SV0423 Torque/Pos Balance Error fault in Fanuc drive

SV0423 Torque/Pos Balance Error fault in Fanuc drive

Description

SV0423 is the "Position" sibling to the SV0420 "Torque" alarm. It appears on Twin-Driven axes (Master/Slave or Tandem Control). While SV0420 complains if one motor works harder than the other, SV0423 complains if the actual position of the two motors deviates too much from each other. In a gantry, both sides should move exactly the same distance. If the Master moves 100mm and the Slave only moves 98mm, the gantry is twisting physically. SV0423 stops the machine before the frame is permanently bent.

Cause

This implies physical slippage or geometry errors.

• Coupling Slip: The most common cause. The coupling on the slave side is loose, so the motor turns but the ballscrew doesn't. The encoder (on the motor) counts movement, but the linear scale (on the table) sees less movement, or the cross-check between motors fails.
• Backlash Mismatch: One side has a worn ballscrew with 0.05mm backlash, the other is new. When reversing direction, they lose sync.
• Obstruction: One side of the gantry hit a clamp, stopping it, while the other side kept trying to move.
• Parameter: The "Sync Error Limit" parameter is set too tight for an aging machine.

Solution

1. Gantry Square: You likely need to perform a gantry squaring procedure to mechanically realign the two sides.
2. Coupling Check: Mark the shafts and couplings. Move the axis. Check if the marks shifted.
3. Grid Shift: If the alarm happens immediately at startup, the "Home" positions of the two motors are not synchronized. You may need to adjust the Grid Shift parameter on the Slave axis to match the Master.
4. Check Mechanics: Disconnect the motors and push the gantry by hand. Does it rack or bind?