The piecing up of a thread after a thread breakage or after a clearer cut is carried out predominantly in an automated manner in modern open-end spinning machines, whereas the piecing is carried out either by a robot that can be moved along the spinning stations of the open-end spinning machine or by handling elements of the individual spinning station. In any case, initially, multiple preliminary work steps are always required for the piecing of a thread, which are carried out successively in a chronological sequence or in some cases parallel to each other. The work steps may comprise, for example, searching for a thread end on the bobbin surface that accrues on the bobbin, rewinding the thread end from the bobbin, preparing the yarn end for re-start of spinning, cleaning the spinning element, returning the prepared yarn end to the spinning element, and the like. By contrast, the actual piecing operation begins with the return of the thread end into the spinning element. Likewise, upon the splicing of a thread on a winding machine or other thread connecting processes on textile machines, a multiple number of preparatory work steps, successively in a chronological sequence or in some cases parallel to each other, are required.
With known textile machines, the individual work steps are always carried out with a cycle time that is constant over time; that is, the time period of the respective piecing step is fixed and also always lasts the same amount of time in different piecing processes. The cycle time is selected in such a manner that, on the one hand, an advantageous, short cycle time for this step is achieved in order to stop the work station of the textile machine for only a very short time; on the other hand, however, an acceptable success rate is achieved for this piecing step, such that time-consuming repetitions of piecing operations can be avoided.
In order to improve the success rate of individual work steps, some measures have already been proposed.
For example, DE 35 02 118 A1 describes a pneumatic cleaning process for cleaning friction surfaces of a friction spinning machine, in order to control the point in time and the time period of the pneumatic cleaning as a function of the degree of dirtiness to be expected. However, details are not provided as to the manner in which the degree of dirtiness to be expected is determined, and how the adjustment to the cleaning time takes place.
DE 44 18 743 C2 describes an optimization of the thread searching process that is intended to improve the certainty of finding the thread on the bobbin surface. In doing so, the sucking in of the thread end by a suction nozzle is monitored by means of a sensor. If, after a predetermined time period, the thread ending is absent, the rewinding speed of the bobbin is reduced (for example, to less than one third of the usual rewinding speed), in order to expose the thread end to the suction air stream for a longer period of time and thereby facilitate the sucking in of the thread end.
By means of such measures, an overall cost-effective operation of a textile machine can be achieved. However, such a control, directed at the success rate, of the individual work steps often has unfavorable effects on machine efficiency.