The low-stiffness teleoperator slave - a trade-off between stability and performance

Stability is essential for teleoperation and a prerequisite for performance. This paper analyzes the the stability/performance trade-off of a teleoperator where the slave device has a built-in passive intrinsic stiffness. Stability is quantified as time delay robustness and performance is expressed using teleoperator damping and teleoperator stiffness, the boundaries of the Colgate Z-width. Two classic control schemes, position error and Lawrence 4-channel, are used along with a novel 5-channel scheme where the slave stiffness deflection is measured, and compensated for, to improve the performance. The teleoperator system was analyzed theoretically using a linear model and the findings were experimentally validated on a one degree of freedom teleoperation setup. It was found that: A lower slave stiffness improves stability for all three teleoperator architectures. The stability boundary of the three controllers is similar. The performance of the controllers increases from: (poor) position error, 4-Channel to (excellent) 5-channel. A classical linear analysis method can accurately predict the stability characteristics of the teleoperator system. Therefore it can be concluded that a compliant slave device offers a stability advantage,for a range of teleoperation situations and that the loss of performance can be partly compensated.