Soft Mobile Robot Research Articles

Hopping potential wells and gait switching in a fish-like robot with a bistable tail

Fish outperform current underwater robots in speed, agility, and efficiency of locomotion, in part due to their flexible appendages that are capable of rich combinations of modes of motion. In fish-like robots, actuating many different modes of oscillation of tails or fins can become a challenge. This paper presents a highly underactuated (with a single actuator) fish-like robot with a bistable tail that features a double-well elastic potential. Oscillations of such a tail depend on the frequency and amplitude of excitation, and tuning the frequency–amplitude can produce controllable oscillations in different modes leading to different gaits of the robot. This robot design is inspired by recent work on underactuated flexible swimming robots driven by a single rotor. The oscillations of the rotor can propel and steer the robot, but saturation of the rotor makes performing long turns challenging. This paper demonstrates that by adding geometric bistability to the flexible tail, turns can be performed by controllably exciting single-well oscillations in the tail, while exciting double-well oscillations of the tail produces average straight-line motion. The findings of this paper go beyond the application to a narrow class of fish-like robots. More broadly we have demonstrated the use of periodic excitation to produce bistable response that generate different gaits including a steering gait. The mechanics demonstrated here show the feasibility of applications to other mobile soft robots.

Derivation of Ultra-High Gain Hybrid Converter Families for HASEL Actuators Used in Soft Mobile Robots.

This work proposes, analyzes, designs, and validates superior topologies of UHGH converters that are capable of supporting extremely large conversion ratios up to ∼2000× and output voltage up to ∼4-12 kV for future mobile soft robots from an input voltage as low as the range of a 1-cell battery pack. Thus, the converter makes soft robots standalone systems that can be untethered and mobile. The extremely large voltage gain is enabled by a unique hybrid combination of a high-gain switched magnetic element (HGSME) and a capacitor-based voltage multiplier rectifier (CVMR) that, together, achieve small overall size, efficient operation, and output voltage regulation and shaping with simple duty-cycle modulation. With superior performance, power density, and compact size, the UHGH converters prove to be a promising candidate for future untethered soft robots.

Fully 3D-printed tortoise-like soft mobile robot with muti-scenarios adaptability.

Soft robotic systems are well suited to unstructured, dynamic tasks and environments, owing to their ability to adapt and conform without damaging themselves or their surroundings. These abilities are crucial in areas such as human-robot interaction，simplification of control system and weight reduction. However, as the requirements increase, the drawbacks of existing soft mobile robots such as single locomotion mode and application scenarios, manufacturing difficulties and low energy conversion efficiency gradually emerge.
Based on the current shortcomings of soft robots, this paper designs and proposes a fully 3D-printed tortoise-like soft mobile robot with muti-scenarios adaptability. The robot uses a Bionic Tortoise Leg Actuator structure that enables simultaneous bending of the actuator in both directions, simplifying robot control and increasing the maximum bending angle achievable. In addition, a reconfiguration design solution has been proposed to enable the robot to implement two bionic modes for land and sea tortoises, adapting to move on hard and soft surfaces and in water, enabling it to move in amphibious and complex environments. The performance of the pneumatic soft actuators are also improved by an improved Digital Light Processing method that enhances the maximum strain of the 3D printed soft material.
The prototype was tested to give maximum movement speeds for different gaits and environments, demonstrating that the fully 3D printed turtle-like soft-mobile robot designed in this paper is highly adaptable to multiple scenarios. The robot studied in this paper has a wide range of applications, with potential applications including navigation in a variety of domain environments, inspection of large underground oil and gas pipelines, and navigation in high temperature, high humidity and strong magnetic field environments or in military alert conditions.&#xD.

Design and Motion Analysis of a Soft-Limb Robot Inspired by Bacterial Flagella.

Soft robots demonstrate an impressive ability to adapt to objects and environments. However, current soft mobile robots often use a single mode of movement. This gives soft robots good locomotion performance in specific environments but poor performance in others. In this paper, we propose a leg-wheel mechanism inspired by bacterial flagella and use it to design a leg-wheel robot. This mechanism employs a tendon-driven continuum structure to replicate the bacterial flagellar filaments, while servo and gear components mimic the action of bacterial flagellar motors. By utilizing twisting and swinging motions of the continuum structure, the robot achieves both wheeled and legged locomotion. The paper provides comprehensive descriptions and detailed kinematic analysis of the mechanism and the robot. To verify the feasibility of the robot, a prototype was implemented, and experiments were performed on legged mode, wheeled mode, and post-overturning motion. The experimental results demonstrate that the robot can achieve legged and wheeled motions. Moreover, it is also demonstrated that the robot still has mobility after overturning. This expands the applicability scenarios of the current soft mobile robot.

Ultra-soft Organogel Artificial Muscles Exhibiting High Power Density, Large Stroke, Fast Response and Long-Term Durability in Air.

Polymeric gel-based artificial muscles exhibiting tissue-matched Young's modulus (10Pa-1MPa) promise to be core components in future soft machines with inherently safe human-machine interactions. However, the ability to simultaneously generate fast, large, high-power and long-lasting actuation in the open-air environment, has yet been demonstrated in this class of ultra-soft materials. Herein, to overcome this hurdle, we report the design and synthesis of a twisted and coiled liquid crystalline glycerol-organogel (TCLCG). Such material with a low Young's modulus of 133kPa can surpass the actuation performance of skeletal muscles in a variety of aspects, including actuation strain (66%), actuation rate (275%/s), power density (438kW/m3 ) and work capacity (105kJ/m3 ). Notably, its power density is 14 times higher than the record of state-of-the-art polymeric gels. No actuation performance degradation is detected in the TCLCG even after air exposure for 7 days, owing to the excellent water retention ability enabled by glycerol as co-solvent with water. Using TCLCG, we have successfully demonstrated mobile soft robots with extraordinary maneuverability in unstructured environments, including a crawler showing fast bidirectional locomotion (0.50mm/s) in a small-confined space, and a roller that can escape after deep burying in sand. This article is protected by copyright. All rights reserved.

Path Planning Method With Constant Bending Angle Constraint for Soft Growing Robot Using Heat Welding Mechanism

Soft growing robots, a new soft mobile robot, have recently attracted considerable interest. There are many soft growing robots, some of which have irreversible growing and bending motion mechanisms. For such robots, path planning methods that provide information on bending timing improve operation efficiency. Although various path planning methods have already been developed, they cannot be applied to our growing robot that uses a heat welding mechanism because it has a constraint that all bending angles are the constant value. This article proposes a novel path planning method with constant bending angle constraint. The proposed algorithm was developed based on the rapidly-exploring random tree star (RRT*) algorithm. The method incorporates an algorithm for reducing unnecessary nodes from obtained paths keeping bending angles constant and improving path optimality. We confirmed that the proposed method generates paths whose bending angles are constant. In addition, we experimented with moving our robot along the path in the field with some obstacles. The result showed that the proposed method enabled the robot to reach to target place, avoiding obstacles. The proposed method improves the operating efficiency of our soft growing robot.

Vision-Based Soft Mobile Robot Inspired by Silkworm Body and Movement Behavior

Designing an inexpensive, low-noise, safe for individual, mobile robot with an efficient vision system represents a challenge. This paper proposes a soft mobile robot inspired by the silkworm body structure and moving behavior. Two identical pneumatic artificial muscles (PAM) have been used to design the body of the robot by sewing the PAMs longitudinally. The proposed robot moves forward, left, and right in steps depending on the relative contraction ratio of the actuators. The connection between the two artificial muscles gives the steering performance at different air pressures of each PAM. A camera (eye) integrated into the proposed soft robot helps it to control its motion and direction. The silkworm soft robot detects a specific object and tracks it continuously. The proposed vision system is used to help with automatic tracking based on deep learning platforms with real-time live IR camera. The object detection platform, named, YOLOv3 is used effectively to solve the challenge of detecting high-speed tiny objects like Tennis balls. The model is trained with a dataset consisting of images of Tennis balls. The work is simulated with Google Colab and then tested in real-time on an embedded device mated with a fast GPU called Jetson Nano development kit. The presented object follower robot is cheap, fast-tracking, and friendly to the environment. The system reaches a 99% accuracy rate during training and testing. Validation results are obtained and recorded to prove the effectiveness of this novel silkworm soft robot. The research contribution is designing and implementing a soft mobile robot with an effective vision system.

Deformation-Driven Closed-Chain Soft Mobile Robot Aimed for Rolling and Climbing Locomotion

The inherent compliance of soft mobile robots makes them a safe option for interaction with humans and fragile environments. To expand their possibilities around our daily life, it is desirable for them to have enhanced traversal ability with safe structure and movement. To meet this requirement, we propose a new type of soft mobile robot that moves while selecting rotational, wave, and climbing locomotion. The proposed robot, named DECSO, forms a closed chain of modular segment actuators that individually generate contraction and bidirectional bending motion by applying negative pressure. In this paper, after presenting methods for generating the above three kinds of locomotion, the characteristics and modeling of the segment actuator are illustrated. Furthermore, the experimental results show that a 4-segment prototype achieved smooth rotational movement in the horizontal plane at a velocity of 75 mm/s, while a 6-segment prototype was able not only to move forward by travelling waves, but also to cross over the human body and obstacles of 62% of its own height by rotational movement. These findings suggest a new possibility for soft mobile robots that can safely touch and move around the human body.

A fluidic relaxation oscillator for reprogrammable sequential actuation in soft robots

A fluidic relaxation oscillator for reprogrammable sequential actuation in soft robots

Bioinspired multimodal soft robot driven by a single dielectric elastomer actuator and two flexible electroadhesive feet

Locomotion is an important ability of animals and bioinspired mobile robots. It is, however, challenging for current soft mobile robots to achieve multimodal locomotion within a simple structure. Inspired by caterpillars, we combine a two-degree-of-freedom (2-DOF) dielectric elastomer actuator (DEA) and two flexible electroadhesives (EAs) to form the multimodal soft robot. The 2-DOF DEA was regarded as the deformable body that can elongate, contract, and bend. The EAs, fabricated by a cost-effective cut-transfer method, acted as two feet that can provide required and sufficient frictions whilst moving on different surfaces. Both the DEA and EA were experimentally characterized. As a result, we developed a caterpillar inspired soft robot capable of multimodal turning, crawling, and climbing. The robot was able to crawl at a speed of 2.38 mm/s, achieve two turning modes, climb at a speed of 2.30 mm/s, and can still function after 10000 operation cycles. The robot was further demonstrated to carry a micro camera for inspection tasks in a narrow tunnel, and it may be possible to deploy the robot on satellites for detection uses. This study provides a new insight for the design of bioinspired soft robots with multimodal locomotion capabilities.

Dynamic Finite Element Modeling and Simulation of Soft Robots

Soft robots have become important members of the robot community with many potential applications owing to their unique flexibility and security embedded at the material level. An increasing number of researchers are interested in their designing, manufacturing, modeling, and control. However, the dynamic simulation of soft robots is difficult owing to their infinite degrees of freedom and nonlinear characteristics that are associated with soft materials and flexible geometric structures. In this study, a novel multi-flexible body dynamic modeling and simulation technique is introduced for soft robots. Various actuators for soft robots are modeled in a virtual environment, including soft cable-driven, spring actuation, and pneumatic driving. A pneumatic driving simulation was demonstrated by the bending modules with different materials. A cable-driven soft robot arm prototype and a cylindrical soft module actuated by shape memory alley springs inspired by an octopus were manufactured and used to validate the simulation model, and the experimental results demonstrated adequate accuracy. The proposed technique can be widely applied for the modeling and dynamic simulation of other soft robots, including hybrid actuated robots and rigid-flexible coupling robots. This study also provides a fundamental framework for simulating soft mobile robots and soft manipulators in contact with the environment.

Development of an expansion mechanism for a pneumatic soft mobile robot in a confined space

Development of an expansion mechanism for a pneumatic soft mobile robot in a confined space

Thin Piezoelectric Mobile Robot Using Curved Tail Oscillation

In this paper, a novel piezoelectric material-based soft mobile robot is proposed. The robot consists of a thin film body and a soft polyvinylidene fluoride-based tail. The tail has a unique structure that is a combination of a polyethylene terephthalate fin and a curved piezoelectric film. We experimentally demonstrated the performance of a mobile robot. In particular, the resonance frequency was investigated to maximize tail movement. In addition, a parameter study of the tail shape was performed. Moreover, the repeatability of movements was tested. By using a curved piezoelectric tail with a fin, we built a mobile robot with a thin and flexible body. Furthermore, we fabricated multiple mobile robots by varying the robot configuration and analyzing their mobility. We found that our novel curved tail structure has good mobility performance at low body weights and multi-tailed conditions.

Blindly Controlled Magnetically Actuated Capsule for Noninvasive Sampling of the Gastrointestinal Microbiome

The objective of this article is to address the challenges of physical sample retrieval from all locations along patients' gastrointestinal (GI) tracts for studying of interactions between GI microbial communities (microbiomes) and host immune systems. We propose a novel tetherless, blindly controlled, magnetically actuated capsule for noninvasive sampling of GI microbiomes and liquid digesta. The mesoscale capsule, a soft mobile robot platform, is made from two permanent magnets encapsulated in a soft elastomer and actuated remotely by an external magnet. The capsule is controlled blindly using an external magnet to orient and activate the capsule. Following oral administration, capsules transit the GI tract and are activated at specified locations. The capsule is recovered via routine stool passage and collected samples are processed for downstream analyses (e.g., 16S rRNA surveys, metagenomics, metatranscriptomics and/or metabolomics). The localization of the capsule is estimated using the traveling time and the location of collected microbiomes will be confirmed by downstream analyses. A mathematical model of capsule activation is used to predict capsule activation and guide design optimization. We demonstrate the ability of the capsule to collect samples, as well as maintain sample integrity <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro, ex vivo</i> , and with twelve capsules in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> swine models. Eleven capsules successfully collected digesta (in the range of 18 to 61 mg). This sampling apparatus offers a technological advance for the robust sampling of GI tract contents.

Motion Planning and Iterative Learning Control of a Modular Soft Robotic Snake.

Snake robotics is an important research topic with a wide range of applications, including inspection in confined spaces, search-and-rescue, and disaster response. Snake robots are well-suited to these applications because of their versatility and adaptability to unstructured and constrained environments. In this paper, we introduce a soft pneumatic robotic snake that can imitate the capabilities of biological snakes, its soft body can provide flexibility and adaptability to the environment. This paper combines soft mobile robot modeling, proprioceptive feedback control, and motion planning to pave the way for functional soft robotic snake autonomy. We propose a pressure-operated soft robotic snake with a high degree of modularity that makes use of customized embedded flexible curvature sensing. On this platform, we introduce the use of iterative learning control using feedback from the on-board curvature sensors to enable the snake to automatically correct its gait for superior locomotion. We also present a motion planning and trajectory tracking algorithm using an adaptive bounding box, which allows for efficient motion planning that still takes into account the kinematic state of the soft robotic snake. We test this algorithm experimentally, and demonstrate its performance in obstacle avoidance scenarios.

Laser Pouch Motors: Selective and Wireless Activation of Soft Actuators by Laser-Powered Liquid-to-Gas Phase Change

Untethered control of soft-bodied robots is attractive for interactions in a variety of unstructured and dynamic environments. However, soft robotics systems are currently limited in terms of wireless, selective, and scalable control of multiple actuators. Therefore, we propose a method to wirelessly drive multiple soft actuators by laser projection. A small amount of low-boiling-point liquid inside a planar thin pouch can be heated by a laser and evaporated to inflate the whole body. Laser projection enables both wireless energy supply and the selection of target actuators. Further, the low-boiling-point liquid serves as an actuation source and as a receiver of laser irradiation. Thus, we do not need additional components such as electric circuits and batteries to achieve simple and scalable implementation of multiple soft actuators. We evaluated the mechanical properties and demonstrated that the system can wirelessly control the gestures of fingers of a robot hand. We also verified that our method can activate a group of mobile soft robots simultaneously and individually while tracking the actuator positions. Our approach contributes to the scalable deployment of soft robotic systems by removing tethers for power and communication.

Self-Excited Vibration Valve That Induces Traveling Waves in Pneumatic Soft Mobile Robots

This letter presents a soft compact valve inducing self-excited vibration to be aimed for simplification of piping, power saving and downsizing the total system for pneumatic soft mobile robots generating traveling waves. The presented device is composed of flat tubes, permanent magnets, and restraint parts. It is capable of switching the inner pressure among three isolated chambers alternately and periodically by using the constant air pressure supplied from a single line. In this letter, we describe the driving principle of the valve to switch different chambers automatically, while detecting the pre-set pressure inside each chamber without sensors. The prototype has a flexible sheet structure with a mass of 5.1 g and a thickness of 10 mm, and was examined to induce a self-excited vibration of 0.6 Hz by air supply of 80 kPa. Moreover, it was also confirmed that when the developed valve was mounted on a flexible seat-type mobile, it was possible to propel through a narrow space with 25 mm gap smoothly while generating traveling waves. Finally, the effectiveness of the proposed valve is discussed through the experimental results.

Untethered-Bioinspired Quadrupedal Robot Based on Double-Chamber Pre-charged Pneumatic Soft Actuators with Highly Flexible Trunk.

Given that mobile soft robots are adaptable to the environment, they are always tethered with slow locomotion speed. Compared with other types of mobile robots, mobile soft robots may be more suitable for rescuing tasks, accompanying elderly people, and being used as a safe toy for children. However, the infinite freedom of soft robots increases the difficulty of precision control. In addition, the large volume and long tube of the conventional soft actuator structure limit the range of motion of current mobile soft robots. In this article, a newly designed innovative untethered-bioinspired quadrupedal robot based on double-chamber pre-charged pneumatic (DCPCP) soft actuators with highly flexible trunk is proposed. Asymmetrical cross-tendons actuated by servo motors are used to drive the DCPCP soft legs so that buckling can be avoided and mimic the gait of quadruped animals with the simplest drive and control strategy. In addition, the proposed design greatly improves energy efficiency and exhibits superior performance of variable stiffness. The bioinspired highly flexible trunk is designed with the supporting spine structure and tendon driven muscle to deform, which can constantly adjust to the contact situation between the foot and the ground to adjust the center of gravity of the soft quadruped robot and increase stability when walking and turning. The proposed soft quadruped robot does not require any air compressors, valves, and hoses. The characteristics of untethered, high-energy efficiency, linear control, and stability make the soft quadruped robot suitable for many applications.

Learning to Walk a Tripod Mobile Robot Using Nonlinear Soft Vibration Actuators With Entropy Adaptive Reinforcement Learning

Soft mobile robots have shown great potential in unstructured and confined environments by taking advantage of their excellent adaptability and high dexterity. However, there are several issues to be addressed, such as actuating speeds and controllability, in soft robots. In this letter, a new vibration actuator is proposed using the nonlinear stiffness characteristic of a hyperelastic material, which creates continuous vibration of the actuator. By integrating three proposed actuators, we also present an advanced soft mobile robot with high degrees of freedom of movement. However, since the dynamic model of the soft mobile robot is generally hard to obtain(intractable), it is difficult to design a controller for the robot. In this regard, we present a method to train a controller, using a novel reinforcement learning (RL) algorithm called adaptive soft actor-critic (ASAC). ASAC gradually reduces a parameter called an entropy temperature, which regulates the entropy of the control policy. In this way, the proposed method can narrow down the search space during training, and reduce the duration of demanding data collection processes in real-world experiments. For the verification of the robustness and the controllability of our robot and the RL algorithm, experiments for zig-zagging path tracking and obstacle avoidance were conducted, and the robot successfully finished the missions with only an hour of training time.

Soft mobile robot inspired by animal-like running motion

There is a considerable demand for legged robots with exploring capabilities such as passing through narrow pathways. Soft robots can provide a solution for such applications. Here, we propose a soft legged mobile robot with bimorph piezoelectric main body and pre-curved piezoelectric legs. We experimentally demonstrate the performance of the soft mobile robot. The mobile robot can move 70% of the body length per second. In addition, we investigate physical mechanisms behind the locomotion of the mobile robot using a numerical simulation. Interestingly, the mobile robot generates an animal-like running motion. We find that the amplitude difference of the legs, depending on the leg activation condition, may affect the performance of the robot. We also confirm that the soft mobile robot can maintain the movement under impulsive shock owing to its flexibility.