SMA Actuator Control for Miniature Camera Lens Positioning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Miniature camera devices face challenges in actuating camera lens elements due to the limitations of shape memory alloy (SMA) actuators, including reduced lifetime and uncertain absolute position, which affect precise movement and focus control.
Innovation Solution
A method involving SMA actuator control by monitoring resistance changes to prevent operation at the high end of its contraction range, using resistance feedback to adjust heating, and employing an endstop to fix the starting position, thereby reducing exposure to high-end contraction and improving positional accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the SMA actuator is operated at the high end of its contraction range to achieve precise positioning, then the positional control is improved, but the lifetime of the actuator is reduced
Solution Approach 1:
The patent applies preliminary action by performing a calibration operation before normal operation to identify the local minimum resistance point and establish a reduced contraction range. The control system is pre-configured to limit the actuator operation to this calibrated range, preventing operation at the high end that would reduce lifetime. This preliminary calibration ensures that subsequent positioning operations maintain both precision and actuator longevity.
Solution Approach 2:
The patent implements feedback by continuously monitoring the resistance of the SMA actuator and using this information to control the heating current. The control system adjusts the heating power based on the measured resistance to maintain operation within the calibrated safe range, preventing the actuator from reaching the high-end contraction region that would degrade its lifetime while still achieving precise positional control through resistance-based feedback.
2Ease of operation
If the SMA actuator is heated to achieve contraction and movement, then the actuation function is improved, but the positional accuracy becomes uncertain due to temperature variations
Solution Approach 1:
The patent applies parameter changes by transitioning from temperature-based control to resistance-based control. Instead of relying on temperature measurements to determine actuator position, the system monitors the electrical resistance of the SMA actuator, which provides a more direct and accurate indicator of contraction state. This parameter change enables precise positional control while maintaining easy actuation through resistive heating.
Solution Approach 2:
The patent implements feedback by continuously measuring the resistance of the SMA actuator and using this measurement to control the heating process. The resistance feedback provides real-time information about the actuator's contraction state, enabling the control system to achieve precise positional control despite temperature variations and manufacturing tolerances.
3Volume of moving object
If the SMA actuator is used in a miniature camera to reduce device size, then the compactness is improved, but the manufacturing precision requirements increase due to tolerance variations
Solution Approach 1:
The patent applies preliminary action by performing a calibration operation during or after assembly to identify the actual resistance characteristics of the specific SMA actuator and mechanical components. This calibration process compensates for manufacturing tolerances and variations, establishing accurate target resistance values and ranges for the specific device. This allows the miniature camera to achieve precise focus control despite variations in assembly tolerances.
Solution Approach 2:
The patent implements feedback by continuously monitoring the resistance of the SMA actuator and comparing it to target values established during calibration. This resistance feedback mechanism compensates for manufacturing tolerances and variations in real-time, enabling precise focus control in the miniature camera without requiring extremely tight manufacturing tolerances.
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 method extends the lifetime of SMA actuators, enhances positional control, and maintains focus accuracy across varying temperatures and manufacturing tolerances, ensuring reliable operation in miniature camera devices.
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 in which the stress and strain of the SMA actuator changes
Implementation Method 2
At high temperatures the SMA actuator transforms into the austenite phase which induces a deformation causing the SMA actuator to contract
Implementation Method 3
the SMA actuator having a property that resistance varies with length along a curve on which the resistance decreases from a local maximum resistance to a local minimum resistance during contraction
Implementation Method 4
The temperature of the SMA actuator may be changed by selectively passing a current through the SMA actuator to heat it causing the phase change
Data Source
AI summary
A miniature camera lens actuation apparatus comprises a support structure, a camera lens element supported on the support structure by a suspension system; and an SMA actuator connected between the support structure and the movable element to drive movement of the camera lens element. The control circuit may include a drive circuit and a sensor circuit which have separate electrical connections to the SMA actuator to reduce the impact of the resistance of the electrical connections on the sensing. The control circuit may vary the drive signal in response to a temperature signal indicative of the ambient temperature. An endstop limits movement to prevent extension of the SMA actuator in its unheated state beyond a maximum length which is at or below the length corresponding the local maximum resistance of the resistance-length curve. Control of position is effected using resistance of the SMA actuator as a measure of position. The control employs a ‘ratcheting’ method to prevent a failure condition and an initial calibration step to derive a range of target resistance values. In manufacture, the position of a lens holder is adjusted relative to a carrier to provide focussing on the image sensor of an image of an object at a distance in the range from infinity to the hyperfocal distance when the SMA actuator is heated to a predetermined temperature greater than ambient temperature.