Research on Modal Calculation of Six Joint Industrial Robot at Different Poses

In order to study the influence of different poses on the structural modes of a six joint industrial robot, a calculation method based on the theory of substructure and DOF reduction is proposed. Firstly, the DOF of the joint arm is reduced by using the FE software. Secondly, the stiffness matrix containing 3-dimension torsion stiffness of the reducers is established to consider the joint flexibility, and the equivalent generalized mass matrix is established to consider the inertia of the robot's accessories. Combined with the kinematics of the robot, the direct calculation of modal frequency and modal shape of the robot under different poses is realized by programming. The error of the first 6-order modal frequencies calculated by this method is less than 4% by comparing with the modal test results of the robot. The calculated results indicate that the first two-order modal frequencies of the robot vary about 47.2% and 76.7% under different poses in the workspace, which are mainly affected by the joint angles of J2 and J3.