A Modular, Tendon Driven Variable Stiffness Manipulator with Internal Routing for Improved Stability and Increased Payload Capacity

Abstract

Stability and reliable operation under a spectrum of environmental conditions is still an open challenge for soft and continuum style manipulators. The inability to carry sufficient load and effectively reject external disturbances are two drawbacks which limit the scale of continuum designs, preventing widespread adoption of this technology. To tackle these problems, this work details the design and experimental testing of a modular, tendon driven bead-style continuum manipulator with tunable stiffness. By embedding the ability to independently control the stiffness of distinct sections of the structure, the manipulator can regulate it's posture under greater loads of up to 1kg at the end-effector, with reference to the flexible state. Likewise, an internal routing scheme vastly improves the stability of the proximal segment when operating the distal segment, reducing deviations by at least 70.11%. Operation is validated when gravity is both tangential and perpendicular to the manipulator backbone, a feature uncommon in previous designs. The findings presented in this work are key to the development of larger scale continuum designs, demonstrating that flexibility and tip stability under loading can co-exist without compromise.

Figures (8)

• Figure 1: The modular manipulator design (a) in a horizontal configuration, highlighting the flexible hinges (b). Black beads indicate the tip of each segment and have increased radial surface area for the addition of motion tracking markers to aid motion capture.
• Figure 2: Overview of the modular design, showing the (a) compression of flexible hinges, (b) construction of successive beads, (c) discretised motion of successive beads and (d) internal routing of the distal tendons at the transition point between segments.
• Figure 3: Piecewise Constant Curvature (PCC) kinematic model of a single spatial segment, where the dashed lines represent the bending plane.
• Figure 4: PCC behaviour validation of the manipulator design obtained via the MoCap. Shown is the recorded and modelled planar tip positions for the (a)(c) proximal segment and (b)(d) distal segment, relative to the base.
• Figure 5: Example of the temporally recorded data for an instance where $\theta_{2}=60^{o}$, showing (a) the three components of angular rotation of the distal segment varying for each pose being performed in sequence, and (b) the effect on the tip position of the proximal segment for both externally and internally routed cabling. Each shaded region indicates the poses displayed in Fig. \ref{['stiff_vs_flex']}(a)-(e) in sequential order.