Abstract:
A rotation and/or tilt angle detection device for a ball and socket joint is provided wherein at least one magnet ( 2 ), especially a permanent magnet, is arranged in the joint ball ( 1   a ), wherein a display device ( 4 ) displays the magnetic field of the at least one magnet ( 2 ) by means of the magnetooptic effect. An image detection deice ( 10 ) detects the information displayed by the display device ( 4 ). A data processing unit ( 50 ) calculates the relative position of the joint ball ( 1   a ) and the ball socket ( 3 ) of the ball and socket joint on the basis of the information detected.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This is a continuation of and claims the benefit (35 U.S.C. §120 and 365(c)) of copending International Application PCT/DE 2003/003102 of Sep. 17, 2003, which designated inter alia the United States and which claims the priority of German Application DE 102 43 399.2 of Sep. 18, 2002. The entire contents of each application is hereby incorporated by reference in its entirety.  
       FIELD OF THE INVENTION  
       [0002]     The present invention pertains to a rotation angle and tilt angle detection means for a ball and socket joint.  
       BACKGROUND OF THE INVENTION  
       [0003]     Ball and socket joints are important mechanical components, because they allow three degrees of freedom. Only joysticks and vehicle components shall be mentioned here as examples of two typical applications of ball and socket joints. However, the measurement of the rotation and tilt angles has been an essential problem for the use of ball and socket joints so far. A great variety of rotation angle sensors have been known for the measurement of the rotation angle. They use mostly a stationary magnetic field, in which a sensor is arranged, whose resistance changes as a function of the rotary movement of the ball and socket joint. The drawback of these sensors is that they determine exclusively the rotary movement and do not detect the tilting movement of the ball and socket joint. If the tilting movement is to be detected as well, a complicated coupling of a plurality of sensors is disadvantageously necessary.  
         [0004]     Thus, a measuring means with a magnetoresistive sensor for the contactless, continuous measurement of the change in the position of a motor vehicle body, in which a permanent magnet is arranged in the upper apex of a ball head of a ball and socket joint and the sensor is arranged in the area below the apex of the opening of the ball and socket joint socket, is known from the European Patent EP 0 617 260 B1.  
         [0005]     Sensors operating on the basis of Hall sensors disadvantageously have a high sensitivity to external magnetic fields and temperature changes. It is also disadvantageous in case of the use of Hall sensors that the aging of the exciting magnets is not compensated. Furthermore, the calculation of the rotation and tilt angles is very complicated, and it is necessary to record a characteristic diagram in most cases.  
       SUMMARY OF THE INVENTION  
       [0006]     The object of the present invention is therefore to provide a sensor of a relatively simple design or a simple sensor array by means of which the rotary and tilting movement of a ball and socket joint can be determined.  
         [0007]     According to the invention a rotation and/or tilt angle detection device is provided for and in combination with a ball and socket joint. The ball and socket joint has a ball pivot mounted rotatably and pivotably in a ball socket and has a joint ball and a pivot. At least one magnet, especially a permanent magnet, is arranged in the joint ball. A display device based on the magnetooptic effect for displaying the magnetic field of the at least one magnet is provided as well as an image detection means for detecting the information displayed by the display device. A data processing unit is operatively connected to detection means for calculating the position of the ball pivot in relation to the ball socket on the basis of the information detected.  
         [0008]     The automobile industry has a great interest in sensors that detect the position of the wheel in relation to the road. The ball and socket joint images this position. Thus, ball and socket joints are used, e.g., in the front axle of vehicles, and the ball and socket joint is arranged, for example, between the axle guide and the wheel bearing housing. The ball and socket joint is rotated by steering movements. In contrast, it performs a tilting movement during inward deflection.  
         [0009]     The means according to the present invention makes it possible to detect both the rotary and tilting movement of the ball and socket joint, and the sensor advantageously operates in a contactless manner. The present inventions makes provisions for at least one magnet to be arranged at or in the joint ball or the ball pivot. The resulting magnetic field generated is made visible by means of a magnetooptic effect. An optical detection means then determines the visualized magnetic field, and the rotation or tilting of the ball and socket joint can be determined by the magnetic field, which is altered in relation to the initial position.  
         [0010]     Two permanent magnets are advantageously arranged in the pole area of the joint ball in parallel to and at a certain distance from one another. The magnets may be manufactured, in principle, from any desired material and have any desired shape, especially a rod shape. NdFeB magnets, which have a diameter of 1 mm and a length of 2 mm, are advantageously used, one magnet with its north pole being directed toward the surface of the joint ball and the other magnet being directed with its south pole toward the surface of the joint ball. It is possible for the pole area of the joint ball to be flattened. A space is formed as a result between the outer surface of the ball and the ball socket, which space can be used as a grease space or grease depot. If this space is filled with lubricating grease, it is guaranteed that the ball and socket joint will continuously lubricate itself. It is possible in case of such an embodiment of the ball and socket joint for the display device to be arranged in the form of a magnetooptic plate directly behind the grease space or to form a wall area of the grease space itself. The magnetic field generated by the magnets is advantageously not affected adversely or deflected in the latter case by the material of the bearing shell. As a result, the resulting magnetic field of the at least one magnet can be displayed or detected relatively accurately. The display device may also be provided at the ball and socket joint housing or made in one piece therewith.  
         [0011]     The display device advantageously has a magnetooptic sensor layer, which is arranged according to the present invention, as was described above, in the immediate vicinity of the magnet, especially at a distance of only a few mm or a few tenths of one mm from the magnet. The display device may be integrated with the bearing shell, e.g., during the process of manufacturing the bearing shell. However, it may also be fixed or fastened to the bearing shell as a separate module together with the optical detection and/or evaluation means.  
         [0012]     In order for a rotation and tilting of the ball and socket joint to be better detectable, the magnets should not be arranged too close to one another. The distance also depends, among other things, on the distance and the thickness of the magnetooptic sensor layer.  
         [0013]     Embodiments according to the present invention will be explained in greater detail below on the basis of drawings. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a cross-sectional view through a ball and socket joint with a rotation and/or tilt angle detection means according to the present invention;  
         [0015]      FIG. 1   a  is an alternative arrangement of a permanent magnet in a joint ball;  
         [0016]      FIG. 2  is the resulting magnetic field of the two permanent magnets shown in  FIG. 1 , which is displayed by means of the magnetooptic effect, with the ball and socket joint in its starting position;  
         [0017]      FIG. 3  is the displayed magnetic field with the ball and socket joint tilted in direction X;  
         [0018]      FIG. 4  is a displayed magnetic field with the ball and socket joint tilted in direction Y; and  
         [0019]      FIG. 5  is the displayed magnetic field with the ball and socket joint tilted in direction X and twisted at the same time.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]      FIG. 1  shows a cross-sectional view through a ball and socket joint with a rotation and/or tilt angle detection means according to the present invention. The ball and socket joint comprises a ball pivot  1 , which is inserted into a bearing shell (ball socket  3 ) with its joint ball  1   a  made in one piece with the pivot  1   b . The pole face  1   c  of the joint ball  1   a  is flattened, so that a free space  3   a , which can be used as a grease space or grease depot, is formed between the joint ball  1   a  and the bearing shell  3 . Two permanent magnets  2  are arranged at spaced locations and in parallel to one another in the joint ball  1   a  in the pole area, one permanent magnet  2  being directed or pointing with its north pole N and the other permanent magnet  2  with its south pole S in the direction of the pole face  1   c . The permanent magnets  2  may either be inserted into openings and firmly connected with the joint ball  1   a , e.g., by means of an adhesive. However, it is also possible to integrate or to cast the magnets  2  during the process of manufacturing the ball pivot  1 .  
         [0021]     The display device  4  in the form of a magnetooptic plate is arranged under the pole face or in the immediate vicinity of the magnets  2 . The grease space  3   a  as well as the material of the bearing shell  3  is located between the plate  4  and the magnets in  FIG. 1 . It is also possible in an alternative embodiment for the plate  4  to form a wall area of the grease space  3   a , so that there is no bearing shell material between the plate  4  and the magnet  2 . Corresponding magnetooptic plates based on the magnetooptic Faraday effect are sufficiently described in the literature and will not therefore be explained in greater detail here. The optical plate changes its optical properties depending on the magnetic field intensity. The magnets  2  generate a magnetic field, so that the magnetic field intensity changes over the optical plate. If the plate is exposed to light, the electromagnetic waves are reflected differently as a function of the magnetic field, so that an image can be detected in the reflected path of rays, and the magnetic field in the area of the optical plate can be inferred from this image, as a result of which the relative position of the ball and socket joint can in turn be calculated. An illuminating means  5 , whose rays S reach the optical plate  4  through a lens  6  and a polarizer  7  at an angle, is used for the illumination, and these rays are reflected from the plate  4  more or less well correspondingly or as a function of the particular magnetic field prevailing at the reflection point and reach the image detection sensor  10  via a polarizing filter called an analyzer  8  and a lens  9 . The polarizer  7  and the analyzer  8  are arranged rotated by an angle of 45° in relation to one another. The evaluating electronic unit  50 , which performs a calculation as to the rotation or tilting of the ball and socket joint on the basis of the image information obtained, is shown in  FIG. 1 . The image information converted by the image detection sensor or the image detection means  10  into digital signals is shown as an example in  FIGS. 2 through 5 .  
         [0022]     The illuminating means  5  may be formed by light-emitting diodes (LEDs) or even by another, externally arranged light source, whose rays are sent, e.g., by means of an optical light guide to the needed location. The image detection means may be, for example, a commercially available CCD chip (CCD=charge coupled device).  
         [0023]      FIG. 1   a  shows an alternative arrangement of an individual permanent magnet  2 ′ in the pole area of a joint ball  1   a ′. The magnet  2 ′ is arranged in this embodiment in parallel to the flattened pole face, so that the south and north poles of the magnet generate the necessary magnetic field intensity differences in the area of the optical plate, not shown.  
         [0024]      FIG. 2  shows the image information  11  that can be determined, which is obtained on the optical plate due to the magnetic field intensity difference. The ball and socket joint is now located in its zero position, i.e., it is neither rotated nor tilted. The north pole of one permanent magnet causes a positive Faraday rotation, whereas the south pole induces a negative Faraday rotation. Due to the fact that the polarizer  7  and the analyzer  8  are arranged rotated by 45° in relation to one another, the photoresponse curve is linear, as a result of which the sensor (CCD sensor) determining the image information detects more or less light depending on the sign of the magnetization. The north pole of one magnet thus generates a dark spot MD and the south pole a light spot MH. If the starting position of the dark and light spots MD and MH are known, the rotation and tilt of the ball and socket joint can be calculated, as is shown in  FIGS. 3 through 5 , from the relative displacements of these spots.  
         [0025]      FIGS. 3 through 5  show the starting positions of the light and dark spots MD and MH in broken lines. The starting positions are preferably stored in a storage for constant values after calibration.  FIG. 3  shows the tilting of the ball and socket joint in direction X. The dark spot MD′ as well as the light spot MH migrate both to the right and are shifted by the wavelength dx. If the geometry of the ball and socket joint as well as of the rotation and tilt detection means is known, the tilt can be calculated from the shift dx. The dark and light spots MD″ and MH″ are analogously shifted in direction Y, as is shown in  FIG. 4 .  
         [0026]     If the ball and socket joint is tilted and rotated, the relative position of the spots MD′″ and MH′″ changes again in relation to the starting position, and the rotation angle α as well as the tilt in the directions X and Y can be calculated from the relative displacements and distances dx′, dx″ as well as dy′ and dy″. The rotation angle α of the ball and socket joint is obtained from the angle between the lines connecting the shifted spots MD′″ and M′″ as well as the spots indicated by broken lines.  
         [0027]     It is obvious that it is also possible to use more than two permanent magnets. However, it shall be borne in mind in this connection that the distance between the magnets shall not be selected to be too small, so that the light and dark spots can still be determined by the image processing software with sufficient sharpness, so that accurate results or the position of the ball and socket joint can be calculated.  
         [0028]     The rotation and/or tilt detection means according to the present invention can, of course, be used for all types and designs of ball and socket joints.  
         [0029]     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.  
       Appendix  
       [heading-0030]     List of Reference Numbers  
         [none]    
       
           1  Ball pivot  
           1   a ,  1   a ′ Joint ball  
           1   b  Pivot  
           1   c  Pole face  
           2 ,  2 ′ Permanent magnet  
           3  Bearing shell (ball socket)  
           3   a  Free space  
           4  Display device (magnetooptic plate)  
           5  Illuminating means  
           6  Lens  
           7  Polarizer  
           8  Analyzer (polarizing filter)  
           9  Lens  
           10  Image detection sensor  
           11  Image information  
          S Rays  
          M, MD′, MD″ Dark spot  
          NH, MH′, MH″ Light spot  
          dx, dx′, dx″ Wavelength in direction X  
          dy, dy′, dy″ Wavelength in direction Y  
          αRotation angle