Is this really backlash ?

Discussions and help on this commercial controller.

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Re: Is this really backlash ?

Postby artofmystate » Tue Apr 17, 2012 7:21 pm

I am having a similar issue with 'backlash'.

Here is the file I am cutting from:

laser_test_sheet_1b.jpg


And here is the outcome:

laser_test_sheet_1.jpg


You can compare the insanely large varying gap by comparing the red and green circles.

Notice the orange arrow. This indicates typical backlash.

Yet, look at the blue circle. The far left side was last to be cut. This area is grossly lower than where it should be! (compare to vector file above)

So my thinking is this is software/firmware related because, IIRC, this phenomenon did not begin until I upgraded from an older version of LaserCad to the latest with the PPI update. However, I also changed PCs as well. There has been no electro/mechanical changes.
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Re: Is this really backlash ?

Postby whmeade10 » Tue Apr 17, 2012 9:46 pm

If you don't mind, I would like to run your file and see what the outcome is. I am using LaserCAD v5.93 with the PPI incorporated which is great to say the least.

- BIll
FSE 45w Deluxe CO2 Laser 5th Gen w/RetinaEngrave 3D | CorelDRAW X4
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Re: Is this really backlash ?

Postby iGull » Wed Apr 18, 2012 2:44 pm

Hi All

@naPS OK on the pulleys - I guess that your Y pulley shaft must have been threaded rod or something then ?

@Gav - had already checked grub screws and all clamping were tight (as a duck's ar$e :D ) but rechecked again anyway. thanks.

OK, I completely replaced my alloy 12mm Y shafts with 10mm steel - turned to 6mm at the ends to suit the pulleys (all my pulleys are aluminium and are all the same). I replaced the single mount plates with dual mount plates and dual bearings. I realigned everything this morning - the belts are as tight as I can get them - not as tight as top E on my guitar, but close to bottom E/A ! (bear in mind I didn't have this problem before).

Sadly, the problem is EXACTLY the same :x :x

I pulled out my old dial gauge and set it up on the stage and locked in position. Set the stage to go off in Y at 100mm and back again - did this tens of times and it returns to within 10 microns each time (0.010mm). I did this with the stage going positive and negative, measuring it from the back and front reference bars. This is definitely not backlash, or it would show on the gauge. I repeated the snake test using the dial gauge this time - in both directions (I reversed the system Y direction just in case) - again, it returned within 10 microns of it's start position.
Looking at the pulleys, I checked the runout on the shafts, pulleys and even did it with the belt surfaces - all within about 10-15 microns.
I even checked everything again using a vernier gauge just in case :D

I've attached a pic of the actual snake test - you can see both start and finish are accurately aligned, but the individual segments are not. Again, the total length should be 60mm, but they are exactly 59.0mm - the X is exactly 60.0mm and uses the same pulleys. I even gauged the OD of the pulleys just in case - as expected, all the same.

P1010067.JPG
Snake Test


So, for me, it is still pointing toward software/firmware contrary to Bill's results.

@Bill/@artofmystate, are you all using the latest and greatest versions of firmware and software ?
For reference, here's my setup again ...
Main board 7.12.04.01
LCD 5.12.02.29
LaserCAD 5.93
It would be interesting to see if artofmystate gets the same results from the backlash snake file.

I'm not sure I have any mileage left from a hardware standpoint - any smart ideas gratefully accepted - I'm stumped.

Cheers

Neil

PS, Just remembered, I swapped the stepper drivers too - exactly the same results :cry:
EMOs are a sign of weakness ...
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Re: Is this really backlash ?

Postby iGull » Wed Apr 18, 2012 3:04 pm

Hi Again

As a footnote, FWIW, I allowed the system to change the uM per step in the Y axis so that the 59mm became 60mm.
The 59mm correctly went to 60mm, but the segments were still misaligned and the system still returned to within 10 microns in Y.
I returned the uM per step back to their correct mechanical values.

Cheers

Neil
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Re: Is this really backlash ?

Postby artwood_decor » Wed Apr 18, 2012 4:34 pm

I don't have a machine yet, but...

How difficult would it be to run using MACH 3 only?
If lots of rewiring and setting changes, then this doesn't make sens.
However, I think that would tell you if it is backlash in mechanical or issue in the software.
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Re: Is this really backlash ?

Postby whmeade10 » Wed Apr 18, 2012 4:56 pm

iGull wrote:Hi All

@Bill/@artofmystate, are you all using the latest and greatest versions of firmware and software ?
For reference, here's my setup again ...
Main board 7.12.04.01
LCD 5.12.02.29
LaserCAD 5.93
It would be interesting to see if artofmystate gets the same results from the backlash snake file.

I'm not sure I have any mileage left from a hardware standpoint - any smart ideas gratefully accepted - I'm stumped.

Cheers

Neil

PS, Just remembered, I swapped the stepper drivers too - exactly the same results :cry:


I will check my Main Board and LCD firmware versions when I get home tonight.

- Bill
FSE 45w Deluxe CO2 Laser 5th Gen w/RetinaEngrave 3D | CorelDRAW X4
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Re: Is this really backlash ?

Postby iGull » Wed Apr 18, 2012 5:06 pm

@Bill - thanks, I'm interested to see if it's maybe a firmware issue.

@-artwooddecor - I could actually go back to my lasersaur setup, but it is a bit painful as I don't have the mating connectors for the LO box yet - they should be here next week (my intention was to be able to quickly swap out for beta testing).

@artofmystate, if you pm me your file, I can also give it a try with my setup - see if the results are similar.

Cheers

Neil
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Re: Is this really backlash ?

Postby TLHarrell » Wed Apr 18, 2012 7:54 pm

Is this perhaps dropping steps? With the shifting that's occurring across the job on @artwooddecor, it looks like dropped steps during a rapid travel between parts. Run a program that travels around the entire table, then back to a reference point. Measure how much it's off from it's starting point. Do it 20x. Measure the result each time (fire a test laser pulse). If it's backlash, the result should not drift. If it's dropping steps, it'll drift.

Dropping steps is the result of either way too much belt tension or other mechanical factors, or trying to send too many pulses to the motor in too short of a time. Try disassembling part of the drive system and testing each section by hand for mechanical interference. For dropped steps, try turning your acceleration settings and maximum speed down a little and seeing if the problem changes or persists.
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Re: Is this really backlash ?

Postby iGull » Wed Apr 18, 2012 9:02 pm

Hi Tim

Yes, it might look like dropping steps, but definitely not. It always returns to exactly the same point strangely.
I have a test file that I wrote a while back for the lasersaur - it starts with a closure pattern - essentially a diamond - writes a whole pile of data then completes by writing the final part of the closure pattern - if the corners of the diamond meet, then no lost steps - it worked fine (at least it met at the diamond :D )
I can't comment on @artwooddecor - he'd (or she'd :-) have to try some other simple tests to determine if it were lost steps. The LO controller is easy to use in this scenario, just move it to say 100,100 - pop the laser, then move to say 1000,1000, move about some more (or as you say, write some oddball pattern) then return to 100,100 and pop the laser again - if the spots match, then you can be fairly sure that you are not losing steps (however, if the controller is lying ..... )

Mechanically, my system seems sound - I re-checked that this morning when I had the shafts and belts off - I even scrubbed all the rails and vee wheels (this is unheard of in my workshop LOL). I'm happy with the mod I made to the Y axis shaft bearings, they are very rigid now - they could in theory move in X if the shaft couplers were compressed or extended, but there is no sidethrust to do that - I toyed with the idea of a pair of thrust washers, but the ones I had were too big.

I've played with acceleration and max speed values too - always the same scenario. I've even written it with the laser at high and low power, laser off then do a laser pop at start and finish - even taped a pen to the head in case it was some strange interference thang ! (same results). I've checked the PSU's for noise (I have a 24V stepper PSU and a 12V controller PSU - I don't think using the same PSU for steppers and controllers is a good idea) - very little noise - usual switching crap on the high current steppers, but nothing untoward - system PSU is clean - just the same as always - I checked it when I built the machine so I had some kind of reference.

I disagree with your comment 'If it's backlash, the result should not drift' - that really depends on the degree of backlash you have and how much stiction is in the system - it may not be repeatable - you should see my Chinese lathe - horrendous :lol: .

Thanks for all the helpful comments Tim, they are all useful.

I guess I'll get to the bottom of the issue eventually - I should get the mating connectors next week and I'll be able to fire up the lasersaur controller again to check (assuming someone doesn't win the 1 dollar prize I'm offering for the answer in the interim :-)))

Cheers

Neil
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Re: Is this really backlash ?

Postby Greolt » Wed Apr 18, 2012 11:23 pm

artofmystate wrote:I am having a similar issue with 'backlash'.

You can compare the insanely large varying gap by comparing the red and green circles.

So my thinking is this is software/firmware related because, IIRC, this phenomenon did not begin until I upgraded from an older version of LaserCad to the latest with the PPI update. However, I also changed PCs as well. There has been no electro/mechanical changes.


Artofmystate

If this proves not to be a software issue, then I would suspect that your Y axis is losing steps when moving between cuts.

Moving between cuts often happens at a much greater velocity than when cutting.

Lower rapid speed and acceleration (software calls it space speed) and see if it makes a difference.

Greolt
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