Shape Memory Alloys in Continuum and Soft Robotic Applications

Abstract

Continuum robots are inspired by biological trunks, snakes and tentacles. Unlike conventional robot manipulators, there are no rigid structures or joints. Advantageous is the ease of miniaturization combined with high dexterity, since limiting components such as bearings or gears can be omitted. Most currently used actuation elements in continuum robots require a large drive unit with electric motors or similar mechanisms. Contrarily, shape memory alloys (SMAs) can be integrated into the actual robot. The actuation is realized by applying current to the wires, which eliminates the need of an additional outside drive unit. In the presented study, SMA actuator wires are used in variously scaled continuum robots. Diameters vary from 1 to 60 mm and the lengths of the SMA driven tentacles range from 75 to 220 mm. The SMAs are arranged on an annulus in a defined distance to the neutral fiber, whereby the used cores vary from superelastic NiTi rods to complex structures and also function as restoring unit. After outlining the theoretical basics for the design of an SMA actuated continuum robot, the design process is demonstrated exemplarily using a guidewire for cardiac catheterizations. Results regarding dynamics and bending angle are shown for the presented guidewire.

Systematic Methodology for an Optimized Design of Shape Memory Alloy‐Driven Continuum Robots

“…Schematic drawing of a continuum robotic structure consisting of a core element as restoring force, referred to as neutral fiber, a single SMA actuator wire, and spacer disks. a) The idle state of the structure, [11,42] b) the activated state with fully actuated SMA wire for a continuously guided SMA actuator. [11,42] c) The continuum robotic structure with a partially constraint SMA actuator wire (red), while d) highlights one single section bounded by two spacer disks.…”

“…Common structural designs include concentric-tube robots, based on multiple precurved elastic tubes nested inside each other, [8,9] as well as single backbone continuum robots, in which an elastic element structure supports the structure and acts as a restoring force, which brings back the robot to its initial state after actuation. [7,10,11] The actuation strategy can be categorized as intrinsic or extrinsic, depending on where the actuation takes place with respect to the structure. Intrinsic actuation refers to actuation within the bending structure, while the extrinsic actuation method takes place outside the moving robot and requires suitable mechanisms to transmit the force to the structure.…”

“…Previous work from the authors mainly focused on the mechanical design of SMA-driven continuum robots for different applications, the unique assembly procedure required to determine the suitable prestrain of the SMA wires while assembling as well as exemplary validation experiments. [7,11,37] The calculations presented in these publications are based on a highly simplified kinematic model neither incorporating the SMA characteristics nor accounting for multiple SMA actuators affecting each other.…”

Design and analysis of a continuum manipulator for use in narrow spaces

“…However, the elephant trunk manipulator has lower control accuracy and load capacity. Goergen et al (2020) put forward a serpentine continuum robot for pipeline detection in nuclear industry to improve its detection efficiency and safety, but with a larger structural size. In addition, a new continuum robot used for aircraft turbine engine detection was presented, which can realize the inspection of engine blades in situ and avoid the tedious disassembly process (Dong et al , 2016; Zhao et al , 2015) developed a high-stiffness serpentine continuum manipulator for single-port laparoscopic surgery systems.…”

A Novel Underactuated Continuum Robot With Shape Memory Alloy Clutches

“…This means that they are highly flexible and can navigate in cluttered environments such as gas turbines [1], [2], nuclear facilities [3], [4], and the human body [5]. Multiple design solutions have been proposed since the 1960s, [6], [7], the majority of which belong to the following three categories: external actuation [8], [9], [10] intrinsic actuation [11], [12], and concentric tubes [13], [14], [15]. CRs with intrinsic actuation have actuators embedded in the snake body structure, resulting in heavy and bulky designs with higher payloads but with a reduced inner lumen for the delivery of tools to the tip.…”