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DRV8711 - Stepper Motor Missing Steps At Lower speed

yogeshwar dharmaraj
Prodigy 20 points
Other Parts Discussed in Thread: DRV8711

Dear All,

                I have been driving stepper motors with DRV8711 for XY Table.I have incremental encoders to check for missing steps.

The faster speed(625 rpm) produces accurate encoder reading.But when I reduce to lower speed (50 RPM - which is the ideal speed for my application),the motor seems to miss steps.Please find the register settings and Motor configuration Below.

Register settings

Mode : 1/8 step

Full Scale Current: 2A

SMPLTH : 100us

TOFF: 7.5us

TBLANK : 2.5us

DTIME: 850ns

ABT: 0

TDECAY : 3 us

DECMOD : Use auto mixed decay at all times

DRIVE_REGISTER : 0x0e54

The N MOSFETs I use are STD20NF06L 

Motor configuration:

Rated Voltage: 3.6V

Current / Phase:2A

Resistance / Phase:1.8Ohms

Inductance / Phase:4.1mH

Holding Torque:1.26 Nm

Rotor Inertia: 300 G-cm2

I would appreciate any kind of help.

With Regards

Yogeshwar

  • 0
    TI__Mastermind 26065 points

    Hi Yogeshwar,

    Just to be clear, the missing steps only happens when speed down from high to low like 600rpm to 50rpm. If just in 50rpm constantly, there will be no steps missing, right?

    How the deceleration process of your command profiles? We need to speed down gradually with a proper linear or "S" curve speed down process from high speed to low speed. Also we need proper accelerating process when the motor ramp ups. Do we have implemented this?

    Best regards,

  • 0 in reply to Wilson Zuo
    Prodigy 20 points
    Hi Wilson

    Thanks for the reply

    My application is a simple cnc machine with 3 axes.

    The x any y axes comes faster till the workpiece with 625 rpm.

    Then stops (no shift to 50 rpm in motion)and and then do the application operation at 50 rpm.

    The acceleration is 125rpm/sec

    When I constantly jog at 50 rpm the steps are missing and the current waveform is smoother except at particular period when the wave is rising at positive edge.

    With Regards
    Yogeshwar
  • 0 in reply to yogeshwar dharmaraj
    TI__Mastermind 26065 points
    Hi Yogeshwar,

    If the position counter is counting all the time, the missing could happen at the time when stop from 625 rpm to 0, and all the later moving may have a offset error always.

    Is the stop from 625 rpm to 0 acting suddenly? There must be a gradually deceleration process of the stop.

    On the other hand, if the step missing truely happens only in the low speed 50rpm section, could you show the current waveform at this speed?

    Also can you make sure the torque of the motor is enough since the tools is ready touching the workpiece. The loading could be much bigger and changing widely. This may cause the motor missing steps.

    Another point is if the motor is 2A motor (Always means 2A rms), so in your current level setting at 1/8 micro stepping mode, the MAX level of the current sure be 2A * 1.4, which is about 2.8A. Then, we get about 2A rms current. So now, you motor may be not driven to its best torque level.


    Best regards,