Patent Publication Number: US-2023160725-A1

Title: Encoder

Description:
TECHNICAL FIELD 
     The present disclosure relates to an encoder. 
     BACKGROUND ART 
     An encoder for detecting rotation of a rotation shaft of a motor is known. For example, PTL 1 discloses an encoder including a pattern arranged in a measurement direction, a light source configured to emit light to the pattern, and light reception elements arranged in the measurement direction and configured to receive the light emitted from the light source and transmitted through or reflected by the pattern. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Laid-Open Publication No. 2016-118486 
       
    
     SUMMARY OF INVENTION 
     An encoder according to an aspect of the present disclosure includes a rotatable plate including a first pattern and a second pattern, a light emission unit configured to emit light to the first pattern and the second pattern, and a light receiving unit configured to receive light emitted from the light emission unit and passing through the first pattern and light emitted from the light emission unit and passing through the second pattern. Each of the first pattern and the second pattern includes first unit regions and second unit regions which are arranged in a circumferential direction about a rotation axis of the rotatable plate. The first unit regions are configured to guide the light emitted from the light emission unit to the light receiving unit. The second unit regions are configured not to guide the light emitted from the light emission unit to the light receiving unit. An order of the first unit regions and the second unit regions are arranged in the first pattern are reversed to an order of the first unit regions and the second unit regions of the second pattern. 
     An encoder according to another aspect of the present disclosure includes a rotatable plate including a pattern, a light emission unit configured to emit light to the pattern, and a light receiving unit configured to receive light emitted from the light emission unit and passing through the pattern. The pattern includes first unit regions and second unit regions arranged in a circumferential direction about a rotation axis of the rotatable plate. The first unit regions are configured to guide the light emitted from the light emission unit to the light receiving unit. The second unit regions are configured not to guide the light emitted from the light emission unit to the light receiving unit. When the first unit regions and the second unit regions are referred to as unit regions, the pattern includes: a first arrangement that is an arrangement of M unit regions for outputting position information indicating a position of a detection target; and a second arrangement that is an arrangement of N unit regions for outputting correction information for correcting the position information, the second arrangement being adjacent to the first arrangement. 
     According to the present disclosure, it is possible to provide an encoder capable of preventing a decrease in detection accuracy. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating a motor including an encoder according to an exemplary embodiment. 
         FIG.  2 A  is a diagram illustrating a rotatable plate of the encoder shown in  FIG.  1   . 
         FIG.  2 B  is a diagram illustrating the rotatable plate of the encoder shown in  FIG.  1   . 
         FIG.  3    is a block diagram of the encoder shown in  FIG.  1    for illustrating a functional configuration thereof. 
         FIG.  4    is a diagram for illustrating an example of a determination method performed by a determination unit of the encoder shown in  FIG.  1   . 
         FIG.  5    is a diagram illustrating an example of a received light intensity of light received by a light receiving unit of the encoder shown in  FIG.  1   . 
         FIG.  6    is a diagram for illustrating an example of a determination method and a correction method performed by a correction unit of the encoder shown in  FIG.  1   . 
         FIG.  7    is a diagram illustrating a calculation circuit that calculates values for forming a first pattern on the rotatable plate of the encoder shown in  FIG.  1   . 
         FIG.  8    is a diagram illustrating a table illustrating values obtained by the calculation circuit shown in  FIG.  7   . 
         FIG.  9    is a diagram illustrating a flow of data during an operation of the correction unit of the encoder shown in  FIG.  1   . 
         FIG.  10    is a diagram for illustrating another example of the correction method performed by the correction unit of the encoder shown in  FIG.  1   . 
         FIG.  11    is a diagram for illustrating another example of the correction method performed by the correction unit of the encoder shown in  FIG.  1   . 
         FIG.  12    is a diagram for illustrating still another example of the correction method performed by the correction unit of the encoder shown in  FIG.  1   . 
         FIG.  13    is a diagram illustrating another example of the received light intensity of the light received by the light receiving unit of the encoder shown in  FIG.  1   . 
         FIG.  14    is a diagram illustrating a calculation circuit that calculates values for forming a first pattern different from the first pattern of the encoder shown in  FIG.  1   . 
         FIG.  15    is a diagram illustrating a table illustrating values obtained by the calculation circuit shown in  FIG.  14   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present disclosure will be described. The embodiment described below illustrates a specific example of the present disclosure. Therefore, numerical values, constituent elements, arrangement positions and connection forms of the constituent elements, processes, an order of the processes, and the like described in the following embodiment are examples, and are not intended to limit the present disclosure. Accordingly, among the constituent elements in the following embodiment, constituent elements not recited in any one of the independent claims defining the broadest concept of the present disclosure are described as any constituent elements. 
     In addition, each drawing is a schematic diagram and is not necessarily a precise illustration. In each drawing, substantially the same components are denoted by the same reference numerals, and redundant descriptions will be omitted or simplified. 
     Exemplary Embodiment 
       FIG.  1    is a diagram illustrating motor  1  including encoder  10  according to an exemplary embodiment.  FIG.  2 A  and  FIG.  2 B  are diagrams illustrating rotatable plate  12  of encoder  10  shown in  FIG.  1   .  FIG.  2 A  is rotatable plate  12  viewed in an axial direction, and  FIG.  2 B  is an enlarged view of rotatable plate  12  for illustrating a portion surrounded by a dotted line shown in  FIG.  2 A . In  FIG.  1   , case  6 , first pattern  24 , and second pattern  26  are illustrated in across-sectional view. In the following description, the axial direction is a direction in which a rotation axis A extends (see an arrow X in  FIG.  1   ). A radial direction indicates a radial direction about the rotation axis A (see an arrow Y in  FIG.  2 A  and  FIG.  2 B ). A circumferential direction is a circumferential direction about the rotation axis A and surrounds the rotation axis A (see an arrow Z in  FIG.  2 A  and  FIG.  2 B ). The radial direction is perpendicular to the circumferential direction and the rotation axis. A configuration of encoder  10  will be described with reference to  FIG.  1   ,  FIG.  2 A , and  FIG.  2 B . 
     As illustrated in  FIG.  1   , motor  1  includes main body  2 , stator  3 , rotor  4 , rotation shaft  5 , case  6 , and encoder  10 . 
     Main body  2  is a housing that accommodates stator  3 , rotor  4 , and the like. Stator  3  is fixed to an inner surface of main body  2 . Rotor  4  is rotatable with respect to stator  3 . 
     Rotation shaft  5  has a rod shape, such as a cylindrical shape, is fixed to an inner surface of rotor  4 , and is configured to rotate about the rotation axis A. For example, when power is supplied to motor  1 , rotation shaft  5  rotates about the rotation axis A together with rotor  4  based on the power. Encoder  10  is provided at one end of rotation shaft  5  in the axial direction. A load (not illustrated) or the like that is rotationally driven by the rotation of rotation shaft  5  is attached to the other end of rotation shaft  5  in the axial direction. Rotation shaft  5  is made of, e.g., magnetic metal, such as iron. 
     Case  6  is attached to main body  2  and covers the one end of rotation shaft  5  in the axial direction, encoder  10 , and the like. Case  6  is made of, e.g., magnetic metal, such as iron. 
     Encoder  10  is configured to detect rotation of a detection target. Specifically, encoder  10  is configured to detect a position (a rotation position) of the detection target, a rotation direction of the detection target, a rotation speed of the detection target, and the like. In this embodiment, the detection target is rotation shaft  5 . That is, encoder  10  is configured to detect a position of rotation shaft  5 , a rotation direction of rotation shaft  5 , a rotation speed of rotation shaft  5 , and the like. 
     As described above, encoder  10  is provided at the one end of rotation shaft  5  in the axial direction. As illustrated in  FIG.  1   ,  FIG.  2 A , and  FIG.  2 B , encoder  10  includes rotatable plate  12 , first substrate  14 , second substrate  16 , light emission unit  18 , and light receiving unit  20 . 
     Rotatable plate  12  is configured to rotate about the rotation axis A, and includes main body  22 , first pattern  24 , and second pattern  26 . 
     Main body  22  has a plate shape extending in directions perpendicular to the axial direction, and has a circular shape when viewed in the axial direction. Main body  22  is attached to the one end of rotation shaft  5  in the axial direction, and is configured to rotate about the rotation axis A together with rotation shaft  5 . An axial center of main body  22  coincide with the rotation axis A. Main body  22  is made of, e.g., transparent glass, configured to transmit light. 
     First pattern  24  is provided on a main surface of main body  22  directed to a first substrate  14 . First pattern  24  has an annular shape extending along the circumferential direction. First pattern  24  is configured to rotate together with main body  22 . In this embodiment, first pattern  24  is an absolute pattern. First pattern  24  includes plural first light-guidable portions  28  and plural first non-light-guidable portions  30 . 
     First light-guidable portions  28  are arranged at intervals in the circumferential direction. Each of first light-guidable portions  28  is constituted by arranging, in the circumferential direction, first unit regions  32  configured to guide light emitted from light emission unit  18  to light receiving unit  20 . That is, each of the first light-guidable portions  28  is a region constituted by one or more first unit regions  32 , and guides the light emitted from light emission unit  18  to light receiving unit  20 . First unit region  32  is a region having a predetermined size. First unit region  32  is made of, e.g., transparent glass, which transmits light. 
     The number of first unit regions  32  constituting each of the first light-guidable portions  28  is not uniform. A dimension of each of first light-guidable portions  28  in the circumferential direction is determined by the number of first unit regions  32  constituting first light-guidable portion  28 , and the dimensions of the first light-guidable portions  28  in the circumferential direction are not necessarily identical to one another. In  FIG.  2 B , only a part of first unit regions  32  are illustrated in order to avoid complication of the drawing (see a two-dot chain line). 
     The first non-light-guidable portions  30  are arranged at intervals in the circumferential direction. Specifically, each of the first non-light-guidable portions  30  is arranged between adjacent first light-guidable portions  28  among the plural first light-guidable portions  28 . That is, first pattern  24  has a configuration in which first light-guidable portions  28  and first non-light-guidable portions  30  are alternately arranged in the circumferential direction. Each of the first non-light-guidable portions  30  is constituted by arranging, in the circumferential direction, second unit regions  34  which do not guide the light emitted from light emission unit  18  to light receiving unit  20 . That is, each of the first non-light-guidable portions  30  is a region constituted by one or more second unit regions  34 . When the light is emitted from light emission unit  18 , first non-light-guidable portion  30  does not transmit the light and does not guide the light to light receiving unit  20 . Second unit region  34  is a region having a predetermined size. Ehen the light is emitted from light emission unit  18 , second unit region  34  does not transmit the light and does not guide the light to light receiving unit  20 . The size of second unit region  34  is the same as the size of first unit region  32 . For example, second unit region  34  is formed by black chromium plating or the like that does not transmit light. 
     The number of second unit regions  34  constituting each of the first non-light-guidable portions  30  is not uniform. A dimension of each of the first non-light-guidable portions  30  in the circumferential direction is determined by the number of second unit regions  34  constituting first non-light-guidable portion  30 , and the dimensions of the first non-light-guidable portions  30  in the circumferential direction are not necessarily identical to one another. In  FIG.  2 B , only a part of second unit regions  34  are illustrated in order to avoid complication of the drawing (see a two-dot chain line). 
     As described above, each of the first light-guidable portions  28  is constituted by arranging one or more first unit regions  32  in the circumferential direction, and each of the first non-light-guidable portions  30  is constituted by arranging one or more second unit regions  34  in the circumferential direction. That is, first pattern  24  has a configuration in which first unit regions  32  and second unit regions  34  are arranged in the circumferential direction. 
     Second pattern  26  is provided on the main surface of main body  22  directed to the first substrate  14 . Second pattern  26  is disposed radially inward of first pattern  24  and has an annular shape extending along the circumferential direction. Second pattern  26  rotates together with main body  22 . In this embodiment, second pattern  26  is an absolute pattern. Second pattern  26  includes plural second light-guidable portions  36  and plural second non-light-guidable portions  38 . 
     The second light-guidable portions  36  are arranged at intervals in the circumferential direction. Each of the second light-guidable portions  36  is constituted by arranging, in the circumferential direction, first unit regions  40  configured to guide the light emitted from light emission unit  18  to light receiving unit  20 . That is, each of the second light-guidable portions  36  is a region constituted by one or more first unit regions  40 , and configured to guide the light emitted from light emission unit  18  to light receiving unit  20 . First unit region  40  is a region having a predetermined size. When the light is emitted from light emission unit  18 , first unit region  40  transmits the light and guides the light to light receiving unit  20 . The size of first unit region  40  in second pattern  26  is different from the size of first unit region  32  in first pattern  24 . For example, first unit region  40  is formed of transparent glass or the like that transmits light. 
     The number of first unit regions  40  constituting each of the second light-guidable portions  36  is not uniform. A dimension of each of the second light-guidable portions  36  in the circumferential direction is determined by the number of first unit regions  40  constituting second light-guidable portion  36 , and the dimensions of the second light-guidable portions  36  in the circumferential direction are not identical to one another. In  FIG.  2 B , only a part of first unit regions  40  are illustrated in order to avoid complication of the drawing (see a two-dot chain line). 
     Each of the plural second light-guidable portions  36  correspond to respective one of the plural first non-light-guidable portions  30 . In this embodiment, each of the second light-guidable portions  36  is adjacent in the radial direction to corresponding one of first non-light-guidable portion  30  among the first non-light-guidable portions  30 . The number of first unit regions  40  constituting second light-guidable portion  36  is the same as the number of second unit regions  34  constituting first non-light-guidable portion  30  corresponding to second light-guidable portion  36 . 
     That is, each of the first unit regions  40  in second pattern  26  corresponds to respective one of the second unit regions  34  in first pattern  24 . In this embodiment, each of the first unit regions  40  in second pattern  26  is adjacent in the radial direction to corresponding second unit region  34  among the second unit regions  34  in first pattern  24 . 
     The second non-light-guidable portions  38  are arranged at intervals in the circumferential direction. Specifically, each of the second non-light-guidable portions  38  is arranged between adjacent second light-guidable portions  36  among the plural second light-guidable portions  36 . That is, second pattern  26  has a configuration in which second light-guidable portions  36  and second non-light-guidable portions  38  are alternately arranged in the circumferential direction. Each of the second non-light-guidable portions  38  is constituted by arranging, in the circumferential direction, second unit regions  42  which do not guide the light emitted from light emission unit  18  to light receiving unit  20 . That is, each of the second non-light-guidable portions  38  is a region constituted by one or more second unit regions  42 . When the light is emitted from light emission unit  18 , each of the second non-light-guidable portions  38  does not transmit the light and does not guide the light to light receiving unit  20 . Second unit region  42  is a region having a predetermined size. When the light is emitted from light emission unit  18 , second unit region  42  does not transmit the light and does not guide the light to light receiving unit  20 . The size of second unit region  42  is the same as the size of first unit region  40 . In addition, the size of second unit region  42  in second pattern  26  is different from the size of second unit region  34  in first pattern  24 . For example, second unit region  42  is formed by black chromium plating or the like that does not transmit light. 
     The number of second unit regions  42  constituting each of the second non-light-guidable portions  38  is not uniform. A dimension of each of the second non-light-guidable portions  38  in the circumferential direction is determined by the number of second unit regions  42  constituting second non-light-guidable portion  38 , and the dimensions of the plurality of second non-light-guidable portions  38  in the circumferential direction are not identical to one another. In  FIG.  2 B , only a part of second unit regions  42  are illustrated in order to avoid complication of the drawing (see a two-dot chain line). 
     Each of the second non-light-guidable portions  38  corresponds to respective one of the first light-guidable portions  28 . In this embodiment, each of the second non-light-guidable portions  38  is adjacent in the radial direction to corresponding first light-guidable portion  28  among the first light-guidable portions  28 . The number of second unit regions  42  constituting second non-light-guidable portion  38  is the same as the number of first unit regions  32  constituting first light-guidable portion  28  corresponding to second non-light-guidable portion  38 . 
     That is, each of the second unit regions  42  in second pattern  26  corresponds to respective one of the first unit regions  32  in first pattern  24 . In this embodiment, each of the second unit regions  42  in second pattern  26  is adjacent in the radial direction to corresponding first unit region  32  among the first unit regions  32  in first pattern  24 . 
     As described above, each of the second light-guidable portions  36  is constituted by arranging one or more first unit regions  40  in the circumferential direction, and each of the second non-light-guidable portions  38  is constituted by arranging one or more second unit regions  42  in the circumferential direction. That is, second pattern  26  has a configuration in which first unit regions  40  and second unit regions  42  are arranged in the circumferential direction. 
     Each of the first unit regions  40  in second pattern  26  corresponds to respective one of the second unit regions  34  in first pattern  24 . Each of the second unit regions  42  in second pattern  26  corresponds to respective one of the first unit regions  32  in first pattern  24 . An order in which first unit regions  32  and second unit regions  34  are arranged in first pattern  24  is reversed to an order in which first unit regions  40  and second unit regions  42  are arranged in second pattern  26 . First unit region  32  and second unit region  34  in first pattern  24  are reversed to first unit region  40  and second unit region  42  in second pattern  26  in a direction (radial direction, the arrow Y) perpendicular to a rotation direction of rotatable plate  12  (an arrow B). That is, first unit region  32  in first pattern  24  and second unit region  42  in second pattern  26  are arranged in the radial direction, and second unit region  34  in first pattern  24  and first unit region  40  in second pattern  26  are arranged in another radial direction. 
     When the light is emitted to first unit region  32  from light emission unit  18 , second pattern  26  allows the light to be also emitted to second unit region  42  corresponding to first unit region  32  from light emission unit  18 . When the light is emitted to second unit region  34  from light emission unit  18 , second pattern  26  allows the light to be also emitted to first unit region  40  corresponding to second unit region  34  from light emission unit  18 . Second pattern  26  reverses an output value of first light receiving element  48  and an output value of second light receiving element  50  to each other. That is, second pattern  26  allows the output value of second light receiving element  50  to be a value reversed to the output value of first light receiving element  48 . 
     As illustrated in  FIG.  1   , first substrate  14  extends in directions perpendicular to the axial direction. First substrate  14  is spaced apart from rotatable plate  12  in the axial direction, and faces rotatable plate  12 . First substrate  14  is fixed at an inner surface of case  6  and does not rotate together with rotation shaft  5 . 
     Second substrate  16  extends in directions perpendicular to the axial direction. Second substrate  16  is spaced apart from rotatable plate  12  in the axial direction, and faces rotatable plate  12 . Second substrate  16  is provided on a side opposite to first substrate  14  with respect to rotatable plate  12 . Second substrate  16  is fixed at the inner surface of case  6  and does not rotate together with rotation shaft  5 . 
     Light emission unit  18  includes first light emitter  44  and second light emitter  46 , and emits light to first pattern  24  and second pattern  26 . 
     First light emitter  44  is attached to first substrate  14  to face first pattern  24  in the axial direction, and emits light to first pattern  24 . For example, first light emitter  44  is implemented by a light emitting module or the like. 
     Second light emitter  46  is attached to first substrate  14  to face second pattern  26  in the axial direction, and emits light to second pattern  26 . For example, second light emitter  46  is implemented by a light emitting module or the like. 
     Light receiving unit  20  is configured to receive light emitted from light emission unit  18  to first pattern  24  and passing through first pattern  24 , and to receive light emitted from light emission unit  18  to second pattern  26  and passing through second pattern  26 . Light receiving unit  20  includes first light receiving element  48  and second light receiving element  50 . 
     First light receiving element  48  is attached to second substrate  16  to face first pattern  24  in the axial direction, and is configured to receive the light transmitted through first pattern  24 . In addition, first light receiving element  48  binarizes an intensity of the received light and outputs the binarized intensity. For example, first light receiving element  48  is implemented by a light reception element or the like. 
     Second light receiving element  50  is attached to second substrate  16  to face second pattern  26  in the axial direction, and is configured to receive the light transmitted through second pattern  26 . In addition, second light receiving element  50  binarizes an intensity of the received light and outputs the binarized intensity. For example, second light receiving element  50  is implemented by a light reception element or the like. 
       FIG.  3    is a block diagram of encoder  10  in  FIG.  1    for illustrating a functional configuration thereof. The functional configuration of encoder  10  will be described with reference to  FIG.  3   . 
     As illustrated in  FIG.  3   , encoder  10  further includes determination unit  52  and correction unit  54 . 
     First light receiving element  48  binarizes the intensity of the received light, outputs the binarized intensity, and transmits the binarized intensity to determination unit  52 . Specifically, first light receiving element  48  compares the intensity of the received light with a predetermined threshold value, and outputs one of the two values according to the comparison result. In this embodiment, first light receiving element  48  outputs value “1” when the intensity of the received light is equal to or greater than the predetermined threshold value, and outputs value “0” when the intensity of the received light is smaller than the predetermined threshold value. 
     Second light receiving element  50  binarizes the intensity of the received light, outputs the binarized intensity, and transmits the binarized intensity to determination unit  52 . Specifically, second light receiving element  50  compares the intensity of the received light with the predetermined threshold value, and outputs one of the two values according to the comparison result. In this embodiment, second light receiving element  50  outputs value “1” when the intensity of the received light is equal to or greater than the predetermined threshold value, and outputs value “0” when the intensity of the received light is smaller than the predetermined threshold value. 
     Determination unit  52  acquires the output value of first light receiving element  48  and the output value of second light receiving element  50 , and determines whether these output values are erroneous or not. Specifically, when the output value of second light receiving element  50  is reversed to the output value of first light receiving element  48 , determination unit  52  determines that the output value of first light receiving element  48  and the output value of second light receiving element  50  are not erroneous, and outputs the determination result. When the output value of second light receiving element  50  is not a value reversed to the output value of first light receiving element  48 , determination unit  52  determines that one of the output value of first light receiving element  48  and the output value of second light receiving element  50  is erroneous, and outputs the determination result. Determination unit  52  is implemented by, e.g., a processor. 
     For example, when the output value of first light receiving element  48  is “1” and the output value of second light receiving element  50  is “0”, determination unit  52  determines that these output values are not erroneous. When the output value of first light receiving element  48  is “0” and the output value of second light receiving element  50  is “0”, determination unit  52  determines that one of these output values is erroneous. 
     When determination unit  52  determines that one of the output value of first light receiving element  48  and the output value of second light receiving element  50  is erroneous, correction unit  54  determines whether the output value of first light receiving element  48  is erroneous or not. When the output value of first light receiving element  48  is erroneous, correction unit  54  corrects the output value of first light receiving element  48  to a correct value and outputs the corrected output value. A determination method and a correction method performed by correction unit  54  will be described later. Correction unit  54  is implemented by, e.g., a processor. 
       FIG.  4    is a diagram illustrating an example of the determination method performed by determination unit  52  of encoder  10  shown in  FIG.  1   .  FIG.  4 ( a )  schematically illustrates first pattern  24  and the output value of first light receiving element  48 .  FIG.  4 ( b )  schematically illustrates second pattern  26  and the output value of second light receiving element  50 .  FIG.  4 ( c )  illustrates a total value of the output value of first light receiving element  48  and the output value of second light receiving element  50 .  FIG.  5    is a diagram illustrating an example of a received light intensity of the light received by light receiving unit  20  of encoder  10  shown in  FIG.  1   .  FIG.  5 ( a )  illustrates an example of a received light intensity of light received by first light receiving element  48 .  FIG.  5 ( b )  illustrates an example of a received light intensity of light received by second light receiving element  50 . An example of the determination method performed by determination unit  52  will be described with reference to  FIG.  4    and  FIG.  5     
     As illustrated in  FIG.  4 ( a ) , in first pattern  24 , first unit regions  32  and second unit regions  34  are arranged in the rotation direction (see the arrow B in  FIG.  4   ) of rotatable plate  12 . Hereinafter, the rotation direction of rotatable plate  12  is also simply referred to as a rotation direction. The rotation direction coincides with the circumferential direction and is along the circumferential direction. Each of first unit region  32  and second unit region  34  are also simply referred to as a unit region. When first unit region  32  and second unit region  34  are referred to as unit regions, first pattern  24  includes a first arrangement that is an arrangement of M unit regions for outputting position information indicating a position of rotation shaft  5 , which is the detection target, and a second arrangement adjacent to the first arrangement. The second arrangement is an arrangement of N unit regions for outputting correction information for correcting the position information. In this embodiment, M=9, and N=2. 
     First light receiving element  48  receives LED light emitted from light emission unit  18  and transmitted through first pattern  24 , binarizes an intensity of the received light, and outputs the binarized intensity. For example, when first light receiving element  48  faces first unit region  32  and sufficiently receives light transmitted through first unit region  32 , the intensity of the received light becomes equal to or greater than the predetermined threshold value, and first light receiving element  48  outputs value “1”. On the other hand, when first light receiving element  48  faces second unit region  34  and does not sufficiently receive the light by second unit region  34 , the intensity of the received light becomes smaller than the predetermined threshold value, and first light receiving element  48  outputs value “o”. 
     When rotatable plate  12  rotates, first light receiving element  48  sequentially faces one of first unit regions  32  and second unit regions  34  arranged in the circumferential direction, and binarizes the received light intensity and outputs the binarized received light intensity each time first light receiving element  48  faces one of first unit regions  32  and second unit regions  34 . 
     For example, by facing each unit region in the first arrangement, first light receiving element  48  outputs nine values. A head of the first arrangement in the rotation direction is first unit region  32 . By facing first unit region  32 , first light receiving element  48  receives the light emitted from light emission unit  18  and transmitted through first unit region  32 . In the following description, the head in the rotation direction is also simply referred to as a head. As illustrated in  FIG.  5 ( a ) , the intensity of the light received by first light receiving element  48  by facing first unit region  32  becomes equal to or greater than the predetermined threshold value, and first light receiving element  48  outputs value “1”. 
     On the other hand, a second unit region from the head of the first arrangement is second unit region  34 . When facing second unit region  34 , first light receiving element  48  does not sufficiently receive the light emitted from light emission unit  18 . Therefore, the intensity of the light received by first light receiving element  48  by facing second unit region  34  is smaller than the predetermined threshold value, and thus first light receiving element  48  outputs value “0”. 
     The nine output values thus output based on the first arrangement is the position information indicating the position of rotation shaft  5 , and the position and the like of rotation shaft  5  is identified by a combination of the nine output values. 
     Here, foreign substance  7  which prevents transmission of light adheres to fifth first unit region  32  from the head of the first arrangement. When facing first unit region  32 , first light receiving element  48  does not sufficiently receive the light, the intensity of the received light becomes smaller than the predetermined threshold value, and first light receiving element  48  outputs value “0”. That is, in this case, the output value obtained based on first unit region  32  is “0”. 
     An output value output based on the second arrangement will be described later. 
     As illustrated in  FIG.  4 ( b ) , in second pattern  26 , first unit regions  40  and second unit regions  42  are arranged in the rotation direction. Hereinafter, each of first unit region  40  and second unit region  42  are also simply referred to as a unit region. Here, when first unit region  40  and second unit region  42  are referred to as unit regions, second pattern  26  includes a first arrangement that is an arrangement of M unit regions for outputting the position information indicating the position of rotation shaft  5 , which is the detection target, and a second arrangement adjacent to the first arrangement. The second arrangement is an arrangement of N unit regions for outputting the correction information for correcting the position information. In this embodiment, M=9, and N=2. 
     Second light receiving element  50  receives LED light emitted from light emission unit  18  and transmitted through second pattern  26 , binarizes an intensity of the received light, and outputs the binarized intensity. For example, when second light receiving element  50  faces first unit region  40  and receives light transmitted through first unit region  40 , the intensity of the received light becomes equal to or greater than the predetermined threshold value, and second light receiving element  50  outputs value “1”. On the other hand, when second light receiving element  50  faces second unit region  42  and does not sufficiently receive the light by second unit region  42 , the intensity of the received light becomes smaller than the predetermined threshold value, and second light receiving element  50  outputs value “0”. 
     When rotatable plate  12  rotates, second light receiving element  50  sequentially faces one of first unit regions  40  and second unit regions  42  arranged in the circumferential direction, and binarizes the received light intensity and outputs the binarized received light intensity each time second light receiving element  50  faces one of first unit regions  40  and second unit regions  42 . 
     For example, by facing each unit region in the first arrangement, second light receiving element  50  outputs nine values. A head of the first arrangement is second unit region  42 . When facing second unit region  42 , second light receiving element  50  does not sufficiently receive the light emitted from light emission unit  18 . As illustrated in  FIG.  5 ( b ) , an intensity of the light received by second light receiving element  50  facing second unit region  42  is smaller than the predetermined threshold value, and thus second light receiving element  50  outputs value “0”. 
     On the other hand, a second unit region from the head of the first arrangement is first unit region  40 . When facing first unit region  40 , second light receiving element  50  receives the light emitted from light emission unit  18  and transmitted through first unit region  40 . The intensity of the light received by second light receiving element  50  facing first unit region  40  becomes equal to or greater than the predetermined threshold value, and second light receiving element  50  outputs value “1”. 
     An order of the first arrangement in second pattern  26  is reversed to an order of the first arrangement in first pattern  24 . Therefore, by reversing output values of second light receiving element  50  output based on the first arrangement in second pattern  26 , the reversed output values of second light receiving element  50  are the same as the output values of first light receiving element  48  output based on the first arrangement in first pattern  24 , and the position information indicating the position of rotation shaft  5  is obtained. 
     An order of the second arrangement in second pattern  26  is reversed to an order of the second arrangement in first pattern  24 . Therefore, by reversing output values of second light receiving element  50  output based on the second arrangement in second pattern  26 , the reversed output values of second light receiving element  50  are the same as output values of first light receiving element  48  output based on the second arrangement in first pattern  24 , and the correction information for correcting the position information is obtained. 
     In this embodiment, reversing the output value means changing “1” to “0” and changing “0” to “1”. 
     As illustrated in  FIG.  4 ( c ) , by summing the output value of first light receiving element  48  and the output value of second light receiving element  50  corresponding to the output value, determination unit  52  determines whether or not the output value of second light receiving element  50  is the value obtained by reversing the output value of first light receiving element  48 . Specifically, determination unit  52  sums the output value of first light receiving element  48  and the output value of second light receiving element  50  corresponding to the output value, and determines that these output values are reversed and not erroneous when a total value is “1”. Determination unit  52  sums the output value of first light receiving element  48  and the output value of second light receiving element  50  corresponding to the output value, and determines that these output values are not reversed to each other and one of these output values is erroneous when the total value is “0”. 
     For example, an output value “l” obtained based on the head unit region in the first arrangement of first pattern  24  corresponds to an output value “0” obtained based on the head unit region in the first arrangement of second pattern  26 . When these corresponding output values are summed, “1”+“0”=“1”, and the total value is “1”. Therefore, determination unit  52  determines that these output values are not erroneous. 
     On the other hand, for example, an output value “0” obtained based on a fifth unit region from the head of the first arrangement of first pattern  24  corresponds to an output value “0” obtained based on a fifth unit region from the head of the first arrangement of second pattern  26 . When these corresponding output values are summed, “0”+“0”=“0”, and the total value is “0”. Therefore, determination unit  52  determines that one of these output values is erroneous. 
     For example, in the case that two patterns in which first unit regions and second unit regions are arranged in the same order are provided, output values output based on a second unit region in one pattern and a second unit region in the other pattern corresponding to the second unit regions are both “0”. In addition, while foreign substance  7  adheres to both the first unit region in one pattern and the first unit region in the other pattern corresponding to the first unit region, the output values output based on the two first unit regions may be both “0”. In this way, when two patterns in which the first unit regions and the second unit regions are arranged in the same order are provided, it is not possible to determine whether the value is output based on the second unit region or the value is output based on the first unit region at which a foreign substance adheres. Therefore, the position and the like of rotation shaft  5  may be detected erroneously without noticing that the output value is erroneous, resulting in a decrease in detection accuracy. 
     In this embodiment, the output value of first light receiving element  48  is reversed to the output value of second light receiving element  50  corresponding to the output value. That is, (the output value of first light receiving element  48 , the output value of second light receiving element  50  corresponding to the output value)=(1, 0) or (0, 1). Therefore, the total value of these output values is “1” in principle. Accordingly, it is determined that the output value of first light receiving element  48  and the output value of second light receiving element  50  corresponding to the output value are not erroneous when the total value is “1”, and that one of these output values is erroneous when the total value is not “I”. In this way, it is possible to notice that the output value is erroneous, and thus the decrease in the detection accuracy can be prevented. 
     In the encoder in PTL 1, when dust or the like adheres to the pattern, the light from the light source is difficult to transmit or to be reflected due to the dust or the like, and erroneous detection may occur. Further, detection accuracy may decrease due to the erroneous detection not being noticed. In addition, even the occurrence of the erroneous detection is noticed, it is difficult to correct an error, and the detection accuracy decreases. 
     In contrast, encoder  10  according to the embodiment can prevent the decrease in the detection accuracy as described above. 
       FIG.  6    is a diagram for illustrating an example of the determination method and the correction method performed by correction unit  54  of encoder  10  shown in  FIG.  1   .  FIG.  6 ( a )  is a diagram for illustrating a case in which an output value output based on a head unit region in the second arrangement is used.  FIG.  6 ( b )  is a diagram for illustrating a case in which an output value output based on a second unit region from the head of the second arrangement is used. 
       FIG.  6 ( a )  illustrates a method for determining, when determination unit  52  determines that one of an output value output based on a third unit region from the head of the first arrangement of first pattern  24  and an output value output based on a third unit region from the head of the first arrangement of second pattern  26  is erroneous, whether or not the output value output based on the unit region of first pattern  24  is correct and correcting the output value when the output value is erroneous. 
     As illustrated in  FIG.  6 ( a ) , correction unit  54  acquires nine output values output based on the first arrangement and two output values output based on the second arrangement. The two output values output based on the second arrangement are output values output from first light receiving element  48  similarly to the nine output values output based on the first arrangement. The two output values output based on the second arrangement are correction information for correcting at least one of the nine output values which are the position information indicating the position of rotation shaft  5 . 
     In this embodiment, an output value output based on the head unit region in the second arrangement is information for determining whether one output value determined by determination unit  52  to have a possibility of being erroneous among output values output based on the head unit region and a third, a fifth, a sixth, a seventh, and an eighth unit regions from the head of the first arrangement is erroneous, and is information for correcting the one output value when the one output value is erroneous. 
     When a value obtained by taking an exclusive OR of the output values output based on the head unit region and the third unit region from the head of the first arrangement is referred to as a first value, a value obtained by taking an exclusive OR of the first value and the output value output based on the fifth unit region from the head is referred to as a second value, a value obtained by taking an exclusive OR of the second value and the output value output based on the sixth unit region from the head is referred to as a third value, a value obtained by taking an exclusive OR of the third value and the output value output based on the seventh unit region from the head is referred to as a fourth value, and a value obtained by taking an exclusive OR of the fourth value and the output value output based on the eighth unit region from the head is referred to as a fifth value, the output value obtained based on the head unit region of the second arrangement is equal to the fifth value. 
     For example, when the output value output based on the head unit region in the second arrangement is “0”, a total value of the output values output based on the head unit region and the third, the fifth, the sixth, the seventh, and the eighth unit regions from the head of the first arrangement is an even number. 
     On the other hand, when the output value output based on the head unit region in the second arrangement is “1”, the total value of the output values output based on the head unit region and the third, the fifth, the sixth, the seventh, and the eighth unit regions from the head of the first arrangement is an odd number. 
     In  FIG.  6 ( a ) , the output value obtained based on the head unit region in the second arrangement is “0”. The total value of the output values output based on the head unit region and the third, the fifth, the sixth, the seventh, and the eighth unit regions from the head of the first arrangement is “0”+“0”+“1”+“1”+“0”+“1”=“3”, which is an odd number. Therefore, it is determined that one of the output values output based on the head unit region and the third, the fifth, the sixth, the seventh, and the eighth unit regions from the head of the first arrangement is erroneous. 
     As described above, here, it is determined that one of the output value output based on the third unit region from the head of the first arrangement of first pattern  24  and the output value output based on the third unit region from the head of the first arrangement of second pattern  26  is erroneous. Therefore, correction unit  54  determines that the output value obtained based on the third unit region from the head of the first arrangement of first pattern  24  among the output values output based on the head unit region and the third, the fifth, the sixth, the seventh, and the eighth unit regions from the head is erroneous, corrects the output value from “0” to “1”, and outputs the corrected output value. 
       FIG.  6 ( b )  illustrates a method for determining, when determination unit  52  determines that one of an output value output based on a fourth unit region from the head of the first arrangement of first pattern  24  and an output value output based on a fourth unit region from the head of the first arrangement of second pattern  26  is erroneous, whether or not the output value output based on the unit region of first pattern  24  is correct and correcting the output value when the output value is erroneous. 
     As illustrated in  FIG.  6 ( b ) , similarly to the case illustrated in  FIG.  6 ( a ) , correction unit  54  acquires nine output values obtained based on the first arrangement and two output values obtained based on the second arrangement. 
     In this embodiment, an output value output based on a second unit region from the head of the second arrangement is information for determining whether or not one output value determined by determination unit  52  to have a possibility of being erroneous among output values output based on the second, the fourth, a sixth, a seventh, an eighth, and a ninth unit regions from the head of the first arrangement is erroneous, and is information for correcting the one output value when the one output value is erroneous. 
     When a value obtained by taking an exclusive OR of the output values output based on the second and the fourth unit regions from the head of the first arrangement is referred to as a sixth value, a value obtained by taking an exclusive OR of the sixth value and the output value output based on the sixth unit region from the head is referred to as a seventh value, a value obtained by taking an exclusive OR of the seventh value and the output value output based on the seventh unit region from the head is referred to as an eighth value, a value obtained by taking an exclusive OR of the eighth value and the output value output based on the eighth unit region from the head is referred to as a ninth value, and a value obtained by taking an exclusive OR of the ninth value and the output value output based on the ninth unit region from the head is referred to as a tenth value, the output value output based on the second unit region from the head of the second arrangement is equal to the tenth value. 
     For example, when the output value obtained based on the second unit region from the head of the second arrangement is “0”, a total value of the output values output based on the second, the fourth, the sixth, the seventh, the eighth, and the ninth unit regions from the head of the first arrangement is an even number. 
     On the other hand, when the output value obtained based on the second unit region from the head of the second arrangement is “1”, the total value of the output values output based on the second, the fourth, the sixth, the seventh, the eighth, and the ninth unit regions from the head of the first arrangement is an odd number. 
     In  FIG.  6 ( b ) , the output value output based on the second unit region from the head of the second arrangement is “0”. The total value of the output values output based on the second, the fourth, the sixth, the seventh, the eighth, and the ninth unit regions from the head of the first arrangement is “1”+“0”+“0”+“0”+“0”+“1”=“2”, which is an even number. Therefore, correction unit  54  determines that the output value output based on the fourth unit region from the head of the first arrangement of first pattern  24  is not erroneous, and outputs “0” without correcting the output value. 
     By reversing the output values output based on the first arrangement and the second arrangement of second pattern  26 , the same processing as described above is performed. 
       FIG.  7    is a diagram illustrating calculation circuit  56  that calculates values for forming first pattern  24  on rotatable plate  12  of encoder  10  shown in  FIG.  1   .  FIG.  8    is a table illustrating values obtained by calculation circuit  56  shown in  FIG.  7   . 
     Calculation circuit  56  illustrated in  FIG.  7    is a circuit for calculating a value based on an M code (irreducible polynomial): X 9 +X 7 +X 5 +X 4 +X 3 +X 2 +1. It is possible to form first pattern  24  including the first arrangement and the second arrangement by forming first pattern  24  based on the values obtained by calculation circuit  56 . 
     As illustrated in  FIG.  7   , calculation circuit  56  includes plural registers  58  to  74  and plural XOR circuits  76  to  86 . 
     Each of the registers  58  to  74  stores a value used for operation performed by calculation circuit  56 , and outputs the stored value. 
     A value output from register  60  is input to register  58 . A value output from register  62  is input to XOR circuit  76  and register  60 . A value output from register  64  is input to register  62 . A value output from register  66  is input to XOR circuit  78  and register  64 . A value output from register  68  is input to XOR circuit  80  and register  66 . A value output from register  70  is input to XOR circuit  82  and register  68 . A value output from register  72  is input to XOR circuit  84  and register  70 . A value output from register  74  is input to register  72 . 
     Each of the XOR circuits  76  to  86  calculates an exclusive logical sum of input two values and outputs a calculated value. A value output from register  58  and the value output from register  62  are input to XOR circuit  76 , and XOR circuit  76  calculates an exclusive logical sum of these two values and outputs a calculated value. The value output from register  66  and the value output from XOR circuit  76  are input to XOR circuit  78 , and XOR circuit  78  calculates an exclusive logical sum of these two values and outputs a calculated value. The value output from register  68  and the value output from XOR circuit  78  are input to XOR circuit  80 , and XOR circuit  80  calculates an exclusive logical sum of these two values and outputs a calculated value. The value output from register  70  and the value output from XOR circuit  80  are input to XOR circuit  82 , and XOR circuit  82  calculates an exclusive logical sum of these two values and outputs a calculated value. The value output from register  72  and the value output from XOR circuit  82  are input to XOR circuit  84 , and XOR circuit  84  calculates an exclusive logical sum of these two values and outputs a calculated value. A predetermined value input from the outside and the value output from XOR circuit  84  are input to XOR circuit  86 , and XOR circuit  86  calculates an exclusive logical sum of these two values and outputs a calculated value. For example, the predetermined value is one value previously determined. The value output from XOR circuit  86  is input to register  74 . 
     Each time a value is newly input, each of the registers  58  to  74  outputs the input value. Each time two values are newly input, each of the XOR circuits  76  to  86  calculates an exclusive logical sum of the two input values and outputs the calculated value. 
     Here, a case in which registers  58 ,  60 ,  64 ,  70 , and  74  previously store value “0” and registers  62 ,  66 ,  68 , and  72  previously store value “1” will be described below. 
     In this case, first, registers  58 ,  60 ,  64 ,  70 , and  74  output value “0”, and registers  62 ,  66 ,  68 , and  72  output value “1”. 
     XOR circuit  76  outputs value “1” which is an exclusive logical sum of values “0” and “1”. XOR circuit  78  outputs “0” which is an exclusive logical sum of “l” and “1”. XOR circuit  80  outputs “1” which is an exclusive logical sum of “1” and “0”. XOR circuit  82  outputs “1” which is the exclusive logical sum of “0” and “1”. XOR circuit  84  outputs “0” which is the exclusive logical sum of “1” and “1”. Value “0” is input to XOR circuit  86  from the outside. XOR circuit  86  outputs value “0” which is an exclusive logical sum of values “0” and “0”. 
     As described above, each time a value is newly input, each of the registers  58  to  74  outputs the input value. Each time two values are newly input, each of the XOR circuits  76  to  86  calculates the exclusive logical sum of the two input values and outputs the calculated value. As described above, values illustrated in  FIG.  8    are obtained by repeating calculation and output of the exclusive logical sum. 
     As illustrated in  FIG.  8   , nine output values output from the registers  58  to  74  are values for forming the first arrangement. For example, when looking at the top of the output values of the table illustrated in  FIG.  8   , the nine output values output from the registers  58  to  74  are “001011010”. In this case, the first arrangement is formed by arranging second unit region  34 , second unit region  34 , first unit region  32 , second unit region  34 , first unit region  32 , first unit region  32 , second unit region  34 , first unit region  32 , and second unit region  34  in this order in the circumferential direction. 
     The value output from register  60  is subsequently output from register  58 . The value output from register  62  is subsequently output from register  60 . The value output from register  64  is subsequently output from register  62 . The value output from register  66  is subsequently output from register  64 . The value output from register  68  is subsequently output from register  66 . The value output from register  70  is subsequently output from register  68 . The value output from register  72  is subsequently output from register  70 . The value output from register  74  is subsequently output from register  72 . The value output from XOR circuit  86  is subsequently output from register  74 . XOR circuit  86  calculates a new value based on these values and outputs the calculated value. This processing is repeatedly performed. 
     As described above, the nine output values output from the registers  58  to  74  are the values for forming the first arrangement. The value output from XOR circuit  86  together with the nine output values and a value output from XOR circuit  86  after the value are values for forming the second arrangement corresponding to the first arrangement formed based on the nine output values. 
     By repeatedly outputting values by the registers  58  to  74  and XOR circuit  86 , plural values for forming the first arrangement are obtained, and plural first arrangements are formed. That is, first pattern  24  formed using the values illustrated in  FIG.  8    includes plural first arrangements. The plural first arrangements in first pattern  24  are continuously formed such that the unit regions are shifted one by one. That is, an arrangement of nine unit regions in first pattern  24  is the first arrangement, and nine arrangements in which unit regions are shifted one by one in the circumferential direction with respect to the arrangement of the nine unit regions are also first arrangements. The plural first arrangements are different from one another in the order of first unit regions  32  and second unit regions  34  arranged. That is, the plural first arrangements are formed so that the arrangements of nine output values obtained based on the plural first arrangements are not the same. 
     By repeatedly outputting values by the registers  58  to  74  and XOR circuit  86 , plural values for forming the second arrangement are obtained, and plural second arrangements are formed. That is, first pattern  24  formed using the values illustrated in  FIG.  8    includes plural second arrangements. The plural second arrangements in first pattern  24  respectively correspond to the plural first arrangements described above, and each of the plural second arrangements is an arrangement of two unit regions and is adjacent to the corresponding first arrangement. Each of the plural second arrangements is an arrangement for outputting the correction information for correcting the output values output based on the corresponding first arrangement. The plural second arrangements in first pattern  24  are continuously formed such that the unit regions are shifted one by one. That is, an arrangement of two unit regions in first pattern  24  is the second arrangement, and two arrangements in which unit regions are shifted one by one in the circumferential direction with respect to the arrangement of the two unit regions are also second arrangements. 
       FIG.  9    is a diagram illustrating a flow of data during operation of correction unit  54  of encoder  10  shown in  FIG.  1   . In  FIG.  9   , in the first arrangement and the second arrangement, value “1” indicates first unit region  32 , and value “0” indicates second unit region  34 . In  FIG.  9   , a case where foreign substance  7  adheres to the third unit region from the head of the first arrangement of first pattern  24  will be described. 
     As illustrated in  FIG.  9   , determination unit  52  determines, based on these output values, whether or not no error is present in nine output values output by first light receiving element  48  and nine output values output by second light receiving element  50 . The determination method performed by determination unit  52  is omitted here by referring to the above description. Determination unit  52  transmits, to correction unit  54 , error location information indicating an output value having a possibility of being erroneous. 
     Correction unit  54  recognizes, based on the error location information, the output value having a possibility of being erroneous among the output values of first light receiving element  48  output based on the first arrangement. Here, the error location information indicates that the output value output based on the third unit region from the head has a possibility of being erroneous. 
     Correction unit  54  performs error determination of whether the output value having a possibility of being erroneous is erroneous. Specifically, correction unit  54  determines whether or not the output value having a possibility of being erroneous among the output values of first light receiving element  48  is erroneous using an output value other than the output value. The determination method performed by correction unit  54  is omitted here by referring to the above description. 
     When the output value of first light receiving element  48  is erroneous, correction unit  54  performs correction operation on uncorrected data, and calculates corrected data. The corrected data is a value obtained by correcting the output value of first light receiving element  48 . The correction method performed by correction unit  54  is omitted here by referring to the above description. 
     After calculating the corrected data, correction unit  54  performs circulation to determine whether another erroneous output value is present among the output values of first light receiving element  48 . 
     After correcting all correctable output values, correction unit  54  selects raw data or the corrected data and outputs the selected data to the outside. The raw data is a value identical to the output value of first light receiving element  48 . Correction unit  54  outputs corrected data for the erroneous output value. 
       FIG.  10    is a diagram for illustrating another example of the correction method performed by correction unit  54  of encoder  10  in  FIG.  1   .  FIG.  10 ( a )  is a diagram for illustrating correction on one output value among the output values of first light receiving element  48 .  FIG.  10 ( b )  is a diagram for illustrating correction on another output value among the output values of first light receiving element  48 . A case in which two output values among the output values of first light receiving element  48  are corrected will be described with reference to  FIG.  10   . 
     As illustrated in  FIG.  10 ( a ) , correction unit  54  acquires two output values (correction information) output based on the second arrangement in addition to nine output values (position information) output based on the first arrangement. 
     The output value obtained based on the head unit region in the second arrangement is “0”. A total value of the output values output based on the head unit region and the fifth, the sixth, the seventh, and the eighth unit regions from the head of the first arrangement is “0”+“1”+“1”+“0”+“1”=“3”, which is an odd number. Therefore, in order to set the total value to an even number, correction unit  54  sets the output value output based on the third unit region from the head of the first arrangement to “I” and outputs value “1”. 
     Next, as illustrated in  FIG.  10 ( b ) , correction unit  54  corrects the output value output based on the second unit region from the head of the first arrangement. 
     The output value output based on the second unit region from the head of the second arrangement is “0”. A total value of the output values output based on the fourth, the sixth, the seventh, the eighth, and the ninth unit regions from the head of the first arrangement is “0”+“1”+“0”+“1”+“0”=“2”, which is an even number. Therefore, in order to maintain the total value as an even number, correction unit  54  sets the output value output based on the second unit region from the head of the first arrangement to “0” and outputs value “0”. 
       FIG.  11    is a diagram for illustrating still another example of the correction method performed by correction unit  54  of encoder  10  shown in  FIG.  1   .  FIG.  11 ( a )  is a diagram for illustrating correction on one output value among the output values of first light receiving element  48 .  FIG.  11 ( b )  is a diagram for illustrating correction on another output value among the output values of first light receiving element  48 . A case in which two output values among the output values of first light receiving element  48  are corrected will be described with reference to  FIG.  11   . 
     As illustrated in  FIG.  11 ( a ) , the output value obtained based on the second unit region from the head of the second arrangement is “0”. A total value of the output values output based on the second, the fourth, the seventh, the eighth, and the ninth unit regions from the head of the first arrangement is “0”+“o”+“0”+“1”+“0”=“1”, which is an odd number. Therefore, in order to set the total value to an even number, correction unit  54  sets the output value output based on the sixth unit region from the head of the first arrangement to “1” and outputs value “1”. 
     Next, as illustrated  FIG.  11 ( b ) , correction unit  54  corrects the output value output based on the fifth unit region from the head of the first arrangement using the corrected value. 
     The output value output based on the head unit region in the second arrangement is “0”. A total value of the output values output based on the head unit region and the third, the sixth, the seventh, and the eighth unit regions from the head of the first arrangement is “0”+“I”+“1”+“0”+“1”=“3”, which is an odd number. Therefore, in order to set the total value to an even number, correction unit  54  sets the output value output based on the fifth unit region from the head of the first arrangement to “1” and outputs value “1”. 
       FIG.  12    is a diagram for illustrating a further example of the correction method performed by correction unit  54  of encoder  10  shown in  FIG.  1   .  FIG.  12 ( a )  is a diagram for illustrating correction on one output value among the output values of first light receiving element  48 .  FIG.  12 ( b )  is a diagram for illustrating correction on another output value among the output values of first light receiving element  48 . A case in which two output values among the output values of first light receiving element  48  are corrected will be described with reference to  FIG.  12   . 
     As illustrated in  FIG.  12 ( a ) , the output value obtained based on the head unit region in the second arrangement is “0”. A total value of the output values output based on the head unit region and the third, the fifth, the sixth, and the seventh unit regions from the head of the first arrangement is “0”+“1”+“1”+“1”+“0”=“3”, which is an odd number. Therefore, in order to set the total value to an even number, correction unit  54  sets the output value output based on the eighth unit region from the head of the first arrangement to “1” and outputs value “1”. 
     Next, as illustrated in  FIG.  12 ( b ) , correction unit  54  corrects the output value output based on the fourth unit region from the head of the first arrangement using the corrected value. 
     The output value output based on the second unit region from the head of the second arrangement is “0”. A total value of the output values output based on the second, the sixth, the seventh, the eighth, and the ninth unit regions from the head of the first arrangement is “0”+“1”+“0”+“1”+“0”=“2”, which is an even number. Therefore, in order to maintain the total value as an even number, correction unit  54  sets the output value output based on the fourth unit region from the head of the first arrangement to “0” and outputs value “0”. 
     Correction unit  54  thus further correct other output values using the corrected output value. 
     Encoder  10  according to the embodiment is described above. 
     Encoder  10  according to the embodiment includes rotatable plate  12  including first pattern  24  and second pattern  26 , light emission unit  18  configured to emit light to first pattern  24  and second pattern  26 , and light receiving unit  20  configured to receive light emitted from light emission unit  18  and passing through first pattern  24  and light emitted from light emission unit  18  and passing through second pattern  26 . First pattern  24  includes first unit regions  32  and second unit regions  34  which are arranged in the circumferential direction about the rotation axis A of rotatable plate  12 . Each first unit region  32  is configured to guide the light emitted from light emission unit  18  to light receiving unit  20 . Each second unit region  34  is configured not to guide the light emitted from light emission unit  18  to light receiving unit  20 . Second pattern  26  includes first unit regions  40  and second unit regions  42  which are arranged in the circumferential direction about the rotation axis A of rotatable plate  12 . Each first unit region  40  is configured to guide the light emitted from light emission unit  18  to light receiving unit  20 . Each second unit region  42  is configured not to guide the light emitted from light emission unit  18  to light receiving unit  20 . The order in which first unit regions  32  and second unit regions  34  are arranged in first pattern  24  is reversed to the order in which first unit regions  40  and second unit regions  42  are arranged in second pattern  26 . 
     In this configuration, the light guided from first pattern  24  is reversed to the light guided from second pattern  26 . Specifically, when first pattern  24  guides the light to light receiving unit  20 , second pattern  26  does not guide the light to light receiving unit  20 . When first pattern  24  does not guide the light to light receiving unit  20 , second pattern  26  guides the light to light receiving unit  20 . Therefore, when the light is not guided to light receiving unit  20  from both first pattern  24  and second pattern  26 , it is possible to notice that abnormality occurs. For example, when foreign substance  7  adheres to both first pattern  24  and second pattern  26  and the light is not guided to light receiving unit  20  from both first pattern  24  and second pattern  26 , it is also possible to notice that abnormality occurs. In this way, it is possible to prevent occurrence of erroneous detection and the decrease in the detection accuracy by noticing the occurrence of an abnormality. 
     Encoder  10  according to the embodiment further includes determination unit  52 . Light receiving unit  20  includes first light receiving element  48  and second light receiving element  50 . The first light receiving element  48  is configured to receive the light emitted from light emission unit  18  and passing through first pattern  24 , binarize the intensity of the received light, and output the binarized intensity. The second light receiving element  50  is configured to receive the light emitted from light emission unit  18  and passing through second pattern  26 , binarize the intensity of the received light, and output the binarized intensity. Second pattern  26  is provided such that the output value of second light receiving element  50  is reversed to the output value of first light receiving element  48 . When the output value of second light receiving element  50  is not the value reversed to the output value of first light receiving element  48 , determination unit  52  determines that one of the output value of first light receiving element  48  and the output value of second light receiving element  50  is erroneous, and outputs the determination result. 
     This configuration reverses the output value of first light receiving element  48  based on the light passing through first pattern  24  and the output value of second light receiving element  50  based on the light passing through second pattern  26 . When these output values are not reversed to each other, determination unit  52  determines that one of these output values is erroneous. In this way, it is possible to easily notice that the output value is erroneous and to further prevent the occurrence of the erroneous detection, and thus it is possible to further prevent the decrease in the detection accuracy. 
     When first unit region  32  and second unit region  34  are referred to as unit regions, first pattern  24  includes one or more first arrangements and one or more second arrangements each of which is adjacent to respective one of the one or more first arrangements. Each first arrangement is an arrangement of nine unit regions for outputting the position information indicating the position of rotation shaft  5 . Each second arrangement is an arrangement of two unit regions for outputting the correction information for correcting the position information. 
     In this configuration, first pattern  24  includes the one or more second arrangements each of which is an arrangement of two unit regions for outputting the correction information for correcting the position information. Therefore, when at least one of the one or more first arrangements does not normally guide the light from light emission unit  18  to light receiving unit  20  and the position information is erroneous, it is possible to correct the position information based on the correction information and to prevent the decrease in the detection accuracy. 
     First pattern  24  includes plural first arrangements and plural second arrangements each corresponding to respective one of the plural first arrangements. 
     In this configuration, the correction information is obtained for each of plural pieces of position information obtained based on the plural first arrangements. Therefore, even when any position information among the plural pieces of position information is erroneous, the correction is performed based on the corresponding correction information, and the detection accuracy can be prevented from being decreased. 
     Next, another example of the correction method performed by correction unit  54  will be described. 
       FIG.  13    is a diagram illustrating another example of the received light intensity of the light received by light receiving unit  20  of encoder  10  shown in  FIG.  1   .  FIG.  13 ( a )  is a diagram illustrating another example of the received light intensity of the light received by first light receiving element  48 .  FIG.  13 ( b )  is a diagram illustrating another example of the received light intensity of the light received by second light receiving element  50 . 
     In the above description, a case in which correction unit  54  corrects an error in the output value output based on the first arrangement based on the output value output based on the second arrangement is described, and the present disclosure is not limited thereto. For example, correction unit  54  may acquire the received light intensity of the light received by first light receiving element  48  and the received light intensity of the light received by second light receiving element  50 , and correct, based on the acquired received light intensities, the error in the output value obtained based on the first arrangement. 
     Here, a case will be described in which both the output value output based on the fifth unit region from the head of the first arrangement of first pattern  24  and the output value output based on the fifth unit region from the head of the first arrangement of second pattern  26  are “0” and determination unit  52  determines that one of these output values is erroneous. 
     In this case, as illustrated in  FIG.  13   , correction unit  54  acquires the received light intensity of the light received by first light receiving element  48  based on the fifth unit region from the head of the first arrangement of first pattern  24  and the received light intensity of the light received by second light receiving element  50  based on the fifth unit region from the head of the first arrangement of second pattern  26 . Correction unit  54  compares these acquired received light intensities and corrects an error in the output values based on a comparison result. Specifically, the received light intensity of the light received by first light receiving element  48  is larger than the received light intensity of the light received by second light receiving element  50 . Therefore, correction unit  54  corrects the output value of first light receiving element  48  to value “1”, outputs the corrected output value, and outputs the output value of second light receiving element  50  as “0”. 
     Next, calculation circuit  88  which calculates values for forming a first pattern different from first pattern  24  of encoder  10  will be described. 
       FIG.  14    is a diagram illustrating calculation circuit  88  that calculates values for forming the first pattern different from first pattern  24  of encoder  10  shown in  FIG.  1   .  FIG.  15    is a table illustrating values obtained by calculation circuit  88  in  FIG.  14   . 
     Calculation circuit  88  illustrated in  FIG.  14    is a circuit for calculating a value based on an M code (irreducible polynomial): X 9 +X 5 +1. It is possible to form the first pattern including a first arrangement and a second arrangement, which is different from first pattern  24 , by forming the first pattern based on the values obtained by calculation circuit  88 . 
     As illustrated in  FIG.  14   , calculation circuit  88  includes plural registers  90  to  106  and plural XOR circuits  108  and  110 . 
     A value output from register  90  is input to XOR circuit  108 . A value output from register  92  is input to register  90 . A value output from register  94  is input to register  92 . A value output from register  96  is input to register  94 . A value output from register  98  is input to XOR circuit  108  and register  96 . A value output from register  100  is input to register  98 . A value output from register  102  is input to register  100 . A value output from register  104  is input to register  102 . A value output from register  106  is input to register  104 . 
     The value output from register  90  and the value output from register  98  are input to XOR circuit  108 , and XOR circuit  108  calculates an exclusive logical sum of these two values and outputs the calculated value. A predetermined value input from the outside and the value output from XOR circuit  108  are input to XOR circuit  110 , and XOR circuit  110  calculates an exclusive logical sum of these two values and outputs the calculated value. 
     For example, the predetermined value is one value previously determined. The value output from XOR circuit  110  is input to register  106 . 
     For example, when registers  90 ,  94 ,  98 , and  102  previously store value “0” and registers  92 ,  96 ,  100 ,  104 , and  106  previously store “1”, values illustrated in  FIG.  15    are obtained by repeating calculation and output of an exclusive logical summation. 
     By using the values illustrated in  FIG.  15   , it is possible to form a first pattern including a first arrangement that is an arrangement of nine unit regions, a second arrangement that is an arrangement of four unit regions, and a third arrangement that is an arrangement of one unit region and is for outputting correction information for correcting position information obtained based on the first arrangement. The third arrangement is adjacent to the first arrangement and opposite to the second arrangement with respect to the first arrangement. 
     For example, an output value output based on a head unit region in the second arrangement is a value obtained by taking an exclusive local sum of two output values output based on a head unit region and a fifth unit region from the head of the first arrangement. An output value output based on a fourth unit region from the head of the second arrangement is a value obtained by taking an exclusive logical sum of two output values output based on a fourth unit region and an eighth unit region from the head of the first arrangement. An output value output based on a ninth unit region from the head of the first arrangement is a value obtained by taking an exclusive logical sum of two output values output based on a head unit region in the third arrangement and the fourth unit region from the head of the first arrangement. Since such a relation is established, the position information obtained based on the first arrangement is corrected using correction information obtained based on the second arrangement and correction information obtained based on the third arrangement. 
     Other Embodiments 
     As described above, the embodiment is described as an example of the technique disclosed in the present application. However, the technique according to the present disclosure is not limited thereto, and can be applied to embodiments or modified examples in which changes, substitutions, additions, omissions, and the like are appropriately performed without departing from the gist of the present disclosure. 
     In the embodiment described above, a case in which encoder  10  includes first pattern  24  and second pattern  26  is described, and the present disclosure is not limited thereto. For example, encoder  10  may not include second pattern  26 . 
     In this case, an encoder includes rotatable plate  12  including first pattern  24 , light emission unit  18  configured to emit light to first pattern  24 , and light receiving unit  20  configured to receive the light emitted from light emission unit  18  and passing through first pattern  24 . First pattern  24  includes first unit regions  32  and second unit regions  34  which are arranged in a circumferential direction about a rotation axis A of rotatable plate  12 . Each first unit regions  32  is configured to guide the light emitted from light emission unit  18  to light receiving unit  20 . Each second unit regions  34  is configured not to guide the light emitted from light emission unit  18  to light receiving unit  20 . When first unit regions  32  and second unit regions  34  are referred to as unit regions, first pattern  24  includes a first arrangement that is an arrangement of nine unit regions for outputting position information indicating a position of rotation shaft  5 , and a second arrangement adjacent to the first arrangement. The second arrangement is an arrangement of two unit regions for outputting correction information for correcting the position information. 
     Accordingly, first pattern  24  includes the second arrangement that is the arrangement of two unit regions for outputting the correction information for correcting the position information. Therefore, when the first arrangement does not normally guide the light from light emission unit  18  to light receiving unit  20  and the position information is erroneous, it is possible to correct the position information using the correction information and to prevent a decrease in detection accuracy. 
     In the embodiment described above, a case in which the detection target by encoder  10  is rotation shaft  5  is described, and the present disclosure is not limited thereto. For example, the detection target by encoder  10  may not be rotation shaft  5 , and may be a rotating body that rotates. 
     In the embodiment described above, a case in which first unit region  32  and first unit region  40  transmit the light emitted from light emission unit  18  and guide the light to light receiving unit  20  is described, and the present disclosure is not limited thereto. For example, the first unit region may reflect the light emitted from the light emission unit and guide the light to the light receiving unit. In this case, for example, the main body of the rotatable plate is made of SUS or the like, the first unit region is formed by chromium plating or the like that reflects light, and the second unit region is formed by black chromium plating or the like that does not reflect light. 
     In the embodiment described above, a case in which second pattern  26  is provided radially inward of first pattern  24  is described, and the present disclosure is not limited thereto. For example, the second pattern may be provided radially outward of the first pattern. 
     In the embodiment described above, a case in which first unit region  32  and second unit region  42  corresponding to first unit region  32  are adjacent to each other in the radial direction is described, and the present disclosure is not limited thereto. For example, first unit region  32  and second unit region  42  corresponding to first unit region  32  may not be adjacent to each other in the radial direction, and may be provided at positions deviated in radial directions. 
     In the embodiment described above, a case in which second unit region  34  and first unit region  40  corresponding to second unit region  34  are adjacent to each other in the radial direction is described, and the present disclosure is not limited thereto. For example, second unit region  34  and first unit region  40  corresponding to second unit region  34  may not be adjacent to each other in the radial direction, and may be provided at positions deviated in radial directions. 
     In the embodiment described above, a case in which first pattern  24  and second pattern  26  are provided on the main surface of main body  22  directed to the first substrate  14  is described, and the present disclosure is not limited thereto. For example, the first pattern and the second pattern may be formed such that the main body of the rotatable plate is made of a material that does not transmit light, and the first unit region is formed by a through hole that passes through the main body of the rotatable plate. In this case, a part of the main body of the rotatable plate functions as the second unit region. 
     In the embodiment described above, a case in which the first arrangement is an arrangement of nine unit regions, the second arrangement is an arrangement of two or four unit regions, and the third arrangement is an arrangement of one unit region is described, and the present disclosure is not limited thereto. 
     INDUSTRIAL APPLICABILITY 
     An encoder according to the present disclosure may be used for rotation detection of a rotation shaft or the like of a motor that rotationally drives a load. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
         
           
               10  encoder 
               12  rotatable plate 
               14  first substrate 
               16  second substrate 
               18  light emission unit 
               20  light receiving unit 
               22  main body 
               24  first pattern 
               26  second pattern 
               28  first light-guidable portion 
               30  first non-light-guidable portion 
               32 ,  40  first unit region 
               34 ,  42  second unit region 
               36  second light-guidable portion 
               38  second non-light-guidable portion 
               44  first light emitter 
               46  second light emitter 
               48  first light receiving element 
               50  second light receiving element 
               52  determination unit 
               54  correction unit