Abstract:
There is provided an induced current position transducer having an improved signal intensity and durability to gap variations. This can be achieved by preventing harmful diffusion of magnetic fluxes to reduce a loss due to leakage fluxes and forming an efficient closed magnetic path between a magnetic field generator and a magnetic flux sensor. A high permeable substance is disposed in a target magnetic path on members of a read head and a scale. This arrangement can suppress a loss due to leakage fluxes caused from diffusion of magnetic fluxes occurred in the conventional winding structure, improving a signal intensity of a magnetic flux and reducing an affection from an external magnetic flux.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority under 35USC §119 to Japanese Patent Application No. 2000-198895, filed on Jun. 30, 2000, the entire contents of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an induced current position transducer for use in calipers, linear height gauges and linear scales, for example. More particularly, the present invention relates to an induced current position transducer capable of reducing harmful magnetic fluxes diffusing to the outside from the inside of the transducer to improve signal intensity. 
     2. Description of the Related Art 
     Electric calipers using an induced current position transducer have been developed and demonstrated in the art. In the induced current position transducer, a magnetic field generator generates a primary magnetic field, which couples to a first section in a coupling loop that consists of two loop sections. The first section generates an induced current in response to the primary magnetic field. A second section in the coupling loop generates a secondary magnetic field, corresponding to the induced current, which couples to a magnetic flux sensor. The magnetic flux sensor is arranged at a spatial period that corresponds to an array of coupling loops to provide a signal in accordance with a relative position of the coupling loop to the magnetic flux sensor. 
     The above signal processing technology may be applied to a measurement device. In this case, since the measurement device has restrictions from its characteristic on a structure and a structural material, it often employs a metal for the material. If the above technology is applied to a precise measurement under such the condition, it is required to maintain a magnetic flux intensity having a role of a signal with a possible minimal loss. Nevertheless, the primary and secondary magnetic fields diffuse along the members that construct the measurement device. As a result, an efficient magnetic coupling to the coupling loop can not be ensured and a sufficient signal intensity can not be obtained. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of such the disadvantages and according has an object to provide a higher precise measurement technology by preventing harmful diffusion of magnetic fluxes and reducing a signal intensity variation in accordance with a distance (gap) variation between a coupling loop and a magnetic generator and magnetic flux sensor to improve a stability over the gap variation, and by forming a closed magnetic path between the coupling loop and the magnetic generator and magnetic flux sensor to improve the signal intensity. 
     The present invention is provided with an induced current position transducer, which comprises a first and a second members arranged opposite to each other and relatively movable along a measurement axis, the first and second members each having a first and a second magnetic flux regions formed normal to the measurement axis; a magnetic field generator for generating a first variable magnetic flux within the first magnetic flux region in response to a driving signal; a coupling loop having a first section located within the first magnetic flux region and a second section located within the second magnetic flux region, the first section generating an induced current in response to the first variable magnetic flux, and the second section generating a second variable magnetic flux corresponding to the induced current; and a magnetic flux sensor disposed within the second magnetic flux region for sensing the second variable magnetic flux, wherein any one of the magnetic field generator, the coupling loop and the magnetic flux sensor is located on one of the first and second members, and the remainder two on the other of the first and second members, and wherein a high permeable substance is disposed on at least a part of the first member, the second member and a gap between the first and second members to form a magnetic path for a flux permeating at least one of the magnetic field generator, the coupling loop and the magnetic flux sensor. 
     In a preferred embodiment of the present invention, the magnetic field generator and the magnetic flux sensor are located on one of the first and second members, and the coupling loop on the other of the first and second members. 
     In a second embodiment, the magnetic field generator and the coupling loop may be located on one of the first and second members, and the magnetic flux sensor on the other of the first and second members. 
     In a third embodiment, the coupling loop and the magnetic flux sensor may be located on one of the first and second members, and the magnetic field generator on the other of the first and second members. 
     Preferably, the magnetic flux sensor in the first and second embodiments and the magnetic field generator in the third embodiment have a plurality of regions alternating polarities along the measurement axis, which regions are formed in more detail in a periodic pattern with a certain wavelength along the measurement axis. 
     The high permeable substance may comprise a high permeable resin layered on, a magnetic material adhered on, or a magnetic material embedded in at least one of the first and second members. 
     The high permeable substance may also comprise a high permeable resin layered on the first member and/or the second member and patterned to cover the pattern of at least one of the magnetic field generator, the coupling loop and the magnetic flux sensor. 
     One of the first and second members is secured on a beam extending along the measurement axis, and the other of the first and second members is secured on a slider slidably mounted on the beam. The beam and slider may be composed of a magnetic material. 
     In the present invention, one of the first and second members is secured on a beam extending along the measurement axis, and the other of the first and second members is secured on a slider slidably mounted on the beam. Preferably, the beam is composed of a magnetic material, and in the slider at least one side opposite to the beam is composed of a non-magnetic material. 
     Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully understood from the following detailed description with reference to the accompanying drawings in which: 
     FIG. 1 shows an induced current position transducer according to an embodiment of the present invention; 
     FIG. 2 is a perspective view showing the same induced current position transducer partly cut off; 
     FIG. 3A is a cross-sectional view of FIG. 2 seen in the direction of the arrow A; 
     FIG. 3B is a cross-sectional view of a conventional device shown for the purpose of comparison; 
     FIG. 4 is a cross-sectional view of a transducer according to another embodiment of the present invention; 
     FIG. 5 is a cross-sectional view of a transducer according to a further embodiment of the present invention; 
     FIGS. 6A-B are a cross-sectional view and a plan view of a scale in a transducer according to a further embodiment of the present invention; 
     FIGS. 6C-D are a cross-sectional view and a plan view of a scale in a transducer according to a further embodiment of the present invention; 
     FIG. 7 is a perspective view showing the main part of the same transducer; 
     FIG. 8 is a perspective view showing the main part of a transducer according to a further embodiment of the present invention; and 
     FIG. 9 is a perspective view showing the main part of a transducer according to a further embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 
     FIG. 1 shows the main part of an incremental, induced current position transducer according to an embodiment of the present invention. 
     The position transducer  200  comprises a read head  220  or a first member and a scale  210  or a second member, which are arranged opposite to each other via a certain gap interposed therebetween and relatively movable along a measurement axis  114  in the figure. In this embodiment, a magnetic field generator  222 , each two sets of magnetic flux sensors  224 ,  226  and coupling loops  212 ,  216  are provided to reduce an offset while each one set of the sensors and the loops may also be applied in the present invention. The magnetic field generator  222  and magnetic flux sensors  224 ,  226  are located on the read head  220  and the coupling loops  212 ,  216  on the scale  10 . The magnetic field generator  222  and first sections  213 ,  217  in the coupling loops  212 ,  216  are located within a first magnetic flux region while the magnetic flux sensors  224 ,  226  and second sections  214 ,  218  in the coupling loops  212 ,  216  are located within a second magnetic flux region. 
     The scale  210  includes a plurality of first coupling loops  212  consisting of closed loops with a first polarity and a plurality of second coupling loops  216  consisting of closed loops with a second polarity. The coupling loops  212  are spatially phase-shifted and electrically isolated from the coupling loops  216 . 
     A first coupling loop  212  includes a first section  213  and a second section  214  connected to each other through a pair of connection conductors  215 . A second coupling loop  216  includes a first section  217  and a second section  218  connected to each other through a pair of connection conductors  219  in the same manner. 
     In the plurality of first coupling loops  212 , the first sections  213  are arrayed on a first side edge of the scale  210  along the measurement axis  114 . The second sections  214  are arrayed on the center of the scale  210  along the measurement axis  114 . The connection conductors  215  extend in the direction normal to the measurement axis  114  to connect the first sections  213  with the second sections  214 . 
     In the plurality of second coupling loops  216 , the first sections  217  are arrayed on a second side edge of the scale  210  along the measurement axis  114 . The second sections  218  are arrayed on the center of the scale  210  along the measurement axis  114  and interleaved with the second sections  214  of the coupling loops  212 . The connection conductors  219  extend in the direction normal to the measurement axis  114  to connect the first sections  217  with the second sections  218 . 
     The read head  220  in the induced current position transducer  200  includes a magnetic field generator  222  that has a first part  223 A and a second part  223 B of the magnetic field generator. The first part  223 A of the magnetic field generator is located at the first side edge of the read head  220  while the second part  223 B of the magnetic field generator is located at the second side edge of the read head  220 . The first  223 A and second  223 B parts of the magnetic field generator comprise rectangular patterns with a long side that extends along and has the same length as the measurement axis  114 . In addition, the first  223 A and second  223 B parts of the magnetic field generator have a short side that extends in the direction normal to the measurement axis  114  and has a length of d1. 
     The magnetic field generator  222  has terminals  222 A and  222 B that are connected to a driving signal generator  150  for transmission. The driving signal generator  150  supplies a time-variable driving signal to the magnetic field generator terminal  222 A. As a result, a time-variable current can flow from the terminal  222 A to the terminal  222 B through the magnetic field generator  222 . 
     In response to the above operation, the first part  223 A of the magnetic field generator generates a primary magnetic field that rises up from the sheet of FIG. 1 inside the loop of the first part  223 A and falls down to the sheet of FIG. 1 outside the loop of the first part  223 A. To the contrary, the second part  223 B of the magnetic field generator generates a primary magnetic field that rises up from the sheet of FIG. 1 outside the loop of the second part  223 B and falls down to the sheet of FIG. 1 inside the loop of the second part  223 B. As a result, such currents are induced in the coupling loops  212  and  216  that can cancel magnetic field variations. 
     The induced currents flowing into the first sections  213 ,  217  in the coupling loops respectively have the opposite direction to those that flow into the corresponding proximal portions in the parts  223 A,  223 B of the magnetic field generator. Loop currents with the opposite polarities flow into adjacent ones of the second sections  214  and  218  that are located on the scale center. Thus, a secondary magnetic field is generated so that magnetic field components with the opposite polarities distribute periodically along the center of the scale. The periodic secondary magnetic field has a wavelength of λ that is equal to an interval between successive two of the second sections  214  (or  218 ). 
     For the purpose of maintaining the magnetic flux intensity of the primary and secondary magnetic fields and reducing leakage fluxes to external, a high permeable substance is disposed for the scale  210  and the read head  220 . Positions to locate the substance and effects caused from the location of the substance will be described later in detail. 
     The read head  220  includes a first  224  and a second  226  magnetic flux sensors. These first  224  and second  226  magnetic flux sensors respectively consist of conductor segments  228  and  229  that form part of a plurality of sinusoidal waveforms. The conductor segments  228  and  229  are patterned on both surfaces of an insulating layer in a printed circuit board that is employed to configure the read head  220 . 
     The segments  228  and  229  are connected via through wires  230  to form positive polar loops  232  and negative polar loops  234  alternating in the first  224  and second  226  magnetic flux sensors. As a result, inductive regions are arrayed and formed in a spatially width-modulated periodic pattern. In this case, a pair of adjacent positive polar loop  232  and negative polar loop  234  has a length along the measurement axis equal to a wavelength of λ. In addition, a phase difference of λ/4 is defined between the first magnetic flux sensor  224  and the second magnetic flux sensor  226 . The first  224  and second  226  magnetic flux sensors are arranged on the center of the read head  220  and sandwiched between the first  223 A and second  223 B parts of the magnetic field generator, having a width of d2 along the direction normal to the measurement axis. 
     Useless coupling from the magnetic field generator loops to the magnetic flux sensor loops (independent of the position and the scale) can be avoided with such the configuration. The primary magnetic fields generated from the first  223 A and second  223 B parts of the magnetic field generator direct to opposite directions in the proximity of the first  224  and second  226  magnetic flux sensors. Therefore, the primary magnetic fields cancel one another within occupied areas of the first  224  and second  226  magnetic flux sensors. Ideally, the primary magnetic fields should be cancelled completely in the areas. 
     The first  224  and second  226  magnetic flux sensors are inwardly spaced apart a gap of d3 equally from the first  223 A and second  223 B parts of the magnetic field generator. Therefore, according to the first  223 A and second  223 B parts of the magnetic field generator, the magnetic fields generated in the areas occupied by the first  224  and second  226  magnetic flux sensors in the read head  220  are symmetrical and opposite. Direct inductive actions can be thereby cancelled effectively. Voltages induced across the first  224  and second  226  magnetic flux sensors from useless direct coupling with the first  223 A and second  223 B parts of the magnetic field generator can be reduced first to some extent if the magnetic field generator is spaced from the magnetic flux sensors. Second, a symmetrical design can reduce the useless coupling to zero. 
     The plural first coupling loops  212  are arrayed at the same pitch as the wavelength λ of the first  224  and second  226  magnetic flux sensors. The first sections  213  are intended to have a length as close to the wavelength λ as possible along the measurement axis  114  while ensuring an insulating space  201  between adjacent ones. The first sections  213  provide a width of d1 in the direction normal to the measurement axis  114 . 
     The plural second coupling loops  216  are similarly arrayed at the same pitch as the wavelength λ. The first sections  217  are intended to have a length as close to the wavelength λ as possible along the measurement axis  114  while ensuring an insulating space  201  between adjacent ones. They provide a width of d1 in the direction normal to the measurement axis  114 . 
     The second sections  214  and  218  in the first  212  and second  216  coupling loops are also arrayed at the same pitch as the wavelength λ. The second sections  214  and  218 , however, have a length along the measurement axis  114  that is determined as close to ½ the wavelength λ as possible. An insulating space  202  is provided between a pair of adjacent second sections  214  and  218  as shown in the figure. Thus, the second sections  214  and  218  in the first  212  and second  216  coupling loops are interleaved along the length of the scale  210 . The second sections  214  and  218  have a width of d2 in the direction normal to the measurement axis  114 . 
     A gap of d3 is provided between the second sections  214  and  218  and the corresponding first sections  213  and  217 . Therefore, when the read head  220  is located close to the scale  210 , the first part  223 A of the magnetic field generator is arranged in line with the first section  213  of the first coupling loop  212 . The first part  223 B of the magnetic field generator is arranged in line with the second section  217  of the second coupling loop  217 . The first  224  and second  226  magnetic flux sensors are arranged in line with the second sections  214  and  218  in the first  212  and second  216  coupling loops. 
     In this embodiment, the scale  210  and the read head  220  employ printed circuit boards. In addition, the magnetic field generator, coupling loops and magnetic flux sensors are produced with printed circuit board processes. 
     In measurement operations, a time-variable driving signal is supplied from the driving signal generator  150  to the terminal  222 A of the magnetic field generator. The first part  223 A of the magnetic field generator thereby generates a first variable magnetic field in a first direction. The second part  223 B generates a second variable magnetic field in a second direction opposite to the first direction. The second variable magnetic field has the same magnetic field intensity as the first variable magnetic field generated from the first part  223 A of the magnetic field generator. 
     The plural first coupling loops  212  couple inductively with the first part  223 A of the magnetic field generator by means of the first magnetic field generated from the first part  223 A. An induced current thereby flows clockwise into each of the first coupling loops  212 . At the same time, the plural second coupling loops  216  couple inductively with the second part  223 B of the magnetic field generator by means of the second magnetic field generated from the second part  223 B. This induces a current flowing counterclockwise into each of the second coupling loops  216 . As a result, these currents flow in the opposite directions through the second sections  214  and  218  in the coupling loops  212  and  216 . 
     The clockwise current flowing into the second section  214  in the first coupling loop  212  generates a third magnetic field that falls down to the sheet of FIG. 1 within the second section  214 . The counterclockwise current flowing into the second section  218  in the second coupling loop  216  generates a fourth magnetic field that rises up from the sheet of FIG. 1 within the second section  218 . A net variable magnetic field is thereby created along the measurement axis  114 . This variable magnetic field has a wavelength equal to the wavelength λ of the first  224  and second  226  magnetic flux sensors. 
     Accordingly, when the positive polar loops  232  of the first magnetic flux sensor  224  meet one of the second sections  214 ,  218 , the negative polar loops  234  of the first magnetic flux sensor  224  meet the other of the second sections  214 ,  218 . This situation is similarly caused when the positive polar loops  232  and negative polar loops  234  of the second magnetic flux sensor  226  meet the second sections  214 ,  218 . The variable magnetic fields generated from the second sections  214  and  218  are spatially modulated with the same wavelength as that used for spatially modulating the first  214  and second  216  sections of the magnetic flux sensors. Therefore, induced electromotive forces (EMF) generated when the positive  232  and negative  234  polar loops meet the second section  214  are equal to each other and opposite to EMFs generated when they meet the second section  218 . 
     Thus, the net output from the positive polar loop  232  exhibits a sinusoidal function of a position “x” of the read head  220  along the scale  210  when the read head  220  moves relative to the scale  210 . In this function, an offset component in the output signal caused from the useless coupling becomes nominal zero. Similarly, the net output from the negative polar loop  234  exhibits a sinusoidal function of the position “x” of the read head  220  along the scale  210  when the read head  220  moves relative to the scale  210 . In this function, an offset component in the output signal caused from the useless coupling becomes nominal zero. EMF contributions are provided in the same phase from the positive polar loop  232  and the negative polar loop  234 . 
     The first  224  and second  226  magnetic flux sensors are in a quadrature relation. Therefore, the output signal obtained at the first magnetic flux sensor  224  as the function of the position x has a phase difference of 90° from the output signal obtained at the second magnetic flux sensor  226  as the function of the position x. These signals are both sent to a signal process circuit  140  for processing received signals. 
     From the first  224  and second  226  magnetic flux sensors, the signal process circuit  140  reads in the output signals, which are sampled, converted into digital values and then sent to a control unit  160 . The control unit  160  processes the digitized output signals to determine the relative position x of the read head  220  to the scale  210  within the wavelength λ. 
     It should be appreciated that an appropriate variation on the locations of the through wires can give a zero width in the direction normal to the measurement axis to one of the positive polar loops  232  and negative polar loops  234  (effecting as simple conductor elements between adjacent loops). In this case, the first  224  and second  226  magnetic flux sensors serve as single-polar magnetic flux receivers, which have increased sensitivities to an external magnetic field and provide output signals with ½ amplitude (resulted from reduction of the loop region) compared to the previous embodiment. 
     This design modification can provide some benefits. As a result of the magnetic field generator symmetrically configured, the useless magnetic fluxes through loops are held at nominal zero. The output signals from the magnetic flux sensors  224  and  226  also have zero offset and swing between a positive maximum value and a negative minimum value. A degree of output signal variation per unit displacement is extremely high with respect to a given measurement range because of complementary periodic structures of the scale element and magnetic flux sensors. 
     On the basis of properties of quadrature outputs from the first  224  and second  226  magnetic flux sensors, the control unit  160  can determine the direction of relative movement of the read head  220  to the scale  210 . The control unit  160  counts part or all of “increments” of the wavelength λ passing through. The control unit  160  employs the count and the relative position within the wavelength λ to provide a relative position from a certain origin located between the read head  220  and the scale  210 . The control unit  160  sends a control signal to the driving signal generator  150 , which generates the time-variable driving signal. 
     FIG. 2 shows an outlined positional relation between the scale  210  and the read head  220  in the embodiment. For the convenience of simplification, the transducer is sliced with a plane normal to the measurement axis  114 . 
     A beam  31 , extending along the measurement axis, supports a slider  32  slidably. The scale  210  is located on the beam  31  and the read head  220  is located on the slider  32 , opposing to the scale  210 . 
     FIG. 3A shows a cross section of the scale  210  and the read head  220  together with elements for supporting them seen in the A-direction of FIG.  2 . FIG. 3B shows a conventional example for the purpose of comparison. 
     The beam  31  and slider  32  are composed of magnetic stainless steel, for example. A substance with a high permeability is layered on the read head  220  in a surface opposite to the scale  210 . This high permeable substance  33  may employ a high permeable resin composed of high permeable magnetic powders mixed in a resin. In this case, if an IC is mounted on a surface of the read head  220  and the high permeable resin is to be layered on the surface, the high permeable substance  33  can be formed by pouring the resin. If no IC is mounted, a usual magnetic plate or tape may be adhered on that surface of the read head  220 . 
     The high permeable substance  33  can be arranged on the upper surface of the read head  220 . This arrangement allows, as shown in FIG. 3A, the most of magnetic fluxes  34  that are generated from and located in the figure above the magnetic field generator parts  223 A and  223 B to pass through the high permeable substance  33  that has a low magnetic resistance. Therefore, it is possible to suppress leakage and dispersion of the magnetic fluxes  34  to external and concentrate the magnetic fluxes generated from the magnetic field generator parts  223 A and  223 B onto the first sections  213 ,  217  in the coupling loops  212 ,  216 . It is also possible to reduce magnetic resistances in magnetic circuits and increase intensities of signals received at the magnetic flux sensors  232 ,  234 . 
     To the contrary, in the conventional induced current position transducer shown in FIG. 3B, no magnetic material is connected to a surface of the read head  220 . In addition, an inner frame of the slider  32  is composed of a magnetic metal. Accordingly, flows of the magnetic fluxes  34  can not form a closed magnetic circuit that passes through the surface of the read head  220  effectively, resulting in diffusion of the magnetic fluxes  34  toward above the read head  220 . As a result, the magnetic fluxes from the magnetic field generator parts  223 A,  223 B can not concentrate on the first sections  213 ,  217  in the coupling loops  212 ,  216 , causing leakage fluxes that yield losses. This means that the third and fourth magnetic fields generated from the second sections  214 ,  218  in the coupling loops  212 ,  216  are also weaken. Further, the third and fourth magnetic fields diffuse toward above the read head  220  to prevent them from concentrating efficiently on the magnetic flux sensors  232 ,  234 . Accordingly, the magnetic flux sensors  232 ,  234  can not provide sufficient signal intensities. 
     It is more effective if a high permeable substance exists between the read head  220  and the scale  210 . FIG. 4 shows another high permeable substance  35  that is layered on the read head  220  in a surface opposing to the scale  210 . The high permeable substance  35  may also be layered on the scale  210  in a surface opposing to the read head  220 . 
     FIG. 5 shows another example of the slider  32 , which has an inner frame  36  that may be composed of a non-magnetic metal or resin and an outer frame  37  that may be composed of a magnetic stainless steel. According to such the arrangement, the inner frame  36  can prevent magnetic fluxes from diffusing from the beam  31  to the slider  32 . In addition, the outer frame  37  of the slider  32  can magnetically shield external magnetic fields that affect on measurements. 
     FIGS. 6A-D show 16-way positions A-I and A′-I′ to arrange high permeable substances on the scale  210 . FIGS. 6B and 6D are cross-sectional views of FIGS. 6A and 6C respectively taken along arrowhead lines S—S′ and T—T′. 
     The scale  210  is applied to such an induced current position transducer as shown in FIG.  7 . The transducer comprises a set of magnetic field generator  222  and a set of magnetic flux sensor  224  on the first member or read head  220  and a plurality of coupling loops  212  on the second member or scale  210 . The arrangement of the high permeable substance shown in FIG. 6 may also be applied to the induced current position transducer shown in FIG.  1 . 
     Desirably, as shown with arrows in the figure, the position for arranging the high permeable substance is determined on a path that can be considered ideal for a signal magnetic flux to pass therethrough. 
     For the above reason, a high permeable substance characteristically exists corresponding to each coupling loop  212  located inside a scale substrate  41  or on the upper or lower surface thereof. In particular, A, B, C and A′, B′, C′ are respectively located on extensions of axes of the first sections  213  and the second sections  214 . 
     E and F exemplify pattern formations of a high permeable substance per coupling loop  212 . I, H and I′, H′ exemplify pattern formations of the same first sections  213  and of the same second sections  214  in each coupling loop  212  using common high permeable substances. Any one of the above 16-way positions A-I and A′-I′ may also be applied to arrange high permeable substances. Any combination of the positions to arrange high permeable substances may be selected in accordance with restrictions such as a design specification for the transducer. 
     The more the positions for arranging high permeable substances exist, the more the effect by the positions becomes sufficient to increase the signal intensity and reduce the leakage flux. 
     In the above embodiment, the magnetic field generator  222  and magnetic flux sensor  224  are located on the read head  220  while the coupling loops  212  on the scale  210 . The magnetic flux sensor  224  may be formed on the scale  210  while the coupling loops  212  and magnetic field generator  222  on the read head  220  as shown in FIG.  8 . In this case, the magnetic flux sensor  224  has a waveform pattern crossing at a certain period and the magnetic field generator  222  has a rectangular pattern formed to cover the second sections  214  in the coupling loops  212 . 
     FIG. 9 shows a further embodiment. In this embodiment, the magnetic flux sensor  224  is formed on the scale  210  while the coupling loops  212  and magnetic field generator  222  on the read head  220 . In this case, the magnetic flux sensor  224  has a waveform pattern crossing at a certain period and the magnetic field generator  222  has a rectangular pattern formed to cover the first sections  213  in the coupling loops  212 . The present invention is also applicable to the induced current position transducer thus configured. 
     As obvious from the forgoing, according to the present invention, an efficient closed magnetic path is formed between a magnetic field generator and a magnetic flux sensor to reduce occurrence of a harmful leakage magnetic flux and prevent affection from an external magnetic field. This leads to an induced current position transducer capable of improving signal intensity and achieving a higher precise measurement. 
     Having described the embodiments consistent with the present invention, other embodiments and variations consistent with the invention will be apparent to those skilled in the art. Therefore, the invention should not be viewed as limited to the disclosed embodiments but rather should be viewed as limited only by the spirit and scope of the appended claims.