Electrical Causes of Flying Shear Misalignment in Roll Forming Machines (Troubleshooting Guide)

Flying shear misalignment is one of the most expensive faults in roll forming production.

Electrical Causes of Flying Shear Misalignment

Why Your Cut Length Drifts, Misses or Crashes — And How to Diagnose It

Flying shear misalignment is one of the most expensive faults in roll forming production.

It presents as:

Cut length drifting longer or shorter
Shear hitting rib incorrectly
Crooked or angled cuts
Shear crashing into material
Shear “chasing” strip but not synchronizing
Random miscuts at high speed

While mechanical alignment is often blamed first, in high-speed roll forming systems the root cause is frequently electrical or control-related.

The flying shear system depends on:

Strip speed signal → Encoder feedback → PLC high-speed logic → Servo/VFD synchronization → Hydraulic or servo cut actuation.

Any electrical instability in that chain causes misalignment.

This guide explains the electrical causes of flying shear misalignment and provides a structured troubleshooting method.

1) Understand the Flying Shear Control Chain

Typical control sequence:

Main Drive Motor → Strip Speed
Encoder → High-Speed Counter
PLC Calculates Cut Length
Servo Drive Synchronizes Shear Carriage
Hydraulic / Servo Cut Actuated
Shear Returns

If any electrical signal is unstable, timing shifts.

2) Encoder Signal Instability (Most Common Cause)

Flying shears rely on encoder pulses to track strip position.

If encoder pulses are unstable:

Length calculation becomes inaccurate
Shear trigger point shifts
Cut timing drifts

Common electrical causes:

Broken shield
Shield grounded both ends (ground loop)
Cable routed next to motor cable
Loose connector
Incorrect encoder voltage supply
Noise from VFD

Diagnosis:

Monitor pulse count stability while running at different speeds.

If misalignment worsens at high speed → EMI likely.

3) Incorrect Encoder Wiring (A/B Channel Swap)

Quadrature encoders use:

A+, A−
B+, B−

If channels reversed:

Direction logic incorrect
Position tracking unstable
Servo compensation inaccurate

Confirm correct differential wiring.

Never use single-ended encoder signals in high-noise environments.

4) High-Speed Counter Configuration Errors

PLC high-speed input module must match:

Encoder pulses per revolution
Input filtering settings
Counting mode

If pulse frequency exceeds module capability:

Missed counts occur
Length gradually drifts

Verify module max frequency rating.

High-speed roofing lines require high-frequency input capacity.

5) Servo Drive Tuning Instability

Flying shear carriage often servo-driven.

Improper servo tuning causes:

Position lag
Overshoot
Oscillation
Delayed synchronization

Electrical causes include:

Incorrect motor parameters
Incorrect encoder feedback settings
Poor grounding
Noise on feedback cable

Verify servo tuning parameters and monitor following error.

6) VFD Speed Reference Instability

Main roll former speed may fluctuate due to:

Analog speed reference noise
PLC analog output drift
Poor 0V reference
Shielded cable incorrectly grounded

Speed instability affects strip position tracking.

Monitor speed feedback consistency.

7) 24V Control Power Instability

If 24VDC drops during shear cycle:

PLC may delay output
Servo enable may momentarily drop
Encoder signal may distort

Measure 24V under load during shear activation.

Unstable PSU can create intermittent miscuts.

8) Electrical Noise from Motor Cables

Motor cables produce high-frequency switching noise.

If encoder or analog cables routed parallel:

False pulse detection
Count errors
Length miscalculation

Corrective actions:

Separate power and signal cables
Use shielded twisted pair
Ground shield at one end only

9) PLC Scan Time & Task Configuration

In high-speed systems:

PLC scan time matters.

If shear trigger logic placed in slow task:

Trigger delay increases
Cut point shifts at high speed

Verify:

High-speed counter interrupts used
Fast task handling shear logic

Electrical misconfiguration can create mechanical symptom.

10) Communication Delay (Fieldbus Systems)

If shear drive controlled via:

EtherCAT
Profinet
Modbus

Network delay or packet loss can cause:

Synchronization error
Position lag
Random miscuts

Check network diagnostics.

Use shielded industrial Ethernet cable.

11) Ground Loop Between Encoder & Drive

If encoder shield grounded at both ends:

Ground loop creates:

Noise injection
Pulse distortion
Intermittent errors

Disconnect shield at one end (panel side preferred).

Ground loops are common retrofit error.

12) Hydraulic Actuation Delay (Electrically Triggered)

In hydraulic flying shear systems:

PLC output → Solenoid → Hydraulic valve → Shear movement.

If electrical delay exists:

Solenoid slow to energize
Voltage drop during activation
Coil undervoltage

Measure voltage at solenoid during activation.

Low voltage causes delayed actuation.

13) Overcurrent or Torque Limit in Servo

If servo hits torque limit:

Shear carriage lags
Synchronization lost

Electrical cause:

Current limit set too low.

Monitor servo current during synchronization phase.

14) Phase Imbalance in Main Drive

If main roll former motor has phase imbalance:

Speed may fluctuate slightly.

Small speed fluctuation creates length drift.

Measure phase current balance under load.

15) Overvoltage During Deceleration

If shear decelerates too quickly:

VFD overvoltage trip may momentarily disable system.

Drive disable creates misalignment on next cycle.

Check deceleration ramps and brake resistor.

16) PLC Output Delay

If output controlling shear solenoid passes through:

Interposing relay
Safety relay
Additional logic block

Delay increases response time.

Measure output timing from PLC bit change to solenoid energization.

17) Diagnostic Method (Structured Approach)

Step 1: Check encoder pulse stability
Step 2: Verify high-speed counter configuration
Step 3: Inspect servo following error
Step 4: Measure 24V stability during cycle
Step 5: Inspect cable routing
Step 6: Check shield grounding
Step 7: Monitor VFD speed consistency
Step 8: Verify PLC scan time

Never adjust mechanical alignment before verifying electrical stability.

18) Most Common Electrical Root Causes

Encoder noise from VFD cable
Shield grounded both ends
Loose encoder connector
High-speed input overloaded
Servo tuning incorrect
24V voltage drop during shear cycle
Analog speed reference instability
Network delay (fieldbus systems)

Electrical instability often increases with production speed.

19) Buyer Strategy (30%)

When purchasing a roll forming machine with flying shear, verify:

Differential encoder used
Shielded encoder cable specified
Cable separation guidelines provided
Servo tuning documented
High-speed counter capacity adequate
Brake resistor installed (if required)
24V supply sized for solenoid load
Commissioning includes length calibration report

Red flags:

“Single-ended encoder in high-speed line.”
“Motor and encoder cables in same tray.”
“No servo tuning documentation.”

Flying shear precision depends heavily on electrical engineering quality.

6 Frequently Asked Questions

1) Why does misalignment worsen at high speed?

Electrical noise and scan time limitations increase at higher pulse rates.

2) Can grounding cause length drift?

Yes, poor grounding causes encoder instability.

3) Should I adjust mechanical shear first?

No, verify electrical signals first.

4) How do I check encoder noise?

Monitor pulse stability or use oscilloscope.

5) Can servo tuning cause miscuts?

Yes, incorrect tuning causes position lag.

6) What is most common cause?

Encoder noise from improper shielding.

Final Engineering Summary

Flying shear misalignment in roll forming machines is often caused by electrical instability in:

Encoder feedback
High-speed counting
Servo tuning
24V control voltage
Cable shielding
Grounding
Speed reference stability
Network communication

The flying shear system is a precision synchronization mechanism — even small electrical instability can create measurable cut deviation.

Disciplined electrical troubleshooting prevents tooling damage, scrap production, and costly downtime in high-speed roll forming operations.