Measuring Wheel Encoder in Roll Forming Machines — Cut Length Feedback & Speed Control Guide

The measuring wheel encoder is a precision rotary feedback device mounted to the cut length measuring wheel assembly in a roll forming machine.

Measuring Wheel Encoder in Roll Forming Machines — Complete Engineering Guide

Introduction

The measuring wheel encoder is a precision rotary feedback device mounted to the cut length measuring wheel assembly in a roll forming machine. Its function is to convert the rotational movement of the measuring wheel into electrical pulse signals, which are then interpreted by the PLC or motion controller to calculate exact strip travel.

In both stop-cut and flying shear systems, accurate strip length measurement is critical. The encoder ensures:

Consistent panel length
High-speed synchronisation
Reduced scrap
Reliable production accuracy

It is one of the most important electronic accuracy components in the entire roll forming line.

1. What Is a Measuring Wheel Encoder?

A measuring wheel encoder is:

A rotary motion feedback device
Coupled directly to the measuring wheel shaft
Connected to PLC or servo drive
Designed to output pulse signals

It converts mechanical rotation into digital data.

2. Primary Functions

2.1 Strip Length Measurement

Translates wheel rotation into linear distance.

2.2 Speed Feedback

Measures strip velocity in real time.

2.3 Cut Position Control

Triggers shear at programmed length.

2.4 Synchronisation Input

Provides speed reference for flying shear carriage.

3. Location in the Roll Forming Line

The encoder is mounted:

Directly on measuring wheel shaft
Via flexible shaft coupling
On bracket adjacent to measuring arm

It must remain mechanically stable.

4. How It Works

Operation process:

Strip moves forward
Measuring wheel rotates
Encoder shaft rotates with wheel
Encoder generates pulses
PLC counts pulses
Pulse count converted to linear distance

Accuracy depends on pulse resolution and wheel circumference.

5. Types of Encoders Used

Common types include:

Incremental Encoder

Outputs A/B pulse signals
Measures speed and direction
Requires homing reference

Absolute Encoder

Provides exact position value
No homing required
Higher precision

Most roll forming systems use incremental encoders.

6. Pulse Resolution

Resolution is measured in:

Pulses per revolution (PPR)
Counts per revolution (CPR)

Higher resolution results in:

More accurate cut length
Smoother speed feedback
Better flying shear synchronisation

7. Signal Output

Typical signal outputs include:

A/B quadrature signals
Z index pulse
SSI protocol
BiSS protocol
EtherCAT (advanced systems)

Signal compatibility must match PLC input.

8. Conversion to Linear Distance

Linear length is calculated using:

Wheel circumference ÷ encoder pulses

PLC scaling factor ensures correct length conversion.

9. Accuracy Factors

Measurement accuracy depends on:

Encoder resolution
Wheel diameter accuracy
Slippage between wheel and strip
Signal noise
PLC scaling accuracy

Encoder alone cannot correct wheel slip.

10. Mounting Configuration

Proper installation requires:

Rigid mounting bracket
Accurate shaft alignment
Flexible coupling (if required)
Secure fasteners

Mechanical vibration affects signal quality.

11. Coupling Methods

Encoder may be connected via:

Direct shaft mount
Flexible bellows coupling
Clamp coupling
Hollow shaft design

Flexible couplings prevent bearing stress.

12. Environmental Protection

Encoders operate in:

Steel dust environments
Oil mist conditions
High vibration zones

Industrial IP-rated encoders are required.

13. EMI & Shielding

Because roll forming lines include:

VFD drives
Servo amplifiers
High-current cables

Encoder cables must be:

Shielded
Properly grounded
Routed separately from power cables

EMI interference causes signal errors.

14. Flying Shear Synchronisation

In flying shear systems:

Measuring wheel encoder reads strip speed
PLC calculates carriage acceleration
Servo matches strip velocity
Cut occurs at synchronised speed

Encoder precision directly impacts cut timing.

15. Stop-Cut Systems

In hydraulic stop-cut systems:

Encoder triggers stop command
Strip stops at programmed count
Shear activates

Pulse accuracy determines final panel length.

16. Calibration Procedure

During commissioning:

Wheel diameter verified
Encoder pulse count confirmed
PLC scaling adjusted
Test panels measured

Calibration ensures dimensional accuracy.

17. Common Sources of Error

Potential errors may include:

Wheel slippage
Encoder misalignment
Signal noise
Incorrect scaling factor
Worn wheel coating

Routine checks prevent production deviation.

18. Maintenance Considerations

Routine inspection should include:

Cable integrity
Connector tightness
Bracket stability
Signal test verification

Loose cables cause intermittent faults.

19. Thermal Stability

Temperature variation may affect:

Encoder electronics
Signal stability
Wheel expansion

Industrial-grade encoders compensate for drift.

20. Redundancy Systems

Advanced systems may use:

Dual encoders
Strip encoder + motor encoder
Cross-check monitoring

Redundant systems improve reliability.

21. Integration with PLC

The encoder connects to:

High-speed counter input
Motion control module
Servo amplifier
Length control logic

Correct programming is critical.

22. High-Speed Production Demands

At high speeds:

Pulse frequency increases
Signal integrity becomes critical
Cable shielding becomes essential

Encoder must handle high RPM reliably.

23. Engineering Selection Criteria

Engineers select encoder based on:

Required resolution
Maximum shaft RPM
Environmental rating
Output protocol
Electrical compatibility
Mechanical mounting style

Proper selection ensures stable performance.

24. Impact on Production Quality

High-quality encoder feedback ensures:

Consistent panel length
Reduced scrap
Accurate installation fit
Improved product reputation

Length accuracy is a key customer expectation.

25. Summary

The measuring wheel encoder is a precision rotary feedback device that converts measuring wheel rotation into digital signals for accurate strip length and speed control in roll forming machines.

It:

Enables precise cut length control
Supports flying shear synchronisation
Provides real-time speed feedback
Improves production accuracy
Reduces material waste

It is one of the most critical accuracy components in modern roll forming systems.

FAQ

What does a measuring wheel encoder do?

It converts wheel rotation into pulse signals to measure strip length.

Is high resolution important?

Yes — higher resolution improves cut length accuracy.

Can EMI affect encoder signals?

Yes — proper shielding is essential in industrial environments.

Is it used in flying shear systems?

Yes — it provides strip speed reference for synchronisation.

Does it require calibration?

Yes — correct PLC scaling ensures accurate panel length.