encoder

Abstract

To provide an encoder that can reduce the number of components.SOLUTION: An encoder 2 comprises: a rotary shaft 230; a first sensor 241 detecting the angle of rotation of the rotary shaft 230; a first gear 251; a second gear 252; a third gear 253 formed integrally with the second gear 252; a fourth gear 254; a second sensor 242 detecting the angle of rotation of the fourth gear 254; and a calculation unit 270. A first pair of the first gear 251 and the second gear 252, and a second pair of the third gear 253 and the fourth gear 254 are an eccentric oscillation speed reducer. The calculation unit 270 calculates the number of rotations Tm of the rotary shaft 230 on the basis of the angle of rotation detected by the second sensor 242.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an encoder, and particularly to an encoder for detecting the rotational position of a rotating shaft.

Background Art

[0002] As such an encoder, for example, the encoder described in Patent Document 1 below is known. The encoder described in Patent Document 1 includes a main shaft and two sub-shafts. In the encoder described in Patent Document 1, sensors are attached to each of the main shaft and the two sub-shafts. The sensor attached to the main shaft detects the rotational angle of the main shaft. Each of the two sensors attached to the two sub-shafts detects the rotational angle of the corresponding sub-shaft. The rotation of the main shaft is decelerated through a plurality of spur gears and a plurality of worm gears and transmitted to each of the two sub-shafts. Therefore, the sensors attached to each of the two sub-shafts detect the rotational angle of the sub-shaft decelerated with respect to the rotation of the main shaft.

[0003] According to such an encoder described in Patent Document 1, the rotational angle of the main shaft can be detected by the sensor attached to the main shaft, and by detecting the rotational angle of the sub-shaft decelerated with respect to the rotation of the main shaft, it is possible to detect how many rotations the main shaft (rotating shaft) has made (hereinafter, may be described as "the number of rotations of the rotating shaft").

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the encoder as described in Patent Document 1 above, for example, there is a demand to further reduce the number of parts such as gears and shafts.

[0006] Therefore, an object of the present invention is to provide an encoder capable of reducing the number of parts.

Means for Solving the Problems

[0007] The encoder according to the present invention includes a rotating shaft, a first sensor that detects the rotation angle of the rotating shaft, a fixed first gear having a plurality of first numbers of internal teeth on the rotating shaft side in the radial direction, and a plurality of second numbers of external teeth that are fewer than the internal teeth of the first gear on the side opposite to the rotating shaft side in the radial direction, and a second gear that rotates as the rotating shaft rotates, and a third gear that is integrally formed with the second gear on one side of the second gear in the axial direction of the rotating shaft and has a plurality of third numbers of external teeth on the side opposite to the rotating shaft side in the radial direction, and a fourth gear having a plurality of fourth numbers of internal teeth that are more than the external teeth of the third gear on the rotating shaft side in the radial direction, and a fourth gear that rotates as the third gear rotates, a second sensor that detects the rotation angle of the fourth gear, and a calculation unit. Each of the first pair of the first gear and the second gear and the second pair of the third gear and the fourth gear is an eccentric swing type reduction gear, and the calculation unit calculates the number of rotations of the rotating shaft based on the rotation angle detected by the second sensor.

[0008] Such an encoder may further include at least one of the following configurations.

[0009] The rotating shaft may include a crank portion that swings the second gear and the third gear. In this case, each of the first pair and the second pair may constitute a cycloid mechanism or a harmonic gear mechanism.

[0010] The first meshing position, in which a portion of the external teeth of the second gear meshes with a portion of the internal teeth of the first gear, moves sequentially along the circumferential direction of the first gear as the rotation of the rotation axis rotates, and when the first meshing position completes one rotation along the circumferential direction of the first gear, the second gear may rotate along the circumferential direction of the first gear by the difference in the number of teeth between the first gear and the second gear.

[0011] The second meshing position, in which a portion of the external teeth of the third gear meshes with a portion of the internal teeth of the fourth gear, moves sequentially along the circumferential direction of the fourth gear as the second and third gears rotate, and when the second meshing position completes one rotation along the circumferential direction of the fourth gear, the fourth gear may rotate along the circumferential direction by the difference in the number of teeth between the fourth gear and the third gear.

[0012] The aforementioned rotating shaft may be a hollow shaft.

[0013] The system may include a ring-shaped first magnet fixed to the rotating shaft. In this case, the first sensor may be a magnetic sensor that detects changes in the magnetic field generated by the first magnet.

[0014] When viewed from the axial direction of the rotating shaft, the second sensor may overlap the fourth gear. In this case, a ring-shaped second magnet may be fixed to the axial side of the fourth gear on the side of the second sensor, and the second sensor may be a magnetic sensor that detects changes in magnetism generated from the second magnet. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view showing the encoder in the first embodiment of the present invention, with the case and substrate visible through it. [Figure 2] This is a cross-sectional view in the axial direction of the encoder shown in Figure 1. [Figure 3]Figure 1 is a cross-sectional view of the encoder in the radial direction, showing the state when the main shaft is in a rotational position. [Figure 4] Figure 1 is a cross-sectional view of the encoder in the radial direction, showing the case where the main shaft is in a different rotational position than in Figure 3. [Figure 5] This is a perspective view showing the encoder in a second embodiment of the present invention, with the case and substrate visible through it. [Figure 6] Figure 5 is a cross-sectional view of the encoder in the axial direction. [Figure 7] This is a cross-sectional view along line VII-VII in Figure 6, showing the encoder shown in Figure 5. [Figure 8] This is a cross-sectional view along line VIII-VIII in Figure 6, showing the encoder shown in Figure 5. [Figure 9] This is a perspective view showing the encoder in the third embodiment of the present invention, with the case and substrate visible through it. [Figure 10] Figure 9 is a cross-sectional view of the encoder in the axial direction. [Figure 11] This is a cross-sectional view along the line XI-XI in Figure 10, showing the encoder shown in Figure 9. [Figure 12] Figure 9 shows the encoder, which is a cross-sectional view along the line XII-XII in Figure 10. [Figure 13] This is a perspective view showing the encoder in the fourth embodiment of the present invention, with the case and substrate visible through it. [Figure 14] Figure 13 is a cross-sectional view of the encoder in the axial direction. [Figure 15] This is a cross-sectional view along the line XV-XV in Figure 14, showing the encoder shown in Figure 13. [Figure 16] This is a schematic axial cross-sectional view showing a first modified example of the encoder shown in Figure 1. [Figure 17] Figure 16 is a schematic radial cross-sectional view of the encoder shown. [Figure 18] This is a perspective view showing a second modified example of the encoder shown in Figure 1, with the case and circuit board visible through the glass. [Figure 19] Figure 18 is a cross-sectional view of the encoder in the axial direction. [Modes for carrying out the invention]

[0016] The following examples illustrate embodiments for implementing the encoder according to the present invention, along with the accompanying drawings. The embodiments illustrated below are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved from the following embodiments without departing from its spirit. In addition, in the accompanying drawings, the dimensions of each component may be exaggerated or reduced, or hatching may be omitted, in order to facilitate understanding.

[0017] (First Embodiment) First, the encoder according to the first embodiment will be described.

[0018] Figure 1 is a perspective view showing the encoder in this embodiment, Figure 2 is a cross-sectional view of the encoder shown in Figure 1 in a certain reference state along the axial direction of the encoder's rotation axis (hereinafter simply referred to as "axial direction"), and Figure 3 is a radial cross-sectional view showing a part of the encoder shown in Figure 1 in the above reference state. The radial direction is the direction perpendicular to the axial direction.

[0019] As shown in Figures 1 to 3, the encoder 1 according to this embodiment mainly comprises a casing 110, a substrate 120, a reduction mechanism 100, a rotating shaft 130, a first sensor 141, and a second sensor 142. In Figure 1, the casing 110 and substrate 120 are shown as transparent, and for convenience, the transparent casing 110 and substrate 120 are shown with dashed lines.

[0020] The casing 110 has a substantially flattened rectangular parallelepiped shape in which the length in the axial direction is shorter than the length in the radial direction. A hole 110h is formed in the radial center of the casing 110, penetrating the casing 110 axially. The inner circumferential surface of the casing 110 that defines this hole 110h is formed in a shape that allows the rotating shaft 130 to be fitted into it. The casing 110 consists of a first portion 111 on one side in the axial direction and a second portion 112 on the other side. In this embodiment, the lengths of the first portion 111 and the second portion 112 are approximately equal in the axial direction, but are not limited to this. The first portion 111 and the second portion 112 are superimposed on each other in the axial direction and fixed together. A connector 121 is attached to the first portion 111.

[0021] The second portion 112 has a stepped inner surface 112i. That is, the inner surface 112i has a first inner surface 112iu located on the side of the first portion 111 in the axial direction, and a second inner surface 112id located on the opposite side of the first portion 111 in the axial direction. Viewed from the axial direction, the inner surfaces 112iu and 112id are concentric circles centered on the center 130c of the rotation axis 130, and the diameter of the second inner surface 112id is smaller than the diameter of the first inner surface 112iu. In this specification, the side closer to the center of the rotation axis in the radial direction is referred to as "inside," and the side further from the center of the rotation axis is referred to as "outside." Multiple first internal teeth 151it of number N1 are formed on the entire circumference of the second inner surface 112id. That is, the second portion 112 of the casing 110 is formed as a first gear 151 having multiple internal teeth 151it on the side of the rotation axis 130 in the radial direction. Thus, the first gear 151 is part of the casing 110 and is fixed to the casing 110. Alternatively, the first gear 151 may be made separate from the casing 110 and fixed to the casing 110.

[0022] The substrate 120 is fixed to the casing 110 in the axial direction at at least one of the first portion 111 and the second portion 112 of the casing 110. The rotation shaft 130 passes through the approximate center of the substrate 120 in the radial direction. Two sensors (first sensor 141, second sensor 142) are mounted on the surface of the substrate 120 on the second portion 112 side. In this embodiment, sensors 141 and 142 are positioned on opposite sides of the center 130c of the rotation shaft 130, but the positional relationship of sensors 141 and 142 is not limited to this. As will be described later, the first sensor 141 detects the magnetism generated from the first magnet 161, and the second sensor 142 detects the magnetism generated from the second magnet 162, so it is preferable to position each sensor in a position that makes it easy to detect the magnetism of the magnet to be detected. A connector 121 is connected to the surface of the substrate 120 on the first portion 111 side. External power may be supplied to sensors 141 and 142 and the calculation unit 170 (described later) via the terminals connected to this connector 121, and the data calculated by the calculation unit 170 may be output to the outside.

[0023] The rotating shaft 130 is fitted into a hole 110h in the casing 110 and is rotatably supported by the casing 110. In this embodiment, the rotating shaft 130 includes a shaft body 131 and a crank portion 132. The shaft body 131 is formed in a circular ring shape with the center 130c of the rotating shaft 130 as viewed from the axial direction. In this embodiment, the shaft body 131 is formed in a cylindrical shape, i.e., hollow, and has an inner circumferential surface 131i that extends axially with the center 130c as the center. That is, in this embodiment, the rotating shaft 130 is a hollow shaft. Another rotating shaft (for example, the main shaft of a motor) may be attached to the inner circumferential surface 131i of the shaft body 131, for example by press-fitting. By attaching another rotating shaft to the rotating shaft 130 in this way, the present invention functions as an encoder for detecting the amount of rotation of another rotating body.

[0024] The crank portion 132 is formed on the outer circumferential surface of the shaft body 131. The crank portion 132 may be formed integrally with the shaft body 131, or it may be formed separately and then fixed to the shaft body 131. In the axial direction, at least a part of the crank portion 132 and at least a part of the second gear 152, which will be described later, are at the same position (height). Figure 3 is a cross-sectional view along the radial direction in the axial portion where at least a part of the crank portion 132 and at least a part of the second gear 152 are located. As shown in Figure 3, focusing on the portion 132of of the outer circumferential surface of the rotating shaft 130 on which the crank portion 132 is formed (hereinafter, for convenience, referred to as the "crank-forming surface 132of"), the crank portion 132 includes an eccentric portion 132a, which is a surface that is radially eccentric with respect to the center 130c of the rotating shaft 130 (i.e., the center of the shaft body 131). The eccentric portion 132a is the portion (surface) where the radial distance RL from the center 130c to the crank forming surface 132of is longer than that of other parts of the crank forming surface 132of (i.e., the distance RL is the maximum). It is sufficient that at least the portion of the rotating shaft 130 that contacts the second gear 152 is eccentric.

[0025] A second gear 152 is supported at the position of the crank-forming surface 132of in the axial direction, so as not to change its position in the axial direction. In this embodiment, the second gear 152 is a spur gear. A through hole, whose shape generally corresponds to the shape of the crank-forming surface 132of, runs through the radial center of the second gear 152 along the axial direction. The crank portion 132 is inserted through this through hole of the second gear 152. A ring-shaped first magnet 161 is fixed to the outer circumferential surface of the crank portion 132. That is, the ring-shaped first magnet 161 is fixed to the rotating shaft 130.

[0026] In this embodiment, as shown in Figure 2, the first sensor 141 described above overlaps with the first magnet 161 fixed to the rotation shaft 130 when viewed from the radial direction. However, the first sensor 141 does not necessarily have to overlap with the first magnet 161 when viewed from the radial direction. In this embodiment, the first sensor 141 is configured as a magnetic sensor. The first sensor 141 detects that the magnetism generated from the first magnet 161 changes as the first magnet 161 rotates in conjunction with the rotation of the rotation shaft 130, converts this change in the magnetism of the first magnet 161 into an electrical signal, and outputs it to a calculation unit 170 provided on the substrate 120, for example. When the first sensor 141 is configured as a magnetic sensor, it is not particularly limited to magnetic sensors, but for example, a sensor using a coil, a sensor using a reed switch, a sensor using a Hall element, and a sensor using a magnetoresistive element can be used. The same applies when other sensors described later are configured as magnetic sensors. Furthermore, the first sensor 141 is not limited to a magnetic sensor. If the first sensor 141 is composed of a sensor other than a magnetic sensor, such as an optical sensor, the first magnet 161 is unnecessary because a slit disc or the like is used for the rotating body. Also, when using a sensor with a magnetoresistive element and a gear made of magnetic material, the magnet can be placed on a fixed part such as a substrate instead of the first magnet 161 provided on the rotating shaft. The calculation unit 170 may be composed of a CPU (Central Processing Unit), for example, and acquires the above electrical signal output from the first sensor 141 and calculates the rotation angle θ of the rotating shaft 130. sensor1 The first sensor 141 calculates the rotation angle θ of the rotation axis 130 via the calculation unit 170. sensor1 It detects.

[0027] The eccentric portion 132a of the crank portion 132 is in slidable contact with the inner circumferential surface 152if of the second gear 152 that defines the through hole. At least one of the eccentric portion 132a and the inner circumferential surface 152if of the second gear 152 may be coated to improve wear resistance and sliding properties between the eccentric portion 132a and the inner circumferential surface 152if. On the outer circumferential surface of the second gear 152 (i.e., the surface on the radial side of the second gear 152 opposite to the rotation axis 130), a plurality of external teeth 152ot, fewer than the first number N1, are formed around its entire circumference. The second gear 152 is positioned inside the internal teeth 151it of the first gear 151 and is surrounded by the internal teeth 151it of the first gear 151 around its entire circumference. Each of the multiple external teeth 152ot can mesh with each of the multiple internal teeth 151it of the first gear 151.

[0028] As the rotating shaft 130 rotates around the center 130c, the eccentric portion 132a of the crank portion 132 also rotates together with the rotating shaft 130 around the center 130c, and the second gear 152 oscillates as a result of this rotation of the eccentric portion 132a. This oscillation of the second gear 152 causes the external teeth 152ot, which lie on a straight line SL extending radially from the center 130c through the eccentric portion 132a, to mesh with the internal teeth 151it, which lie on the straight line SL. The straight line SL is shown as a dashed line in Figure 3. Hereinafter, the position where a part of the external teeth 152ot of the second gear 152 meshes with a part of the internal teeth 151it of the first gear 151 will be referred to as the meshing position EP. The meshing position EP lies on the straight line SL.

[0029] As shown in Figure 4, when the rotating shaft 130 rotates by a predetermined angle from the state in Figure 3, that is, when the eccentric portion 132a of the crank portion 132 rotates by a predetermined angle from the state in Figure 3, the meshing position EP also moves by the same angle along the circumferential direction of the first gear 151. In this way, the meshing position EP moves sequentially along the circumferential direction of the first gear 151 as the rotating shaft 130 rotates. When the rotating shaft 130 completes one rotation, the meshing position EP completes one rotation along the circumferential direction of the first gear 151. Here, as described above, the first number N1 of the internal teeth 151it of the first gear 151 is greater than the second number N2 of the external teeth 152ot of the second gear 152. Therefore, when the meshing position EP completes one rotation along the circumferential direction of the first gear 151, that is, when the rotating shaft 130 completes one rotation, the second gear 152 rotates relative to the first gear 151 along the circumferential direction by the difference in the number of teeth between the first gear N1 and the second gear N2. Thus, the reduction ratio Gr of the second gear 152 with respect to the rotating shaft 130 can be expressed by the following equation (1). TIFF0007848436000001.tif11166 For example, if the number of teeth of the first gear 151 (first number N1) is 101 and the number of teeth of the second gear 152 (second number N2) is 100, then the reduction ratio Gr of the second gear 152 with respect to the rotating shaft 130 is 100. Note that the rotation direction of the second gear 152 is opposite to the rotation direction of the rotating shaft 130.

[0030] Thus, the first gear 151 and the second gear 152 are configured as an eccentric oscillating type reduction gear. More specifically, the first gear 151 and the second gear 152 function as a reduction gear 100 that constitutes a hypocycloid mechanism, or more precisely, an involute gear type hypocycloid mechanism.

[0031] As shown in Figure 1, a ring-shaped second magnet 162 is fixed to the substrate 120 side of the second gear 152 in the axial direction. As shown in Figure 2, the second sensor 142 described above overlaps with the second gear 152 when viewed from the axial direction, and the second magnet 162 is located between the second gear 152 and the second sensor 142 in the axial direction. However, the positional relationship between the second sensor 142, the second gear 152, and the second magnet 162 is not limited to this. In this embodiment, the second sensor 142 is configured as a magnetic sensor. The second sensor 142 detects that the magnetism generated from the second magnet 162 changes as the second magnet 162 rotates in conjunction with the rotation of the second gear 152, and converts this change in the magnetism of the second magnet 162 into an electrical signal which is output to, for example, the calculation unit 170. Furthermore, the second sensor 142 is not limited to a magnetic sensor. If the second sensor 142 is composed of a sensor other than a magnetic sensor, such as an optical sensor, the second magnet 162 is unnecessary because a slit disc or the like is used for the rotating body. Also, if a sensor using a magnetoresistive element and a gear made of magnetic material are used, the magnet is unnecessary. The calculation unit 170 acquires the above electrical signal output from the second sensor 142 and calculates the rotation angle θ of the second gear 152. sensor2 The calculation unit 170 calculates the rotation angle θ of the second gear 152. In other words, in this embodiment, the second sensor 142, via the calculation unit 170, calculates the rotation angle θ of the second gear 152. sensor2 It is detecting [something].

[0032] As described above, the second gear 152 rotates along the circumferential direction of the first gear 151 by the difference in the number of teeth between the first gear N1 and the second gear N2 when the rotating shaft 130 rotates once. Therefore, the reduction ratio Gr of the second gear 152 can be expressed by the above equation (1). For this reason, the rotation angle θ of the second gear 152 when the rotating shaft 130 rotates once is gear2(1) This can be expressed by the following equation (2). TIFF0007848436000002.tif11166For example, when the reduction ratio Gr is 100, when the rotating shaft 130 makes one rotation (360° rotation), the second gear 152 rotates 3.6° in the opposite direction to the rotating shaft 130. Therefore, the rotation angle θ of the second gear 152 detected by the second sensor 142 via the calculation unit 170 sensor2 By dividing by the value obtained from the above formula (2), the number of rotations Tm of the rotating shaft 130 (how many rotations the rotating shaft has made) can be calculated. That is, the number of rotations Tm can be calculated based on the following formula (3). TIFF0007848436000003.tif11166Also, the rotation angle θ of the rotating shaft 130 considering the number of rotations of the rotating shaft 130 is the rotation angle θ of the rotating shaft 130 sensor1 Can be expressed by the following formula (4) using it. TIFF0007848436000004.tif8166In formula (4), INT means rounding down the decimal part.

[0033] The calculation unit 170 calculates the number of rotations Tm and the rotation angle θ of the rotating shaft 130 based on the data of the rotation angle θ of the rotating shaft 130 sensor1 And the data of the rotation angle θ of the second gear 152 sensor2 And the above formulas (1) to (4). Thus, according to the encoder 1, the number of rotations Tm of the rotating shaft 130 can also be detected together with the rotation angle of the rotating shaft 130. Note that the detection upper limit of the number of rotations of the encoder 1 corresponds to the reduction ratio Gr. Therefore, for example, when the reduction ratio is 100, the detection upper limit of the number of rotations Tm is 100 rotations.

[0034] As described above, the encoder 1 according to the present embodiment includes the rotating shaft 130 and the rotation angle θ of the rotating shaft 130 sensor1A first sensor 141 for detecting, a fixed first gear 151 having a plurality of first number N1 internal teeth 151it on the radial side of the rotation axis 130, a second gear 152 having a plurality of second number N2 external teeth 152ot on the radial side opposite to the rotation axis 130, fewer than the internal teeth 151it of the first gear 151, and rotating with the rotation of the rotation axis 130, and the rotation angle θ of the second gear 152 sensor2 The encoder 1 includes a second sensor 142 for detecting the rotation angle θ detected by the second sensor 142, and a calculation unit 170. In this encoder 1, the first gear 151 and the second gear 152 are eccentric oscillating type reducers, and the calculation unit 170 calculates the rotation angle θ detected by the second sensor 142. sensor2 Based on this, the number of rotations Tm of the axis of rotation is calculated.

[0035] In order to increase the number of rotations of the detectable axis, a large reduction ratio is required, and generally, the larger the required reduction ratio, the larger the increase in the number of gears tends to be. However, in the encoder 1 according to this embodiment having the above configuration, a large reduction ratio (for example, a reduction ratio of 100) can be obtained with two gears (first gear 151 and second gear 152). Therefore, even when a large reduction ratio is required, the increase in the number of gears can be suppressed. In addition, in the encoder 1 according to this embodiment, only one axis, the rotating axis 130, is sufficient to constitute the encoder 1. Thus, in the encoder 1 according to this embodiment, it is possible to reduce the number of parts such as gears and axes, and by reducing the number of parts, it is possible to reduce the manufacturing cost of the encoder, simplify assembly, and make it smaller (smaller diameter, thinner). Furthermore, in this embodiment, the first gear 151 and the second gear 152 can be pre-unitized as an involute gear type hypocycloid mechanism and used in the assembly process, so the number of parts to be assembled can be further reduced, and the encoder can be assembled more easily.

[0036] Furthermore, in this embodiment, since a hypocycloid mechanism is used as the reduction mechanism, it is easy to hollow out the rotating shaft without increasing the size of the encoder.

[0037] Furthermore, by using a hypocycloid mechanism, as described above, it is possible to achieve a larger reduction ratio with fewer gears, thereby effectively increasing the upper limit of detection for the number of rotations of the rotating shaft.

[0038] In this embodiment, bearings may be placed between the outer circumferential surface of the rotating shaft 130 and the inner circumferential surface of the casing 110, and between the outer circumferential surface of the crank portion 132 and the inner circumferential surface of the second gear 152.

[0039] (Second Embodiment) Next, the encoder according to the second embodiment will be described.

[0040] Figure 5 is a perspective view showing the encoder in this embodiment, Figure 6 is a cross-sectional view along the axial direction in a reference state of the encoder shown in Figure 5, Figure 7 is a cross-sectional view of the encoder shown in Figure 5 along the line VII-VII in Figure 6, and Figure 8 is a cross-sectional view of the encoder shown in Figure 5 along the line VIII-VIII in Figure 6.

[0041] As shown in Figures 5 to 8, the encoder 2 according to this embodiment mainly comprises a casing 210, a substrate 220, a reduction mechanism 200, a rotating shaft 230, a first sensor 241, and a second sensor 242. In Figure 5, the casing 210 and substrate 220 are shown as transparent, and for convenience, the transparent casing 210 and substrate 220 are shown with dashed lines.

[0042] The casing 210 has a substantially flattened rectangular parallelepiped shape in which the axial length is shorter than the radial length. A hole 210h is formed in the radial center of the casing 210, penetrating the casing 210 axially. The inner circumferential surface of the casing 210 defining this hole 210h is formed in a shape that allows the rotating shaft 230 to be fitted into it. The casing 210 consists of a first portion 211 on one side in the axial direction and a second portion 212 on the other side in the axial direction. In this embodiment, the axial length of the first portion 211 is shorter than the axial length of the second portion 212, but is not limited to this. The first portion 211 and the second portion 212 are stacked axially and fixed to each other. A connector 221 is attached to the second portion 212.

[0043] The second portion 212 has a stepped inner surface 212i. The inner surface 212i has a first inner surface 212iu located on the side of the first portion 211 in the axial direction, a second inner surface 212id located on the opposite side of the first portion 211 in the axial direction, and a connecting surface 212is connecting the first inner surface 212iu and the second inner surface 212id. The connecting surface 212is is a plane parallel to the radial direction. Viewed from the axial direction, the inner surfaces 212iu and 212id are concentric circles centered on the center 230c of the rotation axis 230, and the diameter of the second inner surface 212id is smaller than the diameter of the first inner surface 212iu. Multiple first internal teeth 251it of number N1 are formed on the entire circumference of the second inner surface 212id. In other words, the second portion 212 of the casing 210 is formed as a first gear 251 having a plurality of internal teeth 251it on the radial axis 230 side. Thus, the first gear 251 is part of the casing 210 and is fixed to the casing 210. Alternatively, the first gear 251 may be made as a separate component from the casing 210 and fixed to the casing 210.

[0044] The substrate 220 is fixed to the casing 210 in the axial direction at at least one of the first portion 211 and the second portion 212 of the casing 210. The rotation axis 230 passes through the approximate center of the substrate 220 in the radial direction. Two sensors (first sensor 241 and second sensor 242) are mounted on the surface of the substrate 220 on the second portion 212 side. In this embodiment, sensors 241 and 242 are positioned on opposite sides of the center 230c of the rotation axis 230, but the positional relationship of sensors 241 and 242 is not limited to this. As will be described later, the first sensor 241 detects the magnetism generated from the first magnet 261, and the second sensor 242 detects the magnetism generated from the second magnet 262, so it is preferable to position each sensor in a position that makes it easy to detect the magnetism of the magnet to be detected. A connector 221 is also connected to the surface of the substrate 220 on the second portion 212 side. External power may be supplied to sensors 241 and 242 and the calculation unit 270 (described later) via the terminals connected to this connector 221, and the data calculated by the calculation unit 270 may be output to the outside.

[0045] The rotating shaft 230 is fitted into a hole 210h in the casing 210 and is rotatably supported by the casing 210. In this embodiment, the rotating shaft 230 includes a shaft body 231 and a crank portion 232. The shaft body 231 is formed in a circular ring shape with the center 230c of the rotating shaft 230 as viewed from the axial direction. In this embodiment, the shaft body 231 is formed in a cylindrical shape, i.e., hollow, and has an inner circumferential surface 231i that extends axially with the center 230c as the center. That is, in this embodiment, the rotating shaft 230 is a hollow shaft. Another rotating shaft (for example, the main shaft of a motor) may be attached to the inner circumferential surface 231i of the shaft body 231, for example by press-fitting. By attaching another rotating shaft to the rotating shaft 230 in this way, the present invention functions as an encoder for detecting the amount of rotation of another rotating body.

[0046] The crank portion 232 is formed on the outer circumferential surface of the shaft body 231. The crank portion 232 may be formed integrally with the shaft body 231, or it may be formed separately and then fixed to the shaft body 231. In the axial direction, at least a portion of the crank portion 232 and at least a portion of the second gear 252 (described later) are at the same position (height), and at least a portion of the crank portion 232 and at least a portion of the third gear 253 (described later) are at the same position (height). Figure 7 is a radial cross-sectional view of the axial portion where at least a portion of the crank portion 232 and at least a portion of the second gear 252 are located. Figure 8 is a radial cross-sectional view of the axial portion where at least a portion of the crank portion 232 and at least a portion of the third gear 253 are located. As shown in Figures 7 and 8, focusing on the portion 232of of the outer circumferential surface of the rotating shaft 230 where the crank portion 232 is formed (hereinafter, for convenience, referred to as the "crank-forming surface 232of"), the crank portion 232 includes an eccentric portion 232a, which is a surface that is radially eccentric with respect to the center 230c of the rotating shaft 230 (i.e., the center of the shaft body 231). The eccentric portion 232a is the portion (surface) where the radial distance RL from the center 230c to the crank-forming surface 232of is longer than that of other parts of the crank-forming surface 232of (i.e., where the distance RL is maximum). Note that it is sufficient for at least the portion of the rotating shaft 230 that contacts the second gear 252 and the third gear 253 to be eccentric.

[0047] The second gear 252 and the third gear 253 are supported at the crank forming surface 232of in the axial direction so as not to change the axial position of the crank portion 232. In this embodiment, the second gear 252 and the third gear 253 are integrally formed spur gears. For convenience, the second gear 252 and the third gear 253 may be collectively referred to as "gears 252, 253". The third gear 253 is integrally formed with the second gear 252 on one side of the second gear 252 in the axial direction and is on the substrate 220 side in the axial direction relative to the second gear 252. The outer circumferential surface of the second gear 252 faces the inner surface 212id of the second portion 212 of the casing 210 in the radial direction. That is, the outer circumferential surface of the second gear 252 faces the internal teeth 251it of the first gear 251 in the radial direction. The outer circumferential surface of the second gear 252 has a second number N2 external teeth 252ot formed thereon. On the other hand, the outer circumferential surface of the third gear 253 faces the inner surface 212iu of the second portion 212 of the casing 210 via a fourth gear 254, which will be described later, in the radial direction. The outer circumferential surface of the third gear 253 has a third number N3 external teeth 253ot formed thereon. A through hole, whose shape generally corresponds to the shape of the crank forming surface 232of of the crank portion 232, passes through the radial center of the gears 252 and 253 along the axial direction. The crank portion 232 is inserted through this through hole. A ring-shaped first magnet 261 is fixed to the outer circumferential surface of the crank portion 232. That is, a ring-shaped first magnet 261 is fixed to the rotating shaft 230.

[0048] In this embodiment, the first sensor 241 described above is configured as a magnetic sensor. The first sensor 241 detects that the magnetism generated by the first magnet 261 changes as the first magnet 261 rotates in conjunction with the rotation of the rotation shaft 230, converts this change in the magnetism of the first magnet 261 into an electrical signal, and outputs it to a calculation unit 270 provided on, for example, the substrate 220. Note that the first sensor 241 is not limited to a magnetic sensor; if the first sensor 241 is configured as a sensor other than a magnetic sensor, such as an optical sensor, the first magnet 261 is unnecessary because a slit disc or the like is used for the rotating body. Also, when using a sensor with a magnetoresistive element and gears made of magnetic material, the magnet can be placed on a fixed part such as a substrate instead of the first magnet 261 provided on the rotation shaft 230. The calculation unit 270 acquires the electrical signal output from the first sensor 241 and the rotation angle θ of the rotation shaft 230. sensor1 The first sensor 241 calculates the rotation angle θ of the rotation axis 230 via the calculation unit 270. sensor1 It detects.

[0049] The eccentric portion 232a of the crank portion 232 is in slidable contact with the inner circumferential surfaces 252if and 253if (the inner circumferential surface 252if of the second gear 252 and the inner circumferential surface 253if of the third gear 253) that define the through holes of the gears 252 and 253. At least one of the eccentric portion 232a and the inner circumferential surfaces 252if and 253if of the gears 252 and 253 may be coated to improve wear resistance and sliding properties between the eccentric portion 232a and the inner circumferential surfaces 252if and 253if.

[0050] As shown in Figure 7, the outer circumferential surface of the second gear 252 (i.e., the surface of the second gear 252 opposite to the rotation axis 230 in the radial direction) has a plurality of second external teeth 252ot, which are fewer than the first number N1, formed around its entire circumference. The second gear 252 is positioned inside the internal teeth 251it of the first gear 251 and is surrounded by the internal teeth 251it of the first gear 251 around its entire circumference. Each of the plurality of external teeth 252ot can mesh with each of the plurality of internal teeth 251it of the first gear 251.

[0051] As the rotating shaft 230 rotates around the center 230c, the eccentric portion 232a of the crank portion 232 also rotates together with the rotating shaft 230 around the center 230c, and the gears 252 and 253 oscillate as a result of the rotation of this eccentric portion 232a. Due to the oscillation of gears 252 and 253, the external teeth 252ot of the second gear 252, which lie on a straight line SL extending radially from the center 230c through the eccentric portion 232a, mesh with the internal teeth 251it of the first gear 251, which lie on the straight line SL. The straight line SL is shown as a dashed line in Figures 7 and 8. Hereinafter, the position where a part of the external teeth 252ot of the second gear 252 meshes with a part of the internal teeth 251it of the first gear 251 will be referred to as the first meshing position EP1. The first meshing position EP1 lies on the straight line SL.

[0052] When the rotating shaft 230 rotates by a predetermined angle from the state shown in Figure 7, that is, when the eccentric portion 232a of the crank portion 232 rotates by a predetermined angle from the state shown in Figure 7, the first meshing position EP1 also moves by the same angle along the circumferential direction of the first gear 251. In this way, the first meshing position EP1 moves sequentially along the circumferential direction of the first gear 251 as the rotating shaft 230 rotates. When the rotating shaft 230 completes one rotation, the first meshing position EP1 completes one rotation along the circumferential direction of the first gear 251. Here, as described above, the first number N1 of the internal teeth 251it of the first gear 251 is greater than the second number N2 of the external teeth 252ot of the second gear 252. Therefore, when the first meshing position EP1 completes one rotation along the circumferential direction of the first gear 251, that is, when the rotating shaft 230 completes one rotation, the second gear 252 (i.e., gears 252 and 253) rotates relative to the first gear 251 along the circumferential direction of the first gear 251 by the difference in the number of teeth between the first number N1 and the second number N2. Therefore, the reduction ratio Gr2 of the second gear 252 with respect to the rotating shaft 230 can be expressed by the following equation (5). TIFF0007848436000005.tif11166 For example, if the number of teeth N1 of the first gear 251 is 101 and the number of teeth N2 of the second gear 252 is 100, then the reduction ratio Gr of the second gear 252 with respect to the rotating shaft 230 is 100. Note that the rotation direction of the second gear 252 is opposite to the rotation direction of the rotating shaft 230.

[0053] As shown in Figure 6, a fourth gear 254, formed as a spur gear, is mounted on the connecting surface 212is of the second portion 212 of the casing 210. The fourth gear 254 is formed in a ring shape and is positioned so that the center 230c of the rotating shaft 230 is at its center. The fourth gear 254 is supported by the casing 210 in a configuration not shown so that its position in the axial direction does not change. A through hole 254h is formed in the radial center of the fourth gear 254, through which the rotating shaft 230 passes, and the first magnet 261 described above is positioned inside the through hole 254h. The inner circumferential surface of the fourth gear 254 is notched from the inside to the outside. Due to this notch, the fourth gear 254 includes a ring-shaped outer peripheral edge portion 254A and a disc-shaped disc portion 254B that extends inward from the portion of the outer peripheral edge portion 254A on the substrate 220 side in the axial direction. On the inner circumferential surface of the outer peripheral edge portion 254A, there are four internal teeth 254it, numbered N4, which is greater than the third number N3 of the external teeth 253ot of the third gear 253. That is, the fourth gear 254 has multiple internal teeth 254it, numbered N4, on the rotation axis 230 side in the radial direction, which is greater than the external teeth 253ot of the third gear 253. In the radial direction, the internal teeth 254it of the fourth gear 254 face the external teeth 253ot of the third gear 253. The external teeth 253ot of the third gear 253 are surrounded by the internal teeth 254it of the fourth gear 254 around their entire circumference. A ring-shaped second magnet 262 is fixed to the axial surface of the disc portion 254B of the fourth gear 254 that faces the substrate 220.

[0054] As shown in Figure 8, the outer circumferential surface 254of of the fourth gear 254 is in slidable contact with the inner surface 212iu of the second portion 212 of the casing 210. At least one of the outer circumferential surface 254of of the fourth gear 254 and the inner surface 212iu of the casing 210 may be coated to improve wear resistance and sliding properties between the fourth gear 254 and the casing 210. Each of the multiple external teeth 253ot of the third gear 253 can mesh with each of the multiple internal teeth 254it of the fourth gear 254. In this embodiment, the external teeth 253ot of the third gear 253, which are on a straight line SL, mesh with the internal teeth 254it of the fourth gear 254, which are on a straight line SL. Hereinafter, the position where a portion of the external teeth 253ot of the third gear 253 meshes with a portion of the internal teeth 254it of the fourth gear 254 will be referred to as the second meshing position EP2. The second meshing position EP2 lies on the straight line SL.

[0055] As the rotating shaft 230 rotates once, gears 252 and 253 rotate relative to the first gear 251 along the circumferential direction of the first gear 251 by the difference in the number of teeth between the first number N1 and the second number N2. Consequently, the second meshing position EL2 also moves along the circumferential direction of the fourth gear 254 from the state in Figure 8 by an angle equal to the difference in the number of teeth between the first number N1 and the second number N2. In this way, the second meshing position EP2 moves sequentially along the circumferential direction of the fourth gear 254 as gears 252 and 253 rotate. When gears 252 and 253 rotate once along the circumferential direction of the first gear 251, the second meshing position EP2 completes one rotation along the circumferential direction of the fourth gear 254. Here, as described above, the fourth number N4 of the internal teeth 254it of the fourth gear 254 is greater than the third number N3 of the external teeth 253ot of the third gear 253. Therefore, when the second meshing position EP2 completes one rotation along the circumferential direction of the fourth gear 254, that is, when gears 252 and 253 complete one rotation along the circumferential direction of the first gear 251, the fourth gear 254 rotates relative to the casing 210 along the circumferential direction of the fourth gear 254 by the difference in the number of teeth between the fourth gear N4 and the third gear N3. Thus, the reduction ratio Gr4 of the fourth gear 254 relative to gears 252 and 253 can be expressed by the following equation (6). TIFF0007848436000006.tif11166 For example, if the number of teeth of the fourth gear 254 (the fourth number N4) is 102 and the number of teeth of the third gear 253 (the third number N3) is 101, then the reduction ratio Gr4 of the fourth gear 254 relative to gears 252 and 253 is 101. Note that the rotation direction of the fourth gear 254 is opposite to that of gears 252 and 253, and is the same as the rotation direction of the rotation axis 230.

[0056] Furthermore, the reduction ratio Gr of the fourth gear 254 relative to the rotating shaft 230 can be determined by multiplying Gr2, which is obtained by equation (5), by Gr4, which is obtained by equation (6). Therefore, if the reduction ratio Gr2 of gears 252 and 253 relative to the rotating shaft 230 is, for example, 100, and the reduction ratio Gr4 of the fourth gear 254 relative to gears 252 and 253 is, for example, 101, then the reduction ratio Gr is 10100, which is an even larger reduction ratio than that of the encoder 1 according to the first embodiment.

[0057] Thus, the first pair of the first gear 251 and the second gear 252, and the second pair of the third gear 253 and the fourth gear 254 are each eccentric oscillating reducers, and moreover, the first gear 251, gears 252 and 253, and the fourth gear 254 function as a reduction mechanism 200 that constitutes an involute gear type hypocycloid mechanism.

[0058] As shown in Figure 6, the second sensor 242 described above overlaps with the fourth gear 254 when viewed from the axial direction, and the second magnet 262 is located between the fourth gear 254 and the second sensor 242 in the axial direction. However, the positional relationship between the second sensor 242, the fourth gear 254, and the second magnet 262 is not limited to this. In this embodiment, the second sensor 242 is configured as a magnetic sensor. The second sensor 242 detects that the magnetism generated from the second magnet 262 changes as the second magnet 262 rotates in conjunction with the rotation of the fourth gear 254, and converts this change in the magnetism of the second magnet 262 into an electrical signal which is output to, for example, the calculation unit 270. Note that the second sensor 242 is not limited to a magnetic sensor, and if the second sensor 242 is configured as a sensor other than a magnetic sensor, such as an optical sensor, the second magnet 262 is unnecessary because a slit disc or the like is used for the rotating body. Furthermore, a magnet is not required when using a sensor with a magnetoresistive element and a gear made of magnetic material. The calculation unit 270 acquires the above electrical signal output from the second sensor 242 and calculates the rotation angle θ of the fourth gear 254. sensor2 The calculation unit 270 calculates the rotation angle θ of the fourth gear 254. In other words, in this embodiment, the second sensor 242, via the calculation unit 270, calculates the rotation angle θ of the fourth gear 254. sensor2 It detects.

[0059] As described above, the reduction ratio Gr of the fourth gear 254 relative to the rotating shaft 230 can be determined by multiplying the reduction ratio Gr2 of gears 252 and 253 relative to the rotating shaft 230 by the reduction ratio Gr4 of the fourth gear 254 relative to gears 252 and 253. Therefore, the rotation angle θ of the fourth gear 254 when the rotating shaft 230 completes one rotation is... gear4(1) This can be expressed by the following equation (7). TIFF0007848436000007.tif11166 Therefore, the rotation angle θ of the fourth gear 254 detected by the second sensor 242 via the calculation unit 270. sensor2 By dividing by the value obtained from equation (7) above, the number of rotations Tm of the rotating shaft 230 can be calculated. That is, the number of rotations Tm can be calculated based on the following equation (8). TIFF0007848436000008.tif8166 Furthermore, the rotation angle θ of the rotation axis 230, taking into account the number of rotations of the rotation axis 230, can be obtained by substituting Tm, obtained by equation (8), into equation (4) above.

[0060] The calculation unit 270 calculates the rotation angle θ of the rotation axis 230. sensor1 The data and the rotation angle θ of the fourth gear 254 sensor2 Based on the data and the equations (4), (5) to (8) above, the rotation count Tm and rotation angle θ of the rotating shaft 230 are calculated. In this way, the encoder 2 can detect both the rotation angle and the rotation count Tm of the rotating shaft 230. The upper limit of the rotation count detection by the encoder 2 corresponds to the product of the reduction ratio Gr2 and the reduction ratio Gr4. Therefore, for example, if Gr2 is 100 and Gr4 is 101, the upper limit of the rotation count Tm detection is 10100 rotations.

[0061] As described above, the encoder 2 according to this embodiment includes a rotating shaft 230 and a rotation angle θ of the rotating shaft 230. sensor1 A first sensor 241 for detecting a first gear 251 having a plurality of first number N1 internal teeth 251it on the radial side of the rotation axis 230, a second gear 252 having a plurality of second number N2 external teeth 252ot fewer than the internal teeth 251it of the first gear 251 on the radial side opposite to the rotation axis 230, and rotating in conjunction with the rotation of the rotation axis 230, a third gear 253 formed integrally with the second gear 252 on one side of the second gear 252 in the axial direction of the rotation axis 230, having a plurality of third number N3 external teeth 253ot on the radial side opposite to the rotation axis 230, a fourth gear 254 having a plurality of fourth number N4 internal teeth 254it more than the external teeth 253ot of the third gear 253 on the radial side of the rotation axis 230, and rotating in conjunction with the rotation of the third gear 253, and the rotation angle θ of the fourth gear 254 sensor2The encoder 2 includes a second sensor 242 for detecting the rotation angle θ and a calculation unit 270. In this encoder 2, the first pair of the first gear 251 and the second gear 252 and the second pair of the third gear 253 and the fourth gear 254 are eccentric oscillating type reducers, and the calculation unit 270 calculates the rotation angle θ detected by the second sensor 242. sensor2 Based on this, the number of rotations Tm of the rotation axis 230 is calculated.

[0062] In the encoder 2 according to this embodiment, which has the configuration described above, a large reduction ratio (for example, a reduction ratio of 100-100) can be obtained by four gears (first gear 251, second gear 252, third gear 253, and fourth gear 254). Therefore, even when a large reduction ratio is required, the increase in the number of gears can be kept to a minimum. In particular, the reduction mechanism 200 of encoder 2 can obtain a reduction ratio by multiplying the reduction ratio of the first pair of gears, the first gear 251 and the second gear 252, by the reduction ratio of the second pair of gears, the third gear 253 and the fourth gear 254. As a result, a larger reduction ratio can be achieved compared to, for example, encoder 1 according to the first embodiment, and as a result, the detection limit of the number of rotations of the rotating shaft can be increased compared to, for example, encoder 1 according to the first embodiment (see equation (8)). Furthermore, in encoder 2, since the second gear 252 and the third gear 253 are formed as an integrated gear, despite being able to achieve the large reduction ratio and large detection limit described above, the number of gears required is substantially only three. Furthermore, in encoder 2, only one shaft, the rotating shaft 230, is needed to constitute encoder 2. Thus, in encoder 2 according to this embodiment, it is possible to reduce the number of parts such as gears and shafts, and by reducing the number of parts, it is possible to reduce the manufacturing cost of the encoder, simplify assembly, and make it smaller (smaller diameter, thinner). In addition, in this embodiment, the first gear 251, the second gear 252, the third gear 253, and the fourth gear 254 can be pre-unitized as an involute gear type hypocycloid mechanism and used in the assembly process, so the number of parts to be assembled can be further reduced, and the encoder can be assembled more easily.

[0063] Furthermore, in this embodiment, since a hypocycloid mechanism is used as the reduction mechanism, it is easy to hollow out the rotating shaft without increasing the size of the encoder.

[0064] Furthermore, in this embodiment, by using a hypocycloid mechanism, it is possible to achieve a larger reduction ratio with fewer gears, as described above, thereby effectively increasing the upper limit of detection for the number of rotations of the rotating shaft.

[0065] In this embodiment, bearings may be placed between the outer circumferential surface of the rotating shaft 230 and the inner circumferential surface of the casing 210, and between the outer circumferential surface of the crank portion 232 and the inner circumferential surfaces of the gears 252 and 253.

[0066] (Third embodiment) Next, the encoder according to the third embodiment will be described.

[0067] Figure 9 is a perspective view showing the encoder in this embodiment, Figure 10 is a cross-sectional view along the axial direction shown in Figure 9 in a certain reference state, Figure 11 is a cross-sectional view along line XI-XI in Figure 10 showing the encoder shown in Figure 9, and Figure 12 is a cross-sectional view along line XII-XII in Figure 10 showing the encoder shown in Figure 9.

[0068] As shown in Figures 9 to 12, the encoder 3 according to this embodiment mainly comprises a casing 310, a substrate 320, a reduction mechanism 300, a rotating shaft 330, a first sensor 341, a second sensor 342, and a third sensor 343. The reduction mechanism 300 has a configuration in which two involute gear-type hypocycloid mechanisms are arranged in the axial direction. In Figure 9, the casing 310 and substrate 320 are shown transparently, and for convenience, the transparent casing 310 and substrate 320 are shown with dashed lines.

[0069] The casing 310 has a substantially flattened rectangular parallelepiped shape in which the axial length is shorter than the radial length. A hole 310h is formed in the radial center of the casing 310, penetrating the casing 310 axially. The inner circumferential surface of the casing 310 defining this hole 310h is formed in a shape that allows the rotating shaft 330 to be fitted into it. The casing 310 consists of a first portion 311 on one side in the axial direction and a second portion 312 on the other side. In this embodiment, the lengths of the first portion 311 and the second portion 312 are approximately equal in the axial direction, but are not limited to this. The first portion 311 and the second portion 312 are superimposed on each other in the axial direction and fixed together. A connector 321 is attached to the first portion 311.

[0070] The first portion 311 of the casing 310 has a stepped inner surface 311i. The inner surface 311i has a first inner surface 311id located on the side of the second portion 312 in the axial direction, and a second inner surface 311iu located on the opposite side of the second portion 312 in the axial direction. Viewed from the axial direction, the inner surfaces 311id and 311iu are concentric circles centered on the center 330c of the rotation axis 330, and the diameter of the first inner surface 311id is larger than the diameter of the second inner surface 311iu. Multiple first internal teeth 351it of number N1 are formed on the entire circumference of the second inner surface 311iu. That is, the first portion 311 of the casing 310 is formed as a first gear 351 having multiple internal teeth 351it on the side of the rotation axis 330 in the radial direction. Thus, the first gear 351 is part of the casing 310 and is fixed to the casing 310. Alternatively, the first gear 351 may be made separate from the casing 310 and fixed to the casing 310.

[0071] The second portion 312 of the casing 310 has a stepped inner surface 312i. The inner surface 312i has a first inner surface 312iu located on the side of the first portion 311 in the axial direction, and a second inner surface 312id located on the opposite side of the first portion 311 in the axial direction. Viewed from the axial direction, the inner surfaces 312iu and 312id are concentric circles centered on the center 330c of the rotation axis 330, and the diameter of the first inner surface 312iu is larger than the diameter of the second inner surface 312id. In this embodiment, the diameter of the first inner surface 312iu of the second portion 312 is approximately equal to the diameter of the first inner surface 311id of the first portion 311, and the inner surfaces 312iu and 311id are adjacent to each other in the axial direction with the substrate 320 in between. Furthermore, in this embodiment, the diameter of the second inner surface 312id of the second portion 312 is smaller than the diameter of the second inner surface 311iu of the first portion 311. Multiple third internal teeth 353it of number N3 are formed on the second inner surface 312id of the second portion 312 around its entire circumference. That is, the second portion 312 of the casing 310 is formed as a third gear 353 having multiple internal teeth 353it on the rotation axis 330 side in the radial direction. Thus, the third gear 353 is part of the casing 310 and is fixed to the casing 310. Alternatively, the third gear 353 may be a separate component from the casing 310 and fixed to the casing 310.

[0072] The substrate 320 is fixed to the casing 310 in the axial direction at at least one of the first portion 311 and the second portion 312 of the casing 310. The rotation axis 330 passes through the approximate center of the substrate 320 in the radial direction. One sensor (second sensor 342) is attached to the surface of the substrate 320 on the first portion 311 side. On the other hand, two sensors (first sensor 341 and third sensor 343) are attached to the surface of the substrate 320 on the second portion 312 side. In this embodiment, sensors 341 and 343 are positioned on opposite sides of the center 330c of the rotation axis 330, but the positional relationship of sensors 341 and 343 is not limited to this. As will be described later, the first sensor 341 detects the magnetism generated from the first magnet 361, and the third sensor 343 detects the magnetism generated from the third magnet 363, so it is preferable to position each sensor in a position that makes it easy to detect the magnetism of the magnet to be detected. Furthermore, a connector 321 is connected to the side of the circuit board 320 facing the first portion 311. External power is supplied to sensors 341, 342, 343 and the calculation unit 370 (described later) via terminals connected to this connector 321, and data calculated by the calculation unit 370 may be output to the outside.

[0073] The rotating shaft 330 is fitted into a hole 310h in the casing 310 and is rotatably supported by the casing 310. In this embodiment, the rotating shaft 330 includes a shaft body 331 and a crank portion 332. The shaft body 331 is formed in a circular ring shape with the center 330c of the rotating shaft 330 as viewed from the axial direction. In this embodiment, the shaft body 331 is formed in a cylindrical shape, i.e., hollow, and has an inner circumferential surface 331i extending axially with the center 330c as the center. That is, in this embodiment, the rotating shaft 330 is a hollow shaft. Another rotating shaft (for example, the main shaft of a motor) may be attached to the inner circumferential surface 331i of the shaft body 331, for example by press-fitting. By attaching another rotating shaft to the rotating shaft 330 in this way, the present invention functions as an encoder for detecting the amount of rotation of another rotating body.

[0074] The crank portion 332 is formed on the outer circumferential surface of the shaft body 331. The crank portion 332 may be formed integrally with the shaft body 331, or it may be formed separately and then fixed to the shaft body 331. In the axial direction, at least a portion of the crank portion 332 and at least a portion of the second gear 352 (described later) are at the same position (height), and at least a portion of the crank portion 332 and at least a portion of the fourth gear 354 (described later) are at the same position (height). Figure 11 is a radial cross-sectional view of the axial portion where at least a portion of the crank portion 332 and at least a portion of the second gear 352 are located. Figure 12 is a radial cross-sectional view of the axial portion where at least a portion of the crank portion 332 and at least a portion of the fourth gear 354 are located. As shown in Figures 11 and 12, focusing on the portion 332of of the outer circumferential surface of the rotating shaft 330 where the crank portion 332 is formed (hereinafter, for convenience, referred to as the "crank-forming surface 332of"), the crank portion 332 includes an eccentric portion 332a, which is a surface that is radially eccentric with respect to the center 330c of the rotating shaft 330 (i.e., the center of the shaft body 331). In this embodiment, as shown in Figure 10, the crank-forming surface 232of has two eccentric portions 332a that are spaced apart in the axial direction. Each of the two eccentric portions 332a is the portion (surface) where the radial distance RL from the center 330c to the crank-forming surface 332of is longer than that of other parts of the crank-forming surface 332of (i.e., where the distance RL is maximum). Note that it is sufficient for at least the portion of the rotating shaft 330 that contacts the second gear 352 and the fourth gear 354 to be eccentric.

[0075] The second gear 352 and the fourth gear 354 are supported at the crank-forming surface 332of in the axial direction, so as not to change their axial position. In this embodiment, the second gear 352 and the fourth gear 354 are spur gears. The second gear 352 is located on the first gear 351 side in the axial direction relative to the base plate 320, and the fourth gear 354 is located on the third gear 353 side in the axial direction relative to the base plate 320. That is, the second gear 352 and the fourth gear 354 are separated from each other and formed as separate components. In each of the second gear 352 and the fourth gear 354, a through hole runs through the radial center along the axial direction, with a shape that generally corresponds to the shape of the crank-forming surface 332of of the crank portion 332. The crank portion 332 is inserted through the through hole in the second gear 352 and the through hole in the fourth gear 354, respectively. Furthermore, a ring-shaped first magnet 361 is fixed to the outer circumferential surface of the crank portion 332. In other words, a ring-shaped first magnet 361 is fixed to the rotating shaft 330. This first magnet 361 is located in the axial direction between the two eccentric portions 332a and between the second gear 352 and the fourth gear 354.

[0076] In this embodiment, the first sensor 341 described above is configured as a magnetic sensor. The first sensor 341 detects that the magnetism generated from the first magnet 361 changes as the first magnet 361 rotates in conjunction with the rotation of the rotation shaft 330, converts this change in the magnetism of the first magnet 361 into an electrical signal, and outputs it to a calculation unit 370 provided on, for example, the substrate 320. Note that the first sensor 341 is not limited to a magnetic sensor; if the first sensor 341 is configured as a sensor other than a magnetic sensor, such as an optical sensor, the first magnet 361 is unnecessary because a slit disc or the like is used for the rotating body. Also, when using a sensor with a magnetoresistive element and gears made of magnetic material, the magnet can be placed on a fixed part such as a substrate instead of the first magnet 361 provided on the rotation shaft 330. The calculation unit 370 acquires the electrical signal output from the first sensor 341 and the rotation angle θ of the rotation shaft 330. sensor1The first sensor 341 calculates the rotation angle θ of the rotation axis 330 via the calculation unit 370. sensor1 It detects.

[0077] The eccentric portion 332a of the crank portion 332 is in slidable contact with the inner circumferential surface 352if of the second gear 352 that defines the through hole. At least one of the eccentric portion 332a and the inner circumferential surface 352if of the second gear 352 may be coated to improve wear resistance and sliding properties between the eccentric portion 332a and the inner circumferential surface 352if. As shown in Figure 11, the outer circumferential surface of the second gear 352 (i.e., the surface on the radial side of the second gear 352 opposite to the rotation axis 330) has multiple external teeth 352ot, fewer than the first number N1, formed around its entire circumference. The second gear 352 is positioned inside the internal teeth 351it of the first gear 351 and is surrounded by the internal teeth 351it of the first gear 351 around its entire circumference. Each of the multiple external teeth 352ot can mesh with each of the multiple internal teeth 351it of the first gear 351.

[0078] When the rotating shaft 330 rotates around the center 330c, the eccentric portion 332a of the crank portion 332 also rotates together with the rotating shaft 330 around the center 330c, and the second gear 352 oscillates as a result of this rotation of the eccentric portion 332a. Due to this oscillation of the second gear 352, the external teeth 352ot, which lie on a straight line SL extending radially from the center 330c through the eccentric portion 332a, mesh with the internal teeth 351it, which lie on the straight line SL. The straight line SL is shown as a dashed line in Figures 11 and 12. Hereinafter, the position where a part of the external teeth 352ot of the second gear 352 meshes with a part of the internal teeth 351it of the first gear 351 will be referred to as the first meshing position EP1. The first meshing position EP1 lies on the straight line SL.

[0079] When the rotating shaft 330 rotates by a predetermined angle from the state shown in Figure 11, that is, when the eccentric portion 332a of the crank portion 332 rotates by a predetermined angle from the state shown in Figure 11, the first meshing position EP1 also moves by the same angle along the circumferential direction of the first gear 151. In this way, the first meshing position EP1 moves sequentially along the circumferential direction of the first gear 351 as the rotating shaft 330 rotates. When the rotating shaft 330 completes one rotation, the first meshing position EP1 completes one rotation along the circumferential direction of the first gear 351. Here, as described above, the first number N1 of the internal teeth 351it of the first gear 351 is greater than the second number N2 of the external teeth 352ot of the second gear 352. Therefore, when the first meshing position EP1 completes one rotation along the circumferential direction of the first gear 351, that is, when the rotating shaft 330 completes one rotation, the second gear 352 rotates relative to the first gear 351 along the circumferential direction of the first gear 351 by the difference in the number of teeth between the first number N1 and the second number N2. Thus, the reduction ratio Gr2 of the second gear 352 with respect to the rotating shaft 330 can be expressed by the following equation (9). TIFF0007848436000009.tif8166 Note that the rotation direction of the second gear 352 is opposite to the rotation direction of the rotating shaft 330.

[0080] Thus, the first pair of gears 351 and 352 is configured as an eccentric oscillating reduction gear, and more precisely, it constitutes an involute gear type hypocycloid mechanism.

[0081] The eccentric portion 332a of the crank portion 332 is in slidable contact with the inner circumferential surface 354if of the fourth gear 354 that defines the through hole. At least one of the eccentric portion 332a and the inner circumferential surface 354if of the fourth gear 354 may be coated to improve wear resistance and sliding properties between the eccentric portion 332a and the inner circumferential surface 354if. As shown in Figure 12, the outer circumferential surface of the fourth gear 354 (i.e., the surface on the radial side of the fourth gear 354 opposite to the rotation axis 330) has multiple external teeth 354ot, fewer than the third number N3, formed around its entire circumference. The fourth gear 354 is positioned inside the internal teeth 353it of the third gear 353 and is surrounded by the internal teeth 353it of the third gear 353 around its entire circumference. Each of the multiple external teeth 354ot can mesh with each of the multiple internal teeth 353it of the third gear 353.

[0082] When the eccentric portion 332a of the crank portion 332 rotates as described above, the fourth gear 354 oscillates in accordance with the rotation of the eccentric portion 332a. This oscillating motion of the fourth gear 354 causes the external teeth 354ot, which lie on a straight line SL extending radially from the center 330c through the eccentric portion 332a, to mesh with the internal teeth 353it, which lie on the straight line SL. Hereinafter, the position where a portion of the external teeth 354ot of the fourth gear 354 meshes with a portion of the internal teeth 353it of the third gear 353 will be referred to as the second meshing position EP2. The second meshing position EP2 lies on the straight line SL.

[0083] When the rotating shaft 330 rotates by a predetermined angle from the state shown in Figure 12, that is, when the eccentric portion 332a of the crank portion 3332 rotates by a predetermined angle from the state shown in Figure 12, the second meshing position EP2 also moves by the same angle along the circumferential direction of the third gear 153. In this way, the second meshing position EP2 moves sequentially along the circumferential direction of the third gear 353 as the rotating shaft 330 rotates. When the rotating shaft 330 completes one rotation, the second meshing position EP2 completes one rotation along the circumferential direction of the third gear 353. Here, as described above, the third number N3 of the internal teeth 353it of the third gear 353 is greater than the fourth number N4 of the external teeth 354ot of the fourth gear 354. Therefore, when the second meshing position EP2 completes one rotation along the circumferential direction of the third gear 353, that is, when the rotating shaft 330 completes one rotation, the fourth gear 354 rotates relative to the third gear 353 along the circumferential direction by the difference in the number of teeth between the third gear N3 and the fourth gear N4. Thus, the reduction ratio Gr4 of the fourth gear 354 with respect to the rotating shaft 330 can be expressed by the following equation (10). TIFF0007848436000010.tif11166 Note that the rotation direction of the fourth gear 354 is opposite to the rotation direction of the rotating shaft 330.

[0084] Thus, the second pair of the third gear 353 and the fourth gear 354 is configured as an eccentric oscillating reduction gear, or more precisely, as an involute gear type hypocycloid mechanism.

[0085] Therefore, in this embodiment, the reduction mechanism 300 is formed by a first pair of gears, a first gear 351 and a second gear 352, and a second pair of gears, a third gear 353 and a fourth gear 354, arranged in the axial direction. The reduction mechanism 300 has a configuration in which two involute gear-type hypocycloid mechanisms are arranged in the axial direction.

[0086] The reduction ratio Gr2 calculated from equation (9) corresponds to the reduction ratio of the first pair, and the reduction ratio Gr4 calculated from equation (10) corresponds to the reduction ratio of the second pair. The encoder 3 is configured such that the reduction ratios Gr2 and Gr4 are different. This means that when the rotating shaft 330 rotates once, there is a difference between the rotation angle (amount of rotation) of the second gear 352 and the rotation angle (amount of rotation) of the fourth gear 354. In this embodiment, the reduction ratio Gr2 is greater than the reduction ratio Gr4. Therefore, in this embodiment, the amount of rotation of the fourth gear 354 is greater than the amount of rotation of the second gear 352. However, the relationship between the magnitudes of the reduction ratios Gr2 and Gr4 may be reversed.

[0087] As shown in Figure 10, a ring-shaped second magnet 362 is fixed to the substrate 320 side of the second gear 352 in the axial direction. The second sensor 342 described above overlaps with the second gear 352 when viewed from the axial direction, and the second magnet 362 is located between the second gear 352 and the second sensor 342 in the axial direction. However, the positional relationship between the second sensor 342, the second gear 352, and the second magnet 362 is not limited to this. In this embodiment, the second sensor 342 is configured as a magnetic sensor. The second sensor 342 detects that the magnetism generated from the second magnet 362 changes as the second magnet 362 rotates in conjunction with the rotation of the second gear 352, and converts this change in the magnetism of the second magnet 362 into an electrical signal which is output to, for example, the calculation unit 370. Note that the second sensor 342 is not limited to a magnetic sensor. If the second sensor 342 is composed of a sensor other than a magnetic sensor, such as an optical sensor, the second magnet 362 is unnecessary because a slit disc or the like is used for the rotating body. Also, if a sensor using a magnetoresistive element and a gear made of magnetic material are used, the magnet is unnecessary. The calculation unit 370 acquires the above electrical signal output from the second sensor 342 and calculates the rotation angle θ of the second gear 352. sensor2 The second sensor 342 calculates the rotation angle θ of the second gear 352 via the calculation unit 370. sensor2 It detects.

[0088] As shown in Figure 10, a ring-shaped third magnet 363 is fixed to the surface of the fourth gear 354 on the substrate 320 side in the axial direction. The aforementioned third sensor 343 overlaps the fourth gear 354 when viewed from the axial direction, and the third magnet 363 is located between the fourth gear 354 and the third sensor 343 in the axial direction. However, the positional relationship between the third sensor 343, the fourth gear 354, and the third magnet 363 is not limited to this. In this embodiment, the third sensor 343 is configured as a magnetic sensor. The third sensor 343 detects that the magnetism generated from the third magnet 363 changes as the third magnet 363 rotates in conjunction with the rotation of the fourth gear 354, and converts this change in the magnetism of the third magnet 363 into an electrical signal which is output to, for example, the calculation unit 370. Furthermore, the third sensor 343 is not limited to a magnetic sensor. If the third sensor 343 is configured with a sensor other than a magnetic sensor, such as an optical sensor, the third magnet 363 is unnecessary because a slit disc or the like is used for the rotating body. Also, if a sensor using a magnetoresistive element and a gear made of magnetic material are used, the magnet is unnecessary. The calculation unit 370 acquires the above electrical signal output from the third sensor 343 and calculates the rotation angle θ of the fourth gear 354. sensor3 This calculates the rotation angle θ of the fourth gear 354 via the calculation unit 370. In other words, in this embodiment, the third sensor 343, via the calculation unit 370, calculates the rotation angle θ of the fourth gear 354. sensor3 It detects.

[0089] As described above, in this embodiment, since the amount of rotation of the fourth gear 354 is greater than the amount of rotation of the second gear 352, the difference α in the rotation angle between the fourth gear 354 and the second gear 352 is θ sensor3 From θ sensor2 This is the value obtained by subtracting [a certain factor]. Also, the rotation angle θ of the fourth gear 354 that occurs when the rotating shaft 330 rotates once. sensor3 and the rotation angle θ of the second gear 352 sensor2 The difference β can be expressed by the following equation (11) using the reduction ratios Gr2 and Gr4. Therefore, the number of rotations Tm of the rotating shaft 330 in this embodiment can be calculated by dividing α by β, and specifically, it can be calculated based on the following formula (12). TIFF0007848436000012.tif13166 Furthermore, the rotation angle θ of the rotating shaft 330, taking into account the number of rotations of the rotating shaft 330, is the rotation angle θ of the rotating shaft 330 detected by the first sensor 341 via the calculation unit 370. sensor1 Using this, it can be expressed by the above equation (4).

[0090] The calculation unit 370 calculates the rotation angle θ of the rotation axis 330. sensor1 The data and the rotation angle θ of the second gear 352 sensor2 The data and the rotation angle θ of the fourth gear 354 sensor3 Based on the data and the equations (4), (9) to (12) above, the number of rotations Tm and the rotation angle θ of the rotating shaft 330 are calculated. In this way, the encoder 3 can detect both the rotation angle and the number of rotations Tm of the rotating shaft 330.

[0091] As explained above, the encoder 3 has a rotating shaft 330 and a rotation angle θ of the rotating shaft 330. sensor1 A first sensor 341 for detecting a first gear 351 has a fixed first gear 351 with a plurality of first number N1 internal teeth 351it on the radial side of the rotation axis 330, a second gear 352 has a plurality of second number N2 external teeth 352ot on the radial side opposite to the rotation axis 330, fewer than the internal teeth 351it of the first gear 351, and rotates with the rotation of the rotation axis 330, a fixed third gear 353 has a plurality of third number N3 internal teeth 353it on the radial side of the rotation axis 330, a fourth gear 354 has a plurality of fourth number N4 external teeth 354ot on the radial side opposite to the rotation axis 330, fewer than the internal teeth 353it of the third gear 353, and rotates with the rotation of the rotation axis 330, and the rotation angle θ of the second gear 352 sensor2 A second sensor 342 detects the rotation angle θ of the fourth gear 354. sensor3The encoder 3 includes a third sensor 343 for detecting the rotation angle θ and a calculation unit 370. In the encoder 3, the first pair of the first gear 351 and the second gear 352 and the second pair of the third gear 353 and the fourth gear 354 are eccentric oscillating type reducers, and the calculation unit 370 calculates the rotation angle θ detected by the second sensor 342. sensor2 The rotation angle θ detected by the third sensor 343 sensor3 Based on the difference between the two values, the number of rotations Tm of the rotation axis 330 is calculated.

[0092] In the encoder 3 according to this embodiment, which has the configuration described above, a large reduction ratio can be obtained by four gears (first gear 351, second gear 352, third gear 353, and fourth gear 354). Therefore, even when a large reduction ratio is required, the increase in the number of gears can be kept to a minimum. In particular, according to the reduction mechanism 300 of encoder 3, as shown in equation (12), the number of rotations of the rotating shaft is calculated based on the difference between the rotation angle of the second gear 352 in the first pair of the first gear 351 and the second gear 352 and the rotation angle of the fourth gear 354 in the second pair of the third gear 353 and the fourth gear 354, and the value obtained by multiplying the reduction ratio Gr2 of the first pair by the reduction ratio Gr4 of the second pair. Therefore, compared to encoder 1 according to the first embodiment 1, for example, the detection upper limit of the number of rotations of the rotating shaft can be increased. Furthermore, despite achieving such a large detection upper limit in encoder 4, the number of gears required is effectively only four. Furthermore, in encoder 4, only one shaft, the rotating shaft 330, is needed to constitute the encoder 4. Thus, in encoder 4 according to this embodiment, it is possible to reduce the number of parts such as gears and shafts, and by reducing the number of parts, it is possible to reduce the manufacturing cost of the encoder, simplify assembly, and make it smaller (smaller diameter, thinner). In addition, in this embodiment, the first gear 351, the second gear 352, the third gear 353, and the fourth gear 354 can be pre-unitized as an involute gear type hypocycloid mechanism stacked in two stages in the axial direction and used in the assembly process, so the number of parts to be assembled can be further reduced, and the encoder can be assembled more easily.

[0093] Furthermore, in this embodiment, since a hypocycloid mechanism is used as the reduction mechanism, it is easy to hollow out the rotating shaft without increasing the size of the encoder.

[0094] Furthermore, in this embodiment, by using a hypocycloid mechanism, it is possible to achieve a larger reduction ratio with fewer gears, as described above, thereby effectively increasing the upper limit of detection for the number of rotations of the rotating shaft.

[0095] In this embodiment, bearings may be placed in at least one of the following locations: between the outer circumferential surface of the rotating shaft 330 and the inner circumferential surface of the casing 310; between the outer circumferential surface of the crank portion 332 and the inner circumferential surface of the second gear 352; and between the outer circumferential surface of the crank portion 332 and the inner circumferential surface of the fourth gear 354.

[0096] (Fourth Embodiment) Next, the encoder according to the fourth embodiment will be described.

[0097] Figure 13 is a perspective view showing the encoder in this embodiment, Figure 14 is a cross-sectional view along the axial direction in a reference state of the encoder shown in Figure 13, and Figure 15 is a cross-sectional view along line XV-XV in Figure 14 showing the encoder shown in Figure 13.

[0098] As shown in Figures 13 to 15, the encoder 4 according to this embodiment mainly comprises a casing 410, a substrate 420, a reduction mechanism 400, a rotating shaft 430, a first sensor 441, a second sensor 442, and a third sensor 443. The reduction mechanism 400 has a configuration in which two involute gear-type hypocycloid mechanisms are arranged radially. In Figure 13, the casing 410 and substrate 420 are shown transparently, and for convenience, the transparent casing 410 and substrate 420 are shown with dashed lines.

[0099] The casing 410 has a substantially flattened rectangular parallelepiped shape in which the axial length is shorter than the radial length. A hole 410h is formed in the radial center of the casing 410, penetrating the casing 410 axially. The inner circumferential surface of the casing 410 defining this hole 410h is formed in a shape that allows the rotating shaft 430 to be fitted into it. The casing 410 consists of a first portion 411 on one side in the axial direction and a second portion 412 on the other side in the axial direction. In this embodiment, the axial length of the second portion 412 is longer than the axial length of the first portion 411, but is not limited to this. The first portion 411 and the second portion 412 are stacked axially and fixed to each other. A connector 421 is attached to the second portion 412.

[0100] The second portion 412 includes a bottom portion 413 on the side opposite to the first portion 411 in the axial direction, an outer peripheral wall 415 extending from the outer peripheral edge of the bottom portion 413 toward the first portion 411 in the axial direction, and a wall portion 414 located radially between the rotation axis 430 and the outer peripheral wall 415. The wall portion 414 extends from the bottom portion 413 toward the first portion 411 in the axial direction. When viewed from the axial direction, the wall portion 414 and the outer peripheral wall 415 form concentric circles centered on the center 430c of the rotation axis 430. In this embodiment, the wall portion 414 is located approximately in the center of the bottom portion 413 in the radial direction, but is not limited thereto.

[0101] Multiple internal teeth 451it of a first number N1 are formed on the inner circumferential surface (the surface on the rotation axis 430 side) of the wall portion 414 along its entire circumference. In other words, the wall portion 414 of the casing 410 is formed as a first gear 451 having multiple internal teeth 451it on the rotation axis 430 side in the radial direction. Thus, the first gear 451 is part of the casing 410 and is fixed to the casing 410. Alternatively, the first gear 451 may be made separately from the casing 410 and fixed to the casing 410.

[0102] Multiple third internal teeth 453it of number N3 are formed on the inner circumferential surface (the surface on the rotation axis 430 side) of the outer circumferential wall 415 along its entire circumference. In other words, the outer circumferential wall 415 of the casing 410 is formed as a third gear 453 having multiple internal teeth 453it on the rotation axis 430 side in the radial direction. Thus, the third gear 453 is part of the casing 410 and is fixed to the casing 410. Alternatively, the third gear 453 may be made separate from the casing 410 and fixed to the casing 410.

[0103] The substrate 420 is fixed to the casing 410 in the axial direction at at least one of the first portion 411 and the second portion 412 of the casing 410. The rotation shaft 430 passes through the approximate center of the substrate 420 in the radial direction. Three sensors (a first sensor 441, a second sensor 442, and a third sensor 443) are mounted on the surface of the substrate 420 on the second portion 412 side. The three sensors are arranged radially from the inside to the outside in the order of the first sensor 441, the second sensor 442, and the third sensor 443. As will be described later, the first sensor 441 detects the magnetism generated from the first magnet 461, the second sensor 442 detects the magnetism generated from the second magnet 462, and the third sensor 443 detects the magnetism generated from the third magnet 463. Therefore, each sensor should be positioned in a location that makes it easy to detect the magnetism of the magnet to be detected. Furthermore, a connector 421 is connected to the side of the substrate 420 facing the second portion 412. External power is supplied to sensors 441, 442, 443 and the calculation unit 470 (described later) via terminals connected to this connector 421, and data calculated by the calculation unit 470 may be output to the outside.

[0104] The rotating shaft 430 is fitted into a hole 410h in the casing 410 and is rotatably supported by the casing 410. In this embodiment, the rotating shaft 430 includes a shaft body 431 and a crank portion 432. The shaft body 431 is formed in a circular ring shape with the center 430c of the rotating shaft 430 as viewed from the axial direction. In this embodiment, the shaft body 431 is formed in a cylindrical shape, i.e., hollow, and has an inner circumferential surface 431i that extends axially with the center 430c as the center. That is, in this embodiment, the rotating shaft 430 is a hollow shaft. Another rotating shaft (for example, the main shaft of a motor) may be attached to the inner circumferential surface 431i of the shaft body 431, for example by press-fitting. By attaching another rotating shaft to the rotating shaft 430 in this way, the present invention functions as an encoder for detecting the amount of rotation of another rotating body.

[0105] The crank portion 432 is formed on the outer circumferential surface of the shaft body 431. The crank portion 432 may be formed integrally with the shaft body 431, or it may be formed separately and then fixed to the shaft body 431. In the axial direction, at least a portion of the crank portion 432 and at least a portion of the second gear 452 (described later) are at the same position (height), and at least a portion of the crank portion 432 and at least a portion of the fourth gear 454 (described later) are at the same position (height). Also, as will be described later, in the axial direction, at least a portion of the second gear 452 and at least a portion of the fourth gear 454 are at the same position (height). Figure 15 is a radial cross-sectional view of the axial portion where at least a portion of the crank portion 432, at least a portion of the second gear 452, and at least a portion of the fourth gear 454 are located. As shown in Figure 15, focusing on the portion 432of of the outer circumferential surface of the rotating shaft 430 where the crank portion 432 is formed (hereinafter, for convenience, referred to as the "crank-forming surface 432of"), the crank portion 432 includes an eccentric portion 432a, which is a surface that is radially eccentric with respect to the center 430c of the rotating shaft 430 (i.e., the center of the shaft body 431). The eccentric portion 432a is the portion (surface) where the radial distance RL from the center 430c to the crank-forming surface 432of is longer than that of other parts of the crank-forming surface 432of (i.e., the distance RL is the maximum). Note that it is sufficient for the portion of the rotating shaft 430 that contacts the second gear 452 and the fourth gear 454 to be eccentric.

[0106] In this embodiment, the crank portion 432 includes a flange portion 433 that protrudes radially outward from its outer circumferential surface. That is, the flange portion 433 is part of the rotating shaft 430 and rotates integrally with the shaft body 431. The flange portion 433 is formed from a non-magnetic material and is circular in shape when viewed from the axial direction. The flange portion 433 includes a ring-shaped disc portion 433A that extends radially and an outer wall portion 433B that extends axially from the outer circumferential edge of the disc portion 433A toward the bottom portion 413 of the casing 410. The disc portion 433A is positioned axially at a distance from the wall portion 414 of the casing 410 and is located on the substrate 420 side of the wall portion 414. The outer wall portion 433B of the flange portion 433 is formed in a cylindrical shape and is positioned radially at a distance from the wall portion 414 and is located outside the wall portion 414.

[0107] A ring-shaped groove is formed on the surface of the disc portion 433A facing the substrate 420, and a ring-shaped first magnet 461 is fitted into this groove. When viewed from the axial direction, the first sensor 441 overlaps the first magnet 461. The first sensor 441 is configured as a magnetic sensor. The first sensor 441 detects that the magnetism generated by the first magnet 461 changes as the first magnet 461 rotates in conjunction with the rotation of the rotation axis 430, converts this change in the magnetism of the first magnet 461 into an electrical signal, and outputs it to a calculation unit 470 provided on the substrate 420, for example. The calculation unit 470 acquires the electrical signal output from the first sensor 441 and calculates the rotation angle θ of the rotation axis 430. sensor1 The first sensor 441 is not limited to a magnetic sensor. If the first sensor 441 is composed of a sensor other than a magnetic sensor, such as an optical sensor, the first magnet 461 is unnecessary because a slit disc or the like is used for the rotating body. Also, if a sensor using a magnetoresistive element and a gear made of magnetic material are used, the magnet can be placed on a fixed part such as a substrate instead of the first magnet 461 provided on the rotating shaft 430. In other words, the first sensor 441 calculates the rotation angle θ of the rotating shaft 430 via the calculation unit 470. sensor1 It detects.

[0108] A second gear 452 is supported at the crank-forming surface 432of in the axial direction so as not to change its position in the axial direction. In this embodiment, the second gear 452 is a spur gear. The second gear 452 is located radially inside the wall portion 414 (first gear 451) and axially between the disc portion 433A of the flange portion 433 and the bottom portion 413 of the casing 410. The eccentric portion 432a of the crank portion 432 is in slidable contact with the inner circumferential surface 452if of the second gear 452. At least one of the eccentric portion 432a and the inner circumferential surface 452if of the second gear 452 may be coated to improve wear resistance and sliding properties between the eccentric portion 432a and the inner circumferential surface 452if. As shown in Figure 15, the outer circumferential surface of the second gear 452 (i.e., the surface of the second gear 452 opposite to the rotation axis 430 in the radial direction) has a plurality of second external teeth 452ot, which are fewer than the first number N1, formed around its entire circumference. The second gear 452 is positioned inside the internal teeth 451it of the first gear 451 and is surrounded by the internal teeth 451it of the first gear 451 around its entire circumference. Each of the plurality of external teeth 452ot can mesh with each of the plurality of internal teeth 451it of the first gear 451.

[0109] As the rotating shaft 430 rotates around the center 430c, the eccentric portion 432a of the crank portion 432 also rotates together with the rotating shaft 430 around the center 430c, and the second gear 452 oscillates as a result of this rotation of the eccentric portion 432a. Due to this oscillation of the second gear 452, the external teeth 452ot, which lie on a straight line SL extending radially from the center 430c through the eccentric portion 432a, mesh with the internal teeth 451it, which lie on the straight line SL. The straight line SL is shown as a dashed line in Figure 15. Hereinafter, the position where a part of the external teeth 452ot of the second gear 452 meshes with a part of the internal teeth 451it of the first gear 451 will be referred to as the first meshing position EP1. The first meshing position EP1 lies on the straight line SL.

[0110] When the rotating shaft 430 rotates by a predetermined angle from the state shown in Figure 15, that is, when the eccentric portion 432a of the crank portion 432 rotates by a predetermined angle from the state shown in Figure 15, the first meshing position EP1 also moves by the same angle along the circumferential direction of the first gear 451. In this way, the first meshing position EP1 moves sequentially along the circumferential direction of the first gear 451 as the rotating shaft 430 rotates. When the rotating shaft 430 completes one rotation, the first meshing position EP1 completes one full rotation along the circumferential direction of the first gear 451. Here, as described above, the first number N1 of the internal teeth 451it of the first gear 451 is greater than the second number N2 of the external teeth 452ot of the second gear 452. Therefore, when the first meshing position EP1 completes one rotation along the circumferential direction of the first gear 451, that is, when the rotating shaft 430 completes one rotation, the second gear 452 rotates relative to the first gear 451 along the circumferential direction of the first gear 451 by the difference in the number of teeth between the first number N1 and the second number N2. Therefore, the reduction ratio Gr2 of the second gear 452 with respect to the rotating shaft 430 can be expressed by equation (9), as in the third embodiment. Note that the rotation direction of the second gear 452 is opposite to the rotation direction of the rotating shaft 430.

[0111] Thus, the first pair of gears 451 and 452 is configured as an eccentric oscillating reduction gear, and more precisely, it constitutes an involute gear type hypocycloid mechanism.

[0112] A ring-shaped second magnet 462 is fixed to the substrate 420-side surface of the second gear 452. In this embodiment, when viewed from the axial direction, the second sensor 442 overlaps the second magnet 462 and the second gear 452 via the disc portion 433A of the flange portion 433, and the second magnet 462 is located between the second gear 452 and the second sensor 442 in the axial direction. However, the positional relationship between the second sensor 442, the second gear 452, and the second magnet 462 is not limited to this. The second sensor 442 is configured as a magnetic sensor. The second sensor 442 detects that the magnetism generated from the second magnet 462 changes as the second magnet 462 rotates in conjunction with the rotation of the second gear 452, and converts this change in the magnetism of the second magnet 462 into an electrical signal which is output to, for example, a calculation unit 470 provided on the substrate 420. Furthermore, the second sensor 442 is not limited to a magnetic sensor. If the second sensor 442 is composed of a sensor other than a magnetic sensor, such as an optical sensor, the second magnet 462 is unnecessary because a slit disc or the like is used for the rotating body. Also, if a sensor using a magnetoresistive element and a gear made of magnetic material are used, the magnet is unnecessary. The calculation unit 470 acquires the above electrical signal output from the second sensor 442 and calculates the rotation angle θ of the second gear 452. sensor2 The calculation unit 470 calculates the rotation angle θ of the second gear 452. In other words, in this embodiment, the second sensor 442, via the calculation unit 470, calculates the rotation angle θ of the second gear 452. sensor2 It detects.

[0113] A fourth gear 454 is supported at the position of the outer wall portion 433B in the axial direction so as not to change its position in the axial direction. In this embodiment, the fourth gear 454 is a spur gear. The fourth gear 454 is located radially between the wall portion 414 and the outer peripheral wall 415 (third gear 453), and axially between the base plate 420 and the bottom portion 413 of the casing 410. Furthermore, in the axial direction, the fourth gear 454 is at approximately the same position (height) as the second gear 452. However, the positional relationship between the fourth gear 454 and the second gear 452 in the axial direction is not limited to this. The portion of the outer peripheral surface 433of of the outer wall portion 433B of the crank portion 432 located on the aforementioned straight line SL is in slidable contact with the inner peripheral surface 454if of the fourth gear 454if. Furthermore, a coating may be applied to at least one of the outer circumferential surface 433of of the outer wall portion 433B and the inner circumferential surface 454if of the fourth gear 454 to improve wear resistance and sliding properties between the outer wall portion 433B and the inner circumferential surface 454if of the fourth gear 454. As shown in Figure 15, the outer circumferential surface of the fourth gear 454 (i.e., the surface opposite to the rotation axis 430 side in the radial direction of the fourth gear 454) has a plurality of fourth external teeth 454ot, which is fewer than the third number N3, formed around its entire circumference. The fourth gear 454 is positioned inside the internal teeth 453it of the third gear 453 and is surrounded by the internal teeth 453it of the third gear 453 around its entire circumference. Each of the plurality of external teeth 454ot can mesh with each of the plurality of internal teeth 453it of the third gear 453.

[0114] As the rotating shaft 430 rotates around the center 430c, the eccentric portion 432a of the crank portion 432 also rotates together with the rotating shaft 430 around the center 430c, and the fourth gear 454 oscillates as a result of this rotation of the eccentric portion 432a. This oscillating of the fourth gear 454 causes the external teeth 454ot, which are on the straight line SL, to mesh with the internal teeth 453it, which are also on the straight line SL. Hereinafter, the position where a part of the external teeth 454ot of the fourth gear 454 meshes with a part of the internal teeth 453it of the third gear 453 will be referred to as the second meshing position EP2. The second meshing position EP2 is on the straight line SL.

[0115] When the rotating shaft 430 rotates by a predetermined angle from the state shown in Figure 15, that is, when the eccentric portion 432a of the crank portion 432 rotates by a predetermined angle from the state shown in Figure 15, the second meshing position EP2 also moves by the same angle along the circumferential direction of the third gear 453. In this way, the second meshing position EP2 moves sequentially along the circumferential direction of the third gear 453 as the rotating shaft 430 rotates. When the rotating shaft 430 completes one rotation, the second meshing position EP2 completes one rotation along the circumferential direction of the third gear 453. Here, as described above, the third number N3 of the internal teeth 453it of the third gear 453 is greater than the fourth number N4 of the external teeth 454ot of the fourth gear 454. Therefore, when the second meshing position EP2 completes one rotation along the circumferential direction of the third gear 453, that is, when the rotating shaft 430 completes one rotation, the fourth gear 454 rotates relative to the third gear 453 along the circumferential direction of the third gear 453 by the difference in the number of teeth between the third gear N3 and the fourth gear N4. Therefore, the reduction ratio Gr4 of the fourth gear 454 with respect to the rotating shaft 430 can be expressed by equation (10), as in the third embodiment. Note that the rotation direction of the second gear 452 is opposite to the rotation direction of the rotating shaft 430.

[0116] Thus, the second pair of the third gear 453 and the fourth gear 454 is configured as an eccentric oscillating reduction gear, or more precisely, as an involute gear type hypocycloid mechanism.

[0117] Therefore, in this embodiment, the first pair of the first gear 451 and the second gear 452 and the second pair of the third gear 453 and the fourth gear 454 are arranged radially to constitute the reduction mechanism 400, and the reduction mechanism 400 has a configuration in which two involute gear-type hypocycloid mechanisms are arranged radially.

[0118] The reduction ratio Gr2 calculated from equation (9) corresponds to the reduction ratio of the first pair, and the reduction ratio Gr4 calculated from equation (10) corresponds to the reduction ratio of the second pair. The encoder 4 is configured such that the reduction ratios Gr2 and Gr4 are different. This means that when the rotating shaft 430 rotates once, there is a difference between the rotation angle (amount of rotation) of the second gear 452 and the rotation angle (amount of rotation) of the fourth gear 454. In this embodiment, the reduction ratio Gr2 is greater than the reduction ratio Gr4. Therefore, in this embodiment, the amount of rotation of the fourth gear 454 is greater than the amount of rotation of the second gear 452. However, the relationship between the magnitudes of the reduction ratios Gr2 and Gr4 may be reversed.

[0119] As shown in Figure 14, a ring-shaped third magnet 463 is fixed to the surface of the fourth gear 454 on the substrate 420 side in the axial direction. The aforementioned third sensor 443 overlaps the third magnet 463 and the fourth gear 454 when viewed from the axial direction, and the third magnet 463 is located between the fourth gear 454 and the third sensor 443 in the axial direction. However, the positional relationship between the third sensor 443, the fourth gear 454 and the third magnet 463 is not limited to this. In this embodiment, the third sensor 443 is configured as a magnetic sensor. The third sensor 443 detects that the magnetism generated from the third magnet 463 changes as the third magnet 463 rotates in conjunction with the rotation of the fourth gear 454, and converts this change in the magnetism of the third magnet 463 into an electrical signal which is output to, for example, the calculation unit 470. Furthermore, the third sensor 443 is not limited to a magnetic sensor. If the third sensor 443 is composed of a sensor other than a magnetic sensor, such as an optical sensor, the third magnet 463 is unnecessary because a slit disc or the like is used for the rotating body. Also, if a sensor using a magnetoresistive element and a gear made of magnetic material are used, the magnet is unnecessary. The calculation unit 470 acquires the above electrical signal output from the third sensor 443 and calculates the rotation angle θ of the fourth gear 454. sensor3 The calculation unit 470 calculates the rotation angle θ of the fourth gear 454. In other words, in this embodiment, the third sensor 443, via the calculation unit 470, calculates the rotation angle θ of the fourth gear 454. sensor3It detects.

[0120] As described above, in this embodiment, the amount of rotation of the fourth gear 454 is greater than the amount of rotation of the second gear 452, so the difference α in the rotation angles between the fourth gear 454 and the second gear 452 is θ sensor3 From θ sensor2 This is the value obtained by subtracting . Furthermore, the difference β between the rotation angle of the fourth gear 454 and the rotation angle of the second gear 452 that occurs when the rotating shaft 430 rotates once can be expressed by equation (11) using the reduction ratio Gr2 and the reduction ratio Gr4, similar to the third embodiment. Therefore, the number of rotations Tm of the rotating shaft 430 in this embodiment can be calculated based on equation (12), similar to the third embodiment. Furthermore, the rotation angle θ of the rotating shaft 430, taking into account the number of rotations of the rotating shaft 430, is the rotation angle θ of the rotating shaft 430 detected by the first sensor 441 via the calculation unit 470. sensor1 Using this, it can be expressed by the above equation (4).

[0121] The calculation unit 470 calculates the rotation angle θ of the rotation axis 330. sensor1 The data and the rotation angle θ of the second gear 452 sensor2 The data and the rotation angle θ of the fourth gear 454 sensor3 Based on the data and the equations (4), (9) to (12) above, the number of rotations Tm and the rotation angle θ of the rotating shaft 430 are calculated. In this way, the encoder 4 can detect both the rotation angle and the number of rotations Tm of the rotating shaft 430.

[0122] As explained above, the encoder 4 has a rotation axis 430 and a rotation angle θ of the rotation axis 430. sensor1A first sensor 441 for detecting a first gear 451 having a plurality of first number N1 internal teeth 451it on the radial side of the rotation axis 430, a second gear 452 having a plurality of second number N2 external teeth 452ot fewer than the internal teeth 451it of the first gear 451 on the radial side opposite to the rotation axis 430, and rotating in conjunction with the rotation of the rotation axis 430, a fixed third gear 453 having a plurality of third number N3 internal teeth 453it on the radial side of the rotation axis 430, a fourth gear 454 having a plurality of fourth number N4 external teeth 454ot fewer than the internal teeth 453it of the third gear 453 on the radial side opposite to the rotation axis 430, and rotating in conjunction with the rotation of the rotation axis 430, and the rotation angle θ of the second gear 452 sensor2 A second sensor 442 detects the rotation angle θ of the fourth gear 454. sensor3 The encoder 4 includes a third sensor 443 for detecting the rotation angle θ and a calculation unit 470. In the encoder 4, the first pair of the first gear 451 and the second gear 452 and the second pair of the third gear 453 and the fourth gear 454 are eccentric oscillating type reducers, and the calculation unit 470 calculates the rotation angle θ detected by the second sensor 442. sensor2 The rotation angle θ detected by the third sensor 443 sensor3 Based on the difference between the two values, the number of rotations Tm of the rotation axis 430 is calculated.

[0123] With an encoder 4 having such a configuration, the same effects as the encoder 3 according to the third embodiment can be obtained.

[0124] Furthermore, in encoder 4, since the first pair and the second pair are aligned radially, the axial length of encoder 4 can be shortened and the encoder can be made thinner when achieving the same reduction ratio compared to encoder 3 according to the third embodiment, in which the first pair and the second pair are aligned axially.

[0125] On the other hand, according to the encoder 3 of the third embodiment, since the first pair and the second pair are aligned in the axial direction, the area of ​​the cross-section of the encoder perpendicular to the axial direction can be reduced when the same reduction ratio is actually applied, compared to the encoder 4 in which the first pair and the second pair are aligned in the radial direction.

[0126] In this embodiment, bearings may be placed in at least one of the following locations: between the outer circumferential surface of the rotating shaft 430 and the inner circumferential surface of the casing 410; between the portion of the outer circumferential surface of the crank portion 432 facing the second gear 452 and the inner circumferential surface of the second gear 452; and between the outer wall portion 433B of the crank portion 432 and the inner circumferential surface of the fourth gear 454.

[0127] Although the present invention has been described above with reference to the above embodiments, the present invention is not limited thereto.

[0128] For example, in the first to fourth embodiments, an example was described in which the reduction mechanism is configured as an involute gear type hypocycloid mechanism, but the reduction mechanism may be configured by other mechanisms. This point will be explained below using the first and second modifications of the first embodiment as examples.

[0129] (First variation) First, the first modified example will be described. Figure 16 is a schematic axial cross-section of the encoder according to this modified example. Figure 17 is a schematic radial cross-section of the encoder shown in Figure 16. Note that components similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and detailed explanations are omitted.

[0130] As shown in Figures 16 and 17, in the encoder 1A according to this modified example, the reduction mechanism 100 is replaced by a reduction mechanism 100A. Furthermore, in encoder 1A, due to the adoption of the reduction mechanism 100A, the rotating shaft 130 consists only of the shaft body 131A. In encoder 1A, a ring-shaped first magnet 161 is fixed to the outer circumferential surface 131of of the shaft body 131.

[0131] The reduction mechanism 100A of encoder 1A includes a first gear 1151 fixed to a casing (not shown), a second gear 1152 located inside the first gear 1151, and a rotating member 1153 located inside the second gear 1152. The rotating member 1153 is an elliptical ring-shaped member when viewed from the axial direction, and its inner circumferential surface is fixed to the outer circumferential surface 131of of the shaft body 131. Therefore, the rotating member 1153 rotates integrally with the rotating shaft 130. When viewed from the axial direction, the center of the rotating member 1153 coincides with the center 130c of the rotating shaft 130.

[0132] The second gear 1152 is rotatably supported in a casing (not shown). The second gear 1152 is flexible and can bend (deform) in response to a pressure, for example, when subjected to a radial pressure acting from the inside outward. When not deformed, the second gear 1152 has a circular ring-shaped outer shape when viewed from the axial direction and includes a cylindrical outer wall 1152A and a flange portion 1152B that protrudes toward the rotation axis 130 from one end of the outer wall 1152A in the axial direction. The rotating member 1153 is positioned inside the inner circumferential surface 1152if of the outer wall 1152A.

[0133] When the second gear 1152 is not deformed, the diameter of the inner surface 1152if of the outer peripheral wall 1152A is shorter than the major axis LA of the rotating member 1153 and longer than the minor axis of the rotating member 1153. Therefore, the inner surface 1152if of the outer peripheral wall 1152A is pressed radially from the inside to the outside by the portion of the major axis LA of the rotating member 1153 that is located inside the outer peripheral wall 1152A. As a result, the second gear 1152 is deformed into an elliptical shape when viewed from the axial direction. In Figure 17, the major axis LA of the rotating member 1153 and its extension are shown as dashed lines. The portion of the outer peripheral surface 1153of of the rotating member 1153 other than the portion through which the major axis LA passes is not in contact with the inner surface 1152if of the outer peripheral wall 1152A. The outer circumferential surface 1153of of the rotating member 1153 can slide in contact with the inner circumferential surface 1152if of the outer circumferential wall 1152A. Multiple second external teeth 1152ot of number N2 are formed on the outer circumferential surface of the outer circumferential wall 1152A (i.e., the surface opposite to the rotation axis 130 side in the radial direction).

[0134] The flange portion 1152B of the second gear 1152 is a ring-shaped plate member, and the rotating shaft 130 passes through a through hole defined by the inner circumferential surface of the flange portion 1152B. The base plate 120 is on one side of the flange portion 1152B in the axial direction, and the rotating member 1153 is on the other side. The flange portion 1152B also faces the first magnet 161 in the radial direction. A ring-shaped second magnet 162 is fixed to the axial side of the flange portion 1152B facing the base plate 120.

[0135] The first gear 1151 is made of a highly rigid material and is designed not to deform. The first gear 1151 is fixed to a casing (not shown). When viewed from the axial direction, the first gear 1151 is circular in shape, and its center coincides with the center 130c of the rotation axis 130. The inner surface of the first gear 1151 (i.e., the surface on the rotation axis 130 side in the radial direction) has internal teeth 1152it, the first number N1 which is greater than the second number N2. In this embodiment, the difference between the first number N1 and the second number N2 is 2n (where n is any natural number). The internal teeth 1152it of the first gear 1151 surround the external teeth 1152ot of the second gear 1152 around its entire circumference.

[0136] Each of the multiple external teeth 1152ot of the second gear 1152 can mesh with each of the multiple internal teeth 1151it of the first gear 1151. In this embodiment, as shown in Figure 17, the external teeth 1152ot of the second gear 1152 through which the extension of the long axis LA passes mesh with the internal teeth 1151it of the first gear 1151. Therefore, the external teeth 1152ot at two locations through which the extension of the long axis LA passes, i.e., two locations symmetrically positioned with respect to the center 130c, mesh with the internal teeth 1151it. Thus, the encoder 1A according to this modified example has two meshing positions EP.

[0137] When the rotating shaft 130 rotates around the center 130c, the rotating member 1153 also rotates together with the rotating shaft 130 around the center 130c. That is, the long axis LA of the rotating member 1153 rotates around the center 130c. When the long axis LA rotates by a predetermined angle, the meshing position EP also moves by the same angle along the circumferential direction of the first gear 1151. In this way, the meshing position EP moves sequentially along the circumferential direction of the first gear 1151 as the rotating shaft 130 rotates. When the rotating shaft 130 completes one rotation, the meshing position EP completes one rotation along the circumferential direction of the first gear 1151. Here, as described above, the first number N1 of the internal teeth 1151it of the first gear 1151 is 2n greater than the second number N2 of the external teeth 1152ot of the second gear 1152. Therefore, when the meshing position EP completes one revolution along the circumferential direction of the first gear 1151, that is, when the rotation axis 130 completes one rotation, the second gear 1152 rotates relative to the first gear 1151 along the circumferential direction of the first gear 1151 by the difference in the number of teeth between the first gear N1 and the second gear N2 (tooth difference of 2n). Note that the direction of rotation of the second gear 1152 is opposite to the direction of rotation of the rotation axis 130.

[0138] In this modified example, the rotating member 1153 can be considered in the same way as the crank portion 132 in the first embodiment. Thus, the first gear 1151 and the second gear 1152 are configured as an eccentric oscillating type reduction gear, and more precisely, they function as a reduction mechanism 100A that constitutes a harmonic drive gear mechanism.

[0139] In the axial direction, a first sensor 141 and a second sensor 142, which are magnetic sensors, are mounted on the flange portion 1152B side of the substrate 120. The first sensor 141 detects that the magnetism generated from the first magnet 161 changes as the first magnet 161 rotates in conjunction with the rotation of the rotation axis 130, and calculates the rotation angle θ of the rotation axis 130 via the calculation unit 170. sensor1 The second sensor 142 detects that the magnetism generated from the second magnet 162 changes as the second magnet 162 rotates in conjunction with the rotation of the second gear 1152, and calculates the rotation angle θ of the second gear 1152 via the calculation unit 170. sensor2It detects.

[0140] Therefore, according to the encoder 1A of this modified example, the number of rotations Tm and the rotation angle θ of the rotating shaft 130 can be calculated based on equations (1) to (4), similar to the first embodiment.

[0141] In addition, in the second to fourth embodiments described above, the reduction mechanism may also be configured as a harmonic drive gear mechanism as described in this modified example.

[0142] (Second variation) Next, a second modified example will be described. Figure 18 is a perspective view showing the encoder in this modified example. Figure 19 is a cross-sectional view along the axial direction of the encoder shown in Figure 18. Note that components similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and detailed descriptions are omitted.

[0143] As shown in Figures 18 and 19, in the encoder 1B according to this modified example, the reduction mechanism 100 is replaced by the reduction mechanism 100B. The reduction mechanism 100B of encoder 1B includes a first gear 2151 and a second gear 2152.

[0144] A second gear 2152 is supported at the axial position of the crank portion 132 of the rotating shaft 130 so as not to change its axial position. The eccentric portion 132a of the crank portion 132 is in contact with the inner circumferential surface of the second gear 2152 so as to be slidable with respect to the inner circumferential surface of the second gear 2152. As described in the above embodiment, at least one of these surfaces may be coated. When viewed from the axial direction, the outer circumferential surface of the second gear 2152 (the surface opposite to the rotating shaft 130 side in the radial direction) is formed to form an epitrochoidal curve. Therefore, the outer edge of the second gear 2152 is formed by a plurality of arc-shaped protrusions 2152T that project outward by a plurality of N2. In this modified example, each of these plurality of protrusions 2152T functions as an external tooth 2152ot of the second gear 2152.

[0145] A ring-shaped second magnet 162 is fixed to the axial side of the second gear 2152 facing the first portion 111. A ring-shaped first magnet 161 is fixed to the outer circumferential surface of the crank portion 132. A first sensor 141 and a second sensor 142 are mounted as magnetic sensors on the axial side of the substrate 120 facing the second gear 2152. The first sensor 141 calculates the rotation angle θ of the rotating shaft 130 via a calculation unit 170 based on the change in magnetism generated from the first magnet 161 as the rotating shaft 130 rotates. sensor1 It detects.

[0146] The second portion 112 of the casing 110 has a bottom portion 112B on the side opposite to the first portion 111 in the axial direction. The bottom portion 112B forms the bottom of the casing 110. The bottom portion 112B is provided with a plurality of first number N1 pins 2153 of the same dimensions. The first number N1 is greater than the second number N2. Each of the plurality of pins 2153 is formed in a cylindrical shape and protrudes from the bottom portion 112B toward the first portion 111 in the axial direction. The plurality of pins 2153 are arranged radially inward relative to the outer wall 110of of the casing 110. Furthermore, the plurality of pins 2153 are arranged at equal intervals along the circumferential direction of the circle Cr, which is centered on the center 130c of the rotation axis 130. Note that in Figure 18, a portion of the circle Cr is shown as a dashed line. Each of the multiple protrusions 2152T (external teeth 2152ot) of the second gear 2152 can mesh with two adjacent pins 2153 in the circumferential direction of circle Cr. Thus, the multiple pins 2153 function as internal teeth 2151it that mesh with the external teeth 2152ot of the second gear 2152. Therefore, the second portion 112 of the casing 110 functions as the first gear 2151 having a plurality of first number N1 internal teeth 2151it on the rotation axis 130 side in the radial direction.

[0147] In this embodiment, as shown in Figure 18, among the multiple external teeth 2152ot, the external teeth 2152ot located on the straight line SL mesh with the internal teeth 2151it located on the straight line SL (more specifically, the gap between two adjacent internal teeth 2151it in the circumferential direction of the circle Cr, through which the straight line SL passes). As in the first embodiment, the straight line SL is a straight line extending radially from the center 130c through the eccentric portion 132a of the crank portion 132. In Figure 18, the straight line SL is shown as a dashed line. Therefore, the encoder 1B has a meshing position EP through which a part of the external teeth 2152ot and a part of the internal teeth 2151it mesh. In this modified example, the meshing position EP may be defined as the gap between two adjacent internal teeth 2151it in the circumferential direction of the circle Cr, through which the straight line SL passes.

[0148] When the rotating shaft 130 rotates by a predetermined angle from the state shown in Figure 18, that is, when the eccentric portion 132a of the crank portion 132 rotates by a predetermined angle from the state shown in Figure 18, the meshing position EP also moves by a similar angle along the circumferential direction of the first gear 2151 (circumferential direction of circle Cr). In this way, the meshing position EP moves sequentially along the circumferential direction of the first gear 2151 as the rotating shaft 130 rotates. When the rotating shaft 130 completes one rotation, the meshing position EP completes one rotation along the circumferential direction of the first gear 2151. Here, as described above, the first number N1 of the internal teeth 2151it of the first gear 2151 is greater than the second number N2 of the external teeth 2152ot of the second gear 2152. Therefore, when the meshing position EP completes one rotation along the circumferential direction of the first gear 2151, that is, when the rotation axis 130 completes one rotation, the second gear 2152 rotates relative to the first gear 2151 along the circumferential direction of the first gear 2151 by the difference in the number of teeth between the first gear N1 and the second gear N2. Note that the direction of rotation of the second gear 2152 is opposite to the direction of rotation of the rotation axis 130.

[0149] Thus, the first gear 2151 and the second gear 2152 are configured as an eccentric oscillating type reduction gear, and more specifically, they function as a reduction gear 100B that constitutes a hypocycloid mechanism, or more precisely, a pin gear type hypocycloid.

[0150] The second sensor 142 calculates the rotation angle θ of the second gear 2152 via the calculation unit 170 based on the change in magnetism generated from the second magnet 162 as the second gear 2152 rotates. sensor2 It detects.

[0151] Therefore, according to the encoder 1B of this modified example, the number of rotations Tm and the rotation angle θ of the rotating shaft 130 can be calculated based on equations (1) to (4), similar to the first embodiment.

[0152] In addition, in the second to fourth embodiments described above, the reduction mechanism may also be configured as a harmonic drive gear mechanism as described in this modified example.

[0153] Furthermore, although the above embodiments and modifications describe examples where the axis of rotation is a hollow shaft, the axis of rotation is not limited to a hollow shaft.

[0154] Furthermore, encoders 1, 2, 3, 4, 1A, and 1B described above may be used as absolute rotary encoders or incremental rotary encoders. In addition, encoders 1, 2, 3, 4, 1A, and 1B can also be used as battery-less absolute encoders that do not require homing even if the power supply from the power source is temporarily turned off and then restored.

[0155] Furthermore, those skilled in the art may modify the encoder of the present invention as appropriate in accordance with conventionally known knowledge. Such modifications, insofar as they still possess the configuration of the present invention, are of course included within the scope of the present invention. [Explanation of Symbols]

[0156] 2…Encoder, 230…Rotation shaft, 232…Crank section, 241…First sensor, 242…Second sensor, 251…First gear, 251it…Internal teeth, 252…Second gear, 252ot…External teeth, 253…Third gear, 253ot…External teeth, 254…Fourth gear, 254it…Internal teeth, 261…First magnet, 262…Second magnet, 270…Calculation unit

Claims

1. The axis of rotation and A first sensor for detecting the rotation angle of the rotating shaft, A fixed first gear having a plurality of first-order internal teeth on the rotation axis side in the radial direction, A second gear has a number of external teeth, fewer than the internal teeth of the first gear, on the side opposite to the rotation axis in the radial direction, and rotates in conjunction with the rotation of the rotation axis. A third gear is formed integrally with the second gear on one side of the second gear in the axial direction of the rotating shaft, and has a plurality of third external teeth on the side opposite to the rotating shaft in the radial direction, A fourth gear having a number of internal teeth greater than the external teeth of the third gear on the rotation axis side in the radial direction, and rotating in conjunction with the rotation of the third gear, A second sensor for detecting the rotation angle of the fourth gear, Calculation unit and Equipped with, Each of the first pair of the first gear and the second gear, and each of the second pair of the third gear and the fourth gear, is an eccentric oscillating type reduction gear. The calculation unit is an encoder that calculates the number of times the rotating shaft has rotated based on the rotation angle detected by the second sensor.

2. The encoder according to claim 1, wherein the rotating shaft includes a crank portion for oscillating the second gear and the third gear.

3. The encoder according to claim 2, wherein each of the first pair and the second pair constitutes a cycloidal mechanism or a harmonic drive mechanism.

4. The first meshing position, in which a portion of the external teeth of the second gear meshes with a portion of the internal teeth of the first gear, moves sequentially along the circumferential direction of the first gear as the rotation of the rotation shaft rotates. The encoder according to any one of claims 1 to 3, wherein when the first meshing position completes one revolution along the circumferential direction of the first gear, the second gear rotates along the circumferential direction of the first gear by the difference in the number of teeth between the first and second gears.

5. The second meshing position, in which a portion of the external teeth of the third gear meshes with a portion of the internal teeth of the fourth gear, moves sequentially along the circumferential direction of the fourth gear as the second and third gears rotate. The encoder according to any one of claims 1 to 3, wherein when the second meshing position completes one revolution along the circumferential direction of the fourth gear, the fourth gear rotates along the circumferential direction by the difference in the number of teeth between the fourth and third gears.

6. The encoder according to any one of claims 1 to 3, wherein the rotating shaft is a hollow shaft.

7. It comprises a ring-shaped first magnet fixed to the aforementioned rotating shaft, The encoder according to any one of claims 1 to 3, wherein the first sensor is a magnetic sensor that detects a change in magnetism generated from the first magnet.

8. The encoder according to any one of claims 1 to 3, wherein, when viewed from the axial direction of the rotation axis, the second sensor overlaps the fourth gear.

9. The fourth gear comprises a ring-shaped second magnet fixed to the second sensor-side surface in the axial direction, The encoder according to claim 8, wherein the second sensor is a magnetic sensor that detects a change in magnetism generated from the second magnet.

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