Resonant Drive Train for Power Toothbrush
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Solution Overview
Problem
Existing power toothbrush drive trains using DC motors face increased torque requirements at higher frequencies, especially with direct crank and linkage mechanisms, which complicates the design and increases costs, while custom-made components for sinusoidal signals are expensive.
Innovation Solution
A drive train system utilizing a DC motor with an eccentric shaft and a spring assembly, where the spring member alternates between compression and extension to produce an oscillating motion for the brushhead, eliminating the need for a direct crank and linkage, and allowing for adjustable frequency and amplitude through the spring's stiffness and system inertia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a DC motor with a crank and linkage mechanism is used to produce oscillating brushhead motion, then the brushhead oscillation frequency can be increased to effective values, but the torque requirements for the motor increase substantially
Solution Approach 1:
The patent employs a spring assembly that utilizes mechanical vibration and resonance to produce oscillating brushhead motion. The spring is excited by the rotating motor shaft, and the system operates at or near the resonant frequency of the spring, which amplifies the oscillation amplitude without requiring proportionally high torque from the motor. This allows effective oscillation frequencies to be achieved with reduced motor torque requirements compared to direct crank and linkage mechanisms.
2Ease of operation
If a sinusoidal signal drive system with custom-made stators is used, then the brushhead oscillating motion can be produced, but the overall expense of the power toothbrush increases substantially
Solution Approach 1:
The patent replaces expensive custom-made stators with a standard DC motor and a simple spring assembly. The spring assembly uses conventional components that can be manufactured using standard processes, significantly reducing manufacturing costs. The spring itself is a relatively inexpensive component that provides the necessary oscillating motion through its elastic properties, eliminating the need for costly custom electromagnetic stators.
Solution Approach 2:
The patent substitutes the electromagnetic drive system (requiring custom stators and complex electronics) with a mechanical spring assembly driven by a standard DC motor. The spring assembly translates the rotational motion of the motor shaft into oscillating brushhead motion through mechanical elasticity and resonance, replacing complex electromagnetic field control with simpler mechanical principles.
3Device complexity
If a direct crank and linkage assembly is used to generate oscillating brushhead motion, then the design is simple, but the device complexity increases when frequency is increased to effective values
Solution Approach 1:
The patent uses a dynamic spring assembly that can adapt to different operating frequencies. The spring's natural frequency and stiffness characteristics allow the system to operate effectively at various oscillation frequencies without requiring complex mechanical linkages or cranks. The spring assembly provides a flexible, dynamic mechanism that simplifies the overall drive train structure while maintaining the ability to generate effective oscillation frequencies.
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 solution simplifies the design, reduces costs, and maintains effective oscillating motion for teeth cleaning by using a mechanical excitation of the spring member to produce a resonant sweeping motion, adjustable in amplitude and frequency, without the complexity of direct crank and linkage mechanisms.
Implementation Method 1
a spring assembly extending from the eccentric portion, the spring assembly including a spring member which alternates between two conditions as the eccentric portion rotates
Implementation Method 2
a mechanical excitation of the spring member to produce a resonant sweeping motion
Implementation Method 3
the drive shaft having an eccentric portion located proximally from the free end thereof
Data Source
AI summary
The power toothbrush includes a driving assembly which in turn includes a DC motor (14) and a battery. The DC motor has a rotating drive shaft (16), supported at its free end. The drive shaft has an eccentric portion (18). Mounted on the eccentric portion is a plastic sleeve (20) having an extending portion which engages one end of a spring member (38). The other end of the spring member is secured to a yoke (36) which is secured to a brushhead shaft (32). Rotation of the drive shaft results in the extending portion of the plastic sleeve, moving the spring between a compressed state and an extended state. The action of the DC motor excites the spring to produce an oscillating action of the brushhead shaft and a brushhead assembly (40) mounted thereon.