Patent GB-769530-A (GB)
Title: Improvements in or relating to automatic computing apparatus
IPC: G06J1/00
Filed: 1954-06-02
Abstract: 769,530. Electric analogue calculating systems. SCHLUMBERGER WELL SURVEYING CORPORATION. June 2, 1954 [June 2, 1953], No. 16336/54. Class 37. [Also in Group XL(b)] A computer for deriving a particular function of two independent variables comprises a screen inscribed with a family of curves of the function depicting successive values of a dependent variable plotted in first and second co-ordinate directions in terms of two respective independent variables, sources of radiant energy projected upon the screen in beams which are deflectible with respect thereto in the first coordinate direction to scan the inscribed family of curves and effect modulation of the radiant energy thereby and in the second co-ordinate direction in response to instantaneous values of a first independent variable, timing means responsive to instantaneous values of a second independent variable to determine the time interval of scanning by the beam, and sensitive means receiving and utilizing the modulated radiant energy to derive electrical signals representing the modulation during the scanning interval ; the curves being disposed on the screen in two groups respectively defining two series of successive values of the dependent variable, which groups are scanned successively in the first direction over an interval determined by the second independent variable while the screen and scanning beams are positioned in the second direction in accordance with the instantaneous value of the first independent variable, and the radiant energy-sensitive means operate to separate the modulation representative electrical signal into two separate components each representing the beam modulation due to a particular curve group, which energize means for integrating the two components and re-combining them subtractively so that the combination measured by an indicating instrument represents the required dependent variable for the prevailing values of the independent variables. Fig. 1 shows a computing apparatus of the kind described in Specification 745,403, in which an endless transparent belt 10 is rotated at constant speed by motor 14 over sprockets 12, 13 engaging holes in the belt. The latter is inscribed with alternating groups 15, 16 of opaque curves respectively corresponding to portions 17, 18 of the family of curves shown in Fig. 2 representing the parabolic function for different values of Z, where h is a constant; plotted against mutually perpendicular ordinates and abscissµ y and x about axis 19, which is the locus of the points of tangency of ordinal lines to the curves, the groups being distinguished by plotting in opposite senses as shown. Groups 15 are located in the lower half of each frame 20, groups 16 are located in the upper half of each frame 21, and the movement of the belt is parallel to. the ordinates, while a mirror galvanometer 22 energized by the analogue voltage of independent variable x traverses a light beam 23 across the belt in a direction parallel to the abscissµ. Aligned with each group of curves 15, 16 in corresponding frames 20, 21 is a triangular opaque region 28 inscribed on the belt, across which a mirror galvanometer 27 energized by the analogue voltage of independent variable y traverses a light beam 26 in an abscissal direction collinear with the traverse of beam 23, and the emergent light is received by a lineal first photo-cell 24 disposed perpendicularly to the belt movement, whose output comprises trains of pulses whose number and positional spacing in time corresponds to the intersections of the curves and the beam 23 in response to the instantaneous values of the variable x, combined with a sequence of rectangular pulses of durations dependent on the instantaneous values of the variable y. The photo-cell output is applied to the inputs of two electronic switches 29, 30, of which 29 is operative to transmit pulses only during modulation of beam 23 by curve groups 15, and 30 is operative to transmit pulses only during modulation by curve groups 16, in response to synchronizing signals derived from second photo-cell 43 illuminated by a static light beam from source 41 modulated by a narrow border of alternately opaque and transparent elements 39, 40 respectively coincidental with curve groups 15, 16, which signals are amplified and connected to actuate switch 29 directly and switch 30 through a phase inverter 46. The switch outputs are respectively supplied to amplitude-selective amplifiers 31, 32 energizing counting integrators 33, 34 whose continuously variable voltage outputs are additively combined across resistances 36, 37 to a signal analogous to the result which is measured by a recording voltmeter 38. In the photo-cell output (Fig. 3A) the alternate trains of pulses 50, 54 derived from the intersections of curve groups 15, 16 with beam 23 are partially superimposed on rectangular pulses 51, 55 derived from the intersections of beam 26 and corresponding opaque regions 28, while switches 29, 30 are alternately operated by pulses 52, 53 (Fig. 3, B, C) in the output of photo-cell 43. The trains of superimposed pulses having the greater amplitude are passed by amplifiers 31, 32 for counting by the respective integrators 33, 34, while the trains of non-superimposed pulses having the lesser amplitude are excluded, and the integrators alternately produce voltages proportional to the count of each respective train of superimposed voltages in accordance with the instantaneous prevailing values of x, y, so that the subtractive combination of such continuously variable voltages for measurement by meter 38 represents the required dependent variable z. The inscribed curve groups may be derived from a curve family representing a circular function z = [(x - a)<SP>2</SP> - (y - b)<SP>2</SP>], wherein a and b are constant, divided into groups by the locus of points of contact of ordinal tangents (Fig. 4, not shown), or from a curve family (Fig. 5) representing an arbitrary empirical function y = f(x, y) wherein the loci 63, 64, 65 of points of contact of ordinal tangents divide the family into four groups 66, 67, 68, 69 of which 66, 68 are inscribed vertically and adjacently in each successive frame 20 of the belt and groups 67, 69 are similarly inscribed in each successive frame 21. The inscribed belt of Fig. 1 may carry (Fig. 6, not shown) a second narrow border of alternately transparent and opaque elements distributed complementarily to those of the first border and modulating the illumination of a third photo-cell; the first combined curvemodulated output being applied in parallel to amplitude selective amplifiers which are inoperative in the absence of a pulse from a respective photo-cell illuminated by a light beam modulated by the appropriate synchronizing border; the amplifier outputs energizing integrators operating as in Fig. 1 in accordance with the pulse modulation imposed by the correct curve group. Synchronization may also be effected by pulses generated mechanically by the band driving motor. In a modification (Fig. 7) each successive frame 80 of a transparent belt 10b is divided laterally into sections 81, 82, 83 respectively inscribed with curve groups 15b, 16b derived as above in alignment with a triangular opaque region 28b. Beams of light 86, 87 are traversed laterally of the belt by mirror galvanometers 84, 85 energized by the analogue voltage of variable x to intersect the respective curve groups, and beam 26b is traversed by mirror galvanometer 27b to intersect the boundaries of region 28b. The emergent light beams are respectively received by lineal photo-cells 88, 89, 90, of which 88, 89 supply pulse trains dependent on the instantaneous value of x to amplitude selective amplifiers 31b, 32b energizing counting integrators 33b, 34b, while 90 supplies switching pulses dependent in length on the instantaneous value of y in response to which the amplifiers are operative while they are inoperative in the absence of such pulses. The integrators accordingly receive output pulse trains derived from curve groups 15b, 16b corresponding to the instantaneous values of x and y, and the resultant continuous voltages are combined in resistance network 35b to derive the analogue voltage of dependent variable z, as in the apparatus of Fig. 1, which is measured by voltmeter 38b. In a modification (Fig. 8, not shown) of the apparatus of Fig. 7, a single mirror galvanometer energized by the analogue voltage of variable x traverses a beam of white light over a belt in which the two curve groups are respectively inscribed as red and green transparent lines in an opaque field and the emergent light is separated by a prism into red and green beams modulated by the respective curve groups, incident upon the appropriate photocells through red and green filters. Alternatively the two inscribed curve group transparencies may be distinguished by respectively polarizing light horizontally and vertically while the coloured filters are similarly replaced by horizontally and vertically polarizing screens. The curve groups may be superimposed. Variations of motor speed may be corrected in all the above forms of the apparatus by inscribing on the belt a border of equal alternate opaque and transparent markings modulating a light beam incident on a further photo-cell, whose output is integrated and applied to vary the gain of amplifiers disposed between the combining resistance network and the computing integrators. A further modification (Fig. 9) comprises a computer of the kind described in Specification 769,531, wherein the fluorescent surfaces of cathode-ray tubes 100, 101 are covered by transparent screens 113, 115 respectively inscribed with curve groups 114, 116 derived from a complete family of curves in the manner described above. Voltages analogous to the instantaneous values of the independent variables x, y ar