A second-hand 5-axis center with a Siemens Sinumerik 840D SW 4.4 controller and a 1FT6064 synchronous servo on the Y-axis needs a structured auto-tuning pass after a belt change. Symptoms range from following-error alarms above 1 500 mm/min to auto-tuning rejecting the drive with a 'rotary/linear axis type' mismatch. This reference collects every constraint that must be verified before pressing the Auto-Tune button on a SW 4.4 HMI Advanced screen: the motor selector code, the machine data that defines axis type and feedback source, the mechanical preconditions on a belt-driven Y-axis, and the drive parameter path that should be reviewed in the SimoComu / Simodrive screen. Use it as a field-validated workflow to clear the alarm, re-measure the speed and position controllers, and lock in stable contour behavior at high feed rates.
Problem Overview and Machine Context
The reported installation is a five-axis machine retrofitted with a SINUMERIK 840D running HMI Advanced, software version SW 4.4 (build series NCK 4.x / HMI 6.x, before the Operate transition). The Y-axis is driven by a 1FT6064-xAH7x-xxx synchronous servo motor with a documented rated output of 9.5 Nm continuous stall torque, 9.1 A rated current, 4 500 rpm maximum speed, and a Siemens-internal motor data sheet code of 1303. After a belt replacement the operator expected to recover vibration and following error by simply re-running the built-in auto-tuning routine, but the commissioning screen refuses to continue with an alarm that indicates a rotary-versus-linear axis mismatch inside the controller.
Three separate issues overlap on a machine of this vintage:
- Residual mechanical mismatch caused by a swapped belt set with a marginally different pitch.
- Axis type configuration in the machine data. The 840D NCK expects a rotary servo motor on this axis but the auto-tune read-out is reporting linear motor characteristics, or vice versa.
- Feed-rate dependent contour error above approximately 1 500 mm/min, which suggests inadequate reserves on the speed-loop proportional gain (KV / Kp) and an aggressive look-ahead, not a tuning problem in isolation.
Auto-tuning alone will not address (1) and is partially obstructed by (2). The procedure below resolves (2) and (3) in sequence.
Motor Identification: 1FT6064-xAH7x-xxx Nameplate
Identify the motor by reading every field on the rating plate; do not rely on the order code alone. The 1FT6 family is a legacy SIMOTICS servo line now superseded by 1FT8 / 1FK8, but the motor data sheet and the motor selector list inside the 840D remain the source of truth for SW 4.4 commissioning.
| Field | Source value | Engineering meaning |
|---|---|---|
| Motor type | 1FT6064 | 1FT6 synchronous, frame size 63 mm center height, length variant "4" (medium) |
| Variant block | xAH7x | Radial cable outlet, insulation class H, internal encoder code "7" (typically 2048 ppr incremental sin/cos) |
| Order code suffix | xxx | Holding brake, shaft end, balance grade, and connector variant |
| Speed nmax | 4 500 rpm | Mechanical max speed; used for MD32000 $MD_MAX_AX_VELO scaling |
| Continuous stall torque M0 | 9.5 Nm | Stall torque at I0. Used with torque limit MD32100 $MD_MOTOR_RATED_TORQUE. |
| Rated current I0 | 9.1 A | Rated armature current at M0. Drives MD31130 $MD_MOTOR_NOMINAL_CURRENT. |
| Motor data sheet | 1303 | Selection list ID inside the 840D motor list. Must match an entry listed in the drive configuration. |
Record the nameplate photo for the documentation package and note the following numbers before touching the 840D:
- Continuous current I0 (A) and short-term current Imax (A).
- Torque at rated current M0 (Nm) and maximum torque Mmax (Nm).
- Rotor moment of inertia Jrot (kg cm²) listed on the rating plate or in the matching data sheet.
- Resolver or encoder type code (incremental 2048 / sin-cos 1 Vpp / EnDat, depending on the "7" digit variant).
These four numbers are copied verbatim into the NCK machine data described in the next section; matching them line-by-line against the motor data sheet is faster than running the auto-tuning measurement twice.
SINUMERIK 840D SW 4.4 HMI Advanced Environment
SW 4.4 runs the classic HMI Advanced (PCU 50 / PCU 70) interface rather than SINUMERIK Operate. The startup-tree structure differs from modern controllers, and several commissioning menus live one level deeper than a field engineer familiar with Operate will expect.
| Menu level | Path text | Purpose |
|---|---|---|
| Level 1 | Start-up → HMI → Start-up | Enters commissioning area (operator password required). |
| Level 2 | Start-up → Commissioning → Axes | Axis list. |
| Level 3 | Axis → Drive commissioning | SimoComu / Simodrive drive screen for motor data and current controller. |
| Level 4 | Axis → Optimization/test | Speed and position controller, including Auto-Tune. |
| Level 5 | Optimization → Auto-tuning → Run | Live measurement and gain write-back. |
SW 4.4 supports two built-in tuning methods for rotary motors:
- Speed controller auto-tuning with constrained moves on the axis. Performs a series of low-amplitude ramp profiles to estimate inertia and the required speed-loop Kp / Tn.
- Position controller auto-tuning (circle-test variant). Executes a small circular interpolation cycle at a fixed feed override to back out the KV factor (position gain, "servo gain") and the acceleration-pre-control factor.
For a belt-driven Y-axis, the procedure normally tunes the speed loop first, verifies with a circle test, then lets the operator fine-tune the KV factor manually. Run both passes with the axis carriage mounted on the machine (ballscrew preloaded, way cover clearances tight) and not in air.
Pre-Tuning Mechanical and Electrical Preconditions
Autotuning does not recover from broken mechanics. The belt change means the following have to be checked and confirmed before pressing Run.
| Check | Test method | Acceptance value |
|---|---|---|
| Belt tension | Frequency-based tension meter on the slack span between motor pinion and ballscrew pulley | Manufacturer's static frequency specification, typically 70 to 110 Hz for a standard timing belt of this drive class. Verify against the machine builder manual. |
| Belt path alignment | Dial indicator across the pulley faces, or laser alignment bar across the two shafts | Axial parallelism ≤ 0.05 mm over the span. Skewed pulleys add side-load to the motor bearing and cause the autotune to flag a non-rigid coupling. |
| Way & ballscrew lubrication | Manual grease cycle, confirm pressure or volume per manufacturer's spec | No stall alarms during a slow jog from -Y to +Y at 1 % override. |
| Counterweight (if Y is vertical) | Visually inspect compensation cylinder / hydraulic balance, check for leaks | Axis must hold position with motor torque < 15 % of M0 in static state. |
| Ballscrew bearing pre-load | Jog axis 5 mm, examine backlash on dial indicator at the table | Reverse error ≤ 0.01 mm at the table for a machine of this class. |
| Couplings / bellows | Visual check, runout on coupling stubs | No visible wear, no set-screw slippage. |
The electrical preconditions are equally non-negotiable:
- 24 VDC control voltage present on the drive module (check LED status, green steady).
- DC link pre-charge complete; intermediate-circuit voltage at nominal level for the line (typically 600 VDC on a 480 V three-phase feed).
- Resolver or encoder cable shield grounded only at the drive end, no shield continuity to the motor frame.
- Current actual-value is < 5 % of rated current in standstill with no following error (this confirms the resolver / encoder auto-commissioned cleanly).
- Drive enable (X8 / STO input on Simodrive 611) wired and asserted.
Machine Data Verification: Rotary vs Linear Axis Type
The reported alarm — "trying to tune linear motor where in MD it has been configured as rotary motor” — is rooted in the NCK and the drive disagreeing on the axis topology. Work through this table and resolve every mismatch before re-trying Auto-Tune.
| MD | Name | Expected value for this Y-axis | Comment |
|---|---|---|---|
| MD30320 $MD_IS_ROT_AX | Axis identifier rotary / linear | 1 (rotary) for a 1FT6 spindle-mounted motor that drives a ballscrew through a belt; 0 (linear) only if the motor drives a linear direct-drive stage | Setting this to 1 with a rotary motor and a transmission ratio is the standard configuration. A 0 here would cause the controller to interpret the position-feedback pulses as metric travel and flag an axis-type alarm during autotune. |
| MD31000 $MD_ENC_IS_LINEAR | Encoder is linear scale | 0 (rotary, e.g. resolver on 1FT6064) | Must match the encoder type. 1 is reserved for linear glass / magnetic scales. |
| MD31020 $MD_ENC_TYPE | Encoder evaluation type | 1 (incremental) or 2 (absolute) depending on the "7" position in the variant | Wrong value here causes the Simodrive commissioning tool to flag a feedback-source mismatch. |
| MD30200 $MD_NUM_ENCS | Number of encoders | 1 (single motor encoder, belt path; no direct measuring system on this axis) | 2 is appropriate only when a separate linear scale is fitted in parallel with the motor encoder. |
| MD31050 $MD_DRIVE_ENC_TYPE_NBR / drive telegram | Drive telegram assignment | DST 104 with torque limit word, or the axis-specific telegram configured in the Simodrive FB | If the telegram format on the PROFIBUS / analog setpoint side expects a linear-motor data block, replace it with the rotary standard telegram. |
| MD32100 $MD_MOTOR_RATED_TORQUE | Rated motor torque | 9.5 Nm (or 0.95 daNm, the unit on the same line as the motor code) | Confirm the trailing comma decimal: 9,5 in European notation is read by the HMI as 9.5 Nm. |
| MD31130 $MD_MOTOR_NOMINAL_CURRENT | Rated motor current | 9.1 A | Taken from the rating plate; mismatch with drive p290 will be detected during autotune. |
| MD32000 $MD_MAX_AX_VELO | Maximum axis velocity | 4 500 rpm * 60 / belt ratio / screw lead; calculate in mm/min | Typical Y-axis values fall between 10 000 and 30 000 mm/min. Confirm by adding a cap at 1.2 times the rated value. |
The driving rule is: every MD that has a "rotary / linear" decision bit must agree with the drive's p096 motor configuration and with the physical transducer on the machine. The autotune measurement will only run if all three agree.
Auto-Tuning Procedure Step-by-Step
Once the mechanical checklist and the axis-type MDs are validated, the autotune procedure on SW 4.4 is run in five ordered steps. The drive monitors each step and aborts with a precise alarm code if any one fails.
- Activate the commissioning area. Log in with the operator-level password on the HMI Advanced header bar. The commissioning menu only appears after the access level is raised from operator to commissioning.
- Validate drive configuration. Open the drive commissioning screen and select the Y-axis. Confirm the motor entry matches rating plate motor data sheet 1303. If the drive accepts a 1FT6064 with rotor inertia matching the catalog data sheet, the drive screen will show "Motor data complete". If the entry is blank or shows a 1FK / 1FT7 variant, re-flash the configuration or re-read the motor list in the SimoComu tool.
- Confirm machine data. Open MD30320, MD31000, MD31020, MD30200 and MD31130. The values must match the table above before the NCK will allow the autotune routine to be selected.
- Speed controller autotune. Drive the Y-axis to a safe mid-travel position; ensure that 30 mm of travel is free in both directions. Trigger Optimization → Auto-tuning → Run. The axis will execute 6 to 10 short open-loop controlled moves and write back Kp and Tn values to the drive. Duration: roughly 90 seconds.
- Position controller autotune (circle test). From the same menu, select the circle test. Pick a modest radius (5 mm to 10 mm at 1 000 mm/min) and a higher radius / higher feed (for example 20 mm at 3 000 mm/min) to confirm stability at the operating feed rates where the contour error originally appeared.
Current and Torque Verification
After autotune the built-in HMI Advanced display can graph the actual current, position following error and torque limit. Use a coupled 5 minute jog between -Y and +Y at the maximum programmed feed rate and confirm:
- Peak actual current stays below the motor's maximum current (typically 2.2 × I0 = ~20 A for short peaks). Persistent saturation means the drive autotune under-gained the speed loop.
- The torque utilized on acceleration does not exceed 70 % to 80 % of rated stall torque (M0 = 9.5 Nm), so the machine has margin for cutting load.
- Following error during a constant feed portion should remain below the configured MD36400 $MD_CONTOUR_TOL (default 1 mm, typically reduced to 0.05 mm or 0.10 mm for a finishing center).
If the actual current saturates during the high-feed jog, re-run the autotune with the mechanical load on the ballscrew (dampers, counterweight attached) and with lubrication active. The autotune will otherwise derive Kp values that are valid for an unloaded bearing assembly but unstable on the dressed machine.
Servo Trace and Loop Verification
The Servo Display screen is essential for verifying the autotune write-back rather than trusting the routine's success prompt.
| Display | Expected behavior |
|---|---|
| Speed actual / setpoint | Setpoint and actual overlay with negligible lag during constant-velocity phases. |
| Kv factor (KV) | Recorded in MD32200 $MD_POSCTRL_GAIN. Reasonable start: 0.5 to 1.5 (m/min)/mm for a 16 mm ballscrew, but final tuning is at the machine tool. |
| Following error | Flat-band value ~0.01 mm to 0.03 mm at modest feed; should not exceed 0.05 mm above 3 000 mm/min. |
| Acceleration pre-control factor | Default 1.0 after autotune. Reduce to 0.6 on a belt-driven axis if overshoot appears on ramp-down. |
| Torque actual | Triangle waveform on Jerk-limited ramps; no clipping at the +/- Mmax limit during sustained feed. |
Common Alarms and Clearing Actions
The alarms typically encountered on a 1FT6 motor under SW 4.4 axis-type or autotune are organized in this matrix. Alarm numbers are reproduced from the SINUMERIK 840D / SIMODRIVE 611 alarm documentation; if a specific code does not appear on screen, the HMI Advanced Help text remains the authoritative source.
| Alarm area | Symptom | Likely root cause | Action |
|---|---|---|---|
| Drive – motor data | Autotune aborts immediately with axis type mismatch | MD30320 / MD31000 inconsistent with motor data sheet 1303 | Match MD30320 = 1 for rotary; MD31000 = 0; re-download drive configuration |
| Drive – current limit | Auto-tune write-back triggers drive warning during ramp | Mechanical load too high, belt tension incorrect | Re-tension belt, verify counterweight if vertical axis |
| NCK following error | Following error alarm only above 1 500 mm/min | KV factor too low after autotune, or acceleration pre-control disabled | Increase KV in increments of 0.05; confirm FF3 in part program |
| Encoder / resolver | Ripple on speed actual, autotune measurement noisy | Shield on encoder cable multi-grounded or motor overheating | Re-route encoder cable, ground shield only at drive side, verify motor ventilation |
| Communication / drive telegram | Profibus / drive telegram fault during autotune write-back | Wrong telegram type loaded for axis MD | Load the standard rotary drive telegram; re-power the drive module |
| Position controller instability | High-frequency oscillation audible during constant feed | Position gain KV too high relative to speed loop | Reduce KV by 0.1 per step until oscillation clears; verify Tn still adequate |
Troubleshooting Matrix
Use this matrix for a quick field diagnosis if the autotune routine or the resulting contour behavior fails.
| Observed symptom | Likely subsystem | First action | Second action | Last escalation |
|---|---|---|---|---|
| Auto-tune aborts with axis-type alarm | MD mismatch | Read MD30320 and MD31000 | Compare with motor data sheet 1303 | Reload NCK archive or compare against backup NCK MD image |
| Auto-tune completes but contour error at 1 500 mm/min | Mechanical/control | Capture Servo Display during 0–5 m/min ramp | Increase KV, lower acceleration pre-control | Recheck the belt stiffness; consider wider belt or re-pitch pulleys |
| Drive reports "current actual" near zero during standstill | Resolver / encoder | Check resolver pin continuity at drive | Re-home the axis after re-commissioning the encoder | Replace resolver |
| Axis oscillates 10–20 Hz after autotune | Position loop too aggressive | Drop MD32200 POSCTRL_GAIN by 20 % | Drop acceleration pre-control factor FF3 | Manual speed-loop detuning, then re-run autotune |
| Belt tension indication inconsistent before autotune | Mechanical | Stop, recheck belt using tension meter | Verify pulleys have same reference pitch | Replace belt with original-equivalent part number |
Field-Validated Notes for SW 4.4 Specifically
The 840D SW 4.4 line is mature and well-instrumented, but a few caveats come from working on a 20-year-old control with a 1FT6 motor:
- The HMI Advanced start-up menu text can be in German or English depending on the loaded language pack; the motor parameter labels are identical. Use whichever language profile matches the operator's training records.
- The SimoComu / Simodrive commissioning tool will run on Windows XP / 7 with an MPI or PROFIBUS adapter. RS-232 point-to-point is supported but slow. Use the PROFIBUS adapter when the machine is networked.
- The motor data sheet 1303 must be loaded into the active NCK image before invoking autotune; for older machines the default image loaded at power-on may reference a different motor code, which is a common cause of the axis-type alarm.
- When the machine came as a second-hand unit, request the original NCK archive from the vendor and compare MD30310 / MD30320 / MD31000 against the as-found archive. A belt replacement rarely justifies a fresh axis-type configuration, but restoring the original archive avoids introducing new inconsistencies.
Safety and Commissioning Caveats
Auto-tuning produces real motion at potentially high speed. Lock out the following before pressing Run:
- Operator safety circuits (E-stop, safety door interlock, safe stop on the drive STO input).
- Hand-operated jogging controller — the autotune routine runs in NCK-controlled mode and ignores the handwheel pulses.
- Limit switch hand-test; ensure the Y-axis has at least 50 mm travel free of hardware OT switches for the move sequence.
- Save the NCK archive before changes. SW 4.4 does not auto-restore; a corrupted write produces a 840D boot that requires Siemens service tooling to recover.
Why does the autotune reject the 1FT6064 with an axis-type alarm on SW 4.4?
The NCK machine data MD30320 (rotary/linear axis flag) and MD31000 (encoder type) must agree with the motor data sheet 1303 entry on the drive. If MD30320 reads 0 (linear) while the motor is a 1FT6 rotary servo, the controller treats the resolver pulses as metric travel and rejects autotune. Set MD30320 to 1, MD31000 to 0, then re-run the optimization.
What is motor data sheet 1303 and how do I confirm it?
1303 is the Siemens internal selector list identifier for the 1FT6064-xAH7x-xxx variant with 9.5 Nm and 9.1 A. Confirm it in the SimoComu / Simodrive commissioning tool by reading the active motor list. The nameplate photo and the matching data sheet row in the Siemens motor catalog must agree on torque, current, rotor inertia, and the encoder code letter.
Do I need to autotune after a belt change?
A belt change can shift the loop behavior enough to benefit from a short autotune, but only if the belt is the correct pitch and properly tensioned. An incorrect belt type or a slack installation will produce unstable results even after autotune. Re-mechanical checks first, autotune second, then verify with a circle test at the operating feed rate.
What KV factor is reasonable for this Y-axis after autotune?
The KV factor (MD32200 $MD_POSCTRL_GAIN) typically lands in the 0.5 to 1.5 (m/min)/mm range for a belt-driven 16 mm ballscrew on a 1FT6064 axis. Use the SW 4.4 Servo Display to monitor following error while jogging in 0.05 increments. If the value overshoots or oscillates, reduce KV by ~0.1 and re-test at the original 1 500+ mm/min feed.
Why does the following-error alarm disappear on the older X / Z axes but persist on Y?
The Y-axis post-belt is the most likely candidate, but always verify by running the same ramp on X and Z and capturing the Servo Display. If the X and Z loops stay clean while Y errors, the difference is mechanical (belt elasticity, table mass, lubrication) or the Y loop has been left at a default gain from a previous commissioning that did not match the new belt. Equalize the table mass, re-tension the belt, and re-run autotune only on Y.
Where are the official documentation references for this procedure?
Refer to the SINUMERIK 840D / SIMODRIVE 611D Commissioning Manual and the 1FT6 Synchronous Servomotors documentation in the Siemens Industry Online Support archive for the Motor Data Sheet referenced by code 1303 and for the Auto-Tuning screens. The HMI Advanced user manual describes the menu navigation structure used in SW 4.4 and the alarm descriptions printed on the help screen.