Robot doesn't turn correctly in user frame

ath · November 14, 2023 at 5:07 PM

I am trying to make my robot detect a user frame and rotate about the Y-Axis in a certain number of degrees.

I am using PR to populate the value of the 5th position and apply these changes to the point in my tp program.

The problem I am facing is that if the frame is created at 45 degree from world it will rotate correctly. However, if the frame is created at 0 degrees, it rotates about the X-axis instead. when checking how the user frame looks, they both looks correct.

Any ideas please ?

Nation · November 14, 2023 at 5:20 PM

What are you trying to rotate about? The frame origin? A point? The TCP?

Also, post your code please.

TitusLepic · November 14, 2023 at 6:08 PM

Agree with Nation, we need more information - however, if you're trying to do what I think you are, this post should help: Finding rotation around Z axis

ath · November 15, 2023 at 4:19 PM

So here is the code below, I define a frame and set it in UF:1, and then I am trying to rotate about Y and Z. However, I am getting rotation about X and Z instead, if I change the orientation of the frame I get rotation about Y and Z.

The rotation is supposed to take place at the TCP point, which is recorded in P[1]

Code

/MN
   1:  UTOOL_NUM=10 ;
   2:  UFRAME_NUM=1 ;
   3:  PR[1,5]=0    ;
   4:  PR[1,6]=0    ;
   5:L P[1] 1000mm/sec FINE    ;
   6:  PR[1,5]=(-35)    ;
   7:L P[1] 1000mm/sec FINE Offset,PR[1]    ;
   8:  PR[1,5]=35    ;
   9:L P[1] 1000mm/sec FINE Offset,PR[1]    ;
  10:L P[1] 1000mm/sec FINE    ;
  11:  PR[1,5]=0    ;
  12:  PR[1,6]=35    ;
  13:L P[1] 1000mm/sec FINE Offset,PR[1]    ;
  14:  PR[1,6]=(-35)    ;
  15:L P[1] 1000mm/sec FINE Offset,PR[1]    ;
  16:L P[1] 1000mm/sec FINE    ;
  17:  PR[1,5]=0    ;
  18:  PR[1,6]=0    ;
/POS
P[1]{
   GP1:
    UF : 1, UT : 10,    
    J1=    14.828623 deg,    J2=     7.152353 deg,    J3=   -29.061642 deg,
    J4=   -53.349148 deg,    J5=   -58.607075 deg,    J6=   102.550850 deg
};
/END

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hermann · November 15, 2023 at 5:37 PM

What about PR[1,4] ?

TitusLepic · November 15, 2023 at 5:40 PM

Here are a couple of articles that explain what is causing your robot to behave the way that it is.

How is Orientation in Space Represented with Euler Angles? | Mecademic Robotics

Learn how orientation in space is represented with Euler angles and understand their importance in defining tool reference frames.

www.mecademic.com

Understanding Gimbal Lock and how to prevent it

As you noticed, creating the UFrame at a 45° offset to world gives you the behavior you want. I have no idea what your process or part geometry is, but if it's possible to define your UFrame that way that would be the easiest solution.

HawkME · November 16, 2023 at 12:51 PM

Definitely sounds like Gimbal lock. A quick fix is to use a tool offset for your rotation.

Only use the regular offset for x,y,z frame offsets.

Always use tool offset for w,p,r offsets.

If you follow that rule then you shouldn't experience Gimbal lock.

You can apply both a frame and tool offset onto a single motion instruction if needed.

Robot doesn't turn correctly in user frame

95devils November 14, 2023 at 5:10 PM

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