introduction
Heat sealing bags are widely used in product packaging, food and pharmaceutical packaging, and other fields. Their rapid development is due to their speed, lack of contamination of the packaged goods, and cost savings. This paper addresses the shortcomings of heat sealing by employing Panasonic's Fp0-32-bit programmable logic controller (PLC) technology to precisely design the heat sealing machine production process. Under different external environments, reasonable upper and lower limits for heat sealing temperature, pressure, and time are established. Ultimately, a more efficient and rational heat sealing method is developed.
1. Technical Introduction to CNC Heat Sealing Machine Platform
1.1 Introduction to Heat Sealing Technology
Heat sealing is a process that uses external conditions (such as electric heating, high-frequency voltage, and ultrasound) to heat the sealing area of a plastic film into a viscous state. With the help of certain pressure, the two layers of film are fused together. After cooling, the film maintains a certain strength and sealing performance, ensuring that the product can withstand certain external forces during packaging, transportation, storage, and consumption, preventing the product from cracking or leaking, and thus protecting the product.
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 limit and upper limit of heat sealing, and the difference between these two temperatures is an important factor in measuring the ease of heat sealing of the material.
(2) Heat sealing pressure: Its function is to enable effective interpenetration and diffusion of polymer chain segments in the viscous flow state of the film at the sealing interface, and to bring the distance between polymers close enough to generate intermolecular forces. If the heat sealing pressure is too low, the heat seal may be weak; 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-sealed part, leading to stringing.
(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
A programmable logic controller (PLC) is a new type of industrial control device based on computer technology.
1.2.1 PLC Characteristics
PLCs are highly reliable due to their use of modern large-scale integrated circuit technology, strict manufacturing processes, and advanced anti-interference technology in their internal circuitry.
1.2.2 Application Areas of PLC
Currently, PLCs are widely used in various industries both domestically and internationally, including steel, petroleum, chemical, electric power, building materials, machinery manufacturing, automobiles, light textiles, transportation, environmental protection, and cultural entertainment. Their applications can be broadly categorized as follows: logic control of digital signals, analog signal control, motion control, process control, data processing, communication, and networking.
2. System Design of CNC Heat Sealing Machine Platform
The instrument's exterior is mainly composed of a housing with excellent water tightness and high pressure resistance. The electrical control part consists of two electric motors and one electric motor with a braking function, a temperature sensor, a regulated power supply, and a microcontroller with data acquisition/storage functions.
In PLC programming, all available components fall into three categories: input devices, output devices, and some internal devices. Each type of device has only two states for each bit: 1 or 0. This system uses proximity switches to control the bag clamping and releasing positions of the heat sealer. When proximity switch xx=1, the corresponding logic switch in the program is activated, indicating that the heat sealer has clamped the bag; conversely, it is deactivated or released. A timer controls the heat sealing or heat cutting time. When timer TX=1, it indicates that timer X has started, and heat sealing or heat cutting has begun. When the timer ends, TX=0.
3. Technologies realized by the CNC heat sealing machine platform
3.1 Internal Auxiliary Relay Identification Method
This system employs state programming for sequential control programming, utilizing auxiliary relays within the programmable logic controller (PLC) as "transitional" components to implement state identification. This internal auxiliary relay identification method is used to design the entire CNC process of the heat sealing machine. Furthermore, Panasonic GVWIN2.1 touchscreen development software is used to display the status of the internal auxiliary relays on the screen, allowing for reasonable modification. This replaces the previously commonly used hardware identification methods using diodes or transistors, making the system more intuitive and convenient, and improving its robustness. During PLC operation, the program monitors the on/off state of the contacts based solely on the state of the internal auxiliary relay coils, without directly identifying external devices. Each auxiliary relay not only stores the status of an input device but also identifies the status of an output device, displaying these statuses on the GVWIN2.1 touchscreen for precise tracking of program execution . The data from each relay is stored in designated memory, providing the most valuable data for future maintenance.
3.2 Data Acquisition Technology
In the CNC design of the heat sealing machine, we adopted the most commonly used hot-press sealing method. The most common problem encountered during production is the improper setting of heat sealing parameters before heat sealing. Regarding the three main factors in the heat sealing process: heat sealing temperature, pressure, and time, temperature is the most important, and the heat sealing temperature depends on the heat sealing time. Therefore, the parameter for the heating time of the resistance wire is crucial. Considering different external environments, we selected an appropriate heating time for the resistance wire and made reasonable adjustments based on the residual heat of the resistance wire. We developed a microprocessor-based data acquisition program.
3.2.1 Hardware Design
We use a temperature sensor, a regulated power supply, and an 89C51 microcontroller with data acquisition/storage functions. The system consists of an extended program memory 2764, a 74LS373 for latching, a data memory 6264, an A/D converter, and extended I/O ports.
3.2.2 Software Design
Our microprocessor-based data acquisition program strictly controls the heating time of the heat-sealing knife under different environments to achieve a reasonable heat-sealing effect. Simultaneously, considering the residual heat from continuous operation of the resistance wire, as well as future maintenance and monitoring of the CNC system, we adopted Panasonic GVWIN2.1 touchscreen development software to display the heat-sealing temperature, pressure, time, and internal auxiliary relay status on the screen, making appropriate modifications to make the system more intuitive and convenient. The subroutine for reading temperature values from the temperature sensor is attached below.
4. Conclusion
This paper proposes a numerical control design for a heat sealing machine based on an internal auxiliary relay status identification method. A data acquisition program, centered on a microprocessor, is developed to set reasonable upper and lower limits for heat sealing temperature, pressure, and time under different environments. The program displays the data status on a GVWIN2.1 touchscreen, allowing for appropriate modifications. This system boasts advantages such as high reliability, strong adaptability, and robust heat sealing. Currently, the system has been put into experimental use and is operating well. During use, it significantly improves the efficiency and strength of heat sealing, greatly avoiding issues such as incomplete sealing, false sealing, leaks, adhesive residue, stringing, seal breakage, and poor heat sealing strength.
