【摘要】 目前对零开口三通阀控油缸系统的分析都是建立在零位控制压力等于1/2油源压力的基础上的。而在实际系统中往往并非如此,本文揭示出在这种系统中存在着正反向流量增益不等的非线性环节。并用描述函数的分析方法找出了闭环稳定性的新判据。还给出用电子计算机数字仿真的方法进行计算的实例。更多还原

【Abstract】 Objective.Hydraulic design for the three-way valve controlled cylider is nowadays based on the prerequisite that the null controlling piston pressure is given just as the half of supply pressure.But it is not always the case in practice,e.g.,the hydraulic servo for lifting electrodes in an are furnace.In such a case.as a result caused by various factors the null controlling pressure pc is not really equal to the half of supply pressure ps,and so the gain in a direction is not identical with that in reverse.This paper gives an analysis of performance characteristic to such a sort of cylinder system and discusses the stability concerned.For the cylinder system controlled by a three-way valve,different gains in opposite directions due to varied loading lead to a conversion of linear system into nonlinear(shown as in Fig.2).Expressions are derived as follows:where coefficient k=pc/ps,kq the valve flow gain when k-0.5,kq and kq2 the real valve flow gains in opposite flow directions respectively.Having analyzed the describing function GD in connection with coefficient k(GD=kq when k=0.5,Fig.3),it is found that Nyquist contour may be used to determine the stability of the system including a part of nonlinear gains which are unequal in opposite directions.The system will be unstableif the point(-2 (1+k+k),j0) is enclosed in Nyquist contour,or the point (-1,j0) is enclosed in such a Nyguist contour which is drawn on the basis of multiplying the transfer function of linear partG(s) by (1-k+k)2,The transient response charactersitic cal -culated by computer shows that the overshoot decreases so long as the coefficient k increases and no oscillation will occurs with transient res- ponse when k increased to a certain degree.Fig.1 Three-way valve controlled cylinderFig.2 Characteristic curve of valve flow gains in opposite flow directionsFig.3 Relationship between GO and kFig.4 Three-way valve controlled cylinder systemFig.5 Block diagram of three-way valve controlled cylinder systemFig.6 Nyquist contourFig.7 Step response No.1Fig.8 Step response No.2Fig.9 Step response No.3Fig.10 Step response No.4Fig.11 Step response No.5Fig.12 Step response No.6更多还原