Precise Control of the Piston Position and the Pressure of Cylinder Chambers for the Pneumatically Actuated Leg

In the pneumatically actuated leg control system, precise control of the piston position and the pressure of cylinder chambers is a tricky problem. In this paper, a new control scheme is introduced, in which the gas internal energy of the cylinder’s two chambers is used as the set point for PD controller. The proposed control scheme is essential to control the piston position and the chamber pressure simultaneously. A pneumatic position servo model is developed by Simulink tools in the form of an S-function. The maximum steady-state error of 0.19 mm for the piston position and 0.001 MPa for the chamber pressure have been verified in simulations. The test rig of the vertical hopping is constructed, and the experimental results of the pneumatic position servo control on the pneumatically actuated leg show that the chamber pressure error is less than 0.002 MPa, the piston positioning error is less than 0.31 mm and there is no overshooting. The experimental results also show that the established mathematical model and the simulation results are correct. Consequently, the practical experiments of vertical hopping are successful, which validates the proposed method further. Key-Words: piston position, the chamber pressure, the gas internal energy, the pneumatically actuated leg, vertical hopping