Electromagnetic selector equipped with a plurality of selection positions

Abstract: An electromagnetic selector device comprising a single permanent magnet (1) and a plurality of electromagnets (6), which are excited in contrast or in agreement with the permanent magnet, to form a plurality of selection positions on two fronts along which run the elements (5) to be selected.

Description: The present invention relates to an electromagnetic selection device capable of holding or not holding, depending on the electrical excitation supplied to it, ferromagnetic elements which are brought close to it for very short periods. These electromagnetic devices are widely used in the electro-mechanical industry and one of their typical applications is in circular knitting machines. The present description refers to this application, without any intention of limitation. In circular knitting machines, the needles are selected by operating elements active in the said selection (comprising for example auxiliary jacks, rocker levers and flexible bars arranged to form a kinematic chain with each needle) which are held or not held and assume two alternative positions, which correspond to putting into operation or excluding from operation the corresponding needle. These devices and procedures for selecting the needles in a circular knitting machine are described for example in European Patent Application No. 91202485.8 of the present Applicant, in European Patent Application No. 219029 in the name of Lonati, in UK Patent Application No. 2112822 in the name of Elitex, in UK Patent in the name of Precision Fukuhara and in French Patent No. 1564603 in the name of Mayer. The present invention is described with reference to the said specific application, which presents considerable difficulties as regards the speed at which the selection must be made, the problems of shortage of space, and the problems of synchronism with the other organs of the machine, but with the proviso that the electromagnetic selection device can be advantageously applied also in other areas of technology. An electromagnetic selection device based on the combination of attraction by permanent magnets with concordant or contrasting attraction by electromagnets, depending on their excitation, is described in Czechoslovakian Inventor's Certificate No. 216358. This device comprises a plate along the edge of which slide the active needle-selection elements, loaded with an elastic force which tends to pull them away from the said edge. The two external parts of the said edge comprise the pole shoes of a permanent magnet - which thus permanently exert an attractive action on the active elements that slide along the edge - while the central part of the said edge, magnetically isolated from the external parts, constitutes the pole shoe of an electromagnet which attracts or does not attract the active elements that slide along it, depending on the electrical excitation supplied to it, releasing them or holding them to make the selection the moment they pass through the central part. According to European Patent Appln. No. 91202485.8 of the present Applicant, this selection is performed by means of a plurality of electromagnetic selectors of the type described above, placing the said selectors on different levels and equipping the active selection elements with protrusions and/or indentations at the said levels. Known from GB-A-2,043,120 is a control magnet system for a pattern apparatus on a knitting machine which has a permanent magnet including a control pole and controllable by means of a control coil and a cooperating pole. An armature is movable relative to the two poles and can be applied against the surface of the control pole against a spring force. When the coil is not energized, the armature remains unattracted, whereas, when the control coil is energized the armature is released. Known from EP-A-0,343,123 is a numerically controlled device for the electromagnetic selection of needles at three different positions corresponding to floating, stitch retention and stitch discharge positions. The device employs two vertically superimposed electromagnets for selecting corresponding oscillatable selectors for selecting the lowered floating-stitch position of the needles, a first cam-operated device for moving the needles to an intermediate stitch-retention position, and a second cam-operated device for moving the needles to an upper stitch-discharge position. Also known from FR-A-2,568,596 is a circular knitting machine having a needle selection device including oscillatable selectors which act on elastic members, under the action of cams and electromagnetic selection and retention devices, arranged around the needle cylinder and excited selectively according to a program. Moreover, known from EP-A-0,249,203 is an electromagnetic selector device in which a selector is supported by a carriage for moving a select face of the selector in sliding contact with select jacks supported by a support jack through a support member. The select face has a highest point at a jack posture correcting edge and a downwardly inclined jack support edge. Poles of electromagnets are provided on the jack posture correcting edge and on both sides of the jack support edge, and poles of permanent magnets are provided on both outsides in the jack support edge direction of the poles of the electromagnets. There are considerable problems in using these electromagnets selectors due to the limited availability of angular space for their arrangement proceding any supply of wire, and to the small distance between two successive elements to be selected (which may be of the order of one millimetre or even less) and lastly to the limited axial space available for modulating the selection on the various levels of the selectors. The present invention provides an electromagnetic selector as defined in the appended claims. The selector according to the invention consists in a compact electromagnetic selector, equipped with a plurality of work positions which requires a minimum number of components and a minimum space for its arrangement. The present invention is described below with reference to Figures 1 to 3 which show a few of its typical embodiments, for the purpose of illustration but in no way limiting. According to the embodiment in Figure 1, the selection device uses a single permanent magnet 1, with N and S poles at its opposite bases. To these N and S bases are connected two parallel plates 2 of ferromagnetic material, each of these plates having a cavity 3 to house the electromagnetic part of the device. The two edges 4 of the device have elements 5 to be selected running through them. Edge 4a selects elements 5a and edge 4b selects elements 5b. Each edge 4 is made up of two end parts 4' which belong to plate 2 and constantly have a magnetic polarity (N or S) imparted to them by permanent magnet 1, and of a central part 4'' which constitutes the pole shoe of electromagnet 6 and assumes a magnetic polarity depending on the excitation of its winding by an electric current. As previously described, elements 5 slide along edge 4 and are loaded with an elastic force which tends to pull them away from the said edge. If electromagnet 6 is excited so as to counteract the attractive action by the pole shoes of the permanent magnet, elements 5 which slide along edge 4 in central section 4'' are no longer attracted and, due to their elastic force, become detached from the said edge. They then follow a different trajectory to those elements which instead continue to find magnetic attraction in section 4'', since electromagnet 6 is not excited in contrast to the permanent magnets. The elements thus selected are engaged by different organs placed along two different trajectories and work differently. Parts 4'' and 4' are magnetically separated by diamagnetic inserts 4'''. Electromagnets 6a and 6b are held by supports 7 and packed in by bolts 8, which form the assembly of the device. Edges 4a and 4b may be the same and have the various parts 4', 4'' and 4''' of the same dimensions and placed at the same angular intervals, or they may be different and/or placed at different angular intervals. In other words the device may be symmetrical in its two parts or asymmetric. The cores and windings of electromagnets 6a and 6b may be arranged along the same A-A axis or along axes which are offset in relation to each other, and thus their pole shoes 4'' may be positioned on different angular co-ordinates in relation to the cylinder of the machine. Whereas in Figure 1 the A-A axis is essentially at right angles to plate 2, in Figure 2 a different embodiment of the invention is shown, placing the axes of the electromagnets parallel to the plane of plates 2. The arrangement shown in Figure 1 enables a device with a minimum distance between plates 2, while the arrangement shown in Figure 2 enables a device with smaller overall vertical dimensions. Figure 3 shows an embodiment of the selector device according to the invention for several pairs of electromagnets 6a and 6b placed on upper and lower levels, in which a single permanent magnet 1 and, preferably, a single pair of plates 2, each with several cavities 3, and a single pair of supports 7, serve to create several pairs of selection positions, bearing several pairs of electromagnets 6. With this arrangement the various parts 4', 4'', 4'...4'', 4' of the active selection edge are alternated, the terminal parts however being those connected to the permanent magnet. This arrangement enables an even more compact selector to be created, with a minimum number of parts, easier to construct and install on the machine, and with even smaller angular dimensions.

Claims: An electromagnetic selector particularly suitable for application in circular knitting machines for selecting active elements used to put into operation or exclude the corresponding needles, comprising a part with a permanent magnet (1) with matching pole shoes (4') in an external position and an electromagnetic part (4'') in an internal position in relation to said pole shoes (4'), such pole shoes (4' and 4'') being magnetically isolated from each other and forming the path (4) along which the selection of active elements (5) is made, characterised in that it comprises two parallel plates (2) connected to the N and the S poles of the single permanent magnet (1), each with a cavity (3) to contain electromagnets (6) with their pole shoes (4''), to form two parallel paths (4a and 4b) on two different levels to select elements (5a and 5b), depending on the electrical excitation supplied to electromagnets (6a and 6b), to hold said elements (5a and 5b) against path 4 or not to hold said elements (5a,5b) and then to bring them onto different trajectories, constituting two selection stations on two levels. An electromagnetic selector device according to Claim 1, characterised in that electromagnets (6) are arranged with their axis essentially perpendicular to said plates (2). An electromagnetic selector device according to Claim 1, characterised in that electromagnets (6) are arranged with their axis essentially parallel to said plates (2). An electromagnet selector device according to Claim 2 or to 3, characterised in that to a single permanent magnet (1), and preferably to a single pair of plates (2), corresponds a plurality of cavities (3), to house a plurality of pairs of electromagnets (6a and 6b) with their pole shoes, to form a plurality of pairs of selection positions on two levels.

Inventors: ARIA PIERO, ARIA, PIERO
Applicants: MATEC SRL, MATEC S.R.L.
Application year: 1991
Main classification: D04B15
IPC codes: D04B15