ROTATING HOOK DEVICE FOR SEWING MACHINE AND MACHINE COMPRISING THE DEVICE

Abstract: Rotating hook device for sewing machines, of the type which comprises a needle (A) which moves in a cyclic fashion, a main thread (F) through a fabric, comprising a stationary case which has a first substantially vertical axis of symmetry and is suitable to accommodate a spool of auxiliary thread (F'), a rotating hook (7) which is suitable to engage the loop of main thread (F) in order to wind it around the case (2) and tie it to the auxiliary thread (F') to form a stitch. The hook (7) is fitted so that it can rotate about a second axis which intersects the first one and is inclined with respect to it; supporting devices (12, 13) selectively support the case at its ends. This configuration allows to use spools (S) of auxiliary thread (F') which have a large capacity, reducing downtimes for reloading and considerably increasing the productivity of the sewing machines on which the device is applied.

Description: ROTATING HOOK DEVICE FOR SEWING MACHINE AND MACHINE COMPRISING THE DEVICE The present invention relates to a rotating hook device, particularly for industrial sewing machines of the knotted- stitch type, embroidering machines, and the like. Another aspect of the invention relates to a sewing machine which includes the rotating hook device. Conventional knotted-stitch sewing machines essentially include a footing which forms a surface for the sliding of a fabric to be sewn and supports an upper arm with a head which has, at its free end, a needle which can move axially with a reciprocating motion between an upper stroke limit and a lower stroke limit in order to pass a main thread through the fabric. A device known as "crochet" is fitted below the sliding surface and detachably encloses a spool of auxiliary thread which interacts with the main thread to form the stitches. Conventional crochet devices generally include a substantially cylindrical hollow body, which is mounted in a cantilevered fashion at the end of an axis which is substantially perpendicular to the direction of the movement of the needle or parallel to the needle; such crochet devices are known respectively as "horizontal-axis crochet" and "vertical-axis crochet". The hollow body of the crochet is peripherally provided with a hook-shaped part, which is adapted to engage a loop formed by the main thread after passing through the fabric, and with an axial cavity with a stationary drum on which a likewise stationary case is detachably mounted and rotatably accommodates the spool of auxiliary thread. In a first conventional type of crochet device, termed "oscillating-shuttle crochet", the hollow body oscillates periodically about its own axis with an angle of more than 180°, so as to engage the main thread and move it beyond the semicircle of the spool, guiding it and promoting its full rotation about the spool in order to form a stitch. A drawback of the conventional oscillating-shuttle crochet devices is the limited speed at which they can operate, because of the continuous alternating positive and negative accelerations of the shuttle. Accordingly, machines equipped with this crochet device, despite being accurate, are scarcely suited for the high speeds of modern industrial sewing. In order to obviate this drawback, a second conventional type of crochet device, known as "rotating-hook crochet", has been devised in which the hook rotates about the axis of the crochet, engaging the main thread to wrap it around the spool and tie it to the auxiliary thread. These conventional rotating-hook crochet devices allow a distinctly higher sewing speed than oscillating-shuttle crochet devices; for example, modern machines using this crochet can achieve sewing rates of more than 4,000 stitches per minute. Another drawback of all conventional crochet devices is the limited productivity caused by the frequent reloading of the spool of auxiliary thread, which has a limited capacity. Commonly used spools in fact, for example, contain approximately 50 of 0.5-mm thread and this capacity decreases rapidly with threads having a larger diameter for sewing heavy curtains, hides and the like. In order to increase the capacity of the spool, one would have to increase the mass and dimensions of the crochet, with possible problems in the dynamic balancing of the rotating parts and reliability problems, because of the high rotation speed. This drawback is more evident in the case of embroidering machines, which usually have a plurality of crochet devices with an equal number of spools of thread, whose very frequent reloading introduces considerable downtimes in production. Furthermore, in the case of large-diameter threads used to stitch heavy curtains, hides and the like, the length of the thread contained in the spool decreases further, forcing the operator to perform very frequent reloadings of the spool . Another drawback of conventional crochet devices is their limited life, due to the quick wear of the parts which are subjected to continuous mutual friction. An aim of the present invention is to eliminate the above drawbacks by providing a rotating hook device which is relatively simple and allows to considerably increase the productivity of sewing machines to which it is applied, reducing downtimes. An object of the invention is to provide a rotating hook device which is reliable, precise and has a minimum number of moving parts. A further object of the invention is to provide a sewing machine which includes a device of the above described type. This aim and these objects are achieved by a rotating hook device for knotted-stitch sewing machines according to claim 1. The dependent claims define detail characteristics of the device according to the invention and of a sewing machine which includes the device. A preferred but not exclusive embodiment of a rotating hook device and of a machine according to the invention is described hereinafter and illustrated only by way of non- limitative example in the accompanying drawings, wherein: Fig. 1 is a partially sectional front view of a sewing machine with a rotating hook device of the prior art; Fig. 2 is a partially sectional front view of a sewing machine with a rotating hook device according to the invention; Fig. 3 is an enlarged-scale schematic side view of the rotating hook device of Fig. 2; Fig. 4 is a top view of a detail of the device of Fig. 3 ; Figs. 5a to 5e are respective schematic perspective views of the rotating hook device of Fig. 2 in an operating sequence. With reference to the above figures, a rotating hook device according to the invention is illustrated and generally designated by the reference numeral 1. The device is applied to a knotted-stitch sewing machine which has a needle A which can move in a reciprocating fashion between an upper stroke limit and a lower stroke limit to pass a main thread F through a fabric to be sewn, making it interact with an auxiliary thread F' . The device 1 is rigidly coupled in a preset position to the sewing machine below the sliding surface of the fabric and cooperates with other mechanisms of the machine to produce the stitches. According to the invention, the device 1 includes a case 2 which is cylindrical or preferably frustum-shaped and tapers upward with a vertical axis 3 which is substantially parallel to the needle A. The case 2 is provided with an axial tang 4 in an upward region, and with a resting surface 5 in a downward region and has, on the side wall, an openable portion 6 for the insertion of a spool S of auxiliary thread F 1 . Conveniently, the case 2 is removable to facilitate the insertion of the spool during reloading and/or for ordinary maintenance operations. The spool S, which is also preferably frustum-shaped, can be distinctly larger than the spools commonly used in conventional similar devices of the prior art. According to the invention, there is a rotating hook 7 which can rotate about a second axis 8 which intersects, and is inclined obliquely to, the axis 3 of the case 2 by an angle between 0° and 90°, preferably close to 12°. The hook is arranged so that its plane of rotation intersects the case 2 proximate to the centerline thereof. More specifically, the hook 7 is rigidly coupled to the free end of a stem 9 which is fixed, at the opposite end, to a hub 10 which is connected by means of a drive 11 to external motor devices M which are associated with the sewing machine. The hook 7, by rotating, enters a loop formed by the main thread F after the needle A has passed through the fabric and pulls the main thread F around the case 2, tying it to the auxiliary thread F'. According to the invention, the device includes a unit for supporting the case 2 which acts selectively at its longitudinal ends to support it in a stationary position, allowing the free rotation of the hook 7 and of the thread F about the case 2 as well as the extraction of the knotted threads F and F' toward the outside of the tang 4. In particular, the supporting unit includes a pair of grip members 12, which interact in a cyclic fashion with the tang 4 of the case 2, and a pusher 13 which acts in a cyclic fashion on the lower supporting surface 5 of the case 2. The grip members 12 and the pusher 13 cooperate selectively in order to suspend the case 2 in a substantially stationary position with respect to the hook 7. More specifically, the grip members 12 are constituted by two jaws 12', 12" which can move alternately between a first clamping position and a second release position of the tang 4, and the pusher 13 is constituted by a disk 14 which is rigidly coupled to the end of a lever 15 which can move alternately between a lower position, which is spaced from the lower surface 5 of the case, and an upper position, which is in contact therewith. Conveniently, the grip members 12 and the pusher 13 are synchronized so that the clamping position of the former coincides with the spaced position of the latter. Units are provided for actuating the grip members 12 and the pusher 13 and are constituted by one or more cams 16, 16 ■ which are operatively connected to the motor M of the sewing machine and act according to a preset criterion synchronously with the rotary motion of the hook 7 and the reciprocating motion of the needle A. For example, it is possible to use cams which are drum-shaped and/or have complementary profiles and act by means of adapted transmission means on the jaws 12', 12" and on the lever 15. As an alternative, the actuation units can be of the electromagnetic or pneumatic type. In order to guide the rotation of the main thread F about the case 2, there are first guiding units constituted by a spacer 17 made of rigid metal wire which is substantially V-shaped, with its ends rigidly coupled to the case 2 and the vertex arranged so as to protrude toward the outside of the case. Likewise, there are second units 18 for guiding the auxiliary thread F' which are mounted inside the case 2 and are suitable to release in a controlled manner the thread F', keeping its tension and unwinding speed constant. These second guiding units are constituted by a substantially horizontal elongated member 19, which is rotatably and coaxially pivoted to the upper end of the case 2 and has, at its free end, an eyelet 20 in which the auxiliary thread F" unwound from the spool is passed. The elongated member 19 is coupled to an adjustable tensioning spring 21 which acts on the thread F'. Figs. 5a to 5e illustrate an operating sequence of the rotating hook device according to the invention. The device according to the invention allows to reduce the downtimes of the sewing machines to which it is applied, considerably increasing their productivity by virtue of the fact that the case can accommodate spools which have a distinctly higher capacity than the spools that are normally used. The constructive simplicity and the reduced number of moving parts allow to achieve high sewing rates, ensuring reliability and precision. The resulting seams are free from thread interruptions, as instead occurred in the past, and therefore are stronger and more pleasant from an aesthetic point of view. According to a further aspect of the invention, a knotted- stitch sewing machine includes a rotating hook device of the type described above and includes a head T which is joined to a footing B by means of an arm C. The head T supports a thread tensioning lever 22 which can move reciprocatingly between an upper position, in which the main thread F is stretched, and a lower position for the release of the previously stretched portion of thread used to form a stitch. According to the invention, the thread tensioning lever 22 has at least two thread passage eyelets 23 and 24 which are formed at the free end of the lever at a short distance from each other for the insertion of respective loops of thread, so as to tension/release, at each stroke, a portion of thread which is twice that of conventional thread tensioning levers of the past which had the same length but had a single thread passage eyelet. As an alternative, the end of the head can be split in two, with one eyelet for each part. The rotating hook device and the machine according to the invention are susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept expressed by the claims that follow. All the details may be replaced with technical equivalents which are understood to be protected by the present invention.

Claims: CLAIMS 1. Rotating hook device for knotted-stitch sewing machines, of the type which comprises a needle (A) provided with a reciprocating motion, which is suitable to pull a main thread (F) through a fabric to be sewn, forming a loop, wherein said device comprises a case (2) which has a first substantially vertical axis of symmetry (3) and is suitable to accommodate a spool (S) of auxiliary thread (F'), a rotating hook (7) which is suitable to engage said loop of main thread (F) in order to wind it around said case (2) and tie it to the auxiliary thread (F'), forming a stitch; characterized in that said hook (7) can rotate about a second axis (8) which intersects said first axis (3) and is inclined with respect to it, devices (12, 13, 14, 15) being provided to selectively support said case (2) at its longitudinal ends and in a stationary position in order to allow the free rotation of the hook (7) about said case (2) on a preset plane. 2. Device according to claim 1, characterized in that the rotation plane of the hook (7) intersects said case (2). 3. Device according to claim 1, characterized in that the angle of inclination ( " f ) of said second axis (8) with respect to said first axis (3) is between 0° and 90°. 4. Device according to claim 1, characterized in that said angle of inclination ( * > ) is close to 12°. 5. Device according to claim 1, characterized in that said hook (7) is rigidly coupled to the end of a stem (9) which is rigidly coupled, at its opposite end, to a hub (10) which is connected through a drive (11) to an external motor unit (M) which is suitable to make it rotate synchronously with the reciprocating motion of said needle (A). 6. Device according to claim 6, characterized in that said case (2) has an upper axial tang (4) and a central lower supporting surface (5). 7. Device according to claim 1, characterized in that said case (2) is removable and has opening devices (6) for the insertion and accommodation of said spool (S). 8. Device according to claim 1, characterized in that said case (2) has a substantially cylindrical shape with a vertical axis. 9. Device according to claim 1, characterized in that said case (2) has a substantially frustum-like shape which tapers upward. 10. Device according to claim 1, characterized in that said supporting devices (12, 13, 14, 15) comprise two grip members (12', 12") which selectively interact with said tang (4) and a pusher (13) which selectively acts on said lower surface (5) of the case (2). 11. Device according to claim 10, characterized in that said grip members (12, 12*) can move in a reciprocating fashion between a first clamping position and a second release position of said tang (4), and in that said pusher (13) can move in a reciprocating fashion between a lower position, which is spaced from said lower surface (5), and an upper position for contact therewith. 12. Device according to claim 10, characterized in that said grip members (12', 12") and said pusher (13) are synchronized so that the clamping position of said grip members coincides with the spaced position of said pusher. 13. Device according to claim 10, characterized in that said lower pusher (13) is essentially constituted by a disk (14) which is rigidly coupled to the end of a lever (15). 14. Device according to claim 1, characterized in that it has cyclic actuation units (16, 16') for said grip members (12', 12") and for said pusher (13), which are connected to external motor units (M) and act according to a preset criterion synchronously with the rotary motion of said hook (7) and the reciprocating motion of said needle (A). 15. Device according to claim 14, characterized in that said cyclic actuation units (16, 16') are of the mechanical cam type . 16. Device according to claim 14, characterized in that said cyclic actuation units are of the electromagnetic type. 17. Device according to claim 14, characterized in that said cyclic actuation units are of the pneumatic type. 18. Device according to one or more of the preceding claims, characterized in that it comprises first guiding units which are constituted by a spacer (16) which is rigidly coupled to said case (2) for guiding said main thread (F) during rotation about said case (2). 19. Device according to claim 1, characterized in that it has second guiding units (17) for the auxiliary thread (F') which are installed inside said case (2) and are suitable to release in a controlled manner the thread (F 1 ), keeping its tension and rate of unwinding from the spool (S) constant. 20. Knotted-stitch sewing machine of the type which comprises a footing (B), an arm (C) and a head (T) which supports a needle (A) which can move in a reciprocating fashion between an upper stroke limit and a lower stroke limit in order to pass, in a cyclic fashion, a main thread (F) through a fabric to be stitched, characterized in that it comprises a rotating hook device according to one or more of the preceding claims. 21. Sewing machine according to claim 20, characterized in that said head (T) supports a thread tensioning lever (22) which can move in a reciprocating fashion and synchronously with the movement of said needle (A), for pulling and releasing, in a controlled manner, the main thread (F) involved in the sewing operation, said thread tensioning lever (22) having at least two thread guiding eyelets (23, 24) for the passage of respective loops of said main thread (F).

Inventors: CRACCO GILBERTO, CRACCO, GILBERTO
Applicants: CRACCO GILBERTO, CRACCO, GILBERTO
Application year: 1997
Main classification: D05B57
IPC codes: D05B57