Resolving SINAMICS V90 F7452 Following Error Fault on S-1FL6 Axes

Overview: What F7452 Means on a SINAMICS V90

The fault code F07452 (displayed on the SINAMICS V90 BOP as F7452) is a following error trip. The drive continuously compares the actual position feedback (typically the encoder on the SIMOTICS S-1FL6 servo motor) against the internal position setpoint, and F7452 latches when the difference between the two exceeds the configured following-error window for a defined time. On a ball-screw cylinder where the load is being driven in the positive direction and the fault is intermittent, the drive is signalling that the mechanics cannot keep up with the command, or that the scaling factors that convert motor revolutions to load position are wrong.

Two related alarms precede a hard F7452 in most cases:

• A07452 - Following error warning (the position lag has crossed the warning threshold but not the trip threshold).
• A07453 - Position controller output limited (often a precursor on a stalled or near-stalled axis).

Root Cause Matrix for F7452 on V90 + S-1FL6 Ball-Screw Axes

Mechanical and Scaling Parameters to Verify First

On a ball-screw axis the V90 derives LU (Length Units) from the mechanical chain. Wrong numbers here make every position setpoint mathematically wrong, and the drive will report F7452 because the encoder (actual) and the trajectory (setpoint) cannot agree on where the load is.

Following-Error Thresholds: p2546, p2634, and Their Timers

F7452 has two independent trigger paths, both of which must be right or the drive will trip.

Static position following-error window

The drive compares |setpoint_position - actual_position| against p2546 (Position following error tolerance, in LU). When the difference exceeds p2546 for the time set in p2547, F7452 trips.

• p2546 default on a 1FL6+V90 with 0.1 µm LU: 1000 (i.e. 0.1 mm of tolerated lag).
• p2547 default: 200 ms. The error must be exceeded for this duration before F7452 fires.

Velocity-based path (motion monitoring)

p2634 is the velocity following error tolerance, in 1/min (mechanical rpm). If |n_set - n_act| exceeds p2634 for longer than the configured timer, F7452 is raised. Default values:

• p2634 default: 100 rpm
• Timer: integrated into p2546/p2547 path on most V90 firmware.

Sizing a rational p2546

A practical engineering rule for V90 + S-1FL6 ball-screw axes:

1. Run the axis through its full speed range, capture r2563 (current position error, signed LU) and r0080 (speed actual) in the trace.
2. Take the 99th percentile of the steady-state lag at the maximum operating speed.
3. Set p2546 = 3x to 5x this value, with p2547 = 100 to 200 ms.
4. Re-run and confirm no F7452. If F7452 still occurs at standstill, the issue is binding, not lag.

Position Loop and Speed Pre-Control for Reducing Lag

If the trace shows clean steady-state lag (a flat line that grows linearly with speed), the position loop gain is the lever to pull, not the window.

For a ball-screw cylinder with direct coupling and 10 mm pitch, a tuned loop typically shows < 50 µm of lag at 1 m/min and < 200 µm at the rated speed. Anything consistently above that is a mechanical or scaling problem.

Encoder and Feedback Health Checks

Before assuming the encoder is at fault, eliminate the cheaper causes first. On V90 with 1FL6 incremental encoders (resolver / 10 kHz TTL or 20-bit absolute), do the following in order:

1. Inspect cable - look for kinks, abrasion, oil ingress. A torn shield is the single most common intermittent F7452 root cause on shop-floor machines.
2. Confirm connector pin assignments: pins 1, 2, 5, 6, 7, 8 on the X7 encoder connector per the SINAMICS V90 List Manual (search for "X7" in your firmware version).
3. Measure encoder supply: 5.0 V +/- 5% at the drive end. Brown-out gives intermittent counts that look like a follow error at high speed.
4. Read r0027 (speed actual) and r0061 (position actual) with the motor hand-turned. They must update smoothly with no jumps > 1 encoder count between samples.
5. Check fault buffer: r0945[8] lists the last 8 fault codes. If F31850, F31885, A3xxx, or F07452 appears in pairs separated by short intervals, the encoder is suspect.

One-Button Auto-Tuning Procedure for S-1FL6 + Ball-Screw

Auto-tuning is the recommended first action after the parameter verification above, because it identifies the load inertia, sets Kp, and configures the speed pre-control factor in one motion sequence. The procedure below is for V90 in PTI or IPOS positioning mode with an S-1FL6 motor.

1. Set p29000 to the correct motor code from the motor nameplate. Example for 1FL6024-6AF: code 17xxx (refer to the motor code table in the operating instructions).
2. Set p29002 to the direction of rotation that matches your application. Confirm by jogging at low speed and watching the position increment.
3. Confirm p29020 (tuning function configuration): 1 = one-button auto tuning; 2 = real-time auto tuning. Use 1 for commissioning.
4. Provide the drive the motion envelope: minimum and maximum stroke, max speed, max acceleration in the controller (PLC or V90 IPOS) so the auto-tuning test move stays inside the cylinder.
5. On the BOP, navigate to p29020 and press P to start tuning. The drive will run a 1-2 cycle sinusoidal move and write p2533, p2534, and p1460/p1462 internally.
6. Verify result: r3925[0] shows "identification complete". Check the new p2533 against the table above.
7. Run the application profile and look for A07452 in the alarm buffer. If absent, you have a clean loop.

Step-by-Step Diagnostic Procedure for an Intermittent F7452 in the Positive Direction

The fact that the fault only appears in the positive direction is the most useful clue. It almost always means one of the following:

1. Mechanical asymmetry. Run a back-and-forth trace at constant speed: r2563 vs position. The lag envelope in the positive direction should be within 20% of the negative direction. If positive lag is 3x negative, the mechanics is binding on extension.
2. Direction-dependent scaling. Some commissioning tools let the LU scaling be set per direction (backlash compensation). If p29012 (backlash compensation) is non-zero, confirm it matches the measured mechanical backlash. Setting it to a value larger than actual backlash will produce a permanent lag in one direction that the drive sees as a following error.
3. Direction-of-rotation reversal. p29002 reversed from physical sign will make the drive command negative LU for a positive hand-wheel direction; the controller will keep integrating error trying to chase a sign-flipped setpoint.
4. Thrust load imbalance. A ball-screw cylinder that pushes against a spring or workpiece is more loaded in the positive direction. Confirm torque limit p1520 / p1521 and current limit p0640 are at the motor rating and not clamped by a lower value from a previous setup.

Verification: Acceptance Test After the Fix

1. Run the full motion profile (positive and negative, full speed, full acceleration) for 50 cycles. Watch r2563 stays inside p2546/2 in steady state.
2. Run the profile for 8 hours with the trace recorder running on r2563 and r0080. No F7452 in fault buffer (r0945).
3. Capture a BOP screenshot showing p29020 = 0 (auto tuning done) and the new p2533 value.
4. Document p2920, p2921, p2922, p29002, p2546, p2533, p2534 in the machine file. These are the parameters that will get re-entered next time a drive is replaced.

When to Escalate: V90 Replacement vs. Field Repair

If the encoder health checks pass, the mechanical chain is free, scaling is verified, the loop is correctly tuned, and F7452 still appears with a 1FL6 motor on a known-good ball-screw cylinder, the next suspects are the drive's encoder interface (replace the encoder cable as a single assembly; do not splice) and, last, the V90 control unit itself. The S-1FL6 is an integrated-encoder motor - the encoder is not field-replaceable on most frame sizes, so if the encoder is genuinely damaged, the motor assembly is the spare part, not just the encoder.

Quick Reference Parameter Sheet

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