Sensorless Force Estimator for Bilateral Control Systems Using Adaptive Sliding-Mode-Assisted Disturbance Observer

Superior transparency, which includes precise force feedback and position tracking, is the main objective of bilateral operating systems. Therefore, force information estimation or measurement plays a critical role in improving the transparency of bilateral operating systems. This article proposes a bilateral control scheme combined with an adaptive sliding-mode-assisted disturbance observer (ASMADO) for bilateral operating systems. First, ASMADO, comprising an adaptive disturbance observer and adaptive sliding-mode-assisted control law, is used as a force detector to estimate the time-varying force in bilateral control systems. The adaptive disturbance observer with a fixed-time convergent auxiliary dynamic variable is designed without the prior knowledge of the upper bound of the force information derivative, which drives the force estimation error into a small bounded set. Then, the adaptive sliding-mode-assisted control law is used to eliminate the estimated residuals of the adaptive disturbance observer in the inner loop of the force estimator. The stability analysis proves that the proposed ASMADO is practical finite-time stable. Subsequently, a bilateral control scheme based on the proposed ASMADO is developed to further improve the system transparency with force feedback and position tracking. Finally, comparative experimental studies are conducted to verify the superior performance of the proposed bilateral controller based on ASMADO.