Patent Application
20130248635
The present invention relates to a yarn-feeding/recovering method for textile machines and to an apparatus for carrying out such method.
In the textile field, well feeders are known which are provided with a stationary drum on which a motorized swivel arm winds a plurality of yarn loops forming a stock. The yarn, which is unwound from the drum upon request of a textile machine arranged downstream, is subject to a stabilizing brake that maintains the unwinding yarn under a slight tension. The stabilizing brake typically comprises a frustoconical hollow member which is biased with its inner surface against the delivery edge of the drum by manually adjustable elastic means.
As described in EP 2031106, in order to maintain the feeding tension substantially constant, a controlled brake may be arranged downstream of the feeder, e.g., a foil-based brake of the type described in EP 0622485. This brake is controlled by a feedback loop which receives a measured tension signal from a sensor, then compares it with a reference tension which is indicative of a desired tension, and finally modulates the braking action in such a way as to minimize the difference between the reference tension and the measured tension.
Feeders are also known in which the yarn is wound on a rotary drum, which draws the yarn from a reel and feeds it to the downstream textile machine In this case, the tension of the yarn unwinding from the feeder is controlled by modulating the speed of rotation of the drum, always on the basis of a signal received from a tension sensor as in the previous case. Accordingly, in other words, the change of tension to be applied is determined by the difference between the yarn-feeding speed and the yarn-drawing speed set in the downstream machine
As known, certain particular processes, e.g., weaving the heel of socks, require that the yarn fed to the machine is periodically recovered and then returned. This operation is usually carried out by a dedicated recovering device arranged upstream of the machine
A recovering device of this type is described in EP 1741817 and essentially comprises a motorized reel having an oblique passage defined therein, through which the yarn runs. The passage extends between an inlet port which is axially formed on an end surface of the reel, and an outlet port which is formed on the cylindrical, lateral surface of the reel. When an amount of yarn must be recovered, the downstream machine sends a signal to the recovering device which enables the rotation of the reel, so that the yarn is wound upon the reel.
As well known to the person skilled in the art, a critical issue of the above systems consists in coordinating the operation of the braking system, which operates on the basis of the measured tension of the yarn, with the operation of the recovering system, which is enabled in response to commands sent from the downstream machine on the basis on a predetermined pattern, with consequent difficulties in accurately controlling the feeding parameters and the state of the yarn during the recovering steps, e.g., in relation to possible, accidental events which may occur, such as a yarn breakage.
It is a main object of the present invention to provide a method in which the yarn-feeding function and the yarn-recovering function are coordinated with each other in a more reliable and more accured manner with respect to the prior art, particularly in relation to the control of the yarn tension during the recovering step and to the reaction in case of accidental events, such as a yarn breakage; it is also an object to provide an apparatus for carrying out such method.
The above objects and other advantages, which will better appear from the following description, are achieved by a method having the features recited in claim 1, as well as by an apparatus having the features recited in claim 7, while the dependent claims state other advantageous, though secondary features, of the invention.
The invention will be now described in more detail with reference to a few preferred, non-exclusive embodiments, shown by way of non limiting example in the attached drawings, wherein:
Yarn F, which is unwound from the drum upon request of a general textile machine 22 arranged downstream, is subject to the braking action of a stabilizing brake adapted to maintain the yarn under a slight tension. The stabilizing brake conventionally comprises a frustoconical hollow member 24 which is biased with its inner surface against the delivery edge of drum 14 by elastic means 26.
In a way known per se, yarn F coming out of stabilizing brake is further subject to the braking action of an electronic yarn-braking device (or brake) 28 which is controlled by a tension control block TC of a control unit CU (which is typically incorporated in yarn feeder 12). Control unit CU is programmed to modulate the braking action applied to yarn F by electronic brake 28, on the basis of a signal received from a tension sensor 30, in such a way as to maintain the tension of the delivered yarn substantially constant on a reference value T_ref.
The stock on drum 14 is controlled by a triad of sensors. A first sensor 51, preferably a Hall sensor, detects the passage of magnets M integral with flywheel 16 in order to determine the amount of yarn which is wound on the drum and the winding speed. A second sensor S2, preferably a mechanical sensor, provides a binary information about the presence of a minimum amount of yarn at an intermediate area of drum 14. A third sensor S3, preferably an optical sensor, generates one pulse UWP per each loop unwound from the drum. A speed-evaluating block SE processes signals UWP in order to calculate the yarn consumption speed on the basis of the time interval between pulses UWP, and generates an enabling signal LE which enables tension control block TC when this speed is higher than a predetermined threshold value, which is preferably equal to zero in the present embodiment. An apparatus of this type is described in EP 2031106, to which reference should be made for a more detailed description.
A yarn-recovering device 32 of the type described in EP 1741817 and shown in detail in
Yarn-recovering device 32 comprises a reel 34 keyed to a drive shaft 36 of a motor 38, preferably a stepping motor or, alternatively, a brushless motor provided with an absolute sensor, in order to measure the real position based on techniques conventional in the field. Reel 34 is arranged with its axis A slanting at a first angle a with respect to the direction of yarn F, indicated by arrow D, so that its end surface 34a facing away from motor 38 obliquely faces the incoming yarn. Reel 34 has an axial cylindrical seat 40 at its end surface 34a. A passage 44 defined within reel 34 extends between an inlet port 44a open to axial cylindrical seat 40, and an outlet port 44b open to the lateral, winding surface 34b of the reel. Passage 44 is rectilinear and is slanting at a second angle b, which is substantially equal to first angle a, with respect to axis A of the reel. An internally rounded wearproof ring 46 made of ceramic is applied to the edge of cylindrical seat 40. An inlet yarn-guide eyelet 48 and an outlet yarn-guide eyelet 50 respectively applied upstream and downstream of reel 34 are arranged at the same level of wearproof ring 46.
Yarn F passes through upstream yarn-guide eyelet 48, cylindrical seat 40, passage 44 and downstream yarn-guide eyelet 50. By operating motor 38, as shown in
With the method according to the invention, as described in the flowchart of
In detail, as long as signal LE indicates that yarn is being unwound (LE=1), control unit CU continues to modulate the braking action of electronic brake 28 in such a way as to maintain the tension substantially constant at reference value T_ref, while yarn-recovering device remains at a position of minimum interference with the yarn, as shown in
It should be noted that, with the method according to the invention, reel 34 can rotate at a modulated speed in both directions. In fact, after an initial yarn-recovering step, during which the exceeding yarn is wound on reel 34 in order to maintain the tension at the desired level T_ref, the subsequent request of yarn from the downstream machine will cause reel 34 to rotate in the opposite direction always at a controlled speed, in order to return the yarn; however, before reaching the initial position (N=0) it could have to recover yarn again. When the reel reaches the initial position, control unit CU stops reel 34, enables electronic brake 28 again, and then the cycle is repeated.
As shown in the flowchart of
Accordingly, with this embodiment, signal LE is used as a comsumption indicator that is indicative of the delivery of yarn from the feeder and, therefore, of the withdrawal of yarn by the downstream machine; on the basis of this indicator, electronic brake 28 and yarn-recovering device 32 are alternately enabled as discussed above.
Having now reference to
A yarn-recovering device 120 is arranged between motorized drum 102 and the tension sensor; in the present embodiment, it is incorporated in housing 103 of feeder 100, as shown in more detail in
Yarn F′ from spool 104 passes through an inlet yarn-guide eyelet 130 attached to the feeder, is wound between drum 12 and an arm 132 of a conventional tension limiter (which does not fall within the scopes of the present invention and, therefore, will not be further disclosed), runs through passage 124 which, at rest, lies at the resting position of
With the method according to this alternative embodiment of the invention, which is diagrammatically shown in the flowchart of
In particular, as long as speed VRP of drum 102 is higher than zero, which circumstance is indicative of the fact that yarn is being delivered by the feeder and, consequently, is being drawn by the downstream machine, drum 102 continues to rotate at a modulated speed, in such a way as to maintain the tension substantially constant on reference value T_ref, while reel 122 remains at its resting position of
Similarly to the previous embodiment, reel 122 can rotate in both directions at a modulated speed. In fact, after an initial yarn-recovering step, in which the exceeding yarn is wound on reel 122 in order to maintain the tension at the desired level T_ref, the next request of yarn from the downstream machine will cause reel 122 to rotate in the opposite direction, always at a controlled speed, in order to return the yarn; however, before reaching the initial position (N=0), it could have to recover yarn again. When the reel reaches the initial position N=0, control unit CU′ stops reel 122, enables drum 102 again, and then the cycle is repeated.
With this embodiment, there is also provided an emergency condition, by which the tension control can be bypassed. In particular, when N reaches a value N_max corresponding to the maximum amount of yarn which can be stored on the reel, the process is stopped and an alarm signal is generated. Accordingly, with this embodiment the speed VRP of the drum is used as a comsumption indicator, which is indicative of the delivery of yarn by the feeder and, consequently, of the withdrawal of yarn by the downstream machine; on the basis of this indicator, drum 102 and reel 122 are alternately enabled according to the above method.
A few preferred embodiments of the invention have been described herein, but of course many changes may be made by a person skilled in the art within the scope of the claims. In particular, in the first described embodiment a stabilizing brake as described in EP 1059375, which applies a controlled braking action to the unwinding yarn, could be used in lieu of electronic brake 28. Moreover, in the described embodiments, the yarn-recovering device is always positioned in such a way that, at rest, it can assume positions not interfering with the yarn, as shown in
The disclosures in Italian Patent Application No. TO2012A000261 from which this application claims priority are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| TO2012A000261 | Mar 2012 | IT | national |
