Parallel Helix Actuators for Soft Robotic Applications.

James H Chandler,Keith L Obstein,Pietro Valdastri,Manish Chauhan,Nicolo Garbin

doi:10.3389/frobt.2020.00119

Abstract

Fabrication of soft pneumatic bending actuators typically involves multiple steps to accommodate the formation of complex internal geometry and the alignment and bonding between soft and inextensible materials. The complexity of these processes intensifies when applied to multi-chamber and small-scale (~10 mm diameter) designs, resulting in poor repeatability. Designs regularly rely on combining multiple prefabricated single chamber actuators or are limited to simple (fixed cross-section) internal chamber geometry, which can result in excessive ballooning and reduced bending efficiency, compelling the addition of constraining materials. In this work, we address existing limitations by presenting a single material molding technique that uses parallel cores with helical features. We demonstrate that through specific orientation and alignment of these internal structures, small diameter actuators may be fabricated with complex internal geometry in a single material—without- additional design-critical steps. The helix design produces wall profiles that restrict radial expansion while allowing compact designs through chamber interlocking, and simplified demolding. We present and evaluate three-chambered designs with varied helical features, demonstrating appreciable bending angles (>180°), three-dimensional workspace coverage, and three-times bodyweight carrying capability. Through application and validation of the constant curvature assumption, forward kinematic models are presented for the actuator and calibrated to account for chamber-specific bending characteristics, resulting in a mean model tip error of 4.1 mm. This simple and inexpensive fabrication technique has potential to be scaled in size and chamber numbers, allowing for application-specific designs for soft, high-mobility actuators especially for surgical, or locomotion applications.

Highlights

The compliant nature and large range of motion of soft robotic fluidic actuators engenders a wide application scope with significant research interest (Rus and Tolley, 2015; Laschi et al, 2016; Gorissen et al, 2017; Shintake et al, 2018; Chen et al, 2019; Gifari et al, 2019; Runciman et al, 2019)
In this paper we introduce, for the first time, the design concept of “Parallel Helix Actuators” (PHAs)
Within the following sections we introduce the PHA concept and describe the associated fabrication technique

Summary

Introduction

The compliant nature and large range of motion of soft robotic fluidic actuators engenders a wide application scope with significant research interest (Rus and Tolley, 2015; Laschi et al, 2016; Gorissen et al, 2017; Shintake et al, 2018; Chen et al, 2019; Gifari et al, 2019; Runciman et al, 2019). Through variation of the winding geometry, precise control over the actuator’s behavior is possible (Krishnan et al, 2012), and by combining actuators with differing fiber geometry in series, configurable trajectory matching may be achieved (Bishop-Moser and Kota, 2015; Connolly et al, 2015, 2017; Polygerinos et al, 2015; Kurumaya et al, 2018; Singh and Krishnan, 2020) Though effective, fabricating these actuators is complicated by the need for precision control of fiber path, tension, and adhesion (Agarwal et al, 2016), and resultant devices typically have reduced extensibility and flexibility relative to purely elastomeric structures (Rus and Tolley, 2015). To improve fabrication repeatability and design flexibility, Agarwal et al (2016) presented a molding approach with pre-formed, integrated reinforcement shells for single-step molding of bending and linear actuators, this approach does not readily extend to multi-chamber designs

Methods

Discussion

Conclusion