Investigating the Potential of Flexible Links for Increased Payload to Mass Ratios for Collaborative Robotics.

One of the main restrictions of commercial cobots can be found in their limited payload to mass ratios. Flexible link manipulators seem to offer interesting advantages over traditional rigid robotics, in terms of lower self-weight, lower energy consumption and safer operation. However, the design and loading specifications in the general literature on flexible link manipulators differ from those expected in a collaborative industrial setting. In this paper, we want to investigate whether the use of flexible links can be truly beneficial for collaborative robotics. Firstly, the theoretical potential of flexible links to increase the payload to mass ratio is investigated. The feasibility to design a cylindrical flexible link for specific, realistic loading conditions is investigated, and the effect of link flexibility on the demanded motor torque and maximum reachable payload is visualised, while considering cylindrical links. Subsequently, to get insights in the accuracy and usability of such a manipulator, we experimentally quantify to what extent the undesired side effects of the flexible design can be counteracted using an appropriate controller. To comply with the envisioned application of collaborative robotics, a control strategy based on strain measurements along the link and robust to payload changes is proposed. The obtained accuracy was measured by tracking the end effector position using a Vicon motion capture system, considering two types of single link designs; firstly, a very flexible link setup with rectangular cross section, and secondly, a cylindrical flexible link, loaded to reach a payload to mass ratio of 1.