Thread Content
1 Introduction Due to their flexible control capabilities and the ability to provide reliable operational testing, microcontrollers are widely used in the field of mechatronics. Utilizing the functions of microcontrollers to achieve automated control and processing has become one of the most common control methods in modern industry. The main objective of this design is to make full use of the resources and functions of the microcontroller in order to accomplish the complex tasks of the sealing and cutting machine positioning system in the simplest possible way. During operation, the system uses photoelectric signal sensors to detect the movement parameters of the sealing and cutting machine, and relies on the software and hardware control functions of the microcontroller to automatically determine the movement state of this machine. This allows for controlling the feeding speed of the stepper motor, so that it matches the sealing and cutting motion controlled by the main motor, thereby enabling precise sealing of the packaging bags ； At the same time, it enables automatic electronic counting and display of packaging, display and adjustment of bag length, as well as functions such as single-action operation and reset. 2. Working principle of the automatic positioning system for sealing and cutting machines The automatic positioning system for sealing and cutting machines is designed for use with packaging bags; it utilizes the software and hardware capabilities of the 8751 microcontroller, as well as the signals detected by photoelectric sensors, to automatically control the movement of the packaging bags during transportation and sealing. It also regulates the speed of the feed stepper motor, ensuring that the feeding process is synchronized with the sealing action carried out by the motor with variable speed control, thereby achieving automated and precise sealing of the packaging bags ； At the same time, accurate production information is provided to production operators through displays and alarm systems. The working principle of the film sealing machine’s automatic positioning system: the dashed areas in the diagram represent the 8751 microcontroller and its external interfaces, while human-operated input information and on-site information are entered at the input terminal ； The output terminal has a display system and actuators that respond to the operating results of the microcontroller ； Manual input includes operations such as adjusting the bag length, resetting, restoring to default settings, and jogging ； The on-site information mainly includes information related to photoelectric sensors ； The operation status display shows the bag length value and the number of bags being processed ； The external actuator is a stepper motor that functions as a conveying bag, and its frequency is controlled by the microcontroller. In the packaging manufacturing industry, the composite pouches used as packaging bags can be divided into two types: one is a blank bag, and the other is a printed bag (colored bag). The color bag is printed with identifiers that can be recognized by photoelectric signal detection sensors. The automatic positioning system of the sealing and cutting machine detects automatically the frequency of the sealing and cutting machine controlled by the main motor through photoelectric signal sensors; this frequency is then converted into a number of pulses, which is compared with the number of pulses detected by another photoelectric signal sensor. The frequency of the feeding stepper motor is adjusted as a result, in order to change its feeding speed and enable it to adapt to the sealing and cutting movements of the main motor. Automatic positioning systems can be further divided into two types depending on the type of sealing bag: one is the blank bag positioning system, which is a fixed-length positioning system that requires only the sealing speed to match the bag-feeding speed in order to achieve fixed-length sealing ； Another is the printing bag positioning system, which involves tracking the position of the bag; it requires that the location where sealing and cutting take place be exactly at the designated mark. When carrying out various release-related tasks, we inevitably encounter a problem ； It’s that the bag length required for each task can change, and this inevitably affects the initial value of the bag length preset in our system. Furthermore, since the distance S between the photoelectric sensor that detects the color tag and the sealing cut is a constant value, any change in the bag length will inevitably affect the relationship between the bag feeding speed and the sealing speed. Therefore, to achieve automated positioning of the processing, a certain functional adjustment must be made between the bag length and the distance S. But this only works for sealed and printed bags; it’s meaningless when sealing blank bags. 3 Hardware Design of the Automatic Positioning System 3.1 Control of Stepper Motors Due to the hardware interface limitations of the 8751 microcontroller and in order to improve the accuracy of the system’s operation, hardware-based control is used for stepping motion rather than software-based control. The operation, stopping, and speed of the stepper motors are controlled by the pulse frequency output from port P1.0 of the 8751 microcontroller. When the period of the output pulse at port P1.0 is changed, the width of the high and low levels of the ABC three-phase windings will change. This results in a change in the rate of power-on and power-off, thereby altering the speed of the stepper motor. In summary, to control the motion state and operating speed of a stepper motor, it is sufficient to adjust the pulse period and the number of pulses output by port P1.0. Figure 1: Simple structure of a sealing machine 3.2 Application of photoelectric signal sensors Photoelectric signal sensors are devices that use light as a medium for signal transmission. In the automatic positioning system of the sealing machine, two photoelectric signal sensors are installed (as shown in Figure 1). Its main function is to perform real-time monitoring of the entire system. When the photoelectric signal sensor receives a signal, it transmits this signal to the CPU in the form of a voltage level, while also generating an interrupt request. This request tells the CPU to switch to the interrupt subroutine corresponding to that request in the next machine cycle after completing the current instruction, so that the interrupt subroutine can be executed, thereby enabling real-time monitoring of the entire system as well as the processing and transmission of relevant data. A photoelectric signal sensor (also known as a photoeye) is installed in front of the heat-sealing unit of the packaging machine. When the operating mode of the automatic positioning system of the sealing machine is set to control based on the color of the printed bags, the photoeye is activated to detect the color signals on those bags and transmit the detected signals to the CPU. The CPU then uses software functions to convert these signals into pulse signals that can be used to control the operation of the stepper motor. Another photoelectric sensor is installed at the location where sealing and cutting takes place. When the automatic positioning system of the sealing and cutting machine is activated, this photoelectric sensor detects signals of either high or low level resulting from changes in light intensity caused by the movement up and down of the sealing blade, and transmits these signals to the CPU. The CPU uses counting software and pulse width measurement software to enable automatic electronic counting of the system and to adjust the speed at which the stepper motor feeds material. 3.3 Display System The display system in the automatic positioning system of the sealing machine serves two purposes: first, it provides the production operator with information regarding the length of the bags; second, it shows the number of bags that have been sealed. Together with the alarm system, it enables control over quantitative production. The hardware structure of the display system in the film sealing machine’s automatic positioning system does not use decoders; decoding is accomplished through software ； The display mode is common-cathode dynamic display via serial port output. 3.4 Alarm System In the automatic positioning system for bag sealing machines, the function of the alarm system is as follows: once the total number of sealed bags reaches n×100+90 (where n is any integer), the system will automatically issue an alarm ； When the total number of sealing bags reaches n×100 (where n is any integer), the system automatically cancels the alarm. The implementation of this function can help production operators achieve quantitative production control. Second, the system issues an automatic alarm when the sealing and cutting machine’s movement, as detected by the photoelectric signal sensor, is too fast. Its hardware structure consists of a buzzer, a power amplifier transistor, and an 8751 microcontroller. 3.5 Reliability Design of the System To ensure the reliability of operation of the automatic positioning system in the sealing and cutting machine, and to reduce the interference caused by external interrupt signals entering via ports INT0 and INT1 on the CPU’s operation, optoelectronic isolation circuits are employed in the system’s hardware design. When the photoelectric sensor sends level pulse signals to the INT0 and INT1 interrupt ports of the CPU, these signals are transmitted through the optocoupler-based input/output isolation circuit and the 6-phase Schmitt trigger 40160 to the corresponding ports of the 8751 microcontroller, thereby ensuring that the operation of the internal data bus of the 8751 microcontroller is not affected by noise levels. 4 Software Design of the Automatic Positioning System 4.1 Definition of the System In this case, it is an automatically operating positioning system that functions continuously. Therefore, the feeding and sealing movements occur continuously. Therefore, the system must be able to respond quickly to requests from various interrupts. Multiple interrupt nesting constitutes the core of the entire system. First, the sealing and cutting speed is obtained from the main motor; the initial speed of the stepper motor is calculated using a speed conversion subroutine and sent to the stepper motor. Then, the speed of the stepper motor is fed back to the microcontroller, where it is compared with the speed of the sealing and cutting machine. The speed of the stepper motor is adjusted accordingly using a speed adjustment subroutine. In the automatic sealing machine system, the main task of the software is to convert the bag length information obtained by the CPU and the pulse signals representing the sealing speed of the main motor into the initial value for timer TO. It also handles the comparison between these two values in order to monitor the speed of the stepper motor in real time. The bag length information is entered manually by the operator during system initialization, with a default value of 150 MM for the system. The value can be adjusted by pressing the button to increase it by “1” or decrease it by “1”, thereby changing the bag length. The output speed of the stepper motor is determined by the pulse frequency sent from port P1.0 of the 8751 microcontroller. If it is detected that the number of pulses between two sealing operations is less than the number of pulses corresponding to the length of bags fed during that period, this indicates that the feeding speed is slower than the sealing speed; the feeding speed should be increased, at which point the value of timer TO increases ； Conversely, reduce the value of TO. 4.2 Design of the system software flowchart The main functions of the system software are to determine the operating mode of the automatic positioning system (empty bag/printed bag) and to carry out automatic positioning operations. For printed bags, printing errors are inevitable, which result in variations in the length of the packaging bags. To correct these errors, a second photoelectric sensor is used to perform real-time positioning of the printed bags, and software is employed to process these errors. The P1.0 port of the CPU is adjusted to send out pulses to the stepper motor, thereby enabling precise sealing of the packaging bags. When the object of processing for the automatic positioning system of the sealing machine is an empty bag, the bag length set in the main program or modified manually is converted into a number of pulses, which serves as the initial value for comparison by the automatic positioning system ； Compared with the number of pulses detected by the photoelectric eye 1, the comparison result is fed back to the CPU, which adjusts the frequency of pulses output from the P1.0 port of the microcontroller based on the feedback signal, thereby controlling the bag-feeding speed of the stepper motor.