Tension Detection Maintaining constant material tension and accurately controlling tension fluctuations are crucial for improving production efficiency and controlling bag-making quality. Tension detection is a fundamental prerequisite for tension control.
Traditional bag-making machines use two types of tension sensors: direct and indirect. Direct measurement includes bearing-type tension sensors, such as the piezoresistive tension sensor, which consists of an excitation coil and a secondary coil. The secondary coil acts as an inductor; when the magnetic element is subjected to mechanical stress in the measurement direction, magnetic coupling occurs, generating an induced AC voltage signal proportional to the mechanical force. After signal processing, a tension signal proportional to the magnitude of the mechanical force is output.
Piezoresistive tension sensors are installed between the bearing and the frame, recording the horizontal roll tension. A corresponding amplifier is used for full-bridge voltage supply and measurement signal processing. The amplifier output signal is proportional to the radial force and can be used for digital display or as the instantaneous value of a closed-loop circuit. There are also leaf spring-type micro-displacement tension sensors. The advantages of direct tension sensors are a wide detection range, fast response speed, and good linearity. The disadvantage is that it cannot absorb peak tension. When the tension control system is subjected to strong interference, the system cannot react instantly, resulting in large fluctuations in the tension of the conveyor belt.
Indirect tension detection is essentially a form of position control, commonly using a floating roller type. When the tension is stable, the tension on the conveyor belt is balanced by the force of the cylinder, keeping the floating roller in the center position. When the tension changes, the floating roller position rises or falls. The floating roller potentiometer detects the change in position and feeds it back to the tension controller as a position signal. The controller then calculates and outputs a control signal.
Combining direct and indirect tension detection methods, this approach can simultaneously detect the floating roller position signal and the tension electrical signal output by the sensor. It has excellent buffering and stabilizing effects, and also features high precision and high repeatability of closed-loop control.
Another method of tension detection is based on roll diameter. A proximity switch installed on the roll shaft detects the shaft's rotational speed. Using a pre-set initial roll diameter and material thickness, the current diameter of the winding or unwinding drum is calculated cumulatively. A control signal is output based on the change in roll diameter to control the winding torque or unwinding braking torque, thereby adjusting the tension.
Mask Deviation Detection: During material conveying, horizontal deviations may occur due to uneven force, uneven thickness, traction roller roundness, and other reasons. Timely online deviation detection is necessary.
Early bag-making machines had low speeds, and material deviation was manually adjusted by operators based on actual on-site observation.
Because photoelectric sensors have advantages such as simple structure, reliable performance, high accuracy, and fast response, they are now used to track the boundary lines of different color areas on the edge of packaging materials. The offset between the actual position of the strip and the set position is read, the offset is converted into an electrical signal, amplified, compared, calculated and analyzed, and then a command is sent to the servo controller to control the motor to drive the correction and guidance mechanism, so that the strip is returned to the set position, thus achieving the purpose of automatic tracking and adjustment of the conveyor.
