Resolving DMU60P Rotary Table C30 C04 Errors on Simodrive 611

The Deckel Maho DMU60P 5-axis machining center uses a Siemens Simodrive 611 digital servo drive system to control its C-axis rotary table. Two recurring alarms — C30 "Setting time overflow" and C04 "Maximum following error too large" — typically appear together when the C-axis cannot complete a commanded motion within the controller's monitoring window. This reference walks through the field-diagnosis procedure used to isolate these faults, with emphasis on mechanical binding, wave (harmonic) drive condition, encoder integrity, and Simodrive 611 drive-side diagnostics.

1. Problem Description and Initial Symptoms

The reported fault pattern on a DMU60P equipped with a Simodrive 611 system and DDC2 (Digital Drive Control, 2-axis) control boards is as follows:

• When a C-axis motion is commanded, the table rotates a few millimetres (approximately 0 to 2 mm of equivalent linear travel at the table periphery) and then the controller drops into emergency stop.
• The HMI displays alarm C30 ("Setting time overflow" / "Positioning timeout") and alarm C04 ("Max. following error exceeded").
• The Axis Info panel on the Simodrive 611 shows C-axis torque demand rising sharply and the following error (position lag) saturating the monitoring window.
• The fault is direction-independent: the table fails in both clockwise and counter-clockwise rotation.
• The A-axis (tilt table, also driven by Simodrive 611) operates normally for comparison, isolating the issue to the C-axis mechanical or electrical path.

2. Simodrive 611 Architecture Used on the DMU60P

The DMU60P C-axis drive chain consists of:

1. Simodrive 611 power module (6SN1123 or 6SN1145 series) — supplies the DC link and the IGBT inverter stage.
2. DDC2 control board (6SN1118-0DM/0DJ or compatible) — performs current, speed, and position closed-loop control for two axes (C and A in this case).
3. 1FK / 1FT-series servomotor coupled to the table through a toothed belt and harmonic (wave) reducer.
4. Heidenhain ROD or EnDat encoder mounted on the motor and a separate rotary encoder (typically ERN1387 or ROC series) on the table itself for absolute position.
5. Hydraulic brake on the motor rear shaft, energized through relay 7K4 and downstream contactors; contacts X143 / X144 carry the brake wiring.
6. Clamping rail pressure regulator (typically 5.0–6.0 bar) feeding the table faceplate clamping and the rotary axis hydraulic clamp.

When alarms C30 and C04 appear simultaneously, the control loop is open at one of three points: the mechanical transmission (most common), the motor/tacho feedback path, or the inverter output stage. The diagnostic ladder below resolves these in order of probability and ease of test.

3. Diagnostic Decision Matrix

4. Step-by-Step Isolation Procedure

4.1 Verify the Hydraulic Brake Releases

1. Lock the table against gravity using an overhead crane or suitable fixture. The DMU60P C-axis is a horizontal trunnion-style table; gravity-load the faceplate.
2. Command the C-axis to move at 5% feed from the operator panel.
3. With a multimeter set to DC voltage, measure across terminals X143 pins 1 and 4 at the motor junction box. A healthy brake releases at 24 V DC ± 10% (typical 1FK7 holding brakes draw 0.7–1.5 A).
4. Repeat at X144 pins 1 and 4 (or whichever diagram sheet applies to the C-axis brake path on your build).
5. If the voltage is present but the table does not free up, the brake itself is sticking — apply 24 V directly to the brake leads at the motor to confirm.

4.2 Check Contact and Connector Integrity

Wiggle-test the connector at X143/X144 and the power cable 7A6.1 / 7A6.2 while monitoring 24 V. In one field case the intermittent contact at these pins (oxidation, loose crimp) was the cause of intermittent C30/C04 alarms. The procedure:

1. Disconnect power and discharge the DC bus (wait 5 minutes after mains off — confirm at the 611 display).
2. De-pin X143/X144 connectors and inspect for discoloration, cold-flow, or green oxide.
3. Measure contact resistance from pin to wire end with a 4-wire ohmmeter; target is < 50 mΩ.
4. Re-pin with new gold or tin-plated crimps and reassemble.

4.3 Manually Free-Rotate the Table

The decisive test for mechanical binding is to release the brake and try to turn the table faceplate by hand using an Allen key inserted into the motor-end gear or the harmonic drive input. Procedure:

1. With the machine off, remove the motor cover and the timing-belt guard.
2. Apply 24 V DC directly to the brake leads to release the brake.
3. Insert an Allen key into the head of the harmonic drive input gear (typically 8 mm or 10 mm).
4. Try to rotate the table faceplate.
5. Feel for: smooth rotation, slight gear-tooth chatter, or hard binding at certain angles (indicates localized damage in the harmonic drive flexspline or wave generator bearing).

4.4 Read Simodrive 611 Axis Info Live Data

With the operator panel in the Simodrive 611 "Axis Info" menu (or via SimoCom U on a laptop), observe the following during a commanded motion:

On the reported DMU60P, the Axis Info video showed C-axis torque demand saturated and a steadily growing following error. The A-axis (driven from the same 611 module) ran cleanly, ruling out the inverter module itself and pointing at a C-axis-specific mechanical or feedback problem.

5. Checking and Adjusting the Clamping Pressure

The DMU60P rotary table uses a hydraulically released clamp that prevents table rotation when the C-axis is not commanded to move. If the clamp pressure is too low, the brake and clamp fight each other, increasing the effective load on the servomotor until the position loop runs out of torque margin. The factory setting is typically 5.0–5.5 bar; many field reports, including the one documented here, document reliable running at 6.0 bar.

1. Locate the pressure regulator on the hydraulic manifold serving the C-axis clamp (usually labelled on the schematic as "C-Achse Spannzylinder").
2. Connect a calibrated test gauge in parallel.
3. Read the current setting. If below 5.5 bar, increase in 0.2 bar steps and re-test motion.
4. Do not exceed the system maximum; the DMU60P hydraulic system is usually regulated to 40–60 bar total with local regulator to the clamp circuit.

Field note: in the original case, raising the pressure from 5.2 to 6.0 bar combined with running the table at 100% feed (a deliberate stress test) cleared the alarm on the next cold cycle. The most plausible mechanism is that the higher clamp pressure fully released the brake and clamped the table centering pre-load, restoring the air-gap the servo needed to overcome.

6. Swapping Servomotors to Localize the Fault

When several identical servomotors exist on the same machine (e.g., a spare 1FK7060 or 1FT6086), swapping them is a fast way to localize the fault to the motor, the encoder, or the downstream mechanical chain. Procedure:

1. Identify a C-axis motor and a verified-good axis (A-axis) using the spare parts list or the 611 module wiring diagram.
2. Power down, wait 5 minutes, verify zero energy.
3. Disconnect the C-axis motor power cable (X411 / X412 on the DDC2) and encoder cable (X411 or X412 depending on encoder protocol).
4. Swap the entire motor — including the rear encoder — with the spare or with a known-good A-axis motor of the same catalog number.
5. Reconnect and re-reference the axis. Run the C-axis test motion.

7. DDC2 Board Swap Procedure

The DDC2 (Digital Drive Control, 2-axis) board is a known failure component in older Simodrive 611 installations. Symptoms that point to the DDC2 specifically include:

• Alarms appearing on one channel of a 2-axis DDC2 board while the other channel works.
• Fault following a warm-up period (thermal-sensitive components on the DDC2).
• Intermittent following error with normal torque demand.

To swap a DDC2 board:

1. Power off the Simodrive 611 module, discharge DC link, wait 5 minutes.
2. Loosen the four retaining screws on the front of the 611 module and pull the DDC2 board out by the front handle.
3. Note the slot assignment — the C-axis and A-axis each occupy a half of the DDC2 (slot left and right), and the firmware module number on the spindle end of the board must match the drive configuration.
4. Insert the spare DDC2 board, seat firmly, retighten the four screws.
5. On power-up, the 611 will auto-detect the new module and the Sinumerik 840D will display the new axis assignment. Re-reference both C and A axes.

In the documented DMU60P case, swapping the DDC2 board did not clear the C04 alarm — confirming the fault was not on the control board itself, and refocusing investigation on the mechanical side.

8. Encoder Verification Procedure

The C-axis on a DMU60P typically uses either a Heidenhain ROD 426 incremental encoder (1Vpp) or an EnDat absolute encoder. Both can be checked with a 2-channel oscilloscope at the DDC2 connector:

1. With the 611 powered and the motor stationary, probe the encoder connector at the DDC2 end (not the motor end — cable problems are common).
2. Measure the A and B track signals: 1Vpp nominal, sinusoidal, with 90° ± 20° phase shift between them.
3. Manually rotate the motor (with brake released) at a slow, steady rate. The A and B signals should remain clean sinusoids with no dropouts, spikes, or amplitude collapse.
4. Check the R (reference) or C/D track pulse: it should appear exactly once per motor revolution, with amplitude similar to A/B.
5. For EnDat absolute encoders, verify the clock and data lines toggle in pairs without collisions. An EnDat cable that is too long or has a broken shield will show intermittent comm errors logged in the Simodrive 611 alarm buffer.

9. Simodrive 611 Spare Rack and Module Swapping

The DMU60P typically uses one 6SN1123-1AA0x power module feeding one or two DDC2 boards and a connected motor module. Field engineers commonly keep a complete spare rack (power module + DDC2 + IGBT module) for quick swap. The procedure is:

1. Label every connector before disconnection. Photograph the wiring from at least two angles.
2. Remove DC bus bars, control bus ribbon, and motor power cables.
3. Sliding rails release with the front screws; the module pulls out as a single assembly.
4. Insert the spare, reconnect with the photograph as reference.
5. Re-commission both axes, run the circularity test, and re-set MD parameters only if necessary (they are stored on the NCK side, not the drive module).

10. Wave (Harmonic) Drive Condition Assessment

The DMU60P C-axis is driven through a harmonic drive (e.g., CSF-25 or CSG-25 series from Harmonic Drive AG). Failure modes include:

• Flexspline fatigue: typically after 10,000–20,000 hours of indexing duty. Symptoms include growing backlash, periodic binding at the wave-generator position, and rising torque demand under load.
• Wave generator bearing wear: roughness at every revolution of the wave generator. Audible as a "rustling" or rumbling at low speed, as was reported on the right-side reducer in the original case.
• Grease degradation: high-temp grease life is typically 5–7 years; hardened grease is a common cause of high torque demand after extended downtime.

Indirect assessment without disassembly:

1. With the belt removed and the motor disconnected, rotate the harmonic drive input by hand using an Allen key. Smooth motion with a slight tooth-mesh feel = healthy; roughness, hard spots, or grinding = worn.
2. Listen with a mechanic's stethoscope on the harmonic drive housing while jogging the axis at 5% feed. A clean wave drive has a steady mesh-frequency hum; rumbling, ticking, or popping indicates wear.
3. Check backlash: clamp a dial indicator against the table faceplate, rotate the table ±5° from a centered position, and measure the lost motion. Spec is typically < 0.05 mm at the periphery; > 0.10 mm indicates wave drive wear.

11. Table Faceplate Leveling and Geometric Correction

Field reports show typical table faceplate run-out of up to 0.20 mm on the X and Y axes after years of service. Sources of error include:

• Table bearing preload relaxation.
• Table mounting bolt torque relaxation (12 M16 cap screws typically).
• Spalling of the table faceplate under repeated indexing loads.

Re-leveling procedure:

1. Loosen the 12 table mounting bolts in a star pattern, 1/4 turn at a time.
2. Place a precision dial indicator (0.001 mm resolution) on the spindle nose.
3. Sweep the indicator across the table at four quadrants.
4. Re-torque the bolts in a star pattern to the OEM spec (typically 80–120 Nm for M16 high-tensile).
5. Re-check with the indicator. A small improvement of 0.05–0.10 mm is typical; full elimination usually requires scraping or remachining the table faceplate.

Machining the faceplate on-machine to a flatness below 0.01 mm is feasible but is a last resort — the table is usually more accurate than the spindle nose run-out that the operator assumes is being measured.

12. Verification Procedure After Repair

After each fix attempt, run the following verification ladder:

1. Static test: Reference the C-axis, then command a 1° move at 1% feed. Axis Info should show position settling within 200 ms and zero following error after settling.
2. Directional test: Command 360° clockwise, then 360° counter-clockwise at 25% feed. Torque demand should stay under 40% of rated; following error under 20% of MD-stored tolerance.
3. Circularity test: Run a 100 mm diameter circular interpolation at 1000 mm/min, measuring circularity with a dial indicator or laser. Spec is typically < 0.030 mm on the DMU60P.
4. Thermal test: Run the C-axis continuously for 30 minutes at 50% feed, monitoring 611 module temperature and motor temperature. Both should stabilize below 70 °C.
5. Stress test: Run a 360° move at 100% feed (this is the test that cleared the original case after the 6 bar pressure adjustment). If the alarm does not return under this load, the fix is holding.

13. Related Machine Data (MD) Parameters

14. Field-Commissioning Checklist

1. Visual inspection of the table — grease leaks, bolt looseness, drag marks on the faceplate.
2. Brake release voltage at X143/X144: 24 V DC ± 10%.
3. Hydraulic clamp pressure at C-axis regulator: 5.5–6.0 bar.
4. Simodrive 611 power module diagnostic LEDs all green; no alarm on the operator panel.
5. DDC2 board seated, all screws torqued, ribbon cable undamaged.
6. Encoder 1Vpp signals clean on oscilloscope at the DDC2 end.
7. Axis Info: torque demand under load, following error within tolerance.
8. Circularity test: < 0.030 mm on a 100 mm circle.
9. Backlash check: < 0.05 mm at the faceplate.
10. 30-minute thermal soak at 50% feed — no C30, C04, or 611 temperature alarm.

15. Frequently Asked Questions