Patent GB-804044-A (GB)
Title: Improvements in or relating to apparatus for estimating the probable paths of motionof objects
IPC: G06G7/78
Filed: 1955-02-23
Abstract: 804,044. Electric analog calculating systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. Feb. 23, 1955 [Feb. 24, 1954], No. 5505/55. Class 37. [Also in Group XX] Apparatus for estimating the probable path of motion of an object during a future time interval comprises an extrapolation device fed with signals representing the present conditions of motion of the body for calculating estimated positions at successive future instants and a display device which presents these future positions as an estimated future course. In the apparatus shown in Fig. 7 the extrapolation device 71 is fed with voltages representing the co-ordinates of the observed position of the object (U X0 , U Y0 ), obtained for example, by radar, the observed course and speed of the object (U #0 , U V0 ) and where appropriate, the acceleration along the course (U A0 ). The extrapolation device contains resolvers 715, 716, multipliers 713, 714, 718, 722, adding units 711, 712 and a squaring unit 723 and computes voltages Ux, U Y  representing the co-ordinates of a future position in accordance with equations derived in the Specification. The future position is indicated on the cathode-ray tube 70 and a display of extrapolated course is obtained by varying periodically the future instant of time, for which the computation is effected, by means of a sawtooth voltage generator 719 producing an output Uα. A device 721, fed by the voltage Uα, limits the display to a selected extrapolation interval by means of a brightness control voltage applied to the grid 703 of the cathode-ray tube. The display may also be extinguished for short distances along the display, corresponding to known time intervals, to provide a time scale. A motor-driven mechanical control may be provided to reduce the extrapolation interval so that the limit corresponds to a fixed future instant time, the display shortening as that instant is approached. If the supply of information is discontinuous a series of voltage impulses U i  is supplied, at instants when fresh information is received, to trigger a sawtooth generator 724 which produces a voltage U 1 , added, in the unit 720, to the voltage Uα fed to the limiting device 721, which results in the information being retained until the next fresh information is available. An alternative extrapolation device is described which takes account of accelerations of the object at right angles to its path. To predict paths of two objects appropriate voltages may be separately derived and by an electronic switch, displayed alternately on the cathoderay tube. Alternatively a double-beam cathoderay tube may be used, or separate tubes, the presentations of which are combined optically. A three-dimensional display may be obtained by using three displays representing the motions in three mutually perpendicular planes or, as a simplification, a two-dimensional display using, for example, a horizontal projection and a vertical projection through the present position. A mechanical presentation device may comprise a member 21, Fig. 22 movable in perpendicular co-ordinate directions over a plotting table and carrying a housing 29 rotatable to adjust the direction of movement indicated by the member 22. This consists of two juxtaposed flexible tubes with a central flexible wire. The amount of projection of the member may be varied by rollers 220 to represent the prediction interval and the curvature may be varied, to represent the predicted curvature of the course by applying different pressures to the two tubes. A three-dimensional display may be obtained by providing movement of the housing 29 in three co-ordinate directions and by providing the member 22 with four tubes so that a curvature in any direction may be produced by appropriate differential pressures. Another presentation device comprises an optical projector containing sliding shutters, with intersecting slits, which may be moved in two co-ordinate directions to project a spot of light, the position of which corresponds to the position of the intersection of the slits. The shutters are moved so that the spot of light moves rapidly and repetitively through successive future object positions.