Author Topic: Multiple Galvos  (Read 1543 times)

Beginnings!

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Multiple Galvos
« on: January 19, 2018, 11:04:13 AM »
Hello,

I wasn't too sure that this topic was still achieve, but it seemed most relevant since it is about 3d printing that I have my query. I am just at the beginnings of understanding SLA as a 3d printing option, and the thought  of using your board to achieve this is exciting. However, a lot of the build areas that are possible across all SLA technologies, seems to be a little small, for what I am after, and I wanted to know whether it was possible to increase this using the configuration in the attached picture. Or am I just asking for a whole lot of pain? Any direction on this would be greatly appreciated.

Regards,

P.S On the drawing I now realise I spelt Galvos wrong, apologies
« Last Edit: January 21, 2018, 11:17:07 PM by Macpod »

Macpod

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Re: Multiple Galvos
« Reply #1 on: January 21, 2018, 11:24:21 PM »
Hi,

I split your topic to make this easier to track. Thank you for the sketch.

To gain higher resolutions and print size you could do something like this. Already the library contains a feature that will let you uniquely identify LaserShark units using their serial numbers. It may be a bit of a headache to align everything plus account for correction of the projection surface (remember you have to either use optics or software to correct for this!).

Have you considered putting a single galvo on an x-y table and move this to gain more resolution? It will be slower, but it should be simpler to build and likely cheaper too.

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Re: Multiple Galvos
« Reply #2 on: January 22, 2018, 11:01:38 AM »
Hello,

Thanks for coming back to me mate, wasn't sure you would, I have been having a spot of bad luck getting fed back from anybody. Ideally, it would be a build area of 300mm x 300mm, and just trying to squeeze as much res. out of it as possible. Your response to alignment issues, was certainly playing on my mind, would your board drive one of these Chinese scanner heads, or similar?

https://www.alibaba.com/product-detail/405nm-High-Speed-Laser-Scan-Head_60484790424.html

And I could just add a pimpin f-theta lens like this one:

https://www.aliexpress.com/item/FL-254mm-scan-area175-175-YAG-semiconductor-fiber-galvo-f-theta-scan-lens-system-for-laser/1473906553.html?spm=2114.10010108.1000014.10.2ae04e73ZWkwTS&traffic_analysisId=recommend_3035_null_null_null&scm=1007.13338.80878.000000000000000&pvid=511bd05e-96bf-4e7b-a973-f0714e94a5d5&tpp=1

To push the print are out to 300mm x 300mm? Is scan area the same as print area?

Sorry for the long links, don't know why aliexpress does that.

Thanks,

Macpod

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Re: Multiple Galvos
« Reply #3 on: January 22, 2018, 07:33:52 PM »
I haven't played with these scanner head types before. I see that it supports the XY2-100 digital program (which you wouldn't need/want a LaserShark to control). In quickly looking around the web I see that some of these heads support both analog and digital input. One of these might be controllable by the LaserShark. Do you have or can you request a datasheet and pinout from the manufacturer?

Yes, the F-theta lenses are a means to correct the projection plane that is frequently used by engravers/3d printers.

The area the laser is able to draw upon will depend on how far away the galvo system is from the drawing surface. As you move further away, the laser movements will become greater between points. The LaserShark has a resolution of 2^12 bits = 4096 theoretical points*. With a setup that allows for a 100mm printable area that means that each bit shift will move the laser focus by (100mm/4096) = 0.0244140625mm. For a 300mm area these points would be 0.0732421875mm apart

* Note that neither the DAC in the LaserShark nor the galvo amplifier pid loop is perfect thus you will likely not have a full 12-bits to work with outside of a theoretical sense. You will also need to take into consideration "drift" caused by temperature in the LaserShark dac, amplifiers, galvo amplifiers, and galvo feedback components.

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Re: Multiple Galvos
« Reply #4 on: January 23, 2018, 09:04:41 AM »
Hey Mac,

Again thanks for getting back to me, I am learning bucket loads! Sorry, about departing somewhat from the topic subject. Yeah, I think I will do some digging for some datasheets on those units, not sure I will get much from the Chinese manufacturers, but since I wanna get it close to right the first time, it might be worth investing in some more locally produced equipment, which might also make finding datasheets easier.

Further to the laser resolution, I have a couple of follow up queries if you would indulge me. Your note, in regards to the departure from the theoretical valve, would it be a safe bet to assume for design purposes, an operational valve of 80% that of theoretical, hence 4096 * 0.80 = 3276, odd? Therefore an expected point shift of approx. 0.09mm for an 300mm area. Further to the point shift, given 0.09mm between points, would you need to allow for the laser dot to be focused to a approx., diameter of between 0.1mm to 0.09mm? Just wanted to cross tees and dot i's before taking my foot off the till.

Macpod

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Re: Multiple Galvos
« Reply #5 on: January 23, 2018, 10:15:58 PM »
To properly calculate the value you would need to sum up (plus multiply for amplifiers) the errors and non-linearity of all the components. I wouldn't want to make a guess without significant experimentation which I have not formally done. What I would do in your design is try to keep temperatures as stable as possible.

I think if i were experimenting with this I would try to use as focused a beam as possible and then increase the diameter if you find you have problems. I suspect as-is this won't be a problem due to the beam width of your laser (assuming you will keep it stock) and it's transverse electromagnetic (TEM) mode.