SMA Actuator Lens Control for Endoscope Responsiveness
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Solution Overview
Problem
Conventional endoscope image pickup units using SMA wires for adjusting optical properties suffer from poor responsiveness and stability due to temperature variations and heat from illumination sources, leading to delayed and unreliable adjustments of optical properties.
Innovation Solution
An image pickup unit with a shape memory alloy actuator that incorporates a resistance feedback circuit and helical compression springs, allowing for controlled expansion and contraction of the SMA wire to maintain optimal optical properties, and a configuration that minimizes the length of the rigid insertion portion for improved insertability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an SMA wire is used as an actuator to move the movable lens frame for adjusting optical properties, then the device can achieve compact structure and simple operation, but the responsiveness of expansion and contraction is poor, causing delay in adjusting optical properties
Solution Approach 1:
A push-pull rod is introduced as an intermediary mechanism between the SMA wire and the movable lens frame. The push-pull rod converts the contraction of the SMA wire into bidirectional movement of the lens frame, enabling both forward and backward movement through a single actuator, thereby improving responsiveness while maintaining structural simplicity
Solution Approach 2:
The system dynamically switches between different actuation modes: using the SMA wire's contraction for backward movement and the urging spring's elastic recovery for forward movement. This dynamic utilization of different force sources improves the overall responsiveness of the optical property adjustment
2Device complexity
If the SMA wire relies on natural cooling for expansion, then the structure remains simple, but the expansion responsiveness becomes poor when current is stopped after a period of current passage
Solution Approach 1:
An urging spring is introduced to provide a counteracting force that actively pushes the movable lens frame forward when the SMA wire contracts. This spring mechanism compensates for the slow natural cooling expansion of the SMA wire, significantly reducing the time delay in optical property adjustment while maintaining simple structure
3Adaptability or versatility
If the endoscope is used in a body environment with temperature around 40 degrees, then the endoscope can perform medical examinations, but the expansion/contraction state of the SMA wire varies according to temperature, affecting stability
Solution Approach 1:
A resistance feedback circuit is implemented that continuously monitors the resistance of the SMA wire and adjusts the driving current accordingly. This feedback mechanism compensates for temperature-induced variations in SMA wire properties, maintaining stable optical property adjustment throughout the medical procedure
Solution Approach 2:
The system dynamically adjusts the driving current parameters based on temperature conditions and resistance feedback. By changing the electrical parameters (current magnitude and duration) in response to temperature variations, the system maintains consistent mechanical output from the SMA wire despite environmental temperature changes
4Illumination intensity
If a light guide bundle is provided for illumination, then the endoscope can perform imaging functions, but the heat generated by guiding illumination light is transmitted to the SMA wire, causing temperature rise and affecting contraction state
Solution Approach 1:
The illumination system (light guide bundle) is spatially separated from the actuator system (SMA wire and movable lens frame). By extracting the heat-generating illumination function from the vicinity of the temperature-sensitive actuator, the system maintains illumination capability while minimizing thermal interference with SMA wire performance
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 enhances the responsiveness and stability of optical property adjustments, ensuring reliable movement of the movable lens frame and reducing pain during insertion by shortening the insertion portion, while maintaining efficient temperature control and minimizing heat-related issues.
Implementation Method 1
the movable lens frame is moved backward against the urging force of the urging spring when the SMA wire is caused to contract by passing a current thereto
Implementation Method 2
when the SMA wire is caused to contract by passing a current thereto
Implementation Method 3
when the current being passed to the contracted SMA wire is stopped to cause the SMA wire to expand, the movable lens frame is moved forward by the urging force of the urging spring
Implementation Method 4
by controlling a drive current applied to the shape memory alloy actuator on the basis of a detected value detected by the detection circuit
Data Source
AI summary
An actuator apparatus 62 of the present invention includes a movable body 32 that is arranged so as to be movable forward or rearward, and a shape memory alloy wire 56 that is provided directly or indirectly to the movable body so as to enter a non-tension state at an ordinary temperature. The shape memory alloy wire 56 is subjected to expansion/contraction control in which an electric current is applied thereto from a power supply portion of an external control circuit portion 100 to change a temperature thereof to a predetermined temperature.