CommutationOffset Parameter

Default Value: 0

Minimum Value: 0

Maximum Value: 359

Units: degrees

Type: int

WARNING: If you set this parameter to an incorrect value, failure and damage to the motor can occur.

The CommutationOffset parameter specifies a commutation offset for brushless motors. You can use this parameter to compensate for misalignment between the motor and the feedback device that is used for commutation. Examples of feedback devices that you can use for commutation include Hall-effect switches and absolute encoders.

Determining the Commutation Offset for Hall-Effect Switches

Use the TuningSetMotorAngle() function to calculate the correct value for this parameter. The table that follows shows the Hall states that occur at different angles.

Table: Hall States That Occur at Different Angles

Angle Range	Hall A	Hall B	Hall C
330° - 30°	L	L	H
30° - 90°	L	H	H
90° - 150°	L	H	L
150° - 210°	H	H	L
210° - 270°	H	L	L
270° - 330°	H	L	H

Before you apply a commutation offset, make sure that the order of the Hall states is the same as the order that is in this table. If the order of the Hall states is reversed, you must set the Hall Commutation Direction setting of the CommutationInitializationSetup Parameter to Inverted. After you configure this setting, you must set the CommutationOffset parameter to the angle that causes your motor to produce the Hall states that the table shows for 330° - 30°, which are indicated by the Hall A Input Level, Hall B Input Level, and Hall C Input Level bits of the Drive Status item.

The value of this parameter must be a positive number between 0° - 359°. Adjust negative offsets when necessary. For example if you have a -30° offset, set the value of the CommutationOffset parameter to 330°.

Determining the Commutation Offset for an EnDat Encoder or BiSS Encoder

When you configure an axis to use a feedback device that supplies an absolute position, the zero value of the feedback device must be aligned with the zero electrical angle of the motor for the drive to operate correctly. Examples of feedback devices that supply an absolute position include EnDat encoders and BiSS encoders.

To determine the commutation offset, do one of these options:

To automatically determine the Commutation Offset for axes that use absolute encoder feedback for commutation, use the Absolute Encoder Alignment Module.
To manually calculate the correct value for the CommutationOffset parameter to adjust for differences in the alignment between the feedback and the motor, use the applicable procedure that follows.

Linear EnDat or Linear BiSS Encoder Feedback

Open Studio.
In the Configure tab, find the Axes category. In this category, select the Motor topic. On the top-right of the application, click the Go to Advanced Editing link. Then set the CommutationOffset parameter to 0.
Save the parameters. Then reset the controller for these changes to have an effect.
Select the Visualize tab.
On the Data Visualizer menu, click the Configure Signals link. The Configure Signals dialog comes into view. Do the steps that follow:

In the Axis section, specify the axes that you want to assign to one or more signals.
In the Signals section, select the signal that is applicable to the type of encoder that you are using:

If you are using an Absolute Encoder EnDat, select the EnDat Absolute Position signal.
If you are using an Absolute Encoder BiSS, select the Biss Absolute Position signal.

Click the Add Signals to List button to add the signal to your list of configured signals.
Click the Save Signal Collection Settings button. The application applies your changes and closes the dialog.

On the Data Visualizer menu, click the Collect Repeated Snapshots button.
Issue TuningSetMotorAngle() functions in a sequence where the first function starts with an $angle value of 0°. You can issue them through the Command field in the application. For each function that you issue, do the steps that follow:

Select a value for the $current argument. This value must be sufficient to move the motor. You must use the same value for the $current argument in each TuningSetMotorAngle() function that you issue.
Increase the value of the $angle argument. Do this for each TuningSetMotorAngle() function in the sequence until the value of the signal that you are plotting is a multiple of the number of feedback counts per electrical cycle of the motor. After you get this result, record the value of the $angle argument.

To calculate the CommutationOffset angle, add 30° to the $angle argument that you recorded in the previous step.
Use the CommutationOffset angle that you calculated as the new value for the CommutationOffset parameter. If the value of this angle is greater than 359°, you must subtract 360° from the angle because the valid range of values for the CommutationOffset parameter is 0° - 359°.
In the Configure tab, find the Axes category. In this category, select the Motor topic. In the CommutationInitializationSetup parameter, make sure that the Initialization Method is set to Absolute Encoder.
Save the parameters. Then reset the controller for these changes to have an effect.

Rotary EnDat or Rotary BiSS Encoder Feedback

Open Studio.
In the Configure tab, find the Axes category. In this category, select the Motor topic. On the top-right of the application, click the Go to Advanced Editing link. Then set the CommutationOffset parameter to 0.
Save the parameters. Then reset the controller for these changes to have an effect.
Select the Visualize tab.
On the Data Visualizer menu, click the Configure Signals link. The Configure Signals dialog comes into view. Do the steps that follow:

In the Axis section, specify the axes that you want to assign to one or more signals.
In the Signals section, select the signal that is applicable to the type of encoder that you are using:

If you are using an Absolute Encoder EnDat, select the EnDat Absolute Position signal.
If you are using an Absolute Encoder BiSS, select the Biss Absolute Position signal.

Click the Add Signals to List button to add the signal to your list of configured signals.
Click the Save Signal Collection Settings button. The application applies your changes and closes the dialog.

On the Data Visualizer menu, click the Collect Repeated Snapshots button.
Manually rotate the motor until the value of the signal is as near to 0 as possible.
Issue TuningSetMotorAngle() functions in a sequence where the first function starts with an $angle value of 0°. You can issue them through the Command field in the application. For each function that you issue, do the steps that follow:

Select a value for the $current argument. This value must be sufficient to move the motor. You must use the same value for the $current argument in each TuningSetMotorAngle() function that you issue.
Increase the value of the $angle argument. Do this for each TuningSetMotorAngle() function in the sequence until the value of the signal that you are plotting is as near to 0 as possible. After you get this result, record the value of the $angle argument.

To calculate the CommutationOffset angle, add 30° to the $angle argument that you recorded in the previous step.
Use the CommutationOffset angle that you calculated as the new value for the CommutationOffset parameter. If the value of this angle is greater than 359°, you must subtract 360° from the angle because the valid range of values for the CommutationOffset parameter is 0° - 359°.
In the Configure tab, find the Axes category. In this category, select the Motor topic. In the CommutationInitializationSetup parameter, make sure that the Initialization Method is set to Absolute Encoder.
Save the parameters. Then reset the controller for these changes to have an effect.