GB2060722A - A sewing machine - Google Patents

Abstract

A sewing machine is provided with a workpiece trimming device comprising a fixed blade (14) mounted in one side of a presser foot (24) and a movable blade (15), which is operatively associated with the underside of the fixed blade (14) and reciprocally driven within a passage (52) disposed on the opposite side of the presser foot (24) and in alignment with the fixed blade (14). A first biasing spring (35) acting on the presser bar (33) continually urges the presser foot (24) towards the needle plate and a second biasing spring (53) acting in the opposite direction maintains contact between the fixed blade (14) and the movable blade (15). The first and second biasing springs (34, 53) acting in opposite directions favour improved control of the intended functions of the presser foot and cooperating trimming blades. <IMAGE>

Description

SPECIFICATION A sewing machine The present invention relates to a sewing machine provided with a cutting device for trimming adjacent edges of pieces of fabric being joined by means of flat seam stitching with a covering stitch in the sewing machine.

When two pieces of material are to be joined by seaming so that their sewn edges are disposed in co-planar and contiguous relation, it is common practice to feed the two pieces into the machine so that the finished and joined edges are formed adjacent to the original edges of each piece which are severed from the latter immediately prior to the seaming operation. This is accomplished by positioning the pieces so that a major portion of each is disposed in the same horizontal plane and with the adjacent edges of each being turned at right angles to the horizontal plane and in abutting relationship with each other. These abutting edges are caused to enter a guide in the presser foot of the machine and are severed from the two pieces just prior to the latter being subjected to the seaming operation of the flat-seam and covering stitch type.

To perform such seaming operations, which are commonly referred to as cut-stitch operations, trimming devices are provided which include a fixed blade, which is disposed horizontally in the base of the presser foot and which extends perpendicularly to the direction of advance of a workpiece. Such trimming devices also include a movable blade carried by a movable support which locates it in operative association with the fixed blade; the movable support is operatively connected to any suitable actuating mechanism of the machine itself. The movable support is also provided with a biasing means to maintain contact between the fixed and movable blades.The presser foot is attached to the lower end of the fabric presser bar, which is supported in the frame of the sewing machine and which is continuously biased by spring means associated with the presser bar in the direction of a usual needle plate which is mounted in the work surface that supports the workpieces during the sewing operation. Conventional transport means or feed dogs cooperate in a known manner with the underside of the presser foot to effect advance of the workpiece during the seaming operation. The biasing means operatively associated with the movable support so acts on the movable blade as to continually urge it into contact with the fixed blade even when the presser foot is being displaced in an upwardly direction away from the needle plate.

In known types of trimming device described above, the fixed blade is supported in the base portion of the presser foot so as to be in relatively close proximity with the needle plate and the movable blade is located above and in operative association with the fixed blade, the biasing means for the movable support maintaining the two blades in operative contact by pressing downwardly on the movable blade thus effecting its actuation in a positive manner. This downward force on the movable blade coupled with the biasing means acting on the presser bar causes the feed dogs to be subjected to what is considered to be an excessive amount of downward force by the presser foot. As a result, the feed dogs in order to perform their intended function must overcome the combined forces of both biasing means associated with the presser bar and the movable blade.

Both of these biasing means must be capable of producing selected and accurate amounts of force which differ one from the other in view of the function each is to perform. In particular, the biasing means for the presser bar should be such that the force it exerts while cooperating with the feed dogs will not have any damaging effects on the structure of the workpiece being advanced therebetween. Additionally, the biasing means for the movable support must be sufficient to maintain operative contact between the two blades without subjecting them to too great a biasing force which would result in excessive wear and a shortened life expectancy of the blades.

These factors are considered serious in known trimming devices for it is quite difficult and timeconsuming to obtain the most desirable setting of each of the two biasing means so that the forces they provide will be the most advantageous for the particular characteristics of the material forming the workpiece.

Additionally, the biasing means for the movable supports in the known trimming devices are subjected to compression forces caused by the upward movement of the feed dogs and passing through the fabric to the presser foot and in an upward direction that opposes the spring force pressing of the fabric, the compression forces being transmitted to the biasing means acting on the movable blade. This condition occurs particularly when contact between the two blades is such that their cutting edges are in a spaced relation which defines their inactive or rest position and places undue stress on the movable blade. This condition also creates an unbalanced condition in the presser foot which is to be attributed to the biasing means of the movable support that creates a greater degree of compression on that side of the presser foot at which the movable blade is operating.

As a result of the increased forces on one side of the presser foot, the fabric being advanced by the latter has a tendency to become misaligned or in other words, the fabric is urged to rotate out of alignment with the intended path it should follow during its advancement.

According to the present invention, there is now provided a sewing machine provided with a work surface and comprising a needle plate mounted on the work surface, a presser bar, feed dogs operatively associated with the needle plate, a presser foot supported by the presser bar for cooperation with the feed dogs, and a trimming device comprising a fixed blade mounted horizontally within the presser foot and extending perpendicularly to the direction of workpiece advancement, a presser spring operatively associated with the presser bar to urge the presser bar in the direction of the needle plate, a guide passage provided in one side of the presser foot in alignment with the fixed blade, a movable blade, supporting means to support the movable blade for reciprocating movement within the guide passage and in operative contact with the underside of the fixed blade, and biasing means mounted on the supporting means for urging the movable blade into engagement with the fixed blade and in a direction opposite to the direction of force provided by the presser spring on the presser foot.

Causing the biasing means associated with the movable support to act on the movable blade in a direction opposite to the biasing means acting on the presser foot provides a means, by which the desired amount of pressure between the two blades can be obtained and maintained, i.e. the pressure best suited to the particular type of material forming the workpiece. Additionally, while the feed dogs project above the needle plate, there is a limited amount of release of pressure between the two blades, since the fixed blade, which is being raised together with the presser foot, permits the spring forming the biasing means for the movable blade to increase in length thereby slightly reducing the biasing force with which the movable blade engages the fixed blade.

The device can be made effective to reduce frictional wear between the two blades to a minimum and to maintain the presser foot in a balanced state, in which its underside maintains full contact with the workpiece so that the latter advances along its intended path of travel without any deviations therefrom.

An embodiment of the present invention will now be more particulariy described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a portion of a workpiece showing two cutting blades of the trimming device of Fig. 2 in operative association with the edges thereof; Fig. 2 is a perspective view of a portion of a sewing machine provided with a trimming device and embodying the present invention, and Fig. 3 is a sectional view as seen looking in the direction of the arrows on line Ill-Ill in Fig. 2.

Referring now to the drawings, a portion of a workpiece shown in Fig. 1 is formed by two pieces of material 10 and 11 with their respective edges 12 and 13 being folded to extend in side by side relation in a plane substantially perpendicular to that containing the remainder of the pieces. The two edges 12 and 13 to be trimmed are cut by two operatively associated blade elements which comprise a stationary or fixed blade 14 and a blade 15, which is caused to move alternately to and fro in the directions indicated by the double arrow X and which is effective in severing the edges to be trimmed while the fabric pieces are stationary between two successive steps for advancing it. Immediately following the cutting region, a so-called flat-seam is being formed which includes seaming stitches 1 6 and covering stitches 1 7.This type of seaming is well known to those skilled in the art and it is therefore considered unnecessary to describe it in further detail here.

To accomplish the trimming operation, the fabric pieces are fed onto the work surface of the machine which includes the usual needle plate 18 that forms a part of the framework 1 9 of the sewing machine. The edges to be trimmed are inserted in an opening or guide passage 20 formed between two spaced arms (Fig. 2) of a presser foot 24. These edges are guided by a wall 22 forming the sides of the guide passage to the location of the blades 14 and 1 5, the severed edge portions then being removed laterally by means of a guide 23. In Fig. 2, the indicating arrow Y identifies the direction of advance of the workpiece. The presser foot 24 includes a base portion 25, one side of which is adapted to fixedly support the fixed blade 14 therein by means of a screw 26.This fixed blade also includes a longitudinally extending finger 27 disposed at one end thereof serving to guide and maintain contact with the movable blade 1 5 when the latter during its movement is at a distance furthest from the location of performing its trimming function. As shown in Fig. 2, the needle plate 1 8 includes the usual openings 28, which provide the well known means for feed dogs 29 of a fabric transport device to perform its intended function. The feed dogs in known manner travel in a generally elliptical path by being caused to move upwardly in the direction of the presser foot, thence in the direction of arrow Y and then downwardly and back to their initial position to repeat the cycle.

During the advancing movement in the direction Y and in particular at the start of this movement, the feed dogs of the transport device apply stress through the fabric on the presser foot and produce an upwardly directed force on the latter. Advance of the workpiece is accomplished by means of a conventional sawtooth configuration 30 of the upper surface of the feed dogs 29. As shown in Fig. 2, the presser foot also includes openings 31, through which a needle (not shown) of the machine is caused to travel during the sewing operation.

The presser foot 24 is supported in conventional manner by a support 32 connected to a fabric presser bar 33 which is housed so as to be slidable in the vertical direction within a sleeve 34. The fabric presser bar 33 is biased in a downwardly direction by means of a fabric presser spring 35 and the biasing force of the latter can be adjusted by means of a regulating plunger 36. The fabric presser bar transmits a pre-selected amount of force on the presser foot 24, which force passes through the fabric and to the teeth of the feed dogs. When the feed dogs are raised, they cause simultaneous raising of the presser foot to result in a slight compression of the fabric presser spring 35, which increases the biasing force being applied to the presser foot.

The movable blade 1 5 is carried by a support arm 37 connected to the sleeve 34 and is caused to oscillate in the directions indicated by the double arrow Z by means of an eccentric member 38 operatively connected therewith and mounted on a rotatably driven shaft 39. The means operatively connecting the eccentric member 38 with the support arm 37 include a connecting rod 40 (Fig. 2) having a pin 42 which interconnects it with one end of an arcuate arm 43, the opposite end of which is fixed on the sleeve 34 so as to cause the sleeve and support arm to oscillate about the axis of the fabric presser bar 33. This driven shaft 39 and the eccentric member 38 are housed in the upper horizontal arm (not shown) of the sewing machine.

The support arm 37 has a U-shaped bracket 44 at the end opposite the end attached to the sleeve 34. The arms 45 and 46 of this bracket have bushings 47 and 48 respectively attached thereto in vertically aligned relation and serve to support a rod 49 for sliding movement therein. The lower end of rod 49 carries a support block 50 which supports the movable blade 1 5 by means of a locking screw 51. From the support block 50, the movable blade 1 5 extends in the direction of and into an opening or guide passage 52 (Fig. 3) provided in one side of the presser foot 24. The location of the movable blade 1 5 is such that it is disposed below the fixed blade 14 and its longitudinally extending finger 27, in other words the movable blade 1 5 is closer than the fixed blade 14 to the needle plate.The biasing force of the movable blade 1 5 against the fixed blade 14 and the finger 27 is provided by means of a helical spring 53, which presses at one end against the bushing 47 fixed to the arm 45 of the bracket 44, and at the other end against a stop element 55 fixed on the rod 49 in an adjustable manner by means of a screw 56. A finger 57 on the stop element 55 rests against a vertically extending guide 58, which is fixed to the bracket 44 intermediate its arms 45 and 46 and serves to prevent oscillation of the movable blade 15.

In operation, the biasing force provided by the helical spring 53 is directed toward the stop element 55 urging the latter and the rod 49 upwardly so that the movable blade 1 5 is also urged upwardly into frictional contact with the fixed blade 14 and its longitudinally extending finger 27. Additionally, it is possible to regulate the biasing force which the spring 53 produces so as to provide the most desirable operating pressure between the two blades 14 and 1 5 independently of the biasing force provided by the fabric presser spring 35. When the presser foot 24 is raised by the feed dogs 29, the fixed blade 14 moves upwardly therewith and such movement subjects the spring 35 to further compression. As a result, the movable blade 1 5 is also raised under the action of the spring 53 and the biasing force provided thereby is reduced so that there is a reduction in the biasing force by the blade 1 5 on the finger 27, if the advancing operation occurs while the blade 1 5 is in the rest position shown in Fig. 2. By causing the helical spring 53 and the spring 35 to act in opposite directions, it is possible substantially to reduce frictional wear between the two blades 14 and 1 5 and to maintain the presser foot 24 in a balanced state so that the workpieces will not become misaligned from their intended path of advancement.

Claims (5)

1. A sewing machine provided with a work surface and comprising a needle plate mounted on the work surface, a presser bar, feed dogs operatively associated with the needle plate, a presser foot supported by the presser bar for cooperation with the feed dogs, and a trimming device comprising a fixed blade mounted horizontally within the presser foot and extending perpendicularly to the direction of workpiece advancement, a presser spring operatively associated with the presser bar to urge the presser bar in the direction of the needle plate, a guide passage provided in one side of the presser foot in alignment with the fixed blade, a movable blade, supporting means to support the movable blade for reciprocating movement within the guide passage and in operative contact with the underside of the fixed blade, and biasing means mounted on the supporting means for urging the movable blade into engagement with the fixed blade and in a direction opposite to the direction af force provided by the presser spring on the presser foot.

2. A sewing machine as claimed in claim 1, wherein the fixed blade comprises a longitudinally extending finger at one end thereof for maintaining contact with the movable blade when the fixed and the movable blade are moved out of cooperative engagement for performing a trimming operation.

3. A sewing machine as claimed in either claim 1 or claim 2, the supporting means comprising a support arm mounted for oscillating movement on the presser bar and a vertically extending rod to support the movable blade for limited rotational movement at one end of the support arm.

4. A sewing machine as claimed in claim 3, the biasing means comprising a helical spring and a selectively positionable stop element mounted on the rod to urge the rod upwardly and the movable blade carried thereby into contact with the fixed blade.

5. A sewing machine substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.