M. Singaperumal

Critical review of current trends in shape memory alloy actuators for intelligent robots

Purpose – The purpose of this paper is to review the current application areas of shape memory alloy (SMA) actuators in intelligent robotic systems and devices.Design/methodology/approach – This paper analyses how actuation and sensing functions of the SMA actuator have been exploited and incorporated in micro and macro robotic devices, developed for medical and non‐medical applications. The speed of response of SMA actuator mostly depends upon its shape and size, addition and removal of heat and the bias force applied. All these factors have impact on the overall size of the robotic device and the degree of freedom (dof) obtained and hence, a comprehensive survey is made highlighting these aspects. Also described are the mechatronic aspects like the software and hardware used in an industrial environment for the control of such nonlinear actuator and the type of sensory feedback devices incorporated for obtaining better control, positioning accuracy and fast response.Findings – SMA actuators find wide ap...

Modelling and simulation of a novel shape memory alloy actuated compliant parallel manipulator

This paper presents the non-linear analysis of a shape memory alloy (SMA) actuated fully compliant spatial parallel mechanism. A compliant mechanism made of SMA wires as its actuators and SMA pipe as its structural member that exploits both the shape memory and superelastic effects is proposed and its static analysis using ANSYS is presented in this study. Finite element analysis in a multi-physics environment considering geometric and material non-linearities helps the user to analyse complex behaviour of a system. For the proposed mechanism, simulation results show: (a) 4 per cent strain for SMA actuation is optimal considering the geometric non-linearity of the proposed mechanism for obtaining maximum displacement; (b) buckling effect is less predominant while implementing the superelastic behaviour; and (c) the mechanism can be designed as a compliant device with one or more inflexion points by exploiting the superelasticity of the SMA pipe. The knowledge obtained from the simulation study could help in further miniaturization of the manipulator.

Experimental investigations of the large deflection capabilities of a compliant parallel mechanism actuated by shape memory alloy wires

This experimental study investigates the coupled effect of the force developed by the shape memory alloy (SMA) actuators and the force required for the large deflection of an elastica member in a compliant parallel mechanism. The compliant mechanism developed in house consists of a moving platform mounted on a superelastic pillar and three SMA wire actuators to manipulate the platform. A three-axis MEMS accelerometer has been mounted on the moving platform to measure its tilt angle. Three miniature force sensors have been designed and fabricated out of cantilever beams, each mounted with a pair of strain gauges, to measure the force developed by the respective actuators. The force sensors are highly sensitive and cost effective compared to commercially available miniature force sensors. Calibration of the force sensors has been accomplished with known weights, and for the three-axis MEMS accelerometer a rotary base has been considered which is usually used in optical applications. The calibration curves obtained, with R-squared values between 0.9997 and 1.0, show that both the tilt and force sensors considered are most appropriate for the respective applications. The mechanism fixed with the sensors and the drivers for the SMA actuators is integrated with a National Instruments data acquisition system. The experimental results have been compared with the analytical results and it was found that the relative error is less than 2%. This is a preliminary study in the development of a mechanism for eye prosthesis and similar applications.

A Compliant Miniature Parallel Manipulator with Shape Memory Alloy Actuators

Light weight parallel manipulators are most desirable for aerospace, medical applications etc., where flexibility, low inertia, simplicity in operation, low stowed volume are important parameters. This paper presents the design and simulation of a flexible parallel manipulator with central elastic column that is made of superelastic nitinol. The actuators are shape memory SMA wires of 300 mum diameter. Unlike conventional rigid link parallel manipulators, the proposed manipulator does not have any joints, which is the major advantage. The proposed manipulator is investigated for its degree of freedom with virtual rigid segment concept and its large deflection is analyzed based on elastica approach. Its control aspect is briefly described and numerical simulation results are presented.

Design of a Shape Memory Alloy Actuated Compliant Smart Structure: Elastica Approach

Large displacement static analysis of a fully compliant spatial mechanism is presented here. This mechanism is made up of a superelastic nitinol pipe as its compliant structural member and actuated by three shape memory alloy (SMA) wires. The coupled effect of the force developed by the SMA actuation and the force required for elastica deflection is simplified by incorporating the geometric parameters of the mechanism using a defiection plane approach. An iterative algorithm with elliptical integration has been developed, which is suitable for a wider range of actual and arbitrary inputs. The solutions are obtained for the effect of one-wire and two-wire actuation methods. Results obtained from the deflection plane approach and simulation have been compared and found that the relative error is less than 1% within the safe operating range of 5% strain value recommended for SMA actuators. Based on the analytical and simulation inputs, the mechanism is miniaturized further with the aim of increasing its workspace and is fabricated for further experimental investigations.

A generalized analytical approach to the coupled effect of SMA actuation and elastica deflection

A compliant miniature parallel manipulator made of superelastic nitinol pipe as its central pillar and actuated by three symmetrically attached shape memory alloy (SMA) wires is under development. The mobility for the platform is obtained by the selective actuation of one or two wires at a time. If one wire is actuated, the other two unactuated wires provide the counter effect. Similarly, if two wires are actuated simultaneously or in a differential manner, the third unactuated wire resists the movement of the platform. In an earlier work of the authors, the static displacement analysis was presented without considering the effect of unactuated wires. In this contribution, the force–displacement analysis is presented considering the effect of both actuated and unactuated wires. Subsequently, an attempt has been made to obtain a generalized approach from which six types of actuation methods are identified using a group of conditional parameters. Each method leads to a set of large deflection expressions suitable for a particular actuation method. As the large deflection expressions derived for the mechanism are nonlinear and involve interdependent parameters, their simplified form using a parametric approximation have also been obtained using Howells algorithm. The generalized approach and the solution algorithm developed can be applied to any kind of compliant mechanism having large deflection capabilities, including planar and spatial MEMS devices and stability analysis of long slender columns supported by wires or cables. The procedure developed is also suitable for the static analysis of spatial compliant mechanisms actuated by multiple SMA actuators.

Design of SMA actuated light weight parallel manipulator with intelligent controller

Abstract Parallel manipulators are best known for their high load carrying capacity, stiffness, fast, accurate positioning etc., compared to their serial counterparts. Lightweight parallel manipulators are typical parallel mechanisms in which the linear-rotary actuators and spherical-rotary joints are replaced by smart actuators and with or without flexure joints. This paper describes about a lightweight miniature parallel manipulator of size 17.5mm dia.x25mm height, made of Beryllium-Copper spring steel and actuated by Shape Memory Alloy (SMA) actuators. The system modelling which includes dynamics and kinematics analysis is briefly described. The possibility of incorporating an Intelligent Fuzzy Controller is investigated. Preliminary simulation results are presented.

Kinetostatic Analysis of a Spatial Compliant Mechanism Actuated by Three Shape Memory Alloy Wires in Differential Form

This contribution presents the kinetostatic analysis of a spatial compliant mechanism actuated by three Shape Memory Alloy (SMA) wire actuators. This mechanism exploits both shape memory and superelastic effects of SMA actuators. The moving platform of the mechanism is mounted on a pillar made of superelastic SMA and its mobility is obtained from the large deflection of the pillar by the selective actuation of any one or two wires in differential manner. The deflection expressions obtained are basically force-displacement kinematic relationships, derived after incorporating follower forces and variable moments developed by the actuators. Two sets of geometric parameters, related to deflected and undeflected conditions, have been utilized to solve the coupled relationship between the force developed by the SMA actuation and the force required for the elastica deflection. The deflection expressions are solved using Romberg integration method and the numerical results obtained have been validated by comparing them with those obtained from FEM simulation. The results show that, for the design of compliant mechanisms exhibiting large displacements the force-displacement relationships in linear form, as applicable to small deflections, are no longer valid.