Robotic timber milling: accuracy assessment for construction applications and comparison to a CNC-machine

The set goals of this paper consist of investigating the accuracy of industrial robots (IRs) when milling glued laminated timber and comparing these results to the machining accuracy of common CNC joinery machines (JMs). For the assessment, four different to-be-milled geometries, two positive and two negative shapes, were selected. In total, 45 specimens were milled, with eight of each geometry machined by the IR and the remaining 13 by a JM. In order to additionally consider the machining parameters of the JM in the assessment, two of the geometries were machined with different machining speeds. The dimensional analysis is based on 3D-scans of the specimens and the results have been checked in accordance with industry requirements. The results show that the median machining accuracy of the IR is very close to the robot manufacturer's specifications of position and path repeatability. The accuracy of the JM lies insignificantly below the accuracy of the IR, however, presents wider-spread results. External influencing factors on the machining accuracy, such as workpiece alignment to the superordinate coordinate system and deviations of the raw workpiece cross-sectional dimensions, were identified allowing for a clear assessment of the true accuracy of both machining processes.