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DRV8434: Non-smooth motion and distorted current waveform at different speeds

irem esin
Prodigy 10 points
Part Number: DRV8434

Hello, 

I am using DRV8434PWPR driver for driving bipolar 2 phase stepper motors with 1/64 microstepping for a camera. 

The pan motor is being drived with 1.6 A peak current. The speed for the pan motor varies from 0.4 degrees/s to 960 degrees/second. 

During low speeds I am seeing a  non-smooth motion where the image starts moving and after a short while the image looks like it stops.

During this time I am constantly giving PWM signal but the motion looks like it stops for a really short time. Could this be caused by 

zero crossing error? According to my measurements zero crossing lasts about 70 miliseconds.

Also for higher speeds the current graph gets distorted and motor starts making noises. I am using smart tune dynamic decay with Toff = 7 microseconds.  

Below are oscilloscope waveforms for the motor current (with highest speed and zero crossing for the lowest speed)

.

Thanks,

İrem

  • 0
    TI__Mastermind 23421 points

    Hey Irem,

    Thank you for the waveform with the motor current, that is very helpful.  Can you please try driving it with lower current? I believe you are using too much current for this motor and the backEMF can't handle it.  Lower current often gives better results with stepper motors for a given speed. 

    https://www.planetanalog.com/tips-and-tricks-for-testing-and-debugging-stepper-motors/ 

    Smart Tune Dynamic Decay should give you the best results, but you can also try the other modes.  

    Best,

    Jacob

  • 0 in reply to Jacob Thompson
    Prodigy 10 points

    Hi Jacob,

    I tried lowering the current but that did not solve my problem. The current waveform is still distorted. 

    I have tried slow decay mode for low speed but still the motion is the same.

    İrem

  • 0 in reply to irem esin
    Genius 3700 points

    Hi Irem,

    "During low speeds I am seeing a  non-smooth motion where the image starts moving and after a short while the image looks like it stops." - Probably it is caused by motor nonlinear response to sinusoidal driver current. I guess all stepper motors have nonlinear response to sinusoidal current, though some of them are better and some of them are worse.

    "Also for higher speeds the current graph gets distorted and motor starts making noises." - Probably it is caused by low speed motor resonances.

    I would try the following:

    - keep peak motor current below its nominal current rating,

    - try different decay modes,

    - try to replace motor, preferably for one with lower detent torque ratio to holding torque. Can you tell what motor

    do you use at the moment (motor datasheet)?

    - try to use modified sinusoidal current, TI has some new drivers that have "Customizable microstepping indexer table", you can use an MCU to control driver current as well (drivers with PWM inputs),

    - use 3-phase stepper motors,

    - use 2-phase stepper motor in closed position loop with an encoder,

    - use BLDC motor with an encoder,

    The last three options would be more difficult or/and expensive to do.

    Regards,

    Grzegorz

  • 0 in reply to Grzegorz Pelikan
    TI__Intellectual 2540 points

    Hi Irem,

    Can you try fast decay at 1/4 ustepping at 1A full scale current and share the waveform with us? Also, what speeds (pps) are you operating at? Are you using our EVM? 

    Regards,
    Karan