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Journal of Bionic Engineering 2023年第5期20卷 2069-2087页

作者： Zelin Huang Chencheng Dong Zhangguo Yu Xuechao Chen Fei Meng Qiang Huang School of Mechatronical Engineering Beijing Institute of TechnologyBeijing100081China Key Laboratory of Biomimetic Robots and Systems Ministry of EducationBeijing100081China

Whole-body control is beneficial for improving the disturbance adaptation of humanoid robots,since it can simultaneously optimize desired joint torque,joint acceleration,and contact force while considering whole-body dynamics and other physical limits.However,the lack of torque feedback information prevents the position-controlled humanoids from utilizing whole-body control directly,because it enhances the difficulty of guaranteeing desired contact force which is important for maintaining stability.In this paper,a whole-body control that integrates task-space inverse dynamics and variable contact force control is proposed for position-controlled humanoids to enhance the robot’s adaptability toward the unknown disturbance.The task-space inverse dynamics generates the desired joint acceleration and contact force with the consideration of whole-body dynamics and other limits to track the references.The variable contact force control modifies references related to Center of Mass(CoM)and end effectors to ensure reasonable contact force tracking performance,thereby assuring good tracking performance of CoM and momentum to maintain robot stability.Simulations and experiments of balancing and walking under unknown disturbance have been successfully conducted on a position-controlled humanoid robot,BHR-7P3,with the proposed method.

关键词： Whole-body control contact force Admittance control Humanoid robot

Experimental research on the contact force of the bi-directional pig in oil and gas pipeline

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Petroleum Science 2023年第1期20卷 474-481页

作者： Xiao-Xiao Zhu Chun-Ming Fu Yu-Tao Wang Shi-Ming Zhang College of Mechanical and Transportation Engineering China University of Petroleum-BeijingChangpingBeijing102249China

The migration process of the pig in oil and gas pipeline is a complex dynamic problem.During the pigging operation,the variation of friction force caused by the nonlinear contact between the sealing disc and the pipe wall is the key factor affecting the dynamic characteristics of the pig motion.At present,the existed pigging models for predicting pigging behavior regard friction as an invariant constant.Experimental research indicates that the friction force of the pig varies with the contact force and the lubrication conditions.Therefore,the assumption that the friction force is constant cannot reflect the friction dynamic characteristics of the pig during pigging,and will also affect the accuracy of the pigging model.Exploring the variation of friction force of pig under different conditions is the basis of establishing the transient dynamic model of a pig.As a result,in this paper,a method of direct measurement of contact force between the pig and the pipeline is presented,the contact force,the friction force,as well as the friction coefficient of the pig are obtained from the experiment.Research results in this paper can help to establish a more accurate dynamic model of pig.

关键词： Pipeline pig Sealing disc contact force Friction coefficient Experimental rig

Nonlinear dynamics investigation of contact force in a cam–follower system using the Lyapunov exponent parameter,power spectrum analysis,and Poincarémaps

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International Journal of Mechanical System Dynamics 2022年第2期2卷 214-230页

作者： Louay S.Yousuf Department of Mechanical Engineering San Diego State UniversitySan DiegoCaliforniaUSA

The aim of this article is to detect the detachment between the cam and the follower using the largest Lyapunov exponent parameter,the power density function of fast Fourier transform,and Poinarémaps due to the nonlinear dynamics phenomenon of the follower.The detachment between the cam and the follower was investigated for different cam speeds and different internal distances of the follower guide from inside.This study focuses on the use of the cam–follower system with a bionic quadruped robot through a linkage mechanism.Multishock absorber(spring–damper–mass)systems at the very end of the follower were used to improve the dynamic performance and to reduce the detachment between the cam and the follower.The SolidWorks program was used in the numerical solution,while a high‐speed camera at the foreground of the OPTOTRAK 30/20 equipment was used to identify the follower position.The friction and impact were considered between the cam and the follower and between the follower and its guide.In general,when the cam and the follower are in permanent contact,there is no loss in potential energy,and no impact or restitution.The detachment between the cam and the follower increases with increasing coefficient of restitution in the presence of the impact.

关键词： nonlinear dynamics Lyapunov exponent non‐periodic motion contact force

Extraction on the contact forces Among the Opaque and Non-photoelastic Particles Under Electromagnetic force

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Acta Mechanica Solida Sinica 2022年第2期35卷 248-260页

作者： Shuaike Jiao Cong Liu Jun Zhou Xingyi Zhang You-He Zhou Key Laboratory of Mechanics on Disaster and Environment in Western China Attached to the Ministry of Education of China Lanzhou UniversityLanzhou 730000China Department of Mechanics and Engineering Sciences College of Civil Engineering and MechanicsLanzhou UniversityLanzhou 730000China

contact force is related to the mechanical response of superconducting strands under a large electromagnetic body force,which is important for the safety of the international t hermonuclear experimen tai reac tor(ITER)magne t struc ture.Due to the complex st rue ture of the cable-in-conduit conductor(CICC),the component unit of the ITER magnet,and the extreme operating environment,the research on the strand contact force caused by the electromagnetic force has been progressing slowly.In this study,a two-dimensional(2D)theoretical model based on the granular elemen t method is construe ted to compute the contac t forces among some opaque and non-photoelastic ferromagnetic particles which are placed in a non-uniform magnetic field.In the experiment,the contact deformations of these particles may be obtained by the digital image correlation method.We also propose a method,which is similar to the least-squares method,to calculate the electromagnetic body forces of different particles.Subsequently,the distributional and statistical characteristics of the contac t force chains and contact angles are presen ted.It is considered that the method proposed in this paper is suitable for the contact force analysis of the cross section of superconducting strands in the ITER CICC that is subjected to a transverse elec-tromagnetic force.In the end,this 2D theoretical model is generalized to the three-dimensional(3D)case,and the concise mathematical framework is presented.

关键词： contact force Electromagnetic force Superconducting strand Cross section

contact force and mechanical loss of multistage cable under tension and bending

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Acta Mechanica Sinica 2016年第5期32卷 891-904页

作者： Yanyun Ru Huadong Yong Youhe Zhou Key Laboratory of Mechanics on Disaster and Environment in Western China Ministry of Education of China Department of Mechanics and Engineering Sciences College of Civil Engineering and Mechanics Lanzhou University

A theoretical model for calculating the stress and strain states of cabling structures with different loadings has been developed in this paper. We solve the problem for the first- and second-stage cable with tensile or bending strain. The contact and friction forces between the strands are presented by two-dimensional contact model. Several theoretical models have been proposed to verify the results when the triplet subjected to the tensile strain, including contact force, contact stresses, and mechanical loss. It is found that loadings will affect the friction force and the mechanical loss of the triplet. The results show that the contact force and mechanical loss are dependent on the twist pitch. A shorter twist pitch can lead to higher contact force, while the trend of mechanical loss with twist pitch is complicated. The mechanical loss may be reduced by adjusting the twist pitch reasonably. The present model provides a simple analysis method to investigate the mechanical behaviors in multistage-structures under different loads.

关键词： contact force Friction force Tension Bending Mechanical loss

Relationship between the real contact area and contact force in pre-sliding regime

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Chinese Physics B 2017年第7期26卷 212-217页

作者：宋保江阎绍泽 State Key Laboratory of Tribology Department of Mechanical Engineering Tsinghua University

The pre-sliding regime is typically neglected in the dynamic modelling of mechanical systems. However, the change in contact state caused by static friction may decrease positional accuracy and control precision. To investigate the relationship between contact status and contact force in pre-sliding friction, an optical experimental method is presented in this paper.With this method, the real contact state at the interface of a transparent material can be observed based on the total reflection principle of light by using an image processing technique. A novel setup, which includes a pair of rectangular trapezoidal blocks, is proposed to solve the challenging issue of accurately applying different tangential and normal forces to the contact interface. The improved Otsu＇s method is used for measurement. Through an experimental study performed on polymethyl methacrylate（PMMA）, the quantity of contact asperities is proven to be the dominant factor that affects the real contact area. The relationship between the real contact area and the contact force in the pre-sliding regime is studied, and the distribution of static friction at the contact interface is qualitatively discussed. New phenomena in which the real contact area expands along with increasing static friction are identified. The aforementioned relationship is approximately linear at the contact interface under a constant normal pressure, and the distribution of friction stress decreases from the leading edge to the trailing edge.

关键词： real contact area contact interface pre-sliding regime contact force

Elastic-plastic contact force history and response characteristics of circular plate subjected to impact by a projectile

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Acta Mechanica Sinica 2007年第4期23卷 415-425页

作者： L.B.Chen F.Xi J.L.Yang Solid Mechanics Research Center,Beihang University,Beijing 100083.China Shandong Institute of Architecture and Engineering,Jinan 250014,China Solid Mechanics Research Center Beihang University Beijing China Shandong Institute of Architecture and Engineering Jinan China

A new elastic-plastic impact-contact model is proposed in this paper. By adopting the principle of minimum acceleration for elastic-plastic continue at finite deformation, and with the aid of finite difference method, the proposed model is applied in the problem of dynamic response of a clamped thin circular plate subjected to a projectile impact centrally. The impact force history and response characteristics of the target plate is studied in detail. The theoretical predictions of the impact force and plate deflection are in good agreements with those of LDA experimental data. Linear expressions of the maximum impact force/transverse deflection versus impact velocity are given on the basis of the theoretical results.

关键词： Elastic-plastic contact model ImpactCircular plate contact force Minimum principleof acceleration

A numerical study of contact force in competitive evacuation

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Chinese Physics B 2017年第10期26卷 295-301页

作者：林鹏马剑司有亮吴凡雨王国元王建宇 Department of Fire Safety Engineering Faculty of Geosciences and Environmental Engineering Southwest Jiaotong University Chengdu 610031 China School of Transportation and Logistics Southwest Jiaotong University Chengdu 610031 China

Crowd force by the pushing or crushing of people has resulted in a number of accidents in recent decades. The aftermath investigations have shown that the physical interaction of a highly competitive crowd could produce dangerous pressure up to 4500 N/m, which leads to compressive asphyxia or even death. In this paper, a numerical model based on discrete element method （DEM） as referenced from granular flow was proposed to model the evacuation process of a group of highly competitive people, in which the movement of people follows Newton＇s second law and the body deformation due to compression follows Hertz contact model. The study shows that the clogs occur periodically and flow rate fluctuates greatly if all people strive to pass through a narrow exit at high enough desired velocity. Two types of contact forces acting on people are studied. The first one, i.e., vector contact force, accounts for the movement of the people following Newton＇s second law. The second one, i.e., scale contact force, accounts for the physical deformation of the human body following the contact law. Simulation shows that the forces chain in crowd flow is turbulent and fragile. A few narrow zones with intense forces are observed in the force field, which is similar to the strain localization observed in granular flow. The force acting on a person could be as high as 4500 N due to force localization, which may be the root cause of compressive asphyxia of people in many crowd incidents.

关键词： crowd flow discrete element method （DEM） contact force force localization

INTER-contact force ANALYSIS OF IMPACTED DISK ASSEMBLY BY DYNAMIC CAUSTICS

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Acta Mechanica Sinica 2003年第4期19卷 371-379页

作者：李明 ZHANG Jue 方竞 Department of Mechanics and Engineering Science Peking University Beijing 100871 China

The caustic method was utilized to study the contact force transmission in disk assemblies under impact load. The mapping equations were obtained based on the first invariant of the stress components in the disk subject to a normal concentrated force, and a characteristic dimension of the maximum size in the caustic curve was proposed to evaluate the contact force between the disks.Transient patterns of the caustic shadows were recorded by means of a high-speed camera of off-focus imaging, then the histories of the inter-contact forces among the disks were obtained with respect to the conditions of different masses and heights of the falling hammers. The influence of the impact loading and impulsive velocity was analyzed with respect to the force responses of the disk assembly,the double-peak phenomenon with comparison to the initial masses, and the energy dissipation of the systems under impact of different momentums.

关键词： caustic method disk assembly dynamics contact force

contact force distribution and the value of contact force catheter during pace-map in right ventricular outflow tract

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South China Journal of Cardiology 2021年第1期22卷 21-29页

作者：刘海燕刘方舟林炜东廖洪涛方咸宏廖自立刘洋詹贤章薛玉梅 Department of Cardiology Guangdong Cardiovascular InstituteGuangdong Provincial People’s HospitalGuangdong Academy of Medical SciencesGuangzhou 510030GuangdongChina

Backgrounds Whether the contact force(CF)-sensing catheter could improve the efficiency of pace mapping(PM)in right ventricle outflow tract(RVOT)has not been fully studied.The present study was the first investigation of the CF distribution in the right ventricle(RV)by using a CF-sensing catheter and the relationship between CF and capture threshold in RVOT.Methods In total,4543 mapping points with CF were recorded in 15 patients.Operators were blinded to CF data and data were analyzed according to 10 predefined RV segments.PM were performed at 6 different RVOT segments with 3 different intentional CF levels and 3 different pacing setup.The pacing threshold in RVOT and pacing capture level were recorded.The morphology matching score were recorded and analyzed.Results Median CF during RV mapping was 8(5-12)g and coefficient of variation was 71.64%.Median CF ranged from 9.5(5.8-16)g at the posterior-outflow tract freewall(OTFW)to 7(4-10)g at the apex.Distribution of CF≥20 g in RV predefined segments mainly located in the OTFW.Distribution of CF≤2 g in RV predefined segments mainly located in the inflow tract freewall(ITFW),anterior-OTFW,and apex.A total of 810 pacing were performed at RVOT with different CF and output.Stable capture rate could be significantly improved via increasing CF level under 2 mA output(46.7%/2-5 g vs.50%/6-9 g vs.91.1%/≥10 g),and no capture rate could be significantly declined simultaneously(16.7%/2-5 g vs.8.9%/6-9 g vs.2.2%/≥10 g).Conclusions A marked variability in CF was observed among the different predefined segments.CF mapping could improve the safety and efficacy of catheter ablation of premature ventricular contraction(PVC)/ventricular tachycardia(VT)in RV.CF was an essential factor in RVOT pace mapping process,especially under low-pacing output.[S Chin J Cardiol 2021;22(1):21-29]

关键词： contact force right ventricle pace mapping