PID Control
A classic closed loop control method that processes the error signal along three separate paths — proportional, integral, and derivative — and sums them. The proportional term handles fast response, the integral term eliminates steady-state error, and the derivative term damps overshoot.
What the three terms mean in hydraulic position control is concrete:
- P: produces a command proportional to the distance from target. Used alone, a small steady-state error remains because of the load's weight.
- I: sums the error accumulating over time and closes that steady-state gap. Too much leads to overshoot and windup problems.
- D: looks at the rate of change of the error and applies the brake; it slows things down as the target is approached. It is hard to use with a noisy sensor.
The tuning order in practice is this: P is raised first and backed off somewhat when oscillation starts; then I is added until no steady-state error remains; if needed, a small amount of D is applied to suppress overshoot. Since deadband and hysteresis strain the integral term in hydraulics, compensating those two before PID delivers more benefit.
In AXI's HCT400 and HCT402 kits, lever position is held within a typically ±1° band by a PID based control.
Where this term is used: What Does the HCT402 Achieve, How, and How Much? A Technical Review