Electric Toothbrush Cone-Shaped Motor Cavity Design
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Solution Overview
Problem
Existing electric toothbrushes face challenges in forming the motor cavity through single injection molding due to stem material limitations, experience reduced vibration power and noise due to vibration transmission, and struggle with weight balance due to motor placement constraints.
Innovation Solution
An electric toothbrush design featuring a stem member made of synthetic resin with a cone-shaped cavity to securely hold a DC motor, a vibration shaft with an eccentric shaft, and a recessed hole for axial shaft insertion, allowing for efficient vibration transmission and adjustable weight balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the stem is formed from synthetic resin, then the stem can be easily manufactured, but it is difficult to form the cavity through a single injection molding process
Solution Approach 1:
The cavity formation process is segmented into multiple injection molding steps. First, a preliminary cavity structure is formed, then additional molding steps complete the cavity formation. This allows the synthetic resin stem to be manufactured while still achieving the complex cavity shape that would be difficult to form in a single step.
2Device complexity
If the vibration of the eccentric shaft is transmitted through the motor and the stem to the bristle, then the structure is simplified, but it results in a reduction in power and the production of excessive noise
Solution Approach 1:
The vibration transmission path is extracted and separated from the motor and stem. A dedicated vibration transmission component is introduced that directly connects the eccentric shaft to the brush assembly, bypassing the motor and stem. This extraction of the vibration path eliminates noise from motor/stem transmission while maintaining simplified overall structure.
3Volume of moving object
If the motor is located close to the tooth cleaning elements, then the motor size can be reduced, but it results in low vibration power
Solution Approach 1:
A dedicated vibration transmission shaft serves as an intermediary component between the motor and the brush assembly. This mediator allows the motor to be positioned close to the cleaning elements (reducing motor size) while the vibration transmission shaft efficiently transmits vibration power to the brush, preventing power loss despite the close proximity.
4Device complexity
If the location of the motor is limited, then the motor placement is constrained, but it makes it difficult to adjust the weight balance
Solution Approach 1:
The motor placement is made dynamic and adjustable rather than fixed. The motor can be repositioned along the stem axis or at different angular positions, allowing weight balance to be adjusted according to specific requirements while still maintaining the benefit of limited placement locations. This dynamic positioning capability resolves the conflict between constrained placement and balance adjustment.
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 design enhances vibration power transmission, reduces noise, and allows for better weight balance and easier assembly, enabling a more effective and balanced electric toothbrush operation.
Implementation Method 1
a DC motor inserted in the elongated cavity from the open end and firmly held in the elongated cavity by a rigid contact between a shoulder portion and/or side surface of the DC motor and the cone- shaped wall
Implementation Method 2
a vibration shaft having one end connected to the DC motor and another end formed with an axial shaft portion which is rotatably inserted into the recessed hole, said vibration shaft having an eccentric shaft whose gravity center is located at a position deviated from an axis of the DC motor
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
An electric toothbrush includes a stem member on which a replaceable toothbrush is mounted. The stem member is made of synthetic resin and has a cavity for accommodating a DC motor and a vibration shaft connected to the DC motor. One end of the cavity is opened for inserting the DC motor and the vibration shaft together, and the other end thereof is closed. A free end of the vibration shaft is rotatably supported at the closed end of the cavity. The cavity has a cone-shaped wall so that the DC motor is firmly held in the cavity by a rigid contact between a shoulder portion of the DC motor and the cone-shaped wall.