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毕业设计(论文)任务书设计（论文）课题名称苹果自动去皮机机械设计学生姓名院（系）工学院专 业机制指导教师职 称讲师学 历博士毕业设计（论文）要求：1 设计要自己独立完成，不得抄袭，要具有一定的实用性；2 通过查阅资料，扩充知识面，进一步熟练AutoCAD ,Proe软件制图；3 自学习苹果自动去皮机方向的相关知识；4 初步完成对苹果自动去皮机工作原理，整体框架的设计；5 绘制苹果自动去皮机的装配图和非标准件的零件图；6 写毕业任务说明书。毕业设计（论文）内容与技术参数：1 完成对苹果自动去皮机整体方案的设计，完成相应的零件图纸，装配图纸折合A0号图纸1.5张以上。并需要用AutoCAD和Proe绘制。2 编写相应的说明书，字数不少于4000字，必须是打印稿，并提供电子文档。说明书必须包括苹果自动去皮机总体方案的设计，苹果自动去皮机运动机构的确定，电机的选择，轴的设计和轴承的选择。毕业设计（论文）工作计划：2.20-2.24毕业设计实习，包括去工厂对苹果自动去皮机的参观和学习。2.25-3.5 调研，收集资料3.6-3.17 绘制苹果自动去皮机结构草图，并讨论之3.18-3.25中期考核3.26-4.10 绘制苹果自动去皮机的装配图4.11-5.5 绘制苹果自动去皮机相应的非标准零件图5.5-5.10撰写设计指导书接受任务日期 2013 年 12 月 20 日 要求完成日期 2013 年 5 月 14 日学 生 签 名 2013 年 5月 14日指导教师签名 2013年 5月 14日院长（主任）签名 2013年 5月 14日翻译部分英文原文Gear mechanismsGear mechanisms are used for transmitting motion and power from one shaft to another by means of the positive contact of successively engaging teeth. In about 2,600B.C., Chinese are known to have used a chariot incorporating a complex series of gears like those illustrated in Fig.2.7. Aristotle, in the fourth century B .C .wrote of gears as if they were commonplace. In the fifteenth century A.D., Leonardo da Vinci designed a multitude of devices incorporating many kinds of gears. In comparison with belt and chain drives ,gear drives are more compact ,can operate at high speeds, and can be used where precise timing is desired. The transmission efficiency of gears is as high as 98 percent. On the other hand, gears are usually more costly and require more attention to lubrication, cleanliness, shaft alignment, etc., and usually operate in a closed case with provision for proper lubrication.Gear mechanisms can be divided into planar gear mechanisms and spatial gear mechanisms. Planar gear mechanisms are used to transmit motion and spatial gear mechanisms. Planar gear mechanisms are used to transmit motion and power between parallel shafts ,and spatial gear mechanisms between nonparallel shafts.Types of gears(1) Spur gears. The spur gear has a cylindrical pitch surface and has straight teeth parallel to its axis as shown in Fig. 2.8. They are used to transmit motion and power between parallel shafts. The tooth surfaces of spur gears contact on a straight line parallel to the axes of gears. This implies that tooth profiles go into and out of contact along the whole facewidth at the same time. This will therefore result in the sudden loading and sudden unloading on teeth as profiles go into and out of contact. As aresult, vibration and noise are produced.(2) Helical gears. These gears have their tooth elements at an angle or helix to the axis of the gear(Fig.2.9). The tooth surfaces of two engaging helical gears inn planar gear mechanisms contact on a straight line inclined to the axes of the gears. The length of the contact line changes gradually from zero to maximum and then from maximum to zero. The loading and unloading of the teeth become gradual and smooth. Helical gears may be used to transmit motion and power between parallel shaftsFig. 2.9(a)or shafts at an angle to each otherFig. 2.9(d). A herringbone gear Fig. 2.9(c) is equivalent to a right-hand and a left-hand helical gear placed side by side. Because of the angle of the tooth, helical gears create considerable side thrust on the shaft. A herringbone gear corrects this thrust by neutralizing it , allowing the use of a small thrust bearing instead of a large one and perhaps eliminating one altogether. Often a central groove is made around the gear for ease in machining.(3) Bevel gars. The teeth of a bevel gear are distributed on the frustum of a cone. The corresponding pitch cylinder in cylindrical gears becomes pitch cone. The dimensions of teeth on different transverse planes are different. For convenience, parameters and dimensions at the large end are taken to be standard values. Bevel gears are used to connect shafts which are not parallel to each other. Usually the shafts are 90 deg. to each other, but may be more or less than 90 deg. The two mating gears may have the same number of teeth for the purpose of changing direction of motion only, or they may have a different number of teeth for the purpose of changing both speed and direction. The tooth elements may be straight or spiral, so that we have plain and spiral bevel gears. Hypoid comes from the word hyperboloid and indicates the surface on which the tooth face lies. Hypoid gears are similar to bevel gears, but the two shafts do not intersect. The teeth are curved, and because of the nonintersection of the shafts, bearings can be placed on each side of each gear. The principal use of thid type of gear is in automobile rear ends for the purpose of lowering the drive shaft, and thus the car floor.(4) Worm and worm gears. Worm gear drives are used to transmit motion and ower between non-intersecting and non-parallel shafts, usually crossing at a right angle, especially where it is desired to obtain high gear reduction in a limited space. Worms are a kind of screw, usually right handed for convenience of cutting, or left handed it necessary. According to the enveloping type, worms can be divided into single and double enveloping. Worms are usually drivers to reduce the speed. If not self-locking, a worm gear can also be the driver in a so called back-driving mechanism to increase the speed. Two things characterize worm gearing (a) large velocity ratios, and (b) high sliding velocities. The latter means that heat generation and power transmission efficiency are of greater concern than with other types of gears.(5) Racks. A rack is a gear with an infinite radius, or a gear with its perimeter stretched out into a straight line. It is used to change reciprocating motion to rotary motion or vice versa. A lathe rack and pinion is good example of this mechanism.Geometry of gear toothThe basic requirement of gear-tooth geometry is the provision of angular velocity rations that are exactly constant. Of course, manufacturing inaccuracies and tooth deflections well cause slight deviations in velocity ratio; but acceptable tooth profiles are based on theoretical curves that meet this criterion.The action of a pair of gear teeth satisfying this requirement is termed conjugate gear-tooth action, and is illustrated in Fig. 2.12. The basic law of conjugate gear-tooth action states that as the gears rotate, the common normal to the surfaces at the point of contact must always intersect the line of centers at the same point P called the pitch point.The law of conjugate gear-tooth can be satisfied by various tooth shapes, but the only one of current importance is the involute, or, more precisely, the involute of the circle. (Its last important competitor was the cycloidal shape, used in the gears of Model T Ford transmissions.) An involute (of the circle) is the curve generated by any point on a taut thread as it unwinds from a circle, called the base circle. The generation of two involutes is shown in Fig. 2.13. The dotted lines show how these could correspond to the outer portion of the right sides of adjacent gear teeth. Correspondingly, involutes generated by unwinding a thread wrapped counterclockwise around the base circle would for the outer portions of the left sides of the teeth. Note that at every point, the involute is perpendicular to the taut thread, since the involute is a circular arc with everincreasing radius, and a radius is always perpendicular to its circular arc. It is important to note that an involute can be developed as far as desired outside the base circle, but an involute cannot exist inside its base circle.Let us now develop a mating pair of involute gear teeth in three steps: friction drive, belt drive, and finally, involute gear-tooth drive. Figure 2.14 shows two pitch circles. Imagine that they represent two cylinders pressed together. If slippage does not occur, rotation of one cylinder (pitch circle) will cause rotation of the other at an angular velocity ratio inversely proportional to their diameters. In any pair of mating gears, the smaller of the two is called the pinion and the larger one the gear. (The term “gear” is used in a general sense to indicate either of the members, and also in a specific sense to indicate the larger of the two.) Using subscripts p and g to denote pinion and gear, respectively.In order to transmit more torque than is possible with friction drive alone, we now add a belt drive running between pulleys representing the base circles, as in Fig 2.15. If the pinion is turned counterclockwise a few degrees, the belt will cause the gear to rotate in accordance with correct velocity ratio. In gear parlance, angle is called the pressure angle. From similar triangles, the base circles have the same ratio as the pitch; thus, the velocity ratio provided by the friction and belt drives are the same.In Fig. 2.16 the belt is cut at point c, and the two ends are used to generate involute profiles de and fg for the pinion and gear, respectively. It should now be clear why is called the pressure angle: neglecting sliding friction, the force of one involute tooth pushing against the other is always at an angle equal to the pressure angle. A comparison of Fig. 2.16 and Fig.2.12 shows that the involute profiles do indeed satisfy the fundamental law of conjugate gear-tooth action. Incidentally, the involute is the only geometric profile satisfying this law that maintains a constant pressure angle as the gears rotate. Note especially that conjugate involute action can take place only outside of both base circles.Nomenclature of spur gear The nomenclature of spur gear (Fig .2.17) is mostly applicable to all other type of gears.The diameter of each of the original rolling cylinders of two mating gears is called the pitch diameter, and the cylinders sectional outline is called the pitch circle. The pitch circles are tangent to each other at pitch point. The circle from which the involute is generated is called the base circle. The circle where the tops of the teeth lie is called the dedendum circle. Similarly, the circle where the roots of the teeth lie is called the dedendum circle. Between the addendum circle and the dedendum circle, there is an important circle which is called the reference circle. Parameters on the reference circle are standardized. The module m of a gear is introduced on the reference circle as a basic parameter, which is defined as m=p/. Sizes of the teeth and gear are proportional to the module m.The addendum is the radial distance from the reference circle to the addendum circle. The dedendum is the radial distance from the reference circle to the dedendum circle. Clearance is the difference between addendum and dedendum in mating gears. Clearance prevents binding caused by any possible eccentricity.The circular pitch p is the distance between corresponding side of neighboring teeth, measured along the reference circle. The base pitch is similar to the circular pitch is measured along the base circle instead of along the reference circle. It can easily be seen that the base radius equals the reference radius times the cosine of the pressure angle. Since, for a given angle, the ratio between any subtended arc and its radius is constant, it is also true that the base pitch equals the circular pitch times the cosine of the pressure angle. The pressure angle is the angle between the normal and the circumferential velocity of the point on a specific circle. The pressure angle on the reference circle is also standardized. It is most commonly 20(sometimes 15).The line of centers is a line passing through the centers of two mating gears. The center distance (measured along the line of centers) equals the sum of the pitch radii of pinion and gear.Tooth thickness is the width of the tooth, measured along the reference circle, is also referred to as tooth thickness. Width of space is the distance between facing side of adjacent teeth, measured along the reference circle. Tooth thickness plus width of space equals the circular pitch. Backlash is the width of space minus the tooth thickness. Face width measures tooth width in an axial direction.The face of the tooth is the active surface of the tooth outside the pitch cylinder. The flank of the tooth is the active surface inside the pitch cylinder. The fillet is the rounded corner at the base of the tooth. The working depth is the sum of the addendum of a gear and the addendum of its mating gear.In order to mate properly, gears running together must have: (a) the same module; (b) the same pressure angle; (c) the same addendum and dedendum. The last requirement is valid for standard gears only. Rolling-Contactbearings The rolling-contact bearing consists of niier and outer rings sepatated by a number of rolling elements in the form of balls ,which are held in separators or retainers, and roller bearings have mainly cyinndrical, conical , or barrelcage.The needles are retainde by integral flanges on the outer race, Bearigs with rolling contact have no skopstick effect,low statting torqeu and running friction,and unlike as in journal bearings. The coefficient of friction varies little with load or opeed.Probably the outstanding of a rolling-contant beating over a sliding bearing is its low statting friction.The srdinary sliding bearing starts from rest with practically metal to metal contact and has a high coefficient of friction as compared with that between rolling members.This teature is of particular important in the case of beatings whcch vust carry the same laode at test as when tunning,for example.less than one-thirtieth as much force is required to start a raliroad freight car equopped with roller beatings as with plain journal bearings.However.most journal bearing can only carry relatively light loads while starting and do not become heavily loaded until the speed is high enough for a hydrodynamic film to be built up.At this time the friction id that in the luvricant ,and in a properly designed journal bearing the viscous friction will be in the same order of magnitude ad that for a that for a rolling-conanct bearing.中文译文齿轮机构齿轮机构用来传递运动和动力，通过连续啮合轮齿的正确接触，从一根轴传动到另一根轴。大约公元前2600年，中国人就能够使用一系列战车而闻名复杂的齿轮机构而构成的。公元前4世纪，亚里士多德写的齿轮好象推动的是平凡的。在公元15世纪，Leonardo da Vinci 设计了能与许多种类的齿轮枢结合的大量装置。与皮带和链传动相比较，齿轮传动装置更加紧凑，能高速运行，也能够被运用在要求准确定时的场合。齿轮传动的传动效率高达98。另一方面，齿轮传动机构成本高，而且要求注意润滑、清洁度、轴的对中等等，经常用在提供准确箱体润滑的闭式情况下。齿轮机构能被分为平面齿轮机构和空间齿轮机构。平面齿轮机构被用于传递运动和动力，而平行轴间的运动和动力空间齿轮机构用于传递不平行轴间的运动和动力。齿轮的分类：1、 直齿轮 直齿轮有节轮表面和平行于轮的轴线的直齿轮，如图2.8所示。它们用于传递两平行轴间的运动和动力。两配合的直接齿面啮合在一条平行于其轴线的直线上，这意味着整个齿宽在同一时刻啮合脱开，这样在齿面上导致加载或卸载，当齿轮啮合或脱开时，结果推动和噪声就产生了。（1） 斜齿轮 这种齿轮的轮齿有一位角度或与其轴线旋转一定角度在平面齿轮机构中相互啮合，斜齿轮齿面相啮合于一条倾斜于轴承的直线上，啮合线的长度从0逐渐变化到最大再从最大变化到0，轮齿的加载和卸载变得平稳均匀的运动和动力。人字齿轮相当于右旋齿轮和左旋齿轮并在一起，因为轮齿存在一定角度，斜齿轮产生相当大的轴间推力，人字齿轮通过相互抵消纠正了这一推力，允许其使用以推力轴承代替大推力轴承，或不同推力轴承，为了加工方便经常沿着齿轮加工一个中心槽。（2） 伞状齿轮 伞状齿轮是依据平截头圆锥体分配的。圆柱齿轮的节圆柱成为分圆锥，齿轮的齿的横剖面的尺寸是不同的。为了方便起见，锥齿轮的大头端部的参数和尺寸作为标准值。习惯上锥齿轮相互作用的轴彼此不是平行的，通常两轴线彼此成为90度，有时会比90度或多或少。两个相互啮合的齿轮仅仅为了变向或许有一样的齿数，又或者为了改变速度和方向而齿数不同。锥齿轮可能是直齿的也可能是螺旋形齿轮，以便我们有简单的和螺旋形的齿轮。准双曲面来自于双曲面和齿面的放置的表面。准双曲面的齿轮属于锥齿轮，但是两轴不能横断，因为轴的材料，它的齿是曲线的，轴承可以位于各齿轮的各个侧面。这种齿轮主要用在汽车后方末端是为了降低传动轴并且用在汽车踏板处。（3） 蜗轮蜗杆齿轮 蜗轮传动惯于传递动力和功率，它的轴既不相交也不平行，通常都是垂直的，尤其是要求获得高的齿轮减速在一定的极限运算范围内。蜗杆是螺旋的，通常为了方便起见都是顺时针方向的，如果需要的话也可是左旋方向的。按照类型，可以是单螺旋的也可以是双螺旋的，螺杆通常用来降低速度的，即使不自动锁住，螺杆也能够被驱动，所以称作回力驱动机构，为了提高速度。下面是蜗轮蜗杆传动装置的两个特点：（a）有很高的传动速度（b）后者意思指和其它种类的齿轮相比中心有高的发热性和电力传输效率。齿轮轮齿形状轮齿几何形状的基本要求提供一个准确不变的角速度，当然制造端差和轮齿变形将会在速度比上产生微小的偏差，然而可接受的齿形依据基于满足这一判剧的理论曲线得出的。满足这要求的一对配合齿轮的运动被称为共轭齿轮传动。如图2.12所示，共轭齿轮传动的基本定律论述为当齿轮转动时，接触点表面的公法线总是与中心线交于一点P，这点叫节点。共轭齿轮传动原则能