基于正四棱台Bricard单元的双环可展开天线机构构型设计

Double-ring Deployable Antenna Mechanism Based on Square Frustum-shaped Bricard Units

单环桁架式可展开天线的结构刚度随口径增大而降低的特点制约了其大型化,提出一种基于空间过约束正四棱台Bricard机构单元的双环可展开天线机构设计方法。首先,由等腰梯形面对称Bricard机构综合出展开构型与正四棱台几何体具有相同几何约束的正四棱台机构。而后,以始终存在一组正交对称面为约束条件推导出正四棱台Bricard机构的扭角约束关系,满足该约束的正四棱台机构自由度为1、可束状收拢。最后,由正四棱台机构构建出5 m口径的双环桁架式可展开天线机构。为双环桁架式可展开天线机构设计提供了过约束机构方案,提高了桁架的利用率,有助于面对称Bricard机构的广泛工程应用。

The stiffness of the single-ring truss deployable antenna decreases with the increasing diameter,which hinders the enlargement of the antenna.Based on spatial over-constrained square frustum-shaped Bricard units,a double-ring deployable antenna mechanism is proposed.First,a square frustum-shaped Bricard unit,whose deployed configuration has the same geometric constraints as the square frustum,is synthesized by the isosceles trapezoidal plane-symmetric Bricard linkage.Then,the constraint equation between twist angles in square frustum-shaped Bricard units is deduced on condition that there is always a set of orthogonal symmetry planes.The square frustum-shaped Bricard unit,which satisfy the constraint equation,have the characteristic of one degree of freedom,and bundle-folding.Finally,a double-ring truss deployable antenna mechanism with a diameter of 5 m is constructed of square frustum-shaped Bricard units.This research provides an over-constrained mechanism scheme for the double-ring truss deployable antenna mechanism,which improves the utilization rate of the truss and facilitates wide engineering applications of the plane-symmetric Bricard linkages.