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  1. #1
    la vache fantôme phantomcow2's Avatar
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    Encoder for a stepper motor?

    I got two NEMA 34 stepper motors today from IDC. I was told they have encoders mounted on them, but I am not sure what to think of this. Why would one use an encoder for a stepper motor? What advantage would it have for a linear positioning system>?
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  2. #2
    That darn Yankee TexasGuy's Avatar
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    I hope you or somebody else here knows what you're talking about because i dont have a ****ing clue. When people talk to me about encoders they usually are for encoding data streams or multimedia streams
    Life is about hanging onto what you think is important and finding out what really is important.
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  3. #3
    2-Cyl, 1/2 HP @ 90 RPM slvoid's Avatar
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    Cause your damn motor is positioned relative to each phase in the step but it doesn't feed back anything. If you want a closed loop system you're gonna need an encoder, be it relative or absolute. Now stop confusing the poor texans!

  4. #4
    la vache fantôme phantomcow2's Avatar
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    I usually get pretty good replies to my geeky questions . This one might be a little out there though.
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  5. #5
    la vache fantôme phantomcow2's Avatar
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    Quote Originally Posted by slvoid
    Cause your damn motor is positioned relative to each phase in the step but it doesn't feed back anything. If you want a closed loop system you're gonna need an encoder, be it relative or absolute. Now stop confusing the poor texans!
    See, always a good reply.
    Okay, well both motors have the encoders on there. I had a feeling is what closed loop means.
    Its like on a servo, so the controller knows where the servo is? Where as a regular "open loop (stepper) system, the generator of the pulse train (in my case computer) ASSUMES that the stepper motor is where it should be, but the motor could have lost steps and the generator of pulse train would have no idea?

    And lastly, how hard would it be to get one of these encoders working?
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  6. #6
    2-Cyl, 1/2 HP @ 90 RPM slvoid's Avatar
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    Your basic open loop system operates by dead reckoning which is ok for something that has low mass/low torque/etc. For something where position is critical or when there is a lot of outside interference, the encoder lets you know the amount of drift that occurs. You don't have to do anything to get an encoder working, all it gives is pulses.
    Some of them will give a constant pulse, some give a graduated pulse, some give a sinusoidal pulse, etc. The first is just relative position in formation. It might have a different pulse for the home position. The rest have multiple phases that let you resolve direction and/or absolute position.

  7. #7
    la vache fantôme phantomcow2's Avatar
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    well this is for my CNC router, which took some MAJOR steps up in the quality arena (im talking like made from .75" aluminum plate instead of MDF, Linear rails on each axis instead of a crude conduit pipe system, that stuff), so it would be nice if my computer knew where the motor was...
    Might as well go all out

    But the encoders have several wires coming from them, where would these wires go to? The motor driver?
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  8. #8
    la vache fantôme phantomcow2's Avatar
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    Yea something i somewhat left out. When you look at these, they are 5 wire unipolar and you can see that connection. Then there are 8 wires from the encoder. THe encoder has a nice little case bolted onto teh bottom...
    These mount right into linear actuators, being a 34 frame. WooHoo!
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  9. #9
    2-Cyl, 1/2 HP @ 90 RPM slvoid's Avatar
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    The encoder is generally wired into your feedback control system which should come with the motor controller or the servo system.
    Otherwise you'll have to make your own circuit to nab the output of the encoder and inject it into your feedback control loop.

  10. #10
    la vache fantôme phantomcow2's Avatar
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    hmm, do you how hard it would be to make a circuit for this encoder?
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