My son talks about a "Klout" score, a measurement of how well connected you are or how much influence you wield on the internet. I wish there were a way to measure how well connected the various parts of our laser systems are. Let me tell you why.
In an earlier post, I showed how to set up tests that give you the right "exposure" - the right power, speed, and scan gap to get good, consistent results. I ended by saying I needed to try applying those same settings to photos, and I have been working at that for the past week. Not all that successfully, but working at it just the same.
Here is an example of the kinds of results I have been getting.
For about 18 months, I have had this problem; I simply have not been
able to figure out. It shows up most on materials that react in a somewhat
analog manner to laser engraving - wood, Laser Tiles, and the like.
Coated materials, e.g. anodized aluminum, are basically digital, either
the coating has been zapped away by the laser or it has not - it is one
state or the other - it is digital. And giving it a little too much power doesn't
seem to have noticeable negative effects. So it is pretty easy to set up a
scanned image (a photo, for example) and know that, as long as you give
it enough power, it is going to reproduce the series of laser firings
that make up a particular scan row in that image. Digital is good! Life
Wood, Laser Tiles, leather, and some other materials
have a much wider range of responses - all the way from barely scorched
wood and leather or light gray tones on the tile to total charred wood and leather or dense
black on the tile. This, of course, gives you a great deal of control
over the visual presentation of your image. Like I said, it is analog,
so you can do some really artsy things with that much latitude. But,
that much freedom comes with a price - you have to have really tight
control over your power output to maintain a visual consistency. And
therein lies the problem. The tests I have been running for 18 months are not consistent.
It is reasonably obvious, I believe, that the inconsistency is a direct response to an inconsistent delivery of power to the targeted material. That means it is an issue with the laser power supply, the laser tube itself, the main power source for the entire laser system, or some combination of the three. I have the whole laser on a circuit of its own and power in the shop is quite stable, I believe, so I don't think the issue is there. Unfortunately, neither power supply nor the tube issues are easily diagnosed.
In a separate conversation this last week with Bart over at BuildLog.net, he commented that he really likes analog meters better than digital, because he thinks they tell you more. I decided it would be worth my time to hook up an old analog meter I had lying around from my previous laser to see if it would release any secrets that would magically fix my problem. So this weekend, I located the meter, opened up my laser and went to work.
As I went about wiring and installing the meter, out of the corner of my eye, I noticed what appears to be a deformity in the high voltage positive cable that runs from the power supply to the laser tube. It was barely perceptible, but just looked odd - like maybe it had been kinked at some time in the past and had been straightened back out. Obviously, this was not a problem, after all, the power supply is still supplying power to the tube, right? But, what the heck. I actually have a couple of extra high voltage laser cables (don't get me started on why), so as long as the laser box is opened up, why not just swap it out? Can't hurt!
I finished wiring up the meter, closed up the laser and ran a test. Notice how much cleaner the engraved image is. There are no significant stripes.
Once the old cable was out, I became more and more curious about the deformity. Turns out that about half of the wire strands (there are only about a dozen or so anyway) were broken internally to the cable insulation. Not totally disconnected, I believe, but certainly poor enough to make an inconsistent connection.
Here are a couple of other tests. Again, the Rushmore tests started out with significant bands but in different places from one test to the next. The final is pretty good - most of what you may think are inconsistencies here are really just layers in the rock formation. The output is a very good representation of the original image.
The motorcycle image is from an ink drawing that I scanned. Again, the layers are totally eliminated.
As it turns out, it appears that my laser power supply was, indeed, connected to the laser tube; it just wasn't well connected.
Here is one final ink drawing from the internet without a before shot. I just like the image and though you might too.
I wish I could say that my issues with power consistency are completely past. That is just not the case. I do still have issues with significant dark area in an image. But, hopefully, I have eliminated one major cause.
I still need to find a way test the power supply and the tube independently. Unfortunately, I don't have a spare tube and/or ps to toss in there. Actually, I have an old tube but it is questionable all by itself. I certainly don't want to throw in yet another variable, and ALL tubes are a new variable. But, if anybody out there has a spare power supply, or one that you are not ready to use yet while you are still building your system, I would love to swap it into my system for a day or two, just to see if anything changes.