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CHAPTER 9 COUPLING, CLUTCHING, AND BRAKING DEVICES COUPLING OF PARALLEL SHAFTS Fig. 1 One method of coupling shafts makes use of gears that can replace chains, pulleys, and friction drives. Its major limitation is the need for adequate center distance. However, an idler can be used for close centers, as shown. This can be a plain pinion or an internal gear. Transmission is at a constant velocity and there is axial freedom. Fig. 2 This coupling consists of two universal joints and a short shaft. Velocity transmission is constant between the input and output shafts if the shafts remain parallel and if the end. | __CHAPTER 9 COUPLING CLUTCHING AND BRAKING DEVICES COUPLING OF PARALLEL SHAFTS Fig. 1 One method of coupling shafts makes use of gears that can replace chains pulleys and friction drives. Its major limitation is the need for adequate center distance. However an idler can be used for close centers as shown. This can be a plain pinion or an internal gear. Transmission is at a constant velocity and there is axial freedom. Fig. 2 This coupling consists of two universal joints and a short shaft. Velocity transmission is constant between the input and output shafts if the shafts remain parallel and if the end yokes are arranged symmetrically. The velocity of the central shaft fluctuates during rotation but high speed and wide angles can cause vibration. The shaft offset can be varied but axial freedom requires that one shaft be spline mounted. Fig. 3 This crossed-axis yoke coupling is a variation of the mechanism shown in Fig. 2. Each shaft has a yoke connected so that it can slide along the arms of a rigid cross member. Transmission is at a constant velocity but the shafts must remain parallel although the offset can vary. There is no axial freedom. The central cross member describes a circle and is thus subjected to centrifugal loads. Fig. 4 This Oldham coupling provides motion at a constant velocity as its central member describes a circle. The shaft offset can vary but the shafts must remain parallel. A small amount of axial freedom is possible. Atilt in the central member can occur because of the offset of the slots. This can be eliminated by enlarging its diameter and milling the slots in the same transverse plane. 294 NOVEL LINKAGE COUPLES OFFSET SHAFTS An unorthodox yet remarkably simple arrangement of links and disks forms the basis of a versatile parallel-shaft coupling. This coupling essentially three disks rotating in unison and interconnected in series by six links se drawing can adapt to wide variations in axial displacement while it is .