Single actuator wave-like robot (SAW): design, modeling, and experiments

Scale-inspired programmable robotic structures with concurrent shape morphing and stiffness variation

Biological organisms often have remarkable multifunctionality through intricate structures, such as concurrent shape morphing and stiffness variation in the octopus. Soft robots, which are inspired by natural creatures, usually require the integration of separate modules to achieve these various functions. As a result, the whole structure is cumbersome, and the control system is complex, often involving multiple control loops to finish a required task. Here, inspired by the scales that cover creatures like pangolins and fish, we developed a robotic structure that can vary its stiffness and change shape simultaneously in a highly integrated, compact body. The scale-inspired layered structure (SAILS) was enabled by the inversely designed programmable surface patterns of the scales. After fabrication, SAILS was inherently soft and flexible. When sealed in an elastic envelope and subjected to negative confining pressure, it transitioned to its designated shape and concurrently became stiff. SAILS could be actuated at frequencies as high as 5 hertz and achieved an apparent bending modulus change of up to 53 times between its soft and stiff states. We further demonstrated both the versatility of SAILS by developing a soft robot that is amphibious and adaptive and tunable landing systems for drones with the capacity to accommodate different loads.

Bionic Snail Robot Enhanced by Poroelastic Foams Crawls Using Direct and Retrograde Waves

Snails employ a distinctive crawling mechanism in which the pedal waves travel along the foot and interact with the mucus to promote efficient movement on various substrates. Inspired by the concavities on the pedal wave, we develop a new bionic snail robot that introduces transverse patterns in a longitudinal wave to periodically change the friction. The poroelastic foam serves as flexible constraint and fills the robot's internal cavity. It contributes to the bending action, and maintains the thinness and softness of the robot. Then, the model of the robot's single segment is built utilizing the Euler-Bernoulli beam theory. The model aligns well with the experimental data, thereby confirming the effectiveness of soft constraints. The evaluation of pedal wave is conducted, which further guides the optimization of the control sequence. The experiments demonstrated the robot performing retrograde wave locomotion on dry substrates. Notably, shear-thickening fluids were found to be suitable for this particular crawling pattern compared with other mucus simulants, resulting in direct wave locomotion with a 49% increase in speed and a 33% reduction in energy usage. The load capacity of the soft snail robot was also enhanced, enabling it to carry loads up to 2.84 times its own weight. The use of mucus in crawling also brings valuable insights for the enhancement of other biomimetic robots.

Structural Design and Control Research of Multi-Segmented Biomimetic Millipede Robot

Due to their advantages of good stability, adaptability, and flexibility, multi-legged robots are increasingly important in fields such as rescue, military, and healthcare. This study focuses on the millipede, a multi-segmented organism, and designs a novel multi-segment biomimetic robot based on an in-depth investigation of the millipede's biological characteristics and locomotion mechanisms. Key leg joints of millipede locomotion are targeted, and a mathematical model of the biomimetic robot's leg joint structure is established for kinematic analysis. Furthermore, a central pattern generator (CPG) control strategy is studied for multi-jointed biomimetic millipede robots. Inspired by the millipede's neural system, a simplified single-loop CPG network model is constructed, reducing the number of oscillators from 48 to 16. Experimental trials are conducted using a prototype to test walking in a wave-like gait, walking with a leg removed, and walking on complex terrain. The results demonstrate that under CPG waveform input conditions, the robot can walk stably, and the impact of a leg failure on overall locomotion is acceptable, with minimal speed loss observed when walking on complex terrain. The research on the structure and motion control algorithms of multi-jointed biomimetic robots lays a technical foundation, expanding their potential applications in exploring unknown environments, rescue missions, agriculture, and other fields.

Optimal free-surface pumping by an undulating carpet

Examples of fluid flows driven by undulating boundaries are found in nature across many different length scales. Even though different driving mechanisms have evolved in distinct environments, they perform essentially the same function: directional transport of liquid. Nature-inspired strategies have been adopted in engineered devices to manipulate and direct flow. Here, we demonstrate how an undulating boundary generates large-scale pumping of a thin liquid near the liquid-air interface. Two dimensional traveling waves on the undulator, a canonical strategy to transport fluid at low Reynolds numbers, surprisingly lead to flow rates that depend non-monotonically on the wave speed. Through an asymptotic analysis of the thin-film equations that account for gravity and surface tension, we predict the observed optimal speed that maximizes pumping. Our findings reveal how proximity to free surfaces, which ensure lower energy dissipation, can be leveraged to achieve directional transport of liquids.

Wave-like Robotic Locomotion between Highly Flexible Surfaces and Comparison to Worm Robot Locomotion

In a recent study, we developed a minimally actuated robot that utilizes wave-like locomotion and analyzed its kinematics. In this paper, we present an analysis of the robot's locomotion between two highly flexible surfaces. Initially, we created a simulation model of the robot between two surfaces and determined its speed and the conditions of locomotion based on the flexibility of the surface, the geometrical parameters, and the coefficient of friction for horizontal locomotion and climbing at different angles. Our findings indicate that wave locomotion is capable of consistently advancing along the surface, even when the surface is highly flexible. Next, we developed an experimental setup and conducted multiple experiments to validate the accuracy of our simulation. The results indicate an average relative difference of approximately 11% between the speed and advance ratio of the wave crawling between the two surfaces of our simulation model and the experimental results were performed using an actual robot. Lastly, we compared the wave locomotion results to those of the worm locomotion and discovered that wave locomotion outperforms worm locomotion, especially at a higher surface flexibility.

A novel wave-like crawling robot has excellent swimming capabilities

Multiple animals ranging from micro-meter scale bacteria to meter scale vertebrates rely on undulatory motion to propel themselves on land and in the water. This type of locomotion also appears in amphibious animals such as sea snakes and salamanders. While undulatory motion can be used for both crawling and swimming, it requires the coordination of multiple joints so that only a few robots have the ability to mimic this motion. Here, we report a new minimalistic method for both crawling and swimming based on producing a wave motion in the sagittal (vertical) plane. A robotic prototype AmphiSAW was developed to demonstrate this methodology in a variety of scenarios. AmphiSAW (using its wave mechanism only) crawled at 1.5 B s^-1and swam at 0.74 B s^-1. The robot can be fitted with legs or wheels at the front, which can further increase its performance especially when crawling on uneven terrains. In addition to its high speeds, the robot has the lowest cost of transport among all amphibious robots reported in literature.

Fundamentals of burrowing in soft animals and robots

Creating burrows through natural soils and sediments is a problem that evolution has solved numerous times, yet burrowing locomotion is challenging for biomimetic robots. As for every type of locomotion, forward thrust must overcome resistance forces. In burrowing, these forces will depend on the sediment mechanical properties that can vary with grain size and packing density, water saturation, organic matter and depth. The burrower typically cannot change these environmental properties, but can employ common strategies to move through a range of sediments. Here we propose four challenges for burrowers to solve. First, the burrower has to create space in a solid substrate, overcoming resistance by e.g., excavation, fracture, compression, or fluidization. Second, the burrower needs to locomote into the confined space. A compliant body helps fit into the possibly irregular space, but reaching the new space requires non-rigid kinematics such as longitudinal extension through peristalsis, unbending, or eversion. Third, to generate the required thrust to overcome resistance, the burrower needs to anchor within the burrow. Anchoring can be achieved through anisotropic friction or radial expansion, or both. Fourth, the burrower must sense and navigate to adapt the burrow shape to avoid or access different parts of the environment. Our hope is that by breaking the complexity of burrowing into these component challenges, engineers will be better able to learn from biology, since animal performance tends to exceed that of their robotic counterparts. Since body size strongly affects space creation, scaling may be a limiting factor for burrowing robotics, which are typically built at larger scales. Small robots are becoming increasingly feasible, and larger robots with non-biologically-inspired anteriors (or that traverse pre-existing tunnels) can benefit from a deeper understanding of the breadth of biological solutions in current literature and to be explored by continued research.

Fluid-Driven Traveling Waves in Soft Robots

Many marine creatures, gastropods, and earthworms generate continuous traveling waves in their bodies for locomotion within marine environments, complex surfaces, and inside narrow gaps. In this work, we study theoretically and experimentally the use of embedded pneumatic networks as a mechanism to mimic nature and generate bidirectional traveling waves in soft robots. We apply long-wave approximation to theoretically calculate the required distribution of pneumatic network and inlet pressure oscillations needed to create desired moving wave patterns. We then fabricate soft robots with internal pneumatic network geometry based on these analytical results. The experimental results agree well with our model and demonstrate the propagation of moving waves in soft robots, along with locomotion capabilities. The presented results allow fabricating soft robots capable of continuous moving waves using the common approach of embedded pneumatic networks and requiring only two input controls.

Repetitive hygroscopic snapping movements in awns of wild oats

Wild oat (Avena sterilis) is a very common annual plant species. Successful seed dispersion support its wide distribution in Africa, Asia and Europe. The seed dispersal units are made of two elongated stiff awns that are attached to a pointy compartment containing two seeds. The awns bend and twist with changes in humidity, pushing the seeds along and into the soil. The present work reveals the material structure of the awns, and models their functionality as two-link robotic arms. Based on nano-to-micro structure analyses the bending and twisting hygroscopic movements are explained. The coordinated movements of two sister awns attached to one dispersal unit were followed. Our work shows that sister awns intersect typically twice every wetting-drying cycle. Once the awns cross each other, epidermal silica hairs are suggested to lock subsequent movements, resulting in stress accumulation. Sudden release of the interlocked awns induces jumps of the dispersal unit and changes in its movement direction. Our findings propose a new role to epidermis silica hairs and a new facet of wild oat seed dispersion. Reversible jumping mechanism in multiple-awn seed dispersal units may serve as a blueprint for reversibly jumping robotic systems. STATEMENT OF SIGNIFICANCE: The seed dispersal unit of wild oats carries two elongated stiff awns covered by unidirectional silica hairs. The awns bend and twist with changes in humidity, pushing the seed capsule along and into the ground. We studied structures constructing the movement mechanism and modeled the awn as a two-link robotic arm. We show that sister awns, attached to the same seed capsule, intersect twice every drying cycle. Once the awns cross each other, the epidermal silica hairs are suggested to lock any subsequent movements, causing stress accumulation. Sudden release of the interlocked awns may cause the dispersal unit to jump and change its direction. Our findings suggest a new role to silica hairs and a new dispersal mechanism in multiple-awn seed dispersal units.

Fundamental understanding of millipede morphology and locomotion dynamics

A detailed model for the locomotory mechanics used by millipedes is provided here through systematic experimentation on the animal and validation of observations through a biomimetic robotic platform. Millipedes possess a powerful gait that is necessary for generating large thrust force required for proficient burrowing. Millipedes implement a metachronal gait through movement of many legs that generates a traveling wave. This traveling wave is modulated by the animal to control the magnitude of thrust force in the direction of motion for burrowing, climbing, or walking. The quasi-static model presented for the millipede locomotion mechanism matches experimental observations on live millipedes and results obtained from a biomimetic robotic platform. The model addresses questions related to the unique morphology of millipedes with respect to their locomotory performance. A complete understanding of the physiology of millipedes and mechanisms that provide modulation of the traveling wave locomotion using a metachronal gait to increase their forward thrust is provided. Further, morphological features needed to optimize various locomotory and burrowing functions are discussed. Combined, these results open opportunity for development of biologically inspired locomotory methods for miniaturized robotic platforms traversing terrains and substrates that present large resistances.

Frontiers of Robotic Colonoscopy: A Comprehensive Review of Robotic Colonoscopes and Technologies

Flexible colonoscopy remains the prime mean of screening for colorectal cancer (CRC) and the gold standard of all population-based screening pathways around the world. Almost 60% of CRC deaths could be prevented with screening. However, colonoscopy attendance rates are affected by discomfort, fear of pain and embarrassment or loss of control during the procedure. Moreover, the emergence and global thread of new communicable diseases might seriously affect the functioning of contemporary centres performing gastrointestinal endoscopy. Innovative solutions are needed: artificial intelligence (AI) and physical robotics will drastically contribute for the future of the healthcare services. The translation of robotic technologies from traditional surgery to minimally invasive endoscopic interventions is an emerging field, mainly challenged by the tough requirements for miniaturization. Pioneering approaches for robotic colonoscopy have been reported in the nineties, with the appearance of inchworm-like devices. Since then, robotic colonoscopes with assistive functionalities have become commercially available. Research prototypes promise enhanced accessibility and flexibility for future therapeutic interventions, even via autonomous or robotic-assisted agents, such as robotic capsules. Furthermore, the pairing of such endoscopic systems with AI-enabled image analysis and recognition methods promises enhanced diagnostic yield. By assembling a multidisciplinary team of engineers and endoscopists, the paper aims to provide a contemporary and highly-pictorial critical review for robotic colonoscopes, hence providing clinicians and researchers with a glimpse of the major changes and challenges that lie ahead.

Kinetic and Dynamic Modeling of Single ActuatorWave-Like Robot

In this study, the kinematics and dynamics of a single actuator wave (SAW)-like robot are explored. Comprising a helical spine and links, SAW has the potential for miniaturization. A kinematic model for SAW is firstly established, and the dynamic equation of motion is derived based on Kane’s method. For validation, the motion of SAW is simulated using both MATLAB and ADAMS, and the comparison of results demonstrates the effectiveness of the theoretical models. Then the inverse dynamic analysis is performed to reveal the power consumption. Finally, robot prototypes are developed and tested to confirm the robot velocity predicted by simulations.

Planar locomotion of earthworm-like metameric robots

The goal of this research is to develop a generic earthworm-like locomotion robot model consisting of a large number of segments in series and based on which to systematically investigate the generation of planar locomotion gaits and their correlation with a robot’s locomotion performance. The investigation advances the state-of-the-art by addressing some fundamental but largely unaddressed issues in the field. These issues include (a) how to extract the main shape and deformation characteristics of the earthworm’s body and build a generic model, (b) how to coordinate the deformations of different segments such that steady-state planar locomotion can be achieved, and (c) how different locomotion gaits would qualitatively and quantitatively affect the robot’s locomotion performance, and how to evaluate them. Learning from earthworms’ unique morphology characteristics, a generic kinematic model of earthworm-like metameric locomotion robots is developed. Left/right-contracted segments are introduced into the model to achieve planar locomotion. Then, this paper proposes a gait-generation algorithm by mimicking the earthworm’s retrograde peristalsis wave, with which all admissible locomotion gaits can be constructed. We discover that when controlled by different gaits, the robot would exhibit four qualitatively different locomotion modes, namely, rectilinear, sidewinding, circular, and cycloid locomotion. For each mode, kinematic indexes are defined and examined to characterize their locomotion performances. For verification, a proof-of-concept robot hardware is designed and prototyped. Experiments reveal that with the proposed robot model and the employed gait controls, locomotion of different modes can be effectively achieved, and they agree well with the theoretical predictions.

Trajectory Analysis for the MASAR: A New Modular and Single-Actuator Robot

Single-actuator mobile robots offer the benefits of low energy consumption, low weight and size, and low cost, but their motion is typically only one-dimensional. By using auxiliary binary mechanisms that redirect and channel the driving force of their only actuator in different ways, it is possible for these robots to perform higher-dimensional motions, such as walking straight, steering, or jumping, with only one motor. This paper presents the MASAR, a new Modular And Single-Actuator Robot that carries a single motor and several adhesion pads. By alternately releasing or attaching these adhesion pads to the environment, the proposed robot is able to pivot about different axes using only one motor, with the possibility of performing concave plane transitions or combining with other identical modules to build more complex reconfigurable robots. In this paper, we solve the planar trajectory tracking problem of this robot for polygonal paths made up of sequences of segments, which may include narrow corridors that are difficult to traverse. We propose a locomotion based on performing rotations of 180 ∘ , which we demonstrate to be the minimum-time solution for long trajectories, and a near-optimal solution for shorter ones.

Bio-Inspired Robotic Solutions for Landslide Monitoring

Bio-inspired solutions are often taken into account to solve problems that nature took millions of years to deal with. In the field of robotics, when we need to design systems able to perform in unstructured environments, bio-inspiration can be a useful instrument both for mechanical design and for the control architecture. In the proposed work the problem of landslide monitoring is addressed proposing a bio-inspired robotic structure developed to deploy a series of smart sensors on target locations with the aim of creating a sensor network capable of acquiring information on the status of the area of interest. The acquired data can be used both to create models and to generate alert signals when a landslide event is identified in the early stage. The design process of the robotic system, including dynamic simulations and robot experiments, will be presented here.