Aerial transportation and manipulation have attracted increasing attention in the unmanned aerial vehicle field, and visual servoing methodology is widely used to achieve the autonomous aerial grasping of a target object. However, the existing marker-based solutions pose a challenge to the practical application of target grasping owing to the difficulty in attaching markers on targets. To address this problem, this study proposes a novel image-based visual servoing controller based on natural features instead of artificial markers. The natural features are extracted from the target images and further processed to provide servoing feature points. A six degree-of-freedom (6-DoF) aerial manipulator system is proposed with differential kinematics deduced to achieve aerial grasping. Furthermore, a controller is designed when the target object is outside a manipulator’s workspace by utilizing both the degrees-of-freedom of unmanned aerial vehicle and manipulator joints. Thereafter, a weight matrix is used as basis to develop a multi-tasking visual servoing framework to integrate the controllers inside and outside the manipulator’s workspace. Lastly, experimental results are provided to verify the effectiveness of the proposed approach.

Emulating periodic main wing movement of a bird for generating lift and thrust remains a significant challenge in developing a robotic bird. The sequences of main wing motion are comprised of flapping, folding, bending, and twisting. In this paper, we concentrate on the flapping and folding motion, and design two wing mechanisms based on a 4-bar linkage structure: one is only for Flapping Motion (FM) and the other is for simultaneous Flapping and Folding Motion (FFM) during a wing stroke. We derive relationships between length and angle of links to analyze kinematic characteristics of the mechanisms and conduct an optimization to select the length parameters of links that allow maximization of the flapping angle. We run a simulation to confirm the performance of the optimized parameters by examining physical properties, and fabricate two wing mechanisms accordingly. In particular, the folding motion is achieved without using an additional actuator. Force measurements to investigate a lift profile of each mechanism and their quantitative comparison of the performance of both types confirm the benefits of the folding motion in the perspectives of wing frequency and lift. We expect that our kinematic formulation, design procedures, and comparative measurement results can help develop a wing mechanism to create a truly biomimetic robotic bird.

Fish commonly execute rapid linear accelerations initiated during steady swimming, yet the function of the median fins during this process is less understood. We find that the erection/folding time (from the starting time of the linear acceleration (0 s) to the starting time of the folding movement of the fin), as well as the spreading area of the median fins, actively change during the linear acceleration of the live largemouth bass (Micropterus salmoides). To better understand the influence of the folding time and the area change of the median fins on the linear acceleration, we implemented an undulatory biomimetic robotic fish with soft median fins that can be programmed to erect and fold, just like a live fish. To characterize the acceleration performance of the robotic fish, we developed a ‘‘self-propelled’’ experiment technique based on the Kalman filter and Proportional-Integral-Derivative (PID) control algorithm. The experiments on the robotic fish show the acceleration induced by fully-erected median fins increases by 46.3%. Fully-erected median fins positively contribute to propulsion primarily at the onset stage of the linear acceleration while result in a significant decrease in steady swimming speed by 25%, which suggests a large drag force is induced at the steady swimming stage due to the enlarged wetted area. Parametric sweeping experiments on erection/folding time and spreading area demonstrate a proper combination of the erection/folding time and the spreading area enhances the mean linear acceleration by up to 85%. Particle Image Velocimetry (PIV) results reveal that the vortexes shed by the erected dorsal fin are stronger than those shed by the folded fin. As the acceleration process progresses, the thrust generated by the dorsal fins gradually is weakened until only resistance is generated in the end. Our findings may shed light on the realization of controllable surfaces on high performance fish-inspired robotic systems in the future.

Tuna, known for high endurance cruising, have already inspired several underwater robots and swimming studies. This study uses a biomimetic robotic tuna to investigate how different caudal fin planform geometries affect the thrust production and flow structures during Body and/or Caudal Fin (BCF) swimming. The robot was tethered to a circulating water tunnel, and swimming was simulated by moving water at a constant speed relative to the stationary robot. Three differently shaped caudal fins were tested, one rectangular, one elliptical, and one swept. Area, aspect ratio, and rigidity were kept constant between the three fins to ensure that the effect of caudal fin shape could be isolated. The fins were tested at three freestream velocities and four Strouhal numbers (St) so that comparisons between the fins could be made for a variety of swimming scenarios. The swept fin, which is the tested caudal fin most similar to one found on a fusiform swimmer, had the greatest thrust potential at high St, followed by the elliptical fin. The rectangular fin generally produced the least thrust. It was shown that in addition to producing the most thrust, the swept fin also best stabilized the leading edge vortex that developed during the second half of the stroke.

This paper presents a frog-inspired swimming robot based on articulated pneumatic soft actuator. To realize the miniaturization of the robot and enhance its environmental adaptability, combined with the advantages and characteristics of soft materials, an articulated pneumatic soft actuator is designed based on analysis of a frog’s propulsion characteristics. A structural model is established to analyse the mechanical properties of the soft actuator. With the goal of making full use of the driving torque of the actuator and enhancing the propulsion efficiency of the robot, the motion trajectories of each joint of the robot are planned. Based on the trajectory planning, the control strategy of the soft actuator is determined to realize the frog-like swimming of the robot. The torso size after assembly is 0.175 m × 
0.100 m × 0.060 m, which realizes the miniaturization of the frog-inspired robot. During the movement of the robot, the torso moves stably and flexibly, and can realize continuous linear and turning movements. The rationality of the structure and trajectory planning are verified by prototype experiments.

Ionic Polymer Metal Composite (IPMC) is a novel electrically actuated intelligent material with the advantages of big bending dis-placement, low driving voltage, flexible and so on. It has been recognized as one of the most attractive actuators with prospective applications for underwater robots and bionic organs. In this work, a capsule-like robot was introduced with the pectoral and caudal fins made of IPMC. By analyzing the properties of displacement response to square waves with different frequencies and low level voltages, it was found that performance of IPMC are frequency sensitive. Besides, when the absolute value of low level voltage decreases, IPMC could swing on one side with the decrease in amplitudes, whereas the amplitude at high level voltage fluctuates within small ranges at low frequencies.  IPMC tip can approximately maintain when the frequency of driving signal around 30 Hz. Such properties were employed to control the locomotion of robot combining the motions of pectoral and caudal fin. Thus, the locomotions of swimming forward, turning and positioning were realized.

Energy efficiency has been the focus of quadruped robot research. Decreasing the energy loss caused by the DC motor can contribute to the walking efficiency of electrically actuated quadruped robots. Most works have focused on the quadruped mechanisms or actuations such as the Series Elastic Actuation (SEA). This work proposes a better efficient controller to perform the stable 5 m?s?1 movements of quadruped robots. The dynamic model of the electrically actuated leg is established by Lagrangian formulation. The energy efficiency of the DC motors in the electrically actuated quadruped robot is formulated as an optimization problem. The Stochastic Linear Complementarity Problem (SLCP) and sinusoidal pulse force are proposed to reduce the energy consumption at the contact. The Bernstein polynomials are used for planning a quasi-elliptic foot motion trajectory. The stability and energy efficiency of the proposed controller are verified with computer simulation and an actual single leg robot prototype. Compared with other works, the proposed controller performs the optimal Cost of Transport (COT).

The Synthetic Jet (SJ) control on the propulsion behavior of a foil in plunge-pitch motion is examined in this work by numerical simulations. An elliptic foil with ratio of 8 performs the plunge and pitch motions synchronously. A pair of SJs with the same frequency and strength is integrated into the upper and lower surfaces of the foil. As a result, the local flow field around the foil could be obviously modified by the SJs. At the Reynolds number of 200, the effects of the inclined angle between the jet direction and the chord line, the phase angle between the SJs and the flapping motion as well as the location of SJ on the propulsion performance are systematically investigated. Compared with the pure plunging and pitching foil, it is indicated that the enhancement of mean thrust and propulsive efficiency can be obtained by the SJs with suitable working parameters. Based on the numerical analysis, it is found that the jet flow on the foil surfaces, which changes the local pressure distribution to increase the pressure difference between upper and lower surfaces, can benefit the propulsion behavior of the flapping foil.

Solar power, as one of renewable energy, holds potential application for producing steam which relies on high-temperature liquid by traditional methods. Herein, steam was generated by a bio-inspired strategy derived from the plants transpiration using a Printed Recyclable Carbon Membrane (PRCM). The membrane structure facilitated the concentration of carbon particles for the photoreaction and the heat generation for water evaporation, thereby improving the photo-thermal conversion efficiency. The PRCM achieved the best steady evaporation efficiency of 51.9%, which was 5.6 times higher than the value for water and recycling tests were demonstrated. The carbon particles were separated from the water under the magnetism action, a convenient approach that avoided secondary pollution resulting from the disintegration of the PRCM. Rapid preparation, low cost, and reusability of the printed carbon membrane allow for photo-thermal applications such as solar steam generation and seawater desalination.

In modern mechanical design, non-sticky and non-slippery surfaces are highly preferred in many applications. In this work, bio-inspired micro patterns of hexagonal pillar and round dimple with various geometric parameters are fabricated, and the static friction and adhesion performances of the prepared surfaces are investigated. It is found that hexagonal pillar patterns can enhance the static friction and weaken the adhesion performances either at dry or wet conditions. The effects of round dimple patterns on the tribological performances depend on the wetting condition, the load, and the area density. The function mechanism of the designed surfaces is revealed, and a general design principle of the biomimetic patterned surface is proposed. 

In this work, bio-inspired concepts, including a Self-Healing (SH) and super hydrophobic structure, were used to produce slow-release of urea fertilizer. Following a bottom-up process, an SH layer on the urea granule was produced from a combination of two natural waxes, palm and carnauba, and fabricated by a hot-melt coating process in a pan coater. Another layer for super hydrophobicity was formed by a deposition of submicron-wax and carbon black particles on the SH layer to create a micro-nanostructure during coating. After the heat treatment, a smooth coating and even deposition of waxes throughout the urea surfaces were obtained. The properties of the waxes, a healing mechanism, and releasing profiles were examined using an optical microscope. After cracking of the coated urea surface, the intrinsic self-healing behavior was stimulated by heating the samples above 45 ?C, corresponding to high ambient daytime temperatures. Air-trapping behavior was observed at the interphase of the water and coated urea, creating super hydrophobic granule surfaces which act as an invisible layer for water-penetration protection. The releasing profiles of the coated urea in soil revealed that the releasing periods could be significantly extended to four-times longer than those of the uncoated urea.

The morphology of bone repair materials, such as particle size and roughness of the materials surface, can affect the adsorption of protein molecules. The effects of surface morphology on the absorption of proteins with different charges were studied. Submicron and nano hydroxyapatite (HA) powders prepared by the chemical precipitation method were coated on the surface of a gold sheet by electrophoretic deposition. Various hydroxyapatite coating morphologies were obtained by controlling the powder particle size and the deposition time. The coating surface morphology was analyzed by Atomic Force Microscopy (AFM), and the adsorption behavior of differently charged proteins on the surface was dynamically monitored by Quartz Crystal Microbalance with Dissipation (QCM-D). The adsorption dependence of two proteins with different charges upon hydroxyapatite coating surface morphology was investigated. Results show that coating surfaces with smaller deposited particle sizes are favorable for the adsorption of negatively-charged bovine albumin, while with larger deposited particles facilitate the adsorption of positively-charged lysozyme. This may be because that the negatively-charged hydroxyapatite coating exhibits stronger electrostatic effect as the increase in the coating particle size, which facilitates the adsorption of positively-charged proteins and hinders the adsorption of negatively-charged proteins. Increasing coating surface roughness facilitates protein adsorption, though the particle size exhibits a dominant influence. These results are significant for selective adsorption of proteins on material surfaces.

Higher strength and lower degradation rate of Fe compared to magnesium and zinc have made it the most reliable for orthopaedic reconstruction. Hence, this paper studies the morphological and mechanical characteristics of porous Fe fabricated using subtractive manufacturing for load bearing bone replacement. Three types of porous Fe (19%, 39% and 59%) were prepared and then modelled into a 3D model for finite element analysis. The mechanical properties evaluated through finite element analysis were then validated by the experimental results. Computational fluid dynamics was done in this study to evaluate the permeability and wall shear stress of the porous Fe. Correlations between morphological indices, mechanical properties, shear stress and permeability were then obtained. The mechanical behaviour of porous Fe investigated through finite element analysis was in good agreement with the experimental work. The mechanical properties of porous Fe specimen particularly sample C (modulus: 5.63 GPa and yield strength: 145.7 MPa) was tailored to the cancellous bone (modulus: 0.5 GPa – 18 GPa and yield strength: 101 MPa – 169.6 MPa). As the porosity increased, the performance of porous Fe regarding mechanical properties and morphological properties were enhanced.

Fugitive dust has been recognized as an important contributor to air pollution, and artificial porous fence is one of the most effective management strategies to reduce fugitive dust in open areas. To improve the shelter effects and efficiency of Particulate Matter (PM) reduction of traditional fences, this study proposed five bionic fences and their capability was evaluated through wind tunnel tests. The results indicated that all of bionic fences presented better efficiency in reducing wind speed and PM concentrations compared with tradi-tional fences, and they were more efficient in capturing PM10. Among the bionic fences, the non-woven cloth material with four-leave opening presented the best capability both in wind speed and PM reduction. The proposed bionic fences may be further developed and studied for future application in capturing fine PM and adapting to the wind.

Following the contemporary research trend of exploring the potential of eco-friendly natural fibres, this work studies the effects of alkali and silane treatments, with varying concentrations, on the mechanical characterization of composites reinforced with kenaf and pineapple leaf fibre (PALF). Kenaf- and PALF-based composites were fabricated through the heat compression method. Their mechanical characterization was then performed to evaluate the tensile, flexural and impact properties. The findings concluded that chemical treatments indeed enhanced the mechanical properties of composite materials. 5% NaOH and 3% silane treatments can respectively provide the optimum mechanical properties to the kenaf fibre and PALF reinforced composites. Chemical treatment results evidenced that silane-treated composites exhibit higher mechanical properties compared to the NaOH-treated composites. When comparing the mechanical properties of kenaf- and PALF-reinforced polypropylene composites, the overall results show that composites based on PALF have superior mechanical properties.

This innovative work presents mechanical, physical and chemical characterization and analysis of newly extracted fiber from natu-rally resourced plant stem, named Spinifex littoreus fibers (SLF). This is a novel natural, biodegradable and sustainable reinforcement for an improved composite. Initially, the chemical constituents of SLF, such as cellulose, lignin, moisture and wax content were studied. The raw SLF surfaces were modified by chemical treatment with sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2) and silane. A polyester matrix was reinforced with all the treated SLF, before the mechanical properties (tensile strengths) of the composites were determined. Among all the surface chemically treated SLF/polyester composite samples, the Ca(OH)2 treated sample exhibited the highest tensile strength. Further microscopic examination was carried out to validate this result. Also, this analysis established the mechanism of failure of the tensile fractured composite samples, using Scanning Electron Microscope (SEM), among other techniques.