Washing Machine Lid Lock Using PTC-Heated Memory Wire
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Solution Overview
Problem
The use of shape memory alloy wires in commercial applications, such as washing machine lid locks, is hindered by the need for power conditioning to prevent overheating and maintain strain recovery properties, and existing solutions like thermal elements require complex regulation and can cause hot spots.
Innovation Solution
A thermal actuator using a separate heating element, like a PTC resistor, directly contacts the shape memory alloy wire for consistent heating control, eliminating the need for costly power regulation and ensuring efficient thermal contact without inhibiting movement, allowing for practical use in household appliances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power conditioning is used to prevent overheating of the muscle wire, then the strain recovery properties are maintained, but the device complexity and cost increase
Solution Approach 1:
A PTC heater element is introduced as an intermediary heating device that converts electrical energy to thermal energy, which then heats the muscle wire indirectly. This mediator approach eliminates the need for complex power conditioning circuits while maintaining reliable heating control and preventing overheating of the muscle wire.
Solution Approach 2:
The patent replaces the electrical resistive heating method (which requires power conditioning) with a thermal conduction-based heating system using a PTC heater element. This substitution eliminates the need for voltage regulation and current control circuits, significantly reducing device complexity while maintaining heating reliability.
2Speed
If direct heating of the muscle wire is used, then fast response is achieved, but hot spots and overheating occur
Solution Approach 1:
The PTC heater element provides uniform thermal distribution across the muscle wire through controlled thermal conduction. The heater's design ensures consistent heating along the wire length, preventing localized hot spots while maintaining fast overall response time. The thermal properties of the PTC material itself provide self-regulation to avoid overheating.
3Duration of action of stationary object
If thermal elements like wax motors or bimetallic strips are used, then time delay feature is provided, but the device complexity and response time increase
Solution Approach 1:
The patent extracts the time delay function from complex thermal elements like wax motors and bimetallic strips, implementing it simply through the thermal mass of the PTC heater element itself. The heater's thermal characteristics naturally provide the required delay without requiring additional mechanical components, significantly simplifying the device while maintaining the safety delay feature.
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
This solution enables fast response actuation and consistent thermal control, reducing the risk of overheating and hot spots, while minimizing the use of expensive shape memory alloy material, allowing for reliable operation in repeated cycles.
Implementation Method 1
an electrical heater pressed against the shape memory alloy element with movement of the shape memory alloy element
Implementation Method 2
a shape memory alloy wire having a first end attached to the anchor point and having a second end moving with respect to the anchor point caused by a change of length of the wire
Data Source
AI summary
An actuator suitable for a washing machine lid lock employs a shape memory alloy wire indirectly heated by a temperature regulating heater that provides a sliding coupling to the wire and that may be driven, for example, directly by line voltage without the need for temperature regulation circuitry.