Shape Memory Alloy Actuator Position Control Using Variable Gain
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Solution Overview
Problem
Conventional position control methods for shape memory alloy actuators with hysteresis face limitations in achieving satisfactory control accuracy and response due to the use of constant PID gains, leading to oscillations and restricted positioning precision.
Innovation Solution
A position control method that employs two different gains, a first gain for rapid response and a second gain for stability, to control the shape memory alloy actuator's length based on resistance value measurements, ensuring accurate positioning and responsive control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a constant gain is used in PID control for the shape memory alloy actuator, then the control system is simple to implement, but positioning accuracy deteriorates and oscillations occur
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant gain to a dynamic variable gain that changes based on the actuator's current state. The gain is adjusted according to the resistance value and displacement state of the shape memory alloy actuator, allowing the control system to adapt to different operating conditions and achieve both simplicity and high positioning accuracy.
Solution Approach 2:
The patent implements parameter changes by modifying the PID gain parameter based on the actuator's resistance value and displacement state. By changing the gain parameter dynamically according to the current operating point, the system optimizes control performance across the entire control range while maintaining simplicity in implementation.
2Speed
If a high gain is used to improve response speed, then the response speed improves, but positioning accuracy deteriorates due to oscillations
Solution Approach 1:
The patent uses dynamics to adjust the gain based on the real-time state of the actuator. During the initial phase when large displacement is needed, a higher gain is applied to achieve fast response. As the actuator approaches the target position, the gain is reduced to prevent oscillations and ensure accurate positioning, thus resolving the contradiction between response speed and positioning accuracy.
Solution Approach 2:
The patent applies partial or excessive action by using a higher gain than necessary only during the initial displacement phase when the actuator is far from the target. Once the actuator approaches the target position, the gain is reduced to the minimum necessary level, preventing excessive control action that would cause oscillations while maintaining fast response during the critical initial phase.
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 positioning accuracy and response speed by using a higher first gain for initial displacement and a lower second gain for maintaining stability, preventing oscillations and achieving precise control.
Implementation Method 1
controls the length of a shape memory alloy to a predetermined length based on the value of resistance of the shape memory alloy after expansion/contraction thereof resulting from phase transformation caused by heating by power supply
Implementation Method 2
heating by power supply to thereby control the position of a moving body provided on the shape memory alloy
Data Source
AI summary
To provide a position control method for a shape memory alloy actuator that improves positioning accuracy of the actuator while ensuring satisfactory response until achieving positioning, the method includes a commanded resistance value setting step of setting a commanded resistance value that corresponds to the predetermined length, a resistance value measurement step of measuring the value of resistance, a resistance value comparison step of comparing the commanded resistance value and the measured resistance value, a first control step of controlling the length of the shape memory alloy using a first gain based on the result of comparison until the commanded resistance value is reached, a termination determination step of making a determination as to a condition for terminating the first control step, and a second control step of keeping the moving body stationary, upon determination of termination in the termination determination step, by retaining the length of the shape memory alloy using a second gain smaller than the first gain based on the result of the comparison, wherein the second control step is continued until a commanded resistance value is set again, thereby performing position control of the moving body.