TMS320F28379D: Absolute Quadrature Encoder Position

Kevin,

Tommorow is US holiday, please expect our first response by end of day on Monday.

Best,
Matthew

Could anyone please clarify if there's any convention for what the rotor angle of the motor is when the quadrature encoder index signal pulse occurs?  Is there a convention that the angle is 0 degrees (rotor is aligned with stator A-axis) when the pulse occurs?  The motor I'm using is EMJ-04APB22.  I don't see anything on the datasheet /cfs-file/__key/communityserver-discussions-components-files/171/EMJ_2D00_04-Servo-Motor.pdf which indicates the angle when the pulse occurs.

Thanks,

Kevin

Hi Kevin,

Apologies for the delay, the expert in this area is still out of office.  

The specific encoder's datasheet should have information describing the timing of the index (sometimes known as the Z signal for zero) with respect to the A and B signals. 

Best regards

Lori

I just noticed you attached a specification.  I don't see mention of a Z or I signal or any mention of a zero cross.  I suggest reaching out to the manufacturer to confirm the encoder supports this and the timing associated. 

Lori,

Thanks for your reply.  Yes, it is correct that output "C" is the zero-point pulse that occurs once per revolution.  I've verified that when running the motor at 750 rpm, the frequency of the output "C" pulse is 12.5 Hz (80 ms period) as expected. 

However, my question is still what is the absolute rotor angle of the motor when the quadrature encoder index signal pulse occurs?  Is there a convention that the angle is 0 degrees (rotor is aligned with stator A-axis) when the pulse occurs? 

Unless my angle estimator algorithm (that I implemented using https://www.ti.com/lit/an/sprabq3/sprabq3.pdf?ts=1650383436589) has a major error, it does NOT look like the index signal pulse is occurring at 0 degrees (rotor is aligned with stator A-axis)

Thanks,

Kevin

I don't think there is such a convention but instead the reference point depends on the motor/application.  In the user's guide I see a section on determining the reference point. 

-Lori