Simulation Analysis of Frog-Inspired Take-Off Performance Based on Different Structural Models.

The frog-inspired jumping robot is an interesting topic in the field of biomechanics and bionics. However, due to the frog's explosive movement and large range of joint motion, it is very difficult to make their structure completely bionic. To obtain the optimal jumping motion model, the musculoskeletal structure, jumping movement mechanism, and characteristics of frogs are first systematically analyzed, and the corresponding structural and kinematic parameters are obtained. Based on biological characteristics, a model of the articular bone structure is created, which can fully describe the features of frog movement. According to the various factors affecting the frog's jumping movement, mass and constraints are added, and the complex biological joint structure is simplified into four different jumping structure models. The jumping ground reaction force, velocity, and displacement of the center of mass, joint torque, and other motion information of these four models are obtained through ADAMS simulation to reveal the jumping movement mechanism and the influencing factors of frogs. Finally, various motion features are analyzed and compared to determine the optimal structural model of the comprehensive index, which provides a theoretical basis for the design of the frog-inspired jumping robot.

CFD-Based Simulation Analysis for Motions through Multiphase Environments.

The motion process and force of the jumper crossing a multiphase environment are of great significance to the research of small amphibious robots. Here, CFD (Computational Fluid Dynamics)-based simulation analysis for motions through multiphase environments (water-air multiphase) is successfully realized by UDF (user-defined function). The analytical model is first established to investigate the jumping response of the jumpers with respect to the jump angle, force, and water depth. The numerical model of the jumper and its surrounding fluid domain is conducted to obtain various dynamic parameters in the jumping process, such as jumping height and speed. Satisfactory agreements are obtained by comparing the error of repeated simulation results (5%). Meanwhile, the influence of the jumper's own attributes, including mass and structural size, on the jumping performance is analyzed. The flow field information, such as wall shear and velocity when the jumper approaches and breaks through the water surface, is finally extracted, which lays a foundation for the structural design and dynamic underwater analysis of the amphibious robot.

Design and research of soft-body cavity-type detonation drivers.

According to the high-energy-density movement characteristics of animals during jumping, soft-body cavity-type detonation driver that combines the explosive chemical reaction mechanism of hydrogen and oxygen is designed, in order to control the robot in jump to achieve output optimization. Then, combined with the theoretical values of the detonation dynamic equation and experimental data for the performance parameters, the influences of the mixing ratio of hydrogen (H2) and oxygen (O2), the volume of mixed hydrogen and oxygen in the cavity, and the shape, wall thickness, and area ratio value of the soft-body cavity on the output performance of the detonation driver are analyzed. When gas volume is 20:10 mL, the jump height reaches 2.5 m. In addition, the upper and lower area ratio of cavity is optimized to 2:1, improving the output performance by 21.6% on average. Therefore, the above research results provide reference for the driver structure design of jumping robot.

Design of the Jump Mechanism for a Biomimetic Robotic Frog.

Frogs are vertebrate amphibians with both efficient swimming and jumping abilities due to their well-developed hind legs. They can jump over obstacles that are many or even tens of times their size on land. However, most of the current jumping mechanisms of biomimetic robotic frogs use simple four-bar linkage mechanisms, which has an unsatisfactory biomimetic effect on the appearance and movement characteristics of frogs. At the same time, multi-joint jumping robots with biomimetic characteristics are subject to high drive power requirements for jumping action. In this paper, a novel jumping mechanism of a biomimetic robotic frog is proposed. Firstly, the structural design of the forelimb and hindlimb of the frog is given, and the hindlimb of the robotic frog is optimized based on the design of a single-degree-of-freedom six-bar linkage. A simplified model is established to simulate the jumping motion. Secondly, a spring energy storage and trigger mechanism is designed, including incomplete gear, one-way bearing, torsion spring, and so on, to realize the complete jumping function of the robot, that is, elastic energy storage and regulation, elastic energy release, and rapid leg retraction. Thirdly, the experimental prototype of the biomimetic robotic frog is fabricated. Finally, the rationality and feasibility of the jumping mechanism are verified by a jumping experiment. This work provides a technical and theoretical basis for the design and development of a high-performance amphibious biomimetic robotic frog.

Porous cauliflower-like molybdenum disulfide/cadmium sulfide hybrid micro/nano structure: Enhanced visible light absorption ability and photocatalytic activity.

Micro-/nanostructured materials can control the diffraction and propagation of light, thereby providing new optical properties that can be exploited to enhance photocatalytic processes. In this work, a series of the cauliflower-like MoS2/CdS hybrid micro-/nanostructures is synthesized. These structures contain numerous cracks and pores that can enhance the absorption and utilization of light as well as shorten the distance for transferring photogenerated electrons to the catalyst surface. The results of ultraviolet-visible diffuse reflectance absorption spectra show that the composite material has enhanced absorption in the visible light region. Further investigation of the optical characteristics of the synthesized materials using a finite-difference time-domain (FDTD) simulation reveals that the cauliflower-like micro-/nanostructure increases the optical absorption intensity at the MoS2/CdS interface. Notably, the MoS2/CdS hybrid micro-/nanostructures exhibits high photocatalytic hydrogen production activity (9.5 mmol g-1 h-1) and long-lasting cycle stability. This work helps us to further understand the enhancement mechanism of light absorption and utilization by porous structural materials.

A Dynamic Hysteresis Model and Nonlinear Control System for a Structure-Integrated Piezoelectric Sensor-Actuator.

The piezoelectric sensor-actuator plays an important role in micro high-precision dynamic systems such as medical robots and micro grippers. These mechanisms need high-precision position control, while the size of the sensor and actuator should be as small as possible. For this paper, we designed and manufactured a structure-integrated piezoelectric sensor-actuator and proposed its PID (Proportion Integral Differential) control system based on the dynamic hysteresis nonlinear model and the inverse model. Through simplifying the structure of the piezoelectric sensor-actuator by the centralized parameter method, this paper establishes its dynamic model and explores the input-output transfer function by taking the relationship between the output force and displacement as the medium. The experiment shows the maximum distance of the hysteresis curve is 0.26 µm. By parsing the hysteresis curve, this paper presents a dynamic hysteresis nonlinear model and its inverse model based on a 0.5 Hz quasi-static model and linear transfer function. Simulation results show that the accuracy of the static model is higher than that of the dynamic model when the frequency is 0.5 Hz, but the compensation accuracy of the dynamic model is obviously better than that of the static model with the increase of the frequency. This paper also proposes a control system for the sensor-actuator by means of the inverse model. The simulation results indicate that the output root mean square error was reduced to one-quarter of the original, which proves that the structure-integrated piezoelectric sensor-actuator and its control system have a great significance for signal sensing and output control of micro high-precision dynamic systems.

Swimming Performance of the Frog-Inspired Soft Robot.

This article presents a frog-inspired swimming soft robot whose joints are articulated pneumatic soft actuators. The soft actuator is designed and prepared by studying the biological structure and limb movement characteristics of frogs. A schematic limb motion diagram of the robot is established based on the kinematic model, and the design scheme is determined by a combined control system. The torso size is 0.175 × 0.100 × 0.060 m, which realizes frog-inspired swimming robot miniaturization. The experimental results show that the average propulsion speed during linear motion is 0.075 m/s, and the average turning speed is 15°/s. The rationality of the robot structural design and correctness of the control system are verified by prototype experiments.

Lanthanide Coordination Polymer-Based Composite Films for Selective and Highly Sensitive Detection of Cr2O72- in Aqueous Media.

Due to the high carcinogenicity and bioaccumulation effects of dichromate ions in the human body, sensitive and rapid detection of Cr2O72- ions is necessary. Herein, two lanthanide coordination polymers based on a linear dicarboxylic acid ligand, named {Ln(cpon)(Hcpon)(H2O)3}n [Ln = Tb, Tbcpon; Eu, Eucpon; H2 cpon = 5-(4-carboxy-phenoxy)-nicotinic acid], have been successfully synthesized. These two isostructural compounds contain one-dimensional zigzag chains that consist of uncoordinated carboxyl groups and pyridine groups in the framework, and the one-dimensional chains can further form a three-dimensional supramolecular stacking structure by intermolecular interaction. Both Tbcpon and Eucpon show good luminescence performance and high stability. Tbcpon exhibits a good ability to sense Cr2O72- ions in aqueous solution. Moreover, the composite film material composed of Tbcpon and poly(methyl methacrylate) (PMMA) exhibits superior luminescence properties compared to those of pure Tbcpon. The Tbcpon-PMMA film exhibits an excellent ability to recognize Cr2O72- ions with high selectivity and a low detection limit of 5.6 ppb, which is much lower than the maximum contamination standard of 100 ppb in drinking water specified by the U.S. Environmental Protection Agency. Furthermore, the Tbcpon-PMMA film shows good recyclability for more than five cycles and anti-interference ability. After the introduction of the slightly soluble polymer poly(vinyl alcohol) (PVA), the Tbcpon-PVA composite film can effectively detect Cr2O72- ions in as little as 1 min. These composite films could be potentially used as test strips for trace detection and rapid detection of Cr2O72- ions in aqueous solution.

Highly sensitive and selective fluorescent probes for Hg2+ in Ag(i)/Cu(ii) 3D supramolecular architectures based on noncovalent interactions.

Three novel metal-organic assemblies (MOAs), namely, [Ag(2,4'-Hpdc)(4,4'-bpy)]n (1), [Ag(2,2'-Hpdc)(4,4'-bpy)0.5]n (2), and [Cu(2,2'-Hpdc)2(1,4-bib)]n (3) [2,4'-H2pdc = 2,4'-biphenyldicarboxylic acid; 2,2'-H2pdc = 2,2'-biphenyldicarboxylic acid; 4,4'-bpy = 4,4'-bipyridine; 1,4-bib = 1,4-bis(1-imidazolyl)benzene] have been hydrothermally synthesized by using mixed ligands and characterized by single crystal X-ray diffraction, infrared (IR), elemental analysis and thermogravimetric analysis (TGA). The crystal structures of the three compounds indicate that the hydrogen bonding (C-HO and C-Hπ) and ππ stacking interactions play critical roles in the formation of an extended supramolecular array. The combination of C-Hπ and ππ stacking interactions endow 1 with a 3D network. 2 displays a rare 3D structure with a unique 1D structure based on an eight-membered {Ag2C2O4} ring and compound 3 shows a 1D chain structure, which is propagated to form an extended 3D structure only by C-Hπ hydrogen bonding. The two Ag(i)-compounds display blue emissions in the solid state at 298 K and 77 K. More significantly, compound 1 shows excellent selectivity, fast detection time (<5 min), and high sensitivity (detection limit, 9.63 nM) for Hg2+ ions in aqueous solution due to a great enhancement of 1-luminescence, which can be attributed to Hg2+ cation binding by a non-coordinated carboxyl group efficiently. This is a rare example of Hg2+ detection in aqueous solution based on luminescent silver MOAs. In addition, adsorption spectra reveal the semiconductive nature (2.76 eV for 2, but not detected for 1), thus the role of the AgAg interaction in controlling the performance of the semiconductor properties is highlighted.

Design of a quasi-passive 3 DOFs ankle-foot wearable rehabilitation orthosis.

Muscular rigidity and atrophy caused by long-term underactivity usually lead to foot drop, strephenopodia, foot extorsion or some other complications for the lower limb movement disorders or lower limb surgery sufferers. The ankle-foot orthosis can help patients conduct the right ankle motion mode training, inhibit spasm and prevent ankle complications. In this paper, a quasi-passive 3 DOFs ankle-foot wearable orthosis was designed on the basis of kinematics and dynamics analysis of the ankle joint. Ankle joint trajectory and dynamic characteristics similar to those of natural gait can be obtained by the combination of passive energy storage and additional power complement. In terms of function, the orthosis has shock absorption and low energy consumption. Given its excellent characteristics of comfortableness, lightweight, and anthropomorphic construction, the orthosis can be used in medical institutions for rehabilitation training or as a daily-walking auxiliary equipment for surgery sufferers.

A passively safe cable driven upper limb rehabilitation exoskeleton.

BACKGROUND: When using upper limb exoskeletons that assist the movement of physically weak people, safety should be the most important index. OBJECTIVE: In this paper, a passively safe, cable-driven upper limb exoskeleton with parallel actuated joints, which perfectly mimics human motions, is proposed. METHODS: Compared with the existing upper limb exoskeletons which are mostly designed only considering the realization of functional properties, and having poor wearabity, a passively safe prototype for motion assistance based on human anatomy structure has been developed in our design. This design is based on the prior exoskeleton structure with the adoption of a gravity balanced device. RESULTS AND CONCLUSION: The gravity balanced mechanism was confirmed in theory and simulation, showing it has a positive effect on balance.

BP neural network tuned PID controller for position tracking of a pneumatic artificial muscle.

BACKGROUND: Although Pneumatic Artificial Muscle (PAM) has a promising future in rehabilitation robots, it's difficult to realize accurate position control due to its highly nonlinear properties. OBJECTIVE: This paper deals with position control of PAM. METHODS: To describe the hysteresis inside PAM, a polynomial based phenomenological function is developed. Based on the phenomenological model for PAM and analysis of pressure dynamics within PAM, an adaptive cascade controller is proposed. Both outer loop and inner loop employ BP Neural Network tuned PID algorithm. The outer loop is to handle high nonlinearities and unmodeled dynamics of PAM, while the inner loop is responsible for nonlinearities caused by pressure dynamics. RESULTS: Experimental results show high tracking accuracy as compared with a convention PID controller. CONCLUSION: The proposed controller is effective in improving performance of PAM and will be implemented in a rehabilitation robot.