Bi-stable Overload Protection for Active Material Actuators
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Solution Overview
Problem
Existing mechanical overload protection systems for active material actuators face challenges in balancing high force thresholds with low post-overload stiffness without increasing bulk, as conventional linear springs either result in high maximum force levels or large, unwieldy designs.
Innovation Solution
An actuation assembly incorporating an elastic member with a force-deflection characteristic featuring a limit point and negative stiffness region, allowing for a non-linear force versus displacement relationship, which reduces stress on the actuator during overload conditions without compromising the stroke length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If linear mechanical springs are used for overload protection, then high force threshold is achieved, but the device becomes bulky due to conflicting requirements of high force threshold and low stiffness
Solution Approach 1:
The patent changes the force-deflection parameter relationship from linear to non-linear by using an elastic member with a negative stiffness region. This allows the system to present high initial stiffness (high force threshold) that transitions to low stiffness (low post-overload stiffness) when activated, resolving the contradiction between maintaining high force threshold and achieving low device bulk
Solution Approach 2:
The elastic member's stiffness is made dynamic rather than static. The member transitions from a high-stiffness state during normal operation to a low-stiffness state during overload conditions through its negative stiffness region. This dynamic parameter change allows the same component to satisfy both high force threshold requirements and low post-overload stiffness requirements without increasing device bulk
2Force
If linear mechanical springs are used for overload protection, then high force threshold is achieved, but low post-overload stiffness cannot be achieved without increasing bulk
Solution Approach 1:
The patent implements parameter changes by designing an elastic member with a non-linear force-deflection characteristic that includes a negative stiffness region. This allows the system to transition from high initial stiffness to low post-overload stiffness within the same compact component, achieving both high force threshold and low post-overload stiffness without increasing device bulk
3Adaptability or versatility
If electrical-control schemes are used for overload protection, then versatility is improved, but system cost increases
Solution Approach 1:
The overload protection system is designed to be self-activating through the inherent mechanical properties of the elastic member with negative stiffness region. The system automatically transitions from high-stiffness to low-stiffness mode when the force-deflection relationship enters the negative stiffness region, eliminating the need for external sensors, controllers, or feedback systems. This self-service approach maintains versatility while significantly reducing system cost compared to electrical-control schemes
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 effectively mitigates mechanical overload by providing a high overload force threshold with low post-overload stiffness, minimizing stress on the actuator and maintaining the actuator's useful stroke length, thus overcoming the trade-offs of conventional linear spring-based systems.
Implementation Method 1
an elastic member defining a force-deflection characteristic having a limit point and negative stiffness region therein
Implementation Method 2
The member is drivenly coupled to the actuator opposite the load, and presents an initial deformation force
Data Source
AI summary
An actuation assembly adapted for driving a load, and protecting against overload conditions, includes an actuator defining a stroke, and an overload protection device including at least one elastic member having a nonlinear force-deflection characteristic defining a limit point and negative stiffness region, drivenly coupled to the actuator opposite the load, and operable to provide a secondary work output path when an overload condition exists.