3D Printed Soft Pneumatic Bending Sensing Chambers for Bilateral and Remote Control of Soft Robotic Systems

This work reports on soft pneumatic bending sensing chambers that are directly 3D printed without requiring any support material and postprocessing using a low-cost and open-source fused deposition modeling (FDM) 3D printer and a commercially available soft thermoplastic polyurethane (TPU). These bending sensing chambers have multiple advantages including very fast response to any change in their internal volume, linearity, negligible hysteresis, repeatability, reliability, stability over time, long lifetime and very low power consumption. The performance of these soft sensing chambers is accurately predicted and optimized using finite element modeling (FEM) and a hyperelastic material model for the TPU used for 3D printing. The soft sensing chambers are tailored to several soft robotic applications such as bending sensors for bilateral control of soft robotic fingers and structures and soft wearable gloves for remote control of soft monolithic robotic fingers and adaptive grippers.

I. Introduction

Soft robotic concepts and devices are ideal for developing safe human-machine interfaces that are made of highly deformable and soft materials [1] . Recently, diverse soft untethered robots were developed to prove and demonstrate that such robots are more suitable in some robotic areas compared to traditional rigid-bodied robots [2] . Conventional robotic systems are made of stiff and rigid materials and components and therefore cannot operate safely alongside humans and in unstructured environments [3] . Ideally, an entirely soft robot should be made completely of soft and flexible materials that can undergo and sustain large deformations repeatedly [4] . Soft robots require dexterous soft actuators, robust soft sensors and electronics, resilient deformable and flexible structures and compliant power sources (i.e., compliant batteries) [4] . One of the challenges of soft robotics is the development of functional soft and deformable sensors. Soft robotic sensors must be able to sustain large and repeatable deformations and provide acceptable performance. Several resistive strain sensors were developed for soft robots including flex sensors [5] , [6] , conductive ks [7 – 9] , ionic conductive liquids [10] , liquid metals [11 – 13] , fabrics and textiles [14 , 15] , resistive 3D printable thermoplastics [16] , soft and elastic compressive foam sensors [17] and ultra-thin piezoresistive sensors [18] combined with 3D printable soft monolithic structures [19] . Also, capacitive soft sensors were developed for pressure sensing [20 , 21] , tactile sensing [22] and strain sensing [23] in several robotic applications. Similarly, strain, curvature, texture and force optical sensors were developed for use in soft prosthetic hands [24] . Some of these sensors have several limitations such as hysteresis, drift, short lifetime or slow response in addition to their laborious manufacturing methods which require multiple fabrication steps before their integration in soft robotic systems. Figure 1.

Soft pneumatic bending sensing chambers computer-aided design (CAD) models and dimensions. (a) Soft 3D printed bending chamber. (b) Soft 3D printed bending chamber with the solid air pressure sensor attached. (c) Top view of the assembly. (d) Soft sensor dimensions: 1: 34.0, . All dimensions are in mm. (e) Isometric view of the assembly. (f) A cross-sectional view along the length of the soft 3D printed chamber.