Data-driven model-free adaptive fractional-order sliding mode control for the SMA actuator with prescribed performance

In this paper, a novel data-driven model-free adaptive fractional-order sliding mode controller with prescribed performance is proposed for the shape memory alloy (SMA) actuator. Due to the strong asymmetric saturated hysteresis nonlinear characteristics of the SMA actuators, it is not easy to establish an accurate model and develop an effective controller. Therefore, we present a controller without using the model of the SMA actuators. In other words, the proposed controller depends merely on the input/output (I/O) data of the SMA actuators. To obtain the reasonable compensation for hysteresis, enhance the noise robustness of the controller, and reduce the chattering, a fractional-order sliding mode controller with memory characteristics is employed to improve the performance of the controller. In addition, the prescribed performance control (PPC) strategy is introduced in our work to guarantee the tracking errors converge to a sufficiently small boundary and the convergence rate is not less than a predetermined value which are significant and considerable in practical engineering applications of the SMA actuator. Finally, experiments are carried out, and results reveal the effectiveness and success of the proposed controller. Comparisons with the classical Proportional Integral Differential (PID), model-free adaptive control (MFAC), and model-free adaptive sliding mode control (MFAC-SMC) are also performed.

Fault-tolerant control of a rotary shape memory alloy actuator using a terminal sliding mode controller

This paper focuses on developing a Fault-tolerant control (FTC) method for a rotary Shape Memory Alloy (SMA) actuator against actuator faults. The SMA actuator uses a pair of SMA wires in the antagonistic configuration for rotating a pulley. A proposed Terminal Sliding Mode Controller (TSMC) is utilized to compensate for the effects of actuator faults and to guarantee acceptable tracking performance in the presence of faults. The developed closed-loop scheme is applied to both a simulated model of the actuator as well as a real actuator in an experimental setup and then, the performance is evaluated and compared with a Proportional (P) controller and a sliding mode controller. It is shown that the proposed scheme works well in both normal and faulty conditions. The experimental results indicate that TSMC has almost no steady-state error while both P and sliding mode controllers have a considerable error (about 20% relative error), in the presence of the actuator faults.

Design and Simulation of a Flexible Bending Actuator for Solar Sail Attitude Control

This paper presents the design of a flexible bending actuator using shape memory alloy (SMA) and its integration in attitude control for solar sailing. The SMA actuator has advantages in its power-to-weight ratio and light weight. The bending mechanism and models of the actuator were designed and developed. A neural network based adaptive controller was implemented to control the non-linear nature of the SMA actuator. The actuator control modules were integrated into the solar sail attitude model with a quaternion PD controller that formed a cascade control. The feasibility and performance of the proposed actuator for attitude control were investigated and evaluated, showing that the actuator could generate 1.5 × 10−3 Nm torque which maneuvered a 1600 m2 CubeSat based solar sail by 45° in 14 h. The results demonstrate that the proposed SMA bending actuator can be effectively integrated in attitude control for solar sailing under moderate external disturbances using an appropriate controller design, indicating the potential of a lighter solar sail for future missions.

Development of XY Micro-Position Stage Based on a Shape Memory Alloy

This paper reports a novel monolithic two DoF micro-positioning stage using shape-memory-alloy (SMA) actuator. The design was fabricated in a one fabrication step and it comprises all actuation functions in a single piece of SMA. The square shaped actuator has dimensions of 10 mm × 10 mm × 0.25 mm. The device includes a moving stage in the center which is connected to four SMA springs to generate large displacement in two directions, x- and y- axes. The four SMA actuators underwent annealing process using internal joule heating by flowing electrical current through the springs. Each of SMA springs has been actuated individually by internal joule heating generated using an electrical current. The developed design has been simulated to verify thermal response and heat distribution. In addition, the micro-positioning stage was experimentally tested. The maximum displacement results of the stage are 1.1 mm and 1.1 mm along the directions of x- and y- axes, respectively. The developed micro-positioning stage has been successfully demonstrated to control the position of a small object for microscopic imaging applications.

Development of a Combined Micro-Macro Mechanics Analytical Approach to Design Shape Memory Alloy Spring-Based Actuators and Its Experimental Validation

In this work, an analytical procedure for the preliminary design of shape memory alloy spring-based actuators is investigated. Two static analytical models are considered and interconnected in the frame of the proposed procedure. The first model, based on the works from An, is able to determine the material properties of the SMA components by means of experimental test data and is able to size the SMA component based on the requirements of the system. The second model, based on a work from Spaggiari, helps to design and size an antagonist spring system that allows one to obtain the geometric characteristics of springs (SMA and bias) and the mechanical characteristics of the entire actuator. The combined use of these models allows one to define and size a complex SMA actuator based on the actuation load requirements. To validate the design procedure, static experimental tests have been performed with the entire SMA actuator.

Design of a 2 DOF Shape Memory Alloy Actuator Using SMA Springs

In this paper, we developed two degree of freedom shape memory alloy (SMA) actuator using SMA springs. This module can be applied easily to various applications: device holder, artificial finger, grippes, fish robot, and many other biologically inspired applications, where small size and small wight of the actuator are very critical. This actuator is composed of two sets of SMA springs: one set is for the rotation around the X axis (roll angle) and the other set is for the rotation around the Y axis (pitch angle). Each set contains two elements: one SMA spring and one antagonistic SMA spring. We used an inertia sensor (IMU) and two potentiometers for angles feedback. The SMA actuator system is modeled mathematically and then tested experimentally in open-loop and closed-loop control. We designed and experimentally tuned a proportional integrator derivative (PID) controller to follow the set points and to track the desired trajectories. The main goal of the presented controller is to control roll and pitch angles simultaneously in order to satisfy set points and trajectories within the work space. The experimental results show that the two degree of freedom SMA actuator system follows the desired setpoints with acceptable rise time and overshoot.