Movement banging on direction change

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ashesman
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Movement banging on direction change

Post by ashesman »

I have been battling away for months and months now trying to get good motion control on this machine of mine and I just cant get there. If I want it fast it jerks and bangs. If I slow it down, well, its slow!

I have been using DYN4 drives which I think are a big part of my problem. They were failing to control my old motors, so I replaced the motors with DMM motors. Turns out I should have just replaced the drives. The new DMM motors cannot do full RPM on 200V. And the control of them is only marginally better than my old motors. Too late now!

What I was aiming for was 24m/min rapids and 0.1s acceleration. It wasn't at all a problem for the old controller on the machine from the 90s. See the video below. I made this video the night I pulled the old controller off the machine. Fast as f..k and no banging on the starts and stops.



I cannot go above 22m/min with the DMM motors and if I try go below about 300ms acceleration the whole machine thumps and bangs on every movement. Actually the rapids are not the problem I can get 22m/min and 0.15s acceleration time and it is fine. It is the small and slow movements that are now a problem.

I found the problem is the drives are oscillating slightly on stopping which sets off a vibration through the machine. I have tried every combination of gains and settings and I can't get rid of it. Using the PID scope you can see a little ring when movement stops. This is enough to really bang. I ran a program that had rounded corners that were made of ten or so straight lines, every transition from one line to another made the machine bang. The fast transition between the lines made a sort of vibration. The feed rate indicator was all over the show. Turning on smoothing fixed it and made the feedrate constant. The old controller could run segmented code like that smoothly. You would see every little line in the machined part.
20210827_190049[1].jpg
20210827_190311[1].jpg
I tried turning on S curve smoothing and it actually made the oscillations worse!

HELP ME!!! Am I ever going to achieve the kind of control the machine had or am I just wasting my time? In fact am I ever going to achieve even smooth slower control that is not harsh and banging? I cant find any example videos of a Centroid or DMM running a fast machine. Can it do it?
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Re: Movement banging on direction change

Post by cnckeith »

post a fresh report.zip and the g code file. there are lots of details to get right for the best machine motion. smoothing is one of them but there may be other issues to address. the report.zip and g code information is necessary for us to have the whole picture and then to comment effectively.
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Re: Movement banging on direction change

Post by tblough »

Smoothing combines multiple short program moves into a longer single move. This helps with stuttering when processing files with many small moves. Banging is caused by fast acceleration. You need to set your accels slower.
Cheers,

Tom
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I have CDO. It's like OCD, but the letters are where they should be.
ashesman
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Re: Movement banging on direction change

Post by ashesman »

Today I gathered up some more information, reports, gcode file etc. I also think I found the limit of the Centroid controller!

So, I am doing this testing on a program for a test block. The g code is generated by Fusion 360. The initial program I ran yesterday had tolerance set to 0.1 and smoothing off (in F360). This made a 130kB g code file and had steps of around 0.5 to 0.8mm around the corners. I understand the g code generated for this simple application is unnecessarily complicated and could be massively simplified but it is a good test.
Capture.JPG
This morning I set tolerance to 0.001 and smoothing to 0.0001 and regenerated the g code. Now 800 kB with around 0.1mm steps around the corners. The rest of this post is about this g code file.

So first thing I noticed is how long CNC12 takes to open the file in graphing view. It draws it tice every time which makes it take twice as long. I think I will turn it to default to g code again, graph view is shit anyway as has no ability to rotate or 3d capability! I am running a grunty i7 PC and it still takes a good 20 seconds to draw. I think there is some pretty average code in CNC12 there!

So, I dry ran the program at 100% feed rate and it went through beautiful and smooth. I thought great it was just too "steppy" in the g code. So, I went to 200% feed rate and ran it again to make a video. If you watch to the end you will see it go nasty!!! Pretty sure I found the limit of the rate Centroid can process the G code! It could just slow the feed rate rather than going nasty! They know its going wrong!



Then I realised that the whole time smoothing had been turned on in CNC12 from yesterday. So, I re-ran the program at 100% feedrate with no smoothing. Even then it still bangs and vibrates around the corners.



Attached are the F360 file, the g code and a report generated today. Have a look and see what you think...
Attachments
F360 Test Block v9.zip
(500.82 KiB) Downloaded 100 times
Test Blockc 2000 RPM 0.1 Chip load with smoothing.nc
(813.14 KiB) Downloaded 107 times
report_0008DC111213-1214201066_2021-08-28_14-16-36.zip
(3.85 MiB) Downloaded 104 times
polaraligned
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Re: Movement banging on direction change

Post by polaraligned »

Well, you can rotate and 3D the graph view. Hold down the left mouse button and move the mouse to 3d rotate the view. I think holding the right mouse button pans the view. You can also zoom in and out.

As for your slow graphing, the speed of CNC12 on Windows 10 is much slower than when I was running CNC11/CNC12 on windows 7 - and the CNC12/Win10 is on a 3X faster computer!!. Win 10 is a resource pig and the worst OS imaginable for real time control. Just booting CNC12 takes much, much longer on a Win 10 OS.

As for the banging, my machine will bang long before reaching the g-code processing limit. The banging is a function of the feedrate override being turned up over 100% and not the code processing speed limit. As I stated in a different thread, I can program a cut at say 50 ipm and machine will run fine, but if I program to 35 ipm and set the feedrate override to 142% to bring the cut rate up to 50 ipm, the machine bangs like all hell pretty much on every move. This really messed me up until I figured it out. Clearly there is something going on with the feedrate override that causes this and I no longer turn the override above 100%, but rather program for a higher than expected rate and tweak the feedrate downward to adjust to the sweet spot.
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Re: Movement banging on direction change

Post by aamir »

I need to know
1)Your Drives use +/-10V velocity Mode or Pulse Train?
2)What is the no of pulses /rev of Motor?
cncsnw
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Re: Movement banging on direction change

Post by cncsnw »

According to his report, it is running in position mode (P256 = 2, all PID gains zero).
According to his report, encoder counts/rev is 30000.

Since acceleration and deceleration distance allowances are computed in advance, based on the programmed feedrate, it is not surprising there is more "banging" when running with the feedrate override turned significantly above 100%.

If you double the programmed feedrate, then run it at 100% feedrate override, does it run more smoothly than if you program it slow and run it at 200% override?
ashesman
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Re: Movement banging on direction change

Post by ashesman »

aamir wrote: Sat Aug 28, 2021 11:49 am I need to know
1)Your Drives use +/-10V velocity Mode or Pulse Train?
2)What is the no of pulses /rev of Motor?
DYN4 drives with DMM 11A 1kW motors. Oak is running in precision mode. 30000 steps per revolution. I had to reduce it from 32768 as the Oak cant reach 2400 RPM at 32768. But as it turned out, the motors can only reach 2200 RPM at 200V so I could have left it at 32768!
ashesman
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Re: Movement banging on direction change

Post by ashesman »

cncsnw wrote: Sat Aug 28, 2021 6:35 pm According to his report, it is running in position mode (P256 = 2, all PID gains zero).
According to his report, encoder counts/rev is 30000.

Since acceleration and deceleration distance allowances are computed in advance, based on the programmed feedrate, it is not surprising there is more "banging" when running with the feedrate override turned significantly above 100%.

If you double the programmed feedrate, then run it at 100% feedrate override, does it run more smoothly than if you program it slow and run it at 200% override?
The second video was running 100% feedrate and it still shudders around the corners when smoothing is turned off in CNC12. I didn't think that feedrate was unreasonable?

At the end of the video you can see the feed rate is erratic as it goes through all the little steps around the corners. With smoothing turned on, feedrate is almost constant so no shudder.

It makes me nervous, I am starting to lose confidence and don't trust the control now. Scares the crap out of me when it goes bad and I don't think its really that great for the ball screws either! I usually turn the FR override up nice and high to dry run a program to get through it quickly rather than wait all day but I guess that is not safe!

I am sure my issues are mostly related to the DMM drives overshooting and oscillating on small steps. DMM have given me some tests to do.

I tried changing the dead start and delta vmax number but they don't seem to do anything? The manual gives almost no explanation on their function and says "don't change them".
cncsnw
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Re: Movement banging on direction change

Post by cncsnw »

Try increasing Deadstart and DeltaVMax on all axes to around 120 mm/min, then running the same toolpath, at 100%, with smoothing off.
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