Absolute encoder

Abstract

An absolute encoder is provided with: a spindle gear that rotates together with a spindle; a first magnet that rotates together with the main shaft; a first magnetic sensor that detects a change in magnetic flux generated from the first magnet; an idle gear having a smaller number of teeth than the main shaft gear and rotating along with the rotation of the main shaft gear; a first countershaft disposed parallel to the main shaft; a first driven gear mounted on the first countershaft and engaged with the idle gear; a second magnet that rotates together with the first countershaft; a second magnetic sensor that detects a change in magnetic flux generated from the second magnet; a second countershaft disposed parallel to the main shaft; a second driven gear which is mounted on the second countershaft, has a different number of teeth from that of the first driven gear, and meshes with the idle gear; a third magnet that rotates together with the second countershaft; and a third magnetic sensor that detects a change in the magnetic flux generated from the third magnet.

Description

Technical Field

[0001] The present invention relates to absolute encoders. Background Art

[0002] In the past, there are known rotary encoders for detecting the position or angle of movable elements in various control mechanical devices. Among such encoders, there are incremental encoders for detecting relative positions or angles and absolute encoders for detecting absolute positions or angles. For example, Patent Document 1 describes an absolute rotary encoder having a plurality of magnetic encoder parts for detecting the angular positions of a main shaft and a secondary shaft using magnetism, and for measuring the absolute position of the main shaft based on the detection results.

[0003] <Prior Art Literature>

[0004] <Patent Documents>

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-165917 Summary of the invention

[0006] <Problems to be Solved by the Invention>

[0007] The absolute encoder described in Patent Document 1 has a problem that it is difficult to be thinned in the axial direction of the main shaft because it has a worm gear. In addition, when a worm gear is provided, there is a risk of angular error caused by axis conversion between two orthogonal axes. In addition, when a worm gear is provided, in the axial direction of the rotating shaft orthogonal to the main shaft, the worm or worm wheel wants to move in the thrust direction during rotation, so the deviation of the gap during installation will affect the angular error. Therefore, in order to always apply force in one direction to remove the gap, it is necessary to provide a leaf spring, etc., which increases the number of components and complicates the structure.

[0008] An object of the present invention is to provide an absolute encoder that can be simplified in structure and reduced in size.

[0009] <Methods used to solve the problem>

[0010] An absolute encoder according to an embodiment of the present invention includes: a main shaft gear mounted on the main shaft and rotating together with the main shaft; a first magnet mounted on the main shaft and rotating together with the main shaft; a first magnetic sensor detecting a change in magnetic flux generated from the first magnet; an idler gear having a smaller number of teeth than the main shaft gear and rotating as the main shaft gear rotates; a first secondary shaft arranged in parallel with the main shaft; a first driven gear mounted on the first secondary shaft and meshing with the idler gear; a second magnet mounted on the first secondary shaft and rotating together with the first secondary shaft; a second magnetic sensor detecting a change in magnetic flux generated from the second magnet; a second secondary shaft arranged in parallel with the main shaft; a second driven gear mounted on the second secondary shaft, having a different number of teeth from the first driven gear and meshing with the idler gear; a third magnet mounted on the second secondary shaft and rotating together with the second secondary shaft; and a third magnetic sensor detecting a change in magnetic flux generated from the third magnet.

[0011] <Effects of the Invention>

[0012] The absolute encoder according to the present invention can have a simple structure and can be reduced in size. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is an exploded perspective view showing the absolute encoder according to the first embodiment.

[0014] Figure 2 is a perspective view showing an absolute encoder.

[0015] Figure 3 is a top view showing an absolute encoder.

[0016] Figure 4 It is a cross-sectional view showing a section cut along the XZ plane of the absolute encoder.

[0017] Figure 5 It is a cross-sectional view showing a section cut along the YZ plane of the absolute encoder.

[0018] Figure 6 It is a perspective view showing a main shaft, a main shaft gear, an idler gear, a driven gear, a first counter shaft, and a second counter shaft.

[0019] Figure 7 is a side view showing the main shaft, the main shaft gear, the idler gear, the driven gear, the first countershaft and the second countershaft.

[0020] Figure 8 It is a perspective view showing a magnet attached to the main shaft.

[0021] Fig. 9 This is a table showing the specifications of gears, reduction ratios, and maximum detectable rotation numbers.

[0022] Fig.10 It is an exploded perspective view showing a bearing, a driven gear, a first countershaft, a magnet holder, a magnet, and a magnetic sensor.

[0023] Fig.11 It is an exploded perspective view showing a bearing, a driven gear, a second counter shaft, a magnet holder, a magnet, and a magnetic sensor.

[0024] Fig.12 It is a perspective view showing magnets attached to the first auxiliary shaft and the second auxiliary shaft.

[0025] Fig.13 It is a bottom view showing a substrate, a microcomputer, and a magnetic sensor.

[0026] Fig.14 This is a block diagram showing the functional structure of a microcomputer packaged in an absolute encoder.

[0027] Fig.15 This is a table showing the permissible errors of the rotation angles of the main shaft, the first sub-shaft, and the second sub-shaft.

[0028] Fig.16 It is a perspective view showing an absolute encoder according to a second embodiment.

[0029] Fig.17 is a cross-sectional view showing an absolute encoder.

[0030] Fig.18 This is a table showing the specifications of gears, reduction ratios, and maximum detectable rotation numbers. DETAILED DESCRIPTION

[0031] Hereinafter, the structure of the absolute encoder involved in the embodiment of the present invention is described in detail based on the accompanying drawings. In addition, the present invention is not limited to the embodiment. In addition, in each figure, as three mutually orthogonal directions, the X-axis direction, the Y-axis direction and the Z-axis direction are sometimes illustrated with arrows. The X-axis direction is the direction along which the X-axis extends. The Y-axis direction is the direction along which the Y-axis extends. The Z-axis direction is the direction along which the Z-axis extends. In addition, when a gear is illustrated, the teeth of the gear are not illustrated.

[0032] [First embodiment]

[0033] <Overview of Absolute Encoders>

[0034] First, refer to Figures 1 to 13 , an absolute encoder 100 according to the first embodiment will be described. Hereinafter, “absolute encoder” may be abbreviated as “encoder”.

[0035] Figure 1 It is an exploded perspective view showing the absolute encoder according to the first embodiment. Figure 21 is a perspective view showing an absolute encoder. The encoder 100 is an absolute encoder that detects the rotation angle of the spindle 10. The spindle 10 is, for example, the rotation axis of the motor 200. The spindle 10 extends along the Z-axis direction. The encoder 100 outputs the rotation angle of the spindle 10 as a digital signal.

[0036] <Motor>

[0037] The motor 200 may be, for example, a stepping motor or a DC brushless motor. The motor 200 may be used as a driving source for driving a robot for industrial use, for example, via a speed reduction mechanism such as a wave gear device. The rotating shaft of the motor 200 protrudes to both sides in the Z-axis direction. The encoder 100 is adjacent to the main body of the motor 200 in the Z-axis direction. The main body of the motor 200 includes a magnet and a frame, but does not include a rotating shaft.

[0038] <Absolute encoder>

[0039] Figure 3 FIG. 1 is a top view showing an absolute encoder. Figure 3 As shown, the encoder 100 includes main shaft gears 12 and 14, a magnet Mg1, and a magnetic sensor 16. The main shaft gear 12 is an example of a first main shaft gear, and the main shaft gear 14 is an example of a second main shaft gear. The magnet Mg1 is an example of a first magnet, and the magnetic sensor 16 is an example of a first magnetic sensor.

[0040] The encoder 100 includes an idler shaft 20 and idler wheels 22 and 24. The idler wheels 22 and 24 are examples of first idler wheels. The encoder 100 includes an idler shaft 30 and idler wheels 32 and 34. The idler wheels 32 and 34 are examples of second idler wheels.

[0041] The encoder 100 includes a first secondary shaft 40, a driven gear 42, a magnet Mg2, and a magnetic sensor 46. Fig.10 The driven gear 42 is an example of a first driven gear. The magnet Mg2 is an example of a second magnet, and the magnetic sensor 46 is an example of a second magnetic sensor.

[0042] The encoder 100 includes a second secondary shaft 50, a driven gear 52, a magnet Mg3, and a magnetic sensor 56. Fig.11 The driven gear 52 is an example of a second driven gear. The magnet Mg3 is an example of a third magnet, and the magnetic sensor 56 is an example of a third magnetic sensor.

[0043] like Figure 1 As shown, the encoder 100 includes a cover plate 62 , a frame 110 , a substrate 120 , a support column 64 , a main base 70 , and a main partition plate 72 in this order along the Z-axis direction.

[0044] <Main axis>

[0045] The main shaft 10 is cylindrical and has a hollow structure. A wiring electrically connected to the motor 200 may be inserted into the main shaft 10 .

[0046] <Main partition>

[0047] The main partition plate 72 is arranged adjacent to the main body of the motor 200 in the Z-axis direction. The main partition plate 72 is in the shape of a plate. The plate thickness direction of the main partition plate 72 is along the Z-axis direction. The main partition plate 72 is formed with an opening for inserting the main shaft 10. The main partition plate 72 is formed in a rectangular shape when viewed in the Z-axis direction. The main partition plate 72 may be formed of, for example, resin.

[0048] <Main base>

[0049] The main base 70 is arranged adjacent to the main partition plate 72 in the Z-axis direction. The main base 70 is plate-shaped. The plate thickness direction of the main base 70 is along the Z-axis direction. An opening for inserting the main shaft 10 is formed in the main base 70. The main base 70 is formed in a rectangular shape when viewed along the Z-axis direction. The main base 70 includes a magnetic body and functions as a magnetic shield. As the material of the main base 70, for example, stainless steel or cold-rolled steel plate can be used. The material of the main base 70 is formed of a material different from that of the main partition plate 72.

[0050] <Pillar>

[0051] Figure 1 to Figure 3 The support column 64 shown is arranged between the main base 70 and the substrate 120 in the Z-axis direction. The support column 64 is provided in a manner of protruding to the side opposite to the main partition plate 72 relative to the main base 70 in the Z-axis direction. The support column 64 is arranged at a position opposite to the corner of the rectangle of the main base 70. The support column 64 has a predetermined length in the Z-axis direction. The support column 64 supports the substrate 120. The support column 64 is formed of, for example, resin. The support column 64 is formed as a separate component from the main base 70. In addition, the support column 64 and the main base 70 are not limited to being formed as independent components, and may be formed as an integral body.

[0052] <Substrate>

[0053] Figure 4 It is a cross-sectional view showing a section cut along the XZ plane of the absolute encoder. Figure 5 It is a cross-sectional view showing a section cut along the YZ plane of the absolute encoder. Figure 1 , Figure 4 as well as Figure 5The substrate 120 shown is a printed wiring substrate. The substrate 120 is fixed to a plurality of pillars 64. The thickness direction of the substrate 120 is along the Z-axis direction. The substrate 120 is spaced apart from the main base 70 in the Z-axis direction. In the Z-axis direction, the pillars 64 are arranged between the main base 70 and the substrate 120, thereby forming a predetermined space between the main base 70 and the substrate 120. The substrate 120 has an opening for inserting the spindle 10.

[0054] Fig.13 FIG. 2 is a bottom view showing the substrate, the microcomputer and the magnetic sensor. Fig.13 As shown, the magnetic sensors 46 and 56 are packaged on the substrate 120. The magnetic sensors 46 and 56 are mounted on the bottom surface of the substrate 120. The bottom surface of the substrate 120 is the surface close to the main base 70 side in the Z-axis direction. The microcomputer 121 is packaged on the substrate 120.

[0055] <Frame>

[0056] Figure 1 , Figure 4 as well as Figure 5 The frame 110 shown has a top plate 112 and side walls 114 and 116. The top plate 112 is formed in a rectangular shape when viewed along the Z-axis direction. The plate thickness direction of the top plate 112 is along the Z-axis direction. The top plate 112 is separated from the substrate 120 in the Z-axis direction. An opening is formed in the top plate 112 for inserting the spindle 10. The top plate 112 is arranged in a manner to cover the substrate 120 from the side opposite to the main base 70 in the Z-axis direction.

[0057] The plurality of side walls 114, 116 are formed in a square tube-like manner. Figure 4 As shown in FIG. 1 , the side walls 114 are opposite to each other in the X-axis direction. The thickness direction of the side walls 114 is along the X-axis direction. Figure 5 As shown, the side walls 114 and 116 are opposed to each other in the Y-axis direction. The plate thickness direction of the side wall 116 is along the Y-axis direction. The side walls 114 and 116 have a predetermined length in the Z-axis direction. The side walls 114 and 116 are formed so as to extend from the top plate 112 in the Z-axis direction.

[0058] In the space surrounded by the top plate 112 and the side walls 114 and 116, the base plate 120, the main base 70, the main partition plate 72, the main shaft gears 12 and 14, the idle shafts 20 and 30, the idle gears 22, 24, 32 and 34, the first secondary shaft 40, the second secondary shaft 50, the driven gears 42 and 52, the magnetic sensors 16, 46 and 56, and the magnets Mg1, Mg2 and Mg3 are arranged. In addition, a part of the main partition plate 72 and the magnet Mg1 may extend in the Z-axis direction to a position closer to the motor 200 than the side walls 114 and 116.

[0059] <Cover>

[0060] Figure 1 , Figure 4 as well as Figure 5 The cover plate 62 shown is formed in a rectangular shape when viewed along the Z-axis direction. The plate thickness direction of the cover plate 62 is along the Z-axis direction. An opening for inserting the spindle 10 is formed in the cover plate 62. The cover plate 62 is arranged so as to cover the surface of the top plate 112 on the opposite side to the motor 200. The cover plate 62 includes a magnetic body and functions as a magnetic shield.

[0061] <Main shaft gear>

[0062] Figure 6 It is a perspective view showing a main shaft, a main shaft gear, an idler gear, a driven gear, a first counter shaft, and a second counter shaft. Figure 7 is a side view showing the main shaft, main shaft gear, idler gear, driven gear, first countershaft and second countershaft. Figures 4 to 7 As shown, the main shaft gears 12 and 14 are spur gears mounted on the main shaft 10. The gears provided on the main shaft 10 are in a two-stage structure. The main shaft gears 12 and 14 are arranged on the opposite side of the motor 200 with respect to the main base 70 in the Z-axis direction. The main shaft gears 12 and 14 rotate together with the main shaft 10.

[0063] The number of teeth of the main shaft gears 12 and 14 is different from each other. The number of teeth of the main shaft gear 14 is greater than the number of teeth of the main shaft gear 12. The number of teeth of the main shaft gear 12 may be, for example, 50. The number of teeth of the main shaft gear 14 may be, for example, 51. The main shaft gear 14 is arranged close to the main body of the motor 200 relative to the main shaft gear 12 in the Z-axis direction.

[0064] <Casing>

[0065] The encoder 100 has a sleeve 18 mounted on the main shaft 10. The main shaft 10 is inserted into the opening of the sleeve 18. The main shaft 10 is pressed into the sleeve 18, for example. The main shaft gears 12, 14 and the sleeve 18 are formed as a whole. The sleeve 18 extends from the main shaft gear 14 to a position close to the main body of the motor 200 in the Z-axis direction. The main shaft gears 12, 14 and the sleeve 18 rotate together with the main shaft 10.

[0066] <Magnet Mg1>

[0067] like Figure 4 , Figure 5 as well as Figure 7As shown, the magnet Mg1 is installed on the main shaft 10, for example, via a sleeve 18. The magnet Mg1 is annular and fixed relative to the main shaft 10. The magnet Mg1 is arranged in a manner to contact the outer peripheral surface of the sleeve 18. The magnet Mg1 can be fixed to the main shaft 10 via the sleeve 18, or can be directly fixed to the outer peripheral surface of the main shaft 10. The magnet Mg1 is arranged at a position close to the motor 200 relative to the main base 70 in the Z-axis direction. The magnet Mg1 is arranged in the opening of the main partition 72. The magnet Mg1 can also extend in the Z-axis direction in a direction closer to the motor 200 than the main partition 72. As shown in FIG. Figure 8 As shown, the magnetization direction of the magnet Mg1 is along the radial direction of the main shaft 10.

[0068] <Idle shaft 20>

[0069] like Figure 2 , Figure 3 , Figure 6 as well as Figure 7 As shown, the idle shaft 20 extends in the Z-axis direction. The idle shaft 20 is fixed to the main base 70 by, for example, press-fitting. The idle shaft 20 protrudes to the opposite side of the main body of the motor 200 relative to the main base 70. When viewed in the Z-axis direction, the idle shaft 20 is arranged outside the main shaft gears 12 and 14 in the radial direction of the main shaft 10. The idle shaft 20 is arranged at a position overlapping with the main shaft gears 12 and 14 in the Z-axis direction.

[0070] <First idler gear>

[0071] The first idler gear includes an idler gear 22 and an idler gear 24, and has a two-stage structure. The idler gear 22 is a spur gear rotatably supported relative to the idler shaft 20. The idler gear 22 is arranged on the opposite side of the motor 200 relative to the main base 70 in the Z-axis direction. The idler gear 22 meshes with the main shaft gear 12. The rotation of the main shaft 10 is transmitted to the idler gear 22 via the main shaft gear 12. The idler gear 22 rotates in the opposite direction to the rotation direction of the main shaft 10 with the idler shaft 20 as the center.

[0072] Fig. 9 is a table showing the specifications of the gears, the reduction ratios, and the maximum detectable rotation speeds. Fig. 9 As shown, the number of teeth of the idler gear 22 is, for example, 30. The speed ratio of the idler gear 22 to the main shaft 10 is less than 1. The speed ratio of the idler gear 22 to the main shaft 10 is, for example, 0.60. The number of teeth of the idler gear 22 is less than the number of teeth of the main shaft gear 12. When the number of teeth of the main shaft gear 12 is set to "n", the number of teeth of the idler gear 22 can be "n-20". In addition, "n" and "n-20" are natural numbers.

[0073] like Figure 3 , Figure 6 as well as Figure 7As shown, the idler wheel 24 is a spur gear rotatably supported relative to the idler shaft 20. The idler wheel 24 is arranged on the opposite side of the main body of the motor 200 relative to the main base 70 in the Z-axis direction. The idler wheel 24 is adjacent to the idler wheel 22 in the Z-axis direction. The idler wheel 24 is arranged at a position closer to the main body of the motor 200 than the idler wheel 22 in the Z-axis direction. The outer diameter of the idler wheel 24 is smaller than the outer diameter of the idler wheel 22. The idler wheel 24 rotates together with the idler wheel 22. The idler wheel 24 and the idler wheel 22 are integrally formed.

[0074] like Fig. 9 As shown, the number of teeth of the idler gear 24 is less than the number of teeth of the idler gear 22. The number of teeth of the idler gear 24 is, for example, 21. When the number of teeth of the idler gear 22 is set to "n", the number of teeth of the idler gear 24 may be "n-9". In addition, "n" and "n-9" are natural numbers.

[0075] <First auxiliary shaft>

[0076] Fig.10 It is an exploded perspective view showing a bearing, a driven gear, a first countershaft, a magnet holder, a magnet, and a magnetic sensor. Fig.10 The bearing 48, the driven gear 42, the first secondary shaft 40, the magnet holder 44 and the magnet Mg2 are integrally assembled. The magnetic sensor 46 is spaced apart from the magnet Mg2.

[0077] The first sub-shaft 40 extends in the Z-axis direction. The first sub-shaft 40 is arranged parallel to the main shaft 10. The first sub-shaft 40 is rotatably supported by a bearing 48. The bearing 48 is fixed to the main base 70, for example. The first sub-shaft 40 protrudes to the opposite side of the motor 200 with respect to the main base 70.

[0078] <First driven gear>

[0079] The driven gear 42 is a spur gear mounted on the first countershaft 40. The first countershaft 40 may be pressed into the opening of the driven gear 42. The driven gear 42 is arranged on the opposite side of the motor 200 with respect to the main base 70 in the Z-axis direction. The driven gear 42 meshes with the idler gear 24. The rotation of the main shaft 10 is transmitted to the driven gear 42 via the main shaft gear 12 and the idler gears 22 and 24. The first countershaft 40 rotates together with the driven gear 42. The driven gear 42 and the first countershaft 40 rotate in the same direction as the rotation direction of the main shaft 10.

[0080] like Fig. 9 As shown, the number of teeth of the driven gear 42 is, for example, 33. The number of teeth of the driven gear 42 is greater than the number of teeth of the idler gear 24. When the number of teeth of the idler gear 24 is set to "n", the number of teeth of the driven gear 42 may be "n+12".

[0081] The speed ratio of the driven gear 42 relative to the main shaft 10 is close to 1. The speed ratio of the driven gear 42 relative to the main shaft 10 may be, for example, 0.942857. The speed ratio of the driven gear 42 relative to the idler gear 24 is greater than 1. The speed ratio of the driven gear 42 relative to the idler gear 24 may be, for example, 1.571.

[0082] <Magnetic Mg2>

[0083] like Figure 2 , Figure 3 as well as Fig.10 As shown, the magnet Mg2 is mounted on the front end of the first auxiliary shaft 40. The magnet Mg2 is, for example, in the shape of a disk. The front end of the first auxiliary shaft 40 is the end on the side away from the main body of the motor 200 in the Z-axis direction. The plate thickness direction of the magnet Mg2 is along the Z-axis direction. Fig.12 As shown, the magnetization direction of the magnet Mg2 is along the Z-axis direction.

[0084] <Magnet holder>

[0085] Fig.10 The magnet holder 44 shown is formed integrally with the first secondary shaft 40, for example. The magnet holder 44 is provided at the front end portion of the first secondary shaft 40. The magnet holder 44 has a recessed portion into which the magnet Mg2 is embedded. The magnet Mg2 is embedded in the recessed portion of the magnet holder 44. The magnet Mg2 is held by the magnet holder 44 and rotates together with the first secondary shaft 40.

[0086] <Idle shaft 30>

[0087] like Figure 2 , Figure 3 , Figure 6 as well as Figure 7 As shown, the idle shaft 30 extends in the Z-axis direction. The idle shaft 30 is fixed to the main base 70. The idle shaft 30 protrudes to the opposite side of the main body of the motor 200 relative to the main base 70. When viewed in the Z-axis direction, the idle shaft 30 is arranged outside the main shaft gears 12 and 14 in the radial direction of the main shaft 10. The idle shaft 30 is arranged at a position overlapping with the main shaft gears 12 and 14 in the Z-axis direction.

[0088] <Second idler gear>

[0089] The second idler gear includes an idler gear 32 and an idler gear 34, and has a two-stage structure. The idler gear 32 is a spur gear rotatably supported relative to the idler shaft 30. The idler gear 32 is arranged on the opposite side of the motor 200 relative to the main base 70 in the Z-axis direction. The idler gear 32 meshes with the main shaft gear 14. The rotation of the main shaft 10 is transmitted to the idler gear 32 via the main shaft gear 14. The idler gear 32 rotates in the opposite direction to the rotation direction of the main shaft 10 with the idler shaft 30 as the center.

[0090] like Fig. 9 As shown, the number of teeth of the idler gear 32 is, for example, 30. The speed ratio of the idler gear 32 to the main shaft 10 is less than 1. The speed ratio of the idler gear 22 to the main shaft 10 is, for example, 0.58. The speed ratio of the idler gear 32 to the main shaft 10 is less than the speed ratio of the idler gear 22 to the main shaft 10. The number of teeth of the idler gear 32 is less than the number of teeth of the main shaft gear 14. When the number of teeth of the main shaft gear 14 is set to "n", the number of teeth of the idler gear 32 can be "n-21". In addition, "n" and "n-21" are natural numbers.

[0091] like Figure 2 , Figure 3 as well as Figure 7 As shown, the idler wheel 34 is a spur gear rotatably supported relative to the idler shaft 30. The idler wheel 34 is arranged on the opposite side of the main body of the motor 200 relative to the main base 70 in the Z-axis direction. The idler wheel 34 is adjacent to the idler wheel 32 in the Z-axis direction. The idler wheel 34 is arranged at a position farther from the main body of the motor 200 than the idler wheel 32 in the Z-axis direction. The outer diameter of the idler wheel 34 is smaller than the outer diameter of the idler wheel 32. The idler wheel 34 rotates together with the idler wheel 32. The idler wheel 34 and the idler wheel 32 are integrally formed.

[0092] like Fig. 9 As shown, the number of teeth of the idler gear 34 is less than the number of teeth of the idler gear 32. The number of teeth of the idler gear 34 is, for example, 20. The number of teeth of the idler gear 34 is less than the number of teeth of the idler gear 32. When the number of teeth of the idler gear 32 is set to "n", the number of teeth of the idler gear 34 may be "n-10". In addition, "n" and "n-10" are natural numbers.

[0093] <Second auxiliary shaft>

[0094] Fig.11 It is an exploded perspective view showing a bearing, a driven gear, a second counter shaft, a magnet holder, a magnet, and a magnetic sensor. Fig.11 The bearing 58, the driven gear 52, the second secondary shaft 50, the magnet holder 54 and the magnet Mg3 are assembled as one body. The magnetic sensor 56 is arranged apart from the magnet Mg3.

[0095] The second auxiliary shaft 50 extends in the Z-axis direction. The second auxiliary shaft 50 is arranged in parallel with the main shaft 10. The second auxiliary shaft 50 is rotatably supported by a bearing 58. The bearing 58 is fixed to the main base 70, for example. The second auxiliary shaft 50 protrudes to the opposite side of the main base 70 from the main body of the motor 200.

[0096] <Second driven gear>

[0097] The driven gear 52 is a spur gear mounted on the second countershaft 50. The second countershaft 50 may also be pressed into the opening of the driven gear 52. The driven gear 52 is arranged on the opposite side of the motor 200 with respect to the main base 70 in the Z-axis direction. The driven gear 52 meshes with the idler gear 22. The rotation of the main shaft 10 is transmitted to the driven gear 52 via the main shaft gear 12 and the idler gears 32 and 34. The second countershaft 50 rotates together with the driven gear 52. The driven gear 52 and the second countershaft 50 rotate in the same direction as the rotation direction of the main shaft 10.

[0098] like Fig. 9 As shown, the number of teeth of the driven gear 52 is, for example, 33. The number of teeth of the driven gear 52 is greater than the number of teeth of the idler gear 34. When the number of teeth of the idler gear 34 is set to "n", the number of teeth of the driven gear 52 may be "n+13". The number of teeth of the driven gear 52 may also be the same as the number of teeth of the driven gear 42.

[0099] The speed ratio of the driven gear 52 relative to the main shaft 10 is close to 1. The speed ratio of the driven gear 52 relative to the main shaft 10 may be, for example, 0.970588. The speed ratio of the driven gear 52 relative to the idler gear 34 is greater than 1. The speed ratio of the driven gear 52 relative to the idler gear 34 may be, for example, 1.65. The speed ratio of the driven gear 52 relative to the idler gear 34 is greater than the speed ratio of the driven gear 42 relative to the idler gear 24.

[0100] <Magnetic Mg3>

[0101] like Figure 2 , Figure 3 as well as Fig.11 As shown, the magnet Mg3 is mounted on the front end of the second auxiliary shaft 50. The magnet Mg3 is, for example, in the shape of a disk. The front end of the second auxiliary shaft 50 is the end on the side away from the main body of the motor 200 in the Z-axis direction. The plate thickness direction of the magnet Mg3 is along the Z-axis direction. Fig.12 As shown, the magnetization direction of the magnet Mg3 is along the Z-axis direction.

[0102] <Magnet holder>

[0103] Fig.11 The magnet holder 54 shown is formed integrally with the second secondary shaft 50, for example. The magnet holder 54 is provided at the front end portion of the second secondary shaft 50. The magnet holder 54 has a recessed portion into which the magnet Mg3 is embedded. The magnet Mg3 is embedded in the recessed portion of the magnet holder 54. The magnet Mg3 is held by the magnet holder 54 and rotates together with the second secondary shaft 50.

[0104] <Magnetization direction of magnet Mg1>

[0105] Next, refer to Figure 8 The magnetization direction DM1 of the magnet Mg1 will be described. Figure 8 1 is a perspective view showing a magnet mounted on the spindle. The magnet Mg1 is magnetized along the radial direction D1 of the spindle 10. The radial direction D1 of the spindle 10 is the radial direction of the annular magnet Mg1 and is a direction intersecting the Z-axis direction. The radial direction D1 may be a direction along the X-axis direction, a direction along the Y-axis direction, or a direction along other directions. In addition, the situation of being magnetized in the radial direction is sometimes described as "radial magnetization".

[0106] When the magnetizing direction DM1 is the radial direction D1 , the magnetic field generated by the magnet Mg1 is more likely to spread in the radial direction D1 than when the magnetizing direction DM2 is the Z-axis direction.

[0107] <First Magnetic Sensor>

[0108] Figure 1 as well as Figure 8 The magnetic sensor 16 shown detects the rotation angle of the spindle 10. The magnetic sensor 16 is, for example, located at a position overlapping with the magnet Mg1 in the Z-axis direction and arranged outside the magnet Mg1 in the radial direction of the magnet Mg1. The magnetic sensor 16 faces the outer peripheral surface of the magnet Mg1 in the radial direction of the magnet Mg1. The magnetic sensor 16 detects the change in the magnetic flux of the magnet Mg1. The magnetic sensor 16 detects the rotation angle of the spindle 10 based on the change in the magnetic flux of the magnet Mg1.

[0109] <Magnetic direction of magnet Mg2>

[0110] Next, refer to Fig.12 The magnetization direction DM2 of the magnet Mg2 will be described. Fig.12 3D diagram showing magnets mounted on the first auxiliary shaft and the second auxiliary shaft. The magnet Mg2 is magnetized along the axial direction of the first auxiliary shaft 40. The axial direction of the first auxiliary shaft 40 is along the Z-axis direction. In the magnet Mg2, an N pole is formed on one side and an S pole is formed on the other side with the center of the radial direction D2 of the magnet Mg2 as the boundary. In addition, in the magnet Mg2, the N pole and the S pole are reversed with the center of the Z-axis direction as the boundary. Fig.12 In the case shown, an N pole is arranged on the left side of the upper section, and an S pole is arranged on the right side of the upper section. An S pole is arranged on the left side of the lower section, and an N pole is arranged on the right side of the lower section. The magnetization direction DM2 of the magnet Mg2 is along the Z-axis direction. In addition, the case of magnetization along the axial direction is sometimes described as "plane direction magnetization".

[0111] When the magnetizing direction DM2 is the Z-axis direction, the magnetic field generated by the magnet Mg2 is distributed so as to spread in the Z-axis direction, and the peak value becomes higher, compared with the case where the magnetizing direction is the radial direction D2.

[0112] <Second magnetic sensor>

[0113] Fig.10 , Fig.12 as well as Fig.13 The magnetic sensor 46 shown detects the rotation angle of the first secondary shaft 40. The magnetic sensor 46 is arranged at a position overlapping with the first secondary shaft 40 when viewed along the Z-axis direction. The magnetic sensor 46 is separated from the magnet Mg2 in the Z-axis direction. The magnetic sensor 56 is packaged on the substrate 120. The magnetic sensor 46 is mounted on the bottom surface of the substrate 120. The magnetic sensor 46 detects the change in the magnetic flux of the magnet Mg2. The magnetic sensor 46 detects the rotation angle of the first secondary shaft 40 based on the change in the magnetic flux of the magnet Mg2.

[0114] <Magnetization direction of magnet Mg3>

[0115] The magnetization direction of the magnet Mg3 is the same as the magnetization direction DM2 of the magnet Mg2, so the description here is omitted.

[0116] <Third magnetic sensor>

[0117] Fig.11 , Fig.12 as well as Fig.13 The magnetic sensor 56 shown detects the rotation angle of the second secondary shaft 50. The magnetic sensor 56 is arranged at a position overlapping with the second secondary shaft 50 when viewed along the Z-axis direction. The magnetic sensor 56 is separated from the magnet Mg3 in the Z-axis direction. The magnetic sensor 56 is packaged on the substrate 120. The magnetic sensor 56 is mounted on the bottom surface of the substrate 120. The magnetic sensor 56 detects the change in the magnetic flux of the magnet Mg3. The magnetic sensor 56 detects the rotation angle of the second secondary shaft 50 based on the change in the magnetic flux of the magnet Mg3.

[0118] <Microcomputer>

[0119] On the substrate 120, as Fig.13 As shown in FIG. 1 , a microcomputer 121 is packaged. The microcomputer 121 is mounted on the bottom surface of the substrate 120 . Fig.14 1 is a block diagram showing the functional structure of a microcomputer. The microcomputer 121 includes a CPU, and obtains digital signals indicating the rotation angles outputted from the magnetic sensors 16, 46, and 56. The microcomputer 121 calculates the rotation angle of the spindle 10 based on the signals obtained from the magnetic sensors 16, 46, and 56.

[0120] Fig.14 This is a block diagram showing the functional structure of a microcomputer packaged in an absolute encoder. Fig.14Each block of the microcomputer 121 shown represents a function realized by executing a program as the CPU of the microcomputer 121. Each block of the microcomputer 121 can be realized by a component or mechanical device represented by a CPU (central processing unit) of a computer in terms of hardware, and can be realized by a computer program or the like in terms of software, but here, functional blocks realized by their cooperation are depicted. Therefore, these functional blocks can be realized in various ways by a combination of hardware and software.

[0121] The microcomputer 121 includes a rotation angle acquisition unit 121p, a rotation angle acquisition unit 121q, a rotation angle acquisition unit 121r, a table processing unit 121b, a rotation amount determination unit 121c, and an output unit 121e. The rotation angle acquisition unit 121q acquires the rotation angle Aq, which is the angle information indicating the rotation angle of the main shaft 10, based on the signal output from the magnetic sensor 16. The rotation angle acquisition unit 121p acquires the rotation angle Ap, which is the angle information indicating the rotation angle of the first secondary shaft 40, based on the signal output from the magnetic sensor 36. The rotation angle acquisition unit 121r acquires the rotation angle Ar, which is the angle information indicating the rotation angle of the second secondary shaft 50 detected by the magnetic sensor 46.

[0122] The table processing unit 121b determines the number of rotations of the main shaft 10 corresponding to the obtained rotation angle Ap by referring to the first correspondence table storing the rotation angle Ap of the first sub-shaft 40 and the number of rotations of the main shaft 10 corresponding to the rotation angle Ap. In addition, the table processing unit 121b determines the number of rotations of the main shaft 10 corresponding to the obtained rotation angle Ar by referring to the second correspondence table storing the rotation angle Ar of the second sub-shaft 50 and the number of rotations of the main shaft 10 corresponding to the rotation angle Ar.

[0123] The rotation amount determination unit 121c determines the rotation amount of the spindle 10 for multiple rotations based on the rotation number of the spindle 10 determined by the table processing unit 121b and the obtained rotation angle Aq. The output unit 121e converts the rotation amount of the spindle 10 for multiple rotations determined by the rotation amount determination unit 121c into information indicating the rotation amount and outputs the information.

[0124] <Permissible error of rotation angle>

[0125] Fig.15 : is a table showing the allowable error of the rotation angle of the main shaft, the first sub-shaft, and the second sub-shaft. The allowable error of the rotation angle in one rotation of the main shaft 10 is 1.8°±0.9°. The allowable error of the rotation angle in one rotation of the first sub-shaft 40 is 10.29°±5.15°. The allowable error of the rotation angle in one rotation of the second sub-shaft 50 is 10.59°±5.19°.

[0126] Since the allowable error of the rotation angle of the main shaft 10 is smaller than the allowable errors of the rotation angles of the first auxiliary shaft 40 and the second auxiliary shaft 50, it is ideal to use a radially magnetized magnet for the magnet Mg1 corresponding to the magnetic sensor 16 for detecting the rotation angle of the main shaft 10 so as not to exceed the allowable error of the main shaft 10.

[0127] On the other hand, the permissible error of the rotation angle of each of the first auxiliary shaft 40 and the second auxiliary shaft 50 is larger than the permissible error of the rotation angle of the main shaft 10. Therefore, for the magnet Mg2 corresponding to the magnetic sensor 46 for detecting the rotation angle of the first auxiliary shaft 40, it is more desirable to use an axially magnetized magnet in order to preferentially suppress the occurrence of magnetic interference. For the same reason, for the magnet Mg3 corresponding to the magnetic sensor 56 for detecting the rotation angle of the second auxiliary shaft 50, it is more desirable to use an axially magnetized magnet.

[0128] <Maximum detection rotation number>

[0129] The main shaft 10 rotates 35 times, and the first sub-shaft 40 has one cycle (360÷35=10.285). The main shaft 10 rotates 34 times, and the second sub-shaft 50 has one cycle (360÷34=10.588). In this case, the maximum detectable number of rotations is 1190 (34×35=1190).

[0130] <Absolute encoder operation>

[0131] When the motor 200 is driven, the main shaft 10, which is the rotating shaft of the motor 200, rotates. In the encoder 100, when the main shaft 10 rotates, the main shaft gears 12 and 14 and the magnet Mg1 rotate together with the main shaft 10.

[0132] The idler gear 22 meshes with the main shaft gear 12 and rotates with the rotation of the main shaft gear 12. The idler gear 24 rotates integrally with the idler gear 22. The driven gear 42 meshes with the idler gear 24 and rotates with the rotation of the idler gear 24. The first secondary shaft 40 and the magnet Mg2 rotate integrally with the driven gear 42.

[0133] The idler gear 32 meshes with the main shaft gear 14 and rotates with the rotation of the main shaft gear 14. The idler gear 34 rotates integrally with the idler gear 32. The driven gear 52 meshes with the idler gear 34 and rotates with the rotation of the idler gear 34. The second secondary shaft 50 and the magnet Mg3 rotate integrally with the driven gear 52.

[0134] <Effects of absolute encoder>

[0135] In the conventional structure with a worm gear, a spring and a mechanism for supporting the spring are required to suppress the influence of the axis conversion on the angle error or the displacement in the axial direction. In the encoder 100 involved in this embodiment, since there is no worm gear, it can be set to a simple structure and the number of components can be reduced. Therefore, the assembly of the encoder 100 becomes easy.

[0136] The encoder 100 includes main shaft gears 12, 14, idler gears 22, 24, 32, 34, and driven gears 42, 52, all of which are spur gears, so that the thickness in the Z-axis direction can be reduced. The encoder 100 is thinner in the Z-axis direction than a conventional structure including a worm gear.

[0137] In the encoder 100, the rotation angle of the main shaft 10, the rotation angle of the first secondary shaft 40, and the rotation angle of the second secondary shaft 50 can be detected, and the number of rotations and the rotation angle of the main shaft 10 can be detected based on these angles. The encoder 100 includes main shaft gears 12 and 14 with different numbers of teeth, and the idler gears include idler gears 22 and 24 that rotate with the rotation of the main shaft gear 12 and idler gears 32 and 34 that rotate with the rotation of the main shaft gear 14. The driven gear 42 meshes with the idler gear 24, and the driven gear 52 meshes with the idler gear 34. In the encoder 100 with such a structure, it is possible to achieve thinness and increase the maximum number of detections with a simple structure. In the encoder 100, it is possible to prevent the main shaft 10, the first secondary shaft 40, and the second secondary shaft 50 from becoming the same combination of rotation angles until the main shaft 10 rotates 1190 times. In the encoder 100, a maximum number of rotations of 1190 can be achieved.

[0138] In the encoder 100, a main base 70 for suppressing the transmission of magnetic flux is arranged between the magnet Mg1 and the magnets Mg2 and Mg3 in the axial direction of the main shaft 10. The magnet Mg1 is arranged at a position closer to the main body of the motor 200 than the main base 70, and the magnets Mg2 and Mg3 are arranged at a position farther from the main body of the motor 200 than the main base 70. Similarly, the magnetic sensor 16 corresponding to the magnet Mg1 is arranged at a position closer to the main body of the motor 200 than the main base 70, and the magnetic sensor 46 corresponding to the magnet Mg2 and the magnetic sensor 56 corresponding to the magnet Mg3 are arranged at a position farther from the main body of the motor 200 than the main base 70.

[0139] In the encoder 100 having such a structure, the penetration of magnetic flux is suppressed by the main base 70, so that the magnetic sensors 46 and 56 can be suppressed from detecting the magnetic flux generated from the magnet Mg1, and the magnetic sensor 16 can be suppressed from detecting the magnetic flux generated from the magnets Mg2 and Mg3. In addition, in the encoder 100, the penetration of magnetic flux generated from the magnet of the motor 200 is suppressed by the main base 70. In the encoder 100, the penetration of magnetic flux is suppressed by the main base 70, so the leakage of magnetic flux to the outside of the encoder 100 can be suppressed.

[0140] In the encoder 100, in the axial direction of the spindle 10, the magnet Mg1 having a strong magnetic flux is arranged at a position close to the main body of the motor 200, and the magnets Mg2 and Mg3 having weak magnetic fluxes are arranged at a position far from the main body of the motor 200. In the encoder 100 having such a structure, the magnetic flux generated by the magnet Mg1 close to the main body of the motor 200 is strong, so that the influence of the magnetic flux of the magnet of the motor 200 can be suppressed, and the change of the magnetic flux of the magnet Mg1 can be detected by the magnetic sensor 16.

[0141] In the encoder 100, the magnet Mg1 is magnetized in the radial direction of the main shaft 10, and the magnets Mg2 and Mg3 are magnetized in the axial direction of the first auxiliary shaft 40 and the second auxiliary shaft 50. In the encoder 100 having such a structure, the magnet Mg1 is magnetized in the radial direction, so the magnetic field generated by the magnet Mg1 is easier to expand in the radial direction D1 than in the case of magnetization in the surface direction. In the encoder 100, the magnets Mg2 and Mg3 are magnetized in the surface direction, so the magnetic field generated by the magnets Mg2 and Mg3 is distributed in a manner that expands in the Z-axis direction compared to the case of radial magnetization, and the peak value becomes higher. As a result, each magnetic sensor 16, 46, 56 can reliably detect the change in the magnetic flux generated by the corresponding magnets Mg1, Mg2, Mg3.

[0142] In addition, in the encoder 100, the magnet Mg1 is annular, and the main shaft 10 is inserted through the opening of the magnet Mg1. The magnetic sensor 16 is arranged on the outside of the magnet Mg1 in the radial direction of the main shaft 10, the magnet Mg2 is arranged at the end in the axial direction of the first secondary shaft 40, the magnetic sensor 46 is arranged in a manner opposite to the magnet Mg2 in the axial direction of the first secondary shaft 40, the magnet Mg3 is arranged at the end in the axial direction of the second secondary shaft 50, and the magnetic sensor 56 is arranged in a manner opposite to the magnet Mg3 in the axial direction of the second secondary shaft 50.

[0143] According to the encoder 100 of this structure, the magnetic sensor 16 is arranged on the radially outer side of the magnet Mg1, so that it can be thinned in the Z-axis direction compared with the case where it is arranged at a position overlapping with the magnet Mg1 in the Z-axis direction. In addition, by arranging the magnetic sensor 46 in the Z-axis direction opposite to the magnet Mg2 arranged at the end of the first secondary shaft 40, it can be arranged in the Z-axis direction away from the magnet Mg1. As a result, in the magnetic sensor 46, the influence of the magnetic flux generated from the magnet Mg1 can be reduced. Similarly, the magnetic sensor 56 is arranged in the Z-axis direction opposite to the magnet Mg2 arranged at the end of the second secondary shaft 50, so that it can be arranged in the Z-axis direction away from the magnet Mg1. As a result, in the magnetic sensor 56, the influence of the magnetic flux generated from the magnet Mg1 can be reduced.

[0144] Furthermore, in the encoder 100 , when viewed in the Z-axis direction, the idler gears 22 , 24 , 32 , and 34 are arranged between the magnet Mg2 and the magnetic sensor 46 and the magnet Mg3 and the magnetic sensor 56 .

[0145] According to the encoder 100 of this structure, by configuring the magnetic sensor 46 at a position away from the magnet Mg3, the influence of the magnetic flux generated from the magnet Mg3 can be reduced in the magnetic sensor 46. Similarly, by configuring the magnetic sensor 56 at a position away from the magnet Mg2, the influence of the magnetic flux generated from the magnet Mg2 can be reduced in the magnetic sensor 56.

[0146] In addition, the encoder 100 includes a cover plate 62 that is arranged to cover the top plate 112 of the frame 110 and suppresses the penetration of magnetic flux. According to the encoder 100 of this structure, the penetration of magnetic flux generated from the magnets of the motor 200, the magnets Mg1, Mg2, and Mg3 can be suppressed by the cover plate 62, thereby suppressing the leakage of magnetic flux to the outside of the encoder 100. In addition to the main base 70, the encoder 100 further includes the cover plate 62, whereby the magnetic flux generated from the magnets of the motor 200 and the magnet Mg1 is suppressed from penetrating by the main base 70, and further suppressed from penetrating by the cover plate 62. As a result, in the encoder 100, the leakage of magnetic flux to the outside of the encoder 100 can be further suppressed. For devices outside the encoder 100, the risk of magnetic interference can be reduced.

[0147] [Second embodiment]

[0148] Next, refer to Figure 16 to Figure 18 An encoder 100B according to the second embodiment will be described. Fig.16 It is a perspective view showing an encoder according to a second embodiment. Fig.17 is a cross-sectional view showing the encoder. Fig.18This is a table showing the specifications of gears, reduction ratios, and maximum detectable rotation numbers. Fig.16 as well as Fig.17 The encoder 100B according to the second embodiment shown is different from the encoder 100 according to the first embodiment described above in that the gear structure is different. Specifically, the difference is that the encoder 100B has a primary structure main shaft gear 12B instead of the secondary structure main shaft gears 12 and 14, has idler gears 32B and 34B instead of the idler gears 22, 24, 32 and 34, and has driven gears 42B and 52B that mesh with the same idler gear 34B instead of the driven gears 42 and 52 that mesh with different idler gears 24 and 34. In addition, in the description of the encoder 100B, the same description as that of the encoder 100 is sometimes omitted.

[0149] like Fig.16 As shown, the encoder 100B includes a main shaft gear 12B, a magnet Mg1, and a magnetic sensor 16. The encoder 100B includes an idle shaft 30B and idle gears 32B and 34B. The encoder 100B includes a first secondary shaft 40B, a driven gear 42B, a magnet Mg2, and a magnetic sensor 46. The encoder 100B includes a second secondary shaft 50B, a driven gear 52B, a magnet Mg3, and a magnetic sensor 56.

[0150] The main shaft gear 12B and the magnet Mg1 rotate together with the main shaft 10. The idler gears 32B and 34B are integrally formed like the idler gears 32 and 34. The idler gear 32B meshes with the main shaft gear 12B and rotates with the rotation of the main shaft gear 12B. The idler gear 34B rotates as a whole with the idler gear 32B. The idler gears 32B and 34B rotate around the idle shaft 30B.

[0151] The first countershaft 40B, the driven gear 42B, the magnet Mg2 and the magnetic sensor 46 are Fig.10 The first secondary shaft 40, the driven gear 42, the magnet Mg2 and the magnetic sensor 46 of the first embodiment shown in the figure have the same structure. The driven gear 42B meshes with the idler gear 34B and rotates with the rotation of the idler gear 34B. The driven gear 42B, the first secondary shaft 40B and the magnet Mg2 rotate as a whole.

[0152] The second secondary shaft 50B, the driven gear 52B, the magnet Mg3 and the magnetic sensor 56 are Fig.11 The second secondary shaft 50, the driven gear 52, the magnet Mg3 and the magnetic sensor 56 of the first embodiment shown in the figure have the same structure. The driven gear 52B meshes with the idler gear 34B and rotates with the rotation of the idler gear 34B. The driven gear 52B, the second secondary shaft 50B and the magnet Mg3 rotate as a whole.

[0153] like Fig.18As shown, the number of teeth of the main shaft gear 12B is, for example, 50. The number of teeth of the idler gear 32B is, for example, 29. The speed ratio of the idler gear 32B to the main shaft 10 is less than 1. The speed ratio of the idler gear 32B to the main shaft 10 is, for example, 0.58. The number of teeth of the idler gear 32B is less than the number of teeth of the main shaft gear 12B. When the number of teeth of the main shaft gear 12 is set to "n", the number of teeth of the idler gear 32B can be "n-21". In addition, "n" and "n-21" are natural numbers.

[0154] The number of teeth of the idler gear 34B is smaller than that of the idler gear 32B. The number of teeth of the idler gear 34B is, for example, 20. When the number of teeth of the idler gear 32B is set to "n", the number of teeth of the idler gear 34B may be "n-9". In addition, "n" and "n-9" are natural numbers.

[0155] The number of teeth of the driven gear 42B is, for example, 33. The number of teeth of the driven gear 42B is greater than the number of teeth of the idler gear 34B. When the number of teeth of the idler gear 34B is "n", the number of teeth of the driven gear 42B may be "n+13".

[0156] The speed ratio of the driven gear 42B to the main shaft 10 is close to 1. The speed ratio of the driven gear 42B to the main shaft 10 may be, for example, 0.957. The speed ratio of the driven gear 42B to the idler gear 34B is greater than 1. The speed ratio of the driven gear 42B to the idler gear 34B may be, for example, 1.65.

[0157] The number of teeth of the driven gear 52B is, for example, 34. The number of teeth of the driven gear 52B is greater than the number of teeth of the idler gear 34B. When the number of teeth of the idler gear 34B is set to "n", the number of teeth of the driven gear 52B may be "n+14".

[0158] The speed ratio of the driven gear 52B relative to the main shaft 10 is close to 1. The speed ratio of the driven gear 52B relative to the main shaft 10 may be, for example, 0.986. The speed ratio of the driven gear 52B relative to the idler gear 34B is greater than 1. The speed ratio of the driven gear 52B relative to the idler gear 34B may be, for example, 1.7. The speed ratio of the driven gear 52B relative to the idler gear 34B is greater than the speed ratio of the driven gear 42B relative to the idler gear 34B.

[0159] <Maximum detection rotation number>

[0160] exist Fig.18 Under the condition of the gear shown, the maximum detectable rotation number is 999. Here, the initial states of the three detection values ​​of the main shaft 10, the first secondary shaft 40B, and the second secondary shaft 50B are set to 0 (zero), and then the rotation number of the main shaft 10 just before the detection values ​​of the main shaft 10, the first secondary shaft 40B, and the second secondary shaft 50B simultaneously become 0 becomes the maximum detectable rotation number.

[0161] <Effects of absolute encoder>

[0162] The encoder 100B according to the second embodiment also has the same effects as the encoder 100 according to the first embodiment. The encoder 100B has fewer idle shafts and idle gears than the encoder 100, so the number of components can be reduced to simplify the structure.

[0163] The configurations described in the above embodiments are examples of the contents of the present invention, and may be combined with other known technologies, or part of the configurations may be omitted or modified without departing from the gist of the present invention.

[0164] In the above-mentioned embodiment, the encoder 100 is described as having a main base 70 as a magnetic body, but the encoder 100 is not limited thereto. The encoder 100 may also have a main base 70 composed of a non-magnetic body, for example. In addition, the encoder 100 may also have a structure having a magnetic shielding member mounted on the main base 70 composed of a non-magnetic body, for example.

[0165] In the above-described embodiment, the spindle 10 is described as a cylindrical spindle having a hollow structure, but the spindle 10 is not limited to a cylindrical shape. The encoder 100 may include a cylindrical spindle, for example.

[0166] This international application claims the benefit of priority based on Japanese Patent Application No. 2022-086345 filed on May 26, 2022, and the entire contents of Japanese Patent Application No. 2022-086345 are incorporated herein by reference.

[0167] Explanation of symbols

[0168] 100, 100B: encoder (absolute encoder); 10: main shaft; 12: main shaft gear (first main shaft gear); 12B: main shaft gear; 14: main shaft gear (second main shaft gear); 16: magnetic sensor (first magnetic sensor); 22, 24: idler gear (first idler gear); 32, 34: idler gear (second idler gear); 40, 40B: first secondary shaft; 42: driven gear (first driven gear); 46: magnetic sensor (second magnetic sensor); 50, 50B: second secondary shaft; 52: driven gear (second driven gear); 56: magnetic sensor (third magnetic sensor); 70: main base (magnetic shield); Mg1: magnet (first magnet); Mg2: magnet (second magnet); Mg3: magnet (third magnet); X: X-axis direction; Y: Y-axis direction; Z: Z-axis direction (axial direction of the main shaft).

Claims

1. An absolute encoder, comprising: a main shaft gear mounted on the main shaft and rotating together with the main shaft; a first magnet mounted on the main shaft and rotating together with the main shaft; a first magnetic sensor that detects a change in magnetic flux generated from the first magnet; an idler gear having a smaller number of teeth than the main shaft gear and rotating as the main shaft gear rotates; a first secondary shaft arranged parallel to the primary shaft; a first driven gear mounted on the first countershaft and meshing with the idler gear; a second magnet mounted on the first secondary shaft and rotating together with the first secondary shaft; a second magnetic sensor that detects a change in magnetic flux generated from the second magnet; a second secondary shaft arranged parallel to the primary shaft; a second driven gear mounted on the second secondary shaft, having a different number of teeth from that of the first driven gear and meshing with the idler gear; a third magnet mounted on the second secondary shaft and rotating together with the second secondary shaft; as well as The third magnetic sensor detects a change in magnetic flux generated from the third magnet.

2. The absolute encoder according to claim 1, wherein: The main shaft gear includes a first main shaft gear and a second main shaft gear with different numbers of teeth. The idler gear includes a first idler gear that rotates with the rotation of the first main shaft gear, and a second idler gear that rotates with the rotation of the second main shaft gear. The first driven gear is meshed with the first idler gear, The second driven gear meshes with the second idler gear.

3. The absolute encoder according to claim 1 or 2, wherein: The absolute encoder further includes a magnetic shield disposed between the first magnet, the second magnet, and the third magnet in the axial direction of the spindle to suppress transmission of magnetic flux.

4. The absolute encoder according to claim 3, wherein: The main shaft is the rotating shaft of the motor, The first magnet is disposed at a position closer to the main body of the motor than the second magnet and the third magnet in the axial direction of the main shaft.

5. The absolute encoder according to claim 1 or 2, wherein: The first magnet is magnetized along the radial direction of the main shaft. The second magnet and the third magnet are magnetized along the axial direction of the first auxiliary shaft and the second auxiliary shaft.

6. The absolute encoder according to claim 5, wherein: The first magnet is ring-shaped, and the main shaft is inserted through an opening of the first magnet. The first magnetic sensor is arranged outside the first magnet in the radial direction of the main shaft. The second magnet is disposed at an end portion of the first secondary shaft in the axial direction. The second magnetic sensor is arranged to face the second magnet in the axial direction of the first secondary shaft. The third magnet is arranged at an end portion of the second auxiliary shaft in the axial direction. The third magnetic sensor is arranged to face the third magnet in the axial direction of the second auxiliary shaft.

7. The absolute encoder according to claim 1, wherein: The idler gear has a smaller number of teeth than the first driven gear and the second driven gear.

8. The absolute encoder according to claim 2, wherein: The number of teeth of the first idler gear is less than the number of teeth of the first main shaft gear and the number of teeth of the first driven gear, The number of teeth of the second idler gear is less than the number of teeth of the second mainshaft gear and the number of teeth of the second driven gear.

Images