Method and apparatus for the accurate detection of the passage of the edge of a straight contrast jump

Claim 3

A method according to claim 1 wherein said output signal is produced only when the brightness values of the said second and third areas are unequal.

Claim 4

A method according to claim 2 wherein said output signal is produced only when the difference between the brightness values of the second and third areas is greater than a predetermined second threshold value which is greater than the predetermined first threshold value.

Claim 5

A method according to claim 2 wherein the said output signal is produced only when the difference between the brightness values of the second and third areas is smaller than a predetermined negative threshold value, the absolute value of which is greater than the said first threshold value.

Claim 6

A method according to claim 1 including the steps of illuminating the fields with a light source and adjusting the first threshold value in proportion to the brightness of the light source.

Claim 7

Apparatus for accurately detecting the passage of a moving edge of optical contrast between first and second fields having unequal brightness of illumination, the edge of the contrast extending essentially at right angles to the direction of movement of the edge, said apparatus comprising a first photoelectric cell constructed and positioned to detect the brightness of a first area of Said fields and stationary with respect to said fields and second and third photo-electric cells constructed and positioned to detect the brightness of second and third areas, said areas located respectively previous and subsequent to the area scanned by said first photo-electric cell, relative to the direction of movement of the edge, said photocells each having an output emitting a signal which is a function of the brightness of the area scanned by that photocell, said outputs of the photo-electric cells being coupled to means, including an operational amplifier generating a sum signal which is a function of the sum of the signal outputs of said second and third photocells less twice the output signal of the first photocell, for providing that the value of the sum signal as the edge traverses the first area is independent of the detected relative brightness of the first and second fields, the passage of said edge across said first area being indicated by the passage of the value of said sum signal through a predetermined first threshold value.

Claim 8

Apparatus for accurately detecting the passage of a moving edge of optical contrast between first and second fields having unequal brightness of illumination, the edge of the contrast extending essentially at right angles to the direction of movement of the edge, said apparatus comprising a first photoelectric cell constructed and positioned to detect the brightness of a first area of Said fields and stationary with respect to said fields and second and third photo-electric cells constructed and positioned to detect the brightness of second and third areas, said areas located respectively previous and subsequent to the area scanned by said first photo-electric cell, relative to the direction of movement of the edge, said photocells each having an output emitting a signal which is a function of the brightness of the area scanned by that photocell, said outputs of the photo-electric cells being coupled to means, including an operational amplifier generating a sum signal which is a function of the sum of the signal outputs of said second and third photocells less twice the output signal of the first photocell, for providing that the value of the sum signal as the edge traverses the first area is independent of the detected relative brightness of the first and second fields, the passage of said edge across said first area being indicated by the passage of the value of said sum signal through a predetermined first threshold value.

Claim 9

Apparatus according to claim 6 wherein the three said areas are immediately adjacent to one another.

Claim 10

Apparatus according to claim 7 including a comparator coupled to the output of the operational amplifier and constructed and arranged to emit an output signal only when the absolute value of the sum signal is smaller than a predetermined threshold value.

Claim 11

Apparatus according to claim 7 wherein a second operational amplifier is coupled to the outputs of said second and third photo-electric cells and produces a signal indicative of the differential between the output signals of the two said second and third photo-electric cells.

Claim 12

Apparatus according to claim 9 including a first comparator coupled to the output of the operational amplifier and constructed and arranged to emit an output signal only when the absolute value of the sum signal is smaller than a predetermined threshold value and a second comparator coupled to the output of the second operational amplifier, said second comparator emitting an output signal only when said differential is greater than a second predetermined threshold value.

Claim 13

Apparatus according to claim 10 wherein a third comparator is coupled to the output of the second operational amplifier, said third comparator emitting an output signal only when said differential is smaller than a predetermined further negative threshold value.

Claim 14

Apparatus according to claim 11 including means to selectively apply the outputs of the said second and third comparators to one input of an AND-gate, a second input of which is coupled to the output of the first comparator.

Claim 15

Apparatus according to claim 12 wherein the second and third comparators are applied to the AND-gate through an OR-gate

Claim 16

Apparatus according to claim 11 wherein the outputs of the second and third comparators are each applied to an AND-gate of which the other two inputs are connected to the output of the first comparator.

Claim 17

Apparatus according to claim 14 wherein the outputs of the AND-gates are connected to a flip-flop of which one output emits a voltage upon the passage of a contrast edge between a first lighter field and a second darker field while its other output emits a voltage in the case of passage of an edge between a first darker and second lighter field.