Wave Generator Roller Skewing Prevention
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Solution Overview
Problem
In strain wave gear devices, roller bearings tend to skew due to loose radial play, leading to impaired rotation as rollers transition from minor to major axis positions, especially in low velocity ratio systems, causing rollers to become tightly restrained and non-smooth.
Innovation Solution
A wave generator with a roller bearing that features a non-circular, convex outer surface and a roller-pressing member to maintain rollers in line contact with the outer raceway surface, preventing skewing by pressing loose rollers radially toward the outer raceway surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a roller bearing is used in the wave generator, then the device can handle higher loads and provide better support, but the rollers become skewed due to radial play and cannot rotate smoothly
Solution Approach 1:
The roller pressing member applies preliminary radial force to the rollers before they enter the tight state at major axis positions. This preliminary action maintains continuous line contact between rollers and raceway surfaces, preventing skewing from occurring in the first place as rollers transition through their elliptical motion path.
Solution Approach 2:
The invention changes the radial position parameter of the rollers by applying external radial force through the roller pressing member. This parameter change compensates for the radial play in the roller bearing, maintaining optimal contact conditions between rollers and raceway surfaces throughout the wave generator's operation.
2Ease of operation
If the gap between pocket inner circumferential surfaces and rollers is increased to accommodate elliptical motion, then rollers can move freely, but rollers become skewed and enter tight state more easily
Solution Approach 1:
The roller pressing member acts as an intermediary element between the roller retainer pockets and the rollers. It provides controlled radial force to maintain line contact while allowing the necessary elliptical motion, mediating between the constraint of fixed pockets and the need for roller movement freedom.
3Reliability
If rollers are held tightly between inner and outer races to prevent skewing, then rotation smoothness improves, but rollers cannot accommodate elliptical motion
Solution Approach 1:
The roller pressing member provides dynamic radial force that adapts to the rollers' position during elliptical motion. The pressing member allows the system to transition from a static tight-fit configuration to a dynamic configuration where radial force is applied continuously to maintain line contact while accommodating the changing geometric requirements of elliptical motion.
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
Ensures smooth rotation by preventing rollers from becoming skewed and entering a tight state, maintaining line contact and reducing manufacturing precision requirements for the roller-pressing member.
Implementation Method 1
a roller-pressing member for pressing loose rollers disposed in a state of having some play in the radial direction between an outer race and inner race of the roller bearing, the loose rollers being pressed in a direction toward an outer raceway surface of the outer race
Data Source
AI summary
The wave generator of the strain wave gear device comprises: a rigid plug; a roller bearing fitted on the elliptical outer circumferential surface thereof; and first and second cylindrical springs, which press loose rollers that have some play in the radial direction between the outer race and the inner race of the roller bearing against the outer raceway surface. The loose rollers are pressed against the outer raceway surface with a linear contact and roll according to the outer raceway surface. Skewing of the rollers is limited, ensuring smooth rotation of the roller bearing.