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Original question:

DRV8889-Q1: DRV8889-Q1 stall detection issue

DRV8889-Q1: Slightly vibration issue

Alex Wang
Prodigy 140 points
Part Number: DRV8889-Q1

Tool/software:

Hi Murugavel,
I used DRV8889-Q1 to drive the 14HK0405 stepping motor, and found an issue. The test conditions were as following:
Decay mode: Smart Tune Ripple Control
When the motor stopped, sometimes I could feel the motor slightly vibrated(not rotate exactly), and existed until
(1)the motor was started again, or
(2)change the decay mode to other modes, or
(3)changed the torque DAC to other values(higher values such as 62.5%, or lower values such as 18.75%).
It seemed to be related to the current change related to Smart Tune Ripple Control, what exactly is this issue and what is the reason?
Thanks,
Alex
  • 0
    Prodigy 140 points

    BTW, the motor is combined to the screw, this issue will be reflected as a relatively sharp buzzer, even during the rotation of the motor.

  • 0 in reply to Alex Wang
    TI__Mastermind 44595 points

    Hi Alex,

    This is probably due to current chopping of the regulation in STRC (ripple control decay) combined with stopping the stepper motor in a microstep position where a physical pole of rotor and stator may not exist. The reason is STRC uses slow decay most of the time, and when the motor is stopped with low current amplitudes of the microsteps slow decay may not be sufficient to keep the current regulated at that level - you could observe this using a current probe in the oscilloscope. STDD (dynamic decay) would use fast decay combined with slow decay and would be able to keep the regulation tight at these low current amplitudes. 

    When you change the torque DAC the STRC may lock to the regulation or perhaps the motor shaft may move slightly to align with the poles. A potential solution could be to switch over to STDD just before stopping the motor. This behavior is also specific to some stepper motors. 

    Regards, Murugavel 

  • 0 in reply to Murugavel4637
    Prodigy 140 points

    Hi Murugavel,

    Got it, your explanation is great.

    There's another strange issue: When the motor stops, I often turn off the driver output by controlling DRVOFF pin, then when the driver output is enabled again, I often hear a click-click sound. Is this issue related to uncertain location, as you mentioned in the above "combined with stopping the stepper motor in a microstep position where a physical pole of rotor and stator may not exist"?

    Is there any other way to avoid this issue, when retaining to disable DRVOFF pin after the motor stops?

    Thanks,

    Alex

  • +1 in reply to Alex Wang
    TI__Mastermind 44595 points

    Hi Alex,

    Alex Wang said:
    There's another strange issue: When the motor stops, I often turn off the driver output by controlling DRVOFF pin, then when the driver output is enabled again, I often hear a click-click sound. Is this issue related to uncertain location, as you mentioned in the above "combined with stopping the stepper motor in a microstep position where a physical pole of rotor and stator may not exist

    Yes this is correct.

    Alex Wang said:
    Is there any other way to avoid this issue, when retaining to disable DRVOFF pin after the motor stops?

    If you keep track of the indexer position in the MCU and ensure you stop at physical pole alignment positions this can be mitigated. Usually this would be full-step positions - electrical angle 45, 135, 225 and 315 degrees.  

    Regards, Murugavel 

  • 0 in reply to Murugavel4637
    Prodigy 140 points

    Hi Murugavel,

    Got it.

    Thanks,

    Alex