控制系统基础论文中英文资料外文翻译文献

控制系统基础论文中英文资料外文翻译文献

文献翻译

原文：

Numerical Control

One 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 associated 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 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 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 than 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:

1.Electrical discharge machining.

https://www.360docs.net/doc/1a71994.html,ser cutting.

3.Electron beam welding.

Numerical control has also made machine tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide variety of par 4s , each involving an assortment of undertake the production of products that would not have been feasible from an economic perspective 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 machines 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 the curve . 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 necessary 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 instructions written on the tape for the machine .Together, all of 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 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 necessary 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 . Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape , theThis most mportant 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 necessary 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 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 transmission 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 the host computer goes down , the machine tools also experience down time . This problem led to the development of computer numerical control.

The evelopment of the microprocessor allowed for the development of programmable logic controllers (PLC) and microcomputers . These two technologies allowed for 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 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 connectDigital ignal Processors.

There are numerous situations where analog signals 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 words difficult pm design analog hardware analysis of signals.

The act of sampling an signal into thehat are specialised 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 manufacturers, each one designed for a particular price/performance/usage group. Many of the largest manufacturers, like Texas Instruments and Motorola, offer both specialised DSP?s for certain fields like motor-control or modems ,and general high-performance SP?s that can erform broad ranges of processing tasks. Development kits an software are also available , and there are companies making software development tools for DSP?s that allows the programmer to implement complex processing algorithms using simple “drag …n? drop” methodologies.

DSP?s more or less fall into two categories depending on 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 difference 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 DSP?s behave more like common general-purpose CPU?s ,with register-files.

There are thousands of different DSP?s 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 wishlist, and try to compare the processors from the biggest manufacturers against it.

The “big four” manufacturers of DSP?s: Texas Instruments, Motorola, AT&T and Analog Devices.

Digital-to-analog conversion

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

The TMS320 family DQP of Texas Instruments

The TLS320family consists of fixed-point, floating-point, multiprocessor digital signal processors (DSP?s) , and foxed-point DSP controllers. TMS320 DSP have an architecture designed specifically for real-time signal processing . The F/C240 is a number of the?C2000DSP platform , and is optimized for control applications. The C24x 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 right choice for a wide range of processing applications:

--- Very flexible instruction set

--- Inherent operational flexibility

---High-speed performance

---Innovative parallel architecture

---Cost effectiveness

Devices within a generation of the TMS320 family have the same CPU structure but different on-chip memory 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.

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 , Kalman filtering , 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 digital 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 the 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-purpose C2xx generation ,source code compatible with the C2x generation , and upwardly source code compatible with the C5x generation of 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 minimizes 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 advantage 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)

---Analog-to-digital converters(ADC)

---Event manager

---System protection, such as low-voltage and watchdog timer

The DSP controller peripheral library is continually growing and changing to suit the of tomorrow?s e mbedded control marketplace.

The TMS320F/C240 is the first standard device introduced in the …24x 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 Kalman 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 240 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 controllers

---Automotive systems, such as electronic power steering , antilock brakes, and climate control

---Appliance and HV AC blower/ compressor motor controls

---Printers, copiers, and other office products

---Tape drives, magnetic optical drives, and other mass storage products

---Robotic and CNC milling machines

To 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 high-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-art maximum efficiency in the switching of power transistors.

There independent up down timers, each with it?s own compare register, support

the generation of asymmetric (noncentered) as well as symmetric (centered) PWM waveforms.

Open-Loop and Closed-Loop Control

Open-loop Control Systems

The word automatic 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 has the automatic feature. Usually , the automatic feature is achieved by feed.

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 ,which 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 conitions or to external disturbances. In the case of the furnace control, 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 electric 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 and turn itsedt off when the desired degised of cleanliness is reached.

Closed-Loop Control Systems

What 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 bontrol, 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 pats like that just described is called a 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 control system , let us consider that the objective is to reach for an object on aperform 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 reacher the object. This is a typical example of closed-loop control. However , if one is told to reach for the object and then is blindolded, 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 alements and the bloca 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 multitude of feedback loops and element blocks.

译文：

控制系统基础

数字控制机床常常重达上百吨，但却常常要求切削工具的定位精度达到0.002毫米。控制系统必须使刀具在遇到负载的情况下的进给速度高达每秒8厘米，而负载在给定的轨道上的变化非常之大。数控机床必须具有动态响应特性以便能够跟踪复杂的轮廓，具有最小的轨迹误差。很清楚，这些要求意味着控制系统必须与它所驱动的机械特性相匹配。

控制系统是一个通过控制能源流以及其他往来资源实现控制操作的组合设备。实际上，控制系统是由相关的子系统组成，这些子系统可以完成在传统机加工过程中由胜任的人员操纵的任务。

因此，数控机床的控制系统能代替及其操作员，更为重要的是甚至比做好的人操作还要更好。数字控制与它所替代的操作人员之间的一下操作十项类似的：

1.感测机床的当前状态；

2.做出完成动作所需要的逻辑判断；

3.向机床传达决定，驱动是党的机械装置；

4.具有储存信息的能力：指令、数据和逻辑判断的决定。

总之，机床控制系统是电子电路、感测元件和引导刀具沿预先确定的到运动的机械机构组成的组合体。

第七课数字控制

先进制造技术中的一个最基本的概念是数字控制（NC）。在数字技术出现之前，所有的机床都是由人工操纵和控制的。在与人控制的机床有关的很多局限性中，操作者的技能大概是最突出的问题。采用人工控制时，产品的质量直接与操作者的技能有关。数字控制代表了从人工控制机床走出来的第一步。

数字控制意味着采用预先录制的、存储的符号指令，控制机床和其他制造系统。一个数控技师的工作不是去操纵机床，而是编写能够发出机床操纵指令的程

序。对于一台数控机床，其上必须装有一个被称为阅读机的界面装置，用来接受和解译编程指令。

发展数控技术是为了克服人类操作者的局限性，而且它确实完成了这项工作。数控机床比人工操纵机床的精度更高，他们可以生产一致性更好的零件，它们更快，而且长期加工成本更低。数控技术的发展导致了制造工艺中其他几项新发明的产生：

1.电火花加工技术；

2.激光切割；

3.电子束焊接。

数字控制还使得机床比它们采用人工操纵的前辈们的用途更为广泛。一台数控机床可以自动生产很多种类的零件，每个零件都可以有不同的和复杂的加工过程。数控可使生产厂家承担哪些对于采用人工控制的机床和工艺来说，在经济上不划算的产品任务。

与许多先进技术一样，数控诞生于麻省理工学院的实验室中。数控这个概念是20世纪50年代在美国空军的资助下提出来的。在其最初的阶段，数控机床可以经济和有效地进行直线切割。

然而，曲线轨迹成为机床加工的一个问题，在编程时应该采用一系列的水平与竖直的台阶来生成曲线。构成台阶的每个线段越短，曲线就越光滑。台阶中的每个线段都必须经过计算。

在这个问题促使下，于1959年诞生了自动编程工具（APT）语言。这是一个专门适用于数控的编程语言，使用类似于英语的语句来定义零件的几何形状，描述切削刀具的现状和规定必要的运动。APT语言的研究和发展是在数控技术进一步发展过程中的一大进步。最初的数控系统与今天应用的数控系统是很大差别的。在那时的机床中，只有硬线逻辑电路。指令程序写在穿孔纸带上（它后来被塑料磁带所取代），采用带阅读机将写在纸带或磁带上的指令给机器翻译出来。所有这些共同构成了机床数字控制方面的巨大进步。然而，在数控发展的这个阶段中还存在着许多问题。

一个主要问题是穿孔纸带的易损坏性。在机械加工过程中，载有编程指令信息的纸带断裂和被撕坏是常见的事情。在机床上加工一个零件的这段连续时间

里，需要将载有程序指令的纸带放入阅读机中重新运行的情况使这个问题显得更加严重。如果需要制造100个某种零件，则应该将纸带分别通过阅读机100次。易损坏的纸带显然不能承受严酷的车间环境和这种重复使用。

这就导致了一种专门的塑料磁带的研制。在纸带上通过采用一系列的小孔来载有编程指令，而在塑料带上通过采用以一系列的磁点来载有编程指令。塑料带的强度比纸带的强度要高很多，这就可以解决常见的撕坏和断裂问题。然而，它仍然存在着两个问题。

其中最重要的一个问题是，对输入带中的指令进行修改是非常困难的，甚至是根本不可能的。即使对指令程序进行最微小的调整，也必须终端加工，制作一条新带。而且磁带通过阅读机的次数还必须与要加工的零件的个数相同。幸运的事，计算机技术的实际应用很快解决了数控技术中与穿孔纸带和塑料带有关的问题。

被称为直接数字控制（DNC）概念的发展消除了用纸袋作为程序指令的载体，从而解决了数字控制中纸带或塑料带所带来的问题。在直接数字控制中，几台机床通过数据传输线路连接到一台主机算计上。操纵这些机床所需要的程序都存储在这台主计算机中。当需要时，通过数据传输线路提供给每台机床。直接数字控制是在穿孔纸带和塑料带基础上的一大进步。然而，它也有着与其他依赖于主计算机的技术一样的局限性。当主计算机出现故障时，由其控制的所有机床都将停止工作。这个问题促使了计算机数字控制技术的产生。

微处理器的发展为可编程逻辑控制器和微型计算机的发展做好了准备。这两种技术为计算机数字控制（CNC）的发展打下了基础。采用（CNC）技术后，每台机床上都有一个可编程逻辑控制器或者微机对其进行数字控制。这可以使得程序被输入和存储在每台机器内部。它还可以在机床以外编制程序，并且将其下载到每台机床中。计算机数控解决了主计算机发生故障所带来的问题，但是它产生了另一个被称为数据管理的问题。同一个程序可能要分别装入十个相互之间没有通信联系的微机中。这个问题正在解决之中，它是通过采用局部区域网络将各个微机连接起来，以利于更好地进行数据管理。

第八课数字信号处理器

在很多情况下需要对模拟信号进行多种处理，例如滤波和谱分析。设计一个