Electromechanical Relay Restart Protection for Handheld Power Tools
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Solution Overview
Problem
Mains-operated handheld machine tools with purely mechanical latching of slide switches can lead to uncontrolled restarting of the drive motor after power interruptions, posing risks to users and causing damage to tool inserts.
Innovation Solution
Incorporating an electromechanical relay in the handheld machine tool to prevent uncontrolled restarting of the drive motor by ensuring the latching is canceled upon power interruptions, using a combination of electrical switches with make and break contacts and a compression spring-pretensioned plunger to manage the relay's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a purely mechanical latching mechanism is used for the slide switch, then the device complexity is reduced and ease of manufacture is improved, but uncontrolled restarting of the drive motor after power interruptions occurs, worsening safety and reliability
Solution Approach 1:
An electromechanical relay is introduced as an intermediary component between the slide switch and the drive motor. The relay's auxiliary contact acts as a mediator that detects power interruptions and prevents automatic restarting, while the slide switch itself remains purely mechanical. This resolves the contradiction by adding a safety intermediary without complicating the primary switching mechanism.
Solution Approach 2:
The patent replaces a purely mechanical latching system with an electromechanical relay system for the safety function. The relay uses electromagnetic fields to control the auxiliary contact that prevents restarting, substituting mechanical interlocking with electromagnetic control for the protection function, thereby improving reliability without significantly increasing overall device complexity.
2Reliability
If an electromechanical relay with auxiliary contact is added to prevent uncontrolled restarting, then safety and reliability are improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The electromechanical relay serves multiple functions simultaneously: it controls the main power circuit to the drive motor, provides the latching function to keep the motor running, and through its auxiliary contact, provides the safety function to prevent uncontrolled restarting. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity while achieving improved reliability.
3Ease of operation
If the slide switch is made latchable to maintain position during operation, then ease of operation is improved, but the risk of uncontrolled restarting after power interruption increases, worsening safety
Solution Approach 1:
The relay's auxiliary contact acts as a safety intermediary that decouples the latchable slide switch from the drive motor power supply. The slide switch can remain latched for ease of operation, but the auxiliary contact monitors power status and prevents automatic motor restarting, thereby resolving the contradiction between operational convenience and safety.
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 prevents uncontrolled restarting of the drive motor after power interruptions, reducing the risk of accidents and damage to tool inserts, while maintaining a simple and reliable design.
Implementation Method 1
A protection device having an electromechanical relay is provided, which is designed to prevent, by means of the electromechanical relay, uncontrolled restarting of the drive motor after an interruption to a corresponding power supply
Implementation Method 2
The electrical switch has a plunger, which is pretensioned by means of a compression spring and is axially displaceable, counter to a spring force applied by the compression spring
Data Source
AI summary
A mains-operated handheld machine tool includes a tool housing, an electric drive motor arranged in the housing and configured to drive an associated tool insert, and a slide switch arranged, at least in a longitudinally displaceable fashion, on the tool housing and coupled to a sliding element configured to switch the drive motor on and off. The mains-operated handheld machine also includes a protection device with an electromechanical relay. The protection device is configured to prevent, by way of the electromechanical relay, uncontrolled restarting of the drive motor after an interruption to a corresponding power supply to the drive motor as a result of latching of the relay being canceled.