华侨大学
design, according to the application situation to from the travelling schedule and the state of motion request, determines from the movement rule. 3. cam gears basic parameter design, determines from the travelling schedule, various movements angle, the cam radius, , the roller radius, the center distance, from the length and so on. 4. cam contours curve design. 5. cam gears bearing capacity computation. 6. cam gears structural design, plan organization assembly drawing and various components shop drawing
Fromstructural design: from structure: When design must consider from the guidance and prevented revolves. From movement rule design: The cam gear design basic question 1. cam gears type choice, the definite cam shape, with from maintains the high vice- contact from the shape and the movement form and the cam the way 2. from the movement rule design, according to the application situation to fromthe travelling schedule and the movement 1, the cam gear application cam gear is includes the cam the high vice- organization, the cam gear has the structure to be simple, may accurately realize request merit and so on movement rule, thus obtains the widespread application in the industrial production, specially automatic device and in the automatic control device, obtains the widespread application. 2nd, the cam gear classification according to two moves the relative motion characteristic classification between the component (1) the plane cam gear 1) the disk cam; 2) translation cam. (2) space cam gear according to from movement vice- element shape classification (1) apex from; (2) roller from (3) flat base from. Note: Classifies this part of content when the introduction cam gear, should point out each kind of cam gear the good and bad points and its the adaption situation, showed each kind of cam gear the inner link, will build the foundation for the later translation cam and the column cam contour design.
3rd, the throwout lever movement rule (1) the cam gear cycle of motion and the basic term terminology push the regulation movement angle: With from pushes the cam corner which the regulation corresponds; Far stops the angle: With from far rests the cam corner which the regulation corresponds; Return trip movement angle: With cam corner which corresponds from the return trip; Nearly stops the angle: With from nearly rests the cam corner which the regulation corresponds; Cam: Take the cam axle center as the center of a circle, take its outline slightly to diameter r0 as the radius circle; From ravelling schedule: In pushes in the regulation or the return trip from the biggest displacement, indicated with h;: The cam center
26
华侨大学
of rotation with from guides way the bias distance, indicated with e. Types of Cams
Plate cams are simple to fabricate.The follower can be moved in various patterns with various rise /fall ratios.Motion should be controlled to avoid abrupt changes in force transmitted from the cam to the follower.One should carefully determine horizontal force components,since these present problems designing the follower assembly guide.Critical reactions occur at points A and B.These reaction values must be computed.The relative vertical position of point A with respect to B needs to be raised if the reaction value at Bis excessive.The position of B should be as close to cam as possible to minimize flexure in the roller-follower support.
This type produces reciprocating motion in the follower.Again,dorces need to be determined and dimensions chosen so as to avoid excessive component sizes.A tapered roller follower is frequently employed ;the groove in the periphery of the cam should be shaped to accommodate the follower.This type of cam is expensive to produce.The cylindrical cam has two outstanding features.One is the fact that the cam is positive actiong.N outside forces (such as gravity or spring action ) are needed to hold the follower against the working surface of the cam.The second feature is the fact that the follower can move through a complete cycle in the course of several revolutions of the cam.For example,it is possible to design the cam so the follower could move from a starting position at the left end to the extreme right position in three revolutions( or more),then the starting position in two revolutions.Other variations are possible.
A translation cam is illustrated.In the figure shown the cam reciprocates horizontally and the follower moves up and down.A pivoted follower can be used with this type .The translation cam can be made positive by providing a guided plate with an inclined slot for the cam;the slot cam then engage a pin or roller on a guided vertical reciprocated follower.With the latter type ,however,a complete force analysis is a critical phase of the design.
In this type,the cam rotates and the follower (ususlly a roller or pin) is guided by a groove cut into the end face of a cylindrical section .Rotation of the cam provides translation of the follower.This type is also positive acting.Production costs for this type of cam are much higher than for a simple plate cam.
27
华侨大学
A constant –diameter cam is illustrated .This is merely a circular plate with the camshaft hole eccentrically located.The amount of eccentricity determines the amount of follower displacement.As the cam rotates,the follower reciprocates.This arrangement is sometimes known as a Scotch yoke mechanism.Follower action is positive ;harmonic motion is produced by this type of arrangement.
Types of Followers
In neneral,the follower is considered to be the part that comes in contact with the cam profile .However,when a seconday follower is used, the motion of the secondary follower is dictated by that of the primary follower.For example ,a roller follower can be reciprocated by acting against the edge of a pivoted follower.
The simplest type of follower is the reciprocationg type that merely moves up and down (or in and out ) with the rotation of the cam;the centerline can be either collinear with the cam centerline or offset from it .Contact with the cam can be via a point,a knife edge,a suface ,or a roller.A flat-afced reciprocating follower is shown If a point or surface is employed for contact the high normal force can result in abrasion and excessive wear.If the load being transmitted from the cam to the follower is small,the problem is not serious.For example ,the operation of a small snap-action switch does not produce cam surface wear.Miniature snap-action electrical switches have actuators with various configurations;some of these are in the form of rounded points or thin meta sections.Miniature three-way valves in air circuits have similar actuators.If cams are used to operate mechanical components directly,a roller is much more effective.
Cam rollers are commercially available in roller sizes ranging from1/2 in .to 6 in Basic dynamic capacities range from 620 to 60000 ,based on 33.33 rpm and 500hr of minimum life .Correction factors must be used for any other speed or life values.It should be noted that the cam can be lubricated through and oil hole in the end of the shank.Rolling contact with the cam surface minimizes wear problems.Several mounting arrangements are possible with this type of followr .shows the roller follower mounted on a pivoted arm .A pivoted flat-faced follower is shown .As with any flat-faced follower,friction between the follower face and the cam profile must be controlled.Proper lubrication can reduce the effects of friction.
28
华侨大学
6.2 汉语翻译:
凸轮
通过凸轮和从动件的作用，可得到不同的运动。许多计时装置由凸轮驱动。使用凸轮的目的是使其从动件产生位移，次级从动件常用来在另一位置产生附加位移。最常用的凸轮是盘形凸轮。圆柱凸轮用来将其旋转运动转变为从动件的直线运动。最常用的凸轮是盘形凸轮。圆柱凸轮 用来将其放置运动转变为从动件的直线运动。有时也用三维凸轮，它们提供一些不建党的从动件运动，也使从动件设计难度加大。汽车发动机上的凸轮轴显示了盘形凸轮的简单和重要的应用场合，录音机上的凸轮组件是更复杂的应用实例。
凸轮轮廓可用作图法或数学计算法来精确设计，将设计图转换成加工图可用下面几种方法：
1．制造一个实尺样板。这是制造需要，但不能保证精确的凸轮轮廓。 2．使用径向尺寸设计。这相当精确，但在生产时有时会产生排布问题。 3．用座标尺寸设计。这种方法能保证精度。 选用这些方法时，应按要求的精度考虑凸轮的作用。 凸轮的结构设计：
因凸轮的工作轮廓已经确定，所以凸轮的结构设计主要是确定曲线轮廓的轴向厚度和凸轮与传动轴的连接方式。当工作载荷较小时，曲线轮廓的轴向厚度一般取为轮廓曲线最大矢径的1/10～1/5；对于受力较大的重要场合，需按凸轮轮廓面与从动件间的接触强度进行设计。
在确定凸轮与传动轴的联接方式时，应综合考虑凸轮的装拆、调整和固定等问题。对于执行机构较多的设备，其各执行构件之间的运动协调性通常由运动循环图确定，因此在装配凸轮机构时，凸轮轮廓曲线起始点（推程开始点）的相对位置需按运动循环图进行调整，以保证各执行构件能按预定程序协调动作。为此，在结构设计上要求凸轮能相对于传动轴沿圆周方向进行转动，并可靠地加以固定。最简便的方法是采用紧定螺钉固定凸轮，或用紧定螺钉预固定，待调整好后再用销子固定。
从动件的结构设计：
直动从动件的结构：设计时要考虑从动件的导向和防止旋转。 从动件运动规律的设计:
从动件运动规律的设计涉及许多方面的问题，除考虑刚性冲击和柔性冲击外，还应对各种运动规律所具有的最大速度vmax、最大加速度amax及其影响加以比较。
29
华侨大学
1) vmax愈大，则动量mv愈大。若从动件突然被阻止，过大的动量会导致极大的冲击力，危及设备和人身安全。因此，当从动件质量较大时，为了减小动量，应选择vmax值较小的运动规律。
2) amax愈大，惯性力愈大。作用在高副接触处的应力愈大，机构的强度和耐磨性要求也就愈高。对于高速凸轮，为了减小惯性力的危害，应选择amax值较小的运动规律。 前述几种运动规律的vmax、amax、冲击特性及适用场合如下表
对于摆动从动件凸轮机构，其运动线图的横坐标表示凸轮转角，纵坐标则分别表示从动件的角位移、角速度和角加速度。这类运动线图具有的运动特性与上述相同。 凸轮机构设计的基本问题
1. 凸轮机构类型选择，确定凸轮形状、从动件形状与运动形式及凸轮与从动件维持高副接触的方式
2. 从动件运动规律设计，根据应用场合对从动件行程和运动特性的要求，确定从动件运动规律。
3. 凸轮机构基本参数设计，确定从动件行程、各运动角、凸轮基圆半径、偏距、滚子半径、中心距、从动件长度等。 4. 凸轮轮廓曲线设计。 5. 凸轮机构承载能力计算。
6. 凸轮机构结构设计，绘制机构装配图和各零件的工作图。 凸轮机构的应用
凸轮机构是含有凸轮的高副机构，凸轮机构具有结构简单，可以准确实现要求的运动规律等优点，因而在工业生产中得到广泛的应用，特别是自动机械和自动控制装置中，得到广泛的应用。 凸轮机构的分类
按两活动构件间的相对运动特性分类 (1)平面凸轮机构 1)盘形凸轮； 2)移动凸轮。 (2)空间凸轮机构
按从动件运动副元素形状分类 (1)尖顶从动件；
30