Abstract:
In order to improve a device to press a rotatably supported shaft of a rotor of a spindle motor for a hard disk drive into a shaft receiving portion of an associated stator housing by means of a first pressing tool acting on the rotor and a second pressing tool acting on the stator housing, inasmuch as high manufacturing precision, with low process tolerances in particular, can be achieved, it is proposed that a first aligning apparatus for the rotor and a second aligning apparatus for the stator housing are provided, that the first and second aligning apparatuses are formed in such a way that they guide the rotor by means of a rotor carrier and the stator housing by means of a stator carrier exactly aligned with respect to each other during the pressfitting process, and that the first pressing tool has a first pressing element acting on the shaft of the rotor that is independent of the first aligning apparatus and the second pressing tool has a second pressing element acting on the stator housing that is independent of the second aligning apparatus, the first and second pressing elements fitting snugly against the shaft or the stator housing respectively, at the latest at the start of the pressfitting process.

Description:
[0001]     The present disclosure relates to the subject matter disclosed in German applications No. 103 43 317.1 of Sep. 10, 2003 and No. 103 47 477.3 of Sep. 30, 2003, which are incorporated herein by reference in their entirety and for all purposes.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a device to press a rotatably supported shaft of a rotor of a spindle motor for a hard disk drive into a shaft receiving portion of an associated stator housing by means of a first pressing tool acting on the rotor and a second pressing tool acting on the stator housing.  
         [0003]     In the devices known to date, the force to press the shaft into the shaft receiving portion via the rotor and the stator housing is introduced in such a way that process tolerances are created on the one hand, and damage to the bearing system can also not be excluded on the other hand.  
         [0004]     The object of the invention is therefore to improve a device to press the shaft of the rotor into the shaft receiving portion inasmuch as high manufacturing precision, with low process tolerances in particular, can be achieved.  
       SUMMARY OF THE INVENTION  
       [0005]     This object has been achieved in accordance with the invention by a device of the type described in the opening paragraphs in that a first aligning apparatus for the rotor and a second aligning apparatus for the stator housing are provided, that the first and second aligning apparatuses are formed in such a way that they guide the rotor by means of a rotor carrier and the stator housing by means of a stator carrier exactly aligned with respect to each other at least during the pressfitting process, and that the first pressing tool has a first pressing element acting on the shaft of the rotor that is independent of the first aligning apparatus and the second pressing tool has a second pressing element acting on the stator housing that is independent of the second aligning apparatus, the first and second pressing elements fitting snugly against the shaft or the stator housing respectively, at the latest at the start of the pressfitting process.  
         [0006]     The advantage of the solution according to the invention is to be seen in the fact that the aligning apparatuses acting independently of the pressing elements make it possible for the rotor and the stator housing to be precisely aligned to each other during the pressfitting process and to be then held in a precisely aligned state, allowing the pressfitting process to be carried out with high precision in respect of the alignment of the two parts to each other.  
         [0007]     The exact alignment of the rotor can be achieved in a particularly advantageous manner if the rotor, at least from the start of the pressfitting process, is held in a precisely aligned state in that a precision-related surface of the rotor engages against a first support surface of the rotor carrier of the first aligning apparatus with a defined first holding force.  
         [0008]     In that a defined holding force holds down the precision-related surface, the disk supporting surface of the rotor for example, onto the first support surface of the rotor carrier, the exact alignment of the rotor determined by the first support surface of the rotor carrier can be maintained throughout the pressfitting process from the very beginning.  
         [0009]     Within the scope of the solution according to the invention, the first aligning apparatus can either be associated with one of the pressing tools or arranged entirely independently of the pressing tools.  
         [0010]     A particularly favorable solution provides that the first aligning apparatus is associated with the first pressing tool.  
         [0011]     In order to achieve and maintain the exact alignment of the rotor, it is particularly favorable if the first support surface of the rotor carrier can be movably guided with respect to the first pressing element, so that, independent of the pressing force exerted with the first pressing element, the first holding force between the precision-related surface of the rotor and the support surface of the rotor carrier can be maintained.  
         [0012]     A particularly favorable realization provides that the rotor carrier is movably guided by means of at least one first linear guide of the first aligning apparatus.  
         [0013]     To maintain high guiding precision in the aligning apparatus, it is preferable if the first linear guide is supported by rolling element bearings, preferably having no free play.  
         [0014]     The first linear guide preferably comprises a guide column and a first guide sleeve that is movable with respect to the guide column.  
         [0015]     In respect of the association of the rotor carrier with the guide column and the guide sleeve, such association can basically take a large variety of conceivable forms. A particularly favorable association provides for the rotor carrier to be mounted on the first guide sleeve.  
         [0016]     In principle, the linear guide can be independent of the arrangement of the pressing element. A particularly compact design can be realized, however, if the first pressing element is mounted on the guide column.  
         [0017]     To advantageously generate the holding force with which the precision-related surface of the rotor is to engage against the first support surface of the rotor carrier, it is preferably provided that the rotor carrier can be moved in the direction of the pressing tool located opposite the rotor carrier until it reaches a starting position, that a first holding force acting in the direction of the starting position is exerted on the rotor carrier, that the rotor supported by the rotor carrier, in the starting position with the shaft, is spaced from the first pressing element and that a movement of the rotor with the shaft in the direction of the first pressing element works against the first holding force.  
         [0018]     In order to prevent any damage whatsoever to the pair of bearings used to support the rotor on the shaft, it is preferable if the holding force is less than 1.5 times the preload force of a pair of bearings provided between the shaft and the rotor, and even more preferable if it is less than this preload force.  
         [0019]     The holding force can basically be generated in a large variety of different ways. It is particularly favorable if the first holding force can be generated by an energy or force storage unit acting between the rotor carrier and a base of the first pressing tool, preferably an elastic force storage unit.  
         [0020]     In relation to the embodiments of the solution according to the invention mentioned up to this point, only the first holding force to achieve the exact alignment of the rotor has been dealt with.  
         [0021]     To prevent the rotor from being attracted to the stator due to magnetic interaction before the pressfitting process has begun and thus possibly becoming partially disengaged from the rotor receiving portion and consequently losing its alignment, it is preferable if, before the pressfitting process begins, the precision-related surface of the rotor can be butted against the first support surface of the rotor carrier by means of a first applying force.  
         [0022]     The applying force goes to prevent the rotor from disengaging from the rotor receiving portion in the manner described above.  
         [0023]     The first applying force is preferably dimensioned in such a way that it is less than the first holding force but greater than the effective force produced by the magnetic interaction between the rotor and the stator.  
         [0024]     The first applying force can be preferably generated by a force transmission element which becomes effective as the first pressing tool and the second pressing tool approach each other before the start of the pressfitting process.  
         [0025]     It is particularly favorable if the first force transmission element is disposed on the second pressing tool and can thus be easily put into effect.  
         [0026]     So far, no precise details have been given in relation to the above explanation of the device according to the invention concerning the alignment of the stator housing. A further beneficial embodiment of the invention provides for the stator housing, at the latest at the start of the pressfitting process, to be held in a precisely aligned state in that one or more precision-related surfaces of the stator housing, reference or mounting surfaces for example, abut a second support surface of the stator carrier of the second aligning apparatus. This also goes to ensure that during the pressfitting process the stator housing is always held precisely aligned in the required manner.  
         [0027]     The second aligning apparatus can be associated with the second pressing tool.  
         [0028]     It is, however, conceivable that in another solution, the second aligning apparatus is associated with the first pressing tool.  
         [0029]     In order to maintain the second holding force throughout the pressfitting process, it is preferable if the second support surface of the stator carrier can be movably guided with respect to the second pressing element.  
         [0030]     Such guided movement can be achieved, for example, in that the stator carrier is movably guided by at least one second linear guide of the second aligning apparatus.  
         [0031]     The second linear guide is preferably supported by rolling element bearings.  
         [0032]     In the simplest case, provision is made for such a second linear guide to comprise a second guide column and a second guide sleeve which can be moved with respect to the second guide column.  
         [0033]     The way in which the guide sleeve and the guide column are associated with the stator carrier can basically be chosen arbitrarily.  
         [0034]     A beneficial solution provides for the guide sleeve to carry the stator carrier. However, it is also conceivable to arrange the guide column in such a way that it carries the stator carrier.  
         [0035]     Moreover, the guide sleeve and guide column can be arranged entirely independently of the second pressing element.  
         [0036]     A particularly compact design provides for the second guide column to carry the second pressing element.  
         [0037]     Another beneficial solution provides that, as a stator carrier, the second aligning apparatus has a carrying member guided by a plurality of linear guides.  
         [0038]     Such a carrying member can be particularly advantageously employed if it were to have a plurality of second support surfaces for the precision-related surfaces of the stator housing.  
         [0039]     So far, no precise details have been given concerning the generation of the second holding force. A particularly beneficial embodiment thus provides that the stator carrier can be moved in the direction of the pressing tool located opposite the stator carrier until it reaches a starting position, that a second holding force acting in the direction of the starting position is exerted on the stator carrier, that the stator housing held by the stator carrier is spaced at a distance from the second pressing element and that the second holding force works against a movement of the stator housing with the stator carrier in the direction of the second pressing element.  
         [0040]     The second holding force is also preferably selected in such a way that no deformation of the stator housing can occur.  
         [0041]     The second holding force can be generated in a particularly favorable way when it is generated by a force storage unit acting between the stator carrier and a base of the associated pressing tool, preferably an elastic spring force storage unit.  
         [0042]     To prevent the stator housing from becoming at least partially disengaged from the stator receiving portion due to the magnetic attraction of the rotor and the stator as the rotor and the stator approach each other before the actual pressfitting process, it is preferably if, before the start of the pressfitting process, the precision-related surfaces of the stator housing can be supported on the second support surface by means of a second applying force. Here, the second applying force, for example, can be less than the first holding force but always strong enough so as not to be overcome by the magnetic attraction between the rotor and the stator.  
         [0043]     Such an applying force can preferably be generated by at least one force transmission element which becomes effective when the first pressing tool is conveyed in the direction of the second pressing tool, that is when the two pressing tools are brought together.  
         [0044]     The second force transmission element is preferably disposed on the first pressing tool.  
         [0045]     To ensure a centric alignment of the stator housing and rotor shaft at the start of the pressfitting process, a centering element is also preferably provided.  
         [0046]     The centering capability of this element is particularly effective if it acts on the shaft receiving portion of the stator housing.  
         [0047]     In order to pressfit the rotor up to a defined spacing of the precision-related surface of the rotor and stator housing, one of the two interacting elements of a measuring device is preferably associated with the first support surface and the second support surface respectively to measure a precise spacing between these two surfaces.  
         [0048]     It is preferable if the measuring device generates a signal for the control of a drive motor when a defined, predetermined spacing between the first support surface and the second support surface is reached.  
         [0049]     The first and second support surfaces can be particularly precisely positioned with respect to each other when the measuring device is part of a closed-loop circuit of the control of the drive motor.  
         [0050]     In particular, the spacing between the first support surface and the second support surface can be achieved with great repeat accuracy when the control operates the drive motor in a section before an expected pressfit end as a stepping motor operating in start-stop mode, providing the possibility of ending the movement of the second pressing tool with respect to the first pressing tool with stepped precision.  
         [0051]     Furthermore, to prevent damage to the pressing tools, or also to the rotor or stator housing, from occurring, it is preferable if a force sensor is provided between a press drive and the associated pressing element, making it possible to detect whether atypically high force peaks occur during the course of the pressing process.  
         [0052]     Such a force sensor is preferably disposed in an open control loop of the press control, allowing the press control to detect the occurrence of unexpected, large forces and to switch off the press drive.  
         [0053]     In order to achieve the greatest possible accuracy, it is preferable if the press drive is a spindle drive.  
         [0054]     Further characteristics and advantages of the invention form the subject matter of the description below as well as the illustration in drawings of several embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0055]      FIG. 1 a  schematic view of a first embodiment of a device according to the invention to pressfit the shaft of a rotor for a spindle motor into the corresponding stator housing;  
         [0056]      FIG. 2  an enlarged view of a first and second pressing tool as a section along line  2 - 2  in  FIG. 1 ;  
         [0057]      FIG. 3  an enlarged view of a measuring device according to the invention;  
         [0058]      FIG. 4 a  view from above in the direction of the arrows A ( FIG. 4   a ) and B ( FIG. 4   b ) in  FIG. 3  of the first pressing tool and the second pressing tool and  
         [0059]      FIG. 5 a  section similar to  FIG. 2  through the pressing tools of a second embodiment of a device according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0060]     A first embodiment of a device according to the invention illustrated in  FIG. 1  to  4  to pressfit a shaft  10 , to which a rotor  12  of a spindle motor is mounted by means of a pair of bearings  11 , into the shaft receiving portion  14  of a stator housing  16  of a stator  15  ( FIG. 2 ) of the spindle motor comprises a pressing device  18  ( FIG. 1 ), described in more detail below, having a first pressing tool  20  acting on the rotor  12  and a second pressing tool  22  acting on the stator housing  16 , which can be moved towards each other in a pressing direction  24 , the first pressing tool  20  being connected to the pressing device  18  via a first base  26  and the second pressing tool  22  being connected to the pressing device  18  via a second base  28 .  
         [0061]     For its part, the first pressing tool  20  comprises a first pressing element  30  provided with a first pressing surface  32  with which a force can be exerted on an end face  38  of the shaft  10  located opposite an end face  36  disposed at a pressfit end  34  of the shaft  10  for the purpose of pressfitting the pressfit end  34  into the shaft receiving portion  14 .  
         [0062]     To align the rotor  12  when the shaft  10  is pressed into the shaft receiving portion  14 , a first aligning apparatus, indicated in its entirety by  40  and associated with the first pressing tool  20  is provided which has a rotor carrier  42  provided with a rotor receiving portion  44 . The rotor receiving portion  44  is preferably formed as a negative pressure receiving portion and provided with a suction connection  45  so that the rotor  12  can be held with its hub  47  in the rotor receiving portion  44  through negative pressure.  
         [0063]     The rotor  12  with its hub  47  can be inserted into the rotor receiving portion  44  in such a way that it can be butted with a disk supporting surface  46  formed as a precision-related surface against a first support surface  48  of the rotor carrier  42 , enabling the rotor  12  to be precisely aligned by means of the rotor carrier  42 .  
         [0064]     The rotor carrier  42  is guided by a first guide  50  in the pressing direction  24  linearly movable with respect to the first pressing element  30 , the first guide  50  comprising a first guide column  52  held on the first base  26  and a first guide sleeve  56  precisely guided with respect to the first guide column  52  by means of rolling elements  54 , the first guide sleeve  56  being provided with the rotor carrier  42  on the side facing the second pressing tool  22 .  
         [0065]     By means of first spring elements  58  acting on the rotor carrier  42 , the rotor hub  47  is held, without additional outside force being exerted, by the rotor carrier  42  with respect to the first pressing element  30 , in a first starting position in which the first pressing element  30  does not act on the end face  38  of the shaft  10 , but is rather spaced at a distance from it.  
         [0066]     The first spring elements  58  are supported on the one hand by the base  26  and on the other hand they exert a force on the first guide sleeve  56  in a direction heading away from the base  26  in order to hold the rotor carrier  42  with respect to the base  26  in the starting position defined by stops.  
         [0067]     The overall first holding force exerted by the first spring elements  58  is less than 1.5 times the bearing preload force of the pair of roller bearings  11  so that overcoming the holding force H 1  with effect on the shaft  10 , its end face  36  for example, avoids damaging the pair of bearings  11 .  
         [0068]     For its part, the first guide column  52  is firmly seated via the baseplate  26  on a plunger  60  of the pressing device  18  and can be moved in the pressing direction  24  by a movement of the plunger  60 . Moreover, the first guide column  52  carries the first pressing element  30  at the end  62  facing the second pressing tool  22 , the first pressing element  30  being firmly connected to the first guide column  52 .  
         [0069]     The first guide  50  is preferably formed in such a way that the first guide column  52  is a cylindrical column, the rolling elements  54  fitting snugly against its sleeve surface  64  and preferably being held in a conventional rolling element cage  65 , the first guide sleeve  56  supporting itself against the rolling elements  54  with its inner surface  66 , and in this way being guided along the first guide column  52  via the rolling elements  54 . The inner surface  66  is likewise preferably formed as a cylindrical surface, the sleeve surface  64  and the inner surface  66  extending coaxial to a cylindrical axis  68  that is aligned parallel to the pressing direction  24 .  
         [0070]     To align the stator housing  16 , formed for example as a flange in the spindle motor of the first embodiment, a second aligning apparatus  70 , associated with the second pressing tool  22 , is provided, the second aligning apparatus  70  comprising a stator carrier  72  having a stator receiving portion  74  in which the stator housing  16  can be placed in such a way that the stator housing  16  with a mounting surface  76  as a precision-related surface of the stator housing  16  engages against a second support surface  78  of the stator carrier  72 , in this case the stator housing  16  penetrating with its hub member  77  into the stator receiving portion  74 .  
         [0071]     To exert a force on the stator housing  16  in the region of the shaft receiving portion  14 , a second pressing element, indicated in its entirety by  80 , is provided which, with a second pressing surface  82 , can act on a contact surface  86  of the stator housing  16  located opposite a pressfit opening  84  in the shaft receiving portion  14 , disposed on the stator housing  16  and preferably enclosing the shaft receiving portion  14 .  
         [0072]     Here, for example, the second pressing element  80  is supported on a counter support  90  to the plunger  60  of the pressing device  18  via a second base  28 , with respect to which the plunger  60  can be moved.  
         [0073]     To guide the second aligning apparatus  70  with respect to the second pressing element  80  a second guide, indicated in its entirety by 100, is provided which comprises a second guide column  102  and a second guide sleeve  106  journalled on this guide column  102  via rolling elements  104 , the second guide sleeve  106  being provided with the stator carrier  72  and a second spring element  108  exerting a second holding force H 2  on the second guide sleeve in such a way that the second guide sleeve  106 , and thus the second aligning apparatus  70 , are in a starting position in which the stator housing  16 , accommodated in the stator receiving portion  74 , abuts the second support surface  78  with the mounting surface  76 , no force being exerted, however, on the stator housing  16  in the region of its contact surface  86  by the second pressing surface  82 .  
         [0074]     The second spring element  108  is preferably supported on the base  28  of the second pressing tool  22  mounted on the counter support  90 .  
         [0075]     The second guide column  102  is preferably seated on the base  28  and carries.. the second pressing element  80  on the end located opposite the counter support  90 .  
         [0076]     Furthermore, the second pressing element  80  is allocated a centering pin  110  which is held by a guide bolt  112  reaching through the second guide column  102 , a force being exerted on the guide bolt  112  via a pressure cylinder  114  in a direction of pressure  116  running opposite to the pressing direction  24 .  
         [0077]     The centering pin  110  projects beyond the pressing element  80  in such a way that, in a starting position of the pressing tools  20 ,  22 , the centering pin  110  engages into the shaft receiving portion  14  and uses this to center the stator housing  16  with respect to the second pressing tool  22  so that the shaft receiving portion  14  is aligned coaxial to the shaft  10  of the rotor  12  held by the first pressing tool  20 .  
         [0078]     The center pin  110  further engages through the shaft receiving portion  14  and, as an applying element, exerts a force with its end face  118  on the end face  36  of the shaft  10  disposed at the pressfit end  34  before this end face  36  enters into the shaft receiving portion  14  when the pressing tools  20 ,  22  are brought together, in order to support the rotor  12  in a stable way, despite incipient magnetic attraction between the rotor  12  and the stator  15 , with its disk supporting surface  46  on the first support surface  48  using an applying force A 1  and to thus precisely align the rotor  12 , together with the shaft  10 , before the pressfitting process.  
         [0079]     The first applying force A 1  acting on the shaft  10  is to be preferably dimensioned in such a way that it is less than a preload force of the pair of bearings  11  in order to prevent the pair of bearings  11  from being damaged due to applying force A 1 .  
         [0080]     In order to further ensure that the stator housing  16  abuts the second support surfaces  78  with its mounting surfaces  76  by means of a second applying force A 2  before the shaft  10  is pressfitted and, despite incipient magnetic attraction between the rotor  12  and the stator  15 , continues to be held in close contact, a holding-down apparatus  120  is provided having holding-down devices  122  on which a force is exerted by means of pressure springs  124 .  
         [0081]     The holding-down apparatus  120  is integrated, for example, in the first aligning apparatus  40 , the holding-down devices  122  being formed as pins lodged in bores  126  in the rotor carrier  42 , on which a force is exerted by pressure springs  124  disposed in bores  128  in the first guide sleeve  56  in such a way that the holding-down devices  122  project beyond the first aligning apparatus  40  in the direction of the second pressing tool  22  and thus, when the first pressing tool  20  is moved in the pressing direction  24  towards the second pressing tool  22 , exert a force on the stator housing  16  on an end located opposite the mounting surface  76  and thus support the mounting surface  76  with this exerted force on the second support surface  78 .  
         [0082]     In order to form the second applying force A 2  exerted by the holding-down devices  122  independently of the force acting on the first guide sleeve  56  generated by the spring elements  58 , the pressure springs  124  are supported directly on the base  26  of the first pressing tool  20 .  
         [0083]     In order to achieve a defined spacing between the mounting surface  76  of the stator housing  16  and the disk supporting surface  46  of the rotor hub  47  when the shaft  10  is pressed into the shaft receiving portion  14 , and to ensure that it is reproducible, a measuring device  130 , illustrated in  FIG. 1  and  3 , is provided comprising a measuring probe  132 , firmly positioned in the pressing direction  24  with respect to the first support surface  48 , and a sensor contact surface  134 , firmly positioned in the pressing direction  24  with respect to the second support surface  78 , the measuring probe  132  being held by a probe holder  136  disposed on the rotor carrier  42  in which the measuring probe  132  can be fixed in a defined alignment so that a probe needle  138  is in a defined position to the first support surface  48  in the pressing direction  24 , while the sensor contact surface  134  is likewise disposed in a defined alignment to the second support surface  78  by means of an appendage  140  formed on the stator receiving portion  74 .  
         [0084]     The measuring probe  132  can now be aligned with respect to the first support surface  48  in the pressing direction  24  in such a way that, with the probe needle  138  engaging on the sensor contact surface  138 , the measuring probe  132  releases a signal exactly when the disk supporting surface  46  is at the desired predetermined distance from the mounting surface  76 .  
         [0085]     A measuring probe is any device which is capable of registering the desired position and emitting a signal with a sufficient degree of precision.  
         [0086]     The pressing device  18  mentioned earlier comprises two guide columns  142 ,  144  rising from the counter support  90  that are connected by a cross bar  146 . on which a drive motor  148 , having a rotor with a hollow shaft  150 , is arranged.  
         [0087]     The hollow shaft  150  drives a spindle nut  154  via a coupling  152 , the spindle nut  154  being seated on a sliding spindle  156  which can be pushed into the hollow shaft  150 .  
         [0088]     The sliding spindle  156  is fixedly connected to the plunger  60  via a flange  158 , the plunger  60  in turn being precisely aligned and movably guided on the two guide columns  142  and  144  in the pressing direction  24  in order to thus also guide the first pressing tool  20  to the second pressing tool  22  in a perfectly aligned manner.  
         [0089]     To register the force acting on the plunger  60 , a force sensor  160  is provided between the flange  158  and the plunger  60 , the force sensor  160  being connected to a pressing control  162  which not only registers the values of the force sensor  160  but also the switching signals of the measuring probe  132 .  
         [0090]     The device according to the invention now works such that the first pressing tool  20  and the second pressing tool  22  are pushed by the control  162 , by moving the plunger  60  in the opposite direction to the pressing direction  24 , so far apart from each other that the rotor  12  with its rotor hub  47  can be placed in the rotor receiving portion  44  of the rotor carrier  42 , the rotor hub  47  initially being held in the rotor receiving portion  44  by negative pressure so that the rotor  12  cannot fall out of the rotor receiving portion  44  due to the force of gravity.  
         [0091]     Moreover, the stator  15  with the stator housing  16  is inserted into the stator receiving portion  74 , the centering pin  110  jutting through the shaft receiving portion  14  and thus centering the stator housing  16  via the shaft receiving portion  14 .  
         [0092]     Then, by activating the control  162 , the plunger  60  with the first pressing tool  20  is moved by means of the drive motor  148  in the direction of the second pressing tool  22 , the hollow shaft  150  driving the spindle nut  154  via the coupling  152  which moves the sliding spindle  156  that is fixedly connected to the plunger  60  in the direction of the counter support  90  of the pressing device  18 .  
         [0093]     Before the actual process of pressing the pressfit ends  34  of the shaft  10  into the shaft receiving portion  14  begins, as can be seen in  FIG. 2 , the holding-down devices  122  of the holding-down apparatus  120  touch the stator housing  16  on the surface facing away from the mounting surface  76  and press the stator housing  16  with the mounting surface  76  against the second support surface  78  of the stator carrier  72  with applying force A 2 .  
         [0094]     Here, applying force A 2  is less than holding force H 2  with which the stator carrier  72  is held in the starting position described above in which the stator housing  16  does not yet touch the second pressing surface  82 .  
         [0095]     This force is sufficient, when the first pressing tool  20  and the second pressing tool  22  are brought closer together, to move the holding-down devices  122  in the direction opposite to the direction in which the pressure springs  124  work.  
         [0096]     When the first pressing tool  20  and the second pressing tool  22  are brought even closer together, the centering pin  110  comes into contact with the end face  36  of the shaft  10  and thus exerts applying force A 1  on the entire rotor  12  by means of which the disk supporting surface  46  is held in close contact with the first support surface  48  by means of this applying force A 1 .  
         [0097]     Applying forces A 1  and A 2 , acting in opposite directions to each other, are further so great that they counteract a magnetic attraction of the rotor  12  and the stator  15  so that, despite this magnetic attraction, the mounting surface  76  and the second support surface  78  as well as the disk supporting surface  46  and the first support surface  48  respectively remain in close contact with each other.  
         [0098]     As the pressing tools  20  and  22  move even closer together, the pressfit end  34  of the shaft  10  then touches the pressfit opening  84  of the shaft receiving portion  14  and great forces now act not only on the shaft  10 , and thus on the rotor,  12  but also on the stator housing  16 .  
         [0099]     These forces are so great that holding force H 1  is overcome and the rotor  12  together with the rotor carrier  42  moves in the direction of the base  26  against the force of the first spring elements  58 , and continues until the end face  38  of the shaft  10  abuts the first pressing surface  32 .  
         [0100]     Since this force acting on the rotor carrier  42  is transferred from the shaft  10  via the pair of bearings  11  to the rotor hub  47 , holding force H 1  should preferably be dimensioned in such a way that it is less than 1.5 times the preload force of the pair of bearings  11 , so that the pair of bearings  11  cannot be damaged. Thus at the start of the pressfitting process, the disk supporting surface  46  and the first support surface  48  are pressed against each other with the first holding force H 1 , which goes to ensure that the rotor hub  47 , and thus the rotor  12 , is aligned in a stable and precise manner with respect to the stator housing  16 , in particular that the shaft  10  with the pressfit end  34  is aligned coaxial with respect to the shaft receiving portion  14 .  
         [0101]     Likewise, at the start of the pressfitting process, the stator housing  16 , together with the stator receiving portion  74 , is also pushed in the direction of the base  28 , overcoming the second holding force H 2 , until the contact surface  86  abuts the second pressing surface  82 .  
         [0102]     Holding force H 2  is also dimensioned in such a way that it is at any event less than any resulting bending forces that can deform the stator housing  16 , so that any changes in measurement resulting from distortion and/or deflection of the stator housing  16  can be prevented or excluded.  
         [0103]     On the other hand, at the start of the pressfitting process the mounting surface  76  and the second support surface  78  are thereby pressed together with holding force H 2  thus ensuring that the stator housing  16  is precisely aligned with respect to the rotor  12 .  
         [0104]     As the pressfitting process continues, the first pressing surface  32  and the end face  38  of the shaft  10  as well as the second pressing surface  82  and the contact surface  86  interact directly with each other so that the pressfit end  34  can be pressed into the shaft receiving portion  14  with as large a force as necessary.  
         [0105]     To avoid damaging the pressing tools  20  and  22 , the movement of the first pressing tool  20  in the direction of the second pressing tool  22  is monitored by the pressing control  162  coupled to the force sensor  160  in an open control loop and, if any large, atypical forces appear, the drive motor  148  is switched off.  
         [0106]     Using a stepping motor as the drive motor  148  also creates the possibility of comparing the forces measured at the force sensor  160  with allowable and/or at least necessary forces associated with individual forward feed positions and to interrupt the pressing process should deviations occur.  
         [0107]     In the spindle motors manufactured according to the invention, it is moreover necessary to carry out the process of pressing the shaft  10  into the shaft receiving portion  14  in such a way that the disk supporting surface  46  is disposed with an exact spacing from the mounting surface  76 .  
         [0108]     It is for this reason that the control  162  is coupled to the measuring device  130  and is thus able to maintain with stepped precision the forward feed of the drive motor, taking the form of a stepping motor in a closed control loop operating in start-stop mode, in the pressing direction  24  only until the first support surface  48  and the second support surface  78  have the predetermined spacing from each other, it being possible to preset the spacing by adjusting the measuring probe  132 .  
         [0109]     If the measuring probe  132  is precise enough, the process of pressing the shaft  10  into the shaft receiving portion  14  can be precisely repeated in the micrometer range.  
         [0110]     In a second embodiment illustrated in  FIG. 5 , the elements that are identical to the elements of the first embodiment are given the same reference numbers so that with regard to their description, full reference can be made to the details provided for the first embodiment.  
         [0111]     In the second embodiment, the arrangement of the first pressing tool  20  in respect of the second pressing tool  22  with respect to the plunger  60  and to the counter support  90  is inverted. This means that the first pressing tool  20 ′ is held on the counter support  90  by its base  26  while the second pressing tool  22 ′ is held by its base  28  at the plunger  60 .  
         [0112]     As to the construction of the rotor carrier  42  and the first pressing element  30 , the first pressing tool  20 ′ is formed in an identical way to the first embodiment, with the difference, however, that the rotor receiving portion  44  no longer needs negative pressure to hold the rotor  12  but rather the rotor  12  remains in the rotor receiving portion  44  due to the force of gravity.  
         [0113]     In contrast to the first embodiment, however, the second aligning apparatus  70 ′ is not associated with the second pressing tool  22 ′ but rather with the first pressing tool  20 ′, since the stator housing  16 ′ has reference surfaces  76 ′ that are located on the side of the stator housing  16 ′ from which the shaft  10  is pressed into the shaft receiving portion  14 .  
         [0114]     The second aligning apparatus  70 ′ thus has a carrying member  170  as stator carrier  72 ′ which encloses the first guide sleeve  56  from the outside, the first guide sleeve  56  engaging through a central opening  172  in the carrying member  170 .  
         [0115]     This carrying member  170  is then movably guided on a plurality of second guides  100 ′, three by way of example, with respect to the base  26 , the guides likewise comprising second guide columns  102  and second guide sleeves  106 . The guide sleeve  106  is connected firmly to the base  26  whereas the guide column  102  is connected firmly to the carrying member  170  of the stator carrier  72 ′.  
         [0116]     In the second embodiment, the stator receiving portion  74 ′ is formed by means of alignment pins  174  which project beyond the carrying member  170  in the direction of the second pressing tool  22 ′ and fit snugly against corresponding alignment surfaces of the stator housing  16 ′.  
         [0117]     In addition, the reference surfaces  76 ′ of the stator housing  16 ′ abut second support surfaces  78 ′ that can be adjusted with respect to the carrying member  170  by means of adjusting elements  176  in order to preset the exact alignment of the stator housing  16 ′.  
         [0118]     In the second aligning apparatus  70 ′ as well, a force is exerted on the stator receiving portion  72 ′ in the direction of the starting position by means of an elastic force storage unit, not illustrated in the drawings, with the generation of holding force H 2  which acts in the same direction as holding force H 1  of the first aligning apparatus  40 .  
         [0119]     In contrast to the first embodiment, in the second embodiment the second pressing tool  22 ′ only comprises the pressing element  80  with the pressing surface  82 , and the centering pin  110 ′ is further disposed in a column member  180  carrying the second pressing element  80  and has a force exerted on it by a force storage unit  114 ′ so that, on the one hand, the centering pin  110 ′ also centers the stator housing  16 ′ by engaging into the shaft receiving portion  14  and, on the other hand, can still act on the end face  36  of the pressfit end  34  to ensure that the disk supporting surface  46  of the rotor  12  abuts the first support surface  48  when the stator housing  16 ′ is lowered, despite the incipient magnetic interaction between the rotor  12  and then stator  15 , and does not thus disengage from the rotor receiving portion  44 .  
         [0120]     The second embodiment of the device according to the invention now functions such that initially the first pressing tool  20 ′ and the second pressing tool  22 ′ are again pushed apart from each other in order to first place the rotor  12  in the rotor carrier  42  and then to put the stator housing  16 ′ on the stator carrier  72 ′.  
         [0121]     Due to the force of gravity, the disk supporting surface  46  and the first support surface  48  lie against each other as do the reference surfaces  76 ′ and the second support surfaces  78 ′.  
         [0122]     The starting position of the rotor carrier  42  corresponds to the starting position of the first aligning apparatus  40  described in the first embodiment and the starting position of the second aligning apparatus  70 ′ holds the stator housing  16 ′ such that there is a space between the end face  36  and the pressfit opening  84 . Moreover, the second pressing element  80  with the second pressing surface  82  is already spaced at a distance from the contact surface  86  of the stator housing  16 ′.  
         [0123]     By conveying the second pressing tool  22 ′ in the direction of the first pressing tool  20 ′ the centering pin  110 ′ initially penetrates the shaft receiving portion  14  and thus centers the stator housing  16 ′ in the manner described above. The centering pin  110 ′ furthermore penetrates the shaft receiving portion  14  and then, with its front end  118 , exerts a force on the end face  36  of the shaft  10 , generating the first applying force A 1 , which results in the fact that at the start of the pressfitting process, the disk supporting surface  46  cannot lift away from the first support surface  48  due to the magnetic interaction between the rotor  12  and the stator  15 .  
         [0124]     Owing to the changes in the arrangement of the second aligning apparatus  70 ′ brought about by the relocation of the reference surfaces  76 ′ to the front of the stator housing  16 ′, the magnetic interaction between the rotor  12  and the stator  15  does not cause the mounting surfaces  76 ′ to lift away from the second support surfaces  78 ′, but rather presses them together so that there is no longer need to generate a second applying force to prevent the mounting surfaces  76 ′ from lifting away from the second support surfaces  78 ′.  
         [0125]     When the second pressing tool  22 ′ is conveyed in the direction of the first pressing tool  20 ′, the second pressing surface  82  comes to rest against the contact surface  86  and, with a continued movement of the second pressing tool  22 ′ in the direction of the first pressing tool  20 ′, causes the stator housing  16 ′ to be pushed, against holding force H 2  of the second aligning apparatus  70 ′, in the direction of the rotor  12  and continuing until the pressfit end  34  of the shaft  10  comes to rest against the pressfit opening  84 .  
         [0126]     As the second pressing tools  22 ′ continues to be conveyed in the direction of the first pressing tool  20 ′, the rotor  12  together with the rotor carrier  42  is moved, overcoming the first holding force H 1 , until the end face  38  of the shaft  10  also abuts the first pressing surface  32 . This means that at the start of the pressfitting process in which the pressfit end  34  of the shaft  10  is pressed into the shaft receiving portion  14 , a precise alignment of the rotor  12  and the stator housing  16 ′ with respect to each other is achieved since, similarly to the first embodiment, the disk supporting surface  46  is pressed against the first support surface  48  with first holding force H 1  and, in addition, the mounting surfaces  76 ′ are pressed against the second support surfaces  78 ′ with second holding force H 2 . When the second pressing tool  22 ′ is conveyed further in the direction of the first pressing tool  20 ′, with the precise alignment of the rotor  12  to the stator housing  16 ′, the pressfit end  34  is pressed into the shaft receiving portion  14  in the same way as described in detail in relation to the first embodiment.  
         [0127]     Concerning the parts that are identical to those in the first embodiment and the processes of pressing the pressfit end  34  into the shaft receiving portion  14  that have not been expressly described in relation to the second embodiment, reference is made in full to the embodiments relating to the first embodiment.  
       Identification Reference List  
       [0128]      10  Shaft  
         [0129]      11  Pair of bearings  
         [0130]      12 Rotor  
         [0131]      14  Shaft receiving portion  
         [0132]      15  Stator  
         [0133]      16  Stator housing  
         [0134]      18  Pressing device  
         [0135]      20  1st pressing tool  
         [0136]      22  2nd pressing tool  
         [0137]      24  Pressing direction  
         [0138]      26  1st base  
         [0139]      28  2nd base  
         [0140]      30  1st pressing element  
         [0141]      32  1st pressing surface  
         [0142]      34  Pressfit end  
         [0143]      36  End face of the shaft  10   
         [0144]      38  End face of the shaft  10   
         [0145]      40  First aligning apparatus  
         [0146]      42  Rotor carrier  
         [0147]      44  Rotor receiving portion  
         [0148]      45  Suction connection  
         [0149]      46  Disk supporting surface  
         [0150]      47  Rotor hub  
         [0151]      48  First support surface  
         [0152]      50  First guide  
         [0153]      52  First guide column  
         [0154]      54  Rolling elements  
         [0155]      56  First guide sleeve  
         [0156]      58  First spring element  
         [0157]      60  Plunger  
         [0158]      62  End  
         [0159]      64  Sleeve surface  
         [0160]      65  Rolling element cage  
         [0161]      66  Inner surface  
         [0162]      68  Cylinder axis  
         [0163]      70  Second aligning apparatus  
         [0164]      72  Stator carrier  
         [0165]      74  Stator receiving portion  
         [0166]      76  Reference surfaces, mounting surface  
         [0167]      77  Hub member  
         [0168]      78  Second support surface  
         [0169]      80  2nd pressing element  
         [0170]      82  2nd pressing surface  
         [0171]      84  Pressfit opening  
         [0172]      86  Contact surface  
         [0173]      90  Counter support  
         [0174]      100  Second guide  
         [0175]      102  Second guide column  
         [0176]      104  Rolling elements  
         [0177]      106  Second guide sleeve  
         [0178]      108  Second spring element  
         [0179]      110  Centering pin, force transmission element  
         [0180]      112  Guide bolt  
         [0181]      114  Pressure cylinder  
         [0182]      116  Direction of pressure  
         [0183]      118  End face  
         [0184]      120  Holding-down apparatus  
         [0185]      122  Holding-down device, applying element, force transmission element  
         [0186]      124  Pressure springs  
         [0187]      126  Bore  
         [0188]      128  Bore  
         [0189]      130  Measuring device  
         [0190]      132  Measuring probe  
         [0191]      134  Sensor contact surface  
         [0192]      136  Probe holder  
         [0193]      138  Probe needle  
         [0194]      140  Appendage  
         [0195]      142  Guide column  
         [0196]      144  Guide column  
         [0197]      146  Cross bar  
         [0198]      148  Drive motor  
         [0199]      150  Hollow shaft  
         [0200]      152  Coupling  
         [0201]      154  Spindle nut  
         [0202]      156  Sliding spindle  
         [0203]      158  Flange  
         [0204]      160  Force sensor  
         [0205]      162  Pressing control  
         [0206]      170  Carrying member  
         [0207]      172  Opening  
         [0208]      174  Alignment pins  
         [0209]      176  Adjusting elements  
         [0210]      180  Column member  
         [0211]     H 1  First holding force  
         [0212]     H 2  Second holding force  
         [0213]     A 1  First applying force  
         [0214]     A 2  Second applying force