Abstract:
A filter includes a plurality of filter plates for adjusting X-ray energy spectrum, a plurality of rails for fixedly supporting the filter plates, a plurality of cams which are respectively provided with a groove curve on a surface thereof, a driving wheel for driving the cams, and a plurality of link levers, each link lever being connected to one of the filter plates at one end and being mounted to an axis at an opposite end such that the link lever is rotatable about the axis, and each link lever being provided with a pin which is in cooperation with the groove curve of the corresponding cam so that the link lever proceeds with a reciprocating movement according to rotation of the corresponding cam to move the filter connected to it into or out of the X-ray passing space. The plurality of cams are respectively located at different sides of the driving wheel to move the filter plates into the X-ray passing space from different directions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Chinese Patent Application No. 200910132511.8 filed Mar. 31, 2009, which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Embodiments described herein relate to a filter and an X-ray imaging apparatus, and more particularly to a filter that adjusts energy spectra of X-ray, and an X-ray apparatus provided with the filter. 
     A X-ray imaging apparatus irradiates X-ray to a subject by adjusting energy spectrum of the X-ray with a filter. The filter is provided in a collimator box attached to an X-ray tube. In order to obtain desired spectrum, the filter can be used by switching multiple filter plates which are attached to a rotating disc, as disclosed in the Japanese Patent Application No. HEI11-76219. In this prior art, the energy spectrum can be adjusted in a wide range according to the actual needs, but in the construction in which the filter plates are switched by the rotating disc, a four-step adjustment is about all this construction can provide. Therefore, widening the adjustment range causes a rough step, while providing more steps narrows the adjustment range. When a multi-step adjustment is made possible in the rotating disc system anyway, the rotating disc to which a great number of filters are attached is increased in size, thus unrealistic. 
     In addition, the U.S. Pat. No. 7,260,183 reveals a filter which is provided with a cam having a curve to adjust laminated filter plates, in order to realize a filter that can make a fine spectrum adjustment in a wide rage and can be miniaturized. However, there are some disadvantages in the technical solution of this prior art: 1. when there are more than two cams in a set of cams, the curve becomes very complex and thus the cam will be in an execrable stressed state, even the angle of the force driving the cam is approximate to the angle of friction. When the cam is rotated to a certain direction or to a certain state, it will be in a more execrable stressed state; 2. since one driving system will drive at most two filter plates in practice, more driving systems are needed to drive two or more filter plates, and thus the disadvantages of high cost, large size and complex structure are caused. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention provides a filter, which is provided with less driving systems to realize a fine spectrum adjustment in a wide range, and which has advantages of simple structure, low cost and high reliability. A X-ray imaging apparatus fitted with said filter is also provided. 
     Moreover, embodiments of the present invention provide a filter, comprising: at least two filter plates for adjusting X-ray energy spectrum; a pair of rails for fixedly supporting the filter plates, said filter plates being provided in a laminated structure on the guiders of the pair of rails; two cams which are respectively provided with a groove curve on a surface thereof; and a driving wheel for driving the cams contacted with it, wherein the filter further comprises at least two link levers, each link lever being connected to one of the filter plates at one end and being mounted to an axis at the other end in the manner that the link lever is rotatable about the axis, and each link lever being provided with a pin which is in cooperation with the groove curve of the corresponding cam so that the link lever proceeds with a reciprocating movement according to rotation of the corresponding cam to move the filter connected to it into or out of the X-ray passing space; the cams are respectively located at different sides of the driving wheel to move the filter plates into the X-ray passing space from different directions. 
     The number of the filter plates is two; the corresponding cams are respectively located at the left and right sides of the driving wheel, each cam being provided with a groove curve at only one surface thereof; and the filter has two link levers, each link lever being connected to one of the filter plates and being in cooperation with the groove curve of one of the cams. 
     The filter further comprises a third filter plate and a third link lever, the third link lever being connected to the third filter plate at one end thereof and being provided with a pin; on the other surface of one of the cams is provided with a groove curve which is in cooperation with the pin on the third link lever. 
     The groove curve on each cam is designed according to the following method: according to N, the number of the filter thickness states that can be switched, calculate the minimum rotation angle of each cam in each thickness switch by 360°/N; set R 1 , the corresponding radius of the cam groove curve as the minimum one when the filter plate is in the O region retreating from the X-ray passing space; set R 2 , the corresponding radius of the cam groove curve as the maximum one when the filter plate is in the W region advancing into the X-ray passing space; determine whether the driving wheel is rotated clockwise or anticlockwise; set the O region and W region of the filter plates according to the space size and structure of the collimator box; determine whether the cams are located at the left side or the right side of the filter; and create and design the cam groove curves according to the table below: 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 N 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate 1 
                 O region or W 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 which side of 
               
               
                   
                 region? 
                   
                   
                   
                   
                 the filter? 
               
               
                 Filter Plate 2 
                 O region or W 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 which side of 
               
               
                   
                 region? 
                   
                   
                   
                   
                 the filter? 
               
               
                 Filter Plate . . . 
                 O region or W 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 which side of 
               
               
                   
                 region? 
                   
                   
                   
                   
                 the filter? 
               
               
                 Operating State of 
                 Is any filter 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                 the Filter 
                 working? 
               
               
                   
               
             
          
         
       
     
     wherein the O region represents the non X-ray passing space; and the W region represents the X-ray passing space. 
     Assuming the filter plate 1 and the filter plate 2 have thickness of h1 and h2 respectively, then the filter composed of the filter plates has four switches in thickness, i.e. N=4, and the four switches are 0, h1, h2, and h1+h2, wherein 0 indicates that there is no filter in the X-ray passing space; h1 indicates that there is a filter with thickness of h1 in the X-ray passing space; h2 indicates that there is a filter with thickness of h2 in the X-ray passing space; h1+h2 indicates that there is a filter with thickness of h1+h2 in the X-ray passing space; and corresponding to each thickness switch, the cams will be rotated by an angle of 90° calculated by 360°/4; assuming the driving wheel is rotated anticlockwise and the two cams are rotated clockwise, then the table below for the two groove curves can be designed: 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate 1 
                 O 
                 W 
                 O 
                 W 
                 right side 
               
               
                 Filter Plate 2 
                 O 
                 O 
                 W 
                 W 
                 left side 
               
               
                 Operating State of the 
                 0 
                 h1 
                 h2 
                 h1 + h2 
               
               
                 Filter 
               
               
                   
               
             
          
         
       
     
     The filter plates are made of copper or tin; h1 and h2 are respectively 0.1 mm and 0.2 mm. 
     The filter plate 1 and the filter plate 2 have thickness of h1, h2 respectively; with an additional filter plate 3 with thickness of hn, the filter composed of the filter plates has four thickness switches plus a switch of thickness hn, i.e. N=5, and the switches are 0, h1, h2, h1+h2, and hn; and corresponding to each thickness switch, the cams will be rotated by an angle of 72° calculated by 360°/5; assuming the driving wheel is rotated anticlockwise and the cams located respectively at left side and right side of the driving wheel are rotated clockwise, then a table below for three groove curves can be designed, wherein groove curves for respectively controlling the filter plate 1 with thickness of h1 and the filter plate 3 with thickness of hn are respectively provided on the front surface and the back surface of the cam located at the right side: 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate 1 
                 O 
                 W 
                 O 
                 W 
                 O 
                 right side 
               
               
                 Filter Plate 3 
                 O 
                 O 
                 O 
                 O 
                 W 
                 right side 
               
               
                 Filter plate 2 
                 O 
                 O 
                 W 
                 W 
                 O 
                 left side 
               
               
                 Operating State of the 
                 0 
                 h1 
                 h2 
                 h1 + h2 
                 hn 
               
               
                 Filter 
               
               
                   
               
             
          
         
       
     
     The filter plate 1 and the filter plate 2 are made of copper or tin; h1 and h2 are respectively 0.1 mm and 0.2 mm; and the filter plate 3 is made of tin or copper. 
     The filter plate 1 and the filter plate 2 have thickness of h1 and h2 respectively; with an additional filter plate 3 with thickness of hn, the filter composed of the filter plates has four thickness switches plus one more thickness switch of hn+h2+h1, i.e. N=5, and the switches are 0, h1, h2, h1+h2, and hn+h1+h2; and corresponding to each thickness switch, the cams will be rotated by 72° calculated by 360°/5; assuming the driving wheel is rotated anticlockwise and the cams located respectively at the left and right sides of the driving wheel are rotated clockwise, then the table below for three groove curves can be designed, wherein groove curves for respectively controlling the filter plate 1 with thickness of h1 and the filter plate 3 with thickness of hn are respectively provided on the front surface and the back surface of the cam located at the right side: 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate 1 
                 O 
                 W 
                 O 
                 W 
                 W 
                 right side 
               
               
                 Filter Plate 3 
                 O 
                 O 
                 O 
                 O 
                 W 
                 right side 
               
               
                 Filter plate 2 
                 O 
                 O 
                 W 
                 W 
                 W 
                 left side 
               
               
                 Operating state of 
                 0 
                 h1 
                 h2 
                 h1 + h2 
                 hn + h1 + h2 
               
               
                 the Filter 
               
               
                   
               
             
          
         
       
     
     The filter plate 1 and the filter plate 2 are made of copper or tin; h1 and h2 are respectively 0.1 mm and 0.2 mm; and the filter plate 3 is made of tin or copper. 
     Another embodiment of the present invention provides an X-ray imaging apparatus for imaging a subject by X-ray via a filter, wherein said filter comprises: at least two filter plates for adjusting X-ray energy spectrum; a pair of rails for fixedly supporting the filter plates, said filter plates being provided in a laminated structure on the guiders of the pair of rails; two cams which are respectively provided with a groove curve on a surface thereof; and a driving wheel for driving the cams contacted with it, wherein the filter further comprises at least two link levers, each link lever being connected to one of the filter plates at one end and being mounted to an axis at the other end in the manner that the link lever is rotatable about the axis, and each link lever being provided with a pin which is in cooperation with the groove curve of the corresponding cam so that the link lever proceeds with a reciprocating movement according to rotation of the corresponding cam to move the filter connected to it into or out of the X-ray passing space; the cams are respectively located at different sides of the driving wheel to move the filter plates into the X-ray passing space from different directions. 
     The filter has two filter plates; the corresponding cams are respectively located at the left and right sides of the driving wheel, each cam being provided with a groove curve at only one surface thereof; and the filter has two link levers, each link lever being connected to one of the filter plates and being in cooperation with the groove curve of one of the cams. 
     The filter further comprises a third filter plate and a third link lever, the third link lever being connected to the third filter plate at one end thereof and being provided with a pin; on the other surface of one of the cams is provided with a groove curve which is in cooperation with the pin on the third link lever. 
     The groove curve on each cam is designed according to the following method: according to N, the number of the filter thickness states that can be switched, calculate the minimum rotation angle of each cam in each thickness switch by 360°/N; set R 1 , the corresponding radius of the cam groove curve as the minimum one when the filter plate is in the O region retreating from the X-ray passing space; set R 2 , the corresponding radius of the cam groove curve as the maximum one when the filter plate is in the W region advancing into the X-ray passing space; determine whether the driving wheel is rotated clockwise or anticlockwise; set the O region and W region of the filter plates according to the space size and structure of the collimator box; determine whether the cams are located at the left side or the right side of the filter; and create and design the cam groove curves according to the table below: 
                                                                                                         Switch Order of the Filter Plates                    1   2   3   4   N   Cam Position                        Filter Plate 1   O region or W   . . .   . . .   . . .   . . .   which side of           region?                   the filter?       Filter Plate 2   O region or W   . . .   . . .   . . .   . . .   which side of           region?                   the filter?       Filter Plate . . .   O region or W   . . .   . . .   . . .   . . .   which side of           region?                   the filter?       Operating State of   Is any filter   . . .   . . .   . . .   . . .       the Filter   working?                    
wherein the O region represents the non X-ray passing space; and the W region represents the X-ray passing space.
 
     Assuming the filter plate 1 and the filter plate 2 have thickness of h1 and h2 respectively, then the filter composed of the filter plates has four switches in thickness, i.e. N=4, and the four switches are 0, h1, h2, and h1+h2, wherein 0 indicates that there is no filter in the X-ray passing space; h1 indicates that there is a filter with thickness of h1 in the X-ray passing space; h2 indicates that there is a filter with thickness of h2 in the X-ray passing space; h1+h2 indicates that there is a filter with thickness of h1+h2 in the X-ray passing space; and corresponding to each thickness switch, the cams will be rotated by an angle of 90° calculated by 360°/4; assuming the driving wheel is rotated anticlockwise and the two cams are rotated clockwise, then the table below for the two groove curves can be designed: 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate 1 
                 O 
                 W 
                 O 
                 W 
                 right side 
               
               
                 Filter Plate 2 
                 O 
                 O 
                 W 
                 W 
                 left side 
               
               
                 Operating State of the 
                 0 
                 h1 
                 h2 
                 h1 + h2 
               
               
                 Filter 
               
               
                   
               
             
          
         
       
     
     The filter plates are made of copper or tin; h1 and h2 are respectively 0.1 mm and 0.2 mm. 
     The filter plate 1 and the filter plate 2 have thickness of h1, h2 respectively; with an additional filter plate 3 with thickness of hn, the filter composed of the filter plates has four thickness switches plus a switch of thickness hn, i.e. N=5, and the switches are 0, h1, h2, h1+h2, and hn; and corresponding to each thickness switch, the cams will be rotated by an angle of 72° calculated by 360°/5; assuming the driving wheel is rotated anticlockwise and the cams located respectively at left side and right side of the driving wheel are rotated clockwise, then a table below for three groove curves can be designed, wherein groove curves for respectively controlling the filter plate 1 with thickness of h1 and the filter plate 3 with thickness of hn are respectively provided on the front surface and the back surface of the cam located at the right side: 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate 1 
                 O 
                 W 
                 O 
                 W 
                 O 
                 right side 
               
               
                 Filter Plate 3 
                 O 
                 O 
                 O 
                 O 
                 W 
                 right side 
               
               
                 Filter plate 2 
                 O 
                 O 
                 W 
                 W 
                 O 
                 left side 
               
               
                 Operating State of the 
                 0 
                 h1 
                 h2 
                 h1 + h2 
                 hn 
               
               
                 Filter 
               
               
                   
               
             
          
         
       
     
     The filter plate 1 and the filter plate 2 are made of copper or tin; h1 and h2 are respectively 0.1 mm and 0.2 mm; and the filter plate 3 is made of tin or copper. 
     The filter plate 1 and the filter plate 2 have thickness of h1 and h2 respectively; with an additional filter plate 3 with thickness of hn, the filter composed of the filter plates has four thickness switches plus one more thickness switch of hn+h2+h1, i.e. N=5, and the switches are 0, h1, h2, h1+h2, and hn+h1+h2; and corresponding to each thickness switch, the cams will be rotated by 72° calculated by 360°/5; assuming the driving wheel is rotated anticlockwise and the cams located respectively at the left and right sides of the driving wheel is rotated clockwise, then the table below for three groove curves can be designed, wherein groove curves for respectively controlling the filter plate 1 with thickness of h1 and the filter plate 3 with thickness of hn are respectively provided on the front surface and the back surface of the cam located at the right side: 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate 1 
                 O 
                 W 
                 O 
                 W 
                 W 
                 right side 
               
               
                 Filter Plate 3 
                 O 
                 O 
                 O 
                 O 
                 W 
                 right side 
               
               
                 Filter plate 2 
                 O 
                 O 
                 W 
                 W 
                 W 
                 left side 
               
               
                 Operating state of 
                 0 
                 h1 
                 h2 
                 h1 + h2 
                 hn + h1 + h2 
               
               
                 the Filter 
               
               
                   
               
             
          
         
       
     
     The filter plate 1 and the filter plate 2 are made of copper or tin; h1 and h2 are respectively 0.1 mm and 0.2 mm; and the filter plate 3 is made of tin or copper. 
     In the present invention, a single driving wheel drives multiple cams that have different curves. The cams are respectively located at different sides of the driving wheel, so that the cams driven by the driving wheel move the filter plates connected thereto into FOV of the X-ray respectively from different sides (FOV is the abbreviation of Field of View). In the present invention, the number of driving systems and motors are reduced, and a driving system can satisfy the case of four cam curves. Therefore, the present invention reduces the components number and complexity in structure, enhances reliability and cuts the cost. In the meantime, the structure according to the present invention increases the margin between the filter plates, and thus decreases the requirement on filter plate position repeatability accuracy, because the size of the filter plates can be optimized and increased, and the filter plates can be withdrawn sufficiently. 
     In addition, by the cam design method according to the present invention, the cam curve becomes more simple and the strained condition is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing the structure of one example of an X-ray imaging apparatus according to the best mode for carrying out the present invention. 
         FIG. 2  and  FIG. 3  are two different views of an example of the filter structure according to the present invention; 
         FIGS. 4A and 4B  are schematic drawings of the curves designed on the two cams in example 1; 
         FIG. 4C  is a schematic drawing of the filter in example 1; 
         FIGS. 4D ,  4 E,  4 F, and  4 G are schematic drawings showing the operating states of the filter in example 1; 
         FIGS. 5A ,  5 B, and  5 C are schematic drawings showing the curves designed on the three cams in example 2; 
         FIGS. 5D and 5E  are schematic drawings viewed from the front side and the back side of the filter in example 2; 
         FIGS. 5F ,  5 G,  5 H,  5 I, and  5 J are schematic drawings showing the operating states of the filter in example 2; 
         FIGS. 6A ,  6 B, and  6 C are schematic drawings showing the curves designed on the three cams in example 3; 
         FIGS. 6D and 6E  are schematic drawings viewed from the front side and the back side of the filter in example 3; 
         FIGS. 6F ,  6 G,  6 H,  6 I, and  6 J are schematic drawings showing the operating states of the filter in example 3. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments according to the present invention will be described in detail in the following text with reference to the Drawings. It should be apprehended that the present invention shall not be limited to these specific embodiments. 
       FIG. 1  shows the structure of a X-ray imaging apparatus according to the present invention. The X-ray imaging apparatus is an example of the present invention, and comprises an X-ray irradiating device  10 , X-ray detecting device  20  and an operator controller  30 . The X-ray irradiating device  10  and the X-ray detecting device oppose to each other via a subject  40 . 
     The X-ray irradiating device  10  has an X-ray tube  12  and a collimator box  14 . A filter  16  and a collimator  18  are accommodated in the collimator box  14 . The filter  16  is one example of the present invention. 
     X-ray emitted from the X-ray tube  12  whose energy spectra are adjusted by the filter  16  is irradiated to the subject  40  through an opening of the collimator  18 . The filter  16  can make the energy spectra variable. The collimator  18  has the opening that is variable. 
     The X-ray passing through the subject  40  is detected by the X-ray detecting device  20  to be inputted to the operator controller  30 . The operator controller  30  reconstructs the radioscopic image of the subject based upon an inputted signal. The reconstructed radioscopic image is displayed on a display  32  of the operator controller  30 . The operator controller  30  further controls the X-ray irradiating device  10 . The control of the X-ray irradiating device  10  by the operator controller  30  includes the control of the filter  16  and the control of the collimator  18 . It should be noted that the filter  16  and the collimator  18  can manually be adjusted according to actual need. 
       FIG. 2  is a view showing the structure of a filter  16  according to the present invention. As shown in  FIG. 2 , filter plates  161 ,  162  are provided in a laminated structure on a pair of rails  172 ,  174 . The rails  172 ,  174  are parallel with each other, each rail having parallel rails in equal amount with the filter plates. The two ends of each filter plate are respectively inserted into the corresponding guider of the pair of rails  172 ,  174 , so that the filter plates are formed into a laminated structure, and each filter plate is movable parallelly between the pair of rails  172 ,  174 . The filter plates  161 ,  162  are respectively connected to one ends of link levers  261 ,  262 , while the other ends of the link levers  261 ,  262  are mounted to axes  272 ,  274  to be rotatable about the axes  272 ,  274 . Cams  461 ,  462  for driving the link levers  261 ,  262  are provided with groove curves, while the link levers  261 ,  262  are provided with pins to cooperate with the groove curves on the cams  461 ,  462 . The two cams  461 ,  462  are located respectively at different sides of the driving wheel  800 , which drives the cams  461 ,  462  simultaneously to rotate and thus to move the filter plates  161 ,  162  into and out of the FOV region of the X-ray from different directions. 
     As shown in  FIG. 3 , the link levers  261 ,  262  driven by the cams  461 ,  462  make the filter plates  161 ,  162  proceed with a reciprocating movement respectively along the rails  171 ,  172 . The filter plate  161  and/or the filter plate  162  are in the advancing state into the X-ray passing space when they are present in the W region, while they are in the retreating state when they are respectively present at the left and right O region. In the present invention, the structure is simplified, since the filter plates  161 ,  162  are moved in/out through the reciprocating movement of the link levers  261 ,  262  driven by the rotation of the cams  461 ,  462 , while the rotation of the cams are driven by a single driving wheel  800 . 
     As stated above, through rotation, the cams  461 ,  462  have the function of switching positions of the filter plates in a binary mode between the advancing position where the filter plates move into the X-ray passing space and the retreating position where the filter plates move out of the X-ray passing space. 
     As shown in  FIG. 3 , the groove curve of each cam according to the present invention is designed following the method below: 
     1. According to N, the number of the filter thickness states that can be switched, calculate the rotation angle of each cam in each thickness switch by 360°/N; 
     2. Set the O region to correspond to R 1 , the minimum radius of the cam groove curve; 
     3. Set the W region to correspond to R 2 , the maximum radius of the cam groove curve; 
     4. Determine the rotation direction of the driving wheel  800 , e.g. the clockwise direction or the anticlockwise direction; 
     5. Set the O region and W region of the filter plate according to the space size and structure of the collimator box; 
     6. Determine which side of the filter the cam is positioned, e.g. the left side or the right side; 
     7. Create a table for designing the groove curve of the cam and a graph of the groove curve. 
     The method for designing the groove curve will be described through the specific examples below. 
     EXAMPLE 1 
     Assuming there are two filter plates  161 ,  162  made of copper which have thickness of 0.2 mm and 0.1 mm respectively, then the filter composed of the same will have four different thickness switches, i.e. N=4 (N=4, e.g. 0.0 mm, 0.1 mm, 0.2 mm, 0.3 mm; wherein 0.0 mm indicates that no filter is present in the X-ray passing space; 0.1 mm indicates that a filter with thickness of 0.1 mm is present in the X-ray passing space; 0.2 mm indicates that a filter with thickness of 0.2 mm is present in the X-ray passing space; 0.3 mm indicates that a filter with thickness of 0.3 mm is present in the X-ray passing space), and corresponding to each thickness, the cam shall be rotated by an angle of 90° calculated by 360°/4; assuming the driving wheel  800  is rotated anticlockwise, then the two cams  461 ,  462  are rotated clockwise. Two groove curves  471 ,  472  are designed on the cams  461 ,  462  as shown in  FIG. 4A  according to Table 1. 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter plate, 0.1 
                 O 
                 W 
                 O 
                 W 
                 right side 
               
               
                 mm 
               
               
                 Filter plate, 0.2 
                 O 
                 O 
                 W 
                 W 
                 left side 
               
               
                 mm 
               
               
                 Operating state 
                 0.0 mm 
                 0.1 mm 
                 0.2 mm 
                 0.3 mm 
               
               
                 of the Filter 
               
               
                   
               
             
          
         
       
     
       FIG. 4C  shows the filter mounted according to Table 1 and  FIGS. 4A and 4B , with a operating state as shown in  FIGS. 4D-4G . It can be seen that from the 0.0 mm state to the 0.3 mm state, each cam is rotated by 90° with each operating state switch; between the 0.0 mm state and the 0.1 mm state, or between the 0.0 mm state and the 0.3 mm state, the minimum cam rotation angle is 90°; between the 0.1 mm state and the 0.3 mm state, or between the 0.3 mm state and the 0.1 mm state, the minimum cam rotation angle is 180°; between the 0.0 mm state and the 0.2 mm state or between the 0.1 mm state and the 0.3 mm state, the minimum cam rotation angle is 180°. 
     EXAMPLE 2 
     For example, there are two filter plates  161 ,  162  made of copper which have the thickness of 0.2 mm and 0.1 mm respectively; and a filter plate  163  which has the thickness of hn (as shown in  FIGS. 5D and 5E ). Assuming the filter composed of the above filter plates has 4 copper filter thickness switches and 1 tin filter thickness switch, i.e. N=5, (N=5, e.g. 0.0 mm, 0.1 mm, 0.2 mm, 0.3 mm, hn), then corresponding to each thickness switch, the cam shall be rotated by an angle of 72° calculated by 360°/5; assuming the driving wheel  800  is rotated anticlockwise, then the cams  461 ,  462  at the left side and the right side of the driving wheel  800  respectively will be rotated clockwise. Three groove curves  571 ,  572 ,  573  as shown in  FIGS. 5A-5C  are designed according to Table 2, wherein on the front surface and the back surface of the cam  462  are respectively provided with groove curves  572 ,  573  for respectively controlling the copper filter plate  162  with the thickness of 0.1 mm and the tin filter plate. A third link lever  263  is further included, with one of its end connected to the tin filter plate. A pin (with no reference number) is provided on the third link lever  263  to cooperate with the groove curve  573  on the back surface of the cam  462 . 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate, 0.1 
                 O 
                 W 
                 O 
                 W 
                 O 
                 right side 
               
               
                 mm 
               
               
                 Filter Plate, hn 
                 O 
                 O 
                 O 
                 O 
                 W 
                 right side 
               
               
                 Filter Plate, 0.2 
                 O 
                 O 
                 W 
                 W 
                 O 
                 left side 
               
               
                 mm 
               
               
                 Operating state 
                 0.0 
                 0.1 
                 0.2 
                 0.3 
                 hn 
               
               
                 of the Filter 
                 mm 
                 mm 
                 mm 
                 mm 
               
               
                   
               
             
          
         
       
     
       FIGS. 5D and 5E  are two schematic drawings showing the front side and the back side of the filter mounted by two cams  461 ,  462  according to Table 2 and  FIGS. 5A-5C . The operating states of the filter is shown in  FIGS. 5F-5J . It can be seen that from the 0.0 mm state to the 0.3 mm state and then to the hn state, each cam is rotated by 72° along with each operating state switch, wherein between the 0.0 mm state and the hn state or between the hn state and the 0.0 mm state, the minimum cam rotation angle is 72°; between the 0.1 mm state and the 0.2 mm state and the hn state, the minimum cam rotation angle is 144°. 
     If the required thickness switch states include four copper filter thickness switches and one tin filter thickness plus 0.3 mm, i.e. N=5, (N=5, 0.0 mm, 0.1 mm, 0.2 mm, 0.3 mm, hn+0.3 mm), then three groove curves  671 ,  672 ,  673  as shown in  FIGS. 6A-6C  are designed according to Table 3, wherein groove curves  672 ,  673  are provided on the front surface and the back surface of the cam  462  for respectively controlling the copper filter plate  62  with thickness of 0.1 mm and the tin filter plate  163 . 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 Switch Order of the Filter Plates 
                   
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 Cam Position 
               
               
                   
                   
               
             
          
           
               
                 Filter Plate, 0.1 
                 O 
                 W 
                 O 
                 W 
                 W 
                 Right side 
               
               
                 mm 
               
               
                 Filter Plate, hn 
                 O 
                 O 
                 O 
                 O 
                 W 
                 Right side 
               
               
                 Filter Plate, 0.2 
                 O 
                 O 
                 W 
                 W 
                 W 
                 Left side 
               
               
                 mm 
               
               
                 Operating state 
                 0.0 
                 0.1 
                 0.2 
                 0.3 
                 hn + 
               
               
                 of the Filter 
                 mm 
                 mm 
                 mm 
                 mm 
                 0.3 mm 
               
               
                   
               
             
          
         
       
     
       FIGS. 6D and 6E  are schematic drawings showing the front side and the back side of the filter mounted by the two cams  461 ,  462  designed according to Table 3 and  FIGS. 6A-6C . The operating states of the filter are shown in  FIGS. 6F-6J . It can be seen that from the 0.0 mm state to the 0.3 mm state and then to the hn+0.3 mm state, each cam will be rotated by 72° along with each operating state switch. 
     Of course, all the filter plates as described in the present invention can be made of copper or tin or other materials which are suitable for filtering. 
     In  FIGS. 4D-4G ,  5 F- 5 J, and  6 F- 6 J, 0.0CF, 0.1CF, 0.2CF and 0.3CF refer to copper filter, 0.0 mm; copper filter, 0.1 mm; and copper filter, 0.2 mm; and copper filter, 0.3 mm respectively; TinF refers to tin filter.