Modelling of Shape Memory Alloy Negator Springs for Long-Stroke Constant-Force Actuators

2012 ◽  
Vol 78 ◽  
pp. 52-57
Author(s):  
Andrea Spaggiari ◽  
Eugenio Dragoni
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Elastic Moduli ◽  
Mechanical Response ◽  
Constant Force ◽  
Output Force ◽  
Different Temperatures ◽  
Strip Metal ◽  
Long Stroke ◽  
Intrinsic Characteristic

The paper deals with the analytical modelling of a shape memory alloy Negator spring. Negator springs are spiral springs made of strip metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. This configuration allows a constant force mechanical response and very long strokes, limited mainly from the total length of the spring. The authors investigate the behaviour of the spring made of a shape memory alloy (SMA). The intrinsic characteristic of SMA is to have two different elastic moduli at different temperatures. This difference can be exploited in order to have a net actuation force for the entire very long stroke, overcoming the two major drawbacks of the SMA actuators, short strokes and output force which varies linearly during the travel.

Analytical Modelling of Rolamite Mechanism Made of Shape Memory Alloy for Constant Force Actuators

2015 ◽  
Author(s):  
Andrea Spaggiari ◽  
Eugenio Dragoni
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Metal Strip ◽  
Force Generation ◽  
Constant Force ◽  
Low Friction ◽  
Actuation Force ◽  
Long Stroke ◽  
Force Generator ◽  
Roll Back

This paper analyses the Rolamite architecture exploiting shape memory alloys as power element to obtain a solid state actuator. The Rolamite mechanism was discovered in the late sixties, initially as precision and low friction linear bearing. The most common Rolamite configuration consists of a flexible thin metal strip and two rollers mounted between two fixed parallel guide surfaces. The system can roll back and forth without slipping guided by the plates along its so called sensing axis. The system presents another relevant advantage in addition to low friction coefficient, which is the possibility to provide force generation in a quite simple way. In the original literature works the force was provided thanks to cutouts of various shape in the strip, though this method does not allow the Rolamite to be considered a proper actuator, but only a force generator. In this paper we developed the idea of exploiting the shape memory alloy as Rolamite power element and therefore to use the shape memory effect to change the elastic properties of the strip and to provide the actuation force. The mechanical analyses and the equations where the martensite-austenite transition is modelled in a simplified way, show that this application is feasible, mainly thanks to the initial precurvature of the SMA strip. The discussion of the results highlights some important merits of this architecture such as long stroke, constant force and compactness.

Analytical modelling of Rolamite mechanism made of shape-memory alloy for constant force actuators

2016 ◽  
Vol 28 (16) ◽  
pp. 2208-2221 ◽  
Author(s):  
Andrea Spaggiari ◽  
Eugenio Dragoni
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Mechanical Analysis ◽  
Metal Strip ◽  
Constant Force ◽  
Low Friction ◽  
Actuation Force ◽  
Long Stroke ◽  
Force Generator ◽  
Roll Back

This article analyses the Rolamite architecture exploiting shape-memory alloys as power element to obtain a solid-state actuator. The Rolamite mechanism was discovered in the late 1960s, initially as precision and low friction linear bearing. The most common Rolamite configuration consists of a flexible thin metal strip and two rollers mounted between two fixed parallel guide surfaces. The system can roll back and forth without slipping guided by the plates along its so-called sensing axis. The system presents another relevant advantage in addition to low friction coefficient, which is the possibility to provide force generation in a quite simple way. In the original literature works, the force was provided, thanks to cut-outs of various shapes in the strip, although this method does not allow the Rolamite to be considered a proper actuator, but only a force generator. In this article, we developed the idea of exploiting the shape-memory alloy as Rolamite power element, and therefore, to use the shape-memory effect to change the elastic properties of the strip and to provide the actuation force. The mechanical analysis, where the martensite–austenite transition is modelled in a simplified way, shows that this application is feasible, mainly thanks to the initial precurvature of the shape-memory alloy strip. The discussion of the results highlights some important merits of this architecture such as long stroke, constant force and compactness.

Analytical and Numerical Modelling of Shape Memory Alloy Negator Springs for Long-Stroke Constant-Force Actuators

2012 ◽  
Author(s):  
Andrea Spaggiari ◽  
Eugenio Dragoni
Keyword(s):  
Shape Memory ◽  
Mechanical Behaviour ◽  
Volume Ratio ◽  
Constant Force ◽  
Helical Springs ◽  
Finite Element Software ◽  
Spiral Spring ◽  
High Area ◽  
Flat Shape ◽  
Long Stroke

This paper explores the merits of shape memory Negator springs as powering elements for solid state actuators. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. The unique characteristic of Negator springs is the nearly-constant force needed to unwind the strip for very large, theoretically infinite deflections. Moreover the flat shape, having a high area over volume ratio, grants improved bandwidth compared to any solution with solid wires or helical springs. The SMA material is modelled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behaviour. The mathematical model of the mechanical behaviour of SMA Negator springs is provided and their performances as active elements in constant-force, long-stroke actuators are assessed. The SMA Negator spring is also simulated in a commercial finite element software, ABAQUS, and its mechanical behaviour is estimated through FE analyses. The analytical and the numerical prediction are in good agreement, both in martensitic and in austenitic range.

Microstructural and Fractographic Analysis of CuAlNi Shape Memory Alloy before and after Heat Treatment

2020 ◽  
Vol 405 ◽  
pp. 100-106
Author(s):  
Ivana Ivanić ◽  
Mirko Gojić ◽  
Stjepan Kožuh ◽  
Borut Kosec
Keyword(s):  
Heat Treatment ◽  
Shape Memory Alloy ◽  
Fracture Surface ◽  
Shape Memory ◽  
Fractographic Analysis ◽  
Before And After ◽  
Different Temperatures ◽  
The Difference ◽  
Type Of Fracture ◽  
Scanning Electron

The paper presents comparison of microstructure and fracture surface morphology of the CuAlNi shape memory alloy (SMA) after different heat treatment procedures. The investigation was performed on samples in as-cast state and heat treated states (solution annealing at temperatures of 850 °C / 60’ / H2O and 920 °C / 60’ / H2O along with tempering at two different temperature 150 °C / 60’ / H2O and 300 °C / 60’ / H2O). The microstructure of the samples was examined by optical (OM) and scanning electron microscope (SEM) equipped with device for EDS analysis. The obtained fracture surfaces were examined by SEM. Optical and scanning electron microscopy showed martensitic microstructure in all investigated samples. However, the fractographic analysis of samples after tensile testing reveals significant changes in fracture mechanism. In both solution annealed states the results shows transgranular type of fracture, but after tempering at two different temperatures the difference is obvious. After tempering at 150 °C, along with transgranular type of fracture appear some areas with intergranular type of fracture. After tempering at 300 °C, fracture surface reveals completely intergranular type of fracture.

scholarly journals Effect of Heat Treatment Temperature on Martensitic Transformation and Superelasticity of the Ti49Ni51 Shape Memory Alloy

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2539 ◽  
Author(s):  
Peiyou Li ◽  
Yongshan Wang ◽  
Fanying Meng ◽  
Le Cao ◽  
Zhirong He
Keyword(s):  
Heat Treatment ◽  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Thermal Hysteresis ◽  
Treatment Temperature ◽  
Heat Treated ◽  
Different Temperatures ◽  
Tini Phase ◽  
Rapidly Solidified

The martensitic transformation and superelasticity of Ti49Ni51 shape memory alloy heat-treatment at different temperatures were investigated. The experimental results show that the microstructures of as-cast and heat-treated (723 K) Ni-rich Ti49Ni51 samples prepared by rapidly-solidified technology are composed of B2 TiNi phase, and Ti3Ni4 and Ti2Ni phases; the microstructures of heat-treated Ti49Ni51 samples at 773 and 823 K are composed of B2 TiNi phase, and of B2 TiNi and Ti2Ni phases, respectively. The martensitic transformation of as-cast Ti49Ni51 alloy is three-stage, A→R→M1 and R→M2 transformation during cooling, and two-stage, M→R→A transformation during heating. The transformations of the heat-treated Ti49Ni51 samples at 723 and 823 K are the A↔R↔M/A↔M transformation during cooling/heating, respectively. For the heat-treated alloy at 773 K, the transformations are the A→R/M→R→A during cooling/heating, respectively. For the heat-treated alloy at 773 K, only a small thermal hysteresis is suitable for sensor devices. The stable σmax values of 723 and 773 K heat-treated samples with a large Wd value exhibit high safety in application. The 773 and 823 K heat-treated samples have large stable strain–energy densities, and are a good superelastic alloy. The experimental data obtained provide a valuable reference for the industrial application of rapidly-solidified casting and heat-treated Ti49Ni51 alloy.

An Analytical Design Method for a Shape Memory Alloy Wire Actuated Compliant Finger

2008 ◽  
Author(s):  
Chao-Chieh Lan ◽  
You-Nien Yang
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Design Method ◽  
Three Dimensional ◽  
Output Force ◽  
Shape Parameterization ◽  
Robotic Manipulations ◽  
Experimental Validations ◽  
Electro Magnetic ◽  
High Work

This paper presents an analytical method to design a mechanical finger for robotic manipulations. As traditional mechanical fingers require bulky electro-magnetic motors and numerous relative-moving parts to achieve dexterous motion, we propose a class of fingers the manipulation of which relies on finger deflections. These compliant fingers are actuated by shape memory alloy (SMA) wires that exhibit high work-density, frictionless, and quite operations. The combination of compliant members with embedded SMA wires makes the finger more compact and lightweight. Various SMA wire layouts are investigated to improve their response time while maintaining sufficient output force. The mathematical models of finger deflection caused by SMA contraction are then derived along with experimental validations. As finger shapes are essential to the range of deflected motion and output force, we find its optimal initial shapes through the use of a shape parameterization technique. We further illustrate our method by designing a humanoid finger that is capable of three-dimensional manipulation. As compliant fingers can be fabricated monolithically, we expect the proposed method to be utilized for applications of various scales.

Sign in / Sign up

Export Citation Format

Share Document