The Prince’s tears, a large cable-driven parallel robot for an artistic exhibition

This paper presents the development and results of a large 3 d.o.f cable-driven parallel robot (CDPR) that has been extensively used between June and August 2019 for an artistic exhibition. The purpose of the exhibition was to 3D print a wall of glass powder, which will slowly collapse after the deposit of each layer. Positioning control on the assigned trajectory was an issue because of the CDPR geometry imposed by the specific configuration of the exhibition place. We describe how this problem was solved using a combination of cable length estimation based on the winch rotation measured by encoder, together with 3 on-board lidars that were used to provide a measure of the robot position. To the best of our knowledge this is the first time that such method was used for controlling a large CDPR. This CDPR has run for 174 hours since 6/18/2019, averaging a run time of 4h15mn per day. The 3D printing of the wall started on 7/18/2019 and stops on 8/31/2019. During this period the robot was used for 32 days with an average of 2h18mn run-time per day. The robot has traveled on a total distance of 4757 meters, of which 3893 meters on the assigned trajectory. During the period 76 layers have been deposited, representing a mass of 1.5 tons of glass powder.