Tips for Smooth, Precise Hydraulic Motion Control
Controlling hydraulic motion with precision involves understanding the fundamental difference between servo motors and hydraulic actuators. Electric motors generally respond linearly to control inputs and can be referred to as “first-order systems.” Simple PI and PID control algorithms can provide precise control of first-order systems, and typical electronic motion controllers or even PLCs implementing simple P, PI, or PID algorithms can easily handle the task.
Some hydraulic systems, on the other hand, must deal with the effects of the compressibility of the hydraulic fluid medium, which can be modeled as a mass between two springs, where the piston and the load are the mass and the oil on either side of the piston is the springs. With such systems, simple P only, PI or PID controls often exhibit performance limitations due to the natural frequency and damping factor of the hydraulic/mechanical design. For such systems, called “second-order systems,” algorithms that employ second derivative gains are often needed.