21660

Review the PLC program source (typically in OB1 or synchronized action subroutines) for DO_$AA_OFF[<axis>] assignments. Search for any unconditional or event-driven synchronous action logic that sets this variable.

Do not disable synchronous actions without understanding the complete motion control strategy.

Cross-reference the PLC logic with the CORROF command location in the part program (NCK block %2). Verify that DO_$AA_OFF is not set to TRUE in the same or adjacent NC blocks where CORROF deselection occurs.

Add conditional logic to the PLC synchronized action: guard DO_$AA_OFF with a flag that is cleared when CORROF is about to execute. Use NC variable synchronization (via DB or shared memory) to prevent simultaneous conflicting commands.

Test the corrected logic in simulation mode (Playback/DRY RUN) before running on the machine. Verify that $AA_OFF state matches the intended offset status in both NCK and PLC contexts.

Verify CORROF syntax in the NC block: correct format is CORROF(<axis_name>, "AA_OFF"). Confirm the axis name matches the machine configuration and that it corresponds to axis %3 mentioned in the alarm.

Use axis technical names (e.g., X, Y, Z) not axis numbers unless explicitly configured.

Check MD 22070 (Synchronized Action Monitoring) and MD 22080 (Enable Synchronized Actions). If MD 22070 = 1, the system is actively monitoring for conflicts. Verify that DO_$AA_OFF is scoped to the same axis as CORROF.

Inspect the synchronized action definition in the PLC (typically in the synchronous action block or interrupt handler) to ensure DO_$AA_OFF[axis_index] references the correct axis. Cross-check axis indexing (0-based vs. 1-based).

Review the PLC cycle time and the NCK interpolation cycle time (typically 12.8 ms for 840D). Determine if the DO_$AA_OFF assignment is combinatorial (always on) or edge-triggered. Combinatorial logic will persistently conflict with CORROF.

Avoid combinatorial synchronous action assignments; use edge-triggered (R_TRIG/F_TRIG) logic to set and reset DO_$AA_OFF.

Implement a handshake protocol: use an NC-side acknowledge variable (e.g., a custom SYN variable) to signal the PLC that CORROF has executed, allowing the PLC to safely clear DO_$AA_OFF in the next cycle.

Add a brief dwell (G04 P0.1 or similar) after CORROF in the part program to allow the PLC cycle to synchronize and clear the conflicting DO_$AA_OFF assignment.