毕业设计-外文原文(4万字符)

1、.编号：毕业设计外文翻译（原文）院 （系）：电子工程与自动化学院专业：测控技术与仪器学生姓名：李 XX学号：XXX指导教师单位：电子工程与自动化学院指导教师：XXX职称：XXX2013 年5 月 20 日.Information ControlAutomatic ControlAutomatic control has played a vital role in the advance of engineering and science. In addition to its extreme importance in space-vehicle systems, missile-guid

2、ance systems, robotic systems, and the like, automatic control has become an important and integral part of modern manufacturing and industrial processes. For example, automatic control is essential in the numerical control of machine tools in the manufacturing industries, in the design of autopilot

3、 systems in the aerospaceindustries, and in the design of cars and trucks in the automobile industries. It is also essential in such industrial operations as controlling pressure, temperature, humidity, viscosity, and flow in the process industries.Since advances in the theory and practice of automa

4、tic control provide the means for attaining optimal performance of dynamic systems, improving productivity, relieving the drudgery of many routine repetitive manual operations, and more, most engineers and scientists must now have a good understanding of this field.Control engineering is based on th

5、e foundations of feedback theory and linear system analysis, and it integrates the concepts of network theory and communication theory. Therefore control engineering is not limited to any engineering discipline but is equally applicable to aeronautical, chemical, mechanical, environmental, civil, an

6、d electrical engineering. For example, a control system often includes electrical, mechanical, and chemical components. Furthermore, as the understanding of the dynamics of business, social, and political systems increases, the ability to control these systems will also increase.A control system is

7、an interconnection of components forming a system configuration that will provide a desired system response. The basis for analysis of a system is the foundation provided by linear system theory, which assumes a cause-effect relationship for the components of a system. Therefore a component or proce

8、ss to be controlled can be represented by a block, as shown in Figure 8.1. The input-output relationship represents the cause-and-effect relationship of the process, which in turn represents a processing of the input signal to provide an output signal variable, often with a power amplification.In ge

9、neral, control systems can be categorized as being either open-loop or closed loop. The distinguishing feature between these two types of control systems is the use of.feedback comparison for closed-loop operation.1Open-loop Control SystemAn open-loop control system utilizes a controller or control

10、actuator to obtain the desired response, as shown in Figure 8.2. An open-loop system is a system without feedback, simplest form of controlling devices. Figure 8.3 illustrates a simple tank-level control system. We wish to hold the tank level h within reasonable acceptable limits even though the out

11、let flow through value V1 is varied. This can be achieved by irregular manual adjustment of the inlet flow rate by valve V2. The system is not a precision system,as it does not have the capability of accurately measuring the output flow rate through valve V1 ,the input flow rate through valve V2, or

12、 the tank level. Figure 8.4 shows the simple relationship that exists in this system between the input (the desired tank level) and the output (the actual tank level). This control system does not have any feedback comparison,and the term open loop is used to describe this absence.InputProcessOutput

13、DisireActuatingouputProcessOuputdeviceresponseFigure 8.1 Process to be controlledFigure 8.2 An open-loop systemv2v1hInput(desiredControl system(valueOutput(actualtank level)v2 and operator)tank level)Figure 8.3Tank-level control systemFigure 8.4 Tank-level control system black diagram2Closed-loop Co

14、ntrol SystemIn contrast to an open-loop control system, a closed-loop control system utilizes an additional measure of the actual output to compare the actual output with the desired output response. The measure of the output is called the feedback signal. A simple closed-loop feedback control syste

15、m is shown in Figure 8.5. A feedback control system is a control system that tends to maintain a prescribed relationship of one system variable to another by comparing functions of these variables and using the difference as a means of control.Desire outputComparisonControllerProcessOutputresponseMe

16、asurementFigure 8.5Close-loop control systemClosed-loop control systems derive their valuable accurate reproduction of the input from feedback comparison. An error detector derives a signal proportional to the differences between the input and outputThe closed-loop control system drives the output u

17、ntil it equals the input and the error is zeroAny differences between the actual and desired output will be automatically corrected in a closed-loop control system Through proper design the system can be made relatively independent of secondary inputs and changes in component characteristicsFigure 8

18、.6 illustrates an automatic tank-level control version of the system shown in Figure 8.3. It can maintain the desired tank level h within quite accurate tolerances even through the output flow rate through value V1 is varied. If the tank level is not correct,an error voltage is developed This is amp

19、lified and applied to a motor drive that adjusts value V2 in order to restore the desired tank level by adjusting the inlet flow rate A block diagram analogous to this system is shown in Figure 8.7. Because feedback comparison is present,the term closed-loop is used to describe the systems operation

20、.v2+vFloat-vv1hErrorPowerMotoramplifierdriveFigure 8.6Automatic tank-level control systemInput(desired +ErrorPowerMotorTankOutput(actualtank level)amplifierdrivetank level)-FloatFigure 8.7Black diagram of automatic tank-level control system.Due to the increasing complexity of the system under contro

21、l and the interest in achieving optimum performance, the importance of control system engineering has grown in the past decade. Furthermore, as the system become more complex, the interrelationship of many controlled variables must be considered in the control scheme. A block diagram depicting a mul

22、tivariable control system is shown in Figure 8.8.The introduction of feedback enables us to control a desired output and can improve accuracy, but it requires attention to the issue of stability of response.DesiredOutputoutputControllerProcessvariablesresponseMeasurementFigure 8.8Mulutivariable cont

23、rol systemMicrocontrollerA microcontroller (sometimes abbreviated C, uC or MCU) is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash is also often included on chip, as well as a typi

24、cally small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications.Microcontrollers are used in automatically controlled products and devices, such as automobile engine control system

25、s, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally contr

26、ol even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems.Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as 4 kHz, for low power consumption (milliwattsor mic

27、rowatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting.battery applicati

28、ons. Other microcontrollers may serve performance-critical roles, where they may need to act more like a digital signal processor (DSP), with higher clock speeds and power consumption.Embedded designA microcontroller can be considered a self-contained system with a processor, memory and peripherals

29、and can be used as an embedded system. The majority of microcontrollers in use today are embedded in other machinery, such as automobiles, telephones, appliances, and peripherals for computer systems. These are called embedded systems. While some embedded systems are very sophisticated, many have mi

30、nimal requirements for memory and program length, with no operating system, and low software complexity. Typical input and output devices include switches, relays, solenoids, LEDs, small or custom LCD displays, radio frequency devices, and sensors for data such as temperature, humidity, light level

31、etc. Embedded systems usually have no keyboard, screen, disks, printers, or other recognizable I/O devices of a personal computer, and may lack human interaction devices of any kind.1InterruptsMicrocontrollers must provide real time (predictable, though not necessarily fast) response to events in th

32、e embedded system they are controlling. When certain events occur, an interrupt system can signal the processor to suspend processing the currentinstruction sequence and to begin an interrupt service routine (ISR,or “ interrupt handler.”)The ISR will perform any processing required based on the sour

33、ce of the interrupt before returning to the original instruction sequence. Possible interrupt sources are device dependent, and often include events such as an internal timer overflow, completing an analog to digital conversion, a logic level change on an input such as from a button being pressed, a

34、nd data received on a communication link. Where power consumption is important as in battery operated devices, interrupts may also wake a microcontroller froma low power sleep state where the processor is halted until required to do something by aperipheral event.2ProgramsMicrocontroller programs mu

35、st fit in the available on-chip program memory, since it would be costly to provide a system with external, expandable, memory. Compilers and assemblers are used to convert high-level language and assembler language codes into a compact machine code for storage in the microcontroller s memory. Depen

36、ding on the.device, the program memory may be permanent, read-only memory that can only be programmed at the factory, or program memory may be field-alterable flash or erasable read-only memory.Higher integrationIn contrast to general-purpose CPUs, micro-controllers may not implement an external add

37、ress or data bus as they integrate RAM and non-volatile memory on the same chip as the CPU. Using fewer pins, the chip can be placed in a much smaller, cheaper package.Integrating the memory and other peripherals on a single chip and testing them as a unit increases the cost of that chip, but often

38、results in decreased net cost of the embedded system as a whole. Even if the cost of a CPU that has integrated peripherals is slightly more than the cost of a CPU and external peripherals, having fewer chips typically allows a smaller and cheaper circuit board, and reduces the labor required to asse

39、mble and test the circuit board.This integration drastically reduces the number of chips and the amount of wiring and circuit board space that would be needed to produce equivalent systems using separate chips. Furthermore, on low pin count devices in particular, each pin may interface to several in

40、ternal peripherals, with the pin function selected by software. This allows a part to be used in a wider variety of applications than if pins had dedicated functions. Micro-controllers have proved to be highly popular in embedded systems since their introduction in the 1970s.Some microcontrollers us

41、e a Harvard architecture: separate memory buses for instructions and data, allowing accessesto take place concurrently. Where a Harvard architecture is used, instruction words for the processor may be a different bit size than the length of internal memory and registers; for example: 12-bit instruct

42、ions used with 8-bit data registers.The decision of which peripheral to integrate is often difficult. The microcontroller vendors often trade operating frequencies and system design flexibility against time-to-market requirements from their customers and overall lower system cost. Manufacturers have

43、 to balance the need to minimize the chip size against additional functionality.Microcontroller architectures vary widely. Some designs include general-purpose microprocessor cores, with one or more ROM, RAM, or I/O functions integrated onto the.package. Other designs are purpose built for control a

44、pplications. A micro-controller instruction set usually has many instructions intended for bit-wise operations to make control programs more compact. For example, a general purpose processor might require several instructions to test a bit in a register and branch if the bit is set, where a micro-co

45、ntroller could have a single instruction to provide that commonly-required function.Microcontrollers typically do not have a math coprocessor, so floating point arithmetic is performed by software.Programming environmentsMicrocontrollers were originally programmed only in assembly language, but vari

46、ous high-level programming languages are now also in common use to target microcontrollers. These languages are either designed specially for the purpose, or versions of general purpose languages such as the C programming language. Compilers for general purpose languages will typically have some res

47、trictions as well as enhancements to better support the unique characteristics of microcontrollers. Some microcontrollers have environments to aid developing certain types of applications. Microcontroller vendors often make tools freely available to make it easier to adopt their hardware.Many microc

48、ontrollers are so quirky that they effectively require their own non-standard dialects of C, such as SDCC for the 8051, which prevent using standard tools (such as code libraries or static analysis tools) even for code unrelated to hardware features. Interpreters are often used to hide such low leve

49、l quirks.Interpreter firmware is also available for some microcontrollers. For example, BASIC on the early microcontrollers Intel 8052; BASIC and FORTH on the Zilog Z8 as well as some modern devices. Typically these interpreters support interactive programming.Simulators are available for some micro

50、controllers, such as in Microchip s MPLAB environment and the Revolution Education PICAXE range. These allow a developer to analyze what the behavior of the microcontroller and their program should be if they were using the actual part. A simulator will show the internal processor state and also tha

51、t of the outputs, as well as allowing input signals to be generated. While on the one hand most simulators will be limited from being unable to simulate much other hardware in a system, they can exercise conditions that may otherwise be hard to reproduce as well in.the physical implementation, and c

52、an be the quickest way to debug and analyze problems.Recent microcontrollers are often integrated with on-chip debug circuitry that when accessedby an in-circuit emulator via JTAG, allow debugging of the firmware with a debugger .Types of microcontrollersThere are several dozen microcontroller archi

53、tectures and vendors including:Parallax PropellerIntel 8051Silicon Laboratories Pipelined 8051 MicrocontrollersARMprocessors (frommany vendors) using ARM7or Cortex-M3cores aregenerally microcontrollersSTMicroelectronics STM8 (8-bit), ST10 (16-bit) and STM32 (32-bit)Atmel AVR (8-bit), AVR32 (32-bit),

54、 and AT91SAM (32-bit)Hitachi H8, Hitachi SuperH (32-bit)MIPS (32-bit PIC32)NEC V850 (32-bit)PowerPC ISEPSoC (Programmable System-on-Chip)Rabbit 2000 (8-bit)Texas Instruments Microcontrollers: TI MSP430 16-bit Microcontrollers, C2000 (32-bit), and Stellaris (32-bit)Toshiba TLCS-870 (8-bit/16-bit)and

55、many others, some of which are used in very narrow range of applications or are more like applications processors than microcontrollers. The microcontroller market is extremely fragmented, with numerous vendors, technologies, and markets. Note that many vendors sell (or have sold) multiple architect

56、ures.Examples of microcontrollers1Intel 8051The 8051 architecture provides many functions (CPU, RAM, ROM, I/O, interrupt logic, timer, etc.) in a single package.A new and particularly useful feature of the 8051 core was the inclusion of a.Boolean processing engine which allows bit-level boolean logic operations to be carried out directly and efficiently on internal registers and RAM. This critical feature helped cement the 8051s popularity in industrial