Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-05-19
2001-05-22
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S202000, C324S207200, C324S174000
Reexamination Certificate
active
06236200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic metal sensor for detecting a magnetic metal piece and a method for detecting magnetic metal using the magnetic metal sensor. As an example, the present invention relates to a magnetic metal sensor for detecting the possible presence of a magnetic metal piece or its displacement, a magnetic metal sensor for detecting a plurality of magnetic metal pieces from a unit under detection comprised of the magnetic metal pieces arranged side-by-side at a pre-set separation from one another.
2. Related Art
There has hitherto been known an eddy-current type sensor as a magnetic metal sensor for detecting the possible presence or displacement of magnetic metal.
This type of the magnetic metal sensor is desired to be used in a system, such as a machine tool for detecting the number of teeth of a gear for controlling the rpm of the rotational angle of the gear, or in a system for detecting the number of teeth used for knitting fibers in a knitting machine for cloths or chemical fibers for controlling the movement positions of the knitting bar of a comb-shaped knitting bar.
The magnetic metal sensor is also desired to be used in a system for judging whether or not a robot arm, for example, has approached a pre-set position to control the arm position, or in a system for detecting the slack or failure in tightening of a screw mounted on a work in order to check the operating process.
Meanwhile, the magnetic metal sensor of the eddy-current system is usually low in response rate. Thus, with the magnetic metal sensor of the eddy-current sensor, it has been difficult to detect a metal piece moved at an elevated speed or plural metal pieces paced side-b-side.
Also, the magnetic metal sensor of the eddy-current system is suddenly lowered in output level if the metal piece being detected is smaller in size than the coil making up the sensor. Thus, with the magnetic metal sensor of the eddy current system, it has been difficult to detect metal pieces of small sizes.
In addition, with the eddy-current type magnetic metal sensor, since the eddy current needs to flow through the metal piece by magnetic induction, the magnetic field applied from the coil to the metal piece needs to be sufficiently large to render it difficult to provide a sufficient distance between the coil and the metal piece.
By the above reason, it has been difficult to apply the eddy-current type magnetic metal sensor to a system for controlling the system for a machine tool or a system for controlling the destination of movement.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic metal sensor which is high in response speed and capable of detecting a metal piece of a small size and of increasing the separation thereof from the metal piece.
It is another object of the present invention to provide a magnetic metal sensor capable of detecting plural magnetic metal pieces arranged side-by-side at a pre-set separation &lgr; and which is high in the response rate while being capable of detecting a metal piece of a small size and increasing the separation thereof from the metal piece.
It is still another object of the present invention to provide a magnetic metal sensor adapted for detecting plural metal pieces arranged side-by-side and for detecting magnetic metal pieces lying proximate to the sensor.
It is yet another object of the present invention to provide a method for detecting plural magnetic metal pieces arranged side-byside at a pre-set separation &lgr; which is high in the response rate and which is capable of detecting a metal piece of a small size and increasing the separation thereof from the metal piece.
In one aspect, the present invention provides a magnetic metal sensor including a pair of coils energized by the current of a pre-set frequency for generating the magnetic field in a pre-set direction, a core formed of a high magnetic permeability material having a first portion, a second portion and a third portion, magnetic field generating means for applying to the core a magnetic field along the direction parallel to the magnetic field generated by the paired coils and detection means for detecting from the paired coils the magnetic field which is varied by magnetic metal approaching to an open magnetic path portion of the core. The core constitutes an open magnetic path in its entirety. The first portion carries one of the paired coils, the second portion carries the other coil and the third portion interconnects one ends of the first and second portions along the direction parallel to the direction of the magnetic field generated by the paired coils.
In the magnetic metal sensor, as magnetic metal approaches to the open magnetic path portion of the core, the magnetic circuit defined by the core and air is varied in magnetic reluctance to cause variations in the impedance of the paired coils. Based on changes in impedance of the paired coils, the magnetic metal sensor detects the possible presence of magnetic metal or its displacement. based on variations in the impedance of the paired coils.
In another aspect, the present invention provides a magnetic metal sensor including a pair of magnetic impedance effect (MI) devices fed with the current of a pre-set frequency, magnetic field generating means for applying to the paired MI devices a magnetic field along the direction parallel to the direction of the supplied current, and detection means for detecting from the paired MI devices the magnetic field varied by magnetic metal approaching the paired MI devices.
If, in the magnetic metal sensor, magnetic metal approaches to the paired MI devices, the magnetic circuit defined by the MI devices and air is changed in magnetic reluctance to change the impedances of the paired MI devices. The magnetic metal sensor detects the possible presence or displacement of magnetic metal based on impedance changes of the paired MI devices.
In still another aspect, the present invention provides a magnetic metal sensor moved relative to a unit under detection comprised of a plurality of magnetic metal pieces arrayed side-by-side at a pre-set interval &lgr; along the direction of side-by-side arraying of the magnetic metal pieces for detecting the magnetic metal pieces, in which the sensor includes a pair of magneto-electric conversion units each having a magnetically sensitive portion which responds to variations in the magnetic field along the direction of magnetic sensitivity and magnetic field generating means for applying the magnetic field along the direction of magnetic sensitivity to the magnetically sensitive portions of the paired magneto-electric conversion units. The magnetically sensitive portions are provided in the paired magneto-electric conversion units so that the magnetically sensitive portions is of the same polarity and so that the direction of magnetic sensitivity is perpendicular to the direction of side-by-side arraying of the magnetic metal pieces. The magnetically sensitive portions are provided so that the separation g′ between neighboring magnetic metal pieces along the movement direction is given by:
g′=
(
n
+1/2)&lgr;
where &lgr; is the above-defined pre-set interval and n is an integer not less than 0.
With the present magnetic metal sensor, the magnetically sensitive portions are sequentially responsive to the magnetic metal pieces arranged side-by-side. If the magnetically sensitive portion of one of the magneto-electric conversion units responds to one of the magnetic metal pieces, the magnetically sensitive portion of the other magneto-electric conversion unit responds to none of the magnetic metal pieces. Thus, with the present magnetic metal sensor, the difference of detection signals of the paired magneto-electric conversion units is deflected on the plus and minus sides about the value of the difference of the detection signals in the absence of response of both magneto-electric conversion units as center. The magnetic metal sensor detects the positio
Kusumi Masaaki
Nekado Yasuo
Jolly Anthony
Maioli Jay H.
Sony Precision Technology Inc.
Williams Hezron
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