a mechanism in which points on the links describe nonplanar trajectories or trajectories that lie on intersecting planes. Spherical mechanisms, in which the trajectories of points on the links are situated on concentric spheres, are used extensively in technology to transfer rotation between intersecting axes, for example, in gear drives, bevel universal-joint drives in automobiles, and radar mechanisms. Rotation is transferred between intersecting axes by means of three-dimensional gear mechanisms, such as worm gears, mechanisms with helical gears, and hypoid drives. Automated machinery in light industry and the food industry uses three-dimensional mechanisms not only to transfer rotary motion but also to reproduce three-dimensional trajectories, for example, in the thread carrier on sewing machines. Working components in agricultural machines are subject to three-dimensional motions, usually as a result of the unevenness of the soil, and many of the mechanisms correspondingly function in three dimensions. Lever-type three-dimensional mechanisms are used in manipulators and industrial robots to reproduce movements that simulate the movements of human hands. They are also used in certain space-technology devices, such as mechanisms for the spatial orientation of spacecraft and mechanisms in planetary probes.
N. I. LEVITSKII