OK, now that I did a complete mastering with an EMD (200 € ; yikes !), I re-did my XYZ 4 directions calibration, and this time : documented !
I think my calibration tool is as good as it gets, made from a linear guide ; I measured 0.09mm of runout at 200mm distance from the spindle.
Well, the result (error = 0.788 mm) is still completely crappy, so I hope you guys can give me advice on how to get a better XYZ.
OK MOM, will do
Could You do me a favor?
Sure ! Will do. Thanks for your help.
I just need to take care of some stuff first.
have seen many not absolute accurate robots with deviations like your robot.
Oh well. I guess I put my 40 000€ on the wrong robot for milling, then.
I hope I have better luck next time.
Someone told me something about stereoscopic cameras. Could that help getting closer to a decent calibration ?
But I would master without any attached weight on axis 6.
In the calibration position, my spindle doesn't exert any torque around axis 6, so I think it's irrelevant in my case, but I understand how a tool with an offset weight along the flange Y axis couls cause trouble.
To be clear my spindle was on the robot when I made the mastering, and I followed "EMD / Standard / Set mastering". I also performed the "Check mastering" sequence, and the deviations were in the order of 0.001° in motor angles, so I guess my mastering is OK.
I DID NOT do the load compensation procedure (one mastering with load, one without).
Using my laser, I moved the TCP along the Y axis on a broad LIN movement, and the result is appalling.
I measuer at both ends and at the middle of the LIN, and this time, I didn't bother trying to align my laser cross with the Y axis, so the end points aren't close, but I wanted to see the "Sag" at the midpoint.
I get 1.5mm sag downwards at midpoint which is where the arm is the least extended.
This seems to indicate that the robot is over-compensating the static loads when it is fully extended...
I made a second run after setting the load data ""weight" to 0 kg, and the result was almost the same.
Anyways, for my milling application, dynamic loads will probably not make any difference. Milling is a relatively slow process.
Sorry for the messy video BTW ; difficult to use a pendant and a smartphone at the same time...
I've gotten the EMD from KUKA and un-mastered + remastered my robot with it.
Sadly, with roughly the same 4 directions and still with painstaking care, I get a worse-than-before uncertainty value of 0.74 mm, and the "rotate around tool A" test still sees the TCP move in the direction of tool "A" (z) axis even more than before.
I'm puzzled by the concept of calibrating with / without a tool load in my case because the spindle is there all the time.
I made my calibration with the spindle attached, as this will be the "Permanent" state of the robot ;
the "tools" for me are just the end-mills which weight will be negligible.
Then, I wonder if I should enter the spindle weight in the tool load data (which I use for all my tools) since it has already been accounted for in the calibration...
In short , calibrating with / without load plus entering load data seems redundent, and I wonder if the robot is over-compensating the load in my case.
I'm off to re-do the calibration, and this time, I'll take pictures of the 4 postures that I use to calibrate the tool XYZ
Careful... Justin was in my class when I was 12 in Ottawa.
Just a phone call and he can send a trained beaver to bite your rear !
OK... I'll just start from scratch and document everything.
I don't want to get in bad terms with a fellow Canadian.
the nonsensical part is still not clarified - what is the selected coordinate system, what is the tool value, if the tool direction is set correctly, if the axes were correctly identified (jog X, Y and X to confirm) and really match the expectation.
OK Panic, although I'm slightly moronic, I think I know what I'm doing here, and I have described all the things that you cite.
As well as you are prompt to point to documentation, I will kindly point you to my very first post where I have taken great care to explain what I was doing, which coordinate system, etc... with bonus photographs too.
The pin holes are not made for fun, they made to get a better result
OK Mom, I'm sorry, I won't do it again.
also have you checked the required torque of the screws?
Nope.
I'll look into this, but the guys at Eurobots know what they are doing ; I "suppose" they have tightened the nuts correctly...
Mounted not only with screws, nuts and bolts. There should be at least two precise pins to fix the position precisely.
Nope, there are two remaining holes on the baseplate, and underneath, threaded holes on the plange.
Is your tool pinned?
Ummm... what does that mean ?
Did you select correct tool?
Yes, I did.
I just received a linear guide rod which has a very small runout, and made a new calibration tool with it.
So it's back at monkeying the robot around to define a tool and hopefully get something that makes sense.
I'm trying to reach the local KUKA people to borrow an EMD too.
basic KUKA training would likely do wonders here
Surely ! I had a KR6 for almost 7 years, but I would love some training.
Maybe we can discuss that in PM.
Err... is there such a thing on this forum ?
Depends on your skills.
It's highly recommended to use an absolute accurate robot for your application.
Edit:
Inaccurate setting of A/B/C of the tool has no effect to the behavior your robot shows.
The used coordinate system has no effect to the behavior your robot shows, as long as you use the correct tool, and do only movements in A/B/C.
I know... That's why I am in doubt on my mastering.
Make sure to use sufficiently different orientations (60-120 deg different from each other). This will get you first three coordinates (XYZ is TCP only). Then you also need to get tool orientation (ABC values)...
To do the 4 direction XYZ, I used a great video from Werner Hampel where he describes the best practices.
I don't want to brag, but I really out-done myself to make it as good as I could.
I was almost disappointed when I saw the error margin was 0.45mm, which is not so bad.
Sadly, I have found no good advice anywhere to set the ABC, so what I did is that I used a laser to set my world Z vertical : I extended the arm and checked the level at A1=0, 90, 180, 270.
I can say that my robot is as "vertica"l as it can be.
Then, I also used the laser to place my tool axis strictly vertical , with A1=0, and the wrist "straight", then I calibrated with ABC world.
Would you say that it is feasible to master the robot with sufficient accuracy for milling with the dial gauge tool ?
I'm willing to try again, but I've lost so much time with this already...
In wg´hich coordinate system did you actually move?
If you are referencing the photos in my first post, that was the tool's coordinate system
Yeah, I guess you're right, but don't you think that the very nature of what I'm seeing screams "lousy mastering" ?
Anyways, a friend told me that it's possible to rent an EMD from KUKA , I'll report back the results.
Do you have some transform like external axis?
I do have an external axis, a turn-table.
For now, I have not touched it ; I'm struggling too hard on the calibration of my spindle's axis to worry about that for now.
How could it influence my tool's TCP ?
