Abstract:
The present invention provides a fabric tensioning device for stretching fabric on a sewing machine. The fabric tensioning device includes a cylindrical frame having a window extending in a longitudinal direction. A fabric clamping member clamps down the cloth material against the frame for presenting the material to the embroidery needle at the window in a tensioned state. The clamping member opens and closes on the frame and has a pair of opposing fabric clamps on the left and right side of the frame that are oblong in the longitudinal direction with open front edges. The fabric clamps are tightened against the frame by belts in the front and rear thereof.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a fabric tensioning device for stretching work fabric in the sewing location of a sewing machine. 
     2. Description of Related Art 
     Devices for tensioning a piece of tube-like fabric, such as a material for socks and wrist bands, using a cylindrical frame are used in embroidering on a sewing machine. One of such fabric tensioning device is disclosed in International Patent Publication Number WO0/53836. This device has a cylindrical frame  101  that is placed to cover the outside of the cylinder bed (not shown) of the sewing machine as shown in FIG. 11. A sewing window  102  is formed in cylindrical frame  101  for exposing the sewing, area of the cylinder bed. A fabric clamping member  103  capable of opening and closing vertically is provided in order to clamp down the fabric, which is arranged to cover sewing window  102 , against cylindrical frame  101 . Fabric clamping member  103  is formed by bending a steel rod to form a rectangular shape with a closed front end, to clamp down the fabric against cylindrical frame  101  to hold it on three sides, i.e., the front, left and right sides, of the sewing area. 
     However, with this fabric tensioning device, because fabric clamping member  103  is a frame-like member made of a highly rigid material, the contact of fabric clamping member  103  against the fabric is often localized. This causes a clamp mark in a certain area, and insufficient clamping in other areas of the fabric, which are all undesirable. Moreover, since fabric clamping member  103  does not hold the fabric on the rear side of the sewing area, it may cause looseness in the fabric on the left and right sides of the sewing area particularly when the fabric is a thin or slippery piece of processed fabric, thus affecting the sewing accuracy. 
     SUMMARY OF THE INVENTION 
     The present invention provides a fabric tensioning device for a sewing machine that can solve the abovementioned problems by holding down the fabric on the four sides of the sewing area evenly and stretching the fabric securely on the cylindrical frame without causing any clamping marks or slacks. 
     In order to solve the abovementioned problems, the fabric tensioning device according to the present invention comprises a cylindrical frame having a sewing window and a fabric clamping member for clamping down against said cylindrical frame a work fabric that is covering said sewing window, wherein said fabric clamping member is provided in such a way as to be able to open or close against said cylindrical frame, and said fabric clamping member is equipped with a pair of fabric clamps on the left and right hand side that are oblong in the longitudinal direction having open-end front edges, wherein said fabric clamps are tightened against said cylindrical frame at the front and rear ends of a sewing area by means of a pair of belts provided in the front and the rear of the area. 
     While the direction that the fabric clamping member opens or closes can either be a vertical direction or a lateral direction, it is preferable for the fabric clamping member to be mounted in such a way to open or close in the lateral direction as it makes it easier to open the sewing window fully and to spread the fabric over the area. It is preferable in this case that the fabric clamping member is pivot-mounted on the cylindrical frame at a location outside of one of the fabric clamps so that a wide space can be formed between the fabric clamp and the cylindrical frame and the work fabric can be easily inserted. More specifically, it is preferable to form the fabric clamping member in a rectangular shape with an open-ended front edge by connecting the rear end of the left and right hand side fabric clamps, and to attach the rear end of the fabric clamping member to the cylindrical frame via a pivot shaft located outside of one of the fabric clamps so that the fabric clamping member can be opened in the lateral direction. 
     The belts that tighten the fabric clamps do not have to be made of a specific kind of material; for example, rubber belts, fabric belts, surface fastener belts, etc., can be used, as long as they are flexible so that they are unlikely to leave clamping marks. Surface fastener belts with open-ends are preferable as they can be used to tighten the fabric clamps with one-touch operation. It is preferable in this case to provide a surface fastener on one of the fabric clamps in such a way that the position of the rear belt can be adjusted in the forward and backward direction in order to be able to tighten the fabric clamp close to the rear end of the stitch forming area as needed in accordance with the sewing area of an embroidery pattern, etc. The front belt should preferably be threaded through the hole provided on the front end of the left and right fabric clamps so that it will not be lost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a cylinder bed according to an embodiment of the invention. 
     FIG. 2 is a front view of the bed according to an embodiment of the invention. 
     FIG. 3 is a disassembled perspective view showing a cylindrical frame guide device provided on the bed according to an embodiment of the invention. 
     FIG. 4 is a perspective view of a fabric tensioning device of the bed according to an embodiment of the invention. 
     FIG. 5 is a side view of the fabric tensioning device according to an embodiment of the invention. 
     FIG. 6 is a partially broken front view of the fabric tensioning device according to an embodiment of the invention. 
     FIG. 7 is a plan view of the fabric tensioning device according to an embodiment of the invention. 
     FIG. 8 is a cross-sectional view showing how an core material and a work fabric are mounted on the fabric tensioning device according to an embodiment of the invention. 
     FIG. 9 is a plan view showing how the core material and the work fabric are tensioned according to an embodiment of the invention. 
     FIG. 10 is a cross-sectional view showing how the core material and the work fabric are tensioned according to an embodiment of the invention. 
     FIG. 11 is a perspective view of a fabric tensioning device of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the invention on an embroidering sewing machine will be described below with reference to the accompanying drawings. As shown in FIG.  1  and FIG. 2, a head  1  and a cylinder bed  2  are displaced in a vertical direction in the machine frame (not shown) of a the sewing machine, and a needle  3  is attached to the bottom end of head  1 , while a bobbin case  4  and a needle plate  11  are provided at the front end of cylinder bed  2 . A Y-direction moving body  5  is supported by the top surface of cylinder bed  2 , and a base plate  6  is connected vertically to moving body  5 . Three rollers  8  are displaced on the front side of base plate  6  in order to support a drive ring  7 , while two guide rollers  10  are provided on the back side of base plate  6  engaging with two bottom grooves  9  on the left and right sides of cylinder bed  2 . 
     An X-direction moving body  13  is supported via a rail  12  provided on the top of Y-direction moving body  5 , while a pulley  14  is provided at the left and right ends of moving body  13  respectively. A wire rope  15  is provided on pulleys  14  tightly stretched by means of a spring  16 , while rope  15  is wrapped around drive ring  7  in the middle. Y-direction moving body  5  and X-direction moving body  13  are connected to a sewing frame driving device (not shown) of the sewing machine, and Y-direction moving body  5  strokes drive ring  7  in a reciprocating manner in the axial direction (front and rear direction) of cylinder bed  2  via base pate  6 , while X-direction moving body  13  rotates drive ring  7  in a reciprocating manner around the axis of cylinder head  2  via wire rope  15 . 
     In an embroidering process of a piece of tube-like fabric such as a material for socks and wrist bands, a cylindrical frame  19  of fabric tensioning device  18  is placed to cover the outside of cylinder bed  2  and is attached to drive ring  7  via a mounting part  19   a  at its rear end. A latching piece  20  and a flange  21  are provided protrusively on the rear outer periphery of cylindrical frame  19  (see FIG.  4 ), while a lever  22  that engages with latching piece  20  and a spring  23  that elastically contacts with flange  21  are provided on drive ring  7 . Thus, cylindrical frame  19  is connected tightly to drive ring  7  via lever  22  and spring  23  and driven together with drive ring  7  in the axial and circumferential directions relative to the axis of cylinder bed  2  in order to sew on the fabric stretched around cylindrical frame  19  in the cooperation of needle  3  and bobbin case  4 . 
     As shown in FIG. 3, a pair of arms  25  is protrusively provided on the left and right sides of the front end of cylinder bed  2  and a needle plate  11  is horizontally affixed on arms  25 . Curved surfaces  11   a  are formed on the left and right shoulder areas of needle plate  11  close to the inner surface of cylindrical frame  19 , and a boss  26  equipped with a needle hole  26   a  is provided protruding low in the center flat area of needle plate  11 . An opening  29  is formed below needle plate  11 , the front end of a bobbin case drive shaft  31  extends into this opening  29 , and bobbin case  4  is mounted on bobbin case drive shaft  31 . 
     Also, a guide member  27  is provided in opening  29  for supporting cylindrical frame  19  from the inside. Guide member  27  consists of a connecting part  27   a  in the rear end and two side wall parts  27   b  on the left and right sides, together forming a rectangular shape, and connecting part  27   a  is detachably affixed with a screw  32  to the front end surface of cylinder bed  2  below bobbin case drive shaft  31  as side walls  27   b  are placed to cover the outside of the arms  25 . A curved plate  33  is affixed by welding on the outside of each side wall part  27   b,  and these curved plates  33  form a partial cylindrical surface  30  that contacts concentrically with the inside of cylindrical frame  19  for side wall parts  27   b.    
     A protection cover  28  is provided below guide member  27  and cover  28  covers bobbin case  4  from its underside. Protection cover  28  consists of flat parts  28   a  and a curved part  28   b  forming a U-shape as it is viewed from the front, wherein curved part  28   b  forms a partial cylindrical surface  36  having the same curvature as partial cylindrical surface  30  of guiding member  27  for cover  28 . Semispherical protrusions  34  are provided on flat parts  28   a,  while holes  35  are provided on side walls  27   a  to fit with protrusions  34 . Protection cover  28  is mounted detachably on guide member  27  by means of fitting between protrusions  34  and holes  35  as flat parts  28   a  are inserted on the inside of side wall parts  27   b.    
     As shown in FIG.  4  through FIG. 7, cylindrical frame  19  comprises a sewing window  37  that exposes needle plate  11 , an core material clamping member  38  that clamps down the core material C (see FIG. 7) covering sewing window  37  against cylindrical frame  19 , a fabric clamping member  39  that clamps down the work fabric W that is covering the core material C together with the core material C against cylindrical frame  19 , and a support member  40  that supports the core material C and the work fabric W in the middle position of sewing window  37 . The core material C is a shape keeping material to prevent the work fabric W from sinking and is made of cardboard, unwoven fabric, etc. If the work fabric W consists of a rigid material such as leather and felt, it is possible to sew by stretching the work fabric W direction over cylindrical frame  19  without using the core material C. 
     Sewing window  37  is formed to a length corresponding to the axial stroke length of cylindrical frame  19 , while a slip guard  42  made of rubber is glued on cylindrical frame  19  along the front and rear edges of sewing window  37  respectively and a tightener  43  made of strip steel or rubber is protrusively provided along the left and right side edges of sewing window  37 . Support member  40  is formed into a curved shape having a curvature approximately equal to that of the outside diameter of cylindrical frame  19  and is fastened at fastening areas  40   a  at each end with screws  44  that are screwed onto screw holes  43   a  of tighteners  43  in an axially adjustable manner spanning over sewing window  37 . A notch  45  is formed on rear mounting part  19   a  of cylindrical frame  19  to allow spring  23  of drive ring  7  to enter. The inside of the front end of cylindrical frame  19  is attached with an annular plate  46 , at a portion of which is provided with a protruding positive stop  47  for positioning the core C from the front end. 
     Core material clamping member  38  made of a steel strip is formed in an oblong shape in the axial direction (longer than sewing window  37 ) on the left and right hand sides of cylindrical frame  19  respectively under tightener  43 . The rear end of core material clamping member  38  is affixed to flange  21  with a screw  49  on the left and right sides of cylindrical frame  19  respectively, while the front end of core material clamping member  38  is provided in such a way as to be able to open individually to the left and right relative to cylindrical frame  19 . At multiple places inside of core material clamping member  38 , clamping pieces  50  are provided, which are formed being bent in an angle going from top to bottom for elastically contacting the core material C. At the front end of core material clamping member  38 , temporary latches  51  are formed bending them inward, in such a way that temporary latches  51  can elastically engage with annular plate  46  through notches  52  provided on cylindrical frame  19  in order to hold core material clamping member  38  temporarily in a closed state. 
     Fabric clamping member  39  comprises, provided on the left and right sides, a pair of fabric clamps  56  that are oblong in the axial direction and open at the front end. The rear ends of the left and right fabric clamps  56  are connected by a connecting part  55  thus causing fabric clamping member  39  to have substantially a rectangular shape with an open ended front. Fabric clamps  56  are each made of a steel strip and to a length approximately equal to that of core material clamping member  38  and are facing core material clamping member  38  from the outside. Slip guards  53  made of rubber plates with grooves that are intended to sandwich the work fabric W with fabric clamps  56  are glued on the outside of core material clamping member  38 . Connecting part  55  is made of a steel plate in a shape to go across cylindrical frame  19 , and a bracket  57  is attached to its left side. A threaded shaft  58  is provided on bracket  57  on the outside of the left fabric clamp  56 , and fabric clamping member  39  is fastened to flange  21  of cylindrical frame  19  by means of threaded shaft  58  in such a way that it can open or close in the lateral (left and right) direction. 
     An oblong surface fastener tape  60  is adhered to the outside surface of each fabric clamp  56  and a surface fastener belt  61  with open ends are latched to this tape  60  in such a way as to be adjustable in the axial direction in order to coordinate with support member  40 . An engaging hole  62  is provided at the front end of the left and right fabric clamps  56  and a surface fastener belt  63  is threaded through engaging hole  62 . The left and right fabric clamps  56  and the left and right core material clamping members  38  can be tightened against cylindrical frame  19  in the front and rear of needle plate  11  where the sewing actions occur by means of the front and rear fastener belts  61  and  63 . Surface fastener belts  61  and  63  can be provided with surface fasteners for the entire surface on the front and back or can be provided only on both ends. 
     The method of using fabric tensioning device  18  in a sewing machine constituted as described in the above will be described as follows: In embroidering a piece of tube-like fabric, as shown in FIG. 1, set cylindrical frame  19  to cover the outside of cylinder bed  2 , fit mounting area  19   a  into drive ring  7 , clamp flange  21  to spring  23 , cause lever  22  to engage with engaging piece  20 , and mount cylindrical frame  19  tightly on drive ring  7 . 
     Next, as shown in FIG.  7  and FIG. 8, move open fabric clamping member  39  toward left side of cylindrical frame  19 , and make the core material C to abut against positive stop  47 , to be supported by supporting member  40 , to cover sewing window  37 , and to be clamped down against cylindrical frame  19  to be stretched by means of core material clamping members  38  on the left and right sides. According to fabric tensioning device  18  of this embodiment, the following operating advantages can be achieved: 
     (1) Since two core material clamping members  38  on the left and right sides are attached to cylindrical frame  19  in such a way as to be able to open independently, it is possible to clamp down the core material C against cylindrical frame  19  on the left and right side independently and align it against the outer periphery of cylindrical frame  19  easily and accurately. More specifically, after clamping the left side of the core material with the left core material clamping member  38 , adjust the shape of the remaining portion of the core material C, and clamp the right side of the core material with the right core material clamping member  38  to stretch the entire core material C in a smooth cylindrical shape; the order can be reversed to start with the right side as well. 
     (2) Since the front ends of the left and right side core material clamping members  38  are arranged in such a way as to be able to open toward the left and right sides of cylindrical frame  19  respectively, in contrast to the prior art wherein the clamping member opened and closed in the vertical direction, the core material C is less likely to be stretched in a skewed manner and the material can be easily stretched against cylindrical frame  19  evenly from the front to the rear at the same height. 
     (3) Since temporary latches  51  are provided at the front end of core material clamping member  38 , the core material C can be held in a smooth cylindrical shape by temporarily latching one side of the core material C, which makes it easy to adjust the other side of the work fabric W with both hands and to stretch it out neatly. 
     (4) Since the core material clamping members  38  are provided below tighteners  43 , it is possible to securely prevent the core material C from slacking and deformation while it is temporarily latched. 
     (5) Since multiple clamping pieces  50  are provided in the inside of core material clamping members  38 , it is possible to hold various parts of the core material C with an even force using core material clamping members  38  which are oblong in the axial direction. 
     Next, place the work fabric W on top of the core material C as shown in FIG.  9  and FIG. 10, close down fabric clamping member  39 , and clamp down the work fabric W via the core material C against cylindrical frame  19  with the left and right fabric clamps  56 . Next, make both ends of the front and rear surface fastener belts  61  and  63  contact and stick together, and tighten them in order to cause fabric clamps  56  to tighten against cylindrical frame  19  together with core material clamping members  38  to stretch the work fabric W against cylindrical frame  19 . According to fabric tensioning device  18  of this embodiment, the following operating advantages can be achieved: 
     (6) Since the two fabric clamps  56  on the left and right sides are tightened against cylindrical frame  19  by means of two surface fastener belts  61  and  63  in the front and rear, the work fabric W is evenly clamped down on four sides of needle plate  11  thus making it possible to stretch it out securely on cylindrical frame  19  without causing any clamp marks or slacks. 
     (7) Since fabric clamping member  39  is provided in such a way as to be able to open or close in the lateral direction, the core material C and the work fabric W can be neatly and quickly spread out to cover the fully exposed sewing window  37  (see FIG.  7 ). 
     (8) Since fabric clamping member  39  is pivot mounted on flange  21  via threaded shaft  58  located on the outside of the left side fabric clamp  56 , it is possible to provide a wide space between the left side fabric clamp  56  and cylindrical frame  19  when fabric clamping member  39  is opened, allowing the core material C and the work fabric W to be inserted in that space easily. (See FIG. 8) 
     (9) Since the left and right fabric clamps  56  are facing the left and right core material clamping members  38  from the outside, they can be tightened together with two surface fastener belts  61  and  63  to hold the work fabric W and the core material C against cylindrical frame  19  solidly and simultaneously. 
     (10) Since the slip guards  53  are provided on the outside surfaces of the core material clamping members  38 , the work fabric W can be clamped without any slacks between core materials clamping members  38  and fabric clamps  56 . 
     (11) Since surface fastener belts  61  and  63  having open ends on one side are used, fabric clamps  56  can be tightened by one-touch operation without causing any slacks. 
     (12) Since the rear surface fastener belt  61  is engaged with surface fastener tape  60  in such a way as to be adjustable in the axial direction, it is possible to tighten fabric clamps  56  closer to the back of the embroidering position as needed according to the embroidering pattern. 
     (13) Since the front surface fastener belt  63  is threaded through engaging hole  62  of fabric clamp  56 , this belt  63  is less likely to get lost. 
     According to a sewing machine of this embodiment, the following operating advantages can be achieved: 
     (14) Since cylindrical frame  19  is guided by means of guide member  27 , which is independent of needle plate  11 , it is possible to install needle plate  11  permanently on cylinder bed  2  in order to use it not only for cylindrical frame  19  but also to other type of frames such as a rectangular frame and an annular frame, thus eliminating the needs of replacing needle plate  11  on different applications. 
     (15) Since curved surfaces  11   a  are provided on the left and right shoulder areas of needle plate  11  facing the inner surface of cylindrical frame  19  in close ranges, it is possible to feed the work fabric W smoothly without being stuck on needle plate  11  and to provide a wide area on needle plate  11  for supporting the work fabric. 
     (16) Since partial cylindrical surface  30  is formed on the left and right side walls  27   b  of guide member  27  concentric with cylindrical frame  19  in a close range, cylindrical frame  19  can be guided in parallel with cylinder bed  2  in high precision. 
     (17) Since guide member  27  is formed in a open-ended rectangular shape, it is possible to attach guide member  27  rigidly on cylinder bed  2  via its connecting part  27   a,  thus effectively preventing vibration. 
     (18) Since partial cylindrical surface  30  is formed on the left and right side A walls  27   b,  it is possible to install bobbin case  4  and form a wide area of partial cylindrical surface  30  effectively using the limited space underneath needle plate  11  effectively. 
     (19) Since protection cover  28  is provided detachably on guide member  27 , bobbin cage  4  is not exposed and makes it safer when cylindrical frame  19  is not used, while the bobbin case  4  can be easily removed or installed by removing cover  28  during the bobbin exchange. 
     (20) Since partial cylindrical surface  36  is formed on protection cover  28 , this guide surface  36  provides a wide surface for guiding cylindrical frame  19  in cooperation with partial cylindrical surface  30  of guide surface  27 . 
     This invention should not be construed to be restricted with the embodiment described above, but rather can be materialized in various other ways without leaving the gist of the invention as exemplified below: 
     (a) To pivot-mount fabric clamping member  39  by a shaft at the rear end so that it can open or close vertically; 
     (b) To form the entire structure of fabric clamping member  39  with a rod material in an open-ended rectangular shape; 
     (c) To form a slit oblong in the axial direction in one of fabric clamps  56  of fabric clamping member  39 , and cause the rear belt  61  to be engaged with this slit in such a way as to make its position adjustable; 
     (d) To form core material clamping member  38  with a rod material in a shape oblong in the axial direction; 
     (e) To support core material clamping member  38  at its rear end via a shaft and spring mechanism rotating relative to cylindrical frame  19 . 
     (f) To provide core material clamping member  38  and fabric clamps  56  in positions vertically separated on both left and right sides of cylindrical frame  19 ; and 
     (g) To form a portion of the guide device for cylindrical frame  19  that corresponds to protection cover  28  integral with guide member  27  and provide on the outside of guide member  27  a partial cylindrical surface with an open portion at the top like a C-shape. 
     As can be seen from the above, the fabric tensioning device for a sewing machine according to this invention, the two fabric clamps on the left and right sides of the fabric clamping member are tightened against the cylindrical frame with two belts at the front and rear sides thereof, so that the work fabric can be clamped on four sides of the sewing area, providing an excellent result in securely tensioning the fabric on the circular frame causing no clamping marks or slacks.