Modeling and control of the pneumatic constant pressure system for zero gravity simulation

This paper presents a complete dynamic model and a hybrid design method for the high precision pneumatic constant pressure control system for a gravity compensation suspension device. The pneumatic system components consist of newly-developed frictionless cylinders without mechanical seals, a large tank and an electro-pneumatic proportional pressure valve. The complete mathematical models are derived, which consist of valve dynamics and flow nonlinearities through the valve orifice, pressure evolution in cylinder chambers and tank, and gas leakage. Because the system is highly nonlinear, parameter time-varying and uncertain, a practical hybrid piecewise control method combined with bang-bang, proportional-derivative and fuzzy logic proportional plus conventional integral-derivative algorithm is proposed to minimize the pressure fluctuations in cylinders. Finally, some typical experiments illustrated the effectiveness for high precision pressure control of the proposed approach.