AUTOMATIC DEVICE FOR STRETCHING LONGITUDINALLY AND TRANSVERSELY A WEB OF KNITTED FABRIC

Abstract: The web (T) being produced by a straight knitting machine is acted upon transversely and at a short distance from the needles of the needle-bars, by a pair of oppositely-threaded screws (1, 101) which are powered and synchronized so as to submit said web (T) to a suitable stretching both in the longitudinal and transverse directions, for the purpose of arranging the upper loops of said web (T) in the best condition for co-operation with the automatic side-transport devices provided on the machine. One (1) of the two screws is stationary and the other (101) is carried by swinging supports with which the comb of the machine co-operates, partly, when raised and then lowered at the beginning of the cycle for producing each web (T), with a view to avoid any interference of said comb with the swinging screw. The interference of the comb with the stationary screw, on the other hand, is avoided by suitably spacing said screw from the plane of travel of the comb. Suitable means will match automatically the rotational speed of the stretching screws with the speed of the machine carriage.

Description: Flat knitting machines provided with automatic devices or stretching longitudinally and transversely a web of knitted fabric are already known in the prior art from FR-A-2 089 243. These machines are equipped with a single threaded bar counter-acted by a parallel spring-loaded roller and are not provided with a mechanism to clear automatically the path of an automatic side-transporting device, e.g. a comb. This comb normally submits the web being produced to a longitudinal stretching and automatically regulates the tension as a function of the width of said web. When the machine is pre-arranged for the production of shaped webs and is equipped with automatic decreasing and increasing devices, the action of the web-stretching comb is efficient only during the initial step of the web-producing cycle because when said web exceeds a certain length, its elasticity will not ensure a uniform and even tensioning of the loops, whereby the latter might not be caught correctly by said automatic side-transporting devices. The invention aims to overcome this disadvantage by means of a device of simple construction and of high technological reliability, which comprises below the needle-bars and at the top portion thereof, i.e. as close as possible to the operative area of said needle-bars, a pair of parallel screws adapted to operate transversely of the web being produced and each provided with opposite threads and so powered and synchronized as to submit said web to an efficient stretching both in the longitudinal and transverse directions. Further characteristics of the invention and the advantages resulting therefrom will become apparent from the following description of a preferred embodiment thereof, shown as a non-limiting example in the Figures of the accompanying single sheet of drawings, wherein: Fig. 1 is a diagrammatic top plan view of the two stretching screws; Fig. 2 is a top plan view showing the connection of the two stretching screws to the respective rotation means; Fig. 3 is a side view of the needle-bars of the machine with the stretching screws; Fig. 4 is a front elevational and partly sectional view of one of the end supports for the stretching screws; Fig. 5 is an enlarged plan view showing the outline of the threading of the stretching screws; Fig. 6 is a cross sectional view on the line VI-VI of Fig. 5, showing further details of the screws co-operating with the web to be stretched; Fig. 7 shows the stretching screws of Fig. 3, but in the opened condition corresponding to the end of the lifting stroke of the web-stretching comb; Fig. 8 is a block diagram of the electronic control circuit for the motor which actuates the stretching screws. With particular reference to Fig. 3 of the drawing, below the needle-bars FA and FP of the knitting machine there are arranged, at a short distance from the top end of said needle-bars and parallel to said top end, screw members 1-101 whose length is substantially the same as or suitably longer than that of said needle-bars, and one of which, e.g. the screw 1, is rotatably supported by stationary supports (not shown), is arranged at a short distance from the needle-bar FA thereabove and is suitably spaced from the imaginary vertical plane whereon the web-stretching comb P of the machine is moved (see Fig. 7), so as to avoid any interference with the latter member at the beginning of the cycle for the production of each knitted web (see below). The screw 101 is arranged below the axis of the screw 1, for the following reasons: to be far enough from the needle-bar FP, so as to be spaced adequately from the screw 1 when needed; to make the web T being produced by the machine pass between the screws 1-101 along a sinuous path of travel to make it enwrap said screws extensively, whereby the latter can best perform their longitudinal and transverse stretching action on said web (see below). The screw 101 is rotatably supported at the ends thereof by a pair of bell-crank levers 2, oriented downwards, inter-pivoted at 3 on the frame of the machine and connected at the other ends thereof to a resilient means 4 which can be calibrated by means of an adjustment nut 5. The arm 102 of the levers 2 is suitably shaped on the edge 6 facing the needle-bar FA so that when at the beginning of each working cycle the web-stretching comb P is lifted and inserted in the known manner with its hooks U between the needles of the needle-bars FA-FP, as shown in Fig. 7, the small rollers 7 provided at the ends of said comb will co-operate with the edge 6 of the levers 2 to cause the screw 101 to move away from the screw 1 to avoid any interference of said comb with said screw 101. When the comb is lowered and the hooks U have passed beyond the screws 1-101, said screw 101 moves back to the operative condition of Fig. 3 to nip the web T with a pressure depending on the calibration of the springs 4. In order to facilitate both the routine and extraordinary maintenance operations on the screws 1-101, the latter are mounted on their supports so as to be removable easily. As shown in Figs. 3 and 4, the supports for the screws comprise an open-top groove 8 whereinto the corresponding end portions and intermediate portions 12, 112 of said screws can be inserted easily (see also Fig. 1). At least in the outer sides of the end supports for the screws 1-101 there are formed annular recesses 9 which are concentric with the axis of curvature of the groove 8 and are adapted for engagement with the reduced end portion of a lock-ring 10 which is locked against axial movement on the end portions of the screws by means of a dowel or pin 11. By removing this pin, the lock-ring 10 can be disengaged from the recess 9 and the screws can be lifted and removed from their supports. In order to easily reach the screws 1-101, preferably, the rear needle-bar FP can be spaced away from the front needle-bar FA according to conventional methods which, therefore, are not discussed further herein. It will be noted in Fig. 1 that the screws 1-101 are provided with intermediate, symmetrically-disposed grooves 12-112 whereat said screws are supported by suitable supports, even only of fork-shaped type, and such as to avoid any interference with the movement of the comb P, all in a manner which may be easily conceived and worked out by those skilled in the art. The intermediate grooves 12 define in each screw 1-101 two oppositely-threaded portions, i.e. a right-hand threaded portion and a left-hand threaded portion, whereby during the co-operation with the web T being produced by the machine, as a result of the synchronous rotation of the screws in the directions indicated in Fig. 6 by the arrows F, the web T will be submitted by said threadings, in addition to a suitable stretching in a longitudinal downwards direction, also to a suitable stretching in a transverse direction, so that the loops of the web being sustained by the needles of the needle-bars will be in the best condition to be suitably picked up by the rods or needles of the automatic side-transporting devices, as discussed in the preamble of this specification. The screws 1-101 are synchronized as described below, and the crests of the thread of a screw operate in the inter-thread groove of the opposite screw, whereby the surface of the web T engaged by said screws is large. As shown in the detail of Fig. 5, the threads of the screws 1-101 have, preferably, a rounded contour, particularly a type of contour which is quite similar to the Edison contour. Moreover, good results have been obtained by using two-start threadings and with a pitch conforming the fineness of the flat knitting machine that is provided with the device of the invention. In case of machines having fineness 7, the pitch of the screws 1-101, for example, is such as to include 3.5 two-start threads per inch. The screws 1-101, preferably, are chrome-plated and polished or otherwise they are treated so as to have a reduced sliding friction while co-operating with the web T. With reference to Fig. 2, it will be seen that the screws 1-101 are connected at one end, through small universal joints 13-113, to the shafts of gearwheels 14-114 having the same diameter and meshing with each other, one of which is keyed on the slow-moving shaft of a motor-reducer 15 fixed to the frame of the machine, while the other one is rotatably supported on a support 16 which is fixed to the body of the unit 15. The motor of the unit 15 is of the variable-speed type and is controlled by the computer C provided on the machine (see Fig. 8), which automatically matches the rotational speed of said unit in a manner directly proportional, with the speed of the motor MC of the machine carriage. It is also possible to adjust finely, through a potentiometer 17, the rotational speed of the unit 15 to conform to possible specific requirements. When the machine carriage stops, the unit 15 stops too. Preferably, according to the invention, the unit 15 may also stop during the transport steps. During the normal operative cycle of the knitting machine, the unit 15 usually moves continuously. However, it is to be understood that said unit 15 may also be actuated intermittently.

Claims: 1. An automatic device for stretching both in the longitudinal direction and transverse direction a knitted web (T) being produced by flat-knitting machines, the automatic device being provided at a short distance from the top end thereof and such as to act transversely on the web (T) being produced by the machine, characterized in that it comprises a pair of parallel screws (1-101) arranged below the needle-bars (FA-FP), each screw (1-101) being provided with two oppositely-threaded portions, the crest of the threading of a screw (1) being operative in the inter-thread groove of the opposite screw (101), said screws (1,101) being actuated synchronously in a rotational direction and at a speed such that the web (T) being produced by the machine will be submitted to an adequate stretching both in the longitudinal direction and transverse direction, whereby the loops co-operating with the needles of the machine are always in the best condition to be picked up by the rods and/or needles of the automatic side-transport devices. 2. A device according to claim 1, wherein the stretching screws (1-101) have a threading with rounded contour. 3. A device according to claim 1, wherein the stretching screws (1-101) have a threading with Edison type contour. 4. A device according to claim 1, wherein the threading of the stretching screws (1-101) is a two-start or multiple start threading. 5. A device according to claim 1, wherein the threads of the stretching screws (1-101) have a pitch which is proportional to the fineness of the knitting machine whereon they are mounted. 6. A device according to claim 5, wherein the pitch of the threading of the stretching screws (1-101) includes 3.5 two-start threads per inch when said screws are designed for application on flat-knitting machines having a fineness of 7 needles per inch. 7. A device according to claim 1, wherein the stretching screws (1-101) are chrome-plated and polished or otherwise are treated so as to have a reduced sliding friction upon co-operating with the knitted web (T) to be stretched. 8. A device according to claim 1, wherein one (1) of said stretching screws is rotatably mounted on stationary supports, while the other screw (101) is mounted on swinging supports (2) which are connected to adjustable resilient means (4), so as to be resiliently urged towards the stationary screw, said swinging supports or parts associated therewith being shaped so as to co-operate with small rollers (7) mounted on the body of the web-stretching comb (P) when the latter is moved vertically at the beginning of each operative cycle, so as to space the movable screw (101) from the stationary screw (1) to avoid any interference of said screws with said comb, the stationary screw (1) being normally in such a position as to avoid interfering with said comb. 9. A device according to claim 1, wherein the stationary screw (1) is arranged close to the overlying needle-bar (FA), while the movable screw (101) is arranged below said stationary screw, so as to be far from the respective needle-bar (FP) to be moved unhindered thereby and to compel the web (T) to extensively enwrap said screws so as to be efficiently stretched thereby. 10. A device according to claim 1, wherein the stretching screws (1-101) are engaged in end supports comprising open top groove (8) so as to be easily disengaged from said supports whenever required. 11. A device according to claim 1, wherein the stretching screws (1-101) are connected at one end thereof, through small universal joints (13-113) to the shafts of a pair of gearwheels (14-114) having the same diameter and meshing with each other, one of which is keyed on the slow-rotating shaft of a variable-speed motor-reducer (15) which, preferably, is controlled by the computer (C) provided for the machine so as to rotate at a speed which is proportional to the speed of the carriage of said knitting machine, means (17) being preferably provided to permit the precision adjustment of the speed of rotation of the stretching screws to match it, if desired, to specific requirements. 12. A device according to claim 11, wherein the actuation logic of the stretching screws (1-101) is such that said screws usually rotate continuously during the normal operation of the knitting machine, while they are stopped when the machine carriage is stopped and, preferably, also during the operative step of the side-transport devices. 13. A device according to claim 11, characterized in that, the actuation logic of the stretching screws (1-101) is such that said screws rotate intermittently during the normal operation of the knitting machine whereon they are mounted, while they are stopped when the machine carriage is stopped and, preferably, also during the operative step of the side-transport devices.

Inventors: BERNARDELLI, GIANCARLO
Applicants: COMET MARTINELLI S.R.L.
Application year: 1989
Main classification: D04B15
IPC codes: B29C55, D06C3, D04B15