Scalable Output Linear Actuators, a Novel Design Concept Using Shape Memory Alloy Wires Driven by Fluid Temperature

Andres Osorio Salazar,Yukio Takeda,Yusuke Sugahara,Daisuke Matsuura

doi:10.3390/machines9010014

Abstract

In this paper, the concept of scalability for actuators is introduced and explored, which is the capability to freely change the output characteristics on demand: displacement and force for a linear actuator, angular position and torque for a rotational actuator. This change can either be used to obtain power improvement (with a constant scale factor), or to improve the usability of a robotic system according to variable conditions (with a variable scale factor). Some advantages of a scalable design include the ability to adapt to changing environments, variable resolution of step size, ability to produce designs that are adequate for restricted spaces or that require strict energy efficiency, and intrinsically safe systems. Current approaches for scalability in actuators have shortcomings: the method to achieve scalability is complex, so obtaining a variable scaling factor is challenging, or they cannot scale both output characteristics simultaneously. Shape Memory Alloy (SMA) wire-based actuators can overcome these limitations, because its two output characteristics, displacement and force, are physically independent from each other. In this paper we present a novel design concept for linear scalable actuators that overcome SMA design and scalability limitations by using a variable number of SMA wires mechanically in parallel, immersed in a liquid that transmits heat from a separate heat source (wet activation). In this concept, more wires increase the maximum attainable force, and longer wires increase the maximum displacement. Prototypes with different number of SMA wires were constructed and tested in isometric experiments to determine force vs. temperature behavior and time response. The heat-transmitting liquid was either static or flowing using pumps. Scalability was achieved with a simple method in all tested prototypes with a linear correlation of maximum force to number of SMA wires. Flowing heat transmission achieved higher actuation bandwidth.

Highlights

Ever since automated systems were introduced, the ability to respond to a change, to be adaptable, was highly sought after by designers and users
In this work we present a design concept of a scalable actuator based on Shape Memory Alloy (SMA) wires that achieve scalability by having its energy conversion elements reconfigured (Scalability strategy number 4 from Section 2.1), with a change of scaling factor that is simple
The decrease in output force of the Constant-Flow SMA Linear Actuator (CFSMALA) with respect to Zero-Flow SMA Linear Actuator (ZFSMALA) can be attributed to the losses caused by the internal pressure in the actuator induced by the fluid flow, not present in the ZFSMALA

Summary

Introduction

Ever since automated systems were introduced, the ability to respond to a change, to be adaptable, was highly sought after by designers and users. If their systems could continue to be useful by meeting the ever-changing demands from the market, it would provide value for a longer time-frame. Whenever there is a change in the output requirement, e.g., a change of the object being manipulated, the same robotic system can continue to be useful. The focus of companies is to design systems that, besides meeting the high-quality-low-cost standard requirement, have to facilitate rapid response to market changes and consumer needs. It enables manufacturing systems to quickly launch new products on existing systems, and to react rapidly and cost-effectively to: market changes, including changes in product demand, product changes, including changes in current products and introduction of new products; and system failures (ongoing production despite equipment failures).”

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