Cobots Designed for Strength, Not Stiffness

Conventional industrial robots are designed to be as stiff as possible to ensure high positioning accuracy. The stiffness of a structure is, however, strongly related to its mass, leading to heavy structures. This paper aims to quantify the potential gain of reducing and eliminating the stiffness constraints, which is of lesser importance for collaborative robots, by investigating the effect of applying different optimization objectives. The resulting optimized designs are quantitatively compared using a set of performance measures and evaluated against the traditional stiffness-designed approach. It was concluded that significant improvements can be made, e.g. the robot’s mass can be reduced up to 74% compared to traditionally stiff-designed robots. The dependency of the payload as well as the structural/actuator mass distribution on the optimized results is investigated and proved to have a significant influence on the potential improvements when allowing reduced structural rigidity. The relationship between structural mass and actuator mass is investigated and compared to commercially available cobots.