Hollow-Roller Wave Generator for Lower Hertz Contact Stress
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Solution Overview
Problem
Conventional strain wave gearing with solid cylindrical rollers requires high hardness steel for raceway surfaces to withstand radial loads, limiting the load torque and necessitating increased hardness, which is not necessary for wave generators with hollow rollers.
Innovation Solution
A wave generator using cylindrical hollow rollers made of steel or stainless steel with a diameter ratio of inner to outer diameter (Di/Do) set to 0.95 or higher, allowing the rollers to flex into an ellipsoidal shape under radial load, reducing Hertz contact stress and enhancing fatigue life without increasing raceway surface hardness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid cylindrical rollers made of high hardness steel are used in the wave bearing, then the radial load can be withstood, but the load torque must be limited and the hardness of raceway surface portions must be increased
Solution Approach 1:
The invention changes the structural parameter of the rollers from solid to hollow, specifically setting the inner diameter to outer diameter ratio Di/Do to 0.95 or higher. This parameter change reduces the mass and moment of inertia of the rollers, thereby reducing centrifugal force and inertial force during operation, which allows for higher load torque capability while maintaining radial load support
2Strength
If the hardness of raceway surface portions is increased to withstand radial load, then the load capacity is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The invention changes the structural parameter of the rollers from solid to hollow with Di/Do ≥ 0.95, which fundamentally alters the stress distribution characteristics. This parameter change allows the use of materials with lower hardness requirements for the raceway surfaces, as the hollow roller structure reduces the centrifugal and inertial forces that would otherwise require high hardness materials to withstand
3Force
If hollow rollers with high Di/Do ratio are used, then centrifugal force and inertial force are reduced, but the rigidity of the roller may be insufficient
Solution Approach 1:
The invention optimizes the Di/Do ratio parameter to be 0.95 or higher, which strikes a balance between reducing centrifugal/inertial forces and maintaining sufficient rigidity. This specific parameter range ensures that the hollow rollers are light enough to reduce dynamic forces while still having sufficient structural integrity to support radial loads and maintain their function in the wave bearing
Solution Approach 2:
The invention specifies that the hollow rollers be made of steel or stainless steel, utilizing these materials' high strength-to-weight ratio properties. This material selection allows the hollow structure to achieve both weight reduction (lowering centrifugal and inertial forces) and sufficient rigidity to perform the bearing function effectively
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
The solution reduces the need for high hardness materials in raceway surfaces, enabling the wave generator to handle radial loads effectively while enhancing the fatigue life of the rollers by distributing stress through hoop stress and reducing Hertz contact stress.
Implementation Method 1
The cylindrical hollow rollers, which are located on both end portions in the major-diameter direction of the ellipsoidal outer circumferential surface of the rigid plug, are flexed and deformed into an ellipsoidal shape by the radial load
Data Source
AI summary
A wave bearing of a wave generator of a strain wave gearing is provided with steel or stainless steel cylindrical hollow rollers between an inner-race-side raceway surface and an outer-race-side raceway surface, the hollow rollers serving as rolling elements. The ratio Di/Do of the inner diameter Di to the outer diameter Do of the hollow rollers is set to 0.95 or more. The relative radius of curvature of hollow rollers that have been flexed into an ellipsoidal shape increases with respect to the inner-race raceway surface and the outer-race raceway surface with which the hollow rollers are in contact, and the Hertz maximum contact stress is reduced. The hardness of the hollow rollers, the inner-race raceway surface, and the outer-race raceway surface can be reduced.