Patent GB-1355115-A (GB)
Title: Collision avoidance system
IPC: G01S13/937
Filed: 1971-07-19
Abstract: 1355115 Pulse radar MARINE DIGITAL SYSTEMS Inc 19 July 1971 [19 Aug 1970] 33782/71 Heading H4D  A collision avoidance system comprises a source of a signal representing a first vehicle velocity; means for providing a signal representing the position of a target relative to the first vehicle; means for providing a signal representing the velocity of the target and means for providing a signal representative of the distance and bearing of the target from the first vehicle at the closest point of approach (CPA). In a ship (mounted) system the ship's velocity may be found by a Doppler or inertial navigation system, pitometer, gyrocompass or normal navigational techniques. The target position is found by a continuously rotating radar beam, the radar being equipped for manual or automatic tracking. The target velocity is calculated from its change of position over a fixed time, determined by the radar. The information is used in a digital computer which produces signals representing the magnitude of the closest point of approach, its location, the time thereto and a warning if the CPA is less than a predetermined minimum. The radar display may be a PPI with a range ring adjustable to coincide with a target and a bearing cursor. The absolute course directions of the targets are displayed by vector arrows at the target location and the targets are identified by alpha-numeric characters (Fig. 6A, not shown). The collision warning comprises flashing lines which are projections of the courses of the relevant target vehicle and the prime vehicle. Alternatively, the computer may provide a purely alpha-numeric "list" display (Fig. 6B, not shown) comprising a table indicating in columns, the target identification; magnitude of CPA; time thereto; target course; target velocity; bearing of CPA; target range; target bearing; target moving/stationary; collision warning. In the manual tracking mode a target is selected by range and bearing markers 31, 33, Fig. 5. The target is then assigned an alpha-numeric character (e.g. A1) by depressing appropriate buttons 102. When the target moves, the operator repeats the procedure and the computer calculates the relevant information. In the automatic tracking mode, any target of interest is selected and identified as above. If the AUTO button 104 is also selected the target position is entered into the computer store and the target is automatically tracked. Removal of a target from the auto tracking is accomplished by identification by buttons 102 and selecting the EXIT button 106. ASK button 108 is selected to call for all information on an identified target. The auto tracking unit is shown in Fig. 4. The computer provides signals (for each target) representing (1) a bearing search sector, which are entered in registers 50, 51; (ii) a range gate, entered in registers 66, 67; (iii) echo amplitude threshold, which is fed to detector 86. As the radar beam scans the azimuth plane, the bearing thereof is coded and compared with the search sector signals in comparators 52, 53. While the beam is scanning the desired sector, bi-stable 54 enables gate 85. The range gate operates in a similar manner, at the transmitter pulse, bi-stable 83 is set via line 88 to enable oscillator 82 which starts range counter 80. When this reaches the beginning of the range gate, bi-stable 72 is set enabling gate 85. If an echo is received from the search sector, detector 86 produces a pulse which passes gate 85 and opens gates 76, 58 transferring the instantaneous range and bearing into buffers 74, 59. The echo also sets bi-stable 78 which indicates the presence of new data to the computer and resets bi-stable 65 which inhibits a "no target" indication. When the computer has accepted the new information, a clear signal resets bistable 78 and sets bi-stable 65. When counter 80  reaches the maximum range, bi-stable 83 and counter 80 are reset via decoder 84. At the end of the search sector (i.e. maximum bearing, maximum range), bi-stables 54, 72 are reset thereby enabling gate 60. Bi-stable 62 thus signals the computer to move on to a new target. Since bi-stable 65 remains set if no echo is received, at the end of search bi-stable 63 is set, thereby indicating that no target was found. In order to determine safe avoidance procedure in the event of a collision warning, theoretical course and/or speed changes may be manually entered to predict a new CPA. Alternatively, a desired CPA may be entered and the computer provides a new course and speed. In threedimensional systems, e.g. involving aircraft or submarines (using sonar), the vehicle may follow a course that avoids intersection in the azimuth plane or height or depth information may be processed as above and the conditions at different levels shown on a multi-colour display.