Rotation detector

Abstract

The present invention suppresses the occurrence of erroneous detection by a rotation detector. A rotation detector (1) comprises: a magnet (10) that rotates about a prescribed axis; a power generation circuit (50) that includes a power generation element (20) which utilizes a large Barkhausen effect to generate power, a voltage detection unit (31) that detects the voltage generated by the power generation element (20), and a power storage unit (32) that stores the power generated by the power generation element (20); a rotation position detection unit (60) that has a magnetic sensor (61) provided corresponding to the power generation element (20) and an information processor (62) that determines the rotation position of an axis of rotation; a power supply unit (70) that supplies the power generated by the power generation element (20) to the magnetic sensor (61); and a control circuit (80). The control circuit (80) controls the supply of power, generated by the power generation element (20), from the power supply unit (70) to the magnetic sensor (61), such control being performed on the basis of the voltage generated by the power generation element (20), a first voltage threshold value, and a second voltage threshold value.

Description

Rotation detector

[0001] The present disclosure relates to a rotation detector.

[0002] Conventionally, there is known a rotation detector that detects the rotation of a rotating shaft of a motor. Another known rotation detector is one that detects rotation using power supplied from a power generating circuit that generates power using changes in the magnetic field of a magnet attached to the rotating shaft when there is no power supply from a battery or an external power source (for example, see Patent Document 1).

[0003] Japanese Patent No. 6610697

[0004] However, in a rotation detector that detects rotation using power supplied from a power generation circuit, such as the rotation detector disclosed in Patent Document 1, there is a problem that if the voltage generated in the power generation circuit does not reach the operating voltage of the rotation detector, the power generated by the power generation circuit is not properly supplied to the circuit that detects rotation, resulting in erroneous detection.

[0005] The present disclosure has been made to solve such problems, and has an object to provide a rotation detector that can suppress the occurrence of erroneous detection.

[0006] A rotation detector according to one aspect of the present disclosure includes a magnet, a first power generating circuit, a first rotational position detection unit, and a power supply unit. The magnet rotates around a predetermined axis. The first power generating circuit includes a first power generating element, a voltage detection unit, and a power storage unit. The first power generating element generates power by utilizing the Great Barkhausen effect, which occurs when a magnetic field changes due to the rotation of the magnet around the predetermined axis. The voltage detection unit detects the voltage generated by the first power generating element. The power storage unit stores the first power generated by the first power generating element. The first rotational position detection unit includes a first magnetic sensor and a first information processing unit. The first magnetic sensor detects a magnetic field generated by the magnet and is provided corresponding to the first power generating element. The first information processing unit determines the rotational position of the rotation shaft based on the detection result of the first magnetic sensor. The power supply unit supplies the first power to the first magnetic sensor. The control circuit controls the supply of the first power by the power supply unit. Further, the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, a first voltage threshold for detecting the voltage, and a second voltage threshold for detecting the voltage that is greater than the first voltage threshold.

[0007] According to the present disclosure, it is possible to provide a rotation detector that can suppress the occurrence of false detection.

[0008] FIG. 1 is a cross-sectional view showing a schematic configuration of a rotation detector according to an embodiment. FIG. 2 is a top view of a substrate in the rotation detector according to an embodiment. FIG. 3 is a top view of a rotating plate in the rotation detector according to an embodiment. FIG. 4 is a diagram showing a circuit configuration of the rotation detector according to an embodiment. FIG. 5 is a timing chart showing a specific example of the operation of the rotation detector according to an embodiment. FIG. 6 is a diagram for explaining the relationship between a voltage generated by a power generating element and a voltage threshold value according to an embodiment. FIG. 7 is another diagram for explaining the relationship between a voltage generated by a power generating element and a voltage threshold value according to an embodiment. FIG. 8 is a diagram showing an example of a waveform of a voltage generated by a power generating element according to an embodiment. FIG. 9 is a diagram for explaining a case where a voltage detecting unit according to an embodiment has three or more voltage threshold values. FIG. 10 is another diagram for explaining a case where a voltage detecting unit according to an embodiment has three or more voltage threshold values. FIG. 11 is a diagram showing a circuit configuration of a rotation detector according to a modified embodiment. FIG. 12 is a diagram for explaining the relationship between the capacity of a power storage unit and a voltage waveform according to a modified embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, component placement positions, connection forms, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Therefore, among the components in the following embodiments, components that are not recited in the independent claims of the present disclosure will be described as optional components.

[0010] Note that each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, the scales and the like do not necessarily match in each figure. Furthermore, in each figure, the same reference numerals are used for substantially the same configurations, and redundant explanations will be omitted or simplified.

[0011] Furthermore, in this specification, terms indicating the relationship between elements, such as orthogonal and parallel, terms indicating the shape of elements, such as rectangle, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0012] Furthermore, the terms "up" and "down" in the following description of the rotation detector according to the present disclosure do not refer to the upward direction (vertically upward) and downward direction (vertically downward) in absolute spatial recognition, but are directions determined by relative positional relationships, and do not limit the orientation of the rotation detector according to the present disclosure during manufacture or use.

[0013] (Embodiment) A rotation detector according to this embodiment will be described below.

[0014] [Configuration] First, the configuration of the rotation detector according to this embodiment will be described. FIG. 1 is a cross-sectional view showing a schematic configuration of the rotation detector 1 according to this embodiment. FIG. 2 is a top view of the substrate 17 in the rotation detector 1 according to this embodiment. FIG. 3 is a top view of the rotating plate 15 in the rotation detector 1 according to this embodiment. FIG. 4 is a diagram showing the circuit configuration of the rotation detector 1 according to this embodiment. Note that in FIG. 1, the magnetic member 21 and coil 22 housed in the housing 23 of the power generating element 20 are schematically shown by dashed lines. Also, in FIG. 2, the outlines of the magnet 10, rotating shaft 16, and magnetic sensor 61 arranged below the substrate 17 are shown by dashed lines. Also, in FIG. 3, the outline of the rotating shaft 16 arranged below the rotating plate 15 is shown by dashed lines. Also, in FIG. 4, some components are shown by functional blocks.

[0015] 1 to 4 , the rotation detector 1 includes a magnet 10, a rotating plate 15, a substrate 17, a plurality of power generation circuits 50, a plurality of rotational position detection units 60, a power supply unit 70, a control circuit 80, a plurality of backflow prevention circuits 81 a, 81 b, and an oscillator (OSC) 90. Each of the plurality of power generation circuits 50 includes a power generation element 20, a voltage detection unit 31, a power storage unit 32, a rectifier 33, and a discharge unit 34. Each of the plurality of rotational position detection units 60 includes a magnetic sensor 61 and an information processing unit 62.

[0016] The rotation detector 1 is used in combination with a motor such as a servo motor. The rotation detector 1 is provided at one end of a rotation shaft 16 of the motor or the like in the rotation axis direction. The rotation axis direction is the direction in which a rotation axis A of the rotation shaft 16 extends. The rotation shaft 16 rotates around a predetermined rotation axis A. The rotation detector 1 detects, for example, the rotation position of the rotation shaft 16. The rotation detector 1 may detect the rotation direction of the rotation shaft 16 or the number of rotations of the rotation shaft 16. The shape of the rotation shaft 16 is a rod-like shape, such as a cylindrical shape, extending in the rotation axis direction. The axis center of the rotation shaft 16 and the rotation axis A are aligned. Note that the rotation shaft 16 is not limited to the shaft of a motor, but may also be the rotation shaft of a rotating body connected to the motor shaft by a gear or the like. Furthermore, the rotation shaft 16 is not limited to the motor, but may also be the rotation shaft of a rotating mechanism that rotates around an axis, such as the axle of a wheel of an automobile or train.

[0017] First, the structure of the rotation detector 1 will be described with reference to FIGS.

[0018] The rotating plate 15 is a plate-shaped member that rotates together with the rotating shaft 16. A central portion of one main surface of the rotating plate 15 is attached to an end of the rotating shaft 16 in the rotational axis direction of the rotating shaft 16 (the direction in which the rotating shaft 16 extends). The rotating plate 15 extends in a direction perpendicular to the rotational axis direction of the rotating shaft 16. The rotating plate 15 rotates around a rotation axis A that passes through the center of the rotating shaft 16 and extends along the axial direction of the rotating shaft 16. The shape of the rotating plate 15 in a plan view is, for example, circular. The rotating plate 15 is made of, for example, metal, resin, glass, ceramic, or the like.

[0019] The magnet 10 applies a magnetic field to the power generating element 20 and the magnetic sensor 61. The magnet 10 is, for example, a plate-shaped magnet. The magnet 10 faces the rotating plate 15 and the substrate 17 and is located on the main surface of the rotating plate 15 opposite the rotation axis 16. The thickness direction of the rotating plate 15 and the thickness direction of the magnet 10 are the same and are in the direction of the rotation axis of the rotation axis 16. The magnet 10 is fixed to the rotation axis 16 via the rotating plate 15 and rotates together with the rotating plate 15 around the rotation axis A of the rotation axis 16. The magnet 10 may be fixed to the rotation axis 16 by a member other than the rotating plate 15. The rotation direction of the magnet 10 is, for example, both clockwise and counterclockwise, but may be only one of clockwise and counterclockwise. The rotation direction of the magnet 10 is also along the circumference of a circle centered on the rotation axis A. The planar shape of the magnet 10 is a circle with an open center, but may be another shape such as a rectangle. Furthermore, the magnet 10 does not have to have an opening. Furthermore, the magnet 10 may be a magnet of another shape, such as a rod-shaped magnet, as long as it can change the magnetic field applied to the power generation element 20 and the magnetic sensor 61. Furthermore, there may be more than one magnet 10.

[0020] Magnet 10 has a plurality of pairs of magnetic poles magnetized in the thickness direction, and the plurality of pairs of magnetic poles are aligned in the rotation direction of magnet 10. Figure 3 shows the magnetic poles on main surface 11, which is the surface of magnet 10 facing power generating element 20. Each pair of magnetic poles is magnetized so that the north pole and south pole are reversed relative to the adjacent pair of magnetic poles in the rotation direction of magnet 10. The direction in which magnet 10 is magnetized is not particularly limited, and for example, magnet 10 may be magnetized in a direction parallel to rotating plate 15. Also, in Figure 3, a halftone dot pattern is applied to the north pole, but this is for ease of viewing and does not mean that a halftone dot pattern is actually applied.

[0021] In magnet 10, multiple magnetic poles are aligned in the direction of rotation on main surface 11 of magnet 10 facing power generating element 20. The multiple magnetic poles include at least one north pole and at least one south pole, and the north poles and south poles are aligned alternately in the direction of rotation. Among the multiple magnetic poles of magnet 10, the number of north poles and the number of south poles are the same.

[0022] The multiple magnetic poles are arranged so that the north pole and south pole face each other across the rotation axis A of the rotating shaft 16. That is, the north pole of the multiple magnetic poles faces the south pole across the rotation axis A, and the south pole of the multiple magnetic poles faces the north pole across the rotation axis A. In the example shown in FIG. 3 , there are two multiple magnetic poles, including one north pole and one south pole. In the multiple magnetic poles, the south pole is located 180 degrees offset from the north pole in the direction of rotation of the magnet 10, and the north pole is located 180 degrees offset from the south pole. When viewed from the direction of the rotation axis of the rotating shaft 16, the size of each magnetic pole of the multiple magnetic poles is equal. As the magnet 10 rotates, the magnetic field applied to the power generating element 20 and the magnetic sensor 61 changes. Furthermore, the position of each magnetic pole corresponds to the rotation position of the rotating shaft 16. The number of multiple magnetic poles is not particularly limited and may be four, six, or more.

[0023] The substrate 17 is positioned on the magnet 10 side of the rotating plate 15 so as to face the rotating plate 15 and the magnet 10 with a gap therebetween. That is, the rotating shaft 16, rotating plate 15, magnet 10, and substrate 17 are arranged in this order along the rotational axis direction of the rotating shaft 16. The substrate 17 does not rotate together with the magnet 10 and rotating plate 15. The substrate 17 is plate-shaped with its thickness direction aligned with the rotational axis direction of the rotating shaft 16. The shape of the substrate 17 in a plan view is, for example, circular. For example, when viewed from the rotational axis direction of the rotating shaft 16, the centers of the rotating shaft 16, rotating plate 15, and substrate 17 are aligned and located at the rotational axis A. The substrate 17 is fixed to, for example, a case (not shown) that constitutes part of the rotation detector 1, a motor, or the like.

[0024] The substrate 17 is, for example, a wiring board, and has electronic components such as the power generating element 20 and the magnetic sensor 61 mounted thereon. In the example shown in Figures 1 and 2, the magnetic sensor 61 is mounted on the main surface of the substrate 17 facing the magnet 10, and the power generating element 20 is mounted on the main surface of the substrate 17 opposite the magnet 10. Although not shown in Figure 1, components other than the magnet 10 in the rotation detector 1 shown in Figure 4 may also be provided on the substrate 17.

[0025] The power generating element 20 generates power by changing the magnetic field formed by the magnet 10 as the magnet 10 rotates, specifically by reversing the direction of the magnetic field, and outputs the generated power. The power generating element 20 generates power by utilizing the large Barkhausen effect, which occurs due to the change in the magnetic field caused by the rotation of the magnet 10 together with the rotation shaft 16.

[0026] The power generating element 20 is located on the main surface of the substrate 17 opposite to the magnet 10 side. The power generating element 20 is aligned with the magnet 10 and the rotating plate 15 along the rotational axis direction of the rotating shaft 16. The power generating element 20 does not rotate together with the magnet 10 and the rotating plate 15. Note that the power generating element 20 may also be located on the main surface of the substrate 17 facing the magnet 10.

[0027] The power generating element 20 is disposed so as to face the magnet 10 and the rotating plate 15 in the rotational axis direction of the rotating shaft 16. When viewed from the rotational axis direction of the rotating shaft 16, the power generating element 20 is disposed at a position that does not overlap with the rotational axis A but is offset from the rotational axis A. When viewed from the rotational axis direction of the rotating shaft 16, the power generating element 20 overlaps with a position through which the magnet 10 passes when it rotates. The power generating element 20 also extends along the main surface of the substrate 17 so as to extend in a tangential direction to the rotational direction of the magnet 10. The longitudinal direction of the magnetic member 21 and the winding axis direction of the coil 22 in the power generating element 20 are the extension direction of the power generating element 20. The power generating element 20 may also extend radially of a circle centered on the rotational axis A.

[0028] The power generating element 20 includes, for example, a magnetic member 21 , a coil 22 wound around the magnetic member 21 , a housing 23 , and terminals 24 and 25 .

[0029] The magnetic member 21 is a magnetic material that generates a large Barkhausen effect. The magnetic member 21 is, for example, a wire-like member extending tangentially to the rotation direction of the magnet 10. A specific example of the magnetic member 21 is a Wiegand wire. A Wiegand wire is a magnetic material whose magnetization direction aligns to one side of the longitudinal direction when a magnetic field of a predetermined value or greater is applied along the longitudinal direction of the Wiegand wire. Specifically, the Wiegand wire includes a soft magnetic portion and a hard magnetic portion extending along the longitudinal direction. When the direction of the magnetic flux flowing along the longitudinal direction of the Wiegand wire changes, the magnetization direction of the soft magnetic portion of the Wiegand wire suddenly reverses, inducing a pulse-like voltage (voltage pulse) across both ends of the coil 22 wound around the Wiegand wire. In this way, the power generating element 20 generates electricity, outputting a voltage higher than that of conventional induction power generation. The magnetic member 21 is not particularly limited as long as it generates a large Barkhausen effect, and may be a magnetic material other than Wiegand wire.

[0030] The housing 23 houses and supports the magnetic member 21 and the coil 22. The magnetic member 21 and the coil 22 are, for example, embedded in a resin or the like within the housing 23. The housing 23 also houses a portion of the terminals 24, 25. The housing 23 is, for example, open on the magnet 10 side of the power generating element 20. The housing 23 is fixed to the substrate 17 by, for example, a fixing member or the like (not shown). Although not shown, the housing 23 may house soft magnetic members such as ferrite beads that are arranged on both ends of the magnetic member 21.

[0031] Terminals 24 and 25 are members for electrically connecting the power generating element 20 and the substrate 17. Terminals 24 and 25 are located at the end of the power generating element 20 on the substrate 17 side. A magnet 10 is disposed on the terminal 24, 25 side of the power generating element 20. Terminal 24 is electrically connected to one end of the conductor that constitutes the coil 22, and terminal 25 is electrically connected to the other end of the conductor. In other words, the coil 22 and the substrate 17 are electrically connected via terminals 24 and 25.

[0032] The magnetic sensor 61 detects the magnetic field generated by the magnet 10. The magnetic sensor 61 is, for example, a magnetoresistive element (a TMR (Tunnel Magneto Resistive) element) sensor or a Hall element sensor.

[0033] The magnetic sensor 61 is located on the main surface of the substrate 17 facing the magnet 10. The magnetic sensor 61 is aligned with the magnet 10 and the rotating plate 15 along the rotational axis direction of the rotating shaft 16. The magnetic sensor 61 does not rotate together with the magnet 10 and the rotating plate 15. Note that the magnetic sensor 61 may also be located on the main surface of the substrate 17 opposite to the magnet 10 side.

[0034] The magnetic sensor 61 is provided so as to face the magnet 10 and the rotating plate 15 in the direction of the rotation axis of the rotating shaft 16. When viewed from the direction of the rotation axis of the rotating shaft 16, the magnetic sensor 61 is not overlapped with the rotation axis A, but is arranged at a position offset from the rotation axis A. When viewed from the direction of the rotation axis of the rotating shaft 16, the magnetic sensor 61 overlaps with a position through which the magnet 10 passes as it rotates.

[0035] In this embodiment, the rotation detector 1 includes multiple power generating circuits 50 and multiple rotational position detection units 60, and therefore multiple power generating elements 20 and magnetic sensors 61 are also provided. In the example shown in FIGS. 1 to 4 , the number of power generating circuits 50 and rotational position detection units 60 is two, but the number may be one or three or more. In the following, to distinguish between the multiple power generating circuits 50, the power generating circuits 50 and the power generating elements 20 included in the power generating circuits 50 may be referred to as power generating circuits 50a and 50b, and power generating elements 20a and 20b. The power generating circuit 50a is an example of a first power generating circuit, and the power generating circuit 50b is an example of a second power generating circuit connected in parallel to the first power generating circuit. The power generating element 20a is an example of a first power generating element, and the power generating element 20b is an example of a second power generating element. Furthermore, in order to distinguish between the multiple rotational position detection units 60, the rotational position detection units 60 and the magnetic sensors 61 included in the rotational position detection units 60 may be referred to as rotational position detection units 60a and 60b, and magnetic sensors 61a and 61b. The rotational position detection unit 60a is an example of a first rotational position detection unit, and the rotational position detection unit 60b is an example of a second rotational position detection unit. The magnetic sensor 61a is an example of a first magnetic sensor, and the magnetic sensor 61b is an example of a second magnetic sensor.

[0036] The multiple magnetic sensors 61 are provided corresponding to the multiple power generating elements 20, respectively. Specifically, the magnetic sensor 61a is provided corresponding to the power generating element 20a and operates based on the power generated by the power generating element 20a. The magnetic sensor 61b is provided corresponding to the power generating element 20b and operates based on the power generated by the power generating element 20b. The power generated by the power generating element 20a is an example of a first power, and the power generated by the power generating element 20b is an example of a second power.

[0037] The multiple power generating elements 20 are aligned along the rotation direction of the magnet 10, and are arranged so that adjacent power generating elements 20 in the aligned direction form a predetermined angle around the rotation axis A. Similarly, the multiple magnetic sensors 61 are aligned along the rotation direction of the magnet 10, and are arranged so that adjacent magnetic sensors 61 in the aligned direction form a predetermined angle around the rotation axis A. The predetermined angle is not particularly limited. Furthermore, when viewed from the rotation axis direction of the rotation shaft 16, the corresponding power generating elements 20 and magnetic sensors 61 are aligned along the radial direction of a circle centered on the rotation axis A (the direction in which the dashed dotted line in FIG. 2 extends). In the example shown in FIG. 2, the magnetic sensor 61 is arranged outside the power generating element 20. Note that the magnetic sensor 61 may be arranged between the power generating element 20 and the rotation axis A, or may be arranged so that the rotation axis A is located between the magnetic sensor 61 and the power generating element 20. Furthermore, the power generating element 20 and the magnetic sensor 61 provided correspondingly may be aligned along the rotation direction of the magnet 10 when viewed from the rotation axis direction of the rotating shaft 16 .

[0038] Next, the functional configuration of the rotation detector 1 will be described in detail with reference to FIG.

[0039] The power generation circuits 50 have the same functional configuration as each other, and each includes a power generation element 20, a voltage detection unit 31, a power storage unit 32, a rectifier 33, and a discharge unit 34. The power generation circuits 50 are connected in parallel with each other. The power generation circuits 50 supply the power generated by the power generation elements 20 to the power supply unit 70.

[0040] As described above, the power generating element 20 generates power based on the change in the magnetic field caused by the rotation of the magnet 10 .

[0041] The voltage detection unit 31 detects the voltage generated by the power generation element 20. Specifically, the voltage detection unit 31 detects the voltage generated by the power generation element 20 between the rectifier 33 and the power storage unit 32. As shown in FIG. 4 , the voltage detected by the voltage detection unit 31 is the voltage VWC1 or the voltage VWC2 corresponding to the power stored in the power storage unit 32. Hereinafter, when content that applies to both the power generation circuit 50a and the power generation circuit 50b is described without distinguishing between them, the voltage VWC1 and the voltage VWC2 may be simply referred to as the "voltage VWC."

[0042] The voltage detection unit 31 has a plurality of voltage thresholds for detecting the voltage VWC generated by the power generation element 20. The voltage thresholds will be described in detail later, but the voltage detection unit 31 has at least a first voltage threshold and a second voltage threshold that is greater than the first voltage threshold as the plurality of voltage thresholds. The voltage detection unit 31 is configured, for example, with a comparator corresponding to each voltage threshold. That is, in this example, having a voltage threshold means having a comparator that compares the voltage VWC with the voltage threshold. The voltage detection unit 31 outputs the voltage detection result to the control circuit 80. For example, when the voltage VWC input to the comparator exceeds a voltage threshold, the voltage detection unit 31 outputs a signal indicating that the voltage threshold has been exceeded.

[0043] The power storage unit 32 stores the power (in other words, charge) generated by the power generating element 20. The power storage unit 32 is composed of a capacitance element. One end of the power storage unit 32 is connected to the output of the rectifier 33, and the other end of the power storage unit 32 is connected to ground.

[0044] The rectifier 33 is connected to the power generating element 20 and performs full-wave rectification of the current generated by the power generating element 20. The current rectified by the rectifier 33 stores power in the power storage unit 32.

[0045] The discharge unit 34 discharges the power stored in the power storage unit 32. The discharge unit 34 is configured, for example, with a switch that discharges the power stored in the power storage unit 32 by short-circuiting the power storage unit 32 and the ground.

[0046] The plurality of rotational position detection units 60 have the same functional configuration, and each includes a magnetic sensor 61 and an information processing unit 62 .

[0047] As described above, the magnetic sensor 61 detects the magnetic field generated by the magnet 10 .

[0048] The information processing unit 62 is a processing circuit that performs rotational position detection processing. The information processing unit 62 of the rotational position detection unit 60a is an example of a first information processing unit, and the information processing unit 62 of the rotational position detection unit 60b is an example of a second information processing unit. The information processing unit 62 determines the rotational position of the rotating shaft 16 based on the detection result of the magnetic sensor 61. The information processing unit 62 is realized, for example, by a memory, a processor, etc. The information processing unit 62 may also be realized by a logic circuit dedicated to performing rotational position detection processing. For example, the information processing unit 62 determines the polarity of the magnet 10 that applies a magnetic field to the magnetic sensor 61 and stores the determined result in memory as rotational position information. Note that multiple rotational position detection units 60 may share the information processing unit 62.

[0049] The power supply unit 70 supplies power generated by the power generating element 20 to the rotational position detection unit 60. The power supply unit 70 supplies power to at least the magnetic sensor 61. The power supply unit 70 may also supply power to the information processing unit 62. The power supply unit 70 is connected to the power storage unit 32 of the power generation circuit 50a via a backflow prevention circuit 81a and to the power storage unit 32 of the power generation circuit 50b via a backflow prevention circuit 81b. The power supply unit 70 uses the ground potential as a reference potential and the voltage between the terminals of the capacitive element of the power storage unit 32 as an input voltage, and outputs a constant voltage VLDO. The voltage VLDO output from the power supply unit 70 is supplied to, for example, the magnetic sensor 61 and the information processing unit 62 of the rotational position detection unit 60. The power supply unit 70 is, for example, an LDO (Low Drop Out) regulator.

[0050] The control circuit 80 is a processing circuit that controls the operation of the rotation detector 1. The control circuit 80 performs processing to control the supply of power generated by the power generating element 20 from the power supply unit 70 to the magnetic sensor 61 based on the voltage VWC generated by the power generating element 20, a first voltage threshold, and a second voltage threshold. The control circuit 80 controls the supply of power generated by the power generating element 20 from the power supply unit 70 to the magnetic sensor 61, for example, by controlling whether or not to discharge the power stored in the power storage unit 32 by the discharge unit 34 based on the voltage VWC generated by the power generating element 20, the first voltage threshold, and the second voltage threshold. The control circuit 80 also determines whether or not to supply the power generated by the power generating element 20 from the power supply unit 70 to the magnetic sensor 61 based on, for example, the detection result of the voltage VWC by the voltage detection unit 31 using the first voltage threshold and the detection result of the voltage detection unit 31 using the second voltage threshold.

[0051] The control circuit 80 may also control the on / off of the multiple backflow prevention circuits 81 a, 81 b based on the voltage detection results of the respective voltage detection units 31 of the multiple power generation circuits 50. Controlling the on / off of the multiple backflow prevention circuits 81 a, 81 b means controlling whether or not the multiple backflow prevention circuits 81 a, 81 b, described in detail below, will perform a backflow prevention function; in the on state, the backflow prevention function is performed, and in the off state, the backflow prevention function is not performed. Furthermore, by the control circuit 80 controlling the on / off of the multiple backflow prevention circuits 81 a, 81 b, it is also possible to control whether the power generated by the power generation element 20 a of the power generation circuit 50 a is supplied to the magnetic sensor 61 a of the rotational position detection unit 60 a, or whether the power generated by the power generation element 20 b of the power generation circuit 50 b is supplied to the magnetic sensor 61 b ​​of the rotational position detection unit 60 b, by the power supply unit 70.

[0052] The control circuit 80 is realized by, for example, a memory, a processor, etc. The control circuit 80 may also be realized by a dedicated logic circuit that performs the above-mentioned and later-described processes. Although not shown in FIG. 4, the control circuit 80 may be supplied with the voltage VWC.

[0053] A plurality of backflow prevention circuits 81a, 81b are provided corresponding to a plurality of power generation circuits 50. The backflow prevention circuit 81a is provided between the power generation circuit 50a and the power supply unit 70. The backflow prevention circuit 81b is provided between the power generation circuit 50b and the power supply unit 70. Each of the plurality of backflow prevention circuits 81a, 81b is located on the connection path between the power storage unit 32 and the power supply unit 70. Specifically, the backflow prevention circuit 81a is provided corresponding to the power generation circuit 50a, and has a backflow prevention function that prevents power generated by the power generation element 20b from being supplied from the power generation circuit 50b to the power generation circuit 50a. The backflow prevention circuit 81b is provided corresponding to the power generation circuit 50b, and has a backflow prevention function that prevents power generated by the power generation element 20a from being supplied from the power generation circuit 50a to the power generation circuit 50b. Each of the multiple backflow prevention circuits 81a, 81b includes, for example, a switch whose on / off state is controlled by the control circuit 80. In this case, the backflow prevention circuit 81a switches between conduction and non-conduction between the power generation circuit 50a and the power supply unit 70 and the power generation circuit 50b, and the backflow prevention circuit 81b switches between conduction and non-conduction between the power generation circuit 50b and the power supply unit 70 and the power generation circuit 50a. In the following description, unless otherwise specified, the multiple backflow prevention circuits 81a, 81b are each configured as a switch. In other words, the description is given for a case in which the backflow prevention function of the multiple backflow prevention circuits 81a, 81b is variable. Note that each of the multiple backflow prevention circuits 81a, 81b may be configured as a diode. In this case, the cathode of the diode is connected to the power supply unit 70, and the anode of the diode is connected to the power storage unit 32.

[0054] The oscillator 90 supplies an operating clock to the information processing unit 62 and the control circuit 80. The oscillator 90 is supplied with voltages VWC1 and VWC2 generated by the power generated by the power generating element 20. The oscillator 90 includes, for example, an oscillation circuit that can switch the applied voltage between voltage VWC1 and voltage VWC2. The oscillation circuit is applied with, for example, the higher of voltage VWC1 and voltage VWC2.

[0055] The rotation detector 1 may further include an input interface (not shown) that accepts input from the user.

[0056] [Operation] Next, an example of the operation of the rotation detector 1 according to this embodiment will be described.

[0057] Fig. 5 is a timing chart showing a specific example of the operation of the rotation detector 1 according to this embodiment. Fig. 5 shows an example of the timing of operation when power is normally generated by the power generating element 20a of the power generating circuit 50a. Below, an example of operation will be described in which the rotational position detection unit 60a performs rotational position detection processing using power generated by the power generating element 20a of the power generating circuit 50a. Therefore, unless otherwise specified, the following description will focus on the rotational position detection processing involving the power generating circuit 50a and the rotational position detection unit 60a.

[0058] "VWC" in FIG. 5 shows the change in voltage VWC1 in the power generation circuit 50a. "OSC" in FIG. 5 schematically shows the output of the oscillator 90. Specifically, the period from when the oscillator 90 outputs a clock until the clock stabilizes is shown by a diagonally shaded rectangle, and the period during which the oscillator 90 outputs a stable clock is shown by a vertically shaded rectangle. "First Voltage Threshold" in FIG. 5 shows the output of the voltage detection unit 31 based on the first voltage threshold V1. When the voltage VWC1 exceeds the first voltage threshold V1, the output changes from low to high. "Second Voltage Threshold" in FIG. 5 shows the output of the voltage detection unit 31 based on the second voltage threshold V2. When the voltage VWC1 exceeds the second voltage threshold V2, the output changes from low to high. "Backflow Prevention Circuit" in FIG. 5 shows control signals for controlling the backflow prevention circuits 81a and 81b. When the control signal is low, the backflow prevention circuits 81a and 81b are on, and the backflow prevention functions of the backflow prevention circuits 81a and 81b are activated. When the control signal is high, the backflow prevention circuits 81a and 81b are off, and the backflow prevention functions of the backflow prevention circuits 81a and 81b are not activated. In the example shown in Figure 5, the backflow prevention circuit 81b is always on during the period shown in the figure, so the supply of power generated by the power generation element 20a from the power generation circuit 50a to the power generation circuit 50b is always prevented.

[0059] The operation of the rotation detector 1 will be described below with reference to FIG.

[0060] First, when the rotating shaft 16 rotates while the circuits of the rotation detector 1 (in the example shown in FIG. 4 , the control circuit 80, the backflow prevention circuits 81a and 81b, the information processing unit 62, and the voltage detection unit 31) are reset, the magnetic field applied to the power generating element 20a from the magnet 10 changes, causing the power generating element 20a to generate electricity, and the voltage VWC1 begins to rise. In the example shown in FIG. 5 , at time t1, the voltage VWC1 reaches the first voltage threshold V1. Therefore, the voltage detection unit 31 outputs the detection result based on the first voltage threshold V1 to the control circuit 80, and the control circuit 80 acquires the output detection result based on the first voltage threshold V1. The control circuit 80 also starts measuring time, triggered by the acquisition of the detection result based on the first voltage threshold V1. The first voltage threshold V1 is set, for example, to a voltage equal to or higher than the voltage required for the clock output by the oscillator 90 to stabilize. When the voltage VWC1 reaches the first voltage threshold V1, the clock output by the oscillator 90 is stable. That is, the internal clock in the rotation detector 1 is initialized.

[0061] Furthermore, when the control circuit 80 acquires the detection result based on the first voltage threshold V1, it turns off the backflow prevention circuit 81a and brings the power generation circuit 50a and the power supply unit 70 into electrical continuity.

[0062] Next, the control circuit 80 determines whether to supply the power generated by the power generating element 20a to the magnetic sensor 61a based on whether the detection result of the voltage VWC1 by the voltage detection unit 31 satisfies a predetermined criterion. For example, the control circuit 80 measures the time Δt from when the voltage VWC1 reaches the first voltage threshold V1 to when it reaches the second voltage threshold V2 in the voltage detection unit 31, and determines whether the measured time Δt is equal to or less than a predetermined value. In the example shown in FIG. 5 , the voltage VWC1 reaches the second voltage threshold V2 at time t2. Therefore, the voltage detection unit 31 outputs the detection result based on the second voltage threshold V2 to the control circuit 80, and the control circuit 80 acquires the output detection result based on the second voltage threshold V2. The control circuit 80 measures the time Δt from time t1 to time t2. The second voltage threshold V2 is set, for example, to a voltage that is equal to or greater than the voltage that can supply the power required for the rotational position detection process by the rotational position detection unit 60a, and when the voltage VWC1 exceeds the second voltage threshold V2, the occurrence of erroneous detection of the rotational position by the rotational position detection unit 60a can be suppressed.

[0063] When the control circuit 80 determines that the detection result of the voltage VWC1 by the voltage detection unit 31 satisfies a predetermined criterion, it causes the power supply unit 70 to supply the power generated by the power generating element 20a to the magnetic sensor 61a. The control circuit 80 prevents the discharge unit 34 from discharging the power stored in the power storage unit 32 and keeps the backflow prevention circuit 81a in the off state, thereby causing the power supply unit 70 to supply the power generated by the power generating element 20a to the magnetic sensor 61a. In this way, the control circuit 80 controls the supply of power from the power supply unit 70 to the magnetic sensor 61a.

[0064] Next, based on the detection result of the magnetic sensor 61 a, the information processing unit 62 determines the rotational position of the rotating shaft 16. For example, based on the detection result of the magnetic sensor 61 a, the information processing unit 62 determines the polarity of the magnet 10 that applies a magnetic field to the magnetic sensor 61 a, and stores the determination result in memory as rotational position information that indicates the rotational position of the rotating shaft 16.

[0065] Next, the control circuit 80 turns on the backflow prevention circuit 81a, thereby disconnecting the power generation circuit 50a and the power supply unit 70. The control circuit 80 then performs a discharge process by discharging the power stored in the power storage unit 32 using the discharge unit 34. This reduces the voltage VWC1, returning it to the state before power generation by the power generation element 20a. In other words, each circuit of the rotation detector 1 is reset. In the example shown in FIG. 5, the backflow prevention circuit 81a is turned on at time t3, and the discharge process begins at time t4. The order of operations from time t3 to time t4 is not particularly limited.

[0066] On the other hand, if the control circuit 80 determines that the detection result of the voltage VWC1 by the voltage detection unit 31 does not satisfy the predetermined criterion, it turns on the backflow prevention circuit 81a to disable conduction between the power generation circuit 50a and the power supply unit 70. In this case, if the voltage VWC1 does not reach the second voltage threshold V2 even after a predetermined time has elapsed since time t1, the control circuit 80 may determine that the predetermined criterion is not satisfied because the time Δt exceeds a predetermined value. The control circuit 80 then performs a discharge process by discharging the power stored in the power storage unit 32 using the discharge unit 34. This causes the control circuit 80 to control the supply of power from the power supply unit 70 to the magnetic sensor 61a. The control circuit 80 prevents the power supply unit 70 from supplying the power generated by the power generation element 20a to the magnetic sensor 61a, and the information processing unit 62 does not perform rotational position detection processing. Therefore, erroneous detection of the rotational position of the rotating shaft 16 due to insufficient power supplied to the magnetic sensor 61a does not occur.

[0067] Furthermore, the rotation of the rotary shaft 16 causes the above-mentioned operation to be repeated.

[0068] In the above example of operation, when the voltage VWC1 reaches the first voltage threshold V1, the clock output by the oscillator 90 is stable and the internal clock in the rotation detector 1 is initialized. However, the oscillator 90 may output a clock when the voltage VWC1 exceeds the first voltage threshold V1. For example, the oscillator 90 may have an enable terminal, and the voltage detection unit 31 may output a signal that serves as an enable signal to the enable terminal of the oscillator 90 when the voltage VWC1 reaches the first voltage threshold V1. In other words, the voltage detection unit 31 may output a signal that serves as a trigger for initializing the internal clock of the rotation detector 1 when the voltage VWC1 reaches the first voltage threshold V1.

[0069] In the above example of operation, the rotational position detection unit 60a performs rotational position detection processing using power generated by the power generating element 20a of the power generating circuit 50a. However, the same operation is performed when the rotational position detection unit 60b performs rotational position detection processing using power generated by the power generating element 20b of the power generating circuit 50b. That is, the explanation can be made by replacing the power generating circuit 50a, power generating element 20a, rotational position detection unit 60a, magnetic sensor 61a, backflow prevention circuit 81a, and voltage VWC1 with the power generating circuit 50b, power generating element 20b, rotational position detection unit 60b, magnetic sensor 61b, backflow prevention circuit 81b, and voltage VWC2, respectively. Furthermore, because the multiple power generating elements 20 are aligned along the rotational direction of the magnet 10, voltages VWC1 and VWC2 do not normally rise simultaneously.

[0070] The control circuit 80 also controls the backflow prevention circuits 81a and 81b so that they are not turned off at the same time. For example, after turning off the backflow prevention circuit 81a, the control circuit 80 does not turn off the backflow prevention circuit 81b until turning on the backflow prevention circuit 81a. For example, while the backflow prevention circuit 81a is turned off, the control circuit 80 causes the discharge unit 34 to discharge the power generated by the power generation element 20b in the power generation circuit 50b. Similarly, for example, after turning off the backflow prevention circuit 81b, the control circuit 80 does not turn off the backflow prevention circuit 81a until turning on the backflow prevention circuit 81b. For example, while the backflow prevention circuit 81b is turned off, the control circuit 80 causes the discharge unit 34 to discharge the power generated by the power generation element 20a in the power generation circuit 50a.

[0071] Furthermore, in the above example of operation, each of the multiple backflow prevention circuits 81a, 81b is configured with a switch, but similar rotation position detection processing is possible even if each of the multiple backflow prevention circuits 81a, 81b is configured with a diode. In this case, the on / off of the multiple backflow prevention circuits 81a, 81b is not controlled by the control circuit 80, and, for example, operations other than those of the multiple backflow prevention circuits 81a, 81b described above are performed. Normally, voltages VWC1 and VWC2 rise at different times, so power is not supplied to the power supply unit 70 from the power generation circuits 50a and 50b at the same time, and backflow can also be prevented by the function of the diode.

[0072] [Effect] In the rotation detector 1 according to this embodiment, the control circuit 80 controls the supply of power generated by the power generating element 20 from the power supply unit 70 to the magnetic sensor 61 based on the voltage VWC generated by the power generating element 20, a first voltage threshold V1 for detecting the voltage VWC, and a second voltage threshold V2 for detecting the voltage VWC, the second voltage threshold V2 being greater than the first voltage threshold. As a result, the rotation detector 1 can detect with high accuracy whether the power generated by the power generating element 20 is regular or irregular, and determine whether to supply the power generated by the power generating element 20 to the magnetic sensor 61. As a result, the occurrence of erroneous detection of the rotational position by the rotational position detection unit 60 can be suppressed. This point will be described in detail using FIGS. 6 and 7 .

[0073] 6 and 7 are diagrams for explaining the relationship between the voltage threshold and the voltage generated by the power generating element 20. In Fig. 6 and Fig. 7, the vertical axis represents the voltage generated by the power generating element 20 generating electricity, and the horizontal axis represents time.

[0074] As shown in Fig. 6 , the power generation element 20 generates power using the large Barkhausen effect, and therefore, in the case of normal power generation, the voltage waveform Pr1 shows a very fast voltage rise and reaches a high voltage. However, the manner in which the large Barkhausen effect occurs may vary depending on the external environment, etc. Therefore, the power generation element 20 may also produce voltage waveforms due to irregular power generation, such as a waveform Pi1 in which the voltage reached is low despite power generation due to the large Barkhausen effect, and a waveform Pi2 in which the voltage reached is low due to inductive power generation not based on the large Barkhausen effect. Furthermore, as shown in Fig. 7 , a voltage waveform Pi3 due to irregular power generation may also be produced, in which the voltage reached is high but the voltage rise is slow because the inductive power generation is not based on the large Barkhausen effect.

[0075] Here, let us assume that the first voltage threshold V1 is set to a voltage necessary for the clock output by the oscillator 90 to stabilize, and the second voltage threshold V2 is set to a voltage that can supply the power necessary for the rotational position detection process by the rotational position detection unit 60. If the voltage generated by the power generating element 20 does not exceed the first voltage threshold V1, the internal clock of the rotation detector 1 will not be initialized properly, and the operation of each circuit in the rotation detector 1 may not be performed as specified. For example, the on / off state of circuit path switching may be indefinite, and the output state may not be determined, which may prevent the circuits receiving power from the generated power from operating as specified. Furthermore, as shown by the voltage waveforms Pi1 and Pi2 resulting from irregular power generation, even if the voltage generated by the power generating element 20 exceeds the first voltage threshold V1, if it does not exceed the second voltage threshold V2, the rotational position detection process by the rotational position detection unit 60 may not be performed correctly. Furthermore, as in the waveform Pi3 of the voltage due to irregular power generation, even if the voltage generated by the power generating element 20 exceeds the first voltage threshold V1 and the second voltage threshold V2, if it takes a long time from when the voltage reaches the first voltage threshold V1 to when it reaches the second voltage threshold V2, there is a possibility that sufficient power will not be supplied to the rotational position detection unit 60 when the rotational position detection process is performed. Furthermore, if the rotational position detection process is performed after waiting for the voltage to reach the second voltage threshold V2, there is a possibility that the process will not be completed within the specified time, which may cause problems with the operation of the rotation detector 1.

[0076] As described above, when irregular power generation occurs in the power generating element 20, the rotational position detection unit 60 is likely to detect the rotational position erroneously. However, by detecting whether irregular power generation is occurring based on the voltage VWC, the occurrence of erroneous detection in the rotational position detection can be suppressed. However, if an attempt is made to detect irregular power generation by the power generating element 20 using only one of the first voltage threshold V1 and the second voltage threshold V2, the accuracy of the detection of irregular power generation will be reduced. In the rotation detector 1 according to this embodiment, the control circuit 80 makes a determination based on the detection result using the first voltage threshold V1 and the detection result using the second voltage threshold V2. Therefore, when the internal clock of the rotation detector 1 is initialized and the voltage required for the rotational position detection process by the rotational position detection unit 60 is secured, the power generated by the power generating element 20 can be supplied to the magnetic sensor 61, enabling rotational position detection. Furthermore, the control circuit 80 can determine whether the required voltage is reached within a specified processing time, thereby suppressing rotational position detection at inappropriate times.

[0077] The rotation detector 1 also includes a plurality of power generation circuits 50, a plurality of rotational position detection units 60, and a plurality of backflow prevention circuits 81 a, 81 b. Therefore, while the plurality of backflow prevention circuits 81 a, 81 b prevent the power of the plurality of power generation circuits 50 from being mutually supplied with power, it is possible to select the power generation circuit 50 that is the power supply source for performing the rotational position detection process and the rotational position detection unit 60 that is the power supply destination, and perform rotational position detection, thereby enabling more accurate and stable rotational position detection.

[0078] [Example of Determination Method by Control Circuit] Next, an example of a method by which the control circuit 80 determines whether or not to supply the power generated by the power generating element 20 to the magnetic sensor 61 will be described.

[0079] Fig. 8 is a diagram showing an example of a waveform of a voltage generated by the power generating element 20. Fig. 8 shows the waveform of the voltage VWC generated by the power stored in the power storage unit 32 after full-wave rectification by the rectifier 33. As shown in Fig. 8, the voltage VWC generated by the power generating element 20 increases in (a) as the power storage unit 32 is charged by the power generated by the power generating element 20, decreases gradually in (b) as the power of the power storage unit 32 is consumed by the rotational position detection process by the rotational position detection unit 60, and decreases sharply in (c) as the power storage unit 32 is discharged by the discharge unit 34.

[0080] As described above, the control circuit 80 measures the time Δt from time t1 when the voltage VWC reaches the first voltage threshold V1 in the voltage detection unit 31 to time t2 when the voltage VWC reaches the second voltage threshold V2. The time Δt can also be considered to be the interval between the timings at which the voltage VWC reaches the two voltage thresholds in the voltage detection unit 31. If the time Δt exceeds a predetermined value, it is determined that the voltage VWC is slow to reach the second voltage threshold V2 or that the voltage VWC is low, and it is possible to determine that irregular power generation is occurring in the power generating element 20. Therefore, the control circuit 80 determines whether or not to supply the power generated by the power generating element 20 to the magnetic sensor 61 through the power supply unit 70 based on the measured time Δt. For example, if the time Δt is equal to or less than a predetermined value, the control circuit 80 supplies the power generated by the power generating element 20 to the magnetic sensor 61 through the power supply unit 70. However, if the time Δt exceeds the predetermined value, the control circuit 80 does not supply the power generated by the power generating element 20 to the magnetic sensor 61 through the power supply unit 70. This makes it possible to prevent erroneous detection of the rotational position even when the power generation element 20 generates power with a slow voltage rise or a low voltage. The predetermined value is set to a value that ensures enough time for the rotational position detection unit 60 to perform the rotational position detection process, for example, according to the rotational speed of the rotating shaft 16, etc.

[0081] The control circuit 80 may also calculate a slew rate from the time Δt and ΔV, which is the difference between the first voltage threshold V1 and the second voltage threshold V2. The slew rate is ΔV / Δt. If the slew rate is less than a predetermined value, it can be determined that irregular power generation is occurring in the power generating element 20. The control circuit 80 uses this slew rate to determine whether to supply power to the magnetic sensor 61 via the power supply unit 70. For example, if the slew rate is equal to or greater than a predetermined value, the control circuit 80 supplies the power generated by the power generating element 20 to the magnetic sensor 61 via the power supply unit 70. If the slew rate is less than the predetermined value, the control circuit 80 does not supply the power generated by the power generating element 20 to the magnetic sensor 61 via the power supply unit 70. By using the slew rate for determination, it is possible to easily determine whether or not the power generating element 20 is generating power with a slow voltage rise, such as induction power generation that does not rely on the large Barkhausen effect.

[0082] In the above, we have described a case where the voltage detection unit 31 has two voltage thresholds, the first voltage threshold V1 and the second voltage threshold V2, but the voltage detection unit 31 may also have one or more other voltage thresholds different from the first voltage threshold V1 and the second voltage threshold V2.

[0083] Fig. 9 is a diagram for explaining a case where voltage detection unit 31 has three or more voltage threshold values. Similar to Fig. 8, Fig. 9 shows the waveform of voltage VWC due to the power stored in power storage unit 32 after full-wave rectification by rectifier 33. In Fig. 9, an example of the waveform of normal voltage VWC is shown by a solid line, and an example of the waveform of abnormal voltage VWC is shown by a dashed line.

[0084] 9 , the voltage detection unit 31 has a first voltage threshold V1, a second voltage threshold V2, and additional voltage thresholds Vx1 and Vx2 that are between the first voltage threshold V1 and the second voltage threshold V2. That is, the voltage detection unit 31 outputs the detection results based on the first voltage threshold V1, the second voltage threshold V2, and the additional voltage thresholds Vx1 and Vx2 to the control circuit 80. In this case, in the normal mode, the control circuit 80 determines whether or not to supply the power generated by the power generating element 20 to the magnetic sensor 61 via the power supply unit 70 based on the time Δt as described above. This normal mode is an example of the first control mode.

[0085] On the other hand, in another mode, the control circuit 80 controls the supply of power generated by the power generating element 20 from the power supply unit 70 to the magnetic sensor 61 based on, for example, the voltage VWC generated by the power generating element 20, a first voltage threshold V1, and other voltage thresholds Vx1 and Vx2. Specifically, the control circuit 80 measures, for example, the time Δx from when the voltage VWC reaches the first voltage threshold V1 to when it reaches the other voltage threshold Vx1, and determines whether or not the power supply unit 70 should supply the power generated by the power generating element 20 to the magnetic sensor 61 based on the measured time Δx. This other mode is an example of the second control mode. For the determination, the time Δx may be used directly, or a slew rate calculated from the time Δx may be used as described above. Because the time Δx is shorter than the time Δt, the time from when the voltage VWC reaches the first voltage threshold V1 to when the control circuit 80 makes the above determination can be shortened. For example, if the waveform when irregular power generation occurs in the power generating element 20 is stable and has a shape like the example shown by the dashed line in Fig. 9, even if the time Δx is used for the determination, it is possible to determine in a short time whether or not irregular power generation is occurring without reducing the detection accuracy. The control circuit 80 switches between these modes based on, for example, a user input to the input interface.

[0086] Fig. 10 is another diagram for explaining a case where voltage detection unit 31 has three or more voltage threshold values. Similar to Fig. 8, Fig. 10 shows the waveform of voltage VWC due to the power stored in power storage unit 32 after full-wave rectification by rectifier 33. In Fig. 10, an example of the waveform of normal voltage VWC is shown by a solid line, and an example of the waveform of abnormal voltage VWC is shown by a dashed line.

[0087] 10 , the voltage detection unit 31 has a first voltage threshold V1, a second voltage threshold V2, and additional voltage thresholds Vx1, Vx2, and Vx3 that have values ​​between the first voltage threshold V1 and the second voltage threshold V2. That is, the voltage detection unit 31 outputs detection results based on the first voltage threshold V1, the second voltage threshold V2, and the additional voltage thresholds Vx1, Vx2, and Vx3 to the control circuit 80. The control circuit 80 controls the supply of power generated by the power generation element 20 from the power supply unit 70 to the magnetic sensor 61, based on the voltage VWC generated by the power generation element 20, the first voltage threshold V1, the second voltage threshold V2, and the additional voltage thresholds Vx1, Vx2, and Vx3. Specifically, the control circuit 80 determines whether or not to supply the power generated by the power generating element 20 to the magnetic sensor 61 via the power supply unit 70 based on, for example, the detection results of the voltage detection unit 31 using the first voltage threshold V1, the detection results of the second voltage threshold V2, and the detection results of other voltage thresholds Vx1, Vx2, and Vx3.

[0088] For example, the control circuit 80 measures the intervals (in the example shown in FIG. 10 ) between the timings at which the voltage VWC reaches the first voltage threshold V1, the second voltage threshold V2, and the other voltage thresholds Vx1, Vx2, and Vx3. For example, if all of the times Δx1 to Δx4 are within a predetermined range, the control circuit 80 supplies the power generated by the power generating element 20 to the magnetic sensor 61 via the power supply unit 70. If at least one of the times Δx1 to Δx4 is outside the predetermined range, the control circuit 80 does not supply the power generated by the power generating element 20 to the magnetic sensor 61 via the power supply unit 70. Alternatively, the control circuit 80 may make the above determination based on the variation in the time from Δx1 to Δx4. This allows for detection of waveform disturbances of the voltage VWC intermediate between the first voltage threshold V1 and the second voltage threshold V2, thereby improving the accuracy of detecting irregular power generation. For example, in the case of the waveform of voltage VWC shown by the dashed line in Figure 10, the interval between the timing at which the voltage VWC reaches the first voltage threshold V1 and the timing at which it reaches another voltage threshold Vx1 is shorter than Δx1 in the waveform of a normal voltage VWC. However, because there is a large variation in the intervals between the timing at which the voltage VWC reaches the first voltage threshold V1, the second voltage threshold V2, and the other voltage thresholds Vx1, Vx2, and Vx3, the above method can detect irregular power generation.

[0089] In addition, the control circuit 80 may determine whether or not there is a disturbance in the waveform of the voltage VWC due to a cause other than irregular power generation by the power generating element 20, such as a load fluctuation, noise, or leakage current as shown by the dashed line in Figure 10, and it becomes possible to detect a malfunction of the rotation detector 1, etc.

[0090] [Modification] Next, a rotation detector according to a modification of the embodiment will be described. In the following description of the modification, differences from the embodiment will be mainly described, and description of commonalities will be omitted or simplified.

[0091] Fig. 11 is a diagram showing the circuit configuration of a rotation detector 101 according to this modification. As shown in Fig. 11, the rotation detector 101 according to this modification differs from the rotation detector 1 according to the embodiment in that it includes a plurality of power generation circuits 150 instead of the plurality of power generation circuits 50. The power generation circuit 150 is configured such that, compared to the power generation circuit 50, it has a power storage unit 132 instead of the power storage unit 32, and further includes a capacity adjustment unit 135.

[0092] The capacity of the power storage unit 132 is variable. The power storage unit 132 is configured, for example, with variable capacitance elements. The power storage unit 132 may include multiple capacitance elements with fixed capacitance and switches, and the capacity may be variable by changing the number of capacitance elements that store the power generated by the power generating element 20 using the switches.

[0093] The capacity adjustment unit 135 is a processing circuit that adjusts the capacity of the power storage unit 132. The capacity adjustment unit 135 is realized by, for example, a memory, a processor, etc. The capacity adjustment unit 135 may be realized by a dedicated logic circuit that performs capacity adjustment processing for the power storage unit 132. Note that the capacity adjustment unit 135 may be shared by multiple power generation circuits 150.

[0094] In the rotation detector 101, the waveform of the voltage VWC can be adjusted by varying the capacity of the power storage unit 132. Fig. 12 is a diagram for explaining the relationship between the capacity of the power storage unit 132 and the waveform of the voltage VWC. In Fig. 12, the waveform of the voltage VWC when the capacity of the power storage unit 132 is relatively small is shown by a solid line, and the waveform of the voltage VWC when the capacity of the power storage unit 132 is relatively large is shown by a dashed line. In the rotation detector 101, the waveform of the voltage VWC can be changed by adjusting the capacity of the power storage unit 132.

[0095] The peak value Vmax of the voltage VWC due to the power generated by the power generating element 20 is expressed by the following formula (1) or formula (2).

[0096]

[0097]

[0098] Here, C is the capacity of the power storage unit 132, R is the load resistance between the power generating element 20 and the power storage unit 132, t is the charging time to the power storage unit 132 (i.e., the time from when the power generating element 20 starts generating power to when the rotational position detection unit 60 starts detecting the rotational position), W is the energy stored in the power storage unit 132, and Q is the amount of charge stored in the power storage unit 132. The energy W and the amount of charge Q are determined from the amount of power generated by the power generating element 20, and the load resistance R is also constant. Therefore, as can be seen from equations (1) and (2), the peak value Vmax and the time constant can be adjusted by the capacity C of the power storage unit 132.

[0099] As shown by the waveform indicated by the solid line in Figure 12, when the capacitance C of the power storage unit 132 is small, the voltage VWC rises quickly and the peak value Vmax1 is large. On the other hand, as shown by the waveform indicated by the dashed line in Figure 12, when the capacitance C of the power storage unit 132 is large, the voltage VWC rises slowly and the peak value Vmax2 is small. The capacitance C of the power storage unit 132 needs to be large enough to cover the power consumed by the rotational position detection unit 60 in the rotational position detection process. However, if the capacitance C of the power storage unit 132 is too large, the rise of the voltage VWC will be slow and the peak value Vmax will be low. In the rotation detector 101, the capacitance C of the power storage unit 132 is adjustable, so it is possible to adjust the capacitance C to an appropriate value depending on the power consumed in the rotational position detection process and the time required to perform the rotational position detection process. For example, at the time of initial setting or calibration of the rotation detector 101, the capacity adjustment unit 135 adjusts the capacity C of the power storage unit 132 based on an input from a user to the input interface. This makes it possible to further suppress the occurrence of erroneous detection in the rotation position detection process.

[0100] Furthermore, the capacity adjustment unit 135 may adjust the capacity of the power storage unit 132 based on a history of detection results of the voltage VWC by the voltage detection unit 31. For example, the voltage detection unit 31 outputs detection results of the voltage VWC based on each voltage threshold, and the capacity adjustment unit 135 acquires the output detection results and stores the detection results of the voltage VWC in memory. The capacity adjustment unit 135 then adjusts the capacity of the power storage unit 132 based on the history of detection results of the voltage VWC stored in memory. The detection results of the voltage VWC may be stored in memory by the control circuit 80. The capacity adjustment unit 135 adjusts the capacity of the power storage unit 132 based on a history of the time Δt from when the voltage VWC reaches the first voltage threshold V1 to when it reaches the second voltage threshold V2, for example.

[0101] For example, consider a case where the time Δt from when the voltage VWC reaches the first voltage threshold V1 to when the voltage VWC reaches the second voltage threshold V2 is desired to be equal to or shorter than the time Δt1, as shown by the solid line in FIG. 12 for the rotational position detection process. In this case, if the history of the detection results of the voltage VWC indicates that the time Δt is equal to or shorter than the time Δt1, the capacity adjustment unit 135 does not adjust the capacity C of the power storage unit 132. On the other hand, if the history of the detection results of the voltage VWC indicates that the time Δt is equal to or longer than the time Δt1, as shown by the dashed line in FIG. 12 for the voltage VWC waveform, the capacity adjustment unit 135 reduces the capacity C of the power storage unit 132. This adjusts the waveform of the voltage VWC to the waveform of the voltage VWC shown by the solid line in FIG. 12. In other words, the capacity C of the power storage unit 132 is adjusted to an appropriate value depending on the power consumed by the rotational position detection process and the time required for the rotational position detection process, thereby further reducing the occurrence of erroneous detection in the rotational position detection process.

[0102] There is no particular limitation on the frequency of adjusting the capacity C of the power storage unit 132 based on the history of the detection results of the voltage VWC by the capacity adjustment unit 135. The adjustment of the capacity C of the power storage unit 132 based on the history of the detection results of the voltage VWC by the capacity adjustment unit 135 is performed, for example, every time a predetermined number of histories of the detection results of the voltage VWC are stored in memory.

[0103] Furthermore, the history of detection results of the voltage VWC by the voltage detection unit 31, which the capacity adjustment unit 135 uses to adjust the capacity C of the power storage unit 132, is not limited to the history of detection results using the first voltage threshold V1 and the second voltage threshold V2. As described with reference to FIGS. 9 and 10 , if the voltage detection unit 31 has another voltage threshold, the history of detection results of the voltage VWC by the voltage detection unit 31 may further include a history of detection results using the other voltage threshold. The capacity adjustment unit 135 may adjust the capacity C of the power storage unit 132 based on, for example, the history of the time Δx described with reference to FIG. 9 . This allows the capacity C of the power storage unit 132 to be adjusted based on the history of the time Δx, which is likely to reflect the rising state of the voltage VWC.

[0104] (Others) While the rotation detector according to the present disclosure has been described above based on the embodiments and modifications, the present disclosure is not limited to the above embodiments and modifications. The present disclosure also includes forms obtained by applying various modifications to the above embodiments and modifications that would occur to a person skilled in the art, and forms realized by arbitrarily combining the components and functions of the embodiments within the scope of the present disclosure.

[0105] For example, in the above-described embodiment and modified examples, the number of power generation circuits 50 and the number of rotational position detection units 60 in the rotation detector 1 may each be one. Similarly, the number of power generation circuits 150 and the number of rotational position detection units 60 in the rotation detector 101 may each be one. In this case, each of the rotation detectors 1 and 101 does not need to include multiple backflow prevention circuits 81a and 81b. Even in this case, the control circuit 80 controls the supply of power generated by the power generation element 20 from the power supply unit 70 to the magnetic sensor 61, for example, by controlling whether or not the discharge unit 34 discharges the power stored in the power storage unit 32.

[0106] Furthermore, for example, in the above-described embodiment and modified examples, the voltage detection unit 31 is configured with comparators corresponding to each voltage threshold value, but this is not limited thereto. For example, the voltage detection unit 31 may be a voltage detector that detects the voltage value of the voltage VWC. The voltage detection unit 31 outputs the voltage value of the voltage VWC at predetermined time intervals, for example. In this case, the control circuit 80 controls the supply of power generated by the power generating element 20 from the power supply unit 70 to the magnetic sensor 61 based on the voltage value of the voltage VWC detected by the voltage detection unit 31 and each voltage threshold value. The control circuit 80, for example, uses the detected voltage value of the voltage VWC to measure the time Δt from when the voltage VWC reaches the first voltage threshold value V1 to when it reaches the second voltage threshold value V2, and determines whether the measured time Δt is equal to or less than a predetermined value.

[0107] In the above-described embodiment and modifications, the processes performed by a specific processing unit such as the information processing unit 62, the control circuit 80, and the capacity adjustment unit 135 may be performed by another processing unit. The order of multiple processes may be changed, or multiple processes may be performed in parallel.

[0108] In the above-described embodiment and modifications, all or part of the processing units, such as the information processing unit 62, the control circuit 80, and the capacity adjustment unit 135, may be configured with dedicated hardware, or may be realized by executing a software program suitable for each processing unit. Each processing unit may be realized by a program execution unit, such as a CPU (Central Processing Unit) or a processor, reading and executing a software program recorded on a recording medium, such as a semiconductor memory.

[0109] Furthermore, the processing units such as the information processing unit 62, the control circuit 80, and the capacitance adjustment unit 135 may be configured with one or more electronic circuits. Each of the one or more electronic circuits may be a general-purpose circuit or a dedicated circuit.

[0110] The one or more electronic circuits may include, for example, a semiconductor device, an integrated circuit (IC), or a large-scale integration (LSI). The IC or LSI may be integrated on a single chip or on multiple chips. Although the IC or LSI is referred to here as an IC or LSI, the name may vary depending on the degree of integration, and may be called a system LSI, a very large-scale integration (VLSI), or an ultra-large-scale integration (ULSI). A field programmable gate array (FPGA), which is programmed after the LSI is manufactured, may also be used for the same purpose.

[0111] Furthermore, the general or specific aspects of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, or a computer program. Alternatively, the general or specific aspects may be realized as a computer-readable non-transitory recording medium such as an optical disk, a hard disk drive (HDD), or a semiconductor memory on which the computer program is stored. Alternatively, the general or specific aspects of the present disclosure may be realized as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium.

[0112] Examples of the rotation detector according to the present disclosure described based on the above embodiment and modified examples are shown below. The rotation detector according to the present disclosure is not limited to the following examples.

[0113] For example, a rotation detector according to a first aspect of the present disclosure includes a magnet, a first power generating circuit, a first rotational position detection unit, a power supply unit, and a control circuit. The magnet rotates around a predetermined axis. The first power generating circuit includes a first power generating element, a voltage detection unit, and a power storage unit. The first power generating element generates power by utilizing the Great Barkhausen effect, which occurs when a magnetic field changes due to the magnet rotating around the predetermined axis. The voltage detection unit detects the voltage generated by the first power generating element. The power storage unit stores the first power generated by the first power generating element. The first rotational position detection unit includes a first magnetic sensor and a first information processing unit. The first magnetic sensor detects a magnetic field generated by the magnet and is provided corresponding to the first power generating element. The first information processing unit determines the rotational position of the rotation shaft based on the detection result of the first magnetic sensor. The power supply unit supplies the first power to the first magnetic sensor. The control circuit controls the supply of the first power by the power supply unit. Further, the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, a first voltage threshold for detecting the voltage, and a second voltage threshold for detecting the voltage that is greater than the first voltage threshold.

[0114] For example, a rotation detector according to a second aspect of the present disclosure is the rotation detector according to the first aspect, and has the following configuration: the voltage detection unit has the first voltage threshold and the second voltage threshold as voltage thresholds for detecting the voltage, and the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on a detection result of the voltage detection unit using the first voltage threshold and a detection result of the voltage detection unit using the second voltage threshold.

[0115] Furthermore, for example, a rotation detector according to a third aspect of the present disclosure is a rotation detector according to the first or second aspect, wherein the control circuit causes the voltage detection unit to measure the time from when the voltage reaches the first voltage threshold to when it reaches the second voltage threshold, and determines whether or not to supply the first power from the power supply unit to the first magnetic sensor based on the measured time.

[0116] Also, for example, a rotation detector according to a fourth aspect of the present disclosure is a rotation detector according to the third aspect, wherein the control circuit calculates a slew rate from the time, the first voltage threshold value, and the second voltage threshold value, and uses the slew rate to determine whether or not to supply the first power from the power supply unit to the first magnetic sensor.

[0117] Furthermore, for example, a rotation detector according to a fifth aspect of the present disclosure is the rotation detector according to any one of the first to fourth aspects, wherein the control circuit has a first control mode and a second control mode. The first control mode controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, the first voltage threshold, and the second voltage threshold. The second control mode controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, the first voltage threshold, and one or more other voltage thresholds for detecting the voltage, the other being different from the first voltage threshold and the second voltage threshold.

[0118] Furthermore, for example, a rotation detector according to a sixth aspect of the present disclosure is a rotation detector according to any one of the first to fifth aspects, wherein the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, the first voltage threshold, the second voltage threshold, and one or more other voltage thresholds for detecting the voltage between the first voltage threshold and the second voltage threshold.

[0119] Also, for example, a rotation detector according to a seventh aspect of the present disclosure is a rotation detector according to any one of the first to sixth aspects, wherein the first power generation circuit further has a discharge unit that discharges the first power stored in the storage unit.

[0120] Furthermore, for example, a rotation detector according to an eighth aspect of the present disclosure is the rotation detector according to the seventh aspect, wherein the control circuit controls whether or not to discharge the first power stored in the power storage unit by the discharge unit, based on the voltage generated by the first power generating element, the first voltage threshold value, and the second voltage threshold value, thereby controlling the supply of the first power from the power supply unit to the first magnetic sensor.

[0121] Furthermore, for example, a rotation detector according to a ninth aspect of the present disclosure is the rotation detector according to the eighth aspect, wherein the control circuit causes the voltage detection unit to measure the time from when the voltage reaches the first voltage threshold to when it reaches the second voltage threshold, and controls whether or not the first power stored in the storage unit is discharged by the discharge unit based on the measured time.

[0122] Furthermore, for example, a rotation detector according to a tenth aspect of the present disclosure is the rotation detector according to any one of the first to ninth aspects, wherein the capacity of the power storage unit is variable.

[0123] Also, for example, a rotation detector according to an eleventh aspect of the present disclosure is the rotation detector according to the tenth aspect, wherein the first power generation circuit further has a capacity adjustment unit that adjusts the capacity of the storage unit based on a history of the voltage detection results by the voltage detection unit.

[0124] Furthermore, for example, a rotation detector according to a twelfth aspect of the present disclosure is the rotation detector according to the fifth or sixth aspect, wherein the capacity of the power storage unit is variable, and the first power generation circuit further has a capacity adjustment unit that adjusts the capacity of the power storage unit based on a history of the voltage detection results by the voltage detection unit.

[0125] Also, for example, a rotation detector according to a thirteenth aspect of the present disclosure is a rotation detector according to any one of the first to twelfth aspects, wherein the voltage detection unit outputs a signal that triggers initialization of an internal clock of the rotation detector when the voltage reaches the first voltage threshold.

[0126] Furthermore, for example, a rotation detector according to a fourteenth aspect of the present disclosure is the rotation detector according to any one of the first to thirteenth aspects, further comprising a second power generating circuit, a second position detection unit, and a backflow prevention circuit. The second power generating circuit has a second power generating element that generates power using the large Barkhausen effect caused by a change in magnetic field due to rotation of the magnet around the predetermined axis. The second power generating element supplies the second power generated by the second power generating element to the power supply unit and is connected in parallel to the first power generating circuit. The second rotational position detection unit includes a second magnetic line sensor and a second information processing unit. The second magnetic sensor receives the second power from the power supply unit, detects the magnetic field generated by the magnet, and is provided corresponding to the second power generating element. The second information processing unit determines the rotational position of the rotating shaft based on the detection result of the second magnetic sensor. The backflow prevention circuit is provided between the second power generating circuit and the power supply unit and prevents the first power from being supplied from the first power generating circuit to the second power generating circuit.

[0127] The rotation detector according to the present disclosure can be used to detect the rotation of, for example, the rotating shaft of a motor that rotates a load, etc. Therefore, the rotation detector according to the present disclosure is industrially useful.

[0128] DESCRIPTION OF SYMBOLS 1, 101 Rotation detector 10 Magnet 11 Main surface 15 Rotating plate 16 Rotating shaft 17 Substrate 20, 20a, 20b Power generating element 21 Magnetic member 22 Coil 23 Housing 24, 25 Terminal 31 Voltage detection unit 32, 132 Power storage unit 33 Rectifier 34 Discharge unit 50, 50a, 50b, 150 Power generating circuit 60, 60a, 60b Rotation position detection unit 61, 61a, 61b Magnetic sensor 62 Information processing unit 70 Power supply unit 80 Control circuit 81a, 81b Backflow prevention circuit 90 Oscillator 135 Capacity adjustment unit

Claims

1. A rotation detector comprising: a magnet that rotates about a predetermined axis; a first power generating circuit having: a first power generating element that generates power by utilizing the Large Barkhausen effect caused by a change in a magnetic field due to the magnet rotating about the predetermined axis; a voltage detection unit that detects a voltage generated by the first power generating element; and a storage unit that accumulates a first power generated by the first power generating element; a first rotational position detection unit that detects a magnetic field generated by the magnet and has a first magnetic sensor provided corresponding to the first power generating element and a first information processing unit that determines a rotational position of the rotating shaft based on a detection result of the first magnetic sensor; a power supply unit that supplies the first power to the first magnetic sensor; and a control circuit that controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, a first voltage threshold for detecting the voltage, and a second voltage threshold for detecting the voltage that is greater than the first voltage threshold.

2. A rotation detector as described in claim 1, wherein the voltage detection unit has the first voltage threshold and the second voltage threshold as voltage threshold values ​​for detecting the voltage, and the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on a detection result obtained by the voltage detection unit using the first voltage threshold and a detection result obtained by the voltage detection unit using the second voltage threshold.

3. The rotation detector according to claim 1, wherein the control circuit causes the voltage detection unit to measure the time from when the voltage reaches the first voltage threshold to when it reaches the second voltage threshold, and determines whether or not to supply the first power from the power supply unit to the first magnetic sensor based on the measured time.

4. The rotation detector according to claim 3, wherein the control circuit calculates a slew rate from the time, the first voltage threshold value, and the second voltage threshold value, and uses the slew rate to determine whether or not to supply the first power from the power supply unit to the first magnetic sensor.

5. A rotation detector as described in claim 1, wherein the control circuit has: a first control mode in which the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, the first voltage threshold, and the second voltage threshold; and a second control mode in which the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, the first voltage threshold, and one or more other voltage thresholds for detecting the voltage that are different from the first voltage threshold and the second voltage threshold.

6. The rotation detector according to claim 1, wherein the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor based on the voltage generated by the first power generating element, the first voltage threshold, the second voltage threshold, and one or more other voltage thresholds for detecting the voltage between the first voltage threshold and the second voltage threshold.

7. The rotation detector according to claim 1, wherein the first power generating circuit further comprises a discharge section that discharges the first electric power stored in the power storage section.

8. The rotation detector according to claim 7, wherein the control circuit controls the supply of the first power from the power supply unit to the first magnetic sensor by controlling whether or not to discharge the first power stored in the power storage unit by the discharge unit based on the voltage generated by the first power generating element, the first voltage threshold value, and the second voltage threshold value.

9. The rotation detector according to claim 8, wherein the control circuit measures the time from when the voltage reaches the first voltage threshold value in the voltage detection unit until when it reaches the second voltage threshold value, and controls whether or not to discharge the first power stored in the power storage unit by the discharge unit based on the measured time.

10. The rotation detector according to claim 1, wherein the capacity of the storage unit is variable.

11. The rotation detector according to claim 10, wherein the first power generation circuit further includes a capacity adjustment section that adjusts the capacity of the power storage section based on a history of the voltage detection results obtained by the voltage detection section.

12. The rotation detector according to claim 5, wherein the capacity of the power storage unit is variable, and the first power generation circuit further has a capacity adjustment unit that adjusts the capacity of the power storage unit based on a history of the voltage detection results by the voltage detection unit.

13. The rotation detector according to claim 1, wherein the voltage detection unit outputs a signal that triggers initialization of an internal clock of the rotation detector when the voltage reaches the first voltage threshold value.

14. The rotation detector according to any one of claims 1 to 13, further comprising: a second power generating element which generates power by utilizing the Great Barkhausen effect caused by a change in the magnetic field due to the magnet rotating around the specified axis, a second power generating circuit which supplies a second power generated by the second power generating element to the power supply unit and is connected in parallel with the first power generating circuit; a second rotational position detection unit which receives the second power from the power supply unit, detects the magnetic field generated by the magnet, and is provided corresponding to the second power generating element, and a second information processing unit which determines the rotational position of the rotating shaft based on the detection result of the second magnetic sensor; and a backflow prevention circuit which is provided between the second power generating circuit and the power supply unit and prevents the first power from being supplied from the first power generating circuit to the second power generating circuit.

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