Patent GB-905847-A (GB)
Title: Apparatus for indicating the distance between a target and a projectile fired at the target from a firing point
Inventor: THORNTON WILLIAM EDGAR
IPC: F41G3/26
Filed: 1959-01-05
Abstract: 905,847. Automatic alignment-control systems. DEL MAR ENGINEERING LABORATORIES. Jan. 5, 1959, No. 349/59. Class 38 (4). [Also in Groups XX and XL (c)] The method of obtaining on a recording device such as cinematograph film a visual record of the relative positions of a target, and a projectile being fired thereat, as described in Specification 899,540, [see Groups XX and XL (c)], is modified by providing a pivoted optical system for controlling the direction of the optical path of the visual recording device, so that it may be maintained effectively trained on the object. This is of advantage when the device (i.e. a camera) is mounted in a rapidly moving aircraft. The camera and cathode-ray tube unit are as described in Specification 899,540, and are mounted in a fixed position on the aircraft. In the path of the optical axis is a pivotable beam-shifting optical system 18 which is slaved to the antenna 204 of the radar unit (Fig. 8). The antenna itself is kept tracked on the target by known self-correcting techniques, so that the optical system in effect keeps the camera always trained on the target. The optical system 18, Fig. 6 (and also Figs. 4 and 5, not shown), comprises a mirror 102 tiltable about an axis 104, and a prism 112 rotatable about an axis 114. The incident beam of light passes through the prism, and is reflected from the tiltable mirror 102 on to a fixed mirror 100. Mirror 100 reflects the beam out at right-angles to the plane of the paper, and into the objective of the camera, which is not seen in Fig. 6, but is assumed to be pointing towards the plane of the paper. Mirror 100 and prism 112 are controlled by servomotors 108 and 118 respectively, to vary the elevational angle of the one and the angular azimuth range of the other. The antenna 204 itself is mounted on a pair of mutually perpendicular axes, so that its azimuth and elevational angles can be controlled. The reflected radar pulses from the target arc caused to control the adjustment of azimuth and elevation of the antenna so as to keep it tracked on the target, within certain limits of manoeuvre. The antenna has an elevation resolver which develops an output voltage which is a function of the elevation. This resolver is coupled, via an adder, to the elevation resolver of the elevation mirror motor 108 (Fig. 7, not shown). When the output voltage of the two resolvers is not identical, the error is amplified and used to energize the motor 108 so that the error is reduced. The mirror 102 is thus given an elevation which corresponds to the elevation of the antenna. In like manner the azimuth prism 112 is controlled to correspond with the azimuth of the antenna, so that the optical system is thus slaved to the antenna. As explained in Specification 899,540, the radar reflections from the target give a signal on the cathode-ray tube which is reproduced on the film frame as an indicator mark Y, and the reflection from the missile gives a mark X. When these coincide, as in Fig. 10, the target and missile are at equal distances from the firing point. Also included is a range fiducial generator which produces a series of pulses which show on the cathode-ray tube screen, and hence on the film frame, as indicator marks Z. In Fig. 10 these pulses correspond to 0.2 mile of radar range. Every fifth pulse is emphasized, so that these latter pulses represent one-mile ranges. From the component distances a and e as shown on the frame of Fig. 10, it is possible to calculate the actual " miss " distance between projectile and target.