Comparison and analysis of two Coulomb friction models on the dynamic behavior of slider-crank mechanism with a revolute clearance joint

The objective of this study is to investigate the effects of the Coulomb dry friction model versus the modified Coulomb friction model on the dynamic behavior of the slider-crank mechanism with a revolute clearance joint. The normal and tangential forces acting on the contact points between the journal and the bearing are described by using a Hertzian-based contact force model and the Coulomb friction models, respectively.The dynamic equations of the mechanism are derived based on the Lagrange equations of the first kind and the Baumgarte stabilization method. The frictional force is solved via the linear complementarity problem(LCP) algorithm and the trial-and-error algorithm.Finally, three numerical examples are given to show the influence of the two Coulomb friction models on the dynamic behavior of the mechanism. Numerical results show that due to the stick friction, the slider-crank mechanism may exhibit stick-slip motion and can balance at some special positions, while the mechanism with ideal joints cannot.

Dynamics Response and Non⁃linear Characteristics Analysis of Complex Planar 2⁃DOF Mechanism with Revolute Clearances

There are clearances in mechanism because of manufacture and assembly error,which reduces operation life and working accuracy of mechanism and has a great impact on dynamical responses.At the moment,research in this area mainly focuses on single degree⁃of⁃freedom mechanism considering one clearance,while research of multi⁃DOF mechanism considering multi⁃clearance is less.With the purpose of studying the dynamical characteristics of complex multi⁃DOF mechanism with multi⁃clearances,a dynamic model was developed.The dynamic responses of 2⁃DOF mechanism with two clearances under different positions,values,and numbers of clearance were analyzed.The displacement,velocity,acceleration,collision force,and the axis trajectory at clearance were then given.In addition,there is a limited amount of literature on chaotic phenomena,which mainly focuses on the chaotic phenomena of end⁃effector of mechanism.But in this paper,the non⁃linear characteristics were analyzed by chaotic phenomenon of clearance joint,then chaotic phenomenon was identified by Poincarémappings and phase diagrams.Bifurcation diagrams were given.The results will offer a reliable technical support for the study of dynamical responses of planar mechanisms and the analysis of chaotic phenomena.

Dynamic Analysis of Four-Bar Beating-up Mechanism with Joint Clearance

For the four-bar beating-up mechanism of air-jet loom,the plain bearing of linkage is the bearing with dynamic load,and is immersed in the lubricant-box.If the joint clearance is considered,the research on linkage movement could be very complicated.In this paper,the kinematic characteristics of four-bar beating-up mechanism with joint clearance were studied by analyzing the trace of journal center and the balance of radial,tangential forces,and bearing load.The region of principal vibration and its forming causes were discussed.And the results could interpret the measuring curves of four-bar beating-up mechanism completely.

Experimental Study of the Motion Modes of a Planar Mechanical System with Multi-Clearance Revolute Joints

Clearances in joints of a mechanical multibody system can induce impulsive forces, leading to vibrations that compromise the system’s reliability, stability, and lifespan. Through dynamic analysis, designers can investigate the effects of the clearances on the dynamics of the multibody system. A revolute joint with clearance exhibits three motions which are;free-flight, impact and continuous contact motion modes. Therefore, a multibody system with n-number of revolute clearance joints will exhibit 3n motion modes which are a combination of the three motions in each joint. This study investigates experimentally the nine motion modes in a mechanical system with two revolute clearance joints. A slider crank mechanism has been used as the demonstrative example. We observed that the experimental curve exhibits a greater impact compared to the simulation curve. In conclusion, this experimental investigation offers valuable insights into the dynamics of planar mechanical systems with multiple clearance revolute joints. Utilizing a slider-crank mechanism for data acquisition, the study successfully confirmed seven out of nine motion modes previously identified in numerical research. The missing modes are attributed to inherent complexities in real-world systems, such as journal-bearing misalignment.

Simulation and Analysis of Spatial Weft Insertion Mechanism Considering Flexibility and Clearance

A 3D model of the spatial four-bar weft insertion mechanism was built with unigraphics NX(UG) according to the actual requirement,and dynamics simulation was carried out by importing the model into ADAMS.Without considering the clearance,the motion characteristic curve of the sword belt was generated through ADAMS combined with MATLAB.In this paper the hinge between the rod and the sector gear was selected as an example with different values of clearance,outputting the motion characteristic curve of the sword belt.Finite element analysis(FEA)was conducted,the flexible body was generated by importing the forked frame into ANSYS,and flexible dynamics simulation was carried out by importing the flexible body into ADAMS to replace the rigid rod.A comprehensive comparison of the output characteristics of the sword belt was conducted in the consideration of the clearance or flexible.Analysis of the force on the left hinge of the rod was carried out with the ADAMS post processing module.With the same clearance,considering the flexibility,amplitude of fluctuation of the force on the hinge increased obviously.

A Hand Prosthesis with an Under-Actuated and Self-Adaptive Finger Mechanism

One of the major problems faced by hand amputees is the unavailability of a lightweight and powered multi-functional hand prosthesis. Under-actuated finger designs play a key role to make the hand prosthesis lightweight. In this paper, a hand prosthesis with an under-actuated and self-adaptive finger mechanism is proposed. The proposed finger is capable to generate passively different flexion/extension angles for a proximal interphalangeal (PIP) joint and a distal interphalangeal (DIP) joint for each flexion angle of metacarpophalangeal (MCP) joint. In addition, DIP joint is capable to generate different angles for the same angle of PIP joint. Hand prosthesis is built on the proposed finger mechanism. The hand prosthesis enables user to grasp objects with various geometries by performing five grasping patterns. Thumb of the hand prosthesis includes opposition/apposition in addition to flexion/extension of MCP and interphalangeal (IP) joint. Kinematic analysis of the proposed finger has been carried out to verify the movable range of the joints. Simulations and experiments are carried out to verify the effectiveness of the proposed finger mechanism and the hand prosthesis.

Design and Kinematics Analysis of a Parallel Mechanism to be Utilized as a Luggage Door by an Analogy to a Four – Bar Mechanism

In this study, a luggage door mechanism to be used in commercial vehicles such as midibuses and buses is designed and analyzed. The mechanism is designed as a parallel hinged system. Velocities, rotational veloci- ties and rotational accelerations of selected points on the design are calculated. Furthermore, the experiment- tal model of the design is established and it is seen that the data taken from the model are compatible with the calculated results. The aim of this study is to design a mechanism with the minimal workspace so that the door can be utilized in narrow areas and the ergonomics of the luggage door is improved. Considering both commercial and passenger vehicle sales, vehicle interior and exterior trim features have an exceptionally important role in automotive industry, in addition to vehicle performance characteristics. In today’s compete- tive environment, parts used in a vehicle’s internal and external trim have to meet user demands in terms of ergonomics as well as aesthetics. Due to its similarity to a four-bar mechanism, kinematics analysis of the design was carried out based on a four-bar mechanism, which is used extensively in industry.

The Analysis of Link Mechanism and Its Programming Realization

This paper introduces realization method of kinematics analysis for the planar four bar mechanism based on the MFC. A mathematicat model is established by a simple and effective method, using the computer simulation technology can the dynamic demonstration mechanism taotion and automatic drawing trajectory curve of arbitrary point on the connecting rod, and can output various motion displacement, speed and acceleration diagram. The paper provides a simple way for motion analysis of planar four link.

论中国共产党以自我革命引领社会革命的彰显机理

主动自我革命是马克思主义先进政党的优良品格,积极引领社会革命是马克思主义先进政党的崇高使命。以马克思主义为指导的中国共产党,在奋斗进程中义无反顾进行自我革命,并以主动自我革命积极引领社会革命,努力实现党的自我不断革命与引领社会深广革命的良性互动、协同发展。在深入分析中国共产党以自我革命引领社会革命的彰显机理内在本质基础上,深刻把握中国共产党以自我革命引领社会革命的彰显机理的重要表征、生成逻辑、生发动能,教育党员干部在有力推进自我革命中彰显引领社会革命的思想自觉与行动自觉,从而进一步增强和显示党组织的战斗力、凝聚力、影响力,对于在新发展征程推进党的建设新的伟大工程具有重要现实意义和深远影响。

Dynamics modeling and error analysis for antenna pointing mechanisms with frictional spatial revolute joints on SE(3)

This paper presents a non-smooth multibody dynamic formulation and error analysis of an antenna pointing mechanism including frictional spatial revolute joints(FSRJs)with small clearance in the framework of the special Euclidian group SE(3).The formulation leads to an inertial frame-invariant,a compact and unified description for rigid bodies and spatial revolute joints(SRJs).The geometric constraint of the bearing is covered by four open semi-cylinders,which can be treated as bilateral constraints assuming that the impact effects are negligible.The frictional contact problem is formulated as a horizontal linear complementary problem(HLCP),which is embedded in the Lie-group integration scheme.Error of the antenna pointing mechanism is modeled by means of the adjoint transformation and POE-based formula.The evolution of errors is obtained through the solution of non-smooth dynamics.The obtained numerical results illustrate the influences of FSRJs in dynamics modeling and error analysis of the antenna pointing mechanism.

RELIABILITY-BASED ANALYSIS AND SYNTHESIS OF MECHANICAL ERROR FOR PATH GENERATING LINKAGES

A reliability-based analysis approach to mechanical error in path generating linkages is pre- sented . The reliability index is taken as a measure for the deviation of the actual path of a coupler point from the desired one. A reliability-based synthesis procedure of the mechanical error for path generating linkages to allocate optimal tolerances and clearances is developed. A four-bar path generating mechanism is considered for numerical illustration.

我国大倾角煤层开采技术变革与展望

大倾角煤层是我国煤炭资源的主要赋存样式之一。在地域分布上呈现出广泛性与区域性,据不完全统计,全国25个省、自治区、直辖市均涉及该类煤层开采,在中西部地区储量丰富、产量大、生产集中程度高。在赋存条件上呈现出多样性与复杂性,不同区域成煤时期不一,构造控煤过程迥异,形成了多样且复杂的开采条件,催生了不同的开采技术要求。大倾角煤层开采的技术难度大。煤层倾角导致采场围岩运动破坏呈现非对称性显现特征,支护系统稳定性控制与“三机”配套与协同、采准巷道布置与支护、工作面“人-机”环境安全保障等工作的难度显著加剧,严重制约了矿井安全高效开采。大倾角煤层开采的区域经济需求强,该类煤层赋存与生产较集中的区域多见以煤炭工业为主的资源型城市,经济结构相对单一,煤炭资源安全高效开发利用对区域能源保供、民生保障、经济保稳具有兜底作用。长期以来,大倾角煤层开采技术变革聚焦于解决“难”与“需”的矛盾,在采煤方法与工艺、岩层控制理论与技术、成套装备研制与应用3个方面不断完善、创新、发展,实现了由非机械化向机械化开采的转变,安全产效水平大幅提升,人员劳动强度大幅下降,作业环境显著改善。20世纪90年代中期,川煤集团绿水洞煤矿首次成功实现了大倾角中厚煤层长壁综采,冲破了大倾角煤层机械化开采技术“禁区”。在此示范作用下,大倾角厚煤层长壁综放开采、大采高综采、薄煤层伪俯斜长壁综采三项首创性工程实践先后取得成功。这一过程中创新了工作面非线性限位布置与调斜方式,确立了“支架-围岩”系统稳定性多维交互控制模式,研发了工作面成套装备,取得良好收效,综合机械化开采技术适用范围进一步拓宽。与此同时,大倾角煤层开采仍存在许多亟待突破的关键科学问题与技术瓶颈,导致自动化、智能化水平提升与近水平/缓倾斜煤层相较仍存在较大差距。需进一步强化倾斜层状煤系地层煤岩体采动力学行为研究,揭示其对采场围岩灾变的控制机制,并实现量化表征;需进一步阐明岩体承载结构-采场装备群组系统间的多维动态作用过程与规律,完善装备与围岩多维动态多目标协同控制理论与技术基础,实现技术转化应用。在科学问题取得突破的基础上进行采煤方法、回采工艺、岩层控制、成套装备的系统性技术创新与研发,破解大倾角煤层开采安全-产效双提升的制约技术瓶颈,使大倾角煤层综合机械化开采倾角上限在有可靠技术保障的前提下向上延伸(扩展),为实现自动化、智能化开采奠定基础。

Analysis of Mechanical Combined-Type CVT Consisting of Closed Links,Grooved Cam and Non-invertible Elements

As one of transmission mechanisms,continuously variable transmission(CVT)can transfer energy depending upon rotation speed or torque generated by rotation power transferred from input axis to output axis.It is known that the CVT is mechanism that can change gear ratios continuously in power transmission installed in vehicles,or power generation and its transfer systems.In this paper,we propose a CVT using a new type of mechanism in which four-bar linkages(quadric crank chains)and non-invertible elements such as one-way clutches or ratchets are installed.The conventional CVTs which are classified as belt-type CVTs or toroidal CVTs are driven by friction force between conduction mechanisms.Due to slippage or high-pressure between the transmission components in the conduction mechanism,the transfer efficiency in the conduction energy becomes inferior.However,the proposed CVT does not depend upon any friction forces,and it is considered that its transfer efficiency is superior.

基于工匠训练营的分层递进教学模式在课堂教学中的改革实践——以测绘减速器从动轴为例

针对在测绘减速器从动轴教学中存在的思政元素的嵌入牵强、教学形式单调、过程性评价不细致等问题,创新了基于“工匠精神”的教学内容、基于工匠训练营的分层递进教学模式、基于“工匠价值”的教学评价体系,形成了工匠训练营协同教学、学生分层次递进发展的教学特色,给工科课程的课程革命提供一定的参考。

美国能源部地热钻井技术研发最新部署及干热岩开发示范创新实践

与其他主要的可再生能源相比,地热能是唯一能够提供基本负载电力的能源。干热岩是指不含原生水或含少量水的高温深部岩体,可通过水力刺激改造形成增强型地热系统储层,从而提取数量可观的地热能。干热岩型地热资源的开发面临两方面主要技术挑战,一是花岗岩和玄武岩等极坚硬岩石对机械钻速的限制,二是钻井所处地层温度超过随钻测量和旋转导向等工具电子设备的运行温度上限。近年来,美国能源部资助的FORGE计划犹他州项目为测试新的钻头技术和优化钻井作业流程提供了机会,以逐步提升机械钻速并降低钻井成本。本文综述了美国能源部地热技术办公室近年发展规划中对地热钻井技术研发的部署,重点分析了犹他州项目在钻井实践过程中对基于物理限制因素重新设计的工作流程的应用,总结了美国能源部围绕地热钻井技术开展的多次规划编制以及部署实施的相关项目涉及的主要领域,以及犹他州项目在探索和实践钻井作业流程优化方面取得的认识。

油气体制机制改革十周年:成效与展望

2014年6月,习近平总书记在中央财经领导小组第六次会议上,提出了推动能源消费革命、能源供给革命、能源技术革命、能源体制革命和全方位加强国际合作,以及积极推进能源体制改革、抓紧制定电力体制改革和石油天然气体制改革总体方案、启动能源领域法律法规立改废工作的要求,这为中国油气领域深化改革、全面绿色转型和高质量发展提供了根本遵循。为全面把握新时代能源安全新战略的总体要求、油气体制机制改革的重点工作与取得的主要成效,系统整理了2014年至今油气体制机制改革的重点法律、政策、标准等文件,定性定量概括总结了主要成效,认为10年来中国坚持推进石油天然气体制机制改革,开展了油气领域法律法规和标准体系建设、加快转变油气行业政府管理职能、引导和构建油气市场体系、推进改革油气价格机制等一系列改革举措,有力支撑了油气增储上产和行业加快发展。展望未来,随着中国迈上全面建设社会主义现代化国家新征程,油气行业将健全石油天然气行业法律法规体系、建立起有为政府和有效监管体系、全面建成“X+1+X”油气市场格局、形成“管住中间、放开两头”的油气价格机制,全面保障油气行业高质量发展。

绕回转体空泡稳定性及流动控制研究与进展综述

回转体水下带攻角高速运动时,诱发附着在物面的大尺度非对称云状空泡流动,空泡末端云状局部空泡界面失稳诱发高量值脉动压力对回转体结构强度产生重要影响,是工程研制面临的重要基础性难题。本文对绕回转体非对称云状空泡流相关研究情况进行梳理,详细地介绍在非对称云状空泡流实验和数值模拟方法、非对称云状空泡流场结构与界面稳定性、流动调控机制等方面的研究情况,并分析未来发展趋势,给出后续需要重点关注的研究方向的建议。

近代“身体”观念的转变与医学进步

近代医学进步的主要目标在于实现疾病的可治疗、可预防、可共存。身体作为人的生理组织,其观念经历了三个转变并催生了三次医学进步。其一,以机械论范式为主导的思想认为“人是机械”,身体形同机械构造,催生了临床医学进步,并部分实现了疾病可治疗的目标;其二,以系统论范式为主导的思想认为人的身体是一个有机统一的整体,微生物、细胞等共同维持身体的平衡,催生了预防医学进步,并部分实现疾病可预防的目标;其三,以现象学范式为主导的思想认为身体与世界具有关联性,催生了身体医学进步,并部分实现疾病与健康的共存状态。

大学课堂改革倒逼教学改革:逻辑、困境与路径

课堂是人才培养的主渠道,新时代的教学改革应聚焦课堂,将课堂作为教学改革的重点,以课堂改革倒逼整个教学系统改革。需求、问题、质量与技术是课堂改革倒逼教学改革的四大逻辑要素。目前教学改革与课堂存在割断、课堂改革障碍重重。因此,改革需要对接课堂改革需求,精准教学改革供给;需要建立激励机制、管理机制与保障机制,促进教学改革与课堂改革的深度融合;需要加强教学改革与课堂改革目标耦合,提升教师进行课堂改革的动力与能力,发挥人员驱动改革的功效。