Flexible Spring Motor Assembly for Torsional Vibration Reduction
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Solution Overview
Problem
Personal care appliances, such as power toothbrushes, experience vibrations and oscillations that transfer torsional forces to the user, leading to an undesirable user experience due to the rotational motion of the drive shaft.
Innovation Solution
Incorporating a motor assembly with flexible springs that resist rotation in specific directions, utilizing a stator sub-assembly with magnetic fields to drive hubs out of phase, and a torsion bar to transfer torque, which reduces the transfer of torsional vibrations to the user.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a traditional motor assembly is used to generate rotational motion of the drive shaft, then the personal care appliance can function effectively, but vibrations and oscillations transfer torsional forces to the user creating an undesirable user experience
Solution Approach 1:
The patent changes the physical parameters of the spring member by configuring it with different stiffness values in different rotational directions. The spring member has a first stiffness in a first rotational direction and a second stiffness in a second rotational direction, where the first stiffness is greater than the second stiffness. This anisotropic stiffness configuration allows the system to resist torsional vibrations more effectively in the primary rotation direction while maintaining operational flexibility.
Solution Approach 2:
The spring member is designed with asymmetric mechanical properties, having different stiffness characteristics for clockwise versus counter-clockwise rotation. This asymmetry enables the motor assembly to better dampen torsional vibrations in the direction that matters most for user comfort, while still allowing necessary operational movements in the opposite direction.
2Object-affected harmful factors
If the compliant member has high stiffness to resist rotation, then torsional vibrations are reduced, but the power requirements and operational flexibility may be compromised
Solution Approach 1:
Instead of using a uniformly high-stiffness compliant member that would increase power requirements, the patent employs a spring member with directionally selective stiffness parameters. The first stiffness (in the primary rotation direction) is high to reduce vibrations, while the second stiffness (in the opposite direction) is lower to maintain operational flexibility and reduce overall power consumption.
Solution Approach 2:
The spring member exhibits different mechanical qualities in different directions of rotation. The local quality of the spring material and geometry is optimized to provide high resistance to torsional vibrations in the critical rotation direction while maintaining lower resistance in the opposite direction, thereby reducing overall energy requirements.
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 torsional vibrations and power requirements, providing a more stable and comfortable user experience by ensuring the rotational masses of the motor assembly rotate out of phase, thereby minimizing the transmission of unwanted forces to the user.
Implementation Method 1
the compliant member has a first stiffness such that the compliant member is arranged to resist rotation of the rotational member within the grounded section in at least a first rotational direction
Implementation Method 2
a stator sub-assembly with magnetic fields to drive hubs out of phase
Implementation Method 3
a torsion bar to transfer torque, which reduces the transfer of torsional vibrations to the user
Data Source
AI summary
A personal care appliance which includes at least one flexible spring. The flexible spring having an grounded section with an outer surface and an inner surface, a rotational member arranged radially within the grounded section, wherein the rotational member is arranged to rotate within the grounded section in a first rotational direction about an imaginary rotational axis, and a compliant member having a first end and a second end, wherein the first end is operatively engaged with the inner surface of the grounded section and the second end operatively engaged with the rotational member. The compliant member has a first stiffness such that the compliant member is arranged to resist rotation of the rotational member in at least the first rotational direction.