Strain Wave Gear Coupling and Bearing Layout for Eccentric Load Relief
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Solution Overview
Problem
Strain wave gear systems face challenges in precise wave generator positioning, radial over-constraint leading to eccentric loading, length and backlash issues due to compliance devices, and inefficient lubrication and sealing methods, which increase costs and risk of leakage.
Innovation Solution
A strain wave gear system with a ring gear, wave generator, and flexspline, featuring strategically placed bearings for axial constraint without radial movement, a sealing system using a housing and cap with a protrusion and cavity for consistent sealant distribution, and a lubricating system with plungers for controlled grease delivery into bearings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ball bearings are used to constrain the wave generator, then the manufacturer can properly position the wave generator, but the system becomes radially over-constrained causing eccentric loading on the bearings
Solution Approach 1:
The patent removes the radially constraining function from the ball bearings, extracting only the axial positioning function. The bearings are positioned to support axial loads and locate the wave generator axially, but are deliberately not positioned to provide radial constraint, thereby eliminating the over-constraint problem while maintaining positioning precision.
Solution Approach 2:
The constraint functions are segmented into axial constraint (provided by bearings) and radial constraint (provided by the housing and wave generator geometry). This segmentation allows each component to perform its specific function without creating conflicting constraints, resolving the over-constraint issue.
2Ease of operation
If an Oldham style coupling is used for input connection, then misalignment compensation is achieved, but the system length and backlash increase
Solution Approach 1:
The patent extracts the misalignment compensation function from a separate Oldham coupling component and integrates it directly into the wave generator structure. The wave generator's elliptical geometry and mounting arrangement provide inherent misalignment compensation, eliminating the need for an additional coupling device and reducing overall system length.
Solution Approach 2:
The input connection and misalignment compensation functions are merged into a single integrated structure. The wave generator is directly mounted to the input shaft with built-in compliance features, combining what were previously separate functions into one compact assembly.
3Measurement precision
If custom modifications are made to the input for wave generator positioning, then proper positioning is achieved, but system costs increase significantly
Solution Approach 1:
The input shaft is designed with universal features (keyways, mounting surfaces, and compliance elements) that serve multiple functions: torque transmission, axial positioning, and misalignment compensation. This multi-functionality eliminates the need for custom modifications while achieving precise positioning.
Solution Approach 2:
The positioning function is segmented from the input shaft and assigned to the wave generator's own mounting structure. The wave generator includes integrated positioning features that locate itself on the input shaft, eliminating the need for custom input modifications and reducing manufacturing costs.
4Ease of operation
If strain relief is added to the input, then misalignment compliance is improved, but the input structure becomes more complex
Solution Approach 1:
The strain relief compliance feature is merged with the input shaft structure itself. The input shaft incorporates flexible elements or geometric features that provide strain relief as an integrated part of its design, rather than as a separate component, thereby maintaining simplicity while improving compliance.
Data Source
AI summary
A strain wave gear system (10) includes first and second sets of ball bearings (80, 82) located intermediate a flange (84) and a retainer plate (88) rotatable with an output (54) and a radially oriented flat disc (74) of the input including strain relief (76). Strain relief (76) is a helical slot in a coupling (70) located radially within the wave generator (94) and the ring gear (22). The ring gear (22) is sealed by a sealing system including sealant (42) forced by a protrusion (34) of the cap (24) entering into a cavity (36) through a channel (40) into a relief volume (38) of the housing (12). The bearing (48) rotatably mounting the housing (12) to the output (54) is lubricated by a lubricating system including plungers (110) threadably received in axial bores (102) intersecting with radial bores (104) in communication with radial holes (47) of the bearing (48).