Grasping and Rolling In-plane Manipulation Using Deployable Tape spring Appendages

TL;DR

This work addresses the workspace-volume tradeoff of rigid robotic arms by introducing bidirectional tape-spring appendages integrated into a two-digit GRIP-tape gripper, enabling large manipulation workspaces within a compact footprint. The authors develop and characterize the GRIP-tape design, including bidirectional tape-spring fabrication, seven-motor actuation, and kinematic models (inverse and forward) validated by motion capture, along with force sensing and automatic gripping capabilities. Key contributions include extensive mechanical testing (3-point bend, fatigue over 4000 cycles), quantitative workspace and grip-force analysis, and demonstrations of grasping, translating, rotating in place, and multi-object conveyance with passive compliance and force-feedback rotation control. The resulting extensible, soft-contact gripper offers safe interaction, self-recoverability, and applicability to remote environments such as space, deep-sea, and agriculture, illustrating a new direction for SCRAM-based deployable manipulators with potential for 3D motion and multi-axis object rotation in future work.

Abstract

Rigid multi-link robotic arms face a tradeoff between their overall reach distance (the workspace), and how compactly they can be collapsed (the storage volume). Increasing the workspace of a robot arm requires longer links, which adds weight to the system and requires a larger storage volume. However, the tradeoff between workspace and storage volume can be resolved by the use of deployable structures with high extensibility. In this work we introduce a bidirectional tape spring based structure that can be stored in a compact state and then extended to perform manipulation tasks, allowing for a large manipulation workspace and low storage volume. Bidirectional tape springs are demonstrated to have large buckling strength compared to single tape springs, while maintaining the ability to roll into a compact storage volume. Two tape spring structures are integrated into a bimanual manipulator robot called GRIP-tape that allows for object Grasping and Rolling In Planar configurations (GRIP). In demonstrations we show that the continuum kinematics of the tape springs enable novel manipulation capabilities such as simultaneous translation-rotation and multi-object conveyance. Furthermore, the dual mechanical properties of stiffness and softness in the tape springs enables inherent safety from unintended collisions within the workspace and soft-contact with objects. Our system demonstrates new opportunities for extensible manipulators that may benefit manipulation in remote environments such as space and the deep sea.

Figures (8)

• Figure 1: Functional basis, implementation, and demonstrated capabilities of the GRIP-tape extensible gripper. (A) An implementation of two tape spring appendages to form the GRIP-tape two-digit manipulator. (B) Capabilities of the tape spring gripper include the ability to interact with soft objects, translate objects over large distances in a 2D plane, and in-grasp manipulation including rolling and conveying objects. (C) Tape spring beams are capable of being rolled into compact spaces and extended over long-distances. (D) The beam stiffness is asymmetric in the case of unidirectional tape springs, and symmetric in bidirectional tape springs. (E) By bending the tape spring, a reconfigurable appendage is formed. The kinematics of this appendage are modeled as two rotation-prismatic joints coupled through an elastic spring.
• Figure 2: The bucking force of different configurations of the tape spring and results of the fatigue test. (A) Structure of bidirectional tape. (B) Results of 3-point bend test of different tapes. (C) 4000 cycles of fatigue test. (D) Buckling force $F_{max}$ (data and fitted curve) of different setups of tape spring with response to the distance between the fixed point and external force. (E), and (F) Trend of the buckling force and buckling angle.
• Figure 3: Kinematics and design of the GRIP-tape manipulator. (A) GRIP-tape is composed of a left and right digit. Each digit has independent control over the tip location denoted by the black dots. (B) The four insets show the basic modes of appendage control. (C) A schematic of the overall control inputs for the two tape spring appendages. (D) Representative model of the left-appendage with actuation inputs from two roller units ($\theta_1$, $\theta_2$) that control the left-right length of the appendage, and a rotational input ($\theta_4$) that controls the angle of the appendage.
• Figure 4: Demonstration of GRIP-tape appendage kinematics (A) The workspace of the left appendage. (B) Combined workspace of both appendages with the maximum gripping force computed from buckling measurements and indicated with a color map. (C) Inverese kinematics position error of the right digit tip location from over six trials. (D) Results from right digit tip location tracing over three trials with four different shapes. See movie S3 for video.
• Figure 5: Stiffness of the spring-like curve of a bent tape spring. (A) Curve fitting and comparison between the stiffness of bidirectional and unidirectional tapes. (B) Raw data of the loading and unloading loop of the bidirectional tape. (C) Soft pinch on an egg. (D) Young's modulus compared to other materials(Adapted from Rus2015).