Shape-Memory Alloy Actuator with Base Current Control
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Solution Overview
Problem
Shape memory alloy (SMA) actuators face challenges in achieving fast actuation times without significantly reducing their lifespan, as high currents used for rapid actuation lead to a short life cycle, and previous methods have been unable to create SMAs that are both responsive and long-lasting.
Innovation Solution
Applying a base current during non-actuation periods to maintain the SMA in a pre-actuated state, monitoring impedance changes, and using AC currents, particularly at RF frequencies, to control and facilitate actuation, allowing for rapid and sustained operation of SMA actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high currents are passed through the SMA element to achieve fast actuation, then actuation speed is improved, but the life cycle of the actuator is greatly reduced
Solution Approach 1:
The patent applies preliminary action by maintaining the SMA element in a pre-heated state during non-actuation periods through the application of a base current. This preliminary heating reduces the energy required for subsequent actuation, allowing fast response times without requiring excessively high actuation currents that would damage the SMA element and reduce its life cycle.
Solution Approach 2:
The patent implements periodic action by applying a base current during non-actuation periods to maintain the SMA in a pre-actuated state, and then applying additional actuation current only when needed. This periodic application of current maintains the SMA in an optimal state for rapid actuation while avoiding continuous high current exposure that would degrade the element's lifespan.
2Speed
If base current is applied during non-actuation periods to maintain pre-actuated state, then actuation response time is improved, but energy consumption increases
Solution Approach 1:
The patent applies partial action by providing only a base current during non-actuation periods rather than full actuation current. This partial current application is sufficient to maintain the SMA in a pre-heated state for rapid actuation, but consumes significantly less energy than continuous full-power actuation would require.
Solution Approach 2:
The SMA element serves itself by using the base current applied during non-actuation periods to maintain its own temperature in a pre-actuated state. This self-heating mechanism eliminates the need for external heating systems or continuous high-power input, reducing overall energy consumption while enabling fast response times.
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 SMA actuators to actuate within 50 ms while maintaining performance for over a million cycles, contradicting the prevailing belief that responsive and long-lasting SMA actuators are incompatible.
Implementation Method 1
An actuator can be formed using a material that changes shape in response to application of an external force and that returns to a predictable shape after the force is removed. One example is a shape memory alloy (SMA). SMAs typically change shape in response to the application of heat and return to the same or substantially the same shape after the heat source is removed.
Implementation Method 2
In many instances, an SMA will change shape in response to a current passing through the SMA (e.g. where the current passing through the SMA heats the SMA).
Data Source
AI summary
A shape memory element (a structure formed from a shape memory alloy) includes an electrically conductive ferromagnetic material. The ferromagnetic material may be magnetostrictive. In some embodiments, the shape memory element is formed from a shape memory alloy core and has a cladding over the core that includes the ferromagnetic material. In other embodiments, the shape memory alloy may be selected to be ferromagnetic.