2.2.3. Cranks and Rollers

Depending on the movement characteristics of the crank linkage, the crank length should not be designed to be too long or too short. A crank that is too long may result in the rollers becoming stuck in the cam slide and not moving continuously. Meanwhile, a crank that is too short will result in the mechanism running less smoothly and with more impact on the cam slide. The crank is hinged to the roller at one end and pinned to the poppet shaft at the other end. With reference to various models of pickup devices, a crank length of 110 mm was finally chosen.

**Figure 6.** Schematic diagram of the structure of the roller disc: (1) spring gear shaft seat (2) central hole of the drive shaft (3) disc.

The size of the roller radius *rr* should take into account the size of the cam slide. As the roller is rolling frictionally and is subjected to large forces when working, a small radius will lead to serious wear on the slide, and the roller is prone to deformation when the radius is too large. Therefore, the size of the rollers should therefore be designed to satisfy Equation (2):

$$r\_r = (0.1 - 0.5) \ R\_a \tag{2}$$

where *Ra* is the radius of the base circle, mm; *rr* is the radius of the rollers, mm.

The final radius of the rollers was determined to be 45 mm, and the crank poppet shaft-fixing structure is shown in Figure 7.

**Figure 7.** Fixed structure of the crank gear shaft: (1) crank (2) bearing (3) roller (4) connecting rod (5) gear shaft.
