Bidirectional rotating actuators using shape memory alloy wires

NASA's Mars Pathfinder mission, to be launched in 1996, reflects a new philosophy of exploiting new technologies to reduce mission cost and accelerate the pace of space exploration.

Series on Stability, Vibration and Control of Systems, Series B, 2000

In this paper we study the design and modelling of a new rotary actuator that has been developed at the University of Waterloo using shape memory alloy springs. Shape memory alloys (SMAs) have the property that they can be subjected to a large deformation when it is below martensite temperature and it recovers its original shape when it is heated over austenite temperature. In other words, a SMA can directly convert thermal energy to mechanical work! It is also interesting to note that among low and medium range actuators SMAs have the highest power to weight ratio. The designed actuator in this work is a two-way actuator and is made of NiTi SMA springs. It is modular and large rotations can be o btained using extra m o dules. The actuator design is rst explained and then, the Ikuta's model is modi ed to derive a mathematical representation of the actuator. Using experimental and simulation results the mathematical model is veri ed.

2010

This paper presents low-profile torsional actuators applicable for mesoscale and microscale robots. The primary actuator material is thermally activated Ni-Ti shape memory alloy (SMA), which exhibits remarkably high torque density. Despite the advantages of SMAs for actuator applications-high strain, silent operation, and mechanical simplicity-the response time and energy efficiency limit overall performance. As an alternative to SMA wires, thin SMA sheets are used to fabricate effective yet compact torsional actuators. Also, instead of using conventional Joule heating, an external Ni-Cr heating element is utilized to focus heat on the regions of highest required strain. Various design parameters and fabrication variants are described and experimentally explored in actuator prototypes. Controlled current profiles and discrete heating produces a 20% faster response time with 40% less power consumption as compared to Joule heating in a low-profile (sub-millimeter) torsional actuator capable of 180 • motion.

Smart Materials and Structures, 2012

This paper presents a low-profile bidirectional folding actuator based on annealed shape memory alloy sheets applicable for meso-and microscale systems. Despite the advantages of shape memory alloys-high strain, silent operation, and mechanical simplicity-their application is often limited to unidirectional operation. We present a bidirectional folding actuator that produces two opposing 180 • motions. A laser-patterned nickel alloy (Inconel 600) heater localizes actuation to the folding sections. The actuator has a thin (<1 mm) profile, making it appropriate for use in robotic origami. Various design parameters and fabrication variants are described and experimentally explored in the actuator prototype.

Sensors and Actuators A: Physical, 2015

This paper presents the design and control of a novel compliant differential shape memory alloy (SMA) actuator with significantly improved performance compared to traditional bias and differential type SMA actuators. This actuator is composed of two antagonistic SMA wires and a mechanical joint coupled with a torsion spring. The differential SMA wires are utilized to increase the response speed, and the torsion spring is employed to reduce the total stiffness of SMA actuator and improve the output range. Theoretical models that include the stiffness equations of the SMA wire as well as the dynamics of three different SMA actuation systems are introduced and compared. Simulation and experimental results have proved that this new actuator can provide larger output angle compared to conventional SMA actuators under the same conditions. Moreover, regulation and tracking control experiments have demonstrated that this compliant differential SMA actuator achieves higher response speed compared to the bias SMA actuator using compatible PI controller. The tracking performance is further improved by the saturated PI controller.

2005

Thls paper presents the application of systematic model-based design techniques to the design of Shape Memory Alloy (SMA) actuators. Shape memory alloys are promising materials for (micro-)actuation, because of the relatively large deformations and forces that can be achieved. However, the complex ctmstitutive behavior and the fact that several physical domains (electrical, thermal and mechanical) play a role makes it difficult to design effective SMA actuators with complex shapes and layouts.

performance compared to traditional SMA actuators. This actuator is composed of two antagonistic SMA wires and a mechanical joint coupled with a torsion spring. The torsion spring is employed to reduce the total stiffness of SMA actuator and improve the range of motion. The antagonistic wires increase the response time as one wire can be heated up while the other wire is still in the cooling process. Dynamic model of this actuator was established for control design. Experimental results proved that this new actuator can provide larger output range of motion and faster response speed than traditional SMA actuators under the same conditions. Sine wave tracking with 0.05 Hz, 0.08 Hz and 0.1 Hz were performed and our results demonstrated that this compliant actuator has good tracking performance under simple PID control.

Proceedings of the First International Conference on Biomedical Electronics and Devices, 2008

The present paper presents the development of a mechanical actuator using a shape memory alloy with a novel cooling system based on the thermo-electric effect (Seebeck-Peltier effect). Such a method has the advantage of reduced weight and requires a simpler control strategy as compared to other forced cooling systems. A complete mathematical model of the actuator was derived, and an experimental prototype was implemented. Several experiments are used to validate the model and to identify all parameters. A robust and nonlinear controller, based on sliding-mode theory, was derived and implemented. Experiments were used to evaluate the actuator closed-loop performance, stability, and robustness properties. The results showed that the proposed cooling system is able to improve the dynamic response of the actuator.

2016 8th International Conference on Electronics, Computers and Artificial Intelligence (ECAI), 2016

The current paper discusses the design, modeling and control of a Light weight robotic arm actuated by Shape Memory Alloy (SMA) actuators, usable for applications such as Aerial Manipulator. Compared to servo motor based robotic arm the proposed design has an added advantage of light weight and high force to mass ratio, but further introduces the problem of nonlinearities such as Hysteresis into the system. A nonlinear dynamic model of the hysteretic robotic arm is systematically developed to perform closed loop simulations. A Joint Space control is performed using Variable Structure Control and the closed loop performance is successfully verified by simulation studies.

2011

Abstract In this paper, a one-degree-of-freedom actuator that is based on shape memory alloy (SMA) springs is developed and tested. The use of SMA springs allows a larger actuation workspace and controllable stiffness than SMA wires. It is shown that the actuator demonstrates a good positioning accuracy in addition to a higher level of stiffness control. A strategy based on the variable structure control method is implemented for simultaneous displacement and stiffness control.

Smart Materials and Structures, 2012

Shape memory alloys have been widely proposed as actuators, in fields such as robotics, biomimetics and microsystems: in particular spring actuators are the most widely used, due to their simplicity of fabrication. The aim of this paper is to provide a general model and the techniques for fabricating SMA spring actuators. All the steps of the design process are described: a mechanical model to optimize the mechanical characteristic for a given requirement of force and available space, and a thermal model for the estimation of the electrical power needed for activation. The parameters of both models are obtained by experimental measurements, which are described in the paper. The models are then validated on springs manufactured manually, showing also the fabrication process. The design method is valid for the dimensioning of SMA springs, independently from the external ambient conditions. The influence on the actuator bandwidth was investigated for different working environments, providing numerical indications for the utilization in underwater applications. The spring characteristics can be calculated by the mechanical model with an accuracy of 5%. The thermal model allows one to calculate the current needed for activation under different ambient conditions, in order to guarantee activation in the specific loading conditions. Moreover, two solutions were found to reduce the power consumption by more than 40% without a dramatic reduction of bandwidth.

2013

The aim of this paper is to propose an analog current driver topology specifically designed for mechanical actuators based on Shape Memory Alloys (SMAs). The use of SMAs in present actuators represents an alternative to electromagnetic actuators in a wide range of applications. The current driver described in the following paper, matched to a dedicated SMA actuator, is perfectly suitable as a powerful evaluation tool for supporting and spreading the diffusion of a new actuation concept in modern electromechanical applications. INTRODUCTION The shape memory alloys, also called SMAs, are metallic alloys that exhibit the shape memory effect: SMAs can be deformed at a low temperature but regain their original configuration when heated to a higher temperature. Components made from SMAs can be designed to exert forces over a considerable range of motion, often for many cycles. For this reason, SMAs as actuators are used as alternatives to electromagnetic actuators in a wide range of appli...

In this paper various applications of shape memory alloys (SMA) in bio-medical field based upon their material properties are discussed, and a novel SMA spring actuator design for biopsy is proposed. Design parameters such as spring configuration, wire diameter required for designing the actuator were defined and obtained through experiments. Finally, itconcludeswith the possibility of using SMA spring for high force compact system.

Actuators

Typical shape memory alloy actuators provide a unique combination of large stresses and strains that result in work-per-volume larger by more than two orders of magnitude than all other actuation methods that are based on active materials. High-rate actuation of shape memory alloys can provide improved energy efficiency, and shorter response and total actuation times, along with large travel-per-wire-length, with respect to slow-rate SMA applications. In this article, we review the different aspects of high-rate actuation of shape memory alloy wires in the high-driving-force regime. We briefly survey previous experimental results about the kinetics and thermodynamics of the phase transformation in view of its practical implications. New experimental results, regarding energy efficiency, total actuation time, repeatability, and fatigue, are presented and discussed. The paper provides general design guidelines for obtaining high actuator performance, as well as guidelines for selectin...

Shape memory alloys (SMAs) are used as active elements in novel actuation devices. Two generic types of SMA actuators can be distinguished according to the type of bias passive-bias actuators where an elastic component serves as a bias and active-bias actuators where two SMA elements are connected together. This paper describes an experimental testing bench developed for the characterization of SMA active elements and their testing in a real actuation environment. The characterization of SMA active elements is performed under three complementary testing modes: (a) constant-stress, (b) fixed-support, and (c) elasticbias recovery modes. Force, displacement and temperature data acquired during testing of a given SMA active element are then used to assess the mechanical work-generation potential of this active element and, ultimately, for the design of an SMA actuator containing this element. Finally, a case study is presented to illustrate the experimental design methodology and results.