motion Frame input with A,B,C

  • Hi, I am working with KUKA LBR IIWA 7 R800 in Sunrise Workbench.

    I am trying to calculate A,B,C values to give robot as an input to make robot flange pointing at a certain direction given in vector format(nx,ny,nz).

    I simply thought that as A,B,C values given to KUKA is a Euler angle value, I calculated the rotation matrix
    (0,0,1) -> (nx,ny,nz) : z-aixs, which is the pointing direction of the TOOL coordinate system to match the vector.
    and extracted three Euler angles from that rotation matrix.
    (refered to https://pdfs.semanticscholar.o…46e689eea1e334bcf6bf6.pdf)

    However, this does not work since there can be so many x-axis and y-axis representation.

    Do you have any other suggestion? Or is there a function given in Sunrise Workbench for this kind of purpose?
    Robot flange to pointing the direction vector(x,y,z).

    :help: :help: :help: :help:

  • AD
  • Well, for starters, KUKA uses the Euler sequence Rz,Ry,Rx. A=Rz, B=Ry, and C=Rx. And that requires a different formula for conversion into a rotation matrix, as I recall.

    Not sure what you mean by "so many representations." In KRL, the solution space is deliberately limited: A and C can range only between -180 and +180, and B is limited to +/- 90. However, giving the robot a value of (for example) +200deg for A will result in an automatic conversion to -160.

  • maybe this helps...

    basically FRAME has six coordinates,
    X,Y,Z represent translation
    A,B,C is rotation.

    translation takes you to some point in space.
    rotation changes orientation of the tool so it points in new direction.

    in case of translation, order does not matter - you always end up in same point regardless in which order you move first (although different choices will create different path if motions are executed individually for each of the three axes).

    in case of rotation, order does matter - there are 12 possible scenarios.
    each robot manufacturer must pick one of the 12 choices and stick with it...

  • As already mentioned by SkyeFire and shown in attachment it is first rotating about Z axis by angle A, then about new (moved) Y axis by angle B and finally about new (moved) X axis by C degrees.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • Hi, I am wondering an issue related to A, B and C angles at KUKA iiwa 14.


    When doing cartesian jogging of the flange using SmartPad, that noticed that B and C values are not changing as expected.

    I have used Jogging type: World, and Tool selection: Flange.

    For example: when I press Angle B + button, not only the B value in "Cartesian Position"-view at SmartPad is increasing,

    It seems that changes of B and C angles during pressing B or C + and - buttons are not logical.

    At some poses of the iiwa arm B even decreases when I press B - button.

    My colleague actually noticed this behavior first a couple of weeks ago, earlier we had not paid attention to those values at "Cartesian Position" view on SmartPad.

    Our iiwa is wall-mounted at the moment, at this is taken into account in project settings. We have noticed this behaviour in two different projects.

    I wondering is there something wrong with our iiwa setup at the moment, or does this behavior arise from the way how Sunrise handles Euler angles?

    Would you iiwa owners check how A, B and C values at Cartesian Position -view are behaving during cartesian jogging?

    -BR, Paavo from Kuopio, Finland.

  • The ABC angles in a KUKA Frame are a sequence of rotations, relative to the active Base frame. A first, then B, then C.

    So, it is entirely possible to put the robot into a condition where driving rotation around one axis only causes changes to the ABC values of the other two axes. If the TCP Z axis is nearly aligned with the Base Z axis, then rotating A will mostly effect A. However, if TCP Z is more closely aligned with Base X, the effects will be quite different.

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