Ben's 2.x Laser Build

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Re: Ben's 2.x Laser Build

Postby BenJackson » Tue Sep 13, 2011 9:52 pm

bdring wrote:The main board cap is on the 5VDC line. The 5VDC power supply has short circuit protection, so it is not supposed to take down the 24VDC power supply.

Ah, I didn't realize where that cap was. I had the reverse problem: 24V short took out 5V (hence no fan, one of the obvious visible signals)

bdring wrote:The 5VDC current is quite low in the drivers and the cap is so close to the driver that I don't see it inducing ripple in caps on the driver. I think the cap that failed on your board was on the VMM (motor) line.

That's correct. I just assumed the cap was on the 24V line. It probably needs a cap on 24V (if not per driver, at least somewhere on the board). A 24V cap on the board will reduce the ripple in the cap that blew on mine and reduce its power dissipation. In fact it's possible that the 4.7u caps on the pololu modules are "sharing" between the modules and the weakest one is dissipating more power than the rest and blowing up. Survival of the fittest!

In fact, although it's not an ideal location, you could easily clamp an electrolyic cap in the 24V fan screw terminals. I'll put a scope on it tonight and see what it looks like.

(speaking of those fan terminals: Those blue screw terminals are easily the worst screw terminals in the system. My fan ground lead kept falling out even though it appeared to be clamped. The removable green terminals are nicer and the DIN rail terminals are nicer still)
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Measuring the ripple on 24V

Postby BenJackson » Wed Sep 14, 2011 2:49 am

I put a scope on 24V at the 24V fan terminal. Normally you'd want to measure noise as close to the device as possible, but it's not very convenient with the board installed and given no pre-existing bulk capacitance on the board it's probably fairly accurate. After I add the cap I'm probably getting too generous a result (due to measuring right at the cap).

Here are snapshots with the stepper drivers enabled and disabled and with and without a 470u 50V cap mounted in the 24V fan power port:
24v_cap.png


Capacitor installed:
P1000121.JPG
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More experiments in pulsed cutting

Postby BenJackson » Wed Sep 14, 2011 7:07 am

I did a bunch of tests in 5mm plywood with varying parameters and got good results at "full" power and 0.0125mm pulses and 20 pulses/mm (so about 1/4th pulse duty) at F300. The cuts are even less charred than the ones I illustrated above.

Oddly adding more pulses per mm made the cuts shallower (when I did slices that ran up to the edge). 20 PPMM was chosen as about 500 PPI based on the recommended Epilog settings, I went so far as to try 18,19,20,21,22 and 20 was always the winner in cut depth. Cut depth increases up to about 0.125mm/pulse (making max pulses/mm 80) but not much above that.

If you go to full power (continuous wave) the through cuts are much faster -- maybe F500.
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Re: Ben's 2.x Laser Build

Postby dirktheeng » Sat Sep 17, 2011 12:36 pm

Wow,

I think this could be some of the reason why my stepper drivers humm too. I'm going to go get a cap and put it on mine and see what happens
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A jig for quickly positioning material

Postby BenJackson » Sat Sep 17, 2011 11:31 pm

One thing I miss from the Epilog I used a long time ago is the edge rails that let you quickly register 0,0. I made this one to key off of the table T slots:
P1000123.JPG


I first cut the plate and the "rails" and glued them up using M5 screws to ensure alignment. Next time I'd probably put 3mm holes at the ends to ensure alignment because of the tiny kerf on the guide rails where the M5 passes through. With those glued on I installed it and did a big square cut at 0,285 (my upper left corner) thus ensuring it's perfectly aligned.

This is 1/8th acrylic, which is slightly too thick, but it actually works out fine (the plate actually "hovers" a bit). You have to be sure to focus for that when you make the final cut.
Attachments
zero-fixture.zip
(2.27 KiB) Downloaded 355 times
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Re: Ben's 2.x Laser Build

Postby BenJackson » Wed Sep 21, 2011 6:05 am

I've been turning the laser, water pump and assist air on with a power strip since my laser was just wired for "always on". I finally got around to wiring up my light-up front panel rocker and cut a back panel to hold an outlet and the power connection. It feels so decadent to turn on the laser and have the water/assist air come on automatically when a job starts.

The water/assist air are set up to come on whenever my "master laser enable" (M3) is on and for another 20 seconds after it goes off (M5).

Currently the blower (switched by one phase of that ginormous 3-phase DIN relay) is on direct control but I will probably automate that as well. Since it's separately controllable from the other side of the outlet I feel like I should have a special, different rule for it. It probably makes sense to do roughly the same thing as the water and air. Maybe run it less after...

One thing about having a back panel is is that my suction is now so good that there's a tremendous whistling sound where the air goes around the door. I had noticed it to a lesser extent when blocking the back of the electronics bay, but now that it's really closed off it's quite loud. For now I'm using the panel on top of the electronics bay (still not secured) as a "blast gate" to let off some pressure. I might have to gasket the door or cut more air holes somewhere. I wonder if there's something I could just stuff into the T-track on the sides of the door.
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Re: Ben's 2.x Laser Build

Postby StigOE » Wed Sep 21, 2011 7:24 am

BenJackson wrote:The water/assist air are set up to come on whenever my "master laser enable" (M3) is on and for another 20 seconds after it goes off (M5).

Isn't it recommended to start the water pump some time before you start the laser? And leave it on for a while (more than 20 seconds) after you've stopped the laser to let it cool the tube?
BenJackson wrote:I might have to gasket the door or cut more air holes somewhere. I wonder if there's something I could just stuff into the T-track on the sides of the door.

I believe it should be possible to use one of the Misumi slot covers, but I don't know which type would be best, the foam type or the plastic type.
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Re: Ben's 2.x Laser Build

Postby BenJackson » Wed Sep 21, 2011 6:45 pm

StigOE wrote:Isn't it recommended to start the water pump some time before you start the laser? And leave it on for a while (more than 20 seconds) after you've stopped the laser to let it cool the tube?

The water jacket is full of water all the time. If it weren't you'd have to personally supervise it to ensure it was free of large bubbles every time you started the pump. Also M3 is merely the master enable, it doesn't fire the laser. This is because EMC knows about "spindles" and if you stop a run it stops the spindle. It doesn't do anything about digital outputs.

During a cut you're at a dynamic equilibrium with the heat producing parts of the laser warming nearby parts until you reach the water cooling. So there's some gradient from hot to coolant temp. When you stop cutting the heat producing parts immediately stop getting hotter. The only reason to run the water after is to keep the parts between the heat producing elements and the water at the equilibrium temperature rather than letting them get warmer when the stagnant coolant warms up.

All that said I've never really noticed my coolant getting warmer at all...
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Another step towards "print to laser"

Postby BenJackson » Sun Sep 25, 2011 2:55 am

This boring and sort of wobbly star:
P1000125.JPG


is notable because I drew it in Inkscape, exported as PostScript (could have equally well printed it via the Generic MS Imagesetter) and converted to a combination of raster and vector cuts with a script.

The basic formula is:
  • The pre-existing pstoedit gcode filter is used to convert the PostScript to vector operations. A PostScript preamble modifies the execution environment so that only lines < 0.6 point (about .2mm, or the laser spot size) are allowed through. All the fills, images, text is suppressed.
  • Ghostscript is then used to convert the raster parts (by way of another preamble doing the inverse of the first) into an image. (Ghostscript is also the backend of pstoedit)
  • A python script crops the white borders off the raster part and emits the gcode line necessary to raster the image
  • The main script then edits that into the beginning of the vector gcode and cleans up some other header/footer issues

There are a number of rough edges, not the least of which is that the pstoedit gcode plugin is very primitive. There's no vector sorting, no way to use things like color to influence the output, etc. It also works in inches which forced me to make all of my rastering scripts unit-aware so they work under G20 and G21. Also the raster conversion step should be able to slice the engraving steps into smaller jobs where it makes sense to split them up (and even using color to do the split and/or choose power settings).

At this point the only thing missing between hitting "print" on a desktop and having that show up as a gcode job in EMC2 is a bit of Samba configuration (a samba print server will just drop the PostScript from the client into a directory) plus invocation of axis-remote to automatically load the job into EMC2.
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Re: Ben's 2.x Laser Build

Postby naPS » Sun Sep 25, 2011 3:52 pm

Sweet! That's awesome!
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