the velocity constrain during running CP motion and an external axis

  • Problem:
    When CP motion runs during an external axis moves, the robot doesn't reach expected velocity.

    I set some of parameters as below.
    -$VEL.CP = 0.1
    -$OV_PRO = 100%

    At the points from P0 to P6 , the velocity gets 0.1[m/s] running this sample code with automatic mode.
    The problem is it doesn't get 0.1[m/s] from P7 where the external axis starts to move.
    LIN {X 0,Y 0,Z 0,E1 0} C_DIS ;P0
    LIN {X 1000,Y 0,Z 100,E1 0} C_DIS ;P1
    LIN {X -1000,Y 0,Z 100,E1 0} C_DIS ;P2
    LIN {X 1000,Y 0,Z 100,E1 0} C_DIS ;P3
    LIN {X -1000,Y 0,Z 100,E1 0} C_DIS ;P4
    LIN {X 1000,Y 0,Z 100,E1 0} C_DIS ;P5
    LIN {X -1000,Y 0,Z 100,E1 0} C_DIS ;P6

    LIN {X 1000,Y 0,Z 100,E1 180} C_DIS ;P7 the external axis starts to run from here
    LIN {X -1000,Y 0,Z 100,E1 359} C_DIS ;P8

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  • Thank your for your reply.

    controller : KRC4 compact
    KSS: 8.3.33

    I set so that robot follows the moving base coordinate-system while E1 axis rotates.
    So the robot and E1 axis are integrated.

    I set $VEL_MA as 3.0.
    I' ve not tried an Oscilloscope trace.

    The point is the velocity behaves differently between PTP and CP.

    I think I need to learn Oscilloscope trace first.

  • $VEL_CP and $VEL_ORI, not $VEL_MA.

    Also, $VEL_EXTAX[1] for E1 velocity.

    The velocity will always behave differently between CP and PTP -- in PTP motions, the only thing that matters is the endpoint of the motion, and the TCP is allowed to "cut the corner", so to speak. For the same motion, but CP, the TCP is now forced to follow a linear path, in the rotating reference frame of E1. So there are more restrictions on how the TCP can move.

    In a PTP move, the motion planner calculates the end position of each axis, determines which axis will need the most time, and adjusts the speed of all the other axes so that all 7 axes achieve the commanded destination at the same time. This is the most time-efficient type of motion. All the axes accelerate to commanded speed, maintain that speed until near the destination, then decelerate and stop.

    In a CP motion, the linear motion of the TCP means that many axes may have to follow a much more complex speed/time profile. The addition of the kinematically integrated E1 complicates this further. In some cases, several axes may have to undergo multiple accel/decel ramps during a single motion. The path planner looks ahead and de-rates the entire motion to match the predicted slowest part of the commanded motion.

    Performing an O-Scope trace should help reveal which axis, if any, is "maxing out" during the CP motion.

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