Stiffness modeling of redundant robots with large load capacity and workspace

In the robotic machining process, the external force due to the end-effector (EE) and the workpiece can lead to significant deviations of the desired trajectory. In addition, moving platforms have been added to many heavy-duty industrial robots to improve the workspace. The combination of a moving platform and a six-degree-of-freedom industrial robot constitutes the redundant robot system. However, the effect of moving platforms is rarely considered in the redundant robot system for deflection analysis. This paper analyzes the shortcomings of traditional methods for joint stiffness modeling. Considering the advantages and limitations of traditional methods, we propose an effective method for redundant heavy-duty robot stiffness modeling by considering joint and moving platform compliances. Firstly, the relationship equations of the joints and the end-effector (EE) deformation are derived. Secondly, the static equilibrium equations of the moving platform are established in its stiffness matrix expression, and then the whole redundant robot system stiffness model is derived. Finally, simulations are performed to verify the correctness of the stiffness model. This work can be used for motion planning of redundant serial robots and optimization of machining operations.