Patent GB-1424588-A (GB)
Title: Apparatus for determining the position of a vehicle
IPC: G01C19/38
Filed: 1973-03-07
Abstract: 1424588 Gyrocompass FRIED KRUPP GmbH 7 March 1973 [8 March 1972] 11135/73 Heading G I C [ Also in Division G4] A method of determining the position of a vehicle using movement and measuring apparatus and a gyrocompass carried on board the vehicle includes the step of calculating the system error angle of the gyrocompass using an approximate N direction derived from the speed and drift of the vehicle measured at a certain moment and the latitude of the vehicle measured at a previous moment. The method involves determining the position at successive times separated by intervals # which are sufficiently small to make the distance travelled negligible compared with the circum-  ence of the earth. Fig. 2 shows the vehicle at position i=1 after movement over time # from position i-1=0 for which the latitude and longitude #, # are known and where the speed V  res  of the vehicle is assumed to be zero.Since the speed at (i-1) is zero, the gyro points to true N and the system error α of the gyro is zero at that point. At point i the speed V 1 , drift Vq, drift angle γ and resultant speed V res  are measured or calculated, using integrators 1a, 1b, Fig. 4 and conventional function generators 5, 6. The reading # of the gyrocompass is fed to the error computer 10 where an auxiliary angle #=#-γ is calculated. Part of the system error (denoted by e) is all due to the velocity of the vehicle combined with the rotational velocity of the earth at the latitude concerned. According to the invention, e is calculated in computer 10 from Vres and u.R. cos # (i-1) where u is the angular velocity of the earth, R is its radius and # is the latitude, the bracketted expression indicating that the latitude is that measured at point (i-1). The so-called "course error" e is added to # to produce an approximate north N' from which are derived velocity components VN' and VO' by resolving V res  in the approximate north and east directions. From these are formed the system error α, using known gyrodynamic equations, in the computer 10. The system error includes error due to acceleration as well as speed. The true bearing # = # + α - γ is formed in the adding circuits 9, 9' and is combined with V res  integrated over time T in circuits 7, 8 to provide the new latitude and longitude # i , # i . Fig. 3 shows the vehicle at point (i+1) where relationships differ from those of Fig. 2 since the system error at point i is not equal to zero. To determine #(i+1), #-γ is calculated as before and added to α(i)-#(i). From the new #(i+1), the new V res  (i+1), and the factor u.R.  cos #(i) determined at the previous point i, the new course error #(i+1) is found and a new approximate north N'(i+1) determined. As well as new speed components VN'(i+1), VO'(i+1), acceleration components bN'(i+1), bO'(i+1) are found by comparing the former with VN'(i), VO'(i). From these components, a new system error α(i+1) is calculated. The system error computer is shown in Fig. 8 where # is formed from # and γ in circuit 11  and e from V res , # and the previous calculation of #, in the circuit 13. Velocity components in approximate north and east directions are formed in circuit 14 from V res  and the sum of e and #. Circuit 15, for forming the corresponding acceleration, is controlled by a clock 18 having a period #. At the end of each period the values of VN and ON' are fed to a difference circuit where they are compared with the stored values computed for the previous period. The differences GN' and GO' represent uniform accelerations and arefed together with the velocities VN', VQ' to the system error computer 16 see also Fig. 13 (not shown). Of the three components of the system error, only the azimuth error α is utilized. At the end of each period #, the course error e is subtracted from the system error α and the difference Á used in the calculation of #. In a modification Fig. 9 (not shown), the accelerations b but not the velocities V, are fed to the system error computer 16 which produces an output Á instead of α. In another modification Fig. 15 (not shown), the acceleration b are derived directly from the measuring devices 1, Fig. 4, whence they are fed to the computer 10.