Roller-Bearing Wave Generator for Low-Error Strain Wave Gearing
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Solution Overview
Problem
In strain wave gearing with roller-bearing-type wave generators, one-sided contact occurs between the external peripheral surface of the wave generator and the internal peripheral surface of the externally toothed gear at the long-axis position, leading to increased angular transmission error, positioning inaccuracies, and reduced lifespan due to uneven radial load distribution.
Innovation Solution
A strain wave gearing design featuring a roller-bearing-type wave generator with an ellipsoidal external peripheral surface and a recessed plug that allows for differential radial rigidity, enabling rollers to maintain linear contact with the internally toothed gear, preventing one-sided contact and distributing load evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a roller bearing is used to support the wave generator, then the wave generator can rotate smoothly, but one-sided contact occurs at the long-axis position causing increased angular transmission error and positioning inaccuracy
Solution Approach 1:
The plug is designed with non-uniform wall thickness, having a first wall thickness in a first radial direction and a second wall thickness in a second radial direction perpendicular to the first. This creates differential rigidity in different radial directions, allowing the plug to elastically deform and adjust the contact position of the roller bearing, thereby preventing one-sided contact and reducing angular transmission error while maintaining rotation smoothness
Solution Approach 2:
The invention changes the physical parameter of the plug by varying its wall thickness in different radial directions. This parameter change creates intentional rigidity differences that enable the plug to compensate for the coning effect during operation, allowing the roller bearing to maintain proper contact alignment and reduce positioning inaccuracy
2Ease of manufacture
If the external peripheral surface of the wave generator is made rigid, then manufacturing is easier, but it cannot follow the coning shape of the flexed externally toothed gear, leading to one-sided contact and reduced component life
Solution Approach 1:
The plug incorporates local quality variation through non-uniform wall thickness distribution. Different radial directions have different wall thicknesses, creating zones of different rigidity. This allows the plug to elastically deform in specific directions to match the coning shape of the flexed gear, preventing one-sided contact and extending component life while remaining manufacturable using conventional processes
3Force
If the contact location shifts to the diaphragm side on the long axis, then the roller bearing supports the wave generator, but strong pressing force causes one-sided contact and worsens positioning accuracy
Solution Approach 1:
The invention changes the rigidity parameter of the plug by varying wall thickness in different radial directions. This creates controlled elastic deformation that shifts the contact location from the diaphragm side toward the center, distributing the pressing force more evenly and improving positioning accuracy while maintaining adequate support force
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances angular transmission accuracy, reduces wear, and extends the lifespan of the strain wave gearing by ensuring even contact and reduced Hertzian stress across the ellipsoidal surface.
Implementation Method 1
a roller bearing that is mounted between the ellipsoidal external peripheral surface of the plug and an internal peripheral surface of a cylindrical barrel part of the externally toothed gear and that supports the externally toothed gear so as to allow rotation relative to the plug
Implementation Method 2
the externally toothed gear undergoes three-dimensional flexure when an external teeth formation portion thereof is caused by a wave generator to flex into an ellipsoidal shape
Data Source
AI summary
A strain wave gearing has a wave generator provided with a plurality of rollers mounted between an ellipsoidal outer peripheral surface of a plug and an inner peripheral surface of an externally toothed gear. The plug is formed with recesses along the ellipsoidal outer peripheral surface. The recesses open in a first end surface of the plug facing toward a diaphragm of the externally toothed gear. The radial rigidity of the plug is relatively low in the side having the first end surface in the direction of a plug axis. When viewed along the direction of the plug axis, the respective rollers can be brought into linear contact with the inner peripheral surface of the externally toothed gear at positions on the long axis (Lmax) of the elliptically-flexed externally toothed gear, so as not to occur one-sided contact state.