Patent GB-849499-A (GB)
Title: Apparatus for recording the true courses of ship targets in conjunction with a radarset
IPC: G01S1/02
Filed: 1956-11-19
Abstract: 849,499. Radar. ATLAS-WERKE A. G. Nov. 19, 1956 [Nov. 19, 1955; June 25, 1956], No. 35354/56. Class 40(7). [Also in Groups XIX and XX] In a ship-borne pulse radar system for recording the true motion tracks of the ship and of other craft in its vicinity such that the images of stationary targets are stationary relative to the record surface, a Plan Position Indicator (PPI) cathode-ray tube short-afterglow display is projected optically on to a record surface which is automatically oriented in reverse correspondence to changes in the ships heading such that the direction of a vector on the record surface corresponding to the instantaneous heading of the ship remains parallel to a reference axis in a fixed frame of reference, e.g. the casing of the display, and means are provided for producing relative translatory movement between the projected PPI image and the record surface in accordance with the motion of the ship; in the embodiments described the projected image is stationary and the record surface is moved but alternatively the record surface may be stationary and the projected image may be displaced optically. Such a display is defined as a "courseoriented" display and the fixed reference axis is defined as the "image axis" which is identified in the Figs. by the reference A; when the display surface is a vertical plane the image axis A is usually vertically upwards. In some embodiments of the invention the course-oriented display may be converted into a "north-oriented" display, i.e. one in which a predetermined geographical direction on the record surface remains parallel to the image axis A. When a course-oriented record is required the projected PPI image must be course-oriented and when a north-oriented display is required the projected PPI image must be north oriented; a course-oriented projected image may be derived from a north-oriented PPI display by projecting the display through an inverting prism which is rotated through half the angular change in the ships heading. The PPI display must be intensity modulated at its origin to produce an indication corresponding to the ship carrying the radar. When the displayed "stationary" targets are targets which are stationary relative to the water mass the ships motion is derived from its heading γ and its speed w through the water as determined by a ship's log; when the displayed stationary targets are stationary relative to land the effect of drift must be allowed for. The projected images may be recorded by manual plotting or the record surface may be (1) coated with long-afterglow fluorescent material giving a visual image which may be fixed by any suitable photo-chemical or photo-electric process or (2) comprise a photo-cathode giving an electron charge image which is rendered visible by known television or photo-electric printing techniques. The instantaneous position co-ordinates of the ship may be generated by vectorial integration of the velocity vector # to give the position vector r t  or by generating the rectangular position coordinates by scalar integration of the corresponding rectangular components of the ships velocity. For position co-orindates u and v corresponding to the E-W and N-S directions the equations are For position co-ordinates x and y perpendicular to and parallel to the ships heading the equations are Vectorial integration. In Figs. 1-3 the PPI display is projected on to a disc 73 coated with long-afterglow fluorescent material. The disc 73 is mounted on rollers 74 permitting displacement of the disc in any direction in the plane of the disc by means of friction wheels 75 pressed resiliently against its under surface as shown in Fig. 3. The wheels 75 are driven in unison in accordance with the ships speed by means of a differential 86, Fig. 2, and synchro-motor 85 and the wheels 75 are driven in opposition through a differential 89 and synchro motor 87 in accordance with changes in the ships heading to produce a corresponding rotation of the disc 73. The wheels 75 and their driving means are mounted on a plate 79 carried by a shaft 81, Fig. 3, coupled through a clutch 82 to a compass repeater 83. For a course-oriented final display, a course-oriented cathode-ray tube display is employed, the clutch 82 is disengaged and the plate 79 is locked in a position such that the pointer 84 is on zero. For a north-oriented final display, a north-oriented cathode-ray tube display is employed and the clutch 82 is engaged so that the axis 76 of the friction wheels 75 is oriented in accordance with the heading, a change in heading does not now produce a corresponding rotation of the disc 73 since the rotational effect of the differential drive on the wheels 75 is compensated by the rotation of the axis 76. Scalar integration. Reference of the ships motion to "north-oriented" and "courseoriented" geographical rectangular axes U and V is shown in Figs. 4 and 5 respectively where P is a stationary reference point, S is the position of the ship and the vector C is parallel to the ships heading; Fig. 6 and 7 respectively show corresponding arrangements for co-ordinate axes X and Y perpendicular and parallel to the ships heading. Figs. 8 to 11 show corresponding arrangements for simulating the motion of the ship S by the movement relative to a fixed point S<SP>1</SP> representing the ship of a recording surface 3. Fig. 9 and 11 produce a course-oriented display and Figs. 8 and 10 produce a north-oriented display. The cathode-ray tube PPI display is projected on to a circular area 99 of the recording surface centred at the fixed point S<SP>1</SP> and the recording surface 3 is attached to a sleeve 103 slidable along a guide 102 attached to a sleeve 101 slidable along a guide 100, the sleeves 103 and 101 being positioned by lead screws in accordance with the co-ordinate values u, v or x, y as indicated. In Figs. 8 and 9 the surface 3 is rigidly attached to the sleeve 103 but in Figs. 10 and 11 the surface 3 is rotatably attached to the sleeve 103 and is oriented in accordance with the heading. In Figs. 8 and 11 the guide 100 is fixed but in Figs. 9 and 10 the whole guide assembly is oriented about the point S<SP>1</SP> in accordance with the heading. Figs. 12 and 13 (not shown) illustrate constructional details of the arrangements shown in Figs. 9 and 11 respectively for producing course-oriented final displays. Mechanical computers for solving equations (2) and (3) are shown in Figs. 14 and 15 respectively. In Fig. 14 a conical roller 139 is rotated at a speed proportional to the ships speed w and drives a friction wheel 140 at a speed of w(1 + d) where d is the displacement of the wheel along its square shaft 141, the displacement being effected by a crank guide 143, 144 actuated by a shaft 161 controlled in accordance with the heading such that d = sin γ. The shaft 141 and a shaft rotating at the speed w are coupled to the inputs of a differential gear 145 so that the angular position of the output shaft 146 is proportional to u. A second conical roller 149 and corresponding associated components are provided to compute v, the displacement d being in this case equal to cos γ. Fig. 15 comprises two conical rollers 164, 174 whose angular positions are set in accordance with the heading γ. A friction wheel 175 driven by the roller 174 is displaced from a datum position by an amount proportional to y by a lead screw 177 so that the angular position of shaft 176 is proportional to (γ-#y dγ). The shaft 176 and a shaft controlled in accordance with γ are coupled to the inputs of a differential gear 180 giving an output rotation proportional to x = - #ydγ which controls (by means of a lead screw 167) the displacement of a friction wheel 165 driven by the roller 164 so that the angular position of shaft 166 is proportional to (y + J x dγ) and this is converted to # x dγ in a differential gear 170 (similar to the differential gear 180) and combined with a shaft rotation J w dt in a further differential 185 giving an output shaft rotation y = # x dγ + #w dt w dt. Electrical outputs proportional to x and y are provided by synchros 173, 183 mounted on the lead screw shafts 167, 177. Specification 849,500 is referred to.