[Th015]

Citation:

D.Y. Hwang, 'Teleoperation Performance with a Kinematically Redundant Slave Robot,' Ph.D. Dissertation, University of Washington, Department of Electrical Engineering, December 1995.

Abstract

When the scaled teleoperation is used, the stability issue becomes important due to the high gains in position or force scaling. We used two experimental methods to identify the stable region of position and force scaling factors of a one-axis system haveing 4000:1 force scaling capability. We used a simple classical teleoperation control law. An indirect closed loop approach with ARX technique was used to model the nonlinear slave system with a flexible printed circuit cable. The stability regions were identified by experiments and simulations. Then the slave system was physically linearized by replacing the flexibile printed circuit cable with thin wires. The linear case stability regions were identified. In addition, the contact stability region and sensitivity analysis were studied.

Kinetic energy minimization was used to resolve the redundant joint space solution in the early literature work by Whitney in 1969. Kinetic energy optimization has been used for local and global redundancy control. However, the further effects of kinetic energy on teleoperation performance have not been studied. This section shows the effects of kinetic energy level on teleoperation performance. First, we expressed an inertia weighted pseudo-inverse solution corresponding to a general level of kinetic energy by using the gradient projection method. Second, we added joint limit avoiding by using the null space of the main task. Then we derived three kinematic redundancy control modes having different kinetic energy levels using the property of the generalized inverse matrix: "Whitney Mode", "Intermediate Mode", and "Least Squares" mode.

To validate our algorithms, we performed autonomous robot tests and teleoperation. The tradeoff between kinetic energy level and joint limit index was clearly shown in the autonomous test. For teleoperation, 4 tasks and 7 indices were defined. A 3-DOF pen-based master and 5-DOF Mini Direct Drive Robot were used. Tasks were x-y-z positioning and contact, giving 2 DOF kinematic redundancy in the slave robot. Overall, the "Whitney Mode" showed the best performance, while the least-squares mode showed the worst performance. In addition, the subjective quality ratings of inertia force, bias force, noise force were made by the test operators. "Whitney Mode" showed the lowest perceived level of noise force.

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