分级比例控制及其在材料试验机中的应用

Stage Proportional Control and Its Application in Material Testing Machine

电液材料试验机对试件的加载通常由伺服阀或比例阀构成闭环控制系统实现。由于对载荷及加载速率的控制精度要求较高,故由伺服阀或比例阀表现出的非线性,如滞后、饱和、分辨率等,就不能对液压加载控制子系统产生很大影响,为此本文提出了分级比例控制的方法,其基本思想是:将阀的整个控制区间分成若干段,而在每一段内均执行独立的比例控制。通过分级比例控制,多种因非线性导致的不利影响被大大削弱。目前这种技术已被应用于水泥材料试验机。根据ISO水泥试验机标准,电液加载子系统的加载速率为2.4kN/s时,误差应不超过7％,保载误差应在0.2％以内。应用分级比例控制后,此两项具体数值分别被控制在2％及0.05％以内。

The loading force control of a material test machine is usually carried out through close loop scheme by using a servo or a proportional valve. Because of the high accuracy requirement on both loading force and loading rate, the nonlinearities displayed by the servo or proportional valves, such as hysteresis, saturation, definite resolution, should not impose a significant effect on the performance of the hydraulic loading control subsystem. For this reason, the stage control is introduced in the hydraulic loading control subsystem. The fundamental concept of the stage control is to divide the whole control range into a number of areas in which independent proportional control is carried out. By means of the stage control, the various nonlinear errors are reduced by the stage number. An application in a compression machine for the cement sample test is presented. According to the Chinese (also ISO) standard for cement test, the loading rate of the electrohydraulic loading subsystem should be at 2.4 KN/s withan error less than 7% and error rate for the constant force control should be maintained within a range 0.2% . With the application of the stage control, these two specified errors are limited to 2% and 0.05 % respectively