Patent Publication Number: US-2013228643-A1

Title: Device for feeding a yarn to a textile machine having a yarn-cutting device

Description:
The present invention relates to a yarn feeding device in accordance with the introduction to the main claim. 
     Yarn feeding devices (or simply “feeders”) are known, operating in accordance with various principles. 
     A first type is defined as constant tension yarn feeders, which are able to maintain said parameter (peculiar to the yarn) constant at a required value during the operating stages of the textile machine to which said yarn is fed. 
     A second type is defined as storage feeders, which are able to load a programmable yarn quantity onto a rotary drum or member, this quantity then being withdrawn by the machine during article production. 
     Another type is defined as constant quantity yarn feeders, hence able to ensure that the yarn quantity fed to the machine during the production process is constant. 
     Members or cutters able to cut the fed yarn if irregularities arise are also known; these devices are usually controlled via electrical impulses or solenoid valves by a control unit usually associated with the textile machine. 
     These feeders generally comprise a housing with which a rotary member is associated, about which one or more turns of the yarn can wind. This yarn unwinds from its own package to reach, on leaving the feeder, a textile machine (loom, knitting machine, stocking machine) where suitable known members receive it and process it to produce a finished article. 
     Correct yarn feed (however obtained, whether constant tension or constant quantity) is monitored by feed control means associated with the feeder housing on the basis of at least one measured parameter which can be correlated to the rotary member (for example the torque value of an electrical actuator which operates this member) or to an intrinsic characteristic of the yarn (for example its tension or the feed velocity to the textile machine). 
     Although known feeders correctly perform the function for which they are proposed, they present the technical limit of creating a drastic tension increase in the leaving yarn if the parameter monitored by them (for example the yarn tension or velocity) does not remain constant or attains and exceeds a predefined threshold value. This tension increase can cause a loss of finished product quality, or damage to certain machine members which cooperate with the yarn in producing an article (such as the needles of a knitting machine). 
     Moreover, any tension error which exceeds a predefined threshold value, characteristic of the yarn being processed, could cause yarn deterioration with, additionally, structural variations of the yarn compared with its standard characteristics (burrs, fibre elongation, fibre draw-out, etc.). 
     For example, in the case of a constant tension feeder, if the tension in the yarn entering the feeder exceeds the maximum torque of the actuator (electric motor) of the rotary member (for example because of a yarn spooling, unwinding or blocking problem), this actuator is unable to maintain the tension constant, and consequently records a drastic tension increase in the yarn leaving the feeder and hence in proximity to the point at which the yarn is introduced into the textile machine. 
     In the case of the storage feeder, if the tension involved in unwinding the yarn from the package is such as to require the motor or actuator to provide a torque close to the maximum rated value, the feeder device deposits the turns onto the drum at very high tension. This hence leads to imperfect separation between the turns (compacting of turns deposited under high tension) such that when the machine withdraws these high tension turns it is not possible to ensure the quality of the production process. 
     With regard to the constant quantity feeder, if the tension involved in unwinding the yarn from the package exceeds the maximum motor torque, the actuator device is unable to maintain the rotational velocity of the rotary member constant, with a consequent drastic tension increase at the actuator exit, leading to a tension increase in the yarn entering the textile machine. 
     This means that for all the aforesaid feeders, the article produced by said machine is defective and/or does not conform to the desired parameters. 
     DE4016964 describes a yarn feeding member in a knitting machine in which a cutting device is provided along the path of the yarn fed to the textile machine. Within this device, the yarn cooperates with a movable member which, in the case of a sudden increase in yarn tension, moves to activate a cutter control member, also contained within said device. 
     The control member can be a mechanism such as lever system or a microswitch which, on closing, powers a cutter actuator member. Essentially, to achieve activation of this control member, there must always be a movement of the movable member with which the yarn cooperates. 
     However this solution is influenced by dirt or dust and enzymatic oil residues which accumulate in the cutting device carried by the yarn, such dirt, dust or residues possibly interfering both with the movement of the movable member and with that of the control member, so preventing correct cutter activation when required. Even in the case of a microswitch control member, any dust or other deposit can give rise to false contact, with cutter operation when not required (with obvious problems), or with lack of cutter operation, resulting in negative effects on the machine production. 
     An object of the present invention is to resolve the technical problem related to tension variation in the yarn entering the feeder, this variation resulting in the impossibility of maintaining constant tension in the exit yarn, with consequent production of defective articles by the textile machine. 
     A particular object of the invention is to offer a feeder device provided with a yarn cutting member which is able to solve the aforeindicated problem. 
     Another object is to provide a feeder device of the aforestated type which is reliable in use and of small dimensions such as to enable it to be easily positioned on a textile machine or in proximity thereto. 
     A further object is to offer a feeder device which is able to interrupt yarn feed to the textile machine whenever incorrect feed tension arises, without said interruption being generated directly by the action of the yarn on a control member for the cutter, which action could result in undesired activation of said cutter or lack of cutter intervention on the yarn. 
     A particular object of the invention is to provide a device of the stated type which is able to feed the yarn while monitoring any yarn characteristic directly (such as tension, velocity or quantity fed) or indirectly (such as a characteristic of a member which feeds it) and which on the basis of such monitoring is able to activate the cutting member such as to interrupt yarn feed whenever this monitored characteristic does not conform to a desired value, this activation of said member taking place without the yarn cooperating with a control member for said cutting member. 
     These and other objects which will be apparent to the expert of the art are attained by a feeding device in accordance with the accompanying claims. 
    
    
     
       The present invention will be more apparent from the accompanying drawings, which are provided by way of non-limiting example and in which: 
         FIG. 1  is a lateral view of a feeder formed in accordance with the invention; 
         FIG. 2  is a block diagram of the device of  FIG. 1 ; and 
         FIG. 3  is a flow diagram indicating the manner in which the device of  FIG. 1  operates. 
     
    
    
     With reference to said figures,  FIG. 1  shows a device  1  which in the example is able to feed a yarn F at constant tension, by unwinding it from a corresponding package (not shown). 
     However, the device of the invention can be a generic feeder able to ensure the constancy of a characteristic of the fed yarn (velocity or quantity, in addition to tension) evaluated directly or indirectly, for example by monitoring a parameter of a member of said device, as described hereinafter. 
     The device  1  comprises a box housing  1 A containing the functional elements of the device. This latter comprises a rotary member  2  subjected to an actuator  3 . The actuator  3  is an electric motor operating under the control of a programmable control unit  5 , preferably of microprocessor type, inserted in the housing  1 A. 
     The control unit  5  also cooperates with a tension sensor or measurement member  8  with which the yarn F interacts and of which it measures the tension. This sensor is for example a load cell. Depending on the tension of the yarn F measured by the tension sensor  8  and on its comparison with a predetermined value stored in a memory unit, the control unit  5  (in known manner) commands the actuator or motor  3  (accelerating or decelerating it) in order to maintain constant the tension of the yarn leaving the device  1  (arrow K of  FIG. 1 ) and directed towards a textile machine T. 
     As an alternative or in addition to the aforedescribed, the unit  5  can cooperate with a velocity sensor  10  operationally associated with the rotary member  2 ; by means thereof, the unit  5  is able to measure the feed velocity of the yarn F to the machine T and hence the yarn quantity fed to this latter. 
     A yarn cutting member or simply cutter  13  is also connected to the unit  5  and can be activated by said unit on the basis of the variation in at least one monitored parameter from the yarn tension and velocity, or in the torque absorbed by the motor  3  (for example by the current absorbed by this latter or another known method). This cutter activation takes place without the yarn F directly acting on it or on a mechanical or electrical member (such as a microswitch) connected to said cutter; activation takes place always and only by the intervention of the unit  5  based on a measurement of a yarn characteristic (measured directly or indirectly) or on a value related to said feed. The cutter therefore acts on the yarn only and always on the basis of a command functionally linked to said yarn, but not directly generated by it. 
     In this manner any dust, dirt, etc. transported by the yarn is unable to affect the signal controlling the cutter activation, hence providing more reliable yarn feed and control. 
     The control unit  5  has, stored in its memory unit (not shown), a particular threshold value of at least one of said parameters. If during its unwinding from the package the yarn F should undergo braking (for example because blocked within the package or spool), at least one of the aforestated monitored parameters varies its value (for example the torque absorbed by the motor increases to drag the yarn, which is braked) until a threshold value is reached. In that case, to prevent the yarn F leaving the device  1  with a tension different from that programmed (this latter stored in the unit  5 ) such as to create potential problems for the article produced by the machine T, the unit  5  activates the cutter  13  which cuts the yarn F entering the device  1 . 
     This cutter is of known type and comprises a housing  20  preferably mechanically coupled to the housing  1 A of the device  1  and having a movable cutting element operated in known manner and electrically controlled (for example by an electromagnet) to intercept the yarn F and cut it when necessary. 
     Consequently, as soon as the unit  5  of the device  1  senses that the monitored parameter no longer lies within an acceptable range of values and attains and/or exceeds a predetermined threshold value, this unit activates the cutting element of the cutter  13  (and preferably halts the machine T) before the tension increase in the yarn F leaving the device  1  can cause formation of a defective article. In both cases, said unit activates the cutter  13 . 
     In particular, in the case of a constant, tension yarn feeder, when the unit  5  senses that the device is unable to ensure constant tension of the exit yarn F, it activates the cutter and halts the machine. The unit  5  could also intervene in advance by monitoring the motor or actuator torque, or its current consumption (when the torque exceeds a predetermined or programmable value based for example on the maximum rated torque possibly for a fixed or programmable time, the unit  5  senses entry into a “critical” zone), or the tension of the yarn leaving the feeder (when this exceeds a predetermined or programmable value based for example on the set tension possibly for a fixed or programmable time, the unit  5  senses entry into a “critical” zone), after which the yarn F would attain a tension such as to cause the defective article to be formed. 
     In the case of a storage feeder, as soon as the unit  5  senses that the yarn traction torque on the rotary member is not constant, it activates the cutter and halts the machine. The device could intervene in advance by simply monitoring the motor torque acting on the rotary member  2  or the current consumption used to load the yarn turns (when this exceeds a predetermined or programmable value based for example on the maximum rated torque possibly for a fixed or programmable time, it senses entry into a “critical” zone), or the number of turns present on the feed drum (when because of the traction force of the yarn from the package this is less than a predetermined or programmable value based for example on the set number of turns possibly for a fixed or programmable time, the unit  5  senses entry into a “critical” zone). 
     If the yarn feeder is of constant quantity type, as soon as the unit  5  senses that for any reason it is unable to ensure constant feed, it activates the cutter  13  and halts the textile machine. The unit  5  could intervene in advance by monitoring, as in the preceding cases, the torque of the motor  3  or the actual velocity of the rotary member (when this is less than a predetermined or programmable value based for example on the set velocity possibly for a fixed or programmable time during operation of the machine T, the unit  5  senses entry into a “critical” zone). 
       FIG. 3  shows a flow diagram which enables a more detailed understanding of the method of intervention of the control unit  5 . 
     According to that shown in this figure, in block  1  the unit  5  initializes the variables necessary for monitoring feed of the yarn F to the machine T in the predefined manner (constant tension, constant quantity or for correct operation of a storage feeder). For example, in block  1  the unit  5  defines the value ranges of the tension of the yarn F or of the drive torque of the actuator or motor  3  within which the corresponding values measured and sensed by said unit must remain for the yarn F to be fed to the textile machine T with a suitable tension for correct production of an article. 
     In block  2  the parameters (for example tension or torque) monitored by the unit  5  are measured. For example, if the tension is monitored the signal originating from the sensor  8  is analyzed; if the monitored parameter is the torque, the current absorbed by the motor  3  is for example measured. 
     In block  3 , the unit  5  verifies whether the value of the measured parameter exceeds the set threshold value, which in the case of the drive torque can be a constant depending on the rated motor torque or a programmable value (as in the case of the tension measurement or absorbed yarn quantity measurement). 
     If the comparison finds that the measured value of the monitored parameter is less than the threshold value the process passes to block  4  in which an alarm counter (not shown) to which the unit  5  is connected is reset. It then returns to block  2 . 
     If instead the monitored parameter has a value exceeding the threshold value, the process passes to block  5  in which the alarm counter is incremented. It then passes to block  6  in which the unit  5  verifies whether the counter value exceeds a predetermined value. This operation is executed on the basis of a “time filter” which defines this value (i.e. a maximum threshold-exceeding value by the monitored parameter). If the counter value is less than the time filter the process returns to block  2 ; alternatively it passes to block  7  in which the unit  5  activates an alarm signal (visual and/or audio) and halts the textile machine T. The process then rapidly passes to block  8  in which the unit  5  activates the cutter  8 . The process than returns to block  2 . 
     The flow diagram of  FIG. 3  can evidently vary on the basis of the different monitored variable or parameter, such as the number of turns present on the rotary member, the tension of the yarn leaving the device  1 , etc., according to the feeder used. 
     By virtue of the invention total production control is achieved. Moreover, if yarn irregularities occur upstream of the feeder, these cannot in any manner affect its exit side, causing quality problems in the finished product or mechanical damage to the stitch formation members. This solution also enables the yarn quality and technical characteristics to be preserved. 
     It should be noted that according to the invention, the unit  5  besides activating the cutter also preferably halts the machine T, enabling it to stop normally without the yarn stock present on the feeder being consumed. 
     Various embodiments of the invention have been described and mentioned. Others are however possible in the light of the preceding description (such as one in which the cutter  13  is separate from the housing  1 A of the device  1 ), these falling within the scope of the ensuing claims.