Since the 1960s, there are milling machines for processing flocks of staple fibre bales (CH 12.179/60). In recent decades, the tower milling machines (DE 3334222) established themselves as most widely used design. Besides, there are inclined milling machines (DE 10 2005 059 151), which enable an operation without height adjustment of the bales and without manual pick up of the residual bales, and portal milling machines, e.g., Hergeth maxiFLOC.

The portal milling machines are advantageous when the milling head is applied with greater operating width or increased weight. The objective of the invention is to combine the advantages of tower milling and portal milling. The pivoting capability and the portal movements shall be combined. A problem is present therein, that the larger operating widths develop a greater leverage effect and therefore very stiff and material consuming constructions are necessary in order to avoid a jamming or great pressure on the drive guide bar. In accordance with the invention, this takes place in which a big, rigid construction is avoided, the deflection effect of the milling head and/or the connecting part and/or the cantilever support is measured and countered through corresponding correction of the relative drive speed between the main supports and the cantilever support.

The portal milling machines present two carrier constructions moving back and forth, which are connected through connecting beams fitted on top of the carriers. The connecting beams and the milling head can also be designed as single part. In one part, generally the fibre transporting device and the guidance along a guiding path as well as a traction drive are included. The other carrier contains mostly one traction drive, but mostly it does not contain any guiding elements. Both the traction drives are controlled in parallel. In accordance with the invention, both can be controlled individually and with varied speed independent of each other. Further, one drive can remain idle while the other is working. Even the drives can assume different rotational directions during pivoting. In order to avoid jamming or pressing forces in the construction or on the guidance bar are measured or the deviation of the subcarrier in comparison with the main carrier or the differences in the lengthwise position of the carrier are measured and based on these measurement values the relative speed of the drive motors is changed so as to achieve even speed.

The separate control can be used for pivoting the milling head from one bale processing path to the opposite path.

The drive motor of the main carrier around which the pivoting is made remains still in this process, and the drive motor of the subcarrier drives the wheels of the subcarrier. Through this the milling head is pivoted. In order to avoid tilting of the main part, it is suggested to secure the main part in the end position against tilting, for example, in the position in which the main part moves between two retaining jaws.

If the pivoting process is completed, the drive motors are again actuated in such a way that the carriers move parallel in the desired distance.