伺服阀如何保证不同外载荷下，速度恒定的？

wushao308

请教伺服控制的大拿们：工程机械上，速度调节用比例阀或变量泵调节，比例阀和泵都有压力补偿阀，来恒定压差，不管外载荷是否变化，执行元件的速度只与阀开口大小成比例。那么伺服阀也带有压力补偿阀吗？它是如何在不同负载下，保证速度不变的？初次接触伺服阀，向各位老师请教。

游勇

是通过闭环控制。

zhangweiwei

闭环系统可以有效提高系统的速度刚度

PEN

伺服阀本身不能保证正确的速度。必须有反馈，因此闭环控制可以补偿位置和速度的误差。

重要的是要了解速度变化的原因。由于开环增益变化，速度会发生变化。开环增益具有（mm / s）/％控制单位。可以使用VCCM方程计算开环增益。 VCCM表明开环增益将随供应压力和负载的变化而变化。这种变化与之成正比

Sqrt（（供应压力*面积 - 负荷）/（初始供应压力*面积 - 平均负荷））

很容易看出，随着供应压力的降低和负载力的增加，开环增益将随着比率的增加而减小。

随着供应压力的变化，可以调节控制器增益。 35年来，很少有人这样做过。有时可以估计质量并相应地调整增益。很少这样做。最好的控制器可以轻松补偿开环增益的20％变化。

The servo valve does not guarantee the correct speed by itself.  There must be feedback so the closed loop control can compensate for errors in position and speed.

It is important to understand why the speed changes.  The speed changes because the open loop gain changes.  The open loop gain has units of (mm/s)/%control.  The open loop gain can be computed using the VCCM equation.  The VCCM shows that the open loop gain will change as a function of changes in the supply pressure and the load.  The change is proportional to

Sqrt((supply pressure*area-load)/(initial supply pressure*area-average load))

It is easy to see that as the supply pressure decreases and the load force increases, the open loop gain will decrease by the ratio.

It is possible to adjust the controller gains as the supply pressure changes.  In over 35 years, very few have done that.  It is sometimes possible to estimate the mass and adjust gains accordingly.  Few do that.  The best controllers can compensate for 20% changes in the open loop gain easily.