Patent GB-1489758-A (GB)
Title: Visual display apparatus
IPC: G09B9/02
Filed: 1974-10-16
Abstract: 1489758 Flight simulators REDIFON Ltd 10 Oct 1975 [16 Oct 1974] 44837/74 Heading B7W [Also in Division G2] Visual display apparatus, for use in, e.g., an aircraft simulator for training pilots, includes image generating apparatus and apparatus for projecting the generated image. The projection apparatus includes a screen (3) (Fig. 1, not shown), of highly retroflective material at least partly surrounding the pilot, a helmet (1) or the like worn by the pilot, a projector for projecting the image as a light beam, movable optical means defining a movable optical path for the light beam between the projector and the helmet (1), a reflector 45 on the helmet for reflecting the light beam forwardly on to screen (3) from a position close to the pilot's eyes, means for varying the generated image in accordance with the simulated movement and attitude of the aircraft, means for sensing movement in rotation and inclination of the helmet (1) and for providing signals corresponding thereto and means responsive to the control signals for varying the generated image correspondingly to the orientation of the helmet (1). Optical System.-As shown in Fig. 2, a collimated image-forming light beam from a TV projector 4 is passed to a Dove prism 38, which is rotated by a servomotor 41 to compensate for head movements. The beam passes to an input lens 21, is reflected by a prism 24 and forms a real image at 22. The beam passes through pivotally jointed light-tight tubes 23, 25, which are mechanically linked to a reflecting prism 24, which is moved through half the pivoting angle. Tube 25 has a rotary joint 32 and the beam passes along it to a prism 32<SP>1</SP>, similar to prism 32 and similarly mounted at another pivoting joint for a tube 33, having a rotating joint 36. The beam reflected by prism 32 is focused by a relay objective 34 at a plane 35 after reflection by a prism 37 mounted as prisms 24, 32<SP>1</SP> in a rotating joint. The beam passes through an eyepiece 42, emerging with a diverging angle of about 40 degrees. This emergent beam falls on a beam splitter 431 and is partly reflected and partly transmitted, the parts being directed to a beamsplitter 45 through which the pilot views the screen 3, on which the beams reflected at 45 are focused. The beams pass through sheets 46, 49 of material passing light polarized in planes mutually at right-angles to form overlapping images on screen 3. Light from the screen passes through these sheets to the pilot's eyes respectively, so that he sees one image with one eye and the other image with the other eye. The flexible optical structure is counterbalanced by a spring 50 and is arranged to fold back when the pilot enters his seat. Simulation.-Potentiometers 51-56 mounted at the rotating and pivoting joints provide electrical signals proportional to the rotation of the joints. These signals are used to compute the position of the pilot's head, so that the viewprojected is always appropriate to the head position. A computer (101), Fig. 4, not shown, is programmed with simulated flight and aircraft data, and controls an optical probe (104) with servo-controlled optical elements to alter the direction in which a terrain model (102) is viewed through the probe by a TV camera (103). The signals from the optical link (5) are combined by a device (108) which provides signals added to computer signals applied to probe (104) and a signal (112) for the motor 41 (Fig. 2) which rotates the Dove prism 38. Provision is made for correcting the image electronically when the pilot's head movements are too fast for the servos to follow. Modification.-The effort required by the pilot may be eliminated by providing servo-assisted movements of the mechanical parts. The mechanical parts may be eliminated, the beams being large enough to fall on beam splitter 45 for a restricted range of head movements and the head movements being detected by reflection of infra-red beams from mirrors mounted on the helmet. The image beam may be projected along a path fixed relative to the helmet, the projector being carried on an arcuate gantry. The projector may be a cathode-ray tube projector, an oil film projector, a shadow-mask cathode-ray tube projector, or a laser beam deflector. Deflection may be by mirrors. The TV camera may be replaced by a laser beam generator and scanner, or the image may be computer.