Evaluation of 3D Printed Soft Robots in Radiation Environments and Comparison With Molded Counterparts

Robots have an important role during inspection, clean-up, and sample collection in unstructured radiation environments inaccessible to humans. The advantages of soft robots, such as body morphing, high compliance, and energy absorption during impact, make them suitable for operating under extreme conditions. Despite their promise, the usefulness of soft robots under a radiation environment has yet to be assessed. In this work, we evaluate the effectiveness of soft robots fabricated from polydimethylsiloxane (PDMS), a common fabrication material, under radiation for the first time. We investigated gamma-induced mechanical damage in the PDMS materials' mechanical properties, including elongation, tensile strength, and stiffness. We selected three radiation environments from the nuclear industry to represent a wide range of radiation and then submerged a 3D printed hexapus robot into a radiation environment to estimate its operation time. Finally, to test the reliability of the 3D printed soft robots, we compared their performances with molded counterparts. To analyze performance results in detail, we also investigated dimensional errors and the effects of fabrication methods, nozzle size, and print direction on the stiffness of PDMS material. Results of this study show that with increasing exposure to gamma irradiation, the mechanical properties of PDMS decrease in functionality but are minimally impacted up to 20 kGy gamma radiation. Considering the fractional changes to the PDMS mechanical properties, it is safe to assume that soft robots could operate for 12 h in two of the three proposed radiation environments. We also verified that the 3D printed soft robots can perform better than or equal to their molded counterparts while being more reliable

Additively Manufactured Hemp Fibers Reinforced Silicone

Additive manufacturing provides a broad range of applications and offers significant advantages over conventional molding methods. One of the advantages with additive manufacturing is its high efficiency of feedstock utilization. Although, the most common polymer and metallic composites feedstocks used within additive manufacturing are normally obtained from inefficient, and non-sustainable sources. This contribution explores the 3D printability of a new material based on silicone and hemp fibers from renewable, sustainable and non-petroleum resources with the aim of enhancing mechanical properties of silicone. To improve composites printing technology, it's required to discover the desired mixing composition. At first, to determine the proper amount of fibers, samples were fabricated by molding. Incorporation of fibers improved the mechanical properties of the silicone matrix. However, fibers distribution within the matrix adversely affected the printability of silicone due to the resulting high viscosity. Therefore, behavior of the new manufactured material with varying fiber and solvent composition was analyzed using rheological study to obtain a printable material. The composition containing 15 (wt\%) hemp fibers and 20 (wt\%) solvent with enhanced mechanical properties displayed desirable printability. Moreover, the mechanical properties of the 3D printed and molded samples were studied. The results revealed that 3D printed samples outperformed the molded counterparts in tensile strength and hardness. Finally, a simple gripper and honeycomb structure were fabricated to demonstrate the application of the developed material

3D Printed Soft Robotic Hand

Soft robotics is an emerging industry, largely dominated by companies which hand mold their actuators. Our team set out to design an entirely 3D printed soft robotic hand, powered by a pneumatic control system which will prove both the capabilities of soft robots and those of 3D printing. Through research, computer aided design, finite element analysis, and experimental testing, a functioning actuator was created capable of a deflection of 2.17” at a maximum pressure input of 15 psi. The single actuator was expanded into a 4 finger gripper and the design was printed and assembled. The created prototype was ultimately able to lift both a 100-gram apple and a 4-gram pill, proving its functionality in two prominent industries: pharmaceutical and food packing

Direct 3D printing of a two-part silicone resin to fabricate highly stretchable structures

The direct ink writing (DIW) method of 3D-printing liquid resins has shown promising results in various applications such as flexible electronics, medical devices, and soft robots. A cost-effective extrusion system for a two-part high-viscous resin is developed in this article to fabricate soft and immensely stretchable structures. A static mixer capable of evenly mixing two viscous resins in an extremely low flow regime is designed based on the required mixing performance through a series of biphasic computational fluid dynamics analyses. The printing parameters of the extrusion system are determined empirically, and the mechanical properties of the printed samples are compared to their molded counterparts. Furthermore, some potential applications of the system in soft robotics and medical training are demonstrated. This research provides a clear guide for utilizing DIW to 3D print highly stretchable structures

Additively Manufactured Hemp Fibers Reinforced Silicone

Additive manufacturing provides a broad range of applications and o�ers significant advantages over conventional molding methods. One of the advantages with additive manufacturing is its high e�ciency of feedstock utilization. Although, the most common polymer and metallic composites feedstocks used within additive manufacturing are normally obtained from ine�cient, and non-sustainable sources. This contribution explores the 3D printability of a new material based on silicone and hemp �bers from renewable, sustainable and non-petroleum resources with the aim of enhancing mechanical properties of silicone. To improve composites printing technology, it's required to discover the desired mixing composition. At �rst, to determine the proper amount of �bers, samples were fabricated by molding. Incorporation of �bers improved the mechanical properties of the silicone matrix. However, �bers distribution within the matrix adversely a�ected the printability of silicone due to the resulting high viscosity. Therefore, behavior of the new manufactured material with varying �ber and solvent composition was analyzed using rheological study to obtain a printable material. The composition containing 15 (wt%) hemp �bers and 20 (wt%) solvent with enhanced mechanical properties displayed desirable printability. Moreover, the mechanical properties of the 3D printed and molded samples were studied. The results revealed that 3D printed samples outperformed the molded counterparts in tensile strength and hardness. Finally, a simple gripper and honeycomb structure were fabricated to demonstrate the application of the developed material

3D Printable Sensorized Soft Gelatin Hydrogel for Multi-Material Soft Structures

The ability to 3D print soft materials with integrated strain sensors enables significant flexibility for the design and fabrication of soft robots. Hydrogels provide an interesting alternative to traditional soft robot materials, allowing for more varied fabrication techniques. In this work, we investigate the 3D printing of a gelatin-glycerol hydrogel, where transglutaminase is used to catalyse the crosslinking of the hydrogel such that its material properties can be controlled for 3D printing. By including electron-conductive elements (aqueous carbon black) in the hydrogel we can create highly flexible and linear soft strain sensors. We present a first investigation into adapting a desktop 3D printer and optimizing its control parameters to fabricate sensorized 2D and 3D structures which can undergo >300% strain and show a response to strain which is highly linear and synchronous. To demonstrate the capabilities of this material and fabrication approach, we produce some example 2D and 3D structures and show their sensing capabilities

A 3D-Printed Omni-Purpose Soft Gripper

Numerous soft grippers have been developed based on smart materials, pneumatic soft actuators, and underactuated compliant structures. In this article, we present a three-dimensional (3-D) printed omni-purpose soft gripper (OPSOG) that can grasp a wide variety of objects with different weights, sizes, shapes, textures, and stiffnesses. The soft gripper has a unique design that incorporates soft fingers and a suction cup that operate either separately or simultaneously to grasp specific objects. A bundle of 3-D-printable linear soft vacuum actuators (LSOVA) that generate a linear stroke upon activation is employed to drive the tendon-driven soft fingers. The support, fingers, suction cup, and actuation unit of the gripper were printed using a low-cost and open-source fused deposition modeling 3-D printer. A single LSOVA has a blocked force of 30.35 N, a rise time of 94 ms, a bandwidth of 2.81 Hz, and a lifetime of 26 120 cycles. The blocked force and stroke of the actuators are accurately predicted using finite element and analytical models. The OPSOG can grasp at least 20 different objects. The gripper has a maximum payload-to-weight ratio of 7.06, a grip force of 31.31 N, and a tip blocked force of 3.72 N

An agile multi-body additively manufactured soft actuator for soft manipulators

With the introduction of collaborative robots in production environments, the harm to workers by using traditional robots with rigid links is inherent. A new generation of robots made from flexible soft materials that decreases collision danger by self-deforming actions has been proposed as a promising solution for the human-robot collaboration environments. Recently, by the development of additive manufacture of elastic soft materials, new design opportunities arise for these so-called soft robots. However, robustness that is required for production environments is still not achieved. This paper presents a design approach of a fully additively manufactured three-axis soft pneumatic actuator. For its use in flexible soft robotic manipulator systems, design guidelines, a direct 3D printing process with elastic materials and a low-level PLC semi-automated pressure regulation control system are presented. To validate the proposed design, the actuator is manufactured and tested for maximum contact force, bending motion reaction and its signal response.Con la introducción de robots colaborativos en entornos de producción, el daño a los trabajadores por el uso de robots tradicionales con enlaces rígidos es inherente. Se ha propuesto una nueva generación de robots hechos de materiales blandos flexibles que reduce el peligro de colisión mediante acciones de autodeformación como una solución prometedora para los entornos de colaboración humano-robot. Recientemente, con el desarrollo de la fabricación aditiva de materiales blandos elásticos, surgen nuevas oportunidades de diseño para estos llamados robots blandos. Sin embargo, aún no se logra la robustez que se requiere para los entornos de producción. Este documento presenta un enfoque de diseño de un actuador neumático blando de tres ejes fabricado de forma totalmente aditiva. Para su uso en sistemas de manipuladores robóticos blandos flexibles, se presentan pautas de diseño, un proceso de impresión 3D directo con materiales elásticos y un sistema de control de regulación de presión semiautomatizado PLC de bajo nivel. Para validar el diseño propuesto, el actuador se fabrica y prueba para la fuerza de contacto máxima, la reacción de movimiento de flexión y su respuesta de señal

Development of a Fabrication Technique for Soft Planar Inflatable Composites

Soft robotics is a rapidly growing field in robotics that combines aspects of biologically inspired characteristics to unorthodox methods capable of conforming and/or adapting to unknown tasks or environments that would otherwise be improbable or complex with conventional robotic technologies. The field of soft robotics has grown rapidly over the past decade with increasing popularity and relevance to real-world applications. However, the means of fabricating these soft, compliant and intricate robots still poses a fundamental challenge, due to the liberal use of soft materials that are difficult to manipulate in their original state such as elastomers and fabric. These material properties rely on informal design approaches and bespoke fabrication methods to build soft systems. As such, there are a limited variety of fabrication techniques used to develop soft robots which hinders the scalability of robots and the time to manufacture, thus limiting their development. This research focuses towards developing a novel fabrication method for constructing soft planar inflatable composites. The fundamental method is based on a sub-set of additive manufacturing known as composite layering. The approach is designed from a planar manner and takes layers of elastomeric materials, embedded strain-limiting and mask layers. These components are then built up through a layer-by-layer fabrication method with the use of a bespoke film applicator set-up. This enables the fabrication of millimetre-scale soft inflatable composites with complex integrated masks and/or strain-limiting layers. These inflatable composites can then be cut into a desired shape via laser cutting or ablation. A design approach was also developed to expand the functionality of these inflatable composites through modelling and simulation via finite element analysis. Proof of concept prototypes were designed and fabricated to enable pneumatic driven actuation in the form of bending soft actuators, adjustable stiffness sensor, and planar shape change. This technique highlights the feasibility of the fabrication method and the value of its use in creating multi-material composite soft actuators which are thin, compact, flexible, and stretchable and can be applicable towards real-world application

Design, Modeling and Control of a 3D Printed Monolithic Soft Robotic Finger with Embedded Pneumatic Sensing Chambers

IEEE This paper presents a directly 3D printed soft monolithic robotic finger with embedded soft pneumatic sensing chambers (PSC) as position and touch sensors. The monolithic finger was fabricated using a low-cost and open-source fused deposition modeling (FDM) 3D printer that employs an off-the-shelf soft and flexible commercially available thermoplastic polyurethane (TPU). A single soft hinge with an embedded PSC was optimized using finite element modeling (FEM) and a hyperelastic material model to obtain a linear relationship between the internal change in the volume of its PSC and the corresponding input mechanical modality, to minimize its bending stiffness and to maximize its internal volume. The soft hinges with embedded PSCs have several advantages, such as fast response to very small changes in their internal volume (~0.0026ml/°), linearity, negligible hysteresis, repeatability, reliability, long lifetime and low power consumption. Also, the flexion of the soft robotic finger was predicted using a geometric model for use in real-time control. The real-time position and pressure/force control of the soft robotic finger were achieved using feedback signals from the soft hinges and the touch PSC embedded in the tip of the finger. This study contributes to the development of seamlessly embedding optimized sensing elements in the monolithic topology of a soft robotic system and controlling the robotic system using the feedback data provided by the sensing elements to validate their performance