Feedforward Position Control Concepts for Radial Pneumatic Engines

This paper presents an innovative design of a pneumatic drive as well as two corresponding feedforward position control concepts. Pneumatic drives are favoured in the context of clinical applications due to several advantages. Drawbacks, nevertheless, exist due to the compressibility of the working fluid - mostly air - and nonlinear friction inside the pneumatic drives. Technical applications require typically feedback control, and the use of position sensors. The use of such electric sensors, however, represents a severe issue when developing medical robots for research in magnet resonance imaging (MRI) or other medical equipment, which prevent the use of any metallic components as well as electrical signals. Thus, a new concept for a pneumatic rotary drive is presented that does not require position sensors. Three single acting pneumatic pistons are arranged in a favourable geometrical relation to each other. By means of nonlinear pressure tracking control, the drive positions meet the accuracy requirements regarding the desired position. Realistic simulations show that an accurate tracking is achievable despite nonlinear friction.