應用于電氣系統的可編程序控制器【中文4300字】【中英文WORD】
應用于電氣系統的可編程序控制器【中文4300字】【中英文WORD】,中文4300字,中英文WORD,應用于,電氣,系統,程序,控制器,中文,4300,中英文,WORD
附錄2
英文原文
Programmable controller designed for electro-pneumatic systems
This project deals with the study of electro-pneumatic systems and the programmable controller that provides an effective and easy way to control the sequence of the pneumatic actuators movement and the states of pneumatic system. The project of a specific controller for pneumatic applications join the study of automation design and the control processing of pneumatic systems with the electronic design based on microcontrollers to implement the resources of the controller.
1.Introduction
The automation systems that use electro-pneumatic technology are formed mainly by three kinds of elements: actuators or motors, sensors or buttons and control elements like valves. Nowadays, most of the control elements used to execute the logic of the system were substituted by the Programmable Logic Controller(PLC).Sensors and switches are plugged as inputs and the direct control valves for the actuators are plugged as outputs. An internal program executes all the logic necessary to the sequence of the movements, simulates other components like counter, timer and control the status of the system.
With the use of the PLC the project wins agility, because it is possible to create and simulate the system as many times as needed. Therefore, time can be saved, risk of mistakes reduced and complexity can be increased using the same elements.
A conventional PLC, that is possible to find on the market from many companies, offers many resources to control not only pneumatic systems, but all kinds of system that uses electrical components. The PLC can be very versatile and robust to be applied in many kinds of application in the industry or even security system and automation of buildings.
Because of those characteristics, in some applications the PLC offers to much resources that are not even used to control the system, electro-pneumatic system is one of this kind of application. The use of PLC, especially for small size systems, can be very expensive for the automation project.
An alternative in this case is to create a specific controller that can offer the exactly size and resources that the project needs[3,4].This can be made using microcontrollers as the base of this controller.
The controller, based on microcontroller, can be very specific and adapted to only one kind of machine or it can work as a generic controller that can be programmed as a usual PLC and work with logic that can be changed. All these characteristics depend on what is needed and how much experience the designer has with developing an electronic circuit and firmware for microcontroller. But the main advantage of design the controller with the microcontroller is that the designer has the total knowledge of his controller, which makes it possible to control the size of the controller, change the complexity and the application of it. It means that the project gets more independence from other companies, but at the same time the responsibility of the control of the system stays at the designer hands
2.Electro-pneumatic system
On automation system one can find three basic components mentioned before ,plus a logic circuit that controls the system. An adequate technique is needed to project the logic circuit and integrate all the necessary components to execute the sequence of movements properly.
For a simple direct sequence of movement an intuitive method can be used[1,5],but for indirect or more complex sequences the intuition can generate a very complicated circuit and signal mistakes. It is necessary to use another method that can save time of the project, make a clean circuit, can eliminate occasional signal overlapping and redundant circuits.
The presented method is called step-by-step or algorithmic [1,5], it is valid for pneumatic and electro-pneumatic systems and it was used as a base in this work. The method consists of designing the systems based on standard circuits made for each change on the state of the actuators, these changes are called steps.
Fig.1.Standard circuit for the pneumatic system.
Fig.2.Standard circuit for the electro-pneumatic system.
The first part is to design those kinds of standard circuits for each step, the next task is to link the standard circuits and the last part to connect the control element that receive signals from sensors, switches and the previous movement and give the air or electricity to the supply lines of each step. In Figs.1 and 2 the standard circuits are drawn for pneumatic and electro-pneumatic system [8].It is possible to see the relations with the previous and the next steps.
3. The method applied inside the controller
The result of the method presented before is a sequence of movements of the actuator that is well defined by steps. It means that each change on the position of the actuators is a new state of the system and the transition between states is called step.
The standard circuit described before helps the designer to define the states of the systems and to define the condition to each change between the states. In the end of the design, the system is defined by a sequence that never chances and states that have the inputs and the outputs well defined. The inputs are the condition for the transition and the outputs are the result of the transition.
All the configuration of those steps stays inside of the microcontroller and is executed the same way it was designed. The sequences of strings are programmed inside the controller with 5 bytes; each string has the configuration of one step of the process. There are two bytes for the inputs, one byte for the outputs and two more for the other configurations and auxiliary functions of the step. After programming, this sequence of strings is saved inside of a non-volatile memory of the microcontroller, so they can be read and executed.
The controller task is not to work in the same way as a conventional PLC, but the purpose of it is to be an example of a versatile controller that is design for an specific area. A conventional PLC process the control of the system using a cycle where it makes an image of the inputs, execute all the conditions defined by the configuration programmed inside, and then update the state of the outputs. This controller works in a different way, where it read the configuration of the step, wait the condition of inputs to be satisfied, then update the state or the outputs and after that jump to the next step and start the process again.
It can generate some limitations, as the fact that this controller cannot execute, inside the program, movements that must be repeated for some time, but this problem can be solved with some external logic components. Another limitation is that the controller cannot be applied on systems that have no sequence. These limitations are a characteristic of the system that must be analyzed for each application.
4. Characteristics of the controller
The controller is based on the MICROCHIP microcontroller PIC16F877 [6,7] with 40 pins, and it has all the resources needed for this project. It ha enough pins for all the components, serial communication implemented in circuit, EEPROM memory to save all the configuration of the system and the sequence of steps. For the execution of the main program, it offers complete resources as timers and interruptions.
The list of resources of the controller was created to explore all the capacity of the microcontroller to make it as complete as possible. During the step, the program chooses how to use the resources reading the configuration string of the step. This string has two bytes for digital inputs, one used as a mask and the other one used as a value expected. One byte is used to configure the outputs value. One bytes more is used for the internal timer, the analog input or time-out. The EEPROM memory inside is 256 bytes length that is enough to save the string of the steps, with this characteristic it is possible to save between 48 steps.
The controller has also a display and some buttons that are used with an interactive menu to program the sequence of steps and other configurations.
4.1.Interaction components
For the real application the controller must have some elements to interact with the final user and to offer a complete monitoring of the system resources that are available to the designer while creating the logic control of the pneumatic system:
.Interactive mode of work; function available on the main program for didactic purposes, the user gives the signal to execute the step.
.LCD display, which shows the status of the system, values of inputs, outputs, timer and statistics of the sequence execution.
.Beep to give important alerts, stop, start and emergency.
.Leds to show power on and others to show the state of inputs and outputs.
4.2. Security
To make the final application works property, a correct configuration to execute the steps in the right way is needed, but more then that it must offer solutions in case of bad functioning or problems in the execution of the sequence. The controller offers the possibility to configure two internal virtual circuits that work in parallel to the principal. These two circuits can be used as emergency or reset buttons and can return the system to a certain state at any time[2]. There are two inputs that work with interruption to get an immediate access to these functions. It is possible to configure the position, the buttons and the value of time-out of the system.
4.3.User interface
The sequence of strings can be programmed using the interface elements of the controller. A computer interface can also be used to generate the user program easily. With a good documentation the final user can use the interface to configure the strings of bytes that define the steps of the sequence. But it is possible to create a program with visual resources that works as a translator to the user,it changes his work to the values that the controller understands.
To implement the communication between the computer interface and the controller a simple protocol with check sum and number of bytes is the minimum requirements to guarantee the integrity of the data.
4.4. Firmware
The main loop works by reading the strings of the steps from the EEPROM memory that has all the information about the steps.
In each step, the status of the system is saved on the memory and it is shown on the display too. Depending of the user configuration, it can use the interruption to work with the emergency circuit or time-out to keep the system safety. A block diagram of micro controller main program is presented.
5.Example of electro-pneumatic system
The system is not a representation of a specific machine, but it is made with some common movements and components found in a real one. The system is composed of four actuators. The actuators A,B and C are double acting and D-single acting. Actuator A advances and stays in specified position till the end of the cycle, it could work fixing an object to the next action for example(Fig.3), it is the first step. When A reaches the end position, actuator C starts his work together with B, making as many cycles as possible during the advancing of B. It depends on how fast actuator B is advancing; the speed is regulated by a flowing control valve. It was the second step. B and C are examples of actuators working together, while B pushes an object slowly, C repeats. its work for some time.
Fig.3.Time diagram of A,B,C and D actuators.
When B reaches the final position, C stops immediately its cycle and comes back to the initial position. The actuator D is a single acting one with spring return and works together with the back of C, it is the third step. D works making very fast forward and backward movement, just one time. Its backward movement is the fourth step. D could be a tool to make a hole on the object.
When D reaches the initial position, A and B return too, it is the fifth step.
Fig.4 shows the first part of the designing process where all the movements of each step should be defined [2]. (A+)means that the actuator A moves to the advanced position and (A . )to the initial position. The movements that happen at the same time are joined together in the same step. The system has five steps.
Fig.4.Step sequence of A,B,C and D actuators.
These two representations of the system(Figs.3 and 4) together are enough to describe correctly all the sequence. With them is possible to design the whole control circuit with the necessary logic components. But till this time, it is not a complete system, because it is missing some auxiliary elements that are not included in this draws because they work in parallel with the main sequence.
These auxiliary elements give more function to the circuit and are very important to the final application; the most important of them is the parallel circuit linked with all the others steps. That circuit should be able to stop the sequence at any time and change the state of the actuators to a specific position. This kind of circuit can be used as a reset or emergency buttons.
The next Figs.5 and 6 show the result of using the method without the controller. These pictures are the electric diagram of the control circuit of the example, including sensors, buttons and the coils of the electrical valves.
Fig.5.Electric diagram of the example.
Fig.6.Electric diagram of the example.
The auxiliary elements are included, like the automatic/manual switcher that permit a continuous work and the two start buttons that make the operator of a machine use their two hands to start the process, reducing the risk of accidents.
6. Changing the example to a user program
In the previous chapter, the electro-pneumatic circuits were presented, used to begin the study of the requires to control a system that work with steps and must offer all the functional elements to be used in a real application. But, as explained above, using a PLC or this specific controller, the control becomes easier and the complexity can be increase also.
It shows a resume of the elements that are necessary to control the presented example.
With the time diagram, the step sequence and the elements of the system described in Figs.3 and 4 it is possible to create the configuration of the steps that can be sent to the controller.
While using a conventional PLC, the user should pay attention to the logic of the circuit when drawing the electric diagram on the interface (Figs.5and 6), using the programmable controller, describe in this work, the user must know only the concept of the method and program only the configuration of each step.
It means that, with a conventional PLC, the user must draw the relation between the lines and the draw makes it hard to differentiate the steps of the sequence. Normally, one needs to execute a simulation on the interface to find mistakes on the logic.
The new programming allows that the configuration of the steps be separated, like described by the method. The sequence is defined by itself and the steps are described only by the inputs and outputs for each step.
The structure of the configuration follows the order:
1-byte: features of the step;
2-byte: for the inputs;
3-byte: value expected on the inputs;
4-byte: value for the outputs;
5-byte: value for the extra function.
Fig.7.Actuators A and B, and sensors.
Fig.8.Actuators C and D, and sensors.
Table 5 shows how the user program is saved inside the controller, this is the program that describes the control of the example shown before.
The sequence can be defined by 25 bytes. These bytes can be divided in five strings with 5 bytes each that define each step of the sequence (Figs.7 and 8).
7. Conclusion
The controller developed for this work shows that it is possible to create a very useful programmable controller based on microcontroller. External memories or external timers were not used in case to explore the resources that the microcontroller offers inside. Outside the microcontroller, there are only components to implement the outputs, inputs, analog input, display for the interface and the serial communication.
Using only the internal memory, it is possible to control a pneumatic system that has a sequence with 48 steps if all the resources for all steps are used, but it is possible to reach sixty steps in the case of a simpler system.
The programming of the controller does not use PLC languages, but a configuration that is simple and intuitive. With electro-pneumatic system, the programming follows the same technique that was used before to design the system, but here the designer works directly with the states or steps of the system.
With a very simple machine language the designer can define all the configuration of the step using four or five bytes. It depends only on his experience to use all the resources of the controller.
The controller task is not to work in the same way as a commercial PLC but the purpose of it is to be an example of a versatile controller that is designed for a specific area. Because of that, it is not possible to say which one works better; the system made with microcontroller is an alternative that works in a simple way.
References
[1]E.Nelli Silva,Fluid-mechanics systems Manual, Escola Politecnica USP,2002(in Portuguese).
[2]J.Swider,Control and Automation of Technological Process and Mechatronic systems,Silesian University Publishing Company,Gli-wice,2002(redaction in Polish).
[3]J.Swider, G.Wszolek, W.Carvalho. Example of the system prepared to be controlled by the controller based on microcontroller,in:12 International Scientific Conference—Achievements in Mechanical and Materials Engineering,Gliwice-Zakopane,Poland,2003,pp.965-970.
[4]J.Swider,G.Wszolek,W.Carvalho, Controller based on microcontroller designed to execute the logic control of pneumatic systems, in:12International Scientific Conference— Achievements in Mechanical and Materials Engineering,Gliwice-Zakopane,Poland,2003,pp. 959–964.
[5]J.Swider,G.Wszoek, The methodical collection of laboratory and project tasks of technological process control in Pneumatic and Electro-pneumatic Systems with Logical PLC Control, Silesian University Publishing Company,Gliwice,2003.
[6]PIC 16f87xDatasheet.MICROCHIP,2001.
[7]Application notes AN587 and AN546.MICROCHIP,1997.
[8]Fundamental of electro-pneumatic—FESTODidactic,2000.
中文翻譯
應用于電氣系統的可編程序控制器
摘要
此項目主要是研究電氣系統以及簡單有效的控制氣流發動機的程序和氣流系統的狀態。它的實踐基礎包括基于氣流的專有控制器、自動化設計、氣流系統的控制程序和基于微控制器的電子設計。
1.簡介
使用電氣技術的自動化系統主要由三個組成部分：發動機或馬達，感應器或按鈕，狀如花瓣的控制零部件?，F在，大部分的系統邏輯操作的控制器都被程序邏輯控制器（PLC）所取代。PLC的感應器和開關是輸入端，而發動機的直接控制閥是輸出端，其中有一個內部程序操控所有運行必需的邏輯，模擬其他的裝置如計算器、定時器等，對整個系統的運行狀態進行控制。
因為可以根據需要無數次創建和模擬這樣的系統，所以藉由PLC的使用，此項目有靈活的優點。因此，可以節省時間，減少失誤的危險，同時在使用相同材料的情況下，它可以更加精密。
市場上的許多家公司都使用了常規的PLC，它不僅可以用氣流系統來控制，還可以用各種電氣設備。PLC 的用途廣泛，可以應用于許多工業生產中，甚至用于建筑物的安全和自動化系統中。
由于以上的各種特性，在一些實際應用中PLC提供了很多的資源，甚至包括不控制系統的資源，電氣系統就是一種這樣的應用。對于自動化的工程，PLC的使用是比較昂貴的，尤其是對那些小型的系統。
針對這種情況可行的一種辦法是創建一個可提供特定尺寸和功能的控制器[3,4]。這種控制器可以根據微控制器來制作。
這種基于微控制器的控制器的適用范圍比較小，只能用于一個類型的機器或者可以用做一個像普通PLC一樣可以被編程的控制器，那樣它就可以通過可變化的邏輯程序來進行各種作業。所有的這些特性根據具體需要的不同而不同，具體的設計者的經驗的不同而不同。但是這種設計的主要優點在于設計人員非常了解自己的控制器，可以自由掌握控制器的大小尺寸，改變它的功能。這就意味著此項目有更多的獨特性，但同時系統的控制也由它的設計者所控制。
2.電氣系統
人們可以從一個自動化系統中找到三個上文中提到的基本部件，外加一個控制系統的邏輯線路。只有成熟先進的技術能做出特定的邏輯線路和執行正確操作所需要的部件升級。
對于一個簡單的運動，系統自動程序[1,5]可以完成，但是對于間接或更加復雜的運動，系統的程序就會產生復雜的線路和錯誤的信號。這是就需要另一種方法可以節省時間，產生清晰線路，能夠防止偶然的信號交疊和線路堵塞。
這種方計的不同標準的線路基法叫循序漸進式或規則系統[1,5]，它對氣流和電氣系統非常有效，而且也是此項目的一個基礎。它包括根據發動機狀態各個不同變化所設基礎上的系統。
圖一 氣壓系統標準回路
圖二 電控氣壓系統標準回路
第一步是為每個步驟設計那些種標準的線路。第二步是聯編標準的線路，最后一步是連接接收來自感應器，開關和先前的運動信號，同時把空氣或電傳送給每個步驟的補給線。如圖中所示， 1 和 2 標準線路是為氣流的和電氣系統[8]服務.我們能夠很清楚的看到每一步驟和下一個步驟之間的聯系。
3.控制器內部的應用原理
上述方法可以使發動機的每一個運動都被很好地用步驟來定義。這也就是說發動機的每一次運動變化都是系統的一個新的狀態，而兩個不同狀態之間的轉變叫做步驟。
先前提到的標準線路可以幫助設計人員定義系統的不同狀態和不同步驟的變化所帶來的
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