Induction-type position measuring apparatus

Abstract

An inductive linear encoder ( 10 ) has a position sensor ( 1 ) and scale ( 2 ) which are movably disposed relative to each other. The sensor ( 1 ) is with a drive wire ( 3 ) to which an alternating current is supplied, and one set of detection wires ( 4 a - 4 d ) at right angles to the drive wire ( 3 ) in the same plane. The scale ( 2 ) is configured including an elongate substrate ( 7 ) having its surface on which a series combination of conductive closed loop patterns ( 8 ) are periodically arranged at equal intervals. These conductive closed loop ( 8 ) are linearly laid out on the substrate ( 7 ) in the relative movement direction. Each loop ( 8 ) consists essentially of a reception conductor segment ( 8 a ) and signal transmit conductor segments ( 8 b , 8 c ) integral with the former ( 8 a ). The receive conductor segment ( 8 a ) is responsible for generation of an induced current due to a first variable magnetic field creatable from the drive coil ( 3 ). The transmit conductor segments ( 8 b , 8 c ) are to create second variable magnetic fields that are opposite in polarity to each other and are perpendicular to the first magnetic field. Creation of such second magnetic fields results in flow of an induced current in the detector wire ( 4 ) of sensor ( 1 ), which in turn acts as a position detection output current.

What is claimed is:  
     
         1 . An induction-type position measuring apparatus comprising: 
 a first member;    a second member having a measurement axis and being movably arranged along the measurement axis with a predefined gap between the first and second members;    a drive wire disposed on the first member and having a predetermined length along the measurement axis, for producing a first variable magnetic field upon receipt of an alternating current from a drive signal source;    an array of electromagnetic coupling devices laid out on the second member along the measurement axis at constant intervals, each of the electromagnetic coupling devices generating an induced current due to couplement with the first variable magnetic field generated by the drive wire, and generating a second variable magnetic field substantially perpendicular to the first variable magnetic field in response to the induced current at a position physically spaced apart from a coupling portion with the first variable magnetic field; and    a variable magnetic field detecting device which has at least one detection wire disposed on the first member substantially perpendicular to the drive wire, for providing an output signal due to couplement with the second variable magnetic field from the electromagnetic coupling devices, the output signal being variable with relative displacement of the first and second members.    
     
     
         2 . The apparatus according to    claim 1   , wherein the drive wire is wound into a drive coil, and wherein the detection wire is wound into a detector coil with its axis substantially perpendicular to the drive coil.  
     
     
         3 . The apparatus according to    claim 1   , wherein the first member includes an insulative block letting the drive wire and the detection wire be wound therearound into a drive coil and a detector coil respectively.  
     
     
         4 . The apparatus according to    claim 1   , wherein the first member includes an insulative substrate, and the drive wire and the detector wire are formed of patterned conductive leads on the top and bottom surfaces of the insulative substrate and conductive through-going leads extending through the substrate for electrical interconnection of the patterned inductive leads as to serve as drive coil and detector coil, respectively.  
     
     
         5 . The apparatus according to    claim 1   , wherein each of the electromagnetic coupling device comprises a conductive closed loop pattern having a receiver conductor segment lying substantially parallel to the drive wire for being coupled with the first variable magnetic field as generated by the drive wire, and a transmit conductor segment integral with the receiver conductor for creation of the second magnetic field.  
     
     
         6 . The apparatus according to    claim 5   , wherein the conductive closed loop pattern is of a rectangular shape with the receiver conductor segment lying at right angles to the transmit conductor segment.  
     
     
         7 . The apparatus according to    claim 5   , wherein the conductive closed loop pattern is shaped letting each of the receiver conductor segment and the transmit conductor segment resemble a circular arc in shape.  
     
     
         8 . The apparatus according to    claim 5   , wherein each the conductive closed loop pattern includes two spaced-apart receiver conductor segments with a distance equivalent to half of a layout period of the electromagnetic coupling devices for permitting flow of induced currents in opposite directions at right angles to the drive wire, and wherein the variable magnetic field detector device includes at least one set of four detection wires in combination, the wires being laid out in a range corresponding to the length of the drive wire at specified intervals each being quarter of the layout period of the electromagnetic coupling devices for coupling with a variable magnetic field created from the transmit conductor segment of each the conductive closed loop pattern to thereby provide four-phase output signals each being shifted of 90° from another.  
     
     
         9 . The apparatus according to    claim 5   , 
 wherein each the conductive closed loop pattern includes two spaced-apart transmit conductor segments at intervals each equal to half of a layout period of said electromagnetic coupling devices for permitting flow of induced currents in opposite directions at right angles to the drive wire, and    wherein the variable magnetic field detector devices includes at least one set of four first detection wires in combination being laid out in a range corresponding to the length of the drive wire at specified intervals each being quarter of the layout period of the electromagnetic coupling devices for coupling with a variable magnetic field from the transmit conductor segment of each the conductive closed loop pattern to thereby provide four-phase output signals each being shifted of 90° from another, at least one set of four second detection wires as disposed within a range of the length of the drive wire at intervals each equal to a quarter of the layout period of the electromagnetic coupling devices with a predefined phase shift relative to the first detection wires for coupling with variable magnetic fields from the transmit conductor segments of each the conductive closed loop pattern to thereby provide four-phase output signals each being shifted of 90° from another, the predefined phase shift being substantially equal to λ/2N, where λ is the layout period of the electromagnetic coupling devices, and N is an odd number greater than or equal to 3.    
     
     
         10 . The apparatus according to    claim 1   , wherein each the electromagnetic coupling device is formed of a conductive pattern responsive to receipt of the first variable magnetic field from the drive wire for permitting induction of an eddy current therein.  
     
     
         11 . The apparatus according to    claim 1   , wherein each the electromagnetic coupling device is formed of a magnetic material pattern for modulating a magnetic flux density of the first variable magnetic field generated from the drive wire.  
     
     
         12 . A position measurement apparatus having an inductive position sensor for sensing a position of an object to be measured, the position sensor comprising: 
 a drive coil for generating a variable magnetic field upon receipt of an alternating current from a drive current source;    a detection coil disposed adjacent to the drive coil for generating an induced current due to coupling with a variable magnetic field created by the drive coil in response to displacement of the object; and    a support body for immovably holding the drive coil and the detection coil,    wherein the drive coil and said detection coil are arranged so that in absence of the object no electromagnetic coupling is made, while electromagnetic coupling with the detection coil occur due to modulation in distribution of the variable magnetic field as generated by the drive coil depending upon displacement of the object.    
     
     
         13 . The apparatus according to    claim 12   , wherein the drive coil and the detection coil are disposed having axes at right angles to each other.  
     
     
         14 . The apparatus according to    claim 12   , wherein the inductive position sensor is adaptable for use as a proximity sensor by letting the drive coil and the detection coil be laid out having axes at right angles to each other and by comprising a contactor movably disposed as the object along a bisector line of the axes of the drive coil and the detection coil for modulation of a variable magnetic field generatable from the drive coil in accordance with a position.  
     
     
         15 . The apparatus according to    claim 12   , wherein the inductive position sensor is adaptable for use as a linear encoder by letting the drive coil and the detector coil be disposed having axes at right angles to each other and by comprising an elongate scale movably penetrating the detection coil as the object and having thereon an array of periodically disposed magnetic field modulation units for modulating a variable magnetic field distribution from the drive coil during movement of the scale.