Abstract:
A storage feed device for a yarn which unwinds from a corresponding bobbin and is fed to a textile machine. The device includes a rotary or fixed drum and an optical sensor member arranged to sense the movement of the yarn towards the textile machine. The optical sensor includes a plurality of emitters and receivers between which a light beam is generated and is interrupted by the yarn during its movement. The optical sensor includes a first fixed part and a second fixed part which includes the emitter and receiver elements, the first part being coaxial with the rotary member, the second being annular and surrounding the first part, the yarn moving between the parts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 USC 119 from Italian Patent Application No. N. MI2011A002046, filed on Nov. 11, 2011, incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a yarn storage feed device in accordance with the introduction to the main claim. In particular, the invention relates to a yarn storage feed device able to measure with absolute precision the fed yarn quantity and the yarn quantity present on the drum. 
     BACKGROUND OF THE INVENTION 
     Various types of yarn feed devices or feeders are known in which the yarn originating from a spool or bobbin is deposited onto a fixed drum loaded by an external member driven by its own motor, or onto a rotating drum from which it is withdrawn by the textile machine. In these feeders a system has necessarily to be provided for measuring or counting the number of turns present on the drum such that the yarn stock present on this latter remains virtually constant, and to prevent it from being totally consumed by the machine, with obvious problems for the operation thereof. 
     Various methods for measuring the yarn quantity (or number of turns) present on the drum are known. A first of these utilizes the reflection of light generated by an emitter and received by a corresponding receiver which are associated with the feeder. One or two reading zones (comprising emitters and receivers) are used to verify that at least one turn is present within them. Usually, one is positioned at the drum entry (yarn inlet zone) and one at the drum exit (yarn outlet zone) to control the so-called minimum stock and maximum stock respectively. 
     Feeders provided with this type of control are however able to ensure only that the number of turns is within a given range, but are not able to know their exact number (with the consequent impossibility of knowing how much yarn is stored on the drum, of which the lateral surface area is known). 
     The aforedescribed reflection method also has the limit of its well known dependence on the colour of the yarn to be monitored, and which can negatively affect the effectiveness of sensing the yarn by the optical elements utilized by the method under examination. 
     Feeders are also present in which the turns unloaded from the drum (and hence the fed yarn quantity) can be counted, again by reflection, however these known devices also present the limit that the reading resolution is strongly influenced by the yarn colour and by any dirt and dust deposits on the optical elements by which the number of turns is measured. 
     Other feed devices comprise optical elements inserted into a single emitter/receiver member and hence do not comprise separated emitter and receiver portions. This emitter/receiver member is of barrier operation and is able to measure the yarn quantity which has moved in front of it (i.e. the yarn quantity fed and hence the yarn quantity remaining on the drum), however as it does not know the exact position of the yarn within the sensor it is unable to know the yarn position at the feeder outlet, consequently it is unable to offer optimal resolution and precision. 
     Other feeders comprise mechanical solutions using mechanical lever detectors to which sensors (proximity sensors, Hall sensors) are connected to determine a minimum and a maximum yarn stock on the drum. 
     Such solutions again do not enable the number of turns present on the drum to be known exactly; moreover, the mechanical action of the levers modifies the yarn tension, with obvious repercussions on the yarn fed to the textile machine. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a feed device able to measure with absolute precision the yarn stored on the drum and simultaneously the yarn quantity withdrawn by the textile machine. 
     Another object of the present invention is to provide a device able to monitor a yarn feed which does not suffer from those limits of reflection-operated optical solutions related for example to the yarn colour and to dirt accumulation. 
     A further object of the present invention is to provide a device which is not influenced by the presence of dust or the like, by being subjected to cleaning by yarn passage along the device. 
     Another object of the present invention is to provide a device able to measure with high resolution the yarn quantity absorbed (AYL) by the textile machine. 
     A further object of the present invention is to provide a device which does not influence the yarn during its passage from the feeder to the textile machine. 
     Another object of the present invention is to provide a device able to sense the lack of yarn or its breakage and possibly to indicate this to the textile machine. 
     A further object of the present invention is to provide a device able to count with absolute precision the number of turns deposited on the drum during its loading, starting from the unloaded drum and during all the subsequent operative stages of withdrawal by the textile machine. 
     These and other objects which will be apparent to the expert of the art are attained by a feed device in accordance with the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 perspective view of a device formed in accordance with the invention; 
         FIG. 2  is a section therethrough on the line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a front view of the section of  FIG. 2 ; 
         FIG. 4  is a section on the line  4 - 4  of  FIG. 1 ; 
         FIG. 5  is a section on the line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is a view similar to that of  FIG. 4 , but of a variant of the invention; and 
         FIG. 7  is a section on the line  7 - 7  of  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to said figures, a feed device according to the invention is indicated overall by  1  and comprises a casing  2  provided with a fixing bracket  3  to enable the device to be fixed to a support (not shown) associated with, or close to, a textile machine (not shown). 
     The casing  2  carries a rotary member or drum  5  driven (in any known manner) by its own electric motor or actuator  6  (with hollow shaft  6 A) contained within the casing  2 . A yarn F is wound about this drum before leaving the feed device and reaching the textile machine; the yarn F forms a plurality of turns  7  on the drum  5  to hence define a yarn stock for the machine such as to always enable its optimal operation even in the presence of discontinuous yarn withdrawals by said machine, for producing a particular article (for example a mesh). 
     The yarn F entering the device  1  cooperates with one or more thread guides  10  (only one being shown in the figures), for example of ceramic, which define its trajectory in entering said device such as to prevent the yarn F from coming into contact with the casing  2  (hence undergoing damage or creating overtensions deleterious for the proper operation of the device  1  and for correct yarn feed to the textile machine). 
     The feed device  1  preferably presents an entry yarn brake  11  and a tension sensor  12 , of known type and therefore not described. The thread guide  10  and the yarn brake  11  project from the casing  2 . 
     The feeder  1  presents an optical sensor  13  to measure the quantity of yarn F on which the feeder operates. The sensor  13  comprises a first part  15  and a second part  16  surrounding the first; the first part is defined by a part  17  (totally or partly, for example in a lateral surface  22  thereof, of any known light transparent material), disposed coaxially to the rotary drum  5  and containing a plurality of light emitting members or transmitting photodiodes  18 . The part  17  is supported by the casing  2  via a tube  19  positioned within the hollow shaft  6 A and fixed at one end  18 A to this casing. The cable for handling the necessary signals sent and received by the sensor  13  passes within the tube. 
     The photodiodes  18  are associated with an electronic circuit or electronic card  21  contained in the part  17  which is present in a stationary position at one end of the drum  5  from which the yarn F leaves to reach the textile machine. 
     The second part  16  of the sensor  13 , also stationary, is defined by a hollow annular part  23  present at the casing  2 . The part  23  comprises at least one transparent portion  26  facing the first part  15  and containing a plurality of receiver photodiodes  30 , of a number equal to the number of transmitter photodiodes  18  and disposed within the part  16  such as to receive the light signals emitted by the corresponding transmitter  18  (for example such as to face these emitters). 
     The receivers  30  are also associated with an electronic circuit or card  33  inserted into the part  16  and connected electrically to a control unit  35  of the device  1  to control the feeder operation. 
     The unit  35 , in particular, cooperates with a memory unit (not shown) in which the “physical” data of the rotary drum  5 , i.e. its diameter, are contained; the unit  35  also commands and controls the operation of the motor  6 , of which the rotational velocity is hence always known by known control elements (for example Hall sensors). 
     During use of the device  1 , the yarn F unwinds from a corresponding bobbin or spool (not shown), and passes through the thread guide  10  and the yarn brake  11 . 
     At this point the yarn F is wound onto the drum for a predetermined number of turns  7  (possibly programmable); the purpose of this drum is to feed the yarn F by withdrawing it from the spool in order to feed it to the textile machine, while at the same time separating said yarn present on the drum such that the individual turns  7  are unable to superimpose on and/or touch each other. 
     Before abandoning the device, the yarn F passes through the sensor  12  which, by known methods, measures its tension, then it possibly passes through a further braking member (not shown) which further determines and controls its braking. 
     In proximity to its point of exit from the drum  5 , the yarn F passes through the optical sensor  13  shown in greater detail in  FIG. 5 . By way of example, this shows four transmitters (indicated by  18 A, B, C, D) and four receiver photodiodes ( 30 A, B, C, D), the yarn F withdrawn by the textile machine (and shown as a circumference as it detaches from the drum  5 ), and the parts of the sensor  13 . 
     The photodiodes  18  and  30  determine four light rays or beams which the yarn F interrupts by passing in front of them, i.e. “light barriers” which are indicated in  FIG. 5  by A, B, C, D. 
     The suitably conditioned signal (i.e. amplified and filtered by known electrical/electronic members, not shown, associated with the card  33 ) of each receiver element  30 A, B, C, D is fed to the control unit  35  of the entire device. This control unit, by analyzing the state of each barrier and knowing the drum rotation direction, is able to verify the yarn position and to know if the yarn has been loaded onto or unloaded from the drum, during the operating stages of the textile machine. In this respect, it will be assumed that the drum  5  on which the yarn F is deposited rotates clockwise; when the control unit  35  senses a barrier activation sequence (i.e. the sequence of interruption of light beams between the pairs of transmitter photodiodes and receivers  18 A, B, C, D and  30 A, B, C, D) of the type A→B→C→D→A→B→C . . . , it determines that this yarn has been loaded on the drum and defines this sequence as a LOAD sequence. 
     When the electronic control unit  35  senses a barrier activation sequence of the type D→C→B→A→D→C . . . , it determines that this yarn F has been unloaded from the drum  5  and defines this sequence as an UNLOAD sequence. 
     It is therefore evident that by utilizing the data originating from the optical sensor  13  and by knowing and regulating the velocity and position of the feed drum, the control unit  35  is able to perform the following operations: 
     1) during the loading of the device  1  (sequence in which the yarn is wound onto the drum starting from a drum  5  unloaded condition), the unit  35  counts with absolute precision the number of turns  7  loaded, from which the yarn quantity in mm available as stock can be obtained with precision. In this respect, the control unit  35  causes the drum  5  to rotate at a fixed or variable velocity (by commanding and controlling the motor  6  in any known manner) and monitors the optical sensor  13 , to halt the movement of the drum  5  as soon as it has counted a number of change-overs (A→B, B→C, . . . ) equal to four times the number of revolutions to be carried out. 
     2) The unit  35  senses that the textile machine has begun to withdraw yarn from the feeder when, by analyzing the barrier activation sequence, it determines that an UNLOAD sequence is underway. In response to an UNLOAD sequence, this unit begins to rotate the drum  5  such that the number of turns  7  present as stock remains constant and equal for example to a possibly programmable predetermined value. 
     In particular, the control unit  35  increases o decreases the velocity of the motor  6  which controls the drum in response to an UNLOAD sequence or LOAD sequence respectively, in accordance with known control algorithms (for example P, PI, PD, PID), by closing a control loop for the yarn quantity present on the drum. 
     Then by processing the data relative to drum velocity and position and the state of the optical sensor  13 , the control unit always known with absolute precision the yarn quantity present on the drum (stock) and the yarn quantity withdrawn by the machine in real time. 
     The yarn quantity present on the drum (known hereafter as REAL TIME YARN STOCK) is in fact the algebraic sum of the UNLOAD and LOAD sequence with respect to the initial yarn quantity known as the YARN STOCK. 
     For example, assuming that the drum  5  has a linear development equal to 200 mm and assuming that during the loading stage the device has loaded ten turns and hence 2000 mm of yarn (turn number×development→10×200=2000), then at each UNLOAD sequence a value of 50 mm (development/number of sensors→200/4=50) is subtracted from the yarn quantity present on the REAL TIME YARN STOCK, whereas at each LOAD sequence a value of 50 mm is added. 
     A brief numerical example follows: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 SENSOR 
                   
                 YARN 
                 REAL TIME 
               
               
                   
                 SEQUENCE 
                 CODE 
                 STOCK 
                 STOCK 
               
               
                   
                   
               
             
             
               
                   
                   
                   
                 2000 
                 2000 
               
               
                   
                 A→B 
                 LOAD 
                 2000 
                 2050 
               
               
                   
                 B→C 
                 LOAD 
                 2000 
                 2100 
               
               
                   
                 C→B 
                 UNLOAD 
                 2000 
                 2050 
               
               
                   
                   
               
             
          
         
       
     
     The yarn quantity withdrawn by the textile machine is given by the difference between the initial yarn quantity YARN STOCK and the actual yarn quantity REAL TIME YARN STOCK added to the number of drum revolutions. 
     Let us imagine that the control unit  35  does not cause the drum  5  to rotate in order to reload the yarn withdrawn by the machine; in this case the withdrawn yarn quantity (ABSORBED YARN QUANTITY AYL) must be incremented by 50 mm for each UNLOAD pulse. 
     A numerical example follows: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 SENSOR 
                   
                 REAL TIME 
                 FED YARN 
               
               
                   
                 SEQUENCE 
                 CODE 
                 YARN STOCK 
                 QUANTITY 
               
               
                   
                   
               
             
             
               
                   
                   
                   
                 2000 
                  0 
               
               
                   
                 B→A 
                 UNLOAD 
                 1950 
                  50 
               
               
                   
                 A→D 
                 UNLOAD 
                 1900 
                 100 
               
               
                   
                 D→B 
                 UNLOAD 
                 1850 
                 150 
               
               
                   
                   
               
             
          
         
       
     
     At the moment in which the control unit  35  begins to cause the drum  5  to reload from the bobbin or spool those turns withdrawn by the machine, the yarn quantity (AYL) is given by the algebraic sum of the YARN STOCK and the REAL TIME YARN STOCK to which a quantity of 200 mm (drum development) must be added for each motor revolution. This is shown in the following table. 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 REAL TIME 
                   
                   
               
               
                 SENSOR 
                   
                 YARN 
                 MOTOR 
                 FED YARN 
               
               
                 SEQUENCE 
                 CODE 
                 STOCK 
                 R.P.M. 
                 QUANTITY 
               
               
                   
               
             
             
               
                   
                   
                 2000 
                 0 
                  0 
               
               
                 B→A 
                 UNLOAD 
                 1950 
                 0 
                  50 
               
               
                 A→D 
                 UNLOAD 
                 1900 
                 0 
                 100 
               
               
                 D→A 
                 LOAD 
                 1950 
                 1 
                 250 
               
               
                   
               
             
          
         
       
     
     From the previously given examples it is apparent that the unit  35  is able to measure with absolute precision the value of the stock of yarn F and the yarn quantity absorbed (AYL) by the textile machine. 
     It should be noted that the resolution of the two measurements can be improved; for example, the number of optical barriers can be incremented, such as to reduce the minimum increment and decrement step calculated as the drum development divided by the number of barriers. 
     An encoder can be used to know the exact position of the motor  6  and hence of the drum  5  such that the contribution given by the rotation of the motor  6  in the calculation of the fed yarn quantity is not an exact multiple of the drum development, but a function of its position (hence also taking account of the fractions of a revolution, with greater encoder resolution and greater measurement resolution). 
     For example by using a 4096 position encoder, precisions can be achieved which are less than one tenth of a millimeter. 
     One of the possible embodiments of the invention has been described; others are however possible in the light of the preceding description. For example, the number of barriers could be greater or less than four, odd or even, and comprise at least one pair of emitters and at least one pair of receivers; obviously, as the number of barriers increases, the counting precision varies, as already indicated. Moreover, the barriers could operate not “by interruption” but “by reflection”; hence in this latter case, each transmitter and the corresponding receiver lie on the same part  15  or  16  of the sensor  13 , with a mirror being mounted on the opposite part ( 16  or  15 ), such that the system again operates as a barrier. 
     According to another variant, the passage of the yarn F is intercepted not as the interruption of a light beam but as the sliding of the yarn. This solution has the great advantage of verifying yarn passage not within a single point (crossing of the barrier light beam), but within an angular sector centred on the receiver element. This enables the passage condition to be intercepted with greater safety as it derives not from an instantaneous condition but from a condition of greater duration in terms of time. This makes the sensor much more robust and able to read any type of yarn with precision, in particular even very thin yarns. 
     As an alternative to that described, the barriers or the generated light beams could be partially superimposed in pairs, such as to have for each sensitive element two signals CHA and CHB and hence obtain the passage and direction data from the state of the transition CHA→CHB or vice versa (unwind, wind→LOAD, UNLOAD). In this manner the sensor  13  operates as an optical encoder. 
       FIGS. 6 and 7 , in which parts corresponding to those of the already described figures are indicated by the same reference numerals, show a further variant of the invention. According to this latter, the transmitters and the corresponding receivers are located on the second part  16  of the sensor  13 , the first part  15  now having been eliminated. 
     The second part  16  surrounds the member  5  even though distant therefrom (lower, in  FIG. 6 ). This second part contains the emitters  18  and receivers  30 . 
     The operation of the device shown in  FIGS. 6 and 7  is evidently the same as that shown in the already described figures. 
     Finally, if the feed device is formed as a fixed drum solution and hence the hollow shaft (which passes through it) is used for yarn passage, the hollow shaft transports the electrical signals for controlling the optical sensor. 
     These embodiments are also to be considered as falling within the scope of the invention as defined by the following claims.