The curvature stagnation point curve would degenerate in two straight lines, when the given Ball point was located on the fixed bar and an instantaneous center coincided with a fixed pivot. A random bar laid on the vertical straight line would produce an approximate straight line mechanism. The synthesis formulae and figures of crank linkages solution region on the coordinate plane, based on crank linkages analysis, were presented. Some useful conclusions were obtained by analyzing special points in the solution regions. According to different design demands, the corresponding evaluating functions were adopted in order to calculate the feasible solution region and the optimal mechanism solution automatically. The proposed method was visual and automatic. Both the blindness of choosing optimal mechanism and the lowness of design efficiency were overcome observably.%当给定鲍尔点与机架共线、瞬心点与一个机架点重合时,曲率驻点曲线退化成两条直线,在其中与机架垂直的直线上任意给定一个连架杆,即可综合出一个四杆直线机构.提出了直线机构综合公式,并根据曲柄机构存在条件,推导了曲柄解域计算公式.以一个固定铰链点为坐标原点,在整个机构坐标平面内绘制出曲柄机构解域图,讨论了其中一些特殊点的机构综合问题.根据不同的设计要求确定评价函数,自动计算生成可行解域图及其局部和全局最优机构解.实现了机构综合的可视化和自动化,解决了传统机构优选的盲目性和效率较低等问题.
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