面对称Bricard-like机构的设计与研究

Design and Research of Plane-symmetric Bricard-like Mechanism

由于空间单环机构巧妙的几何约束,Bennett机构、Bricard机构等被陆续提出并被广泛研究。将多个反四边形机构通过转动副回环连接,可以构造一类新型空间机构,该类机构具有类似空间单环机构的运动特点。提出了一种类似面对称Bricard机构的面对称Bricard-like机构。该Bricard-like机构由两个相同的反四边形单元和一个反平行四边形单元构成。根据反四边形单元的运动特点,将Bricard-like机构简化为变杆长的面对称Bricard机构。而后通过分析其等价6R机构的D-H参数及闭环方程,得到了该机构的自由度以及运动轨迹。此外,根据运动轨迹,分析了该机构的运动特性,揭示了该机构能够实现内翻运动和外翻运动,进而实现无限翻转运动。并讨论了该机构的无限翻转的可行性条件,给出了构造无限翻转机构的约束条件。最后通过制作样机模型,验证了构造方法的可行性和理论分析的正确性。

Due to the ingenious geometric constraints of the spatial single-loop mechanism,Bennett mechanism and Bricard mechanism have been proposed and studied extensively.A new type of spatial mechanism can be constructed by connecting multiple anti-quadrilateral mechanisms by using revolute joints,which has the motion characteristics similar to a spatial single-loop mechanism.A spatial plane-symmetric Bricard-like mechanism similar to plane-symmetric Bricard mechanism is proposed.The Bricard-like mechanism is composed of two identical anti-quadrilateral units and one anti-parallelogram unit.According to the movement characteristics of the anti-quadrilateral unit,the Bricard-like mechanism can be simplified as a special spatial plane-symmetric mechanism with variable links’ lengths.Then the degree of freedom and kinematic paths are further analyzed through the D-H parameters and the closure equations by considering the simplified spatial 6 R mechanism with variable links’ lengths.In addition,according to the kinematic paths,the motion mode is analyzed,and it is obtained that the mechanism can realize inward and outward motion,then can realize infinitely turnover.The feasibility conditions of infinitely turnover is analyzed,and the constraint conditions for constructing the infinitely turnover mechanism is obtained.Finally,a plane-symmetric Bricard-like mechanism is fabricated to verify the feasibility of the proposed method and the correctness of analysis.