VDI 2154:2015-03

The standard spherical four-bar crank mechanisms consist of four links connected together by four revolute joints with each other. The axes of rotation of all joints intersect at a single point. Having a degree of freedom (mobility) of F = +l, spherical four-bar crank mechanisms, like planar four-bar crank mechanisms, are constrained mechanisms. They derive from a fourbar kinematic chain with revolute joint axes intersecting at a single point when one of the links is selected as the frame.