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Motor Start Problem With Incremental Encoder

mrthunderous
Prodigy 230 points

Hi all,

1)I can drive motor with FOC using inceremental encoder (closed loop current and torque). But there is a problem with encoder. Motor start up with open loop using RG and RC macro. When Motor  spin 2 or 3 second  ı set flag to enable  closed loop. But encoder dont know where is the index point  at start up position. I dont want to use open loop procedure to get index point position of the encoder. How can ı get index point position of the encoder at start up position.

2) For instance, motor spinning with current and toque controller using encoder. I stop motor and rotate motor shaft with my hand.When I start up motor after this rotation, motor firstly rotate a little bit left or right. After this littie rotation motor get actual position and continue spining. This rotation is not desirable. How can ı solve this problem 

Thanks.

  • 0
    TI__Guru** 118790 points
    since this isn't InstaSPIN let me move this to C2000 forum and tag Ramesh to answer
  • 0 in reply to ChrisClearman
    TI__Mastermind 27240 points
    With any encoder, you need to know the relative angular difference between the encoder and motor phase A. You need this angle to be subtracted from the encoder feedback to track the angle of phase A. Therefore an alignment is needed. If you already know this difference, you can hard code it but if the encoder is remounted, it will have to be retuned again.
  • 0 in reply to Ramesh Ramamoorthy
    Prodigy 230 points
    Thx Ramesh. According to what you've said ı dont know the absolute position of the motor before receiving the first index pulse of the incremental encoder. Ok. How can ı control position of the motor with incremental encoder? Is there any ti application note about this ?
  • 0 in reply to mrthunderous
    TI__Mastermind 27240 points

    When you use a QEP -

    After a power cycle, the POSCNT in EQEP resets and loses the current position. Hence an alignment is needed to bring the motor winding and encoder to a common known platform.

    With any other abs encoder:

    If you know the position of encoder at alignment, that value will be enough to use for as long as the encoder is not remounted.