输送机外文翻译--生产自动化（外文原文+中文翻译.doc

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1、生产自动化毕业论文中英文资料外文翻译文献外文资料：Production AutomationCharles L. Philips, Royce D. Harbor. Feedback Control Systems. Prentic Hall, Inc.2000Abstract:Automation is a widely used term in manufacturing. In this context, automation can be defined as a technology concerned with the application of mechanical, elec

2、tronic, and computer-based systems to operate and control production. Examples of this techno logy include: Automatic machine tools to process parts. Automated transfer lines and similar sequential production systems. Automatic assembly machines. Industrial robots. Automatic material handling and st

3、orage systems. Automated inspection systems for quality control. Feedback control and computer process control. Computer systems that automate procedures for planning, data collection, and decision making to support manufacturing activities.Keywords: Automation manufacturing mechanical computerAutom

4、ated production systems can be classified into two basic categories: fixed automation and programmable automation.Fixed AutomationFixed automation is what Harder was referring to when he coined the word automation. Fixed automation refers to production systems in which the sequence of processing or

5、assembly operations is fixed by the equipment configuration and cannot be readily changed without altering the equipment. Although each operation in the sequence is usually simple, the integration and coordination of many simple operations into a single system makes fixed automation complex. Typical

6、 features of fixed automation include 1. high initial investment for custom-engineered equipment, 2. high production rates, 3. application to products in which high quantities are to be produced, and 4. relative inflexibility in accommodating product changes.Fixed automation is economically justifia

7、ble for products with high demand rates. The high initial investment in the equipment can be divided over a large number of units, perhaps millions, thus making the unit cost low compared with alternative methods of production. Examples of fixed automation include transfer lines for machining, dial

8、indexing machines, and automated assembly machines. Much of the technology in fixed automation was developed in the automobile industry; the transfer line (dating to about (1920) is an example.Programmable AutomationFor programmable automation, the equipment is designed in such a way that the sequen

9、ce of production operations is controlled by a program, i. e., a set of coded instructions that can be read and interpreted by the system. Thus the operation sequence can be readily changed to permit different product configurations to be produced on the same equipment. Some of the features that cha

10、racterize programmable automation include 1. high investment in general-purpose programmable equipment, 2. lower production rates than fixed automation, 3. flexibility to deal with changes in product configuration, and 4. suited to low and / or medium production of similar products or parts (e. g. p

11、art families). Examples of programmable automation include numerically controlled machine tools, industrial robots, and programmable logic controllers.Programmable production systems are often used to produce parts or products in batches. They are especially appropriate when repeat orders for batche

12、s of the same product are expected. To produce each batch of a new product, the system must be programmed with the set of machine instructions that correspond to that product. The physical setup of the equipment must also be changed; special fixtures must be attached to the machine, and the appropri

13、ate tools must be loaded. This changeover procedure can be time-consuming. As a result, the usual production cycle for a given batch includes 1. a (3 period during which the setup and reprogramming is accomplished and 2. a period in which the batch is processed. The setup-reprogramming period consti

14、tutes nonproductive time of the automated system.The economics of programmable automation require that as the setup-reprogramming time increases, the production batch size must be made larger so as to spread the cost of lost production time over a larger number of units. Conversely, if setup and rep

15、rogramming time can be reduced to zero, the batch size can be reduced to one. This is the theoretical basis for flexible automation, an extension of programmable automation. A flexible automated system is one that is capable of producing a variety of products (or parts) with minimal lost time for ch

16、angeovers from one product to the next. The time toreprogram the system and alter the physical setup is minimal and results in virtually no lost production time. Consequently, the system is capable of producing various combinations and schedules of products in a continuous flow, rather than batch pr

17、oduction with interruptions between batches. The features of flexible automation are 1. high investment for a custom-engineered system, 2. continuous production of mixtures of products, 3. ability to change product mix to accommodate changes in demand rates for the different products made, 4. medium

18、 production rates, and 5- flexibility to deal with product design variations. Flexible automated production systems operate in practice by one or more of the following approaches: 1. using part family concepts, by which the parts made on the system are limited in variety; 2. reprogramming the system

19、 in advance and /or off-line, so that reprogramming does not interrupt production; 3. downloading existing programs to the system to produce previously made parts for which programs are already prepared;) 4. using quick-change fixtures so that physical setup time is minimized; 5. using a family of f

20、ixtures that have been designed for a limited number of part styles; and 6. equipping the system with a large number of quick-change tools that include the variety of processing operations needed to produce the part family. For these approaches to be successful, the variation in the part styles prod

21、uced on a flexible automated production system is usually) more limited than a batch-type programmable automation system. Examples of flexible automation are the flexible manufacturing systems for performing machining operations that date back to the late 1960s.Automation StrategiesA number of funda

22、mental strategies exist for improving productivity in manufacturing operations. These strategies often involve the use of automation technology and are, therefore, called automation strategies. Indicating the likely effects of each strategy on operating factors such as cycle time, nonproductive time

23、, manufacturing lead time, and other production parameters.Numerical controlNumerical control (often abbreviated NC) can be defined as a form of programmable automation in which the process is controlled by numbers, letters, and symbols. In NC, the numbers form a program of instructions designed for

24、 a particular workpart or job. When the job changes, the program of instructions is changed. This capability to change the program for each new job is what gives NC its flexibility. It is much easier to write new programs than to make major changes in the production equipment.NC equipment is used in

25、 all areas of metal parts fabrication and comprises roughly 15% of the modern machine tools in industry today. Since numerically controlled machines are considerably more expensive than their conventional counterparts, the asset value of industrial NC machine tools is proportionally much larger than

26、 their numbers. Equipment utilizing numerical control has been designed to perform such diverse operations as drilling, milling, turning, grinding, sheet metal press working, spot welding, arc welding, riveting, assembly, drafting, inspection, and parts handling. And this is by no means a complete l

27、ist. Numerical control should be considered as a possible mode of controlling the operation for any production situation possessing the following characteristics: 1. Similar workparts in terms of raw material (e. g., metal stock for machining).2. The workparts are produced in various sizes and geome

28、tries.3. The workparts are produced in batches of small to medium-sized quantities.4. A sequence of similar processing steps is required to complete the operation on each workpiece.Many machining jobs meet these conditions. The machined workparts are metal, they are specified in many different sizes

29、 and shapes, and most machined parts produced in industry today are made in small to medium-size lot sizes. To produce each part, a sequence of drilling operations may be required, or a series of turning or milling operations. The suitability of NC for these kinds of jobs is the reason for the treme

30、ndous growth of numerical control in the metalworking industry over the last 25 years.Basic Components of an NC SystemAn operational numerical control system consists of the following three basic components:1. Program of instructions.2. Controller unit, also called machine control unit (MCU).3. Mach

31、ine tool or other controlled process.The general relationship among the three components is illustrated. The program of instructions serves as the input to the controller unit, which in turn commands) the machine tool or other process to be controlled.Program of instructionsThe program of instructio

32、ns is the detailed step-by-step set of directions which tell the Wm machine tool what to do. It is coded in numerical or symbolic form on some type of input medium that can be interpreted by the controller unit. The most common input medium is i-inch-wide punched tape. Over the years, other forms of

33、 input media have (been used, including punched cards, magnetic tape, and even 35-mm motion picture film.There are two other methods of input to the NC system which should be mentioned. The first is by manual entry of instructional data to the controller unit. This is time-consuming and is rarely us

34、ed except as an auxiliary means of control or when only one or a very limited number of parts are to be made. The second method of input is by means of a direct link with a computer. This is called direct numerical control, or DNC.The program of instructions is prepared by someone called a part prog

35、rammer. The programmers job is to provide a set of detailed instructions by which the sequence of processing steps is to be performed. For a machining operation, the processing steps 4 involve the relative movement of the machine tool table and the cutting tool.Controller unitThe second basic compon

36、ent of the NC system is the controller unit. This consists of the electronics and hardware that read and interpret the program of instructions and convert it into mechanical actions of the machine tool. The typical elements of the controller unit include the tape reader, a data buffer, signal output

37、 channels to the machine tool, feedback channels from the machine tool, and the sequence controls to coordinate the overall operation of the foregoing elements.The tape reader is an electrical-mechanical device for winding and reading the punched tape containing the program of instructions. The data

38、 contained on the tape are read into the data buffer. The purpose of this device is to store the input instructions in logical blocks of information. A block of information usually represents one complete step in the sequence of processing elements. For example, one block may be the data required to

39、 move the machine table to a certain position and drill a hole at that location.The signal output channels are connected to the servomotors and other controls in the machine tool. Through these channels, the instructions are sent to the machine tool from the controller unit. To make certain that the

40、 instructions have been properly executed by the machine, feedback data are sent back to the controller via the feedback channels. The most important function of this return loop is to assure that the table and workpart have $ been properly located with respect to the tool. Most NC machine tools in

41、use today are provided with position feedback controls for this purpose and are referred to as closed-loop systems. However, in recent years there has been a growth in the use of open-loop systems, which do not make use of feedback signals to the controller unit. The advocates of the open-loop conce

42、pt claim that the reliability of the system is great enough that feedback controls are not needed and are an unnecessary extra cost.Sequence controls coordinate the activities of the other elements of the controller unit. The tape reader is actuated to read data into the buffer from the tape, signal

43、s are sent to and from the machine tool, and so on. These types of operations must be synchronized and this is the function of the sequence controls.Another element of the NC system, which may be physically part of the controller unit or part of the machine tool, is the control panel. The control pa

44、nel or control console contains the dials and switches by which the machine operator runs the NC system. It may also contain data displays to provide information to the operator. Although the NC system is an automatic system, the human operator is still needed to turn the machine on and off, to chan

45、ge tools (some NC systems have automatic tool changers), to load and unload the machine, and to perform various other duties. To be able to discharge these duties, the operator must be able to control the system, and this is done through the control panel.Machine toolThe third basic component of an

46、NC system is the machine tool or other controlled process. It is the part of the NC system which performs useful work. In the most common example of an NC system, one designed to perform machining operations, the machine tool consists of the worktable and spindle as well as the motors and controls n

47、ecessary to drive them. It also includes the cutting tools, work fixtures, and other auxiliary equipment needed in the machining operation.Transfer MachinesThe highest degree of automation obtainable with special-purpose, multifunction machines is achieved by using transfer machines. Transfer machin

48、es are essentially a combination of individual workstations arranged in the required sequence, connected by work transfer devices, and integrated with interlocked controls. Workpieces are automatically transferred between the stations, which are equipped with horizontal, vertical, or angular units t

49、o perform machining, gagging, workpiece repositioning, assembling, washing, or other operations. The two major classes of transfer machines are rotary and in-line types.An important advantage of transfer machines is that they permit the maximum number of operations to be performed simultaneously. There is relatively no limitation on (the number of workpiece surfaces or planes that can be machined, since devices can be interposed in transfer machin