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

Pneumatic cylinder systems have the potential to provide high output power to weight and size ratios at a relatively low cost. However, they are mainl y employed in open-loop control applications where positioning repeatabilit y is not of great importance. In this paper the repeatability of a pneumati c rodless cylinder system under closed-loop PD control is examined for its potential use in robotic applications, Our analysis shows that the lineariz ed continuous time dynamics is dependent on the trimmed and operating condi tions. This can cause positioning problems when a controller is designed ba sed upon the transfer function obtained at a particular trimmed point. Furt hermore, there are uncertainties associated with the dynamics which can lea d to precision errors in both transient and steady-state responses. Due to these complexities, a pragmatic gain tuning methodology is proposed to achi eve satisfactory nominal transient response characteristics over the range of loading requirements. With this scheme, it is suggested that the perform ance of the conventional controller be evaluated in terms of its repeatabil ity. The repeatability of the system under different start-stop positions a nd loading conditions is experimentally found to be less than +/- 0.3 mm. T his repeatability value is within typical industrial requirements. (C) 1999 Elsevier Science Ltd. All rights reserved.