A FLEXIBLE RACE CYLINDRICAL ROLLER BEARING DEVICE FOR USE IN A STRAIN WAVE GEAR

Abstract

The present invention provides a flexible race cylindrical roller bearing used in a strain wave gear. It comprises an inner race (3), an outer race (1), rollers, and a cage. An elliptical cam (2) is inserted, causing both the inner and outer races of the bearing to deform according to the elliptical shape of the cam. This entire assembly is connected to the wave generator hub (6). This design is more effective at handling radial loads, and its impact on the stress and flexibility of the races can be analyzed using the finite element method. Compared to ball bearing, a cylindrical roller bearing exhibit lower radial stresses due to their reduced contact loads. Being less stiff, they achieve the desired flexibility in the races. It experiences less contact stress and maintain approximately consistent stress levels across different roller positions. So that these bearing with their consistent stress distribution and lower stiffness, provide a better performance.

Specification

Description:Field of Invention:
The present invention relates to the field ofmechanical devices. More particularly, the present invention discloses abouta flexible race cylindrical roller bearing device for use in a strain wave gear.

Background of Invention:
The strain wave gear, commonly referred to as harmonic drive, represents a specialized mechanical gear system prized for its ability to deliver exceptional precision, high reduction ratios, compact dimensions, and superior positional accuracy. These qualities have made harmonic drives indispensable in fields such as robotics, aerospace, and industrial automation, where precise motion control is crucial.
In harmonic drives, bearings are pivotal in ensuring smooth operation and longevity. Traditionally, ball bearings have been favoured due to their low friction and manufacturing convenience. However, they come with inherent limitations, including restricted load capacity and vulnerability to wear under rigorous conditions. These drawbacks can lead to reduced efficiency and premature failure, compromising the overall performance of harmonic drives.
To overcome these challenges, there exists a need to explore the adoption of roller bearings in place of ball bearings within harmonic drives by using a flexible race cylindrical roller bearing device for use in a strain wave gear.
The technical advancements disclosed by the present invention overcome the limitations and disadvantages of existing and conventional systems and methods.

Summary of Invention:
The present invention relates toa flexible race cylindrical roller bearing device for use in a strain wave gear.
An object of the present invention is toprovide a flexible race cylindrical roller bearing device,
Another object of the present invention is to provide aroller bearing with superior load distribution and durability,
Yet another object of the present invention is to significantly enhance performance, reliability, and operational lifespan of the device, and
Yet another object of the present invention is toprovide a robust and precise roller bearing.
A flexible race cylindrical roller bearing device for use in a strain wave gear, the device comprises: a wave generator hub having a first portion and a second portion, said second portion is co-axially attached to at least one side of said first portion such that said second portion is extended outward to said first portion; an elliptical cam circumferentially coupled to said wave generator hub such that an inner portion of said elliptical cam is attached to said second portion of said wave generator hub whereas an outer portion of said elliptical cam mounted on said first portion of said wave generator hub; an inner race configured to fit over said elliptical cam, deforming in accordance with a cam's elliptical shape; a cage circumferentially secured by said inner race, said cage having a plurality of cylindrical cavities serially fabricated such that one end of each cavity is open; a plurality of cylindrical rollers disposed within said plurality of cylindrical cavities and allowed to rotate freely; an outer race circumferentially disposed on said cage such that deforms in response to a shape of said inner race and said applied displacement; and wherein said cylindrical rollers engage with both inner and outer races to transmit torque, resulting in reduced radial stress and increased load-carrying capacity.

To further clarify the advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

Brief Description of Figures:
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Figure 1 illustrates a block diagram of a flexible race cylindrical roller bearing device for use in a strain wave gear,
Figure 2-9 illustrates a schematic representation of 2) Harmonic drive assembly, 3) Exploded view of Harmonic drive Assembly, 4) Roller, 5) Inner Race, 6) Outer Race, 7)Wave Generator Hub, 8) Cage and 9)Elliptical cam, and
Figure 10-12 illustrates 10) Total Radial stress of (a) Roller bearing and (b) Ball bearing, 11) (a) Inner and (b) Outer stiffness at the contact of roller and 12) Nominal Contact stress of (a) Inner and (b) Outer race at the contact of roller.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

Detailed description:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to "an aspect", "another aspect" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

Figure 1 illustrates a block diagram of a flexible race cylindrical roller bearing device for use in a strain wave gear, the device comprises: an outer race (1), an elliptical cam (2), an inner race (3), a plurality of cylindrical rollers (4), a cage (5) and a wave generator hub (6).

The wave generator hub (6) is having a first portion (6a) and a second portion (6b), said second portion (6b) is co-axially attached to at least one side of said first portion (6a) such that said second portion (6b) is extended outward to said first portion (6a). The first portion is a thick disc and the second portion is a hollow cylinder vertically mounted on the at least one face of the disc, wherein the second portion has a cylindrical cavity.

The elliptical cam (2) is circumferentially coupled to said wave generator hub (6) such that an inner portion (2a) of said elliptical cam (2) is attached to said second portion (6b) of said wave generator hub (6) whereas an outer portion (2b) of said elliptical cam (2) mounted on said first portion of said wave generator hub (6). The elliptical cam (2) induces deformation in the inner and outer races.
The enhanced load distribution and reduced stress concentrations contribute to the increased durability and longevity of roller bearings, making them more suitable for high-stress applications.
In an embodiment, when the wave generator cam is inserted into a flexible race roller bearing, it causes both the inner and outer races of the bearing to deform in accordance with the elliptical shape of the cam.Cylindrical roller bearings in harmonic drives include high rigidity, and increased load-carrying capacity, low backlash and high precision, ensuring minimal play and maintaining high precision even in high-speed applications.

The inner race (3) is configured to fit over said elliptical cam (2), deforming inaccordance with a cam's elliptical shape.
A cage (5) is circumferentially secured by said inner race (3), said cage (5) having a plurality of cylindrical cavities serially fabricated such that one end of each cavity is open. The inner race has at least two circumferentially outward extended edges, said extended edges are positioned parallelly such that forms a circumferential cavity to fit the cage (5) securely. The plurality of cylindrical rollers disposed between the inner and outer races, having a larger contact area with the races compared to ball bearings, Fig.10, shows the radial stress for the roller bearing is 68.185 MPa, whereas for the ball bearing, it is 214.99 MPa, resulting in reduced radial stress due to their reduced contact loads and increased bearing life.

The cage (5) comprises: a thin disc-shaped portion (5a); and a plurality of I-shaped separators (5b) vertically mounted on said thin disc-shaped portion (5a) to form the cylindrical cavity to securely fit in the plurality of rollers.

The plurality of cylindrical rollers (4) are disposed within said plurality of cylindrical cavities and allowed to rotate freely. The cylindrical rollers (4) exhibit lower stiffness compared to ball bearings, allowing for increased flexibility of the races and improved accommodation of deformations. The cylindrical rollers (4) provide a more even distribution of load across the races compared to ball bearings, resulting in reduced stress concentrations and increased bearing life.
Fig.12, shows the contact stress at different positions of the roller. The results indicate that roller bearings experience less contact stress and maintain approximately consistent stress levels across various positions.

The plurality of cylindrical rollers (4) are disposed between the inner and outer races, having a larger contact area with the races compared to ball bearings, which allows to distribute loads more evenly and handle higher radial loads. The design of cylindrical roller bearings makes them more adaptable to high-speed applications where ball bearings might fail due to excessive wear or thermal issues.

The outer race (1) is circumferentially disposed on said cage (5) such that deforms in response to a shape of said inner race and said applied displacement, wherein said cylindrical rollers (4) engage with both inner (3) and outer (1) races to transmit torque, resulting in reduced radial stress and increased load-carrying capacity.

In an embodiment, the elliptical cam (2) is operatively connected to the wave generator hub (6) through a series of micro-adjustment gears located within the second portion (6b), allowing for precise tuning of the cam's elliptical shape to modulate the deformation of the inner race (3) at predetermined intervals during operation, wherein the outer race (1) is coupled to the cage (5) via a set of interlocking grooves that are symmetrically arranged to synchronize the radial movement of the cage (5) with the deformation pattern of the inner race (3), ensuring uniform engagement of the cylindrical rollers (4) with both races (1, 3).

In an embodiment, the cage (5) is designed with a series of radially extending arms that interfacewith corresponding slots on the inner race (3), these arms being elastically deformable to absorb slight misalignments between the cylindrical rollers (4) and the races (1, 3), thereby maintaining consistent load distribution across the rollers, wherein the cylindrical rollers (4) are arranged within the cage (5) in a staggered configuration such that every alternate roller is offset by a predetermined angle, reducing the overall friction during the operation and enhancing the smooth transition of load between the inner (3) and outer (1) races.

In an embodiment, the outer race (1) is operatively connected to the cage (5) through a spring-loaded locking mechanism that permits controlled axial displacement of the outer race (1) in response to the deformation of the inner race (3), facilitating the smooth transfer of torque without generating excessive radial stress on the cylindrical rollers (4).

In an embodiment, the elliptical cam (2) is configured with an adjustable phase shift mechanism that allows for fine-tuning of the elliptical profile's orientation relative to the wave generator hub (6), ensuring that the peak deformation aligns precisely with the cylindrical roller (4) positions for optimized load transfer, and wherein the cage (5) is equipped with a dampening system that includes a set of micro-compression springs located between the cylindrical cavities and the inner race (3), these springs absorb micro-vibrations and prevent unwanted oscillations of the cylindrical rollers (4) during high-speed operation.

In an embodiment, the inner race (3) features a dual-layered configuration with an internal annular channel through which a viscous fluid circulates, the fluid dynamically adjusting to the deformation induced by the elliptical cam (2) to maintain consistent roller engagement and reduce wear on the contact surfaces.

Figure 2-9 illustrates a schematic representation of 2) Harmonic drive assembly,3) Exploded view of Harmonic drive Assembly, 4) Roller, 5) Inner Race, 6) Outer Race, 7)Wave Generator Hub, 8) Cage and 9)Elliptical cam.

When the wave generator cam is inserted into a flexible race roller bearing, it causes both the inner and outer races of the bearing to deform in accordance with the elliptical shape of the cam. The inner race is fits over the elliptical cam, while a cage maintains the position of the rollers within the bearing. This entire assembly is connected to the wave generator hub. The aim is to apply finite element analysis to compare the performance characteristics of harmonic drives equipped with cylindrical roller bearing and ball bearing, while keeping the boundary conditions the same. Specifically, we will observe the flexibility and distribution of contact stress at the roller-races interface.

Figure 10-12 illustrates 10) Total Radial stress of (a) Roller bearing and (b) Ball bearing, 11) (a) Inner and (b) Outer stiffness at the contact of balls and 12) Nominal Contact stress of (a) Inner and (b) Outer race at the contact of roller.
Roller bearings have a larger contact area with the races compared to ball bearings. This allows them to distribute loads more evenly and handle higher radial loads. Fig.10, shows a roller bearing is exhibit lower radial stresses due to their reduced contact loads. The radial stress for the roller bearing is 68.185 MPa, whereas for the ball bearing, it is 214.99 MPa. Fig.11 shows that roller bearings being less stiff, achieve the desired flexibility in the races. This flexibility helps accommodate deformations and improves the overall performance of the bearing. Fig.12, shows the contact stress at different positions of the roller. The results indicate that roller bearings experience less contact stress and maintain approximately consistent stress levels across various locations. The enhanced load distribution and reduced stress concentrations contribute to the increased durability and longevity of roller bearings, making them more suitable for high-stress applications. The design of roller bearings makes them more adaptable to high-speed applications where ball bearings might fail due to excessive wear or thermal issues. Roller bearings in harmonic drives include high rigidity, and increased load-carrying capacity, low backlash and high precision, ensuring minimal play and maintaining high precision even in high-speed applications.
The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims. 
, Claims:1. A flexible race cylindrical roller bearing device for use in a strain wave gear, the device comprises:
a wave generator hub (6) having a first portion (6a) and a second portion (6b), said second portion (6b) is co-axially attached to at least one side of said first portion (6a) such that said second portion (6b) is extended outward to said first portion (6a);
an elliptical cam (2) circumferentially coupled to said wave generator hub (6) such that an inner portion (2a) of said elliptical cam (2) is attached to said second portion (6b) of said wave generator hub (6) whereas an outer portion (2b) of said elliptical cam (2) mounted on said first portion of said wave generator hub (6);
an inner race (3) configured to fit over said elliptical cam (2), deforming in accordance with a cam's elliptical shape;
a cage (5) circumferentially secured by said inner race (3), said cage (5) having a plurality of cylindrical cavities serially fabricated such that one end of each cavity is open;
a plurality of cylindrical rollers (4) disposed within said plurality of cylindrical cavities and allowed to rotate freely;
an outer race (1) circumferentially disposed on said cage (5) such that deforms in response to a shape of said inner race and said applied displacement; and
wherein said cylindrical rollers (4) engage with both inner (3) and outer (1) races to transmit torque, resulting in reduced radial stress and increased load-carrying capacity.

2. The device as claimed in claim 1, wherein the first portion is a thick disc and the second portion is a hollow cylinder vertically mounted on the at least one face of the disc, wherein the second portion has a cylindrical cavity, and wherein the cylindrical rollers (4) exhibit lower stiffness compared to ball bearings, allowing for increased flexibility of the races and improved accommodation of deformations.

3. The device as claimed in claim 1, wherein the cylindrical rollers (4) provide a more even distribution of load across the races compared to ball bearings, resulting in reduced stress concentrations and increased bearing life, and wherein the inner race has at least two circumferentially outward extended edges, said extended edges are positioned parallelly such that forms a circumferential cavity to fit the cage (5) securely, and wherein the cage (5) comprises:

a thin disc-shaped portion (5a); and
a plurality of I-shaped separators (5b) vertically mounted on said thin disc-shaped portion (5a) to form the cylindrical cavity to securely fit in the plurality of rollers, and wherein the elliptical cam (2) induces deformation in the inner and outer races.

4. The device as claimed in claim 1, wherein the plurality of cylindrical rollers (4) disposed between the inner and outer races, having a larger contact area with the races compared to ball bearings, which allows to distribute loads more evenly and handle higher radial loads, and wherein when the wave generator cam is inserted into a flexible race roller bearing, it causes both the inner and outer races of the bearing to deform in accordance with the elliptical shape of the cam.

5. The device as claimed in claim 1, wherein the elliptical cam (2) is operatively connected to the wave generator hub (6) through a series of micro-adjustment gears located within the second portion (6b), allowing for precise tuning of the cam's elliptical shape to modulate the deformation of the inner race (3) at predetermined intervals during operation, wherein the outer race (1) is coupled to the cage (5) via a set of interlocking grooves that are symmetrically arranged to synchronize the radial movement of the cage (5) with the deformation pattern of the inner race (3), ensuring uniform engagement of the cylindrical rollers (4) with both races (1, 3).

6. The device as claimed in claim 1, wherein the cage (5) is designed with a series of radially extending arms that interface with corresponding slots on the inner race (3), these arms being elastically deformable to absorb slight misalignments between the cylindrical rollers (4) and the races (1, 3), thereby maintaining consistent load distribution across the rollers,

7. The device as claimed in claim 1, wherein the cylindrical rollers (4) are arranged within the cage (5) in a staggered configuration such that every alternate roller is offset by a predetermined angle, reducing the overall friction during the operation and enhancing the smooth transition of load between the inner (3) and outer (1) races.

8. The device as claimed in claim 1, wherein the outer race (1) is operatively connected to the cage (5) through a spring-loaded locking mechanism that permits controlled axial displacement of the outer race (1) in response to the deformation of the inner race (3), facilitating the smooth transfer of torque without generating excessive radial stress on the cylindrical rollers (4).

9. The device as claimed in claim 1, wherein the elliptical cam (2) is configured with an adjustable phase shift mechanism that allows for fine-tuning of the elliptical profile's orientation relative to the wave generator hub (6), ensuring that the peak deformation aligns precisely with the cylindrical roller (4) positions for optimized load transfer, and wherein the cage (5) is equipped with a dampening system that includes a set of micro-compression springs located between the cylindrical cavities and the inner race (3), these springs absorb micro-vibrations and prevent unwanted oscillations of the cylindrical rollers (4) during high-speed operation.

10. The device as claimed in claim 1, wherein the inner race (3) features a dual-layered configuration with an internal annular channel through which a viscous fluid circulates, the fluid dynamically adjusting to the deformation induced by the elliptical cam (2) to maintain consistent roller engagement and reduce wear on the contact surfaces.

Documents