Robust Passivity-based Nonlinear Controller Design for Bilateral Teleoperation System under Variable Time Delay and Variable Load Disturbance

Abstract

The communication pathways between the master and slave play a crucial role in determining the performance of a bilateral system. This research focuses on implementing a robust passivity-based nonlinear control method for the bilateral/teleoperation system. The algorithm addresses the issues of variable communication and control delays plus load disturbance in the feedback, which can lead to instability and reduced transparency, and also handles the parameter changes in the system. To tackle these problems, we propose a controller that incorporates a second-order super-twisting sliding-mode observer to counteract the effects of communication and control delays in the feedback loop. Additionally, a sliding mode assist disturbance observer is used for compensating the load torque variations. A robust passivity-based nonlinear controller has been investigated for this problem, with a particular emphasis on compensating for random/constant time delays through a disturbance rejection strategy. This control method aims to ensure stability and transparency while accounting for time-varying delays. Furthermore, the controller compensates for load torque variations on the slave side through load estimation. The system model consists of two interconnected direct-drive motors. One motor represents a specific joint actuator of the robot, while the other motor emulates the overall dynamics affecting the joint through torque control. This actuator-dynamics load pair enables real-time simulation of any robotic configuration without the physical presence of the robot. The proposed approach utilizes a nonlinear controller framework to reframe the complex bilateral control problem as a means of controlling the interactive dynamic system. This approach simplifies the solution and significantly improves stability and transparency performance. To evaluate the system's behavior and controller performance, various computer simulations are performed using step and sinusoidal inputs. The simulations demonstrate a satisfactory level of accuracy and transparency between the estimated and actual slave positions, even in the presence of constant/random measurement delays and variable/step-type load variations on the slave side. These findings provide strong support for implementing this approach in real-time internet-based bilateral control systems.