Solved: Step Loss / Angled Engravings

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Solved: Step Loss / Angled Engravings

Postby bdring » Sat Sep 03, 2011 1:18 pm

I change my laser all the time to test various motor driver and controller setups. I recently had an strange issue with the DSP. On some speed and stepover values, I was getting angled or skewed engravings. Here is a picture on the problem. The square was done in cut mode then the same square was done in engrave mode.

angle.JPG
angle.JPG (23.83 KiB) Viewed 14732 times


The problem turned out to be the way I attached the steppers. The DSP has + and - terminals for the step and drive signals. I tried a few drivers in including opto isolated types and was able to repeat and solve the problem by wiring.

My guess is it has to do with timing of the direction and step signals. If you don't have the right connection, at one end of the raster it is either losing a step or stepping before the direction changes. Whatever it is it slowly walks in one direction an extra step or two per raster.

If you see the problem try changing your wiring scheme.
Bart
"If you didn't build it, you will never own it."
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Re: Solved: Step Loss / Angled Engravings

Postby naPS » Sat Sep 03, 2011 4:21 pm

This is the EXACT problem I was describing in my other posts. It's the only thing I've really been dissatisfied with the DSP, as a couple of other folks have had the same problem and no one was able to figure it out.

When you say change up the wiring, did you just switch one pair? Like, if it goes (for example) Blue Black Green Red you swapped Blue / Black, or Green / Red?

Thanks for figuring this out Bart!!!
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Re: Solved: Step Loss / Angled Engravings

Postby bdring » Sat Sep 03, 2011 4:26 pm

No it is the step and direction wires. If you are using pololu drivers look at this schematic. It works for me.

http://www.buildlog.net/cnc_laser/erp/g ... ber=D32016
Bart
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Re: Solved: Step Loss / Angled Engravings

Postby naPS » Sat Sep 03, 2011 9:42 pm

Hmmm... I have it wired up exactly as in that diagram. So you're saying move the step or dir wire to the terminal (+ or -) on the DSP opposite of where I have it now?
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Re: Solved: Step Loss / Angled Engravings

Postby bdring » Sat Sep 03, 2011 11:35 pm

You want ground and negative for both step and direction.
Bart
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Re: Solved: Step Loss / Angled Engravings

Postby naPS » Sun Sep 04, 2011 2:42 am

Yeah, I've had it wired up the way you describe since day 1. What was the actual process that solved the issue? Did you have them on the + terminals before?
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Re: Solved: Step Loss / Angled Engravings

Postby bdring » Sun Sep 04, 2011 3:24 am

I had it on the +. What drivers do you use?
Bart
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Re: Solved: Step Loss / Angled Engravings

Postby naPS » Sun Sep 04, 2011 4:21 am

I'm using a parallel cable adapter that I made that goes from the v2 Pololu interface board to the DSP. I'm starting to think that it might be a little too long or something, or there is noise getting into the system or something. Although, if that were the case, you would think it would mess up in both directions.
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Re: Solved: Step Loss / Angled Engravings

Postby naPS » Sun Sep 04, 2011 4:52 am

Welp - I'm officially a moron. I had both of them on the + terminal, and only noticed after checking it twice. I'm either going blind, or just losing it. Switched them to the - terminals like I had originally thought I had them, and voila, works like a champ.

I'm wondering if it has something to do with the rising edge / falling edge thing.

Thanks for finding this Bart.
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