CBRC (Cable-Based Robotic Crane): design and implementation of overhead travelling cranes based on variable radius drums

In this paper we present a new family of overhead travelling cranes based on variable radius drums, called Cable-Based Robotic Cranes (CBRCs). A Variable Radius Drum (VRD) is characterized by the variation of the spool radius along its profile. This kind of device is used, in this context, for the development of a cable-robot, which can support and move a load through a planar working area with just 2 degrees-of-freedom. Firstly, we present the kinematic analysis and the synthesis of the geometry of VRD profile. Then, the schema of a bidimensional horizontal moving mechanism, based on the VRD theory, and an experimental prototype of a three-dimensional CBRC are presented. The features of this wire-based overhead crane and an analysis of cables tensions are discussed. Finally, the performance of this mechanism is evaluated, demonstrating a deviation between the end-effector and the nominal planar surface of less than 1% throughout the whole working area.