Reference Governor for SMA Hysteretic Actuator Control

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional control techniques for hysteretic systems, such as those using shape memory alloy actuators, often neglect or eliminate hysteresis, which limits their ability to achieve fast response times and accurate tracking due to the nonlinear behavior of these systems.

Innovation Solution

The approach involves exploiting the multi-valued mapping of hysteretic systems by using a reference governor that manipulates the reference signal based on a hysteresis model and physical limitations, allowing the system to take advantage of hysteresis effects while maintaining stability, as demonstrated with temperature-controlled shape memory alloy actuators and robotic catheter systems.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If conventional control structures are used to eliminate or neglect hysteresis, then control design and analysis are simplified, but tracking accuracy and response time are degraded

Engineering Contradiction:

Improvecontrol design complexityVSAvoidtracking accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent converts the harmful hysteresis effect into a beneficial resource by exploiting its multi-valued mapping characteristic. Instead of eliminating hysteresis, the control method uses the hysteresis model to predict and utilize the system's inherent nonlinear behavior, allowing the hysteresis loop to be traversed in a controlled manner to improve tracking accuracy and enable faster response times while maintaining stability.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Device complexity

If conventional control structures are used to eliminate hysteresis, then control analysis is simplified, but response time is degraded

Engineering Contradiction:

Improvecontrol analysis complexityVSAvoidresponse time

Core Design Contradiction:

Device complexityVSSpeed

Solution Approach 1:

The patent applies preliminary action by using the hysteresis model to predict the system's future state and pre-planning the control trajectory. The reference governor manipulates the reference signal in advance to account for hysteresis effects, allowing the system to prepare for upcoming changes and reduce response time while maintaining stability.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If hysteresis is exploited for improved tracking, then tracking accuracy is improved, but system stability may be compromised

Engineering Contradiction:

Improvetracking accuracyVSAvoidsystem stability

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The patent employs feedback mechanisms through the reference governor that continuously monitors system state and adjusts the reference signal accordingly. The feedback loop ensures that while hysteresis is exploited for improved tracking, the system remains stable by correcting any deviations and preventing runaway behavior.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the parameter of the reference signal dynamically based on system state and hysteresis model predictions. The reference governor adjusts reference values and rates of change to optimize tracking while maintaining stability, transforming the system's operating parameters to exploit hysteresis benefits safely.

Inventive Principle:

Principle #35Parameter changes

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 method improves tracking accuracy and enables faster actuation in systems with input limitations, reducing tracking errors by 81-88% in experiments and simulations, particularly benefiting over-actuated systems like robotic catheters.

Implementation Method 1

SMA hysteretic wire actuators

Methodology Applied

Scientific EffectShape memory alloy: Shape Memory Alloy

Implementation Method 2

hysteresis behavior of the SMA hysteretic wire actuators

Methodology Applied

Scientific EffectHysteresis: Hysteresis

Implementation Method 3

temperature controlled shape memory alloy actuators

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS11633572B2Over-actuated hysteretic systems and methods for control of same

Publication Date: 2023.04.25 EINDHOVEN MEDICAL ROBOTICS BV

AI summary

An over-actuated system [304], such as a catheter, having shape memory alloy (SMA) hysteretic wire actuators is controlled using a controller [300, 302] that generates a control signal [310] based on a temperature model that takes into account physical limitations of the SMA hysteretic wire actuators, and based on a hysteresis model (e.g., the Duhem model) that describes hysteresis behavior of the SMA hysteretic wire actuators. The controller preferably includes a feedback controller [302] and a reference governor [300] that generates a smart reference signal [308] from a reference signal [306] representing a desired value of an output of the system. The smart reference signal preferably minimizes an error between the reference signal and an achievable output, and the control signal preferably is generated based on the smart reference signal.