Wave Generator Asymmetry for Strain Wave Gear Vibration Reduction
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Solution Overview
Problem
Strain wave gearing systems experience significant vibration errors due to angle transmission errors, particularly secondary or tertiary vibration components, which can lead to resonance and poor positioning accuracy, especially in high-precision applications like robot arms, caused by the symmetrical meshing portions of externally and internally toothed gears.
Innovation Solution
The system introduces a wave generator that flexes the externally toothed gear into a non-circular shape with multiple meshing portions at equal angular intervals, ensuring each meshing portion has a distinct shape, thereby reducing the occurrence time and amplitude of angle transmission errors, and using a combination of wave generators with rigid wave plugs and rollers to define the elliptical closed curve shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the externally toothed gear is flexed into a symmetrical non-circular shape (e.g., elliptical or three-lobe shape) to form meshing portions at equal angular intervals, then the gear can mesh with the internally toothed gear at multiple positions for reduced-speed rotation, but vibration components of specific orders (secondary or tertiary) become dominant in the angle transmission error
Solution Approach 1:
The patent applies asymmetry by making the meshing portions have different shapes from each other. Specifically, when the externally toothed gear is flexed into an elliptical shape, the meshing portions at the two ends of the major axis are made to have different shapes by adjusting the flexing characteristics. This breaks the point symmetry that causes dominant secondary vibration components, thereby reducing angle transmission errors while maintaining multi-position meshing capability for reduced-speed rotation
2Productivity
If the externally toothed gear is flexed into a non-circular shape with multiple meshing portions, then the meshing portions pass through the same position multiple times per rotation, but this causes repeated flexing with constant amplitude that generates dominant vibration components
Solution Approach 1:
The patent makes the meshing portions have different shapes so that when they pass through the same position, they do not produce identical flexing patterns. This asymmetry in meshing portion shapes disrupts the periodic repetition of identical flexing events, thereby reducing the amplitude of dominant vibration components generated during operation
3Ease of manufacture
If symmetrical meshing portions are used in the externally toothed gear, then the gear structure is simpler and easier to manufacture, but the angle transmission error includes large vibration components that cause resonance and poor positioning accuracy
Solution Approach 1:
The patent intentionally introduces asymmetry in the shapes of meshing portions to eliminate dominant vibration components in angle transmission errors. While this requires more precise control of the flexing characteristics during manufacturing, it significantly improves positioning accuracy by preventing resonance caused by large vibration components, thereby enhancing overall system reliability
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
This approach effectively reduces vibration errors by ensuring that each meshing portion passes through the same position differently, minimizing secondary or tertiary error components, thereby enhancing the accuracy and precision of the drive system.
Implementation Method 1
a flexible externally toothed gear which is flexed by a wave generator into a non-circular shape
Data Source
AI summary
A wave generator of a wave gear device flexes an externally toothed gear into a shape along an elliptical closed curve to form engaging portions of the externally toothed gear with an internally toothed gear at two places, namely at both ends of the major axis, and to move the engaging portions in the circumferential direction. The elliptical closed curve has a non-point symmetric shape. For example, the elliptical closed curve is a line symmetric closed curve that is not symmetric about the minor axis, and is symmetric about only the major axis. In the non-point symmetric state, the engaging portions 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 can be reduced.