Getting More Power and Cutting Accuracy Out of Your Home Bui

[bdring]

dirktheeng wrote a great blog post detailing his work with the pulse per step power control method....

http://www.buildlog.net/blog/2011/12/ge ... er-system/

[lasersafe1]

Very interesting! I will need some time to digest that information. Looks promising. I wonder if the pulsed method actually allows us to drive a tube beyond normal specifications since the plasma will not be held in the high state but for a brief period.

[mikegrundvig]

Wow, that was quite a read. I was wondering about over-driving the laser as well as it's basically running higher voltage for far longer. Though I see he calls out that the laser is cooler over all.

Now my big question: are the DSPs we can use for our lasers supporting PPI settings already?

[BenJackson]

With EMC I actually implemented PPI where the pulse *length* is really in *length* rather than time. I also found a nonlinearity similar to Dirk's where lower pulse rates seemed to have more penetrating power.

I should revisit that and implement the simpler pulse time mode now that Dirk has done the work to tell me how long the pulse should last

[lasersafe1]

Now that I think about it, it is "effectively" CW beam from the tube and you should abide by the recommended currents. It might actually even be bad for the tube since it spends much more of its life in the "starting" state and less in the lower "running" state. We need a volunteer to run a tube 24/7/365 in this pulsed state to check life.

[BenJackson]

The tubes are too cheap to care IMO.

[bdring]

When tubes are engraving, they are running pretty close to this mode, so one would think it is not too much of a problem.

If it cuts faster it has less total hours, plus the operator productivity comes into play.

[bill.french]

I was going to ask this on Dirk's build thread, but I'll ask here!

What's the significance of tracking direction?

[canadianavenger]

Nice posting! I'm curious as to how the proposed PPI solution behaves with a 45 degree line and a circle. I think a good test image would have been a 1inx1in triangle [along X & Y] with a circle inside of it. PPI in just X or Y is relatively simple, PPI at arbitrary angles and on arcs is much more difficult. The naive solution would simply pulse n times every inch in travel for either X or Y. [this basically results in a grid of the PPI frequency, and pulse at the intersection points] This would, however, result in the power density being only 0.707 that of a purely vertical or horizontal line on one that is at 45 degrees.

[edit]Nevermind, I missed the code... took a look, and travel distance is being approximated by Pythagorean theorem. The calculated distance is not actually the travelled distance, in this case, but the crows distance from the last pulse, which should be good enough for most applications. This also answers the previous question about the use of direction... direction is needed to know the distance from the last point/pulse. To simplify a bit... imagine drawing a circle with a radius 1/PPI around the point of the last pulse. Whenever your path crosses that circle, another pulse will be made, and the process starts over. Any additional meandering around inside of that circle is not relevant to the calculation, and is effectively ignored.

[dirktheeng]

Now that I think about it, it is "effectively" CW beam from the tube and you should abide by the recommended currents. It might actually even be bad for the tube since it spends much more of its life in the "starting" state and less in the lower "running" state. We need a volunteer to run a tube 24/7/365 in this pulsed state to check life.

I don't think this will be much of a problem. I ran this mode for hours and hours at a time cutting out all the gifts for christmas (that's why I haven't posted anything lately... too busy with making the gifts). To answer the question, you have to think about what would be the failure mechanism. The bigest failure mechanism to worry about is overheating any of the components due to over current (specifically the mirrors). However, the actual duty cycle for the laser is much lower with this control method. Under most circumstances, the laser is on for 2ms and then off for 20-100ms which means that the duty cycle is only 2-10%. Now if the power level for that short burst is on average 2x the normal on (which is probably a big over estimate), the duty cycle is still only 5-20%.

I'm not sure how else we would really get the laser to fail. I don't claim to be an expert in this by any means, but I have had no problems and those doing engravings where the laser is being switched on and off frequently don't have problems. Besides, a tube is only about $150, so if I have hto replace that a little more often to get better results (which is not a statement of fact or experience at this point), then I would be willing to do that.