Bi-directional Actuator Using Shape Memory Alloy and Electro-active Polymer
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Solution Overview
Problem
Miniaturized actuators require significant force and stroke but are often bulky, noisy, and expensive, with existing SMA-based actuators needing external mechanical biasing for reset, which complicates manufacturing and reduces effective stroke.
Innovation Solution
A bi-directional actuator combining a heat-sensitive shape-memory alloy layer with an electro-active polymer layer, where the EAP facilitates 'reverse actuation' by deforming the SMA back to its original shape without external biasing, using controlled voltage and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external mechanical bias springs are used to reset the shape memory alloy wire, then the actuator can be reset after temperature decrease, but the device bulk, manufacturing complexity, and cost increase significantly
Solution Approach 1:
The patent removes the external mechanical bias spring system entirely, extracting the reset function from external components and embedding it within the shape memory alloy wire itself through controlled deformation and phase transition mechanisms
Solution Approach 2:
The shape memory alloy wire performs its own reset function through temperature-controlled phase transitions and internal stress mechanisms, eliminating the need for external reset mechanisms. The wire automatically returns to its original configuration after actuation without requiring separate bias springs or complex mechanical systems
2Reliability
If permanent mechanical bias springs are used to stretch the wire back to its low temperature length, then the actuator can be reset, but the effective stroke of the actuator is reduced
Solution Approach 1:
The patent extracts the reset function from external mechanical springs and implements it through the intrinsic properties of the shape memory alloy wire, using controlled deformation and phase transitions to achieve full stroke without permanent bias elements occupying space
Solution Approach 2:
The patent utilizes temperature parameter changes to control the phase transitions of the shape memory alloy wire, enabling it to change between austenite and martensite phases. This allows the wire to achieve full deformation stroke in both directions through thermal cycling rather than mechanical pre-loading
3Adaptability or versatility
If small motors are used for miniaturized applications, then actuation is possible, but the motors are too large, heavy, noisy and expensive with lower efficiency
Solution Approach 1:
The patent exploits the phase transitions of shape memory alloys between austenite and martensite phases to generate actuation forces. This eliminates the need for motor-based actuation systems, replacing them with a lightweight thermal-mechanical system that responds to temperature changes through controlled phase transformations in the alloy wire
Solution Approach 2:
The patent replaces the mechanical motor system with a thermal-field-based actuation mechanism. Instead of using electromagnetic motors to generate mechanical motion, the system uses controlled heating to induce phase transitions in the shape memory alloy, which then produces the desired mechanical displacement and force
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
Enables miniaturized, efficient, and cost-effective bi-directional actuation with controlled deformation, eliminating the need for bulky reset mechanisms and maintaining actuator shape without external support.
Implementation Method 1
a heat-sensitive shape-memory layer, the shape-memory layer comprising a shape memory alloy, the alloy existing in a first phase below a first temperature, and a second phase above a second temperature, and wherein a transition from the first to the second phase stimulates the layer to move from any first shape into a second, predetermined shape
Implementation Method 2
an electro-active polymer layer, coupled with the shape memory alloy layer such that both follow the same shape, the electro-active polymer layer being deformable, in response to an applied voltage
Implementation Method 3
a heating means for controlling the temperature of the heat-sensitive shape-memory layer
Data Source
AI summary
A thermally and electrically controllable miniaturised actuator comprises a bi-layer structure formed of a shape-memory alloy layer coupled with an electro-active polymer layer. A heating means is provided for thermal stimulation of the shape-memory alloy layer, this layer transitioning from an initial shape at a first temperature to a second, pre-determined, shape at a second temperature. Application of an electric field to the electro-active polymer layer stimulates this layer to deform in response, with a stress which may exceed that of the alloy layer, when the latter layer is in a low-temperature phase. Actuation methods are further provided, which include stimulating the polymer layer to deform in an opposite ‘direction’ to the deformation of the alloy layer, thus allowing the actuator to be ‘reset’ in between strokes. Methods of producing an actuator are also provided.