Views: 0 Author: Site Editor Publish Time: 2026-04-29 Origin: Site
In the operation of a slitting machine, Tension Control is a core technology. Whether slitting paper, film, or aluminum foil, the stability of the tension directly determines the flatness of the finished product, the slitting precision, and the winding quality.
Tension control is primarily divided into two modes: Open-loop and Closed-loop. Their underlying logic and application scenarios differ significantly.
1. Open-loop Tension Control
Open-loop control does not directly monitor the actual tension value. Instead, it "estimates" and outputs the required torque based on predicted and preset parameters.
Operating Principle:
The control system calculates the torque (Torque) required by the drive motor (usually a magnetic powder brake or servo motor) based on the current Roll Diameter, Material Width, and Target Tension value.
T is the output torque,
F is the set tension, and
R is the real-time roll diameter.
Key Requirement: It must have high-precision Diameter Calculation (via encoders, ultrasonic sensors, or linear speed conversion).
Pros: Simple structure, low cost, and no need for expensive tension sensors or dancing rollers.
Cons: Lack of real-time correction. If material thickness is uneven, mechanical friction changes, or environmental factors fluctuate, the system cannot perceive the actual tension deviation, leading to lower precision.
2. Closed-loop Tension Control
Closed-loop control monitors the actual value in real-time via sensors and compares it with the set value, using a PID algorithm to automatically correct the output.
A. Tension Sensor Feedback (Direct Closed-loop)
Process: Specialized Load Cells (Tension Detectors) are installed under the guide rollers.
B. Dancing Roller / Pendulum Arm (Indirect Closed-loop)
Process: Air pressure controls the dancing roller to exert a constant force. Material tension balances against this pressure. When tension fluctuates, the arm moves; a potentiometer detects this displacement and feeds it back to the system.
Characteristics: The dancing roller acts as a buffer and energy storage, absorbing shocks during startup or emergency stops to prevent material breakage.
3. Comparison: Open-loop vs. Closed-loop
| Feature | Open-loop Control | Closed-loop Control |
| Detection Element | None (or only diameter sensing) | Load Cells or Dancing Roller |
| Precision | Medium-Low; sensitive to interference | Extremely High; auto-compensation |
| Stability | Inherently stable; no oscillation | Requires PID tuning to prevent hunting |
| Hardware Cost | Low | High |
| Typical Scenarios | Unwinding, low-end machines, consistent materials | High-speed slitters, Rewinding, ultra-thin materials |
4. Why Rewinding Often Uses "Closed-loop + Taper Control"
In the Rewinding stage of a slitting machine, maintaining a strictly constant tension can cause the inner layers to be too loose or the outer layers to crush the core (the "telescoping" or "cauliflower" effect).
Therefore, closed-loop control is usually combined with a Tension Taper algorithm: as the roll diameter increases, the set tension is automatically and linearly reduced.
K is the taper coefficient and
R is the current diameter.
Summary
Entry-level/Economic Solution: Open-loop control with a magnetic powder brake for unwinding; simple torque mode for rewinding.
High-end/High-speed Solution: Full closed-loop control. The unwinding end uses an active motor with sensors, while the rewinding end utilizes servo motors with closed-loop control and dynamic taper compensation to ensure neat edges and scientific distribution of internal stress.
