Elliptical Flexible Coupling Reduces Bending Stress in Personal Care Appliances
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Solution Overview
Problem
Conventional round cross-sectional coupling members in personal care appliances experience high bending stresses at the ends, leading to reduced lifespan, and increasing the length of the appliance to mitigate this results in undesirable size elongation.
Innovation Solution
An elliptical cross-sectional flexible coupling member with a thin dimension in the direction of bending and a wider dimension perpendicular to it, reducing bending stress while maintaining torque transfer capability, thereby extending the lifespan and maintaining a desirable appliance length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the length of the coupling member is increased to reduce bending stresses, then the stress level decreases and coupling member life increases, but the appliance length increases which is undesirable
Solution Approach 1:
The coupling member transitions from a conventional round cross-section to an elliptical cross-section with asymmetric dimensions. The major axis of the ellipse is oriented perpendicular to the bending direction, providing greater moment of inertia and reduced bending stress without increasing the overall length of the coupling member. This asymmetric geometry allows the appliance to maintain a compact length while extending coupling member life through reduced stress levels.
Solution Approach 2:
The cross-sectional parameters of the coupling member are changed from a circular geometry (equal dimensions in all directions) to an elliptical geometry (different dimensions along different axes). By increasing the dimension along the major axis perpendicular to bending, the section modulus increases, which directly reduces bending stress for a given moment, thereby extending component life without lengthening the appliance.
2Ease of manufacture
If the coupling member is made with round cross-section, then manufacturing is simple, but bending stresses at the ends are high leading to reduced lifespan
Solution Approach 1:
The coupling member transitions from a conventional round cross-section to an elliptical cross-section with asymmetric dimensions. The major axis of the ellipse is oriented perpendicular to the bending direction, providing greater moment of inertia and reduced bending stress without increasing the overall length of the coupling member. This asymmetric geometry allows the appliance to maintain a compact length while extending coupling member life through reduced stress levels.
Solution Approach 2:
The cross-sectional parameters of the coupling member are changed from a circular geometry (equal dimensions in all directions) to an elliptical geometry (different dimensions along different axes). By increasing the dimension along the major axis perpendicular to bending, the section modulus increases, which directly reduces bending stress for a given moment, thereby extending component life without lengthening the appliance.
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 elliptical coupling member design reduces bending stress, increases the lifespan of the coupling member, and allows for efficient torque transfer, ensuring the appliance operates effectively within commercial size constraints.
Implementation Method 1
the coupling member is elliptical in cross-section in an active region thereof, having a thin dimension and a wider dimension, with the thin dimension in the direction of the bending of the coupling member during operation of the appliance and the wider dimension perpendicular thereto
Implementation Method 2
a spring hub assembly driven by the coupling member and eccentric mass, which constrains the rotational movement of the coupling member to an oscillating action of the workpiece shaft assembly
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The appliance includes a DC motor (12) having a rotating output shaft (14). A flexible coupling member (22) is connected at one end to the output shaft, and at the other end is connected to an eccentric mass (24). The end of the coupling member with the eccentric mass is connected to a V-spring assembly (16) which drives a workpiece assembly (18) on a distal end of which is mounted a workpiece (19). The spring assembly constrains the rotational movement of the coupling member to produce an oscillating, back-and-forth action of the workpiece shaft and the workpiece through a desired angle. The coupling member is elongated, and is elliptical in cross- section in an active region (34), having a thin dimension (38) in the direction in which the active portion bends during operation of the motor and rotation of the motor output shaft.