Patent GB-1097998-A (GB)
Title: Electrical line following apparatus
IPC: G06F3/033
Filed: 1966-06-14
Abstract: 1,097,998. Digitising curves. INTERNATIONAL BUSINESS MACHINE CORPORATION. June 14, 1966 [June 30, 1965], No. 26470/66. Heading G4A. [Also in Division G1] A photoelectric line follower system is used to scan an image-bearing surface, the analog information from the detector being translated into digital signals, defining the image, which can be stored in a conventional generalpurpose digital computer. The digital information may be altered if desired, and reproduced later in its original or altered form. The line-follower system comprises a C.R.T. 15 operated as a flying spot scanner, following a photographic line image 13 on surface 11. A photomultiplier provided with a lens system produces an output whenever the scanning beam coincides with a part of the line 13. The general position of the beam on the CRT screen is controlled by X, Y coils 17. Predetermined scanning patterns for the beam effective over a limited area of the screen, are produced by X<SP>1</SP>, Y<SP>1</SP> coils 19. The type of scanning patterns used depends on the complexity of the line image to be followed. In the embodiment described, there are eight patterns, each being formed by five continuous sides of an octagon and being defined by a series of six end points given by X<SP>1</SP> and Y<SP>1</SP> co-ordinates (Figs. 2, 3, not shown). In operation, the scanning beam is first positioned manually or automatically (by a raster scan to locate the line) on the line 13 and the first pattern to be generated selected by programme control or by analysis of the starting area. The computer 21 issues a threebit binary code signal, representing one of the patterns, through register 23 to decoder 25. One of the eight lines to end point generator 27 is selected in accordance with the code. The generator 27 supplies in time sequence two, three-bit digital signals representative of the X<SP>1</SP> and Y<SP>1</SP> co-ordinates of the end points for the pattern chosen. Converters 29 convert these signals to analog signals for controlling coils 19. The beam is thus caused to follow six straight line strokes from endpoint to endpoint and define the pattern selected. However, the first stroke is simply to position the beam at the proper starting point and the beam intensity is therefore reduced during this time by blanking on line B. The photomultiplier detects when the pattern coincides with the line 13 and produces a pulse which is amplified at 37 and applied through gate 41 to register 39. By means of the clock 43 synchronized with the generator 27, the register determines which stroke (or strokes) coincided with the line and gates the signals accordingly into outputs E1, 1, 2, 4, and E2 corresponding to strokes 2 to 6. E 1  and E 2  provide for exceptions to the usual following of a line, since they denote the presence of an intersection of the line from either or both sides. The computer programme, may or may not permit exceptions i.e. in the latter case, intersections are disregarded, the line being followed through such intersection; in the former case the intersecting lines may be followed up at times decided by the programme. When it does, line 61 enables AND gates 59, so that exception bits on lines E1, E2 may be transmitted, after decoding by circuit 45, to the programme word address counter of the computer. If both bits are zero an output from decoder 45 enables AND gates 51, through OR gate 49, to gate the contents of the middle output positions of the register to the computer. These correspond respectively to decimal values 1, 2 and 4. If exceptions are not permitted by the programme, line 63 enables AND gates 51 regardless of the exception bit values. Thus, a number of different strike conditions eleven, in fact are possible for submitting to the computer which analyses the information and determines the next pattern to be generated (through register 23) and the position at which it will start (through D/A converter to coils 17). The digital information from each pattern is also stored to build up a total digital record of the image. Specification 1,078,545 describing circuits for the register 23, decoder 25 and generator 27, is referred to.