I have a simple linear translation stage that is driven by a screw, and I would like to attach a stepper motor to the screw drive. The axis of the screw and the axis of the motor are approximately colinear. The issue is that, as the screw turns it recedes away from (or advances towards) the motor. The spacing between the motor shaft and the screw drive can change by as much as 10 mm. A diagram of the problem and an example of the type of stage are shown below.

How can I couple the stepper motor to the screw drive in a way that allows for this expansion/contraction of the space between the two?

The problem

Translation stage

  • $\begingroup$ Can you put together a diagram for this? I'm having trouble picturing where all your inputs and outputs and connections need to be. $\endgroup$ – Trevor Archibald Oct 28 '15 at 20:06
  • $\begingroup$ I guess my main question is if the stepper is connected to the screw on its axis or if the connection is in the radial direction. $\endgroup$ – Trevor Archibald Oct 28 '15 at 20:19
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    $\begingroup$ I would guess that, if the screw moves away from the motor, you've got the motor installed in the wrong location. You want the motor on the drive end, not the actuated end. $\endgroup$ – Chuck Oct 28 '15 at 20:26
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    $\begingroup$ @ChrisMueller can't you turn it around so the screw remains stationary? $\endgroup$ – ratchet freak Oct 28 '15 at 20:49
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    $\begingroup$ Have you considered a splined coupling? You could get 10mm of extension/axial movement from a spline. Are you concerned at all with backlash? $\endgroup$ – GisMofx Oct 29 '15 at 3:46

All you need is a sliding base that can keep the motor from counter-rotating. You could use a linear carriage or a shaft and a linear bearing to create the sliding platform.

You attach the fixed end or shaft to the screw drive housing, either directly or via an intermediary like screwing both to lumber, and then you mount the motor on the moving platform. Couple the motor and screw drive together with any ordinary coupling mechanism; flanges, flexible couplings, etc.

Don't forget end stops and making the wiring long enough. First prototype phase is typically where you break all your expensive equipment.

  • $\begingroup$ That's a good idea that I hadn't thought of. I would prefer something a little more compact, but this might be doable. Thanks. $\endgroup$ – Chris Mueller Oct 29 '15 at 0:00
  • $\begingroup$ @ChrisMueller you haven't really given any details about this except that the stroke is 10mm. Basically any track should work, it's just up to you to pick one capable of withstanding the torque the motor needs to output to turn the leadscrew. McMaster's site is really nice in that you can generally sort on a number of features; the links I provided in the answer should be a fair starting point, and the terminology should help if you can't find anything there. $\endgroup$ – Chuck Oct 29 '15 at 1:40
  • $\begingroup$ Just for emphasis on the lack of information comment, here is a carriage that's roughly 25mm wide by 32mm long, that rides on a 12.5mm wide track, and supports about 45kg. I don't know how much smaller your "more compact" definition is, but it can't be too much smaller because stepper motors smaller than that can be hard to come by. I don't know the physical dimensions of your motor so I can't link anything more specific than pointing you in the right direction. $\endgroup$ – Chuck Oct 29 '15 at 1:49
  • $\begingroup$ By more compact I meant something that fits between the motor and the screw like a special coupling. That is, perhaps, an unrealistic hope though. Thanks again for the suggestion. $\endgroup$ – Chris Mueller Oct 29 '15 at 1:54

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