DC Brushless Servos, RF Laser?

[Dex]

I am doing some research for my employer, primary function of the laser table would be engraving LED panels (lit from the side, acrylic engraved on the back).

So far I've narrowed it down to some nice machines from Vytek, Kern, etc. Budget is a concern however. Looked at a 4' x 8' chinese machine in action - didn't seem capable of what we needed and it was SLOW. The brand name machines seem quite fast but cost several times more. I understand that all the components are better on the brand name machines but they are out of my employer's price range. I also understand that the chinese machine probably didn't have a DSP controller.

My employer's budget is somewhere between the cost of the 4' x 8' chinese and a mid-size Vytek. He asked me if I could build a large 5' x 10' gantry system.

It seems that to be safely capable of making the panels at a satisfactory quality and speed, I'd probably need servos and a high quality laser (probably a Coherent). The system would also need to be capable of vector engraving. He would like the capability to cut out the panels (up to 8mm thickness) as well but I am not sure if I could get both cutting and engraving in the same machine. I've also looked into galvo systems but they have limited engrave area and non perpendicular cutting.

So the question is this: Is the LightObject DSP controller capable of controlling Servos and a Coherent RF laser? Anything else that I should consider?

Thanks in advance!

[fnaranjob]

Hi Dex,

Regarding the servos, I am building a machine now with brushless DC servos from Leadshine and the DSP controller works well with them, you will need servo drives that can take step/dir signals though, about the speed you should be sure you're comparing machines with similar laser powers, RF lasers can cut faster but it isn't such a great difference from what i've tested, and they are WAY more expensive, if you want to cut acrylic fast you will need high power (well I dont know what fast means to you, how many of those panels do you want to be able to produce in one day?, and what are their dimensions?), a Coherent150W laser tube can cost you around 20000 USD, while a glass tube with similar power can cost you around 3000 USD, that's a big difference (a lot bigger than the difference in feedrate), if you go with glass laser tubes you want to have good quality tube and optics, the long life model that Marco sells here works very well, if you are thinking about raster engraving speed you are going to need servos to achieve Kern/Vytek results (I think they can handle engraving speeds greater than 3000mm/sec), and for that you may also need a RF laser tube since those can be pulsed a lot faster (The DSP controller has an option for controlling RF lasers but i've never tested it, my guess is that it will work just fine)

If you use the DSP controller sold here you can do both cutting an engraving in the same job so that is not a problem.

Hope that helps, it sounds like a nice project!
Cheers

[Dex]

Thanks for the reply fnaranjob. I have a lot of work to do figuring all this out

I'm thinking that we should just invest in a smaller machine for now and go bigger later. Unfortunately there's a big gap between the budget and what the specs require in a pre-built machine. I'm daydreaming about a 5'x10' galvo/gantry hybrid but of course there's always a budget.

Would I be losing precision when going with servo drives that take a step/direction input? (I'm guessing that pre-built machines using servos use servo specific controllers.) And if I went with a Chinese glass laser tube, would I be able to upgrade easily to a RF laser later?

My major concern with being able to do the job is with the engrave quality. I need very consistent engrave depth and precise control of the depth to have a usable engrave on acrylic to use as a backlight. Let's say I put two machines side-by-side with the same specs (RF lasers/servos/etc), one being a Kern and one custom built with a LightObject DSP. Would there be a difference in engrave quality?

And since budget is a concern, how much would you estimate the machine to cost excluding man hours?

Thanks again!

[fnaranjob]

I don't think you'll lose precision with step/dir drivers, your machine's resolution will depend on gearing, encoder count and drive system, not on the mode the servodrive uses, to tell you the truth I have no idea what mode the servo drives from big brand laser manufacturers use, but from what I've read you'll get best results using either torque mode or velocity mode (not step/dir), which are options only available on more expensive motion controllers, now, I when I say best results I mean smooth motion, not resolution, they are completely different things, I don't know what precision you expect but I've seen some pretty nice looking photo engravings made with glass tubes, I think the quality of the engraving will depend on good quality laser and optics and a correct and uniform focus height across the entire workpiece, if you want to be able to engrave very small details you will probably need a beam expander or at least a short focus length lens to reduce the spot diameter as much as possible.

About the interchangeability from glass to RF it should be pretty easy but you should consider that their dimensions and weight are not the same, and if you plan on making a gantry style machine, the tube should be mounted on the gantry, so you should design with that in mind.

Engraving depth can be easilly controlled changing the power setting with the DSP controller and as long as your electricity is stable and the focus distance is kept constant I think you should get consistent engraving depth, I haven't had any problems with that so far.

About budget, well what is the size of the machine you want to build?, what accuracy you expect?, max speed? will it work full time? 24/7?