Topological principle of strengthened connecting frames in the stretchable arm of an industry coating robot

This paper researches on a stretchable coating robot arm for extremely large parts. It has high enough lateral and vertical stiffnesses within the reachable workspace to keep the required spraying accuracy. According to the functional independence principle, the vertical stiffness is kept by screw driving mechanism working in the vertical direction while the lateral stiffness is safeguarded by an overconstrained stretchable arm. In this paper, the focus is put on the stiffness synthesis of the stretchable arm's strengthened connecting frames by discussing both their lateral stiffness and unit-stiffness under different topologies. The stretchable arm consists of a four-sided scissor-form structure of pivoted links interconnected by strengthened connecting frames at each deployable layer, forming a multi-planar laterally overconstrained structure. Different frames have different stiffnesses and self-weights because of their different topologies. Therefore, the unit-stiffness, which is the ratio between the lateral stiffness and self-weight, is applied as it proved to be a resourceful design index in evaluating the planar stretchable arm. This paper proposes a topological design solution for the strengthened connecting frames, positively influencing the stretchable coating robotic arm's mechanical performance in engineering application.