Adaptive Control for a Crane-Mounted Inverted Stewart Platform

Positioning and suspending materials over large space volumes is a fundamental process in the construction industry. Traditional equipment such as cranes cannot satisfy the accuracy requirement due to their structural limitation. Also, the large size and complexity of modern cranes require new capabilities, or intelligence, to interact with the environment automatically. Because of the unpredictable behavior of the environment on a construction site (for instance, wind), traditional control concepts and methods are insufficient. To ensure the necessary accuracy and safety of the larger and heavier construction machines, the increased use of sensors and embedded controls is unavoidable. This paper discusses the mechanics of a Crane-Mounted Inverted Stewart Platform (C-MISP) prototype as an approach to fulfill the above demands. The C-MISP is designed to have all degrees of freedom kinematically constrained by supporting cables, making it very stable during manipulation. Through integration of a spatial positioning system and various on-board sensors, the C-MISP can monitor the environmental changes as well as its own work condition in real time. Such sensing information can then be used by a control and decision making unit to decide if the C-MISP parameters should be changed in order to maintain its position and path accuracy. In addition to the structural mechanics, the initial results of a study to analyze the behavior of C-MISP under wind loads are also discussed in this paper.