Servo Motor Wiring & Feedback Systems for Roll Forming Machines (Flying Shear Guide)

Servo Motor Wiring & Feedback Systems

Flying Shear & Precision Control in Roll Forming Machines

Servo systems are used in roll forming machines where precision and synchronization are critical.

Typical applications:

• Flying shear systems

• Punch synchronization

• Cut-to-length positioning

• Servo-driven stackers

• Coil feed control

Unlike standard AC motors with VFDs, servo systems operate in closed-loop control using:

• Position feedback

• Velocity feedback

• Torque control

Improper wiring of servo systems leads to:

• Position errors

• Shear misalignment

• Encoder faults

• Drive trips

• Random following error alarms

• Production scrap

Servo systems are extremely sensitive to wiring discipline and grounding.

This guide explains proper servo motor power wiring, feedback system wiring, shielding, and commissioning practices.

1) Basic Servo System Architecture

A typical flying shear servo system includes:

• PLC → Servo Drive → Servo Motor
• Encoder (internal or external) → Servo Drive
• Brake (if fitted) → Drive or separate supply

Word-Based Flow:

PLC Position Command → Servo Drive → Motor Torque
Encoder Feedback → Servo Drive → Position Correction

Closed-loop control ensures accurate positioning.

2) Servo Motor Power Wiring

Servo motors are powered by servo drives.

Word-Based Power Flow:

AC Supply → MCCB → Servo Drive Input
Servo Drive Output (U/V/W) → Servo Motor

Servo output cable must:

• Be shielded

• Be inverter-rated

• Have symmetrical grounding

• Be short as practical

Never mix servo motor cables with signal cables in the same trunking.

3) Servo Feedback Cable Wiring

Feedback cable connects encoder inside motor to servo drive.

Word-Based:

• Encoder A+/A–
• Encoder B+/B–
• Encoder Z+/Z–
• Power for encoder
• Shield

Requirements:

• Twisted pair for differential signals

• Shielded cable

• Proper termination at drive

• No splicing

Feedback cables are highly sensitive to noise.

Improper routing causes encoder faults.

4) Differential Signal Importance

Modern servo encoders use differential signals:

A+ and A–
B+ and B–

Differential signaling improves noise immunity.

Never connect only single-ended signals if differential is available.

Correct wiring preserves signal integrity at high speeds.

5) Shield Termination Best Practices

Servo motor power cable:

• Shield bonded at drive

• Shield bonded at motor (360° clamp preferred)

Servo feedback cable:

• Shield bonded at drive end

• Typically bonded at motor through connector housing

Follow manufacturer recommendations strictly.

Improper shield bonding causes:

• Position jitter

• Encoder alarms

• Random following errors

6) Servo Brake Wiring

If motor includes holding brake:

Brake coil typically 24VDC.

Word-Based:

Drive Brake Output → Brake Coil → 0V

Brake must release before motor motion.

Incorrect brake wiring causes:

• Dragging brake

• Overcurrent

• Positioning error

Brake timing parameters must match mechanical release time.

7) Grounding Strategy for Servo Systems

Servo drive PE terminal must connect to cabinet earth bar.

Motor frame must be bonded to machine frame.

Grounding flow:

Earth Bar → Servo Drive PE → Motor Shield → Motor Frame

Never rely on mounting bolts as sole ground path.

Poor grounding increases high-frequency noise.

8) Separation from VFD Systems

If roll forming machine has both:

• Main VFD

• Servo drive

Ensure separation between:

• VFD motor cables

• Servo feedback cables

Never run servo feedback cable parallel to VFD output cable.

VFD PWM noise couples into encoder lines easily.

9) High-Speed Flying Shear Synchronization

Servo must synchronize with line speed.

Word-Based Control:

Encoder on main roll → PLC High-Speed Counter → Position Command → Servo Drive

Servo drive calculates required motion profile.

Poor encoder wiring affects synchronization.

10) Typical Servo Wiring Errors in Roll Forming

1. Using unshielded power cable

2. Running feedback cable with motor cable

3. Improper shield termination

4. Loose motor ground

5. Incorrect encoder type setting in drive

6. Incorrect motor parameter selection

7. Swapped encoder channels

8. Poor brake wiring

Most servo faults originate in wiring discipline.

11) Initial Servo Parameter Setup

Minimum configuration:

1. Motor model selection

2. Encoder resolution

3. Gear ratio (if mechanical coupling used)

4. Acceleration limits

5. Deceleration limits

6. Torque limits

7. Following error threshold

Incorrect encoder resolution leads to position mismatch.

12) Tuning Considerations

Servo tuning affects:

• Response time

• Stability

• Overshoot

• Vibration

Auto-tuning may be used initially.

Fine tuning may be required for:

• Heavy shear mass

• High-speed roofing lines

• Structural punch systems

Mechanical rigidity influences tuning results.

13) Diagnosing Servo Faults

Common servo alarms:

• Encoder error

• Overcurrent

• Overvoltage

• Following error

• Overtemperature

Diagnosis steps:

1. Read drive fault code

2. Verify feedback cable integrity

3. Confirm motor cable shielding

4. Check grounding continuity

5. Confirm parameter match with motor

6. Inspect brake release timing

Never guess servo issues without reading drive alarm history.

14) Encoder Noise Symptoms

In flying shear systems:

• Cut length drift

• Inconsistent shear trigger

• Random position offset

• Following error at high speed

Often caused by:

• Shielding problem

• Ground loop

• Feedback cable routing near VFD cable

Fix wiring before changing parameters.

15) Commissioning Checklist

Before production:

1. Verify motor rotation direction

2. Confirm brake release timing

3. Check encoder count stability

4. Perform low-speed positioning test

5. Monitor following error

6. Run at production speed gradually

7. Confirm synchronization with main line

Never run full-speed shear test immediately.

16) Environmental Considerations

Roll forming environments include:

• Vibration

• Metal dust

• Oil mist

• Temperature changes

Ensure:

• Feedback connectors secure

• Shield clamps tight

• No cable rubbing on sharp edges

Vibration can loosen connectors over time.

17) Export Considerations

When exporting servo-driven machines:

• Confirm supply voltage compatibility

• Confirm frequency rating

• Provide servo parameter backup

• Provide motor data sheet

• Confirm local service support

Servo systems are more complex than basic VFD systems.

Backup is essential.

18) Buyer Strategy (30%)

Before purchasing a servo-driven roll forming machine, verify:

1. Shielded servo motor cable used

2. Shielded feedback cable used

3. Proper grounding system implemented

4. Encoder differential signals used

5. Brake wiring correct

6. Parameter backup provided

7. Servo tuning documented

8. Commissioning test performed at full speed

Red flag:

“Servo system works — wiring details not documented.”

Professional suppliers provide full servo wiring diagram.

6 Frequently Asked Questions

1) Why is servo feedback cable so sensitive?

Because encoder signals are high-frequency, low-voltage differential signals.

2) Can servo motor cable be unshielded?

No. Shielded inverter-duty cable is required.

3) Why does shear miss position at high speed?

Often encoder noise or improper tuning.

4) Should servo brake be wired directly to 24V?

Only if controlled properly via drive or relay logic.

5) Can I run servo feedback next to VFD motor cable?

No. Maintain separation.

6) What is most common servo wiring mistake?

Poor shield termination.

Final Engineering Summary

Proper servo motor wiring and feedback integration in roll forming machines requires:

• Shielded power cable

• Shielded differential feedback cable

• Correct grounding architecture

• Separation from VFD wiring

• Accurate parameter configuration

• Proper brake integration

• Structured commissioning

Incorrect servo wiring causes:

• Position errors

• Following faults

• Scrap production

• Random instability

In high-speed flying shear systems, wiring discipline directly determines cut accuracy and machine reliability.