Optical character recognition system and method

Claim 3

The method of identifying an unknown character as defined in claim 1 wherein the first and second light beams differ in frequency.

Claim 4

A character recognition system wherein an unknown character is compared to a reference character, the system comprising: first light source means for providing a first substantially coherent light beam; second light source means for providing a second substantially coherent light beam, the second light beam differing from the first light beam such that a beat frequency signal is produced when the first and second light beams are superimposed; first spatial pattern forming means intercepting the path of the first light beam to form a spatial pattern of an unknown character with the first beam; second spatial pattern forming means intercepting the path of the second light beam to form a spatial pattern of a reference character with the second beam; means for superimposing the first and second light beams containing the spatial patterns whereby a beat frequency signal is generated where the spatial patterns overlap, the intensity of the beat frequency signal being dependent on the degree of similarity existing between the unknown and reference characters, and detector means positioned to receive the superimposed first and second light beams and tuned to the beat frequency to provide an output indicative of the intensity of the beat frequency signal.

Claim 5

A character recognition system wherein an unknown character is compared to a reference character, the system comprising: first light source means for providing a first substantially coherent light beam; second light source means for providing a second substantially coherent light beam, the second light beam differing from the first light beam such that a beat frequency signal is produced when the first and second light beams are superimposed; first spatial pattern forming means intercepting the path of the first light beam to form a spatial pattern of an unknown character with the first beam; second spatial pattern forming means intercepting the path of the second light beam to form a spatial pattern of a reference character with the second beam; means for superimposing the first and second light beams containing the spatial patterns whereby a beat frequency signal is generated where the spatial patterns overlap, the intensity of the beat frequency signal being dependent on the degree of similarity existing between the unknown and reference characters, and detector means positioned to receive the superimposed first and second light beams and tuned to the beat frequency to provide an output indicative of the intensity of the beat frequency signal.

Claim 6

The character recognition system of claim 3 wherein the detector means further includes means for providing an output indicative of the intensity of the first and second light beams where the spatial patterns do not overlap.

Claim 7

The character recognition system of claim 3 wherein the first anD second light source means comprise: a light source for producing a single substantially coherent light beam; light separating means for separating the single light beam produced by the light source into first and second light beams; and phase modulator means associated with one of the first and second light beams to time-vary the phase of one beam relative to the other beam.

Claim 8

The character recognition system of claim 5 wherein; the light source is a laser; the light separating means and the light superimposing means are half-silvered mirrors, and the phase modulator means is an electro-optic crystal having an electric field dependent index of refraction.

Claim 9

The character recognition system of claim 3 wherein the first and second light beams differ in frequency.

Claim 10

The character recognition system of claim 7 wherein: the first and second light source means are lasers, and the light superimposing means is a half-silvered mirror.

Claim 11

The character recognition system of claim 3 wherein: the second spatial pattern forming means further includes means for systematically positioning each of a plurality of reference characters in the path of the second beam to sequentially form a spatial pattern of each, storage means are included for storing the intensity of the beat frequency signal corresponding to each of the plurality of reference characters, and retrieval means are included for selecting the maximum intensity stored, thereby identifying the unknown character with the reference character which produced the maximum intensity beat frequency signal.

Claim 12

The character recognition system of claim 9 wherein the first and second light source means comprise: a light source for producing a single substantially coherent light beam; light separating means for separating the single light beam produced by the light source into first and second light beams, and phase modulator means associated with one of the first and second light beams to time-vary the phase of one beam relative to the other.

Claim 13

The character recognition system of claim 9 wherein the first and second light beams differ in frequency.

Claim 14

The character recognition system of claim 3 wherein the first and second spatial pattern forming means comprise: means for forming a Fresnel diffraction pattern the unknown and reference character, respectively, and means for transforming the Fresnel diffraction patterns to Fraunhofer diffraction patterns.

Claim 15

The character recognition system of claim 3 wherein: The second light source means further includes light separating means for separating the second light beam into a plurality of light beams, and frequency varying means associated with each of the plurality of light beams for providing each light beam with a different frequency such that each beam is capable of producing a different beat frequency signal when superimposed with the first light beam, the second spatial pattern forming means includes means intercepting the path of each of the plurality of light beams to form a spatial pattern of a different reference character with each of the plurality of light beams, the light beam superimposing means further includes means for superimposing each of the plurality of light beams with a first light beam to simultaneously produce a plurality of different beat frequency signals, the detector means is tuned to each of the beat frequencies produced to provide an output indicative of the intensity of each beat frequency signal generated where the spatial patterns overlap, storage means are included for storing the intensity of the beat frequency signal corresponding to each of the plurality of reference characters, and retrieval means are included for selecting the maximum intensity stored, thereby identifying the unknown character with the reference character which produced the maximum intensity beat frequency signal.

Claim 16

The character recognition system of claim 3 wherein: the second spatial pattern forming means comprises a hologram in which a plurality of reference characters are stored, each of the reference characters being stored at a different frequency, the second light source means further includes means for varying the frequency of the second light beam to sequentially produce a spatial pattern of each of the plurality of reference characters, each spatial pattern producing a different beat frequency when superimposed with the first spatial pattern, storage means are included for storing the intensity of the beat frequency signal corresponding to each of the plurality of reference characters, and retrieval means are included for selecting the maximum intensity stored, thereby identifying the unknown character with the reference character which produced the maximum intensity beat frequency signal.