Multi-turn absolute encoder

Abstract

This multi-turn absolute encoder comprises: a rotary body that rotates about an axis of rotation; a printed wiring board that is opposite from the rotary body with a gap therebetween; a reflection pattern that is formed in a circular annular region in a surface of the rotary body and that encodes and records angle information; a magnetic field generation source that is held by the rotary body and that has a plurality of magnetic poles; an optical sensor that is mounted to the printed wiring board; and a power generation sensor that is mounted to the printed wiring board. The power generation sensor includes a magnetic wire, a coil, and a pair of magnetic flux conduction pieces comprising a soft magnetic body. The pair of magnetic flux conduction pieces are provided with a pair of axis-orthogonal parts and a pair of axis-parallel parts. The axis-orthogonal parts have wire placement parts to which both ends of the magnetic wire are fixed. The axis-parallel parts are disposed between the magnetic wire and the printed wiring board.

Description

Multi-turn absolute encoder

[0001] The present invention relates to a multi-rotation absolute encoder.

[0002] Patent Document 1 discloses an encoder equipped with a multi-rotation detection unit using a power-generating sensor and an optical single-rotation absolute detection unit. Figure 2 of the document shows a structure in which a two-pole magnet is placed on the rotation axis of a rotor, and a power-generating sensor is placed on the rotor side of a printed circuit board facing the two-pole magnet. The magnetic field changes once per rotation, and the power-generating sensor generates a pulse voltage of two pulses per rotation.

[0003] However, since the power generation sensor can experience pulse dropouts, multi-revolution counting using a pulse voltage of 2 pulses per revolution lacks precision and resolution, and the number of revolutions cannot be determined from the count value alone.

[0004] Therefore, it is possible to increase the number of pulses per rotation by using a multi-pole magnet, but in an axial arrangement where the magnet is placed on the rotation axis, it is difficult to improve the resolution of the multi-rotation detection unit using a multi-pole magnet. For example, in the case of a four-pole magnet, magnetic poles of the same polarity face each end of the power generation sensor, so no pulse voltage is generated.

[0005] Furthermore, it is not possible to increase the number of pulses by increasing the number of power generation sensors.

[0006] In addition, it is not possible to produce a double-shaft encoder having a penetrating rotating shaft (rotating body) or a hollow-shaft encoder, so the versatility is insufficient.

[0007] Furthermore, the optical single-revolution absolute detection unit in Patent Document 1 is a transmission type, in which the light-emitting element and the light-receiving element are mounted on separate printed circuit boards, and the configuration detects light transmitted through a slit pattern formed circumferentially on the rotating body. As a result, at least two printed circuit boards are required, resulting in a long structure in the direction of the rotation axis, and additionally, there are issues with increased material costs and assembly costs.

[0008] Patent Document 2 discloses a configuration in which the magnetic field changes two periods per rotation and three power generation sensors are provided. Each power generation sensor generates a pulse voltage of four pulses per rotation, and the three power generation sensors generate a pulse voltage of 12 pulses per rotation in total. This allows the number of rotations to be accurately counted even if a pulse voltage drop occurs (pulse missing). Figures 21 and 22 of the same document show the arrangement of magnets and power generation sensors that avoid the rotation axis. Figure 21 of the same document shows a configuration in which a magnet magnetized in a direction parallel to the rotation axis is arranged on the outer periphery of a rotor, and a power generation sensor is arranged parallel to the rotation axis so as to face the outer periphery of the rotor. Figure 22 of the same document shows a configuration in which a radially magnetized magnet is used and the magnetic field of the magnet is detected by a power generation sensor arranged along the radial direction.

[0009] However, the configuration of FIG. 21 of the same document has a problem of being long in the direction of the rotation axis, and the configuration of FIG. 22 of the same document has a problem of being large in the radial direction.

[0010] Patent Document 3 discloses a configuration in which three power generation sensors are arranged along the tangential direction of a circumference centered on the rotation axis, and these power generation sensors detect the magnetic field of four magnetic poles that move in a circumferential orbit around the rotation axis. The four magnetic poles are held on a rotating disk and form a magnetic field generating unit that generates a magnetic field that varies periodically with rotation. The power generation sensors are arranged opposite the rotating disk and form a magnetic field detecting unit that detects the magnetic field generated by the magnetic field generating unit.

[0011] Paragraphs 0007 to 0011 of the same document point out that if the power generating sensor is simply arranged in the circumferential direction, the magnetization direction does not change in a predictable manner, making it impossible to accurately detect shaft rotation. Therefore, the same document proposes installing a first magnetic member and a second magnetic member that cover both ends of the power generating sensor between the magnetic field generating unit and the power generating sensor, and controlling the flow of magnetic flux to stabilize the operation of the power generating sensor and increase its output.

[0012] However, the configuration of Patent Document 3 requires the first magnetic member and the second magnetic member to be disposed between the magnetic field generating unit and the magnetic field detecting unit, which increases material costs and requires space for disposition.

[0013] In addition, in Patent Document 3, the magnetic field detection unit and the light detection unit are arranged on opposite sides of the rotating disk. This requires two printed circuit boards to mount the magnetic field detection unit (power generation sensor) and the light detection unit, respectively, and also requires components to ensure electrical connections for exchanging signals between the printed circuit boards. This inevitably increases costs and space.

[0014] Japanese Patent Publication No. 2020-64018 Japanese Patent Publication No. 5802297 Japanese Patent Publication No. 5895774

[0015] Therefore, one embodiment of the present invention provides a multi-rotation absolute encoder having a structure advantageous for miniaturization and cost reduction while ensuring versatility.

[0016] One embodiment of the present invention provides a multi-rotation absolute encoder including: a rotor that rotates about a rotation axis; a printed wiring board that faces the rotor with a gap in a direction parallel to the rotation axis; a reflection pattern that is formed in a circumferential annular region having a center on the rotation axis on a surface of the rotor that faces the printed wiring board, and that encodes and records angular information; a magnetic field generating source that is held by the rotor on a side of the rotor that is remote from the surface that faces the printed wiring board, and that has a plurality of magnetic poles magnetized in a direction parallel to the rotation axis; an optical sensor that is mounted on the surface of the printed wiring board that faces the rotor, and that has a light source that radiates light toward the rotor and a light receiving element that receives reflected light from the rotor; and a power generation sensor that is mounted on the surface of the printed wiring board that is opposite to the rotor, and that responds to a magnetic field generated by the magnetic field generating source. The power generating sensor includes a magnetic wire exhibiting the large Barkhausen effect, a coil wound around the magnetic wire, and a pair of magnetic flux conducting pieces made of soft magnetic material symmetrical with respect to a symmetry plane set at the axial center of the magnetic wire. The pair of magnetic flux conducting pieces is mounted on the opposite surfaces of the printed wiring board so that the axial direction of the magnetic wire is along a tangential direction of a circumference centered on the rotation axis. The pair of magnetic flux conducting pieces includes a pair of axis-orthogonal portions extending parallel to each other in a direction perpendicular to the axial direction from both ends of the magnetic wire, and a pair of axis-parallel portions extending toward each other along the axial direction from the tips of the axis-orthogonal portions, with their proximal ends facing each other with a gap in the axial direction. The axis-orthogonal portions have wire placement portions formed by holes or grooves penetrating in the axial direction, to which both ends of the magnetic wire are fixed. The axis-parallel portions are disposed between the magnetic wire and the opposite surfaces of the printed wiring board.

[0017] In one embodiment of the present invention, the magnetic field generating source is arranged so that, when viewed in a direction parallel to the rotation axis, it overlaps partially or entirely with the annular region in which the reflection pattern is formed.

[0018] In one embodiment of the present invention, the magnetic field generating source has four magnetic poles.

[0019] In one embodiment of the present invention, the spacing between the magnetic poles of the magnetic field generating source is longer than the total length of the magnetic wire, and the length of the magnetic poles on their orbits when they rotate together with the rotor around the rotation axis is shorter than the total length of the magnetic wire and is 50% or less of the spacing.

[0020] In one embodiment of the present invention, the magnetic field generating source is four magnets magnetized in a direction parallel to the rotation axis, and the four magnets are held by the rotor and arranged with their north and south poles alternately arranged on a circle centered on the rotation axis.

[0021] The above and other objects, features and advantages of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings.

[0022] FIG. 1 is a block diagram illustrating an example of the configuration of a multi-rotation absolute encoder according to one embodiment of the present invention. FIG. 2A is a perspective view illustrating an example of the configuration of the multi-rotation absolute encoder. FIG. 2B is a plan view of the multi-rotation absolute encoder. FIG. 2C is a front view as viewed in the direction of arrows IIC in FIG. 2B. FIG. 3 is a plan view of a multi-pole magnet, which is an example of a magnet to be detected. FIG. 4 is a plan view of a disk, which is an example of a rotating body. FIG. 5A shows the results of a two-dimensional magnetic simulation when a magnet is placed in the detection area of ​​a power generation sensor. FIG. 5B shows the results of a two-dimensional magnetic simulation when a magnet is placed in the detection area of ​​a power generation sensor. FIG. 5C shows the results of a two-dimensional magnetic simulation when a magnet is placed in the detection area of ​​a power generation sensor. FIG. 6 is a diagram illustrating the operation of the power generation sensor as the disk rotates, showing the change in magnetic flux density with respect to the rotation angle of the disk. FIG. 7A is a cross-sectional view illustrating an example of the configuration of a multi-rotation absolute encoder according to another embodiment of the present invention. FIG. 7B is a plan view of the multi-rotation absolute encoder. Fig. 7C is a bottom view of the multi-rotation absolute encoder. Fig. 8 is a perspective view of a disk, which is an example of a rotating body. Fig. 9A shows the results of a two-dimensional magnetic simulation when a magnet is placed in the detection area of ​​the power generation sensor. Fig. 9B shows the results of a two-dimensional magnetic simulation when a magnet is placed in the detection area of ​​the power generation sensor. Fig. 9C shows the results of a two-dimensional magnetic simulation when a magnet is placed in the detection area of ​​the power generation sensor. Fig. 10 is a diagram for explaining the operation of the power generation sensor as the disk rotates, showing the change in magnetic flux density with respect to the rotation angle of the disk.

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] 1 is a block diagram illustrating an example of the configuration of a multi-rotation absolute encoder according to an embodiment of the present invention. The multi-rotation absolute encoder 100 is a device that detects the multi-rotation absolute angle of a rotating shaft 30 (an example of a rotating body) that rotates about a rotation axis 33, and generates a multi-rotation absolute angle detection value that is the detected value. The multi-rotation absolute angle refers to an absolute angle within an angle range that exceeds one rotation, i.e., spans multiple rotations. The multi-rotation absolute encoder 100 includes a precision absolute angle detector 1, a multi-rotation detector 2, and a computing device 4.

[0025] The precision absolute angle detector 1 is an angle sensor that generates precise absolute angle detection values ​​within one rotation period of the rotating shaft 30, i.e., from 0 degrees to 360 degrees, with a higher resolution than the multi-rotation detector 2. In this embodiment, the precision absolute angle detector 1 is configured as an optical absolute encoder. The precision absolute angle detector 1 is configured to generate absolute angle detection values ​​in an angle region within one rotation period (0 degrees to 360 degrees) with a resolution of 24 bits (16777216 levels), for example.

[0026] The precision absolute angle detector 1 typically operates by receiving power from an external power supply. Specifically, the multi-rotation absolute encoder 100 includes a power supply circuit 3 that can be connected to an external power supply. When connected to the external power supply, the power supply circuit 3 supplies power to the precision absolute angle detector 1, and the precision absolute angle detector 1 operates by receiving that power. The precision absolute angle detector 1 inputs a 24-bit absolute angle detection value to the arithmetic unit 4, for example, by serial communication.

[0027] The multi-rotation detector 2, also called a segment counter, counts the number of segments that divide one rotation period of the rotating shaft 30 into multiple (equal) parts according to the rotation of the rotating shaft 30, and generates a count value that represents the angle value of each segment in an angle range spanning multiple rotations of the rotating shaft 30 (more than one rotation).

[0028] The multi-rotation detector 2 includes a power generation sensor 20, a magnetic field generating source 50 that rotates around the rotation axis 33 together with the rotating shaft 30, a rectifier / power supply circuit 6, a signal processing circuit 7, a counter circuit 8, and a non-volatile memory 9 that stores count values. In this embodiment, three power generation sensors 20 are provided spaced apart in the circumferential direction around the rotation axis 33. The non-volatile memory 9 may be composed of an FeRAM (ferroelectric random access memory). In this embodiment, the counter circuit 8 and the non-volatile memory 9 are incorporated into a single counter memory IC (integrated circuit) 10.

[0029] The power generation sensors 20 generate pulse voltages in response to changes in the magnetic field caused by the rotation of the magnetic field generating source 50. The signal processing circuit 7 determines the polarity of the pulse voltages generated by the three power generation sensors 20, and supplies digital data (serial signals) representing the determination results to the counter memory IC 10 as pulse information.

[0030] The rectifier / power supply circuit 6 rectifies the pulse voltage generated by the power generation sensor 20, converts it into an appropriate voltage, and supplies it to the signal processing circuit 7 and the counter memory IC 10 (counter circuit 8 and nonvolatile memory 9). Therefore, the signal processing circuit 7 and the counter memory IC 10 (counter circuit 8 and nonvolatile memory 9) can operate without receiving power from an external power source. In other words, the multi-rotation detector 2 operates using power generated by its own power generation, even when there is no external power supply. The counter memory IC 10 can operate using power supplied from the power supply circuit 3 when the power supply circuit 3 is connected to an external power source.

[0031] The counter circuit 8 built into the counter memory IC 10 performs a counting operation in accordance with a predetermined counter logic based on pulse information supplied from the signal processing circuit 7 and the previous pulse information stored in the nonvolatile memory 9. This counting operation is performed regardless of whether external power is supplied from the power supply circuit 3. The count value obtained by this counting operation is stored in the nonvolatile memory 9. This count value is saved even when there is no power supply (nonvolatile storage). When external power is supplied, the counter memory IC 10 can supply the count value and pulse information stored in the nonvolatile memory 9 to the arithmetic unit 4 via serial communication.

[0032] The arithmetic unit 4 operates by receiving power from the power supply circuit 3 when the power supply circuit 3 is connected to an external power supply. When the external power supply is turned on, the arithmetic unit 4 requests a precision absolute angle detection value from the precision absolute angle detector 1 and also requests a count value from the non-volatile memory 9. The precision absolute angle detector 1 supplies the precision absolute angle detection value to the arithmetic unit 4 via serial communication. The non-volatile memory 9 supplies the count value to the arithmetic unit 4 via serial communication. The arithmetic unit 4 combines the precision absolute angle detection value and the count value to generate and output a multi-rotation absolute angle detection value. The multi-rotation absolute angle detection value output by the arithmetic unit 4 is supplied to a host controller (not shown), for example, and used for controlling the rotation of an electric motor, etc.

[0033] Fig. 2A is a perspective view for explaining an example of the structure of a multi-rotation absolute encoder 100, and Fig. 2B is a plan view thereof. Fig. 2C is a front view seen in the direction of arrow IIC in Fig. 2B. The multi-rotation absolute encoder 100 integrally includes a precision absolute angle detector 1 and a multi-rotation detector 2.

[0034] The multi-rotation absolute encoder 100 includes a disk 32 as a rotating body that rotates about a rotation axis 33, and a printed wiring board 31 arranged to face the disk 32. The multi-rotation absolute encoder 100 further includes a magnetic field generation source 50 held on the surface of the disk 32 opposite the printed wiring board 31, an optical sensor 60 mounted on the surface of the printed wiring board 31 facing the disk 32, and a power generating sensor 20 mounted on the surface of the printed wiring board 31 opposite the disk 32. The precision absolute angle detector 1 includes the optical sensor 60 and a reflection pattern 70 read by the optical sensor 60. The multi-rotation detector 2 includes the magnetic field generation source 50 and the power generating sensor 20 that responds to the magnetic field of the magnetic field generation source 50.

[0035] The printed wiring board 31 is disposed with a gap 35 from the disk 32 in a direction parallel to the rotation axis 33. The printed wiring board 31 and the disk 32 are each plate-like, parallel to each other, and disposed along a plane perpendicular to the rotation axis 33. An opening 32a is formed in the disk 32 and passes through along the rotation axis 33. In this example, the opening 32a is circular and has a center on the rotation axis 33. An opening 31a is formed in the printed wiring board 31 and passes through along the rotation axis 33 so as to align with the opening 32a in the disk 32. In this example, the opening 31a is circular and has a center on the rotation axis 33, and has a larger diameter than the opening 32a in the disk 32. In this example, an encoder with a hollow shaft structure is configured.

[0036] The power generation sensor 20 is disposed on and supported by a printed wiring board 31. In this embodiment, a plurality of power generation sensors 20, more specifically, three power generation sensors 20, are disposed at intervals (equally spaced in this embodiment) around the rotation axis 33 along a circumference having a center on the rotation axis 33.

[0037] The magnetic field generation source 50 is fixed to the disk 32. The disk 32 rotates relative to the printed wiring board 31 about a rotation axis 33. The rotation shaft 30, the object of rotation detection, is disposed so as to pass through the openings 32a, 31a along the rotation axis 33, and is coupled (fixed) to the disk 32. Therefore, the disk 32 rotates together with the rotation shaft 30 about the rotation axis 33. In contrast, the printed wiring board 31 is fixed and held in a non-rotating state. As a result, the magnetic field generation source 50 rotates together with the disk 32 about the rotation axis 33, and rotates relative to the printed wiring board 31 about the rotation axis 33.

[0038] The rotating shaft 30 is typically rotated by a driving force from a drive shaft of an electric motor (not shown). When the electric motor is driven in both directions, the rotating shaft 30 rotates in both the counterclockwise direction CCW and the clockwise direction CW accordingly.

[0039] The magnetic field generating source 50 is held by the disk 32 on the side of the disk 32 that is farther from the surface facing the printed wiring board 31. In this example, the magnetic field generating source 50 is configured as a ring-shaped multi-pole magnet M (more specifically, a four-pole magnetized magnet) that surrounds the rotation axis 33. The magnetization direction is parallel to the rotation axis 33.

[0040] As shown in the plan view of FIG. 3 , when viewed from one direction of the rotation axis 33, the multi-pole magnet M has k magnetic pole pairs (pairs of north and south poles) (k is an integer equal to or greater than 2; in the illustrated example, k=2) arranged on a circle centered on the rotation axis 33, with the north poles and south poles alternately arranged. The magnet M has k north poles n1, n2, ..., nk and k south poles s1, s2, ..., sk. Each of the magnetic poles n1, n2, ..., nk; s1, s2, ..., sk spans an angular region of 360 degrees / 2k (90 degrees in this embodiment) around the rotation axis 33. Therefore, as the disk 32 rotates together with the rotation axis 30 and the magnetic field generating source 50 rotates around the rotation axis 33 accordingly, an alternating magnetic field of k periods (two periods in the illustrated example) is applied to each power generation sensor 20.

[0041] The power generation sensor 20 is mounted on one main surface of the printed wiring board 31. More specifically, it is mounted on the main surface of the printed wiring board 31 opposite the disk 32. The power generation sensor 20 responds to the magnetic field generated by the magnetic field generating source 50.

[0042] The power generation sensor 20 includes a magnetic wire FE and a first magnetic flux conductor FL1 and a second magnetic flux conductor FL2 magnetically coupled to opposite ends of the magnetic wire FE. A coil SP (induction coil) is wound around the magnetic wire FE between the first magnetic flux conductor FL1 and the second magnetic flux conductor FL2. The first magnetic flux conductor FL1 and the second magnetic flux conductor FL2 are soft magnetic components of substantially the same shape and size. More specifically, the first magnetic flux conductor FL1 and the second magnetic flux conductor FL2 are symmetrically arranged with respect to a plane of symmetry 27 (a virtual plane for illustrating the geometric arrangement) perpendicular to the axial direction x at an axial center position 25 (hereinafter referred to as the "axial center position 25") of the magnetic wire FE.

[0043] The magnetic wire FE is configured to exhibit the large Barkhausen effect. Specifically, the magnetic wire FE has a core and a skin covering the core. One of the core and the skin is a soft layer (soft magnetic layer) whose magnetization direction is reversed even in a weak magnetic field, while the other is a hard layer (hard magnetic layer) whose magnetization direction does not reverse unless a strong magnetic field is applied. In this specification, the magnetic field strength at which the magnetization direction of the soft layer is reversed is referred to as the "operating magnetic field," and the magnetic field strength at which the magnetization direction of the hard layer is reversed is referred to as the "stabilizing magnetic field."

[0044] Each of the magnetic flux conducting pieces FL1, FL2 has a magnetic flux conducting end 21, 22 facing the detection region SR. The magnetic wire FE of the power generating sensor 20 is located on a tangent to a circumference 36 whose center is on the rotation axis 33, and the axial center position 25 of the magnetic wire FE is located on the tangent point of the tangent. The power generating sensor 20 is positioned so that the magnetic fields conducted from the two magnetic flux conducting pieces FL1, FL2 are balanced when the center of one of the magnetic poles n1, n2, ..., nk; s1, s2, ..., sk over an angular region of 360 degrees / 2k (90 degrees in this embodiment) around the rotation axis 33 is aligned with the axial center position 25 of the magnetic wire FE. For example, the coil SP generates a negative voltage pulse in a first state when the magnetic flux from the north poles n1, n2, ..., nk is conducted from the first magnetic flux conducting piece FL1, and generates a positive voltage pulse in a second state when the magnetic flux from the north poles n1, n2, ..., nk is conducted from the second magnetic flux conducting piece FL2.

[0045] In this embodiment, the first magnetic flux conduction piece FL1 and the second magnetic flux conduction piece FL2 include axis-orthogonal portions 41 extending parallel to each other from both ends of the magnetic wire FE in an axis-orthogonal direction z perpendicular to the axial direction x, and axis-parallel portions 42 extending from the tips of the axis-orthogonal portions 41 in directions approaching each other along the axial direction x. Both ends of the magnetic wire FE are fixed to the base ends of the axis-orthogonal portions 41 of the first magnetic flux conduction piece FL1 and the second magnetic flux conduction piece FL2. More specifically, the base ends of the axis-orthogonal portions 41 are provided with wire placement portions 23 having holes or grooves penetrating in the axial direction x. Both ends of the magnetic wire FE are fixed to the axis-orthogonal portions 41 in the wire placement portions 23, penetrating the axis-orthogonal portions 41 of the first magnetic flux conduction piece FL1 and the second magnetic flux conduction piece FL2, respectively. For example, the magnetic wire FE and the first and second magnetic flux conduction pieces FL1 and FL2 are coupled and fixed to each other by resin (not shown) placed in the holes or grooves that form the wire placement portion 23. As a result, both ends of the magnetic wire FE are magnetically coupled to the first and second magnetic flux conduction pieces FL1 and FL2, respectively.

[0046] The power generation sensor 20 is configured such that the side of the axially parallel portion 42 opposite the magnetic wire FE is a detection region SR for detecting a magnetic field.

[0047] Each of the magnetic flux conduction pieces FL1 and FL2, made of a soft magnetic material, has an axis-orthogonal portion 41 having a substantially rectangular parallelepiped shape and an axis-parallel portion 42 connected to the tip of the axis-orthogonal portion 41 on the detection region SR side, forming an L-shape bent at a right angle at the junction between the axis-orthogonal portion 41 and the axis-parallel portion 42. The axis-parallel portion 42 extends along the axial direction x to cover the magnetic wire FE, i.e., to shield the magnetic wire FE from the detection region SR. The first magnetic flux conduction piece FL1 and the second magnetic flux conduction piece FL2, which have symmetrical shapes, extend toward the axial center of the magnetic wire FE, and their proximal ends 42a face each other with a gap between them near the axial center position 25 of the magnetic wire FE. The proximal ends 42a form planes perpendicular to the axial direction x, and the two planes forming each of the two proximal ends 42a are parallel to each other and face each other in the axial direction x.

[0048] The axially parallel portions 42 of the first and second magnetic flux conduction pieces FL1 and FL2 define magnetic flux conduction ends 21 and 22 that form detection-area-facing surfaces facing the detection region SR. The magnetic flux conduction ends 21 and 22 (detection-area-facing surfaces) are flat surfaces parallel to the axial direction x. When a magnetic pole is positioned in the detection region SR, the magnetic flux conduction ends 21 and 22 (detection-area-facing surfaces) guide magnetic flux from the magnetic pole into the first and second magnetic flux conduction pieces FL1 and FL2.

[0049] The axially parallel portions 42 of the first magnetic flux conduction piece FL1 and the second magnetic flux conduction piece FL2 are joined to a wiring pattern (not shown) formed on one main surface of the printed wiring board 31, thereby surface-mounting the power generating sensor 20 on the printed wiring board 31. The power generating sensor 20 is arranged so that the axial direction x of the magnetic wire FE is aligned with a tangent to a point (contact point) on a circumference 36 whose center axis is the rotation axis 33, and the axial center position 25 of the magnetic wire FE coincides with the contact point. The detection region SR of the power generating sensor 20 is on the opposite side of the axially parallel portions 42 from the magnetic wire FE, and in this example, is an area on the other main surface of the printed wiring board 31.

[0050] The power generation sensor 20 may include a case 28 that houses the magnetic wire FE, the coil SP, the first magnetic flux conduction piece FL1, the second magnetic flux conduction piece FL2, etc. In order to explain the configuration of the power generation sensor 20, for convenience, Figures 2A and 2C show the configuration of one power generation sensor 20 with the case 28 removed.

[0051] In this example, the disk 32 is configured in an annular shape surrounding the rotation axis 33. More specifically, the disk 32 is configured as an annular plate-like body, is arranged along a plane perpendicular to the rotation axis 33, and is parallel to the printed wiring board 31. A multi-pole magnet M is fixed to the surface of the disk 32 on the side away from the printed wiring board 31. In this embodiment, the magnetic poles n1, s1, n2, s2, ..., nk, sk of the multi-pole magnet M are arranged at equal intervals in the circumferential direction around the rotation axis 33. In the illustrated example, four magnetic poles n1, s1, n2, s2 are arranged at 90-degree angular intervals around the rotation axis 33, and the multi-pole magnet M is fixed to the surface of the disk 32 opposite the printed wiring board 31 so that they face the printed wiring board 31 across the disk 32. The distance from the rotation axis 33 to the centers of the magnetic poles n1, s1, n2, s2, ..., nk, sk may be equal to the distance from the rotation axis 33 to the axial center position 25 of the magnetic wire FE. That is, in a plan view along the rotation axis 33, the magnetic wire FE and the magnetic poles n1, s1, n2, s2, ..., nk, sk may be located on a circumference 36 of equal radius with the rotation axis 33 as the center axis, and thereby may be in a positional relationship that allows them to face each other in a direction parallel to the rotation axis 33.

[0052] The disk 32 is made of a non-magnetic material, such as aluminum or resin (glass epoxy resin, etc.), and is configured to allow the magnetic field generated by the multi-pole magnet M to pass through, enabling the magnetic field to be detected by the power generation sensor 20.

[0053] As the disk 32 rotates around the rotation axis 33 together with the rotation shaft 30, the magnetic poles n1, s1, n2, s2, ..., nk, sk move on a circular orbit 51 centered on the rotation axis 33 and passing through the detection region SR. The axial direction x of the magnetic wire FE is parallel to a tangent passing through a certain point (contact point) on the orbit 51, and the axial center position 25 is on a perpendicular line (in this example, a perpendicular line parallel to the rotation axis 33) erected to the tangent line at the contact point. In other words, the axial center position 25 of the magnetic wire FE has its center on the rotation axis 33 and is located at a certain point (contact point) on a circumference 36 of a radius equal to that of the orbit 51, and the magnetic wire FE is along the tangent line at the contact point.

[0054] The distance between the printed wiring board 31 and the disk 32 in the direction along the rotation axis 33 is set to an appropriate value that allows the magnetic poles n1, s1, n2, s2, ..., nk, sk to enter the detection region SR of the power generation sensor 20 as the disk 32 rotates.

[0055] With this configuration, as the rotating shaft 30 rotates counterclockwise (CCW) around the rotation axis 33, each time one of the magnetic pole pairs n1, s1; n2, s2; ...; nk, sk passes through the detection region SR of each of the power generating sensors 20 along the circumferential orbit 51, the power generating sensor 20 generates one negative pulse and one positive pulse in sequence. Also, as the rotating shaft 33 rotates clockwise (CW) around the rotation axis 33, each time one of the magnetic pole pairs n1, s1; n2, s2; ...; nk, sk passes through the detection region SR of each of the power generating sensors 20 along the circumferential orbit 51, the power generating sensor 20 generates one positive pulse and one negative pulse in sequence. Therefore, by performing a predetermined counting operation using the pulse voltages (positive pulses and negative pulses) generated by the three power generating sensors 20, a count value corresponding to the number of rotations of the rotating shaft 30 can be obtained.

[0056] An optical sensor 60 is mounted on the main surface of the printed wiring board 31 opposite to the main surface on which the power generation sensor 20 is mounted, i.e., on the main surface facing the disk 32. The optical sensor 60 is a reflective sensor including a light source 61 (light-emitting element) that emits light toward the disk 32 and a light-receiving element 62 that receives light reflected from the disk 32. The optical sensor 60 includes at least one light source 61 and at least one (typically multiple) light-receiving element 62.

[0057] As shown in FIG. 4 , a plan view along the rotation axis 33 shows a reflection pattern 70 on the surface of the disk 32 facing the printed wiring board 31, which encodes and records angular information. The reflection pattern 70 is formed in a circumferential annular region 75 (annular region) centered on the rotation axis 33. The reflection pattern 70 is created, for example, by forming a fine pattern encoding the angular information by high-precision etching of a thin film formed on the surface of the disk 32. The reflection pattern 70 is composed of a fine pattern including high-reflectivity portions 71 and low-reflectivity portions 72, and this fine pattern is detected by the optical sensor 60. Then, by performing a decoding process on the output signal of the optical sensor 60, precise absolute angle information within one rotation range can be obtained. The thin film constituting the reflection pattern 70 is preferably made of a non-magnetic material. However, because of its minute thickness, even if it is made of a magnetic material, the magnetic field generated by the magnetic field source 50 can easily pass through it.

[0058] In this way, the reflective pattern 70 formed on the disk 32 and the optical sensor 60 mounted on the printed wiring board 31 constitute the precision absolute angle detector 1. Furthermore, the magnetic field generation source 50 held on the disk 32 and the power generation sensor 20 mounted on the printed wiring board 31 constitute the multi-rotation detector 2. As a result, the multi-rotation absolute encoder 100 has a structure in which the precision absolute angle detector 1 and the multi-rotation detector 2 are integrated.

[0059] As described above, according to this embodiment, the power generation sensor 20 and the optical sensor 60 (light source 61 and light receiving element 62) are mounted on a single printed wiring board 31, which allows for miniaturization in the direction parallel to the rotation axis 33 and reduces material and assembly costs. Furthermore, the power generation sensor 20 and the magnetic field generating source 50 are positioned away from the rotation axis 33, thereby realizing a hollow-shaft encoder. It is also possible to fix the rotation axis 30 to the disk 32 to create a double-shaft encoder. Therefore, an encoder with a highly versatile structure can be provided.

[0060] The optical precision absolute angle detector 1 is realized on a single printed wiring board 31 by arranging a reflective optical sensor 60 on the printed wiring board 31 and carrying a reflective pattern 70 on the surface of the disk 32 facing it. Meanwhile, the magnetic field generated by the magnetic field generating source 50 passes through the disk 32 and the printed wiring board 31 and can be detected by the power generating sensor 20. This realizes a small multi-rotation absolute encoder 100 in which the precision absolute angle detector 1 and the multi-rotation detector 2 are integrated.

[0061] Furthermore, when viewed in a direction parallel to the rotation axis 33, the annular region 75 in which the reflection pattern 70 is formed overlaps with the annular multi-pole magnet M that constitutes the magnetic field generation source 50. With this arrangement, the radial size of the multi-rotation absolute encoder 100 can be reduced.

[0062] The power generation sensor 20 has a structure in which a pair of magnetic flux conduction pieces FL1, FL2 are magnetically and mechanically coupled to both ends of a magnetic wire FE, and the axially parallel portions 42 of the magnetic flux conduction pieces FL1, FL2 are located between the magnetic wire FE and the printed wiring board 31. Therefore, even if the magnetic field generation source 50 is located somewhat far away, the magnetic field generated by the magnetic field generation source 50 can be reliably guided to both ends of the magnetic wire FE by the magnetic flux conduction pieces FL1, FL2, and a pulse voltage can be reliably generated by the large Barkhausen effect.

[0063] 5A, 5B, and 5C show the results of a two-dimensional magnetic simulation in which magnets 411, 412, and 413 are placed in the detection area of ​​the power generation sensor 20. The total length Lw of the magnetic wire FE is 11 mm, and the distance Ld from the magnet surface to the magnetic wire FE in the orthogonal direction z is 4.5 mm. Three magnetic poles are arranged on a linear track 51A that crosses the detection area parallel to the magnetic wire FE. In this example, three individual magnets 411, 412, and 413 magnetized in the orthogonal direction z are arranged in order of south, north, and south poles. In this example, three individual magnets 411, 412, and 413 of the same shape and size are prepared and arranged in contact along the linear track 51A to simulate the ring-shaped multi-pole magnet M that constitutes the magnetic field generator 50. The magnetic pole pitch Lp is equal to the length of the individual magnets 411, 412, and 413 along the track 51A. The magnetic pole pitch Lp is set to 8.5 mm. In this example, the magnetic pole pitch Lp is equal to the distance Lc between the axial center positions of the pair of axis-orthogonal portions 41, which is the condition under which the amplitude of the alternating magnetic field applied to the magnetic wire FE becomes the largest.

[0064] As shown in Figures 5A and 5B, the north pole is located in the center and the south poles are located on either side of it. In Figure 5A, the north pole faces the axial center position 25 of the magnetic wire FE, and therefore the boundaries between the north pole and the south poles on either side face the axial center positions of the axis-orthogonal portions 41 of the magnetic flux conduction pieces FL1 and FL2 on both sides. Figure 5B shows the magnetic flux in a magnetic pole arrangement that is moved 0.5 mm to the right from the reference position, with the magnetic pole arrangement in Figure 5A being the reference position.

[0065] As shown in Fig. 5A, when the central magnetic pole (N pole) faces the center of the power generation sensor 20, no magnetic flux passes through the magnetic wire FE. On the other hand, as shown in Fig. 5B, when the N pole moves slightly to the right from the center of the power generation sensor 20, magnetic flux passes through the magnetic wire FE from the right magnetic flux conduction piece FL2 toward the left magnetic flux conduction piece FL1.

[0066] Figure 5C shows the results of investigating the magnetic flux density at each part of the magnetic wire FE for each magnetic pole arrangement in which the magnetic pole was moved 0.5 mm to the right from the reference position (see Figure 5A). The horizontal axis indicates the position within the magnetic wire FE, with 0 being the axial center position of the magnetic wire FE. The vertical axis indicates the magnetic flux density. While a two-dimensional simulation can easily determine the direction of magnetic flux flow and the tendency of magnetic flux density, the absolute value of magnetic flux density cannot be determined, so the vertical axis of the graph is in arbitrary units (arb. units). In addition, in the graph, magnetic flux flowing from left to right is considered positive, and magnetic flux flowing from right to left is considered negative.

[0067] It can be seen that the magnetic flux density of the magnetic wire FE increases as the magnetic pole arrangement moves away from the reference position. Furthermore, it can be seen that the magnetic flux density is almost constant at any axial position inside the magnetic wire FE, and that the magnetic flux density is almost uniform regardless of the axial position. Although not shown, in the magnetic pole arrangement on the left side of the reference position, the sign of the magnetic flux density is reversed, and similar results are obtained.

[0068] The axially parallel portions 42 of the L-shaped magnetic flux conduction pieces FL1, FL2 block magnetic flux entering the axially intermediate portion of the magnetic wire FE and collect the magnetic flux and guide it to both ends of the magnetic wire FE. This improves the uniformity of the magnetic flux density over the entire axial length of the magnetic wire FE. Furthermore, because the magnetic flux conduction pieces FL1, FL2 can collect magnetic flux and efficiently guide it to both ends of the magnetic wire FE, a large Barkhausen effect can be exerted in response to changes in the magnetic field, generating a pulse voltage, even if the distance to the magnetic field generating source 50 is somewhat long.

[0069] FIG. 6 is a diagram for explaining the operation of the power generation sensor 20 as the disk 32 rotates, showing the change in magnetic flux density with respect to the rotation angle of the disk 32.

[0070] When the detection pitch of the power generation sensor 20 (the distance Lc between the axial center positions of the pair of axis-orthogonal portions 41) matches the magnetic pole pitch (Lp) on the circumferential orthogonal portion 41, the magnetic flux density of the magnetic wire FE changes sinusoidally with respect to the rotation angle. If the magnetic pole pitch is longer, an angular region will be created in which both ends of the power generation sensor 20 detect the same polarity, resulting in an angular region in which the magnetic flux density changes gradually near 0. As the detection radius increases, the angular region in which the same polarity is detected increases, and therefore the phase difference between the generation positions of the pulse voltages during forward and reverse rotation increases.

[0071] Here, we assume that the power generation sensor 20 is arranged so that its detection pitch is equal to the magnetic pole pitch (Lp) on the circumferential orbit 51. The angle when the axial center positions of the pair of axis-orthogonal portions 41 are aligned with the magnetic pole boundary lines 55 (see FIG. 3) on both circumferential sides of one magnetic pole (e.g., the north pole) is defined as 0 degrees, and the angle value increases in the counterclockwise direction (CCW). In this case, the change in magnetic flux density accompanying the rotation of the disk 32 about the rotation axis 33 is sinusoidal, as shown in FIG. 6. The magnetic flux density here refers to the magnetic flux density passing through the magnetic wire FE, i.e., the density of the magnetic flux component in the vicinity of the magnetic wire FE, parallel to the axial direction x of the magnetic wire FE. This also applies to the other embodiments described below. The operating magnetic field and stabilizing magnetic field of the magnetic wire FE are also shown in FIG. 6.

[0072] When the ring-shaped multi-pole magnet M rotates counterclockwise (CCW) together with the disk 32, if the magnetic flux density falls below the negative stabilizing magnetic field, a positive pulse is prepared (positive set state), and if the magnetic flux density subsequently exceeds the positive operating magnetic field, a positive pulse PP is generated. Also, when the ring-shaped multi-pole magnet M rotates counterclockwise (CCW) together with the disk 32, if the magnetic flux density exceeds the positive stabilizing magnetic field, a negative pulse is prepared (negative set state), and if the magnetic flux density subsequently falls below the negative operating magnetic field, a negative pulse NP is generated. Therefore, as shown in FIG. 6 , positive pulses PP are generated near 90 degrees and 270 degrees, and negative pulses NP are generated near 0 degrees and 180 degrees.

[0073] Similarly, when the ring-shaped multi-polar magnet M rotates clockwise (CW) together with the disk 32, a positive pulse ready state (positive set state) is entered when the magnetic flux density falls below the negative stabilizing magnetic field, and a positive pulse PP is generated when the magnetic flux density subsequently exceeds the positive operating magnetic field. Also, when the ring-shaped multi-polar magnet M rotates clockwise (CW) together with the disk 32, a negative pulse ready state (negative set state) is entered when the magnetic flux density subsequently exceeds the positive stabilizing magnetic field, and a negative pulse NP is generated when the magnetic flux density subsequently falls below the negative operating magnetic field. Therefore, as shown in FIG. 6 , negative pulses NP are generated near 90 degrees and 270 degrees, and positive pulses PP are generated near 0 degrees and 180 degrees.

[0074] By performing a predetermined counting operation in response to the generation of the positive pulse PP and the negative pulse NP, it is possible to obtain a count value corresponding to the number of rotations of the rotary shaft.

[0075] Fig. 7A is a cross-sectional view showing the structure of a multi-rotation absolute encoder 101 according to another embodiment of the present invention, Fig. 7B is a plan view thereof, and Fig. 7C is a bottom view thereof. In Figs. 7A, 7B, and 7C, parts that are the same as those shown in Figs. 2A, 2B, and 2C described above are given the same reference numerals, and descriptions thereof will be omitted.

[0076] In the above-described embodiment, the magnetic field generator 50 is constituted by a single ring-shaped multi-pole magnet M magnetized with multiple poles. In contrast, in the configuration example shown in FIGS. 7A to 7C , the magnetic field generator 50 includes a plurality of individual magnets, i.e., 2k (k=2 in the illustrated example) M1, M2, ... (four individual magnets M1, M2, M3, M4 in the illustrated example), and these individual magnets M1, M2, ... are fixed to the side of the disk 32 opposite the printed wiring board 31. Also, while the above-described embodiment includes a plurality of (specifically, three) power generation sensors 20, in this embodiment, a single power generation sensor 20 is mounted on the surface of the printed wiring board 31 opposite the disk 32. The configuration and arrangement of the power generation sensor 20 (the position and the orientation of the magnetic wire FE) are the same as those in the above-described embodiment.

[0077] The multiple individual magnets M1, M2, ... are magnetized in a direction parallel to the rotation axis 33 and are arranged at equal angular intervals around the rotation axis 33 (at 90-degree intervals in the illustrated example), that is, at equal intervals along a circumferential path 51 centered on the rotation axis 33. In a plan view seen from a direction parallel to the rotation axis 33 (see FIG. 7B ), the north and south poles are arranged alternately in the circumferential direction around the rotation axis 33. That is, as the disk 32 rotates in one direction around the rotation axis 33, the north and south poles alternately enter the detection region SR of the power generation sensor 20, generating an alternating magnetic field in the vicinity of the power generation sensor 20.

[0078] 7A and 8, which is a perspective view of the disk 32, the disk 32 has a boss 32b (hub) that surrounds the opening 32a and protrudes along the rotation axis 33 on the side opposite to the printed wiring board 31. The rotation shaft 30 can be inserted into this boss and fixed.

[0079] Furthermore, on the side of the disk 32 opposite the printed wiring board 31, a plurality of recesses 32c (see FIG. 7A) for fitting and fixing the plurality of individual magnets M1, M2, ... are formed in accordance with the desired arrangement of the plurality of individual magnets M1, M2, .... As a result, the plurality of individual magnets M1, M2, ... are held (fixed) on the disk 32 in a state where they are accurately positioned within a plane perpendicular to the rotation axis 33.

[0080] The individual magnets M1, M2, ... are, for example, cylindrical (columnar) magnets having a central axis parallel to the rotation axis 33, and in this case, the recess 32c has a cylindrical inner wall surface parallel to the rotation axis 33. In this example, the recess 32c does not penetrate the disk 32, but has a bottom with which one end face (the upper end face in FIG. 7A ) of the individual magnets M1, M2, ... abuts. As a result, the individual magnets M1, M2, ... are held (fixed) to the disk 32 while being accurately positioned in a direction parallel to the rotation axis 33.

[0081] 7A, 7B, and 7C, which require fixing a plurality of individual magnets M1, M2, ... to the disk 32. On the other hand, from the viewpoint of design freedom (versatility) for various sizes (diameters) of the opening 32a, the structures of the previous embodiment using one multi-pole magnet M are advantageous.

[0082] In particular, in embodiments using a multi-pole magnet M, it is necessary to manufacture a ring-shaped multi-pole magnet M specially designed to match the size (diameter) of the opening 32a, and a dedicated magnetizing yoke must be prepared for this purpose. In contrast, in embodiments using multiple individual magnets M1, M2, ..., permanent magnets of the same design can be used universally as the individual magnets M1, M2, ... for various sizes (diameters) of the opening 32a. In addition, because universal magnets that can be manufactured by magnetizing in the thickness direction with an air-core coil can be used as the individual magnets M1, M2, M3, M4, magnet costs can be reduced.

[0083] As in the previous embodiment, a reflective pattern 70 that is detected by the optical sensor 60 is formed on the surface of the disk 32 facing the printed wiring board 31. When viewed in a direction parallel to the rotation axis 33, an annular region 75 on which the reflective pattern 70 is formed overlaps with the plurality of individual magnets M1, M2, ... that make up the magnetic field generation source 50. This arrangement makes it possible to reduce the radial size of the multi-rotation absolute encoder 101.

[0084] 9A and 9B show the results of a two-dimensional magnetic simulation when a single magnet 410 simulating one of the individual magnets M1, M2, ... is placed in the detection area of ​​the power generation sensor 20. The magnetization direction of the magnet 410 is the direction z perpendicular to the axis, and the magnetic poles of the magnet 410 are N pole on the side facing the power generation sensor 20 and S pole on the opposite side. The total length Lw of the magnetic wire FE is 11 mm, and the distance Ld from the surface of the magnet 410 to the axial center position 25 of the magnetic wire FE (the center position in the axial direction x) is 4.5 mm.

[0085] 9A shows the magnetic flux when the magnet 410 faces the axial center position of the magnetic wire FE, i.e., when the magnet 410 is in the center of the detection area of ​​the power generation sensor 20. As shown in Fig. 9A, when the magnet 410 is in the center, the magnetic flux entering the pair of magnetic flux conduction pieces FL1, FL2 is balanced, and no magnetic flux passes through the magnetic wire FE. The magnetic flux from the magnet 410 toward the axial middle of the magnetic wire FE is blocked by the axial parallel portions 42 of the magnetic flux conduction pieces FL1, FL2, and is collected by the axial parallel portions 42 before being conducted through the magnetic flux conduction pieces FL1, FL2.

[0086] 9B shows the magnetic flux when the magnet 410 is positioned 0.5 mm to the right of the reference position, where the position of the magnet 410 in FIG. 9A is taken as the reference position. As shown in FIG. 9B, when the magnet 410 moves slightly to the right from the reference position, magnetic flux passes through the magnetic wire FE from the magnetic flux conduction piece FL2 on the right to the magnetic flux conduction piece FL1 on the left.

[0087] 9C shows the results of measuring the magnetic flux density at each part of the magnetic wire FE at each magnet position obtained by moving the magnet 410 to the right at 0.5 mm intervals from the reference position. The horizontal and vertical axes are the same as those in FIG. 5C.

[0088] It can be seen that the magnetic flux density in the magnetic wire FE increases as the magnet position moves away from the reference position. It can also be seen that the magnetic flux density is almost constant inside the magnetic wire FE, and is almost uniform regardless of axial position. Although not shown, at the magnet position to the left of the reference position, the sign of the magnetic flux density is reversed, and similar results are obtained.

[0089] In this way, when the individual magnets M1, M2, ... pass through the detection area of ​​the power generation sensor 20, the magnetic flux density in the magnetic wire FE changes sufficiently, and a uniform magnetic flux density can be achieved over the entire axial length of the magnetic wire FE. Furthermore, since the magnetic flux can be collected by the magnetic flux conduction pieces FL1, FL2 and efficiently induced to both ends of the magnetic wire FE, a large Barkhausen effect can be exerted in response to changes in the magnetic field, and a pulse voltage can be generated, even if the distance to the magnetic field generation source 50 (individual magnets M1, M2, ...) is somewhat long.

[0090] FIG. 10 is a diagram for explaining the operation of the power generation sensor as the disk 32 rotates, showing the change in magnetic flux density with respect to the rotation angle of the disk.

[0091] The state shown in the plan view of Figure 7B, i.e., a state in which one south pole (the upper magnetic pole of individual magnet M3) faces the center of the power generation sensor 20 and one north pole (the upper magnetic pole of individual magnet M4) is located 90 degrees away in the clockwise direction CW, is taken as the origin (0 degrees) of the rotation angle. The angle value increases in the counterclockwise direction CCW. The change in magnetic flux density accompanying the rotation of the disk 32 in this case is shown in Figure 10. The magnetic flux density here refers to the density of the magnetic flux component passing through the magnetic wire FE.

[0092] 7B , in this embodiment, the arrangement interval D of the magnetic poles (upper magnetic poles) of the individual magnets M1, M2, ... that face the power generation sensor 20 is longer than the total length Lw of the magnetic wire FE. In addition, the length d of the magnetic poles (here, the diameter of the cylindrical individual magnets M1, M2, ...) on the orbit 51 when the magnetic poles of the individual magnets M1, M2, ... rotate together with the disk 32 around the rotation axis 33 is shorter than the total length Lw of the magnetic wire and is 50% or less of the arrangement interval D.

[0093] The magnetic field generating source 50 (magnets M1, M2, M3, and M4) generates two cycles of alternating magnetic field per rotation of the rotating shaft 30 around the rotation axis 33. When the four magnets M1, M2, M3, and M4 rotate counterclockwise (CCW) together with the disk 32, a positive pulse ready state (positive set state) is entered when the magnetic flux density falls below the negative stabilizing magnetic field. A positive pulse PP is then generated when the magnetic flux density subsequently exceeds the positive operating magnetic field. Also, when the four magnets M1, M2, M3, and M4 rotate counterclockwise (CCW) together with the disk 32, a negative pulse ready state (negative set state) is entered when the magnetic flux density subsequently exceeds the positive stabilizing magnetic field. A negative pulse NP is then generated when the magnetic flux density subsequently falls below the negative operating magnetic field. Therefore, as shown in FIG. 10 , negative pulses NP are generated near 0 degrees and 180 degrees, and positive pulses PP are generated near 90 degrees and 270 degrees.

[0094] Similarly, when the four magnets M1, M2, M3, and M4 rotate clockwise (CW) together with the disk 32, a positive pulse ready state (positive set state) is entered when the magnetic flux density falls below the negative stabilizing magnetic field, and a positive pulse PP is generated when the magnetic flux density subsequently exceeds the positive operating magnetic field. Also, when the four magnets M1, M2, M3, and M4 rotate clockwise (CW) together with the disk 32, a negative pulse ready state (negative set state) is entered when the magnetic flux density subsequently exceeds the positive stabilizing magnetic field, and a negative pulse NP is generated when the magnetic flux density subsequently falls below the negative operating magnetic field. Therefore, as shown in FIG. 10 , a positive pulse "P" is generated near 0 degrees (360 degrees) and 180 degrees, and a negative pulse "N" is generated near 90 degrees and 270 degrees.

[0095] The change in magnetic flux density with respect to the rotation angle is very steep near 0 degrees (360 degrees), 90 degrees, 180 degrees, and 270 degrees. Therefore, there is little variation in the pulse generation position (the angle at which the pulse is generated), and the deviation in the pulse generation position depending on the direction of rotation, i.e., the phase difference, is extremely small. In addition, because the angle difference from the operating magnetization to the stabilizing magnetic field is very small, the range (reversal range) in which so-called pulse missing occurs when the direction of movement (direction of rotation) is reversed is narrow.

[0096] Furthermore, since the major axis direction of the power generation sensor 20 is the tangent direction of the circumference 36 having its center on the rotation axis 33 (see FIG. 7B), it is possible to reduce the outer size of the encoder 101. From another perspective, it is possible to increase the diameter of the hollow portion (opening 32a) of the disk 32.

[0097] As described above, since the arrangement interval D of the four magnetic poles (individual magnets M1, M2, M3, M4) is longer than the total length Lw of the magnetic wire FE (preferably 1.5 times or more), as shown in Figure 10, a flat portion where the magnetic flux density is 0 appears in the intermediate region between 0 degrees (360 degrees), 90 degrees, 180 degrees, and 270 degrees where the pulse is generated. This makes it possible to separate the influence of the magnetic field from adjacent magnetic poles on the track 51, and to make the change in magnetic flux density steeper in the vicinity of 0 degrees (360 degrees), 90 degrees, 180 degrees, and 270 degrees. This tendency is further strengthened by setting the length d of the magnetic poles on the track 51 to 50% or less of the arrangement interval D of the magnetic poles.

[0098] In this embodiment, the length d of the magnetic pole on the track 51 is shorter than the total length Lw of the magnetic wire FE. This ensures a steep change in magnetic flux density without creating a flat portion in the change in magnetic flux density near 0 degrees (360 degrees), 90 degrees, 180 degrees, and 270 degrees. Setting the length d of the magnetic pole to half or less of the total length Lw of the magnetic wire FE is preferable because it allows for a steeper change in magnetic flux density.

[0099] With this configuration, a pulse is generated each time one of the individual magnets M1, M2, M3, and M4 passes through the detection region SR along the orbit 51 during counterclockwise CCW rotation about the rotation axis 33, so that a pulse voltage of four pulses can be generated per rotation. Similarly, a pulse is generated each time one of the individual magnets M1, M2, M3, and M4 passes through the detection region SR along the orbit 51 during clockwise CW rotation about the rotation axis 33, so that a pulse voltage of four pulses can be generated per rotation.

[0100] Although the embodiments of the present invention have been described in detail, these are merely examples used to clarify the technical contents of the present invention, and the present invention should not be construed as being limited to these examples, and the scope of the present invention is limited only by the appended claims.

[0101] 1: Precision absolute angle detector 2: Multi-rotation detector 20: Power generation sensor 23: Wire arrangement section 25: Shaft center position 27: Symmetry plane 30: Rotation axis 31: Printed wiring board 32: Disk (rotating body) 33: Rotation axis 35: Air gap 41: Axis-orthogonal section 42: Axis-parallel section 50: Magnetic field generation source 60: Optical sensor 61: Light source 62: Light-receiving element 70: Reflection pattern 75: Annular area 100: Multi-rotation absolute encoder 101: Multi-rotation absolute encoder Lw: Total length of magnetic wire D: Arrangement interval d: Length of magnetic pole FE: Magnetic wire FL1: First magnetic flux conducting piece FL2: Second magnetic flux conducting piece M: Multi-pole magnet M1, M2, ...: Individual magnets SR: Detection area x: Axial direction z: Orthogonal direction to the axis

Claims

a rotating body that rotates around a rotation axis; a printed wiring board facing the rotor with a gap in a direction parallel to the rotation axis; a reflection pattern formed in a circumferential annular region having a center on the rotation axis on a surface of the rotating body facing the printed wiring board, the reflection pattern having angle information encoded and recorded thereon; a magnetic field generating source held by the rotating body on a side farther from a surface of the rotating body facing the printed wiring board, the magnetic field generating source having a plurality of magnetic poles magnetized in a direction parallel to the rotation axis; an optical sensor mounted on a surface of the printed wiring board facing the rotating body, the optical sensor having a light source that irradiates light toward the rotating body and a light receiving element that receives light reflected from the rotating body; a power generation sensor mounted on a surface of the printed wiring board opposite to the rotating body, the power generation sensor responding to the magnetic field generated by the magnetic field generation source; the power generating sensor includes a magnetic wire that exhibits the large Barkhausen effect, a coil wound around the magnetic wire, and a pair of magnetic flux conducting pieces made of soft magnetic materials that are symmetrical with respect to a symmetry plane set at the center position of the axial direction of the magnetic wire, and is mounted on the opposite surface of the printed wiring board so that the axial direction of the magnetic wire is along a tangent direction of a circumference having a center on the rotation axis; the pair of magnetic flux conduction pieces comprise a pair of axis-orthogonal portions extending parallel to each other in a direction perpendicular to the axial direction from both ends of the magnetic wire, and a pair of axis-parallel portions extending toward each other along the axial direction from the tips of the axis-orthogonal portions, with their proximal ends facing each other with a gap in the axial direction, the axis-orthogonal portions having wire placement portions consisting of holes or grooves that pass through in the axial direction and to which both ends of the magnetic wire are fixed, and the axis-parallel portions are placed between the magnetic wire and the opposite surface of the printed wiring board, a multi-rotation absolute encoder.

2. The multi-rotation absolute encoder according to claim 1, wherein the magnetic field generating source is arranged so as to overlap part or all of the annular region in which the reflection pattern is formed when viewed in a direction parallel to the rotation axis.

3. The multi-rotation absolute encoder according to claim 1, wherein the number of magnetic poles of the magnetic field generating source is four. 　 the spacing between the magnetic poles of the magnetic field generating source is longer than the total length of the magnetic wire; 4. The multi-rotation absolute encoder according to claim 3, wherein a length of the magnetic poles on an orbit when the magnetic poles rotate together with the rotating body around the rotation axis is shorter than a total length of the magnetic wire and is 50% or less of the arrangement interval. 　 the magnetic field generation source is four magnets magnetized in a direction parallel to the rotation axis, 5. The multi-rotation absolute encoder according to claim 4, wherein the four magnets are held by the rotating body and arranged with their north and south poles alternately arranged on a circumference having a center on the rotation axis.

Images