Abstract:
A magnet-based angular displacement measuring system for measuring a rotational movement of a driveshaft. The magnet-based angular displacement measuring system includes a drive shaft comprising a free end. The free end has a coaxial recess so as to form a hollow shaft section. An exciter unit is rotationally coupled to the free end of the drive shaft. A stationary sensor unit functionally cooperates with the exciter unit to measure the rotational movement of the drive shaft.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
       [0001]    This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2015/079121, filed on Dec. 9, 2015 and which claims benefit to German Patent Application No. 10 2015 101 248.0, filed on Jan. 28, 2015. The International Application was published in German on Aug. 4, 2016 as WO 2016/119962 A1 under PCT Article 21(2). 
     
    
     FIELD 
       [0002]    The present invention relates to a magnet-based angular displacement measuring system for detecting a rotational movement of a drive shaft, comprising a driveshaft, an exciter unit coupled to the free or axial end of the driveshaft for rotation therewith, and a stationary sensor unit which functionally cooperates with the exciter unit for detecting the rotational movement of the driveshaft. 
       BACKGROUND 
       [0003]    Angular displacement measuring systems serve to measure rotational movements of a shaft and are often also referred to as angle measuring means, angular displacement sensors, or rotary encoders. They are in particular used to control and monitor machines and vehicles. Contactless angular displacement measuring systems, for example, electrically or magnetically induced systems, here play a special role since they have a long service life due to wear-free sensor system. With magnet-based angular displacement systems, in particular with multi-turn absolute value encoders, a rotation of a shaft is inductively detected by a measuring unit, the measuring unit in particular comprising a rotating exciter unit, such as a permanent magnet, and a stationary sensor unit with at least one sensor, such as, for example, a Hall and/or a Wiegand sensor. The measuring unit is thereby mostly arranged at the free end of the shaft to be monitored. 
         [0004]    Slight measuring errors frequently occur, however, when arranging or mounting a magnet based angular displacement measuring system directly on a drive shaft, in particular on a drive shaft of an electric motor or an electric generator. Such measuring errors are most often caused by interferences acting on the angular displacement measuring system from outside. Examples of such interference include a magnetic field caused by the drive shaft being magnetized in use by the electric motor or by an electromagnetic brake, and the magnetic field being transferred via the shaft which is typically made of steel so that, at the angular displacement measuring system, the rotational magnetic field formed by the exciter unit eventually changes, thereby causing measuring errors in the sensor unit. It is therefore necessary to avoid such interferences in the angular displacement measuring system in order to improve measuring accuracy. 
         [0005]    DE 38 13 610 A1 describes an angle measuring means with a scanning means, wherein the scanning means is shielded from electric disturbing influences. The scanning means is thereby fastened in a housing in an electrically insulated manner and is connected to the mass potential of an evaluation unit. The housing is also in electric contact with the drive unit so that the interference signals outputted by the drive unit do not negatively affect the measuring values. 
         [0006]    A drawback is, however, that magnetically induced interferences are not shielded off and measuring errors are still caused in the sensor unit, in particular with a magnet-based angle measuring means. The means for shielding the angle measuring means also has a very complex structure and comprises a great number of components. 
       SUMMARY 
       [0007]    An aspect of the present invention is to provide an angular displacement measuring system for detecting a rotational movement of a drive shaft that provides for an exact and interference-free measuring, which has a simple structure, and which is simple to assemble. 
         [0008]    In an embodiment, the present invention provides a magnet-based angular displacement measuring system for measuring a rotational movement of a driveshaft. The magnet-based angular displacement measuring system includes a drive shaft comprising a free end, the free end comprising a coaxial recess so as to form a hollow shaft section, an exciter unit rotationally coupled to the free end of the drive shaft, and a stationary sensor unit configured to functionally cooperate with the exciter unit to measure the rotational movement of the drive shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
           [0010]      FIG. 1  schematically shows a perspective view of a first embodiment of an angular displacement measuring system according to the present invention, wherein the components are shown in an exploded view; 
           [0011]      FIG. 2  schematically illustrates a detail of the first embodiment in sectional side view; 
           [0012]      FIG. 3  schematically illustrates a detail of a second embodiment of an angular displacement measuring system according to the present invention in sectional side view; and 
           [0013]      FIG. 4  schematically illustrates a detail of a third embodiment of an angular displacement measuring system according to the present invention in sectional side view. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    According to the present invention, the drive shaft has a coaxial recess or indentation in the region of the free end so that a hollow shaft section is formed in this region of the drive shaft. In the present instance, the drive shaft may be a separately formed shaft part, a transmission shaft, or the shaft of an electric motor or of an electric brake. The drive shaft may at least partly be formed as a solid shaft. By providing the coaxial recess, a magnetic field induced in the drive shaft in the region of the free end can be passed into a radial outer region of the drive shaft and be concentrated there, for example, for discharge. The recess makes it possible to discharge a magnetic field generated in the drive shaft radially outward. A hollow space radially enclosed by the hollow shaft section can thereby almost be magnetically insulated. This region is therefore particularly suited for coupling a measuring unit to the drive shaft. 
         [0015]    In an embodiment of the present invention, the recess in the free end of the drive shaft can, for example, have a frustoconical shape so that the material ring remaining in the region of the hollow shaft section and protruding axially from the solid shaft tapers conically or converges to a point in the direction of the free end. This frustoconical shape allows for a relatively uniform, radially outward directed discharge of a magnetic field generated in the drive shaft. Depending on the requirements, the recess may alternatively also be hemispheric or may have any other shape. 
         [0016]    In an embodiment of the present invention, the exciter unit can, for example, be coupled or fastened to the drive shaft using a fastening device extending through the recess, for example, a magnetically not conductive screw or shaft. The fastening device of the exciter unit may advantageously be arranged in the region of the recess immediately on the drive shaft therefore. No additional shaft is thereby required for the measuring unit. A bore may be formed in the drive shaft at the bottom of the recess for placing the fastening unit, which can, for example, be designed as an axial screw, the bore extending, for example, coaxially with the drive shaft and having a thread corresponding to the screw. The exciter unit can thereby be mounted to the free end of the drive shaft in a relatively simple manner. The fastening device may alternatively be formed by a screw adapted to be placed radially in the drive shaft, in particular a grub screw. It may additionally or alternatively be provided to adhesively bond the exciter unit to the drive shaft. The fastening device per se can, for example, be made of a material that is not or is only slightly conductive. The fastening device can, for example, be made of titanium or brass so that it is possible to prevent the transfer of the magnetic field induced in the drive shaft or a shaft section towards the exciter unit via the fastening device. 
         [0017]    In an embodiment of the present invention, a radial air gap can, for example, be formed in the region of the hollow shaft section between the drive shaft and the fastening device. The diameter of the recess may be of such a size that the fastening device can extend in a contactless manner through the recess or the hollow shaft section at least in the region of the free end. A second axial end face of the drive shaft can, for example, be formed at the bottom of the recess, where the fastening device is in contact with the drive shaft and where it is fastened to the drive shaft. In an embodiment, the fastening device can, for example, be surrounded by a spacer or a pacer sleeve at least in the region of the hollow shaft section, which spacer is made of a magnetically not conductive material. The screw can thus be magnetically insulated in a particularly effective manner so that it is possible to prevent magnetic induction into the screw in the region of the hollow shaft section. Providing the spacer sleeve may in particular have the effect that the magnetic field is scattered rather widely when transferred between two conductors, thereby preventing a local magnetic saturation of the receiving material. 
         [0018]    In an embodiment of the present invention, a first shielding body can, for example, be provided comprising an annular disc coaxial to the drive shaft and which can, for example, be arranged axially between the exciter unit and the drive shaft, and a first axial section extending circumferentially on the radial outer side of the annular disc. The annular disc can, for example, have a coaxial opening through which at least the fastening device extends. The diameter of this opening can, for example, be only slightly larger than the diameter of the fastening device. The opening may also serve to center the annular disc with respect to the fastening device. A part of the drive shaft may also extend through this opening. The first axial section may protrude from the annular disc from one side. The first axial section may alternatively protrude from the annular disc on both sides, in particular in equal portions. The first axial section may thereby at least partly surround the drive shaft in the region of the hollow shaft section. This allows for a relatively space-saving structure of the angular displacement measuring system. The first axial section may be designed as a cylindrical section so that a very large circumferential surface is formed. The first shielding body can, for example, be magnetically conductive or can, for example, have a relatively high magnetic permeability so that a magnetic field induced, for example, in the region of the opening of the annular disc, can be transferred radially outward by the annular disc and be transferred further by the first axial section arranged on the radial outer side of the annular disc or be transferred to an adjacent component. The first shielding body can, for example, be made of a so-called “mu-metal”, which is a nickel iron alloy. The first shielding body can alternatively be made of steel. It is thus possible to dissipate a magnetic field generated in the drive shaft and thus to effectively shield the measuring unit of the angular displacement measuring system. 
         [0019]    In an embodiment of the present invention, the first shielding body can, for example, be connected to the drive shaft for rotation therewith. For this purpose, the first shielding body may contact the free end of the hollow shaft section and/or a spacer by an axial end face of the annular disc and may be fastened to the drive shaft, for example, by the fastening device of the exciter unit. A magnetic field generated in the drive shaft and present in the hollow shaft section can thereby be transferred into the annular disc directly via the end face. The magnetic field induced in the annular disc can be transferred radially outward into the first axial section so as to shield the measuring unit. This provides for a particularly effective and relatively space-saving shielding of the measuring unit. 
         [0020]    It has been shown that a defined distance between the first shielding body and the drive shaft is suited for a uniform and constant transmission of a magnetic field from the drive shaft to the first shielding body. A first spacer can therefore, for example, be arranged between the first shielding body and the drive shaft. The first spacer can, for example, be made of a material that is not or is only slightly magnetically conductive. The first spacer can, for example, be suited to enclose the free end of the drive shaft both axially and radially. The first spacer is in particular configured as a sleeve adapted to be set on the free end. The first shielding body can thereby be arranged and fixed with respect to the drive shaft at a defined distance both in the axial and the radial direction. For fastening the first spacer, the first spacer can, for example, have an opening through which the fastening device extends so that the first spacer can be pretensioned in the direction of the drive shaft. 
         [0021]    A second spacer may be arranged between the shielding body and the exciter unit in order to avoid a transmission of a magnetic field from the first shielding body to the exciter unit. The second spacer can, for example, be made of a material having no or only a little magnetic conductivity. The second spacer may be a washer which may be placed in a recess in the first shielding body for fixation. 
         [0022]    In an embodiment of the present invention, the first shielding body can, for example, have a second axial section by which the first shielding body can radially abut on the drive shaft and/or the spacer. The first shielding body may in particular be set or sleeved on the free end of the drive shaft and/or the spacer by the second axial section. This allows for a very large transfer surface for the transfer of a magnetic field from the drive shaft to the first shielding body. The transfer of a magnetic field may thus be effected at the end face and/or radially at the drive shaft. A relatively simple and precise centering is thereby possible. 
         [0023]    In an embodiment of the present invention, the first shielding body can, for example, be spaced at a defined axial distance from the free end of the hollow shaft section by at least an axial end face of the annular disc that is arranged opposite the free end of the drive shaft. The first shielding body may also be radially spaced from the drive shaft. An axial and/or radial air gap may thereby be formed between the first shielding body and the drive shaft so that the first shielding body may be stationary with respect to the drive shaft. For transferring a magnetic field from the drive shaft to the first shielding body, the diameter of the inner opening of the annular disc can, for example, be smaller than the inner diameter of the hollow shaft section of the drive shaft at the free end. A magnetic field prevailing at the free end of the drive shaft in the hollow shaft section can thereby be transferred or induced axially into the annular disc to a limited extent via the air gap formed between the drive shaft and the first shielding body. The magnetic field can thus in particular be transferred uniformly and continuously without a magnetic supersaturation occurring in the annular disc. The air gap may also be replaced with or realized as a magnetically non-conductive spacer in an alternative embodiment. For an effective diversion of the magnetic field, the annular disc and the axial section of the first shielding body may also be formed with relatively little material or thin. An effective shielding and a relatively light weight of the angular displacement measuring system are thereby possible so that manufacturing costs are also consequently reduced. 
         [0024]    In an embodiment of the present invention, a second shielding body having an axial cylindrical section which radially encloses at least the first axial section of the first shielding body can, for example be provided, a defined air gap being formed between the first radial section and the axial cylindrical section. The first shielding body can, for example, be magnetically conductive and be made of steel or the mu-metal. The radial distance between the first shielding body and the second shielding body may be constant for the axial length of the cylinder. It is thus possible to effect a large-surface and a uniform transfer of a magnetic field. During assembly, the second shielding body can further be sleeved over the first shielding body in a relatively simple manner. The second shielding body may be configured to be stationary and in particular as an outer housing of at least the measuring unit. A magnetic field generated in the rotating components of the angular displacement measuring system can thereby be transferred to at least one stationary component, especially the second shielding body, at a transfer location. The surface for shielding can thereby be enlarged without requiring additional rotating components and the resulting additional weight at the drive shaft. An effective shielding from an externally generated magnetic field can also be provided. 
         [0025]    The first shielding body and/or the second shielding body may at least comprise an axial bearing section on which a bearing of the drive shaft abuts. The first shielding body and/or the second shielding body can, for example, comprise a shoulder on which a shaft bearing of the drive shaft abuts. An exact alignment of the angular displacement measuring system of the measuring unit is thereby possible with respect to the drive shaft, as well as a space-saving structure. 
         [0026]    The first shielding body and/or the second shielding body may comprise at least one shoulder to which the sensor unit and/or a housing are fastened. The first shielding body and/or the second shielding body can, for example, be formed with a flange having a screw hole pattern, to which flange the housing with a corresponding counter-flange and a corresponding screw hole pattern is fastened using screws. The respective shielding body may itself be adapted, for example, to be fixed to a machine thereby or via a further shoulder. The first shielding body may also be fastened to the second shielding body at the shoulder. The first shielding body and/or the second shielding body may also be provided with a shoulder or web for fastening the sensor unit. The second shielding body in particular has a shoulder at which a sensor body can be inserted and fastened. It is thereby possible to align the components of the angular displacement measuring system with each other so that an air gap formed between rotating and stationary components can be relatively small, while the angular displacement measuring system may have of a relatively compact structure. 
         [0027]    In an embodiment of the present invention, a housing can, for example, be provided which at least partly surrounds the angular displacement measuring system. The measuring unit, the first shielding body and/or the second shielding body may in particular be surrounded axially and/or radially by the housing. The housing can, for example, be made of steel. A particularly effective shielding of the measuring unit or of the angular displacement measuring system from interferences can thus be achieved which occur on the outside of the angular displacement measuring system and which could have negative effects on the angular displacement measuring system. 
         [0028]    In an embodiment of the present invention, the housing can, for example, be adapted to be set on the first shielding body and/or on the second shielding body. The housing can, for example, be designed as a pot which is adapted to axially set on the angular displacement measuring system, in particular on the measuring unit. An effective shielding and a relatively simple assembly of the angular displacement measuring system are thereby possible. 
         [0029]    The exciter unit may comprise a magnet carrier with at least two magnets fixed on the magnet carrier. This provides for a relatively simple and economic manufacture and assembly of the exciter unit. The magnet carrier is magnetically conductive and is arranged directly opposite the sensor so that a double shielding exists that exactly defines a magnetic field system. The magnetic conditions at the sensor, in particular a Wiegand sensor, can thereby be secured and a multi-turn functionality of the sensor becomes possible. 
         [0030]    In an embodiment of the present invention, the drive shaft can, for example, be coaxially connected to a second shaft at a shaft end portion which is averted from or opposite to the free end at which the exciter unit is arranged and which is in particular a second free end. The drive shaft may thereby be made of a material that is not or that is only slightly magnetically conductive, such as titanium or brass, while the second shaft may be made of steel. An additional shielding of the measuring unit from magnetic interferences can thereby be achieved. 
         [0031]    The present invention will be described in detail below under reference to three embodiments and to the accompanying drawings. 
         [0032]      FIGS. 1 to 4  respectively show an angular displacement measuring system  100  which provides for a direct assembly or a direct coupling of a measuring unit  101  to a drive shaft  4 , wherein the measuring unit  101  comprises an exciter unit  5  and a sensor unit  7 . The angular displacement measuring system  100  is in particular arranged at an axial end of the drive shaft  4  so that an additional shaft for the measuring unit  101  is not required. 
         [0033]    The drive shaft  4  typically is a solid shaft made of steel which is suited to be at least partially magnetized. The drive shaft  4  can in particular be magnetized in use by the electric motor (not shown in the drawings), or by a magnetic brake in contact with the drive shaft  4  (which brake is also not shown in the drawings). It is necessary to shield the measuring unit  101  from such magnetic fields to avoid measuring errors caused thereby, in particular in magnet-based measuring units  101  which are in direct contact with the drive shaft  4 . Such shielding is presently in particular effected by a geometric design of the magnetically conductive components  1 ,  2 ,  4 ,  8  of the angular displacement measuring system  100  so that the magnetic fields interfering with a measurement are dissipated around the measuring unit  101 . 
         [0034]    As shown in  FIGS. 1 and 2 , the drive shaft  4  has a hollow shaft section  42  at a free end  43  thereof, which hollow shaft section  42  tapers conically toward the free end  43  of the drive shaft  4 . A cylindrical or frustoconical recess  41  is thereby formed in the drive shaft  4  at the free end  43 , while a narrow circumferential end face  43   a  exists at an axial front face of the drive shaft  4 . The recess  41  can, for example, be made using a lathe tool or also by a coaxial bore. A second end face  43   b  of the drive shaft  4  is formed at the bottom of the recess  41 , which second end face  43   b  is surrounded by the hollow shaft section  42  and is penetrated by a bore  45  coaxial to the drive shaft  4 . The bore  45  is provided with a thread in engagement with a fastening device  9 , which is shown as a screw  9 . The screw  9  is made of a material that is not or that is only slightly magnetically conductive, for example, a titanium aluminum vanadium alloy, so that, at the free end  43  of the drive shaft  4 , a magnetic field induced in the drive shaft  4  is not transferred via the screw  9 , but is merely transferred into the outer region or into the hollow shaft section  42 . The conical design of the hollow shaft section  42  effects a concentration of the magnetic field transferred into the hollow shaft section  42 . 
         [0035]    In order to dissipate a magnetic field induced in the hollow shaft section  42  to the outside or around the measuring unit  101 , a first shielding body  1  is provided which has an annular disc  10  and a first axial section  12   a  circumferentially extending on the radial outer side of the annular disc  10 . As can be seen in  FIG. 2 , the first shielding body  1  is set axially on the drive shaft  4  or on a first spacer  81  via a second axial section  12   b  and is connected to the drive shaft  4  via said second section. 
         [0036]    The first spacer  81  is designed as a sleeve coaxially aligned with the drive shaft  4  and having a cover, the spacer being fittingly sleeved axially on the free end  43  of the drive shaft  4 . The cover of the first spacer  81  is provided with an opening through which the screw  9  extends. The first shielding body  1  is fittingly sleeved on the first spacer  81  so that the first shielding body  1  and the first spacer  81  can be fixed to the drive shaft  4  via the screw  9 . The arrangement of the first spacer  81  between the drive shaft  4  and the first shielding body  1  allows the arrangement of the first shielding body  1  at a defined axial and radial distance from the drive shaft  4 . An end face  11 , as well as a transfer surface  15  formed on the radial inner side of the second axial section  12   b,  are in particular arranged at a constant distance from the drive shaft  4 . This allows for a uniform and continuous transfer of a magnetic field from the drive shaft  4  to the first shielding body  1 . 
         [0037]    It has been shown that it is possible to optimize a dissipation of a magnetic field by spacing the first shielding body  1  from the drive shaft  4  and thus a restriction of the magnetic transfer from the drive shaft  4  to the first shielding body  1 . An air gap  46  or a magnetically non-conductive spacer may serve as the restriction between the first shielding body  1  and the drive shaft  4 . For this reason, the first spacer  81  can, for example, be made of a material that has no or only little magnetic conductivity, for example, aluminum. It is thereby possible to constantly transfer a magnetic field for a longer period from the drive shaft  4  to the first shielding body  1  without experiencing an increased magnetic concentration or even a magnetic saturation in the end face  11 , in the transfer surface  15 , or in the transition material of the first shielding body  1 . 
         [0038]    The annular disc  10  of the first shielding body  1  has a coaxial opening  14  through which the screw  9  extends. The first shielding body  1  can thus be pretensioned onto the axial end face  45   a  of the drive shaft  4 . The first axial section  12   a  is formed on the radial outer side of the annular disc  10 , in particular as a coaxial cylindrical section. The first axial section  12   a  extends from the annular disc  10  on either side towards and away from the drive shaft  4 . The first shielding body  1  is made of a magnetically conductive material, for example, iron or steel. A magnetic field concentrated in the flanks of the hollow shaft section  42  can thus be transferred into the annular disc  10  and into the second axial section  12   b  of the first shielding body  1  and can be dissipated radially outward into the first axial section  12   a  via the first shielding body  1 . The first axial section  12   a  of the first shielding body  1  is radially surrounded by a stationary second shielding body  2  in the assembled state. 
         [0039]    The second shielding body  2  comprises a flange  22  from which an axial cylindrical flange  21  extends. The axial cylindrical flange  21  of the second shielding body  2  surrounds the first axial section  12   a  of the first shielding body  1  with a smaller radial distance  6  so that the first shielding body  1  is freely rotatable in the second shielding body  2 . An outer radial transfer surface  16  of the first axial section  12   a  and an inner radial transfer surface  26  of the axial cylindrical section  21  are thus arranged opposite each other with a small air gap between them. A magnetic field can thereby be transferred from the first shielding body  1  to the second shielding body  2  and be transmitted further. In the present case, the second shielding body  2  has an axial bearing section  24  which is in contact with a bearing  44  of the drive shaft  4 . This allows for an exact alignment of the measuring unit  101  with respect to the drive shaft  4 . 
         [0040]    The first axial section  12   a  radially surrounds a space in which the exciter unit  5  is arranged at least partly. The exciter unit  5  includes a magnet carrier  50  at which two permanent magnets  51   a,    51   b  are fastened. The exciter unit  5  is connected for rotation with the drive shaft  4  via the screw  9 , so that, in operation, the permanent magnets  51   a,    51   b  build a rotatory magnetic field corresponding to the rotation of the drive shaft  4 , which magnetic field is detected by the sensor unit  7 . A magnetically non-conductive second spacer  82  is provided between the first shielding body  1  and the exciter unit  5  in order to avoid a transmission of a magnetic field from the first shielding body  1  to the magnet carrier  50 . In the present instance, the second spacer  82  is designed as a washer set into an axial recess in the annular disc  10  so that a slipping or shifting of the washer  82 , as well as of the screw  9 , is prevented with respect to the annular disc  10 . 
         [0041]    The screw  9  thus extends through the magnet carrier  50 , the second spacer  82 , the first shielding body  1 , and the first spacer  81 , into the drive shaft  4 , so that the above-mentioned components of the angular displacement measuring system  100  are fixed to the drive shaft  4 . The screw  9  can, for example, here be connected coaxially with the drive shaft  4  and be arranged in the recess  41  in a contactless manner with respect to the radially inner side walls of the hollow shaft section  42 . 
         [0042]    The sensor unit  7  is stationary and in particular includes a sensor  71 , for example, a Hall sensor and/or a Wiegand sensor, fastened to a sensor carrier  72 . In an embodiment, the sensor  71  is suited to detect each rotation of the drive shaft  4 . The sensor unit  7  may further include processing electronics (not shown in the drawings). The sensor carrier  72  is designed as a round disc which, in the mounted state, rests on a shoulder  23  of the second shielding body  2 . The sensor carrier  72  thus forms a cover for the exciter unit  5  arranged inside the first axial section  12   a  of the first shielding body  1 . 
         [0043]    A stationary housing  8  at least partly encloses both the first shielding body  1  and the second shielding body  2 . The housing  8  may here be sleeved in a simple manner on the axial cylindrical section  21  of the second shielding body  2  and be fastened to the flange  22  of the second shielding body  2  using screws  91 . The housing  8  may be made of steel so that a magnetic field transferred from the second shielding body  2  into the housing  8  can be dissipated to the outside. 
         [0044]    It should be clear that at least the drive shaft  4 , the second shielding body  2 , the first spacer  81 , the first shielding body  1 , the second spacer  82 , the screw  9 , the sensor carrier  72 , and the housing  8 , have a common longitudinal axis. It is thus possible to integrate a high-resolution magnetic multi-turn sensor unit  7  having a magnetic shielding in a motor. 
         [0045]      FIG. 3  shows an alternative embodiment of the present invention which for the most part corresponds to the embodiment illustrated in  FIGS. 1 and 2  except, for example, the design and the arrangement of the first shielding body  1  with respect to the drive shaft  4 . 
         [0046]    In the embodiment of the angular displacement measuring system  100  illustrated in  FIG. 3 , a drive shaft  4  with a hollow shaft section  42  formed at a free end  43  is again provided. A first shielding body  1  directly contacts an axial end face  43   a  of the drive shaft  4  by an end face  11  of an annular disc  10 . A first spacer  81  is not provided. A magnetic field prevailing in the drive shaft  4  can thus be transferred directly to the first shielding body  1 . A circumferentially extending first axial section  12   a  is formed on the radial outer side of the annular disc  10  to transmit the magnetic field from the first shielding body  1  to a second shielding body  2 , which first axial section  12   a  is cylindrical in shape and extends from one side of the annular disc  10  away from the drive shaft  4 . An axial cylindrical section  21  of the second shielding body  2  is again arranged opposite the first axial section  12   a  and spaced therefrom. An effective shielding of the measuring unit  101  can thereby be realized. 
         [0047]      FIG. 4  illustrates an alternative embodiment of the present invention which again corresponds for the most part to the embodiment illustrated in  FIGS. 1 and 2  except, for example, the design and the arrangement of the first shielding body  1  with respect to the drive shaft  4 . 
         [0048]    The embodiment of the angular displacement measuring system  100  illustrated in  FIG. 4  is again provided with a drive shaft  4  having a frustoconical hollow shaft section  42  with a recess  41  at a free end  43 . A first spacer  81  is placed in the recess  41 , which first spacer  81  is connected for rotation with the drive shaft  4  and whose axial length is clearly greater than the axial length of the recess  41 . The first spacer  81  thus protrudes from the free end  43  of the drive shaft  4 . The first spacer  81  can, for example be made of a material having only little magnetic conductivity, for example, aluminum. A fastening device  9  in the form of a screw extends through the first spacer  81 . The screw  9  is also made of a material that is not or that is only slightly magnetically conductive so that a magnetic field induced in the drive shaft  4  is not transmitted via the first spacer  81  and/or the screw  9 , but is concentrated in the flanks of the hollow shaft section  42  arranged on the radial outer side. 
         [0049]    The screw  9  is used to pretension a magnet carrier  50  of an exciter unit  5  on the drive shaft  4  at the free end of the first spacer  81  protruding from the hollow shaft section  42 . Two permanent magnets  51   a,    51   b  are fastened to the magnet carrier  50 , which in operation build a magnetic field corresponding to the rotation of the drive shaft  4 , which field can be detected by a sensor  71  of a sensor unit  7 . The sensor  71  is surrounded by a housing  8  (not shown in  FIG. 4 ). 
         [0050]    A first shielding body  1  is arranged with an end face  11  of an annular disc  10  at a defined distance from an axial end face  43   a  of the drive shaft  4  so that an axial air gap  61  is arranged between the first shielding body  1  and the drive shaft  4 . In the present instance, the first shielding body  1  is designed as a stationary component of the angular displacement measuring system  100 . The first shielding body  1  may be of a two-part structure so that the first shielding body  1  has two halves adapted to be plugged or set radially into each other. The first shielding body  1  can also be fastened to the housing  8  (not shown in  FIG. 4 ) via a flange. The screw  9  and the first spacer  81  extend through a coaxial opening  14  in the annular disc  10 . The diameter of this coaxial opening  14  is smaller than the diameter of the radial inner flanks of the hollow shaft section  42 . A circumferentially extending, axial section  12  is formed on the radial outer side of the annular disc  10 , which axial section  12  is cylindrical in shape and extends from one side of the annular disc  10  away from the drive shaft  4 . The first shielding body  1  is stationary and is not connected to the drive shaft  4 . The first shielding body  1  is made of a magnetically conductive material, for example, iron or steel. A magnetic field concentrated in the flanks of the hollow shaft section  42  can thus be transferred into the annular disc  10  via the axial air gap  61  and can finally be directed radially outward into the first axial section  12   a  around the exciter unit  5  and the sensor unit  7 . The measuring unit  101  can thereby be effectively shielded from a magnetic field induced in the drive shaft  4 . 
         [0051]    The present invention is not limited to embodiments described herein; reference should be had to the appended claims. 
       REFERENCE NUMERALS 
       [0052]      100  angular displacement measuring system 
         [0053]      101  measuring unit 
         [0054]      1  first shielding body 
         [0055]      10  annular disc 
         [0056]      11  end face (of the annular disc) 
         [0057]      12   a  first axial section 
         [0058]      12   b  second axial section 
         [0059]      14  coaxial opening 
         [0060]      15  transfer surface 
         [0061]      16  outer radial transfer surface 
         [0062]      2  second shielding body 
         [0063]      21  axial cylindrical flange 
         [0064]      22  flange 
         [0065]      23  shoulder 
         [0066]      24  axial bearing section 
         [0067]      26  inner radial transfer surface 
         [0068]      4  drive shaft 
         [0069]      41  recess 
         [0070]      42  hollow shaft section 
         [0071]      43  free end 
         [0072]      43   a  end face/axial end face 
         [0073]      43   b  second end face 
         [0074]      44  bearing 
         [0075]      45  bore 
         [0076]      46  air gap 
         [0077]      5  exciter unit 
         [0078]      50  magnet carrier 
         [0079]      51   a  permanent magnet 
         [0080]      51   b  permanent magnet 
         [0081]      6  radial air gap 
         [0082]      61  axial air gap 
         [0083]      7  sensor unit 
         [0084]      71  sensor 
         [0085]      72  sensor carrier 
         [0086]      8  housing 
         [0087]      81  first spacer 
         [0088]      82  second spacer/washer 
         [0089]      9  fastening device/screw 
         [0090]      91  screw