New delay-dependent position/force hybrid controller design for uncertain telerobotics without force sensors

In this article, a new position/force hybrid control strategy is proposed for a class of uncertain bilateral telerobotics systems under time-varying communication delays. This control approach features the capability of removing the use of force sensors and relaxing the assumption on external forces. Specially, the proposed terminal sliding mode (TSM)-based force observer can estimate human force and environment force in a fixed time by applying a variable exponent coefficient, which effectively avoids the temporal problems of other existing force observers. By embedding the estimated force information, corresponding position/force hybrid controller is designed to ensure transparency and stability of system, which can be evaluated by the position synchronization in the slave and the force repeated in the master. Furthermore, by selecting Lyapunov-Krasovskii functional, it proves the stability of the bilateral telerobotics system under particular linear matrix inequality (LMI) conditions. The proposed stability criterion can serve to calculate the maximum allowable transmission delay with the given controller parameters; thus, the conservativeness is reduced. Finally, simulation comparison results and experimental results demonstrate the superior performance of the proposed position/force hybrid controller under different external forces.