Rotor position encoder having features in decodeable angular positions

A method of controlling an electric machine which includes a rotor, a stator, at least one phase winding, and an encoder defining a position code for the rotor of the electric machine relative to the stator, the encoder comprising:

• a single sensor, indicia arranged to rotate with the rotor past the sensor for influencing the output of the sensor, the indicia including sensor output influencing first indicia which are in evenly spaced angular positions, and sensor output influencing second indicia which are in unevenly spaced angular positions, the said angular positions of each second indicium relative to one of the first indicium being decodable as a sequence such that the position of the rotor relative to the stator is determinable from the sequence;
• the method comprising sensing the movement of the indicia past the sensor;
• decoding the sequence of the second indicia relative to the first indicia;
• determining the position of the rotor relative to the stator according to the state of the sequence;
• and timing the switching of the machine according to the first indicia passing the sensor.

A method of starting an electric machine comprising a rotor defining rotor poles, a stator defining stator poles, an encoder including a moving part arranged to rotate with the rotor and to provide a rotor position code, a sensor arranged to be influenced by the moving part of the encoder according to the position code and to produce an output thereof, and a controller for receiving the output from the sensor, the moving part comprising a set of indicia mountable to rotate with the rotor past the sensor for influencing the output of the sensor, the indicia including sensor output influencing first indicia which are in evenly spaced angular positions, and sensor output influencing second indicia which are in unevenly spaced angular positions, the said angular position of each second indicium relative to one of the first indicium being decodable as a sequence such that the position of the rotor relative to the stator is determinable from the sequence;

• the method comprising:
• energizing at least a selection of the stator poles to orientate the rotor with respect to the stator into a predetermined position;
• initiating a count of the first indicia of the encoder from the predetermined position;
• accelerating the rotor according to the continued energization of the stator poles based on the position count derived from the first indicia of the encoder passing the sensor and thereafter checking the rotor position from the count with the decoded sequence.

A method of starting a polyphase electric machine comprising a rotor, a stator defining stator poles, a rotor position encoder, including a moving part mounted to rotate with the rotor and a sensor having an output which is influenced by the encoder, the encoder having angularly evenly spaced sensor output influencing indicia mounted to rotate past the sensor which define a position code of the rotor relative to the stator, the method comprising:

• energizing sets of poles of adjacent phases of the machine so that the rotor assumes a position intermediate the maximum inductance positions associated with the two phases;
• de-energizing one of the sets of poles such that the rotor rotates towards the maximum inductance position of the other energized set of poles;
• monitoring the passage of the rotor past the stator poles according to the position code derived from the encoder;
• de-energizing the other set of poles at a moment that assists in allowing the rotor to freewheel past the said maximum inductance position, and continuing single phase rotation of the rotor by energizing and de-energizing the said other set of poles according to the monitored position of the rotor.

A method of starting a single phase electric machine comprising a rotor, a stator defining stator poles, an encoder, including a moving part arranged to rotate with the rotor and to provide a rotor position code, a sensor arranged to be influenced by the moving part according to the position code and to produce an output thereof, and a controller for receiving the output from the sensor, the moving part of the encoder comprising a set of indicia arranged to rotate with the rotor past the sensor for influencing the output of the sensor, the indicia including sensor output influencing first indicia which are in evenly spaced angular positions, and sensor output influencing second indicia which are in unevenly spaced angular positions, the said angular positions of each second indicium relative to one of the first indicium being decodable as a sequence such that the position of the rotor relative to the stator is determinable from the sequence, the method comprising:

• energizing the stator poles;
• monitoring the passage of the rotor past the stator poles by counting the first indicia past the sensor;
• de-energizing the stator poles when a position of maximum inductance of the rotor relative to the stator is reached;
• allowing the rotor to freewheel until the rotor reaches a position at which re-energization of the stator poles will continue rotation of the rotor, as indicated by the count of the first indicia past the sensor;
• thereafter checking the rotor position count with the decoded sequence.