KUKA Robot codes
AxisMD

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KUKA Robot Controller

Servo/Axis · Basic

Alarm KRC0421

KUKA Robot KRC0421 - <axis number> AXIS SYNCHRONIZED

An attempt was made to reference an axis that has already been successfully mastered in single-axis referencing mode. The KUKA controller prevents redundant referencing to maintain the integrity of the current machine datum calibration and avoid calibration drift.

KUKA RobotServo/AxisBasic

KRC0421

KUKA Robot KRC0421 - <axis number> AXIS SYNCHRONIZED

<axis number> AXIS SYNCHRONIZED

An attempt was made to reference an axis that has already been successfully mastered in single-axis referencing mode. The KUKA controller prevents redundant referencing to maintain the integrity of the current machine datum calibration and avoid calibration drift.

Common Causes

  • Operator accidentally selected an already-mastered axis for referencing via KUKA smartPAD
  • Referencing program loop in KRL repeated axis mastering call without checking mastered status
  • Automatic referencing sequence in WorkVisual configuration attempted to re-reference an existing axis
  • Manual referencing procedure was resumed after interruption without tracking which axes were already done
  • Mastered status flag was not properly cleared between separate maintenance referencing sessions

Troubleshooting Steps

  1. 1Check the Referencing Status display on KUKA smartPAD Diagnosis menu to identify which axes are already mastered
  2. 2Skip any axes showing mastered status and only reference the remaining unmounted or replaced axes
  3. 3If re-referencing is necessary due to suspected calibration error, use Reset Mastering function to clear all axes first
  4. 4Review the active KRL referencing program to ensure it contains logic to check $AXIS_REF_STATE before attempting mastering
  5. 5Modify any automatic referencing procedures in WorkVisual to filter out already-mastered axes from the referencing queue
  6. 6Document the mastered axis status before any maintenance work and cross-reference before re-running referencing cycles

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