车床夹具的对定误差分析计算

本文通过两个典型例子说明设计车床专用夹具时 ,计算对定误差的方法。

齿轮加工的对定误差分析计算

重点分析常用的加工齿轮的滚齿机和插齿机夹具在机床上定位和对刀误差,并用常用的几个重要的齿轮公差来限定机床夹具的定位和对刀误差。

铣床夹具对定误差分析计算

本文通过曲型铣床夹具 ,分析产生对定误差的因素 ,列出计算各方面对定误差的计算式和控制各方面对定误差的关系式。

镗床夹具对定误差的分析计算

本文以典型的镗床夹具为例 ,分析产生各方面对定误差的因素 ,介绍了计算各方面对刀误差、对机误差的计算式以及控制方法。

圆柱销分度对定机构分度误差计算

分度误差的计算,一般用圆柱销对定机构进行分析推导出计算公式,且都以分度盘转过相邻的两个对定孔的最大中心距,减去理想的两相邻对定孔的中心距而得出计算公式,即:

Effect of melt convection on primary dendrite arm spacing in directionally solidified Pb-26%Bi hypo-peritectic alloys

Primary dendrite arm spacing（PDAS） of α phase in directionally solidified Pb-26%Bi（mass fraction） hypo-peritectic alloys was measured by considering the effect of melt convection in cylindrical samples with different diameters.The experimental results show the measured PDAS increases with increasing diameter of the sample.At the growth velocity of 5 μm/s,its value changes from 161.5 μm for the sample with 1.8 mm in diameter to 240.4 μm for the sample with 7 mm in diameter.The strong melt convection in large diameter samples causes a high bulk alloy composition and a high concentration gradient in peritectic β phase,resulting in a larger PDAS.Simultaneously,the high concentration gradient could effectively promote the peritectic transformation,enhancing the dissolution of the thin α dendrite.

Cycle slip detection approach based on time-relative positioning theory

An efficient cycle slip detection method is proposed for high precision positioning and navigation results with global positioning system （GPS）,which is based on the assumption of a high sampling interval, measurement errors are so small that they can be ignored in the temporal single difference observables. And ambiguities are ordinarily equal to zero,but could be the number of cycles that have ＂slipped＂ if loss-of-lock has occurred.Therefore,cycle slips are estimated as parameters of time-relative positioning observation equations.Because the temporal single difference observables are taken at different epochs and different stations with a single GPS receiver,if time-relative positioning observation equations are linearized as that of conventional relative positioning,the design matrix will be rank defective.To obtain a stable linearization scheme,time-relative positioning observation equations are further analyzed,and the concept of virtual measurement is applied.A sample of data collected on a vehicle test shows that a cycle slip detection approach based on time-relative positioning theory can detect slips at the value of one cycle.The results also indicate if two satellites are so near to each other that they have the same equivalent to satellite-receiver geometry,cycle slip detection will be difficult and may get wrong results.Cycle slips of different satellites also affect detection by satellite-receiver geometry.

New criterion for delay-dependent absolute stability of Lurie system with interval time-varying delay

The delay-dependent absolute stability for a class of Lurie systems with interval time-varying delay is studied. By employing an augmented Lyapunov functional and combining a free-weighting matrix approach and the reciprocal convex technique, an improved stability condition is derived in terms of linear matrix inequalities （LMIs）. By retaining some useful terms that are usually ignored in the derivative of the Lyapunov function, the proposed sufficient condition depends not only on the lower and upper bounds of both the delay and its derivative, but it also depends on their differences, which has wider application fields than those of present results. Moreover, a new type of equality expression is developed to handle the sector bounds of the nonlinear function, which achieves fewer LMIs in the derived condition, compared with those based on the convex representation. Therefore, the proposed method is less conservative than the existing ones. Simulation examples are given to demonstrate the validity of the approach.

机床夹具设计方法探讨

机床夹具设计是金属切削加工批量生产的重要环节,设计质量的高低直接影响到零件的加工质量和效率。笔者总结了多年实际工作的经验,系统介绍了机床夹具设计的基本方法和关键技术。

SYMMETRIC POSITIVE DEFINITE SOLUTIONS OF MATRIX EQUATIONS (AX,XB)=(C,D) AND AXB=C

The symmetric positive definite solutions of matrix equations (AX,XB)=(C,D) and AXB=C are considered in this paper. Necessary and sufficient conditions for the matrix equations to have symmetric positive definite solutions are derived using the singular value and the generalized singular value decompositions. The expressions for the general symmetric positive definite solutions are given when certain conditions hold.

Turbulence regime near the forest floor of a mixed broad leaved/Korean pine forest in Changbai Mountains

The measurement and observation for this study were carried out by using a three-dimensional (u, v, w) Sonic anemometer (IAP-SA 485), at Forest Ecosystem Opened Research Station of Changbai Mountains (12828扙 and 4224?N, Jilin Province, P. R. China) in August 2001. The basic characteristics of turbulence, such as turbulence intensity, atmospheric stability, time scales, and convection state, near the forest floor were analyzed. It is concluded that the airflow near forest floor is characterized by high intermittence and asymmetry, and the active and upward movement takes the leading position. Near forest floor, the vertical turbulence is retained and its time scale and length scale are much less than that of u, v components. The eddy near forest floor shows a flat structure and look like a ’Disk’. Buoyancy plays a leading role in the generation and maintenance of local turbulence

巧妙设计夹具解决在箱壳零件上钻孔的难题

分析了减速机箱体、箱盖钻孔工艺特点,提出了夹具的设计思路,剖析了夹具的定位、装夹、分度、对定、导向等问题,并阐述了夹具主要零件的加工工艺、装配工艺和使用方法,巧妙地利用旋转分度对定夹具有效地解决了在箱壳零件上钻孔的难题。

Some Opinions on the Paper “Several Inequalities of Matrix Traces”

In this paper,we find some mistakes in the paper “Several Inequalities of Matrix Traces” which was published in Chinese Quarterly Journal of Mathematics,Vol.10,No.2.

Criteria Condition for Generalized Diagonally Dominant Matrices

In this paper, we provide some new necessary and sufficient conditions for generalized diagonally dominant matrices and also obtain some criteria for nongeneralized dominant matrices.

Duality theorem for smash coproduct over quantum groupoids

The duality theorem of generalized weak smash coproducts of weak module coalgebras and comodule coalgebras over quantum groupoids is studied.Let H be a weak Hopf algebra,C a left weak H-comodule coalgebra and D a left weak H-module coalgebra.First,a weak generalized smash coproduct C×lH D over quantum groupoids is defined and the module and comodule structures on it are constructed.The weak generalized right smash coproduct C×rL D is similar.Then some isomorph-isms between them are obtained.Secondly,by introducing some concepts of a weak convolution invertible element,a weak co-inner coaction and a strongly relative co-inner coaction,a sufficient condition for C×rH D to be isomorphic to Cv D is obtained,where v∈WC（C,H）and the coaction of H on D is right strongly relative co-inner.Finally,the duality theorem for a generalized smash coproduct over quantum groupoids,（C×lH H）×lH H≌Cv（H×lH H）,is obtained.

提炼内容 归纳特点 总结方法——夹具精度分析的教学

一、夹具精度计算的特点归纳影响工件加工精度的误差种类繁杂,其中随机因素甚多,难于精确控制,这就决定了夹具精度计算的一些特点:1.均是估算,仅获得相近的结果;2.同一理论基点:各种误差的总和不得大于工件相应尺寸的公差;3.相同形式的计算公式:δ≥∑△1,（δ—工件相应尺寸公差,△1—工艺系统中各种误差）4.工艺系统中各种误差的分类原则均立足于简化夹具的设计程序;5.各种误差的数字处理方法.均以矢量概念进行计算.经几何运算或座标转换后,使各种误差与工件相应尺寸同向,再做代数运算.误差的综合统计计算可用极限法,考虑其最不利的工作状态,各种误差取其极限值.此法计算简单,但对夹具制造精度要求偏严.也可用概率法,对某些系统误差用系数加以修正,取其概率值.此法在保证工件精度的前提下.对夹具制造精度要求较宽,但求解计算比较麻烦.

拨叉双面铣专用夹具设计

本文针对车床变速箱中拔叉双面铣专用夹具进行设计。设计中综合运用力学、机械设计、机械制造工程学等多门课程的理论知识，遵循夹具设计要点，完成了专用铣夹具的设计。专用夹具的定位与夹紧可靠、结构紧凑，可以通过调整适应相近零件的装夹需要，手动夹紧，操作方便。

加工误差的组成及分配

在机床夹具设计中,始终围绕着如何控制工件的加工误差,来解决确保工件的加工质量并力求经济的目的。因而。

Directional growth behavior of a(Al) dendrites during concentration-gradientcontrolled solidification process in static magnetic field

The large and small sized Cu（solid）/Al（liquid） couples were prepared to investigate the directional growth behavior of primary a（Al） phase during a concentration-gradient-controlled solidification process under various static magnetic fields（SMFs）.The results show that in the large couples,the α（Al） dendrites reveal a directional growth character whether without or with the SMF.However,the 12 T magnetic field induces regular growth,consistent deflection and the decrease of secondary arm spacing of the dendrites.In the small couples,the α（Al） dendrites still reveal a directional growth character to some extent with a SMF of ≤5 T.However,an 8.8 T SMF destroys the directional growth and induces severe random deflections of the dendrites.When the SMF increases to 12 T,the a（Al） dendrites become quite regular despite of the consistent deflection.The directional growth arises from the continuous long-range concentration gradient field built in the melt.The morphological modification is mainly related to the suppression of natural convections and the induction of thermoelectric magnetic convection by the SMF.