Cuts not repeatable, losing steps(FIXED) but will continue thread

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cnckeith
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Re: Cuts not repeatable, I'm losing steps

Post by cnckeith »

fyi.. we tested on both the db25 and screw terminals now for days of continuous running with dyn4 with no issues.

testing says...."we have been running the DYN4 since Thursday on the open collector outputs (screw terminals). It came right back to the mark today. Running it at 200 kHZ and 4000 steps/rev 300in/min."
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
lavrgs
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Re: Cuts not repeatable, I'm losing steps

Post by lavrgs »

cnckeith wrote: Mon Jan 24, 2022 5:25 pm fyi.. we tested on both the db25 and screw terminals now for days of continuous running with dyn4 with no issues.

testing says...."we have been running the DYN4 since Thursday on the open collector outputs (screw terminals). It came right back to the mark today. Running it at 200 kHZ and 4000 steps/rev 300in/min."
Are you using DMMDRV to ensure that the steps return to zero? When you say "It came right back to the mark today." what mark are you using?
Richards
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Re: Cuts not repeatable, I'm losing steps

Post by Richards »

lavrgs wrote: Tue Jan 25, 2022 9:23 am Are you using DMMDRV to ensure that the steps return to zero? When you say "It came right back to the mark today." what mark are you using?
I'm running CNC12 with the DMMDRV servo setting screen open and I can't see a box on the DMMDRV screen that shows the dynamic indexer count. Where would I find that?
-Mike Richards
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Re: Cuts not repeatable, I'm losing steps

Post by lavrgs »

test movement.png
You want to be on the TEST MOVEMENT Tab. You need to have the DMM drive tuning cable connected to the drive. If you are using the Acorn to move make sure you are in STEP/DIR -on the servo page. On the Test movement page use the READ MOTOR POSITION. If you want to zero press the DRIVE RESET button or cycle power..
Make your movements with the Acorn and go back to check position. For example If you move x 0>>2in and return to 0 the motor position should read 0 or very close (1-2). I suggest running multiple cycles, then check, to ensure repeatability
HTH
lavrgs
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Re: Cuts not repeatable, I'm losing steps

Post by lavrgs »

After being down for a couple weeks I have kentonsj's differential board installed and connected to the db25. I have some work to do to get back to previous setup - I changed a lot of parameters in the wizard testing the DB25 interface options.
Initial test shows that I am no longer losing steps...only tested X so far. I have to figure out why I lost my speed...I get confused when setting the steeps I have 2000 and I think it should be 8000, but i will spend some time with this.
I'm using the DRIVE TYPE DYN4-DB25 that is attached somewhere above and wonder if this is ideal - it has 200K as the max step rate. Can I edit this file to be 400K and change the steps/in from 2000 to 8000?
I am attaching a report to see if there are any obvious issues - any help would be appreciated.
Attachments
report_402E71CADC40-0323214550_2022-01-26_17-07-26.zip
(714.61 KiB) Downloaded 64 times
kentonsj
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Re: Cuts not repeatable, I'm losing steps

Post by kentonsj »

That's good news that the board has helped.

Your steps/revolution in the Acorn wizard should be 4 times your DMM Gear number. Your report shows your fast jog at 60IPM. Let's use 60IPM for easy math. 60I/M / 60sec/min = 1 inch per second. 10 turns per inch equals 10 turns/second on you servo motor. 10turns/sec x 8000steps/turn = 80,000steps/sec or 80khz. Room to go up to 150IPM at 8000 steps per rev at 200khz. I have tested the board up to 400khz, but if you can get away with 200khz, you should have a higher margin of reliability.

If you have 2000 as your DMM gear number, 2000 steps/rev in Acorn would cause your machine to move slowly. It would also not be moving the correct distance one inch on the DRO would be 0.25 inches on the machine.
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Re: Cuts not repeatable, I'm losing steps

Post by Richards »

I'm interested in learning more about the Kentonsj differential board. I have not yet built a differential prototype for my DMM DNY4 750W driver/servo.

After Lavrgs showed me how to read the encoder, I ran some tests. I'm consistently getting 223 few encoder counts than expected when I command the motor to turn 10 turns. That is a a very small error. The actual move is 99.966% of the move commanded. That means that the cut would be about 3-thousandths short over 10 inches or 3-ten thousandths over 1 inch. I don't own equipment that can produce that tight of tolerances, but I am interested adding a differential driver to the RS232 step/direction signals to see the encoder count.

Back when I was designing process control equipment for professional photo labs, Kodak released a paper that used the term "circle of confusion". Basically, that term showed the least amount of deviation to expect in final prints when the printer was set to the same values. In a perfect world, the prints would be identical. In the real world, the prints would deviate by 2.5 log units, or just enough that the trained eye could see a mismatch. Knowing what the "circle of confusion" value was, kept photo labs from wasting time and materials chasing impossible perfection. I would suspect that the same thing happens in machine shops. Chasing tenths when temperature variations can change a cut by over a thousandth would be an example of the "circle of confusion" principle.
-Mike Richards
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Re: Cuts not repeatable, I'm losing steps

Post by lavrgs »

Mike before I installed Kentonsj's board I was consistently losing steps - close to 1200 after 50 cycles of moving 0. -2in. 2in .0
Now I am getting back to 0 +/- 1
For my motors 8000 steps is one revolution; when you're off by 1200 steps it is significant. In my case the error was accumulating; so the more you move the worse it gets. YMMV. I would suggest running a cycle for 5-10 minutes - go back to ZERO to see how many steps are lost.
kentonsj board is plug and play - I needed to change the drive type to use the DB25 as the input vs. the TERMINALS- this was accomplished by using the attached drive type. I am still wondering if it is ideal - I seem to be able to modify the file but the items set by the file can be changed within the wizard
Attachments
DYN4_DB25 (1).zip
(1.27 KiB) Downloaded 69 times
kentonsj
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Re: Cuts not repeatable, I'm losing steps

Post by kentonsj »

Richards wrote: Thu Jan 27, 2022 2:51 pm I'm interested in learning more about the Kentonsj differential board. I have not yet built a differential prototype for my DMM DNY4 750W driver/servo.
My board uses two TI AM26C31 quadruple differential line drivers to convert the TTL logic from the DB25 to differential. I also added some breakout so that I could combine the enable signals from the screw terminals and take the BKO output from the Z axis drive and faults signals in one neat package. This board is really just a 4 channel differential converter, it would work with any step/direction drive that accepts differential inputs. I use a DB9 connector and then solder a DB25 connector on the other end to match the DYN4 pins. Here's a wiring diagram of how it interfaces with the Acorn. Here's the cable soldering/pinout for the custom cables.
SJ Thermy-AcornDMM Cable.pdf
(59.25 KiB) Downloaded 91 times
This is what it looks like in my cabinet. Each cable runs to the DYN4, no DB25 breakouts and all the signal wires are shielded.
IMG_20190316_113214.jpg
I made and sold a tested board to lavrgs in hopes that it would help him eliminate lost step issues. It seems to have helped him. Keith, Marty and others on the forum have demonstrated that a differential converter is not required. Keith's most recent test from last week proves it isn't required. I mainly made the board to clean up the wiring in the panel, in the process, I designed this board with help from this forum. I thought I may as well take the opportunity to change to differential outputs and make the signal chain more robust. I'm not looking to go into business selling these boards, but I will sell tested boards to interested parties. I can sell you an un-populated board, or a tested board. I have one more design tweak to make on the next revision, I placed the DB9 connectors very close together and only the thinnest of DB9 connectors will work, a little bit more breathing room on that would have been a good idea. I was also dreaming about a re-design to make it strictly a 4 channel converter with no BKO DYN4 support, which would let me use a shielded CAT cable for all the connections, change to all surface mount devices and have a circuit board shop populate the board so I could lower the cost. When you hand solder the through-hole board and all the cables, it's a couple of hours' worth of work. 9 pins are required if you use the DYN BKO output, 8 without. I think a lot of people just use the acorn brake output, I used the DMM one to save outputs for a future tool changer, this was all designed before the ethernet board was available. DM if you'd like more information.
Scott
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Re: Cuts not repeatable, I'm losing steps

Post by Richards »

Kentosj,

You have done a masterful job of designing a robust interface. The schematics show careful thought. The photos show careful implementation. Even Teknic ClearPath motors could benefit. They would require a differential received board per drive according to the Teknic manual which discourages using only a differential driver. That's a limitation of how Teknic designed their servo drives, not a limitation of differential circuits.

I've looked at 'scope images of step signals with and without a differential driver/receiver from the Acorn H headers using 5VDC. The wave forms with a differential driver/receiver are nearly perfect. The wave forms with just a pull-up resistor can be made almost as good, but the length and type of cable has great influence on the pull-up resistor's value.

Your design looks like it will solve DMM DYN4 issues. Your design, along with a matching differential receiver board, would solve issues with ClearPath servos.
-Mike Richards
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