Patent GB-945255-A (GB)
Title: Apparatus for computing the range, course and/or speed of a target or other body
Inventor: SNOWDON CHARLES
IPC: G06G7/78
Filed: 1960-03-23
Abstract: 945,255. Target tracking. SHORT BROS. & HARLAND Ltd. March 9, 1961 [March 23, 1960], No. 10376/60. Heading G4G. In an apparatus for computing the range r of a target from a moving observing station there is included means for generating signals respectively representative of the first, second and third time derivations #, ##, and ## of the target bearing #; means for generating signals one of which is representative of a component fr of the acceleration f of the target relative to the observing station, the component fr being an acceleration component along the target bearing line, and another of which is representative of a component fn of the acceleration f, the component fn being an acceleration component at right angles to the said target bearing line; means for generating a signal representative of the first time derivative fn of the acceleration component fn, and means for operating on and combining the said signals in accordance with the expression or its equivalent,to produce an output signal representative of the range r. Fig. 1 indicates an observing ship O/S moving with a velocity U on a heading K and a target ship T/S moving with a velocity V at a range r and bearing # from the observing ship. By means of passive listening and dead reckoning equipment the bearing # is determined, and signals representing the parameters #, K and U are fed into an acceleration computing unit 26, Fig. 2, which produces signals fn, fn and fr (see below), The signal # is also fed to the differentiating circuits 28, 29 and 30. The units 34 to 39 operate on combinations of these signals to produce the numerator of the above expression after summing in a unit 32, and similarly the units 40 to 46 produce signals which are summed in the unit 33 to produce the denominator of the above expression. These signals representing the required numerator and denominator are applied to the divider 31 to produce a value for the range r. To obtain an accurate value however, it is necessary to carry out the above computation with a large value of fn. This is best achieved by applying a steady turn to the observing ship O/S. A switch 47 is provided to prevent the transmission of the range signal determined by the divider 31 when fn is small; and additional apparatus is provided to supply a continuous indication of the range r. This is achieved by integrating in the unit 54 the value formed in the units 48, 49 and 53 and then feeding back the value of r obtained in the unit 50 to the units 55 and 49 to assist in producing suitable correction signals. In the unit 55 this value of r is subtracted from the value intermittently transmitted by the switch 47 and the difference is stored at 58. This difference is added to the value of r obtained from the unit 54 in the unit 50, so that the range signal appearing at the output 59 is based on the last accurate value transmitted by the switch 47. The course B and speed W of the target ship T/S relative to the observing ship O/S may be determined from the equations using the units 62-65 for W and the units 66-68 for B. Fig. 3 shows the acceleration computing unit 26 in more detail. The equations whose evaluation is performed by the units of Fig. 3 are