Application of the IMPACT structure on bilateral teleoperation

A common issue encountered in teleoperation systems is a time-delay in the communication channel. Depending on the type of communication protocol, the delay can be constant or time-varying. In both cases, the delay can seriously degrade performance of teleoperations or even destroy stability. The Smith predictor [1] can be used to compensate for undesirable effects of time-delays. Reference [2] addresses some issues of robustness and disturbance rejection characteristic to time-delay compensation using Smith predictors. There, a control structure is proposed to increase robustness of systems with Smith predictors. This control structure makes use of the Internal Model Principle and Control Together (IMPACT) approach. In this work, we apply the IMPACT approach to position error (PERR) based teleoperations, where only position information is exchanged between the master and slave manipulators. Our method combines a Smith predictor with a disturbance estimator designed based on an expected class of disturbances acting at the output of the slave manipulator. The block diagram of the control structure we propose is presented in Figure 1. Here, Td represents the forward and backward time-delays in the communication channel that are both assumed to be constant, known and identical to each other in the design and robustness analysis of the controller. The time delays used in the controller are different than the ones that exist in the communication channel and the influence of this mismatch on the robustness has been investigated. We consider 1 d.o.f. equation of motion: Jiq̈i +Biq̇i = τi, (1) where qi, q̇i, and q̈i represent the position, velocity and acceleration of the manipulators, respectively, τi is the control, Ji and Bi are the inertia and the viscous friction coefficient, and i ∈ {m,s} identifies variables at the master or slave side. In Figure 2, we show simulation results in the case of a sinusoidal disturbance acting at the slave side. Here, both master and slave robots are commanded to follow a step reference signal. It can be observed from Figure 2 that the influence of the disturbance on the steady-state values of both master and slave manipulators is reduced reasonably fast with the help of the proposed control strategy. Master + Control