# Patent

## Title
Planar motor rotor displacement measuring device and its measuring method

## Abstract

A planar motor rotor displacement measuring device and its measuring method are provided. The motor is a moving-coil type planar motor. The device comprises probes, two sets of sine sensors, two sets of cosine sensors, a signal lead wire and a signal processing circuit. The method is arranging two sets of magnetic flux density sensors within a magnetic field pitch τ along two vertical movement directions in the rotor located in the sine magnetic field area. Sampled signals of the four sets of sensors are respectively processed with a frequency multiplication operation, four subdivision signals are obtained, the zero-crossing points of the four subdivision signals are detected, and then two sets of orthogonal pulse signals are generated. The pulse number of the orthogonal pulse signals is counted, and phase difference of the two sets of orthogonal pulse signals is respectively detected.

## Background
TECHNICAL FIELD
The invention relates to a rotor displacement measuring device for a planar motor including the sine magnetic field model and the like, and its measuring method, particularly to a subdivision displacement measuring device and computing method with relatively a long moving range and high resolution.
BACKGROUND ART
In the two-dimensional positioning and machining devices, especially the modern semiconductor micromachining equipments, and other ultra-precision machining equipments, the high-precise movement is typically implemented by the planar motor. The planar motor has attracted much attention in both the academe and the industry because of its advantages such as its quick response, high sensitivity and simple structure. Chinese Patents No. 201110045692.8, No. 200910029368.X and No. 200910088894.3 have described several types of planar motors with different structures in detail.
Currently, the detection for the rotor position of the planar motor is usually performed by the optical measurement method such as using the grating and the laser interferometer. According to Chinese Patent No. 200880111964.6, the movement measurement for the planar motor is performed with a two-dimensional grating, in which a planar grating of a larger area is required to be installed in the planar motor so as to generate optical signals with displacement information to communicate with optical sensors, and the requirement for operating environment is higher, and the surfaces of the grating ruler must be protected and prevented from being polluted; according to Chinese Patent No. 201110040403.5, the grating sensor is adopted to detect the moving position in two directions, and in each direction, a main scale and its corresponding reading head, which must meet the measuring range requirement, are required to be installed to generate Moire fringe signals or other types of optical signals with the displacement information, and the requirement for operating environment is also high; and according to Chinese Patent No. 200910029828.9, a laser position sensor is adopted to perform measurement for movement of the planar motor through laser triangulation methods or echo analysis, but the preciseness of the measurement is strongly affected by the environment, and it is difficult to guarantee high preciseness under long moving range and the signal processing is not simple and quick at the same time.
Therefore, it is desirable to develop a newly planar motor rotor displacement measuring method, which has advantages of reducing complexity of installation of the sensor, having high preciseness under long moving range and simple and quick signal processing.
SUMMARY
The present invention aims to provide a planar motor rotor displacement measuring device and measuring method thereof, which provides highly precise displacement measurement of the motor's rotor in a long moving range in a plane in two degrees-of-freedom, and can directly output orthogonal coding signals commonly used in the industry.
In order to achieve the above object, the present invention provides the following technical solution:
A planar motor rotor displacement measuring device, where the planar motor is a moving-coil type planar motor comprising a stator and a rotor on the stator, the stator includes a magnetic steel array, and a coil array is arranged on the lower surface of the rotor; the displacement measuring device comprises a probe, two sets of sine sensors, two sets of cosine sensors, a signal lead wire and a signal processing circuit; the probe is arranged at the edge of the rotor which is located in the sine magnetic field area generated by the magnetic steel array of the stator of the moving-coil type planar motor; the two sets of sine sensors include an x-direction sine sensor set and a y-direction sine sensor set, the two sets of cosine sensors include an x-direction cosine sensor set and a y-direction cosine sensor set; the sensors are arranged in the probe in such a manner, firstly, one sensor is arranged in the probe as the reference sensor, my sensors in total including the reference sensor are uniformly arranged within a magnetic field pitch τ along the x-direction, forming the y-direction sine sensor set; taking the reference sensor as the first sensor, mx sensors in total including the reference sensor are uniformly arranged within a magnetic field pitch τ along the y-direction, forming the x-direction sine sensor set; beginning at the distance τ/4 from the reference sensor in the y-direction, my sensors are uniformly arranged within a magnetic field pitch τ along the x-direction, forming the y-direction cosine sensor set; beginning at the distance τ/4 from the reference sensor in the x-direction, mx sensors are uniformly arranged within a magnetic field pitch τ along the y-direction, forming the x-direction cosine sensor set, where mx=2, 3, 4, . . . , my=2, 3, 4, . . . ; the signal processing circuit is connected with the output of the probe via the signal lead wire; the signal processing circuit includes an analog signal processing unit and a digital signal processing unit; and the magnetic field pitch τ is the spatial period of the sine magnetic field of the planar motor.
A moving-coil type planar motor rotor displacement measuring method, the method includes:
1) sampled signals of the x-direction sine sensor set, sampled signals of the x-direction cosine sensor set, sampled signals of the y-direction sine sensor set and sampled signals of the y-direction cosine sensor set are processed by the analog signal processing unit of the signal processing circuit, so as to obtain the x-direction sine measurement signal SX0, the x-direction cosine measurement signal CX0, the y-direction sine measurement signal SY0 and the y-direction cosine measurement signal CY0 respectively;
2) the x-direction sine measurement signal SX0 and the x-direction cosine measurement signal CX0 are processed with nX frequency multiplication operations by the digital signal processing unit of the signal processing circuit so as to obtain the x-direction sine subdivision signal SXnX and the x-direction cosine subdivision signal CX,nX:




  
    
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where SX1, CX1, SX2, CX2, . . . , SX,nX-1 and CX,nX-1 are intermediate variables, nx=1, 2, 3, . . . ;
also, the y-direction sine measurement signal SY0 and the y-direction cosine measurement signal CY0 are processed with nY frequency multiplication operations by the signal processing circuit so as to obtain the y-direction sine subdivision signal SYnY and the y-direction cosine subdivision signal CYnY:




  
    
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where SY1, CY1, SY2, CY2 . . . SY,nY-1 and CY,nY-1 are intermediate variables, nY=1, 2, 3, . . . ;
3) the zero-crossing points of the x-direction sine subdivision signal SXnX and the x-direction cosine subdivision signal CXnX obtained at step 2) are detected by the digital signal processing unit of the signal processing circuit respectively, generating a set of x-direction orthogonal pulse signals, that is, the x-direction sine pulse signal AX and x-direction cosine pulse signal BX; also, the zero-crossing points of the y-direction sine subdivision signal SYnY and the y-direction cosine subdivision signal CYnY obtained at step 2) are detected respectively, generating a set of y-direction orthogonal pulse signals, that is, the y-direction sine pulse signal AY and y-direction cosine pulse signal BY;
4) if the x-direction sine subdivision signal SXnX>0, then the output of the x-direction sine pulse signal AX is of high level; if the x-direction sine subdivision signal SXnX<0, then the output of the x-direction sine pulse signal AX is of low level; and if the x-direction sine subdivision signal SXnX>0, then the output of the x-direction sine pulse signal AX remains unchanged; and if the x-direction cosine subdivision signal CXnX>0, then the output of the x-direction cosine pulse signal BX is of high level; if the x-direction cosine subdivision signal CXnX<0, then the output of the x-direction cosine pulse signal BX is of low level; and if the x-direction cosine subdivision signal CXnX=0, then the output of the x-direction cosine pulse signal BX remains unchanged;
5) if the y-direction sine subdivision signal SYnY>0, then the output of the y-direction sine pulse signal AY is of high level; if the y-direction sine subdivision signal SYnY<0, then the output of the y-direction sine pulse signal AY is of low level; and if the y-direction sine subdivision signal SYnY=0, then the output of the y-direction sine pulse signal AY remains unchanged; and if the y-direction cosine subdivision signal CYnY>0, then the output of the y-direction cosine pulse signal BY is of high level; if the y-direction cosine subdivision signal CYnY<0, then the output of the y-direction cosine pulse signal BY is of low level; and if the y-direction cosine subdivision signal CYnY=0, then the output of the y-direction cosine pulse signal BY remains unchanged;
6) the pulse numbers of the x-direction sine pulse signal AX or the x-direction cosine pulse signal BX obtained at step 3) are counted by the digital signal processing unit of the signal processing circuit, and the phase difference between the x-direction sine pulse signal AX and the x-direction cosine pulse signal BX is detected; taking one pulse of the x-direction sine pulse signal AX or the x-direction cosine pulse signal BX as an x-direction displacement resolution




  
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nX=1, 2, 3, . . . , if the phase of the x-direction sine pulse signal AX is behind the phase of the x-direction cosine pulse signal BX, then it indicates that it is the forward displacement; and if the phase of the x-direction sine pulse signal AX is ahead of the phase of the x-direction cosine pulse signal BX, then it indicates that it is the backward displacement, in such a way, the x-direction displacement of the rotor of the planar motor is measured;

7) the pulse numbers of the y-direction sine pulse signal AY or the y-direction cosine pulse signal BY obtained at step 3) are counted by the digital signal processing unit of the signal processing circuit, and the phase difference between the y-direction sine pulse signal AY and the y-direction cosine pulse signal BY is detected; taking one pulse of the y-direction sine pulse signal AY or the y-direction cosine pulse signal BY as a y-direction displacement resolution




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nY=1, 2, 3, . . . , if the phase of the y-direction sine pulse signal AY is behind the phase of the y-direction cosine pulse signal BY, then it indicates that it is the forward displacement; and if the phase of the y-direction sine pulse signal AY is ahead of the phase of the y-direction cosine pulse signal BY, then it indicates that it is the backward displacement, in such a way, the y-direction displacement of the rotor of the planar motor is measured.

The invention is characterized in that, nX can be determined as follows:
given that the BXM is the magnitude of the magnetic induction intensity along the x-direction of the sine magnetic field generated by the magnetic steel array of the stator of the planar motor, and vx is the noise in the sensor measurement along the x-direction, then the maximized number of times of frequency multiplication operations along the x-direction is




  
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nY described at step 2) can be determined as follows:
given that the BYM is the magnitude of the magnetic induction intensity along the y-direction of the sine magnetic field generated by the magnetic steel array of the stator of the planar motor, and vy is the noise in the sensor measurement along the y-direction, then the maximized number of times of frequency multiplication operations along the y-direction is




  
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Compared with the prior art, the invention has the following advantages: The method only involves simple subtraction and multiplication to derive the displacement information contained in the magnetic field signals and it directly utilize the sine magnetic field of the motor itself without need of solving non-linear equations, which makes the calculation simple and quick; and for the device, it doesn't need to configure the components for generating the signals containing displacement information, which can lower the production cost significantly; and when increasing the moving range, it only needs to increase the dimension of the stator and doesn't affect the resolution for the displacement, which may achieve the planar motor rotor displacement measurement of long moving range and high precision.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic view of the overall structure of the displacement measuring device according to the present invention.
FIG. 2 is a bottom view seen from bottom to top of the probe in which mx=my=4 according to the present invention.
FIGS. 3a and 3b are waveform schematic views of the x-direction sine and cosine measurement signals, x-direction sine and cosine subdivision signals and x-direction sine and cosine pulse signals when nx=4 according to the present invention.
FIGS. 4a and 4b are schematic views of two sets of orthogonal pulse signals of the rotor displacement during the measurement according to the present invention.



The main numerals used in the drawings are:

    
    
        1 stator
        2 magnetic steel array
        3 rotor
        4 coil array
        5 probe
        6 signal lead wire
        7 signal processing circuit
        8 x-direction sine sensor set
        9 x-direction cosine sensor set
        10 y-direction sine sensor set
        11 y-direction cosine sensor set
        12 reference sensor
    
    


MODE FOR THE INVENTION
In the following, the embodiments of the invention will be further described in detail in conjunction with the accompanying drawings.
Referring to FIGS. 1 and 2, the planar motor described in the invention is a moving-coil type planar motor comprising a stator 1 and a rotor 3 on the stator 1; the stator 1 includes a magnetic steel array 2, and a coil array 4 is arranged on the lower surface of the rotor 3; the displacement measuring device comprises a probe 5, two sets of sine sensors, two sets of cosine sensors, a signal lead wire 6 and a signal processing circuit 7; the probe 5 is arranged at the edge of the rotor 3 which is located in the sine magnetic field area formed by the magnetic steel array of the stator of the moving-coil type planar motor; the two sets of sine sensors include an x-direction sine sensor set 8 and a y-direction sine sensor set 10, the two sets of cosine sensors include an x-direction cosine sensor set 9 and a y-direction cosine sensor set 11; the sensors are arranged in the probe 5 in such a manner, firstly, a sensor is arranged in the probe 5 as the reference sensor 12, my sensors in total including the reference sensor 12 are uniformly arranged within a magnetic field pitch τ along the x-direction, forming the y-direction sine sensor set; taking the reference sensor 12 as the first sensor, mx sensors in total including the reference sensor 12 are uniformly arranged within a magnetic field pitch τ along the y-direction, forming the x-direction sine sensor set; beginning at the distance τ/4 from the reference sensor 12 in the y-direction, my sensors are uniformly arranged within a magnetic field pitch τ along the x-direction, forming the y-direction cosine sensor set; beginning at the distance τ/4 from the reference sensor 12 in the x-direction, mx sensors are uniformly arranged within a magnetic field pitch τ along the y-direction, forming the x-direction cosine sensor set, where mx=2, 3, 4, . . . , my=2, 3, 4, . . . ; the signal processing circuit 7 is connected with the output of the probe 5 via the signal lead wire 6; the signal processing circuit 7 includes an analog signal processing unit and a digital signal processing unit; and the magnetic field pitch τ is the spatial period of the sine magnetic field of the planar motor.
Referring to FIGS. 3a and 3b, taking the case in which the rotor 3 is in the uniform motion along the x-direction as an example, the waveforms of the x-direction sine measurement signal SX0, the x-direction sine subdivision signal SX4, the x-direction sine pulse signal AX, and the waveforms of the x-direction cosine measurement signal CX0, the x-direction cosine subdivision signal CX4, and the x-direction cosine pulse signal BX during the rotor movement when nX=4 are presented respectively.
Referring to FIGS. 4a and 4b, the measurement of the x-direction displacement with the x-direction sine pulse signal AX and the x-direction cosine pulse signal BX, and the measurement of the y-direction displacement with the y-direction sine pulse signal AY and the y-direction cosine pulse signal BY are presented respectively.
The planar motor rotor displacement measuring method described in the invention includes the following steps:
1) sampled signals of the x-direction sine sensor set, sampled signals of the x-direction cosine sensor set, sampled signals of the y-direction sine sensor set and sampled signals of the y-direction cosine sensor set are processed by the analog signal processing unit of the signal processing circuit, so as to obtain the x-direction sine measurement signal SX0, the x-direction cosine measurement signal CX0, the y-direction sine measurement signal SY0 and the y-direction cosine measurement signal CY0 respectively;
2) the x-direction sine measurement signal SX0 and the x-direction cosine measurement signal CX0 are processed with nX frequency multiplication operations by the digital signal processing unit of the signal processing circuit so as obtain the x-direction sine subdivision signal SXnX and the x-direction cosine subdivision signal CXnX:




  
    
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where SX1, CX1, SX2, Cx2, . . . , SX,nX-1 and CX,nX-1 are intermediate variables, nX=1, 2, 3, . . . ;

also, the y-direction sine measurement signal SY0 and the y-direction cosine measurement signal CY0 are processed with nY frequency multiplication operations by the signal processing circuit so as to obtain the y-direction sine subdivision signal SYnY and the y-direction cosine subdivision signal CYnY:





  
    
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  ⁢
  
    
      S
      
        Y
        ⁢
        
          
        
        ⁢
        2
      
    
    =
    
      2
      *
      
        S
        
          Y
          ⁢
          
            
          
          ⁢
          1
        
      
      *
      
        C
        
          Y
          ⁢
          
            
          
          ⁢
          1
        
      
    
  
  ,
  
    
      C
      
        Y
        ⁢
        
          
        
        ⁢
        2
      
    
    =
    
      
        
          C
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
        *
        
          C
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
      
      -
      
        
          S
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
        *
        
          S
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
      
    
  
  ,
  
    

  
  ⁢
  ...
  ⁢
  
    
  
  ,
  
    

  
  ⁢
  
    
      S
      
        Yn
        Y
      
    
    =
    
      2
      *
      
        S
        
          Y
          ,
          
            
              n
              Y
            
            -
            1
          
        
      
      *
      
        C
        
          Y
          ,
          
            
              n
              Y
            
            -
            1
          
        
      
    
  
  ,
  
    

  
  ⁢
  
    
      C
      
        Yn
        Y
      
    
    =
    
      
        
          C
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
        *
        
          C
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
      
      -
      
        
          S
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
        *
        
          S
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
      
    
  
  ,




where SY1, CY1, SY2, CY2, . . . , SY,nY-1 and CY,nY-1 are intermediate variables, nX=1, 2, 3, . . . ;

3) the zero-crossing points of the x-direction sine subdivision signal SXnX and the x-direction cosine subdivision signal CXnX obtained at step 2) are detected by the digital signal processing unit of the signal processing circuit respectively, generating a set of x-direction orthogonal pulse signals, that is, the x-direction sine pulse signal AX and x-direction cosine pulse signal BX; also, the zero-crossing points of the y-direction sine subdivision signal SYnY and the y-direction cosine subdivision signal CYnY obtained at step 2) are detected respectively, generating a set of y-direction orthogonal pulse signals, that is, the y-direction sine pulse signal AY and y-direction cosine pulse signal BY;
4) if the x-direction sine subdivision signal SXnX>0, then the output of the x-direction sine pulse signal AX is of high level; if the x-direction sine subdivision signal SXnX<0, then the output of the x-direction sine pulse signal AX is of low level; and if the x-direction sine subdivision signal SXnX=0, then the output of the x-direction sine pulse signal AX remains unchanged; if the x-direction cosine subdivision signal CXnX>0, then the output of the x-direction cosine pulse signal BX is of high level; if the x-direction cosine subdivision signal CXnX<0, then the output of the x-direction cosine pulse signal BX is of low level; and if the x-direction cosine subdivision signal CXnX=0, then the output of the x-direction cosine pulse signal BX remains unchanged;
5) if the y-direction sine subdivision signal SYnY>0, then the output of the y-direction sine pulse signal AY is of high level; if the y-direction sine subdivision signal SYnY<0, then the output of the y-direction sine pulse signal AY is of low level; and if the y-direction sine subdivision signal SYnY=0, then the output of the y-direction sine pulse signal AY remains unchanged; and if the y-direction cosine subdivision signal CYnY>0, then the output of the y-direction cosine pulse signal BY is of high level; if the y-direction cosine subdivision signal CYnY<0, then the output of the y-direction cosine pulse signal BY is of low level; and if the y-direction cosine subdivision signal CYnY=0, then the output of the y-direction cosine pulse signal BY remains unchanged;
6) the pulse numbers of the x-direction sine pulse signal AX or the x-direction cosine pulse signal BX obtained at step 3) are counted by the digital signal processing unit of the signal processing circuit, and the phase difference between the x-direction sine pulse signal AX and the x-direction cosine pulse signal BX is detected; taking one pulse of the x-direction sine pulse signal AX or the x-direction cosine pulse signal BX as an x-direction displacement resolution




  τ
  
    2
    
      n
      X
    
  




where nX=1, 2, 3, . . . ; if the phase of the x-direction sine pulse signal AX is behind the phase of the x-direction cosine pulse signal BX, then it indicates that it is the forward displacement; if the phase of the x-direction sine pulse signal AX is ahead of the phase of the x-direction cosine pulse signal BX, then it indicates that it is the backward displacement, in such a way, the x-direction displacement of the rotor of the planar motor is measured;

7) the pulse numbers of the y-direction sine pulse signal AY or the y-direction cosine pulse signal BY obtained at step 3) are counted by the digital signal processing unit of the signal processing circuit, and the phase difference between the y-direction sine pulse signal AY and the y-direction cosine pulse signal BY is detected; taking one pulse of the y-direction sine pulse signal AY or the y-direction cosine pulse signal BY as an y-direction displacement resolution




  τ
  
    2
    
      n
      Y
    
  




nY=1, 2, 3, . . . ; if the phase of the y-direction sine pulse signal AY is behind the phase of the y-direction cosine pulse signal BY, then it indicates that it is the forward displacement; if the phase of the y-direction sine pulse signal AY is ahead of the phase of the y-direction cosine pulse signal BY, then it indicates that it is the backward displacement, in such a way, the y-direction displacement of the rotor of the planar motor is measured.

nX described at step 2) can be determined as follows:
given that the BXM is the magnitude of the magnetic induction intensity along the x-direction of the sine magnetic field generated by the magnetic steel array of the stator of the planar motor, and vx is the noise in the sensor measurement noise along the x-direction, then the maximized number of times of frequency multiplication operations along the x-direction is




  
    
      n
      X
    
    =
    
      [
      
        
          
            log
            2
          
          ⁡
          
            (
            
              
                B
                XM
              
              
                v
                x
              
            
            )
          
        
        -
        3
      
      ]
    
  
  ;




nY described at step 2) can be determined as follows:
given that the BYM is the magnitude of the magnetic induction intensity along the y-direction of the sine magnetic field generated by the magnetic steel array of the stator of the planar motor, and vy is the noise in the sensor measurement along the y-direction, then the maximized number of times of frequency multiplication operations along the y-direction is




  
    n
    Y
  
  =
  
    
      [
      
        
          
            log
            2
          
          ⁡
          
            (
            
              
                B
                YM
              
              
                v
                y
              
            
            )
          
        
        -
        3
      
      ]
    
    .
  




The embodiment:
for example, mx=my=4, the magnetic field pitch τ=35.35 mm, according to the formula of the maximized number of times of frequency multiplication operations, taking nX=nY=4, the device and method of the invention are implemented.
The device can be seen from FIG. 1, the planar motor described in the invention is a moving-coil type planar motor comprising a stator 1 and a rotor 3 on the stator 1, the stator 1 includes a magnetic steel array 2, and a coil array 4 is arranged on the lower surface of the rotor 3; the displacement measuring device comprises a probe 5, two sets of sine sensors, two sets of cosine sensors, a signal lead wire 6 and a signal processing circuit 7; the probe 5 is arranged at the edge of the rotor 3 which is located in the sine magnetic field area generated by the magnetic steel array of the stator of the moving-coil type planar motor; the two sets of sine sensors include an x-direction sine sensor set 8 and a y-direction sine sensor set 10, the two sets of cosine sensors include an x-direction cosine sensor set 9 and a y-direction cosine sensor set 11; a probe 5 is arranged at the edge of the rotor which is located in the sine magnetic field area generated by the magnetic steel array of the stator of the moving-coil type planar motor; referring to FIG. 2, the sensors are arranged in the probe 5 in such a manner, firstly, one sensor is arranged in the probe 5 as the reference sensor 12, and then one sensor is arranged every τ/4 along a pitch τ within the magnetic field, i.e., the x-direction, 4 sensors in total including the reference sensor are arranged, forming the y-direction sine sensor set; taking the reference sensor as the first sensor, one sensor is arranged every τ/4 along another pitch τ within the magnetic field, i.e., the y-direction, 4 sensors in total including the reference sensor are arranged, forming the x-direction sine sensor set; beginning at the distance τ/4 from the reference sensor 12 in the y-direction, one sensor is arranged every τ/4 along the x-direction, 4 sensors in total, forming the y-direction cosine sensor set; beginning at the distance τ/4 from the reference sensor 12 in the x-direction, one sensor is arranged every τ/4 along the y-direction, 4 sensors in total, forming the x-direction cosine sensor set, where τ/4 is 8.8375 mm.
The method includes:
1) sampled signals of the x-direction sine sensor set, sampled signals of the x-direction cosine sensor set, sampled signals of the y-direction sine sensor set and sampled signals of the y-direction cosine sensor set are processed by the analog signal processing unit of the signal processing circuit, so as to obtain the x-direction sine measurement signal SX0, the x-direction cosine measurement signal CX0, the y-direction sine measurement signal SY0 and the y-direction cosine measurement signal CY0 respectively;
2) the x-direction sine measurement signal SX0 and the x-direction cosine measurement signal CX0 are processed with nX=4 frequency multiplication operations, i.e. 24 subdivision operations by the digital signal processing unit of the signal processing circuit:

SX1=2*SX0*CX0,CX1=CX0*−CX0−SX0*SX0,

SX2=2*SX1*CX1,CX2=CX1*−CX1−SX1*SX1,

SX3=2*SX2*CX2,CX3=CX2*−CX2−SX2*SX2,

SX4=2*SX3*CX3,CX4=CX3*−CX3−SX3*SX3,

so as to obtain the x-direction sine subdivision signal SX4 and the x-direction cosine subdivision signal CX4, where SX1, CX1, SX2, CX2, SX3 and CX3 are intermediate variables, also, the y-direction sine measurement signal SY0 and the y-direction cosine measurement signal CY0 are processed with nY=4 frequency multiplication operations, i.e. 24 subdivision operations by the signal processing circuit:

SY1=2*SY0*CY0,CY1=CY0*CY0−SY0*SY0,

SY2=2*SY1*CY1,CY2=CY1*CY1−SY1*SY1,

SY3=2*SY2*CY2,CY3=CY2*CY2−SY2*SY2,

SY4=2*SY3*CY3,CY4=CY3*CY3−SY3*SY3,

so as to obtain the y-direction sine subdivision signal SY4 and the y-direction cosine subdivision signal CY4, where SY1, CY1, SY2, CY2, SY3 and CY3 are intermediate variables;

3) The zero-crossing points of the x-direction sine subdivision signal SX8 and the x-direction cosine subdivision signal CX8 are detected by the digital signal processing unit of the signal processing circuit respectively, generating a set of x-direction orthogonal pulse signals, that is, the x-direction sine pulse signal AX and x-direction cosine pulse signal BX; also, the zero-crossing points of the y-direction sine subdivision signal SY8 and the y-direction cosine subdivision signal CY8 are detected respectively, generating a set of y-direction orthogonal pulse signals, that is, the y-direction sine pulse signal AY and y-direction cosine pulse signal BY;
4) referring to FIGS. 3a and 3b, if the x-direction sine subdivision signal SX8>0, then the output of the x-direction sine pulse signal AX is of high level; if the x-direction sine subdivision signal SX8<0, then the output of the x-direction sine pulse signal AX is of low level; if the x-direction sine subdivision signal SX8=0, then the output of the x-direction sine pulse signal AX remains unchanged; and if the x-direction cosine subdivision signal CX8>0, then the output of the x-direction cosine pulse signal BX is of high level; if the x-direction cosine subdivision signal CX8<0, then the output of the x-direction cosine pulse signal BX is of low level; if the x-direction cosine subdivision signal CX8=0, then the output of the x-direction cosine pulse signal BX remains unchanged;
5) if the y-direction sine subdivision signal SY8>0, then the output of the y-direction sine pulse signal AY is of high level; if the y-direction sine subdivision signal SY8<0, then the output of the y-direction sine pulse signal AY is of low level; if the y-direction sine subdivision signal SY8=0, then the output of the y-direction sine pulse signal AY remains unchanged; and if the y-direction cosine subdivision signal CY8>0, then the output of the y-direction cosine pulse signal BY is of high level; if the y-direction cosine subdivision signal CY8<0, then the output of the y-direction cosine pulse signal BY is of low level; if the y-direction cosine subdivision signal CY8=0, then the output of the y-direction cosine pulse signal BY remains unchanged;
6) referring to FIG. 4a, the pulse number of the x-direction cosine pulse signal BX is counted by the digital signal processing unit of the signal processing circuit, and the pulse number at time t is 4 with respect to time 0, indicating the displacement is




  
    
      4
      *
      
        τ
        
          2
          
            n
            ⁢
            
              
            
          
        
      
    
    =
    
      
        4
        *
        
          
            35.35
            ⁢
            
              
            
            ⁢
            mm
          
          
            2
            8
          
        
      
      =
      
        0.5523
        ⁢
        
          
        
        ⁢
        mm
        ⁢
        
          
        
        ⁢
        long
      
    
  
  ,




and the phase of the x-direction sine pulse signal AX is ahead of the phase of the x-direction cosine pulse signal BX, indicating the backward displacement, so in FIG. 4a, the displacement in the x-direction at time t with respect to time 0 is −0.5523 mm;

referring to FIG. 4b, the pulse number of the y-direction sine pulse signal AY is counted by the digital signal processing unit of the signal processing circuit, and the pulse number at time t is 3 with respect to time 0, indicating the displacement is




  
    
      3
      *
      
        τ
        
          2
          n
        
      
    
    =
    
      
        3
        *
        
          
            35.35
            ⁢
            
              
            
            ⁢
            mm
          
          
            2
            8
          
        
      
      =
      
        0.4143
        ⁢
        
          
        
        ⁢
        mm
        ⁢
        
          
        
        ⁢
        long
      
    
  
  ,




and the phase of the y-direction sine pulse signal AY is behind the phase of the y-direction cosine pulse signal BY, indicating the forward displacement, so in FIG. 4b, the displacement in the y-direction at time t with respect to time 0 is +0.4143 mm;

Through the above steps, on condition that the zero-crossing points are able to be detected, it only requires simple subtraction and multiplication to extract the displacement information contained in the magnetic field signals, and differently from the prior art, the components configured for generating signals containing the displacement information are not required, simplifying the installation of hardware and reducing the cost, and at the same time, the displacement measurement of the rotor of the planar motor of long moving range and high preciseness is still guaranteed.
Only some preferred embodiments of the present invention are described in the above. Without departing from the scope of the invention disclosed in the claims, various modification, addition and substitution should be considered as in the scope of protection of the invention.

## Claims

1. A planar motor rotor displacement measuring device, wherein the planar motor is a moving-coil type planar motor comprising a stator (1) and a rotor (3) on the stator (1), the stator (1) includes a magnetic steel array (2), and a coil array (4) is arranged on the lower surface of the rotor (3), characterized in that:
the displacement measuring device comprises a probe (5), two sets of sine sensors, two sets of cosine sensors, a signal lead wire (6) and a signal processing circuit (7);
the probe (5) is arranged at the edge of the rotor (3) which is located in a sine magnetic field area generated by the magnetic steel array of the stator of the moving-coil type planar motor;
the two sets of sine sensors include an x-direction sine sensor set (8) and a y-direction sine sensor set (10), the two sets of cosine sensors include an x-direction cosine sensor set (9) and a y-direction cosine sensor set (11);
a plurality of sensors are arranged in the probe (5) including a reference sensor (12), wherein my sensors in total including the reference sensor (12) are uniformly arranged within one magnetic field pitch τ along an x-direction, forming the y-direction sine sensor set and mx sensors in total including the reference sensor (12) are uniformly arranged within one magnetic field pitch τ along a y-direction, forming the x-direction sine sensor set;
wherein, beginning at a distance of τ/4 from the reference sensor (12) in the y-direction, my sensors are uniformly arranged within one magnetic field pitch τ along the x-direction, forming the y-direction cosine sensor set;
wherein, beginning at the distance of τ/4 from the reference sensor (12) in the x-direction, mx sensors are uniformly arranged within one magnetic field pitch τ along the y-direction, forming the x-direction cosine sensor set, where mx=2, 3, 4, . . . , my=2, 3, 4, . . . ;
wherein the signal processing circuit (7) is connected with an output of the probe (5) via the signal lead wire (6);
wherein the signal processing circuit (7) includes an analog signal processing unit and a digital signal processing unit; and
wherein the magnetic field pitch τ is a spatial period of the sine magnetic field of the planar motor.

2. A planar motor rotor displacement measuring method using the device of claim 1, characterized in that, the method includes:
1) processing, by the analog signal processing unit of the signal processing circuit, sampled signals of the x-direction sine sensor set, sampled signals of the x-direction cosine sensor set, sampled signals of the y-direction sine sensor set and sampled signals of the y-direction cosine sensor set, so as to obtain an x-direction sine measurement signal SX0, an x-direction cosine measurement signal CX0, a y-direction sine measurement signal SY0 and a y-direction cosine measurement signal CY0, respectively;
2) processing the x-direction sine measurement signal SX0 and the x-direction cosine measurement signal CX0 with the following nX frequency multiplication operations by the digital signal processing unit of the signal processing circuit, so as to obtain an x-direction sine subdivision signal SXnX and an x-direction cosine subdivision signal CXnX:





  
    
      S
      
        X
        ⁢
        
          
        
        ⁢
        1
      
    
    =
    
      2
      *
      
        S
        
          X
          ⁢
          
            
          
          ⁢
          0
        
      
      *
      
        C
        
          X
          ⁢
          
            
          
          ⁢
          0
        
      
    
  
  ,
  
    
      C
      
        X
        ⁢
        
          
        
        ⁢
        1
      
    
    =
    
      
        
          C
          
            X
            ⁢
            
              
            
            ⁢
            0
          
        
        *
        
          C
          
            X
            ⁢
            
              
            
            ⁢
            0
          
        
      
      -
      
        
          S
          
            X
            ⁢
            
              
            
            ⁢
            0
          
        
        *
        
          S
          
            X
            ⁢
            
              
            
            ⁢
            0
          
        
      
    
  
  ,
  
    

  
  ⁢
  
    
      S
      
        X
        ⁢
        
          
        
        ⁢
        2
      
    
    =
    
      2
      *
      
        S
        
          X
          ⁢
          
            
          
          ⁢
          1
        
      
      *
      
        C
        
          X
          ⁢
          
            
          
          ⁢
          1
        
      
    
  
  ,
  
    
      C
      
        X
        ⁢
        
          
        
        ⁢
        2
      
    
    =
    
      
        
          C
          
            X
            ⁢
            
              
            
            ⁢
            1
          
        
        *
        
          C
          
            X
            ⁢
            
              
            
            ⁢
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      -
      
        
          S
          
            X
            ⁢
            
              
            
            ⁢
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        *
        
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            X
            ⁢
            
              
            
            ⁢
            1
          
        
      
    
  
  ,
  
    

  
  ⁢
  ...
  ⁢
  
    
  
  ,
  
    

  
  ⁢
  
    
      S
      
        Xn
        X
      
    
    =
    
      2
      *
      
        S
        
          X
          ,
          
            
              n
              X
            
            -
            1
          
        
      
      *
      
        C
        
          X
          ,
          
            
              n
              X
            
            -
            1
          
        
      
    
  
  ,
  
    

  
  ⁢
  
    
      C
      
        Xn
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    =
    
      
        
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            X
            ,
            
              
                n
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              -
              1
            
          
        
        *
        
          C
          
            X
            ,
            
              
                n
                X
              
              -
              1
            
          
        
      
      -
      
        
          S
          
            X
            ,
            
              
                n
                X
              
              -
              1
            
          
        
        *
        
          S
          
            X
            ,
            
              
                n
                X
              
              -
              1
            
          
        
      
    
  




where SX1, CX1, SX2, CX2, . . . , SX,nX-1 and CX,nX-1 are intermediate variables, nX=1, 2, 3, . . . ;
while, the y-direction sine measurement signal SY0 and the y-direction cosine measurement signal CY0 are processed with the following nY frequency multiplication operations by the signal processing circuit, so as to obtain a y-direction sine subdivision signal SYnY and a y-direction cosine subdivision signal CYnY:




  
    
      S
      
        Y
        ⁢
        
          
        
        ⁢
        1
      
    
    =
    
      2
      *
      
        S
        
          Y
          ⁢
          
            
          
          ⁢
          0
        
      
      *
      
        C
        
          Y
          ⁢
          
            
          
          ⁢
          0
        
      
    
  
  ,
  
    
      C
      
        Y
        ⁢
        
          
        
        ⁢
        1
      
    
    =
    
      
        
          C
          
            Y
            ⁢
            
              
            
            ⁢
            0
          
        
        *
        
          C
          
            Y
            ⁢
            
              
            
            ⁢
            0
          
        
      
      -
      
        
          S
          
            Y
            ⁢
            
              
            
            ⁢
            0
          
        
        *
        
          S
          
            Y
            ⁢
            
              
            
            ⁢
            0
          
        
      
    
  
  ,
  
    

  
  ⁢
  
    
      S
      
        Y
        ⁢
        
          
        
        ⁢
        2
      
    
    =
    
      2
      *
      
        S
        
          Y
          ⁢
          
            
          
          ⁢
          1
        
      
      *
      
        C
        
          Y
          ⁢
          
            
          
          ⁢
          1
        
      
    
  
  ,
  
    
      C
      
        Y
        ⁢
        
          
        
        ⁢
        2
      
    
    =
    
      
        
          C
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
        *
        
          C
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
      
      -
      
        
          S
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
        *
        
          S
          
            Y
            ⁢
            
              
            
            ⁢
            1
          
        
      
    
  
  ,
  
    

  
  ⁢
  ...
  ⁢
  
    
  
  ,
  
    

  
  ⁢
  
    
      S
      
        Yn
        Y
      
    
    =
    
      2
      *
      
        S
        
          Y
          ,
          
            
              n
              Y
            
            -
            1
          
        
      
      *
      
        C
        
          Y
          ,
          
            
              n
              Y
            
            -
            1
          
        
      
    
  
  ,
  
    

  
  ⁢
  
    
      C
      
        Yn
        Y
      
    
    =
    
      
        
          C
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
        *
        
          C
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
      
      -
      
        
          S
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
        *
        
          S
          
            Y
            ,
            
              
                n
                Y
              
              -
              1
            
          
        
      
    
  




where SY1, CY1, SY2, CY2, . . . , SY,nY-1 and CY,nY-1 are intermediate variables, nY=1, 2, 3, . . . ;
3) detecting zero-crossing points of the x-direction sine subdivision signal SXnX and the x-direction cosine subdivision signal CXnX obtained at step 2) by the digital signal processing unit of the signal processing circuit respectively, generating a set of x-direction orthogonal pulse signals, that is, an x-direction sine pulse signal AX and an x-direction cosine pulse signal BX; while, the zero-crossing points of the y-direction sine subdivision signal SYnY and the y-direction cosine subdivision signal CYnY obtained at step 2) are detected respectively, generating a set of y-direction orthogonal pulse signals, that is, a y-direction sine pulse signal AY and a y-direction cosine pulse signal BY;
4) if the x-direction sine subdivision signal SXnX>0, then the output of the x-direction sine pulse signal AX is of high level; if the x-direction sine subdivision signal SXnX<0, then the output of the x-direction sine pulse signal AX is of low level; and if the x-direction sine subdivision signal SXnX=0, then the output of the x-direction sine pulse signal AX remains unchanged; if the x-direction cosine subdivision signal CXnX>0, then the output of the x-direction cosine pulse signal BX is of high level; if the x-direction cosine subdivision signal CXnX<0, then the output of the x-direction cosine pulse signal BX is of low level; and if the x-direction cosine subdivision signal CXnX=0, then the output of the x-direction cosine pulse signal BX remains unchanged;
5) if the y-direction sine subdivision signal SYnY>0, then the output of the y-direction sine pulse signal AY is of high level; if the y-direction sine subdivision signal SYnY<0, then the output of the y-direction sine pulse signal AY is of low level; and if the y-direction sine subdivision signal SYnY=0, then the output of the y-direction sine pulse signal AY remains unchanged; if the y-direction cosine subdivision signal CYnY>0, then the output of the y-direction cosine pulse signal BY is of high level; if the y-direction cosine subdivision signal CYnY<0, then the output of the y-direction cosine pulse signal BY is of low level; and if the y-direction cosine subdivision signal CYnY=0, then the output of the y-direction cosine pulse signal BY remains unchanged;
6) counting the pulse numbers of the x-direction sine pulse signal AX or the x-direction cosine pulse signal BX obtained at step 3) by the digital signal processing unit of the signal processing circuit, and detecting a phase difference between the x-direction sine pulse signal AX and the x-direction cosine pulse signal BX; taking one pulse of the x-direction sine pulse signal AX or the x-direction cosine pulse signal BX as an x-direction displacement resolution





  τ
  
    2
    
      n
      X
    
  




nX=1, 2, 3, . . . , if the phase of the x-direction sine pulse signal AX is behind the phase of the x-direction cosine pulse signal BX, then it indicates that it is the forward displacement; and if the phase of the x-direction sine pulse signal AX is ahead of the phase of the x-direction cosine pulse signal BX, then it indicates that it is the backward displacement, in such a way, the x-direction displacement of the rotor of the planar motor is measured;
7) counting the pulse numbers of the y-direction sine pulse signal AY or the y-direction cosine pulse signal BY obtained at step 3) by the digital signal processing unit of the signal processing circuit, and detecting the phase difference between the y-direction sine pulse signal AY and the y-direction cosine pulse signal BY; taking one pulse of the y-direction sine pulse signal AY or the y-direction cosine pulse signal BY as a y-direction displacement resolution





  τ
  
    2
    
      n
      Y
    
  




nY=1, 2, 3, . . . , and if the phase of the y-direction sine pulse signal AY is behind the phase of the y-direction cosine pulse signal BY, then it indicates that it is the forward displacement; and if the phase of the y-direction sine pulse signal AY is ahead of the phase of the y-direction cosine pulse signal BY, then it indicates that it is the backward displacement, in such a way, the y-direction displacement of the rotor of the planar motor is measured.

3. The planar motor rotor displacement measuring method of claim 2, characterized in that, nX described at step 2) is determined as follows:
given that the BXM is the magnitude of the magnetic induction intensity in the x-direction of the sine magnetic field generated by the magnetic steel array of the stator of the planar motor, and vx is the noise in the sensor measurement in the x-direction, then the maximized number of times of the frequency multiplication operations in the x-direction is





  
    n
    X
  
  =
  
    [
    
      
        
          log
          2
        
        ⁡
        
          (
          
            
              B
              XM
            
            
              v
              x
            
          
          )
        
      
      -
      3
    
    ]
  



nY described at step 2) is determined as follows:
given that the BYM is the magnitude of the magnetic induction intensity in the y-direction of the sine magnetic field generated by the magnetic steel array of the stator of the planar motor, and vy is the noise in the sensor measurement in the y-direction, then the maximized number of times of frequency multiplication operations in the y-direction is





  
    n
    Y
  
  =
  
    
      [
      
        
          
            log
            2
          
          ⁡
          
            (
            
              
                B
                XM
              
              
                v
                y
              
            
            )
          
        
        -
        3
      
      ]
    
    .