Sewing machine provided with a device for intermittently feeding a secondary thread

Abstract

A sewing machine comprising: a base defining a support plane for at least one piece of fabric to be sewn; a needle designed to move through the fabric to be sewn with a reciprocating motion comprising a forward stroke to insert a main thread through the fabric to be sewn and a return stroke to enable the main thread to form a loop below the fabric to be sewn; a feeding device of a secondary thread designed to provide an intermittent feed and to insert a coupling portion of the secondary thread through the loop of the main thread; a cutting device for separating the coupling portion from the secondary thread; wherein the feeding device of the secondary thread comprises two rollers with parallel axes and provided with side surfaces facing each other and between which the secondary thread is tangentially fed; wherein, at least at the secondary thread, the distance between the side surfaces of the rollers is cyclically variable between a first distance less than a diameter of the secondary thread, where the secondary thread is flattened between the rollers, and a second distance greater than the diameter of the secondary thread, where there is clearance between the secondary thread and the rollers.

Description

[0001] R. 401848

[0002] - 1 -

[0003] Description

[0004] Title

[0005] Sewing machine provided with a device for intermittently feeding a secondary thread

[0006] Technical field

[0007] The technical reference field for the present invention is the field of sewing machines. In particular, the present invention relates to a type of sewing machine designed to create stitches in which a main thread moved by a needle forms a loop beneath the fabric to be sewn and a secondary thread is fed into the loop of the main thread. Once the needle has gone up and the loop has been tightened, the secondary thread is cut so that the free end of this thread is ready to be inserted into the new loop being formed. To correctly cut the secondary thread, it is known to feed the secondary thread intermittently. In this context, the present invention addresses the problem of providing a novel secondary-thread feeding device or module, which may optionally be built into a machine already in use, and which is designed to feed the secondary thread intermittently.

[0008] Prior art

[0009] As indicated above, the technical field of the present invention is the field of sewing machines. According to the prior art, a sewing machine that could be improved by the present invention is a sewing machine of the type comprising:

[0010] - a base defining a substantially horizontal support plane for a piece of fabric to be sewn;

[0011] - a sewing station formed in the base to make a plurality of lock stitches in the fabric to be sewn;

[0012] - a feed device for feeding the fabric to be sewn through the sewing station and along the support plane. R. 401848

[0013] - 2 -

[0014] The feed device for example comprises a dragging member that is arranged beneath the support plane, provided with a plurality of dragging teeth facing the fabric to be sewn, and is movable continuously along a closed ring-shaped feed path in a substantially vertical containment plane perpendicular to the support plane. The feed path is designed to lift the dragging teeth above the support plane so as to engage and feed the fabric to be sewn along the support plane, and to lower the dragging teeth below the support plane so as to disengage the fabric to be sewn. However, the feed device is not the subject matter of the present invention and the embodiment described above is not limiting.

[0015] As is known, the sewing machine also comprises a needle designed to move through the fabric to be sewn with a reciprocating motion comprising a forward stroke to feed a main thread through the fabric to be sewn and a return stroke to enable the main thread to form a loop below the fabric to be sewn. There is then a secondary thread feed designed to feed the secondary thread through the loop of the main thread, and a cutting device for separating the coupling portion from the secondary thread and making a lock stitch.

[0016] EP0580260 describes a sewing machine in which the lock stitches are made in the manner described above.

[0017] It is also known to provide a drive motor provided with an output shaft assembled to rotate continuously about its own longitudinal axis, and a transmission unit for mechanically connecting the output shaft of the drive motor to the cutting device, the feed device, and the needle. However, the present invention does not relate to the transmission and coordination of motion between the cutting device, the feed device, and the needle.

[0018] To correctly cut the secondary thread, it is known to provide an intermittent feed of the secondary thread designed so that the cut is made when the secondary thread is stationary. The present invention relates to a novel secondary-thread feeding module, which may optionally be built into a machine already in use, and which is designed to feed the secondary thread intermittently. R. 401848

[0019] - 3 -

[0020] Description of the invention

[0021] The present invention is intended to provide a sewing machine that does not have the aforementioned drawbacks and that is simple and inexpensive to implement.

[0022] The starting point for the present invention is therefore a sewing machine, comprising:

[0023] - a base defining a substantially horizontal support plane for at least one piece of fabric to be sewn;

[0024] - a needle designed to move through the fabric to be sewn with a reciprocating motion comprising a forward stroke to insert a main thread through the fabric to be sewn and a return stroke to enable the main thread to form a loop below the fabric to be sewn;

[0025] - a feeding device of a secondary thread designed to provide an intermittent feed and to insert a coupling portion of the secondary thread through the loop of the main thread;

[0026] - a cutting device for separating the coupling portion from the secondary thread.

[0027] All of the elements listed above are well known to a person skilled in the art, and therefore no additional structural details are required to correctly understand the invention. Furthermore, this type of structure is also described in EP0580260.

[0028] Starting from a structure of this type, the present invention proposes a novel device for feeding the secondary thread comprising:

[0029] - two feed rollers with parallel axes provided with side surfaces facing each other and between which the secondary thread is tangentially fed; wherein

[0030] - at the secondary thread, the distance between the side surfaces of the rollers is cyclically variable between a first distance, which is less than a diameter of the secondary thread (where the thread is partially flattened between the rollers), and a second height, which is greater than the diameter of the secondary thread (where there is clearance between the secondary thread and the rollers).

[0031] Therefore, according to the present invention, during rotation of the rollers, there are moments when the secondary thread is flattened by the rollers and other R. 401848

[0032] - 4 - moments when there is clearance between the thread and the rollers, thereby providing a stepped feed of the thread. Indeed, the secondary thread is only fed during the ... phases.

[0033] Such alternating thread flattening / release phases by the rotating rollers can be implemented in many different ways. For example, the axes of the rollers can be movable instead of fixed, to cyclically move closer and further away.

[0034] Alternatively, according to a preferred embodiment that is shown in the figures, the profile of at least one side surface varies like a cam, so as to have portions that project further and cause flattening, and portions in which there is clearance from the thread. Preferably, a drag channel in which the secondary thread is received can be formed on the side surface of at least one of the two feed rollers, wherein the height (radial distance from the axis) of said drag channel varies between a first height, which is less than the diameter of the secondary thread, and a second height, which is greater than the diameter of the secondary thread.

[0035] According to two alternative embodiments, the drag channel can be formed entirely on the side surface of one of the feed rollers, or can be formed partly on the side surface of one of the feed rollers and partly on the side surface of the other feed roller.

[0036] In the embodiment in which at least one roller has a cam profile, the axes of the rollers can be fixed, or the axis of at least one roller can be movable, and in particular pushed against the other roller. In this embodiment, a pushing device is therefore provided to move the feed rollers against one another, with the secondary thread in between. The pushing device preferably comprises at least one spring.

[0037] Additional aspects of the present invention, for example aspects relating to the cutting device, to the feed device for feeding the fabric along the support plane, and to the drive motor, are set out in some of the attached dependent claims.

[0038] List of figures R. 401848

[0039] - 5 -

[0040] The present invention is described below with reference to the attached drawings, which show a non-limiting example embodiment, in which: Figures 1 and 3 are two schematic perspective views, with parts removed for clarity, of a preferred embodiment of the sewing machine of the present invention;

[0041] Figures 2 and 4 are two schematic side views, with parts removed for clarity, of the sewing machine in Figures 1 and 3;

[0042] Figure 5 is a schematic perspective view, with parts removed for clarity, of a first detail of the sewing machine in Figures 1 and 3;

[0043] Figure 6 is a schematic perspective view, with parts removed for clarity, of a second detail of the sewing machine in Figures 1 and 3;

[0044] Figure 7 is a schematic side view, with parts in cross section and parts removed for clarity, of a third detail of the sewing machine in Figures 1 and 3;

[0045] Figure 8 is a schematic side view, with parts in cross section and parts removed for clarity, of a fourth detail of the sewing machine in Figures 1 and 3;

[0046] Figure 9 is a perspective view of a detail in Figure 7;

[0047] Figures 10, 11 and 12 illustrate schematically the operation of the sewing machine in Figures 1 and 3.

[0048] Description of an embodiment of the invention

[0049] In Figures 1 , 2, 3 and 4, reference sign 1 indicates a sewing machine as a whole, comprising a base 2 provided with a support surface 3 designed to define a substantially horizontal support plane P to support a piece of fabric to be sewn. In the following description, the term “fabric” identifies any medium of any material that requires stitching. The sewing machine 1 further comprises a sewing station 5 formed through the surface 3 in a vertical direction 6 perpendicular to the plane P, and a feed device 7 for feeding the fabric along the plane P in a horizontal direction 8 transverse to the direction 6. The device 7 comprises a support bracket 9 that is mounted beneath the surface 3 and is provided with a plurality of flat plates 10 that are parallel to one another, that extend in respective vertical containment planes parallel to the direction 8, and that are distributed about the station 5. Each plate 10 projects upwards from the bracket 9, is provided with a plurality of upper dragging teeth 11 , and engages a related slot 12, which is formed through the surface 3, extends in the direction 8, and has a length, R. 401848

[0050] - 6 - measured parallel to the direction 8, greater than a length of the plate 10, also measured parallel to the direction 8. The bracket 9 and the plates 10 are moved by a drive device 13 along a closed, ring-shaped feed path (not shown) in a substantially vertical containment plane perpendicular to the plane P. The feed path (not shown) is designed to lift the teeth 11 above the plane P so as to engage and feed the fabric along the plane P, and to lower the teeth 11 below the plane P so as to disengage the fabric. The drive device 13 comprises, in this case, an electric motor 14 provided with an output shaft 15 connected to the bracket 9 via an interposed first transmission unit (known and not shown) designed to transform the rotational movement of the shaft 15 into the movement of the bracket 9 and of the plates 10 along said feed path (not shown).

[0051] The sewing machine 1 is also provided with a needle that extends in the direction 6 and is arranged to move through the fabric with a reciprocating motion, preferably but not necessarily a rectilinear reciprocating motion, comprising a forward stroke, in which the needle is lowered to feed a main thread through the fabric, and a return stroke, in which the needle is lifted to enable the thread to form a loop below the fabric. The needle is moved by the reciprocating motion thereof through the fabric under the action of the shaft 15 and a second transmission unit (known and not shown) interposed between the shaft 15 and the needle and designed to transform the rotational movement of the shaft 15 into the reciprocating motion of the needle. The sewing machine 1 is also provided with a feeding device 19 mounted underneath the surface 3 to intermittently feed a secondary thread 20 to the station 5. The unit 19 comprises two feed rollers 21 , 22 arranged to rotate, continuously and in a manner described below, about respective rotation axes 23, 24 that are parallel to one another. With reference to Figure 7, the roller 21 is limited by a substantially cylindrical side surface 25 coaxial with the axis 23, and is fitted rotatably on a support pin 26 via a pair of interposed rolling bearings 27. The pin 26 is coupled slidingly to the base 2 to execute, with respect to the base 2 and under the action of a spring 28 interposed between the base 2 and the pin 26, rectilinear movements transverse to the axis 23, and to move the roller 21 against the roller 22 with the thread 20 in between. The roller 22 is fitted rotatably on a support pin 29 via a pair of interposed rolling bearings 30 and is limited by a shaped side surface 31 extending about the axis 24. The roller 22 is provided with a drag R. 401848

[0052] - 7 - channel 32 (Figures 9, 11 and 12), which is formed on the surface 31 , opens outwards at the surface 31 , and has a variable height H measured transversely to the axis 24. The height H varies, preferably but not necessarily continuously, about the axis 24 between a first height H1 that is less than a diameter of the thread 20, in particular a first height H1 of zero, and a second height H2 that is greater than the diameter of the thread 20. The pin 29 is fastened to the base 2 coaxial with the axis 24, and is engaged rotatably by a return pulley 33 coupled at a fixed angle to the roller 22. The pulley 33 defines part of a belt transmission 34 also comprising another return pulley 35 fitted onto a transmission shaft 36 arranged to rotate, with respect to the base 2 and under the action of the output shaft 15 of the electric motor 14, about a rotation axis 37 parallel to the axes 23 and 24.

[0053] The transmission 34 also comprises a belt 38 looped around the pulleys 33 and 35. Since the roller 22 is moved continuously by the motor 14 about the axis 24:

[0054] - when the height H of the channel 32 at the thread 20 is greater than the diameter of the thread 20 (Figure 10), the roller 21 is kept in contact with the roller 22 under the action of the spring 28 and the thread 20 is not pushed towards the station 5;

[0055] - when the height H of the channel 32 at the thread 20 is less than the diameter of the thread 20 (Figures 11 and 12), the roller 21 is kept in contact with the thread 20 under the action of the spring 28 and the thread 20 is pushed towards the station 5.

[0056] As shown in Figure 5, the thread 20 is guided by a bobbin (not shown) to the station 5 via a first guide device 39 arranged upstream of the rollers 21 and 22 in a feed direction 40 of the thread 20, a second guide device 41 arranged downstream of the rollers 21 and 22 in the direction 40, a third guide device 42 arranged downstream of the device 41 in the direction 40, and a shaped flexible tube (not shown) for guiding the thread 20 between the devices 41 and 42. The device 42 is designed to feed the thread 20 through the station 5 parallel to the plane P and orthogonal to the directions 6 and 8, and to insert a coupling portion of the thread 20 into the loop of the thread. In this regard, it should be noted that the movement of the needle enables the lifting of the loop, and therefore the portion of the secondary thread 20 against the fabric. The sewing machine 1 R. 401848

[0057] - 8 - finally comprises a cutting device 44, which cuts the secondary thread 20 at each operating cycle a lock stitch. With reference to Figures 6 and 8, the device 44 comprises a rectilinear guide 45 that is mounted beneath the surface 3 at the station 5, extends in the direction 6, and is engaged slidingly by a cutting member 46 that is movable along the guide 45 with a rectilinear reciprocating motion in phase with the feed device 7 of the fabric, with the feed needle of the main thread, and with the feed unit 19 of the secondary thread 20.

[0058] The member 46 is preferably fork-shaped and is provided with two arms 47 arranged on opposite sides of the needle. The member 46 is connected to the support bracket 9 of the feed device 7 via an interposed transmission unit 48 comprising a U-shaped coupling bracket 49 that extends beneath the surface 3 and projects downwards from the support bracket 9. The unit 48 further comprises a crank 50 that is hinged on the bracket 49 to rotate, with respect to the bracket 49, about a fulcrum axis 51 parallel to the direction 6, and has a slot 52 formed through the crank 50 in the same direction 6. The slot 52 is engaged slidingly on a coupling pin 53, which is in turn mounted on the cutting member 46. Following the movement of the support bracket 9 along said closed ring-shaped feed path (not shown) in said vertical containment plane perpendicular to the axes 23 and 24, and therefore following the lifting and lowering of the bracket 9 in the direction 6, the coupling bracket 49, the coupling pin 53, and the cutting member 46 are moved in the direction 6 as a result of the engagement of the member 46 in the guide 45, of the rotation of the crank 50 with respect to the bracket 49, and of the engagement of the slot 52 on the pin 53. The device 44 also comprises an elastic metal plate 54 that is arranged inside an upper end of the guide 45, cooperates with the member 46 to ensure the correct position of the thread 20 when cutting, and is lifted by the member 46 to enable disengagement of the lock stitch once it has been made by the plate 54. According to a variant that is not shown, the drag channel 32 is made in part on the side surface 25 of the roller 21 and in part on the side surface 31 of the roller 22. The sewing machine 1 has several advantages mainly resulting from the fact that: the secondary thread 20 is fed to the station 5 relatively simply and inexpensively; the feed device 7, the assembly defined by the needle and by the main thread, the feeding device 19 of the secondary thread, and the cutting device 44 are all R. 401848

[0059] - 9 - driven by the electric motor 14 and are mechanically interconnected and in phase with one another so as to together synchronize the movements of the main thread, of the secondary thread 20, of the cutting member 46, and of the fabric; and the secondary thread 20 is unwound from relatively large bobbins (not shown), which ensures a relatively low stopping frequency of the sewing machine 1.

Claims

R. 401848- 10 -Claims1 . Sewing machine (1) comprising:- A base (2) defining a substantially horizontal support plane (P) for at least one piece of fabric to be sewn;- a needle configured to move through the fabric to be sewn with a reciprocating motion comprising a forward stroke to insert a main thread through the fabric to be sewn and a return stroke to allow the main thread to form a loop below the fabric to be sewn;- a feeding device (19) of a secondary thread (20) configured to feed intermittently and insert a coupling portion of the secondary thread (20) through the loop of the main thread;- a cutting device (44) to cyclically cut the secondary thread (20); characterized in that the feeding device (19) comprises:- two feed rollers (21 , 22) with parallel axes (23, 24) and provided with side surfaces (25, 31) facing each other and between which the secondary thread (20) is tangentially fed; wherein- at least at the secondary thread (20) the distance between the side surfaces of the rollers is cyclically variable between a first distance (H1) less than a diameter of the secondary thread, where the secondary thread (20) is flattened between the rollers (21 , 22), and a second distance (H2) greater than the diameter of the secondary thread (20) where there is clearance between the secondary thread (20) and the rollers (21 , 22).

2. Sewing machine according to claim 1 , wherein a drag channel (32) wherein the secondary thread (20) is housed is formed on the side surface (31) of at least one of the two feed rollers (22), wherein the drag channel (32) has a height (H) varying between a first height (H1) less than a diameter of the secondary thread (20) and a second height (H2) greater than the diameter of the secondary thread (20) itself.R. 401848- 11 -3. Sewing machine according to claim 2, wherein the drag channel (32) is formed entirely on the side surface (31) of one of the rollers (22), or the drag channel (32) is formed partly on the side surface (31) of one of the rollers (22) and partly on the side surface (25) of the other roller (21).

4. Sewing machine according to any of the preceding claims, wherein the feeding device (19) comprises, in addition, a pushing device (28) for moving the feed rollers (21 , 22) against each other with the interposition of the secondary thread (20).

5. Sewing machine according to claim 4, wherein the pushing device (28) comprises at least one spring to move one of the feed rollers (21) against the other feed roller (22) with the interposition of the secondary thread (20).

6. Sewing machine according to any of the preceding claims, wherein the cutting device (44) comprises a cutting member (46) movable perpendicularly to the support plane (P) of the fabric to be sewn (4).

7. Sewing machine according to claim 6, wherein the cutting device (44) further comprises, in addition, a striker plate (54), in particular elastically deformable, which is attached to the base (2) on the opposite side of the cutting member (46) with respect to the secondary thread (20), and cooperates with the cutting member (46) during cutting of the secondary thread (20).

8. Sewing machine according to claim 7, wherein the cutting device (44) comprises, in addition, a guide (45) engaged slidingly by the cutting member (46); the striker plate (54) being mounted inside the guide (45) itself.

9. Sewing machine according to any of the preceding claims and comprising, in addition, a feed device (7) provided with at least one dragging member (10,11) to feed the fabric to be sewn along the support plane (P).

10. Sewing machine according to claim 6 and 9 and further comprising a drive motor (14) provided with an output shaft (15) mounted to rotate continuously, and a transmission unit to mechanically connect the output shaft (15) of theR. 401848- 12 - drive motor (14) with the feed rollers (21 , 22) of the feed unit (19), the cutting member (46) of the cutting device (44), the dragging member (10, 11) of the feed device (7), and the needle.

Images