microstepping for dummy

[selse]

I need very precise computer controlled rotation of a light weighted object (laser pointer). Rotation range should be max 90 degrees and speed and torque are also not important.
First I thought of geared stepper motor but recently I read of micro stepping so now this is the option? Then I thought of servo motor but I don't know if there is the microstepping option with it, and I need motor on demand to go on start position, also extra precise (this is easily done with servo, right?).

Please, I am artist with a bit programming skills and not engineer, and have very basic knowledge of these topics. Can you help me pair controller and motor, if possible with PlugAndPlay capabilities
Controller should be able to support 2-3 motors and allow me to have step of 0.04 degrees or smaller

Thanks

[vger]

At one time in the past I ran a laser show in a planetarium. Instead of moving the laser we moved mirrors to control the beam. We used "General Scanners" servos that had feedback loops for this, and could position the beams very accurately and rapidly (500 Hz full swing) just a little over 90 degrees. Microstepping drives are available from many makers. One you might find interesting is at Baldor found here...
http://www.baldor.com/pdf/literature...S-SeriesDC.pdf
These will do 51200 steps / revolution or about .007 degrees / step
You would need the USB cable to set parameters in the motor/controller and one of thier motion control boards for the computer.

Don't know what your budget is but full plug / play may be a bit expensive.

Steve

[kreutz]

Originally Posted by selse I need very precise computer controlled rotation of a light weighted object (laser pointer). Rotation range should be max 90 degrees and speed and torque are also not important. First I thought of geared stepper motor but recently I read of micro stepping so now this is the option? Then I thought of servo motor but I don't know if there is the microstepping option with it, and I need motor on demand to go on start position, also extra precise (this is easily done with servo, right?). Please, I am artist with a bit programming skills and not engineer, and have very basic knowledge of these topics. Can you help me pair controller and motor, if possible with PlugAndPlay capabilities Controller should be able to support 2-3 motors and allow me to have step of 0.04 degrees or smaller Thanks

Micro-stepping does not offer that kind of positioning accuracy unless it is tailor made (using two different microstepping tables (forward and reverse) adjusted for specific motor) and/or a closed loop setup with high resolution encoder.

Using a servo with a 2500 ppr encoder (decoded x4 = 10000ppr => 0.036 degrees per pulse) or higher resolution will probably be simpler. If you gear down the servo you could do it with less resolution encoders, but the backlash will probably be higher than 0.04 degrees even with a high quality gearbox.

Depending on the weight of the load, a galvanometer will do better than both of them by moving a little mirror, your laser pointer could be stationary.

[vger]

The servos (galvos) we used for the laser show had analog feedback loops to the drive amp. We did have to periodiclly adjust zero offset and gain to keep everything in line. Had 4 X/Y pairs of galvos, one pair for each of 4 colors.