Low Spring Index NiTi Coil Actuators for Use in Active Compression Garments

Abstract

Abstract-This paper describes the modeling, development, and testing of low spring index nickel titanium (NiTi) coil actuators designed for use in wearable compression garments, and presents a prototype tourniquet system using these actuators. NiTi coil actuators produce both large forces (>1 N) and large recoverable displacements (>100% length) that are well suited for compression garment design. Thermomechanical coil models are presented that describe temperature and force as a function of non-dimensionalized coil geometry, extensional strain, and applied voltage. These models suggest that low spring index coils maximize activation force, and an analytical model is presented to predict garment counter-pressure based on actuator architecture. Several low spring index (C = 3.08) coils were manufactured, annealed, and tested to assess their de-twinning and activation characteristics. Results suggest both annealing and applied stress affect activation thresholds. Actuator force increases both with extensional strain and applied voltage up to 7.24 N. A first-generation compression tourniquet system using integrated actuators with direct voltage-control of applied pressure is presented, demonstrating >70% increase in applied pressure during activation. This approach enables new, dynamic garments with controllable activation and low effort donning and doffing, with applications ranging from healthcare solutions to advanced space suit design.

Low spring index, large displacement Shape Memory Alloy (SMA) coil actuators for use in macro- and micro-systems

“…(1) to streamline actuator design by defining three non-dimensionalized parameters: packing density, η; actuator extensional strain, ; and spring index, C . 15 We define packing density η as the ratio of the number of active coils n contained in the free spring length L 0 relative to the physical limit. This can also be defined as the ratio of the solid spring length L S (i.e., the length of a spring that is wound as tightly as is physically possible) to the free spring length:…”

Empowering Persons with Deafblindness

“…It is already possible to integrate a broad spectrum of mechanisms especially for haptic communication within common textile processing methods such as weaving, knitting, embroidery and sewing. Mechanisms include vibrotactile [15] and pressure [16] modesall of these will be explored to extend the communication space of deafblind users in the SUITCEYES project.…”

Relationship between input power and power density of SMA spring

“…2,5,10,11 is the free spring length, is the SMA wire diameter, is the SMA spring diameter, is the number of active coils in the spring is the displacement of the SMA spring, and G is the shear modulus. The spring index C is defined as the ratio of the spring diameter to the wire diameter (C = D/d).…”

“…2,10,11 SMA springs have so far been mainly investigated in terms of the parameter relationships such as the relationships between the generated force and the displacement, between the generated force and the input power, and between the displacement and the input power. 4,11,15 However, the relationship between the maximum power or power density and the input power has not been investigated. In the present study, the maximum power density of an SMA spring was evaluated with respect to the input power.…”