EP0326197A2

EP0326197A2 - Improved needle selection system in circular knitting machines, particularly for stockings

Info

Publication number: EP0326197A2
Application number: EP89200056A
Authority: EP
Inventors: Paolo Brandani
Original assignee: Savio SpA; Savio Macchine Tessili SpA
Current assignee: Savio SpA; Savio Macchine Tessili SpA
Priority date: 1988-01-27
Filing date: 1989-01-11
Publication date: 1989-08-02
Also published as: EP0326197A3; JPH01314761A; IT8819220A0; IT1216712B

Abstract

A system for needle selection in circular knitting machines, particularly for stockings, in which those reciprocating jacks (4) which are not required to raise the respective needle (5) are caused to re-enter the rotary tricked cylinder (1) by at least one lever (11) compelled by an electromagnet (16) ndergo a short travel stroke against the action of a return spring to strike the butt of said reciprocating jacks.

Description

This invention relates to a new system for needle selection in circular knitting machines, particularly for stockings, which combines the facility for a large number and variety of selections with low cost, considerable constructional simplicity, high reliability, very small overall size and a high operating speed. In such machines the needles are selected by presser levers acting on the butts of reciprocating jacks which are urged out of the tricked rotating vertical guide cylinder by fixed radial thrust cams and either slide along fixed lifting cams or do not. Said levers act on said butts by means of an inclined surface part so that they either selectively and gradually urge towards the interior of the tricked rotating guide cylinder those jacks which are not required to raise the overlying needle, with the result that said jacks are no longer acted on by said fixed lifting cams disposed externally to the cylinder and in close proximity thereto, or they allow to remain in a projecting position those jacks which are required to raise the respective overlying needle by the action of said fixed lifting cams. The selective command to the presser levers is generally provided by the action of teeth projecting from a selection drum which undergoes one or more rotary steps for each revolution of the tricked cylinder.
A drum lever system of this type, such as described in USA patent 3,662,572, suffers however from considerable drawbacks. In particular, even for forming the most common patterns many levels of butts are necessary, requiring lengthy jacks with consequent very tall and heavy tricked guide cylinders, leading to structurally complicated systems of considerable overall size. In addition the drum system is of poor versatility. In this respect, the pattern has to be changed by changing the arrangement of the projecting drum teeth, it therefore being necessary to halt the machine and remove the teeth and rearrange them according to the new required pattern. Lengthy down-times are therefore required for changing the pattern, with considerable negative influence on the machine production costs.
Again, this system is not particularly reliable in that the not inconsiderable possibility of an accidental but undiscovered breakage of a tooth during said manipulation or during operation can give rise to defective patterns not corresponding to requirements.
Current market requirements impose the need for fast product pattern changes to allow immediate adaptation to current fashion, thus implying very versatile machines, and use is therefore now made of a needle selection system utilising electromagnetically operated presser levers as described in U.K. Patent Number 1.481.146 by Macchine Tessili Circolari MATEC S.p.A. Each of said levers has a first vertically or axially inclined lead-in profile, along which the jack butt slides to rotate the lever, against the action of a return spring, with strokes of about 2 mm, into a position outside its path where said lever is retained by a permanent retention magnet, followed by a second profile with a radially inclined surface arranged to cooperate with said butt to cause the jack to re-enter the relative trick of the rotary cylinder. For this purpose, the magnet is provided with a coil energised in accordance with a program to temporarily neutralize on command the retention action of the magnet to allow said return spring to act by returning the lever to the path of the jack to thus compel its butt to follow said second radially inclined profile of the lever, and cause the jack to return to its inactive position and produce no lifting. Thus, in this latter needle selection system the jack butt not only undergoes radial action by the lever but also acts vertically or axially on the lever.
In other words, the approximately 2 mm displacement of the lever into its active position (so-called because it produces lifting of the jack and thus of the relative needle) is imposed by the actual movement of the tricked guide cylinder for the jacks, this position being maintained by the magnet which retains the ferromagnetic end of the lever in contact with it, whereas the 2 mm displacement of the lever into its inactive position in which the jack is caused to re-enter and remain inactive must be commanded by an electrical pulse which nullifies the magnetic effect to allow the return spring to act.
The advantages of such a selection system are immediately apparent.
They include firstly a great versatility which allows immediate implementation of a number of patterns as the system can now be easily controlled by a microprocessor with said patterns preprogrammed. The system also allows specific selection of the needles one by one, but against this there are the drawbacks of considerable heating of the electromagnets and a considerable vertical height.
In this respect to allow each individual needle to be selected, the butts of successive jacks must be spaced apart in a manner which at least take account both of the time required for positioning the electromagnetically operated lever, and of its overall extension in terms of the overall size of its vertically or axially active profile and of its radial thrust profile. This means that in order to provide a large number of needles per unit length of the tricked cylinder periphery, many levels of jack butts must be used (for example with 34 needles per inch, as required for ladies' stockings, at least 16 levels are required) with the result that the vertical height of the system increases considerably.
Again, to allow high selection rates the levers must switch by about 2 mm between one butt and the next with high frequency, but as their size cannot be reduced extremely light levers must be used to minimize inertia at the expense of mechanical strength, together with very small but powerful magnets which generate a considerable heat to be dispersed by a suitable cooling circuit, this causing further constructional complications.
The object of the present invention is to obviate said drawbacks by providing a needle selection system in circular knitting machines which is of extremely small height and length, is constructionally simple and reliable, and allows very high selection rates and a very large number and variability of selections themselves.
This is substantially attained in that instead of being made to act by moving their large inclined surface into the operating position through a stroke of about 2 mm, the presser levers are used as hammers which, against return springs, are caused by electromagnets, by means of a partial stroke of about 0.5 mm, to strike during their flight those jack butts which are to be made to re-enter in order to keep them inactive. In other words the levers serves only to transmit kinetic energy by impact to those jack butts which are to be deactivated, and according to one characteristic of the invention this is such as to enable the jack to undergo its entire stroke of travel of about 2 mm to completely re-enter as the result of only a very small stroke of the lever, equal to about 1/4 that of the jack.
In addition, the active part of the hammer lever can be of very small size, ie of length just greater than the jack thickness, with the consequent possibility of covering the entire needle selection field with only a few levels of levers (2-3). This means that the jacks and thus the tricked cylinder are of very small height with a consequent very small overall size of the selection system not only in width but also in height, and a much reduced cost and machining requirement.
Again, the potentially very small dimensions of the presser levers and their very reduced travel stroke mean that operating frequencies exceeding 200 Hertz can be obtained, ie much higher than those obtainable with known systems, and that smaller less powerful electromagnets can be used, with consequent smaller overall size and lesser heat to be dispersed.
The invention will be more apparent with reference to the accompanying drawing which shows a preferred embodiment by way of non-limiting example in that technical or constructional modifications can be made thereto but without leaving the scope of the present invention.
In said drawing:

Figure 1 is a partial perspective view, shown in partial section, of a needle selection system constructed in accordance with the invention;
Figure 2 is a partial plan view of the selection system of Figure 1 to an enlarged scale.

In the figures, the reference numeral 1 indicates a cylinder rotating in the direction of the arrow 2 and comprising axial tricks 3 acting as vertical guides for reciprocating jacks 4, 4′, 4˝, 4‴..., supporting corresponding needles 5, 5′, 5˝, 5‴... Said reciprocating jacks 4....4‴... are urged out of the rotary cylinder 1 by fixed radial thrust cams 6 so that their butts 7 (see specifically Figure 1) are compelled to slide along the fixed lifting cams 8 to raise the needles 5....5‴..., unless in proximity to said lifting cams 8 there acts a presser device 9 to cause them to return to said tricks 3 of the cylinder 1 in correspondence with recesses 10 in said radial thrust cams 6, in which case the jacks (see specifically the jack 4‴) do not raise the respective needle.
Said presser device 9 substantially consists according to the invention of a lever 11 pivoted at 12 on a rigid fixed support 13 to act with its end 15, against the action of a return spring 14, as an armature for a control electromagnet 16 which is suitably energized by the programmer 17.
The appropriate energization of the electromagnet 16, synchronized with the rotation of the cylinder 1 by said programmer 17, causes the lever 11 to move such that its active part 18 undergoes a short travel stroke of about 0.5 mm against the action of the spring 14, so that said active part 18 of the lever 11, acting as a hammer, strikes the jack butt 19 which is passing at that movement, so causing the jack to re-enter the cylinder 1.
Thus, as the lever is required only to supply kinetic energy by striking the butt of the jack concerned, its active part 18 can be of a length which is just greater than the thickness of the jack itself, with resultant very small dimensions.

Claims

1. A system for needle selection in circular knitting machines, particularly for stockings, comprising a rotating tricked vertical guide cylinder for the reciprocating jacks which control the needles and are urged out of said cylinder by fixed radial thrust cams to either, by way of a butt thereof, slide or not slide along fixed lifting cams according to whether presser means have not or have caused them to re-enter said cylinder, to correspondingly raise or not raise the corresponding needles, characterised in that said presser means consist of at least one lever acting against a return spring and compelled by an electromagnet, energized by pulses synchronized with the cylinder rotation, to undergo a short stroke of travel in order for its active part to strike in the manner of a hammer the corresponding butt of each jack which has to re-enter said cylinder in order not to raise the corresponding needle.

2. A needle selection system as claimed in claim 1, characterised in that said short travel stroke which the active part of said lever is required to undergo under the action of the electromagnet is generally about 1/4 of that which said jacks are required to undergo in order to completely re-enter said rotary tricked cylinder, and is about 0.5 mm.

3. A needle selection system as claimed in claim 1, characterised in that said active part of said lever end has a length just greater than the thickness of said reciprocating jacks.