Numerical and experimental investigations on new jar designs for high efficiency planetary ball milling

The internal shape of planetary ball mill jars was modified to increase the efficiency of the milling process. Four new jar designs are presented, where obstacles on the surface of a traditional cylindrical jar modify the ratio of normal-to-tangential transferred mechanical action, thus improving the comminution of the mill charge and reducing the process time. Multibody dynamics simulations, validated by operando video recordings of the process, were employed to investigate modified ball motion regimes promoting the increase of the number of high-energy impacts. Moreover, experimental grinding of calcium fluoride powder was performed to assess the effect of milling time and jar-to-plate velocity ratio, through the evaluation of size and microstrain of the end product deduced from X-ray diffraction line profile analysis.     

高加速度数控机床关键技术问题研究

本文以沈阳第一机床厂研制开发的CHH6125卧式车削中心为研究对象，对其部分关键技术问题进行研究；主要论述了影响机床加、减速度的主要因素，以及如何更好地提高机床进给加速度；并建立了机床系统的多刚体动力学模型并进行数字模拟仿真和实验验证。针对高速、高精度机床提出了提高机床进给加速度的一些措施，同时也为其它同类机床的研制开发提供一定的参考。     

On the unique solvability of a direct dynamics problem for mechanisms with redundant constraints and Coulomb friction in joints

The uniqueness of simulated motion of an overconstrained rigid body mechanism with joint friction is studied. The investigated issue originates in the problem of joint reactions solvability. It is known that in case of redundant constraints existence the constraint reaction forces cannot be — in general — uniquely determined. It can be proved, however, that — under certain conditions — selected reactions can be specified uniquely. Analytical and numerical methods for reactions solvability analysis are available. It is shown in this paper that indeterminacy of normal reactions results in indeterminacy of friction forces, and moreover, non-uniqueness of friction forces results in non-uniqueness of simulated motion. A method of finding these joints, for which friction forces are unique, is presented. It is also proved that if only uniquely solvable friction effects are introduced, then simulated motion of the mechanism is unique, otherwise it is not. Finally, examples of dynamic analysis of overconstrained mechanisms with joint friction are presented; unique and non-unique results are obtained.     

具有力约束的多体系统动力学优化方法的研究

本文以Ｋａｎｅ方程为基础，建立了具有力约束的多体系统动力学方程，以能量最小为优化目标，实现了动力学解算。以工业机器人为例，进行了动力学分析和解算。     

Real-time state observers based on multibody models and the extended Kalman filter

This work is a preliminary study on the use of the extended Kalman filter (EKF) for the state estimation of multibody systems. The observers based on the EKF are described by first-order differential equations, with independent, non-constrained coordinates. Therefore, it should be investigated how to formulate the equations of motion of the multibody systems so that efficient, robust and accurate observers can be derived, which can serve to develop advanced real-time applications. In the paper, two options are considered: a state-space reduction method and the penalty method. Both methods are tested on a four-bar mechanism with a linear spring-damper. The results enable us to analyze the pros and cons of each method and provide clues for future research.     

Incorporating non-motion cues into 3D motion segmentation

We address the problem of segmenting an image sequence into rigidly moving 3D objects. An elegant solution to this problem in the case of orthographic projection is the multibody factorization approach in which the measurement matrix is factored into lower rank matrices. Despite progress in factorization algorithms, their performance is still far from satisfactory and in scenes with missing data and noise, most existing algorithms fail.In this paper we propose a method for incorporating 2D non-motion cues (such as spatial coherence) into multibody factorization. We show the similarity of the problem to constrained factor analysis and use the EM algorithm to find the segmentation. We show that adding these cues improves performance in real and synthetic sequences.     

DESIGN AND CONTROL SENSITIVITY ANALYSIS OF MULTIPLE HYPERELASTIC BODY SYSTEMS

A statement of Hamilton's principle for a multiple-body system in the finite theory of elasticity is presented. Surface interaction, among the bodies and with the ground, is materialized by kinematic boundary condition, holonomic constraints, a potential and a dissipation function. As additional data, there are body forces and tractions, and three kinds of time limit conditions. The design and control of the system is defined by a parametric representation of data. Material properties, time interval of analysis and control discontinuities are considered. An incremental form of Hamilton's principle is presented, in connection with a perturbation of the data. The virtual work of stress, global and incremental, is represented by differential operators and transformation laws for these operators, under rigid-body motions, are derived. Sensitivity analysis results by the adjoint method for a mechanical system with small strains overlying large rigid-body motions are presented.     

Friction Power Loss Simulation of Internal Combustion Engines Considering Mixed Lubricated Radial Slider,Axial Slider and Piston to Liner Contacts

Different types of mixed lubricated contacts are present in internal combustion engines. These are several radial slider bearings; for instance, in main bearings; big end, small end, and piston pin bearings; as well as axial slider bearings and piston–liner contacts. Phenomena such as friction power loss and wear as well as acoustic excitation and oil consumption of the overall lubrication system are mainly affected by these contacts. Therefore, the simulation-based investigation of oil film–lubricated contacts is important during the development process of internal combustion engines. Due to the highly nonlinear interactions, the applied mathematical models have to consider the dynamics of the overall flexible body system in addition to the detailed properties of the contacts and the lubricant itself.

This work outlines both the theory of the separated mathematical models and their coupling. The large number of nonlinear contacts, which is possible to consider when applying the presented coupling approach, is emphasized. Furthermore, application of a friction power loss analysis for an in-line four-cylinder internal combustion engine is described.     

Experimental validation of a model of an uncontrolled bicycle

In this paper, an experimental validation of some modelling aspects of an uncontrolled bicycle is presented. In numerical models, many physical aspects of the real bicycle are considered negligible, such as the flexibility of the frame and wheels, play in the bearings, and precise tire characteristics. The admissibility of these assumptions has been checked by comparing experimental results with numerical simulation results. The numerical simulations were performed on a three-degree-of-freedom benchmarked bicycle model. For the validation we considered the linearized equations of motion for small perturbations of the upright steady forward motion. The most dubious assumption that was validated in this model was the replacement of the tires by knife-edge wheels rolling without slipping (non-holonomic constraints). The experimental system consisted of an instrumented bicycle without rider. Sensors were present for measuring the roll rate, yaw rate, steering angle, and rear wheel rotation. Measurements were recorded for the case in which the bicycle coasted freely on a level surface. From these measured data, eigenvalues were extracted by means of curve fitting. These eigenvalues were then compared with the results from the linearized equations of motion of the model. As a result, the model appeared to be fairly accurate for the low-speed low-frequency behaviour.     

A Lie group formulation of Kane’s equations for multibody systems

We propose a Lie group approach to formulate the Kane’s equations of motion for multibody systems. This approach regards the set of rigid body transformations as the special Euclidean group SE(3). By expressing rigid body displacements as exponential maps generated from the Lie algebra se(3), it subsequently manipulates rigid body kinematics as convenient matrix operations. With this approach, all the individual quantities involved in Kane’s equations can be computed explicitly in an intrinsic manner, and the motion equations can be obtained systematically and efficiently. An example is presented to illustrate its use and effectiveness.