US3023722A - Sewing machine feeding mechanism - Google Patents

Description

March 6, 1962 R. E. JOHNSON 3,023,722

SEWING MACHINE FEEDING MECHANISM Filed Jan. 25, 1960 '3 Sheets-Sheet 1 INVENTOR. RALPH E. Jamvsozv BY WZI'TTORNEY WITNESS March 6, 1962 R. E. JOHNSON SEWING MACHINE FEEDING MECHANISM '3 Sheets-Sheet 2 Filed Jan. 25, 1960 INVEN TOR BY RALPH E. JOHNSON 6 ZTORNEY WITNESS March 6, 1962 R. E. JOHNSON SEWING MACHINE FEEDING MECHANISM 3 Sheets-Sheet 3 Filed Jan. 25, 1960 RALPH E. JOHNSON BY ATTORNEY WITNESS United States Patent 3,023,722 SEWING MACHINE FEEDING MECHANISM Ralph E. Johnson, Mountainside, N.J., assignor to The Singer Manufacturing Company, Elizabeth, N.J., a corporation of New Jersey Filed Jan. 25, 1960, Ser. No. 4,429 3 Claims. (Cl. 112210) The present invention relates to sewing machines and particularly to a feeding mechanism for sewing machines.

The object of this invention is to provide a feeding mechanism for sewing machines in which the rise of the feed dog above the throat plate is adjustable and wherein the adjustment will have a minimum effect upon the overall feed lift motion of the feed dog and thereby will not appreciably vary the path of motion of the feed dog.

Further objects of this invention are to provide such a feed adjustment that is economical, simple to adjust, and dependable and durable.

Having in mind the above and other objects that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations and arrangements of parts as illustrated in the presently preferred embodiment of the invention which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction with the accompanying drawings in which:

FIG. 1 is a vertical sectional view longitudinally of a sewing machine embodying the present invention,

FIG. 2 is a bottom plan view of the bed of the sewing machine of FIG. 1,

FIG. 3 is a fragmentary detail sectional view substantially on the line 33 of FIG. 2,

FIG. 4 is a sectional view substantially on the line 44 of FIG. 2,

FIG. 5 is a sectional view substantially on the line 5-5 of FIG. 2,

, FIG. 6 is a fragmentary detail sectional view similar to FIG. 3 but on a larger scale and illustrating the feed lift cam in different positions,

FIG. 7 is a fragmentary detail sectional view substantially on the line 77 of FIG. 3.

The present invention is illustrated as embodied in the sewing machine forming the subject matter of the copending United States patent application of Johnson, Serial No. 4,430, filed January 25, 1960, wherein the machine is fully disclosed and to which reference may be had for a more complete understanding of the machine.

With reference to the drawings, there is illustrated a sewing machine having a frame including a bed 1, a standard 2 rising from one end of the bed and carrying a bracket arm 3 terminating in a head 4 overhanging the bed 1. The top of the bed 1 is formed by a bed plate 5. Journaled longitudinally of the bracket arm 3 is a rotary main shaft 6 that is driven by an electric motor 7 mounted in the standard 2 and connected by a belt 8 to a hand wheel 9 secured on the end of the main shaft 6.

The stitching mechanism of the machine comprises a needle bar 10 mounted in the head 4 for endwise reciprocation and driven from the main shaft 6 by a crank 11 and link 12. Beneath the needle bar 10, the bed plate 5 has a throat plate 13, the upper surface of which, together with the upper surface of the bed plate 5, defines the work supporting surface of the machine. At its lower end the needle bar 10 carries a needle 14 which, upon endwise reciprocation of the needle bar 10, penetrates the throat plate 13 and cooperates with a vertical axis oscillating book 15 in the bed 1 and thereby defines the point of stitch formation on the work supporting sur face of the machine. The hook 15 is mounted upon a hook shaft 16 journaled in a supporting wall 17 integral 3,023,722 Patented Mar. 6, 1962 with the bed plate 5. Oscillation is imparted to the hook shaft 16 by a vertical axis shaft 18 journaled in the standard 2 and connected by gears 19 and 20 to the main shaft 6. On the lower end of the shaft 18 is a crank 21 connected by a pitman 22 to one arm 23 of a bell crank lever pivotally mounted intermediate its ends at 24 on the wall 17. The other arm 25 of the bell crank lever is connected by a link 26 to a crank arm 27 secured to the lower end of the hook shaft 16.

Work is adapted to be advanced across the work supporting surface of the machine past the point of stitch formation by a four motion feeding mechanism comprising a feed bar 28 carrying a feed dog 29 operating through feed dog slots in the throat plate 13 to engage the work. Journaled longitudinally of the bed at the front of the machine is a feed advance shaft 30 having rock arms 31 which are pivotally connected to one end of the feed bar 28. Oscillation is imparted to the feed advance shaft 3%} by an eccentric 32 on the main shaft 6 which is embraced by a fork on the upper end of a pitman 33. Intermediate its ends the pitman 33 has a laterally extending pin 34 extending into a groove 35 in a block 36 that is pivotally mounted in a transverse wall of the frame by means of a stud 37 and which includes a handle 38 extending to a position accessible to the operator. At its lower end, the pitman 33 is connected to a crank arm 39 on the feed advance shaft 30.

The feed lift mechanism comprises a feed lift shaft 40 journaled in the rear of the bed 1 by cone shaped end bearings 41 in bearing lugs 42 and 43. The one end of the feed lift shaft 40 has a crank arm 44 which at its free end is connected by a link 45 to the feed bar 28 for imparting feed lift motions to the feed bar 28 upon oscillation of the feed lift shaft 40. At the other end of the feed lift shaft 40 there is a second crank arm 46 having a hub 47 at its free end that receives a cylindrical pin 43 mounted therein for turning adjustment, which turning is facilitated by a screw driver slot 49 in the end thereof. The pin 48 is secured in its adjusted position by a set screw 50. Integral with the pin 48 is a stud 51 that is eccentric relatively to the axis of the pin 48. A cam follower element 52 is pivotally mounted on the stud 51 and is held thereon by a screw 53. The crank arm 46 is disposed to locate the cam follower element 52 in engagement with an axial displacement cam surface 54 formed on the upper surface of the crank 21. A coil compression spring 55 is disposed between the crank arm 44 and the underside of the bed plate 5 to bias the feed lift mechanism in the direction to lower the feed bar 28 and to hold the cam follower element 52 in tracking engagement with the cam surface 54. Thus, upon rotation of the crank 21 oscillation is imparted to the feed lift shaft 40.

The crank arm 44 is located adjacent to the lug 43 and is offset to position the link 45 in a plane normal to the lug 43, and the crank arm 46 is located adjacent to the lug 42 and is also offset to position the cam follower element 52 close to a plane normal to the lug 42. In this manner substantially only torsional forces are applied to the shaft 40 with a minimum of bending. The spring 55 also serves to pre-stress the feed lift shaft 40 and thus minimizes torsional deflection of the shaft.

The feed path, which is the path of motion of a selected point on the feed dog 29, is a function of the motion imparted to the feed dog by the feed advance shaft 30 and the feed lift shaft 49. The desired feed path and the timing of the feed motion are determined by basic considerations, for example, experience has shown that a particular rise of the feed dog above the throat plate produces an optimum engagement of the feed dog against the work, a relatively flat motion of the feed dog during feeding is desirable, the feed must be operative while the needle is out of the work and preferably as late as possible in the cycle, and the stitch length should be adjustable from Zero to a predetermined maximum. There are also various mechanical considerations, for example, the feed dog overlies the hook and must be designed so that there is always adequate clearance between the two but which, at the same time, locates the hook as close as possible to the throat plate to provide a minimum needle bar stroke.

The mechanics of the system are designed to produce a desired feed motion, which always represents some compromise that is determined by trial and error to be best suited to the particular sewing machine. Once established, the system cannot be freely changed since any changes in relative timing between the feed lift motion and feed advance motion, and any changes in the amplitude of the motions will produce changes in the feed path, thus destroying the designed optimum.

In the present machine, the timing of the feed advance is obtained by the angular position of the eccentric 32 on the main shaft 6. Since the angular position of the crank 21 on the shaft 18 is fixed by the hook requirements, the timing of the feed lift is obtained by the configuration of the cam surface 54 on the crank 21.

Having determined the feed lift motion necessary to obtain the desired feed path, it then becomes necessary to obtain the desired rise of the feed dog 29 above the throat plate 13. This of course can be obtained by design and by maintaining strict manufacturing tolerances. However, this is relatively expensive. To reduce manufacturing costs, it would be preferable to provide a construction in which the manufacture of the element is less critical and which is adjustable to obtain the desired alignment of the parts. In the present machine, this adjustment has been provided by the eccentric stud 51. By rotating the pin 48, the feed lift is adjusted to provide the desired rise of feed dog 29 above the throat plate 13.

Such an adjustment in the feed must be made without altering the mechanics 'of the system such as to vary the feed path significantly. In the operation of the present machine, the displacement of the cam follower element 52 by the cam surface 54 produces a certain angular movement of the crank arm 46, the feed lift shaft 40 and the crank arm 44, thus producing a certain feed lift motion. The angular movement of the crank arm 46 for any given displacement of the cam follower element 52 is a dependent upon the location of the cam follower element 52 radially relatively to the pivot axis of the crank arm 46, which is the axis of the feed lift shaft 40. Shortening the radius will produce an increased angular movement of the crank arm 46 while lengthening the radius will produce a reduced angular movement of the crank arm 46. Upon turning the pin 48 to adjust the rise of the feed dog, the eccentric stud 51 moves in an arc about the axis of the pin 48, thus having a first component in a direction tangential to the arc of motion of the pin 48 about the axis of the feed lift shaft 40, which direction is substantially vertical, and which component adjusts the feed lift motion to obtain the desired rise of the feed dog above the throat plate. However, the pin 48 also has a second component of motion that is in a plane that is substantially horizontal and is defined by the axis of the feed lift shaft 40 and the pin 48. In effect this second component varies the lever arm between the axis of the 'feed shaft 40 and the point at which the force is applied by the cam follower element 52 to the crank arm 46, i.e., the axis of the stud 51. Such a variation, changes the feed path.

To minimize the effect upon the effective length of the crank arm 46 by the eccentricity of the stud 51, there is provided a stop shoulder 56 on the crank arm 46 that is designed to be engaged by the edge 57 of the cam follower element 52 when the stud 51 is adjusted to its maximum and minimum positions in the direction tangential to I the arc of motion of the pin 48 about the axis of the feed anism such that the desired setting of the eccentric is at the midpoint of its arc of adjustment, and by making the eccentricity of the stud 51 more than the normally required adjustment, a minimum of the undesired displacement of the stud 51 is obtained. I J

The axis of rotation of the crank 21, which is the axis of the shaft 18, is normal to a horizontal plane containing the axis of the feed lift shaft 40, and the axis of the pin 48 is parallel to the axis of the feed lift shaft 40 and intersects the axis of the shaft 18. The cam surface 54 on the crank 21 is planar and inclined to effect a displacement of the cam follower element 52 axially of the shaft 1-8. The cam follower element 52 has a cam engaging surface 58 which is arcuate in a direction radially of said cam surface 54 and is defined by straight Pafa lines in a direction perpendicular to the radius of said cam surface. The cam follower element 52 is free to pivot about the axis of the stud 51 and because of the arcuate configuration of the cam engaging surface 58 and the planar configuration of the cam surface 54 there is line contact between the cam engaging surface 58 and the cam surface 54 which, as the cam surface 54 is rotated and presents a differently inclined surface to the surface 58, shifts the line of contact across the surface 58 between the lines A and B, FIG. 6. In this manner there is provided a substantial bearing between the surfaces 54 and 58 which can accommodate the variations in the inclination of the cam surface 54 as it rotates, and also reduces wear on the cam engaging surface 58 by continuously shifting the line of engagement to distribute the wear over a large area. At the same time, by virtue of the fact that the line of contact is a straight line perpendicular to the radius of the cam surface 54, the points of contact along the line are spaced different distances from the axis of the crank 21 e.g., as seen in FIG; 7, the ends of line of contact A engage the surface 54 along a circle C while the midpoint engages along a circle D,- and the ends of the line B engage the cam surface 54 along a circle E while the midpoint engages along a circle F. Thus there is defined an annular engaging surface on the cam surface 54 extending between the circles C and F, which again reduces wear by distributing it over a large area.

Having thus described the nature of this invention what I claim herein is:

:1. In a sewing machine having a frame including a bed having a work supporting surface, stitching mechanism defining a point of stitch formation on said work supporting surface, and feeding mechanism for advancing work past said point of stitch formation comprising a feed advance shaft journaled in said bed and having a rock arm, a feed bar pivotally connected to said rock arm, a feed dog carried by said feed bar, means for imparting oscillation to said feed advance shaft, a feed lift shaft journaled in said bed, means for connecting said feed lift shaft to said feed bar for imparting feed lift motions to said feed bar upon oscillation of said feed lift shaft, a cam and cam follower means on said feed lift shaft and cooperating with said cam for imparting oscillation to said feed lift shaft and for adjusting the rise of said feed dog relatively to said work supporting surface, comprising a crank arm on said feed lift shaft, a pin mounted in said crank arm for angular adjustment, means for releasably securing said pin in angularly adjusted position in said crank arm, an eccentric stud on said pin, and a cam fol-lower element mounted on said stud and engaging said cam and means for limiting angular adjustment of said pin substantially to one half of one revolution in an are that at its midpoint has a tangent parallel to a tangent to the arc of the oscillation of the stud about the axis of the feed lift shaft.

2. In a sewing machine in accordance with claim 1 in Which said last mentioned means comprises a stop shoulder on said crank against which said cam follower element engages in its maximum and minimum positions.

3. In a sewing machine having a frame including a bed having a work supporting surface, stitching mechanism defining a point of stitch formation on said Work supporting surface, and feeding mechanism for advancing work past said point of stitch formation comprising a feed advance shaft journaled in said bed and having a rock arm, a feed bar pivotally connected to said rock arm, a feed dog carried by said feed bar, means for imparting oscillation to said feed advance shaft, a feed lift shaft journaled in said bed, means for connecting said feed lift shaft to said feed bar for imparting feed lift motions to said feed bar upon oscillation of said feed lift shaft, a cam mounted on an axis normal to a plane containing the axis of said feed shaft and having an axial displacement planar cam surface, and cam follower means on said feed lift shaft and cooperating with said cam surface for imparting oscillation to said feed lift shaft, said cam follower means comprising a crank arm on said feed lift shaft, a pin mounted in said crank arm on an axis parallel to the axis of said feed lift shaft, a cam follower element carried by said pin and engaging said cam surface, said cam follower element having a cam engaging surface that is arcuate in a direction radially of said cam and is defined by straight parallel lines in a direction perpendicular to the radius of said cam surface.

15 References Cited in the file of this patent UNITED STATES PATENTS 1,612,500 Ezbelent et a1. Dec. 28, 1926 2,808,793 Ay es Oct. 8, 1957 20 2.899.920 Dunn Aug. 18, 1959

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