Arrangement For Optical-electronic Identification Of A Moving Body

Abstract

An arrangement for the optical-electronic identification of a moving body provided with identification marks, said marks consisting of a plurality of code marks arranged in parallel relationship and being perpendicular to the direction of movement of said body, said code marks being constituted as broad and narrow code marks, the width of the broad code marks being three times that of the narrow code marks and the space on both sides of a narrow code mark being at least twice the width of a narrow code mark. An optical system is provided for producing a scanning spot of light of at least four times the width of a narrow code mark, the optical system projecting the images of the respective illuminated areas of the field of the identification marks onto four adjacent photodetectors controlling two gates via three differential amplifiers responsive to the difference of the scanning signal of the fourth, outer detector with respect to the scanning signals of the remaining three detectors, one of the gates being responsive to a broad mark while the other of the gates is responsive to a narrow mark.

Description

BRIEF SUMMARY OF THE INVENTION

This invention relates to an arrangement for optical-electronic identification of a moving body provided with identification marks, said marks consisting of a plurality of code marks arranged in parallel relationship and being perpendicular to the direction of movement of said body.

In the German published Pat. No. 1,262,643 an arrangement of this type is disclosed, in which the data are coded complementary in binary form in two lines. Two scanning photodetectors respond to the presence and absence respectively of a code mark in each of both lines. The output signals of the photodetectors are supplied to a differential amplifier which, when a code mark is present in one of the lines and simultaneously none is present in the other line, generates a corresponding output signal. Irregularities regarding the reflectivity of the record carriers are balanced by establishing the difference. The body must be moved past the scanning system at a predetermined level so that each of the two photodetectors will scan only the line related to it.

An object of the present invention is to provide an arrangement for optical-electronic identification, in which the photodetectors need not be adjusted to the respective reflectivity of the moving body and of the code marks, and in which furthermore no second data recording in inverted form is necessary.

An arrangement for optical-electronic identification according to the invention is characterized in that the body carries broad and narrow code marks, the width of the broad code marks being three times that of the narrow code marks and the space on both sides of a narrow code mark being at least twice the width of a narrow code mark, and in that an optical system produces a scanning spot of light of at least four times the width of a narrow code mark, said system projecting the images of the respective illuminated areas of the field of the identification marks onto four photodetectors arranged adjacent each other, the scanning signals supplied by said photodetectors controlling means which selectively determines the presence of a broad and a narrow code mark in accordance with the signals supplied by the photodetectors.

The latter means comprises two gates connected to three differential amplifiers responsive to the difference of the scanning signal of the fourth, outer photodetector with respect to the scanning signals of the remaining three photodetectors, one of said gates being responsive to a broad mark and the second gate being responsive to a narrow mark.

The arrangement according to the invention does not respond to the absolute values of the amount of light reflected by the recording area but responds to contrasts of the intensity of light. As long as the contrast is sufficient, the code marks may be of any color. The fact that during scanning of the code marks the respective width of the mark is entered constitutes an additional protection against any other accidentally present markings interfering with the scanning process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an optical system according to the invention;

FIG. 2 is a plan view of four photodetectors arranged adjacent one another as seen when viewed along lines 2-2 in FIG. 1;

FIG. 3 shows code marks applied to a body and the spot of light serving scanning purposes;

FIG. 4 is a schematic view of the four photodetectors during scanning of a broad code mark;

FIG. 5 is a schematic view of the four photodetectors during scanning of a narrow code mark; and

FIG. 6 is a block diagram of a logic circuit according to the invention for evaluating the output signals of the photodetectors.

DETAILED DESCRIPTION

In the optical system of FIG. 1 the rays from a source of light are passed through a condenser lens 3 to a lens system 2. The rays are reflected by reflecting mirrors 3' and 6 and by a semitransparent mirror or beam splitter 5. The rays from the light source pass through the lens system 2 into an information carrier 4, to form a sharp scanning spot of light thereon. The spot of light is reflected through the lens system 2 and the semitransparent mirror 5 onto the photodetector arrangement 7. The image of the spot of light overlaps all four photodetectors (P1, P2, P3, P4) shown in FIG. 2. In the present case, the moving body carrying the identification marks is a plain data carrier 4, e.g. a prescription form which is to be put into a box together with a medicine and the identification marks of which are to be scanned beforehand for reasons of safety.

As may be seen from FIG. 3, the identification code consists of narrow and broad marks, the narrow ones having a width E and the broad ones having a width 3E. The spaces between the marks are such that a distance 2E is provided from the edge of the one mark to the edge of the next-following mark. The marks may have any desired length which is selected such that no excessive demands are made with regard to observing an exact level at which the body is moved past the scanning system.

The scanning spot of light also shown in FIG. 3 has a width 4E. The image of the said scanning spot of light is formed on the photodetector arrangement in such a way that the image of the spot just overlaps all four photodetectors P1 to P4. In FIGS. 4 and 5 for instance, the image of the spot of light has a width 4E'. The hatched area of FIG. 4 corresponds to that portion of the scanning spot of light 9 in FIG. 3 which is at that moment directed on a broad mark. In case the code marks consist of black stripes applied to a white background, the photodetector P4 will (in the position of FIG. 4) receive light while the photodetectors P1 through P3 will be darkened. In other words, P4 will "see" white while P1 through P3 will "see" black. From FIG. 4 it may also be seen that this state of exposure to light of the photodetectors will continue for a certain period of time upon moving the body past the detectors, because the effective area of each of the photodetectors P1 through P3 is smaller than the width E' of the image of a narrow code mark.

From FIG. 5 the state of exposure of the photodetectors during scanning of a narrow code mark may be seen. FIG. 5 shows exactly the position in which the image of a narrow code mark lies symmetrically on the photodetector P2. In this case, P1, P3 and P4 "see" white while P2 "sees" black. It is obvious that this state of exposure, too, will continue for a certain period of time during movement of the body past the detectors, which fact is due to the relatively small effective width of the photodetectors P1 through P4.

As will be described later, the logic circuit to which the scanning signals of the photodetectors are supplied responds only to the positions shown in FIGS. 4 and 5 whereas the remaining positions resulting during movement of the body past the detectors will not elicit an output signal from the logic circuit. In the following table some of the states of exposure are given which result when a narrow code mark and a broad code mark respectively are moved past the scanning arrangement; the narrow code mark will be termed O and the broad code mark will be termed L. The s will be "black" and w will be "white," i.e. the respective photodetector is darkened and respectively receives light. ##SPC1##

In the above table the direction of movement of the code marks is from right to left. In those scanning positions in which the actual scanning occurs with the result O or L P4 will always "see" white. Thus P4 always will supply a reference signal which is used to form the actual scanning signals from the contrast between the areas of the code marks and the background. The last line of the above table shows a state of exposure of the photodetectors in which P1 and P3 "see" black while P2 and P4 "see" white. This state may be caused by two narrow code marks being too close to each other, or by an interference which additionally darkens one of the two photodetectors. In both cases the scanning process is stopped.

The electronic circuit for evaluating the scanning signals (FIG. 6) substantially comprises the three differential amplifiers V1, V2 and V3, the two multiple coincidence gates 10 and 11, and the OR gate 12. The output signals of the photodetectors P1 through P4 may, for instance, be derived by means of the resistance network shown in FIG. 6. Each of the differential amplifiers V1 through V3 has two inputs, the output signal of the related photodetector P1, P2, or P3 being supplied to the one input of each of the differential amplifiers V1 through V3 and the output signal of the fourth photodetector P4 being supplied to the other input of each of the differential amplifiers V1 through V3. The differential amplifiers V1 through V3 will generate an output signal only when one of the photodetectors P1 through P3 "sees" black and P4 "sees" white or when at least one of the three photodetectors P1 to P3 receives a substantially smaller amount of light than the photodetector P4.

The outputs of the differential amplifiers V1 through V3 are directly supplied to the coincidence gate 11. The coincidence gate 10, however, has two inverting inputs to which the output signals of the differential amplifiers V1 and V3 are supplied whereas the output signal of the differential amplifier V2 is supplied directly to the coincidence gate 10. At the outputs of the coincidence gates 10 and 11 the pulses indicating O and L respectively are available. The OR gate 12 is connected in parallel to the said outputs and supplies a timing impulse upon occurrence of an O signal and an L signal respectively. The said timing impulse may, for instance, be used for controlling the output of a reference code in case the scanned mark is to be compared with a reference code.

With the state of exposure of the photodetectors shown in FIG. 4 all differential amplifiers V1 through V3 g generate an output signal so that the coincidence gate 11 responds. With the state of exposure of the photodetectors as shown in FIG. 5 an output signal is generated merely by the differential amplifier V2, whereas the differential amplifiers V1 and V3 do not generate an output signal, so that the coincidence condition for the gate 10 is satisfied. In order to initiate a scanning process, two light barriers arranged one behind the other in the direction of movement are interrupted upon entering of a body into the scanning arrangement; scanning will take place only while these light barriers are interrupted. Thus it will be prevented that the edges of the data carrier are erroneously identified as code marks.

Instead of the scanning position for a narrow code mark shown in FIG. 5 there may also be used the position in which the narrow code mark is imaged on the photodetector P3. Furthermore, the spaces between the code marks may also be selected differently; as may be seen in FIGS. 4 and 5 it is merely necessary that the spaces on both sides of a broad code mark are at least E' and the spaces on both sides of a narrow code mark are at least 2E'.

Claims

I claim:

1. An arrangement for the optical-electronic identification of a moving body provided with identification marks, said marks consisting of a plurality of code marks arranged in parallel relationship and being perpendicular to the direction of movement of said body, said code marks being constituted as broad and narrow code marks, the width of the broad code marks being three times that of the narrow code marks and the space on both sides of a narrow code mark being at least twice the width of a narrow code mark, an optical means for producing a scanning spot of light having a length at least four times the width of a narrow code mark, four adjacent photodetectors, said optical means projecting the images of the respective lighted areas of the field of the identification marks onto said four photodetectors, the latter producing signals in accordance with the presence or absence of a code mark, and means coupled to said photodetectors to determine selectively the presence of a broad and a narrow code mark in accordance with the signals produced by said photodetectors.

2. An arrangement as claimed in claim 1 wherein said means coupled to the photodetectors comprises three differential amplifiers responsive to the difference of the scanning signal of the fourth, outer photodetector with respect to the scanning signals of the remaining three photodetectors and two gates connected to said differential amplifiers, the first of said gates being responsive to a broad mark and the second of said gates being responsive to a narrow mark.

3. An arrangement according to claim 2 wherein the three difference signals of said differential amplifiers are directly supplied to the first gate, and the difference signal produced from the difference between the fourth, outer photodetector and one of the centrally arranged photodetectors is directly supplied to the second gate whereas the two other difference signals are supplied to said second gate in inverted form.

4. An arrangement according to claim 2 comprising an OR gate, the output signals of said two gates being supplied to said OR gate for producing a timing impulse.

5. An arrangement according to claim 1 comprising two light barriers for initiating the scanning process when the front edge of the moving body interrupts the said light barriers.

6. An arrangement according to claim 1 wherein said optical means comprises a source of light, a reflecting mirror positioned so as to be illuminated by said source of light, a condenser lens between said mirror and source, a lens system positioned to receive the image which is reflected by said mirror and to project the image onto the area to be scanned so as to produce the spot of light, a beam splitter disposed between said mirror and the lens system, said lens system projecting an image of said spot of light through said beam splitter, said photodetectors being disposed at the focal point of the image formed by the lens system of said spot of light.