IE50309B1 - Method and apparatus for identifying objects - Google Patents

Abstract

1. Method of identifying articles, which appear in any position and orientation and at any time at an image aperture and each have a designating area or panel on a surface which is facing the image aperture, which panel comprises symbols (52) in at least one datum track (51) and at least one contrasting line pattern (54), which characterizes the positon and the orientation of the datum track and has a plurality of parallel lines of different spacing and/or line width, in connection with which the image aperture is scanned line by line (60) and a binary video signal corresponding to the scanned contrast line pattern and the following symbols is produced, the image aperture in the first step of the method being scanned at different angles until a prescribed contrasting line pattern is detected, in the second step of the method, the position alignment of the data track relatively to the image aperture is established, and in the third of the method, a grid scanning is effected in the direction of the data track and the symbols are read off and decoded, characterized in that, - for the detection of the constrast line pattern (PIC), the interval lengths of overlapping intervals (Figs. 11 to 14) of the video signal and in each case comprising at least one light-dark region are measured and portrayed in the form of binary counter readings (TC1 to TC4), - that the counter readings (TC1 to TC4, Fig. 6) address a two-dimensional table (Fig. 10) which is stored in a store (28 in Fig. 7) and in which is contained an expectation zone with criteria for a prescribed ratio between two successive interval lengths of the intervals (11 to 14), - that the counter reading (TCN) corresponding to an interval length (IN) addresses one line of the table and the reading corresponding to the following interval length (IN+1) addresses one column of the table, - that a coincidence signal (LPIC1, LPIC2, LPIC3) is produced when the relation of the two respectively following interval lengths lies in a prescribed value range, and - that a recognition signal (PIC OUT Fig. 9) is delivered when a coincidence signal (LPIC1, LPIC2, LPIC3) is produced with a number of successive addressing steps which is prescribed by the contrast line pattern (PIC).

Description

The invention relates to a method and an apparatus for identifying objects appearing in a random position and orientation and at random times on an image window. On a surface facing the image window, each object has an identiξ fication in the form of a field which comprises on at least one data track contrasting indicia with at least one contrasting line pattern identifying the position and the orientation of the data track. The track also includes a plurality of parallel lines with variable spacing and/or line ie widths. The image window is scanned line-by-line and a binary video signal is generated which corresponds to the scanned contrast sequence. In a first step, the image window is scanned from varying angles or directions until a contrasting line pattern is detected. In a second step, the tS position and alignment of the data field relative to the image window is determined and in a third step, raster scan is preformed in the direction of the data track to read and decode the indicia present on the data track.. .., Such method and apparatus are- already known. The io objects to be identified are, for example, commercial goods, department store articles, or the. like which are identified in machine readable form. For this purpose, appropriate identifications are applied to the objects by imprinting thereon with the desired code, for example the OCR code. The uncoded information may' compri’se indications of quality, size, price, the number of ttoiarticles, and so forth. 50308 It is difficult to machine read such cedes since the objects vary in size and since the code is frequently printed on adhesive labels which are applied to varying points on the article. Therefore, it cannot be assumed that the information can be found in a specific location with a fixed orientation and at predetermined time intervals. Thus, the reading of such codes cannot be compared with the reading of punched cards or the like, where a card is available in a precisely defined reading position at precisely fixed times. In the present case, the exact opposite applies. The data field on the object appears only more or less approximately at a specific place, and the alignment of the data field is to some extent arbitrary.

This type of method and apparatus for the identification of an object is used, for example, at the cash counters of supermarkets and the like in order to identify the price and/or the number of the articles which a customer wishes to buy and which he has brought to the cash counter for this purpose. The articles, such as boxes of varying shape and size, bottles, cartons, cans, and the like, are then placed individually into the image window with the surface bearing the data field directed toward the image window. The data fields on the various objects thus appear in variable alignment at differing locations within the image window. The data fields also do not appear at the scanning station at fixed time intervals. Thus, the scanning station must be able to search for the data field and, once found, must readout the data track signals in the direction of the data tracks of the field. The readout signals can then be fed to the cash register in the form of electric impulses so that the cash register can print out on the cash receipt the price, the number of the article, its classification, etc.

The data field applied onto the object is provided with a contrasting line pattern or product identification code (PIC) which is defined by a plurality of parallel lines of varying spacing and/or line width. The purpose of the contrasting line pattern is to reliably and clearly distinguish the data field, for example the printed label, 5030© from other indicia or line patterns which may be present on the object in the vicinity of the data field. Further, within the data field the contrasting line pattern has a given position and orientation which can be used to ascertain the position and orientation of the contrasting line pattern — -and thereby of the data tracks — relative to the scanning angle of the scanning line. This can then be used to subsequently raster scan the field in the direction of the data tracks perpendicularly over the code lines. Thus, the reliable identification of the contrasting line pattern represents an important step in the omnidirectional reading of visibly imprinted data fields.

The German Offenlegungsschrift 2,338,561 discloses a method and an apparatus of the above described type wherein the identification of the contrasting line pattern occurs only when the lines of the pattern are oriented substantially perpendicularly to the scanning direction and the resulting pulse sequence of a video signal generated thereby equals a predetermined pulse sequence which corresponds to the contrasting line pattern used. In other words, the Offenlegungsschrift discloses a correlation method. It is particularly disadvantageous that the scanning of the image field for locating the contrasting line pattern must proceed in very small angular increments until a scanning line transsects the pattern vertically. This results in an undesireably long search time. Further, blurred printed edges of the contrasting line pattern may prevent a recognition of the pattern since in such an event the scanned pulse sequence and the resulting video signal may deviate from the stored reference pattern. As a result, either the search process must be repeated or the contrasting line pattern is not recognized at all, leaving the associated data field unread.

In contrast, it is an object of the invention to provide a method and an apparatus of the above described type which make possible a rapid and reliable identification of contrasting line patterns while generally preventing blurred edges of the lines from adversely affecting the readout.

S0309 In accordance with the invention this is achieved by measuring the length of the overlapping light and dark intervals of the video signal resulting from a scanning of the line pattern. Successively measured interval lengths are compared with each other and a reference or comparison signal having a-first amplitude is generated when the two interval lengths which are being compared have a predetermined ratio to each other which conforms to the spacing of corresponding pattern lines. An identification signal (PIC OUT) is emitted when during each of a number of successive comparison steps, the number of which is determined by the contrasting line pattern, a reference signal having the first amplitude is generated.

The apparatus of the invention has an optoelectronic scanner which outputs binary video signals that correspond to the line-by-line scanned image field and comprises a series of light and dark intervals. The apparatus has a decoder for identifying a scanned contrasting line pattern of a plurality of parallel lines with varying spacing and/or line widths which characterizes the position and orientation of at least one data track of the data field. The apparatus further includes means for aligning the scanner parallel to the data track and for reading the indicia of the scanned data track.

In accordance with the invention the apparatus is characterized by a counting circuit which receives the video signals and determines the length of successive, overlapping video signal intervals. Further, the apparatus has at least one reference table which receives successively counted interval lengths in pairs via a gate circuit and emits a comparison signal having a first amplitude when two compared intervals lengths have a given ratio which corresponds to the ratio of the corresponding interval of the contrasting line pattern. An evaluation circuit is provided which generates an identification signal (PIC OUT) when a predetermined number of reference signals with a first amplitude have been generated.

SOSOS The advantages of the invention reside particularly in that the identification of the contrasting line pattern -is dependent only on whether the ratio of successive overlapping interval lengths of the video signal lies within narrow ranges. As a result, the contrasting line pattern is reliabily identified even when scanning at an oblique angle to lines of the pattern since the ratios of successively measured interval lengths of thovideo signal are constant and do not vary with the scanning angle. Thus, a single scanning of the contrasting line pattern — at any desired angle — so long as all lines of the pattern are crossed, is sufficient for a reliable identification of the line pattern. The line pattern can, therefore, be rapidly identified with relatively few scans in which the angular inclination is varied in large increments.

The decoding of the video signal for detecting the contrasting line pattern in relation to the video signal must take place in real-time, that is substantially simultaneously with the generation of thSvideo signal to ensure that the line pattern is identified anywhere within the video signal. Therefore, the determination of whether the ratio of successively measured interval lengths falls within a given value range, is carried out not by a division but by entering the value of the ratio into a two-dimensional comparison table, sometimes also called a division table. The table emits a reference signal of a given, first amplitude only when two interval lengths which are being compared lie in a predetermined field of the table where the quotient of the compared interval lengths has a value range which corresponds to that of the corresponding interval length of the searched for line pattern. The time and hardware consuming division process is thereby eliminated and real-time operation with regard to the video signal is maintained.

The comparison table is preferably in the form of a two-dimensional programmed read-only memory (PROM). The various possible discrete values of the first measured interval length address the lines of the memory. The various discrete values of the next following measured interval length address the columns of the memory. The expected field is defined so that it encompasses all storage points where the quotient of the interval length associated with the line address fall within a given value range. If a storage point within the expected field is addressed, then the PROM emits a comparison signal of a first amplitude which signals a partial identification of the line pattern. If, however, the storage point determined by the line column addresses lies outside the expected field then a comparison signal with a second amplitude is emitted to indicate that the quotient of the compared successive interval lengths lies outside the predetermined value range. When a reference signal with a second amplitude appears, the decoder is reset and ready for a new identification and decoding step.

Preferably, two interval lengths which are to be compared are fed into a separate comparison table with its own expected field and examined there with regard to their quotient value. Each individual comparison table preferably comprises as a separate PROM. This simplifies the control logic of the decoder.

In accordance with a preferred embodiment of the invention, eight bit memory positions are provided for the first PROM to compare the first and the second interval lengths as well as for the second PROM to compare the second and third interval lengths, and so forth. Thus, eight comparison tables, each with its own expected field can be accommodated in the PROM's, the first table being formed for example from the first bit of the memory positions, the second table from the second bit of the memory positions, and so forth. By selectively addressing and selectively reading out the table which is being used, it is possible to identify up to eight different contrasting line patterns with one decoding circuit, thereby enhancing the utilization of the apparatus in accordance with one aspect of the invention.

When the scanning beam sweeps over a darkly colored area of the data field, the binary video signal has a first amplitude Hi, and it has a second amplitude Lo when the scanning beam sweeps over a light, signal-free area of the 0 3 0® data field. The allocation of the amplitudes Hi and Lo is arbitrary, and a different allocation of the two amplitudes to light and dark areas of the data field is possible.

The intervals of the video signal, the length of which is to be measured, preferably extend from one rising slope o£-the video signal to the next rising slope, as well as overlapping therewith from one falling slope of the video signal between the rising slopes to the next falling slope. The third interval then extends from the second rising slope to a next rising slope, and so forth. The fact that the intervals extend from a rising slope to a rising slope, or from a falling slope to a falling slope ensures that blurred edges of the contrast lines of the contrasting line pattern — which generally extend in the same direction and in the same manner on all contrast lines — do not materially influence the interval lengths. Consequently the decoder can identify contrasting line patterns in accordance with the invention which were produced under variable printing conditions.

To enhance the reliability of the identification, contrasting line patterns having a signal-free lead zone of a given length can be employed. This lead zone is disposed ahead of the first line of the pattern. In such a case the measurement of the interval length is preferably initiated only when a signal-free lead zone of a predetermined length appears in the video dignal.

Measurement of the interval lengths is preferably terminated when a measured interval length exceeds a predetermined maximum which equals the maximum interval length present in the contrasting line pattern. An ongoing measurement of the interval lengths is preferably also terminated when the ratio of two successively measured interval lengths falls outside the predetermined value range. In both cases, the object identifying process is brought to a halt at the earliest possible moment and the decoder is reset and ready for a new cycle.

The ongoing measurement of the interval lengths is preferably also terminated when a signal-free intermediate zone of a predetermined duration which equals the maximum distance between the lines of the line pattern is detected. The decoding device is then reset and is ready for a new cycle.

The contrasting line pattern further preferably has a signaLvfree trailing zone the length of which corresponds, for example, to the length of the signal-free lead zone. Xn such an event a contrasting line pattern identification signal is preferably emitted only when the video signal also includes the signal-free trailing zone of predetermined length.

To enhance the redundancy of the identification process and thus reduce the probability of error, the same line is preferably scanned n times, and a contrasting line pattern identification signal is emitted only when the pattern has been successively identified n times.

The lengths of the overlapping intervals of the video signal are preferably digitally measured and for this purpose they are counted out in a counting circuit. The counting circuit includes a timing circuit which generates gate pulses of the same length as the corresponding intervals of the video signal. The length of a given interval of the video signal is measured with a counter which receives as an input the gate pulses of that interval. The inputs of the counters are further connected with a sync generator which emits sync pulses to the counters. The final count of the individual counters then corresponds to the length of the respective gate pulses and thereby to the length of the corresponding intervals. Successively counted interval values address the corresponding read-only memory after the subsequent interval value has been counted, and while counting of further interval values may still continue.

Embodiments of the invention are hereinafter described in greater detail with reference to the following drawings: Fig. 1 shows a first arrangement of a contrasting line pattern within a data field having a data track; 50308 Fig. 2 shows a second arrangement of a contrasting line pattern within a data field; Fig. 3 shows a third arrangement of a contrasting line pattern within a data field; Fig. 4 shows the light-dark distribution of various contrasting line patterns taken perpendicular to the contrast lines; Fig. 5 shows a portion of the video signal as a function of time which corresponds to the contrasting line pattern of Fig. 4(a); Fig. 6 is a block diagram of the counting circuit of the decoder; Fig. 7 is a block diagram of the comparison table of the decoder; Fig. 8 is another embodiment of the comparison table of the decoder; Fig. 9 is a block diagram of the evaluation circuit of the decoder; Fig. 10 is a schematic representation of the struc20 ture of the comparison table; Fig. 11 is a pulse diagram of the pulses generated in the timing circuit of the counting circuit; and Fig. 12 is a pulse diagram ofi the pulses processed within a selecting circuit.

Figs. 1 to 3 show a variety of object identifications 50 such as adhesive price labels which are secured, for example, to a container, a package or on any other article (not separately shown), and which appear in random positions and orientations on an image window. The image window is defined, for example, by the optical aperture of a flyingspot scanner such as a vidicon, which first scans the image window line-by-line, and then in a linewise raster scan.

The identifications 50 have a data field which includes contrasting signals 52 in at least one date track 51 for identifying the object or article. The contrasting signals are preferably optical character signals of one of the known, machine readable types, for example OCR-A or OCR-B characters.

A contrasting line pattern 54 — often referred to as position identification code or PIC -- is in a predetermined position and orientation in relation to the date track and has a plurality of parallel contrast lines with varying spacing and/or line widths. In the embodiment shown in Fig. 1, the line pattern is located in advance of the date track, in the embodiment shown in Fig. 2 it is underneath the data track, and in the embodiment shown in Fig. 3 it is at the end of the data track. The contrasting line pattern 54 is asymmetrical in a direction perpendicular to the contrast lines so as to identify the data field with regard to the beginning and the end of the data tracks. The line patterns shown in Figs. 1 and 2 have a signal-free lead zone 56 and a signalfree trailing zone 58.

Although the illustrated line patterns have only three lines each, patterns having more than three lines may be used. Further — and deviating from the illustration of Figs. 1 to 3 — the patterns may be located at a different position and have a different orientation in relation to the data tracks. It is further possible to provide two or more line patterns on one identification field 50.

A shown in Fig. 1, the image window, or an image corresponding to the window, for example on the target of a vidicon, is scanned step-by-step under an angle a by at least one scan line 60. Before reading the data tracks, it is important to first reliably identify the line pattern and determine its position and orientation relative to the scan line 60 of the scanning beam since the signals contained in the data track can then be read by subsequent raster scanning in the direction of the data track.

Fig. 4 shows the light-dark distribution of various three-line PIC patterns taken perpendicular to the direction of the individual lines which are all asymmetric and can therefore be used in accordance with the invention.

Fig. 5 shows a section of the video signal obtained from scanning a PIC pattern in accordance with Fig. 4(a) as an electric binary signal, the amplitude Hi being allocated to the dark areas of the pattern and the amplitude Lo to the 0308 light areas of the pattern. Light-dark fluctuations within the individual lines and the spacings of the PIC pattern are eliminated from the electric signal immediately after scanning. The video signal section shown in Fig. 5 includes a signal free lead zone that corresponds to the lead zone 56 in Fig. 1, a first interval TI which extends from the first ascending flank or slope to the second ascending flank or slope, a second interval T2 which extends from the first descending flank to the second descending flank, a third interval T3 which extends from the second ascending flank to the third ascending flank, and a fourth interval T4 which extends from the second descending flank to the third descending flank. It also includes a trailing zone that corresponds to the trailing zone 58 of Fig. 1.

The PIC pattern, for example the one shown in Fig. , is decoded according to the delta distance method, which determines whether successive and overlapping intervals, that is ΤΙ, T2 and T2, T3 and T3, T4 have a predetermined ratio relative to each other as given by the PIC pattern which is to be decoded. If the value of the quotients of successive overlapping interval lengths falls within predetermined value ranges, the size of the range being determined by printing blurrs or digitalization inaccuracies, then in all probability the searched-for PIC pattern is present.

Fig. 6 shows the counting circuit, which forms the input of the decoder of the invention, and which counts the interval lengths TI to T4 and makes them available as binary values for further processing. The counting circuit contains a timing circuit 2 to which the video signal VIDEO is fed and which emits at a first output a first gate signal from a first rising slope to a second rising slope of the video signal, a second gate signal T2 at a second output from a falling slope following the first rising slope to a second falling slope of the video signal, a third gate signal T3 at a third output from the second rising slope to the next, third, rising slope, and a fourth gate signal T4 at a fourth output from the second falling slope to the next, third, falling slope. See also the pulse schematic shown in Fig. 11.

The gate signals TI and T4 are fed individually to the gate inputs Gl to G4 of the four counters 6, 8, 10 and 12, respectively. Each counter receives at its input CT1 to CT4 sync pulses from a sync generator 14 which are counted by the counters so long as the respective gate signals TI to T4 are applied. The result obtained at the outpus TCI to TC4 of the counters 6 to 12 then represents a measure for the length of the gate signals TI to T4.

In the timing circuit 2, a release signal E2 is generated by the falling slope of the gate signal T2, a release signal E3 is generated by the falling slope of the gate signal T3, and a release signal E4 is generated by the falling slope of the gate signal T4. The release signals are emitted at separate outputs. The release signal E4 further generates a signal PWAIT the length of which corresponds to the signal-free trailing zone after the end of the gate signal T4, and it too is emitted at a separate output.

The counting circuit further includes a reset circuit 4 which receives the video signal VIDEO, and an external reset signal RESET IN at a separate input at the start of each scan line. The reset circuit 4 emits a reset signal RESET to the reset inputs RSI to RS4 of the counters 6 to 12 as well as to the timing circuit 2 and resets the counters 6 to 12 as well as the timing circuit 2 into an active starting condition when the video signal contains a signal-free section — of an amplitude Lo — which is larger than the maximum scanning distance between the lines of the PIC patterns as given by the maximum spacing within the PIC pattern, multiplied by the largest permissible scanning angle.

The counting circuit further contains an overflow sensor 40 which is responsive to an overflow or carryover output OV1 to 0V4 of the counters 6 to 12 and emits a reset signal OV RESET, and then resets the decoder into a new state of readiness.

Fig. 7 shows an embodiment of the comparison table of the decoder which includes a read-only memory or PROM 28. PROM 28 is organized so that count TCI of the counter 6 addresses individual lines of the memory matrix and count TC2 of the counter Θ addresses individual columns of the first memory matrix. Counts TCI and TC2 are applied to PROM 28 by the release signal E2 via the gate circuits 16, 18 after TC2 has been counted. The first memory matrix includes an expectancy field which encompasses the memory positions where the quotient of the line address and the column address falls within a predetermined value range. This value range corresponds to the quotient of a first interval length to a second interval length of the PIC pattern under consideration. If a memory position within the expectancy field is addressed by counts TCI and TC2, a reference signal having a first amplitude, for example Hi, is emitted which signals that information had been scanned which corresponds to a portion of the PIC pattern under consideration.

To correspondingly compare the gate pulses T2 with gate pulse T3, the count TC2 of the second counter 8 addresses the lines of a second memory matrix, and the count TC3 of the third counter 10 addresses the columns of the second memory matrix. The addressing takes place via gates 20, 22 after the count TC3 has been counted and the counts TC2 and TC3 are sent to PROM 28 by the release signal E3. The second matrix also includes an expectancy field which encompasses the memory positions whose quotient of line address and column address falls within a predetermined range which is equal to the value range of the quotient of the intervals of the PIC pattern corresponding to gate signals T2 and T3.

When a memory position in the expectancy field is addressed, a reference signal having a first amplitude, for example the amplitude Hi, is emitted. When a memory position outside the expected field is addressed, a reference signal having a second amplitude Lo is emitted.

Comparison of the count TC3 of the third counter 10 with the position TC4 is accomplished likewise by addressing lines and columns of a third memory matrix which also includes an expectancy field. When a memory position within the expectancy field is addressed, a reference signal having a first amplitude Hi is emitted. The third memory matrix is addressed via gates 24, 26 after the count TC 4 of the fourth counter 12 has been counted and the counts TC3 and TC4 are sent to the FROM 28 by the release signal E4. Gates 16 to 26 comprise AND gates.

The release of comparison signals LPIC1 and LPIC2 and LPIC3 is effected by the release signals EL2, EL3 and EL 4 which are obtained by delaying the release signals E2, E3, and E4 in the delay circuit 30; see also the pulse plan of Fig. 12. Read-out may only take place after the first, second and third memory matrix have been addressed.

As an alternative to the embodiment shown in Fig. 7, the first memory matrix may be defined by a first readonly memory, PROM1, the second memory matrix by a second read-only memory, PROM2, and the third memory matrix by a third read-only memory, PROM3. In this embodiment three read-only memories of relatively low storage capacity can be employed.

The read-only memory 28 has storage areas each of which has an n-bit capacity. Since for the determination of an expected field only one bit of the storage area portion defining the expected field is occupied, up to eight different expected fields for eight different PIC patterns can be simultaneously accommodated in the PROM. For example, the first expected field in PROM1 is accommodated in the first bit of the memory positions, the second expected field in the second bit of the memory positions, and so forth. The same applies for PROM2 and PROM3. The line and column addressing for a specific PIC pattern must then occur selectively to the corresponding bits of the memory positions. Further, a switch 32 coupled to PROM28 selectively reads out the comparison signals LPIC1 and LPIC2 and LPIC3 from the pertinent bits of the memory positions and transmits as its output to an evaluation circuit the evaluation signal MUX PIC, formed of the sequential comparison signals LFIC1, LPIC2 and LFIC3.

Fig. 9 illustrates the evaluation circuit of the decoding device. An interim memory 34 receives the evaluation signal MUX PIC and stores the comparison signal LPIC1 — which indicates that the value TC1/TC2 falls within a pre15 SQ309 determined range — as well as comparison signals LPIC2 and LPIC3. Storing is commenced by release signals EL2 and EL3 and EL4 which are generated substantially simultaneously with the comparison signals LPIC1, LPIC2 and LPIC3, see the pulse schematic of Fig. 12. After all comparison signals have been stored in the interim memory as storage signals LPIC1', LPIC2', LPIC3', the storage signals are transmitted to an AND gate 35 which emits an output signal LPIC when all storage signals LPIC1' etc. have a first amplitude corresponding to the first amplitude of the comparison signals LPIC1 etc., see Fig. 12. The output signal LPIC is fed to an output circuit 38 which receives the video signal VIDEO and the hold signal PWAIT from the control circuit 2. The output circuit 38 generates an identification signal PIC OUT when the video signal VIDEO remains on amplitude Lo while hold signal PWAIT is applied. The amplitude Lo identifies a signal-free subsurface. This ensures that the decoded line pattern is followed by a signal-free trailing zone which corresponds to the trailing zone 58 of the PIC pattern.

The output circuit 38 is reset by the external reset signal RESET IN and thereupon applies a reset signal RESETA to the interim memory 34 and resets the latter for a new cycle. The interim memory is further reset by the overflow reset signal OV RESET when one of the counters 6 to 12 signals an overflow.

Fig. 10 is a schematic representation of the organization of the comparison table, for example the partial comparison table of PROM1 for comparing the quotient TC1/TC2.

The table comprises a memory matrix and its lines and columns have the appropriate binary addresses. In accordance with a preferred embodiment of the decoder of the invention, a 5-bit representation has been selected. All memory positions with a specific value of the quotient of line address to column address lie on one line, the so-called expectancy line around which the expectancy field is located. Within the field all those memory positions are located VL &h address quotients that fall in the predetermined value range. The counts TCI to TC4 are also emitted as 5-bit words. The count TCI addresses the lines of the table, the count TC2 addresses the columns of the table.

Claims (26)

1. Method of identifying articles, which appear in any position and orientation and at any time at an image aperture and each have a designating area or panel on a surface which is facing the image aperture, which panel comprises symbols in at least one datum track and at least one contrasting line pattern, which characterises the position and the orientation of the datum track and has a plurality of parallel lines of different spacing and/or line width, in connection with which the image aperture is scanned line by line and a binary video signal correspond!ng to the scanned contrast line pattern and the following symbols is produced, the image aperture in the first step of the method being scanned at different angles until a prescribed contrasting line pattern is detected, in the second step of the method, the position and alignment of the data track relatively to the image aperture is established, and in the third step of the method, a grid scanning is effected in the direction of the data track and the symbols are read off and decoded, wherein for the detection of the contrast line pattern (PIC), the interval lengths of overlapping intervals of the video signal and in each case comprising at least one light-dark region are measured and portrayed in the form of binary counter readings (TCI to TC4). that the counter readings (TCI to TC4) address a twodimensional table which is stored in a store and in which is contained an expectation zone with criteria for a prescribed ratio between two successive interval lengths of the intervals SOS that the counter reading (TCN) corresponding to an interval length (IN) addresses one line of the table and the reading corresponding to the following interval length (IN + 1) addresses one column of the table, that a coincidence signal (LPIC1, LPIC2, LPIC3) is produced when the relation of the two respectively following interval lengths lies in a prescribed value range, and that a recognition signal (PIC OUT) is delivered when a coincidence signal LPIC1, LPIC2, LPIC3) is produced with a number of successive addressing steps which is prescribed by the contrast line pattern (PIC).

2. Method according to claim 1, wherein, in the two-dimensional table, the expectation zone comprises those table positions at which is situated the quotient of those two successively measured interval lengths within the prescribed value range which are compared with one another and a coincidence signal is produced when the interval lengths compared with one another correspond to a table position within the expectation zone.

3. Method according to claim 2, wherein the expectation zone is situated in a region of the table which in each case is defined by a line and a column with minimal and maximal interval length.

4. Method according to claim 2 or 3, wherein always two successively measured interval lengths which are to be compared with one another are associated with their own table having a common expectation field.

5. Method according to claim 4, wherein different expectation fields or zones for appropriately successively measured interval lengths of different contrast line patterns are provided in the individual tables.

6. Method according to one of claims 2 to 5, wherein the counter readings of two successively measured interval lengths are simultaneously introduced into the store, after the subsequently measured interval length is measured.

7. Method according to claim 1, wherein the intervals of the video signal are in each case measured from one rising flank to the next rising flank and in overlapping manner from the descending flank living between these rising flanks to the next descending flank.

8. Method according to one of the preceding claims, wherein the contrast line pattern has a symbol-free preliminary zone of prescribed length, and that the measurement of the interval lengths is first initiated when a symbol-free preliminary zone of the prescribed length is identified in the video signal.

9. Method according to one of the preceding claims, wherein the measurement of the interval lengths is terminated when an interval length exceeds a pre-set maximum value, which value just corresponds to the maximum interval length appearing in the contrast line pattern.

10. Method according to one of the preceding claims, wherein the progressive measurement of the interval lengths is ended and a new measurement is started when the ratio between two successively measured interval lengths is outside the prescribed value range.

11. Method according to one of the preceding claims, wherein the progressive measurement of the interval lengths is ended and a new measurement is started when a symbol-free intermediate zone of prescribed duration is detected in the video signal, which zone just SOSOS corresponds to the maximum scanning path between the lines of the contrast line pattern.

12. Method according to one of the preceding claims, wherein the contrast line pattern has a symbol-free follow-up zone of prescribed 5 length, and that an identification signal (PIC OUT) is only delivered when the video signal contains a symbol-free follow-up zone of the prescribed length.

13. Method according to one of the preceding claims, wherein the interval lengths are counted out digitally as a multiple of a prescribed 10 timing period.

14. Method according to one of the preceding claims, wherein the same line of the image zone is scanned n times, and that the identification signal (PIC OUT) is only delivered when a contrast line pattern is identified n times in successsion.

15. 15. Apparatus for carrying into effect the method according to one of the claims 1 to 14, comprising an opto-electronic scanning device with rotatable scanning screen, which delivered, at the output, the binary video signal which corresponds to the image aperture scanned line-by-line and contains in binary form the contrast pattern of the 20 scanned lines, de-coding means for the detection of the scanned contrast line pattern (PIC), which characterises the position and orientation of at least one datum track of the identification field and contains a plurality of parallel lines which are differently spaced and/or have a different line width, and means for the alignment of the scanning grid 25 parallel to the datum track and for reading or sensing the scanned symbols of the datum track, wherein the decoding means contain a counter circuit which receives the video signal and determines the interval Z0 lengths of following and overlapping intervals of the video signal, that the decoding means contain at least one storage matrix(PROM 28) which by way of a gate circuit receives the counter readings (TCI, TC2; TC2, TC3; TC3, TC4...) in pairs, corresponding to the successive interval lengths and in each case delivers the identification signal (LPIC1, LPIC2, LPIC3) when the relationship of the two successive interval lengths is in a prescribed value range which corresponds to the relationship of the corresponding intervals of the contrast line pattern, and that an evaluation circuit is provided which delivers the recognition signal (PIC OUT) in the event of a succession of a special number of identification signals (LPIC....).

16. Apparatus according to claim 15, wherein the counter circuit contains a time control circuit, which generates gate pulses (Tl, T2, T3, T4...), which correspond to overlapping intervals of the video signal and of which the pulse length is determined by successive rising flanks or successive descending flanks of the video signal, that the gate pulses (Tl, T2, T3, T4...) are each capable of being fed in the gate input to a counter, that the counters are jointly connected to the counting input to a timing generator and count out the gate impulses at intervals and feed them as digitally selected interval lengths to the storing matrix.

17. Apparatus according to claim 16, wherein the counting circuit contains an over-run detector which, in the event of overrunning of a counter, sets back the decoding means.

18. Apparatus according to one of claims 15 to 17, wherein the store matrix is designed as a two-dimensional programme region (PROM), that SOSOS the various possible discrete counting values of a first interval length address well-defined associated lines of the programme register, that the various possible discrete counting values of the subsequently counted interval length address well-defined columns of the programme 5 register, and that an expectation field is prescribed, which covers those store positions at which the quotient from line address to column address lies in a prescribed value range, and with addressing of a store position within the expectation field, an identification signal (LPIC1, LPIC2, LPIC3) is delivered. 10

19. Apparatus according to claim 18, wherein a specific programme register (PROM 1, PROM 2, PROM 3..,) with its own expectation field is provided in each case for two successive interval counting values (TCI, TC2; TC2, TC3; TC3, TC4...).

20. Apparatus according to claim 19, wherein two successively counted 15 interval counting values (TCI, TC2; TC2, TC3; TC3, TC4...) in each case addresss the associated programme registers (PROM 1, PROM 2, PROM 3...) simultaneously when the later interval counting value is counted out and the time control circuit delivers a release or tripping signal (E2, E3, E4) for activating the gate circuit in front 2u of the programme register.

21. Apparatus according to one of claims 18 to 20, wherein each storage space of the programme register stores n bits and each bit is associated with a selectively addressable expectation field for n different contrast line patterns, and that the signals (LPIC 1, LPIC 2, 25 LPIC 3) associated with the different expectation fields are capable of being supplied selectively to the evaluation circuit by means of a following selector switch.

22. Apparatus according to one of claims 15 to 21, wherein the evaluation circuit contains an intermediate store, which stores the signals (LPIC1, LPIC2) until the arrival of the last signal (LPIC3) and then delivers all said signals (LPIC1, LPIC2, LPIC3) to separate inputs of an AND gate, which supplied an output signal (LPIC) when all said signals (LPIC1, LPIC2, LPIC3) are present.

23. Apparatus according to claim 22, wherein an output circuit is connected following the AND gate, which contains the video signal and, from the time control circuit, receives a waiting signal (PWAIT) and delivers the recognition signal (PIC OUT) when the video signal, during the proximity of the waiting signal (PWAIT), has a signal-free run-out section.

24. Apparatus according to one of claims 15 to 23, wherein a resetting circuit is provided, which receives the video signal and, with commencement of each scanning line, an external resetting signal (RESET IN), that the resetting circuit delivers a resetting signal (RESET) when the video signal contains a signal-free section which is larger than the maximal scanning path between the lines of the contrast line pattern, and that the resetting circuit delivers a resetting signal (RESET) when an external resetting signal (RESET IN) is present, and that the resetting signal (RESET) can be supplied to the counters and the time control circuit for the resetting.

25. A method for identifying articles substantially as described herein with reference to the accompanying drawings.

26. Apparatus for identifying objects constructed and adapted to operate substantially as described herein with reference to the accompanying drawings. Dated this 15th day of April 1980. (Signed): BY: TOMKINS & CO., Applicants' Agents, 5, wTmouth Road, DUBLIN 6.