The tension control system of a stretch film slitting and rewinding machine is a core component ensuring slitting quality. Its precise adjustment requires real-time sensor feedback, dynamic compensation through control algorithms, and coordinated optimization of the mechanical structure. Tension fluctuations directly affect the flatness, edge neatness, and winding tightness of the stretch film. Insufficient tension can lead to wrinkles and misalignment of the film, while excessive tension may cause stretching deformation or even film breakage. Therefore, the system must maintain stable tension during acceleration, deceleration, and constant-speed operation.
Tension detection in stretch film slitting and rewinding machines typically employs a combined solution of floating roller position detection and tension sensor. The floating roller is connected to an angular displacement sensor via a cylinder. When tension changes, the floating roller's position rises or falls accordingly, and the sensor converts the displacement signal into an electrical signal, which is fed back to the controller. For example, when tension increases, the floating roller presses down, and the controller, upon receiving the signal, reduces the winding motor speed; when tension decreases, the floating roller rises, and the controller increases the speed. Simultaneously, the tension sensor directly measures the friction between the film and the detection roller, converting the tension value into an electrical signal. This signal is compared with a set value, and a PID algorithm is used to adjust the motor torque. The two detection methods complement each other: the floating roller responds quickly to large-scale tension fluctuations, while the sensor provides high accuracy in detecting minute changes, together ensuring the real-time performance and accuracy of tension control.
Regarding control algorithms, stretch film slitting and rewinding machines often employ a combination of closed-loop control and dynamic compensation. Closed-loop control continuously compares the deviation between the actual tension and the set value, using a PID controller to output a control signal and adjust the motor speed or torque. For example, when changes in film thickness cause tension fluctuations, the system automatically corrects the control parameters to eliminate the deviation. Dynamic compensation addresses the inertial effects during acceleration and deceleration by anticipating changes in film roll diameter and speed, and adjusting the motor output in advance. For instance, as the roll diameter gradually increases during winding, the system gradually reduces the tension according to a preset taper coefficient to prevent the outer film from squeezing the inner layer and forming a "hard core"; during deceleration, the system increases braking torque to counteract the sudden increase in tension caused by inertia.
Optimization of the mechanical structure is fundamental to improving the accuracy of tension control. The flattening roller, energizing roller, and web guiding system of a stretch film slitting and rewinding machine must maintain high-precision synchronous operation to avoid film stretching or loosening due to roller parallelism deviations or inconsistent speeds. For example, the flattening roller adopts an arc design to eliminate initial wrinkles in the film through mechanical pressure; the web guiding system is linked to tension control. When the film deviates, the web guiding motor adjusts the film position, while the tension system fine-tunes the winding speed to prevent sudden tension changes on one side. Furthermore, the rigidity and balance of the winding shaft are also crucial. Insufficient rigidity will cause axial runout during winding, leading to tension fluctuations; poor balance may result in uneven film roll ends, affecting subsequent processing.
Material property matching is a key consideration for tension control. Different stretch film materials (such as PE, PET, and BOPP) have significantly different elastic moduli, tensile strengths, and coefficients of friction, requiring matching with corresponding tension curves. For example, PE film has high elasticity and requires low tension and slow start-up parameters; PET film has high rigidity and can withstand greater tension, allowing for a more appropriate increase in start-up speed. The system must have a material parameter preset function. Operators can input parameters such as elastic modulus and thickness according to the membrane material type, and the system will automatically generate the optimal tension control scheme.
Environmental factors also have a significant impact on tension control. Temperature changes alter the elasticity of the membrane material, and increased humidity may cause electrostatic adsorption, interfering with sensor detection. Therefore, the stretch film slitting and rewinding machine needs to be equipped with an environmental compensation function, using a temperature sensor to monitor the workshop environment in real time and adjust the tension setpoint. For example, in high-temperature environments, the membrane material's elasticity decreases, and the system automatically reduces the tension; in high-humidity environments, an electrostatic elimination device is added to reduce sensor misjudgments.
The tension control system of the stretch film slitting and rewinding machine needs to achieve precise tension adjustment through real-time sensor feedback, dynamic compensation of the control algorithm, mechanical structure optimization, material property adaptation, and environmental factor compensation. This process relies not only on the precision and stability of the hardware but also on the intelligence and adaptability of the software algorithm. Only in this way can the flatness, neat edges, and tight winding of the slit film roll be ensured, meeting the high-quality requirements of downstream processing.
