Over the past decades, robots have emerged as a valuable technological solution for multiple highly complex industrial processes, and the manufacture of marine propellers has not been an exception. Majority of the propellers being produced worldwide are custom-designed products aiming to satisfy each ship’s propulsion requirements. Such geometrical diversity is a considerable challenge when traditionally manual manufacturing processes like hand-grinding and polishing need to be automated.
In several market-leading propeller manufacturers within Europe and Asia, industrial robots are being applied for widely diverse operations such as milling polystyrene blocks to make moulding patterns, grinding out the excess material in the blade surfaces, or polishing the complete propellers’ surface before their final verification. Propeller blades are customized products, formed by curved and warped surfaces, requiring minimum 5 axes to be smoothly polished, and this can be easily achieved with a robot cell where the CAD/CAM data coming from the individual design are directly translated into robotic parameters.
While this solution has demonstrated to be perfectly capable to comply with the marine propellers finishing tolerances, which are internationally defined by ISO 484 standard rules [6], robotic solutions for propeller measurement have not been successfully implemented within this specific industry due to reasons like lack of accuracy and repeatability. This paper analyses the root causes behind this problem, identifying the calibration process, the cell alignment method and the tool positioning as the principal factors resulting in this low measuring repeatability.
Findings explained by the authors are the outcome of several practical measuring tests made on real marine propellers within ABB and Fanuc robot cells. This paper concludes offering solutions to reduce the inaccuracies caused by the mentioned factors, and recommending what type of marine propellers are more suitable to be measured with industrial robots, on the basis of ISO 484 requirements for each customized design. Moreover, suggestions for further research on this specific measuring application are provided in the concluding chapter.
