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1、附录附录1Programmable designed for electro-pneumatic systems controllerThis 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 pneumaticsystem. The
2、 project of a specifi c controller for pneumatic applicationsjoin the study of automation design and the control processing of pneumaticsystems with the electronic design based on microcontrollers to implementthe resources of the controller. 1. IntroductionThe automation systems that use electro-pne
3、umatic Technology are formed mainly by three kinds of elements: actuators or motors, sensors or buttonsand 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
4、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, simulatesOther components like counter,timer and control the status of the system.With the use of the PLC,the project wins a
5、gility,because it is possible to create and simulate the system as many times as needed.Therefore,timeCan be saved,risk of mistakes reduced and complexity can be increased usingThe same elements.A conventional PLC,that is possible to find on the market from many companies,offers many resources to co
6、ntrol 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 application of in the industry or even security system and automation of buildings.Because of those characteristics, in some applications th
7、e 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
8、 that can offer the exactly size and resources that the project needs3,4. This can be madeusing 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 thatcan be pro
9、grammed as a usual PLC and work with logic that can be changed. All these characteristics depend on what is needed and how much experiencethe designer has with developing an electronic circuit and firmware for microcontroller. But the main advantage of design the controller with the microcontroller
10、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 contro
11、l of the system stays at the designer hands.2. 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 neededto project the logic circuit and integrate all the necessary components to e
12、xecute the sequence of mo vements properly.For a simple direct sequence of movement an intuitive method can be used1,5, 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 th
13、e project, make a clean circuit, can eliminate occasional signal overlapping and redundant circuits. The presented method is called step-by-step or algorithmic1,5, 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 sys
14、tems based on standard circuits made for each change on the state of the actuators, these changes are called steps.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 is to connect the control elements that rece
15、ive signals from sensors, switches and the previous movements, and giv e the air or electricity to the supply lines of each step. In Figs. 1 and2 the standard circuits are drawn for pneumatic and electro-pneumatic system8. It is possible to see the relations with the previous and the next steps.3. T
16、he method applied inside the controllerhe 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 stan
17、dard 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 input
18、s 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 t
19、he configuration of one step of the process There are two bytes for the inputs, one byte forthe outputs and two more for the other configurationsand auxiliary functions of the step. After programming, this sequence of strings is saved inside of an on-volatile memory of the microcontroller, so they c
20、an be read and executedThe 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
21、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 a
22、fter 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
23、that the contro ller 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 controllerThe controller is based on the MICROCHIP microcontroller PIC16F877 6,7 with40 pins, and it has
24、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 the system and the sequence of steps. For the execution of the main program it offers complete resources as timers and inte
25、rruptions.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 input
26、s, 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 is256 bytes length that is enough to save the string of the steps, with this charac
27、teristic it is possible to save between48 steps（Table1）.The controller(Fig.3) 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 componentsFor the real application the controller must have some element
28、s 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(Fig.3): Interactive mode of work; function available on the main program for didactic purposes, the user gives the
29、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. SecurityTo
30、 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 vir
31、tual circ uits 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 time2. There are two inputs that work with interruption to get an immediate access to these functions. It is possible to configure t
32、he position, the buttons and the value of time-out of the system.4.3. User interfaceThe 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 th
33、e 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 compu
34、ter 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. 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 st
35、ep, 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. In Fig.4,a block diagram of micro controller main program is presented.5.
36、 Example of electro-pneumatic systemThe 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 an
37、d stays in specified position till the end of the cycle, it could work fixing an object to the next action for example(Fig. 5), 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 o
38、n 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, Crepeats its work for some time.When B reaches the final position, C stops immediately its cycle and com
39、es 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
40、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 movements of each step should be defined2. (A+)means that the actuator A moves to the advanced position and(A) to the initial position. The move
41、ments that happen at the same time are joined together in the same step. The system has five steps.These two representations of the system(Figs. 5 and6) together are enough to describe correctly all the sequence With them is possible to design the whole control circuit with the necessary logic compo
42、nents. 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; t
43、he 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 a nd 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. 7 and8 show
44、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.The auxiliary elements are included, like the automatic/manual switcher that permit a continuous wor
45、k 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 programIn the previous chapter, the electro-pneumatic circuits were presented, used to begin the study of the requires to control
46、 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.Table2 shows a resume of the elements that are necessary to
47、 control the presented exampleWith the time diagram, the step sequence and the elements of the system described in Table2 and Figs. 5 and6 it is possible to create the configuration of the steps that can be sent to the controller(Tables3 and4).While using a conventional PLC, the user should pay atte
48、ntion to the logic of the circuit when drawing the electric diagram on the interface(Figs. 7 and8), using the programmable controller, described 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
49、 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 logicThe 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 conf
