of the beams in both their rotational directions adjusting the feed of the warp threads continuously or by close intervalled step by step changes in forward and backwards directions application_number US 35123394 A description fig1 shows relevant parts of a dobby 1 which is symbolized by a generally indicated shaft frame system 2 and a back rest system 3 the warp threads running out from the back rest system are indicated by 4 the warp threads are divided into a shed by the shaft frame and in the arrangement shown in fig1 the threads for the upper shed have been indicated by 4a and for the lower shed by 4b the butting edge is defined by 5 and the fabric which has been finish woven in the weaving machine has been designed by 6 the back rest arrangement is represented in this embodiment by three back rest beams 7 8 and 9 the beams are driven by a gearbox system 10 which acts upon the beams 7 8 and 9 individually via power transmission systems 7a 8a or 9a gearbox and power transmission systems of this kind are already well known and will not be described here in any greater detail the gearbox system 10 is driven by an ac servo which can be of the seidel type an ac servo of this kind is provided on its axle with a pulse transmitter 12 which indicates or detects rotated turns of the ac servo the beam 7 of the beam arrangement is provided with a force detection mechanism in the form of a load cell 13 which can be constituted by a known model and can be of the nobel.