SMA Coil Spring Linear Actuator Low Power Stroke
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Solution Overview
Problem
Existing linear actuators, particularly in small or portable applications, face challenges with high power requirements, heat generation, external magnetic fields, and limited precision control due to the use of solenoids, as well as limitations in stroke length and structural complexity with Shape Memory Alloy (SMA) components like wires and springs when electrically controlled.
Innovation Solution
A linear actuator comprising a SMA coil spring with a specific geometrical ratio of external diameter to wire thickness (4:1 to 10:1) and crimped terminals, allowing for improved stroke length, life cycles, and low electrical power consumption, replacing traditional solenoids with enhanced force distribution and thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If solenoids are used in linear actuators, then magnetic field actuation is achieved, but power requirements become large and heat generation increases
Solution Approach 1:
The patent replaces the electromagnetic solenoid system with a Shape Memory Alloy (SMA) spring system. The SMA spring utilizes phase transformation under electrical heating to generate mechanical force, eliminating the need for electromagnetic fields and large power converters. This substitution directly addresses the high power requirements and heat generation issues of solenoids by using a more efficient thermal-mechanical conversion mechanism.
Solution Approach 2:
The invention exploits the phase transition properties of Shape Memory Alloy materials. The SMA spring transitions between martensite (relaxed) and austenite (actuated) phases through controlled heating, enabling linear displacement with minimal power input. This phase transition mechanism allows the actuator to achieve significant mechanical work while consuming up to 90% less electrical power compared to traditional solenoids.
2Device complexity
If SMA wire is used with simple configuration, then structure is simplified, but stroke length is limited
Solution Approach 1:
The patent transforms the straight SMA wire configuration into a coiled spring geometry. This curvature transformation allows the SMA material to expand radially outward when actuated, converting limited linear expansion into amplified linear stroke. The coiled structure achieves several times longer stroke length compared to a straight wire of the same length while maintaining structural simplicity and avoiding complex mechanisms like pulleys.
3Length of moving object
If SMA coil spring is used, then stroke length is improved, but temperature gradients may deform the coiled shape
Solution Approach 1:
The patent optimizes the geometric parameters of the SMA spring, specifically the ratio between external diameter and wire thickness (4:1 to 10:1). This parameter optimization ensures uniform heat distribution throughout the coil during actuation, preventing temperature gradients that could cause deformation. The optimized geometry maintains structural integrity and reliable operation while achieving the desired stroke length improvement.
4Power
If solenoids are used for actuation, then magnetic field generation is achieved, but external magnetic fields affect other components
Solution Approach 1:
The patent eliminates the electromagnetic actuation system entirely by replacing solenoids with SMA spring actuators. The SMA spring uses direct thermal-mechanical conversion through phase transformation, generating actuation force without producing external magnetic fields. This substitution removes the harmful electromagnetic interference issue while maintaining effective actuation capability for valve control applications.
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
The SMA coil spring actuator achieves strokes several times longer than traditional SMA wires, reduces electrical power requirements by up to 90%, and offers significant weight and volume reductions compared to solenoids, while maintaining high mechanical work performance and fatigue resistance.
Implementation Method 1
SMA materials have a first, relaxed (martensite) state at ambient temperature and a second, fully-actuated (austenite) state when heated to a predetermined temperature
Implementation Method 2
SMA materials have a first, relaxed (martensite) state at ambient temperature and a second, fully-actuated (austenite) state when heated to a predetermined temperature
Data Source
AI summary
The present invention relates to linear actuators comprising an electrically-controlled shape memory alloy coil spring (23) suitable to provide linear displacements in valves, switches, lock systems and provided with a crimped terminal at each extremity, each of said crimped terminals comprising a crimping component (21) and an engaging member (22) suitable to mount the spring (23) into the linear actuator. The invention further discloses the use of said spring (23) with particular geometrical characteristics and crimping system assuring the maximization of the available stroke and fatigue life, structural simplicity, low electrical power requirements and thermal inertia, small size.