TORQUE LIMIT


TORQUE LIMIT

1.  TORQUE LIMIT

1.1.  Specification

  • This function is designed to limit the maximum value of torque generated for a servo-controlled gripper.

  • The limit on torque is a percentage of a maximum value of motor torque.

    Syntax:

    TORQ_LIMIT t% (t:0.0~100.0)
    

  • The following system variables are used to set the axis that the torque limit is applied to. The default value is 7th axis of group 1.

    $TORQUE_LMT.$GROUP[i] : This system variable represents the group number that the torque limit is applied to, where i is the group number. If this system variable is set to True for a group, it means that the torque limit is applied to that particular group.

    i: group number

    $TORQUE_LMT.$GAi[j]: This system variable represents the group and the axis number for the motor to which torque limitation is applied.

    i: group number, j: axis number

    For example, if the motor is the first axis of group 2, $GA2[1] is set to TRUE and others are set to FALSE.

    $TORQUE_LMT.$GROUP[2] = TRUE
    $TORQUE_LMT.$GA2[1] = TRUE
    $TORQUE_LMT.$GA2[2] = FALSE
    :      :
    $TORQUE_LMT.$GA2[9] = FALSE
    

    • GA1[1] to GA1[6] are normally robot axes and are not set TRUE.

    • Multiple axes can be set TRUE.

  • You must determine the optimal value of force for each part. The part weight and gripped surface may affect the torque required to hold the part firmly.

  • During torque limit, the maximum of motor torque is not changed until the next torque limit instruction is reached.

    Example.

    1: J P[1] 100% FINE
    2:   TORQ_LIMIT 20.0%        <- Torque limitation is set to 20%.
    3: J P[2] 100% FINE            
    4: L P[2] 500mm/sec CNT100   <- Maximum Torque is limited to 20%.
     :                            
    6:   TORQ_LIMIT 100.0%       <- Torque limitation is set to 100%.
       
    

  • If the torque limit instruction lowers the motor torque too much , the axis might not be able to reach the taught point. The value of the following system variable should be large enough that errors do not occur during normal operation.

    • $PARAM_GROUP[group].$STOPTOL[axis]

    • $PARAM_GROUP[group].$STOPERLIM[axis]

    • $PARAM_GROUP[group].$MOVER_OFFST[axis]

  • You can specify the maximum value of torque limit by using the following system variable.

    $TORQUE_LMT.$MAX_TRQ_LMT = Upper limit

    Lower limit is 0.1 fixed value.

1.2.  Restriction

Warning

Because this function can also be applied to the robot axis, special care should be taken in NOT enabling this function for an axis that could fall due to the robot's own mass, for instance a gravity loaded axis .

  • This function only limits the maximum value of motor torque and, consequently, has no effect on the output torque of motor.

  • This function is designed for the FANUC servo motors only. Special considerations and extensive care are needed if the motor is manufactured by another company than FANUC.