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Fire!

Postby kbob » Sun Aug 10, 2014 11:14 am

It lives!

Yesterday I hauled the laser cutter out to the garage, wired up the laser power supply, screwed on the rest of the skins, did some last minute debugging, and burned marks on some cardboard.

I'll give the blow-by-blow in a minute, but right now I'm looking at two problems.

1. Focus. I can't find the focal point. The best I can do is about a 1 mm wide beam. I got my optics from Bart's Makerslide Store, which is down now. I don't remember what the nominal focal length is.

2. The Y motor is skipping steps. I have one example where it's a repeating pattern, skipping once every cm of travel. I have another example where it skipped about 3 mm at once. In other cases, it doesn't skip at all. The slower I go, the more it skips. I'm perplexed.

Here's the whole story.

Two weekends ago, I made a little daughterboard for the Azteeg. It sits in the position intended for the 2nd extruder motor driver. It routes the signals for the laser power supply, and it also holds an MCP4725 DAC chip which I use to set the laser's power level.

Then I wrote a bunch of software.

I got the status monitor software "finished" -- it's kind of a dashboard display for the laser cutter.

I redesigned the safety interlock software. The problem is that if you hit the E-stop switch in the middle of a print job, the print commands would continue to be processed, but the lasers and motors were shut off. If you released the button before the print job ended, it would resume at the wrong position. And there was no way to know whether the job had finished. Now, if you hit the big red button, the firmware discards all commands until it receives a Stop command. The Stop command resets the Emergency Stop state, and commands that follow that work normally again.

Finally, the MCP4725 is a 12 bit DAC with an I²C control interface. I learned about I²C, wrote a driver, and put in a new command to set the laser's power level. That part of the API is kind of hacky -- I may redo it.

Yesterday morning, I got my wife to help me carry the laser cutter down the stairs and out to the garage. I hooked up the water and air, verified the water doesn't leak, and tested that software control can switch the pumps on and off.

I installed the laser power supply. It is on a little plywood shelf above the rest of the electronics. I put it up there so it would be close to the laser tube, but then the power supply came with a connector on the + side, so there's about 12" of cable to accomodate the connector. Next time, all the electronics go on the same level.

I attached all the skins. That was straightforward.

I found a piece of scrap wood and placed it between the main laser and the first mirror. I closed the box.

Then I fired up the power supply for the first time. One second later, I used the Emergency Stop button for the first time. The laser came on as soon as I switched the power supply on. A few minutes later, I figured out why. My controller is using active-low logic for the laser pulse, but I'd mistakenly wired it to the power supply's TTL High input. Fixed that.

I had written a test program to fire the laser for 1/10th second whenever I press the computer's Enter key. I'd tested it with an LED standing in for the laser. That program did not set the laser power level, so I added the DAC support to it. Then I spent about 45 minutes debugging a missing initialization call. Link.

That resolved, I could fire the laser under software control.

I was surprised to see that the laser beam is quite wide, about 4 or 5 mm in diameter. I guess I'd read that once, but I'd forgotten.

Aligning the lasers required lots of trial and error, as expected. Having the red laser diode did make it a little easier. It took a while to get both lasers aligned and hitting the center of the first mirror. Then it was quick and easy to align the red laser by eye, and the CO₂ laser was aligned too.

Before I was done, I ended up writing another test program to streamline the process. both-lasers: when the lid is open, it turns on the red laser. When the lid is closed, it fires the CO₂ on the Enter key. I wrote that after about the 10th iteration of reflashing the firmware to do one or the other. (-: Link.

Then I started cutting some shapes. I started with a simple rectangle. Tried various speeds, power levels, pulse speeds/durations, and focal lengths. I never did cut all the way through the cardboard. I'm pretty sure that's because I didn't have a good focus.

I cut some more complicated shapes too, but because of the focus and the skipped steps, none of them completed successfully.


So I'm stoked. And I'm also frustrated. (-:
Bob
"If you didn't code it, it will never own you." (-:
kbob
 
Posts: 151
Joined: Mon Jul 09, 2012 6:39 am
Location: Eugene, OR, US

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