Friction characteristics and servo control of a linear peristaltic actuator

Abstract

Despite presenting several inherent advantages, pneumatic actuators are typically discarded for applications where fine motion control is required. This is mainly caused by friction effects caused by piston and rod seals, namely the discontinuities found in friction forces around zero velocity. These effects are very hard to predict and thus to counteract using conventional control laws. This paper explores the use of a different pneumatic actuation solution, a pneumatic linear peristaltic actuator (PLPA), to overcome this problem. The solution envisaged has several potential advantages over conventional or low-friction actuators. Since literature is scarce on this topic, this paper presents the working principle and the model of a PLPA, along with experimental results of its static and viscous friction forces. These results are compared against the ones obtained with a conventional low-friction actuator. Finally, the paper explores the use of a PLPA and a low-friction actuator for servo control, using a conventional PID-type controller. It is experimentally shown that, contrary to what happens with conventional (even low friction) actuators, the use of an integral action does not lead to a limit cycle. Moreover, zero steady-state control error is obtained in a closed loop step response, showing that the approach proposed in this study potentially leads to a low-cost and simple motion control solution.