Patent Publication Number: US-2023141286-A1

Title: Attachment for sealing seams

Description:
CROSS-REFERENCE TO RELATED CASES 
     This application is a divisional application of U.S. patent application Ser. No. 16/974,389, filed Jan. 8, 2021, which is a divisional application of U.S. patent application Ser. No. 15/932,105, filed Feb. 5, 2018, now U.S. patent Ser. No. 10/934,647, issued Mar. 2, 2021. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an attachment for an existing sewing machine, including an improved mechanism for pulling fabric members to be sewn to one another using thread comprising a thermoplastic polymer, together with a strip of the same or a different thermoplastic polymer, through a sewing machine while applying heat and pressure thereto, so as to sew the seam and melt the polymer to seal the seam in a single operation. 
     BACKGROUND OF THE INVENTION 
     Numerous products are made by sewing fabric members to one another, such as garments, tents, sails, backpacks, and the like. In many circumstances, these products are required to be highly water repellent and waterproof. As the needle used to drive thread through the fabric members in the sewing process is necessarily much larger in diameter than the thread, the needle punctures commonly tend to leak unless steps are taken to seal the seam. The spaces in the seam between needle punctures also tend to leak. 
     At present, the most prevalent method of sealing a sewn seam is to apply a wide tape of thermoplastic polymer with an adhesive layer over a previously sewn seam. The garment or other object is supplied to a machine provided with a pair of opposed rollers. A polymer substrate on the order of one inch wide with adhesive on one side thereof is heated by a stream of hot air, to activate the adhesive, and is then urged against the seam by the rollers so as to be adhered to the fabric members over the seam as the tape cools, covering the seam. Although this process is referred to in the art as “seam sealing”, in fact the seam itself is not literally sealed but is simply covered by the tape. 
     This method of seam sealing has many drawbacks, perhaps most notably that it requires the seam to be sealed in a separate operation from the sewing of the seam. Clearly if the seam could be sewn and sealed in a single-operation, substantial economies would be realized in terms of reduced labor requirements, reduced floor space requirements, and reduced equipment costs. The application of the polymer tape also stiffens the seam in ways that can be uncomfortable and restrict the wearer&#39;s motion in the case of garments and adds additional weight. 
     More recently, a new method for sealing seams has been developed, which is described in Ferreiro U.S. patent application Ser. No. 13/594,415 filed Aug. 24, 2012, incorporated herein by this reference, claiming priority from provisional application 61/575,602, filed Aug. 24, 2011, and published as publication No. 2013/0048219, and in co-pending continuation application Ser. No. 14/999,320, issued Feb. 13, 2018, as U.S. Pat. No. 9,889,598. The Ferreiro applications describe a method for forming a waterproof seam while sewing the seam by employing a thread comprising a quantity of thermoplastic polymer and heating the seam while applying pressure, melting the polymer so as to fill the punctures. A strip of thermoplastic polymer can also be inserted between the fabric members during the sewing step and be bonded to the fabric members in the same step of applying heat and pressure, sealing the seam between the thread punctures. 
     Because the polymer-bearing thread and optional polymer strip are internal to the seam in the Ferreiro method of seam sealing, the practice of heating the polymer using a jet of hot air, as practiced in the prior art seam sealing practice, in which the polymer tape is applied to a previously sewn seam, cannot be employed in the Ferreiro process. The Ferreiro application teaches that the heat and pressure can be applied to the seam using a heated roller opposed to a heated plate, and that the heated plate could be replaced by a roller. See para. [0031] of the published application. Ferreiro also teaches that a “puller” wheel could be provided to pull the fabric members joined by the seam through the sewing machine. See para. [0033] of the published application. 
     The present application relates to improvements in the mechanism and process described in the Ferreiro application, essentially taking it from the “proof-of-concept” status described therein to a fully commercialized device that can be attached readily to various commercial sewing machines. One particular improvement relates to the means of application of heat and pressure to seal the seam as it is being sewn. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to replace the heated roller opposed to a heated plate or to another heated roller of the Ferriero application with a series of driven heated rollers, typically three, opposed to pairs of heated idler rollers, with a belt disposed over the heated idler rollers, such that the belt urges the fabric members to be joined against the heated driven rollers. This ensures that the fabric members are in contact with the heated driven rollers long enough to ensure effective melting of the polymer, and thereby ensuring that the seam is effectively sealed. 
     Another improvement provided according to the present invention is driving the downstream roller slightly faster than the upstream rollers, slightly stretching the fabric while heating the seam, to ensure that the seam remains well-formed after the polymer cools and hardens. 
     Further detailed improvements provided by the present invention will be described below in connection with a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood by reference to the accompanying drawings, in which: 
         FIG.  1    shows a perspective view of the sewing machine, seen from the operator&#39;s side, with the attachment of the invention added thereto, and including a simplified schematic indication of control circuitry provided according to the invention; 
         FIG.  2    shows an enlarged perspective view comparable to  FIG.  1   , illustrating the attachment of the invention in additional detail; 
         FIG.  3    shows an enlarged perspective view comparable to  FIG.  2   , but taken from a point towards the rear of the sewing machine; 
         FIG.  4    shows an enlarged elevation of the upper and lower rollers from one side, with the belt passing therebetween; 
         FIG.  5    shows an enlarged perspective view comparable to  FIG.  2   , but of the attachment only, and with one of the rollers in section, showing the cartridge heaters used to heat the rollers; 
         FIG.  6    shows a view from the rear of the sewing machine, showing belts used to drive the rollers, and also showing a magnet attached to the flywheel of the sewing machine and a cooperating Hall-effect sensor, used to synchronize operation of the attachment according to the invention to the sewing machine; 
         FIG.  7    is a schematic diagram of the electrical circuit provided according to the invention; 
       and 
         FIG.  8    is a schematic diagram of a compressed air system employed to move the driven rollers into engagement with the fabric members and to preheat the polymer strip. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As indicated above, the invention relates to an attachment for an existing sewing machine that enables a seam to be sewn and sealed in a single operation. As shown by  FIG.  1   , a typical commercial sewing machine  10  comprises an upright column  12 , in which runs a drive belt from a motor (not shown) disposed under a table  14 , the motor being controlled by a foot switch  20  or the like, a transverse arm  16 , a sewing mechanism  18 , including a needle  19  and a presser foot  21  (see  FIG.  2   ), a lever  13  for lifting the foot  21  out of engagement with fabric members  7  and  9  to be sewn to one another, and a flywheel  22 . These components are well known, and their functions are not affected by the present invention, although certain of these are used in additional ways according to the invention, as will be detailed below. 
     According to the invention, an attachment  24  is attached to the sewing machine  10  by removing a cover plate (not shown) and assembling the attachment  24  in place of the cover plate. The details of this replacement of the cover plate by the attachment will of course vary somewhat from machine to machine; in each case, the attachment is designed so that the rollers (discussed further below) are disposed directly behind needle  19 . Also added is a reel  23  dispensing a strip  25  of an adhesive thermoplastic polymer, and a feeder assembly  27  for directing the polymer strip  25  into the seam being sewn. As compared to the adhesive tape used in prior seam sealing operations, which may be one inch wide by 0.002-0.003 inches thick, the strip employed according to the invention may typically be ⅛-¼ inch wide by 0.010-0.020 inches thick, 0.014 inches being preferred. The feeder assembly  27  may be provided with a hot air duct and nozzle, to preheat the polymer strip  25  and activate its adhesive properties prior to its being sewn into the seam.  FIG.  8    shows details of the air system used to preheat the polymer strip  25 . 
     Further provided according to the invention is an electronic control unit  26 , which may comprise a touch screen  28  for receiving user input concerning the parameters necessary to control the process of sealing the seam, such as the temperature of heated rollers that apply heat and pressure to the seam to melt the polymer and seal the seam, and a microprocessor  29  (indicated as a component of computer device  26  as “MP”) for receiving these user inputs and other data, and for providing control signals to the various components of the attachment.  FIG.  7    shows a block diagram of this circuitry. Also attached to the sewing machine  10  are a magnet  30  (see  FIG.  6   ), mechanically affixed to the flywheel  22 , and a Hall-effect sensor  32 , likewise mechanically affixed to the upright column  12 . 
     More specifically, as is well-known, in the process of sewing a seam, the sewing machine  10  advances the fabric members  7  and  9  to be sewn together incrementally, by the desired length of the stitch, and the presser foot  21  then holds them in place, so that the needle  19  can puncture the fabric members while stationary. In so doing flywheel  22  is rotated intermittently. As will be discussed in detail below, the attachment of the invention comprises heated rollers  40 ,  42 , and  44  (see  FIG.  4   ) that are driven to pull the fabric members through the attachment while applying heat and pressure to the seam so as to melt the polymer and seal the seam. In order to function properly, the driven rollers must cease pulling on the fabric members during the stitching process. In order that the operation of the rollers can be synchronized with that of the sewing machine, when the magnet  30  passes the Hall-effect sensor, the latter provides a signal (“HE” in  FIGS.  6  and  7   ) that is provided to the microprocessor  29  to control two motors  34  and  36  via signals M 1  and M 2  ( FIGS.  1  and  7   ) that drive the rollers. Signal HE is thus used to synchronize the operation of the rollers to the remainder of the sewing machine, so as to avoid distorting the fabric. The circuitry connecting the microprocessor  29  to the various components providing and receiving the signals noted is not shown in  FIG.  1   , for clarity of the drawing, but will be readily understood and easily implemented by those of skill in the art. As above,  FIG.  7    shows a schematic diagram of this circuitry. 
     As noted, operation of the sewing machine is controlled by a foot pedal  20  or the like, such as a knee-operated or foot-operated switch operated by an operator. When the operator stops a given sewing operation, the heated rollers  40 ,  42  and  44  must be removed from the fabric members being sewn together in order to avoid scorching the fabric. Therefore, a control signal SW from foot pedal  20  is provided to microprocessor  29  which in turn provides a control signal AC to an air cylinder  48 . The assembly of rollers  40 ,  42 , and  44  and of motors  34  and  36  is carried by air cylinder  48  and is withdrawn upwardly, out of engagement with the fabric members, when operation of the sewing machine  10  is stopped by the operator. At the same time the stream of hot air preheating the strip of polymer 25 is shut off. These operations are accordingly reversed when sewing is again initiated by the operator. 
     The signals provided by microprocessor  29  also include three control signals H 1 , H 2  and H 3  provided to rollers  40 ,  42  and  44  respectively, to control their surface temperature and thereby the amount of heat applied to the seam. Control of the surface temperature of these rollers is clearly important to obtaining adequate melting of the polymer of the thread and strip to provide good sealing without scorching or burning the fabric. The surface temperature of the rollers can be measured directly using infrared sensors, if such can be found that are sufficiently durable, or the temperature can be controlled indirectly using a feedback loop. The rollers can be heated using internal cartridge heaters  51 . See  FIG.  5   . Idler rollers  50  (discussed further below) are likewise heated. 
     More specifically, in order that electrical connections can be made to the cartridge heaters  51 , they must be stationary, while driven rollers  40 ,  42  and  46  and idler rollers  50  must rotate freely over heaters  51 . The heaters  51  are designed to expand when current is applied, typically so as to fit snugly into a hole bored in a volume of material to be heated. In order that such expansion does not prevent rotation of the rollers, the cartridge heaters can be disposed in sections  53  of steel tubing, while the rollers may be made of aluminum, bored to be a sliding fit over the steel tubes, and assembled with a small quantity of heat-conducting grease therebetween. The greater coefficient of thermal expansion of aluminum as compared to that of steel will prevent the heating of the cartridge heaters  51  from interfering with rotation of the rollers. 
     As mentioned, the temperatures of the surfaces of the rollers can be measured directly using infrared sensors, if suitably durable components can be found. Alternatively, thermocouples can be provided to measure the temperatures of the cartridge heaters  51 , and this data used in a well-known proportional-integral-derivative (PID) feedback loop to control the temperatures of the surfaces of the rollers. Experimentation and appropriate testing will be required to determine the optimal parameters for the PID feedback loop, and these will likely vary with differing fabric types to be sewn and sealed to one another according to the invention. Such experimentation and testing to calibrate the feedback loop is within the skill of the art. 
     Turning now to the detailed mechanical details of the attachment of the invention,  FIG.  4    shows an end view of the assembly of driven heated rollers  40 ,  42  and  44 , heated idler rollers  50 , and belt  52  in detail;  FIGS.  2 ,  3 ,  5  and  6    show further features provided according to the invention. Rollers  50  are carried by a chassis  56  that is assembled to the sewing machine  10 , typically by attachment to the hinge (not shown) conventionally provided to allow the sewing machine to be pivoted out of its&#39; “nest” in the sewing machine table  14 .  FIG.  4    is effectively taken from inside chassis  56 , so as to show the ends of rollers  50 . Chassis  56  has an inclined leading surface  56   a  (see  FIG.  2   ) that assists in feeding the sewn fabric members from beneath presser foot  21  to between the driven rollers  40 ,  42  and  44  and the idler rollers  50 .  FIG.  4    also shows the thread  17 , which will typically be the polymer-coated thread described in the Ferreiro applications. Chassis  56  is preferably spaced from the sewing machine  10  by insulating spacers (not shown) to allow air to pass there between and avoid overheating the sewing machine  10 . 
     A continuous belt  52  fits over rollers  50  and moves together with the fabric members  7  and  9  to be sewn, which are indicated by a heavy broken line  58  in  FIG.  4   . Belt  52  rides over a final, unheated roller  60 , and is tensioned by springs  54  on either side of the chassis  56 , biasing roller  60  (leftwardly in the view of  FIG.  4   ) toward the “downstream” end of chassis  56 ; the degree of tension in belt  52  may be adjusted by provision of differing springs  54 , or by adjustment of the preload provided. As indicated by  FIG.  3   , the biasing roller  60  is mounted in a slot  56   b  in chassis  56 , to allow it to move to adjust the tension in belt  52 . 
     As illustrated, the fabric members  7  and  9  to be bonded to one another are urged by belt  52  into engagement with rollers  40 ,  42 , and  44  along a lower portion of the circumference of each of rollers  40 ,  42 , and  44  between the opposed pairs of idler rollers  50 , ensuring good heat transfer between rollers  40 ,  42 , and  46  on the upper side, to the fabric members indicated at  58 . By comparison, if belt  52  were omitted, heat transfer would end to take place only along lines at which the idler rollers  50  are juxtaposed to the driven rollers  40 ,  42 , and  46 , which would be much less effective. Belt  52  can be made of a composite of fiberglass cloth coated by one or more layers of Teflon® material. Given that these materials, as well as those of most fabrics, are relatively insulative, the extension of the heat transfer area provided by provision of the belt  52  is highly beneficial in ensuring sufficient heat transfer to effectively melt the polymer materials of the thread  17  and strip  25 , and thereby effectively sealing the seam. Belt  52  also prevents the fabric members from being tangled in rollers  50 . 
     In the preferred embodiment, the axes of driven rollers  40 ,  42 , and  44  are coplanar, as are those of the idler rollers  50 , as illustrated by  FIG.  4   . When the driven rollers are withdrawn upwardly, at the end of a sewing operation, the spring tension provided to unheated idler roller  60  by springs  54  will cause roller  60  to move leftwardly, so that belt  52  will take a straight-line path over the upper surfaces of idler rollers  50 . When the driven rollers  40 ,  42 , and  44  are brought back downwardly as sewing resumes, the belt  52  will be forced away from the straight-line path so as to conform to the lower circumferential surfaces of rollers  40 ,  42 , and  44  between the respective pairs of idler rollers  50 , taking the form shown in  FIG.  4   , while the springs  54  allow the unheated idler roller  60  to move rightwardly in the view of  FIG.  4   . 
     More specifically, as the fabric members with the polymer strip therebetween are drawn through the heated rollers, the heat and pressure provided by the rollers melts the preheated polymer strip  25  and squeezes it laterally, filling the space between the fabric members  7  and  9 . Normally the practice of the invention will also involve the use of the polymer-laden thread  17  of the Ferriero applications, so that the polymer of the thread  17  is melted at the same time, filling the punctures left by the needle. However, it may be possible to avoid use of the thread  17  in favor of a plain thread, and simply filling the needle punctures with the polymer from the strip  25 , and such is accordingly also within the scope of the invention. Likewise, in some applications the polymer strip  25  may be avoided and only the thread  17  used. 
     The polymers applied to the thread  17  and that of strip  25  may be the same or may differ. As of the filing of this application, experimentation is being performed to identify the optimal materials for these purposes. They may be as disclosed in the Ferreiro application, that is, thermoplastic polyurethane, or possibly materials selected from the group including nylon, polyester, polyolefin and vinyl, and mixtures and combinations thereof. It will be appreciated that these materials have good adhesive properties, so that the seam is strengthened as well as sealed by practice of the invention. The materials used in the prior art seam sealing processes may also be used. Preferably, the polymer is applied to the thread in a bath of molten polymer, so that the polymer is absorbed into the yarns of the thread, followed by passage through a die or the like, squeezing out extra polymer, so the final polymer content of the thread is 2-6% by weight, as in the Ferreiro applications. 
     As shown in  FIG.  6   , the “upstream” rollers  42  and  44  are driven by motor  36  by way of a first belt  60 , while the “downstream” roller  40  is driven separately by motor  34  by way of a second belt  62 . The motors  34  and  36  are operated responsive to signals M 1  and M 2  ( FIGS.  1  and  7   ) respectively, so that the rollers can be driven at different speeds as desired. Preferably, the downstream roller  40  is driven at a slightly higher speed than the upstream rollers  42  and  44 , so as to exert tension on the assembly of fabric members while the polymer is being melted and the seam compressed, ensuring that the seam is properly formed. 
     Other preferred aspects of the design include the following: 
     The surfaces of driven rollers  40 ,  42 , and  44  are knurled as illustrated, so as to ensure adequate friction between these surfaces and the fabric members  7  and  9 . A coating is applied to produce a non-stick surface. 
     An operator-controlled cutter (not shown) may be provided between the rollers  40 ,  42 , and  44  and presser foot  21 , to cut the polymer strip  25  at the end of the seam. 
     Rollers  40 ,  42 , and  44  are carried by a frame  64  ( FIG.  2   ) that is pivoted transversely at  66  with respect to the moving actuator  68  of air cylinder  48 . This pivoting allows the rollers to remain in contact with the fabric members  7  and  9  despite some degree of irregularity in the thickness of the fabric members, such as where several fabric members cross one another. The rollers  40 ,  42 ,  44  may also be carried on individual suspensions, spring-biased downwardly with respect to frame  64 , for similar reasons. 
     As mentioned above,  FIG.  7    is a schematic diagram of the electrical circuitry provided according to the invention. Where feasible, the components and control signals identified earlier are identified here as well. Thus, an electronic control unit (ECU)  80 , which may comprise microprocessor  29  and associated supporting components, including a user interface such as touch screen  26 , receives sensor inputs and provides control signals through appropriate interface circuit boards. Thus, for example, a set of temperature sensors  70  for the lower roller assembly, that is, idler rollers  50 , a set of temperature sensors  72  for the driven rollers  40 ,  42 , and  44 , and an air process temperature sensor  73  for measuring the temperature of the stream of air preheating the polymer tape  25 , each provide temperature data to a sensor input board  74 . Sensor input board  74  then performs simple operations on the data, for example, analog-to-digital conversion, and provides the results to ECU  80  as indicated at  76 . As discussed above, the signals responsive to roller temperature may represent direct measurement of the temperature of the rollers or may represent measurement of the temperature of the cartridge heaters  51 . 
     In either case, the temperature measurement signals are used by ECU  80  to generate temperature control signals by way of a well-known proportional-integral-derivative (PID) feedback loop. These control signals are then provided to a relay control board  82 , which uses the control signals from ECU  80  to drive relays on board  82  to control supply of current to the various heating elements, including the lower assembly heating elements  84 , that is, the cartridge heaters in idler rollers  50 , the upper assembly heating elements  86 , that is, the cartridge heaters in driven rollers  40 ,  42 , and  44 , and the air process heating element  88 , heating the stream of air employed to preheat the polymer tape  25 . 
     Similarly, the signal HE from the Hall-effect sensor  32  is provided to the ECU  80  and used to synchronize the operation of drive motors  34  and  36 , by way of provision of signals M 1  and M 2  to a motor control board  84 , which directly controls operation of motors  34  and  36 . These motors may be of any of a variety of types; stepper motors are currently preferred. 
     Likewise, foot switch  20  provides signal SW to ECU  80 , thereby indicating that sewing is to start or to stop. In response to a stop signal, ECU  80  provides signal AC to relay control board  82 , which then operates the air cylinder via solenoid valve(s)  92  to lift the heated driven rollers  40 ,  42 , and  44  out of engagement with the fabric members to be joined, and likewise operates hot air solenoid  90  to cut off the supply of hot air preheating polymer tape  25 . While the fabric members  7  and  9  may remain in contact with belt  52  while rollers  40 ,  42 , and  44  are thus withdrawn, out of engagement with fabric members  7  and  9 , the fact that no pressure is then being exerted prevents the fabric from being scorched by heat from the idler rollers  50 . 
       FIG.  8    shows as mentioned a schematic diagram of the pneumatic components employed. Compressed air is supplied at  94  and is supplied to a first solenoid valve  90  which controls flow of air for preheating the polymer strip  25 . The pressure in the supply line is controlled by a regulator  96 , and the air is heated by a heater  88 . The heater is controlled by control unit  80  in response to a signal from sensor  73 , as discussed above. The hot air impinges on the polymer strip  25  as it exits feeder  27 , as illustrated. 
     A second stream of air is provided to solenoid valves  92 , connected to air cylinder  48  as shown, in order to controllably raise and lower roller assembly  24  as desired. 
     Thus, in operation of the sewing machine with the attachment according to the invention, the sewing machine  10  is first preferably supplied with the polymer-bearing thread  17  ( FIG.  4   ) according to the Ferreiro application referred to above. The polymer strip  25  is placed between the fabric members  7  and  9 , and this assemblage is hand-fed under the presser foot  21 . The foot switch  20  (or equivalent, such as a knee-operated lever switch) is then actuated by the operator, causing the sewing machine to operate as usual. At the same time, according to the invention, rollers  40 ,  42 , and  44  are brought into engagement with the assemblage of fabric members and polymer strip  25 , and are driven in synchronism with the operation of the sewing machine  10  to pull the assemblage between rollers  40 ,  42 , and  44  and idler rollers  50 , with belt  52  therebetween, so that the assemblage is heated to melt the polymer of tape  25  and that of the thread  17 . 
     More specifically, the preheated polymer strip  25  is drawn into the machine between the two fabric members  7  and  9 , the fabric members are stitched together, and a final application of heat to raise the polymer above its solid-to-liquid transition temperature is provided from the rollers. At the same time, the rollers also provide pressure, which flattens the seam, and squeezes the polymer in the seam between the needle punctures. The application of pressure also provides better heat transfer through the fabric to the polymer, as well as deforming the lower belt to give greater surface area for improved heat transfer efficiency. After exiting the roller assembly, the polymer rapidly cools and is set. At present, no separate cooling step appears necessary, but such is within the invention if needed. 
     It will be appreciated that while a single needle sewing a simple seam has been illustrated, other sewing operations, such as double-needle sewing or sewing of more complex seams, such as interlocking “felled” seams, may be readily accommodated. It will also be appreciated that the sewing machine could be used as usual, that is, without employment of the attachment of the invention, while it remains in place; that minimal modification of the sewing machine is needed to employ the attachment of the invention to simultaneously sew and seal seams; and that minimal operator training is needed. 
     While a preferred embodiment of the invention has been described in detail, the invention is not to be limited thereto, but only by the following claims. 
     1. A sewing and sealing machine allowing sewing and sealing of a seam between fabric members in a single operation, comprising: 
     a reel for providing a quantity of thread comprising between about 2% and about 6% by weight of a thermoplastic polymer material selected from the group consisting of polyurethane, nylon, polyester, polyolefin, and vinyl; 
     a sewing mechanism adapted to incrementally draw said at least two fabric members from an upstream side of said sewing machine towards a downstream side of said sewing machine, and to cause a needle to puncture said at least two fabric members at regular intervals and to draw said thread through said punctures, to form a sewn seam; and 
     a sealing mechanism, comprising:
         a control unit for receiving operational signals from said sewing mechanism, said signals including a synchronization signal and a signal from an operator-controlled switch for initiating sewing operations;   a reel for supply of a strip of thermoplastic polymer material selected from the group consisting of polyurethane, nylon, polyester, polyolefin, and vinyl;   a feeder assembly for feeding the strip of thermoplastic polymer material between the fabric members;   a plurality of driven rollers;   a pair of idler rollers opposed to each of said driven rollers;   a continuous belt disposed over said idler rollers;   each of said driven rollers and idler rollers being controllably heated responsive to control signals from said control unit;       

     wherein said driven rollers are brought into engagement with said fabric members in response to said signal from an operator-controlled switch for initiating sewing operations and said driven rollers are driven intermittently by motors controlled by said control unit responsive to said synchronization signal while said at least two fabric members are incrementally drawn from said upstream side of said sewing machine towards said downstream side of said sewing machine, in order to apply heat and pressure to said seam so as to melt said polymer from said thread, whereby said polymer from said thread fills and seals said punctures, and so as to melt said polymer from said strip, whereby said polymer from said strip fills and seals spaces between said fabric members between said punctures. 
     2. The machine of claim  1 , wherein said driven and idler rollers are heated by cartridge heaters disposed in bores in said rollers. 
     3. The machine of claim  2 , wherein the temperature of the surfaces of said driven and idler rollers is controlled by said control unit responsive to measurement of the temperature of said cartridge heaters, using a calibrated feedback loop. 
     4. The machine of claim  1 , further comprising a heater for heating a stream of air, and a nozzle disposed with respect to said feeder assembly so as employ said stream of heated air to preheat the polymer strip prior to its being fed between the fabric members. 
     5. The machine of claim  1 , wherein said driven rollers are mounted on a frame, and wherein said frame is supported by an air cylinder controlled by said control unit to bring said driven rollers into engagement with said fabric members responsive to said signal from an operator-controlled switch for initiating sewing operations. 
     6. The machine of claim  5 , wherein said frame is pivotably mounted with respect to said air cylinder. 
     7. The machine of claim  1 , wherein said synchronization signal is provided by attachment of a magnet to a flywheel of said sewing mechanism, and by attachment of a Hall-effect sensor to said sewing mechanism so as to be juxtaposed to said magnet when said flywheel rotates in operation of said sewing mechanism, whereby said Hall-effect sensor provides said synchronization signal to said control unit. 
     8. The machine of claim  1 , wherein said plurality of idler rollers are carried by a chassis attached to said sewing machine. 
     9. The machine of claim  8 , wherein said chassis carries a further unheated roller over which said belt passes, the axis of said further unheated roller being movable to control the tension in said belt. 
     10. The machine of claim  9 , wherein said unheated roller is spring-biased to control the tension in said belt. 
     11. The machine of claim  10 , wherein when said driven rollers are engaged with said fabric members, said belt is deformed so as to urge said fabric members against a portion of the circumference of each of said driven rollers. 
     12. The machine of claim  1 , wherein the thermoplastic polymer materials comprised by said thread and comprised by said strip are the same. 
     13. The machine of claim  1 , wherein the heated rollers are removed from contacting the fabric members except during sewing, to avoid scorching the fabric. 
     14. The machine of claim  1 , wherein three driven heated rollers are provided, and the downstream roller is driven faster than the upstream rollers, to exert tension on the fabric members.