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  • Z axis stage lift help

    Discussion in 'The main mechanical design forum' started by Imzautomation, Aug 22, 2014.

    1. Imzautomation

      Imzautomation New Member

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      Hello guys I am working on a z axis lift driven by stepper to lift and lower the platform precisely . It will be driven by a capstan drum fixed to stepper shaft and cable routing around pulleys . I have a stepper nema23 with 1n-m holding torque . As per my calculation toque required By motor to lift the stage would be FXR since I am looking to design the stage for max payload of 10 kg I assume the motor torque is sufficient but as we know the efficiency of motor is actually less assuming 80% available torque would that be enough since I am running cables through capstan drum with 2-4 wraps and around pulleys will I be having some mechanical advantage so that my motor is capable with available torque? If yes will that be sufficient enough to hold the stage if there is a power failure without slipping I am routing cables similar to this diagram http://www.google.com/patents/US5273352 I also thought of increasing torque with torque amplifier design http://en.m.wikipedia.org/wiki/Torque_amplifier is this feasible enough . Waiting for valuable suggestions
       
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    3. Lochnagar

      Lochnagar Well-Known Member

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      Why don't you use a leadscrew and nut to do the lifting - since the leadscrew provides a mechanical brake (as you can't back drive a leadscrew assuming the correct pitch of leadscrew is selected) - should you loose power.

      Hope this helps.
       
    4. Imzautomation

      Imzautomation New Member

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      Thank you for the reply I am designing this system for a 3d printer and engraver combo the reason for going with this design instead of a leadscrew is because the leadscrew wobble shows up in print where as I assume since this is a capstan driven I can precisely lower the device to a accuracy of microns with a micro stepping but as I said I wanna know about the torque capacity I was planning to construct the torque amplifier as shown in the above link and drive the stage from and since it amplifies the torque it will have enough holding torque at its out put shaft to hold the stage with out falling when power goes off suggestions welcomed thanks
       
    5. Imzautomation

      Imzautomation New Member

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      Any suggestions guys waiting for your replies
       
    6. Dana

      Dana Well-Known Member

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      Forget the torque amplifier; use a bigger stepper motor if necessary. Unless you gear the motor way down it's unlikely it will be self locking with power off as the cable drive is fairly efficient. A better approach might be a spring loaded mechanical brake that engages when the stepper power is lost.
       
    7. Imzautomation

      Imzautomation New Member

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      Hi Dana thanks for the reply yes I was thinking of gearing down the stepper with worm drive as it is self locking I have ordered a plastic worm and spur combo will give it a try do you have any idea how to go about spring loaded brake when the power goes off awaiting your reply
       
    8. Lochnagar

      Lochnagar Well-Known Member

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      You could have a look at some of the brakes offered by Warner Electric - see complete list below. If you have a look at the WR or ERS series - you might find something there that is suitable for your application.

      http://www.warnerelectric.com/brake-products.asp

      Hope this helps.
       

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