Malleable Robots: Reconfigurable Robotic Arms with Continuum Links of Variable Stiffness

TL;DR

This work tackles the challenge of task-driven manipulation with low-DOF, morphologically reconfigurable arms by introducing a 2-DOF malleable robot whose topology can be reconfigured via a variable-stiffness link. It develops a distance-geometry framework to model the workspace and to perform forward and inverse kinematics, enabling topology optimization from a single end-effector target and a distal orientation. The authors demonstrate topology reconfiguration and joint recalibration, with experimental evaluation showing sub-10 mm alignment accuracy after practice and useful payload-handling capabilities, highlighting practical viability while noting joint-axis alignment and stiffness termination as critical factors. The approach offers a path toward cheaper, lighter, and more versatile reconfigurable robots for unstructured environments, with potential extensions to AR-assisted guidance and autonomous reconfiguration.

Abstract

Through the implementation of reconfigurability to achieve flexibility and adaptation to tasks by morphology changes rather than by increasing the number of joints, malleable robots present advantages over traditional serial robot arms in regards to reduced weight, size, and cost. While limited in degrees of freedom (DOF), malleable robots still provide versatility across operations typically served by systems using higher DOF than required by the tasks. In this paper, we present the creation of a 2-DOF malleable robot, detailing the design of joints and malleable link, along with its modelling through forward and inverse kinematics, and a reconfiguration methodology that informs morphology changes based on end effector location -- determining how the user should reshape the robot to enable a task previously unattainable. The recalibration and motion planning for making robot motion possible after reconfiguration are also discussed, and thorough experiments with the prototype to evaluate accuracy and reliability of the system are presented. Results validate the approach and pave the way for further research in the area.

Figures (24)

• Figure 1: A 2-DOF malleable robot visual description of capability, demonstrating the possible topology types of the malleable robot.
• Figure 2: The developed two-degree-of-freedom (DOF) malleable robot arm, showing various topology configurations it can achieve. A PUMA-like configuration is shown in foreground.
• Figure 3: Exploded CAD of the two revolute joints, (a) joint 1 and (b) joint 2, of the malleable robot, showing highlighted cable and vacuum pass-through.
• Figure 4: Comparison of the layer jamming termination methods: (a) A typical termination performed by trimming the layers to the desired length, (b) the proposed layer termination method with added passive layers, (c) cross-sectional view of the malleable link showing the layer jamming area of interest, and (d) a plot of overlapped layers against distance from link end, comparing the typical termination (red) and the proposed termination with added passive layers (blue). In the typical design a decrease in layers towards the link end is shown, as well as the misalignment of layers resulting in the oscillation between 10--11 overlapped layers far from the link end.
• Figure 5: Partially constructed malleable link highlighting the design of the variable stiffness components.