Abstract:
A presser foot for a sewing machine is provided with a pair of forwardly mounted, pivotal pressure shoes having inclined front and rear surfaces for maintaining continuous contact with the sewn material while stitching across raised, high seam material areas.

Description:
FIELD OF THE INVENTION 
     The present invention relates to presser feet for sewing machines and, in particular, to a presser foot for traversing a raised area without collateral noise and a loss of forward stitching speed. 
     BACKGROUND OF THE INVENTION 
     Sewing machines are generally provided with presser feet for holding the sewn material as the sewing needle is withdrawn. The presser foot is attached to a presser bar, which moves in alternate phase opposition to the needle carried by a needle bar. The foregoing arrangement works highly satisfactory in most instances. Difficulties, however, are presented when traversing raised areas wherein a cross panel is present, oftentimes referred to as a high seam. Generally, the presser foot will not ride over the raised area requiring interruption of the sewing, manually raising the presser bar to clear the raised area, stitching slowly thereacross, lowering the presser bar, and resuming normal stitching thereafter. In addition to the loss in sewing productivity, the raised presser bar during this period generates considerable undesirable noise. 
     Efforts have been made to overcome some of the above limitations including provisions for automatically raising the presser foot as disclosed in U.S. Pat. No. 5,899,157 to Kurono et al. Other provisions have been made as disclosed in U.S. Pat. No. 5,590,614 to Murata et al for preventing operation if the presser foot is not adequately cushioned. Additional presser foot control is disclosed in U.S. Pat. No. 5,718,182 to Nakayama et al. wherein a downwardly biased presser foot contacts the material during operation. The pivot axis is aligned with the presser bar and resent problems in high seam applications inasmuch as the reciprocating presser foot in the downward position engages the raised panel and precludes continued movement. Moreover, the trailing surface of the presser foot abruptly leaves the raised area and may create stitching discontinuities. 
     In view of the foregoing, it would be desirable to provide a presser foot for use in high seam applications wherein the foot freely advances over a raised area maintaining normal stitching speed and continuous affirmative contact with the material. 
     SUMMARY OF THE INVENTION 
     The foregoing objectives are accomplished in the present invention by a presser foot having a pair of spring biased pressure shoes having inclined leading and trailing ramped surfaces forward of the presser bar that allow the shoes to traverse and conform to a high seam area while maintaining continuous contact with the material. The shoes have a center horizontal lower presser surface for normal engagement with the material. As the leading surface engages the raised area, the shoes are reversely pivoted against spring biasing to conform to the material elevations. The shoes are normally biased to the horizontal position for traversing the raised area and reversely downwardly pivoted to bridge the material elevations upon exiting the raised area. By locating the shoes forward of the presser bar, continuous tracking with the material is achieved. Resultant, sewing speed may be maintained and the continuous pressure against the material reduces the noise attendant conventional raised presser foot positioning. 
     Accordingly, it is an object of the present invention to provide a presser foot for high seam sewing that allows sewing speeds to maintained without interruption for repositioning the presser foot. 
     Another object of the invention is to provide a presser foot that maintains continuous contact with the sewn material while traversing raised stitching area thereby eliminating collateral noise. 
     A further object of the invention is to provide a presser foot for a sewing machine having inclined leading and trailing surfaces forward of the presser bar that conform to changes in sewing elevations without requiring a slowing of stitching speed or presser foot repositioning. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become apparent upon reading the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective view of a presser foot in accordance with an embodiment of the invention; 
     FIG. 2 is top view of the presser foot shown in FIG. 1; 
     FIG. 3 is a side cross sectional view taken along line  3 — 3  in FIG. 2; 
     FIG. 4 is front elevational view of the presser foot; 
     FIG. 5 is an enlarged fragmentary cross sectional view taken along line  5 — 5  in FIG. 2; 
     FIG. 6 is a schematic view of the presser foot advancing toward a raised panel; 
     FIG. 7 is a schematic view of the presser foot advancing over a raised panel; 
     FIG. 8 is a schematic view of the presser foot traversing the raised panel; and 
     FIG. 9 is a schematic view of the presser foot exiting the raised panel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings for the purpose of describing the preferred embodiment and not for limiting same, FIG. 1 illustrates a presser foot  10  having a support yoke  12  that is adapted to be attached to a reciprocable presser bar, not shown, and carries at laterally spaced legs  16  a pair of pivotal presser shoes  18  and  19 . 
     The support yoke  12  includes a rectangular body  20  having a vertical bore  22  extending centrally through the top wall  24  for receiving the lower end of the presser bar. The body  20  includes a split rearwardly projecting tab  26  having tab sections  28  separated by a vertical slot  30 , which intersects the bore  22 . A threaded fastener  32  includes a shank that extends through an aperture in the adjacent tab section for clamping the tab sections to thereby engage the presser bar and retain the presser foot thereon. It will be appreciated that the foregoing mounting is typical of one version of the presser foot attachment and that other conventional presser bar attachments may be accomplished in any acceptable manner. 
     Referring additionally to FIGS. 2 through 4, the support arms  16  extend forwardly from the lower outer surface of the body  20  and are laterally spaced by a center groove  40 . Each arm  16  frontally terminates at a beveled tip  42  having a depending knuckle  44  pivotally connected to the shoes  18  and  19  by mounting pin  48 . The shoes  18  and  19  each include a horizontal center section  60 , an upwardly and forwardly inclined toe section  62 , and an upwardly and rearwardly inclined heel section  64 . The center section  60  includes upwardly extending, laterally spaced outer and inner flanges  66  and  67  defining a transverse groove in which the knuckles  44  are slidably received. By locating the pin  48  forwardly on the arms, the shoes are located entirely forwardly of the reciprocal axis of the presser bar. 
     Referring to FIG. 5, the flanges  66 ,  67  and knuckle  44  have horizontally aligned clearance holes for slidably receiving the mounting pin  48 . A vertically threaded hole  68  is formed in the tip  42  of the arm  16  and the knuckle that intersects the mounting pin  48 . A set screw  69  is threaded in the hole into engagement to axially fix the pin in the knuckle  44  and permit the shoes to rotate about the pin  48  as shown in FIGS. 6 through 9. 
     The flanges on the center sections  60  terminate with a horizontal top wall  80  parallel to the bottom surface of the center section  60 . The biasing spring  52  includes a center coiled section  72  and outwardly extending upper and lower arms  74  and  76 . The upper arm  74  is retained between the outer wall of the arm  16  and the head of the fastener  52 . The lower arm  76  is disposed in a transverse groove in the top wall  80  for normally maintaining the horizontal orientation of the shoes, while yieldingly accommodating pivoting of the shoes during sewing operations. 
     The pressure shoes may be varied within the above criteria to handle differing materials and sewing constructions. In order to handle welts, a semicircular recess  82  may be formed on the inner wall of one of the shoes as shown in FIGS. 4 and 5. The width of the side flange  67  may be increased appropriately to handle the recess. The surface texture of the lower surfaces may also be varied. For example, a smooth surface would be preferred for materials such a leathers, while a roughened or knurled surface would be preferred for certain fabrics. 
     Referring to FIGS. 6 through 9, in operation as the pressure shoe  100  reaches a transverse raised panel  102  on bottom panel  103  requiring high seam stitching thereover, the toe section  104  engages the leading surface of the panel  102  and effects pivoting of the shoe  100  against the biasing of the spring  105  relative to the presser arm  106 . As the stitching and material advance continues, the toe section  104  and the center section  110  progressively slide over the leading edge of the panel until the heel section  112  is adjacent thereto and lies flat on the bottom panel  103  as shown in FIG.  7 . Thereafter, the shoe reversely pivots against the biasing of the spring arm  114 , lying flat on the raised panel as shown in FIG.  8 . The slightly increased resultant elevation of the pivot pin is readily accommodated by the compensating springs in conventional presser bar mechanisms. As the presser shoe leaves the raised panel, the shoe downwardly pivots with the toe section  104  engaging the bottom panel  103 , as shown in FIG.  9 . Further advances disengage the shoe from the raised panel. 
     It will be appreciated that at all times during traverse of the raised panel positive contact in maintained between the presser shoe surfaces and the materials thereby reducing machine noise attendant the conventional raised pressure foot during such an operation. The continuous pressure ensures proper thread tensioning throughout the travel. Moreover, the ability of the presser shoes to gradually accommodate to the changes in elevation allows continuous feeding without interruption or slowdown. 
     While the inclination and length of the toe and heel sections will depend on the details of the sewn construction, testing has revealed that extremely high productivity can be obtained over a wide range of fabrics and raised panels with heel and toe inclinations in the range of about 15 0  to 45 0 , with preferred inclinations in the range of about 20 0  to 35 0 . It is preferred to have a toe section length about the same as the center section, and a heel section of the same or shorter length. Such relationships provide affirmative pressures in the stitching area and gradual transitions between the panel surfaces. Highly satisfactory results have been demonstrated on high-speed single needle lockstitch machines using alternating presser and walking fit with a high seam pressure foot having 0.25 inch shoe widths, 0.75 inch toe section length inclined 28 0 , and a 0.32 in heel section length inclined 23 0 , and the pin  48  1 in. from the axis of the presser bar bore  22 . 
     Having thus described a presently preferred embodiment of the present invention, it will now be appreciated that the objects of the invention have been fully achieved, and it will be understood by those skilled in the art that many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the sprit and scope of the present invention. The disclosures and description herein are intended to be illustrative and are not in any sense limiting of the invention, which is defined solely in accordance with the following claims.