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 (4a-4d) 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 (8a) and signal transmit conductor segments (8b, 8c) integral with the former (8a). The receive conductor segment (8a) 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 (8b, 8c) 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.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to an induction-type position measuring apparatus for performing position measurements based on electromagnetic coupling principles.[0003] 2. Description of the Related Art[0004] 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 resulting in coupling with the detection coil. This magnetic coupling causes induction of a corresponding voltage at the d...

AI Technical Summary

Benefits of technology

[0012] 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 variable 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 first and second members.

[0014] In the induction-type position measurement apparatus in accordance with the second aspect of the invention, the position sensor's drive coil and detector coil are disposed so that these are in the state that no electromagnetic coupling is present in the absence of any object of interest to be measured at right angles to each other, while permitting creation of electromagnetic coupling with the detector coil due to modulation of the drive coil's generated variable magnetic field distribution in response to the object's displacement. Accordingly, with this apparatus also, it becomes possible to obtain offset-free detection outputs, leading to an ability to attain high-precision position measurements.

Problems solved by technology

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.

This approach, however, suffers from difficulty in offset removal due to the fact that offset components are significantly affectable from to 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.

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