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An apparatus for detecting an edge of a semitransparent plane substance provided with a light source array including a plurality of light sources and a photosensor array including a plurality of photosensors. A selection circuit selects a pair of one of the light sources and one of the photosensors,

An apparatus for detecting an edge of a semitransparent plane substance provided with a light source array including a plurality of light sources and a photosensor array including a plurality of photosensors. A selection circuit selects a pair of one of the light sources and one of the photosensors, respectively, and a comparator circuit compares the outputs of each of the photosensors in each pair when no detected substance exists between the light source array and the photosensor array, and the corresponding outputs when a substance exists between the light source array and the photosensor array, so that the edge portion of the substance can be detected.

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1. An apparatus for detecting an edge of a semitransparent plane substance provided with a light source array including a plurality of light sources and a photosensor array including a plurality of photosensors having outputs, comprising: means, operatively connected to the light source array and

1. An apparatus for detecting an edge of a semitransparent plane substance provided with a light source array including a plurality of light sources and a photosensor array including a plurality of photosensors having outputs, comprising: means, operatively connected to the light source array and said photosensor array, for selecting a light source and photosensor pair and for providing a selection signal; means, operatively connected to said selecting means, for driving the selected light source and photosensor pair; and means, operatively connected to said photosensor array, for comparing the outputs of each of the plurality of photosensors, when the semitransparent plane substance between the light source array and the photosensor array is not detected, with the corresponding outputs of each of the plurality of photosensors when the semitransparent plane substance between the light source array and the photosensor array is detected, thereby detecting the edge portion of the semitransparent plane substance. 2. An apparatus for detecting an edge of a semitransparent plane substance according to claim 1, wherein each of the plurality of light sources and each of the plurality of photosensors has a light path which is at an angle to the semitransparent plane substance, wherein the light path of each of the plurality of light sources and the light path of each of the plurality of photosensors are arranged to coincide, and wherein said selecting means selects as a pair, one of the plurality of light sources and one of the plurality of photosensors positioned on the same light path. 3. An apparatus for detecting an edge of a semitransparent plane substance according to claim 1, wherein there are M light sources and M photosensors, where M is an integer greater than one, the photosensor array and the light source array extending parallel to the semitransparent plane substance, wherein each one of the plurality of light sources emits light and each of the plurality of photosensors generates a signal upon receipt of the light from a respective light source, wherein each of the plurality of light sources and each of the plurality of photosensors has a light path which is at an angle to the semitransparent plane substance, wherein the light path of each of the plurality of light sources and the light path of each of the plurality of photosensors is shifted from each other, and wherein said selecting means first, selects a Jth light source and a Jth photosensor as a pair, where J is an integer less than or equal to M, a Jth+1 light source and a Jth+1 photosensor as a pair, for the Jth to the J=M light sources, and second, selects the Jth+1 light source and the Jth photosensor as a pair, a Jth+2 light source and the Jth+1 photosensor as a pair, for the Jth to the J=M light sources. 4. An apparatus for detecting an edge of a semitransparent plane substance according to claim 1, wherein there are M light sources and M photosensors, where M is an integer greater than one, the photosensor array and the light source array extending parallel to the semitransparent plane substance, wherein each of the plurality of light sources emits light and each of the plurality of photosensors generates a signal upon receipt of the light from a respective light source, wherein each one of the plurality of light sources and each one of the plurality of photosensors has a light path which is at an angle to the semitransparet plane substance, wherein the light path of each of the plurality of light sources and the light path of each of the plurality of photosensors are arranged to be shifted from each other and wherein said selecting means selects a Jth light source and a Jth photosensor as a pair, where J is an integer less than or equal to M, the Jth photosensor and a Jth+1 light source as a pair, the Jth+1 light source and a Jth+2 photosensor as a pair, for the Jth to the J=M light sources. 5. An apparatus for detecting an edge of a semitransparent plane substance according to claim 1, wherein the light source array and the photosensor array have standard right and left measuring points, wherein P denotes a pitch of the light sources and the photosensors, L denotes a width between the standard right and left measuring points, l denotes a width of the semitransparent plane substance, Δl denotes an increment of the width of l, and m and n denote integers, the relationship between P, L, l, Δl, m and n being expressed by the following equation: ##EQU## 6. An apparatus for detecting an edge of a semitransparent plane substance according to claim 1, wherein said driving means comprises: a control operation circuit, operatively connected to said selecting means; a signal bus, operatively connected to said control operation circuit and said selecting means, for supplying the selection signal to said selecting means; an analog-to-digital circuit, operatively connected to said means for comparing, for converting an analog value of the outputs of each of the plurality of photosensors to digital values and for supplying the digital values to said control operation circuit; and a memory, operatively connected to said signal bus, for storing the digital values of said analog-to-digital circuit when the semitransparent plane substance is not detected. 7. An apparatus for detecting an edge of a semitransparent plane substance according to claim 1, wherein said driving means comprises: a control operation circuit operatively connected to said selecting means; a signal bus, operatively connected to said control operation circuit and said selecting means, for supplying the selection signal to said selecting means; a digital-to-analog circuit having analog reference levels, operatively connected to said signal bus, for controlling the output current of the plurality of light sources; an analog comparator circuit, operatively connected to said comparing means and said signal bus, for comparing the outputs of the photosensors with the analog reference levels; and a light amount compensation memory, operatively connected to said signal bus, for storing the output of the analog comparator circuit when the semitransparent plane substance is not detected. 8. An apparatus for detecting an edge of a semitransparent plane substance according to claim 3, wherein said driving means comprises: a control operation circuit operatively connected to said selecting means; a signal bus, operatively connected to said control operation circuit and said selecting means, for supplying the selection signal to said selectig means; an analog-to-digital circuit, operatively connected to said means for comparing, for converting an analog value of the outputs of each of the plurality of photosensors to digital values and for supplying the digital values to said control operation circuit; and a memory, operatively connected to said signal bus, for storing the digital values of said analog-to-digital circuit when the semitransparent plane substance is not detected. 9. An apparatus for detecting an edge of a semitransparent plane substance according to claim 4, wherein said driving means comprises: a control operation circuit operatively connected to said selecting means; a signal bus, operatively connected to said control operation circuit and said selecting means, for supplying the selection signal to said selecting means; an analog-to-digital circuit, operatively connected to said means for comparing, for converting an analogue value of the outputs of each of the plurality of photosensors to digital values and for supplying the digital values to said control operation circuit; and a memory, operatively connected to said signal bus, for storing the digital values of said analog-to-digital circuit when the semitransparent plane substance is not detected. 10. An apparatus for detecting an edge of a semitransparent plane substance according to claim 4, wherein said driving means comprises: a control operation circuit operatively connected to said selecting means; a signal bus, operatively connected to said control operation circuit and said selecting means, for supplying the selection signal to said selecting means; a digital-to-analog circuit having analog reference levels, operatively connected to said signal bus, for controlling the output current of the plurality of light sources; an analog comparator circuit, operatively connected to said means for comparing and said signal bus, for comparing the outputs of the photosensors with the analog reference levels, and a light amount compensation memory, operatively connected to said signal bus, for storing the output of the analog comparator circuit when the semitransparent plane substance is not detected.