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Stepper motor for 1200 kg linear force

  1. Aug 14, 2013 #1
    stepper motor for 1200 kg linear "force"

    Hi all,

    For a project I need to bring over a linear force of 1200 kg onto a steel rod of about 10 mm. I would like to have some guidance in how I could do this with a stepper motor. How 'heavy' does this motor have to be ? I most powerful ones I've found have 4nm torque, but I have no clue if this would be enough... Also, I probably will need a microstepper in between to have bigger resolution. Any suggestions are welcome.

    cheers,

    Kirsten
     
  2. jcsd
  3. Aug 14, 2013 #2

    berkeman

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    Staff: Mentor

    Kilogram is a unit of mass, not force. How many Newtons (N) of linear force do you need?

    I googled Stepper Motor Linear Actuator, and got lots of hits. Here is one of the manufacturers on that hit list:

    http://www.haydonkerk.com/?TabId=66

    .
     
  4. Aug 14, 2013 #3
    well, 1200 kg linear force would give about 12000 N

    Since I will be pushing only in 1 direction, I think a linear hybrid would be the thing to have ? But I can see that even the biggest one can only push 500 lbs (200 kg) ...
     
  5. Aug 14, 2013 #4

    berkeman

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    Staff: Mentor

    A 1200kg mass would *weigh* about 12000N. But unless you are trying to lift that mass vertically, I don't see how you can make that assertion about the force.

    What exactly are you wanting to do? How are you coming up with this force? What direction are you wanting to move/compress something?
     
  6. Aug 14, 2013 #5
    The direction will be vertical and I will have to overcome a pressure of 1400 bar (max.) that is put on a plunger of 10mm.

    Basically, it will be a syringe pump, driven by a stepper motor for high pressures. This will be used in analysing equipmant for laboratories (HPLC)
     
  7. Aug 17, 2013 #6

    Baluncore

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    Science Advisor

    A stepper motor positions things in steps. It does not work well when asked to do heavy work as it can slip multiple steps. This application should use a DC servo motor fitted with a shaft encoder, driving a ball screw through a reduction gearbox.
     
  8. Aug 17, 2013 #7
    wow, a lot of things that I never heard of before :-)

    I have not yet decided which engineering company could develop this 'monster pump', but this could be very useful information. Thanks.

    However, someone told me a stepper motor with torque of 20Nm and bal screw of 5 x 20 would give me just enough power... So if I take a 40Nm torque stepper motor and bal screw, I should be safe, no ?

    I don't know the prices of DC servo motors, but the price of a 40Nm stepper motor would still fit my budget...

    Of course, there are a lot more things to consider, like developing a syringe that can withstand this pressure (sealing will be crucial).
     
    Last edited: Aug 17, 2013
  9. Aug 17, 2013 #8

    Baluncore

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    The design of the actuator should follow this sort of path.


    We know the maximum pressure (and you know the stroke) so you can calculate the energy required. The size and cost of the motor used should be decided by the energy required and the time available, with an allowance for system losses.

    What is the stroke length required and how much time do you have ?


    The design problem then transfers to the way the motor drives the piston. The piston requires linear motion from a rotating motor, so a ball screw is worth evaluating. The ball screw must carry a force of 1200kg. Manufacturers tables will determine the diameter and pitch of the ball screw. The pitch is determined by ball diameter. Ball diameter is decided by the number of balls available in the nut and the maximum linear force. This appears to be an application for many small balls, either in a long nut or on a big screw diameter.

    Now we must match the motor RPM and torque to the pitch of the ball screw by filling the gap between the motor and the ball screw with some form of coupler or gearbox if needed.

    A prototype system that will work has now been designed. Engineering optimisation can be applied to minimise the cost.


    There are several alternative ways to do this.
    I would definitely consider a hydraulic pressure multiplier based on a large diameter piston driving the 10mm plunger.
    Town water supply usually has a pressure of between 30 and 60psi.
    So let us design for 30psi water against 20,000psi on your piston.
    Area ratio = 20,000 / 30. = 667 : 1 Area Ratio.
    Diameter ratio = Sqrt(667) = 25.82 : 1 Diam Ratio.
    Diameter of low pressure piston is therefore 25.82 * 10mm = 258.2mm minimum.

    Rams of that diameter are typically used in pneumatic systems. As an example, look at the bead breaker in a tyre stripping machine. There is the ready made “spare” part for your low pressure side.

    Turn on the domestic water connection and watch the piston move. Keep It Simple.
     
  10. Aug 18, 2013 #9
    ok, this is definitely stuff for engineers and not for chemists (like me) :-)
    Thanks for the input. If I don't find a good engineering company that can give me some direct answers based on the same information that I posted here, I will come back to you ;-)

    For the hydraulic pressure: I don't think this will work in my application because I have to be able to change the speed of the plunger. Also I have to be able to work without being dependable of a nearby water connection. This will also be very difficult to sell to the people who will buy this equipment.
     
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