Magnetic sensor system for motor control
AssigneeAnalog Devices International Unlimited Company
InventorsJochen Schmitt, Enda Joseph Nicholl
Life of this patent
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Abstract
The present disclosure provides a magnetic sensor system for monitoring the position of the rotor relative to the stator for use in electronic motor commutation. The system uses two magnetic sensors with a back bias magnet, the magnetic sensors being configured to detect changes in the magnetic field direction caused by the magnetic field interacting with two moveable targets that are being rotated by the motor shaft. The unique phase shift between the signals measured at each sensor can thus be used to determine the relative position between the stator and the rotor. In this respect, the system makes use of the Nonius or Vernier principle to measure rotational displacement, however, the scale of the encoder is defined by the number of motor pole pairs.
Claims18
A magnetic sensor system, comprising:
- at least one bias magnet configured to produce a magnetic field;
- a first magnetic sensor configured to detect changes to the magnetic field induced by a first magnetic target arranged to be rotated by a motor shaft, the first magnetic target having a first number of features for inducing a change in the magnetic field;
- a second magnetic sensor configured to detect changes to the magnetic field induced by a second magnetic target arranged to be rotated by the motor shaft, the second magnetic target having a second number of features for inducing a change in the magnetic field;
- and
- a processing circuit in communication with the first magnetic sensor and the second magnetic sensor, the processing circuit configured to:
- detect a difference between measurements obtained by the first magnetic sensor and the second magnetic sensor;
- generate first shaft rotation angle information associated with a rotation angle of the motor shaft based on the detected differences between measurements obtained from the first magnetic sensor and the second magnetic sensor;
- and
- generate second rotation angle information relative to the first shaft rotation angle information based on a count of the first number of features of the first magnetic target measured by the first magnetic sensor or a count of the second number of features of the second magnetic target measured by the second magnetic sensor,
- wherein a difference between the first number of features and the second number of features is determined based on a number of pole pairs of the motor.
A method of monitoring a position of a shaft in an electronically commutated motor, the method comprising:
- obtaining, from a first magnetic sensor, a first magnetic field measurement associated with a rotation of the shaft, wherein the first magnetic field measurement is representative of changes induced by a first magnetic target in at least one magnetic field produced by at least one bias magnet, the first magnetic target having a first number of features for inducing a change in the magnetic field;
- obtaining, from a second magnetic sensor, a second magnetic field measurement associated with the rotation of the shaft, wherein the second magnetic field measurement is representative of changes induced by a second magnetic target in the at least one magnetic field produced by the at least one bias magnet, the second magnetic target having a second number of features for inducing a change in the magnetic field;
- generating, with a processing circuit, first shaft rotation angle information based on the first magnetic field measurement and the second magnetic field measurement;
- generate second rotation angle information relative to the first shaft rotation angle information based on a count of the first number of features of the first magnetic target measured by the first magnetic sensor or a count of the second number of features of the second magnetic target measured by the second magnetic sensor,
- wherein a difference between the first number of features and the second number of features is determined based on a number of pole pairs of the motor.
Dependencies are inferred from the claim text.