Scotch Yoke Mechanism for Quiet Electric Toothbrush Drive
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Solution Overview
Problem
Current electric toothbrush drive systems produce excessive noise due to high accelerations and inertia forces, particularly at frequencies around 83 Hz, leading to undesired noise emissions above 55 dB(A) sound power level.
Innovation Solution
A gear mechanism incorporating a scotch yoke mechanism with a cross slider guided by pivotable links converts rotary motion into a sinusoidal reciprocating pivoting motion of the driven shaft, reducing noise by minimizing accelerations and inertia forces through a sinusoidal movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gearwheels are used in the drive mechanism, then the continuous rotary movement can be converted into reciprocating pivoting motion, but sound emissions increase
Solution Approach 1:
The patent replaces the traditional gearwheel-based mechanical transmission system with a scotch yoke mechanism. This substitution eliminates the meshing of gear teeth that generates noise, while still achieving the required conversion of continuous rotary motion into reciprocating pivoting motion through the eccentric drive pin and slotted link mechanism.
Solution Approach 2:
The invention changes the motion parameters by introducing an eccentric drive pin that creates a sinusoidal reciprocating motion pattern. This parameter change in the motion trajectory reduces acceleration peaks and inertia forces compared to traditional gear mechanisms, thereby reducing noise emissions to below 55 dB(A).
2Productivity
If high acceleration reciprocating motion is generated, then the driven shaft performs effective cleaning action, but inertia forces increase causing noise above 55 dB(A)
Solution Approach 1:
The scotch yoke mechanism with eccentric drive pin generates a sinusoidal (curved) motion pattern instead of linear reciprocating motion. This curved trajectory smooths out acceleration changes, reducing inertia forces and noise while maintaining the reciprocating cleaning action of the driven shaft.
Solution Approach 2:
The invention employs periodic sinusoidal motion through the eccentric mechanism, creating smooth, rhythmic reciprocating movement. This periodic action with controlled acceleration profiles reduces impact forces and noise emissions compared to abrupt start-stop motion patterns.
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 noise emissions to below 55 dB(A) by converting rotary motion into a sinusoidal reciprocating motion, minimizing bearing reaction forces and rattling noise, thereby enhancing the quiet operation of electrically driven devices like toothbrushes.
Implementation Method 1
The driven shaft may be indirectly coupled to the drive shaft by means of a gear mechanism comprising a scotch yoke mechanism, i.e. a slotted link mechanism, converting a rotary motion of the drive shaft into a reciprocating pivoting motion of the driven shaft
Implementation Method 2
An elastically deformable element may be provided between the housing and the rocker frame biasing the rocker frame into a rest position
Data Source
AI summary
An electrically driven device includes a housing, an electric motor with a drive shaft having a first rotary axis and a drive pin connected to the drive shaft eccentrically with respect to the rotary axis, and a driven shaft having a second rotary axis and mounted in the housing for performing a pivoting about the second rotary axis. The driven shaft is coupled to the drive shaft by a gear mechanism including a scotch yoke mechanism converting a rotary motion of the drive shaft into a reciprocating motion of the driven shaft. The scotch yoke mechanism includes a cross slider having a sliding support extending perpendicular to the first rotary axis and receiving the drive pin either directly or through a sliding block with a bearing receiving the drive pin. The cross slider is guided in the housing by at least two pivotable links. The driven shaft is coupled to the cross slider by an arm, converting a rotary motion of the drive shaft into a reciprocating of the driven shaft.