Safe Tumbling of Heavy Objects Using a Two-Cable Crane

In heavy industries, large, heavy objects must be tumbled to access features on their bottoms and sides for assembly and maintenance. Traditional manual operations using a single-cable crane are high-risk, and difficult for less experienced workers. Automating the tumbling process is made challenging due to the presence of kinematic and static singularities which are shown to occur when a single-cable crane loses control over the block being tumbled. Here, an autonomous method for safely tumbling a heavy block sitting on a surface using a two-cable crane is presented. Two winches controlling a pair of cables on a crane are coordinated in such a way that a) the block cannot slip on the floor, b) the block is not lifted into the air, and c) the block is under quasi-static balanced control at all times. A control algorithm for coordinating the two winches is developed for safely tumbling a block without slipping or becoming airborne as well as for eliminating the effect of singularities. A small-scale prototype is developed and the control algorithm is implemented and evaluated experimentally.