Abstract:
In order to be able to measure over more than 360° with a magnetic angle sensor, it is proposed not to adjust the distance between the encoder magnet and the sensor element in addition to the rotation, e.g. by means of a thread, like in the prior art, but to maintain said distance constant, but instead to adjust a magnetic variator with respect to its axial distance from the sensor element, or also in transversal direction, which variator can be a flux conductor or also a secondary magnet.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS: 
     This U.S. application claims priority to German Patent Application No. 102008033769.2 filed 18 Jul. 2008 and to German Patent Application No. 102009021081.4 filed 13 May 2009, each of which is incorporated herein by reference. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable 
     FIELD OF THE INVENTION 
     The invention relates to a magnetic angle sensor, which is capable of measuring angles of rotation in excess of 360°, in particular over a plurality of revolutions. 
     As a matter of principle, a magnetically sensitive sensor element is used for a magnetic angle sensor, which sensor element is mostly provided as a sensor chip, opposite to which sensor element, an encoder magnet mostly provided as a permanent magnet is rotatably disposed. Thus, the sensor element measures the magnetic field or its change in the form of magnetic induction or in the form of magnetic flux, which correlates with the magnetic field strength H over a material&#39;s constant H. 
     Thus, the sensor element is at least capable to determine the partial rotation angle of the encoder magnet between 0° and 360°. The necessary knowledge of the additionally performed complete revolutions of the encoder magnet, which add up to form the total rotation angle, is acquired in different ways. 
     Thus, EP 0 1503182 uses a sensor element, which additionally measures also the magnetic field provided at the sensor element, and moves the encoder magnet during its rotation axially along a threaded spindle towards the microchip, which is disposed transversal to said axial direction and which constitutes the sensor element. 
     Said solution has several disadvantages, e.g. that there is no linear context between the approach of the encoder magnet and the field alteration at the sensor element. 
     In order to compensate this, either a very complicated processing algorithm for the amount of field alteration is required at the sensor element, or the approach of the encoder magnet to the sensor element, which is a function of the number of revolutions has to follow an analog non linear function, which causes a very complex mechanical fabrication as a matter of principle. 
     BRIEF SUMMARY OF THE INVENTION 
     Thus, it is the object of the invention to provide an angle sensor measuring over plural rotations, which is simple and economical in construction, and in which in particular the distance of the encoder magnet from the sensor element remains constant. 
     Said object is accomplished through the features of patent claim  1 . Advantageous embodiments can be derived from the dependent claims. 
     The distance between the encoder magnet and the sensor element can remain unchanged, when the angle sensor according to the invention additionally comprises a field variator, through which the magnetic field provided at the sensor element is changed as a function of the total rotation angle, which was covered by the encoder magnet. 
     Such a variator can be implemented in different ways. 
     In a preferred embodiment, the variator is comprised of a flux conductor component, e.g. made of soft iron, which, contrary to the material of a permanent magnet, can be machined in a simple and highly precise manner, so that precise threads, guides and similar can be machined therein without increased complexity, and/or the variator is also comprised of a magnetically permeable liquid. 
     By approaching or removing such a flux conductor component, e.g. provided as a flat element from the backside of the encoder magnet or also from the backside of the sensor element, again respectively as the function of the total rotation angle of the encoder magnet, which is subsequently not explicitly repeated with each movement of the variator, the magnetic field variation, which is caused by the invariably offset encoder magnet and which is measurable at the sensor element, changes. 
     The same applies when such a flux conductor component is increasingly inserted in transversal direction between the encoder magnet and the sensor element, which quasi generates a magnetic shunt. When this is performed synchronously by two or plural flux conductor components, disposed opposite to one another and evenly distributed over the circumference, a certain type of magnetic aperture is thus created. 
     The desired effect can also be accomplished by sliding a tubular- or pot shaped flux conductor component with its open face forward over the encoder magnet or over the sensor element from behind to an increasing extent. Thus, the encoder magnet can also be provided annular in a plane parallel to the sensor element, and such a flux conductor component can additionally comprise a center pin in its center, which center pin thus also penetrates into the inner cavity of the annular encoder magnet. Thus, e.g. a threaded spindle with a spindle nut running thereon can be used for moving the flux conductor component. 
     Another option is comprised in that the encoder magnet is made of two encoder magnet components offset in transversal direction and the flux conductor component is pushed forward between the two encoder magnet components in axial direction, thus along the axis of rotation, which is preferably a common axis of rotation for the two encoder magnet components. 
     Thus, when the threaded spindle comprises a constant pitch, it can also be accomplished through a respective shape of the flux conductor component, e.g. through the amount of cross section variation of the flux conductor component in its movement direction, that a linear relationship is provided between the rotating movement of the encoder magnet and the field alteration at the sensor element. 
     If this linear relationship can be accomplished through a non-constant variable pitch of the threaded spindle, the spindle as well as the nut is simpler in configuration than in the prior art, since none of said elements is made of a magnetic material. 
     The variator, however can also be a secondary magnet instead of a flux conductor component, where the pole orientation of said secondary magnet is then preferably axial, or the variator can also be a combination of such a secondary magnet and a flux conductor component. 
     Thus, quite different mechanical solutions can be envisioned. 
     Another option of implementing a variator is comprised in not using a permanent magnet as encoder magnet, but an electric magnet, and in controlling the magnetic force of said encoder magnet as a function of its total rotation angle. Thus, no mechanical approaching or removing an element to and from the sensor element is necessary anymore. 
     With respect to processing the signals put out by the sensor element for the partial rotation angle of the encoder magnet, or also processing said signals added up to form a total rotation angle, by the connected processing unit, which sensor element and processing unit jointly form the sensor unit, interpolation values should be stored in a memory of the processing unit, which correspond to integer complete revolutions. Said interpolation values can be determined again with increasing wear or aging of the angle sensor, preferably they are determined automatically in defined time intervals. 
     Said interpolation values are determined and stored for the first time when the angle sensor is operated for the first time. 
     Among other things, said interpolation values are used for detecting the current total rotation position of the encoder magnet, if the threaded spindle and the spindle nut employed in a mechanical drive of the encoder magnet come out of engagement due to a provided end stop, and by means of an overturning safety, which prevents mechanical damages when running over the end stop, the spindle and the nut subsequently come back into engagement. 
     Thus, the sensor unit may not only comprise one sensor element, thus typically a sensor chip. It is proposed according to the invention to use at least two sensor elements, thus typically two sensor chips. 
     Thus, it is possible according to the tasks of said two sensor elements to detect and put out, on the one hand, the partial rotation angle of the encoder magnet, and, on the other hand, to detect and put out the distance between variator and sensor element, to provide a sensor element respectively optimized for said tasks. 
     With respect to the geometric disposition, thus preferably the sensor element, which determines the partial rotation angle of the encoder magnet, is disposed centrally, thus on the rotation axis of the encoder magnet, while the second sensor element applicable for determining the distance can be disposed closely adjacent, since the consequences herein are less severe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments according to the invention are subsequently described in more detail in an exemplary manner with reference to drawings, wherein: 
         FIGS. 1(   a )-( e ) show a solution with a variator, which can be axially inserted between the magnets. 
         FIGS. 2(   a )-( b ) show a solution with a sleeve shaped variator about the encoded magnet. 
         FIG. 3  shows a solution for changing the transversal offset of the encoder magnets; and 
         FIG. 4  shows a solution with an aperture shaped variator. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the solution of  FIG. 1 , the encoder magnet  1 , whose total revolutions are to be measured by the angle sensor, is disposed on the front face of a rotating body  20 , which is, as illustrated best in  FIG. 1   b , received with its rear end in the bottom of a preferably pot shaped housing  7 , so it is rotatable but fixated in axial direction  10 , so that its front end protrudes into the inner cavity of the housing  7 . 
     The rotating body  20  is provided with a slot  14  from its front end in axial direction and one respective partial encoder magnet  1   a, b  is disposed on the partial faces of the front end thus formed, so that the pole orientation of each partial encoder magnet is initially parallel to the rotation axis  2 , thus to the axial direction  10  of the rotational body, preferably completely covering the partial face. 
     However, in the two partial encoder magnets  1   a, b  the pole orientation relative to one another is reversed, so that the north pole in the one partial face and the south pole in the other partial face of the respective partial encoder magnet  1   a, b  is oriented forward in axial direction  10 , so that the poles disposed at the free end comprise a pole orientation  3  relative to one another transversal to the axial direction  10 . 
     The axial slot in the front side of the rotating body  20  is much deeper compared to the axial extension of the magnets  1   a, b , and it amounts to at least approximately five times that depth. 
     In the slot  14 , e.g. a plate shaped variator  6  is guided axially movable, whose thickness corresponds exactly to the thickness of the slot  14 , which, however, laterally protrudes on both sides from the rotating body  20 , since it comprises a larger width than the diameter of the rotating body  20 . 
     Contrary to the above,  FIG. 1   e  shows a slightly differently shaped variator with the same basic constellation, which variator is not only inserted plate shaped into a slot of the rotating body  20 , but which also additionally encloses it also on the outside, so that the variator  6 , in this case is preferably configured disk shaped with a circular outer circumference, which comprises two openings opposed with respect to the center, which openings respectively pass through in longitudinal direction, through which openings the two free ends of the slotted fork shaped rotating body  20  can be inserted. 
     An exterior thread  12  is provided on the outward protruding lateral surfaces of the variator  6 , wherein the center of said thread coincides with the rotation axis  2  of the rotating body  20 , so that only respective segments of thread windings according to the thickness of the variator  6  are provided on top of one another on the outer surfaces. 
     As illustrated in  FIGS. 1   b  and  1   c , the housing  7  comprises an inner thread  13  on its inner circumference, which is concentric to the rotating body  20 , which inner circumference corresponds to the width of the variator  6 , which inner thread is engaged with the outer thread  12  on the variator  6 . 
       FIG. 1   b  shows that an offset and opposed sensor unit  4  with a sensor element  5  is disposed in the free face of the rotating body  20 , wherein the sensor unit  4  in the form of a circuit board can also be supported e.g. at a shoulder of the pot shaped housing  7 , and by all means does not co-rotate with the rotating body  20 . 
     Thus, when the rotating body  20 , whose total rotation is to be measured, is brought into rotation, thus by more than 360°, the magnetic field  3  extending between the poles of the partial encoder magnets  1   a, b  opposed in transversal direction  11  will continuously change its direction with respect to the sensor element  5 , which is registered by said sensor element. Thus, however, the partial encoder magnets  1   a, b  do not change the axial distance from the sensor element  5 . 
     However, with increasing rotation of the rotating body  20 , the variator  6 , depending on the rotation direction, is moved from the bottom of the slot  14  further and further forward or backward between the partial encoder magnets  1   a, b , wherein the angle sensor comprises a mechanical limiter, so that the variator  6  cannot completely reach the sensor element  5  and overall completely reach the sensor unit  4 . 
     Thus, the variator  6  influences the electrical field between the two partial encoder magnets  1   a, b  with increasing insertion into the portion between said two partial encoder magnets  1   a, b , depending on the variator  6  being a flux conductor component made of soft magnetic material, or being a secondary magnet. 
       FIG. 1   d  shows a version differing from  FIG. 1   b  in that the sensor unit  4  features two separate sensor elements  5   a, b.    
     The sensor element  5   a  is centrally located on the longitudinal axis  10 , the rotation axis of the magnet, and preferably measures the partial rotation angle of the magnet. On the other hand, the second sensor element  5   b  is disposed on the circuit board slightly laterally offset, which sensor element shall determine the axial distance between the variator and the sensor unit  4 . 
     For simplification reasons, the variator  6  is always designated as a flux conductor component without restricting the invention thereto. 
       FIG. 2   a  shows a solution, which differs from the solution according to  FIG. 1  initially in that the rotating body  20  is not slotted at its forward free end, and accordingly the two partial encoder magnets  1   a, b  are directly adjacent to one another and can form a one-piece encoder magnet  1 , of which only the poles (north and south pole) facing the free face are visible, so that no sequence of poles is necessary in axial direction  10 . 
     Furthermore, the rotating body  20  now comprises an outer thread  12  on its round outer circumference, on which outer thread the sleeve shaped variator  6  runs with a respective interior thread  13 , which variator concentrically surrounds the rotating body  20 . 
     The sleeve shaped variator  6  comprises protrusions  16  on its outer circumference, e.g. on two sides opposite to one another, which protrusions are machined into longitudinal grooves  15 , extending in longitudinal direction  10  in the inner surfaces of the in turn preferably pot shaped housing  7 , thus allowing a longitudinal movement, but no rotation of the sleeve shaped variator  6 . 
     Also here, the magnetically sensitive sensor element  5  of a sensor unit  4  is disposed in turn axially offset opposite to the free face of the rotating body  20 , thus opposed to the encoder magnet  1  rotatably disposed thereon, which sensor unit  4  is mounted to the housing  7  and therefore does not rotate with the rotating body  20 . 
     This way, when the rotating body  20  is driven in rotation, the pole axis  3  of the encoder magnet  1 , which pole axis extends in transversal direction  11 , is rotated with respect to the sensor element  5 , however, it maintains its axial distance from the sensor element  5 . On the other hand, driven by the threaded connection, the sleeve shaped variator  6  changes its distance from the sensor element  5  by moving more or less laterally past the encoder magnet  1 , which does not laterally protrude beyond the face of the rotating body  20 , thus influencing the field of said encoder magnet. 
       FIG. 2  shows a slightly different variant, since the variator  6  therein does not surround the rotating body  20  as a sleeve over its entire circumference, but only as partial variators  6   a, b  disposed on two sides opposed to one another, which variators engage longitudinal grooves  15  provided in the outer circumference of the rotating body  20  by means of radially inward oriented protrusions  16 , and therefore co-rotate with the rotating body  20 , but are simultaneously longitudinally movably guided thereon. 
     Thus, the outer thread  12  is now disposed on the outside of the partial variators  6   a, b , which mesh with an inner thread  13 , which is disposed in this configuration on the internal circumferential surfaces of the housing  7 , concentrically surrounding the rotating body  20 . 
     Also here, the encoder magnet  1  is disposed on the frontal free face of the rotating body  20 , and in turn axially offset opposite thereto, the sensor unit  4  with a sensor element  5  is disposed on the rotation axis  2 , which sensor unit is not visible in  FIG. 2 . Thus, also here, an effect occurs, that with increasing rotation of the rotating body  20 , the partial variators  6   a, b , which are preferably disposed on the pole direction  3  of the encoder magnet  1 , co-rotate with the encoder magnet  1 , but in turn move forward more or less in axial direction over the encoder magnet  1 , thus changing its distance from the sensor element  5 . 
       FIG. 3  shows a solution in which the variator  6  neither has to be a flux conductor component nor a secondary magnet, since it only changes the distance of the partial encoder magnets  1   a, b  in transversal direction  11  from the rotating axis  2 , while its distance from the sensor element  5  in axial direction  10  remains constant. 
     This can be performed in several ways. 
     In the variant illustrated in  FIG. 3 , the rotating body  20  is provided in several pieces for this purpose by rotatably supporting a round base body  20 , as it is typical rotatably in a housing  7 , but this time, it is also being moved in axial direction  10 , since it bears an exterior thread  12  on its outside, which exterior thread meshes with the respective interior thread in the housing  7 . 
     The forward free end of the base body  20  is configured as a round cone  17 , in whose conical surfaces longitudinal grooves  15 ′ are machined in two opposite directions. 
     The cone  17  protrudes beyond the base surface of the pot shaped housing  7 , in whose bottom the base body  20  is guided in a thread. 
     Rotating body components  20   a, b  contact the cone  17 , engaging one of the longitudinal grooves  15  provided in the outer circumference of the rotating body  20  respectively by means of radially inward oriented protrusions  16 , thus co-rotating with the rotating body  20 , while simultaneously being supported longitudinally movable therein. 
     Partial encoder magnets  1   a, b  are disposed on the front face of said rotating body components, which partial encoder magnets are disposed opposite to the sensor element  5  and respectively comprise a pole orientation in transversal direction  11  and comprise poles alternating in sequence in transversal direction  11 , wherein each particular partial encoder magnet  1   a  or  1   b  comprises a north pole and a south pole. 
     The rotation body components  20   a, b  can thus be pressed against the conical surface of the cone  17  from the outside by a respective spring  18 , which rotating body components are supported on the radial outside at the housing  7  and which slide in circumferential direction on the rotating body components  20   a, b , preferably at their inner ends by means of a shoe  19   a, b , contacting said rotating body components, since the springs  18  do not co-rotate with the rotating body components  20   a, b.    
     Thus, a form locked connection in axial direction  10  between the shoe  19   a, b  and the respective rotating body component  20   a, b  can additionally prevent a position change of the rotating body components  20   a, b  in axial direction. 
     In this case the cone  17 , or better the interaction between the conical surfaces at the cone  17  and the opposite surfaces at the rotating body components which support the encoder magnets  1   a, b  and which are modulated the with respect to their transversal distance through the axial movement of the cone  17 , acts as a variator. 
       FIG. 4  shows a solution in which the variator is divided into two or more variator components  6   a, b  opposite to one another with respect to the rotation axis  2  and disposed in axial direction between the encoder magnet  1 , which in turn is disposed on the face of a rotation body  20 , axially fixated in the housing  7  and the opposite sensor element  5 . The transversal movement of the two or more variator components  6   a, b  distributed about the circumference thus acts like a type of variable aperture between the encoder magnet  1  and the sensor element  5 . 
     This is accomplished by disposing the variator components  6   a, b  at the free end of support arms  22   a, b , respectively carrying a variator component  6   a, b , and protruding forward at a slant angle and outward from the front portion of the rotating body  20 . 
     The support arms  22   a, b  are configured pivotable, e.g. through their own elasticity, so that they can extend more or less outward, but they are preloaded in radial outward direction through their inner tension. 
     The support arms  22   a, b  are pressed inward by disposing a conical sleeve  21 , which comprises a negative concave cone on its front face, concentrically about the rotating body  20 , and providing it axially movable in the housing  7  in longitudinal direction  10  by engaging longitudinal grooves  15  provided in its inner circumference in a form locking manner. The longitudinal drive is in turn performed by an exterior thread on the outside of the rotating body  20 , which exterior thread is engaged with an inner thread  13  in the pass-through opening of the conical sleeve  21 . 
     The variator components  6   a, b  or the support arms  22   a, b  contacting the inner conical surfaces of the conical sleeve  21  are increasingly pressed radially inward and the aperture is closed more and more through pushing of the conical sleeve  21  forward in axial direction  10 . 
     When sliding the conical sleeve  21  backward, the arms  22   a, b  move outward again due to their preloading or spring elasticity. 
     REFERENCE NUMERALS AND DESIGNATIONS 
       1  encoder magnet 
       1   a, b  encoder magnet component 
       2  rotation axis 
       3  pole orientation 
       4  sensor unit 
       5  sensor element 
       6  variator 
       6   a, b  variator components 
       7  housing 
       7   a  bottom surface 
       8  processing unit 
       10  axial direction 
       11  transversal direction 
       12  exterior thread 
       13  interior thread 
       14  slot 
       15 ,  15 ′ longitudinal groove 
       16  protrusion 
       17  cone 
       18  spring 
       19   a, b  shoe 
       20  rotating body, base rotating body 
       20   a, b  rotating body components 
       21  conical sleeve 
       21   a  inner cone surface 
       22   a, b  support arms 
       23  support 
       24  lip seal