Motor control system

An electric motor comprising:

• a stator and an element movable relative to said stator;
• a plurality of energising coils;
• a position sensor for sensing the position of said movable element, comprising a first member mountable with said movable element and a second member fixable relative to said stator;
• at least one of said first and second members comprising a plurality of circuits each having at least two loops connected in series and being arranged so that signals generated in said at least two loops by a common electromagnetic field oppose each other;
• and
• the other one of said first and second members comprising a field generator for generating an electromagnetic field, which generator is adapted, in use, to be electromagnetically coupled to each of said circuits and wherein the electromagnetic coupling between the field generator and each circuit continuously varies as a function of their relative position, such that in response to an electromagnetic field generated by said field generator, a plurality of output signals are generated respectively dependent upon the electromagnetic coupling between the field generator and the respective said circuits;
• means for processing said plurality of output signals to generate a plurality of control signals;
• and
• means for controlling the application of a supply current to said energising coils in accordance with said control signals for causing said movable element to move relative to said stator.

A position sensor comprising:

• first and second members which are adapted, in use, to be movable relative to each other;
• said first member comprising a first circuit having at least two loops connected in series and being arranged so that signals generated in said at least two loops by a common electromagnetic field oppose each other, and a second circuit;
• said second member comprising a field generator having a first portion which is adapted, in use, to have a substantially constant electromagnetic coupling with said second circuit and a second portion having at least two loops connected in series and being arranged so that signals generated in said at least two loops by a common electromagnetic field oppose each other;
• wherein the loops of said second portion are adapted, in use, to be electromagnetically coupled to the loops of said first circuit, which coupling continuously varies as a function of the relative position of said first and second members, such that in response to an input driving signal applied to one of said first and second circuits, said field generator generates an electromagnetic field which generates an output signal in the other one of said first and second circuits, which output signal continuously varies as a function of the relative position of said first and second members.

A method of controlling a motor having a stator and an element movable relative to the stator and a plurality of energising coils, the method comprising the steps of:

• providing a position sensor for sensing the position of the movable relative to the stator, the position sensor comprising a first member mountable with said movable element and a second member fixable relative to said stator;
• at least one of the first and second members comprising a plurality of circuits each having at least two loops connected in series and being arranged so that signals generated in said at least two loops by common electromagnetic field oppose each other;
• and
• the other one of said first and second members comprising a field generator for generating an electromagnetic field, which generator is adapted, in use, to be electromagnetically coupled to each of said circuits and wherein the electromagnetic coupling between the field generator and each circuit continuously varies as a function of their relative position, such that in response to an electromagnetic field generated by said field generator, a plurality of output signals are generated respectively dependent upon the electromagnetic coupling between the field generator and the respective said circuits;
• causing said field generator to generate said electromagnetic field;
• processing said plurality of output signals to generate a plurality of control signals;
• and
• controlling the application of a supply current to said energising coils in accordance with said control signals for causing said movable element to move relative to said stator.

An electric motor comprising:

• a stator and an element movable relative to said stator;
• a plurality of energising coils;
• means for switching a supply current to a selected one or more of said energising coils for causing said movable element to move relative to said stator;
• a position sensor for sensing the position of said movable element, comprising a first member mountable with said movable element and a second member fixable relative to said stator;
• at least one of said first and second members comprising a plurality of circuits each having at least two loops connected in series and being arranged so that signals generated in said at least two loops by a common electromagnetic field oppose each other;
• and
• the other one of said first and second members comprising a field generator for generating an electromagnetic field, which generator is adapted, in use, to be electromagnetically coupled to each of said circuits and wherein the electromagnetic coupling between the field generator and each circuit continuously varies as a function of their relative position, such that in response to an electromagnetic field generated by said field generator, a plurality of output signals are generated respectively dependent upon the electromagnetic coupling between the field generator and the respective said circuits;
• and
• means for processing said plurality of output signals to generate a plurality of control signals for controlling said switching means.