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.

Redundant actuators enable to distribute power among two motors, which can be selected optimally in terms of efficiency. We propose a methodology that finds effective combinations of motors and gearboxes for a dynamic load, taking into account the constraints, inertia, and efficiency of each component. Focusing on battery-operated robots as an application, it also considers battery pack mass in relation to the energy required by the actuator for multiple hours of operation. Based on this methodology, a prototype of a kinematically redundant actuator for the distal joint of a robot was built. Simulations and experiments are presented to prove the validity of the proposed approach.