TAILIEUCHUNG - Robotics Part 3

Tham khảo tài liệu 'robotics part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 38 Robotics gear. Gear A turns in a counter clockwise direction and also gear C turns in a counter clockwise direction. The idler gear is used so that the rotation of the two important gears is the same. Velocity Ratio We know that the velocity ratio of a pair of gears is the inverse proportion of the diameters of their pitch circle and the diameter of the pitch circle equals the number of teeth divided by the diametric pitch. Also we know that it is necessary for the mating gears to have the same diametric pitch to satisfy the condition of correct meshing. Thus we infer that the velocity ratio of a pair of gears is the inverse ratio of their number of teeth. For the ordinary gear trains in Figure we have w N 2 w2 N 3 w N 4 - 2 2 3 3 4. 2 3 w2 N w3 N2 w4 N3 v . 1 These equations can be combined to give the velocity ratio of the first gear in the train to the last gear 1 N2 N3 N4 N 4 N1 N2 N3 N1 _ T The tooth numbers in the numerator are those of the driven gears and the tooth numbers in the denominator belong to the driver gears. Gear 2 and 3 both drive and are in turn driven. Thus they are called idler gears. Since their tooth numbers cancel idler gears do not affect the magnitude of the input-output ratio but they do change the directions of rotation. Note the directional arrows in Figure . Idler gears can also constitute a saving of space and money if gear 1 and 4 mesh directly across a long center distance their pitch circle will be much larger . There are two ways to determine the direction of the rotary direction. The first way is to label arrows for each gear as in Figure . The second way is to multiple mth power of -1 to the general velocity ratio. Where m is the number of pairs of external contact gears internal contact gear pairs do not change the rotary direction . However the second method cannot be applied to the spatial gear trains. Thus it is not difficult to get the velocity ratio of the gear train in Figure 1 -1 2 N2 N4 4 N1

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