Patent GB-478948-A (GB)
Title: Improvements in and relating to document examining and sorting apparatus
IPC: G06V10/75
Filed: 1936-04-27
Abstract: 478,948. Photo - electric apparatus for examining and sorting documents. BLUMENTHAL. L. J., and FREEDMAN, P. April 27, 1936, No. 11869. [Classes 39 (i) and 40 (iii)] Relates to methods of and apparatus for examining and sorting documents such as competition coupons or ballot papers containing one or more columns of symbols, involving the comparison of the symbols with those on a standard page. According to the invention, given that the symbols on a page to be examined and on a standard page fulfil certain specified conditions as to arrangement and characteristic light-influencing qualities dependent on shape, size, and quality of ink, &c., the operations of examining and sorting are effected by scanning an observed document page and a standard page synchronously and successively by two lines of light of different wavelengths, and utilizing the effect produced thereby on light-sensitive means. Apparatus for carrying out the invention may comprise an endless band, Fig. 4 (not shown), on which the documents to be examined are carried below a slit illuminated from above by coloured light and below a second slit illuminated by differently coloured light, the lines of light reflected from the document affecting suitablyarranged photo-electric devices (as described below). Simultaneously, with the two scannings of the observed page, a standard page and a blank page are scanned by fixing such pages in duplicate below the moving belt in positions where they are traversed at the appropriate times by slits in the band. Means are also provided for enabling the second blank page to operate a " switching photocell " between the two scannings, and for operating " set-zero " photocells which reset the whole electrical system after a document has been completely scanned and before the commencement of scanning of another document to be observed. For each column of symbols on a document, there is provided a system, partly shown in the Figure, comprising a group of photocells P<1> ... P' and " cathode-ray phototubes " PK<1> ... PK<4>, all of which devices are sensitive only to the first scanning light; there is also a similar group (not shown) sensitive only to the second scanning light. The cells P<1>, P<3> are affected by light reflected from an observed page and a standard page respectively, whilst the cells P<2>, P<4> are affected by light from the blank pages, and similarly for the '' cathode-ray phototubes " PK<1> ... PK<4>. Each of the latter comprises a hot cathode, a focusing cylinder, two pairs of deflecting plates, one or more intercepting diaphragms, an anode, and a cathode formed as a condenser with a light-sensitive layer as one electrode. Resistances and batteries are arranged as shown. In addition, there are provided for the first scanning operation a pair of " impulse cathode-ray tubes " Ko, Ks, for each column of an observed page and of the standard page and a similar group (not shown) for use in the second scan. Each of these devices comprises a hot cathode preferably surrounded by a focusing cylinder, a control grid, an axial tubular anode, a pair of deflector plates, an apertured intercepting diaphragm, and a collector electrode. A condenser Co or Cs is connected to the collector electrode of each of the tubes Ko, Ks and is also connected to the grid of a valve Vo or Vs. The effect of the arrangement so far described is that during the first scan, when a symbol has been scanned on the observed page, a current flows through Ko and is proportional to the light-controlling value of the symbol ; electrons do not, however, reach the collector electrode if no potential is applied to the deflector plates, i.e. if the corresponding square on the standard page is blank. A similar effect is produced on Ks. Thus, during the first scanning of corresponding columns, charges are accumulated on Co and Cs which are proportional to the sum of the light-controlling effects produced by the symbols in the respective columns, and the currents so produced in the valves Vo and Vs rise to maxima which are proportional to the charges on the condensers. Two " comparison valves " Vg are provided, each of which has two control grids, the potential of one of which is dependent on the current flowing in Vo or Vs, while that of the other is controlled by current impulses in one of the " impulse cathode-ray tubes " used during the second scan. The arrangement is such that no current flows in either of the valves Vg during the first scan, but whilst the documents are being scanned by the second line of light current impulses occur synchronously in these valves whenever symbols are scanned simultaneously in corresponding squares on the observed and the standard documents. In each valve, the integrating effect on one control grid produced during the first scan combines with the individual effect corresponding to a particular symbol produced during the second scan. Thus, the first scan tests whether predetermined conditions as to overall similarity exists as between the symbols in corresponding columns on the compared documents, and if these conditions are fulfilled, whenever during the second scan the same symbols occur in corresponding squares of the documents substantially equal current impulses pass through the valves Vg. The anodes of these valves are connected by resistances R<21>, R<22> and to a pair of deflector plates in a " charger cathoderay tube" Kc, which plates control the passage of the electron beam through an aperture in a diaphragm. Two further pairs of deflector plates, with corresponding diaphragms, also control the beam, one pair being arranged to determine the " tolerance value" " (i.e. the allowable departure from identity between the symbols on the compared documents), and the other being controlled by the " switching photocell." The beam can only pass to the collector electrode when substantially equal current impulses are produced, as described above, in the valves Vg, causing substantially equal potential drops 'in R<21>, R<22>, and when the switching photocell has operated. Each time the beam reaches the collector electrode. a condenser Cc receives a charge. If and when the built-up charge reaches a predetermined value, it operates a " trigger-tube " G, whereby through a relay sorting-mechanism is actuated, and causes the examined document to be delivered into a receptacle. Mechanism as described in Specification 468,692 may be utilized for this purpose. After a complete scanning operation has been performed, the residual charges on the various condensers are neutralized by means of " set-zero photocells " co-operating with special valves in the manner described in Specification 470,638. Optical systems for scanning simultaneously a number of columns as described in this prior Specification may be employed.