Ben's 2.x Laser Build

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Re: Lost steps for the first time!

Postby BenJackson » Wed Jan 16, 2013 5:26 am

BenJackson wrote:
BenJackson wrote: All my settings are identical from parallel port to FPGA, except the FPGA is actually able to make the 1us pololu pulses. I assume I will need to stretch those a bit, which shouldn't have any effect on my max speeds. I could also put a scope on the pololu if I want to do some contortion to check the signal quality.

I made another spool with the timings bumped from 1us/200ns to 2us/400ns and no lost steps. Makes sense that you'd have to consider the waveform at the pololu and be less aggressive. The min step time on the pololu is around 30us anyway so the signalling time hardly matters.

I made another spool and lost steps again, so I put a scope on it and dug into the code. The signal quality is actually fine for the original 1us signals. I saw occasional back-to-back steps at the fastest possible signal speed, though (much faster than the fastest motor speed). The part of the manual I was glossing over:

(float r/w) maxvel
Maximum speed, in position units per second. If set to 0, the
driver will always use the maximum possible velocity based on
the current step timings and position-scale. The max velocity
will change if the step timings or position-scale changes.
Defaults to 0.

In other words, the driver will try to make pulses as fast as the signalling is allowed. I assumed it was safe to leave this at 0 because the position command (and thus indirectly the velocity) is already being driven by the trajectory planner, which already limits the axis velocity. However if the hostmot2 stepgen slightly disagrees with the trajectory planner it is willing to catch up "as fast as possible". With maxvel set and the scope on infinite persistence I didn't see any more doubled steps. I hope I have this nailed down!
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Re: Lost steps for the first time!

Postby BenJackson » Thu Jan 17, 2013 9:14 am

BenJackson wrote:I hope I have this nailed down!

Nope. I was losing a ton of steps (the problem seemed to be getting worse) and although signal quality looked fine at a "macro" level there were dropouts of 10-30ns in the step pulses themselves, but only on the X axis (parallel port pin 2). After swapping just about everything around and having it follow pin 2, I finally measured at the back of the PC and it was fine. So I measured at the end of the cable and it was crap (due to reflections, I think, not crosstalk). I assume the FPGA is just putting much faster edges out than the parallel port. Another cable looks much better (and does not lose steps! Yay!) and it looks even better with termination. I may pull the laser interface board and add terminators to it just to be sure. I could put caps on 24V closer to the pololus, too.

All hail the mighty oscilloscope, without which I would have been hosed. "Trigger on pulse width < 1us" was super handy. Also my new headlamp, for hands-free delving into the electronics bay.
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Re: Ben's 2.x Laser Build

Postby cvoinescu » Thu Jan 17, 2013 12:04 pm

BenJackson wrote:"Trigger on pulse width < 1us" was super handy.

That's a good oscilloscope you have there. I have a Tektronix 2465B, but now I have scope envy.
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Re: Ben's 2.x Laser Build

Postby BenJackson » Thu Jan 17, 2013 7:32 pm

cvoinescu wrote:
BenJackson wrote:"Trigger on pulse width < 1us" was super handy.

That's a good oscilloscope you have there. I have a Tektronix 2465B, but now I have scope envy.

I have a Tek TDS 2014. 4.5 lbs! Another big advantage yesterday. It was expensive (I think about $1700 refurb from Tek) but it has more than paid for itself. These days I'd probably settle for one of the $400 Rigol DSOs, but that wasn't an option when I got mine.
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Re: Ben's 2.x Laser Build

Postby educa » Thu Mar 07, 2013 2:18 pm

Ben,

I see that you upgraded your github code to work on linuxcnc2.5 now.

Does that mean that it now works out of the box on 2.5 ? Or are people still experiencing problems with rastering ?


I currently use jvcc's code, but the rastering isn't very clear to me. Therefore I would like to retry your code but in the past I had problems to raster engrave 2 pictures in 1 job.

The first picture was engraved, but the second was only partly engraved or not at all.


Any ideas ? Does anyone use BJJ github setup and be able to raster engrave multiple images in 1 .ngc job run ?


Kind regards,
Bart
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Re: Ben's 2.x Laser Build

Postby BenJackson » Thu Mar 07, 2013 8:54 pm

educa wrote:Does that mean that it now works out of the box on 2.5 ? Or are people still experiencing problems with rastering ?


I hope that's true. I think I've also cleaned up some math issues (where LinuxCNC's floating results were slightly different from python's, leading to disagreement on the exact raster geometry). That might have been related to the dual engrave issue you saw.

I'm afraid I can't test dual engrave for you right now because I'm set up for the Mesa 5i25 and with the stepgen in HW the raster trick I used does not work. I still need to add rastering to the FPGA.
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Re: Ben's 2.x Laser Build

Postby educa » Thu Mar 07, 2013 8:58 pm

Thats not a problem Ben, as soon as possible (I believe in about 1 week) I'll setup another HDD with your configs on it (I suppose its best to test on a fresh machine, since I don't think I can add both your and jvccs config on 1 machine ? You don't use the same freq component ?
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Re: Ben's 2.x Laser Build

Postby BenJackson » Fri Mar 08, 2013 2:34 am

educa wrote:Thats not a problem Ben, as soon as possible (I believe in about 1 week) I'll setup another HDD with your configs on it (I suppose its best to test on a fresh machine, since I don't think I can add both your and jvccs config on 1 machine ? You don't use the same freq component ?

If he changed the behavior without renaming it you can just rename the component (not just its filename, I think the component name is on the first line of the .comp) and change the references in the HAL. Or if you don't want to do that, use comp --install to reinstall between uses.

I actually think his is the same as mine except when given negative values, but you might want to check.
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Re: Ben's 2.x Laser Build

Postby jv4779 » Mon Mar 11, 2013 10:45 pm

You can use either version of laserfreq.comp with either config. You will just loose the duty cycle mode using Ben's code on my config, PPI will work the same.
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Re: Ben's 2.x Laser Build

Postby sliptonic » Thu Aug 22, 2013 9:37 pm

Today I was trying to engrave some tiny text and I didn't like the result I was getting so I started playing with LinuxCNC's path blending (G64). Even though I set the P value very small (0.0003) I was still getting bad results with linuxcnc deviating from the path a lot.

I finally figured out what was happening.
My preamble was like this:
G17 G21 G90 M3 S7 T1 M06 F1000 M68 E0 Q0.9 G64 P0.0003

Simply moving the G64 P0.0003 to a new line fixed the problem. I think what's happening is that the Q0.9 earlier in the line is being used by G64 for its Q word and activating the naive cam detector.

Just thought I'd mention it here in case anyone else has the issue.
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