Sliding-mode bilateral teleoperation control design for master–slave pneumatic servo systems

This paper presents a novel bilateral control design scheme for pneumatic master–slave teleoperation systems that are actuated by low-cost solenoid valves. The motivation for using pneumatic actuators in lieu of electrical actuators is that the former has higher force to mass ratio than the latter and is inert to magnetic fields, which is crucial in certain teleoperation applications such as MRI-guided, robot-assisted surgery. A sliding mode approach, called the three-mode control scheme, is incorporated into a two-channel bilateral teleoperation architecture, which can implement a position–position, force–force, or force–position scheme. An analysis of stability and transparency of the closed-loop teleoperation system is carried out. The proposed control design performance is experimentally verified on a single-degree-of-freedom pneumatic teleoperation system actuated by on/off valves. Experimental results show high accuracies in terms of position and force tracking under free-space motion and hard-contact motion in the teleoperation system. Another purpose of this paper is to demonstrate the possibility to improve the valve lifetime by increasing the number of control levels. To do this, a new control design, called the five-mode control scheme, is developed and compared with the three-mode scheme in time domain as well as in frequency domain.