Asymmetric Wave Generator Profile for Strain Gear Vibration Reduction
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Solution Overview
Problem
Strain wave gearing systems experience significant angle transmission errors due to secondary or tertiary vibration components, leading to resonance and poor positioning accuracy, particularly in applications requiring high precision motion trajectories, such as robot arms, due to machining errors and misalignment between gears.
Innovation Solution
A strain wave gearing system with a flexible externally toothed gear and a wave generator that flexes the gear into a non-circular shape with multiple meshing portions at equal angular intervals, where each meshing portion has a distinct shape, reducing the occurrence time and amplitude of angle transmission errors by ensuring different meshing states for each portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an externally toothed gear is flexed into a symmetric non-circular shape (e.g., elliptical or three-fold symmetry) to form meshing portions at equal angular intervals, then the gear can mesh with the internally toothed gear at multiple positions, but the same-shaped meshing portions cause periodic angle transmission errors and vibration at frequencies corresponding to the number of meshing portions
Solution Approach 1:
The patent applies asymmetry by designing meshing portions with different shapes rather than identical symmetric shapes. Specifically, the flexed externally toothed gear is configured to have meshing portions at multiple positions (e.g., two positions for elliptical flexing) where the portions have different geometries. This asymmetric design breaks the periodic repetition of identical meshing conditions, thereby reducing angle transmission errors and vibration at frequencies corresponding to the number of meshing portions while maintaining multi-position meshing capability.
2Speed
If the externally toothed gear is flexed into a non-circular shape to reduce the number of meshing portions to two or three, then the vibration frequency is reduced, but secondary or tertiary vibration components still cause significant angle transmission errors and resonance
Solution Approach 1:
The patent combines asymmetry with multi-position meshing to address this contradiction. By configuring meshing portions with different shapes at multiple positions (e.g., two positions for elliptical flexing), the system reduces the fundamental vibration frequency while the asymmetric design prevents the generation of significant secondary and tertiary vibration components. This approach maintains positioning accuracy by eliminating the periodic repetition of identical meshing errors that would otherwise cause resonance.
Solution Approach 2:
The patent applies local quality by making each meshing portion have a distinct shape tailored to its specific position on the flexed gear. Rather than applying a uniform symmetric shape to all meshing portions, each portion is locally optimized with different geometries. This local differentiation ensures that angle transmission errors do not repeat periodically, thereby reducing vibration components and improving positioning accuracy while maintaining reduced vibration frequency.
3Ease of manufacture
If the wave generator uses a symmetric flexing shape (e.g., standard elliptical or three-lobe shape), then the structure is simple and easy to manufacture, but the same-shaped meshing portions generate periodic angle transmission errors
Solution Approach 1:
The patent applies asymmetry to the wave generator's flexing profile while maintaining manufacturing feasibility. The wave generator is designed to flex the externally toothed gear into a shape where meshing portions at different positions have different geometries (e.g., asymmetric elliptical flexing with two distinct meshing positions). This asymmetric flexing profile can be manufactured using standard wave generator fabrication methods, but it fundamentally changes the meshing characteristics to eliminate periodic angle transmission errors while keeping the structure relatively simple.
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 effectively reduces vibration caused by angle transmission errors, improving the accuracy and precision of the drive system by ensuring that each meshing portion passes through the same position differently, thereby minimizing secondary or tertiary vibration components.
Implementation Method 1
a flexible externally toothed gear and a wave generator that flexes the gear into a non-circular shape
Implementation Method 2
when the wave generator is rotated by a motor or the like, the meshing portions of both gears are moved in the circumferential direction of the internally toothed gear
Implementation Method 3
the meshing portions of both gears are moved in the circumferential direction... A relative rotation occurs between the both gears by the amount corresponding to the difference in the number of teeth
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(b)
AI summary
A wave generator (4) of a wave gear device (1) flexes an externally toothed gear (3) into a shape along an elliptical closed curve (C0) to form engaging portions (5a, 5b) of the externally toothed gear (3) with an internally toothed gear (2) at two places, namely at both ends of the major axis (Lmax), and to move the engaging portions (5a, 5b) in the circumferential direction. The elliptical closed curve (C0) has a non-point symmetric shape. For example, the elliptical closed curve (C0) is a line symmetric closed curve that is not symmetric about the minor axis (Lmin), and is symmetric about only the major axis (Lmax). In the non-point symmetric state, the engaging portions (5a, 5b) are formed at both ends in the major axis direction. By selecting different shapes for the engaging portions at the two locations of the major axis, vibration attributed to a secondary angular transmission error component generated along with the rotation of the wave generator (4) can be reduced.