Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of co-pending application Ser. No. 09/570,387 filed May 12, 2000. 
    
    
     This application claims the priority of German Application No. 199 21 913.3 filed May 12, 1999, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a sewing machine needle, particularly for rapidly operating sewing machines which have high stitch output. 
     As a rule, the output of current industrial sewing machines is 5,000 stitches per minute; in some applications even 8,000 or more stitches per minute are reached. 
     During the sewing operation the sewing machine needle penetrates the workpiece (hereafter referred to as fabric) to produce a stitch hole. The time available for opening the stitch hole is the period from the moment the needle point touches the fabric to the moment when the needle eye passes the stitch hole. Such an opening period is approximately 0.5 ms for a stitching machine which operates with 5000 stitches per minute. The opening of the stitching hole occurs as a rapid, almost explosion-like lateral displacement of the fabric During such an occurrence, high frictional forces are generated and thus high penetrating forces as well as high operating power for the sewing operation are required. 
     Sewing with a very high number of stitches per minute involves the risk of mechanical and thermal damage to the fabric. Fibers or even fiber bundles (yarns) may be torn apart as stitch holes are being formed. Further, the high friction forces may heat the needle to temperatures which, within a few seconds, may cause the usual synthetic fibers to reach their melting point. Such fibers then are melted or fused in the stitching zone. A further consequence may be frequent ruptures of the sewing thread. 
     The fusing of laminates and layers as well as color or other components may lead to further disturbances during the sewing operation. The discussed problems may lead to a deteriorated seam quality and may adversely affect the strength of the manufactured apparel. 
     Further, needles for sewing machines, particularly those which operate at high machine speeds, are exposed to relatively large mechanical stresses. Increasing machine speeds cause dynamic problems to an increased extent. The masses rotating in the sewing machine may cause vibrations which affect particularly the sewing machine needles clamped at one end. The sewing machine needles furthermore have to withstand external forces such as the pull of the thread, lateral excursions upon contacting the fabric as well as forces derived from handling the sewing machine by the operating personnel. If, for achieving an increased stability, thicker needles are used, the above-outlined problems become even more pronounced. 
     During sewing the thread must be protected from being damaged as it is pushed through the fabric by the needle. Therefore, in industrial sewing machines it is a desideratum that the needle, even in case of extremely high reciprocating speeds, ensures a substantially frictionless run of the thread during the entire stitch forming cycle. Since the thread thickness is in most cases predetermined for providing the desired seam strength, the sewing machine needle must guide the thread of predetermined thickness with low friction and must adequately protect the thread even in the high-speed range. Also, an excessive motion caused friction between the thread and the fabric is to be avoided in the high-speed range. In case such a requirement cannot be ensured, uncontrollable thread ruptures and misses in the stitching operation result. 
     German Offenlegungsschrift (application published without examination) 30 27 534 discloses a sewing machine needle having a laterally bent blade. A thread trough provided along the needle blade leads to a needle eye which is positioned in the vicinity of the needle point. The thread trough is defined by two lateral walls which extend into the eye region. The needle contour is substantially linear in the region of transition from the laterally bent zone to the needle point. The above-described difficulties during high-speed sewing operations may involve sewing machine needles of the above-outlined conventional type. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved sewing machine needle which is adapted for high-speed operation. 
     This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the sewing machine needle includes a central longitudinal axis; a blade extending at least partially coaxially with the axis and terminating in a point; and an eye passing through the blade transversely to the axis and having an opening direction. The eye has opposite openings on opposite sides of the blade. Two mutually spaced walls forming part of the blade have respective inner faces bounding the eye. An indentation is provided in the blade in a region of at least one of the eye openings. The indentation reduces the height of at least one part of the eye walls as measured from the axis. 
     The sewing machine needle according to the invention has a reduced volume of the eye cross section while the eye width remains the same and, at the same time, exhibits improved thread protecting characteristics. As a result, the stitch hole for the thread of a given thickness needs to be opened less wide than required conventionally, whereby friction effects on the sewing machine needle and the fabric are reduced. The reduction of the eye cross section is achieved by the indentation formed on the trough-side of the needle blade. Such an arrangement does not adversely affect the eye width and thus threads of usual or predetermined thicknesses may be used. 
     The indentation changes the deployment characteristic of the piercing force. The first force peak which dominantly occurs during the passage of the eye of a normal needle is in most cases significantly reduced. The maximum stitch hole widening occurs relatively gently only as the upper needle blade penetrates, that is, when the lowering motion of the needle becomes slower and approaches zero. The explosive effect which in case of a conventional needle occurs by virtue of the maximum stitch hole widening at the highest penetration velocity is minimized or prevented altogether. 
     According to the invention, advantageously a lesser piercing force is present, and thus a lesser energy input is required for the stitching process, accompanied, at the same time, by a lesser needle heat-up and a stitch hole opening process which treats the material gently. Further, the eye may be configured such that a high degree of thread protection is obtained, resulting in fewer stitch misses and thread breakage. 
     The indentation is preferably dimensioned in such a manner that at least at one location the eye walls have a total height which is slightly less than the height of a region which is situated between the needle point and the eye. As a result, it is feasible to equalize to some extent the width increase of the needle from the needle point to the needle eye by a simultaneously slight flattening to thus achieve an overall, only small cross-sectional increase of the needle. This feature reinforces the above-discussed advantages. 
     In accordance with an advantageous feature of the invention, the sewing machine needle has at least in one certain region of the eye a substantially constant overall height; this contributes to the delay of the stitch hole opening process during needle penetration. 
     The indentation of the sewing machine needle has, according to another advantageous feature of the invention, a substantially constant radius; the center of the curvature may be situated approximately at the height of the eye (that is, in a linear extension of the eye). The radius of curvature is preferably relatively large and is, according to an advantageous example, approximately three to four times the nominal needle thickness to be measured in a blade region of unreduced thickness. 
     While the sewing machine needle according to the invention has an indentation at the needle eye on the side where the thread trough extends, the eye walls at the opposite side of the eye are preferably of straight configuration, whereby in this location too, no projection or almost no projection beyond the eye is present. 
     The thickness of one and the same eye wall may vary from one side of the eye to the other. For example, it is advantageous if the eye walls have a slightly greater thickness at their side adjoining the indentation than at their side remote therefrom. In such a configuration the side walls of the needle may extend parallel to the central axis and may be arranged at an acute angle to one another in the transverse direction. 
     In accordance with a particularly advantageous feature of the invention, the sewing machine needle has a thread trough which extends into the eye region with an undiminished height. The height of the walls defining the thread trough are constant along the entire thread trough particularly up to the eye and the indentation formed in the eye region. This ensures a maximum thread protection while, at the same time, the eye is of very slim configuration and thus the widening process of the stitch hole is slow and the required piercing forces are small. 
     The blade of the sewing machine needle is advantageously provided with a laterally offset portion which defines a hollow part on that side of the needle which is remote from the thread trough. The hollow part provides a space for a thread gripper which engages the thread during seam formation. 
     According to an advantageous feature of the invention, the height of the thread trough walls is, in the region of transition into the eye, slightly increased which further enhances the protection of the thread. 
     As viewed in the direction of the central needle axis, the eye is advantageously bounded by rounded eye webs which are offset relative to the central axis. The rounding of the eye webs is so dimensioned that the ends of the eye webs are semicircular, and the axes of the rounding of the webs are offset with respect to one another by approximately one-half of the eye height. The arrangement is preferably such that a tangent passing through the eye forms, with the central needle axis, an angle which is preferably significantly smaller than 20°. A thread which runs taut through the eye and has a thread thickness which corresponds to the thickness of the sewing yarn, forms with the central axis an angle which is preferably also smaller than 20°. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional elevational view of a terminal portion of a sewing machine needle structured according to the invention. 
     FIG. 2 is a sectional view taken along line II—II of FIG.  1 . 
     FIG. 3 is a sectional view taken along line III—III of FIG.  1 . 
     FIG. 4 is a sectional view taken along line IV—IV of FIG.  1 . 
     FIG. 5 is a sectional view taken along line V—V of FIG.  1 . 
     FIG. 6 is a view similar to FIG. 1, illustrating a thread passing through the needle eye and depicting the arrangement before the penetrating step. 
     FIG. 7 is a view similar to FIG. 1, illustrating a thread passing through the needle eye and depicting the arrangement during the penetrating step. 
     FIG. 8 is a view similar to FIG. 1, illustrating a thread passing through the needle eye and depicting the arrangement shortly after reversing the direction of needle motion, during withdrawal of the needle. 
     FIG. 9 is a view similar to FIG. 1, illustrating a thread passing through the needle eye and depicting the arrangement during the reverse stroke of the needle and showing an ideally formed thread loop for being received by a loop gripper. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an end portion of a sewing machine needle  1  having a blade  2  which terminates in a needle point  3 . The blade  2  has a central longitudinal axis  4  which passes through the point  3 . The blade  2  extends from a non-illustrated needle shank at which the needle is clamped in a socket of the sewing machine (also not shown). 
     As seen from FIG. 2, in the left-hand portion of the FIG. 1 illustration, the needle blade  2  has, as viewed cross-sectionally, a rounded upper surface  5  and planar lateral faces  6  and  7 . At its underside  8  the needle  1  is provided with a thread trough  9  which is bounded by two side walls  10  and  11  which are connected by a trough bottom  12 . The transition between the walls  10  and  11 , on the one hand, and the trough bottom  12 , on the other hand, may be polygonal or rounded. 
     As shown in FIG. 1, the thread trough  9  extends along the blade  2  and an offset region  14  thereof in which the needle is laterally outwardly bent relative to the blade axis  4 . The offset region  14  defines a depressed needle portion  15  at the top side  5  of the needle  1 . The bottom surface  15   a  of the depressed portion  15  is at a small distance from the central axis  4 . The cross-sectional configuration of the needle  1  in this region is illustrated in FIG.  3 . As seen, in the offset region  14  the needle  1  is widened but is of a slightly flatter configuration as compared to the region illustrated in FIG.  2 . The cross sections of the blade  2  shown in FIGS. 2 and 3 are approximately of the same area; they are about 12% smaller than the nominal cross-sectional area. 
     The offset region  14  is adjoined by a transitional region  17  in which the center of the cross section is shifted back from an offset position onto the central axis  4  or the vicinity thereof. The thread trough  9  extends through the offset region  14  and the transitional region  17  to a needle eye  18  which, as shown in FIG. 1, is situated adjacent the needle point  3 . The eye  18  extends through the needle  1  in a direction which is the same as the direction of offset in the offset region  14 . As seen from the cross section illustrated in FIG. 4, the eye  18  is bounded by two eye walls  19  and  20  between which a passage  18   a  is formed The eye walls  19  and  20  are at their facing inner surfaces  21 ,  22  essentially of planar or slightly curved configuration and extend approximately parallel to one another, whereas the outer faces  6  and  7  of the respective eye walls  19  and  20  are oriented at an acute angle to one another. As a result of this arrangement, the eye walls  19 ,  20  have at the sides of the thread trough  9  a slightly greater wall thickness than on the side remote from the thread trough  9 . In this zone the total needle cross section is up to 10% less than the nominal needle thickness. 
     In the transitional region  17  an eye web  23  is formed whose end  24  borders the eye  18  in the axial direction (that is, in the direction of the central axis  4 ). The end  24  is rounded with the greatest possible radius and lacks any edges. The bottom  12  of the thread trough  9  thus extends without any edge up to the end  24  of the eye web  23 . The side walls  10 ,  11  of the thread trough  9  change from a first height H measured in the offset region  14  to a slightly enlarged height H 1  in a parallel region  25  in which the thread trough  9  extends obliquely to the central axis  4 . At the end of the parallel region  25  the lateral walls  10 ,  11  of the thread trough  9  merge into the eye walls  19 ,  20 . At that location, that is, in the region of the eye  18 , the eye walls  19 ,  20 , as shown in FIG. 1, are provided with an indentation  26  by means of which the eye inlet adjoining the trough  9  is offset towards the central axis  4 . The eye  18  is, along the needle axis  4 , adjoined by a conical needle region  27  which tapers toward and terminates in the needle point  3 . The largest radius of the conical region  27 , measured at the needle portion designated at  28 , is greater than the distance of the inlet of the eye  18  in the region of the indentation  26  from the central axis  4 . By virtue of this arrangement the inlet of the eye  18  is offset against the conical region  27 . The indentation  26  has, as shown in FIG. 1, a curvature, whose radius R has a starting point M which is, situated on the side of the thread trough  9  in the extension of the passage defined by the eye  18 . The radius R is approximately four times greater than the nominal needle thickness. 
     The indentation  26  is directly adjoined by a second eye web  29  which is rounded at its end  30  oriented towards the eye  18 . The eye web  29  merges into a concave bottom surface  31  on the side remote from the indentation  26 . The approximately circular cross-sectional configuration of this region is shown in FIG.  5 . At the transition of the eye  18  into the conical region  27  the cross section of the needle is slightly flattened. In this region the cross section is approximately 20% less than the cross section which corresponds to the nominal needle thickness. 
     The eye webs  23  and  29  are offset relative to one another transversely to the axis  4  at a distance which is at least 40% (preferably 50%) of a nominal needle thickness measured in a blade zone of unreduced blade thickness. Further, the eye webs  23  and  29  have a thickness, measured transversely to the axis  4 , which is at least 40% (preferably 50%) of the nominal needle thickness. 
     In the description which follows the operation of the above-described sewing machine needle will be set forth. 
     FIG. 6 shows the sewing machine needle  1  and a sewing yarn  32  which is positioned in the thread trough  9 . Then, in the end region of the trough  9  the yarn  32  changes direction and passes in a linear, taut condition through the eye  18  and thereafter bridges the concave bottom surface  31 . In this position of the sewing yarn  32  the needle  1  has not yet penetrated into the fabric. 
     The needle starts its approach towards the fabric and begins penetration thereof. First, the point  3  enters the fabric and thereafter, as the needle continues its axial motion, the conical region  27  enters the fabric and the stitch hole is widened until the eye  18  reaches the fabric. Such a widening occurs gradually and relatively uniformly so that the sewing yarn  32  may be pulled through the stitch hole and, while doing so, positions itself about the eye web  23  as shown in FIG.  7 . The fabric, during the piercing process, slides over the eye  18  and simultaneously the fabric is, by virtue of the height of the thread trough  9 , maintained at a distance by the parallel region  25  from the sewing yarn  32  situated in the thread trough  9 . Thus, the sewing yarn  32  may be pulled with high speed into the stitch hole without a substantial friction between the sewing yarn  32  and the fabric. Particularly in the eye region the sewing yarn  32  is effectively protected despite the slender configuration of the eye  18 . Such a result is made possible by a combination of the indentation  26  with a heightened (deepened) thread trough in the adjoining parallel region  25 . 
     Upon termination of the piercing step, the sewing machine needle  1  is withdrawn whereby the sewing yarn  32  first assumes its position illustrated in FIG.  8 . As seen, the sewing yarn lifts off the eye web  23  and subsequently forms a loop  33  as shown in FIG.  9 . The eye web  29 , by virtue of its lateral offset relative to the eye web  23 , prevents the sewing yarn  32  from exiting in the direction of the thread groove  9 . Rather, the sewing yarn  32  is pressed out of the eye  18  by the eye web  29  so that the desired loop  33  is reliably formed. Subsequently, as the sewing process progresses, the loop is received by a non-illustrated gripper. An accurately formed loop makes possible a disturbance-free sewing operation. 
     Thus, according to the invention, a sewing machine needle is provided particularly for high operating speeds, having a slender eye  18  which merges directly in a thread trough  9  running along the needle blade. At the side of the thread trough  9  the eye  18  is provided with an indentation  26  which results in a small eye cross section and thus the fabric will be exposed only to a small stress during the piercing process. In the transitional region from the thread trough  9  to the eye  18  the wall portions bounding that region are of such a height (as measured from the bottom  12  of the thread trough  9 ) that the sewing yarn  32  remains unexposed and is thus effectively held at a distance from the fabric. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

Technology Category: d