Light-dark bar coded information reading appts. - has laser beam bent in rotating prism to describe cone

摘要

The device consists of a laser beam bent in a rotating triangular prism so that the emerging beam describes a cone. At the tip of the cone is placed a plane mirror which reflects the beam so that it describes a circle in a bar code reading window. The mirror is tilted to and fro more slowly than the prism is rotated so that the circle precesses in the window. A long prism with three facets is placed between the window and the tilting mirror and the bending of the beam outside the plane middle facet enables the window to be reduced by one third and the beam describes precessing semicircles and arcs. A five facet prism will for instance reduce the window size to one fifth of the diameter of the original circle.