Amir Takhmar

A small gain framework for networked cooperative force-reflecting teleoperation

For cooperative force-reflecting teleoperation over networks, conventional passivity-based approaches have limited applicability due to nonpassive slave-slave interactions and irregular communication delays imposed by networks. In this paper, a small gain framework for stability analysis design of cooperative network-based force reflecting teleoperator systems is developed. The framework is based on a version of weak input-to-output practical stability (WIOPS) nonlinear small gain theorem that is applicable to stability analysis of large-scale network-based interconnections. Based on this result, we design a cooperative force-reflecting teleoperator system which is guaranteed to be stable in the presence of multiple network-induced communication constraints by appropriate adjustment of local control gains and/or force-reflection gains. Experimental results are presented that confirm the validity of the proposed approach.

CARTESIAN APPROACH FOR GAIT PLANNING AND CONTROL OF BIPED ROBOTS ON IRREGULAR SURFACES

Biped robots possess higher capabilities than other mobile robots for moving on uneven environments. However, due to natural postural instability of these robots, their motion planning and control become a more important and challenging task. This article presents a Cartesian approach for gait planning and control of biped robots without the need to use the inverse kinematics and the joint space trajectories, thus the proposed approach could substantially reduce the processing time in both simulation studies and online implementations. It is based on constraining four main points of the robot in Cartesian space. This approach exploits the concept of Transpose Jacobian control as a virtual spring and damper between each of these points and the corresponding desired trajectory, which leads to overcome the redundancy problem. These four points include the tip of right and left foot, the hip joint, and the total center of mass (CM). Furthermore, in controlling biped robots based on desired trajectories in the...

Projection-Based Force-Reflection Algorithms With Frequency Separation for Bilateral Teleoperation

Projection-based force-reflection (PBFR) algorithms have been previously demonstrated to substantially improve stability characteristics of bilateral teleoperators with communication delays; however, the transient response of the PBFR algorithms suffers from relatively slow force convergence. As a result, the high-frequency component of the reflected force is lost during the initial phase of contact with the environment, which has a strong negative effect on the haptic perception of the environmental stiffness and texture. In this paper, a new type of PBFR algorithms are developed which solve the aforementioned problem. The new algorithms are based on the idea to separate different frequency bands in the force-reflection signal and apply the PBFR principle to the low-frequency component, while reflecting the high-frequency component directly. Both theoretical analysis and experimental results are presented; the results obtained confirm that the new algorithms fundamentally improve force convergence without a negative effect on stability of the teleoperator system with communication delays.

Cooperative Teleoperation With Projection-Based Force Reflection for MIS

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

Counteracting modeling errors for sensitive observer-based manipulator collision detection

Modeling errors are one of the elements responsible for deficiencies in sensorless collision detection of robotic systems. By providing a specific formulation of manipulator equations, this paper presents a time-variant threshold for observer residues in joint space of a manipulator in order to provide more accurate collision detection ability compared to constant thresholds. The time-variant threshold considers modeling errors in both robots parameters and its friction forces. Simulation results using real-life collision forces and experiments on the Phantom Omni device are provided to validate the proposed scheme.

Experimental evaluation of a projection-based force reflection algorithm for haptic interfaces

Experimental results are presented that evaluate the stability and performance of a projection-based force reflection algorithm for haptic interaction with a virtual wall. It is shown that the projection-based algorithm allows for stability improvement similar to the one that can be achieved by using the virtual coupling; however, contrary to the virtual coupling, the projection-based force reflection algorithms algorithms do not result in the transparency deterioration.

Small-gain design of networked cooperative bilateral teleoperators

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

Frequency separation in projection-based force reflection algorithms for bilateral teleoperators

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

Cooperative teleoperation with projection-based force reflection for MIS

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

Small gain design of cooperative teleoperator system with projection-based force reflection

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