A dual hoist robot crane for large area sensing
Harber, John A.
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Cranes are used to lift and move large objects in a wide variety of applications at constructions sites, shipping ports, and manufacturing facilities, etc. If the load to be moved is too long or heavy for a single crane, then two, or more, cranes must work in cooperation to move the payload. In a factory setting this can be accomplished using two trolleys running along the same bridge forming a dual hoist crane. Using two hoists not only increases lifting capacity, it also improves stability of the payload over traditional single hoist configurations. This research takes advantage of that increased stability and explores a novel application for dual hoist cranes: suspending a robot arm from the two trolleys. This increases the workspace of the robot to the entirety of the space covered by the crane, opening up numerous applications not possible with a stationary robot. In order to better understand and characterize the dynamics of the system, a numerical model was developed and tested against a physical system to confirm its validity. A vision system has the potential to greatly increase the usefulness of a robotic system such as the one presented in previous paragraph. The Asus Xtion was used in this work due to its versatility and low cost. An evaluation of this sensor was performed. Various tests were conducted to determine its accuracy in a range of scenarios. It was found that crane oscillations degraded the quality of data returned. This is effect is especially detrimental if the crane is moved to a specified point and sensing begins immediately. The data collection process could be delayed until the residual oscillations subside, however the time penalty incurred by waiting is large because the oscillations are lightly damped and have a long period. To address this issue a control method called input shaping was introduced to reduce the residual oscillations thereby increasing the quality of the sensor data. Finally, two promising uses of the robot arm dual-hoist crane system were introduced: painting and sandblasting. The efficiency of a factory equipped with this system can be increased at relatively low cost by automating manual tasks such as these.