U.S. patent application number 09/729450 was filed with the patent office on 2002-05-16 for electronic pressure-sensitive device for detecting the magnitude of load as electrical resistance.
This patent application is currently assigned to Alps Electric Co., Ltd.. Invention is credited to Saito, Mitsuru.
Application Number | 20020056918 09/729450 |
Document ID | / |
Family ID | 18381111 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020056918 |
Kind Code |
A1 |
Saito, Mitsuru |
May 16, 2002 |
ELECTRONIC PRESSURE-SENSITIVE DEVICE FOR DETECTING THE MAGNITUDE OF
LOAD AS ELECTRICAL RESISTANCE
Abstract
Disclosed is an electronic pressure-sensitive device which has a
long service life and which is capable of detecting with high
accuracy loads of various magnitudes including values in proximity
to zero. In the electronic pressure-sensitive device, first and
second resistive element layers 2b and 6b are formed on the
outermost surfaces of first and second contact portions 2 and 6,
and the first and second resistive element layers 2b and 6b are
constantly maintained in an electrical contact state, the force
bringing the first and second resistive element layers 2b and 6b
into press contact with each other being detected as the electrical
resistance between the first and second contact portions 2 and
6.
Inventors: |
Saito, Mitsuru; (Miyagi-ken,
JP) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Alps Electric Co., Ltd.
|
Family ID: |
18381111 |
Appl. No.: |
09/729450 |
Filed: |
December 4, 2000 |
Current U.S.
Class: |
257/773 |
Current CPC
Class: |
G01G 3/12 20130101; G01G
19/4142 20130101 |
Class at
Publication: |
257/773 |
International
Class: |
H01C 010/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 1999 |
JP |
11-346095 |
Claims
What is claimed is:
1. An electronic pressure-sensitive device comprising a first
substrate consisting of an insulating material, a first contact
portion formed on the first substrate, a first resistive element
consisting of a high-resistance material, constituting the first
contact portion and provided on the outermost surface of the first
contact portion, a second substrate consisting of an insulating
material and opposed to the first substrate, a second contact
portion formed on the second substrate and opposed to the first
contact portion, a second resistive element consisting of a
high-resistance material, constituting the second contact portion
and provided on the outermost surface of the second contact
portion, and an adhesive member provided between the first and
second substrates and gluing the first and second substrates to
each other, wherein the first and second resistive elements are
constantly maintained in an electrical contact state, and wherein a
press contact force acting between the first and second resistive
elements by pressurizing the first and second contact portions;
from at least one side is detected as the electrical resistance
between the first and second contact portions.
2. An electronic pressure-sensitive device according to claim 1,
wherein the adhesive member is formed at a position spaced apart
from the first and second resistive elements so as to surround the
first and second resistive elements.
3. An electronic pressure-sensitive device according to claim 1,
wherein at least one of the first and second substrates is
flexible, wherein the adhesive member consists of an insulating
sheet-like member, and wherein the distance between the first and
second substrates is larger where the first and second contact
portions are formed than where the adhesive member is provided.
4. An electronic pressure-sensitive device according to claim 3,
wherein both the first and second substrates are flexible.
5. An electronic pressure-sensitive device according to claim 3,
wherein an opening is provided in the adhesive member consisting of
a sheet-like member, and the first and second resistive elements
are held in an electrical contact state inside the opening, wherein
the sum total of the thicknesses of the first and second contact
portions is larger than the width dimension of the distance between
the first and second substrates at the position where the adhesive
member is provided.
6. An electronic pressure-sensitive device according to claim 3,
wherein the adhesive member consists of a sheet like base member on
either side of which an adhesive layer is formed.
7. An electronic pressure-sensitive device according to claim 1,
wherein at least one of the first and second contact portions has a
conductor electrically connected to the first and second resistive
elements.
8. An electronic pressure-sensitive device according to claim 7,
wherein the first and second contact portions respectively have
first and second conductors, the first and second conductors being
opposed to each other through the intermediation of the first and
second resistive elements and formed substantially in the entire
area where the first and second resistive elements are opposed to
each other.
9. An electronic pressure-sensitive device according to claim 7,
wherein the first and second resistive elements are formed on the
surfaces of the first and second conductors, and wherein the
surface area of the resistive elements differs from the surface
area of the conductors.
10. An electronic pressure-sensitive device according to claim 9,
wherein the resistive elements cover the entire surfaces of the
conductors.
11. An electronic pressure-sensitive device according to claim 1,
wherein the first and second resistive elements are formed of the
same material.
12. An electronic pressure-sensitive device according to claim 1,
wherein the first and second resistive elements are formed of a
material whose specific resistance ranges from 10.sup.2 to 10.sup.6
(.OMEGA..multidot.cm).
13. An electronic pressure-sensitive device according to claim 1,
wherein a wiring pattern consisting of a conductive material is
formed on at least one of the first and second substrates, the
wiring pattern being electrically connected to the first and second
contact portions.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electronic
pressure-sensitive device for detecting the magnitude of a load as
electrical resistance and, in particular, to an electronic
pressure-sensitive device capable of detecting the magnitude of a
load ranging from a small load to a large load.
[0003] 2. Description of the Related Art
[0004] For example, as shown in FIG. 7, in a conventional
electronic pressure-sensitive device used in a seat sensor or the
like detecting whether a person is sitting on a seat, a first
contact portion 52 formed on a flexible first insulating substrate
51 and consisting of a conductive material is opposed to a second
contact portion 56 formed on a flexible second insulating substrate
55 and consisting of a conductive material through the
intermediation a gap, the width of the gap being maintained by a
spacer 54 provided between the first and second insulating
substrates.
[0005] When a load is applied to the first and second insulating
substrates 51 and 55, the insulating substrates 51 and 55 are
deflected toward the gap. And, the load applied to the first and
second insulating substrates 51 and 55 exceeds a threshold value,
the first contact portion 52 is brought into contact with the
second contact portion 56, and the electronic pressure-sensitive
device is turned ON.
[0006] In the conventional seat sensor, a plurality of electronic
pressure sensitive devices as described above are arranged in the
plane of a seat base (the seat base receiving the weight of a
person), and, from the in-plane distribution of the electronic
pressure-sensitive device which has been turned ON, it is detected
whether a person is sitting on the seat or not. And, when the
presence of a person sitting on the seat is detected, an air bag is
operated when the vehicle undergoes a collision.
[0007] However, in the conventional electronic pressure-sensitive
device, which is turned ON when a load of a magnitude not less than
a threshold value is applied, it is difficult to detect a small
load applied to the electronic pressure-sensitive device or
variation in the load.
[0008] Further, since the first and second insulating substrates 51
and 55 are deflected toward the gap, the burden applied to the
first and second insulating substrates 51 and 55 is large, and,
when the first and second insulating substrates 51 and 55 are
deformed so as to protrude toward the gap, the threshold value
varies to thereby cause malfunction.
[0009] In a motor-vehicle-mounted seat sensor using this
conventional electronic pressure-sensitive device, it is difficult
to detect the magnitude of a load, so that it is impossible to
sense the physique of the person sitting on the seat, to operate
the air bag in conformity with the physique of the person sitting
on the seat, some other device is necessary. Further, in the case
of a motor-vehicle-mounted sensor, a load can be continuously
applied at high temperature, so that it is necessary to use an
expensive material such as polyethylene terephthalate, which has a
superior heat resistance, for the first and second insulating
substrates 51 and 55, which are continuously deflected by the load
(baggage), resulting in a high cost.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to
provide an electronic pressure-sensitive device which has a long
service life and which is capable of detecting loads of various
magnitudes including a minute load in appropriate resistance
values.
[0011] In accordance with the present invention, there is provided
an electronic pressure-sensitive device comprising a first
substrate consisting of an insulating material, a first contact
portion formed on the first substrate, a first resistive element
provided on the surface of the first contact portion, a second
substrate consisting of an insulating material and opposed to the
first substrate, a second contact portion formed on the second
substrate and opposed to the first substrate, a high resistance
material, a second resistive element constituting the first contact
portion and provided on the surface of the second contact portion,
and an adhesive member provided between the first and second
substrates and adapted to glue the first and second substrates to
each other, wherein the first and second resistive elements are
constantly in an electrical contact state, and wherein a press
contact force acting between the first and second resistive
elements is detected as the electrical resistance between the first
and second contact portions by pressurizing the first and second
contact portions from at least one side.
[0012] In this electronic pressure-sensitive device, the first and
second resistive elements consisting of a high resistance material
are constantly in an electrical contact state, so that, even when
no load is applied to the substrates, the electrical resistance
measured between the first and second contact portions is a limited
value. When a load is applied to at least one of the first and
second substrates, even if it is a minute load, the pressure
contact force which acts between the first and second resistive
elements according to the load increases, and the electrical
contact area of the first and second resistive elements increases,
whereby the contact resistance decreases, so that the electrical
resistance measured between the first and second contact portions
is a value according to the load. Thus, due to the electrical
resistance measured between the first and second contact portions,
it is possible to detect loads of various magnitudes including
those in the proximity of zero.
[0013] Further, since there is no need to maintain a gap between
the contact portions, there is no need to provide a maintaining
member for maintaining a gap, and there is no deterioration in
performance due to deformation of the maintaining member. Further,
since there is no gap between the contact portions, the amount of
deformation (deflection amount) due to the load is small, so that
there is little burden on the substrates, thereby providing a long
service life.
[0014] Further, even when the magnitudes of the press contact
forces acting on the first and second resistive elements are the
same, the higher the specific resistance of the first and second
resistive element materials, the higher the electrical resistance
measured between the first and second contact portions, so that, by
varying the specific resistance of the first and second resistive
element materials according to the magnitude of the load detected
by the electronic pressure-sensitive device (the specifications of
the electronic pressure-sensitive device), the electrical
resistance measured between the first and second contact portions
is an appropriate value, making it possible to detect the load
according to the specifications in an appropriate electrical
resistance.
[0015] Further, by gluing together the first and second substrates
by an adhesive member, the first and second resistive elements are
secured at predetermined positions, and the opposition area of the
first and second resistive elements is maintained constant, so that
it is possible to reduce the factor leading variation in the
detection of the load.
[0016] Further, in the electronic pressure-sensitive device of the
present invention, the adhesive member is formed at a position
deviated from the first and second resistive elements in such a way
as to surround the first and second resistive elements.
[0017] In this electronic pressure-sensitive device, the adhesive
member surrounds the first and second resistive elements with the
first and second substrates to make it possible to reduce the
influence from the external environment. Further, the electrical
contact of the first and second resistive elements is not hindered
by the adhesive member.
[0018] Further, in the electronic pressure-sensitive device of the
present invention, at least one of the first and second substrates
is flexible, and the adhesive member consists of a sheet-like
member, the gap between the first and second substrates being
larger at the positions where the first and second contact portions
are formed than at the position where the adhesive member is
provided.
[0019] In this electronic pressure-sensitive device, the substrates
are deflected between the adhesive member and the contact portions,
so that the first and second contact portions are pressurized from
the side of the deflected substrates, whereby a press contact force
acts on the first and second resistive elements, making it possible
to constantly keep the first and second resistive elements in an
electrical contact state without imparting any external force.
[0020] Further, when the sum total of the thicknesses of the first
and second contact portions is the same and no external force
(load) is applied, the press contact force (referred to as
pressurization) acting on the first and second contact portions
(resistive elements) due to the deflected substrates is larger when
the adhesive member is thin than when it is thick.
[0021] Thus, even when the magnitude of the load applied to the
substrates is the same, the electrical resistance between the first
and second contact portions is lower when the adhesive member is
thin than when it is thick. However, when the load applied to the
substrates is sufficiently large, and the press contact force
(pressurization) due to the deflection of the substrates is
negligible, the electrical resistance between the first and second
contact portions converges on a value which does not depend on the
thickness of the adhesive member. Thus, the variation in the
electrical resistance between the contact portions with respect to
the variation in the load applied to the substrates is milder when
the adhesive member is thin.
[0022] Utilizing the above load/electrical-resistance
characteristics, the thickness of the adhesive member is varied
according to the width between the minimum value and the maximum
value of the load detected by the electronic pressure-sensitive
device (the specifications of the electronic pressure sensitive
device), whereby adjustment can be conducted from the electrical
resistance corresponding to the minimum load to the electrical
resistance corresponding to the maximum load, so that it is
possible to detect a load within a desired detection range in an
appropriate electrical resistance.
[0023] Further, in the electronic pressure-sensitive device of the
present invention, both the first and second substrates are
flexible, so that it has a superior shock resistance and the
substrates are not damaged by the load or the like.
[0024] Further, in the electronic pressure-sensitive device of the
present invention, an opening is provided in the adhesive member
consisting of a sheet-like member, and the first and second
resistive elements are brought into an electrical contact state
inside this opening, and the sum total of the thicknesses of the
first and second contact portions is larger than the distance
between the first and second substrates at the position where the
adhesive member is provided.
[0025] Thus, it is possible to bring the first and second resistive
elements exposed through the opening due to the thicknesses of the
first and second contact portions and the thickness of the
sheet-like member even in the case in which no external force is
applied.
[0026] Further, in the electronic pressure-sensitive device of the
present invention, the adhesive member is formed such that adhesive
layers are formed on both sides of the sheet-like member, so that
there is little variation in the thickness of the adhesive member,
and it is possible to produce the device such that the distance
between the first and second substrates is constant.
[0027] Further, in the electronic pressure-sensitive device of the
present invention, at least one of the first and second contact
portions has a conductor consisting of a conductive material
electrically connected to the first and second resistive
elements.
[0028] In this electronic pressure-sensitive device, it is possible
to effect electrical connection between the first and second
resistive elements and the exterior through the conductor, so that
it is possible to effect more reliably an electrical connection
between the first and second resistive elements and the
exterior.
[0029] Further, in the electronic pressure-sensitive device of the
present invention, the first and second contact portions have the
first and second conductors, respectively, and the first and second
conductors are opposed to each other through the first and second
resistive elements, and formed in the entire area where the first
and second resistive elements are opposed to each other.
[0030] In this electronic pressure-sensitive device, the current
path between the first and second conductors is substantially
perpendicular to the opposing surfaces of the first and second
resistive elements, and is the shortest path in the first and
second resistive elements, so that, on either side of the
electrical contact surfaces of the first and second resistive
elements, the electrical resistance of the current path can be made
low. Thus, the electrical resistance output between the first and
second contact portions can be such that the component due to the
contact resistance is predominant.
[0031] Further, in substantially the entire area of the opposing
surfaces of the first and second resistive elements, current paths
are distributed, so that in the resistant output, the variation in
the electrical characteristics in the first and second resistive
element surfaces is averaged, giving a stable output.
[0032] Further, in the electronic pressure-sensitive device of the
present invention, the first and second resistive elements are
respectively formed on the surfaces of the first and second
conductors, and the surface area of the resistive elements is
different from the surface area of the conductors.
[0033] In this electronic pressure-sensitive device, the surface
area of the conductors and that of the resistive elements are
different, so that in the process for superimposing the resistive
elements on the conductors, misregistration in formation between
them (e.g., misregisration in printing) can be absorbed due to the
difference in magnitude as compared with the case in which the
surface area of the conductors and that of the resistive elements
are the same, so that it is easy to make the overlapping area of
the resistive elements and the conductors, making it possible
restrain variation in characteristics.
[0034] Further, in the electronic pressure-sensitive device of the
present invention, the resistive elements cover the entire surface
of the conductors.
[0035] In this electronic pressure-sensitive device, the conductors
are not exposed to the exterior, so that it is possible to prevent
short-circuiting between the conductors and the other contact
portions. Further, since the conductors are cut off from the
external environment, it is possible to prevent a deterioration in
the conductors.
[0036] Further, in the electronic pressure-sensitive device of the
present invention, the first and second resistive elements are
formed of the same material, so that it is possible to reduce the
number of kinds of resistive element material, whereby it is easy
to control the materials and it is possible to prevent generation
of improper use.
[0037] Further, in the electronic pressure-sensitive device of the
present invention, the first and second resistive elements are
formed of a material whose specific resistance ranges from 10.sup.2
to 10.sup.6 (.OMEGA..multidot.cm), so that the resistance value
measured between the first and second contact portions is an
appropriate value, making it possible to correctly detect the
load.
[0038] To perform the detection more accurately, it is desirable
that the specific resistance of the material range from 10.sup.3 to
10.sup.5 (.OMEGA..multidot.cm).
[0039] Further, in the electronic pressure-sensitive device of the
present invention, a wiring pattern consisting of a conductive
material is formed on at least one of the first and second
substrates, and the wiring pattern is electrically connected to the
first and second resistive elements.
[0040] In this electronic pressure-sensitive device, power supply
from the outside to the contact portions and the resistance value
output between the first and second contact points (power output in
accordance with the resistance value) are effected by using the
wiring pattern, so that there is no need to separately connect a
lead wire or the like to the resistive elements, so that the
construction is simple, and it is possible to make the electrical
connection between the contact portions and the exterior more
reliable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a plan view illustrating an electronic
pressure-sensitive device according to a first embodiment of the
present invention;
[0042] FIG. 2 is a sectional view taken along the line II-II of
FIG. 1;
[0043] FIG. 3 is a plan view illustrating an electronic
pressure-sensitive device according to a second embodiment of the
present invention;
[0044] FIG. 4 is a sectional view taken along the line IV-IV of
FIG. 3;
[0045] FIG. 5 is a sectional view of an electronic
pressure-sensitive device used as a comparative example;
[0046] FIG. 6 is a graph showing the load/resistance-value
characteristics of the electronic pressure-sensitive device of the
present invention; and
[0047] FIG. 7 is a sectional view of a conventional electronic
pressure-sensitive device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] The electronic pressure-sensitive device of the present
invention will be described with reference to FIGS. 1 through
5.
[0049] First, the construction of the first embodiment of the
present invention will be described. FIGS. 1 and 2 are a plan view
and a sectional view of the first embodiment. The member formed on
the first substrate is indicated by a solid line, and the member
formed on the second substrate is indicated by a dashed line.
[0050] The first substrate 1 consists of a flexible flat polyester
substrate having a thickness of 50 to 150 .mu.m, and, on the first
substrate 1, there is formed a first circular contact portion 2
having a diameter of 10 to 20 mm. The first contact portion 2 has a
double-layer structure in which a first conductor 2a in the form of
a layer (hereinafter referred to as the first conductor layer 2a)
and a first resistive element 2b in the form of a layer
(hereinafter referred to as the first resistive element layer 2b)
are sequentially stacked together, and the circular first conductor
layer 2a having a thickness of 10 .mu.m consists of a conductive
material in which silver particles as a conductive filler are
dispersed in a binder resin such as polyester, polyurethane or
acrylic resin.
[0051] The first resistive element layer 2b consists of a
high-resistance material whose specific resistance is approximately
10.sup.4 (.OMEGA..multidot.cm). It is formed, for example, by
dispersing metal oxide particles such as titan oxide or zinc oxide
or carbon particles such as carbon black or graphite in a
thermosetting resin such as phenol as a binder resin.
[0052] The first resistive element layer 2b is thick enough (25
.mu.m) to prevent generation of pin holes, and covers the surface
of the first conductor layer 2a to constitute the outermost surface
layer of the first contact portion 2, and the first conductor layer
2a is formed substantially in the entire area within the plane of
the first resistive element layer 2b.
[0053] A first wiring pattern 3 formed on the same surface on which
the conductor layer 2a of the first substrate 1 is formed consists
of the same material as the first conductor layer 2a, and is
integrally formed with the first conductor layer 2a.
[0054] An adhesive member 4 consists of a base member 4b consisting
of a polyester film and having a thickness of 5 .mu.m and adhesive
layers 4c formed on both sides of the base member 4b and having a
thickness of 12 .mu.m. The entire thickness of the adhesive member
is smaller than double the thickness of the first contact portion
2. Further, there is provided at a predetermined position a
substantially circular opening (hereinafter referred to as a
through-hole 4a) having a diameter of 11 to 22 mm, the diameter of
the through-hole 4a being larger than that of the first contact
portion 2.
[0055] The second substrate 5 and the second contact portion 6
formed on the second substrate 5 are of the same material,
configuration and construction as the first substrate 1 and the
first contact portion 2, the second contact portion 6 consisting of
a second conductor 6a in the form of a layer (hereinafter referred
to as the second conductor layer 6a) and a second resistive element
6b in the form of a layer (hereinafter referred to as the second
resistive element layer 6b).
[0056] A second wiring pattern 7 formed on the same surface on
which the second conductor layer 6a of the second substrate 5 is
provided is formed of the same material as the first wiring pattern
3, and is integrally formed with the second conductor layer 6a.
[0057] The adhesive member 4 exists between the first and second
substrates 1 and 5 to glue together the first and second substrates
1 and 5 and serves to maintain a gap between the first and second
substrates 1 and 5.
[0058] Inside the through-hole 4a of the adhesive member 4, the
first contact portion 2 is superimposed on the second contact
portion 6 so as to be matched therewith, and is secured in position
with the second contact portion 6. At this time, the first
resistive element layer 2b is in contact with the second resistive
element layer 6b in the entire mutual area. Further, the first and
second contact portions 2 and 6 are surrounded by the adhesive
member 4 and the first and second substrates 1 and 5.
[0059] Further, the sum total of the thicknesses of the first and
second contact portions 2 and 6 is larger than the thickness of the
adhesive member 4, so that the flat first and second substrates 1
and 5 are deflected between the adhesive member 4 and the first and
second contact portions 2 and 6. In the first and second substrates
1 and 5, there is generated due to the deflection a force
pressurizing the first and second contact portions 2 and 6, so that
a press contact force (referred to as pressurization) acts on the
first and second resistive element layers 2b and 6b.
[0060] The first and second wiring patterns 3 and 7 are
electrically connected through the first and second contact
portions 2 and 6, and connected to the exterior to effect power
supply to the first and second contact portions 2 and 6 and output
of the resistance value between the first and second contact
portions 2 and 6.
[0061] Next, the construction of the second embodiment of the
present invention will be illustrated with reference to FIGS. 3 and
4. As in the first embodiment, the members formed on the first
substrate 11 are indicated by a solid line, and the members formed
on the second substrate 15 are indicated by a dashed line.
[0062] A first substrate 11 and a first contact portion 12 formed
on the first substrate 11 are of the same material, configuration
and construction as those of the first embodiment. However, the
first conductor layer 12a and the first resistive element layer 12b
are divided in two at a position near the center of the first
contact portion 12. The distance between the two portions of the
first conductor layer 12a obtained through division is
approximately 1 to 2 mm, which is much larger than the thickness of
the first contact portion 12. However, it is sufficiently smaller
than the diameter of the first contact portion 12. Further, the two
portions of the first resistive element layer 12b obtained through
division cover the entire surface of the first conductor layer
12a.
[0063] On the same surface of the first substrate 11 on which the
first contact portion 12 is formed, there are formed a first wiring
pattern 13 and a second wiring pattern 17 consisting of the same
material as the first conductor layer 12a, and the two portions of
the first conductor layer 12a obtained through division are
respectively formed integrally with the first or second wiring
pattern 13, 17.
[0064] On the second substrate 15, there is only formed a second
contact portion 16 which of the same material, configuration and
construction as those of the first embodiment, and a second
conductor layer 16a and a second resistive element layer 16b are
stacked together to form a second contact portion 16. As in the
first embodiment, the adhesive member 14 consists of a base member
14b and adhesive layers 14c on both sides thereof, an opening
(hereinafter referred to as a through-hole 14a) being provided. As
in the first embodiment, the first and second substrates 11 and 15
are glued together by the adhesive member 14, and the first and
second contact portions 12 and 16 are arranged in the same state as
in the first embodiment.
[0065] The first and second wiring patterns 13 and 17 are
electrically connected through the first and second contact
portions 12 and 16, and connected to the exterior to effect power
supply to the first and second contact portions 12 and 16 and
output of the resistance value between the first and second contact
portions 12 and 16.
[0066] Next, a method of producing the first and second embodiments
and, in particular, the contact portions 2, 6, 12 and 16 will be
described.
[0067] The preparation of the conductor layers 2a, 6a, 12a and 16a
is conducted simultaneously with the preparation of the wiring
patterns 13 and 17. After the pattern formation of a conductive ink
in which a conductive filler is dispersed in an organic solvent
containing a binder resin on the substrates 1, 5, 11 and 15 by
screen printing, the conductive ink is dried to vaporize the
organic solvent.
[0068] In preparing the resistive element layers 2b, 6b, 12b and
16b, printing is effected by screen printing on the conductive
layers 2a, 6a, 12a and 16a in a resistive ink in which metal oxide
particles or carbon particles are dispersed in an organic solvent
containing a binder resin consisting of a thermosetting resin, and
then the resistive ink is dried to vaporize the organic solvent. In
this way, the production of the contact portions 2, 6, 12 and 16 is
completed.
[0069] Next, the power supply to the contact portions 2 and 6 and
the resistance value output between the contact portions 2 and 6 in
the first embodiment will be described.
[0070] The electric current applied from the first wiring pattern 3
to the first contact portion 2 flows through the first conductor
layer 2a, and passes through the electrical contact surfaces of the
first and second resistive element layers 2b and 6b before it
reaches from the second conductor layer 2a to the second wiring
pattern 7.
[0071] At this time, the current path is substantially
perpendicular to the opposing surfaces of the first and second
resistive elements 2b and 6b, and takes the shortest route in the
first and second resistive elements 2b and 6b, so that the
resistance value output due to the contact resistance is
predominant. Further, the current path is distributed over the
entire area in the opposing surfaces of the first and second
resistive elements, so that, in the resistance value output, the
variation in the electrical characteristics in the planes of the
first and second resistive element layers 2b and 6b.
[0072] Subsequently, the power supply to the contact portions 12
and 16 and the resistance value output between the contact portions
12 and 16 in the second embodiment will be described.
[0073] The electric current applied from the first wiring pattern
13 to the first contact portion 12 flows through one of the
portions of the first conductor layer 12a obtained through
division, and passes through the electrical contact surfaces of the
first and second resistive element layers 12b and 16b before it
reaches the second conductor layer 16a. After flowing through the
second conductor layer 16a, it passes again through the electrical
contact surfaces of the first and second resistive element layers
12b and 16b before it reaches the second wiring pattern 17 from the
other portion of the first conductor layer 12a.
[0074] In addition to the characteristics of the first embodiment,
the resistance value output characteristics of the second
embodiment is such that the electric current passes through the
electrical contact surfaces of the first and second resistive
element layers 12b and 16b twice, so that, when the electrical
contact state of the first and second resistive element layers 12b
and 16b varies, the variation in the resistance value out is double
that of the first embodiment.
[0075] While in the above-described first and second embodiments
the material of the conductor layers 2a, 6a, 12a and 16a is one
obtained by dispersing silver particles as a conductive filler in a
binder resin such as polyester or urethane, it is possible for the
conductive filler to be a mixture of carbon and silver or carbon.
There is no restriction as to the material and production method of
the conductor layers 2a, 6a, 12a and 16a as long as the specific
resistance of the material is negligible as compared with that of
the material of the resistive element layers 2b, 6b, 12b and
16b.
[0076] Further, while in the first and second embodiments the
material of the resistive element layers 2b, 6b, 12b and 16b is one
obtained by dispersing a metal oxide or a carbon material in a
thermosetting resin as a binder resin such as phenol, there is no
restriction regarding the material and production method of the
resistive element layers 2b, 6b, 12b and 16b as long as the
specific resistance of the material is 10.sup.2 to 10.sup.6
(.OMEGA..multidot.cm), and more preferably, 10.sup.3 to 10.sup.5
(.OMEGA..multidot.cm).
[0077] In the first and second embodiments the conductor layers 2a,
6a, 12a and 16a are covered with resistive element layers 2b, 6b,
12b and 16b prepared without involving pin holes. This is for the
purpose of preventing migration of the silver contained in the
conductor layers 2a, 6a, 12a and 16a. When the conductor layers 2a,
6a, 12a and 16a are formed of a material little subject to
migration, it is also possible to adopt a structure in which the
conductor layers 2a, 6a, 12a and 16a are larger than the resistive
element layers 2b, 6b, 12b and 16b and exposed from the resistive
element layers 2b, 6b, 12b and 16b. In this case, however, it is
necessary to prevent the conductor layers from coming into contact
with each other through pressurization by, for example, covering
the exposed conductor layers with the adhesive member. The
construction of the electronic pressure-sensitive device is not
restricted to the above constructions. Any construction will do as
long as the first resistive element layers 2b and 12b and the
second resistive element layers 6b and 16b are constantly in an
electrical contact state.
[0078] Further, while in the above embodiments the resistive
elements and the conductors are formed as resistive element layers
2b, 6b, 12b and 16b and conductor elements 2a, 6a, 12a and 16a,
their configuration is not restricted to the layer form.
COMPARATIVE EXAMPLE
[0079] FIG. 5 is a sectional view of an electronic
pressure-sensitive device as a comparative example.
[0080] Like the embodiments of the present invention, the
comparative example comprises first and second substrates 21 and
25, and first and second contact portions 22 and 26 formed on the
first and second substrates 21 and 25 and opposed to each other.
The first and second contact portions 22 and 26 are of a double
layer structure, consisting of first and second conductor layers
22a and 26a and first and second resistive element layers 22b and
26b. The first resistive element layer 22b and the second resistive
element layer 26b are opposed to each other through the
intermediation of a gap S as long as no load is applied to the
substrates 21 and 25, the width of the gap S being maintained by
the thickness dimension of a spacer 24 provided between the first
and second substrates 21 and 25.
[0081] Next, the load-resistance characteristics of the electronic
pressure sensitive device of the present invention will be
described. The load-resistance characteristics of the first and
second embodiments are qualitatively the same. In the following, to
simplify the illustration, only the reference numerals of the first
embodiment will be used.
[0082] FIG. 6 is a log-log graph qualitatively showing the
load-resistance characteristics of the present invention and the
comparative example. In the log-log graph, the number of digits is
varied by one for one increment of the scales of the vertical axis
and the horizontal axis.
[0083] First, the load-resistance characteristics of the
comparative example shown in the graph of FIG. 6 will be
described.
[0084] In the comparative example, when there is no load applied to
the substrates 21 and 25, the first and second resistive element
layers 22b and 26b are opposed to each other through the
intermediation of the gap S, as shown in FIG. 5, so that the
resistance between the first and second contact portions 22 and 26
is infinite.
[0085] In the comparative example, even if a load is applied to the
first and second substrates 21 and 25, the first and second
resistive element layers 22b and 26b are not brought into contact
with each other as long as the load is minute, and the resistance
remains infinite. When a load N.sub.U exceeding a threshold value
is applied to the first and second substrates 21 and 26, the first
and second resistive element layers 22b and 26b are brought into
contact with each other, and a resistance value R.sub.U
corresponding to the load N.sub.U is output.
[0086] In this electronic pressure-sensitive device, it is
impossible to detect a load up to the threshold value, so that it
is not suitable for the detection of small loads including those
near zero.
[0087] Next, the load-resistance characteristics of the present
invention shown in the graph of FIG. 6 will be described.
[0088] As shown in FIGS. 2 and 4, in the electronic
pressure-sensitive device of the present invention, the first and
second resistive element layers 2b and 6b are constantly in an
electrical contact state, so that even when no load is applied to
the substrates 1 and 5, the resistance value measured between the
first and second contact portions 2 and 6 is a limited value
R.sub.0.
[0089] And, when a load N.sub.1 is applied to the first and second
substrates 1 and 5, even if it is a minute load, the force
pressurizing the first and second resistive element layers 2b and
6b increases in accordance with the magnitude of the load N.sub.1,
and, as a result, the contact area of the first and second
resistive element layers 2b and 6b increases to reduce to the
contact resistance, so that the output resistance value decreases
from R.sub.0 and becomes a value R.sub.1 corresponding to the load
N.sub.1.
[0090] Further, the resistance value R.sub.1 corresponding to the
load N.sub.1increases in proportion to the specific resistance of
the material of the resistive element layers 2b and 6b, so that by
appropriately selecting the material of the resistive element
layers 2b and 6b, the resistance value R.sub.1 can be made a value
suited for measurement. Thus, it is possible to accurately detect
the load N.sub.1.
[0091] Further, as shown in FIGS. 2 and 4, in the electronic
pressure-sensitive device of the present invention, the first and
second substrates 1 and 5 are deflected between the adhesive member
4 and the contact portions 2 and 6, and, due to this deflection,
even if no external force is applied, the first and second
substrates 1 and 5 pressurize the first and second contact portions
2 and 6, whereby a press contact force (pressurization) is applied
to the first and second resistive element layers 2b and 6b. The
press contact force applied to the first and second resistive
element layers 2b and 6b by the first and second substrates 1 and 5
is larger when the adhesive member 4 is thin than when it is thick,
so that, if the magnitude of the load applied to the substrates is
the same, the resistance between the first and second contact
portions 2 and 6 is lower when the adhesive member 4 is thin.
[0092] However, when the load applied to the substrates is
sufficiently large, and the force generated due to the deflection
of the substrates (pressurization) is negligible, the resistance
between the first and second contact portions 2 and 6 converges on
a value which does not depend upon the thickness of the adhesive
portion. Thus, the variation in the resistance with respect to the
variation in the load is milder when the adhesive member 4 is
thin.
[0093] In an electronic pressure-sensitive device detecting from
load N.sub.1 (minimum value) to N.sub.2 (maximum value), the
material of the resistive element layers 2b and 6b is selected such
that the resistance value R.sub.1 corresponding to the load N.sub.1
is an appropriate value. At this time, when the load N.sub.2 is
large and the width from the load N.sub.1 to N.sub.2 is large, the
variation in the resistance with respect to the variation in the
load is made milder by using a thin adhesive member 4, whereby it
is possible to include the resistance value R.sub.1 corresponding
to the load N.sub.1 to the resistance value R.sub.2 corresponding
to the load N.sub.2 in a resistance value range suitable for
measurement.
[0094] Further, by varying the thickness of the adhesive member 4,
with both the resistance values R.sub.1 and R.sub.2 being included
in a range suitable for measurement, it is possible to adjust the
variation amount of the resistance value with respect to the
variation in the load.
[0095] The electronic pressure-sensitive device of the present
invention can be used, for example, in an in-car seat sensor or a
zoom switch in a camera.
[0096] When the electronic pressure-sensitive device of the present
invention is used in an in-car seat sensor, a plurality of
pressure-sensitive devices are embedded in the seat cushion, and
arranged in the plane of the seat base (the seat base receiving the
weight of a person) to detect the magnitude of the load applied to
each position in the seat base plane. It is possible to specify the
physique of the sitting person from the in-plane distribution of
the magnitude of the load, so that it is possible to adjust the
operation of the air bag at the time of collision according to the
physique of the person sitting on the seat to prevent the person
sitting on the seat from being injured by the spouting shock of the
air bag.
[0097] Further, in the case of an in-car seat sensor, a load can be
continuously applied thereto at high temperature by a baggage or
the like. In the electronic pressure-sensitive device of the
present invention, there is no gap between the contact portions 2
and 6, so that the substrates 1 and 2 do not sink in a gap at high
temperature to be greatly deflected and deformed. Thus, it is not
necessary to use an expensive heat resistant material such as
polyethylene naphthalate, which has conventionally been used as a
substrate material, and it is possible to use an inexpensive
substrate material such as polyethylene terephthalate. Thus, there
is little burden on the substrates 1 and 5, and the service life of
the device can be increased.
[0098] Further, in the electronic pressure sensitive device of the
present invention, both the first and second substrates 1 and 5 are
flexible, so that, if it is embedded in a cushion, the person
sitting on the seat experiences no uncomfortable feeling.
[0099] In the above embodiments both the first and second
substrates 1 and 5 are flexible. However, when the electronic
pressure-sensitive device of the present invention is used in a
zoom switch in a camera, one of the first and second substrates 1
and 5 is placed on a base, so that the base-side substrate of the
first and second substrates 1 and 5 may be a rigid substrate.
[0100] Further, while in the above embodiments the through-holes 4a
and 14a are substantially circular so as to obtain a stable
resistance value output with little variation, the configuration of
the through-holes is not restricted to a circular one. It may also
be of a polygonal configuration, such as a hexagon. Further, it is
not absolutely necessary for the through-holes 4a and 14a to be
completely closed. It is possible for them, for example, to exhibit
a C-shaped structure substantially surrounding the contact portions
(the resistive element layers) (There is provided a fine cutout
extending from the through-hole 4a, 14a to the end portion of the
adhesive member 4, 14).
[0101] In the electronic pressure-sensitive device of the present
invention, the first and second contact portions have on the
outermost surfaces thereof first and second resistive elements
consisting of a high-resistance material, and, in a condition in
which the first and second resistive elements are constantly
maintained in an electrical contact state, the press contact force
acting on the first and second resistive elements is detected as
the electrical resistance between the first and second contact
portions.
[0102] In this electronic pressure-sensitive device, the first and
second resistive element layers consisting of a high-resistance
material are constantly in an electrical contact state, so that,
even when no load is applied to the substrates, the resistance
value measured between the first and second contact portions is a
finite value. When a load is applied to at least one of the first
and second substrates, even if it is minute load, the press contact
force acting on the first and second resistive elements increases
according to the load, and the electrical contact area of the first
and second resistive elements increases to thereby reduce the
contact resistance, so that the resistance value measured between
the first and second contact portions is a value according to the
load. Thus, it is possible to detect loads of various magnitudes
including those in proximity to zero.
ATTACHMENT A
[0103] Guy W. Shoup 26,805
[0104] F. David AuBuchon 20,493
[0105] Gustavo Siller, Jr. 32,305
[0106] Jasper W. Dockrey 33,868
[0107] John C. Freeman 34,483
[0108] William F. Prendergast 34,699
[0109] Michael E. Milz 34,880
[0110] Paul E. Rauch 38,591
[0111] Vita G. Conforti 39,639
[0112] Tadashi Horie 40,437
[0113] Richard K. Clark 40,560
[0114] Joseph F. Hetz 41,070
[0115] Daniel B. Burg 41,649
[0116] Jason C. White 42,223
[0117] James A. Collins 43,557
[0118] Abdollah Katbab 45,325
[0119] Anthony P. Curtis 46,193
* * * * *