基于C语言的平面连杆机构的运动分析

提出一种基于C语言的平面连杆机构运动分析方法，为平面连杆机构运动分析提供一条简单易行的解析途径。     

Solid particle erosion of diamond coatings under non-normal impact angles

This paper describes an erosion study, which examines the effect of impact angle on the erosion behaviour of diamond coatings deposited on tungsten substrates by chemical vapour deposition (CVD). The coatings were 37–60 μm in thickness and were erosion tested using angular silica sand with a mean diameter of 194 μm at a particle velocity of 268 m s⁻¹. The impact angles used were 30, 45, 60 and 90°. The results show that the damage features, termed “pin-holes” are generated at all angles, though the number of impacts required for pin-hole initiation is significantly increased at lower angles. This work provides useful information in attempting to explain the mechanism by which damage is generated during the high velocity sand erosion of CVD diamond.     

On quasi-degeneracies in plate vibration problems

In plotting the variation of frequencies with geometric parameters such as side ratio, skew angle, thickness taper, etc. in detailed studies of the vibration characteristics of plates, situations are encountered such as crossing of the frequency curves or the tendency of these curves to come close together and veer away from each other. These have been generally referred to as “frequency crossings” and “transitions” respectively. The latter may preferably be referred to as “quasi-degeneracies”. In the literature there appears to be some ambiguity in the analysis and interpretation of these features. In this paper, a clarification of some of these questions as regards rectangular and skew plates is presented by making use of concepts from physics dealing with molecular vibrations.     

On the dynamics of high-speed cam profiles

An exact expression for the maximum output acceleration of a two-mass-and-spring cam system is developed for zero damping and dwell-rise-dwell profiles. A family of high-speed cam profiles having minimum components in the higher harmonics and similar in shape to Neklutin's “modified trapezoids” is suggested. One simple formula applies to the whole profile. General considerations on optimization of cam profiles (for minimum force on follower) and limitations on ultimate performance are presented.     

Spectral analysis of bi-tone waveforms: study of the uncertainty contributions arising from the virtual time-domain approach

Multi-tone signals are discrete-spectrum signals with spectral components located at nonharmonically related frequencies. The authors proposed a method that combines the use of a virtual time-domain and a statistical technique that provides an estimator for the spectral analysis of multi-tone signals in short observation intervals. In this paper, the above estimator is treated as error source, whose effects are referred to as “intrinsic contributions” to uncertainty. A study on these contributions is developed in the case of bi-tone signals and application examples are provided. The experimental results confirm theory.     

Kinematic analysis of combined roller-chain and planar mechanisms

This paper presents a suggested mechanical system comprising of two sprocket roller-chains (flexible system) in combination with rigid planar links either crank-coupler or drag-link linkage. The paper discusses and analyzes two alternatives in which the roller-chain is driving the rigid links and “inverse” possibility when the crank of the rigid planar links is the input element and the output motion is taken from the roller-chain. Moreover, replacing the crank of the rigid links by a variable length is discussed, and obtained by considering the coupler as being joined with a point on a drag-link mechanism. The merits of each version are presented and discussed. Of interest, is the unique advantage of obtaining particular output/input velocity ratios which no available mechanism can achieve. Moreover, the obtained results indicate quite a useful applicability of the analyzed system in the industrial packing process, motion transmission and, in particular, in conveying machinery. The kinematic analysis procedure is presented in simple formulation using trigonometric relations.     

平面3-RRR并联机器人运动分析的计算机模拟逼近法

提出一种新的平面3自由度并联机器人运动分析方法,计算机模拟逼近法。运用该方法进行了速度和加速度分析。先采用CAD的几何约束、尺寸约束、尺寸方程和尺寸驱动技术,构造平面3—RRR3自由度机器人的模拟机构。再用两个相同且彼此靠近的平面3自由度机器人模拟机构,构造速度模拟机构,求解动平台上确定点的速度和角速度。最后用两个相同且彼此靠近的平面3—RRR机器人速度模拟机构,构造加速度模拟机构,求解动平台上确定点的加速度和角加速度。计算机模拟结果与解析法的结果比较表明,该方法具有简单、快捷、直观、求解精度高的优点,而且可以完成复杂机构的运动分析,为多自由度机构运动分析提供了更有效的工具。     

The particular or the general? (Some examples from robot kinematics)

The common use of some general analytical methods for solving problems is called into question. It is contended that “realistic” serial robots can be dealt with more elegantly and faster by perceiving their particular properties rather than resorting to generality. Robot “closure” (inverse pair-variable determination) and velocity-determination provide examples. The physical nature of the problem is evident throughout, whereas it is obscured when a general method is routinely followed. Moreover, there is the prospect of improved algorithms for real-time control. It is contended that the gist of the message conveyed has broader applications too.     

Abrasive wear mechanisms of fluoropolymer based composite coatings on aluminum substrates

Experimental studies on wear performance and wear mechanisms of fluoropolymer based composite, non-stick coatings on aluminum substrates were carried out by using particular wear testing methods, i.e. the “mechanical tiger paw (MTP) Test” and the “Nord Test”. Both are supposed to simulate household abrasive operating conditions in a laboratory environment. It was found that the wear process involved in the MTP Test was an accelerated one, but that in the Nord Test was decelerated due to a transition from severe three-body abrasion to milder two-body sliding wear. In addition, both effects of the microstructure of the coatings and of the surface treatment of the substrates were discussed.     

An evaluation of the effect of simulated launch vibration on the friction performance and lubrication of ball bearings for space applications

Ball bearings in space mechanisms are subjected to vibration during launch which can lead to a temporary loss of contact between the balls and the raceway. On re-establishing contact the transient high contact stresses which arise may cause damage to the bearing. This transient loss of contact is referred to as “gapping”. Despite the fact that it is clearly of interest to understand how exposure to the launch vibration impacts upon bearing and lubricant performance, the dynamic behaviour of bearings subjected to vibration typical of that occurring during launch has been little studied.This paper describes a theoretical and experimental investigation to examine the influence of simulated launch vibration on the torque performance of solid and liquid lubricated ball bearings. A fixture containing a pair of preloaded face-to-face angular contact bearings was mounted on an electro-dynamic vibrator. Two laser triangulation transducers were used to measure the relative axial displacement of the bearing components at a range of acceleration levels. A simple analytical model was also developed to predict gapping for a range of different test conditions. Data from this model was compared to measured gapping. The effect of vibration on bearing torque was measured following each level of acceleration. Finally, features arising in the bearing raceway due to vibration testing were assessed.     

Fault coverage in plant protection systems

Many process plant protection systems rely on redundancy methods to achieve high reliability and predictable operation. The basic principle behind such systems is: if one system fails, redundant mechanisms that can allow continued operation or bring the process to a known safe state. It has been shown [1] that the degree of dependability achievable by such systems is a function of the number of “covert” faults—i.e., faults that are not discovered during normal operation and could lead to improper operation of the system on demand if not discovered by testing.

Typical redundant systems automatically test for covert faults using a variety of hardware and software diagnostic methods. “coverage factor” (or simply “coverage”) is a measure of how well such a system detects faults. Therefore, systems with high coverage have few undiscovered covert failure modes and can operate predictably. Systems with low coverage have many covert failure modes and expose the plant to potentially unpredictable and unsafe operation. This paper presents the concept of coverage, explores its impact on system reliability, and discusses methods of achieving high coverage and assessing the coverage factor.     

Analytical dynamics of mechanisms—a computer oriented overview

General-purpose computer programs such as IMP, DRAM, MEDUSA and DYMAC, for the solution of inertia-variant (linkage-type) mechanisms are beginning to emerge. These programs, which automatically generate, and numerically integrate, the equations of motions, are based upon different but related analytical and numerical principles. There has also been much recent discussion of “influence coefficient” methods, energy methods and related matters. This paper reviews the various principles and techniques available for formulating the equations of motion, for integrating them numerically, and for solving the associated kinetostatic problem for the determination of bearing reactions. The relative advantages of vector methods, d'Alembert's Principle, Lagrange's Equations with and without multipliers, Hamilton's Equations, Virtual work, and energy methods are discussed. Particular emphasis is placed on how well-suited the various methods are to the automatic generation of the equations of motion, and to the form and order of the systems of differential equations they lead to. It is shown how velocity ratios, influence coefficients, centripetal coefficients, generalized inertia coefficients, and Christoffel symbols interrelate the various methods, and tie them to classical results of Analytical Dynamics such as the “explicit” equations of motion and the power-balance principle. Methods for solving both the general dynamics problem, and the kinetostatic problem, are reviewed, and the particular methods of implementation used in the recently developed general-purpose computer programs, and in other recent literature, are described.     

求解机器人臂速度和加速度的CAD变量几何法

提出求解机器人臂平面多自由度机构的速度和加速度的CAD变量几何方法。用CAD变量几何技术，构造一些典型的机器人臂多自由度平面机构的模拟机构。再用两个相同且彼此靠近的多自由度机器人臂模拟机构，构违速度模拟机构，求解各个机构输出杆的速度。最后用两个相同且彼此靠近的多自由度平面连杆速度模拟机构，构追加速度模拟机构，求解机构的输出杆的加速度。计算机变量几何方法求解结果与解析法的结果比较表明，文中方法不仅具有简单、快捷、直观、求解精度高的优点，而且可以完成复杂机构的运动分析，为多自由度机构运动分析提供了更有效的工具。     

The lubrication of lightly loaded cylinders in combined rolling, sliding and normal motion with couple stress fluid

The lubrication of lightly loaded cylinders with combined rolling, sliding and normal motion is investigated with a couple stress fluid as lubricant under cavitation boundary conditions. It is shown that the major bearing performance characteristics can be accounted for by means of a dimensionless parameter, q, involving the “normal” and “entraining” velocities, the minimum film thickness and the radius of the geometrically equivalent cylinder near a plane. The load capacity and frictional drag increase as the squeeze velocity increases. This increase is enhanced by decreasing the couple stress parameter, τ. However, when the two surfaces move apart these results are reversed. It is convenient to adopt the least-squares procedure for the accurate representation of the line of cavitation and the line of maximum pressure. The effect of couple stresses on the point of cavitation is quite significant compared with viscous fluid of the same viscosity.     

Generalized study of crank-rocker mechanisms driven by a d.c. motor Part I. Mathematical model

A mathematical model is developed for analyzing a 4-bar linkage driven through a speed reducer by a separately-excited d.c. motor. A set of nonlinear differential equations, governing the dynamic response of this system, is derived and converted to dimensionless form. This dimensionless form is described by newly defined linkage and drive parameters. It is believed that these parameters may find convenient use in estimating the overall behavior of motor-mechanism systems from performance graphs and guidelines which can be established by numerical study of typical cases.

The performance characteristics which are considered in this analysis are the steady-state speed fluctuation of the mechanism and its steady-state energy consumption as well as the time required for mechanism “start-up” and the energy consumption during start-up. Expressions are derived in a dimensionless form to represent these performance characteristics. In Part II of this paper, specific numerical examples are presented which relate the performance characteristics to the linkage and drive parameters for two different mechanisms.     

Strength and residual stress of Mg-PSZ after grinding

The influence of grinding with two grinding wheels, differing mainly in diamond-grain size, on the properties of Mg-PSZ was examined. The residual stress, the amount of monoclinic zirconia and the strength of the material were determined. From these measurements depth profiles were obtained for the phase content and the residual stress. The fracture surfaces were examined optically to estimate the critical flaw size. Material ground with “coarse” diamond grains was significantly weaker than that ground with “fine” diamond grains. “Coarse” diamond grains in the grinding wheel resulted in more residual stress and a thicker layer of transformed zirconia than when “fine” grains were in the wheel. This apparent discrepancy is explained with a model based on the occurrence of localized spots of tensile stress beneath the residual stress layer near grain boundaries. These spots are assumed to be larger in number and to contain higher tensile stresses after grinding with “coarse” grains.     

High availability systems for safety and performance—the “coverage” factor

High Availability Systems are needed in many applications not only for safety purposes but also good economic performance. “Coverage” is a measure of how well the automated testing in such systems detects failures. The coverage factor is considered by many to be the most important measure of availability in fault tolerant architectures. The control system designer can create better logic control systems by understanding the “hows” and “whys” of coverage.     

An applied finite element displacement analysis of a simple integral construction vehicle body shell

A finite element idealization of a full-size vehicle body shell was created and used to predict underfloor displacement patterns due to beam loadings, which were compared with experimentally measured values. Modified representations of roof and floor construction details were used to highlight their influence on the structural behaviour of the vehicle. Also comparative studies were made using “assumed stress” and “assumed displacement” element formulations.