Stepper motor help?

Discussion in 'The Projects Forum' started by big ragu, Sep 27, 2012.

  1. big ragu

    Thread Starter New Member

    Sep 3, 2012
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    Ok, I was given all sorts of help from this board regarding a project I was thinking about doing (been too busy to get into that yet, but i will!), so I figured I'd turn to you guys once again. Quick background on what I'm working on:
    At the plant I work in, we have a saw that has the ability to vary the width before a cut. Currently, there's a motor with an encoder, a frequency drive, and a controller. The controller has 10 preset widths, as well as the ability to manually jog it (slow and high speed jog). None of this is working, and I want to revamp it. I was thinking about using a stepper motor, but I'm not extremely experoenced with them. What would be the most economical way to go about this? I'm open to ideas!
     
  2. crutschow

    Expert

    Mar 14, 2008
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    I would think it would be much easier and cheaper just to fix the system you have rather then try to design something new, which would not be trivial.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    yes so many missing variables to answer the question properly..

    Fix whats there already...a qualified electrician should be able to troubleshoot/fix that in no time.
     
  4. big ragu

    Thread Starter New Member

    Sep 3, 2012
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    There in lies the problem. It's obsolete, parts are not available and it's a German manufacturer. It'd be an 18000 upgrade from the manufacturer. But thanks anyway
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Not saying its not doable at all. In fact it "sounds" fairly simple.. But you will need to provide MUCH more information heck we don't even know if this is a small circular saw or a giant tree splitting saw,etc.. or start reading/learning coding and proper sizing of stepper motors based on the current setup.. Pictures are worth a 1000 words for this.
    But in general you will need to figure out a mechanical solution to attach a suitably sized stepper motor in-place of the existing motor. (Could be very simple) Get a suitable driver for this stepper (gecko drives maybe) and power supplies. Then feed the proper signals to the driver from something like a PLC or microprocessor (an Arduino even)
    Note that with typical stepper applications you don't know the steppers position exactly.. It could miss steps and be in a totally different position than you think it is..
    That's why an encoder was used in the initial application. Electromechanical limit switches can be implemented to ensure it doesn't go to far in either direction,etc..
     
  6. big ragu

    Thread Starter New Member

    Sep 3, 2012
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    It's an industrial rip saw, weighs about 7000lbs. So yeah, it's big. I understand exactly why it is set up the way it is, it's just there's really no way to use what is there. What I need is the ability to preset widths, and the ability to jog it manually. Attaching a motor to the shaft is not a problem. In my head it's all very simple, I just don't know every available option which is why I'm looking for ideas. There's very little torque needed to adjust the width, there are prox's that stop it from overtraveling. My initial thoughts were a stepper motor, programmable driver, and some sort of operator controller. Money wise, it wasn't looking too bad. But again, I'm not super familiar with steppers.

    Right now it's 3 phase/480, but it can be DC. At the end of the day I need the operator to be able to walk up, tell it to go to a preset width (3" for example), and the machine reacts. There's a motor in place that works, and the encoder works as well. THe freq drive and controller are gone. Right now I have it wired through starters so they can manually move it in and out.
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    There are two problems with a stepper, and I think you've got the first one solved, now that you've mentioned the limit switches. It has to count steps from some known starting point, and the limit could be that. When you switch power on, there would need to be an initial move to find the home position, and then you can count steps.

    The other problem is that the motor can stall, and steps (and thus the overall position) are lost. To avoid that, there can't be unpredictable obstacles blocking the moving parts, and you have to accelerate smoothly. And maybe with machinery like this, you have to worry about shock from the cutting process pushing the saw blade around--can that happen? But if the motor can run freely and not get pushed off position, it sounds like a workable system.

    You can buy packaged closed-loop stepper systems. There would be an encoder on the stepper, just so you can be sure no steps are ever lost. Something like this (picked at random from search, I have never dealt with these people):
    http://www.evarobotics.com/evodrive/fw-a206-evodrive-st-23-integrated-stepper-servo
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Personally.. I would do it with the following
    1-arduino board w/wall-wart power supply
    2-gecko drive w/suitable power supply for the stepper
    3-nema 23 stepper motor (maybe something like 200-300 oz-in)
    4-16x2 serial LCD
    5-a few buttons (for menu system and jogging,etc..)
    6-1k resistor/tip102 transistor/relay/diode (to turn on the saw)

    Total cost..should be very close to $400 if not less

    You will need to implement a homing routine (or add an encoder to the stepper) and a simple menu system to allow the user to enter the desired width, monitor the safety curtain and energize the relay to trigger the saw.

    The tutorials on the Arduino site should have all the coding you need. Time for you to start reading/learning :)
     
  9. crutschow

    Expert

    Mar 14, 2008
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    How do you know the encoder works? Can you read the position from the encoder on a display?

    I was thinking of the possibility of controlling the present motor with a new controller using the encoder readout. Did the previous controller ramp the motor speed up and down or was it a simple on/off type of control?
     
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