Patent Publication Number: US-2003221310-A1

Title: Method and apparatus for winding a multi-pole stator

Description:
RELATED APPLICATION  
       [0001] This patent application claims priority of European Patent Application Serial No. EP 02425363.5, filed May 31, 2002.  
       FIELD OF THE INVENTION  
       [0002] The present invention relates to the field of stator winding machines, and precisely it relates to a method for winding multi-pole stators.  
       [0003] Furthermore, the invention relates to an apparatus that carries out this method.  
       BACKGROUND OF THE INVENTION  
       [0004] Outwardly spooled multi-pole stators are known, formed by a substantially star-shaped stack of sheets featuring a plurality of poles extending from a tubular core. The stators of this type are suitable for coupling with an inner concentric armature or outer ring armature. They are common in brushless motors.  
       [0005] The peripheries of the poles, or pole extensions, form substantially a cylinder with a plurality of slits parallel or oblique with respect to the axis of the stator. The peripheries of the poles are connected to the core by means of pole walls that define corresponding grooves, accessible through the slits. The grooves have to be filled with insulated lead wire, by creating coils spooled about the pole walls.  
       [0006] At winding, where possible, the wire must pass necessarily through the slits for entering the grooves, and has to be guided to avoid collisions against the edges of the grooves. To this purpose, existing winding machines having a winding arm, or flier, which rotates causing the wire a circular trajectory and creating thus the coil of each pole. The wire follows the circular trajectory while it is guided in the slits by means of special winding shrouds.  
       [0007] The shrouds are normally of two types, usually enough to wind the most common outwardly spooled multi-pole stators: 
       [0008] a couple of lateral guiding plates, which form substantially a channel that aids the wire to enter the slits; hits are thus avoided of the wire against the edges of the poles adjacent to the pole being wound;  
       [0009] a shroud that allows the wire to overtake the pole making substantially a double slide guide that deviates the wire from its own circular trajectory and brings it to wind about the pole wall. The shroud normally is mounted on a support shaft, that is co-axial to the flier and is movable towards/away from the axis of the stator, for laying uniformly the wire helically about the pole wall. 
       [0010] The flier, during winding, rotates about the support shaft of the shroud in order to have its free end needle that moves in orbital position both with respect to the pole being wound and to the shroud that guides the wire in the grooves.  
       [0011] The wire is spooled about the pole with the aid of a shroud whose shielding portion has two semi-shrouds that move with respect a body integral to the support shaft. The two semi-shrouds skim over the stator so that the wire is laid in an optimal way.  
       [0012] Therefore, for causing the flier and the shrouds to work correctly, at the high speed provided for automatic production lines, the stator must be located suitably in the winding station.  
       [0013] Presently, automatic systems exist for locating the stator in the winding station, comprising means that put the stator on a support at a predetermined height responsive to the height of the stack of sheets.  
       [0014] However, starting from a standard height of the stack of ferromagnetic sheets, the actual height is subject to errors.  
       [0015] For example, if the machine that counts the ferromagnetic sheets, used for making the stack of a stator, makes an error by excess or by defect, this error causes unavoidably a variation of the height of the stack same.  
       [0016] Another possible error is due to the different compression of the stack of ferromagnetic sheets owing to, for example, defects of construction of the sheets same.  
       [0017] In these cases, then, there is a variability on the stack height of 1 mm and more. As shown in FIG. 1 (described in detail later), the variability on the stack height causes a misalignment between the mid-plane of the shroud and the mid-plane of the stator.  
       [0018] Therefore, when the wire has size less than the size deviation of the stack height, winding problems arise, among which: 
       [0019] jamming of the wire between the semi-shrouds and the stator, obliging the operators that control the process to intervene immediately on the machines at stop, for cutting the jammed wire and rejecting the workpiece with subsequent costs and loss of time;  
       [0020] bad filling rate, in case the wire does not jam, due to not controllable inclination of the coils, with bad final quality of the product. 
       [0021] In addition to the problem of size tolerance, moreover, parts with different nominal stack height, even if within a predetermined range, are worked with difficulty. This problem is in particular felt where, in a same production campaign, stators of different stack height must be worked without stopping the production, called “mixed flow” production, and the machines are operated completely by a computer. In fact, even if shrouds capable of opening and closing on the stator are used, however, the problem remains of misalignment between the mid-plane of the shroud and of the stator that occurs when the stack height is changed. Also in this case, in particular, the misalignment creates a space between shroud and stator, at one side, impairing the slot filling and causing jamming.  
       SUMMARY OF THE INVENTION  
       [0022] It is an object of the present invention to provide an automatic winding method of stators in a winding station that allows the stators to centre with respect to the axis of symmetry of the shrouds.  
       [0023] It is a particular object of the present invention to provide a method for winding stators that eliminates the problem of wire jamming between the end of the shrouds and a face of the stator same, during the winding step.  
       [0024] It is another particular object of the present invention to provide a method for winding stators that allows to obtain a better quality of the product reducing the work rejection rate.  
       [0025] It is a further object of the present invention to provide a method for centering stators in a winding station that allows multi-pole stators to be spooled with different nominal stack height, even if within predetermined limits.  
       [0026] These and other objects are obtained by the method for centering a multi-pole stator, having a stack of ferromagnetic sheets, an axis of symmetry and a plurality of radially extending poles, in a winding station, with respect to shroud means, according to the present invention, comprising the steps of: 
       [0027] arranging the stator in the winding station near at least a shroud means and a winding flier;  
       [0028] relatively aligning the mid-planes of the stator and the shroud means;  
       [0029] winding the stator by the flier and the shroud means with opening/closing symmetric of the shroud with respect to the mid-plane of the stator. 
       [0030] A first advantageous embodiment of the method, according to the invention, comprises the further steps of: 
       [0031] measuring the actual height of the stack of sheets of the stator;  
       [0032] arranging the stator in a winding station near at least a shroud means and a winding flier, said stator being arranged on a support movable parallel to the axis of the stator;  
       [0033] aligning the mid-plane of the stator, by the means for supporting, with the mid-plane of the shroud means;  
       [0034] winding the stator by the flier and the shroud means, with opening/closing symmetric of the shroud with respect to the mid-plane of the stator. 
       [0035] Advantageously, a preliminary measuring step of the height of the face of reference of the stator is made with optical sensor means.  
       [0036] The method, according to the present invention, eliminates the possibility that sum of tolerances or small size differences on the stack height affect both the location of the stator in the winding station and the winding same.  
       [0037] Winding the wire about a pole of the stator is made by a rotatable arm guided by the shroud in many steps. Advantageously, after every layer deposited about the stator, the two parts of the shroud move away symmetrically in a direction orthogonal to their axis of symmetry. This combination assures that the stator is centred with respect to the shroud for all the spooled wire step about the poles.  
       [0038] Alternatively, a second embodiment of the method, according to the invention, provides that the shroud means has two semi-shrouds capable of asymmetrically closing/opening, with respect to the mid-plane of the support of the shroud same.  
       [0039] Therefore, the two semi-shrouds are located symmetrically with respect to the stator, even if the mid-plane of the support is shifted with respect to the mid-plane of the stator.  
       [0040] According to another aspect of the invention, a device that carries out the method for centering a multi-pole stator, having a stack of ferromagnetic sheets, an axis of symmetry and a plurality of radially extending poles, in a winding station, with respect to shroud means, comprises: 
       [0041] stator winding means and shroud means, wherein the shroud means can be opened/closed symmetrically with respect to the mid-plane of the stator;  
       [0042] means for arranging the stator in a winding station near at least a shroud means and a winding flier;  
       [0043] means for relatively aligning the mid-plane of the stator with the mid-plane of the shroud means. 
       [0044] In a first embodiment of the device, the following are provided, in addition: 
       [0045] sensing means for measuring the actual height of the stack of sheets of the stator;  
       [0046] means for supporting the stator to provide the alignment of the mid-plane of the stator and the mid-plane of the shroud means. 
       [0047] In this case, the device that carries out the method, according to the present invention, comprises a control unit that receives a measuring signal and is operatively connected to means for actuating the support and means for actuating the shaft of the shrouds.  
       [0048] A second different embodiment of the device comprises means for opening/closing the shrouds, independent from one another.  
       [0049] In particular, the opening/closing step of the shrouds independently can be effected by actuators in turn independent, which operate responsive to sensors that detect the approach to the stator during the asymmetrical opening/closing movement.  
       [0050] In particular, such means for opening/closing the shrouds comprise a wedge element formed by two semi-wedges that can be operated independently. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0051] Further characteristics and the advantages of the method according to the invention will be made clearer with the following description of an embodiment thereof, exemplifying but not limitative, with reference to the attached drawings, wherein:  
     [0052]FIGS. 1 and 2 respectively show the location of a stator in a winding station and the jamming of a spooled wire between an end of the shrouds and the stator, according to the prior art;  
     [0053]FIG. 3 shows a preliminary measuring step of the height of a face of reference of a stator, as provided by the method according to the invention;  
     [0054]FIGS. 4 through 8 show successive winding phases of the wire about a pole of a stator according to the method of the invention; and,  
     [0055]FIGS. 9 through 11 show successive centering steps of a multi-pole stator, in the case of asymmetrical opening/closing movement of the shroud means, according to an alternative embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0056]FIG. 1 shows the method of location of a multi-pole stator  1  in a winding station, according to the prior art. Stator  1  has a core formed by a stack of ferromagnetic sheets  3  of known nominal height, having a mid-plane  2  and a plurality of poles (not shown) that radially extend defining grooves between them.  
     [0057] Stator  1  is located with its mid-plane  2  parallel to a mid-plane  12  of a shroud  10 , which is capable of moving radially towards stator  1  and of guiding the wire  17  during the winding step about a pole of stator  1 .  
     [0058] The vertical location of stator  1  is made by a support  6  adjustable orthogonally with respect to the mid-plane  2 , responsive to the nominal stack height. In presence of deviations of the stack of sheets  3  from the nominal value, the plane  2  of stator  1  and the plane  12  of shroud  10  are shifted of a distance ΔL.  
     [0059] In particular, always with reference to FIG. 1, the end  13  of a first portion  11  of shroud  10  is located at a distance L 1 , with respect to the corresponding reference face  4  of stator  1 , less than a distance L 2 , between end  13 ′ of a second part  11 ′ of shroud  10 , taken with respect to the corresponding reference face  5 .  
     [0060] Such a location of shroud  10  with respect to stator  1  has the drawback of jamming wire  17 , at the end  13  or  13 ′, obliging the operator to stop the machine with subsequent loss of time and decrease of productivity. A minor drawback, but equally to be avoided, is that the wire  17  can be guided incorrectly by shroud  10 , owing to the space between shroud  10  and stator  1 , which causes a bad filling and lower quality.  
     [0061]FIG. 3 shows a preliminary step of a first embodiment of the method, according to the present invention, wherein the height of stator  1  is measured on a reference face  4  by a sensor  20 .  
     [0062] The preliminary measure allows to calculate the deviation ΔL of FIG. 4 of stator  1 , in order to lower/raise it at a height to align the mid-plane  2  of stator  1  with the mid-plane  12  of shroud  10 .  
     [0063] This way, as shown in FIG. 5, the distance L 1 , between the end  13  of shroud  10  and the respective reference face  4 , and the distance L 2 , between the end  13 ′ of shroud  10  and the respective reference face  5 , coincide perfectly. Therefore, the position of auto-centering shroud  10  can be calculated, being the distance L 1 =L 2  the least possible, so that the end  13  and  13 ′ practically “skim” over the faces  4  and  5  of stator  1  when a first layer of wire  17  is spooled, as shown in FIG. 6. A jamming of wire  17  during the winding step is thus impossible, as instead shown in FIG. 2.  
     [0064]FIGS. 6, 7 and  8  show the steps of winding wire  17  about a pole of stator  1 .  
     [0065] In the first step, illustrated in FIG. 6, shroud  10  is approached radially to stator  1  and is juxtaposed to the respective pole, not yet spooled with wire  17 . Then, as shown in FIG. 7, after having spooled a first layer of wire about the pole of stator  1 , semi-shrouds  11  and  11 ′ move away from each other symmetrically in a direction orthogonal to plane  12 . This step is repeated at every next layer winding, as shown for second layer in FIG. 8.  
     [0066] Therefore, during all the winding steps auto-centering stator  1  is kept still with respect to shroud  10 , and then the risk of jamming wire  17  is avoided for all the spooling step.  
     [0067] A second different embodiment of the method, shown in FIGS. from  9  to the  11 , provides a multi-pole stator  1  whose alignment is achieved by a shroud  10 , comprising two semi-shrouds  11  and  11 ′ equipped with asymmetrical movement with respect to the mid-plane  12  of the support. This asymmetrical movement of the two semi-shrouds  11  and  11 ′ is operated by two semi-wedge elements  18  and  18 ′, which move independently. Therefore, stator  1  is centred by approaching symmetrically, in a first step, two semi-shrouds  11  and  11 ′ to stator  1  up to when semi-shroud  11 ′ reaches face  5  of the stack of sheets  3 . Then, the stator  1  is further centred, with respect to shroud  10 , moving back semi-wedge element  18  and causing the semi-shroud  11  to reach face  4 . This step is obtained blocking semi-wedge element  18 ′, and then semi-shroud  11 ′, in the previous position.  
     [0068] Notwithstanding reference has been made above to two preferred embodiments, the method, according to the present invention can be carried out using alternative solutions. For example, the mid-plane of the shrouds  12  and the mid-plane of the stator  2  can be aligned by providing on support  15  of the shrouds, and/or on the shrouds same, actuator means movable orthogonally to the mid-plane  12 .  
     [0069] The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.