DIY Galvo?

[john banks]

HightSpeed-galvo-scanner-for-laser-lighting-NEW-Without-Show-Card-/230688515891?pt=US_Stage_Lighting_Single_Units&hash=item35b61b6733

If you took something like the above and pointed a suitable laser at it, changing the galvo mirrors to suit the wavelenth, and used a suitable lens, plus safety enclosure and interlock, would it be correct to say that the control signals needed would be:

Analog voltage from a DAC for X axis galvo
Analog voltage from a DAC for Y axis galvo
TTL or whatever the laser needs to enable/modulate its output (assuming solid state to avoid needing shutters)

I know producing a working system needs lots of details, but I wondered if conceptually I'd got it? Whilst you may not be driving it to 20000 points per second, it looks like the Ebay item is closed loop and simply moves the galvo to a position related to the voltage input for each axis?

Wonder if this could produce an interesting high speed marking system, especially with something like this:
itm/Coherent-High-Power-Lab-Industrial-Diode-Laser-FAP800-30W-808nm-30-W-33A-/390518444010?pt=LH_DefaultDomain_0&hash=item5aecb68fea
or

/itm/Industrial-808nm-15000mw-15Watt-Infrared-Focusable-high-power-laser-burning-TTL-/180943013777?pt=LH_DefaultDomain_0&hash=item2a210b4791[/url]

[matthew knott]

Hi John, you have the right concept, but none of the parts you have chosen will really be off any use. You would need larger closed loop galvos, these would then be able to take the correct mirrors you require, the smallest mirrors in practical terms would be 8mm, 10 & 15mm mirrors are more common. This is because the beam needs expanding from the laser to have any chance of it engraving anything. What you have picked are light show galvos, the raw beam can be much smaller.
Secondly the laser you picked would be pretty usless for engraving anything, it would normally be used as a pump source for a yag crystal, this with a q-switch and bits and pieces could make a laser that could be used for marking.

what you really need is something like this
and this (not this one mind you, some kind sole has chopped the fiber in half)
h (http://www.ebay.com/itm/IPG-PHOTONICS-YTTERBIUM-YLP-0-5-80-10-EOT-Laser-Fiber-cable-cutted-as-pictures-/170962388886?pt=LH_DefaultDomain_0&hash=item27ce270796) to control the whole lot, add a shutter, lens, etc etc
The DAC you speak of is normally done with a digital signal (called XY2-100) this is converted to an analogue signal to give the x & y positions, but its not a simple as an XY co2 laser as quite a bit of correction is needed because if you describe a box with the galvos you will actually get a is a a box with made of convex and concave sides. If your seriously interested I can help you out, but for a useable safe system budget £10k.

[john banks]

Thanks, sorry Mike about the direct Ebay links, I had forgotten the rule, it is so automatic to put them in forum posts even though I didn't have any commercial interests in doing so.

Thanks Matthew, just the sort of feasibility points I was looking for. If you have chance, can you explain about what beam expansion does?

The box with convex and concave makes sense considering the geometry, thanks for the tip. With my background with microcontrollers I was thinking I could producing the correct x and y voltage to position the mirrors of an inexpensive closed loop galvo, but the size of the cheap ones is a shame.

[matthew knott]

To have a decent marking area you need quite a long focus lens, a 160mm lens gives about 120mm x 120mm, the beam expander (collimator) makes the input beam to the focus lens bigger, and hence smaller when its focused, the bigger the expanded beam the smaller the engraving spot, but you need bigger mirrors to cope. Its the same for both yag and co2 lasers.
Cheers
Matt