Curve following device

A curve-following device having an optical sensing head capable of sensing a guide zone containing a guide line having a substantial component transverse to its longitudinal direction and of sensing at least one separate code zone provided adjacent at least one side of said guide line and marks within said code zone, said curve-following device comprising optical scanning means within said head for periodically scanning said guide zone with a certain frequency and for generating signals, means for moving said head along said guide zone at a speed relatively slow in relation to said frequency of the scanning period of said scanning means, a control instrument connectable to said device and having means for receiving said signals generated by said optical scanning means and for distinguishing between marks arranged within said at least one code zone and said guide line, and means for generating first control signals for controlling said means for moving the sensing head along said guide line, means for tripping second control signals for controlling means other than said moving means, and including means for comparing the length of said marks with said transverse component of the guide line and means for preventing tripping said second control signals unless a mark detected in said code zone exceeds a predetermined length.