DWELL-EXPERT:计算机辅助间歇运动连杆机构概念设计系统

以间歇运动连杆机构的设计为例,重点讨论了基于功能、约束和结构的概念设计方法在机构概念设计中的应用,包括了设计空间的离散化、推理网络的构成及其推理方法等。本文所提出的思路和方法,对于其他机械产品的概念设计也有一定的参考价值。     

Design of single- and multiple-dwell six-link mechanisms through design optimization

Nonlinear programming techniques are applied to a class of six-bar linkages to produce single- and multiple-dwell mechanisms. The six-bar linkage consists of a four-bar crank-rocker mechanism driving a slider crank mechanism from a coupler point. The dwell position(s) may be specified at any value of input link rotation and may last for any reasonable duration. The total stroke and the location of the slider at each dwell position may also be specified. A design optimization problem is formed which attempts to generate a linkage in which the slider link will travel in a circular path and thus produce a dwell period in the cycle at the appropriate link position. This problem is then solved by an exterior penalty function technique. The linkage model is constructed using the vector loop approach and examples for both a single- and double-dwell mechanism are included. Extensions including velocity, acceleration and transmission angle constraints are also discussed.     

注塑工艺优化设计

从预热温度、料筒温度、模具温度、压力油温度、锁模力、模具填充速度、模具填充压力、保压压力、保压时间、螺杆转速、卸压、背压参数设计等方面讨论了注塑工艺参数优化设计的方法,并分析了注塑成型的常见问题及质量缺陷。     

Observer-based stabilization for switched positive system with mode-dependent average dwell time

This paper concerns the exponential stabilization problem for a class of switched positive systems. The switching signal satisfies mode-dependent average dwell time (MDADT) and the state variables are partially unmeasurable. A further explanation of mode-dependent average dwell time is included. By employing a set of quasi-time variables, which is first proposed for switched systems with MDADT, new stability results are obtained for the switched nonlinear systems and the underlying linear systems. Observer-based stabilization controllers, both for single-input case and multi-input case, are designed such that the closed-loop system converges exponentially. The designed observers and controllers are both mode-dependent and quasi-time-dependent, which is proved to be less conservative than the ones only mode-dependent. A simplified design strategy is provided to reduce the computation burden. Illustrative examples are provided to demonstrate the effectiveness of the results.     

Influence of the bulk diffusion of rubidium and sodium atoms in glass on their surface dwell time

This paper presents the results of measurement of the surface potential and the dwell time of Rb and Na atoms on the surface of S-52 molybdenum glass. It is found that at temperatures below the glass transition temperature, the temperature dependence of the dwell time of Rb atoms is well described by the Arrhenius formula. The surface potentials for Rb and Na are measured to be 0.67 and 1.37 eV, respectively. At temperatures above the glass transition temperature, the dwell time of these atoms increases abnormally. The reason for this is that during impact of an atom on the surface of molten glass, it can penetrate into the volume of the window and then return by diffusion and desorb from the surface. In this case, the dwell time of the atom on the glass is determined by the diffusion time and can be very significant, despite the relatively low potential barrier at the surface and high temperature.     

Verbesserung der genauigkeit und laufgüte sechsglierdriger koppel-schwingrastgetriebeImprovement of accuracy and quality of transmission in six-bar mechanisms for oscillating-dwell motions

In order to produce dwell-rise-dwell motions cam mechanisms can be designed much simpler than linkages. Because of the many advantages of linkages, more attention should be spent to their design and at first to the six-linked structures which fulfill the given problem by smallest expense. The six-bar coupler linkage is discussed here. It realizes the dwells by approximation of the coupler-curve to a circle which is represented by the length of an additional coupler link. Many investigations have been made to meet this problem best. So the circle point curve (Burmester-curve) represents a four-fold coincidence of coupler-curve and circle. If a dwell at the end of an oscillating motion is ordered, the curvature of coupler-curve must show an extremum value. If, in addition, two end-dwells are asked for the classic Burmester Theory never can solve this problem. Now the computer-aided design is able to give new ideas as follows: The major size of coupler-curves is well-known by tables like Hrones and Nelson's atlas and also the ranges usable for dwell-motions. Such four-bars are computer-programmed to find maximum values of curvature automatically. Deviations of the transmitting link from radius of maximum curvature enlarge the duration of dwell but increase the errors during the dwell period. In each case a four-fold coincidence is realized. The computer automatically finds all extremum curvature point and there are no difficulties in finding a second end-dwell. Using special four-bars with equal lengths of coupler, output link and coupler point distance, symmetrical coupler curves are produced in which extremum curvatures correspond to crank displacements of 180°. If non-symmetrical motions are wanted, four-bars with general dimensions have to be computer-investigated. It should be stated that by the method explained eight precision points of coupler curve have been found when the maximum of them is nine. For each problem a certain number of usable four-bars can be found. The computer cam then be ordered to find that one having smallest maximum acceleration. Further investigations in this direction should be started in order to find the limits of six-linked mechanisms and to learn exactly for which requirements linkages of higher order have to be used, i.e. how to produce longer dwells and those ones with higher accuracy, also how to produce two dwells having a larger difference in back and forth motion between dwells and finally how to design linkages for more than two dwells.     

Utilisation of time-variant influence functions in the computer controlled polishing

In the computer controlled polishing, a polishing tool moves in a well-defined manner across the workpiece surface in order to individually remove the surface error-profile. The commonly used technique to calculate the moving of the polishing tool is the dwell time method. Based on a constant (time-invariant) removal characteristic of the polishing tool (influence function) the amount of material to be removed is controlled via the dwell time. The longer the polishing tool is in contact with a particular area of the workpiece, the more material is removed at this position.Mathematical basics to calculate dwell time-profiles are shown, and a new approach considering time-variant influence functions for the computer controlled polishing is introduced. The results point out that time-variant influence functions may contribute to further decrease the process time, and thus to make a computer controlled polishing process more efficient. The reduction of the process time was observed to approximately 35% using a combination of the dwell time method with time-variant influence functions.     

Trajectory planning of optical polishing based on optimized implementation of dwell time

This paper presents a study on the trajectory planning of optical polishing based on an optimized implementation of dwell time to improve the polishing quality and efficiency of optical surfaces. The large-scale, sparse, and ill-posed linear equation solution is transformed into a quadratic programming problem with boundary constraint, and the monotone projection gradient method is adopted to obtain an optimal dwell time solution by considering its fluctuation characteristic. Then, parametric polishing paths are constructed using cubic B-spline curves to guarantee one-to-one correspondence between each curve segment and dwell time of a removal spot. Finally, an interpolation process of polishing trajectory is proposed on the basis of the equal–proportional feed rate adjustment strategy to improve the implementation accuracy of dwell time. Simulation and experimental results show that the proposed dwell time algorithm and spline interpolation method can considerably improve the solution accuracy of dwell time and the convergence rate of the form error during polishing. These results provide important scientific basis and technical support for the high-efficiency and high-precision polishing of large-aperture aspheric optical surfaces.     

数控光学成形的计算机模拟及工艺实验

本文详细介绍了以控制磨头驻留时间为基础的CCOS基本原理、计算机模拟软件和工艺实验,为CCOS数控机床的设计提供了理论参考和实验依据,同时也提供了CCOS计算机模拟的实用软件及合理的工艺参数,为进一步研究这一技术打下良好的基础。     

A fractional coverage model for gas–surface interaction in reciprocating sliding contacts

A model of fractional coverage in reciprocating sliding contact is developed. The sliding velocity profiles, the contact pressure distribution, the lengths of the slider or wear-track, and the periods of dwell where the slider is held stationary at the turn around locations are all variables. The model is evaluated for the condition of a constant fully reversing sliding speed with a uniform contact pressure and dwell. Plots are presented for surface area fractional coverage as a function of position illustrating the effects of individually varying vapor pressure, velocity, load, and dwell. The prediction of a steady state friction coefficient dependence on position is discussed, as well as the locations of maximum and minimum friction coefficient. The model predicts coverage to be enhanced by decreasing loads, decreasing sliding speeds, increasing gas pressures, and increasing periods of dwell.     

The effect of dwell angle on vibration characteristics of camshaft bearing housings

Cam-follower mechanisms are affected by undesired dynamic forces which may disrupt the accuracy of the follower motion. These undesired dynamic forces create vibrations which cause noise, wear, and increasing operating costs for cam-follower mechanisms. Journal bearings are the most widely-used mechanical parts in internal combustion engines under high load and high operating speeds. In this study, the effect of the dwell angle on the vibration characteristics of camshaft bearing housings was investigated. Two camshafts having a 6 mm lift and different dwell angles were tested at operating speeds of 450, 900, 1350, 1920, and 2400 rpm. The collected data were analyzed in detail. It was observed that with the increasing of the camshaft rotational speed, vibration responses of greater magnitude were obtained. In general, the first and second peak values of the low dwell angle camshaft were higher than those of the high dwell angle camshaft.     

Molecular adsorption: early stage surface exploration

In this study, the atomic force microscope has been employed in force spectroscopy mode to gain information on the interaction between long mucin molecules and a positively charged surface during the first few seconds of interaction. Recent studies have revealed that negatively charged mucin molecules introduced to a positively charged surface are kinetically trapped and bind very rapidly, assuming non-equilibrium conformations. This systematic study of surface dwell times has revealed that significant differences exist in mucin adsorption during the first three seconds of introduction to the surface and provides direct evidence of molecular rearrangement for several seconds before trapping occurs. Limited interactions were recorded at dwell times of less than one second, with increased molecular rearrangement observed between 1.5 and 2.25 s. Increasing the surface dwell time beyond this critical limit caused rupture of the tip-tethered mucin molecules during the retract cycle of the cantilever. All subsequent recorded events, at increased dwell times up to 3 s, revealed events at much reduced distances from the point of contact between the mucin functionalised-cantilever and the positively charged surface.     

New results on stability of switched continuous-time systems with all subsystems unstable

This paper studies the stability problem of switched continuous-time systems with all subsystems unstable. Switchings can be classified into two categories depending on their dwell time, which are the switching without divergence time and the switching with divergence time. Based on this, stability conditions under the bounded maximum average dwell time (BMADT) switching are established. In addition, by jointly considering the dynamic characteristics of the subsystems before and after switching instants, we also give the stability result via the dwell time with the floating lower and upper bounds. Finally, some simulation results are given to illustrate the advantages of the obtained theoretical results.     

某型炮兵雷达模拟训练系统的设计与实现

利用模拟器进行训练是目前国际上一种普遍做法,它既可以节省费用。降低磨损,又可以提高训练效率。本文提出了某炮兵雷达模拟训练系统的总体设计方案。并详细描述了系统各部分的组成和功能。介绍了系统软件的设计思路和组成。实用证明,该系统满足设计要求,能模拟实现雷达各种功能和操作。     

光学非球面离子束加工模型及误差控制

摘要：通过对离子束加工系统的分析,给出了加工非球面光学元件的离子源子系统运动模型公式,并将驻留时间求解的反卷积过程转化为求解线性矩阵方程模型,便于进一步优化求解;对加工过程中不可避免的离子源定位误差过程进行了分析,指出其对最终面形精度的影响可归结为一个系数因子的控制上,并提出了综合考虑离子束材料去除函数和定位误差的方法来控制系数因子,降低对定位系统的苛刻精度要求,保证过程稳定的同时降低设备成本。     

立体仓库中堆垛机的理想待命位的控制

讨论了在自动化立体仓库系统（AS／RSs）中,堆垛机动态待命位的问题。由存储时间优先的出库策略确定了m个可能的访问点,由随机存储策略得到了这m个可能的访问点分别具有的的流通率,证明了这m个可能的访问点属于格拉斯曼空间。利用多质点重心法,通过格拉斯曼空间到仿射空间的映射,求出堆垛机动态待命位。     

保载应力和加载速率对316H不锈钢蠕变行为的影响

针对316H不锈钢,通过开展一系列高温蠕变试验,探讨了保载应力和保载前加载速率对材料蠕变行为的影响。结果表明,保载应力对材料蠕变行为影响较大,在进行高温结构蠕变损伤估算时,蠕变应变速率和蠕变断裂延性的选取均要考虑保载应力的影响;保载前的加载速率也对材料蠕变行为产生一定影响,尤其是加载速率较低时。因此,在进行高温结构蠕变损伤估算时,需考虑较低加载速率的影响。     

Alternative method to determine parting direction automatically for generating core and cavity of two-plate mold using B-rep of visibility map

Hysteresis friction behaviors of linear rolling bearings (LRBs) are important for precision positioning applications, which are related to the displacement and the traversed trajectory history within pre-rolling friction region. Although these behaviors have been pointed out in literature, the time dependence of transient hysteresis friction behaviors has not been reported before. In this work, the effects of initial conditions induced by the applied forces prior to commencement of the hysteresis motion are considered, which are denoted by the differences between the magnitudes of positive endpoints and the magnitudes of negative endpoints of virgin curves for the obtained asymmetrical hysteresis loops. The evolution of the time dependence is denoted by the decaying of the differences with the increasing dwell time. The effects of the damping and the junction growth during the dwell time are used to explain the time-dependent hysteresis friction behaviors of the LRB. The experiments of higher preload and lubrication-free conditions have been implemented as well, and the results indicate that the conditions are positive to diminish the time-dependent hysteresis friction behaviors.     

Wear observations applied to lifeboat slipway launches

It is necessary to use an inclined slipway to launch a large lifeboat in locations where there is no natural harbour or where there is a large tidal range. Slipway stations consist of an initial section where the boat is held on rollers followed by an inclined Keelway of nickel/chromium coated steel, the lifeboat is released from the top of the slipway and proceeds under its own weight into the water. The lifeboat is subsequently recovered to the top of the slipway using a winch line. With the introduction of the new, larger Tamar class lifeboat existing boathouses are being upgraded and existing low friction coated steel slipway lining materials replaced with a low friction jute fibre/phenolic resin composite, which is designed to operate with unlubricated conditions. This has led to problems of high wear on slipway panels, particularly where the lifeboat mounts the slipway for recovery.This paper describes a method for assessing slipway lining materials and lubricants. The selection of an appropriate test machine, the TE92 rotary tribometer, and design of a modified ring on disc arrangement is described. An experimental methodology is developed using programmed running intervals to simulate dwell effects.Experimental data is thus presented to establish slipway panel wear rates for a range of lubricants and contact pressures. Results and implications of this research for future lifeboat slipway design are discussed.     

基于Bayesian原理的低陡度光学镜面面形误差离子束修正驻留时间算法

离子束修形是一种高效修除镜面误差的技术,驻留时间求解算法是此技术的关键问题之一。以光学镜面计算机控制成型原理为基础,建立基于Bayesian原理的平面镜面驻留时间算法,对数据边缘进行Gaussian延拓以消除边缘效应。分析驻留时间近似速度实现方式的实现误差与工艺参数的关系,通过在算法中引入附加光滑修正因子以提高驻留时间实现精度。在适当的路径规划下,将低陡度非球面修形过程近似用平面修形过程线性模型来描述,最终形成低陡度光学镜面面形误差离子束修正中驻留时间的快速近似算法。利用此算法对 100平面镜和 200球面镜进行修形加工,加工收敛率均可达9。研究结果表明：线性化近似模型是合理的,速度近似计算是可行的,基于Bayesian原理的低陡度非球面驻留时间求解算法是一种快速高效面形控制技术,可对镜面进行确定性精确修形。