Servo systems used in flying shears, punch presses, stackers, and positioning axes are extremely sensitive to electrical noise.
Unlike standard induction motors, servo systems operate with:
High-frequency PWM switching
Closed-loop position feedback
High-speed encoder signals
Fast current response
Improper cable selection is one of the most common causes of:
Following errors
Encoder faults
Random shear misalignment
Position drift
Servo drive trips
Unstable high-speed operation
In roll forming environments with VFD-driven main motors, hydraulic solenoids, and long cable runs, electromagnetic interference (EMI) is significant.
This guide explains how to properly select, route, and terminate shielded cables for servo motor and feedback systems.
Servo drives generate high-frequency switching pulses.
These pulses:
Create electromagnetic noise
Induce voltage in nearby cables
Affect encoder feedback signals
If feedback signals are corrupted, the servo drive loses position accuracy.
Shielded cable acts as a barrier between:
Noise source → Sensitive signal conductors
Without proper shielding, system stability degrades at high speed.
Every servo axis typically requires:
Servo Motor Power Cable
Servo Feedback (Encoder) Cable
Each has different shielding requirements.
Power cable between drive and motor must:
Be rated for inverter duty
Include overall braid shield
Include symmetrical grounding conductor
Have low capacitance
Be oil and abrasion resistant
Word-Based Connection:
Servo Drive U/V/W → Shielded Motor Cable → Servo Motor
Shield must be terminated properly at both ends.
Encoder cable must:
Use twisted pair for each signal
Use differential pairs (A+/A–, B+/B–, Z+/Z–)
Have foil or braid shield
Maintain signal integrity at high frequency
Feedback cable carries low-voltage signals.
Even small noise can disrupt accuracy.
Common shield types:
Good for high-frequency noise
Lightweight
Less mechanically durable
Better mechanical strength
Good overall EMI protection
Best industrial protection
Recommended for flying shear systems
Combination shielding is preferred in high-speed roll forming lines.
Servo feedback systems use differential signaling.
Example:
A+ and A–
B+ and B–
Twisted pairs reduce electromagnetic pickup.
Each pair must be:
Individually twisted.
Do not untwist near terminals.
Servo Motor Cable:
Shield → 360° clamp at drive end
Shield → Proper motor housing bond
Servo Feedback Cable:
Shield → Bonded at drive end
Motor connector housing typically provides second bond
Avoid long pigtail grounding wires.
Long pigtails reduce shielding effectiveness.
Power cables and signal cables must be separated.
Recommended layout:
Left trunking → Power
Right trunking → Feedback and signal
Maintain minimum separation distance.
If crossing required:
Cross at 90° angle.
Never run servo feedback cable parallel to VFD motor cable.
In roll forming frames:
Avoid sharp edges
Avoid high-vibration points
Use flexible drag chain rated cable
Avoid routing near hydraulic solenoids
Mechanical stress damages shielding over time.
Grounding flow:
Earth Bar → Servo Drive PE → Motor Cable Shield → Motor Frame
Ensure:
Low impedance grounding
No floating shields
No ground loops
Multiple improper ground points cause interference.
In flying shear applications:
Cut length variation
Random servo following error
Encoder loss at high speed
Position jitter
Servo instability only at high RPM
If issue appears only at high speed, suspect EMI first.
For long runs (>15–20 meters):
Use high-quality shielded cable
Consider lower capacitance design
Ensure differential encoder signals
Verify drive supports long cable length
Excessive capacitance stresses drive output stage.
Roll forming environments include:
Metal dust
Oil mist
Temperature variation
Vibration
Cable jacket must be:
Oil resistant
Flexible
Rated for continuous motion if in drag chain
Low-quality cable fails prematurely.
Using standard motor cable instead of servo cable
Using unshielded feedback cable
Running feedback cable with power cables
Poor shield termination
Untwisting pairs excessively
Using incorrect connector type
No strain relief
No separation from hydraulic solenoids
These mistakes cause intermittent faults that are hard to trace.
Testing procedure:
Inspect shield termination
Measure continuity
Inspect for mechanical damage
Monitor encoder count stability
Run at full production speed
Observe following error trend
Noise-related faults often only appear under load.
In structural roll forming lines with:
Multiple servo axes
Flying shear
Punch system
Each axis must have:
Independent shielded cable
Separate routing if possible
Cross-coupling noise between axes can occur.
When exporting roll forming machines:
Confirm cable rating for ambient temperature
Confirm compliance with local standards
Provide spare cable part number
Document cable specification
Verify EMC compliance
Replacing servo cable locally with generic type often causes instability.
Before purchasing a servo-driven roll forming machine, verify:
Servo motor cable is shielded inverter-duty rated
Feedback cable uses twisted differential pairs
Shield termination uses 360° clamp
Power and signal routing separated
Cable rated for industrial environment
Cable length within drive specification
Proper grounding architecture implemented
Documentation includes cable specification
Red flag:
“Standard multi-core cable used for servo feedback.”
That design will fail at high speed.
No. Servo systems require inverter-duty shielded cable.
High-frequency noise increases with speed and PWM switching.
Follow manufacturer recommendation. Typically bonded at drive end.
Using long pigtail ground instead of 360° clamp.
Reduces electromagnetic interference on differential signals.
Yes. Poor shielding and high capacitance reduce stability.
Proper shielded cable selection for servo systems in roll forming machines requires:
Inverter-duty shielded motor cable
Differential twisted-pair feedback cable
360° shield termination
Physical separation from power cables
Clean grounding architecture
Environmental durability
Incorrect cable selection causes:
Following errors
Cut length variation
Encoder instability
Random drive faults
Production downtime
In high-speed flying shear applications, cable quality and shielding discipline directly determine system accuracy and reliability.
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