Character recognition equipment

摘要

871,162. Automatic character recognition. STANDARD TELEPHONES & CABLES Ltd. July 11, 1958 [July 17, 1957], No. 22390/58.' Class 106 (1). In apparatus for reading legible characters, they are first sensed to produce signals indicating blackened areas and these signals are stored in a two-dimensional shift-register as shown in Fig. 1, the pattern of stored signals being displaceable as a whole vertically and horizontally. A small group of the storage elements 21 is shown in Fig. 2, there being four parallel lines between adjacent elements to transmit either " black " or " white " data in either direction and four shift lines are connected in common to all elements to shift the signals upwards (+y), downwards ( - y), to the left ( - x) or to the right (+x). The elements 21 may be any bistable units; as described, they are transistor flip-flop circuits. First method of recognition.-In one embodiment the characters are recognized by coincidence circuits, one for each character connected to the " black " and " white " outputs of the storage elements to correspond to an ideal pattern for that character. A few such circuits are shown in Fig. 4, connections being made from appropriate outputs of certain storage elements 21 through resistors R to transistors T1. A bias voltage U1 is applied to the emitter of each transistor and it conducts only when the signals from the storage elements overcome this bias. An output is then produced on the line Z1-Z3 corresponding to the character recognized. Defective characters.--Since the character may be imperfect in shape or badly printed, an ideal pattern may not be stored in the elements 21 and the transistor bias is accordingly reduced to allow them to respond to fewer than the ideal number of input signals. This may be done as shown in Fig. 4 by providing further transistors T2, T3, T4 for each coincidence circuit having successively reduced bias voltages U2, U3, U4 so that tests are made simultaneouslv for the ideal pattern and for approximations to it. Misalignment.-To compensate for lack of perfect alignment of the character in the sensing field the pattern as a whole is displaced in a spiral or similar path, Fig. 5, so that at one point it will coincide with the position chosen for the ideal pattern in making coincidence connections. For this purpose a counting chain C1, Fig. 6, supplied with pulses from a generator 22, has its stages connected to the shift lines to produce shifts in the order shown. The first part D causes each point of the pattern to trace the path D and the second path causes it to retrace along path E. The central and end stages V and R supply a second counter C2 which may be used progressively to reduce the bias voltage on the coincidence transistors so that in successive movements along the spiral path the apparatus looks for progressively worsening approximations to the ideal pattern. When an output is given the process is terminated and the counters reset. In the case of simultaneous tests for approximations, the spiral is only traversed once. Second recognition method.-In the form shown in Fig. 7 an array of storage devices is provided which is twice as large as in the previous form, a central line of elements Fl, Fm, and Fr dividing the upper and lower halves. The character signals are first entered in the lower half and control signals displace the pattern vertically until it touches the central line of elements, Fig. 9 (b). The pattern is then moved under the control of shift pulses derived by a gating circuit using output signals from elements Fl, Fm and Fr, the movement being such that each portion of the pattern moves in turn through the middle element Fm, Figs. 9 (c)-9 (l). This process in effect detects the right-hand edge of the pattern and the number of shifts to left and to right are recorded in two counters. The pattern is then displaced downwardly to the initial position, the left-hand edge being detected and the corresponding left and right shifts are again entered in two counters. The character is identified by gating together appropriate stages of the four counters.