Brushless motor device

1. An n-phase brushless motor device (n is a positive integer) comprising:

a stator placed at a fixed position;

a rotor which rotates when said stator is excited sequentially according to a plurality of excitation patterns, said rotor having a predetermined number of poles;

a magnet for magnetic pole position detection fixed to a face perpendicular to a rotation axis of said rotor, said magnet having a number of poles which is twice as many as that of said rotor;

n main Hall elements arranged opposite to said magnet for magnetic pole position detection, for detecting a magnetic pole position of said rotor;

n sub Hall elements arranged opposite to said magnet for magnetic pole position detection in such a way as to have a predetermined offset in a direction of a periphery with respect to said main Hall elements, for detecting the magnetic pole position of said rotor;

a main counting unit that calculates an actual position “A” of the rotor; and

a sub counting unit that counts a value of “2” in response to a detected change in an output pattern of said main Hall elements as compared to an output pattern of said sub Hall elements, where counting a value of “2” is accomplished by setting the actual rotor position to 2A;

where the sub counting unit further counts a value of “1” in response to a detection of the output pattern of said main Hall elements being the same as the output pattern of said sub Hall elements at a predetermined timing, where counting a value of “1” is accomplished, by setting the actual rotor position to 2A+1; and

a control unit for controlling a rotation of said rotor according to the value counted by said sub counting unit.

2. The brushless motor device according to claim 1 , wherein the offset of the sub Hall elements with respect to the main Hall elements is one-twelfth of a mechanical angle formed by a pair of an S pole and an N pole of the magnet for magnetic pole position detection.

3. The brushless motor device according to claim 2 , where n is “3”, the number of poles of the rotor is “12”, and the offset of the sub Hall elements with respect to the main Hall elements is a mechanical angle of “2.5 degrees”.

4. The brushless motor device according to claim 1 , where the main counting unit performs the counting in response to rising and falling edges of an output signal of the main Hall elements, and the sub counting unit performs the counting at predetermined time intervals.

5. An n-phase brushless motor device (n is a positive integer) comprising:

a stator placed at a fixed position;

a rotor which rotates when said stator is excited sequentially according to a plurality of excitation patterns, said rotor having a predetermined number of poles;

a magnet for magnetic pole position detection formed surrounding a rotation axis of said rotor or fixed to a face perpendicular to the rotation axis of said rotor, said magnet having a same number of poles as that of said rotor;

n main Hall elements arranged opposite to said magnet for magnetic pole position detection, for detecting a magnetic pole position of said rotor;

n sub Hall elements arranged opposite to said magnet for magnetic pole position detection in such a way as to have a predetermined offset in a direction of a periphery with respect to said main Hall elements, for detecting the magnetic pole position of said rotor;

a main counting unit that calculates an actual position “A” of the rotor; and

a sub counting unit that counts a value of “2” in response to a detected change in an output pattern of said main Hall elements as compared to an output pattern of said sub Hall elements, where counting a value of “2” is accomplished by setting the actual rotor position to 2A.

where the sub counting unit further counts a value of “1” in response to a detection of the output pattern of said main Hall elements being the same as the output pattern of said sub Hall elements at a predetermined timing, where counting a value of “1” is accomplished by setting the actual rotor position to 2A+1; and

a control unit for controlling a rotation of said rotor according to the value counted by said sub counting unit.

6. A method of controlling an n-phase brushless motor device, where n is a positive integer, the method comprising:

providing a stator at a fixed position;

rotating a rotor when said stator is excited sequentially according to a plurality of excitation patterns, said rotor having a predetermined number of poles;

detecting a magnetic pole position of said rotor by

providing a magnet fixed to a face perpendicular to a rotation axis of said rotor, said magnet having at least the predetermined number of poles;

providing n main Hall elements arranged opposite to said magnet; and

providing n sub Hall elements arranged opposite to said magnet in such a way as to have a predetermined offset in a direction of a periphery with respect to said main Hall elements;

first counting a value of “2” in response to a detected change in an output pattern of said main Hall elements as compared to an output pattern of said sub Hall elements, where counting a value of “2” is accomplished by, for an initial actual rotor position of A, setting the actual rotor position to 2A;

second counting a value of “1” in response to a detection of the output pattern of said main Hall elements being the same as the output pattern of said sub Hall elements at a predetermined timing, where counting a value of “1” is accomplished by further incrementing the actual rotor position to 2A+1; and

controlling a rotation of said rotor according to the first counted value or the second counted value.

7. The method of claim 6 , where the magnet has twice the predetermined number of poles.