Synthesis of spherical four-bar mechanisms for two or three prescribed coupler-curve cusps

This paper presents a new approach for the synthesis of spherical four-bar mechanisms with two or three prescribed coupler curve cusps. According to t he configuration of a spherical four-bar mechanism whose coupler point coin cides with the instant center at two separated positions. two kinds of dege nerated curves for the corresponding spherical Burmester curves are obtaine d For each degenerated curve, a synthesis procedure is proposed for the dim ensional synthesis of spherical four-bar mechanisms to trace a coupler curv e with two prescribed cusps. The possible types of spherical four-bar mecha nisms with two-cusp coupler curves are discussed. Furthermore, special sphe rical double-rockers are also presented for tracing a symmetric coupler cur ve with two cusps, tracing a doubly symmetric coupler curve with two cusps or tracing a symmetric coupler curve with three cusps.