外文翻译--护理床动力学优化

外文资料翻译 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. 外文资料翻译 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 外文资料翻译 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, 外文资料翻译 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. 外文资料翻译 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 外文资料翻译 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. 护理床动力学优化 5.1 引言 动力学是理论力学的一个分支学科，它主要研究作用于物体的力与物体运动的关系。动力学的研究对象是运动速度远小于光速的宏观物体。动力学是物理学和天文学的基础，也是许多工程学科的基础。 动力学以牛顿第二定律为核心，这个定律指出了力、加速度、质量三者间的关系。牛顿首先引入了质量的概念，而把它和物体的重力区分开来，说明物体的重力只是地球对物体的引力 。 多功能医用护理床的运动学分析是 基于 ADAMS 建立于在运动学分析的基础之上 的，根据先前的运动学分析，以运动学分析结果作为动力学分析的初始值，综合考虑线性推杆的推、拉力的限制以及机架各支点的受力状况，主要对线性推杆的受力状况及各床架支点的受力状况进行动力学分析。 5.2 侧翻机构动力学分析 5.2.1为机构添加外力 侧翻机构在运行的过程中，会有以下几个方面对机构运动产生影响。它们是机构自身质量，患者体重以及各个运动副之间的摩擦力。由于摩擦力很小，在此忽略不计，只考虑机构的重量及患者的体重。 通过 solidworks 软件对虚拟样机进行质量测量，测得背板质量为 20kg，通过设计手册查得我 国身高 1.85m的成年人平均体重为 83kg 左右。为了真实的模拟虚拟样机的性能，本文采用背板质量为 20kg，人体背部重量为 50kg。对机构添加力之后，运行一次动力学仿真。测量各个点的受力以及电机的受力。仿真时间为 25s，步数为 500 步。 添加力测量，测得的各点受力曲线如图 5-1 所示。 外文资料翻译 7 图 5-1 各点受力曲线 5.2.2侧翻机构动力学优化仿真 从图 5-1 中，得知 MAKER_5 点的受力最大，机构的受力优化就从MARKER_5 着入。首先，测试各个设计变量对 MARKER_5 的受力变化的敏感度。运行一次动力学仿真 ，时间为 25s，步数为 500 步，线性推杆移动速度为5.5mm/s，背板质心处加力 500N，背板自重 20kg。运行优化设计，优化的目标为将 MARLKER_5 点的受力的最大值进行最小化，仿真后优化数据如下： 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 外文资料翻译 8 5-2 MARKER_5 点优化前后受力曲线 5-3 MARKER_1 点优化前后受力曲线 5-4 MARKER_21 点优化前后受力曲线 5-5 各参数下的翻转角度值 从图 5-2 至 5-4 中，可以发现经过动力学优化之后，各支点受力均有明显的改善，其中图 5-2 中 MARKER_5 点受力从 1443N 减至 1133N，从图 5-5 中，背板的转动角度在角度约束的范围之内。 5.2.3样机的实际结构 通过以上的分析，在实际设计中， 各关键点的坐标取值为如表 5-1 所示 表 5-1 各关键点实际取值 DV_L1/mm DV_L2/mm DV_L4/mm DV_L7/mm DV_L8/mm 初始值 250 245 330 400 370 优化值 265 215 346.1 390.28 359.94 此时，样机的背板转动角加速度最小且各支点的受力也达到了最小化、满足了机构的设计要求。动力学优化前后机构构件尺寸表如表 5-2 所示： 表 5-2 优化前后杆件尺寸对比 A、 B 水平距离 /mm A、 B 竖直距离 /mm BD/mm 初始值 50 65 98.4 优化值 35 19 118 5.3 抬背机构动力学分析 5.3.1为机构添加力 为了较为真实的模拟人体的质量，以及考虑背板的推、拉力的限制，在抬背机构的背部添加竖直向下的均布力，大小为 400N，在臀部床板添加 400N 的力，外文资料翻译 9 运行一次动力学优化仿真。 5.3.2抬背机构动力学优化仿真 为了进一步研究线性推杆的受力状况，以及机架上各支点的受力状况，使得机构工作得更安全及更可靠，以抬背机构运动学优化数据为动力学优化的初始数据，优化目标函数为抬背过程中线性推杆受力的最大值最小化，进行动力学优化仿真，已得 到满足机构设计要求的最优化参数。通过设计研究对各个设计变量进行敏感度测试。根据设计研究对各设计变量的测试，得到的数据报表如下： 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 外文资料翻译 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 通过设计研究，观察计算结果，可以发现实际变量 DV_3、 DV_4、 DV_6、DV_8 的敏感度最大，所以在优化设计的时候着重考虑上述几个设计变量，对它们进行优化设计，以期望得到满足设计要求的机构最优化参数。 5.3.3样机的实际结构 通过以上的分析，在实际设计中，各关键点的坐标取值为如表 5-3 所示 表 5-3 各关键点实际取值 DV_2/mm DV_5/mm DV_6/mm DV_8/mm 初始值 390 458 330 275 优化值 381 452.603 32317 278.8 优化前后杆件尺寸变化如表 5-4 所示。 表 5-4 优化前后杆件尺寸变化表 A、 C 竖直距离/mm BC /mm CD /mm DE/mm 外文资料翻译 11 初始值 60 236 256 667 优化值 62 228 248 659 图 5-6 抬背机构动力学优化前后电机受力曲线 观察图 5-6 可以得知在机构动力学仿真之后，机构表现出了良好的动力学性能， 机构的受力状况得到了有效的改善，达到了预期的效果，即电机受力的最大值最小化。 5.4 曲腿机构动力学分析 为了真实的模拟曲腿机构在运行过程中的受力性能，以及线性推杆的受力状况，所以对曲腿机构在运动学仿真的基础之上进行一次动力学仿真，为了得到较为真实的机构运行状况，并进行优化仿真，得到理想机构设计参数。 5.4.1为机构添加外力 综合考虑人体的自身重量以及床板的重量，在小腿板的质心处及脚板的质心处各添加竖直向下的力，大小为 500N。 5.4.2曲腿机构动力学仿真 以运动学优化的数据作为动力学优化的初始数据，进行 动力学优化，优化的目标函数为电机受力最大值的最小化。首先，对各个设计变量进行设计研究，设计研究的报表如下： 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 外文资料翻译 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 根据上述的设计研究的结果对 DV_1、 DV_2、 DV_3、 DV_4、 DV_5、 DV_7、DV_9 七 变量，作为优化设计时的设计变量，进行动力学优化仿真。 图 5-7 曲腿机构动力学优化前后电机受力曲线图 观察图 5-7 可以得知，经过动力学优化后的电机受力的最大值由原来的4550N 减小为优化后的 2850N，电机的受力大大的减小，从而保证了机构运行的安全性及运行的稳定性。 5.4.3 样机的实际结构 通过以上的分析，在优化设计时选取上述设计变量作为优化设计时的设计变量，进行动力学优化，经过动力学优化之后，各关键点的坐标取值为如表 5.5 所示 外文资料翻译 13 表 5-5 各关键点实际取值 DV_1/mm DV_2/mm DV_3/mm DV_4/mm DV_5/mm 初始值 300 -63 165 -270 -85.788 优化值 270 -56.7 181.5 -243 -94.36 此时，样机的线性推杆的受力最小且各支点的受力也达到了最小化、满足了机构的设计要求。优化前