Plural rotary member position encoder having electromagnetically coupled resonant frequency multiplexed outputs for respectively associated rotatable members

A method of determining the angular position of a plurality of rotatable members, said method comprising the steps of:

• providing a plurality of electrically resonant circuits mounted in respective rotatable members for rotation therewith, each electrically resonant circuit of said plurality being resonant at a frequency different to those of the other resonant circuits so as to be distinguishable therefrom;
• providing an excitation circuit electromagnetically coupled in common to said plurality of resonant circuits;
• providing a sensing circuit electromagnetically coupled in common to said resonant circuits;
• arranging the plurality of electrically resonant circuits, the excitation circuit and the sensing circuit to be such that the degree of electromagnetic coupling between each resonant circuit and at least one of the excitation circuit and the sensing circuit varies as a function of the angular position of the corresponding rotatable member;
• using said excitation circuit to energize each resonant circuit at its respective resonant frequency;
• and
• detecting the output signals induced in said sensing circuit as a result of the energizing of said resonant circuits, and deriving from the detected output signals the angular position of said plurality of rotatable members.

An apparatus for remotely indicating the angular position of a plurality of rotatable members each having an electromagnetic intermediate device (EID) mounted for rotation therewith the apparatus comprising:

• input means for electromagnetically energizing each EID;
• output means electromagnetically coupled to each EID,
• each EID being an electrically resonant circuit having a resonant frequency different to those of the other EIDs in that each EID generates when energized by said input means, an electromagnetic field proportional to the degree of coupling between the input means and the EID, which electromagnetic field induces an output signal in said output means characteristic of and dependent upon the angular position of the corresponding rotatable member, and in that the degree of electromagnetic coupling between each EID and at least one of the input means and the output means varies as a function of the angular position of the corresponding rotatable member, thereby causing said output signal to vary in dependence upon said angular position,
• wherein the degree of electromagnetic coupling between each EID and one of said input means or said output means is substantially independent of the angular position of the corresponding rotatable member;
• wherein each rotatable member has a second EID mounted therewith that is electromagnetically coupled to said input means and said output means such that said second EID generates, when energized by said input means, an electromagnetic field proportional to the degree of coupling between the input means and the second EID, which electromagnetic field induces a second output signal in the output means characteristic of and dependent upon the angular position of the corresponding rotatable member, the electromagnetic field generated by said second EID having an axis different from the axis of the electromagnetic field generated by the corresponding first EID thereby causing the output signal induced by said second EID to be different from the output signal induced by the corresponding first EID.