U.S. patent application number 17/120359 was filed with the patent office on 2021-08-19 for capacitive sensor system for touch detection.
This patent application is currently assigned to Kostal Automobil Elektrik GmbH & Co. KG. The applicant listed for this patent is Kostal Automobil Elektrik GmbH & Co. KG. Invention is credited to Christian Brueggemann, Matthias Seifert.
Application Number | 20210255754 17/120359 |
Document ID | / |
Family ID | 1000005613067 |
Filed Date | 2021-08-19 |
United States Patent
Application |
20210255754 |
Kind Code |
A1 |
Seifert; Matthias ; et
al. |
August 19, 2021 |
Capacitive Sensor System for Touch Detection
Abstract
A capacitive sensor system for touch detection includes a sensor
surface, a first sensor electrode, a second sensor electrode, and
an evaluation device. The sensor electrodes are both situated on
and border the sensor surface. The first sensor electrode has a
first closed conductor loop and the second sensor electrode has a
second closed conductor loop. The first closed conductor loop
surrounds the second closed conductor loop without the closed
conductor loops touching each other. Each sensor electrode
generates a sensor signal that depends on a position of a touch of
an object on the sensor surface relative to the closed conductor
loop of the sensor electrode. The evaluation device detects the
touch based on a comparison of a ratio value to a threshold value,
wherein the ratio value is a ratio of (i) a difference and (ii) a
sum of the sensor signals.
Inventors: |
Seifert; Matthias; (Bochum,
DE) ; Brueggemann; Christian; (Bochum, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kostal Automobil Elektrik GmbH & Co. KG |
Luedenscheid |
|
DE |
|
|
Assignee: |
Kostal Automobil Elektrik GmbH
& Co. KG
Luedenscheid
DE
|
Family ID: |
1000005613067 |
Appl. No.: |
17/120359 |
Filed: |
December 14, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2019/067318 |
Jun 28, 2019 |
|
|
|
17120359 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 3/0443 20190501;
G06F 3/04186 20190501 |
International
Class: |
G06F 3/041 20060101
G06F003/041; G06F 3/044 20060101 G06F003/044 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2018 |
DE |
10 2018 005 248.7 |
Claims
1. A capacitive sensor system for touch detection, comprising: a
sensor surface; a first sensor electrode and a second sensor
electrode both situated on and bordering the sensor surface, the
first sensor electrode having a first closed conductor loop and the
second sensor electrode having a second closed conductor loop; the
first closed conductor loop surrounds the second closed conductor
loop without the closed conductor loops touching each other; each
sensor electrode generates a sensor signal that depends on a
position of a touch of an object on the sensor surface relative to
the closed conductor loop of the sensor electrode; and an
evaluation device for detecting the touch based on a comparison of
a ratio value to a threshold value, wherein the ratio value is a
ratio of (i) a difference and (ii) a sum of the sensor signals.
2. The capacitive sensor system of claim 1 wherein: the closed
conductor loops are parallel, non-touching closed conductor
loops.
3. The capacitive sensor system of claim 1 wherein: sections of the
closed conductor loops are in parallel to one another without
touching each other.
4. The capacitive sensor system of claim 1 wherein: both of the
closed conductor loops have a circular, rectangular, or polygonal
arrangement.
5. The capacitive sensor system of claim 1 wherein: both of the
closed conductor loops have a rectangular arrangement.
6. The capacitive sensor system of claim 1 wherein: the closed
conductor loops are concentric with one another.
7. A method for a capacitive sensor system having a sensor surface,
a first sensor electrode and a second sensor electrode both
situated on and bordering the sensor surface, the first sensor
electrode having a first closed conductor loop and the second
sensor electrode having a second closed conductor loop, the first
closed conductor loop surrounds the second closed conductor loop
without the closed conductor loops touching each other, the method
comprising: generating, by the first sensor electrode, a first
sensor signal that depends on a position of a touch of an object on
the sensor surface relative to the first closed conductor loop of
the first sensor electrode; generating, by the second sensor
electrode, a second sensor signal that depends on the position of
the touch of the object on the sensor surface relative to the
second closed conductor loop of the second sensor electrode; and
detecting, by an evaluation device, the touch based on a comparison
of a ratio value to a threshold value, wherein the ratio value is a
ratio of (i) a difference and (ii) a sum of the sensor signals.
8. The method of claim 7 wherein: the closed conductor loops are
parallel, non-touching closed conductor loops.
9. The method of claim 7 wherein: sections of the closed conductor
loops are in parallel to one another without touching each
other.
10. The method of claim 7 wherein: both of the closed conductor
loops have a circular, rectangular, or polygonal arrangement.
11. A capacitive sensor system for touch detection, comprising: a
sensor surface; a first sensor electrode having a first conductor
section which forms a first closed conductor loop; a second sensor
electrode having a second conductor section which forms a second
closed conductor loop the closed conductor loops being both
situated on and bordering the sensor surface, the first closed
conductor loop surrounding the second closed conductor loop, and
the closed conductor loops being parallel with one another and
non-touching each other; an evaluation device for evaluating a
first sensor signal of the first sensor electrode and a second
sensor signal of the second sensor electrode, wherein the first
sensor signal depends on a position of a touch of an object in one
direction in a plane of the sensor surface relative to the first
closed conductor loop and the second sensor signal depends on the
position of the touch of the object in the one direction in the
plane of the sensor surface relative to the second closed conductor
loop; and wherein the evaluation device determines a ratio value
from a ratio of (i) a difference of the second sensor signal and
the first sensor signal and (ii) a sum of the first sensor signal
and the second sensor signal, compares the ratio value to a
threshold value, and detects a touch based on the comparison of the
ratio value to the threshold value.
12. The capacitive sensor system of claim 11 wherein: the closed
conductor loops are parallel, non-touching closed conductor
loops.
13. The capacitive sensor system of claim 11 wherein: sections of
the closed conductor loops are in parallel to one another without
touching each other.
14. The capacitive sensor system of claim 11 wherein: both of the
closed conductor loops have a circular, rectangular, or polygonal
arrangement.
15. The capacitive sensor system of claim 11 wherein: both of the
closed conductor loops have a rectangular arrangement.
16. The capacitive sensor system of claim 11 wherein: the closed
conductor loops are concentric with one another.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International
Application No. PCT/EP2019/067318, published in German, with an
International filing date of Jun. 28, 2019, which claims priority
to DE 10 2018 005 248.7, filed Jun. 30, 2018; the disclosures of
which are hereby incorporated in their entirety by reference
herein.
TECHNICAL FIELD
[0002] The present invention relates to a capacitive sensor system
for touch detection, the capacitive sensor system including a
sensor surface on which at least one sensor electrode is situated
and an evaluation device for evaluating an electrical sensor signal
of the sensor electrode that is influenceable by the position of a
measured object in a direction in the plane of the sensor
surface.
BACKGROUND
[0003] Capacitive sensor systems of the type stated here are used
as touch-sensitive control elements on operator panels, for
example, in consumer electronic devices or also in the dashboard
area of motor vehicles.
[0004] In common systems for touch detection using a capacitive
sensor system in the single-pole method, a preferably full-surface
sensor electrode is used for each individual operating surface. The
lateral delimitation of the touch-sensitive surfaces is achieved by
geometric adaptation of the sensor electrodes. Areas of a sensor
through which light passes are either excluded or implemented using
transparent conductive materials. For detecting a touch, the sensor
signal must exceed a signal threshold.
[0005] These systems function well as long as the size of the
touch-sensitive sensor surfaces is smaller than or similar to the
measured object, in particular an operating finger, for example.
For a sensor surface that is much larger than a finger, the sensor
signal drops off only slowly beyond the edge of the sensor surface
in the plane of the operating surface. Such a sensor system is
generally designed to function robustly for different finger sizes,
and in some circumstances, also for operation while wearing gloves.
A threshold value condition that is modified for small fingers may
then, for large fingers, result in inaccurate touch detection a few
centimeters outside the operating surface.
[0006] If it is necessary to exclude the interior region of the
sensor surface, for example, for lighting elements, then the sensor
signal once again drops off in this region, and the threshold value
must be lowered further. As a result, the touch detection in the
operating plane migrates even farther to the outside. Such a sensor
system in which the sensor is made up of a conductor loop that
borders the actual operating surface thus functions at least very
imprecisely, and even incorrectly, with regard to the association
of functions and sensor surfaces.
SUMMARY
[0007] An object is to provide a capacitive sensor system for touch
detection in a simple and cost-effective manner in such a way that
the touch detection has a preferably low dependency on the specific
configuration of the measured object.
[0008] An embodiment of the present invention provides a capacitive
sensor system for touch detection. The capacitive sensor system
includes a sensor surface and an evaluation device. A first sensor
electrode and a second sensor electrode are arranged on and border
the sensor surface. Each sensor electrode generates an electrical
sensor signal that depends on the position of a measurement object
in a direction in the plane of the sensor surface relative to the
sensor electrode. The sensor electrodes each have a closed
conductor loop which run parallel to one another, without touching
each other. The closed conductor loop of the first sensor electrode
surrounds the closed conductor loop of the second sensor electrode.
The sensor electrodes are connected to respective inputs of the
evaluation device for the evaluation device to receive the sensor
signals. The evaluation device evaluates the sensor signals by
determining a ratio value from the ratio of the difference and the
sum of the sensor signals and then by comparing the ratio value to
a threshold value. The evaluation device detects a touch depending
on the comparison. For instance, the evaluation device detects a
touch when the ratio value exceeds the threshold value.
[0009] In carrying out any of the above and/or other objects, a
capacitive sensor system for touch detection is provided. The
capacitive sensor system includes a sensor surface, a first sensor
electrode, a second sensor electrode, and an evaluation device. The
sensor electrodes are both situated on and border the sensor
surface. The first sensor electrode has a first closed conductor
loop and the second sensor electrode has a second closed conductor
loop. The first closed conductor loop surrounds the second closed
conductor loop without the closed conductor loops touching each
other. Each sensor electrode generates a sensor signal that depends
on a position of a touch of an object on the sensor surface
relative to the closed conductor loop of the sensor electrode. The
evaluation device detects the touch based on a comparison of a
ratio value to a threshold value, wherein the ratio value is a
ratio of (i) a difference and (ii) a sum of the sensor signals.
[0010] In embodiments, the closed conductor loops are parallel,
non-touching closed conductor loops.
[0011] In embodiments, sections of the closed conductor loops are
in parallel to one another without touching each other.
[0012] Both of the closed conductor loops may have a circular,
rectangular, or polygonal arrangement. In an embodiment, both of
the closed conductor loops have a rectangular arrangement.
[0013] The closed conductor loops may be concentric with one
another.
[0014] In carrying out any of the above and/or other objects, a
method for the capacitive sensor system is provided. The method
includes generating, by the first sensor electrode, a first sensor
signal that depends on a position of a touch of an object on the
sensor surface relative to the closed conductor loop of the first
sensor electrode and generating, by the second sensor electrode, a
second sensor signal that depends on the position of the touch of
the object on the sensor surface relative to the closed conductor
loop of the second sensor electrode. The method further includes
detecting, by the evaluation device, the touch based on a
comparison of a ratio value to a threshold value, wherein the ratio
value is a ratio of (i) a difference and (ii) a sum of the sensor
signals.
[0015] In carrying out any of the above and/or other objects,
another capacitive sensor system for touch detection is provided.
This capacitive sensor system includes a sensor surface, a first
sensor electrode having a first conductor section which forms a
first closed conductor loop, and a second sensor electrode having a
second conductor section which forms a second closed conductor
loop. The closed conductor loops are both situated on and border
the sensor surface, the first closed conductor loop surrounds the
second closed conductor loop, and the closed conductor loops are
parallel with one another and non-touching each other. This
capacitive sensor system further includes an evaluation device for
evaluating a first sensor signal of the first sensor electrode and
a second sensor signal of the second sensor electrode. The first
sensor signal depends on a position of a touch of an object in one
direction in a plane of the sensor surface relative to the first
closed conductor loop and the second sensor signal depends on the
position of the touch of the object in the one direction in the
plane of the sensor surface relative to the second closed conductor
loop. The evaluation device determines a ratio value from a ratio
of (i) a difference of the second sensor signal and the first
sensor signal and (ii) a sum of the first sensor signal and the
second sensor signal, compares the ratio value to a threshold
value, and detects a touch based on the comparison of the ratio
value to the threshold value.
[0016] DE 10 2004 038 872 A1 describes a capacitive sensor system
for touch detection. This capacitive sensor system includes a
sensor surface and an evaluation device. First and second sensor
electrodes are situated on and border the sensor surface. The
evaluation device is for evaluating an electrical sensor signal of
each sensor electrode. The electrical sensor signal of each sensor
electrode depends on the position of a measured object in a
direction in the plane of the sensor surface. The sensor electrodes
have conductor sections in parallel to one another. The conductor
sections form triangular arrangements of conductor surfaces. The
first sensor electrode surrounds the second sensor electrode. The
sensor electrodes are connected to respective inputs of the
evaluation device. The evaluation device receives the sensor
signals of the sensor electrodes and determines a ratio value from
the ratio of the difference to the sum of the detected sensor
signals. The evaluation device then compares the ratio value to a
threshold value.
[0017] This capacitive sensor system uses a sensor element that is
divided into at least two closely adjacent sensor surfaces, wherein
in one direction a first sensor element becomes progressively
smaller and a second sensor element becomes progressively larger.
As a result, the detectable sensor signal changes with the
particular location of the actuation. The sensor surfaces are
therefore formed essentially by interlinked triangular
surfaces.
[0018] In contrast to this capacitive sensor system, in embodiments
of the present invention, parallel, non-touching closed conductor
loops provide touch detection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] A functional principle of a capacitive sensor system
according to the present invention for touch detection is
illustrated and explained below with reference to the Figures. In
addition, the problem leading to the present invention is explained
in greater detail based on a conventional capacitive sensor
system.
[0020] FIG. 1 illustrates a schematic diagram of a capacitive
sensor system for touch detection according to an embodiment of the
present invention;
[0021] FIG. 2 illustrates a graph of sensor signal curves of first
and second sensor electrodes of the capacitive sensor system as a
function of lateral touch position;
[0022] FIG. 3 illustrates a schematic diagram of an evaluation
device of the capacitive sensor system;
[0023] FIG. 4 illustrates a graph of sensor signal ratio function
curves as a function of lateral touch position;
[0024] FIG. 5 illustrates a schematic diagram of a conventional
capacitive sensor system for touch detection; and
[0025] FIG. 6 illustrates a graph of sensor signal curves of the
sensor electrode of the conventional capacitive sensor system.
DETAILED DESCRIPTION
[0026] Detailed embodiments of the present invention are disclosed
herein; however, it is to be understood that the disclosed
embodiments are merely exemplary of the present invention that may
be embodied in various and alternative forms. The figures are not
necessarily to scale; some features may be exaggerated or minimized
to show details of particular components. Therefore, specific
structural and functional details disclosed herein are not to be
interpreted as limiting, but merely as a representative basis for
teaching one skilled in the art to variously employ the present
invention.
[0027] Referring now to FIG. 5, a schematic diagram of a
conventional capacitive sensor system for touch detection is shown.
A capacitive touch switch having a rectangular metallic frame as a
sensor element is known, for example, from DE 10 2007 044 393 B3
(counterpart U.S. Pat. No. 8,182,104). FIG. 6 illustrates a graph
of qualitative sensor signal curves of the sensor electrode of the
conventional capacitive sensor system. The problem leading to the
capacitive sensor system in accordance with embodiments of the
present invention is explained in greater detail based on this
diagram.
[0028] As shown in FIG. 5, the conventional capacitive sensor
system includes a sensor electrode E. Sensor electrode E is in the
form of a closed conductor loop L. The closed conductor loop forms
the edge section of a rectangular sensor surface SF. A direction
coordinate X whose origin point 0 is arbitrarily situated in the
center of the associated lateral extension region of sensor surface
SF is illustrated parallel to a lateral line of sensor surface SF.
Direction coordinate X is strictly an example of one of the lateral
directions in which a measured object F may be positioned relative
to sensor surface SF. Lateral positionings of measured object F in
a direction other than the illustrated X direction result in a
qualitatively similar course.
[0029] The conventional capacitive sensor system detects touches of
a measured object F onto sensor surface SF. Herein, it is assumed,
without limitation of universality, that measured object F is a
human finger.
[0030] Sensor electrode E emits a sensor signal S dependent on the
position of measured object F relative to sensor electrode E. An
evaluation device of the conventional capacitive sensor system
receives sensor signal S from sensor electrode E. Electronic
evaluation device AV compares sensor signal S to a predefined
signal threshold value S_threshold. As an example, it is
illustrated in FIG. 5 that evaluation device AV checks whether
sensor signal S is equal to signal threshold S_threshold.
Alternatively, evaluation device AV may determine that a valid
sensor actuation is present when the value of sensor signal S
either falls below or exceeds signal threshold S_threshold.
[0031] Determining a suitable signal threshold S_threshold is not
without problems. The dependency of the sensor signal curve S(x) on
the position x of a finger F is plotted along the direction
coordinate X in the diagram in FIG. 6. The size of finger F
touching sensor surface SF is considered as a relevant parameter
that also influences the sensor signal S(x). Therefore, the sensor
signal curves S(x) in FIG. 6 are plotted once for a large finger as
sensor signal curve S(x)_L and once for a small finger as the
sensor signal curve S(x)_S.
[0032] Large finger sensor signal curve S(x)_L and small finger
sensor signal curve S(x)_S are illustrated here in a strictly
qualitative manner, and in addition the numerical figures indicated
on the abscissa are based on arbitrary units. However, emphasis is
placed on the point x=0, which refers to the line in the center of
sensor surface SF in FIG. 5, as well as the black area of the
graphic which, extended laterally along direction coordinate X,
represents the position of the right-most side of closed conductor
loop L of sensor electrode E shown in FIG. 5.
[0033] The two graphs of sensor signal curves S(x)_L and S(x)_S in
FIG. 6 show that sensor signal curve S(x) initially rises slightly
during displacement of a large finger F and a small finger F in the
positive X direction from the center toward the edge of sensor
surface SF, and then falls more or less quickly outside sensor
surface SF, i.e., on the other side of closed conductor loop L.
[0034] These sensor signal curves S(x)_L and S(x)_S may result in
ambiguities with regard to the particular threshold value
condition. It is assumed that the dashed horizontal line in FIG. 6
marks a signal threshold S_threshold. It is then apparent from the
illustrated bordering data points that for sensor signal curve
S(x)_S for a small finger, signal threshold S_threshold is reached
at two positions x inside and outside sensor surface SF (i.e.,
inside closed conductor loop L and outside closed conductor loop
L), since at that location, sensor signal values occur that are
identical to the value of signal threshold S_threshold. Thus, it is
not clear from the determined sensor signal S whether finger F at
that moment is approximately in the center or outside sensor
surface SF. For sensor signal curve S(x)_L for a large finger, a
sensor value at the level of signal threshold S_threshold results
in an even greater distance to the side of sensor surface SF.
[0035] Since it is generally not known whether sensor surface SF is
touched by a large or a small finger, ambiguities result in the
interpretation of a detected sensor signal S by evaluation device
AV. This may cause operating errors which should be avoided.
[0036] For solving this problem, FIG. 1 shows a schematic
illustration of a capacitive sensor system for touch detection
according to an embodiment of the present invention. The capacitive
sensor system includes a first sensor electrode E1 and a second
sensor electrode E2. Sensor electrodes E1, E2 are both situated on
and border a sensor surface SF of the capacitive sensor system.
First sensor electrode E1 is in the form of a first closed
conductor loop L1. Second sensor electrode E2 is in the form of a
second closed conductor loop L2. Closed conductor loops L1, L2 are
each in the form of circular, rectangular, or polygonal closed
conductor loops, which enclose one another in a preferably mutually
parallel arrangement without touching each other. For instance, as
shown in FIG. 1, closed conductor loops L1, L2 are both rectangular
closed conductor loops and first closed conductor loop L1 surrounds
second conductor loop L2 with the sides of closed conductor loops
L1, L2 running in parallel to one another, without closed conductor
loops L1, L2 touching one another. Put another way, closed
conductor loops L1, L2 are concentric with one another and do not
touch on another.
[0037] As closed conductor loop L1 of sensor electrode E1 surrounds
closed conductor loop L2 of sensor electrode E2, sensor electrode
E1 is an outer sensor electrode and sensor electrode E2 is an inner
sensor electrode, as shown in FIG. 1.
[0038] Sensor electrodes E1, E2 each emit their own sensor signals
S1, S2. Sensor signal S1 of first sensor electrode E1 depends on a
position of a measured object F relative to closed conductor loop
L1 of first sensor electrode E1. Sensor signal S2 of second sensor
electrode E2 depends on the position of measured object relative to
closed conductor loop L2 of second sensor electrode E2. Sensor
electrodes E1, E2 supply sensor signals S1, S2 to respective inputs
of an evaluation device AV of the capacitive sensor system.
Evaluation device AV determines a ratio value from a ratio of (i) a
difference of sensor signal S2 and sensor signal S1 and (ii) a sum
of sensor signal S1 and sensor signal S2. Evaluation device AV
detects a touch depending on a comparison of the ratio value to a
threshold value.
[0039] Referring now to FIG. 2, with continual reference to FIG. 1,
a graph of sensor signal curves of sensor electrodes E1, E2 as a
function of lateral touch position is shown. FIG. 2 illustrates,
for a given sensor system, typical curves S(x) of these sensor
signals S1, S2 as a function of the finger position x in the X
direction indicated in FIG. 1, analogously to the illustration in
FIG. 6. The graphs depicted as dashed lines represent sensor signal
curves S1(x)_S and S1(x)_L, which result from sensor signals S1 of
outer sensor electrode E1, while the graphs depicted as solid lines
represent the sensor signal curves S2(x)_S and S2(x)_L for sensor
signals S2 of inner sensor electrode E2. The indices _S and _L are
in turn used to distinguish between a small or a large finger as
the particular measured object F.
[0040] It is apparent from FIG. 2 that, regardless of the size of
finger F, the signal value curves S2(x)_S, S2(x)_L of inner sensor
electrode E2 always have greater values than the signal value
curves S1(x)_S, S1(x)_L of outer sensor electrode E1, as long as
finger F is inside sensor surface SF bordered by inner sensor
electrode E2, and conversely, outer sensor electrode E1 always
delivers greater signal values S1(x)_S and S1(x)_L as soon as
finger F is outside the area bordered by outer sensor electrode
E1.
[0041] For a finger F of a given size, sensor signal curves S1(x)_S
and S2(x)_S as well as S1(x)_L and S2(x)_L in each case assume
exactly the same value when the finger is in the area between the
sensor electrode E1, E2, which is apparent at the intersection
points of the corresponding plots in FIG. 2.
[0042] The sensor signal curves S(x) illustrated in FIG. 2 are
characteristic for a certain specific design of a sensor system,
and therefore may in principle be used by evaluation device AV,
depicted in FIG. 1, for comparison with a threshold value. However,
these comparisons would also be subject to significant
uncertainties, since as shown in FIG. 2, different sizes of finger
F result in sensor signals S(x) that are very different
quantitatively. Only the positioning of a finger F exactly in the
area between sensor electrode E1, E2 allows a precise
identification in every case, since at this location the sensor
signals S1 and S2 of sensor electrodes E1, E2 have exactly the same
value regardless of the size of finger F.
[0043] As schematically illustrated in FIG. 3, a much more accurate
determination of a threshold value condition is achieved in that
evaluation device AV forms a ratio value V which, except for
additive or multiplicative constants that may be present, is given
by:
V:=(S2-S1)/(S1+S2)
[0044] The ratio value V thus results from the difference S2-S1 of
sensor signals S1, S2 of sensor electrodes E1, E2 (i.e., the
difference of sensor signal S2 and sensor signal S1) divided by the
sum S1+S2 of sensor signals S1, S2 of sensor electrodes E1, E2
(i.e., the sum of sensor signal S1 and sensor signal S2).
[0045] The difference S2-S1 between the two sensor signals S1, S2
is a value that provides information about the position of a finger
F in the plane of sensor surface SF. The sum S1+S2 of the two
sensor signals S1, S2 qualitatively corresponds approximately to
the signal of an individual sensor electrode E1, E2, and scales
with the finger size. It may therefore be used to normalize the
difference signal S2-S1.
[0046] The same as for the individual sensor signals, a ratio
function V(x) for the dependency of the ratio value V on the finger
position may also be calculated for the ratio value V:
V(x):=(S2(x)-S1(x))/(S1(x)+S2(x)),
which once again is typical for a given sensor system.
[0047] FIG. 4 illustrates a graph of sensor signal ratio function
curves as a function of lateral touch position. In FIG. 4, two
graphs V(x)_L, V(x)_S are plotted which represent the ratio
function V(x), calculated once from sensor signal data for a large
finger and calculated once from sensor signal data for a small
finger. It is apparent that both ratio functions V(x)_L, V(x)_S
have a quite similar curve, qualitatively as well as
quantitatively.
[0048] For the evaluation it is advantageous that the ratio
functions V(x)_L, V(x)_S drop off monotonically toward the origin
point 0, and thus toward the center of sensor surface SF, and have
the steepest slope, in particular in the area of the illustrated
sections of closed conductor loops L1, L2. In addition, the
function values of the ratio functions V(x) both have a zero
crossing here. By use of these properties, ambiguities, which
otherwise result in major errors in the touch detection, may be
satisfactorily avoided.
[0049] The two ratio functions V(x)_L and V(x)_S illustrated in
FIG. 4 show that their function values for different sizes of
fingers F have a relatively small fluctuation margin. For touch
detection, it is thus possible to satisfactorily set a threshold
value V_threshold that is also suitable for different sizes of
fingers F.
[0050] Thus, a threshold value V_threshold having the value -0.10
by way of example is marked by a horizontal dashed line in FIG. 4.
It is apparent that for a ratio value of V.ltoreq.-0.10 determined
by evaluation device AV, it is ensured for a sensor actuation by a
small finger as well as by a large finger that the touch occurs
inside the area SF of the sensor field.
[0051] The proposed capacitive sensor system thus allows an
accurate delimitation of the touch detection within large operator
panels, regardless of the size of a finger that touches the sensor.
In addition, the sensitive areas may be adapted to the geometry of
the operator panel via a positionally accurate evaluation. The
inner free spaces within the double ring-shaped electrode
arrangement may be utilized for additional purposes, for example
for placement of lighting elements.
LIST OF REFERENCE SYMBOLS
[0052] AV evaluation device [0053] E, E1, E2 sensor electrodes
(conductor loops) [0054] F measured object (finger) [0055] L, L1,
L2 closed conductor loops (conductor sections) [0056] S, S1, S2
sensor signals [0057] S(x), S1(x), S2(x) sensor signal curves
(general) [0058] S(x)_L, S1(x)_L, S2(x)_L sensor signal curves (for
a large finger) [0059] S(x)_S, S1(x)_S, S2(x)_S sensor signal
curves (for a small finger) [0060] S2-S1 difference between sensor
signals S2 and S1 [0061] S1+S2 sum of sensor signals S1 and S2
[0062] SF sensor surface [0063] S_threshold threshold value, signal
threshold [0064] V ratio value [0065] V(x), V(x)_L, V(x)_S ratio
function [0066] V_threshold threshold value [0067] X direction
coordinate [0068] x (finger) position [0069] 0 origin point
[0070] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms of the
present invention. Rather, the words used in the specification are
words of description rather than limitation, and it is understood
that various changes may be made without departing from the spirit
and scope of the present invention. Additionally, the features of
various implementing embodiments may be combined to form further
embodiments of the present invention.
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