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DRV8880 A noise of motor when motor stop

masahiko shimizu
Guru 11235 points
Other Parts Discussed in Thread: DRV8880

Hi

My customer is using DRV8880.
He has issue of a noise(sound) of motor when motor stop.
The tone as the "pee" or "kee". *This is an onomatopoeic word of Japanease.

Setting is the following.
- TOFF : 10us
- Decay : Adaptive decay
- Step : 1/4
- VM : 33V
- chopping current : 0.5A
- torqu: 100%

I confirmed waveform of operating current at occurring issue.
Current ripple frequency was 72kHz.

I think a noise(sound) cause is current ripple.
In case of current ripple frequency is under 20kHz, excitation sound by current ripple is heard directly from motor coil.
But in case of current ripple frequency is over 20kHz, I guess that something in the motor vibrates by sympathizing with a frequency of current ripple.
What do you think of this issue?
I can't understand why noise(sound) is heard from motor at over 20kHz current ripple frequency. 

Could you advice me about this, please?

 

Best regards

Shimizu

  • 0
    TI__Mastermind 26065 points
    Hi Shimizu,

    In Adaptive decay, the device will automatically select fast or slow decay based on the charging rate and the setting threshold of the current. Could you show the waveform you get the 75kHz PWM? I think the "driving time + Toff" of this motor should lead to a lower PWM frequency not as high as 75kHz.

    Also even the PWM frequency is above 20kHz, it is not meant we will not hear anything. Because the there may be sub-frequency caused by the decay mode changing all the time (a duty change of the PWM maybe in a lower rate of the PWM frequency). I think DRV8880 is already giving very good noise performance for the stepper driver. Did customer see a better performance of the old solution?

    Best regards,
  • 0 in reply to Wilson Zuo
    Guru 11235 points

    Hi Wilson,

    Thank you for your support.
    Please see the attached file.
    Seting is the following.
    - TOFF : 10us
    - Deacy : Adaptive decay
    - Step : 1/4
    - VM : 33V
    - chopping current : 0.5A
    - torqu: 100%

    We will not hear anything at the PWM frequency is above 20kHz. I think so too.
    But I heard noise.
    I don't understand this mechanism of this issue.
    For the reason, I guessed that something in the motor vibrated by switching frequency and noise was heard.

    Could you advice me this mechanism of this issue, please?

    Thanks
    Shimizu

  • 0 in reply to masahiko shimizu
    TI__Mastermind 26065 points
    Hi Shimizu,

    Yes. That is true 74kHz. Can you hear noise just when you stop the motor and hold on a position with above current?

    For the noise, mostly there are two kinds. One is the PWM switching noise which is usually a high tone. It could be just the PWM frequency or the lower sub-frequency. The current regulation level changing during micro-stepping will also cause noticable noise even the PWM frequency is higher than 20kHz.

    Another one is the running noise which is due to the current shape or non-smooth change of the current, the tone is much lower based on the speed. Also it is the same range of the mechanical vibration when running.

    The combination of the two kinds noise are always there. Especially a stepper motor which is controlled rushing step by step.

    Best regards,
  • 0 in reply to Wilson Zuo
    Guru 11235 points
    Hi Wilson,

    Thank you for your advice.

    This issue is when I stop the motor and hold on a position.
    Sound change by a position.
    There is position which noise is not heard at, too.

    A frequency of 72~5kHz is most noisy.
    Tone is high.

    Could you let me know mean of "the lower sub-frequency"?

    Thanks
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Mastermind 26065 points
    Hi Shimizu,

    Checked on bench and I think I can understand the noise you mentioned. The main reason is because of in adaptive decay setting, there will be some current level setting points which made the device changing the decay mode adaptively always. So you will hear something just when the decay mode is changing. The changing happens at a lower frequency band which is hearable especially when you at high VM voltage.

    You can verify this by holding the motor at one step, then just change the current level setting with GUI. You will find at some level the noise will be much noticable. Then, at this point, you can just turn off the adaptive decay, and select a fixed Mixed decay mode, you will find the noise pattern changed and lower.

    Best regards,
  • 0 in reply to Wilson Zuo
    TI__Mastermind 26065 points
    The sub-frequency is usually 1/n of the PWM frequecy, the current chopping is not a single frequency wave. If your scope can do the FFT, you will see it.

    Best regards,
  • 0 in reply to Wilson Zuo
    Guru 11235 points

    Hi Wilson,

    Thank you for your support.

    "you will hear something just when the decay mode is changing. "
    ->Do you mention that it may became output PWM under 20kHz frequency by adaptive decay ?

    And DRV8880 need to enter sleep or reset for changing from adaptive decay to another decay.

    Thanks
    Shimizu

  • 0 in reply to Wilson Zuo
    Guru 11235 points
    Hi Wilson,

    Thank you for your support.

    "you will hear something just when the decay mode is changing. "
    ->Do you mention that it may became output PWM under 20kHz frequency by adaptive decay ?

    And DRV8880 need to enter sleep or reset for changing from adaptive decay to another decay.

    Thanks
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Mastermind 26065 points
    Hi Shimizu,

    Adaptive decay it's self means changing the decay mode between SLOW and FAST mode just as need all the time automatically. So you will not hear things when the state is stay in SLOW or FAST mode, but it is possibe to produce some noise when just at the time shifting the mode from FAST to SLOW or reverse, because there will be a tiny current shape change there and cause the motor have a tiny shaking. It is really dependent on the motors and VM level on how loud this could be.

    Best regards,
  • 0 in reply to Wilson Zuo
    Guru 11235 points
    Hi Wilson,

    Thank you for your support.
    I understood that the noise course of this issue is ratio shifted of fast and slow decay dynamically.
    But It is really dependent on the motors and VM level on how loud this could be.

    I add a question.　 　
    Does this issue occur in case of Mixed decay?
    I think this issue doesn't occur at mixed decay because the ratio of fast and slow decay is fixed.
    Is this correct?

    Thanks
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Mastermind 26065 points
    Hi Shimizu,

    Yes. If mixed decay used and no other condition change, the PWM freqency will be stable.

    Best regards,