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Reset Absolute Encoder Position - Store In Drive or Motor?

The Compax3 offers the flexibility with the absolute encoders of storing the absolute position within the drive or the feedback. The Compax3 with the F11 feedback option for the drive is used with the Stegmann SinCos Hyperface absolute encoders. The Compax3 with the F12 feedback option is compatible with the Heidenhain Endat absolute encoders.

This stores an offset value from the encoder's actual absolute position.

This is good for applications where you need a known 0 position on actuators and cannot easily remove the motor from the mechanics since these encoders are multi-turn (4096 turns).

1. Set the Store absolute position to In Feedback in the drive configuration.

As of C3 ServoManager Release 9-20, now in the main screen on the left, under Online device functions, there is now the Reset absolute position allowing the same functionality as below with a single click (only 24vdc logic needs to be connected, no hardware enable, motor does not need to be energized).

Then when you power up, the absolute position will be read into the drive and you can immediately do absolute moves relative to your stored 0 position.


In the rare case that the drive fails and needs to be replaced, if it's stored in the encoder, the drive could be replaced and no adjustment would be needed as the absolute position is stored in the motor feedback. Homing is not necessary.


If it's stored in the drive, if the motor fails, when the motor is be replaced the above no-motion homing would need to be performed again, as the encoder position of the new motor is different to the encoder position of the old motor.

Exception: If your travel is longer than the multiturn limit of the absolute encoder (4096 turns for the 7D and 6S encoders on our MPP/MPJ), use In Device. The rollover point is tracked with In Device and is compensated at the Compax3 drive. This isn't compensated for with In Feedback.

 

 

Alternate way:

1. Set the Store absolute position to In Feedback in the drive configuration.

2. In the Compax3 ServoManager software, in the Drive Configuration, in the Units/Homing/Travel limits, set the Machine Zero (Homing) Mode to 35 (no motion, just set 0 position to the absolute encoder position). Download to Compax3.


3. Power the drive and command a Homing Move. This can be done in the Optimization screen.

 

4. Change the home mode back to No Homing and redownload to the Compax3. This prevents a user from overwriting this offset value.