Methods and devices are known for removing of broken weft threads from air nozzle weaving looms, see among others DE-OS 2,228,131, EP-Application 0,284,766, EP-Application 0,322,576, EP-Application 0,318,861, and EP-Application 0,319,026.
All these methods and devices are based on monitoring the proper insertion of the weft threads and on automatically removing any weft thread not properly inserted. These weft threads are inserted into the loom shed by the main nozzle of an air nozzle weaving loom under the control of a thread storage. The monitoring of the weft thread insertion takes place by means of so-called thread monitors which provide information to the loom control at least regarding the beginning of the weft thread insertion into the loom shed and regarding the arrival or non-arrival of the weft thread at the exit of the loom shed. If the arrival of the weft thread is not signalled, then the loom control automatically stops the loom. Generaly, the cause for the absence of an arrival signal is a breaking of the weft thread, either on its way into the loom shed, or in the loom shed itself.
In a high speed loom in which the main nozzle and the reed are rigidly connected with the back and forth swinging sley, a predetermined length of the made ready weft thread is released when the loom suddenly stops. The released length of weft thread is held taut in the area between the main nozzle which moves along with the sley and the fabric selvage. This feature makes sure that the made ready weft thread is not torn off by the faulty inserted weft thread when the sley is moved back. This solution is known from European Patent Publication 0,310,804.
European Patent Publication 0,310,804 relates to a method for removing a faultily inserted weft thread in an air weaving loom and to an apparatus for performing the method. The known method aims at solving the technical problem to provide a method that makes it possible to separate a faultily inserted weft thread with relatively large forces from the beat-up edge of the fabric, whereby these relatively large forces are to be applied substantially along the entire length of the loom shed. This problem has been solved, in said European Application, in that the made available weft thread is released sequentially in several length sections, whereby each section is smaller than twice the weft thread length, and wherein these length sections are shot through the loom shed together with the faultily inserted weft thread by means of the main nozzle and the auxiliary nozzles applying several transport impulses to the weft thread. In a modification it is provided that following a signal by the weft thread monitor indicating a faulty weft thread, a predetermined length of the made available weft thread is released and held taut in the area between the main nozzle that moves along with the sley and the selvage of the fabric. Thereby, it is achieved that the made ready weft thread is not torn off of the faultily inserted weft thread when the sley is moved back, because the length of thread is made available for this motion. Thereby, it is also prevented that the thread length enters into the area of the already newly formed shed so that a disturbance could occur in the further work sequence.
In order to make it possible to hold the weft thread taut while simultaneously preventing its tearing, it is known that the weft threads which are provided by a supply spool, and which are spooled off by means of a prespooling device, are made available in a predetermined number of turns which correspond to the length of the weft thread to be inserted. For this purpose, the prespooling device is equipped with a magnetic clamping mechanism which is also referred to as thread stopper by means of which the made available weft thread is clamped to the prespooling device or released.
Downstream of the prespooling device in the direction toward the loom, there is arranged a preblowing nozzle which is so constructed that when the breakage of a weft thread occurs, the preblowing nozzle is capable of exposing a portion of the weft thread winding pulled off the prespooling device, to pressurized air directed opposite to the spooling off direction. Thus, the section of the weft thread between the fabric selvage and the main nozzle can be held taut in a controlled manner, whereby tearing of the weft thread and formation of loops of the weft thread are avoided.
However, the known solution is subject to a disadvantage nevertheless in that namely between the prespooling device and the main blowing nozzle, a preblowing nozzle is arranged, having a complicated construction, and such nozzle is needed as an additional structural component, which requires a specialized pneumatic control.