Patent GB-781931-A (GB)
Title: Character recognition device
IPC: G06V10/75
Filed: 1954-12-03
Abstract: 781,931. Photo-electric character coding apparatus. BURROUGHS CORPORATION. Dec. 3, 1954 [Dec. 4, 1953], No. 35079/54. Class 40 (3). [Also in Group XIX] Characters are identified by means of the blackness or otherwise of a number of selected test points in each, the arrangement being that the position of the test points relatively to a datum point or edge is the same for each character. Thus, if the lower edge of the character is taken as the datum edge the test points will all be located at definite distances above the datum edge-thus Fig. 4 shows an " O " the lower edge of which is used as the datum and which is divided into a series of vertical and transverse lines, the transverse lines having a similar shape to the lower edge of the V. The height of the character is divided into 64 distinct traverses and the width into 35. Thus each of the test points A-E may be specified by a co-ordinate system, the abscissa and co-ordinate of point A being as shown. If then the letter is scanned in a series of vertical traverses the total number of intersections of transverse lines will indicate the position of the test points; e.g. point A is 357; point B is 996 and so on. In the arrangement to be described the lower edge of the character is in all cases used as the starting point, Figs. 9Q and 9R indicate that in the case of the digit 7 the starting edge is discontinuous. However, the positions of the test points are the same relative to the starting line as is shown in Fig. 9R and 9M (digit 5). General operation. Figs. 1 and 5. A document bearing characters 16 to be identified moves horizontally while a beam of light is traversed substantially vertically across it by a scanning disc 25 and a slit 23. Slit 23 is not quite vertical so that the combined movement of the document and the light spot causes it to be scanned in a series of vertical lines. A photomultiplier 30 receives light reflected from the document and produces an output of the type shown in Fig. 3. The beginning of one line and the end of the previous one slightly overlap and the anode voltage of the cell falls to V1; the white background gives an anode voltage V2 and the black character V3. The output signals of photo-cell 30 are shaped and amplitude controlled in input unit 42 (Fig. 5) thus the output comprises a train of rectangular pulses of variable spacing and variable duration depending on the character under examination. When the scanning spot encounters the starting edge of the character a negative pulse is applied from unit 42 to control unit 44. The control unit contains a constant frequency oscillator which starts oscillating at such a frequency as to produce 64 oscillations during one vertical scan. Thus oscillations are applied to an eleven-stage binary counter, each stage consisting of a "flipflop " FF1-FF11 (Fig. 6) to which feeds a pulse back to the oscillator to stop it when 64 (or any multiple thereof) pulses have been received. Counter 45 maintains its count. Each time the scanning spot encounters the lower edge of the character 64 pulses are counted whilst counter 45 is registering a number of pulses representative of the position of one of the test points (see above). The flip-flops are connected to a timing matrix 48 which consists of a network of resistors so connected to recognition gates 50A to 50E (50 in Fig. 5) that when the counter registers a number of pulses corresponding to one of the test points the corresponding recognition gate is prepared. The photo-cell output signal is also applied to the recognition gates and if the photo-cell output indicates that the character is black when the counter indicates that a test point has been reached the recognition gate opens momentarily and operates one of five storage units 52A-52B (52 in Fig. 5) which consists of five "flip-flops." If the test point is white the storage unit remains unoperated. As the counter arrives at the appropriate count each test point conditions the appropriate gate so as to operate the storage unit if the test point is white. At the end of the scanning of any one character the character is represented in a fiveunit code according to which of the storage units are operated. The various elements of the storage unit 52 are connected to a decoding matrix 54 similar in construction to the timing matrix. This matrix has five pairs of input leads, one pair for each storage element, and has ten output leads connected to ten thyratrons each representing one of the characters to be recognised. The combination of storage elements energized prepares one of the thyratrons but this thyratron does not fire until an appropriate potential is applied to all the shield grids simultaneously by an actuator unit 58 comprising a gate connected to the timing matrix which opens when the last test point is reached. The thyratron which fires operates a relay which closes the circuit of a magnet in a tabulating card punch and opens the anode circuit of the thyratron. A pulse developed at the anode of the thyratron in output unit 56 is used to reset the storage unit. A reset unit 46 comprises a condenser which charges sufficiently between characters to operate a thyratron and reset counter 45 and storage unit 52 if not already reset (as in the case of a hyphen). Modification (Fig. 10).-In this embodiment the characters are distorted as indicated previously in Figs. 9Q, 9R and 9M and then examined by a group of photo-cells each of which looks for one of the test points. The scanning is performed by a unit similar to that already described and the first time that input unit 160 produces a "black" pulse, the horizontal sweep generator 162 begins to generate a horizontal deflecting voltage which continues to build up linearly for a period equal to scanning time per character and then returns to its initial value. The vertical sweep generator 164 is triggered once for each vertical scan of the scanning spot in the document when the input unit 160 produces a black signal. The trace is only visible while the output is black, however, and the distorted characters of the type already referred to are produced on the screen of cathode-ray tube 163. The blackness or whiteness of the test points is determined by a group of recognition photo-cells 168 associated with holes in a mask 166 corresponding to the position of the test points. These cells control a group of flip-flops constituting storage unit 170 which then represent the character in the fiveunit code. This code is decoded and represented as already described with reference to the previous embodiment. Photo-multiplier circuit (Fig. 7E).-The output voltage of the photo-multiplier is developed across anode resistor 65 and applied to cathode follower 66 which feeds the diode rectifier section 68A of tube 68. The diode develops a plate voltage equal to the lowest excursion of the photo-cell anode voltage, this excursion is produced at the commencement of each scanning line when the photo receives light from two apertures of the scanning line. Part of the voltage developed by the diode is applied to the control grid of a pentode 74 connected in series with the network supplying the multiplier operating voltage 5. Thus regardless of photocell supply voltage variations, light source variations and change in paper reflectance, the peak-to-peak amplitude of the photo-cell output is maintained constant by neon diode 76 in parallel with the pentode tube 74 by preventing the development of too great a potential across it.