Variable stiffness design of redundantly actuated planar rotational parallel mechanisms

Redundantly actuated planar rotational parallel mechanisms (RAPRPMs) adapt to the requirements of robots under different working conditions by changing the antagonistic internal force to tune their stiffness. The geometrical parameters of the mechanism impact the performances of modulating stiffness. Analytical expressions relating stiffness and geometrical parameters of the mechanism were formulated to obtain the necessary conditions of variable stiffness. A novel method of variable stiffness design was presented to optimize the geometrical parameters of the mechanism. The stiffness variation with the internal force was maximized. The dynamic change of stiffness with the dynamic location of the mechanism was minimized, and the robustness of stiff-ness during the motion of the mechanism was ensured. This new approach to variable stiffness design can enable off-line planning of the internal force to avoid the difficulties of on-line control of the internal force.     

陶瓷CBN砂轮修锐效果的砂轮地貌评价

对磨削性能下降的陶瓷CBN砂轮进行不同程度的修锐,用激光三角法的砂轮地貌测量系统对各状态下砂轮地貌进行测量。得到了砂轮地貌的三维形貌和磨粒出刃高度、磨粒刃密度的变化特点,以此评价修锐效果。结果表明,陶瓷CBN砂轮的修锐对砂轮磨粒的出刃性、等高性和均匀性有很大改善。     

固定小翼颤振激励系统激励力建模研究

通过基于双时间方法求解非定常欧拉方程得到固定小翼激励力源数据,分析了这种新型颤振激励系统工作原理,对固定小翼新型颤振激励系统工作原理的分析,建立了激励力简化计算模型。可实现M=0.3～0.5飞机稳定飞行状态下激励力载荷计算,大大简化了计算过程,精度足够满足工程分析,可满足试飞数据实时处理的需要。     

高超声速锥体表面凸起物分离干扰区气动力/热关联计算方法

针对高超声速锥体表面凸起物周围的分离干扰流动产生的气动力/热提供了关联计算方法,包括凸起物周围分离干扰区压力分布计算方法、分离干扰区几何特征的计算方法、分离干扰区附加气动力计算方法、分离干扰区气动热计算方法.对典型的钝锥加凸起物外形进行了计算,计算分析了由于凸起物周围分离干扰区压力升高引起的附加气动力、凸起物表面及干扰区的气动热,对气动热计算结果与激波风洞实验结果进行了比较,本文关联方法计算结果与实验结果符合较好.     

挠性杆的镗加工技术

针对挠性杆的结构特点和加工难点,提出了有效的工艺措施,从装夹定位、刀具材料与几何参数选择、刃磨方法、切削用量的选择,以及挠性杆内应力的分析等方面详细地阐述了加工过程中的关键技术,解决了挠性杆镗削加工的技术难题。     

试用暗物质理论解释惯性和惯性力的物理机制(上)

基于对暗物质的多年探讨,我们认为宇宙空间是具有质量、相对均匀、连续稳定和有相当弹性暗物质群体(DMG)的空间.自然、宇宙万物终生处于群体引力制约之中,它们因此也获得了相应的惯性.本文立足于上述的宇宙空间,借助宇宙学原理、马赫原理和爱因斯坦等效原理,提出了物质客体的惯性机制和被称为虚力的惯性力机制 同时本文也解读所有惯...     

双满壳层附近原子核的双粒子能谱

采用由M-3Y力等效G矩阵,用格林函数方法对Ca42、Sc42、N i58和Cu58的双粒子能谱做了理论计算和讨论.结果表明:二级图中3p1h不可约顶角考虑多重散射后,使能级更趋于实验能级.因此用格林函数方法计算双粒子能谱是十分有效的。     

Effective Coulomb force modeling for spacecraft in Earth orbit plasmas

Coulomb formation flight is a concept that utilizes electrostatic forces to control the separations of close proximity spacecraft. The Coulomb force between charged bodies is a product of their size, separation, potential and interaction with the local plasma environment. A fast and accurate analytic method of capturing the interaction of a charged body in a plasma is shown. The Debye–Hückel analytic model of the electrostatic field about a charged sphere in a plasma is expanded to analytically compute the forces. This model is fitted to numerical simulations with representative geosynchronous and low Earth orbit (GEO and LEO) plasma environments using an effective Debye length. This effective Debye length, which more accurately captures the charge partial shielding, can be up to 7 times larger at GEO, and as great as 100 times larger at LEO. The force between a sphere and point charge is accurately captured with the effective Debye length, as opposed to the electron Debye length solutions that have errors exceeding 50%. One notable finding is that the effective Debye lengths in LEO plasmas about a charged body are increased from centimeters to meters. This is a promising outcome, as the reduced shielding at increased potentials provides sufficient force levels for operating the electrostatically inflated membrane structures concept at these dense plasma altitudes.     

Silver Film Growth on Glass Ceramic by Radio Frequency Magnetron Sputtering

Thin silver films are deposited by radio frequency magnetron sputtering on glass ceramic at room temperature.Variations of sputtering power,bios voltage and power density are carried out for each deposition,then parts of as-deposited samples are subjected to annealing at 600 ℃ within a vacuum chamber.Structural properties are studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and laser scanning confocal microscope(LSCM).It is shown that structural properties have a strong dependency on sputtering power and annealing temperature.Electrical contact resistance measured by a four point probe instrument is directly affected by the thickness of films.It is also found that the film conductivity,especially in thinner films,is improved by the increasing grain size.Finally,the film adhesion is observed by scratch tests.And the adhesive ability deposited by radio frequency magnetron sputtering shows a better performance than that produced by traditional methods.     

Predictive Modeling and Parameter Optimization of Cutting Forces During Orbital Drilling

To optimize cutting control parameters and provide scientific evidence for controlling cutting forces,cutting force modeling and cutting control parameter optimization are researched with one tool adopted to orbital drill holes in aluminum alloy 6061.Firstly,four cutting control parameters(tool rotation speed,tool revolution speed,axial feeding pitch and tool revolution radius)and affecting cutting forces are identified after orbital drilling kinematics analysis.Secondly,hybrid level orthogonal experiment method is utilized in modeling experiment.By nonlinear regression analysis,two quadratic prediction models for axial and radial forces are established,where the above four control parameters are used as input variables.Then,model accuracy and cutting control parameters are analyzed.Upon axial and radial forces models,two optimal combinations of cutting control parameters are obtained for processing a13mm hole,corresponding to the minimum axial force and the radial force respectively.Finally,each optimal combination is applied in verification experiment.The verification experiment results of cutting force are in good agreement with prediction model,which confirms accracy of the research method in practical production.