Design and strength analysis of a gimbaled nozzle mechanism

This paper proposes an over-constrained mechanism for the gimbaled thrust nozzle of a solid-fuel rocket engine, aiming at reducing its self-weight by replacing the traditional anti-torsion device and distributing the load across its distributed limbs. This mechanism prevents excessive load concentration on any single limb. However, the link dimensions play a critical role, requiring internal stress analysis under dynamic loading for effective optimization. The kinematics analysis begins with determining the velocity screw of the mechanism. Then, the dynamics equations for each link are established by using the momentum screw and force screw of each rigid body. The transformation matrix is developed to transfer all force screws from the absolute coordinate frame to the cross-section frame, uniformly representing the loads at each specified cross-section. Analyzing the stresses at the most critical points in the cross-section yields the principal stress, which is used to calculate the equivalent stress based on the third strength theory. This method enables condition monitoring of links on-time and provides a theoretical foundation for the dimension design of a mechanism.