Bionic lightweight design of limb leg units for hydraulic quadruped robots by additive manufacturing and topology optimization

Galloping cheetahs,climbing mountain goats,and load hauling horses all show desirable locomotion capability,which motivates the development of quadruped robots.Among various quadruped robots,hydraulically driven quadruped robots show great potential in unstructured environments due to their discrete landing positions and large payloads.As the most critical movement unit of a quadruped robot,the limb leg unit(LLU)directly affects movement speed and reliability,and requires a compact and lightweight design.Inspired by the dexterous skeleton–muscle systems of cheetahs and humans,this paper proposes a highly integrated bionic actuator system for a better dynamic performance of an LLU.We propose that a cylinder barrel with multiple element interfaces and internal smooth channels is realized using metal additive manufacturing,and hybrid lattice structures are introduced into the lightweight design of the piston rod.In addition,additive manufacturing and topology optimization are incorporated to reduce the redundant material of the structural parts of the LLU.The mechanical properties of the actuator system are verified by numerical simulation and experiments,and the power density of the actuators is far greater than that of cheetah muscle.The mass of the optimized LLU is reduced by 24.5%,and the optimized LLU shows better response time performance when given a step signal,and presents a good trajectory tracking ability with the increase in motion frequency.

Study of the Ballistic Impact Behavior of Protective Multi-Layer Composite Armor

The abalone shell,a composite material whose cross-section is composed of inorganic and organic layers,has high strength and toughness.Inspired by the abalone shell,several multi-layer composite plates with different layer sequences and thicknesses are studied as bullet-proof material in this paper.To investigate the ballistic performance of this multi-layer structure,the complete characterization model and related material parameters of large deformation,failure and fracture ofAl_(2)O_(3)ceramics andCarbon Fiber Reinforced Polymer(CFRP)are studied.Then,3D finite element models of the proposed composite plates with different layer sequences and thicknesses impacted by a 12.7 mm armor-piercing incendiary(API)are built using Abaqus to predict failure.The simulation results show that the CFRP/Al2O3 ceramic/Ultrahigh Molecular Weight Polyethylene(UHMWPE)/CFRP(1 mm/4 mm/4 mm/1 mm)composite is the optimized stack of layers.The simulation results under specified layer sequence and thickness have a reasonable correlation with the experimental results and reflect the failure and fracture of the multi-layer composite protective armor.

Design of A Bionic Spudcan and Analysis of Penetration and Extraction Performances for Jack-up Platform

The mechanisms of soil structure interaction have drawn much attention in the past years in the installation and operation of jack-up platform. A bionic spudcan produced by biomimetic of egg and snail shell is proposed, and the performance of the penetration and extraction are analyzed by numerical method. The geometric contour of egg and snail shell is measured, and its mathematical model is established respectively. According to the structure of existing spudcan of jack-up platform, three kinds of typical biomimetic spudcan are designed. Furthermore, numerical analysis models of biomimetic spudcan are established respectively to study the soil structure interaction mechanism in the process of penetration and extraction, and contrastive analysis of resistance characteristics are carried out. To conclude, the results show that the biomimetic spudcan facilitates the platform installation, and it is also beneficial to the improvement of the bearing capacity of spudcan.

TOPOLOGY DESIGN OPTIMIZATION BASED ON BIOTIC BRANCH NET

The biotic branch nets are extreme high-tech product. In order to achieve acertain functional objective, they can adjust their growth direction and growth velocity byaccording to the varying growth environment. An innovative and effective methodology of topologydesign optimization based on the growth mechanism of biotic branch nets is suggested, and it isapplied to a layout design problem of a conductive cooling channel in a heat transfer system. Theeffectiveness of the method is validated by the FEM analysis.

Improving the design of reinforcing frames by simulating the arch and peltate venation structures

Based on the analyses on arch and peltate venation structures, the design of reinforcing frames was improved. First, distribution rules of the arch structure were summarized. According to the load condition and the structure of the frame, a mechanical model of arch structure was devel- oped, and two solutions for the model were analyzed and compared with each other. Through the a- nalysis, application rules of arch structure for improving the design were obtained. Then, distribu- tion rules of peltate venation structure were summarized. By using the same method, application rules of peltate venation structure for improving the design were also obtained. Finally, mechanical problem of the frame was described, and rib arrangement of the frame was redesigned. A parameter optimization for the widths of ribs in bionic arrangement was also carried out to accomplish the im- proving design. Comparison between bionic and conventional reinforcing frames shows that the weight is reduced by as much as 15.3%.

Optimal Design and Mechanical Simulation of Rubber bushing with Convex Hull Structure Based on Bionics

Inspired by the safe landing of cats falling from high altitudes,a bionic flexible rubber bushing structure is proposed and its motion characteristics are systematically studied to explore its potential application in the suppression of vibration.The convex hull structure on the bushing surface is abstracted from the cat’s claw pad,and the hyper-viscoelastic model is selected as the constitutive model of the rubber material.In addition,the design with the best vibration damping effect is finally obtained by reasonably adjusting the amount of radial compression and distribution of bionic structures.Finally,under the same conditions,the test results of the dynamic characteristics of the bushing verify the accuracy of the simulation results.Research results show that the convex hull bionic structure designed in this paper can effectively change the motion characteristics of the rubber bushing under various working conditions,which provides new inspiration or potential possibility for the design of rubber bushing in the future.

Bionic Design and Experimental Validation of a Robotic Airship Inspired by the Physalia physalis

The robotic airship is one of the most unique and promising green aircraft,however,as a“lighter-than-air aircraft”and“thermal aircraft”,its long-endurance flight has great difficulties in decreasing drag and controlling buoyancy and pressure under thermal effects.In this work,we reported a robotic airship inspired by the Physalia physalis,imitating its morphology,physiological structure,and biological behaviors.The hull is designed by imitating the morphology of the Physalia physalis,and the gasbags including a helium balloon,two ballonets,and a thermoregulation gasbag are designed by imitating the physiological structure and biological behaviors of the pneumatophore,bladder,and gland of the Physalia physalis,respectively.Experimental results show that the bionic airship has an increase of about 40%in lift-to-drag and decreases the pressure in helium balloon by 47.5%under thermal effects,and has better aerodynamic performances and thermoregulation performances than conventional airships.

Elastic Buckling of Bionic Cylindrical Shells Based on Bamboo

High load-bearing efficiency is one of the advantages of biological structures after the evolution of billions of years. Biomimicking from nature may offer the potential for lightweight design. In the viewpoint ofrnechanics properties, the culm of bamboo comprises of two types of cells and the number of the vascular bundles takes a gradient of distribution. A three-point bending test was carried out to measure the elastic modulus. Results show that the elastic modulus of bamboo decreases gradually from the periphery towards the centre. Based on the structural characteristics of bamboo, a bionic cylindrical structure was designed to mimic the gradient distribution of vascular bundles and parenchyma cells. The buckling resistance of the bionic structure was compared with that of a traditional shell of equal mass under axial pressure by finite element simulations. Results show that the load-bearing capacity of bionic shell is increased by 124.8%. The buckling mode of bionic structure is global buckling while that of the conventional shell is local buckling.

A Bio-Inspired Flapping-Wing Robot With Cambered Wings and Its Application in Autonomous Airdrop

Flapping-wing flight, as the distinctive flight method retained by natural flying creatures, contains profound aerodynamic principles and brings great inspirations and encouragements to drone developers. Though some ingenious flapping-wing robots have been designed during the past two decades, development and application of autonomous flapping-wing robots are less successful and still require further research. Here, we report the development of a servo-driven bird-like flapping-wing robot named USTBird-I and its application in autonomous airdrop.Inspired by birds, a camber structure and a dihedral angle adjustment mechanism are introduced into the airfoil design and motion control of the wings, respectively. Computational fluid dynamics simulations and actual flight tests show that this bionic design can significantly improve the gliding performance of the robot, which is beneficial to the execution of the airdrop mission.Finally, a vision-based airdrop experiment has been successfully implemented on USTBird-I, which is the first demonstration of a bird-like flapping-wing robot conducting an outdoor airdrop mission.

Design of an Active Flexible Spine for Wall Climbing Robot Using Pneumatic Soft Actuators

Wall climbing robots can be used to undertake missions in many unstructured environments.However,current wall climbing robots have mobility difficulties such as in the turning or accelarating.One of the main reasons for the limitations is the poor flexibility of the spines.Soft robotic technology can actively enable structure deformation and stiffness varations,which provides a solution for the design of active flexible spines.This research utilizes pneumatic soft actuators to design a flexible spine with the abilities of actively bending and twisting by each joint.Using bending and torsion moment equilibriums,respectively,from air pressure to material deformations,the bending and twisting models for a single actuator with respect to different pressure are obtained.The theoretical models are verified by finite-element method simulations and experimental tests.In addition,the bending and twisiting motions of single joint and whole spine are analytically modeled.The results show that the bionic spine can perform desired deformations in accordance with the applied pressure on specified chambers.The variations of the stiffness are also numerically assessed.Finally,the effectiveness of the bionic flexible spine for actively producing sequenced motions as biological spine is experimentally validated.This work demonstrated that the peneumatic spine is potential to improve the spine flexibility of wall climbing robot.

Design of a Flexible Bionic Ankle Prosthesis Based on Subject-specific Modeling of the Human Musculoskeletal System

A variety of prosthetic ankles have been successfully developed to reproduce the locomotor ability for lower limb amputees in daily lives. However, they have not been shown to sufficiently improve the natural gait mechanics commonly observed in comparison to the able-bodied, perhaps due to over-simplified designs of functional musculoskeletal structures in prostheses. In this study, a flexible bionic ankle prosthesis with joints covered by soft material inclusions is developed on the basis of the human musculoskeletal system. First, the healthy side ankle–foot bones of a below-knee amputee were reconstructed by CT imaging. Three types of polyurethane rubber material configurations were then designed to mimic the soft tissues around the human ankle, providing stability and flexibility. Finite element simulations were conducted to determine the proper design of the rubber materials, evaluate the ankle stiffness under different external conditions, and calculate the rotation axes of the ankle during walking. The results showed that the bionic ankle had variable stiffness properties and could adapt to various road surfaces. It also had rotation axes similar to that of the human ankle, thus restoring the function of the talocrural and subtalar joints. The inclination and deviation angles of the talocrural axis, 86.2° and 75.1°, respectively, as well as the angles of the subtalar axis, 40.1° and 29.9°, were consistent with the literature. Finally, dynamic characteristics were investigated by gait measurements on the same subject, and the flexible bionic ankle prosthesis demonstrated natural gait mechanics during walking in terms of ankle angles and moments.

Structural design and stiffness matching control of bionic variable stiffness joint for human–robot collaboration

The physical compliance of interaction is an important requirement for safe and efficient collaboration between robots and humans,and the realization of human–robot compliance requires robot joints with variable stiffness similar to those of human joints.In this study,based on the tissue structure and driving principle of the human arm muscle ligament,a robot joint with variable stiffness is designed,consisting of an elastic belt and serial elastic actuator in parallel.The variable stiffness of the joint is realized by adjusting the tension length of the elastic belt.Surface electromyography(sEMG)signals of the human arm are used as the characterization quantity of joint stiffness to establish the pseudostiffness model of the elbow joint.The stiffness of the robot joints is adjusted in real-time to match the human arm stiffness based on the changes in sEMG signals of the human arm during operation.Real-time compliant interaction of human–robot collaboration is realized based on an end stiffness matching strategy.Additionally,to verify the effectiveness of the human joint stiffness matching-based compliance control strategy,a human–robot cooperative lifting experiment was designed.The bionic variable stiffness joint shows good stiffness adjustment,and the human–robot joint stiffness matching strategy based on human sEMG signals can improve the effectiveness and comfort of human–robot collaboration.

Design and 3D Printing of Graded Bionic Metamaterial Inspired by Pomelo Peel for High Energy Absorption

Light-weight,high-strength metamaterials with excellent specific energy absorption(SEA)capabilities are sig-nificant for aerospace and automobile.The SEA of metamaterials largely depends on the material and structural design.Herein,inspired by the superior impact resistance of pomelo peel for protecting the pulp and the elevated SEA ability of a functionally graded structure,a graded bionic polyhedron metamaterial(GBPM)was designed and realized by 3D printing using a soft material(photosensitive resin)and a hard material(Ti-6Al-4V).Guided by compression tests and numerical simulations,the elevated SEA ability was independent of the materials.The fluctuation region appeared in hard-material-fabricated bionic polyhedron metamaterial(BPMs)and was absent in soft-material-fabricated BPMs in the stress-strain curves,resulting in the growth rate of the SEA value of the soft-material-fabricated GBPM being enhanced by 5.9 times compared with that of the hard-material-fabricated GBPM.The SEA values of soft-and hard-material-fabricated GBPM were 1.89 and 44.16 J/g,which exceed those of most soft-and hard-material-fabricated metamaterials reported in previous studies.These findings can guide the design of metamaterials with high energy absorption to resist external impacts.

A Bionic Stick–Slip Piezo-Driven Positioning Platform Designed by Imitating the Structure and Movement of the Crab

By imitating the body structure and movement mode of the crab in nature,a novel stick–slip piezo-driven positioning platform was proposed by employing the bionic flexible hinge mechanism with a symmetrical structure and two piezoelectric stacks.The structural design and bionic motion principle were discussed,followed by analyzing the feasibility,safety,and output magnification ratio of the bionic flexible hinge mechanism via the stiffness matrix method and finite element simulation.To investigate the output performances of the positioning platform,a prototype was fabricated and an experiment system was established.Stepping characteristics of the positioning platform under various driving voltages were characterized,and the results indicated that the positioning platform could move steadily under various driving voltages.Within 1 s,the differences between the forward and reverse output displacement were less than 3%under different driving frequencies,proving the high bidirectional motion symmetry.The maximum driving speed of 5.44 mm/s was obtained under the driving voltage of 120 V and driving frequency of 5 Hz.In addition,the carrying load capacity of the positioning platform was tested by standard weights,and the results showed that when the carrying load reached 10 N,the driving speed could still reach 60μm/s.

Extraction and evolution of grader’s bionic morphological feature line using shape structure behavior function model

To improve the innovation of agricultural machinery product styling,this paper proposes a shape structure behavior function(SSBF)model suitable for the industrial design field.The feature line evolution method combining shape grammar and genetic algorithm was used for modelling the of the grader,which not only maintains the product style characteristics but also reflects the typical identification characteristics of the bionic prototype and produces a new product modelling scheme.By conducting cognitive and recognition experiments on product styling features,the ranking of product styling features and the contribution of each component to product styling were determined.The method of combining shape grammar and quadratic Bézier curve was used to express and encode feature lines,and genetic algorithm was used to evolve biomimetic forms to form product feature lines with typical biological morphological features;The extracted form bionic elements were integrated into the grader modelling design,and the interaction evaluation was carried out through the genetic algorithm evolution scheme.The basic form elements were extracted and analyzed,and the deduction rules were formulated and reorganized.The derived feature line geometric data considered the product’s image features and the bio-inspired prototype,which can be used for the follow-up guidance of industrial design schemes.

Functional Design for Customizing Sit-To-Stand Assisting Devices

Standing up refers to the transition from the seating to the standing postures to perform a movement that involves several body segments and requires both voluntary action and equilibrium control during an important displacement of the body Centre of Gravity （COG）. This task can be considered very important for people with reduced mobility to achieve minimal independence in Activity of Daily Living （ADL）. In this paper, we propose solutions for the homecare of persons with reduced mobility, describing a functional design to customize assisting devices for the Sit-to-Stand （STS）. In particular, the support mechanism that generates the requested motion and sustains the body of a person can be synthesized ad-hoc according to the experimental data of the subject. Experimental tests carried out during the Sit-To-Stand are used to track and record point trajectories and the orientation of the trunk of an individual, and they are used to design a 1-DOF mechanism able to reproduce the assigned rigid-body motion. A four-bar linkage has been synthesized according to the desired features. Simulation results are reported to illustrate the engineering soundness of the proposed mechatronic solution.

Bionic design and performance test of maize grain cleaning screen through earthworm motion characteristics

The maize mixture feeding with a large mass cannot be migrated backward rapidly along the planar reciprocating vibrating screen,and it is easy to accumulate in the front of the screen,which leads to the decrease of screening efficiency.Based on the reverse engineering technology,using the wavy geometry formed during the earthworm(Pheretima guillelmi)moving as a bionic prototype,a bionic screen was designed to make the maize mixture migrate backward rapidly in the front of the screen.The contour curve of earthworm’s head in an axial contracted state was extracted and fitted to obtain its equation.Based on the difference of concave position of the lower surface’s wavy geometry during the earthworm moving,the motion of the bionic screen was divided into four postures,and the conversion between different postures of the bionic screen was realized by the cam drive mechanism.The kinematics simulation of the bionic screen was carried out through ADAMS,and the displacement and velocity of the bionic screen were analyzed.When the feeding mass of the maize mixture was set at 5 kg/s,6 kg/s and 7 kg/s,the test results showed that the time of the maize mixture migrated(TOMMM)in the front of the bionic screen was shortened by 0.18 s,0.71 s,and 1.36 s,respectively,compared with that of planar reciprocating vibrating screen.The total screening time(TST)of the bionic screen was shortened by 1.28 s,1.33 s,and 1.53 s,respectively.The ability of the maize mixture to be migrated backward was improved.This study can provide a reference for the innovative design of the cleaning screen.

A Synthetic Framework for Evaluating and Designing an Anthropomorphic Prosthetic Hand

The mimic of aesthetics, fianction, and rehabilitation application makes the prosthetic hand design an interdisciplinary, synthetic work. Prosthetic hands should be designed in a comprehensive consideration with a synthetic framework from multiple areas. In this case, a synthetic framework containing 12 anthropomorphism indexes is established and utilized to understand the human hand characteristic and quantifiably evaluate the anthropomorphism of a prosthetic hand. Our quantified evaluation results show that a Global Anthropomorphic Score （GAS） of the current commercial prosthetic hands is only 45.2%. The compliance, coupling speed ratio and configuration of the Degrees Of Freedom （DOF） are found to be the lowest three anthropomorphism evaluation indexes in all 12 indexes. In addition, a design priority is proposed based on the quantified evaluation results and contributes to a prosthetic hand design. Moreover, our correlation analysis results between each index and GAS show that, compared with the conventional evaluation index-grasp gesture, the rotation axis distribution index has a stronger distinguishing capability to the hand performance. Finally, a flowchart of prosthetic hand design was presented for a designer to design a prosthetic hand with a high anthropomorphism.

Metamaterial electromagnetic wave absorbers and devices:Design and 3D microarchitecture

Metamaterials refer to a class of artificial composite structures with supernormal physical properties that natural materials do not have.The emergence of metamaterials has opened up new research directions for classical electromagnetic theory and made it possible to manipulate electromagnetic waves effectively.One of most important applications of metamaterials is metamaterial absorbers(MMAs).The properties of MMAs depend on the material composition,cell size and structure,which could often achieve"perfect"absorption through reasonable design.This review starts with the development of MMAs and describes the status of this absorber,then mainly focuses on bionic design and new artificial design.Specifically,it is to draw inspiration from natural plants and animals,design novel structures to get better absorbing properties.Furthermore,the artificial design can achieve the optimize absorption capacity as well as absorption bandwidth.What’s more,this review summarizes the 3D printing technology to prepare MMAs that are different from traditional printed circuit board technology.The MMAs produced by 3D printing technology can prepare more complex shapes,and has light weight and better absorbing properties.

Automated Layout Design of Stiffened Container Structures Based on the Morphology of Plant Ramifications

This study proposes a new topology optimization solution providing designers with choices for feasible stiffener layouts inside large-scale containers of garbage trucks. Firstly, the mathematical expressions of loading conditions inside garbage containers are derived. Then, a growth-based layout optimization framework is built, taking inspiration from the morphology of plant ramifications. The principles of the highly effective but individual design rules of existent leaf venation layout problems are explored and transferred into analytical laws. Based on this, an evolutionary algorithm is developed to simulate the load-adapted growth of stiffener layouts, which provides an approximately homogeneous stress distribution along the surface of self-optimizing structures, Unlike the conventional methods, the new approach needs neither the densest ground structure nor the modification of the existing finite element programs, it is fast, easy to apply and nearly constraint free. Finally, a case study is provided showing how a large-scale container structure can be designed by this extremely intelligent CAD approach.