SMA Wire Endoscope Actuator Control for Lens Positioning
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Solution Overview
Problem
Existing endoscope systems with shape memory alloy actuators face issues with focus responsiveness, power saving characteristics, and durability, particularly when moving lenses between focus positions and maintaining them at specific positions.
Innovation Solution
The endoscope system employs a shape memory alloy wire actuator with a control circuit that alternates between heating and resistance value detection periods, using a PD control for initial focus switching and constant current control for holding, while avoiding the minimum resistance value to prevent durability degradation and optimize power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the actuator system always supplies the same current to the wire to hold the lens at the second position, then the lens position is maintained, but power consumption increases
Solution Approach 1:
The patent implements periodic action by using a bending mechanism that alternates between active and passive states. The wire is bent to store elastic energy, then released periodically to move the lens between positions. This eliminates the need for continuous current supply, reducing power consumption while maintaining position stability through the mechanical energy storage and release cycle.
2Measurement precision
If the actuator system detects the minimum resistance value for each calibration, then the resistance control is optimized, but the durability of the shape memory element deteriorates
Solution Approach 1:
The patent applies partial action by performing calibration only when necessary (e.g., at startup or when focus abnormalities are detected) rather than continuously. The system uses a determination unit to assess whether calibration is needed based on focus state analysis, thereby reducing the frequency of minimum resistance value detections and minimizing wear on the shape memory element while maintaining adequate control precision.
3Ease of operation
If the actuator system uses a shape memory alloy wire to move the lens between focus positions, then the focusing function is achieved, but the responsiveness when moving from the second position to the first position is poor
Solution Approach 1:
The patent employs a counterweight principle through the bending mechanism that stores elastic energy. When the lens needs to move from the second position to the first position, the pre-bent wire releases stored energy to actively push the lens, providing rapid movement. This mechanical energy storage and release system compensates for the inherently slow response of shape memory alloy, achieving fast and responsive lens positioning.
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 approach enhances lens movement responsiveness, reduces power consumption, and improves the durability of the shape memory element by controlling the SMA wire's contraction and elongation effectively between focus positions.
Implementation Method 1
the shape memory alloy wire produces heat in response to passage of the current and is contracted at high temperatures
Implementation Method 2
it releases heat in response to shutoff of the current and is elongated consequently
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An endoscope system 1 includes: an actuator 20 having an SMA wire 21 and driving a moving member 30 for moving a lens 24; an output control circuit 52; a detection circuit 53; and a CPU 51. The CPU 51 outputs a driving signal to the output control circuit 52, on a basis of an instruction to move the lens 24, and on the basis of a position of the moving member 30 corresponding to a resistance value detected by the detection circuit 53. In response to a moving instruction to move the lens 24 from a far-point position to a near-point position, the CPU 51 outputs the driving signal so that a current for moving the moving member 30 from the far-point position to a position beyond the near-point position is passed through the SMA wire 21 to heat the SMA wire. The CPU 51 then performs preheating control, holding constant current transition control, and reheating control.