Patent GB-1289304-A (GB)
IPC: G09B9/32
Filed: 1968-11-21
Abstract: 1289304 Visual simulation apparatus REDIFON Ltd 17 Nov 1969 [21 Nov 1968] 55247/68 Heading B7W [Also in Divisions F4 G2 and H4] A visual simulation apparatus, shown in Fig. 2, comprises a TV camera 20 having an associated lens system 21 for viewing a model 22 of an airport and surrounding terrain, means 23, 24 for providing relative movement of camera and model, a lighting unit 25 adapted to illuminate a strip of the surface of the model at a distance from the lens system which is varied repetitively, and an electromechanical actuator 27 for varying the focusing characteristics of the lens system co-operatively with the distance of the illuminated strip from the lens system. The scene is illuminated in such a way that only those parts which are in good optical focus are illuminated at any one time, and synchronization with the frame scanning action of the camera gives rise to a continuously and wholly focused picture effect, with correct focus being provided over the whole area viewed by the optical system at the instant of viewing. Movement of the controls by a trainee pilot 30 in a simulated flight deck 31 effects by means of a computer corresponding movement of the above apparatus, resulting in a projection on a suitably placed screen 28. Synchronizing pulses for the TV system, Fig. 3, are provided by a photocell 63 operated by light which is interrupted by a disc 65, provided with alternate transparent and opaque areas, which is rotated by a synchronous A.C. motor 67; a gear wheel arrangement connects disc 65 and motor 67 to synchrogenerator units 72, 73. Generator 72 is connected to a motor unit 76 via a differential unit 77 coupled to servo 55, a mirror drum 78 (Fig. 4, not shown) mounted on the shaft of motor 76 is thereby rotated at a speed related to the TV system frame frequency and modified by variations in simulated pitch angle. Generator 73 is connected via motor unit 79 to a variable area stop 80 (Fig. 6, not shown) whose aperture is varied synchronously with the TV frame frequency so that it is reduced as scanning in each frame proceeds towards the foreground of each scene, so that picture brightness is maintained at the desired level during each scanning period. The TV camera 20 has an angularly movable front portion 56, Figs. 3, 5 which provides simulated variations in azimuth. Simulated rolling and pitching effects are provided by means of a dove prism 50, and a reflecting prism 53. The portion 56 includes a lens system 58, 59 comprising a fixed lens 59 of short focal length and a Petzval or double Gauss arrangement 58 whose position is varied cyclically to keep the lens system in good focus for that portion of the image which embraces each scanning line as scanning proceeds from background to foreground in each frame of the display. The arrangement 58 is vibrated by a moving coil actuator 27, Fig. 5, comprising an annular magnet 121 with polepieces 122, 123 and a cylindrical coil 125, attached to a rigid flange 127, and supported by an elastic member 128. Vibrations in unwanted directions are suppressed by a conical extension 130 supported by a second elastic member 131. The coil 125 is fed via terminals 136, 136<SP>1</SP> with current from an amplifier 87, the amplitude of which varies cyclically with the frame repetition frequency. The gain of the amplifier is varied by the D.C. voltage, provided from the wiper of a potentiometer 81, which controls the amplitude of the coil current so that it has a desired maximum value according to the height of the camera above the model, in order that good optical focus be maintained on an area of the model corresponding to. that part of the image of the model which is being scanned, as the height of the point of observation of the model changes. The gain control of the amplifier by the potentiometer also provides compensation in the video signal 84 for increase in model brightness at short ranges. The lighting unit 25 comprises a batten 88 supporting a row of compact source mercury vapour or xenon arc lamps 89, each provided with a front reflector 90 and a back reflector 91 having a dichroic coating. Light from the lamps is thrown on to elongated concave mirrors on parts 78<SP>1</SP>, 78<SP>11</SP> (Fig. 4, not shown) of the mirror drum 78 so that an illuminated strip is produced on the model by the reflected light.