GB2059463A - Thread cutting device - Google Patents

Abstract

A thread cutting device for a sewing machine comprises a cutter blade (35) pivotally mounted so as to extend into a recess of a cover plate (10) which recess is enclosed by a cutter plate having a substantially plane upper surface (32) coplanar with the surface over which a fabric is guided during sewing, whereby the fabric is not distorted by its passage over the thread cutting device. The cutter plate (31) has a slot (34) therein providing a cutting edge to cooperate with the blade (35). A jet of air is directed into the recess (11) to entrain the cut thread into a waste delivery tube (19). A sewing machine incorporating the thread cutting device has a support plate (38) pivotally mounted thereon and whose upper surface (39) is also coplanar with the upper surface (32) of the cutting device and the fabric guide surface. <IMAGE>

Description

SPECIFICATION Thread cutting device This invention relates to thread cutting devices and in particular to automatic thread cutting devices which are used, for example, in sewing machines and the like in which there is a requirement to cut a thread which is connected to a piece of fabric. The invention has particular application to automatic sewing machines, in which machines a sewn fabric is withdrawn from the sewing region and the thread attached to that fabric is cut automatically prior to the commencement of the sewing operation on the next piece of fabric to be sewn.

In such machines the sewn fabric is guided over a support plate which is usually pivotally mounted on the machine so as to provide access to a cover plate and thence to working parts of the machine located beneath the cover plate. It is known to mount an automatic cutting device on the support plate, the thread trailing from the sewn fabric back to the sewing needle being caused to traverse a predetermined path whereby it is cut automatically by the cutting device. However, such an arrangement has the disadvantage that the sewn fabric is caused to pass over the support plate and the cutting device mounted thereon so that in the region of the cutting device local distortion of the fabric is caused. Such local distortion causes rucks in the fabric and can cause the fabric to travel in a path diverging from the desired path.It is an object of the present invention to provide a thread cutting device in which the above problem is minimised.

The invention provides a thread cutting device for cutting a thread attached to a fabric comprising a cover plate of a form having a recess in one face thereof, thread cutting means attached to said cover plate and extending into said recess, said thread cutting means having a planar first surface which in use forms part of a plane surface over which a fabric is caused to pass in contact whilst being guided over said thread cutting means.

By plane surface it is intended to include a surface which is, or of which a part is, a cylindrically curved surface having a large radius of curvature.

The cover plate may comprise, either integral therewith or attached thereto, a fabric guide which in use guides an edge of the fabric as it passes over thread cutting means.

The thread cutting means may comprise a movable blade pivotally mounted on a second surface of a cutter plate, the opposed face of which plate comprises said first surface. The cutter plate preferably has a slot therein and an edge of said slot may form a cutting edge to cut the thread in co-operation with the blade. The blade is preferably resiliently biased away from said cutting edge and if the cutting device is attached to a sewing machine or the like the blade may be moved there-towards by a cam driven by the drive means of that machine.

The recess may be in fluid flow communication with a waste thread delivery means, which may comprise a tube attached to the cover plate and opening into the recess. Suction may be applied to the waste thread delivery tube so as to draw cut waste thread along said recess and into the tube for transportation to waste. Alternatively a jet of air may be directed into the tube opening so as to entrain a secondary airflow along the recess towards the tube and to thereby draw the cut waste yarn as described above. The jet of air may be caused to issue into the recess from a conduit passing through the guide member and communicating with the recess.

The invention also provides a sewing machine having a thread cutting device as aforesaid.

The sewing machine may have a support plate attached thereto in which case the support plate is located so that a plane surface thereof lies in the same plane as said first surface of the thread cutting device. In this way fabric passing over the support plate and the thread cutting device is not distorted in the region of the thread cutting device.

The support plate may be pivotally mounted on the machine so as to uncover the cover plate or to cover a part of the cover plate to which the thread cutting means does not extend.

One embodiment of thread cutting device according to the invention will now be further described with reference to the accompanying drawings in which: Fig. 1 is a plan view of a cover plate to which a thread cutting means and fabric guide is to be attached; Fig. 2 is an exploded plan view of the fabric guide and thread cutting means for attachment to the cover plate of Fig. 1; Fig. 3 is an end view of the cover plate of Fig. 1 with the fabric guide and thread cutting means of Fig. 2 attached thereto.

Referring now to Fig. 1, there is shown a cover plate 10 having a recess 11 in a raised portion 12 of the upper surface 13 of the plate 10. The raised portion 12 is formed by means of a step at 14, the reason for which will be explained hereinafter.

Holes 1 5 are provided in the cover plate 10 to facilitate attachment thereof to a sewing machine by means of screws (not shown). A depending skirt 1 6 is formed on the undersurface of the cover plate 10, whereby to shield the surroundings from lubricant or the like thrown out by working parts of the machine which in use are enclosed by the skirt 16. The recess 11 has an enlarged portion 17 at one end thereof, into which the cutting means extends as shown in Fig. 3, and at the other end the recess 11 communicates with an aperture 18 which is in fluid flow connection with a waste tube 19.

Referring now to Fig. 2 the fabric guide 20 comprises a plate having holes 21 therein to facilitate its attachment to the cover plate 10 shown in Fig. 1, by screws (not shown).

Upstanding on the upper surface of the plate is an integral wall 22 which is of a generally castellated plan-form. Passing through the wall 22 is a pipe 23 which is in fluid flow connection with the recess 11 in the cover plate 10 when the latter and the guide 20 are attached to each other. In this assembled state the end of the pipe 23 is substantially in alignment with the aperture 1 8 and the entrance to waste tube 1 9.

A detachable wall 24 is attached to the fabric guide plate 20 with accurately formed surfaces 25, 26 in contact with each other. By this means the front surfaces 27, 28 of the integral wall 22 and the detachable wall 24 form an uninterrupted guide surface for the edge of a fabric passing over the top surface 29 of guide 20.

The thread cutting means 30 comprises a plate 31 having a top surface 32. The plate 31 also has holes 33 provided therein to facilitate attachment thereof to the cover plate 10. A slot 34 is formed in one edge of the plate 31. Pivotally attached to the undersurface of the plate 31 is a cutting blade 35 so that the cutting edge 36 performs a scissors action with the opposed edge 37 of slot 34 when the blade 35 is moved theretowards. A spring (not shown) resiliently biases the blade 35 away from edge 37. In the assembled state the surface 32 is coplanar with surface 29 so that a fabric passing over the two surfaces is not deformed, and is readily guided in contact with surfaces 28 and 27 over their whole length. The forward part 24a of detachable wall 24 overlies plate 31 for this purpose.

Fig. 3 shows the parts described above in the assembled state. In this state the blade 35 and the spring associated therewith extend into the slot 11 in cover plate 10. The cover plate 10 may then be attached to an automatic sewing machine or the like, which machine may have a fabric support plate 40, shown in dotted lines in Fig. 3, pivotally attached thereto. When the support plate 40 is moved into its operating position an edge of the plate 40 abuts the step 14 in the upper surface of cover plate 1 0. In this configuration the upper surface 39 of support plate 40 is coplanar with surfaces 29 and 32 of the fabric guide 20 and cutting means 30 respectively. In consequence over the whole width of the fabric the fabric will be supported without distortion as it passes over the cutting means.

After completion of a sewing operation on a fabric the thread attached to the fabric and the bobbin is caused to pass into the slot 34 and a cam driven by the drive means of the machine engages follower surface 40 to move blade 35 and thereby cut the thread. Compressed air is passed through pipe 23 into waste tube 1 9. This causes the entrainment of a secondary airflow from the cutting means 30 along recess 11 towards the waste tube 19, which secondary airflow draws the cut end of the thread towards waste pipe 1 9. When the thread is again cut prior to the commencement of a subsequent sewing operation the cut length of thread is drawn into waste pipe 1 9 and away to waste.

Claims (15)

1. A thread cutting device for cutting a thread attached to a fabric, comprising a cover plate of a form having a recess in one face thereof, thread cutting means attached to said cover plate and extending into said recess, said thread cutting means having a substantially planar first surface which in use forms a part of a substantially plane surface over which a fabric is caused to pass in contact whilst being guided over said thread cutting means.

2. A device according to claim 1 wherein said cover plate comprises a fabric edge guide.

3. A device according to claim 1 or claim 2 wherein said thread cutting means comprises a blade movably mounted on said cover plate.

4. A device according to claim 3 wherein said blade is pivotally mounted on a cutter plate member of said cover plate.

5. A device according to claim 4 wherein said cutter plate has a surface, which comprises said first surface, and a second surface opposed thereto and on which said blade is mounted.

6. A device according to claim 4 or claim 5 wherein said cutter plate has a slot therein having an edge adapted to form a cutting edge to cut the thread in cooperation with said blade.

7. A device according to claim 6 wherein said blade is resiliently biased away from said cutting edge.

8. A device according to claim 7 comprising a cam which upon rotation thereof is adapted to move said blade towards said cutting edge.

9. A device according to claim 8 comprising drive means adapted to drive said cam in rotation.

10. A device according to any one of claims 1 to 9 wherein said recess is in fluid flow communication with waste thread delivery means.

11. A device according to claim 10 wherein said waste thread delivery means comprises a tube attached to said cover plate and opening into said recess.

12. A device according to claim 11 wherein said tube is connected to suction means.

13. A device according to claim 11 wherein a jet of air is directed into said tube opening.

14. A device according to claim 13 when dependent on claim 2 wherein said jet is directed into said recess from a conduit passing through said guide.

1 5. A thread cutting device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

1 6. A sewing machine comprising a thread cutting device according to any one of claims 1 to

15.

1 7. A sewing machine according to claim 16 having a fabric support plate.

1 8. A sewing machine according to claim 1 7 wherein said support plate has a substantially plane surface which is coplanar with said first surface.

1 9. A sewing machine according to any one of claims 16 to 1 8 wherein said support plate is pivotally mounted on said machine.

- 20. A sewing machine according to claim 1 9 wherein said support plate is pivotal between a first position in which said cover plate is uncovered and a second position in which a part of said cover plate to which the thread cutting means does not extend is covered by said support plate.