This paper explores the feasibility of using magnetoresponsive silicone as the primary mechanism for generating vibrotactile feedback in haptic interfaces. The distinctive feature of this research lies in the integration of magnetoresponsive silicone, a flexible material that responds to electromagnetic fields to produce localized vibrations. Preliminary experiments evaluate the performance of these actuators, focusing on their ability to produce controlled vibrations across a range of frequencies and amplitudes relevant to human tactile perception. Building on this foundation, we introduce the VibroFlex Pad, a haptic interface featuring a magnetoresponsive silicone sheet and an array of electromagnets. The VibroFlex Pad demonstrates its versatility in generating varied tactile effects and simulating dynamic wavelike movements across its surface. To assess the VibroFlex Pad's effectiveness, a user study was conducted, separately evaluating tactile accuracy, overall performance, and user comfort. The findings suggest that the VibroFlex Pad offers reliable and precise vibrotactile feedback, highlighting its potential to enhance wearable haptic technologies and improve the user experience in a variety of applications.

Path planning and localization in low-light and inclement weather conditions are critical problems facing autonomous vehicle systems. Our proposed method applies a single modality, millimetre-wave radar perception system for the detection of roadside retro-reflectors. Radar-based perception tasks can be challenging to perform due to the sparse and noisy nature of radar data. We propose the use of an unsupervised learning approach for filtering radar point clouds through Density-Based Spatial Clustering of Applications with Noise (DBSCAN). The DBSCAN algorithm segments retro-reflector points from noise points, thus providing the autonomous vehicle with a predicted path for the road ahead. We tested the approach via indoor experiments that make use of Continental's ARS 408 radar, a mobile Husky A2000 robot, and a Vicon motion capture system for ground truth validation. The experimental results of the proposed system demonstrated a classification accuracy of 84.13 % and F1 score of 83.71 %.

This paper proposes a variable impedance control architecture to facilitate eye surgery training in a dual-user haptic system. In this system, an expert surgeon (the trainer) and a novice surgeon (the trainee) collaborate on a surgical procedure using their own haptic devices. The mechanical impedance parameters of the trainer's haptic device remain constant during the operation, whereas those of the trainee vary with his/her proficiency level. The trainee's relative proficiency might be objectively quantified in real-time based on position error between the trainer and the trainee. The proposed architecture enables the trainer to intervene in the training process as needed to ensure the trainee is following the right course of action and to avoid the trainee's from potential tissue injuries. The stability of the overall nonlinear closed-loop system has been investigated using the input-to-state stability (ISS) criterion. High-gain observer with unknown inputs is considered in this work to estimate the interaction forces. Simulation and experimental results under different scenarios confirm the effectiveness of the proposed control methods.

Analysis of string stability in vehicle platoons has mainly been confined to strings of vehicles having similar dynamics. In this scenario, errors propagate uniformly downstream in the string, making string stability analysis convenient. In real driving and platooning scenarios, homogeneity of vehicles is highly unlikely. This means errors amplify/attenuate in a nonuniform manner downstream, as a result of differing dynamics of the current and preceding vehicles appearing in the platoon error dynamic model. This complicates string stability analysis. To remedy this issue, a dynamic proxy to decouple the error dynamics of current vehicle from its predecessor is proposed. Then, by utilizing passivity-based techniques to constrain the output strict passivity index of each vehicle subsystem in the string to unity through a two-stage control strategy, the condition for string stability is met. Validation of the proposed strategy through numerical simulations is nresented.

Online environment dynamic estimates are often used for the control of robots, telerobots, and haptic systems. The nonlinear Hunt-Crossley (HC) model, which is physically consistent with the behavior of soft objects with limited deformation at a single point of contact, is being increasingly used in robotic control systems. The HC model can be identified online using a single-stage log linearization technique; however, the accuracy and applicability of the existing method is limited. We propose a two-stage polynomial identification method, which uses a quadratic approximation in the first stage to generate a linearly parameterized model of the HC dynamics (Quad-Poly). The coefficients of the Quad-Poly model are then used in the second stage to extract the HC parameters using a lookup table and recursive least squares parameter estimation. The proposed method is experimentally assessed against a previous natural logarithm linearization method, and further tested for time-varying environment dynamics and human-generated trajectories and for robustness against uncertainties in the measured data and system parameters.

In this paper, we set out a framework for the analysis of coupled stability in dual-user linear teleoperation systems. An extension of the Zeheb-Walach (ZW) criteria for absolute stability of an n-port network will be stated and proven. While the original theorem states conditions for asymptotic stability of a network terminated by passive impedances, the extended version allows for poles on the imaginary axis, which makes it applicable to a larger class of systems, such as robotic applications with position feedback. The extended theorem includes conditions on the Laurent expansion of the elements and the principal minors of the network immittance matrix. A novel dual-user shared control paradigm, realizing a three-way gearbox mechanism, is presented. A numerical analysis of absolute stability of the three-port network, representing the shared control architecture, demonstrates the effectiveness of the extended Zeheb-Walach method.

A novel robust stability analysis framework is presented for unconditional stability analysis of multimaster/multislave teleoperation systems. Unlike the unconditional stability criterion for single-user systems, the newly proposed criteria for unconditional stability of multimaster/multislave teleoperation systems depend on the multiport network parameters and the port terminations. In addition to the analytical solution, the graphical demonstration of the unconditional stability region facilitates the analysis of coupled stability against variations in the dynamics of the environments and operators, even when they behave actively. The proposed robust stability analysis framework is examined on two multilateral shared control architectures that were previously developed for dual-user teleoperation systems.

Real-time estimates of environment dynamics play an important role in the design of controllers for stable interaction between robotic manipulators and unknown environments. The Hunt-Crossley (HC) dynamic contact model has been shown to be more consistent with the physics of contact, compared with the classical linear models, such as Kelvin-Voigt (KV). This paper experimentally evaluates the author's previously proposed single-stage identification method for real-time parameter estimation of HC nonlinear dynamic models. Experiments are performed on various dynamically distinct objects, including an elastic rubber ball, a piece of sponge, a polyvinyl chloride (PVC) phantom, and a PVC phantom with a hard inclusion. A set of mild conditions for guaranteed unbiased estimation of the proposed method is discussed and experimentally evaluated. Furthermore, this paper rigorously evaluates the performance of the proposed single-stage method and compares it with those of a double-stage method for the HC model and a recursive least squares method for the KV model and its variations in terms of convergence rate, the sensitivity to parameter initialization, and the sensitivity to the changes in environment dynamic properties.

This paper proposes two new multilateral shared control architectures for dual-user haptic training systems. Similar to the architecture previously proposed in, the controllers allow interaction between both users, the trainee and the trainer, as well as between the users and the virtual slave robot and environment. However, the newly proposed architectures provide increased maneuverability and enhanced sense of environment to the users. The kinesthetic performance of the proposed control architectures are analyzed under different operating conditions. Furthermore, the architectures are implemented on a dual-user haptic simulation testbed for user study experiments to investigate the effectiveness of the proposed architectures in terms of sense of environment, maneuverability, and guidance.

In this paper the performance of a dual-user haptic simulation system with a proposed shared control architecture is experimentally evaluated for a specific trajectory following task under different operating conditions. The multilateral control architecture developed for training purposes, allows interaction between both users, the trainee and the trainer, as well as between the users and the virtual slave robot in a shared environment. The performance of the architecture is evaluated experimentally in terms of the effect of environment point of view, environment mushiness, and the existence of virtual fixtures. The performance is measured against task completion time, the path following accuracy and energy exchange by the trainer and the trainee.

In this paper, a powerful robust stability analysis technique is introduced and developed for teleoperation systems. The methodology is based on wave parameters and discusses absolute stability and potential instability using scattering and is originally used in microwave systems [1]. The proposed method provides suitable mathematical and visual aids to determine bounds or regions of passive environment impedances for which a potentially unstable system connected to any passive operator is stable, and vice-versa. Furthermore, a novel stability parameter is proposed to maximize the derivation of the above bounds or regions. This results in less conservative guaranteed stability conditions compared to the Llewellyn’s criterion; thus, achieving a better compromise between stability and performance. The proposed methodology allows for the design of bilateral control systems when such bounds are known or even when the operator or environment dynamics are active. The new robust stability analysis and Llewellyn’s criterion are numerically evaluated and compared with each other on two common teleoperation control architectures.

This paper proposes a novel framework for the analysis and design of linear teleoperation controllers that are robust to time-delay. The framework that is based upon the earlier work of the authors employs scattering parameters and reflection coefficients to guarantee absolute stability of the system under any amount of delays. The proposed framework that incorporates both stability and performance considerations is utilized to design two new delay-robust bilateral controllers and the stability and performance of these controllers are rigorously evaluated.

In this paper, we study the performance of various algorithms for fast online identification of environment impedance during robotic contact tasks. In particular, we evaluate and compare algorithms with regard to their convergence rate, computational complexity and sensitivity to noise for different environments using a single degree-of-freedom experimental setup. The results provide some guidelines for choosing an appropriate identification algorithm for a specific application.

Online estimates of unknown environment dynamics are used for the control of robotic contact tasks. The Hunt-Crossley nonlinear dynamic model of environments has been shown to be more consistent with the physics of contact, compared to the classical linear models, such as Kelvin-Voigt. This paper proposes a new method for online parameter estimation of Hunt-Crossley model and provides a mild set of conditions for guaranteed unbiased estimation. The rate and the sensitivity of convergence to parameter initialization and system parameter changes are numerically evaluated and compared for both the proposed method and an existing 2-stage identification method.

This paper presents a framework for the design of a haptic-based medical ultrasound training simulator. The proposed simulator is composed of a PHANToM haptic device and a modular software package that allows for visual feedback and kinesthetic interactions between an operator and multimodality image databases. The system provides real-time ultrasound images in the same fashion as a typical ultrasound machine, enhanced with corresponding augmented computerized tomographic (CT) and/or MRI images. The proposed training system allows trainees to develop radiology techniques and knowledge of the patient's anatomy with minimum practice on live patients, or in places or at times when radiology devices or patients with rare cases may not be available. Low-level details of the software structure that can be migrated to other similar medical simulators are described. A preliminary human factors study, conducted on the prototype of the developed simulator, demonstrates the potential usage of the system for clinical training.

This paper proposes a new multilateral position-position shared control architecture for dual-user haptic training. The proposed controller allows interaction between both users, the trainee and the trainer, as well as between the users and the virtual slave robot and environment. It also allows for the adjustment of the dominance of the trainer over the trainee in interaction with the virtual slave and environment through a dominance factor parameter. The issue of transparency in such collaborative haptic simulation system has been discussed. A performance index has also been defined to quantify the users' skill for a specific task under study. This metric is used to identify the maximum allowable dominance of the trainee over the trainer. Haptic simulation experiments have been carried out with two planar twin pantograph haptic devices and a simulated pantograph as the slave robot.

This work presents a haptic-based medical ultrasound diagnostic simulator that can be used as an ultrasound training tool for radiology residents as well as an examination system for remote applications. The proposed system allows to develop radiology expertise with minimum practice on live patients, or in places or at times when radiology devices or patients with rare cases may not be available. The proposed simulator consists of a PC workstation with dual monitors, a PHANToMtrade haptic device and a modular software package that allows for visual feedback and kinesthetic interactions between the operator and multi-modality image databases. The system helps emulate a real ultrasound examination condition at hospital, which is enhanced with augmented CT and/or MRI images. The haptic interface creates position correspondence between the operator's hand and a virtual probe. Preliminary human factors studies have demonstrated significant potential of the developed system for scientific and commercial applications

This paper proposes a novel four-channel multilateral shared control architecture for dual-user teleoperation systems. The proposed control architecture is designed to allow interaction between two users as well as slave and environment through a dominance factor. The dominance factor adjusts the authority of the users over the slave robot and the task. To analyze transparency performance in dual-user systems, a number of performance measures are examined or proposed. These measures are evaluated for various types of environments, users' grasps, and levels of dominance of the users over the task.

In the presence of communication delays, master- slave teleoperation systems suffer from poor contact stability and sluggish performance. In this paper, a new impedance reflecting force-position (F-P) control architecture is proposed in which the master is in interaction with a local model of environment, thus bypassing the delayed contact force received at the master in a typical F-P controller. The local environment model is updated by the environment model parameters that are identified online at the slave and are transmitted to the master. However, due to the delay in model parameter transmission and the slow transition of the identified parameters at contact, the controller experiences contact oscillations in practice. As a remedy, a laser proximity sensor is employed to predict the collision time between the slave and the environment "a delay ahead of time". The incorporation of predicted contact time not only synchronizes the required sudden change in the environment local model dynamics with the remote environment contact event, but also allows for an increase in parameter identification convergence rate. The prediction method is introduced for slave unrestricted motion; however, it is verified on a single degree-of-freedom experimental setup. The performance of the proposed novel impedance reflecting F-P controller with collision prediction is compared to that of a typical F-P controller.

In dual-user teleoperation systems, unlike traditional teleoperation systems, two users are in interaction with each other as well as with environment. In this paper, the issue of transparency in such collaborative systems is discussed. In addition a number of measures are presented to analyze kinesthetic performance in dual-user systems. These indices are evaluated for a collaborative haptic control architecture presented in [1] for various types of environments, user grasps, and levels of dominance of users over tasks.

In the majority of robotic and haptic applications, including manipulation and human-robot interaction, contact force needs to be monitored and controlled. Transparent implementation of bilateral teleoperation or haptic controllers necessitates the exchange of operator and environment contact forces. This requires the use of expensive commercially available force/torque sensors, which are rather bulky, are vulnerable to impact forces, and increase system inertia and compliance. An alternative solution is the use of dynamic force observers, which estimate external forces using system dynamic model. However, due to the uncertainties in system dynamic structure and parameters, these model-based observers do not produce accurate force estimates, and often create a dynamic lag that may cause bandwidth limitation and instability. This paper proposes two neural-network-based force/torque observers that do not require a system dynamic model. The observers can estimate human hand force and environment contact force with up to 98.3% accuracy in the sense of mean-square error, and with negligible dynamic lag. The performance of the proposed observers are extensively analyzed in separate human-robot and robot-environment experimental settings, and in a two-channel bilateral teleoperation control loop with multiple runs with two Planar Twin-Pantograph haptic devices

In many studies and applications that include direct human involvement such as human-robot interaction, control of prosthetic arms, and human factor studies, hand force is needed for monitoring or control purposes. The use of inexpensive and easily portable active electromyogram (EMG) electrodes and position sensors would be advantageous in these applications compared to the use of force sensors which are often very expensive and require bulky frames. Among non model-based estimation methods, “Multilayer Perceptron” Artificial Neural Networks (MLPANN) have widely been used to estimate muscle force or joint torque of different anatomy of humans or animals. This paper investigates the use of Radial Basis Function (RBF) ANN and MLPANN for force estimation and compares the performance of the two methodologies for the same human anatomy, i.e. hand force estimation, under an ensemble of operational conditions. In this unified study, the EMG signal readings from upper arm muscles involved in elbow joint movement and sensed elbow angular position and velocity are utilized as inputs to ANNs. Moreover, the use of elbow angular acceleration signal as input for ANN is investigated. Towards this end, a single degree-of-freedom robotic experimental testbed has been constructed, which allows for data collection, training and validation.

This paper addresses position and force control of robotic manipulators that are in contact with environments that exhibit mechanical impedances covering a large continuous range, from very soft to very stiff. For robot programming, automation, teleoperation and haptics, such environments enforce a trade-off between position and force control, which can be accommodated by impedance controllers. In this work, we extend the concept of duality and consider impedance matching in order to optimise a combined position and force trajectory error metric. The analysis of numerical optimisation results provides clear guidance on the choice of target impedance parameters, based on environment and manipulator dynamics.

Transparent teleoperation under rate mode has proven to be difficult in terms of stability, performance and implementation. This is mainly due to the need for exchange of derivatives and integrals of measured positions and forces. This paper proposes and implements a new control architecture designed based on the environment impedance reflecting controller previously developed. The performance of this new controller, implemented on a haptic simulation test-bed, is compared to that of a conventional controller under different operational conditions.

Transparent teleoperation under rate mode has proven to be difficult in terms of stability, performance and implementation. This is mainly due to the need for the exchange of derivatives and integral of measured positions and forces. This paper proposes a new control architecture designed based on the environment impedance reflection concept. The performance of this controller is compared to that of a conventional controller, under different operational conditions using both analytical methods and numerical simulations.

An indirect, self-calibrating, easy to install, and robust joint angle sensing method for heavy-duty manipulators is presented in this paper. This method is suitable for the harsh working environment of these machines where conventional contact-type angle sensors cannot be deployed, or problems are associated with their use. The approach is based on processing the outputs of a pair of biaxial accelerometers placed very close to the joint axis on the adjacent links. In the proposed technique, joint angles are obtained without integrating the accelerometer outputs to avoid measurement error accumulation over a long period of time. Two calibration procedures are also described for accelerometers to ensure the accuracy of their measurements. The experimental results attest to the efficiency and accuracy of the new angle sensing mechanism.

This paper first investigates the issue of transparency in time-delayed teleoperation. It then studies the advantages of employing local force feedback for enhanced stability and performance. In addition, two classes of three-channel control architectures, that are perfectly transparent under ideal conditions are introduced. The stability robustness of the proposed architectures to delays is rigorously analyzed, leading to certain bounds on force feedforward control parameters. Experimental results are included in support of the theoretical work.

Teleoperation systems are subject to operator and environment dynamic uncertainties as well as communication-channel delays. For the first time in the context of teleoperation, the passivity-based Llewellyn's two-port network absolute stability criterion as well as the minima and the dynamic ranges (Z-widths) of the operator and environment transmitted impedances are employed to analyze stability and performance robustness of two and four channels bilateral control architectures. The results of these evaluations and the above analysis tools provide a framework for robust bilateral controller design.

This paper studies the advantages of employing local force feedback for enhanced stability and performance in teleoperation systems. It also shows how a class of three-channel architecture bilateral controllers can provide perfect transparency under ideal conditions. Furthermore, the robustness of the proposed architecture to the communication channel time-delays is analytically investigated. Experimental results are also included to support the theoretical work.

In order to facilitate the testing and evaluation of control strategies and operator environments designed for heavy duty hydraulic machines, an excavator simulator has been developed and is described in this paper. The simulator comprises an impedance model of the excavator arm, a model for the bucket-ground interaction forces, a graphical environment and a haptic interface. This paper describes the simulator components and their integration.

This paper addresses issues of transparency and implementation of dual hybrid teleoperation. A method for automatically adjusting the master and slave impedances to match stiff and soft environments and to interpolate in between them is presented and evaluated using simulations. The application of this technique to the force-feedback control of a mini-excavator is also presented and discussed with supporting experimental results.

To achieve transparency for teleoperation in unknown or time varying environments a class of indirect adaptive bilateral control schemes is developed based on the Slotine-Li (1989) "composite adaptive control" schemes and the "impedance bilateral control" architecture presented by Hannaford (1989). The proposed controllers need master and slave position, velocity and acceleration measurements and require no force sensing. Numerical simulations are worked out to demonstrate the transparency and robustness of the controllers to time delay.