U.S. patent application number 16/788465 was filed with the patent office on 2020-06-11 for pressure sensor, e.g. in sole for an article of footwear.
The applicant listed for this patent is IEE INTERNATIONAL ELECTRONICS & ENGINEERING S.A.. Invention is credited to Andreas Steier.
Application Number | 20200182714 16/788465 |
Document ID | / |
Family ID | 48626432 |
Filed Date | 2020-06-11 |
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United States Patent
Application |
20200182714 |
Kind Code |
A1 |
Steier; Andreas |
June 11, 2020 |
PRESSURE SENSOR, E.G. IN SOLE FOR AN ARTICLE OF FOOTWEAR
Abstract
A pressure sensor, e.g. for being arranged in the sole structure
of an article of footwear, for measuring a pressure exerted by the
wearer's foot. The pressure sensor has one or more pressure-sensing
cells. Each cell has a first flexible carrier film and a second
flexible carrier film, the first and second carrier films being
attached to one another by a spacer film having an opening, a
plurality of first electrodes arranged on the first carrier film
and a plurality of second electrodes arranged on the second carrier
film. The plurality of first electrodes has a first group of
electrodes and a second group of electrodes. The first and second
groups of electrodes are arranged so as to interdigitate with
delimiting gaps there between. One or more electrically insulating
overprints are arranged on the first carrier film so as to cover
the gaps.
Inventors: |
Steier; Andreas; (Pellingen,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IEE INTERNATIONAL ELECTRONICS & ENGINEERING S.A. |
Echternach |
|
LU |
|
|
Family ID: |
48626432 |
Appl. No.: |
16/788465 |
Filed: |
February 12, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14406193 |
Dec 5, 2014 |
10598555 |
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PCT/EP2013/061665 |
Jun 6, 2013 |
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16788465 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/6807 20130101;
A43B 3/0005 20130101; A61B 5/1038 20130101; G01L 1/205 20130101;
G01L 1/20 20130101 |
International
Class: |
G01L 1/20 20060101
G01L001/20; A61B 5/00 20060101 A61B005/00; A61B 5/103 20060101
A61B005/103; A43B 3/00 20060101 A43B003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2012 |
LU |
92 016 |
Claims
1. A pressure sensor comprising one or more pressure-sensing cells,
each of said pressure sensing cells comprising: a first flexible
carrier film and a second flexible carrier film, said first and
second carrier films being attached to one another by a spacer film
having an opening; and a plurality of first electrodes arranged on
said first carrier film and a plurality of second electrodes
arranged on said second carrier film, said plurality of first
electrodes and said plurality second electrodes being arranged in
facing relationship with each other in said opening in such a way
that said first and second electrodes may be brought into contact
with one another when pressure is exerted on said pressure-sensing
cell and that contact areas between said first and second
electrodes increase with increasing pressure, wherein said first
electrodes are resistive electrodes, wherein said plurality of
first electrodes comprises a first group of electrodes and a second
group of electrodes, said first and second groups of electrodes
being arranged so as to interdigitate while delimiting gaps there
between, wherein said first carrier film carries conductive tracks
that contact border portions of said first electrodes extending
along said gaps, each conductive track defining an equipotential
line, and wherein one or more electrically insulating overprints
are arranged on said first carrier film so as to cover said gaps,
said overprints at least partially overlapping with the border
portions in which said first electrodes are contacted by said
conductive tracks.
2. The pressure sensor as claimed in claim 1, wherein said second
electrodes are resistive electrodes.
3. The pressure sensor as claimed in claim 1, wherein said
plurality of second electrodes comprises a third group of
electrodes and a fourth group of electrodes, said third and second
fourth groups of electrodes being arranged so as to interdigitate
while delimiting gaps there between.
4. The pressure sensor as claimed in claim 3, wherein said second
carrier film carries conductive tracks that contact border portions
of said second electrodes extending along said gaps.
5. The pressure sensor as claimed in claim 3, wherein said third
and fourth groups of electrodes are separated from each other by a
high impedance when said first and second electrodes are not in
contact with one another and wherein said third and fourth groups
of electrodes are shunted via said first electrodes when said first
and second electrodes are in contact with one another.
6. The pressure sensor as claimed in claim 4, wherein said third
and fourth groups of electrodes are separated from each other by a
high impedance when said first and second electrodes are not in
contact with one another and wherein said third and fourth groups
of electrodes are shunted via said first electrodes when said first
and second electrodes are in contact with one another.
7. The pressure sensor as claimed in claim 1, wherein said first
and second groups of electrodes are separated from each other by a
high impedance when said first and second electrodes are not in
contact with one another and wherein said first and second groups
of electrodes are shunted via said second electrodes when said
first and second electrodes are in contact with one another.
8. The pressure sensor as claimed in claim 1, said pressure sensor
being configured for being arranged in a sole structure of an
article of footwear in order to measure a pressure exerted by a
wearer's foot on the sole structure, wherein said one or more
sensor cells are located in areas expected to be subjected to
pressure peaks when the wearer is standing still, is walking or is
running.
9. The pressure sensor as claimed in claim 8, wherein each of said
one or more sensor cells is located in an area corresponding to a
bone or part of bone of a wearer's foot selected from the heel
bone, the head of the first metatarsal bone, the head of the fourth
or fifth metatarsal bone, the head of the second or third
metatarsal bone and the head of the first phalange.
10. The pressure sensor as claimed in claim 1, wherein each of said
pressure sensing cells is oval, elliptical or rectangular with
rounded angles.
11. The pressure sensor as claimed in claim 1, wherein each of said
pressure sensing cells comprises a ventilation hole for
equalization of gas pressure inside said opening.
12. The pressure sensor as claimed in claim 11, wherein said
ventilation hole is in communication with an exterior or a gas
reservoir.
13. The pressure sensor as claimed in claim 1, comprising a foam
rubber support.
14. The pressure sensor as claimed in claim 13, wherein said foam
rubber support is made of ethylene vinyl acetate.
15. The pressure sensor as claimed in claim 1, wherein said first
electrodes have generally the shape of an equal-sided triangle and
wherein said conductive tracks that contact border portions of said
first electrodes comprise studs extending from a tip of said
triangle.
16. The pressure sensor as claimed in claim 1, wherein said second
electrodes have generally the shape of an equal-sided triangle and
wherein said conductive tracks that contact border portions of said
second electrodes comprise studs extending from a tip of said
triangle.
17. A pressure sensor preferably as claimed in claim 1, comprising
a flexible multilayer film structure, wherein the pressure sensor
further comprises a trough-shaped receptacle for an electronic
control module, said receptacle comprising in its interior a
plurality of connection pins for interfacing said pressure sensor
with said electronic control module.
18. The pressure sensor as claimed in claim 17, wherein said
receptacle is arranged in an opening provided in said flexible
multilayer film structure.
19. The pressure sensor as claimed in claim 17, wherein said
receptacle comprises a bottom part and a top part, said bottom part
and said top part being assembled with each other so as to squeeze
between each other a border of said opening in said multilayer film
structure and thus securing said multilayer film structure to said
receptacle.
20. The pressure sensor as claimed in claim 18, wherein said
receptacle comprises a bottom part and a top part, said bottom part
and said top part being assembled with each other so as to squeeze
between each other a border of said opening in said multilayer film
structure and thus securing said multilayer film structure to said
receptacle.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/406,193 filed on Dec. 5, 2014, which is a
United States national phase of International Patent Application
No. PCT/EP2013/061665 filed Jun. 6, 2013, which claims priority to
Luxembourg Application No. 92 016 filed Jun. 6, 2012, the
disclosures of which are all hereby incorporated by reference in
their entirety.
TECHNICAL FIELD
[0002] The present invention generally relates to a pressure
sensor, especially but not exclusively for an article of footwear,
such as e.g. a shoe, a boot, a sandal or the like. Such a pressure
sensor may be used for measuring pressure exerted by the wearer's
foot on the sole structure.
BACKGROUND ART
[0003] Document US 2010/0063779 discloses a shoe with an integrated
sensor system. The sensor system collects performance data that are
transferred for further use via a communication port. The shoe
contains a force sensor arranged in the sole structure for
measuring, in a plurality of areas, pressure (force) exerted by the
wearer's foot on the sole structure, and an electronic module
configured to gather data from the sensors. The module is
configured for transmitting the data to an external device for
further processing. In one of the embodiments disclosed in US
2010/0063779, the pressure sensor comprises four elongated
pressure-sensing cells, each of which contains a first and a second
electrode as well as a force-sensitive resistive material disposed
between the electrodes to electrically connect the electrodes
together. When pressure is applied to the force-sensitive material,
its resistivity changes, and the resulting change in resistance is
detected by the electronic module. Materials exhibiting
volume-based resistance behavior are used as the force-sensitive
material: when such material is compressed, conductive particles
contained therein move closer together, whereby conductive paths
are formed and the resistance decreases. If another resistance vs.
pressure characteristic is needed, a suitable force-sensitive
material has to be found, which may be difficult.
BRIEF SUMMARY
[0004] The invention provides a pressure sensor, wherein the one or
more pressure sensing cells have an increased dynamic range, i.e.
whose electrical resistance decreases more slowly with increasing
pressure but over a broader range.
[0005] The proposed pressure sensor comprises one or more
pressure-sensing cells. Each cell comprises a first flexible
carrier film and a second flexible carrier film, the first and
second carrier films being attached to one another by a spacer film
having an opening, a plurality of first electrodes arranged on the
first carrier film and a plurality of second electrodes arranged on
the second carrier film, the plurality of first electrodes and the
plurality second electrodes being arranged in facing relationship
with each other in the opening in such a way that the first and
second electrodes may be brought into contact with one another when
pressure is exerted on the pressure-sensing cell and that contact
areas between the first and second electrodes increase with
increasing pressure. The first electrodes are resistive electrodes
(e.g. made of graphite ink, carbon ink, graphite-carbon ink or the
like). The plurality of first electrodes comprises a first group of
electrodes and a second group of electrodes, the first and second
groups of electrodes being arranged so as to interdigitate while
delimiting gaps there between. The first carrier film carries
conductive tracks that contact border portions of the first
electrodes, which extend along the gaps, each conductive track
defining an equipotential line in the respective border portion.
One or more electrically insulating overprints are arranged on the
first carrier film so as to cover the gaps. The overprints at least
partially overlap with (preferably completely cover) the border
portions in which the first electrodes are contacted by the
conductive tracks. The electrically insulating overprints locally
prevent a direct contact between the first and second electrodes
and enable the direct contact where they are absent. The pressure
sensor according to the invention may especially (but not
exclusively) be used in an article of footwear (in particular a
sports shoe, such as e.g. a running shoe, a tennis shoe or the
like) that comprises a sole structure for supporting a wearer's
foot and an upper for holding the wearer's foot onto the sole
structure. In this case, a pressure sensor according to the
invention is preferably arranged in the sole structure for
measuring a pressure exerted by the wearer's foot on the sole
structure.
[0006] The above-described pressure-sensing cell exhibits an
improved dynamic response due to the presence of the electrically
insulating overprints and the conductive tracks in the border
regions of the first electrodes. These layers locally reinforce the
first carrier film, whereby the mechanical response of the carrier
film is shifted to higher pressures (i.e. it bends less easily
under pressure). It follows that the rate of growth of the contact
area between the first and second electrodes decreases with
increasing pressure (at higher pressures, the contact area spreads
towards the borders of the pressure-sensitive cell, where at least
the first carrier film yields less easily under pressure due to the
presence of the conductive track and the overprints). This means,
in turn, that maximum mechanical contact between the first
electrodes and the second electrodes occurs at a higher pressure
than in conventional pressure sensing cells.
[0007] Preferably, the pressure-sensing cells are configured (in
particular by tailoring of the shape of the electrically insulating
overprints) in such a way that pressures in the range from about
0.1 bar to 7 bar translate into a steady change of the contact area
between the resistive electrodes (and thus of the electrical
resistance of the cell) from 0% (at the turn-on pressure, i.e. at
the about 0.1 bar) and about 100% (full contact at about 7
bar).
[0008] Preferably, also the second electrodes are resistive
electrodes. Alternatively, they can be conductive electrodes (e.g.
made of a silver ink or a conductive carbon/graphite ink). The
electrically insulating overprints are preferably made of
electrically insulating (dielectric) ink.
[0009] Advantageously, the plurality of second electrodes comprises
a third group of electrodes and a fourth group of electrodes, the
third and second fourth groups of electrodes being arranged so as
to interdigitate while delimiting gaps there between. Most
preferably, the first and second electrodes are mirror-symmetrical
to each other.
[0010] Also the second carrier film may carry conductive tracks
that contact border portions of the second electrodes extending
along the gaps.
[0011] The third and fourth groups of electrodes may be separated
from each other by a high impedance when the first and second
electrodes are not in contact with one another and shunted via the
first electrodes when the first and second electrodes are in
contact with one another. Additionally or alternatively, the first
and second groups of electrodes may be separated from each other by
a high impedance when the first and second electrodes are not in
contact with one another and shunted via the second electrodes when
the first and second electrodes are in contact with one
another.
[0012] Preferably, the one or more sensor cells of a pressure
sensor to be arranged in a sole structure of an article of footwear
are located in areas expected to be subjected to pressure peaks
when the wearer of the footwear is standing still, is walking or is
running. Advantageously, each of the one or more sensor cells is
preferably located in an area corresponding to a bone or part of
bone of a wearer's foot selected from the heel bone, the head of
the first metatarsal bone, the head of the fourth or fifth
metatarsal bone, the head of the second or third metatarsal bone
and the head of the first phalange. Those skilled will appreciate
that pressure maxima are typically located under the heel bone,
under the heads of the fourth and/or fifth metatarsal bone and
under the head of the first phalange when the wearer is standing at
rest; when the wearer is walking, the pressure maxima are usually
under the heel bone, under the heads of the second and/or third
metatarsal bone and under the head of the first phalange.
[0013] The pressure-sensing cells may have various shapes. For
instance, each of the pressure-sensing cells may be oval,
elliptical or rectangular with rounded angles.
[0014] For equalization of gas pressure inside the opening, each of
the pressure sensing cells advantageously comprises a ventilation
hole. The ventilation hole may be in fluid communication with the
exterior of the pressure sensor (e.g. the atmosphere) or with a gas
(e.g. air) reservoir within the pressure sensor. Such gas reservoir
could e.g. be a cavity between the first and second carrier
films.
[0015] According to a preferred embodiment of the invention, the
pressure sensor comprises a foam rubber support, e.g. made of
ethylene vinyl acetate (EVA), preferably fixed to the first or the
second carrier film by means of an adhesive.
[0016] As those skilled will appreciate, the pressure sensor could
be arranged in different parts of a sole structure of footwear. For
instance, the pressure sensor could be arranged on or in the
insole. Alternatively, the pressure sensor could be arranged on, in
or under the midsole.
[0017] Another aspect of the present invention relates to a
pressure sensor for an article of footwear that comprises a
flexible multilayer film structure, wherein the pressure sensor
further comprises a trough-shaped receptacle for an electronic
control module, the receptacle comprising in its interior a
plurality of connection pins for interfacing the pressure sensor
with the electronic control module. Preferably, the trough-shaped
receptacle is made of plastic material, e.g. PET or epoxy.
[0018] The receptacle is preferably arranged in an opening provided
in the flexible multilayer film structure. The receptacle may
comprise a bottom part and a top part, the bottom part and the top
part being assembled with each other so as to squeeze between each
other a border of the opening in the multilayer film structure and
thus securing the multilayer film structure to the receptacle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Preferred, non-limiting, embodiments of the invention will
now be described, by way of example, with reference to the
accompanying drawings in which:
[0020] FIG. 1 is a longitudinal cross sectional view of the sole
structure of a sports shoe equipped with a pressure sensor in
accordance with a preferred embodiment of the invention;
[0021] FIG. 2 is a top view of the pressure sensor of the sports
shoe of FIG. 1;
[0022] FIG. 3 is an exploded view of one of the pressure-sensing
cells of the pressure sensor of FIG. 2;
[0023] FIG. 4 is a schematic cross sectional view of the B-B plane
of FIG. 3;
[0024] FIG. 5 is a graph illustrating the difference in the
electrical responses of a pressure-sensing cell without an
electrically insulating overprints and one with such
overprints;
[0025] FIG. 6 is a block diagram of the electrical circuit of the
pressure sensor illustrated in FIG. 2;
[0026] FIG. 7 is a schematic block diagram of an alternative
electrical circuit for the pressure sensor of FIG. 2;
[0027] FIG. 8 is a schematic block diagram of another alternative
electrical circuit for the pressure sensor of FIG. 2;
[0028] FIG. 9 is an exploded view of a variant of the
pressure-sensing cell of FIG. 3;
[0029] FIG. 10 is an illustration of the pressure-dependent growth
of the contact areas between the electrodes of a pressure-sensing
cell as shown in FIG. 3 or 9.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] An article of footwear, in form of a sports shoe 10 is
depicted in FIG. 1 as including an upper 12 and a sole structure
14. The upper 12 is secured to sole structure 14 and defines a
chamber for receiving a foot. The sole structure 14 includes an
outsole 14.1, a midsole 14.2, and an insole 14.3, which forms the
bottom of the foot-receiving chamber of the sport shoe 10.
[0031] The film-type pressure sensor is arranged on the upper
surface of an EVA substrate 17. In the illustrated embodiment, the
midsole 14.2, which is preferably formed of impact-attenuating
material, has the film-type pressure sensor 16 on its substrate 17
attached to its upper surface. When the insole is in place, the
pressure sensor 10 is thus sandwiched between the insole 14.3 and
the midsole 14.2.
[0032] As best shown in FIG. 2, the pressure sensor 16 comprises a
plurality of pressure-sensing cells 18, located in different areas
of the sole structure 14, for measuring pressure exerted by the
wearer's foot on the sole structure 14.
[0033] The configuration of the pressure sensing cells 18 will now
be described with reference to FIGS. 3 and 4. FIG. 3 shows the
different layers of a pressure-sensing cell 18. FIG. 4 shows the
pressure-sensing cell of FIG. 3 in cross section. The pressure
sensor 16 comprises a multilayered structure including a first
carrier film 20, a second carrier film 22, and a spacer 24. The
spacer 24 is typically a double-sided adhesive, with which the
first and second carrier films 20, 22 are laminated together. The
first and second carrier films 20, 22 are preferably made of PET
but other materials such as PEN, PI, PEEK etc. are also possible.
Each of the carrier films may consist of a single film layer or
comprise a plurality of film layers of the same or different
materials. The spacer 24 preferably comprises a PET, PEN, PI, PEEK,
etc. film layer with an adhesive coating applied on each side
thereof. At each pressure-sensing cell 18, the spacer comprises an
oblong opening 26, within which the first and second carrier films
20, 22 may be pressed together. In each pressure-sensing cell 18, a
plurality of first, resistive, electrodes 28 is printed on the
first carrier film 20 and a plurality of second electrodes 30 is
printed on the second carrier film 22, in facing relationship with
the a plurality of first electrodes 28. Each plurality of
electrodes 28, 30 is contacted by a respective conductive track 34,
36. The plurality of first electrodes 28 is partially covered with
electrically insulating overprints 32 (made e.g. of a dielectric
ink), in such a way as to locally prevent a direct contact between
the electrodes on the first carrier film 20 and those on the second
carrier film 22.
[0034] As best illustrated in FIG. 3, the plurality of first
electrodes 28 comprises a first group of electrodes and a second
group of electrodes arranged so as to interdigitate while
delimiting gaps 42 there between. The electrodes of each group
contact the conductive track 34 only on one longitudinal side of
the pressure-sensitive cell 18. The conductive track 34 comprises
studs 35 arranged in contact with border portions of the first
electrodes 28 that extend along the gaps 42. Likewise, the
plurality of second electrodes 30 comprises a third group of
electrodes and a second group of electrodes arranged so as to
interdigitate while delimiting gaps 42' there between. The
electrodes of each group contact the conductive track 36 only on
one longitudinal side of the pressure-sensitive cell 18. The
conductive track 36 comprises studs 35' arranged in contact with
border portions of the second electrodes 30 that extend along the
gaps 42'.
[0035] In response to pressure acting on the pressure-sensing cell
18, at least one of the first and second carrier films 20, 22,
deflects towards the other carrier film until the carrier films 20,
22 or the elements on their respective surface come into contact.
FIG. 10 illustrates the evolution of the mechanical contact areas
on the second carrier film 22. Contours 64, 64' and 64'' represent
the contact areas as pressure on the pressure-sensing cell
increases. Once contact is established (inner contours 64), the
radius of the mechanical contact areas increases (see arrows 66)
with increasing pressure. When a direct contact is established
between the electrodes 28 and 30, the electrical resistance between
the conductors 34 and 36 becomes finite and a current may flow in
consequence. As the contact area between the first and second
electrodes 28, 30 increases, the resistance measurable between the
conductors 34 and 36 decreases. The positions of the contacts
between the resistive electrodes 28, 30 and the respective
conductive trace 34, 36, the specific resistance of the resistive
electrodes, the shape of the first and second electrodes 28, 30,
the shape of the electrically insulating overprints 32 and the
mechanical properties of the carrier films 20, 22 determine the
pressure-dependent cell resistance. Referring to the cell
configuration of FIGS. 3, 9 and 10, the first and second electrodes
28, 30 have a roughly equal-sided triangular shape. The base of the
triangles extends substantially parallel to the longitudinal axis
of the pressure-sensing cell. Each electrode 28, 30 is contacted
with the conductive studs 35, 35' at the tip opposite the base. The
initial contact (contours 64) between the first and second
electrodes 28, 30 occurs approximately at the center of each
triangle. The dielectric overprints 32 on the first electrodes 28
(shown as a dashed line in FIG. 10) prevent that a single,
continuous contact area is formed. Each contact area grows as
roughly shown by arrows 66 when pressure increases. When the
contact area has reached a certain size, the residual resistance
between the conductors 34 and 36 is mainly due to the resistive
path between the contact areas and the conductive studs 35, 35'.
(The resistance of the conductive tracks and the studs may be
neglected.) At higher pressures, each contact area grows into the
region between the studs 35, 35', which tapers in the direction of
the tip of the triangle. Since the dielectric overprints 32 locally
maintain the carrier films 20, 22 at a certain minimum distance
from each other, the rate of growth of the contact area decreases
as the contact area enters the region between the studs 35,
35'.
[0036] The electrical response function of the pressure-sensing
cells, i.e. the resistance versus pressure, may be adjusted in a
predetermined manner by suitably shaping the overprints 32, because
the electrically overprints 32 locally prevent a direct contact
between the first and second electrodes 28, 30 whereas the direct
contact is possible in those areas where the electrically
insulating overprints 32 are absent.
[0037] FIG. 5 schematically illustrates the difference in the
electrical response of a pressure-sensing cell without the
overprints (dotted curve 38) and one with the overprints shaped as
in FIG. 3 (continuous curve 40), all other cell parameters being
the same. One notes that for the pressure-sensing cell without the
insulating overprints the resistance change occurs in a relatively
small pressure range starting at the activation pressure p.sub.act
(the pressure at which the electrodes enter into contact). Above
p.sub.act, the resistance quickly levels out at a low value. For
the cell equipped with the insulating overprints, the resistance
change spreads over a significantly longer pressure interval. As a
consequence, the cell with the insulating overprints enables
pressure measurement at significantly higher pressures than the
cell without the insulating overprints. It shall be noted that the
conductive studs 35, 35' and the insulating overprints 32 also
locally reinforce the carrier films 20, 22. The suppleness of the
carrier films 20, 22 is thus locally reduced, which means that, in
vicinity of the conductive studs and the insulating overprints,
more pressure is needed to bring the first and second electrodes
into contact, which increases the dynamic range of the sensor.
[0038] As best illustrated in FIG. 2, the pressure-sensing cells 18
are arranged in areas of the shoe 10, in which the pressure peaks
are expected to occur when the wearer is standing, walking or
running. Specifically, a first one of the pressure-sensing cells is
positioned in the area of the head of the first phalange (big toe),
a second one in the area of the head of the first metatarsal bone,
a third one in the area of the head of the fifth metatarsal bone
and a fourth one in the area of the calcaneum (heel bone).
[0039] For fixation of the pressure sensor 16 to the sole structure
14 (in this example the midsole), the pressure sensor 16 comprises
one or more fixation pads 44 (see FIG. 2). The fixation pads 44
preferably comprise a layer of pressure-sensitive or
heat-activatable adhesive, initially protected by a release liner,
which is removed just before the pressure sensor 16 is attached to
its carrier member of the sole structure 14. Instead of using local
fixation pads 44, the entire surface of the first 20 or the second
22 carrier film can be coated with an adhesive (and initially
protected by a release liner).
[0040] The pressure sensor 16 further comprises an electronic
control module 46, which is arranged within a trough-shaped
receptacle 62 and mechanically attached to the multilayer film
structure of the pressure-sensor 10. Connection strips 48
interconnect the pressure sensing cells 18 and the electronic
control module 46. The connection strips 48 are integral part of
the multilayer film structure of the pressure sensor 16 and carry
conductive tracks that electrically connect the first and second
electrodes of each pressure-sensing cell 18 with the electronic
control module 46. The connection strips 48 may have a serpentine
shape to act as springs and to thereby increase the
pressure-sensor's elasticity in the sensor plane.
[0041] The electronic control module 46 preferably comprises an
application-specific integrated circuit (ASIC), a
field-programmable gate array (FPGA), a microprocessor, or the
like. Advantageously, the electronic control circuit is configured
for wirelessly transmitting the collected pressure data or any data
derived there from to a receiver appliance having a user interface.
Such receiver appliance could include a (wrist-) watch, the wrist
receiver of a heart rate monitor, a handheld computer, a mobile
phone, a portable media player or the like. In the illustrated
embodiment, the electronic control module 46 is arranged in a
cavity or well of the midsole 14.2. The cavity or well may be
located elsewhere in the sole structure 14 in other
embodiments.
[0042] For equalization of gas pressure inside the opening 26 of
the spacer 24, each pressure-sensing cell 18 comprises a
ventilation hole 58 (best shown in FIGS. 2 and 3). The ventilation
holes 58 fluidly connect the interiors of the pressure sensing
cells to the outside, so that compression of the gas inside the
pressure sensing cells is essentially avoided and thus has no
significant impact on the response curve of each cell 18.
Additionally, or alternatively, the ventilation holes 58 could be
connected to a gas reservoir within the film-type pressure
sensor.
[0043] FIG. 6 is a schematic block diagram of the flexible circuit
of the pressure sensor 16. The pressure-sensing cells 18 are drawn
as variable resistors 18.1-18.4. The cells are arranged
electrically in parallel between a respective terminal 50.1, 50.2,
50.3 or 50.4 of the electronic control module (not shown in FIG. 6)
and circuit ground 52. The electronic control module determines the
pressure values based upon the resistance (or the current or the
voltage if one of these quantities is kept constant) measured
between each terminal 50.1, 50.2, 50.3 or 50.4 and circuit ground.
It should be noted that the cell response curve is influenced by
changes in resistivity of the electrode material, which may vary
depending on ageing, temperature, humidity or other environmental
influences. To be able to correct or compensate such influence on
the pressure values, a reference resistor 54 is provided. The
reference resistor 54 is made of the same material as the
electrodes 28, 30. It is arranged somewhere on the pressure sensor
16 so that it experiences essentially the same environmental
influences as the electrodes 28, 30. In the illustrated embodiment,
the reference resistor 54 is arranged electrically between a
reference terminal 56 and circuit ground 52, in parallel to the
pressure sensing cells. The electronic control module measures the
resistance of the reference resistor 54. Any deviation from a
nominal value is used to correct the readings of the
pressure-sensing cells 18. The reference resistor 54 may be
arranged on either one of the carrier films 20, 22. One could also
use a plurality of resistors arranged on one or both of the carrier
films. Another possibility would be to provide a preloaded
pressure-sensing cell (i.e. a pressure-sensing cell wherein the
electrodes are permanently kept in contact).
[0044] The reference resistor 54 and the resistive electrodes 28,
30 of the pressure-sensing cells are preferably obtained by
printing of carbon ink on the respective carrier film. The
conductive tracks 34, 36 (including studs 35 and 35') are
preferably made of silver ink.
[0045] FIG. 7 is a schematic block diagram of an alternative
flexible circuit for the pressure sensor 16. Unlike in the flexible
circuit of FIG. 6, the reference resistor 54 is arranged
electrically between circuit ground 52 and the pressure-sensing
cells 18, drawn again as variable resistors 18.1-18.4, in the
manner of a voltage divider. During the measurement, one
pressure-sensing cell at a time may be connected to a voltage
source (e.g. a battery) by means of its terminal 50.1, 50.2, 50.3
or 50.4. The electronic control module determines the pressure
values based upon the voltages measured on measurement terminal 60.
The resistance R.sub.X of one of the pressure-sensing cells
18.1-18.4 may be obtained by
R.sub.x=R.sub.ref(U.sub.0/U.sub.meas-1), where R.sub.ref is the
resistance of the reference resistor, U.sub.0 the voltage applied
at the terminal 50.1, 50.2, 50.3 or 50.4, and U.sub.meas the
voltage measured at the terminal 60. As one supposes that the
resistances of the pressure-sensing cells and the reference
resistors are subjected to the same changes due to environmental
influences (temperature, ageing, etc.), the normalized resistance
R.sub.x/R.sub.ref is essentially independent of these effects. In
all other respects, the circuit for the pressure sensor 16 of FIG.
7 is configured and operates in the same way as the one of FIG.
6.
[0046] FIG. 8 is a schematic block diagram of another alternative
flexible circuit for the pressure sensor 16. According to this
alternative, the reference resistor 54 is arranged in parallel with
one of the pressure-sensing cells 18.1-18.4. In this arrangement,
the reference resistance is substantially higher than the
resistances of the pressure-sensing cells 18.1-18.4 in actuated
state (i.e. above the activation pressure).
[0047] FIG. 9 shows a variant of the pressure-sensitive cell 18 of
FIG. 3. The only difference with respect to FIG. 3 is that the
third and fourth groups of second electrodes 30 are contacted by
separate conductive tracks 36, 36'. The third and fourth groups of
electrodes are thus separated from each other by a high impedance
when the first and second electrodes are not in contact with one
another. They are shunted via the first electrodes when the first
and second electrodes are in contact with one another. The
electrical resistance of the cell is measured between the
conductive tracks 36 and 36'. The pressure-sensitive cell is,
therefore, of the so-called "shunt-mode" type. (In contrast, the
cell of FIG. 3 is said to be of the "through-mode" type; the
electrical resistance is measured between the conductive traces 34
and 36). The first carrier film 20 may also carry separate
conductive tracks that contact border portions of the first
electrodes 28 extending along the gaps, each of the conductive
tracks defining an equipotential line, and wherein one or more
electrically insulating overprints are arranged on the first
carrier film 20 so as to cover the gaps. The overprints at least
partially overlap with the border portions in which the first
electrodes are contacted by the conductive tracks.
[0048] While specific embodiments have been described in detail,
those with ordinary skill in the art will appreciate that various
modifications and alternatives to those details could be developed
in light of the overall teachings of the disclosure. Accordingly,
the particular arrangements disclosed are meant to be illustrative
only and not limiting as to the scope of the invention, which is to
be given the full breadth of the appended claims and any and all
equivalents thereof.
* * * * *