Flying Cutoff Motor Wiring Diagram (Word-Based) for Roll Forming Machines

Flying Cutoff Motor Wiring Diagram (Word-Based)

Electrical Architecture for High-Speed Cut Systems in Roll Forming

Flying cutoff systems are used in roll forming machines to cut material without stopping the strip.

The system must:

• Match strip speed

• Synchronize with encoder pulses

• Execute precise blade actuation

• Return safely for next cycle

The cutoff motor may be:

• Servo motor (most common modern design)

• VFD-controlled AC motor (mid-range systems)

• Hydraulic-only system with electrical trigger

This guide provides a clear word-based wiring diagram structure, explaining how power, control, and feedback circuits integrate in a flying cutoff system.

1) Flying Cutoff System Overview

Typical electrical components:

• Main line encoder

• PLC with high-speed counter

• Servo drive or VFD

• Cutoff motor

• Brake resistor (if required)

• Hydraulic solenoid (blade actuation)

• Limit switches (home position)

• Safety relay

All elements must integrate in real-time.

2) Word-Based Power Circuit – Servo Flying Cutoff

• 3-Phase Supply →
• Main Isolator →
• MCCB (Servo Drive Protection) →
• Servo Drive Input (L1/L2/L3) →
• Internal Rectifier → DC Bus → Inverter →
• Servo Drive Output (U/V/W) →
• Servo Motor

Protective Earth (PE) → Motor Frame → Earth Bar

Brake Resistor (if used):
Servo Drive Brake Terminals → Brake Resistor → Earth Mounting Frame

This is the high-power motion circuit.

3) Word-Based Feedback Circuit – Servo Motor Encoder

Encoder Feedback Cable:

Motor Encoder Connector →
Servo Drive Feedback Terminals:

• A+ → A+
• A– → A–
• B+ → B+
• B– → B–
• Z+ → Z+
• Z– → Z–
• +24V or +5V → Encoder Power
• 0V → Encoder Common

Shield → Earth Bar (360° clamp at cabinet entry)

Feedback integrity is critical for position accuracy.

4) Word-Based Line Encoder Integration (Length Measurement)

Main Roll Encoder →
High-Speed Counter (HSC) on PLC

• A+ / A– → HSC A+ / A–
• B+ / B– → HSC B+ / B–
• Shield → Earth Bar

PLC calculates cut trigger position based on pulse count.

5) Word-Based Control Circuit – Motion Command

• PLC Digital Output → Servo Drive Enable
• PLC Digital Output → Servo Drive Run Command
• PLC Analog Output (optional) → Speed Reference
• Servo Drive Fault Output → PLC Digital Input

This creates closed-loop control between PLC and servo drive.

6) Word-Based Hydraulic Blade Actuation Circuit

• 24VDC Power Supply →
• PLC Digital Output →
• Interposing Relay →
• Hydraulic Solenoid Valve Coil →
• 0V Return

Hydraulic solenoid energizes only during synchronization window.

Solenoid coil suppression diode required (for DC coils).

7) Word-Based Safety Circuit Integration

• 24VDC PSU →
• E-STOP Loop →
• Safety Relay →
• Main Contactor Coil →
• Servo Drive Safe Torque Off (STO) Terminals

If E-stop activated:

• Main power contactor drops

• Servo drive STO disables torque

• Hydraulic actuation disabled

Safety must override motion command.

8) Word-Based Home Position Sensor Circuit

Home Proximity Sensor:

• +24V → Sensor
• 0V → Sensor
• Signal Output → PLC Digital Input

Home position required for:

• Initial zero reference

• Post-cut return verification

PLC logic prevents next cycle until home confirmed.

9) Flying Cutoff Synchronisation Logic (Electrical Flow)

• Line Encoder Pulses →
• PLC HSC Count →
• Compare to Target Length – Pre-trigger Offset →
• Trigger Servo Motion Profile →
• Servo Accelerates to Match Strip Speed →
• PLC Activates Hydraulic Solenoid →
• Cut Executed →
• Servo Returns to Home →
• System Ready for Next Cycle

Electrical timing precision determines cut accuracy.

10) VFD-Based Flying Cutoff (Alternative Design)

In lower-speed systems:

3-Phase Supply → MCCB → VFD → AC Motor

• PLC DO → VFD Run
• PLC DO → VFD Direction
• PLC AO → Speed Reference

However, VFD systems lack true closed-loop positional precision compared to servo systems.

Servo preferred for high-speed roofing lines.

11) Brake Resistor Integration (Servo Systems)

During rapid deceleration:

• Motor acts as generator →
• Energy flows into DC bus →
• Brake chopper activates →
• Brake resistor dissipates energy

Improper resistor sizing causes:

DC Bus Overvoltage Fault during return motion.

12) Shield Separation Rules (Inside Cabinet)

Left Trunking → Power Cables (U/V/W)
Right Trunking → Feedback & Encoder Cables

Never run servo motor cable parallel to encoder cable.

Maintain physical separation.

13) Commissioning Sequence

1. Verify motor direction

2. Confirm encoder count stable

3. Confirm line encoder scaling

4. Test servo motion at low speed

5. Test hydraulic actuation delay

6. Test full-speed synchronization

7. Verify no following error

8. Confirm repeatability across multiple cuts

All tests must be performed under production speed.

14) Common Wiring Mistakes

1. No shielded servo cable

2. Feedback cable run next to VFD motor cable

3. No high-speed counter input

4. Improper brake resistor wiring

5. No suppression diode on solenoid

6. Incorrect encoder resolution parameter

7. Loose earth connection

8. Inadequate deceleration ramp

Most flying cutoff faults originate electrically.

15) Voltage Stability During Cut

During blade actuation:

• Hydraulic motor load spike
• Servo torque increase
• Solenoid activation

Control 24VDC must remain stable.

Voltage sag causes:

• PLC glitch
• Drive fault
• Misfire cut

Separate control transformer recommended.

16) Export Considerations

When exporting flying cutoff systems:

• Confirm servo voltage compatibility

• Confirm frequency setting

• Provide parameter backup

• Provide wiring diagram

• Verify shielded cable type documented

• Confirm brake resistor rated for climate

Improper installation abroad often results in noise-related faults.

17) Buyer Strategy (30%)

Before purchasing a roll forming machine with flying cutoff, verify:

1. Servo-based system (for high-speed lines)

2. Differential encoder wiring

3. High-speed counter used

4. Shielded motor and feedback cables

5. Brake resistor properly sized

6. Hydraulic solenoid suppression installed

7. STO safety integration implemented

8. Full-speed commissioning documented

Red flag:

“Cutoff timing adjusted manually without encoder logic.”

That indicates outdated or unstable design.

6 Frequently Asked Questions

1) Why does cutoff length vary at high speed?

Likely encoder noise or improper synchronization logic.

2) Can VFD replace servo for flying cutoff?

Only in low-speed applications.

3) Why does servo fault during return?

Possible brake resistor undersized or acceleration too aggressive.

4) Should solenoid coil have suppression diode?

Yes, for DC coils to prevent voltage spikes.

5) Why does PLC reset during cut?

Voltage sag on 24V control supply.

6) What is most common flying cutoff wiring error?

Improper shielding and cable routing.

Final Engineering Summary

Flying cutoff motor wiring in roll forming machines requires:

• Structured power architecture

• Shielded servo motor cable

• Differential feedback wiring

• High-speed counter integration

• Hydraulic solenoid suppression

• Brake resistor design

• Safety STO integration

• Stable control voltage

Incorrect wiring leads to:

• Cut length inaccuracy

• Servo faults

• DC bus overvoltage

• Electrical noise instability

• Production downtime

In modern high-speed roll forming lines, flying cutoff electrical synchronisation is one of the most technically demanding and critical systems in the entire machine.