Using a Mobile Phone to Measure an Overhead Crane Hook Condition

Relying on a mobile phone as a measurement device in maintenance operations has invoked great interest lately. Especially in Industry 4.0 context, mobile phones provide several favorable features, such as easier integration with maintenance systems, authentication, and automated documentation. However, the limiting factor in using mobile phones as part of maintenance is the accuracy of measurements. This paper investigates the accuracy of the iPhone 14 Pro Max in measuring the overhead crane hook dimensions using several commercial applications relying on the structure-from-motion method. Measuring the hook dimensions is a part of regular inspections, and the maximum allowed deviations from the nominal values have been standardized. The results show that the mean absolute error of the measurements was under 0.2 mm when a known reference scale was used. This corresponds to a relative error of 0.6%. If a scale is not used, the accuracy is drastically reduced to mean absolute error of over 3 mm, corresponding to a relative error of over 10%. The accuracy of the scaled 3D models created with the iPhone and commercial structure-from-motion applications met the requirements set for the crane hook inspections. This paper suggests that mobile phones could be used to conduct regular crane hook inspections. This would also allow the integration of inspection details directly into maintenance systems, contributing to the goal of Industry 4.0 of connected systems.