Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-03-23
2003-06-17
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207240, C324S207120, C336S136000
Reexamination Certificate
active
06580264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position transducer which detects an amount of travel and moved position of a moving or movable part of machine tools, industrial robots, etc.
2. Description of the Related Art
As a position transducer which detects an amount of travel and moved position of a moving part of machines tool, industrial robots, etc., there has been proposed a position transducer
100
of a differential transformer type as shown in FIG.
1
.
As shown in
FIG. 1
, the differential transformer type position transducer
100
includes a detection unit
110
consisting of an exciting coil
111
excited with a signal of 2 to 3 kHz in frequency for example, a first detection coil
112
disposed adjacently to one end of the exciting coil
111
and concentrically with the exciting coil
111
, and a second detection coil
113
disposed adjacently to the other end of the exciting coil
111
and concentrically with the exciting coil
111
, and a round bar-shaped magnetic core
122
installed with a spindle
121
to a moving part
120
of a machine tool, industrial robot or the like movably inside the detection unit
110
along the center axis of the latter as the moving part
120
moves.
The first and second detection coils
112
and
113
are longer than the moving distance of the core
122
, and the exciting coil
111
is substantially as long as the first and second detection coils
112
and
113
. The first and second detection coils
112
and
113
are magnetically coupled to the exciting coil
111
and given magnetic fluxes by the exciting coil
111
to induce an electric power.
In the position transducer
100
constructed as in the above, when the penetration or amount of insertion of the core
122
in the first and second detection coils
112
and
113
changes as the core
122
moves inside the detector
110
, the inductance of the first and second detection coils
112
and
113
will be changed correspondingly to the amount of insertion of the core
122
. Thus, the electric power from the first and second detection coils
112
and
113
, induced due to the magnetic fluxes from the exciting coil
111
, will change correspondingly to an amount of travel of the core
122
.
Therefore, by determining a difference in output between the first and second detection coils
112
and
113
, the differential transformer the position transducer
100
can detect, with a high accuracy, an amount of travel and moved position of the core
122
, that is, of a moving part
120
to which the core
122
is fixed.
FIG. 2
shows an output characteristic of the above differential transformer type position transducer
100
. On the assumption that a position where the penetration of the core
122
in the first detection coil
112
and that of the penetration of the core
122
in the second detection coil
113
are equal to each other is a reference position, when the core
122
is at the reference position, the inductance of the first detection coil
112
is equal to that of the second detection coil
113
. Thus, an output C
1
from the first detection coil
112
is equal to an output C
2
from the second detection coil
113
and the difference between these outputs (C
2
−C
1
) is zero.
As the core
122
moves from the reference position, the amount of insertion of the core
122
in one of the detection coils increases while that of the core
122
in the other decreases. Thus the detection coil in which the amount of insertion of the core
122
is increased will have the inductance thereof linearly increased for the increased amount of insertion or amount of travel of the core
122
, while the detection coil in which the amount of insertion of the core
122
is decreased will have the inductance thereof linearly decreased for the decreased amount of insertion or amount of travel of the core
122
. Therefore, by converting the change in inductance of each detection coil to determine a difference in output (C
2
−C
1
) between the detection coils, it is possible to detect, with a high accuracy, the amount of travel and moved position of the core
122
, that is, of the moving part
120
to which the core
122
is fixed, while canceling the influence of electric noises.
There has also been proposed an MI effect type position transducer having a so-called magnetic impedance effect (will be referred to as “MI effect” hereunder) applied therein, as a position transducer similar to the aforementioned differential transformer type position transducer
100
.
The MI effect type position transducer is not illustrated herein. It includes a pair of detection coils corresponding to the first and second detection coils
112
and
113
, respectively, in the aforementioned differential transformer type position transducer
100
and which is excited directly. Because of this direct excitation, this position transducer has not any coil corresponding to the exciting coil
111
in the differential transformer type position transducer
100
.
In the MI effect type position transducer, when the pair of detection coils is driven with a high frequency pulse whose rate is a few MHz to tens MHz and width is a few ns to tens ns, or a sinusoidal wave having a similar pulse rate, the inductance component of the detection coils and the skin effect of a magnetic substance, developed by a high frequency excitation, will cause the actual resistance component of the detection coils to change correspondingly to a relative position of the core to the pair of detection coils. Therefore, by adapting the MI effect type position transducer to detect changes in impedance of the detection coils, which is a combination of the changes in inductance component and actual resistance component of the detection coils, it is possible to have a very wide output dynamic range and detect, with a higher accuracy, the amount of travel and moving distance of the core, namely, a moving pat to which the core is fixed.
Disadvantageously, however, the aforementioned conventional different transformer type and MI effect type position transducers as a whole can hardly be designed compact. More specifically, the conventional differential transformer type position transducer needs three coils longer than the moving distance of the core and the whole apparatus has to be more than three times longer than the moving distance (effective length for detection) of the core.
In the conventional MI effect type position transducer, there is not provided any coil corresponding to the exciting coil used in the differential transformer type position transducer. Since the magnetic field at the ends of the detection coils is less uniform and so the output linearity is lower, the length of the apparatus in the moving direction of the core has to be sufficiently longer than the effective length for detection in order to assure a high accuracy of detection. Thus, the conventional MI effect type position transducer as a whole cannot be designed so much compact as compared with the differential transformer type position transducer.
To provide a solution to the above problems of the prior art, the Inventor of the present invention has proposed a position transducer disclosed in the Japanese Published Unexamined Application No. 2000-9412. The position transducer includes first and second detection coils excited with a high frequency, and a core fixed with a spindle to a moving part of a machine tool, industrial robot or the like and moved inside the first detection coil. When the core is in place (at a reference or home position) inside the first detection coil, the impedance of the first detection coil is equal to that of the second detection coil. In this position transducer, when the core moves from the reference position, the impedance of the first detection coil changes linearly correspondingly to the amount of travel of the core while the impedance of the second detection coil is always set constant independently of the amount of travel of the core. Therefore, with this position transducer, by converting a ch
Maioli Jay H.
Patidar Jay
Sony Precision Technology Inc.
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