Soft pressure sensors are one class of the essential devices for robotics and wearable device applications. Despite the tremendous progress, sensors that can reliably detect both positive and negative pressures have not yet been demonstrated. In this paper, a soft capacitive pressure sensor, made using a convenient and low-cost screen-printing process that can reliably detect both positive and negative pressures from −60 to 20 kPa, is reported. The sensor is made with an Ecoflex-0030 dielectric layer, conductive and stretchable poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (with ionic additives) electrodes, and polydimethylsiloxane encapsulation layers. Air gaps are designed and incorporated into the dielectric layer to significantly enhance the sample deformation and pressure response especially to negative pressure. The sensor exhibits repeatable response for thousands of cycles, even under bending or stretching conditions. Lastly, to demonstrate the practical application, a 12 × 12-pixel sensor array that can automatically measure both positive and negative pressure distributions has been reported under −20 and 10 kPa.

The field of soft robotics has seen increasing interest and developments in recent years. Stiffness tuning is a desirable characteristic for soft robots since it enables adaptively modulating the load-bearing capability, shape, and locomotion behavior of the robots. In this article a compact and cost-effective mechanism for stiffness tuning is proposed based on a three-dimensional printed conductive polylactic acid (CPLA) material, and its potential in soft robotics is demonstrated through a soft pneumatic actuator (SPA) capable of stiffness and shape modulation. In particular, the conductive nature of the CPLA material allows convenient control of temperature and stiffness through Joule heating. Mechanical, thermoplastic, and electrical properties of the CPLA are first characterized. The material shows 98.6% reduction of Young's modulus, from 1 GPa at room temperature (25°C) to 13.6 MPa at 80°C, which is fully recovered after the material is cooled down to its initial temperature, and its glass transition temperature is 55°C, at which its Young's modulus is at 60% of that under room temperature. The experimentally identified material parameters are then used in finite-element modeling and simulation to investigate the behavior of a SPA integrated with a CPLA layer. A soft actuator with three virtual joints enabled by CPLA is prototyped, and bending experiments are conducted to both demonstrate the effectiveness of stiffness tuning and shape control and support the efficacy of the finite element model. Finally, a gripper composed of two soft actuators as fingers is fabricated to demonstrate localized gripping posture and the ability to carry load in a desired locked posture even when the pressure input is turned off, after the CPLA is cooled down.

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Soft robotics is a recent trend in engineering that seeks to create machines that are soft, compliant, and capable of withstanding damage, wear and high stress. Soft pneumatic actuators (SPAs) are a key element of soft robots, and their elastomeric substrate enables generation of sophisticated motion with simple controls. Although several methods for fabrication, material selection, and structure design have been investigated for the construction of SPAs, limited attention has been paid to the integration of distributed sensors for performing localized measurement. Carbon nanotubes (CNTs) are molecular-scale tubes of carbon atoms with remarkable mechanical and electronic properties, showing potential application in sensing devices. In this paper, we present the design, fabrication, and testing of a novel type of CNT-based sensor array combined with silver nanowires for measuring localized strain along the bottom layer of a SPA. Simulation and experimentation have been performed in order to analyze the soft actuator deformation during bending. The results demonstrate the promise of the proposed SPA with integrated strain sensing, which lays groundwork for a myriad of applications in grasping, manipulation, and bioinspired locomotion.