Stepper motors or servo required?

[vwdevotee]

I'm working on a new project and I can't figure out if I should be looking for stepper motors, or going for servos. I'm going to be driving a acme lead screw, essentially unloaded, to a position and then holding there. the acme screw has a 32 percent effiicency, so it shoul dbe self locking. It's my understanding that steppers only run into problems (losing steps) under high acceleration/speeds, and under great loads. Since the load is minimal, and the motor will be electoronically limited to about 250rpm, will an open loop stepper motor be sufficient to maintain my precision? do I have a good handle on what will make me lose steps and therefore precision?

[RotarySMP]

Not enough information provided.

What load, what desire precision, what acceleration?

No idea if you have a good handle on what will make you loose steps.

250rpm with a 10x microstepping drive is only 8khz. You could easily get this speed with something like a Gecko being driven from a ancient Pentium one running Turbocnc.

Actually it sounds like you have repeative process and could probably drive the gecko from a simple counter circuit which send a set number of steps then whats for a further input, and send the same number again. The end switches could be set up to run the geckos direction pins.

A well designed stepper system won't loose steps.

[vwdevotee]

It's a fairly low demand system. Full steps (0.9deg) will be acceptable so I don't really need microstepping, although I may decide later to play with it. The load on the lead screw during motion will be small, a few kg. Acceleration will also be very small. I can allow up to 10 seconds for the motor to reach any position in a 160 revolution range. Once the screw is positioned I'm expecting up to 45kg to be placed on it. The process isn't actually repetitive, it will be going to different locations each time so it will still need real control.

I'm sure a well designed stepper system won't lose steps, but since this is my first system I'm not really sure how well designed my system will be.

[RotarySMP]

You are probably going to need micro stepping drivers with mid band resonance suppression like geckos to avoid stalling due to resonance.

What is the diameter of the lead screw? Is it lifting the few kg's, or moving something horizontally along a track?

[vwdevotee]

The lead screw is 13mm, and is lifting a few kg vertically.

So it sounds like I shouldn't have any trouble using steppers for this application, but I'll want to get good drivers for them.