机电工程英语PPTPART_TWO.ppt

1、PART TWO,16.1 Text 16.2 Words and Phrases 16.3 Complex Sentence Analysis 16.4 Exercise,Lesson 16 Product Test and Quality Control, 16.1 Text Product Test Product test can be thought of as the culmination of all process control work. It can also be thought of as a quality check of the inspection proc

2、ess itself. If the quality plan is adequate and carried out properly, then the products performance should have been verified and a total test is redundant. For this reason, a test of the completed product is often nothing more than a contractual requirement that must be performed before the custome

3、r accepts the product. But product test is also more than proving. And testing to whole is equal to the sum of the parts. 1It allows for gathering data that support the design theory of the product, for interpretations to be made for further improvements in design so that future products will be bet

4、ter than present ones, and for evaluation of design evolution toward better performance costs. In addition, it is a means of verifying design, since not all design parameters can be fully calculated or predicted. Product test engineers work closely with design engineers to provide useful data for te

5、sting. They must also work in close harmony with engineers all other phases of manufacturing. Not infrequently, product testing will turn up deficiencies in design that requires major revisions in manufacturing processes. This is particularly true if the company produces many prototypes and has shor

6、t production runs. Therefore, manufacturing engineers are as interested in product tests results as are design engineers. For complex products, product test becomes a very important part of the total process control function. It gives the company a high degree of confidence that the product will per

7、form as the customer expects it to, and this is a valuable marketing tool as it helps to establish the proper reputation with the customers., 16.1 Text Geometric Errors Geometric errors are defined here as errors in form of individual machine components (e.g., straightness of motion of a linear bear

8、ing). Geometric errors are concerned with the quasi-static accuracy of surface, which bear upon the moving relative of the surfaces. Geometric errors can be smooth and continuous (systematic) or they can exhibit hysteresis (e.g., backlash) or random behavior. 2Many factors affect geometric errors in

9、cluding: surface straightness (see Fig.16.1), surface roughness, bearing preload, kinematics versus elastic design principles and structural design philosophies.,Fig.16.1 Straightness Errors Caused by Surface Form and Finish Errors, 16.1 Text Fit and Tolerance Fit is defined as the relation resultin

10、g from the difference between the sizes of two mating parts. And tolerance is defined as the difference between the maximum limit and the minimum limit. The tolerance is also equal to the algebraic difference between the upper and lower deviations (see Fig.16.2).,Fig.16.2 Diagram Illustrating Basic

11、Size, Deviations and Tolerances, 16.1 Text Fit and Tolerance Depending upon the actual limits of the hole or shaft, a fit may be classified as follows: (1) Clearance fit is a fit that always provides a clearance between the mating parts. In this case, the tolerance zone of the hole is entirely above

12、 that of the shaft. (2) Interference fit is a fit that always provides interference between the mating parts. Here, the tolerance zone of the hole is entirely below that of the shaft. (3) Transition fit is a fit that may provides either a clearance or interference between the mating parts depending

13、on the actual dimensions of the finished products. A tolerance is designated by a letter (in some cases, two letters), a symbol, and a numerical symbol. Capital letters are used for holes and small letters for shafts. The letter symbol indicates the position of the zone of tolerance in relation to t

14、he zero line representing the basic size. The numerical symbol represents the value of this zone of tolerance and is called the grade or quality of tolerance. Both the position and the grade of tolerance are functions of the basic size. A size with tolerance is thus defined by its basic value follow

15、ed by a letter and a number, e.g., 20H7 or 20g6 In engineering drawing practice, the tolerance for hole and shaft is written a little above and little below the basic size, respectively. 3Similarly, a fit is indicated by the basic size common to both the mating components, followed by the appropriat

16、e symbols corresponding to each component, e.g., 16.1 Text Quality Planning This is the planning and strategy activity of process control, and is sometimes referred to as process planning or inspection planning. The engineers involved develop the plans for checking the adequacy of performance of sho

17、p operations to ensure that the final product performs as designed. Using plans and methods produced by measurement of productivity and work measurement (MP in this way quality planning can report to management whether quality levels are improving or declining. Quality status can be reported by stat

18、istically evaluating the numbers of deviations and their seriousness. This leads naturally to an evaluation of the cost of doing the repair work caused by the deviation. Repair work, which constitutes manufacturing losses, is an important measurement of organizational quality levels. Manufacturing l

19、osses are a significant measure of the adequacy of attention to detail of the operators and their foremen. High losses indicate a poorly managed operation. Quality planning engineers are responsible for setting the manufacturing losses, budgets, and measurements policy., 16.1 Text Quality Control Qu

20、ality control has traditionally been the liaison between manufacturing and design. This function interprets designs specifications for manufacturing and develops the quality plan to be integrated into manufacturing engineerings methods and planning instructions to operations. Quality control is also

21、 responsible for recommending to management what level of manufacturing losses (cost of mistakes in producing the product) can be tolerated. This is based on the complexity of the product design; specifically the degree of preciseness necessary in tolerances. Quality control traditionally monitors m

22、anufacturing losses by setting a negative budget that is not to be exceeded, and establishes routines for measurement and corrective action. Within the past decade or two, quality control has become increasingly involved with marketing and customers in establishing documentation systems to ensure gu

23、aranteed levels of product quality. This new role has led to the new title quality assurance, to differentiate it from traditional in-house quality control. Quality assurance strives through documentation of performance and characteristics at each stage of manufacture to ensure that the product will

24、 perform at the intended level. Whereas quality control is involved directly with manufacturing operations, quality assurance is involved with the customer support responsibilities generally found within the marketing function. Many industrial organizations have chosen to establish an independent qu

25、ality assurance sub-function within the manufacturing function and have placed the technical responsibilities of quality control, namely process control, within the manufacturing engineering organization., 16.2 Words and Phrases culmination kQlmi5neiFEn n. 顶点 contractual kEn5trAktjuEl adj. 契约的 defic

26、iency di5fiFEnsi n. 缺乏，不足 quasi-static 准静态的 hysteresis 7histE5ri:sis n. 滞后作用，物磁滞现象 clearance fit 间隙配合 interference fit 过盈配合 transition fit 过渡配合 liaison li(:)5eizB:n, -zEn n. 联络，(语音)连音, 16.3 Complex Sentence Analysis 1 It allows for gathering data that support the design theory of the product, for in

27、terpretations to be made for further improvements in design so that future products will be better than present ones, and for evaluation of design evolution toward better performance costs. it为形式主语，代替support the design theory 两个for引导的介词短语引导状语从句 2 Many factors affect geometric errors including: surfa

28、ce straightness (see Fig. 16.1), surface roughness, bearing preload, kinematics versus elastic design principles and structural design philosophies. surface straightness表示“平面度”。 surface roughness表示“表面粗糙度”。 versus elastic design principles(相对于弹性设计原理)介词短语修饰kinematics(运动学) 3 Similarly, a fit is indicat

29、ed by the basic size common to both the mating components, followed by the appropriate symbols corresponding to each component, e.g., is indicated by表示“简要的说明“，修饰fit。 followed by引导的介词短语修饰the basic size。, 16.4 Exercise：Translate the Following Paragraphs Machine parts are manufactured so they are inter

30、changeable. In other words, each part of a machine or mechanism is made to a certain size and shape so it will fit into any other machine or mechanism of the same type. To make the part interchangeable, each individual part must be made to a size that will fit the mating part in the correct way. It

31、is not only impossible, but also impractical to make many parts to an exact size. This is because machines are not perfect, and the tools become worn. A slight variation from the exact size is always allowed. The amount of this variation depends on the kind of part being manufactured. For example, a

32、 part might be made 6 in. long with a variation allowed of 0.003 (three-thousandths) in, above and below this size. Therefore, the part could be 5.997 in. to 6.003 in. and still be the correct size. These are known as the limits. The difference between upper and lower limits is called the tolerance.

33、 A tolerance is the total permissible variation in the size of a part. The basic size is that size from which limits of size are derived by the application of allowances and tolerances. Sometimes the limit is allowed in only one direction. This is known as unilateral tolerance. Unilateral tolerance

34、is a system of dimensioning where the tolerance (that is variation) is shown in only one direction from the nominal size. Unilateral tolerance allows the changing of tolerance on a hole or shaft without seriously affecting the fit. When the tolerance is in both directions from the basic size, it is

35、known as a bilateral tolerance (plus and minus). Bilateral tolerance is a system of dimensioning where the tolerance (that is variation) is split and is shown on either side of the nominal size. Limit dimensioning is a system of dimensioning where only the maximum and minimum dimensions are shown. T

36、hus, the tolerance is the difference between these two dimensions.,PART TWO,17.1 Text 17.2 Words and Phrases 17.3 Complex Sentence Analysis 17.4 Exercise,Lesson 17 Industrial Robots, 17.1 Text A robot is an automatically controlled, reprogrammable, multipurpose, manipulating machine with several rep

37、rogrammable axes, 1which may be either fixed in place or mobile for use in industrial automation applications. The key words are reprogrammable and multipurpose because most single-purpose machines do not meet these two requirements. The term “reprogrammable” implies two things: The robot operates a

38、ccording to a written program, and this program can be rewritten to accommodate a variety of manufacturing tasks. The term “multipurpose” means that the robot can perform many different functions, depending on the program and tooling currently in use. Over the past two decades, the robot has been in

39、troduced into industry to perform many monotonous and often unsafe operations. Because robots can perform certain basic tasks more quickly and accurately than humans, they are being increasingly used in various manufacturing industries., 17.1 Text Structures of Robots The typical structure of indust

40、rial robots consists of 4 major components: the manipulator, the end effector, the power supply and the control system, as shown in Fig.17.1.,Fig.17.1 Structures of Robots, 17.1 Text The manipulator is a mechanical unit that provides motions similar to those of a human arm. It often has a shoulder j

41、oint, an elbow and a wrist. It can rotate or slide, stretch out and withdraw in every possible direction with certain flexibility. The basic mechanical configurations of the robot manipulator are categorized as cartesian, cylindrical, spherical and articulated. A robot with a cartesian geometry can

42、move its gripper to any position within the cube or rectangle defined as its working volume. Cylindrical coordinate robots can move the gripper within a volume that is described by a cylinder. The cylindrical coordinate robot is positioned in the work area by two linear movements in the X and Y dire

43、ctions and one angular rotation about the Z axis. Spherical arm geometry robots position the wrist through two rotations and one linear actuation. Articulated industrial robots have an irregular work envelope. This type of robot has two main variants, vertically articulated and horizontally articula

44、ted. The end effector attaches itself to the end of the robot wrist, also called end-of-arm tooling. 2It is the device intended for performing the designed operations as a human hand can. End effectors are generally custom-made to meet special handling requirements. Mechanical grippers are the most

45、commonly used and are equipped with two or more fingers. The selection of an appropriate end effector for a specific application depends on such factors as the payload, environment, reliability, and cost., 17.1 Text The power supply is the actuator for moving the robot arm, controlling the joints an

46、d operating the end effector. The basic types of power sources include electrical, pneumatic, and hydraulic. Each source of energy and each type of motor has its own characteristics, advantages and limitations. An ac-powered or dc-powered motor may be used depending on the system design and applicat

47、ions. These motors convert electrical energy into mechanical energy to power the robot. Most new robots use electrical power supply. Pneumatic actuators have been used for high speed, nonservo robots and are often used for powering tooling such as grippers. Hydraulic actuators have been used for hea

48、vier lift systems, typically where accuracy was not also required. The control system is the communications and information-processing system that gives commands for the movements of the robot. It is the brain of the robot; it sends signals to the power source to move the robot arm to a specific pos

49、ition and to actuate the end effector. It is also the nerves of the robot; it is reprogrammable to send out sequences of instructions for all movements and actions to be taken by the robot. An open-loop controller is the simplest form of the control system, which controls the robot only by following

50、 the predetermined step-by-step instructions. This system does not have a self-correcting capability. A close-loop control system uses feedback sensors to produce signals that reflect the current states of the controlled objects. By comparing those feedback signals with the values set by the program

51、mer, the close-loop controller can conduct the robot to move to the precise position and assume the desired attitude, and the end effector can perform with very high accuracy as the close-loop control system can minimize the discrepancy between the controlled object and the predetermined references.

52、, 17.1 Text Classification of Robots Industrial robots vary widely in size, shape, number of axes, degrees of freedom, and design configuration. Each factor influences the dimensions of the robots working envelope or the volume of space within which it can move and perform its designated task. A bro

53、ader classification of robots can been described as below. Fixed-and Variable-Sequence Robots. The fixed-sequence robot (also called a pick-and place robot) is programmed for a specific sequence of operations. Its movements are from point to point, and the cycle is repeated continuously. The variabl

54、e-sequence robot can be programmed for a specific sequence of operations but can be reprogrammed to perform another sequence of operation. Playback Robot. An operator leads or walks the playback robot and its end effector through the desired path. The robot memorizes and records the path and sequenc

55、e of motions and can repeat them continually without any further action or guidance by the operator. Numerically Controlled Robot. The numerically controlled robot is programmed and operated much like a numerically controlled machine. The robot is servo-controlled by digital data, and its sequence o

56、f movements can be changed with relative ease. Intelligent Robot. 3The intelligent robot is capable of performing some of the functions and tasks carried out by human beings. It is equipped with a variety of sensors with visual and tactile capabilities., 17.1 Text Robot Applications The robot is a v

57、ery special type of production tool; as a result, the applications in which robots are used are quite broad. These applications can be grouped into three categories: material processing, material handling and assembly. In material processing, robots use tools to process the raw material. For example

58、, the robot tools could include a drill and the robot would be able to perform drilling operations on raw material. Material handling consists of the loading, unloading, and transferring of workpieces in manufacturing facilities. These operations can be performed reliably and repeatedly with robots,

59、 thereby improving quality and reducing scrap losses. Assembly is another large application area for using robotics. An automatic assembly system can incorporate automatic testing, robot automation and mechanical handling for reducing labor costs, increasing output and eliminating manual handling concerns. Fig.17.2 is SCARA Robot for automatic assembly.,Fig.17.2 SCARA Robot for Automatic Assembly, 17.2 Words and Phrases reprogrammable 7ri:prEu5rAmEbl adj. 可重复编程的，可改编的 manipulate mE5nipjuleit v. (熟练地)操作, 使用