Position control and repeatability of a pneumatic rodless cylinder system for continuous positioning

Abstract

Pneumatic cylinder systems have the potential to provide high output power to weight and size ratios at a relatively low cost. However, they are mainly employed in open-loop control applications where positioning repeatability is not of great importance. In this paper the repeatability of a pneumatic rodless cylinder system under closed-loop PD control is examined for its potential use in robotic applications. Our analysis shows that the linearized continuous time dynamics is dependent on the trimmed and operating conditions. This can cause positioning problems when a controller is designed based upon the transfer function obtained at a particular trimmed point. Furthermore, there are uncertainties associated with the dynamics which can lead to precision errors in both transient and steady-state responses. Due to these complexities, a pragmatic gain tuning methodology is proposed to achieve satisfactory nominal transient response characteristics over the range of loading requirements. With this scheme, it is suggested that the performance of the conventional controller be evaluated in terms of its repeatability. The repeatability of the system under different start–stop positions and loading conditions is experimentally found to be less than ±0.3 mm. This repeatability value is within typical industrial requirements.