Encoder for a rotary motor

A rotary motor comprising:

• a disk including a first circular track with a first series of magnetic regions with alternating polarity, and a second circular track with a second series of magnetic regions with alternating polarity;
• a first set of sensors configured and arranged to detect magnetic polarity in multiple regions along the first track;
• a second set of sensors configured and arranged to detect magnetic polarity along the second track;
• and
• a decoder for identifying an angular position of the disk based on a first output from the first set of sensors and a second output from the second sensors.

A rotary magnetic encoder configured to identify an angular position of a rotatable shaft, comprising:

• a first circular track with a non-uniformly distributed series of alternating magnetic poles;
• a second circular track with a uniformly distributed series of alternating magnetic poles;
• a first set of sensors configured to detect magnetic poles along the first track;
• a second set of sensors configured to detect magnetic poles along the second track;
• and
• a decoder for identifying the angular position of the rotatable shaft based on a first output from the first set of sensors and a second output from the second set of sensors.

A method for identifying an angular position of a rotatable shaft with an encoder having a first series of alternating magnetic poles non-uniformly distributed along a first circular track on a disk and a second series of alternating magnetic poles uniformly distributed along a second circular track on the disk, the method comprising:

• sensing a multiplicity of magnetic fields produced by multiple magnetic poles of the first series of alternating magnetic poles with a first set of sensors,
• producing a pattern of sensor outputs with the first set of sensors that is nonvarying for a fixed range of rotation of the rotatable shaft, wherein each fixed range of rotation defines an angular region;
• detecting a pole transition from the second series of alternating magnetic poles with a second set of sensors;
• and
• determining the angular position of the rotatable shaft, relative to a reference frame stationary relative to the sensors, based on the pattern of sensor outputs and an output of the second set of sensors.