In clinical practice, magnetic resonance imaging (MRI) is used to locate a lesion/tumor for bone biopsy in children. However, there is a lack of MR-compatible tools that can be used simultaneously during imaging and biopsy while maintaining surgical accuracy and safety. The Pediatric Surgery Robot (PSR) platform is a 5-DOF robot with a modular tool interface. For the case of bone biopsy, a Bone Biopsy Tooling (BBT) is attached. It is designed to fit within a Philips Achieva 3.0T MRI bore and carry a modified titanium bone biopsy needle. A surgical pre-planning and control interface has been developed for joint and Cartesian level control. The PSR-BBT has demonstrated 1.65 +/- 1.77 mm accuracy in Cartesian control in free space. The PSR-BBT can generate 12.46 +/- 0.32 N of axial force while drilling at a speed of 30 rpm, which is sufficient for cortical and cancellous bone phantoms. Under MRI testing (T1-FFE, T1-SE, T2-FFE and T2-TSE scans), the system demonstrated less than 33% signal-to-noise ratio variation while drilling and a 0.46% geometric distortion while powered on without significantly impacting MRI guidance in situ. These results show that the PSR-BBT can allow the user to simultaneously image and perform the biopsy and presents the PSR as a viable platform for MR-guided robotic surgery.

This paper presents a new mobile robot design based on hybridization of the mobile platform and manipulator arm as one entity for robot locomotion as well as manipulation. The novel mechanical design is described in detail. To analyse the design, a virtual prototype tool was developed with ADAMS software for multi-body dynamic motion simulations of the complete robotic system. The simulation results were used to study the robot's mobility characteristics through animations of different possible tasks that require various locomotion and manipulation capabilities. The ability to visualize and validate various robot mobility cases and to study its functionality in the early design stages aided in optimizing the design and hence dramatically reduce physical prototype development time and cost. The design optimization process also involved proper components selection. Moreover, the simulations enabled us to define motor torque requirements and maximize end-effector payload capacity for different robot configurations.

A modular and reconfigurable robot (MRR) with multiple working modes is developed for performing sophisticated tasks in uncontrolled environments. In the proposed MRR design, each joint module can independently work in active modes with position or torque control, or passive modes with friction compensation. Under a federated control system architecture, not only the MRR configuration can be reconfigured to adapt to various tasks, but also the working mode of each module, which can be switched on-line to satisfy the needs to carry out sophisticated tasks. Three joint modules have been developed, and the proposed method of passive working mode implementation with friction compensation has been tested experimentally. Door opening using a mobile manipulator consisting of the developed joint modules is studied as an application case study of the proposed multiple working mode MRR.

In this paper, the design paradigm for a novel modular tele-robtoic system for MRI-guided neurosurgery is presented. Clinical requirements and design parameters are discussed. The overall infrastructure for MRI-guided intervention is addressed. The major focus is the application of the designed MR-compatible robotic system to MRI-guided brain biopsy. Candidate neurosurgical procedures enabled by this system include thermal ablation, radiofrequency ablation, deep brain stimulators DBS, and targeted drug delivery considering the modular structure of the slave manipulator. The mechanical design and preliminary MR-compatibility experiments are reported.

Micro-electro-mechanical system (MEMS) is one of the few commercial platforms for building optical switches. 2D MEMS L-switching matrix has been introduced recently to double sizes of 2D MEMS crossbar switches. The sizes of the switches are mainly limited by the Gaussian signal loss associated path difference. Though the design of L-switching matrix improves system scalability but it suffers internal blocking problem. In this paper, a rearrangeably nonblocking algorithm will be presented. Moreover, two enhanced designs are proposed to improve the overall system performance of the L-switching matrix. They are the staircase switching mechanism and redundant switching system. With the improved internal blocking probability can be minimized. Consequently, the L-switching probability can be minimized. Consequently, the L-switching matrix performs similar to an optical switching fabric with wide-sense nonblocking property.

Explosion in Internet applications has stimulated active research activities in expanding the capability of the current telecommunication networks. These activities include implementing faster electronics to process the higher data bit rates, or developing wavelength division multiplexing (WDM) techniques, and novel optical networks components to increase the information carrying capacity of the optical networks. As the data bit rates increases, it will become increasingly difficult to implement an electronic switching fabric solution. It is known that the information carrying laser beams should be dealt with at the optical level. One of most promising optical network components is micromachined optical cross connect switches. We present a new crossbar switching design methodology that decreases the number of mirrors and electrodes needed while maintaining the same non-blocking port switching capability. More importantly, this new architecture also reduces the distance of free-space propagation of light beams, thus reducing the loss due to Guassian-beam divergence during free-space propagation of light.

The problem of friction compensation at very low velocity is investigated experimentally. Two published friction compensation strategies, based on two well-known friction models, are evaluated experimentally on a direct drive robot arm. One is an adaptive nonlinear dynamic friction compensation method using the LuGre friction model, and the other is a decomposition-based friction compensation method based on a friction model parameter linearization approach. In the experiments, a new velocity estimation method is implemented. The method significantly improves the effectiveness of friction compensation for all tested methods.

Input shaping is a simple but effective method for vibration reduction of linear flexible systems. When systems exhibit nonlinear dynamics, the performance of an input shaper may be degraded. In this paper, a new shaper design scheme is developed for a nonlinear system which consists of a rigid robotic manipulator and a flexible sheet metal payload being grasped at several points by the robot gripper. The new scheme utilizes a parallel shaper structure based on the modal forces of payload vibration. A feedforward/feedback control law is also presented to drive the system to follow its shaped trajectory and to stabilize it at its desired position. Simulation results of a rest-to-rest robot motion control illustrate improved performance of the proposed input shaper, and verify the effectiveness of the control strategy.

A novel robust control technique, robust damping control (RDC), is introduced. An RDC controller is further developed for the motion control of a mobile manipulator subject to kinematic constraints. The knowledge of dynamic parameters of the mobile manipulator is assumed to be completely unknown. The proposed RDC controller is capable of disturbance-rejection in the presence of unknown bounded disturbance, without requiring the knowledge of its bound. The stability of the closed-loop system is guaranteed. The controller has a simple structure and can be easily implemented in applications. Experimental tests on a 2-DOF robotic manipulator illustrate that the proposed control is significantly better than conventional robust control.

Presents the application of an image registration method for a mobile manipulator. The robot is used for scanning natural terrain and detecting metal objects hidden beneath the terrain surface (e.g., landmines) using a metal detector. The range image may be interpreted for visual servoing, map building and path planning, or object recognition. In the work, the image is used to build a terrain map for obstacle free path planning. Because the working area of the robot is extremely dynamic (i.e., not only the robot travels but also the environment is also subject to change) an active range sensing method is selected to provide the range image. The range values are acquired using a laser range finder with a rotating mirror for scanning so that sensor fusion in the form of collecting sensor readings over an extended period of time is required. In addition, range readings of two ultrasonic range finders are fused at signal level to tackle both sensor imperfection and environmental illumination that induce uncertainty at the system. We explain the use of a real-time programming platform that executes an online map-building process in parallel for robot manipulation and control.

This paper presents the results from an experimental investigation into the performance of stiffness control, implemented on a two degree-of-freedom manipulator that uses harmonic drive gears. Stiffness control, which is the simplest form of impedance control, was implemented using force feedback. The results demonstrate the benefits of using force feedback to compensate for static friction effects and for the difficulty in accurately controlling the joint torques for geared manipulators.

In this paper, a neural network (NN)-based methodology is developed for the motion control of mobile manipulators subject to kinematic constraints. The dynamics of the mobile manipulator is assumed to be completely unknown, and is identified online by the NN estimators. No preliminary learning stage of NN weights is required. The controller is capable of disturbance-rejection in the presence of unmodeled bounded disturbances. The tracking stability of the closed-loop system, the convergence of the NN weight-updating process and boundedness of NN weight estimation errors are all guaranteed. Experimental tests on a 4-DOF manipulator arm illustrate that the proposed controller significantly improves the performance in comparison with conventional robust control.

In this paper, a novel robust damping control scheme is proposed for the tracking control of wheeled mobile robots in the presence of unknown dynamics and bounded disturbances. The knowledge of the bounds of uncertainties is not required. Global uniform boundedness of all tracking errors is guaranteed. The controller has a fairly simple structure and can be easily implemented. Simulation results illustrate the effectiveness of the proposed theory.

The system tackled in the paper consists of a rigid robotic manipulator and a flexible shear metal payload being grasped at several points by the robot gripper. The dynamic model is first developed using the component mode synthesis method, and the vibration controllability of the flexible payload is discussed. It is concluded that some flexible states may become uncontrollable if the grasping points are located in the subspace of the payload modal nodes. In addition, given proper grasping of the payload and sufficient degrees of freedom of the robot, the flexible states are locally controllable in almost all of the robot workspace with the exception of some singular configurations. This result implies that vibration suppression control can be achieved by properly selecting the grasping points and robot moving path.

In this paper, a novel neural-net (NN) based control methodology is developed for the motion control of mobile manipulators subject to kinematic constraints. The dynamics of the mobile manipulator is assumed to be unknown and is to be identified by the NN online estimators. No preliminary learning stage of NN weight matrices is required. The controller is capable of disturbance-rejection in the presence of unknown bounded disturbances. Closed-loop stability of the control system and convergence of the NN learning processes are both guaranteed. Experimental tests on a two-DOE manipulator arm illustrate that the proposed control is significantly better than conventional robust control.

This paper describes a step by step validation procedure of a mobile manipulator simulation. The procedure includes performing basic model simulations, a sensitivity analysis, and a stochastic output analysis. Static, quasi-static, and dynamic experiments performed on a real system and simulated using DADS/sup TM/ are also presented. An algorithm to time the model parameters, to match the output of the simulations to the output of the real system, was successfully implemented. Finally, an optimization procedure on the design parameters of the system is discussed.

The position/force control of mechanical systems subject to a set of Pfaffian constraints is addressed in this paper. A reduced order dynamical description of such nonholonomic mechanical systems, including the constraints, is developed. Some properties of the dynamic model are then exploited to facilitate the controller design. Based on the theory of guaranteed stability of uncertain systems, a robust control algorithms is derived, guaranteeing the uniform ultimate boundedness of the tracking errors. A detailed numerical example is presented to illustrate the developed method.

This paper presents a fuzzy-logic control structure, containing the fuzzy-logic model of the dynamic system and fuzzy control rules that ensure the stability and robust performance. The robust fuzzy rules are designed based on a generalized formulation of sliding mode control for a class of nonlinear multi-input multi-output systems. The proposed fuzzy-logic control scheme was applied to the trajectory control of a four-degree-of-freedom robot, and compared with the high-gain PID controllers. A superior tracking performance was achieved.

A systemic approach of fuzzy-logic modeling from the system input-output data is applied to modeling dynamics behavior of a four degree-of-freedom robot manipulator. The output of the fuzzy model is compared with the experimental data and with that of an analytical simulation. The simplicity of the fuzzy model and its improved accuracy is significant.

This paper proposes a systematic methodology of fuzzy logic modeling for complex system modeling. It has a unified parameterized reasoning formulation, an improved fuzzy clustering algorithm, and an efficient strategy of selecting significant system inputs and their membership functions. The reasoning mechanism introduces 4 parameters whose variation provides a continuous range of inference operation. As a result, we are no longer restricted to standard extremes in any step of reasoning. The fuzzy model itself can then adjust the reasoning process by optimizing the inference parameters based on input-output data. The fuzzy rules are generated through fuzzy c-means (FCM) clustering. Major bottlenecks are addressed and analytical solutions are suggested. We also address the classification process to extend the derived fuzzy partition to the entire output space. In order to select suitable input variables among a finite number of candidates (unlike traditional approaches) we suggest a new strategy through which dominant input parameters are assigned in one step and no iteration process is required. Furthermore, a clustering technique called fuzzy fine clustering is introduced to assign the input membership functions. In order to evaluate the proposed methodology, two examples-a nonlinear function and a gas furnace dynamic procedure-are investigated in detail. The significant improvement of the model is concluded compared to other fuzzy modeling approaches.

Usually friction is considered to be a velocity-dependent phenomenon. As a result, most of the available friction models describe friction only as a function of velocity. However, there is also positional dependency which is routinely ignored. Experiments reported in this paper confirm previously published findings of others that friction is position dependent, and that this dependency should not be ignored. Therefore, it is necessary to develop models that describe friction as a function of both position and velocity. Furthermore, available models of nonlinear friction are usually developed by investigating simple cases, such as sliding of two flat surfaces or rolling of a perfectly rounded body on a flat surface. These models do not accurately describe friction generated by mechanisms that have numerous sliding and rolling parts. In this paper, a new spectral-based modeling technique capable of describing nonlinear friction as a function of position and velocity is proposed. This technique identifies the specific contribution to the overall friction of every moving part of the mechanism.

Presents a robotic system used for detection, sorting and grading of paper objects as a part of an automated paper recycling system. The system uses stereo vision to estimate in real time the spatial position of moving objects on a conveyor to be picked by the robot arm. It was proved in the literature that stereo vision may be successfully used to estimate position of moving objects, with a priori known shape, and generate commands to a robot arm for picking up the object. A special computing architecture is introduced for performing the task in real time. A vector of geometric and textural features is used for sorting the paper, according to its grade. The grading process uses color vision and additional contact ultrasonic sensors. A new data fusion paradigm, based on supervised learning, is used. The data fusion algorithm combines stereo vision and ultrasonic sensors to detect and grade paper objects.

This paper presents the calibration methodology developed for calibrating the RoboTwin (a re-configurable robot system). A steel bar of known length is used for calibrating the robot. The length of the bar is calculated using the nominal robot geometry and compared with the actual length to determine the error in the length. A method is developed to express the error in the bar length in terms of the kinematic parameters of the robot. This error is then minimized using a least squares algorithm iteratively to determine the real robot parameters. The calibration results are presented for a 3 DOF robot system.

This paper focuses on designing torque control laws for robots equipped with harmonic drive transmissions. A nominal linear model of the joint is first identified from input-output experimental tests. Subsequently, by varying the input signal amplitude level, a set of models, incorporating the effect of nonlinearities in the system, can be extracted. The differences between the nominal model and this set are formulated as uncertainty bounds for control design purposes. Utilizing the uncertainty bounds, an H/sub /spl infin//-based optimal controller is designed. Experiments are performed for different uncertainty levels on the IRIS facility (a versatile, modular and reconfigurable prototype robot developed at the Robotics and Automation Laboratory of the University of Toronto).

Motion control of manipulators relies on the ability of the actuation system to provide desired joint torques. For robotic manipulators, particularly those equipped with harmonic drives (HD), this ability is considerably restricted by the inherent nonlinearity, friction and flexibility in the actuator-transmission systems. In this work, a joint torque feedback scheme is used for torque control. The design of this method requires that the actuation system is modeled accurately. The motion control design consists of two parts. In the first part, the error dynamic model of the rigid robot arm is derived, followed by obtaining a computed torque control law based on H/sub /spl infin//. The control torque must be provided accurately. The second part of the control design addresses this issue. It has to perform robustly in the presence of hysteresis, nonlinearity and friction. Describing function and conic sector bounded nonlinearity methods are proposed to model the effect of hysteresis, friction and nonlinear stiffness in the control design.

In this paper a new method of modeling nonlinear friction as a function of both position and velocity is introduced. The proposed empirical model uses spectral analysis to identify the main sources of position dependent friction in complex mechanisms. In addition, the model describes the contribution to the overall friction of every moving part of the mechanism. In the paper, the proposed spectral-based modeling technique is used to describe the static friction of the first joint of PUMA 560 robot. Development of a complete friction model, which describes both static and sliding friction of complex mechanisms as a function of position and velocity, is the topic of our future work.

Coordinated control of multiple flexible joint robots holding a constrained object is addressed in this paper. A combined adaptive and robust control scheme, consisting of an adaptive coordinated controller and a robust joint torque controller, is proposed to control simultaneously the motion of the object, the internal force among the robots, the contact force between the object and environment, and the joint torques. The proposed control scheme is developed assuming that all system parameters, including the joint flexibility values, are unknown except for some of their bounds. Stability analysis of the control system shows that with the proposed control scheme, asymptotic motion and force tracking is achieved. Simulation results illustrate the effectiveness of the proposed control method.

By capitalizing on the known properties of harmonic potential functions this work develops a new approach to probability-based path planning that is intuitive, free from local traps (local minima) and computationally less complex than many existing methods. Although the approach presented here is based on the hill-climbing method, it is still able to guarantee goal attainment. Furthermore the algorithm presented here is able to handle arbitrary-shaped geometries and does not require any geometrical or topological approximation at the environment representation level.

This paper presents a new paradigm for model-free design of a trajectory tracking controller and its experimental implementation in control of a direct-drive manipulator. In accordance with the paradigm, a nonlinear approximation for the feedforward control is used. The input to the approximation scheme are task parameters that define the trajectory to be tracked. The initial data for the approximation is obtained by performing learning control iterations for a number of selected tasks. The paper develops and implements practical approaches to both the approximation and learning control. We propose a new learning control algorithm based on the online Levenberg-Marquardt minimization of a regularized tracking error index. The paper demonstrates an experimental application of the paradigm to trajectory tracking control of fast (1.25 s) motions of a direct-drive industrial robot AdeptOne. In our experiments, the learning control converges in five to six iterations for a given set of the task parameters.

A new method aiming at reducing peak torques is developed in this paper for kinematically redundant manipulators. The method considers the contributions of both velocity and acceleration to the joint torque. Instead of minimizing the joint torque or kinetic energy at the current station, the method always uses the current torque to approach an optimum velocity of the following station, which, along with joint acceleration, minimizes the torque of the following station, while at the same time keeps the current torque within the limits. Simulations are conducted for three cases and the results show the clear superiority of the proposed method over the conventional torque optimization and energy minimization methods.

This paper presents a new robust saturation-based control method for robot manipulators and related experimental results. The proposed method distinguishes between uncertainty in the inertia, Coriolis and centripetal forces, gravity and friction. A robust compensator is designed for each type of uncertainty, and each control parameter is directly related to a specific behavior of the closed-loop robot system and can be adjusted accordingly. The goal is to achieve better performance by using this fine-tuning capability of the control law. The proposed control method has been implemented on a direct-drive robot arm. Experiments were conducted to investigate the effectiveness of the proposed method, and the results are reported in this paper.

A new method aiming at reducing peak torques is developed in this paper for kinematically redundant manipulators. The method considers the contributions of both velocity and acceleration to the joint torque. Instead of minimizing the joint torque or kinetic energy at the current station, the method always uses the current torque to approach an optimum velocity of the following station, which, along with joint acceleration, minimizes the torque of the following station, while at the same time keeps the current torque within the limits. Simulations are conducted and the results show the clear superiority of the proposed method over the torque optimization method (Hollerbach & Suh 1987) and the energy minimization method (Khatib 1983).

In this paper, fundamental principles of design of position/force controller for robot manipulators executing constrained task are enunciated. The principles are based on stability considerations, and are addressing the dynamic interaction between position and force subcontrollers. The principles could serve as design guidelines that would guarantee overall stability and reduction of the interactions between the subcontrollers. The concept of consistency introduced in this paper forms the cornerstone of proper implementation of position/force (P/F) controllers, in terms of reduction of the interaction between the two subcontrollers. The principle of consistency indicates that the direct interaction is canceled via the design of a stable P/F controller, however the indirect interaction can only be removed if a Jacobian condition is satisfied, independent of the subcontrollers design.

This paper addresses motion and force control issues of flexible joint robots in constrained motion in the presence of parametric uncertainty. Assuming that values of all system parameters, including joint flexibility, are unknown, except for some of their bounds, a new adaptive and sliding mode control scheme is developed, that provides a unified approach to motion and force control of flexible joint robots in general coordinate space. The proposed control scheme, consisting of an adaptive constrained motion/force controller and a joint torque sliding mode controller, guarantees that motion, force and joint torque tracking errors converge asymptotically to zero without persistent excitation. Simulation results illustrate the effectiveness of the proposed control method.

This paper presents a solution based on robust control approach for asymptotic position/force control of constrained robots with parametric uncertainty. Important practical feature is that position, velocity, acceleration and force errors converge to zero without requiring measurements or estimates of acceleration and force derivative. In this control scheme, a variable structure controller combined with a PI controller is used to guarantee the convergence of position and force errors without control chattering. Compared with adaptive position/force controllers in the literature, the proposed robust controller is less sensitive to force measurement noise.

This paper considers a problem of nonholonomic motion planning. A practical paradigm for planning and stabilization of motion in a class of multivariate nonlinear (nonholonomic) systems is presented and applied to a planar free-floating manipulator system. The controller architecture designed in the paper is based on the radial basis function approximation of an optimal control program for any desired motion. This architecture also incorporates a sampled-data feedback stabilization algorithm. The proposed control technique overcomes certain problems associated with other control approaches available for nonholonomic systems. The presented simulation results reveal a promising potential of the proposed control paradigm. This paradigm can be extended to a broader class of nonlinear control problems.

Since the advent of robotics, manipulators have, in practice, been confined to specific application areas. This limitation can be attributed to their geometrical and physical characteristics such as having fixed link lengths, fixed angular ranges, relatively large size and mass, and their torque capabilities. This paper describes the design of a heavy-duty hydraulic manipulator, the Guelph Arm, which is uniquely flexible in its applications, The features of this robot include compactness, reconfigurability, variable link lengths, large torque and low, overall mass. The Guelph Arm is modeled and, the design and implementation of an industrial controller is given. The use of this robot in neurophysiological experiments is reported.

The paper describes a novel approach to accurate positioning control of mechanical devices with nonlinear (stick-slip) friction. The controller applies narrow torque pulses to achieve the desired displacement of the mechanism. The pulse shapes are computed through fuzzy logic approximation of the dependence between the desired displacement and the pulse shape. The stability conditions of the proposed controller are derived taking into account an influence of random variation of the friction properties. A detailed experimental study of the system response to the torque pulses of different shapes and a detailed controller design are presented for a direct-drive manipulator setup. It is experimentally demonstrated that the developed controller achieves positioning precision up to the limits of the position encoder resolution.

This paper addresses motion control issues of flexible joint robot manipulators using joint torque feedback. A two-stage control scheme consisting of a motion controller and a joint torque controller is established in a systematic way for the general n-link case. To deal with uncertainties in the robotic system, a robust adaptive control algorithm is developed assuming that all system parameters including the joint flexibility values are unknown except for some of their bounds. The system stability is analyzed via Lyapunov stability theory. The result has the distinct feature that no restriction of joint flexibility, nor exact knowledge of the parameters of rotor subsystem is required. The outcome is a useful framework for generalization of control methods previously developed for rigid robots. Simulation results verify the effectiveness of the proposed control methods.

In this paper, a new method of design of position/force controller for robots with parametric uncertainty is presented. An adaptive control scheme is proposed for constrained robot motion control. The proposed control scheme possesses an important practical feature: under the suggested controller, position, velocity, acceleration and force errors converge to zero without requiring measurements or estimates of acceleration and force derivative. Computer simulation results are also presented for illustration.

The remote manipulator described consists of two arms: a 3-DOF main lifting arm (aerial device), and a 6-DOF robot manipulator (treejib) mounted at the upper end of the aerial device. Each arm is single-joint rate controlled, with the reference joint rate being proportional to the corresponding joint displacement of a corresponding hand controller. Both controllers are kinematically equivalent to each of the two arms. Two of the treejib joints are instrumented for position feedback, and the corresponding hand controller joints are motorized and also position controlled. This ensures that no excessive force is exerted on the tool during contact with the branches. The system is of a master-slave rate controlled force reflective type. The design presented has novel features such as a quick connect-disconnect coupler for hydraulic tools and a force reflective master in a form of a small kinematic replica of the slave. The system has been extensively field tested. The results were very promising, however several modifications to the basic concept used to automate the specific operations are necessary.>

The paper presents a sliding-mode based implementation of impedance control. The sliding surface is defined as a measure of the impedance error. When the system variables correspond to the sliding surface, then the desired impedance is implemented. The proposed control approach is composed of two parts. First, the system is controlled such that the state variables reach certain values corresponding to a neighborhood of the sliding surface. This part is performed using a control law consisting of a version of the computed torque and an impedance error-based switching function. The paper uses a new formulation of the acceleration signal for the computed torque calculation. The need for such a neighborhood is to avoid chattering which is typical to sliding-ode based control laws. The second part is performed using a PI-controller which ensures that the state variables further converge to some desired values corresponding to the sliding surface, such that the impedance error would tend to zero asymptotically. The proposed method has been verified experimentally. The method is practical and superior to other known methods.>

In this paper, we present a technique for planning and stabilization of motion in a class of multivariable nonlinear (nonholonomic) systems, and apply this technique to the free-flying manipulators. The controller architecture designed in the paper is based on the radial basis function (RBF) network approximation of an optimal control program for any desired motion. An additional control level for sampled feedback compensation of the approximation errors is also proposed. The presented RBF-based control technique overcomes certain problems associated with other control approaches recently proposed for nonholonomic systems. An example and numerical simulations are provided for illustration.>

In this paper, a new design of smooth dynamic feedback is proposed that compensates for kinematic drift in motion of a nonholonomic system. The technique is applied to a space-based free-flying manipulator in order to compensate for attitude drift. The proposed drift compensation technique is based on our design of the smooth time-variant dynamic feedback for stabilization of a nonholonomic system. We also present a classification and analysis of various cases of the kinematic drift. Example and numerical simulation are provided for illustration.>

Most robust control methods of robot manipulators guarantee small tracking errors by applying sufficiently high feedback gains. Infinite gains are required for zero tracking errors. However, in practice, feedback gains could be severely limited by hardware factors. Robust control schemes using low feedback gains are desirable. In this paper, we derive a globally asymptotically stable robust control scheme by combining integral control with a robust saturation control law. The proposed robust control method takes advantage of both saturation control and integral control techniques, while the disadvantages attributed to them are remedied by each other. Globally asymptotic stability of an n-link robot system with parametric model uncertainties is achieved. As an illustration, the proposed control scheme is applied to a two degrees-of-freedom direct drive robot arm. Simulations were conducted, and the results are in accordance with the theoretical analysis.>

In this paper, two sliding mode based control schemes in joint space are developed for robust control of constrained robot motion in the presence of dynamic uncertainties. One of the proposed control schemes is developed by using two sliding surfaces; the other scheme is derived by employing only one sliding surface, Under the proposed control schemes, both position and contact force are simultaneously controlled. Computer simulation results are presented for illustration.>

In this work, we address robust hybrid impedance control via a tracking control method. The objective of hybrid impedance control is converted into tracking a targeted trajectory. A globally asymptotically stable robust control law is proposed and applied to the tracking control of the targeted trajectory. The position and velocity tracking errors converge to zero under the proposed control law, and the force error is bounded. Furthermore, it is shown that the force error can be reduced by applying inner-loop acceleration feedback. The same controller can be used for control of both free and constraint motions of robot manipulator. As an illustration, an example is presented, and the simulation results are in accordance with the theoretical analysis.>

In this paper, the problem of robust control of robot manipulators which perform noncontact and contact tasks is considered. Using the hybrid control strategy, two variable structure control algorithms are developed in task space. One of the algorithms is developed for control of robot manipulators in constrained motion; the other is proposed for control of manipulators in unconstrained and constrained motion. Computer simulation results are presented for illustration.>

In this paper, the robust control of robot manipulators with consideration of motor dynamics is studied. A robust control scheme is designed based on a third-order dynamic model of robot manipulators that incorporates motor dynamics. The motor torque ripple and parameter uncertainty of the armature circuit are taken into account. The well known robust saturation control technique is applied to the third-order dynamic model to design a control law that guarantees the uniform ultimate boundedness of the closed-loop tracking errors. Simulations are conducted to evaluate the proposed control method, and the results have confirmed its effectiveness.

Describes the implementation of a real-time controller for dexterous manipulation with a hierarchical intelligent control architecture. The architecture is based on a blackboard model that enables incremental, opportunistic, and dynamic decision making and control. The following features have been incorporated into the dexterous robot hand controller: (1) controlling robot fingers using robotic common sense reasoning, based on qualitative representations of control variables and parameters; and (2) opportunistically switching between coarse qualitative control that is based on a physical model and conventional fine quantitative control that is based on a mathematical model. The controller was implemented on a multirobot grasping facility, and preliminary experimental results are presented.>

The authors present the design, development, and implementation of a kinematic calibration procedure for robot manipulators working in coordination in a multiple robot facility. The objectives of this work were two-fold: (i) to identify the individual kinematic parameters of each robot, such as the link lengths, joint angles, etc., and (ii) to identify the global kinematic parameters of the multiple robot environment, such as the relative positions and orientations of the individual robot base frames. The identification required a multidimensional numerical root seeking procedure that behaved better than the traditionally used Newton-Raphson technique. A development of such a procedure (customized to the requirement of calibration) is outlined. The procedure was found to be extremely robust, as it handles the complexity of the model of five bar mechanism quite efficiently.>

The author addresses force control of robot manipulators. It is shown that from a linear system point of view the methods proposed in the literature are equivalent to state an/for output variable feedback, and the stability, for measurement performed either in joint or task space coordinates, can be established through similarity transformations. However, when selection matrices are used, the stability is affected by the choice of compensation in terms of task or joint space coordinates. Using linear models, it is argued that many different methods are analytically equivalent, hence the suggested improvements are inconclusive unless considerations of hardware-, software-, and equipment-specific data are taken into account.>

A general algebraic framework for control analysis of constrained and compliant motion is presented. The author reviews the theory of screws, operators, and indefinite inner products to establish a mathematical formulation for a task space decomposition suitable for synthesis of constrained and compliant motion. Four components of the space of screws are identified and their mathematical properties are presented. The proposed decomposition generalizes the original hybrid force and position control. Applications to contact kinematics and system dynamics are given for illustration. The main contribution is to shed light on the issue of the hybrid control assumption of presumed orthogonality between constraint and freedom subspaces.>

A remote manipulator was developed for forestry operations to relocate operators away from hazardous operations. The operations of tree trimming are performed in the vicinity of live electrical distribution lines, generating a hazard for the operator. The remote manipulator has two major subsystems: a three degree-of-freedom (DOF) aerial device acting as the main lifting arm, and a six DOF manipulator mounted at the end of the aerial device. Each arm was rate controlled with the reference rate provided by the displacement of a corresponding hand controller, which was kinematically equivalent to the manipulator. The mechanical design, the control system of the remote manipulator, and the results of field tests are described.>

Several robust control schemes and a computed torque method were implemented on a two degree-of-freedom direct drive robot. Simulations and experiments have been performed to test the effectiveness of the control schemes and to compare their performance. Based on the results obtained, an integral control has been introduced with a saturation control scheme. This has been found to generate a better tracking performance than the other methods evaluated experimentally. Some generic problems with the implementation of robust control schemes were found and are discussed.>

Three potential problems exist in multifingered hands. The impact forces that result during each instant of grasping a rigid object can affect the functioning of the finger tip sensor. A hand with hard fingers cannot securely grasp objects that have uneven surfaces due to the poor conformability of the fingers. Repetitive strains are induced into the fingers throughout manipulation task. Carefully chosen materials-plastic, rubber sponge, a fine powder, a paste, and a gel-were experimentally compared for their ability to overcome these three problems. Results showed that sponge is the most suitable and plastic is the least suitable for the application. For practical reasons, however, the gel was a good compromise over the sponge. It is recommended that future robotic hands constitute a soft finger or at least fingers with soft tips, constructed out of carefully chosen materials.>

Extending the grasp compliance center concept to grasps in dynamic situations, previous work formulated a concept termed the grasp admittance center and showed that a grasp with an admittance center will have four distinct advantages: stability, decoupled force/motion relation, decoupled time response, and the ease of assigning the grasp dynamic behavior. The authors obtain the analytical conditions that must be satisfied for an admittance center to be achievable. They develop a procedure for computing the necessary fingertip impedances to achieve a desired admittance center. The results of experiments showing the regulation of the apparent impedances of a typical finger are presented.>

The authors investigate the Lyapunov stability property of a control scheme for the bilateral master-slave teleoperator, first introduced by the authors in 1990. Given the nominal models of the master and slave dynamics, and using an approximate feedback linearization control, based on the earlier work of M.W. Spong and M. Vidyasagar (1987), it is shown that Lyapunov stability can be obtained under the assumption that the deviation of the model from the true system satisfies certain norm inequalities. From these norm inequalities, it is shown that the tracking error (position/velocity and force/torque) is bounded and that sufficient conditions for Lyapunov stability can be achieved. The control scheme is illustrated using the simulation of a 30-degree-of-freedom master-slave teleoperator, and the results are presented.>

This paper evaluates the performance of a new control scheme for bilateral master-slave teleo- perator, introduced earlier, and compares it to pub- lished control methods by using a mathematical cri- terion based on the two-port network model. It is shown that most of the published control laws under investigation do not achieve optimal performance, and the few that do, require perfect estimation (or exact knowledge) of the human operator or master arm dynamics. It is also shown that optimal performance, based on the selected mathematical criterion, can be obtained using the proposed control law: I. INTRODUCTION Teleoperating systems may be viewed as synergistic systems composed of human operators and master-slave manipulators which interact with the physical world. The master, sometimes called hand controller, is used to gen- erate commands (usually position, rate or force commands) to its remotedly located counterpart called slave. In gen- eral, the position/velocity command from the operator is fed forward to the slave, while the reaction force, due to mechanical interaction with the environment, is fed back to the master, providing contact force information to the human operator. By reflecting the measured force back to the master arm, it is said that the teleoperator is controlled bilaterally. One of the main issues in telerobotics is control of master-slave teleoperators. A number of control metho- dologies have been proposed in the teleoperator literature. There are two main methods for controlling master-slave teleoperators. The first, a more traditional approach, uses position and/or velocity error (between the master and slave) to generate a forcehorque command into the master arm. The position/velocity of the master and slave are measured by sensors usually located at the joints. The second method uses direct force feedback, rather than posi- tion and velocity errors, to generate command signals to the master. This method uses a force/torque signal obtained from a sensor, usually located at the end-effector of the slave, to provide the operator with the force feeling of the remotedly located counterpart. The force feedback control is usually considered superior because of the more precise nature of the feedback signal. The two-port model network theory has been exten- sively used for the analysis of circuits in which bi- directional energy flows are present at two distinct pairs of terminals. This method provides a useful linear representa- tion of complex networks which exchange energy. The two-port model theory is also used in bilateral teleoperator systems (1,3-81, with force and velocity sensing at the mas- ter and slave. The interfaces between the human operator and master, and between the environment and slave are ports through which the teleoperator is designed to exchange energy between the operator and environment. Recently, several algorithms have been proposed to

The design and analysis of a noncontact electrooptical orientation sensor is addressed. The sensor is based on the intensity measurement of modulated light signals reflected from the surface of an object. The experimental setup of the sensor used in this research was designed and manufactured such that two mechanical-design parameters could be investigated. The operation principle of the 1D inclination-angle measurement sensor was verified using the experimental setup as well as through simulation. Experiments undertaken yielded an optimal sensor design that can effectively operate within a range from +20 degrees to -20 degrees independent of its distance from the object (within the operational-distance range of the sensor).>

An identification method for determining the inertial parameters of robot manipulators with closed kinematic chains is presented. The main issues are the mathematical model describing the robot system, the derivation of a dynamic model using linear combinations of the inertial parameters, and the proposed identification algorithm. An illustrating example, using the proposed method for a closed-chain direct drive arm, is included.>

An approach to the control of multiple coordinated redundant robots working in an environment with obstacles is developed in which the extended task space technique is presented for establishing the dynamic equations of the coordinated redundant robots using the redundant degrees of freedom. This approach can be used to control the motion of an object while avoiding obstacles. Three subsystem error equations are generated: a position error subsystem, an internal force error subsystem, and a constraint error subsystem. The adaptive law is derived to estimate the unknown parameters of the coordinated redundant robots and the object in terms of the three error subsystem equations.>

The objective of hybrid impedance control is defined, and a robust hybrid impedance control method is proposed. The task space is split into force-controlled and position-controlled subspaces based on the concept of hybrid control. Desired inertia and damping are introduced in the force control subspace to improve the dynamic behavior, and impedance control is used in the position-controlled subspace. In the proposed control scheme, the hybrid impedance control is equivalent to tracking a desired acceleration trajectory, which is generated in real-time. The computed torque technique and a PI control law are used to reduce the influence of model uncertainties. Experimental results obtained with a two-degree-of-freedom direct drive robot have shown the effectiveness of the proposed hybrid impedance control method.>

In most applications of manipulating systems, the manipulator has to make contact with rigid fixtures in its environment. In practice, it has been noticed that the performance of the contact force controllers is affected when the manipulator is in contact with a rigid environment or in the presence of uncertainties. A model of the manipulator in contact with a rigid environment is presented, and a robust control architecture based on a general theory of a servomechanism for controlling the contact force is proposed. The results of this work are demonstrated experimentally using a two-degree-of-freedom direct drive robot.>

A grasp with an admittance center will have the following three consequential advantages: (1) the disturbing forces and motions experienced by the grasped object result in motions and forces on the respective degrees of freedom only; (2) the task of specifying the behavior of the object then reduces to that of specifying the behaviors of a finite number of linear second-order systems; and (3) each degree of freedom of the grasp will then be a linear second-order system and will always be stable. Since all such degrees of freedom are dynamically decoupled, the grasp as a whole will be stable. Contributing to achieve such a behavior in articulated multifingered grasps is the prime objective of the work.>

Nonholonomic constraints characterize robot systems in rolling contact with the environment as well as space manipulators. In this paper, the authors address the issue of stability of nonholonomic systems. In the past, it has been shown (Neimark and Fufaev, 1972) that an equilibrium manifold, rather than an isolated equilibrium point, exists for these systems. It is shown that Lyapunov's second method and La Salle's theorem of invariance can be adapted to study the stability of this manifold. Specifically, the Lyapunov function must be positive definite with respect to the equilibrium manifold and its derivative must vanish identically only thereupon. The example of the rolling vertical disc is used to illustrate the analysis.>

A sliding mode based impedance controller is proposed. A continuous PI function is used near the sliding surface to avoid chattering as well as to reduce the steady-state error. Stability analysis is performed via Lyapunov theory. The proposed controller is realized on a DD-arm robot to test its performance. Its performance in the grinding process with different parameters of targeted impedance is also investigated. Through frequency spectrum analysis of the grinding force, criteria to choose the proper parameters of the targeted impedance for grinding tasks are suggested.>

Joint rate solutions for redundant manipulators are formulated in terms of a particular solution and a homogeneous solution formed using a basis for the Jacobian null space. Solutions for several local optimization objectives are formulated in terms of Jacobian null-space bases. A method based on a decomposition of screw coordinates is presented for finding null-space bases and particular solutions. The screw decomposition is applied in the derivation of the analytical expressions for the null-space bases and in the identification of special configurations for a seven-revolute manipulator. The analysis is then extended to multiple-arm systems with common degrees of freedom, and is applied to an analytical example involving industrial manipulators mounted on a common platform.>

The optimal torque control problem of a system of multiple coordinated redundant manipulators using joint redundancy is discussed. A local optimal control law and a global optimal control law, both minimizing torque loading at the joints of the multiple redundant manipulators, are presented. The Pontryagin minimum principle is used to solve the global optimal control problem. The local and global optimal control approaches can be used to control the motion of an object held by the redundant manipulators and the internal forces which do not contribute to the motion of the object. From the task space point of view, the errors in the object motion and in the internal forces converge asymptotically to zero. From the joint space point of view, the joint torques which are provided by the joint actuators of the multiple redundant manipulators are the global minimum under the global optimal controller or the local minimum under the local optimal controller.>

An approach is proposed to simultaneously control the contact forces exerted on a constraint surface and the position of the end-effector, both in the presence of frictional forces on the constraint surface. The approach, using a novel formulation of the dynamics model, is based on a linear state feedback. A feedforward and PI (proportional-integral) feedback control strategy is proposed along with a design procedure. Using the proposed control method the trajectory following problem is solved and the closed-loop system is shown to be asymptotically stable. Numerical examples of a two-link robot moving along a constraint surface are presented for illustration.>

An approach to motion and force control of multiple coordinated robot arms based on an adaptive scheme is developed. The adaptation law uses Popov hyperstability theory to estimate online the uncertain parameters of multiple robot arms and payload. The approach can be used to control the motion of an object held by the arms, the contact forces between the object and the environment, and the internal forces that do not contribute to the motion and the contact forces. Three subsystem error equations are generated, i.e. a position error subsystem, a contact force error subsystem, and an internal force error subsystem. The unknown parameters of the multiple coordinated robot arms and the object are estimated in terms of the three error subsystem equations. It is shown that the proposed adaptive control scheme improves the position and internal and contact force tracking accuracy of a class of systems with an uncertain knowledge of the dynamic model.>

Some aspects of automatic deburring by a robot are considered. The strategy proposed is based on constrained motion control, in which both force and position of the robot are simultaneously controlled. However, in practice, a robot may be in free unconstrained motion before it comes in contact with the environment. In order to control the deburring operation without switching controllers for the unconstrained and constrained motions respectively, an additional controller is proposed, and a control strategy is used so that these three controllers for the robot are automatically switched. This ensures that the robot is stable during the whole process of deburring. A numerical example of a deburring process with a two degrees-of-freedom robot is presented for illustration.>

Trajectory control of a manipulator constrained by the contact of the end-effector with the environment represents an important class of control problems. A method is proposed whereby both contact force exerted by the manipulator, and the position of the end-effector while in contact with the surface are controlled. The controller parameters are derived based on a linearized dynamic model of the manipulator during constrained motion. Hence the method is valid only in a neighborhood about the point of linearization. Additionally, a perfect kinematic model of the contact surface is assumed. The proposed method utilizes the fundamental structure of the dynamic formulation of the manipulator's constrained motion. With this formulation, the trajectory control problem is naturally expressed in terms of the state vector variables of the model of the constrained dynamic system. A detailed numerical example illustrates the proposed method.>

The development of an experimental tactile sensor utilizing optical fibers is analyzed. In the first stage of this research, a single-point experimental force sensor was designed and manufactured. In the single-point sensor, light from an emitting fiber is reflected from the surface of a cantilever beam into a receiving fiber, and the intensity of the light reflected is continuously measured as the beam deflects due to applied force. The experimental sensor is designed such that it allows variation in design parameters to determine the best set of parameter values for optimal performance of the sensor. In the second stage of the research the optimal design parameters obtained from the single-point sensor experiments were used to design and manufacture a four-point prototype tactile sensor. This prototype sensor makes use of electrical amplification and digital conversion which can enable the force signals to provide tactile information to the controller of a multifingered hand.>

The design of a robust nonlinear feedback controller is addressed for an N-degree-of-freedom robot with bounded uncertainty in the dynamic model's parameters. It is demonstrated that the proposed controller makes the robot system practically stable when both unknown payload variation and joint frictional force are taken into consideration. It is also shown that this controller can guarantee the practical stability of the robot system when a collision between the robot and its environmental occurs. Sufficient conditions for global practical stability are derived using Lyapunov's second method. A numerical simulation of a two-link robot manipulator with bounded parameter to illustrate the proposed control system.>

A conceptual treatment is conceptual using linearized models to avoid complexity is presented. However, it is also shown that the approach is suitable when nonlinear models are used. A system configuration which implements both force and impedance control, using feedback and feedforward compensation, for both linear and nonlinear models is obtained. The scheme is currently being implemented in real-time control for testing.>

A singular system model of manipulation of rigid objects is presented. It is suggested that this is the proper formulation of the problem. The use of singular systems in robotic studies is a recent development. Its application thus far has been limited to the frictionless contour-following problem. A review of related studies is given. Some control issues related to this problem are discussed.>

The RAL hand is a fifteen joint, four fingered hand, which can be easily attached to a commercial robot, in particular, a PUMA 560 industrial robot. A computer architecture which integrates both control of the RAL hand joints and PUMA arm is under development. The complete system will be able to perform operations requiring coordinated motions of the arm and hand. This paper describes the layout of the RAL hand, the computer architecture and interfaces to the manipulator, and the concept for low level control.

Various definitions of task-space tolerances, using geometric pseudoenvelopes, are introduced, and new approaches to "direct" and "inverse" joint-error analysis of robots are formulated. These error analyses lead to the development of a "feasible joint-tolerance domain" concept for use in computer-aided design of robots.

A new method is proposed for the accurate trajectory control of a general n degree of freedom robot manipulator, in the presence of large unknown parameter perturbations. In particular, joint friction and large payload mass perturbations are considered. It is demonstrated that for the particular control scheme considered, the choice of high gain feedback results in a system which gives good performance even in the presence of large unmodelled parameter uncertainties. Sufficient conditions for stability are derived using a local subsystem approach. A numerical simulation of a two degree of freedom manipulator, with a large unknown payload mass is included illustrating the new controller design.

The dynamics modelling of a single-link flexible robot with a rigid mass attached to the tip is addressed. The flexibility is represented by lateral bending motion of the robot link. The model is obtained using a Newton-Euler formulation and the natural frequencies and mode shapes are obtained using a constrained mode approach. The paper models the flexibility effects as an internal disturbance torque generated by lateral bending which affects the rigid body motion. The model is suitable for control system analysis and synthesis. A numerical example is presented for the purpose of illustrating the calculation of natural frequencies, mode shapes, and other modal parameters based on the model developed.

The kinematic transformation between task space and joint configuration coordinates is nonlinear and configuration dependent. A solution to the inverse kinematics is a vector of joint configuration coordinates that corresponds to a set of task space coordinates. For a class of robots closed form solutions always exist, but constraints on joint displacements cannot be systematically incorporated in the process of obtaining a solution. An iterative solution is presented that is suitable for any class of robots having rotary or prismatic joints, with any arbitrary number of degrees of freedom, including both standard and kinematically redundant robots. The solution can be obtained subject to specified constraints and based on certain performance criteria. The solution is based on a new rapidly convergent constrained nonlinear optimization algorithm which uses a modified Newton-Raphson technique for solving a system nonlinear equations. The algorithm is illustrated using as an example a kinematically redundant robot.

An exact kinematic model of the Unimation PUMA 600 robotic manipulator is presented. Discrepancies found between the actual manipulator in laboratory tests and the first model presented are discussed. The link coordinate frames are redefined in order to introduce a new transformation for a tool frame. Modifications are made to previously published solutions of the inverse kinematics and differential kinematics. The actual reference orientation frame of the manipulator is formulated such that the orientation of the end effector can be expressed in terms of the actual coordinate angles.