Actuator

Abstract

This actuator includes a motor, a speed reducer, a first hollow shaft constituting the rotor of the motor, a second hollow shaft fixed to an output shaft of the speed reducer, a primary encoder for detecting the position of the motor shaft of the motor, and a secondary encoder for detecting the position of the output shaft of the speed reducer. A first detecting portion of the primary encoder is fixed to the stator of the motor or a housing of the actuator.

Description

Actuator

[0001] This disclosure relates to an actuator.

[0002] The actuator includes a servo motor and a speed reducer connected to each other. A primary encoder is connected to the motor shaft of the servo motor to detect the absolute position within one rotation of the motor shaft. Similarly, a secondary encoder is connected to the output shaft of the speed reducer to detect the absolute position within one rotation of the output shaft. And the total number of rotations of the primary encoder and / or the secondary encoder is detected (see, for example, Japanese Patent Publication No. 2023-505330).

[0003] Since the dimensional error in the axial direction of the output shaft of the speed reducer is relatively large, it is difficult to appropriately manage the gap between the rotating disk of the secondary encoder and the magnetic sensor therefor.

[0004] In International Publication No. 2024-166391, it is disclosed that a first coupling portion that couples the output shaft of the speed reducer and the rotating disk of the secondary encoder to each other includes a spline or an oldham coupling. In this case, the management of the gap between the rotating disk of the secondary encoder and the magnetic sensor therefor becomes relatively easy.

[0005] Japanese Patent Publication No. 2023-505330, International Publication No. 2024-166391

[0006] However, even in International Publication No. 2024-166391, it is difficult to appropriately manage the gap between the rotating disk of the primary encoder and the output shaft. Also, during the manufacture or maintenance of the actuator, the positional relationship between the rotating disk of the primary encoder and the magnetic sensor therefor may shift, resulting in a decrease in the accuracy of the encoder.

[0007] Furthermore, there is a requirement to facilitate the attachment and detachment of a substrate equipped with an encoder circuit for position calculation during the manufacture or maintenance of the actuator.

[0008] Therefore, there is a need for an actuator that can properly manage the gap between the primary encoder's rotating disk and its magnetic sensor, and that allows for easy attachment and detachment of the encoder circuit board.

[0009] According to the first aspect of this disclosure, a is provided.

[0010] The purposes, features, and advantages of this disclosure will become even clearer from the following description of embodiments related to the accompanying drawings.

[0011] This is an axial cross-sectional view of an actuator according to the first embodiment of this disclosure. This is a partially exploded view of the actuator in the first embodiment. This is an axial cross-sectional view of an actuator according to the second embodiment of this disclosure. This is a partially exploded view of the actuator in the second embodiment. This is an axial cross-sectional view of an actuator according to the third embodiment. This is an axial cross-sectional view of an actuator in the prior art. This is a partially exploded view of an actuator in the prior art.

[0012] Embodiments of the present disclosure will be described below with reference to the attached drawings. Throughout the drawings, corresponding components are denoted by the same reference numerals. Figure 1A is an axial cross-sectional view of an actuator according to a first embodiment of the present disclosure. The actuator 5a is incorporated into a machine having a shaft, such as a robot. The following description will focus on the case where the actuator 5a is incorporated into a robot, but the same applies to the case where the actuator 5a is incorporated into another machine having a shaft, such as a machine tool.

[0013] The actuator 5a mainly includes a motor 10 consisting of a stator 11 and a rotor 12, such as a servo motor, an electromagnetic brake B connected to the motor 10, a reduction gear 20 connected to the motor shaft 13 of the motor 10, a force sensor S coupled to the reduction gear, and an encoder E.

[0014] In this application, the reduction gear 20 is defined as being positioned in front of the motor 10, and the motor 10 is defined as being positioned behind the reduction gear 20. Furthermore, in principle, "radial direction" in this application refers to the radial direction of the actuator 5a, etc., and "axial direction" refers to the axial direction of the actuator 5a, etc.

[0015] The motor 10 includes a rotor 12 that rotates integrally with the motor shaft 13, and a stator 11 that surrounds the rotor 12. The stator 11 is fixed to the inner circumferential surface of the housing 10a of the actuator 5a. The tip of the output shaft 23 of the reduction gear 20 is connected to a link 2 (not shown) via a force sensor S. Therefore, the actuator 5 controls the position by rotating the link 2 (not shown) relative to the actuator 5 within a predetermined operating range. The reduction ratio of the reduction gear 20 is, for example, 1:50.

[0016] The motor shaft 13 is, for example, a hollow shaft, and a primary encoder 15 equipped with a rotating disk 15A is attached to its rear end. The primary encoder 15 is, for example, an absolute encoder and outputs A-phase, B-phase, and Z-phase signals. The output signals are detected by the detection unit 15B, and the absolute position of the motor shaft 13 within one rotation and the total number of rotations of the motor shaft 13 are detected by known methods. The detected information is stored in the memory of the detection unit 15B, for example, volatile memory or non-volatile memory.

[0017] An extension 23a, for example, a hollow tube, is connected to the output shaft 23 of the reduction gear 20, and this extension 23a extends towards the motor 10 through the hollow motor shaft 13. A secondary encoder 25 equipped with a rotating disk 25A is attached to the rear end of the extension 23a. Note that the output shaft 23 of the reduction gear 20 and the extension 23a may be integrally formed. In other words, the extension 23a can be a part of the output shaft 23. Therefore, in the following, "extension 23a" may be referred to as "output shaft 23".

[0018] The secondary encoder 25 is, for example, an absolute encoder and outputs A-phase, B-phase, and Z-phase signals. The output signals are detected by the detection unit 25B, and the absolute position and total number of rotations within one revolution of the output shaft 23 are detected using a known method. The detected information is stored in the memory of the detection unit 25B, for example, volatile memory or non-volatile memory. Note that the primary encoder 15 and the secondary encoder 25 are sometimes collectively referred to as encoder E.

[0019] The force sensor S consists of a torque sensor or the like that detects the force acting around the axis of the actuator 5a. Preferably, the force sensor S has a spring portion (not shown) that exhibits spring properties. When a force is acted around the axis of the actuator 5a, the spring portion deforms, so the force acting around the axis can be detected through the amount of deformation of the spring portion. The force sensor S may be a strain gauge type, a capacitance type, a magnetic type, or an optical encoder type, etc.

[0020] As shown in the figure, the force sensor S, reduction gear 20, motor 10, electromagnetic brake B, and encoder E, which are coaxially connected to each other, are preferably hollow in structure. Furthermore, it is preferable that the hollow portions of these force sensor S, reduction gear 20, motor 10, electromagnetic brake B, and encoder E have a common inner diameter. This allows for the smooth arrangement of extensions 23a, such as hollow tubes. Hereinafter, the internal spaces of the force sensor S, reduction gear 20, motor 10, electromagnetic brake B, and encoder E may be collectively referred to as the hollow portion 22. At least one wire (not shown), such as a signal line or current supply line, passes through the hollow portion 22. Note that, as will be described later, even if the actuator 5a does not include the force sensor S and / or the electromagnetic brake B, it is still within the scope of this disclosure.

[0021] As shown in Figure 1A, a radially extending circular first support member 18 is attached to the rear end of the motor shaft 13. The first support member 18 is provided with an annular projection 18a, and it is preferable that the projection 18a engages with the rear end of the motor shaft 13. From the radially outer portion of the first support member 18, an annular extension 18b extends in the axial direction of the motor shaft 13 so as to be spaced away from the motor 10. An annular rotating disk 15A for the primary encoder 15 is provided on the outer circumferential surface of this extension 18b. In other words, the rotating disk 15A is supported by a part of the first support member 18. In embodiments not shown, the first support member 18 may not have an extension 18b, and the rotating disk 15A may be directly provided on the outer circumferential surface of the first support member 18.

[0022] Furthermore, the housing 10a extends towards the rear end in the axial direction of the motor shaft 13 so as to be spaced away from the motor 10. A detection unit 15B is provided on the inner circumferential surface of the portion extending in the axial direction. The detection unit 15B is positioned to face the outer circumferential surface of the rotating disk 15A with a predetermined gap between them. The detection unit 15B detects the position of the outer circumferential surface of the rotating disk 15A.

[0023] As mentioned above, the stator 11 of the motor 10 is fixed to the housing 10a. Therefore, the detection unit 15B is provided so as to be integral with the housing 10a and the stator 11. In other words, it can be said that the detection unit 15B is fixed to the stator 11.

[0024] Furthermore, a flange 10b is provided at the rear end of the housing 10a of the actuator 5a. A cylindrical extension member 41 is attached to the flange 10b. The rear end surface of the extension member 41 extends radially inward. A second support member 28 is attached to the inner circumferential surface of the portion extending radially inward via a bearing 29. The inner diameter of the second support member 28 is approximately equal to the inner diameter of the hollow portion 22. The circuit board 42, which is equipped with the detection unit 25B of the secondary encoder 25, is attached to the inner circumferential surface of the extension member 41. The detection unit 15B of the primary encoder 15 is physically and electrically connected to the circuit board 42 via a connector 39.

[0025] The second support member 28 extends from the rear end of the actuator 5a toward the reduction gear 20, and the tip of the portion extending toward the reduction gear 20 extends radially outward. An annular rotating disk 25A for the secondary encoder 25 is provided on the rear end face of the portion extending radially outward. In other words, the rotating disk 25A is supported by a portion of the second support member 28. The detection unit 25B is positioned to face the end face of the rotating disk 25A with a predetermined gap between them. The detection unit 25B detects the position of the end face of the rotating disk 25A.

[0026] In the first embodiment shown in Figure 1A, the extension 23a (output shaft 23) of the reduction gear 20 and the rotating disk 25A are connected to each other by a first coupling portion 31. More precisely, the extension 23a of the reduction gear 20 and the second support member 28 that supports the rotating disk 25A are connected to each other by the first coupling portion 31. It is also possible to interpret the second support member 28 as being part of the first coupling portion 31.

[0027] The first coupling portion 31 plays the role of sliding a portion 6a of the actuator 5a, which includes the rotating disk 25A of the secondary encoder 25, in the axial direction of the actuator 5a to connect it to the output shaft 23. Furthermore, the first coupling portion 31 is configured to prevent the portion 6a of the actuator 5a from moving in the circumferential and radial directions of the actuator 5a.

[0028] A typical first coupling 31 is a combination of splines and grooves. That is, a plurality of splines are formed on either the outer circumferential surface of the output shaft 23 or the inner circumferential surface of the second support member 28, and a plurality of grooves that engage with the plurality of splines are formed on the other of the outer circumferential surface of the output shaft 23 or the inner circumferential surface of the second support member 28. The splines and grooves have a predetermined length in the axial direction of the actuator 5a. Alternatively, the first coupling 31 may be a combination of a key and a keyway formed to extend in the axial direction of the actuator 5a. The first coupling 31 may also be an Oldham joint.

[0029] Figure 1B is an exploded view of the actuator in the first embodiment. As shown in Figure 1B, unit 6a, which is part of actuator 5a, includes an extension member 41, a bearing 29, a second support member 28, a circuit board 42 equipped with a detection unit 25B, a secondary encoder 25, and a connector 39. Unit 6a is configured to operate as a single unit.

[0030] When unit 6a is slid toward the output shaft 23 in the axial direction of actuator 5a, the second support member 28 of unit 6a is coupled to the output shaft 23 by the first coupling portion 31. As a result, unit 6a does not move in the circumferential or radial direction of actuator 5a. The extension member 41 is to be separately fixed to the flange 10b of housing 10a with screws or the like.

[0031] Then, when unit 6a is slid away from the output shaft 23 in the axial direction of actuator 5a, unit 6a separates. As shown in Figure 1B, unit 6a includes the rotating disk 25A and the detection unit 25B of the secondary encoder 25. In other words, even if unit 6a is removed during the manufacture or maintenance of actuator 5a, the rotating disk 25A and the detection unit 25B do not separate from each other. Therefore, the gap between the rotating disk 25A and the detection unit 25B is maintained.

[0032] Therefore, in the first embodiment, the positional relationship between the rotating disk 25A and the detection unit 25B does not shift and the gap does not change during the manufacturing or maintenance of the actuator 5a. Thus, in the first embodiment, a decrease in the accuracy of the secondary encoder 25 can be further avoided.

[0033] Furthermore, in the first embodiment, the rotating disk 15A of the primary encoder 15 is coupled to the first support member 18, and the detection unit 15B is coupled to the inner circumferential surface of the housing 10a. In other words, the aforementioned unit 6a does not include the rotating disk 15A and the detection unit 15B. Therefore, even if unit 6a is removed during the manufacture or maintenance of the actuator 5a, the rotating disk 15A and the detection unit 15B will not separate from each other. That is, the gap between the rotating disk 15A and the detection unit 15B is maintained.

[0034] Therefore, in the first embodiment, the positional relationship between the rotating disk 15A and the detection unit 15B does not shift and the gap does not change during the manufacturing or maintenance of the actuator 5a. Thus, in the first embodiment, a decrease in the accuracy of the primary encoder 15 can be further avoided.

[0035] In other words, in the first embodiment, the gap between the rotating disk 15A and the detection unit 15B and the gap between the rotating disk 25A and the detection unit 25B can be appropriately controlled. Furthermore, after separating the unit 6a including the encoder circuit board 42, the board 42 can be easily attached, detached, and replaced.

[0036] By the way, Figure 4A is an axial cross-sectional view of actuator 5' in the prior art, and Figure 4B is a partially exploded view of actuator 5' in the prior art. As shown in these drawings, in the prior art, the substrate 42 attached to the extension member 41 is equipped with both detection units 15B and 25B.

[0037] Therefore, as can be seen from Figure 4B, when the unit 6' described above is removed during maintenance, the rotating disk 15A and the detection unit 15B of the primary encoder 15 become separated from each other. Consequently, although the gap between the rotating disk 25A and the detection unit 25B can be maintained, the gap between the rotating disk 15A and the detection unit 15B cannot be maintained. Then, when the actuator 5' is reassembled or manufactured, it becomes difficult to reproduce the gap between the rotating disk 15A and the detection unit 15B, and as a result, in the conventional technology, there was a problem that the detection accuracy of the primary encoder 15 was reduced.

[0038] In contrast, in this disclosure, as described above, the gap between the rotating disk 15A and the detection unit 15B of the primary encoder 15 can be maintained. Therefore, even when the actuator 5 is reassembled or manufactured, the detection accuracy of the primary encoder 15 does not decrease.

[0039] Figure 2A is an axial cross-sectional view of the actuator 5b in a second embodiment of the present disclosure. The main difference between the first embodiment shown in Figure 1A and the second embodiment shown in Figure 2A is that the first support member 18 in the second embodiment does not have an extension 18b. The rotating disk 15A of the primary encoder 15 is provided on the rear end face of the first support member 18.

[0040] Furthermore, as can be seen in Figure 2A, a portion of the housing 10a extends toward the rear end in a direction away from the motor 10. A projection 10c extending radially inward from the actuator 5b is provided on the inner circumferential surface of this extended portion. The detection unit 15B of the primary encoder 15 is provided on the front end side of the projection 10c. As shown in the figure, the detection unit 15B is provided with a predetermined gap so as to face the rotating disk 15A. In Figure 2A, the detection unit 15B faces the end face of the rotating disk 15A, and the detection unit 15B detects the position of the end face of the rotating disk 15A. Preferably, the detection unit 15B is connected to the substrate 42 via a connector or wire (not shown).

[0041] Figure 2B is a partially exploded view of the actuator in the second embodiment. As described above, unit 6b, which is part of actuator 5b, is removed using the first coupling part 31. Unit 6b includes an extension member 41, a bearing 29, a second support member 28, a substrate 42 equipped with a detection unit 25B, and a rotating disk 25A. As described above, unit 6b is configured to operate integrally. Therefore, as described above, the gap between the rotating disk 25A and the detection unit 25B is maintained. Accordingly, the detection accuracy of the secondary encoder 25 does not decrease during manufacturing or maintenance of actuator 5b.

[0042] Furthermore, in the second embodiment, the rotating disk 15A of the primary encoder 15 is coupled to the first support member 18, and the detection unit 15B is coupled to a projection 10c extending from the housing 10a. In other words, the aforementioned unit 6b does not include the rotating disk 15A and the detection unit 15B. Therefore, even if unit 6b is removed during the manufacturing or maintenance of the actuator 5a, the rotating disk 15A and the detection unit 15B do not separate from each other. That is, the gap between the rotating disk 15A and the detection unit 15B is maintained. Therefore, the detection accuracy of the primary encoder 15 does not decrease during the manufacturing or maintenance of the actuator 5b. Thus, the same effects as described above can be obtained.

[0043] Figure 3 is an axial cross-sectional view of an actuator in another embodiment. The actuator 5c shown in Figure 3 mainly includes a motor 10 consisting of a stator 11 and a rotor 12, a reduction gear 20 connected to the motor 10, and an encoder E. In other words, actuator 5c has the same configuration as actuator 5a, but without the force sensor S and electromagnetic brake B. In this case as well, the same effects as described above can be obtained. Furthermore, in this case, it can be seen that actuator 5c can be made even smaller. Also, even if the actuators 5a to 5b described above do not include the force sensor S and / or electromagnetic brake B, they are still included in the scope of this disclosure.

[0044] As an effect of at least one of the embodiments described above, the gap between the rotating disk of the primary encoder and the magnetic sensor therefor can be appropriately managed, and the substrate of the encoder circuit can be easily attached and detached.

[0045] Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the individual embodiments described above. These embodiments can be variously added, replaced, changed, partially deleted, etc., without departing from the gist of the invention, or without departing from the spirit and scope of the invention derived from the content described in the claims and its equivalents. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as an example and are not limited thereto. The same applies when numerical values or mathematical formulas are used in the description of the above-described embodiments. Furthermore, appropriately combining some of the foregoing embodiments is included in the scope of the present disclosure.

[0046] With respect to the above embodiments and variations, the following additional notes are disclosed. (Note 1) An actuator comprising: a motor including a rotor and a stator; a reduction gear connected to the motor; a first hollow shaft constituting the rotor of the motor; a second hollow shaft fixed to the output shaft of the reduction gear; and a primary encoder for detecting the position of the motor shaft of the motor, wherein the primary encoder has a first rotating disk that rotates integrally with the first hollow shaft and a first detection unit that faces the first rotating disk and detects its position, and further comprises a secondary encoder for detecting the position of the output shaft of the reduction gear, wherein the secondary encoder has a second rotating disk that rotates integrally with the second hollow shaft and a second detection unit that faces the second rotating disk and detects its position, and the first detection unit is fixed to the stator of the motor or the housing of the actuator. (Note 2) The actuator according to Note 1, further comprising: a substrate on which the second detection unit is mounted; and a connector or inter-substrate connector for connecting the first detection unit and the substrate. (Note 3) The actuator according to Note 1, wherein the first detection unit detects the position of the outer circumferential surface of the first rotating disk. (Note 4) The actuator according to Note 1, wherein the first detection unit detects the position of the end face of the first rotating disk. (Note 5) The actuator according to Note 1, further comprising a first coupling unit that slides a portion of the actuator, including the second rotating disk of the secondary encoder, in the axial direction of the actuator to connect it to the second hollow shaft. (Note 6) The actuator according to Note 5, wherein the first coupling unit includes a spline or an Oldham joint. (Note 7) The actuator according to Note 1, wherein the first detection unit and the second detection unit are magnetic sensors or optical sensors.

[0047] 5a-5c Actuator 6a, 6b Unit 10 Motor 10a Housing 10b Flange 11 Stator 12 Rotor 13 Motor shaft 15 Primary encoder 15A Rotating disk 15B Detection unit 18 First support member 18a Projection 20 Reducer 23 Output unit 23a Extension unit 25 Secondary encoder 25A Rotating disk 25B Detection unit 28 Second support member 29 Bearing 31 First coupling unit 39 Connector 41 Extension member 42 Circuit board B Electromagnetic brake E Encoder S Force sensor

Claims

1. An actuator comprising: a motor including a rotor and a stator; a reduction gear connected to the motor; a first hollow shaft constituting the rotor of the motor; a second hollow shaft fixed to the output shaft of the reduction gear; and a primary encoder for detecting the position of the motor shaft of the motor, wherein the primary encoder has a first rotating disk that rotates integrally with the first hollow shaft and a first detection unit that faces the first rotating disk and detects its position; further comprising a secondary encoder for detecting the position of the output shaft of the reduction gear, wherein the secondary encoder has a second rotating disk that rotates integrally with the second hollow shaft and a second detection unit that faces the second rotating disk and detects its position; and the first detection unit is fixed to the stator of the motor or to the housing of the actuator.

2. The actuator according to claim 1, further comprising a substrate on which the second detection unit is mounted, and a connector or inter-substrate connector connecting the first detection unit and the substrate.

3. The actuator according to claim 1, wherein the first detection unit detects the position of the outer circumferential surface of the first rotating disk.

4. The actuator according to claim 1, wherein the first detection unit detects the position of the end face of the first rotating disk.

5. The actuator according to claim 1, further comprising a first coupling portion which slides a portion of the actuator, including the second rotating disk of the secondary encoder, in the axial direction of the actuator and connects it to the second hollow shaft.

6. The actuator according to claim 5, wherein the first coupling portion includes a spline or an Oldham joint.

7. The actuator according to claim 1, wherein the first detection unit and the second detection unit are magnetic sensors or optical sensors.

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