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Siemens SINUMERIK Controller
System · Intermediate · 30-120 minutes
Siemens 4016 - Axis already used by NCU
Alarm 4016 fires when multiple NCUs (Numerical Control Units) in an NCU link configuration attempt simultaneous setpoint control over the same physical axis. This violates the single-master principle of NCU link architecture where each axis must be exclusively controlled by one NCU to prevent conflicting motion commands and system instability.
4016
Siemens 4016 - Axis already used by NCU
Axis already used by NCU
An attempt was made to apply setpoints to one axis from several NCUs. Only occurs with the NCU link system Control reaction: NC not ready. Channel not ready. NC Start disable in this channel. Interface signals are set. Alarm display. NC Stop on alarm.
Root Cause Summary
Alarm 4016 fires when multiple NCUs (Numerical Control Units) in an NCU link configuration attempt simultaneous setpoint control over the same physical axis. This violates the single-master principle of NCU link architecture where each axis must be exclusively controlled by one NCU to prevent conflicting motion commands and system instability.
Safety
- Only qualified personnel should diagnose and clear control alarms; follow the machine builder's safety procedures and lockout/tagout where hardware work is required.
Causes and Fixes
- 1
Access Siemens SINUMERIK 840D HMI → Maintenance → Machine Data and navigate to MD32000 (Axis assignment to NCU). Verify each physical axis is assigned to only one NCU number. Document current assignments.
Do not modify MD32000 while axes are in motion or DRY RUN mode is active.
- 2
Cross-reference the NCU link configuration file (typically in /siemens/config/ncu_link.xml or equivalent) against the axis assignments. Ensure no axis appears in multiple NCU declarations within the <AxisAllocation> or <MasterNCU> sections.
- 3
If duplicate assignments exist, edit MD32000 to reassign conflicting axes to their intended single NCU master. Set unassigned axes to value 0 (not allocated) if they should remain idle.
After modification, perform a cold restart (power cycle) of all NCUs to reload configuration data.
- 4
Verify correction by checking alarm log (via HMI → Diagnostics → Alarms) and confirm no new 4016 alarms appear during subsequent axis motion commands across NCUs.
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