Sergei Troizky

Motor Offset or Controller Offset?

6 posts in this topic

CompactLogix with integrated motion. Hyperphase absolute encoders. There are the Motor Offset and Controller Offset options in the Axis properties/Motor feedback. The manual says "in the most cases it would be the controller offset", however does not explain when and why. Could anybody explain the difference and the preferences.

Edited by Sergei Troizky

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From "motion-rm003_-en-p.pdf"

"The Commutation Offset attribute is a value that specifies the commutation offset of the PM motor mounted feedback device in units of electrical degrees. This attribute specifies the offset from a commutation reference position defined by applying DC current into the A terminal and out of the shorted B and C terminals of the motor and allowing the rotor to move to its magnetic null position relative to the stator. On an absolute encoder or resolver, the offset is the difference from the device’s zero absolute position and the commutation reference position. On an incremental encoder or Hall sensor with UVW signals, the offset is the difference between the position corresponding to a transition of the commutation device’s W (S3) channel (with the U (S1) channel high and the V (S2) channel low) and the commutation reference position. The commutation offset is only applicable to the motor mounted Feedback 1 device.
When the optional Commutation Alignment attribute is supported and set to Controller Offset or Database Offset, the drive shall apply the Commutation Offset value from the controller to determine the electrical angle of the motor. In this case, a valid Commutation Offset value must be entered by the user, read from the Motor Database, or determined by the Commutation Test. In the unusual case where the commutation offset is also stored in the motor, and differs significantly from Commutation Offset value from the controller, the drive shall transition to the Start Inhibited state.
If the Commutation Alignment attribute is NOT set to Controller Offet or Database Offset, the Commutation Offset value from the controller is ignored by the drive and the drive must determine its internal commutation offset value by other means. Without a valid commutation offset, the drive shall be Start Inhibited."

Bye

Edited by chantecler

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So many unnecessary technical details, and still absolutely unclear when and why use the controller offset or the motor offset.

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Sounds to me like you can use the drive's commutation test to determine the offset and set the parameter to that value (might be set automatically by the commutation test procedure) or the value is part of the motor file that you download. It isn't clear to me what happens when you don't use this parameter or what "other means" the drive will use to determine the offset or how effective the "other means" will be.

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You don't set the value of the Motor Offset. If you do the Commutation Test or know the commutation offset and it is different from the Motor Offset determined by the system then use Controller Offset, introduce your offset value and this is what the drive is going to use.

Bye

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In Logix/Studio5000, depending on which motor/encoder setup is selected, the software obtains values from the Motor Database and loads into Logix.  "If a permanent magnet motor is selected from the Motor Database, the Commutation Alignment is set to Controller Offset; however, if a permanent magnet motor is specified from Nameplate Datasheet, you need to specify the Commutation Alignment method".

So, to boil it down, for the sake of Controller Offset (which is a TYPE of Commutation Alignment), this datapoint is 100% a function of the type of motor selected from the database or what you enter if creating your own motor type.

I am assuming you are creating a custom servo motor/encoder Motor Database entry.  Have you consulted Allen-Bradley/Rockwell Technical Support with help in building your own custom servo motor/encoder Motor Database entry?

 

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