1、中文 2180 字 PLC-based control system design vending machine With highly modern peoples lives, all intelligent automated new model is gradually into our daily lives, and more and more vending machines morewidely used, it is to peoples lives brought great convenient, and therefore its reliable and stabl
2、e design, highlights the importance of vending machines are to be completed no vending, optical, mechanical, electrical integration of business automation equipment. Vending machines have not any space restrictions, convenient advantage of can 24h daily sales. For vending machine design a control sy
3、stem with reliable performance, wide voltage range and easy programming, easy to maintain. Vending machine for the automated business representatives are widely used in public places. The traditional vending machine control system using SCM as the control so that not only will do a great job with th
4、e ratio of the input and output interfaces and immunity system is relatively poor, it is also very cumbersome to maintain, and expensive. Programmable Logic Controller (PLC) is a combination of computer technology, automatic control technology and communication technology and a new type of industria
5、l control devices developed its high reliability, simple programming, and easy maintenance have been in the field of industrial control vending machines widely used because of the completion of the community as a retail and integrated services independent facilities require it to be reliable structu
6、re, high stability and efficiency. Developmentof PLC and computertechnology, semiconductor technology, control iscloselyrelated to the development of technology, digital technology, high-techcommunications network technology, the development of these high-tech promote the development of PLC, the PLC
7、 and the development of these high-tech a higher update request promote their development. From the perspective of the development trend of the vending machine, and its appearance is due to the labor-intensive to technology-intensive industrial structure of the product of social change. Mass product
8、ion, mass consumption, and changes in consumption patterns and sales environment, requires the emergence of new distribution channels； while relatively supermarket, department store shopping and other newdistribution channels, labor costs are rising； coupled with the limitations of the venue shoppin
9、g convenience and the constraints, etc. These factors. Vending machine industry has long been the rapid development in the United States, Japan and other countries, has gained wide popularity in many countries. According to industry estimates, Chinas vending machine ownership is not too much, relati
10、ve to trend 1300000000 populous country and the development of retail formats in terms of development China vending machine industry will be more broad. Central Processing Unit (CPU) is the brain of a PLC controller. CPU itself is usually one of the microcontrollers. Aforetime these were 8-bit micro
11、controllers such as 8051, and now these are 16-and 32-bit microcontrollers. Unspoken rule is that youll find mostly Hitachi and Fujicu microcontrollers in PLC controllers by Japanese makers, Siemens in European controllers, and Motorola microcontrollers in American ones. CPU also takes care ofcommun
12、ication, interconnectedness among other parts of PLC controllers, program execution, memory operation, overseeing input and setting up of an output. PLC controllers have complex routines for memory checkup in order to ensure that PLC memory was not damaged (memory checkup is done for safety reasons)
13、.Generally speaking, CPU unit makes a great number of check-ups of the PLC controller itself so eventual errors would be discovered early. You can simply look at any PLC controller and see that there are several indicators in the form. of light diodes for error signalization. System memory (today mo
14、stly implemented in FLASH technology) is used by a PLC for a process control system. Aside form. this operating system it also contains a user program translated forma ladder diagram to a binary form. FLASH memory contents can be changed only in casewhere user program is being changed. PLC controlle
15、rs were used earlier instead of PLASH memory and have had EPROM 2memory instead of FLASH memory which had to be erased with UV lamp and programmed on programmers. With the use of FLASH technology this process was greatly shortened. Reprogramming a program memory is done through a serial cable in a p
16、rogram for application development. User memory is divided into blocks having special functions. Some parts of a memory are used for storing input and output status. The real status of an input is stored either as “1”or as “0”in a specific memory bit/ each input or output has one corresponding bit i
17、n memory. Other parts of memory are used to store variable contents for variables used in used program. For example, time value, or counter value would be stored in this part of the memory. PLC controller can be reprogrammed through a computer (usual way), but also through manual programmers (consol
18、es). This practically means that each PLC controller can programmed through a computer if you have the software needed for programming. Todays transmission computers are ideal for reprogramming a PLC controller in factory itself. This is of great importance to industry. Once the system is corrected,
19、 it is also important to read the right program into a PLC again. It is also good to check from time to time whether program in a PLC has not changed. This helps to avoid hazardous situations in factory rooms (some automakers have established communication networks which regularly check programs in
20、PLC controllers to ensure execution only of good programs). Almost every program for programming a PLC controller possesses various useful options such as: forced switching on and off of the system input/outputs (I/O lines), program follow up in real time as well asdocumenting a diagram. This docume
21、nting is necessary to understand and define failures and malfunctions. Programmer can add remarks, names of input or output devices, and comments that can be useful when finding errors, or with system maintenance. Adding comments and remarks enables any technician (and not just a person who develope
22、d the system) to understand a ladder diagram right away. Comments and remarks can even quote precisely part numbers if replacements would be needed. Thiswould speed up a repair of any problems that come up due to bad parts. The old way was such that a person who 3 developed a system had protection o
23、n the program, so nobody aside from this person could understand how it was done. Correctlydocumented ladder diagram allows any technician to understand thoroughly how system functions. Electrical supply is used in bringing electrical energy to central processing unit. Most PLC controllers work eith
24、er at 24 VDC or 220 VAC. On some PLC controllers youll find electrical supply as a separate module. Those are usually bigger PLC controllers, while small and medium series already contain the supply module. User has to determine how much current to take from I/O module to ensure that electrical supp
25、ly provides appropriate amount of current. Different types of modules use different amounts of electrical current. This electrical supply is usually not used to start external input or output. User has to provide separate supplies in starting PLC controller inputs because then you can ensure so called “pure” supply for the PLC controller. With pure supply we mean supplywhere industrial environment can not affect it damagingly. Some of the smaller PLC controllers supply their inputs with voltage
