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

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

1. Encoder noise from VFD cable

2. Shield grounded both ends

3. Loose encoder connector

4. High-speed input overloaded

5. Servo tuning incorrect

6. 24V voltage drop during shear cycle

7. Analog speed reference instability

8. 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:

1. Differential encoder used

2. Shielded encoder cable specified

3. Cable separation guidelines provided

4. Servo tuning documented

5. High-speed counter capacity adequate

6. Brake resistor installed (if required)

7. 24V supply sized for solenoid load

8. 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.