Keywords: Compliant Joint/Mechanism, Legged Robots, Tendon/Wire Mechanism
Abstract: This study presents a crawl robot driven by a single actuator using a bistable lattice structure. The propagation of deformation waves through a bistable lattice realizes the crawling motion of the robot. Bistable structures with energy differences between the two stable states and reset mechanism enable easy and intermittent wave propagation. By softening its body, the robot can change its direction along a curved rail during locomotion. The experimental results of the prototype show that the robot can produce locomotion on straight, curved, and slope-ascending rails.

Keywords: Medical Robots and Systems, Compliant Joint/Mechanism, Soft Robot Applications
Abstract: In this work, we describe a soft robotic artificial heart ventricle whose novel pumping strategy is based on the programmable deformation of a fluid-containing and passive soft-shell. During pumping, the soft-shell collapses, showing the formation of inward folds that strongly contribute to the volumetric reduction of the soft-shell, thus to the pumping functionality. Our soft robotic artificial ventricle is a stand-alone system actuated by inverse pneumatic artificial muscles, that are arranged in a helical fashion around the soft-shell. We present a cable-driven soft pump as a study platform for preliminary investigation of the pumping strategy and the requirements for actuation. Three typologies of inverse pneumatic artificial muscles were fabricated and experimentally characterized as candidate actuators for the artificial ventricle. Finally, a ventricle prototype constituted by a soft-shell and an actuating system made of five inverse pneumatic actuators was designed and tested under physiologically relevant conditions of preload and afterload pressure. The experimental results demonstrated that our soft robotic artificial ventricle meets the functional requirements of a right heart ventricle operating in pulmonary circulation.

Keywords: Soft Robot Materials and Design, Hydraulic/Pneumatic Actuators, Soft Sensors and Actuators
Abstract: Everting, soft growing vine robots benefit from reduced friction with their environment, which allows them to navigate challenging terrain. Vine robots can use air pouches attached to their sides for lateral steering. However, when all pouches are serially connected, the whole robot can only perform one constant curvature in free space. It must contact the environment to navigate through obstacles along paths with multiple turns. This work presents a multi-segment vine robot that can navigate complex paths without interacting with its environment. This is achieved by a new steering method that selectively actuates each single pouch at the tip, providing high degrees of freedom with few control inputs. A small magnetic valve connects each pouch to a pressure supply line. A motorized tip mount uses an interlocking mechanism and motorized rollers on the outer material of the vine robot. As each valve passes through the tip mount, a permanent magnet inside the tip mount opens the valve so the corresponding pouch is connected to the pressure supply line at the same moment. Novel cylindrical pneumatic artificial muscles (cPAMs) are integrated into the vine robot and inflate to a cylindrical shape for improved bending characteristics compared to other state-of-the-art vine robots. The motorized tip mount controls a continuous eversion speed and enables controlled retraction. A final prototype was able to repeatably grow into different shapes and hold these shapes. We predict the path using a model that assumes a piecewise constant curvature along the outside of the multi-segment vine robot. The proposed multi-segment steering method can be extended to other soft continuum robot designs.

Keywords: Soft Robot Materials and Design, Soft Sensors and Actuators, Grasping
Abstract: We describe a novel three-finger robot hand that has high resolution tactile sensing along the entire length of each finger. The fingers are compliant, constructed with a soft shell supported with a flexible endoskeleton. Each finger contains two cameras, allowing tactile data to be gathered along the front and side surfaces of the fingers. The gripper can perform an enveloping grasp of an object and extract a large amount of rich tactile data in a single grasp. By capturing data from many parts of the grasped object at once, we can do object recognition with a single grasp rather than requiring multiple touches. We describe our novel design and construction techniques which allow us to simultaneously satisfy the requirements of compliance and strength, and high resolution tactile sensing over large areas.

Keywords: Biologically-Inspired Robots, Hydraulic/Pneumatic Actuators, Soft Robot Materials and Design
Abstract: Earthworms can crawl on the ground and burrow through the soil by means of sequential actuation of two types of muscles. The elongated soft body of an earthworm extends by contraction of circularly arranged external muscles and swells by contraction of longitudinally oriented muscles. Despite their slow movement, earthworms offer a rich model for developing next-generation limbless soft robots for many applications, including automated sensing of soil properties and microbiomes, gastrointestinal tract endoscopy, and sewer pipe inspection. Here, we take inspiration from the interwoven morphology of earthworms' musculature to create a multimodal soft actuator. We devised a prototyping technique for fabricating composite pneumatic actuators by coiling prestretched inflatable tubes around a cylindrical soft actuator at varying tension. We conducted comprehensive experiments and characterized the evolution of pressure and elongation of these multimodal actuators, inflating the inner and outer actuators in various sequential orders.Finally, we harnessed one of the identified actuation sequences to achieve in-pipe locomotion.

Keywords: Soft Sensors and Actuators, Soft Robot Materials and Design
Abstract: Soft pneumatic actuators have seen applications in many soft robotic systems, and their pressure-driven nature presents unique challenges and opportunities for controlling their motion. In this work, we present a new concept: designing and controlling pneumatic actuators via end geometry. We demonstrate a novel actuator class, named the folded Pneumatic Artificial Muscle (foldPAM), which features a thin-filmed air pouch that is symmetrically folded on each side. Varying the folded portion of the actuator changes the end constraints and, hence, the force-strain relationships. We investigated this change experimentally by measuring the force-strain relationship of individual foldPAM units with various lengths and amounts of folding. In addition to static-geometry units, an actuated foldPAM device was designed to produce continuous, on-demand adjustment of the end geometry, enabling closed-loop position control while maintaining constant pressure. Experiments with the device indicate that geometry control allows access to different areas on the force-strain plane and that closed-loop geometry control can achieve errors within 0.5% of the actuation range.

Keywords: Soft Sensors and Actuators, Wearable Robots, Soft Robot Materials and Design
Abstract: 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.

Keywords: Soft Robot Materials and Design, Biomimetics, Compliant Joint/Mechanism
Abstract: Compliant joints are widely used in the structural design of 3D-printed continuum robots as their monolithic structure can greatly simplify the assembly process. However, some highly flexible compliant joints, such as the leaf-spring joints, still suffer from unstable rotation centers when interfered by external forces, which greatly reduces the motion stability of the constructed continuum robots. To cope with this problem, we propose a topology-optimization-based method in this paper to achieve efficient structural design of the complaint joints in continuum robots. With our method, the rotation stability of compliant joints can be improved without causing stress concentration problems. Experiments were also carried out to evaluate the bending performance of the 3D-printed continuum robots equipped with optimized compliant joints. Results demonstrated that, compared to continuum robots with the conventional leaf-spring joints, the optimized robots showed much less twisting deformation caused by out-of-plane loads, which exhibited the high rotation stability of the optimized joints. In future work, the proposed method can be further developed to achieve optimization of other mechanical properties of the compliant joints in continuum robots.

Keywords: Soft Robot Materials and Design, Grasping
Abstract: Design optimization of soft grippers is critical to functionally exploit their compliance. However, it is difficult to predictably model or search the design space of even simple Fluidic Elastomer Actuators. This work presents a method to rapidly customize and identify desirable morphologies of pneumatic soft grippers via Bayesian Optimization of reconfigurable modular molds. With the goal of maximizing grasping success rate for a general object set, the reality-assisted optimization process uses results from physical pick and place experiments to iterate through a large array of design parameters. Suggested design parameters dictate the assembly of pre-fabricated modules in the mold to generate silicone-casted soft fingers. These fingers are integrated to form a gripper and tested to inform the next iteration. This process allows faster iterations compared to 3D printing equivalent grippers or molds, and discretizes the design space for faster search through parameter combinations. An improvement of 34% in average grasping success rate was achieved in six iterations, shedding light on desirable parameter configurations for the grasping task.

Keywords: Modeling, Control, and Learning for Soft Robots, Compliant Joint/Mechanism, Soft Robot Materials and Design
Abstract: Dynamic modeling of folding joints is critical for predicting dynamic behavior, optimizing design parameters, and developing control strategies for origami robots and machines. Although kinematics of the folded joints exists, little research describes their dynamics. Currently, prevailing models neglect the stiffness of the hinges by making zero-thickness assumption or ignore physical factors such as gravity and friction. In this work, we focus on the dynamic modeling of an origami prismatic joint with rotary-to-translational transmission by using the Newton-Euler method and pseudo-rigid-body-approximation. We provide a comprehensive dynamic model by including gravity, friction, and hinge parameters. We validate the model in an all-inclusive experimental setup addressing static, quasi-static, and dynamic conditions. Our proposed model successfully predicts the dynamics and structural stiffness of the joint. This novel model can be combined with other origami-joint models, such as pin and spherical joint models, to allow model-based design and control strategies for desired output performance of origami robots.

Keywords: Legged Robots, Modeling, Control, and Learning for Soft Robots, Biologically-Inspired Robots
Abstract: Legged robots are a promising technology whose use is limited by their high energy consumption. Biological and biomechanical studies have shown that the vibration generated by elastically suspended masses provides an energy advantage over rigidly carrying the same load. The robotic validation of these findings has only scarcely been explored in the dynamic walking case. In this context, a relationship has emerged between the design parameters and the actuation that generates the optimal gait. Although very relevant, these studies lack a generalizable analysis of different locomotion modes and a possible strategy to obtain optimal locomotion at different speeds. To this end, we propose the use of articulated legs in an extended Spring-Loaded Inverted Pendulum (SLIP) model with an elastically suspended mass. Thanks to this model, we show how stiffness and damping can be modulated through articulated legs by selecting the knee angle at touch-down. Therefore, by choosing different body postures, it is possible to vary the control parameters and reach different energetically optimal speeds. At the same time, this modeling allows the study of the stability of the defined system. The results show how suitable control choices reduce energy expenditure by 16% at the limit cycle at a chosen speed. The demonstrated strategy could be used in the design and control of legged robots where energy consumption would be dynamically optimal and usage time would be significantly increased.

Keywords: Modeling, Control, and Learning for Soft Robots, Soft Robot Materials and Design, Hydraulic/Pneumatic Actuators
Abstract: Pouch motors are one of the recently developed soft actuators, which are known particularly for their low-weight, ease of fabrication and large stroke. To date, several studies have been performed to develop and model new pouch motors designs to improve their functionality. All models assume that the material is behaving inextensibly, i.e. not stretchable. Here, we propose an analytical model for pouch motors where we consider the materials to be stretchable, and show that stretchability of pouch motors sets a limit for the maximum contraction and force, and therefore cannot be neglected even when using nearly inextensible materials. We evaluate our model qualitatively by conducting `blocked-displacement' experiments on single pouches made of various materials with different elasticity.

Keywords: Soft Robot Materials and Design, Modeling, Control, and Learning for Soft Robots, Hydraulic/Pneumatic Actuators
Abstract: Many soft-body organisms found in nature flourish underwater. Similarly, soft robots are potentially well-suited for underwater environments partly because the problematic effects of gravity, friction, and harmonic oscillations are less severe underwater. However, it remains a challenge to design, fabricate, waterproof, model, and control underwater soft robotic systems. Furthermore, submersible robots usually do not have configurable components because of the need for sealed electronics and mechanical elements. This work presents the development of a modular and submersible soft robotic arm driven by hydraulic actuators which consists of mostly 3D printable parts and can be assembled or modified in a relatively short amount of time. Its modular design enables multiple shape configurations and easy swapping of soft actuators. As a first step to exploring machine learning control algorithms on this system, we also present preliminary forward and inverse kinematics models developed using deep neural networks.

Keywords: Hydraulic/Pneumatic Actuators, Soft Sensors and Actuators, Soft Robot Applications
Abstract: This work presents an evaluation of reversible water electrolysis as a method for pneumatic actuation via the electrochemical decomposition of water into hydrogen and oxygen gas. In addition to a theoretical evaluation of the performance of electrochemically-driven pressurized hydrogen generation, pneumatic generation methods were experimentally tested across two axes: performance and compatibility. Through these experiments, the achievable pressure was shown to be at least 0.75 MPa gauge with a flow rate of 0.06 L/min. It was also determined that negligible losses were incurred due to switching from air to hydrogen. Despite low experimental round-trip efficiencies of 0.005%, the reversible electrolysis of water reaction was shown to be a feasible method for pneumatic actuation of soft robots, especially under scenarios where actuator bandwidth is not of concern.

Keywords: Modeling, Control, and Learning for Soft Robots, Simulation and Animation, Learning and Adaptive Systems
Abstract: Soft robots have many advantages over their rigid counterparts. These include their inherent compliance, light weight and high adaptability to cluttered workspaces. Soft continuum robots, biologically inspired snake-like robots, are hyper-redundant and highly deformable. These robots can be challenging to control due to their complex kinematic and dynamic models. This paper presents a novel kinematic-model-free controller that uses a quasi-static assumption in order to control the tip-position of soft continuum robots with threadlike actuation whilst compensating for gravity simultaneously. The controller was tested on simulated continuum soft robots to demonstrate its ability to guide the tip while following a given trajectory. Novel kinematic-model-free control methods for controlling a actuators-reconfiguring robot as well as a growing robot are introduced. The robustness of the controller is demonstrated with a actuator-failure test. The kinematic-model-free controller provides an adaptive control method for static, reconfiguring, and growing soft continuum robots with threadlike actuation.

Keywords: Soft Sensors and Actuators, Soft Robot Materials and Design, Soft Robot Applications
Abstract: Friction-assisted locomotion in limbless creatures has inspired the development of bioinspired soft robots that can creep into narrow passages, inspect disaster sites, and explore unstructured terrains. Directional friction is an essential element of any crawling locomotion where a low forward friction force favors displacement in the direction of movement, and a high backward friction force provides the required anchorage. Kirigami metasurfaces, created by perforating repetitive cuts into thin sheets, can pop out upon being stretched and produce directional friction for specific cut patterns. Here, we create a composite kirigami skin for a soft robot that, in addition to enabling the robot to crawl in a straight line, can reconfigure when stretched along different directions and steer the robot. We fabricated a triangular actuator frame made of three fiber-reinforced extending actuators placed at each edge that, when actuated in pairs, can elongate the frame in three symmetric directions. We covered the actuator with the proposed reconfigurable kirigami skin to create an omnidirectional planar soft crawling robot. We characterized the linear locomotion and maneuvering capabilities of the robot and tracked the robot's trajectories for different combinations of actuation inputs. Our proposed approach uses a single robotics skin to embody multiple locomotion possibilities in soft robots.

Keywords: Force and Tactile Sensing, Haptics and Haptic Interfaces, Soft Sensors and Actuators
Abstract: Soft haptic sensing interfaces based on optical methods using cameras are characterized by their simplicity in design with less complication in terms of wiring, maintenance, and so on. Also, thanks to the fact that the mechanical properties of the flexible outer skin used in such vision-based tactile sensor are not compromised, promising in high reliability with respect to noise. On the other hand, when the sensing area increases, two or more cameras need to be setup behind the soft skin for monitoring markers’ displacements. Previously, we developed a barrel-shaped tactile sensor with two cameras setup at two ends of the device for extraction of three-dimensional (3-D) movement of markers. However, simultaneously processing multiple images from cameras requires much computational effort. In this paper, we describe a 3-D estimation method using the rotation of a fisheye camera setup inside the soft skin’s boundary, active by a simple servo motor. Based on rotation of the camera, the sensing time, sensitivity can be adjusted actively. The proposed method not only improves the usable volume inside the sensor, but also shows more robust measurement performance with respect to deformation of the sensor's outer skin.

Keywords: Grippers and Other End-Effectors, Soft Robot Applications, Soft Robot Materials and Design
Abstract: Granular jamming has recently become popular in soft robotics with widespread applications including industrial gripping, surgical robotics and haptics. Previous work has investigated the use of various techniques that exploit the nature of granular physics to improve jamming performance, however this is generally underrepresented in the literature compared to its potential impact. We present the first research that exploits vibration-based fluidization actively (e.g., during a grip) to elicit bespoke performance from granular jamming grippers. We augment a conventional universal gripper with a computer-controllled audio exciter, which is attached to the gripper via a 3D printed mount, and build an automated test rig to allow large-scale data collection to explore the effects of active vibration. We show that vibration in soft jamming grippers can improve holding strength. In a series of studies, we show that frequency and amplitude of the waveforms are key determinants to performance, and that jamming performance is also dependent on temporal properties of the induced waveform. We hope to encourage further study focused on active vibrational control of jamming in soft robotics to improve performance and increase diversity of potential applications.

Keywords: Soft Robot Materials and Design, Soft Robot Applications, Compliant Joint/Mechanism
Abstract: Exploration in environments that are too hazardous or inaccessible to humans is one of the most promising uses of robotics. In particular, natural environments that contain granular media present a variety of challenges for the design and control of robots. Recently, everting vine robots have been demonstrated that can navigate many different environments, including digging in sand. However, everting vine robots typically rely on a tether which limits their ability to explore. Here we present an untethered, continuously everting soft robot for exploration in granular media. We test the ability of this design to reduce the drag on the robot while moving through granular media. We then investigate design features to improve the ability of the robot to generate thrust in granular media, and validate them experimentally. Finally, We test our robot’s ability to locomote and dig.

Keywords: Biomimetics, Biologically-Inspired Robots
Abstract: As the interest in oceanic and marine technologies increases, there is a growing need to perform construction, maintenance and surveying in ever more complicated situations. Currently, most underwater robots have limitations including manoeuvring in tight spaces, entanglement with foreign objects, ecosystem disruption, and high acoustic noise. A novel pulsatile jet actuator using magnetohydrodynamics (MHD) is proposed to overcome these problems. In this system, there are no moving parts; hence mechanical noise, entanglement and potential ecosystem disruption are reduced significantly. The jet engine operates in, and exploits, the electrical and fluidic properties of seawater. The MHD pulse jet engine was experimentally characterized and maximal thrust generation was achieved by enforcing the optimal formation number. The thrust vortex rings generated were studied using particle image velocimetry in both pulsed flow and continuous flow. We successfully developed an untethered robot using a pulsatile MHD jet and demonstrated its effective movement in salt water. The MHD pulse jet is ideally suited to the next generation of autonomous soft robots for environmental monitoring and protection.

Keywords: Soft Robot Applications, Grippers and Other End-Effectors, Soft Sensors and Actuators
Abstract: Fruit harvesting has recently experienced a shift towards soft grippers that possess compliance, adaptability, and delicacy. In this context, pneumatic grippers are popular, due to provision of high deformability and compliance, however they typically possess limited grip strength. Jamming possesses strong grip capability, however has limited deformability and often requires the object to be pushed onto a surface to attain a grip. This paper describes a hybrid gripper combining pneumatics (for deformation) and jamming (for grip strength). Our gripper utilises a torus (donut) structure with two chambers controlled by pneumatic and vacuum pressure respectively, to conform around a target object. The gripper displays good adaptability, exploiting pneumatics to mould to the shape of the target object where jamming can be successfully harnessed to grip. The main contribution of the paper is design, fabrication, and characterisation of the first hybrid gripper that can use granular jamming in free space, achieving significantly larger retention forces compared to pure pneumatics. We test our gripper on a range of different sizes and shapes, as well as picking a broad range of real fruit.

Keywords: Biologically-Inspired Robots, Biomimetics, Micro/Nano Robots
Abstract: Here, we report a microfabricated untethered lightweight mobile climbing machine with plant-like micropatterned adhesive wheels for complex and unstructured three-dimensional (3D) surfaces. By taking inspiration from the ratchet-like climbing mechanism of the hook climber Galium aparine, we first designed a custom-made machine using two millimeter-scale wheels with bioinspired directional microhooks for mechanical interlocking. Secondly, we fully microfabricated the machine via two-photon lithography, a high-resolution 3D additive manufacturing technique. Then, we characterized the shear forces of the microhooks over natural complex surfaces, like plant leaves. Finally, we demonstrated the climbing behavior of the machine over an inclined slope covered by leaf tissues, as well as its ability to carry a payload. Our research shows potential for prototyping sustainable climbing plant-like small-scale machines for exploration and inspection of unstructured and/or confined terrains, which paves the way for future applications in environmental monitoring and ecosystem conservation.

Keywords: Soft Robot Applications, Biologically-Inspired Robots
Abstract: A new underwater thrust device is proposed in this work that makes use of a soft outer structure in combination with a parallel linkage and driven by a classical actuator. By merging soft and rigid parts, we hope to increase the performance of pulsed jet propulsion that plays a crucial role in attitude control for AUVs. But also simpler models for design and control can be applied by this approach. A specific linkage design for actuation, along with two different soft structures (mantles) are introduced and evaluated in experiments which indicate efficient thrust creation. Particle Image Velocimetry (PIV) experiments show the formation of vortex rings that suggest efficient propulsion, whereby the wider and more flexible mantel is characterized by higher momentum and thrust.

Keywords: Soft Robot Materials and Design, Soft Sensors and Actuators, Grippers and Other End-Effectors
Abstract: The synthesis of tactile sensing with compliance is essential to many fields, from agricultural usages like fruit picking, to sustainability practices such as sorting recycling, to the creation of safe home-care robots for the elderly to age with dignity. From tactile sensing, we can discern material properties, recognize textures, and determine softness, while with compliance, we are able to securely and safely interact with the objects and the environment around us. These two abilities can culminate into a useful soft robotic gripper, such as the original GelSight Fin Ray, which is able to grasp a large variety of different objects and also perform a simple household manipulation task: wine glass reorientation. Although the original GelSight Fin Ray solves the problem of interfacing a generally rigid, high-resolution sensor with a soft, compliant structure, we can improve the robustness of the sensor and implement techniques that make such camera-based tactile sensors applicable to a wider variety of soft robot designs. We first integrate flexible mirrors and incorporate the rigid electronic components into the base of the gripper, which greatly improves the compliance of the Fin Ray structure. Then, we synthesize a flexible and high-elongation silicone adhesive-based fluorescent paint, which can provide good quality 2D tactile localization results for our sensor. Finally, we incorporate all of these techniques into a new design: the Baby Fin Ray, which we use to dig through clutter, and perform successful classification of nuts in their shells.