Microwave Safety Switch with Delayed Power Interruption
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Solution Overview
Problem
Existing safety devices for cooking appliances with microwave functions, particularly those with higher-power sources, face challenges in safely switching off the microwave source when the door is open, due to complex mechanical implementations and unreliable monitoring of door switches, which can lead to unsafe conditions if the power supply is not properly interrupted.
Innovation Solution
A safety device with at least one electrically actuatable closing switch and two changeover switches that are coupled to the appliance door, where the switches are designed to ensure the power supply to the microwave source is interrupted if they become stuck in abnormal positions, using a delay time to differentiate between fault states and transient switching states, and incorporating a short-circuit switch to permanently interrupt the power supply if faults are detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If direct switching of power supply is used for high-power microwave sources, then the microwave source can be switched off when door is open, but the switching reliability is insufficient and the circuit becomes too simple to ensure safety
Solution Approach 1:
The patent introduces an intermediary closing switch (Schließschalter) with auxiliary contacts that mediates between the door switches and the power supply. This closing switch acts as a safety intermediary that must be actively closed by a closing signal to enable power flow, providing an additional layer of control and reliability for high-power microwave sources without requiring complex mechanical implementations
Solution Approach 2:
The patent implements feedback through auxiliary contacts of the closing switch that monitor the switching state and provide signals to ensure proper operation. The monitoring circuit receives feedback from the closing switch and door switches to verify the appliance door is closed before allowing microwave operation, ensuring reliable safety control
2Reliability
If three door switches are used for monitoring and interrupting power supply, then switching reliability improves, but the device complexity and mechanical implementation become too complicated
Solution Approach 1:
The patent merges the functions of multiple door switches into a single closing switch with auxiliary contacts. Instead of using three separate door switches for monitoring and power interruption, the closing switch combines these functions by using its main contacts for power control and auxiliary contacts for monitoring, significantly reducing circuit complexity while maintaining reliability
Solution Approach 2:
The closing switch serves multiple functions simultaneously: it acts as a power interrupting switch, a monitoring switch, and a signal generator. The auxiliary contacts of the closing switch perform monitoring functions that would otherwise require separate switches, making the closing switch a multi-functional component that reduces overall device complexity
3Ease of operation
If mechanical door switches are used for power interruption, then the power supply can be interrupted when door is open, but the switches can get stuck or stick due to frequent use under load, leading to unsafe conditions
Solution Approach 1:
The patent replaces direct mechanical door switch operation with an electrically actuatable closing switch. The closing switch is controlled by closing signals from the monitoring circuit rather than direct mechanical actuation by the door, reducing mechanical wear and sticking issues. The auxiliary contacts provide electrical monitoring that is less prone to mechanical failure
Data Source
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AI summary
The device (10) has changeover switches (S1, S2) connected with each other such that the switches provide a closure signal to a closure switch (14) e.g. relay, when the switches are in a switching position. The switches do not provide the closure signal to the closure switch when one of the changeover switches is in another switching position. The closure switch disconnects a power supply of a microwave source (12) i.e. magnetron, when the closure switch is closed according to a cycle of preset time lag after switching of one of the changeover switches into the latter position. An independent claim is also included for a method for securely switching off a microwave source in a cooking device with microwave function.