Vehicle guidance systems

Claim 1

A guidance system for controlling steering means of a vehicle to selectively guide the vehicle along any one of a plurality of paths at different distances laterally offset from a predetermined plane in which a guide member is located, the guide member being operative to emit an electromagnetic field, said system being adapted for mounting on the vehicle and comprising: a pair of detectors in laterally spaced relation on the vehicle and producing similar relative responses corresponding to the strength of a selected component of said electromagnetic field, said strengths varying with the distance from said predetermined plane, the ratio of said relative responses being substantially constant and independent of the emitted field strength when the vehicle is in any one of said plurality of paths, and said ratio of said relative responses having different values respectivelY corresponding to said paths, circuit means connected to said pair of detectors and including signal comparison means and ratio adjustment means for selecting any one of said plurality of laterally offset paths to be followed, said comparison means being operative to produce an error signal when the ratio of said strengths of said selected components deviate from a value determined by said adjustment means, and steering control means responsive to said error signal for controlling the steering means to steer the vehicle toward the path selected by adjustment of said adjustment means, whereby the vehicle may be selectively guided in any one of said plurality of paths by adjustment of said adjustment means.