Joint Motion command painfully slow with speed in seconds

    One of my students wrote a basic motion program as a lab assignment.


    The lab asked him to change the speed from % to seconds. He used 10.0 seconds as a time value.


    J P[1] 10.0sec CNT100

    J P[2] 10.0sec CNT100

    etc.


    The manipulator moves almost imperceptibly. Displaying World position in separate window shows small changes happening in the decimal parts of X, Y, and Z position values.


    Increasing or decreasing the time values has no effect.


    If the speed values are replaced with 50% speed, the program operates in a more normal fashion.


    If the 10.0sec program is run in AUTO, it operates as it would be expected.


    Robot is a ER-4iA / R-30iB Mate Plus. HandlingTool V9.30P/21 installed; a second identical robot has V9.30P/20. The program acts the same on both robots.


    I have looked at DCS configuration but cannot find any relevant settings that are active that would explain the behavior.

    Mark

    Robotics Instructor

    Quote from HawkME

    Sometimes things behave a little differently in teach mode. I've never seen anyone use a time based motion command like that. I'm not sure there are any real world use cases for that.

    I found only one use of time based motion years ago in a press tending application. The robot moved into place under the press and waited for the press to finish its cycle and open. The press opening motion was time based and the robot start and end points were taught with a time based move to the end point that matched the press move time. It worked really well.


    Other than that, I haven't had any other instances where I used that instruction.

    I have found a timed move during a spray operation on a rotating tank to be very useful.


    The very large tank was revolving at a constant 2.2 rpm. The spray was a 36" wide fan pattern that needed to be rotated at one corner of the fan over one revolution of the tank. The starting position was roughly 45 degrees off of horizontal and finished at a horizontal attitude.


    One joint move over 27.27 seconds worked perfectly for this; 60 sec / 2.2 rpm = 27.2727272.....


    I think someone else had told me of a similar situation once on a painting line. Timed moves can work very simply for coordinating motion with a rotating target. The're great when there is almost zero TCP linear movement, but a lot of rotation. Calling out the speed in deg/sec is another option, but sometimes it's just simpler to time it if the beginning attitude needs to be adjusted at a later time.

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