Sensitivity analysis is applied to an investigation of the influence of parameters on the dynamics of a variable displacement axial piston pump. Since an exact mathematical model of piston pump is complex and highly non-linear, the investigation of its dynamic characteristics for the variation of the system purameters by changing separate parameter values in sequence becomes very inefective. In this paper a parameter sensitivity analysis was employed to analyse the eflects of the system parameters systematically. The analysis was done on the exact non-linear dynamic model of the pump system which is represented by fourth-order dynamics. Based upon the simulation results, the degree of influence ofeuch parameter and the justification of order reduction are discussed in some detail.

The load-sensing hydraulic system is an energy saving hydraulic system which improves the efficiency of transmitting power from the pump to the load. However, its stability characteristics deteriorate critically due to the addition of the load-sensing mechanism, compared with those of the conventional system. In this pfi!per, a non-linear mathematical model of the load-sensing hydraulic system is formulated, taking into consideration the dynamics of the load-sensing pump. Based upon linearization of this model for various operating conditions, the stability analysis has been madt using the Routh-Hurwitz stability criterion. The results of the theoretical stability analysis were assured through experiments. Both results show that stability is critical to the choice of system parameters such as the setting pressure of the pump compensator and the load inertia. 3/88 0 IMechE 1988 0263-7138/88 $2.00 + .05

A poppet-type electropneumatic servovalve developed in this study utilizes a poppet directly operated by a moving-coil actuator in the metering stage and is controlled by a digital controller. This servovalve is insensitive to air contamination and has no problem of air leakage at null, but it has relatively large friction between the O-rings installed in the peripheral grooves of the balance pistons and the valve sleeve. For friction compensation control, a static friction model that enables simulation of the stick-slip phenomena and a dynamic model that captures the friction behaviour such as presliding displacement and varying break-away force are presented. The parameters for the friction models are identified by utilizing an evolution strategy, one of the evolutionary algorithms, which is a probabilistic global search algorithm based on the model of natural evolution. These friction models are then used in designing a non-linear friction compensation controller. It is found in the experiment that the electropneumatic servovalve has almost no hysteresis and that the friction compensation control significantly improves valve performance. The experimental results of the open loop test on poppet positioning agree well with simulation results of the valve model with identified friction parameters. It is also shown that the experimental results of friction compensation control using a static friction model show a small steady state error but those using a dynamic friction model show almost no such error.