Patent GB-693079-A (GB)
Title: Automatic tracking apparatus
IPC: G01S3/42
Filed: 1951-07-03
Abstract: 693,079. Electric analogue calculating systems. COLLINS RADIO CO. July 3, 1951 [July 19, 1950], No. 15761/51. Class 37. Apparatus for computing the position of a moving body (e.g. an aircraft) relatively to a pair of reference co-ordinate axes comprises apparatus mounted on the body receiving radiant energy from transmitters at known geographic locations to produce an output signal which is converted by a resolver into a pair of co-ordinate signals representing the co-ordinates of the body referred to a ground reference system, relative angle and airspeed measuring apparatus carried by the body, an x-computer receiving an x-co-ordinate signal from the resolver and first x-velocity signal from the angle and airspeed measuring apparatus, and a y-computer receiving a y-co-ordinate signal from the resolver and a second yvelocity signal from the angle and airspeed measuring apparatus; the x- and y-computers respectively computing derived co-ordinate signals indicating the position of the moving body by selecting the low-frequency components of the derived co-ordinate signals from the x- and y-co-ordinate signals and by selecting the high frequency components of the derived co-ordinate signals from the x- and y-velocity signals. Fig. 2 shows a tracking computer wherein a positional co-ordinate signal x1 from a resolver 12, responsive to the bearings of two fixed transmitters from a pair of radio direction finders, Fig. 1 (not shown), and an airspeed co-ordinate signal x 2  from a calculator 34 responsive to the aircraft compass 32 and airspeed indicator 33, together energize the control amplifier 21 of a servo motor-generator system 22, 23 driving the slider of an A.C. energized potentiometer 24, whose displacement output is retroactively fed back to the amplifier input together with a rate signal from the generator 23. The control amplifier 36 of a servo motor-generator system 37, 38, driving an A.C. energized potentiometer 49 directly and an A.C. energized potentiometer 41 through a differential gear 39 also driven by the motor 22, is energized by the signal x1, the retroactively fed-back displacement output of potentiometer 41 and the rate signal from generator 38. The servo system 21, 22, 23 is shown to operate analogously to a capacitanceresistance high-pass filter, Fig. 5 (not shown), in that the input xl signal having H.F. errors due to radio channel fluctuations, and the input x 2  signal having L.F. or steady errors due to wind speed, are combined to give a resultant corrected velocity signal x 3  appearing as the rate voltage fed back from the generator 23, or alternatively as the shaft velocity of the servomotor 22. The H.F. components of this signal are derived from the x2 signal, and the L.F. components are derived from the x1 signal, while the wind velocity error in x 2  iseliminated by the L.F. attenuation characteristics of the system. Similarly the servo system 36, 37, 38 is shown to operate analogously to a resistance-capacitance low-pass filter, Fig. 6 (not shown), in that the input signal x1 controls the amplifier 36 in combination with the retroactive rate voltage from generator 38 and the retroactive displacement voltage from potentiometer 41, while the shaft velocity of the motor 22 representing x, is added to the shaft velocity of the motor 37 in the differential gear 39, so that the output of the system as represented by the displacement voltage from potentiometer 41 is proportional to the required corrected valve of x3, free from L.F. wind error and H.F. radio fluctuation error. This voltage is indicated by instrument 18 as the corrected x-co-ordinate of the aircraft. The difference between the displacements of potentiometers 24 and 41 is shown to be proportional to wind error, so that since the velocities of motors 22, 37 are added in differential gear 39 to displace potentiometer 41, the displacement of potentiometer 49 and its output signal are proportional to the wind error. When radio co-ordinate positional in. formation is not continuously available the tracking computer is rearranged by switching (not shown) to operate as an automatic deadreckoning computer between radio fixes. In Fig. 3 the corrected co-ordinate signal x3 from potentiometer 41 is fed into amplifiers 21 and 36 in lieu of the radio positional signal x1. The servo system 21, 22, 23 is thus controlled by the velocity signal x 2  combined with the rate signal from generator 23, and by the negative displacement signal from potentiometer 24 combined with the co-ordinate signal x3 corrected for wind at the last radio fix. Thus the motor runs at a speed proportional to the true co-ordinate ground speed so long as the wind is unchanged. Servo system 36, 37, 38 is controlled by the rate signal from generator 38, the corrected co-ordinate signal x3 fed in positively in lieu of x1 and the same signal fed in negatively as before from potentiometer 41, so that the motor remains stationary, and the potentiometer 41 is driven through differential gear 39 at the speed of motor 22, so that its displacement and output signal measured on instrument 18 is proportional to the x-co-ordinate of the position of the craft, with the wind correction " remembered " from the last radio fix and indicated by the output of the potentiometer 49. For dead reckoning of the craft co-ordinates from known wind direction and velocity without radio guidance (Fig. 4) the circuit is rearranged by switching (not shown) so that the x-component of wind velocity is set in manually from the A.C. energized potentiometer 70 in series opposition to the signal from potentiometer 49 to control the servo-system 36, 37, 38, together with the inverse rate signal from generator 38. Motor 37 runs to readjust potentiometer 49 until its output signal balances the x-wind velocity signal, and servo system 21, 22, 23 is controlled by the output of potentiometer 41, the x 2  signal computed from the aircraft instruments, the output of potentiometer 24, and the rate signal from generator 23, so that motor 22 runs at a speed proportional to the x-component of air speed plus the x-component of wind speed; i.e. the x-component of ground speed. The motor rotations are combined in the differential gear 39 to adjust potentiometer 41 whose displacement and consequent output signal measured by instrument 18 are proportional to the x-co-ordinate of the craft. Corrected y-co-ordinates of the aircraft position are produced by similar tracking computers responsive to y1 and y 2  signals, and the resultant x-, y-co-ordinates of the craft position may be supplied to a known course computer.