Improvement to a method for controlling an autonomous mobile robot et related device

Navigation device for mobile robot which includes - a means for measuring the amplitude of a periodic electromagnetic signal transmitted by one or a boundary elements, for example a thread, arranged on the periphery of the working surface of said mobile robot, and measurements are repeated during several periods - a means for sampling the amplitude of the signal during each period - a separate memories for storing the result of each measurement sample, and the results collected are added in said memories until the content of these memories reaches a reference threshold, - a microprocessor capable of interpreting numerical analysis the number of samples needed to reach that threshold and the content of each memory and said microprocessor is therefore able to determine the distance or variation of distance with respect to said limit.