Rotation angle detection apparatus
A first third harmonic component removing portion calculates an approximate value (sin θ) n of a signal sin θ that is an output signal of a first magnetic sensor from which third harmonic components have been removed. A second third harmonic component removing portion calculates an approximate value (cos θ) n of a signal cos θ that is an output signal of a second magnetic sensor from which third harmonic components have been removed. A rotation angle calculation portion calculates a rotation angle θ of a rotor based on the approximate value (sin θ) n of sin θ, which has been calculated by the first third harmonic component removing portion and the approximate value (cos θ) n of cos θ, which has been calculated by the second third harmonic component removing portion.
1. A rotation angle detection apparatus, comprising:
a magnet that rotates as a rotor rotates, and that has multiple magnetic poles arranged in a circumferential direction of the magnet;
a first magnetic sensor that outputs, as the magnet rotates, a sinusoidal signal on which a third harmonic component is superimposed;
a second magnetic sensor that outputs, as the magnet rotates, a sinusoidal signal on which a third harmonic component is superimposed and of which a phase is different from a phase of the sinusoidal signal output from the first magnetic sensor;
a third harmonic component removing unit that corrects the sinusoidal signals output from the first magnetic sensor and the second magnetic sensor so as to remove the third harmonic components from the sinusoidal signals; and
a rotation angle calculating unit that calculates a rotation angle of the rotor based on the sinusoidal signals corrected by the third harmonic component removing unit, wherein
the third harmonic component removing unit comprises:
a unit that calculates a post-correction signal V 1 a of the sinusoidal signal output from the first magnetic sensor according to an equation a; and
a unit that calculates a post-correction signal V 2 a of the sinusoidal signal output from the second magnetic sensor according to an equation b,
V
1
a
=
V
1
·
1
1
+
4
K
1
-
K
·
(
1
-
V
1
b
2
)
(
a
)
V
2
a
=
V
2
·
1
1
+
4
K
1
-
K
·
(
1
-
V
2
b
2
)
(
b
)
wherein K is a third harmonic component gain that is larger than zero but smaller than 1 (0<K<1), V 1 is the sinusoidal signal output from the first magnetic sensor, V 1 a is the post-correction signal that is obtained by correcting the output signal V 1 using the third harmonic component removing unit, V 1 b is a pre-correction signal that is the output signal V 1 before correction, V 2 is the sinusoidal signal output from the second magnetic sensor, V 2 a is the post-correction signal that is obtained by correcting the output signal V 2 using the third harmonic component removing unit, and V 2 b is a pre-correction signal that is the output signal V 2 before correction.
2. The rotation angle detection apparatus according to claim 1 , wherein
the third harmonic component removing unit comprises:
a unit that calculates the post-correction signal V 1 a in a final calculation cycle, using the output signal V 1 as the pre-correction signal V 1 b in the equation a; and
a unit that calculates the post-correction signal V 2 a in the final calculation cycle, using the output signal V 2 as the pre-correction signal V 2 b in the equation b.
3. The rotation angle detection apparatus according to claim 1 , wherein
the third harmonic component removing unit comprises:
a unit that calculates the post correction signal V 1 a in a first calculation cycle, using the output signal V 1 as the pre-correction signal V 1 b in the equation a;
a unit that calculates the post-correction signal V 1 a in a final calculation cycle by executing, at least one time, a process in which the post-correction signals V 1 a in a second calculation cycle and calculation cycles following the second calculation cycle are each calculated using the post-correction signal V 1 a calculated in an immediately preceding calculation cycle as the pre-correction signal V 1 b in the equation a;
a unit that calculates the post-correction signal V 2 a in the first calculation cycle, using the output signal V 2 as the pre-correction signal V 2 b in the equation b; and
a unit that calculates the post-correction signal V 2 a in the final calculation cycle by executing, at least one time, a process in which the post-correction signals V 2 a in the second calculation cycle and the calculation cycles following the second calculation cycle are each calculated using the post-correction signal V 2 a calculated in an immediately preceding calculation cycle as the pre-correction signal V 2 b in the equation b.
4. The rotation angle detection apparatus according to claim 1 , wherein
if the rotation angle of the rotor is θ, the output signal V 1 is expressed by an equation c where θ represents the rotation angle of the rotor, and the output signal V 2 is expressed by an equation d where θ represents the rotation angle of the rotor, the equation a is an equation e obtained from the equation c, the equation b is an equation f obtained from the equation d, the pre-correction signal V 1 b corresponds to sin θ in a term (1−sin 2 θ) in a right side of the equation e, the post-correction signal V 1 a corresponds to sin θ in a left side of the equation e, the pre-correction signal V 2 b corresponds to case in a term (1−cos 2 θ) in a right side of the equation f, and the post-correction signal V 2 a corresponds to cos θ in a left side of the equation f
V
1
=
sin
θ
+
K
·
sin
3
θ
1
-
K
(
c
)
V
2
=
cos
θ
-
K
·
cos
3
θ
1
-
K
(
d
)
sin
θ
=
V
1
·
1
1
+
4
K
1
-
K
·
(
1
-
sin
2
θ
)
(
e
)
cos
θ
=
V
2
·
1
1
+
4
K
1
-
K
·
(
1
-
cos
2
θ
)
.
(
f
)
5. The rotation angle detection apparatus according to claim 2 , wherein
if the rotation angle of the rotor is θ, the output signal V 1 is expressed by an equation c where θ represents the rotation angle of the rotor, and the output signal V 2 is expressed by an equation d where θ represents the rotation angle of the rotor, the equation a is an equation e obtained from the equation c, the equation b is an equation f obtained from the equation d, the pre-correction signal V 1 b corresponds to sin θ in a term (1−sin 2 θ) in a right side of the equation e, the post-correction signal V 1 a corresponds to sin θ in a left side of the equation e, the pre-correction signal V 2 b corresponds to cos θ in a term (1−cos 2 θ) in a right side of the equation f, and the post-correction signal V 2 a corresponds to cos θ in a left side of the equation f
V
1
=
sin
θ
+
K
·
sin
3
θ
1
-
K
(
c
)
V
2
=
cos
θ
-
K
·
cos
3
θ
1
-
K
(
d
)
sin
θ
=
V
1
·
1
1
+
4
K
1
-
K
·
(
1
-
sin
2
θ
)
(
e
)
cos
θ
=
V
2
·
1
1
+
4
K
1
-
K
·
(
1
-
cos
2
θ
)
.
(
f
)
6. The rotation angle detection apparatus according to claim 3 , wherein
if the rotation angle of the rotor is θ, the output signal V 1 is expressed by an equation c where θ represents the rotation angle of the rotor, and the output signal V 2 is expressed by an equation d where θ represents the rotation angle of the rotor, the equation a is an equation e obtained from the equation c, the equation b is an equation f obtained from the equation d, the pre-correction signal V 1 b corresponds to sin θ in a term (1−sin 2 θ) in a right side of the equation e, the post-correction signal V 1 a corresponds to sin θ in a left side of the equation e, the pre-correction signal V 2 b corresponds to cos θ in a term (1−cos 2 θ) in a right side of the equation f, and the post-correction signal V 2 a corresponds to case in a left side of the equation f
V
1
=
sin
θ
+
K
·
sin
3
θ
1
-
K
(
c
)
V
2
=
cos
θ
-
K
·
cos
3
θ
1
-
K
(
d
)
sin
θ
=
V
1
·
1
1
+
4
K
1
-
K
·
(
1
-
sin
2
θ
)
(
e
)
cos
θ
=
V
2
·
1
1
+
4
K
1
-
K
·
(
1
-
cos
2
θ
)
.
(
f
)