The invention relates to a method and apparatus for start spinning of yarn at a spinning unit of an open-end friction spinning machine, which unit is provided with two adjacently arranged rollers, driven in the same rotational direction and forming a wedge throat or slot therebetween. An inlet and opening device for feeding single fibers to the wedge slot, a yarn withdrawal device for drawing off the produced yarn in the direction of the wedge slot and a suction device for holding of yarn to be produced within the wedge slot are also included for the spinning unit. For the process of start spinning, an already spun yarn end is returned and first brought to a position at a distance from the wedge slot and is subsequently delivered to the wedge slot. The delivery of single fibers interrupted earlier is resumed and the yarn is drawn off.
This application is related to application Ser. No. 604,377, filed on even date herewith and based upon the same German patent application No. P 33 15 034.6.
A start spinning process for a spinning unit of an open end friction spinning machine is known in European Published application (EP-OS) No. 34 427 which can be executed manually, whereby a yarn end which was stretched to reach the supply position, is returned over a yarn withdrawal tube in the closed spinning unit. This process requires that special steps at the spinning unit are taken to achieve that the yarn end, while in an outstretched condition, is first brought into a position at a distance from the wedge slot and is then carried into the wedge slot in said extended or straightened condition. This construction allows the yarn end to be returned essentially over the circumference of a self-suctioned drum or roller rotating towards the wedge slot, which roller delivers the yarn end into the wedge slot. Then the fiber feed is switched on. Thereafter the yarn withdrawal device resumes operation. The known process is difficult to execute and offers no real control as to whether the yarn end actually reaches the area of fiber supply. Because the wedge slot is not exposed and not visible there is no control possible. In addition, there is always the danger that the yarn end running over the roller which rotates towards the wedge slot, will assume an uncontrollable position.
The invention is based on the problems of providing an arrangement of the kind described above which makes the safe return of a yarn end to a start spinning process possible, while it is positively assured that the yarn end actually reaches the area in which the supply of fibers take place, i.e., in the area of fiber supply.
These problems are solved according to the invention by exposing the wedge slot prior to the return of the yarn end by movement of a cover-like element, whereby said yarn end is brought into a position between the wedge slot and said cover-like element. The yarn end then is transferred to an area immediately next to the wedge slot, whereby the actual start spinning process is initiated by switching on the yarn withdrawal device, by transfer of the yarn end to the wedge slot, and by activating the fiber feed supply.
This arrangement allows controllable transfer of the yarn end prior to the start spinning process, so that a yarn end to be start spun actually exists in the area of supply to which fibers can be attached. Control of the return of the yarn end is easily possible since the spinning unit is opened prior to the start spinning and yarn end insertion processes. The necessary operations are made without hinderance so that especially also automatically operating devices can be utilized.
In further arrangements of the invention it is provided that the supply of fibers is activated at the time the yarn end is in the area of fiber feed after the end is returned over the length of the wedge slot and subsequently the yarn is removed through the same path. It is thereby possible to provide a qualitative improvement in the start spinning location.
To be provided with a start spinning yarn portion that differs as little as possible from the rest of the yarn, a further arrangement of the invention provides that a decreased amount of fiber material is supplied during start spinning, compared with the amount during normal operation until the withdrawal of the yarn end from the area of fiber feed. This measure permits to further enhance the quality of the start spinning section of the yarn and, especially reduces the yarn thickening to an absolute minimum before the actual start spinning section of the yarn. This particular measure is certainly also attainable according to certain embodiments where the spinning unit is not opened for inserting in the yarn end.
In further arrangements of the invention means are provided to at least partially free the yarn end from the spinning rotation before the same reaches the area of fiber feed. This allows a very fine connection between the newly supplied (fed in) fibers and the yarn end so that the quality of the start spinning portion of the yarn is even further improved. The amount of fibers first introduced and surrounding or covering the yarn end are reduced to a minimum. This operational step is certainly also usable if the spinning unit is not opened for the withdrawal of the yarn end, according to certain preferred embodiments of the invention.
In order to avoid thickening in the area of start spinning, another arrangement of the invention provides that the yarn end is withdrawn with a differing speed of withdrawl as compared to the operational speed, until the end of the yarn end has left the area of fiber feed. This even further reduces the possibility of yarn thickening and offers special advantages in connection with control of the amount of fiber feed-in during the start spinning process.
A further arrangement of the invention provides that the yarn is held at a distance to the wedge slot and without touching the roller surfaces and is only transferred to the wedge slot shortly prior to the actual start spinning process, when the end of the yarn end reaches the area of fiber feed. It is thereby attained that the yarn end transferred to the wedge slot does not achieve high spinning rotation compared with the yarn spun during operational provisions which could otherwise change the characteristics and also complicate the start spinning process. This measure is certainly also possible without opening the spinning unit to position the yarn end, according to certain preferred embodiments of the invention.
In preferred embodiments, apparatus for accommodating the start spinning process is accommodated in a mobile maintenance device that is selectively positionalbe adjacent respective spinning units of a spinning machine.