Geometrical instruments – Indicator of direction of force traversing natural media – Level or plumb – terrestrial gravitation responsive
Reexamination Certificate
2001-02-23
2002-09-03
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Level or plumb, terrestrial gravitation responsive
C033S366110
Reexamination Certificate
active
06442855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic type tilt sensor which is used for detecting a tilt angle with respect to a plane perpendicular to the direction of gravity, more particularly to a tilt sensor providing an alarm or conducting a predetermined control when a detected tilt angle exceeds a predetermined value.
2. Background Art
Conventional tilt sensors employing a tilt detection element are described in Japanese Unexamined Utility Model Publication No. 4-53528 and Japanese Examined Utility Model Publication No. 5-14168. An electrostatic type tilt sensor having these types of conventional structure is shown in FIG.
5
and FIG.
6
.
FIG. 5
is an exploded view of a conventional tilt sensor.
FIG. 6
is a cross-sectional view of a conventional tilt sensor along a plane cut normal to a front surface of the tilt detection element.
A printed circuit board
1
made of a heat resistant material, for example a laminate plate made of glass cloth and epoxy resin, is disposed vertically with respect to a reference plane for measuring a tilt angle when a tilt sensor is fixed to an object whose tilt angle is to be measured. In
FIG. 5
, this reference plane is designated by the plane including an imaginary line L
0
represented by a double-dotted and dashed line. This plane defined by the imaginary line L
0
becomes a reference plane from which to measure tilt angle.
The reference plane is in a “0 degree” tilt angle when the reference plane includes a line normal to the direction of gravity. In the printed circuit board
1
, a pair of differential electrodes
2
a
,
2
b
are formed of a copper foil pattern electrically independent of each other in two regions. The two regions (left and right) are defined by a plane formed along the intersection of (an imaginary line L
1
shown by a double dot and dash line in
FIG. 5
) both the reference plane and the surface of the printed circuit board
1
.
The signal processing circuit section of the tilt sensor, which includes a printed wiring pattern and related electronic parts will be described hereinafter. The signal processing circuit section is mounted on a surface opposite to the surface on which the differential electrodes
2
a
,
2
b
of the printed circuit board
1
are formed. The respective differential electrodes
2
a
,
2
b
are connected to the copper foil pattern on the surface of the printed circuit board
1
. The signal processing circuit section is formed via through holes, at the electrode points
2
c
,
2
d
shown in FIG.
5
.
The pair of differential electrodes
2
a
,
2
b
are formed as an electrode pattern which is symmetric with respect to the imaginary line L
1
. Also, each electrode of the pair of differential electrodes
2
a
,
2
b
is formed as an electrode pattern which is symmetric with respect to the imaginary line L
2
. Imaginary line L
2
is the line that is normal to the imaginary L
1
in FIG.
5
. In the example shown in
FIG. 5
, each of the differential electrodes
2
a
,
2
b
is shaped like a horizontal fan.
In the example shown in
FIG. 5
, the arc-shaped periphery of each of the differential electrodes
2
a
,
2
b
follows the shape a circular arc. The circular arc is defined by a circle with its center at the point of intersection of the imaginary line L
1
and the imaginary line L
2
. In this example, the diameter of the circle is set at 30 mm.
A reference numeral
3
designates a common electrode plate formed of a conductive material having a desired rigidity. As shown in
FIG. 6
, this common electrode plate
3
is mounted on the printed circuit board
1
in a state where it is held in parallel to the differential electrodes
2
a
,
2
b
with a certain gap between them. A plurality of terminals
3
a
,
3
b
,
3
c
,
3
d
are inserted into the printed circuit board I which are integral with the common electrode plate
3
and are formed by bending the plate
3
at right angles. The terminals
3
a
,
3
b
,
3
c
,
3
d
are inserted into terminal holes
4
a
,
4
b
,
4
c
,
4
d
made in the printed circuit board
1
and are secured by soldering them to the surface of the printed circuit board
1
on which the signal processing circuit section is formed.
An oil case
5
formed of plastics having a desired flexibility is formed in the shape of a letter U in cross section. When an end face of the oil case
5
is bonded to the printed circuit board
21
with bonding means such as a double-faced adhesive tape
5
B or the like, the oil case
5
forms a closed space with the surface of the printed circuit board
1
.
The peripheries of the differential electrodes
2
a
,
2
b
, the periphery of the common electrode
3
, and the periphery of the case
5
are formed concentrically with each other. The opposite faces of the differential electrodes
2
a
,
2
b
, that of the common electrode
3
, and the corresponding face of the case
5
are formed in parallel to each other.
The closed space formed by the case
5
and the printed circuit board
1
is filled with a dielectric liquid
7
such as a silicone oil or the like. The dielectric liquid
7
is poured from a through hole
6
made in the printed circuit board
1
to the level of approximately half the effective volume in the closed space, e.g. to the level of the imaginary line L
2
shown in FIG.
5
. The through hole
6
of the printed circuit board
1
is filled with the dielectric liquid
7
and is then sealed.
An electrostatic shielding plate
8
is mounted on a side of the printed circuit board
1
to cover the case
5
and its surroundings and the electrostatic shielding plate
9
is mounted on a second side of the printed circuit board
1
to cover the signal processing circuit section described hereinafter.
FIG. 7
is a schematic view of a signal processing circuit section of an exemplary, conventional tilt sensor. In
FIG. 7
, an oscillator
11
and the output terminal thereof are connected to the common electrode plate
3
of the tilt detection element
10
having the characteristics described in FIG.
5
and FIG.
6
. Further, the pair of differential electrodes
2
a
,
2
b
of the tilt detection element
10
are connected to the input terminals of capacity-voltage conversion circuits
12
a
,
12
b
, respectively.
The output terminals of the capacity-voltage conversion circuits
12
a
,
12
b
are connected to the input terminals of a differential amplifier circuit
13
, respectively. An output terminal
14
of the tilt sensor is led out of the differential amplifier circuit
13
. The signal processing circuit section is provided with a power stabilizing circuit
15
and the stabilized voltage supplied from this power stabilizing circuit
15
is supplied to the oscillator
11
and the differential amplifier circuit
13
as a power supply voltage.
Since the signal processing circuit section is arranged in the manner described hereinabove, an oscillation output signal of a predetermined frequency from the oscillator
11
is supplied to the capacity-voltage conversion circuits
12
a
through a first capacitor connected by the differential electrode
2
a
and the common electrode plate
3
and also to the capacity-voltage conversion circuits
12
b
through a second capacitor connected by the differential electrode
2
b
and the common electrode plate
3
.
Accordingly, peak value signals corresponding to the capacity of the first capacitor and the capacity of the second capacitor are applied to the capacity-voltage conversion circuits
12
a
,
12
b
, respectively.
The capacity-voltage conversion circuits
12
a
,
12
b
rectify the input signals, and produce smoothed voltage. Therefore, the respective output voltages of the capacity-voltage conversion circuits
12
a
,
12
b
correspond to peak values of the input signals. The capacity of the first capacitor and the capacity of the second capacitor correspond to their respective input signals.
Therefore, the differential amplifier circuit
13
produces a differential voltage between the output voltage of the capacity-voltage conversion circuits
12
a
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