Power transmission devices and robots

Abstract

To provide a power transmission device that can suppress the ingress of liquid or dust. [Solution] The power transmission device comprises an internal gear, an external gear, a main bearing, and a housing. The internal gear has a plurality of internal teeth. The flexible external gear has a plurality of external teeth that mesh with the internal teeth. The main bearing has an inner ring fixed to the internal gear and an outer ring fixed to the flexible external gear. The housing is fixed to the flexible external gear. The housing has an end wall and a cylindrical circumferential wall. The end wall covers one axial end face of the flexible external gear. The circumferential wall extends axially from the end wall and covers the outer circumferential surfaces of the flexible external gear and the outer ring. The power transmission device further comprises an annular sealing portion 90. The sealing portion is positioned between the flexible external gear 30 or the outer ring 52 and the circumferential wall portion 72.

Description

Technical Field

[0001] The present disclosure relates to a power transmission device and a robot.

Background Art

[0002] Conventionally, a power transmission device that decelerates the rotational motion output from a motor is known. The power transmission device is mounted, for example, on a joint of a robot. In recent years, it has been proposed to mount a sensor for detecting torque, rotational angle, temperature, etc. on the gears of the power transmission device. A power transmission device equipped with a sensor is described in, for example, Patent Document 1.

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0003] The power transmission device of Patent Document 1 has a circuit board that processes a detection signal output from a sensor. The circuit board is attached to the housing of the power transmission device. In this type of power transmission device, it is required to prevent liquid or dust from entering the circuit board through the gaps in the housing. In particular, it is required to prevent conductive water, metal powder, etc. from adhering to the circuit board.

[0004] Therefore, an object of the present disclosure is to provide a power transmission device that can suppress the intrusion of liquid or dust.

Means for Solving the Problems

[0005] This disclosure relates to a power transmission device comprising: an internal gear having a plurality of internal teeth; a flexible external gear having a plurality of external teeth meshing with the internal teeth; a main bearing having an inner ring fixed to the internal gear and an outer ring fixed to the flexible external gear; and a housing fixed to the flexible external gear, wherein the housing has an end wall portion covering one axial end face of the flexible external gear and a cylindrical circumferential wall portion extending axially from the end wall portion and covering the outer circumferential surfaces of the flexible external gear and the outer ring, and further comprises an annular sealing portion disposed between the flexible external gear or the outer ring and the circumferential wall portion. [Effects of the Invention]

[0006] According to this disclosure, the space between the flexible external gear or outer ring and the peripheral wall is sealed by the sealing portion. This prevents liquid or dust from entering through the space between the flexible external gear and outer ring and the peripheral wall. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram of the robot. [Figure 2] Figure 2 is a longitudinal cross-sectional view of the power transmission device. [Figure 3] Figure 3 is a cross-sectional view of the power transmission device as seen from position AA in Figure 2. [Figure 4] Figure 4 is a partial longitudinal cross-sectional view of a flexible external gear near the sensor. [Figure 5] Figure 5 is a plan view of the sensor. [Figure 6] Figure 6 is a partial plan view of the sensor. [Figure 7] Figure 7 is a circuit diagram of a bridge circuit that includes four strain gauges. [Figure 8] Figure 8 is a partial longitudinal cross-sectional view of a power transmission device including the sealing portion of the first embodiment. [Figure 9] Figure 9 is a partial longitudinal cross-sectional view of a power transmission device including a sealing portion according to the second embodiment. [Figure 10]Figure 10 is a partial longitudinal cross-sectional view of a power transmission device including a sealing portion according to the third embodiment. [Figure 11] Figure 11 is a partial longitudinal cross-sectional view of a power transmission device including a sealing portion according to the fourth embodiment. [Figure 12] Figure 12 is a partial longitudinal cross-sectional view of a power transmission device including a sealing portion according to the fifth embodiment. [Figure 13] Figure 13 is a partial longitudinal cross-sectional view of a power transmission device including a sealing portion according to the sixth embodiment. [Figure 14] Figure 14 is a partial longitudinal cross-sectional view of a power transmission device including a sealing portion of one modified example. [Modes for carrying out the invention]

[0008] Hereinafter, exemplary embodiments of the present application will be described with reference to the drawings.

[0009] <1. About robots> Figure 1 is a schematic diagram of a robot 100 equipped with a power transmission device 1 according to one embodiment. The robot 100 is a so-called industrial robot that performs tasks such as transporting, processing, and assembling parts in, for example, an industrial product manufacturing line. As shown in Figure 1, the robot 100 comprises a base frame 101, an arm 102, a motor 103, and a power transmission device 1.

[0010] The arm 102 is rotatably supported on the base frame 101. The motor 103 and power transmission device 1 are incorporated into the joint between the base frame 101 and the arm 102. When a drive current is supplied to the motor 103, rotational motion is output from the motor 103. The rotational motion output from the motor 103 is then reduced in speed by the power transmission device 1 and transmitted to the arm 102. As a result, the arm 102 rotates relative to the base frame 101 at the reduced speed.

[0011] <2. Configuration of the power transmission system> Next, we will explain the detailed structure of the power transmission device 1.

[0012] Hereinafter, the direction parallel to the central axis 9 of the power transmission device 1 is referred to as the "axial direction", the direction orthogonal to the central axis 9 of the power transmission device 1 is referred to as the "radial direction", and the direction along the arc centered on the central axis 9 of the power transmission device 1 is referred to as the "circumferential direction". However, the above-mentioned "parallel direction" includes a substantially parallel direction. Also, the above-mentioned "orthogonal direction" includes a substantially orthogonal direction. In each figure of the present application, the axial direction is indicated by the symbol D. Further, in the following description, the side of the signal processing board 80 with respect to the internal gear 20 is referred to as the "one axial side", and the opposite side is referred to as the "other axial side".

[0013] FIG. 2 is a longitudinal sectional view of the power transmission device 1 according to an embodiment. FIG. 3 is a cross-sectional view of the power transmission device 1 as viewed from the A-A position in FIG. 2. In order to avoid complication of the figure, in FIG. 3, the hatching indicating the cross section is omitted.

[0014] The power transmission device 1 is a device (speed reducer) that decelerates the rotational motion at the first rotational speed obtained from the motor 103 to the rotational motion at the second rotational speed slower than the first rotational speed. As shown in FIGS. 2 and 3, the power transmission device 1 includes a shaft 10, an internal gear 20, a flexible external gear 30, a wave generator 40, a main bearing 50, a sensor 60, a housing 70, and a signal processing board 80.

[0015] The shaft 10 is a member that rotates at the first rotational speed before deceleration. The shaft 10 of the present embodiment is substantially cylindrical and extends along the central axis 9. The shaft 10 is connected directly to the output shaft of the motor 103 or via a power transmission mechanism such as a gear. When the motor 103 is driven, the shaft 10 rotates at the first rotational speed about the central axis 9.

[0016] The internal gear 20 is an annular gear centered on the central axis 9. The internal gear 20 is located on the radially outer side of the shaft 10. The internal gear 20 is fixed to the arm 102. The rigidity of the internal gear 20 is sufficiently higher than the rigidity of the body portion 33 of the flexible external gear 30 described later. The internal gear 20 has a plurality of internal teeth 21. The plurality of internal teeth 21 are provided at a constant pitch in the circumferential direction on the inner peripheral surface of the internal gear 20. Each internal tooth 21 projects radially inward from the inner peripheral surface of the internal gear 20.

[0017] The flexible external gear 30 is an annular gear that can be elastically deformed. The flexible external gear 30 is fixed to the base frame 101. As shown in FIG. 2, the flexible external gear 30 has a thick portion 31, a diaphragm portion 32, a body portion 33, and a plurality of external teeth 34.

[0018] The thick portion 31 is annular centered on the central axis 9. The thick portion 31 is located between the end wall portion 71 of the housing 70 described later and the outer ring 52 of the main bearing 50 described later, and is fixed to the end wall portion 71 and the outer ring 52.

[0019] The diaphragm portion 32 extends radially inward from the thick portion 31. The diaphragm portion 32 surrounds the central axis 9 and extends along a plane orthogonal to the central axis 9. The axial thickness of the diaphragm portion 32 is thinner than the axial thickness of the thick portion 31. Therefore, the diaphragm portion 32 can be elastically deformed in the axial direction.

[0020] The body portion 33 is a cylindrical portion that extends from the radially inner end of the diaphragm portion 32 to the other axial side. The end of the body portion 33 on the other axial side is located radially outside the wave generator 40 and radially inside the internal gear 20. The body portion 33 can be elastically deformed in the radial direction. The end of the body portion 33 on the other axial side is deformed into an elliptical shape when viewed axially.

[0021] Multiple external teeth 34 are formed on the outer circumferential surface of the body 33. The multiple external teeth 34 are arranged on the outer circumferential surface of the body 33 at a constant pitch in the circumferential direction. Each external tooth 34 protrudes radially outward from the outer circumferential surface of the other end of the body 33 on the axial side. When the body 33 is deformed into an elliptical shape, some of the multiple external teeth 34 and some of the multiple internal teeth 21 described above mesh with each other. The number of internal teeth 21 in the internal gear 20 and the number of external teeth 34 in the flexible external gear 30 are slightly different.

[0022] The wave generator 40 is a mechanism that generates deflection deformation in the flexible external gear 30. The wave generator 40 is positioned radially inward of the external teeth 34. The wave generator 40 in this embodiment includes a cam 41 and a flexible bearing 42. The cam 41 is rotatably supported about the central axis 9. The outer circumferential surface of the cam 41 is elliptical when viewed in the axial direction. The flexible bearing 42 is a bearing that can be deflected. The flexible bearing 42 is positioned between the outer circumferential surface of the cam 41 and the inner circumferential surface of the body 33 of the flexible external gear 30. Therefore, the cam 41 and the body 33 can rotate at different rotational speeds.

[0023] The inner ring of the flexible bearing 42 contacts the outer circumferential surface of the cam 41. The outer ring of the flexible bearing 42 contacts the inner circumferential surface of the body 33. As a result, the body 33 deforms into an elliptical shape along the outer circumferential surface of the cam 41. Consequently, at two locations corresponding to the ends of the major axis of the ellipse, the external teeth 34 of the flexible external gear 30 and the internal teeth 21 of the internal gear 20 mesh. At other locations in the circumferential direction, the external teeth 34 and the internal teeth 21 do not mesh.

[0024] In this embodiment, the shaft 10 and the cam 41 are formed from a single integrated component. Therefore, when the motor 103 is driven, the cam 41 rotates at a first rotational speed around the central axis 9. As a result, the major axis of the ellipse of the flexible external gear 30 also rotates at the first rotational speed. Consequently, the meshing position between the external teeth 34 and the internal teeth 21 also rotates at the first rotational speed in the circumferential direction. Furthermore, as described above, the number of internal teeth 21 of the internal gear 20 and the number of external teeth 34 of the flexible external gear 30 are slightly different. Due to this difference in the number of teeth, the meshing position between the external teeth 34 and the internal teeth 21 changes slightly in the circumferential direction with each rotation of the cam 41. As a result, the internal gear 20 rotates relative to the flexible external gear 30 at a second rotational speed, which is slower than the first rotational speed, around the central axis 9.

[0025] The main bearing 50 is a bearing that connects the internal gear 20 and the flexible external gear 30 in a manner that allows them to rotate relative to each other. In this embodiment, the main bearing 50 is a cross-roller bearing. The main bearing 50 has an inner ring 51, an outer ring 52, and a plurality of rollers 53. The inner ring 51 is fixed to the internal gear 20. In this embodiment, the inner ring 51 is located on one axial side of the internal gear 20. The outer ring 52 is fixed to the thickened portion 31 of the flexible external gear 30. In this embodiment, the outer ring 52 is located on the other axial side of the thickened portion 31.

[0026] Multiple rollers 53 are arranged between an annular V-shaped groove provided in the inner ring 51 and an annular V-shaped groove provided in the outer ring 52, alternating their orientations. This allows the inner ring 51 and the outer ring 52 to rotate relative to each other while maintaining high rigidity. Therefore, the main bearing 50 of this embodiment can obtain sufficient rigidity in the axial and radial directions without being used in pairs like ball bearings.

[0027] Sensor 60 is a detector that detects various physical quantities related to the operation of the power transmission device 1. Sensor 60 is attached to the diaphragm portion 32 of the flexible external gear 30. In this embodiment, sensor 60 is attached to one axial side surface of the diaphragm portion 32. Sensor 60 measures, for example, the torque applied to the flexible external gear 30, the rotation angle of the power transmission device 1, the temperature, etc., and outputs a detection signal indicating the measured value. The detailed structure of sensor 60 will be described later.

[0028] The housing 70 is a substantially disc-shaped member located on one axial side of the flexible external gear 30. The housing 70 is fixed to the base frame 101. As shown in Figure 2, the housing 70 has an end wall portion 71 and a circumferential wall portion 72. The end wall portion 71 extends along a plane perpendicular to the central axis 9. The end wall portion 71 covers the end face on one axial side of the flexible external gear 30.

[0029] The housing 70 is fixed to the thickened portion 31 and the outer ring 52 by bolts (not shown). Therefore, the flexible external gear 30 and the outer ring 52 are kept stationary relative to the housing 70. In addition, a sub-bearing 54 is interposed between the inner circumference of the end wall portion 71 and the outer circumference of the shaft 10. This allows the housing 70 and the shaft 10 to rotate at different rotational speeds.

[0030] The circumferential wall portion 72 extends from the radially outer end of the end wall portion 71 toward both sides in the axial direction. The circumferential wall portion 72 is cylindrical with respect to the central axis 9. The circumferential wall portion 72 covers the outer circumferential surface of the flexible external gear 30. More specifically, the circumferential wall portion 72 covers the outer circumferential surface of the thick-walled portion 31. In addition, the circumferential wall portion 72 partially covers the outer circumferential surface of the main bearing 50. More specifically, the circumferential wall portion 72 covers a portion of the outer circumferential surface of the outer ring 52 on one side in the axial direction.

[0031] The signal processing board 80 is a board on which electrical circuits for processing detection signals output from the sensor 60 are mounted. The signal processing board 80 is electrically connected to the sensor 60. The signal processing board 80 is fixed to the end wall portion 71 of the housing 70. In this embodiment, the signal processing board 80 is positioned on one axial side of the end wall portion 71. As shown in Figure 2, the end wall portion 71 has a wiring hole 73. The wiring hole 73 penetrates a portion of the outer circumference of the end wall portion 71 in the axial direction. The sensor 60 and the signal processing board 80 are electrically connected via a cable 81 inserted into the wiring hole 73.

[0032] <3. About the sensor> Next, the sensor 60 described above will be explained in detail. Figure 4 is a partial longitudinal cross-sectional view of the flexible external gear 30 near the sensor 60. Figure 5 is a plan view of the sensor 60.

[0033] The sensor 60 has a flexibly deformable film substrate 601 and a conductive layer 602 formed on the surface of the film substrate 601. The film substrate 601 extends in an annular shape around a central axis 9. The film substrate 601 is attached to one axial side surface of the diaphragm portion 32. The conductive layer 602 is formed of a conductive metal. For example, copper alloy, chromium alloy, or copper can be used as the material for the conductive layer 602.

[0034] The sensor 60 of this embodiment includes a torque sensor. The torque sensor is a sensor for detecting the torque applied to the diaphragm portion 32. The torque sensor has a first strain gauge Ra, a second strain gauge Rb, a third strain gauge Rc, and a fourth strain gauge Rd, which are formed by the conductive layer 602 described above. The third strain gauge Rc and the fourth strain gauge Rd are located radially outward from the first strain gauge Ra and the second strain gauge Rb.

[0035] The first strain gauge Ra and the second strain gauge Rb are spaced apart in the circumferential direction. The first strain gauge Ra and the second strain gauge Rb are arranged in an arc shape within a range of approximately 180° around the central axis 9. The first strain gauge Ra and the second strain gauge Rb are arranged concentrically and symmetrically. Furthermore, the radial distance from the central axis 9 to the first strain gauge Ra and the radial distance from the central axis 9 to the second strain gauge Rb are approximately the same.

[0036] The third strain gauge Rc and the fourth strain gauge Rd are spaced apart in the circumferential direction. The third strain gauge Rc and the fourth strain gauge Rd are arranged in an arc shape within a range of approximately 180° around the central axis 9. The third strain gauge Rc and the fourth strain gauge Rd are arranged concentrically and symmetrically. Furthermore, the radial distance from the central axis 9 to the third strain gauge Rc and the radial distance from the central axis 9 to the fourth strain gauge Rd are approximately the same.

[0037] Figure 6 is a partial plan view of the sensor 60. As shown in Figure 6, each strain gauge Ra, Rb, Rc, and Rd consists of a single wire extending circumferentially while bending in a zigzag pattern. Each strain gauge Ra, Rb, Rc, and Rd contains multiple resistance wires r. These multiple resistance wires r are arranged circumferentially in a position that is approximately parallel to each other. The multiple resistance wires r of strain gauges Ra and Rd are inclined to one side in the circumferential direction with respect to the radial direction. The multiple resistance wires r of strain gauges Rb and Rc are inclined to the other side in the circumferential direction with respect to the radial direction. The inclination angle of the resistance wires r with respect to the radial direction is, for example, 45°. The ends of adjacent resistance wires r in the circumferential direction are alternately connected on the inside or outside of the radial direction. As a result, the multiple resistance wires r are connected in series as a whole.

[0038] Figure 7 is a circuit diagram of a bridge circuit C that includes four strain gauges Ra to Rd. The four strain gauges Ra to Rd are connected to each other to form a bridge circuit C as shown in Figure 7. The first strain gauge Ra and the second strain gauge Rb are connected in series in that order. The third strain gauge Rc and the fourth strain gauge Rd are connected in series in that order. Then, between the positive and negative terminals of the power supply voltage, the rows of two strain gauges Ra, Rb and the rows of two strain gauges Rc, Rd are connected in parallel. In addition, the midpoint M1 of the two strain gauges Ra, Rb and the midpoint M2 of the two strain gauges Rc, Rd are connected to a voltmeter V.

[0039] The resistance value of each resistance wire r changes according to the torque applied to the diaphragm section 32. For example, when a torque is applied to the diaphragm section 32 in one direction in the circumferential direction around the central axis 9, the resistance values ​​of the resistance wires r of the two strain gauges Ra and Rd decrease, while the resistance values ​​of the resistance wires r of the other two strain gauges Rb and Rc increase. On the other hand, when a torque is applied to the diaphragm section 32 in the other direction in the circumferential direction around the central axis 9, the resistance values ​​of the resistance wires r of the two strain gauges Ra and Rd increase, while the resistance values ​​of the resistance wires r of the other two strain gauges Rb and Rc decrease. Thus, the resistance values ​​of the two strain gauges Ra and Rd and the other two strain gauges Rb and Rc show changes in opposite directions with respect to torque.

[0040] When the resistance values ​​of the four strain gauges Ra, Rb, Rc, and Rd change, the potential difference between the midpoint M1 of the two strain gauges Ra and Rb and the midpoint M2 of the two strain gauges Rc and Rd changes, and therefore the measured value of the voltmeter V also changes. The signal processing board 80 detects the direction and magnitude of the torque applied to the diaphragm section 32 based on this measured value of the voltmeter V.

[0041] <4. Regarding the sealing part> As described above, the power transmission device 1 includes a signal processing board 80 that processes the detection signal output from the sensor 60. The signal processing board 80 is mounted on one axial side of the end wall portion 71 of the housing 70. Therefore, it is necessary to prevent liquid or dust from entering the signal processing board 80 from the outside. In particular, it is necessary to prevent conductive water or metal powder from adhering to the signal processing board 80.

[0042] One axial end of the housing 70 is properly sealed when connected to the base frame 101. However, it is conceivable that liquid and dust may enter between the other axial end of the housing 70 and the main bearing 50. In that case, it is assumed that the liquid and dust will enter from between the outer ring 52 and the peripheral wall 72, through the thickened portion 31 and the peripheral wall 72, and further through the wiring hole 73 to the signal processing board 80. Therefore, the sealing portion 90 for suppressing such ingress of liquid and dust will be described below.

[0043] <4-1. First Embodiment> First, the sealing portion 90 of the first embodiment will be described. Figure 8 is a partial longitudinal cross-sectional view of the power transmission device 1 including the sealing portion 90 of the first embodiment. As shown in Figure 8, the power transmission device 1 has a sealing portion 90. The sealing portion 90 is an O-ring or a sealing material.

[0044] In the example shown in Figure 8, an annular sealing portion 90 is positioned between the outer ring 52 of the main bearing 50 and the peripheral wall portion 72 of the housing 70. In this way, the space between the outer ring 52 and the peripheral wall portion 72 is closed by the sealing portion 90. This prevents liquid or dust from entering the signal processing board 80 from between the outer ring 52 and the peripheral wall portion 72, and through the space between the thickened portion 31 and the peripheral wall portion 72.

[0045] Furthermore, the structure shown in Figure 8 also prevents liquid or dust that seeps in from between the outer ring 52 and the peripheral wall portion 72 from passing through the gap between the thick-walled portion 31 and the outer ring 52 and entering radially inward.

[0046] In the example shown in Figure 8, the peripheral wall portion 72 has an annular groove 91 on its inner circumferential surface. An annular sealing portion 90 is positioned in this groove 91. The sealing portion 90 contacts the outer circumferential surface of the outer ring 52 when fitted into the groove 91. In this way, the sealing portion 90 can be positioned without providing a groove 91 in the main bearing 50.

[0047] The sealing portion 90 is, for example, an annular O-ring. In this case, the sealing portion 90 is formed of rubber, which is an elastic material. The sealing portion 90 conforms tightly to the outer circumferential surface of the outer ring 52 and the groove 91 while undergoing elastic deformation. This closes the space between the outer ring 52 and the peripheral wall portion 72.

[0048] However, the sealing portion 90 may be formed by applying a fluid resin sealing material to the groove 91. In that case, the sealing material hardens while in contact with the outer circumferential surface of the outer ring 52 and the groove 91. This closes the gap between the outer ring 52 and the peripheral wall portion 72.

[0049] <4-2. Second Embodiment> Next, the sealing portion 90 of the second embodiment will be described. Figure 9 is a partial longitudinal cross-sectional view of the power transmission device 1 including the sealing portion 90 of the second embodiment. As shown in Figure 9, the power transmission device 1 has a sealing portion 90. The sealing portion 90 is an O-ring or a sealing material.

[0050] In the example shown in Figure 9, an annular sealing portion 90 is positioned between the thickened portion 31 of the flexible external gear 30 and the peripheral wall portion 72 of the housing 70. In this way, the space between the thickened portion 31 and the peripheral wall portion 72 is closed by the sealing portion 90. This prevents liquid or dust from entering the signal processing board 80 from between the outer ring 52 and the peripheral wall portion 72, and through the space between the thickened portion 31 and the peripheral wall portion 72.

[0051] In the example shown in Figure 9, the peripheral wall portion 72 has an annular groove 91 on its inner circumferential surface. An annular sealing portion 90 is positioned in the groove 91. The sealing portion 90 contacts the outer circumferential surface of the thickened portion 31 when fitted into the groove 91. In this way, the sealing portion 90 can be positioned without providing a groove 91 on the flexible external gear 30.

[0052] The sealing portion 90 is, for example, an annular O-ring. In this case, the sealing portion 90 is made of rubber, which is an elastic material. The sealing portion 90 conforms tightly to the outer surface of the thickened portion 31 and the groove 91 while undergoing elastic deformation. This closes the space between the thickened portion 31 and the peripheral wall portion 72.

[0053] However, the sealing portion 90 may be formed by applying a fluid resin sealing material to the groove 91. In that case, the sealing material hardens while in contact with the outer surface of the thickened portion 31 and the groove 91. This closes the gap between the thickened portion 31 and the peripheral wall portion 72.

[0054] <4-3. Third Embodiment> Next, the sealing portion 90 of the third embodiment will be described. Figure 10 is a partial longitudinal cross-sectional view of the power transmission device 1 including the sealing portion 90 of the third embodiment. As shown in Figure 10, the power transmission device 1 has a sealing portion 90. The sealing portion 90 is an O-ring or a sealing material.

[0055] In the example shown in Figure 10, an annular sealing portion 90 is positioned between the outer ring 52 of the main bearing 50 and the peripheral wall portion 72 of the housing 70. In this way, the space between the outer ring 52 and the peripheral wall portion 72 is closed by the sealing portion 90. This prevents liquid or dust from entering the signal processing board 80 from between the outer ring 52 and the peripheral wall portion 72, and through the space between the thickened portion 31 and the peripheral wall portion 72.

[0056] Furthermore, the structure shown in Figure 10 also prevents liquid or dust that seeps in from between the outer ring 52 and the peripheral wall portion 72 from passing through the gap between the thick-walled portion 31 and the outer ring 52 and entering radially inward.

[0057] In the example shown in Figure 10, the outer ring 52 of the main bearing 50 has an annular groove 91 on its outer circumference. An annular sealing portion 90 is positioned in the groove 91. The sealing portion 90 contacts the circumferential wall portion 72 when fitted into the groove 91. In this way, the sealing portion 90 can be positioned without providing a groove 91 in the housing 70. Furthermore, compared to the first and second embodiments, the pressure of the sealing portion 90 can suppress the circumferential wall portion 72 from bulging radially outward.

[0058] For example, when the power transmission device 1 is mounted on the robot 100, if the outer surface of the peripheral wall portion 72 is fitted into a part of the base frame 101, or if the outer surface of the peripheral wall portion 72 is used for positioning relative to the base plate 101, then if the peripheral wall portion 72 bulges radially outward, it may cause problems in mounting the power transmission device 1. However, the power transmission device 1 of this embodiment can prevent such problems.

[0059] It should be noted that, as in the first and second embodiments, providing a groove 91 for arranging the sealing portion 91 in the peripheral wall portion 72 does not necessarily cause the peripheral wall portion 72 to bulge radially outward. By appropriately adjusting the strength of the peripheral wall portion 72, the pressing force from the O-ring or sealing material, etc., bulging can be prevented.

[0060] The sealing portion 90 is, for example, an annular O-ring. In this case, the sealing portion 90 is formed of an elastic material, such as rubber. The sealing portion 90 conforms tightly to the inner surface of the peripheral wall portion 72 and the groove 91 while undergoing elastic deformation. This closes the space between the peripheral wall portion 72 and the outer ring 52.

[0061] However, the sealing portion 90 may be formed by applying a fluid resin sealing material to the groove 91. In that case, the sealing material hardens while in contact with the inner surface of the peripheral wall portion 72 and the groove 91. This closes the gap between the peripheral wall portion 72 and the outer ring 52.

[0062] <4-4. Fourth Embodiment> Next, the sealing portion 90 of the fourth embodiment will be described. Figure 11 is a partial longitudinal cross-sectional view of the power transmission device 1 including the sealing portion 90 of the fourth embodiment. As shown in Figure 11, the power transmission device 1 has a sealing portion 90. The sealing portion 90 is an O-ring or a sealing material.

[0063] In the example shown in Figure 11, an annular sealing portion 90 is positioned between the thickened portion 31 of the flexible external gear 30 and the peripheral wall portion 72 of the housing 70. In this way, the space between the thickened portion 31 and the peripheral wall portion 72 is closed by the sealing portion 90. This prevents liquid or dust from entering the signal processing board 80 from between the outer ring 52 and the peripheral wall portion 72, and through the space between the thickened portion 31 and the peripheral wall portion 72.

[0064] In the example shown in Figure 11, the thick-walled portion 31 of the flexible external gear 30 has an annular groove 91 on its outer circumferential surface. An annular sealing portion 90 is positioned in the groove 91. The sealing portion 90 contacts the circumferential wall portion 72 when fitted into the groove 91. In this way, the sealing portion 90 can be positioned without providing a groove 91 in the housing 70. Furthermore, compared to the first and second embodiments, the pressure of the sealing portion 90 can suppress the circumferential wall portion 72 from bulging radially outward.

[0065] The sealing portion 90 is, for example, an annular O-ring. In this case, the sealing portion 90 is formed of an elastic material, such as rubber. The sealing portion 90 conforms tightly to the inner surface of the peripheral wall portion 72 and the groove 91 while undergoing elastic deformation. This closes the space between the peripheral wall portion 72 and the thickened portion 31.

[0066] However, the sealing portion 90 may be formed by applying a fluid resin sealing material to the groove 91. In that case, the sealing material hardens while in contact with the inner surface of the peripheral wall portion 72 and the groove 91. This closes the gap between the peripheral wall portion 72 and the thickened portion 31.

[0067] <4-5. Fifth Embodiment> Next, the sealing portion 90 of the fifth embodiment will be described. Figure 12 is a partial longitudinal cross-sectional view of the power transmission device 1 including the sealing portion 90 of the fifth embodiment. As shown in Figure 12, the power transmission device 1 has a sealing portion 90. The sealing portion 90 is an O-ring or a sealing material.

[0068] In the example shown in Figure 12, an annular sealing portion 90 is positioned in the gap between the thickened portion 31 of the flexible external gear 30, the outer ring 52 of the main bearing 50, and the peripheral wall portion 72. In this way, the space between the thickened portion 31, the outer ring 52, and the peripheral wall portion 72 is closed by the sealing portion 90. This prevents liquid or dust from entering the signal processing board 80 from between the outer ring 52 and the peripheral wall portion 72, and through the space between the thickened portion 31 and the peripheral wall portion 72.

[0069] Furthermore, the structure shown in Figure 12 also prevents liquid or dust that seeps in from between the outer ring 52 and the peripheral wall portion 72 from passing radially inward through the gap between the thick-walled portion 31 and the outer ring 52.

[0070] In the example shown in Figure 12, the sealing portion 90 is positioned in the gap between the tapered surface provided at one axial end of the outer circumferential surface of the outer ring 52, the tapered surface provided at the other axial end of the outer circumferential surface of the thickened portion 31, and the inner circumferential surface of the circumferential wall portion 72. In this way, the sealing portion 90 can be positioned without providing grooves in the thickened portion 31, the outer ring 52, or the circumferential wall portion 72.

[0071] The sealing portion 90 is formed, for example, by applying a sealing material, such as a fluid resin, to the gap at the boundary between the thick-walled portion 31, the outer ring 52, and the peripheral wall portion 72. In this case, the sealing material hardens while in contact with the thick-walled portion 31, the outer ring 52, and the peripheral wall portion 72. This closes the space between the thick-walled portion 31, the outer ring 52, and the peripheral wall portion 72.

[0072] However, the sealing portion 90 may be an annular O-ring. In that case, the sealing portion 90 is formed of an elastic material, rubber. The sealing portion 90 conforms tightly to the thickened portion 31, the outer ring 52, and the peripheral wall portion 72 while undergoing elastic deformation. This closes the space between the thickened portion 31, the outer ring 52, and the peripheral wall portion 72.

[0073] <4-6. Sixth Embodiment> Next, the sealing portion 90 of the sixth embodiment will be described. Figure 13 is a partial longitudinal cross-sectional view of the power transmission device 1 including the sealing portion 90 of the sixth embodiment. As shown in Figure 13, the power transmission device 1 has a sealing portion 90.

[0074] In the example shown in Figure 13, the sealing portion 90 is positioned between the other axial end of the peripheral wall portion 72 and the outer circumferential surface of the outer ring 52. In this way, the space between the other axial end of the peripheral wall portion 72 and the outer ring 52 is closed by the sealing portion 90. This prevents liquid or dust from entering the signal processing substrate 80 from between the outer ring 52 and the peripheral wall portion 72, and through the space between the thickened portion 31 and the peripheral wall portion 72.

[0075] Furthermore, the structure shown in Figure 13 prevents liquid or dust from entering the space between the outer ring 52 and the peripheral wall 72.

[0076] The sealing portion 90 is formed, for example, by applying a sealing material, such as a fluid resin, between the other axial end of the peripheral wall portion 72 and the outer circumferential surface of the outer ring 52. In this case, the sealing material hardens while in contact with the peripheral wall portion 72 and the outer ring 52. This closes the space between the other axial end of the peripheral wall portion 72 and the outer ring 52. Furthermore, since the sealing portion 90 is exposed to the outside, it is easy to check the application state of the sealing material.

[0077] In the embodiments described above, the effect of preventing liquid or dust from adhering to the circuit board has been explained, but there are other effects as well. For example, the power transmission device 1 uses lubricant in the meshing portion between the internal teeth 21 and the external teeth 34, the flexible bearing 42, the main bearing 50, and the sub-bearing 54. Mechanical seals and O-rings are provided nearby to prevent the ingress of liquid or dust from the outside, but by providing the sealing portion 90, these lubricants can be kept even cleaner.

[0078] <5. Variation> While embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above.

[0079] <5-1. Regarding assembly holes> Figure 14 is a partial longitudinal cross-sectional view of a power transmission device 1 including a modified sealing portion 90. In the example of Figure 14, the outer ring 52 of the main bearing 50 has an assembly hole 55. The assembly hole 55 is a hole for inserting a roller 53 or grease between the inner ring 51 and the outer ring 52. The assembly hole 55 penetrates radially through a portion of the outer ring 52 in the circumferential direction.

[0080] In the example shown in Figure 14, the sealing portion 90 is positioned in a different axial direction from the assembly hole 55. In this way, for example, if an O-ring is used as the sealing material 90, a gap is formed between the O-ring and the step created on the surface of the closed assembly hole 55, preventing liquid or dust from entering through this gap. In other words, the sealing portion 90 can properly seal the space between the outer ring 52 and the peripheral wall portion 72 without being affected by the assembly hole 55.

[0081] <5-2. About Sensors> In the above embodiment, the sensor 60 had one set of torque sensors. However, the sensor 60 may have multiple sets of torque sensors. In that case, even if an abnormality such as a broken wire occurs in one torque sensor, the torque can still be detected normally by the other torque sensors.

[0082] Furthermore, the sensor 60 may also have a rotation angle sensor. The rotation angle sensor is composed of, for example, a plurality of strain gauges arranged in the circumferential direction. The rotation angle sensor detects the rotation angle of the power transmission device 1 by detecting the periodic deflection deformation corresponding to the rotation angle of the diaphragm portion 32 using the plurality of strain gauges. The signal processing circuit may also have a function to correct periodic errors occurring in the detection signal of the torque sensor based on the detection signal obtained from the rotation angle sensor.

[0083] Furthermore, the sensor 60 may also have a temperature sensor. The temperature sensor is, for example, composed of an arc-shaped resistance wire centered on the central axis 9. The resistance value of this resistance wire is less affected by the bending deformation of the diaphragm portion 32, and therefore changes due to temperature are dominant. Accordingly, the temperature of the diaphragm portion 32 can be detected according to the resistance value of this resistance wire.

[0084] <5-3. Regarding the main bearings> In the above embodiment, the main bearing 50 was a cross roller bearing. However, the main bearing 50 may be a bearing other than a cross roller bearing. For example, the main bearing 50 may be a roller bearing, a ball bearing, or a sliding bearing. Also, the main bearing 50 may be composed of multiple bearings.

[0085] <5-4. Other variations> In the above embodiment, a power transmission device 1 mounted on a robot 100 was described. However, a power transmission device 1 with a similar structure may be mounted on other devices such as assist suits and automated guided vehicles. In particular, as mentioned above, the power transmission device 1 can suppress the ingress of liquids and dust, so it is suitable when the device on which it is mounted is used in an environment with a lot of liquids and dust.

[0086] Furthermore, the power transmission device and the detailed configuration of the robot may be modified as appropriate, without departing from the spirit of this disclosure. In addition, elements appearing in the above embodiments and modifications may be selected and combined as appropriate, without causing any inconsistencies.

[0087] <6. Summary> This technology can be configured as follows:

[0088] (1) A power transmission device comprising: an internal gear having a plurality of internal teeth; a flexible external gear having a plurality of external teeth meshing with the internal teeth; a main bearing having an inner ring fixed to the internal gear and an outer ring fixed to the flexible external gear; and a housing fixed to the flexible external gear, wherein the housing has an end wall portion that covers one axial end face of the flexible external gear, and a cylindrical circumferential wall portion that extends axially from the end wall portion and covers the outer circumferential surfaces of the flexible external gear and the outer ring, and further comprises an annular sealing portion disposed between the flexible external gear or the outer ring and the circumferential wall portion.

[0089] (2) A power transmission device according to (1), wherein the flexible external gear is located between the end wall and the outer ring and has a thickened portion fixed to the end wall and the outer ring, a diaphragm portion extending radially inward from the thickened portion, a cylindrical body portion extending axially to the other side from the diaphragm portion, and the external teeth formed on the outer circumferential surface of the body portion, and the sealing portion is disposed between the thickened portion or the outer ring and the circumferential wall.

[0090] (3)(2) A power transmission device according to (2), further comprising a sensor attached to the diaphragm portion and a signal processing board electrically connected to the sensor, wherein the signal processing board is fixed to the end wall portion.

[0091] (4)(3) A power transmission device according to (3), wherein the signal processing board is arranged on one axial side surface of the end wall portion, the end wall portion has a wiring hole that penetrates in the axial direction, and the sensor and the signal processing board are electrically connected via a cable inserted into the wiring hole.

[0092] (5) A power transmission device according to any one of (1) to (4), wherein the peripheral wall portion has an annular groove on its inner circumferential surface, and the sealing portion is arranged in the groove.

[0093] (6) A power transmission device according to any one of (1) to (5), wherein the flexible external gear or the outer ring has an annular groove on its outer surface, and the sealing portion is arranged in the groove.

[0094] (7) A power transmission device according to any one of (1) to (6), wherein the sealing portion is located in the gap between the boundary of the flexible external gear, the outer ring, and the peripheral wall portion.

[0095] (8) A power transmission device according to any one of (1) to (7), wherein the sealing portion is disposed between the other axial end of the peripheral wall portion and the outer circumferential surface of the outer ring.

[0096] (9) A power transmission device according to any one of (1) to (8), wherein the sealing portion is an O-ring or a sealant.

[0097] (10) A power transmission device according to any one of (1) to (9), wherein the outer ring has an assembly hole that penetrates radially, and the sealing portion is located at an axial position different from the assembly hole.

[0098] (11) A power transmission device according to any one of (1) to (10), wherein the main bearing is a cross roller bearing.

[0099] (12) A robot equipped with a power transmission device as described in any one of (1) through (11). [Industrial applicability]

[0100] This disclosure can be used in power transmission devices and robots. [Explanation of symbols]

[0101] 1: Power transmission device 9: Central axis 10: Shaft 20: Internal gear 21: Inner teeth 30: Flexible external gear 31: Thick wall part 32: Diaphragm section 33: Torso 34: External teeth 40: Wave Generator 41: Cam 42: Flexible bearing 50: Main bearing 51: Inside 52: Outer ring 53: Laura 54: Sub-bearing 55: Assembly hole 60: Sensor 70: Housing 71: End wall section 72: Peripheral wall part 73: Wiring hole 80: Signal processing board 81: Cable 90: Sealing part 91: Groove 100: Robot 101: Base frame 102: Arm 103: Motor 601: Film substrate 602: Conductor layer C: Bridge circuit Ra: First strain gauge Rb: Second strain gauge Rc: Third strain gauge Rd: 4th strain gauge V: Voltmeter r: resistance wire

Claims

1. An internal gear having multiple internal teeth, A flexible external gear having multiple external teeth that mesh with the internal teeth, A main bearing having an inner ring fixed to the internal gear and an outer ring fixed to the flexible external gear, A housing fixed to the aforementioned flexible external gear, A power transmission device equipped with, The aforementioned housing is The end wall portion covers the end face on one axial side of the aforementioned flexible external gear, A cylindrical circumferential wall portion extends axially from the end wall portion and covers the outer circumferential surface of the flexible external gear and the outer ring, It has, An annular sealing portion disposed between the flexible external gear or the outer ring and the peripheral wall portion. A power transmission device that further incorporates these features.

2. A power transmission device according to claim 1, The aforementioned flexible external gear is A thickened portion is located between the end wall portion and the outer ring and is fixed to the end wall portion and the outer ring, The diaphragm portion extends radially inward from the aforementioned thickened portion, A cylindrical body extending from the diaphragm portion to the other side in the axial direction, The external teeth formed on the outer circumferential surface of the body portion, It has, The sealing portion is a power transmission device disposed between the thickened portion or the outer ring and the peripheral wall portion.

3. A power transmission device according to claim 2, The sensor attached to the diaphragm portion, A signal processing board electrically connected to the aforementioned sensor, Furthermore, A power transmission device in which the signal processing board is fixed to the end wall portion.

4. A power transmission device according to claim 3, The signal processing board is arranged on one axial side surface of the end wall portion, The end wall portion has a wiring hole that penetrates in the axial direction. A power transmission device in which the sensor and the signal processing board are electrically connected via a cable inserted into the wiring hole.

5. A power transmission device according to any one of claims 1 to 4, The aforementioned peripheral wall portion has an annular groove on its inner circumferential surface. The sealing portion is a power transmission device positioned in the groove.

6. A power transmission device according to any one of claims 1 to 4, The flexible external gear or the outer ring has an annular groove on its outer surface, The sealing portion is a power transmission device positioned in the groove.

7. A power transmission device according to any one of claims 1 to 4, The sealing portion is located in the gap between the flexible external gear, the outer ring, and the peripheral wall portion of the power transmission device.

8. A power transmission device according to any one of claims 1 to 4, The sealing portion is a power transmission device located between the other axial end of the peripheral wall and the outer circumferential surface of the outer ring.

9. A power transmission device according to any one of claims 1 to 4, The sealing portion is an O-ring or a sealant in a power transmission device.

10. A power transmission device according to any one of claims 1 to 4, The outer ring has an assembly hole that penetrates radially, The sealing portion is located in a position in the axial direction different from the assembly hole in the power transmission device.

11. A power transmission device according to any one of claims 1 to 4, The aforementioned main bearing is a cross roller bearing in a power transmission device.

12. A robot equipped with a power transmission device according to any one of claims 1 to 4.

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