linear motion (stepper+rack and pinion)

By fixing platform on rack and fixing motor on pinion, and using a stepper controller.

Assuming that the platform is in inches or cm and not mm or m.

First you need to attach some slides or linear bearings to your platform.

A standard stepper can do 200 (or 1.8deg per step) or more steps per revolution.

Then you need to calculate the movement per revolution of your rack and pinion. (in steps per mm or mm per revolution / step)

With this ratio you can achieve any movement.

Also have a look at a lead screw on the stepper. With 400 steps per revolution and a 4mm lead screw you van get 0.01 mm resolution. 5mm lead screw does well for inch moves.

Lets not forget though that one can only approximate linear motion with a stepping motor. Stepping motors move in steps. A micro-step controller can minimize the size of these steps but they will still be steps.

Depends on the transmission used on the stepper. You can gear the thing so that a single step is smaller than your gear lash.

Not true, unless the gear reduction has some form of dampening factor built in to smooth the steps. But even if this is dampened, at some velocities the steps will reappear. You are correct that the non-linear steps will be smaller and possibly the gear chatter could be larger than the non-linear steps. But without knowing what the OP is doing with this stage, I would not claim that either of these will be insignificant. I believe it is better to warn somebody of a probably insignificant problem, than to ignore any aspect you noticed but that others didn't see.

Are we talking about the static position resulting from a motion or a motion? If we're talking about moving the device and watching it as it moves you are correct. If we're just trying to hit a position then a stepper will work.

I guess I deal with moving things to a process position rather than dynamic motion....

Why ask the same question twice in two seperate Blogs???????????????

I suggest you contact an OMRON dealer.

Ask for information on Linear motors (not stepper motors) . You can resolve your problem of precision (0.05 mm) , speed (20 meters/sec), acceleration on any single axis (20 G). This is relatively new technology. A limit would be the distance you can move the object.

cheers

I did not read 20 meters a second from the OP, where did you get that from please?

If true that is quite a speed to hit, a servo motor will be better in such a case I feel.....

Andy, you are right, I must have made a mistake in filling up the performance sheet. However we applied this motor to shift the slot connection on a series of peristaltic pumps. The maximum displacement was 2 meters and this was done in 0.5 seconds with acceleration and deceleration. Incredible speed and precision.

Sounds expensive though, is it?

Andy

Expensive is always subject to discussion. For us it turned out to cost just as much, if not less than the traditional system considering the money we saved in linear bearings, supporting platforms and transmissions. Above all we saved a lot of time to put things together and setting up the system. The maintenance time and cost is practically nil compared to a traditional system. We are controlling 60 pumps with two motors.

cheers