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Author Topic: Driving a galvo head with Grex possible?  (Read 7334 times)

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Driving a galvo head with Grex possible?
« on: June 20, 2007, 07:40:31 AM »

Would it be possible to drive a laser galvo head (for marking) with Mach & Grex.
Galvo heads are typically controlled using an analog voltage, wich directly relates to a position in its working field (eg 180x180mm - 7x7 inch)
What i will do is create an electronic circuit wich has a counter(connected to the step en direction outputs), who's value is connected to a 16 bit D/A (one for each axis).
Since this galvo heads normally use linear control AND jumps, i will need a Grex, because of the speeds involved (in relation to its smallest step -about 2.75 µm).
Normally jump speeds from 700 to 1000 mm/s are used, with uncontrolled acceleration. So if i just go to linear movement, with very high puls rate (400kHz), it could be considered a jump. Writing speeds are lower (and linear).
I believe that my idea can work but there are some problems. There need's  to be some pause times after positioning. After all, it is an open loop system, so mach or Grex, don't know actual positions.
Wich brings me to my question.
What are the smallest delay times that are supported in such a setup. Can i use G4 to dwell, or do i need to write some plugin to support this stuff ?
I need delay times that are in the range of 10 to 10000 µs.
Any suggestions?
Do you want to have me committed?

Logic takes you from A to B, imagination takes you anywhere

Offline chad

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Re: Driving a galvo head with Grex possible?
« Reply #1 on: August 30, 2007, 03:16:34 AM »
Hi, I have not done much with high speed marking or machining but I have lots of laser display knowledge.

I suppose you could do it but there are probably better alternatives. What kind of head do you have? I have never seen a head that does not have feedback. If they are open loop you will have to wait a long time for them to settle down. If they are general scanning they have a torsion bar and will oscillate like crazy with those big mirrors on a step. If thy are Cambridge they cannot work with out feedback, they do not have any kind of physical centering.


Re: Driving a galvo head with Grex possible?
« Reply #2 on: August 30, 2007, 03:51:04 AM »
Hey Chad,
Thanks for your reply.
The mirrors are not stepper driven.
We have a head from scanlabs, something like this : http://www.scanlab.de/index.php?id=17919
It is controlled by 2 analog voltages wich relate to there position, i.e. 0V on axis1 completly to the right and 12 V would be at your leftt side. 6V would point to the center of the field.
Actually it might be that the electronics inside the head are closed loop, but when controlling with the normal program, there are settlng times (like 0.4 ms).
what i wanted to do make a program like this
G0 X10 Y10
G04 F0.4
M10(laser on)
G1 X70Y50 F400 (in mm/s)
G04 F0.1
M11 (laser of)

This is comparable with how the galvo's are controlled at the moment. (i took the liberty of studying a dissasembly of there driver, i can read, but i cannot create ... damn).

Do you know if a G04 with just 0.4 ms could work?, or does that get rounded to 0 or 1 ms

To pulse the laser there are even times like 40µs, but that i can solve with some extra hardware. ( a custom timercard)

Logic takes you from A to B, imagination takes you anywhere
Re: Driving a galvo head with Grex possible?
« Reply #3 on: April 28, 2008, 10:32:40 AM »
Maybe you can create a macro. I believe with the VBScript you can define a time as small as you need. It could be like an M150 and in could be something like:
while time()-x < .004