Metal muscles and nerves—a self-sensing SMA-actuated hand concept

Abstract

Bio-inspired hand-like grippers actuated by Shape Memory Alloy (SMA) wires represent an emerging new technology with potential applications in many different fields, ranging from industrial assembly processes to biomedical systems. The inherently high energy density makes SMAs a natural choice for compact, lightweight, and silent actuator systems capable of producing a high amount of work, such as hand prostheses or robotic systems in industrial human/machine environments. In this work, a concept for a compact and versatile gripping system is developed, in which SMA wires are implemented as antagonistic muscles actuating an artificial hand with three fingers. In order to combine high gripping force with sufficient actuation speed, the muscle implementation pursues a multi-wire concept with several 0.1 mm diameter NiTi wires connected in parallel, in order to increase the surface-to-volume ratio for accelerated cooling. The paper starts with an illustration of the design concept of an individual 3-phalanx-finger, along with kinematic considerations for optimal placement of SMA wires. Three identical fingers are subsequently fabricated via 3D printing and assembled into a hand-like gripper. The maximum displacement of each finger phalanx is measured, and an average phalanxes dynamic responsiveness is evaluated. SMA self-sensing is documented by experiments relating the wires change in resistance to the finger motion. Several finger force measurements are also performed. The versatility of the gripper is finally documented by displaying a variety of achievable grasping configurations.

Soft Robotic Grippers

“…Furthermore, miniaturization could be achieved by substituting electromagnetic motors with more compact actuators, such as smart materials. In this regard, researchers have showed the integration of shape memory alloys into tendon‐driven fingers and grippers …”

“…One approach to building SMA‐based adaptive grippers consists in combining them with flexible beams and hinges . Simone et al developed a prosthetic gripper made of 3D printed tendon‐driven structures mimicking the shape of the human hand. The device has three fingers that can be actuated independently enabling grasping and holding a coffee cup, a screwdriver, a pencil, and a rectangular box.…”

A Soft Five-Fingered Hand Actuated by Shape Memory Alloy Wires: Design, Manufacturing, and Evaluation

“…Each finger is designed in order to achieve the desired motion range by exploiting a SMA strain of only 3.5%, which represents the safe value for high lifetime (Fumagalli et al, 2009). The SMA wires dimensioning is obtained by means of kinematic and dynamic models formulated in Simone et al (2017Simone et al ( , 2019.…”

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“…During the contraction, each SMA wire changes its electrical resistance according to the current length. Therefore, it is possible to relate its change in resistance to the finger motion and rotation (Simone et al, 2017). According to this behavior, the SMA wires act also as nerves.…”

“…Over the past years, several rigid hand structures driven by SMA wires have been developed (Bundhoo et al, 2009;Lee et al, 2012;Andrianesis and Tze, 2015;Simone et al, 2017). However, so far, none of them can be considered advanced enough to support amputees in typical real life operations, mainly due to their limited performance in terms of dexterity and speed (Kyberd et al, 2004;Lee et al, 2012).…”