Adding Length Measuring and Auto-Cut to an Older Roll Forming Line

Introduction — Why Older Roll Forming Lines Need Length Automation

Many older roll forming machines operate with manual cutting systems or simple mechanical stops. Operators measure the panel length manually and trigger a shear using pushbuttons or foot pedals.

While this approach works, it introduces several problems:

• inconsistent panel lengths
• operator fatigue
• lower production speed
• higher scrap rates
• limited repeatability.

Modern roll forming lines solve this problem using encoder-based length measurement and automatic cutting systems controlled by a PLC.

By adding length measuring and automated cutting, an older roll former can achieve:

• accurate panel lengths
• consistent production
• higher line speed
• automated operation
• reduced scrap.

This guide explains how to retrofit length measurement and automatic cutting onto an existing roll forming machine.

How Modern Roll Forming Length Control Works

Modern roll forming machines measure the movement of the metal strip using a rotary encoder connected to a measuring wheel.

As the strip moves through the machine, the encoder generates pulses.

The PLC counts these pulses to calculate strip movement.

Once the programmed length is reached, the PLC triggers the cutting system.

Typical sequence:

1 strip begins moving
2 encoder measures movement
3 PLC counts pulses
4 target length reached
5 PLC triggers shear
6 machine continues or pauses depending on cutting type.

This method provides extremely accurate length control.

Types of Cutting Systems Used with Length Control

When adding automation to an older line, the cutting system must also be considered.

Common options include:

Stop-to-Cut Shear

The machine stops before cutting.

Advantages:

• simple control logic
• easier retrofit
• lower cost.

Disadvantages:

• slower production.

Flying Shear

The shear moves with the strip while cutting.

Advantages:

• continuous production
• higher line speeds.

Disadvantages:

• complex synchronization
• higher cost.

For most retrofits on older machines, stop-to-cut systems are more practical.

Core Components Needed for the Upgrade

Adding length measurement and auto-cut requires several key components.

Typical hardware includes:

• rotary encoder
• measuring wheel assembly
• PLC controller
• operator interface (HMI)
• hydraulic or pneumatic shear control
• encoder mounting bracket
• electrical wiring and control cabinet upgrades.

Each component plays a role in accurate length control.

Encoder Selection

Encoders measure rotational movement and convert it into electrical pulses.

Important encoder specifications include:

• pulse resolution (pulses per revolution)
• output signal type
• environmental protection rating.

Typical industrial encoders provide:

1000 to 5000 pulses per revolution.

Higher resolution improves measurement accuracy.

Encoders should also include differential outputs to reduce electrical noise.

Measuring Wheel Design

The measuring wheel contacts the moving strip and transfers movement to the encoder.

Important design considerations include:

• wheel diameter
• rubber or polyurethane surface
• spring-loaded mounting.

Spring-loaded arms maintain constant pressure against the strip.

This prevents slippage that could cause inaccurate measurements.

Encoder Mounting Position

The measuring wheel should be placed where strip movement is stable.

Common locations include:

• just before the shear
• after the last forming stand
• before the stacker.

Avoid mounting the measuring wheel where strip vibration or bending occurs.

Stable strip movement improves measurement accuracy.

PLC Integration

The encoder signal must connect to a PLC input capable of counting high-speed pulses.

Most PLCs include:

• high-speed counter inputs
• dedicated encoder modules.

The PLC program converts encoder pulses into distance measurements.

Example calculation:

Wheel circumference = 200 mm

Encoder resolution = 2000 pulses per revolution

Distance per pulse =

200 mm ÷ 2000 = 0.1 mm per pulse.

This allows the PLC to measure strip movement very precisely.

Length Calculation in the PLC

The PLC continuously counts encoder pulses.

Using the scaling factor, it calculates the strip length.

Example PLC logic sequence:

1 encoder count begins when strip moves
2 PLC converts pulses to millimeters
3 PLC compares measured length with target length
4 cut command triggered when length reached.

After the cut, the encoder count resets for the next panel.

Operator Interface for Length Entry

Adding an HMI allows operators to set panel length easily.

Typical HMI features include:

• panel length input
• production counter
• alarm display
• machine status.

Operators can enter the required panel length without mechanical adjustments.

This improves flexibility and reduces setup time.

Shear Control Integration

The PLC must control the shear cycle.

Typical shear sequence:

1 PLC receives cut command
2 line stops (if stop-to-cut)
3 shear valve activates
4 blade moves down
5 blade returns to home position
6 line restarts.

Sensors confirm the shear position to ensure safe operation.

Hydraulic Shear Systems

Many roll forming shears use hydraulic cylinders.

Important components include:

• hydraulic power pack
• solenoid valves
• pressure switches.

The PLC controls valve activation to move the shear blade.

Hydraulic systems provide strong cutting force for thick materials.

Pneumatic Shear Systems

Some light-duty machines use pneumatic shears.

Advantages include:

• simpler installation
• lower cost.

However, pneumatic systems provide less cutting force and may not suit heavier materials.

Calibration of the Length Measurement System

After installation, the encoder system must be calibrated.

Typical calibration process:

1 run material through machine
2 measure actual panel length
3 compare with PLC measurement
4 adjust scaling factor if needed.

Calibration ensures accurate length control.

Common Sources of Length Error

Several issues may cause inaccurate panel lengths.

Common causes include:

Measuring Wheel Slip

If the wheel slips on the strip, measured length becomes inaccurate.

Encoder Signal Noise

Electrical noise may create extra pulses.

Incorrect Scaling

Incorrect encoder scaling factors cause measurement errors.

Mechanical Movement

Strip vibration may affect measurement stability.

Technicians should verify each factor during troubleshooting.

Troubleshooting Length Control Problems

If panel lengths become inconsistent, technicians should check:

• encoder cable condition
• measuring wheel pressure
• encoder mounting stability
• PLC scaling parameters
• sensor wiring.

Most length measurement issues can be resolved with simple adjustments.

Commissioning Procedure

When installing a new length control system, engineers should follow a structured commissioning process.

Typical steps include:

1 verify encoder wiring
2 test encoder pulse detection
3 confirm PLC length calculation
4 test shear operation
5 run sample panels
6 verify panel length accuracy.

These steps ensure reliable production operation.

Benefits of Automated Length Control

Adding length measurement and automatic cutting provides many benefits.

These include:

• improved product accuracy
• faster production speeds
• reduced operator workload
• consistent panel dimensions.

For many older roll forming machines, this upgrade significantly improves productivity.

Cost Considerations

The cost of adding length control depends on several factors.

These include:

• encoder hardware
• PLC system
• HMI installation
• wiring and installation labor.

Compared with purchasing a new machine, this upgrade is often very cost-effective.

Extending Machine Life

Modernizing older roll forming machines with automation upgrades extends their useful life.

Many machines with strong mechanical frames can operate for decades if control systems are upgraded.

This makes retrofits a valuable investment.

FAQ — Adding Length Control to Older Roll Formers

Can an old roll forming machine be upgraded with automatic length control?

Yes. Many older machines can be retrofitted with encoders and PLC control to automate cutting.

What device measures panel length?

A rotary encoder connected to a measuring wheel measures strip movement.

Why is the measuring wheel important?

The measuring wheel transfers strip movement to the encoder, allowing accurate length measurement.

Do I need a PLC to automate cutting?

Yes. The PLC processes encoder signals and triggers the shear at the correct length.

Can automatic cutting work with hydraulic shears?

Yes. Hydraulic shears are commonly controlled by PLC systems.

How accurate is encoder length measurement?

With proper calibration, accuracy within a few millimeters is achievable.