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Updated kinematics shifting tool CAD when UR10 moves
#1
After updating the kinematics for my UR10 using a program created on the teach pendant and the UR_LoadControllerKinematics.py script, I noticed that the position of the tool geometry is now shifting relative to the robot flange as the robot moves. The shift seems to occur whenever any of the robot joints are changed, however it is particularly noticeable for joints 4 and 5. Below are a few screenshots that show the position of the tool before and after executing a move program first with the default kinematics, and then with the updated kinematics enabled. I have also attached the station file that the screenshots were taken from.

Default kinematics:

           


Controller kinematics:

           

Is there any way to fix this so that the tool will maintain a consistent distance and rotation with respect to the robot flange? If not, how will this affect the collision detection feature in RoboDK? I am currently using RoboDK to control a real UR10 for a nondestructive inspection project which requires the robot to move the tool along the surface of a part while maintaining a consistent standoff distance of roughly 1 inch. The ability to add targets on the surface of an object and the automatic collision detection feature were two of the main reasons I chose to use RoboDK, but the fact that the tool appears to be shifting by an inch or more as the robot moves makes the software unusable for my purposes. Any suggestions on how to resolve this issue would be greatly appreciated.


Attached Files
.rdk   updated_kinematics_error.rdk (Size: 1.15 MB / Downloads: 69)
#2
Hi Michael, 

Hope you are well. 


I'll try to keep things simple and clear. 

As far as we know, UR robots are the only ones requiring us to update the kinematics of the robot. 
This is simply because each and every robot that comes out of their factory is individually "calibrated" to try to compensate for the production tolerances. 
The robot you imported from our online library is equipped with the theoretical kinematics of the robot (if the tolerances were zero). 
In the case of the older UR (everything before the e-series), the difference between the theoretical model of the robot and the real robot you have can be quite impressive. 
In your case, the difference between the theoretical position of the flange and it's real position is about 38 mm. 


Therefore, when you updated the robot kinematics, the flange in RoboDK moved to its real position. Attaching your tool to this newly define flange will give you the real position of the tool along your path. 
But considering that you updated the kinematics of the robot, the 3D model we have in the library is not accurate anymore, or in fact, was not updated to match the new kinematics. 
If you right-click the robot and "Visible robot flange" you will see that the tool position stays constant with respect to the newly define robot flange. 

So, if you want to make sure that the tool won't collide with your part, you can use the updated kinematic. The tool position should match reality. On the other hand, there will be a small difference between the position of the robot arm in RoboDK and in real life. 

If you really need to be precise there, you could recreate a new robot with the exported kinematics and by adapting the 3D model of the robot, but that can be quite challenging. 

I hope it helped you better understand the situation. 

Jeremy
  




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