Servo Purchase Recommendations, Yaskawa?

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19 Nov 2021 17:54 #227007 by tommylight
Since this came up again and i suppose someone from DMM does read this forum (if they do not they should be ashamed and take some lessons from PCW), i really think it is about damn time they send a set of drive/motor to me or Andy or PCW, or even better to all 3 of us.
The bad rep they are getting is costing them much more than 3 sets.
P.S.
Just in case they ever decide to send something my way, i do not do NDA, i do not care about hurting feelings, and i sure as hell do not respond gently to someone suing me for whatever.

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19 Nov 2021 18:57 #227017 by ihavenofish
I will say analogue on linuxcnc is not ideal. a handful of people have told me they have it working fine, but rarely on what i would call a high performace machine, and many others never got it to behave. Linuxcnc has no jerk control, and instant changes in acceleration might be causing the drive to respond poorly (resonance and over correction). in short, i prefer a blind pulse system where the drives auto tuning and filtering can work its magic over the way linuxcnc and analogue behaves right now.

The good thing about delta (drive model -L) and yaskawa and several others is that you can use pulse or analogue. so if analogue doesn't work out well, just switch over.

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19 Nov 2021 21:05 #227022 by chris@cnc
I also looked at Delta, Panasonic and Yaskawa. I decide to Delta. Reason: The manual and circuit diagram are easy to understand. Parameters are well explained and the tuning software convinced me. Search for delta servo tuning software videos. It's really 10 minutes and the thing works. Lastly, measure the resonance and set the filter. Almost like the professionals. And if you have an external measuring system, you can connect it directly to the A2 driver.
Good to know are P44 + P45. Standard setup are 16 + 10 
=160000 steps/rev. Little high for hobby machine...

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20 Nov 2021 02:55 #227044 by Michael
I don't have a high end machine. It's a 1996 that's getting a retrofit. Will deltas have the same issue with jerk on a large old heavy machine with a lot of inertia? I was looking at the 1.5kw. Would the same behavior be observed in pulse with closed loop to LCNC ( I don't see why that would matter but I don't have experience).

Tommy I would gladly send you a dmm set if you weren't so damn far away. I would be curious to see what you could do. Still not sure what I will do with them when I take them off.
The following user(s) said Thank You: tommylight

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20 Nov 2021 03:11 #227045 by tommylight

Tommy I would gladly send you a dmm set if you weren't so damn far away.

Yes i am !
Andy and Peter (PCW) can do all the testing required also, but try to coordinate with them, we have one thing in common = no time!
Forgot to mention above, the time it takes for testing such things costs much more than 3 sets, and still we are willing to put the time and effort to help others, it is 4:06AM here and have to be up by 9!
Thank you for the offer.
Manufacturers should also take a page from PC equipment manufacturers, they send every damn thing to youtubers and accept feedback and fix things, not all are fair though.

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20 Nov 2021 03:25 #227046 by ihavenofish
someone can correct me or dispute me here, but, basically, jerk is a function of the linuxcnc trajectory planner. we all know the result, a harsh acceleration and deceleration. doesn't matter how big and heavy your machine is, this is the path the control commands and for most machines, it is an impossible path.

when you have a pulse controlled drive, it reads that harsh acceleration command and says "yeah, that's not gonna happen" and filters it, creating its own jerk control. new drives can have some very advanced filtering resulting in negligible position deviation. so basically, the problem doesn't exist because the drive is taking care of it and because the control is not reading the encoder other than to log an error (if even that), it cant interfere. you will have a path deviation, however it should be so small it is not an issue in practice.

in analogue mode, linuxcnc is controlling the position loop, and keeps spitting out speed commands to the drive, which the drive/motor can't perform, which in turn causes linuxcnc to keep adjusting and compensating. in theory, your high inertia heavy machine would make this even worse. the result (for me) was a clunky acceleration where the motor would overshoot and then come back. this was literally 2 or 3 encoder counts on the x and y, well under 0.001" deviation, however it was enough to make a violent motion that could damage the ball screws, and occasionally send the motor into resonance (especially the z). i had sanyo servos on a brother tapping centre, so a light high dynamic machine.

Things to note on my experience are that my encoders were 1024 line - 4096 pulse, and the drive had a velocity loop of about 100hz. linuxcnc typically runs its position loop at 1000+hz - so the drive basically does not respond to the control before the control decides to issue another correction.

a delta b3 (and yaskawa sigma 7) has a velocity loop of 3100hz if i remember right, so it is entirely possible that it would behave flawlessly as it has both the velocity loop performance and encoder counts to adapt to the controls unreasonable commands.

my analogue spindle servo (basically an axis drive) worked flawlessly as well, because i assume the way linux controls it is much "lazier" and it's also not driving a heavy linear load. 0 to 6000rpm to -6000 to 0rpm in 400ms. vroom.

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20 Nov 2021 03:28 #227047 by ihavenofish

 Manufacturers should also take a page from PC equipment manufacturers, they send every damn thing to youtubers and accept feedback and fix things, not all are fair though.


oh, they send out all sorts of things for testing, they just literally don't give a s*** about this market. at all. 

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20 Nov 2021 04:14 #227048 by Michael
I think it should be on DMM to check compatibility of their product with the various control systems. I read somewhere that they did reach out to someone in the community (forgot who) about certifing their product for LCNC but the response was something like, "thats not how the Linuxcnc community works".

The jerk motion described does sound similar to the issue I had. Even at low acceleration numbers in my INI the motors would lag the command and over accelerate to make up for it. This would cause an over current fault at anything above half speed. We discussed ways to deal with it; lincurve, some PID constraints. The Ferror wasnt horrible but the motors would never work past half speed without the fault. DMM just kept saying it wasn't their fault and the servos are "capable of near instantaneous acceleration".

They work fine in pulse mode and achieve full speed but as an open loop to LCNC. I really want closed loop and specifically to home to index. Most of my work uses pallets and the same couple WCS so I would like the homing to be as accurate as possible. Currently its .0005" in open loop.

I don't blame them entirely. I was attracted to them because of price and had no idea what I was doing at the time (still don't). They are decent for the price and market they are shooting for. Just not the direction I should have went. Hind sight is always 20/20

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20 Nov 2021 09:52 #227064 by tommylight
Jerk or "S curve acceleration" has nothing to do with drive lag, no amount of "softening" will help a drive that takes 50ms to report its actual position.
Guessing here, but using buffers for filtering and seting long timings to have clean signals does that.
As for acceleration on older machines, it has to be tuned to every machine, the LinuxCNC default of 750mm/s/s was to much on a Hurco BMC20, but my plasma can do 5000mm/s/s easily, 3D printers do even more.
Basically, LinuxCNC acceleration has nothing to do with slow drives.
Slow drives have something wrong on the feedback side, the input side is a simple power amplifier so the delays there are very short.

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20 Nov 2021 16:04 #227096 by chris@cnc

I don't have a high end machine. It's a 1996 that's getting a retrofit. Will deltas have the same issue with jerk on a large old heavy machine with a lot of inertia?
 

On the Delta Servos, you could set a low-pass or S-curve Filter. Its own chapter in the manual. First step of tuning is set the electronic gear ratio. Should be your smallest unit/pulse. In metric =1µ/puls or 10µ/pulse. Second, could you adjust a low pass filter or s-curve filter. In any way should you are able to avoid the jerk. Your following error rise in this step, but with low gain from lcnc it's okay. Another way is to use one external scale and connect to drive direct and set lcnc PID near 0. To calculate the gain parameter is the tuning software helpful. For sure not perfect, but you are able to get better result as to set the parameter by hand.
As I write this line...
What will be happened if all step and feedback commands pass the lcnc low-pass filter? Could it be possible to avoid a jerk by this way?

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