Using stepper motor driven stages for macrophotography

AndrewC · Post by **AndrewC** » Sun Nov 09, 2008 2:57 am

I'm building a stage with stepper motor driven positioning. I've no concern about the stability of the slides but I'm trying to figure out some parameters for the drives.

Has anyone any direct experience of using a stepper motor driven slide ? Do you think they are stable enough when microstepping (uses partially energised coils to hold the motor "between" normal rest positions) ? This is a horizontal setup so holding power shouldn't really be an issue.

I've got one stage on a precision slide I can drive to 25.6um steps or 2.6um when x8 microstepping.

If I do some work to stabilise the carriage, I've got another drive I can index at 3.2um whole steps. That seems the more attractive but even though it will be very precise in depth (z) there might be some play in the x and y and I want to minimise the alignment needed by stacking software.

I'll probably end up making a hybrid of the two - mount the camera on the relatively coarse stage and the subject on the precision stage.

Any suggestions / ideas ?

thanks, Andrew

Graham Stabler · Post by **Graham Stabler** » Sun Nov 09, 2008 3:39 am

I've used stepper drives quite a bit including for my macro object movie rig. One thing you should know is that microstepping gives smoother motion but does not increase resolution, the drive will stop at the nearest half step, at least it will not step in individual micro steps. This means you have 400 positions per revolution for a typical 200step motor. That's 2.5um for a 1mm lead screw for example.

Graham

AndrewC · Post by **AndrewC** » Sun Nov 09, 2008 3:54 am

Hi Graham, are you sure about no increase in resolution ? For sure you may not get directly scaled accuracy but I think you do achieve better resolution. Accuracy can be increased with a linear rather than digital driver. The big problem is overcoming stiction of the drive train. Typically going to an x8 microstep reduces your holding/moving torque to (if memory serves me correctly) 20% of full step holding power.

rgds, Andrew

Graham Stabler · Post by **Graham Stabler** » Sun Nov 09, 2008 4:08 am

20% is quite a reduction so the question is, can you move by a single microstep? 8X is probably not too bad, half a half step. For low acceleration, driving a light load (including stiction etc) you might be OK, you should just try it there is not much else you can do, you can always use a bigger motor.

Graham

AndrewC · Post by **AndrewC** » Sun Nov 09, 2008 4:24 am

At my current rate of progress I expect to suck and see sometime in the next few months

Thanks for the answers anyway

Andrew

Graham Stabler · Post by **Graham Stabler** » Sun Nov 09, 2008 6:03 am

What is the sticking point?

AndrewC · Post by **AndrewC** » Sun Nov 09, 2008 7:17 am

Graham Stabler wrote:What is the sticking point?

... two little children, working in Europe for an American company supporting a 24x7 R&D site - just not enough hours in the day

Graham Stabler · Post by **Graham Stabler** » Sun Nov 09, 2008 9:13 am

AndrewC wrote:
Graham Stabler wrote:What is the sticking point?
... two little children, working in Europe for an American company supporting a 24x7 R&D site - just not enough hours in the day

Ouch, that would do it

g4lab · Post by **g4lab** » Sun Nov 09, 2008 8:48 pm

I saw this on fleabay

Might save some time with the electronics. The seller has all sorts of other similar things. Maybe it will shorten your deveilopment time.

AndrewC · Post by **AndrewC** » Mon Nov 10, 2008 12:46 am

g4lab wrote:I saw this on fleabay

Might save some time with the electronics. The seller has all sorts of other similar things. Maybe it will shorten your deveilopment time.

Thanks for the link - actually I've got boxes full of stepper motors, drivers, bearings, etc. The trouble is finding the time to integrate them. sort of thing you can't do in 15mins grabbed here and there

Still, it is satisfying to watch a project gradually take form and transmogrify before it even does anything !

Andrew

elf · Post by **elf** » Mon Nov 10, 2008 1:59 am

g4lab wrote:I saw this on fleabay

Might save some time with the electronics. The seller has all sorts of other similar things. Maybe it will shorten your deveilopment time.

This might help keep the sensor cool when shooting stacks: http://cgi.ebay.com/158W-Thermoelectric ... m153.l1262

AndrewC · Post by **AndrewC** » Mon Nov 10, 2008 6:40 am

elf wrote:
g4lab wrote:I saw this on fleabay

Might save some time with the electronics. The seller has all sorts of other similar things. Maybe it will shorten your deveilopment time.
This might help keep the sensor cool when shooting stacks: http://cgi.ebay.com/158W-Thermoelectric ... m153.l1262

I've been eyeing those for a while with the intent of making a chilled stage to keep live specimens moving slowly

Graham Stabler · Post by **Graham Stabler** » Mon Nov 10, 2008 7:27 am

They work very well and are the same thing you find in those tiny beer coolers along with a big heat sink and a fan. I started converting one to a more efficient micro fridge (reduced volume and increased insulation) but lost motivation to finish the project, plus it was looking a bit too ghetto.

Graham