User guide

Stepper Controls CME 2 User Guide
142 Copley Controls
12.3: Encoder Correction
For a stepper motor with an encoder, encoder correction may be used to compensate for
lost microsteps. Normally, in an open loop micro stepping mode with an encoder, the total
number of micro steps per revolution is set to the number of encoder counts per
revolution. However, a following error can accumulate when micro steps are lost.
In encoder correction mode, when a commanded position is not equal to the actual
position, indicated by encoder counts, the following error is multiplied by the Encoder
Corrections proportional gain (ECp), and micro steps are added to the open loop micro
stepping loop.
If the error is large or the gain is high, micro steps are added at a higher rate, up to the
Max step rate limit. If the ECp gain is too high, the loop will become unstable and
corrections will not reduce the position error. The position error will not be reduced if the
Max step rate is outside of the motors stepping ability. If steps are lost during a move,
encoder corrections are made during the move, but will tend to accumulate during the
trajectory profile and become resolved by the end of the move.
Set Encoder Correction Gain
1
Click to open the Encoder Correction screen.
2
Set the Encoder Correction parameters:
Parameter
Description
ECp
Proportional gain used to compensate for lost microsteps. Default: 0.
Max Step Rate
Maximum velocity allowed while using ECp to correct position errors.
Excessive velocity can result in more lost microsteps. Default: 0.
Test Encoder Correction
While holding position, introduce a position error by rotating the motor shaft by hand.
NOTE: Reduce the holding current slightly if unable to rotate shaft.
The ECp will act on the error and the motor will settle into position slower than a servo
motor but in a reasonable amount of time.