Centroid Community CNC Support Forum

I am trying to setup an acorn board on a Bridgeport 1000 VMC. I purchased servos and drivers for the machine that were speced out by DMM. Im only dealing with the x axis right now and it is giving me fits. The bench test seemed to go ok but I don't think I could see the problem on the bench. I am using servo 115-DST-A6HK1 with the driver DYN4-T01.

Below are some important doc.

http://www.dmm-tech.com/Files/2210P1805-EN.pdf

http://www.dmm-tech.com/Files/DYN4MS-ZM7-A10A.pdf

http://www.dmm-tech.com/Files/motor_spe ... 15-120.pdf

I am using the acorn rev4 DMM DYN4 DMM Cable#CA-CUACRN-M4-05 drawing for hooking the servos up.

I am using 240 volt single phase hooked with per their instructions in the manual. I have a 45amp line reactor and a 16amp emi filter along with a 1amp EMI filter going into the logic connection L1 and L2 of the DYN4 driver.

So the problem appears to be when I select incremental movement in acorn. The servos jump and make jerky movements. The servo do not move sometime with ACORN tells them to. The DRO will move but the servo wont. Sometimes it moves like it should other times it just does as it wants. Right now as soon as acorn commands a move the servo will just automatically move slowly by itself until I stop it. It doenst matter if I say move .001" or .010" the servo just keeps moving. If I remove the 1amp EMI filter going into L1 and L2 the movement stops but the incremental movement is still off and not consistent. The problem does not appear if I am in fast or slow jog mode. The x axis will move like it should and stop like it should. It seems consistent. It just seems like the issue is when I am in incremental mode. I have checked everything numerous times and swapped cables, drivers, motors, and redid wiring and changed setting multiple times. I've tried 400000khz and 200000khz settings. I've changed my motor steps per rev to 8000 and put my gear number at 2000 like someone suggested on another topic. I've tried the 8000 motor steps in acorn and 8000 gear number in the driver settings. I've ran autotune multiple times with various settings. Yesterday I even took the CNC machine table off of the saddle to check of any binding or anything that would cause an issue. It was a 4 hour job to get the thing apart because of how much it weights. I've been emailing DMM for about a week now trying to fix the issue and they haven't been able to make any headway either. All I do is change settings for the servo and it doesn't make the problem go away. If I hook the servo driver up directly to the computer and leave acorn out of the circuit I can control the servo and the movement is smooth and precise. As soon as acorn is back in the system then the problem arises.

Here are a few videos of what's happening




Any suggestions would be greatly appreciated.
Thanks
Aaron

Your settings don't look right:
Slow jog is too fast, Y at 800 inches a minute seems fast
Your steps per rev don't look right (if you set LINE NUM and GEAR NUM in DMMDRV to 2000 then they should all be set to 8000)


Set Gear and line number in DMM DRV both to 2000
Set steps per motor rev to 8000
Set the slow jog to say 50IPM and fast jog to 100IPM and Max Rate to 300IPM all for testing at this point
DYN4 drives run at 400KHZ change that
Fix the above and then follow the attached guides for COARSE and FINE DRO settings (Yes they are for All in One DC but still applies)

Axis Slow Jog Fast Jog Max Rate Deadstart Delta Vmax
(in/min) (in/min) (in/min) (in/min) (in/min)
1 100.0000 236.0000 236.0000 5.0000 5.0000
2 100.0000 800.0000 800.0000 5.0000 5.0000
3 100.0000 236.0000 236.0000 5.0000 5.0000
4 36.0000 360.0000 360.0000 5.0000 5.0000
5 50.0000 100.0000 200.0000 5.0000 5.0000
6 25.0000 100.0000 200.0000 5.0000 5.0000
7 25.0000 100.0000 200.0000 5.0000 5.0000
8 25.0000 100.0000 200.0000 5.0000 5.0000


Axis Label Motor Encoder Lash Comp. Limit Home Dir Screw
revs/in counts/rev. (inches) - + - + Rev Comp
1 X 6.3537 8000 0.0000 0 0 0 0 N N
2 Y 1.5864 2000 0.0000 0 0 0 0 N N
3 Z 1.5800 2000 0.0000 0 0 0 0 Y N

Marty,

Please see the attached new report file. I changed all the settings as suggested. I cannot do the fine and coarse adjustments. The movement is too jerky and when I change directions the servos respond with a fwd movement then the movement goves back to where it was at. The indicator needle just bounces back and forth and doesn't advance position.

Although you need to get the basic settings right such as steps per rev and gear ratios, this looks more like a servo tuning issue to me.

I've only got experience of the DYN2 range but from what I've seen, the tuning software is pretty much the same for their other products, as you might expect. I originally calculated starting points the P, I & D values using the app note provided, then used the autotuning function to try to improve the response. Neither seemed to get my system anywhere near where it needed to be and in the end I resorted to a more manual method.

With a stepped position signal set up (something like 1Hz and 100 degree motion) I turned the I & D values down to zero, then increased P until it was unstable, then backed it off something like 20%. Then dialled in some D until the step response was much crisper, increasing it until it was unstable again, then backing it off. Some playing with the P term helped to find a good overall response from the P and D settings. Finally, the I term is what you need to ensure there is no steady state positional error at the end of the move. Again, dialling too much in will result in instability and the best overall settings will require some final fiddling with all 3 terms. I did this with my X and Y settings and the final values were nowhere near what the calculations or autotuner gave me.

There is lots of info out there on setting up PID controllers, as its always been a bit of a black art / acquired skill. There are some good autotuners out there but I'd suggest the DMM one doesn't fit that description. Have a go at manually tuning your controller but don't forget to take lots of screenshots along the way so that you can revert to something that seems to be getting there.

With the DMM tuning software, you need to re-read the drive settings frequently to check what values are actually active in the drive. And save the settings to ensure the ones displayed are sent to the drive. The actual values of the PID settings don't translate into anything obvious, so don't get hung up on them - or try to compare them to other systems out there.

I could tell you my own values but mine are for a Bridgeport milling machine with belt reduction, so likely to be quite different in many ways. One thing I learnt the hard way was that the large CI handwheels (2 on the X and 1 on the Y) increased the moments of inertia of the ballscrews massively and prevented me from getting an acceptable step response. They far outweighed the effects of mass of the saddle, table and workpiece on the response. I took the hand wheels off and the behaviour is enormously improved. I don't know what your drive train looks like but it's worth checking if you have any means of minimising your moments of inertia.

EDIT - There's a short video part way down in this post showing what I managed and a glimpse of some of the settings:
https://mightyshiz.blogspot.com/2018/10 ... heels.html

Thanks for your input. I will be back out in the shop Monday trying to figure it out. Does anybody have an suggested starting points on the tuning? The machine is heavy. Probably a 1000# table weight. The xy saddle probably weights 2000#.

Raceman17 wrote: ↑Sun Apr 05, 2020 6:30 am Thanks for your input. I will be back out in the shop Monday trying to figure it out. Does anybody have an suggested starting points on the tuning? The machine is heavy. Probably a 1000# table weight. The xy saddle probably weights 2000#.

Get the settings (gear num and line num) set right save and run the autotune in the DMMDRV software specific to your motors.
No one can really guess.
The DYN4 manual does give some guidance.

Ok thanks. The gear an line number are set to your suggestions of 2000 and 8000 steps. I will try to work on it tomorrow. I gotta do real work at the house for my real job!

Can someone tell me if these dyn4 drives can be wired up to 240 volt single phase power. I have regular US house power where each hot leg it 120volts and they share the ground. All my problems seemed to go away when the drive was hooked up to a single 120volt wall outlet. I was under the impression that these could be wired 240v single phase. If they can be wired to 240 volt what is the placement of the wires for R T L1 and L2?

Here's a screen shot of the document DMM sent me when I purchased a DYN4 drive and 750W servo.

I have the same drawing. My question is coming off the main power at the top of the diagram.. are each of the legs 120volt from a 240volt single phase connection. I had it wired with each hot leg coming into r and s and L1 and L2. It didnt work correctly.