A Novel Continuum Robot With Stiffness Variation Capability Using Layer Jamming: Design, Modeling, and Validation

Abstract

This paper presents a novel continuum robot (OctRobot-I) that has controllable stiffness variation capability in both the transverse and axial directions. Robot design, stiffness variation analysis and experimental testing are discussed in detail. Stiffness models based on the Euler-Bernoulli beam theory are developed, and then four static deflection cases are analysed. Experiments are conducted with two types of layer jamming sheaths (overlap numbers n = 3, 5) and four different vacuum pressures (0kPa, 25kPa, 50kPa, 75kPa) at three different bending angles (0°, 90°, 180°). The results demonstrate that the stiffness changing tendency is in compliance with the derived models and show that the robot has a good stiffness variable capability. With the jamming sheath of n = 3, the stiffness ranges (ratios) are 36.4 to 241.7 N/m (6.6) and 92.9 to 19.3×10 3 N/m (207.8) in the transverse and axial directions, respectively. With the jamming sheath of n = 5, the stiffness ranges (ratios) are 65.7 to 398.3 N/m (6.1) and 106.7 to 20.8×10 3 N/m (194.9) in the transverse and axial directions, respectively. Additionally, the actuating and gripping experiments demonstrate that this robot has good performance in real-world applications.

A Review of Mechanisms to Vary the Stiffness of Laminar Jamming Structures and Their Applications in Robotics

“…There are multiple variations of vacuum-pressure-activated LJ that have been developed to be applied in robotics [1,7,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. These variations will be described in Section 4.…”

“…Figure 10c illustrates another example of a continuum robot formed by LJSs based on vacuum pressure. This continuum robot, named "OctRobot-I" [26], consists of a support spine that has multiple segments, an inner membrane, a jamming sheath, and an outer membrane. The jamming sheath consists of two tubular latex membranes that cover a double-side flap pattern that is similar to the flap structure described in [15].…”

Tendon-Driven Continuum Robots for Aerial Manipulation—A Survey of Fabrication Methods

“…In general, the joint is designed to accommodate a tendon guide structure with eyelets, and they are supported with springs between every two joints radially. Similar to vertebrae-type cross-universal joint robots, springs are typically mounted in a way that the tendons are routed through them [145][146][147]. A globe joint-based manipulator could be less stable and exhibits low stiffness.…”

“…A globe joint-based manipulator could be less stable and exhibits low stiffness. Incorporating helical springs [145][146][147] or flexure hinge [148] can increase the bending stiffness and stability of the manipulator. A CAD model shown in Figure 9a provides a general structure of globe joint.…”

“…When multiple springs are connected in series, the support disks can act as the connection interface between two subsequent springs [125,146]. When connecting multiple springs in series to produce a single backbone, the support disks can be made with longitudinally extended profiles with threads.…”