Application of the hottest soft PLC in the design

2022-08-23
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Application of soft PLC in the control system design of all electric injection molding machine

Abstract: Soft PLC is a new automatic control technology based on PC. compared with the traditional PLC control mode, it can not only realize all the functions of hard PLC, but also follow the IEC programming standard and provide users with more openness. This paper introduces the application of soft PLC product CoDeSys of German 3S company in the control system design of injection molding machine, which is traditional control 2 According to the friction movement mode, it can be divided into: the transformation of the linear reciprocating friction and wear experimental machine system provides a new control scheme

key words: Soft PLC; Injection molding machine; Control system

abstract: soft PLC is a new technology in the world industrial automation field, it is based on the PC, contract to the traditional hardware PLC control system, it provides more open opportunities to the is paper based on new automation software CoDeSys, and illustrate an example in the Plastic Injection Molding Machine to introduces the new control mothod to replace the traditional control system and realize the auto-control.

key w ensure that the water content is below 0.1%; Orders: SoftPLC, plastic injection molding machine, control system

1 preface

injection molding machine is a polymer material processing machine widely used at present. At present, the injection molding machine widely used in China is basically driven by machinery or hydraulic pressure, and the control system mostly adopts contact relay logic control circuit. The biggest disadvantage of this control system is that the automation degree of the control system is not high, the accuracy is low Low production efficiency. Although the control system using hardware PLC can realize various control functions, it is difficult for users to upgrade and transform due to the hardware exclusivity and closeness of each manufacturer. With the development of automation and computer technology, using the software and hardware resources of computer, the function of hardware PLC can be realized through software, and the high-precision synchronous motion control of precise electronic gear and electronic cam can be realized, that is, software PLC technology. It follows the international standards of IEC

the typical system structure using soft PLC is industrial computer plus i/o interface plus soft PLC software package. Soft PLC product is a control device based on PC open structure. It has the characteristics of hard PLC in function, reliability, speed, fault finding and so on. Using software technology, the standard industrial PC can be transformed into a full-function PLC process controller. Soft PLC integrates the functions of computer and PLC, such as on-off control, analog control, mathematical operation, numerical processing, communication network, etc. through a multi task control core, it provides a powerful instruction set, fast and accurate scanning cycle, reliable operation, and an open structure that can connect various i/o systems and networks. By using soft PLC and servo motor with high precision control performance as the driving system, the fully electric injection molding machine greatly improves the operability of the equipment, product quality and production efficiency

2 structure and working principle of all electric injection molding machine

2.1 structure of all electric injection molding machine

all electric injection molding machine is mainly composed of injection device, clamping device and electrical control system. As shown in Figure 1, compared with general-purpose injection machines, servo motors and ball screws with high-precision control performance are used to realize the conversion from circular motion to linear motion. The function of the injection device is to plasticize the plastic evenly and inject it into the mold cavity. The injection device is composed of plasticizing parts (screw, barrel, heating device, nozzle), hopper, metering device, transmission device, injection motor and base motor. The mold closing device realizes the opening and closing of the mold, and the mold should be reliably closed during injection. The mold closing device is mainly composed of front and rear fixed templates, moving templates, connecting rods, linkage mechanisms, mold adjusting devices, mold closing servo motors, and demoulding servo motors. The electrical control system provides power and enables the injection machine to work according to the predetermined process requirements (pressure, speed, time, temperature) and action sequence

Figure 1 Schematic diagram of injection molding machine system composition

2.2 working principle

the process of producing a product by an injection molding machine generally goes through mold closing, injection, pressure maintaining, cooling (plasticizing), mold opening, and ejection of products

operation mode:

(1) manual operation can be used for one-step debugging, including manual mold opening and closing, manual mold height adjustment, and manual operation of screws, Manual adjustment of the back and forth movement of the injection seat, etc

(2) semi automatic operation press the semi-automatic operation button, the injection molding machine starts mold closing, injection and other work until the product processing is completed, and then it is in the waiting state. When the semi-automatic operation button is pressed again, the next cycle will begin

(3) after automatic operation completes one injection and metering cycle, the program automatically enters the next cycle

3 system design

three major problems need to be solved in the design of the control system of the all electric injection molding machine: first, how to ensure high-precision motion control after using the servo motor, how to realize position control, speed control, torque control in the program, and the switching between these controls. The second is how to realize the accurate control of temperature and pressure analog quantity to ensure that each injection cycle can ensure that the plastic raw materials are fully heated to the appropriate temperature and ensure the accurate control of injection pressure and pressure holding pressure. The third is how to design man-machine interface to monitor real-time status, modify data, deal with error alarms, and diagnose and eliminate errors in time

3.1 hardware design of the system

the hardware of the control system is composed of industrial computer, SERCOS IO module, Dr Rexroth digital servo driver and servo motor. The structural diagram of the control system is shown in Figure 2: the industrial computer, as the core of the control system, constitutes the upper computer, and controls the mold locking servo motor, injection servo motor, plasticizing servo motor through soft PLC and SERCOS optical cable ring The demoulding servo motor moves according to the written program, which can realize the high-precision motion control in the injection molding process, as well as the position, speed, torque and the switching between these controls. Input buttons, travel switches and other external digital input signals are collected into the PLC program through the IO module, processed into a logical relationship, and the required output state is obtained to control the field equipment. The indicator and alarm lights display the current equipment operation status and error alarm information. The analog signals of temperature sensor and pressure sensor are converted into digital signals that can be recognized by soft PLC through SERCOS IO module. Through the PID module program written in the programming system, the precise temperature and pressure PID adjustment in the injection molding process can be realized

sercos motion control bus conforms to the standard of open CNC system. It can flexibly add equipment according to the needs of the system, which is conducive to the distributed control of intelligent CNC equipment, saves the design and debugging cycle, and greatly improves the reliability of the system

3.2 software design of the system relative to the mechanical data experimental machine

CoDeSys of 3S company is compared with other soft PLC products such as SIMATIC WinAC of Siemens company and SoftPLC of SoftPLC company. The biggest advantage is that it integrates logic control, motion control and visualization

codesys is a programming tool that conforms to IEC standards. As long as the CoDeSys SP RTE software is installed on the computer, it can become an advanced high-performance programmable controller (PLC). In addition, the visualization can be easily realized with CoDeSys without other configuration software. CoDeSys softmotion can be used to realize motion control programming, including single axis motion to complex multi axis interpolation motion

Figure 2 Schematic diagram of control system structure

the program design of this control system adopts a modular design method, including the design of motion main program, manual control program, semi-automatic control program, automatic control program, IO control program and temperature control program

(1) task setting

set four tasks in the program task motiontask, tempctrl, pressureread Iotask

as shown in Figure 3: the four program tasks are parallel. According to the set priority and periodic scanning time, it can ensure that logic control and motion control do not interfere with each other

Figure 3 task configuration diagram

so

(2) main program design of motion

the main program of motion is mainly composed of parameter initialization, axis group enable, motor return to zero, operation mode selection, axis group state processing modules. Under the selection of operation mode, select the corresponding operation mode (manual, semi-automatic, automatic), The main program will call the corresponding processing program (manual control program, semi-automatic control program, automatic control program) program module diagram is shown in Figure 4:

Figure 4 program module diagram

4 Conclusion

the author's innovation is that the design of the control system adopts soft PLC technology and SERCOS motion control bus technology, simplifies the hardware structure, and makes the developed control system meet the requirements of development architecture, The scalability, reliability and maintainability of the system are greatly improved. The most important thing is to achieve high-speed, high-precision and short cycle of injection. After practical test, this control scheme has achieved the expected effect and has a very broad application prospect

References:

[1] Fu Yinghong, Li Xiaofan, etc Discussion on Soft PLC technology, products and control scheme [j] Microcomputer information 2000,5

[2] huyanhai et al Modular design of the main structure of injection molding machine and its case study Mechanical design and research, 2004,6

[3] Chen Weifu, Yang Jianwu Application of open CNC system and SERCOS interface technology China Machine Press, 2003.1

[4] CoDeSys user manual (end)

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