Servo Faults on Roll Forming Machines — Following Error, Homing Error & Torque Limit

Introduction — Why Servo Faults Stop Roll Forming Lines

Servo motors are widely used in modern roll forming machines where precise positioning and synchronization are required. Typical servo applications include:

• servo feed systems for punching
• flying shear carriage motion
• indexing mechanisms
• precision positioning systems.

Servo drives continuously compare the commanded position with the actual position reported by the encoder. If the servo cannot keep up with the command, the drive generates a fault condition to protect the system.

The most common servo faults in roll forming machines include:

• following error faults
• homing errors
• torque limit faults.

These issues may originate from mechanical problems, electrical faults, or incorrect servo tuning.

Understanding these faults helps technicians restore machine operation quickly.

How Servo Systems Work in Roll Forming Machines

Servo systems operate using a closed-loop control system.

The system typically includes:

• servo motor
• servo drive
• encoder feedback
• PLC motion control commands.

The PLC sends a position or speed command to the servo drive. The encoder reports the motor's actual position.

The drive continuously compares the commanded position with the actual position.

If the difference exceeds allowable limits, the drive generates a fault.

Servo Following Error Fault

A following error occurs when the servo motor cannot reach the commanded position quickly enough.

This means the difference between commanded position and actual position exceeds the allowable tolerance.

Typical servo fault codes include:

• following error
• position deviation fault
• position lag error.

These faults usually occur during rapid motion or heavy loads.

Symptoms of Following Errors

Operators may observe:

• servo stops suddenly during motion
• machine faults during high-speed operation
• servo moves but fails to reach target position
• intermittent motion errors during production.

These symptoms usually indicate the servo system cannot keep up with commanded motion.

Mechanical Causes of Following Errors

Mechanical resistance is a common cause.

Possible issues include:

Excessive Load

The servo may be required to move more mass than expected.

Example:

Heavy shear carriage components.

Binding or Misalignment

Linear guides or ball screws may be misaligned.

This increases friction and reduces servo response.

Worn Mechanical Components

Damaged bearings or worn drive belts may increase mechanical resistance.

Technicians should inspect the mechanical drive system when following errors occur.

Incorrect Servo Tuning

Servo drives require tuning to match the mechanical system.

Tuning parameters include:

• proportional gain
• integral gain
• derivative gain.

If tuning values are incorrect, the servo may respond too slowly or oscillate.

Poor tuning can cause following errors even when mechanical systems are healthy.

Encoder Feedback Problems

Servo systems rely heavily on encoder feedback.

If encoder signals become unreliable, the drive may misinterpret motor position.

Possible causes include:

• loose encoder cables
• electrical noise
• damaged encoder connectors.

These issues can cause sudden following errors.

Servo Homing Errors

Before servo systems operate automatically, they must perform a homing procedure.

Homing establishes a known reference position.

The servo moves until it detects a reference point such as:

• home sensor
• limit switch
• encoder index pulse.

If the homing process fails, the servo drive generates a homing fault.

Symptoms of Homing Errors

Typical signs include:

• servo fails to initialize during startup
• axis moves but cannot find home position
• PLC reports homing fault alarm.

Without a successful homing process, the PLC cannot safely command motion.

Common Causes of Homing Errors

Several issues can prevent successful homing.

Faulty Home Sensor

The home sensor may be damaged or misaligned.

Incorrect Sensor Wiring

Loose or broken wiring prevents the signal from reaching the drive.

Incorrect Homing Parameters

Servo drives use parameters that define:

• homing direction
• homing speed
• sensor type.

Incorrect configuration may prevent the drive from detecting the home signal.

Mechanical Travel Limits

Sometimes the servo axis cannot physically reach the home position.

Possible causes include:

• mechanical obstruction
• incorrect limit switch placement
• axis travel limits misconfigured.

Technicians should inspect the mechanical path of the axis.

Servo Torque Limit Fault

Servo drives monitor motor torque continuously.

If torque exceeds the configured limit, the drive may generate a torque limit fault.

This protects the motor and mechanical system from damage.

Symptoms of Torque Limit Faults

Typical symptoms include:

• servo stalls under load
• axis stops during motion
• torque overload alarms on the drive.

These faults often occur during heavy mechanical loading.

Causes of Excessive Torque

Several mechanical conditions may cause excessive torque demand.

Jammed Mechanical System

Material or debris may block movement.

Excessive Load

Servo axis may be moving heavier components than designed.

Misaligned Drive Components

Misalignment increases friction.

Technicians should inspect the mechanical system for resistance.

Incorrect Torque Limit Settings

Sometimes torque limits are configured too low.

If the limit is lower than the required operating torque, the servo may fault even under normal conditions.

Engineers should review torque parameters in the drive configuration.

Servo Motor Power Supply Issues

Voltage problems may also trigger servo faults.

Possible electrical causes include:

• unstable power supply
• loose power terminals
• damaged drive components.

Inspecting the electrical supply is recommended if faults occur frequently.

Troubleshooting Procedure

Technicians should follow a systematic troubleshooting approach.

Step 1 — Identify the Exact Fault Code

Check the servo drive display or HMI alarm message.

Step 2 — Inspect Mechanical Systems

Check for binding, misalignment, or excessive load.

Step 3 — Verify Encoder Signals

Inspect encoder wiring and feedback signals.

Step 4 — Check Homing Sensors

Confirm home sensors function correctly.

Step 5 — Review Servo Parameters

Verify tuning, torque limits, and motion settings.

Commissioning Best Practices for Servo Systems

Proper commissioning reduces the likelihood of servo faults.

Typical commissioning tasks include:

1 verifying encoder wiring
2 testing homing sequences
3 tuning servo parameters
4 verifying motion limits.

These steps ensure reliable motion control during production.

Preventative Maintenance for Servo Systems

Regular maintenance improves servo reliability.

Recommended practices include:

• inspecting encoder cables
• cleaning motion sensors
• checking mechanical alignment
• monitoring servo temperature.

Preventative maintenance helps avoid unexpected machine shutdowns.

Production Impact of Servo Faults

Servo faults can stop roll forming production immediately.

Consequences may include:

• machine downtime
• production delays
• product defects.

Quick diagnosis and repair are essential for maintaining productivity.

Benefits of Proper Servo Setup

When servo systems are configured correctly, they provide several advantages.

These include:

• precise positioning
• repeatable punching patterns
• synchronized flying shear motion
• improved product quality.

For modern roll forming lines, reliable servo control is essential.

FAQ — Servo Faults in Roll Forming Machines

What causes a servo following error?

Following errors occur when the servo motor cannot reach the commanded position due to mechanical load, tuning problems, or encoder issues.

Why does my servo fail during homing?

Common causes include faulty home sensors, incorrect wiring, or incorrect homing parameters.

What does a torque limit fault mean?

It means the servo motor is attempting to produce more torque than allowed by the drive settings.

Can mechanical problems cause servo faults?

Yes. Binding components, misalignment, or heavy loads can trigger servo faults.

How can servo faults be prevented?

Proper servo tuning, regular mechanical inspection, and correct parameter configuration help prevent faults.

Why is homing necessary for servo systems?

Homing establishes a reference position so the PLC knows the exact position of the servo axis.