Patent GB-621760-A (GB)
Title: Improvements in or relating to navigating systems and apparatus therefor
IPC: G06G3/00
Filed: 1946-09-12
Abstract: 621,760. Radio-navigation. TAYLOR, J. A., NISBET, R. H., and SPERRY GYROSCOPE CO., Ltd. Sept. 12, 1946, No. 27443. [Classes 40 (vii)] [Also in Group XL (b)] A navigational system whose output comprises two physical quantities representing the values of two positional co-ordinates of a craft in a particular co-ordinate system is arranged to feed one of the quantities to a device arranged to develop a third quantity related to the device input according to a law relating the co-ordinate of points on a selected locus line and a differential device is actuated by the third quantity and the other of the first-mentioned quantities to give an output indicative of, and preferably a measure of, the difference between the actuating quantities. This output is an indication of the deviation of the craft from a desired course and may be used to control the flight of the craft to maintain the selected course line. The nature of the device operating according to the law relating the co-ordinates of points on the locus line may be simple or complex, but it is stated that the invention is especially applicable to a simple relationship such as when the co-ordinates are directly proportional. In hyperbolic (path difference) navigation systems, if the portion of the locus of interest is some distance from the hyperbolic foci the hyperbolic co-ordinate lines may be regarded as straight and parallel so that the direct proportional relation may be said to hold. Fig. 1 shows a navigational system receiver 10 feeding two outputs through interchanging switch 14 to phase-meter devices 15 and 16 whose shafts 17 and 34 take up angular positions corresponding to the co-ordinates of the receiver's position. Shaft 25 takes up a position corresponding to shaft 17 under the influence of a simple motor servo-mechanism, and is geared to disc 50. Disc 50 drives cylinder 54 through an arrangement of two balls 51, 52. The position of the balls is adjusted by manual control 58 so that the cylinder 54 takes up an angular position corresponding to the other co-ordinate of a point on the locus with a first co-ordinate corresponding to the setting of shaft 17. Arms 39 and 40, carried on insulating boss 41, driven by cylinder 54 and connected through slip-rings to lines 47 and 48 are arranged on either side of contact 44 connected to lead 49 and positioned by shaft 34. Relative movement of contacts 39 and 40 and 44. representing deviation of the receiver from the course line, causes the making of a circuit through either line 47 or 48, according to the sense of the deviation, and may be used to operate a steering control device. Switch 14 is inserted, as it is preferable that the quantity whose rate of change is greater be connected to operate the co-ordinate conversion device. In Fig. 2 (not shown), a cam and cam follower device is used in a system otherwise similar to that of Fig. 1 to perform the co-ordinate conversion. Such an arrangement may be non-linear and the cam may be replaced by another for a different course line. Fig. 3 (not shown) again shows a system very similar to Fig. 1, but shaft 34 is used to drive one input of a differential gear through a servo-mechanism and shaft 38 the other. The output of the differential is a rotation of a magnitude and sense corresponding to the deviation from the course line. In a more complex arrangement (Fig. 4), shaft 25 is used to drive a film strip 74, blackened over a portion 88 of its width according to the coordinate relationship law of the locus. This film passes before a slit 78 on which a beam of light is focused from lamp 79. Inside the box 76 is a photo-electric cell, Fig. 5 (not shown). A shutter 83 is moved to traverse the film by shaft 67 in accordance with meter 16, and its edge 85, when the receiver is on the course line, is normally co-incident with the edge of the blackened portion of the film so that only a small light flux reaches the photo-electric cell which in this condition is balanced in a bridge circuit. Any deviation from the course increases or decreases the light flux passing to the cell and produces a corresponding bridge circuit output.