Strain Wave Gear Fastening Layout to Prevent Bearing Misalignment
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Solution Overview
Problem
Existing strain wave gearings face misalignment issues due to radial-direction deformation caused by loads, which are not adequately addressed in the design of fastening points, compromising the reliability when no Oldham coupling is used.
Innovation Solution
The strain wave gearing design ensures equal or greater radial-direction fastening strength between the externally toothed gear and the first flange, using a socket-and-spigot fitting or press-fit pins, and forms transition fits to minimize radial deformation and misalignment between the wave generator and support bearings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the input shaft is connected to the wave generator without a coupling such as an Oldham coupling, then the device complexity is reduced, but radial force applied to the wave generator due to misalignment compromises reliability
Solution Approach 1:
The patent pre-compensates for radial-direction deformation by designing the fastening points with equal or greater radial fastening strength compared to rotational fastening strength. This preliminary design adjustment prevents misalignment before it occurs, eliminating the need for Oldham couplings while maintaining reliability
Solution Approach 2:
The patent changes the fastening strength parameters by ensuring that radial-direction fastening strength is equal to or greater than rotational-direction fastening strength. This parameter adjustment compensates for radial deformation under load, preventing misalignment and eliminating the need for additional coupling mechanisms
2Ease of manufacture
If fastening bolts are designed based on torsional moment only, then the ease of manufacture is improved, but radial-direction deformation occurs due to insufficient radial fastening strength
Solution Approach 1:
The patent modifies the design parameters by establishing that radial fastening strength must be equal to or greater than rotational fastening strength. This simple parameter rule ensures both manufacturing ease and alignment precision without complex design calculations
Solution Approach 2:
The patent introduces asymmetry in fastening strength requirements, where radial-direction fastening strength is designed to be equal to or greater than rotational-direction fastening strength, rather than treating both directions equally. This asymmetric design compensates for the specific loading conditions and prevents radial deformation
3Device complexity
If the number of fastening bolts on the externally toothed gear side is reduced, then the device complexity is reduced, but the radial fastening strength becomes lower than that on the internally toothed gear side, causing radial-direction deformation
Solution Approach 1:
The patent establishes a parameter relationship where radial fastening strength is equal to or greater than rotational fastening strength. This allows for optimized bolt distribution that reduces overall complexity while maintaining sufficient radial strength to prevent deformation
Data Source
Figure 1(A)~1(C)
Figure 2
AI summary
A strain wave gearing (1) comprises a first flange (8) and a second flange (10) which support an input shaft (6) via a first support bearing (7) and a second support bearing (9), respectively. An externally toothed gear (3) is fastened and fixed to the first flange (8) by a first fastening bolt (11), and an internally toothed gear (2) is fastened and fixed to the second flange (10) by a second fastening bolt (12). The radial fastening strength between the externally toothed gear (3) and the first flange (8) by the first fastening bolt (11) is set equal to or greater than the fastening strength between the internally toothed gear (2) and the second flange (10) by the second fastening bolt (12). Misalignment between a wave generator (4) and the first and second support bearings (7, 9) caused by radial deformation generated in the first and second flanges (8, 10) due to radial loads acting from the load side can be suppressed and excessive radial forces acting on the wave generator can be avoided.