Abstract:
An angular transmitter integrated with a small electrical motor and supplying phase-shifted signals has at least one magnetic part having an end face and alternatingly arranged poles on the end face. At least one sensor is arranged opposed to the at least one magnetic part. The at least one sensor has at least two sensor elements arranged angularly relative to one another. The at least two sensor elements are rotated relative to one another by 90° or by 60°. The at least two sensor elements cross one another.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to an angle transmitter integrated with a small electrical motor and comprised of at least one magnetic part which is provided at its end face with alternatingly arranged poles and which has at least one sensor positioned opposite thereto, wherein the angle transmitter supplies phase-shifted signals.  
           [0003]    2. Description of the Related Art  
           [0004]    The angle transmitter has a magnetic part which is fixedly connected with the motor shaft and enables the precise governing of rotational speed and rotational direction of the motor shaft as well as a positioning of the motor. The smaller the motors in which the angle transmitter is used, the greater the problem of achieving a high precision with reasonable expenditure.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present invention to configure an angle transmitter of the aforementioned kind such that it provides high resolution while being of a small size.  
           [0006]    In accordance with the present invention, this is achieved in that the sensor has at least two sensor elements which are positioned angularly relative to one another.  
           [0007]    In the angle transmitter according to the invention, the sensor is provided with at least two sensor elements which are arranged angularly to one another. The sensor thus supplies phase-shifted high-quality signals which result in a high angle precision. The angle transmitter according to the invention enables moreover a high resolution. The sensor elements can have very small dimensions so that the angle transmitter overall is very compact. It is suitable particularly for small or miniature motors which have an outer diameter of only approximately 4 mm to 6 mm and an axial length of, for example, only 10 mm to 20 mm. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]    In the drawing:  
         [0009]    [0009]FIG. 1 is a schematic illustration of the angle transmitter according to the invention;  
         [0010]    [0010]FIG. 2 is a view of a magnetic ring of the angle transmitter according to FIG. 1;  
         [0011]    [0011]FIG. 3 is an illustration corresponding to FIG. 1 of a second embodiment of the angle transmitter according to the invention;  
         [0012]    [0012]FIG. 4 is an enlarged illustration of a sensor of the angle transmitter according to the invention;  
         [0013]    [0013]FIG. 5 shows a second embodiment of a sensor of the angle transmitter according to the invention;  
         [0014]    [0014]FIG. 6 shows an amplitude-angle diagram for the sensor according to FIG. 4;  
         [0015]    [0015]FIG. 7 shows the conversion of the amplitude-angle diagram according to FIG.  6  into a sine-cosine diagram;  
         [0016]    [0016]FIG. 8 is an illustration according to FIG. 1 of a third embodiment of the angle transmitter according to the invention; and  
         [0017]    [0017]FIG. 9 is a view of the magnetic disc of the angle transmitter according to FIG. 8. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The angle transmitter is configured to be integrated with small electrical motors and serves for providing exact governing of the rotational speed and rotational direction as well as the precise positioning of the small motors. The angle transmitter according to FIGS. 1 and 2 has a magnetic ring  2  mounted on a motor shaft  1  of a small motor (not illustrated). The magnetic ring  2  has, for example, a circular contour, as illustrated in FIG. 2, and is seated fixedly on the motor shaft  1 . The magnetic ring  2  is magnetized at the end face over a semi-circle as the north pole N and on the other semi-circle area as the south pole S. This can be realized, for example, by magnetization in a diametrical direction by means of a homogenous magnetic field. The magnetic ring  2  has, for example, a diameter of only 3 mm.  
         [0019]    In the embodiment according to FIGS. 1 and 2, the magnetic ring  2  is positioned at a distance from the ends of the motor shaft  1 . It is also possible to attach a magnetic disc  2   c  (FIGS. 8 and 9) on one end of the motor shaft  1 . In this case, the magnetic part  2  is not penetrated by the motor shaft  1  so that it is of a disc-shaped configuration.  
         [0020]    A sensor  3  is positioned opposite the magnetic ring  2 ; the sensor  3  is advantageously a Hall sensor or a magneto-resistive sensor. It is seated on a support  4 , for example, a PCB (printed circuit board), on which may be provided optionally also an evaluation IC (integrated circuit)  11  (FIGS. 8 and 9). The latter is positioned advantageously on the side of the support  4  facing away from the sensor  3 . The sensor  3  is advantageously positioned under, and thus protected by, a cover  5  which is attached to the support  4 . The sensor  3  detects the magnetic field emitted by the magnetic ring  2  upon rotation of the motor shaft  1 . As illustrated in FIG. 4, the sensor  3  has a horizontal sensor element  6  and a vertical sensor element  7  which are arranged so as to cross one another perpendicularly. The two sensor elements  6 ,  7  in the illustrated embodiment have the same rectangular contour and cross one another at half their length. As a result of the sensor elements  6 ,  7  being positioned perpendicularly to one another, the sensor  3  provides two sine-shaped signals  8 ,  9  (FIG. 6) which are phase-shifted by 90° relative to one another. Because of the phase shift by 90°, the signal  8  corresponds to a sine curve and the signal  9  to the matching cosine curve. For example, in FIG. 6, three rotational angles φ 1  to φ 3  are illustrated, and the corresponding amplitude values can be correlated therewith. As illustrated in FIG. 7, in this way the respective rotational angle of the motor shaft  1  can be determined very precisely.  
         [0021]    The sensor elements  6 ,  7  which are rotated relative to one another by 90° provide high-quality sine-cosine signals which provide a high angular precision. The sine-shaped signals (quadrature signals) enable the determination of the absolute position within a complete revolution of the motor shaft  1 .  
         [0022]    When magneto-resistive sensor elements are used, the absolute position of the motor shaft  1  can be precisely determined within one half revolution of the motor shaft.  
         [0023]    The evaluation of the quadrature signals  8 ,  9  is realized preferably after amplification of the sensor signals. For this purpose, an interpolator circuit can be provided which advantageously is integrated into the angle transmitter and provides two 90° phase-shifted encoder signals with a pulse number which is determined by the interpolator circuit. Since such an interpolator circuit is known in general, it will not be described in detail in this context.  
         [0024]    As an alternative, the interpolator circuit can also provide the absolute position value, for example, by means of a serial interface.  
         [0025]    The evaluation of the quadrature signals after amplification can also be realized by an evaluation algorithm which is provided external to the angle transmitter, for example, by means of a software program provided on a computer. In this type of evaluation, additional corrections of systematic errors are possible, for example, amplitude errors, offset errors or shape errors (deviations from the sine shape). In this way, an even greater precision can be achieved.  
         [0026]    [0026]FIG. 3 shows an embodiment in which a motor magnet  2   a  is fixedly mounted on the motor shaft  1 . The motor shaft  1  penetrates the motor magnet  2   a  centrally. One half is magnetized as a north pole N and the other half is magnetized as the south pole S. The sensor  3  is again positioned opposite the motor magnet  2   a  and is mounted on the support  4  under the cover  5 . The sensor  3  can be embodied corresponding to the embodiment according to FIG. 4.  
         [0027]    In the embodiment according to FIGS. 8 and 9, the magnetic disc  2   c  is positioned centrally at the end of the motor shaft  1 . The magnetic disc  2   c , corresponding to the embodiment of FIGS. 1 and 2, is magnetized at the end face about a semi-circle area as a north pole and on the other semi-circle area as a south pole (FIG. 9). The magnetic disc  2   c  is centrally arranged before the sensor  3  in the axial direction. Otherwise, this embodiment is identical to the embodiment of FIGS. 1 and 2. The center position of the magnet disc  2   c  results in a very compact configuration of the angle transmitter.  
         [0028]    [0028]FIG. 5 shows a sensor  3   b  which can be used in the embodiments of FIGS. 1 and 2,  3  or  8 ,  9 . The sensor  3   b  has three sensor elements  6   b ,  7   b ,  10  which are identical, respectively, and have a rectangular shape. The three sensor elements  6   b ,  7   b ,  10  are arranged at half their length in a crossing arrangement and are staggered by 60°, respectively. Accordingly, this sensor  3   b  provides three sine-shaped signals which are phase-shifted electrically by 120° relative to one another.  
         [0029]    The described angle transmitter is characterized by a very compact configuration because the sensors  3 ,  3   b  have very small dimensions. Their dimension measured perpendicularly to the motor shaft  1  is, for example, only approximately 1.5 mm. The sensor  3 ,  3   b  is positioned at a small spacing opposite the magnetic ring  2  or the motor magnets  2   a  and has only a minimal spacing from the motor shaft  1 . When the sensors  3 ,  3   b  are formed as vertical Hall sensors, as illustrated in the embodiments, the angle transmitter has a high resolution and great precision. When the sensors  3 ,  3   b  are embodied as magneto-resistive sensors, an extremely compact configuration combined with high resolution and precision is obtained also.  
         [0030]    The angle transmitter can be integrated into a brushless or into a brush-type small direct-current motor with air-core coil. The sine-shaped signals  8 ,  9  are evaluated as part of the angle transmitter either within the small motor or external thereto.  
         [0031]    The evaluation of the signals  8 ,  9  can be performed, instead of employing an interpolator circuit, also by means of a microprocessor, a digital logic circuit or the like.  
         [0032]    The evaluation of the sensor signals can be realized such that the output signal provides the absolute position of the motor shaft  1  within an integral part of a revolution of the motor shaft  1 . Advantageously, the output signal provides the absolute position of the motor shaft  1  within one revolution.  
         [0033]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.