Strain Wave Gear Wave Generators Using Circular Bearing Arrays
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Solution Overview
Problem
The high cost and complexity of manufacturing elliptical wave generators for strain wave gears, which are critical for robotics and spacecraft applications, lead to inefficient and costly production, particularly due to the need for precise machining and the resulting mismatch in fatigue life between the wave generator and flexspline.
Innovation Solution
The use of circular bearings, either ball or roller, distributed around the circumference of an elliptical shape to form a wave generator, providing multiple points of contact and adjustable support to match the deformation and torque requirements of the flexspline, thereby reducing manufacturing costs and improving fatigue performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional elliptical wave generators are used, then the gear reduction and torque capacity are achieved, but the manufacturing cost and complexity increase significantly
Solution Approach 1:
The wave generator is segmented into multiple modular units, each containing a small number of circular bearings (2-4 bearings per module). These modular units can be independently manufactured and assembled, reducing the overall manufacturing complexity while maintaining the elliptical motion pattern required for torque transmission.
Solution Approach 2:
Instead of using a traditional elliptical-shaped wave generator that requires complex precision machining, the invention inverts the approach by using multiple circular bearings arranged to create the elliptical motion path. This inversion simplifies the manufacturing process as circular bearings are commercially available and easier to manufacture with high precision.
2Productivity
If traditional elliptical wave generators are used, then the gear reduction ratio is achieved, but the manufacturing precision requirements and cost increase
Solution Approach 1:
The invention uses commercially available circular bearings as standardized components that can be copied and mass-produced with high precision. These standardized bearings replace the custom-machined elliptical wave generator, allowing for easier replication and consistent performance across multiple units while reducing manufacturing costs.
Solution Approach 2:
The invention changes the fundamental parameter of the wave generator from a solid elliptical shape to a configuration of discrete circular bearings. This parameter change allows the system to achieve the same gear reduction ratio while significantly reducing the precision requirements for manufacturing, as circular bearings can be produced with standard tolerances.
3Strength
If traditional elliptical wave generators are used, then the structural integrity is maintained, but the fatigue life mismatch between wave generator and flexspline occurs
Solution Approach 1:
The wave generator structure is designed with local quality variations, where the circular bearings are strategically positioned to provide enhanced support and stress distribution at critical locations. This localized reinforcement ensures structural integrity while allowing the overall system fatigue life to be balanced with the flexspline, preventing premature failure of the wave generator.
4Ease of manufacture
If fewer components are used, then the assembly ease and size reduction are achieved, but the contact points and support for flexspline decrease
Solution Approach 1:
Each circular bearing in the wave generator performs multiple functions: it provides structural support, maintains the elliptical motion path, distributes loads, and ensures continuous contact with the flexspline. This multi-functionality allows the system to achieve reliable flexspline support with a minimal number of components, simplifying assembly while maintaining 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 allows for the production of low-cost strain wave gears with improved fatigue performance and flexibility, matching the life cycle of the flexspline, and enabling wider industrial applications by reducing the cost and complexity of wave generator manufacturing.
Implementation Method 1
HDs were developed to take advantage of the elastic dynamics of metals, particularly the expansion of a metal ring to engage gear teeth without exceeding the elastic limit of the ring
Implementation Method 2
The wave generator is an elliptical cam with small ball-bearings built into the outer circumference
Data Source
AI summary
Harmonic drives (HDs) are used widely in robotics as a method for achieving high gear reductions and for driving force transmissions. The HD is made a three components: a wave generator, a flexspline, and a circular spline. Low-cost wave generators for metal strain wave gearing are provided. Wave generators are provided that incorporate commercially available bearings that form an ellipse either statically or through adjustment. Wave generators are optimized to maximum performance, including increasing the efficiency and the lifetime, while maximizing the running torque. The shape, size, number, type and location of the bearings can be changed so that the wave generator fails at a similar lifetime as a low cost flexspline. The shape of the wave generator may be adjusted to change the performance of the strain wave gear. The combination of low-cost flexsplines with low-cost wave generators reduces the cost of the strain wave gear.