SMA Rotary Actuator Torque Translation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing SMA-driven rotary actuators face issues such as complex electrical power and ground return, lack of direct torque translation, position feedback errors due to slipping, and limited angular travel adjustment in automotive applications.
Innovation Solution
A SMA-driven rotary actuator with a U-shaped configuration of SMA wires providing direct torque to an input member through geared coupling, allowing position feedback by resistance measurement, simple electrical connection, and adjustable angular travel via gear ratio and radial distance variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SMA wires are mounted between a fixed point and the rotating member through a pin, then the device can be simplified, but the electrical power and ground return must be provided through the rotation axis which complicates the electrical connection
Solution Approach 1:
The patent divides the electrical connection function from the mechanical rotation function by introducing a separate electrical contact point on the non-rotating support structure. The SMA wire is anchored to both the rotating member and the non-rotating support, creating independent paths for mechanical torque transmission and electrical power/ground return, thereby resolving the contradiction between mechanical simplicity and electrical connection ease.
2Device complexity
If a chord is used to transmit force from SMA wires to a pulley, then the device can be simplified, but most force works against the pulley axis and only friction force drives the shaft reducing efficiency
Solution Approach 1:
The patent extracts the force transmission function from the chord-pulley friction system and implements it through direct radial attachment of SMA wires to the input member. The SMA wires are anchored at specific radial distances from the rotation axis, allowing their force to be directly converted into torque without intermediate friction elements, thereby eliminating energy loss and improving efficiency.
3Device complexity
If position feedback is achieved by measuring SMA wire resistance, then additional sensors can be dispensed with, but position feedback errors may occur due to slipping of the chord
Solution Approach 1:
The patent eliminates the chord element that causes slipping by implementing direct rigid attachment of SMA wires to the input member. This direct connection ensures that the SMA wire position accurately reflects the input member position without slip-induced errors, while maintaining the simple resistance-based feedback method, thus resolving the contradiction between system simplicity and measurement precision.
4Power
If gear transmission is used to couple input and output members, then torque is directly translated, but the device complexity increases
Solution Approach 1:
The patent segments the actuator into distinct functional modules: the input member with SMA wire attachments, the gear transmission mechanism, and the output member. This modular segmentation allows the gear transmission to be optimized for direct torque translation while keeping the overall device complexity manageable through clear functional separation and standardized components.
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 solution ensures direct torque translation, accurate position feedback without additional sensors, reliable operation across a wide temperature range, and self-holding capabilities, with optional additional position sensing for precise control.
Implementation Method 1
The controlled heating via Joule effect of one of the SMA wires causes its contraction and the movement of the driven element
Implementation Method 2
Some examples of patents and applications relating to SMA-driven rotary actuators are U.S. Pat. No. 7,082,890, US 20140333088, US 20070175213 and EP 1752661 all describing rotary actuators driven by a pair of SMA wires in antagonistic configuration. The controlled heating via Joule effect of one of the SMA wires causes its contraction and the movement of the driven element
Data Source
AI summary
A SMA-driven rotary actuator comprises as actuating elements two U-shaped SMA wires (3) connected in an antagonistic configuration to a rotating input member (1) coupled to an oppositely rotating output member (2), preferably through a geared coupling, which is connected to a shaft (4) of a user device.