Thanks for the thoughts on mounting the VFD to the gantry. I had kinda thought about those items as well, the main driver for me was actually 3 phase switching noise caused by the VFD. I use double shielded VFD cable but at these high frequencies (300 - 400Hz AC at 2.5khz switching) there can be alot of noise that causes interference elsewhere in the home. Anyway I have scrapped the idea in favor of wall mounted.
Finally some updates on the machine.
X axis motor mount plates (laser cut) and servo motor mocked up.
Long ballscrew mocked up for bracket design
Also made some good headway on the electrics. Still cant get CSMIO to connect so will have to contact them here soon but Im a bit of time away from needing it.
I have been MIA for a long period, normal life and other projects got in the way over summer. Finally back to working on the CNC.
Leveling the Y to Z plate for gantry foot epoxy pour
Pouring the gantry feet
Ballscrew to Z axis plate, made with steel I had on hand
Installing limit switches for Z
Z home Prox Switch
Finished underside of Z axis with dust shielding in place
Z axis installed onto Y axis/gantry
Lots more Z axis mockup
Building brackets for dust collection holding and pneumatic counter balance system
Machining and installing guides for dust shroud, shroud/brush will be on pneumatic cylinders so it can be pulled up when needed and also when I add the tool changer.
As it sits today, my plan is to work backward from the Z axis finishing each axis as I go. Sorry for the dump with little text but I wanted to update this with where things are. I can give any specific information as needed
Made some progress forward... Z is moving although I cant get the video to download.
Also got Y going for initial tuning, here is a video jogging at ~1600 inch/min then I have a question for all the servo tuning experts out there.
Ok, so trying to get that Y axis tuned through the CSMIO config it seems I can get either no overshoot and no oscillation but I never actually get to the number I requested. Or by changing the I value just 1 I get slight overshoot and oscillation. I am tuning at 2000 inch per min max rate and an acceleration set to 500inch/sec/sec.
Right now my numbers are, with these numbers there is no overshoot and the movement is very crisp with no oscillation at 0 speed. But I am always 0.003 of an inch from the requested number. (i.e. if I ask it to go to 8 I get 7.997). Error in this setup ends up around 10 to 12 counts
P - 800
I - 4
D - 10
If I change the I to 5 leaving the P and D the same, I get slight overshoot, but also get oscillation around the number, around 100 counts + and - . Also at 0 speed I am getting oscillation around 30 counts + and -. The CSMIO config dialog wont let me put a decimal into the value otherwise I think 4.5 could be the magic number.
Any thoughts? I think not getting to the requested number wont work in real machining? Also overshoot or oscillation could have some pretty negative impact. Kinda got to the point of pulling my hair out yesterday after around 3 hours of messing with it so I decided to move on for now. Oh and a BTW, the autotuning feature did not work at all. The numbers it left me with gave oscillations around 1 full inch of movement. I am happy with the crispness of the response on how I have it tuned just very odd I cant get to the number I asked for.
Now your ino the realms of Black Magic.!!
First thing first are you sure the Drive is tuned correctly to the motor.? If not then wasting you time tuning the controller.
However 500in/s/s is very high(12700mm/s/s) and could be the cause of your tiny overshoot. This is very abrupt stop and from high speed. You can see in the video how abrupty it stops. Try lowering the Accelration and see if the error disappears or reduces.
Also I notice you using kD value which often if required is much higher valule than 10. 100's even 1000's isn't unusual.
The kD value will fine tune the oscillation or any humming noice from motors.
You also don't mention the Kvff value. With such high acceleration then this value will come into play slightly as it trying to predict the next action and can help reduce errors if matched well to PID.
To be honest no one can truely help you with this unless in front of machine. Even then it's mostly trial and error. Also I wouldn't waste much time fine tuning untill the axis is fully finished and working as it will be when cutting. Just adding little more Mass or lowering resonance can change the Tuning when comes to fine detail.
Good luck and keep cool it will be worth the effort.
Yeah I figured the cart was ahead of the horse so to speak but it was fun to get something moving. I was planning on just doing a quick tune so that I could jogg the axis... 3 hrs later I was so frustrated I had to say stop.
I dont know that the motor is tuned correctly, these are the units from BST and I just made sure to set the drive to the correct number for the motor. I will need to do a little more learning on servo drive tuning before jumping into that can of worms... Should I need to dig into the servo driver setup? I was hopeful that just setting the number for the motor would get me where I needed to be.
The acceleration was set just trying to push the limits of the servos a bit, I ran all the way down to 50 inch/s/s and it is always 0.003 inch off the mark with the PID set the way I have it. Then if I changed the PID, the overshoot and hunting was always essentially the same, so with that I came to the conclusion that the acceleration may not be in play? But obviously more tuning needs to be done.
I do need to play more with the KD and Kvff, but I think I will take your advice and wait until the whole thing is together before performing the final tuning.
Have a Mach4 question as well, DRO readout with the CSMIO-IP/a, in Mach3 if I would turn a servo motor by hand the DRO would update. In Mach4 I am not getting that, hoping that its just a setting somewhere that I overlooked? Anyone have any thoughts? I was using the demo of Mach3 and decided to buy Mach4 so I dont need/want to upgrade as quickly.
So onto finishing the mechanicals. Thanks for the help
Here is the Z axis jogging, I didnt do much of any tuning here just got it running making it easier to work on.
Last edited by Scott Damman; 12-12-2016 at 06:02 PM.
Are you sure about that acceleration? My machine is tuned at 3000mms2 and is much snappier at 10000mm min feed rate. And from servos is still on 50-60% of their ability. Frankly when working at around 16000mm/min it looks really dangerous and leaves you no time for any reaction.
I got my servos from BST too so likely the same, I think the thing with the drive number setting the drive up is that it has no idea what load the motor has - its just a ballpark setting. The downside is the manual is written Chinglish and unless you know exactly what parameter does what, then its all guesswork.
I spent hours and hours tuning, its made harder as you also need to test each tune at multiple speeds, I test at 3, 13,23,33,43 and so on as % of full speed - its easy to tune so that it runs great at say 60-100% but oscillates badly below 50%
In the end i tweaked in the order P - D - I until the following error was as low as possible, then added some kVff if needed.
I'm still not happy with it though but at least the mill is running now. No doubt an expert could tune it in minutes but I don't know any mobile servo experts ;)
My motors are only 400w but i assure you when i raise the acceleration snappiness from the servos themselves, its like shooting a bullet. Thats the sound how machine starts and stops. In fact my problems when tuning were related to Undershooting, cause i was not brave enough at first. So problem was it goes to position fast and then you could see how the motors for a millisecond were further positioning it in place. So i thought i am Overshooting. Yes but No. When i raised the servo response this disappeared. So auto tuning did not work i my case. Also it would be better if there is a total gain adjustment which auto adjusts all details, instead of separately adjusting each parameter. Which by the way is well described on many places around the web, but i still fail to comprehend it entirely .
Last edited by Boyan Silyavski; 13-12-2016 at 08:56 AM.
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