Resonant Toothbrush Drive Train Using V-Spring and Eccentric
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Solution Overview
Problem
Existing power toothbrush drive trains using DC motors for resonant oscillation face reliability issues due to flex coupling problems and noise from the eccentric/bushing interface, and require expensive electronic circuits for sinusoidal signal-driven systems, while also experiencing insufficient startup torque and overshoot when stalled.
Innovation Solution
A DC motor-driven toothbrush with a spring assembly, where the motor is attached to a free-moving spring hub and fixed spring mount, using a V-spring configuration that is stiffer in bending than torsion, excited by an eccentric to produce oscillatory action within specific frequency and amplitude ranges, minimizing parts and avoiding magnetic coupling issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flex coupling is used to transmit power from the DC motor to the spring assembly, then the system can be assembled, but reliability problems occur due to oscillation and wear
Solution Approach 1:
The patent removes the flex coupling from the drive train entirely, replacing it with a direct mechanical connection between the DC motor and the spring assembly. This extraction eliminates the reliability problems and noise associated with the flex coupling's oscillation and wear.
Solution Approach 2:
Instead of using a flexible element to accommodate misalignment, the patent inverts the approach by using a rigid direct connection and allowing the spring assembly itself to accommodate the alignment through its mounting geometry, thereby eliminating the harmful flex coupling.
2Reliability
If an electromagnetic driver with sinusoidal signal is used to drive the spring assembly, then oscillating brushhead action is achieved, but expensive electronic circuits are required
Solution Approach 1:
The patent replaces the electromagnetic driver with sinusoidal signal and expensive electronic circuits with a simple DC motor driven by a constant voltage source. The mechanical oscillation is achieved through the DC motor's direct connection to the spring assembly, eliminating the need for complex electronic control circuits.
Solution Approach 2:
The patent changes the control parameter from a sinusoidal electrical signal to a constant DC voltage, and achieves the desired oscillation frequency by adjusting mechanical parameters such as spring stiffness and mass distribution rather than through electronic frequency control.
3Device complexity
If a DC motor is used to drive the spring assembly, then cost and simplicity are reduced, but insufficient startup torque and overshoot occur when the brush is stalled
Solution Approach 1:
The patent employs a compliant mounting for the spring assembly that allows dynamic adjustment of the drive train's stiffness characteristics. This dynamic compliance enables the system to accommodate the DC motor's limited startup torque while preventing overshoot and stall issues through controlled flexibility in the mounting geometry.
4Device complexity
If the eccentric is mounted to rotate in a bushing, then the structure is simple, but wear occurs at the eccentric/bushing interface resulting in noise
Solution Approach 1:
The patent removes the bushing from the eccentric mounting, eliminating the wear interface entirely. The eccentric is mounted directly to the DC motor shaft or through a compliant connection that does not require a bushing, thereby eliminating the noise and wear associated with the eccentric/bushing interface.
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 provides a reliable, simple, and cost-effective oscillating action for effective tooth cleaning with reduced noise and improved reliability by generating sufficient mechanical force to excite the spring assembly in a resonant mode, maintaining desired oscillation frequencies and amplitudes without excessive wear or noise.
Implementation Method 1
DC motor with an eccentric is used to mechanically excite a spring system
Implementation Method 2
the rotation of the eccentric at a selected frequency excites the spring member to an oscillatory action, resulting in the brush shaft and the brushhead oscillating therewith
Implementation Method 3
a spring assembly which includes a spring member characterized by a stiffness in torsion which results in a rotational system resonant frequency
Data Source
Figure 1~2
Figure 3~4
AI summary
The toothbrush includes a drive assembly comprising a DC motor (12) driven by a battery (15) with a rotating drive shaft (16) extending from one end of the DC motor, on which is mounted an eccentric member (20) which rotates with the drive shaft. A spring assembly (24) includes a hub member (26) at a proximal end, a mount member (28) at a distal end and a V-spring member (41) mounted to and extending therebetween. The DC motor is fixed to a rear surface of the hub member, the motor and the hub member being free to move in unison in operation of the toothbrush. The mount member is fixed in position in the toothbrush. A brushhead shaft (38) is mounted to and extends between the hub member and the mount member and extends distally from the mount member. The brushhead shaft member is offset laterally from the axis of rotation of the motor drive shaft. A brushhead assembly (42), including a set of bristles (44), is removably mounted on the brushhead shaft.