PLC intelligent control system for finishing of th

  • Detail

Light rail finishing PLC intelligent control system

Abstract: This paper introduces the implementation method of light rail finishing milling and drilling machine PLC control system. The system uses PLC to replace the original relay and other devices, which improves the stability and reliability of the electrical control system, and increases the automatic control function and fault diagnosis function. Thus, the labor intensity is reduced, and the product quality and production efficiency are improved. The actual production shows that the control system works well

key words: PLC; Control system; Fault diagnosis

1 Introduction

the medium-sized plant of Tangshan Iron and steel company is an enterprise producing section steel. The original four sets of drilling and milling machine equipment are used for light rail finishing. Its electrical control system is composed of relays and contactors, and the control means are relatively backward. The control effect completely depends on the operator's experience and mental state. The consistency between each process is poor, time-consuming and laborious, the failure rate is high and the maintenance is difficult, which affects the production efficiency. Therefore, it is necessary to carry out technical transformation. PLC control has the advantages of high reliability, good flexibility and short development cycle. It is especially suitable for machine tool control and fault self diagnosis system. It can greatly reduce the number of components such as relays and improve the stability and reliability of electrical control system. Therefore, using PLC control system to replace relays with large volume, large investment and large energy consumption is the development trend of electrical control system. In view of the above reasons, we used PLC technology to carry out a comprehensive technical transformation of the original electrical system

2. System function

the PLC intelligent control system for light rail finishing includes the control of milling machine and drilling machine, and the basic functions are as follows:

(1) switching function: it can realize the switching between manual and automatic control. Under normal circumstances, the automatic gear is used. When maintenance or debugging is required, it is switched to the manual gear

(2) automatic alarm function: in case of abnormal conditions, it can alarm at any time. When abnormal conditions occur in any of the four parts: clamping head fast down, power head fast forward, power head work forward and power head fast backward, the corresponding audible and visual alarm will act, so that the on-site staff can take measures quickly to avoid or reduce the losses caused by the accident

(3) automatic memory function: equipped with "stop" and "continue running" buttons. When some problems occur during the working process and the operation needs to be suspended, press the "stop" button, the machine tool will stop running and all parts will remain in their original places. Press the "continue operation" button again, and the machine tool will continue to run

(4) emergency stop reset function: equipped with "emergency stop reset" button. Press this button to return all parts of the machine tool to the original state before processing when an abnormality occurs during the working process or when it is restored after a sudden power failure

in order to realize the above functions, it is necessary to make intelligent judgment on the operation process and carry out corresponding control. At the same time, considering the limitation of the operation function of PLC, it is necessary to add a fault diagnosis module and display it accordingly

3. System composition

PLC is realized by using FX2N series programmable controller of Mitsubishi company [1]. The structure of light rail finishing intelligent control system composed of programmable controller is as follows:

Figure 1 Light rail finishing intelligent control system structure diagram

the system is composed of input, control operation and output

1) the input part includes two parts: operation button and signal detection

a. the operation button is used to manually set parameters or conduct manual operation to deal with emergencies

b. signal detection is to automatically monitor the working condition of the machine tool on the production line by the sensor. Once there is an abnormal condition, the alarm will prompt the operator immediately, so as to deal with the corresponding fault, such as emergency shutdown, so as to avoid the occurrence of accidents

2) control operation part

the control operation part is mainly completed by PLC, and the application software of the control system completes the main functions of signal input, processing and control output

3) the output part includes alarm device, transmission and power device, fixed device

a. the alarm device is composed of flashing red, yellow and green lights and alarm bells, and the three colors correspond to three different alarm levels respectively. Green indicates that the system is normal, yellow indicates that the system parameters are out of range, but it still works and needs to be handled; If the red alarm is accompanied by the alarm sound, it must be stopped for emergency treatment

b. the conveying device controls the main circuit by the signal output from PLC and sends instructions to the motor to automatically complete the transmission of raw materials and power

c. the hydraulic device is a fixed device. The signal given by the PLC controller controls the hydraulic equipment through the solenoid valve to fix the raw materials in a certain position to serve the processing of raw materials

. System software design

4.1 problems considered in PLC software design

using ladder diagram to compile control program, the following problems should be considered in PLC software design:

(1) principle of strong current shutdown priority: in the software design of milling machine, as long as there is a strong current shutdown signal in the control signal, the strong current should be switched off regardless of other signals. As shown in Figure 2 of anchor chain tensile strength tester model introduction, as long as the off signal xo2= 1, the intermediate relay M100 will be turned off. (2) There are mainly three types of action interlocking reaction: Principle: some controls cannot act at the same time, so they must be interlocked. For example, for the spindle forward and reverse control, figure 3 is the schematic diagram of spindle interlock control. After any circuit is started, the other circuit must be closed at the same time, so as to ensure that the two cannot act at the same time

Figure 2

Figure 3

(3) sequential interlocking control principle: that is, some control requirements cannot be reversed, which requires that the normally open contact of the previous action is connected in the next control action, and the normally closed contact of the latter action is connected in the control circuit of the previous action, as shown in Figure 4

figure 4

in short, there are many factors affecting the PLC control system. As long as we fully consider all aspects of factors in software design, we can avoid failures and the operation of the control system will be more stable [2]

4.2 PLC basic control program design

the specific control function block diagram of milling machine is shown in Figure 5, and the control function of drilling machine is similar

Figure 5 Milling machine control sequence function block diagram

4.3 program design of fault diagnosis module

for PLC system, due to limited memory resources, complex intelligent diagnosis is difficult to achieve, so fault diagnosis intelligent module is added. This module is based on single chip microcomputer and adopts C51 programming, which can easily realize various control algorithms

fault tree reasoning and expert experience rule reasoning are combined, and intelligent modules are used to detect more and more i/o functions and internal information for fault diagnosis. [3] [4]

(1) fault structure analysis

when designing fault diagnosis, we must first analyze the possible faults of the whole system, get the fault hierarchy of the system, and use this hierarchy to design the fault diagnosis part. Figure 6 shows the fault hierarchy of the system

Figure 6 Fault hierarchy block diagram

(2) program design

the hierarchy of system fault structure provides a reasonable hierarchical model for fault diagnosis. When designing the program of the system, the hierarchy of fault structure should be fully considered and the logical flow should be reasonably arranged. Two points should be paid attention to when introducing fault input points:

a. all detection points of the system that may cause faults must be introduced into the PLC, which is mainly from the safe and renewable raw materials exhibition area organizer zz91 Regeneration Director Liu Ningxiang said that the operation should be considered, so that the system can handle faults in time

b. the lowest fault input information should be introduced into the PLC program as much as possible under the conditions allowed by the system, so as to obtain more fault detection information and provide services for the fault self diagnosis of the system

5. Conclusion

after debugging and industrial test operation, the control system has been officially put into operation in 2004. Since its operation, it has achieved good results, achieved the predetermined control function requirements, overcome the limitations brought by the control of relays and contactors, and avoided the problems of the original control system, such as many auxiliary components, high failure rate, high working noise, single control mode, difficult maintenance, etc. The manual and automatic switching is convenient, and the anti-interference ability is strong. It is suitable for the harsh working environment of the steel plant production line, and it is easy for computer communication to realize network monitoring

the author's Innovation: combining PLC and single chip microcomputer, the control system for light rail finishing drilling and milling machine equipment is designed, and it has the function of fault diagnosis and alarm. The system structure is simple and the operation is convenient


[1] Wang Mingjin FX2N PLC in 2 × Application of 12532t gantry crane Qinghai electric power, 2002.4:

[2] Liao Jingsheng, Chen Chonglin, Li Zhen The design and application of PLC in automatic cargo hoist Microcomputer information l. 20 (9):

[3] Xiong Xingming Reliability design of PLC control system Automation and instrumentation, 2004 (4)

[4] Jin Guangliang et al The application of programmable controller in the transformation of machine tool control system Water conservancy and electric machinery, 1999.2: (end)

Copyright © 2011 JIN SHI