Robot guided bolt tensioning tool with adaptive process control for the automated assembly of wind turbine rotor blade bearings

The three rotor blade bearings of a wind turbine hub are mounted to the rotor by several hundred bolted joints. Within this assembly process, a specific preload force has to be applied to these bolts in order to achieve a defined clamping force between the bearing and the rotor. Despite high manual labour intensity and safety concerns (platforms need to be raised to reach bolted joint at a height of 4 m), workers use hydraulic bolt tensioning cylinders which need to be threaded on each bolt individually. In order to automate this recurring assembly process, a robot guided bolt tensioning tool has been developed, which is part of a self-adaptive assembly system. Hence, we are able to locate each bolted joint, mount the bolt tensioning tool and apply the preload to each bolt of the bearing sequentially. In order to be flexible for different product variants and compensate the tolerances of large product dimensions in the wind turbine assembly, an adaptive process has been created. Therefore, the relevant parameters describing the product and assembly process are identified which can be adapted depending on the rotor hub type. Furthermore, the tolerance chain is analysed and improved by integrating measurement techniques to the new tool and using these sensors in the adaptive process control.