Patent GB-707212-A (GB)
Title: Converting mechanical motion or position into pulse sequence
IPC: H03M1/00
Filed: 1948-01-15
Abstract: 707,212. Calculating apparatus. COALES, J. F., HILL, N. D., HERSOM, S. E., and BUCKING- HAM, J. Jan. 17, 1949 [Jan. 15, 1948], No. 1267/48. Class 106 (1). [Also in Group XXXVIII] The position, or a function of the position, of a carrier relative to a datum position, is signalled by digital electric pulses derived by point-bypoint scanning, at the datum position, of markings on the carrier which are arranged in columns characteristic of the various positions to be signalled, in a predetermined system of enumeration e.g. binary or ternary. The data transmitted may represent the instantaneous position of a movable member or the value of a function, e.g. a trigonometrical function of an angular displacement which may be fed to a computor. Photoelectric scanning is used for the various embodiments described but according to the Provisional Specification other scanning systems may be used. Transmitting angular position in the binary system.-For transmitting the angular position of a shaft, an opaque disc ME, Figs. 11, 12, rigid with the shaft bears a pattern of transparent portion m1 representative of a predetermined number of angular positions of the shaft in the binary system. The disc is scanned radially by a tight beam derived from the screen of a cathode ray tube CRT, which actuates the photocell PC to produce a pulse train corresponding to each radial position scanned. The photocell output is amplified at PCA and controls a gate circuit DG which passes, from a clock pulse train generator PTG to the output D, only those pulses of the uniform train generated coincident in time with those of the photocell output. The pulse time generator also controls the CRT time base TB. Carrier marking details.-Corrector circuits, Fig. 1, shows a manner of forming a binary pattern on an opaque carrier strip ME, the 15 columns c of markings m1 representing the linear displacement of the columns in question from a datum X-X, negative displacements to the left, being distinguished by an additional transparent marking ms. The negative displacements may alternatively be represented as complements of a number, Fig. 1a (not shown), particularly for use in calculating machines. Markings m1, representing the same digit value, in adjacent columns and, or, rows may be joined to form single continuous markings, Figs. 2, 3, 4 (not shown). To reduce or eliminate errors arising during scanning, e.g. as a result of movement of the carrier, both the digit 1 markings m1 and the digit 0 " markings " m0 (indicated by the absence of a mark) have subsidiary control markings a, b, Fig. 5, at diagonally opposite corners, the corresponding pulses produced in the photocell output being used to effect a correcting lateral shift of the scanning beam of the CRT as shown in Fig. 14. The photocell output is amplified at PCA and in this digit gate DG, gate pulses received from the pulse train generator PTG in accordance with the digit markings m1, Fig. 5. The photocell output is also fed to left and right digit gates LDG, RDG, which, dependent on whether a left or right hand auxiliary marking a or b is scanned allows passage of a corrective pulse from PTG to effect the corrective shift of half a column width to the scanning beam. The correction may be effected alternatively, by providing the subsidiary markings in a row of "initiator" markings scanned just prior to the binary pattern, Figs. 7, 8 (not shown), and further timing markings may be provided, Fig. 9 (not shown) for correcting the starting instant of a scan, Fig. 13 (not shown), averaged over a number of scans, and for correcting the scanning speed, again averaged over a number of scans, respectively Fig. 13 (not shown). In other arrangements, Figs. 15, 16 (not shown) transmission of an incorrect digit is prevented by repeated transmission of the last correctly received digit or by suppression of transmission. Computing arrangements, addition, Fig. 17.- To provide a digital output D corresponding to a function of the sum of two independent variables the rotary disc ME, Fig. 17, carries a pattern corresponding to successive values of a function of one variable say f (x) and is scanned radially as in Figs. 11, 12. In the absence of any input at 8 the pulse output D from the digit gate DG is f (x) in digital form. If now an analogue voltage y is applied at 8 to produce lateral shift of the CRT beam the output D will by f (x+y). Correcting means as above mentioned may be used. Ternary system.-This system may be used by utilizing transparent reflecting and opaque portions of a strip for the three different digital signals, Fig. 18 (not shown).