We developed a position sensor used a 3-element laser target and CCD cameras that detected 2-dimensional positioning (trolley travel position and gantry travel position) of hoisting load, and used the sensor for automatic operation of rail-mounted gantry cranes (RMGCs) in Hong Kong from 1996. The detection principle involves image processing. CCD cameras on the trolley image the laser target on the spreader. The image processing unit (IPU) detects pixel positions of the laser target. We then calculate 2-demensional hoisting load positioning with the hoisting load height We now use a 9-element laser target for RMGCs that has high stability in hard rain.
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