Siemens SINUMERIK 840D sl / ONE alarm 25040: Axis standstill monitoring
Alarm 25040 “Axis %1 standstill monitoring” on a SINUMERIK 840D sl means an axis that should be holding position at zero speed moved outside the tolerance in MD36030 $MA_STANDSTILL_POS_TOL. Monitoring starts after the delay in MD36040 once interpolation has ended; Siemens names two cases: a mechanically jammed axis, or an axis pushed away by machining forces with a low position-loop gain.
Diagnose this with AI
Try Free CNC Alarm Diagnostic Upload a keypad photo, the fault history or a parameter export from your Siemens SINUMERIK 840D sl / ONE. InduQT compares the evidence and suggests the next useful checks.
When it happens
- At standstill after a move (after the MD36040 delay)
- While clamping or while another axis cuts
- Servo enable dropped with the axis under load
Likely causes and checks
1Machining force pushing a stopped axis
- Points to it
- Alarm while another axis is cutting or while the tool is in contact; axis is not clamped.
- Check
- Estimate the machining force and reduce it with a lower feed or higher speed, as Siemens suggests.
2Insufficient clamping
- Points to it
- Axis has a clamp; alarm when the clamp is applied or under load.
- Check
- Check clamp operation and clamping pressure; Siemens lists increasing clamping pressure.
3Axis mechanically jammed with servo enable off
- Points to it
- Servo enable (DB31, … DBX2.1) is 0 at the time; axis cannot settle.
- Check
- Check the NC/PLC interface signal and look for a mechanical jam.
4Low position-loop gain
- Points to it
- Axis drifts under load with servo enabled; recent tuning change.
- Check
- Have the position controller optimized; Siemens points to the Kv factor in MD32200 $MA_POSCTRL_GAIN.
5Tolerance or delay set too tight
- Points to it
- Alarm after a machine data change; MD36030 not greater than MD36000.
- Check
- Have the machine builder check MD36030 and MD36040; Siemens says the tolerance must be greater than exact stop coarse (MD36000).
Telling it apart
- 25050 contour monitoring is checked while the axis is moving; 25040 only once interpolation has ended.
- 25080 positioning monitoring means the axis did not reach the exact stop window within MD36020 $MA_POSITIONING_TIME; 25040 means it reached position but did not stay.
- 25042 is the version used during travel to fixed stop (torque/force limitation).
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| MD36030 $MA_STANDSTILL_POS_TOL | Standstill tolerance | Must be greater than MD36000 exact stop coarse. |
| MD36040 $MA_STANDSTILL_DELAY_TIME | Delay before standstill monitoring | Time after interpolation ends before monitoring starts. |
| MD36000 $MA_STOP_LIMIT_COARSE | Exact stop coarse | Reference for the standstill tolerance. |
| MD32200 $MA_POSCTRL_GAIN | Position loop gain (Kv) | Low gain lets machining forces push the axis away. |
Evidence to collect
- Axis name and what other axes were doing
- Clamp state and servo enable signal at the alarm
- MD36030, MD36040, MD36000 and MD32200 values vs the builder’s archive
- Recent tuning or mechanical changes
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