Tendon-Driven Gripper with Variable Stiffness Joint and Water-Cooled SMA Springs

Abstract

In recent years, there has been an increase in the development of medical robots to enhance interventional MRI-guided therapies and operations. Magnetic resonance imaging (MRI) surgical robots are particularly attractive due to their ability to provide excellent soft-tissue contrast during these procedures. This paper describes a novel design for a tendon-driven gripper that utilizes four shape memory alloy (SMA) spring actuators and variable stiffness joints controlled by SMA coils for use in MRI surgical robot applications. The contact force of the gripper link is determined by the mechanical properties of the SMA spring actuators (SSA) and the angle of each linkage, and the joint stiffness can be adjusted by varying the electrical current applied to the SMA coil. To enhance the efficiency of the SSAs, a new cooling system using water has been proposed and implemented. To validate the effectiveness of our proposed gripper, we conducted three types of experiments, namely, a single SSA experiment, a single SMA coil experiment, and a whole gripper experiment. The experimental results demonstrate that the proposed water-cooling system can effectively solve temperature issues of SMA, and the joint stiffness in the austenite state is higher than that in the martensite state. Moreover, our experiments show that the presented gripper is capable of grasping and holding objects of various shapes and weights.

Variable stiffness soft robotic gripper: design, development, and prospects

“…Consequently, many soft grippers and continuum bodies have increasingly adopted cable-driven actuators, with researchers fabricating fixtures driven by flexible cables embedded in silicone, elastic bags, textiles, and origami structures [2]. The cable-driven actuators, known for their controllability and responsiveness, have rapidly advanced the field of intelligent control in soft robotics [63,69,163]. However, the additional requirements for power sources, such as motors or pneumatic actuators, unavoidably increase the system's burden, resulting in a cumbersome weight.…”

“…Currently, the superior materials for stiffness adjustment in soft robotics include low-melting-point alloys (LMPAs) [9], polylactic acid (PLA) [120], polycaprolactone (PCL) [57], SMA [7,98,104], conductive thermoplastic starch polymers (CTPS) [122], SMPs [25,71,102,133], and wax [289]. These materials find application in various functional components of soft robots, such as programming functionality [290], elastic functionality [63], adhesion functionality [25], and load-bearing functionality [289,291]. While these technologies offer distinct advantages, they also have certain drawbacks, notably the need for external energy to drive stiffness changes and relatively slow response and transition speeds, posing challenges to efficiency and safety.…”

“…Based on the statistical data presented in the chart, it is evident that most research on soft robotic grippers emphasizes adaptability, particularly in the case of SC and FBC gripping methods, which have demonstrated remarkable results. In contrast, studies focusing on accuracy are primarily confined to intelligent variable stiffness grasping [63,68]. The primary reason is that soft robotic grippers do not necessitate precise control, as the gripper's adaptability compensates for operational errors.…”

Universally Grasping Objects with Granular—Tendon Finger: Principle and Design

“…In recent times, hybrid grippers have emerged as a design approach to inherit the soft and rigid properties of the previously mentioned soft and traditional grippers. The authors of [ 42 ] developed a hybrid gripper with two rigid fingers actuated by the shape memory alloy (SMA) springs. Li [ 43 ] proposed a gripper in which each finger has a soft–rigid actuator for flexibly adapting multiple objects.…”

Design and implementation of shape‐adaptive and multifunctional robotic gripper

“…Generally, robotic grippers are classified as classical rigid grippers and soft grippers (Birglen & Schlicht, 2018; Shintake et al, 2018; Wang et al, 2023; Zhang et al, 2020). The rigid gripper/hands are classified further into two main categories: wire driven, and linkage‐driven (ACAR et al, 2021; Cianciotto et al, 2021; Do et al, 2023; Kang, Seo, Yoon, et al, 2019; Kashef et al, 2020; Ko, 2020; Nate et al, 2022; Yoon & Choi, 2021). From an actuation point of view in rigid grippers, there are two major types of grippers: fully actuated (Hermann et al, 2019; Mańkowski et al, 2020) and under‐actuated gripper (Courchesne et al, 2023; Glick et al, 2020; Kang et al, 2021; Mouazé & Birglen, 2022).…”