(70% Engineering / 30% Buyer Strategy — no images, word-based engineering detail)
Flying shear systems are one of the most technically demanding parts of a roll forming machine.
The shear must:
Match strip speed
Reach exact cut position
Cut without distorting the panel
Return to home without losing synchronisation
At 40–60 m/min, timing errors of milliseconds create:
Cut length variation
Edge burrs
Profile distortion
Servo following errors
Scrap production
Most flying shear problems are not mechanical.
They are electrical synchronisation problems between:
Line encoder
PLC high-speed counter
Motion logic
Servo drive
Brake timing
Hydraulic or blade actuation
This guide explains how electrical synchronisation works and how to engineer it correctly.
Flying shear electrical synchronisation means:
The servo motor moves at the same linear velocity as the moving strip during the cut window.
That requires:
Accurate line position measurement
Accurate line speed calculation
Precise servo motion command
Correct timing of blade actuation
Stable feedback loop
If any part is unstable, synchronisation fails.
Word-Based Flow:
Main Roll Encoder → High-Speed Counter → PLC → Motion Profile → Servo Drive → Servo Motor → Shear Carriage
During motion:
Servo Encoder Feedback → Servo Drive → Closed Loop Correction
The system operates in real-time.
Scan-based timing alone is not sufficient.
Line encoder typically mounted on:
Pinch roll shaft
Main drive shaft
Encoder outputs:
A+/A–
B+/B–
Connected to high-speed counter (HSC).
Critical requirements:
Differential signals
Shielded cable
Proper grounding
No routing near VFD cables
If encoder signal is unstable, synchronisation cannot work.
HSC counts pulses independent of PLC scan.
Word-Based Logic:
If HSC_Count ≥ Target_Length
→ Trigger Motion Sequence
HSC must be:
Configured for quadrature
Correctly scaled
Reset at appropriate time
Incorrect HSC configuration leads to:
Length drift
Delayed shear trigger
Flying shear does not just move to a point.
It must:
Accelerate
Match line velocity
Perform cut
Decelerate
Return
Motion profile includes:
Acceleration ramp
Synchronisation window
Cutting dwell
Return motion
PLC calculates position offset relative to moving strip.
Line speed = 50 m/min
Encoder pulses represent 1 mm per pulse
Target length = 3000 mm
Logic:
When HSC = 3000 mm – Pre-trigger offset
→ Start servo acceleration
Servo matches strip velocity
Blade actuates
Servo returns
Pre-trigger offset compensates for acceleration delay.
Servo drive continuously adjusts torque based on:
Command Position vs Actual Position
If difference exceeds threshold:
Following Error Fault triggered.
Electrical stability of feedback cable is critical.
Noise causes position jitter and false following errors.
Blade may be:
Hydraulic
Mechanical
Pneumatic
Electrical timing must account for:
Valve delay
Mechanical travel time
Material thickness
Word-Based:
Servo in Sync Window
AND Position Within Cut Range
→ Activate Shear Solenoid
Delay must be tuned carefully.
If servo acceleration too slow:
Misses sync window
Late cut
If too aggressive:
Overcurrent trip
Mechanical shock
Motion profile must be tuned to machine inertia.
After cut:
Servo must:
Clear material path
Return to home
Be ready for next cycle
Improper return timing causes:
Carriage collision
Delayed next cut
Sequence stall
Return logic must not conflict with next length count.
Common causes:
Encoder noise
HSC misconfiguration
Incorrect scaling
Servo tuning mismatch
24V voltage sag during shear
Poor grounding
Brake delay mismatch
Incorrect pre-trigger offset
Always verify electrical integrity before mechanical adjustment.
Shear actuation often triggers:
Hydraulic solenoid
Brake release
High torque demand
If 24VDC drops:
PLC output may glitch
Servo enable may flicker
Fault triggered
Measure 24V during actual shear event.
Stable control voltage is essential.
At low speed, system may appear stable.
At high speed:
Encoder pulse frequency increases
Servo acceleration demand increases
Timing window narrows
Electrical weaknesses become visible only at production speed.
Commissioning must test full-speed operation.
Verify encoder stability at max speed
Confirm HSC pulse accuracy
Validate scaling against physical measurement
Tune servo acceleration profile
Adjust pre-trigger offset
Test shear delay timing
Confirm no following errors
Verify repeatability over multiple cuts
Repeat at different lengths.
Symptom: Cut too short
Cause: Pre-trigger too early or scaling error
Symptom: Cut too long
Cause: Delay in actuation or encoder pulse loss
Symptom: Random length variation
Cause: Encoder noise or 24V sag
Symptom: Servo following error at high speed
Cause: Poor feedback wiring or aggressive tuning
Symptom: Occasional missed cut
Cause: HSC not configured correctly
Roofing lines:
Continuous high speed
Lightweight panels
Short sync window
Structural lines:
Heavier material
Lower speed
Higher torque demand
Electrical synchronisation must match mechanical design.
Before purchasing a flying shear roll forming machine, verify:
Differential encoder used
High-speed counter implemented
Servo drive tuned for machine inertia
Shielded cables for motor and feedback
24V power stability designed with margin
Pre-trigger offset adjustable via HMI
Commissioning performed at full speed
Parameter backup provided
Red flag:
“Shear timing adjusted manually without encoder.”
Modern flying shears must use electronic synchronisation.
Because electrical timing margins shrink as speed increases.
Yes. Noise in encoder signals disrupts synchronisation.
Distance compensation for servo acceleration delay.
Servo cannot match commanded position due to tuning or noise.
Yes. Standard PLC scan inputs are insufficient.
Incorrect encoder scaling or noisy wiring.
Flying shear electrical synchronisation in roll forming machines depends on:
Stable differential encoder signals
Proper high-speed counter configuration
Accurate scaling
Well-tuned servo motion profiles
Clean grounding and shielding
Stable 24V control power
Correct actuation timing
When properly engineered, flying shear systems deliver:
Precise cut length
Clean panel edges
High-speed reliability
Minimal scrap
In modern roll forming production, synchronisation accuracy is primarily an electrical engineering discipline, not just a mechanical one.
Copyright 2026 © Machine Matcher.