Flying Shear Electrical Synchronisation Explained for Roll Forming Machines

Flying Shear Electrical Synchronisation Explained

How Encoder, PLC & Servo Work Together in Roll Forming Machines

(70% Engineering / 30% Buyer Strategy — no images, word-based engineering detail)

Flying shear systems are one of the most technically demanding parts of a roll forming machine.

The shear must:

• Match strip speed

• Reach exact cut position

• Cut without distorting the panel

• Return to home without losing synchronisation

At 40–60 m/min, timing errors of milliseconds create:

• Cut length variation

• Edge burrs

• Profile distortion

• Servo following errors

• Scrap production

Most flying shear problems are not mechanical.

They are electrical synchronisation problems between:

• Line encoder

• PLC high-speed counter

• Motion logic

• Servo drive

• Brake timing

• Hydraulic or blade actuation

This guide explains how electrical synchronisation works and how to engineer it correctly.

1) What “Electrical Synchronisation” Really Means

Flying shear electrical synchronisation means:

The servo motor moves at the same linear velocity as the moving strip during the cut window.

That requires:

1. Accurate line position measurement

2. Accurate line speed calculation

3. Precise servo motion command

4. Correct timing of blade actuation

5. Stable feedback loop

If any part is unstable, synchronisation fails.

2) System Architecture Overview

Word-Based Flow:

Main Roll Encoder → High-Speed Counter → PLC → Motion Profile → Servo Drive → Servo Motor → Shear Carriage

During motion:

Servo Encoder Feedback → Servo Drive → Closed Loop Correction

The system operates in real-time.

Scan-based timing alone is not sufficient.

3) Step 1 – Accurate Line Position Measurement

Line encoder typically mounted on:

• Pinch roll shaft

• Main drive shaft

Encoder outputs:

A+/A–
B+/B–

Connected to high-speed counter (HSC).

Critical requirements:

• Differential signals

• Shielded cable

• Proper grounding

• No routing near VFD cables

If encoder signal is unstable, synchronisation cannot work.

4) Step 2 – High-Speed Counter Configuration

HSC counts pulses independent of PLC scan.

Word-Based Logic:

If HSC_Count ≥ Target_Length
→ Trigger Motion Sequence

HSC must be:

• Configured for quadrature

• Correctly scaled

• Reset at appropriate time

Incorrect HSC configuration leads to:

• Length drift

• Delayed shear trigger

5) Step 3 – Calculating Synchronised Motion

Flying shear does not just move to a point.

It must:

1. Accelerate

2. Match line velocity

3. Perform cut

4. Decelerate

5. Return

Motion profile includes:

• Acceleration ramp

• Synchronisation window

• Cutting dwell

• Return motion

PLC calculates position offset relative to moving strip.

6) Word-Based Synchronisation Example

Line speed = 50 m/min
Encoder pulses represent 1 mm per pulse

Target length = 3000 mm

Logic:

When HSC = 3000 mm – Pre-trigger offset
→ Start servo acceleration

• Servo matches strip velocity
• Blade actuates
• Servo returns

Pre-trigger offset compensates for acceleration delay.

7) Step 4 – Servo Drive Closed-Loop Control

Servo drive continuously adjusts torque based on:

Command Position vs Actual Position

If difference exceeds threshold:

Following Error Fault triggered.

Electrical stability of feedback cable is critical.

Noise causes position jitter and false following errors.

8) Step 5 – Blade Actuation Timing

Blade may be:

• Hydraulic

• Mechanical

• Pneumatic

Electrical timing must account for:

• Valve delay

• Mechanical travel time

• Material thickness

Word-Based:

• Servo in Sync Window
• AND Position Within Cut Range
• → Activate Shear Solenoid

Delay must be tuned carefully.

9) Acceleration & Deceleration Coordination

If servo acceleration too slow:

• Misses sync window

• Late cut

If too aggressive:

• Overcurrent trip

• Mechanical shock

Motion profile must be tuned to machine inertia.

10) Return Motion Timing

After cut:

Servo must:

• Clear material path

• Return to home

• Be ready for next cycle

Improper return timing causes:

• Carriage collision

• Delayed next cut

• Sequence stall

Return logic must not conflict with next length count.

11) Electrical Sources of Synchronisation Failure

Common causes:

1. Encoder noise

2. HSC misconfiguration

3. Incorrect scaling

4. Servo tuning mismatch

5. 24V voltage sag during shear

6. Poor grounding

7. Brake delay mismatch

8. Incorrect pre-trigger offset

Always verify electrical integrity before mechanical adjustment.

12) Voltage Stability During Shear Event

Shear actuation often triggers:

• Hydraulic solenoid

• Brake release

• High torque demand

If 24VDC drops:

• PLC output may glitch

• Servo enable may flicker

• Fault triggered

Measure 24V during actual shear event.

Stable control voltage is essential.

13) Synchronisation at High Speed

At low speed, system may appear stable.

At high speed:

• Encoder pulse frequency increases

• Servo acceleration demand increases

• Timing window narrows

Electrical weaknesses become visible only at production speed.

Commissioning must test full-speed operation.

14) Commissioning Checklist

1. Verify encoder stability at max speed

2. Confirm HSC pulse accuracy

3. Validate scaling against physical measurement

4. Tune servo acceleration profile

5. Adjust pre-trigger offset

6. Test shear delay timing

7. Confirm no following errors

8. Verify repeatability over multiple cuts

Repeat at different lengths.

15) Common Field Symptoms & Electrical Causes

Symptom: Cut too short
Cause: Pre-trigger too early or scaling error

Symptom: Cut too long
Cause: Delay in actuation or encoder pulse loss

Symptom: Random length variation
Cause: Encoder noise or 24V sag

Symptom: Servo following error at high speed
Cause: Poor feedback wiring or aggressive tuning

Symptom: Occasional missed cut
Cause: HSC not configured correctly

16) Differences: Roofing vs Structural Lines

Roofing lines:

• Continuous high speed

• Lightweight panels

• Short sync window

Structural lines:

• Heavier material

• Lower speed

• Higher torque demand

Electrical synchronisation must match mechanical design.

17) Buyer Strategy (30%)

Before purchasing a flying shear roll forming machine, verify:

1. Differential encoder used

2. High-speed counter implemented

3. Servo drive tuned for machine inertia

4. Shielded cables for motor and feedback

5. 24V power stability designed with margin

6. Pre-trigger offset adjustable via HMI

7. Commissioning performed at full speed

8. Parameter backup provided

Red flag:

“Shear timing adjusted manually without encoder.”

Modern flying shears must use electronic synchronisation.

6 Frequently Asked Questions

1) Why does flying shear work at low speed but fail at high speed?

Because electrical timing margins shrink as speed increases.

2) Can poor grounding affect cut accuracy?

Yes. Noise in encoder signals disrupts synchronisation.

3) What is pre-trigger offset?

Distance compensation for servo acceleration delay.

4) Why do following errors occur?

Servo cannot match commanded position due to tuning or noise.

5) Should HSC be used for encoder?

Yes. Standard PLC scan inputs are insufficient.

6) What is most common synchronisation mistake?

Incorrect encoder scaling or noisy wiring.

Final Engineering Summary

Flying shear electrical synchronisation in roll forming machines depends on:

• Stable differential encoder signals

• Proper high-speed counter configuration

• Accurate scaling

• Well-tuned servo motion profiles

• Clean grounding and shielding

• Stable 24V control power

• Correct actuation timing

When properly engineered, flying shear systems deliver:

• Precise cut length

• Clean panel edges

• High-speed reliability

• Minimal scrap

In modern roll forming production, synchronisation accuracy is primarily an electrical engineering discipline, not just a mechanical one.