To accommodate misalignment between mating shafts for more than the 3°, a universal joint is used. Angular misalignments of up to 45° are possible at low rotational speeds with single universal joints. It consists of two yokes, a centre bearing block, and two pins that pass through the block at right angles. Approximately 20° – 30° is more reasonable for speeds about 10 rpm. Since universal joints have the disadvantage that the rotational speed of the output shaft is non-uniform in relation to the input shaft. A double universal joint allows the connected shafts to be parallel and offset by large amounts as shown in Figure 16.3. Furthermore, the second joint cancels the non-uniform oscillation of the first joint so the input and the output rotate at the same speed.
Figure 16.3 Universal Joint
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