气动伺服控制中特性参数与结构参数的辨识

Identification of characteristic parameters and structure parameters in pneumatic servo control

为获得气动伺服系统比较精确的模型参数,有必要对中位电压、固定容积和泄漏流量进行参数辨识.根据相同控制电压下端口A和端口B的稳定压力不同的物理现象,通过2条压力稳定比值曲线求取偏移量的最小值来获得比例阀的中位电压;根据无杆气缸始端和末端的压力响应曲线不同但稳定压力相同的物理现象,通过压力相同则泄漏的质量流量相同来求取无杆气缸的固定容积;同时,为描述阀口开启交界处的快变的质量流量且克服泄漏流量公式与阀口质量流量公式的不连续问题,将泄漏流量转化为一种泄漏面积意义的拟合.试验表明,上述结构参数和特性参数的辨识,减小了模型不确定,提高了自适应鲁棒控制器的控制精度且控制量非常光滑.

Median control input,dead volume and leakage flow rate were identified for obtaining precise model parameters of pneumatic servo system. According to the physical phenomenon that the stable pressure values of port A and port B under the same control voltage would be different,the median control input of proportional directional valve could be obtained through minimizing the offset value of two stable pressure ratio curves. According to the physical phenomenon that the pressure responses of port A would be different but the stable pressure values of port A are identical when the pneumatic cylinder is fixed at two ends,the dead volume of rodless pneumatic cylinder could be obtained through equal leakage mass flow rate when equalizing pressure. In order to describe the steep mass flow rate just before the valve port was open and eliminate the noncontinuity between the flow rate equations of leakage and valve orifice,the leakage flow rate was transformed into the leakage throttling area that was fitted by a rational expression. The experimental results indicated that the model uncertainties are reduced,the control accuracy of the adaptive robust controller is improved,and the control input is very smooth through the identification of characteristic parameters and structure parameters.