1、XXX大学邮电与信息工程学院外文文献翻译文 献 名 Planetary Gears 文献译名 行星齿轮结构 专业班级 学 号 学生姓名 指导教师 指导教师职称 学 部 名 称 完成日期： 年 5 月 21日英文原文Planetary GearsIntroductionThe Tamiya planetary gearbox is driven by a small DC motor that runs at about 10,500 rpm on 3.0V DC and draws about 1.0A. The maximum speed ratio is 1:400, giving an
2、output speed of about 26 rpm. Four planetary stages are supplied with the gearbox, two 1:4 and two 1:5, and any combination can be selected. Not only is this a good drive for small mechanical applications, it provides an excellent review of epicycle gear trains. The gearbox is a very well-designed p
3、lastic kit that can be assembled in about an hour with very few tools. The source for the kit is given in the References. Lets begin by reviewing the fundamentals of gearing, and the trick of analyzing epicyclic gear trains.Epicyclic Gear Trains A pair of spur gears is represented in the diagram by
4、their pitch circles, which are tangent at the pitch point P. The meshing gear teeth extend beyond the pitch circle by the addendum, and the spaces between them have a depth beneath the pitch circle by the dedendum. If the radii of the pitch circles are a and b, the distance between the gear shafts i
5、s a + b. In the action of the gears, the pitch circles roll on one another without slipping. To ensure this, the gear teeth must have a proper shape so that when the driving gear moves uniformly, so does the driven gear. This means that the line of pressure, normal to the tooth profiles in contact,
6、passes through the pitch point. Then, the transmission of power will be free of vibration and high speeds are possible. We wont talk further about gear teeth here, having stated this fundamental principle of gearing. If a gear of pitch radius a has N teeth, then the distance between corresponding po
7、ints on successive teeth will be 2a/N, a quantity called the circular pitch. If two gears are to mate, the circular pitches must be the same. The pitch is usually stated as the ration 2a/N, called the diametral pitch. If you count the number of teeth on a gear, then the pitch diameter is the number
8、of teeth times the diametral pitch. If you know the pitch diameters of two gears, then you can specify the distance between the shafts. The velocity ratio r of a pair of gears is the ratio of the angular velocity of the driven gear to the angular velocity of the driving gear. By the condition of rol
9、ling of pitch circles, r = -a/b = -N1/N2, since pitch radii are proportional to the number of teeth. The angular velocity n of the gears may be given in radians/sec, revolutions per minute (rpm), or any similar units. If we take one direction of rotation as positive, then the other direction is nega
10、tive. This is the reason for the (-) sign in the above expression. If one of the gears is internal (having teeth on its inner rim), then the velocity ratio is positive, since the gears will rotate in the same direction. The usual involute gears have a tooth shape that is tolerant of variations in th
11、e distance between the axes, so the gears will run smoothly if this distance is not quite correct. The velocity ratio of the gears does not depend on the exact spacing of the axes, but is fixed by the number of teeth, or what is the same thing, by the pitch diameters. Slightly increasing the distanc
12、e above its theoretical value makes the gears run easier, since the clearances are larger. On the other hand, backlash is also increased, which may not be desired in some applications. An epicyclic gear train has gear shafts mounted on a moving arm or carrier that can rotate about the axis, as well
13、as the gears themselves. The arm can be an input element, or an output element, and can be held fixed or allowed to rotate. The outer gear is the ring gear or annulus. A simple but very common epicyclic train is the sun-and-planet epicyclic train, shown in the figure at the left. Three planetary gea
14、rs are used for mechanical reasons; they may be considered as one in describing the action of the gearing. The sun gear, the arm, or the ring gear may be input or output links. If the arm is fixed, so that it cannot rotate, we have a simple train of three gears. Then, n2/n1 = -N1/N2, n3/n2 = +N2/N3,
15、 and n3/n1 = -N1/N3. This is very simple, and should not be confusing. If the arm is allowed to move, figuring out the velocity ratios taxes the human intellect. Attempting this will show the truth of the statement; if you can manage it, you deserve praise and fame. It is by no means impossible, just invoved. However, there is a very easy way to get the desired result. First, just consider the gear train locked, so it moves as a rigid body, arm and all. All
