Mobility and Kinematic Analyses of a Novel Deployable Composite Element

A novel deployable mechanism9RR-12URU with multiple degrees of freedom(DoFs)is proposed,which can be used as the minimum composite element of the supporting mechanism of large-diameter truss antennas. This deployable mechanism consists of three 3RR-3URU tetrahedral units. The DoF of a tetrahedral unit is analyzed based on the screw theory,and then the DoF of the 9RR-12URU mechanism is obtained by using the method of splitting rod groups. According to the geometric positions and coordinate transformation matrices of the nodes,the analytic expressions of the position and velocity of each node in the folding/deploying process of the mechanism are derived. Furthermore,the RPY angle is adopted to describe the orientation of each node with respect to the fixed node. The theoretical analyses on the DoF and kinematics of the9RR-12URU mechanism are verified by Adams software. The results show that the mechanism has two kinds of DoFs:translational and rotational DoFs,which contribute to achieving the maximum folding ratio of the mechanism. The9RR-12URU deployable mechanism has a simple structure and a large folding ratio,that can be applied to truss deployable reflectors with a bent surface.