Friction-Retained SMA Actuator Assembly for Camera Lens Positioning
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Solution Overview
Problem
Existing SMA actuator assemblies for camera lenses require continuous energizing to maintain lens position, leading to energy consumption and instability due to susceptibility to external factors.
Innovation Solution
Incorporating a biasing arrangement that generates a static frictional force between friction surfaces to constrain the movable part's position when SMA wires are not energized, allowing the actuator to hold the position without power consumption and ensuring accurate movement when energized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SMA wires are continuously energised to hold the lens assembly at a given position, then the lens assembly can be maintained at the desired position, but energy is consumed continuously and the system becomes susceptible to sudden movements from external factors
Solution Approach 1:
The patent extracts the position holding function from the SMA actuator by introducing a separate friction-based retention mechanism. The biasing arrangement with friction surfaces maintains the lens assembly position when SMA wires are not energised, allowing the SMA wires to be used only for movement actuation rather than continuous position maintenance.
Solution Approach 2:
The biasing arrangement acts as an intermediary mechanism between the SMA actuator and the lens assembly. It provides a passive friction-based retention system that supplements the active SMA actuation, enabling the system to hold position without continuous power while still allowing controlled movement when needed.
2Use of energy by moving object
If a biasing arrangement is introduced to retain the movable part using friction, then power consumption is reduced, but the device complexity increases
Solution Approach 1:
The biasing arrangement is integrated with the existing actuator assembly structure. The friction surfaces are incorporated into the movable part and support structure that already exist in the system, merging the retention function with the existing mechanical components rather than adding entirely separate systems.
Solution Approach 2:
The biasing arrangement serves multiple functions: it provides position retention through friction, guides the movement of the movable part, and works cooperatively with the SMA actuator. This multi-functionality reduces the need for additional dedicated components for each function.
3Force
If the biasing arrangement applies normal force in directions other than perpendicular to the range of movement, then additional constraint forces are provided, but the stresses in the SMA wires are opposed and movement efficiency is reduced
Solution Approach 1:
The biasing arrangement is designed to apply normal force specifically in the direction perpendicular to the range of movement at each position. This localized optimization ensures that the constraint force is provided exactly where needed to prevent unwanted motion, while avoiding any force components that would oppose the SMA wire actuation direction.
Solution Approach 2:
The biasing arrangement is configured to dynamically adjust its constraint application based on the position of the movable part. As the movable part moves within the range of movement, the biasing arrangement maintains perpendicular force application throughout the trajectory, ensuring optimal efficiency at all positions rather than being fixed in a single orientation.
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
Reduces power consumption and enhances stability by maintaining the movable part's position without continuous energizing, while enabling precise and controlled movement through SMA wires.
Implementation Method 1
a biasing arrangement arranged to bias the first and second friction surfaces against each other with a normal force, thereby generating a static frictional force that constrains the movement of the movable part relative to the support structure
Implementation Method 2
one or more SMA wires arranged, on contraction, to move the movable part relative to the support structure to any position within a range of movement
Implementation Method 3
the one or more SMA wires are arranged, on contraction, to reduce the normal force between first and second friction surfaces
Data Source
AI summary
An actuator assembly comprising: a support structure comprising a first friction surface; a movable part comprising a second friction surface engaging the first friction surface; one or more SMA wires arranged, on contraction, to move the movable part relative to the support structure to any position within a range of movement; a biasing arrangement arranged to bias the first and second friction surfaces against each other with a normal force, thereby generating a static frictional force that constrains the movement of the movable part relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted; wherein the one or more SMA wires are arranged, on contraction, to reduce the normal force between first and second friction surfaces.