Magnetic detection device and absolute encoder

Abstract

To reduce the impact of usage posture on detection accuracy, the magnetic detection device (60) includes: a magnetized magnet (Mr); a magnetic sensor, i.e., an angle sensor (Sr), for detecting magnetic flux originating from the magnet (Mr); a magnet holder (61) for holding the magnet (Mr); and a second auxiliary shaft gear shaft (62). The magnet holder (61) is rotatably supported by the second auxiliary shaft gear shaft (62). The second auxiliary shaft gear shaft (62) is formed of a magnetic material, and an attractive force is generated between the magnet (Mr) and the second auxiliary shaft gear shaft (62) in the direction of the rotation axis of the magnet holder (61).

Description

Technical Field

[0001] This invention relates to a magnetic detection device and an absolute encoder. Prior Technology

[0002] Since ancient times, magnetic detection devices, which use magnetic sensors to detect magnetic flux originating from magnets, have been used in various technologies. In various control mechanisms, magnetic detection devices are also used in rotary encoders used to detect the position and angle of movable elements. Regarding rotary encoders, there are incremental encoders that detect relative position or angle, and absolute encoders that detect absolute position or angle. Such absolute encoders incorporate magnetic detection devices. As an absolute encoder with a magnetic detection device, a known magnetic encoder device is described, in which a magnetized magnet is mounted on a rotating shaft (spindle) that is the object of measurement, and a magnetic sensor detects the rotation angle of the magnet, thereby detecting the amount of rotation of the spindle that is the object of measurement. Furthermore, a method is known that measures the amount of rotation of the spindle after multiple rotations by obtaining the rotation angle of a rotating body that decelerates along with the rotation of the spindle.

[0003] In such absolute encoders, in order to maintain the resolution of a specific spindle rotation while expanding the range of that rotation, a structure is proposed that detects the rotation of multiple magnets using a magnetic sensor that serves as a corresponding angle sensor. For example, a structure is proposed that connects the spindle and a secondary shaft or subsequent shafts via a reduction gear, and detects the rotation of magnets mounted on each shaft using a corresponding magnetic sensor to specify the spindle rotation (see, for example, Patent Document 1). [Prior Art Documents] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-15536 Summary of the Invention

[0005] [The problem the invention aims to solve] In this type of absolute encoder that detects the rotation of a magnet, the magnetic flux detected by the magnetic sensor changes periodically as the rotating shaft rotates. The rotation of the rotating shaft is detected based on the change in magnetic flux within a predetermined rotation cycle. Therefore, when the change in magnetic flux detected by the magnetic sensor differs within the predetermined rotation cycle, the rotation of the rotating shaft cannot be accurately detected. For example, when the distance between the magnetic sensor and the permanent magnet changes, as mentioned above, the change in magnetic flux within the predetermined rotation cycle will differ. Specifically, since the vertical positional relationship between the magnetic sensor and the magnet changes according to the operating posture of the absolute encoder, the distance between the magnetic sensor and the magnet may change, leading to an inability to accurately detect the rotation of the rotating shaft. Therefore, in such an absolute encoder, to improve detection accuracy, a structure is required that prevents the change in magnetic flux detected by the magnetic sensor due to the operating posture of the absolute encoder.

[0006] This invention was made in view of the above-mentioned problems, and its object is to provide a magnetic detection device and an absolute encoder that can reduce the impact of usage posture on detection accuracy. [Means for solving the problems]

[0007] To achieve the above objectives, the magnetic detection device of the present invention comprises: Magnetized lodestone; A magnetic sensor detects the magnetic flux originating from the magnet; A magnet retainer, which retains the aforementioned magnet; and Shaft, characterized by The aforementioned magnet retainer is rotatably supported on the aforementioned shaft. The aforementioned shaft system is formed by a magnetic body, and in the direction of the rotation axis of the aforementioned magnet holder, an attractive force is generated between the aforementioned magnet and the aforementioned shaft by magnetic force.

[0008] To achieve the above objectives, the absolute encoder of the present invention is characterized by incorporating the magnetic detection device of the present invention. [Effects of the Invention]

[0009] The magnetic detection device and absolute encoder according to the present invention can reduce the impact of usage posture on detection accuracy. Simple Explanation of the Diagram

[0010] Figure 1 is a perspective view schematically showing the structure of an absolute encoder according to an embodiment of the present invention. Figure 2 is a perspective view schematically showing the structure of the absolute encoder shown in Figure 1 with the housing and shield removed. Figure 3 is a perspective view schematically showing the structure of the absolute encoder shown in Figure 2 with the base plate, connector, and support plate removed. Figure 4 is a perspective view schematically showing the structure of the absolute encoder shown in Figure 3 as seen from another angle. Figure 5 is a perspective view schematically showing the structure of the absolute encoder shown in Figure 3 with the motor removed. Figure 6 is a plan view schematically showing the structure of the absolute encoder shown in Figure 5. Figure 7 is a cross-sectional view showing the absolute encoder shown in Figure 1 cut along a plane parallel to the central axis of the main shaft. Figure 8 is a cross-sectional view schematically showing the absolute encoder shown in Figure 1 with the motor removed, cut along a plane passing through the central axis of the main shaft gear and orthogonal to the central axis of the first intermediate gear. Figure 9 is an exploded longitudinal sectional view, schematically showing the composition of the magnet, spindle gear, spindle connector, and motor spindle of the absolute encoder shown in Figure 8. Figure 10 is an enlarged sectional view showing one end of the spindle connector shown in Figure 8. Figure 11 is a sectional view, schematically showing the composition of the absolute encoder shown in Figure 6, cut along a plane passing through the central axis of the first intermediate gear and parallel to the XY plane. Figure 12 is an enlarged perspective view of the sectional view shown in Figure 11 from another angle. Figure 13 is a partial sectional view, schematically showing the composition of the absolute encoder shown in Figure 6, cut along a plane passing through the central axis of the first intermediate gear and parallel to the XY plane. Figure 14 is an exploded perspective view, schematically showing the disassembled composition of the absolute encoder shown in Figure 12, including the base, first intermediate gear, first intermediate gear shaft, leaf spring, and screws. Figure 15 is a partial cross-sectional view, schematically showing the configuration of the absolute encoder shown in Figure 2, cut along a plane passing through the central axis of the first counterspindle gear and orthogonal to the central axis of the first intermediate gear. Figure 16 is an exploded perspective view, schematically showing the disassembled state of the magnet, magnet retainer, first counterspindle gear, and bearing in the configuration of the absolute encoder shown in Figure 15. Figure 17 is a partial cross-sectional view, schematically showing the configuration of the absolute encoder shown in Figure 2, cut along a plane passing through the central axes of the second intermediate gear and the second counterspindle gear. Figure 18 is an enlarged cross-sectional view showing the second intermediate gear shown in Figure 17. Figure 19 is an enlarged cross-sectional view showing the magnet retainer having the second counterspindle gear shown in Figure 17. Figure 20 is an exploded perspective view, schematically showing the disassembled state of the magnet retainer shown in Figure 19. Figure 21 is a schematic perspective view showing a cylindrical magnet suitable for use as the magnet retainer shown in Figure 19. Figure 22 is an enlarged sectional view of one end of the lower side of the second auxiliary shaft gear shown in Figure 18.Figure 23 is a schematic diagram showing the second auxiliary shaft gear shaft being pressed into the shaft support portion at the base of the base. Figure 24 is a schematic diagram showing the second auxiliary shaft gear shaft being pressed into the shaft support portion at the base of the base. Figure 25 is a diagram schematically showing a modified example of the support protrusion at the main shaft side end of the first intermediate gear shaft in an absolute encoder. Figure 26 is a diagram schematically showing a modified example of the support protrusion at the main shaft side end of the first intermediate gear shaft in an absolute encoder. Figure 27 is a diagram schematically showing a modified example of the support protrusion at the main shaft side end of the first intermediate gear shaft in an absolute encoder. Figure 28 is a view of the substrate shown in Figure 2 from below. Figure 29 is a block diagram schematically showing the functional structure of the absolute encoder shown in Figure 1. Implementation

[0011] [The form in which the invention is carried out] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the dimensions of the components in each drawing have been appropriately enlarged or reduced for ease of understanding. Also, some components that are not essential to explaining the embodiments of the present invention have been omitted from the drawings. Furthermore, gears in the drawings are shown with the tooth shape omitted. Also, although terms including ordinal numbers such as "1," "2," etc., are used to describe various constituent elements, these terms are only used to distinguish one constituent element from other constituent elements, and not to limit the constituent elements. Furthermore, the present invention is not limited to this embodiment.

[0012] The magnetic detection device 60 of this embodiment includes: a magnetized magnet Mr; a magnetic sensor, i.e., an angle sensor Sr, for detecting magnetic flux originating from the magnet Mr; a magnet holder 61 for holding the magnet Mr; and a second auxiliary shaft gear 62 serving as a shaft. The magnet holder 61 is rotatably supported on the second auxiliary shaft gear 62. The second auxiliary shaft gear 62 is formed of a magnetic material and is formed between the magnet Mr and the second auxiliary shaft gear 62 in the direction of the rotation axis of the magnet holder 61, generating an attractive force through magnetic force. Furthermore, the absolute encoder 2 of this embodiment includes the magnetic detection device 60 described above. Hereinafter, the structures of the absolute encoder 2 and the magnetic detection device 60 will be specifically described.

[0013] Figure 1 is a perspective view schematically showing the configuration of the absolute encoder 2 according to an embodiment of the present invention. Figure 2 is a perspective view showing the configuration of the absolute encoder 2 shown in Figure 1 with the outer shell 4 and shield removed. In Figure 1, the shield, outer shell 4, and substrate 5 of the absolute encoder 2 are shown in perspective. In Figure 2, the substrate 5 of the absolute encoder 2 is shown in perspective.

[0014] For convenience, this description uses the XYZ Cartesian coordinate system for the absolute encoder 2. The X-axis corresponds to the horizontal left-right direction, the Y-axis corresponds to the horizontal front-back direction, and the Z-axis corresponds to the vertical up-down direction. The Y-axis and Z-axis are orthogonal to the X-axis. In this description, the X-axis is referred to as the left or right side, the Y-axis as the front or rear side, and the Z-axis as the top or bottom side. Regarding the orientation (upright) of the absolute encoder 2 shown in Figures 1 and 2, the left side in the X-axis direction is the left side, and the right side in the X-axis direction is the right side. Also, regarding the orientation of the absolute encoder 2 shown in Figures 1 and 2, the side in front in the Y-axis direction is the front side, and the side inside in the Y-axis direction is the rear side. Also, regarding the orientation of the absolute encoder 2 shown in Figures 1 and 2, the top side in the Z-axis direction is the top side, and the bottom side in the Z-axis direction is the bottom side. The view viewed from above in the Z-axis direction is called a top view, the view viewed from the front in the Y-axis direction is called a front view, and the view viewed in the X-axis direction is called a side view. This description of directions does not limit the usage posture of the absolute encoder 2; the absolute encoder 2 can be used in any posture.

[0015] The absolute encoder 2, as described above, is an absolute encoder that specifies and outputs the rotational amount of the main shaft 1a of the motor 1 after multiple rotations. In this embodiment of the invention, the absolute encoder 2 is located at the upper end of the motor 1 in the Z-axis direction. In this embodiment of the invention, the absolute encoder 2 has a generally rectangular shape when viewed from above, and a horizontally elongated rectangle that is thinner in the vertical direction (i.e., the extension direction of the main shaft 1a) when viewed from the front and side. In other words, the absolute encoder 2 has a flat cuboid shape that is longer in the horizontal direction than in the vertical direction.

[0016] The absolute encoder 2 includes a housing 4 that houses the internal structure. The housing 4 has a plurality (e.g., four) of outer wall portions 4a surrounding 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 retainer 61. Furthermore, the housing 4 has a cover portion 4b that plugs the openings on the upper sides of the four outer wall portions 4a. The cover portion 4b is covered by a shield.

[0017] As an example, motor 1 can be a stepper motor or a DC brushless motor. As another example, motor 1 can also be a motor suitable as a drive source, which drives industrial robots via a reduction mechanism such as a wave gear device. The main shaft 1a of motor 1 protrudes from the motor housing on both sides in the vertical direction. The absolute encoder 2 outputs the rotation amount of the main shaft 1a of motor 1 as a digital signal.

[0018] The shape of motor 1 is roughly rectangular when viewed from above, and also roughly rectangular in the vertical direction. That is, motor 1 has a roughly cubic shape. The length of each of the four outer wall portions constituting the shape of motor 1 when viewed from above is, for example, 25 mm, meaning the shape of motor 1 is 25 mm square when viewed from above. Furthermore, suppose that the absolute encoder 2 of motor 1 is fitted to motor 1, for example, motor 1 with a shape of 25 mm square when viewed from above.

[0019] As shown in Figures 1 and 2, the substrate 5 is arranged to cover the interior of the absolute encoder 2 together with the outer casing 4. The substrate 5 is a plate-shaped printed wiring substrate that is roughly rectangular in shape and thin in the vertical direction when viewed from above. Furthermore, the 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).

[0020] Figure 3 is a schematic perspective view of the absolute encoder 2 shown in Figure 2, excluding the base plate 5 and connector 6. Figure 4 is a schematic perspective view of the absolute encoder 2 shown in Figure 3 from another angle. Figure 5 is a schematic perspective view of the absolute encoder 2 shown in Figure 3, excluding the motor 1. Figure 6 is a schematic plan view of the absolute encoder 2 shown in Figure 5.

[0021] The absolute encoder 2 includes: a main shaft gear 10 having a first worm portion 11 (first drive gear); a first intermediate gear 20 having a first worm wheel portion 21 (first driven gear) and a second worm 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 retainer 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.

[0022] The main shaft 1a of motor 1 is the output shaft of motor 1 and the input shaft for transmitting rotational force to absolute encoder 2. The main shaft gear 10 is fixed to the main shaft 1a of motor 1 and is rotatably supported integrally with the main shaft 1a by the bearing members of motor 1. A first worm gear portion 11 is disposed on the outer periphery of the main shaft gear 10 such that it rotates with the rotation of the main shaft 1a of motor 1. In the main shaft gear 10, the central axis of the first worm gear portion 11 is aligned with or approximately aligned with the central axis of the main shaft 1a. A first worm wheel portion 21 is disposed on the outer periphery of the first intermediate gear 20, and is configured to mesh with the first worm gear portion 11, rotating with the rotation of the first worm gear portion 11. The axial angle between the first worm wheel portion 21 and the first worm gear portion 11 is set to 90° or approximately 90°.

[0023] There is no particular limitation on the outer diameter of the first worm gear portion 21, but in the example shown, the outer diameter of the first worm gear portion 21 is set to be smaller than the outer diameter of the first worm portion 11 (see Figure 8), and the outer diameter of the first worm gear portion 21 becomes smaller. Therefore, it is possible to miniaturize the size of the absolute encoder 2 in the vertical direction.

[0024] The second worm portion 22 is disposed on the outer periphery of the first intermediate gear 20, and rotates with the rotation of the first worm wheel portion 21. In the first intermediate gear 20, the central axis of the second worm portion 22 is aligned with or approximately aligned with the central axis of the first worm wheel portion 21. The second worm wheel portion 31 is disposed on the outer periphery of the first counterspindle gear 30 and is configured to mesh with the second worm portion 22, rotating with the rotation of the second worm portion 22. The axial angle between the second worm wheel portion 31 and the second worm portion 22 is set to 90° or approximately 90°. The axis of rotation of the second worm wheel portion 31 is arranged parallel or approximately parallel to the axis of rotation of the first worm portion 11. The gear portion 32 is disposed on the outer periphery of the first counterspindle gear 30, and rotates with the rotation of the second worm wheel portion 31. In the first counterspindle gear 30, the central axis of the gear portion 32 is aligned with or approximately aligned with the central axis of the second worm wheel portion 31.

[0025] Here, in order to engage the first worm gear portion 21 with the first worm portion 11, the direction in which the first worm gear portion 21 faces the first worm portion 11 is designated as the first engagement direction (arrow P1 in FIG. 12). Similarly, in order to engage the second worm portion 22 with the second worm gear portion 31, the direction in which the second worm portion 22 faces the second worm gear portion 31 is designated as the second engagement direction (arrow P2 in FIG. 12). In this embodiment, both the first engagement direction P1 and the second engagement direction P2 are directions along the horizontal plane (XY plane).

[0026] The second intermediate gear 70 has a gear portion 71 (the third driven gear) and a gear portion 72 (the fourth driving gear). The gear portion 71 is disposed on the outer periphery of the second intermediate gear 70, meshing with the gear portion 32 of the first counterspindle gear 30, and rotates as the gear portion 32 rotates. The gear portion 72 is disposed on the outer periphery of the second intermediate gear 70, rotating as the gear portion 71 rotates. In the second intermediate gear 70, the central axis of the gear portion 72 is aligned with or approximately aligned with the central axis of the gear portion 71. The rotation axes of the gear portions 71 and 72 are parallel or substantially parallel to the rotation axis of the gear portion 32 of the first counterspindle gear 30.

[0027] The magnet retainer 61 has a second counterspindle gear 63, and as described later, has a gear portion 64 (fourth driven gear) provided on the second counterspindle gear 63. The gear portion 64 is provided on the outer periphery of the second counterspindle gear 63, meshes with the gear portion 72 of the second intermediate gear 70, and rotates as the gear portion 72 rotates. The axis of rotation of the gear portion 64 is arranged to be parallel or substantially parallel to the axis of rotation of the gear portion 72 of the second intermediate gear 70.

[0028] An angle sensor Sq detects the rotation angle of the second worm gear 31, which is also the rotation angle of the first counterspindle gear 30. A magnet Mq is fixed so that its central axes are aligned or approximately aligned with the top of the first counterspindle gear 30. The magnet Mq has bipolar magnetic poles arranged perpendicularly or substantially perpendicular to the rotation axis of the first counterspindle gear 30. To detect the rotation angle of the first counterspindle gear 30, the angle sensor Sq is positioned with a gap at its bottom and faces the top of the magnet Mq in the vertical direction.

[0029] As an example, the angle sensor Sq is fixed to a substrate 5 supported by a substrate support 110 of the 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, which is the rotation angle of the first secondary shaft gear 30, based on the detection information related to the input magnetic flux.

[0030] An angle sensor Sr detects the rotation angle of the magnet holder 61, which is also the rotation angle of the second counterspindle gear 63. The magnet Mr is fixed so that its central axes coincide or are approximately coincident on the top of the second counterspindle gear 63. The magnet Mr has bipolar magnetic poles arranged perpendicular to the rotation axis of the second counterspindle gear 63. To detect the rotation angle of the second counterspindle gear 63, the angle sensor Sr is positioned with a gap below it and faces the top of the magnet Mr in the vertical direction.

[0031] As an example, the angle sensor Sr is fixed on the same surface as the angle sensor Sq on the substrate 5. 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, which is the rotation angle of the second auxiliary shaft gear 63, based on the detection information related to the input magnetic flux.

[0032] The magnet Mp is fixed on the top of the spindle gear 10 in a manner that aligns or approximately aligns with the central axes of both. The magnet Mp has two magnetic poles arranged in a direction perpendicular to the rotation axis of the spindle gear 10. In order to detect the rotation angle of the spindle gear 10, the angle sensor Sp is positioned with a gap below it and facing the top of the magnet Mp in the vertical direction.

[0033] As an example, the angle sensor Sp is fixed on the same surface as the angle sensor Sq on the substrate 5. 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 detection information related to the input magnetic flux, thereby determining the rotation angle of the main shaft gear 10, that is, 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 later, the microcomputer 51 determines the rotation amount of the main shaft 1a based on the determined rotation angles of the first secondary shaft gear 30, the second secondary shaft gear 63, and the determined rotation angle of the main shaft 1a, and outputs it. For example, the microcomputer 51 can also output the rotation amount of the main shaft 1a of the motor 1 as a digital signal.

[0034] The absolute encoder 2 configured in this way determines the number of rotations of the main shaft 1a based on the rotation angle of the first countershaft gear 30 determined by the detection information of the angle sensor Sq, and the rotation angle of the second countershaft gear 63 determined by the detection information of the angle sensor Sr. It can also determine the rotation angle of the main shaft 1a based on the detection information of the angle sensor Sp. Then, the microcomputer 51 determines the amount of rotation of the main shaft 1a after multiple rotations based on the determined number of rotations and the rotation angle of the main shaft 1a.

[0035] Assume that the number of teeth in the first worm section 11 of the main shaft gear 10 on the main shaft 1a is, for example, 5, and the number of teeth in the first worm wheel section 21 is, for example, 20. That is, the first worm section 11 and the first worm wheel section 21 constitute a first transmission mechanism R1 with a reduction ratio of 20 / 5 = 4 (see Figure 6). When the first worm section 11 rotates 4 revolutions, the first worm wheel section 21 rotates 1 revolution. The first worm wheel section 21 and the second worm section 22 are mounted on the same shaft to form the first intermediate gear 20. Since they rotate as a single unit, when the first worm section 11 rotates 4 revolutions, that is, when the main shaft 1a and the main shaft gear 10 rotate 4 revolutions, the first intermediate gear 20 rotates 1 revolution, and the second worm section 22 rotates 1 revolution.

[0036] The number of teeth in the second worm gear section 22 is, for example, 2, and the number of teeth in the second worm wheel section 31 of the first counterspindle gear 30 is, for example, 25. That is, the second worm gear section 22 and the second worm wheel section 31 constitute a second transmission mechanism R2 with a reduction ratio of 25 / 2 = 12.5 (see Figure 6). When the second worm gear section 22 rotates 12.5 times, the second worm wheel section 31 rotates 1 time. The first counterspindle gear 30, on which the second worm wheel section 31 is formed, is integrated with the magnet retainer 35 and the magnet Mq as described later and rotates. Therefore, when the second worm gear section 22 constituting the first intermediate gear 20 rotates 12.5 times, the magnet Mq rotates 1 time.

[0037] The number of teeth in the gear section 32 of the first countershaft gear 30 is, for example, 18, and the number of teeth in the gear section 71 of the second intermediate gear 70 is, for example, 36. That is, gear section 32 and gear section 71 constitute a third transmission mechanism R3 with a reduction ratio of 36 / 18 = 2 (see Figure 5). For every 2 rotations of the gear section 32 of the first countershaft gear 30, the gear section 71 of the second intermediate gear 70 rotates 1 rotation. Furthermore, the number of teeth in the gear section 72 of the second intermediate gear 70 is, for example, 19, and the number of teeth in the gear section 64 of the second countershaft gear 63 is, for example, 38. That is, gear section 64 and gear section 72 constitute a fourth transmission mechanism R4 with a reduction ratio of 38 / 19 = 2 (see Figure 5). For every 2 rotations of the gear section 72 of the second intermediate gear 70, the gear section 64 of the second countershaft gear 63 rotates 1 rotation.

[0038] Gear section 71 and gear section 72 are mounted coaxially to form the second intermediate gear 70. Since they rotate as a single unit, gear section 72 rotates once for every one rotation of gear section 71. Therefore, the reduction ratio of the second intermediate gear 70 as a whole is 4. That is, when gear section 32 of the first countersunk gear 30 rotates 4 times, the second intermediate gear 70 rotates 2 times, and gear section 64 of the second countersunk gear 63 rotates 1 time. The second countersunk gear 63, on which gear section 64 is formed, constitutes the magnet retainer 61 as described later, and rotates as a single unit with the magnet Mr. Therefore, when gear section 32 constituting the first countersunk gear 30 rotates 4 times, the magnet Mr rotates 1 time.

[0039] Based on the above explanation, when the main spindle 1a rotates 200 revolutions, the first intermediate gear 20 rotates 50 revolutions, the first counterspindle gear 30 and magnet Mq rotate 4 revolutions, the second intermediate gear 70 rotates 2 revolutions, and the second counterspindle gear 63 and magnet Mr rotate 1 revolution. In other words, by using the detection information from angle sensor Sq related to the rotation angle of the first counterspindle gear 30, the number of revolutions in 50 revolutions of the main spindle 1a can be specified; and by using the detection information from angle sensor Sr related to the rotation angle of the second counterspindle gear 63, the number of revolutions in 200 revolutions of the main spindle 1a can be specified. Furthermore, the reduction ratio of the first counterspindle gear 30 to the main shaft gear 10 is smaller than the reduction ratio of the second counterspindle gear 63 to the main shaft gear 10. Therefore, the resolution of the rotation amount of the main shaft 1a obtained from the detection information of the magnetic sensor Sq corresponding to the magnet Mq rotating with the first counterspindle gear 30 is higher than the resolution of the rotation amount of the main shaft 1a obtained from the detection information of the magnetic sensor Sr corresponding to the magnet Mr rotating with the second counterspindle gear 63. Thus, in the absolute encoder 2, the range of the identifiable rotation amount of the main shaft 1a can be expanded without reducing the resolution of the identifiable rotation amount.

[0040] The following is a more detailed explanation of the structure of the absolute encoder 2.

[0041] As described above (refer to Figures 1-6), the absolute encoder 2 includes: a base 3; a housing 4; a base plate 5; and a connector 6. Furthermore, the absolute encoder 2 includes: a main shaft gear 10; a first intermediate gear 20; a first countershaft gear 30; a second intermediate gear 70; a magnet retainer 61 having a second countershaft gear 63; and a biasing mechanism 40. Additionally, the absolute encoder 2 includes magnets Mp, Mq, Mr and angle sensors Sp, Sq, Sr, and includes a microcomputer 51 for controlling the drive unit, detection unit, etc., of the absolute encoder 2.

[0042] The base 3 is a platform that holds the rotating bodies 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 retainer 61 (second countershaft gear 63) in a rotatable manner, and fixes the components such as the base plate 5 and the biasing mechanism 40. As shown in Figures 3 to 6 and Figures 11 to 14, the base 3 has: a base 101; and various support parts (described later) for supporting the components of the absolute encoder 2 provided on the base 101. As shown in Figure 7, the housing 4 is fixed to the base 3 by the support plate 3a. The support plate 3a is held between the base 3 and the motor 1, and the housing 4 is fixed to the support plate 3a at one location by screws 8c. Furthermore, the base plate 5 is fixed to the base 3 at three locations by screws 8a. The base 101 is a plate-shaped portion that extends in the horizontal direction (X-axis and Y-axis directions). The plate-shaped portion has a pair of surfaces facing each other in the vertical direction of the absolute encoder 2.

[0043] On the surface above the base 101, i.e., the upper surface 104, substrate supports 110 and substrate positioning pins 120 are provided, which are used to support the substrate 5. The base 3 may have, for example, three substrate supports 110 and two substrate positioning pins 120.

[0044] As shown in Figure 5, the substrate support 110 is a portion protruding upward from the top surface 104 of the base 101, and is, for example, cylindrical or substantially cylindrical. A screw hole 112 extending downward is formed on the upper end face (upper end face 111) of the substrate support 110. The upper end faces 111 of each substrate support 110 are formed such that they extend on the same horizontal plane or along the same horizontal plane. In the absolute encoder 2, the substrate 5 has its lower surface 5a contacting the upper end face 111 of the substrate support 110, and is fixed to the substrate support 110 by a screw 8a screwed into the screw hole 112. Furthermore, as described later, one of the substrate supports 110 is integrated with a substrate positioning pin 120 and a support protrusion 45 constituting the biasing mechanism 40 described later. Also, the substrate support 110 may have reinforcing ribs.

[0045] As shown in Figure 5, the substrate positioning pin 120 is a portion protruding upward from the top surface 104 of the base 101, and is, for example, cylindrical or substantially cylindrical. The upper end (front end 121) of the substrate positioning pin 120 is thinner than the lower part (base 122) of the front end 121, and a stepped surface 123 is formed between the front end 121 and the base 122. As shown in Figure 28 described later, the front end 121 of the substrate positioning pin 120 can be inserted into the positioning hole 5b formed in the substrate 5. By inserting the front end 121 of the substrate positioning pin 120 into the positioning hole 5b of the substrate 5, the substrate 5 is positioned relative to the base 3.

[0046] Furthermore, as shown in Figure 5, the base 3 has upwardly projecting portions on the upper surface 104 of the base 101, namely support protrusions 131, 132, and 141 (see Figures 3-6, etc.). As described later, support protrusion 132 supports the leaf spring 9, which pushes the first intermediate gear 20 toward its central axis. As described later, support protrusions 131 and 141 are used to rotatably support the first intermediate gear 20. Furthermore, as described later, the base 3 has a bearing retainer portion 134 that supports the bearing 135, which rotatably holds the first secondary shaft gear 30 (see Figure 15). Furthermore, as described later, the base 3 includes: a shaft support portion 136 supporting the second secondary gear shaft 62, which rotatably supports the magnet retainer 61 on which the second secondary gear 63 is formed; and a shaft support portion 137 supporting the shaft 75, which rotatably supports the second intermediate gear 70 (see Figures 17-19). Also, a support protrusion 45 is provided on the upper surface 104 of the base 101 of the base 3. As described later, the support protrusion 45 is part of the biasing mechanism 40 that biases the second worm portion 22 toward the second worm wheel portion 31, and is a part that supports the biasing spring 41.

[0047] Next, each component supported by the base 3 of the absolute encoder 2 will be described in detail.

[0048] (Main shaft gear) Figure 8 is a sectional view, which schematically shows the configuration of the absolute encoder 2 shown in Figure 1 with the motor 1 removed, cut along a plane passing through the central axis of the main shaft gear 10 and orthogonal to the central axis of the first intermediate gear 20. Figure 9 is an exploded longitudinal sectional view, which schematically shows the configuration of the magnet Mp, main shaft gear 10, main shaft connector 12 and main shaft 1a of the motor 1 in the configuration of the absolute encoder 2 shown in Figure 8.

[0049] As shown in Figures 8 and 9, the main shaft gear 10 is a cylindrical member coaxial or substantially coaxial with the main shaft 1a of the motor 1 and the main shaft connector 12. The main shaft gear 10 has a cylindrical portion 13 and a first worm portion 11 located radially outward of the cylindrical portion 13. The first worm portion 11 is the gear portion of the main shaft gear 10. As shown in Figure 9, a cylindrical press-in portion 1b with a space formed on the inner circumference is formed at the upper end of the main shaft 1a of the motor 1. The press-in portion 1b is formed for pressing the main shaft connector 12 in and fixing it. Furthermore, a cylindrical press-in portion 14 with a space formed on the inner side is formed in the cylindrical portion 13 of the main shaft gear 10. The press-in portion 14 is formed for pressing the main shaft connector 12 in and fixing it.

[0050] Furthermore, as shown in Figures 8 and 9, a magnet holding portion 15 is formed in the cylindrical portion 13 of the main shaft gear 10 to hold the magnet Mp. The magnet holding portion 15 is a portion that is recessed downward from the upper end face 13a of the cylindrical portion 13, corresponding to the shape of the magnet Mp, and is formed to accommodate the magnet Mp. The magnet holding portion 15 is connected to the pressing portion 14 and has a cylindrical inner circumferential surface 15a with a larger diameter than the pressing portion 14, and an annular bottom surface 15b that connects the inner circumferential surface 15a to the pressing portion 14.

[0051] The inner peripheral surface 15a of the magnet holding portion 15 is formed 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 connector 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 contacts the upper end surface 12a of the spindle connector 12, but does not contact the bottom surface 15b of the magnet holding portion 15 of the spindle gear 10. Thus, the vertical positioning of the magnet Mp is achieved using the upper end surface 12a of the spindle connector 12, and the horizontal positioning is achieved using the inner peripheral surface 15a of the magnet holding portion 15. The lower surface Mpb of the magnet Mp, which is positioned in this way, is attached to and fixed to the upper end surface 12a of the spindle connector 12.

[0052] As described above, the magnet Mp is fixed to the spindle connector 12, and the magnet Mp, spindle gear 10, and spindle connector 12 rotate as a unit with the spindle 1a of the motor 1. The magnet Mp, spindle gear 10, and spindle connector 12 rotate about the same axis as the spindle 1a of the motor 1.

[0053] The first worm gear portion 11 is constructed using helical teeth and is configured to mesh with the first worm wheel portion 21 of the first intermediate gear 20. The first worm gear portion 11 is, for example, formed of polyacetal resin. The first worm gear portion 11 is an example of a first drive gear.

[0054] As shown in Figure 9, the magnet Mp is a disk-shaped or substantially disk-shaped permanent magnet inserted into the magnet holding part 15 of the main shaft gear 10, having an upper part MPa and a lower part Mpb facing each other. 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 (the position in the vertical direction) is defined by the upper end surface 12a of the main shaft connector 12, as described above, in that the upper part MPa of the magnet Mp and the surface of the angle sensor Sp face each other at a certain distance in the vertical direction.

[0055] The central axis MpC of the magnet Mp (representing the axis of the center of the magnet Mp or the axis passing through the center of the intersection of the magnetic poles) is aligned or approximately aligned with the central axis GC1 of the main shaft gear 10, the central axis SaC of the main shaft connector 12, and the central axis MoC of the main shaft 1a of the motor 1. By aligning or approximately aligning the central axes in this way, the angle sensor Sp can detect the rotation angle or rotation amount of the magnet Mp with higher accuracy.

[0056] Furthermore, in this embodiment of the invention, it is ideal for the two magnetic poles (N / S) of the magnet Mp to be formed adjacent to each other in a horizontal plane (XY plane) perpendicular to the central axis MpC of the magnet Mp. This further improves the detection accuracy of the rotation angle or rotation amount of the angle sensor Sp. Moreover, the magnet Mp is formed, for example, from a ferromagnetic material or an Nd(neodymium)-Fe(iron)-B(boron) magnetic material. The magnet Mp can also be, for example, a rubber magnet containing a resin binder, a bonded magnet, etc.

[0057] (Spindle Adapter) Figure 10 shows an enlarged sectional view of one end 124 of the spindle adapter 12.

[0058] The spindle connector 12 is pressed into the shaft of the press-in portion 1b and the press-in portion 14, with the spindle 1a of the motor 1 and the cylindrical portion 13 of the spindle gear 10 as supporting members. As shown in Figures 8, 9 and 10, the spindle connector 12 has tapered portions 126 and 127 and a through hole 128.

[0059] The through hole 128 is connected to the spindle connector 12, connecting one end 124 to the other end 125. The through hole 128 has: a first hole portion 128a occupying a predetermined length in the axial direction from the end 124 side; and a second hole portion 128c extending from the first hole portion 128a and occupying a region up to the other end 125. In the through hole 128, the diameter of the first hole portion 128a in the predetermined length in the axial direction from the end 124 side is larger than the diameter of the second hole portion 128c located on the other end 125 side. Furthermore, the end portion 128b between the first hole portion 128a and the second hole portion 128c is generated when machining the first hole portion 128a with a drill bit having an angled tip; when machining with an end mill, the end portion 128b is absent.

[0060] In terms of the structure for mounting the spindle gear 10 to the spindle 1a of the motor 1, the absolute encoder 2 does not directly mount the spindle gear 10 to the spindle 1a to accommodate spindles 1a of various diameters. Instead, the spindle gear 10 is fixed via a spindle connector 12. Here, the spindle 1a is the rotating shaft of the motor and requires rigidity. Furthermore, the spindle connector 12, as mentioned above, requires adhesive to fix the magnet Mg; therefore, it is ideal to use metal for both the spindle 1a and the spindle connector 12. Consequently, a high pressing force is required when pressing the spindle connector 12 into the pressing portion 1b of the spindle 1a. In this case, there is a risk of bending deformation of the spindle 1a due to the pressing force, or scratches or damage to the pressing fit (inner diameter portion and outer diameter portion) of the spindle 1a and the spindle connector 12.

[0061] Regarding the absolute encoder 2, by making the diameter of the first hole 128a of the through hole 128 of the spindle connector 12 larger than the diameter of the second hole 128c and thinning the wall thickness, the spindle connector 12 becomes more flexible, reducing the pressing force toward the spindle 1a and thus lessening the load toward the spindle 1a. On the other hand, in the upper part (front end side) of the spindle connector 12, since the magnet Mp needs to be fixed with adhesive, the contact area with the magnet Mp (the wall thickness between the outer and inner diameters of the spindle connector 12) is necessary. Therefore, the diameter of the through hole 128 of the spindle connector 12 is made different from that of the area corresponding to a predetermined position in the axial direction, for example, the pressing amount (the size required for pressing) on ​​one end 124 side.

[0062] In other words, by setting the diameter of the first hole 128a on the side of the press-in end 124 (the lower side in FIG. 9) of the spindle connector 12 to be larger than the diameter of the second hole 128c, the peripheral surface 129 of the spindle connector 12 is easily deformed and easily pressed into the press-in portion 1b. Furthermore, by setting the diameter of the second hole 128c on the other end 125 side of the press-in end (the upper side in FIG. 9) to be smaller than the diameter of the first hole 128a, it is possible to balance ensuring the contact area with the magnet Mp and reducing the pressing force without damaging the contact holding force.

[0063] The tapered surfaces 126 and 127 are inclined outer peripheral surfaces where the diameters of one end 124 and the other end 125 are smaller than the diameter of the peripheral surface 129. The tapered surface 126 is the connection portion 126a between the tapered surface 126 of the spindle connector 12 and the peripheral surface 129, where a curved surface is used for connection. Similarly, the tapered surface 127 on the other end 125 side is also connected to the peripheral surface 129 via a curved surface connection portion 127a. In other words, the tapered surfaces 126 and 127 are formed by applying curved surface machining to the connection portions 126a and 127a of the outer peripheral surfaces between them and the peripheral surface 129.

[0064] As shown in Figure 9, the spindle connector 12 is formed by pressing a predetermined length of area in the axial direction from one end 124 into a pressing portion 1b formed at the upper end of the spindle 1a of the motor 1. Furthermore, a predetermined length of area in the axial direction from the other end 125 of the spindle connector 12 is pressed into a pressing portion 14 formed in the cylindrical portion 13 of the spindle gear 10.

[0065] Here, when only a straight chamfer is applied to the tapered surface 126, when one end 124 of the spindle connector 12 is pressed into the press-in portion 1b, scrape material is generated from both the spindle connector 12 and the press-in portion 1b when the edge of the hole in the press-in portion 1b comes into contact with the tapered surface 126. Similarly, when only a straight chamfer is applied to the tapered surface 127, when the other end 125 of the spindle connector 12 is pressed into the press-in portion 14, scrape material is generated from both the spindle connector 12 and the press-in portion 14 when the edge of the hole in the press-in portion 14 comes into contact with the tapered surface 127.

[0066] On the other hand, when the spindle connector 12 is pressed into the pressing portion 1b and the pressing portion 14, after the tapered surfaces 126 and 127 are inserted into the pressing portions 1b and 14, the connecting portions 126a and 127a of the outer peripheral surfaces between the tapered surfaces 126 and 127 and the peripheral surface 129 come into contact with the pressing portions 1b and 14. The spindle connector 12 is smoothly pressed into the pressing portions 1b and 14 by applying curved surfaces to the connecting portions 126a and 127a of the outer peripheral surfaces between the tapered surfaces 126 and 127 and the peripheral surface 129, thus preventing scratches on both the spindle connector 12 and the pressing portions 1b and 14. Therefore, the scattering of chips and other debris can be suppressed according to the spindle connector 12. Furthermore, the spindle connector 12 can prevent the spindle connector 12 from being tilted (inclined) due to component scratches. Moreover, by suppressing the tilt of the spindle connector 12, the amount of pressing in (the required size for pressing in) can be reduced.

[0067] Ideally, the surface machining of the connecting portions 126a and 127a should be set to a radius of approximately 1 mm. Furthermore, by making the surface roughness of the spindle connector 12, which contains the circumferential surface 129 and the tapered surfaces 126 and 127a of the connecting portions 126a and 127a, smoother surfaces, scratches can be prevented on the surfaces of both the spindle connector 12 and the press-fit portion 14. The surface roughness Rmax (maximum roughness) of the spindle connector 12 can be set to, for example, 1.6 μm or less. Additionally, the surface machining of the connecting portions 126a and 127a can be either one end 124 or the other end 125.

[0068] (First Intermediate Gear) Figure 11 is a sectional view, schematically showing the configuration of the absolute encoder 2 shown in Figure 6, cut along a plane passing through the central axis of the first intermediate gear 20 and parallel to the horizontal plane (XY plane). Figure 12 is an enlarged perspective view of the absolute encoder 2 cut as shown in Figure 11, viewed from above on the secondary shaft end 23b side of the first intermediate gear shaft 23. Figure 13 is a partial sectional view, schematically showing the configuration of the absolute encoder 2 shown in Figure 6, cut along a plane passing through the central axis of the first intermediate gear 20 and orthogonal to the horizontal plane (XY plane).

[0069] As shown in Figures 4 to 6 and Figures 11 to 13, the first intermediate gear 20 is supported rotatably on the upper side of the base 101 of the base 3 by the first intermediate gear shaft 23. The first intermediate gear shaft 23 extends parallel to the horizontal plane. Furthermore, the first intermediate gear shaft 23 is not parallel to the left-right direction (X-axis direction) and the front-back direction (Y-axis direction) when viewed from above. That is, the first intermediate gear shaft 23 is inclined relative to the left-right direction and the front-back direction. The inclination of the first intermediate gear shaft 23 relative to the left-right direction and the front-back direction means that the first intermediate gear shaft 23 extends obliquely relative to the outer peripheral surfaces 105-108 of the base 101 of the base 3 (see Figure 11). In the absolute encoder 2, the first intermediate gear shaft 23 is supported on the base 101 of the base 3 by a support protrusion 131 located on the side of the main shaft gear 10 and a support protrusion 141 located on the side of the first auxiliary shaft gear 30.

[0070] As shown in Figure 11, the outer peripheral surface of the base 3 is composed of a right outer peripheral surface 105, a left outer peripheral surface 107 parallel to the YZ plane, and a rear outer peripheral surface 106 and a front outer peripheral surface 108 parallel to the XZ plane and extending between the right outer peripheral surface 105 and the left outer peripheral surface 107. The right outer peripheral surface 105 is located on the right side (right side in the X-axis direction) of the base 3. The left outer peripheral surface 107 is located on the left side (left side in the X-axis direction) of the base 3. The rear outer peripheral surface 106 is located on the rear side (rear side in the Y-axis direction) of the base 3. The front outer peripheral surface 108 is located on the front side (front side in the Y-axis direction) of the base 3.

[0071] As shown in Figures 3 to 6, the absolute encoder 2, viewed from above, is the same size as, for example, a 25mm square motor 1. Therefore, by configuring the first intermediate gear 20, which is arranged parallel to the top 104 of the base 3, to extend obliquely relative to the outer peripheral surfaces 105-108 of the base 3, the horizontal dimension of the absolute encoder 2 can be reduced. Furthermore, the horizontal direction refers to a direction orthogonal to the central axis of the main shaft 1a of the motor 1, and also a direction parallel to the XY plane.

[0072] As shown in Figures 5, 6, and 11-14, the first intermediate gear 20 is formed as a cylindrical component capable of rotating around the first intermediate gear shaft 23, and has a first worm gear portion 21, a second worm portion 22, a cylindrical portion 24, a main shaft-side sliding portion 25, and a secondary shaft-side sliding portion 26. The cylindrical portion 24 is a cylindrically extending component with an inner peripheral surface 24b forming 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 peripheral surface 24b of the cylindrical portion 24. The inner peripheral surface 24b is formed to slide on the outer peripheral surface of the first intermediate gear shaft 23, which is inserted into the through hole 24a, and the first intermediate gear 20 is supported by the first intermediate gear shaft 23 in a manner that allows it to rotate freely around the first intermediate gear shaft 23. The first intermediate gear 20 is a component integrally formed of metal, resin, etc., and in this example, it is formed of polyacetal resin.

[0073] As shown in Figures 5 to 8, the first worm gear portion 21 is a gear that meshes with the first worm portion 11 of the main shaft gear 10. The first worm gear portion 21 is an example of the first driven gear. The first worm gear portion 21 is provided on one end side of the cylindrical portion 24 of the first intermediate gear 20, and is composed, for example, of a plurality of teeth provided on the 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 such that the first worm gear portion 21 is located near the center of the base 101 of the base 3. Therefore, the end of the cylindrical portion 24 near which the first worm gear portion 21 is located is the end of the first intermediate gear 20 on the main shaft gear 10 side.

[0074] As shown in Figure 8, the outer diameter of the first worm gear portion 21 is smaller than the outer diameter of the first worm portion 11. The central axis of the first worm gear portion 21 is coaxial or substantially coaxial with the central axis of the inner circumferential surface 24b of the cylindrical portion 24. In the absolute encoder 2, the central axis of the first worm gear portion 21 is parallel or substantially parallel to the upper surface 104 of the base portion 101 of the base 3. Therefore, by reducing the outer diameter of the first worm gear portion 21, the absolute encoder 2 can be miniaturized in the vertical direction (height direction).

[0075] As shown in Figures 5, 6, and 11-15, the second worm gear portion 22 is constructed using helical teeth and is arranged coaxially or substantially 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, for example, it is constructed by helical teeth formed on a cylindrical surface formed on the other end side of the cylindrical portion 24. The other end side of the cylindrical portion 24 refers to the end side that becomes the first secondary shaft gear 30 side of the first intermediate gear 20. Furthermore, the central axis of the second worm gear portion 22 is formed coaxially or substantially coaxially with the central axis of the inner circumferential surface 24b of the cylindrical portion 24. By meshing the second worm gear portion 31 provided on the first secondary shaft gear 30 with the second worm gear portion 22, the rotational force of the first intermediate gear 20 is transmitted to the first secondary shaft gear 30.

[0076] As described above, the axial angle between the first worm portion 11 and the first worm wheel portion 21 is 90° or approximately 90°. The central axis of the first worm portion 11 and the central axis system of the first worm wheel portion 21 are perpendicular to the central axis of the first worm portion 11, and when viewed from a direction perpendicular to the central axis of the first worm wheel portion 21, they are orthogonal or approximately orthogonal to each other. Similarly, the axial angle between the second worm portion 22 and the second worm wheel portion 31 is 90° or approximately 90°. The central axis of the second worm portion 22 and the central axis system of the second worm wheel portion 31 are perpendicular to the central axis of the second worm portion 22, and when viewed from a direction perpendicular to the central axis of the second worm wheel portion 31, they are orthogonal or approximately orthogonal to each other.

[0077] As shown in Figure 15, in order to miniaturize the absolute encoder 2 in the vertical direction (height direction), the outer diameter of the second worm 22 is set to a small value within the possible range.

[0078] As shown in Figures 6 and 11-13, the main shaft-side sliding portion 25 of the first intermediate gear 20 is provided at one end of the first intermediate gear 20, that is, the end of the first intermediate gear 20 that becomes the main shaft gear 10. Specifically, the main shaft-side sliding portion 25 is the end face of one end of the cylindrical portion 24, which is an annular surface facing the central axis direction of the first intermediate gear 20 formed at one end of the cylindrical portion 24. In the absolute encoder 2, the main shaft-side sliding portion 25 of the first intermediate gear 20 is in contact with one end 9a of the leaf spring 9, which will be described later.

[0079] The leaf spring 9 is an example of an elastic component, for example, made of metal. In the absolute encoder 2, the leaf spring 9 is a component used to push the first intermediate gear 20 towards the central axis of the first intermediate gear shaft 23. As shown in Figures 4-6 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 the support protrusion 45 of the base 3 by a screw 8b and is supported by the base 3. One end 9a of the leaf spring 9 is formed to contact the sliding portion 25 on the main shaft side of the first intermediate gear 20; specifically, as shown in Figures 4 and 13, one end 9a of the leaf spring 9 is composed of two forked branches. A gap larger than the diameter of the first intermediate gear shaft 23 is formed between the two branches constituting one end 9a of the leaf spring 9. Thus, in the absolute encoder 2, the two branches of one end 9a of the leaf spring 9 pass through the intermediate first intermediate gear shaft 23 and contact the main shaft side sliding part 25 of the first intermediate gear 20.

[0080] As shown in Figures 4, 6, 11, and 13, in the absolute encoder 2, the leaf spring 9, in its flexed state, has one end 9a in contact with the main shaft-side sliding portion 25 of the first intermediate gear 20, while the other end 9b is supported by the support protrusion 132 of the base 3 and fixed to the support protrusion 45 of the base 3. Therefore, when the leaf spring 9 generates elastic force, the main shaft-side sliding portion 25 of the first intermediate gear 20 is pressed by one end 9a of the leaf spring 9. Due to this pressing force, the first intermediate gear 20 is biased along the first intermediate gear shaft 23 towards the support protrusion 141 from the support protrusion 131 on the main shaft gear 10 side towards the support protrusion 141 on the first auxiliary shaft gear 30 side. In this state, when the first intermediate gear 20 rotates, the main shaft-side sliding portion 25 of the first intermediate gear 20 rotates while still in contact with one end 9a of the leaf spring 9.

[0081] As shown in Figures 4, 6, and 11 to 14, the secondary shaft-side sliding portion 26 of the first intermediate gear 20 is provided at the other end of the first intermediate gear 20, that is, the end of the first intermediate gear 20 that becomes the first secondary shaft gear 30. Specifically, the secondary shaft-side sliding portion 26 is the end face of the other end of the cylindrical portion 24, and is an annular surface facing the other end of the cylindrical portion 24 in the direction of the central axis of the first intermediate gear 20, and is opposite to the main shaft-side sliding portion 25 in the direction of the central axis of the first intermediate gear 20.

[0082] In the absolute encoder 2, the sliding portion 26 on the secondary shaft side of the first intermediate gear 20 contacts the support protrusion 141, which is positioned on the first intermediate gear 20 along the central axis of the first intermediate gear shaft 23. As described above, since the first intermediate gear 20 is pressed by the leaf spring 9 in a direction from the support protrusion 131 on the main shaft gear 10 side towards the support protrusion 141 on the secondary shaft gear 30 side, the sliding portion 26 on the secondary shaft side of the first intermediate gear 20 is also pressed in the same direction and contacts the support protrusion 141. Thus, the pressing force of the leaf spring 9 is transmitted from the first secondary shaft gear 30 to the support protrusion 141, and the first intermediate gear 20 is stably supported in the direction from the support protrusion 131 towards the support protrusion 141. When the first intermediate gear 20 rotates, the sliding portion 26 on the secondary shaft side of the first intermediate gear 20 rotates while in contact with the support protrusion 141.

[0083] The aforementioned support protrusions 131 and 141 are examples of a first shaft support and a second shaft support, respectively, which hold the first intermediate gear 20 in a rotatable position via the first intermediate gear shaft 23. As shown in Figures 5, 6, and 11 to 13, support protrusions 131 and 141 form a pair, for example, having a generally cuboid portion or a generally cuboid portion protruding upward from the base 101 of the base 3. Support protrusion 131 is located near the main shaft gear 10, and in top view (refer to Figures 6 and 11), it is located on the left side of the base 3 and near the center in the front-rear direction. Support protrusion 141 is located near the first auxiliary shaft gear 30, and in top view, it is located on the right side and front side of the base 3.

[0084] As shown in Figures 6 and 11 to 13, support protrusions 131 and 141 function as support members that can support the first intermediate gear shaft 23 in a manner that allows it to swing along the horizontal plane; that is, they function as support members that can support the first intermediate gear 20 in a manner that allows it to swing along the horizontal plane. The first intermediate gear shaft 23 is a cylindrical rod-shaped member, having a main shaft side end 23a as one end and a secondary shaft side end 23b as the other end. The main shaft side end 23a is the end of the first intermediate gear shaft 23 located on the side of the main shaft gear 10 in the absolute encoder 2, and the secondary shaft side end 23b is the end of the first intermediate gear shaft 23 located on the side of the first secondary shaft gear 30 in the absolute encoder 2.

[0085] The first worm gear portion 21, located on the main shaft side end 23a of the first intermediate gear shaft 23, is configured by the biasing mechanism 40 (described later) to be movable in the first meshing direction (arrow P1 direction in FIG. 12), but not movable in the extension direction of the first intermediate gear shaft 23 (central axis direction of the first intermediate gear shaft 23) or in a direction orthogonal to the first meshing direction P1 (vertical direction). Furthermore, the first meshing direction, as described above, refers to the direction in which the first worm gear portion 21 faces the first worm portion 11 in order to mesh with the first worm portion 11.

[0086] As shown in Figures 11 to 14, a through hole 143 is formed in the support protrusion 131 for insertion into the spindle-side end 23a of the first intermediate gear shaft 23. The shape of the through hole 143 in a cross-section orthogonal to the extending direction is called a circular hole shape. The so-called circular hole shape refers to a shape with a true circle or a nearly true circle outline.

[0087] Furthermore, the absolute encoder 2 may also have a retaining ring (not shown) that serves as a fixing part, capable of engaging with the main shaft side end 23a of the first intermediate gear shaft 23. The retaining ring is a member in which a portion that cannot pass through the through hole 143 of the support protrusion 131 is formed in the main shaft side end 23a of the first intermediate gear shaft 23, and the outer diameter of the main shaft side end 23a of the first intermediate gear shaft 23 is partially enlarged. The retaining ring is, for example, an e-shaped ring or similar annular member 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 in such a way that the retaining ring is located on the opposite side of the support protrusion 131 relative to the secondary shaft side end 23b. That is, the retaining ring is configured to contact the outer surface 131a of the support protrusion 131. The outer surface 131a is the side of the support protrusion 131 opposite to the side facing the support protrusion 141. Therefore, by contacting the outer surface 131a of the support protrusion 131 of the retaining ring, the movement of the first intermediate gear shaft 23 in the direction from the main shaft side end 23a toward the secondary shaft side end 23b is restricted.

[0088] The second worm portion 22, located on the secondary shaft end 23b of the first intermediate gear shaft 23, is configured to move in the second meshing direction (arrow P2 direction in FIG. 12) via the biasing mechanism 40 described later, while the first intermediate gear shaft 23 cannot move in a direction orthogonal to both the extension direction of the first intermediate gear shaft 23 (the direction of the central axis of the first intermediate gear shaft 23) and the second meshing direction P2 (Z-axis direction). Furthermore, the second meshing direction, as described above, refers to the direction in which the second worm portion 22 faces the second worm wheel portion 31 in order to mesh with the second worm gear portion 31.

[0089] A through hole 145 is formed in the support protrusion 141 for insertion into the secondary shaft end 23b of the first intermediate gear shaft 23. The through hole 145 has an elongated shape in a cross-section orthogonal to the extending direction. This elongated shape of the through hole 145 has a long axis and a short axis orthogonal to the long axis. The width of the long axis side is greater than the width of the short axis side. The width of the long axis side of the through hole 145 of the support protrusion 141 on the first secondary gear 30 side is greater than the diameter of the outer peripheral surface of the first intermediate gear shaft 23. Furthermore, the width of the short 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 long axis direction of the through hole 145 of the support protrusion 141 is parallel or approximately parallel to the horizontal plane. As described later, a biasing spring 41 is engaged in the first intermediate gear shaft 23 at the secondary shaft side end 23b, which is inserted into the through hole 145 of the support protrusion 141, forming a biasing spring 41 that biases the first intermediate gear shaft 23 at the secondary shaft side end 23b in the second meshing direction P2.

[0090] Thus, the first intermediate gear shaft 23, through the biasing mechanism 40, support protrusion 131, and support protrusion 141 described later, allows the secondary shaft end 23b to move parallel or substantially parallel to the horizontal direction with the main shaft end 23a as the fulcrum (= center of swing). Furthermore, the second worm portion 22, which is further from the secondary shaft end 23b than the first worm gear portion 21 on the main shaft end 23a side, can move with a large amplitude parallel or substantially parallel to the horizontal direction. Therefore, 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, is able to swing along the horizontal plane (XY plane).

[0091] In this configuration, the amount of movement (oscillation) of the first intermediate gear shaft 23 is determined by the depth of the through hole 143 formed in the support protrusion 131, that is, the thickness of the support protrusion 131 in the direction of the central axis 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 long axis side of the through hole 145. However, if the clearance between the through hole 143 and the first intermediate gear shaft 23 is large, the oscillation of the first intermediate gear shaft 23 will increase and cause misalignment, so it is desirable to avoid increasing the clearance. Therefore, by forming the support protrusion 131 with a thin plate or the like, the thickness of the support protrusion 131 is reduced, that is, the through hole 143 is made shallower, which can reduce the clearance between the through hole 143 and the first intermediate gear shaft 23 and ensure the amount of movement of the first intermediate gear shaft 23. Furthermore, by pre-designing the movement of the first intermediate gear shaft 23 based on the thickness of the support protrusion 131 to be greater than the movement of the first intermediate gear shaft 23 based on the width of the long axis side of the through hole 145, the movement of the first intermediate gear shaft 23 can be defined by the width of the long axis side of the through hole 145.

[0092] (First Auxiliary Shaft Gear) Figure 15 is a partial sectional view, schematically showing the configuration of the absolute encoder 2 shown in Figure 2, cut along a plane passing through the central axis of the first auxiliary shaft gear 30 and orthogonal to the central axis of the first intermediate gear 20. Figure 16 is an exploded perspective view, schematically showing the disassembled configuration of the magnet Mq, magnet retainer 35, first auxiliary shaft gear 30, and bearing 135 in the absolute encoder 2 shown in Figure 15.

[0093] As shown in Figures 15 and 16, the first auxiliary shaft gear 30 is a cylindrical component into which the shaft portion 35b of the magnet retainer 35 is pressed and fixed. The first auxiliary shaft gear 30 includes a second worm gear portion 31, a gear portion 32, and a through hole 33. The first auxiliary shaft gear 30 is a component integrally formed of metal or resin; in this example, it is formed of polyacetal resin.

[0094] The second worm gear 31 is a gear that meshes with the second worm portion 22 of the first intermediate gear 20. The second worm gear 31 is an example of a second driven gear. The second worm gear 31 is, for example, composed of a plurality of teeth on the outer periphery of a cylindrical portion located on the upper side of the first counterspindle gear 30. As the first intermediate gear 20 rotates, the rotational force of the first intermediate gear 20 is transmitted to the first counterspindle gear 30 through the second worm portion 22 and the second worm gear 31 of the first intermediate gear 20.

[0095] Gear section 32 is a gear that meshes with gear section 71 of the second intermediate gear 70. Gear section 32 is an example of the third drive gear. Gear section 32 is, for example, composed of a plurality of teeth on the outer periphery of the cylindrical portion located on the lower side of the first counterspindle gear 30. Furthermore, as shown in FIG. 15, gear section 32 is formed on the lower side of the second worm gear section 31, and its tooth crown circle diameter is smaller than the tooth crown circle diameter of the second worm gear section 31. By rotating the first counterspindle gear 30, the rotational force of the first counterspindle gear 30 is transmitted to the second intermediate gear 70 through gear section 32 of the first counterspindle gear 30 and gear section 71 of the second intermediate gear 70.

[0096] As shown in Figures 15 and 16, the through hole 33 is a hole in the first secondary shaft gear 30 that runs along the central axis of the cylindrical first secondary shaft gear 30. The shaft portion 35b of the magnet retainer 35 is pressed into the through hole 33, and the first secondary shaft gear 30 is integrated with the magnet retainer 35 and rotates.

[0097] The magnet retainer 35 has a magnet retaining portion 35a and a shaft portion 35b. The magnet retainer 35 is a component integrally molded from metal or resin; in this example, it is formed of non-magnetic stainless steel. Two outer races of bearings 135 are pressed into the inner circumferential surface of the cylindrical bearing retainer portion 134 formed in the base 3. The shaft portion 35b of the magnet retainer 35 is a cylindrical component. The shaft portion 35b is pressed into the through hole 33 of the first counterspindle gear 30, and the lower part of the shaft portion 35b is inserted into and fixed to the inner races of the two bearings 135. Therefore, the magnet retainer 35 supports the base 3 by means of the two bearings 135 and rotates integrally with the first counterspindle gear 30. The magnet retainer 35 is held in the bearing retainer portion 134 by means of the bearings 135, rotatably about a rotation axis parallel or substantially parallel to the Z-axis. Furthermore, a bearing stopper 35c is pressed into the shaft portion 35b of the magnet retainer 35. Regarding the assembly of the first set gear 30, firstly, the outer race of the bearing 135, located on the upper 104 side of the base 3, is pressed into the bearing retainer portion 134. Then, the shaft portion 35b of the magnet retainer 35 is inserted into the inner race of the bearing 135. Next, the bearing stopper 35c is pressed into the shaft portion 35b of the magnet retainer 35 until it abuts against the lower side of the inner race of the bearing 135. Afterward, while inserting the shaft portion 35b of the magnet retainer 35 into the inner race of the bearing 135, located on the lower 102 side of the base 3, the outer race is pressed into the bearing retainer portion 134 and secured. Therefore, by using the bearing stopper 35c to prevent the magnet retainer 35, which is inserted into the bearing 135, from falling off the bearing 135, the bearing 135 and the magnet retainer 35 can be fixed without gaps, thus minimizing the vertical sway of the magnet Mg. Although the positions of the two bearings 135 can be determined by abutting against the bearing positioning member 35d provided on the base 3, they can also be positioned such that the surfaces of the upper 104 and lower 102 of the base 3 are at the same height as the surface of the bearing 135 without the bearing positioning member 35d.

[0098] Furthermore, a 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 is sunken downward from the upper end surface of the magnet holder 35. The inner peripheral surface of the recess of the magnet holding portion 35a is formed to contact the outer peripheral surface Mqd of the magnet Mq. In this way, in the absolute encoder 2, the magnet Mq is fixed to the magnet holding portion 35a by being housed in the recess of the magnet holding portion 35a.

[0099] By using two bearings 135 provided in the bearing retainer portion 134 formed in the base 3 to support the shaft portion 35b of the magnet retainer 35, tilting of the magnet retainer 35 can be prevented. Moreover, when 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 retainer 35 is increased.

[0100] As shown in Figure 16, the magnet Mq is a disk-shaped or nearly disk-shaped permanent magnet pressed into the magnet holding part 35a of the magnet holder 35, having 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 certain 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 intersection of the magnetic poles) is aligned with the central axis SC of the magnet holder 35, the central axis GC2 of the first auxiliary shaft gear 30, and the central axis BC of the bearing 135. By aligning the central axes in this way, the rotation angle or rotation amount can be detected with higher accuracy.

[0101] Furthermore, in this embodiment of the invention, it is ideal for the two magnetic poles (N / S) of the magnet Mq to be 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. Moreover, the magnet Mq is formed, for example, from a granular iron-based or Nd(neodymium)-Fe(iron)-B(boron) based magnetic material. The magnet Mq can also be, for example, a rubber magnet containing a resin binder, a bonded magnet, etc.

[0102] (Second intermediate gear) Figure 17 is a partial sectional view, which schematically shows the state of the absolute encoder 2 shown in Figure 2, cut along the central axis passing through the second intermediate gear 70 and the second counterspindle gear 63. Figure 18 is an enlarged sectional view showing the second intermediate gear 70 shown in Figure 17.

[0103] As shown in Figures 17 and 18, the second intermediate gear 70 is a component that is rotatably supported on the shaft support portion 136 of the base 3, which is fixed to the shaft 75. It includes a gear portion 71, a gear portion 72, and a body portion 73. The second intermediate gear 70 is a component integrally molded from a resin material with low sliding resistance, for example, polyacetal resin. The shaft 75 is fixed to the shaft support portion 136 of the base 3 in such a way that the central shaft GC3 of the second intermediate gear 70 is parallel or substantially parallel to the central shaft GC2 of the first secondary shaft gear 30. For example, the lower end (lower end face 75a) of the shaft 75 is pressed into the through hole 136a of the shaft support portion 136 of the base 3 and fixed.

[0104] The main body 73 is a cylindrical or generally cylindrical portion with a through hole 74 inside. The through hole 74 is formed to allow sliding relative to the shaft 75 and to allow the shaft 75 to be inserted. The gear portion 71 is a gear that meshes with the gear portion 32 of the first secondary shaft gear 30. The gear portion 71 is an example of a third driven gear. The gear portion 71 is, for example, composed of a plurality of teeth provided on the outer periphery of the lower side of the main body 73. By rotating the first secondary shaft gear 30, the rotational force of the first secondary shaft gear 30 is transmitted to the gear portion 71 of the second intermediate gear 70 through the gear portion 32 of the first secondary shaft gear 30. This causes the second intermediate gear 70 to rotate.

[0105] Gear section 72 is a gear that meshes with gear section 64 of the second counterspindle gear 63. Gear section 72 is an example of a fourth drive gear. Gear section 72 is, for example, composed of a plurality of teeth provided on the outer periphery of the upper side of the body section 73, and is provided on the upper side of gear section 71. By rotating the second intermediate gear 70, the rotational force of the second intermediate gear 70 is transmitted to gear section 64 of the second counterspindle gear 63 through gear section 72. This causes the second counterspindle gear 63 to rotate.

[0106] As shown in Figures 17 and 18, the through hole 74 in the second intermediate gear 70 is a hole that extends through the body part 73 in such a way that the central axis of the through hole 74 is aligned or approximately aligned with the central axes of the gear part 71 and the gear part 72 respectively. Furthermore, the through hole 74 is formed such that the central axis GC3 of the second intermediate gear 70 is aligned or approximately aligned with the central axis of the shaft 75.

[0107] The lower end face (lower end face 73a) of the body portion 73 contacts the upper surface 104 of the base 3, allowing it to slide against the upper surface 104. The lower end face 73a of the body portion 73 is, for example, a plane or approximately a plane that is orthogonal to or substantially orthogonal to the central axis GC3 of the second intermediate gear 70. Furthermore, the upper end face (upper end face 73b) of the body portion 73 contacts the member facing the upper end face 73b, allowing it to slide against that member. The upper end face 73b of the body portion 73 is, for example, a plane or approximately a plane that is orthogonal to or substantially orthogonal to the central axis GC3 of the second intermediate gear 70.

[0108] On the upper end (upper end face 75b) side of the shaft 75, an annular groove 75c is formed around the axis of the shaft 75. The groove 75c allows the retaining ring 76 to engage. The retaining ring 76 is a component used to maintain the second intermediate gear 70 in a state where it can be rotatably supported by the shaft 75. It is a component whose outer diameter on the upper end face 75b side of the shaft 75 is partially enlarged. As shown in FIG18, the retaining ring 76 is, for example, a C-type ring or an E-type ring. In the absolute encoder 2, the groove 75c is provided on the shaft 75 such that the retaining ring 76 faces the upper end face 73b of the body portion 73 of the second intermediate gear 70. In the absolute encoder 2, the retaining ring 76 installed in the groove 75c can be formed to contact the upper end face 73b of the second intermediate gear 70, or it can be formed to face the upper end face 73b of the second intermediate gear 70 with a gap. The movement of the second intermediate gear 70 along the axis of the shaft 75 is restricted by the retaining ring 76.

[0109] The second intermediate gear 70 is configured as described above. 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 installed in the groove 75c of the shaft 75 to mount the second intermediate gear 70 in the absolute encoder 2. In the absolute encoder 2, the second intermediate gear 70 is configured to rotate about an axis of rotation parallel or substantially parallel to the central axis GC2 of the first secondary shaft gear 30, with the shaft 75 as the rotation axis. Furthermore, the second intermediate gear 70 is configured to slide against the upper surface 104 of the base 3 and the retaining ring 76 mounted on the shaft 75, and its movement in the axial direction of the shaft 75 is restricted.

[0110] (Second Axis Gear) Figure 19 is an enlarged sectional view showing the magnet retainer 61 with the second axis gear 63 shown in Figure 17. Figure 20 is an exploded perspective view, which roughly shows the disassembled state of the magnet retainer 61 shown in Figure 19.

[0111] As shown in Figures 17, 19, and 20, the magnet retainer 61 is a component rotatably supported on the second auxiliary shaft gear 62. It includes a second auxiliary shaft gear 63, a magnet retainer portion 65, and a magnet Mr. The second auxiliary shaft gear 62 is fixed to the shaft support portion 137 of the base 3. The magnet retainer portion 65 is a component used to hold the magnet Mr between itself and the second auxiliary shaft gear 63 and to fix the magnet Mr within the magnet retainer 61. The second auxiliary shaft gear 62 is fixed to the shaft support portion 137 of the base 3 in a manner where its axis (central shaft GC4) is parallel or substantially parallel to the central shaft GC3 of the second intermediate gear 70. For example, the lower end (lower end face 62a) of the second auxiliary shaft gear 62 is pressed into the through hole 137a of the shaft support portion 137 of the base 3 and fixed therein. Furthermore, in the absolute encoder 2, the second auxiliary shaft gear shaft 62 is fixed to the base 3 in such a way that the magnet Mr of the magnet holder 61 is opposite to the angle sensor Sr mounted on the base plate 5 in the direction of the central shaft GC3.

[0112] The second auxiliary shaft gear 63 includes a gear portion 64, a body portion 66, and a magnet support portion 67. The second auxiliary shaft gear 63 is a component integrally molded from, for example, a resin material with low sliding resistance. That is, the gear portion 64, the body portion 66, and the magnet support portion 67 are integrally formed from the same material, each constituting a part of the second auxiliary shaft gear 63. An example of the resin material for the second auxiliary shaft gear 63 is polyacetal resin. The body portion 66 is a cylindrical or substantially cylindrical portion with a through hole 66a inside. The through hole 66a is formed to be slidable relative to the second auxiliary shaft gear shaft 62 and to allow the second auxiliary shaft gear shaft 62 to be inserted. 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, for example, composed of a plurality of teeth provided on the outer periphery of the body portion 66. In the example shown, the gear portion 64 is a disc-shaped portion protruding outward from the outer peripheral surface of the body portion 66, and a plurality of teeth are formed on the outer peripheral surface of this disc-shaped portion. 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 of the second intermediate gear 70. This causes the second countershaft gear 63 to rotate.

[0113] As shown in Figures 17 and 19, the through hole 66a in the second auxiliary shaft gear 63 is a hole that extends through the body portion 66 in such a way that the central axis of the through hole 66a is aligned with or approximately aligned with the central axis of the gear portion 64. Furthermore, the through hole 66a is formed such that the central axis GC4 of the second auxiliary shaft gear 63 is aligned with or approximately aligned with the central axis of the second auxiliary shaft gear shaft 62.

[0114] The lower end face (lower end face 66b) of the body portion 66 contacts the upper surface 104 of the base 3 and is slidable relative to the upper surface 104. The lower end face 66b of the body portion 66 is, for example, a plane or approximately plane that is orthogonal to or substantially orthogonal to the central axis GC4 of the second counterspindle gear 63. Furthermore, the upper end face (upper end face 66c) of the body portion 66 contacts the member facing which the upper end face 66c is located, and is slidable against that member. The upper end face 66c of the body portion 66 is, for example, a plane or substantially orthogonal to or substantially orthogonal to the central axis GC4 of the second counterspindle gear 63.

[0115] The magnet support portion 67 is a portion of the main body portion 66 that extends upward from the upper side of the gear portion 64, and is a cylindrical portion extending along the central axis GC4 of the second secondary shaft gear 63. The magnet support portion 67 extends upward beyond the upper end face 66c of the main body portion 66, and a cylindrical space is formed inside the magnet support portion 67 by the upper end face 66c of the main body portion 66 and the inner peripheral surface (inner peripheral surface 67a) of the magnet support portion 67. The outer peripheral surface 67b of the magnet support portion 67 is formed at an inner peripheral position beyond the front end of the gear portion 64. The magnet support portion 67 is, for example, a cylindrical or substantially cylindrical component centered or approximately centered on the central axis GC4 of the second secondary shaft gear 63. As shown in Figure 19, the upper end face 66c of the main body 66 is connected to the inner peripheral surface 67a of the magnet support 67. The outer peripheral side of the portion of the main body 66 connected to the magnet support 67 may be larger than the lower portion of the gear portion 64; conversely, the outer peripheral side of the portion connected to the magnet support 67 may not be larger than the lower portion of the gear portion 64. Furthermore, the shape of the magnet support 67 is not limited to a cylindrical or approximately cylindrical shape; it can also be other shapes. For example, the shape of the magnet support 67 may also be a polygonal cylindrical shape, etc.

[0116] The upper end face (upper end face 67c) of the magnet support 67 is a plane or approximately plane that is orthogonal or substantially orthogonal to the central axis GC4 of the second counterspindle gear 63. In the absolute encoder 2, the inner circumferential surface 67a of the magnet support 67 is located further inward than the outer circumferential surface (outer circumferential surface Mrd) facing the magnet Mr, so that the magnet Mr can make full circumferential contact with the upper end face 67c. Furthermore, in the absolute encoder 2, the magnet support 67 is formed such that the upper end face 67c is located further upward than the end face (upper end face 62b) above the shaft of the second counterspindle gear 62. In addition, the upper end face 67c of the magnet support 67 is parallel or substantially parallel to the upper surface 104 of the base 3, so that when the second counterspindle gear 63 rotates, the upper end face 67c rotates relative to the upper surface 104 of the base 3 without surface jump.

[0117] The magnet retainer portion 65 is a component formed of a bottomed cylindrical resin material. The resin material of the magnet retainer portion 65 is, for example, a resin material adhered by an adhesive. Specifically, the magnet retainer portion 65 has: a cylindrical portion 68 extending into a cylindrical shape; and a bottom portion 69 extending from one end of the cylindrical portion 68 toward the inner circumference. The cylindrical portion 68 is formed within a magnet support portion 67 that houses the second counterspindle gear 63, and the magnet retainer portion 65 can be fitted into the fitting portion 65a of the magnet support portion 67. The cylindrical portion 68 and the bottom portion 69 form a magnet receiving portion 65b that can house and retain the magnet Mr inside.

[0118] In the absolute encoder 2, the cylindrical portion 68 of the magnet retainer portion 65 has a cylindrical or substantially cylindrical inner circumferential surface 68a extending along a central axis that coincides with or is approximately coincident with the central axis MC4 of the second counterspindle gear 63. The inner circumferential surface 68a is the surface facing the inner circumferential side, extending from the end opposite to the bottom 69 side of the cylindrical portion 68 (open end 68c) towards the bottom 69 side, and an opening is formed at the open end 68c of the cylindrical portion 68. The space formed inside the inner circumferential surface 68a becomes the fitting portion 65a. The inner circumferential surface 68a is formed such that when the magnet support portion 67 of the second counterspindle gear 63 is housed in the fitting portion 65a, the magnet support portion 67 is tightly fitted into the magnet retainer portion 65, and it contacts the outer circumferential surface 67b of the magnet support portion 67. Furthermore, the shape of the inner circumferential surface 68a of the cylindrical portion 68 is not limited to a cylindrical or approximately cylindrical shape, and may also be other shapes. The shape of the inner circumferential surface 68a of the cylindrical portion 68 corresponds to the shape of the magnet support portion 67 housed within it.

[0119] Furthermore, in the absolute encoder 2, the cylindrical portion 68 of the magnet retainer portion 65 has an inner circumferential surface 68b that is cylindrical or substantially cylindrical. This inner circumferential surface extends along a central axis that coincides with or approximately coincides with the central axis MC4 of the second auxiliary shaft gear 63, and also extends along a central axis that coincides with or approximately coincides with the central axis MrC of the magnet Mr. The inner circumferential surface 68b faces the inner circumferential side and extends between the inner circumferential surface 68a and the bottom surface 69a of the bottom 69. The space formed between the inner circumferential surface 68b and the bottom surface 69a of the bottom 69 forms the magnet receiving portion 65b. The inner circumferential surface 68b is formed such that when the magnet Mr is received in the magnet receiving portion 65b, it faces the outer circumferential surface Mrd of the magnet Mr in the radial direction. The inner circumferential surface 68b is located further inward than the inner circumferential surface 68a, and a step difference is formed between the inner circumferential surfaces 68a and 68b. Furthermore, the width of the inner circumferential surface 68b in the direction of the central axis is smaller than the width in the direction of the central axis MrC of the magnet Mr. The inner circumferential surface 68b can also be formed such that when the magnet Mr is housed in the magnet housing part 65b, it faces the outer circumferential surface Mrd of the magnet Mr with a space in the radial direction, or it can be formed such that it faces the outer circumferential surface Mrd of the magnet Mr without a space in the radial direction.

[0120] The bottom 69 of the magnet holder 65 is a disc-shaped portion extending inward from the end (locking end 68d) of the cylindrical portion 68 opposite to the opening end 68c, and has the aforementioned bottom surface 69a. The bottom surface 69a is the surface opposite to the magnet receiving portion 65b, and is a plane orthogonal or substantially orthogonal to the central axis of the cylindrical portion 68, or a plane along a substantially plane. Furthermore, a through hole, i.e., an opening 69b, is formed in the bottom 69, penetrating 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 such that when the magnet Mr is received in the magnet receiving portion 65b, the central axis MrC of the magnet Mr is in a position parallel or substantially parallel to the central axis of the cylindrical portion 68, and contacts the upper surface Mra of the magnet Mr. Furthermore, the opening 69b at the bottom 69 is configured such that when the magnet Mr is housed in the magnet housing portion 65b, the magnetic flux of the magnet Mr can pass through the opening 69b.

[0121] As described above, the second auxiliary shaft gear 62 is formed of a magnetic material, and an attraction is generated between the magnet Mr in the direction of the rotation axis of the magnet holder 61 and the second auxiliary shaft gear 62 by magnetic force. Specifically, the second auxiliary shaft gear 62 generates a magnetic force that biases the magnet Mr in the direction of the second auxiliary shaft gear 62.

[0122] Furthermore, on the upper end (upper end face 62b) side of the second auxiliary gear shaft 62, an annular groove 62c is formed around the axis of the second auxiliary gear shaft 62, and a retaining ring 62d is formed to engage with the groove 62c. The retaining ring 62d is a component used to restrict the movement of the magnet retainer 61 in the axial direction of the second auxiliary gear shaft 62, and is a component whose outer diameter on the upper end face 62b side of the second auxiliary gear shaft 62 is partially enlarged. As shown in FIG19, the retaining ring 62d is an annular component such as a C-type ring or an E-type ring. In the absolute encoder 2, the groove 62c is provided on the second auxiliary gear shaft 62 in such a way that the retaining ring 62d is positioned opposite to the upper end face 66c of the body portion 66 of the second auxiliary gear 63.

[0123] As shown in Figures 19 and 20, the magnet Mr is a disk-shaped or substantially disk-shaped permanent magnet housed within the magnet receiving portion 65b of the magnet holder portion 65, having a top surface Mra, a bottom surface Mrb, and an outer peripheral surface Mrd. Furthermore, in this embodiment of the invention, it is ideal that the two magnetic poles (N / S) of the magnet Mr are 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. Moreover, the magnet Mr is formed, for example, from ferroferrite, Nd(neodymium)-Fe(iron)-B(boron), or other magnetic materials. The magnet Mr can also be, for example, a rubber magnet containing a resin binder, a bonded magnet, etc. Figure 21 shows a schematic perspective view of a cylindrical magnet Mr adapted to this embodiment of the invention. In the illustrated magnet Mr, 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 Mr as the boundary. Also, in the illustrated magnet Mr, 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 axis (central axis MrC) as the boundary. Furthermore, the arrow DM shown in Figure 21 indicates the magnetization direction. Such a magnetization direction is generally called planar magnetization, and the magnet Mr uses a magnet with planar magnetization.

[0124] The magnet retainer 61 is constructed as described above. In the absolute encoder 2, the second secondary gear shaft 62 is inserted into the through hole 66a of the body portion 66 of the second secondary gear 63, and a retaining ring 62d is installed in the groove 62c of the second secondary gear shaft 62 to mount the second secondary gear 63 in the absolute encoder 2. In the absolute encoder 2, the magnet retainer 61 is rotatable about a rotation axis. The rotation axis of the magnet retainer 61 is aligned with or approximately aligned with the central axis GC4 of the second secondary gear shaft 62. The retaining ring 62d and the portion on the upper end face 62b side of the second secondary gear shaft 62 are accommodated in the space formed on the inner circumferential side of the magnet support portion 67 of the second secondary gear 63.

[0125] Furthermore, in the absolute encoder 2, a magnet Mr is housed in the magnet receiving portion 65b of the magnet holder portion 65, and the magnet Mr is fixed to the magnet holder portion 65. The magnet Mr is fixed to the magnet holder portion 65 by means of an adhesive. For example, the inner peripheral surface 68b of the magnet receiving portion 65b and the outer peripheral surface Mrd of the magnet Mr are bonded by an adhesive material. By fixing the magnet Mr to the magnet holder portion 65 with its bottom surface Mrb in contact with the bottom surface 69a of the magnet receiving portion 65b, it is possible to achieve alignment between the central axis MrC of the magnet Mr and the central axis of the second auxiliary shaft gear 62, and to achieve alignment between the central axis MrC of the magnet Mr and the rotation axis of the second auxiliary shaft gear 62. The detection of the rotation amount or rotation angle of the magnet Mr using the angle sensor Sr can be more accurate. Furthermore, the fixing of the magnet Mr toward the magnet receiving portion 65b is not limited to the method of fixing with an adhesive, but can also be other fixing methods such as the insertion of the first auxiliary shaft gear 30 toward the magnet receiving portion 65b of the magnet Mr.

[0126] Furthermore, in the absolute encoder 2, as described above, the magnet retainer portion 65, to which the magnet Mr is fixed, is fitted into the magnet support portion 67 of the second counterspindle gear 63, and the magnet retainer portion 65 is fixed to the second counterspindle gear 63, assembling into a magnet retainer 61. Specifically, the magnet support portion 67 is pressed into the fitting portion 65a of the magnet retainer portion 65, forming an inner peripheral surface 68a of the fitting portion 65a of the magnet retainer portion 65 pressing the outer peripheral surface 67b of the magnet support portion 67 towards the inner peripheral side, and the outer peripheral surface 67b of the magnet support portion 67 pressing the inner peripheral surface 68a of the magnet retainer portion 65 towards the outer peripheral side, thereby fixing the magnet retainer portion 65 to the second counterspindle gear 63. In addition, the fixing of the magnet retainer portion 65 to the second counterspindle gear 63 is not limited to the fitting method, and other fixing methods can also be used.

[0127] Regarding the magnet retainer 61, which is assembled with the second counterspindle gear 63 and the magnet retainer 65, the magnet Mr is held between the second counterspindle gear 63 and the magnet retainer 65. Specifically, the upper end face 67c of the magnet support 67 contacts the lower end face Mrb of the magnet Mr, and the magnet Mr is held between the upper end face 67c of the magnet support 67 and the bottom surface 69a of the bottom 69 of the magnet retainer 65, and the magnet Mr is fixed in the direction of its central axis MrC. On the other hand, the magnet Mr is fixed in the radial direction orthogonal to its central axis MrC by the connection between the outer peripheral surface Mrd of the magnet Mr and the inner peripheral surface 68b of the magnet retainer 65.

[0128] Furthermore, in the absolute encoder 2, the upper part Mra of the magnet Mr is aligned with the angle sensor Sr in the direction of the central axis MrC of the magnet Mr via an opening 69b formed in the bottom 69 of the magnet holder part 65. In this way, the angle sensor Sr can detect the magnetic flux originating from the magnet Mr.

[0129] As described above, the magnet retainer 61 installed on the absolute encoder 2 is configured to rotate about a rotation axis that is parallel or approximately parallel to the central axis GC3 of the second intermediate gear 70, with the second secondary gear shaft 62 as the rotation axis.

[0130] Furthermore, the second counterspindle gear shaft 62 is formed of a magnetic material, generating a magnetic force that biases the magnet Mr toward the second counterspindle gear shaft 62. Therefore, in the absolute encoder 2, the magnetic force originating from the second counterspindle gear shaft 62 acts on the magnet Mr, and the magnetic force originating from the second counterspindle gear shaft 62 attracts the magnet Mr toward the second counterspindle gear shaft 62. In the illustrated orientation (upright state) of the absolute encoder 2, the lower end face 66b of the body portion 66 of the second counterspindle gear 63 is slidably in contact with the upper surface 104 of the base 3. By means of the axial force originating from the second counterspindle gear shaft 62, the magnet retainer 61 is biased toward the direction in which the lower end face 66b of the second counterspindle gear 63 contacts the upper surface 104 of the base 3. Here, a magnet magnetized in the planar direction has the characteristic that, compared to a magnet magnetized in the radial direction, the magnetic flux density is concentrated in the center of the magnet. As mentioned above, the magnet Mr is a magnetized magnet in the surface direction, and the second auxiliary shaft gear 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 due to the magnetic material of the second auxiliary shaft gear 62. Thus, in the absolute encoder 2, the angle sensor Sr can accurately detect the magnetic flux.

[0131] On the other hand, when the absolute encoder 2 is reversed from its upright state to an inverted state (upside-down state), the magnet retainer 61 can move relative to the second secondary gear shaft 62 in the direction of the central axis MC4 of the second secondary gear 63 through the gap between the retaining ring 62d and the upper end face 66c of the body portion 66 of the second secondary gear 63. That is, the magnet Mr moves towards the angle sensor Sr, and the interval between the magnet Mr and the angle sensor Sr can be changed. However, in the absolute encoder 2, the second secondary gear shaft 62 is formed of a magnetic material, and the second secondary gear shaft 62 attracts the magnet Mr towards the second secondary gear shaft 62 by its magnetic force. Therefore, even when the absolute encoder 2 is in the inverted state, the magnet retainer 61 remains in a state where the lower end face 66b of the second secondary gear 63 is in contact with the upper surface 104 of the base 3, and the magnet retainer 61 remains in the position in the direction of the central axis MC4 in the upright state, preventing the magnet Mr from moving towards the angle sensor Sr. Therefore, in the inverted state, the distance between the magnet Mr and the angle sensor Sr is also maintained as the distance in the upright state.

[0132] Thus, in the absolute encoder 2, the gap between the magnet Mr and the angle sensor Sr does not change due to the usage posture of the absolute encoder 2, which can reduce the impact of the usage posture of the absolute encoder 2 on the detection accuracy.

[0133] Furthermore, the second auxiliary shaft gear 63 restricts the movement of the second auxiliary shaft gear 62 in the axial direction by means of a retaining ring 62d mounted on the second auxiliary shaft gear 62. In other words, the movement of the second auxiliary shaft gear 62 of the magnet retainer 61 in the axial direction is restricted. Therefore, even if a large impact is applied to the absolute encoder 2, and a force is applied that resists the magnetic force of the second auxiliary shaft gear 62, causing the magnet retainer 61 to move upwards in the axial direction of the second auxiliary shaft gear 62, the movement of the magnet retainer 61 is still restricted by the retaining ring 62d. Therefore, adverse conditions such as the magnet retainer 61 detaching from the second auxiliary shaft gear 62 can be prevented.

[0134] As described above, the magnet support portion 67 in the second counterspindle gear 63, specifically the upper end face 67c, also functions as a magnet support portion that supports the magnet Mr on the upper side of the second counterspindle gear 63. The magnet retainer portion 65 functions as a magnet retainer portion that covers the magnet Mr and the second counterspindle gear 63 from above and retains the magnet Mr on the upper end face 67c of the magnet support portion 67.

[0135] Furthermore, the magnet retainer portion 65 is formed of a resin material with a breaking elongation characteristic greater than that of the second counterspindle gear 63. The magnet retainer portion 65 has a bottom surface 69a that functions as a magnet engagement portion and an inner peripheral surface 68a that functions as an insert portion 65a.

[0136] The press-fit assembly method requires no special equipment to ensure the concentricity of the assembled components, making it a relatively simple construction method. In press-fit structures such as the magnet retainer 65 and the second auxiliary shaft gear 63, it is necessary to consider using a portion of the component shape, specifically the outer peripheral surface 67b of the magnet support 67, as a guide to hold the assembled parts, ensure alignment, and guarantee the holding strength of the press-fit components. Therefore, the resin material for the magnet retainer 65 and the second auxiliary shaft gear 63 must be selected as a reinforced material with added filler, exhibiting a low coefficient of linear expansion and high elastic modulus. However, such a low coefficient of linear expansion, high elastic modulus resin material is prone to cracking during press-fitting on the strength surface and is difficult to maintain the pressed-fitted state with durability.

[0137] The magnet retainer portion 65, having an insert portion 65a, is susceptible to tensile stress because it provides a space for deformation release after being pressed in along the outer circumferential direction. On the other hand, the second auxiliary shaft gear 63, which is pressed into the shaft side, lacks a space for deformation release after the magnet retainer portion 65 is pressed in, thus its risk of breakage due to stress is lower compared to the magnet retainer portion 65. Therefore, regarding the absolute encoder 2, considering the elongation at break of the material, by using a material with a larger elongation at break than the second auxiliary shaft gear 63 without changing the content of reinforcing filler in the magnet retainer portion 65, breakage during pressing can be prevented. Here, the elongation at break (elongation at fracture) refers to the elongation of the test piece at fracture in a tensile test, the elongation before fracture between specified marks.

[0138] (Second Axis Gear Shaft) The specific shape of the second auxiliary shaft gear shaft 62 described above will be explained below. Figure 22 is an enlarged cross-sectional view showing one end 62f of the second auxiliary shaft gear shaft 62 on the lower end face 62a side.

[0139] The second auxiliary gear shaft 62 of the second auxiliary gear 63, as described above, is a shaft that is pressed into and fixed in the through hole 137a of the shaft support portion 137 of the base 3. As shown in FIG22, the second auxiliary gear shaft 62 has a tapered surface 62e. The tapered surface 62e is an outer peripheral surface incised such that the diameter of one end 62f is smaller than the diameter of the peripheral surface 62g. The tapered surface 62e is the connection portion 62h between the tapered surface 62e of the second auxiliary gear shaft 62 and the peripheral surface 62g, which is connected by a curved surface. That is, the tapered surface 62e is the connection portion 62h between the tapered surface 62e and the peripheral surface 62g, which is machined by a curved surface.

[0140] Figures 23 and 24 are schematic diagrams showing the second auxiliary shaft gear shaft 62 being pressed into the through hole 137a of the base 101 of the base 3.

[0141] As shown in Figures 23 and 24, when the second auxiliary shaft gear 62 is pressed into the through hole 137a of the base 3, after the tapered surface 62e is inserted into the through hole 137a, the connecting portion 62h between the tapered surface 62e and the peripheral surface 62g contacts the through hole 137a. Similar to the connecting portions 126a and 127a of the tapered surfaces 126 and 127 of the spindle connector 12, by also applying a curved surface machining to the connecting portion 62h, the second auxiliary shaft gear 62 is smoothly pressed into the through hole 137a, thus preventing scratches on both the second auxiliary shaft gear 62 and the through hole 137a. Furthermore, the surface roughness Rmax (maximum roughness) of the spindle connector 12 can be set to, for example, 1.6 [μm] or less. Therefore, based on the second auxiliary shaft gear 62, similarly to the spindle connector 12, the scattering of chips and the like can be suppressed. Furthermore, based on the second auxiliary shaft gear shaft 62, the situation where the second auxiliary shaft gear shaft 62 is tilted (inclined) due to component scratches can be suppressed. Moreover, based on the second auxiliary shaft gear shaft 62, by suppressing the tilting of the second auxiliary shaft gear shaft 62, the pressing amount (the size required for pressing) can be reduced.

[0142] Furthermore, in the absolute encoder 2, the example of applying curved surface machining to the connection portion of the outer peripheral surface between the tapered face and the peripheral surface in the shaft pressed into the support member is not limited to the aforementioned main shaft connector 12 and the second auxiliary shaft gear shaft 62. In the absolute encoder 2, for example, the connection portion of the outer peripheral surface between the tapered face and the peripheral surface in the support shaft of the first auxiliary shaft gear 30 may also be surface machined.

[0143] 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 rotation axes of the main shaft gear 10 and the first countershaft gear 30 are parallel to each other, and the rotation axis of the first intermediate gear 20 is in a torsional position relative to the rotation axes of the main shaft gear 10 and the first countershaft gear 30. Furthermore, the rotation axes of the first countershaft gear 30, the second intermediate gear 70, and the second countershaft gear 63 are parallel to each other. By arranging these gears, the rotation amount of the main shaft gear 10 after multiple rotations can be determined according to the detection results of the angle sensors Sq and Sr. Because the rotation axis of the first intermediate gear 20 is in a torsional position relative to the rotation axes of the main shaft gear 10 and the first countershaft gear 30, and is orthogonal in frontal view, the absolute encoder 2 forms a curved transmission path and can be made thinner.

[0144] (Backlash Reduction Mechanism) As described above, the absolute encoder 2 has a biasing mechanism 40 that biases the second worm gear portion 22 toward the second worm wheel portion 31. The biasing mechanism 40 is a backlash reduction mechanism that reduces the backlash between the second worm gear portion 22 and the second worm wheel portion 31. As shown in Figures 5, 6, 11, and 14, the biasing mechanism 40 includes: a biasing spring 41; a support protrusion 45; and a screw 8b for fixing the biasing spring 41 to the support protrusion 45. Furthermore, the through hole 143 and the through hole 145 of the support protrusion 131 in the base 3 also constitute the biasing mechanism 40.

[0145] The bias spring 41 is an elastic member used to generate a pressing force that pushes the second worm gear portion 22 toward the second worm wheel portion 31. The bias spring 41 is, for example, a leaf spring formed of a metal plate. As shown in Figures 12 and 14, specifically, the bias spring 41 has: a portion that elastically deforms to generate the pressing force, namely the spring portion 42; and portions opposite to the spring portion 42, namely the engaging portion 43 and the fixing portion 44. The engaging portion 43 and the fixing portion 44 are portions that form a pair at the ends of the bias spring 41.

[0146] The fixing part 44 is fixedly formed on the support protrusion 45 protruding from the upper surface 104 of the base 101 of the base 3 by means of a screw 8b. The screw 8b is an example of a fixing member, and a hole 44a for inserting the screw 8b is formed in the fixing part 44. The fixing part 44 extends in a planar shape and is fixed to the support protrusion 45 by means of the screw 8b in a state of contact with the planar support surface 45a of the support protrusion 45.

[0147] The engaging portion 43 has a shape that allows it to engage with the secondary shaft 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 extends along the direction extending from the spring portion 42 of the engaging portion 43. The engaging groove 43a is a groove open on the end edge (i.e., the front end edge 43b) opposite to the connecting portion 43c connected to the spring portion 42 of the engaging portion 43, and forms a forked branch like one end 9a of the leaf spring 9 described above. The engaging portion 43 also extends in a planar shape. At the secondary shaft side end 23b of the first intermediate gear shaft 23, an annular groove, i.e., an engaging groove 23d, is formed extending in a direction orthogonal or substantially orthogonal to the central axis of the first intermediate gear shaft 23. The engaging groove 43a of the engaging portion 43 is formed to engage with this engaging groove 23d. The first intermediate gear shaft 23 is pressed against the engaging groove 23d by one side of the engaging groove 43a that is parallel to the vertical direction, causing the first intermediate gear 20 to be biased toward the second worm gear portion 22 toward the second worm wheel portion 31. Furthermore, the two sides of the engaging groove 43a that are parallel to the horizontal direction contact the first intermediate gear shaft 23 in the engaging groove 23d, and the vertical movement of the biasing spring 41 is restricted by the first intermediate gear shaft 23.

[0148] The spring portion 42 has a shape that is easily elastically deformable in the engagement direction of the engaging portion 43 toward the first intermediate gear shaft 23. Specifically, as shown in FIG14, the extending direction of the engaging groove 43a has a shape that is easily flexible. For example, the spring portion 42 is bent in a way that protrudes in the opposite direction to the direction that biases the first intermediate gear 20.

[0149] The bias spring 41 is fixed to the support protrusion 45 in the fixing part 44 by screw 8b, so that the spring part 42 stands up from the fixing part 44 on the opposite side of the support protrusion 45. In this fixed state, the engaging groove 43a of the engaging part 43 engages with the engaging groove 23d of the first intermediate gear shaft 23, and in this engaged state, the spring part 42 generates a pressing force that presses the engaging part 43 toward the first intermediate gear shaft 23. The dimensions of the spring part 42 and the engaging part 43, the angle of the extension direction of the engaging part 43 relative to the extension direction of the spring part 42, etc. are set. When the above-mentioned retaining ring (not shown) is installed on the first intermediate gear shaft 23, in the fixed and engaged states of the bias spring 41, the retaining ring contacts the outer surface of the support protrusion 141. From the perspective of reducing backlash, as described later, the engagement groove 43a of the engagement portion 43 is preferably formed in a direction that extends orthogonally or substantially orthogonally to the central axis of the first intermediate gear shaft 23 when the bias spring 41 is fixed. In addition, the bias spring 41 can also restrict the movement of the first intermediate gear shaft 23 toward the central axis, so the retaining ring can be omitted as described above.

[0150] As shown in Figures 5, 6, 11, and 14, the leaf spring 9 and the bias spring 41 are integrally formed as a single component. Specifically, the other end 9b of the leaf spring 9 is integrally formed with the fixing part 44 of the bias spring 41, and they are constituted by the same component. That is to say, the leaf spring 9 and the bias spring 41 are formed by a continuous elastic component, and the leaf spring 9 and the bias spring 41 are each part of this continuous elastic component. The other end 9b of the leaf spring 9 and the fixing part 44 of the bias spring 41 are formed in the same part of this continuous elastic component.

[0151] Next, the function of the bias mechanism 40 of the absolute encoder 2 will be explained.

[0152] In the absolute encoder 2, the first intermediate gear shaft 23 has its main shaft side end 23a inserted into the through hole 143 formed in the support protrusion 131 of the base 3, and its secondary shaft side end 23b inserted into the through hole 145 formed in the support protrusion 141 of the base 3, and is supported on the base 3. Thus, the first intermediate gear shaft 23 is supported by the support protrusions 131 and 141.

[0153] Thus, the first intermediate gear 20 is rotatably supported by 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 sliding part 26 of the secondary shaft side of the first intermediate gear 20 abuts against the inner surface 141a of the support protrusion 141 (see Figure 13).

[0154] As described above, the elongated through-hole 145 supporting the secondary shaft end 23b of the first intermediate gear shaft 23 has a longer major axis than minor axis. The secondary shaft end 23b is supported along the major axis of the through-hole 145, that is, along the horizontal plane, within the width of the major axis of the through-hole 145. On the other hand, the through-hole 143 supporting the main shaft end 23a of the first intermediate gear shaft 23 is circular. Therefore, in the absolute encoder 2, the first intermediate gear shaft 23 can swing along the horizontal plane with the support portion of the main shaft end 23a as the center or approximately the center, by means of the through-holes 143 and 145 supporting the protrusions 131 and 141 and the biasing mechanism 40.

[0155] Furthermore, in the first intermediate gear shaft 23, which is thus supported, a locking part 43 of a biasing spring 41 is engaged in the locking groove 23d at the countershaft end 23b. The biasing spring 41 imparts a biasing force to the countershaft end 23b of the first intermediate gear shaft 23, causing the second worm portion 22 of the first intermediate gear 20 to be pressed toward the second worm wheel portion 31 of the first countershaft gear 30 (second meshing direction P2). Therefore, the second worm portion 22 of the first intermediate gear 20 abuts against the second worm wheel portion 31 of the first countershaft gear 30, and the second worm portion 22 and the second worm wheel portion 31 cause a so-called bottoming phenomenon, and the backlash between the gears is zero.

[0156] Furthermore, the secondary shaft end 23b of the first intermediate gear shaft 23, which is supported in a swingable manner, is biased by the biasing spring 41. Therefore, during swinging, the first intermediate gear shaft 23 is continuously biased towards the second worm portion 22 toward the second worm wheel portion 31. Thus, by swinging the first intermediate gear shaft 23, the backlash between the second worm portion 22 and the second worm wheel portion 31 can always be zero without causing adverse conditions in the rotation between the gears.

[0157] For example, when the ambient temperature of the absolute encoder 2 becomes high, the first counterspindle gear 30 expands due to the linear expansion coefficient of the material, and the pitch circle of the second worm gear portion 31 enlarges. At this time, since the through hole 145 formed in the support protrusion 141 of the base 3 is a circular hole instead of an elongated hole as shown in this embodiment, the counterspindle end 23b of the first intermediate gear shaft 23 is fixed by the through hole 145, and the first intermediate gear shaft 23 cannot oscillate as in this embodiment. Therefore, the second worm gear portion 31 of the first counterspindle gear 30, whose pitch circle has enlarged due to temperature rise, may come into strong contact with the second worm portion 22 of the first intermediate gear 20, causing the gear to become unable to rotate.

[0158] Conversely, when the ambient temperature around the absolute encoder 2 is low, the first counterspindle gear 30 contracts due to the linear expansion coefficient of the material, and the pitch circle of the gear in the second worm gear portion 31 shrinks. At this time, since the through hole 145 formed in the support protrusion 141 of the base 3 is a round hole instead of an elongated hole as shown in this embodiment, the counterspindle end 23b of the first intermediate gear shaft 23 is fixed by the through hole 145, and the first intermediate gear shaft 23 cannot swing as in this embodiment. This situation arises because the backlash between the second worm portion 22 of the first intermediate gear 22 and the second worm gear portion 31 of the first counterspindle gear 30 increases, making it impossible to accurately transmit the rotation of the first intermediate gear 22 to the first counterspindle gear 30.

[0159] In contrast, in the absolute encoder 2 of this embodiment, as described above, the first intermediate gear shaft 23 is supported in a manner that allows it to swing horizontally, centered or approximately centered on the support portion of the main shaft end 23a. Furthermore, the first intermediate gear 20 is always biased from the second worm gear 22 side towards the second worm wheel 31 side by the biasing mechanism 40. Also, the first intermediate gear 20 supported on the first intermediate gear shaft 23 is biased towards the support protrusion 141 by the leaf spring 9. Therefore, even if the pitch circle of the second worm wheel 31 of the first counterspindle gear 30 changes due to ambient temperature variations, as described above, the backlash is zero because the tooth surfaces of the second worm gear 22 and the second worm wheel 31 are always in appropriate contact with each other. Therefore, it is possible to avoid situations where the gear stops rotating due to temperature changes, or where the accuracy of the rotation transmitted from the first intermediate gear 20 to the first counterspindle gear 30 deteriorates.

[0160] Therefore, in the absolute encoder 2, the impact of the backlash of the reduction mechanism on the detection accuracy can be reduced. This maintains the resolution of the specific spindle 1a's rotational range and expands the range of the specific spindle 1a's rotational range.

[0161] Furthermore, it is preferable that the biasing mechanism 40 is set in such a way that a certain or approximately certain pressing force can be generated from the biasing spring 41, regardless of the position of the secondary shaft end 23b of the first intermediate gear shaft 23 due to oscillation.

[0162] As described above, the through hole 143 of the support protrusion 131 supporting the main shaft end 23a of the first intermediate gear shaft 23 is a circular hole, and the through hole 145 of the support protrusion 141 supporting the secondary shaft end 23b is an elongated hole with a width on the long shaft side greater than that on the short shaft side. The first intermediate gear shaft 23 is designed to swing parallel or approximately parallel to the horizontal direction with the through hole 143 of the support protrusion 131 as a fulcrum. Therefore, during the swing of the first intermediate gear shaft 23, even if the movement of the second worm portion 22 relative to the second worm wheel portion 31 becomes greater than the movement of the first worm wheel portion 21 relative to the first worm portion 11, and the second worm portion 22 and the second worm wheel portion 31 collide, the first worm portion 11 and the first worm wheel portion 21 will not collide.

[0163] As shown in Figures 10-13, although the through hole 145 supporting the first intermediate gear shaft 23 at the secondary shaft end 23b is formed as a cylindrical surface or a generally cylindrical surface, the through hole 145 is not limited to having such a shape. For example, as shown in Figure 25, the cross-sectional shape of the through hole 145 may not be an elongated hole, but rather a rectangle or a generally rectangular shape. That is, the through hole 145 may also be a through hole forming a pair of opposing surfaces 145a and a pair of opposing surfaces 145b, extending into a quadrangular prism shape. The pair of surfaces 145a and the pair of surfaces 145b forming the through hole 145 may be planar or curved. In the absolute encoder 2, the pair of surfaces 145a extends horizontally, and the pair of surfaces 145b extends vertically. The horizontal width of surface 145a is longer than the vertical width of surface 145b. The through hole 145 shown in Figure 25 can also be made in the same way as the through hole 145 described above to allow the first intermediate gear shaft 23 to swing.

[0164] Similarly, the through hole 143 is not limited to having the shape described above. For example, the through hole 143 may also have a so-called knife-edge structure. Specifically, the through hole 143 may also contact the first intermediate gear shaft 23 by line contact or point contact. For example, as shown in Figures 26(a) and (b), the through hole 143 may also be formed by a pair of conical or substantially conical inclined surfaces 143c that decrease in diameter toward the inward side in the extending direction of the through hole 143. In this case, the through hole 143 contacts and supports the first intermediate gear shaft 23 in the annular line (connecting line 143d) depicting the portion of the circular hole where the pair of inclined surfaces 143c connect. The shape of the circular hole in the connecting line 143d is the same as the shape of the circular hole in the through hole 143 described above when viewed from above. The through hole 143 supports the first intermediate gear shaft 23 through line contact or point contact. Therefore, even if the diameter of the circular hole of the through hole 143 is closer to the diameter of the first intermediate gear shaft 23, the first intermediate gear shaft 23 can still be made to swing. Thus, the cross-sectional shape of the through hole 143 can be made close to the shape without the gap between the through hole 143 and the first intermediate gear shaft 23. In this way, when the first intermediate gear shaft 23 swings, the movement of the part of the first intermediate gear shaft 23 in contact with the through hole 143 can be suppressed, and the distance change between the first worm portion 11 and the first worm wheel portion 21 can be suppressed by the swing of the first intermediate gear shaft 23. Furthermore, the through hole 145 of the support protrusion 141 may also have a so-called blade structure, like the through hole 143 of the support protrusion 131 described above, or it may be formed, for example, by a pair of conical or substantially conical inclined surfaces, which form the annular line depicting the elongated hole.

[0165] Furthermore, as shown in Figures 27(a) and (b), the through hole 145 can also be formed by a pair of square pyramidal or substantially square pyramidal inclined surfaces 145e that taper towards the inward side in the extending direction of the through hole 145. In this case, the through hole 145 contacts and supports the first intermediate gear shaft 23 in the quadrangular or substantially quadrangular annular line (connecting line 145f) depicting the portion where the pair of inclined surfaces 145e connect. The connecting line 145f has a pair of opposing portions, namely line portions 145g, and a pair of opposing portions, namely line portions 145h. The pair of line portions 145g and the pair of line portions 145h can be straight lines or curves. In the absolute encoder 2, the pair of line portions 145g extends horizontally, and the pair of line portions 145h extends vertically. The length of the line portion 145g is longer than the vertical length of the line portion 145h. Furthermore, the through hole 143 supporting the protrusion 131, like the through hole 145 supporting the protrusion 142, can be formed by a pair of quadrangular or approximately quadrangular pyramidal inclined surfaces, which form a loop depicting a quadrangular or approximately quadrangular shape. In this case, the loop becomes a square or approximately square. Similar to the case in Figure 26, the through hole 143 supports the first intermediate gear shaft 23 through line contact or point contact. Therefore, even if the lengths of the line portion extending vertically (corresponding to line portion 145h in Figure 27) and the line portion extending horizontally (corresponding to line portion 145g in Figure 27) are closer to the diameter of the first intermediate gear shaft 23, the first intermediate gear shaft 23 can still swing. Therefore, the shape of the through hole 143 can be made close to a shape with no gaps in the vertical and horizontal directions between the through hole 143 and the first intermediate gear shaft 23. Therefore, when the first intermediate gear shaft 23 swings, the movement of the part of the first intermediate gear shaft 23 in contact with the through hole 143 can be suppressed, and by the swing of the first intermediate gear shaft 23, the distance change between the first worm portion 11 and the first worm wheel portion 21 can be suppressed.

[0166] (Control Unit) Next, the control unit of the absolute encoder 2 will be explained. Figure 28 is a view of the substrate 5 shown in Figure 2 from the bottom 5a side. The microcomputer 51, the line driver 52, the bidirectional driver 53, and the connector 6 are mounted on the substrate 5. The microcomputer 51, the line driver 52, the bidirectional driver 53, and the connector 6 are electrically connected by patterned wiring on the substrate 5.

[0167] The bidirectional driver 53 enables bidirectional communication with an external device connected to connector 6. The bidirectional driver 53 converts operating signals and other data into differential signals for communication with the external device. The line driver 52 converts data representing rotation amount into differential signals and outputs these differential signals in real-time to the external device connected to connector 6. Connector 6 is a connector to which an external device is connected.

[0168] Figure 29 is a block diagram that schematically shows the functional configuration of the absolute encoder 2 shown in Figure 1. Each block of the microcomputer 51 shown in Figure 29 represents the function implemented by the CPU (Central Processing Unit) of the microcomputer 51 executing the program.

[0169] 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 specifying unit 51c, and an output unit 51e. The rotation angle acquisition unit 51p acquires the rotation angle Ap of the main shaft gear 10 based on a signal output from the angle sensor Sp. The rotation angle Ap represents angle information indicating the rotation angle of the main shaft gear 10. The rotation angle acquisition unit 51q acquires the rotation angle Aq of the first secondary shaft gear 30 based on a signal output from the magnetic sensor Sq. The rotation angle Aq represents angle information indicating the rotation angle of the first secondary shaft gear 30. The rotation angle acquisition unit 51r acquires the rotation angle Ar of the magnet retainer 61, i.e., the second secondary shaft gear 63, based on a signal output from the magnetic sensor Sr. The rotation angle Ar represents angle information indicating the rotation angle of the second secondary shaft gear 63.

[0170] The table processing unit 51b refers to the first correspondence table to specify the number of rotations of the main spindle gear 10 corresponding to the obtained rotation angles Aq and Ar. The first correspondence table stores the number of rotations of the main spindle gear 10 corresponding to the rotation angles Aq of the first secondary spindle gear 30 and Ar of the second secondary spindle gear 63. The rotation amount specifying unit 51c specifies the rotation amount of the main spindle gear 10 after multiple rotations based on the number of rotations of the main spindle gear 10 (main spindle 1a) specified by the table processing unit 51b and the obtained rotation angle Ap. The output unit 51e converts the rotation amount of the main spindle gear 10 after multiple rotations specified by the rotation amount specifying unit 51c into information representing the rotation amount and outputs it.

[0171] As described above, in the absolute encoder 2 according to this embodiment, the second auxiliary shaft gear shaft 62 is formed of a magnetic material. The magnetic force of the second auxiliary shaft gear shaft 62 biases the magnet Mr towards the side of the second auxiliary shaft gear shaft 62, thereby fixing the relative position of the magnet Mr and the angle sensor Sr. Therefore, the interval between the magnet Mr and the angle sensor Sr does not change due to the usage posture of the absolute encoder 2, reducing the impact of the usage posture of the absolute encoder 2 on the detection accuracy.

[0172] Furthermore, in the absolute encoder 2 of this embodiment, the movement of the magnet retainer 61 in the axial direction of the second auxiliary shaft gear shaft 62 is restricted by the retaining ring 62d. Therefore, even if a large impact is applied to the absolute encoder 2, and a force is applied that resists the magnetic force of the second auxiliary shaft gear shaft 62 and moves the magnet retainer 61 in the axial direction of the second auxiliary shaft gear shaft 62, the movement of the magnet retainer 61 can still be restricted. Therefore, adverse conditions such as the magnet retainer 61 falling off the second auxiliary shaft gear shaft 62 can be prevented. This also suppresses changes in the gap between the magnet Mr and the angle sensor Sr, and suppresses the reduction of detection accuracy of the absolute encoder 2.

[0173] Furthermore, in the absolute encoder 2 of this embodiment, by setting the first intermediate gear 20 arranged along the horizontal plane in a manner that extends obliquely relative to the outer peripheral surface 105-108 of the base 3, the size of the absolute encoder 2 in the front-back direction and the left-right direction can be reduced.

[0174] Furthermore, in the absolute encoder 2 of this embodiment, the outer diameters of the worm gear portions 21 and 31 and the outer diameters of the worm portions 11 and 22 are set to small values ​​within the possible range. Therefore, the size of the absolute encoder 2 in the vertical direction (height direction) can be reduced.

[0175] The embodiments of the present invention have been described above, but the present invention is not limited to the absolute encoder 2 of the above embodiments, but includes all forms contained in the concept and scope of the claims. Furthermore, the various components can be appropriately combined to achieve at least a portion of the aforementioned problems and effects, and can also be combined with prior art. For example, the shape, material, arrangement, and size of each component in the above embodiments can be appropriately modified by adapting the specific usage of the present invention.

[0176] For example, in the absolute encoder 2 described above, although the magnet retainer 61 employs a second secondary shaft gear 63 and a magnet retainer portion 65 that are separated from each other, the second secondary shaft gear 63 and the magnet retainer portion 65 of the magnet retainer 61 can also be integrally formed from the same material. In this case, for example, the magnet Mr is pre-positioned in the molding die, and the second secondary shaft gear 63 and the magnet retainer portion 65 are integrally formed by injection molding in such a way that the magnet Mr is positioned as described above, thus forming the magnet retainer 61.

[0177] Furthermore, in the aforementioned absolute encoder 2, although the second auxiliary shaft gear 62 is made of a magnetic material, the main shaft gear 10 and the first auxiliary shaft gear 30 can also be made of a magnetic material forming shafts corresponding to magnets Mp and Mq respectively, with the same configuration as the second auxiliary shaft gear 63 and the second auxiliary shaft gear 62, and the magnets Mp and Mq are respectively subjected to magnetic forces originating from the shaft and biased in the axial direction.

[0178] 1: Motor 1a: Spindle 1b: Press-in section 2: Absolute encoder 3: Base 3a: Support board 4: Outer shell 4a: Outer wall portion 4b: cover 4c: Claws 5:Substrate 5a: Below 5b: Positioning hole 6: Connector 8a, 8b, 8c: Screws 9: Leaf spring 9a: One end 9b: The other end 10: Main shaft gear 11: First worm gear section 12: Spindle Connector 12a: Top surface 13:Tubular part 13a: Top surface 14: Press-in section 15: Magnet holding part 15a: Inner circumferential surface 15b: Bottom surface 20: First intermediate gear 21: First worm gear section 22: Second worm gear section 23: First intermediate gear shaft 23a: Spindle-side end 23b: Secondary shaft end 23c: slot 23d: Stuck in slot 24:Tubular part 24a: Through hole 24b: Inner circumferential surface 25: Sliding part on the spindle side 26: Sliding part on the secondary shaft side 30: First pair shaft gear 31: Second worm gear section 32: Gear section 33: Through hole 35: Magnet Holder 35a: Magnet holding section 35b: Shaft 35c: Bearing Stopper 35d: Bearing positioning component 40: Bias Mechanism 41: Bias Spring 42: Spring section 43: Card-connecting section 43a: Engagement slot 43b: Front Edge 43c: Connecting part 44: Fixing part 44a: Hole 45: Support for protrusion 45a: Support surface 51: Microcomputer 51b: Forms Processing Department 51c: Rotational Amount Specific Part 51e: Output Section 51p, 51q, 51r: Rotation angle acquisition part 52: Line driver 53: Bidirectional driver 60: Magnetic detection device 61: Magnet Holder 62: Second auxiliary shaft gear shaft 62a: Lower end face 62b: Top surface 62c: slot 62d: Buckle 62e: Tapered face 62f: One end 62g: Peripheral 62h: Connecting part 63: Second set of shaft gears 64: Gear section 65: Magnet retainer section 65a: Mounting section 65b: Magnet Containment Section 66:Ontology part 66a: Through hole 66b: Lower end face 66c: Top surface 67: Magnet Support Department 67a: Inner circumferential surface 67b: outer peripheral surface 67c: Top surface 68: Cylindrical section 68a, 68b: Inner circumferential surfaces 68c: Open end 68d: Locking end 68e: outer periphery 69: Bottom 69a: Bottom surface 69b: Opening 70: Second intermediate gear 71, 72: Gear section 73: Ontology part 73a: Lower end face 73b: Top surface 74: Through hole 75: Axis 75a: Lower end face 75b: Top surface 75c: slot 76: Buckle 101: Base 102: Below 103: concave part 104: Above 105 to 108: outer peripheral surface 110:Substrate support 111: Top surface 112: Screw hole 120: Substrate positioning pin 121: Front end 122: Base 123: Step difference surface 124: One end 125: The other end 126: Tapered face 126a: Connecting part 127: Tapered face 127a: Connecting part 128: Through hole 128a: Hole 1 128b: End 128c: Second hole 129: Zhoumian 131, 132, 141: Supporting protrusions 131a: Outer surface 132a: Protrusion 134: Bearing retainer section 135: Bearing 136, 137: Shaft support section 141a: Inner surface 143, 145: Through holes 145a, 145b: Face 143c, 145e: Inclined surfaces 143d, 145f: Connecting wires 145g, 145h: thread section Ap,Aq: Angle Information BC: Center of bearing GC1: Central shaft of the main spindle gear GC2: Central shaft of the second auxiliary shaft gear GC3, GC4: Central axis MoC: Central axis of the motor spindle Mp, Mq, Mr: Magnet Mpa, Mqa, Mra: Above Mpb, Mqb, Mrb: Below Mpd, Mqd, Mrd: outer peripheral surface MpC, MqC, MrC: Central axis of the magnet P: Offset direction P1: First meshing direction P2: Second meshing direction R1: First transmission mechanism R2: Second transmission mechanism SaC: Central axis of the spindle connector SC: Central axis of the magnet retainer Sp, Sq, Sr: Angle sensor XYZ: Rectangular coordinate system

Claims

1. A magnetic detection device, characterized by comprising: a magnetized magnet; a magnetic sensor for detecting magnetic flux originating from the magnet; a magnet holder for holding the magnet; and a shaft, wherein the magnet holder is rotatably supported by the shaft, the shaft being formed of a magnetic body, and an attractive force generated by magnetic force is generated between the magnet and the shaft in the direction of the rotation axis of the magnet holder, such that even in an inverted state, the distance between the magnet and the magnetic sensor is maintained as the distance in the upright state.

2. The magnetic detection device of claim 1, wherein the aforementioned shaft system generates a magnetic force that biases the aforementioned magnet in the direction of the shaft.

3. The magnetic detection device as claimed in claim 1, wherein the aforementioned shaft system is fixed to the base.

4. A magnetic detection device, characterized by comprising a magnetized magnet; a magnetic sensor for detecting magnetic flux originating from the magnet; a magnet holder for holding the magnet; and a shaft, wherein the magnet holder is rotatably supported by the shaft, the shaft being formed of a magnetic body, and an attractive force generated by magnetic force is generated between the magnet and the shaft in the direction of the rotation axis of the magnet holder, and further comprising: a limiting mechanism for limiting the movement of the magnet toward the side opposite to the direction in which the magnetic force from the shaft acts on the magnet.

5. The magnetic detection device according to claim 1 or 4, wherein the aforementioned magnet holder has: a gear portion having a gear formed in such a way as to rotate about the aforementioned axis of rotation; and a holder portion formed to hold the aforementioned magnet between itself and the gear portion and to fix the aforementioned magnet to the aforementioned magnet holder.

6. The magnetic detection device of claim 5, wherein the aforementioned retainer portion and the aforementioned gear portion are each part of the same component, or the aforementioned retainer portion and the aforementioned gear portion are different components from each other.

7. An absolute encoder, characterized in that it has a magnetic detection device as claimed in claim 1 or 4.

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