In this paper, we validate the effectiveness of the optimal planning algorithms we have developed for devising surgical plans for Percutaneous Nephrolithotomy (PCNL) using patient-specific Concentric-Tube Robots (CTRs). To do so, we built a life-sized phantom model of the right hemithorax, replicating the anatomy of a patient who suffered from kidney stone and underwent conventional PCNL. Two-dimensional CT scans of the phantom model and its 3D reconstruction enabled the creation of a surgical plan using our planning algorithms based on a puncture into the mid-pole of the kidney. This was compared with two other percutaneous tracts involving punctures into the lower and upper calyces for comparison. The optimal mid-pole plan achieved 84% stone coverage, significantly outperforming the lower pole (58 %) and upper pole (45 %) plans. These results validate the effectiveness of the algorithms and align with simulation-based findings from previous studies, which reported an average volume coverage of 81.6±19.6 % in clinical cases.

Electroadhesive clutches have attracted a great deal of interest in the last decade as semi-active actuators for human-robot interaction due to their lightweight, low power consumption, and tunable high-torque output capability. However, because of the complexity of their dynamics, in most cases, they are utilized in an ON/OFF -control strategy. In this regard, the non-autonomous (time-dependent) degradation of electroadhesive behavior is an inherent challenge that injects unpredictability and uncertainty into the behavior of this family of semi-active clutches. We propose a novel approach to preventing degradation of electroadhesion using a segmented electrode design that modulates the electrical field on the dielectric surface while using a direct current signal and securing low power consumption. This paper, for the first time, presents an optimization process based on a novel analytic model of the proposed actuator. It also develops a data-driven model augmentation using a hybrid shallow learning approach composed of a long short-term memory (LSTM) architecture which is combined with the analytical model. The performance of the proposed semi-active clutch and the data-driven hybrid model is experimentally validated in this paper.

Catheter-based cardiac ablation is the preferred method of treating atrial fibrillation. Conventionally, the catheter is navigated in the heart using X-ray fluoroscopy imaging and an electroanatomical map. Although successful, these imaging modalities do not provide real-time feedback on the quality of lesions created, which in turn could lead to recurrence of arrhythmia. Intracardiac echo (ICE) catheter provides real-time imaging within the heart to visualize both the ablation catheter and lesions created. However, manipulating the ablation and ICE catheters simultaneously is tedious and time consuming. As a first step towards developing a robotic ICE catheter that can autonomously follow the ablation catheter and monitor the lesions, we have developed a dynamic model for the ICE catheter. The model is based on the Cosserat theory for flexible rods that relies on strain parametrization. The model also accounts for frictional forces between the catheter sheath and tendons, external loads and fluid forces acting on the catheter. A good nominal model for describing the catheter dynamics is essential to develop a robust control scheme for the robotic ICE catheter. The parameters of the ICE catheter are estimated using weight release, tendon-driven actuation and fluid flow experiments. To the best of our knowledge, this is the first dynamic model for the ICE catheter that accurately reflects the dynamics of the catheter under pulsatile fluid flow within a heart phantom.

This article presents an overview of the current state of research and application of haptic (primarily kinesthetic) feedback and force-based teleoperation in the context of surgical robotics. Telerobotic surgery provides an approach for transferring the sensorimotor skills of a surgeon through a robotic platform to perform surgical intervention inside a patient’s body. Integration of advanced sensing and haptic technologies in telerobotic surgery can help to enhance the sensory awareness and motor accuracy of the surgeon, thereby leading to improved surgical procedures and outcomes for patients. The primary mode of sensory feedback has been through 3-D visual observation using stereo endoscopes. However, until recently, the sense of touch, i.e., haptics, has been missing in the commercial telesurgery robots approved for use in the operating room despite over two decades of research and development in the field of haptics for teleoperated systems (“telehaptics”). Research has shown that high-fidelity force feedback can enhance the performance of telesurgery and potential outcomes by enabling the surgeon to have a more natural feel of interaction between surgical tools and tissue as normally experienced during open surgery. Interaction forces, such as those generated during palpation of tissue, insertion of a needle, unintentional (and potentially unsafe) exertion of force by a tool, suture breakage, needle slippage, or tool interaction, are replaced by indirect (virtual) sensations, termed visual haptics, which provides an alternative to sensory compensation. Although there is a significant amount of literature supporting this benefit, there are still several important technical challenges in introducing haptics in telesurgery, including instrumentation, fidelity (transparency), stability, and modalities for force reflection, e.g., direct or indirect. This article examines these challenges and discusses recent work on haptics-based teleoperated surgical robotic systems.

Bilateral telerobotic systems have attracted a great deal of interest during the last two decades. The major challenges in this field are the transparency and stability of remote force rendering, which are affected by network delays causing asynchrony between the actions and the corresponding reactions. In addition, the overactivation of stabilizers further degrades the fidelity of the rendered force field. In this article, a real-time frequency-based delay compensation approach is proposed to maximize transparency while reducing the activation of the stabilization layer. The algorithm uses a regulated bound-limited multiple Fourier linear combiner to extract the dominant frequency of force waves. The estimated weights are used in conjunction with the relatively phase-lead harmonic kernels to reconstruct the signal and generate a compensated wave to reduce the effect of the delay. The reconstructed force will then pass through a modulated time-domain passivity controller to guarantee the stability of the system. We will show that the proposed technique will reduce the force-tracking error by 40% and the activation of the stabilizer by 79%. It is shown, for the first time, that through the utilization of online adaptive frequency-based prediction, the asynchrony between transmitted waves through delayednetworks can be significantly mitigated while stability can be guaranteed with less activation of the stabilization layer.

A control design framework for the coupled stability problem in robotics is presented. The proposed framework fundamentally generalizes the conventional passivity-based approaches to the coupled stability problem. In particular, it allows for stabilization of not necessarily passive robot-environment interaction where both the manipulator and the environment are dissipative systems with quadratic supply rates. In contrast with existing results, the proposed framework can be used in combination with an arbitrary robot’s tracking control algorithm, and its stabilizing action when in contact with environment does not affect the robot’s trajectory tracking performance in free space. The framework is based on the recently developed nonplanar conic systems formalism and generalized scattering-based stabilization methods. A detailed design example is presented which illustrates the capabilities of the proposed method.

The time-domain passivity approach has been proposed in the literature in a variety of formats to guarantee the stability of teleoperation leader-follower systems. The conventional use of the proposed technique utilizes the control effort at the follower side as the force feedback to be sent back to the user at the leader’s side. However, this has resulted in transparency problems, especially when the follower dynamics are not negligible. On the other hand, four-channel and three-channel Lawrence architectures have been investigated widely in the literature to maximize the transparency of the system when, in most advanced cases, stability is guaranteed using wave-variables. However, wave-variables are historically known for their transparency deterioration problems. In this paper, we propose a two-layer approach taking advantage of the fusion of (a) a more optimal derivation of Lawrence telerobotic architecture (utilizing only two channels), and (b) a two-port time-domain passivity stabilizer while comparing the performance with a one-port passivity stabilizer. The two-channel derivation of the Lawrence architecture allows for implementing a two-port time domain passivity approach, which is investigated in this paper. The performance of this is compared systematically through a multi-objective approach by analyzing dissipated energy besides force and velocity errors for a wide range of time delays and frequencies of excitation. The paper gives a comprehensive view of the efficacy of two-port versus one-port time-domain passivity control when combined with the two-channel derivation of Lawrence architecture.

This paper presents a novel light-weight back-drivable inherently-safe robotic mechanism for delivering ankle rehabilitation therapies. The robot is designed to be used as the ankle module of a multi-purpose lower-limb rehabilitation robot. A novel friction-based safety feature has been introduced that enables mechanical adjustment of the maximum amount of allowable transfer forces and torques to the patient's limb. The design procedure, mathematical modeling and experimental validations are provided to demonstrate the performance of the proposed system.

Machine vision for plant phenotyping is an emerging research area for producing high throughput in agriculture and crop science applications. Since 2D based approaches have their inherent limitations, 3D plant analysis is becoming state of the art for current phenotyping technologies. We present an automated system for analyzing plant growth in indoor conditions. A gantry robot system is used to perform scanning tasks in an automated manner throughout the lifetime of the plant. A 3D laser scanner mounted as the robot's payload captures the surface point cloud data of the plant from multiple views. The plant is monitored from the vegetative to reproductive stages in light/dark cycles inside a controllable growth chamber. An efficient 3D reconstruction algorithm is used, by which multiple scans are aligned together to obtain a 3D mesh of the plant, followed by surface area and volume computations. The whole system, including the programmable growth chamber, robot, scanner, data transfer, and analysis is fully automated in such a way that a naive user can, in theory, start the system with a mouse click and get back the growth analysis results at the end of the lifetime of the plant with no intermediate intervention. As evidence of its functionality, we show and analyze quantitative results of the rhythmic growth patterns of the dicot Arabidopsis thaliana (L.), and the monocot barley (Hordeum vulgare L.) plants under their diurnal light/dark cycles.

Tremor extraction techniques are considered as the central component of several rehabilitative and compensatory robotic technologies, and the accuracy of such filters can directly affect the performance of the aforementioned technologies. Motivated by this fact, the paper proposes an adaptive estimation framework, referred to as Multiple Adaptive Reduced-order Kalman filtering (KFE-BMFLC), for extraction of pathological hand tremors. The proposed KFE-BMFLC framework is designed with the goal of improving the performance of an existing state-of-the-art filtering technique, i.e. Enhanced Band-limited Fourier Linear Combiner (E-BMFLC), which has shown a promising potential in extracting involuntary hand motions but uses embedded least mean square (LMS) estimation approach. The proposed technique is capable of reducing the computational overhead in comparison to that of the conventional BMFLC technique, while increasing the estimation accuracy.

This paper presents a novel multimodal training platform integrated with hand-over-hand (HOH) haptic guidance for dual-console surgical robotic systems such as the da Vinci Si system. The expert-in-the-loop (EIL) framework incorporates a fuzzy interface system in order to provide a trainee with adaptive authority over the procedure as well as hand-over-hand haptic guidance adjusted in real time based on the proficiency level of the trainee. The EIL expertise-oriented framework enables performance of a surgical procedure by an expert surgeon on a patient, while simultaneously providing a trainee at any stage of the motor-skills development with multimodal training without jeopardizing patient safety. Closed-loop stability of the system is investigated using the circle criterion and it is shown that the proposed architecture is unconditionally stable. Experimental evaluations are presented in support of the proposed platform through the implementation of a dual-console surgical setup consisting of the classic da Vinci surgical system (Intuitive Surgical, Inc., Sunnyvale, CA, USA) and the dV-Trainer master console (Mimic Technology, Inc., Seattle, WA, USA). To the best of our knowledge, the implemented setup is the first research platform for dual-console studies involving the classic da Vinci surgical system.

In spite of the remarkable benefits that minimally invasive surgery provides for patients, the absence of force feedback is still a significant disadvantage. Several studies have been performed to address this issue; however, an accurate sterilizable force sensing technology for measuring axial and grasping forces is still missing. In this work, an innovative partial grasper has been designed and developed for a laparoscopic needle driver that can measure axial and grasping force information at the grasper tip. Fiber Bragg Grating sensors are used in this work because of their sterilizability and high sensitivity. Accuracies of 0.19 N and 0.26 N were achieved for the grasping and axial sensors respectively.

Tendon-driven mechanisms used in robotic surgery exhibit strong nonlinearities, particularly a static backlash-like hysteresis, in their motion transmission behavior. In this paper, an extension of a previously developed model is proposed that allows for estimation of angular displacements in multi-DOF tendon-driven devices where special attention is given to the coupling effect between DOFs. The proposed model consists of the conventional coupling matrix and a novel elongation matrix which compensates for the coupled hysteretic effect. The model is applied to the problem of position estimation in three DOFs (one pitch and two grasping DOFs) of a da Vinci®surgical instrument. As a further extension, a preliminary dynamic model is also suggested to deal with high-frequency inputs. According to the experimental results obtained, the proposed quasi-static model can describe the transmission behavior with goodness-of-fit of 76-92 per cent, and the estimates are improved by 35-72 per cent in terms of the RMSE for the proposed dynamic model as compared to the conventional rigid model.

In this paper, the design of a novel bilateral telerobotic architecture for rehabilitation purposes is proposed and the related feasibility, stability, and control challenges are studied. The objective is to incorporate the supervision of a local/remote human physiotherapist into haptics-enabled rehabilitation systems and allow the therapist to provide nonpassive nonlinear assistive/resistive forces in response to the patient's movements. This can address a challenge of conventional software-based rehabilitation systems, i.e., limited capability in adjusting the therapy. To guarantee human-robot interaction safety, a new design framework and a stabilizing controller are developed based on the small-gain approach. System stability and transparency are analyzed in the presence of the nonpassive, nonlinear, and nonautonomous behavior of the terminals (the therapist and the patient) and time-varying delays for the case of remote and cloud-based therapy. Several practical considerations have been taken into account to match the clinical needs and minimize the implementation cost. Simulation studies, practical implementation, and experimental evaluations are presented.

In this paper, based on the apparent stiffness analysis of a dual tendon-sheath system, we propose a method for using a surgical instrument of the da Vinci surgical robotic system (from Intuitive Surgical Inc.) for estimation of mechanical properties of tissues. The performance of the method is experimentally evaluated by comparing tissues with different stiffnesses and by localizing tumors in an artificial tissue sample.

Tumor localization in traditional lung resection surgery requires manual palpation of the deflated lung through a thoracotomy. It is a painful procedure that is not suitable for many patients. Therefore, a multisensory mechatronic device was designed to localize tumors using a minimally invasive approach. The device is sensorized with tactile, ultrasound and position sensors in order to obtain multimodal data of soft tissue in real time. This paper presents the validation of the efficiency and efficacy of this device via an ex vivo experimental study. Tumor pathology was simulated by embedding iodine-agar phantom tumors of varying shapes and sizes into porcine liver tissue. The device was then used to palpate the tissue to localize and visualize the simulated tumors. Markers were then placed on the location of the tumors and fluoroscopic imaging was performed on the tissue in order to determine the localization accuracy of the device. Our results show that the device localized 87.5% of the tumors with an average deviation from the tumor center of 3.42 mm.

In this paper, a robotics-assisted articulating ultrasonic surgical scalpel for minimally invasive soft tissue cutting and coagulation is designed and developed. For this purpose, the optimal design of a Langevin transducer with stepped horn profile is presented for internal-body applications. The modeling, optimization and design of the ultrasonic scalpel are performed through equivalent circuit theory and verified by finite element analysis. Moreover, a novel two degrees-of-freedom (DOFs) surgical end effector (1-DOF pitch, 1-DOF grip) with decoupled motions is developed that is compatible with the da Vinci® surgical system. The developed instrument is then driven using the dVRK (da Vinci® research kit) and the Classic da Vinci® surgical system.

In our previous work [1], the potential benefits of Magneto-Rheological Fluid based actuators to the field of haptics were studied. Our results showed that the superior mechanical attributes of such actuators contribute to improvement of stability and transparency in haptic devices. To this end, a novel design of a small-scale MRF-based clutch, was proposed in [1]. This paper reports on the development and validation of the proposed MRF-based clutch. In addition, a closed-loop torque control strategy is presented. The feedback signal used in this control scheme comes from the magnetic field measurement and is used to compensate for the nonlinear behavior using an estimated model, based on Artificial Neural Networks (ANNs). Such a control strategy eliminates the need for torque sensors for providing feedback signals. The performance of the developed design and the effectiveness of the proposed modeling and control techniques are experimentally validated. The results clearly demonstrate that the clutch shows great potential for use in a multiple degrees-of-freedom (DOF) haptic interface for a class of medical applications.

This paper presents a Therapist-in-the-Loop (TIL) framework for robotics-assisted mirror rehabilitation therapy integrated with adaptive Assist-as-Needed (ANN) training, to be adjusted based on the impairment and disability level of the patient's affected limb. Closed-loop system stability has been investigated using a combination of the Circle Criterion and the Small-Gain Theorem to account both for time-delay and the time-varying adaptive ANN training. Experiments to investigate the performance of the proposed framework are reported.

In this paper, a new passivity-based technique is proposed to analyze and guarantee the stability of haptics-enabled telerobotic rehabilitation systems where there is a possibility of having more sources of non-passivity than communication delays. In practice, the difficulty of therapeutic exercises should be tuned taking into account the stage of physical disability. However, tuning the difficulty and intensity should not violate the stability of patient-robot interaction. This usually puts conservative prefixed limits on the allowable exercise intensity. In this paper, patient-robot interaction safety is studied in the context of Strong Passivity Theory (SPT). Our goal is to ultimately relax the limitation on the allowable robotic therapies while preserving system stability. The proposed stabilizing scheme does not try to make the entire non-passive component passive. This allows the therapist to have freedom in injecting energy into the system for assistive therapies while ensuring safe patient-robot interaction. In this paper, the case of telerobotic rehabilitation is considered. Experimental implementation and evaluation are presented to support the proposed theory.

Lack of dexterous control over the position of a catheter's distal tip and not having any feedback from the quality of tip - tissue contact are among the factors that make the conventional catheter-based method of performing cardiac ablation very challenging. To resolve these issues, in this paper, we present a robotic catheter manipulation system that accommodates a conventional ablation catheter, places the ablation tip at the desired target and reports the forces that the tip exerts on the environment in real-time. In this system, the manual proximal handle is replaced with a mechanism that is capable of measuring the tension force along the pull-wire while actuating it to flex the distal shaft of the catheter. The placement of force/pressure sensors at the distal end of the catheter is avoided by developing a model-based force estimation technique using the measured tension force and information on the position and orientation of the distal tip. The developed system is further enhanced with an interface to assist the user in placing the catheter tip at the desired location while providing him/her with a real-time measure of the contact force. Extensive experiments show that using the proposed robotic system, the catheter tip is positioned within ±1 mm of the designated target and contact forces are reported in real-time with an accuracy of 3 gf.

This paper reports on the performance evaluation of Magneto-Rheological Fluid (MRF) based actuation systems when used in haptic interfaces. MRF-based actuators exhibit superior characteristics, which can significantly contribute to the transparency and stability of haptic devices. To validate this statement, a prototype two degrees-of-freedom (DoF) haptic interface is constructed. A distributed antagonistic configuration is used in order to develop the 2-DoF haptic interface based on small-scale MRF-based clutches for a class of medical applications. The developed device is compared with three conventional haptic interfaces and their stability is compared using the Virtual Wall experiment. Next, the prototype interface is incorporated in a master-slave teleoperation medical setup. Preliminary studies on the performance of the haptic interface show great potential of MRF-based actuators for integration in haptic devices for medical interventions that require safe, accurate, and stable force representation.

In this paper, a novel formulation for robust surgical planning of robotics-assisted minimally invasive cardiac surgery based on patient-specific preoperative images is proposed. In this context, robustness is quantified in terms of the likelihood of intraoperative collisions and of joint limit violations. The proposed approach provides a more accurate and complete formulation than existing deterministic approaches in addressing uncertainty at the task level. Moreover, it is demonstrated that the dexterity of robotic arms can be quantified as a cross-entropy term. The resulting planning problem is rendered as a chance-constrained entropy maximization problem seeking a plan with the least susceptibility toward uncertainty at the task level, while maximizing the dexterity (cross-entropy term). By such treatment of uncertainty at the task level, spatial uncertainty pertaining to mismatches between the patient-specific anatomical model and that of the actual intraoperative situation is also indirectly addressed. As a solution method, the unscented transform is adopted to efficiently transform the resulting chance-constrained entropy maximization problem into a constrained nonlinear program without resorting to computationally expensive particle-based methods.

The two main objectives in designing a haptic interface are stability and transparency. The dynamics of the actuators employed in a haptic interface have a significant effect on these goals. In this article, the potential benefits of Magneto-Rheological Fluid (MRF) based actuators to the field of haptics are discussed. Devices developed with such fluids are known to possess superior mechanical characteristics over conventional servo systems. This contributes significantly to improved stability and transparency of haptic devices. In this study, this idea is evaluated from both theoretical and experimental points of view. First, the properties of such actuators which motivated this research are discussed. Next, two single degrees-of-freedom (DOF) haptic interfaces are used in a virtual wall experiment. These devices take advantage of an MRF-based clutch and a brushless DC motor at their core, respectively. The results of both devices are compared and show the superiority of the MRF-based clutch. In addition, design and analysis of a small-scale MRF-based clutch, suitable for a multi-DOF haptic interface, is given and its torque capacity, inertia, and mass are compared with those of conventional servo systems. Conclusions drawn from this investigation indicate that MRF clutch actuation approaches can indeed be developed to design haptic interfaces with improved stability and transparency.

This paper proposes an expertise-oriented training platform for robotics-assisted minimally invasive surgery. The framework builds on previous work of the authors and makes use of dual-user teleoperation scenario, allowing the presence of an expert in the training loop. A Fuzzy-Logic (FL) methodology is proposed, which specifies the level/mode of the training required for the trainee according to his/her level of proficiency over the task. A major advantage of the proposed FL approach is that, having the expert in the loop, it can specify the trainee's proficiency level relative to that of the expert in real-time. Moreover, based on the relative skills assessment, the proposed FL approach decides if or to what extent the trainee should receive a haptic guidance force based on Virtual Fixtures or the environment force from the interaction between the surgical instrument and tissue at the slave side. In addition to the level/mode of the haptics-enabled training required for the trainee, the proposed FL framework specifies the authority level of the trainees over the operation in real-time, according to their proficiency levels over the task. Stability of the overall closed-loop teleoperated system is also investigated using the small-gain theorem, resulting in a sufficient condition to guarantee stability in the presence of constant communication delays. Finally, experimental results are given to evaluate the design and feasibility of the proposed framework.

Concentric-tube robots can offer a suitable compromise between force and curvature control. In a previous study by the authors, a real-time trajectory tracking scheme for an unloaded concentric-tube robot was developed. One of the practical barriers to the use of a concentric-tube robot in medical applications is compensation for the impact of environmental forces which can cause drastic deterioration in tracking performance. In this paper, by modifying the robot's forward kinematics and Jacobian, a new method is developed to facilitate tip tracking in real-time while accounting for an external load at the robot's tip. By considering the tip deflection resulting from the external load, a novel dual-layer control architecture is proposed to compensate for this deflection during trajectory tracking. In order to measure the force exerted on the tip position of the robot, a new technique is proposed that can move the sensing system from the distal tip to the proximal base. Experimental results are given to illustrate the effectiveness of the proposed method.

Two simplified quasi-static models for the da Vinci instrument are proposed which take into account distributed frictions and compliance of the tendons. These models are derived from static analysis of the interaction of the tendons with a curved surface. The key parameters of the models are identified, and the performance of the models is experimentally evaluated. Experimental results obtained suggest that a weighted combination of the outputs of the two models provides a sufficiently close estimate of the output torque of the da Vinci instrument.

In this paper, a safety concern arising from pathological tremors in patients interacting with haptics-enabled rehabilitation robots is analyzed and the issue of tremor amplification for assistive/coordinative robotic rehabilitation is investigated. In order to deal with this issue, a control architecture is proposed to dissipate the extra energy of the system and guarantee its stability and safety of the patient. For this purpose, (a) first, a multilayer adaptive filter is proposed to estimate high-frequency components of hand motions (corresponding to involuntary movements); (b) then a resistive force field is generated and applied by the robot to attenuate the tremor; and (c) simultaneously the residual low-frequency voluntary actions are amplified/coordinated to deliver appropriate therapy. Stability analysis and a stabilization scheme are developed to guarantee safe interaction regardless of variations in the patient's dynamics and tremor kinematics. The ultimate goal is to make it possible for patients with pathological tremors to take advantage of non-passive robotic assistive/coordinative therapy. This would not be possible using conventional systems due to the possibility of tremor amplification. Experimental results are presented.

Cardiac ablation using flexible catheters is a common interventional procedure for treating cardiac arrhythmia. This procedure is performed under image guidance and the contact force between the ablation tip and the heart tissue is one of the factors that greatly impacts the efficacy of the ablation procedure. This paper investigates the feasibility of estimating the force that the catheter tip exerts on the heart tissue by monitoring the changes in the shape of the deflectable distal shaft of the catheter (henceforth called the “deflectable shaft” or the “shaft” of the catheter). It is shown that variations in the shaft curvature provide information about how much force the catheter tip is exerting at its point of contact. Consequently, an index is defined for determining the range of contact forces based on the shaft curvature. Experimental results show that the defined index can correctly detect the range of applied contact forces in more than 80% of the cases. This study proves that the flexibility of the deflectable shaft provides a means of estimating contact forces exerted by the catheter tip.

In this paper, a novel robotics-assisted rehabilitation framework is proposed for bilateral mirror-image therapy. For this purpose, a customized dual-user teleoperation architecture is designed incorporating Guidance Virtual Fixtures (GVFs) to deliver the appropriate therapeutic movements to the patient's impaired limb by providing an assist-as-needed treatment strategy. In addition, the therapist is provided with informative haptic feedback that is generated based on the patient's movements, allowing the therapist to decide in real-time on the level and format of the therapy required for the patient. Stability of the closed-loop system is also investigated using the small gain theorem, in the presence of communication time delays, facilitating the case of remote tele-rehabilitation. Experimental results are given to validate the performance of the proposed platform.

Implementation of haptic feedback in minimally invasive surgical teleoperator systems may lead to improved performance in many common surgical procedures; however, most of the currently available surgical teleoperators do not provide force feedback, mainly because of the associated stability issues. In this paper, we study the effect of a special type of force reflection algorithms, called projection-based force reflection (PBFR) algorithms, on the stability and performance of a dual-arm haptics-enabled teleoperator system for minimally-invasive surgical applications. In particular, the teleoperator system's performance is experimentally evaluated in three common tasks, which are knot tightening, pegboard transfer, and object manipulation, in the presence of negligible as well as non-negligible communication delays. The results obtained indicate that, in almost all cases, the PBFR algorithms demonstrate statistically significant improvement of performance in comparison with conventional direct force feedback.

In this paper, a robotic solution is proposed to deal with the challenges caused by lung motion during needle insertion. To accomplish this goal, a macro-micro robotic tool is designed to compensate for tissue motion using the macro part, while performing the needle insertion independently with the micro part. The main application of this work is for robotics-assisted lung tumor biopsy, where the combined motions of respiration and heartbeat may compromise success. An impedance-based controller keeps the macro reference coordinate in contact with the moving soft tissue using measurements from small pressure sensors mounted at the tip of the macro shaft. The micro part, mounted at the end of the macro robot, manipulates the needle in the harmonized reference coordinate system. Preoperative identification of ex vivo soft tissue is performed to estimate the dynamic behavior of the tissue. The controller is then synthesized based on the identified model. The effects of identification error and high frequency uncertainty are addressed in the control design. A prototype was built to evaluate the proposed approach using: 1) two Mitsubishi PA-10 robots, one for manipulating the macro part and the other for mimicking tissue motion, 2) one motorized linear stage to handle the micro part, and 3) a Phantom Omni haptic device for remote manipulation. Experimental results demonstrate the performance of the motion compensation system.

Over the past few decades, catheter-based cardiac ablation has been the first surgical option for treatment of arrhythmia. In order to have an effective ablation procedure, after positioning the catheter at the desired location inside the heart chamber, a consistent tip/tissue contact should be maintained during the whole procedure. With the goal of implementing hybrid force/position control of the catheter tip during the ablation procedure, this paper studies how the catheter tip deflects when forces are applied. A pseudo-rigid-body 3R model for the catheter tip is introduced. The model performance is evaluated through extensive experiments and it is shown that the proposed model can estimate the shape of the bending section of the ablation catheter if force information is available. This model does not require extensive knowledge of the catheter internal structure. Moreover, the well-established static equations are simple to understand and solve, making this model a convenient choice for developing a control system.

The increasing popularity of catheter-based ablation therapy in treating cardiac arrhythmia has motivated researchers to seek new techniques to improve the accuracy and efficiency of such procedures. After guiding the catheter through the vessels into the heart chambers, precise positioning of the catheter tip and consistent tool/tissue contact force are the two factors that greatly affect the ablation outcome. Implementing force/position control of the catheter tip will improve the efficacy of cardiac ablation procedures immensely. This paper proposes a model-based force control system to ensure a desired contact force at the distal tip, without directly measuring the force applied at the tip. In this regard, it is studied how the displacement of the proximal handle of a common 7-Fr pull-wire ablation catheter relates to the change of angle at its distal tip. The resulting mapping together with a mapping that relates the forces at the distal tip to the tip shape are used in developing a control system that ensures a desired contact force at the tip. This paper also introduces an optical strain sensor that can be used without modification in the manufacture of present day ablation catheters. This strain sensor completes the feedback loop of the control system through integration with the shape to force model. Performance of the control system is evaluated experimentally and the results suggest that model-based control of steerable catheters is feasible for catheter ablation. The proposed control system can be employed on a conventional ablation catheter following a fairly simple calibration step.

This paper proposes a teleoperated dual-user system incorporating Virtual Fixtures (VFs) that allows concurrent performance of a robotic surgical task by an expert and a trainee. In order to guide the trainee through the procedure, an adaptive VF is created in the trainee's workspace according to the motion generated by the expert who is performing the surgery at the same time. The VF gets adaptively adjusted based on the level of expertise the trainee shows during the surgery. In addition, the trainee's level of expertise is used to adaptively adjust the dual-user dominance factor in an online fashion, which gives the trainee some authority over the task based on his/her skill level. To quantify the trainee's expertise level, a performance measure is proposed, based on the force generated by the VF. Three performance measures from the literature are also used. To satisfy the desired objectives of the proposed system, an impedance-based control methodology is adopted. Stability of the closed-loop system is investigated using the small-gain theorem. A sufficient stability condition is derived that guarantees stability in the presence of time-varying communication delay. Experimental results are given to validate the performance of the system.

The projection-based force reflection (PBFR) algorithms were previously demonstrated to substantially improve stability characteristics of the force reflecting teleoperator systems and haptic interfaces without transparency deterioration in the steady state; however, the transient response of the PFBR algorithms suffers from relatively slow force convergence. In particular, the high frequency component of the contact force, which is very important for the haptic perception of stiff surfaces, is typically filtered out. In this paper, a solution to this problem is proposed which is based on the idea to separate different frequency bands in the force reflection signal and consequently apply the projection-based principle to the low-frequency component, while reflecting the high-frequency component directly. It is shown that, for bilateral teleoperators with irregular communication delays, stability can always be achieved by implementing the above described force reflection scheme, if the cut-off frequency of the complementary filters is sufficiently high and a certain weighting coefficient in the force reflection algorithm is sufficiently low. Experimental results demonstrate that substantial simultaneous improvement of stability and transparency is achieved using the proposed method.

The reduced access conditions present in Minimally Invasive Surgery (MIS) affect the feel of interaction forces between the instruments and the tissue being treated. This loss of haptic information compromises the safety of the procedure and must be overcome through training. Determining the skill level of trainees is critical for ensuring patient safety. The objective of this work was to evaluate the usefulness of force information for skills assessment during MIS. Experiments were performed using a set of sensorized instruments capable of measuring instrument position and tissue interaction forces. The results show that experience level has a strong correlation with force-based metrics. The proposed metrics can be automatically computed, are completely objective, and measure important aspects of performance.

Concentric-tube robots can offer dexterous positioning even in a small constrained environment. This technology turns out to be beneficial in many classes of minimally invasive procedures. However, one of the barriers to the practical use of a concentric-tube robot is the design of a real-time control scheme. In previous work by the authors, a computationally efficient torsionally compliant kinematic model of a concentric-tube robot was developed. Using this computationally fast technique and deriving the robot's Jacobian, a new position control approach is proposed in this paper. This mechanism provides computational efficiency as well as good tracking accuracy. To evaluate the performance, experiments were conducted, and the results obtained demonstrate the feasibility of enabling the robot's tip to perform trajectory tracking in real time.

The problem of designing of a haptics-enabled teleoperated rehabilitation system in the presence of communication delays is addressed. In a teleoperated rehabilitation system, communication delays introduce phase shift which may result in the task inversion phenomenon. To overcome the task inversion, a new type of projection-based force reflection algorithm is proposed which is suitable for assistive/resistive therapy in the presence of irregular communication delays. Additionally, algorithms for augmented therapy are introduced which combine the projection-based force reflection with a delay-free local virtual therapist. A small-gain design is developed which guarantees stability of the proposed schemes for both assistive and resistive modes of the therapy. Simulations and experimental results are presented which confirm the improvement achieved by the proposed methods.

In this paper, a vibration-assisted needle insertion technique has been proposed in order to reduce needle-tissue friction. The LuGre friction model was employed as a basis for the current study and the model was extended and analyzed to include the impact of high-frequency vibration on translational friction. Experiments were conducted to evaluate the role of insertion speed as well as vibration frequency on frictional effects. In the experiments conducted, an 18 GA brachytherapy needle was vibrated and inserted into an ex-vivo soft tissue sample using a pair of amplified piezoelectric actuators. Analysis demonstrates that the translational friction can be reduced by introducing a vibratory low-amplitude motion onto a regular insertion profile, which is usually performed at a constant rate.

Involuntary motions of the hand can have a significant deteriorating effect on the performance of microsurgical procedures such as vitreoretinal microsurgery. The most common source of the involuntary motions is physiological tremor. Real-time compensation of physiological tremor is therefore necessary to assist surgeons to accurately perform a microsurgery. A novel approach based on the use of Ionic Polymer Metallic Composites (IPMCs) has been developed for actively compensating physiological tremor in the hand. We present the design of our novel handheld device that compensates for tremor using an IPMC-based actuator. We then experimentally evaluate the device to show the amount of compensation achieved.

This work is aimed at developing a new minimally invasive approach to characterize tissue properties in real time during telerobotic palpation and to localize tissue abnormality while estimating its depth. This method relies on using a minimally invasive probe with a rigidly mounted tactile sensor at the tip to capture the force distribution map and the indentation depth by each tactile element and thereby generating a stiffness map for the palpated tissue. The hybrid impedance control technique is used for this approach to enable the operator to switch between position control and force control and thereby to autonomously obtain the required information from the remote tissue. The operator would then be able to localize tissue abnormality based on the force distribution map, the tissue stiffness map and the indentation depth which are visually presented to him/her in real time. This method also enables the operator to estimate the depth at which the tissue abnormality is located. Our results show that tactile sensing alone may be unable to detect tumors embedded deep inside tissue and may also not be a good alternative for palpation on uneven tissue surfaces.

In this paper, a computational framework for patient-specific preoperative planning of Robotics-Assisted Minimally Invasive Cardiac Surgery (RAMICS) is presented. It is expected that preoperative planning of RAMICS will improve the success rate by considering robot kinematics, patient-specific thoracic anatomy, and procedure-specific intraoperative conditions. Given the significant anatomical features localized in the preoperative computed tomography images of a patients thorax, port locations and robot orientations (with respect to the patients body coordinate frame) are determined to optimize qualities such as dexterity, reachability, tool approach angles and maneuverability. To address intraoperative geometric uncertainty, the problem is formulated as a Generalized Semi-Infinite Program (GSIP) with a convex lower-level problem to seek a plan that is less sensitive to geometric uncertainty in the neighborhood of surgical targets. It is demonstrated that with a proper formulation of the problem, the GSIP can be replaced by a tractable constrained nonlinear program that uses a multi-criteria objective function to balance between the nominal task performance and robustness to collisions and joint limit violations. Finally, performance of the proposed formulation is demonstrated by a comparison between the plans generated by the algorithm and those recommended by an experienced surgeon for several case studies.

Catheter-based cardiac ablation is an interventional treatment for heart arrhythmias. Pull-wire steerable catheters are guided to the heart chambers through the vasculature in order to deliver energy to destroy faulty electrical pathways in the heart. The effectiveness of this treatment is dependent on the accuracy of positioning the catheter tip at the target location and also on maintaining contact with the target while the heart is beating. Therefore, it is desirable to perform hybrid force/position control of the catheter tip. We have studied the problem of modeling the distal part of a steerable catheter using beam theory and have developed and validated a static force-deflection model through extensive experiments. It is shown that the model can estimate the shape of the bending section of a catheter using force information and without requiring extensive knowledge of the catheter's internal structure.

This paper presents a new tactile-force integrated method to localize tumors minimally invasively using robotic assistance. This method relies on using a capacitive sensor at the tip of a Tactile Sensing Instrument (TSI) which can be inserted into a patient's body in a minimally invasive manner. In this work, the operator palpates tissue containing tumors in a minimally invasive surgical (MIS) training box, representing the patient's body, through a master-slave teleoperation system which consists of a 7 degrees-of-freedom (DOF) haptic interface, used as the master, and a Mitsubishi PA10-7C robot as the slave. Using the proposed method, the operator would be able to palpate the tissue consistently, observe the pressure distribution over the tissue by a color contour map on a screen and feel the tumor on his/her fingers through a grasping mechanism of the haptic interface as a result of higher stiffness of the tumor. The tissue used for the experiments was ex vivo bovine lung and seven participants were asked to locate artificial tumors embedded in the lungs. The results show an accuracy of 93% in tumor localization using the proposed method while the average force applied to the tissue was 3.42N and the force never exceeded 6N.

In master-slave teleoperator systems used for tele-rehabilitation purposes, the passivity can be violated because of the assistive actions of a therapist; moreover, any type of passivation approach to the design of such a system would defeat the purpose of the assistive therapy. In this paper, a design framework is presented that does not rely on passivity considerations. A number of results are given that deal with stability and transparency properties of the tele-rehabilitation system in the case of intrinsically non-passive behaviour of the therapist. In particular, a stabilization scheme for the networked tele-rehabilitation system is proposed which guarantees stability regardless of the specific actions of the therapist. Simulation results are presented which confirm the theoretical developments.

This paper focuses on control challenges caused by the slave-arm flexibility in master-slave telerobotic systems. Apart from time delay, the nonlinear non-minimum phase deflection of flexible-link slave manipulators creates extra challenges for control of telerobotic systems. These challenges have forced most of the prior research to use basic simplifications. In this paper, we try to remove most of the simplifications using a more realistic model for slave deflections. The degrading effects of flexibility on stability and performance of conventional telerobotics architectures are analyzed. Then, the standard Extended Lawrence Four-Channel (ELFC) control architecture is modified to obtain the stability condition and to enhance performance. Finally, the input-to-output stability (IOS) Small-Gain Theorem is used to generalize the stability criteria for varying delay and to remove the restrictive assumption of deflection-linearity. The proposed architecture consists of a local Partial Feedback Linearization scheme embedded into a modified ELFC architecture. This study is motivated by the use of light-weight cable driven tools in telerobotic surgery.

This paper presents a new approach to account for distributed friction in needle insertion in soft tissue. As is well known, friction is a complex nonlinear phenomenon, and it appears that classical or static models are unable to capture some of the observations in systems subject to significant frictional effects. To characterize dynamic features when the needle is very flexible and friction plays an important role in bending mechanics or when a stop-and-start planning scenario is implemented at low insertion velocities, a distributed LuGre model can be adopted. Experimental results using an artificial phantom illustrate that the proposed method is capable of representing the main features of friction which is a major force component in needle-tissue interaction during percutaneous interventions.

In this paper, robust preoperative planning of RAMICS is formulated. The intent of the proposed planning framework is to improve surgical outcomes by contemplating the intraoperative conditions of the surgical procedure and the geometry of the patient's thoracic anatomy. This includes improvements in target reachability, instrument dexterity for critical surgical tasks, surgical task feasibility and visibility. Given the patient's preoperative computed tomography images of the chest, the planning framework aims to determine the optimal location of the access ports on the ribcage, along with the optimal pose of the robotic arms relative to the patient's anatomy. To minimize susceptibility of the results to intraoperative geometric uncertainty, the planning is formulated as a Generalized Semi-Infinite Program (GSIP) with a convex lower level problem and a multi-criteria objective function. By solving the GSIP, tolerable geometric uncertainty within the task space is increased by eliminating the likelihood of collisions and joint limit violation in a neighborhood of the surgical target.

For cooperative force-reflecting teleoperation over networks, conventional passivity-based approaches are not always applicable due to possibility of nonpassive slave-slave interactions and irregular communication delays imposed by networks. In this work, we propose a design approach that is based on an advanced version of the small-gain theorem developed previously for complex network-based interconnections. It is shown that, using the proposed design approach, a networked cooperative force-reflecting teleoperator system can be made stable in the presence of irregular communications by adjusting the local control gains appropriately. Experimental results are presented that confirm the validity of the proposed approach.

In this paper, a novel decentralized multilateral structure is proposed for the dual user systems in the presence of communication delay. The proposed structure utilizes adaptive impedance control approach in order to overcome the destructive effect of the time-delay on system desired-objectives, which is a disregarded issue in the previous studies on dual user system. The proposed control strategy, which utilizes three desired impedance surfaces defined in the paper, satisfactorily brings the system hybrid matrix close to the ideal one that guarantees the system stability and transparency. The controller is designed in a way that eliminates the necessity of the delay estimation as one of its outstanding characteristics; consequently, the unknown communication time-delay can be handled via this structure while previous studies have disregarded the issue of time delay in dual user system. Furthermore, the adaptive structure of the controller promises to overcome the uncertainties on robot's dynamics. In addition, the efficiency of the controller in guaranteeing the system stability in the presence of unknown communication delay is investigated through passivity theory and the presented analysis illustrates complete independency of the closed-loop system stability on time delay value applying the proposed controller. Experimental results performed on a delayed dual user system demonstrate validity of the proposed scheme.

This paper presents a new needle deflection model that is an extension of prior work in our group based on the principles of beam theory. The use of a long flexible needle in percutaneous interventions necessitates accurate modeling of the generated curved trajectory when the needle interacts with soft tissue. Finding a feasible model is important in simulators with applications in training novice clinicians or in path planners used for needle guidance. Using intra-operative force measurements at the needle base, our approach relates mechanical and geometric properties of needle-tissue interaction to the net amount of deflection and estimates the needle curvature. To this end, tissue resistance is modeled by introducing virtual springs along the needle shaft, and the impact of needle-tissue friction is considered by adding a moving distributed external force to the bending equations. Cutting force is also incorporated by finding its equivalent sub-boundary conditions. Subsequently, the closed-from solution of the partial differential equations governing the planar deflection is obtained using Green's functions. To evaluate the performance of our model, experiments were carried out on artificial phantoms.

Developments to the small-gain design approach to networked cooperative force-reflecting teleoperators are presented. Explicit assumptions on the human dynamics are incorporated into the stability analysis, and the conservatism of the small-gain design is eliminated using the projection-based force reflection principle. Results are established that describe the stability properties of the networked cooperative teleoperator system under different conditions on the human dynamics and for different types of the force reflection algorithms. Samples of experimental results are presented.

This paper outlines a framework for the preoperative planning of robotics-assisted minimally invasive cardiac surgery with application to coronary artery bypass grafting. The intent of the proposed framework is to improve surgical outcomes by considering the intraoperative requirements of the robotic manipulators and the anatomical geometry of the patient's chest. This includes target reachability, instrument dexterity for critical surgical tasks and collision avoidance. Given the patient's preoperative chest computed tomography images, the planning framework aims to determine the optimal location of the access ports on the ribcage, along with the optimal pose of the robotic arms relative to the patient's anatomy. The proposed multi-objective optimality criteria consist of a measure of clearance as well as a new collective kinematic measure. The minimum distances among the robot arms provides a measure for the likelihood of collisions. The proposed kinematic measure is composed of two modified manipulability indices that are dimensionally homogeneous and, in contrast to previously-used measures, are more likely to yield isotropic force and torque distributions when optimized for surgical interventions. The results of a case study illustrate the compatibility of the framework with general guidelines used by experienced surgeons for port selection. Furthermore, the framework surpasses those guidelines by ensuring the feasibility of the solutions in the sense of collision avoidance and surgical target reachability.

Patch clamping is an electrophysiological technique that permits the measurement of ion channel activity in many different kinds of cells. Placement of the patch clamp electrodes using micromanipulators is a time consuming and complicated task due to the lack of depth perception of microscope optics and the constrained physical environment. In order to simplify this process, a software platform has been created that permits the user to easily perform not only single electrode recordings but multiple ones. The software platform provides capabilities for automatic positioning of micropipettes in specified locations on the image plane, autofocusing on selected objects, detecting visible micropipettes using image processing techniques, haptic-enabled master slave control of micromanipulators for accurate positioning of electrodes while generating virtual forces to prevent collision between micropipettes, as well as several other novel features which help the user to perform patch clamping more efficiently. The system does not require any changes in the hardware, and uses a fully software-based approach.

This paper focuses on the problem of incorporating haptics-enabled teleoperation in minimally invasive tumor localization. Since the stiffness of a tumor is higher than that of the surrounding tissue, it can be identified as a hard nodule when palpated. Using a Tactile Sensing Instrument (TSI) developed at CSTAR, the distributed pressure profiles along the contacting surface can be measured during remote tissue palpation. The tumor can be detected by using a visualization software that creates a color contour map based on the magnitude of the pressure over the palpated area. The accuracy of this method depends on the uniformity of the force applied to the tissue. A haptics-enabled teleoperation system provides the surgeon with the opportunity to feel the interaction force between the instrument and tissue during Minimally Invasive Surgery (MIS). The objective of this research was to assess the feasibility of combining force feedback with tactile feedback in order to increase the overall performance of tumor localization. The teleoperation system used in this work consists of a Mitsubishi PA10 robot as the slave that is remotely controlled (over a dedicated network) through a 7 Degree-Of-Freedom (DOF) haptic interface. A two-channel architecture, along with hybrid impedance control was utilized to form a bilateral teleoperation system in which the master is under force control and the slave is under position control. The experimental results confirm the effectiveness of using force feedback in robot-assisted tactile sensing for tumor detection.

The limitations of minimally invasive surgery include the inability to sense forces exerted by the instruments on tissue and the limited visual cues available through the endoscope. A modular laparoscopic instrument capable of measuring force and position has been designed to address these limitations. Novel image-based position tracking software has been developed and integrated within a graphical user interface. This modular system is low cost, versatile, and could be used for training, localization of critical features or for guidance during surgical procedures.

There are applications where different objective lenses have to be used for microscope imaging. Rotary nose-pieces cannot be used when larger objectives are required and when there is a physical space limitation. It is also very difficult and time consuming to change the objective lens manually and locate and focus on the same spot again; This may prevent any attempt for automating an image-guided robot-assisted procedure using the microscope images with different objective lenses. A linear lens changing mechanism has been developed which makes it possible to slide the objectives under a microscope. Image processing algorithms have been used to determine the optimal position of the lenses with respect to the source of light, compensate for changes in the focal length in case of non-parfocal objectives and to locate and focus on the exact same spot, regardless of the objective change. A 3-DOF micromanipulator has been used to move the microscope with respect to the substrate. As one of the most challenging applications, this can facilitate objective lens change in computer-assisted patch clamping with multiple electrodes.

In this paper, we present the design of a 7 degrees-of-freedom (DOF) Haptic Interface for applications in Minimally Invasive Surgery (MIS). The design of the interface is based on an existing dual-panthograph Haptic Wand and is capable of position and force reflection in three translational, three rotational DOF and grasping motion. The paper presents the implementation of a novel cable driven differential transmission to include the yaw and grasping force reflection to the interface. The kinematic and dynamic properties of the interface are characterized and presented. Experimental results demonstrate that the device is capable of high-force reflection with good transparency.

This paper describes some novel research results on bilateral teleoperation of a flexible catheter in a constrained environment. The dynamics of the catheter in a constrained environment is highly nonlinear and is affected by a large number of factors such as friction, flexibility of the catheter, force of insertion, shape and size of the catheter, etc. As a result, the distal end of the catheter almost never follows the actuated end of the catheter which could cause fatigue to the clinician/user attempting to insert the catheter in a blood vessel. In addition, there is a time delay of up to 0.8 second before the distal end of the catheter advances after the near end is actuated. This delay is sufficient to cause instability in the control loop. We have developed a teleoperation framework using wave variables to perform robot- assisted catheter insertion in a constrained environment while reflecting the forces at the tip of the catheter to the clinician. Experimental results showing the effect of different factors such as the velocity and stroke length of insertion on the delays introduced in control loop and errors between the master and slave position are included. To the best of our knowledge, this work is among the first to attempt to provide an understanding of the effects of various factors on the flexing of the catheter. In addition, master-slave insertion of a catheter instrumented with shape memory alloys (SMA) has also been performed and the results are included in this paper.

An integrated system for minimally invasive robot-assisted image-guided lung brachytherapy has been developed. The system incorporates an experimental setup for accurate radioactive seed placement with commercially available dosimetry planning software. The end result is a complete system that allows planning and executing a brachytherapy procedure with increased accuracy. The results of the in vitro seed placement evaluation show that seed misplacement has a significant effect on the volume receiving more than 200% of the dose (V200), and the minimum dosage received by 90% of the volume (D90).

Two-dimensional or 3-D visual guidance is often used for minimally invasive cardiac surgery and diagnosis. This visual guidance suffers from several drawbacks such as limited field of view, loss of signal from time to time, and in some cases, difficulty of interpretation. These limitations become more evident in beating-heart procedures when the surgeon has to perform a surgical procedure in the presence of heart motion. In this paper, we propose dynamic 3-D virtual fixtures (DVFs) to augment the visual guidance system with haptic feedback, to provide the surgeon with more helpful guidance by constraining the surgeon's hand motions thereby protecting sensitive structures. DVFs can be generated from preoperative dynamic magnetic resonance (MR) or computed tomograph (CT) images and then mapped to the patient during surgery. We have validated the feasibility of the proposed method on several simulated surgical tasks using a volunteer's cardiac image dataset. Validation results show that the integration of visual and haptic guidance can permit a user to perform surgical tasks more easily and with reduced error rate. We believe this is the first work presented in the field of virtual fixtures that explicitly considers heart motion.

Interventional cardiologists are at great risk from radiation exposure due to lengthy procedures performed under X-ray radiations. Angioplasty is one such procedure wherein the clinician guides a catheter into the femoral artery under X-rays and the procedure often extends to over 50 min. A clinician performs several hundred such procedures over his/her lifetime, leading to an accumulation of the total radiation he/she is exposed to. In this paper, we investigate autonomous robot-assisted insertion of an active catheter instrumented with shape memory alloy (SMA) actuators using image guidance. The tip of the active catheter is tracked in real time to provide information on the location of the catheter that determines the optimal stroke length of insertion for the robot and the necessary bending angle for the active catheter. The catheter is autonomously guided from the point of entry to the site of plaque buildup, thereby shielding the clinician from harmful radiation due to the X-rays used for imaging and providing a more ergonomic approach for catheter insertion. Experimental results are given to illustrate the robot-assisted catheter insertion procedure using image guidance.

In this paper, based on a passivity framework, admittance-type and hybrid-type delay-compensated communication channel models are introduced, which warrant different bilateral control architectures for wave-based teleoperation under time delay. We utilize wave transforms and signal filtering for passivating the delayed-communication channel and passivity/stability conditions are derived using scattering theory based on an end-to-end model of the teleoperation system rather than the communication channel alone. Contrary to a commonly held view, it is proven that the teleoperation system can remain stable when force measurement data of the master and the slave manipulators interactions with the operator and the remote environment are used. Experimental results on a soft-tissue task for a hybrid-type architecture and for round-trip delays of 60 msec and 600 msec show that using slave-side force measurements considerably enhances teleoperation transparency.

The prostate is a small exocrine gland in men responsible for production of the liquid component of the seminal fluid. In North America, prostate cancer accounts for over 300,000 new cases and 40,000 deaths each year and it is the second leading cause of cancer death in men. Low-dose Rate (LDR) brachytherapy is gaining interest as a viable treatment option for prostate cancer due to its low side effects and high benefits. The present manual approach for brachytherapy needle insertion and the inherent flexibility of the needles make it extremely difficult to achieve accurate and consistent dosimetry. In this paper, we present a new 5 degrees-of-freedom (DOF) manipulator capable of performing percutaneous needle insertion. The manipulator can perform orientation, insertion and rotation of the needle and linear motion of the plunger to drop radioactive seeds at targeted locations. The manipulator is an integral part of a system utilizing a mechanically rotated side-fire transducer to create 3D ultrasound images of the organ and utilizing 3D SLICER software to visualize those images. Experiments conducted in agar phantoms reveal an average RMS targeting error of 1.45mm at an average insertion depth of 75.78mm proving the feasibility and efficacy of the proposed robotic system for percutaneous needle insertion.

A novel technique is described for isotropy-based kinematic optimization of specific robot characteristics. The new technique has advantages over existing techniques when designing robotic systems for specific, unconventional tasks, and for constrained motion. In this paper, the technique is used to assist in the selection of a remote center-of-motion (RCM) location for a research testbed that is being developed at CSTAR to study robotics-assisted minimally-invasive surgery. The optimization technique allows isotropy to be considered with respect to the surgical tool tip while operating under the RCM constraint. Global isotropy over a minimally-invasive surgical workspace is evaluated for a set of candidate RCM locations, and an optimal RCM location with respect to isotropy is selected. The isotropy results are compared with experimental data for a number of candidate RCM locations. The experimental results confirm the usefulness of the optimization technique.

An ultrasound probe holder is designed for use in the prostate brachytherapy procedure. The holder comprises a passive-jointed stabilizer that can be used to position, manipulate and lock in place the ultrasound probe, and a tracker mechanism to provide the position and orientation of the probe in 3D space. The information obtained from the integrated stabilizer-tracker mechanism can be utilized in image-guided robot-assisted prostate brachytherapy procedures. Performance tests show that the tracker assembly can acquire the position and orientation of the ultrasound probe with an average displacement accuracy of 0.66 mm and roll, pitch and yaw angular accuracies of 0.24deg, 0.38deg and 0.19deg, respectively.

In this paper, we investigate autonomous robot- assisted insertion of an active catheter instrumented with shape memory alloy (SMA) actuators using image guidance. An Augmented Hybrid Impedance Control (AHIC) algorithm is implemented on a Mitsubishi robot (PA 10-7C) to insert the active catheter. The robot is constrained to move in Cartesian space along a pre-defined trajectory while controlling the force of insertion. A closed-loop control scheme has been developed to accurately control the bending in the active catheter. The tip of the active catheter is tracked in real-time to provide information on the path of the catheter and for determining the future course of insertion. The catheter is autonomously guided from the point of entry to the site of plaque buildup, thereby shielding the surgeon from the harmful radiation due to the X-rays used for imaging, providing a more ergonomic approach for catheter insertion. Experimental results are given to illustrate the robot-assisted catheter insertion procedure.

In the recent years, there has been considerable interest in developing active catheters instrumented with shape memory alloy (SMA) actuators to perform angioplasty. The problem, however, with SMA actuators is the extremely non-linear response of the strain with input current. Therefore, control of such an active catheter inside the body is inaccurate and which could lead to unforeseen damage. In this paper, a novel model for SMAs and a robust Hinfinloop-shaping controller has been implemented to guarantee robust performance of the active catheter. A closed-loop control algorithm has been implemented to precisely orient the catheter in space based on feedback from a 5-DOF magnetic sensor. The active catheter tracks a reference trajectory generated either by a haptic device under the control of a user or from an image processing algorithm which determines the angle of a branch in the vasculature.

Minimally invasive surgery is a technique that provides numerous benefits to the patient, but presents challenges to the surgeon in that dexterity, hand-eye coordination and haptic perception are compromised. Robot-assisted minimally invasive approaches have addressed the problems of dexterity and coordination; however, the lack of kinesthetic and tactile feedback remains a significant drawback. Despite many advances in this area, little is currently known about what level of feedback performance is adequate to allow the surgeon to palpate tissue to detect an underlying tumour. This paper describes experiments that were conducted on ex-vivo porcine lung, using artificial tumours, to elucidate one measure of sensor performance required to detect the presence of a tumour. The results indicate that a force- sensitive probe with a sensing range of 0 to 10 N and a resolution of 0.01 N would allow a tumour to be localized via palpation using kinesthetic feedback.

Discretization of a stabilizing continuous-time bilateral teleoperation controller for digital implementation may not necessarily lead to stable teleoperation. This paper addresses the stability of master-slave teleoperation under discrete-time bilateral control. Stability regions are determined in the form of conditions involving the sampling period, control gains including the damping introduced by the controller, and environment stiffness. Due to the tradeoff between stability and transparency in bilateral teleoperation, such stability boundaries are of particular importance when the teleoperation system has good transparency.

An experimental test-bed for robot-assisted image-guided minimally invasive lung brachytherapy has been developed. The setup includes surgical robots, a device to accurately drop brachytherapy seeds, an ultrasound system, electromagnetic trackers, and navigational software. An evaluation using the test-bed was performed to compare the open procedure and the video-assisted thoracoscopic procedure with the proposed robot-assisted minimally invasive procedure under ultrasound image guidance and electromagnetic tracking. The results show that the use of robotic systems and image guidance can provide improved seed placement accuracy as compared to open surgery, while reducing the invasiveness of the procedure and trauma to the patient's body.

In prostate brachytherapy, multiple seeds are implanted during each needle insertion, and the locations of these seeds are dependent on the track of the needle shaft inside the tissue. Therefore, the track of needle shaft is as important as the placement of the needle tip on the outcome of this procedure and the effectiveness of therapy. In this study, the needle is rotated at particular locations during insertion in order to maintain the needle on a desired track. To define locations of rotation, a needle deflection model based on Euler-Bernoulli beam bending equations is proposed. This model estimates the reciprocal of the needle curvature and predicts the needle tip position based on real-time force/moment feedback prior to the first rotation. The needle tip position is then predicted based on needle motion on a circular segment. Tissue deformation resulting from needle deflection is also measured during insertions. In order to validate the performance of the proposed method, experimental results are presented for robot-assisted needle insertion in animal phantoms.

This paper presents an actuator Fault Detection and Isolation (FDI) scheme for nonlinear systems. A state space approach is used and a nonlinear-in-parameters neural network (NLPNN) is employed to identify the additive unknown fault. The FDI scheme is based on a hybrid model (composed of an analytical nominal model and a neural network model) of the nonlinear system. The nominal performance of the system in fault free operation is governed by analytical model whereas the uncertainties and unmodeled dynamics are accounted for by intelligent (neural network based) model. The neural network weights are updated based on a modified backpropagation scheme. The stability of the overall fault detection scheme is shown using Lyapunov's direct method. To evaluate the performance of the proposed fault detection scheme, FDI in a spacecraft attitude control systems with reaction wheel type of actuators is considered as a case study. Simulation results are presented to show the effectiveness of the proposed fault detection scheme.

In this paper, the application of a piezoelectric stack actuator for vibration control in a large-scale robotic manipulator, called a macromanipulator, is studied. In this regard, mechanical design and mathematical modeling of the actuator are discussed. The structural flexibility of the macromanipulator includes deflection and torsional vibration modes. The vibration modes are detected using appropriate sensor attachments. Furthermore, a nominal transfer function matrix between the input signals to the actuators and the output voltages of the sensors is obtained. A closed-loop controller based on the obtained model is designed. Because of the presence of deflection and torsional vibration modes and model uncertainties resulting from manipulator motion, an robust controller is utilized. Experimental results are presented to validate the robustness and performance of the designed controller.

The lack of a potential field model capable of providing accurate representations of objects of arbitrary shapes is considered one major limitation in applying the artificial potential field method in many practical applications. In this correspondence, we propose a potential function based on generalized sigmoid functions. The generalized sigmoid model can be constructed from combinations of implicit primitives or from sampled surface data. The constructed potential field model can achieve an accurate analytic description of objects in two or three dimensions and requires very modest computation at run time. In this correspondence, applications of the generalized sigmoid model in path-planning tasks for mobile robots and in haptic feedback tasks are presented. The validation results in this correspondence show that the model can effectively allow the user or mobile robot to avoid penetrations of obstacles while successfully accomplishing the task.

In master-slave teleoperation applications that deal with a delicate and sensitive environment, it is important to provide haptic feedback of slave/environment interactions to the user's hand as it improves task performance and teleoperation transparency (fidelity), which is the extent of telepresence of the remote environment available to the user through the master-slave system. For haptic teleoperation, in addition to a haptics-capable master interface, often one or more force sensors are also used, which warrant new bilateral control architectures while increasing the cost and the complexity of the teleoperation system. In this paper, we investigate the added benefits of using force sensors that measure hand/master and slave/environment interactions and of utilizing local feedback loops on the teleoperation transparency. We compare the two-channel and the four-channel bilateral control systems in terms of stability and transparency, and study the stability and performance robustness of the four-channel method against nonidealities that arise during bilateral control implementation, which include master-slave communication latency and changes in the environment dynamics. The next issue addressed in the paper deals with the case where the master interface is not haptics capable, but the slave is equipped with a force sensor. In the context of robotics-assisted soft-tissue surgical applications, we explore through human factors experiments whether slave/environment force measurements can be of any help with regard to improving task performance. The last problem we study is whether slave/environment force information, with and without haptic capability in the master interface, can help improve outcomes under degraded visual conditions.

Angioplasty is a minimally invasive procedure wherein a catheter (a thermoplastic hollow wire) is inserted into the femoral artery and guided till it reaches a blockage in the blood vessel. There could be some potential complications arising from the conventional way of performing angioplasty, e.g., damage to the blood vessel due to excessive force of insertion and exposure of clinicians to harmful radiations and/or high levels of noise from an MRI machine. In this paper, we investigate the use of a robot manipulator (Mitsubishi PA 10-7C) to aid in the insertion of a catheter into a blood vessel. The robot controls the insertion force while the surgeon can remotely operate the robot from a safe and comfortable environment. The paper describes a hybrid impedance control scheme implemented on the Mitsubishi robot to perform simultaneous force/position control. The robot is used in experiments to insert a catheter into a test-bed by controlling the force of insertion and preventing the catheter from buckling or "bunching up". Experimental results for the insertion algorithms are shown

In this paper, the application of a piezoelectric stack actuator for vibration control in a large-scale robotic manipulator, called the macro manipulator, is studied. The structural flexibility of the system includes deflection and torsional vibration modes. The vibration modes are detected using an appropriate sensor attachment. A nominal transfer function matrix between the input signals of the actuators and the output voltages of the sensors is obtained. A closed-loop controller based on the obtained model is designed. Because of the presence of different vibrational modes and model uncertainties resulting from manipulator motion as well as its varying payloads, an Hinfinrobust controller is utilized and experimental results are presented

In robot-assisted interventions, providing a surgeon with haptic information regarding contacts made between surgical instruments and tissue can improve task performance and reliability. In this paper, a force-reflective user interface is used with a sensorized surgical instrument to form a master-slave test-bed for studying haptic interaction in a soft-tissue endoscopic surgery environment. After modeling and parametric identification of the master and the slave, bilateral controllers are designed and teleoperation experiments involving a single degree of freedom surgical task on soft tissue (palpation) are conducted. The transparency of the teleoperator in terms of transmitting the critical task-related information to the user in the context of soft-tissue surgical applications is investigated

A device for robot-assisted brachytherapy has been designed for use with a minimally-invasive surgical robot such as the ZEUStrade It may be loaded with a standard brachytherapy needle allowing the robot to position its tip at a specified location within cancerous tissue. The device accurately retracts a hollow needle loaded with radioactive seeds while a stationary plunger pushes the seeds out into the tissue. The position error when retracting the needle is less than 0.05 mm. The use of this device, together with image-guidance for needle placement, can improve radiation dose delivery when treating certain types of lung cancer. The incorporation of this device into robotic systems that are already approved for clinical use can potentially allow it to be commercialized much sooner than competitive technology

In this paper, the stability problem of neural network based observers/identifiers for nonlinear systems is revisited when nonlinear-in-parameter neural networks (NLPNN) are employed. The proposed approach is based on decomposing the neural network into two subsystems. The first subsystem (Subsystem 1) consists of the estimation error and output-layer weight error and the second subsystem (Subsystem 2) consists of the hidden-layer weight error. The key to this decomposition is that the hidden-layer weights appear in Subsystem 1, only as an argument of a sigmoidal function and its derivative which are both known to be bounded. This allows us to regard the Subsystem 1 as a linear-in-parameter neural network (LPNN) whose stability proof is more straightforward. Having shown the stability of the first subsystem, the stability of the second subsystem is also shown subsequently without the requirement of having the limiting assumptions of previous work. The bound on estimation error can be made arbitrarily small by proper selection of design parameters. The estimation scheme is then employed to estimate the state of flexible joint manipulators.

An actuated robot arm is designed for use as a macro manipulator that can carry, appropriately orient, precisely position and firmly "lock" in position different types of micro robots and surgical tools necessary for applications in minimally invasive therapy. The sophisticated configuration and joint structure of the arm enable it to perform and interact efficiently with the constrained and limited workspace of surgical environments. The normally locked braking system and the simple quick release joint enhance the safety features of the robot for emergencies and power shutdown. With a simple manipulation protocol, the surgeon can use the robot without undergoing any training. Robot workspace analysis indicates that all singularities are outside the operating work envelope. A performance analysis shows that the robot operates with an average displacement accuracy of 0.58 mm and a roll, pitch and yaw angular accuracies of 0.26deg, 0.26deg and 0.38deg respectively.

A stable neural network (NN)-based observer for general multivariable nonlinear systems is presented in this paper. Unlike most previous neural network observers, the proposed observer uses a nonlinear-in-parameters neural network (NLPNN). Therefore, it can be applied to systems with higher degrees of nonlinearity without any a priori knowledge about system dynamics. The learning rule for the neural network is a novel approach based on the modified backpropagation (BP) algorithm. An e-modification term is added to guarantee robustness of the observer. No strictly positive real (SPR) or any other strong assumption is imposed on the proposed approach. The stability of the recurrent neural network observer is shown by Lyapunov's direct method. Simulation results for a flexible-joint manipulator are presented to demonstrate the enhanced performance achieved by utilizing the proposed neural network observer.

This paper investigates the inherent oscillation problem of potential field methods (PFMs) in the presence of obstacles and in narrow passages. These problems can cause slow progress and system instability in implementation. To overcome these two problems, in this paper, we propose a modification of Newton's method. The use of the modified Newton's method, which applies anywhere C/sub 2/ continuous navigation functions are defined, greatly improves system performance when compared to the standard gradient descent approach. To the best of our knowledge, ours is the first systematic approach to the oscillation problems in PFMs. We have validated this technique by comparing its performance with the gradient descent method in obstacle-avoidance tasks with different potential models and parameter changes.

In this paper, the application of high control authority piezoelectric stack actuators, in short piezostack actuators, for active vibration control of long-reach robotic manipulators is studied. The idea is to include piezostack actuators in the base structure in order to strengthen its stiffness characteristics. A mechanism is designed for converting the force produced by a piezostack actuator to a bending moment. A flexible link actuated with a piezostack actuator is built and mathematically modeled. The solution of the governing partial differential equation with non-homogenous boundary conditions is obtained. A comparison between experimental frequency response of the system and its model is given. A control law using the Popov criterion is obtained and experimental results for closed-loop system are given.

Accurate and proper placement of ports during robotically-assisted endoscopic surgery is critical to the success of the procedure. Improper placement of ports can lead to robot collisions, the inability to reach the surgical site, the inability to manipulate the tools properly, or collisions between the tools inside the patient’s body. In current practice, port placement methods do not consider the ability of the robot to manoeuvre the tools. Furthermore, there is a lack of guidance on what the position of the robot or the configuration of its arms should be. This paper proposes to choose the best port location and determine the position of the base and arms of the robot such that its performance is maximized. Performance measures developed in the past to optimize robot design and manipulation are used to optimize the placement of ports when using a surgical manipulator for artery dissection during coronary bypass surgery.

Most conventional motion planning algorithms that are based on the model of the environment cannot perform well when dealing with the navigation problem for real-world mobile robots where the environment is unknown and can change dynamically. In this paper, a layered goal-oriented motion planning strategy using fuzzy logic is developed for a mobile robot navigating in an unknown environment. The information about the global goal and the long-range sensory data are used by the first layer of the planner to produce an intermediate goal, referred to as the way-point, that gives a favorable direction in terms of seeking the goal within the detected area. The second layer of the planner takes this way-point as a subgoal and, using short-range sensory data, guides the robot to reach the subgoal while avoiding collisions. The resulting path, connecting an initial point to a goal position, is similar to the path produced by the visibility graph motion planning method, but in this approach there is no assumption about the environment. Due to its simplicity and capability for real-time implementation, fuzzy logic has been used for the proposed motion planning strategy. The resulting navigation system is implemented on a real mobile robot, Koala, and tested in various environments. Experimental results are presented which demonstrate the effectiveness of the proposed fuzzy navigation system.

In this paper the application of high control authority piezostack actuators (PSA) for active vibration control in flexible manipulators is studied. The idea is to incorporate the piezostack actuators into the system in order to strengthen its stiffness characteristics. In this regard a cantilever beam actuated with piezostack actuators is considered. A mechanism for converting the blocking force of the PSA to a bending moment is studied and a model for the whole system consisting of a flexible beam and B A is obtained. The simulation results show that the suggested method may open new possibilities in active vibration control of large flexible manipulator.

In this paper, friction compensation in robotic manipulators is studied. An observer based model of the friction force is utilized for the friction compensation algorithm. In order to evaluate the efficiency of this method two different manipulators with different friction characteristics are examined. A 2-DOF manipulator used for high-speed, micro-meter precision manipulation and a 4-DOF macro manipulator used for long reach positioning task are examined. These manipulators are characterized, according to compensation task classifications (Armstrong, B. et al., 1994), as high-reversal-velocity and low-reversal-velocity tracking tasks, respectively. In each case a steady-state model of friction is experimentally obtained. This model is further utilized in dynamic equations of the friction force during manipulation. It is shown that despite the different nature of the two manipulators the same method can effectively improve the speed and performance of the manipulation in both cases.

Minimally invasive surgery (MIS) is an alternative to open surgery where special instruments are inserted into the body cavity through tiny incisions in order to perform surgical procedures. In this work, some design issues in a master-slave robotic system for use in MIS are discussed. First, we discuss the design of a user interface that can be used to incorporate haptic interaction in robot-assisted MIS. Then we discuss the design of a laparoscopic end effector that meets MlS requirements and is instrumented for haptic feedback.

Distributed multi-robot systems have attracted considerable attention over the past few decades. Multiple robots performing tasks together in a cooperative manner can have a significant advantage over a single robot, especially in parts assembly and load sharing between two or more coordinated robots. Most multi-robot systems are hard real-tune systems and require real-time scheduling. Many real-time schedulers have been discussed including round-robin, earliest-deadline-first (EDF), minimum-laxity-first (MLF), least-slack-time-first (LST), etc. Unfortunately, none of these schemes provide enough support for relative task constraints and timing constraints that are commonly used in multi-robot systems. This paper gives a task-oriented scheduling method that can help guarantee the safety, reliability and time deadline of a distributed multi-robot system. Experiments show that with the proposed algorithm, both the timing constraints and relative task interdependencies can be satisfied.

Minimally invasive surgery involves inserting special instruments into the body cavity through tiny incisions in order to perform surgical procedures. In this paper, the design of a robotic master-slave system for use in minimally invasive surgery is discussed. This system is capable of providing haptic feedback to the surgeon in all available degrees of freedom. System design as well as master and slave bilateral control and communication issues are discussed.

In this paper, we first describe some "goal-unreachable" problems found in fuzzy logic-based algorithms for mobile robot navigation systems. Then, a new algorithm is developed to solve one of the problems, i.e., a problem with nearby obstacles. The resulting navigation system has been implemented on a real mobile robot, Koala, and tested in various environments. Experimental results are presented which demonstrate the effectiveness and improvement of the resulting fuzzy navigation system over conventional fuzzy-logic navigation algorithms.

Internet-based telerobotic systems have been evolving rapidly in recent years. Using Web-based technology, telerobotic systems have been shown to have an increasing potential for a variety of applications including remote control, manufacturing, surgery, training, and education. In this paper, we present an Internet-based distributed, multiple-telerobot system that enables operators to use remote robots in order to perform cooperative tasks. Several multiple-telerobot demonstration programs have been designed, including a single telerobot training program, a multiple-telerobot "group object-handling" program, and pairs of telerobots serving Internet participants playing with a Rubik's Cube to illustrate Internet-based interaction and collaboration. Experimental tests have been performed on three demonstration programs that are presented in this paper.

This paper discusses the selection process for piezoelectric transducers (PZT) used as actuator elements for suppressing vibrations in a flexible beam system. The effects of changing physical parameters such as the relative thickness of the piezoelectric ceramic with respect to the beam, the optimum location of the PZT actuator, and the length of the PZT are studied based on the singular value decomposition of the controllability Grammian of the resulting system. A model for a clamped-mass cantilevered beam is developed and its frequency response is compared with that obtained experimentally. Simulation results are given to illustrate how this method can be used to determine physical properties and location of the PZT actuator. Further experimental studies are currently being performed.

The problem of controlling a discrete-time nonlinear non-minimum phase system is considered. An output re-definition strategy is developed which is applicable to a class of open-loop stable nonlinear systems whose input-output maps contain nonlinear terms from the output and linear terms from the input. No a priori knowledge about the nonlinearities of the system is required. The output re-definition scheme is based on first identifying the nonlinearities of the system using neural networks and then modifying the system zero dynamics. A stable/anti-stable factorization is performed on the zero dynamics of the system. The new output is re-defined using, the neural identifier and the stable part of the zero dynamics. A controller is then designed based on the new output whose zero dynamics are stable and can be inverted. Simulation results are resented to show the effectiveness of the proposed control scheme as compared to both linear and nonlinear conventional controllers.

This paper deals with identification of a two-link flexible manipulator belonging to a class of multi-input, multi-output (MIMO) nonlinear systems, by using adaptive time delay neural networks (ATDNNs). Two neuro-dynamic identifiers are proposed. The capabilities of the proposed structures for representing the nonlinear input-output map of the flexible manipulator are shown analytically. Selection criteria for specifying the fixed structural parameters as well as the adaptation laws for updating the adjustable parameters of the networks are provided. During identification, the two-link flexible manipulator is under nonlinear control and the input-output data sets are generated for different desired trajectories. Simulation results reveal that the proposed neuro-dynamic structures are capable of successfully identifying a highly nonlinear system without any a priori information about the nonlinearities of the system and without any off-line training.

The problem of controlling the tip position of a flexible-link manipulator is considered. The control strategy is based on an output re-definition approach which is applicable to a class of non-minimum phase nonlinear systems whose nonlinearities appear in output terms in their input-ouput mappings and are open-loop stable. The controller is composed of a stabilizing joint PD controller and an output re-definition tracking controller. The output re-definition scheme is based on modifying the zero dynamics of the system using a stable/anti-stable factorization. The controller is then designed based on the new output whose zero dynamics are stable and can be inverted. Experimental results are also presented to show the effectiveness of the proposed control scheme as compared to a PD controller.

The problem of tracking a Cartesian space trajectory for an object held by two redundant robots while controlling the contact force and the object's internal force is investigated in this paper. A two-level impedance control (TLIC) algorithm incorporating an error reference controller (ERC) is developed. This algorithm is robust to system and environmental kinematic and dynamic uncertainties. Joint redundancy is used to fulfil additional tasks such as singularity robustness. The control algorithm is applicable to dual independent as well as closed-chain robot control. The algorithm has been extensively tested using a computer simulation of the full dynamic model of a dual-arm experimental redundant system in our Robotics and Control Systems Laboratory. The algorithm has also been implemented on the dual-arm experimental system. Experimental results that illustrate various features of the dual-arm control algorithm are presented in this paper.

The problem of controlling a nonminimum phase nonlinear system with application to tip position control of a flexible-link manipulator is considered. An output re-definition strategy is developed which is applicable to a class of open-loop stable nonlinear systems whose input-output maps contain nonlinear terms from output and linear terms from input. No a priori knowledge about the nonlinearities of the system is required. The output re-definition scheme is based on first identifying the nonlinearities of the system using neural networks and then modifying the system zero dynamics. A stable/anti-stable factorization is performed on the zero dynamics of the system. The new output is re-defined using the neural identifier and the stable part of the zero dynamics. A controller is then designed based on the new output whose zero dynamics are stable and can be inverted. For the flexible-link manipulator case, the controller is composed of a stabilizing joint PD controller and an output re-definition tracking controller. Experimental and simulation results are presented to show the effectiveness of the proposed control scheme as compared to both linear and nonlinear conventional controllers.

We present a control scheme for high-speed vibration-free positioning of a system consisting of a rigid manipulator mounted on a flexible base. The objective is to move the end-point of this macro-micro manipulator system rapidly by proper motion of the micro-manipulator and without inducing structural vibrations when the joints of the flexible macro-manipulator are locked. It is shown by an example that the system is in general non-minimum phase. A control strategy is developed for rapid positioning of the end-effector of the micro-manipulator that will achieve the above goal. Simulation results are presented for a two-link manipulator mounted on a flexible boom.

Experimental evaluation of the performance of neural network-based controllers for tip position tracking of flexible-link manipulators is presented. A modified output re-definition approach is utilized to overcome the problem caused by the non-minimum phase characteristic of the flexible-link system. This modification is based on using minimum a priori knowledge about the system dynamics. The modified output redefinition approach requires a priori knowledge about the linear model of the system and no a priori knowledge about the payload mass. Four different neural network schemes are proposed. The neural networks are trained and employed as online controllers. The four proposed neural network controllers are implemented on a single flexible-link experimental test-bed. Experimental and simulation results are presented to illustrate the advantages and improved performance of the proposed tip position tracking controllers over conventional PD-type controllers in the presence of unmodeled dynamics.

This paper presents dynamic modeling of flexible link manipulators using artificial neural networks. A state-space representation is considered for a neural identifier. The recurrent network configuration is obtained by a combination of feedforward network architectures with dynamical elements in the form of stable filters. To guarantee the boundedness of the states, joint PD control is introduced in the system. The method can be considered both as an online identifier that can be used as a basis for designing neural network controllers as well as an off-line learning scheme to compute deflections due to link flexibility for evaluating forward dynamics. The performance of the proposed neural identifier is evaluated by identifying the dynamics of different flexible-link manipulators. To demonstrate the effectiveness of the algorithm, simulation results for a single-link manipulator, a two-link planar manipulator and the Space Station Remote Manipulator System (SSRMS) are presented.

The problem of redundant manipulator collision avoidance in an unstructured environment is addressed in this paper based on the concept of modified impedance control. Instead of using a limited degree of redundancy (as in conventional methods) to find a collision-free trajectory, in the proposed approach, a robot's commanded joint torques are augmented by an "artificial" joint torque to provide correction for collision avoidance. "Artificial" collision forces are generated online according to the robot's posture and environment information (through knowledge of the robot kinematics and environment or proximity sensors on the robot). The corresponding artificial collision forces are converted to equivalent joint torques that would accomplish the collision avoidance manoeuvre. Then, the commanded joint torques are augmented so that a collision-free joint torque profile is achieved. Robot-to-environment collisions, robot self-collisions and robot constraints such as joint limit and singularity avoidance can be achieved using this method.

This paper focuses on the experimental implementation of an observer-based decoupling control strategy for tip-position tracking of a class of multilink flexible manipulators. The control strategy is based on output redefinition and input-output decoupling that was studied by the authors in an earlier paper. Since the rates of change of flexible modes are required, a nonlinear observer is implemented to estimate these variables. Experimental results are given for the case of a two-link flexible manipulator that further confirm the theoretical and simulation results. The closed-loop performance under different observation schemes is evaluated and compared to the case when conventional methods are used.

This paper presents neural network based adaptive controllers for a single flexible-link manipulator. The control is designed by using the output re-definition approach. Three different neural network schemes are examined. None of the schemes requires full state measurements. The neural network controllers are implemented on a single flexible-link experimental test-bed. Experimental and simulation results are presented to illustrate the advantages and improved performance of the proposed tip position tracking controllers over the conventional PD-type controller.

This paper presents a new control algorithm for eliminating flexible structure residual oscillations. The pulse active damping (PAD) algorithm is developed and applied on the Space Shuttle Remote Manipulator System (RMS), which is probably the best existing example of a practical flexible manipulator. The proposed control algorithm is activated at the end of an RMS manoeuvre in order to damp out the end-effector oscillation in a fast manner. Basically, this is achieved by injecting torque pulses at the shoulder yaw and shoulder pitch joints so that associated cancelling oscillations at the end-effector are excited to "cancel" out the observed in-plane and out-of-plane end-effector vibrations. Robustness of this algorithm to the estimated natural frequency of the system is addressed and improved by a two-pulse control scheme. It is shown that high oscillations can be eliminated efficiently by PAD.

In this paper, a nonlinear control strategy for tip position trajectory tracking of a class of structurally flexible multilink manipulators is developed. Using the concept of integral manifolds and singular perturbation theory, the full-order flexible system is decomposed into corrected slow and fast subsystems. The tip-position vector is similarly partitioned into corrected slow and fast outputs. To ensure an asymptotic tracking capability, the corrected slow subsystem is augmented by a dynamical controller in such a way that the resulting closed-loop zero dynamics are linear and asymptotically stable. The tracking problem is then redefined as tracking the slow output and stabilizing the corrected fast subsystem by using dynamic output feedback. Consequently, it is possible to show that the tip position tracking errors converge to a residual set of O(/spl epsiv//sup 2/), where /spl epsiv/ is the singular perturbation parameter. A major advantage of the proposed strategy is that the only measurements required are the tip positions, joint positions, and joint velocities. Experimental results for a single-link arm are also presented and compared with the case when the slow control is designed based on the rigid-body model of the manipulator.

In this paper, an index of optimization is proposed for improving the dynamic behavior of structurally flexible manipulators. The improvement is achieved through an optimization scheme where a cost function associated with the lowest natural flexible mode and an index defined as modal accessibility, is optimized subject to certain constraints. The formulation assumes a singularly perturbed model of the flexible-link system as this system possesses two-time scale properties. To illustrate the approach, the design of a two-link, non-uniform, planar, flexible manipulator is considered which results in improved performance characteristics as compared to a uniform manipulator.

In this paper a nonlinear control strategy for tip position trajectory tracking of a class of structurally flexible multi-link manipulators is developed. Using the concept of integral manifolds and singular perturbation theory, the full-order flexible system is decomposed into corrected slow and fast subsystems. The tip position vector is similarly partitioned into corrected slow and fast outputs. To ensure an asymptotic tracking capability, the corrected slow subsystem is augmented by a dynamical controller in such a way that the resulting closed-loop zero-dynamics are linear and asymptotically stable. The tracking problem is then re-defined as tracking the slow output and stabilizing the corrected fast subsystem by using dynamic output feedback. A major advantage of the proposed strategy is that the only measurements required are the tip positions, joint positions, and joint velocities.

This paper focuses on the tip-position control of a single flexible link which rotates in the horizontal plane. The dynamic model is derived using a Lagrangian assumed modes method based on Euler-Bernoulli beam theory. The model is then linearized about an operating point. An output feedback control strategy that uses the principle of transmission zero assignment achieves tracking for this nonminimum phase linear time-invariant system. The control strategy consists of two parts. The first part is an inner (stabilizing) control loop that incorporates a feedthrough term to assign the system's transmission zeros at desired locations in the complex plane, and a feedback term to move the system's poles to appropriate positions in the left-half plane. The second part is a feedback servo loop that allows tracking of the desired trajectory. The controller is implemented on an experimental test-bed. The performance is compared with that of a second controller based on pole placement state feedback.

The problem of controlling robot manipulators with flexible joints is considered. A reduced-order flexible-joint model based on a singular perturbation formulation of the manipulator equations of motion is used. The concept of an integral manifold is utilized to construct the dynamics of the slow subsystem. A fast subsystem is constructed to represent the dynamics of the elastic forces at the joints. A composite adaptive control scheme is developed with special attention to stability and robustness of the controller. The proposed controller is based on online identification of the manipulator parameters and takes into account the effect of a class of unmodeled dynamics, identification errors, and parameter variations. Stability analysis of the resulting closed-loop full-order system is presented. To show the capability of the proposed algorithm, an example of a two-link flexible-joint manipulator is considered. Simulation results are given to illustrate the applicability of the proposed control scheme.>

The kinematic design of redundant seven-axis manipulators is addressed. It is shown that isotropic seven-axis manipulators are possible. Three different optimum solutions are presented: first, a nonlinear minimization problem is solved which, in effect, renders the Jacobian matrix fully isotropic. Next, it is argued that, despite the fully isotropic feature of the first solution, some of its structural features can be improved. This leads to pre-assigning some of the parameters defining the structure of the manipulator, resulting in a system of 21 nonlinear equations in 21 unknowns. As the second solution, the Hartenberg-Denavit parameters of an isotropic manipulator are then obtained by solving the said system of nonlinear equations. Further constraints to make the manipulator structure anthropomorphic yield a third solution. This last solution gave rise to a manipulator which is not fully isotropic but is very close to isotropy, and exhibits a greater resemblance to the structure of the human arm.>

Various neural models are considered for solving the robot forward kinematics problem. It is demonstrated that a three-layer backpropagation network is capable of learning the forward kinematics of a rigid-link, open-chain manipulator without knowledge of the manipulator's kinematic structure. Simulation results show that, by properly training such a network, it is possible to model the forward kinematics with an acceptable degree of accuracy. However, it is also shown that, if information about the kinematic structure of a manipulator is available, a functional link network gives, by far, the most accurate results

The problem of using a manipulator to catch a moving object without any advanced knowledge of its trajectory is discussed, and a heuristic procedure is proposed. The method is divided into two parts: a coarse tuning algorithm first drives the end effector into the neighborhood of the object in near-minimum time; a finite tuning algorithm then provides precise matching of the object's trajectory to ensure the relative velocity and acceleration at the time of grasping. The resulting sensor-based system is simulated for a two-degree-of-freedom planar robot with a highly nonlinear object path. The approach can rapidly be extended to six-degree-of-freedom manipulators.>

A modeling scheme that uses the concepts of generalized and augmented links is proposed for computing joint-space inertia matrices of open-chain rigid body systems. Expressions for evaluating these matrices are derived, utilizing orthogonal Cartesian tensors and the Newton-Euler equations of motion. The resulting recursive algorithm is applicable to all rigid-link manipulators having open-chain kinematic structures with revolute and/or prismatic joints. An efficient implementation of the algorithm shows that the joint-space inertia-matrix of a six degree-of-freedom manipulator with revolute joints can be computed in approximately 420 multiplications and 339 additions. For manipulators with 0 degrees to 90 degrees twist angles, the number of computations is reduced to 271 multiplications and 250 additions.>

Orthogonal second-order Cartesian tensors are used to formulated the Newton-Euler dynamic equations for a robot manipulator. Based on this formulation, an efficient recursive procedure is developed to evaluate the joint torques. The procedure is applicable to all rigid-link manipulators with open-chain kinematic structures with revolute and/or prismatic joints. For simplicity of presentation, only manipulators with (kinematically more complex) revolute joints are considered. An efficient implementation of the proposed method shows that the joint torques for a six-degree-of-freedom manipulator with revolute joint, can be computed in approximately 500 multiplications and 420 additions. For manipulators with 0 degrees or 90 degrees twist angles, the required computations are reduced to 380 multiplications and 315 additions.>

An overview is presented of a micromanipulator vision system for use in automating various functions during the testing of a wafer for semiconducting parameters and inspection of VLSI circuits. Positioning the probe and touching a test pad are the chief concern of the work desired. A brief description of the experimental setup is given. The image processing techniques used in identifying and controlling the location of various components such as the probes and the test pads are discussed. The vision modules and an expert system using hierarchical plan generation to control the sequence of plans are included.>

The authors use orthogonal second-order Cartesian tensors to formulate the Newton-Euler dynamic equations for a robot manipulator. Based on this formulation, they develop two efficient recursive algorithms for computing the joint actuator torques/forces. The proposed algorithms are applicable to all rigid-link manipulators with open-chain kinematic structures with revolute and/or prismatic joints. An efficient implementation of one of the proposed algorithms shows that the joint torques/forces for a six-degrees-of-freedom manipulator with revolute joints, can be computed in approximately 489 multiplications and 420 additions. For manipulators with zero or 90 degrees twist angles, the required computations are reduced to 388 multiplications and 370 additions. For manipulators with even simpler geometric structures, these arithmetic operations can be further reduced to 277 multiplications and 255 additions.>

A computational method for recursive evaluation of linearized dynamic robot models about a nominal trajectory is presented. The forward method evaluates the "sensitivity matrices" necessary to calculate the "forward" dynamics of the linearized model. The method has made efficient by using the fact that the derivatives of trigonometric functions need not be computed explicitly and that the partial derivatives of the homogeneous transformation matrices, may be obtained merely by row and column manipulations. The proposed scheme is general in nature and can be applied efficiently to manipulators having revolute and prismatic joints.