给定6R闭链的八杆机构四位置综合

在给定6R闭链上添加2个RR杆形成32种单自由度八杆机构。首先依据扩展布氏曲线理论求出解曲线,在解曲线上添加2个RR杆得到了所要综合的八杆机构。由于解曲线上的每一点都可以作为添加RR杆的点,因此可以得到无穷多解。通过把解曲线进行变换可以得到表示无穷多解的解平面,称为解域。根据闭链上添加的两个RR杆是否相关,把解域分为2类。采用杆组法对机构进行分类并进行运动分析。根据机构是否能顺序通过给定闭链的4个位置判断机构是否有缺陷,去掉解域中有缺陷的机构就得到了机构的可行解域。在可行解域中,根据机构的原动件可转动的角度范围,将原动件为曲柄和非曲柄的机构进行区分。解域综合方法可使设计者能更直观、准确地选择满足要求的机构,提高了设计效率。最后,通过一个八杆机构的综合示例具体说明了该类四位置综合的过程及结果。

Synthesis of Eight-bar Linkage for Specified 6R Loop through Four Positions

There are 32 ways in which the two RR constraints are added to the 6R loop to form 1 DOF eight bar linkage. First, the solution curve was obtained based on expanding burmester curve theory. Then the eight bar linkage can be synthesized by adding two RR constraints on the solution curves. Each point on the solution curve can be viewed as the added RR constraint, so infinitely many solutions can be got. The solution curve can be converted into the solution plane which presents infinitely many solutions. The solution plane was called solution region. The solution region was divided into two categories according to whether the two added RR constraints were related. The linkages were classified by the method of Assur group. The motion of eight bar linkage was analyzed by the iterative position analysis method which relegated the four bar Assur groups or six bar Assur groups to several two bar Assur groups. Whether a linkage could be defected depends on if it can sequently move through the four positions of 6R loop. After the defect linkages were removed, the feasible solution region can be got. In the solution region, the feasible linkage can be classified into two types, the crank and the non crank, according to the rotatable angle range of the driving link. The solution region synthesis theory makes designers choose the feasible linkage directly and accurately, so the design efficiency was improved. In addition, eight bar linkage can achieve more movement function compared with six bar linkage and four bar linkage. The synthesis of eight bar linkage for 6R loop through four positions makes the solution region synthesis theory more perfectly, provides more choices for designer and lays the foundation for the application of eight bar linkage in practice. Finally, an example of eight bar linkage specifies the four positions synthesis.