Bistable Shape Memory Actuator for Anti-Glare Mirrors
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Solution Overview
Problem
Existing shape memory actuators for automatic anti-glare rear view mirrors require multiple SMA wires, suffer from friction and bulkiness, are susceptible to vibrations, and lack manual operation capabilities due to reliance on photodetector control.
Innovation Solution
A bistable shape memory actuator design where the SMA wire is activated only during shortening runs, with a mobile driving element in a plane parallel to the supporting body, connected through a bistable moving system, allowing for two stable positions without continuous actuation and enabling manual activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple SMA wires are used to achieve bidirectional movement, then the actuator can perform automatic anti-glare function, but the device complexity and bulkiness increase
Solution Approach 1:
The actuator is divided into two independent stable positions achieved through a bistable mechanism rather than using multiple active SMA wires. The bistable system segments the movement into two distinct stable states (normal position and anti-glare position), eliminating the need for multiple actuating wires while maintaining bidirectional functionality.
Solution Approach 2:
Instead of using multiple SMA wires to actively drive the mirror to both positions, the invention inverts the approach by using a single SMA wire that actively drives the mirror to one position (anti-glare) while relying on the bistable mechanism's inherent stability to maintain the other position (normal). The bistable system passively provides the return path without requiring active actuation.
2Measurement precision
If SMA wires are continuously actuated to maintain mirror positions, then precise position control is achieved, but energy consumption increases and vibrations occur
Solution Approach 1:
The SMA wire is actuated periodically and intermittently rather than continuously. Current is applied only when transitioning between stable positions (from normal to anti-glare or vice versa), and the bistable mechanism maintains positions without continuous energy input. This periodic actuation eliminates vibrations associated with continuous actuation while reducing energy consumption significantly.
Solution Approach 2:
The bistable mechanism serves itself by maintaining stable positions through its inherent mechanical design rather than requiring continuous external actuation. The system uses its own structural properties (bistability) to maintain position, eliminating the need for continuous energy input and reducing both energy consumption and vibrations.
3Extent of automation
If a photodetector control system is used for automatic anti-glare function, then automatic operation is achieved, but manual operation capability is lost and device complexity increases
Solution Approach 1:
The bistable mechanism serves multiple functions: it enables automatic operation when activated by the photodetector control system, and simultaneously allows manual operation by the driver. The same mechanical bistable system can be actuated either automatically (via photodetector triggering SMA wire) or manually (via direct mechanical input), providing universal operation capability without requiring separate mechanisms for automatic and manual modes.
4Reliability
If compressed springs are used to ensure permanent contact between slider and mirror-holder, then contact reliability is improved, but friction increases and device bulkiness grows
Solution Approach 1:
The invention extracts and eliminates the compressed springs from the system by using the bistable mechanism's inherent mechanical stability to maintain contact and positioning. The bistable system provides the necessary contact force through its structural design rather than through elastic springs, thereby removing the source of excessive friction while maintaining contact reliability.
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 reduces vibrations, enhances compactness, and allows for manual operation without additional controls, making the actuator more reliable and cost-effective.
Implementation Method 1
A SMA wire has to be trained so that it can exhibit its features of shape memory element, and the training process of a SMA wire usually allows to induce in a highly repeatable manner a martensite/austenite (M/A) phase transition when the wire is heated
Implementation Method 2
This occurs thanks to the transformation of the micro-crystalline structure of the piece that passes from a type called martensitic (M), stable at lower temperatures, to a type called austenitic (A), stable at higher temperatures, and vice versa (M/A and A/M transition)
Implementation Method 3
In the M/A transition the wire undergoes a shortening by 3-5% which is recovered when the wire cools down
Data Source
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AI summary
A shape memory actuator comprises a supporting body (1), a driven element (7) pivotably mounted (3, 5) on the supporting body (1) and in permanent contact with a driving element (15) whose movement is determined by a SMA actuating member and by at least one resilient return member (25) acting in opposition to the SMA actuating member, the driven element (7) being able to take two stable positions under the action of a bistable moving system connecting the driving element (15) to the driven element (7) such that each toggling between said two stable positions is due to an activation of the SMA actuating member, the latter being arranged together with the bistable moving system, with the resilient return member (25), with the driving element (15) and with the driven element (17) on a same side of the supporting body (1) in a substantially co- planar arrangement.