U.S. patent application number 12/379127 was filed with the patent office on 2010-08-19 for piezoelectric tactile sensor.
This patent application is currently assigned to Southern Taiwan University. Invention is credited to Cheng-Hsin Chuang.
Application Number | 20100207490 12/379127 |
Document ID | / |
Family ID | 42559267 |
Filed Date | 2010-08-19 |
United States Patent
Application |
20100207490 |
Kind Code |
A1 |
Chuang; Cheng-Hsin |
August 19, 2010 |
PIEZOELECTRIC TACTILE SENSOR
Abstract
A novel flexible tactile sensor for sensing the force direction
was designed by introducing the concept of structural electrodes on
a piezoelectric film. The structural electrodes comprised an
elastomeric column and distributed microelectrodes between the
column and piezoelectric film. As a periodic small force acts at
the elastomeric column, the force is transferred to the
piezoelectric film based on the column bending behavior, therefore
the scale of force can be detected by the output voltages from the
distributed electrodes due to the corresponding force state under
the column. In addition, two opposite output signals from different
sides of the column can differentiate the force direction as the
column is bent by external force. The resulting signal for sensing
force and its direction depends on the size of column.
Inventors: |
Chuang; Cheng-Hsin; (Tainan,
TW) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE, FOURTH FLOOR
ALEXANDRIA
VA
22314-1176
US
|
Assignee: |
Southern Taiwan University
Tainan County
TW
|
Family ID: |
42559267 |
Appl. No.: |
12/379127 |
Filed: |
February 13, 2009 |
Current U.S.
Class: |
310/338 ;
29/25.35; 345/184 |
Current CPC
Class: |
H01L 41/1132 20130101;
Y10S 310/80 20130101; Y10T 29/42 20150115; H01L 41/45 20130101 |
Class at
Publication: |
310/338 ;
29/25.35; 345/184 |
International
Class: |
H01L 41/113 20060101
H01L041/113; H01L 41/22 20060101 H01L041/22 |
Claims
1. A piezoelectric tactile sensor comprises a piezoelectric film, a
elastomeric column and distributed microelectrodes, wherein said
piezoelectric film includes a top surface and a corresponding
opposite bottom surface; said elastomeric column, which is an
elastic column, includes a top end surface and a bottom end
surface, which overlays over the top surface of the piezoelectric
film; said microelectrodes are sandwiched between the top surface
of the piezoelectric film and the bottom end surface of the
elastomeric column in spread manner; and said piezoelectric film
will generate uneven force distribution to initiate said
distributed microelectrodes output a corresponding induced voltage
signal upon said elastomeric column being subjected to an external
force.
2. The piezoelectric tactile sensor is recited and claimed in the
claim 1, wherein said piezoelectric film is made of polyvinylidene
fluoride (PVDF) polymer, said elastomeric column is made of silicon
rubber, and said microelectrodes are sandwiched between the top
surface of the piezoelectric film and the bottom end surface of the
elastomeric column in manner of ring arrangement.
3. The piezoelectric tactile sensor is recited and claimed in the
claim 2, wherein distributed elastomeric columns of silicon rubber
are further included to overlay over the top surface of the
piezoelectric film in array manner and the distributed
microelectrodes of each elastomeric columns are sandwiched between
the top surface of the piezoelectric film and the bottom end
surface of the elastomeric column in separated manner.
4. A fabricating method of the piezoelectric tactile sensor
comprises processing steps as below: a. Prepare a piezoelectric
film with a top surface and a bottom surface; b. Form a metallic
layer on the top surface of the piezoelectric film; c. Etch the
metallic layer to obtain a distributed microelectrode configuration
on the top surface of the piezoelectric film; and d. Overlay the
bottom end surface of the elastic elastomeric column over the top
surface of the piezoelectric film such that the distributed
microelectrodes are sandwiched between the bottom end surface of
the elastic elastomeric column and the top surface of the
piezoelectric film.
5. The fabricating method of the piezoelectric tactile sensor is
recited and claimed in the claim 4, wherein a processing step is
intervened between the steps of b and c that coating over the
metallic layer by a layer of photoresist with a photomask pattern
thereon to develop the pattern.
6. The fabricating method of the piezoelectric tactile sensor is
recited and claimed in the claim 4, wherein the metallic layer
formed in the step b is a layer of chromium (Cr) alloy or
mixture.
7. The fabricating method of the piezoelectric tactile sensor is
recited and claimed in the claim 4, wherein a processing step is
intervened either between the steps of b and c or between the steps
of c and d that forming a metallic film beneath the bottom surface
of the piezoelectric film.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention provides a piezoelectric tactile
sensor, particularly for one that features in discerning
multi-axial force, and also offers a fabricating method
thereof.
PRIOR ARTS OF THE INVENTION
[0002] The popular application of the tactile sensor includes robot
field, information industry, industrial automation, biomedical
devices, wired/wireless physiological monitors, joysticks or
control levers of the videogames and the like. Most of conventional
tactile sensors belong to the tactile sensors in measurement of
normal force. For tactile sensors in measurement of lateral shear
force or multi-axial force are few.
[0003] Wherein, regarding the tactile sensors about application of
lateral shear force, U.S. Pat. No. 5,871,248 discloses a "Robot
gripper", which comprises a pair of gripper surfaces with flexible,
non-elastic films disposed on each gripper surface respectively,
these films being comprised of cubic cells filled with compressible
fluid, so that when each gripper surface makes contact with the
object to be lifted, they simultaneously compress and lift the
object whereby the friction between the object and the gripper
surfaces generates a shear force which distorts the films. As the
compression and lifting forces are simultaneously increased, the
distortion to the films will also increase until the pressure
inside the cubic cells is large enough to provide sufficient
friction force to lift the object. Therefore, it is not required to
know the weight of the object to be gripped beforehand.
[0004] U.S. Pat. No. 4,745,812 discloses a "Tri-axial tactile
sensor", which comprises an array of unique micro-machined bossed
silicon elastomeric column cells in conjunction with requisite
electrical circuitry and components, which collectively provide
ability to sense torque by detecting both normal and lateral
applied loads. Electrical signal information from
sensor-incorporated internal and external related circuitry
components can be analyzed via computer devices to yield specific
loading characteristics on the sensor surface. The related
circuitry is fabricated by diffusing piezoresistive areas and thin
film conducting strips and tap-off points. These areas and related
conductive circuitry for each of the micro-small sensor elements
are configurable as two Wheatstone bridges which thereby help
provide for the measurement of both normal and lateral load
component magnitudes
[0005] Besides, some of conventional tactile sensors employ strain
gauge, ultrasonic elastomeric column, or piezoelectric-resistor to
sense the multi-axial force.
SUMMARY OF THE INVENTION
[0006] Having realized the popular application of the tactile
sensor for discerning the multi-axial force and the urgent need
about different designs and technologies in the tactile sensor as
options for the publics, the inventor of the present invention
successfully worked out the piezoelectric tactile sensor of the
present invention after painstaking study and development with
utmost attention. Accordingly, the primary object of the present
invention is to provide a piezoelectric tactile sensor with
features of simple structure and inference about the bending moment
of the external force subjected via induced voltage signal so that
the sensor can be employed to figure out the direction and
magnitude of the external multi-axial force subjected when it is
used in the touch-controlled devices, the anti-slip sensor in the
gripper of the robot and the like.
[0007] The piezoelectric tactile sensor of the present invention
comprises a piezoelectric film, a elastomeric column and
distributed microelectrodes, wherein said piezoelectric film
includes a top surface and a corresponding opposite bottom surface;
said elastomeric column, which is an elastic column, includes a top
end surface and a bottom end surface, which overlays over the top
surface of the piezoelectric film; said microelectrodes are
sandwiched between the top surface of the piezoelectric film and
the bottom end surface of the elastomeric column in spread manner;
and said piezoelectric film will generate uneven force distribution
to initiate said distributed microelectrodes output a corresponding
induced voltage signal upon said elastomeric column being subjected
to an external force.
[0008] In an exemplary preferred embodiment, said piezoelectric
film is made of polyvinylidene fluoride (PVDF) polymer and said
elastomeric column is made of silicon rubber.
[0009] In the other exemplary preferred embodiment, said
piezoelectric tactile sensors can be expanded into array pattern
for better sensing the profile of the target object.
[0010] The present invention also discloses a fabricating method of
piezoelectric tactile sensor comprises processing steps as
below:
[0011] a. Prepare a piezoelectric film with a top surface and a
bottom surface;
[0012] b. Form a metallic layer on the top surface of the
piezoelectric film;
[0013] c. Etch the metallic layer to obtain a distributed
microelectrode configuration on the top surface of the
piezoelectric film; and
[0014] d. Overlay the bottom end surface of the elastic elastomeric
column over the top surface of the piezoelectric film such that the
distributed microelectrodes are sandwiched between the bottom end
surface of the elastic elastomeric column and the top surface of
the piezoelectric film.
[0015] In an exemplary preferred embodiment, a processing step is
intervened between the previous steps of b and c that coating over
the metallic layer by a layer of photoresist with a photomask
pattern thereon to develop the pattern.
[0016] Regarding the other objects, advantages and features of the
present invention, following exemplary preferred embodiments are
described in detailed manner with associated drawings for your
better under understanding and perusal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] Regarding the structure for the piezoelectric tactile sensor
of the present invention, a detailed disclosure for an exemplary
preferred embodiment, which is not intended for confining the scope
of the present invention, is further described below in reference
to associated drawings. FIGS. 1 and 2 shows a piezoelectric tactile
sensor 10 of the present invention is subjected to a normal force
and a shear force (also simply known as shear) as an exemplary
preferred embodiment of the present invention. The piezoelectric
tactile sensor 10 comprises a piezoelectric film 1, a elastomeric
column 2 and distributed microelectrodes 3, wherein said
piezoelectric film 1, which is made of polyvinylidene fluoride
(PVDF) polymer with properties of lightweight, high piezoelectric
force coefficient, good flexibility and high strength in mechanical
properties, includes a top surface 11 and a corresponding opposite
bottom surface 12 with wires for connecting to related signal (not
shown); said elastomeric column 2, which is an elastic column made
of silicon rubber, includes a top end surface 22 and a bottom end
surface 21, which overlays over the top surface 11 of the
piezoelectric film 1; and said microelectrodes 3 are sandwiched
between the top surface 11 of the piezoelectric film 1 and the
bottom end surface 21 of the elastomeric column 2 in spread
manner.
[0018] FIGS. 3a and 3b shows the characteristics of the force
distribution for the piezoelectric tactile sensor 10 being
subjected to a multi-axial force, where P denotes a normal force
while Q denotes a horizontal shear force as shown in the FIG. 2.
According to basic theory in the mechanics of materials, the
resultant effect of the normal force P and shear force Q can be
analyzed as below:
[0019] Let the shear force Q is constant and normal force P is
variable.
[0020] If the magnitude of the normal force P is less than the
bending moment of the shear force Q, then the resultant force
distribution will be shown as the FIG. 3b such that the strain area
of the piezoelectric film 1 acted by the elastomeric column 2 is
divided into compression zone (also called compressive force zone)
and tension zone (also called tensional force zone) with deviated
neutral axis due to unbalanced resultant force.
[0021] If the magnitude of the normal force P is increased to be
greater than the bending moment of the shear force Q, then the
resultant force distribution will be shown as the FIG. 3a such that
the strain area of the piezoelectric film 1 acted by the
elastomeric column 2 is entirely affected into compression zone
with different magnitudes of compressive force at both ends thereof
due to uneven resultant compressive force.
[0022] If (.sigma..sub.L) denotes the magnitudes of compressive
force at left end of the strain area of the piezoelectric film 1
while (.sigma..sub.R) denotes the magnitudes of compressive force
at right end of the strain area of the piezoelectric film 1, then
the magnitude of resultant compressive/tensional force subjected by
the bending moment of the shear force Q is
( .sigma. R + .sigma. L 2 ) ##EQU00001##
while the magnitude of resultant evenly distributed compressive
force is
( .sigma. R - .sigma. L 2 ) . ##EQU00002##
[0023] Thus, when the elastomeric column 2 is subjected to the
multi-axial force, no matter what the magnitude of the normal force
P, a set of different left force component magnitude
(.sigma..sub.L) and right force component magnitude (.sigma..sub.R)
will happen in both affected ends at the bottom end surface 21 of
the elastomeric column 2 so that both ends at the strain area of
the abutted piezoelectric film 1 will be acted to induce different
magnitudes of the left induced voltage component V.sub.L and right
induced voltage component V.sub.R.
[0024] Generally, if the piezoelectric film 1 is virtually
subjected to resultant force along the direction of thickness (i.e.
orthogonal to the surface thereof) without any friction, and the
plane in longitudinal and transverse directions is hypothetically
infinite, the induced voltage can be derived from the formula of
(V.sub.0=g.sub.22 .sigma..sub.2t).
[0025] Where, (V.sub.0) is the induced open-circuit output voltage
of the piezoelectric film 1; (g.sub.22) is the piezoelectric force
coefficient thereof; (.sigma..sub.2) is the resultant force along
the thickness direction thereof; and (t) is the thickness thereof.
Basing on the (V.sub.0=g.sub.22 .sigma..sub.2t) aforesaid, the
induces voltage (V.sub.0) is direct proportional to the resultant
force along the thickness direction (.sigma..sub.2) since the
piezoelectric force coefficient (g.sub.22) and thickness (t) are
constant virtually in the exemplary embodiment. When the
piezoelectric film 1 is subjected to multi-axial force, the induced
voltage (V.sub.0) at the left end, which is denoted as (V.sub.L),
and the induced voltage (V.sub.0) at the right end, which is
denoted as (V.sub.R), will be different since the resultant force
(.sigma..sub.2) acting on the left end, which is denoted as
(.sigma..sub.L) is different to the resultant force (.sigma..sub.2)
acting on the right end, which is denoted as (.sigma..sub.R). For
example, in the case of the FIG. 3b, the (VL) is positive value
while the (VR) is negative value; whereas in the case of the FIG.
3a, both of (VL) and (VR) are all negative values but different in
the magnitudes owing to the magnitude difference between the left
resultant force (.sigma..sub.L) and the right resultant force
(.sigma..sub.R). Thus, with (V.sub.L) and (V.sub.R), the external
multi-axial force can be figured out by reverse inference.
[0026] Thereby, in the practical embodiment for the piezoelectric
tactile sensor 10 of the present invention, if the elastomeric
column 2 is subjected to an external multi-axial force, the
piezoelectric film 1 will generate different magnitudes of induced
voltages (V.sub.L) and (V.sub.L), both of which are caused by the
different resultant forces (.sigma..sub.L) and (.sigma..sub.R) in
uneven force distribution. Thus, the different induced voltages
(V.sub.L) and (V.sub.L) can be captured by the piezoelectric film 1
to be converted into interpretable information to analyze the
direction and magnitude of the multi-axial force subjected.
[0027] Please refer to the FIGS. 4 and 5, which show the trend
characteristics graphs respectively about the induced voltage
distribution and force distribution for the elastomeric column 2 of
the piezoelectric film 1 by an modeling simulation of the Finite
Element Analysis (FEA) method, wherein the elastomeric column 2 is
subjected to a horizontal shear force.
[0028] In the exemplary simulated embodiment, the element form of
the piezoelectric film 1 is piezoelectric type while the element
shape thereof is hexahedron with 20 nodes, and the thickness
thereof is 52 .mu.m with a grounding terminal fixed, whereas the
elastomeric column 2, which dimensions in 30 mm height by 17 mm
width, is subjected to an external shear force in magnitude of 1
Newton near the top thereof.
[0029] The FIG. 4 shows the variation characteristics of the
induced voltage (V.sub.o) captured from a suitable path on the
(piezoelectric film 1) that the induced voltage (V.sub.R) in the
compression zone (also known as compressive force zone) is positive
value while the induced voltage (V.sub.L) in the tension zone (also
known as tensional force zone) is negative value.
[0030] Similarly, the FIG. 5 shows the variation characteristics of
the resultant force (.sigma..sub.2) captured from a suitable path
on the piezoelectric film 1 that the resultant force
(.sigma..sub.R) in the compression zone (also known as compressive
force zone) is negative value while the resultant force
(.sigma..sub.L) in the tension zone (also known as tensional force
zone) is positive value.
[0031] With information reflects above, the direction of the
external multi-axial force acting on the elastomeric column 2 can
be ascertained is from left to right.
[0032] Thus, by means of the left induced voltage (V.sub.L) and the
right induced voltage (V.sub.R) from the piezoelectric film 1, the
direction and magnitude of the external multi-axial force can be
figured out via interpretable analysis.
[0033] Refer to the FIGS. 6a through 6g. The processing steps for
the fabricating method of the piezoelectric tactile sensor provided
by the present invention are described as below:
[0034] a. Prepare a piezoelectric film 1 with a top surface 11 and
a bottom surface 12 (as shown in the FIG. 6a);
[0035] b. Form a metallic layer 4 on the top surface 11 of the
piezoelectric film 1 (as shown in the FIG. 6b), which can be
accomplished by depositing a layer of chromium (Cr) alloy or
mixture thereon via E-beam Evaporator in an exemplary
embodiment;
[0036] c. Coat over the metallic layer 4 by a layer of photoresist
5 with a photomask 6 pattern thereon to develop the pattern (as
shown in the FIG. 6c);
[0037] d. Etch the metallic layer 4 via the pattern formed (as
shown in the FIG. 6d);
[0038] e. Remove the residues of the photoresist 5 to obtain the
distributed microelectrodes 3 configuration on the top surface 11
of the piezoelectric film 1 (as shown in the FIG. 6e);
[0039] f. Form a metallic film 7 beneath the bottom surface 12 of
the piezoelectric film 1 (as shown in the FIG. 6f), which can be
accomplished by E-beam Evaporator to have metallic film 7 as
grounding electrode; and
[0040] g. Overlay the bottom end surface 21 of the elastic
elastomeric column 2 over the top surface 11 of the piezoelectric
film 1 such that the distributed microelectrodes 3 are sandwiched
between the bottom end surface 21 of the elastic elastomeric column
2 and the top surface 11 of the piezoelectric film 1 (as shown in
the FIG. 6g).
[0041] The piezoelectric tactile sensor 10 of the present invention
is a pioneer in employing the piezoelectric film 1 and distributed
microelectrode 3 to capture the force distribution from the
elastomeric column 2. Namely, when the piezoelectric tactile sensor
10 is subjected to the multi-axial force, the elastic elastomeric
column 2 is strained to create uneven force zones of compression
zone and tension zone on the piezoelectric film 1 so that
corresponding positive and negative induced voltages (V.sub.0) are
generated by the distributed microelectrodes 3. By means of the
induced voltages (V.sub.0) obtained, the bending moment due to
external multi-axial force can be figured out retroactively. And
then, the direction and magnitude of the multi-axial force can be
calculated accordingly.
[0042] FIG. 7 shows the other exemplary preferred embodiment for
the piezoelectric tactile sensor 10 of the present invention,
wherein the distributed microelectrodes 3 of the piezoelectric
tactile sensor 10 are sandwiched into ring arrangement between the
top surface 11 of the piezoelectric film 1 and the bottom end
surface 21 of the elastomeric column 2, wherein the elastomeric
column 2, when being subjected to the external multi-axial force,
can generate induced voltage (V.sub.0) of high resolution for being
analyzed to figure out the direction and magnitude of the external
multi-axial force.
[0043] Moreover, the arrangement of the piezoelectric tactile
sensor 10 can be expanded into array pattern for better sensing the
profile of the target object as shown in the FIG. 8. The
distributed elastomeric columns 2 overlay over the top surface 11
of the piezoelectric film 1 in array manner and the distributed
microelectrodes 3 of each elastomeric columns 2 are sandwiched
between the top surface 11 of the piezoelectric film 1 and the
bottom end surface 21 of the elastomeric column 2 in separated
manner, wherein the cluster of the elastomeric columns 2, when
being subjected to the external multi-axial force, can generate
group induced voltages (V.sub.0) of high resolution for being
analyzed to figure out the slip, movement, position, displacement,
contacting area, shape of the sensing object as well as the
direction and magnitude of the external multi-axial force.
[0044] Besides, both of the structure and fabricating process
disclosed heretofore are very simple without need of extra power
supply that results in having achieved the expected objects and
application effects.
[0045] Moreover, the applicable realm for the piezoelectric tactile
sensor 10 of the present invention covers:
[0046] 1. Robot Field: Movement control of the robot such as
gripping object, interface between man and the machined pet such as
machined dog pet AIBO.TM. from SONY.
[0047] 2. Information Industry: Touch input device in combination
of display device such as touch screen on the Personal Digital
Assistant (PDA), fingerprint identification, Virtual Reality and
the like.
[0048] 3. Industrial Automation: Measuring and inspecting devices
for the instrument calibration and product design such as tire
texture pattern and force distribution on the touching ground for
design of the tire grapping force against the ground.
[0049] 4. Biomedical Devices: Typical application in popular smart
skin, assistant devices for diagnosing the breast tumor or prostate
gland disease.
[0050] 5. Physiological Monitors: Various wired/wireless
physiological devices for monitoring the respiration, heartbeat and
pulsation in either wristlet, or sticking plaster or disposable
types.
[0051] The disclosure heretofore is the description about the
structure of the present invention as the exemplary preferred
embodiments. However, the embodiments can be changed and modified
in many ways in accordance with the nature and spirit of the
present invention. Therefore, any equivalent substitution and
alteration, which can be easily done by people who are skillful in
this technical field in the manner of not departing from the nature
and spirit of the present invention, should be reckoned as in the
claim scope and range of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 is the perspective schematic view showing an
exemplary preferred embodiment for the piezoelectric tactile sensor
of the present invention.
[0053] FIG. 2 is the cross sectional schematic view of the previous
FIG. 1 to show the piezoelectric tactile sensor is subjected to a
normal force and a shear force.
[0054] FIGS. 3a and 3b are the schematic views of the previous FIG.
2 to show the characteristics of the force distribution for the
piezoelectric tactile sensor being subjected to a normal force and
a shear force.
[0055] FIGS. 4 and 5 are the trend characteristics graphs
respectively showing the induced voltage distribution and force
distribution of the piezoelectric tactile sensor being subjected to
a horizontal shear force of 1 Newton force as an exemplary
preferred embodiment of the present invention.
[0056] FIGS. 6a through 6g are the flow charts showing the
fabrication process for the piezoelectric tactile sensor of the
present invention as an exemplary preferred embodiment of the
present invention.
[0057] FIG. 7 is the perspective schematic view showing the other
exemplary preferred embodiment for the piezoelectric tactile sensor
of the present invention.
[0058] FIG. 8 is the perspective schematic view showing an array
for the piezoelectric tactile sensor arrangement of the present
invention.
* * * * *