Design of a Pressure Observer and its Application to a Low-Cost Pneumatic Control System

The nonlinear pressure observer this paper presents for pneumatic systems and observer-based approaches for controlling position and stiffness eliminate the need for pressure and force sensors. The observer estimates pressure in the pneumatic actuator chamber, acting instead of a sensor in a pressure-feedbackbased system. Conventional single-loop controllers are inadequate for pneumatic actuators because such actuators have high nonlinearities such as air compressibility and friction. Most advanced controllers providing better performance require full-state feedback, and using sensors to acquire data makes pneumatic control systems less cost-competitive than electric control systems. Combining our proposed pressure observer with other observers enables a position and stiffness control system to be designed for a two degree-of-freedom pneumatic manipulator. Force caused in contact between the manipulator and an external object can be obtained without using force sensors. Experimental results show that our observerbased approach reduces cost, enables high estimation performance, and ensures high control accuracy.