Geometric,kinematical and thermal analyses of non-round cylindrical grinding

This paper is concerned with the analyses of grinding geometry and kinematics in the grinding zone and develops a thermal model, along with a chip-thickness-dependent value of specific grinding energy into the workpiece. The grinding geometry and kinematics are modeled for arbitrary non-round workpiece forms. Unlike other models, which are based on a fixed, constant geometry, the model presented here is based on first principles using a fundamental, transient, non-constant geometry and thus constitutes a much-needed advancement in grinding technology. A novel experimental approach is also taken, which uses the specific grinding energy into the workpiece, rather than the total specific grinding energy coupled with an estimate of the energy partition, an estimate which previously has proven difficult to achieve accurately. The model is verified with experimental work and predicted temperatures are in reasonable agreement with temperatures associated with the onset of thermal damage, determined via metallographic examination and Barkhausen noise. Finally, some of the challenges of using Barkhausen noise to evaluate thermal damage are investigated, namely the differing response characteristics of stressed and overtempered material vs. rehardened material, and how these can be overcome in practice.     

双臂液压钻车的运动学分析及优化

为了实现双臂钻车的自动化打孔,对其进行运动学分析和优化计算。优化计算的目的是要找到液压钻臂各个关节的合适的角度位置,能够在钻车工作时实现确定的位姿。采用粒子群算法在MATLAB环境下计算并得出最优解,结果证明粒子群算法能有效解决两臂钻车的运动学计算。为了方便操作和审核,建立了用户界面并生成了.exe文件,从而为钻车自动化打孔奠定了技术基础。     

全液压自动猫道钻杆运移系统设计及仿真分析

根据大陆科学钻探钻机自动猫道的设计要求,设计了猫道的钻杆运移系统。系统具有机构新颖、动作稳定可靠、控制方便等优点,能够代替人工完成在钻井过程中运移钻杆的动作,实现钻具的自动运移。简要介绍了钻杆运移系统的结构组成、工作原理及系统的动作流程,并利用Inventor软件为设计平台建立钻杆运移系统模型,并在此基础上运用ADAMS仿真软件建立仿真模型。对系统进行运动学仿真模拟,得到钻杆运移系统与钻杆之间接触力的变化以及钻杆运移系统关键部位的应力变化。通过仿真分析验证了系统的稳定性,为系统实际动作的优化及控制提供了理论依据。     

The effect of displacement control input parameters on tibiofemoral prosthetic knee wear

The mechanisms of UHMWPE wear at the tibiofemoral articulation of a total knee replacement are potentially highly dependent on the cyclic direction of motion, the relative amounts of rolling versus sliding, and the loading of the contacting surfaces as previously described for hip components [3]. The simulated wear rate, for a standard test protocol utilizing the Insall-Burstein^®1 II Modular Knee System (IB-II) knee prosthesis, for normal walking gait was found to be 17.0 mg/10⁶ cycles on a Boston AMTI knee simulator. When the anterior/posterior (A/P) translation input was reduced by 50%, the wear rate was reduced approximately 37% to 10.6 mg/10⁶ cycles. Eliminating either the A/P translation or tibial rotation reduced the wear rate to 1.7 mg/10⁶ cycles and 0.69 mg/10⁶ cycles, respectively. These results cannot be explained by sliding distance effects alone and suggest that the UHMWPE wear rate is sensitive to other parameters, such as the magnitude of multidirectional shear motion and the ratio of rolling/sliding contact kinematics in combination with the applied load.     

基于影响系数法的激光切割机床主体机构运动学研究

将3-PUU并联机构作为激光切割机床的主体机构,以对3-PUU并联机构的运动学分析为目的,构建3-PUU并联机构的位置方程,采用虚设机构法建立并联机构的影响系数矩阵,包括Jacobian矩阵和Hessian矩阵。采用影响系数矩阵和对位置方程微分的方式分别求得并联机构的驱动副与动平台间速度和加速度的映射关系,将影响系数法和微分法所得驱动副速度和加速度图谱与ADAMS仿真结果对比。通过对比3种分析方法所得曲线的一致性,验证运动学理论研究的正确性、仿真验证的可靠性以及作为激光切割机床主体机构的适用性。影响系数矩阵的正确建立也为激光切割机床主体机构的动力学分析、性能指标的建立以及优化设计提供了基础。     

Kinematic Soil-Structure Interaction from Strong Motion Recordings

Earthquake strong motion recordings from 29 sites with instrumented structures and free-field accelerographs are used to evaluate variations between foundation-level and free-field ground motions. The focus of the paper is on buildings with surface and shallowly embedded foundations. The foundation/free-field ground motion variations are quantified in terms of frequency-dependent transmissibility function amplitude ∣H∣. Procedures are developed to fit to ∣H∣ analytical models for base slab averaging for the assumed conditions of a rigid base slab and a vertically propagating, incoherent incident wave field characterized by ground motion incoherence parameter κ. The limiting assumptions of the model are not strictly satisfied for actual structures, and the results of the identification are apparent κ values (denoted κa) that reflect not only incoherence effects, but also possible foundation flexibility and wave inclination effects. Nonetheless, a good correlation is found between κa values and soil shear wave velocity for sites with stiff foundation systems. Based on these results, recommendations are made for modifying free-field ground motions to estimate base slab motions for use in response analyses of buildings.     

Kinematics and dynamics of a double-gimbaled control moment gyroscope

Control moment gyroscopes (CMGs) are torque-generating mechanisms that can be used for attitude and vibration control of spacecraft. CMGs consist of a rotating flywheel as well as a wheel-tilting actuator. Most CMG designs allow the flywheel spin axis to tilt about only one axis––a single-gimbaled CMG. This paper develops and analyzes the kinematics and dynamics of a novel double-gimbaled CMG design. The compact CMG design involves two four-bar linkages allowing the axis of rotation of the spinning flywheel to have two degrees of freedom.     

In-vitro measurement of the human knee joint motion during quadriceps leg raising

This paper represents a three-dimensional motion analysis of the human knee joint under given conditions of loading and constraint. As the knee is extended by a known force applied to the quadriceps tendon, relative displacements of the femur, tibia, and patella are measured using a video motion analysis system. The most prominent motion of the tibia is external rotation and anterior displacement relative to the femur during knee extension. The patellar flexion angle decreases from 70° to 0°. The moment arm of the knee extensor mechanism exhibits a characteristic bell shape which peaks somewhere in the 40°–60° region of flexion. In general, the quadriceps force results primarily from an increase in the torque exerted by the weight of the lower leg. In the range of 20°–60°, the quardricep force needed to extend the leg remains relatively constant. As the knee approaches full extension, the moment arm decreases due to the fact that the posterior capsule and the ACL begin to tighten in this region. Consequently, the quadriceps force increases rapidly.     

Quasi-static kinematics model for motion errors of closed hydrostatic guideways in ultra-precision machining

Aspheric optics has been widely employed in some high-tech industries for its superiority. In order to achieve the ultra-precision machining of these aspheric surfaces, the large optical ultra-precision grinding machine becomes crucial because it determines the efficiency of the whole process. As the key functional unit in ultra-precision machine tool, the hydrostatic guideways are commonly adopted for the excellent performance. However, the motion errors of hydrostatic guideways have a direct influence on the accuracy of the machined workpiece, and some analysis approaches have been reported correspondingly. Although the existed analysis models do work, their imperfections also can be easily captured. Accordingly, a novel analysis model with less imperfection is deserved to be developed. In this paper, the kinematic theory is utilized to establish the quasi-static analysis model for motion errors in closed hydrostatic guideways. Through the large ultra-precision grinding machine designed by our research group, the consistently good agreement between the predicted results and the measured experimental data are obtained. Furthermore, it is found that the motion accuracy is more sensitive to the profile error of the guide rail bearing the external load rather than that of the other guide rail in the closed hydrostatic guideway. The presented research is supposed to be valuable to the peer designers.