Design of numerical control of heat sealing machine based on PLC

Abstract: Aiming at the current demand for heat-sealed bag making, combined with the numerical control design of PLC, the numerical control design of heat sealer based on the internal auxiliary relay state identification method is analyzed, and a set of data acquisition procedures with microprocessor as the center is given to formulate reasonable upper and lower limits of heat sealing temperature, pressure and time under different environments. Finally, it was put into experiment and ran well, which greatly improved the efficiency and strength of heat sealing during use.

introduction

Heat-sealed bag making is widely used in product packaging, food and medicine packaging and other fields. It has been rapidly developed because it is fast, does not pollute the packaged objects and saves costs. In view of the shortcomings in heat sealing, this paper uses the numerical control technology of Panasonic Fp0-32-bit programmable logic controller to accurately design the production process of the heat sealing machine, and formulates reasonable upper and lower limits of heat sealing temperature, pressure and time under different external environments. Finally, a more efficient and reasonable heat sealing method is developed.

1. Technical introduction of CNC heat sealing machine platform

1.1 Introduction to Heat Sealing Technology

The so-called heat sealing is to use various external conditions (such as electric heating, high-frequency voltage and ultrasound, etc.) to heat the sealing part of the plastic film into a viscous state, and with the help of a certain pressure, the two layers of film are fused into one. After cooling, a certain strength and sealing performance are maintained to ensure that the goods can withstand a certain external force during packaging, transportation, storage and consumption, and to ensure that the goods will not crack or leak, thereby achieving the purpose of protecting the goods.

1.1.1 Factors affecting heat sealing

(1) Heat sealing temperature: Its function is to heat the adhesive film layer to a relatively ideal viscous flow state. The viscous flow temperature and decomposition temperature of the polymer are the lower and upper limits of heat sealing. The difference between these two temperatures is an important factor in measuring the difficulty of heat sealing of the material.

(2) Heat sealing pressure: Its function is to make the film in a viscous flow state produce effective polymer chain segments to penetrate and diffuse at the sealing interface, and also to make the distance between polymers close enough to produce intermolecular forces. If the heat sealing pressure is too low, the heat seal may be loose; if the pressure is too high, some effective chain segments in the viscous flow state may be squeezed out, resulting in a semi-cut state at the heat sealing part, leading to wire drawing.

(3) Heat sealing time: refers to the time the film stays under the sealing knife. The heat sealing time determines the heat sealing temperature, pressure and production efficiency of the equipment.

1.2 Introduction to PLC Technology

Programmable controller, referred to as PLC (Programmable logic Controller), is a new type of industrial control device based on computer technology.

1.2.1PLC Features

PLC uses modern large-scale integrated circuit technology and strict production processes to manufacture its internal circuits, and its internal circuits use advanced anti-interference technology, making it highly reliable.

1.2.2 Application fields of PLC

At present, PLC has been widely used in various industries at home and abroad, including steel, petroleum, chemical industry, electric power, building materials, machinery manufacturing, automobile, textile, transportation, environmental protection, culture and entertainment. Its usage can be roughly summarized into the following categories: logic control of switch quantity, analog quantity control, motion control, process control, data processing, communication and networking, etc. [1]

2. System design of CNC heat sealing machine platform

The exterior of the instrument is mainly composed of a shell with excellent water sealing and high pressure resistance. The electronic control part consists of two motors and a motor with a brake function, a temperature sensor, a voltage-stabilized power supply and a single-chip microcomputer with data acquisition/storage functions. The main program control flow chart is shown in Figure 1 below, and the I/O allocation diagram of the PLC is shown in Figure 2.

Figure 1 Main program control flow chart

Figure 2 PLC I/O allocation diagram

All the components available in the PLC programming process include only three types of devices: input devices, output devices, and some internal devices. Each type of device has only two states per bit: 1 or 0. This system uses a proximity switch.

The switch controls the heat sealer to clamp the bag in place and release it. When the proximity switch xx=1, the corresponding logic switch in the program is turned on, which means the heat sealer clamps the bag in place, otherwise it is released. The heat sealing time or heat cutting time is controlled by the timer. When the timer TX=1, it means that the X timer starts timing, heat sealing or heat cutting begins, and TX=0 when the timing ends.

3 Technologies implemented by the CNC heat sealing machine platform

3.1 Internal Auxiliary Relay Identification

This system adopts the idea of ​​state programming to design sequential control programs, and uses the auxiliary relays inside the programmable controller as "transitional" elements to realize state identification and design the CNC process of the entire heat sealing machine. This is the internal auxiliary relay identification method we use. At the same time, we use Panasonic GVWIN2.1 touch screen development software to display the state of the internal auxiliary relay on the screen, and can make reasonable modifications to replace the hardware identification method of diodes or transistors that were often used in the past, making the system more intuitive and convenient and improving the robustness of the system.

During the operation of the PLC, the program monitors the on and off of the contacts, which only depends on the state of the internal auxiliary relay coil and does not directly identify external devices. Each auxiliary relay can not only store the state of an input device, but also identify the state of an output device and display its state on the GVWIN2.1 touch screen to accurately track the operation of the program and store the data of each relay in the designated memory to provide the most favorable data for future maintenance. The partial state table of the internal auxiliary relay identification method of the CNC design of the heat sealing machine is shown in Table 1. [3]

Table 1 Status table of internal auxiliary relay identification method

3.2 Data Collection Technology

In the CNC design of heat sealers, we use the most commonly used heat press sealing method. For the problems that are more likely to occur in the production process, the most common reason is the unreasonable setting of heat sealing parameters before heat sealing. In view of the three major factors of heat sealing process: heat sealing temperature, pressure, and time, the main one is temperature, and the heat sealing temperature depends on the heat sealing time. The parameter of the resistance wire heating time is very important. At the same time, considering the different external environments, we select a reasonable resistance wire heating time and make reasonable adjustments based on the residual heat of the resistance wire. We have developed a data acquisition program centered on a microprocessor.

3.2.1 Hardware Design We use temperature sensor, voltage regulator and 89C51 microcontroller with data acquisition/storage function. The system consists of an extended program memory 2764, 74LS373 as latch, a data memory 6264, A/D conversion, extended I/O port, etc. The data acquisition hardware structure is shown in Figure 3.

Figure 3 Data acquisition hardware structure diagram

3.2.2 Software Design

The data acquisition program we developed, which is based on a microprocessor, strictly controls the heating time of the heat sealing knife under different environments to achieve a reasonable heat sealing effect. At the same time, in view of the residual heat of the resistance wire working continuously, as well as the future maintenance and monitoring of the CNC system, we use Panasonic GVWIN2.1 touch screen development software to display the heat sealing temperature, pressure, time, and internal auxiliary relay status on the screen, and make appropriate modifications to make the system more intuitive and convenient. Attached below is a subroutine to read the temperature value from the temperature sensor. [4]

4. Conclusion

This paper proposes a heat sealer numerical control design based on the internal auxiliary relay status identification method, and develops a set of data acquisition programs centered on microprocessors to formulate reasonable upper and lower limits of heat seal temperature, pressure and time under different environments, and displays its status on the GVWIN2.1 touch screen. After appropriate modifications, it has the advantages of high reliability, strong adaptability, and strong heat seal. At present, the system has been put into experiment and is running well. During use, it has greatly improved the efficiency and strength of heat seal, and greatly avoided the problems of missing seals, false seals, leaking seals, sticking seals, wire drawing, seal ruptures, and poor heat seal strength.