Patent GB-1414490-A (GB)
Title: Navigational aids for land vehicles
IPC: G01C21/36
Filed: 1972-09-25
Abstract: 1414490 Route progress indicators J A SLATER 18 Dec 1973 [25 Sept 1972] 44182/72 Heading G1K [Also in Divisions G4 to G6] An automatic route indicating system or navigational aid for a road vehicle, in which verbal instructions for the following of a chosen route are recorded, e.g. on magnetic tape, and are reproduced for guidance of the driver by vehiclemounted equipment actuated in accordance with the mileage travelled, is provided with means for comparing the actual value of a change in vehicle heading at a pre-selected distance from a datum position with a required value of heading change, and means responsive to any resultant difference between the actual and required heading changes for giving an error warning or alarm signal. If the actual and required heading changes correspond, a comparator 8 comparing actual mileage with the pre-selected distance signals is zeroed, so that there is no accumulation of mileage error. Data is recorded either on two magnetic tapes 1, 2 driven in synchronism, or on two tracks of a single tape. The first track or tape carries sets A1, A2 .... An of verbal instructions for preselected points along the route. The second track or tape carries digital coded data B1, B2 .... Bn for each point representing the distance to the next pre-selected point, each group Bn being followed by one or more stop pulses BSn. With the tape drive 11 running, a playback head 3 transmits a verbal instruction group Ax to an amplifier 5 and a speaker 6, and a playback head 4 transmits a signal Bx via a discriminator 7 to a distance comparator 8. The subsequent stop signal BSx is passed by the discriminator 7 to actuate a bi-stable switch 9 to stop the tape drive 11. As the vehicle proceeds, the output of a distance travelled coding device 16 driven from a road wheel 10 is subtracted from the Bx value stored in the comparator 8 until zero is reached (i.e. the distance travelled equals the distance initially stored), when a start signal is fed to the switch 9 to restart the tape drive 11 to play the next instruction group. The second track or tape 2 also carries coded change of heading signals "cos L" (left) and "cos R' (right) related to pre-selected points on the route, together with their distances "cos E" from the points at which the associated instruction groups are played. The discriminator 7 passes these signals to logic circuits 34-37. A compass 30 provides signals of change in the vehicle's actual heading, which are supplied to an up-down counter 32. The arrival of a cos R or cos L signal in a trigger unit 36 or 37 sets the counter 32 to zero and starts a second distance comparator 38 which compares the cos E signal with actual distance travelled. A self-synchronizing value store 40 holds permanently the magnitudes and senses of the correct changes in direction at the pre-selected points, and the appropriate one of these is compared with the actual heading change in a comparator 41. If the correct heading change occurs within the distance cos E, an alarm circuit which was brought to readiness by the trigger unit 36 or 37 is inhibited. If an incorrect heading change or no heading change occurs within the distance cos E, the alarm circuit is activated and the remainder of the system shut down. When the vehicle has been restored to its correct route, the system is reset by a push-button 49. The actual distance signal may be electrically or electronically corrected before passing to the comparator 8, to compensate for odometer inaccuracies.