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To achieve rapid disengagement and smooth engagement of clutch in automated manual transmission systems, servo control of an electro-pneumatic clutch actuator controlled by solenoid on–off valves is considered. Nevertheless, realization of high-accuracy servo control usually depends on model-based non-linear control technologies requiring full-state knowledge of the system. Pressure sensors are not used in automated manual transmission systems owing to cost considerations. Thus, the pressure states in the chambers are unknown. To address this issue, non-linear pressure observers taking the place of pressure sensors were proposed in this paper. It is stable in the sense of the Lyapunov theory and independent of the load. Furthermore, the pressure observer’s polytropic exponent was analysed and then determined experimentally. Finally, a compound sliding-mode controller with pressure observers was presented. Extensive experiments demonstrated the feasibility and the effectiveness of the proposed pressure-observer-based controller.

The system considered in this work consists of a cylinder which is controlled by a pair of three-way servo valves rather than a four-way one. Therefore, the cylinder output stiffness is independently controllable of the output force. A discontinuous projection based adaptive robust controller (ARC) was constructed to achieve high-accuracy output force trajectory tracking for the system. In ARC, on-line parameter adaptation method was adopted to reduce the extent of parametric uncertainties due to the variation of friction parameters, and sliding mode control method was utilized to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbance. Furthermore, output stiffness maximization/minimization was introduced to fulfill the requirement of many robotic applications. Extensive experimental results were presented to illustrate the effectiveness and the achievable performance of the proposed scheme. For tracking a 0.5 Hz sinusoidal trajectory, maximum tracking error is 4.1 N and average tracking error is 2.2 N. Meanwhile, the output stiffness can be made and maintained near its maximum/minimum.

A new-type frictionless pneumatic cylinder with an aerostatic bearing as its piston can decrease the friction significantly. The stability and the leakage of this cylinder mostly depend on the radial load carrying capacity(RLCC) and the air consuming of the bearing. In order to make a better use of this cylinder in pneumatic servo systems, a simulation study on the influence of the structural parameters and time-varying surrounding parameters to this cylinder was carried out on the basis of a numerical solution method based on finite element method(FEM) which was constructed to solve Reynolds equations in this paper. Simulation shows that introducing a recess chamber at the end of the orifice hole can increase the RLCC significantly and smooth the sharp distribution of the pressure around the orifices in the air film, which makes the bearing working more stable; the time-varying parameters have a combined effects on the performance characteristics of the bearing.

For the stick-slip phenomenon encountered in the pneumatic cylinder motion in practical application, the stick-slip mechanism was analyzed and an nonlinear mathematical model based on the improved LuGre model of pneumatic cylinder movement was established. The movement of the piston and the pressure of the rodless chamber in the pneumatic cylinder based on meter-in circuit were obtained through solving the differential equations by four-order variable-step Runge-Kutta method. The comparison between simulation and experimental results shows that the established mathematical model can describe the stick-slip motion of pneumatic cylinder with a relatively good accuracy.