Shape memory alloys (SMAs) are a well-known class of smart materials. When subjected to certain thermal cycles, they are able to generate mechanical work by recovering a predetermined shape. Due to their high mechanical performances, their compactness and lightness, SMAs can be easily included in mechanical devices of small dimensions and used as actuating elements. There are rather few companies worldwide that deal in SMA mini-actuators; we can find, nonetheless, quite a large number of studies about them. In this paper, we illustrate the state of art of SMA mini-actuators, in the meaning of mini-modular-mechanical devices activated by SMA materials; particular attention is granted to the commercial SMA mini-actuators and to the most recent and relevant publications and patents in this field. Ferromagnetic shape memory alloys are presented as well.

The high potential of shape memory alloys in developing miniature mechanical devices: A review on shape memory alloy mini-actuators

Assistive devices are a key aspect in wearable systems for biomedical applications, as they represent potential aids for people with physical and sensory disabilities that might lead to improvements in the quality of life. This chapter focuses on wearable assistive devices for the blind. It intends to review the most significant work done in this area, to present the latest approaches for assisting this population and to understand universal design concepts for the development of wearable assistive devices and systems for the blind.

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Wearable Assistive Devices for the Blind

This paper presents an up-to-date survey of graphical tactile displays. These devices provide information through the sense of touch. At best, they should display both text and graphics (text may be considered a type of graphic). Graphs made with shapeable sheets result in bulky items awkward to store and transport; their production is expensive and time-consuming and they deteriorate quickly. Research is ongoing for a refreshable tactile display that acts as an output device for a computer or other information source and can present the information in text and graphics. The work in this field has branched into diverse areas, from physiological studies to technological aspects and challenges. Moreover, interest in these devices is now being shown by other fields such as virtual reality, minimally invasive surgery and teleoperation. It is attracting more and more people, research and money. Many proposals have been put forward, several of them succeeding in the task of presenting tactile information. However, most are research prototypes and very expensive to produce commercially. Thus the goal of an efficient low-cost tactile display for visually-impaired people has not yet been reached

Graphical Tactile Displays for Visually-Impaired People

TeslaTouch is a technology that provides tactile sensation to moving fingers on touch screens. Based on TeslaTouch, we have developed applications for the visually impaired to interpret and create 2D tactile information. In this paper, we demonstrate these applications, present observations from the interaction, and discuss TeslaTouch's potential in supporting communication among visually impaired individuals.

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Tactile display for the visually impaired using TeslaTouch

We describe a tactile transducer system that has a compact, yet modular design. The tactile transducer comprises a 6 × 10 piezo bimorph actuator array with a spatial resolution of 1.8 × 1.2 millimeter and a wide temporal bandwidth. The blocked force of the individual actuators can be changed (0.15 N, 0.22 N) by adjusting the cantilever mechanics to optimally match skins and/or applications. This tactile transducer is modular, appeals to ordinary fabrication methods, and can be assembled and dismantled in a short time for debugging and maintenance. It weighs 60 g, it is self-contained in a 150 cm3volume and may be interfaced to most computer, provided that two analog outputs and six digital IO lines are available. A pilot test was carried out where subjects were asked to detect a virtual line randomly located on an otherwise smooth virtual surface.

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Compact, Portable, Modular, High-performance, Distributed Tactile Transducer Device Based on Lateral Skin Deformation

This paper presents a new concept of low-cost, high-resolution, lightweight, compact and highly-portable tactile display. The prototype consists of an array of 8 /spl times/ 8 upward/downward independent moveable pins based on shape memory alloy (SMA) technology. Each actuator is capable of developing a 320 mN pull force at 1.5 Hz bandwidth by using simple forced-air convection. The proposed concept allows the development of 60 g weight tactile devices of compact dimensions easily carried in the user's hand. SMA active element, tactile actuator and tactile display are presented and discussed.

A low-cost highly-portable tactile display based on shape memory alloy micro-actuators

This paper presents a novel pin-matrix tactile-display device that exhibits some advantageous features for the blind: low cost, lightweight, compactness, and high portability. The prototype consists of 64 tactile pins actuated by shape memory alloys with 2.6-mm spatial resolution (Braille-like). Unlike existing devices, the full display weighs only 200 g, and its compact dimensions make it easy to carry. A technical overview of the system is presented, as well as preliminary results on shape recognition, to evaluate its performance on tactile rendering.

Tactile Rendering With Shape-Memory-Alloy Pin-Matrix

This paper presents a new miniature actuator, which is currently being used to design and develop high resolution, lightweight and compact interfaces for tactile binary information representation such as Braille. Since the main drawback of these devices is their high cost, the proposed actuator exploits the simplicity of its design to provide a low-cost actuation alternative. Based on shape memory alloy (SMA) technology, the actuator consists of an antagonist arranged pair of NiTi helical springs. The actuator of 1.5 mm diameter and 150 mg weight is capable of developing a 320 mN pull force and 1.5 Hz bandwidth by using simple forced-air convection. A combined computational/experimental study on the thermomechanical properties of both SMA active element and actuator is presented to evaluate characteristics such as actuation speed, force and stroke. In conclusion, the prototype and performance results are reported and discussed.

Miniature Shape Memory Alloy Actuator for Tactile Binary Information Display

This paper addresses a new concept of visuo-tactile human-machine interface for a certain representation of the peripersonnal space, especially useful for visually impaired and blind people navigation. The proposed space representation have been successfully implemented on a tactile device and validated via series of experiments involving naive blindfolded sighted people. Results show that is possible to interact with the space via the proposed tactile representation

A Dynamic Tactile Map as a Tool for Space Organization Perception: Application to the Design of an Electronic Travel Aid for Visually Impaired and Blind People

This paper describes the design, modeling and implementation of a novel shape memory alloy (SMA) based micro-actuator intended for high resolution tactile displays. In order to evaluate the characteristics of SMA devices, existing constitutive models are used to predict their dynamic behavior. In particular, thermal and mechanical properties are studied and analyzed. Time domain and force-displacement open loop experimental results are presented to validate simulation performance. The accuracy of the models may be used to design actuators under specifications of dimension, force and speed. Inspired by a simple retractable ballpoint pen-like mechanism, the actuator's design concept is described in detail. In conclusion, the prototype and preliminary results are presented and discussed.

M. Hafez

Papers

A low-cost highly-portable tactile display based on shape memory alloy micro-actuators

Tactile Rendering With Shape-Memory-Alloy Pin-Matrix

Miniature Shape Memory Alloy Actuator for Tactile Binary Information Display

A Dynamic Tactile Map as a Tool for Space Organization Perception: Application to the Design of an Electronic Travel Aid for Visually Impaired and Blind People

Design and characterization of a shape memory alloy based micro-actuator for tactile stimulation