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1、精品_精品资料_应用于电气系统的可编程序掌握器此工程主要是讨论电气系统以及简洁有效的掌握气流发动机的程序和气流系统的状态.它的实践基础包括基于气流的专有掌握器、自动化设计、气流系统的掌握程序和基于微掌握器的电子设计.1. 简介使用电气技术的自动化系统主要由三个组成部分：发动机或马达,感应器 或按钮,状如花瓣的掌握零部件.现在,大部分的系统规律操作的掌握器都被 程序规律掌握器 表示主动器 A 向前推动,而 A- 表示返回到开头的位置.同时发生的运动在相同的步骤中被一起叠加.这个系统共有有五个步骤.图 6 A ,B ,C ,D 传动装置传动次序图5和6所表现的系统运行清晰的描述了全部序列.利用他们
2、我们可以用必需的规律语言设计整个的掌握线路.但是现在仍它仍不是一个完整的系统,由于它仍缺少一些帮助设施 .使用传统的 PLC的,如图 7,8所示,在绘制接口处的电图表时,要留意线路的规律.使用这种可编程的掌握器,使用者必需知道运行方法的观念并且规 划每个步骤的结构.那就是说,使用传统的 PLC,使用者清晰各个操作之间的关系.一般情形下,使用者可以在接口上运行一个模拟程序查找规律上的错误同之前所述的一 样,新的编程答应每一步骤的结构被分割.序列独自被定义,但每一步骤只被 输入和输出端描述.图9 A ,B 传动装置和传感器图10 C ,D 传动装置和传感器表 5 表现的是使用系统如何被贮存在掌握器
3、里,这在前文中也具体说明过.序列被 25个位元组所定义.这些位元组被分成5组,每一组描述系统运行的一个步骤. .Sensors and switches are plugged as inputs and the direct control valves for theactuators are plugged as outputs. An internal program executes all the logic necessary to the sequence of the movements, simulates other components like counter, ti
4、mer 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
5、PLC, that is possible to findon the market frommany 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 sy
6、stem and automation of buildings.Becauseof those characteristics, in some applications the PLC offers to much resourcesthat 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可编辑资料 - - - 欢迎下载精品_精
7、品资料_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,
8、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
9、 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
10、 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 hands2. Electro-pneumatic systemOn automation system one can find three basic components mentioned before, plus a logic circuit that controls the
11、system. An adequate technique is needed to project the logic circuit and integrate all the necessarycomponents to execute the sequence of movements properly.For a simple direct sequence of movement an intuitive method can be used 1, 5, but forindirect or more complex sequences the intuitioncan gener
12、ate 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 presentedmethod is called step-by-step or algorithmic 1, 5, it is valid for pneuma
13、tic 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.可编辑资料 - - - 欢迎下载精品_精品资料_The first part is to design those kinds of stand
14、ard circuits for each 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 circ
15、uits 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 controllerThe result of the method presented before is a sequenceof movements of the可编辑资料 - - - 欢迎下载精品_精品资料_actuator that is well def
16、ined 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
17、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
18、 the microcontroller and is executed the same way it was designed. The sequencesof 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 configu
19、rations and auxiliary functions of the step. After programming,thissequence ofstringsissaved insideofanon-volatilememoryofthe 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 ver
20、satile controller that is design for an specific area. A conventional PLC processthe 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 i
21、n 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, insid
22、e the program, movements that must be repeated for some time, but this problem can be solved with some external logic components. Another limitationis that the controller cannot be applied on systems that have no sequence. These limitations are a characteristic of the system that must be analyzed fo
23、r each application.4. Characteristics 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 s
24、ave all the configuration of the system and the sequence of steps. For the execution ofthemainprogram, itofferscomplete resources as timersand interruptions.The list of resources of the controller was created to explore all the capacity of可编辑资料 - - - 欢迎下载精品_精品资料_the microcontroller to make it as com
25、plete as possible. During the step, the program chooseshow to use the resourcesreading the configuration string of the step. This string has two bytes for digital inputs, one used as amask and the other one used as a value expected. One byte is used to configure the outputs value. One bytes more is
26、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 has also a display and some buttons that are used with an interactive menu to prog
27、ram the sequence of steps and other configurations.4.1. Interaction components For the real application the controller must have some elements to interact withthe final user and to offer a complete monitoring of the system resources that areavailable to the designer while creating the logic control
28、of the pneumatic system可编辑资料 - - - 欢迎下载精品_精品资料_Fig.3:.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 seque
29、nce 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 make the final application works property, a correct configuration to execute the steps in the right way is needed, but more then that it m
30、ust 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
31、 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 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. Wi