Actuator Eccentric Core Preload Mitigates Rattle
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Solution Overview
Problem
Electric personal care devices, such as electric toothbrushes, experience detrimental reactionary forces that lead to rattling and unnecessary wear due to misalignment or friction, causing the motor shaft to come off the bearings.
Innovation Solution
Implementing an asymmetrical magnet gap between a core with radially extending pole members and magnets, or using an eccentric core with pole members of varying lengths, and positioning the spindle within bearings with a centerline offset to induce a mechanical preload, thereby mitigating these forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor shaft is allowed to rotate freely within the bearings, then the device operates smoothly with minimal friction, but the shaft can come off the bearings due to reactionary forces, causing rattling and wear
Solution Approach 1:
The patent applies preliminary anti-action by pre-loading the shaft against the bearings using magnetic forces before reactionary forces can cause the shaft to come off. The asymmetric magnet gap creates a bias force that presses the shaft into the bearings, counteracting the detrimental reactionary forces from brush friction and misalignment before they can cause rattling or wear.
Solution Approach 2:
The patent employs asymmetry by creating an asymmetric magnet gap where the distance between the magnet and the core varies around the circumference. This asymmetric configuration generates a unidirectional bias force that pre-loads the shaft against the bearings in a specific direction, preventing the shaft from coming off during operation while maintaining smooth rotation.
2Object-affected harmful factors
If the shaft is tightly constrained within the bearings, then rattling and wear are reduced, but friction increases and operational smoothness decreases
Solution Approach 1:
The magnetic pre-loading applies a controlled bias force that maintains sufficient contact between the shaft and bearings to prevent rattling, while the asymmetric nature of the force distribution allows the shaft to rotate smoothly without excessive friction in the operational direction.
Solution Approach 2:
The patent changes the magnetic field parameters by varying the magnet gap distance asymmetrically around the core. This creates a non-uniform magnetic force distribution that applies sufficient normal force to prevent shaft separation and rattling, while the directional nature of the asymmetric gap minimizes friction during rotational operation.
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
Substantially reduces rattling and wear by applying a bias force that keeps the spindle securely within the bearings, enhancing the user experience and extending the device's lifespan.
Implementation Method 1
an asymmetrical magnet gap between a core, comprising a spindle with radially extending pole members, and magnets disposed about the interior of a housing induces a preload
Data Source
AI summary
An actuator (12) for a personal care appliance (10) having an eccentric core (21) to preload the actuator (12) to prevent rattling caused by detrimental reactionary forces. The eccentric core (21) includes a pole assembly (24) radially extending from a spindle 22 having at least a first set (25-1) and a second set (25-2) of pole members. The first set (25-1) has a greater length as measured from the center of the spindle 22 than the second set (24-2), reducing the magnet gap on one side of the spindle (22) to create an eccentric core and preload the actuator (12). Alternatively, the preload can be mechanically created by a set of bearings (28) disposed within housing (18) of the actuator 12, where the bearings (28) have a centerline (A3) offset from the principal axis (A1) of the housing (18).