Biomimetic leg designs often appear to be arbitrarily chosen. To make a more objective choice regarding biomimetic leg configuration for small canine-inspired robots, we compare one hind leg to the same leg arranged in a different orientation, and show that the less biomimetic leg provides better performance. This differently-oriented leg design, which we call “trans-verse-mirrored” was more efficient and faster, both in simulation and experiment even though both leg configurations used the same passive and active components, rest angles, and monoarticular knee spring.  In experiments the normal configuration had a maximum speed of 0.33 m•s−1 and a specific resistance of 5.1. Conversely, the less biomimetic transverse-mirrored configura-tion had a maximum speed of 0.4 m•s−1 and specific resistance of 3.9. Therefore the transverse-mirrored leg’s best performance yields a 21% increase in speed and 24% decrease in specific resistance when compared to the best performance achieved in the normal biomimetic leg. The major underlying reason is that the knee spring engages more readily in the transverse-mirrored configuration, resulting in this faster and more efficient locomotion. The conclusion is that simply copying from nature does not lead to optimal performance and that insight into the role played by passive design components on natural locomotory dynamics is important.

For most legged robots the drive-motors are mounted on the joints of legs, which increase leg’s mass and rotary inertia. When mounted on legs, the drive-motor has to rotate clockwise and anticlockwise periodically to swing a leg back and forth. Larger inertia of the leg, as well as the ever-changing status of frequent acceleration and deceleration of the motors, limits the moving speed of the legged robots. This article proposes an improved mechanical design to overcome such problems. All the drive-motors are installed on the robot body to reduce the rotary inertia of the legs. Then a crank-rocker mechanism is used to transform continuous rotation of motors to back and forth motion of the leg. With this scheme, the motor may reach higher rotation speed since it drives a lighter leg with no change of the rotation direction. In addition, an elastic tendon is attached to the ankle to reduce the pulse stress on the leg. Kinematics and dynamics analysis demonstrates that the new design enlarges end-workspace, reduces driving torque and increases ground reaction force, which means the new robot has lager stride and higher swing frequency of leg to achieve faster moving.

Compared to single arm robot system, dual arm robot has the ability of performing human-like dexterity and cooperation. Dual arm cooperative operation has attracted more and more attention in industrial applications, such as in assembly of complex parts, manufacturing tasks and handling objects. A unified dynamic control method, which is divided into three modes, namely, independent mode, dependent mode, and half dependent mode, is proposed for a redundant dual arm robot with focus on the movement and force of the desired task being operated. Attention is devoted to develop a unified formulation of the above three modes. In addition, a closed form of inverse kinematic solution instead of numerical integration approach is proposed with the aim to guarantee position accuracy. Different from traditional dynamic controllers, where the independent redundancy resolu-tion is obtained based on particular velocity or acceleration levels, here the two dynamic controllers are improved by combining a closed form of inverse kinematic solution with velocity and acceleration levels. Furthermore, the theoretical results of the proposed control method are validated by simulations and experiments.

An innovative lower extremity exoskeleton with hybrid leg structures is proposed in this paper. The compound pendulum model is applied to analyze the swing motion during walking for the wearer and the exoskeleton respectively. The expression of the resonant period for the human lower limb is obtained and the optimum stride frequency, at which the energy expenditure for walking is the least, coincides with the stride frequency of strolling well. As for the exoskeleton, the relationship between the inertial parameters and the resonant period of the hybrid leg is established. To minimize the walking energy cost for the exo-skeleton, the inertial parameter design must guarantee that the resonant period of the hybrid leg coincides with the actual stride period of the wearer. The resonant period of the hybrid leg is also influenced by the scissor angle which determines the distance between the hip and the ankle of the lower extremity exoskeleton (SJTU-EX) and can be adjusted to match different stride frequencies of various motions by the proper scissor angle planning.

In this paper we propose a data-driven motion control approach for a biomimetic robotic fish. The task of the motion control is to achieve desired motion by means of controlling the fish-like swimming gaits of the robot. Due to the complexity of hydrodynamics, it is impossible to derive an analytic model that can precisely describe the interaction between the robotic fish and surrounding water during motion. To address the lack of the robotic model, we explore data-based modeling and control design methods. First, through biomimetic learning from real fish motion data, a General Internal Model (GIM) is established. GIM translates fish undulatory body motion into robotic joint movement; associates the fish gait patterns, such as cruise and turning, with corresponding joint coordination; and adjusts the robotic velocity by GIM parameters. Second, by collecting robotic motion data at a set of operating points, we obtain the quantitative mapping from GIM tuning parameters to robotic speed. Third, applying the quantitative mapping and using GIM parameters as manipulating variables, a feedforward control is computed according to the desired speed, which greatly expedites the initial movement of the robotic fish. Fourth, Propor-tional-Integral-Derivative (PID) is employed as feedback control, together with an inverse mapping that compensates for the nonlinearity appeared in the quantitative mapping. Fifth, modified Iterative Feedback Tuning (IFT) is developed as an appro-priate data-driven tuning approach to determine controller gains. By switching between feedforward and feedback, the motion performance is improved. Finally, real-time control of robotic fish is implemented on a two-joint platform, and two represen-tative swimming gaits, namely “cruise” and “cruise in turning”, are achieved.

Running on water produces very energy-efficient and fast motion in water environments. Many studies have been per-formed to develop bio-inspired water-running robots. To achieve good performance, the lifting force is very important for a robot to be able to run on water. The loss of lifting force is associated with the rolling stability of the robot on water. The purpose of this study is to improve the rolling stability of a water-running robot through the periodic motion of a balancing tail. Kine-matic analysis was performed to calculate the motions of the legs and the tail, and static analysis was performed to calculate the balancing effect of the tail motion. A numerical model was suggested to determine the dynamic performance of the robotic platform based on kinematic and static results. A simulation based on the numerical model was performed, and the results were compared with empirical data from a robot prototype. The simulation results are in good agreement with the experimental data in terms of rolling stability The lifting force has only a slight effect. The results of this study can be used as a guideline for designing a stable water-running robot.

Feedback flow information is of significance to enable underwater locomotion controllers with higher adaptability and efficiency within varying environments. Inspired from fish sensing their external flow via near-body pressure, a computational scheme is proposed and developed in this paper. In conjunction with the scheme, Computational Fluid Dynamics (CFD) is employed to study the bio-inspired fish swimming hydrodynamics. The spatial distribution and temporal variation of the near-body pressure of fish are studied over the whole computational domain. Furthermore, a filtering algorithm is designed and implemented to fuse near-body pressure of one or multiple points for the estimation on the external flow. The simulation results demonstrate that the proposed computational scheme and its corresponding algorithm are both effective to predict the inlet flow velocity by using near-body pressure at distributed spatial points.

Stimulated locusts often tumble during the jumping process. Locusts can also recover their bodies in the air for flight or landing stability. To increase jumping distance and avoid landing collision of bio-inspired jumping robots, the mechanism of air posture adjustment of locusts is examined in this research. This mechanism can be used to improve the stability of robot. The abdomen swings, wing motions, and the variations in body angle are recorded by a high-speed camera when locusts free fall in air with normal or upside-down initial posture. Results indicate that the wings and abdomen are mainly utilized for air posture adjustment. Moreover, abdomen swing and forewing rotation have positive effects on body pitch. However, locusts have dif-ficulty in recovering their bodies from the upside-down posture without wings, although the body pitch caused by unpredictable perturbation in air can be compensated through abdomen swing. Consequently, body roll is attributed to the wing motion, which is related to two factors, namely, the different flapping amplitudes of the wings on both sides, and the different flapping ve-locities of wings during the upstroke and downstroke periods. This research may provide reference for the design of jumping robots.

Previous studies on chordwise flexibility of flexible wings generally relied on simplified two-dimensional (2D) models. In the present study, we constructed a simplified three-dimensional (3D) model and identified the role of the chordwise flexibility in full flapping motion. This paper includes two parts, the first part discusses the aerodynamic effects of the chordwise flexibility in a typical hovering-flight case; the second part introduces a parametric study of four key parameters. The primary findings are as follows. Flexibility generally degrades the lift performance of the flexible wings. However, in two special cases, i.e. when stroke amplitude is low or pitch rotation is delayed, the flexible wings outperform their rigid counterparts in lift generation. Moreover, flexibility reduces the power consumption of the flexible wings. A wing with small flexibility generally achieves a marginally higher flapping efficiency than its rigid counterpart. Furthermore, reducing stroke amplitude can effectively improve the lift performance of the very flexible wings. Aerodynamic performances of the flexible wings are not as sensitive as the rigid wing to phase difference and mid-stroke angle of attack. The effects of Re are the same for the flexible and rigid wings.

Mosquito has the ability to penetrate the skin with painless insertion. It has attracted the researchers to mimic the bite and develop a painless microneedle. Mosquito applies axial compressive load along with frequency on fascicle to penetrate the human skin and retract if it senses instability prior to insertion. The mechanism of mosquito bite is studied in this work which is divided into two stages for analysis considering different boundary conditions. The probing behaviour of mosquito is considered as stage I and the process of penetration as stage II. An equivalent mechanical model for stage I is proposed and a mathematical model is developed to understand the instability of fascicle in terms of frequency and magnitude of force applied. The governing equation and associated boundary conditions are simplified into Mathieu equation and regions of dynamic instability are ob-tained through the solution. Results confirm instability of the fascicle during stage I of insertion. The probing behaviour of mosquito is discussed in terms of applied force and vibrating frequency. Horizontal reaction forces exerted by labium on fascicle during buckling improve the stability and enable fascicle to withstand high compressive forces. The analysis and results are utilized to set design guidelines for the development of dynamically stable vibration-assisted microneedle.

When the spider orb web stops a prey, the web dissipates impact energy by three routes: internal dissipation within the radial silk, internal dissipation within the spiral silk and aerodynamic dissipation. This paper investigates the energy dissipation mechanism of spider orb webs from the mechanics point of view. Firstly, the dynamic response and energy dissipation of a single spider silk under transverse impact are studied analytically and numerically. The congruence of dynamic response curve validates the accuracy of finite element analysis. Then the whole web is modeled using the finite element method and the re-spective contribution of each route to total energy dissipation during the simulated prey impact is obtained, which agrees with published experimental results. Finally, the influence of initial impact kinetic energy on the fraction distribution of three routes is demonstrated based on the finite element model. The mechanical mechanism of energy dissipation of spider orb webs is discussed and the reason for the differences among the existing opinions is speculated.

Understanding the tribological properties of articular cartilage allows scientists to evaluate degenerative joint diseases and develop new treatment techniques. The objectives of this study are to demonstrate the detrimental effect of rotational motion under both dry and wet friction and to evaluate the friction and wear behavior of bovine articular cartilage with sliding and rotational testing configurations that represent fluid film and boundary lubrication mechanisms, respectively. The articular cartilage pin and plate samples were harvested from healthy adult bovine and then tested on a self-made friction and wear simulator. Cartilage samples were subjected to sliding and rotational motions under constant load. Friction coefficients and wear factors were calculated under three conditions: using bovine serum, phosphate buffered saline and with no lubricant present. The friction coefficient and wear factor of the articular cartilage were significantly increased with rotational motion under both dry and wet friction. Using bovine serum as lubricant in the sliding testing configuration the friction coefficient and wear factor of articular cartilage were both decreased. A similar decrease in the tribological properties of cartilage was initially observed for the rotational testing configuration with bovine serum; however, the friction coefficient and wear factor were increased after 150,000 cycles. In the absence of lubricant, the articular cartilage was entirely worn on contact area in both sliding and rotational testing configurations. Bovine serum proved an effective fluid film lubricant for articular cartilage surfaces.

Polypropylene (PP) matrix composites reinforced with chemically treated Almond Shell (AS) particles with and without compatibilizer (PP-g-MA) was prepared by a twin-screw extrusion at loading of 20 wt.% AS particles. Two types of chemical treatments (alkali treatment with sodium hydroxide and etherification with dodecane bromide) of the particles were carried out to improve the interface adhesion between particles and PP matrix. Results show that chemical modifications of AS particles affect the mechanical and viscoelastic properties of AS/PP composites. The composites reinforced with alkali treated particles and the compatibilized matrix lead to a notable increase in the Young’s modulus (14%) compared to the composites with un-treated AS particles. The ductility of composite was also evaluated by the yield strain, and results show a notable increase (31%) compared to that of composites with untreated particles. The thermal stability increased with the use of etherification (385 ?C), with gains in the temperature up to 23 ?C compared to neat PP (362 ?C). The achieved results show that the AS/PP composites can be used in several applications. A thermoplastic matrix compsite mixed with treated AS particles appears to be a good alternative to obtain environmentally friendly products.

Biomimetic blades for soil-rototilling and stubble-breaking were designed learning from the geometrical structure of the tips of toes of mole rat (Scaptochirus moschatus). The orientation, the number and the central angle of the biomimetic structure were taken as the testing factors. The optimal structure of the biomimetic blade was determined through the tests of soil-rototilling and stubble-breaking operation in an indoor soil bin. The optimal combination of the biomimetic structure pa-rameters is that three arc concave teeth are equally arranged on the front cutting edge with a central angle of 60?. The results of comparative tests between the optimal biomimetic blade and a conventional universal blade show the torque acting on the biomimetic blade is lower during soil-rototilling and stubble-breaking operations. The results of field tests show that the working quality of the biomimetic blades meets the requirements of the national standard of China. Tests of soil-rototilling show that, when the orientation of the biomimetic structure was at low and middle levels, the torque of biomimetic blades decreased from 34.17 N•m to 31.03 N•m. The torque also decreased with the increase of the number of biomimetic structure. The average torques were 34.57 N•m, 33.44 N•m and 31.37 N•m, respectively. The maximum different value between two levels of central angle was 0.41 N•m. Tests in field indicate that for soil-rototilling operation, the tillage depth is deeper than 80 mm, the soil-crushing rate (length of soil block less than 40 mm) is over 50 %, and the vegetation coverage rate is over 55 %. For stubble-breaking operation, the stubble-breaking depth is deeper than 70 mm, the stubble-breaking rate (length of stubble less than 40 mm) is over 60%, and the stubble coverage rate is over 80%, which can meet the stubble-breaking requirement of corn.

Gabor filters are generally regarded as the most bionic filters corresponding to the visual perception of human. Their fil-tered coefficients thus are widely utilized to represent the texture information of irises. However, these wavelet-based iris representations are inevitably being misaligned in iris matching stage. In this paper, we try to improve the characteristics of bionic Gabor representations of each iris via combining the local Gabor features and the key-point descriptors of Scale Invariant Feature Transformation (SIFT), which respectively simulate the process of visual object class recognition in frequency and spatial domains. A localized approach of Gabor features is used to avoid the blocking effect in the process of image division, meanwhile a SIFT key point selection strategy is provided to remove the noises and probable misaligned key points. For the combination of these iris features, we propose a support vector regression based fusion rule, which may fuse their matching scores to a scalar score to make classification decision. The experiments on three public and self-developed iris datasets validate the discriminative ability of our multiple bionic iris features, and also demonstrate that the fusion system outperforms some state-of-the-art methods.