SMA Actuator End-Stop Positioning for Lens Control
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Solution Overview
Problem
Existing SMA actuation systems for miniature camera lenses face challenges in precision control due to non-linear resistance variations with position and over time, requiring complex control algorithms and costly sensors, and existing end-stop arrangements limit the operating range and strain of the SMA actuator.
Innovation Solution
A shape memory alloy actuation apparatus with a support structure, a movable element, and an SMA actuator biased against contraction, featuring an end-stop positioned above the local maximum resistance by up to 15% of the difference between local maximum and minimum resistance lengths, allowing consistent operation and optimal resistance control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an end-stop is positioned at or below the local maximum resistance to limit actuator extension, then the starting position is controlled and strain is reduced, but the operating range is limited
Solution Approach 1:
The patent changes the positioning parameter of the end-stop from being at or below the local maximum resistance to being above it by a specific distance (5-20% of the difference between maximum and minimum resistance lengths). This parameter change allows the SMA actuator to operate through the local maximum resistance point, expanding the operating range while maintaining consistent position control through the resilient biassing arrangement.
2Length of moving object
If the SMA actuator operates over its full resistance curve, then the available stroke is maximized, but the control complexity increases due to non-linear resistance variations
Solution Approach 1:
The resilient biassing arrangement acts as an intermediary between the SMA actuator and the load, providing a mechanical reference point that simplifies control. By positioning the end-stop above the local maximum resistance, the system creates a well-defined starting position that reduces the impact of non-linear resistance variations, making control less complex while maintaining full stroke operation.
3Strength
If the end-stop limits movement at the local maximum resistance, then the SMA actuator strain is minimized, but the resistance operating range for control is reduced
Solution Approach 1:
The patent applies partial action by positioning the end-stop above the local maximum resistance but within a specific range (5-20% of the resistance length difference). This allows the SMA actuator to operate through the maximum resistance point without excessive strain, while still maintaining an adequate control range. The end-stop provides mechanical limiting without completely restricting the resistance operating range needed for precise control.
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 configuration provides consistent position control and optimal resistance operating range, minimizing fatigue and extending the SMA actuator's lifetime by using the local maximum resistance as a reference for closed-loop control, while maintaining an effective stroke range.
Implementation Method 1
Actuation may be achieved by control of the temperature of the SMA actuator over an active temperature range in which the SMA actuator changes between martensite and austenite phases
Implementation Method 2
The contraction drives movement of the movable element
Implementation Method 3
a resilient biassing arrangement biassing the SMA actuator against contraction
Implementation Method 4
an alternative approach is to base the control on the resistance of the SMA actuator. The resistance may be measured by a resistance measurement circuit
Data Source
Figure 1~2
Figure 3~4
AI summary
A shape memory alloy actuation apparatus comprises a camera lens element supported on the support structure by a plurality of resilient flexures that guide movement of the movable element along the optical axis. A shape memory alloy actuator biassed by the resilient flexures and an additional resilient biassing element is arranged to drive movement of the camera lens element. An end-stop limits movement of the camera lens element at a position where the shape memory alloy actuator has a predetermined length that is above the length corresponding on the local maximum resistance by an amount not greater than 15% of the difference between (i) the length corresponding to the local maximum resistance and (ii) the length corresponding to the local minimum resistance.