外文翻譯--護(hù)理床動力學(xué)優(yōu)化

1、<p>　　NC and CNC</p><p>　　The History of NC and CNC Development</p><p>　　Numerical Control (NC) is any machining process in which the operations are executed automatically in sequences as s

2、pecified 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 co

3、ntrol that would guide a milling cutter to produce a "thru-axis curve" in order to generate smooth profiles on work pieces.</p><p>　　In 1949, The U.S. Air Force awarded Parsons a contract to develo

4、p 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

5、 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 mac<

6、/p><p>　　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 machin

7、es 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.</p><p>　　On the first Numerically Co

8、ntrolled (NC) machines were controlled by tape, and</p><p>　　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 p

9、unched 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.</p><p>　　Today's systems have computers to control data; they ar

10、e 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. Normally, new systems are faster, more p

11、owerful, and more versatile</p><p>　　The Applications of NC/CNC</p><p>　　Since its introduction, NC technology has found many applications, including lathes and turning Centers, milling machines

12、 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

13、 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</p><p>　　When preparing a progam for a particul

14、ar operation ,the prommer must select all cutting data using recommendations for conventional machining .this includes proper </p><p>　　Selection of cutting speeds,feedrate,tools and tool geometry,and so on

15、.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 m

16、aching operation to another , changing the cutting tols and applying the coolent.in a surprisingly short time ,the workpiece is </p><p>　　Machined according to the highest quality stangards. But that is n

17、ot 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 compo

18、nents in,for example ,aerospace,nuclear,and medical equipment manufacturing,only CNC machines provide successful results. </p><p>　　Numerical control (NC) is a form of programmable automation in which the pr

19、ocessing 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.

20、 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-</p><

21、;p>　　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

22、 with numerical controls.</p><p>　　Basic Components of NC</p><p>　　A numerical control system consists of the following three basic components:</p><p>　　(1) Program instructions<

23、/p><p>　　(2) Machine control unit</p><p>　　(3) Processing equipment</p><p>　　The program instructions are the detailed step by step commands that direct the processing equipment. [31In

24、 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,

25、 and other functions. </p><p>　　The machine control unit

26、 (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.</p><p>

27、　　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 an

28、d spindle as well as the motors and controls needed to drive them.</p><p>　　Types of NC</p><p>　　There are two basic types of numerical control systems: point to point and contouring.</p>

29、<p>　　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

30、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, re

31、aming, boring and tapping. Hole punching machines, spotwelding machines,</p><p>　　Contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled pat

32、hs 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, millin

33、g machines, grinders,incrementally, by one of several basic methods. There are a number of interpolation schemes that have been developed to deal with the </p><p>　　Programming for NC</p><p>　　A

34、 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 interna

35、l programming department, on the shop floor, or purchased from an outside source. Also, programming may be done manually or with computer assistance.</p><p>　　The program contains instructions and commands.

36、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 interpolati

37、on 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

38、 so on. The </p><p>　　DNC and CNC</p><p>　　The development of numerical control was a significant achievement in batch and job shop manufacturing, from both a technological and a commercial view

39、point. There have been two enhancements and extensions of NC technology, including:</p><p>　　Direct numerical control</p><p>　　(2) Computer numerical control</p><p>　　Direct numeric

40、al 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 i

41、ts 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 separ

42、ate machines. (One commercial DNC system durin</p><p>　　Since the introduction of DNC, there have been dramatic advances in computer technology. The physical size and cost of a digital computer has been sign

43、ificantly 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</p&g

44、t;<p>　　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 replace

45、d by today's microcomputers.</p><p>　　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 a

46、ppropriate to distinguish between the two types of system. There are three principal differences:</p><p>　　1) DNC computers distribute instructional data to, and collect data from, a large number of machines

47、. CNC computers control only one machine, or a small number of machines.</p><p>　　2) DNC computers occupy a location that is typically remote from the machines under their control. CNC computer are located v

48、ery near their machine tools.</p><p>　　3) DNC software is developed not only to control individual pieces of production equipment, but also to serve as part of a management information system in the manufact

49、uring sector of the firm. CNC software is developed to augment the capabilities of a particular machine Tool.</p><p><b>　　護(hù)理床動力學(xué)優(yōu)化</b></p><p><b>　　5.1引言</b></p>&l

50、t;p>　　動力學(xué)是理論力學(xué)的一個分支學(xué)科，它主要研究作用于物體的力與物體運(yùn)動的關(guān)系。動力學(xué)的研究對象是運(yùn)動速度遠(yuǎn)小于光速的宏觀物體。動力學(xué)是物理學(xué)和天文學(xué)的基礎(chǔ)，也是許多工程學(xué)科的基礎(chǔ)。</p><p>　　動力學(xué)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(guān)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。</p><p&g

51、t;　　多功能醫(yī)用護(hù)理床的運(yùn)動學(xué)分析是基于ADAMS建立于在運(yùn)動學(xué)分析的基礎(chǔ)之上的，根據(jù)先前的運(yùn)動學(xué)分析，以運(yùn)動學(xué)分析結(jié)果作為動力學(xué)分析的初始值，綜合考慮線性推桿的推、拉力的限制以及機(jī)架各支點(diǎn)的受力狀況，主要對線性推桿的受力狀況及各床架支點(diǎn)的受力狀況進(jìn)行動力學(xué)分析。</p><p>　　5.2側(cè)翻機(jī)構(gòu)動力學(xué)分析</p><p>　　5.2.1為機(jī)構(gòu)添加外力</p><p

52、>　　側(cè)翻機(jī)構(gòu)在運(yùn)行的過程中，會有以下幾個方面對機(jī)構(gòu)運(yùn)動產(chǎn)生影響。它們是機(jī)構(gòu)自身質(zhì)量，患者體重以及各個運(yùn)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(jī)構(gòu)的重量及患者的體重。</p><p>　　通過solidworks軟件對虛擬樣機(jī)進(jìn)行質(zhì)量測量，測得背板質(zhì)量為20kg，通過設(shè)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(jī)的性能，本文采用背板質(zhì)量為20kg，人體背

53、部重量為50kg。對機(jī)構(gòu)添加力之后，運(yùn)行一次動力學(xué)仿真。測量各個點(diǎn)的受力以及電機(jī)的受力。仿真時間為25s，步數(shù)為500步。</p><p>　　添加力測量，測得的各點(diǎn)受力曲線如圖5-1所示。</p><p>　　圖5-1 各點(diǎn)受力曲線</p><p>　　5.2.2側(cè)翻機(jī)構(gòu)動力學(xué)優(yōu)化仿真</p><p>　　從圖5-1中，得知MAKER_5點(diǎn)

54、的受力最大，機(jī)構(gòu)的受力優(yōu)化就從MARKER_5著入。首先，測試各個設(shè)計變量對MARKER_5的受力變化的敏感度。運(yùn)行一次動力學(xué)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(yùn)行優(yōu)化設(shè)計，優(yōu)化的目標(biāo)為將MARLKER_5點(diǎn)的受力的最大值進(jìn)行最小化，仿真后優(yōu)化數(shù)據(jù)如下：</p><p>　　Model Name : model_1</p>

55、<p>　　Date Run : 2009-04-14 17:13:51</p><p>　　Objectives</p><p>　　O1) Maximum of MARKER_5_MEA_1</p><p>　　Units : newton</p><p>　　Initial Value: 1444

56、.34</p><p>　　Final Value : 1130.2 (-21.7%)</p><p>　　Iter. O1 DV_1 DV_2 DV_8 </p><p>　　0 1444.3 150.00 295.0

57、0 136.30</p><p>　　1 1133.7 165.00 265.50 135.83</p><p>　　2 1130.2 165.00 265.50 134.94</p><p>　　3

58、1130.2 165.00 265.50 134.94</p><p>　　從圖5-2至5-4中，可以發(fā)現(xiàn)經(jīng)過動力學(xué)優(yōu)化之后，各支點(diǎn)受力均有明顯的改善，其中圖5-2中MARKER_5點(diǎn)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)。</p><p>　　5.2.3樣機(jī)的實際結(jié)構(gòu)</p><p

59、>　　通過以上的分析，在實際設(shè)計中，各關(guān)鍵點(diǎn)的坐標(biāo)取值為如表5-1所示</p><p>　　表5-1各關(guān)鍵點(diǎn)實際取值</p><p>　　此時，樣機(jī)的背板轉(zhuǎn)動角加速度最小且各支點(diǎn)的受力也達(dá)到了最小化、滿足了機(jī)構(gòu)的設(shè)計要求。動力學(xué)優(yōu)化前后機(jī)構(gòu)構(gòu)件尺寸表如表5-2所示：</p><p>　　表5-2 優(yōu)化前后桿件尺寸對比</p><p>　

60、　5.3抬背機(jī)構(gòu)動力學(xué)分析</p><p>　　5.3.1為機(jī)構(gòu)添加力</p><p>　　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(jī)構(gòu)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，運(yùn)行一次動力學(xué)優(yōu)化仿真。</p><p>　　5.3.2抬背機(jī)構(gòu)動力學(xué)優(yōu)化仿真</p><p>　　為了進(jìn)一步

61、研究線性推桿的受力狀況，以及機(jī)架上各支點(diǎn)的受力狀況，使得機(jī)構(gòu)工作得更安全及更可靠，以抬背機(jī)構(gòu)運(yùn)動學(xué)優(yōu)化數(shù)據(jù)為動力學(xué)優(yōu)化的初始數(shù)據(jù)，優(yōu)化目標(biāo)函數(shù)為抬背過程中線性推桿受力的最大值最小化，進(jìn)行動力學(xué)優(yōu)化仿真，已得到滿足機(jī)構(gòu)設(shè)計要求的最優(yōu)化參數(shù)。通過設(shè)計研究對各個設(shè)計變量進(jìn)行敏感度測試。根據(jù)設(shè)計研究對各設(shè)計變量的測試，得到的數(shù)據(jù)報表如下：</p><p>　　Trial O1 DV

62、_1 Sensitivity</p><p>　　1 1914.3 369.00 10.740</p><p>　　2 2134.5 389.50 -0.021580</p><p>　　3 1913.4 4

63、10.00 -2.5693</p><p>　　4 2029.1 430.50 -0.019588</p><p>　　5 1912.6 451.00 -5.6838</p><p>　　Trial O1 D

64、V_2 Sensitivity</p><p>　　1 1913.3 -18.000 0.0037970</p><p>　　2 1913.3 -27.000 -0.0031447</p><p>　　3 1913.4 -

65、36.000 -11.532</p><p>　　4 2120.9 -45.000 -0.0029932</p><p>　　5 1913.5 -54.000 23.048</p><p>　　Trial O1

66、DV_3 Sensitivity</p><p>　　1 1925.6 90.000 22.755</p><p>　　2 2039.4 95.000 -1.2229</p><p>　　3 1913.4

67、 100.00 -12.825</p><p>　　4 1911.2 105.00 -0.42287</p><p>　　5 1909.2 110.00 -0.39627</p><p>　　Trial O1

68、 DV_4 Sensitivity</p><p>　　1 1912.8 -50.800 -0.079290</p><p>　　2 1913.3 -57.150 -0.044021</p><p>　　3 1913.4

69、 -63.500 -0.042952</p><p>　　4 1913.9 -69.850 -0.069998</p><p>　　5 1914.3 -76.200 -0.062845</p><p>　　Trial O1

70、 DV_5 Sensitivity</p><p>　　1 1913.5 3.9200 0.011536</p><p>　　2 1913.4 0.00000 0.0081747</p><p>　　3 1913.4

71、 -3.9200 -0.012181</p><p>　　4 1913.5 -7.8400 -3.5109</p><p>　　5 1940.9 -11.760 -6.9926</p><p>　　Trial O1

72、 DV_6 Sensitivity</p><p>　　1 2163.3 -111.15 40.476</p><p>　　2 1913.4 -117.32 20.238</p><p>　　3 1913.4

73、 -123.50 -15.895</p><p>　　4 2109.7 -129.68 -0.0067767</p><p>　　5 1913.5 -135.85 31.777</p><p>　　Trial O1

74、 DV_7 Sensitivity</p><p>　　1 1985.6 306.74 -4.2359</p><p>　　2 1913.4 323.78 -2.1180</p><p>　　3 1913.4

75、 340.82 6.3905</p><p>　　4 2131.2 357.86 0.0011642</p><p>　　5 1913.4 374.90 -12.779</p><p>　　Trial O1

76、 DV_8 Sensitivity</p><p>　　1 2163.3 -111.15 40.476</p><p>　　2 1913.4 -117.32 20.238</p><p>　　3 1913.4

77、 -123.50 -15.895</p><p>　　4 2109.7 -129.68 -0.0067767</p><p>　　5 1913.5 -135.85 31.777</p><p>　　通過設(shè)計研究，觀察計算結(jié)果，可以發(fā)現(xiàn)實際變量D

78、V_3、DV_4、DV_6、DV_8的敏感度最大，所以在優(yōu)化設(shè)計的時候著重考慮上述幾個設(shè)計變量，對它們進(jìn)行優(yōu)化設(shè)計，以期望得到滿足設(shè)計要求的機(jī)構(gòu)最優(yōu)化參數(shù)。</p><p>　　5.3.3樣機(jī)的實際結(jié)構(gòu)</p><p>　　通過以上的分析，在實際設(shè)計中，各關(guān)鍵點(diǎn)的坐標(biāo)取值為如表5-3所示</p><p>　　表5-3各關(guān)鍵點(diǎn)實際取值</p><p

79、>　　優(yōu)化前后桿件尺寸變化如表5-4所示。</p><p>　　表5-4 優(yōu)化前后桿件尺寸變化表</p><p>　　圖5-6 抬背機(jī)構(gòu)動力學(xué)優(yōu)化前后電機(jī)受力曲線</p><p>　　觀察圖5-6可以得知在機(jī)構(gòu)動力學(xué)仿真之后，機(jī)構(gòu)表現(xiàn)出了良好的動力學(xué)性能，機(jī)構(gòu)的受力狀況得到了有效的改善，達(dá)到了預(yù)期的效果，即電機(jī)受力的最大值最小化。</p>&l

80、t;p>　　5.4曲腿機(jī)構(gòu)動力學(xué)分析</p><p>　　為了真實的模擬曲腿機(jī)構(gòu)在運(yùn)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(jī)構(gòu)在運(yùn)動學(xué)仿真的基礎(chǔ)之上進(jìn)行一次動力學(xué)仿真，為了得到較為真實的機(jī)構(gòu)運(yùn)行狀況，并進(jìn)行優(yōu)化仿真，得到理想機(jī)構(gòu)設(shè)計參數(shù)。</p><p>　　5.4.1為機(jī)構(gòu)添加外力</p><p>　　綜合考慮人體的自身重量以及床板的重量，在

81、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。</p><p>　　5.4.2曲腿機(jī)構(gòu)動力學(xué)仿真</p><p>　　以運(yùn)動學(xué)優(yōu)化的數(shù)據(jù)作為動力學(xué)優(yōu)化的初始數(shù)據(jù)，進(jìn)行動力學(xué)優(yōu)化，優(yōu)化的目標(biāo)函數(shù)為電機(jī)受力最大值的最小化。首先，對各個設(shè)計變量進(jìn)行設(shè)計研究，設(shè)計研究的報表如下：</p><p>　　Trial O1

82、 DV_1 Sensitivity</p><p>　　1 4229.0 270.00 10.633</p><p>　　2 4548.0 300.00 10.659</p><p>　　3 4868.5

83、 330.00 10.686</p><p>　　Trial O1 DV_2 Sensitivity</p><p>　　1 4435.8 -56.700 -17.645</p><p>　　2 4519.2

84、 -61.425 -18.141</p><p>　　3 4607.2 -66.150 -18.637</p><p>　　Trial O1 DV_3 Sensitivity</p><p>　　1 4833.0

85、 156.75 -32.756</p><p>　　2 4427.7 169.12 -28.017</p><p>　　3 4139.6 181.50 -23.278</p><p>　　Trial O1

86、 DV_4 Sensitivity</p><p>　　1 3850.1 -243.00 -25.573</p><p>　　2 4367.9 -263.25 -26.353</p><p>　　3 4917.4

87、 -283.50 -27.134</p><p>　　Trial O1 DV_5 Sensitivity</p><p>　　1 4792.4 -81.498 55.604</p><p>　　2 4434.7

88、 -87.932 51.809</p><p>　　3 4125.8 -94.366 48.013</p><p>　　Trial O1 DV_6 Sensitivity</p><p>　　1 4541.

89、0 -597.60 -0.10561</p><p>　　2 4548.0 -664.00 -0.098506</p><p>　　3 4554.0 -730.40 -0.091406</p><p>　　根據(jù)上述的設(shè)計研究的結(jié)果對DV_1、

90、DV_2、DV_3、DV_4、DV_5、DV_7、DV_9七變量，作為優(yōu)化設(shè)計時的設(shè)計變量，進(jìn)行動力學(xué)優(yōu)化仿真。</p><p>　　圖5-7 曲腿機(jī)構(gòu)動力學(xué)優(yōu)化前后電機(jī)受力曲線圖</p><p>　　觀察圖5-7可以得知，經(jīng)過動力學(xué)優(yōu)化后的電機(jī)受力的最大值由原來的4550N減小為優(yōu)化后的2850N，電機(jī)的受力大大的減小，從而保證了機(jī)構(gòu)運(yùn)行的安全性及運(yùn)行的穩(wěn)定性。</p>&

91、lt;p>　　5.4.3 樣機(jī)的實際結(jié)構(gòu)</p><p>　　通過以上的分析，在優(yōu)化設(shè)計時選取上述設(shè)計變量作為優(yōu)化設(shè)計時的設(shè)計變量，進(jìn)行動力學(xué)優(yōu)化，經(jīng)過動力學(xué)優(yōu)化之后，各關(guān)鍵點(diǎn)的坐標(biāo)取值為如表5.5所示</p><p>　　表5-5各關(guān)鍵點(diǎn)實際取值</p><p>　　此時，樣機(jī)的線性推桿的受力最小且各支點(diǎn)的受力也達(dá)到了最小化、滿足了機(jī)構(gòu)的設(shè)計要求。優(yōu)化前后機(jī)

92、構(gòu)桿件尺寸變化見表5-6。</p><p>　　表5-6 優(yōu)化前后構(gòu)件尺寸變化表</p><p><b>　　5.5本章小結(jié)</b></p><p>　　本章在運(yùn)動學(xué)分析的基礎(chǔ)之上的，利用運(yùn)動學(xué)分析的數(shù)據(jù)作為動力學(xué)分析的初始數(shù)據(jù)，對機(jī)構(gòu)進(jìn)行動力學(xué)分析；在滿足機(jī)構(gòu)運(yùn)動學(xué)要求的基礎(chǔ)上改善機(jī)構(gòu)的動力學(xué)性能及機(jī)架的受力性能。使得樣機(jī)的運(yùn)動性能及受力性能

93、達(dá)到最好，滿足人體工學(xué)以及機(jī)構(gòu)在工作過程中的穩(wěn)定性及安全性。本章是進(jìn)行樣機(jī)物理設(shè)計的依據(jù)。</p><p>　　6 護(hù)理床的力學(xué)分析</p><p><b>　　6.1 引言</b></p><p>　　多功能醫(yī)用護(hù)理床在滿足運(yùn)動學(xué)及動力學(xué)性能要求的基礎(chǔ)上，需要對其中的一些主要零件進(jìn)行強(qiáng)度校核，以便在設(shè)計的時候合理的選材，在保證多功能醫(yī)用護(hù)理床

94、安全性和穩(wěn)定型以及盡可能的降低生產(chǎn)成本。</p><p><b>　　6.2 力學(xué)計算</b></p><p>　　護(hù)理床各主要部件及連桿材料均選用Q235A鋼</p><p>　　6.2.1床底架桿校核</p><p>　　考慮到由于多功能醫(yī)用護(hù)理床內(nèi)的機(jī)構(gòu)角度，不可避免的會使床的質(zhì)量增加。由于整床的重量將全部壓在床底

95、架長桿上，所以底架長桿將會是受力最大的桿件，根據(jù)設(shè)計尺寸，底架長桿的長度為1440mm，床底架長桿上有兩個支撐點(diǎn)，假設(shè)床身的質(zhì)量為400kg，人體的質(zhì)量為150kg，總重為550kg。具體計算如下所示：</p><p>　　圖6-1 床底架受力示意圖</p><p>　　根據(jù)solidworks的稱重功能，測得床的質(zhì)量為365kg，假設(shè)床身的質(zhì)量為400kg，人體的質(zhì)量為150kg，總重為

96、550kg。所以</p><p>　　F2=F3=2750N，=1440mm，=1020mm, =70mm。</p><p><b>　　根據(jù)力矩平衡公式：</b></p><p>　　F1×=F2×+F3×</p><p>　　得：F1==2215.3N</p><p&

97、gt;　　=F1+F4=F2+F3</p><p>　　得F4=3284.7N</p><p>　　通過上述已知條件，計算桿各段所受的剪力及彎矩：</p><p>　　以A為原點(diǎn)，在AB端內(nèi)：</p><p>　　剪力 F=F1=2215.3N，方向向下</p><p>　　彎矩 M=F1×x 得：M=0~7

98、75.355N·M，方向為逆時針方向</p><p><b>　　在BC段內(nèi)：</b></p><p>　　剪力F=F2-F1=534.7N，方向向上</p><p>　　彎矩 M=F1×x-F2×（x-0.35） 得：M=229.9~775.355N·M，方向為逆時針方向</p><

99、p><b>　　在CD段內(nèi)：</b></p><p>　　剪力F=F4=3284.7N，方向向上</p><p>　　彎矩 M=F4×x 得：M=0~229.9N·M，方向為逆時針方向</p><p>　　所以，根據(jù)計算分析，得出的結(jié)果為B點(diǎn)的受力最大且彎矩也最大，所以B點(diǎn)所在在截面為危險截面。計算后的剪力圖及彎矩圖如

100、圖6-2所示。</p><p>　　圖6-2 床底架剪力及彎矩圖</p><p>　　根據(jù)剪力及彎矩圖說明了床底架桿在整體上的受力并沒有發(fā)生突變，同時也不存在在某段的力值特別大的現(xiàn)象，所以從整體上而言，床框架的力學(xué)性能良好，受力情況滿足了機(jī)構(gòu)的設(shè)計要求。</p><p>　　6.2.2 抬背桿校核</p><p>　　多功能醫(yī)用護(hù)理床在抬背的

101、時候，其抬背擺桿將是受力較大的桿件，由于人的背部質(zhì)量較大，所以其將會時比較危險的桿件，對其的力學(xué)計算如下。</p><p>　　圖6-3抬背桿受力示意圖</p><p>　　按照人體的質(zhì)量及床板的質(zhì)量均分，則圓整后的數(shù)據(jù)為F1=500N，方向向上。</p><p>　　F3x=950N，F(xiàn)3y=2039N，=830mm，=680mm, =54mm。</p>

102、;<p>　　F2x=F3x=950N，F(xiàn)2y=F1+F3y=500+2039=2539N</p><p><b>　　在AB段</b></p><p>　　剪力 F=F1=500N，方向向上</p><p>　　彎矩 M=F×x，得：M=0~340N·M，方向為順時針方向</p><p&g

103、t;<b>　　在BC段</b></p><p>　　剪力 F= F3y=2039N，方向向下</p><p>　　彎矩 M=F2y×（x-0.68）-F1×x (0.68≤x≤0.734) </p><p>　　得：M=229.9~340N·M，方向逆時針方向</p><p>　　M=