Axis U and W in Fanuc S-420

    Hello friends
    I have one Fanuc robot S-420. I had a problem, so I decided to pull out motor axis U and axis W.
    Now the motors are on the table and in front of me .when I select coordinate system on JOINT, so I use U jog button just motor axis U is turning but when i press W jog button Motor, in a same time to motor axis is turning U and W!!!!!!!
    But in my idea in Joint coordinate system each motor should be driven independently. In this case I have changed servo drive of axis U and W ,axis computer board ,I/O computer board ,also the motor axis 2 and 3 on the manipulator but result is the same !!!!
    Can any body has this experience or help me? Because I have worked with kuka and abb robot. :help:

    Best regards

    I'm afraid this is normal. When you move U axis (J3), only U axis will move. When you move W axis (J2), a Fanuc robot will keep the U axis on the same Joint position. So both U and W axis will move. This is a difference between Fanuc and ABB/KUKA. I guess your problem will be in the cables or motors, because you already changed everything else :icon_smile: Please tell us more about your problem, maybe we can help.

    Thanks RoBoWi

    My first problem was over current on axis W, so I pull out motor axis W to find the problem, to find the location of the error for example problem in gearbox or motor .
    According of your explanation this situation for motor moving of robot is normal and it's strange for me when I compare it with ABB and kuka .
    So I will put the motors on the manipulator and in case trouble inform you .thanks again for answering.

    Dear Friends

    I put the motors on the right position on the manipulator and charge oil and grease according of manual .While I want to move robot axis I get the error message:
    350 U AXIS EXCESSIVE (STOP)
    Some time I can reset the error with rest key on the teach pendent but not all of time .in Case of error acknowledge when I jog the axis W to – direction (Downwards), back balancer of the robot moves down .in my aide this should be wrong ?is it true?

    This is due to the mechanism design of the robot (4 bar linkage) So when you move the upper arm in joint mode only the corresponding motor moves but in reverse direction: If you what to move the arm up, the 4 bar linkage mechanism pulls the back of the arm down. That's why the balancer moves down when you move the upper arm up.
    but when you move the lower arm, J3 moves to compensate this movement to keep the relative position of the upper arm with respect to the lower arm.

    is this correct?
    J2 means W Axis
    J3 mens U Axis

    When we press J3 only mtor Axis U will turn.(Robot aram moves Up/Down)
    When we Press J2 motor axis U also is Turning with motor axis W in wrong direction and same speed .Robot arm Moves Forward and Bacward.

    these are right ???? :help:

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