Design And Implementation of Quantitative Function of Automatic Packaging Machine

Automatic packaging machine is mainly used for quantitative packaging of bulk materials to facilitate transportation, sales and use. According to the quantitative principle, automatic packaging machine can be divided into weighing type and constant volume type. In recent years, with the development of automatic detection and control technology, the accuracy of automatic packaging machine is required to be higher and higher. It is more convenient to improve the weighing accuracy of packaging machine by using weighing method. This paper mainly focuses on the design and implementation of the quantitative function of symmetrical weight automatic packaging machine.

1. Composition and working principle of automatic packaging machine

Weighing automatic packaging machine is mainly composed of storage hopper, feeding door, weighing sensor, weighing hopper, discharging door, discharging hopper and other parts to complete the feeding, weighing and discharging actions and realize the automatic packaging process of materials. When the materials in the storage hopper are enough, they enter the gravity feeding device under the action of gravity, and fully open the material door to enter the large feeding state. When reaching the given large feeding weight, close the feeding door and leave a slit to enter the small feeding state. When the given small feeding weight is reached, the feeding door is completely closed. After a certain amount of air blanking, the weighing bucket is stable, and the bag clamping mechanism is tight, the discharging door is opened, and the material enters the hopper, and then falls into the bag, completing a packaging cycle [1]. According to the actual weight after each filling, the feedback control algorithm is used to calculate the small feeding weight in the next packaging cycle. By controlling this weight, the whole system can automatically adjust back to the target weight.

2. Design of weighing part of quantitative weighing system

The quantitative weighing system is the core part of the packaging machine. The weighing part completes the weighing of materials to ensure the accuracy of packaging. This part mainly includes scale body, scale bucket, sensor, etc.

2.1 scale body

It is a steel fabricated box structure, which can support and contain all parts of the scale in the box structure. There are two large doors on the box, which can easily contact the internal parts during installation and maintenance. There are two air vents on the side of the box, which can be used to install the dust removal system.

2.2 scale bucket

It is used to hold materials in the weighing cycle. The scale bucket is suspended by two vertical rods. The lower end of the rod is fixed with the scale bucket by bolts, and the upper end is connected with the sensor by two bearings. The hopper is equipped with two baffle discharge doors, which are controlled by air cylinders. When the hopper door is fully closed, there is a proximity switch to provide the closing signal. When the hopper door is not closed, there is an interlocking device to prevent the feeding door from acting. A support frame is installed at the bottom of the weighing hopper to place weights during installation and checking. The side of the scale hopper is equipped with an openable door to clean the ash inside the hopper.

2.3 load cell

Connected with the weighing bucket, the weight of materials can be measured in time. The system adopts resistance strain type weighing sensor, and its structure is cantilever beam type. The lower end of the sensor is connected with two vertical rods by two bearings, and the lower end of the rod is fixed with the scale bucket by bolts.

3. Design of control part of quantitative weighing system

In the control process of quantitative weighing system, the weighing sensor weighs the material weight, converts it into electricity, and displays the measured value through the display. The control system compares the measured value with the set value (large feeding weight and small feeding weight) through the sequence unit and relay unit, and controls the material gate action, so as to finally make the system achieve the packaging target weight. According to the characteristics of the general weighing control system, the intelligent compensation algorithm is used to predict and adjust the control quantity of the system, so that the actual weight of the packaging can meet the production requirements. Through the error value between the actual weighing weight and the given weight, the next feeding process is corrected, so as to ensure that the weighing error of materials is within the minimum range. The actual weighing value can be automatically adjusted back to the given value through several times of correction of feeding process.

When the weighing error exceeds the allowable error range and tends to diverge, the statistical value of multiple errors is used to correct. When the weighing error exceeds the allowable error range and has a convergence trend, constant value compensation is adopted. When the weighing error is within the allowable range, there is no compensation. As shown in equation 5. Use common cable; If the signal is transmitted over a long distance, shielded cables can be used. For the cables in charge of communication in the system, the requirements for reliability are higher. At the same time, considering that the signal frequency of some communication cables is relatively high, special cables provided by special manufacturers can be considered; If the signal frequency in the system is low and the requirements of the whole system are not high, twisted pair with shielding can be considered. In the actual deployment and use, PLC control system should be as far away from strong interference sources as possible, such as high-frequency welding machine, large power equipment, etc. In addition, PLC control equipment and high-voltage electrical appliances should be stored separately, and the PLC in the storage cabinet should be away from the power line. Other inductive components in the same switch cabinet as PLC control system, such as common relays, contactor coils, etc., should be connected in parallel with arc suppression circuit.

2.5 measures in software design

In the PLC control system, if more appropriate control model and algorithm are used, the stability of the whole system will be greatly improved. Generally, the digital filtering method of sampling value can be used to filter the interference signal effectively; The incomplete differential method can effectively prevent the oscillation in the control process; If the selective control mediation mode is adopted, the controlled quantity close to the dangerous area can be out of danger, and the fault precursors can be eliminated in time to effectively avoid the occurrence of accidents. Therefore, for different objects, multiple or comprehensive control algorithm modes should be adopted to ensure the accuracy and stability of the whole PLC control system.

3. Using redundancy technology to improve the feasibility

Where the security and feasibility of the whole system are highly required, if only the hardware method is used to improve the system feasibility, it will lead to a substantial increase in the production and use costs of the system. Therefore, it is necessary to use redundancy technology to achieve.

4. Conclusion

In the process of using PLC control system, the application environment and conditions are quite different, and the interference sources are also very different. Therefore, in the specific operation and application development, only by adopting more appropriate measures can the whole system work in a more safe and feasible way.

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