Encoder Wiring for Flying Shears in Roll Forming Machines (High-Speed Accuracy Guide)

Encoder Wiring for Flying Shears

High-Speed Length Accuracy in Roll Forming Machines

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

In high-speed roofing and structural roll forming lines, the flying shear depends entirely on encoder accuracy.

The encoder provides:

• Real-time line position

• Speed feedback

• Length measurement

• Synchronization reference for servo shear

If encoder wiring is poor, you will see:

• Cut length variation

• Shear mistiming

• Following errors

• Random position jumps

• Scrap production

• Unstable servo behavior

Most “shear problems” are not mechanical.

They are encoder signal integrity problems.

This guide explains how to wire encoders correctly for flying shear systems in industrial roll forming environments.

1) Role of the Encoder in Flying Shear Systems

Flying shear logic typically follows this flow:

Main Roll Encoder → High-Speed Counter → PLC → Position Compare → Servo Motion Command → Shear Actuation

The encoder must provide:

• Accurate pulse count

• Stable direction information

• Clean index pulse (if used)

If pulse integrity is compromised, the shear cannot synchronize correctly.

2) Types of Encoders Used in Roll Forming

Common encoder types:

1) Incremental Encoder

• A and B pulse channels

• Optional Z (index) pulse

• Most common in roll forming

2) Absolute Encoder

• Provides position value directly

• Used in more advanced servo systems

Most flying shear applications use incremental encoders with quadrature signals.

3) Incremental Encoder Signal Structure

Typical signals:

• A+ / A–
• B+ / B–
• Z+ / Z–
• +24V or +5V power
• 0V

Differential pairs improve noise immunity.

Never wire only single-ended signals if differential available.

4) Word-Based Correct Encoder Wiring

• Encoder Power + → PLC or Drive +24V
• Encoder 0V → PLC/Drive 0V
• A+ → High-Speed Input Channel A+
• A– → High-Speed Input Channel A–
• B+ → High-Speed Input Channel B+
• B– → High-Speed Input Channel B–
• Shield → Earth Bar (cabinet side)

Proper termination ensures clean pulse detection.

5) High-Speed Counter (HSC) Requirement

Standard PLC inputs scan too slowly for high-speed roll forming.

Flying shear systems must use:

Dedicated high-speed counter inputs.

Encoder must connect directly to HSC terminals.

Using normal input causes:

• Missed pulses

• Length drift

• Timing instability

Always verify HSC configuration matches encoder type.

6) Shielded Twisted Pair Cable

Encoder cable must be:

• Twisted pair per signal

• Shielded

• Industrial-grade

• Oil-resistant

Each differential pair must be twisted separately.

Never use generic multi-core unshielded cable.

7) Shield Termination Best Practices

Critical rule:

Shield grounded at cabinet earth bar.

Avoid:

• Long pigtail connections

• Floating shield

• Improper shield termination

For high-frequency noise protection, use:

360° shield clamp at cabinet entry.

8) Routing Rules in Roll Forming Cabinets

Inside cabinet:

Left trunking → Power cables
Right trunking → Signal cables

Field routing:

• Keep encoder cable away from VFD motor cables

• Maintain minimum separation (200–300mm typical)

• Cross at 90 degrees if necessary

Never run encoder cable parallel to VFD output cable.

PWM switching noise causes pulse distortion.

9) Grounding Strategy

Encoder body should be bonded to machine frame.

Machine frame bonded to earth.

Shield termination must connect to earth bar.

Avoid grounding shield at both ends unless manufacturer specifies.

Multiple ground points create ground loops.

10) Symptoms of Encoder Noise

In flying shear systems, noise appears as:

• Random cut length variation

• Shear triggering early or late

• Servo following error at high speed

• Position count fluctuating without movement

• Cut length stable at low speed but unstable at high speed

If issues occur only at high speed, suspect wiring or shielding first.

11) Encoder Power Stability

Encoders typically require:

• Stable 24VDC or 5VDC

Measure voltage at encoder under load.

Voltage drop causes:

• Weak signal amplitude

• Missed pulses

• Intermittent faults

Avoid sharing encoder supply with high-current solenoids.

12) Differential vs Single-Ended Signals

Differential signals (A+/A–) provide:

• Better noise rejection

• Higher reliability over long runs

Single-ended signals more vulnerable to EMI.

For roll forming lines over 20 meters cable run, differential is strongly recommended.

13) Z (Index) Pulse Usage

Z pulse provides reference position.

Used for:

• Zero calibration

• Shear alignment reference

• Homing sequences

Incorrect Z wiring can cause:

• Wrong zero point

• Offset errors

Document how Z pulse is used in logic.

14) Encoder Mounting Considerations

Mechanical installation affects signal integrity.

Ensure:

• Secure shaft coupling

• No backlash

• No vibration

• Proper alignment

Electrical troubleshooting is wasted effort if mechanical coupling is unstable.

15) Testing Encoder Signals

Testing procedure:

1. Monitor HSC count value in PLC

2. Rotate roll manually

3. Verify smooth count increment

4. Run drive at low speed

5. Observe count stability

6. Increase speed gradually

7. Look for pulse irregularities

If count jumps or drops, inspect shielding and routing.

16) Common Encoder Wiring Mistakes

1. Using unshielded cable

2. Running cable with motor cables

3. No differential wiring

4. No high-speed counter input

5. Poor shield termination

6. Shared 0V with noisy devices

7. Long pigtail ground

8. Loose terminal connections

Most flying shear problems originate here.

17) Long Cable Run Considerations

For long distances:

• Use differential encoder

• Increase cable gauge

• Ensure clean grounding

• Consider signal repeater if extreme length

Excessive cable length without proper design causes attenuation and distortion.

18) Buyer Strategy (30%)

Before purchasing a flying shear roll forming machine, verify:

1. Encoder is differential type

2. High-speed counter input used

3. Shielded twisted-pair cable installed

4. Shield properly terminated

5. Encoder cable separated from VFD motor cables

6. Grounding system documented

7. Commissioning test performed at production speed

8. Spare encoder available

Red flag:

“Encoder cable runs in same tray as motor cable.”

That design invites noise problems.

6 Frequently Asked Questions

1) Why does cut length vary only at high speed?

Because noise interference increases with PWM frequency and motor load.

2) Can I use standard input instead of HSC?

No. High-speed counter is required.

3) Should encoder shield be grounded both ends?

Typically only at cabinet end unless specified.

4) What is most common encoder wiring mistake?

Running cable parallel to VFD motor cable.

5) Can unstable 24V affect encoder?

Yes, especially at high pulse rates.

6) Is differential encoder necessary?

Strongly recommended in industrial environments.

Final Engineering Summary

Proper encoder wiring for flying shear systems requires:

• Differential incremental encoder

• Shielded twisted-pair cable

• High-speed counter input

• Clean grounding architecture

• Separation from VFD motor cables

• Stable power supply

• Secure mechanical mounting

Incorrect encoder wiring causes:

• Length inaccuracy

• Shear misalignment

• Servo instability

• Production scrap

In high-speed roll forming lines, encoder signal integrity directly determines cut accuracy and overall machine reliability.