Field Of Soft Robotics Research Articles

Challenges and Perspectives in Scientific Publication of Robotics as an Interdisciplinary Field of Study

Challenges and Perspectives in Scientific Publication of Robotics as an Interdisciplinary Field of Study

Photoresponsive hydrogel-based soft robot: A review

Soft robots have received a lot of attention because of their great human-robot interaction and environmental adaptability. Most soft robots are currently limited in their applications due to wired drives. Photoresponsive soft robotics is one of the most effective ways to promote wireless soft drives. Among the many soft robotics materials, photoresponsive hydrogels have received a lot of attention due to their good biocompatibility, ductility, and excellent photoresponse properties. This paper visualizes and analyzes the research hotspots in the field of hydrogels using the literature analysis tool Citespace, demonstrating that photoresponsive hydrogel technology is currently a key research direction. Therefore, this paper summarizes the current state of research on photoresponsive hydrogels in terms of photochemical and photothermal response mechanisms. The progress of the application of photoresponsive hydrogels in soft robots is highlighted based on bilayer, gradient, orientation, and patterned structures. Finally, the main factors influencing its application at this stage are discussed, including the development directions and insights. Advancement in photoresponsive hydrogel technology is crucial for its application in the field of soft robotics. The advantages and disadvantages of different preparation methods and structures should be considered in different application scenarios to select the best design scheme.

Highly cross-linked carbon tube aerogels with enhanced elasticity and fatigue resistance

Carbon aerogels are elastic, mechanically robust and fatigue resistant and are known for their promising applications in the fields of soft robotics, pressure sensors etc. However, these aerogels are generally fragile and/or easily deformable, which limits their applications. Here, we report a synthesis strategy for fabricating highly compressible and fatigue-resistant aerogels by assembling interconnected carbon tubes. The carbon tube aerogels demonstrate near-zero Poisson’s ratio, exhibit a maximum strength over 20 MPa and a completely recoverable strain up to 99%. They show high fatigue resistance (less than 1.5% permanent degradation after 1000 cycles at 99% strain) and are thermally stable up to 2500 °C in an Ar atmosphere. Additionally, they possess tunable conductivity and electromagnetic shielding. The combined mechanical and multi-functional properties offer an attractive material for the use in harsh environments.

A length-adjustable vacuum-powered artificial muscle for wearable physiotherapy assistance in infants.

Soft pneumatic artificial muscles are increasingly popular in the field of soft robotics due to their light-weight, complex motions, and safe interfacing with humans. In this paper, we present a Vacuum-Powered Artificial Muscle (VPAM) with an adjustable operating length that offers adaptability throughout its use, particularly in settings with variable workspaces. To achieve the adjustable operating length, we designed the VPAM with a modular structure consisting of cells that can be clipped in a collapsed state and unclipped as desired. We then conducted a case study in infant physical therapy to demonstrate the capabilities of our actuator. We developed a dynamic model of the device and a model-informed open-loop control system, and validated their accuracy in a simulated patient setup. Our results showed that the VPAM maintains its performance as it grows. This is crucial in applications such as infant physical therapy where the device must adapt to the growth of the patient during a 6-month treatment regime without actuator replacement. The ability to adjust the length of the VPAM on demand offers a significant advantage over traditional fixed-length actuators, making it a promising solution for soft robotics. This actuator has potential for various applications that can leverage on demand expansion and shrinking, including exoskeletons, wearable devices, medical robots, and exploration robots.

Highly Stretchable Printed Poly(vinylidene fluoride) Sensors through the Formation of a Continuous Elastomer Phase

Stretchable piezoelectric stress/strain sensing materials have attracted substantial research interest in the fields of wearable health monitoring, motion capturing, and soft robotics. These sensors require operation under dynamic loading conditions with high strain range, changing strain/loading rates, and varying pre-stretch states, which are challenging conditions for existing sensors to produce reliable measurements. To overcome these challenges, an intrinsically stretchable poly(vinylidene fluoride) (PVDF) sensor is developed through the polymer blending of PVDF and acrylonitrile butadiene rubber (NBR). Through precipitation printing and vulcanization, the resulting PVDF/NBR blends exhibit strong β phase PVDF and a blend morphology with submicron-level phase separation, but also strains up to 544%. Both the blend morphology and the mechanical properties indicate that this PVDF/NBR blend can be considered as a continuous elastomer phase above micron scale. After electric poling and adding electrodes, the PVDF/NBR blends have excellent piezoelectric properties to be used as both stretching mode strain sensors and compression mode stress/force sensors. The stretching mode sensors can measure strain up to 70% without strain rate and pre-stretch dependence, while the compression mode sensors have a loading-rate-independent linear voltage-stress relationship up to 4.8 MPa stress and a negligible pre-stretch dependence. Therefore, the PVDF/NBR sensors can provide accurate and reliable stress/strain measurements when attached to soft structures, which paves the way for sensing and calibration of soft robots under dynamic loading conditions.

4D printing of hard magnetic soft materials based on NdFeB particles

Magnetic soft materials (MSM) show excellent potential in soft robotics, biomedicine, and sensors because of their excellent magnetic response, reversible deformation, and controlled motion. A hard magnetic soft material (HASM) that can be obtained by adding hard magnetic particles to a soft material matrix. By programing the spatial magnetization profile of the HASM object and manipulating the driving magnetic field, it exhibits excellent shape manipulation performance with unconstrained, reversible deformation transformation and controlled motion. In this study, a HASM ink consisting of hard magnetic NdFeB particles with a soft silicone rubber matrix was prepared. A 4D printing strategy using 3D injection printing technology combined with origami magnetization technology is used to fabricate 3D structured HASM objects for flexible shape programmability. A variety of programed shapes of HASM straight beams with bionic fish tails were fabricated by 4D printing strategy. The HASM straight beam is driven by the magnetic field, which can quickly realize the transformation and change of the preset shape as well as the shape of the HASM beam. The HASM bionic fish tail can swing rapidly under the action of the driving magnetic field. It shows a broad potential in the field of soft and bionic robots.

Reconfigurable Soft Pneumatic Actuators Using Extensible Fabric-Based Skins.

The development of the field of soft robotics has led to the exploration of novel techniques to manufacture soft actuators, which provide distinct advantages for wearable assistive robotics. One subset of these soft pneumatic actuators is conventionally developed from silicone, fabrics, and thermoplastic polyurethane (TPU). Each of these materials in isolation possesses limitations of low-stress capacity, low-design complexity, and high-input pressure requirements, respectively. Combining these materials can overcome some limitations and maintain their desirable properties. In this article, we explore one such composite design scheme using a combination of silicone polymer-based bladder and reconfigurable fabric skin made from an anisotropic extensible fabric. The silicone polymer bladder acts as the hermetic seal, while this skin acts as the constraint. Bending and torsional actuators were designed utilizing the anisotropy of these fabrics. The torsional actuator designs can achieve over 540° of twist, significantly larger than previously reported in the literature, owing to the lower mechanical impedance of the extensible fabrics. Actuators with 360° of bending were also fabricated using this method. In addition, the lack of TPU-backed or inextensible fabrics reduces the actuator's stiffness, leading to lower actuation pressures. Skin-based designs also confer the advantage of modularity, reconfigurability, and the ability to achieve complex motions by tuning the properties of the bladder and the skin. For applications with high-force requirements, such as wearable exoskeletons, we demonstrate the utility of multilayer design schemes. A multilayer bending actuator generated 190 N of force at 100 kPa and was shown to be a candidate for wearable assistive devices. In addition, torsional designs were shown to have utility in practical scenarios such as screwing on a bottle cap and turning knobs. Thus, we present a novel fabric-skin-based design concept that is highly versatile and customizable for various application requirements.

Review of Dielectric elastomer based application for Soft robotics

Soft robotics is a growing field that is getting more and more attention. Unlike traditional rigid robots, soft robots have a simpler structure and control logic, a simple electric voltage change can activate the whole control system, with the capability of carrying out more complex tasks at the same time. Dielectric elastomer is thought to be a fundamental technology advancing the development of soft robots, with the advantages of fast response, great stretch capacity as well as resilience, less weight and higher energy density. Dielectric elastomer technology has many practical applications, such as grippers, robots on ground, swimming robots, artificial body tissues and so-called artificial muscles. In this paper, we mainly introduce the state-of-art application of Dielectric elastomer in the soft robotics field and also discuss the challenges that the DE-based soft robotics are encountering.

Composite Soft Pneumatic Actuators Using 3D Printed Skins

The development of the field of soft robotics has led to the exploration of novel techniques to manufacture soft actuators. One subset of these- soft pneumatic actuators are conventionally developed from silicone, fabrics, and thermoplastic polyurethane (TPU). Each of these materials in isolation possesses limitations of low-stress capacity, low design complexity and high input pressure requirements, respectively. Combining these materials can overcome some limitations and maintain their desirable properties. In this manuscript, we explore one such composite design scheme using a combination of silicone polymers and TPU manufactured using fused deposition modelling (FDM). Silicone, which has high strain capacity, is used as the inner hermetic seal, while the 3D printed TPU acts as an external constraint that controls the deformation. The composite actuators have the advantage of being able to withstand higher stress than the silicone polymer and still being able to generate high deformations at modest pressures that TPU actuators are unable to achieve. In addition, the composite skins give the advantage of reconfigurability as the inner bladder, and the skin can both be modified to tune the properties of the final actuator. Effects of material selection and stiffness on the deformation and force properties of the composite actuators are also explored, along with variations in force output by changing the inner bladder. The practical utility of these 3D printed skins is demonstrated by showcasing a wearable elbow assistive device based on this technique.

Transforming Soft Robotics: Laminar Jammers Unlocking Adaptive Stiffness Potential in Pneunet Actuators

PneuNet actuators emulate human finger function and have broad application potential in domestic and industrial settings. To unlock their full potential, enhancing their controlled stiffness is crucial. This study presents the innovative design, fabrication, and evaluation of a cost-effective soft hybrid bending actuator by merging a homogeneous laminar structure, composed of 75 GSM printer paper, with a PneuNet actuator produced through soft lithography techniques. This research also characterizes the ensemble based on its tunable stiffness properties and examines the friction tests on jamming layers, highlighting the stabilization of frictional properties over time, which is critical for achieving consistent tunable stiffness. Experiments revealed that the actuator’s resistive force increases due to deformation when subjected to an external load. Furthermore, this linear rise in resistive force can be modulated through the use of an integrated laminar jammer by adjusting the vacuum pressure. Results reveal a negligible stiffness increase beyond −53.33 kPa of vacuum pressure, signifying an ideal vacuum pressure limit for energy conservation during vacuum jamming. A maximum stiffness of 0.116 N was achieved at −80 kPa of vacuum pressure. This study propels the field of soft robotics by offering enhanced tunable stiffness characteristics for diverse applications.

Flexible force‐bearing liquid crystalline elastomer component toward a dynamic braille platform

AbstractLiquid Crystalline Elastomers (LCEs) are elastomeric actuators capable of reversible shape change under external stimulation such as heat or light. This ability makes them prime candidates for use in the field of soft robotics, with examples of explored applications ranging from heart patches to active yarn. Here, we apply LCE actuation to the field of dynamic Braille displays, with the small Braille pins capable of being either flat or protruding on demand. We demonstrate that the complex and numerous moving parts of a dynamic Braille device could be replaced by a single sheet of LCEs embossed with small actuating bumps. A simple molding procedure produces a surface patterned with at‐scale Braille bumps, as a result of a precise and complex internal organization within the elastomer sample that emerges during polymerization. Unlike in previous attempts to use LCEs for Braille technology, our millimeter‐scale protruding features are generated out of the bulk of the material, resulting in structural integrity, and high resistance to compression force. The localized bump‐to‐flat reversible actuation occurs on a timescale of seconds. The potential of this development for application into a complete Braille dynamic display are discussed.

Towards a Soft Science of Soft Robots. A Call for a Place for Aesthetics in Soft Robotics Research

The position paper presents an argument that aesthetic theory and practice are pertinent to the rapidly expanding field of soft robotics. Soft robotics as an aesthetic phenomenon is introduced and contextualized drawing on the author's own research and practice. The potential of aesthetic perspectives and approaches in developing and implementing soft robotics are highlighted with a focus on technical design and human-robot interaction.

A Portable Real-Time Test Bench for Dielectric Elastomer Actuators

Recently, a significant amount of research has been devoted to soft robots. Artificial muscles belong to the most important components of soft robots. Dielectric elastomer actuators (DEAs) represent the technology that comes closest to the capabilities of a natural muscle, making them the best candidates for artificial muscles in robotics and prosthetics applications. To develop these applications, an analysis of DEAs in a test bench must be possible. It is important that the environmental conditions are known, and all components are specified, which is not the case in most publications. This paper focuses on the development of a real-time test bench for DEAs which provides environmental conditions and all components that are specified. Its goal is to open up the research field of dielectric elastomer actuators or soft robots. The stacked DEA used is powered by a high-voltage amplifier, which can be controlled via a real-time block diagram environment together with a data acquisition (DAQ) device. The response of the actuator is measured with a laser triangulation sensor. Furthermore, information about the applied voltage, the operating current, the temperature, and the humidity are collected. It was demonstrated that the selected laser sensor is a suitable device for this application. Moreover, it was shown that the selected high-voltage amplifier is adequate to power a DEA. However, the DAQ is not fast enough to measure the actuator current. It was demonstrated that housing keeps environmental conditions constant, is transportable, and offers the flexibility to investigate different DEAs.

Photothermally induced natural vibration for versatile and high-speed actuation of crystals

The flourishing field of soft robotics requires versatile actuation methodology. Natural vibration is a physical phenomenon that can occur in any material. Here, we report high-speed bending of anisole crystals by natural vibration induced by the photothermal effect. Rod-shaped crystal cantilevers undergo small, fast repetitive bending (~0.2°) due to natural vibration accompanied by large photothermal bending (~1°) under ultraviolet light irradiation. The natural vibration is greatly amplified by resonance upon pulsed light irradiation at the natural frequency to realise high frequency (~700 Hz), large bending (~4°), and high energy conversion efficiency from light to mechanical energy. The natural vibration is induced by the thermal load generated by the temperature gradient in the crystal due to the photothermal effect. The bending behaviour is successfully simulated using finite element analysis. Any light-absorbing crystal can be actuated by photothermally induced natural vibration. This finding of versatile crystal actuation can lead to the development of soft robots with high-speed and high-efficient actuation capabilities.

Topology-Dependent pH-Responsive Actuation and Shape Memory Programming for Biomimetic 4D Printing.

Biomimetic actuators are critical components of bionics research and have found applications in the fields of biomedical devices, soft robotics, and smart biosensors. This paper reports the first study of nanoassembly topology-dependent actuation and shape memory programming in biomimetic 4D printing. Multi-responsive flower-like block copolymer nanoassemblies (vesicles) were utilized as photocurable printing materials for digital light processing (DLP) 4D printing. The flower-like nanoassemblies enhanced thermal stability attributed to their surface loop structures on the shell surfaces. Actuators prepared from these nanoassemblies displayed topology-dependent bending in response to pH and temperature programmable shape memory properties. Biomimetic octopus-like soft actuators were programmed with multiple actuation patterns, large bending angles (∼500 °), excellent weight to lift ratios (∼60), and moderate response time (∼5min). Thus, nanoassembly topology-dependent and shape-programmable intelligent materials were successfully developed for biomimetic 4D printing. This article is protected by copyright. All rights reserved.

Perspective for soft robotics: the field’s past and future

Since its beginnings in the 1960s, soft robotics has been a steadily growing field that has enjoyed recent growth with the advent of rapid prototyping and the provision of new flexible materials. These two innovations have enabled the development of fully flexible and untethered soft robotic systems. The integration of novel sensors enabled by new manufacturing processes and materials shows promise for enabling the production of soft systems with ‘embodied intelligence’. Here, four experts present their perspectives for the future of the field of soft robotics based on these past innovations. Their focus is on finding answers to the questions of: how to manufacture soft robots, and on how soft robots can sense, move, and think. We highlight industrial production techniques, which are unused to date for manufacturing soft robots. They discuss how novel tactile sensors for soft robots could be created to enable better interaction of the soft robot with the environment. In conclusion this article highlights how embodied intelligence in soft robots could be used to make soft robots think and to make systems that can compute, autonomously, from sensory inputs.

Inexpensive monolithic additive manufacturing of silicone structures for bio-inspired soft robotic systems

In soft robotics, the fabrication of extremely soft structures capable of performing bio-inspired complex motion is a challenging task. This paper introduces an innovative 3D printing of soft silicone structures with embedded shape memory alloy (SMA) actuators, which is completed in a single printing cycle from CAD files. The proposed custom-made 3D printing setup, based on the material extrusion (MEX) method, was used in conjunction with a cartesian pick and place robot (CPPR) to completely automate the fabrication of thick silicone skins (7 mm) with embedded shape memory alloy actuators. These structures were fabricated monolithically without any assembly tasks and direct human intervention. Taking advantage of the capability to 3D print different geometries, three different patterns were fabricated over the silicone skin, resulting in remarkable dynamic motions: an out-of-plane deformation (jumping of the structure from the x-y plane to the x-z plane) was achieved for the first-time employing silicone skin, to the best of the author’s knowledge. In addition, two process parameters (printing speed and build plate temperature) and the extruded silicone curing mechanisms were investigated to enhance the printing quality. This paper aims to advance the role of additive manufacturing in the field of soft robotics by demonstrating all the benefits that a low-cost, custom-made silicone 3D printer can bring to the table in terms of manufacturing soft bio-inspired structures.

Review of Soft Actuators Controlled with Electrical Stimuli: IPMC, DEAP, and MRE

Soft actuators have been developed for a variety of applications, including soft grippers, artificial muscles, wearables, tactile devices, and medical devices. In this review, we will discuss a group of chemical materials and their robotic applications in soft actuators controlled with electrical stimuli. Soft actuators provide a deformable body and allow interaction with the environment to achieve the desired actuation pattern. We will also discuss the principles of operation and functionality and focus on important real-life applications of three groups of soft actuators: ionic polymer–metal composites (IPMCs), dielectric electroactive polymers (DEAPs), and magnetorheological elastomers (MREs). This review article aims to provide researchers interested in the field of soft robotics with a guide to various state-of-the-art chemistry methods used in electrically activated soft actuators, as well as the application areas for such devices.

A Review on Fabrication and Application of Tunable Hybrid Micro–Nano Array Surfaces

AbstractThe wettability and adhesion of biological surfaces often depend on their periodically arranged hybrid micro–nano array structures. Various fabrication processes are designed to mimic biomimetic micro–nano array surfaces. This review summarizes the types of micro–nano array structures and analyzes fabrication methods based on top‐down and bottom‐up construction, including templating, etching, self‐assembly, and electrospinning/electrospraying. This review focuses on the shape reconfiguration of surface micro–nano array structures under physical stimuli, as well as the changes in material surface properties during the reconfiguration process. In addition, the applications of biomimetic micro–nano array composite surfaces in the fields of droplet transport, adhesion properties, sensors, and soft robotics are also discussed, and the current challenges and prospects in this field are identified.

High Thermal Conductivity of Sandwich-Structured Flexible Thermal Interface Materials.

Thermal interfaces are vital for effective thermal management in modern electronics, especially in the emerging fields of flexible electronics and soft robotics that impose requirements for interface materials to be soft and flexible in addition to having high thermal performance. Here, a novel sandwich-structured thermal interface material (TIM) is developed that simultaneously possesses record-low thermal resistance and high flexibility. Frequency-domain thermoreflectance (FDTR)is employed to investigate the overall thermal performance of the sandwich structure. As the core of this sandwich, a vertically aligned coppernanowire (CuNW) array preserves its high intrinsic thermal conductivity, which is further enhanced by 60% via a thick 3D graphene (3DG) coating. The thin copper layers on the top and bottom play the critical roles in protecting the nanowires during device assembly. Through the bottom-up fabrication process, excellent contacts between the graphene-coated CuNWs and the top/bottom layer are realized, leading to minimal interfacial resistance. In total, the thermal resistance of the sandwich is determined as low as ~0.23mm2 KW-1 . This work investigates a new generation of flexible thermal interface materials with an ultralow thermal resistance, which therefore renders the great promise for advanced thermal management in a wide variety of electronics.