Rotary Encoder Installation & Wiring in Roll Forming Machines (Length & Speed Control Guide)

Rotary Encoder Installation & Wiring

Length Measurement & Speed Synchronisation in Roll Forming Machines

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

Rotary encoders are one of the most critical electrical components in modern roll forming machines.

They are used to:

• Measure strip length

• Synchronize flying shear motion

• Control cut-to-length accuracy

• Monitor roll speed

• Provide feedback for servo coordination

• Track accumulator movement

Incorrect encoder installation or wiring causes:

• Length inaccuracies

• Random cut variation

• Missed pulses at high speed

• Servo following errors

• PLC counter overflow

• Electrical noise instability

In high-speed roofing lines, encoder integration directly affects production accuracy and scrap rate.

This guide explains proper mechanical installation, electrical wiring, shielding, PLC integration, and commissioning discipline.

1) Types of Rotary Encoders Used in Roll Forming

1) Incremental Encoder (Most Common)

Outputs pulse signals:

• Channel A

• Channel B

• Optional Z (index pulse)

Used for:

• Length measurement

• Speed monitoring

2) Absolute Encoder

Provides unique position value.

Used in:

• Servo-driven carriage systems

• High-end positioning control

Most roll forming lines use incremental encoders.

2) Encoder Output Types

Common electrical output formats:

• NPN open collector

• PNP open collector

• Push-pull (HTL)

• Differential line driver (RS422)

High-speed roll forming systems should use:

Differential line driver outputs.

These resist electrical noise.

3) Word-Based Wiring – Differential Encoder (Recommended)

Encoder Terminal → PLC High-Speed Counter (HSC)

• A+ → HSC A+
• A– → HSC A–
• B+ → HSC B+
• B– → HSC B–
• Z+ → HSC Z+ (optional)
• Z– → HSC Z–

+24V → Encoder Power
0V → Encoder Common

Shield → Cabinet Earth Bar (360° clamp)

Differential wiring significantly reduces noise.

4) Word-Based Wiring – Single-Ended Encoder (Basic)

• Encoder A → PLC Input
• Encoder B → PLC Input
• Encoder Z → PLC Input

Common → 0V

Less noise immunity.

Not recommended near VFD systems.

5) High-Speed Counter (HSC) Integration

Standard PLC inputs are too slow for encoder pulses.

Encoder must connect to:

High-Speed Counter module.

Word-Based Signal Flow:

Encoder → HSC → PLC Memory → Length Calculation Logic

Incorrect wiring to standard input causes missed pulses.

6) Mechanical Installation Principles

Encoder accuracy depends heavily on mounting.

Options:

• Direct shaft coupling

• Measuring wheel contact with strip

• Chain-driven shaft monitoring

Key rules:

• No axial shaft load

• No radial overloading

• Flexible coupling preferred

• Avoid mechanical vibration

Mechanical stress shortens encoder life.

7) Measuring Wheel Installation

Common in roofing lines.

Wheel pressed against strip.

Critical factors:

• Consistent contact pressure

• Non-slip surface

• Proper wheel diameter calibration

• Avoid oil contamination

Wheel slippage causes length error.

8) Pulse Per Revolution (PPR) Selection

Higher PPR:

• Higher resolution

• Greater accuracy

• Higher signal frequency

PLC and HSC must support required frequency.

High-speed lines require careful PPR selection.

9) Scaling Encoder to Length

Example:

Encoder = 1024 PPR
Wheel circumference = 500 mm

Each pulse equals:

500 mm / 1024 pulses

PLC calculates length from pulse count.

Incorrect scaling leads to systematic length error.

10) Shielding & Cable Routing

Encoder cables must be:

• Shielded

• Twisted pair for differential signals

• Routed separately from motor cables

• Not bundled with VFD outputs

Noise on encoder line causes:

• Pulse miscount

• Cut length drift

• Servo misalignment

Shield grounded at cabinet end only.

11) Power Supply Stability

Encoders require stable voltage.

Voltage drop causes:

• Weak signal amplitude

• Pulse distortion

• PLC misreading

Use regulated 24VDC supply.

Avoid sharing supply with heavy loads.

12) Flying Shear Synchronisation Integration

Word-Based Motion Flow:

• Strip Moves → Encoder Pulses →
• PLC HSC Counts →
• PLC Calculates Cut Trigger →
• Servo Drive Activated →
• Cut Executed

Encoder stability directly impacts cut accuracy.

Noise causes inconsistent trigger point.

13) Common Encoder Wiring Mistakes

1. No shield grounding

2. Shield grounded both ends

3. Running cable near VFD output

4. Using single-ended output in high-noise system

5. Incorrect HSC configuration

6. Incorrect PPR scaling

7. Loose mechanical coupling

8. Over-tight shaft coupling

Most cut errors originate at encoder wiring or installation.

14) Encoder Testing Procedure

1. Verify supply voltage

2. Confirm pulse count manually

3. Check PLC HSC count accuracy

4. Rotate shaft slowly and observe count

5. Test at full production speed

6. Monitor for pulse loss

7. Confirm no noise spikes

Testing must be done under actual speed.

15) Environmental Protection

Roll forming environment includes:

• Oil mist

• Metal debris

• Vibration

• Temperature variation

Select encoder with:

• IP65 or IP67 rating

• Industrial connector

• Vibration-resistant housing

Unprotected encoder fails prematurely.

16) Export & Replacement Considerations

When exporting roll forming machines:

• Provide encoder model and PPR specification

• Document scaling factor

• Provide wiring diagram

• Supply spare encoder

• Confirm output type compatibility

Incorrect replacement encoder common field issue.

17) Failure Modes in Roll Forming Lines

Common encoder issues:

• Bearing wear

• Signal noise

• Measuring wheel slip

• Broken cable in drag chain

• Loose connector

• Index pulse misalignment

Periodic inspection recommended.

18) Buyer Strategy (30%)

Before purchasing a roll forming machine, verify:

1. Differential encoder output used

2. Shielded twisted-pair cable installed

3. High-speed counter module used

4. Measuring wheel properly engineered

5. PPR correctly selected

6. PLC scaling documented

7. Spare encoder provided

8. Commissioning test at max production speed

Red flag:

“Single-ended encoder running alongside VFD motor cable.”

That leads to long-term length instability.

6 Frequently Asked Questions

1) Why does cut length vary randomly?

Likely encoder noise or missed pulses.

2) Should I use differential encoder?

Yes, especially in VFD environments.

3) Why does PLC miss counts at high speed?

Incorrect HSC configuration or insufficient frequency rating.

4) Can I ground shield at both ends?

No, ground at cabinet side only.

5) Why does measuring wheel slip?

Improper pressure or oil contamination.

6) What is most common encoder mistake?

Poor cable routing near motor power cables.

Final Engineering Summary

Rotary encoder installation and wiring in roll forming machines must ensure:

• Correct output type selection

• Differential signal wiring

• Shielded twisted-pair cable

• Proper mechanical mounting

• Accurate PPR selection

• Stable power supply

• Correct PLC scaling

• Commissioning under full speed

Improper integration leads to:

• Cut length errors

• Scrap production

• Flying shear instability

• Production downtime

In high-speed roll forming systems, encoder integrity is directly tied to production precision and machine reliability.