Abstract:
A method for starting or stopping each of at least two separately controllable roll-sets ( 22, 26, 34, 56 ) used for processing a yarn (Y) in a stretch-break process, each roll-set comrpising at least two rolls, the method is characterized by the step of each roll-set, changing the speed of each roll from an initial condition to a steady state condition in accordance with a predetermined sequence and in coordination with a change in speed of at least one of the other rolls, such that simultaneous complete breakage of a yarn (Y) being processed in a stretch-break process is minimized.

Description:
This application claims priority as a Section 371 application of International Application PCT/US03/40,020, filed Dec. 12, 2003, which itself claims benefit of application 60/434,051, filed Dec. 17, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates to control of yarn processing equipment in a stretch-break process and in particular to a method for starting the process in a coordinated manner. 
   BACKGROUND 
   The textile industry utilizes multi-positional commercial spinning machines capable of winding multiple spindles of identical product. One type of commercial yarn producing machine, known as a ring spinning machine, directly produces a staple yarn. The production throughput of such a machine is relatively limited. 
   Another direct spinning apparatus, which for the purpose of this application is referred to as a “stretch-break” apparatus, improves throughput by producing staple yarn directly from a multi-filament yarn feed in a continuous operation. Shown within the dotted box in  FIG. 1  is a schematic view of the functional and enabling elements of a single position  12 A of a stretch-break apparatus generally represented by reference character  10 . One or more additional stretch-break positions  12 B,  12 C, . . .  12 N, each identical to position  12 A, may be provided to define a multi-position apparatus  10 . The apparatus  10  is disclosed and claimed in co-pending application Ser. No. 09/979,808, published internationally on Dec. 21, 2000 as WO 0077283. 
   Throughout the following description of the stretch-break apparatus it should be appreciated that each roll in a position may be implemented as multiple rolls, with or without associated nip rolls. It should also be understood that the pressure exerted by the nip rolls may be controlled, either manually or by an associated control device. 
   The position  12 A includes a drawing and annealing zone  20 , a first break zone  30 , a second break zone  40  (also known as a re-break zone), and a consolidation zone  50  connected in series between a continuous supply  16  of yarn Y and a windup zone  60 . 
   The yarn supply  16  may include an unwinder  18  driven by enabling unwind controller  19 , as shown, or another suitable yarn supply device. The unwind controller  19  may be implemented by a braking mechanism or an unwind motor to control the tension of the yarn Y fed from the unwinder  18 . 
   The drawing and annealing zone  20  is defined between a roll  22  and a driven roll  26  and includes a hot plate  24 . The roll  22  includes an enabling heater  22 H and the hot plate  24  includes an enabling heating element  24 H. The roll  26  may also include an enabling heater  26 H. As is well known, to impart draw action, driven roll  26  must rotate at a higher surface speed than the surface speed of the heated roll  22 . The ratio of the surface speed of roll  26  to the surface speed of roll  22  is termed “draw ratio”. 
   The first break zone  30  is defined between rolls  26  and  34 , and the second break zone  40  is defined between rolls  34  and  42 . The ratio of the surface speed of roll  34  to the surface speed of roll  26  is termed “stretch-break ratio”, while the ratio of the surface speed of roll  42  to the surface speed of roll  34  is termed “re-break ratio”. An optional jet  32  with enabling air supply  32 S may be included in the first break zone  30 . The second break zone  40  may include an optional jet  36  with an associated enabling air supply  36 S. 
   The consolidation zone  50  is defined between rolls  42  and  56  and may include one or more consolidation jets  52  and its enabling air supply  52 S. The consolidation device may also be a mechanical or other fluid device designed to consolidate the yarn Y. The ratio of the surface speed of roll  56  to the surface speed of roll  42  is termed “consolidation ratio”. 
   The windup zone  60  includes a traversing winder  62  for collecting the finished staple yarn S on a bobbin B. The winder  62  has an associated enabling winder and traverse drives  62 D,  62 T. A waste jet  58  and it enabling-air supply  58 S may directly precede the winder  62  to facilitate stringing. The ratio of the surface speed of winder  62  to the surface speed of roll  56  is termed “Take Up Tension” (in the table of  FIG. 4 ). 
   Individual rolls that sequentially contact the yarn Y during the stretch-break process may be paired into operational roll-sets. Thus, rolls  26 ,  34  may define a first roll-set  30 S, rolls  34 ,  42  may define a second roll-set  40 S, and rolls  42 ,  56  may define a third roll-set  50 S. Each roll  22 ,  26 ,  34 ,  42 , and  56  has an associated enabling drive motor  23 ,  27 ,  35 ,  43 , and  57  respectively. 
   Alternatively, as seen in  FIG. 1A , the roll  34  may be functionally implemented by multiple rolls, such as dual rolls  34 A,  34 B. Similarly, roll  42  may be functionally implemented by multiple rolls, such as dual rolls  42 A,  42 B. In such an alternative configuration rolls  26 ,  34 A; rolls  34 B,  42 A; and rolls  42 B,  56  may define operational roll-sets  30 S′,  40 S′,  50 S′, respectively. Rolls  34 A,  34 B,  42 A, and  42 B have associated drive motors  35 A,  35 B,  43 A, and  43 B respectively. 
   In operation, yarn Y comprised of filaments F is introduced into the drawing and annealing zone  20 . Within the drawing and annealing zone  20  the yarn Y is heated to an annealing temperature by the combination of the heater  22 H within the heated roll  22  and the hot plate  24 . The first roll  22  in the drawing and annealing zone  20  grips the incoming filaments F and the second roll in the operational roll-set (i.e., roll  26 ) draw-stretches the same. The surface speed of roll  26  may be set relative to the surface speed of roll  22  to draw the heated yarn Y, if desired, to obtain desired tensile properties. 
   The annealed yarn Y passes into the first break zone  30 . During steady state operation, the first roll  26  in the break zone  30  grips the annealed filaments and the second roll in the operational roll-set, i.e., roll  34  ( FIG. 1 ) or roll  34 A ( FIG. 1A ), as the case may be, draw-stretches them until all of the filaments F break in a random manner. The filaments F may be further broken in the second break zone  40  located downstream from the first break zone  30 . An optional jet  36  may be used to control ends of filaments broken in the first break zone to prevent roll wraps. 
   The yarn Y is then consolidated in the consolidation zone  50  to form a staple yarn S. The staple yarn S is wound on the bobbin B under controlled tension and traverse speed by the winder  62 . 
   The stretch-break process as implemented in the apparatus  10  is particularly difficult to start, since the dynamic stretching and breaking properties of a yarn differ at various speeds and differ from its static properties. The goal of the stretch-break process is to break all of the filaments randomly in both time and location. In the apparatus of  FIG. 1  all the filaments are broken randomly in the first stretch-break zone  30 , and those broken filaments are re-broken randomly in the second re-break zone  40 . Aggressive starting could result in simultaneous complete breakage of all filaments in either zone, resulting in loss of string-up of the yarn through the apparatus and generation of waste product. 
   Startup is particularly complicated by the interaction of process parameters. For instance, the stretch-break tolerance (i.e., the breakage of some filaments without complete breakage) of the yarn is affected by the annealing temperature, which changes throughout startup. The stretch-break tolerance of the yarn also changes significantly as roll speeds, and the relative speed ratio of rolls in a given roll-set, vary throughout startup. Jet parameters, particularly operating pressure, affect the degree of fiber entanglement, and winding parameters, such as winding tension, also affect the yarn&#39;s stretch-break tolerance. 
   In view of the foregoing is believed to be beneficial to provide a computer-implemented method for controlling the transition from an initial to a steady state condition of a single or multi-position stretch-break process that minimizes the possibility of complete yarn breakage and waste. It is believed of further advantage to be able to control the process parameters in accordance with a predetermined “recipe” tailored to each individual yarn. As used herein the term “recipe” is a predetermined sequence of changes of operational parameters for the various enabling elements in each position of the stretch-break apparatus. For example, a given recipe will specify sequential changes in the speed of each roll in coordination with the change in speed of at least one other roll (i.e., the ratio of speeds in a given roll-set), the temperature of each heater or heated roll, the operating parameter (i.e., pressure state) of associated jet(s), and the winder tension, to cause a processing position to transition from a stopped or initial condition to a steady state operating condition. The transitions of parameters may be varied in a step-wise or continuous manner. 
   SUMMARY OF THE INVENTION 
   This invention comprises a computer-implemented method and program for starting each of at least three separately controllable roll-sets used for processing a yarn Y in a stretch-break process. Each roll-set comprises at least two rolls. Under the method of the present invention, for each roll-set, the speed of each roll is changed from an initial condition to a steady state condition in accordance with a predetermined sequence and in coordination with a change in speed of at least one of the other rolls, such that complete breakage of a yarn Y being processed in a stretch-break process is minimized. 
   The start up sequence of the method may be practiced in two manners. In the first manner the speed of each roll is changed in at least two discrete steps to achieve a steady state set of roll speeds. In the second the speed of each roll is continuously changed to the steady state roll speeds. 
   The predetermined sequence is created by the steps of:
         a) selecting a candidate speed for each roll;   b) validating the candidate speed for each roll against predetermined operability criteria; and   c) for speeds that meet the operability criteria, setting the speed for each roll.       

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention may be more fully understood from the following detailed description taken in connection with the accompanying drawings, which form a part of this application, and in which: 
       FIG. 1  is a schematic view of one position within a multi-position stretch-break apparatus of the prior art while  FIG. 1A  is a schematic view of a modification thereof; 
       FIG. 2  is a detailed block diagram of a computer system and associated controller for executing a program in accordance with the method of the present invention to control each position; 
       FIG. 3  is an example of a screen display generated by the graphical user interface of the computer system of  FIG. 2 ; and 
       FIG. 4  is a table illustrating an example of a multi-step process recipe in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   Throughout the following detailed description similar reference characters refer to similar elements in all figures of the drawings. 
     FIG. 2  is a detailed block diagram of a control system  110  comprising a computer  112  and associated controller(s)  118  for executing a program in accordance with the method of the present invention to control each position  12 A through  12 N of the multi-position stretch-break apparatus  10  in accordance with a predetermined recipe. The control system  110  may be implemented using a standard desk-top personal computer  112  and one or more commercially available Programmable Logic Controllers (PLCs)  118 . 
   The computer  112  comprises a central processing unit (CPU)  124 , a memory  126 , an operator display  128 , a keyboard  142  and mouse  144  for operator input, an input-output interface  130  and an associated storage device  116  connected by a data and control bus  122 . The memory  126  may be implemented as random access memory (RAM) or another suitable memory device and may be partitioned into memory units  152 A,  152 B, . . .  152 F. The operator display  128  includes a cathode ray tube (CRT), a Liquid Crystal Display (LCD) or some other device for displaying a graphical user interface  114  whereby an operator communicates with the computer  112  using the keyboard  142  and the mouse  144 . A visual graphic, generated by the graphical user interface  114 , for a single position is shown in  FIG. 3 . 
   Suitable cable assemblies  120  implement a bus network to connect the computer  112  with each controller  118  using any standard bus protocol. Controllers  118  each comprise a central control unit  118 C and associated input-output (I/O) interfaces  118 - 1 ,  118 - 2 ,  118 - 3 ,  118 - 4 ,  118 - 5 . Each I/O interface is in turn connected by cable assemblies  200  to the control devices  210 - 250 . Each control device  210 - 250  is associated with respective enabling elements for a single position  12 A- 12 N. 
   As shown, I/O interface  118 - 1  is connected to a motor inverter unit  210 , in turn connected to drive motors  23 ,  27 ,  35 ,  43 ,  57 . The I/O interface  118 - 2  is connected to heater control  220 , which is in turn connected to heaters  22 H and  24 . I/O interface  118 - 3  is connected to jet control  230 , which is in turn connected to jets  32 ,  36 ,  52 ,  54 , and  58 . I/O interface  118 - 4  is connected to yarn supply tension control  240 , which is in turn connected to unwind controller  19 . I/O interface  118 - 5  is connected to winder control  250 , which is in turn connected to winder drive  62 D and winder traverse  62 T. It should be appreciated that a multi-channel PLC capable of interfacing the various enabling elements for two or more positions  12 A- 12 N of the apparatus  10  may be employed. 
   Having described the physical elements and control system architecture, the operation of the method of the present invention that permits each position  12 A- 12 N to be operated independently, using an individual and completely different process recipe which is downloaded to controller  118 , may now be discussed. 
   The present invention stores the commands that implement a process recipe in the computer memory  126 . When these commands are executed the control system  110  causes the position to perform either a multi-step sequence or a continuous sequence. 
   Tables of predetermined operability criteria (i.e., operational limits) for various parameters are stored in the computer memory. An example of an operability criterion is the maximum allowable stretch ratio at a given temperature for a particular type yarn Y. The predetermined operability criteria may be experimentally determined by incrementally changing roll-set speeds and the resulting roll speed ratios to determine operability limits for a given yarn product that will permit achieving the desired steady state running condition. 
   A recipe for a given yarn product can be developed by the operator. Various candidate parameters for each operating condition are selected. Each candidate parameter is validated against its associated predetermined operability criteria. If the candidate parameter satisfies the operability criteria the parameter is entered into the recipe. If the candidate parameter does not satisfy operability conditions the candidate parameter is denied entry into the recipe. Completed recipes, shown as memory segments  154 A- 154 F may be saved using conventional computer file storage techniques. 
   Since yarns made of different filaments (i.e., different deniers or different materials) may have completely different physical characteristics, process recipe programming flexibility is critical. Each yarn type or combination of yarn types performs differently in the drawing and annealing, break, re-break, consolidation and windup zones ( 20 - 60  of  FIG. 1 ). In a multi-step recipe each step in the recipe incrementally changes the parameters in one of more zones. Each incremental step changes roll speed ratios in a coordinated manner until operational speeds are achieved. In a similar manner, a continuous recipe gradually increases changes roll speed ratios continuously (which may be approximated by incrementing speeds in many very small steps) until operational speeds are achieved. 
   The method of the present invention may be implemented using the system control device  110  by downloading a recipe from the desktop computer  112  to the controller  118  associated with a given position. The system control device will facilitate a plurality of multi-step or continuously varying process recipes to be written, modified and stored. The operator can select from pre-determined multi-step process recipes stored in the memory  126  (or storage device  116 ) and download the selected recipe to any one controller  118  associated with a yarn processing position (such as  12 A) or group of positions (such as  12 A- 12 C). This download process is a transfer of recipe data from the system computer  112  to a dedicated positional programmable logic controller (PLC)  118 , thus freeing the computer  112  for other tasks. 
   The PLC  118  then controls: the associated motor inverter unit  210  to control drive motors  23 ,  27 ,  35 ,  43 ,  57 ; the heater control  220  to control heaters  22 H and  24 H; the jet control  230  to control jets  32 ,  36 ,  52 ,  54 , and  58 ; the yarn supply tension control  240  to control unwind controller  19 ; and the winder control  250  to control winder drive  62 D and traverse drive  62 T. 
   Once the data is distributed to the selected control device ( 210 - 250 ) associated with a particular position, that position (such as  12 A) can operate independent of the system control device  110  and independent of other surrounding positions (such as  12 B or  12 C). Since each position  12 A- 12 N can potentially operate with a different multi-step process recipe a separate local readout/operator interface  214 A- 214 N ( FIG. 1 ) is provided for each position  12 A- 12 N. This local readout  214  will enable the operator to control a position and monitor all of the unique positional specific data as well as display positional and system fault messages. 
   It should be noted that recipes are not specific to just motor speeds. Recipes also include operational parameters such as drawing and annealing zone heater temperatures, as well as pressure settings for aspirators, consolidation jets and nip rolls (not shown). Recipes can also include winder-specific parameters such as helix angle, traverse length, package pressure and package length or diameter. Automatic step string-up may also be accommodated in a recipe. This can be done by providing a specified time for each step to operate before automatically. progressing to the next sequential step. 
   Using the graphical display generated by the user interface  114 , shown in  FIG. 3 , new recipes can be developed. The graphical display has windows associated with various icons that pictorially represent hardware elements. Each window represents an operating parameter of an enabling element for a particular step in a recipe. As may be appreciated by viewing the list in the upper left corner of the display, a recipe of up to ten steps may be accommodated. If the candidate parameter satisfies operability criteria the parameter is entered into the new recipe. If the candidate parameter does not satisfy operability criteria the operator is alerted (such as by a color change or flashing warning) and the candidate parameter is denied entry into the recipe. 
   A multi-step process recipe, shown as steps  1  through  6  in the top row of the table, is tabularized in  FIG. 4 . The operating parameters are identified in the left column of the table. Each step in the recipe can be created or modified through the use of the graphical interface  114 .  FIG. 3  shows the operating parameters corresponding to step  6  of the recipe of  FIG. 4 . Calculated roll speeds are displayed based on recipe and step specific ratios. The roll speed of the next step is coordinated with the previous roll speed by multiplying the previous roll speed by the step specific ratio. Therefore by entering the first roll speed or the last roll speed and all zone ratios, all other associated roll speeds can be calculated using a Reference Rollset Selection routine. 
   The Reference Roll-set Selection routine allows roll-set speed calculations to be started from roll  1  (heated roll  22  of  FIG. 1 ) forward or from roll  5  (roll-set  56  of  FIG. 1 ) backward. This enables an operator to design a step specific recipe by specifying a number of parameters: 
   1) specifying a required starting speed, with the other speeds being calculated, or specifying a required ending speed with the other speeds being calculated; 
   2) specifying either a final yarn package diameter or package length may be entered (If a value is entered into both, the first to be achieved during operation becomes the operative parameter resulting in a package doff); 
   3) specifying the acceleration and deceleration time, in seconds, which refers to step-specific time for motors to accelerate or decelerate to the next or previous step speed, respectively. The following calculation is required to determine motor frequency acceleration:
 
Frequency Acceleration(Hz/sec)=(Freq final −Freq init )/(Accel Time)
 
   The precision of this calculation must be at least 0.1% (i.e., 10 −3 ) since all rolls must accurately achieve their final speeds to maintain the desired ratio. This gradual stepping of process ratios in the drawing and annealing, break, re-break, consolidation and windup zones provides the necessary easing of the feed material to the final process speed. These ratio steps result in a specific recipe that is unique to a specific type yarn Y. 
   In addition to operability criteria, safety criteria for the specific hardware of each position are stored in a system database. Safety limits, such as maximum motor speeds, are entered as a system management function and their values are stored in the system database. If a calculated roll speed falls above a system safety limit the operator is alerted via a different graphic color change of the specific roll icon. Thus a selected parameter is validated against predetermined safety criteria as well as operability criteria before the parameter is input into a recipe. The zone ratio, or initial speed is then adjusted to achieve a safe roll speed. 
   A background monitoring routine, resident in the system computer  112 , periodically issue data requests to each positional device to ascertain the state of machine operation via the bus network  120 . A log file may be created if desired by system computer  112  to record this data. Since the same bus is used to download recipes to positions, monitoring is suspended during a recipe download to maintain the integrity of data. When the recipe download is complete monitoring is resumed. 
   Those skilled in the art, having benefit of the teachings on the present invention as hereinabove set forth, may effect modifications and extensions thereof. Such modifications and extensions are to be construed as lying within the scope of the present invention as defined by the claims appended hereto.