Electro-optical position-monitoring apparatus with tracking detector

Claim 1

In an electro-optical object-position-monitoring system including a beam-projecting non-traveling light source, and imaging means for collecting and transmitting light from said source which is reflected by a monitored object, receptor means positioned to receive reflected light transmitted by said imaging means, operable to produce an output response interpretable to indicate monitored object position, said receptor means comprising a carriage mounted adjacent said imaging means for reversible movement along a path generally transverse to the transmission axis of said imaging means, a receiver mounted on said carriage disposed to receive light transmitted by said imaging means, and operable to divide such light for transmission along two different optical paths, with the amount of light transmitted along each path dependent on the position of said receiver relative to light transmitted by said imaging means, photodetector means for each path, each responsive to light transmitted therealong to produce a signal reflective of the intensity of light received by the photodetector means, and means operatively interposed between said photodetector means and said carriage, operable in response to signals produced by the former to effect movement of the latter so as to equalize such signals, said path being oriented whereby, at all positions of said carriage therealong, and under circumstances wherein an image of reflected light causes said two photodetectors to produce equal signals, such image is in focus on said receiver.