Large vertical storage tanks are widely used in the petroleum industry, and also an important measurement tool for the custody transfer of bulk petroleum products. The accuracy of its volume measurement is very important. Based on ISO 7507, this paper designs an automatic wall-climbing robot, which can measure the variation in the radius of different courses at different height. Permanent magnet adsorption and a crawler movement scheme were adopted for the proposed robot. A two-way stepper motor and its controller were used to accurately control the robot's marching distance. An inclination angle sensor was combined with data-acquisition and real-time software control to allow the robot to walk in the vertical direction and avoid measurement errors caused by left or right deviations. Explosion-proof designs were implemented for the robot to make it suitable for flammable and explosive environments. A dome-roof vertical metal tank with a volume of 1000 m(3) and an external floating-roof tank with a volume of 100,000 m(3) were selected to conduct measurement comparisons with two traditional methods including optical-reference-line method and EODR method. The experimental results showed that radial difference measured at all test locations by the proposed robot system were within 1 mm, which validates the accuracy and efficiency of the proposed robot system.
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