Magnetic position sensor and position detecting method

1. A magnetic position sensor having an array in which a plurality of magnetic detection elements are arranged in a straight line, configured to detect a zero crossing point at which a magnetic flux density from a pair of magnetic poles is zero in a plane perpendicular to a longitudinal direction of the array, the magnetic detection elements being elements whose output changes in polarity when a direction of the magnetic flux density is inverted, the magnetic position sensor comprising:

the array;

an approximate detection unit for the zero crossing point configured to read only an output of every k-th magnetic detection element of the array (where k is an integer of 2 or greater), and detect an approximate position of the zero crossing point based on first detection of a magnetic detection element that has an output with a polarity different from that of an initial magnetic detection element in the reading of every k-th magnetic detection element; and

a position detection unit configured to read outputs of at least two magnetic detection elements to both sides of the zero crossing point and detect an accurate position of the zero crossing point according to the read outputs,

wherein the approximate detection unit comprises a memory, and wherein

the approximate detection unit is configured for repeatedly detecting the position of the zero crossing point and storing an approximate position of the zero crossing point in the memory when detecting the position of the zero crossing point, and

in a subsequent detection of a position of a zero crossing point, if the zero crossing point is present in a predetermined range from the approximate position of the zero crossing point stored in the memory, the detection of an approximate position of the zero crossing point is omitted and an accurate position of the zero crossing point is detected by the position detection unit, and

if the zero crossing point is not present in a predetermined range from the approximate position of the zero crossing point stored in the memory, an approximate position of the zero crossing point is detected by the approximate detection unit for the zero crossing point and an accurate position of the zero crossing point is detected by the position detection unit.

2. A magnetic position sensor having an array in which a plurality of magnetic detection elements are arranged in a straight line, configured to detect a zero crossing point at which a magnetic flux density from a pair of magnetic poles is zero in a plane perpendicular to a longitudinal direction of the array, the magnetic detection elements being elements whose output changes in polarity when a direction of the magnetic flux density is inverted, the magnetic position sensor comprising:

the array;

an approximate detection unit for the zero crossing point configured to read only an output of every k-th magnetic detection element of the array (where k is an integer of 2 or greater), and detect an approximate position of the zero crossing point based on first detection of a magnetic detection element that has an output with a polarity different from that of an initial magnetic detection element in the reading of every k-th magnetic detection element; and

a position detection unit configured to read outputs of at least two magnetic detection elements to both sides of the zero crossing point and detect an accurate position of the zero crossing point according to the read outputs,

wherein the magnetic position sensor is configured to stop scanning by the every k-th magnetic detection element and then scan the outputs of intermediate magnetic detection elements, when one of the plurality of magnetic detection elements that has a polarity that is opposite from a previous one of the plurality of magnetic detection elements is detected, and wherein the intermediate magnetic detection elements are between the one of the plurality of magnetic detection elements and the previous magnetic detection element.

3. The magnetic position sensor according to claim 2 , further comprising:

a nonvolatile memory in which correction data is stored, the correction data being data acquired in an environment in which there are no magnetic poles that serve as detection targets and used in correcting an output of each magnetic detection element of the array; and

a correction unit configured to correct the output of the magnetic detection element according to the correction data stored in the nonvolatile memory.

4. The magnetic position sensor according to claim 2 ,

wherein the approximate detection unit for the zero crossing point is configured to detect an approximate position of the zero crossing point, by reading an output of every k-th magnetic detection element in one direction along the straight line and reading an output of the magnetic detection element that detects the downstream magnetic pole of the pair of magnetic poles.

5. The magnetic position sensor according to claim 4 ,

wherein the magnetic detection elements of the array are arranged so that k×a is equal to or smaller than the length of one magnetic pole, where “a” is a pitch of the magnetic detection element.

6. The magnetic position sensor according to claim 5 , wherein

the approximate detection unit for the zero crossing point is configured, upon said first detection of a magnetic detection element that has an output with a different polarity, to obtain outputs of at least two magnetic detection elements to both sides of the zero crossing point by reading outputs of k−1 magnetic detection elements arranged upstream of the detected magnetic detection element.

7. The magnetic position sensor according to claim 6 ,

wherein the position detection unit is configured to obtain the position of the zero crossing point by

P=−α 1/(α1+α2)× a+P 1

or

P=α 2/(α1+α2)× a+P 2,

where α1 is an absolute value of an output of one magnetic detection element that is arranged upstream in a reading direction out of the magnetic detection elements to both sides of the zero crossing point, P1 is a position of the upstream magnetic detection element in the array, α2 is an absolute value of an output of another magnetic detection element that is arranged downstream in the reading direction out of the magnetic detection elements to both sides of the zero crossing point, and P2 is a position of the downstream magnetic detection element in the array, and coordinates increase to the upstream side in the reading direction and decrease to the downstream side in the reading direction.

8. The magnetic position sensor according to claim 2 , further comprising a mobile object,

wherein the magnetic position sensor is mounted on the mobile object, and wherein the pair of magnetic poles serve as a detection target.