Precision Assembly of Heavy Objects Suspended With Multiple Cables From a Crane

Abstract

A new approach to precision mating of heavy objects suspended from overhead cranes is presented. We have found through experiments that heavy shafts suspended with multiple cables at specific positions and orientations can be inserted into a chamfered hole despite a small clearance. This will allow an overhead crane, although limited in positioning accuracy, to execute precision assembly of a heavy shaft simply by holding it with multiple cables and lowering it onto the chamfered hole of a fixed object. Unlike the well-known Remote Center Compliance (RCC) hand, this method does not use a two-layer elastic structure but exploits the physical properties of cables. Specifically, cables go slack when a compressive load is applied. This unidirectional load bearing property is exploited to suspend a heavy shaft such that it is not over-constrained during insertion. Conditions for the cable attachment position and orientation for successful insertion are obtained. A proof-of-concept prototype is developed and experimental verification of the principle and analysis are presented.