Mounting galvos

[Howie]

This should be easy to figure out but I just can't find the answer.

I'll be mounting my galvos this weekend and they arrived disassembled. I was looking at them the other day and it dawned on me, there is no notch or anything in the block or on the galvo motor. I can't figure out which way the mirrors should be facing or how deep into the block.

The beam comes into the bottom(y) mirror which I understand should be about 45 degrees or so to direct the beam to the top(x) mirror and then out. Are the beams combined and aligned through the dichros and then the galvos adjusted in sort of the same manner?

What I mean is do you adjust the deflection and placement of the y mirror to direct the beam into the x mirror then out to an arbitrary target then lock them both in?

I'm probably just being dense about this but I haven't seen a single mention of how to install them in the blocks, and I've looked. I've managed to answer a lot of my questions just searching around but this one has stumped me for a couple days now and my aluminum base is coming tomorrow.

[ElektroFreak]

First of all you need the galvo set assembled, installed and the galvo motors mounted loosely in the block and the galvo amps need to be powered up with 0V on their inputs. This will center the mirrors.

To align your galvos so that the beam is centered and pointing where you want it to be you need at least one working laser powered up and bolted in position with any necessary optics in place so that the beam is pointed at the center of the bottom galvo mirror.

Once you have the beam shining into the galvo assembly you position the mirrors (bottom first) so that the beam is reflected off the bottom mirror onto the center of the top mirror and out of the projector. You make adjustments until the beam is centered and pointing where you want it. The beam at it's centered point will represent the exact center of the laser projection area. Then you tighten the allen screws on the galvo block and you're done. Hope that helps..

[taggalucci]

Just saw EF's post after I submitted this which suggested similar

The beam comes into the bottom(y) mirror which I understand should be about 45 degrees or so to direct the beam to the top(x) mirror and then out.

I think you have X and Y confused if X in horizontal and Y is vertical. If you are mounting the galvo block in the normal operation, the bottom galvo is typically X and the top Y. A galvo block is normally used with the beams entering in one direction, either from the left or the right when you are facing the direction of the output/deflected beam. In the example below, the beam is designed to enter from the right...



You should find the galvo mounting block has one hole lower than the other. This normally indicates the location of the galvo whose mirror the incoming beam should hit first (X). Based on this, the beam should enter 90 degrees/perpendicular to the X galvo shaft and effectively 180 degrees/opposite the Y galvo shaft.

I can't figure out which way the mirrors should be facing or how deep into the block.

The depth into the block is a careful balance between the X and Y to achieve an optimum cross over of the two mirrors. Push each galvo into the two holes (be careful not to break off the mirrors)!

Set up the galvos with their amp and power on to get the galvos to centre. If you don't, you won't be working with the central position and will make life harder. This method will require that you keep the power on, so be careful not to short anything or add rotational force to the galvo shaft or mirrors.

Push and pull the galvos in their mountings to try to get a good cross over of the two mirrors. Looking directly down onto them should help get the two "paddles" to cross over uniformly. The X mirror should deflect the incoming horizontal beam vertically, hit the centre of the Y mirror and be deflected horizontally 90 degrees to the incoming beam. So each will need a 45 degree tilt to the beam angle to achieve this. The mirror surface should point toward the incoming beam (but obviously at the 45 degree offset). Lock the galvos in position temporarily. You can fine tune once everything is set up.

Are the beams combined and aligned through the dichros and then the galvos adjusted in sort of the same manner?

Having set up the galvo block as described, the centre of the X mirror defines your working beam height from the base. Unless you are using bounce mirrors before the dichros (see picture below) the lasers and dichro heights are dictated by this working beam height.



Considering the single point grounding scheme, the dichro block should be electrically isolated from the base but remain thermally conductive. I use a silicone isolation pad cut to size sandwiched between the block and 2mm aluminium cut to the same size as the base of the galvo block. Be sure to drill some corresponding holes (drill them bigger) in the 2mm alu first! So this will add about 3mm to the working beam height, so get this done first before trying to align everything.

What I mean is do you adjust the deflection and placement of the y mirror to direct the beam into the x mirror then out to an arbitrary target then lock them both in?

What I do is have holes in the baseplate that give me a millimetre or two of play to adjust the X and Z position of the block.

Then I get the first laser (usually a green, sometimes a red depending on your combining optics), basically the one you add the other two colours to, and set it up so that it outputs a beam at the working beam height. I do this as temporarily as possible so that you have the chance to adjust position and height as required. Importantly also set up the dichros temporarily and have them in the most likely position and angle you expect. If you don't do this, you will not account for the refraction offset from passing the beam through each dichro. This shouldn't add or remove height (unless you are going with vertical beam stacking of course)! This will normally put the beam back a mm or two (from the front of the projector).

A calliper gauge with a depth probe can be good to assist in setting the working beam height. I set the calliper at the working beam height (based on the X galvo mirror centre height from the base), place it in the path of the beam and then ensure that only the top half of the beam hits the base of the calliper gauge with the probe touching the baseplate. I can then check the beam is horizontal by checking the beam at various points along the base. If all goes well, the beam will hit the X mirror dead on. You can then permanently set this laser in position. If you have the incoming beam entering at a square angle and dead centre of the X mirror, the galvo block can also be locked into position.

Having loosened the galvos in their mounts, by pushing, pulling and rotating the two galvos, you should be able to get the first laser to exit the two galvos horizontally and perpendicular to the front of the projector. Tighten them up again.



Then you can set up the second laser height and dichro to achieve optimum centering/near-field alignment. By doing this, the beam will naturally follow the path of the first laser's beam and deflect as required of both galvos. Again I do this temporarily, mark the positions and then commit to the holes (allowing for some play helps).

Repeat for the third laser and you are almost there!

The last thing I do is a final push/pull/rotate of the galvos (and sometimes the block) to get the least splash and most reflection.

This method requires an incremental approach with each increment require deconstruction to drill the holes. It is slow, but will avoid you having to rework things in the long run.

[ElektroFreak]

That's a WAYYY better explanation than I could muster in a few moments time..

[taggalucci]

That's a WAYYY better explanation than I could muster in a few moments time..

Thanks Just don't tell my boss I spent most of the afternoon writing this up

[taggalucci]

Here are some useful posts/links...

http://www.photonlexicon.com/forums/...113#post132113 - Another of Buffo's great posts

http://www.pangolin.com/resguide03.htm - shows a nice picture in the sidebar with the deflection angles and beam path illustrated.

http://www.edmundoptics.com/onlineca...productid=2717 - shows a well set up block.

[Howie]

Thanks for the replies.

I'm sure it won't be a quick 15 minute project but your explanations are going to save me a LOT of time and headaches.

Now where is that UPS guy with my aluminum?

[taggalucci]

Here are some more photos which show some of the key points mentioned above...

Here are a couple showing the beam combining and alignment, and also illustrate the differing widths of the beam...



Although there's a noticeable difference between the 3 diode beam widths, this is not that noticeable in a beam show (in fact, at distance, it's hard to see the separate beams on a projection surface)...



Here are a couple showing the angle of entry and deflection of the X and Y mirrors...

[Howie]

Those pictures are awesome, thanks a lot.