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.
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.
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.
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.
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.
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
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.
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.
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.
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.
Using unshielded power cable
Running feedback cable with motor cable
Improper shield termination
Loose motor ground
Incorrect encoder type setting in drive
Incorrect motor parameter selection
Swapped encoder channels
Poor brake wiring
Most servo faults originate in wiring discipline.
Minimum configuration:
Motor model selection
Encoder resolution
Gear ratio (if mechanical coupling used)
Acceleration limits
Deceleration limits
Torque limits
Following error threshold
Incorrect encoder resolution leads to position mismatch.
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.
Common servo alarms:
Encoder error
Overcurrent
Overvoltage
Following error
Overtemperature
Diagnosis steps:
Read drive fault code
Verify feedback cable integrity
Confirm motor cable shielding
Check grounding continuity
Confirm parameter match with motor
Inspect brake release timing
Never guess servo issues without reading drive alarm history.
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.
Before production:
Verify motor rotation direction
Confirm brake release timing
Check encoder count stability
Perform low-speed positioning test
Monitor following error
Run at production speed gradually
Confirm synchronization with main line
Never run full-speed shear test immediately.
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.
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.
Before purchasing a servo-driven roll forming machine, verify:
Shielded servo motor cable used
Shielded feedback cable used
Proper grounding system implemented
Encoder differential signals used
Brake wiring correct
Parameter backup provided
Servo tuning documented
Commissioning test performed at full speed
Red flag:
“Servo system works — wiring details not documented.”
Professional suppliers provide full servo wiring diagram.
Because encoder signals are high-frequency, low-voltage differential signals.
No. Shielded inverter-duty cable is required.
Often encoder noise or improper tuning.
Only if controlled properly via drive or relay logic.
No. Maintain separation.
Poor shield termination.
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.
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