Direction of gripper rotation

  • Hi Guyes,

    I am struggling with robot rotation of the gripper. My cell is attached. For simulations I use Roboguide.

    My UF is located at point I shown and it is oriented as the WORLD one.

    To turn gripper Z negative 90 degrees (short turn), I use:

    !check KLT index in pallet;
    IF ((R[6:PalFulLayerInd]>=7) AND (R[6:PalFulLayerInd]<=10)) THEN ;
    PR[6,6:FullPalOffset]=(-90) ; ! I want to Turn KLT, 90 degrees clockwise, according UF
    ENDIF ;
    !position on KLT ;
    J PR[11:37PalFullBgn] 100% CNT20 Tool_Offset,PR[19:37ToolOffset] Offset,PR[6:FullPalOffset] ;

    Because of gripper harness, I need to turn the gripper negative -90 degrees. That is why I use J movement type.

    Unfortunately the grippe is turning Z positive, and rotates 270 degrees.

    When I release the KLT, I use the following commands:

    !rotate gripper basic pos ;
    IF ((R[6:PalFulLayerInd]>=7) AND (R[6:PalFulLayerInd]<=10)) THEN ;
    PR[6,6:FullPalOffset]=0 ; // I want to Turn KLT, 90 degrees counter clockwise, according UF
    ENDIF ;
    J PR[11:37PalFullBgn] 100% CNT20 Tool_Offset,PR[19:37ToolOffset] Offset,PR[6:FullPalOffset] ;

    The gripper is rotate 270 degrees negative according UF.

    A colleague told me that, if I use "J", it will rotate, by choosing the shortest path. What I am missing?

    Why is that happening? How can I control to which direction the gripper is rotating?



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  • You should try linear movement, did you ever try that?

    With joint movements normally the config bits are used, so that the robot positions fits the configuration. On linear movements he should use the shortest way. Don't know for shure if Fanuc moves that way, but other brands do.

  • There are few things you can do but before lets talk about this A colleague told me that, if I use "J". I think he mint save the point with joint representation and not cartesian.

    I use this method when I want to "untangle" the robot. The point is define with angles and the robot will go always on the same (know) direction. Usually I do this in between the pick (at any angle) and the place. The problem is that the offsets that you use are in cartesian so it does not apply to your angles. An offset of, lets say, 3 on axis 1 will rotate the robot 3 degrees instead of moving forward 3 mm.

    As far as your problem if you are picking parts at 0 or 180

    I would approach the point with the gripper half way of each direction, then the rotation is only 90 deg

    I would use numbers like 179.99 instead of 180 or 0.01 instead of 0

    Retired but still helping

  • Your colleague told you wrong.

    I agree with both posts above.

    Linear will take the shortest path.

    Joint will go to the exact destination as defined by the config. This can get messy with offsets.

    Use linear and not joint if you can. If you must use Joint then you need to add the minimum rotation modifier "MROT" to the end of your motion instruction to force it to take the shortest rotational path.

    If you need to untangle the robot then do a simple joint move before this one with no offsets applied.

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