Pedal Waves Research Articles

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.

The WORMESH-II flatworm-like mesh robot with 2-DOF double joints

This paper deals with the development of a flatworm-like mesh robot WORMESH-II, which is the second prototype in the WORMESH series inspired from a flattened and soft-bodied flatworm. The pedal locomotion is the primary locomotor of the flatworm that is continuous gliding propulsion along the bottom of the body. The significance of WORMESH series is use of multiple pedal waves to generate the locomotion. The WORMESH-II is a modular robot having a revolute joint system to interconnect two modules. Further, it contains two module types: control module (CM) and joint module (JM). Depending on their arrangements, WORMESH-II can be arranged in different module formations. First, this paper presents the design of WORMESH-II in which double joints capable of three-dimensional motion are introduced. Then, two locomotion gaits for translational and spinning locomotion are described for WORMESH-II in isotropic module formation. Three synchronized parallel pedal waves and one pedal wave loop by the new double joint mechanism were respectively utilized to generate translational and spinning motions of WORMESH-II for IMF. The proposed locomotion gaits were investigated by dynamics simulation and the experiment using the prototype of WORMESH-II. We have successfully demonstrated basic translational and spinning locomotion of WORMESH-II with the velocity of 2.8 mm/s and the angular velocity of 0.0043 rad/s, respectively.

A Single Central Pattern Generator for the Control of a Locomotor Rolling Wave in Mollusc Aplysia.

Locomotion in mollusc Aplysia is implemented by a pedal rolling wave, a type of axial locomotion. Well-studied examples of axial locomotion (pedal waves in Drosophila larvae and body waves in leech, lamprey, and fish) are generated in a segmented nervous system via activation of multiple coupled central pattern generators (CPGs). Pedal waves in molluscs, however, are generated by a single pedal ganglion, and it is unknown whether there are single or multiple CPGs that generate rhythmic activity and phase shifts between different body parts. During locomotion in intact Aplysia, bursting activity in the parapedal commissural nerve (PPCN) was found to occur during tail contraction. A cluster of 20 to 30 P1 root neurons (P1Ns) on the ventral surface of the pedal ganglion, active during the pedal wave, were identified. Computational cluster analysis revealed that there are 2 phases to the motor program: phase I (centered around 168°) and phase II (centered around 357°). PPCN activity occurs during phase II. The majority of P1Ns are motoneurons. Coactive P1Ns tend to be electrically coupled. Two classes of pedal interneurons (PIs) were characterized. Class 1 (PI1 and PI2) is active during phase I. Their axons make a loop within the pedal ganglion and contribute to locomotor pattern generation. They are electrically coupled to P1Ns that fire during phase I. Class 2 (PI3) is active during phase II and innervates the contralateral pedal ganglion. PI3 may contribute to bilateral coordination. Overall, our findings support the idea that Aplysia pedal waves are generated by a single CPG.

Slug-inspired Magnetic Soft Millirobot Fully Integrated with Triboelectric Nanogenerator for On‐board Sensing and Self‐powered Charging

Untethered bioinspired soft millirobots have significant advantages in the terms of good environmental adaptability, remote control and high locomotion efficiency, showing potential applications in various biomedical settings. However, to make the bio-inspired soft robot be a highly animal-like machine, more effective bio-functionalities should be integrated into the robot. Herein, inspired by Grey Field Slug, we develop a Slug-inspired magnetic soft millirobot fully integrated with triboelectric nanogenerator (named Slug-inspired TENG-Robot) for on-board sensing and self-powered charging. Under untethered actuation of rotating magnetic field, TENG-Robot generates trains of pedal waves through periodic body fluctuations from the tail to head, producing a forward locomotion on the various terrains (e.g. plane, slope, gap, and tunnel). Synchronously, TENG-Robot harvests the self-transformation induced triboelectricity in closed contact-separation mode during this locomotion. TENG-Robot can self-detect the crawl process and self-power for charging the on-board capacitors via triboelectrification effect during the locomotion. Interestingly, Slug-inspired TENG-Robot integrated with various flexible circuits can light itself like firefly, charge the external electronic devices like electric eel, and response to high temperature stimulus like most animals. We believe the bio-inspired design strategies of TENG-Robot may pave important foundation to understand the principles underlying the behavior of animals and transfer them to the development of ever-more capable robots.

Imaging dynamic three-dimensional traction stresses.

Traction stress between contact objects is ubiquitous and crucial for various physical, biological, and engineering processes such as momentum transfer, tactile perception, and mechanical reliability. Newly developed techniques including electronic skin or traction force microscopy enable traction stress measurement. However, measuring the three-dimensional distribution during a dynamic process remains challenging. Here, we demonstrated a method based on stereo vision to measure three-dimensional traction stress with high spatial and temporal resolution. It showed the ability to image the two-stage adhesion failure of bionic microarrays and display the contribution of elastic resistance and adhesive traction to rolling friction at different contact regions. It also revealed the distributed sucking and sealing effect of the concavity pedal waves that propelled a snail crawling in the horizontal, vertical, and upside-down directions. We expected that the method would advance the understanding of various interfacial phenomena and greatly benefit related applications across physics, biology, and robotics.

Collecting differently sized particles on water surface by maneuvering pedal waves on the foot of the water snail Pomacea canaliculata.

The water snail (Pomacea canaliculata) features both broad dietary scope and high feeding rate, possibly making it one of the most successful mollusc invaders globally. The water snail can collect differently sized food particles on the air-water interface by generating pedal waves on the foot surface, such as granular duckweed and animal carrion in wild aquatic environment. While foraging by pedal waves, the biomechanical challenges by manipulating the differently sized particles might be overcome by mediating the waveform for optimized energy costs, the physics and the function of which have not been uncovered yet. Herein, we study the two-dimensional topographic features of the snail foot in the pedal wave feeding pattern by a laser sensor. Feeding on differently sized particles, the average wavelength of the pedal waves remains nearly constant, whereas the amplitude increases while transporting larger particles. We develop a hydrodynamical model and discover that applying a larger amplitude to transport the particle can shorten the transport time, facilitating the food transport rate. However, to maintain a relatively constant mass uptake rate, the water snail exhibits a flexible strategy of collecting larger particles with increased amplitudes. This work demonstrates that the water snail implements a strategy by generating varying waveforms on the foot surface to take up the floating food at an optimized feeding rate. This feeding fashion may open up a new way for developing bio-inspired solid waste collectors at the gas-liquid interface.

Hoop-Passing Motion for a Snake Robot to Realize Motion Transition Across Different Environments

A snake robot performs diverse motions. To realize a wide range functions in a complex environment, it is necessary to transition between various motions suited to each environment. In this article, we propose a method of transitioning the motion of a snake robot across different environments to expand the application environment of the robot. We first find that the motion at the connection point between two motions must coincide with the tangential movement during motion transition across different environments. We then design a gait called the circular pedal wave. This circular pedal wave allows a hoop-passing motion in which the whole body moves as if it is passing through a virtual hoop fixed in space in sequence from its head through combination with a proposed shift part. The hoop-passing motion allows motion transition across different environments. We propose three application examples of this hoop-passing motion, namely passing through a hole in a wall, entering an underfloor, and attaching to a ladder. We report on experiments conducted to verify the effectiveness of the proposed method and to realize the described motions.

How fast is a snail’s pace? The influences of size and substrate on gastropod speed of locomotion

AbstractTerrestrial gastropods display monotaxic direct crawling. During locomotion, smooth muscle contraction stimulates a series of pedal waves that move along the ventral surface of the foot. These waves interact with a thin layer of mucus produced by the foot, propelling the animal forward. Although the mechanism by which this process occurs has been well studied, less is known about how morphological or environmental factors affect this process, and ultimately how they may alter the speed of propulsion. In this study, we tested the influences of body size, substrate type, and substrate orientation on crawling speed in the terrestrial snail Cornu aspersum. We found that substrate texture and orientation had a strong effect on speed, whereas snail body size and the presence of a conspecific trail did not. Crawling speed across rough sandpaper was the most striking, showing a clear inversely proportional relationship between the size of abrasive particle and speed. We suggest that this may be the result of substrate attributes interfering with mucus adhesion or mucus production, subsequently affecting locomotion, although gait choice or the frequency and length of each pedal wave may also play a role.

Design of a biohybrid robot by mimicking the gait mechanism of Aplysia californica

Abstract We present the design, fabrication and analysis of a biohybrid robot by mimicking the bioinspired feature of gait mechanism of Aplysia californica. Aplysia is a marine gastropod having very stable movement through pedal waves. Movement in the organism is due to viscoelastic properties of the mucus which result in resistance variation and also act as a medium for propulsive force transmission. We designed the biohybrid robot on the principle of this anisotropic friction and it was actuated by the natural muscle from rana rugulosus. After kinetic analysis of different structures, fluid dynamic analysis of the final model gave the variation in drag force. The 3D printed robot undergoes forward motion toward the side with lower resistance upon electrical stimulation with the speed of 2mm per pulse.

Dynamical Modeling and Control of Modular Snake Robots With Series Elastic Actuators for Pedal Wave Locomotion on Uneven Terrain

Abstract This paper introduces the equations of motion of modular 2D snake robots moving in vertical plane employing Series Elastic Actuators (SEAs). The kinematics of such 2D modular snake robot is presented in an efficient matrix form and Euler–Lagrange equations are constructed to model the robot. Moreover, using a spring-damper contact model, external contact forces, necessary for modeling pedal wave motion (undulation in the vertical plane) are taken into account, which unlike existing methods can be used to model the effect of multiple contact points. Using such a contact model, pedal wave motion of the robot is simulated and the torque signal measured by the elastic element from the simulation and experimentation are used to show the validity of the model. Moreover, pedal wave locomotion of such robot on uneven terrain is also modeled and an adaptive controller based on torque feedback in gait parameter's space with optimized control gain is proposed. The simulation and experimentation results showed the efficacy of the proposed controller as the robot successfully climbed over a stair-type obstacle without any prior knowledge about its location with at least 24.8% higher speed compared with non-adaptive motion.

A Millimeter-Scale Snail Robot Based on a Light-Powered Liquid Crystal Elastomer Continuous Actuator.

Crawling by means of the traveling deformation of a soft body is a widespread mode of locomotion in nature-animals across scales, from microscopic nematodes to earthworms to gastropods, use it to move around challenging terrestrial environments. Snails, in particular, use mucus-a slippery, aqueous secretion-to enhance the interaction between their ventral foot and the contact surface. In this study, a millimeter-scale soft crawling robot is demonstrated that uses a similar mechanism to move efficiently in a variety of configurations: on horizontal, vertical, as well as upside-down surfaces; on smooth and rough surfaces; and through obstacles comparable in size to its dimensions. The traveling deformation of the robot soft body is generated via a local light-induced phase transition in a liquid crystal elastomer and resembles the pedal waves of terrestrial gastropods. This work offers a new approach to micro-engineering with smart materials as well as a tool to better understand this mode of locomotion in nature.

Design and Development of a Wheel-less Snake Robot with Active Stiffness Control for Adaptive Pedal Wave Locomotion

This paper presents the design and manufacture process of a wheel-less, modular snake robot with series elastic actuators to reliably measure motor torque signal and investigate the effectiveness of active stiffness control for achieving adaptive snake-like locomotion. A polyurethane based elastic element to be attached between the motor and the links at each joint was designed and manufactured using water jet cutter, which makes the final design easier to develop and more cost-effective, compared to existing snake robots with torque measurement capabilities. The reliability of such torque measurement mechanism was examined using simulated dynamical model of pedal wave motion, which proves the efficacy of the design. A distributed control system was also designed, which with the help of an admittance controller, enables active control of the joint stiffness to achieve adaptive snake robot pedal wave locomotion to climb over obstacles, which unlike existing methods does not require prior information about the location of the obstacle. The effectiveness of the proposed controller in comparison to open-loop control strategy was verified by the number of experiments. The results show the capability of the robot to successfully climb over obstacles with the height of more than 55% of the diameter of the snake robot modules.

Theoretical Consideration on the Pedal Waves of Gastropod Locomotion

Theoretical Consideration on the Pedal Waves of Gastropod Locomotion

Pedal Sole Immunoreactive Axons in Terrestrial Pulmonates: Limax, Arion, and Helix

A century ago histological techniques such as formic acid-gold chloride showed the nerve morphology of the pedal sole in Limax and Helix. There have been no similar descriptions since then of the central nervous system relevant to locomotory pedal waves in the foot of slugs and snails. Topical application of 5-HT affects locomotory waves, but the innervation of the pedal sole with 5-HT axons is not known. Three-dimensional morphology of pedal axons in terrestrial pulmonate embryos is shown herein with modern histological techniques using antibodies and the confocal microscope. In Limax maximus, pedal ganglia are shown with Tritonia pedal peptide (TPep) antibodies. Ladder-like cross bridges in the pedal sole are shown with antibodies to both TPep and 5-HT. In Arion ater, pedal ganglia neurons and their axons that form a plexus in the pedal sole are shown with 5-HT antibodies. In Helix aspersa, 5-HT immunoreactive pedal ganglia neurons and a developing pedal sole axon plexus are seen as in A. ater. Axons in this plexus that grow across the pedal sole can be seen growing into pre-existing nerves. No peripheral 5-HT neurons were identified in these three species. This immunoreactive plexus to 5-HT antibodies in A. ater and H. aspersa spreads over the pedal sole epithelium. Axons immunoreactive to 5-HT antibodies in A. ater and H. aspersa extend the length of the foot, primarily in the rim, so that activity in these axons cannot provide local patterned input to produce locomotory waves, but may provide modulatory input to pedal sole muscles.

Discrete Movements of Foot Epithelium during Adhesive Locomotion of a Land Snail

During the adhesive locomotion of land snails a series of short dark transverse bands, called pedal or foot waves, is visible ifa moving snail's ventral surface is observed through a sheet of glass. Moreover, the mucus secreted from the pedal glands and some pedal epithelial cells forms a thin layer which acts as a glue augmenting adherence, while also acting as a lubricant under the moving parts of the snail's foot. The relationships between velocity and the frequency of pedal waves as well as changes in the volume of small air bubbles under foot waves were analyzed by means of digital recordings made through a glass sheet on which the snails were moving. On the ventral surface of a moving snail foot, the adhering parts of the foot constituted about 80% of the total area, while several moving parts only about 20%. The single moving region of the foot (the pedal wave) amounted to about 3% of snail length. The epithelium in the region of the pedal wave was arched above the substrate and was also more wrinkled than the stationary epithelium, which enabled the forward motion of each specific point of epithelium during the passage of a pedal wave above it. The actual area of epithelium engaged by a pedal wave was at least 30% greater than the area of the epithelium as recorded through a glass sheet. In the region of the pedal wave, the tiny subepithelial muscles acting on the epithelium move it up in the front part of the wave, and then down at the end of the wave, operating vertically in relation to the substrate. In the middle part of the wave, the epithelium only moves forward. In summary, during the adhesive locomotion of snails, the horizontal movement of the ventral surface epithelium proceeds as temporally separate phases of upward, forward and downward movement.

The mechanics of the adhesive locomotion of terrestrial gastropods

Research on the adhesive locomotion of terrestrial gastropods is gaining renewed interest as it provides a source of guidance for the design of soft biomimetic robots that can perform functions currently not achievable by conventional rigid vehicles. The locomotion of terrestrial gastropods is driven by a train of periodic muscle contractions (pedal waves) and relaxations (interwaves) that propagate from their tails to their heads. These ventral waves interact with a thin layer of mucus secreted by the animal that transmits propulsive forces to the ground. The exact mechanism by which these propulsive forces are generated is still a matter of controversy. Specifically, the exact role played by the complex rheological and adhesive properties of the mucus is not clear. To provide quantitative data that could shed light on this question, we use a newly developed technique to measure, with high temporal and spatial resolution, the propulsive forces that terrestrial gastropods generate while crawling on smooth flat surfaces. The traction force measurements demonstrate the importance of the finite yield stress of the mucus in generating thrust and are consistent with the surface of the ventral foot being lifted with the passage of each pedal wave. We also show that a forward propulsive force is generated beneath each stationary interwave and that this net forward component is balanced by the resistance caused by the outer rim of the ventral foot, which slides at the speed of the center of mass of the animal. Simultaneously, the animal pulls the rim laterally inward. Analysis of the traction forces reveals that the kinematics of the pedal waves is far more complex than previously thought, showing significant spatial variation (acceleration/deceleration) as the waves move from the tail to the head of the animal.

Pedal-Like Locomotion Mechanism Modeled on Pedal Crawling of Terrestrial Gastropod

When a snail is crawling on a ground, dark transverse bands appear on the sole of the snail and propagate from the posterior end of the foot to the anterior end. The dark bands are essentially the regions of longitudinal muscle contraction of the surface of foot, which form pedal waves. We paid attention to the manner of formation and propagation of the pedal wave. A pedal-like locomotion mechanism is developed of which moves forward by a pedal crawling like the snail. The pedal mechanism consists of eight units of the contraction mechanism which performs such a series of contraction motions as longitudinal contraction of the sole, lifting the sole surface and propagation of pedal wave by the use of a link mechanism and a SMA as actuator. As a result of the experiment on locomotion of the pedal mechanism, it was found that the locomotion velocity of the pedal mechanism was in proportion to both the propagation velocity of a pedal wave and the number of a pedal wave past on the sole per unit time, but an increase of the frequency of a pedal wave caused a decrease in traction of the pedal mechanism.

カタツムリのトライポロジー特性に関する研究 : 足波の運動機構(生産システム)

カタツムリのトライポロジー特性に関する研究 : 足波の運動機構(生産システム)

347 陸棲軟体動物の不整地における腹足推進

We have examined a locomotion mechanism of a snail which is a terrestrial mollusk on a level surface, and made clear of mechanism of locomotion by generating pedal waves with contraction of sole muscle. In this report, the locomotion mechanism of a snail was experimentally investigated in the case of its crawling on a ground with a gap. It was found that the mechanism of pedal locomotion on the irregular ground was the same as that on the level one.

Effects of serotonin, dopamine and ergometrine on locomotion in the pulmonate mollusc Helix lucorum.

The terrestrial snail Helix lucorum crawls using waves of muscular contraction (pedal waves) that spread along the sole of its foot. Crawling speed depends on wave generation frequency (step frequency) and the distance the snail moves forwards during each wave (step length). In a previous study, video recordings of a crawling snail showed that its sole length varied over a wide range and was directly correlated with mollusc speed. Speed depended on step length, which was directly related to sole length, rather than on step frequency, which remained rather constant. In the present study, the effects of dopamine, ergometrine (a blocker of dopamine receptors in molluscs) and serotonin injection on the linear relationship between sole length and locomotor speed in Helix lucorum were studied. In crawling snails, dopamine caused sole contraction, and locomotion slowed down or ceased. Ergometrine stimulated locomotion, which resembled rapid crawling with an extended sole, as observed under normal conditions. Serotonin stimulated locomotion and accelerated crawling significantly without causing changes in sole length. The acceleration of locomotion induced by serotonin injection was due to pedal wave (step) elongation. It is proposed that, during each locomotor episode, dopamine controls snail speed by regulating sole length, which determines the amplitude of contraction of the muscle cells involved in pedal waves and, as a result, step length; serotonin determines the basic step length and shifts the linear relationship between sole length and mollusc speed upwards along the axis of mollusc speed. The efficiency of the serotonergic system depends on the physiological state of the mollusc (e.g. that characteristic of summer or winter).