A Constant Pressure Cylinder Coupled With a “Zero-Stiffness” Eddy Current Damper

Friction and other unmodeled uncertainties in pneumatic actuator systems limit their use in high precise constant pressure control applications, such as ultraprecision grinding and low-gravity simulation. This article presents a novel pneumatic actuator based on a compact Eddy current damper (ECD) and an air-bearing piston for precise constant pressure control. The noncontact ECD improves the stability of the system and does not introduce additional stiffness into the pneumatic system. Numerical prediction and experimental measurement are carried out to obtain the damping coefficient of the ECD. The mathematical model of the proposed cylinder is established, and a backstepping sliding-mode control method based on Lyapunov stability theory is proposed for constant pressure control. A PC-based real-time constant pressure control test bench is built to verify the performance of the proposed cylinder. The experimental results show that ECD improves the accuracy of constant pressure control under step and impact external forces, and the proposed cylinder can reduce the fluctuation of cylinder pressure by using a simple control method.