Energy Saving Control for Pneumatic Servo Systems

This paperproposes an energy saving approach io the control ofpneumaiic servo systems. The control meihodology is presenied, followed by experimental results ihai indicate significani energetic savings and esseniially no compromise in tracking performance relative to a purely active approach. Speci$cally, experiments indicaie an energv savings of 10 to 46% (depending on the desired tracking frequency) relaiive to standard 4-way spool valve pneumatic servo actuaior control. The savings are generally higher at lower tracking frequencies, since tracking of higherfrequencies requires more control effori io minimize tracking error, and therefore limits the degree of possible energy swings. INTRODUCTION A typical pneumatic servo system, which consists primarily of a proportionally controllable 4-way spool valve and a pneumatic cylinder, is depicted in Figure 1. In this system, the position of the valve spool controls the airflow i&o and out of each side of the cylinder, which in turn results in a pressure differential across the piston and thus imposes a force on the load. In a typical pneumatic servo system, feedbackcontrol is incorporated to command a valve spool motion that will result in a desired motion of the piston load. A considerable amount of work has been conducted in the modeling and feedback control of such systems, including the work by Shearer [l, 2, 31, Mannetje [4], Bobrow and McDonell [5], and Richer and Hurmuzlu [6, 71, among others. Despite the prior work on the control of pneumatic servo systems, relatively little work has focused on the energetic efficiency of such systems. This topic has generally received little attention fiom the research community, presumably because most applications draw energy fiom an essentially limitless reservoir of power. In many applications, however, the supply of power is limited (e.g., in the case of a mobile robot), and in such cases, the energetic efficiency of the controller is significant. Fluid powered systems in particular offer intriguing possibilities with regard to the energetic efficiency of control. Specifically, the 'energetic role of an actuator at any given point in time is either to generate or dissipate power. In a fluid powered system, the energetic role of power dissipation can be provided passively by controlling the resistance to fluid flow. Therefore, ideally, a fluid powered system need only draw fiom the (high pressure) fluid supply when the actuator is 0-7803-7759-1/03/$17.00