Patent GB-1276923-A (GB)
Title: Improvements in or relating to visual simulation apparatus
Inventor: SHELLEY MEVILLE LESLIE
IPC: G09B9/32
Filed: 1969-02-13
Abstract: 1276923 Visual simulation apparatus REDIFON Ltd 5 Feb 1970 [13 Feb 1969] 7972/69 Heading B7W [Also in Divisions G2 and H4] Visual simulation apparatus for providing a visual display of a scene such as would be seen by the crew of a vehicle, for example an aircraft, comprises a model 22 representing an area of the surface over which the vehicle travels, a television camera 20 having a camera tube 44 and an associated lens system for viewing at least a portion of the model, means for providing relative movement of the camera and the model in accordance with the assumed position of the vehicle, a moving slit located in the light path of the lens system and adapted to traverse the field of view provided by the lens system, the lengthwise axis of the slit lying substantially parallel to the scanning lines of the camera tube, and means for varying the focusing characteristics of the lens system co-operatively with the position of the slit, so as to maintain focus on that part of the field of view presented by the slit and to provide from the television camera a picture which is in good focus over its whole area. When the assumed altitude of the aircraft is low the close proximity of the camera to the model creates difficulties in obtaining good focus over the whole area viewed. It is stated that, if a point N on part of the model 11 (Fig. 1) is viewed using a lens 10 a distance H from the model and with its optical axis at an angle #, corresponding to the pitch angle, to the plane of the model, then for optimum focus the image N<SP>1</SP> of the point N and the image H<SP>1</SP> of the horizon H are such that the line N<SP>1</SP>H<SP>1</SP> and the plane of the model 11 intersect at O in the plane of the lens, and that a and S (as defined in Fig. 1) are given by and where f is the focal length of the lens 10. If the image N<SP>1</SP>H<SP>1</SP> is scanned by a further lens (12) which produces from each point (P) in turn an image at infinity, then the lateral motion x of the lens (12) needed for this scanning is given by at any instant t, where t f  is the time taken for a full scan and #y is the maximum distance off the optical axis which is scanned. Thus the lens (12) must be given a periodic motion corresponding to (#yt/t f ) tan a and a non-periodic motion corresponding to S. The former may be simulated by interposing between the image N<SP>1</SP>H<SP>1</SP> and the lens an optical element of variable thickness. Motion of the camera 20 in relation to the model 22 is controlled by lead screw servo-type mechanisms 40 and 41, rolling is simulated by motion of part of the camera effected by servo mechanism 55, pitching motion by movement of prism 51 controlled by servo mechanism 53 and yawing by movement of a Dore prism 48 controlled by servo mechanism 50. All these servo systems are controlled by the simulator computer (35). The image produced by the prism 51 is observed by lens 59 and gives rise to an inclined image I G . This image is scanned by lens 60 as previously described, prisms 63 and 64 being moved by a servo system 65 to constitute the optical element of variable thickness. The displacement of the lens 60 corresponding to S is produced by a servo system 67, and the lens 60 produces an image at infinity which is focused by a lens 61 on to the plane of a revolving disc 68 having a plurality of equispaced radial slots, the disc and the systems 65 and 67 being aligned so that each slot passes only that part of the image which is in focus. They may also be synchronized with the scanning circuits of the television system. For instance, the disc 68 may have alternate opaque and transparent areas near its periphery which, in conjunction with a light source and photo-cell amplifier, produce synchronizing pulses for controlling the frame and line scanning circuits. Alternatively the scanning circuits may be operated from the same power supply as the motor 70 driving the disc, there being a mechanical differential between the motor and the disc to enable the phase relationships between the moving slots in the disc and the driving pulses of the scanning circuits to be adjusted. The image passed by the slots is transversed by the Dore prism 48 and is imaged by a lens 62 on to the surface of the camera tube 44. The mechanism 65 for moving the prisms 63 and 64 comprises (Fig. 6) a motor 80 driving, via gearing 81, shafts 82 and 83 connected to camshafts 84 and 85 by means of muff-type couplings 86 and 87 which allow axial movement of the cam-shafts. The cam-shafts carry three-dimensional cams 93 and 97 contoured so as to provide a gradual rise and rapid fall to cam follower rods 98 and 99, which move rocker arms 104 and 105 on which the prisms 63 and 64 are mounted. Some deviation from ideal sawtooth motion is permissible in consequence of the depth of focus of the lens 60. The axial position of the cams determines the amplitude of the motion of the prisms, and this is controlled by a yoke 100 connecting the cam-shafts and having a nut 101 engaging a screw 102 which is the output member of a servomechanism 103, so that axial movement of the cam-shafts proportional to tan a is produced. The servomechanism 103 comprises a summing amplifier 111 which receives signals -H and - sin # via resistors such that an output (H+f sin 0) is produced, and this is fed to the winding of a potentiometer 114 whose slide is carried by a shaft 116 which also carries the screwshaft 102 and which is driven, via reduction gearing 113, by a motor 112. The angular position of the shaft corresponds to tan a, so that the output of the potentiometer 114 corresponds to (H+f sin #) tan a, and this is compared by servo amplifier 130 with a signal -f cos #, so that the motor 112, which receives current from the amplifier 130 comes to rest when f cos # = (H+f sin #) tan α. The shaft 116 also carries the slide of a further potentiometer 115 whose winding receives a signal -tan 0, so that a signal -f tan # tan α is fed to a similar servosystem (Fig. 8, not shown) controlling the displacement of the lens 60.