Movement banging on direction change

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aamir
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Re: Movement banging on direction change

Post by aamir »

Aash
Copy your CNCM folder and make a backup of it and reinstall CNC12 again .
Thats way we are clear towards software side
cncsnw
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Re: Movement banging on direction change

Post by cncsnw »

To the best of my knowledge, CNC12 running in position mode ("precision mode") will only correct for residual errors if you have set non-zero values in Parameters 261 and 262.

With Parameters 261 and 262 equal to zero, it is essentially open loop. CNC12 will read encoder positions when transitioning from drives-not-enabled to drives-enabled, and will just clock out movement requests incrementally from there.

In any event CNC12 will trigger a "410 ... position error" stall/fault condition if an axis is seen to be far away from where it should be (1/4"? 6mm? One revolution of the motor?). But that is just an error check, not a component of the control loop.
ashesman
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Re: Movement banging on direction change

Post by ashesman »

OK, so I spent the night out looking at this problem. Here is what I did. For all my tests, I am using a 0.6mm 1500 mm/min (0.024", 60 inch/min) step on the X axis in both directions. This is the movement that what was causing the bad finish in my chamfers:
  1. To remove doubts I backed up my CNC12 folder and did a fresh install. I put my PLC program in and only adjusted what was absolutely necessary to get the servos to run, PPR, directions etc. I changed absolutely no machine parameters or motor tuning parameters. Did a drive delay tune. The problem was absolutely the same. So, we can rule that one out.
  • I mucked around with the acceleration values. Of course this resolves the issue if you make it big enough but then the machine gets slow. My original target was 0.1s to 24000mm/min as per the OEM controller. If I go below about 0.5s things get rough. Even at 0.5s its not great. Note that Centroid default is 0.5s to 7500mm/min so very slow. For now I left acceleration at 0.3s which is what I have been using
  • I turned smoothing on and off. Interestingly, smoothing made it worse. At 0.5s acceleration the movement is not bad, but if smoothing is on it is worse, similar to an acceleration time of 0.4, but not as bad as 0.3 with no smoothing.
  • Retuned the DMM drives. In fact I tuned them on every combination of the tuning options. In each case it actually came up with the same numbers. These numbers were the same as what I had been using.
  • Used the PID tuning screens graph to look at the motion. I know this graph is intended for PID tuning but it seems to work well to monitor position error in precision mode. I used a program that m=stepped left, pause 0.5s, step right pause 0.5s. Below are some of the graphs from different tests:
    20220121_213337.jpg
    Using the auto tuned gains. P = 32, P = 28, P = 10
    20220121_213246.jpg
    Half the gains. Increases error as response is too slow
    20220121_213439.jpg
    Twice the gains. Significantly reduces error and response time. BUT, if I try run these kinds of gains for big movements massive oscillation occurs.
  • Some more playing on the PID graph but with different accelerations:
    20220121_212054.jpg
    0.2s
    20220121_211658.jpg
    0.3s
    20220121_211916.jpg
    0.5s
    20220121_212004.jpg
    1.0s
So, conclusions...
  • I did not really manage to improve the problem or find a viable solution yet.
  • I still think the motor drives are just not doing a good job of small high speed movements. But I need to be careful not to put my blinders on and not consider other possibilities.
  • I was surprised to see that smoothing made it worse. But maybe a single step move is not ideal for smoothing.
  • The original goal was to be able to nicely machine up to 4000 mm/min (160 inch/min) on adaptive/dynamic type tool paths. So far I can get to about 1500, maybe 2000 so got a way to go yet!
  • On the same tests as above, Z axis is really good. Still slower than OEM, but moves without clunk. The Y axis is not bad, almost bearable. It really is just the X axis to work on.
Thanks for reading if you made it this far!
cnckeith
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Re: Movement banging on direction change

Post by cnckeith »

fyi..
G64 G code smoothing is not designed to cover up motor/drives that aren't performing well. (or mechanical issues)
G code smoothing works wonders on terrible G code on a machine that is electronically and mechanically optimized.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
aamir
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Re: Movement banging on direction change

Post by aamir »

Ash
Share me your G code file
What tolerance u made Gcode?normaly for centroid 0.005mm is a good no .I remember default value is .02mm
Thanks
ashesman
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Re: Movement banging on direction change

Post by ashesman »

aamir wrote: Fri Jan 21, 2022 9:58 pm Ash
Share me your G code file
What tolerance u made Gcode?normaly for centroid 0.005mm is a good no .I remember default value is .02mm
Thanks
This is the file for just the chamfering operation. See the little 0.6mm square steps as it enters and exits the cuts, that is where it oscillates. The transitions around the cuts and curves are good, but I did have smoothing on. Changing the lead in/out to use 2mm radius gets rid of the thump. So, I can work around it in g code but it would be nicer if I didn't have to as one day I will forget or a tool path will be generated with square corners!
Attachments
Test Block Op2.nc
(10.65 KiB) Downloaded 67 times
repauli1
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Re: Movement banging on direction change

Post by repauli1 »

Did you resolve your issues, could you share cure?
Thanks
Bob
ashesman
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Re: Movement banging on direction change

Post by ashesman »

repauli1 wrote: Mon Apr 11, 2022 10:17 am Did you resolve your issues, could you share cure?
Thanks
Bob
I did find the root cause of the issue. The problem is the DYN4 servo drives. They overshoot slightly and oscillate. They cannot be tuned to remove this. To be better the gains need to be so high that they lose control on rapid moves.

DMM promised they would help but will not reply to my emails now. My advice is chose a servo drive that can be fully tuned, especially if you want a fast positioning control on a low friction machine. The DMM drives are my only regret of my machine conversion. They performance of the machine is now so much worse than it was on the 30 year old OEM controller. You can see the oscillation in the cut finish which really p"s me off.
cnckeith
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Re: Movement banging on direction change

Post by cnckeith »

sorry for your frustration, score some Deltas (Delta's are lovely with a 10 minute tuning job with Oak) and return those DMM's to DMM.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
ashesman
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Re: Movement banging on direction change

Post by ashesman »

cnckeith wrote: Wed Apr 13, 2022 4:26 pm sorry for your frustration, score some Deltas (Delta's are lovely with a 10 minute tuning job with Oak) and return those DMM's to DMM.
DMM have offered a refund. I just don't know if I have the time and patience to upgrade to delta drives. Plus I can't find anywhere to buy them that is not really expensive!

I wish I had taken the ABB drives I got offered early on as then I wouldn't have had to change my motors and all the cabling etc.

If you know of a cost effective way to get Delra drives to NZ I'm all ears.
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