V-Spring End Attachment Assemblies for Fretting Fatigue Reduction
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Solution Overview
Problem
Personal care appliances using spring assemblies, such as V-springs, experience fretting fatigue and fretting damage due to high surface pressures and shear forces at the clamped ends, leading to premature failure.
Innovation Solution
A V-spring member with closed end regions and end attachment assemblies featuring curved peripheral edges to reduce stress concentrations, combined with secure attachment methods like gluing or welding, which transition from soft rotational movement to stiff hub assemblies, minimizing fretting fatigue and damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the V-spring is clamped at both ends using conventional attachment assemblies, then the spring can be securely mounted in the drive system, but high surface pressures and shear forces cause fretting fatigue and fretting damage leading to premature failure
Solution Approach 1:
The V-spring is designed with differentiated end regions that have larger cross-sectional areas and different geometries compared to the central region. These end regions are specifically configured to reduce stress concentrations and minimize relative motion during clamping, thereby reducing fretting fatigue and fretting damage while maintaining secure mounting.
Solution Approach 2:
The attachment assemblies incorporate curved contact surfaces that match the geometry of the V-spring end regions. This curved configuration distributes contact pressures more evenly and reduces stress concentrations compared to flat or sharp-edged clamping surfaces, thereby reducing fretting damage.
2Reliability
If the end regions of the V-spring are made larger to support clamping forces, then fretting fatigue and damage are reduced, but the overall complexity of the spring configuration increases
Solution Approach 1:
The attachment assemblies are designed as integrated units that combine the clamping function with the stress distribution function. The curved contact surfaces and support structures are merged into single components that simultaneously secure the V-spring and distribute loads, reducing the need for additional separate elements.
3Ease of manufacture
If conventional clamping methods are used, then assembly is simple, but high shear forces and surface pressures create stress concentrations leading to failure
Solution Approach 1:
The geometry of the end regions is changed with respect to the central region, creating larger cross-sectional areas and different configurations that inherently reduce stress concentrations. This geometric parameter change allows the use of simple clamping methods while achieving better stress distribution and reduced fretting damage.
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 configuration significantly reduces fretting fatigue and damage, allowing the appliance to operate for its expected lifetime by minimizing stress concentrations and micromotion, enhancing linearity and reducing damping.
Implementation Method 1
the physical contact between the lower support portion and the clamping member, respectively, and the V-spring, including the shape of the respective peripheral edges, results in reduced stress concentrations with the V-spring, thereby reducing fretting damage and fretting fatigue
Data Source
AI summary
A V-spring member (18) for use in a driving system for a personal care appliance has regions (34, 36) at the ends of the spring which are large enough to support a contact with an end clamping assembly, the spring member including a cross-piece (40) extending between the longitudinal edges of the spring at the end regions, such that the ends of the spring member define a closed line. End clamping assemblies (16, 24) provided for such a V-spring member include a body portion (64) having a lower support portion (66) on which the V-spring is supported and a mating clamping member (88) positioned in registry with the support portion on top of the V-spring. The support portion and the clamping member include peripheral edges (74, 92) which have a curved cross-sectional configuration, and which are in registry, making contact with the spring member in the end regions in such a manner as to reduce stress concentrations in the end regions of the spring, thereby reducing fretting fatigue and fretting damage in the spring.