科创中国

In design of flexure mechanism, diminishing the parasitic-motion is a key point to improve the accuracy. However, most of existing topics concentrate on improving the accuracy of linear-motion flexure mechanisms via compensating the parasitic error, but few research the multi-dimensional flexure mechanisms. A general design principle and method for high-precision flexure mechanisms based on the parasitic-motion compensation is presented, and the proposed method can compensate the parasitic rotation in company with translation, or the parasitic translation in company with rotation, or both. The crucial step for the method is that the parasitic motion of a flexure mechanism is formulated and evaluated in terms of its compliance. The overall compliance matrix of a general flexure mechanism is formulated by using screw theory firstly, then the criteria for the parasitic motions is introduced by analyzing the characteristics of the resultant compliance matrix as well as with aid of the concept of instantaneous rotation center. Subsequently, a compliance-based compensation approach for reducing parasitic-motion is addressed as the most important part. The design principles and procedure are further discussed to help with improving the accuracy of flexure mechanisms, and case studies are provided to illustrate this method. Finally, an analytical verification is provided to demonstrate that the symmetry design philosophy widely used in flexure design can effectively improve accuracy in terms of the proposed method. The proposed compensation method can be well used to diminish the parasitic-motion of multi-dimensional flexure mechanisms.

Iterative methods based on finite element simulation are effective approaches to design mold shape to compensate springback in sheet metal forming.However,convergence rate of iterative methods is difficult to improve greatly.To increase the springback compensate speed of designing age forming mold,process of calculating springback for a certain mold with finite element method is analyzed.Springback compensation is abstracted as finding a solution for a set of nonlinear functions and a springback compensation algorithm is presented on the basis of quasi Newton method.The accuracy of algorithm is verified by developing an ABAQUS secondary development program with MATLAB.Three rectangular integrated panels of dimensions 710 mm′750 mm integrated panels with intersected ribs of 10 mm are selected to perform case studies.The algorithm is used to compute mold contours for the panels with cylinder,sphere and saddle contours respectively and it takes 57%,22%and 33%iterations as compared to that of displacement adjustment(DA)method.At the end of iterations,maximum deviations on the three panels are 0.618 4 mm,0.624 1 mm and 0.342 0 mm that are smaller than the deviations determined by DA method(0.740 8 mm,0.740 8 mm and 0.713 7 mm respectively).In following experimental verification,mold contour for another integrated panel with 400 mm*380 mm size is designed by the algorithm.Then the panel is age formed in an autoclave and measured by a three dimensional digital measurement devise.Deviation between measuring results and the panel's design contour is less than 1 mm.Finally,the iterations with different mesh sizes(40 mm,35mm,30 mm,25 mm,20 mm)in finite element models are compared and found no considerable difference.Another possible compensation method,Broyden-Fletcher-Shanmo method,is also presented based on the solving nonlinear functions idea.The Broyden-Fletcher-Shanmo method is employed to compute mold contour for the second panel.It only takes 50%iterations compared to that of DA.The proposed method can serve a faster mold contour compensation method for sheet metal forming.

基于2008年至2010年信息技术产业上市公司数据,研究发现:首先,公司规模和业绩均对高管薪酬有显著正向影响;其次,管理层持股对高管薪酬具有一定的替代效应;再次,内部治理机制的效力主要是通过第一大股东来实现的,而两职兼任的高管可以获得较高的薪酬契约,同时其他看似健全的公司治理机制并没有对经理权力形成有效约束;最后,高管薪酬、管理层持股和第一大股东持股比例均对企业绩效有显著的正效应,证实了实施股权激励计划将有益于公司的整体业绩表现.