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Understanding L9942 Stepper Motor Driver

siva2
Associate II

‎2015-05-07 10:15 PM

Posted on May 08, 2015 at 07:15

Dear All,

Thank You for your great support as always..

I have the following clarifications,

  1. Tried to set STALL threshold using the AN2650 procedure, when the STALL threshold value is 00000000 STALL is not set, but when the value is 00000001 the STALL is set. For just a time period of 16us the stall is set.  The frequency of STEP input was 400 HZ and Full-Stepping mode was used. So, is there any other parameter which has to be taken care for proper stall threshold?

  2. Does stall threshold value setting should also consider the STEP input frequency?

  3. For change in STEP input frequency, the motor is not smooth and stops rotating. What is the reason for this? For Full-stepping, the motor is smooth only from 380 to 420 Hz and Micro-stepping does only when there is more than 1 KHz. When referred to the datasheet for STEP input details, only the minimum time period required is given. Is there anything else which should be taken care of?

  4. What is the proper way to stop the motor? Is disabling the EN (Enable Input) is the only way?

  5. Phase A and Phase B open error is always there even when the motor is operating smooth? The same error is not there when a different motor is used (different specification all together). What could be the reason?

  6. How to choose an appropriate decay mode for a stepper motor?

Thanks in advance

Regards,

M.Siva

#l9942
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Brugus
ST Employee

‎2015-05-13 06:05 AM

Posted on May 13, 2015 at 15:05

Dear Mr.  Murugesan Siva,

here below the answers:
  1. please follow the indication reported in AN2650. The register value must be tuned to match your specification
  2. The stall threshold setting is not influenced by the input frequency. It is linked to the internal PWM only.
  3. The step frequency is usually generated by the ucontroller (I assume this is implemented in your configuration). When there is a frequency modification, the step output port is stopped (disabled) and enabled whit the new frequency.

    You have to consider also the inertia and the mechanical mass effects.
  4. You can stop the motor by using the EN signal, the step signal can be still present without any negative effect.
  5. The error status is latched and it can be cleaned by setting CLR6=1 in register 6. If you turn off and on the device, the error register status is cleaned.
  6. The decay mode is driven by the motor used and by the R and L values. The suggestion is to check the output current waveforms to identify the best setup.

Best regards.

From: murugesan.siva

Posted: Friday, May 08, 2015 8:03 AM

Subject: Understanding L9942 Stepper Motor Driver

Dear All,

Thank You for your great support as always..

I have the following clarifications,

  1. Tried to set STALL threshold using the AN2650 procedure, when the STALL threshold value is 00000000 STALL is not set, but when the value is 00000001 the STALL is set. For just a time period of 16us the stall is set.  The frequency of STEP input was 400 HZ and Full-Stepping mode was used. So, is there any other parameter which has to be taken care for proper stall threshold?

  2. Does stall threshold value setting should also consider the STEP input frequency?

  3. For change in STEP input frequency, the motor is not smooth and stops rotating. What is the reason for this? For Full-stepping, the motor is smooth only from 380 to 420 Hz and Micro-stepping does only when there is more than 1 KHz. When referred to the datasheet for STEP input details, only the minimum time period required is given. Is there anything else which should be taken care of?

  4. What is the proper way to stop the motor? Is disabling the EN (Enable Input) is the only way?

  5. Phase A and Phase B open error is always there even when the motor is operating smooth? The same error is not there when a different motor is used (different specification all together). What could be the reason?

  6. How to choose an appropriate decay mode for a stepper motor?

Thanks in advance

Regards,

M.Siva

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siva2
Associate II

‎2015-05-18 12:34 AM

Posted on May 18, 2015 at 09:34

Dear Sir,

Thanks for your great support and your patience with me   !!!

Please help me further...
  1. What kind of stall is detected by L9942? Only completely locked or partially locked (speed reduces) also?
  2. In my case, my stepper motor’s rotational motion is converted to a linear motion. There are barriers at the end of a linear movement (after certain length of travel). When the linear end is reached, the stepper motor still rotates but the speed is quite lesser. The stepper motor still rotates because of the slip clutch provided in it. Can this case be detected as a stall by L9942?
  3. My step pulses are from Function Generator. I am using the Pulse Mode of it. In Full stepping mode the motor rotates only between 380Hz to 420Hz. In Micro Stepping mode, the motor rotates only after 1KHz. Is this a normal behaviour of Stepper Motor or what should I understand further?
  4. In case of Phase A and Phase B open errors, they continue to appear in normal running conditions even after clearing register 6. What could be the problem?

Thanks in Advance,

Regards,

Siva.M

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