Patent ID: 7531772

Claim:
An apparatus for automatically shifting a lens of a laser focusing optical system, the lens carrying out translational movement along an optical axis, comprising: at least one motor; at least one linkage; a carriage; and a means for determining the position of the lens along the direction of translational motion by means of an optical signal, wherein the lens is moved by the at least one motor which carries out rotational movement, the rotational movement being converted by the at least one linkage into translational movement to displace the carriage on which the lens is mounted, wherein the means for determining the position of the lens comprises at least two light sources, and at least two light detectors, all being arranged rigidly with respect to the movable lens and further comprises at least one cover moving together with the lens and entering into an optical path between the light sources and the light detectors when the lens is being shifted, and wherein the at least one cover is arranged with respect to the light sources and the light detectors such that shifting of the lens in one direction will displace a first part of the cover into a first optical path between a first light source and a first light detector, whereas a second part of the cover becomes displaced out of a second optical path between a second light source and a second light detector, the lens position being determined based on the ratio of the light intensities measured by the first and second light detectors.