Patent GB-846722-A (GB)
Title: Improvements in character sensing apparatus
IPC: G06V10/40
Filed: 1957-04-02
Abstract: 846,722. Automatic character reading. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 2, 1957 [April 2, 1956], No. 10731/57. Class 106 (1). Apparatus for sensing and interpreting humanly legible characters comprises sensing means for producing in serial form signals representing each character and circuits responsive to the duration and relationship in time between the signals relating to each character for producing signature signals representing the sizes of at least two different portions of, or spaces within the character. The signature signals are stored in registers and retained therein in an ordered relationship. The signals produced represent different sizes of vertical line in the character, different sizes of included white areas, the number of cross-overs in a vertical scan and the relative altitude or slope of character portions in succeeding scans. These signals having been registered in order are used to control recognition circuits, one for each possible character whereby an output is obtained identifying the character sensed. Photo-electric sensing.-Where the characters are formed on the record in ordinary ink a photo-electric sensing arrangement as shown in Fig. 9 is used. A pulse generator 1 feeds a train of pulses to a frequency divider 2 which gives an output after 32 pulses. This output is applied to a single shot multivibrator which supplies a " scan sync " pulse to a sweep generator 4. A pulse derived as described below is applied to the sweep generator to initiate a vertical scan of the beam of a C.R.T. 5, the light spot being focused upon the record to make a vertical scan over the character being sensed having a length about twice the height of the character to allow for some vertical misalignment. During the scan thirty-two sampling pulses from the pulse generator are applied to a circuit 11 which tests the output from photo-cell 9 to determine whether the beam is on a dark part of the character or on a part of the white background. A former gives positive " X " signal and the latter a negative " O " signal. The scan sync applied to the sweep generator 4 causes the beam to retrace. It is also applied through inverter 14 and single shot multivibrator 12 to give a two microsecond positive pulse beginning at the trailing edge of the scan sync pulse and is used for reading out various storage devices in the circuits. This pulse is also passed through inverter 15 and multivibrator 13 to provide a " scan sync + 2 " pulse which is used for resetting various triggers set during the preceding scan. It is also applied to the scan sweep generator 4 to initiate a scan. The record is moved across the sensing device at such a speed that about twenty vertical scans are made through each character. Magnetic sensing.-The characters may alternatively be printed in magnetic ink and sensed by a magnetic scanning device shown in Fig. 70. A pulse generator as in Fig. 9 is connected to a chain of triggers which are set in turn. These triggers are each used to apply an energizing pulse to the windings on opposite limbs of magnetic frame-like cores 61, 62 &c., of which there are thirty-two. Each limb of a core is gapped and the windings are arranged so that normally, when no character is present, the flux in the central leg 65 balances so that when a pulse is received from the associated trigger, no signal is generated in the common winding 80. Coils on each limb and adjusting resistances 85 are provided to effect a flux balance. If a portion of a character lies under the gap of a core when its trigger is set, the balance is upset and an output signal is produced in winding 80. The output is applied to a sampling circuit 83. As the triggers are set in turn, windings on successive cores are energized in turn so that the character is scanned on a vertical line, the record being moved under the scanning line as before. Character components.-Circuits (Fig. 1) are provided which are adapted to recognize various component parts of a character. The output circuit 200 of the sensing apparatus gives signals on three lines; one signal representing that two successive black indications X have been obtained, this signal is termed XX; another signal OO indicating that two successive white indications were obtained and a third signal XO or OX indicating that opposite indications were successively obtained. These signals occurring in certain predetermined orders indicate that particular " signature components " are present, circuits 201 being provided to recognize this fact. The first component is a vertical line. Vertical line signature components .-Such components are divided into three groups: short, medium and long. For a short vertical line (Vs) there must be eight but less than fourteen successive XX, XO or OX signals. By allowing XO or OX signals to pass as XX considerable tolerance is given as to defective printing or weak lines. A medium vertical line (Vm) produces at least fourteen but not more than twenty such signals successively and a long vertical line (Vl) produces twenty or more. A further circuit in block 201 indicates when there is a lack of a vertical line on the present scan and the preceding scan. This is indicated by the symbol #V. Another circuit indicates that two short vertical lines have been found in a single scan. This is indicated by 2Vs and another circuit indicates that there is a short vertical line above but not below a cross-over in the lower portion of the scan, indicated by Vsu. All these signals are stored in shift registers, in block 204 one for each sort of indication. Included white signature components.-Circuits in block 202 give indications of the size of the white areas between two cross-overs on each of two successive scans. The white area of the scan may be short, medium or long, 2Xs, 2Xm and 2Xl. An indication is received from block 203 that three or more cross-overs were not present on either of the two successive scans. Where on the two scans two long spaces are found or a long space on one scan and a medium or a short space on the other, a signal 2Xl is produced. In the absence of a 2Xl signal a medium space signal 2Xm is produced when a medium space is found in both scans or when a medium and a short space is found. In the absence of either of these signals a 2Xs signal will be produced when a short space is found on both scans. None of these signals is produced if a signal is produced from block 203 to indicate that there are three or more cross-overs in either scan. Signals produced are stored in three ten-position shift registers in block 205. Single and triple cross-over signature components.-Circuits in block 203 receive information from block 202 and determine from it whether there is a single cross-over X, a triple cross-over 3X or no cross-over Z, and the signals produced are stored in three shift registers in block 206, each having ten positions. Stores.-The registers 204, 205 and 206 each have ten stages and are shifted on alternate scans through the character so that outputs from the blocks 201, 202, 203 and 209 can only be entered on alternate scans. The contents of the registers are shifted towards the end and entered into a number of register matrices 207 consisting of a plurality of And circuits which receive the information and give outputs representing a coincidence of certain signature components in certain positions. These outputs and the outputs from the stores are supplied to output circuits in block 208. Relative altitude signature components.-Circuits in block 209 receive information from block 200 and look for changes in the upper contour of a character from one scan to another. There may be a small upward slope giving a signal " D + s " or a large upward slope " D + l." Signals for like downward slopes are " D - s " and " D - l." Where the slopes are sustained for a predetermined number of scans signals " S + " or " S - " are produced and a level line gives a signal " So." These signals are fed on seven lines to the output circuits in block 208. Output circuits.-The group of circuits in block 208 are logical switching circuits, one for each character to be recognized. The outputs from each particular circuit are looked at continuously as they arrive and an output representing the character is provided immediately its identity is determined. Several alternative paths are provided in each logical circuit so that a character may be recognized if it is formed in one of several typewritten styles. Circuits. Block 200.-The circuits of some of the units represented in blocks will be described. The circuit in block 200 is shown in Fig. 2. The sampled video signals are supplied via a double inverter 210 to the right-hand side of trigger 211. Gate 212 receives the outputs from the inverter 210 and from the trigger 211. The trigger is turned on by a black signal at one sample time and if another black signal is produced by the next sample pulse gate 212 opens to pass a XX signal through a double inverter 216. The sampled video is also passed through an inverter 213 to gate 214 which also receives the sample pulses. Where no character area is sensed, gate 214 gives an output which passes through inverter 215 to turn off trigger 211 if it is on. A second negative indication causes gate 199 to open to give a OO signal via inverter 217. Gates 199 and 212 are connected through inverters 219, 218 to gate 220 so that when opposite indications are successively received, gate 220 passes a signal through inverter 221 to the XO or OX output terminal. Block 201.-The XX and XO + OX lines are connected to Or gate 222, Fig. 3, feeding a five-stage counter 223-227 operating in the usual way. Each stage is reset by a OO signal or by the scan sync + 2 pulse. Stages 225 and 227 are connected to gate 228 which accordingly passes an output signal to inverter 229 when a count of twenty is obtained, i.e. when a vertical line of ninetee