Abstract:
A magnetic detection device includes a magnetic moving unit, a magnet that is arranged to face the magnetic moving unit and that applies a magnetic field to the magnetic moving unit, and a magnetoelectric conversion element that is arranged to face the magnetic moving unit and includes at least one segment that detects a change in the applied magnetic field due to rotation of the magnetic moving unit, wherein the magnetic moving unit has a shape that generates an asymmetrical change in magnetic field to the magnetoelectric conversion element in accordance with the direction of rotation of the magnetic moving unit. Thus, a magnetic detection device that can detect the direction of rotation easily and reliably is provided.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a magnetic detection device using a magnetoresistance element (hereinafter referred to as MR element), which is a magnetoelectric conversion element.  
         [0003]     2. Description of the Related Art  
         [0004]     In conventional magnetic detection devices, a bridge circuit is formed by forming an electrode at each end of a magnetoresistance segment that constitutes an MR element, with a constant-voltage and constant-current power source connected between the two counter-electrodes of the bridge circuit, and a change in the resistance value of the MR element due to rotation of a magnetic moving unit is converted to a voltage change, thus detecting a change in the magnetic field acting on the MR element, for example, as disclosed in JP-A-2002-90181 and JP-A-2005-156368.  
         [0005]     In the magnetic detection device disclosed in JP-A-2002-90181, rugged cogs formed on the circumferential edge of the magnetic moving unit are symmetrical about the cog center. Therefore, even when the magnetic moving unit is reversed, a change in the applied magnetic field similar to the change in the applied magnetic field in the case of normal rotation occurs in the MR element, and the same final output signal is generated irrespective of the direction of rotation of the magnetic moving unit. Therefore, the direction of rotation cannot be detected.  
         [0006]     In the magnetic detection device disclosed in JP-A-2005-156368, it is possible to detect the direction of rotation of the magnetic moving unit. However, since it uses the magnetic moving unit in which the rugged cogs are symmetrical about the cog center, plural magnetoresistance segments must be arranged in a complex pattern in order to detect the direction of rotation of the magnetic moving unit. Therefore, the device is complicated and expensive.  
       SUMMARY OF THE INVENTION  
       [0007]     In view of the foregoing circumstances, it is an object of this invention to provide a magnetic detection device that can detect the direction of rotation easily and reliably.  
         [0008]     A magnetic detection device according to an aspect of this invention includes a magnetic moving unit, a magnet that is arranged to face the magnetic moving unit and that applies a magnetic field to the magnetic moving unit, and a magnetoelectric conversion element including at least one segment that is arranged to face the magnetic moving unit and that detects a change in the applied magnetic field due to rotation of the magnetic moving unit, wherein the magnetic moving unit has a shape that generates an asymmetrical change in magnetic field to the magnetoelectric conversion element in accordance with the direction of rotation of the magnetic moving unit.  
         [0009]     Since the magnetic detection device according to an aspect of this invention uses the magnetic moving unit having a shape that generates an asymmetrical change in magnetic field to the magnetoelectric conversion element in accordance with the direction of rotation, the magnetic detection device can detect the direction of rotation of the magnetic moving unit easily and reliably. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIGS. 1A and 1B  are perspective view and top view of essential parts showing the construction of a magnetic detection device according to Embodiment 1 of this invention.  
         [0011]      FIG. 2  is a top view showing the shape of a magnetoresistance segment in Embodiment 1.  
         [0012]      FIG. 3  shows the construction of a processing circuit part of the magnetic detection device according to Embodiment 1.  
         [0013]      FIGS. 4A  to  4 D are timing charts showing the operation (in normal rotation) of the magnetic detection device according to Embodiment 1.  
         [0014]      FIGS. 5A  to  5 D are timing charts showing the operation (in reverse rotation) of the magnetic detection device according to Embodiment 1.  
         [0015]      FIGS. 6A and 6B  are perspective view and top view of essential parts showing the construction of a magnetic detection device according to Embodiment 2 of this invention.  
         [0016]      FIGS. 7A  to  7 D are timing charts showing the operation (in normal rotation) of the magnetic detection device according to Embodiment 2.  
         [0017]      FIGS. 8A  to  8 D are timing charts showing the operation (in reverse rotation) of the magnetic detection device according to Embodiment 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       [0018]      FIGS. 1A and 1B  to  FIG. 3  are structural views showing a magnetic detection device according to Embodiment 1.  FIG. 1A  is a perspective view.  FIG. 1B  is a top view of essential parts.  FIG. 2  shows a pattern of a magnetoresistance segment that constitutes an MR element.  FIG. 3  is a circuit structural view of a signal processing circuit part.  
         [0019]     In this magnetic detection device, a magnetic moving unit  1  is coupled with a detection subject and rotates normally (in the direction of the arrow in  FIG. 1A ) or in reverse about a rotation axis  1   a . A magnet  2  is arranged to face an outer circumferential part of the magnetic moving unit  1  in order to apply a magnetic field to the magnetic moving unit  1 . On the top of the magnet  2 , a board  4  is arranged on which a magnetoresistance segment that constitutes an MR element  3  is formed. Moreover, a processing circuit part  5  is printed on the board  4 . Thus, a construction to detect a change in magnetic field due to rotation of the magnetic moving unit  1  is provided.  
         [0020]     Here, the magnetic moving unit  1  has plural serration-like protrusions  1   b  formed on its circumferential edge. Each serration-like protrusion  1   b  has a shape with its height gradually reduced along the direction of normal rotation of the magnetic moving unit  1  (direction of the arrow) in order to be asymmetrical to the MR element  3 . However, the shape of the serration-like protrusion  1   b  is not limited to the above shape. It may have any shape with its height gradually reduced along the direction of rotation of the magnetic moving unit  1 .  
         [0021]     While the MR element  3  is illustrated as one black block in  FIGS. 1A and 1B , the MR element  3  is formed by a magnetoresistance segment having a shape as shown in  FIG. 2 .  
         [0022]      FIG. 3  shows the construction of the processing circuit part  5  of the magnetic detection device in Embodiment 1.  
         [0023]     In  FIG. 3 , a constant voltage VCC is applied to a bridge circuit  51  formed by the MR element  3  and fixed resistance, and the bridge circuit  51  converts a change in resistance value of the MR element  3  due to a change in magnetic field to a voltage change. The signal, converted to the voltage change, is amplified by a differential amplifier circuit  52  and inputted to a comparator circuit  53 . The signal compared with a predetermined voltage by the comparator circuit  53  is converted to an output of “ 0 ” or “ 1 ” (=VCC) by a transistor  54 T of an output circuit  54  and then outputted from an output terminal  54 Z. Then, a normal/reverse rotation judging circuit  55  calculates the duty of the output acquired from the output terminal  54 Z and judges whether the rotation is normal or reverse on the basis of the result of the calculation.  
         [0024]     Now, the operation of the magnetic detection device according to Embodiment 1 will be described with reference to the drawings.  
         [0025]      FIGS. 4A  to  4 D and  FIGS. 5A  to  5 D are timing charts showing the operations of the magnetic detection device in the normal rotation and the reverse rotation of the magnetic moving unit  1 .  FIGS. 4A and 5A  show the rotation state of the magnetic moving unit  1 .  FIGS. 4B and 5B  show the resistance value of the MR element  3 .  FIGS. 4C and 5C  show the output of the differential amplifier circuit  52 .  FIGS. 4D and 5D  show the change in the output of the output circuit  54 .  
         [0026]     In  Figs. 1A and 1B , when the magnetic moving unit  1  rotates normally, the applied magnetic field to the MR element  3  is changed by the serration-like protrusions  1   b . The resistance value of the MR element  3  changes in accordance with the shape of the magnetic moving unit  1 , as shown in  FIGS. 4A and 4B , and an output OP 1  of the differential amplifier circuit  52  as shown in  FIG. 4C  is provided.  
         [0027]     The output OP 1  of the differential amplifier circuit  52  is compared with a reference value Vref 1  by the comparator circuit  53 , thus shaping the waveform and providing an output signal “ 1 ” or “ 0 ” corresponding to the shape of the magnetic moving unit  1  as an output of the output circuit  54 , as shown in  FIG. 4D .  
         [0028]     In the case of normal rotation, the period during which the output signal is “ 1 ” is represented by t 1 , as shown in  FIG. 4D .  
         [0029]     Next, the operation in the case of reverse rotation is shown in  FIGS. 5A  to  5 D. When the magnetic moving unit  1  rotates in reverse, the applied magnetic field to the MR element  3  is changed by the serration-like protrusions  1   b . The resistance value of the MR element  3  changes in accordance with the shape of the magnetic moving unit  1 , as shown in  FIGS. 5A and 5B , and an output OP 1  of the differential amplifier circuit  52  as shown in  FIG. 5C  is provided.  
         [0030]     The output OP 1  of the differential amplifier circuit  52  is compared with a reference value Vref 1  by the comparator circuit  53 , thus shaping the waveform and providing an output signal “ 1 ” or “ 0 ” corresponding to the shape of the magnetic moving unit  1  as an output of the output circuit  54 , as shown in  FIG. 5D .  
         [0031]     In the case of reverse rotation, the period during which the output signal is “ 1 ” is represented by t 2 , as shown in  FIG. 5D .  
         [0032]     Thus, as seen from  FIGS. 4D and 5D , the relation between the two periods during which the output signal of the output circuit  54  is “ 1 ” is t 1 &gt;t 2 . The length of the period differs between normal rotation and reverse rotation.  
         [0033]     The normal/reverse rotation judging circuit  55  calculates the duty of each of t 1  and t 2 . For example, by judging that the rotation is normal when the duty is 60% and judging that the rotation is reverse when the duty is 80%, it is possible to detect whether the direction of rotation is normal or reverse.  
         [0034]     As described above, the magnetic detection device according to Embodiment 1 uses the magnetic moving unit  1  having the shape that generates an asymmetrical change in magnetic field to the MR element  3  in accordance with the direction of rotation, and can detect the direction of rotation of the magnetic moving unit  1  easily and reliably.  
         [0035]     Also, since the magnetic moving unit  1  has the simple shape in which the serration-like protrusions  1   b  with their height gradually changed along the direction of rotation are formed on the circumferential edge, the magnetic moving unit  1  can be constructed inexpensively.  
       Embodiment 2  
       [0036]      FIGS. 6A and 6B  to  FIGS. 8A  to  8 D are structural views showing a magnetic detection device according to Embodiment 2.  
         [0037]      FIG. 6A  is a perspective view.  FIG. 6B  is a top view of essential parts.  
         [0038]     This magnetic detection device according to Embodiment 2 has basically the same construction as the magnetic detection device of Embodiment 1. However, in this magnetic detection device, the magnetic moving unit  1  has plural serration-like recesses  1   c  formed on its circumferential edge. Each serration-like recess  1   c  has a shape with its depth gradually reduced along the direction of normal rotation of the magnetic moving unit  1  in order to be asymmetrical to the MR element  3 . However, the shape of the serration-like recess  1   c  is not limited to the above shape. It may have any shape with its depth gradually reduced along the direction of rotation of the magnetic moving unit  1 .  
         [0039]     The processing circuit part  5  of the magnetic detection device in Embodiment 2 is the same as the processing circuit part in Embodiment 1 shown in  FIG. 3  and therefore will not be described further in detail. However, in the bridge circuit  51  formed by the MR element  3  and fixed resistance, the vertical positional relation of the MR element  3  and the fixed resistance is opposite to the positional relation in Embodiment 1.  
         [0040]     Now, the operation of the magnetic detection device according to Embodiment 2 will be described with reference to the drawings.  
         [0041]      FIGS. 7A  to  7 D and  FIGS. 8A  to  8 D are timing charts showing the operations of the magnetic detection device in the normal rotation and the reverse rotation of the magnetic moving unit  1 .  FIGS. 7A and 8A  show the rotation state of the magnetic moving unit  1 .  FIGS. 7B and 8B  show the resistance value of the MR element  3 .  FIGS. 7C and 8C  show the output of the differential amplifier circuit  52 .  FIGS. 7D and 8D  show the change in the final output of the output circuit  54 .  
         [0042]     In  FIGS. 6A and 6B , when the magnetic moving unit  1  rotates normally, the applied magnetic field to the MR element  3  is changed by the serration-like recesses  1   c . The resistance value of the MR element  3  changes in accordance with the shape of the magnetic moving unit  1 , as shown in  FIGS. 7A and 7B , and an output OP 1  of the differential amplifier circuit  52  as shown in  FIG. 7C  is provided.  
         [0043]     The output OP 1  of the differential amplifier circuit  52  is compared with a reference value Vref 1  by the comparator circuit  53 , thus shaping the waveform and providing a final output signal “ 1 ” or “ 0 ” corresponding to the shape of the magnetic moving unit  1  as a final output of the output circuit  54 , as shown in  FIG. 7D .  
         [0044]     In the case of normal rotation, the period during which the final output signal is “ 1 ” is represented by t 1 , as shown in  FIG. 7D .  
         [0045]     Next, the operation in the case of reverse rotation is shown in  FIGS. 8A  to  8 D. When the magnetic moving unit  1  rotates in reverse, the applied magnetic field to the MR element  3  is changed by the serration-like recesses  1   c . The resistance value of the MR element  3  changes in accordance with the shape of the magnetic moving unit  1 , as shown in  FIGS. 8A and 8B , and an output OP 1  of the differential amplifier circuit  52  as shown in  FIG. 8C  is provided.  
         [0046]     The output OP 1  of the differential amplifier circuit  52  is compared with a reference value Vref 1  by the comparator circuit  53 , thus shaping the waveform and providing a final output signal “ 1 ” or “ 0 ” corresponding to the shape of the magnetic moving unit  1  as a final output of the output circuit  54 , as shown in  FIG. 8D .  
         [0047]     In the case of reverse rotation, the period during which the final output signal is “ 1 ” is represented by t 2 , as shown in  FIG. 8D .  
         [0048]     Thus, as seen from  FIGS. 7D and 8D , the relation between the two periods during which the final output signal of the output circuit  54  is “ 1 ” is t 1 &gt;t 2 . The length of the period differs between normal rotation and reverse rotation.  
         [0049]     The normal/reverse rotation judging circuit  55  calculates the duty of each of t 1  and t 2 . For example, by judging that the rotation is normal when the duty is 60% and judging that the rotation is reverse when the duty is 80%, it is possible to detect whether the direction of rotation is normal or reverse.  
         [0050]     As described above, the magnetic detection device according to Embodiment 2 has the simple construction using the magnetic moving unit  1  having the shape that generates an asymmetrical change in magnetic field to the MR element  3  in accordance with the direction of rotation, and can detect the direction of rotation of the magnetic moving unit  1  easily and reliably.  
         [0051]     Also, since the magnetic moving unit  1  has the simple shape in which the serration-like recesses  1   c  with their depth gradually changed along the direction of rotation are formed on the circumferential edge, the magnetic moving unit  1  can be constructed inexpensively.