Motion - Limit Error

    Hi,

    I have a problem with a situation that cause me a limit error. I understand what is the limit error, but I need a way to correct it. So here the situation.

    Let say that we have 3 positions (P1, P2, P3)
    P1 has a rotation (R) of 0 deg
    P2 has a rotation (R) of 120 deg
    P3 has a rotation (R) of 240 deg

    The program (in karel) send the robot to the position P1, after to the position P2, after to position P3 and return to P1, P2, P3, P1, ....

    So,
    to be able to pass from P1 to P2, the robot turn the joint 6 counter clock wise of 120deg (let say that J6 value = 120 deg)
    to be able to pass from P2 to P3, the robot turn the joint 6 counter clock wise of another 120deg (J6 value = 240 deg)
    to be able to pass from P2 to P3, the robot turn the joint 6 counter clock wise of another 120deg (J6 value = 360 deg)
    because the robot try to reduce the angular displacement, when it's the time to go from P3 to P1, the joint 6 goes counter clock wise again for 120 deg...

    At some point, the joint 6 will get a limit error

    My question is : How can i correct that?

    -I don't want to manage it myself by always goes to an intermediate position between move that unwind the joint 6...or maybe is the only way to solve that
    -The positions can't be teach others ways

    Thanks for your help

    I don't know about doing it in Karel, but we run into a similar situation with our paint bots. There's a couple of ways around this. First, if you know where the problem point is, either add an intermediate point, or try playing with your angles some. It won't take much. At some point in your move, it's shorter for the bot to keep going toward it's limit. You want to tweak the angle so it wants to go back toward the middle of it's range.

    Otherwise, to fix it before sending home...
    3: PR[15]=JPOS ;
    4: !Store Joint 4 Angle in R30 ;
    5: R[30]=PR[15,4] ;
    6: !If R30>0, Elbow is twisted one ;
    7: !rotation too far. Call Unwind ;
    8: IF R[30]>=0,CALL UNWIND ;
    9: IF R[30]<0,CALL Z2_POINTS ;

    OK, now I understand... So the motion option Wjnt force the robot to return to the exact angle for each joint with respect of the teach position. and the option MROT do what I see now : go to the position by the fastest way (less angular displacement)

    Is that right

    Wow... perfect explication. Thanks a lot...

    For Karel, here the information from the Karel Reference documentation that I found (I hope that the forum will accept this partial citation)

    -Section 8.5.1 Motion Trajectory : Orientation Interpolation
    The system variable $ORIENT_TYPE uses the predefined constants RSWORLD, AESWORLD, and WRISTJOINT to indicate the type of interpolation used to move from one orientation to another during a LINEAR motion. By default, the two-angle method (RSWORLD) is used.

    For the WRISTJOINT method of orientation interpolation, the three wrist joints are joint interpolated. The remaining joints are interpolated so that the TCP moves in a straight line. Note that the starting and ending orientation will be used as taught, but because of the joint interpolation, the orientation during the move is not predictable, although it is repeatable.

    -Section 8.5.1 Motion Trajectory : Configuration
    In JOINT interpolated motion, the Boolean value of the system variable $USE_TURNS (TRUE or FALSE) indicates whether the turn numbers of the initial and destination positions are used in determining the joint distance.

    In CARTESIAN interpolated motion, the robot cannot move along the interpolated location trajectory, maintain control of orientation, and change the configuration. However, if orientation control is not important to the application, the WRISTJOINT method of interpolation can be used. WRISTJOINT is useful if changing configuration is required, while maintaining the location trajectory. The use of the turn numbers of the wrist joints are determined as follows:

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