SMA Tube Ring Drive for Continuous Rotary Actuation
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Solution Overview
Problem
Conventional rotary actuation using Shape Memory Alloy (SMA) materials is limited to reciprocating motion and requires constant heat application to prevent thermal cycling-induced reciprocal effects, which restricts continuous rotary output and efficient torque delivery.
Innovation Solution
The development of a Ring Drive mechanism that utilizes a Spline-Slide Actuator System with integrated bias-spring return assist and Tube Lock Design to enable continuous rotary motion in either direction without constant heat application, using SMA tubes configured to provide rotational output and lock in place during thermal cycles, thereby preventing reciprocal effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SMA rotary actuation is used with ratchet/sprag gear and sun gear drive train, then continuous rotary articulation in one direction is achieved, but the system requires constant heat application to prevent thermal cycling-induced reciprocal effects and experiences increased material stress on gear teeth
Solution Approach 1:
The patent applies periodic thermal cycling to the SMA elements, heating them to generate torque in one direction while allowing passive return during cooling. This periodic heating rather than constant heating reduces energy consumption while maintaining continuous rotary output through the ratchet mechanism that prevents reciprocal motion during the cooling phase.
Solution Approach 2:
The patent replaces the need for constant thermal energy input with a mechanical locking system (ratchet and pawl mechanism). The SMA elements generate torque only during heating, and the ratchet mechanism mechanically maintains the output position during cooling, substituting constant thermal energy with a passive mechanical constraint.
2Reliability
If conventional SMA rotary actuation with sun gear drive train is used, then continuous rotary motion is achieved, but device complexity increases and torque delivery efficiency decreases
Solution Approach 1:
The patent extracts and eliminates the sun gear component from the drive train, using only planetary gears and a ratchet mechanism. This simplification reduces device complexity while maintaining continuous rotary motion capability through the combination of planetary gear reduction and ratchet-based unidirectional locking.
Solution Approach 2:
The patent changes the fundamental operating principle from continuous thermal actuation to periodic thermal actuation with mechanical locking. This parameter change in the actuation cycle, combined with the simplified drive train, reduces complexity while achieving the same reliable continuous rotary output.
3Power
If SMA elements are configured in a Ring Drive mechanism with lock control, then torque delivery efficiency improves and material stress on gear teeth reduces, but the system requires innovative locking and return state features
Solution Approach 1:
The patent introduces a ratchet mechanism as an intermediary between the SMA elements and the output shaft. This intermediary allows the SMA elements to deliver torque efficiently during heating while the ratchet passively maintains position during cooling, reducing material stress on gear teeth by eliminating the need for continuous engagement under load.
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 solution allows for continuous torque delivery in a chosen direction with reduced material stress on gear teeth, enabling efficient and scalable rotary actuation with improved durability and reduced power consumption, as demonstrated in applications like the F-18 Navy Jet winglet folding mechanism.
Implementation Method 1
Conventional rotary actuation with the use of Shape Memory Alloy (SMA) material has been constrained to uses that provide a reciprocating direction of derived power based on the material inducing movement in one direction when heated, and a movement in the opposite direction when cooled, as occurs during a full thermal cycle of the material.
Implementation Method 2
The development of a Ring Drive mechanism that utilizes a Spline-Slide Actuator System with integrated bias-spring return assist
Data Source
AI summary
A scalable plurality of shape memory alloy (SMA) elements are configured to provide a continuous rotation actuator system. The plurality of SMA elements are coupled to a Ring Gear element, as well as to a Sun Gear element and a provision for thermal cycle return assist of the SMA elements. A plurality of Transmission elements provide for controlled rotary actuation in a desired direction with lock capability that provides for continuous rotary motion even as the SMA elements undergo reciprocating rotary action during their thermal cycling without running into system component rotation limits. The innovation distinguishes over other innovative approaches by way of at least the Ring Gear element, the manner of lock control, and the return assist element.