Abstract:
The present invention is intended to provide a ultra-precision high sensitivity displacement measuring device which has such a high resolution as to be able to make submicron measurement.  
     According to the invention, there is provided a displacement measuring device with high resolution, comprising: an electromagnetic system( 10 ) which forms a closed loop of magnetic blocks( 17,19 ) and which houses primary coil bundles( 11 ) and secondary coil bundles( 13 ) for forming magnetic fields within said closed loop of magnetic blocks( 17,19 ); plate springs( 20 ) which include displacement input parts( 21 ) and displacement output zones( 24 ) fixed to the cores( 14 ) having the secondary coils wound around them and which act to guide so that the displacement output zones( 24 ) can output the displacement amplified in proportional to the displacement input to the displacement input parts( 21 ); and a supporting mechanism( 30 ) for supporting the displacement input parts( 21 ) of said plate springs( 20 ) so that the displacement may be input only in one axial direction. (FIG.  2 ).

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a linear variable differential transformer (shortly ‘LVDT’ in the following) widely used for measurement of displacements and particularly to a high sensitivity displacement measuring device using LVDT, which can measure submicron level with an insensitive to surrounding environment, noise and the like and with an increased resolution.  
         DESCRITPTION OF THE PRIOR ART  
         [0002]    The sensitivity represents the ratio of the analog voltage output relative to the displacement input to be measured in a displacement measuring device using LVDT, wherein a high sensitivity, for example, means the large value for the output generated for a given displacement input.  
           [0003]    For such an ordinary analog output producing device, the resolution is closely related with the noise and sensitivity.  
           [0004]    Resolution=Noise/Sensitivity  
           [0005]    In practical circumstances, the resolution is influenced severely by the noise, that is, the surrounding environment or various other factors. A high sensitivity is advantageous in order that the insensitiveness to external factors can be maintained and the resolution can be high enough to realize application in submicron area, with the minimum measurable displacement lowered.  
           [0006]    [0006]FIG. 1 shows schematically a displacement measuring device using LVDT according to a conventional art.  
           [0007]    As shown in FIG. 1, the displacement measuring device according to a conventional art has the form of cylinder, in which there is disposed a primary coil bundle  2  in cylindrical form, with the secondary coil bundles  3 H and  3 L positioned on the top and bottom thereof. In the center of the primary coil bundle  2  and secondary coil bundles  3 H and  3 L, there is disposed a magnetic core  4 , to the lower end of which there is connected a rod  5 , having a contact probe  6  disposed at its lower end. Under the lower secondary coil bundle  3 L, ball bearings  8  are disposed around the rod  5  to facilitate the vertical movement of the rod  5 , with the movement of which there expands or contracts a spring  9  disposed below the ball bearings  8 . The primary coil bundle  2 , upper and lower coil bundles  3 H and  3 L, ball bearings  8  and spring  9  are housed in a housing  7 , under which housing the lower part of contact probe  6  protrudes.  
           [0008]    Thus, as the contact probe  6  protruding from the bottom end of the housing  7  moves up or down depending on a displacement, the magnetic core  4  connected to the rod  5  accordingly moves up or down the same distance.  
           [0009]    On the other hand, when an electric voltage is applied to the primary coil bundle  2 , a magnetic field is generated within the displacement measuring device  1 , causing the magnetic core  4  to move in accordance with the displacement input. Thus, the flux distribution in the respective secondary coil bundles  3 H and  3 L within the displacement measuring device  1  are changed and so the values for the difference in voltage in the form of differential voltages which are induced in the respective secondary coil bundles  3 H and  3 L due to the change in the magnetic fields are also changed, wherein the values for such differential voltages are proportional to the displacement inputs.  
           [0010]    For such displacement measuring devices based on the conventional LVDT, an improvement in the sensitivity can be expected when the ratio of the windings for the secondary coil bundles to the windings for the primary coil bundle are large. Therefore, the number of the windings for the secondary coil bundles needs to be increased to increase the measurement sensitivity, with the result that the size of an overall displacement measuring device must be increased.  
           [0011]    Furthermore, as the coil windings continuously increase, a certain limitation for coil windings is met due to capacity saturations, generation of non-linear elements or the like. Conclusively, there was a disadvantage that a high sensitivity is hardly attained.  
           [0012]    In addition, the type of measuring device with the components of a guide such as ball bearings, springs and the like has the drawback that submicron resolution can not be attained because of the intrinsic non-linearity.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention was created to resolve the above-described problems with the conventional art and the object of the invention is to provide a ultra-precision high sensitivity displacement measuring device which is improved in its construction to facilitate a ultra-precision measurement and which has such a high resolution as to be able to make submicron measurement due to increased sensitivity by using a guiding mechanism to guide and amplify an input displacement.  
           [0014]    To that end, there is provided according to the invention a displacement measuring device with high resolution, comprising: an electromagnetic system which forms a closed loop of magnetic blocks and which houses primary coils and secondary coils for forming magnetic field within said closed loop; guiding mechanism which include displacement input parts and displacement output zones and which act to guide so that the displacement output zones can produce a displacement output amplified in proportional to the displacement input to the displacement input parts; and a supporting mechanism for supporting the displacement input parts of said guiding mechanism so that the displacement may be input only in one axial direction.  
           [0015]    According to another aspect of the invention, there is provided a displacement measuring device, wherein said electromagnetic system includes a plurality of loop magnetic blocks in E-form, beam magnetic blocks connecting the upper and lower free ends of said loop magnetic blocks to form a closed loop, a plurality of primary coils wound around inward projections of said loop magnetic blocks, a plurality of magnetic cores which extend parallel to said beam magnetic blocks between opposite primary coils and which are positioned at a predetermined distance of less than millimeters from the end of inward projection of a loop magnetic blocks, the inward projection being wound by primary coil, and a plurality of secondary coils winding around said magnetic cores, wherein the magnetic cores are fixed, at their ends, to the displacement output zones of said guiding mechanism.  
           [0016]    According to still other aspect of the invention, there is provided a displacement measuring device, wherein said cores and said beam magnetic blocks are of the same material.  
           [0017]    According to still other aspect of the invention, there is provided a displacement measuring device, wherein said guiding mechanism, as plate springs with a thickness of some hundred micrometers, are so constructed that, below the lower edges of said plate springs there protrude the displacement input parts, above the displacement input parts there are positioned fixing zones, attached to the beam magnetic blocks, and on both sides of the fixing zones there are connected rotatable or tiltable zones, and that said fixing zones and said rotatable zones are provided in a symmetric manner in the upper edges as well beside the lower edges of the plate springs and displacement output zones connect the rotatable zones on the upper and lower edges of the plate springs; and wherein between a fixing zone and rotatable zones, between a displacement input part and rotatable zones and between rotatable zones and a displacement output zone, a connecting section or sections are connected, so that when a displacement is input in the displacement input parts, rotatable zones rotate around the connecting sections, as fulcrums, connecting the fixing zones and the rotatable zones to cause the displacement output as determined by a mathematical equation at the displacement output zones.  
           [0018]    According to an aspect of the invention, there is provided a displacement measuring device, wherein said plate springs are made of beryllium-copper and are attached to both sides of said electromagnetic system so that the both plate springs may extend parallel to the closed loop of the electromagnetic system.  
           [0019]    According to an aspect of the invention, there is provided a displacement measuring device, wherein said supporting mechanism comprises a fixing block to be attached to the electromagnetic system, a movable block to have a contact probe mounted and to be fixed to the displacement input parts of said guiding mechanism and supporting bars to connect said fixing block with said movable block.  
           [0020]    According to still other aspect of the invention, there is provided a displacement measuring device, wherein said movable block is fixed, on its both faces, to the displacement input parts of the two sheets of plate springs on the both sides of said electromagnetic system, and said contact probe mounted on the movable block is oriented in the direction opposite to the beam magnetic blocks.  
           [0021]    And, according to still other aspect of the invention, there is provided a displacement measuring device, wherein said supporting bars have the form of flat bars and connect the upper and lower faces of both the fixing block fixed to the bottom surface of the electromagnetic system and the movable block.  
           [0022]    Thus, the high sensitivity displacement measuring device according to the present invention has the advantage that measurements in the submicron area can be easily made through the improvement in, for example, the coil arrangement, the closed loop structure and the decreased gaps at the opposite ends of magnetic cores, and particularly through the improvement in the output sensitivity based on the increased displacement amplification of the magnetic cores by the help of the displacement amplification mechanism of plate springs, and that the control of the contact force for the probe is possible through the adjustment of the elastic modulus for plate springs and the distances between connecting sections on the leaf springs.  
           [0023]    Further, the present invention has another advantage that the movable block moves only in one direction, with supporting bars bearing the block, and the structure is less sensitive to the variation in external environment, i.e. noise or changing temperature thanks to the same material for both the beam magnetic blocks and the magnetic cores. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 shows the schematic view of a displacement measuring device by using a linear variable differential transformer according to a conventional art,  
         [0025]    [0025]FIG. 2 shows the perspective view of a high sensitivity displacement measuring device according to one embodiment of the invention,  
         [0026]    [0026]FIG. 3 shows an assembly drawing for a high sensitivity displacement measuring device shown in FIG. 2,  
         [0027]    [0027]FIG. 4 shows a front view of an electromagnetic system of a high sensitivity displacement measuring device shown in FIG. 2,  
         [0028]    [0028]FIG. 5 shows a front view of a guiding mechanism of a high sensitivity displacement measuring device shown in FIG. 2, and  
         [0029]    [0029]FIG. 6 shows a perspective view for a supporting mechanism of a high sensitivity displacement measuring device shown in FIG. 2. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]    A preferred embodiment of the invention will be described in detail below in conjunction with the accompanying drawings.  
         [0031]    As shown in FIGS. 2 and 3, a displacement measuring device according to the invention is briefly divided into three parts, that is, an electromagnetic system  10  which includes ferromagnetic blocks, coils etc. and within which magnetic flux is generated, a supporting mechanism  30  for supporting a contact probe into which a displacement is input, and plate springs  20  which are fixed to the magnetic cores of an electromagnetic system and to the supporting mechanism  30  and which cause, as guiding mechanism, the movement of magnetic cores with an amplified output displacement relative to input displacement.  
         [0032]    Referring to FIG. 4, the electromagnetic system  10  houses two primary coil bundles  11  to the right and left side. Between the primary coil bundles  11  there are positioned two secondary coil bundles  13 , the coils of which are wound on magnetic cores  14  each having a predetermined length. The magnetic cores  14  are so arranged that air gaps  18  each smaller than a few mm may be present between the respective ends of magnetic cores  14  and the respective ends of inward projections of E-formed loop magnetic blocks  17  on which projections primary coils are wound, wherein the two magnetic cores  14  extend parallel to each other.  
         [0033]    The primary coil bundles  11  are wound on the inward projections of two loop magnetic blocks  17  in the form of E and the spaces between the upper and lower free ends of the two loop magnetic blocks  17  are filled with beam magnetic blocks  19  connecting the loop magnetic blocks. Thus, the two loop magnetic blocks  17  and the two beam magnetic blocks  19  are connected together to form a closed loop, within which two secondary coil bundles  13  and two primary coil bundles  11  are positioned, wherein the loop magnetic blocks  17  and beam magnetic blocks  19  together with primary coil bundles  11  are stationary and on the other hand, two secondary coil bundles  13  with magnetic cores  14  are movable freely. The length of each beam magnetic blocks  19  is the same as that of a magnetic core  14  of secondary coil bundle  13  and the material for both magnetic cores  14  and beam magnetic blocks  19  are the same, so that they have the same thermal expansion. Thus, the thermal expansion and contraction for the magnetic cores  14  is balanced with that for the beam magnetic blocks  19 , so that the air gaps  18  between the free ends of magnetic cores  14  and the fee ends of spool projections for primary coil bundles  11  can be maintained constant independent of temperature variations. On the other hand, when a voltage is applied to the primary coil bundles  11 , a magnetic field is formed within the electromagnetic system  10 . In response, the magnetic cores  14  are moved along with the input of displacement generated relative to the reference position to cause the magnetic flux permeating the coils of secondary coil bundles  13  wrapped around the magnetic cores  14  to exhibit change in proportion with respective displacements. Thus, there is induced in the secondary coils an induced electric voltage, which represents differential voltage.  
         [0034]    On the other hand, a plate spring  20  as a guiding mechanism is made of beryllium-copper(Be—Cu) with the thickness of some hundred micrometers, as shown in FIG. 5. In particular, it is formed from etching part of a beryllium-copper plate by etching technique. The plate spring  20  so etched is formed in several zones, and is characterized in that all zones are integrally connected so that a displacement at one zone may lead to displacement at all zones of the plate spring  20 . As shown in FIG. 5, the plate spring  20  is divided into respective zones which are symmetrically arranged in both the upper and lower part of the plate. According to the definition of zones employed in the illustration, the zone protruding from the middle lower edge of the spring  20  is termed as ‘A’ zone  21 , the zone bounded by the reverse T-formed area in the middle lower edge is termed as ‘B’ zone  22 , the zones to the right and left side of the zone  22  are termed as ‘C’ zone  23  and the zone formed in the middle part of the plate spring  20  is defined as ‘D’ zone  24 . The narrow zones connecting the zone  21  and the zones  23  are termed as the first connecting sections  25 , the areas between the zone  22  and the zones  23  are termed as the second connecting sections  26  and the areas connecting the zones  23  and the zone  24  are designated as the third connecting sections  27 . The description for the lower part of the plate spring substantially holds for the upper part of the plate spring not specifically mentioned. The assembly and function of the plate spring so arranged will be described in detail in the following.  
         [0035]    Two plate springs  20  so formed are attached to the front and back face of the electromagnetic system  10 . Specifically, as clear from FIG. 3, the upper and lower beam magnetic blocks  19  are fixedly attached to the upper and lower ‘B’ zones  22 , and the end faces of the magnetic cores  14  for two secondary coil bundles  13  are adhered to the corresponding positions of the zones  24  in the middle area of plate springs  20 , whereby the two magnetic cores  14  can be maintained at a predetermined constant spacing and simultaneously the air gaps  18  between the end positions of magnetic cores  14  and the end positions of the inward projections of E- formed loop magnetic blocks  17  can be maintained constant, as depicted in FIG. 4. On the other hand, the elliptical hatched portions in FIG. 3 represent adhesive positions to combine the plate springs  20  with the electromagnetic system  10 .  
         [0036]    As shown in FIG. 6, a supporting mechanism  30  includes a stationary block  34  which is fixed to the bottom face of loop magnetic blocks  17  on one end side, a movable block  32  which is positioned at the middle portion of the bottom face of the beam magnetic blocks  19  and four supporting bars  36  connecting the stationary and movable block  34  and  32 . Thus, the movable block  32  connected to the stationary block  34  through supporting bars  36  is positioned on the bottom surface of beam magnetic blocks  19 , wherein the front and back faces of the movable block  32  are fixedly attached to the ‘A’ zones  21  of the plate springs  20 . Therefore, the movable block  32  displaces only in vertical direction by the help of supporting bars  36  and the plate springs  20  and so causes the ‘A’ zones  21  of the plate springs  20  also to make the same amount of displacement, eventually resulting in the displacement of the ‘D’ zones  24  of the plate springs  20 .  
         [0037]    Furthermore, the movable block  32  is fixed, on its bottom surface, with a rod  38 , on the free end of which a contact probe  39  is provided.  
         [0038]    In the following, the function of the plate spring is described.  
         [0039]    As described above, the ‘A’ zones  21  are fixed to the movable block  32 , the ‘B’ zones  22  are fixed to the beam magnetic blocks  19  and the ‘D’ zones  24  are fixed to the magnetic cores  14  of the secondary coil bundles  13 . In this state, when the movable block  32  makes a movement in line with the displacement input, the displacement of the movable block  32  is transmitted to the zones ‘C’ via the first connecting sections  25  on each of the plate springs  20 . Because the leading areas of the zones ‘C’  23  are connected to each other via the second connecting sections  26  of a fixing zone ‘B’  22 , the displacement is transmitted to the respective ‘D’ zones  24  through the third connecting sections  27  positioned in distal areas of the zones ‘C’  23 . In other words, given the displacement input, the zones ‘C’ transmit to the zones ‘D’  24  the input displacement amplified in proportion to the distance between the first and second connecting section  25  and  26  as well as the distance between the second and third connecting section  26  and  27 , in accordance with the principle of leverage. Accordingly, the displacement input acting on the movable block  32  is amplified through the plate springs  20 , so that the magnetic cores  14  of the secondary coil bundles  13  make the movement substantially equal to the amplified displacement output.  
         [0040]    This is expressed as the mathematical equation 1 as given below:  
         Δ                   Z   ′       =         (     La   +   Lb     )     Lb     ×   Δ                 Z                           
 
         [0041]    wherein, ΔZ′ stands for the output displacement, ΔZ does for the input displacement, La the distance between the first connecting section and the third connecting section, and Lb the distance between the first connecting section and the second connecting section.  
         [0042]    The operation of the high sensitivity displacement measuring device constructed as above is described in detail below.  
         [0043]    When a displacement is detected at the contact probe  39 , the rod  38  moves up or down the same amount as that displacement. The movable block  32  also makes the same amount of vertical movement, so that the zones ‘A’  21  of the plate springs  20 , fixed to the movable block  32 , make the same movement as the displacement. The movement of the zones ‘A’  21  is transferred to the zones ‘C’  23 , wherein the displacement so passed down is amplified to the output displacement as determined by the above equation 1 at the third connecting sections  27  to cause the zones ‘D’  24  to make the same movement.  
         [0044]    With the movement of the zones ‘D’  24 , the two secondary coil bundles  13  and magnetic cores  14 , which are secured to these zones, also move up or down the same distance as the amplified displacement output.  
         [0045]    On the other hand, when an electric voltage is applied to the primary coil bundles  11 , within the high sensitivity displacement measuring device  100  there is formed a magnetic field, the flux distribution is changed due to the movement of two magnetic cores  14 . Such a change of the flux distribution causes the change in the voltage induced in the secondary coil bundles  13  or the value for differential voltage. Thus, the value for differential voltage is output in proportional to the amplified displacement output relative to the initial displacement input, as can be determined by the forgoing equation 1.  
         [0046]    It is to be understood that, while the invention was described only with respect to a preferred embodiment, the invention is never restricted to that embodiment and a variety of modifications and alterations would be possible to a man skilled in the art by referring to the description or drawings presented here and within the spirit of the invention and thus those modifications or alterations are to fall within the scope of the invention, which scope should be limited only by the attached claims.