System for measuring the position of an electric motor

In a DC electric motor with drive current being rotated in sequence through electromagnets on a rotor or a stator thereby generating a rotating magnetic field, said drive current at any instant flowing through a plurality of electromagnets operating in series, an improved rotor position detector comprising:

• a fixed impedance reference network comprising two components connected in series, each component having an impedance not affected by motor rotation;
• said components being connected in parallel to a plurality of electromagnets;
• the fixed impedance reference network and the driven electromagnets forming a bridge impedance network;
• a differential amplifier having two inputs where one input is connected to an undriven winding, and the other input is connected to a node between the fixed impedance components of said fixed impedance reference network;
• wherein an output signal of the differential amplifier is consistently related to an impedance ratio between the driven electromagnets;
• said impedance ratio depending on a relative rotational position between the rotor and the stator, thereby defining a rotor position relative to the stator.

In a DC electric motor with drive current being rotated in sequence through electromagnets on a rotor or a stator thereby generating a rotating magnetic field, said drive current at any instant flowing through a plurality of electromagnets connected in a delta configuration, with a center tap in each of the electromagnets, said center tap dividing the winding of each electromagnet into two sections, an improved rotor position detector comprising:

• a fixed impedance reference network comprising two components connected in series, each component having an impedance not affected by motor rotation;
• said components being connected in parallel to a plurality of electromagnets;
• the fixed impedance reference network and the driven electromagnets forming a bridge impedance network;
• a differential amplifier having two inputs where one input is connected to a center tap in a driven electromagnet, and the other input is connected to a node between the fixed impedance components of said fixed impedance reference network;
• wherein an output signal of the differential amplifier is consistently related to an impedance ratio between the two sections of the driven electromagnet;
• said impedance ratio depending on a relative rotational position between the rotor and the stator, thereby defining a rotor position relative to the stator.

An apparatus to detect a position of a rotor, said apparatus comprising:

• a first driven winding and a second driven winding on a rotor or a stator;
• a fixed impedance reference network connected in parallel to the first and second driven windings;
• a computational circuit connected to the first and second driven windings and to the fixed impedance reference network;
• and
• wherein the computational circuit detects changes in the ratio of the impedances of the first and second driven windings and the fixed impedance reference network, thereby determining a position of the rotor relative to the stator.