Assessment of the finger contact surface to promote the spin motion in finger follower mechanisms

This work describes the kinematic properties of finger-follower mechanisms in the spatial domain in relation to the spin motion of the follower. In this framework, the effectiveness of the cylinder-on-sphere coupling as contact condition between finger and follower is assessed in relation to the classical cone-on-sphere coupling, showing the capability of the former to achieve a satisfactory valve spin pivoting radius. An analytical study is performed by taking advantage of a geometrical approach which allows to evaluate 3D layouts, demonstrating that the cylinder-on-sphere coupling requires a higher number of design parameters to fully determine the mechanism. This characteristic increases the complexity of the system, but it adds freedom and flexibility to the design procedure. Several design configurations are evaluated to highlight this aspect thanks to a dedicated parametric study, where the declivity of the contact surface is shown to represent the key parameter controlling the spin pivoting radius. In this context, the possibility to control the cylinder surface declivity on multiple planes may be adopted to improve the stability of the mechanism behavior with respect to the production tolerances.