Patent GB-877413-A (GB)
Title: Improvements in or relating to the production of records of true paths of motion from instantaneous plan-position pictures supplied by radar equipment, mounted on a vehicle or vessel
IPC: G01S1/02
Filed: 1957-11-18
Abstract: 877,413. Radar. ATLAS-WERKE A.G. Nov. 18, 1957 [Nov. 29, 1956], No. 35863/57. Class 40(7) [Also in Groups XIX and XX] Relates to means associated with a ship-borne pulse radar having a Plan Position Indicator (P.P.I.) cathode-ray tube display for recording the true motion tracks of the ship and of other objects in its vicinity such that the recorded images of stationary objects are stationary relative to the record sheet. In producing such a record the record sheet may be orientated so that a vector on the record sheet which corresponds to either the instantaneous heading of the ship or to a predetermined geographical direction, e.g. north, remains parallel to a reference axis fixed with respect to the casing of the display, the corresponding record presentations being defined as course-oriented or north-oriented respectively; the P.P.I. display from which such record presentation is derived must be orientated in a corresponding manner. When the record sheet is in a vertical plane the reference axis is usually vertically upward and is denoted in Figs. 2 and 4 by the reference K<SP>1</SP>. According to the present invention a record sheet is mounted over the P.P.I. display and is automatically displaced in accordance with movement of the ship in a direction opposite to that on the P.P.I. display corresponding to the instantaneous heading of the ship, the displacement means being such as to allow the insertion of a second record sheet when an edge of the first sheet approaches the edge of the display area. Preferably one side of each sheet is coated with an adhesive, e.g. wax, so that the overlapping portions of the two sheets may be attached to each other by pressure. In order to produce a course-oriented record presentation the record sheet is also automatically orientated in reverse correspondence to changes in the ship's heading. The recording may be effected by manual plotting or by photographic or photo-electric printing means; for manual plotting the record sheet is transparent or translucent and a half-silvered mirror 2, Fig. 1, is interposed between the screen of the display tube 1 and the record sheet 4 to reduce parallax. All three of the embodiments described may be used to produce a course-oriented or north-oriented record presentation. Figs. 1 and 2. To produce a course-oriented record presentation the record sheet 4 is pressed down on a glass plate 3 by two friction wheels 6, 7 which are driven in the same direction in accordance with the speed of the craft and in opposite directions in accordance with changes in its heading by means of servo motors 12, 13 and differential gears 11 so that the record sheet 4 is displaced in a direction opposite to that of the reference axis K<SP>1</SP>. To produce a north-oriented record presentation the common axis of the shafts of the wheels 6 and 7 is rotated about the centre of the display in reverse correspondence to changes in the ship's heading. Figs. 3-5. The record sheet 4 is pressed upwards against an annular ring 19 by four friction wheels 18 each of which is pivotly mounted in a yoke 30 supported by a rotatable annular ring 24, the rings 19 and 24 being concentric with the screen of the cathode-ray tube 1. When a northoriented record presentation is being produced a change in the ship's heading causes an equal and opposite rotation of the ring 24 by means of a servo motor 28, Fig. 5, and an equal and like rotation of each yoke 30 by means of a gear train 32, 34 engaging a fixed toothed rim 33 so that the plane of each wheel 18 in its new position 18<SP>1</SP> remains parallel to the reference axis K<SP>1</SP> Each friction wheel 18 is rotated by a servo motor 31 in accordance with the speed of the ship. For a course-oriented record presentation the ring 24 is held stationary. Figs. 6 and 7 and Fig. 8 (not shown). This embodiment as shown produces a north-oriented record presentation. The record sheet 4 is moved intermittently by two rings 41, 42 each having a U-shaped cross section closed at the underside by an annular rubber diaphragm 45, 46 respectively which presses the recording sheet 4 down on the glass plate 3 when the air pressure in the ring is increased. The ring 41 is fixed and the ring 42 is oscillated in its own plane in a sawtooth manner in the direction of the instantaneous ship's heading, the frequency of the oscillation being proportional to the speed of the ship. As shown in Fig. 7 the ring 42 is supported by a parallel linkage 47 and x and y components of the oscillation are produced by linkages 48, 50 and 49, 51 actuated by pairs of pneumatic motors 52, 53 and 54, 55 controlled respectively by two shafts (not shown) whose speeds are proportional to the x and y components of the ship's velocity. During the forward stroke of each sawtooth oscillation of the ring 42, the pressure in ring 42 is increased and the pressure in ring 41 is decreased so that the record sheet 4 moves forward with the ring 42 but during the backstroke the pressure conditions are reversed so that the record sheet 4 is held in its new position by the fixed ring 41 until the next forward stroke when it again moves forward with the ring 42. In order to produce a course-oriented record presentation the ring 42 together with the mechanism producing the displacement is rotated continuously or intermittently in reverse correspondence to changes in the ship's heading. Alternatively the fixed and movable rings 41, 42 may be fitted with retractable friction elements, e.g. pins, in place of the rubber diaphragms.