U.S. patent application number 13/642610 was filed with the patent office on 2014-02-06 for footwear article with pressure sensor.
This patent application is currently assigned to IEE INTERNATIONAL ELECTRONICS & ENGINEERING S.A.. The applicant listed for this patent is Aloyse Kirsch, Mathias Massing, Andreas Steier. Invention is credited to Aloyse Kirsch, Mathias Massing, Andreas Steier.
Application Number | 20140033572 13/642610 |
Document ID | / |
Family ID | 45952549 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140033572 |
Kind Code |
A1 |
Steier; Andreas ; et
al. |
February 6, 2014 |
FOOTWEAR ARTICLE WITH PRESSURE SENSOR
Abstract
An article of footwear including a pressure sensor arranged in
the sole structure, where the sensor includes elongated
pressure-sensing cells, each of which has an axis of main
extension, each cell having a first and a second carrier film,
which are attached to one another by a spacer film having an
elongated opening oriented along the axis of main extension, as
well as a first and a second electrode on the first and the second
carrier film, respectively, where the electrodes are arranged in
facing relationship with each other, so that a contact area between
them increases with increasing pressure, and an electrically
insulating layer is arranged within the opening having a shape such
that it locally prevents direct contact between the electrodes
where the insulating layer is present and enables the direct
contact where it is absent, where the shape is constant or
repetitionary along the axis of main extension of the cell.
Inventors: |
Steier; Andreas; (Pellingen,
DE) ; Kirsch; Aloyse; (Itzig, LU) ; Massing;
Mathias; (Konz, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Steier; Andreas
Kirsch; Aloyse
Massing; Mathias |
Pellingen
Itzig
Konz |
|
DE
LU
DE |
|
|
Assignee: |
IEE INTERNATIONAL ELECTRONICS &
ENGINEERING S.A.
Ecternach
LU
|
Family ID: |
45952549 |
Appl. No.: |
13/642610 |
Filed: |
April 11, 2012 |
PCT Filed: |
April 11, 2012 |
PCT NO: |
PCT/EP2012/056576 |
371 Date: |
February 13, 2013 |
Current U.S.
Class: |
36/103 |
Current CPC
Class: |
A61B 5/1038 20130101;
A63B 2230/62 20130101; A43B 7/08 20130101; A63B 2220/58 20130101;
G01L 1/205 20130101; A63B 2220/836 20130101; A43B 7/00 20130101;
A63B 2220/56 20130101; A63B 2225/50 20130101; A43B 3/0005
20130101 |
Class at
Publication: |
36/103 |
International
Class: |
A43B 7/00 20060101
A43B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2011 |
LU |
91 810 |
Claims
1. An article of footwear, comprising a sole structure for
supporting a wearer's foot and an upper for holding the wearer's
foot onto the sole structure, wherein said article of footwear
comprises a pressure sensor arranged in said sole structure for
measuring a pressure exerted by the wearer's foot on the sole
structure, said pressure sensor comprising one or more elongated
pressure-sensing cells, each of said pressure sensing cells having
an axis of main extension and 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 elongated opening oriented along said axis of main extension, a
first electrode arranged on said first carrier film and a second
electrode arranged on said second carrier film, at least one of
said first and second electrodes made of resistive material, said
first and 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 each other when
pressure is exerted on said pressure-sensing cell and that a
contact area between said first and second electrode increases with
increasing pressure, wherein an electrically insulating layer is
arranged within the opening of said spacer, said electrically
insulating layer having a shape so as to locally prevent a direct
contact between said first and second electrodes where said
electrically insulating layer is present and to enable said direct
contact where said electrically insulating layer is absent, said
shape being constant or repetitionary along said axis of main
extension.
2. Article of footwear as claimed in claim 1, wherein said one or
more elongated sensor cells are located in said sole structure in
areas expected to be subjected to pressure peaks when the wearer is
standing still, is walking or is running.
3. Article of footwear as claimed in claim 1, wherein each of said
one or more elongated 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.
4. Article of footwear as claimed in claim 3, wherein the axis of
main extension of each cell is oriented along a vertical projection
onto the sole structure of an axis of main extension of the bone to
which it corresponds.
5. Article of footwear as claimed in claim 1, wherein each of said
pressure sensing cells is oval, elliptical or rectangular with
rounded angles.
6. Article of footwear as claimed in claim 1, wherein the shape of
said electrically insulating layer comprises a sequence of
generally triangular tooth portions arranged in the manner of a
toothed rack in parallel with said axis of main extension.
7. Article of footwear as claimed in claim 1, wherein one of said
first and second electrodes that is made of resistive material is
made of graphite.
8. Article of footwear as claimed in claim 1, wherein said
electrically insulating layer is made of electrically insulating
ink.
9. Article of footwear as claimed in claim 1, wherein each of said
pressure sensing cells comprises a ventilation hole, in
communication with the exterior or a gas reservoir, for
equalization of gas pressure inside said opening.
10. Article of footwear as claimed in claim 1, wherein said sole
structure comprises an insole, said pressure sensor being arranged
on or in said insole.
11. Article of footwear as claimed in any one of claim 1, wherein
said sole structure comprises a midsole, said pressure sensor being
arranged on or in said midsole.
12. Article of footwear as claimed in claim 1, wherein said one or
more pressure-sensing cells are at least two pressure-sensing
cells, and wherein said pressure sensor comprises one or more
connection strips interconnecting said at least two pressure
sensing cells, said one or more connection strips being integrally
formed with said at least two pressure sensing cells, and said one
or more connection strips bearing conductors for connecting the
first and second electrodes of each pressure-sensing cell with an
electronic control module.
13. Article of footwear as claimed in claim 12, wherein at least
one of said connection strips has a serpentine shape.
14. Article of footwear as claimed in claim 1, wherein said article
of footwear is a sports shoe.
15. A pressure sensor for an article of footwear, comprising a
flexible multilayer film structure that includes a forefoot
portion, a heel portion and a connection strip that connects the
forefoot portion to the heel portion, the connection strip being
integrally formed with the multilayer film structure, wherein the
pressure sensor further comprises a trough-shaped receptacle for an
electronic control module, which receptacle the connection strip is
arranged across and bonded to.
16. Article of footwear as claimed in claim 1, wherein the first
and second electrodes comprise a plurality of generally triangular
portions, which protrude in interdigitating manner from long sides
of the pressure-sensing cell into the opening so as to form a
repetitionary pattern along the axis of main extension and wherein
the electrically insulating layer comprises a plurality of
separate, spindle-shaped portions, each of which is arranged so as
to cover areas, in which sides of neighbouring triangular portions
of the first electrode run alongside one another.
Description
TECHNICAL FIELD
[0001] The present invention generally relates to an article of
footwear, such as e.g. a shoe, a boot, a sandal or the like, in
particular an article of footwear equipped with a pressure sensor
for measuring pressure exerted by the wearer's foot on the sole
structure.
BACKGROUND ART
[0002] Document U.S. 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 U.S.
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
[0003] The disclosure provides an article of footwear including a
pressure sensor, wherein the resistance vs. pressure characteristic
of the pressure sensing cells enables more flexible
adjustments.
[0004] The proposed article of footwear (in particular a sports
shoe, such as e.g. a running shoe, a tennis shoe or the like)
comprises a sole structure for supporting a wearer's foot, an upper
for holding the wearer's foot onto the sole structure and a
pressure sensor arranged in the sole structure for measuring a
pressure exerted by the wearer's foot on the sole structure. The
pressure sensor comprises one or more elongated pressure-sensing
cells, each of which has an axis of main extension. 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 elongated opening oriented
along the axis of main extension, a first electrode arranged on the
first carrier film and a second electrode arranged on the second
carrier film, the first and 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 each other when pressure is exerted on the cell and that a
contact area between the first and second electrode increases with
increasing pressure. According to the invention, an electrically
insulating layer is arranged within the opening of the spacer. The
electrically insulating layer has a shape such that it locally
prevents a direct contact between the first and second electrodes
where the electrically insulating layer is present and enables the
direct contact where the electrically insulating layer is absent.
The shape of the electrically insulating layer is constant or
repetitionary along the axis of main extension of the cell.
[0005] The above-described shape of the electrically insulating
layer ascertains that the response of the pressure sensing cell
remains at least approximately the same when the point of
application of the force (and thus the area of contact between the
elements on the first carrier film and the elements on the second
carrier film) is displaced along the axis of main extension of the
cell. In other words, the response of the pressure sensing cell is
at least approximately invariant under a translation along the axis
of main extension of the point of application of the force (within
the boundaries of the cell). Those skilled in the art will
appreciate that this feature will render pressure sensing less
dependent on the size of the wearer's foot by suitably positioning
and orienting the pressure-sensitive cell(s) in the sole structure.
As a consequence, a pressure sensor as used in the context of the
invention may be suitable for footwear of different sizes.
[0006] Preferably, the one or more elongated sensor cells are
located in the sole structure in areas expected to be subjected to
pressure maxima when the wearer is standing still, is walking or is
running. Advantageously, each sensor cell 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. 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.
[0007] Preferably, the axis of main extension of each cell is
oriented along an axis of main extension of a vertical projection
onto the sole structure of the bone to which it corresponds.
[0008] The pressure sensing cells are preferably oval, elliptical
or rectangular with rounded angles.
[0009] According to a preferred embodiment of the invention, the
shape of the electrically insulating layer comprises a sequence of
generally triangular tooth portions arranged in the manner of a
toothed rack in parallel with the axis of main extension.
[0010] Preferably, at least one of the first and second electrodes
is made of resistive material, e.g. graphite or carbon black. The
electrically insulating layer is preferably made of electrically
insulating ink.
[0011] 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.
[0012] As those skilled will appreciate, the pressure sensor could
be arranged in different part of the sole structure. For instance,
the pressure sensor being arranged on or in the insole.
Alternatively, the pressure sensor may be arranged on or in the
midsole.
[0013] According to a preferred embodiment, the one or more
pressure-sensing cells are at least two pressure-sensing cells. The
pressure sensor in this case preferably comprises one or more
connection strips interconnecting the at least two pressure sensing
cells, the one or more connection strips being integrally formed
with the at least two pressure sensing cells. The connection strips
preferably bear conductors for connecting the first and second
electrodes of each pressure-sensing cell with an electronic control
module. The connection strips are preferably configured having a
serpentine shape in order to offer a greater resiliency to the
pressure sensor as a whole.
[0014] Preferably, the pressure-sensing cells are configured (in
particular by tailoring of the shape of the electrically insulating
layer) 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 from 0% (at the turn-on pressure, i.e. at
the about 0.1 bar) and about 100% (full contact at about 7
bar).
[0015] A preferred embodiment of a pressure sensor for an article
of footwear comprises a flexible multilayer film structure that
includes a forefoot portion and a heel portion. The forefoot
portion and the heel portion are connected to each other by a
connection strip, which is integrally formed with the multilayer
film structure. According to this embodiment, the pressure sensor
further comprises a trough-shaped receptacle for an electronic
control module, which the connection strip is arranged across and
which the connection strip is bonded to. This embodiment of a
pressure sensor for an article of footwear has the advantage that
stresses occurring in the middle region of the article of footwear
during rolling off of the foot are at least partially taken up by
the receptacle instead by the connection strip. Additionally,
buckling of the pressure sensor is efficiently avoided in this
region of the article of footwear.
[0016] Preferably, the trough-shaped receptacle is made of plastic
material, e.g. PET or epoxy. The edges of the receptacle are
preferably rounded where the connection strip crosses them in order
to avoid that the connection strip is cut off under the action of
mechanical loads.
[0017] Advantageously, in the connection strip, the upper (second)
carrier film of the pressure sensor is interrupted and detached
from the spacer film and the first carrier film in such a way that
a tongue or flap is formed, that tongue or flap carrying connection
terminals for electrically connecting the multilayer film structure
(in particular the pressure-sensing cells thereof) to the
electronic control module. Preferably, the tongue or flap is
equipped with a crimp connector portion for releasable connection
with the electronic control module.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A preferred embodiment of the invention will now be
described, by way of example, with reference to the accompanying
drawings in which:
[0019] FIG. 1 is a longitudinal cross sectional view of the sole
structure of a sports shoe with a pressure sensor;
[0020] FIG. 2 is a top view of the pressure sensor of the sports
shoe of FIG. 1;
[0021] FIG. 3 is a top schematic view of one of the pressure
sensing cells of the pressure sensor of FIG. 2;
[0022] FIG. 4 is a schematic cross sectional view of the B-B plane
of FIG. 3;
[0023] FIG. 5 is a graph illustrating the difference in the
electrical responses of a pressure-sensing cell without an
electrically insulating layer and one with such a layer;
[0024] FIG. 6 is a block diagram of the electrical circuit of the
pressure sensor illustrated in FIG. 2;
[0025] FIG. 7 is a schematic block diagram of an alternative
electrical circuit for the pressure sensor of FIG. 2;
[0026] FIG. 8 is a schematic block diagram of another alternative
electrical circuit for the pressure sensor of FIG. 2;
[0027] FIG. 9 is a top schematic view of the components on the
first carrier film in a pressure-sensing cell according to another
configuration;
[0028] FIG. 10 is a top schematic view of the components on the
second carrier film in a pressure-sensing cell according to that
configuration;
[0029] FIG. 11 is a top view of a variant of the pressure sensor of
FIG. 2;
[0030] FIG. 12 is a schematic cross sectional view of the C-C plane
of FIG. 11.
DETAILED DESCRIPTION
[0031] 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
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.
[0032] In the illustrated embodiment, the midsole 14.2, which is
preferably formed of impact-attenuating material, has a film-type
pressure sensor 16 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.
[0033] 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.
[0034] The configuration of the pressure sensing cells 18 will now
be described with reference to FIGS. 3 and 4. FIG. 3 shows the
contours of the elements of a pressure-sensing cell 18. 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 comprise 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
first resistive electrode 28 is permanently arranged on the first
carrier film 20 and a second resistive electrode 30 is permanently
arranged on the second carrier film 22, in facing relationship with
the first electrode 28. Each electrode 28, 30 is contacted by a
respective strip conductor 34, 36, which run alongside the long
sides of the opening 26. At least one of the electrodes 28, 30 (in
this example: electrode 28) is partially covered with an
electrically insulating layer 32 (e.g. a dielectric layer).
[0035] In response to pressure acting on the pressure-sensing cell,
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. Once
contact is established, the radius of the mechanical contact
surface increases 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 strip conductor 34, 36, the specific resistance
of the resistive electrodes, and the shape of the electrically
insulating layer 32 determines the pressure-dependent cell
resistance.
[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 insulating layer 32,
because the electrically insulating layer 32 locally prevents a
direct contact between the first and second electrodes 28, 30
whereas the direct contact is possible in those areas where the
electrically insulating layer 32 is absent. The other parameters of
the pressure-sensitive cells, e.g. the materials of the electrodes,
need not be adapted. FIG. 5 schematically illustrates the
difference in the electrical response of a pressure-sensing cell
without the insulating layer (dotted curve 38) and one with the
insulating layer 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 layer 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
layer, the resistance change spreads over a significantly longer
pressure interval. As a consequence, the cell with the insulating
layer enables pressure measurement at significantly higher
pressures than the cell without the insulating layer.
[0037] The shape of the electrically insulating layer 32 being
constant or repetitionary along the axis of main extension A, the
electrical response of the cell 18 will be substantially
independent of the exact position on axis A of the point of
application of the compressive force. In the illustrated
embodiment, the electrically insulating layer 32 comprises a
sequence of generally triangular tooth portions 42 arranged in the
manner of a toothed rack disposed in parallel with the axis of main
extension A. 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). The axis of main extension of each cell 18
essentially corresponds to the vertical projection onto the sole
structure of an axis of main extension of the bone, which the cell
is associated with. This renders pressure sensing in the cells less
dependent on the size of the wearer's foot. In fact, the described
arrangement of the pressure-sensing cells is tolerant, up to a
certain extent, regarding discrepancies between the nominal shoe
size, which the pressure sensor has been designed for, and the
actual size of the wearer's foot. This size tolerance makes it
possible to use one size of pressure sensor for a range of shoe
sizes (e.g. three consecutive shoe sizes in the Continental
European system).
[0038] 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.
[0039] The pressure sensor 16 further comprises an electronic
control module 46, which is 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. One or more of the connection strips 48 have a
serpentine shape to act as springs and to thereby increase the
pressure-sensor's elasticity in the sensor plane.
[0040] 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 therefrom 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.
[0041] 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.
[0042] 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).
[0043] 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 strip
conductors 34, 36 are preferably made of silver ink. The
electrically insulating layer 32 in each pressure-sensing cell 18
is preferably also a printed layer. Alternatively, the electrically
insulating layer 32 could be laminated on the carrier film and a
resistive electrode.
[0044] 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.o 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.
[0045] 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).
[0046] FIGS. 9 and 10 illustrate an alternative configuration of
the pressure-sensing cells 18. FIG. 9 shows the arrangement of
components on the first carrier film 20, FIG. 10 the corresponding
arrangement on the second carrier film 22. In this variant, the
resistive electrodes 28, 30 comprise a plurality of separate,
generally triangular portions, which protrude in interdigitating
manner from the long sides of the pressure-sensing cell 18 into the
opening 26 so as to form a repetitionary pattern along the axis of
main extension A of the cell. Each triangular portion of the second
electrode 30 is disposed as the vertical projection of a
corresponding triangular portion of the first electrode 28 (and
vice-versa). The triangular portions of the first electrode 28 are
contacted by the first strip conductor 34 outside of the opening 26
at their tops. The triangular portions of the second electrode 30
are contacted by the second strip conductor outside of the opening
26 at their bases. That arrangement forces currents to flow
essentially perpendicular to the axis of main extension A. The
electrically insulating layer 32 comprises a plurality of separate,
spindle-shaped portions, each of which is arranged so as to cover
those areas, in which the sides of neighboring triangular portions
of the first electrode 28 run alongside one another. In all other
respects, the pressure-sensing cell of FIGS. 9 and 10 is the same
as and operates in the same way as the pressure-sensing cell
depicted in FIG. 3.
[0047] FIG. 11 is a top view of a variant 16' of the pressure
sensor 16' of FIG. 2. The pressure sensor 16' is of identical
configuration as the pressure sensor 16 of FIG. 2, except for the
middle portion 62, where the pressure sensor 16' is connected to
the control module 46. The pressure sensor 16 of FIG. 2 comprises
two connection strips extending alongside the electronic control
module 46, which is mechanically and electrically connected to the
pressure sensor 16 by means of a connection tongue 68. It has been
found that such connections strips may be subjected to buckling
when the foot rolls off. Over time, buckling may lead to
deterioration of the connection strips and any strip conductors
arranged thereon. The buckling problem is significantly reduced
with the pressure sensor 16' of FIG. 11. In the pressure sensor
16', the connection strip 64 that interconnects the forefoot
portion of the sensor 16' and the heel portion is passed underneath
the electronic control module 46.
[0048] FIG. 12 shows the longitudinal cross section C-C of FIG. 11.
The connection strip 64 is guided though a trough-shaped receptacle
66 for the electronic control module 46. The receptacle 66 is
preferably made of a plastic material (e.g. PET or epoxy). The wall
thickness of the receptacle 66 is such that it can withstand the
stresses in the middle area of the shoe without substantial
deformation and/or breaking. The connection strip 64 is firmly
bonded to the bottom of the receptacle 66, so that it is the
receptacle 66 that takes up most of the strains occurring in this
area during rolling off of the foot and so that the connection
strip 64 is prevented from ejecting the electronic control module
46 out of the receptacle when tension is applied to it.
[0049] In the area of the connection strip 64, the upper (second)
carrier film of the pressure sensor is interrupted and detached
from the spacer film and the first carrier film in such a way that
a tongue or flap 68' is formed. This tongue or flap 68 carries
those parts of the strip conductors 34, 36 which are connected to
the electronic control module 46. Preferably, the tongue or flap
68' is equipped with a crimp connector portion (not shown) to
removably connect the electronic control module 46 to the film
structure of the pressure sensor 16'. In the connection strip 64,
the strip conductors are all routed between the bottom (first)
carrier film and the spacer. Accordingly, feedthrough contacts are
arranged to lead those strip conductors that are normally
sandwiched between the second carrier film and the spacer to the
first carrier film. Similar feedthrough contacts are provided to
lead those strip conductors that are normally sandwiched between
the first carrier film and the spacer to the tongue or flap
68'.
[0050] 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.
[0051] Specifically, in the embodiment described in detail, the
pressure-sensing cells 18 are configured as so-called through-mode
pressure-sensing cells. In these cells, the electrodes that are in
contact with the conductors leading to each cell are arranged on
the first and the second carrier film, respectively. Those skilled
will understand that the pressure-sensing cells could also be
configured as so-called shunt-mode pressure-sensing cells, wherein
a first and a third electrodes are in contact with the conductors
leading to each cell and are arranged on the same carrier film. The
second electrode is in this case a shunt element, which is brought
into contact with the first and the third electrode when pressure
is applied. The electrically insulating layer in this case locally
prevents a direct contact between the first and the second
electrode, and possibly also between the third and the second
electrode.
* * * * *