外文翻譯--護理床動力學優(yōu)化

外文資料翻譯 1 NC and CNC The History of NC and CNC Development Numerical Control (NC) is any machining process in which the operations are executed automatically in sequences as specified by the program that contains the information for the tool movements. The NC concept was proposed in the late 1940s by John Parsons of Traverse City, Michigan. Parsons recommended a method of automatic machine control that would guide a milling cutter to produce a thru-axis curve in order to generate smooth profiles on work pieces. In 1949, The U.S. Air Force awarded Parsons a contract to develop a new type of machine tool that would be able to speed up production methods. Parsons commissioned the Massachusetts Institute of Technology (M.I.T.) to develop a practical implementation of his concept. Scientists and engineers at M.I.T. built a control system for a two-axis milling machine that used a perforated paper tape as the input media. In a short period of time, all major machine tool manufacturers were producing some machines with NC, but it was not until the late 1970s that computer-based NC became widely used. NC matured as an automation technology when inexpensive and powerful microprocessors replaced hard-wire logic-making computer-based NC systems. When Numerical Control is performed under computer supervision, it is called Computer Numerical Control (CNC). Computers are the control units of CNC machines, they are built in or linked to the machines via communications channels. When a programmer input some information in the program by tape and so on, the computer calculates all necessary data to get the job done. On the first Numerically Controlled (NC) machines were controlled by tape, and because of that, the NC systems were known as tape-controlled machines. They were able to control a single operation entered into the machine by punched or magnetic tape. There was no possibility of editing the program on the machine. To change the program, a new tape had to be made. Todays systems have computers to control data； they are called Computer Numerically Controlled (CNC) machines. For both NC and CNC systems, work principles are the same. Only the way in which the execution is controlled is different. 外文資料翻譯 2 Normally, new systems are faster, more powerful, and more versatile The Applications of NC/CNC Since its introduction, NC technology has found many applications, including lathes and turning Centers, milling machines and machining centers , punches , electrical discharg machines(EDM) Flame cutters,grinders,and inspection equipment. the most complex CNC machine tools are the turning center,shown in Fig.4-1(Amodern turning center with a ten-station turret that accepts quick-chang tools.Each tool can be positioned in Seconds with the press of a button).And the machine center shown in Fig.4-2(Vertical machining center,the tool magazine is on the machine.the control panel on the right can be swiveled by the operator)and Fig.4-3(horizontal machining center,equipped with an automatic tool changer .tool magazines can store 200 ctting tools. When preparing a progam for a particular operation ,the prommer must select all cutting data using recommendations for conventional machining .this includes proper Selection of cutting speeds,feedrate,tools and tool geometry,and so on.when the programmer has chosen all of the necessary information properly,the operator loads the programme into the machine and presses a button to start the cutting crycle .the CNC machine moves automatically from one maching operation to another , changing the cutting tols and applying the coolent.in a surprisingly short time ,the workpiece is Machined according to the highest quality stangards. But that is not all.no matter how big the work series is,all of the parts will be almost identical in size and surface finishing. At this time of advanced technology,with its high demands for surface finishing and tolerances of components in,for example ,aerospace,nuclear,and medical equipment manufacturing,only CNC machines provide successful results. Numerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols. The numbers, letters, and symbols are coded in an appropriate format to define a program of instructions for a particular workpart or job. The instructions are provided by either of the two binary coded decimal systems: the Electronic Industries Association (EIA) code, or the American Standard Code for Information Interchange (ASCII). ASCII-coded machine control units will not accept . EIA coded instructions 外文資料翻譯 3 and vice versa. Increasingly, however, control units are being made to accept instructions in either code. 121Automation operation by NC is readily adaptable to the operation of all metalworking machines. Lathes, milling machines, drill presses, boring machines, grinding machines, turret punches, flame or wire-cutting and welding machines, and even pipe benders are available with numerical controls. Basic Components of NC A numerical control system consists of the following three basic components: (1) Program instructions (2) Machine control unit (3) Processing equipment The program instructions are the detailed step by step commands that direct the processing equipment. 31In its most common form, the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixtured. More advanced instructions include selection of spindle speeds, cutting tools, and other functions. The machine control unit (MCU) consists of the electronics and control hardware that reads and interprets the program of instructions and convert it into mechanical actions of the machine tool or other processing equipment. The processing equipment is the component that performs metal process. In the most common example of numerical control, it is used to perform machining operations. The process-ing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them. Types of NC There are two basic types of numerical control systems: point to point and contouring. Point to point control system, also called positioning, is simpler than contouring control system. Its primary purpose is to move a tool or workpiece from one programmed point to another. Usually the machine function, such as a drilling operation, is also activated at each point by command from the NC program. Point to point systems are suitable for hole machining operations such as drilling, countersinking, couterbofing, reaming, boring and tapping. Hole punching machines, 外文資料翻譯 4 spotwelding machines, and assembly machines also use point to point NC systems. Contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different velocities. Because the tool cuts as it travels along a prescribed path, accurate control and synchronization of velocities and movements are important. The contouring system is used on lathes, milling machines, grinders,incrementally, by one of several basic methods. There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a contouring type NC system. They include linear interpolation,circular interpolation, helical interpolation, parabolic interpolation and cubic interpolation. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tools wear during machining, can be made in the NC . Programming for NC A program for numerical control consists of a sequence of directions that causes an NC machine to carry out a certain operation, machining being the most commonly used process. Programming for NC may be done by an internal programming department, on the shop floor, or purchased from an outside source. Also, programming may be done manually or with computer assistance. The program contains instructions and commands. Geometric instructions pertain to relative movements between the tool and the workpiece. Processing instructions pertain to spindle speeds, feeds, tools, and so on. Travel instructions pertain to the type of interpolation and slow or rapid movements of the tool or worktable. Switching commands pertain to on/off position for coolant supplies, spindle rotation, direction of spindle rotation, tool changes, workpiece feeding, clamping, and so on. The first NC programming language was developed by MIT developmental work on NC programming systems in the late 1950s and called APT(Automatically Programmed Tools). DNC and CNC The development of numerical control was a significant achievement in batch and job shop manufacturing, from both a technological and a commercial viewpoint. 外文資料翻譯 5 There have been two enhancements and extensions of NC technology, including: (1) Direct numerical control (2) Computer numerical control Direct numerical control can be defined as a manufacturing system in which a number of machines are controlled by a computer through direct connection and in real time. The tape reader is omitted in DNC, thus relieving the system of its least reliable component. Instead of using the tape reader, the part program is transmitted to the machine tool directly from the computer memory. In principle, one computer can be used to control more than 100 separate machines. (One commercial DNC system during the 1970s boasted a control capability of up to 256 machine tools.) The DNC computer is designed to provide instructions to each machine tool on demand. When the machine needs control commands, they are communicated to it immediately. Since the introduction of DNC, there have been dramatic advances in computer technology. The physical size and cost of a digital computer has been significantly reduced at the same time that its computational capabilities have been substantially increased. In numerical control, the result of these advances has been that the large hard-wired MCUs of conventional NC have been replaced by control units based on the digital computer. Initially, minicomputers were utilized in the early 1970s. As further miniaturization occurred in computers, minicomputers were replaced by todays microcomputers. Computer numerical control is an NC system using dedicated microcomputer as the machine control unit. Because a digital computer is used in both CNC and DNC, it is appropriate to distinguish between the two types of system. There are three principal differences: 1) DNC computers distribute instructional data to, and collect data from, a large number of machines. CNC computers control only one machine, or a small number of machines. 2) DNC computers occupy a location that is typically remote from the machines under their control. CNC computer are located very near their machine tools. 3) DNC software is developed not only to control individual pieces of production 外文資料翻譯 6 equipment, but also to serve as part of a management information system in the manufacturing sector of the firm. CNC software is developed to augment the capabilities of a particular machine Tool. 護理床動力學優(yōu)化 5.1 引言 動力學是理論力學的一個分支學科，它主要研究作用于物體的力與物體運動的關系。動力學的研究對象是運動速度遠小于光速的宏觀物體。動力學是物理學和天文學的基礎，也是許多工程學科的基礎。 動力學以牛頓第二定律為核心，這個定律指出了力、加速度、質(zhì)量三者間的關系。牛頓首先引入了質(zhì)量的概念，而把它和物體的重力區(qū)分開來，說明物體的重力只是地球?qū)ξ矬w的引力 。 多功能醫(yī)用護理床的運動學分析是 基于 ADAMS 建立于在運動學分析的基礎之上 的，根據(jù)先前的運動學分析，以運動學分析結果作為動力學分析的初始值，綜合考慮線性推桿的推、拉力的限制以及機架各支點的受力狀況，主要對線性推桿的受力狀況及各床架支點的受力狀況進行動力學分析。 5.2 側(cè)翻機構動力學分析 5.2.1為機構添加外力 側(cè)翻機構在運行的過程中，會有以下幾個方面對機構運動產(chǎn)生影響。它們是機構自身質(zhì)量，患者體重以及各個運動副之間的摩擦力。由于摩擦力很小，在此忽略不計，只考慮機構的重量及患者的體重。 通過 solidworks 軟件對虛擬樣機進行質(zhì)量測量，測得背板質(zhì)量為 20kg，通過設計手冊查得我 國身高 1.85m的成年人平均體重為 83kg 左右。為了真實的模擬虛擬樣機的性能，本文采用背板質(zhì)量為 20kg，人體背部重量為 50kg。對機構添加力之后，運行一次動力學仿真。測量各個點的受力以及電機的受力。仿真時間為 25s，步數(shù)為 500 步。 添加力測量，測得的各點受力曲線如圖 5-1 所示。 外文資料翻譯 7 圖 5-1 各點受力曲線 5.2.2側(cè)翻機構動力學優(yōu)化仿真 從圖 5-1 中，得知 MAKER_5 點的受力最大，機構的受力優(yōu)化就從MARKER_5 著入。首先，測試各個設計變量對 MARKER_5 的受力變化的敏感度。運行一次動力學仿真 ，時間為 25s，步數(shù)為 500 步，線性推桿移動速度為5.5mm/s，背板質(zhì)心處加力 500N，背板自重 20kg。運行優(yōu)化設計，優(yōu)化的目標為將 MARLKER_5 點的受力的最大值進行最小化，仿真后優(yōu)化數(shù)據(jù)如下： Model Name : model_1 Date Run : 2009-04-14 17:13:51 Objectives O1) Maximum of MARKER_5_MEA_1 Units : newton Initial Value: 1444.34 Final Value : 1130.2 (-21.7%) Iter. O1 DV_1 DV_2 DV_8 0 1444.3 150.00 295.00 136.30 1 1133.7 165.00 265.50 135.83 2 1130.2 165.00 265.50 134.94 3 1130.2 165.00 265.50 134.94 外文資料翻譯 8 5-2 MARKER_5 點優(yōu)化前后受力曲線 5-3 MARKER_1 點優(yōu)化前后受力曲線 5-4 MARKER_21 點優(yōu)化前后受力曲線 5-5 各參數(shù)下的翻轉(zhuǎn)角度值 從圖 5-2 至 5-4 中，可以發(fā)現(xiàn)經(jīng)過動力學優(yōu)化之后，各支點受力均有明顯的改善，其中圖 5-2 中 MARKER_5 點受力從 1443N 減至 1133N，從圖 5-5 中，背板的轉(zhuǎn)動角度在角度約束的范圍之內(nèi)。 5.2.3樣機的實際結構 通過以上的分析，在實際設計中， 各關鍵點的坐標取值為如表 5-1 所示 表 5-1 各關鍵點實際取值 DV_L1/mm DV_L2/mm DV_L4/mm DV_L7/mm DV_L8/mm 初始值 250 245 330 400 370 優(yōu)化值 265 215 346.1 390.28 359.94 此時，樣機的背板轉(zhuǎn)動角加速度最小且各支點的受力也達到了最小化、滿足了機構的設計要求。動力學優(yōu)化前后機構構件尺寸表如表 5-2 所示： 表 5-2 優(yōu)化前后桿件尺寸對比 A、 B 水平距離 /mm A、 B 豎直距離 /mm BD/mm 初始值 50 65 98.4 優(yōu)化值 35 19 118 5.3 抬背機構動力學分析 5.3.1為機構添加力 為了較為真實的模擬人體的質(zhì)量，以及考慮背板的推、拉力的限制，在抬背機構的背部添加豎直向下的均布力，大小為 400N，在臀部床板添加 400N 的力，外文資料翻譯 9 運行一次動力學優(yōu)化仿真。 5.3.2抬背機構動力學優(yōu)化仿真 為了進一步研究線性推桿的受力狀況，以及機架上各支點的受力狀況，使得機構工作得更安全及更可靠，以抬背機構運動學優(yōu)化數(shù)據(jù)為動力學優(yōu)化的初始數(shù)據(jù)，優(yōu)化目標函數(shù)為抬背過程中線性推桿受力的最大值最小化，進行動力學優(yōu)化仿真，已得 到滿足機構設計要求的最優(yōu)化參數(shù)。通過設計研究對各個設計變量進行敏感度測試。根據(jù)設計研究對各設計變量的測試，得到的數(shù)據(jù)報表如下： Trial O1 DV_1 Sensitivity 1 1914.3 369.00 10.740 2 2134.5 389.50 -0.021580 3 1913.4 410.00 -2.5693 4 2029.1 430.50 -0.019588 5 1912.6 451.00 -5.6838 Trial O1 DV_2 Sensitivity 1 1913.3 -18.000 0.0037970 2 1913.3 -27.000 -0.0031447 3 1913.4 -36.000 -11.532 4 2120.9 -45.000 -0.0029932 5 1913.5 -54.000 23.048 Trial O1 DV_3 Sensitivity 1 1925.6 90.000 22.755 2 2039.4 95.000 -1.2229 3 1913.4 100.00 -12.825 4 1911.2 105.00 -0.42287 5 1909.2 110.00 -0.39627 Trial O1 DV_4 Sensitivity 1 1912.8 -50.800 -0.079290 2 1913.3 -57.150 -0.044021 3 1913.4 -63.500 -0.042952 4 1913.9 -69.850 -0.069998 5 1914.3 -76.200 -0.062845 Trial O1 DV_5 Sensitivity 1 1913.5 3.9200 0.011536 2 1913.4 0.00000 0.0081747 外文資料翻譯 10 3 1913.4 -3.9200 -0.012181 4 1913.5 -7.8400 -3.5109 5 1940.9 -11.760 -6.9926 Trial O1 DV_6 Sensitivity 1 2163.3 -111.15 40.476 2 1913.4 -117.32 20.238 3 1913.4 -123.50 -15.895 4 2109.7 -129.68 -0.0067767 5 1913.5 -135.85 31.777 Trial O1 DV_7 Sensitivity 1 1985.6 306.74 -4.2359 2 1913.4 323.78 -2.1180 3 1913.4 340.82 6.3905 4 2131.2 357.86 0.0011642 5 1913.4 374.90 -12.779 Trial O1 DV_8 Sensitivity 1 2163.3 -111.15 40.476 2 1913.4 -117.32 20.238 3 1913.4 -123.50 -15.895 4 2109.7 -129.68 -0.0067767 5 1913.5 -135.85 31.777 通過設計研究，觀察計算結果，可以發(fā)現(xiàn)實際變量 DV_3、 DV_4、 DV_6、DV_8 的敏感度最大，所以在優(yōu)化設計的時候著重考慮上述幾個設計變量，對它們進行優(yōu)化設計，以期望得到滿足設計要求的機構最優(yōu)化參數(shù)。 5.3.3樣機的實際結構 通過以上的分析，在實際設計中，各關鍵點的坐標取值為如表 5-3 所示 表 5-3 各關鍵點實際取值 DV_2/mm DV_5/mm DV_6/mm DV_8/mm 初始值 390 458 330 275 優(yōu)化值 381 452.603 32317 278.8 優(yōu)化前后桿件尺寸變化如表 5-4 所示。 表 5-4 優(yōu)化前后桿件尺寸變化表 A、 C 豎直距離/mm BC /mm CD /mm DE/mm 外文資料翻譯 11 初始值 60 236 256 667 優(yōu)化值 62 228 248 659 圖 5-6 抬背機構動力學優(yōu)化前后電機受力曲線 觀察圖 5-6 可以得知在機構動力學仿真之后，機構表現(xiàn)出了良好的動力學性能， 機構的受力狀況得到了有效的改善，達到了預期的效果，即電機受力的最大值最小化。 5.4 曲腿機構動力學分析 為了真實的模擬曲腿機構在運行過程中的受力性能，以及線性推桿的受力狀況，所以對曲腿機構在運動學仿真的基礎之上進行一次動力學仿真，為了得到較為真實的機構運行狀況，并進行優(yōu)化仿真，得到理想機構設計參數(shù)。 5.4.1為機構添加外力 綜合考慮人體的自身重量以及床板的重量，在小腿板的質(zhì)心處及腳板的質(zhì)心處各添加豎直向下的力，大小為 500N。 5.4.2曲腿機構動力學仿真 以運動學優(yōu)化的數(shù)據(jù)作為動力學優(yōu)化的初始數(shù)據(jù)，進行 動力學優(yōu)化，優(yōu)化的目標函數(shù)為電機受力最大值的最小化。首先，對各個設計變量進行設計研究，設計研究的報表如下： Trial O1 DV_1 Sensitivity 1 4229.0 270.00 10.633 2 4548.0 300.00 10.659 3 4868.5 330.00 10.686 Trial O1 DV_2 Sensitivity 1 4435.8 -56.700 -17.645 2 4519.2 -61.425 -18.141 3 4607.2 -66.150 -18.637 外文資料翻譯 12 Trial O1 DV_3 Sensitivity 1 4833.0 156.75 -32.756 2 4427.7 169.12 -28.017 3 4139.6 181.50 -23.278 Trial O1 DV_4 Sensitivity 1 3850.1 -243.00 -25.573 2 4367.9 -263.25 -26.353 3 4917.4 -283.50 -27.134 Trial O1 DV_5 Sensitivity 1 4792.4 -81.498 55.604 2 4434.7 -87.932 51.809 3 4125.8 -94.366 48.013 Trial O1 DV_6 Sensitivity 1 4541.0 -597.60 -0.10561 2 4548.0 -664.00 -0.098506 3 4554.0 -730.40 -0.091406 根據(jù)上述的設計研究的結果對 DV_1、 DV_2、 DV_3、 DV_4、 DV_5、 DV_7、DV_9 七 變量，作為優(yōu)化設計時的設計變量，進行動力學優(yōu)化仿真。 圖 5-7 曲腿機構動力學優(yōu)化前后電機受力曲線圖 觀察圖 5-7 可以得知，經(jīng)過動力學優(yōu)化后的電機受力的最大值由原來的4550N 減小為優(yōu)化后的 2850N，電機的受力大大的減小，從而保證了機構運行的安全性及運行的穩(wěn)定性。 5.4.3 樣機的實際結構 通過以上的分析，在優(yōu)化設計時選取上述設計變量作為優(yōu)化設計時的設計變量，進行動力學優(yōu)化，經(jīng)過動力學優(yōu)化之后，各關鍵點的坐標取值為如表 5.5 所示 外文資料翻譯 13 表 5-5 各關鍵點實際取值 DV_1/mm DV_2/mm DV_3/mm DV_4/mm DV_5/mm 初始值 300 -63 165 -270 -85.788 優(yōu)化值 270 -56.7 181.5 -243 -94.36 此時，樣機的線性推桿的受力最小且各支點的受力也達到了最小化、滿足了機構的設計要求。優(yōu)化前