Absolute Encoder

Abstract

To provide means for improving accuracy of detecting a rotation angle of a revolving shaft due to magnetic flux distribution of a magnet.SOLUTION: In an absolute encoder 2, a support shaft 42 is fixed at one end to a gear base part 3 as a substrate and having a flange part at other end. Inner races of a first bearing 43 and a second bearing 44 as at least one bearing are secured to the support shaft 42. The first bearing 43 and the second bearing 44 are arranged between the gear base part 3 and the flange part in an axial direction. A spacer 45 is arranged between the first bearing 43 and second bearing 44 and a magnet Mq in the axial direction of the support shaft 42. The spacer 45, in the inside of a bearing fixing part, comes into contact from the axial direction of outer rings of the first bearing 43 and the second bearing 44.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an absolute encoder. [Background technology]

[0002] Absolute type absolute encoders (hereinafter referred to as "absolute encoders") that detect absolute positions or angles have been known as rotary encoders used to detect the positions and angles of movable elements in various types of control machinery.

[0003] Some absolute encoders measure the amount of rotation of the main shaft based on the rotation angle of the counter shaft. Such absolute encoders detect the rotation angle of the counter shaft based on changes in the magnetic field of a magnet attached to the tip of the counter shaft or a rotating body such as a gear attached to the counter shaft. The change in the magnetic field is detected by an angle sensor installed opposite the magnet. The detection accuracy of the angle sensor increases the less the influence of magnetic flux other than that from the magnet to be detected.

[0004] A rotation detection device is known that includes two magnetic encoders, each having a magnetization pattern with magnetic poles arranged on a circumference and different in number of magnetic poles, and a magnetic sensor that detects the magnetic field of each of the magnetic encoders. In this rotation detection device, a magnetic spacer is provided between the magnetization pattern of the two magnetic encoders (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-267868 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the rotating shaft of an absolute encoder, for example in the sub-shaft, a bearing is placed directly below the magnet attached for angle detection. In an absolute encoder with such a rotating shaft structure, the bearing, which is a magnetic material, acts as a magnetic path, causing disturbance in the magnetic flux distribution on the angle detection surface side (upper side) of the magnet, which may result in a deterioration in the detection accuracy of the angle error.

[0007] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide an absolute encoder that can improve the detection accuracy of the rotation angle of a rotating shaft caused by the magnetic flux distribution of a magnet. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, an absolute encoder of the present invention comprises a support shaft having one end fixed to a substrate and a flange portion at the other end, at least one bearing having an inner ring fixed to the support shaft, a magnetized magnet, a spacer arranged between the bearing and the magnet in the axial direction of the support shaft, a magnet holder for holding the magnet, and a magnetic sensor for detecting magnetic flux from the magnet, wherein the magnet holder has a bearing fixing portion which is a recess open on one side in the axial direction and is fixed to the outer ring of the bearing, and a magnet holding portion which is a recess formed on the other end side of the bearing fixing portion, the bearing is arranged between the substrate and the flange portion in the axial direction, and the spacer abuts against the outer ring of the bearing from the axial direction inside the bearing fixing portion.

[0009] In an absolute encoder according to one aspect of the present invention, the substrate has a hole through which the support shaft can be inserted, and the support shaft has a male threaded portion at one end, and is fixed to the substrate together with the bearing by inserting the male threaded portion into the hole.

[0010] An absolute encoder according to one aspect of the present invention further comprises a washer disposed between the substrate and the bearing in the axial direction.

[0011] In an absolute encoder according to one aspect of the present invention, the spacer abuts against an inner periphery of the bearing fixing portion in the radial direction, and abuts against an outer ring of the bearing in the axial direction.

[0012] In an absolute encoder according to one aspect of the present invention, the flange portion has a surface on one end side in the axial direction facing a disk portion of an inner ring of the bearing.

[0013] In an absolute encoder according to one aspect of the present invention, the spacer is formed in an annular shape, and the flange portion is disposed on the inside of an inner circumferential surface of the spacer.

[0014] In the absolute encoder according to one aspect of the present invention, the support shaft is made of a magnetic material. Effect of the Invention

[0015] According to the absolute encoder of the present invention, it is possible to improve the detection accuracy of the rotation angle of the rotating shaft caused by the magnetic flux distribution of the magnet. [Brief description of the drawings]

[0016] [Figure 1] 1 is a perspective view showing a schematic configuration of an absolute encoder according to an embodiment of the present invention; [Diagram 2] 2 is a perspective view illustrating a schematic configuration of the absolute encoder illustrated in FIG. 1 with a shield plate removed. [Diagram 3] 3 is a perspective view showing a schematic configuration of the absolute encoder shown in FIG. 2 with the case removed. FIG. [Figure 4] 4 is a plan view illustrating a schematic configuration of the absolute encoder illustrated in FIG. 3 with the substrate removed. [Diagram 5] 4 is a bottom view of the angle sensor support substrate shown in FIG. 3. FIG. [Figure 6]5 is a cross-sectional view of the absolute encoder shown in FIG. 4 taken along line AA. [Figure 7] 5 is a cross-sectional view taken along line BB of the absolute encoder shown in FIG. 4. [Figure 8] 5 is a cross-sectional view of the absolute encoder shown in FIG. 4 taken along line CC. [Figure 9] 5 is a cross-sectional view taken along the line DD of the absolute encoder shown in FIG. 4. [Figure 10] 10 is a cross-sectional view of a first countershaft gear in the absolute encoder shown in FIG. 9. [Figure 11] 2 is a block diagram illustrating a schematic functional configuration of the absolute encoder illustrated in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present inventors have found that, in an absolute encoder, the amount of rotation (hereinafter also referred to as the "amount of rotation of the main shaft") over multiple revolutions (hereinafter also referred to as "multiple revolutions") of the main shaft can be specified by acquiring the rotation angle of a rotating body that rotates at a reduced speed in association with the rotation of the main shaft. That is, the amount of rotation of the main shaft can be specified by multiplying the rotation angle of the rotating body by the reduction ratio. Here, the range of the amount of rotation of the main shaft that can be specified increases in proportion to the reduction ratio. For example, if the reduction ratio is 50, the amount of rotation of 50 revolutions of the main shaft can be specified.

[0018] On the other hand, the required resolution of the rotating body decreases in proportion to the reduction ratio. For example, if the reduction ratio is 100, the required resolution of the rotating body per one rotation of the spindle is 360° / 100=3.6°, and a detection accuracy of ±1.8° is required. On the other hand, if the reduction ratio is 50, the required resolution of the rotating body per one rotation of the spindle is 360° / 50=7.2°, and a detection accuracy of ±3.6° is required.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiments and modified examples described below, the same or equivalent components and members are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The dimensions of the members in each drawing are enlarged or reduced as appropriate for ease of understanding. Some of the members that are not important for explaining the embodiment are omitted in each drawing. In addition, the gears are shown in the drawings without showing the tooth shape. Furthermore, terms including ordinal numbers such as first and second are used to explain various components, but these terms are used only for the purpose of distinguishing one component from other components, and the components are not limited by these terms. Note that the present invention is not limited by the present embodiment.

[0020] FIG. 1 is a perspective view showing the configuration of an absolute encoder 2 according to an embodiment of the present invention. FIG. 2 is a perspective view showing the configuration of the absolute encoder 2 with a shield plate 7 removed. In FIG. 2, a case 4 and an angle sensor support substrate 5 of the absolute encoder 2 are shown in a see-through state. FIG. 3 is a perspective view showing the configuration of the absolute encoder 2 with the case 4 removed. In FIG. 3, an angle sensor support substrate 5 of the absolute encoder 2 is shown in a see-through state. FIG. 4 is a plan view showing the configuration of the absolute encoder 2 with the angle sensor support substrate 5 removed. FIG. 5 is a view of the angle sensor support substrate 5 as seen from below. FIG. 6 is an AA cross-sectional view of the absolute encoder 2. FIG. 7 is a BB cross-sectional view of the absolute encoder 2. FIG. 8 is a CC cross-sectional view of the absolute encoder 2. FIG. 9 is a DD cross-sectional view of the absolute encoder 2.

[0021] As shown in FIG. 1 to FIG. 9, the absolute encoder 2 according to the embodiment of the present invention includes a first countershaft gear 40, a support shaft 42, a magnet Mq, an angle sensor Sq, a bearing fixing portion 411, a magnet holding portion 412, a first bearing 43, a second bearing 44, and a spacer 45. The support shaft 42 has one end fixed to a gear base portion 3 as a substrate, and has a flange portion 423 at the other end. The magnet Mq is magnetized. The first countershaft gear 40 also functions as a magnet holder that holds the magnet Mq. The angle sensor Sq functions as a magnetic sensor that detects the magnetic flux from the magnet Mq. The bearing fixing portion 411 is provided on the first countershaft gear 40. The bearing fixing portion 411 is a recess that is open on one side in the axial direction, and is fixed to the outer rings of the first bearing 43 and the second bearing 44. The magnet holding portion 412 is a recess formed on the other end side of the bearing fixing portion 411 in the first countershaft gear 40. The inner rings of the first bearing 43 and the second bearing 44, which serve as at least one bearing, are fixed to the support shaft 42. The first bearing 43 and the second bearing 44 are disposed between the gear base portion 3 and the flange portion 423 in the axial direction. The spacer 45 is disposed between the first bearing 43 and the second bearing 44 and the magnet Mq in the axial direction of the support shaft 42. The spacer 45 abuts against the outer rings of the first bearing 43 and the second bearing 44 from the axial direction inside the bearing fixing portion 411. The structure of the absolute encoder 2 will be specifically described below.

[0022] In this embodiment, for convenience of explanation, the absolute encoder 2 will be explained based on the XYZ Cartesian coordinate system. The X-axis direction corresponds to the horizontal left-right direction, the Y-axis direction corresponds to the horizontal front-rear direction, and the Z-axis direction corresponds to the vertical up-down direction. The Y-axis direction and the Z-axis direction are each perpendicular to the X-axis direction. In this explanation, the X-axis direction is also called the left side or right side, the Y-axis direction is also called the front side or rear side, and the Z-axis direction is also called the upper side or lower side. In the attitude of the absolute encoder 2 shown in Figures 1 and 2, the left side in the X-axis direction is the left side, and the right side in the X-axis direction is the right side. Also, in the attitude of the absolute encoder 2 shown in Figures 1 and 2, the front side in the Y-axis direction is the front side, and the back side in the Y-axis direction is the rear side. Also, in the attitude of the absolute encoder 2 shown in Figures 1 and 2, the upper side in the Z-axis direction is the upper side, and the lower side in the Z-axis direction is the lower side. A state viewed from above in the Z-axis direction is called a plan view, a state viewed from the front in the Y-axis direction is called a front view, and a state viewed from the left side in the X-axis direction is called a side view. These directional notations do not limit the orientation in which the absolute encoder 2 is used, and the absolute encoder 2 can be used in any orientation.

[0023] 1 and 2, the absolute encoder 2 is an absolute type encoder that, as described above, specifies and outputs the amount of rotation over multiple revolutions of the main shaft 1a of the motor 1. In the embodiment of the present invention, the absolute encoder 2 is provided at the upper end of the motor 1 in the Z-axis direction. In the embodiment of the present invention, the absolute encoder 2 has a substantially rectangular shape in a plan view, and has a horizontally elongated rectangular shape that is thin in the up-down direction, which is the extension direction of the main shaft 1a, in a front view and a side view. In other words, the absolute encoder 2 has a flattened rectangular parallelepiped shape that is longer in the horizontal direction than in the up-down direction.

[0024] The absolute encoder 2 has a hollow rectangular cylindrical case 4 that houses the internal structure. The case 4 includes a plurality of (for example, four) outer walls 4a that surround at least a part of the main shaft 1a of the motor 1, the main shaft gear 10, the first intermediate gear 20, the second intermediate gear 30, the first countershaft gear 40, and the second countershaft gear 50, and has an open upper end. A shield plate 7, which is a rectangular plate-shaped member serving as a magnetic flux shielding member, is fixed to the case 4 and the gear base portion 3 by board mounting screws 8a at the upper ends of the open four outer walls 4a.

[0025] The shield plate 7 is a plate-like member provided in the axial direction (Z-axis direction) between the angle sensors Sp, Sq, Sr and the outside of the absolute encoder 2. The shield plate 7 is made of a magnetic material to prevent magnetic interference between the angle sensors Sp, Sq, Sr provided inside the case 4 due to magnetic flux generated outside the absolute encoder 2.

[0026] The motor 1 may be, for example, a stepping motor or a DC brushless motor. For example, the motor 1 may be a motor used as a drive source for driving an industrial robot or the like via a reduction mechanism such as a harmonic gear device. Both top and bottom ends of the main shaft 1a of the motor 1 protrude from the motor case. The absolute encoder 2 outputs the amount of rotation of the main shaft 1a of the motor 1 as a digital signal.

[0027] The shape of the motor 1 is generally rectangular in plan view, and is also generally rectangular in the vertical direction. In other words, the motor 1 is generally cubic. In plan view, the length of each of the four outer walls constituting the outer shape of the motor 1 is, for example, 25 mm, that is, the outer shape of the motor 1 is 25 mm square. In addition, the absolute encoder 2 provided in the motor 1 is, for example, 25 mm square to match the outer shape of the motor 1.

[0028] 1 and 2, an angle sensor support substrate 5 is provided so as to cover the inside of the absolute encoder 2 together with a case 4 and a shield plate 7.

[0029] 5, the angle sensor support board 5 is a printed wiring board having a generally rectangular shape in a plan view and a thin plate shape in the vertical direction. The connector 6 is connected to the angle sensor support board 5 and serves to connect the absolute encoder 2 to an external device (not shown).

[0030] 2, 3, and 4, the absolute encoder 2 includes a main shaft gear 10 having a first worm gear portion 11 (first drive gear), and a first intermediate gear 20 having a first worm wheel portion 21 (first driven gear), a second worm gear portion 22 (second drive gear), and a third worm gear portion 28 (third drive gear). The absolute encoder 2 also includes a second intermediate gear 30 having a third worm wheel portion 31 (third driven gear) and a first spur gear portion 32 (fourth drive gear), a first countershaft gear 40 having a second worm wheel portion 41 (second driven gear) and a support shaft 42 (see FIG. 9), and a second countershaft gear 50 having a second spur gear portion 51 (third driven gear). Moreover, the absolute encoder 2 includes a magnet Mp, an angle sensor Sp corresponding to the magnet Mp, a magnet Mq, an angle sensor Sq corresponding to the magnet Mq, a magnet Mr, an angle sensor Sr corresponding to the magnet Mr, and a microcomputer 121.

[0031] As shown in FIGS. 4 and 6, the main shaft 1a of the motor 1 is an output shaft of the motor 1 and an input shaft that transmits a rotational force to the absolute encoder 2. The main shaft gear 10 is fixed to the main shaft 1a of the motor 1 and rotatably supported integrally with the main shaft 1a by a bearing member of the motor 1. The first worm gear portion 11 is provided on the outer periphery of the main shaft gear 10 as a first driving gear so as to rotate according to the rotation of the main shaft 1a of the motor 1. In the main shaft gear 10, the first worm gear portion 11 is provided so that its central axis coincides or approximately coincides with the central axis of the main shaft 1a. The main shaft gear 10 can be formed from various materials such as resin materials and metal materials. The main shaft gear 10 is formed from, for example, polyacetal resin.

[0032] As shown in Figs. 3 and 4, the first intermediate gear 20 is a gear portion that transmits the rotation of the main shaft gear 10 to the first countershaft gear 40 and the second intermediate gear 30. The first intermediate gear 20 is journaled around a rotation axis extending substantially parallel to the base 3b by a shaft 23. The first intermediate gear 20 is a substantially cylindrical member extending in the direction of the rotation axis. The first intermediate gear 20 includes a first worm wheel portion 21, a second worm gear portion 22, and a third worm gear portion 28, and has a through hole formed therein, through which the shaft 23 is inserted. The first intermediate gear 20 is journaled by inserting the shaft 23 into a first intermediate gear journal portion 3g provided on the base 3b of the gear base portion 3. The first worm wheel portion 21, the second worm gear portion 22, and the third worm gear portion 28 are arranged in this order at positions spaced apart from each other. The first intermediate gear 20 can be made of various materials such as a resin material, a metal material, etc. The first intermediate gear 20 is made of a polyacetal resin.

[0033] 4 and 7, the first worm wheel portion 21 is provided on the outer periphery of the first intermediate gear 20 as a first driven gear. The first worm wheel portion 21 is provided to mesh with the first worm gear portion 11 and rotate following the rotation of the first worm gear portion 11. The shaft angle between the first worm wheel portion 21 and the first worm gear portion 11 is set to 90° or approximately 90°. In other words, the central axis of the first worm wheel portion 21 is perpendicular to the central axis of the first worm gear portion 11.

[0034] Although there is no particular restriction on the outer diameter of the first worm wheel portion 21, in the illustrated example, the outer diameter of the first worm wheel portion 21 is set to be smaller than the outer diameter of the first worm gear portion 11, and the outer diameter of the first worm wheel portion 21 is reduced. This allows the absolute encoder 2 to be reduced in size in the vertical direction.

[0035] The second worm gear portion 22 is provided on the outer periphery of the first intermediate gear 20 as a second driving gear. The second worm gear portion 22 rotates with the rotation of the first worm wheel portion 21. The second worm gear portion 22 meshes with the second worm wheel portion 41 of the first countershaft gear 40 to rotate the first countershaft gear 40. In the first intermediate gear 20, the second worm gear portion 22 is provided such that its central axis coincides or approximately coincides with the central axis of the first worm wheel portion 21.

[0036] 4 and 8, the third worm gear portion 28 is provided on the outer periphery of the first intermediate gear 20. The third worm gear portion 28 rotates in conjunction with the rotation of the first worm wheel portion 21. The third worm gear portion 28 meshes with the third worm wheel portion 31 of the second intermediate gear 30 to rotate the second intermediate gear 30. In the first intermediate gear 20, the third worm gear portion 28 is provided such that its central axis coincides or approximately coincides with the central axis of the first worm wheel portion 21.

[0037] 4 and 9, the first countershaft gear 40 rotates integrally with the magnet Mq at a reduced speed in accordance with the rotation of the main shaft 1a. The first countershaft gear 40 includes a second worm wheel portion 41, a support shaft 42, a first bearing 43, a second bearing 44, and a spacer 45. In the first countershaft gear 40, the second worm wheel portion 41 is journaled by the support shaft 42 via the first bearing 43 and the second bearing 44.

[0038] FIG. 10 is a DD cross-sectional view of the first countershaft gear 40 in the absolute encoder 2. As shown in FIG.

[0039] As shown in Fig. 10, the second worm wheel portion 41 is a member having a substantially circular shape in a plan view. The second worm wheel portion 41 can be formed from various materials such as resin materials and metal materials. The second worm wheel portion 41 is formed from, for example, polyacetal resin. The second worm wheel portion 41 includes a bearing fixing portion 411, a magnet holding portion 412, and a step portion 413.

[0040] The second worm wheel portion 41 is provided on the outer periphery of the first countershaft gear 40 as a second driven gear, meshes with the second worm gear portion 22, and rotates according to the rotation of the second worm gear portion 22. The shaft angle between the second worm wheel portion 41 and the second worm gear portion 22 is set to 90° or approximately 90°. In other words, the central axis of the second worm wheel portion 41 is perpendicular to the central axis of the first worm wheel portion 21. The rotation axis (axis A) of the second worm wheel portion 41 is parallel or approximately parallel to the rotation axis of the first worm gear portion 11.

[0041] The bearing fixing portion 411 is a cylindrical hollow portion provided at a position centered on the axis A in the second worm wheel portion 41. The bearing fixing portion 411 is open on one side in the axis A direction, specifically, on the lower side in the Z-axis direction in Figs. 9 and 10. The radial dimension of the inner periphery 4111 of the bearing fixing portion 411 (direction perpendicular to the axis A, X-axis direction, Y-axis direction) may be a dimension that can fix the outer ring of the bearing of the first countershaft gear 40 and the second worm wheel portion 41. Specifically, the radial dimension of the inner periphery 4111 of the bearing fixing portion 411 is a dimension that can press-fit the outer rings 432, 442 of the first bearing 43 and the second bearing 44. The dimension of the bearing fixing portion 411 in the axis A direction (Z-axis direction) is a dimension that can accommodate the outer ring 432 of the first bearing 43 and the outer ring 442 of the second bearing 44 in the axis A direction. Further, the bearing fixing portion 411 is provided with a step portion 413. The step portion 413 is an annular surface centered on the axis A parallel to the X-axis and Y-axis on the other side in the direction of the axis A, that is, on the upper side in the Z-axis direction in Figures 9 and 10. Note that the second worm wheel portion 41 of the first countershaft gear 40 does not need to be provided with the step portion 413, for example, when the diameter of the magnet Mq and the diameters of the first bearing 43 and the second bearing 44 are the same.

[0042] The magnet holding portion 412, like the bearing fixing portion 411, is an annular hollow portion provided at a position centered on the axis A of the second worm wheel portion 41. The magnet holding portion 412 is formed to be able to accommodate the magnet Mq. The magnet holding portion 412 is provided on the other side in the direction of the axis A than the step portion 413, and on the upper side in the Z-axis direction in FIGS. 9 and 10. The magnet holding portion 412 holds the magnet Mq in the hollow portion described above.

[0043] The support shaft 42 has a shaft body 420, an outer circumferential portion 421, a male thread portion 422, and a flange portion 423. The shaft body 420 of the support shaft 42 is a shaft-shaped member with the axis A direction being the longitudinal direction. In the support shaft 42, the outer circumferential portion 421 is, for example, a cylindrical or approximately cylindrical peripheral surface centered on the axis A. The male thread portion 422 is provided on one end side of the shaft body 420, that is, on the outer circumferential portion 421 within a predetermined range from a lower end portion 424 on the lower side in the Z axis direction in Figs. 9 and 10. The flange portion 423 is provided on the other end side of the shaft body 420, on an upper end portion 425 on the upper side in the Z axis direction in Figs. 9 and 10. The flange portion 423 protrudes from the surface of the outer circumferential portion 421 of the shaft body 420 in the radially outward direction (the Y axis direction in Fig. 10) at the upper end portion 425. An upper surface (upper surface portion 426) and a lower surface (lower surface portion 427) of flange portion 423 are flat surfaces in a direction perpendicular to the axis A, that is, in the radial direction (the Y-axis direction in FIG. 10).

[0044] The support shaft 42 is attached to the base 3b of the gear base 3 so as to protrude substantially perpendicularly. The base 3b of the gear base 3 has a first countershaft gear support portion 3h as a hole through which the male thread portion 422 of the support shaft 42 can be inserted. The support shaft 42 is fixed to the base 3b of the gear base 3 together with the first bearing 43 and the second bearing 44 as follows. The male thread portion 422 of the support shaft 42 is inserted into the first countershaft gear support portion 3h from the upper side to the lower side in the Z-axis direction with the first bearing 43 and the second bearing 44 pressed in. A nut 60 is fastened to the male thread portion 422 protruding downward from the base 3b. The support shaft 42 fixed to the base 3b in this manner rotatably supports the second worm wheel portion 41 via the first bearing 43 and the second bearing 44.

[0045] The first bearing 43 has an inner ring 431, an outer ring 432, and a rolling element 433. The inner ring 431 is an annular member having an inner peripheral portion 4311 that can be attached to the outer peripheral portion 421 of the support shaft 42. The outer ring 432 is provided on the outer peripheral side of the inner ring 431. The outer ring 432 is an annular member that is coaxial with the inner ring 431 and has a larger diameter than the inner ring 431. The rolling elements 433 are spherical members arranged in plurality between the inner ring 431 and the outer ring 432. In the first bearing 43, the inner ring 431 is press-fitted into the outer peripheral portion 421 of the support shaft 42. In the first bearing 43, the cylindrical portion 4322 of the outer ring 432 is press-fitted into the inner peripheral portion 4111 of the bearing fixing portion 411 of the second worm wheel portion 41. In the first bearing 43, an upper disk portion 4321 in the axial A direction (Z-axis direction) of the outer ring 432 abuts against the spacer 45. Also, in the first bearing 43, an upper disk portion 4323 in the axial A direction (Z-axis direction) of the inner ring 431 abuts against a lower surface portion 427 of the flange portion 423. In this manner, the first bearing 43 is fixed with high precision to the second worm wheel portion 41 and the support shaft 42 in the axial A direction and the radial direction.

[0046] The second bearing 44 has an inner ring 441, an outer ring 442, and a rolling element 443. The inner ring 441 is an annular member having an inner peripheral portion 4411 that can be attached to the outer peripheral portion 421 of the support shaft 42. The outer ring 442 is provided on the outer peripheral side of the inner ring 441. The outer ring 442 is an annular member that is coaxial with the inner ring 441 and has a larger diameter than the inner ring 441. The rolling elements 443 are spherical members arranged in plurality between the inner ring 441 and the outer ring 442. In the second bearing 44, the inner ring 441 is press-fitted into the outer peripheral portion 421 of the support shaft 42. In the second bearing 44, an upper disk portion 4421 of the outer ring 442 in the axis A direction (Z-axis direction) abuts against a lower disk portion 4321 of the outer ring 432 of the first bearing 43. In the second bearing 44 , the cylindrical portion 4422 of the outer ring 442 is press-fitted into the inner circumferential portion 4111 of the bearing fixing portion 411 of the second worm wheel portion 41 .

[0047] The spacer 45 is an annular or substantially annular member having an annular disk portion 451 centered on the axis A, and a cylindrical outer peripheral portion 452 and an inner peripheral portion 453. The spacer 45 is disposed on the inner peripheral portion 4111 of the bearing fixing portion 411 in the radial direction. One side (lower side in the Z-axis direction) of the spacer 45 in the axis A direction abuts against the disk portion 4321 of the outer ring 432 of the first bearing 43. The other side (upper side in the Z-axis direction) of the spacer 45 in the axis A direction is in contact with the disk surface Mq1 on the lower side in the Z-axis direction of the magnet Mq. The disk surface Mq2 on the upper side in the Z-axis direction of the magnet Mq is in contact with the upper surface in the Z-axis direction of the magnet holding portion 412. Therefore, the spacer 45 abuts against the magnet holding portion 412 of the second worm wheel portion 41 via the magnet Mq. A flange portion 423 of the support shaft 42 is disposed radially inside the inner periphery 453 of the spacer 45 .

[0048] The washer 46 is disposed between the base 3b and the second bearing 44 in the axial direction A. The washer 46 has a smaller diameter than the outer ring 442 of the second bearing 44. The washer 46, which has a smaller diameter than the outer ring 442 of the second bearing 44, is disposed between the base 3b and the second bearing 44, so that the outer ring 432 of the first bearing 43 and the outer ring 442 of the second bearing 44 are rotatable with respect to the support shaft 42. That is, in the first countershaft gear 40, the second worm wheel portion 41 is rotatable with respect to the support shaft 42. The other side (upper side in the Z-axis direction) of the washer 46 in the axial direction A may be in contact with the disk portion 4412 on the lower side in the Z-axis direction of the inner ring 441 of the second bearing 44.

[0049] As configured as described above, in the absolute encoder 2, the multiple bearings (first bearing 43 and second bearing 44) of the first countershaft gear 40 are pressed into and fixed to the bearing fixing portion 411, thereby precisely fixing the first countershaft gear 40 to the support shaft 42 in the axial A direction and radial direction.

[0050] The magnet Mq is a permanent magnet provided on the axis A of the support shaft 42 at the tip side (upper side in the Z-axis direction) of the second worm wheel portion 41. The magnet Mq is fitted into the inner peripheral portion 4111 of the bearing fixing portion 411 in the radial direction. The magnet Mq is fixed to the upper side of the bearing fixing portion 411 in the direction of the axis A by being abutted against the spacer 45. The angle sensor Sq is provided on the axis A like the magnet Mq. The angle sensor Sq is provided in the vicinity of the magnet Mq, which is a range in which a change in the magnetic flux of the magnet Mq can be detected, for example, on or in the vicinity of the axis A. The angle sensor Sq detects a change in the magnetic flux generated from the magnet Mq.

[0051] In Figs. 4 and 8, the second intermediate gear 30 is a disk-shaped gear portion that rotates according to the rotation of the main shaft 1a and transmits the rotation of the main shaft 1a to the second countershaft gear 50 at a reduced speed. The second intermediate gear 30 is provided between the second worm gear portion 22 and the second spur gear portion 51 provided on the second countershaft gear 50. The second spur gear portion 51 meshes with the first spur gear portion 32. The second intermediate gear 30 has a third worm wheel portion 31 that meshes with the third worm gear portion 28 of the first intermediate gear 20, and a first spur gear portion 32 that drives the second spur gear portion 51. The second intermediate gear 30 is formed of, for example, polyacetal resin. The second intermediate gear 30 is a member that is substantially circular in plan view. The second intermediate gear 30 is journaled on the base portion 3b of the gear base portion 3.

[0052] By providing the second intermediate gear 30, the second countershaft gear 50, which will be described later, can be disposed at a position away from the third worm gear portion 28. This makes it possible to lengthen the distance between the magnets Mp and Mq and reduce the influence of leakage magnetic flux between them. Furthermore, by providing the second intermediate gear 30, the range in which the reduction ratio can be set is expanded accordingly, improving the degree of freedom in design.

[0053] The third worm wheel portion 31 is provided on the outer periphery of the second intermediate gear 30, meshes with the third worm gear portion 28, and rotates in accordance with the rotation of the third worm gear portion 28. The first spur gear portion 32 is provided on the outer periphery of the second intermediate gear 30 such that its central axis coincides or substantially coincides with the central axis of the third worm wheel portion 31. The first spur gear portion 32 meshes with the second spur gear portion 51, and rotates in accordance with the rotation of the third worm wheel portion 31. The rotation axes of the third worm wheel portion 31 and the first spur gear portion 32 are parallel or substantially parallel to the rotation axis of the first worm gear portion 11.

[0054] 8, the second countershaft gear 50 is a gear portion having a circular shape in a plan view, which rotates in accordance with the rotation of the main shaft 1a and transmits the rotation of the main shaft 1a to the magnet Mr at a reduced speed. The second countershaft gear 50 is journaled about a rotation axis extending substantially perpendicularly from the base portion 3b of the gear base portion 3. The second countershaft gear 50 includes a second spur gear portion 51 and a magnet holding portion that holds the magnet Mr.

[0055] The second spur gear portion 51 is provided on the outer periphery of the second countershaft gear 50. The second spur gear portion 51 is provided to mesh with the first spur gear portion 32 and rotate in accordance with the rotation of the third worm wheel portion 31. The rotation axis of the second spur gear portion 51 is provided parallel or approximately parallel to the rotation axis of the first spur gear portion 32. The second countershaft gear 50 can be formed from various materials such as resin materials and metal materials. The second countershaft gear 50 is formed from polyacetal resin.

[0056] Here, the direction in which the first worm wheel portion 21 moves toward the first worm gear portion 11 in order for the first worm wheel portion 21 to mesh with the first worm gear portion 11 is defined as a first meshing direction P1 (the direction of the arrow P1 in FIG. 4). Similarly, the direction in which the second worm gear portion 22 moves toward the second worm wheel portion 41 in order for the second worm gear portion 22 to mesh with the second worm wheel portion 41 is defined as a second meshing direction P2 (the direction of the arrow P2 in FIG. 4). Furthermore, the direction in which the third worm gear portion 28 moves toward the third worm wheel portion 31 in order for the third worm gear portion 28 to mesh with the third worm wheel portion 31 is defined as a third meshing direction P3 (the direction of the arrow P3 in FIG. 4). In this embodiment, the first meshing direction P1, the second meshing direction P2, and the third meshing direction P3 are all along the horizontal plane (XY plane).

[0057] The magnet Mp is fixed to the upper surface of the main shaft gear 10 so that their central axes coincide or nearly coincide. The magnet Mp is supported by a magnet support part 17 provided on the central axis of the main shaft gear 10 via a holder part 16. The holder part 16 is formed of a non-magnetic material such as an aluminum alloy. The inner peripheral surface of the holder part 16 is formed, for example, in an annular shape corresponding to the outer diameter and the shape of the outer peripheral surface of the magnet Mp so as to contact the outer peripheral surface of the magnet Mp in the radial direction and hold the outer peripheral surface. The inner peripheral surface of the magnet support part 17 is formed, for example, in an annular shape corresponding to the outer diameter and the shape of the outer peripheral surface of the holder part 16 so as to contact the outer peripheral surface of the holder part 16. The magnet Mp has two magnetic poles aligned in a direction perpendicular to the rotation axis of the main shaft gear 10. The angle sensor Sp is provided on the lower surface 5a of the angle sensor support substrate 5 so that its lower surface faces the upper surface of the magnet Mp in the vertical direction via a gap in order to detect the rotation angle of the main shaft gear 10.

[0058] As an example, the angle sensor Sp is fixed to an angle sensor support substrate 5 supported by a substrate support 110 disposed on a gear base portion 3 of the absolute encoder 2, which will be described later. The angle sensor Sp detects the magnetic pole of the magnet Mp and outputs the detection information to the microcomputer 121. The microcomputer 121 specifies the rotation angle of the magnet Mp based on the input detection information on the magnetic pole, thereby specifying the rotation angle of the main shaft gear 10, i.e., the rotation angle of the main shaft 1a. The resolution of the rotation angle of the main shaft 1a corresponds to the resolution of the angle sensor Sp. As will be described later, the microcomputer 121 specifies the amount of rotation of the main shaft 1a based on the specified rotation angle of the first countershaft gear 40 and the specified rotation angle of the main shaft 1a, and outputs this. As an example, the microcomputer 121 may be configured to output the amount of rotation of the main shaft 1a of the motor 1 as a digital signal.

[0059] The angle sensor Sq detects the rotation angle of the second worm wheel portion 41, i.e., the rotation angle of the first countershaft gear 40. The magnet Mq is fixed to the upper surface of the first countershaft gear 40 so that their central axes coincide or nearly coincide. The magnet Mq has two magnetic poles aligned in a direction perpendicular to the rotation axis of the first countershaft gear 40. As shown in FIG. 3, the angle sensor Sq is provided so that its lower surface faces the upper surface of the magnet Mq in the vertical direction with a gap therebetween in order to detect the rotation angle of the first countershaft gear 40.

[0060] As an example, the angle sensor Sq is fixed to the angle sensor support substrate 5 on the same surface as the surface on which the angle sensor Sp is fixed. The angle sensor Sq detects the magnetic pole of the magnet Mq and outputs the detection information to the microcomputer 121. The microcomputer 121 identifies the rotation angle of the magnet Mq, i.e., the rotation angle of the first countershaft gear 40, based on the input detection information regarding the magnetic pole.

[0061] The angle sensor Sr detects the rotation angle of the second spur gear portion 51, i.e., the rotation angle of the second countershaft gear 50. The magnet Mr is fixed to the upper surface of the second countershaft gear 50 so that their central axes coincide or nearly coincide. The magnet Mr has two magnetic poles aligned in a direction perpendicular to the rotation axis of the second countershaft gear 50. As shown in FIG. 3, the angle sensor Sr is provided so that its lower surface faces the upper surface of the magnet Mr with a gap therebetween in the vertical direction in order to detect the rotation angle of the second countershaft gear 50.

[0062] As an example, the angle sensor Sr is fixed to an angle sensor support substrate 5 supported by a substrate support 110 disposed on a gear base portion 3 (described later) of the absolute encoder 2. The angle sensor Sr detects the magnetic pole of the magnet Mr and outputs the detection information to a microcomputer 121. The microcomputer 121 identifies the rotation angle of the magnet Mr, i.e., the rotation angle of the second countershaft gear 50, based on the input detection information relating to the magnetic pole.

[0063] A magnetic angle sensor with a relatively high resolution may be used for each magnetic sensor. The magnetic angle sensor is disposed facing the end face including the magnetic poles of each permanent magnet in the axial direction of each rotor with a certain gap therebetween, and identifies the rotation angle of the opposing rotor based on the rotation of these magnetic poles and outputs a digital signal. As an example, the magnetic angle sensor includes a detection element that detects the magnetic poles, and an arithmetic circuit that outputs a digital signal based on the output of the detection element. The detection element may include a plurality of magnetic field detection elements (e.g., four elements) such as a Hall element or a GMR (Giant Magneto Resistive) element.

[0064] The calculation circuit performs lookup calculations using, for example, the difference or ratio of the outputs of multiple detector elements as a key. The rotation angle may be specified by table processing using a table. The detection element and the arithmetic circuit may be integrated on a single IC chip. The IC chip may be embedded in a resin having a thin rectangular parallelepiped outer shape. Each magnetic sensor outputs an angle signal, which is a digital signal corresponding to the rotation angle of each rotating body detected, to the microcomputer 121 via a wiring member (not shown). For example, each magnetic sensor outputs the rotation angle of each rotating body as a multi-bit (e.g., 7-bit) digital signal.

[0065] FIG. 11 is a block diagram showing a schematic functional configuration of an absolute encoder. As shown in FIG. 11, the microcomputer 121 is fixed to the surface of the angle sensor support substrate 5 on the base part 3b side of the gear base part 3 by soldering, bonding, or other methods. The microcomputer 121 is composed of a CPU, and acquires digital signals representing the rotation angles output from the angle sensors Sp, Sq, and Sr, and calculates the amount of rotation of the main shaft gear 10. Each block of the microcomputer 121 shown in FIG. 11 represents a function that is realized by the CPU as the microcomputer 121 executing a program. Each block of the microcomputer 121 can be realized in hardware by elements and mechanical devices such as a computer's CPU (Central Processing Unit) and RAM (Random Access Memory), and in software by a computer program, etc., but here, functional blocks realized by their cooperation are depicted. Therefore, it will be understood by those skilled in the art who have read this specification that these functional blocks can be realized in various ways by combining hardware and software.

[0066] The microcomputer 121 includes a rotation angle acquisition unit 121p, a rotation angle acquisition unit 121q, a rotation angle acquisition unit 121r, a table processing unit 121b, a rotation amount determination unit 121c, and an output unit 121e. The rotation angle acquisition unit 121p acquires a rotation angle Ap, which is angle information indicating the rotation angle of the main shaft gear 10, i.e., the main shaft 1a, based on a signal output from the angle sensor Sp. The rotation angle acquisition unit 121q acquires a rotation angle Aq, which is angle information indicating the rotation angle of the first countershaft gear 40, based on a signal output from the angle sensor Sq. The rotation angle acquisition unit 121r acquires a rotation angle Ar, which is angle information indicating the rotation angle of the second countershaft gear 50 detected by the angle sensor Sr.

[0067] The table processing unit 121b refers to a first correspondence relationship table that stores the rotation angle Ap and the rotation speed of the main shaft gear 10 corresponding to the rotation angle Ap, and specifies the rotation speed of the main shaft gear 10 that corresponds to the acquired rotation angle Ap. Also, the table processing unit 121b refers to a second correspondence relationship table that stores the rotation angle Ar and the rotation speed of the main shaft gear 10 that corresponds to the rotation angle Ar, and specifies the rotation speed of the main shaft gear 10 that corresponds to the acquired rotation angle Ar.

[0068] The rotation amount specifying unit 121c specifies a first rotation amount over multiple rotations of the main shaft gear 10 according to the rotation speed of the main shaft gear 10 specified by the table processing unit 121b and the acquired rotation angle Aq. The output unit 121e converts the rotation amount over multiple rotations of the main shaft gear 10 specified by the rotation amount specifying unit 121c into information indicating the rotation amount and outputs the information.

[0069] The table processing unit 121b, the rotation amount specifying unit 121c, and the output unit 121e also function as an angle position information output unit that outputs the angle position information of the first worm gear unit 11 to an external control device (controller). Similarly, the table processing unit 121b, the rotation amount specifying unit 121c, and the output unit 121e also output angle error information for correcting the angle position information of the first worm gear unit 11 to the external control device.

[0070] The absolute encoder 2 configured in this manner can determine the rotation speed of the main shaft 1a in accordance with the rotation angles of the first countershaft gear 40 and the second countershaft gear 50 determined based on the detection information of the angle sensors Sq and Sr, and can determine the rotation angle of the main shaft 1a based on the detection information of the angle sensor Sp. Then, the microcomputer 121 determines the amount of rotation of the main shaft 1a over multiple rotations based on the determined rotation speed and rotation angle of the main shaft 1a.

[0071] The number of teeth of the first worm gear portion 11 of the main shaft gear 10 provided on the main shaft 1a is, for example, 1, and the number of teeth of the first worm wheel portion 21 is, for example, 20. In other words, the first worm gear portion 11 and the first worm wheel portion 21 constitute a first speed change mechanism with a reduction ratio of 20 / 1=20 (see FIG. 4). When the first worm gear portion 11 rotates 20 times, the first worm wheel portion 21 rotates once. The first worm wheel portion 21 and the second worm gear portion 22 are provided on the same axis to constitute the first intermediate gear 20 and rotate integrally. Therefore, when the first worm gear portion 11 rotates 20 times, i.e., when the main shaft 1a and the main shaft gear 10 rotate 20 times, the first intermediate gear 20 rotates once and the second worm gear portion 22 rotates once.

[0072] The number of teeth of the second worm gear portion 22 is, for example, 5, and the number of teeth of the second worm wheel portion 41 is, for example, 25. That is, the second worm gear portion 22 and the second worm wheel portion 41 constitute a second speed change mechanism with a reduction ratio of 25 / 5=5 (see FIG. 4). When the second worm gear portion 22 rotates five times, the second worm wheel portion 41 rotates one time. The first countershaft gear 40 on which the second worm wheel portion 41 is formed rotates integrally with the magnet Mq. Therefore, when the second worm gear portion 22 constituting the first intermediate gear 20 rotates five times, the magnet Mq rotates one time. From the above, when the main shaft 1a rotates 100 times, the first intermediate gear 20 rotates five times, and the first countershaft gear 40 and the magnet Mq rotate one time. That is, the number of rotations of the main shaft 1a for 50 rotations can be identified based on the detection information on the rotation angle of the first countershaft gear 40 detected by the angle sensor Sq.

[0073] The number of teeth of the third worm gear portion 28 is, for example, 1, and the number of teeth of the third worm wheel portion 31 is, for example, 30. That is, the third worm gear portion 28 and the third worm wheel portion 31 constitute a third speed change mechanism with a reduction ratio of 30 / 1=30 (see FIG. 4). When the third worm gear portion 28 rotates 30 times, the third worm wheel portion 31 rotates once. The second intermediate gear 30 on which the third worm wheel portion 31 is formed is provided with a first spur gear portion 32 having a central axis that coincides or approximately coincides with the central axis of the third worm wheel portion 31. Therefore, when the third worm wheel portion 31 rotates, the first spur gear portion 32 also rotates. The first spur gear portion 32 meshes with the second spur gear portion 51 provided on the second countershaft gear 50, and therefore, when the second intermediate gear 30 rotates, the second countershaft gear 50 also rotates.

[0074] The number of teeth of the second spur gear portion 51 is, for example, 40, and the number of teeth of the first spur gear portion 32 is, for example, 24. In other words, the first spur gear portion 32 and the second spur gear portion 51 constitute a fourth speed change mechanism with a reduction ratio of 40 / 24=5 / 3 (see FIG. 4). When the first spur gear portion 32 rotates five times, the second spur gear portion 51 rotates three times. The second countershaft gear 50 on which the second spur gear portion 51 is formed rotates integrally with the magnet Mr as described later. Therefore, when the third worm gear portion 28 constituting the first intermediate gear 20 rotates five times, the magnet Mr rotates one time. From the above, when the main shaft 1a rotates 1000 times, the first intermediate gear 20 rotates 50 times, the second intermediate gear 30 rotates 5 / 3 times, and the second countershaft gear 50 and the magnet Mr rotate one time. In other words, the number of rotations of the main shaft 1a for 1000 rotations can be determined based on the detection information regarding the rotation angle of the second countershaft gear 50 by the angle sensor Sr.

[0075] [Operation of absolute encoder] The operation of the absolute encoder 2 will now be described.

[0076] As described above (see Figs. 1 to 11), the first countershaft gear 40 of the absolute encoder 2 includes the second worm wheel portion 41 as the second driven gear, the support shaft 42, the first bearing 43, the second bearing 44, and the spacer 45. The male thread portion 422 of the support shaft 42 is fixed to the first countershaft gear support portion 3h of the gear base portion 3 by the nut 60. The support shaft 42 has a flange portion 423 at an upper end portion 425. The first bearing 43 and the second bearing 44 are disposed between the gear base portion 3 and the flange portion 423 in the axial direction. The outer ring 432 of the first bearing 43 and the outer ring 442 of the second bearing 44 are fixed to the bearing fixing portion 411 of the first countershaft gear 40. The magnet Mq is held by the magnet holding portion 412 of the first countershaft gear 40. In the axial direction A, a spacer 45 is disposed between the magnet Mq and the first and second bearings 43 and 44. The flange portion 423 of the support shaft 42 is disposed radially inside the inner periphery 453 of the spacer 45. The upright position of the support shaft 42 of the first countershaft gear 40 is obtained as follows. Specifically, on the lower side of the axial direction A of the first countershaft gear 40, a disk portion 4423 on the lower side of the axial direction A of the inner ring 441 of the second bearing 44 contacts the base portion 3b of the gear base portion 3 via a washer 46. Also, on the upper side of the axial direction A of the first countershaft gear 40, a disk portion 4323 on the upper side of the axial direction A of the inner ring 431 of the first bearing 43 press-fitted into the support shaft 42 contacts the lower surface portion 427 of the flange portion 423. Furthermore, the support shaft 42 is inserted into the first countershaft gear support portion 3h, and is fixed to the base portion 3b by fastening a nut 60 to the male thread portion 422. In this state, the force acting on the support shaft 42 by fastening the nut 60 acts on the upper disk portion 4323 of the inner ring 431 of the first bearing 43. In this manner, the first countershaft gear 40 is positioned between the flange portion 423 provided on the upper end portion 425 of the support shaft 42 and the first bearing 43 and the second bearing 44 press-fitted into the support shaft 42, thereby obtaining an upright position of the support shaft 42.

[0077] As a result of the above configuration, the absolute encoder 2 has the support shaft 42 standing upright as described above, and therefore does not need to provide a shaft support structure such as a flange (not shown) on the lower side of the axis A of the support shaft 42 to ensure that the support shaft 42 is upright. Therefore, the absolute encoder 2 can ensure a sufficient thickness in the vertical direction of the spacer 45 while suppressing an increase in the overall height of the first countershaft gear 40 in the vertical direction (axis A direction). Furthermore, the absolute encoder 2 can ensure a sufficient thickness in the vertical direction of the spacer 45, which increases the distance in the axis A direction between the magnet Mq and the first bearing 43 and the second bearing 44, which are magnetic bodies. Therefore, the absolute encoder 2 can reduce the effect of the first bearing 43 and the second bearing 44 becoming a magnetic path. Specifically, in the absolute encoder 2, the distribution of the surface magnetic flux density on the angle detection surface side of the magnet Mq is stabilized, thereby improving the detection accuracy of the angle information of the first countershaft gear 40 used to determine the amount of multiple rotations of the main shaft 1a. As a result, the absolute encoder 2 can provide an improvement in the determination of the amount of multiple rotations, and therefore the absolute encoder 2 can suppress errors in detecting the rotation angle.

[0078] Although the embodiment of the present invention has been described above, the present invention is not limited to the absolute encoder 2 according to the embodiment of the present invention, but includes all aspects included in the concept of the present invention and the scope of the claims. Furthermore, each configuration may be appropriately and selectively combined, or may be combined with known technology, so as to achieve at least some of the above-mentioned problems and effects. For example, the shape, material, arrangement, size, etc. of each component in the above embodiment may be appropriately changed depending on the specific use of the present invention.

[0079] For example, in the absolute encoder 2, the configuration of the first countershaft gear 40 described above may be combined with the second countershaft gear 50 to suppress vibration of the second countershaft gear 50 and improve the detection accuracy of the rotation angle of the countershaft.

[0080] For example, in the absolute encoder 2, the bearings provided on the first countershaft gear 40 described above are not limited to the two, the first bearing 43 and the second bearing 44, and may be three or more. In this case, it is sufficient that the outer ring of at least one bearing is press-fitted into the first countershaft gear 40.

[0081] For example, in the absolute encoder 2, the spacer 45 provided in the first countershaft gear 40 may have any shape as long as the spacer 45 abuts against the outer ring 432 of the first bearing 43. In other words, the shape of the spacer 45 may be such that the inner ring 431 and the support shaft 42 do not come into contact with the magnet Mq or the spacer 45. For this reason, the shape of the spacer 45 is not limited to the above-mentioned annular shape, and may be, for example, formed in a disk shape with a recess in part.

[0082] For example, in the support shaft 42 of the absolute encoder 2, the material of the support shaft 42 may be a magnetic material. By using a magnetic material for the material of the support shaft 42, the flange portion 423 extending radially outward (in a direction perpendicular to the axis A direction) from the shaft main body 420 can form a magnetic path for the magnetic flux from the magnet Mq. In other words, the support shaft 42 made of a magnetic material can prevent the first bearing 43 and the second bearing 44 from acting as a magnetic path by the flange portion 423 functioning as a magnetic shield for the magnetic flux from the magnet Mq toward the first bearing 43 and the second bearing 44. Therefore, by using a magnetic material for the support shaft 42, it is possible to suppress disturbance in the magnetic flux distribution on the angle detection surface side (upper side) of the magnet Mq, thereby improving the detection accuracy of the angle error. [Explanation of symbols]

[0083] 1...motor, 1a...main shaft, 1b...press-fit portion, 2...absolute encoder, 3...gear base portion, 3b...base portion, 3g...first intermediate gear shaft support portion, 3h...first countershaft gear shaft support portion, 4...case, 4a...outer wall portion, 5...angle sensor support board, 5a...underside, 6...connector, 7...shield plate, 8a...board mounting screw, 10...main shaft gear, 11...first worm gear portion, 16...holder portion, 17...magnet support portion, 20... First intermediate gear, 21...first worm wheel portion, 22...second worm gear portion, 23...shaft, 28...third worm gear portion, 30...second intermediate gear, 31...third worm wheel portion, 32...first spur gear portion, 40...first countershaft gear, 41...second worm wheel portion, 42...support shaft, 43...first bearing, 44...second bearing, 45...spacer, 46...washer, 50...second countershaft gear, 51...second spur gear portion, 60...nut, 110...substrate support, 121...microcomputer, 121b...table processing unit, 121c...rotation amount determination unit, 121e...output unit, 121p...rotation angle acquisition unit, 121q...rotation angle acquisition unit, 121r...rotation angle acquisition unit, 411...bearing fixing unit, 412...magnet holding unit, 413...step portion, 420...shaft main body, 421...outer periphery, 422...male thread portion, 423...flange portion, 424...lower end portion, 425...upper end portion, 426...upper surface portion, 4 27...lower surface portion, 431...inner ring, 432...outer ring, 433...rolling element, 441...inner ring, 442...outer ring, 443...rolling element, 451...disk portion, 452...outer circumference portion, 453...inner circumference portion, 4111...inner circumference portion, 4311...inner circumference portion, 4321, 4323...disk portion, 4322...cylindrical portion, 4411...inner circumference portion, 4412, 4421, 4423...disk portion, 4422...cylindrical portion, Sp...angle sensor, Sq...angle sensor, Sr...angle sensor

Claims

1. A support shaft having one end fixed to the substrate and a flange portion at the other end; At least one bearing having an inner ring fixed to the support shaft; A magnetized magnet, a spacer disposed between the bearing and the magnet in the axial direction of the support shaft; A magnet holder for holding the magnet; A magnetic sensor that detects magnetic flux from the magnet; Equipped with The magnet holder includes: a bearing fixing portion which is a recess having one side open in the axial direction and is fixed to an outer ring of the bearing; a magnet holding portion which is a recess formed on the other end side of the bearing fixing portion, the bearing is disposed between the base plate and the flange portion in the axial direction, The spacer abuts against an outer ring of the bearing from the axial direction inside the bearing fixing portion. Absolute encoder.

2. the substrate has a hole through which the support shaft can be inserted, The support shaft has a male threaded portion at one end, and is fixed to the substrate together with the bearing by inserting the male threaded portion into the hole.

2. The absolute encoder according to claim 1.

3. a washer disposed between the base plate and the bearing in the axial direction; 3. An absolute encoder according to claim 1 or 2.

4. The spacer abuts against an inner circumferential portion of the bearing fixing portion in the radial direction and against an outer ring of the bearing in the axial direction.

4. An absolute encoder according to claim 1.

5. The flange portion has a surface on one end side in the axial direction facing a disk portion of the inner ring of the bearing.

5. An absolute encoder according to claim 1.

6. The spacer is formed in an annular shape, and the flange portion is disposed on the inside of an inner circumferential surface of the spacer.

6. An absolute encoder according to claim 1.

7. The support shaft is made of a magnetic material.

7. An absolute encoder according to claim 1.

Images