Bistable Switch with Shape Memory Actuator
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bistable electric switches using shape memory alloy (SMA) wires face issues where the activated SMA wire's force is partially used to tension the other SMA wire, leading to mechanical stress and reduced reliability due to both wires being stressed at each operating cycle.
Innovation Solution
A bistable electric switch design where the SMA wires are arranged such that the activated SMA wire is shorter than the distance between them, allowing it to use its full force only to overcome the snap-action spring resistance, and the other SMA wire is not in contact with the drive element during its shortening run, reducing mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If both SMA wires are permanently connected to the drive element, then the switch can achieve bistable operation, but the activated SMA wire's force is partially used to tension the other SMA wire, reducing reliability
Solution Approach 1:
The patent extracts the non-activated SMA wire from the force transmission path by positioning it outside the drive element's movement path. During operation, only the activated SMA wire transmits force to the drive element, while the other SMA wire remains idle and does not experience tensile stress. This eliminates the force loss described in the contradiction.
2Duration of action of stationary object
If both SMA wires are permanently connected to the drive element, then the switch structure is complete, but both wires undergo mechanical stress at each operating cycle, reducing durability
Solution Approach 1:
The patent removes the non-activated SMA wire from the stress cycle by positioning it outside the drive element's movement path. During each operating cycle, only the activated SMA wire undergoes mechanical stress, while the other SMA wire remains stress-free. This significantly extends the operational life of the switch by preventing fatigue accumulation in both wires.
3Length of moving object
If the SMA wire is used to cover the entire run between stable positions, then the actuator run is sufficient, but the SMA wire would be too long and inefficient
Solution Approach 1:
The patent introduces the drive element as an intermediary between the SMA wire and the snap-action spring. The SMA wire acts on the drive element, which then engages the snap-action spring to achieve the full movement between stable positions. This allows the SMA wire to be shorter while still achieving the required actuator run through the mechanical advantage of the snap-action mechanism.
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 design enhances the reliability of the switch by allowing the SMA wire to toggle a stronger spring for better electric contact and reduces mechanical stress, optimizing the switch's structure to only account for shape memory-induced loads.
Implementation Method 1
the shape memory phenomenon consists in the fact that a mechanical piece made of an alloy that exhibits said phenomenon is capable of transitioning, upon a temperature change, between two shapes that are preset at the time of manufacturing
Implementation Method 2
both transitions can be caused by temperature changes, this being the case of the application of the present invention. This occurs thanks to the transformation of the micro-crystalline structure of the piece that passes from a type called martensitic, stable at lower temperatures, to a type called austenitic, stable at higher temperatures
Implementation Method 3
A typical example of a snap-action spring is a leaf spring secured at its ends such that it remains compressed and toggles between two stable symmetrical positions
Data Source
AI summary
A bistable electric switch is described. The switch has as actuators a pair of opposing SMA wires acting on a drive element integral with a snap-action spring so as to toggle the snap-action spring between two stable positions corresponding to two operating positions of the switch, the drive element being shorter than the distance existing between the two opposing SMA wires when one of the SMA wires is contracted and the other SMA wire is uncontracted. The entire force exerted by the activated SMA wire is used to overcome the resistance of the snap-action spring.