Leg Tips Research Articles

Natural variability and individuality of walking behavior in Drosophila.

Insects use walking behavior in a large number of contexts, such as exploration, foraging, escape and pursuit, or migration. A lot is known on how nervous systems produce this behavior in general and also how certain parameters vary with regard to walking direction or speed, for instance. An aspect that has not received much attention is if and how walking behavior varies across individuals of a particular species. To address this, we created a large corpus of kinematic walking data of many individuals of the fruit fly Drosophila. We only selected instances of straight walking in a narrow range of walking speeds to minimize the influence of high-level parameters, like turning and walking speed, aiming to uncover more subtle aspects of variability. Using high-speed videography and automated annotation we captured the positions of the six leg tips for thousands of steps and used principal components analysis to characterize the postural space individuals used during walking. Our analysis shows that the largest part of walking kinematics can be described by five principal components (PCs). Separation of these five PCs into a 2-dimensional and a 3-dimensional subspace divided the description of walking behavior into invariant features shared across individuals and features that relate to the specifics of individuals; the latter features can be regarded as idiosyncrasies. We also demonstrate that this approach can detect the effects of experimental interventions in an unbiased manner and that general aspects of individuality, such as the the individual walking posture, can be described.

Dynamics of centipede locomotion revealed by large-scale traction force microscopy.

We present a novel approach to traction force microscopy (TFM) for studying the locomotion of 10 cm long walking centipedes on soft substrates. Leveraging the remarkable elasticity and ductility of kudzu starch gels, we use them as a deformable gel substrate, providing resilience against the centipedes' sharp leg tips. By optimizing fiducial marker size and density and fine-tuning imaging conditions, we enhance measurement accuracy. Our TFM investigation reveals traction forces along the centipede's longitudinal axis that effectively counterbalance inertial forces within the 0-10 mN range, providing the first report of non-vanishing inertia forces in TFM studies. Interestingly, we observe waves of forces propagating from the head to the tail of the centipede, corresponding to its locomotion speed. Furthermore, we discover a characteristic cycle of leg clusters engaging with the substrate: forward force (friction) upon leg tip contact, backward force (traction) as the leg pulls the substrate while stationary, and subsequent forward force as the leg tip detaches to reposition itself in the anterior direction. This work opens perspectives for TFM applications in ethology, tribology and robotics.

Mechanical Properties, Tissue Structure, and Elemental Composition of the Walking Leg Tips of Coconut Crabs

The coconut crab, Birgus latro, has black protrusions on the tops of its walking legs and claw fingers. In addition, there are regularly aligned small black protrusions on parts of the exoskeleton surface of the claws and leg. In this study, the elemental composition, crystal structure, tissue structure, and mechanical properties of these protrusions were studied using a materials science approach, and the results were compared with those of mineralized cuticle. These leg tips were found to be a non-calcified fibrous tissue of α-chitin connected to the mineralized cuticle. The tip of the second walking leg was elongated and had a pointed shape with an oval cavity at its center that was more than 1000 times larger than the pore tubes (100–350 nm) of the mineralized cuticle. It was very soft, with a hardness of 0.4 GPa, corresponding to 11–12% of the hardness of the hard exocuticle and 55–57% of the hardness of the soft endocuticle. The elastic modulus of 8.0 GPa obtained by means of nanoindentation testing was consistent with that of α-chitin fibers of shrimp shells obtained by means of tensile testing. These soft protrusions provide a secure grip on the surfaces of trees or rocks and protect the claw fingertips. It was concluded that the black protrusions are related to a unique ecological (engaging in vertical movements, entering and exiting limestone caves, and escape behavior) aspect of the coconut crab, the largest terrestrial crustacean.

Humanoid Robot's Visual Imitation of 3-D Motion of a Human Subject Using Neural-Network-Based Inverse Kinematics

A sequence of 3-D motion images of a human facing an imitator [i.e., a humanoid robot (HR)] is captured using a stereo-vision system installed on the HR. After acquiring enough motion sequences via image ratio and background registration, the estimation of seven feature points (i.e., the head, two arm tips, two leg tips, and two elbows) of the human are obtained. Using five feature points (i.e., the head, two arm tips, and two leg tips), the extraction of key posture frames from the recorded videos is achieved. To ensure a stable imitation motion of the HR, the human motions of the lower body (LB) and the upper body (UB) are imitated separately. All 11 stable motions for the LB are classified by the motion direction, the motion state, and the support phase, whereas only the two arm tips are employed to imitate the motions of the UB. Due to the disadvantages of traditional inverse kinematics (IK), neural-network-based IK is developed to reduce the computation time and improve the accuracy of the time response of the system. Finally, the combined motions of the LB and the UB with suitable interpolation and time intervals are applied to imitate the 3-D motion of a human. The corresponding experimental results confirm the efficacy of the proposed technique.

脚関節トルクの冗長性を利用した四脚ロボットのトロット歩容における最速歩行制御

A way of deriving the fastest walk pattern of quadruped robots for trot gait is developed and installed into a practical robot system. Two support legs and the body are modeled as a five-link manipulator and each swinging leg is modeled as a two link manipulator respectively. As a first step, the fastest walk pattern of support legs is designed under the constraints of torque limits of leg joints and friction forces at the support leg tips. Then, the time optimal motion pattern of each swing leg is designed under the boundary conditions given by the obtained walk pattern of the support legs. The fastest walk patterns of support legs and swinging legs are designed respectively. Therefore, if the time optimal motion pattern of swinging legs doesn't satisfy the boundary conditions given by support legs, the same procedures are iterated by modifying a velocity parameter of the support legs until the boundary conditions are satisfied. SONY ERS-7 is used as a quadruped walking robot and some fundamental experiments are done to verify the effectiveness of the developed control algorithm. From the results, it is revealed that the proposed method is particularly effective on the ground with large friction coefficients.

Control of compliant legged quadruped robots in the workspace

Locomotion control of a quadruped robot requires a well-defined gait pattern (i.e., a coordinated actuation of its four legs in some particular fashion with respect to time). It is of practical importance to move the leg tips in a desired trajectory in order to achieve specific objectives such as to avoid obstacles, minimize energy consumption and locomotion time. Along with body displacement, body orientation is an equally important limit parameter during each leg step of the gait pattern. There are several possible gait patterns that maintain stable and aesthetically pleasing locomotion, and most of these are biologically inspired. This article presents quadruped locomotion control in the workspace through a novel control scheme in which the leg forward motion is controlled in the workspace while the body forward motion is controlled by providing the required effort directly to the joint actuators. In this control approach, the leg tip trajectory error drives a proportional-integral controller that is then transformed through the Jacobian to generate the corrective joint torques. For the body forward motion, leg motion is arrested and the joints are provided with opposite motion, which are controlled by a proportional-integral-derivative controller. The proposed method is simple and easy to implement in the workspace. The performance of the proposed control scheme is evaluated through simulations and animations.

Common mechanics of mode switching in locomotion of limbless and legged animals

Crawling using muscular waves is observed in many species, including planaria, leeches, nemertea, aplysia, snails, chitons, earthworms and maggots. Contraction or extension waves propagate along the antero-posterior axis of the body as the crawler pushes the ground substratum backward. However, the observation that locomotory waves can be directed forward or backward has attracted much attention over the past hundred years. Legged organisms such as centipedes and millipedes exhibit parallel phenomena; leg tips form density waves that propagate backward or forward. Mechanical considerations reveal that leg-density waves play a similar role to locomotory waves in limbless species, and that locomotory waves are used by a mechanism common to both legged and limbless species to achieve crawling. Here, we report that both mode switching of the wave direction and friction control were achieved when backward motion was induced in the laboratory. We show that the many variations of switching in different animals can essentially be classified in two types according to mechanical considerations. We propose that during their evolution, limbless crawlers first moved in a manner similar to walking before legs were obtained. Therefore, legged crawlers might have learned the mechanical mode of movement involved in walking long before obtaining legs.

Vibrot, a Simple Device for the Conversion of Vibration into Rotation Mediated by Friction: Preliminary Evaluation

While “vibrational noise” induced by rotating components of machinery is a common problem constantly faced by engineers, the controlled conversion of translational into rotational motion or vice-versa is a desirable goal in many scenarios ranging from internal combustion engines to ultrasonic motors. In this work, we describe the underlying physics after isolating a single degree of freedom, focusing on devices that convert a vibration along the vertical axis into a rotation around this axis. A typical Vibrot (as we label these devices) consists of a rigid body with three or more cantilevered elastic legs attached to its bottom at an angle. We show that these legs are capable of transforming vibration into rotation by a “ratchet effect”, which is caused by the anisotropic stick-slip-flight motion of the leg tips against the ground. Drawing an analogy with the Froude number used to classify the locomotion dynamics of legged animals, we discuss the walking regime of these robots. We are able to control the rotation frequency of the Vibrot by manipulating the shaking amplitude, frequency or waveform. Furthermore, we have been able to excite Vibrots with acoustic waves, which allows speculating about the possibility of reducing the size of the devices so they can perform tasks into the human body, excited by ultrasound waves from the outside.

Preparation and standard molar enthalpy of formation of the ZnO nanotetrapods

ZnO nanotetrapods with uniform size and morphology were harvested by a gentle and facile microemulsion-mediated hydrothermal route. Each of the prepared nanotetrapods consisted of four legs about 110–130 nm in length and 20 nm in diameter, and their leg tips were somewhat pointed. Through designing a novel thermochemical cycle according to thermodynamic potential function method, the relationship between standard molar enthalpies of formation of nano ZnO and bulk ZnO was built. Combined with microcalorimetry, standard molar enthalpy of formation of the prepared ZnO nanotetrapods at 298.15 K was successfully acquired as (−317.41±0.29) kJ/mol1. The striking difference between standard molar enthalpies of formation of the ZnO nanotetrapods and bulk ZnO can be attributed to the surface effect of nanomaterials.

Structure, composition and properties of naturally occurring non-calcified crustacean cuticle

Crustaceans are known for their hard, calcified exoskeleton; however some regions appear different in colour and opacity. These include leg and cheliped tips in the grapsid crab, Metopograpsus frontalis. The chelipeds and leg tips contain only trace levels of calcium but a significant mass of the halogens, chlorine (Cl) and bromine (Br). In contrast, the carapace is heavily calcified and contains only a trace mass of Cl and no Br. In transverse section across the non-calcified tip regions of cheliped and leg the mass percent of halogens varies with position. As such, the exoskeleton of M. frontalis provides a useful model to examine a possible correlation of halogen concentration with the physical properties of hardness ( H) and reduced elastic modulus ( E r), within a chitin-based matrix. Previously published work suggests a correlation exists between Cl concentration and hardness in similar tissues that contain a metal (e.g. zinc). However, in M. frontalis H and E r did not vary significantly across cheliped or leg tip despite differences in halogen concentration. The non-calcified regions of M. frontalis are less hard and less stiff than the carapace but equivalent to values found for insect cuticle lacking metals. Cheliped tips showed a complex morphological layering that differed from leg tips.

A new species of Phrynobatrachus (Amphibia: Anura: Phrynobatrachidae) from north-western Guinea, West Africa

A new small Phrynobatrachus species from a gallery forest in north-western Guinea is described. Phrynobatrachus pintoi sp. nov. exhibits a combination of unique morphological characters and a distinctive color pattern, including: compact, oval body, short snout, warty dorsum and eyelid (although no eyelid cornicle is present), three pairs of large symmetric black spots on throat and breast, black spots on belly, more than one black bar on thighs and lower leg, finger and toe tips not expanded, and rudimentary web on foot. Furthermore, analysis of mitochondrial DNA from 16S rRNA reveals that this new species differs from other West African species of the genus by a minimum distance of 7%. Genetically the new species is closest to Phrynobatrachus fraterculus, P. cornutus, and P. gutturosus.

Numerical and experimental study of the virtual quadrupedal walking robot-semiquad

SemiQuad is a prototyped walking robot with a platform and two double-link legs. Thus, it is a five-link mechanism. The front leg models identical motions of two quadruped's front legs, the back leg models identical motions of two quadruped's back legs. The legs have passive (uncontrolled) feet that extend in the frontal plane. Due to this the robot is stable in the frontal plane. This robot can be viewed as a "virtual" quadruped. Four DC motors drive the mechanism. Its control system comprises a computer, hardware servo-systems and power amplifiers. The locomotion of the prototype is planar curvet gait. In the double support our prototype is statically stable and over actuated. In the single support it is unstable and under actuated system. There is no flight phase. We describe here the scheme of the mechanism, the characteristics of the drives and the control strategy. The dynamic model of the planar walking is recalled for the double, single support phases and for the impact instant. An intuitive control strategy is detailed. The designed control strategy overcomes the difficulties appeared due to unstable and under actuated motion in the single support. Due to the control algorithm the walking regime consists of the alternating different phases. The sequence of these phases is the following. A double support phase begins. A fast bend and unbend of the front leg allows a lift-off of the front leg. During the single support on the back leg the distance between the two leg tips increases. Then an impact occurs and a new double support phase begins. A fast bend and unbend of the back leg allows the lift-off of the back leg. During the single support on the front leg the distance between the two leg tips decreases to form a cyclic walking gait. The experiments give results that are close to those of the simulation.

On the origin and properties of scent marks deposited at the food source by a stingless bee, Melipona seminigra

Some species of stingless bees of the genus Melipona were reported to scent mark food sources but little is known about the chemical signals involved. We studied the origin and some properties of such scent marks in M. seminigra. Results from choice experiments suggested that the bees do not scent mark the food (sugar water) itself and that abdominal droplets were excluded as the signal source. Extracts of the most distal tarsomeres, however, attracted recruits in the same way as natural scent marks. We conclude that M. seminigra scent marks a food source by leaving secreted at the leg tips. The footprints of at least 40 visits were needed to effectively scent mark. The chemical signal has an active range of about 1 m and its effect persists for about 2 hours. In the absence of footprints no scent marking effect was seen. This finding excludes the importance of mandibular gland secretions (if at all present) for the scent marking observed. stingless bee / Melipona / scent marking / footprint substance / recruitment

受動歩行からヒューマノイドロボット歩行に向けて

There have already been many studies of bipedal walking, but most of them have concentrated on building a good controller and have failed to utilize the dynamic properties of robots. Recently a new approach to bipedal walking has appeared. Using this new approach, a robot can walk down a shallow slope without any actuators or controllers. This walking mode is called Passive Dynamic Walking (PDW). Because of its simplicity in respect to both energy and control, PDW is thought of as a “glider” in walking (Pratt, 1999).Since the appearance of the first paper on PDW by McGeer (McGeer, 1990), many researchers have studied various aspects of it. Previous studies, however, treat only the lower part of the body, not the torso. If the purpose of PDW studies is to make effective use of the body in a humanoid robot, it is natural to treat a robot with a torso. In this paper, we show the effects of the torso on PDW walking in two-dimensional computer simulation.For the first PDW trial with a torso, we used a very simple mode consisting of three links: a torso and two legs. This is a simple extension of the simplest PDW robot. First we examined the possibility of PDW by this robot without adding any torque. The center of mass of the torso and the initial condition of walking were changed variously. We could not, however, find any suitable parameters or initial conditions for stable walking with the center of mass of the torso higher than the hip point.We therefore added torque to support the torso and tried to suppress that torque. As we wanted to maintain simplicity of PDW, a simple feedback control scheme was applied as follows:τ=−kvθw+k(θwd−θw)Torque is applied only to the joint between the torso and the support leg. Given appropriate initial conditions, the robot can walk stably down a shallow slope. Moreover, the walking mode of this robot has the same properties as the original PDW robot suggested by McGeer. For certain parameter combinations, the PDW robot can walk with a stable limit cycle motion.To suppress the torque needed to stand the torso up, four body parameters were changed variously: changing the posture of the torso, adding soft leg tips, changing the curvature of the sole, and adding passive joint resistance. From experimental results, four qualitative points were obtained: (1) as the torso inclines backward, the torque becomes small, (2) a shock absorber is useful to reduce the torque at heel contact, (3) the shape of the sole is important in suppressing torque in the supporting phase, and (4) passive joint resistance is effective in accelerating the speed and duration of walking, but it cannot suppress the torque. Simple analysis shows that the torque at the hip joint to stand the torso up is closely related to the acceleration of the hip. Moreover, the torque at the contact phase is determined by the vertical component of acceleration of the hip, and torque in the supporting phase is determined by the horizontal component. This analysis improves understanding of the simulation results.

Tables for the Design Strength of Eccentrically-Loaded Single Angle Struts

The design of eccentrically-loaded single angle struts is a tedious and lengthy procedure. A computer program was developed to perform these time consuming calculations and generate design tables for 36 ksi and 50 ksi equal and unequal leg angles. The program uses the less conservative approach permitted by the AISC Specification for Load and Resistance Factor Design of Single-Angle Members (AISC, 1993). This approach involves applying the interaction equation separately at the corner and the two leg tips of the angle, with the proper signs for compression and tension. Two step-by-step numerical examples are presented in this paper to outline the procedure implemented to generate load tables for equal and unequal leg angles.

Control of a Quadruped Walking Robot Without Feet for a Gallop Gait

Abstract This paper presents the control of a quadruped walking robot, without feet, for a gallop gait. This gait is decomposed into two phases: a single support phase and a double support phase. Two control schemes are necessary to achieve the motion of the robot, depending on the current phase. For the single support phase, the system is underactuated: one variable is kept free without control. For the double support phase, the system is overactuated. This redundancy is used to satisfy contact force constraints during the motion. The reference trajectory is built with respect to physical constraints: sliding, impact and contact constraints on the leg tips. Also, the trajectory is defined to cope with changes on the free variable evolution.

INFLUENCE OF BONE STAPLE DESIGN ON INTERFRAGMENTARY COMPRESSION

Staple fixation, most commonly thought of as static, has been studied with regard to effecting dynamic compression. Features of staple design that relate to the creation of interfragmentary compression have been analyzed, and a simple manipulative technique to effect compression is illustrated. Compressive forces of bone fixation staples were measured using pressure-sensitive film. Thirteen staple designs were tested in a wood-block model and in cadaveric bone. Staples with legs splayed outward produced higher compressive forces than standard staple designs. Internal beveling of the staple leg tips also produced high compressive forces, while external beveling produced distraction. Staples with legs tapered over their entire length produced compression, but caused splitting in the wood-block model. Our results show that outward splaying of the staple legs is a simple method to increase compression in any staple design.

Ultrasonic linear motor using a multilayered piezoelectric actuator

Abstract A new type of linear motor using a multilayered piezoelectric actuator has been developed. The slider consists of a multilayered piezoelectric actuator and a vibratory fork. An elliptical motion is generated at the end of legs of the vibratory fork. The slider can move by means of the frictional force at the leg tips and the moving direction can be controlled by changing the drive frequency. This motor is very compact (23mm × 13.5mm × 5mm in size) with higher power (conveyable weight > 1kgf).

The Function of Chemo- and Mechanoreceptors in Lobster (Homarus Americanus) Feeding Behaviour

ABSTRACT The behaviour of lobsters preying on live mussels (Mytilus edulis) was observed before and after chemosensory or chemosensory-mechanosensory deafferentation of different sensory appendages. Deafferentation of the antennules, leg tips, or maxillipeds (but not the carapace or proximal leg segments) interfered with feeding performance by causing an increase in the time necessary to crush a mussel after search initiation. In addition, deafferentation of the leg tips or the maxillipeds caused a decline in number of mussels crushed but for different reasons: leg-treated lobsters walked over the mussels without picking them up, whereas maxilliped-treated lobsters grasped the mussels as usual but either did not crush or did not eat them as readily as did normal lobsters. Deafferentation of leg chemoreceptors resulted in the same behavioural deficiencies as deafferentation of leg chemo- and mechanoreceptors, demonstrating that it is the leg chemoreceptors that are essential in releasing this grasping response. Chemoreceptors on different appendages of lobsters therefore fulfill different functional roles in their feeding behaviour.

Vertical Motion of a Buoy-Cable-Array System Used in Submarine Detection

The vertical motion of a submarine detection system consisting of a surface float, cable, and an array of three neutrally buoyant inflated cylindrical legs is investigated. The variation of the natural frequencies of free vibration with different design parameters is studied. Analysis of the response of the system to surface wave excitations is carried out, the final objective being the reduction in the displacements of the leg tips supporting the hydrophones.