科技英语翻译

1、 科技英语2 学号：0645503122 姓名：刘琉 班级：08电气1班 DC Motor Closed Loop Control SystemOne of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC).Prior to the advent of NC, all machine tools were manual operated and controlled. Among the many limitations assoc

2、iated with manual control machine tools, perhaps none is more prominent than the limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control

3、of machine tools. Numerical control means the control of machine tools and other manufacturing systems though the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes a program that issues operational instructions to the machine tool, for a

4、 machine tool to be numerically controlled; it must be interfaced with a device for accepting and decoding the p2ogrammed instructions, known as a reader. Numerical control was developed to overcome the limitation of human operator, and it has done so. Numerical control machines are more accurate th

5、an manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:Electrical discharge machining.Laser cutting.Electron beam welding.Nu

6、merical control has also made machine tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide variety of par4s, each involving an assortment of undertake the production of products that would not have been feasible from an economic perspect

7、ive using manually controlled machine tools and processes.Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U.S Air Force .In its earliest stages , NC machi

8、nes were able to make straight cuts efficiently and effectively.However, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter is the straight lines making up the step, the smoother is 4he curv

9、e . Each line segment in the steps had to be calculated.This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the neces

10、sary motions. The development of the APT language was a major step forward in the further development of NC technology. The original NC system were vastly different from those used punched paper , which was later to replaced by magnetic plastic tape .A tape reader was used to interpret the instructi

11、ons written on the tape for the machine .Together, all /f this represented giant step forward in the control of machine tools . However, there were a number of problems with NC at this point in its development.A major problem was the fragility of the punched paper tape medium. It was common for the

12、paper containing the programmed instructions to break or tear during a machining process, This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instructions had to rerun thought the reader . If it was necessar

13、y to produce 100 copies of a given part , it was also necessary to run the paper tape thought the reader 100 separate times . Fragile paper tapes simply could not withstand the rigors of shop floor environment and this kind of repeated use.This led to the development of a special magnetic tape. Wher

14、eas the paper tape carried the programmed instructions as a series of holes punched in the tape, the This most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it was neces

15、sary to interrupt machining operations and make a new tape. It was also still necessary to run the tape thought the reader as many times as there were parts to be produced. Fortunately, computer technology become a reality and soon solved the problems of NC, associated with punched paper and plastic

16、 tape.The development of a concept known as numerical control (DNC) solve the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions . In direct numerical control, machine tools are tied, via a data transmis

17、sion link, to a host computer and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitation as all technologies that depend on a host computer. When

18、the host computer goes down, the machine tools also experience down time. This problem led to the development of computer numerical control.The development of the microprocessor allowed for the development of programmable logic controllers (PLC) and microcomputers. These two technologies allowed for

19、 the development of computer numerical control (CNC).With CNC, each machine tool has a PLC or a microcomputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. CNC solved the problems associated downtime of the host computer, but it introduced

20、 another problem known as data management. The same program might be loaded on ten different microcomputers with no communication among them. This problem is in the process of being solved by local area networks that connect Digital Signal ProcessorsThere are numerous situations where analog signals

21、 to be processed in many ways, like filtering and spectral analysis, Designing analog hardware to perform these functions is possible but has become less and practical, due to increased performance requirements, flexibility needs, and the need to cut down on development/testing time .It is in other

22、words difficult pm design analog hardware analysis of signals.The act of sampling an signal into the hat are specialized for embedded signal processing operations , and such a processor is called a DSP, which stands for Digital Signal Processor . Today there are hundreds of DSP families from as many

23、 manufacturers, each one designed for a particular price/performance/usage group. Many of the largest manufacturers, like Texas Instruments and Motorola, offer both specialized DSPs for certain fields like motor-control or modems, and general high-performance DSPs that can perform broad ranges of pr

24、ocessing tasks. Development kits an software are also available , and there are companies making software development tools for DSPs that allows the programmer to implement complex processing algorithms using simple “drag n drop” methodologies.DSPs more or less fall into two categories depending on

25、the underlying architecture-fixed-point and floating-point. The fixed-point devices generally operate on 16-bit words, while the floating-point devices operate on 32-40 bits floating-point words. Needless to say , the fixed-point devices are generally cheaper . Another important architectural differ

26、ence is that fixed-point processors tend to have an accumulator architecture, with only one “general purpose” register , making them quite tricky to program and more importantly ,making C-compilers inherently inefficient. Floating-point DSPs behave more like common general-purpose CPUs, with registe

27、r-files.There are thousands of different DSPs on the market, and it is difficult task finding the most suitable DSP for a project. The best way is probably to set up a constraint and wish list, and try to compare the processors from the biggest manufacturers against it.The “big four” manufacturers o

28、f DSPs: Texas Instruments, Motorola, AT&T and Analog Devices.Digital-to-analog conversionIn the case of MPEG-Audio decoding, digital compressed data is fed into the DSP which performs the decoding, then the decoded samples have to be converted back into the analog domain, and the resulting signal fe

29、d an amplifier or similar audio equipment. This digital to analog conversion (DCA) is performed by a circuit with the same name & Different DCAs provide different performance and quality , as measured by THD (Total harmonic distortion ), number of bits, linearity , speed, filter characteristics and

30、other things.The TMS320 family DQP of Texas InstrumentsThe TLS320family consists of fixed-point, floating-point, multiprocessor digital signal processors (DSPs) , and foxed-point DSP controllers. TMS320 DSP have an architecture designed specifically for real-time signal processing. The F/C240 is a n

31、umber of theC2000DSP platform, and is optimized for control applications. TheC24x series of DSP controllers combines this real-time processing capability with controller peripherals to create an ideal solution for control system applications. The following characteristics make the TMS320 family the

32、right choice for a wide range of processing applications:- Very flexible instruction set- Inherent operational flexibility -High-speed performance-Innovative parallel architecture-Cost effectivenessDevices within a generation of the TMS320 family have the same CPU structure but different on-chip mem

33、ory and peripheral configurations. Spin-off devices use new combinations of On-chip memory and peripherals to satisfy a wide range of needs in the worldwide electronics market. By integrating memory and peripherals onto a single chip , TMS320 devices reduce system costs and save circuit board space.

34、The 16-bit ,fixed-point DSP core of the C24x devices provides analog designers a digital solution that does not sacrifice the precision and performance of their system performance can be enhanced through the use of advanced control algorithms for techniques such as adaptive control , Kaman filtering

35、 , and state control. The C24x DSP controller offer reliability and programmability. Analog control systems, on the other hand, are hardwired solutions and can experience performance degradation due to aging, component tolerance, and drift.The high-speed central processing unit (CPU) allows the digi

36、tal designer to process algorithms in real time rather than approximate results with look-up tables. The instruction set of these DSP controllers, which incorporates both signal processing instructions and general-purpose control functions, coupled with the extensive development time and provides th

37、e same ease of use as traditional 8-and 16-bit microcontrollers. The instruction set also allows you to retain your software investment when moving from other general-purposeC2xx generation, source code compatible with theC2x generation, and upwardly source code compatible with the C5x generation of

38、 DSPs from Texas Instruments.The C24x architecture is also well-suited for processing control signals. It uses a 16-bit word length along with 32-bit registers for storing intermediate results, and has two hardware shifters available to scale numbers independently of the CPU. This combination minimi

39、zes quantization and truncation errors, and increases p2ocessing power for additional functions. Such functions might include a notch filter that could cancel mechanical resonances in a system or an estimation technique that could eliminate state sensors in a system.The C24xDSP controllers take adva

40、ntage of an set of peripheral functions that allow Texas Instruments to quickly configure various series members for different price/ performance points or for application optimization.This library of both digital and mixed-signal peripherals includes:-Timers-Serial communications ports (SCI,SPI)-An

41、alog-to-digital converters (ADC)-Event manager-System protection, such as low-voltage and watchdog timerThe DSP controller peripheral library is continually growing and changing to suit the of tomorrows embedded control marketplace.The TMS320F/C240 is the first standard device introduced in the 24x

42、series of DSP controllers. It sets the standard for a single-chip digital motor controller. The 240 can execute 20 MIPS. Almost all instructions are executed in a simple cycle of 50 ns . This high performance allows real-time execution of very comple8 control algorithms, such as adaptive control and

43、 Kaman filters. Very high sampling rates can also be used to minimize loop delays.The 240 has the architectural features necessary for high-speed signal processing and digital control functions, and it has the peripherals needed to provide a single-chip solution for motor control applications. The 2

44、40 is manufactured using submicron CMOS technology, achieving a log power dissipation rating. Also included are several power-down modes for further power savings. Some applications that benefit from the advanced processing power of the 240 include: -Industrial motor drives-Power inverters and contr

45、ollers-Automotive systems, such as electronic power steering, antilock brakes, and climate control-Appliance and HVAC blower/ compressor motor controls-Printers, copiers, and other office products-Tape drives, magnetic optical drives, and other mass storage products-Robotic and CNC milling machinesT

46、o function as a system manager, a DSP must have robust on-chip I/O and other peripherals. The event manager of the 240 is unlike any other available on a DSP . This application-optimized peripheral unit, coupled with the high performance DSP core, enables the use of advanced control techniques for h

47、igh-precision and high-efficiency full variable-speed control of all motor types. Include in the event manager are special pulse-width modulation (PWM) generation functions, such as a programmable dead-band function and a space vector PWM state machine for 3-phase motors that provides state-of-the-a

48、rt maximum efficiency in the switching of power transistors.There independent up down timers, each with its own compare register, support the generation of asymmetric (no centered) as well as symmetric (centered) PWM waveforms.Open-Loop and Closed-Loop ControlOpen-loop Control SystemsThe word automa

49、tic implies that there is a certain amount of sophistication in the control system. By automatic, it generally means that the system is usually capable of adapting to a variety of operating conditions and is able to respond to a class of inputs satisfactorily. However, not any type of control system

50、 has the automatic feature. Usually, the automatic feature is achieved by feed.g the feedback structure, it is called an open-loop system , which is the simplest and most economical type of control system. Inaccuracy lies in the fact that one may not know the exact characteristics of the further, wh

51、ich has a definite bearing on the indoor temperature. This Alco points to an important disadvantage of the performance of an open -loop control system, in that the system is not capable of adapting to variations in environmental conditions or to external disturbances. In the case of the furnace cont

52、rol, perhaps an experienced person can provide control for a certain desired temperature in the house; but id the doors or windows are opened or closed intermittently during the operating period, the final temperature inside the house will not be accurately regulated by the open-loop control.An elec

53、tric washing machine is another typical example of an open-loop system, because the amount of wash time is entirely determined by the judgment and estimation of the human operator. A true automatic electric washing machine should have the means of checking the cleanliness of the clothes continuously

54、 and turn misted off when the desired devised of cleanliness is reached.Closed-Loop Control SystemsWhat is missing in the open-loop control system for more accurate and more adaptable control is a link or feedback from the output to the input of the system . In order to obtain more accurate control,

55、 the controlled signal c(t) must be fed back and compared with the reference input , and an actuating signal proportional to the difference of the output and the input must be sent through the system to correct the error. A system with one or more feedback pat(s like that just described is called a

56、closed-loop system. human being are probably the most complex and sophisticated feedback control system in existence. A human being may be considered to be a control system with many inputs and outputs, capable of carrying out highly complex operations.To illustrate the human being as a feedback con

57、trol system, let us consider that the objective is to reach for an object on perform the task. The eyes serve as a sensing device which feeds back continuously the position of the hand. The distance between the hand and the object is the error, which is eventually brought to zero as the hand reached

58、 the object. This is a typical example of closed-loop control. However, if one is told to reach for the object and then is blindfolded, one can only reach toward the object by estimating its exact position. It is as anther illustrative example of a closed-loop control system, shows the block diagram of the rudder control system of the basic aliments and the blocs diagram of a closed-loop control system are shown in fig. In general, the configuration of a feedback control system may not be constrained to that of fig &. In complex systems there may be multit