A Multi-objective Sliding Mode Approach for the Energy Saving Control of Pneumatic Servo Systems

This paper proposes a variation on a sliding mode control approach that provides significant energy savings for the control of pneumatic servo systems. The control methodology is formulated by first decoupling the standard four-way spool valve used for pneumatic servo control into two three-way valves, then using the resulting two control degrees of freedom to simultaneously satisfy both the sliding mode sliding condition and a dynamic constraint that minimizes airflow. The control formulation is presented, followed by experimental results that indicate significant energetic savings with essentially no compromise in tracking performance relative to a standard four-way spool valve approach. Specifically, relative to standard four-way spool valve pneumatic servo actuator control, the experimental results indicate energy savings of 27 to 45%, depending on the desired tracking frequency. INTRODUCTION A typical pneumatic servo system, which consists primarily of a proportionally controllable four-way spool valve and a pneumatic cylinder, is depicted in Figure 1. In this system, the position of the valve spool controls the airflow into 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 such a system, feedback control 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 [1, 2, 3], Mannetje [4], Ben-Dov and Salcudean [5], Wang et al. [6], Maeda et al. [7], Ning and Bone [8], Bobrow and McDonell [9], and Richer and Hurmuzlu [10, 11], among others. Despite this prior work on pneumatic supply 4-way proportional spool valve pneumatic cylinder inertial load V C