Patent Publication Number: US-2015061653-A1

Title: Angle detection device

Description:
CLAIM OF PRIORITY 
     This application contains subject matter related to and claims the benefit of Japanese Patent Application No. 2013-178567 filed on Aug. 29, 2013, the entire contents of which is incorporated herein by reference. 
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present disclosure relates to an angle detection device in which a plurality of magnetic detection units detect a rotation magnetic field to obtain an analog output approximating a linear function which is proportional to a rotation angle. 
     2. Description of the Related Art 
     As an angle detection device that detects a rotation angle of a rotational body with a magnet, an angle detection device with a bridge circuit including a magnetoresistive effect element is used. Typically, two sets of bridge circuits are used to obtain a detection output approximating a sine wave from one bridge circuit, whereby a detection output approximating a cosine wave can be obtained from the other bridge circuit. 
     In order to detect the rotation angle of the rotational body, it is necessary to obtain a detection output of a linear function which is proportional to the rotation angle. In order to obtain the detection output of the linear function, an inverse tangent function (arctangent) is calculated from the detection output approximating the sine wave and the detection output approximating the cosine wave. In the related art, as a method of accurately calculating the inverse tangent function, a digital operation using an algorithm such as a codec is performed by A/D converting the detection output approximating the sine wave and the detection output approximating the cosine wave. 
     However, the digital operation using the algorithm has a disadvantage in that the operation is time-consuming. A highly accurate angle detection output can be obtained by the digital operation at a low rotation speed of the rotational body, but the operation cannot follow rotation of the rotational body when the rotational body rotates at a high rotation speed such as in a motor. 
     In Japanese Unexamined Patent Application Publication No. 2010-54495 and Japanese Translation Patent Publication No. 2011-508891, an angle detection device for obtaining a detection output close to a linear function without using a digital operation is disclosed. 
     In the angle detection device described in Japanese Unexamined Patent Application Publication No. 2010-54495, a magnetic sensor with a combination of a magnet and a magnetoresistive effect element is used. A rotational body is made of a ferromagnetic material, and a planar shape of the rotational body is a shape with a tangent function (tangent) added rather than a perfect circle. Using the rotational body, the detection output approximating the linear function can be obtained from the magnetic sensor. 
     However, it is very difficult to manufacture the rotational body with the tangent function added rather than the circle, and the manufacturing costs are increased. 
     In the angle detection device described in Japanese Translation Patent Publication No. 2011-508891, a rotating magnet and four sensor elements facing the rotating magnet are provided. Outputs approximating a sine wave and a cosine wave can be obtained from the sensor element, so that indirect division is performed by an analog multiplier from the two outputs. However, in the analog multiplier, an analog division circuit is required for a signal processing unit, and therefore the circuit configuration becomes complex. 
     These and other drawbacks exist. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present disclosure provide an angle detection device which can obtain an angle detection output approximating a linear function through a simple circuit configuration and follow a high-speed rotation. 
     According to an example embodiment, an angle detection device includes a first magnetic detection unit configured to be provided in a detection area to which a rotational magnetic field is applied so as to obtain a detection output approximating a sine wave being a function of a rotation angle of the rotational magnetic field; a second magnetic detection unit configured to be provided in the detection area to which the rotational magnetic field is applied so as to obtain a detection output approximating a cosine wave being a function of the rotation angle of the rotational magnetic field; a switching circuit configured to cut out a plurality of partial detection outputs approximating a linear function from analog detection outputs obtained from the first and second magnetic detection units; and a bias adding circuit configured to enable the plurality of partial detection outputs to be consecutive by applying a bias power to any one of the partial detection outputs so that the consecutive partial detection outputs are used as angle detection outputs. 
     In an angle detection device according to various embodiments, the analog detection outputs obtained from the magnetic detection units may be cut out to be consecutive by the switching circuit, and therefore the speed may be high and the circuit configuration may be simple in order to obtain the angle detection output. In addition, the analog outputs obtained from the magnetic detection units are used as is, or used by only passing through gain adjustment or the like, and therefore the angle detection output directly connected to the rotation angle of the rotational body can be obtained. 
     An angle detection device according to various embodiments may further include: an output circuit configured to obtain a first detection output from the first magnetic detection unit and a second detection output obtained by reversing positive/negative polarity with the first detection output, and a third detection output from the second magnetic detection unit and a fourth detection output obtained by reversing positive/negative polarity with the third detection output; and a comparator configured to compare either the first and second detection outputs or the third and fourth detection outputs. Here, switching timing of the switching circuit may be determined based on a comparison output from the comparator. 
     In an angle detection device according to various embodiments, each of the first, second, third, and fourth detection outputs may be cut out at intervals of 90 degrees by the switching circuit so that the partial detection outputs may be obtained. 
     Also, the first, second, third, and fourth detection outputs may be cut out in a range of ±45 degrees with a midpoint of the amplitude as a starting point. Accordingly, by obtaining the partial detection output in this range, the partial detection output approximating the linear function can be obtained. 
     In an angle detection device according to various embodiments, each of the first and second magnetic detection units may be constituted of a bridge circuit including a magnetoresistive effect element, and in a first magnetoresistive effect element included in the first magnetic detection unit and a second magnetoresistive effect element included in the second magnetic detection unit, directions of sensitivity axes may be orthogonal to each other. 
     In an angle detection device according to various embodiments, an analog output can be cut out from each of the first magnetic detection unit and the second magnetic detection unit in the switching circuit, and consecutive angle detection output obtained by applying bias can be obtained. Therefore, a circuit configuration is simple, and even when a rotation speed of the rotational body is high, the angle detection output which rapidly follows rotation can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan diagram showing a rotational body and a magnetic detection unit in an angle detection device according to an embodiment of the present invention; 
         FIG. 2  is a circuit block diagram showing a circuit configuration of an angle detection device according to an embodiment of the present invention; 
         FIG. 3  is a line diagram showing four types of detection outputs from first and second magnetic detection units; 
         FIG. 4  is a line diagram showing a partial detection output obtained by cutting a detection output from first and second magnetic detection units; 
         FIG. 5  is a line diagram showing an angle detection output in which partial detection outputs are consecutive; and 
         FIG. 6  is a line diagram showing distribution of errors between the angle detection output shown in  FIG. 5  and a linear function. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The following description is intended to convey a thorough understanding of the embodiments described by providing a number of specific embodiments and details involving an angle detection device. It should be appreciated, however, that the present invention is not limited to these specific embodiments and details, which are exemplary only. It is further understood that one possessing ordinary skill in the art, in light of known systems and methods, would appreciate the use of the invention for its intended purposes and benefits in any number of alternative embodiments, depending on specific design and other needs. 
     As shown in  FIG. 1 , an angle detection device  1  according to an embodiment of the disclosure may have a rotational body  2 , and a detection substrate  3  which may be disposed on an inner side of the rotational body  2 . 
     In the rotational body  2 , two magnets M 1  and M 2  may be mounted at intervals of 180 degrees. An N pole of the magnet M 1  may be directed to the magnet M 2 , an S pole of the magnet M 2  may be directed to the magnet M 1 , and a magnetic field H may be formed from the magnet M 1  toward the magnet M 2 . 
     The rotational body  2  may have a rotational center O and rotates clockwise (CW). As a result, on an inner side of the rotational body  2 , a rotational magnetic field in which the magnetic field H rotates clockwise may be formed. 
     On the detection substrate  3 , first magnetoresistive effect elements R(+s) and R(−s) and second magnetoresistive effect elements R(+c) and R(−c) may be mounted as magnetic detection elements. In  FIG. 1 , the detection substrate  3  and the magnetoresistive effect elements may be shown to be large, but the detection substrate  3  and the magnetoresistive effect elements actually may be much smaller in dimension than a diameter of a rotating locus of the magnets M 1  and M 2 . When the rotational body  2  rotates, the rotational magnetic field in the same direction may be applied to each of the magnetoresistive effect elements on the detection substrate  3 . 
     In addition, despite a configuration in which the magnets M 1  and M 2  are fixed in a fixing unit and the detection substrate  3  may be rotated counterclockwise about the rotational center O, it may be possible to provide the rotational magnetic field which rotates clockwise (CW) relative to the detection substrate  3 . 
     In the first magnetoresistive effect elements R(+s) and R(−s) and the second magnetoresistive effect elements R(+c) and R(−c), directions of sensitivity axes P are orthogonal to each other. Two kinds of the first magnetoresistive effect elements may be provided. Here, the direction of the sensitivity axis P of R(+s) may be an X2 direction, and the direction of the sensitivity axis P of R(−s) may be an X1 direction. Two kinds of the second magnetoresistive effect elements may be provided. Here, the direction of the sensitivity axis P of R(+c) may be a Y2 direction, and the direction of the sensitivity axis P of R(−c) may be a Y1 direction. 
     The magnetoresistive effect element may be a GMR element using a giant magnetoresistive effect, a TMR element using a tunnel effect, or an AMR element. 
     As shown in  FIG. 1 , the magnetoresistive effect element may include electrode portions  4  and  4  and an element portion positioned between the electrode portions  4 . The element portion  5  may be formed in a meander pattern within the plane of an X-Y plane, and may be configured by laminating a fixed magnetic layer/a non-magnetic layer/a free magnetic layer. The fixed magnetization direction of the fixed magnetic layer may coincide with the direction of the sensitivity axis P. In the free magnetic layer, a magnetization direction can be changed in accordance with a direction of an external magnetic field H. 
     When the external magnetic field H is applied in the direction of the sensitivity axis P, an electric resistance value of the magnetoresistive effect element may be a minimum value, and when the external magnetic field H is applied in a reverse direction with respect to the sensitivity axis P, the electric resistance value thereof may be a maximum value. When the external magnetic field H is applied in a direction orthogonal to the sensitivity axis P, the electric resistance value of the magnetoresistive effect element may be a value of the midpoint of the minimum value and the maximum value. 
     The fixed magnetic layer may be superimposed on an anti-ferromagnetic layer to be subjected to heat treatment in the magnetic field, so that the magnetization direction may be fixed. Also, the fixed magnetic layer may have a lamination ferry structure of the magnetic layer/the non-magnetic intermediate layer/the magnetic layer, and the respective magnetic layers may have a self pinning type which may be magnetized and fixed in anti-parallel. In this case, the magnetization may be fixed by forming one magnetic layer in the magnetic field. 
     As shown in  FIG. 2 , in the angle detection device  1 , a first magnetic detection unit  11  and a second magnetic detection unit  12  may be configured on the detection substrate  3 . 
     The first magnetic detection unit  11  may be a full bridge circuit constituted of the first magnetoresistive effect elements R(+s) and R(−s) with the directions of the sensitivity axes P different from each other by 180 degrees. The second magnetic detection unit  12  may be a full bridge circuit constituted of the second magnetoresistive effect elements R(+c) and R(−c) with the directions of the sensitivity axes P different from each other by 180 degrees. 
     As shown in  FIG. 2 , midpoint outputs (midpoint output voltages)  11   a  and  11   b  of the full bridge circuit of the first magnetic detection unit  11  may be applied to a first output circuit  21  and a second output circuit  22 . The first output circuit  21  may be a differential amplifier, and the midpoint output  11   a  may be connected to a (+) input unit and the midpoint output  11   b  may be connected to a (−) input unit. The second output circuit  22  also may be a differential amplifier, and the midpoint output  11   b  may be connected to the (+) input unit and the midpoint output  11   a  may be connected to the (−) input unit. 
     Midpoint outputs (midpoint output voltages)  12   a  and  12   b  of the full bridge circuit of the second magnetic detection unit  12  may be applied to a third output circuit  23  and a fourth output circuit  24 . The third output circuit  23  may be a differential amplifier, and the midpoint output  12   a  is connected to the (+) input unit and the midpoint output  12   b  is connected to the (−) input unit. The fourth output circuit  24  is also a differential amplifier, and the midpoint output  12   b  is connected to the (+) input unit and the midpoint output  12   a  is connected to the (−) input unit. 
     When the rotational body  2  shown in  FIG. 1  rotates clockwise (CW), a first detection output S 1  may be obtained from the first output circuit  21 , and a second detection output S 2  may be obtained from the second output circuit  22 . A third detection output S 3  may be obtained from the third output circuit  23 , and a fourth detection output S 4  may be obtained from the fourth output circuit  24 . 
     In  FIG. 3 , output waveforms of the first to fourth detection outputs S 1  through S 4  are shown. The horizontal axis indicates rotation angle (θ), and the vertical axis indicates output intensity (voltage). 
     In the first detection output S 1  and the second detection output S 2 , the polarities (positive and negative voltage) may be reversed, and also in the third detection output S 3  and the fourth detection output S 4 , the polarities may be reversed. In the first detection output S 1  and the third detection output S 3 , the phases may be different from each other by 90 degrees, and in the second detection output S 2  and the fourth detection output S 4 , the phases also may be different from each other by 90 degrees. One of the first detection output S 1  and the third detection output S 3  may be an output having a change approximating a trigonometric function wave of a sine wave, and the other thereof may be an output having a change approximating a trigonometric wave of a cosine wave. 
     The rotation angle θ of the rotational body  2  is shown in the horizontal axis of  FIG. 3 , but the representation of the rotation angle θ uses a case in which a width center of the magnet M 1  shown in  FIG. 1  coincides with each other on a reference line Z, as the origin (0 degrees).  FIG. 1  shows a state in which the magnet M 1  of the rotational body  3  in rotation advances by 45 degrees clockwise (CW) with the origin (reference axis Z) as a starting point. In this instance, output intensities of the first to fourth detection outputs S 1  to S 4  become an output intensity when the horizontal axis in  FIG. 3  is 45 degrees. When the horizontal axis is 45 degrees, the output intensity of the first detection output S 1  and the output intensity of the second detection output S 2  are values of midpoints, the output intensity of the third detection output S 3  is a maximum value, and the output intensity of the fourth detection output S 4  is a minimum value. 
     Absolute values and amplitudes of intensities of output waveforms of the first to fourth detection outputs S 1  through S 4  shown in  FIG. 3  depend on a gain or the like which is set to a power supply voltage Vdd and depend on the output circuits  21 ,  22 ,  23 , and  24  each being a differential amplifier. The first to fourth detection outputs S 1  to S 4  are analog outputs in which changes in the detection outputs from the first and second magnetic detection units  11  and  12  which detect a rotational magnetic field are reflected as is. 
     As shown in  FIG. 2 , the first to fourth detection outputs S 1  through S 4  may be applied to an analog mixer  30 . The analog mixer  30  may have a switching circuit  31 , comparators  32   a  and  32   b , and a bias adding circuit  33 . 
     The first comparator  32   a  may compare the level of the intensities of the first detection output S 1  and the fourth detection output S 4 , and the comparison result may be applied to the switching circuit  31 . The second comparator  32   b  may compare the level of the intensities of the first detection output S 1  and the third detection output S 3 , and the comparison result may be applied to the switching circuit  31 . 
     The switching circuit  31  may perform a switching operation based on the comparison results of the comparators  32   a  and  32   b  so that the detection output is cut out as a partial detection output in which any one of the first to fourth detection outputs S 1  to S 4  is selected. 
     Based on the comparison result of the first comparator  32   a , the comparison result of the second comparator  32   b , and the comparison result therebetween, the detection output which is cut out in the switching circuit  31  is as described in Table 1 below. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 First 
                 Second 
                 Switching output 
                   
               
               
                 comparator 32a 
                 comparator 32b 
                 (partial detection output) 
                 Bias voltage 
               
               
                   
               
             
            
               
                 S1 &gt; S4 
                 S1 &lt; S3 
                 S1 (S1c) 
                  +350 mV 
               
               
                 S1 &gt; S4 
                 S1 &gt; S3 
                 S4 (S4c) 
                 +1050 mV 
               
               
                 S1 &lt; S4 
                 S1 &gt; S3 
                 S2 (S2c) 
                 +1750 mV 
               
               
                 S1 &lt; S4 
                 S1 &lt; S3 
                 S3 (S3c) 
                 +2450 mV 
               
               
                   
               
            
           
         
       
     
     In  FIG. 4 , partial detection outputs S 1   c , S 4   c , S 2   c , and S 3   c  which are cut out by the switching operation of the switching circuit  31  are shown. 
     As shown in Table 1, switching may be performed in the switching circuit  31  by comparing two detection outputs in each of the first comparator  32   a  and the second comparator  32   b , and therefore four detection outputs are cut out at intervals of 90 degrees while the rotational body  2  rotates 360 degrees clockwise as shown in  FIG. 4 . 
     When the angle θ is between approximately 0 and 90 degrees, as shown in the first column of Table 1, the first detection output S 1  is cut out back and forth relative to a midpoint of its amplitude (voltage width) in a range of 45 degrees, thereby obtaining a partial detection output S 1   c  shown in  FIG. 4 . When the angle θ is between approximately 90 and 180 degrees, as shown in the second column of Table 1, the fourth detection output S 4  is cut out back and forth relative to a midpoint of its amplitude (voltage width) in a range of 45 degrees, thereby obtaining a partial detection output S 4   c  shown in  FIG. 4 . In the same manner, a partial detection output S 2   c  may be obtained when the angle of θ is between approximately 180 and 270 degrees, and a partial detection output S 3   c  may be obtained when the angle of θ is between approximately 270 and 360 degrees. 
     Since the partial detection outputs S 1   c , S 4   c , S 2   c , and S 3   c  are cut out back and forth relative to the midpoint of the amplitude in the range of ±45 degrees among the detection outputs approximating the sine wave and the cosine wave, a change in output intensity may become nearly a linear function. 
     The first comparator  32   a  and the second comparator  32   b  may generate a signal for dividing the detection output for each interval of 90 degrees in which the partial detection output shown in  FIG. 4  can be obtained. To the extent that this is possible, compared detection outputs are not limited to the example shown in Table 1. 
     For example, even in a comparison condition of S 3 &gt;S 1  and S 3 &gt;S 2 , the first detection output S 1  can be cut out when the angle of θ is in a range of approximately 0 to 90 degrees, thereby obtaining the partial detection output S 1   c.    
     The partial detection outputs S 1   c , S 4   c , S 2   c , and S 3   c  which may be cut out in the switching circuit  31  are applied to the bias adding circuit  33 . In the bias adding circuit  33 , a positive or negative bias voltage is applied to the partial detection outputs S 1   c , S 4   c , S 2   c , and S 3   c , whereby an angle detection output approximating the linear function in which the partial detection outputs S 1   c , S 4   c , S 2   c , and S 3   c  are consecutive can be obtained as shown in  FIG. 5 . In the rightmost column of Table 1, in order to obtain the angle detection output shown in  FIG. 5 , the bias voltages applied to the partial detection outputs S 1   c , S 4   c , S 2   c , and S 3   c  are shown numerically. 
     The bias adding circuit may be constituted of a resistor, a variable resistor, and the like, and the bias voltage is applied to the partial detection output S 4   c  so that a starting end of the partial detection output S 4   c  shown in  FIG. 4  is connected to a terminating end of the partial detection output S 1   c . Similarly, the bias voltage may be applied to the partial detection outputs S 2   c  and S 3   c . In addition, by applying the positive or negative bias voltage to the partial detection output S 1   c  which can be first obtained, a starting point of the output when the angle θ is approximately 0 degrees can be aligned with the origin of the output voltage as shown in  FIG. 5 . 
     The change in the angle detection output shown in  FIG. 5  is approximating a linear function.  FIG. 6  shows an intensity error between the angle detection output shown in  FIG. 5  and the linear function. An error for the linear function of the angle detection output is approximately ±0.5%. 
     In the angle detection device  1  according to an embodiment of the present invention, an analog output which can be obtained from the first magnetic detection unit  11  and the second magnetic detection unit  12  is used as is or used by performing gain adjustment, whereby the angle detection output approximating the linear function can be instantaneously obtained. Thus, even when the rotational body  2  rotates to be directly connected to a motor, it is possible to accurately detect a rotation angle. 
     In addition, in the angle detection device  1  shown in  FIGS. 1 and 2 , the first magnetic detection unit  11  is a full bridge circuit constituted of the first magnetoresistive effect elements R(+s) and R(−s), and the second magnetic detection unit  12  is a full bridge circuit constituted of the second magnetoresistive effect elements R(+c) and R(−c). 
     However, in the present disclosure, the first magnetic detection unit  11  may be a half-bridge circuit using any one of R(+s) and R(−s) as the first magnetoresistive effect element, and the second magnetic detection unit  12  may be a half-bridge circuit using any one of R(+c) and R(−c) as the second magnetoresistive effect element. 
     In addition, in the analog mixer  30  shown in  FIG. 2 , the bias power is applied to each of the partial detection outputs cut out in the switching circuit  31 , but the bias power is applied in advance to the first to fourth detection outputs S 1  to S 4  having passed through the first to fourth output circuits  21 ,  22 ,  23 , and  24 , and therefore consecutive angle detection outputs may be obtained from the switching circuit  31  by cutting out the partial detection output in the switching circuit  31 . 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims of the equivalents thereof. 
     Accordingly, the embodiments of the present inventions are not to be limited in scope by the specific embodiments described herein. Further, although some of the embodiments of the present disclosure have been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art should recognize that its usefulness is not limited thereto and that the embodiments of the present inventions can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the embodiments of the present inventions as disclosed herein. While the foregoing description includes many details and specificities, it is to be understood that these have been included for purposes of explanation only, and are not to be interpreted as limitations of the invention. Many modifications to the embodiments described above can be made without departing from the spirit and scope of the invention.