Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-03-13
2003-02-18
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207160, C324S207240, C336S08400R
Reexamination Certificate
active
06522129
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an induction type transducer and an electronic caliper, and in particular, a small-sized induction type transducer with high detection performance and an electronic caliper using the same transducer.
2. Description of the Related Art
Measuring equipments such as an electronic caliper have been widely used for measurement of the thickness or other physical dimensions of objects in the manufacturing industry. As the main component of an electronic caliper, a transducer has been used.
Among various transducers, a capacitance type transducer and an induction type transducer are generally known. In, the capacitance type transducer, a transmitting electrode and a receiving electrode are provided on a grid (slider), and a signal electrode is provided on a scale opposed to the grid. The transmitting electrode and the receiving electrode on the grid are capacitively coupled with the signal electrode on the scale. A drive signal is supplied to the transmitting electrode, and a detection signal which is generated at the receiving electrode in accordance with the relative positions of the grid and scale is processed by a processing circuit, whereby the movement or position of the grid with respect to the scale is detected.
Such a capacitance type transducer is suitable for use in a relatively clean and dry environment such as an inspection room or a design office, however, it cannot be used for dimensional measurement in an environment where the degree of pollution is relatively high such as a machine shop. In the case where a particulate substance such as metal particles and grinding powder or a fluid such as a cooling or cutting fluid exists, the particulate substance or the fluid enters between the signal electrode on the scale and the signal electrode or receiving electrode on the grid, and changes the capacitance between the signal electrode and the transmitting electrode or receiving electrode, resulting in detection failure.
On the other hand, in an induction type transducer, the relative positions of the grid and scale are detected based on the electromagnetic induction between them, so that this transducer has an advantage in that it can be used for dimensional measurement in an environment with a relatively high degree of pollution.
FIG. 6
shows the principle of measurement of the induction type transducer. As shown in (b) of
FIG. 6
, a grid (slider)
10
and a scale
12
are disposed so as to be opposite to each other. The grid
10
is provided with exciting coils
10
a
and
10
b
, and a detecting coil
10
c
. The detecting coil
10
c
is disposed between the exciting coils
10
a
and
10
b
. On the other hand, a scale coil
14
is formed on the scale
12
, a magnetic flux is generated when supplying a current to the exciting coils
10
a
and
10
b
, and an induced current flows in the scale coil
14
on the scale
12
due to electromagnetic induction. Then, a magnetic flux is generated by the induced current in the scale coil
14
, and by this magnetic flux, an induced current (induced voltage) is generated in the detecting coil
10
c
on the grid
10
. Since the induced current (induced voltage) changes in accordance with the relative positions of the exciting coils
10
a
and
10
b
and scale coil
14
, if the grid
10
is moved in the direction of the arrow in the figure with respect to the scale
12
, as shown in (a) of
FIG. 6
, a periodic induced voltage V is generated in the detecting coil
10
c
. Therefore, by detecting the value of the induced voltage, the relative positions of the grid
10
and the scale
12
can be detected.
Even if a pollutant such as water or oil is mixed between the grid
10
and scale
12
, the magnetic flux and the magnetic non-permeability do not change and influence the induced voltage, so that the relative positions can be detected with high accuracy even in an environment with a high degree of pollution.
On the other hand,
FIG. 7
shows a principle for detection of the absolute displaced positions of the grid
10
and scale
12
by using the abovementioned principle. Herein, the absolute displaced positions mean the amounts of displacement from a certain reference point (zero point). As shown in (a) of
FIG. 7
, a plurality of exciting coils
10
a
are provided on the grid
10
, and a plurality of detecting coils
10
c
are provided in accordance with these exciting coils. Scale coils
14
a
and
14
b
, whose center portions have a pitch of &lgr;
1
, and end portions have a pitch of &lgr;
2
are formed on the scale
12
. The pitch at the center portion and the pitch at the end portion are different from each other, so that two induced voltages of the pitches of &lgr;
1
and &lgr;
2
are also generated in the detecting coils
10
c
formed at the center portion and the end portion on the grid
10
. Since one cycle of the two signals differs from each other, the relationship in the induced voltage between two wavelengths at a specified induced voltage value will not become the same at all the grid positions with respect to the scale
12
. That is, as shown in (b) of
FIG. 7
, at the positions X
a
and X
b
at which the induced voltage values V
1
a
of the pitch &lgr;
1
are the same, the induced voltage values of the pitch &lgr;
2
are not identical to each other. Therefore, by converting the relationship in the induced voltage between the two wavelengths into the positions, the absolute position of the grid can be detected.
Thus, the induction type transducer can measure dimensions with high accuracy even in an environment with a relatively high degree of pollution, however, it is necessary that a plurality of exciting coils and detecting coils are formed on the grid, and in particular, when the transducer detects an absolute position, the structure of the grid becomes complicated, and the transducer increases in size. Furthermore, when such an induction type transducer is built-in an electronic caliper, an increase in size of the transducer leads-in an increase in size of the electronic caliper itself, and lowering of workability when measuring.
SUMMARY OF THE INVENTION
The invention is made in view of the abovementioned problems in the related art, and the object thereof is to provide a small-sized induction type transducer with high performance, and furthermore, an electronic caliper using such a small-sized magnetic type transducer with high performance.
In order to achieve the abovementioned object, an induction type transducer of the invention, which outputs an electric signal in accordance with relative displacement between two members, comprises a magnetic flux generating section for generating a magnetic flux based on a drive signal, a magnetic flux detecting section for detecting a magnetic flux which changes in accordance with the relative positions, and a signal processing section for processing a detection signal from the magnetic flux detecting section. In the induction type transducer, the magnetic flux generating section, magnetic flux detecting section, and signal processing section form, a multilayer structure. The magnetic flux generating section, magnetic flux detecting section, and signal processing section are not disposed in parallel on the same plane, but are formed on respective layers in the multilayer structure, whereby the transducer can be reduced in size.
Herein, the multilayer structure is preferably a structure in which a plurality of layers are built-up on a core layer. The use of the built-up substrate reduces the size, thickness, and weight. Furthermore, the number of layers in the multilayer structure becomes easily properly adjustable.
Furthermore, the magnetic flux generating section is formed at the measuring plane side and the signal processing section is formed at the opposite side of the measuring plane. Herein, the measuring plane side means the side opposed to the scale. By forming the magnetic flux generating section at the measuring plane side, a generated magnetic flux can be made to effectively influence
Hayashi Nobuyuki
Kiriyama Tetsuro
Miyata Toshiharu
Sasaki Kouji
Kinder Danell
Lefkowitz Edward
Mitutoyo Corporation
Oliff & Berridg,e PLC
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