Nonlinear model accounting for minor hysteresis of embedded SMA actuators

A quantitative index martensite fraction was used to describe the phase transformation degree of shape memory alloy(SMA).On the basis of the martensite fraction,a nonlinear analysis model for major and minor hysteresis loops was developed.The model adopted two exponential equations to calculate the martensite fractions for cooling and heating,respectively.The martensite fractions were derived as the relative parameters were adjusted timely according to continuous,common initial and common limit constraints.By use of the linear relationship between the curvature of embedded SMA actuator and SMA’s martensite fraction,the curvature was determined.The results of the simulations and experiments prove the validity and veracity of the model.

Review:Recent advances in nonlinear control technologies for shape memory alloy actuators

This paper reviews recent developments in nonlinear control technologies for shape memory alloy (SMA) actuators in robotics and their related applications. SMA possesses large hysteresis, low bandwidth, slow response, and non-linear behavior, which make them difficult to control. The fast response of the SMA actuator mostly depends upon, (1) type of controller, (2) rate of addition and removal of heat, and (3) shape or form of the actuator. Though linear controllers are more desirable than nonlinear ones, the review of literature shows that the results obtained using nonlinear controllers were far better than the former one. Therefore, more emphasis is made on the nonlinear control technologies taking into account the intelligent controllers. Various forms of SMA actuator along with different heating and cooling methods are presented in this review, followed by the nonlinear control methods and the control problems encountered by the researchers.

Gait Study and Pattern Generation of a Starfish-Like Soft Robot with Flexible Rays Actuated by SMAs

This paper presents the design and development of a starfish-like soft robot with flexible rays and the implementation of multi-gait locomotion using Shape Memory Alloy （SMA） actuators. The design principle was inspired by the starfish, which possesses a remarkable symmetrical structure and soft internal skeleton. A soft robot body was constructed by using 3D printing technology. A kinematic model of the SMA spring was built and developed for motion control according to displacement and force requirements. The locomotion inspired from starfish was applied to the implementation of the multi-ray robot through the flexible actuation induced multi-gait movements in various environments. By virtue of the proposed ray control patterns in gait transition, the soft robot was able to cross over an obstacle approximately twice of its body height. Results also showed that the speed of the soft robot was 6.5 times faster on sand than on a clammy rough terrain. These experiments demonstrated that the bionic soft robot with flexible rays actuated by SMAs and multi-gait locomotion in proposed patterns can perform successfully and smoothly in various terrains.

A reusable SMA actuated non-explosive lockrelease mechanism for space application

After the satellite is launched with the carrier rocket,it is necessary to separate the satellite from the rocket at an appropriate time to ensure that the satellite enters the intended orbit.In this process,it is vital to ensure a reliable connection and accurate separation.With the increasing use of microsatellite in orbit,the contradiction between the shock of separation and the requirement of the platform’s dynamic environment is becoming increasingly prominent.Therefore,the traditional pyrotechnic separation device can no longer meet the requirements.This paper presents a reusable non-explosive release actuator using shape memory alloy(SMA)wire for high load and low shock.The system is based on the Fast Acting Shock-less Separation Nut(FASSN)technology.Using the shape memory effect of SMA,a biased SMA wire trigger has been developed,which is used as the driver source of the actuator.At the moment of receiving the electrical signal,the SMA wire generates stress and deformation.The trigger set free the constraints on the mechanical components,and the target is released.Experimental results indicate that the trigger device can unlock successfully and well meet the technical objectives.