Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-11-23
2001-07-10
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207120, C324S207240, C324S207250, C336S045000, C340S870320
Reexamination Certificate
active
06259249
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an induction-type position measuring apparatus for performing position measurements based on electromagnetic coupling principles.
2. Description of the Related Art
One prior known magnetic encoder employing transformers is configured including a displacement sensor and a scale structure operatively associated therewith. The displacement sensor typically has two coils: a primary coil (i.e. drive coil), and a secondary coil (detection coil). The scale is placed adjacent to the sensor and is movable relative thereto. The scale is responsible during movement for modulating the magnetic flux as generated from the drive coil. Upon activation of the drive coil by supplying an alternating drive current thereto, variable magnetic flux might take place, which is then modulated by the scale resuting in coupling with the detection coil. This magnetic coupling causes induction of a corresponding voltage at the detector coil. The induced voltage is variable in potential with movement of the scale, and thus is employable as a detection output indicative of a position measured.
With the prior art magnetic encoder thus arranged, the drive coil and its associative detector coil are coaxially disposed. Such coaxial coil layout must permit presence of electromagnetic coupling components (cross-talk) between the spaced-apart drive coil and detector coil, which components remain independent of the relative position of the scale and are hardly affected from it. Presence of such crosstalk results in inclusion of certain offset components in a detection output of the detector coil, which again are hardly affectable by relative movements of the scale. These offset components can badly behave to cause significant measurement errors in cases where high-precision position detection is performed by dividing a wavelength of the scale into portions.
One typical approach to removal of such offset components is to differentiate two detection voltages of which phases are reverse with each other. This approach, however, suffers from difficulty in offset removal due to the fact that offset components are significantly affectable from the alignment accuracy of the drive and detector coils along with uniformity of materials employed therefor, resulting in the offset value experiencing non-negligible amount of variations among individual products.
SUMMARY OF THE INVENTION
It is an object of the invention to provide such an inductive position measurement apparatus capable of effecting high-accuracy position measurements that offset components are not generated in principle.
In accordance with one aspect of the instant invention, an induction-type position measurement apparatus comprises 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.
A respective one of the electromagnetic coupling devices may typically be configurable from a conductive member providing therein a closed loop current flow path. This closed loop conductor has a receiver conductor segment and more than one transmitter conductor segment The receiver conductor segment lies substantially parallel to the drive wire, and is coupled with the first variable magnetic field as produced by the drive wire. The transmit conductor segment is formed continuously with the receiver conductor segment, for creation of the second variable magnetic field. More practically, each loop conductor is structured including two transit conductor segments which are spaced apart from each other by a distance that is equivalent to half of the layout period or “pitch” of the electromagnetic couplers. These segments are at right angles to the drive wire in a plane, and may derive electromagnetically induced current components flowing therethrough in opposite directions perpendicular to the drive wire.
The variable magnetic field detector device may be such that it includes at least one set of four detection wires lying parallel to one another. These parallel detector wires are laid out within a coverage corresponding to the length of the drive wire at predefined intervals each equal to quarter of the layout period of the electromagnetic couplers. Upon coupling with one or more variable magnetic fields generatable from the transmit conductor segments of each loop conductor, the detector wires provide four-phase output signals, each of which is offset by 90° from another.
In accordance with another aspect of the invention, there is provided an induction-type position measurement apparatus with an inductive position sensor for use in measuring a present location of an object of interest under measurement. The inductive position sensor comprises 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.
In the former position measurement apparatus of the induction type in accordance with the first aspect of the invention, the drive wire and detection wire are disposed at right angles to each other on the first member so that any variable magnetic fields generatable due to alternating current flow in the drive coil will no longer be directly coupled with the detector wire. A first vaiable magnetic field generated by AC-driving the drive wire causes the electromagnetic coupler devices on the second member to produce an induced current. Each electromagnetic coupler is typically configurable from a conductive closed loop pattern having a receive conductor segment lying parallel to the drive wire and more than one transmit conductor segment extending perpendicular thereto. An induced current generatable in the receive conductor segment attempts to flow in this conductive loop producing a second variable magnetic field at right angles to the first variable magnetic field at a specific location physically distant from the receive conductor segments. Detecting this second magnetic field by the detector wire makes it possible to obtain a detection output changeable depending on relative displacement between the fist and second members.
With the scheme of this invention, no electromagnetic coupling activities take place in principle between the drive and detector wires due to the fact that these wires are dispos
Mitutoyo Corporation
Oliff & Berridg,e PLC
Strecker Gerard R.
LandOfFree
Induction-type position measuring apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Induction-type position measuring apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Induction-type position measuring apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2492160