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(11) | EP 0 046 660 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Presser foot for sewing machine |
| (57) A sewing machine comprising a needle bar (14) and a presser foot (10). The presser
foot (10) is mounted for heightwise reciprocating movement on a stationary point (36)
and is urged upwardly by a spring (42). Biasing means (54,60) is operable to move
the presser foot (10) downwards against the action of the spring (42). The biasing
means comprises a spring (60) connected to the presser foot (10). Engaging means (64)
mounted on the needle bar (14) engages the spring (60) of the biasing means at a predetermined
point in the downward travel of the needle bar (14) so as to cause downward movement
of the presser foot (10) until the workpiece is contacted. |
[0001] This invention is concerned with a sewing machine comprising a sewing head comprising a needle bar arranged to support a needle of the machine and arranged to perform a reciprocating movement to cause a needle supported by the needle bar to sew a workpiece, and a presser foot arranged to press a workpiece which is being sewn by the machine as the needle is withdrawn from the workpiece so as to retain the workpiece in proper position for sewing.
[0002] Sewing machines are known in which the presser foot is self-adjusting with respect to differing thicknesses of workpiece. The presser foot's movement is often synchronised with the movement of the needle bar so as to contact the work during needle penetration and to thereafter move upwardly with the needle so as to allow the work to move for subsequent stitching. This pressurised contact with the work prevents the material from being lifted when the needle is being withdrawn from the workpiece. The tendency of the workpiece to otherwise lift with the needle is commonly known as flagging.
[0003] The high speed at which sewing occurs in today's modern sewing machines dictates that the presser foot must move extremely fast in order to alleviate the aforementioned flagging problem. In one known example of a presser foot, the presser foot moves with the movement of the needle bar so as to provide the appropriate holding of the workpiece during stitching. This action is accomplished by a downward biasing of the presser foot which is activated by the needle bar movement itself. The downward biasing is such as to adjust for the various thicknesses of work that are presented to the needle for sewing. This particular presser foot is both self-adjusting and automatically activated by the movement of the needle bar.
[0004] It is to be noted that the aforementioned type of self-adjusting presser foot has been subject to various mechanical failures due to the high speed of the moving parts. The presser foot has moreover produced excessive forces on the various thicknesses of work presented thereunder so as to result in appreciable imprints being made on the work that is being sewn.
[0005] It is an object of the present invention to provide a presser foot which applies a relatively low pressure to the workpiece.
[0006] It is a further object of the present invention to provide a presser foot capable of repetitive usage without mechanical failure.
[0007] These objects are achieved according to the invention in that the presser foot is mounted for heightwise reciprocating movement on a fixed portion of the sewing head, the presser foot is urged upwardly away from the workpiece by resilient means, and the machine comprises biasing means operable to move the presser foot downwardly against the action of the resilient means, the biasing means comprising a spring connected to the presser foot, and engaging means mounted on the needle bar and arranged to engage the spring at a predetermined point in the downward travel of the needle bar so as to cause downward movement of the presser foot until the workpiece is contacted.
[0008] In the interests of simplicity of construction, the presser foot is mounted on the fixed portion on a parallel linkage and the resilient means comprises a spring which urges the parallel linkage upwardly.
[0009] Preferably, the spring of the biasing means is contained in a chamber mounted on the sewing head of the machine above the presser foot, the chamber having a vertical slot thereinto through which the engaging means enters the chamber to engage the spring.
[0010] To allow the pressure between the presser foot and a workpiece to be adjusted, the chamber is mounted on the sewing head for vertical adjustment to-define the path of the presser foot relative to the needle.
[0011] To further reduce the pressure between the presser foot and a workpiece, the presser foot comprises cushioning means arranged to cushion the pressure between the presser foot and the workpiece.
[0012] An example of a sewing machine in accordance with the invention is described in detail hereinafter and is shown in the accompanying drawings.
[0013] In the drawings:
Figure is a perspective view of the presser foot of the sewing machine and associated mechanism;
Figure 2 is an exploded view of part of the mechanism shown in Figure 1;
Figures 3 and 4 are front views of the sewing machine, Figure 3 showing the presser foot in an upper position thereof and Figure 4 showing the presser foot in a lower workpiece- engaging position thereof; and
Figure 5 is a partial view of an alternative presser foot configuration.
[0014] The sewing machine shown in the drawings comprises a needle bar 14 arranged to support a needle 12 of the machine and arranged to perform a reciprocating movement to cause the needle 12 supported by the needle bar 14 to sew a workpiece. The machine also comprises a presser foot 10 arranged to press a workpiece which is being sewn by the machine as the needle 12 is withdrawn from the workpiece so as to retain the workpiece in proper position for sewing.
[0015] , The needle bar 14 is driven via a drive connection 16 in a conventional manner. The needle bar 14 reciprocates within a stationary guide member 18 having appropriate annular guides which receive the needle bar 14. The stationary guide member 18 is attached to an upper portion 20 and a lower portion 22 of a sewing machine frame. It is. to be understood that the frame portions 20 and 22 constitute part of the normal frame structure within the sewing head of the machine.
[0016] The presser foot 10 is mounted for heightwise reciprocating movement on a fixed portion of the sewing head provided by a structural member 36. The presser foot (10) extends downwardly from a parallel linkage formed of four bars 24, 26, 28 and 30. The parallel linkage is shown in exploded fashion in Figure 2 and comprises a joined pair of bottom bars 24 and 26 as well as a joined pair of upper bars 28 and 30. The presser foot 10 is attached to the bottom bars 24 and 26 via a pin 32 whereas the presser foot is connected to the upper pair of bars 28 and 30 via a pin 34. The lower pair of bars 24 and 26 are in turn pivotally connected to the structural member 36 via a pin 38. The upper pair of bars 28 and 30 are pivotally connected to the structural member 36 via a pin 40. It is noted that each of the pins 32, 34, 38 and 40 are maintained in their appropriate positions by retaining rings as shown.
[0017] The presser foot 10 is urged upwardly away from the workpiece by resilient means in the form of a spring 42 which is connected to a cross member 44 between the bottom bars 26 and 28. The spring 42 is connected between a hole in the cross member 44 (Figure 2) and a projection 46 of the structural member 36.
[0018] Figure 3 shows the frame 48 of the sewing head of the machine and a vertically-extending member 50 which extends upwardly of the presser foot 10 into the frame 48, passing through the stationary guide member 18 and serving to support the structural member 36.
[0019] The machine also comprises biasing means operable to move the presser foot 10 downwardly against the action of the spring 42. The biasing means comprises a pusher shaft 54 which bears on a concave saddle 52 formed in the top of the presser foot 10. The shaft 54 extends upwardly into a chamber 56 formed within the member 50 and terminates with a flanged head 58. The biasing means also comprises a spring 60 which rests on the flanged head 58 within the chamber 56 and is therefore connected to the presser foot 10 by the shaft 54. The upper end of the spring 60 supports an impact head 62.
[0020] The sewing machine also comprises engaging means in the form of a horizontally-extending tongue 64 mounted on the needle bar 14 through a horizontal member 68 which includes an axial member 70 which receives the driving link 16. The driving link 16 is connected to an eccentric device 72 which drives the needle bar 14. The tongue 64 extends through a vertical slot 66 into the chamber 56. The arrangement is such that, at a predetermined point in the downward travel of the needle bar 14, the tongue 64 engages the impact head 62 of the spring 60 and presses the spring 60 downwards so as to cause downward movement of the presser foot 10 until the workpiece is contacted. When the presser foot 10 engages a workpiece, for example the multi-layered workpiece 74 shown in Figure 4, further downwards motion of the tongue 64 causes compression of the spring 60 as can be seen from a comparison of Figures 3 and 4. During downwards motion of the presser foot 10, the spring 42 opposes the motion but this opposing force is relatively low so as to not result in any significant compression of the spring 60. The relatively low compression state of the spring 60 changes when the presser foot 10 makes contact with the multi-layered workpiece 74. Specifically, the presser foot 10 is impeded from any further downward movement which causes the spring 60 to be compressed in order to absorb the further downward movement of the needle bar 14 as the needle 12 moves through the multi-layered workpiece 74. The spring constant of the spring 60 is such as to allow for this compression while not imposing an undesirable pressure on the multi-layered workpiece 74. This is accomplished by selecting a spring having an appropriate spring constant which develops an acceptable force when thus compressed the amount dictated by the needle movement through the multi-layered workpiece 74.
[0021] The presser foot 10 moves in a slightly arcuate path relative to the vertical movement of the needle 12; due to the action of the parallel linkage. It is to be noted that the particular pivotal connection of the parallel linkage is such as to minimise the degree of curvature of the path thus travelled by the presser foot 10.
[0022] The vertical member 50 and hence the chamber 56 is mounted on the sewing head for vertical adjustment to define the path of the presser foot 10 relative to the needle 12, since vertical adjustment of the member 50 also adjusts the presser foot 10 vertically. The height adjustment is provided by the guide member 18 which holds an expandable collar 76 which engages serrations (Figure 1) on the outside of the member 50. The expandable collar 76 is closed by a fastener 78. The vertical member 50 can be moved up and down within the expandable collar 76 so as to define-a position of the presser foot 10 relative to both the workpiece 74 and the needle 12. The serrations on the vertical member 50 can be used as both an incremental height adjustment guide as well as for gripping purposes. As soon as the appropriate height is reached, the fastener 78 is tightened so as to close the expandable collar 76 and hence pinch the vertical member 50.
[0023] The positioning which is thus achieved should be such as to allow presser foot 10 to avoid interference with the needle 12 at both its upward and downwardmost positions of travel. The downwardmost position of travel may vary for various multi-layered workpieces and hence will require appropriate adjustment for the thinnest portion of the multi-layered workpiece. This adjustment should also allow for the presser foot to adequately rise as a result of the biasing provided by the spring 42 so as to assure appropriate clearance of the highest level of material of the multi-layered workpiece. The adjustment of the height of the presser foot 10 allows a relatively small amount of travel by the presser foot 10 in engaging the multi-layered workpiece 74. Accordingly, the presser foot 10 does not produce a high inertial impact on the multi-layered workpiece 74 and moreover provides for a relatively low level of force within the presser foot mechanism itself. This is particularly important for high-speed sewing applications wherein repetitive force build-ups are experienced with a presser foot mechanism which is operatively coupled to the needle bar.
[0024] The structural member 36 may be easily disconnected from the end of the vertical member 50. This is accomplished by loosening a fastener 80 which otherwise produces a pinching action on the end of the shaft 50. This allows the presser foot 10 and its associated parallel linkage to be easily removed from the remainder of the presser foot apparatus. The shaft 54 normally resting on the saddle 52 at the top of the presser foot 10 is now free to move slightly downward from the end of the vertical member 52.
[0025] In Figure 5, an alternative embodiment to the toe portion of the presser foot 10 is illustrated. The toe portion of a presser foot 10'has a urethane rubber ring 82 inserted into an annular ring channel formed within the bottom of the presser foot. The urethane rubber ring 82 extends from the bottom of the presser foot 10' so as to present a circular cushion to the contacted workpiece 74. The circular cushion is preferably soft enough to deflect and hence absorb an appreciable amount of the downward pressure of the presser foot. The ring 82 therefore forms cushioning means arranged to cushion the pressure between the presser foot 10' and the workpiece 74. This downward pressure increases as the needle 12 passes through the workpiece 74 and hence into the throat plate 84 of the sewing machine. A preferred hardness of the urethane ring 82 is approximately 91 Shore A.
1. A sewing machine comprising a sewing head comprising a needle bar arranged to support
a needle of the machine and arranged to perform a reciprocating movement to cause
a needle supported by the needle bar to sew a workpiece, and a presser foot arranged
to press a workpiece which is being sewn by the machine as the needle is withdrawn
from the workpiece so as to retain the workpiece in proper position for sewing, characterised
in that the presser foot (10; 10') is mounted for heightwise reciprocating movement
on a fixed portion (36) of the sewing head, the presser foot (10; 10') is urged upwardly
away from the workpiece by resilient means (42), and the machine comprises biasing
means (54, 60) operable to move the presser foot (10; 10') downwardly against the
action of the resilient means (42), the biasing means (54, 60) comprising a spring
(60) connected to the presser foot (10; 10'), and engaging means (64) mounted on the
needle bar (14) and arranged to engage the spring (60) at a predetermined point in
the downward travel of the needle bar (14) so as to cause downward movement of the
presser foot (10; 10') until the workpiece is contacted.
2. A sewing machine according to claim 1, characterised in that the presser foot (10;
101) is mounted on the fixed portion (36). on a parallel linkage (24, 26, 28, 30) and
the resilient means (42) comprises a spring (42) which urges the parallel linkage
(24, 26, 28, 30) upwardly.
3. A sewing machine according to either one of claims 1 and 2, characterised in that
the spring (60) of the biasing means (54, 60) is contained in a chamber (56) mounted
on the sewing head of the machine above the presser foot (10; 10), the chamber (56)
having a vertical slot (66) thereinto through which the engaging means (64) enters
the chamber (56) to engage the spring (60).
4. A sewing machine according to claim 3, characterised in that the chamber (56) is
mounted on the sewing head for vertical adjustment to define the path of the presser
foot (10; 10') relative to the needle (12).
5. A sewing machine according to any one of claims 1, 2, 3 and 4, characterised in
that the presser foot (10; 10') comprises cushioning means (82) arranged to cushion
the pressure between the presser foot (10; 10') and the workpiece.