3.2 PID Tuning - Theory
The following explanation of PID theory will help you to understand the control
system and common terms that are used.
Proportional Gain (Kp)—Proportional gain is the system stiffness. It determines the
contribution of restoring force directly proportional to the position error. Restoring
force is comparable to a spring in a mechanical system.
A high proportional gain gives a stiff responsive system but can cause instability from
overshooting and oscillation.
Derivative Gain (Kd)—Derivative gain is the damping effects on the system. It
determines the contribution of restoring force proportional to the rate of change
(derivative) of position error. This force is much like viscous damping in a damped
spring and mass mechanical system—a shock absorber, for example.
Increasing derivative gain reduces oscillation at the commanded position, or it rings
because of high acceleration.
Integral Gain (Ki)—Integral gain is the static torque load on the system. It determines
the contribution of restoring force that increases with time, ensuring that the static
position error in the servo loop is forced to 0. This restoring force works against
constant torque loads to help achieve zero position error when an axis is stopped.
Integral gain improves positional accuracy. High static torque loads need integral
gains to minimize position error when stopped.
