Tension detection

Maintaining constant material tension and accurately controlling tension fluctuations is an important factor in improving production efficiency and controlling bag quality. Tension detection is the basic prerequisite for tension control.

There are two types of tension sensors for traditional bag making machines: direct measurement and indirect measurement. Direct measurement involves a seat type tension sensor, such as a piezoelectric tension sensor, which consists of an excitation coil and a secondary coil. The secondary coil is an inductor, and magnetic coupling occurs when the magnetic component is subjected to mechanical stress in the measurement direction. The secondary coil generates an induced AC voltage signal directly proportional to the mechanical force, and through signal processing, outputs a tension signal proportional to the magnitude of the mechanical force; The varistor type tension sensor is installed between the bearing and the frame, recording the horizontal tension of the drum. The corresponding amplifier is used to supply the full bridge voltage and process the measurement signal. The signal at the output end of the amplifier is proportional to the radial force and can be used for digital display or as an instantaneous value in a closed-loop circuit; There is also a leaf spring type micro displacement tension sensor. The advantages of direct tension sensors are wide detection range, fast response speed, and good linearity. The disadvantage is that it cannot absorb the peak tension. When the tension control system is subjected to strong interference, the system cannot react in an instant, and the amplitude of tension change on the material belt is large.

The indirect tension detection method is essentially a position control, and the commonly used method is the floating roller tension detection. When the tension is stable, the tension on the material belt is balanced with the force of the cylinder, so that the floating roller is in the central position. When the tension changes, the position of the floating roller will rise or fall. The floating roller potentiometer detects the change in the position of the floating roller, and it will feedback the position signal to the tension controller. The controller calculates and outputs the control signal.

The tension detection method that combines direct and indirect testing can simultaneously detect the position signal of the floating roller and the tension electrical signal output by the sensor. It has a good buffering and stabilizing effect, and also has the characteristics of high precision and high repeatability of closed-loop control.

There is also a method of detecting tension based on the diameter of the roll, which uses a proximity switch installed at the roll to detect the speed of the roll. By setting the initial value of the roll diameter and material thickness, the current diameter of the winding or unwinding roll is accumulated and calculated. Based on the change in roll diameter, a control signal is output to control the winding torque or unwinding braking torque, thereby adjusting the tension.

Runway detection

Due to various reasons such as uneven force distribution, uneven thickness, and roundness of traction rollers, the horizontal position deviation of materials during transportation may occur. It is necessary to conduct online deviation detection in a timely manner.

In the early days, the speed of the bag making machine was not high, and the material deviation was manually adjusted by the operator based on on-site observation.

Due to the advantages of simple structure, reliable performance, high accuracy, and fast response, photoelectric sensors are now used to track the boundaries of different chromaticity zones at the edges of packaging materials. The deviation between the actual position of the strip and the set position is read out, and the deviation is converted into an electrical signal for amplification, comparison, calculation, and analysis. After that, instructions are sent to the servo controller to control the motor to drive the correction guide mechanism, and the strip is returned to the set position, achieving the goal of automatic tracking and adjustment during transportation.