PLC Control System of Rotary Liquid Filling Machines
With the continuous expansion of the food market and the in-depth development of the food trade, as a part of the food industry, food packaging plays an increasingly important role, and the purpose of the development of food packaging machinery manufacturing is to handle food packaging more conveniently and efficiently. Canned drinks are containers made of non-toxic plastic or metal products, and can be added with drinkable liquid food, which can replenish water for the human body at any time and is convenient to carry. At present, there are many kinds of canned drinks in China, including fruit juice, tea and dairy products. The demand of consumers for canned drinks stimulates the prosperity of their industries, but it also puts forward new requirements for canned drinks production, including food safety, beautiful packaging, production accuracy and economy, etc. Therefore, it is an urgent task to develop a more efficient, accurate and intelligent machine control method.
With the rapid development of computer technology, the packaging industry in developed countries such as the United States and Japan has formed a relatively complete mechatronics control operation system, especially the mature application of microelectronic technology and modular technology, which directly determines the development direction of food packaging machinery in the future. China's manufacturing industry started late, and many enterprises choose to import production technology and equipment from abroad, and then improve them according to their own characteristics, forming a unique food packaging industry in China. Among them, liquid canned products are divided into different production lines according to production requirements, such as whether they contain gas, temperature and material. As an important part of the production line, the degree of automation, speed, efficiency and stability of
liquid filling machines largely determine the quality of liquid filling equipment. Taking the control system of rotary filling machines as the research object, the improvement of filling speed, precision and stability were studied.
Control system of rotary liquid filling machines 1. Control system of
rotary liquid filling machines A programmable Logic Controller (PLC) is a kind of electronic system that executes instructions such as calculation, counting and sequence control in the storage process through programmable memory devices. It converts them into digital signals to control the operation process of mechanical equipment. It has the advantages of simple operation, good commonality, powerful functions, strong anti-interference ability and good environmental adaptability. Rotary filling machines refer to the operation mode of continuous filling of liquid food by a rotary motion. After filling, it is production equipment that covers and operates. It is systematically controlled by PLC to achieve the goal of high efficiency, stability and accuracy in the production process. The common rotary filling machine includes four parts: (1) The bottle washing device, which cleans the used bottles, drives the bottles to the bottle washing device and uses the water spray device and the upper turntable to carry out the rotary cleaning. The bottle washing clip turns the cleaned bottles over and drains them. The bottle washing requires two times of water, which take different pipes respectively. The first water is directly discharged, and the second water is recycled as the first water for the next cleaning; (2) A filling device, which fixes the clean bottle, makes a circular motion and fills along the track. After filling, it continues to gradually separate from the filling valve along the track; (3) A capping device: A capping machine fixes the bottle body, and a capping device brings the cap to a corresponding position and rotates clockwise to fit and press the bottle body; (4) Transmission device connects different parts of the rotary filling machine and transports raw materials by liquid. The main steps of the liquid canning process include the transfer of the bottle body and the fitting and installation of the bottle body and the bottle cap. The process flow is: air duct inlet → bottle washing → filling → bottle delivery → (setting caps ↗) capping → bottle outlet.
In view of the above process flow, the common control system of the rotary filling machine should include the following operation units: (1) Input components: Input instructions to control the operation of the rotary filling machine and activate the sensing equipment to monitor whether the operation process is normal. (2) The control center adopts a PLC system to process all input and output signals, switching values, analog values, servo motors and stepping motors, so as to ensure the accurate control of signal transmission and operation process. (3) Actuators: Implement the requirements of the PLC system, and complete the work of liquid suction, liquid filling and pump direction control. (4) Motor, including the main engine and an auxiliary engine, controls different electric systems. (5) Operating system using Human Machine Interface as the operation display and control interface, which is convenient for operators to know the running status of the PLC control system at any time.
2. Elements of rotary liquid filling machines control system
Rotary filling machines can use a servo pump to control double filling heads to work in turn, which is beneficial to improving filling speed. There are 28 stations on the canning head, among which the No.1 station is the reset sensor, the No.2 counter, the No.3 bottle detection sensor, the No.4 filling station sensor and the No.5 to No.28 servo pump detection sensor. Station No.1 is the initial filling position, and station No.9 is the end of filling the position. The bottle body rotates from station No.1 to the end of filling process No.9 and runs to station No.17 to leave the filling process.
Among them, the most complicated and problem-prone parts of the control system include (1) Reset: After entering the filling process, the reset sensor at the No.1 station detects the bottle body. It starts the filling process and ensures the accurate positioning of the whole filling process, and prepares for liquid absorption at any time. It comprises three aspects of resetting, that is, after the reset button is pressed, firstly, the filling main motor starts and transmits the signal to the No.1 reset sensor. After the sensor detects that the filling in No.1 station is normal, the main motor stops and resets; Secondly, after the stepping motor of No.1 to No.12 station reverses to the limit position, the stepping motor stops overloading. The stepping motor rotates 120 degrees to drive the pump core to the liquid suction port, and the stepping motor stops and resets. Thirdly, after 3 seconds delay, the servo motors at stations 1~12 reverse. The sensors at stations 17~28 receive signals. The pump plug stays at the lowest position, and the servo motors at stations 1~12 stop. At this time, the servo motors drive the pump plug to reset. (2) The filling process is controlled by the PLC system, including liquid suction controlled by the servo motor and reversing controlled by the stepping motor. In actual operation, after the filling speed is increased, the frequency of liquid food spilling and foaming phenomenon increases, resulting in poor filling quality. Therefore, under the premise of high-speed filling, improving filling quality is the main research goal at present.
Design of hardware system of rotary liquid filling machines 1. Composition of hardware system of rotary liquid filling machines
According to the requirements of the control object of the rotary liquid filling machine, the control system should include input and output elements, control equipment and execution equipment, among which the control equipment can handle the analog quantity. The control principle of PLC is that buttons, selector switches, limit switches and power supply are connected with the input modules in the PLC system, which are used to control the turn-on and turn-off of the PLC system. The input modules transmit signals into the communication interface of CPU modules. On the one hand, they form an expansion rack with other interface modules. On the other hand, they transmit signals to the output module, which is directly connected with the contactor, solenoid valve, indicator light and power supply of the computer, and communicates with operators through a man-machine interface. According to the principle of PLC control, the configuration of a rotary liquid filling machine includes:
(1) base plate, which is mainly responsible for connecting power supply and other modules and exchanging data
(2) The power supply module is mainly responsible for providing 5V voltage for the system, and it is necessary to ensure that the rated output current value is greater than the current value consumed by the voltage supply module.
(3) input/output module, which is mainly responsible for bidirectional transmission of instructions issued by CPU and operators. The specification of the input/output module depends on the number of transmitted instructions.
(4) Motion control module, which is mainly responsible for controlling the movement process of the bottle body and the bottle cap, and uses the cooperation of the servo motor and the stepping motor to control the movement speed, position and other actions
(5) Man-machine interface, which is mainly responsible for the interaction between the operator and the control system, controls the system through the input interface and gets feedback from the output interface
(6) PLC, which is mainly responsible for controlling the whole system operation process, should have the characteristics of high performance, small volume and easy operation.
2. The execution system of rotary liquid filling machines
The execution system of rotary liquid filling machines includes 20 sets of servo motors and one set of stepping motors, among which 12 sets of servo motors are used to control the process of liquid suction and filling. 8 sets of servo motors are used to control the process of capping, and the stepping motors control the motor activities through the strength and emission frequency of electric pulse signals.
The servo executes the command strictly according to the input signal, and uses the power provided by the motor to drive the connected round shaft to rotate, without self-rotation. At the same time, it has a relatively wide operating range, and can quickly change the operating speed and state. At the same time, the variable-speed filling method is adopted to fill the liquid food, which ensures the high-speed filling and prevents the liquid food from splashing and foaming.
The stepping motor uses an electric pulse to control the motor rotation process. The electric pulse signal strength controls the motor rotation angle. The electric pulse signal emission frequency controls the motor rotation speed, and the electric pulse signal emission quantity controls the motor displacement. Therefore, if the motor rotation process needs to be changed, only the electric pulse signal needs to be changed. Due to the control of the electric pulse signal, the stepper motor has high motion accuracy, strong and sensitive response to start, stop and reverse, and the ability to provide accurate positioning.
3. PLC configuration of rotary liquid filling machines
According to the selection of control equipment and execution equipment of rotary liquid filling machines, the hardware system configuration is designed and connected, and the structure is as follows.
Hardware configuration of rotary liquid filling machines:
Sensor+switch button → power supply module, CPU, input module (washing pump electromechanical, cover trimmer motor, cover blower, vibration blower, cooling blower, liquid inlet pump motor, blow dryer motor, conveying motor), output module, supply-demand
Alarm devise → output module → main motor frequency converter (canned main motor), bottle stopper electromagnet, cover stopper electromagnet, bottle outlet motor frequency converter (bottle outlet motor)
Design of control software system for rotary liquid filling machines 1. Control flow of rotary liquid filling machines
The purpose of programming the control software system of the rotary liquid filling machine is to simplify the control process of the PLC control system into relatively independent small modules, each of which performs the corresponding work, and can connect different modules to each other and call each other to complete the system work together. Generally, liquid food objects faced by rotary liquid filling machines are different, and the processing technology is complex. Using the modular programming method, the processes of system initialization, fault alarm and emergency stop, servo motor control and stepping motor control can be programmed and debugged separately and can be called at any time, so as to control the overall target operation process, and simplify the control process and the process of program modification.
The specific process of the control software system of rotary liquid filling machines is as follows:
(1) Start the program to detect whether the PLC system is faulty. If it is, the PLC system will stop working and give an alarm; If there is no fault, start and initialize the program.
(2) Detecting whether the equipment is faulty. If it is, stop the equipment and give an alarm; If there is no fault, proceed to the next step.
(3) Judging the operation mode, including full-automatic operation and manual operation, in which the full-automatic operation process is complicated, whether there is a cover. If there is no cover, the equipment stops working and gives an alarm; If there is a cover, cover it, and then judge whether the bottle is blocked or not; If so, the equipment will stop working and give an alarm; If not, continue to work until the filling is finished. On the other hand, the manual operation requires the operator to manually set the program and make judgments in the whole process until the filling is finished.
2. Programming the control software system of rotary liquid filling machines
GXDeveloper software of Mitsubishi Company is selected as the control software of a rotary liquid filling machine, which has a Microsoft Windows operating system. It is compatible with all kinds of office software and has standardized programming and operation. It supports multi-language programs with convenient communication, and diversified debugging functions, and can remotely control the PLC system. In addition, in the process of the program design of the system, the motion accuracy of the servo motor and the stepping motor has a great influence on the stability of the system. Therefore, the motion process of the servo motor and the stepping motor can be designed by writing sequence control programs. The control programs of the servo motor and stepping motor are as follows.
Start → initialization processing → input PLC signal →OPR→ no → forced STOP
Start → initialization processing → input PLC signal →OPR→ Yes → start data setting program → start positioning control program execution program → start JOG program → start speed change program → restart program → error reset program → forced STOP→ end program
The increasing demand for beverages promotes the development of the beverage and food industry. The production requirements of rotary liquid filling machines and the overall design scheme of the control system are introduced. A set of servo motors is used to control the double filling heads, so as to improve the filling efficiency and accuracy. At the same time, the related hardware configuration and software programming design are discussed in detail, which provides a research basis for further optimizing the control system program and debugging the optimal filling conditions of different products.