Patent GB-219082-A (GB)
Title: Improvements in or relating to the control of cameras and optical instruments used in aircraft
IPC: G03B15/00
Filed: 1923-04-17
Abstract: 219,082. Henderson, Sir J. B. April 17, 1923. Angle-measuring instruments. - An instrument such as an aircraft camera is provided with external means for eliminating from its field of view the effects of substantially rectilinear relative movements between the instrument and an object in the field of view. The figures show a camera provided with such means in addition to means as described in Specification 223,610, [Class 97 (iii), Thermometers &c.]. for eliminating the effects of relative angular movements. The last-mentioned means comprise a gyroscope 1, with a vertical axis, pivoted on an axis 2 in a ring 4 which is mounted on trunnions 5, 6 in two sides of a sqrare frame 7. The other sides of the frame 7 are extended to form arms 8, 9 carrying trunnions 10 by which they are supported in brackets 12. The hollow trunnion 5 contains a pin 15, Fig. 3, having at its inner end a small fork 16 and at its outer end a fork 17 in which is mounted on horizontal pivots 20 a reflector 18 consisting of a right-angled prism with a roof prism on its hypotenuse. The frame 7 and pin 15 carry arms 23, 24 respectively having at their upper ends flat surfaces 25, 26 inclined equally in opposite directions to the vertical plane. Between these faces is a double roller 27 carried bv an arm 28 secured to a pin 22 mounted within the pin 15. The movements of the frame 7 around the axis 5, 6 are thus transmitted to the reflector 18. Mounted on a pivot 31 in the fork 16 is an arm 30 extending in a vertical plane over the gyro-casing and having at its outer end a roller 32 resting on a platform 34 secured to the casing. The arm 30 is also provided with a downward extension 35 connected by a rod and fork 37 to pivots 36 on the reflector. The pivots 31, 33 are equi-distant from the axis 2 so that when the frame 7 moves around the axis 2 the reflector is moved through half the angle around the pivots 20. To eliminate the orientation of the image due to banking and yawing, the back of the camera carrying the shutter 42 and plate holder 42' is arranged to be rotated around the axis of collimation by a differential gear 45 actuated by repeater motors 46, 47. The motor 46 is actuated bv a transmitter 48 on the shaft of a motor 49 which is arranged to follow the rolling movements of the frame 7, and the motor 47 is similarly actuated from a gyro-compass &c. in accordance with the azimuth movements of the mounting. The rotation of the shutter is communicated by bevel-gears 63, 64 to the ruled view-finder 60. The relative linear movements to be compensated are (1) drift, and (2) movement in the longitudinal direction of the aircraft. To compensate for drift the whole apparatus is rotated around a vertical axis 65 until the movements of the image seen in the view-finder are parallel to the lines 67, and then clamped by a nut 68. A pointer 69 may be provided to indicate the angle of drift. To compensate for longitudinal movements the frame 7 is arranged to be. rocked around the axis 10. A motor 70 drives a square shaft 74 through reduction gearing 71 which is adjusted by two pointers 72, 73, set according to altitude and ground speed. On the shaft 74 is a sleeve 75 which is cylindrical at one end and cam-shaped at the other, the two curves blending into each other along the sleeve. The sleeve acts on a roller 80 to rock the frame 7 about the axis 10, and it can be adjusted along the shaft 74 by a lever 76. The rocking movement thus imparted to the reflector produces periods of immobility or very slow movement of the image separated by periods of rapid movement in the opposite direction.