Non MCU options for soft start/stop

Discussion in 'General Electronics Chat' started by richard3194, Jun 21, 2014.

  1. richard3194

    Thread Starter Member

    Oct 18, 2011
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    I know I can use an MCU IC or something like Arduino to control a stepper motor to achieve soft start and soft stop.

    But, what IC options do I have if I don't want to program an MCU or otherwise deal in code?

    I'm seeking an IC where all I do is flip switches or turn potentiometers to set soft start/stop parameters.

    Not found much on Google, but I'm not a good Google user.

    Thanks.
     
  2. ScottWang

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    Aug 23, 2012
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  3. Papabravo

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    225 Hz is a pretty low frequency for a stepper motor. I understood that the OP wanted to accelerate and decelerate to avoid the mechanical resonance of the system. 200 Hz, with half steps, is only about 30 rpm for a 1.8° stepper.
     
  4. ScottWang

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    225Hz is the limitation for the stepper motor that I tested, the stepper motor of op may not that low, so he can adjust the NE555 to a higher frequency.
     
  5. Papabravo

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    So I guess you can manually accelerate and decelerate if the 555 can go down to zero frequency and up to some maximum.
     
  6. ScottWang

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    Yes, the NE555 can be adjust the frequency to a big range for manually, the problem is the op not describe all the details, so this just give him to think.
     
  7. richard3194

    Thread Starter Member

    Oct 18, 2011
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    Wanting to control a linear actuator (gantry on rails) with soft start/stop by way of automation. I'd press a start button or there would be a switch that would initiate a start. There would be a soft start (PWM ramp upwards) for a set period. Then the gantry (on rails) would hit a switch as it neared the end stop, which would initiate a soft stop (PWM ramp down) and the gantry comes to rest at the end stop - in a gentle deceleration.

    All to be done without MCU or code.

    Every 1.8 degrees of stepper turn would cause a linear movement of 0.314mm. So, there would be 3184 steps to cover 1 metre. If that distance was to be covered in 1 second, I'd need a stepper frequency of 3184 Hz (I think).
     
    Last edited: Jun 21, 2014
  8. Alec_t

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    Looks doable.
    Do you have the stepper motor spec, in particular type, maximum step rate and current?
     
  9. ScottWang

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    The stepper motor is active by the pulse, but the linear actuator (gantry on rails) seems like a DC motor, how is the relationship with them?

    Now it seems that you are talking about two different things, do you have any other things didn't speak out?
     
  10. ScottWang

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    If you want to using stepper motor to have a soft start/stop, maybe you need a VCO(voltage control oscillator) to do the job.
     
  11. richard3194

    Thread Starter Member

    Oct 18, 2011
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    Well, it's not decided whether the motor would be a dc motor or a stepper motor. Either would work. Of course the ramp would be in terms of frequency with a stepper and in terms of pulse width or average voltage with a dc motor.

    I had a dc motor in mind when I wrote post #7. But then I talked about stepper motor issues. I was mixing oranges and apples on post #7.

    One thinks (well I do) there ought to be off-the-shelf motor control ICs that would play a part.

    Maybe dc motor would be easier to design for. Not sure.
     
    Last edited: Jun 21, 2014
  12. Alec_t

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    That's pretty high. Sounds expensive!
     
  13. Fibonacci

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    May 23, 2014
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    Look at this H-bridge CI: L293D.
     
  14. Alec_t

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    Presumably this gantry movement will be reversible?
    Unless you need to send the gantry to an arbitrary accurately-known position (for which a stepper would be an obvious choice) I'd go with a DC motor. Such motors are readily-available in various sizes with built-in reduction gearboxes.
    What size gantry are we talking about? What motor power?
     
  15. richard3194

    Thread Starter Member

    Oct 18, 2011
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    Hi. My thoughts keep flipping between stepper motor and dc motor.

    Lets go with dc motor.

    I'm minded to use V slot rails from OpenBuild. And to affix a gantry plate, which of course will move linearly.

    I don't know the force required to move the gantry. All I know is that the gantry plus what is bolted to it, might come to a mass of 3Kg. And that max velocity can be 1m/s.

    I want to press a button and gantry will go from the left (home) to an end stop on the right. It can move at 1m/s going from home to right end stop.

    There will be some operation whilst the gantry is at right end stop, after that is finished some switch must operate to initiate movement of the gantry back to home when it will stop. The gantry going home must have a soft start and then a soft stop at the home position, or simply go back to home at a low enough velocity to avoid spillage of contents on the gantry. Certainly, start and stop on return to home should be gradual enough to avoid spillage.

    When the gantry stops at the right end stop it's position must not vary more than 0.5mm.

    There is no issue of spillage as the gantry moves from home to right end stop, only from right end stop back to home.

    The length of the V slot rails will be about 1m.

    EDIT: Oh, the gantry would be belt driven, so belt driven linear actuator setup.
     
    Last edited: Jun 22, 2014
  16. richard3194

    Thread Starter Member

    Oct 18, 2011
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    Lets divide this problem into two halves.

    Lets call going from home to right end stop outbound.

    Lets call going from right end stop to home inbound.

    I can put full steady voltage on dc motor in the outbound. But what I cannot get my head around is how do you get the gantry to stop at a position no more than 0.5mm from the end stop? Can/does dynamic braking ensure this? What ensures this? I don't know what ensures a 3kg mass moving at 1m/s comes at rest always within 0.5mm of an end-stop.

    I can more easily see why in the inbound a slow deceleration using PWM ramp can bring the gantry to within 0.5mm of an end stop.
     
    Last edited: Jun 22, 2014
  17. Alec_t

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    Perhaps you could use two limit switches at the right end? On reaching the first switch on the outbound run the motor would decelerate to a low rpm. The gantry would then creep to the second switch position and the motor would be dynamically braked and switched off.

    Edit:
    This isn't perchance a robot bartender you're building?
    :D
     
    Last edited: Jun 22, 2014
  18. richard3194

    Thread Starter Member

    Oct 18, 2011
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    No, but maybe it's not a bad idea getting drinks served without bartender having to walk up and down the bar.:cool:
     
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