Compliance Control of a Pneumatic Robot with Improved Sliding Mode Control Method

In constrained tasks such as deburring, polishing and assisting disable persons, not only a position but also a contact force must be controlled. In addition, a reasonable compliance is necessary to absorb excessive impact or contact forces. A pneumatic robot can well meet these requirements because of its inherent compliance due to air compressibility. In addition to this passive compliance, an active compliance control method of a pneumatic robot is considered. A compliance control system regulates the relation between the manipulator position and the contact force along each task axis. This study proposes a position-based type compliance control system which has a minor position control loop inside a force feedback loop. This position control loop dominates the overall compliance control performance. Unfortunately, a pneumatic robot can not easily provide the high position control performance with usual control schemes owing to the low stiffness and the high nonlinearities. To overcome this problem, a sliding mode control scheme with a pressure feedback compensation is adopted to the position control loop. This compensation is effective to inhibit the chattering. The proposed compliance control method is applied to a pneumatic robot comprising two arms. First, both stability and control accuracy are examined theoretically and experimentally. Next, this method is applied to some tracking controls on the constrained wall. Further, a stabilizing method to realize the higher compliance is proposed and its availability is confirmed. The results obtained assures the effectiveness of the proposed control method for a pneumatic robot. Consequently, the availability of a pneumatic robot may be increased.