Patent Publication Number: US-2019186891-A1

Title: Rotation-Angle Sensor, Stator Element and Rotor Element for Same

Description:
PRIOR ART 
     The invention relates to a rotation angle sensor, a stator element and a rotor element for the same. 
     By arranging transmitting and receiving coils at the stator of a rotation angle sensor, said coils being coupled inductively to a target on the rotor in such a way that when an electromagnetic alternating field is emitted by the transmitting coil an alternating voltage is induced in the receiving coil, the rotation angle can be detected depending on the induced alternating voltage. This is described, for example, in EP 0 909 955 B1. 
     DISCLOSURE OF THE INVENTION 
     The invention is based on the recognition that errors can occur with real sensors as a result of bearing play or tolerances related to manufacture in terms of the relative position of the stator element and the rotor element, said errors being, for example, so large that a specification relating to the accuracy of the measured rotation angle can no longer be satisfied. 
     There may therefore be a need to provide a rotation angle sensor that even in the presence of radial deviations of the stator element or of the stator relative to the rotor element or the rotor from an ideal position, e.g. a centered position, to compensate for the changes in the measurement signal for the angle detection that occur thereby. 
     Advantages 
     It is therefore the object of the present invention to provide an improved rotation angle sensor. 
     This object is fulfilled by the rotation angle sensor as claimed in claim  1 , and the stator element along with the rotor element as claimed in the subsidiary claims. 
     Further advantageous embodiments of the present invention are given in the dependent claims. 
     A corresponding rotation angle sensor comprises a stator element and a rotor element mounted rotatably about a rotation axis with respect to the stator element, wherein the rotation angle can be detected by an inductive coupling between the rotor element and the stator element, wherein at least one compensation element is arranged at the stator element, wherein the at least one compensation element comprises at least one compensation transmitting coil for emitting an electromagnetic compensation alternating field and at least one compensation receiving coil for receiving electromagnetic alternating fields, wherein the rotor element comprises at least one first electrically conducting section, wherein the at least one first electrically conducting section at the rotor element is arranged in such a way and is coupled inductively in such a way with the at least one compensation transmitting coil and the at least one compensation receiving coil of the compensation element that when the electromagnetic compensation alternating field is transmitted by the at least one compensation transmitting coil, a compensation alternating voltage induced in the at least one first compensation receiving coil depends predominantly on a relative radial arrangement of the stator element and of the rotor element to one another with reference to the axis of rotation. 
     It is obvious in this case that the compensation alternating voltage can also depend on the rotation angle. The compensation element is, however, preferably designed such that a pure rotary movement in a defined arrangement between the rotor element and the stator element only changes the compensation alternating voltage slightly if at all. Only a radial displacement between the stator element and the rotor element, e.g. an eccentric arrangement resulting from bearing play with respect to the axis of rotation, should change the compensation alternating voltage measurably. Preferably the compensation alternating voltage changes in terms of its magnitude or amplitude depending on and/or proportionally to the deviation from the defined radial arrangement. The amplitude can, for example, rise with an increasing deviation in a radial direction. It can be provided that the compensation alternating voltage is only sensitive to displacement along one direction in a Cartesian axis system. The provision of two compensation elements that are arranged non-collinearly with respect to the axis of rotation and each other can then enable a sensitivity also to displacements in all directions in a plane perpendicular to the axis of rotation. 
     In the sense of this application, an “electrically conducting” section can also be understood as an “electrically conductive section”. It should be understood here that in the sense of this application, the materials that are generally identified as or used as insulators are not considered to be “electrically conducting” or “electrically conductive”. Purely by way of example, a metal sheet can be electrically conducting or electrically conductive. 
     The compensation alternating voltage is induced in the at least one first compensation receiving coil by the emission of the electromagnetic compensation alternating field. The first electrically conducting section of the rotor element, which can also be known as what is called a target, is used here for the inductive coupling. The inductive coupling depends here on the relative radial arrangement of the target and the compensation element. The target is arranged on the rotor element, the compensation element is arranged on the stator element. The relative radial arrangement of the rotor element and the stator element thus influences the induced compensation alternating voltage, depending on the inductive coupling between the compensation element and the target. By monitoring the induced compensation alternating voltage, the relative radial arrangement of the rotor element and the stator element can thus be monitored. Depending on the relative overlap of the at least one compensation receiving coil by the first electrically conducting section of the rotor element or by the target, the amplitude of the voltage induced by the compensation transmitting coil changes. 
     Advantageously, the stator element comprises at least one angle detection transmitting coil for emitting an electromagnetic angle detection alternating field and at least one angle detection receiving coil for detecting electromagnetic alternating fields, wherein the rotor element comprises at least one second electrically conducting section. The at least one second electrically conducting section can here, for example, be designed in the form of a circular ring sector with respect to the axis of rotation. The at least one second electrically conducting section is here inductivley coupled to the at least one angle detection receiving coil in such a way that when the electromagnetic angle detection alternating field is emitted by the at least one angle detection transmitting coil at least one angle detection alternating voltage is induced in the at least one angle detection receiving coil, wherein the at least one second electrically conducting section is arranged at the rotor element in such a way that the first alternating voltage induced in the at least one angle detection receiving coil depends on an angle of rotation between the stator element and the rotor element. The angle detection alternating voltage induced is, in particular, advantageously, predominantly dependent on an angle of rotation between the stator element and the rotor element. This results in a particularly compact arrangement, since the second section relevant for the angle detection and the first section relevant for the compensation can be constructed in a single target, e.g. in the rotor element or rotor. 
     Advantageously, the at least one compensation element, or the at least one compensation receiving coil, lies radially outside the at least one angle detection receiving coil. A radial deviation can thereby be recognized particularly reliably, since the mutual influence between angle detection coils and compensation coils is thereby minimized. 
     Advantageously, the at least one compensation transmitting coil for generating the compensation alternating field, and the at least one angle detection transmitting coil for generating the angle detection alternating field are arranged at the stator element. This permits a simplified cabling or conductive track configurations for contacting the coils. 
     Advantageously, the at least one angle detection transmitting coil is arranged radially outside, surrounding the at least one angle detection receiving coil. This permits a particularly compact form of construction on a circuit board. The stator element can particularly advantageously thus be arranged on a single circuit board. 
     Advantageously, the winding of the at least one compensation receiving coil with respect to the at least one first electrically conducting section is arranged, radially with respect to the axis of rotation, at least partially overlapping with the first electrically conducting section. In this way, for example, the radial extent of the first electrically conducting section can be smaller than the radial extent of the at least one compensation receiving coil. 
     As a result, a change in the compensation alternating voltage, or a current value of this induced compensation alternating voltage, is particularly well detectable. The compensation alternating voltage is induced here by the electromagnetic compensation alternating field of the at least one compensation transmitting coil in the at least one first compensation receiving coil, with coupling of the at least one electrically conducting first section. Small changes in position of the at least one first electrically conducting section along the radial direction can be detected particularly precisely with these geometrical relationships. Thus even a small deviation in the relative radial arrangement of the stator element and the rotor element with respect to one another in respect of the axis of rotation is recognizable. Deviations from a defined reference position e.g. a centered position, between the stator element and the rotor element with respect to the axis of rotation can, for example, in this way be detected particularly accurately. 
     Advantageously, the at least one first electrically conducting section is an electrically conductive circular ring surrounding the rotor element in the circumferential direction. This permits the recognition of deviations even with only a single compensation element. 
     Advantageously, the at least one first electrically conducting section extends radially from the axis of rotation. The at least one second electrically conducting section here abuts the at least one first electrically conducting section radially, extending in the direction of the axis of rotation. The at least one second electrically conducting section is here arranged, viewed in the radial direction, between the axis of rotation and the at least one first electrically conducting section. Here, viewed in the radial direction, a gap or slot is provided between the at least one second electrically conducting section and the at least one first electrically conducting section. This can have the form of a circular ring sector, and can preferably extend in the circumferential direction. The geometric line at which the edge of the at least one first electrically conducting section and the edge of the at least one second electrically conducting section at facing sides of the respective section are bounded forms a boundary between the sections. The surface that the at least one first electrically conducting section and the at least one second electrically conducting section form at this boundary is preferably interrupted by the gap or slot. This enables an overlap between the at least one first electrically conducting section and the at least one compensation receiving coil, while the at least one second electrically conducting section is still at a distance therefrom. As a result, the robustness of the recognition in respect of parasitic inductive coupling by the second electrical section is increased. 
     Advantageously, the extent of the gap or slot in the radial direction is at least 50% of the difference between a radial extent of the compensation receiving coil and a radial extent of the at least one first conducting section. The functionality is thereby improved. In the centered case, i.e. when both the stator element and the rotor element are centered with respect to the axis of rotation, the at least one first electrically conducting section is, for example, in the center between the windings of the respective compensation receiving coil. With a maximum excursion radially inward, the at least one first electrically conducting section is preferably fully outside the windings of the angle detection receiving coil. In the case of an excursion radially outward, in which the at least one first conducting section lies still exactly just inside the compensation receiving coil, it is simultaneously ensured that the at least one second electrically conducting section does not yet overlap the compensation receiving coil radially inward, or only does so minimally. For this displacement radially outward, the at least one second electrically conducting section is thus arranged not yet overlapping the compensation receiving coil. The at least one first electrically conducting section preferably has a lower radial dimension than the radial extent of the at least one compensation receiving coil. The width of the gap or width of the slot is preferably dimensioned such that, with a radial displacement, the at least one second electrically conducting section does not overlap the at least one compensation element, meaning that the distance is large enough that no (strong) inductive coupling arises between the at least one second electrically conducting section and the at least one compensation element. In this way it is ensured that the at least one compensation element is only, or predominantly only, coupled with the at least one first electrically conducting section, and the compensation measurement results are not corrupted by the at least one second electrically conducting section that is intended for detecting the angle. 
     Advantageously the at least one second electrically conducting section and the at least one first electrically conducting section form a surface, in particular having the form of a circular ring sector, radially abutting one another with respect to the axis of rotation, wherein, in particular, the first conducting section comprises the gap or slot. This enables a simple, in particular one-piece, manufacture out of electrically conducting material. The gap or slot can here for example be stamped from a thin metal sheet. 
     Advantageously, the at least one compensation receiving coil comprises an identical number of first partial windings and second partial windings that are arranged with respect to one another, and with respect to the axis of rotation, such that a first alternating voltage component is induced by the electromagnetic compensation alternating field in the first partial winding, and a second alternating voltage component with the opposite arithmetic sign is induced in the second partial winding. The first alternating voltage component and the second alternating voltage component, here compensate themselves in a predetermined radial arrangement of the at least one first electrically conducting section with respect to the axis of rotation. In the above-mentioned radially central arrangement, the alternating voltages induced in the partial windings overlay to give a resulting voltage of preferably 0 V (zero volts). Deviations in the one or other direction are thus recognizable in the amplitudes of the induced voltage. For this purpose the partial windings are advantageously wound in mutually opposing directions. For example, with a centered arrangement of the rotor element and of the stator element with respect to the axis of rotation, or with a positioning corresponding to the reference position, this central arrangement of the at least one first electrically conducting section with respect to the at least one compensation receiving coil can be adjusted. An induced compensation alternating voltage thus compensates itself in the two partial windings. 
     A number of at least one compensation elements and of at least one first electrically conducting sections advantageously agree with one another. Advantageously two compensation receiving coils are arranged at the stator element in a predetermined circular segment between 0° and a maximum angle in the range of 170° to 190°, preferably 180°, wherein two first electrically conducting sections are provided at the rotor element in a predetermined circular segment between 0° and a maximum angle in the range of 170° to 190°, preferably of 180°. In addition, or as an alternative, at least two compensation receiving coils and at least two first electrically conducting sections are arranged offset by a predetermined angle, in particular between 70 and 100°, preferably 90° in the circumferential direction of the stator element or of the rotor element. 
     These are particularly favorable arrangements for a rotation angle sensor that is implemented as a rotation angle segment sensor. If, for example, a circular segment of 180° is chosen, the structural size of the rotation angle sensor can be halved in comparison with a circular segment of 360°. If, in addition, an offset of for example 90° is chosen, then on the one hand a Cartesian coordinate system with an origin in the axis of rotation can be defined such that two compensation receiving coils are arranged in the negative x-direction and in the positive x-direction at the same distance from the origin. On the other hand, a compensation receiving coil can be arranged in the positive y-direction at the same distance from the origin as these. Radial deviations of the relative arrangement of the rotor element with respect to the stator element can thereby be measured as a linear combination of the deviations along the x-axis and the y-axis. In this case, for example, in an idle position of the rotor element, three first electrically conducting sections can be arranged, offset by 90°, in the rotation angle sensor. Preferably two of the electrically conducting sections are arranged such that in this idle position they are arranged with the same distance from the origin in the negative x-direction and in the positive x-direction, and one of the electrically conducting first sections is arranged in the positive y-direction at the same distance as these from the origin. Through this, in the idle position, a deviation of the rotor element from its centered position in the x-direction and in the y-direction can be recognized. A horizontal and a vertical displacement are thus directly determined with vectorial measurement. With a 90° offset, x-tolerances and y-tolerances can in this way be measured directly, without conversion having to be done. 
     The invention also relates to a stator element and a rotor element of the type described for a rotation angle sensor. 
    
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
       Preferred forms of embodiment of the present invention are explained in more detail below with reference to the appended drawings. Here: 
         FIG. 1  shows schematically a view of a part of a rotation angle sensor, 
         FIG. 2  shows schematically a view of a part of a stator for rotation angle sensors, 
         FIG. 3  shows schematically a part of the rotation angle sensor according to a first form of embodiment, 
         FIG. 4  shows schematically a detailed view of a part of the rotation angle sensor according to the first form of embodiment,  FIG. 5 a   ,  5   b ,  5   c  show schematically views of different relative arrangements of parts of the rotation angle sensor according to  FIG. 4 , 
         FIG. 6  shows schematically a rotor element according to a second form of embodiment. 
     
    
    
       FIG. 1  shows schematically a rotation angle sensor  10 , comprising a stator element  12  and a rotor element  14  mounted rotatably about an axis of rotation A with respect to the stator element  12 . 
     The angle of rotation can be detected through an inductive coupling between the rotor element  14  and the stator element  12 . Details of the inductive coupling and its use for the determination of the angle of rotation are described, for example, in EP 0 909 955 B1. 
     The stator element  12  accordingly, for example, comprises the at least one angle detection transmitting coil  22  illustrated in  FIG. 1  for emitting an electromagnetic angle detection alternating field and at least one angle detection receiving coil  20  for detecting electromagnetic alternating fields. 
     “Radial” or “radial arrangement” below means a spoke-like direction or arrangement going away from the axis of rotation A. “Surrounding” or “circumferential direction” below means a circular direction, essentially on a plane perpendicular to the axis of rotation A. “Axial direction” below means a direction along the axis of rotation A. 
     A sensor circuit board for the rotation angle sensor  10  comprises, for example, at least one circumferentially arranged angle detection transmitting coil  22  which comprises one or a plurality of windings and is preferably implemented as a planar coil. The windings can advantageously be realized on a plurality of layers of a multi-layer circuit board in order to be able to generate a sufficiently large electromagnetic alternating field. The at least one angle detection transmitting coil  22  is subjected to an alternating voltage that has amplitudes in the range between 0.5 V up to 10 V, preferably 1.5 V, at frequencies in the range of a few megahertz, preferably 5 MHz. 
       FIG. 2  shows a layout of a known, exemplary sensor circuit board for a rotation angle sensor that is implemented as a rotation angle segment sensor. This means that coils running through 360° around the axis of rotation A are not provided, but that the coils are arranged with a predetermined opening angle α appropriate for a predetermined measuring range β of the rotation angle sensor. The measuring range β is also accordingly less than 360°. The measuring range β can in principle cover any angle between β=0° and β=360°; the measuring range β advantageously has the values β=360°/n. Here, n is a natural number greater than 1. In the example, the measuring range is β=120°. The opening angle α of the surrounding angle detection transmitting coil  22  is preferably 5° to 10° more than the measuring range β, in order to hold down the influence of the field non-homogeneities in the region of the radially extending conductive tracks of the at least one angle detection transmitting coil  22  on the at least one angle detection receiving coils  20 . A relatively homogeneous flux linkage of the measuring range β is also achieved thereby. 
     The at least one angle detection transmitting coil  22  comprises conductive tracks extending radially that are connected together through arcs. The arc-shaped conductive tracks are bounded on the inside by an inner radius ri and on the outside by an outer radius ra. The outer radius ra is, for example, limited by the available construction space, and is a few tens of millimeters in size, and preferably 25 mm. The inner radius ri is of a sufficiently large dimension to permit a shaft feed-through, but can also be 0 mm if this is not required. In order to increase the field strength, the at least one angle detection transmitting coil  22  can be implemented on a plurality of layers of the sensor circuit board. 
     At least one angle detection receiving coil  20 , which is composed for example of two partial windings, through each of which electrical current flows in different directions when current is flowing (clockwise or anticlockwise) extends, for example, in the interior of the at least one angle detection transmitting coil  22 . The partial windings can be formed on different layers of the circuit board, particularly at the crossover points of the windings. 
       FIG. 3  shows a plan view of a first form of embodiment of the rotation angle sensor  10 . The rotation angle sensor  10  comprises a coil arrangement  23 . In the example, this is implemented according to the arrangement of the at least one angle detection transmitting coil  22  and of the at least one angle detection receiving coil  20  that is described in  FIG. 2 . The rotor element  14  comprises at least one first electrically conducting section  32 , and, in addition, at least one second electrically conducting section  26 . 
     The at least one second electrically conducting section  26  is preferably implemented in the form of a circular ring sector with respect to the axis of rotation A. Other forms, such as for example rectangular form or circular form or general polygons are also possible. 
     The at least one second electrically conducting section  26  is coupled inductively to the at least one angle detection receiving coil  20  in such a way that, when the electromagnetic angle detection alternating field is emitted by the at least one angle detection transmitting coil  22  at least one angle detection alternating voltage is induced in the at least one angle detection receiving coil  20 . The at least one second electrically conducting section  26  is arranged at the rotor element  14  in such a way that the angle detection alternating voltage induced in the at least one angle detection receiving coil  20  depends primarily on a rotation angle between the stator element  12  and the rotor element  14 . Details on the arrangement of the at least one angle detection transmitting coil  22 , the at least one angle detection receiving coil  20 , and the at least one second electrically conducting section  26 , as well as details for determining the rotation angle, are known, for example, from EP 0 909 955 B1. 
     In addition, at least one first compensation element  1 , a second compensation element  2 , and a third compensation element  3  are arranged at the stator element. 
     Each of these compensation elements  1 ,  2 ,  3  comprises at least one compensation transmitting coil  28  for emitting an electromagnetic compensation alternating field and at least one compensation receiving coil  30  for receiving electromagnetic alternating fields. 
     The at least one first electrically conducting section  32  is arranged at the rotor element  14  in such a way, and is inductively coupled with the at least one compensation transmitting coil  22  and the at least one compensation receiving coil  30  of the respective compensation element  1 ,  2 ,  3  in such a way that when the electromagnetic compensation alternating field is emitted by the at least one compensation transmitting coil  28 , a compensation alternating voltage induced in the at least one first compensation receiving coil  30  depends primarily on a relative radial arrangement of the stator element  12  and the rotor element  14  to one another with respect to the axis of rotation A. The inductive coupling takes place, for example, as described for the rotation angle detection. The coupling factor, which is to say an amplitude relationship between the voltage of the compensation receiving coil  30  and the voltage of the compensation transmitting coil  22 , thus supplies information about a relative position of the respective first electrically conducting section  32  to the respective compensation element  1 ,  2 ,  3 , and thus, in particular about the relative radial position of the stator element  12  with respect to the rotor element  14 . 
     The at least one compensation transmitting coil  28  for generating the compensation alternating field and the at least one angle detection transmitting coil  22  for generating the angle detection alternating field are arranged, for example, at the stator element  12  as illustrated in  FIG. 1 . 
     Alternatively, the compensation receiving coil  30  can be arranged inside the angle detection transmitting coil  22  at the stator element  12 . In this way, the rotation angle sensor  10  or the stator element  12  can have an even smaller construction, or an even smaller diameter. 
     The at least one compensation element  1 ,  2 ,  3 , or the at least one compensation receiving coil  30 , lies preferably parallel to a plane that extends essentially perpendicular to the axis of rotation A. Preferably, the at least one compensation element  1 ,  2 ,  3 , or the at least one compensation receiving coil  30 , does not overlap the area of the at least one angle detection receiving coil  20 , when viewed as a projection onto the plane perpendicular to the axis of rotation A. Preferably, the at least one compensation element  1 ,  2 ,  3 , or the at least one compensation receiving coil  30 , lies here radially outside the at least one angle detection receiving coil  30 , i.e. further away therefrom when viewed from the axis of rotation A. 
     The winding of the at least one compensation receiving coil  30  can be arranged to overlap at least partially with respect to the at least one first electrically conducting section  32  radially with respect to the axis of rotation A in a centered position of the rotor element  14  and stator element  12 , wherein, for example, the radial extent of the at least one first electrically conducting section  32  is smaller than the radial extent of the at least one compensation receiving coil  30 . 
     According to the first form of embodiment, the at least one first electrically conducting section  32  is designed essentially in the form of a circular ring sector. The at least one first electrically conducting section  32  extends, according to the first form of embodiment, from the axis of rotation A radially outward. Instead of a circular ring sector form, a different form, for example rectangular form or circular form, can also be used. 
     The at least one second electrically conducting section  26  abuts the at least one first electrically conducting section  32  when viewed radially, and extends in the direction of the axis of rotation A. The at least one second electrically conducting section  26  is, if viewed in the radial direction, arranged between the axis of rotation A and the at least one first electrically conducting section  32 . Viewed in the radial direction, a gap  34  or slot  34 , preferably having the form of a circular ring sector preferably extending in the circumferential direction, is provided between the at least one second electrically conducting section  26  and the at least one first electrically conducting section  32 . The gap  34  or slot  34  can also have a rectangular form or another form. 
     Preferably the at least one second electrically conducting section  26  and the at least one first electrically conducting section  32 , abutting each other radially with respect to the axis of rotation A, constitute a surface  38  having in particular the form of a circular ring sector, wherein in particular the at least one first electrically conducting section  32  comprises the gap  34  or the slot  34 . The surface  38  can be given by a different form, for example by a rectangular form or a circular form. 
     The coil arrangement  23  with the angle detection transmitting coil  22  is illustrated schematically in  FIG. 3 . The angle detection transmitting coil  22  is arranged in a circular arc segment of δ=20° to δ=160° anticlockwise with respect to the x-axis. Its central radial extension D is shown with dashes, and adopts values between a few tens of millimeters and a few hundred millimeters, for example between 10 mm and 200 mm. The opening angle of the arrangement is α=140°. Other angles are also possible. 
       FIG. 3  shows a plan view of an arrangement of a stator element  12  and a rotor element  14 . 3 compensation elements  1 ,  2 ,  3  are arranged at the stator element  12  and the coil arrangement  23 . The coil arrangement  23  can here be designed, for example, as in  FIG. 2 . The rotor element  12  is illustrated, purely by way of example for the purposes of greater clarity, with only one single trapezoidal rotor section that is formed from the first conducting section  32 , the gap  34  and the second conducting section  26 . It is clear that the rotor element can also comprise a plurality of, for example, identical rotor sections  32 ,  34 ,  26 . For example, just as many rotor sections  32 ,  34 ,  26  are provided as compensation elements  1 ,  2 ,  3 . It is also however possible for a smaller or larger number of rotor sections  32 ,  34 ,  26  to be provided than the number of compensation elements  1 ,  2 ,  3 . For example, two, three or four rotor sections  32 ,  34 ,  26  are provided. The rotor sections  32 ,  34 ,  26  can also have the form of a circular sector or the form of a circular ring sector. 
     The illustrated arrangement with the first compensation element  1 , the second compensation element  2  and the third compensation element  3  are formed in a circular arc segment of δ=20° to δ=160°. The individual compensation elements  1 ,  2 ,  3  extend, for example as in  FIG. 3 , in a first circular arc segment of δ=25° to δ=50°, in a second circular arc segment from δ=77.5° to δ=102.5°, and in a third circular arc segment from δ=130° to δ=155°. The first compensation element  1 , the second compensation element  2  and the third compensation element  3  here, viewed radially, have a greater distance from the axis of rotation A than the outer radius ra of the coil arrangement  23 . 
       FIG. 4  schematically shows a view of an excerpt of the rotation angle sensor  10  according to the first form of embodiment. The at least one compensation receiving coil  30  has a first radial extent D 1 . The at least one first electrically conducting section  32  has a second radial extent D 2 . In this case the at least one first electrically conducting section  32  is bounded, viewed radially inward, by the gap  34  or the slot  34 . The gap  34  or the slot  34  has a third radial extent D 3 . 
     The third radial extent D 3  of the gap  34  or of the slot  34  is, in the radial direction, preferably at least 50% of the difference between the first radial extent D 1  of the at least one compensation receiving coil  30  and a second radial extent D 2  of the at least one first electrically conducting section  32 . 
     In the place of the gap  34  or slot  34  or the circular ring-shaped at least one first electrically conducting section  32 , another additional structure, which preferably is used exclusively for measuring the tolerances, can be provided. 
     Preferably, in the centered case, i.e. when the rotor element  14  and stator element  12  are centered with respect to the axis of rotation A and the at least one first electrically conducting section  32  is thus located in the nominal position, the at least one first electrically conducting section  32  is arranged centrally between counteractive windings  30   a ,  30   b  or partial windings  30   a ,  30   b  of the at least one compensation receiving coil  30 . In the example, each winding  30   a ,  30   b  or partial winding  30   a ,  30   b  has a radial width or radial extent of 0.5×D 1 , i.e. half of the first radial extent D 1 . With a maximum excursion radially outward, the at least one first section  32  is located just still within the radially outer winding  30   a  or partial winding  30   a . This is the case after a displacement of 0.5×(D 1 −D 2 ), i.e. of half the difference between the first radial extent of the at least one compensation receiving coil  30  and the second radial extent D 2  of the at least one first conducting section  32 . For this displacement, the at least one second conducting section  26  is preferably not located over the at least one compensation receiving coil  30 , or does not overlap the radially inner winding  30   b  or partial winding  30   b  of the at least one compensation receiving coil  30 . For this purpose the gap width or the slot width of the gap  34  or of the slot  34  is chosen as described above. 
     The at least one first electrically conducting section  32  is here, as illustrated in  FIG. 4 , preferably less wide, i.e. has a lower second radial extent D 2  than the at least one compensation receiving coil  30  which has a first radial extent D 1 . Thus preferably D 2 &lt;D 1 . This improves the sensitivity for the recognition of tolerances. 
     Bearing play, or tolerances occurring as a result of manufacturing, allow(s) a relative displacement of the stator element  12  and the rotor element  14  radially with respect to the axis of rotation A. The measurement error associated with this when determining the rotation angle is described with reference to its position in the Cartesian coordinate system of  FIG. 3 . The axis of rotation A here represents the z-axis. 
     The arrangement of the at least one compensation transmitting coil  28  and the at least one compensation receiving coil  30  are bounded in the example by a circular arc segment. This, as is illustrated in  FIG. 3 , has an opening angle α=140° starting with the angular position δ=20°, which corresponds to the opening angle α of the surrounding angle detection transmitting coil  22  of the coil arrangement  23 . The at least one first electrically conducting section  32 , and the at least one second electrically conducting section  26  are located, as described, at the angle position δ with respect to the x-axis and with respect to an anticlockwise rotation around the axis of rotation A at the origin of a Cartesian coordinate system. Potentially occurring critical tolerances are a displacement in the x direction Δx and displacement in the y-direction Δy. Depending on the angle position δ these affect the measurement error of the rotation angle to different degrees. 
     At an angle position δ=90°, a displacement in the x-direction only corresponds directly to a rotation of the second electrically conducting section  26 . If the rotor element  14  is displaced in this position along the x-axis, the rotation angle sensor  10  detects this displacement with the at least one angle detection receiving coil  20  as the rotation angle, since the rotor element  14  with its inductively coupling at least one second section  26  is displaced with respect to the at least one angle detection receiving coil  20 . The alternating voltage signal thus changes. The rotation angle sensor  10  then assigns to this change a change of the rotation angle, without a rotation of the rotor element  14  with respect to the stator element  12  actually having taken place. In this position of the rotor element  14 , the effect on the angle error to be expected is a maximum. This can be approximated by the relation 
       Δδ x ,max=360°· xπ·D  
 
     The influence of a y-tolerance Δy that occurs on the measurement error is minimal at this point, and can be neglected, since little or nothing changes in the degree of overlap of the at least one angle detection receiving coil  20  by the rotor element  14 . 
     The contrary situation occurs if the at least one first electrically conducting section  26  is located at the radially extending boundary of the at least one angle detection receiving coil  20 . This would be the case with a rotation angle δ of about 0° to 10° of the rotor element  14 . The measurement error here is markedly more strongly dependent on the y-tolerance, and only minimally on the x-tolerance. This is because in this position, even with a small displacement in the y-direction, the rotor element  14  would bring about a large change in the degree of overlap with the at least one angle detection receiving coil  20 . The rotation angle sensor  10 , or the evaluation electronics coupled thereto, would detect this change in the overlap in the form of a changed induced angle detection alternating voltage, and accordingly would output a changed rotation angle—even though only a displacement in the y-direction between the rotor element  14  and the stator element  12  is present. 
     The following approximation applies here to the angular error: 
       Δδ y ,max=cos δ·Δδ x ,max=cos δ·360°·Δ xπ·D  
 
     The errors occurring with real sensors as a result of x-tolerances and y-tolerances are, for example, recognizable and preferably avoided through an arrangement of at least one of the described compensation elements  1 ,  2 ,  3 . Preferably a number of compensation elements  1 ,  2 ,  3  and of first electrically conducting sections  32  are in agreement. 
     Preferably at least two compensation receiving coils  30  are arranged at the stator element  12  in a predetermined circular segment between 0° and a maximum angle in the range from 170° to 190°, preferably 180°, wherein at least two first electrically conducting sections  32  are provided at the rotor element  14  in a predetermined circular segment between 0° and a maximum angle in the range from 170° to 190°. Alternatively or in addition, the at least two compensation receiving coils  30  and the at least two first electrically conducting sections  32  are arranged offset in the circumferential direction of the stator element  12  or of the rotor element  14  through a predetermined angle, in particular between 70 and 100°, preferably 90°. 
     In the first form of embodiment, the at least one compensation receiving coil  30  preferably comprises an identical number of first partial windings  30   a  and second partial windings  30   b , that are arranged with respect to one another and with respect to the axis of rotation A in such a way that a first alternating voltage component is induced by the electromagnetic compensation alternating field in the first winding  30   a  or the first partial winding  30   a , and a second alternating voltage component with the opposite arithmetic sign is induced in the second winding  30   b  or the second partial winding  30   b , wherein the first alternating voltage component and the second alternating voltage component compensate each other in a predetermined radial arrangement of the at least one first electrically conducting section  32  with respect to the axis of rotation A. 
       FIGS. 5 a , 5 b    and,  5   c  show schematic views of the relative arrangement of parts of the rotation angle sensor  10  according to the first form of embodiment. These result from appropriate relative positions of stator element  12  and rotor element  14  in the x-direction with respect to one another. In the arrangement according to  FIG. 5 a    the at least one first electrically conducting section  32  lies in a symmetrical position with respect to the transition region of the first partial windings  30   a  and the second partial windings  30   b . As a result the two alternating voltage components compensate one another, and the coupling factor is zero. 
     This means that the at least one first electrically conducting section  32  is located in the nominal position, i.e. no lateral or vertical offset of the at least one second electrically conducting section  26  with respect to the axis of rotation A is present. 
     If now the at least one first electrically conducting section  32  is displaced, for example in a negative x-direction ( FIG. 5 b   ), then the first electrically conducting section  32  increasingly overlaps the second partial winding  30   b , and an inductive coupling in this part of the coil is suppressed. An induced voltage in the first partial winding  30   a  remains, and the coupling factor is positive. 
       FIG. 5 c    shows the opposing case for a displacement of the at least one first electrically conducting section  32  in the positive x-direction. A negative coupling factor therefore accordingly results. 
     Preferably at least two of the compensation receiving coils  30  are arranged outside the angle detection receiving coil measuring region. When the at least two compensation receiving coils  30  are used, at least two of these compensation receiving coils can particularly advantageously be arranged in a non-collinear manner with respect to the axis of rotation A. In other words: at least two of the plurality of compensation receiving coils  30  do not lie on a straight line on which the axis of rotation A also lies. By measuring the two coupling factors, it is thereby possible to back-calculate the x-offset and the y-offset of the second electrically conducting region  26 . The position of the second electrically conducting region  26  is thereby known at any time. Preferably an incorrect angle signal is accordingly corrected. 
     Instead of the described design of the at least one compensation receiving coil  30 , the first winding  30   a , the first partial windings  30   a , the second winding  30   b  or the second partial windings  30   b , other forms are also possible. For example, the first winding  30   a  or the first partial windings  30   a  and second winding  30   b  or the second partial windings  30   b  do not have to extend over rectangular surfaces when viewed from above. Furthermore, the number of windings of the at least one compensation transmitting coil  28  or of the at least one compensation receiving coil  30  can be greater than one. In addition, the at least one compensation receiving coil  30  can be arranged closer to the axis of rotation A than the at least one compensation transmitting coil  28  of the coil arrangement  23 . Alternatively, the at least one compensation receiving coil  30  can be arranged at a greater distance from the axis of rotation A than the at least one compensation transmitting coil  28 . 
       FIG. 6  shows schematically a part of a rotation angle sensor  10  according to a second form of embodiment. This comprises the rotor element  14 , which is arranged at the stator element  12  as described for the first form of embodiment. In contrast to the first form of embodiment, the rotor element  14  according to the second form of embodiment comprises an electrically conducting circular ring  36  extending in the circumferential direction instead of the at least one first electrically conducting section  32 . 
     The electrically conducting circular ring  36  extending in the circumferential direction is separated from the at least one second electrically conducting section  26  by a gap  34  or a slot  34 . Viewed in the radial direction, that is to say, in the direction toward the axis of rotation A, the at least one second electrically conducting section  26  is arranged between the axis of rotation A and the surrounding electrically conductive circular ring  36 . Viewed in the radial direction, the gap  34  or slot  34 , which for example has the form of a circular ring sector, preferably extends between the at least one second electrically conducting section  26  and the surrounding electrically conductive circular ring  36  in the circumferential direction. Viewed in the circumferential direction, for example four second electrically conducting sections  26  are provided that extend along spokes at a spacing of 90° to one another radially from the axis of rotation A to the surrounding electrically conductive circular ring  36 . More or fewer second electrically conducting sections  26  can also be provided. 
     The at least one second electrically conducting section  26  of the rotor element  14 , the coil arrangement  23  and the compensation elements  1 ,  2 ,  3  of the stator element  12  are, for example, arranged as described in the first form of embodiment. The surrounding electrically conductive circular ring  36  is, for example, arranged radially at the same distance from the axis of rotation A as the at least one first electrically conducting section  32  of the first form of embodiment. The gap  34  or the slot  34  has for example the same dimensions in both forms of embodiment. 
     Preferably, the coil arrangement  23 , in contrast to the first form of embodiment, surrounds the axis of rotation A, i.e. the opening angle is α=360°. The measuring range β of the rotation angle sensor  10  is then, for example, β=360°. For example, four compensation elements at a spacing of 90° are accordingly arranged here.