A door operator assembly, comprising an operator unit mounted to a first position, relative to the door, by a first mounting bracket; and an arm linkage connecting the operator unit and a second position, relative to the door; the arm linkage being mounted at the second position by a second mounting bracket. The linear guide mechanism enables movement of the saw blade and motor assembly along a predetermined linear path in a forward or a rearward direction at a constant level, and includes a first link and a second link pivotally connected by a first hinge connection. The method includes recording the positions of the individual segments and the positions of already assembled groups of segments repeatedly within the spatially-fixed three-dimensional coordinate system during assembly.