0041-BL系列臺(tái)式車床進(jìn)給結(jié)構(gòu)設(shè)計(jì),bl,系列,臺(tái)式,車床,進(jìn)給,結(jié)構(gòu)設(shè)計(jì) 河南理工大學(xué)萬(wàn)方科技學(xué)院本科畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告 題目名稱 BL系列臺(tái)式車床進(jìn)給結(jié)構(gòu) 學(xué)生姓名 程勉強(qiáng) 專業(yè)班級(jí) 07機(jī)制2班 學(xué)號(hào) 0720150131 一、 選題的目的和意義： ? 用以改變機(jī)床切削時(shí)的進(jìn)給量(見(jiàn)切削用量)或改變表面形成運(yùn)動(dòng)中刀具與工件相對(duì)運(yùn)動(dòng)關(guān)系的機(jī)構(gòu)。車床的進(jìn)給結(jié)構(gòu)是保證工件的精度的重要部件。先進(jìn)、精確的進(jìn)給機(jī)構(gòu)更能保證工件的精度，研究車床的進(jìn)給結(jié)構(gòu)對(duì)提高車床的加工精度有著更加重要的地位，因此，更多的企業(yè)愿意花更多的人力和物力在這方面，以期待獲得更大的效益，對(duì)車床的發(fā)展起到推進(jìn)作用。工具：菜譜大全 、漢字字典 、漢語(yǔ)詞典 、成語(yǔ)大全 、歇后語(yǔ)大全 、謎語(yǔ)大全 、免費(fèi)起名 二、 國(guó)內(nèi)外研究現(xiàn)狀簡(jiǎn)述： 進(jìn)給箱利用交換齒輪﹑滑移齒輪﹑棘輪機(jī)構(gòu)﹑拉鍵機(jī)構(gòu)﹑迴曲機(jī)構(gòu)﹑擺移塔齒輪機(jī)構(gòu)﹑雙軸滑移公用齒輪機(jī)構(gòu)和三軸滑移公用齒輪機(jī)構(gòu)等(見(jiàn)圖 改變進(jìn)給量的機(jī)構(gòu) )實(shí)現(xiàn)進(jìn)給量的改變。 ???????? 採(cǎi)用交換齒輪﹑滑移齒輪和無(wú)級(jí)改變進(jìn)給量的機(jī)構(gòu)基本上與機(jī)床變速箱中的相同﹐但進(jìn)給機(jī)構(gòu)為恆扭矩傳動(dòng)﹐速度較低﹑功率較小。 ??????? ? 棘輪機(jī)構(gòu) 曲柄滑塊機(jī)構(gòu)使棘爪按順時(shí)針?lè)较驍[動(dòng)﹐推動(dòng)棘輪轉(zhuǎn)過(guò)一個(gè)角度﹐并由此傳動(dòng)進(jìn)給絲杠以實(shí)現(xiàn)進(jìn)給運(yùn)動(dòng)。當(dāng)棘爪逆時(shí)針?lè)较驍[動(dòng)時(shí)﹐棘輪不動(dòng)。進(jìn)給量是通過(guò)改變棘爪每擺動(dòng)一次時(shí)棘輪所轉(zhuǎn)過(guò)的齒數(shù)來(lái)調(diào)整的﹐因而是等差數(shù)列的。棘輪機(jī)構(gòu)通常用於間歇進(jìn)給的機(jī)床﹐如刨床﹑插床和磨床等。 ???????? 拉鍵機(jī)構(gòu) 齒輪Z 1～Z 是緊固在軸Ⅰ上的﹐齒輪Z ～Z 是空套在軸Ⅱ上的﹐但可以通過(guò)能在該軸空心部分中滑動(dòng)的拉鍵與軸相聯(lián)。把拉鍵拉到不同齒輪的鍵槽中即可得到Z 1/Z ﹑Z 2/Z …Z /Z 共k個(gè)傳動(dòng)比﹐實(shí)現(xiàn)等比數(shù)列或等差數(shù)列的進(jìn)給量。這種機(jī)構(gòu)結(jié)構(gòu)緊湊﹐操縱方便﹐可使用斜齒輪﹐但剛度較差﹐工作時(shí)所有齒輪都在嚙合運(yùn)轉(zhuǎn)﹐噪聲和空轉(zhuǎn)損失較大﹐常用於鉆床中。 ???????? 迴曲機(jī)構(gòu) 又稱梅安特機(jī)構(gòu)﹐由德文Mander(迂迴曲摺之意)一詞而得名。單個(gè)的齒輪Z 1 固定在軸Ⅰ上﹐雙聯(lián)齒輪 Z 1Z 2和Z 3Z 4分別空套在軸Ⅰ和軸Ⅱ上。軸Ⅲ上的滑移齒輪Z 5可以在4個(gè)不同位置上與軸Ⅱ上的4個(gè)齒輪Z 4 嚙合﹐從而得到4個(gè)按等比數(shù)列排列的傳動(dòng)比﹐其公比為(Z 1/Z 2 )×(Z 3/Z 4)。這種機(jī)構(gòu)尺寸緊湊﹐操縱簡(jiǎn)單﹐所有雙聯(lián)齒輪可製成兩種規(guī)格或一種規(guī)格﹐工藝性較好﹔但工作時(shí)所有齒輪都在嚙合運(yùn)轉(zhuǎn)﹐噪聲和空轉(zhuǎn)損失較大﹐主要用作普通車床中的螺距增倍機(jī)構(gòu)。 ???????? 擺移塔齒輪機(jī)構(gòu) 這種機(jī)構(gòu)為美國(guó)人W. P. 諾頓於1892年所創(chuàng)製﹐故又稱諾頓機(jī)構(gòu)。輪Z 可沿軸Ⅰ滑動(dòng)﹐而Z b可繞軸Ⅰ擺動(dòng)﹐這樣可使中間齒輪 Z b與軸Ⅱ上的Z 1﹑Z 2…Z 中的任一個(gè)齒輪嚙合﹐并得到k個(gè)按等差數(shù)列或其他規(guī)律排列的傳動(dòng)比。這種機(jī)構(gòu)齒輪數(shù)目較少﹐沒(méi)有多餘空轉(zhuǎn)的齒輪。原來(lái)的結(jié)構(gòu)由於存在擺移齒輪及其手柄﹐箱體上開(kāi)有長(zhǎng)孔﹐機(jī)構(gòu)剛度和箱體密封性都較差。后改進(jìn)為封閉箱體﹐性能有所改善﹐但結(jié)構(gòu)稍復(fù)雜。諾頓機(jī)構(gòu)主要用作普通車床的螺距變換機(jī)構(gòu)。 工具：菜譜大全 、漢字字典 、漢語(yǔ)詞典 、成語(yǔ)大全 、歇后語(yǔ)大全 、謎語(yǔ)大全 、免費(fèi)起名 三、畢業(yè)設(shè)計(jì)（論文）所采用的研究方法和手段: 1、發(fā)揮獨(dú)立工作能力 設(shè)計(jì)中發(fā)現(xiàn)問(wèn)題，應(yīng)該首先自己考慮，提出自己的看法和意見(jiàn)，和指導(dǎo)老師一同研究，不應(yīng)向指導(dǎo)老師要答案，對(duì)設(shè)計(jì)中的錯(cuò)誤和解決途徑，可由教師提出，但具體答案也應(yīng)該由自己去找。 2、設(shè)計(jì)時(shí)應(yīng)貫徹邊畫、邊算、邊修改的設(shè)計(jì)方法。 3、及時(shí)檢查和整理計(jì)算結(jié)果。 4、借閱圖書館的相關(guān)書籍及手冊(cè)、通過(guò)網(wǎng)絡(luò)查找相關(guān)資料。 5、向老師請(qǐng)教一些難點(diǎn)、疑點(diǎn)。 四、主要參考文獻(xiàn)與資料獲得情況： 老師給的一些基本資料，一些網(wǎng)上搜索的資料和一些企業(yè)的相似產(chǎn)品的資料等等。 下面是一些畢業(yè)設(shè)計(jì)中要用的參考資料： 1．《機(jī)械設(shè)計(jì)》（第四版）邱宣懷主編高等教育出版社1999； 2.《金屬切削機(jī)床設(shè)計(jì)》戴曙主編，機(jī)械工業(yè)出版社1981； 3．《機(jī)床設(shè)計(jì)手冊(cè)》機(jī)械工業(yè)出版社1982； 4．《機(jī)械設(shè)計(jì)手冊(cè)》第二冊(cè)（上冊(cè)）機(jī)械工業(yè)出版社1978； 五、畢業(yè)設(shè)計(jì),進(jìn)度安排（按周說(shuō)明）： (1)收集資料,選擇畢業(yè)設(shè)計(jì)課題（需要0.25周）； (2)進(jìn)行文獻(xiàn)綜述,寫開(kāi)題報(bào)告,寫畢業(yè)實(shí)習(xí)報(bào)告，進(jìn)行英語(yǔ)翻譯（需要一周）；(3)進(jìn)行相關(guān)技術(shù)設(shè)計(jì),查閱資料參考文獻(xiàn)及資料,并進(jìn)行需求分析（需要0.5周）；(4)編寫畢業(yè)論文提綱；(5)根據(jù)畢業(yè)論文的格式確定并編寫初步的畢業(yè)論文(需要2周左右)；(6)對(duì)畢業(yè)設(shè)計(jì)報(bào)告進(jìn)行修改（需要0.25周）；(7)進(jìn)一步進(jìn)行歸納總結(jié)(需要0.5周)；(8)準(zhǔn)備答辯（需要2.5周） 六、指導(dǎo)教師審批意見(jiàn)（對(duì)選題的可行性、研究方法、進(jìn)度安排作出評(píng)價(jià)，對(duì)是否開(kāi)題作出決定）： 指導(dǎo)教師： （簽名） 年 月 日 該方案是BL系列臺(tái)式車床進(jìn)給結(jié)構(gòu)設(shè)計(jì)，主要為機(jī)械元件的設(shè)計(jì)。因BL臺(tái)式車床為小型車床，故在各個(gè)部 分和零件的計(jì)算和選用過(guò)程中在滿足設(shè)計(jì)要求的前提下（剛度、強(qiáng)度等），盡量選用尺寸較小的部件和零件。 進(jìn)給箱是臺(tái)式車床的主要部件之一，其作用是實(shí)現(xiàn)進(jìn)給量的變換和各種螺紋螺距的變換。絲杠與光杠用以聯(lián)接 進(jìn)給箱與溜板箱，并把進(jìn)給箱的運(yùn)動(dòng)和動(dòng)力傳給溜板箱，使溜板箱獲得縱向直線運(yùn)動(dòng)。溜板箱：是車床進(jìn)給運(yùn) 動(dòng)的操縱箱，內(nèi)裝有將光杠和絲杠的旋轉(zhuǎn)運(yùn)動(dòng)變成刀架直線運(yùn)動(dòng)的機(jī)構(gòu)，通過(guò)光杠傳動(dòng)實(shí)現(xiàn)刀架的縱向進(jìn)給運(yùn) 動(dòng)、橫向進(jìn)給運(yùn)動(dòng)和快速移動(dòng)，通過(guò)絲杠帶動(dòng)刀架作縱向直線運(yùn)動(dòng)，以便車削螺紋。它的功能是裝夾刀具，使 刀具作縱向、橫向或斜向進(jìn)給運(yùn)動(dòng)。 河南理工大學(xué)萬(wàn)方科技學(xué)院 本科畢業(yè)設(shè)計(jì)（論文）中期檢查表 指導(dǎo)教師： 張燕 職稱： 副教授 所在院（系）： 機(jī)械與動(dòng)力工程系 教研室（研究室）： 機(jī)械教研室 題 目 BL系列臺(tái)式車床進(jìn)給結(jié)構(gòu) 學(xué)生姓名 程勉強(qiáng) 專業(yè)班級(jí) 07機(jī)制2班 學(xué)號(hào) 0720150131 一、選題質(zhì)量：（主要從以下四個(gè)方面填寫：1、選題是否符合專業(yè)培養(yǎng)目標(biāo)，能否體現(xiàn)綜合訓(xùn)練要求；2、題目難易程度；3、題目工作量；4、題目與生產(chǎn)、科研、經(jīng)濟(jì)、社會(huì)、文化及實(shí)驗(yàn)室建設(shè)等實(shí)際的結(jié)合程度） 1. 在BL臺(tái)式車床進(jìn)給結(jié)構(gòu)設(shè)計(jì)過(guò)程中，運(yùn)用了在大學(xué)中所學(xué)的各種知識(shí)，通過(guò)設(shè)計(jì) 加深了對(duì)所學(xué)知識(shí)的認(rèn)識(shí)。選題符合專業(yè)培養(yǎng)目標(biāo)，能體現(xiàn)綜合訓(xùn)練要求。 2．通過(guò)這一個(gè)月的設(shè)計(jì)、計(jì)算，我感覺(jué)題目難易適中。 3. 題目的工作量大，需要計(jì)算和考慮的東西較多，包括了進(jìn)給箱的設(shè)計(jì)、絲杠和光杠 的設(shè)計(jì)、溜板箱的設(shè)計(jì)。 4. BL臺(tái)式車床在各種機(jī)械加工過(guò)程中經(jīng)常用到，如何提高其加工精度也是各個(gè)廠家 研究的重點(diǎn)，它對(duì)經(jīng)濟(jì)的發(fā)展也做出了重要的貢獻(xiàn)。因此BL系列臺(tái)式車床進(jìn)給結(jié)構(gòu) 的設(shè)計(jì)與生產(chǎn)、科研、經(jīng)濟(jì)等是緊密相連的。 二、開(kāi)題報(bào)告完成情況： 完成 三、階段性成果： 1.英語(yǔ)翻譯已經(jīng)完成。 2.論文以基本完成。 3.正在繪圖。 四、存在主要問(wèn)題： 1.絲杠如何帶動(dòng)溜板箱運(yùn)動(dòng)的？ 2.滑移齒輪是如何工作及固定的？ 3.溜板箱中的運(yùn)動(dòng)傳遞方式？ 五、指導(dǎo)教師對(duì)學(xué)生在畢業(yè)實(shí)習(xí)中，勞動(dòng)、學(xué)習(xí)紀(jì)律及畢業(yè)設(shè)計(jì)（論文）進(jìn)展等方面的評(píng)語(yǔ) 指導(dǎo)教師： （簽名） 年 月 日 機(jī)械加工介紹（中英文對(duì)照） 1 Lathes Lathes are machine tools designed primarily to do turning, facing and boring, Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the work piece. Consequently, more lathes of various types are used in manufacturing than any other machine tool. The essential components of a lathe are the bed, headstock assembly, tailstock assembly, and the leads crew and feed rod. The bed is the backbone of a lathe. It usually is made of well normalized or aged gray or nodular cast iron and provides s heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, are contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat way in one or both sets, They are precision-machined to assure accuracy of alignment. On most modern lathes the way are surface-hardened to resist wear and abrasion, but precaution should be taken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed. The headstock is mounted in a foxed position on the inner ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmission—through which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives. Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball types. The spindle has a hole extending through its length, through which long bar stock can be fed. The size of maximum size of bar stock that can be machined when the material must be fed through spindle. The tailsticd assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clamping the entire assembly in any desired location, An upper casting fits on the lower one and can be moved transversely upon it, on some type of keyed ways, to permit aligning the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76mm(2to 3 inches) in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a hand wheel and screw. The size of a lathe is designated by two dismensions. The first is known as the swing. This is the maximum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways, The second size dimension is the maximum distance between centers. The swing thus indicates the maximum work piece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of work piece that can be mounted between centers. Engine lathes are the type most frequently used in manufacturing. They are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest. They commonly range in size from 305 to 610 mm(12 to 24 inches)swing and from 610 to 1219 mm(24 to 48 inches) center distances, but swings up to 1270 mm(50 inches) and center distances up to 3658mm(12 feet) are not uncommon. Most have chip pans and a built-in coolant circulating system. Smaller engine lathes-with swings usually not over 330 mm (13 inches ) –also are available in bench type, designed for the bed to be mounted on a bench on a bench or cabinet. Although engine lathes are versatile and very useful, because of the time required for changing and setting tools and for making measurements on the work piece, thy are not suitable for quantity production. Often the actual chip-production tine is less than 30% of the total cycle time. In addition, a skilled machinist is required for all the operations, and such persons are costly and often in short supply. However, much of the operator’s time is consumed by simple, repetitious adjustments and in watching chips being made. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw machines, and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing. 2 Numerical Control One of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC). Prior to the advent of NC, all machine tools ere manually operated and controlled. Among the many limitations associated with manual control machine tools, perhaps none is more prominent than the limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools. Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes a program that issues operational instructions to the machine tool. For a machine tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programmed instructions, known as a reader. Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology: Electrical discharge machining,Laser cutting,Electron beam welding. Numerical control has also made machine tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled machine tolls and processes. Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U.S. Air Force. In its earliest stages, NC machines were able to made straight cuts efficiently and effectively. However, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter the straight lines making up the steps, the smoother is the curve, Each line segment in the steps had to be calculated. This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the fur ther development from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development. A major problem was the fragility of the punched paper tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instructions had to be rerun through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate tines. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use. This led to the development of a special magnetic plastic tape. Whereas the paper carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than the paper tape, which solved the problem of frequent tearing and breakage. However, it still left two other problems. The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To made even the most minor adjustments in a program of instructions, it was necessary to interrupt machining operations and make a new tape. It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape. The development of a concept known as direct numerical control (DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control, machine tools are tied, via a data transmission link, to a host computer. Programs for operating the machine tools are stored in the host computer and fed to the machine tool an needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend on a host computer. When the host computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control. 3 Turning The engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered. The engine lathe has been replaced in today’s production shops by a wide variety of automatic lathes such as automatic of single-point tooling for maximum metal removal, and the use of form tools for finish on a par with the fastest processing equipment on the scene today. Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be careful in using tolerances of an experimental part that has been produced on the engine lathe by a skilled operator. In redesigning an experimental part for production, economical tolerances should be used. Turret Lathes Production machining equipment must be evaluated now, more than ever before, this criterion for establishing the production qualification of a specific method, the turret lathe merits a high rating. In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the optimum tolerances possible on the turrets lathe, the designer should strive for a minimum of operations. Automatic Screw Machines Generally, automatic screw machines fall into several categories; single-spindle automatics, multiple-spindle automatics and automatic chucking machines. Originally designed for rapid, automatic production of screws and similar threaded parts, the automatic screw machine has long since exceeded the confines of this narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities play an important part in the economy of the parts machined on the automatic screw machine. Quantities less than on the automatic screw machine. The cost of the parts machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantities. Automatic Tracer Lathes Since surface roughness depends greatly on material turned, tooling , and feeds and speeds employed, minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances. In some cases, tolerances of 0.05mm are held in continuous production using but one cut . groove width can be held to 0.125mm on some parts. Bores and single-point finishes can be held to 0.0125mm. On high-production runs where maximum output is desirable, a minimum tolerance of 0.125mm is economical on both diameter and length of turn 2 Simple Machines and Tools A What Do the Simple Machines Mean? Simple machines are devices which allow energy to be transferred from one place to another. With the help of machines our lives are made much easier. To many people the word "machine" means things like a tractor, an electric drill, a bulldozer, a sewing machine or a bicycle. These are machines, but they are really very complicated ones, such as ones made up of many simple machines. There are only a few kinds of simple machines. They are the lever, the wheel and axle, the inclined plane, gears, pulleys and hydraulics. Simple machines can do the following: They allow energy to be transferred from the place where it is available to the place where it is used. They can change the size and direction of force. Certain types of machines allow us to apply a very large force to something by using a small force. This is called a force advantage. They can change the distance and speed with which something is moving. This is called giving a distance or speed advantage. A typical example of simple machines is the lever, which has found extremely wide use in our production practice. Some other simple machines can be seen like a seesaw, an axe, a wheelbarrow, a pair of scissors and a hammer. These are examples of levers. By using these, tasks which would be difficult for you to do can be done more easily. A lever is a rigid bar. The crowbar in Figure 1 is an example of a simple lever. All levers have the following parts: 1. The fulcrum is the fixed point around which the lever can turn. 2. The effort force is the force applied to the lever. It is sometimes called the input force or simply the effort. 3. The effort arm is the distance between the fulcrum and the point where the effort force is applied. 4. The load force is the force moving the load. It is the output force of the lever and is sometimes simply called the load. 5. The load arm is the distance from the fulcrum to the position of the load. A wheelbarrow allows us to lift a heavy load by using a fairly small force. The wheelbarrow can be draw as a rigid bar as is shown in figure 2. the wheel axle acts as the fulcrum. It can easily be seen that the effort arm is longer than the load arm. This gives a force advantage because the load force is greater than the effort force that is applied. However, the effort force has to be moved much further than the load. Fig.1 A crow-bar Fig.2 A wheelbarrow If the fulcrum is placed so that the load arm is longer than the effort arm, a large force is needed to move a small load, but it moves the load a long way. This gives a speed advantage. This idea can be seen in the fishing rod. The large effort force applied by the fisherman moves only a small load, the fish. However itdoes allow the fisherman to drag the fish in quickly. Often simple machines are made of double levers. Scissors, pliers, nutcrackers and tinsnips are all double levers. double levers 雙重杠桿 effort arm 力臂 effort force 作用力 force advantage 力增益 in a more convenient way 以某種較為方便的方式 inclined plane 斜面 load arm 重力臂 load force 荷載力（重力） rigid bar 剛性桿 speed advantage 速度增益 input force 輸入力 文中為作用力 output force 輸出力 文中為載荷力或阻力 B Tools and Machines Each department in manufacturing uses tools to do its job. In general, tools and machines process (change) materials or information. Production department workers use tools to change materials into finished products. The finance department uses calculators and computers to keep track of the company's finances. Marketing workers send product information to consumers through advertisements made with video and audio recording machines. Workers in manufacturing must know how to use the tools of their trade. Defining tools and machines Tools extend human abilities in doing the work of processing (changing) materials or information. So, strictly speaking, machines are also tools. Tools extend human abilities by increasing the power, speed, efficiency, accuracy, and productivity of work. We cannot drive nails in boards with our bare hands, but we can drive nails with a tool – the hammer. We can do math problems in our head, but an electronic calculator is faster and more accurate. Both the hammer and the calculator are tools that extend our abilities. Generally, tools can be described as hand tools, power hand tools, or machines. A hand tool is the simplest form. The user holds it in the hand and moves it to perform work. It is powered only by the user. Hand saws, screwdrivers, and hand planes are examples of hand tools. Power hand tools are improved hand tools. The user holds one in the hand and moves it to perform work, but the processing power comes from an external source, such as an electric motor. Power circular saws, electric screwdrivers, and power planes are some power hand tools. Machines stay still during processing and use an externally powered tool that is fastened to the machine to do the actual processing. Table saws, drill presses, and planers are all machines. Another category of manufacturing tools is equipment. Equipment covers devices that cannot be defined as machine, power hand tools, or hand tools. Equipment stays still on a structure during processing and uses human or thermal (heat) power too process materials. Examples include the human-powered squaring shears for shearing metal and ovens, and furnaces used to melt materials. All tools, machines, and equipment extend human abilities by increasing the power, speed, efficiency, accuracy, and productivity of processing materials or information. The six basic machines We base the principles that describe how tools work on the basic machines – wheelsevers, pulleys, inclined planes, wedges, and screws, (see the fig.). The purpose of these basic machines is to gain a mechanical advantage in doing work. A mechanical advantage is an increase in a force. Mechanical advantage of force is abbreviated MAF. A simple example is driving nails in wood. Without a hammer, you would not be able to drive the nails. By placing the hammer in your hand, you create a lever that gives you a mechanical advantage of force over the nail. The nail itself uses wedge action to cut into the wood. For anther example, look at the frill press, often found in labs. The drill bit uses a wedge for its cutting action. Inclined planes hold the drill bit in the chuck. Screw threads hold the drill press together. Pulleys transfer power from the motor to the drill bit. The handle on the drill press acts as a lever attached to a wheel and axle. Every time one of the six basic machines is used in a tool or machine, mechanical advantage is realized. Identify the six basic machines in other tools and machines in your lab. dri