3-D Measurement of Large Scale Steel Structure

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A new measuring method is presented for large scale three dimensional measurement, in which the measurement coordinates are constructed by finely collimated laser beam and pentaprism. The positions to be measured are pointed out with laser spots. They are detected by a CCD-camera and the coordinates are calculated by a personal computer. The feasibility of the presented method is investigated applying a prototype device to the measurement of machining accuracy of steel box members of a main tower of a large suspension bridge.The main tower of a suspension bridge, the height is 100m or more, is built by heaping up many steel box members one over another. The vertical straightness of the final configuration depends of the flatness and parallelism of end surfaces of each box member. Therefore, highly accurate machining is required in the final machining process of the end surfaces, which can be successfully achieved by "on the machine measurement". The conventional surveying instruments, such as theodolite and level, are hardly available for this purpose.The prototype device is installed in a facing machine which is specially designed for machining a large workpiece, and end surfaces of a steel box member of a tower are machined and measured. The size of the workpiece is of around 6m x 6m x 5m. Experimental results verified that the "on the machine measurement" with the presented method can considerably improve the machining accuracy. For instance, the achieved flatness and out-of-parallelism of end surfaces are 0.2mm and 3x10^<-5>rad., respectively.