XY positioning system help

[Av8or]

I need to design an ultraprecise (accuracy to about .5 mm) XY positioning system for biomedical/lab biology applications. The travel distance for both axes is around 30cm. This is supposed to be a prototype, so " biomedical quality" isn't an issue right now. What is an issue is that I need to know whether i should use screw or belt drive, and if i should use steppers or seros. Is there a way to get a servo to rotate 360 deg but still be able to feed it positioning commands (think lego mindstorms).

Thanks

 

[(*steve*)]

I'd go stepper motors and a screw.

You will have an issue with some slop in the positioning. You will probably need something that maintains tension on the table so it doesn't move due to the slop between the threads.

I have a colleague who has built his own table like this for positioning a PCB under his drill. He has much better than 0.5mm accuracy.

 

[davenn]

hi
welcome to the forums

Is there a way to get a servo to rotate 360 deg but still be able to feed it positioning commands (think lego mindstorms).
Thanks

yes but you would need some sort of feedback from the servo so that the controller knew where it was. systems I am currently involved with use servos to move units in an up/down ( 360deg) and rotate left/right (360deg) using optical encoder discs attached to the servo shaft, through which a laser shines through and onto a CMOS sensor. It has accuracies of 0.5 of 1 second of arc !! even Im impressed

cheers
Dave

 

[wannabegeek]

Just out of curiosity...does it have to be xy ?

I've heard a professor in one of my classes talk about how he needed an xy position system and ended up with a polar one that was a lot cheaper and just as accurate.

I'm clearly no expert....thanks for reading.
wbg

BTW: 'Slop' is called 'lash' ....in a shop you learn to take the lash out by always moving one direction or backing up past where you
want and then moving forward again. Machine shops have way more precise than 0.5mm position systems. They are definitely optically based.
There might be an off the shelf for this than can be modified. I

One more thing: You can look of the error on a given gear in the Machinery's Handbook.