Skip to main content

 

Dual Loop Block Diagram

When running Galil motion controllers in standard dual loop mode, the PID motion control loop is split up between the load and the motor encoder. The Derivative (KD) loop is closed around the motor encoder. The Proportional (KP) and Integral (KI) loops are closed around the load encoder. The motor encoder is wired into the auxiliary encoder inputs, and the load encoder is wired into the main encoder inputs.

In other words, the response generated from the Derivative loop is completely independent of the resolution of the load encoder. Just as the responses generated from the Integral and Proportional loops are independent of the motor encoder. The 3 responses are summed on the controller to create the final motor command signal.

It is necessary for the motor encoder to have a greater effective resolution then the load encoder to make sure that the controller will see commanded movements of the motor well before the backlash is taken up on the load. Otherwise, the controller could get into a mode where it is building up too much error before it sees any response from the mechanics(load). This can lead to a slight oscillation around the reference position, or even cause the system to become unstable if the backlash is large enough.