US3780310A - Apparatus for detecting unprepared postage stamps - Google Patents

Abstract

There is disclosed an optical arrangement for detecting regular, non-specially-prepared postage stamps for machines which accordingly face or orient the articles for automatic sorting. Detection is limited to the serrated edges common to all existing stamps, which serrations may easily be made into a code. A light source is arranged to impinge radiation at an acute angle relative to the direction of document travel. Thereby the sides of the serrations parallel to this direction are highly illuminated. A photoelectric sensor receives the train of light pulses emitted by the sides of the stamp serrations, which are fed to an amplifier and on to a pulse counting circuit, which serves to operate a deflector.

Description

1451 Dec. 18, 1973 APPARATUS FOR DETECTING UNPREPARED POSTAGE STAMPS [76] Inventor: Heinz Hudler, Ketzergasse 389,

Vienna, Austria 221 Filed: Mar. 21, 1972 211 Appl. No.: 236,619

[30] Foreign Application Priority Data Mar. 30, 1971 Austria A 2691/71 [52] US. Cl ..250/555, 250/223 R, 209/DIG. 1 [51] Int. Cl. G01n 21/30 [58] Field of Search 250/219 DO, 219 DR, 250/219 LG, 222 PC, 223 R; 209/111.5,

DIG. l

[56] References Cited UNITED STATES PATENTS Mustert 250/219 DO Stegenga.. 250/222 X PC Frankie et a1 250/223 R 3,313,944 4/1967 Muir 250/219 LG 3,488,511 l/1970 Mori et al. 250/219 DO 1 2,936,886 5/1960 Harmon 250/219 DQ Primary Examiner-Wa1ter Stolwein Att0rne vC. Cornell Remsen, Jr. et a1.

57 ABSTRACT There is disclosed an optical arrangement for detecting regular, non-specially-prepared postage stamps for machines which accordingly face or orient the articles for automatic sorting. Detection is limited to the serrated edges common to all existing stamps, which serrations may easily be made into a code. A light source is arranged to impinge radiation at an acute angle relative to the direction of document travel. Thereby the sides of the serrations parallel to this direction are highly illuminated. A photoelectric sensor receives the train of light pulses emitted by the sides of the stamp serrations, which are fed to an amplifier and on to a pulse counting circuit, which serves to operate a deflector.

10 Claims, 10 Drawing Figures PAIENIEDHH: 18 ms sum 201 2 APPARATUS FOR DETECTING UNPREPARED POSTAGE STAMPS The automatic distribution of letters in highly mechanized routing post offices basically involves various operations. Those of the received letters must be sorted out which have a unhandly size because they are too large, too thick or too stiff to be handled by machine (separation of sizes). The remaining mail items are then turned around and turned over so that the postage stamps on all letters are on the same side and have the same orientation. This operation involved in the handling by machine is referred to as the facing of the letters and is carried out with so-called facing machines. Only mail items which have been faced can be marked by machine and transferred to the actual automatic sorting operation.

The facing of the letters by machine involves the searching for and detection of the postage stamps. The optical methods presently used to identify postage stamps do not give satisfactory results. For this reason, postage stamps have been prepared by being provided with detectable marks. Various methods have been developed for this purpose. Of these methods, one of the most reliable ones involves the use of luminescent post age stamps. The paper of the postage stamps is impregnated or coated with fluorescent or phosphorescent dyestuff so that the stamps can be relatively easily detected when irradiated with ultraviolet light (quartz lamp) and simple indicating methods can be employed. In this method, the percentage of errors is low (about 1 percent). In other processes, the finished postage stamp is provided with a luminescent coating, or specific spectral colors are used in the stamp picture and can be screened out with the aid of special filters and indicated.

All these methods have the disadvantage that the additional preparation processes add considerably to the costs of making the postage stamps so that the saving of costs which is desired by the use of facing machines may be offset. Another disadvantage resides in that the preparation of the stamps adversely affects the purity of their colors. For instance, the colors of the stamp picture may not give the desired impression on the luminescent base, or the preparation may adversely affect the quality of the stamp paper or may stain the same. The method which is most widely used and involves the use of fluorescent postage stamp paper has a serious technical disadvantage residing in that many of the envelopes being used are made from a paper which has been rendered highly fluorescent by an addition of so-called brighteners. Postage stamps stuck onto such envelope cannot be detected with simple means. For the reasons set forth, the postal administrations in a number of countries have not adopted such methods,

code and by means of modern machines can be made exactly with the desired pitch.

The invention provides an apparatus for identifying normal, serrated, unprepared postage stamps on letters by machine, which apparatus comprises a light source, which illuminates at a small angle the letters moved in a given direction, and a photoelectric sensor, and is characterized in that the light source is arranged so that the light rays include an acute angle with the direction of travel and the stamps are thus laterally illuminated with grazing light in such a manner that the sides of the serrations on the stamp sides which are parallel to the direction of travel are highly illuminated, and the pho toelectric sensor, which receives a train of light pulses emitted by the sides of the serrations of the passing stamps, is connected to a threshold amplifier, which has an optimum gain in a range which is adjustable to include the frequency of the serrations passing the sensor, whereas the output of the amplifier is connected by a timer or by a pulse-counting circuit to a known switch, which serves, e.g., to operate a deflector for selecting a route for each letter.

Because the location at which the stamp is stuck on the envelope is not predetermined, a relatively wide strip must be scanned. For this reason, the photoelectric sensor consists, in accordance: with the invention, of one or more photoelectric cells provided with a slit, or of one or more photoelectric cells provided with an optical system which comprises at least two cylindrical lenses having longitudinal axes at an angle of to each other.

A plurality of photoelectric cells are provided, if desired, in combination with a selector circuit which onsures that only that amplifier channel which carries the useful signal is used to operate the switch.

According to a further feature of the invention, the transient time of the selective amplifier is selected so that an audio-frequency signal voltage which is sufficient to initiate the switching operation will not be generated until the scanning operation has been performed for a time which is approximately one-half of the time for a stamp to pass.

An imporatant feature of the invention resides in that strong grazing light is used for scanning so that the apices and sides of the serrations are particularly brightly illuminated. This optimum effect can easily be obtained if the light source is adjustable and the photoelectric arrangement is rotatable and pivotally movable.

The principle underlying the invention affords the advantage that only the postage stamps, and of these only the serrations, are sensed, whereas there is no photoelectric respouse to disturbing imprints, marks and the like.

If the stamps are provided with serrations differing in pitch, in dependence on the value of the stamps, the provision of a plurality of selective amplifiers, which are tuned to suitable frequencies, will enable a check as to the value of the postage stamps or a sorting for other considerations.

Further features and advantages of the invention will become apparent from the following description with reference to the drawing, in which FIG. 1 is a side elevation showing the apparatus according to the invention,

FIGS. 2a, 2b and 2c show different embodiments of the photoelectric sensor,

FIG. 3 shows the limits of the area in which a postage stamp should be stuck on a letter,

FIG. 4 shows how a plurality of photoelectric sensing units may be used to scan a wide strip,

FIGS. 5a, 5b and 5c represent the transients of the selective amplifier in response to different signals and FIG. 6 illustrates the most desirable adjustment of the photoelectric sensor.

As is apparent from FIG. I, the overall arrangement comprises a belt conveyor 1, by which theletter 2, on which a postage stamp has been stuck, is moved at a constant velocity v under the photoelectric sensor 4. Thelight source 3 must illuminate the letter and the stamp by strongly grazing light so that only the uneven portions of the surfac of the letter, particularly the stamp with its serrations, are scanned. In response to the scanning of the serrations, the photoelectric sensor generates an audiofrequency pulse train, which is amplified by aselective amplifier 5 and, when a certain threshold value is exceeded, the amplified pulse train is delivered to atimer 6 or to a pulse-countingcircuit 7.

In the drawing, both possibilities are provided for (changeover switches U U In practice, however, no change-over will be provided for and only one means or the other will be employed. When the serrations of a stamp are being scanned and the threshold value has been reached and the threshold value of the output voltage of the amplifier has been maintained for a predetermined, short time, the timer or the pulse-counting circuit will cause an operation of theswitch 8.

As is shown in section in FIG. 2a, the scanning may be accomplished in the simplest case by means of aphotoelectric cell 9 and aslit 10, which has a small width, e.g., of 0.5 millimeter, and a longitudinal axis extending parallel to the illuminated sides of the serrations. In this case, the photoelectric sensor must be disposed very close to the postage stamp so that the sensor can receive a sufficiently large amount of reflected light from theserrations 11. For this reason, provision must be made in connection with the conveyor to ensure that that surface of the letter which is to be scanned is always at the same distance from the photoelectric sensor, regardless of the thickness of the letter. This disadvantage may be avoided by the provision of an optical system between the postage stamp and the photoelectric cell (FIGS. 2b and This optical system consists of at least tow cylindrical two one of which (14), forms on thephotoelectrical cell 9 an image corresponding to the scanning width (one serration of the postage stamp) whereas the second lens (13) has a longitudinal axis at an angle of 90 to that of the first lens and results in a reduction so that an image correspnding to the width of the scanning strip is formed on the photoelectric cell. The longitudinal axes of the cylindrical lenses are, respectively, parallel and at right angles to the illuminated sides of the serrations. FIGS. 2b and 20 show the light pahts in two section planes which extend through the optical axis at an angle of 90 to each other.

Anaperture plate 12 disposed in front of the photoelectric cell cooperates with the cylindrical lens system like a slit in conjunction with a normal optical system comprising spherical lenses. With this method, the distance between the postage stamp and the photoelectric sensor can be much increased so that the variations of the distance between the postage stamp and photoelectric cell which are due to the thickness differences between the letters can be neglected and a wider strip of the letter can be scanned.

In accordance with an international agreement, the postage stamp should be stuck in an area having dimensions L 74 millimeters and B 40 millimeters at the upper right corner of the letter, as is shown in FIG. 3 Depending on the size of the stamp, there is a certain latitude as to the location of the stamp in this area. To ensure that the serrations at the upper edge of the stamp can be reliably scanned, the photoelectric sensor must cover a strip having a width H of approximately 15 millimeters. This requirement cannot easily be met with a single photoelectric cell. It is more desirable to provide a plurality of photoelectric cells in an arrangement as shown in FIG. 4. In view of their overall dimensions, thephotoelectric sensing units 15 are staggered. The resulting scanning time differences are insignificant for the detecting operation. Because there may be interference in the overlap areas, the spacing d of the photoelectric cells in the direction of travel is an integral multiple of the pitch of the serrations to be scanned. The outputs of the photoelectric cells are connected by theamplifier channels 16 to a selector circuit 17, such as an OR gate. This selector circuit connects only that amplifier channel to theswitch 8 which carries a signal in response to the scanning of a postage stamp. As a result, any interference signals in the other channels are not added but entirely eliminated.

If a postage stamp being scanned travels at a speed of, e.g., 2.5 meters per second and its serrations have a pitch of, e.g., 1.4 millimeters, the pulse train received by the selective amplifier will have a frequency f 2500/ l .4 I785 Hz. In this case, the scanning time for a stamp having a width of, e.g., 25 millimeters is T 25/2500=0.01 second 10 milliseconds. The voltage waveform at the output of the selective amplifier is represented in FIG. 5a and determined by the transient response of this amplifier. The selected transient time T, is about one-half of the scanning time T (t 5 milliseconds). In this case the amplifier may have a bandwidth B which is approximately l/T 200 Hz. In this case, the selective amplifier has a Q factor which is equal to 1785/200 9. Whereas the threshold value of the amplifier is reached at point A, the switch will not yet be operated. Only when the threshold value has been maintained or exceeded for a certain time, for instance, Ta/2 5 milliseconds, and point B has been reached does theswitch 8 respond. This requirement may be met by a timer, which comprises a rectifier for the audio-frequency output pulses and a variable integrating resistance-capacitance circuit, or by acircuit 7, which at the time when the threshold voltage has been reached begins to count a presettable number of output pulses and only thereafter operates theswitch 8. It is apparent from FIG. 5b that short interferences within the useful frequency range will remain below the threshold voltage and will not even reach the point A. FIG. 5c shows that short interference pulses which are very strong will reach the point A but will not reach the point B so that the switch will not respond in this case too. For this reason, the edges of the letters and the uneven portions of the paper are not indicated because they result in signals which have a duration which is shorter than the scanning time of a postage stamp or have a frequency which differs from the audiofrequency of the voltage waveform generated by the serrations.

The function of the apparatus according to the invention for the detection of postage stamps depends highly on the illuminating device. To ensure a correct illumination with grazing light, the light source is adjustable so that the angle of incidence of the light rays on the plane of the letter or the angle included by the light rays and the direction of travel can be adjusted. Because under suitable illumination the apices and sides of the several serrations of the postage stamps form inclined bright lines rather than dots, the photoelectric sensor is also rotatable about its optical axis. It is apparent in FIG. 6 that the illuminating device L can be rotated through about 30 opposite to the direction of travel F to provide for a particularly bright illumination of the sides of the serrations and a generation of the strongest light pulses. In this case, thephotoelectric sensor 18 must be rotated accordingly. Because the strongest reflection from the illuminated serrations will not be at right angles to the plane of the letter, the angle between the optical axis of the photoelectric sensor and the plane of travel should also be adjustable.

I claim:

1. Apparatus for detecting normal, serrated, unprepared postage stamps on documents moving in a given direction, comprising light source means arranged for emitting a single beam of light radiation obliquely directed at an acute angle along the direction of travel of the documents and highly illuminating the sides of the serrations only which are associated to a side of the stamps which is substantially parallel to the direction of travel of the documents, photoelectric sensing means stationarily arranged relative to the moving documents for receiving the light emitted by said sides of said serrations, which received light is in the form of a train of pulses corresponding to the serrated stamp parallel edges moving relative to the light source beamed radiation, threshold amplifying means coupled to said sensing means, said amplifying means being arranged to have an optimum gain. in a range which is adjustable to include the frequency of the serrations passing said sensing means, and first means coupled to said amplifying means for receiving the output of the latter and deriving therefrom a control output signal which characterizes the positional orientation of the stamp on its associated document.

2. The apparatus according to claim 1 wherein said photoelectric sensing means includes at least one photoelectric cell provided with a slit having a longitudinal axis which is parallel to the illuminated sides of the serrations.

3. The apparatus according to claim 1 wherein said photoelectric sensing means includes at least one photoelectric cell directed to receive said light pulse train, a pair of cylindrical lenses having longitudinal axes which are arranged at an angle of to each other and extend, respectively, parallel and at right angles to the illuminated sides of the serrations, and an aperture plate disposed proximate said photoelectric cell.

4. The apparatus according to claim 1 wherein said photoelectric sensing means includes a plurality of photoelectric cells arranged in a row, said cells having in the direction of travel a predetermined spacing (d) from one another which is an integral multiple of the pitch of the stamp serrations, and further including se lective amplifier means coupled to said plurality of photoelectric cells and having a plurality of amplifier channels, and selector circuit means coupled to said so lector amplifier means for connecting only that amplifier channel which carries the useful output to said first means.

5. The apparatus according toclaim 2 wherein said threshold amplifying means is designed such that the transit time thereof is substantially one-half of the time for a moving stamp to pass said photoelectric sensing means.

6. The apparatus according toclaim 2 wherein said first means is comprised of a timer arrangement which includes a rectifier and an integrating resistancecapacitance circuit for initiating a controlled output only when a received output from said amplifying means, as derived from an input to the latter which is sufficient for an initiation, has been maintained for a predetermined adjustable time.

7. The apparatus according toclaim 2 wherein said first means is comprised of a pulse counting circuit for initiating a controlled output when the photoelectric sensing has resulted in the generation of a predeterminable adjustable number of pulses after the threshold voltage of said amplifying means has been reached.

8. The apparatus according to claim 1 wherein said light source means is arranged such that the output angle formed by the light rays with the direction of document travel is adjustable.

9. The apparatus according toclaim 8 wherein said photoelectric sensing means is rotatable about its optical axis.

10. The apparatus according toclaim 9 wherein the angle included by the optical axis of said photoelectric sensing means with the plane of document travel is predeterminably adjustable.

Claims (10)

1. Apparatus for detecting normal, serrated, unprepared postage stamps on documents moving in a given direction, comprising light source means arranged for emitting a single beam of light radiation obliquely directed at an acute angle along the direction of travel of the documents and highly illuminating the sides of the serrations only which are associated to a side of the stamps which is substantially parallel to the direction of travel of the documents, photoelectric sensing means stationarily arranged relative to the moving documents for receiving the light emitted by said sides of said serrations, which received light is in the form of a train of pulses corresponding to the serrated stamp parallel edges moving relative to the light source beamed radiation, threshold amplifying means coupled to said sensing means, said amplifying means being arranged to have an optimum gain in a range which is adjustable to include the frequency of the serrations passing said sensing means, and first means coupled to said amplifying means for receiving the output of the latter and deriving therefrom a control output signal which characterizes the positional orientation of the stamp on its associated document.

2. The apparatus according to claim 1 wherein said photoelectric sensing means includes at least one photoelectric cell provided with a slit having a longitudinal axis which is parallel to the illuminated sides of the serrations.

3. The apparatus according to claim 1 wherein said photoelectric sensing means includes at least one photoelectric cell directed to receive said light pulse train, a pair of cylindrical lenses having longitudinal axes which are arranged at an angle of 90* to each other and extend, respectively, parallel and at right angles to the illuminated sides of the serrations, and an aperture plate disposed proximate said photoelectric cell.

4. The apparatus according to claim 1 wherein said photoelectric sensing means includes a plurality of photoelectric cells arranged in a row, said cells having in the direction of travel a predetermined spacing (d) from one another which is an integral multiple of the pitch of the stamp serrations, and further including selective amplifier means coupled to said plurality of photoelectric cells and having a plurality of amplifier channels, and selector circuit means coupled to said selector amplifier means for connecting only that amplifier channel which carries the useful output to said first means.

5. The apparatus according to claim 2 wherein said threshold amplifying means is designed such that the transit time thereof is substantially one-half of the time for a moving stamp to pass said photoelectric sensing means.

6. The apparatus according to claim 2 wherein said first means is comprised of a timer arrangement which includes a rectifier and an integrating resistance-capacitance circuit for initiating a controlled output only when a received output from said amplifying means, as derived from an input to the latter which is sufficient for an initiation, has been maintained for a predetermined adjustable time.

7. The apparatus according to claim 2 wherein said first means is comprised of a pulse counting circuit for initiating a controlled output when the photoelectric sensing has resulted in the generaTion of a predeterminable adjustable number of pulses after the threshold voltage of said amplifying means has been reached.

8. The apparatus according to claim 1 wherein said light source means is arranged such that the output angle formed by the light rays with the direction of document travel is adjustable.

9. The apparatus according to claim 8 wherein said photoelectric sensing means is rotatable about its optical axis.

10. The apparatus according to claim 9 wherein the angle included by the optical axis of said photoelectric sensing means with the plane of document travel is predeterminably adjustable.

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