MAGNETIC CORES ASSEMBLY PLANT FOR ELECTRIC TRANSFORMERS AND THE LIKE

Abstract: One or more stores (14) of shaped laminations are movable along a track (12); means for gripping and transfer­ ring the laminations from a store are able to transfer them onto an assembly plane (32), said grip means being capable of placing the laminations in the assembling arrangement; the repetition of the action of the grip and transfer means is obtained in order to form several steps with a predetermined number of laminations.

Description: DESCRIPTION The object of the invention is to provide a plant for the automatic assembly of magnetic cores for electric transformers or other made up of die-cut laminations, by avoiding at most the manual intervention. Substantially, the plant comprises: at least a store of shaped laminations with which to form a core or a step of a core; means for the grip and transfer of the laminations from the store in order to transfer them onto an assembly plane, said grip means being able to place the laminations in the assembling arrangement; and means to obtain the repetition of the action of the grip and transfer means in order to form steps with a predetermined number of laminations. Advantageously, said grip and transfer means may comprise mobile frames which move above the stores and the assembly plane, and,on said frames, members or equipment moving in orthogonal direction to the frames and forming vertical guides for sucker lifting means or the like. Said moving members and/or said frames are operated through catches or step-by-step motors or equivalent means to bring the laminations close to each other in the assembling arrangement and stagger subsequent laminations or groups of laminations. The plant may comprise - in order to form stepped cores a number of stores, each one for the laminations relevant to one step, and means for subsequently transferring said stores to a position of picking up by the grip and transfer means. The stores may be realized either by means of a platform or by carriages which are movable along rail tracks or equivalent and connected between them or otherwise independent of each other. In a advantageous embodiment, each of the grip and transfer means comprises at least two suckers able to engage the lamination towards the end portions thereof, arid a possible central catch in order to achieve curvature convex in the lower part of the lamination which is being lifted, apt to facilitate the separation thereof from the remaining pile of the laminations. A plant may also comprise - in addition or as an alternative to the central catch - magnets or electromagnets capable of induc= ing a homopolar-loeal magnetization in the adjacent laminations in order to cause a repulsion between the close ends of superimposed laminations, able to facilitate the separation of the lamination being lifted out from the laminations of the remaining pile. Programming means may be provided to set up an automatic execution of the grip and transfer of the laminations and their laying down onto the various steps of the core with an automatic handling of the stores7 frames,.grip and transfer means as well as of the catches or other delimitation means of the laying down position of the laminations. The plant may include at least two assembly stations operating out of phase. The following description and the attached drawing disclose in more detail - but, however, in a rough, exemplifying and, therefore, non limitative way - the present invention,reference also being made to the prior art. In the drawing: Figs. 1 and 2 show a core and a local cross section of one element thereof; Figs. 3 and 4 show a group of shaped laminations which may be utilized to form a layer of an assembly of components and the relative position taken up by said laminations in the partial composition of a core for the mounting of the windings; Figs. 5 and 6 are, respectively, a plan view and an elevation view of one embodiment of a plant according to the invention; and Fig. 7 shows a diagram of the stages succession of a work-cycle. As above stated this invention relates to a flexible automatic plant apt to the assembling of magnetic cores for three-phase electric transformers, and for equivalent purposes. A three-phase magnetic core is made up of three straight parallel elements, called columns, and of two elements, called yokes, also parallel between them but at right angle to the columns, which yokes close the magnetic circuit. Each of the above elements consists of a plurality of matched ferromagnetic laminations. Both the yokes and columns have sections of generally square or rectangular shape or inscribed in a circle and with a steps-like pattern. The stepped, or staircase section represents the most general case, while the square and rectangular ones are particular cases. In general, the stepped section is obtained by forming shaped laminations into rectangular packs, the laminations width corresponding to a certain set of strips, while the thickness of the packs is a consequence of the condition to achieve the perfect inscription of the cross section into a circle. By increasing the number of steps, the filling coefficient of the circular section approaches the unity. For constructive reasons, the number of strips is usually dependent on the cross-section diameter of the core components (yokes and columns) and is usually kept to a low value in order to simplify the shearing and assembly operations. An example of a complete magnetic core is shown in Figs..l and 2, Fig. 1 showing the core as a whole, while Fig. 2 shows the stepped section of the columns and yokes. The external columns CE have the interspace 10 and the yokes G have the interspace H,. The central column is indicated by CC In the cross section, N is the diameter of the circumscribed circumference and E, F are, respectively, the minimum and maximum width of the used lamination strips. In a proper and up-to-date construction, the magnetic lamination strips are sheared according to the patterns or outlines shown in Fig. 3 in which, on the left, there is indicated an outline for the columns CE in the centre an outline for column Cc and on the right an outline for one of the yokes G. In Fig. 4 there is shown the relative position between the laminations of Fig. 3, to allow the assembly of the windings on the columns prior to the core completion with the second yoke. It must be observed in Fig. 4, that the successive laminations, making part of the assembly illustrated in Fig. 4, are slightly staggered as indicated with -dotted line differentiated in respect to the solid line; the laminations of columns CE and of the yoke are only axially staggered, while the double cusp laminations of the central columns Cc have the cusps diverted in opposite directions and are assembled in overturning condition to each other according to a longitudinal axis. In a six-step core, for example, six assor- tments of patterns are utilized as illustrated in Fig. 3, and each assortment corresponds to a certain length of strips. The following table shows, for a series of different electric powers, the sizing, the number of steps and the total weight of a core, by way of example only. TABLE Power Weight KVA N NSTEPS Igo HO E F 50 114 4 420 355 100 40 119 250 161 5 580 500 150 50 343 500 188 6 660 585 180 40 555 1000 201 7 740 745 190 50 770 2000 231 7 820 1000 220 60 1275 The three patterns (Fig. 3) of each assortment are usually mounted by hand on plane provided with catches according to the positioning shown in Fig. 4 in which as already mentioned - the solid line indicates the assembly of the patterns of the layers subsequently superimposed to the one indicated with dotted line, thereby the air-gaps between the laminations of the two adjacent planes or layers are displaced of a few millimeters to each other, which is a requirement arising from the characteristics of the magnetic material used. By successive overlaps of layers the thickness is obtained of the step corresponding to a prede termined width of laminations. At this point the assembly is carried out of the patterns having width corresponding to the next step. The above described assembly is usually carried out by hand with an endless repetition of similar movements and work-times which can be hardly quantified since the laminations have a thickness ranging within a few tenths of a millimeter. By the plant according to the invention the automatic arrangement is provided of the laminationa intended to make up cores lacking in a yoke, and of dimensions that can broadly vary between a maximum and a minimum value. Figs. 5 and 6 show respectively a plan view and an elevation view of the structural arrangement of the system. On a straight length of a track 12 there are placed stores of laminations relevant to the various steps, under the form of carriages 14 rigidly interconnected (or of a single platform). On each carriage, the lamination components intended to form one step of the core are piled up; the piles of laminations are suitably spaced apart for handling requirements, relative to the position that the same laminations must take up after the assembly (Fig. 4), with the only difference that for the central column, two piles of laminations are provided in two laying arrangements overturned one in respect to the other in order to achieve the stagger in the step forming the pack. A motorized rack device, not shown, causes the displacement of the train of carriages 14 which are subsequently disposed and blocked at a precise work position P, and whose center line corresponds to the centre of the gap between the aerial guides of a track 16, this track being placed according to a direction X orthogonal to the movement direction Y of the track 12. Numeral 18 indicates a positioning device. On each of carriages 14 there are placed the laminations necessary to form one step of a predetermined group of cores to be formed one after the other. Suitable catches determine exactly the positions of the packed laminations in the various patterns, in the above mentioned arrangement. As illustrated in the elevation of Fig. 6, the guides 16 are at a level above the carriages 14 and the relevant laminations piles, even with the maximum extent of the load. Two motorized frames 20 and 22 can move along the guides 16. The frame 22 may be caused to slide on guides 16 or on the frame 20, always in the direction X. The frame 20 bears three mobile members or equipment 24, 26, 28 which are able to move in a direction Y orthogonal to guides 16, that is, parallel to guides 12. The frame 22 carries only one member 30 being also able to move in the direction Y. Each of members or equipment 24 to 30 carries vertical slide means for grip members each having two or more suckers connected to a vacuum plant and being selectively controllable. The travels of frames 20 and 22 as well as those of members 24 to 30 are operated by sets of screws and nut screws actuated by small motors of suitable power, and said travels are exactly delimited by fixed catches previously positioned, or by other control systems, which may be changed upon variation of the cores dimensions. An assembly plane 32, suitably provided with a pallet support in the working position, is disposed on a weighing unit made up of load cells.or the like. On said assembly plane 32 the core is formed in the arrangement indicated in Fig. 4 with the laminations being picked up one at a time by the carriage 14 in the position P in order to form then the laminations packs which form each step. After that, the carriage 14 is replaced in the position P in order to form the pack of another step, and so on. The catches of frame 20 and those of member 30 are alternatively staggered of the few millimeters intended to obtain the staggered arrangement of the next layers of laminations and ensure the best connection of the magnetic flux at the intersection between yoke and columns. The member 26 is intended to alternatively pick up - from the two laminations piles - the laminations which are to form the central column. The two members 24 and 28 pick up the laminations of the two external columns and bring them close to each other in the assembling arrangement. In particular, the member 30 picks up the laminations of the yokes and places them to be assembled by performing a displacement of a few millimeters according to the axis Y. In an alternative and more advanced system than the one described hereinbefore, the travels of frames 20, 22 and of the mobile members 24 to 30 carried by the frames, instead of being delimited by fixed stops or catches of me chanical type, may be exactly delimited by step-by-step or direct current small motors which are controlled through tachymetric dynamos or encoders. The vertical movements of the suckers grip members may be realized by double-acting air pistons operated by electrovalves. The lifting of the suckers is operated by an electric impulse; their stoppage is caused by reaching a predetermined level; the lowering of the suckers is also operated by an electric impulse; while the stoppage of said lowering takes place when the suckers reache the pile of laminations to be picked up from the carriage 14 at the position P, respectively when they reach the laminations pack to be formed on the assembly plane 32. The operation of the plant is conceptually simple, and a working diagram of the displacements of frames 20 and 22, of members 24, 26, 28, 30 and of the suckers is synthetized in Fig. 7. The displacements are operated by the motion realized by the small motors and through the interventions of the electrovalves on the air and vacuum circuit. In Fig. 7 the actuation phases are shown relevant to the positioning of the laminations of the two successive layers with staggered air-gaps. After the formation of a step the replacement of the store-carriage will also occur. The succession of the various operations may be controlled by a program recorded on a microprocessor or computer having several ctputs. The signals coming from the microprocessor, and being processed within suitable inter faces, generate the operative controls for the opening and closing of the feeding circuits of the actuators (motors and electrovalves). Having described the structural arrangement of the plant, its working may be easily understood. Once the number of cores to be assembled has been predetermined, each carriage 14 is loaded with the patterns of sheared laminations corresponding to a determined step for a total weight approximately equivalent to the requirement of one step (double) multiplied by the number of cores. In this phase the laminations may also be counted. The displacement of the group of carriages 14 causes the position P to be reached by the carriage of the step that, according to the work schedule, must be firstly assembled, and in said work position P said carriage is centered and blocked by the device 18. A this moment, the carriage 20 moves along the guides 16 up to the carriage vertical in the position P, and the members 24 and 28 reach a position above the groups of laminations of the external columns and the member 26 moves above one of the two piles of laminations of the central column. Figs. 5 and 6 show the frame 22 while reaching, together with member 30, the position above the laminations pile of the yoke. At this point, the suchers move downvards and lift the laminations. The three members 24, 26, 28, by sliding on the guides of frame 20, place themselves at distances equal to the center distances of the columns on the core. The frame 20 moves above the assembly plane 32 and the suckers with the picked up laminations move down from the members 24, 26, 28 to lay the laminations thereon. The frame 22 which is previously moved up to a position corresponding to the store of the yoke patterns and which has been centered on the laminations pack, picks up, by the suckers lowering, the yoke lamination and brings it at the desired level. The frame 22 is then moved above the assembly plane 32 along the guides 16 (or above the frame 20, parallel to guides 16), and from the member 30 - suitably positioned on the assembly plane 32 - the suckers lower and lay down the yoke lamination. The two frames 20 and 22 move back above the carriage 14 at the position P. The movements for the formation of the next layer are the same but the travels of the frames and members vary of those short lengths corresponding to the overlap of air-gaps, while the member 26 is brought above the opposite pile of laminations for the central column. Since upon the moment the stores are loaded it is possible to determine, for each step, the average weight of the laminations, the number of laying operations can be determined by a counting. In correspondence of the various steps, or of the half of central step, the already mounted part of the core is weighed, being provided that, to this purpose, the assembly plane is resting on load cells; possible differences from the provided weight may be thus compensated by adding or taking away laminations to and from the various steps or to and from the only central step. A final weighing may be performed after the core completion, especially for statistical control. From some tests which have been carried out, there has been noted that the most crucial moment of the whole opera tion for the transfer and positioning of laminations, occurs upon the separation of the lamination, already seized by the suckers, from the remainder of the pack of laminations stored on the carriage, as an air vacuum generates between the lamination being lifted and the next one. As a result, in some cases it may likely occur the lift also of the second lamination which then falls down in disorder. This drawback may be avoided by taking advantage of the great flexibility of the laminations and thus by lifting firstly the ends and then the central part thereof; in this way the air penetrates between the laminations upon the lifting and nullifies the vacuum zones. This may be obtained by placing the suckers towards the end of the laminations and a mechanical catch at the centre between the suckers. A similar result can be achieved by suitably positioning magnets or electromagnets relative to the pack of laminations in the stores and towards the laminations ends, so as to induce a magnetization on same laminations; a mutual repulsion is thus determined between the laminations getting a flux of the same polarity and, consequently, a lift of those being on the top. The two actions, properly combined, are utilized for rendering the separation operation perfectly reliable. The centering catches in the stores keep the laminations in the proper position before they are picked up. It is understood that the drawing shows an exemplification given only as a practical demonstration of the invention, as this may vary in the forms and dispositions without nevertheless coming out from the ambit of the idea on which the same invention is based. For example, instead of the interconnected carriages 14 which contain the packs of the laminations to be mounted, it is possible to provide either a single bench which moves to subsequent work positions, or a number of carriages individually driven along common or diverse guides for to and from movement. The plant may also be provided with two or more assembly stations properly spaced apart and apt to be fed by the same stores but with a suitably staggered assembly cycle of one station relative to that of the other. The number of store-carriages may be suitably increased.

Claims: CLAIMS 1. Assembly plant of magnetic cores for electric transformers or other, made up of die-cut laminations, characterized in that it comprises: at least a store (14) of shaped laminations with which to form a core or a step of a core; means for the grip and transfer of the laminations of the store (14) in order to transfer them onto an assembly plane (32), said grip means being able to position the laminations in the assembling arrangement; and means to obtain the repetition of the action of the grip and transfer means to form steps with a determined number of lamination-s. 2. A plant according to claim 1, characterized in that said grip and transfer means comprise mobile frames (20,22) which move above the stores (14) and the assembly plane (32), and on said frames members (24,26,28) are provided moving in orthogonal direction to the frames (20,22) and forming vertical guides for suckers lift means or the like. 3. A plant according to claim 2, characterized in that said moving members (24,26,28) and/or said frames (20,22) are operated - by catches or step-by-step motors or other equivalent means - to bring the laminations close to each other in the assembly arrangement and stagger subsequent laminations or groups of laminations. 4. A plant according to claim 1 for the formation of stepped cores, characterized in that it comprises a number of stores (14), each one for the laminations relevant to one step, and means for transferring said stores (14) subsequently to a position of picking up by the grip and transfer means. 5. A plant according to . claim 4, characterized in that the stores are realized by a platform or by carriages (14) displaceable along rail tracks (12) or equivalent, even independently. 6. A plant according to claim 2, characterized in that each of the grip and transfer means comprises at least two suckers capable of engaging the lamination towards the ends thereof, and a possible central catch in order to achieve a convex curvature in the lower part of the lamination which is being lifted, apt to facilitate the separation thereof from the remaining pile of the laminations. 7. A plant according to claim 1 or 6, characterized in that it comprises magnets or electromagnets able to induce a homopolar local magnetization in the adjacent lamination in order to cause a repulsion between the close ends of the superimposed laminations, apt to facilitate the separation of the lamination being lifted out from the remaining pile of laminations. 8. A plant according to claim 5, characterized in that it comprises programming means for setting up an automatic execution of the grip, transfer and laying down of the laminations onto the various core steps, by means of an automatic handling of the stores, frames and of the grip and transfer means as well as of the catches or other means delimitating the laying down position of the laminations. 9. A plant according to claim 8, characterized in that it comprises at least two assembly stations operating out of phase. 10. An assembly plant of magnetic cores for electric transformers or other; all as above described and represented for exemplification in the accompanying drawing.

Inventors: LEGNAIOLI-GIULI, ELENA, LEGNAIOLI, LUCIANO
Applicants: LEGNAIOLI, LUCIANO, LEGNAIOLI-GIULI, ELENA
Application year: 1985
Main classification: H01F41
IPC codes: H01F41