GB2120290A - Sewing machine with workpiece turning device - Google Patents

Abstract

A sewing machine (1) has a feed means for a workpiece to be sewn, the feed means having a workpiece conveyor performing a skipping feed movement below the workpiece and a presser foot (10), aligning and guiding the workpiece on a supporting plate with its edge along a bearing edge. Above the workpiece is provided a turning device, by means of which the workpiece can be turned about an axis coinciding with the needle (8). In order to be able to sew in edge-parallel manner and accompanied by automatic guidance, workpieces made from soft materials with curved or angular seam courses, the turning device has air nozzles 81 directed in acute-angled manner on to the supporting plate and arranged tangentially and in spaced manner with respect to the needle. <IMAGE>

Description

SPECIFICATION Sewing machine This invention relates to sewing machines.

A sewing machine is disclosed in German Patent Specification No. 1 685079 in which, as a result of the torque, the edge of a workpiece in the area which is still to be sewn, is pressed against a bearing edge by the advance of the conveyor. In order to be able to produce seam profiles in corners, for example, at collar tips and the like, a turning device which can be mounted from above on the workpiece is provided and said device turns the workpiece by the necessary angle about the needle axis. Such a means is very complicated, because it requires a separate drive motor. The turning device is unsuitable for use for sewing curved seams, where direction changes occur between the individual stitches, because, raising, reapplication and actuation within in each case one stitching cycle is not possible in view of the sewing speeds used.There is also a considerable risk of workpieces made from soft materials being deformed.

German Patent Specification No. 1485331 discloses a workpiece guidance device for sewing machines, in which the workpiece edges are folded over. At least one nozzle is provided to ensure that in said folding device, the workpiece always engages against a bearing edge. The air jet from the air nozzle presses the workpiece against the bearing edge, at right angles to the sewing direction. It is also possible to provide air nozzles acting in the sewing direction and which compensate the frictional forces occurring in the folding direction.

The present invention aims to provide a sewing machine in which it is possible to sew in edgeparallel manner workpieces made from soft materials having curved or angular seam profiles and accompanied by automatic guidance.

Accordingly, the present invention provides a sewing machine comprising a feed dog for a workpiece to be sewn, said feed dog having a workpiece conveyor performing a skipping feed and adapted to be positioned beneath the workpiece, a presser foot, a supporting plate having a bearing edge for orientating and guiding a workpiece, a needle and a turning device arranged above the workpiece, by means of which the workpiece can be turned about an axis coinciding with the needle, said turning device having air nozzles arranged in tangentially spaced manner with respect to said needle and directed in actte-angled manner on the supporting plate.

As a result of the measures according to the invention, the workpiece is always accurately guided along the bearing edge, particularly when sewing highly curved or angular seam profiles, no importance being attached to the number of stitches over which the curved seam area extends.

As there is no positively working turning device, it is also possible to work softer materials, which are always pressed against the bearing edge, but are not deformed by crinkling or the like.

A particularly simple construction results if the air nozzles are arranged in a hollow plate. Such a hollow plate can also be subsequently fitted to existing sowing machines at limited cost. The hollow plate is preferably arranged immediately above the workpiece but not in contact therewith.

As a result of this arrangement, it is ensured that the workpiece is satisfactorily turned, without introducing new frictional forces. The hollow plate is desirably pivotally mounted for movement towards and away from the workpiece so as to ensure that the insertion and removal of a workpiece are not impeded at the stitch formation point.

According to a preferred embodiment, the air nozzles are arranged on approximately half pitch circles about said needle and are located on the side remote from said bearing edge. This arrangement leads to an optimum turning and therefore orientating action. The tangential direction of the air nozzles is desirably adjustable.

Means are preferably provided to ensure that compressed air is only supplied to said air nozzles when a workpiece is to be stitched with curved or angular seams. This arrangement ensures that normal guidance of the workpiece along the bearing edge takes place with linear or slightly curved seams, and that the turning device is only operated with highly curved or angular seam portions.

The turning device according to the invention can be used with particular advantage if, in addition, the presser foot is arranged to be raised from the workpiece by means of a lifting gear during the stitching cycle of the needle, the lifting gear being constructed in such a manner that during the insertion of the needle, said presser foot is raised from the workpiece during downwardly directed movement of said needle just prior to reaching the bottom dead centre position. The workpiece can then be turned freely about the needle over part of the movement of the latter and with the needle actually inserted.

Preferably, the lifting gear has a cam plate drive drivable by an arm shaft and which is coupled to a presser foot bar of said presser foot by means of a transmission rod. The lift by which the presser foot can be raised from the workpiece may be adjustable and the position to which said presser foot can be raised from the workpiece may also be adjustable.

The invention will now be further described, by way of example, with reference to the drawings, in which: Fig. 1 is a rear view of one embodiment of a sewing machine according to the invention; Fig. 2 is a side view of the sewing machine taken in the direction of the arrow Il in Fig. 1; Fig. 3 is a plan view of the base plate of the sewing machine base plate taken in the direction of the arrow Ill in Fig. 1; Fig. 4 is a perspective view taken in the direction of the arrow IV in Fig. 1; Figs. 5a to Sc show the stitch formation area of the sewing machine taken in the direction of the arrow V in Fig. 1 and showing different phases of the needle movement; Fig. 6 is a plan view of the stitch formation point with a turning device taken in the direction of the arrow Ill in Fig. 1;; Fig. 7 is a partial section taken along the section line VIl-VIl in Fig. 6; and Fig. 8 is a section, corresponding to Fig. 7, but showing a modified embodiment; Referring to the drawings, a sewing machine 1 is provided on its top surface with a lower arm constructed as a base plate 2 and which is received in a workpiece supporting plate 3. A hollow upper arm 4, i.e. constructed in the form of a housing, is fixed to the base plate 2. An arm shaft 5 is mounted in rotary manner in said upper arm 4 and is provided at one end with a handwheel 6 and with its free end terminates in a not shown, conventional, crank gear, which is used for driving a needle bar 7 with a needle 8. A presser foot bar 9 is displaceably mounted in the upper arm 4 (Fig. 2) and to its lower end is secured a presser foot 1 0.The presser foot 10 is constructed with a guide roller 11 and a groove 1 2 for receiving a timing belt 1 3. The presser foot bar 9 is surrounded by a compression spring 14, one end of which is supported by means of a disk 1 5 on the upper arm 4, whilst the other end of which is supported on a bearing block 16, which is fixed by means of a setscrew 1 7 to the presser foot bar 9. To the bearing block 1 6 is hinged a tie rod 18, whose free end is held and guided in a rotary, adjustable manner in an oblong hole 20 of a lever 21 by means of an adjusting screw 1 9.

This oblong hole fixture is used for adjusting the height of lift a of the presser foot 10 and consequently to bring about adaptability to different compressibilities of the workpiece materials. The lever 21 is fixed to a shaft 22, which is rotatably mounted in the arm 4. One end of a lever 24 is adjustably fixed by means of a clamping connection 23 to the shaft 22, said lever having a recess 25 for receiving a roller 27 which is rotatably mounted on a bolt 26. The roller 27 is in contact with a cam disk 28 secured in angularly adjustable manner to the arm shaft 5. At its free end 29, i.e. at the end opposite to the clamping connection 23, the lever 24 has a bearing surface 30.A one-way pneumatic cylinder 31 is secured by screws 32 to the upper arm 4 and has a piston rod 33 which projects into the upper arm 4 above the arm shaft 5 and which can co-operate with the bearing surface 30 of the lever 24. The abovedescribed mechanism, which is in driving connection with the presser foot bar 9, forms a lifting gear H. Adjustment of the height a of the bearing block 1 6 on the presser foot bar 9 and/or a corresponding adjustment to the clamping connection 23, makes it possible to adapt the stroke length of the presser foot 10 to different workpiece thicknesses.

A shaft 36, extending parallel to the arm shaft 5, is pivotably mounted in bearings 34, 35 on the upper arm 4 (Fig. 1). One end of the shaft 36 projects into a not shown ratchet brake with laterally positioned bearings (Torrington type). Such constructions are, for example, known from U.S.

Patent Specification No. 4271776. This ratchet brake is connected to a crank 37. Laterally of the bearing 35, the shaft 36 is axially fixed by means of an adjusting ring 38 and its other end, facing the presser foot 10, is connected in non-rotary manner with a gear wheel 39, around which passes the timing belt 1 3. A rocking lever 40 is pivotably mounted on the shaft 36, said lever being provided with a cap 41 covering the gear wheel 39 and a downwardly radialiy extending lever 42 (Fig. 2). The lower end of the lever 42 carries a guide member 44 for the timing belt 13 which is fixed to the lever 42 by means of a screw 43. One end of a guide lever 45 is fixed by a shoulder screw 46 to the lever 42 and its other end is secured to the presser foot bar 9.

Within the upper arm 4 is arranged a conventional stitch regulating gear 47, which is connected with a crank 49 by means of a tie rod 48. The crank 49 is mounted in non-rotary manner on a sliding shaft 52 which is mounted in bearings 50, 51 below the base plate 2, whilst a further crank 53 is fixed in non-rotary manner to the shaft 52. Cranks 53 and 37 are connected in driving manner by means of a tie rod 54. The sliding shaft 52 is provided with a feed fork 55, connected by means of a bolt (not shown) to a conveyor beam 56, which is supported by a crank (not shown) on an eccentric lug of a shaft (not shown) connected to the arm shaft 5 by means of a timing belt gear 57. In the vicinity of the needle 8, a conveyor 58 is arranged on the conveyor beam 56.A throat plate 62 having a recess 60 for the conveyor 58 and a stitch hole 61, is secured by means of screws 59 to the base plate 2. A stop plate 63 is adjustably fixed, by means of a screw 66 engaging in an elongated slot 65 in said stop plate 63, to the base plate 2, so that the distance between a bearing edge 64 of the stop plate 63 and the stitch hole 61 and consequently the distance from a seam to the workpiece edge is adjustable. In general, the bearing edge 64 is linear and runs parallel to the conveying direction of the conveyor 58. In addition, in the conveying direction, the bearing edge 64 extends on either side of a vertical line through the stitch hole 61, so that the workpiece edge can be guided in all cases tangentially to the bearing edge 64.

A bearing 67 is mounted on the base plate 2 which bearing serves to rotatably receive a double-acting pneumatic operating cylinder 68. A piston rod 69 of the cylinder 68 is articulated in driving manner to a lever mounted in a bearing on the base plate 2 and on said lever 71 is arranged a semicircular hollow plate 72 (Fig. 6) with a compressed air connection 73. The hollow plate 72 has an upper plate 74 and a lower plate 75 parallel thereto, which are interconnected at their peripheries by means of a gasket 76 and rivets 77.

The compressed air connection 73 in the upper plate 74 has a bonded-in stud 78 for receiving a hose 79. The upper and lower plates 74, 75, in conjunction with the gasket 76, enclose a flat compressed air distribution space 80.

The lower plate 75 is provided with air nozzles 81 arranged at an acute angle of 30 to 600 to the plate plane, said nozzles being arranged on concentric pitch circles 82, 83, extending over approximately 1800, with respect to the needle 8, i.e. the stitch hole 61, and which are constructed in each case tangentially to the pitch circles 82, 83. The direction of the air nozzles 81 is such that the trailing, i.e. not sewn edge of the workpiece W is pressed against the bearing edge 64.

As shown in Fig. 2, two reflection barriers 85, 86 are arranged on a plate 84 which is secured to the upper arm 4 of the sewing machine and said barriers form switch points 87, 88 (Fig. 3).

Operation takes place as follows. It is assumed that before the start of working, the needle 8 of the sewing machine is in its uppermost position and, due to the operation of the working cylinder 31, the presser foot 10 is in the raised position and due to the operation of the working cylinder 68, the hollow plate 72 is in the raised position, indicated by the dot-dash lines in Fig. 1. The operation of the working cylinder 31, i.e. the extension of its piston rod 33, ensures, through the co-operation of said rod 33 with the bearing surface 30, that the lever 24 is pivoted around the shaft 22, so that simultaneously the lever 21 is rotated.The upward movement of the lever 21 is transmitted by means of the tie rod 18 to the bearing block 16, so that the presser foot bar 9 is raised against the force of the compression spring 14, so that the presser foot 10 is disengaged from the throat plate 62. During the upward movement of the presser foot bar 9, by means of the guide lever 45, the lever 42 and consequently the guide member 44 is pivoted away from the presser foot bar 9, so that the timing belt 13, constructed as the upper material displacement means, remains in the tensioned position. By operating the cylinder 31, the roller 27 is simultaneously moved out of the action area of the cam disk 28.

A workpiece W, shown in exemplified manner in Fig. 3, is now placed in an initial position A on the base plate 2 of the sewing machine 1, the outer workpiece edge being placed against the bearing edge 64 of the stop plate 63. As can be gathered from Fig. 3, the workpiece W introduced in the represented manner, covers the switch points 87, 88 of the reflection barriers 85, 86, so that the latter emit a signal identifying the presence of a workpiece. The sewing machine 1 can now be started.

After operating a not shown starting button of a control means, initially the pneumatic working cylinders 31 and 68 are reversed, so that the presser foot 10 is lowered on to the workpiece W and the hollow plate 72 in its lower position is lowered immediately over the workpiece W but is not in contact with the latter. On rotating the arm shaft 5, an oscillatory movement is produced in the stitch regulating gear 47, which causes an intermittent movement of the shaft 36 and consequently the timing belt 13, as the upper material displacement means, due to the ratchet brake located in the crank 37.

Simultaneously, the conveyor 58 performs a feed movement, so that the workpiece W is moved in the direction of arrow 89. As soon as the tip of the needle 8 stitches the workpiece W, cf.

Fig. 5b, the cam disk 28 with its operating cam 28' runs on to the roller 27 of the lever 24, so that the latter is pivoted. By means of the lever 21 , the presser foot bar 9 and consequently the presser foot 10 is raised by a small amount from the workpiece W, which corresponds to the height of lift a. Simultaneously, the conveyor 8 has assumed a position in which it is located below the bearing surface for the workpiece W, i.e.

below the surface of the throat plate 62. As no frictional forces are now exerted by the timing belt 13, in the form of the upper material displacement means, or the conveyor 58 on the workpiece W, the latter can be easily oriented with respect to the bearing edge 64 of the stop plate 63 as will be described in detail hereinafter.

During further stitch formation, the needle 8 performs its downward stroke into the lowermost position, i.e. down to bottom dead centre, where it performs an upward movement, at the beginning of which the loop lifting movement necessary for stitch formation takes place. When, during its downward movement, the needle 8 reaches bottom dead centre, the presser foot 10 is again lowered on to the workpiece W, due to the corresponding shaping of the operating cam 28' of the cam disk 28, so that during the formation of the thread loop (Fig. 5c), which is seized by hook G, the workpiece W is held firmly on the throat plate 62. The presser foot 10, which simultaneously carries a circulating material displacement means (timing belt 13), at this time simultaneously fulfilis the function of a presser pad for the workpiece W.The needle 8 is moved further upwards during the further stitch formation cycle. When the needle 8 hasleft the workpiece W, the latter is again moved and the operation can be repeated to form another stitch.

Due to its own weight, the workpiece W rests on the base plate 2 or the workpiece supporting plate 3, also outside the stitch formation zone and essentially in the area located beyond the stitch hole 61 or the needle 8, when viewed from the bearing edge 64. The movement imparted to the workpiece W by the conveyor 58 and timing belt 13 in the sewing direction 89 leads to a torque being produced on the workpiece W, which acts around the needle 8, i.e. around the stitch formation point, which presses the workpiece by its edge located in front of the stitch hole 61 in the sewing direction 89 against the bearing edge 64.

The workpiece edge of the not yet sewn area of the workpiece is consequently always turned towards the bearing edge 64. Thus, in Fig. 4, said torque always acts counterclockwise. As the presser foot 10 is always raised from the workpiece during part of the needle stroke, this rotary movement resulting from the feed in the sewing direction 89 is always facilitated. The force with which the edge of the workpiece W is engaged with the bearing edge 64 of the stop plate 63 is sufficient for guiding workpieces W with a relatively flat, convex or concave configuration. However, it is not adequate for guiding highly curved configurations.For guiding a workpiece W in the vicinity of tighter curves, towards collar tips and the like, the aforementioned hollow plate 72 is used, which is controlled by a not shown control means in the same way as the reflection barriers 85, 86.

As soon as the workpiece W has been transferred from the initial position A into position B, in accordance with Fig. 3 and in which the previously linear seam course changes into a highly curved course in which the workpiece is freed from the first switch point 88, the reflection light barrier 85 emits a signal indicating that a workpiece is not present at switchpoint 88.

Compressed air is then supplied to the hollow plate 72 via the hose 79, which passes into the compressed air distribution space 80. As a result of the arrangement of the air nozzles 81, a torque is imparted to the workpiece W in the direction of arrow 90 (Fig. 6), so that during the next-following highly curves seam course, the workpiece W is held and guided on the bearing edge 64 of the stop plate 63 during each stitch. As soon as the workpiece W has been turned during stitch formation by the air from the air nozzles 81 in such a way that the workpiece W is again positioned above the switch point 88, a corresponding signal is given by the reflection light barrier 85, so that the air supplied to the hollow plate 72 is switched off after a delay time predetermined in the not shown control means.

Such a delay time is necessary in order to ensure that the workpiece W rotates beyond the switch point 88 positioned laterally of the bearing edge 64, for example up to position C in Fig. 3. During the production of the seam in the further curved portion, the workpiece W is guided and rotated in the normal manner. If at the end of the seam, the workpiece is freed from both switch points 87, 88, thread cutting-off takes place in the conventional manner and the pneumatic working cylinders 31, 68 are operated, so that the completely sewn workpiece W can be removed from the sewing machine 1.

The hollow plate 72' partially shown in Fig. 8 corresponds, as regards its basic construction, to the hollow plate 72 shown in Figs. 6 and 7, so that in this respect what has been stated hereinbefore also applies. It has an upper plate 74' and a lower plate 75', bounding between them a compressed air distribution space 80'. However, unlike in the case of Figs. 6 and 7, the direction of air nozzles 81' is adjustable. For this purpose, the air nozzles 81' which slope downwards at an acute angle of 30 to 600 to the plate plane, are each constructed in a swivel member 91, arranged with a lower, approximately flange-shaped head 92 in a corresponding recess 93 on the bottom of the lower plate 75'. The recess 93 widens downwards in frustum-shaped manner, whilst the periphery of the head 92 tapers downwards in frustum-shaped manner.The particular air nozzle 81' issues into the V-shaped slot formed by the shaped surfaces of the head 92 and recess 93. The swivel member 91 has a lug 94 joined to the head 92 by means of which the swivel member is sealingly held and guided in a rotatable manner in a corresponding bore 95 in the lower plate 75'.

A larger diameter bore 103 aligned with the bore 95 is provided in the upper plate 94' and a bush 96 is arranged in said bore. The swivel member 91 extends through the bush 96 and is provided at its upper free end with a screw-thread 97 which is engaged by a nut 98, with the interposition of a washer 99, to hold the swivel member 91 in position. The bush is provided, at its inner end, with a spacer ring 100 which determines the distance between the upper plate 74' and the lower plate 75'. On its end face facing the lower plate 75', the spacer ring 100 is provided with radially extending channels 101 which ensure a connection between the compressed air distribution space 80' and the particular air nozzle 81', for which purpose a frustum-shaped annular channel 102 is also provided on the associated inside of the bush 96.

Prior to the final tightening of the nut 98, each swivel member 91 is aligned in such a way that the associated air nozzle 81' extends precisely tangentially to the particular pitch circle 82 or 83.

With this construction, it is no longer necessary to connect the upper plate 74' and lower plate 75' by means of rivets or the like, because the swivel members 91 with nuts 98 and spacer rings 100 fulfill these functions.

The invention is not restricted to the abovedescribed embodiments but modifications and variations may be made without departing from the scope of the invention as defined by the appended claims.

Claims (12)

1. A sewing machine comprising a feed dog for a workpiece to be sewn, said feed dog having a workpiece conveyor performing a skipping feed and adapted to be positioned beneath the workpiece, a presser foot, a supporting plate having a bearing edge for orienting and guiding a workpiece, a needle and a turning device arranged above the workpiece, by means of which the workpiece can be turned about an axis coinciding with the needle, said turning device having air nozzles arranged in tangentially spaced manner with respect to said needle and directed in acuteangled manner on the supporting plate.

2. A sewing machine according to claim 1, wherein the air nozzles are arranged in a hollow plate.

3. A sewing machine according to claim 2, wherein the hollow plate is arranged immediately above the workpiece but not in contact therewith.

4. A sewing machine according to claim 2 or claim 3, wherein the hollow plate is pivotally mounted for movement towards and away from the workpiece.

5. A sewing machine according to any preceding claim, wherein the air nozzles are arranged on approximately half pitch circles about said needle and are located on the side remote from said bearing edge.

6. A sewing machine according to any preceding claim, wherein the tangential direction of said air nozzles is adjustable.

7. A sewing machine according to any preceding claim, wherein means are provided to ensure that compressed air is only supplied to said air nozzles when a workpiece is to be stitched with curved or angular seams.

8. A sewing machine according to any preceding claim, wherein the presser foot is arranged to be raised from the workpiece by means of a lifting gear during the stitching cycle of the needle, the lifting gear being constructed in such a manner that during the insertion of the needle, said presser foot is raised from the workpiece during downwardly directed movement of said needle just prior to reaching the bottom dead centre position.

9. A sewing machine according to claim 8, wherein the lifting gear has a cam plate drive drivable by an arm shaft and which is coupled to a presser foot bar of said presser foot by means of a transmission rod.

10. A sewing machine according to claim 8 or claim 9, wherein the lift by which said presser foot can be raised from the workpiece is adjustable.

11. A sewing machine according to any one of claims 8 to 10, wherein the position to which said presser foot can be raised from the workpiece is adjustable.

12. A sewing machine substantially as described herein with reference to the drawings.