NEEDLE SELECTION DEVICE FOR A CIRCULAR KNITTING MACHINE, PARTICULARLY FOR LADIES' STOCKINGS

Abstract: Electronically controlled electromagnetic needle selection in the direction of rotation of the needle cylinder in a circular knitting machine, including of the reciprocating motion type, particularly for ladies' stockings, is obtained by using: - a cylinder (1) with needles (2) and elastic pusher jacks (5) housed in corresponding longitudinal tricks, each pusher jack (5) being provided with three butts, namely an upper butt (7) cooperating with a first ring cam (30) for its lowering into the selection position, an intermediate butt (8) which when in the selection position cooperates with a presser cam (35) in the centripetal direction, and a lower butt (9) provided in a position corresponding with a cam (40) for raising the pusher jack (5) to activate the corresponding needle; - a rim structure (12) fixed to the needle cylinder (1) and provided lowerly, in line with each pusher jack (5), with a radial horizontal groove (11) housing an elastic selector (10) having its foot (13) fitted onto the outer circumference of the rim structure and its head (17) underlying the foot (6) of the pusher jack (5) when this latter is in its rest position; - a selection electromagnet (20) interposed between two permanent retaining magnets (22, 23) and fixed under each horizontal elastic selector (10), said electromagnet (20) cooperating with said selector (10) when this latter is urged against the electromagnet by the foot (6) of the pusher jack (5) under the action of the lowering cam (30), in order to either select or not select the corresponding lower butt (9) of the pusher jack (5) after its intermediate butt (8) has passed along said presser cam (35).

Description: This invention relates to an electromagnetic needle selection device for a circular knitting machine with reciprocating motion, particularly for ladies' stockings. Circular knitting machines are known to use one or more needle selection units disposed about the cylinder before each feed, each unit consisting of an electromagnet having a maximum width equal to the distance between one needle and the next and interposed between two permanent magnets, and a presser cam disposed in correspondence with that magnet upstream of the electromagnet, in the direction of advancement of the cylinder, to urge against this latter a rocking selector associated with and overlying an elastic pusher jack. The electromagnet is pulse-operated by current passage or current interruption or direction reversal, in accordance with an electronic program synchronized with the movement of the needle cylinder, in order to selectively keep the rocking selector attracted and/or adhering to the magnets and prevent the butt of the elastic jack from engaging a control cam and inactivating the corresponding needle, or to weaken the magnetic field generated by the permanent magnets and thus release, ie repel, said rocking selector, so causing the butt of the elastic jack to be raised by said control cam and activate the corresponding needle. Such a selection system, as described for example in USA patent 3,972,206, has various drawbacks, such as the fact that the cylinder tricks must be sufficiently deep to house the elastic pusher jack and the rocking selector in associated and superposed relationship, so that such a configuration is possible only for low fineness values; for fineness values exceeding 14, the cylinder walls become too thin and weak and compromise very deep milling. The use of barred cylinders results in constructional advantages and allows tricks to be formed with constant thickness walls and smooth surfaces which are hard, elastic and robust; however the radial arrangement of the bars means that the width of the tricks is greater at their periphery than at their base, and this difference, which increases as the depth of the tricks increases, causes serious clearance problems between the walls and the rocking and sliding members and problems in controlling the friction and force equilibrium. In addition, as the elastic jacks are in direct relationship with the electromagnets by way of the rocking selectors, the requirement for rapid and reliable response at high speed and high fineness values means that the outward elastic force of the elastic jacks when in their working position must be high to ensure response rapidity in the case of non-selection, and therefore the attraction force of the selection electromagnets must overcome this elastic force to keep the elastic jack in its non-working position. However this attraction force is limited by the magnetic flux passage cross-section of the electromagnets, and this is itself limited by the available space between one needle and the next, and when the saturation level has been attained there is no way in which this attraction force can be increased, not even by increasing the number of turns or the current intensity. This limitation, which increases with increasing fineness value, endangers the equilibrium between the elastic reaction, the inertia of the moving parts, friction, centrifugal force etc. On the other hand, although a reduction in the elastic force of the elastic jacks means that the electromagnets can provide better retention with a more easily attainable magnetic force, this reduction compromises the separation of the rocking selectors from the magnet during selection because of the large lever arm and the high centrifugal force involved at high speed. The combination of these limitations and stresses means that systems of the aforesaid type are inadequate and are unable to respond to fineness, speed and reliability requirements. With the system described in USA patent 4,020,652, which comprises two superposed electromagnetic actuators acting on rocking selectors provided with two butts at corresponding height, the time available for selecting each individual needle can be doubled. However the available space for, and therefore the force of, the electromagnets are always so limited that they are unsuitable for high fineness values and in particular, for the same reasons, do not solve the initially stated problems relating to the equilibrium between the elastic, magnetic, centrifugal, friction and centrifugal forces, and to the difficulties of construction. GB patent 2,112,822 describes an electromagnetic selection system in which the upper end of each rocking jack is designed to urge the lower end of the corresponding overlying needle or needle pusher outwards to allow it to engage the control cam, the lower end of said vertical jack being acted upon by an intermediate horizontal jack which slides longitudinally and rocks vertically in a radial groove of an external annular body which is rigid with the needle cylinder, said intermediate jack being associated with an underlying supplementary vertical selector jack housed in a vertical groove in said annular body parallel to that housing the main jack but lying on a circumference of greater radius. In front of said supplementary jack there is an electromagnet and under the butt of said jack there is a fixed cam which when the electromagnet is not energized urges the supplementary jack upwards so that the foot of the intermediate jack is urged centripetally by a cam in such a manner that it acts on the lower end of the main jack which then selects the corresponding needle. However even if this device does provide a greater space for the selection electromagnets by disposing them on a larger-radius circumference of the needle cylinder and avoids superposing the main jack and the selector jack in the same trick of the needle cylinder, it increases the constructional complexity of the machine because of the larger number of components and the variety of movements to be effected, and does not solve the force equilibrium problem, particularly with regard to centrifugal and elastic forces, and therefore does not seem able to allow the needle cylinder to operate at the currently required speed. The object of the present invention is to obviate the aforesaid drawbacks and limitations by providing a device which is adaptable to standard-trick circular knitting machines, which implements the needle selection even for fineness values exceeding 14 needles/inch as required in the manufacture of ladies' stockings, which offers great reliability even at the highest speeds currently obtainable and which at the same time is of simple low-cost construction. This result is attained according to the invention by using for each needle: an elastic pusher jack provided with three butts at different heights, the upper butt cooperating with a ring cam for its lowering into the selection position, the intermediate butt cooperating, when in the selection position, with a presser cam centripetal to the cylinder, and the lower butt being provided in a position corresponding with a ring cam for raising the pusher jack to activate the corresponding needle; an elastic selector housed horizontally in a radial groove provided in the lower surface of a rim structure rigidly fixed about the needle cylinder, its foot being anchored to the outer circumference of said rim structure and its head underlying the foot of the pusher jack when in its rest position; a selection electromagnet interposed between two permanent retaining magnets and underlying each horizontal elastic selector to cooperate with this latter when it is urged against it by the foot of the pusher jack under the action of the lowering cam, in order to either select or not select the corresponding intermediate butt of the pusher jack after its passage past the presser cam. Advantageously the device is provided with a ring fixed onto the needle cylinder in a position underlying the horizontal elastic selectors to keep these, when they are attracted by the electromagnets, slightly spaced from the permanent magnets and electromagnets so as to reduce the magnet wear and the force resisting sliding. According to a preferred embodiment of the invention the upper butts of the pusher jacks of even courses are disposed at a different height from those of the odd course jacks so that they are lowered in sequence into the selection position in correspondence with two electromagnetic actuators which are also operated in sequence; this arrangement doubles the time and space available for selecting each individual needle, so increasing operational reliability for higher fineness values and speeds without reducing the constructional simplicity. The solution proposed by the present invention enables an electromagnetic selection device to be provided which is of simple construction, is adaptable to standard cylinders at low cost, and which because of the particular arrangement of the elastic selectors solves the problem of balancing the forces in play, so allowing operation at the currently required speeds and fineness values, particularly in the manufacture of ladies' stockings. These and further advantages and characteristics of the invention will be more apparent to the expert of the art from the description given hereinafter with reference to the accompanying drawings, which are given by way of non-limiting example and in which: Figure 1 is a radial section through the needle cylinder with a selection device according to the invention in its initial position, ie before the selection stage; Figure 2 is a developed view of the cam skirt for the selection device of Figure 1; Figure 3 is a diagrammatic view of the device of Figure 1 immediately before the selection for activating the corresponding needle and after the pusher jack has lowered the horizontal selector jack against the first permanent magnet; Figure 4 is a diagrammatic view of the device of Figure 1 after the selection for inactivating the corresponding needle; Figure 5 is a radial section through the needle cylinder showing a modified selection device, according to the invention, in its initial position before the selection stage; Figure 6 is a developed view of the cam skirt for the selection device of Figure 5; Figure 7 is a diagrammatic view of the device of Figure 5 immediately before the selection for activating the corresponding needle and with the selector jack lowered by the pusher jacket; Figure 8 is a diagrammatic view of the device of Figure 5 after the selection for inactivating the corresponding needle; Figure 9 is a radial section through the needle cylinder showing a further modified selection device, according to the invention, in its initial position before the selection stage, ie with all needles working; Figure 10 is a developed view of the cam skirt for the device of Figure 9; Figure 11 is a diagrammatic view of the device of Figure 9 during the selection stage. With reference to Figures 1 and 2 of the accompanying drawings, a device according to the invention for electronically controlled electromagnet selection, needle by needle, in a circular knitting machine with reciprocating motion, in particular for ladies' stockings, comprises in combination, for each needle 2 to be selected: a vertical elastic pusher jack 5 longitudinally slidable in a corresponding trick 3 of the cylinder 1 with its head in contact with the lower side of the butt of a relative needle 2, and elastically flexible in a direction radial to the cylinder 1, its rest position being that with its foot 6 separated from the base of the trick 3; said jack 5 is also provided with three butts 7, 8, 9 of which the upper butt 7 is for selecting, and the intermediate butt 8 and lower butt 9 are for activating the corresponding needle at two different levels; a horizontal elastic selector 10 housed in a radial groove 11 in line with the trick 3 for the corresponding jack 5, the groove being provided in the lower face of a rim structure 12 rigidly fixed about the needle cylinder 1; the foot 13 of said selector 10 is of C-shape to enable it to be mounted over the outer circumference of said rim 12 in a corresponding vertical slot 14 and urged into its seat, in the centripetal direction, by two ring springs 15. The body of the selector 10 comprises in proximity to its foot a zone 16 of reduced cross-section to enable the head 17 to flex in a vertical direction; when in its rest position, said head 17 rests against the base of the relative groove in the rim structure 12 and partly penetrates into the trick 3 housing the pusher jack 5 in a position below its foot 6. When in the rest position, the rear of said pusher jack 5 in proximity to its foot is in contact with the inner edge of the rim structure 12 and with an overlying ring 12a which is fixed onto said rim structure to provide a means for fixing this latter to the needle cylinder 1. Finally, the body of said horizontal selector 10 has a middle zone 18 which is slightly offset downwards with respect to the longitudinal axis to define the attraction section for the electromagnet; a selection electromagnet 20 interposed between two permanent retention magnets 22, 23 mounted on the fixed part of the machine under said rim structure 12 in correspondence with the attraction section 18 of the selectors 10; a ring 25 composed of several sectors fitted together and kept in its seat against the outer surface of the needle cylinder 1 by two ring springs 26, in a position below the head 17 of the horizontal elastic selectors 10 to limit their downward travel and prevent contact between the attraction section 18 and the magnets 22, 23 when in the selection position and thus reduce magnet wear and the forces resistant to sliding. Moreover, to select and control the needles, the selection device according to the invention uses conventional means, namely: two preselection ring cams 30, 31 lying respectively above and below the upper butt 7 of the pusher jacks 5, and of which the upper cam 30 comprises two ramps 30a and 30b, the lowest point of which is vertically above the outer end of the magnets 22 and 23 respectively, to enable the upper butt 7 of the pusher jacks 5 to be lowered into their lower selection position (see Figure 3), ie in each of the two directions of motion of the needle cylinder. The lower cam 31 comprises two ramps 31a and 31b to enable the upper butt 7 of those pusher jacks not selected during the preceding selection stage to be raised into the initial intermediate preselection position, (see Figure 1); a presser cam 35 disposed on the vertical axis of each electromagnet 20, its symmetrical ramps 35a and 35b being arranged to engage the intermediate butt 8 of the corresponding pusher jack 5 in the lower selection position, during its passage in the two directions of motion of the needle cylinder respectively; a ring cam 40 underlying the lower butt 9 of the pusher jacks 5 and comprising two ramps 40a and 40b arranged to raise the lower butt 9 of the selected pusher jacks 5 to activate the corresponding needle; a group of cams 45 of inverted isosceles trapezium shape acting on the butt 2′ of the needles 2 to allow stitch formation in conventional manner. The operation is as follows. While the needle cylinder 1 is moving in the direction of the arrow F, as each needle 2 with its pusher jack 5 and horizontal elastic selector 10 arrives at the selection unit 4, the pusher jack 5 is in the initial intermediate preselection position (see Figure 1). The contour 30a of the cam 30 then lowers the pusher jack 5 into the lower selection position so that its foot pushes the head 17 of the elastic selector 10 downwards against the stop ring 25 to enable the magnet 22 to keep the section 18 of the selector 10 attracted (see Figure 3). The contour 35a of the pressure cam 35 then urges the intermediate butt 8 of the pusher jack 5 towards the inside of the cylinder 1, to release the head of the selector 10 which still remains attracted by the magnet 22. At this point one of the following two selections can be made: 1st selection. If the electromagnet 20 is not energized, the selector 10 rises to lock the foot of the pusher jack 5 against the base of the relative trick 3 (see Figure 4); the lower butt 9 of the jack 5 then passes beyond the cam 40 without being engaged by its contour 40a, to inactivate the corresponding needle 2, and proceeds along the lower track A behind said cam 40 until it reaches the next contour 31a of the cam 31 for its return to its initial preselection position ready for a further selection. 2nd selection. On energizing the electromagnet 20, the selector 10 remains attracted by the second magnet 23 and the foot 6 of the pusher jack 5 returns to its rest position against the inner edge of the rim structure 12 with the result that its lower butt 9 is engaged by the contour 40a of the cam 40 (see Figure 3) so that by rising, it urges the corresponding needle into the activation position to allow stitch formation in conventional manner. After stitch formation the jack 5 is returned to its bottom selection position by the contour 30a of the cam 30 which acts on its upper butt 7. Figures 5 to 8 of the accompagnying drawings show a modified embodiment of the selection device according to the invention. This embodiment comprises, for each selection device: two electromagnetic actuators each consisting of an electromagnet 20a, 20b interposed between two permanent magnets 22a, 23a and 22b, 23b, and disposed in sequence along the passage of the elastic selectors 10; odd and even course pusher jacks 5a, 5b respectively, provided with an upper butt 7a, 7b at different heights so as to be separately engaged by two separate pairs of preselection cams 30′, 30″ and 31′, 31″; two presser cams 35′ and 35" for selecting odd and even course jacks respectively, and disposed in a position corresponding with the respective electromagnetic actuator upstream of the contour 41a and 42a of the control cam 40. The operation, which is similar to that of the preceding device but is divided into two stages, is as follows. The odd pusher jacks 5a are lowered into their lower selection position by respective contours 30′a of the cam 30′, whereas the even jacks 5b are positioned by the profile 30″c or 31″a in the intermediate preselection position. The only odd jacks 5a are urged against the cylinder 1 by the first presser cam 35′ and, if selected by the selectors 10 held attracted by the electromagnets 20a, they are raised into the intermediate position by the contour 41a of the cam 40 (butt 7a follows contour 30′c of cam 30′) so as not to be engaged by the second presser cam 35″ or further raised by the control contour 42a of the cam 40. If they are not selected they pass beyond the cams 40 and 35″ without being affected by them. After the even course jacks 5b have passed beyond the presser cams 35′ and 40 without being acted upon by them, they are lowered into the bottom selection position by the contour 30″a of the cam 30″ which acts on the butts 7b and are therefore selected by the presser cam 35″ and by the second actuators 20b. They are then either raised or not by the profile 42a of the cam 40 together with the odd course pusher jacks 5a. Figures 9 to 11 of the accompanying drawings show a further embodiment of the device according to the invention which is particularly advantageous for higher fineness values. In this embodiment: each horizontal elastic selector 10 is housed in a corresponding radial groove 11 provided in the upper face of the rim structure 12 with its head 17 resting, when in the rest position, on the base of the relative groove 11 and partly penetrating into the trick 3 of the corresponding pusher jack 5 under the foot of this latter; the selection electromagnet 20 is mounted above said rim structure 12 in a position corresponding with the attraction section 18 of the selectors 10 but without making contact therewith during the attraction; and a permanent magnet 23 is mounted above the rim structure 12 in a position corresponding with the head 17 of the selectors 10. The magnetic force of said permanent magnet 23 and its distance from the selector 10 must be such that, in relation to the elastic reaction of the selector 10, it does not influence this latter when in its rest position, but be sufficient to keep it attracted against the ring 25, provided above the rim structure 12, during and after attraction by the selection electromagnet 20. The width of the pole pieces of the electromagnet 20 in the direction of motion must be at most equal to the pitch of the selectors 10, and the width of the pole pieces of the permanent magnet 23 must be such as to keep the selected selectors 10 attracted and so keep the butt 9 of the pusher jacks 5 disengaged from the cam 40 even after the butt 8 has abandoned the presser cam 35. The advantages of such an arrangement are essentially that no additional sliding of the pusher jacks 5 is required to activate the horizontal selectors 10 before selection; that these latter rock only when the needles are inactivated; and that it is not necessary to activate the electromagnets 20 when the needles are activated. In practice the invention is susceptible to modifications in terms of the shape, dimensions and arrangement of its component elements and the type of materials used, but without leaving the scope of the inventive idea and therefore lying within the scope of protection of the present industrial invention patent.

Claims: 1. An electromagnetic needle selection device for a circular knitting machine, including of the reciprocating motion type, particularly for ladies' stockings, comprising for each needle an elastic pusher jack (5) and a horizontal elastic selector (10) housed in a radial groove (11) of a rim structure (12) fixed about the needle (2) cylinder (1), characterised in that said pusher jack (5) is provided with three butts (7, 8, 9), namely an upper butt (7) cooperating with a first ring cam (30) for its lowering into the selection position, an intermediate butt (8) which when in the selection position cooperates with a presser cam (35) in the centripetal direction, and a lower butt (9) provided in a position corresponding with a ring cam (40) for raising the pusher jack (5) to activate the corresponding needle (2), said elastic selector (10) having its foot (13) of C-shape to enable it to fit into a corresponding vertical seat (14) provided in the outer circumference of said rim structure (12) and retained in the seat by a ring spring (15), and its head (17) projecting into the corresponding trick (3) of the needle cylinder (1) in a position underlying the foot (6) of the pusher jack (5) when this latter is in its rest position; and comprising a selection electromagnet (20) and at least one permanent retaining magnet (22, 23) which cooperates with said horizontal selector (10) when this latter is activated by said electromagnet (20), in order to either select or not select the corresponding lower butt (9) of the pusher jack (5) after its intermediate butt (8) has passed along said presser cam (35). 2. A selection device as claimed in claim 1, characterised in that said elastic selector (10) is housed in a groove (11) provided in the lower face of the rim structure (12), the electromagnet (20) and the permanent magnets (22, 23) being correspondingly disposed below said rim structure (12). 3. A selection device as claimed in claim 2, characterised in that said electromagnet (20) is interposed between said permanent magnets (22, 23). 4. A selection device as claimed in claim 1, characterised in that said elastic selector (10) is housed in a groove (11) provided in the upper face of the rim structure (12), the electromagnet (20) and the permanent magnets (22, 23) being correspondingly disposed above said rim structure (12). 5. A selection device as claimed in claim 4, characterised in that said permanent magnets (22, 23) are disposed in proximity to the head (17) of the elastic selector (10). 6. A selection device as claimed in claims 2 and 4, characterised in that said elastic sector (10) has a zone (16) of reduced cross-section in proximity to its foot (13). 7. A selection device as claimed in claim 2, characterised in that the middle attraction zone (18) of said elastic selector (10) has a profile which is offset downwards with respect to the longitudinal axis. 8. A selection device as claimed in claims 2 and 4, characterised by comprising a ring (25) fixed onto the needle (2) cylinder (1) in a position respectively lower than and higher than the head (17) of the elastic selectors (10) and held in its seat by springs (26) such that an elastic selector (10) which has been attracted by the electromagnet (20) is kept in an attracted position but without touching the electromagnet (20) and the corresponding permanent magnet (22, 23). 9. A selection device as claimed in claim 1, characterised in that the upper butts (7a) of the pusher jacks (5a) of even courses are disposed at a different height than the butts (7b) of the odd course jacks (5b) so that the two butts (7a, 7b) are respectively lowered in sequence by the respective cam (30′, 30″) into the selection position in correspondence with two electromagnetic actuators (20a, 20b) and two presser cams (35′, 35″) which are respectively disposed in sequence.

Inventors: FURIA, EDOARDO
Applicants: SAVIO S.P.A.
Application year: 1989
Main classification: D04B15
IPC codes: D04B15