Patent GB-1324251-A (GB)
Title: Computer for indicating the movement of a body
IPC: G06G7/78
Filed: 1970-06-11
Abstract: 1324251 Computing vehicle courses L W TOBIN JNR 11 June 1970 28414/70 Heading G4G [Also in Division G1] A computer for plotting the movement of a vehicle or vessel comprises a vehicle-velocity computer and a drift-velocity computer both connected to the motors of the plotting pointer and actuated so that they drive the pointer alternately during equal periods of time whereby over two successive periods the pointer plots the sum of the two velocities, i.e. the absolute velocity of the vehicle. The magnitude of the vehicle-velocity is supplied by an electromechanical transducer 24, Fig. 1, and is fed to a resolver 30 whose setting is determined by a vehicle-mounted compass 32. Sine and cosine signals from the resolver 30 are fed to a quadrant switch 40 which determines the directions of rotation of the motors driving the N-S and E-W lead screws of the pointer over the plotting board 42. The drift-velocity computer comprises transducer 26, supplying the magnitude of the drift, a wind/current detector 48, a resolver 44 and a quadrant switch 52, all these elements being identical in construction to the corresponding elements of the vehicle-velocity computer. A cycling circuit 10, comprising a 180 degree cam and a pair of switches, supplies power (either A.C. or D.C.) alternately to the transducers 24, 26 and to a storage circuit 18. Although the transducers 24, 26 are actuated during the same time periods, only the output of the vehicle velocity transducer 24 is fed to the plotting board during these periods, the output of the drift transducer 24 being fed to the storage circuit 18. During the alternate periods when transducers 24, 26 are not active, the storage circuit 18 is actuated by cycling switch 10 and the drift velocity signal stored therein is fed to the plotting board. This arrangement allows both transducers 24 and 26 to be fed simultaneously through common scaling circuits 14, 20. These circuits are of identical construction and effect time division of the pulse supplied by the cycling switch 10 whereby a scaling factor appropriate to the scale of the map placed on the plotting board is applied to the velocity and drift transducers 24, 26. The scaling circuits comprise a number of cams having different dwell periods mounted on common shafts driven by motors 16, 22. Each cam actuates a respective cyclical switch and a selector in each of the scaling circuits 14, 20 enables a chosen switch to be inserted in respective supply leads 88, 114. The scaled pulse thus derived corresponds to the maximum velocity magnitudes supplied by transducers 24, 26, velocity signals of smaller value being derived by time division of this pulse. The time division is effected by a cam 120, Fig. 2, driven by motor 28 powered by the scaled pulse on lead 114. The cylindrical cam 120 includes a land 124 bounded by a straight edge and a spiral edge and so arranged that, as the cam follower 126 is axially traversed from the L.H.S. to the R.H.S. of the cylinder, the dwell varies linearly from zero to 100%. The follower 126 incorporates a switch which interrupts the signal on line 114 and effects time division of this signal according to the setting (manual or automatic) of the follower along a velocity scale 132. The drift transducer 26 is identical. The output of transducer 24 is fed over lead 134 to the common motor of a pair of cams 170, 172, Fig. 6, similar to the cam 120, land 174 of cam 170 having a linear, spiral edge 182 and land 176 of cam 172 having a cosineshaped, spiral edge 184. Cam followers 162, 164 are mounted on a common traversing bar 154 axially driven by one of a pair of diametrically opposed pegs 152 which are mounted on a rotatable disc 150 and make contact with a cross-bar 158 rigidly mounted on bar 154. The angular setting At of the disc 150 represents the heading of the vehicle derived from a compass 32 and corrected for variation in element 34. The axial position of followers 162, 164 is proportional to sin A t  and switches actuated by the followers 162, 164 therefore effect respective time-divisions of the signal on lead 134 according to the functions sin A t  and cos A t . The sin and cos signals are fed over respective leads 186, 188 to respective double-throw switches 212, 216, Fig. 8, 40, Fig. 6, which are actuated by a 180 degree cam 146 driven to the same angular setting A t  as the disc 150 (see details 36, 144, 148, 40, Fig. 6). The switches are connected by pairs of leads 210, 214 respectively to the NS and EW actuating motors 196, 206 of the plotting head 200 and determine the direction of rotation of these motors. Thus, as shown, when At lies in the NE quadrant, both motors are switched by cam 146 to rotate in a positive direction, i.e. respectively N and E. The mode of operation of the switches and motors for values of A t  lying in other quadrants may readily be deduced. During the time that the vehicle-velocity vector is being plotted, the drift-velocity signal from transducer 26 is fed to a reversible motor of storage device 18 which drives a disc 222, Fig. 14, in a clockwise direction through an angle proportional to the drift signal. At the beginning of this movement a peg 224 on the circumference of disc 222 closes a switch 68 in the power lead 66 (no power is being supplied on 66 at this time). The final position of the peg is shown in broken line. Plotting of the drift vector is initiated when the cyclical switch 10 supplies power over lead 66 to the motor of storage device 18 whereby the disc 222 is driven in an anticlockwise direction until the peg 224 contacts and opens the switch 68. During this period, which is equal in length to the pulse previously supplied by the drift transducer 26, switch 68 is closed and an output pulse representative of drift velocity is supplied over lead 226 and through the RHS 44, 48, 50, 52 of the circuit, to the motors of the plotting board, whereupon the drift vector is plotted. The switch 10 thereafter supplies power to lead 64 and initiates plotting of a fresh vehiclevelocity vector, and so on. The electromechanical elements may be replaced where appropriate with purely electrical elements.