Harmonic Drive Actuator Gearhead

Abstract

A new method for mounting a harmonic drive gearhead to a cylindrical motor reduces the overall size of the actuator assembly. Specifically, the motor is mounted within the harmonic drive and its bearings, i.e., within the space normally occupied by the harmonic drive components. This is made possible by redesigning the harmonic drive so that it can enclose the motor and provide a compact footprint for the actuator assembly.

Description

Cross - reference to related applications

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 928,710, filed on October 31, 2019, which is hereby incorporated by reference in its entirety.

Technical Field

[0002] The present invention generally relates to motors. More specifically, the present invention relates to a harmonic drive actuator gearhead.

Background Art

[0003] The accuracy of computer - controlled motion requires a mechanical transmission with low backlash in the kinematic chain that links the motor to the driven element / end effector. When backlash (mechanical slack, play) exists, the driven element does not accurately follow the motion of the motor, which can result in kinematic errors and dynamic effects. Mechanical backlash affects the kinematic performance of robots, including medical robots. However, most mechanical transmissions are gear - based, and using gears makes it difficult to control backlash. There are few mechanical transmissions with minimal or no backlash, including ball screws, ball worms, cables, and harmonic drives.

[0004] A gearhead is a mechanical transmission attached to a motor within a typical actuator assembly, usually reducing speed and increasing torque by a transmission ratio. Since the motor and the gearhead are usually attached end - to - end, the overall length is the sum of the component lengths. The increased size limits the scope of application.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, it would be advantageous to provide a harmonic drive actuator gearhead. [Means for solving the problem]

[0006] The aforementioned needs are largely met by the present invention, and in one embodiment, the device assembly includes a motor and a gearhead actuator assembly. The gearhead is configured such that the motor is positioned in a space defined within the gearhead actuator assembly.

[0007] According to one aspect of the present invention, the device includes a bell-shaped harmonic drive wave generator. The device may include a bell-shaped motor mount. The motor is cylindrical. The motor is an electric motor. The bearings are laterally arranged to allow them to serve as both the harmonic drive and the main bearings of the device. The motor includes a gearhead. The device includes a harmonic drive with static and dynamic circular splines. The device includes a flexspline and an output shaft.

[0008] According to another aspect of the present invention, the harmonic gearhead assembly includes a motor. The harmonic gearhead assembly includes a static component and an output component. The output component is operably coupled to the motor such that the motor's operation generates a corresponding operation of the output component. The static component and the output component are arranged to define the space in which the motor is located.

[0009] According to yet another aspect of the present invention, the harmonic gearhead assembly further includes a bell-shaped harmonic drive wave generator. The harmonic gearhead assembly includes a bell-shaped motor mount. The motor is cylindrical. The motor is an electric motor. Bearings are arranged laterally to allow for dual use as the main bearings for the harmonic drive and the device. The motor includes a gearhead. The harmonic gearhead assembly may also include a harmonic drive with static and dynamic circular splines. The static circular splines are coupled to the static component, and the dynamic circular splines are coupled to the output component. The harmonic gearhead assembly may include flexsplines. The motor is mounted from the front of the motor. [Brief explanation of the drawing]

[0010] [Figure 1] This is a partial cross-sectional view of a redundant motor reducer drive. [Figure 2A] This is a diagram of a harmonic gearhead according to one embodiment of the present invention. [Figure 2B] This is a diagram of a harmonic gearhead according to one embodiment of the present invention. [Figure 2C] This is a diagram of a harmonic gearhead according to one embodiment of the present invention. [Figure 2D] This is a diagram of a harmonic gearhead according to one embodiment of the present invention. [Figure 2E] This is a diagram of a harmonic gearhead according to one embodiment of the present invention. [Figure 3] This is a diagram of a strain wave gear model. [Modes for carrying out the invention]

[0011] The accompanying drawings are used to more fully illustrate the representative embodiments disclosed herein and provide visual representations that can be used by those skilled in the art to better understand them and their inherent advantages. In these drawings, similar reference numerals shall identify corresponding elements.

[0012] Next, the subject matter currently disclosed will be fully described below with reference to the accompanying drawings illustrating some, but not all, embodiments of the present invention. Throughout this specification, similar figures refer to similar elements. The subject matter currently disclosed can be embodied in many different forms and should not be construed as being limited to the embodiments described herein, but rather these embodiments are provided to satisfy the applicable legal requirements of this disclosure. In fact, many modifications and other embodiments of the subject matter currently disclosed described herein will come to mind for those skilled in the art. Many of these modifications and other embodiments relate to the fact that the subject matter currently disclosed has the benefit of teaching presented in the foregoing description and the associated drawings. Therefore, it should be understood that the subject matter currently disclosed is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims.

[0013] The present invention relates to a novel method for mounting a Harmonic Drive® gearhead to a cylindrical motor, thereby reducing the overall size of the actuator assembly. Specifically, the motor is mounted within the Harmonic Drive and its bearings, i.e., in the space normally occupied by the Harmonic Drive components. This is made possible by redesigning the Harmonic Drive so that it can enclose the motor and provide a compact footprint for the actuator assembly.

[0014] In fact, according to the present invention, the overall size of the actuator assembly is comparable to the overall size of the harmonic drive and bearings alone. Furthermore, this arrangement allows the actuator to be used directly as a joint without the need for additional bearings, as the bearings can support the payload. By using a harmonic drive, the actuator also inherits the performance of a high transmission ratio with no backlash. The encoder is usually included in the motor. The motor is usually an electric motor, but other cylindrical motors can also be used. The present invention includes a compact, backlash-free actuator that can be directly applied to robotic rotary joints.

[0015] Harmonic drives have previously been used as motor gearheads. However, the approach has been to connect them end-to-end as a general gearhead, with the gearhead mounted at the end of the motor. For example, in a redundant motor reducer drive, two motors, two harmonic drives, and their supporting bearings are mounted in this end-to-end configuration, as shown in Figure 1.

[0016] Figure 1 shows a partial cross-sectional view of a redundant motor reducer drive. In Figure 1, motors 24 and 26 are mounted on the sides of harmonic drive components 30 and 56, respectively. Next, bearing 54 is positioned on the harmonic drive, increasing both the overall length and diameter of the assembly. In fact, this design includes two motors, but an increase in size is seen on both sides. For example, on the left side, the central part of the harmonic drive is occupied by component 30. Therefore, in order to shorten the length, motor 24 could not be placed inside the harmonic drive component 32 and was placed on the side. To reduce the overall size of the harmonic drive gearhead (motor assembly for precision joint actuator), the central space of the harmonic drive can be secured by redesigning its central component to accommodate the motor within it.

[0017] A new gearhead design of the present invention is shown in Figures 2A to 2E. Figures 2A to 2D show a diagram of a harmonic gearhead according to one embodiment of the present invention. The harmonic gearhead 100 includes a motor 106 and a gearhead actuator assembly having a static component 102 and an output component 104. As shown, the motor 106 is centrally located within an opening defined by the static component 102 and the output component 104, shortening the entire assembly. The base of the gearhead actuator assembly is the static component 102, and the output is the output component 104. The motor 106 is mounted on the head of a bell-shaped, slender tubular flange, or motor mount, 108, which is attached to the static component 102 by screws 110. In effect, this flange allows the motor to be supported from the rear while being positioned within other components, by moving the motor's mounting location from head to tail. A harmonic drive with static and dynamic circular splines 122, 130 is used. The central portion of the harmonic drive is typically occupied by the wave generator shaft 112, which also serves as its input. To make space for the motor, the wave generator shaft 112 is designed on the motor in a slender tubular shape, i.e., a bell-shaped structure. On one side, the shaft 112 is connected to the motor 106 and output component 104. On the other side, the shaft 112 exhibits the characteristics of a deformable elliptical wave generator shaft 114. The bearing 116 propagates waves as usual by exhibiting a thin elastic race for deformation of the elliptical shape of 114. The elliptical bearing 116 then deforms the dynamic flexspline 118. The teeth 120 of the dynamic flexspline 118 engage with the teeth 124 of the static circular spline 122. Similarly, the teeth 129 of the dynamic flexspline 118 also engage with the teeth 132 of the dynamic circular spline 130. As the motor rotates, the difference in the number of teeth on these gears causes the dynamic circular spline 130 to rotate more slowly than the static spline 118.

[0018] With respect to Figure 2D, the static spline 122 is attached to the static component 102 by a screw 110. The dynamic spline 130 is attached to the output component 104 by a screw 136. Thus, the rotation of the motor 106 causes the output component 104 to rotate relative to the static component 102 with a high transmission ratio and no backlash. A tow bearing 138, a spacer 140, and ring nuts 142, 144 are used to support the shaft 2 within the static component 102. As shown, these are positioned laterally to the harmonic drive and have similar dimensions to the circular splines 122 and 130, not to increase the diameter of the assembly, but to utilize the axial space available to the motor. Potentially, the assembly can be made smaller in diameter if necessary by lowering the bearings closer to the motor within the available space 146. However, this would also reduce the diameter of the output shaft and thus reduce structural rigidity. It should also be noted that the static component 102 can be a single-piece or multi-piece design. The output component 104 may also be a single-piece or multi-piece design. This is determined, at least in part, by manufacturing needs and the intended use of the particular harmonic gearhead 100.

[0019] If a higher transmission ratio than that of the harmonic drive is required, the motor 106 may also include a gearhead. Furthermore, the motor 106 may also include an encoder as needed for motion control and safety. Depending on the application, the motor 106 may itself be a general gearhead-motor-encoder assembly.

[0020] Generally, by redesigning the harmonic drive wave generator shaft 112 and designing the flange motor mount, it has become possible to arrange the motor inside the harmonic drive. Further, as shown, by arranging the bearings horizontally, it has become possible to share the bearings between the harmonic drive and the main bearings of the actuator between the static component 102 and the output component 104. As shown in FIGS. 2D and 2E, these provide a compact assembly that is approximately the same size as the harmonic drive and approximately the same length as the motor.

[0021] FIG. 2E shows a cross-sectional view of a variant of the design of the present invention. With respect to FIG. 2E, the harmonic gear head 200 includes a motor 206. The motor 206 is arranged in the center within an opening defined by the static component 204 and the output component 202, thereby shortening the overall assembly. The base of the actuator assembly is the static component 204, and the output is performed via the output component 202. This is opposite to the embodiment described in FIG. 2D where the base is the static component 204 and the output is via the output component 202. The motor 206 is attached to the head 207 on a bell-shaped, thin tubular flange, or motor mount, 208 that is attached to the static component 204. A harmonic drive with a static spline 222 and a dynamic circular spline 230 is used. Further, with respect to FIG. 2E, the static spline 222 is attached to the static component 204. The dynamic spline 230 is attached to the output component 202. Thus, due to the rotation of the motor 206, the output component 202 rotates relative to the static component 204 with a high transmission ratio and without backlash. It should also be noted that the output component 202 can be of a single-piece or multi-piece design. The static component 204 can also be of a single-piece or multi-piece design. This is determined at least in part by manufacturing needs and the intended use of the particular harmonic gear head 200.

[0022] There exists a harmonic drive including a bell-shaped component. For example, a strain wave gear model manufactured by Harmonic Drive (registered trademark) LLC is shown in FIG. 3. This device 300 uses only three components, namely, a wave generator 302, a flex spline 304, and a circular spline 306. As shown in the figure, the flex spline 304 has a bell shape. The wave generator shaft 302 of the present invention also has a bell shape as shown in FIGS. 2A to 2E, but can be easily distinguished from the design shown in FIG. 3. However, the difference lies in that the two components perform different functions in the harmonic drive. Further, in the configuration of the strain wave gear model shown in FIG. 3, a motor cannot be placed inside because, as shown in FIG. 3, the central space is still occupied by the wave generator 302. The wave generator and motor mount of the present invention are novel in their structure and arrangement themselves, which enable placing the motor inside the wave generator, and substantially enable compacting the actuator.

[0023] Many features and advantages of the present invention are apparent from the detailed description, and thus, it is intended by the appended claims to cover all such features and advantages of the present invention that are within the true spirit and scope of the present invention. Further, since those skilled in the art can easily make many modifications and variations, it is not desirable to limit the present invention to exactly the structure and operation shown and described, and thus, all suitable modifications and equivalents are intended to be included within the scope of the present invention.

Claims

1. Motor and Gearhead Actuator Assembly A device assembly comprising: A device assembly, wherein the gearhead actuator assembly is configured such that the motor is positioned in a space defined within the gearhead actuator assembly.

2. The device of claim 1 further comprising a bell-shaped harmonic drive wave generator.

3. The device of claim 1 further comprising a bell-shaped motor mount.

4. The device of claim 1 , wherein the motor is cylindrical.

5. The device of claim 4 , wherein the motor is an electric motor.

6. 10. The device of claim 1, wherein a bearing is laterally located to allow for a combined main bearing for the harmonic drive and the device.

7. The device of claim 1 , wherein the motor includes a gearhead.

8. The device of claim 1 further comprising a harmonic drive with static and dynamic circular splines.

9. The device of claim 1 further comprising a flexspline.

10. The device of claim 1 further comprising an output shaft.

11. A motor; Static components and an output component operatively coupled to the motor such that movement of the motor produces a corresponding movement of the output component; 1. A harmonic gearhead assembly comprising: The harmonic gearhead assembly, wherein the static component and the output component are positioned to define a space in which the motor is disposed.

12. 12. The harmonic gearhead assembly of claim 11, further comprising a bell-shaped harmonic drive wave generator.

13. The harmonic gearhead assembly of claim 11 further comprising a bell-shaped motor mount.

14. The harmonic gearhead assembly of claim 11 , wherein the motor is cylindrical.

15. The harmonic gearhead assembly of claim 14 , wherein the motor is an electric motor.

16. 12. The harmonic gearhead assembly of claim 11, wherein a bearing is laterally located to allow for a combined main bearing for the harmonic drive and the device.

17. The harmonic gearhead assembly of claim 11 , wherein the motor includes a gearhead.

18. 12. The harmonic gearhead assembly of claim 11, further comprising a harmonic drive comprising a static and a dynamic circular spline, the static circular spline coupled to the static component and the dynamic circular spline coupled to the output component.

19. The harmonic gearhead assembly of claim 11 further comprising a flexspline.

20. The harmonic gearhead assembly of claim 11 , wherein the motor is mounted from a tip of the motor.

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