PLC Control of Roll Forming Machine Uncoilers — Loop Control, Dancer Arms & Braking Systems
Introduction — Why Uncoiler Control Is Critical in Roll Forming Lines
The uncoiler is the starting point of every roll forming line. Its job is to unwind steel coil smoothly and feed material into the forming machine without introducing tension problems, material damage, or production interruptions.
Although the uncoiler appears mechanically simple, proper control is essential for stable production. Poor control can lead to problems such as:
- coil overrun
- strip tension spikes
- strip breakage
- uneven feeding
- coil telescoping
Modern roll forming machines use PLC systems to control uncoilers through a combination of sensors, braking systems, and feedback mechanisms.
The PLC coordinates the uncoiler with the rest of the forming line so that material feeds smoothly as production speed changes.
Understanding how PLC systems control uncoilers is essential for engineers, technicians, and machine operators working with roll forming equipment.
Basic Components of an Uncoiler System
A typical roll forming uncoiler system includes several mechanical and electrical components.
These components include:
- coil mandrel
- expansion mechanism
- drive motor (optional)
- braking system
- dancer arm or loop sensor
- PLC control system
The PLC monitors machine conditions and adjusts the uncoiler to maintain proper strip tension.
Types of Roll Forming Uncoilers
Different types of uncoilers require different PLC control strategies.
Manual Uncoilers
Manual uncoilers are typically used on smaller roll forming machines.
They rely on mechanical braking systems and operator adjustments.
PLC control is minimal.
Motorized Uncoilers
Motorized uncoilers use electric motors to rotate the coil.
The PLC controls the motor speed to match the roll forming line speed.
Hydraulic Uncoilers
Hydraulic uncoilers use hydraulic expansion systems to hold the coil securely.
The PLC often controls hydraulic valves and pressure sensors to operate these systems.
Loop Control in Roll Forming Lines
Loop control is one of the most important functions of uncoiler automation.
In many roll forming lines, a loop of material is allowed to form between the uncoiler and the roll former.
This loop acts as a buffer that absorbs speed changes in the line.
The PLC monitors the loop condition and adjusts the uncoiler accordingly.
Proper loop control prevents:
- excessive strip tension
- coil overrun
- feeding interruptions
Maintaining a stable loop improves overall production stability.
Loop Control Sensors
Several types of sensors may be used to monitor loop position.
Common sensor types include:
- photoelectric sensors
- ultrasonic sensors
- laser distance sensors
These sensors detect the position of the steel strip loop.
The PLC uses this information to determine whether the uncoiler should accelerate, slow down, or stop.
Dancer Arm Control Systems
Another common uncoiler control method uses a dancer arm.
A dancer arm is a pivoting mechanism that moves as strip tension changes.
The dancer arm typically includes:
- rollers supporting the strip
- a pivoting arm
- a position sensor
As strip tension increases or decreases, the dancer arm moves.
The PLC reads the dancer arm position and adjusts the uncoiler accordingly.
Dancer Arm Feedback Signals
Dancer arms often use sensors to measure their position.
Common sensor types include:
- potentiometers
- rotary encoders
- linear position sensors
The PLC receives the dancer arm position signal and determines the correct uncoiler response.
If the dancer arm moves upward, it usually indicates that strip tension is increasing.
If it moves downward, strip tension may be decreasing.
The PLC adjusts the uncoiler speed or braking accordingly.
Uncoiler Braking Systems
Braking systems prevent the coil from spinning too quickly when material demand decreases.
Common braking methods include:
- mechanical friction brakes
- pneumatic brakes
- hydraulic brakes
The PLC may control these brakes directly or indirectly.
Braking control is especially important when the roll forming machine stops suddenly.
Without proper braking, the coil may continue rotating and cause material overrun.
PLC Control Logic for Uncoilers
PLC programs controlling uncoilers typically include several logic sections.
These include:
- machine start and stop control
- loop sensor monitoring
- dancer arm position monitoring
- brake control logic
- safety interlocks
The PLC continuously monitors sensors and adjusts uncoiler behavior to maintain stable strip feeding.
Typical PLC Uncoiler Sequence
A typical PLC control sequence for an uncoiler may include the following steps.
1 Machine Start
The operator starts the roll forming line.
The PLC verifies that:
- coil is loaded
- safety guards are closed
- sensors are operational.
2 Initial Coil Feed
The PLC releases the uncoiler brake and allows the coil to begin rotating.
Material begins feeding toward the forming machine.
3 Loop Formation
The PLC monitors loop sensors or dancer arm position.
Once the proper loop size is reached, the PLC stabilizes uncoiler operation.
4 Production Operation
During production the PLC continuously adjusts:
- uncoiler motor speed
- braking force
These adjustments maintain stable strip tension.
5 Machine Stop
When the forming machine stops, the PLC activates the uncoiler brake to prevent coil overrun.
Common Uncoiler Control Problems
Several problems may occur in uncoiler control systems.
Coil Overrun
If braking is insufficient, the coil may continue spinning after the line stops.
This can cause strip tangling or material damage.
Excessive Strip Tension
If the uncoiler feeds material too slowly, strip tension increases.
High tension can cause strip breakage or deformation.
Loop Instability
Improper loop control may cause the strip loop to fluctuate excessively.
This can lead to inconsistent feeding.
Troubleshooting Uncoiler Control Systems
Troubleshooting uncoiler problems usually involves checking several key areas.
Important checks include:
- verifying sensor operation
- inspecting dancer arm movement
- checking brake functionality
- verifying PLC control signals
Observing loop behavior during machine operation can help identify control issues.
Commissioning Uncoiler Control Systems
When installing or upgrading an uncoiler control system, commissioning must be performed carefully.
Typical commissioning tasks include:
- verifying sensor alignment
- testing brake operation
- calibrating dancer arm sensors
- testing loop control response
Production testing should begin at low machine speeds.
Preventative Maintenance for Uncoiler Systems
Routine maintenance helps prevent uncoiler control problems.
Recommended inspections include:
Monthly checks:
- inspect brake systems
- verify sensor alignment
- check dancer arm movement
Quarterly inspections:
- test PLC control signals
- inspect electrical wiring
Regular maintenance helps maintain stable strip feeding.
Benefits of Proper PLC Uncoiler Control
Well-designed uncoiler control systems provide several important benefits.
These include:
- stable strip feeding
- reduced material damage
- improved production reliability
- smoother machine operation
Proper uncoiler control is essential for consistent roll forming production.
FAQ — PLC Control of Roll Forming Uncoilers
Why is loop control important in roll forming machines?
Loop control provides a buffer between the uncoiler and roll former, preventing excessive strip tension and stabilizing material feeding.
What is a dancer arm used for?
A dancer arm measures strip tension and allows the PLC to adjust the uncoiler speed or braking accordingly.
Why are braking systems necessary on uncoilers?
Brakes prevent the coil from continuing to spin when the roll forming line stops.
What sensors are used for loop control?
Photoelectric sensors, ultrasonic sensors, and laser sensors are commonly used to detect loop position.
What causes coil overrun?
Coil overrun usually occurs when braking force is insufficient or when the PLC control system fails to stop the uncoiler quickly.
How does the PLC adjust uncoiler operation?
The PLC reads feedback from sensors such as dancer arms or loop detectors and adjusts motor speed or braking force.