Patent Publication Number: US-2023141056-A1

Title: Estimation device, estimation method, and program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. national stage of application No. PCT/JP2021/009384, filed on Mar. 9, 2021, and with priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) being claimed from Japanese Patent Application No. 2020-047778, filed on Mar. 18, 2020, the entire disclosures of which are hereby incorporated herein by reference. 
    
    
     1. FIELD OF THE INVENTION 
     The present disclosure relates to an estimation device, an estimation method, and a program. 
     2. BACKGROUND 
     There is a technique of estimating a position of a rotor of a motor using a general-purpose magnetic sensor mounted on the motor as standard. Since such a magnetic sensor is inexpensive and small, an estimation device using the magnetic sensor and a motor itself on which the estimation device is mounted can be inexpensive and small. Further, a position of a rotor can be estimated without using an expensive and large-sized dedicated position sensor such as an optical encoder or a magnetic encoder. 
     However, the above technique is a technique for estimating a position of a rotating body (such as a rotor of a motor), and does not include a function of estimating a degree of change in sensitivity of position detection. If a state of a sensor and a rotating body and a degree of sensitivity can be estimated, reduction in maintenance cost and reduction in stop time can be expected. For this reason, there is demand for estimating degree of change in sensitivity of position detection without providing an additional dedicated sensor for estimating the degree of change. 
     SUMMARY 
     One example embodiment of the present disclosure is an estimation device that estimates a state of a device that detects a position of a rotating body. The estimation device includes a position sensor to output a detection signal that is a signal representing a detection result of a position of a magnet rotatable in conjunction with the rotating body according to a magnetic flux of the magnet, an extractor to extract a feature amount of the detection signal from the detection signal for each of the positions, and an estimator to derive an evaluation value representing a comparison result between a feature amount of the detection signal for each of the positions and a reference value for each of the positions, and to estimate a degree of change in sensitivity to detect the position based on the evaluation value. 
     The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating a configuration example of a sensor assembly according to a first example embodiment of the present disclosure. 
         FIG.  2    is a diagram illustrating an example of a correspondence relationship between a pole pair number, a section, and a segment in the first example embodiment. 
         FIG.  3    is a diagram illustrating a configuration example of a position sensor in the first example embodiment. 
         FIG.  4    is a diagram illustrating an example of a sample point of a detection signal in the first example embodiment. 
         FIG.  5    is a diagram illustrating an example of a case where feature amounts of detection signals of all phases change in one cycle of an electrical angle in the first example embodiment. 
         FIG.  6    is a diagram illustrating an example of a case where a feature amount of a detection signal of a specific phase changes in one cycle of a mechanical angle in the first example embodiment. 
         FIG.  7    is a diagram illustrating an example of a case where feature amounts of detection signals of all phases change in one cycle of a mechanical angle in the first example embodiment. 
         FIG.  8    is a flowchart illustrating an operation example of the sensor assembly in the first example embodiment. 
         FIG.  9    is a diagram illustrating an example of a detection signal in a variation of the first example embodiment. 
         FIG.  10    is a diagram illustrating a configuration example of a position sensor according to a second example embodiment of the present disclosure. 
         FIG.  11    is a diagram illustrating a configuration example of a sensor assembly according to a third example embodiment of the present disclosure. 
         FIG.  12    is a diagram illustrating a configuration example of the position sensor in the third example embodiment. 
         FIG.  13    is a diagram illustrating a configuration example of a sensor assembly according to a fourth example embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of the present disclosure will be described in detail with reference to the drawings. 
       FIG.  1    is a diagram illustrating a configuration example of a sensor assembly  1   a  in a first example embodiment. The sensor assembly  1   a  includes a magnet  2  and an estimation device  3   a . The magnet  2  is a magnet for a position sensor that detects a position of a rotating object such as a rotor. Hereinafter, the number of pole pairs of the magnet  2  is four as an example. The estimation device  3   a  includes a position sensor device  30  and a determination device  31 . The position sensor device  30  includes M (M is an integer of three or more) magnetic sensors  300  and an extractor  301 . In the first example embodiment, “M” is three as an example. The position sensor device  30  includes M of the magnetic sensors  300  as a position sensor  302 . The determination device  31  includes a control unit  310 , a storage unit  311 , an estimator  312 , and an output unit  313 . The sensor assembly  1   a  includes the magnet  2  and the position sensor device  30  as a device for detecting a position of a rotating body. 
       FIG.  2    is a diagram illustrating an example of a correspondence relationship between a pole pair number, a section, and a segment. A section number group is associated with a pole pair number. The number of section numbers is equal to the number of twelve ways of logic including a magnitude relationship of detection signals output from M of the magnetic sensors  300  and positive and negative (zero cross) of an intermediate signal. 
     In  FIG.  2   , a pole pair number “0” is associated with section numbers from “0” to “11”. A segment number is a unique number representing an absolute value of a mechanical angle of the magnet  2 . For example, segment numbers “0” to “11” are associated with section numbers “0” to “11” of a pole pair number “0”. For example, segment numbers “12” to “23” are associated with section numbers “0” to “11” of a pole pair number “1”. A data table representing the correspondence relationship illustrated in  FIG.  2    is stored in advance in the storage unit  311 , for example. 
       FIG.  3    is a diagram illustrating a configuration example of the position sensor  302  in the first example embodiment. An upper part of  FIG.  3    represents an upper surface of the position sensor  302 . A lower part of  FIG.  3    illustrates a side surface of the position sensor  302 . M of the magnetic sensors  300  are provided on a board  100  whose position is fixed. 
     A rotor  201  is a rotating object. The rotating object is, for example, a rotation mechanism, and is not limited to a motor. The rotor  201  includes a main shaft  200 . The magnet  2  is connected to the main shaft  200 . When the rotor  201  rotates, the main shaft  200  rotates. The magnet  2  is rotatable in conjunction with the rotor  201  and the main shaft  200 . 
     Next, details of the sensor assembly  1   a  will be described. Each of the magnetic sensors  300  outputs a detection signal, which is a signal representing a detection result of a position of the magnet  2  (magnetic flux component of a pole pair), to the extractor  301 . Hereinafter, as an example, a magnetic sensor  300 - 1  outputs a U-phase detection signal indicating a position of the magnet  2  to the extractor  301 . A magnetic sensor  300 - 2  outputs a V-phase detection signal indicating a position of the magnet  2  to the extractor  301 . A magnetic sensor  300 - 3  outputs a W-phase detection signal indicating a position of the magnet  2  to the extractor  301 . 
     The extractor  301  reduces in-phase noise in each detection signal. The extractor  301  extracts a feature amount of a detection signal from each detection signal for each position of the magnet  2 . The extractor  301  outputs a feature amount (array data) of a detection signal for each position to the estimator  312  and the control unit  310 . 
       FIG.  4    is a diagram illustrating an example of a sample point of a detection signal in the first example embodiment. The horizontal axis represents a rotor angle (position of the magnet  2 ). The vertical axis represents a digital value of a detection signal. “HU” represents a U-phase detection signal. “HV” represents a V-phase detection signal. “HW” represents a W-phase detection signal. In  FIG.  4   , sample points  401  to  424  are illustrated as an example of sample points representing n (n is an integer of one or more) feature amounts extracted from a detection signal. 
     Each of the sample point  401 , the sample point  405 , the sample point  409 , the sample point  415 , the sample point  419 , and the sample point  423  is an intersection of waveforms of detection signals. 
     The sample point  402 , the sample point  404 , the sample point  406 , the sample point  408 , the sample point  410 , and the sample point  412  are points representing feature amounts of other detection signals in a case where a digital value of a detection signal is zero (zero cross). For example, the sample point  402  indicates a digital value of the detection signal “HU” in a case where a digital value of the detection signal “HW” is zero. The sample point  414 , the sample point  416 , the sample point  418 , the sample point  420 , the sample point  422 , and the sample point  424  are points representing feature amounts of other detection signals in a case where a digital value of a detection signal is zero (zero cross). 
     Each of the sample point  403 , the sample point  407 , and the sample point  411  is a maximum value of a digital value of a detection signal. Each of the sample point  413 , the sample point  417 , and the sample point  421  is a minimum value of a digital value of a detection signal. 
     Returning to  FIG.  1   , the description of the configuration example of the sensor assembly  1   a  will be continued. The control unit  310  controls operation of the storage unit  311 . For example, the control unit  310  records a feature amount of a detection signal in the storage unit  311  for each sample point. 
     The storage unit  311  stores a feature amount (digital value) of a detection signal for each sample point as a feature amount of a detection signal for each position. Since there are not many sample points, storage capacity of the storage unit  311  may be small. The storage unit  311  stores a reference value for each position in advance. The reference value is, for example, a feature amount of a detection signal measured at a past time point. The past time point is, for example, a time point when the magnet  2  and the position sensor device  30  are attached or at the time of shipment. The reference value may be periodically updated. 
     A feature amount of a detection signal is input to the estimator  312  for each position (sample point). The estimator  312  derives an evaluation value representing a comparison result between a feature amount of a detection signal for each position and a reference value for each position. The evaluation value is expressed using a mean square error as in Equation (1), for example. 
     
       
         
           
             
               
                 
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     Here, “ri” represents a reference value (reference feature amount). A value “di” represents a feature amount (measurement value) of a detection signal. A value “n” represents the number of samples included in a predetermined evaluation unit. The evaluation unit is, for example, one cycle of a mechanical angle or one cycle of an electrical angle. When evaluation is performed in each unit (phase unit) of the detection signal “Hu”, the detection signal “Hv”, and the detection signal “Hw”, a reference value and a current value for a maximum value and a minimum value of each phase are compared in units of phases, so that a change in units of phases can be detected based on an evaluation value in units of phases. 
     The estimator  312  estimates degree of change in sensitivity for detecting a position on the basis of an evaluation value. For example, the estimator  312  compares a predetermined threshold with an evaluation value. In a case where an evaluation value is equal to or more than a threshold value, the estimator  312  may determine that sensitivity for detecting a position changes. 
       FIG.  5    is a diagram illustrating an example of a case where feature amounts of detection signals of all phases change in one cycle of an electrical angle in the first example embodiment. The horizontal axis represents four cycles of an electrical angle (position of the magnet  2 ). Four cycles of an electrical angle correspond to one cycle of a mechanical angle of the magnet  2 . The vertical axis represents a digital value of a detection signal. 
     In a case where a magnetic flux changes only in one pole pair of the magnet  2 , a feature amount of the detection signals (HU, HV, and HW) of all phases change in one cycle of an electrical angle associated with the pole pair. In view of the above, in a case where an evaluation value indicates that a feature amount of a detection signal changes with respect to a reference value for each position in one cycle of an electrical angle in one cycle of a mechanical angle, the estimator  312  determines that a magnetic flux of a pole pair of a magnet associated with one cycle of an electrical angle changes. For example, in a case where an evaluation value as in Equation (1) is equal to or more than a threshold value, the estimator  312  may determine that a magnetic flux of a pole pair associated with one cycle of an electrical angle changes. In  FIG.  5   , the estimator  312  determines that a magnetic flux of a pole pair associated with electrical angles from “2n” to “4n” changes. 
       FIG.  6    is a diagram illustrating an example of a case where a feature amount of a detection signal of a specific phase changes in one cycle of a mechanical angle in the first example embodiment. The horizontal axis represents four cycles of an electrical angle (position of the magnet  2 ). The vertical axis represents a digital value of a detection signal. 
     In  FIG.  6   , in one cycle of a mechanical angle, as an example, a feature amount of a detection signal of the magnetic sensor  300  of the detection signal “HU” changes with respect to a reference value for each position. As a factor of this, there are a possibility that a distance between the magnetic sensor  300  that outputs the detection signal “HU” and the magnet  2  changes, and a possibility that sensitivity of the magnetic sensor  300  that outputs the detection signal “HU” changes. 
     In view of the above, in a case where an evaluation value represents that a feature amount of the detection signal “HU” of the magnetic sensor  300  changes with respect to a reference value for each position in one cycle of a mechanical angle, the estimator  312  determines that a distance between the magnetic sensor  300  that outputs the detection signal “HU” and the magnet  2  changes. The estimator  312  may determine that sensitivity of the magnetic sensor  300  that outputs the detection signal “HU” changes. 
       FIG.  7    is a diagram illustrating an example of a case where feature amounts of detection signals of all phases change in one cycle of a mechanical angle in the first example embodiment. The horizontal axis represents four cycles of an electrical angle (position of the magnet  2 ). The vertical axis represents a digital value of a detection signal. 
     In  FIG.  7   , in one cycle of a mechanical angle, feature amounts of detection signals of all the magnetic sensors  300  change with respect to a reference value for each position. As a factor of this, there are a possibility that magnetic fluxes of all pole pairs of the magnet  2  are changed and a possibility that all the magnetic sensors  300  are separated from the magnet  2  by a predetermined distance or more. The predetermined distance is, for example, a designed distance between the magnet  2  and the magnetic sensor  300 . 
     In view of the above, in a case where an evaluation value indicates that feature amounts of the detection signals “HU”, “HV”, and “HW” of all the magnetic sensors  300  change with respect to a reference value for each position in one cycle of a mechanical angle, the estimator  312  determines that magnetic fluxes of all pole pairs of the magnet  2  change. The estimator  312  may determine that a distance between the magnet  2  and all the magnetic sensors  300  changes. The estimator  312  may determine that sensitivity of all the magnetic sensors changes. 
     The output unit  313  outputs degree of change in sensitivity for detecting a position to an external device (not illustrated). The output unit  313  may output a comparison result between degree of change in sensitivity for detecting a position and a threshold value to a predetermined external device. For example, in a case where degree of change is equal to or more than a threshold value, the output unit  313  may output a warning message to an external device (not illustrated) regarding a change in sensitivity for detecting a position. 
     Next, an operation example of the sensor assembly  1   a  will be described.  FIG.  8    is a flowchart illustrating an operation example of the sensor assembly  1   a  in the first example embodiment. Each of the magnetic sensors  300  outputs a detection signal for each position of the magnet  2  to the extractor  301  (Step S 101 ). The extractor  301  extracts a feature amount of a detection signal from the detection signal for each position of the magnet  2  (Step S 102 ). 
     The estimator  312  derives an evaluation value. The evaluation value represents a comparison result between a feature amount of a detection signal for each position of the magnet  2  and a reference value for each position of the magnet  2  (Step S 103 ). The estimator  312  estimates degree of change in sensitivity for detecting a position of the magnet  2  on the basis of an evaluation value (Step S 104 ). The output unit  313  outputs degree of change in sensitivity for detecting the position to a predetermined external device (not illustrated) (Step S 105 ). 
     As described above, the estimation device  3   a  is a device that estimates a state of the position sensor device  30  as a device that detects a position of the rotor  201  (rotating body). The estimation device  3   a  may estimate a state of the magnet  2  (for example, deterioration of a magnetic flux). The position sensor  302  outputs a detection signal, which is a signal representing a detection result of a position of the magnet  2  according to a magnetic flux of the magnet  2  rotatable in conjunction with the rotor  201  (rotating body), to the extractor  301 . The extractor  301  extracts a feature amount of a detection signal from each detection signal for each position of the magnet  2 . The estimator  312  derives an evaluation value representing a comparison result between a feature amount of a detection signal for each position of the magnet  2  and a reference value for each position of the magnet  2 . The estimator  312  estimates degree of change (for example, degradation) in sensitivity (for example, sensitivity) for detecting a position of the magnet  2  on the basis of the evaluation value. 
     As described above, the estimator  312  derives an evaluation value representing a comparison result between a feature amount of a detection signal for each position of the magnet  2  and a reference value for each position of the magnet  2 . This makes it possible to estimate degree of change in sensitivity of position detection without providing an additional dedicated sensor for estimating degree of change in sensitivity of position detection. Here, as illustrated in  FIG.  4   , degree of change in sensitivity of the magnetic sensor  300  can be detected in units of pole pairs. Further, as illustrated in  FIG.  5   , degree of change in sensitivity of the magnetic sensor  300  can be detected in units of magnetic sensors (in units of position sensors). 
       FIG.  9    is a diagram illustrating an example of a detection signal in a variation of the first example embodiment. The extractor  301  may use a digital value of each detection signal in which in-phase noise is corrected as it is as a feature amount of a detection signal as described below. 
     The storage unit  311  stores arrangement data of detection signals in such as manner as a U-phase detection signal U[i], a V-phase detection signal V[i], and a W-phase detection signal W[i]. Here, “i” represents a sample number (1 to s). A value “s” represents the number of samples in one cycle of a mechanical angle. Since the number of sample points becomes large, the storage capacity of the storage unit  311  may be increased. 
     A second example embodiment is different from the first example embodiment in that the position sensor  302  is provided in a housing of a motor. In the second example embodiment, a difference from the first example embodiment will be mainly described. 
       FIG.  10    is a diagram illustrating a configuration example of the position sensor  302  in the second example embodiment. An upper part of  FIG.  10    represents an upper surface of the position sensor  302 . A lower part of  FIG.  10    illustrates a side surface of the position sensor  302 . M of the magnetic sensors  300  are provided on the board  100  whose position is fixed. In the second example embodiment, “M” is three as an example. 
     A stator  202  is an electromagnet including a U-phase coil, a V-phase coil, and a W-phase coil. When current corresponding to a command value flows through each phase coil, a magnetic flux is generated in the stator  202 . A rotor  203  is a magnet. The stator  202  and the rotor  203  constitute a motor. The rotor  203  includes the main shaft  200 . The magnet  2  is connected to the main shaft  200 . When the rotor  203  rotates, the main shaft  200  rotates. The magnet  2  is rotatable in conjunction with the rotor  203  and the main shaft  200 . In  FIG.  10   , the main shaft  200  is arranged so as to pass through the board  100 . That is, the position sensor  302  is fixed to a housing  400  to which the stator  202  is fixed without coming into contact with the main shaft  200 . 
     Note that the magnet  2  connected to the main shaft  200  may be provided outside the housing  400 . In a case where the magnet  2  connected to the main shaft  200  is provided outside the housing  400 , the position sensor  302  is provided between the magnet  2  and the housing  400 . Further, M of the magnetic sensors  300  are provided on a surface of the board  100  of the position sensor  302  on the side close to the magnet  2 . 
     As described above, the position sensor  302  is fixed to the housing  400  to which the stator  202  is fixed without coming into contact with the main shaft  200 . The position sensor  302  outputs a detection signal, which is a signal representing a detection result of a position of the magnet  2 , to the extractor  301 . As described above, the estimator  312  derives an evaluation value representing a comparison result between a feature amount of a detection signal for each position of the magnet  2  and a reference value for each position of the magnet  2 . This makes it possible to estimate degree of change in sensitivity of position detection without providing an additional dedicated sensor in a motor for estimating degree of change in sensitivity of position detection. 
     A third example embodiment is different from the first and second example embodiments in that a rotor (magnet) of a motor is used as a magnet for a position sensor. In the third example embodiment, a difference from the first example embodiment and the second example embodiment will be mainly described. 
       FIG.  11    is a diagram illustrating a configuration example of a sensor assembly  1   b  in the third example embodiment. The sensor assembly  1   b  includes an estimation device  3   b  and a control device  4 . The estimation device  3   b  includes the position sensor device  30  and the determination device  31 . The position sensor device  30  includes M of the magnetic sensors  300  and the extractor  301 . The position sensor device  30  includes M of the magnetic sensors  300  as the position sensor  302 . In the third example embodiment, “M” is six as an example. The determination device  31  includes the control unit  310 , the storage unit  311 , the estimator  312 , and the output unit  313 . 
       FIG.  12    is a diagram illustrating a configuration example of the position sensor  302  in the third example embodiment. An upper part of  FIG.  12    represents an upper surface of the position sensor  302 . A lower part of  FIG.  12    illustrates a side surface of the position sensor  302 . 
     The stator  202  is an electromagnet including a U-phase coil, a V-phase coil, and a W-phase coil. When current corresponding to a command value flows through each phase coil, a magnetic flux is generated in the stator  202 . The rotor  203  is a magnet. The stator  202  and the rotor  203  constitute a motor. The rotor  203  includes the main shaft  200 . When the rotor  203  (magnet) rotates, the main shaft  200  rotates. In  FIG.  12   , the main shaft  200  is arranged so as to pass through the board  100 . That is, the position sensor  302  is fixed to the housing  400  to which the stator  202  is fixed without coming into contact with the main shaft  200 . The rotor  203  is used as a magnet for a position sensor that detects a position of the rotor  203  as a substitute for the magnet  2 . The control device  4  determines a current value to be applied to the stator  202  (electromagnet) based on command values such as a rotational speed and a torque value and position information (angle information) of the rotor  203  (magnet) obtained from the position sensor device  30 . The control device  4  generates a magnetic field by causing current to flow through the stator  202  (electromagnet) based on a determined current value, and controls driving of the rotor  203 . 
     M of the magnetic sensors  300  are provided on the board  100  whose position is fixed. In the third example embodiment, “M” is six as an example. The magnetic sensors  300 - 1  to  300 - 3  (a plurality of first magnetic sensors) are provided near a magnet defining the rotor  203 . Magnetic sensors  300 - 4  to  300 - 6  (a plurality of second magnetic sensors) are provided in the vicinity of the stator  202  at a distance from the main shaft  200  larger than a distance between the magnetic sensors  300 - 1  to  300 - 3  and the main shaft  200 . In  FIG.  12   , the magnetic sensor  300 - 4 , the magnetic sensor  300 - 1 , and the main shaft  200  are arranged on a straight line. The magnetic sensor  300 - 5 , the magnetic sensor  300 - 2 , and the main shaft  200  are arranged on a straight line. The magnetic sensor  300 - 6 , the magnetic sensor  300 - 3 , and the main shaft  200  are arranged on a straight line. 
     The magnetic sensors  300 - 1  to  300 - 3  detect magnetic fluxes from both the rotor  203  (magnet) and the stator  202  (electromagnet), and output a detection signal to the extractor  301 . A detection signal output from any of the magnetic sensors  300 - 1  to  300 - 3  is expressed by Equation (2). 
     The magnetic sensors  300 - 4  to  300 - 6  also detect magnetic fluxes from both the rotor  203  (magnet) and the stator  202  (electromagnet), and output a detection signal to the extractor  301 . A detection result of a magnetic flux component output from any of the magnetic sensors  300 - 4  to  300 - 6  is expressed as Equation (3). 
       [Equation 2] 
         V   HA (θ) =x*φ   m (θ) +j*φ   s (θ, I )  (2)
 
       [Equation 3] 
         V   HB (θ)= y*φ   m (θ)+ k*φ   s (θ, I )  (3)
 
     Here, “VHA” represents a detection signal (magnetic flux component amount) output from any of the magnetic sensors  300 - 1  to  300 - 3 . “VHB” represents a detection result (detection result of a magnetic flux component) output from any of the magnetic sensors  300 - 4  to  300 - 6 . A value “φs(θ,I)” represents a magnetic flux component (leakage magnetic flux component) of the stator  202 . A value “φm (θ)” represents a magnetic flux component of the rotor  203 . A value “θ” represents an electrical angle of the rotor  203 . A value “I” represents a value of current flowing through a coil of the stator  202 . 
     Coefficients “x”, “y”, “j”, and “k” are coefficients depending on a structure of a motor and arrangement of a magnetic sensor, and are determined on the basis of results of experiments or simulations, for example. The coefficient “x” is a coefficient in a term of a magnetic flux of the rotor  203 , and is, for example, a coefficient corresponding to each distance between the magnetic sensors  300 - 1  to  300 - 3  and the rotor  203 . The coefficient “y” is a coefficient in a term of a magnetic flux of the stator  202 , and is, for example, a coefficient corresponding to each distance between the magnetic sensors  300 - 4  to  300 - 6  and the rotor  203 . 
     The coefficient “j” is a coefficient in a term of a magnetic flux of the stator  202 , and is, for example, a coefficient corresponding to each distance between the magnetic sensors  300 - 1  to  300 - 3  and the stator  202 . The coefficient “k” is a coefficient in a term of a magnetic flux of the stator  202 , and is, for example, a coefficient corresponding to each distance between the magnetic sensors  300 - 4  to  300 - 6  and the stator  202 . 
     In view of the above, using a detection result of a magnetic flux component of the stator  202 , the extractor  301  extracts a signal representing a detection result of a magnetic flux component of only the stator  202  from each of detection signals output from the magnetic sensors  300 - 1  to  300 - 6 . The detection result (correction value) of the magnetic flux component of only the stator  202  is expressed as the right side of Equation (4). For example, based on the detection signal “VHA” output from the magnetic sensor  300 - 1  and the detection signal (magnetic flux component amount) “VHB” output from the magnetic sensor  300 - 4 , the extractor  301  derives a detection result of a magnetic flux component of only the stator  202  as indicated on the right side of Equation (4). 
     
       
         
           
             
               
                 
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     The extractor  301  acquires a command value of an amount of current flowing in the stator  202  from the control device  4 . The extractor  301  derives an estimated value of a magnetic flux component of only the stator  202  based on the command value of an amount of current flowing in the stator  202 . The estimator  312  can estimate a state of the stator  202  by comparing the estimated value of the magnetic flux component of only the stator  202  with a detection result of the magnetic flux component of only the stator  202 . A magnetic flux component of the stator  202  is measured at the time of assembly or shipment from a factory, and is stored in the storage unit  311  in advance. The estimator  312  can also estimate a state of the stator  202  by comparing a magnetic flux component of the stator  202  stored in advance in the storage unit  311  with a detected magnetic flux component. 
     As described above, the estimation device  3   b  is a device that estimates a state of the position sensor device  30  as a device that detects a position of the rotor  203  (rotating body) and a state of the stator  202 . The estimation device  3   b  may estimate a state of the rotor  203  (for example, deterioration of a magnetic flux). The estimator  312  estimates degree of change in the stator  202  based on a difference between an estimated value of a magnetic flux component of the stator  202  based on current flowing through the stator  202  and a detection result of a magnetic flux component of only the stator  202 . This makes it possible to improve sensitivity for estimating degree of change in sensitivity of position detection without providing an additional dedicated sensor for estimating degree of change in sensitivity of position detection. 
     A fourth example embodiment is different from the first to third example embodiments in that a sensor assembly includes a plurality of position sensor devices and a single determination device (the determination device is a center determination type). In the fourth example embodiment, a difference from the first to third example embodiments will be mainly described. 
       FIG.  13    is a diagram illustrating a configuration example of a sensor assembly  1   c  in the fourth example embodiment. The sensor assembly  1   c  includes P (P is an integer of two or more) of the magnets  2  and an estimation device  3   c . The estimation device  3   c  includes P of the position sensor devices  30  and the determination device  31 . The position sensor device  30  includes M of the magnetic sensors  300  and the extractor  301 . The position sensor device  30  includes M of the magnetic sensors  300  as the position sensor  302 . The determination device  31  includes the control unit  310 , the storage unit  311 , the estimator  312 , and the output unit  313 . 
     A position sensor  302 - p  (p is any integer from two to P) outputs a detection signal, which is a signal representing a detection result of a position of a magnet  2 - p  (a magnetic flux component of a pole pair), to the extractor  301 . The extractor  301  reduces in-phase noise in each detection signal. The extractor  301  extracts a feature amount of a detection signal from each detection signal for each position of the magnet  2 . The extractor  301  outputs a feature amount (array data) of a detection signal for each position to the estimator  312  and the control unit  310 . 
     As described above, the estimation device  3   c  is a device that estimates a state of the position sensor device  30  as a device that detects a position of the rotor  201  or the rotor  203  (rotating body). The estimation device  3   c  may estimate a state of the magnet  2 . The number of the magnets  2  is plural. The position sensor device  30  includes the position sensor  302  for each of the magnets  2 . This makes it possible to improve degree of change in sensitivity of position detection for a plurality of the magnets  2  without providing an additional dedicated sensor for estimating degree of change in sensitivity of position detection. 
     Further, it is possible to estimate a change in the stator  202  (change in a magnetic flux). It is possible to estimate a change in distance between the stator  202  and the magnetic sensor  300 . It is possible to estimate a state of the stator  202 . The state of the stator  202  is, for example, a change in resistance of a winding wire of a slot, the presence or absence of disconnection, a change in an amount of current due to a temperature rise, a change in an amount of a magnetic flux component, or the like. Note that, in the second example embodiment described above, an additional one of the magnetic sensor  300  may be provided on the board  100 . The additional one of the magnetic sensor  300  is able to detect changes in magnetic flux such that a state of the stator  202 , including a magnitude of the leakage flux of the stator  202 , can be estimated. 
     The procedure of each processing may be performed by recording a program for implementing the function of the estimation device in the present disclosure on a computer-readable recording medium (not illustrated), and causing a computer system to read the program recorded on the recording medium (non-transitory recording medium) to execute the program. Note that the “computer system” described here includes an OS and hardware such as peripheral devices. The “computer system” also includes a WWW system provided with a website provision environment (or display environment). The “computer-readable recording medium” refers to portable media such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and storage devices such as a hard disk incorporated into a computer system. Furthermore, the “computer-readable recording medium” shall include those hold a program for a certain period of time such as a volatile memory (RAM) in a computer system serving as a server or a client in a case where a program is transmitted via a network such as the Internet or a communication line such as a telephone line. 
     Further, the program described above may be transmitted from a computer system in which this program is stored in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” transmitting a program refers to a medium having a function of transmitting information such as a network (communication network) such as the Internet or a communication line such as a telephone line. Further, the program described above may be for implementing a part of the function described above. Furthermore, the program may be what is called a difference file (difference program), which can implement the above-described function in combination with a program already recorded in the computer system. 
     Features of the above-described example embodiments and the modifications thereof may be combined appropriately as long as no conflict arises. 
     While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.