IV: Noticeable difference in gripping accuracy between MoveL and MoveJ

unni2007

As I wanted to  test the accuracy of a vision job I set up using the integrated vision of a Yumi robot, I mounted a pointing-tool to my robot and used a target with a marker.
To make sure my TCP is defined right, I aligned the tool with the world coordinate-system and rotated the wrist angle of the robot (to see if there is any change of the TCP while rotating-> there was none). I configured the quaternions of the robtarget for the grasping so that the tool is perpendicular to my gripping surface (which is parallel to the base).

While testing I noticed something strange:

If the robot approached the target with a MoveJ (using the offs command) and then moves to the target with a linear movement, the pointing tool sometimes missed the marker with an error greater than 1.5 mm, depending on the orientation of the target.
If it approached the target with a MoveL instead of a MoveJ, this error was much less.

AbsAcc is on. I also checked if something is wrong with the AbsAcc values in the MOC.cfg (and did a calibration using the calibration routine).
Shouldn't the results be comparable (within a range of 0.6 mm as this is the maximal error of absolute accuracy for the IRB14000), or am I missing something?

Thank you in advance!
Kris

YuGo

Hi @unni2007
Is very strange that the same robtarget point to two different positions using the linear instead of joint movement; 
Is the tool properly define (both the TCP and the load) and the robot arm right calibrate?
Probably the calibration of the vision system is not so accurate, try to move the target under the camera without rotating it and see if the robot follow it.

Hope this help.

DenisFR

Hello,

Do you use fine zonedata?

EricH

Maybe the mounted tool is not fastened and wobbles a bit. Does the same happen, when moving slowly?