Magnetic detection device and absolute encoder

Abstract

Shielding members of different thicknesses can easily be attached.　A magnetic detection device (60) comprises: a magnet (Mr) that has been magnetized; an angle sensor (Sr) that is a magnetic sensor detecting the magnetic flux from the magnet (Mr); a magnet holder (61) that retains the magnet (Mr); and a second layshaft gear shaft (62). The magnetic detection device (60) has a case (4) that has a plurality of outer wall sections (4a) and a lid section (4b) and accommodates the magnet (Mr) and the magnetic sensor (Sr) on the inside, and a flat plate-shaped shielding member (7) that has a shape corresponding to the lid section (4b) and is attached to the lid section (4b). The shielding member (7) has a protruding section (77) that protrudes to the outside from a peripheral section (731a), and the case (4) has, in an outside end section of the lid section (4b), a recessed section (4e) that opens toward the inside and accommodates the protruding section (77). The recessed section (4e) has a plurality of side wall sections (41e) with different widths, and a plurality of upper wall sections (42e) with different heights.

Description

[Technical Field]

[0001] The present invention relates to a magnetic detection device and an absolute encoder. [Background technology]

[0002] Magnetic detection devices that detect magnetic flux from magnets using magnetic sensors have been used in various technologies. Some rotary encoders used to detect the position and angle of moving elements in various control machines also use magnetic detection devices. Rotary encoders include incremental encoders that detect relative positions or angles and absolute encoders that detect absolute positions or angles. Some absolute encoders include a magnetic detection device. A known example of such an absolute encoder is a magnetic encoder that attaches a magnetized magnet to a rotating shaft (main shaft) to be measured and detects the rotation angle of the magnet using a magnetic sensor to detect the rotation amount of the main shaft. Another known method for determining the rotation amount of the main shaft over multiple revolutions is to acquire the rotation angle of a rotating body that decelerates and rotates in accordance with the rotation of the main shaft.

[0003] In such absolute encoders, in order to maintain the resolution of the amount of rotation of the spindle that can be specified while widening the range of the amount of rotation of the spindle that can be specified, a structure has been proposed in which the amount of rotation of multiple magnets is detected by magnetic sensors that serve as corresponding angle sensors. For example, a structure has been proposed in which the spindle and the countershaft or any subsequent shaft are connected by a reduction mechanism, and the amount of rotation of the magnet attached to each shaft is detected by a corresponding magnetic sensor to specify the amount of rotation of the spindle (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2019-15536 Summary of the Invention [Problem to be solved by the invention]

[0005] In such absolute encoders that detect the amount of rotation of a magnet, the magnetic flux of the magnet detected by a magnetic sensor changes periodically as the rotating shaft rotates, and the amount of rotation of the rotating shaft is detected based on this change in magnetic flux over a predetermined rotation period of the rotating shaft. Therefore, some of the magnetic flux generated by external devices can affect the magnetic sensor, which is a magnetic detection element, resulting in a deterioration in detection accuracy due to the influence of noise from external factors other than the magnetic flux from the permanent magnet that is the intended detection target. For this reason, absolute encoders sometimes include a magnetic shield member made of a magnetic material attached to the outside of the case to prevent the magnetic flux from external devices from affecting the magnetic sensor. However, in absolute encoders, the shielding performance required of magnetic shielding members varies depending on the usage environment and required specifications. The shielding performance of a magnetic shielding member can be changed by changing the plate thickness of the member. For this reason, it is desirable to be able to easily attach multiple different shielding members.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a magnetic detection device and an absolute encoder to which shield members of different thicknesses can be easily attached. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the magnetic detection device of the present invention comprises a magnetized magnet, a magnetic sensor that detects magnetic flux from the magnet, a magnet holder that holds the magnet, a case having a shaft, a plurality of side wall portions and a top surface portion, and accommodating the magnet and the magnetic sensor inside, and a flat shielding member that has a shape corresponding to the top surface portion and is attached to the top surface portion, wherein the shielding member has a convex portion that protrudes outward from an outer periphery, and the case has a concave portion that opens inward at the outer end of the top surface portion and accommodates the convex portion, and the concave portion has a plurality of side wall portions of different widths and a plurality of top wall portions of different heights.

[0008] In one embodiment of the magnetic detection device of the present invention, the heights of the upper wall portions are set according to the heights of the convex portions of the shielding members having different thicknesses, and the widths of the side wall portions are set according to the widths of the convex portions of the shielding members having different thicknesses.

[0009] In a magnetic detection device according to one aspect of the present invention, the case has a recess-forming portion in which the recess is formed and protrudes upward from the outer end of the upper surface portion, and the shielding member has an outer surface portion facing the recess-forming portion on the widthwise outer side of the protrusion portion.

[0010] In the magnetic detection device according to one aspect of the present invention, the case has a boss portion protruding upward from the top surface portion, and the shield member has a boss hole in which the boss portion is housed.

[0011] In one aspect of the magnetic detection device of the present invention, the shielding member has a curved surface portion that is curved to fit along the side wall portion of the case on the outer periphery opposite the position where the convex portion is provided, and a through hole formed in the curved surface portion, and the case has a screw hole that communicates with the through hole in the side wall portion opposite the position where the concave portion is provided.

[0012] In order to achieve the above object, an absolute encoder according to the present invention is characterized by including the magnetic detection device according to the present invention. [Effects of the Invention]

[0013] According to the magnetic detection device and absolute encoder of the present invention, shield members of different thicknesses can be easily attached. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view schematically showing a configuration of an absolute encoder according to an embodiment of the present invention; [Figure 2] 2 is a perspective view schematically illustrating the configuration of the absolute encoder shown in FIG. 1 with a case and a shield removed. FIG. [Figure 3] 3 is a perspective view schematically illustrating the configuration of the absolute encoder shown in FIG. 2, with a substrate, a connector, and a support plate removed. FIG. [Figure 4] 4 is a perspective view schematically illustrating the configuration of the absolute encoder shown in FIG. 3, viewed from another angle. FIG. [Figure 5] FIG. 4 is a perspective view schematically illustrating the configuration of the absolute encoder shown in FIG. 3, with the motor removed. [Figure 6] FIG. 6 is a plan view schematically showing the configuration of the absolute encoder shown in FIG. 5. [Figure 7] 2 is a cross-sectional view showing the absolute encoder shown in FIG. 1 cut along a plane parallel to the central axis of the spindle. [Figure 8] 2 is a cross-sectional view schematically illustrating the configuration of the absolute encoder shown in FIG. 1, with the motor removed, taken along a plane that passes through the central axis of the main shaft gear and is perpendicular to the central axis of the first intermediate gear. [Figure 9] FIG. 9 is an exploded vertical cross-sectional view schematically showing the configuration of a magnet, a main shaft gear, a main shaft adapter, and a main shaft of a motor in the configuration of the absolute encoder shown in FIG. 8. [Figure 10]FIG. 9 is an enlarged cross-sectional view showing one end of the spindle adapter shown in FIG. 8. [Figure 11] 7 is a cross-sectional view schematically showing a state in which the configuration of the absolute encoder shown in FIG. 6 is cut along a plane that passes through the center axis of a first intermediate gear and is parallel to the XY plane. FIG. [Figure 12] FIG. 12 is an enlarged perspective view of the cross-sectional view shown in FIG. 11, viewed from a different angle. [Figure 13] 7 is a partial cross-sectional view schematically illustrating a state in which the configuration of the absolute encoder shown in FIG. 6 is cut along a plane that passes through the center axis of a first intermediate gear and is perpendicular to the XY plane. FIG. [Figure 14] 13 is an exploded perspective view schematically showing a state in which a base, a first intermediate gear, a first intermediate gear shaft, a leaf spring, and a screw are disassembled in the configuration of the absolute encoder shown in FIG. 12. FIG. [Figure 15] 3 is a partial cross-sectional view schematically illustrating a state in which the absolute encoder shown in FIG. 2 is cut along a plane that passes through the central axis of a first countershaft gear and is perpendicular to the central axis of a first intermediate gear. FIG. [Figure 16] 16 is an exploded perspective view schematically showing a state in which a magnet, a magnet holder, a first countershaft gear, and a bearing are disassembled in the configuration of the absolute encoder shown in FIG. 15. FIG. [Figure 17] 3 is a partial cross-sectional view schematically illustrating a state in which the absolute encoder shown in FIG. 2 is cut along a plane passing through the central axes of a second intermediate gear and a second countershaft gear. FIG. [Figure 18] FIG. 18 is an enlarged cross-sectional view showing a second intermediate gear shown in FIG. 17. [Figure 19] FIG. 18 is an enlarged cross-sectional view showing a magnet holder having a second countershaft gear shown in FIG. 17. [Figure 20] 20 is an exploded perspective view schematically showing the magnet holder shown in FIG. 19 in an exploded state. FIG. [Figure 21] 20 is a schematic perspective view showing a cylindrical magnet that can be used as the magnet of the magnet holder shown in FIG. 19. FIG. [Figure 22]FIG. 19 is an enlarged cross-sectional view showing one end portion on the lower end side of the second countershaft gear shaft shown in FIG. 18. [Figure 23] FIG. 10 is a schematic diagram showing a state in which a second countershaft gear shaft is press-fitted into a shaft support portion at the base of the base. [Figure 24] FIG. 10 is a schematic diagram showing a state in which a second countershaft gear shaft is press-fitted into a shaft support portion at the base of the base. [Figure 25] FIG. 10 is a diagram for schematically illustrating a modified example of a support protrusion that supports the main shaft side end of the first intermediate gear shaft in the absolute encoder. [Figure 26] FIG. 10 is a diagram for schematically illustrating a modified example of a support protrusion that supports the main shaft side end of the first intermediate gear shaft in the absolute encoder. [Figure 27] FIG. 10 is a diagram for schematically illustrating a modified example of a support protrusion that supports the main shaft side end of the first intermediate gear shaft in the absolute encoder. [Figure 28] 3 is a diagram of the substrate shown in FIG. 2 as viewed from the bottom side. [Figure 29] FIG. 2 is a block diagram schematically showing a functional configuration of the absolute encoder shown in FIG. [Figure 30] FIG. 2 is a perspective view schematically illustrating the configuration of a case and a shield member provided in the absolute encoder. [Figure 31] FIG. 2 is a plan view schematically showing the configuration of a shield member 7 provided in the absolute encoder. [Figure 32] 3 is a side view seen from the X-axis direction, schematically showing the configuration of a case provided in the absolute encoder. FIG. [Figure 33] FIG. 4 is a cross-sectional view seen from the Y-axis direction, schematically showing the configuration of the case. [Figure 34] 10 is a schematic diagram showing a state in which a convex portion of a shield member is inserted into a concave portion of a case of an absolute encoder. FIG. [Figure 37] FIG. 10 is a perspective view schematically showing the configuration of an absolute encoder including another shield member. [Figure 35] FIG. 10 is a plan view schematically showing the configuration of another shield member provided in the absolute encoder. [Figure 36] 10 is a schematic diagram showing a state in which a convex portion of another shield member is inserted into a concave portion of a case of an absolute encoder. FIG. [Figure 38] FIG. 10 is a plan view schematically showing the configuration of another shield member provided in the absolute encoder. [Figure 39] 10 is a schematic diagram showing a state in which a convex portion of another shield member is inserted into a concave portion of a case of an absolute encoder 2. FIG. [Figure 40] FIG. 10 is a perspective view schematically showing the configuration of an absolute encoder including another shield member. [Figure 41] FIG. 10 is a perspective view schematically showing a configuration of an absolute encoder according to a modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the dimensions of components in each drawing are appropriately enlarged or reduced for ease of understanding. Also, in each drawing, some components that are not important for explaining the embodiments of the present invention are omitted. Also, in the drawings, gears are shown without showing their tooth shapes. Furthermore, terms including ordinal numbers such as first and second are used to describe various components, but these terms are used only to distinguish one component from another component and do not limit the components. Note that the present invention is not limited by the present embodiments.

[0016] A magnetic detection device 60 according to an embodiment of the present invention includes a magnetized magnet Mr, an angle sensor Sr that is a magnetic sensor that detects magnetic flux from the magnet Mr, a magnet holder 61 that holds the magnet Mr, and a second countershaft gear shaft 62 that serves as a shaft. The magnet holder 61 is rotatably supported on the second countershaft gear shaft 62. The second countershaft gear shaft 62 is made of a magnetic material, and an attractive force due to magnetic force is generated between the magnet Mr and the second countershaft gear shaft 62 in the direction of the rotation axis of the magnet holder 61. An absolute encoder 2 according to an embodiment of the present invention also includes the magnetic detection device 60 according to the above-described embodiment of the present invention. The structures of the absolute encoder 2 and the magnetic detection device 60 will be described in detail below.

[0017] Fig. 1 is a perspective view that schematically shows the configuration of an absolute encoder 2 according to an embodiment of the present invention. Fig. 2 is a perspective view that shows the configuration of the absolute encoder 2 shown in Fig. 1 with a case 4 and a shield removed. In Fig. 1, the shield, case 4, and substrate 5 of the absolute encoder 2 are shown in a see-through manner, and in Fig. 2, the substrate 5 of the absolute encoder 2 is shown in a see-through manner.

[0018] For convenience, the absolute encoder 2 will be described in this description based on an 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 and Z-axis directions are each perpendicular to the X-axis direction. In this description, the X-axis direction is also referred to as the left or right side, the Y-axis direction as the front or rear side, and the Z-axis direction as the upper or lower side. In the orientation (upright orientation) of the absolute encoder 2 shown in FIGS. 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. Furthermore, in the orientation of the absolute encoder 2 shown in FIGS. 1 and 2, the near side in the Y-axis direction is the front side, and the far side in the Y-axis direction is the rear side. Furthermore, in the orientation of the absolute encoder 2 shown in FIGS. 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. The state viewed from above in the Z-axis direction is called a plan view, the state viewed from the front in the Y-axis direction is called a front view, and the state viewed 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.

[0019] As described above, the absolute encoder 2 is an absolute type encoder that identifies and outputs the amount of rotation over multiple rotations of the main shaft 1a of the motor 1. In this 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 this 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 vertical 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 shape that is longer in the horizontal direction than in the vertical direction.

[0020] The absolute encoder 2 has a case 4 that houses the internal structure. The case 4 has multiple (for example, four) outer wall portions 4a that surround at least a portion of the main shaft 1a of the motor 1, the main shaft gear 10, the first intermediate gear 20, the first countershaft gear 30, the second intermediate gear 70, and the magnet holder 61. The case 4 also has lid portions 4b that close the upper openings of the four outer wall portions 4a. The lid portions 4b are covered with a shield.

[0021] For example, motor 1 may be a stepping motor or a DC brushless motor. For example, 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. The main shaft 1a of motor 1 protrudes from the motor case on both the top and bottom sides. Absolute encoder 2 outputs the amount of rotation of main shaft 1a of motor 1 as a digital signal.

[0022] The motor 1 has a generally rectangular shape in plan view, and also in the vertical direction. In other words, the motor 1 has a generally cubic shape. In plan view, the length of each of the four outer walls that make up the outer shape of the motor 1 is, for example, 25 mm. In other words, the outer shape of the motor 1 is 25 mm square in plan view. Furthermore, the absolute encoder 2 provided in the motor 1 is, for example, 25 mm square in plan view to match the outer shape of the motor 1.

[0023] 1 and 2, a substrate 5 is provided together with the case 4 to cover the inside of the absolute encoder 2. The substrate 5 is a printed wiring board that has a generally rectangular shape in a plan view and is thin in the vertical direction. A connector 6 is connected to the substrate 5, and the connector 6 is used to connect the absolute encoder 2 to an external device (not shown).

[0024] FIG. 3 is a perspective view schematically showing the configuration of the absolute encoder 2 shown in FIG. 2 with the substrate 5 and connector 6 removed. FIG. 4 is a perspective view schematically showing the configuration of the absolute encoder 2 shown in FIG. 3 as viewed from another angle. FIG. 5 is a perspective view schematically showing the configuration of the absolute encoder 2 shown in FIG. 3 with the motor 1 removed. FIG. 6 is a plan view schematically showing the configuration of the absolute encoder 2 shown in FIG. 5.

[0025] The absolute encoder 2 includes a main shaft gear 10 having a first worm gear portion 11 (first drive gear), a first intermediate gear 20 having a first worm wheel portion 21 (first driven gear) and a second worm gear portion 22 (second drive gear), a first countershaft gear 30 having a second worm wheel portion 31 (second driven gear) and a gear portion 32 (third drive gear), a second intermediate gear 70, a magnet holder 61 having a second countershaft gear 63, 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 51.

[0026] The main shaft 1a of the motor 1 is the output shaft of the motor 1 and is also the input shaft that transmits 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 so as to rotate in accordance with 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 nearly coincides with the central axis of the main shaft 1a. The first worm wheel portion 21 is provided on the outer periphery of the first intermediate gear 20. The first worm wheel portion 21 meshes with the first worm gear portion 11 and rotates in accordance with 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 nearly 90°.

[0027] There is no particular restriction on the outer diameter of the first worm wheel portion 21, but 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 (see FIG. 8), 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.

[0028] The second worm gear portion 22 is provided on the outer periphery of the first intermediate gear 20 and rotates in accordance with the rotation of the first worm wheel portion 21. In the first intermediate gear 20, the second worm gear portion 22 is provided so that its central axis coincides or substantially coincides with the central axis of the first worm wheel portion 21. The second worm wheel portion 31 is provided on the outer periphery of the first countershaft gear 30 and is engaged with the second worm gear portion 22 so as to rotate in accordance with the rotation of the second worm gear portion 22. The shaft angle between the second worm wheel portion 31 and the second worm gear portion 22 is set to 90° or substantially 90°. The rotation axis of the second worm wheel portion 31 is parallel or substantially parallel to the rotation axis of the first worm gear portion 11. The gear portion 32 is provided on the outer periphery of the first countershaft gear 30 and rotates in accordance with the rotation of the second worm wheel portion 31. In the first countershaft gear 30, the gear portion 32 is provided so that its central axis coincides or substantially coincides with the central axis of the second worm wheel portion 31.

[0029] Here, the direction in which the first worm wheel portion 21 moves toward the first worm gear portion 11 in order to mesh with the first worm wheel portion 11 is defined as a first meshing direction (the direction of arrow P1 in FIG. 12). Similarly, the direction in which the second worm gear portion 22 moves toward the second worm wheel portion 31 in order to mesh with the second worm wheel portion 31 is defined as a second meshing direction (the direction of arrow P2 in FIG. 12). In this embodiment, both the first meshing direction P1 and the second meshing direction P2 are directions along the horizontal plane (XY plane).

[0030] The second intermediate gear 70 has a gear portion 71 (third driven gear) and a gear portion 72 (fourth drive gear). The gear portion 71 is provided on the outer periphery of the second intermediate gear 70 and meshes with the gear portion 32 of the first countershaft gear 30, rotating in accordance with the rotation of the gear portion 32. The gear portion 72 is provided on the outer periphery of the second intermediate gear 70 and rotating in accordance with the rotation of the gear portion 71. In the second intermediate gear 70, the gear portion 72 is provided so that its central axis coincides or substantially coincides with the central axis of the gear portion 71. The rotational axes of the gear portions 71 and 72 are provided parallel or substantially parallel to the rotational axis of the gear portion 32 of the first countershaft gear 30.

[0031] The magnet holder 61 has a second countershaft gear 63 and, as will be described later, has a gear portion 64 (fourth driven gear) provided on the second countershaft gear 63. The gear portion 64 is provided on the outer periphery of the second countershaft gear 63, meshes with the gear portion 72 of the second intermediate gear 70, and rotates in accordance with the rotation of the gear portion 72. The rotation axis of the gear portion 64 is parallel or approximately parallel to the rotation axis of the gear portion 72 of the second intermediate gear 70.

[0032] The angle sensor Sq detects the rotation angle of the second worm wheel portion 31, i.e., the rotation angle of the first countershaft gear 30. The magnet Mq is fixed to the upper surface of the first countershaft gear 30 so that their central axes coincide or nearly coincide. The magnet Mq has two magnetic poles aligned perpendicular or nearly perpendicular to the rotation axis of the first countershaft gear 30. The angle sensor Sq is disposed 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 30.

[0033] As an example, the angle sensor Sq is fixed to a substrate 5 supported by a substrate support 110 disposed on a base 3 (described later) of the absolute encoder 2. The angle sensor Sq detects the magnetic flux of the magnet Mq and outputs the detection information to the microcomputer 51. The microcomputer 51 determines the rotation angle of the magnet Mq, i.e., the rotation angle of the first countershaft gear 30, based on the input detection information regarding the magnetic flux.

[0034] The angle sensor Sr detects the rotation angle of the magnet holder 61, i.e., the rotation angle of the second countershaft gear 63. The magnet Mr is fixed to the upper surface of the second countershaft gear 63 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 63. The angle sensor Sr is disposed so that its lower surface faces the upper surface of the magnet Mr in the vertical direction with a gap therebetween in order to detect the rotation angle of the second countershaft gear 63.

[0035] As an example, the angle sensor Sr is fixed to the substrate 5 on the same surface as the surface on which the angle sensor Sq is fixed. The angle sensor Sr detects the magnetic flux of the magnet Mr and outputs the detection information to the microcomputer 51. The microcomputer 51 determines the rotation angle of the magnet Mr, i.e., the rotation angle of the second countershaft gear 63, based on the input detection information on the magnetic flux.

[0036] 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 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 so that its lower surface faces the upper surface of the magnet Mp in the vertical direction with a gap therebetween in order to detect the rotation angle of the main shaft gear 10.

[0037] As an example, the angle sensor Sp is fixed to the substrate 5 on the same surface as the angle sensor Sq. The angle sensor Sp detects the magnetic flux of the magnet Mp and outputs the detection information to the microcomputer 51. The microcomputer 51 determines the rotation angle of the magnet Mp based on the input detection information regarding the magnetic flux, thereby determining 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 described below, the microcomputer 51 determines the rotation amount of the main shaft 1a based on the determined rotation angle of the first countershaft gear 30, the rotation angle of the second countershaft gear 63, and the determined rotation angle of the main shaft 1a, and outputs this. As an example, the microcomputer 51 may output the rotation amount of the main shaft 1a of the motor 1 as a digital signal.

[0038] The absolute encoder 2 configured in this manner can determine the rotation speed of the main shaft 1a in accordance with the rotation angle of the first countershaft gear 30 determined based on the detection information from the angle sensor Sq and the rotation angle of the second countershaft gear 63 determined based on the detection information from the angle sensor Sr, and can also determine the rotation angle of the main shaft 1a based on the detection information from the angle sensor Sp. Then, the microcomputer 51 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.

[0039] The first worm gear portion 11 of the main shaft gear 10 provided on the main shaft 1a has, for example, five threads, and the first worm wheel portion 21 has, for example, 20 teeth. In other words, the first worm gear portion 11 and the first worm wheel portion 21 form a first speed change mechanism R1 with a reduction ratio of 20 / 5=4 (see FIG. 6). When the first worm gear portion 11 rotates four times, the first worm wheel portion 21 rotates once. The first worm wheel portion 21 and the second worm gear portion 22 are provided coaxially to form the first intermediate gear 20 and rotate integrally. Therefore, when the first worm gear portion 11 rotates four times, i.e., when the main shaft 1a and the main shaft gear 10 rotate four times, the first intermediate gear 20 rotates once, and the second worm gear portion 22 rotates once.

[0040] The number of teeth of the second worm gear portion 22 is, for example, 2, and the number of teeth of the second worm wheel portion 31 of the first countershaft gear 30 is, for example, 25. In other words, the second worm gear portion 22 and the second worm wheel portion 31 constitute a second speed change mechanism R2 with a reduction ratio of 25 / 2=12.5 (see FIG. 6). When the second worm gear portion 22 rotates 12.5 times, the second worm wheel portion 31 rotates one time. The first countershaft gear 30 on which the second worm wheel portion 31 is formed rotates integrally with the magnet holder 35 and the magnet Mq, as will be described later. Therefore, when the second worm gear portion 22 constituting the first intermediate gear 20 rotates 12.5 times, the magnet Mq rotates one time.

[0041] The number of teeth of the gear portion 32 of the first countershaft gear 30 is, for example, 18, and the number of teeth of the gear portion 71 of the second intermediate gear 70 is, for example, 36. That is, the gear portion 32 and the gear portion 71 constitute a third transmission mechanism R3 with a reduction ratio of 36 / 18=2 (see FIG. 5). When the gear portion 32 of the first countershaft gear 30 rotates twice, the gear portion 71 of the second intermediate gear 70 rotates once. Also, the number of teeth of the gear portion 72 of the second intermediate gear 70 is, for example, 19, and the number of teeth of the gear portion 64 of the second countershaft gear 63 is, for example, 38. That is, the gear portion 64 and the gear portion 72 constitute a fourth transmission mechanism R4 with a reduction ratio of 38 / 19=2 (see FIG. 5). When the gear portion 72 of the second intermediate gear 70 rotates twice, the gear portion 64 of the second countershaft gear 63 rotates once.

[0042] The gear portion 71 and the gear portion 72 are arranged coaxially to form the second intermediate gear 70 and rotate integrally, so that when the gear portion 71 rotates once, the gear portion 72 rotates once. Therefore, the reduction ratio of the entire second intermediate gear 70 is 4. In other words, when the gear portion 32 of the first countershaft gear 30 rotates four times, the second intermediate gear 70 rotates two times, and the gear portion 64 of the second countershaft gear 63 rotates once. The second countershaft gear 63, on which the gear portion 64 is formed, forms the magnet holder 61, as described below, and rotates integrally with the magnet Mr. Therefore, when the gear portion 32 of the first countershaft gear 30 rotates four times, the magnet Mr rotates one time.

[0043] As a result, when the main shaft 1a rotates 200 times, the first intermediate gear 20 rotates 50 times, the first countershaft gear 30 and magnet Mq rotate four times, the second intermediate gear 70 rotates two times, and the second countershaft gear 63 and magnet Mr rotate one time. In other words, the number of rotations of the main shaft 1a for 50 rotations can be determined from the detection information of the rotation angle of the first countershaft gear 30 from the angle sensor Sq, and the number of rotations of the main shaft 1a for 200 rotations can be determined from the detection information of the rotation angle of the second countershaft gear 63 from the angle sensor Sr. Furthermore, the reduction ratio of the first countershaft gear 30 to the mainshaft gear 10 is smaller than that of the second countershaft gear 63. Therefore, the resolution of the rotation amount of the main shaft 1a based on the detection information of the magnetic sensor Sq corresponding to the magnet Mq that rotates with the first countershaft gear 30 is higher than the resolution of the rotation amount of the main shaft 1a based on the detection information of the magnetic sensor Sr corresponding to the magnet Mr that rotates with the second countershaft gear 63. Therefore, in the absolute encoder 2, the range of the amount of rotation of the spindle 1a that can be specified can be expanded without reducing the resolution of the amount of rotation of the spindle 1a that can be specified.

[0044] The configuration of the absolute encoder 2 will now be described in more detail.

[0045] As described above (see FIGS. 1 to 6), the absolute encoder 2 includes a base 3, a case 4, a substrate 5, and a connector 6. The absolute encoder 2 also includes a main shaft gear 10, a first intermediate gear 20, a first countershaft gear 30, a second intermediate gear 70, a magnet holder 61 having a second countershaft gear 63, and a biasing mechanism 40. The absolute encoder 2 also includes magnets Mp, Mq, Mr and angle centers Sp, Sq, Sr, and a microcomputer 51 for controlling the drive unit, detection unit, etc. of the absolute encoder 2.

[0046] The base 3 rotatably holds each rotating body, such as the main shaft gear 10, the first intermediate gear 20, the first countershaft gear 30, the second intermediate gear 70, and the magnet holder 61 (second countershaft gear 63), and is a base to which each component, such as the substrate 5 and the biasing mechanism 40, is fixed. As shown in FIGS. 3 to 6 and 11 to 14, the base 3 has a base portion 101 and various support portions (described later) for supporting each component of the absolute encoder 2 provided on the base portion 101. As shown in FIG. 7, a case 4 is fixed to the base 3 via a support plate 3a. The support plate 3a is sandwiched between the base 3 and the motor 1, and the case 4 is fixed to the support plate 3a at one location, for example, with a screw 8c. The substrate 5 is fixed to the base 3 at three locations, for example, with screws 8a. The base portion 101 is a plate-like portion having a pair of surfaces facing in the upper and lower directions of the absolute encoder 2, and extends in the horizontal direction (X-axis direction and Y-axis direction).

[0047] The upper surface 104 of the base 101 is provided with board supports 110 and board positioning pins 120 that are portions for supporting the board 5. The base 3 has, for example, three board supports 110 and two board positioning pins 120.

[0048] As shown in FIG. 5 and other figures, the board support pillars 110 are portions that protrude upward from the upper surface 104 of the base 101 and are, for example, cylindrical or approximately cylindrical. A screw hole 112 extending downward is formed in the upper end surface (upper end surface 111) of the board support pillars 110. The upper end surfaces 111 of the board support pillars 110 are formed to extend on or along the same horizontal plane. In the absolute encoder 2, the lower surface 5a of the board 5 contacts the upper end surface 111 of the board support pillars 110 and is fixed to the board support pillars 110 by a screw 8a threaded into the screw hole 112. As will be described later, each board support pillar 110 is integral with one board positioning pin 120 and a support protrusion 45 that constitutes a biasing mechanism 40, which will be described later. The board support pillars 110 may also have a rib for reinforcement.

[0049] As shown in Figure 5 and other figures, the board positioning pin 120 is a portion that protrudes upward from the upper surface 104 of the base 101, and is, for example, a cylindrical or approximately cylindrical portion. The upper end (tip portion 121) of the board positioning pin 120 is thinner than the portion (base portion 122) below the tip portion 121, and a step surface 123 is formed between the tip portion 121 and the base portion 122. The tip portion 121 of the board positioning pin 120 is insertable into a positioning hole 5b formed in the board 5 as shown in Figure 28, which will be described later. By inserting the tip portions 121 of the board positioning pins 120 into the positioning holes 5b of the board 5, the board 5 is positioned with respect to the base 3.

[0050] As shown in FIG. 5 and other figures, the base 3 has support protrusions 131, 132, and 141, which are provided on the upper surface 104 of the base portion 101 and protrude upward (see FIGS. 3 to 6). The support protrusion 132 supports a leaf spring 9 that presses the first intermediate gear 20 in the direction of the central axis of the first intermediate gear 20, as will be described later. The support protrusions 131 and 141 rotatably support the first intermediate gear 20, as will be described later. The base 3 also has a bearing holder portion 134 that supports a bearing 135 that rotatably holds the first countershaft gear 30, as will be described later (see FIG. 15). The base 3 also has a shaft support portion 136 that supports the second countershaft gear shaft 62, which rotatably supports the magnet holder 61 on which the second countershaft gear 63 is formed, and a shaft support portion 137 that supports the shaft 75 that rotatably supports the second intermediate gear 70, as will be described later (see FIGS. 17 to 19). Furthermore, a support protrusion 45 is provided on the upper surface 104 of the base portion 101 of the base 3. As will be described later, the support protrusion 45 is a part that constitutes the biasing mechanism 40 that biases the second worm gear portion 22 toward the second worm wheel portion 31, and is a part that supports the biasing spring 41.

[0051] Next, each of the components supported by the base 3 of the absolute encoder 2 will be specifically described.

[0052] (Main shaft gear) Fig. 8 is a cross-sectional view schematically showing a state in which the configuration of the absolute encoder 2 shown in Fig. 1 is cut along a plane that passes through the central axis of the main shaft gear 10 and is perpendicular to the central axis of the first intermediate gear 20, with the motor 1 removed. Fig. 9 is an exploded vertical cross-sectional view schematically showing the configuration of the magnet Mp, main shaft gear 10, main shaft adapter 12, and main shaft 1a of the motor 1 in the configuration of the absolute encoder 2 shown in Fig. 8.

[0053] As shown in Figures 8 and 9, the main shaft gear 10 is a cylindrical member provided coaxially or approximately coaxially with the main shaft 1a of the motor 1 and the main shaft adapter 12. The main shaft gear 10 includes a cylindrical portion 13 and a first worm gear portion 11 provided radially outward of the cylindrical portion 13. The first worm gear portion 11 is a gear portion of the main shaft gear 10. As shown in Figure 9, a cylindrical press-fit portion 1b that forms a space on the inner peripheral side is formed at the upper end of the main shaft 1a of the motor 1, and the main shaft adapter 12 is press-fitted and fixed into the press-fit portion 1b. Furthermore, a cylindrical press-fit portion 14 that forms a space on the inside is formed in the cylindrical portion 13 of the main shaft gear 10, and the main shaft adapter 12 is press-fitted and fixed into the press-fit portion 14.

[0054] 8 and 9, a magnet holding portion 15 for holding the magnet Mp is formed on the cylindrical portion 13 of the main shaft gear 10. The magnet holding portion 15 is a portion that forms a recess corresponding to the shape of the magnet Mp and recesses downward from the upper end surface 13a of the cylindrical portion 13, and is capable of accommodating the magnet Mp. The magnet holding portion 15 is in communication with the press-fit portion 14 and has a cylindrical inner circumferential surface 15a with a larger diameter than the press-fit portion 14, and an annular bottom surface 15b that connects the inner circumferential surface 15a and the press-fit portion 14.

[0055] The inner peripheral surface 15a of the magnet holding portion 15 is formed so as to contact the outer peripheral surface Mpd of the magnet Mp housed in the magnet holding portion 15. In the absolute encoder 2, the upper end surface 12a of the spindle adapter 12 is located above the bottom surface 15b of the magnet holding portion 15. In the absolute encoder 2, the lower surface Mpb of the magnet Mp is in contact with the upper end surface 12a of the spindle adapter 12, but is not in contact with the bottom surface 15b of the magnet holding portion 15 of the spindle gear 10. In this way, the magnet Mp is positioned in the vertical direction by the upper end surface 12a of the spindle adapter 12, and is positioned in the horizontal direction by the inner peripheral surface 15a of the magnet holding portion 15. The lower surface Mpb of the magnet Mp positioned in this way is adhered and fixed to the upper end surface 12a of the spindle adapter 12.

[0056] As described above, the magnet Mp is fixed to the main shaft adapter 12, and the magnet Mp, main shaft gear 10, and main shaft adapter 12 rotate integrally with the main shaft 1a of the motor 1. The magnet Mp, main shaft gear 10, and main shaft adapter 12 rotate around the same axis as the main shaft 1a of the motor 1.

[0057] The first worm gear portion 11 is configured with teeth formed in a spiral shape and is formed to mesh with the first worm wheel portion 21 of the first intermediate gear 20. The first worm gear portion 11 is made of, for example, polyacetal resin. The first worm gear portion 11 is an example of a first drive gear.

[0058] 9, the magnet Mp is a disk-shaped or approximately disk-shaped permanent magnet inserted inside the magnet holding portion 15 of the main shaft gear 10, and has an upper surface Mpa and a lower surface Mpb that face back to back. In the absolute encoder 2, the position of the magnet Mp in the direction of the central axis GC1 of the main shaft gear 10 (position in the vertical direction) is determined by the upper end surface 12a of the main shaft adapter 12 as described above, so that the upper surface Mpa of the magnet Mp faces the surface of the angle sensor Sp at a certain distance in the vertical direction.

[0059] The central axis MpC of the magnet Mp (the axis representing the center of the magnet Mp or the axis passing through the center of the boundary between the magnetic poles) coincides or approximately coincides with the central axis GC1 of the main shaft gear 10, the central axis SaC of the main shaft adapter 12, and the central axis MoC of the main shaft 1a of the motor 1. By making these central axes coincident or approximately coincident in this way, the angle sensor Sp can detect the rotation angle or amount of rotation of the magnet Mp with higher accuracy.

[0060] In an embodiment of the present invention, the two magnetic poles (N / S) of the magnet Mp are preferably formed adjacent to each other in a horizontal plane (XY plane) perpendicular to the central axis MpC of the magnet Mp. This can further improve the detection accuracy of the rotation angle or rotation amount of the angle sensor Sp. The magnet Mp is formed from a magnetic material such as a ferrite-based material or an Nd (neodymium)-Fe (iron)-B (boron)-based material. The magnet Mp may also be, for example, a rubber magnet containing a resin binder, a bonded magnet, or the like.

[0061] (spindle adapter) FIG. 10 is an enlarged cross-sectional view showing one end 124 of the spindle adapter 12.

[0062] The spindle adapter 12 is a shaft that is press-fitted into the press-fit portions 1b and 14, with the spindle 1a of the motor 1 and the cylindrical portion 13 of the spindle gear 10 serving as support members. As shown in FIGS. 8, 9, and 10, the spindle adapter 12 has tapered surface portions 126, 127 and a through-hole 128.

[0063] The through hole 128 penetrates the spindle adapter 12 between the one end 124 and the other end 125. The through hole 128 has a first hole portion 128a that occupies a region of a predetermined length in the axial direction from the one end 124 side, and a second hole portion 128c that communicates with the first hole portion 128a and occupies a region to the other end 125. In the through hole 128, the diameter of the first hole portion 128a in the region of the predetermined length in the axial direction from the one end 124 side is larger than the diameter of the second hole portion 128c provided on the other end 125 side. Note that an end portion 128b between the first hole portion 128a and the second hole portion 128c is a portion that is generated when the first hole portion 128a is machined using a drill with an angled cutting edge, and the end portion 128b does not exist when machined using an end mill.

[0064] The absolute encoder 2 has a structure in which the spindle gear 10 is attached to the spindle 1a of the motor 1. To accommodate spindles 1a of various diameters, the spindle gear 10 is not directly attached to the spindle 1a, but is fixed via a spindle adapter 12. Here, the spindle 1a is the rotating shaft of the motor and requires rigidity. Furthermore, as described above, the spindle adapter 12 must be adhesively attached to the magnet Mg, so it is desirable to use metal for the spindle 1a and the spindle adapter 12. Therefore, a high press-fit force is required when press-fitting the spindle adapter 12 into the press-fit portion 1b of the spindle 1a. In this case, the press-fit force may cause buckling deformation of the spindle 1a or damage such as scraping of the press-fit portions (inner diameter portion and outer diameter portion) of the spindle 1a and the spindle adapter 12.

[0065] In the absolute encoder 2, by making the diameter of the first hole portion 128a of the through hole 128 of the spindle adapter 12 larger than the diameter of the second hole portion 128c and reducing the wall thickness, the spindle adapter 12 can be made more flexible, the press-fit force on the spindle 1a can be reduced, and the load on the spindle 1a can be alleviated. Meanwhile, the magnet Mp is fixed with adhesive at the upper part (tip side) of the spindle adapter 12, so a contact area with the magnet Mp (wall thickness between the outer diameter and inner diameter of the spindle adapter 12) is required. Therefore, the spindle adapter 12 has different diameters for the through hole 128 at a predetermined position in the axial direction, for example, at a region corresponding to the press-fit allowance (dimension required for press-fit) on the one end 124 side as a boundary.

[0066] That is, the diameter of the first hole portion 128a of the spindle adapter 12 closer to the one end portion 124 than the press-fit allowance (lower side in FIG. 9) is made larger than the second hole portion 128c, thereby facilitating deformation of the circumferential surface 129 of the spindle adapter 12 and facilitating press-fitting into the press-fit portion 1b. Also, the diameter of the second hole portion 128c closer to the other end portion 125 than the press-fit allowance (upper side in FIG. 9) is made smaller than the first hole portion 128a, thereby ensuring an adhesive area with the magnet Mp and achieving a reduction in the press-fit force without impairing the adhesive holding force.

[0067] The tapered surface portions 126, 127 are inclined outer peripheral surfaces such that the diameters of the one end portion 124 and the other end portion 125 are smaller than the diameter of the peripheral surface 129. In the tapered surface portion 126, a connecting portion 126a on the outer peripheral surface between the tapered surface portion 126 and the peripheral surface 129 of the spindle adapter 12 is connected by a curved surface. In the tapered surface portion 127 on the other end portion 125 side, a connecting portion 127a on the outer peripheral surface between the tapered surface portion 126 and the peripheral surface 129 is also connected by a curved surface. In other words, the tapered surface portions 126, 127 have been subjected to curved surface processing at the connecting portions 126a, 127a on the outer peripheral surface between the tapered surface portion 126 and the peripheral surface 129.

[0068] 9, a region of the spindle adapter 12 extending a predetermined length in the axial direction from one end 124 is press-fitted into press-fit portion 1b formed at the upper end of the spindle 1a of the motor 1. Also, a region of the spindle adapter 12 extending a predetermined length in the axial direction from the other end 125 is press-fitted into press-fit portion 14 formed in the cylindrical portion 13 of the spindle gear 10.

[0069] Here, if only linear chamfering is performed on the tapered surface portion 126, when one end portion 124 of the spindle adapter 12 is press-fitted into the press-fit portion 1b, if the tapered surface portion 126 comes into contact with the edge of the hole in the press-fit portion 1b, shavings will be produced from both the spindle adapter 12 and the press-fit portion 1b. Similarly, if only linear chamfering is performed on the tapered surface portion 127, when the other end portion 125 of the spindle adapter 12 is press-fitted into the press-fit portion 14, if the tapered surface portion 127 comes into contact with the edge of the hole in the press-fit portion 14, shavings will be produced from both the spindle adapter 12 and the press-fit portion 14.

[0070] Meanwhile, when the spindle adapter 12 is press-fitted into the press-fitting portion 1b and the press-fitting portion 14, after the tapered surface portions 126, 127 are inserted into the press-fitting portion 1b, 14, the connecting portions 126a, 127a on the outer circumferential surface between the tapered surface portions 126, 127 and the circumferential surface 129 come into contact with the press-fitting portion 1b, 14. The spindle adapter 12 has curved surfaces at the connecting portions 126a, 127a on the outer circumferential surface between the tapered surface portions 126, 127 and the circumferential surface 129. This allows the spindle adapter 12 to be smoothly press-fitted into the press-fitting portion 1b, 14, thereby preventing scraping of both the spindle adapter 12 and the press-fitting portion 1b, 14. Therefore, the spindle adapter 12 can prevent shavings and the like from scattering. Furthermore, the spindle adapter 12 can prevent the spindle adapter 12 from being pressed-fitted in a tilted position, which may be caused by scraping of the components. Furthermore, with the spindle adapter 12, the inclination of the spindle adapter 12 is suppressed, so that the press-fit allowance (the dimension required for press-fitting) can be reduced.

[0071] The curved surfaces of the connecting portions 126a, 127a are preferably machined to a radius R of about 1 mm, for example. Furthermore, by smoothing the surface roughness of the tapered surface portions 126, 127, including the circumferential surface 129 and the connecting portions 126a, 127a, the spindle adapter 12 can prevent the surface materials of both the spindle adapter 12 and the press-fit portion 14 from being scraped off. The surface roughness Rmax (maximum roughness) of the spindle adapter 12 is preferably 1.6 μm or less, for example. The curved surfaces of the connecting portions 126a, 127a may be machined to either one of the one end portion 124 and the other end portion 125.

[0072] (1st intermediate gear) Fig. 11 is a cross-sectional view schematically showing the configuration of the absolute encoder 2 shown in Fig. 6, cut along a plane that passes through the central axis of the first intermediate gear 20 and is parallel to a horizontal plane (XY plane). Fig. 12 is an enlarged perspective view of the absolute encoder 2 cross-sectioned as shown in Fig. 11, viewed from above on the countershaft-side end 23b side of the first intermediate gear shaft 23. Fig. 13 is a partial cross-sectional view schematically showing the configuration of the absolute encoder 2 shown in Fig. 6, cut along a plane that passes through the central axis of the first intermediate gear 20 and is perpendicular to the horizontal plane (XY plane).

[0073] As shown in FIGS. 4 to 6 and 11 to 13, the first intermediate gear 20 is rotatably supported by a first intermediate gear shaft 23 on the upper side of the base portion 101 of the base 3. The first intermediate gear shaft 23 extends parallel to a horizontal plane. Furthermore, the first intermediate gear shaft 23 is not parallel to the left-right direction (X-axis direction) or the front-rear direction (Y-axis direction) in a plan view. That is, the first intermediate gear shaft 23 is oblique to both the left-right direction and the front-rear direction. The fact that the first intermediate gear shaft 23 is oblique to both the left-right direction and the front-rear direction means that the first intermediate gear shaft 23 extends obliquely with respect to the outer peripheral surfaces 105 to 108 of the base portion 101 of the base 3 (see FIG. 11). In the absolute encoder 2, the first intermediate gear shaft 23 is supported on the base portion 101 of the base 3 by a support protrusion 131 located on the main shaft gear 10 side and a support protrusion 141 located on the first countershaft gear 30 side.

[0074] As shown in FIG. 11 , the outer peripheral surface of the base 3 is composed of a right outer peripheral surface 105 and a left outer peripheral surface 107 that is parallel to the YZ plane, and a rear outer peripheral surface 106 and a front outer peripheral surface 108 that are parallel to the XZ plane and extend between the right outer peripheral surface 105 and the left outer peripheral surface 107. The right outer peripheral surface 105 is a side surface provided on the right side (right side in the X axis direction) of the base 3. The left outer peripheral surface 107 is a side surface provided on the left side (left side in the X axis direction) of the base 3. The rear outer peripheral surface 106 is a side surface provided on the rear side (rear side in the Y axis direction) of the base 3. The front outer peripheral surface 108 is a side surface provided on the front side (front side in the Y axis direction) of the base 3.

[0075] 3 to 6, the dimensions of the absolute encoder 2 in a plan view are adjusted to the dimensions of the motor 1, which is, for example, 25 mm square. Therefore, the first intermediate gear 20, which is arranged parallel to the upper surface 104 of the base 3, is provided so as to extend obliquely with respect to the outer peripheral surfaces 105 to 108 of the base 3, thereby making it possible to reduce the dimensions of the absolute encoder 2 in the horizontal direction. Note that the horizontal direction is equal to the direction perpendicular to the central axis of the main shaft 1a of the motor 1 and equal to the direction parallel to the XY plane.

[0076] As shown in Figures 5, 6 and 11 to 14, the first intermediate gear 20 is a cylindrical member formed to be rotatable about the first intermediate gear shaft 23, and includes a first worm wheel portion 21, a second worm gear portion 22, a cylindrical portion 24, a main shaft side sliding portion 25, and a counter shaft side sliding portion 26. The cylindrical portion 24 is a member extending cylindrically and has an inner circumferential surface 24b that forms a through hole 24a through which the first intermediate gear shaft 23 can be inserted. The through hole 24a is a space surrounded by the inner circumferential surface 24b of the cylindrical portion 24. The inner circumferential surface 24b is formed to be slidable on the outer circumferential surface of the first intermediate gear shaft 23 inserted into the through hole 24a, and the first intermediate gear 20 is supported by the first intermediate gear shaft 23 to be rotatable around the first intermediate gear shaft 23. The first intermediate gear 20 is a member integrally molded from metal, resin, or the like, and here, as an example, is formed from polyacetal resin.

[0077] As shown in FIGS. 5 to 8 , the first worm wheel portion 21 is a gear that meshes with the first worm gear portion 11 of the main shaft gear 10. The first worm wheel portion 21 is an example of a first driven gear. The first worm wheel portion 21 is provided on one end side of the cylindrical portion 24 of the first intermediate gear 20, and is configured, for example, by a plurality of teeth provided on a cylindrical surface formed on one end side of the cylindrical portion 24 of the first intermediate gear 20. In the absolute encoder 2, the first intermediate gear 20 is provided so that the first worm wheel portion 21 is located near the center of the base portion 101 of the base 3. Therefore, the one end of the cylindrical portion 24 near which the first worm wheel portion 21 is provided is the end of the first intermediate gear 20 on the main shaft gear 10 side.

[0078] 8, the outer diameter of the first worm wheel portion 21 is smaller than the outer diameter of the first worm gear portion 11. The central axis of the first worm wheel portion 21 is coaxial or approximately coaxial with the central axis of the inner peripheral surface 24b of the cylindrical portion 24. In the absolute encoder 2, the central axis of the first worm wheel portion 21 is parallel or approximately parallel to the upper surface 104 of the base portion 101 of the base 3. Therefore, the smaller outer diameter of the first worm wheel portion 21 enables the absolute encoder 2 to be made smaller in the up-down direction (height direction).

[0079] As shown in FIGS. 5, 6, 11 to 15, etc., the second worm gear portion 22 is configured with teeth formed in a spiral shape and is arranged coaxially or approximately coaxially with the first worm wheel portion 21. The second worm gear portion 22 is an example of a second drive gear. Specifically, the second worm gear portion 22 is provided on the other end side of the cylindrical portion 24, and is configured with teeth formed in a spiral shape on a cylindrical surface formed on the other end side of the cylindrical portion 24, for example. The other end side of the cylindrical portion 24 refers to the end side of the first intermediate gear 20 that is on the first countershaft gear 30 side. Furthermore, the central axis of the second worm gear portion 22 is coaxial or approximately coaxial with the central axis of the inner circumferential surface 24b of the cylindrical portion 24. The second worm gear portion 22 meshes with the second worm wheel portion 31 provided on the first countershaft gear 30 , whereby the rotational force of the first intermediate gear 20 is transmitted to the first countershaft gear 30 .

[0080] As described above, the axial angle between the first worm gear portion 11 and the first worm wheel portion 21 is 90° or approximately 90°, and the central axes of the first worm gear portion 11 and the first worm wheel portion 21 are perpendicular or approximately perpendicular to each other when viewed from a direction perpendicular to the central axis of the first worm gear portion 11 and perpendicular to the central axis of the first worm wheel portion 21. Furthermore, the axial angle between the second worm gear portion 22 and the second worm wheel portion 31 is 90° or approximately 90°, and the central axes of the second worm gear portion 22 and the second worm wheel portion 31 are perpendicular or approximately perpendicular to each other when viewed from a direction perpendicular to the central axis of the second worm gear portion 22 and perpendicular to the central axis of the second worm wheel portion 31.

[0081] As shown in FIG. 15, the outer diameter of the second worm gear portion 22 is set to a value as small as possible in order to enable the absolute encoder 2 to be miniaturized in the up-down direction (height direction).

[0082] 6 and 11 to 13, the main shaft side sliding portion 25 of the first intermediate gear 20 is provided at one end of the first intermediate gear 20, i.e., the end of the first intermediate gear 20 on the main shaft gear 10 side. Specifically, the main shaft side sliding portion 25 is an end surface of one end of the cylindrical portion 24, and is an annular surface formed at one end of the cylindrical portion 24 and facing the central axis direction of the first intermediate gear 20. In the absolute encoder 2, the main shaft side sliding portion 25 of the first intermediate gear 20 comes into contact with one end 9a of a leaf spring 9, which will be described later.

[0083] The leaf spring 9 is an example of an elastic member and is made of, for example, metal. In the absolute encoder 2, the leaf spring 9 is a member for pressing the first intermediate gear 20 in the central axis direction of the first intermediate gear shaft 23. As shown in FIGS. 4 to 6 and 13, the other end 9b of the leaf spring 9 is supported by a protrusion 132a of the support protrusion 132 of the base 3 and is fixed to a support protrusion 45 of the base 3 with a screw 8b, thereby being supported by the base 3. One end 9a of the leaf spring 9 is formed so as to contact the main shaft-side sliding portion 25 of the first intermediate gear 20. Specifically, as shown in FIGS. 4 and 13, the one end 9a of the leaf spring 9 is composed of two bifurcated branches. A gap larger than the diameter of the first intermediate gear shaft 23 is formed between the two branches constituting the one end 9a of the leaf spring 9. As a result, in the absolute encoder 2, the two branches at one end 9a of the leaf spring 9 come into contact with the main shaft side sliding portion 25 of the first intermediate gear 20 with the first intermediate gear shaft 23 passing therebetween.

[0084] As shown in FIGS. 4, 6, 11, and 13, in the absolute encoder 2, the leaf spring 9 is supported at its other end 9b by the support protrusion 132 of the base 3 and is fixed to the support protrusion 45 of the base 3 so that one end 9a of the leaf spring 9 contacts the main shaft side sliding portion 25 of the first intermediate gear 20 when the leaf spring 9 is bent. As a result, an elastic force is generated in the leaf spring 9, and the main shaft side sliding portion 25 of the first intermediate gear 20 is pressed by the one end 9a of the leaf spring 9. This pressing force of the leaf spring 9 urges the first intermediate gear 20 along the first intermediate gear shaft 23 in a direction from the support protrusion 131 on the main shaft gear 10 side toward the support protrusion 141 on the first countershaft gear 30 side. When the first intermediate gear 20 rotates in this state, the main shaft side sliding portion 25 of the first intermediate gear 20 rotates while contacting the one end 9a of the leaf spring 9.

[0085] 4, 6 and 11 to 14, the countershaft side sliding portion 26 of the first intermediate gear 20 is provided at the other end of the first intermediate gear 20, i.e., the end of the first intermediate gear 20 on the first countershaft gear 30 side. Specifically, the countershaft side sliding portion 26 is the end face of the other end of the cylindrical portion 24, and is an annular surface formed at the other end of the cylindrical portion 24 facing the central axis direction of the first intermediate gear 20, and is opposite to the main shaft side sliding portion 25 in the central axis direction of the first intermediate gear 20.

[0086] In the absolute encoder 2, the countershaft-side sliding portion 26 of the first intermediate gear 20 is in contact with the support protrusion 141, and the support protrusion 141 determines the position of the first intermediate gear 20 in the central axial direction of the first intermediate gear shaft 23. As described above, the first intermediate gear 20 is pressed by the leaf spring 9 in the direction from the support protrusion 131 on the mainshaft gear 10 side toward the support protrusion 141 on the first countershaft gear 30 side, and therefore the countershaft-side sliding portion 26 of the first intermediate gear 20 is also pressed in the same direction and comes into contact with the support protrusion 141. In this way, the pressing force of the leaf spring 9 is transmitted from the first countershaft gear 30 to the support protrusion 141, and the first intermediate gear 20 is stably supported in the direction from the support protrusion 131 toward the support protrusion 141. When the first intermediate gear 20 rotates, the countershaft-side sliding portion 26 of the first intermediate gear 20 rotates while contacting the support protrusion 141.

[0087] The support protrusions 131 and 141 described above are examples of a first shaft support portion and a second shaft support portion, respectively, that rotatably support the first intermediate gear 20 via the first intermediate gear shaft 23. As shown in FIGS. 5, 6, and 11 to 13, the support protrusions 131 and 141 form a pair and are, for example, a substantially rectangular parallelepiped portion or a portion having a substantially rectangular parallelepiped portion that protrudes upward from the base portion 101 of the base 3. The support protrusion 131 is provided near the mainshaft gear 10, and is provided on the left side of the base 3 and near the center in the front-to-rear direction in plan view (see FIGS. 6 and 11). The support protrusion 141 is provided near the first countershaft gear 30, and is provided on the right side and front side of the base 3 in plan view.

[0088] 6 and 11 to 13, the support protrusions 131 and 141 function as support members that support the first intermediate gear shaft 23 so that it can swing along a horizontal plane, that is, they function as support members that support the first intermediate gear 20 so that it can swing along a horizontal plane. The first intermediate gear shaft 23 is a cylindrical rod-shaped member and has a main shaft side end 23a as one end and a counter shaft side end 23b as the other end. The main shaft side end 23a is the end of the first intermediate gear shaft 23 that is located on the main shaft gear 10 side in the absolute encoder 2, and the counter shaft side end 23b is the end of the first intermediate gear shaft 23 that is located on the first counter shaft gear 30 side in the absolute encoder 2.

[0089] The first worm wheel portion 21 provided on the main shaft side end portion 23a of the first intermediate gear shaft 23 is movable in a first meshing direction (the direction of arrow P1 in FIG. 12) by a biasing mechanism 40 described later, but is immovable in the direction in which the first intermediate gear shaft 23 extends (the direction of the central axis of the first intermediate gear shaft 23) and in a direction perpendicular to the first meshing direction P1 (the up-down direction). Note that the first meshing direction is 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, as described above.

[0090] 11 to 14, the support projection 131 has a through hole 143 formed therein, into which the main shaft side end 23a of the first intermediate gear shaft 23 is inserted. The cross section of the through hole 143 perpendicular to the extension direction has a circular hole shape. The circular hole shape is a shape having a contour that is a perfect circle or a nearly perfect circle.

[0091] The absolute encoder 2 may also have a retaining ring (not shown) as a fixing part formed to be engageable with the main shaft side end 23a of the first intermediate gear shaft 23. The retaining ring is a member that forms a portion of the main shaft side end 23a of the first intermediate gear shaft 23 that cannot pass through the through hole 143 of the support protrusion 131, and is a member that partially increases the outer diameter of the main shaft side end 23a of the first intermediate gear shaft 23. The retaining ring is, for example, an annular member such as an E-ring that engages with a groove (not shown) formed in the first intermediate gear shaft 23. In the absolute encoder 2, the retaining ring is provided on the main shaft side end 23a of the first intermediate gear shaft 23 so that the retaining ring is located on the opposite side of the counter shaft side end 23b with respect to the support protrusion 131. In other words, the retaining ring is provided so as to come into contact with the outer surface 131a of the support protrusion 131. The outer surface 131a is the surface of the support protrusion 131 facing away from the support protrusion 141. As a result, contact between the retaining ring and the outer surface 131a of the support projection 131 restricts movement of the first intermediate gear shaft 23 in the direction from the main shaft side end 23a toward the counter shaft side end 23b.

[0092] The second worm gear portion 22 provided on the countershaft side end portion 23b of the first intermediate gear shaft 23 is movable in the second meshing direction (the direction of arrow P2 in FIG. 12) by a biasing mechanism 40 described later, but is immovable in the direction in which the first intermediate gear shaft 23 extends (the direction of the central axis of the first intermediate gear shaft 23) and in the direction perpendicular to the second meshing direction P2 (the Z-axis direction). Note that the second meshing direction is the direction in which the second worm gear portion 22 moves toward the second worm wheel portion 31 in order to mesh with the second worm gear portion 22, as described above.

[0093] The support protrusion 141 has a through hole 145 into which the countershaft side end 23b of the first intermediate gear shaft 23 is inserted. The cross section of the through hole 145 perpendicular to the extension direction is elongated. The elongated shape of this through hole 145 has a major axis and a minor axis perpendicular to the major axis. The width of the major axis side is larger than the width of the minor axis side. The width of the major axis side of the elongated hole shape of the through hole 145 of the support protrusion 141 on the first countershaft gear 30 side is larger than the diameter of the outer peripheral surface of the first intermediate gear shaft 23. The width of the minor axis side of the through hole 145 is the same as or approximately the same as the diameter of the outer peripheral surface of the first intermediate gear shaft 23. In the absolute encoder 2, the major axis direction of the through hole 145 of the support protrusion 141 is parallel or approximately parallel to the horizontal plane. As described below, a biasing spring 41 engages with the first intermediate gear shaft 23, whose countershaft side end 23b is inserted into the through hole 145 of the support protrusion 141, and the biasing spring 41 biases the countershaft side end 23b of the first intermediate gear shaft 23 in the second meshing direction P2.

[0094] In this way, the first intermediate gear shaft 23 is configured by the biasing mechanism 40, support protrusions 131, and support protrusions 141 (described later) so that the countershaft end 23b can move parallel or approximately parallel to the horizontal direction with the main shaft end 23a as the fulcrum (=swing center), and the second worm gear portion 22 on the countershaft end 23b side can move parallel or approximately parallel to the horizontal direction with a greater width than the first worm wheel portion 21 on the main shaft end 23a side. As a result, the first intermediate gear shaft 23, i.e., the first intermediate gear 20, biased by the biasing mechanism 40 and supported by the support protrusions 131 and 141, can swing along the horizontal plane (XY plane).

[0095] In this configuration, the amount of movement (amount of swing) of the first intermediate gear shaft 23 is determined by the depth of the through hole 143 formed in the support protrusion 131, i.e., the thickness of the support protrusion 131 in the central axis direction of the first intermediate gear shaft 23, the clearance between the through hole 143 and the first intermediate gear shaft 23, and the width of the through hole 145 on the major axis side. However, if the clearance between the through hole 143 and the first intermediate gear shaft 23 is large, the first intermediate gear shaft 23 will become loose and become misaligned, so it is desirable to avoid increasing this clearance. For this reason, by forming the support protrusion 131 from a thin plate or the like and reducing the thickness of the support protrusion 131, i.e., by making the through hole 143 shallower, it is possible to ensure the amount of movement of the first intermediate gear shaft 23 while reducing the clearance between the through hole 143 and the first intermediate gear shaft 23. Furthermore, by designing the amount of movement of the first intermediate gear shaft 23 due to the thickness of the support protrusion 131 to be greater than the amount of movement of the first intermediate gear shaft 23 due to the width of the long axis side of the through hole 145, the amount of movement of the first intermediate gear shaft 23 can be determined by the width of the long axis side of the through hole 145.

[0096] (First countershaft gear) Fig. 15 is a partial cross-sectional view schematically showing a state in which the absolute encoder 2 shown in Fig. 2 is cut along a plane that passes through the central axis of the first countershaft gear 30 and is perpendicular to the central axis of the first intermediate gear 20. Fig. 16 is an exploded perspective view schematically showing a state in which the magnet Mq, magnet holder 35, first countershaft gear 30, and bearing 135 are disassembled in the configuration of the absolute encoder 2 shown in Fig. 15.

[0097] 15 and 16, the first countershaft gear 30 is a cylindrical member into which the shaft portion 35b of the magnet holder 35 is press-fitted and fixed to the magnet holder 35. The first countershaft gear 30 includes a second worm wheel portion 31, a gear portion 32, and a through hole 33. The first countershaft gear 30 is a member integrally molded from metal or resin, and here, as an example, is formed from polyacetal resin.

[0098] The second worm wheel portion 31 is a gear that meshes with the second worm gear portion 22 of the first intermediate gear 20. The second worm wheel portion 31 is an example of a second driven gear. The second worm wheel portion 31 is configured, for example, by a plurality of teeth provided on the outer periphery of the upper cylindrical portion of the first countershaft gear 30. As the first intermediate gear 20 rotates, the rotational force of the first intermediate gear 20 is transmitted to the first countershaft gear 30 via the second worm gear portion 22 of the first intermediate gear 20 and the second worm wheel portion 31.

[0099] The gear portion 32 is a gear that meshes with the gear portion 71 of the second intermediate gear 70. The gear portion 32 is an example of a third drive gear. The gear portion 32 is configured, for example, by a plurality of teeth provided on the outer periphery of the lower cylindrical portion of the first countershaft gear 30. As shown in FIG. 15 , the gear portion 32 is formed on the lower side of the second worm wheel portion 31, and the tooth tip circle diameter of the gear portion 32 is smaller than the tooth tip circle diameter of the second worm wheel portion 31. As the first countershaft gear 30 rotates, the rotational force of the first countershaft gear 30 is transmitted to the second intermediate gear 70 via the gear portion 32 of the first countershaft gear 30 and the gear portion 71 of the second intermediate gear 70.

[0100] 15 and 16, the through-hole 33 is a hole that passes through the cylindrical first countershaft gear 30 along the central axis of the first countershaft gear 30. The shaft portion 35b of the magnet holder 35 is press-fitted into the through-hole 33, so that the first countershaft gear 30 and the magnet holder 35 rotate together.

[0101] The magnet holder 35 has a magnet holding portion 35a and a shaft portion 35b. The magnet holder 35 is a member integrally molded from metal or resin, and here, as an example, is formed from non-magnetic stainless steel. The outer rings of two bearings 135 are press-fitted into the inner peripheral surface of a cylindrical bearing holder portion 134 formed on the base 3. The shaft portion 35b of the magnet holder 35 is a cylindrical member. The shaft portion 35b is press-fitted into the through-hole 33 of the first countershaft gear 30, and the lower portion of the shaft portion 35b is inserted into and fixed to the inner rings of the two bearings 135. Therefore, the magnet holder 35 is supported on the base 3 by the two bearings 135 and rotates integrally with the first countershaft gear 30. The magnet holder 35 is held by the bearing holder portion 134 via the bearings 135 so as to be rotatable around a rotation axis parallel or approximately parallel to the Z axis. A bearing stopper 35c is press-fitted into the shaft portion 35b of the magnet holder 35. When assembling the first countershaft gear 30, first, the outer ring of the bearing 135 installed on the upper surface 104 side of the base 3 is press-fitted into the bearing holder portion 134, and then the shaft portion 35b of the magnet holder 35 is inserted into the inner ring of this bearing 135. Next, the bearing stopper 35c is press-fitted into the shaft portion 35b of the magnet holder 35 until it abuts against the underside of the inner ring of the bearing 135. Thereafter, the shaft portion 35b of the magnet holder 35 is inserted into the inner ring of the bearing 135 installed on the lower surface 102 side of the base 3, and the outer ring is press-fitted and fixed into the bearing holder portion 134. Therefore, this bearing stopper 35c prevents the magnet holder 35 inserted in the bearing 135 from coming out of the bearing 135, and since the bearing 135 and the magnet holder 35 can be fixed without any gaps, it is possible to minimize any play in the vertical direction of the magnet Mg. The two bearings 135 are press-fit into position by abutting against bearing positioning members 35d provided on the base 3, but the bearing positioning members 35d may not be provided and the surfaces of the upper surface 104 and lower surface 102 of the base 3 and the surfaces of the bearings 135 may be positioned at the same height.

[0102] The magnet holding portion 35a is provided at the upper end of the magnet holder 35. The magnet holding portion 35a is a cylindrical member with a bottom. The magnet holding portion 35a has a recess that recesses downward from the upper end surface of the magnet holder 35. The inner circumferential surface of the recess of the magnet holding portion 35a is formed so as to contact the outer circumferential surface Mqd of the magnet Mq. As a result, in the absolute encoder 2, the magnet Mq is accommodated in the recess of the magnet holding portion 35a and is fixed to the magnet holding portion 35a.

[0103] The shaft portion 35b of the magnet holder 35 is supported by two bearings 135 arranged in a bearing holder portion 134 formed on the base 3, thereby preventing tilting of the magnet holder 35. Furthermore, if the two bearings 135 are arranged as far apart as possible in the vertical direction of the shaft portion 35b, the effect of preventing tilting of the magnet holder 35 is further enhanced.

[0104] As shown in Figure 16, the magnet Mq is a disk-shaped or approximately disk-shaped permanent magnet press-fitted into the magnet holding portion 35a of the magnet holder 35, and has an upper surface Mqa and a lower surface Mqb. In the absolute encoder 2, the upper surface Mqa of the magnet Mq faces the lower surface of the angle sensor Sp at a fixed distance. The central axis MqC of the magnet Mq (the axis representing the center of the magnet Mq or the axis passing through the center of the boundary between the magnetic poles) coincides with the central axis SC of the magnet holder 35, the central axis GC2 of the first countershaft gear 30, and the central axis BC of the bearing 135. By aligning these central axes in this way, it is possible to detect the rotation angle or amount of rotation with higher accuracy.

[0105] In an embodiment of the present invention, the two magnetic poles (N / S) of the magnet Mq are preferably formed adjacent to each other in a horizontal plane (XY plane) perpendicular to the central axis MqC of the magnet Mq. This further improves the detection accuracy of the rotation angle or rotation amount of the angle sensor Sq. The magnet Mq is formed from a magnetic material such as a ferrite-based material or an Nd (neodymium)-Fe (iron)-B (boron)-based material. The magnet Mq may also be, for example, a rubber magnet containing a resin binder, a bonded magnet, or the like.

[0106] (2nd intermediate gear) Fig. 17 is a partial cross-sectional view schematically showing a state in which the absolute encoder 2 shown in Fig. 2 is cut along a plane passing through the central axes of the second intermediate gear 70 and the second countershaft gear 63. Fig. 18 is an enlarged cross-sectional view showing the second intermediate gear 70 shown in Fig. 17 in an enlarged manner.

[0107] 17 and 18 , the second intermediate gear 70 is a member rotatably supported on a shaft 75 fixed to the shaft support portion 136 of the base 3, and includes a gear portion 71, a gear portion 72, and a main body portion 73. The second intermediate gear 70 is a member integrally molded from, for example, a resin material with low sliding resistance; one example of the resin material for the second intermediate gear 70 is polyacetal resin. The shaft 75 is fixed to the shaft support portion 136 of the base 3 so that the central axis GC3 of the second intermediate gear 70 is parallel or approximately parallel to the central axis GC2 of the first countershaft gear 30. For example, the portion of the lower end (lower end surface 75 a) of the shaft 75 is press-fitted into the through-hole 136 a of the shaft support portion 136 of the base 3 and fixed.

[0108] The main body portion 73 is a cylindrical or approximately cylindrical portion and has a through-hole 74 formed therein. The through-hole 74 is formed so that the shaft 75 can be inserted slidably relative to the shaft 75. The gear portion 71 is a gear that meshes with the gear portion 32 of the first countershaft gear 30. The gear portion 71 is an example of a third driven gear. The gear portion 71 is formed, for example, by a plurality of teeth provided on the outer periphery of the lower side of the main body portion 73. As the first countershaft gear 30 rotates, the rotational force of the first countershaft gear 30 is transmitted to the gear portion 71 of the second intermediate gear 70 via the gear portion 32 of the first countershaft gear 30. This causes the second intermediate gear 70 to rotate.

[0109] The gear portion 72 is a gear that meshes with the gear portion 64 of the second countershaft gear 63. The gear portion 72 is an example of a fourth drive gear. The gear portion 72 is configured, for example, by a plurality of teeth provided on the outer periphery of the upper side of the main body portion 73, and is provided above the gear portion 71. As the second intermediate gear 70 rotates, the rotational force of the second intermediate gear 70 is transmitted to the gear portion 64 of the second countershaft gear 63 via the gear portion 72. This causes the second countershaft gear 63 to rotate.

[0110] 17 and 18 , in the second intermediate gear 70, the through-hole 74 is a hole that extends through the main body portion 73 so that the central axis of the through-hole 74 coincides or nearly coincides with the central axes of the gear portion 71 and the gear portion 72. In addition, the through-hole 74 is formed so that the central axis GC3 of the second intermediate gear 70 coincides or nearly coincides with the central axis of the shaft 75.

[0111] The lower end surface (lower end surface 73a) of the main body 73 is in contact with the upper surface 104 of the base 3 and is formed to be slidable relative to the upper surface 104. The lower end surface 73a of the main body 73 is, for example, a flat surface or a substantially flat surface that is perpendicular or substantially perpendicular to the central axis GC3 of the second intermediate gear 70. Furthermore, the upper end surface (upper end surface 73b) of the main body 73 is in contact with a member that the upper end surface 73b faces and is formed to be slidable relative to this member. The upper end surface 73b of the main body 73 is, for example, a flat surface or a substantially flat surface that is perpendicular or substantially perpendicular to the central axis GC3 of the second intermediate gear 70.

[0112] An annular groove 75c is formed around the axis of the shaft 75 at a portion of the upper end (upper end surface 75b) of the shaft 75, and a snap ring 76 is formed to be engageable with the groove 75c. The snap ring 76 is a member for maintaining a state in which the second intermediate gear 70 is rotatably supported on the shaft 75, and is a member for partially increasing the outer diameter of the portion of the shaft 75 on the upper end surface 75b side. As shown in FIG. 18 , the snap ring 76 is an annular member such as a C-ring or E-ring. In the absolute encoder 2, the groove 75c is provided on the shaft 75 so that the snap ring 76 faces the upper end surface 73b of the main body 73 of the second intermediate gear 70. In the absolute encoder 2, the snap ring 76 attached to the groove 75c may be configured to contact the upper end surface 73b of the second intermediate gear 70, or may face the upper end surface 73b of the second intermediate gear 70 with a gap therebetween. The retaining ring 76 limits the movement of the shaft 75 of the second intermediate gear 70 in the axial direction.

[0113] The second intermediate gear 70 is configured as described above, and in the absolute encoder 2, the shaft 75 is inserted into the through hole 74 of the second intermediate gear 70, and a retaining ring 76 is attached to the groove 75c of the shaft 75, and the second intermediate gear 70 is attached in the absolute encoder 2. In the absolute encoder 2, the second intermediate gear 70 is rotatable about a rotation axis line that is parallel or approximately parallel to the central axis GC2 of the first countershaft gear 30, with the shaft 75 as its rotation axis. In addition, the second intermediate gear 70 is slidable between the upper surface 104 of the base 3 and the retaining ring 76 attached to the shaft 75, and movement of the second intermediate gear 70 in the axial direction of the shaft 75 is limited.

[0114] (2nd countershaft gear) Figure 19 is an enlarged cross-sectional view showing the magnet holder 61 having the second countershaft gear 63 shown in Figure 17, and Figure 20 is an exploded oblique view that schematically shows the magnet holder 61 shown in Figure 19 in an exploded state.

[0115] 17, 19, and 20, the magnet holder 61 is a member rotatably supported on the second countershaft gear shaft 62 fixed to the shaft support portion 137 of the base 3, and includes a second countershaft gear 63, a magnet holder portion 65, and a magnet Mr. The magnet holder portion 65 is a member for clamping the magnet Mr between itself and the second countershaft gear 63 and fixing the magnet Mr in the magnet holder 61. The second countershaft gear shaft 62 is fixed to the shaft support portion 137 of the base 3 so that its axis (center axis GC4) is parallel or approximately parallel to the center axis GC3 of the second intermediate gear 70. For example, the portion of the lower end (lower end surface 62a) of the second countershaft gear shaft 62 is press-fitted into a through-hole 137a of the shaft support portion 137 of the base 3 and fixed. Furthermore, the second countershaft gear shaft 62 is fixed to the base 3 so that the magnet Mr of the magnet holder 61 in the absolute encoder 2 faces the angle sensor Sr attached to the substrate 5 in the direction of the central axis GC3.

[0116] The second countershaft gear 63 includes a gear portion 64, a main body portion 66, and a magnet support portion 67. The second countershaft gear 63 is a member integrally molded from, for example, a resin material with low sliding resistance. That is, the gear portion 64, the main body portion 66, and the magnet support portion 67 are integrally formed from the same material and each constitute a part of the second countershaft gear 63. An example of a resin material for the second countershaft gear 63 is polyacetal resin. The main body portion 66 is a cylindrical or approximately cylindrical portion and has a through-hole 66a therein. The through-hole 66a is formed so that the second countershaft gear shaft 62 can be inserted therein and slide relative to the second countershaft gear shaft 62. The gear portion 64 is a gear that meshes with the gear portion 72 of the second intermediate gear 70. The gear portion 64 is an example of a fourth driven gear. The gear portion 64 is formed, for example, by a plurality of teeth provided on the outer periphery of the main body portion 66. In the illustrated example, the gear portion 64 forms a disk-shaped portion that protrudes in the outer circumferential direction from the outer circumferential surface of the main body portion 66, and a plurality of teeth are formed on the outer circumferential surface of this disk-shaped portion. When the second intermediate gear 70 rotates, the rotational force of the second intermediate gear 70 is transmitted to the gear portion 64 of the second countershaft gear 63 via the gear portion 72 of the second intermediate gear 70. This causes the second countershaft gear 63 to rotate.

[0117] 17 and 19, the through-hole 66a in the second countershaft gear 63 is a hole that extends through the main body portion 66 so that the central axis of the through-hole 66a coincides or nearly coincides with the central axis of the gear portions 64. In addition, the through-hole 66a is formed so that the central axis GC4 of the second countershaft gear 63 coincides or nearly coincides with the central axis of the second countershaft gear shaft 62.

[0118] The lower end surface (lower end surface 66b) of the main body 66 is in contact with the upper surface 104 of the base 3 and is formed to be slidable relative to the upper surface 104. The lower end surface 66b of the main body 66 is, for example, a flat surface or a substantially flat surface that is perpendicular or substantially perpendicular to the central axis GC4 of the second countershaft gear 63. Furthermore, the upper end surface (upper end surface 66c) of the main body 66 is in contact with a member that the upper end surface 66c faces and is formed to be slidable relative to this member. The upper end surface 66c of the main body 66 is, for example, a flat surface or a substantially flat surface that is perpendicular or substantially perpendicular to the central axis GC4 of the second countershaft gear 63.

[0119] The magnet support portion 67 is a portion of the main body 66 that extends upward from a portion above the gear portion 64, and is a cylindrical portion that extends along the central axis GC4 of the second countershaft gear 63. The magnet support portion 67 extends upward beyond the upper end surface 66c of the main body 66, and a cylindrical space is formed inside the magnet support portion 67 by the upper end surface 66c of the main body 66 and the surface of the magnet support portion 67 facing the inner peripheral side (inner peripheral surface 67a). The outer peripheral surface 67b of the magnet support portion 67 is located more inward than the tip of the gear portion 64. The magnet support portion 67 is, for example, a cylindrical or approximately cylindrical member whose center is or approximately is the central axis GC4 of the second countershaft gear 63. 19, an upper end surface 66c of the main body 66 is connected to an inner peripheral surface 67a of the magnet support portion 67, and the main body 66 may be larger on the outer circumferential side at the portion connected to the magnet support portion 67 than the portion below the gear portion 64, or may not be larger on the outer circumferential side at the portion connected to the magnet support portion 67 than the portion below the gear portion 64. The shape of the magnet support portion 67 is not limited to a cylindrical or approximately cylindrical shape and may be other shapes. For example, the shape of the magnet support portion 67 may be a rectangular tube or the like.

[0120] The upper end surface (top end surface 67c) of the magnet support portion 67 is flat or substantially flat, perpendicular or substantially perpendicular to the center axis GC4 of the second countershaft gear 63. In the absolute encoder 2, the inner peripheral surface 67a of the magnet support portion 67 is located more inward than the surface (outer peripheral surface Mrd) facing the outer periphery of the magnet Mr, so that the magnet Mr can contact the entire circumference of the top end surface 67c. In addition, in the absolute encoder 2, the magnet support portion 67 is formed so that the top end surface 67c is located higher than the upper end surface (top end surface 62b) of the second countershaft gear shaft 62. The top end surface 67c of the magnet support portion 67 is parallel or substantially parallel to the top surface 104 of the base 3, so that when the second countershaft gear 63 rotates, the top end surface 67c rotates without wobbling relative to the top surface 104 of the base 3.

[0121] The magnet holder portion 65 is a cylindrical member with a bottom made of a resin material. The resin material of the magnet holder portion 65 is, for example, a resin material that can be bonded to an adhesive. Specifically, the magnet holder portion 65 has a cylindrical portion 68 and a bottom portion 69 that extends inward from one end of the cylindrical portion 68. The cylindrical portion 68 forms a fitting portion 65a that accommodates the magnet support portion 67 of the second countershaft gear 63 and allows the magnet holder portion 65 to be fitted to the magnet support portion 67, and the cylindrical portion 68 and the bottom portion 69 form a magnet accommodating portion 65b that accommodates and holds the magnet Mr inside.

[0122] The cylindrical portion 68 of the magnet holder portion 65 has a cylindrical or substantially cylindrical inner circumferential surface 68a extending along a central axis that coincides with or substantially coincides with the central axis MC4 of the second countershaft gear 63 in the absolute encoder 2. The inner circumferential surface 68a faces the inner periphery and extends from an end (opening end 68c) opposite the end of the cylindrical portion 68 that faces the bottom 69 toward the bottom 69, forming an opening at the opening end 68c of the cylindrical portion 68. The space formed by the inner circumferential surface 68a serves as the fitting portion 65a. The inner circumferential surface 68a is formed to contact an outer circumferential surface 67b of the magnet support portion 67 of the second countershaft gear 63 when the magnet support portion 67 is accommodated in the fitting portion 65a so that the magnet support portion 67 is tightly fitted into the magnet holder portion 65. The shape of the inner circumferential surface 68a of the cylindrical portion 68 is not limited to a cylindrical or substantially cylindrical shape and may be other shapes. The shape of the inner peripheral surface 68a of the cylindrical portion 68 corresponds to the shape of the magnet support portion 67 to be housed therein.

[0123] The cylindrical portion 68 of the magnet holder portion 65 has a cylindrical or substantially cylindrical inner circumferential surface 68b that extends along a central axis that coincides or substantially coincides with the central axis MC4 of the second countershaft gear 63 in the absolute encoder 2 and also coincides or substantially coincides with the central axis MrC of the magnet Mr. The inner circumferential surface 68b faces the inner periphery and extends between the inner circumferential surface 68a and a bottom surface 69a of the bottom portion 69. The space formed by the inner circumferential surface 68b and the bottom surface 69a of the bottom portion 69 serves as the magnet accommodating portion 65b. The inner circumferential surface 68b is formed to radially face the outer circumferential surface Mrd of the magnet Mr when the magnet Mr is accommodated in the magnet accommodating portion 65b. The inner circumferential surface 68b is located more inward than the inner circumferential surface 68a, and a step is formed between the inner circumferential surface 68a and the inner circumferential surface 68b. Furthermore, the width of the inner circumferential surface 68b in the central axis direction is smaller than the width of the magnet Mr in the direction of the central axis MrC. The inner circumferential surface 68b may be formed so as to face the outer circumferential surface Mrd of the magnet Mr with a space in the radial direction when the magnet Mr is accommodated in the magnet accommodating portion 65b, or may be formed so as to face the outer circumferential surface Mrd of the magnet Mr with no space in the radial direction.

[0124] The bottom 69 of the magnet holder portion 65 is a disk-shaped portion extending inward from the end (closed end 68d) opposite the open end 68c of the cylindrical portion 68, and has the above-mentioned bottom surface 69a. The bottom surface 69a faces the magnet accommodating portion 65b and is a plane or substantially plane that is perpendicular or substantially perpendicular to the central axis of the cylindrical portion 68. The bottom 69 also has an opening 69b, which is a through-hole that penetrates the bottom 69 in the direction of the central axis of the cylindrical portion 68. The bottom surface 69a of the bottom 69 is formed so as to contact the upper surface Mra of the magnet Mr when the magnet Mr is accommodated in the magnet accommodating portion 65b, with the magnet Mr oriented such that the central axis MrC of the magnet Mr is parallel or substantially parallel to the central axis of the cylindrical portion 68. The opening 69b of the bottom 69 is also formed so that the magnetic flux of the magnet Mr passes through the opening 69b when the magnet Mr is accommodated in the magnet accommodating portion 65b.

[0125] As described above, the second countershaft gear shaft 62 is made of a magnetic material, and an attractive force is generated between the magnet Mr and the second countershaft gear shaft 62 in the direction of the rotation axis of the magnet holder 61. Specifically, the second countershaft gear shaft 62 generates a magnetic force that urges the magnet Mr in the direction of the second countershaft gear shaft 62.

[0126] Furthermore, an annular groove 62c is formed around the axis of the second countershaft gear shaft 62 at the upper end (upper end surface 62b) side of the second countershaft gear shaft 62, and a snap ring 62d is formed to be engageable with the groove 62c. The snap ring 62d is a member for restricting axial movement of the second countershaft gear shaft 62 of the magnet holder 61, and is a member for partially increasing the outer diameter of the portion of the second countershaft gear shaft 62 on the upper end surface 62b side. As shown in FIG. 19, the snap ring 62d is an annular member such as a C-ring or E-ring. In the absolute encoder 2, the groove 62c is provided on the second countershaft gear shaft 62 so that the snap ring 62d faces the upper end surface 66c of the main body 66 of the second countershaft gear 63 with a gap therebetween.

[0127] As shown in FIGS. 19 and 20, the magnet Mr is a disk-shaped or approximately disk-shaped permanent magnet housed in the magnet housing portion 65b of the magnet holder portion 65, and has an upper surface Mra, a lower surface Mrb, and an outer peripheral surface Mrd. In this embodiment of the present invention, the two magnetic poles (N / S) of the magnet Mr are preferably formed adjacent to each other in a horizontal plane (XY plane) perpendicular to the central axis MrC of the magnet Mr. This further improves the detection accuracy of the rotation angle or rotation amount of the angle sensor Sr. The magnet Mr is made of a magnetic material such as a ferrite-based material or an Nd (neodymium)-Fe (iron)-B (boron)-based material. The magnet Mr may also be, for example, a rubber magnet containing a resin binder, a bonded magnet, or the like. FIG. 21 is a schematic perspective view showing a cylindrical magnet Mr applicable to this embodiment of the present invention. In the magnet Mr of the illustrated example, the first magnetic pole portion N and the second magnetic pole portion S are arranged adjacent to each other in the radial direction D1, with the center or approximately the center of the magnet Mr in the radial direction D1 as the boundary. Also, in the magnet Mr of the illustrated example, the first magnetic pole portion N and the second magnetic pole portion S are arranged adjacent to each other in the axial direction D2, with the center or approximately the center of the axial (central axis MrC) direction D2 as the boundary. Note that the arrow DM shown in FIG. 21 indicates the magnetization direction. This type of magnetization direction is generally called face-direction magnetization, and a face-direction magnetized magnet is used for the magnet Mr.

[0128] The magnet holder 61 is configured as described above, and in the absolute encoder 2, the second countershaft gear shaft 62 is inserted into the through-hole 66a of the main body 66 of the second countershaft gear 63, and a retaining ring 62d is attached to the groove 62c of the second countershaft gear shaft 62, and in the absolute encoder 2, the second countershaft gear 63 is attached. In the absolute encoder 2, the magnet holder 61 is rotatable around its rotation axis. The rotation axis of the magnet holder 61 coincides or nearly coincides with the central axis GC4 of the second countershaft gear shaft 62. The retaining ring 62d and the portion of the second countershaft gear shaft 62 on the upper end surface 62b side are housed in a space formed on the inner peripheral side by the magnet support portion 67 of the second countershaft gear 63.

[0129] In the absolute encoder 2, the magnet Mr is accommodated in the magnet accommodating portion 65b of the magnet holder portion 65 and fixed to the magnet holder portion 65. The magnet Mr is fixed to the magnet holder portion 65 by adhesive. For example, an inner circumferential surface 68b forming the magnet accommodating portion 65b of the magnet holder portion 65 and the outer circumferential surface Mrd of the magnet Mr are bonded together with an adhesive. The magnet Mr is fixed to the magnet holder portion 65 with the lower surface Mrb of the magnet Mr in contact with the bottom surface 69a forming the magnet accommodating portion 65b of the magnet holder portion 65. This allows the central axis MrC of the magnet Mr to coincide with the central axis of the second countershaft gear shaft 62, and therefore the central axis MrC of the magnet Mr to coincide with the rotational axis of the second countershaft gear shaft 62, thereby enabling the angle sensor Sr to detect the amount of rotation or angle of rotation of the magnet Mr with higher accuracy. The fixing of the magnet Mr to the magnet accommodating portion 65b is not limited to the use of adhesive, and other fixing methods may be used, such as press-fitting the magnet Mr, such as the first countershaft gear 30, into the magnet accommodating portion 65b.

[0130] Furthermore, in the absolute encoder 2, as described above, the magnet holder portion 65 to which the magnet Mr is fixed is fitted into the magnet support portion 67 of the second countershaft gear 63, and the magnet holder portion 65 is fixed to the second countershaft gear 63, thereby assembling the magnet holder 61. Specifically, the magnet support portion 67 is press-fitted into the fitting portion 65a of the magnet holder portion 65, and the inner circumferential surface 68a forming the fitting portion 65a of the magnet holder portion 65 presses the outer circumferential surface 67b of the magnet support portion 67 inward, and the outer circumferential surface 67b of the magnet support portion 67 presses the inner circumferential surface 68a of the magnet holder portion 65 outward, thereby fixing the magnet holder portion 65 to the second countershaft gear 63. Note that fixing the magnet holder portion 65 to the second countershaft gear 63 is not limited to fitting, and other fixing methods may also be used.

[0131] In the assembled magnet holder 61 in which the magnet holder portion 65 is fixed to the second countershaft gear 63, the magnet Mr is sandwiched and fixed between the second countershaft gear 63 and the magnet holder portion 65. Specifically, the upper end surface 67c of the magnet support portion 67 contacts the lower surface Mrb of the magnet Mr, and the magnet Mr is sandwiched between the upper end surface 67c of the magnet support portion 67 and the bottom surface 69a of the bottom portion 69 of the magnet holder portion 65, and the magnet Mr is fixed in the direction of its central axis MrC. Meanwhile, the magnet Mr is fixed in the radial direction perpendicular to its central axis MrC by adhesion between the outer peripheral surface Mrd of the magnet Mr and the inner peripheral surface 68b of the magnet holder portion 65.

[0132] In the absolute encoder 2, the upper surface Mra of the magnet Mr faces the angle sensor Sr in the direction of the central axis MrC of the magnet Mr through an opening 69b formed in the bottom 69 of the magnet holder part 65. This allows the angle sensor Sr to detect the magnetic flux from the magnet Mr.

[0133] As described above, the magnet holder 61 attached to the absolute encoder 2 is rotatable around a rotation axis that is parallel or approximately parallel to the center axis GC3 of the second intermediate gear 70, with the second countershaft gear shaft 62 as the rotation axis.

[0134] Furthermore, the second countershaft gear shaft 62 is formed from a magnetic material and generates a magnetic force that urges the magnet Mr toward the second countershaft gear shaft 62. Therefore, in the absolute encoder 2, a magnetic force from the second countershaft gear shaft 62 acts on the magnet Mr, and the magnetic force from the second countershaft gear shaft 62 attracts the magnet Mr toward the second countershaft gear shaft 62. When the absolute encoder 2 is in the illustrated position (upright state), the lower end surface 66b of the main body 66 of the second countershaft gear 63 is in slidable contact with the upper surface 104 of the base 3, and the axial force from the second countershaft gear shaft 62 urges the magnet holder 61 in a direction in which the lower end surface 66b of the second countershaft gear 63 contacts the upper surface 104 of the base 3. Here, a magnet that is magnetized in the surface direction has the characteristic that the magnetic flux density is concentrated at the center of the magnet compared to a magnet that is magnetized in the radial direction. As described above, the magnet Mr is a magnet that is magnetized in the surface direction, and the second countershaft gear shaft 62 is formed of a magnetic material. Therefore, the magnetic flux density of the magnet Mr is concentrated near the center of the magnet Mr by the magnetic material of the second countershaft gear shaft 62, which allows the angle sensor Sr in the absolute encoder 2 to detect the magnetic flux with high accuracy.

[0135] On the other hand, when the absolute encoder 2 is inverted from the upright position shown in the figure so that the upside-down orientation is reversed (inverted position), the magnet holder 61 can move relative to the second countershaft gear shaft 62 in the direction of the center axis MC4 of the second countershaft gear 63 due to a gap between the retaining ring 62d and the upper end surface 66c of the main body 66 of the second countershaft gear 63. In other words, the magnet Mr can move toward the angle sensor Sr, changing the distance between the magnet Mr and the angle center Sr. However, in the absolute encoder 2, the second countershaft gear shaft 62 is made of a magnetic material, and the second countershaft gear shaft 62 attracts the magnet Mr toward the second countershaft gear shaft 62 by its magnetic force. For this reason, even if the absolute encoder 2 is in an inverted state, the magnet holder 61 is held in a state in which the lower end surface 66b of the second countershaft gear 63 is in contact with the upper surface 104 of the base 3, and the magnet holder 61 maintains its position in the direction of the central axis MC4 in the upright state, preventing the magnet Mr from moving toward the angle sensor Sr. For this reason, even in the inverted state, the distance between the magnet Mr and the angle center Sr is maintained at the same distance as in the upright state.

[0136] In this way, in the absolute encoder 2, the distance between the magnet Mr and the angle center Sr does not change depending on the usage posture of the absolute encoder 2, and the influence of the usage posture of the absolute encoder 2 on the detection accuracy can be reduced.

[0137] Furthermore, the second countershaft gear 63 is restricted from moving in the axial direction of the second countershaft gear shaft 62 by a snap ring 62d attached to the second countershaft gear shaft 62. In other words, the magnet holder 61 is restricted from moving in the axial direction of the second countershaft gear shaft 62. Therefore, even if a large impact is applied to the absolute encoder 2 and a force is applied that moves the magnet holder 61 upward in the axial direction of the second countershaft gear shaft 62 against the magnetic force of the second countershaft gear shaft 62, the movement of the magnet holder 61 is restricted by the snap ring 62d. This makes it possible to prevent malfunctions such as the magnet holder 61 coming off the second countershaft gear shaft 62.

[0138] As described above, the magnet support portion 67 of the second countershaft gear 63 has an upper end surface 67c which functions as a magnet support portion that supports the magnet Mr on the upper side of the second countershaft gear 63. The magnet holder portion 65 functions as a magnet holding portion that covers the magnet Mr and the second countershaft gear 63 from above and holds the magnet Mr on the upper end surface 67c of the magnet support portion 67.

[0139] The magnet holder portion 65 is formed from a resin material having greater elongation at break than the second countershaft gear 63. The magnet holder portion 65 has a bottom surface 69a of a bottom portion 69 that functions as a magnet joint portion, and an inner circumferential surface 68a that functions as a fitting portion 65a.

[0140] Press-fit assembly is a relatively easy method that requires no special equipment and ensures the concentricity of the components being assembled. In a press-fit structure between resins, such as the magnet holder portion 65 and the second countershaft gear 63, consideration must be given to ensuring the retention and centering of the assembled components and the strength of the press-fit components, using part of the component's shape, specifically the outer circumferential surface 67b of the magnet support portion 67, as a guide. For this reason, the resin material for the magnet holder portion 65 and the second countershaft gear 63 must be reinforced with a filler and have a low linear expansion coefficient and a high elastic modulus. However, such resin materials with a low linear expansion coefficient and a high elastic modulus are prone to cracking during press-fitting and are difficult to maintain in the press-fit state.

[0141] The magnet holder part 65, which has the fitting part 65a, has a way to escape deformation in the outer circumferential direction after press-fitting, and is therefore susceptible to tensile stress. On the other hand, the second countershaft gear 63, which is on the shaft side into which the magnet holder part 65 is press-fitted, has no way to escape deformation after the magnet holder part 65 is press-fitted, and therefore is at a lower risk of breakage due to stress than the magnet holder part 65. Therefore, in the absolute encoder 2, attention is focused on the breaking elongation characteristics of the material, and by using a magnet holder part 65 with a breaking elongation greater than that of the second countershaft gear 63 without changing the reinforcing filler content, breakage during press-fitting can be prevented. Here, the breaking elongation characteristics (elongation at break) refer to the elongation at break of a test piece in a tensile test, or the elongation immediately before breakage between specified gauge points.

[0142] (Second countershaft gear shaft) The following describes a specific shape of the second countershaft gear shaft 62. Figure 22 is an enlarged cross-sectional view showing one end 62f of the second countershaft gear shaft 62 on the side of the lower end surface 62a.

[0143] As described above, the second countershaft gear shaft 62 of the second countershaft gear 63 is a shaft that is press-fitted and fixed into the through-hole 137a of the shaft support portion 137 of the base portion 101 of the base 3. As shown in FIG. 22 , the second countershaft gear shaft 62 has a tapered surface portion 62e. The tapered surface portion 62e is an inclined outer peripheral surface such that the diameter of one end portion 62f is smaller than the diameter of the peripheral surface 62g. The tapered surface portion 62e is connected to the peripheral surface 62g at a connecting portion 62h of the outer peripheral surface between the tapered surface portion 62e of the second countershaft gear shaft 62 and the peripheral surface 62g by a curved surface. In other words, the connecting portion 62h of the outer peripheral surface between the tapered surface portion 62e and the peripheral surface 62g is curved.

[0144] 23 and 24 are schematic diagrams showing how the second countershaft gear shaft 62 is press-fitted into the through-hole 137a of the base portion 101 of the base 3. FIG.

[0145] As shown in FIGS. 23 and 24 , when the second countershaft gear shaft 62 is press-fitted into the through-hole 137a of the base 3, the tapered surface portion 62e is inserted into the through-hole 137a, and then the connecting portion 62h on the outer circumferential surface between the tapered surface portion 62e and the peripheral surface 62g contacts the through-hole 137a. Like the connecting portions 126a and 127a of the tapered surface portions 126 and 127 of the main shaft adapter 12, the connecting portion 62h is also curved. This allows the second countershaft gear shaft 62 to be smoothly press-fitted into the through-hole 137a, preventing scraping of both the second countershaft gear shaft 62 and the through-hole 137a. Furthermore, the surface roughness Rmax (maximum roughness) of the main shaft adapter 12 may be, for example, 1.6 μm or less. Therefore, the second countershaft gear shaft 62, like the main shaft adapter 12, can suppress the scattering of shavings and the like. In addition, the second countershaft gear shaft 62 can prevent the second countershaft gear shaft 62 from being pressed in while tilted, which can be caused by scraping of the member. Furthermore, the second countershaft gear shaft 62 can reduce the tilt of the second countershaft gear shaft 62, thereby reducing the press-fit allowance (dimension required for press-fitting).

[0146] In the absolute encoder 2, examples in which the connecting portion of the outer circumferential surface between the tapered surface portion and the peripheral surface of the shaft press-fitted into the support member is curved are not limited to the above-described main shaft adapter 12 and second countershaft gear shaft 62. In the absolute encoder 2, for example, the connecting portion of the outer circumferential surface between the tapered surface portion and the peripheral surface of the support shaft of the first countershaft gear 30 may be curved.

[0147] In the absolute encoder 2, the main shaft gear 10, the first intermediate gear 20, the first countershaft gear 30, the second intermediate gear 70, and the second countershaft gear 63 are arranged as described above. The rotational axes of the main shaft gear 10 and the first countershaft gear 30 are parallel to each other, and the rotational axis of the first intermediate gear 20 is skewed relative to the rotational axes of the main shaft gear 10 and the first countershaft gear 30. The rotational axes of the first countershaft gear 30, the second intermediate gear 70, and the second countershaft gear 63 are also parallel to each other. This arrangement of the gears makes it possible to determine the amount of rotation of the main shaft gear 10 over multiple rotations based on the detection results of the angle sensors Sq and Sr. Because the rotational axis of the first intermediate gear 20 is skewed relative to the rotational axes of the main shaft gear 10 and the first countershaft gear 30 and is perpendicular to them in a front view, the absolute encoder 2 can be made thinner by configuring a curved transmission path.

[0148] (Backlash reduction mechanism) As described above, the absolute encoder 2 has the biasing mechanism 40 that biases the second worm gear portion 22 toward the second worm wheel portion 31, and the biasing mechanism 40 is a backlash reduction mechanism that reduces backlash between the second worm gear portion 22 and the second worm wheel portion 31. As shown in FIGS. 5 , 6 , 11 , 14 , etc., the biasing mechanism 40 has a biasing spring 41, a support protrusion 45, and a screw 8b for fixing the biasing spring 41 to the support protrusion 45. In addition, the through hole 143 of the support protrusion 131 of the base 3 and the through hole 145 of the support protrusion 141 also constitute the biasing mechanism 40.

[0149] The biasing spring 41 is an elastic member that generates a pressing force that presses the second worm gear portion 22 toward the second worm wheel portion 31. The biasing spring 41 is, for example, a leaf spring, and is formed from a metal plate. As shown in FIGS. 12 and 14 , the biasing spring 41 specifically has a spring portion 42 that is a portion that elastically deforms to generate a pressing force, and an engaging portion 43 and a fixed portion 44 that are portions that face each other across the spring portion 42. The engaging portion 43 and the fixed portion 44 are portions that form a pair of end portions of the biasing spring 41.

[0150] The fixing portion 44 is formed so as to be fixable by a screw 8b to a support protrusion 45 that protrudes from the upper surface 104 of the base portion 101 of the base 3. The screw 8b is an example of a fixing member, and the fixing portion 44 is formed with a hole 44a through which the screw 8b is inserted. The fixing portion 44 extends in a planar shape, and is fixed to the support protrusion 45 by the screw 8b while in contact with the planar support surface 45a of the support protrusion 45.

[0151] The engaging portion 43 has a shape that can engage with the countershaft side end 23b of the first intermediate gear shaft 23. As shown in Figures 13 and 14, the engaging portion 43 has an engaging groove 43a that forms a gap extending in the direction in which the engaging portion 43 extends from the spring portion 42. The engaging groove 43a is a groove that opens toward a tip edge 43b, which is the edge facing away from the connecting portion 43c of the engaging portion 43 with the spring portion 42, and forms a bifurcated body like one end 9a of the leaf spring 9 described above. The engaging portion 43 also extends in a plane. An engaged groove 23d, which is an annular groove that extends in a direction perpendicular or substantially perpendicular to the central axis of the first intermediate gear shaft 23, is formed in the countershaft side end 23b of the first intermediate gear shaft 23, and the engaging groove 43a of the engaging portion 43 can engage with this engaged groove 23d. One side of the engaging groove 43a parallel to the vertical direction presses the first intermediate gear shaft 23 in the engaged groove 23d, thereby biasing the first intermediate gear 20 in the direction in which the second worm gear portion 22 moves toward the second worm wheel portion 31. In addition, two sides of the engaging groove 43a parallel to the horizontal direction contact the first intermediate gear shaft 23 in the engaged groove 23d, and the vertical movement of the biasing spring 41 is restricted by the first intermediate gear shaft 23.

[0152] The spring portion 42 has a shape that is easily elastically deformed in the direction in which the engaging portion 43 engages with the first intermediate gear shaft 23, and specifically, has a shape that is easily bent in the extension direction of the engaging groove 43a, as shown in Fig. 14. For example, the spring portion 42 is curved so as to protrude in the direction opposite to the direction in which the first intermediate gear 20 is biased.

[0153] The biasing spring 41 is fixed to the support protrusion 45 by the screw 8b at the fixing portion 44 in a position where the spring portion 42 stands up from the fixing portion 44 on the opposite side to the support protrusion 45. The dimensions of the spring portion 42 and the engaging portion 43, the angle of the extending direction of the engaging portion 43 relative to the extending direction of the spring portion 42, etc. are set so that in this fixed state, the engaging groove 43a of the engaging portion 43 engages with the engaged groove 23d of the first intermediate gear shaft 23, and so that in this engaged state the spring portion 42 generates a pressing force that presses the engaging portion 43 against the first intermediate gear shaft 23. When the above-mentioned retaining ring (not shown) is attached to the first intermediate gear shaft 23, the retaining ring contacts the outer surface of the support protrusion 141 in the fixed and engaged state of the biasing spring 41. In view of the backlash reduction function described later, it is preferable that the engagement groove 43a of the engagement portion 43 is formed so as to extend in a direction perpendicular or substantially perpendicular to the central axis of the first intermediate gear shaft 23 when the biasing spring 41 is in a fixed state. Note that, since the biasing spring 41 can also restrict movement of the first intermediate gear shaft 23 in the central axis direction, the snap ring may be omitted as described above.

[0154] 5, 6, 11, 14, etc., the leaf spring 9 and the biasing spring 41 are integrally formed as a single member. Specifically, the other end 9b of the leaf spring 9 and the fixed portion 44 of the biasing spring 41 are integrally formed and are made of the same member. In other words, the leaf spring 9 and the biasing spring 41 are made of a continuous elastic member, and the leaf spring 9 and the biasing spring 41 are each part of this continuous elastic member, and the other end 9b of the leaf spring 9 and the fixed portion 44 of the biasing spring 41 are formed in the same part of this continuous elastic member.

[0155] Next, the operation of the biasing mechanism 40 of the absolute encoder 2 will be described.

[0156] In the absolute encoder 2, the first intermediate gear shaft 23 is supported by the base 3, with the main shaft side end 23a inserted into a through hole 143 formed in the support protrusion 131 of the base 3 and the counter shaft side end 23b inserted into a through hole 145 formed in the support protrusion 141 of the base 3. In this way, the first intermediate gear shaft 23 is supported by the support protrusions 131, 141.

[0157] In this way, the first intermediate gear 20 is rotatably supported on the first intermediate gear shaft 23. Furthermore, the first intermediate gear 20 is biased toward the support protrusion 141 by the action of the leaf spring 9, and the countershaft side sliding portion 26 of the first intermediate gear 20 abuts against the inner surface 141a of the support protrusion 141 (see FIG. 13).

[0158] As described above, the long-hole-shaped through-hole 145 that supports the countershaft-side end 23b of the first intermediate gear shaft 23 has a long axis longer than the short axis, and the countershaft-side end 23b is supported movably along the long axis of the through-hole 145, i.e., along the horizontal plane, within the range of the width of the long axis of the through-hole 145. On the other hand, the through-hole 143 that supports the mainshaft-side end 23a of the first intermediate gear shaft 23 is round. Therefore, in the absolute encoder 2, the first intermediate gear shaft 23 can swing along the horizontal plane around the support portion of the mainshaft-side end 23a, by the through-holes 143, 145 of the support protrusions 131, 141 and the biasing mechanism 40.

[0159] Furthermore, the engaging portion 43 of the biasing spring 41 is engaged with the engaged groove 23d of the countershaft side end portion 23b of the first intermediate gear shaft 23 supported in this manner, and the biasing spring 41 applies a biasing force to the countershaft side end portion 23b of the first intermediate gear shaft 23 so that the second worm gear portion 22 of the first intermediate gear 20 is pressed toward the second worm wheel portion 31 of the first countershaft gear 30 (second meshing direction P2). As a result, the second worm gear portion 22 of the first intermediate gear 20 is pressed against the second worm wheel portion 31 of the first countershaft gear 30, causing a so-called bottoming out phenomenon between the second worm gear portion 22 and the second worm wheel portion 31, and eliminating backlash between the gears.

[0160] Furthermore, the countershaft end 23b on the moving side of the swingably supported first intermediate gear shaft 23 is biased by the biasing spring 41, so that during swinging, the first intermediate gear shaft 23 is constantly biased in the direction in which the second worm gear portion 22 moves toward the second worm wheel portion 31. Therefore, swinging of the first intermediate gear shaft 23 does not cause any problems in the rotation between the gears, and backlash between the second worm gear portion 22 and the second worm wheel portion 31 can be always kept to zero.

[0161] For example, if the ambient temperature of the absolute encoder 2 becomes high, the first countershaft gear 30 expands according to the linear expansion coefficient of the material, and the gear pitch circle of the second worm wheel portion 31 expands. At this time, if the through hole 145 formed in the support protrusion 141 of the base 3 is a round hole rather than an elongated hole as in this embodiment, the countershaft side end portion 23b of the first intermediate gear shaft 23 will be fixed by the through hole 145, and the first intermediate gear shaft 23 will not be able to swing as in this embodiment. For this reason, the second worm wheel portion 31 of the first countershaft gear 30, whose gear pitch circle has expanded due to the temperature rise, may come into contact with the second worm gear portion 22 of the first intermediate gear 20 with a strong force, causing the gear to stop rotating.

[0162] Conversely, when the ambient temperature of the absolute encoder 2 drops, the first countershaft gear 30 contracts in accordance with the linear expansion coefficient of the material, and the gear pitch circle of the second worm wheel portion 31 shrinks. At this time, if the through hole 145 formed in the support projection 141 of the base 3 were a round hole rather than an elongated hole as in this embodiment, the countershaft side end 23b of the first intermediate gear shaft 23 would be fixed by the through hole 145, and the first intermediate gear shaft 23 would not be able to swing as in this embodiment. In this case, backlash between the second worm gear portion 22 of the first intermediate gear 22 and the second worm wheel portion 31 of the first countershaft gear 30 would increase, and the rotation of the first intermediate gear 22 would not be transmitted to the first countershaft gear 30 with high precision.

[0163] In contrast, in the absolute encoder 2 according to this embodiment, as described above, the first intermediate gear shaft 23 is supported so as to be swingable along a horizontal plane around the support portion of the main shaft-side end 23a, and the first intermediate gear 20 is constantly biased by the biasing mechanism 40 from the second worm gear portion 22 toward the second worm wheel portion 31. The first intermediate gear 20 supported on the first intermediate gear shaft 23 is constantly biased toward the support protrusion 141 by the leaf spring 9. Therefore, even if the ambient temperature changes as described above and the gear pitch circle of the second worm wheel portion 31 of the first countershaft gear 30 changes, the tooth surfaces of the second worm gear portion 22 and the second worm wheel portion 31 are always in contact with each other with an appropriate pressing force, resulting in zero backlash. This prevents the gears from becoming unrotatable due to temperature changes and prevents deterioration in the accuracy of the rotation transmitted from the first intermediate gear 20 to the first countershaft gear 30.

[0164] This reduces the effect of backlash in the reduction mechanism on the detection accuracy in the absolute encoder 2. This makes it possible to widen the range of the amount of rotation of the spindle 1a that can be specified while maintaining the resolution of the amount of rotation of the spindle 1a that can be specified.

[0165] It is preferable to set the biasing mechanism 40 so that the biasing spring 41 generates a constant or approximately constant pressing force regardless of the position of the countershaft side end 23b of the first intermediate gear shaft 23 due to the swinging movement.

[0166] As described above, the through hole 143 of the support protrusion 131 that supports the main shaft side end 23a of the first intermediate gear shaft 23 is a round hole, and the through hole 145 of the support protrusion 141 that supports the counter shaft side end 23b is an elongated hole whose width on the major shaft side is larger than that on the minor shaft side, so that the first intermediate gear shaft 23 can swing parallel or approximately parallel to the horizontal direction with the through hole 143 of the support protrusion 131 as a fulcrum. Therefore, when the first intermediate gear shaft 23 swings, the amount of movement of the second worm gear portion 22 relative to the second worm wheel portion 31 is larger than the amount of movement of the first worm wheel portion 21 relative to the first worm gear portion 11, and even if the second worm gear portion 22 and the second worm wheel portion 31 bottom out, the first worm gear portion 11 and the first worm wheel portion 21 will not bottom out.

[0167] As shown in FIGS. 10 to 13, the through hole 145 supporting the first intermediate gear shaft 23 at the countershaft-side end 23b forms a cylindrical or substantially cylindrical surface. However, the through hole 145 is not limited to this shape. For example, as shown in FIG. 25, the through hole 145 may have a rectangular or substantially rectangular cross-sectional shape instead of an elongated hole. That is, the through hole 145 may be a through hole extending in the shape of a quadrangular prism, forming a pair of opposing surfaces 145a and a pair of opposing surfaces 145b. The pair of surfaces 145a and the pair of surfaces 145b forming the through hole 145 may be flat or curved. In the absolute encoder 2, the pair of surfaces 145a extend horizontally, and the pair of surfaces 145b extend vertically. The horizontal width of the surface 145a is greater than the vertical width of the surface 145b. The through hole 145 shown in FIG. 25 can also allow the first intermediate gear shaft 23 to swing, similar to the through hole 145 described above.

[0168] Similarly, the through hole 143 is not limited to the above-described shape. For example, the through hole 143 may have a so-called knife-edge structure. Specifically, the through hole 143 may contact the first intermediate gear shaft 23 by line contact or point contact. For example, as shown in FIGS. 26(a) and 26(b), the through hole 143 may be formed by a pair of conical or approximately conical inclined surfaces 143c whose diameter decreases toward the inside in the extension direction of the through hole 143. In this case, the through hole 143 contacts and supports the first intermediate gear shaft 23 at a circular line (connection line 143d) that describes a circular hole at the portion where the pair of inclined surfaces 143c connect. The circular hole shape of the connection line 143d has the same shape as the circular hole shape of the above-described through hole 143 in a plan view. Because the through hole 143 supports the first intermediate gear shaft 23 by line contact or point contact, the first intermediate gear shaft 23 can be pivoted even if the diameter of the circular hole of the through hole 143 is made closer to the diameter of the first intermediate gear shaft 23. Therefore, the cross-sectional shape of the through hole 143 can be made closer to a shape that does not have a gap between the through hole 143 and the first intermediate gear shaft 23. This makes it possible to suppress movement of the portion of the first intermediate gear shaft 23 that contacts the through hole 143 when the first intermediate gear shaft 23 pivots, and to suppress fluctuations in the distance between the first worm gear unit 11 and the first worm wheel unit 21 due to the pivoting of the first intermediate gear shaft 23. Note that the through hole 145 of the support protrusion 141 may also have a so-called knife-edge structure like the through hole 143 of the support protrusion 131 described above. For example, it may be formed by a pair of conical or approximately conical inclined surfaces that form a circular line that describes an elongated hole.

[0169] 27(a) and 27(b), the through hole 145 may be formed by a pair of inclined surfaces 145e having a rectangular pyramidal or substantially rectangular pyramidal shape that tapers toward the inside in the extension direction of the through hole 145. In this case, the through hole 145 contacts and supports the first intermediate gear shaft 23 at a circular line (connection line 145f) that forms a rectangular or substantially rectangular shape where the pair of inclined surfaces 145e connect. The connection line 145f has a pair of line portions 145g that face each other and a pair of line portions 145h that face each other. The pair of line portions 145g and the pair of line portions 145h may be straight or curved. In the absolute encoder 2, the pair of line portions 145g extend horizontally, and the pair of line portions 145h extend vertically. The length of the line portion 145g is longer than the vertical length of the line portion 145h. The through hole 143 of the support protrusion 131 may also be formed by a pair of inclined surfaces shaped like a quadrangular pyramid or a substantially quadrangular pyramid, forming a circular line that forms a quadrangle or a substantially quadrangular shape, like the through hole 145 of the support protrusion 142 described above. In this case, the circular line is a square or a substantially square. In this case, as in the case of FIG. 26 described above, the through hole 143 supports the first intermediate gear shaft 23 by line contact or point contact. Therefore, even if the length of the line portion extending in the vertical direction (corresponding to line portion 145h in FIG. 27) and the length of the line portion extending in the horizontal direction (corresponding to line portion 145g in FIG. 27) are made closer to the diameter of the first intermediate gear shaft 23, the first intermediate gear shaft 23 can be made to swing. Therefore, the shape of the through hole 143 can be made closer to a shape that does not have a gap between the through hole 143 and the first intermediate gear shaft 23 in the vertical and horizontal directions. This makes it possible to suppress movement of the part of the first intermediate gear shaft 23 that comes into contact with the through hole 143 when the first intermediate gear shaft 23 oscillates, and to suppress fluctuations in the distance between the first worm gear portion 11 and the first worm wheel portion 21 due to the oscillation of the first intermediate gear shaft 23.

[0170] (Control unit) Next, we will explain the control unit of the absolute encoder 2. Figure 28 is a view of the substrate 5 shown in Figure 2 as seen from the bottom surface 5a side. The microcomputer 51, line driver 52, bidirectional driver 53, and connector 6 are mounted on the substrate 5. The microcomputer 51, line driver 52, bidirectional driver 53, and connector 6 are electrically connected by pattern wiring on the substrate 5.

[0171] The bidirectional driver 53 performs bidirectional communication with an external device connected to the connector 6. The bidirectional driver 53 converts data such as operation signals into differential signals and communicates with the external device. The line driver 52 converts data representing the amount of rotation into differential signals and outputs the differential signals in real time to the external device connected to the connector 6. The connector of the external device is connected to the connector 6.

[0172] Fig. 29 is a block diagram showing a schematic functional configuration of the absolute encoder 2 shown in Fig. 1. Each block of the microcomputer 51 shown in Fig. 29 represents a function realized by the CPU (Central Processing Unit) serving as the microcomputer 51 executing a program.

[0173] The microcomputer 51 includes a rotation angle acquisition unit 51p, a rotation angle acquisition unit 51q, a rotation angle acquisition unit 51r, a table processing unit 51b, a rotation amount determination unit 51c, and an output unit 51e. The rotation angle acquisition unit 51p acquires a rotation angle Ap of the main shaft gear 10 based on a signal output from the angle sensor Sp. The rotation angle Ap is angle information indicating the rotation angle of the main shaft gear 10. The rotation angle acquisition unit 51q acquires a rotation angle Aq of the first countershaft gear 30 based on a signal output from the magnetic sensor Sq. The rotation angle Aq is angle information indicating the rotation angle of the first countershaft gear 30. The rotation angle acquisition unit 51r acquires a rotation angle Ar of the magnet holder 61, i.e., the second countershaft gear 63, based on a signal output from the magnetic sensor Sr. The rotation angle Ar is angle information indicating the rotation angle of the second countershaft gear 63.

[0174] The table processing unit 51b refers to a first correspondence relationship table that stores the rotation speeds of the main shaft gear 10 corresponding to the rotation angle Aq of the first countershaft gear 30 and the rotation angle Ar of the second countershaft gear 63, and identifies the rotation speed of the main shaft gear 10 that corresponds to the acquired rotation angles Aq and Ar. The rotation amount identifying unit 51c identifies the rotation amount over multiple rotations of the main shaft gear 10, based on the rotation speed of the main shaft gear 10 (main shaft 1a) identified by the table processing unit 51b and the acquired rotation angle Ap. The output unit 51e converts the rotation amount over multiple rotations of the main shaft gear 10 identified by the rotation amount identifying unit 51c into information indicating this rotation amount, and outputs the information.

[0175] (Case and shielding material) 30 is a perspective view that schematically shows the configuration of the case 4 and the shield member 7 that the absolute encoder 2 includes. FIG. 31 is a plan view that schematically shows the configuration of the shield member 7 that the absolute encoder 2 includes.

[0176] The configuration of the shielding member 7 will be described in detail with reference to Figures 30 and 31. The shielding member 7 mainly includes a shielding member main body 711, a flat portion 721, an outer peripheral portion 731, a convex portion 77, an outer surface portion 741, a curved surface portion 751, and a through hole 761.

[0177] The shielding member main body 711 is a magnetic member that constitutes the shielding member 7. The shielding member main body 711 has a shape corresponding to the shape of the lid portion 4b of the case 4 so that it can cover the lid portion 4b, specifically, for example, a flat plate-like member. The planar portion 721 is a plane that extends in the X-axis direction and the Y-axis direction in the shielding member main body 711. The outer peripheral portion 731 corresponds to the end portion on the outer peripheral side of the planar portion 721.

[0178] The protrusions 77 protrude outward from the outer periphery 731a on the X-axis side of the shield member main body 711, in the -X-axis direction in Figure 30 and other figures. The amount of protrusion of the protrusions 77 from the outer periphery 731a in the -X-axis direction is determined by the depth of the recesses 4e on the outside of the X-axis direction. The length (width) of the protrusions 77 in the Y-axis direction corresponds to the length (width) of the recesses 4e in the Y-axis direction. The width of the protrusions 77 is determined according to the plate thickness of the shield member 7.

[0179] The outer surface portion 741 is provided on the outer side in the width direction (Y-axis direction) of the protrusion 77. By providing the outer surface portion 741, the protrusion 77 is provided so as to be surrounded by the outer surface portion 741 in the Y-axis direction, as shown in Fig. 31. As shown in Fig. 30, when the shield member 7 is attached to the case 4, the outer surface portion 741 faces the side surface 41d on the outer side in the width direction (Y-axis direction side) of the recess forming portion 4d.

[0180] The curved surface portion 751 is provided on the outer peripheral portion 731b of the shielding member main body 711, on the opposite side from the position where the protrusion 77 is provided. The curved surface portion 751 is bent downward (in the -Z axis direction) at a right angle or approximately a right angle with respect to the flat surface portion 721 so as to fit along the side wall portion of the case 4, i.e., the outer wall portion 4a. The through hole 761 is a hole that is formed in the curved surface portion 751 and penetrates through the shielding member main body 711 in the thickness direction. The through hole 761 is formed at a position that corresponds to the screw hole 4f of the case 4 when the shielding member 7 is attached to the case 4.

[0181] Fig. 32 is a side view seen from the X-axis direction, schematically showing the configuration of the case 4 included in the absolute encoder 2. Fig. 33 is a cross-sectional view seen from the Y-axis direction, schematically showing the configuration of the case 4.

[0182] The configuration of the case 4 will be described in detail with reference to Figures 32 and 33 in addition to Figure 30. The case 4 of the absolute encoder 2 mainly includes an outer wall portion 4a, a lid portion 4b, a recess forming portion 4d, a recess 4e, and a screw hole 4f. The case 4 has a generally rectangular parallelepiped shape that is flattened in the X-axis and Y-axis directions, with its height (Z-axis) length being shorter than its depth (X-axis) and width (Y-axis) lengths.

[0183] A plurality of (for example, four) outer walls 4a are provided on the case 4. The outer walls 4a surround at least a portion of the main shaft 1a of the motor 1, the main shaft gear 10, and the first intermediate gear 20 from the side (X-axis direction or Y-axis direction). The lids 4b are formed integrally with the outer walls 4a at the upper ends of the four outer walls 4a of the case 4. The outer walls 4a and the lids 4b define the general shape of the case 4, which is a substantially rectangular parallelepiped. A space is formed inside the outer walls 4a and the lids 4b that can accommodate the above-mentioned portion of the main shaft 1a of the motor 1, the main shaft gear 10 of the absolute encoder 2, the first intermediate gear 20, and other components.

[0184] The recess forming portion 4d protrudes upward (in the +Z-axis direction) from the outside of the lid portion 4b, which corresponds to the top surface of the case 4, for example, from the end in the -X-axis direction. The recess forming portion 4d has a generally rectangular parallelepiped shape that is flattened in the X-axis and Y-axis directions, with the height direction (Z-axis direction) being shorter than the depth direction (X-axis direction) and width direction (Y-axis direction). The shape of the recess forming portion 4d is not limited to the example shown in FIG. 30, etc., as long as the recess 4e can be formed. The recess 4e is formed on the inside (negative X-axis side) of the recess forming portion 4d.

[0185] The recess 4e is a groove provided on the outside of the lid portion 4b of the case 4, in the recess-forming portion 4d at the end in the -X-axis direction in Figure 30. The depth direction of the groove of the recess 4e is the surface direction of the lid portion 4b of the case 4, in the -X-axis direction in Figure 30. The recess 4e opens towards the inside of the case 4 at the recess-forming portion 4d, in the X-axis direction in Figure 30, towards the center of the case 4. The recess 4e accommodates the protrusion 77 that is inserted from the center of the case 4 towards the outside. The recess 4e has a side wall portion 41e and an upper wall portion 42e formed therein.

[0186] The side wall portion 41e is a wall-shaped portion extending in the height direction (Z-axis direction) outside the width direction (Y-axis direction) of the recess 4e. A plurality of side wall portions 41e with different widths (lengths in the Y-axis direction) are provided in the recess 4e. The widths of the plurality of side wall portions 41e are set according to the widths of the protrusions 77 of the shield member 7, which have different plate thicknesses.

[0187] The upper wall portion 42e is a wall-like portion extending in the width direction of the recess 4e. A plurality of upper wall portions 42e are provided in the recess 4e, each having a different height from the lid portion 4b. The height of the upper wall portion 42e from the lid portion 4b is set according to the height of the protrusions 77 of the plurality of shield members 7 having different thicknesses (the thicknesses of the shield members 7).

[0188] The screw hole 4f is a hole with a female screw formed in the outer wall portion 4a on the opposite side of the case 4 from the position where the recess 4e is provided. The screw hole 4f communicates with the through hole 761 of the shield member 7 when the shield member 7 is attached to the case 4. The number, positions, and diameter of the screw holes 4f are not limited to the example shown in FIG. 30 etc.

[0189] Next, the relationship between the convex portion 77 and the concave portion 4e when the shield member 7 is attached to the case 4 will be described.

[0190] FIG. 34 is a schematic diagram showing a state in which the convex portion 77 of the shield member 7 is inserted into the concave portion 4e of the case 4 of the absolute encoder 2. As shown in FIG.

[0191] As shown in FIG. 34, when attaching the shielding member 7 to the case 4, the shielding member 7 is moved in the X-axis direction so that the flat portion 721 of the shielding member 7 is aligned with the lid portion 4b of the case 4. By moving the shielding member 7 in this manner, the convex portion 77 is inserted into the concave portion 4e. Here, the width of the side wall portion 41e of the lowest step of the concave portion 4e (the side closest to the lid portion 4b) is formed to correspond to the width of the convex portion 77 of the shielding member 7. The height of the upper wall portion 42e of the lowest step of the concave portion 4e is formed to correspond to the plate thickness of the shielding member 7. Furthermore, the outer surface portion 741 of the shielding member 7 provided on the outer side of the convex portion 77 in the width direction is formed to correspond to the width of the outer surface of the concave portion forming portion 4d of the case 4.

[0192] By forming the case 4 and the shield member 7 as described above, in the absolute encoder 2, the positioning of the shield member 7 relative to the case 4 in the X-axis direction, the Y-axis direction, and the Z-axis direction can be easily performed.

[0193] Furthermore, in the absolute encoder 2, a curved surface portion 751 is provided on the outer peripheral portion 731b on the opposite side in the X-axis direction from the side on which the protrusion 77 is formed, so as to fit along the outer wall portion 4a of the case 4. By providing such a curved surface portion 751, the shield member 7 can be easily positioned in the X-axis direction. Furthermore, the curved surface portion 751 is provided with a through hole 761 through which a screw 78 for fixing the shield member 7 to the case 4 is inserted. By inserting the screw 78 into this through hole 761 and fastening the screw 78 into the screw hole 4f provided in the outer wall portion 4a of the case 4, the absolute encoder 2 can reliably fix the shield member 7 to the case 4.

[0194] Fig. 35 is a plan view schematically showing the configuration of a shield member 7B provided in the absolute encoder 2. Fig. 36 is a schematic diagram showing a state in which a convex portion 77B of the shield member 7B is inserted into a concave portion 4e of a case 4 of the absolute encoder 2. Fig. 37 is a perspective view schematically showing the configuration of an absolute encoder 2 provided with a shield member 7B.

[0195] 35 to 37 differs from the previously described shielding member 7 in the following respects: The thickness of shielding member main body 711B is greater than the thickness of shielding member 7. In addition, in shielding member 7B, the length (width) in the Y-axis direction of protrusion 77B is narrower than the width of protrusion 77 of shielding member 7.

[0196] 36, when attaching shielding member 7B to case 4, flat portion 721B of shielding member 7B is moved so as to fit along lid portion 4b of case 4. The width of side wall portion 41eb, the third step from the bottom of recess 4e, is formed to correspond to the width of protrusion 77B of shielding member 7B. The height of upper wall portion 42eb, the second step from the bottom of recess 4e, is formed to correspond to the plate thickness of shielding member 7B.

[0197] By forming the case 4 and the shield member 7B as described above, in the absolute encoder 2, the positioning of the shield member 7B relative to the case 4 in the X-axis direction, Y-axis direction, and Z-axis direction can be easily performed, similar to the shield member 7 described above.

[0198] Fig. 38 is a plan view schematically showing the configuration of a shield member 7C provided in the absolute encoder 2. Fig. 39 is a schematic diagram showing a state in which a convex portion 77C of the shield member 7C is inserted into a concave portion 4e of a case 4 of the absolute encoder 2. Fig. 40 is a perspective view schematically showing the configuration of an absolute encoder 2 provided with a shield member 7C.

[0199] 38 to 40 differs from the previously described shielding member 7 and shielding member 7B in the following respects: The thickness of shielding member main body 711C is thicker than the thicknesses of shielding member 7 and shielding member 7B. Furthermore, in shielding member 7C, the length (width) in the Y-axis direction of convex portion 77C is narrower than the width of convex portion 77 of shielding member 7 and convex portion 77B of shielding member 7B.

[0200] 39, when attaching the shielding member 7C to the case 4, the flat portion 721C of the shielding member 7C is moved along the lid portion 4b of the case 4. The width of the side wall portion 41ec from the bottom to the top (farthest from the lid portion 4b) of the recessed portion 4e is formed to correspond to the width of the protrusion 77C of the shielding member 7C. The height of the upper wall portion 42ec of the topmost portion of the recessed portion 4e is formed to correspond to the plate thickness of the shielding member 7C.

[0201] By forming the case 4 and the shield member 7C as described above, in the absolute encoder 2, the positioning of the shield member 7C relative to the case 4 in the X-axis direction, the Y-axis direction, and the Z-axis direction can be easily performed, similar to the previously described shield member 7 and shield member 7B.

[0202] That is, in the absolute encoder 2, the combination of the multiple side wall portions 41e with different widths and the multiple upper wall portions 42e with different heights of the recessed portions 4e provided on the case 4 is set according to the widths of the protruding portions 77, 77B, 77C of the shield members 7, 7B, 7C with different plate thicknesses. As the plate thickness of the shield members 7, 7B, 7C increases, the magnetic shielding effect against the angle sensors Sp, Sq, Sr of the case 4 from the outside increases. Therefore, with the absolute encoder 2 configured in this manner, it is easy to select shield members 7, 7B, 7C with various plate thicknesses in accordance with the required shielding effect performance due to various factors, such as when magnetic sensors with different performance are used.

[0203] Fig. 41 is a perspective view schematically showing the configuration of an absolute encoder 200 according to a modified embodiment of the present invention. In Fig. 41, the absolute encoder 200 has a case 400 and a shield member 700 whose configurations differ from the case 4 and shield members 7, 7B, and 7C described above in the following points.

[0204] Case 400 differs from previously described case 4 in that it has a boss portion 401 that protrudes upward (in the +Z-axis direction) from lid portion 4b and in that it does not have a screw hole 4f in outer wall portion 4a. Shield member 700 differs from shield members 7, 7B, and 7C in that it has a boss hole 701 that can accommodate boss portion 401 and does not have a curved surface portion 751 or a through hole 761.

[0205] In the absolute encoder 2 described above, the shield members 7, 7B, and 7C are positioned in the X-axis direction relative to the case 4 by the bent surface portion 751 and the outer wall portion 4a. On the other hand, in the absolute encoder 200, the shield member 100 is positioned in the X-axis direction relative to the case 400 by the boss portion 401 of the case 400 and the boss hole 701 of the shield member 700.

[0206] In the absolute encoder 200 described above, similarly to the absolute encoder 2 described above, the shield member 700 can be easily positioned relative to the case 400 in the X-axis direction, the Y-axis direction, and the Z-axis direction.

[0207] In particular, the absolute encoder 200 has a boss portion 401 that protrudes upward (in the +Z-axis direction) on the lid portion 4b of the case 4. The absolute encoder 200 also has a boss hole 701 that can engage with the boss portion 401, at a position on the flat portion 721 of the shield member 700 that corresponds to the boss portion 401. By providing such boss portion 401 and boss hole 701, the shield member 700 can be easily positioned in the X-axis direction. The boss portion 401 and the boss hole 701 are fixed by fitting them together during assembly, utilizing the flexure of the case 400 and the shield member 700. With this configuration, the absolute encoder 200 allows the shield member 700 to be reliably fixed to the case 400 with a simple configuration.

[0208] Although the embodiments of the present invention have been described above, the present invention is not limited to the absolute encoder 2 according to the above-described embodiments of the present invention, and includes all aspects encompassed within the concept and scope of the claims of the present invention. 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-described problems and effects. For example, the shape, material, arrangement, size, etc. of each component in the above-described embodiments may be appropriately changed depending on the specific use of the present invention. [Explanation of symbols]

[0209] DESCRIPTION OF SYMBOLS 1...motor, 1a...spindle, 1b...press-fit portion, 2...absolute encoder, 3...base, 3a...support plate, 4...case, 4a...outer wall portion, 4b...lid portion, 4c...claw portion, 4d...recess formation portion, 4e...recess, 4f...screw hole, 5...board, 5a...underside, 5b...positioning hole, 6...connector, 7...shield member, 7B...shield member, 7C...shield member, 8a...screw, 8b...screw, 8c...screw, 9...plate spring, 9a...one end, 9b...other end, 10...spindle gear, 11...first worm gear portion, 12...spindle adapter, 12a...upper end surface, 13...cylindrical portion, 13a...upper end surface, 14...press-fit portion , 15...magnet holding portion, 15a...inner peripheral surface, 15b...bottom surface, 20...first intermediate gear, 21...first worm wheel portion, 22...second worm gear portion, 23...first intermediate gear shaft, 23a...main shaft side end, 23b...counter shaft side end, 23c...groove, 23d...engaged groove, 24...cylindrical portion, 24a...through hole, 24b...inner peripheral surface, 25...main shaft side sliding portion, 26...counter shaft side sliding portion, 30...first counter shaft gear, 31...second worm wheel portion, 32...gear portion, 33...through hole, 35...magnet holder, 35a...magnet holding portion, 35b...shaft portion, 35c...bearing stopper, 35d...bearing Positioning member, 40... biasing mechanism, 41... biasing spring, 41d... side surface, 41e... side wall portion, 41eb... side wall portion, 41ec... side wall portion, 42... spring portion, 42e... upper wall portion, 42eb... upper wall portion, 42ec... upper wall portion, 43... engaging portion, 43a... engaging groove, 43b... tip edge, 43c... connecting portion, 44... fixing portion, 44a... hole, 45... support protrusion, 45a... support surface, 51... microcomputer, 51b... table processing portion, 51c... rotation amount specifying portion, 51e... output portion, 51p... rotation angle acquiring portion, 51q... rotation angle acquiring portion, 51r... rotation angle acquiring portion, 52... line driver, 53... bidirectional driver, 60... magnetic detection ejection device, 61...magnet holder, 62...second countershaft gear shaft, 62a...lower end surface, 62b...upper end surface, 62b...upper end, 62c...groove, 62d...retaining ring, 62e...tapered surface portion, 62f...one end portion, 62g...circumferential surface, 62h...connection portion, 63...second countershaft gear, 64...gear portion, 65...magnet holder portion, 65a...fitting portion, 65b...magnet accommodating portion, 65b...magnet holding portion, 66...main body portion, 66a...through hole, 66b...lower end surface, 66c...upper end surface, 67...magnet support portion, 67a...inner peripheral surface, 67b...outer peripheral surface, 67c...upper end surface, 68...tubular portion, 68a...inner peripheral surface, 68b...inner peripheral surface,68c...open end, 68d...closed end, 68e...outer peripheral surface, 69...bottom, 69a...bottom surface, 69b...opening, 70...second intermediate gear, 70...first intermediate gear, 711...shield member main body, 71...gear portion, 711B...shield member main body, 711C...shield member main body, 72...gear portion, 73...main body portion, 73a...lower end surface, 73b...upper end surface, 74...through hole, 75...shaft, 75a...lower end surface, 75a...lower end, 75b...upper end surface, 75b...upper end, 75c...groove, 76...retaining ring, 77...protrusion, 77B...protrusion, 77C...protrusion, 78...screw, 90...approximate, 100...shield member, 101...base , 102...Bottom surface, 103...Concavity, 104...Top surface, 105...Outer circumferential surface, right outer circumferential surface, 106...Rear outer circumferential surface, 106...Outer circumferential surface, 107...Left outer circumference surface, 107...outer surface, 108...outer surface, 108...front outer circumferential surface, 110...board support, 111...top end surface, 112...screw hole, 120...board positioning Female pin, 121...Tip, 122...Base, 123...Step surface, 124...One end, 125...Other end, 126...Tapered surface, 126a...Connection part, 127...Tapered surface part, 127a...Connection part, 128...Through hole, 128a...First hole part, 128b...End part, 128c...Second hole part, 129...Surrounding surface, 131...support protrusion, 131a...outer surface, 132...support protrusion, 132a...protrusion, 134...bearing holder portion, 135...bearing, 136...shaft support portion, 136a...through hole, 137...shaft support portion, 137a...through hole, 141...support protrusion, 141a...inner surface, 142...support protrusion, 143...through hole, 143c...inclined surface, 143d...connecting wire, 144...retaining ring, 145...through hole, 145a...surface, 145b...surface, 145e...inclined surface, 145f...connecting wire, 145g...wire portion, 145h...wire portion, 200...absolute encoder, 400...case, 401...boss portion, 700 ...Shield member, 701...boss hole, 721...flat portion, 721B...flat portion, 721C...flat portion, 731...outer periphery, 731a...outer periphery, 731b...outer periphery, 741...outer surface portion, 751...curved surface portion, 761...through hole, Ap...angle information, Aq...angle information, BC...bearing center, GC1...central axis of main shaft gear, GC2...central axis of second countershaft gear, GC3...central axis, GC4...central axis, MoC...central axis of motor main shaft, Mp...magnet, Mpa...upper surface, Mpb...lower surface, MpC...central axis of magnet, Mpd...outer periphery surface, Mq...magnet, Mqa...upper surface, Mqb...lower surface,MqC...central axis of magnet, Mqd...outer surface, Mr...magnet, Mra...upper surface, Mrb...lower surface, MrC...central axis of magnet, Mrd...outer surface, P...biasing direction, P1...first meshing direction, P2...second meshing direction, R1...first transmission mechanism, R2...second transmission mechanism, SaC...central axis of spindle adapter, SC...central axis of magnet holder, Sp...angle sensor, Sq...angle sensor, Sr...angle sensor, XYZ...Cartesian coordinate system,

Claims

1. A magnetized magnet, a magnetic sensor that detects magnetic flux from the magnet; a magnet holder for holding the magnet; Axle and a case having a plurality of side walls and a top surface, and accommodating the magnet and the magnetic sensor therein; a flat shield member having a shape corresponding to the upper surface portion and attached to the upper surface portion; Equipped with The shield member has a protrusion protruding outward from an outer periphery thereof, the case has a recess that is open to the inside at an outer end of the top surface portion and that accommodates the protrusion, The recess has a plurality of side wall portions with different widths and a plurality of upper wall portions with different heights. Magnetic detection device.

2. heights of the plurality of upper wall portions are set according to heights of the convex portions of the plurality of shield members having different plate thicknesses, The widths of the side wall portions are set according to the widths of the convex portions of the shield members having different plate thicknesses. The magnetic detection device according to claim 1 .

3. the case has a recess-forming portion that protrudes upward from an outer end of the top surface portion and in which the recess is formed, The shield member has an outer surface portion facing the recess forming portion on the outer side of the protrusion in the width direction. The magnetic detection device according to claim 1 .

4. the case has a boss portion protruding upward from the top surface portion, The shield member has a boss hole in which the boss portion is housed. The magnetic detection device according to any one of claims 1 to 3.

5. the shielding member has a bent surface portion bent along the side wall portion of the case on an outer periphery opposite to a position where the protrusion is provided, and a through hole formed in the bent surface portion, the case has a screw hole in communication with the through hole in the side wall portion opposite to the position where the recess is provided; The magnetic detection device according to any one of claims 1 to 3.

6. An absolute encoder comprising the magnetic detection device according to any one of claims 1 to 5.

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