电气毕业论文设计英语文献原文+翻译.doc

1、标准文档期需碇争钟孩幺事外文翻译院（系）专业班级姓名学号指导教师Programmable designed for electro-pneumatic systems controllerJohn F.WakerlyThis project deals with the study of electro-pneumatic systems and the programmable controller that provides an effectiveand easy way tocontrol the sequenceof the pneumatic actuators movement

2、and the statesof pneumatic system.The project of a specific controller for pneumaticapplicationsjoin the study of automation design and the controlprocessing of pneumatic systems with the electronic design based on microcontrollers to implement the resources of the controller.1. IntroductionThe auto

3、mation 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 Contr

4、oller (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.W

5、ith 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 marke

6、t 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

7、 of those characteristics, in someapplications the PLCoffers 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

8、 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

9、 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 advanta

10、ge of design the controller with the microcontroller is that the designer has the total knowledge of his controller, which makesit 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, b

11、ut at the same time the responsibility of the control of the system stays at the designer hands2. Electro-pneumatic systemOn 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 cir

12、cuit 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 nec

13、essary 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

14、 in this work.The method consists of designing the systems based on standard circuits madefor each change on the state of the actuators, these changes are called steps.Fill .堂4nMd Gvvuil 回 tu; pneumdCwI- v J SUndaidtor 11k H彳gyscMoi.The first part is to design those kinds of standard circuits for ea

15、ch step, the next task is to link the standard circuits and the last part is to connect the control elements that receive signals from sensors, switches and the previous movements, and give the air or electricity to the supply lines of each step. In Figs. 1 and 2 the standard circuits are drawn for

16、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 controllerThe 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

17、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 sys

18、tem 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

19、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 st

20、ep. 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 desi

21、gn 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 r

22、ead 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

23、 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. Charac

24、teristics of the controllerThe controller is based on the MICROCHIP microcontroller PIC16F877 6,7 with 40 pins, and it has all the resources needed for this project .It has enough pins for all the components, serial communication implemented in circuit, EEPROM memory to save all the configuration of

25、 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 makeit as complete as possible. During the step, the progra

26、m 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 in

27、put or time-out. The EEPROmemory 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 (Table 1).1OwiIaI inputsK17wiIaIK.XnakkQ mpuhInkrnl2Imtld2I.me： d,W户The controller (Fig.3) has also a display and some buttons

28、that are used with an interactive menuto program the sequence of steps and other configurations.F*- J- Coai|MKiiJihh 4 Lh*kEtnylk工1.1. Interaction componentsFor the real application the controller must have some elements to interact with the final user and to offer a complete monitoring of the syste

29、m resources that are available to the designer while creating the logic control of the pneumatic system (Fig.3):? Interactive modeof work; function available on the main program for didactic purposes, the user gives the signal to execute the step.? LCDdisplay, which shows the status of the system, v

30、alues 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.1.2. SecurityTo make the final application works property, a correct configuration to execute

31、 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 b

32、e 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.1.3. User int

33、erfaceThe sequence of strings can be programmedusing 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 sequ

34、ence. 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

35、 bytes is the minimum requirements to guarantee the integrity of the data.1.4. FirmwareThe 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 disp

36、lay 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. In Fig.4,a block diagram of micro controller main program is presented.mam S3.cuth?n41 -31ali例 furKtMm电 J HkU Jfr p 小山、h E、4f .5. Example of electro-pne

37、umatic systemThe system is not a representation of a specific machine, but it ismade with some common movements and components found in a real one. The system is composedof four actuators. The actuators A, B and C are double acting and D-single acting. Actuator A advances and stays in specified posi

38、tion till the end of the cycle, it could work fixing an object tothe next action for example (Fig. 5) , it is the first step. WhenA reaches the end position, actuator C starts his work together with B, making as manycycles as possible during the advancing of B. It depends on how fast actuator B is a

39、dvancing; the speed is regulated by a flowing control valve. It wasthe second step. B and Care examples of actuators working together, while B pushes an object slowly, C repeats its work for some time.hip 1 Linu, dijirfjiit ct B. ,： miJ I When B reaches the final position, C stops immediately its cy

40、cle 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

41、 a hole on the object.When D reaches the initial position, A and B return too, it is the fifth step.Fig. 6 shows the first part of the designing process where all the movementsof each step should be defined 2. (A+) meansthat the actuator A moves to the advanced position and (A - ) to the initial pos

42、ition. The movements that happen at the same time are joined together in the same step. The system has five steps.HiUM 4JIFig 6 Svp x|u：ncv A. K C aid I Zak-These two representations of the system (Figs. 5 and 6) together are enough to describe correctly all the sequence. With them is possible to de

43、sign the whole control circuit with the necessary logic components. But till this time, it is not a complete system, because it is missing someauxiliary elements that are not included in this draws because they work in parallel with the main sequence.These auxiliary elements give more function to th

44、e 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

45、as a reset or emergency buttons.The next Figs. 7 and 8 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.Tuo Mjri buipns一_ 一 Au(p Shniul arcuil l

46、 ircutLFig. 7. ElttJlrik diMnnul Uu aanpk.f聃科“门 一一一 Mjdus! ckraii . * . * HztsirvwiI r.1 耳 I k Jik di*般曜n - I IkThe 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 s

47、tart the process, reducing the risk of accidents.6. Changing the example to a user programIn 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

48、a real application. But, as explained above, using a PLC or this specific controller, the control becomeseasier and the complexity can be increase also.Table 2 shows a resume of the elements that are necessary to control the presented example.With the time diagram, the step sequence and the elements

49、 of the system described in Table 2 and Figs. 5 and 6 it is possible to create the configuration of the steps that can be sent to the controller (Tables 3 and 4).While using a conventional PLC, the user should pay attention to the logic of the circuit when drawing the electric diagram on the interfa

50、ce (Figs. 7 and 8), using the programmable controller, described in this work, the user must know only the concept o f the method and program only the configuration of each step.2RoquiTiTiXFli、I lb,l iUtji1 LFikd mpiJtyildn7654321(1tpclfeiO?s OS( N03J2)1(XIX1 Y：2 Y34YS6Y7It meansthat, with a convent

51、ional PLC, the user must draw the relationbetween 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 logic74 ar452I01%调尿父)叩Juu口。0u0uil vJ t1111111t3 FrluCl101I0讣diO%1QCl01QotyAVQa口qo串o口

52、印41531卬上UClu(1(11211百11)11I1(N hTT ra(10(1uJuHi(11u11(IattxXKl9i(k10y0ua1(1与1卬J(J(ka11fl01a4dMl1I1i11Ii11 b120iu0(1ail iJLKI1J1u11uU.H阳1JU口u口QCl(1unU口u口0uuQ1214utJ111IiUUEnaa1u0(10IIU4IIK口u1III1I0u(i0J(1()017胤2(1Sl可50(Ia000(10Ud剧21ij111I1,1 Jr 1Uo11u0u1 la |JJu3a1n1(1aiKSJKuua0u0uu25The new programm

53、ing 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: mask for the

54、 inputs;3-byte: value expected on the inputs;4-byte: value for the outputs;5-byte: value for the extra function.thisTable 5 shows how the user program is saved inside the controller, is the program that describes the control of the example shown before.The sequence can be defined by 25 bytes. These

55、bytes can be divided in five strings with 5 bytes each that define each step of the sequence (Figs. 9 and 10).7. ConclusionThe controller developed for this work (Fig. 11) shows that it is possible to create a very useful programmable controller based on microcontroller. External memories or externa

56、l 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 co