Title of Invention

SEWING -MACHINE THREAD-TIGHTENING ARRANGEMENT

Abstract

Thread-tensioning arrangement (9) for a sewing machine, comprising a supporting plate (12) which is fixed to the sewing machine; a first thread tensioner (18) which is mounted on the supporting plate (12); a second thread tensioner (17) which is mounted on the supporting plate (12); a release pin (30) which is allocated to each thread tensioner (17, 18) for releasing the allocated thread tensioner (17, 18); characterized in that a release lever (31), which is mounted for pivoting about a pivot bearing, is successively pivotable against the release pin (30) of the first thread tensioner (18) and against the release pin (30) of the second thread tensioner (17); and characterized in that a linear drive (35) for pivoting the release lever (31) along a pivoting travel by discrete steps to bear against the first thread tensioner (18) and the second thread tensioner (17).

Full Text

Scwing-Machine Thread-Tightening Arrangement The invention relates to a thread-tightening arrangement for a sewing ma- chine. In some sewing jobs, it can happen that producing a seam on one and the same work piece or work pieces will alternately need higher or lower thread tightening. This occurs for instance when bulges are sewn, resulting from cross seams or stripes of material that are additionally inserted in a work piece. In sewing jobs of this kind, switching from one pre-set, repro- ducible value of thread tightening to another must be possible promptly and without any loss of time. DE 197 53 107 C2 describes a sewing-machine thread-tightening arrange- ment in which several thread tighteners can be triggered by pneumatic drives for varying thread tightening to occur in a respective needle thread. Drawbacks reside in the necessity of compressed-air supply for operation of the thread-tightening arrangement, which is not available in every sew- ing workshop. Moreover, this thread-tightening arrangement is construc- tionally complicated. DE 25 16 639 C3 teaches a thread tightener that is provided with a sole- noid, by means of which, against the force of a pre-loaded compression spring, to lift from one another the strain washers that hold the needle thread between them. In this way, the thread tightener can be put into an operating state of needle-thread tightening and into an operating state of needle-thread release. This is no direct solution of the problems described at the outset. It is an object of the invention to embody a thread-tightening arrangement in which, by simple means, to produce at least two varying, preset values of thread-tightening in a needle thread. According to the invention, this object is attained by the features of claim 1. Based on constructionally simple and uncomplicated means, the meas- ures according to the invention offer the possibility of using two thread tighteners and, optionally, turning off one thread tightener or both of them. Of course, three thread tighteners are conceivable, which are connected in series according to the invention. Claim 2 reflects an especially simple solution of a drive, current supply existing in every sewing machine. Claim 3 reflects an especially simple possibility of triggering. Claim 4 reflects an especially simple design of how to dispose the thread tighteners on the thread tightening arrangement. The improvement accord- ing to claim 5 precludes any inadvertent release of both thread tighteners when only the first thread tightener is to be released. To this end, provision is made for the further development according to claim 6. The development according to claim 7 enables the first thread tightener or both thread tighteners to be released manually if necessary. The thread tighteners may be embodied substantially conventionally ac- cording to claim 8. Details of the invention will become apparent from the ensuing description of an exemplary embodiment of the invention, in which Fig. 1 is an illustration of a sewing machine comprising a thread- tightening arrangement; Fig. 2 is a view of the thread-thightening arrangement on an enlarged scale; Fig. 3 is a vertical, cross-sectional view of the thread-tightening arrange- ment on the line III-III of Fig. 1 on an enlarged scale as opposed to Fig. 2; and Fig. 4 is a diagrammatic view of the thread-tightening arrangement, com- prising a control system for triggering the linear drive. The sewing machine seen in the drawing conventionally includes a base plate 1 in the form of a casing, a top arm 2 and a standard 3 uniting them. It is C-shaped. An arm shaft 4 is lodged in the arm 2, via a crank mechanism actuating a needle bar 5 with a needle 6. Actuation of the arm shaft 4 takes place by way of a driving motor (not shown). A hook that is allocated to the needle 6 is disposed in the base plate 1, actuation of the hook deriving from the arm shaft 4. Mounted on the side wall 8 that is allocated to the operator's side 7 of the sewing machine is a thread-tightening arrangement 9 which a needle thread 10 is fed to, coming from a supply of needle thread (not shown). The nee- dle thread 10 is led through the arrangement 9 to a customary thread lever 11 and from there to the needle 6. The thread-tightening arrangement 9 comprises a supporting plate 12 which props against the side wall 8 at a distance therefrom and is fixed thereto by screws 14. A pre-tightener 16, a second thread tightener 17, a first thread tightener 18 and a deflector 19 are disposed on the supporting plate 12 in the way of the needle thread 10 corresponding to the direction of feed 15 thereof. The pre-tightener 16 of conventional design very slightly pre-tightens a needle thread 10 that passes there-through, this pre- tightening primarily ensuring defined supply of the needle thread 10 to the thread tighteners 17, 18. The real thread-tightening job takes place in the thread tighteners 17, 18, which is going to be explained in detail below. Deflecting the needle thread 10 from the thread-tightening arrangement 9 towards the thread lever 11 takes place by way of a leg spring 20 which is mounted on the deflector 19 and, as a sort of a buffer, reliably compensates any kinematic errors that might involve the thread lever 11. The two thread tighteners 17, 18 are identical. Each of them has a support- ing bolt 21 which is mounted on the supporting plate 12 and stands out to- wards the operator's side 7. The free end turned towards the operator's side 7 is provided with a regulating wheel 22 on a thread 23, the wheel 22 thus being adjustable in the longitudinal direction of the bolt 21. The regulating wheel 22 is provided with a plastic ring 24 which engages with the thread 23, working as a self-locking mechanism against any inadvertent rotation of the regulating wheel 22. A pair of strain washers 25, 26 is displaceably mounted on the bolt 21, the needle thread 10 being guided there-between. A strain washer 25 props against the supporting plate 12. A pressure plate 27 is mounted on the bolt 21 for displacement in the longitudinal direction of the bolt 21, bearing against the strain washer 26 that faces away from the supporting plate 12. The pressure plate 27 is guided non-rotatably, but longitudinally displace- ably in a slit 28 of the bolt 21. A compression spring 29 in the form of a conical spring is disposed between the regulating wheel 22 and the pressure plate 27, its pre-load being modified by rotation of the regulating wheel 22. This spring 29 presses the pressure plate 27 against the strain washer 26 which is again forced against the strain washer 25, in this way acting on a needle thread 10, which runs between the strain washers 25, 26, by some frictional force and, consequently, braking force, the extent of which de- pends on the pre-load of the compression spring 29. A release pin 30 bears against the pressure plate 27, passing through the bolt 21 from the side that faces the wall 8 so that any insertion of the release pin 30 into the bolt 21 in the direction towards the pressure plate 27 will lift the pressure plate 27 off the strain washer 26, cancelling the pre-load of the compression spring 29. The needle thread 10 then runs approximately frictionlessly between the washers 25, 26. A release lever 31 is pivotably mounted on the supporting plate 12 on the side that faces away from the operator's side 7 i.e., between the wall 8 and the supporting plate 12. To this end, provision is made for two screws 32 which are disposed in the vicinity of the bottom edges of the supporting plate 12 and the lever 31, each of them enveloped by a spacer sleeve 33; they constitute a pivoting bearing of the release lever 31. In the vicinity of the screws 32, between the lever 31 and the supporting plate 12, a rubber ring is provided, serving as a restoring spring 34, restoring the lever 31 into a position pivoted towards the wall 8 in accordance with the illustration of Fig. 3. When the release lever 31 is pivoted in a direction towards the sup- porting plate 12, it first bears against the release pin 30 of the first thread tightener 18 and, when further pivoted, it will bear against the release pin 30 of the second thread tightener 17. The lever 31 is operated by way of a linear drive 35 which comprises a so- lenoid 36 that is mounted on the wall 8 inside the arm 2; its tappet 37 passes through a hole 38 in the wall 8 and bears against the lever 31 at a clear distance from the pivoting bearing of the lever 31 formed by the screws 32. The top side of the lever 31, turned away from the bearing thereof, is provided with a handle 39, by means of which to operate the handle 31 manually. By means of a screw 41, a leaf spring 42 is mounted on a bearing 40 that is formed on the wall 8 inside the arm 2, projecting through a passageway 43 in the wall 8 towards the supporting plate 12. It has a crimped portion 44 backed up by a locating area 45 of the lever 31. The crimped portion 44 is arranged in such a way that the locating area 45 of the lever 31 will bear against it before the release pin 30 of the second thread tightener 17 is pushed in. Consequently, the leaf spring 42 and its crimped portion 44 constitute a lever-31 switching resistance that must be overcome before the lever 31 touches the release pin 30 of the second thread tightener 17. As seen in Fig. 4, the solenoid 36 comprises a wound coil 47 with a core 48 arranged therein in such a way that it is retracted into the wound coil 47 upon actuation thereof by current. The core 48 comprises the tappet 37 which is pushed out towards the lever 31 when the core 48 is retracted into the coil 47. Current supply is effected by way of a control system 49, triggering the coil 47 of the solenoid 36; by means of a pulse-width modulator 50 and a subsequent amplifier 51, the control system 49 produces a direct current that is formed by square-wave signals of varying time intervals. Actuation takes place via selectors 52, 53 of the control system 49, with the first se- lector 52 triggering the release force that acts on the tappet 37 to such an extent that the first thread tightener 18 is released, cancelling of the fric- tional force by which the first thread tightener 18 acts on the needle thread 10. The selector 53 triggers the coil 47 for full current flux so that the lever 31 first pushes in the release pin 30 of the first thread tightener 18, then overcoming the switching resistance 46 and afterwards pushing in the re- lease pin 30 of the second thread tightener 17, both thread tighteners 17, 18 then being released. This near complete cancellation of thread tightening load is not needed during a sewing operation, but regularly at the end of a sewing job, when the work piece and the needle thread 10 must be re- moved from under the needle 6. As long as the solenoid 36 is not excited, combined tightening load acts on the needle thread 10, exercised by both thread tighteners 17, 18. With little current flowing through the solenoid 36, this will cancel only the tightening load of the first thread tightener 18, while the tightening load of the second thread tightener 17 continues to work on the needle thread 10. The currents that are released by the two selectors 52, 53 are dimensioned such that, given identical design of both thread tighteners 17, 18 and in par- ticular identical dimensions of the compression springs 29, the load that acts on the two release pins 30 upon full current flux is twice the load exer- cised on the release pin 30 of the first thread tightener 18. WE CLAIM: 1. Thread-tensioning arrangement (9) for a sewing machine, comprising - a supporting plate (12) which is fixed to the sewing machine; - a first thread tensioner (18) which is mounted on the supporting plate (12); - a second thread tensioner (17) which is mounted on the supporting plate (12); - a release pin (30) which is allocated to each thread tensioner (17, 18) for releasing the allocated thread tensioner (17,18); characterized in that - a release lever (31), which is mounted for pivoting about a pivot bearing, is successively pivotable against the re ease pin (30) of the first thread tensioner (18) and against the release pin (30) of the second thread tensioner (17); and characterized in that - a linear drive (35) for pivoting the release lever (31) along a pivoting travel by discrete steps to bear against the first thread tensioner (18) and the second thread tensioner (17). 2. A thread-tightening arrangement (9) as claimed in claim 1, wherein the linear drive (35) is a solenoid (36), which a control system (49) is allocated to for varying current flux. 3. A third-tightening arrangement (9) as claimed in claim 2, wherein the control system (49) is embodied for the current flud for release of the first and second thread tightener (18, 19) to be n ore than twice the current flux for release of the first thread tightener (18). 4. A thread-tightening arrangement (9) as claimed n claim 1, wherein the second thread tightener (17) is more remote from the pivoting bearing of the release lever (31) than the first thread tightener (18) 5. A thread-tightening arangment (9) as claimed ir claim 1, wherein a switching resistance (46), which must be overcome by the release lever (31), is disposed on a pivoting travel of the release lever (31) when it is pivoted from a position of contact with the release pin (30) of the first thread tightener (18) into a position of contact with the release pin (30) of the second thread tightener (17). 6. A thread-tightening arrangement (9) as claimed in claim 5, wherein the switching resistance (46) is formed by a leaf spring (42) that has a crimped portion (44). 7. A thread-tightening arrangement (9) as claimed in claim 1, wherein the release lever (31) has a handle (39) for manual operation. 8. A thread-tightening arrangement (9) as claimed in claim 1, wherein the thread-tighteners (17, 18) have adjustable pre-load to be cancelled by the release pins (30). Thread-tensioning arrangement (9) for a sewing machine, comprising a supporting plate (12) which is fixed to the sewing machine; a first thread tensioner (18) which is mounted on the supporting plate (12); a second thread tensioner (17) which is mounted on the supporting plate (12); a release pin (30) which is allocated to each thread tensioner (17, 18) for releasing the allocated thread tensioner (17, 18); characterized in that a release lever (31), which is mounted for pivoting about a pivot bearing, is successively pivotable against the release pin (30) of the first thread tensioner (18) and against the release pin (30) of the second thread tensioner (17); and characterized in that a linear drive (35) for pivoting the release lever (31) along a pivoting travel by discrete steps to bear against the first thread tensioner (18) and the second thread tensioner (17).

Documents:

560-kol-2004-granted-abstract.pdf

560-kol-2004-granted-claims.pdf

560-kol-2004-granted-correspondence.pdf

560-kol-2004-granted-description (complete).pdf

560-kol-2004-granted-drawings.pdf

560-kol-2004-granted-examination report.pdf

560-kol-2004-granted-form 1.pdf

560-kol-2004-granted-form 18.pdf

560-kol-2004-granted-form 2.pdf

560-kol-2004-granted-form 3.pdf

560-kol-2004-granted-form 5.pdf

560-kol-2004-granted-pa.pdf

560-kol-2004-granted-priority document.pdf

560-kol-2004-granted-reply to examination report.pdf

560-kol-2004-granted-specification.pdf

560-kol-2004-granted-translated copy of priority document.pdf