Electrical Switch Plunger Coupling for Power Tool Restart Protection
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Solution Overview
Problem
Electric power tools with existing switches can unintentionally restart after a voltage failure and restoration, posing a hazard, especially when locked in the ON position, as they lack integrated restart protection, which is becoming a standard requirement.
Innovation Solution
A compact electrical switch design incorporating a plunger, contact piece, and a coupling element with an electromagnet, allowing the contact system to be switched independently and incorporating a compression spring for resetting, ensuring the tool remains off during unintended power restoration, suitable for small angle grinders and other power tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a locking device is added to hold the actuating means in the on position, then the power tool can remain on during continuous operation, but the tool may unintentionally restart after voltage failure and restoration
Solution Approach 1:
The switch is divided into two independent switching paths: one controlled by the plunger for normal on/off operation, and another independent path that can switch the contact system off without plunger intervention. This segmentation allows the locking function to be maintained while providing a separate mechanism to prevent unintended restart by breaking the circuit independently of the locking mechanism.
Solution Approach 2:
The coupling element acts as an intermediary between the plunger and the contact piece. It transmits the plunger's switching action to the contact piece when engaged, but can be disengaged to allow the contact piece to be moved independently by the elastic element, thus mediating between the locking requirement and the restart protection requirement.
2Object-affected harmful factors
If restart protection is integrated into the switch, then user safety is improved, but the switch design becomes more complex
Solution Approach 1:
The restart protection function is merged with the existing switch structure by integrating the coupling element, elastic element, and independent contact piece into the same housing and mechanism as the plunger and contact system. This combining approach provides restart protection without requiring a separate device, thus limiting the increase in complexity.
Solution Approach 2:
The coupling element serves multiple functions: it transmits plunger motion to the contact piece for normal switching, provides a decoupling mechanism for independent contact piece movement (restart protection), and can be held in position by the elastic element. This multi-functionality reduces the need for additional separate components.
3Volume of moving object
If the coupling element is made movable on the contact piece, then the switch achieves compact design, but the manufacturing precision requirements increase
Solution Approach 1:
The movable coupling element replaces the need for separate locking and switching mechanisms that would require precise mechanical alignment. By using the elastic element to provide the coupling and decoupling action, the design achieves compactness while relying on elastic deformation rather than precision mechanical tolerances for the critical positioning functions.
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 cost-effective and simple integration of restart protection within the switch, meeting the amended appliance standard without requiring significant alterations to the appliance, ensuring user safety by preventing unintended startup and maintaining other switch functions.
Implementation Method 1
The actuator may be an electromagnet, since such a design operates in a particularly functionally safe and reliable manner
Implementation Method 2
at least one elastic element may act on the actuating means for the purpose of resetting the latter to the off position of the contact system
Data Source
AI summary
An electrical switch for an electric power tool. The electrical switch has a contact system that can be switched between an off position and an on position, and having a movable actuating means or switching the contact system. The actuating means comprises a plunger and a contact piece. The contact piece acts on the contact system for the purpose of switching. A coupling element is provided, such that the plunger can be brought into and out of interaction with the contact piece. The interaction is effected such that it is made possible for the contact system to be switched into the on position and the off position by means of the plunger, and for the contact system to be switched into the off position independently of the plunger.