Method and apparatus for detecting rotor position by use of magnetic field sensor pairs
First Claim
1. A method for determining the rotational position of a rotor which is rotatable about an axis of rotation wherein the rotor carries a magnetic source which creates a rotationally non-symmetrical magnetic field relative to the axis of rotation, said magnetic source having two magnetic poles, and for reducing the influence of external magnetic fields and of sensitivity and offset variations of sensor means on the accuracy of the determination of rotational position, the method comprising:
- providing stationary sensor means in the form of at least three sensors arranged in at least two sensor pairs so that the sensors of each sensor pair are sensitive to substantially parallel components of the magnetic field and wherein connecting lines, each connecting two sensors of one sensor pair, have projections lying in a plane perpendicular to the axis of rotation, the connecting lines lying at an angle relative to each other, the sensor means positioned at a distance from the volume between the two magnetic poles, further characterized in that the sensors of the sensor means each sense the field strength in a specific direction in a specific sensor position, measuring local components of the magnetic field using stationary sensor means, calculating differences between the quantities measured by the two sensors of each sensor pair and at least one ratio of the differences of two pairs, and determining the rotational position of the rotor by comparing the at least one ratio measured by the sensor means with a predetermined function of the field component versus the rotation position of the rotor.
2 Assignments
0 Petitions
Accused Products
Abstract
The rotation position of a rotor (2) rotatable around a rotation axis (1) is determined by mounting a magnetic source (2.1) on the rotor, by providing on a stator (3) at least three sensors (4, 5, 6, 7) for measuring the magnetic field of the magnetic source and being arranged in at least two pairs (4/5, 6/7), calculating the difference of quantities measured by the two sensors of each sensor pair, calculating the ratio of the difference values of two pairs and comparing the ratio with a predetermined function of said ratio versus the rotation position. This rotation position determination is very robust against offset and sensitivity variations common to all sensors (4, 5, 6, 7) and against external magnetic fields and can easily be made robust against mechanical tolerances between rotating and stationary parts also. In a preferred embodiment, there are four sensors (4, 5, 6, 7) arranged at the corners of a square perpendicular to and symmetrical relative to the rotation axis (1). The sensors (4, 5, 6, 7) are advantageously Hall sensors integrated together with readout and calculation electronics in one die.
-
Citations
15 Claims
-
1. A method for determining the rotational position of a rotor which is rotatable about an axis of rotation wherein the rotor carries a magnetic source which creates a rotationally non-symmetrical magnetic field relative to the axis of rotation, said magnetic source having two magnetic poles, and for reducing the influence of external magnetic fields and of sensitivity and offset variations of sensor means on the accuracy of the determination of rotational position, the method comprising:
-
providing stationary sensor means in the form of at least three sensors arranged in at least two sensor pairs so that the sensors of each sensor pair are sensitive to substantially parallel components of the magnetic field and wherein connecting lines, each connecting two sensors of one sensor pair, have projections lying in a plane perpendicular to the axis of rotation, the connecting lines lying at an angle relative to each other, the sensor means positioned at a distance from the volume between the two magnetic poles, further characterized in that the sensors of the sensor means each sense the field strength in a specific direction in a specific sensor position, measuring local components of the magnetic field using stationary sensor means, calculating differences between the quantities measured by the two sensors of each sensor pair and at least one ratio of the differences of two pairs, and determining the rotational position of the rotor by comparing the at least one ratio measured by the sensor means with a predetermined function of the field component versus the rotation position of the rotor. - View Dependent Claims (2, 3, 4, 5)
-
-
6. An apparatus for determining the rotational position of a rotor rotatable about an axis of rotation comprising
a magnetic source mounted on said rotor, the magnetic source having two magnetic poles; -
a stator;
sensor means carried by said stator for measuring a magnetic field created by said magnetic source, said sensor means comprising at least three sensors in at least two sensor pairs so that sensors of each pair are sensitive to substantially parallel components of said magnetic field, and wherein lines connecting each two sensors of each pair lie in a plane perpendicular to said axis of rotation and at angles to each other, said sensor means positioned at a distance from the volume between the two magnetic poles, further characterized in that the sensors in the sensor means each sense the field strength in a specific direction in a specific sensor position; and
means for calculating the differences between signals of said two sensors of each pair and for calculating a ratio of the differences for said at least two sensor pairs to determine said rotational position. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15)
-
Specification