User Manual

PID Tuning Differences between Position Relative and Position Tracking
Advanced Digital Motor Controller User Manual 153
Experiment first with the motor electrically or mechanically disconnected and verify that
the controller is measuring the correct position and is applying the expected amount of
power to the motor depending on the command given.
Verify that when the Command Value equals the Actual Position, the Applied Power equals
to zero. Note that the Applied Power value is shown without the sign in the PC utility.
In the case where the load moved by the motor is not fixed, the PID must be tuned with
the minimum expected load and tuned again with the maximum expected load. Then try
to find values that will work in both conditions. If the disparity between minimal and maxi-
mal possible loads is large, it may not be possible to find satisfactory tuning values.
Note that the controller uses one set of Proportional, Integral and Differential Gains for
both motors, and therefore assumes that similar motor, mechanical assemblies and loads
are present at each channel.
PID Tuning Differences between Position Relative and
Position Tracking
The PID works the same way in both modes in that the desired position is compared to
the actually measured position.
In the Closed Loop Relative mode, the desired position is updated every ms and so the
PID deal with small differences between the two values.
In the Closed Loop Tracking mode, the desired position is changed whenever the com-
mand is changed by the user.
Tuning for both modes requires the same steps. However, the P, I and D values can be ex-
pected to be different in one mode or the other.
Loop Error Detection and Protection
The controller will detect large tracking errors due to mechanical or sensor failures, and
shut down the motor in case of problem in closed loop speed or position system. The
detection mechanism looks for the size of the tracking error (desired position vs. actual
position) and the duration the error is present. Three levels of sensitivity are provided in
the controller configuration:
1: 250ms and Error > 100
2: 500ms and Error > 250
3: 1000ms and Error > 500
When an error is triggered, the motor channel is stopped until the error has disappeared,
the motor channel is reset to open loop mode.
The loop error can be monitored in real time using the Roborun PC utility.