U.S. patent application number 14/722248 was filed with the patent office on 2015-10-01 for sensor element, force detecting device, robot and sensor device.
The applicant listed for this patent is Seiko Epson Corporation. Invention is credited to Hiroki KAWAI.
Application Number | 20150276513 14/722248 |
Document ID | / |
Family ID | 48203855 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150276513 |
Kind Code |
A1 |
KAWAI; Hiroki |
October 1, 2015 |
SENSOR ELEMENT, FORCE DETECTING DEVICE, ROBOT AND SENSOR DEVICE
Abstract
A sensor element includes a piezoelectric substrate made of a
trigonal single crystal and an electrode arranged on the
piezoelectric substrate. The substrate surface of the piezoelectric
substrate includes an electrical axis of crystal axes. An angle
.theta. formed by the substrate surface and a plane including the
electrical axis and an optical axis of the crystal axes is
0.degree.<.theta.<20.degree..
Inventors: |
KAWAI; Hiroki; (Chino,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seiko Epson Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
48203855 |
Appl. No.: |
14/722248 |
Filed: |
May 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13669879 |
Nov 6, 2012 |
9102067 |
|
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14722248 |
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Current U.S.
Class: |
73/862.68 ;
901/46 |
Current CPC
Class: |
G01L 5/167 20130101;
B25J 9/1694 20130101; G01L 1/16 20130101; H01L 41/1873 20130101;
Y10S 901/46 20130101; G01L 1/162 20130101; B25J 19/028 20130101;
G01L 5/226 20130101; H01L 41/1132 20130101 |
International
Class: |
G01L 1/16 20060101
G01L001/16; G01L 5/22 20060101 G01L005/22; B25J 9/16 20060101
B25J009/16; H01L 41/187 20060101 H01L041/187; H01L 41/113 20060101
H01L041/113 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2011 |
JP |
2011-244208 |
Claims
1. A robot comprising: a piezoelectric substrate including a
trigonal single crystal having crystal axes; a first electrode on a
first surface of the piezoelectric substrate; a second electrode on
a second surface, the first and second surfaces being on opposite
sides of the piezoelectric substrate; an arithmetic unit which
detects an amount of electric charge induced in the first or second
electrode and calculates a force applied to the piezoelectric
substrate; a rotatable arm portion; and a hand portion supported on
the arm portion via the piezoelectric substrate, the hand portion
being adapted to grip an object; wherein the first surface of the
piezoelectric substrate includes an electrical axis of the crystal
axes, an angle .theta. between the first surface and a plane
including the electrical axis and an optical axis of the crystal
axes is 0.degree.<.theta.<20.degree., and a material for the
piezoelectric electric substrate is selected from the group
consisting of langasite (La.sub.3Ga.sub.5SiO.sub.14), lithium
niobate (LiNbO.sub.3) single crystal, lithium tantalite
(LiTaO.sub.3) single crystal, gallium phosphate (GaPO.sub.4) single
crystal, and lithium borate (Li.sub.2B.sub.4O.sub.7) single
crystal.
2. The robot according to claim 1, comprising four of the sensor
units.
3. The robot according to claim 1, wherein the first surface of the
piezoelectric substrate includes the electrical axis, a mechanical
axis, and an optical axis of the crystal axes, a portion of an
outer side surface that is different from the first and second
surfaces of the piezoelectric substrate includes a plane, and an
angle .lamda. between the plane of the outer side surface and a
plane including an electrical axis and the optical axis of the
crystal axes is 25.degree..ltoreq..lamda..ltoreq.85.degree..
4. A robot comprising: a piezoelectric substrate including a
trigonal single crystal having crystal axes; a first electrode on a
first surface of the piezoelectric substrate; and a second
electrode on a second surface, the first and second surfaces being
on opposite sides of the piezoelectric substrate; an arithmetic
unit which detects an amount of electric charge induced in the
first electrode or the second electrode and calculates a force
applied to the piezoelectric substrate; a rotatable arm portion;
and a hand portion supported on the arm portion via the sensor
element, the hand portion being adapted to grip an object; wherein
the first surface of the piezoelectric substrate includes a
mechanical axis and an optical axis of the crystal axes, an outer
side surface being different from the first and second surfaces of
the piezoelectric substrate includes a plane, an angle .lamda.
between the plane of the outer surface and a plane including an
electrical axis and the optical axis of the crystal axes is
25.degree..ltoreq..lamda..ltoreq.85.degree., and a material for the
piezoelectric electric substrate is selected from the group
consisting of langasite (La.sub.3Ga.sub.5SiO.sub.14), lithium
niobate (LiNbO.sub.3) single crystal, lithium tantalite
(LiTaO.sub.3) single crystal, gallium phosphate (GaPO.sub.4) single
crystal, and lithium borate (Li.sub.2B.sub.4O.sub.7) single
crystal.
5. The robot according to claim 4, comprising four of the sensor
units.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation patent application of U.S.
application Ser. No. 13/669,879 filed Nov. 6, 2012, which claims
priority to Japanese Patent Application No. 2011-244208 filed Nov.
8, 2011 both of which are expressly incorporated by reference
herein in their entireties.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to a sensor element, a force
detecting device and a robot.
[0004] 2. Related Art
[0005] JP-A-4-231827 discloses a known force sensor using a
piezoelectric material. As shown in FIG. 15 of JP-A-4-231827 plural
measuring elements are arranged on the force sensor. Each measuring
element includes a signal electrode 15 held between crystal disks
16. The crystal disks 16 are made of a piezoelectric material and
are covered with a metal cover disk 17.
[0006] JP-A-4-231827 discloses the use of quartz, which suggests
rock crystal, as a piezoelectric material, and maintains that
quartz is an optimum material for measuring a multiple-component
motive force since quartz receives both compressive and shear
stress according to the crystal cut of the quartz. However, there
is no description regarding the slicing of the piezoelectric
material in a specific crystal direction.
SUMMARY
[0007] An advantage of some aspects of the invention is to provide
a sensor element which can detect a force with high sensitivity by
finding a condition of use of a piezoelectric material that enables
the generation of more electric charge in response to an external
force, a sensor device and a force detecting device using this
sensor element, and a robot with high reliability and safety having
this force detecting device.
[0008] The invention can be implemented in the following forms or
application examples.
Application Example 1
[0009] This application example is directed to a sensor element
including a piezoelectric substrate made of a trigonal single
crystal, a first electrode arranged on one substrate surface of the
piezoelectric substrate, and a second electrode arranged on the
other substrate surface. The substrate surface of the piezoelectric
substrate includes an X-axis (electrical axis) of crystal axes. An
angle .theta. formed by the substrate surface and a plane including
the X-axis (electrical axis) and a Z-axis (optical axis) of the
crystal axes is 0.degree.<.theta.<20.degree..
[0010] According to the sensor element of this application example,
compared with the case where a so-called Y-cut plate with
.theta.=0.degree. is used as the piezoelectric substrate of the
sensor element, the amount of electric charge generated by a shear
force applied to the piezoelectric substrate can be increased and a
sensor element with high detection capability can be provided.
Application Example 2
[0011] This application example is directed to the above
application example, wherein a portion of an outer surface that
intersects the substrate surface of the piezoelectric substrate
includes a plane extending in the X-axis direction.
[0012] According to this application example, the plane of the site
where a large strain is generated by a shear force applied to the
piezoelectric substrate extends in the direction of the shear
force. Therefore, a site where a large amount of electric charge is
generated can be formed on the piezoelectric substrate and a sensor
element with high detection capability can be provided.
Application Example 3
[0013] This application example is directed to a sensor element
including a piezoelectric substrate made of a trigonal single
crystal, a first electrode arranged on one substrate surface of the
piezoelectric substrate, and a second electrode arranged on the
other substrate surface. The substrate surface of the piezoelectric
substrate has crystal axes including a Y-axis (mechanical axis) and
a Z-axis (optical axis). A portion of an outer surface intersecting
the substrate surface includes a plane. An angle .lamda. formed by
the plane of the outer surface and a plane including an X-axis
(electrical axis) and the Z-axis (optical axis) of the crystal axes
is 25.degree..ltoreq..lamda..ltoreq.85.degree..
[0014] According to the sensor element of this application example,
compared with the case where an X-cut plate with .lamda.=0.degree.
is used as the piezoelectric substrate of the sensor element, a
site where a large strain is generated by a compressive force
applied to the piezoelectric substrate extends to an outer part of
the piezoelectric substrate and therefore an electric charge
generation site area where more electric charge is generated by an
increase in the strain is broadened. Thus, a sensor element with
high detection capability can be provided.
Application Example 4
[0015] This application example is directed to the above
application example, where the single crystal is a rock
crystal.
[0016] According to this application example, by using a rock
crystal substrate as the piezoelectric substrate, a large amount of
electric charge can be generated even with a very small strain and
a sensor element with high detection capability can be provided.
Moreover, a single crystal can be easily obtained and a
piezoelectric substrate with excellent workability and quality
stability can be formed. Thus, a sensor element capable of stable
detection can be provided.
Application Example 5
[0017] This application example is directed to a force detecting
device including the above sensor element, and an arithmetic unit
which detects an amount of electric charge induced in the first
electrode or the second electrode and calculates a force applied to
the sensor element.
[0018] According to the force detecting device of this application
example, a triaxial force detecting device can be provided with a
simple configuration. Also, by using plural such triaxial force
detecting devices, for example, a six-axis force detecting device
including torque measuring can be easily provided.
Application Example 6
[0019] This application example is directed to a robot including
the above sensor element, and an arithmetic unit which detects an
amount of electric charge induced in the first electrode or the
second electrode and calculates a force applied to the sensor
element.
[0020] According to the robot of this application example, a
contact with an obstacle and a contacting force to an object during
a predetermined operation of a robot arm or robot hand that make
differential movements are securely detected by a force detecting
device and data is fed back to a robot control device. Thus, a
robot capable of performing safe and fine work can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0022] FIGS. 1A to 1C show a sensor element according to a first
embodiment. FIG. 1A is a sectional view. FIG. 1B is an exploded
perspective view. FIG. 1C is a view from the direction of an arrow
A in FIG. 1B.
[0023] FIG. 2 is a schematic view showing a method for forming a
rock crystal substrate according to the first embodiment in
relation to crystal axes X, Y, and Z.
[0024] FIGS. 3A to 3C show a sensor element according to a second
embodiment. FIG. 3A is a sectional view. FIG. 3B is an exploded
perspective view. FIG. 3C is a view from the direction of an arrow
B in FIG. 2B.
[0025] FIG. 4 is a schematic view showing a method for forming a
rock crystal substrate according to the second embodiment in
relation to crystal axes X, Y, and Z.
[0026] FIGS. 5A and 5B are plan views showing other forms of the
rock crystal substrate according to the second embodiment.
[0027] FIG. 6 is a sectional view showing a sensor device according
to a third embodiment.
[0028] FIGS. 7A to 7C show sensor devices as other forms of the
third embodiment. FIG. 7A is a sectional view. FIGS. 7B and 7C are
exploded perspective views.
[0029] FIGS. 8A and 8B show a force detecting device according to a
fourth embodiment. FIG. 8A is a sectional view. FIG. 8B is a
conceptual view showing the arrangement of sensor devices.
[0030] FIGS. 9A and 9B show another force detecting device
according to the fourth embodiment. FIG. 9A is a plan view. FIG. 9B
is a sectional view taken along C-C' in FIG. 9A.
[0031] FIG. 10 shows the configuration of a robot according to a
fifth embodiment.
[0032] FIGS. 11A and 11B are graphs showing examples of
implementation. FIG. 11A shows an example of implementation of the
sensor element according to the first embodiment. FIG. 11B shows an
example of implementation of the sensor element according to the
second embodiment.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0033] Hereinafter, embodiments of the invention will be
described.
First Embodiment
[0034] FIGS. 1A to 1C show a sensor element according to a first
embodiment. FIG. 1A is a sectional view. FIG. 1B is an exploded
perspective view. FIG. 1C is a view from the direction of an arrow
A in FIG. 1B. A sensor element 100 shown in FIGS. 1A to 1C includes
a rock crystal substrate 10 as a piezoelectric substrate, a
detection electrode 20 as a first electrode, and a grounding
electrode (hereinafter referred to as GND electrode) 30 as a second
electrode. The material of the piezoelectric substrate is not
limited to rock crystal as long as the material is a trigonal
single crystal. A trigonal single crystal refers to a crystal which
has crystal axes such that three symmetry axes with equal lengths
intersect each other at an angle of 120.degree., with one vertical
axis meeting the point of intersection. In addition to rock
crystal, trigonal single crystals include langasite
(La.sub.3Ga.sub.5SiO.sub.14), lithium niobate (LiNbO.sub.3) single
crystal, lithium tantalate (LiTaO.sub.3) single crystal, gallium
phosphate (GaPO.sub.4) single crystal, lithium borate
(Li.sub.2B.sub.4O.sub.7) single crystal and the like. In this
embodiment, a rock crystal which can generate a large amount of
electric charge even with a very small strain and can easily
provide a single crystal and also has excellent workability and
quality stability is used.
[0035] In the sensor element 100 shown in FIG. 1A, the detection
electrode 20 is arranged on one substrate surface 10a of the rock
crystal substrate 10, and the GND electrode 30 is arranged on the
other substrate surface 10b. The rock crystal substrate 10 is held
between the detection electrode 20 and the GND electrode 30. That
is, in terms of the illustrated coordinate axes .alpha., .beta.,
.gamma., the detection electrode 20, the rock crystal substrate 10
and the GND electrode 30 are stacked in this order in the .gamma.
direction, thus forming the sensor element 100. If a force F.alpha.
in a shear direction along the illustrated .alpha.-axis direction
is applied to the sensor element 100, the rock crystal substrate 10
is deformed into a shape like a deformed rock crystal substrate
10'. With the strain due to this deformation, electric charge is
generated in the rock crystal substrate 10.
[0036] Here, in the case where the rock crystal substrate 10 is
made of a so-called Y-cut plate in which a plane intersecting the
Y-axis as the mechanical axis of the crystal axes and including the
X-axis as the electrical axis constitutes a main surface, if the
deformation shown in FIG. 1A, that is, the strain that causes the
deformation into the rock crystal substrate 10' is generated,
positive (+) electric charge is generated inside the rock crystal
substrate 10 on the side of the one substrate surface 10a of the
rock crystal substrate 10 where the detection electrode 20 is
arranged, and negative (-) electric charge is generated inside the
rock crystal substrate 10 on the side of the other substrate
surface 10b where the GND electrode 30 is arranged. The - electric
charge on the side of the other substrate surface 10b is discharged
to the ground (GND), not shown, by the GND electrode 30. The +
electric charge on the side of the one substrate surface 10a is
sent as a detection value to an arithmetic unit, not shown, by the
detection electrode 20. Based on the resulting amount of electric
charge, the force F.alpha. in the .alpha. direction is
calculated.
[0037] In the rock crystal substrate 10 made of a rock crystal that
is a trigonal single crystal as a piezoelectric body, electric
charge is generated as described above by an internal strain. The
amount of this electric charge increases and decreases depending on
the angle of the substrate surfaces 10a, 10b of the rock crystal
substrate 10 to the crystal axes X, Y, Z. A larger amount of
electric charge can be obtained particularly depending on the
following forming conditions of the substrate surfaces 10a,
10b.
[0038] FIG. 1C shows the rock crystal substrate 10, as viewed from
the direction of the arrow A shown in FIG. 1B along the
.alpha.-axis. As shown in FIG. 1C, if the substrate surfaces 10a,
10b of the rock crystal substrate 10 are defined in terms of the
crystal axes X, Y, Z, the rock crystal substrate 10 is sliced out
with an angle .theta. formed by the one substrate surface 10a of
the rock crystal substrate 10 and a plane defined by the Z-axis and
X-axis.
[0039] FIG. 2 schematically shows the method for forming the rock
crystal substrate 10 in relation to the crystal axes X (electrical
axis), Y (mechanical axis), Z (optical axis). As shown in FIG. 2,
the rock crystal substrate 10 is formed in such a way that an angle
formed by a surface 1a including the X-axis and Z-axis and
orthogonal to the Y-axis, of a rock crystal body 1 sliced out along
the crystal axes X, Y, Z, and the substrate surfaces 10a, 10b,
within a plane defined by the Y-axis and Z-axis, becomes the angle
.theta.. The angle .theta. may be preferably formed within a range
of 0.degree.<.theta.<20.degree.. By thus forming the rock
crystal substrate 10, the amount of electric charge generated by
the force F.alpha. can be increased and a sensor element with high
detection capability can be provided.
Second Embodiment
[0040] FIGS. 3A to 3C show a sensor element according to a second
embodiment. FIG. 3A is a sectional view. FIG. 3B is an exploded
perspective view. FIG. 3C is a view from the direction of an arrow
B in FIG. 3B. A sensor element 200 according to the second
embodiment is different in the form of the rock crystal substrate
10 from the sensor element 100 according to the first embodiment,
and the other parts of the configuration are the same as the first
embodiment. Therefore, the same parts of the configuration are
denoted by the same reference numerals and will not be described
further in detail. As shown in FIGS. 3A to 3C, the sensor element
200 according to the second embodiment is the sensor element 200
that detects a force F.gamma. in a direction in which a rock
crystal substrate 40 is compressed, that is, in a .gamma.
direction. The sensor element 200 has a configuration in which a
detection electrode 20 as a first electrode, the rock crystal
substrate 40 as a piezoelectric substrate, and a GND electrode 30
as a second electrode are stacked in the .gamma. direction. As in
the sensor element 100 according to the first embodiment, the
material of the piezoelectric substrate is not limited to rock
crystal as long as the material is a trigonal single crystal.
However, also in this embodiment, an example in which a rock
crystal is used as a piezoelectric material is described.
[0041] If a compressive force F.gamma. in the .gamma. direction is
applied to the sensor element 200, as shown in FIG. 3A, the rock
crystal substrate 40 is compressed and deformed into a shape like a
rock crystal substrate 40'. With the strain due to this
deformation, electric charge is generated in the rock crystal
substrate 40. Here, the rock crystal substrate 40 is made of a
so-called X-cut plate in which a plane intersecting the X-axis as
the electrical axis of the crystal axes and including the Y-axis as
the mechanical axis and the Z-axis as the optical axis constitutes
a main surface. If the deformation shown in FIG. 3A, that is, the
strain is generated, positive (+) electric charge is generated
inside the rock crystal substrate 40 on the side of one substrate
surface 40a of the rock crystal substrate 40 where the detection
electrode 20 is arranged, and negative (-) electric charge is
generated inside the rock crystal substrate 40 on the side of the
other substrate surface 40b where the GND electrode 30 is arranged.
The - electric charge on the side of the other substrate surface
40b is discharged to the ground (GND), not shown, by the GND
electrode 30. The + electric charge on the side of the one
substrate surface 40a is sent as a detection value to an arithmetic
unit, not shown, by the detection electrode 20. Based on the
resulting amount of electric charge, the force F.gamma. in the
.gamma. direction is calculated.
[0042] In the rock crystal substrate 40 made of a rock crystal that
is a trigonal single crystal as a piezoelectric body, electric
charge is generated as described above by an internal strain. The
amount of this electric charge increases and decreases depending on
the angle formed by planes 40c, 40d forming a part of an outer
surface intersecting the substrate surfaces 40a, 40b of the rock
crystal substrate 40 and the surface defined by the X-axis and
Z-axis. A larger amount of electric charge can be obtained
particularly depending on the following forming conditions of the
planes 40c, 40d.
[0043] FIG. 3C shows a view from the direction of the arrow B shown
in FIG. 3B. As shown in FIG. 3C, the outer surface forming the
outer shape of the rock crystal substrate 40 includes at least one
plane. In this embodiment, the outer surface includes the planes
40c, 40d. The rock crystal substrate 40 is sliced out in such a way
that the plane 40d has an angle .lamda. relative to a plane defined
by the X-axis and Y-axis of the crystal axes. In this embodiment,
the rock crystal substrate 40 is rectangular and the plane 40c and
the plane 40d of the outer surface are substantially parallel to
each other. Therefore, the rock crystal substrate 40 is sliced out
in such a way that the plane 40c, too, has an angle .lamda.
relative to the plane defined by the X-axis and Y-axis of the
crystal axes.
[0044] FIG. 4 schematically shows the method for forming the rock
crystal substrate 40 in relation to the crystal axes X, Y, Z. As
shown in FIG. 4, the rock crystal substrate 40 is formed in such a
way that an angle formed by a surface 2a defined by the X-axis and
Z-axis of a rock crystal body 2 sliced out along the crystal axes
X, Y, Z and the plane 40d of the outer surface becomes the angle
.lamda.. Since the plane 40c is substantially parallel to the plane
40d, the rock crystal substrate 40 is formed in such a way that an
angle formed by the surface 2a and the plane 40c becomes the angle
.lamda., too. The angle .lamda. may be preferably formed within a
range of 25.degree..ltoreq..lamda..ltoreq.85.degree.. By thus
forming the rock crystal substrate 40, the amount of electric
charge generated by the force F.gamma. can be increased and a
sensor element with high detection capability can be provided.
[0045] FIGS. 5A and 5B are views showing other forms of the rock
crystal substrate 40. In the rock crystal substrate 40 according to
the second embodiment, as described above, as the plane 40c or the
plane 40d of the outer surface intersects the surface 2a (see FIG.
4) defined by the X-axis and Z-axis, at the angle .lamda., a large
amount of electric charge is generated. Therefore, the outer
surface except the planes 40c, 40d is not limited to a plane. That
is, as in a rock crystal substrate 41 shown in FIG. 5A, parts other
than a plane 41c or a plane 41d intersecting the surface 2a (see
FIG. 4) defined by the X-axis and Z-axis, at the angle .lamda., may
be round surfaces 41a, 41b. Also, as in a rock crystal substrate 42
shown in FIG. 5B, one plane 42b may intersect the surface 2a (see
FIG. 4) defined by the X-axis and Z-axis, at the angle .lamda., and
the other parts of the surface may be a round surface 42a or the
like.
Third Embodiment
[0046] FIG. 6 is a sectional view showing a sensor device according
to a third embodiment. As shown in FIG. 6, in a sensor device 1000,
the sensor element 100 having the rock crystal substrate 10 or the
sensor element 200 having the rock crystal substrate 40 is housed
in a cylindrical container 400 and is pressed and fixed by bases
301, 302. The detection electrode 20 and the GND electrode 30 are
electrically connected to an arithmetic unit 500. The arithmetic
unit 500 includes a QV amplifier, not shown, which converts the
electric charge obtained by the detection electrode 20, and also
includes GND (ground) connected with the GND electrode 30. By
employing such a configuration, the sensor device 1000 can easily
detect a force applied between the base 301 and the base 302.
[0047] FIGS. 7A to 7C show sensor devices 1100, 1200 as other forms
of the third embodiment. FIG. 7A is a sectional view. FIG. 7B is an
exploded perspective view of the sensor device 1100. FIG. 7C is an
exploded perspective view of the sensor device 1200. The sensor
devices 1100, 1200 shown in FIGS. 7A to 7C have a configuration in
which the rock crystal substrate 10 or the rock crystal substrate
40 as a piezoelectric substrate is arranged on both sides of the
detection electrode 20, compared with the above sensor device 1000.
That is, two sensor elements 100 or two sensor elements 200 are
stacked, sharing the detection electrode 20. As shown in FIG. 7A,
in the sensor device 1100, a sensor element 101 and a sensor
element 102 are arranged so as to share the detection electrode 20,
and in the sensor device 1200, a sensor element 201 and a sensor
element 202 are arranged so as to share the detection electrode
20.
[0048] The two sensor elements 101, 102 or the sensor elements 201,
202, thus arranged, are housed in a cylindrical container 410 and
pressed and fixed by the bases 301, 302. The detection electrode 20
and the GND electrode 30 are electrically connected to an
arithmetic unit 510. The arithmetic unit 510 includes a QV
amplifier, not shown, which converts the electric charge obtained
by the detection electrode 20, and also includes GND (ground)
connected with the GND electrode 30.
[0049] FIG. 7B shows the arrangement of the sensor elements 101,
102 in the sensor device 1100. As shown in FIG. 7B, the sensor
element 101 and the sensor element 102 are stacked along an
illustrated stacking direction N, with the .gamma. directions of
the sensor elements aligned, as in the sensor element 100 according
to the first embodiment. Here, the sensor element 101 and the
sensor element 102 are arranged so that the .alpha. directions and
.gamma. directions of the sensor elements become opposite to each
other so that electric charge of the same polarity is generated on
the surface 10a that contacts the detection electrode 20, of the
rock crystal substrate 10 on the upper side in the illustrated N
direction, and on the surface 10b of the rock crystal substrate 10
on the lower side in the illustrated N direction, when a force
along an illustrated L direction is detected in the sensor device
1100.
[0050] FIG. 7C shows the arrangement of the sensor elements 201,
202 in the sensor device 1200. As shown in FIG. 7C, the sensor
element 201 and the sensor element 202 are arranged with the sides
of each sensor element reversed to each other, that is, so that the
one substrate surface 40a of the rock crystal substrate 40 contacts
the detection electrode 20. Thus, when a force along the N
direction, that is, a force in the compressing direction is
applied, electric charge of the same polarity can be generated on
the one substrate surface 40a of the two rock crystal substrates 40
contacting the detection electrode 20.
[0051] By employing such a configuration, electric charge can be
generated in the two rock crystal substrates 10 or rock crystal
substrates 40 by a force applied between the base 301 and the base
302, and about twice the electric charge in the sensor device 1000
can be obtained. Therefore, the sensor devices 1100, 1200 can
easily detect even a very small force.
Fourth Embodiment
[0052] FIGS. 8A and 8B show a force detecting device according to a
fourth embodiment. FIG. 8A is a sectional view. FIG. 8B is a
conceptual view showing the arrangement of sensor devices. In FIG.
8A, a direction in which electrodes and rock crystal substrates are
stacked (upward direction in FIG. 8A) is defined as a V(+)
direction. A rightward direction in FIG. 8A, orthogonal to the V
direction is an Hx(+) direction. A direction heading toward FIG. 8A
from the viewer is an Hy(+) direction. In a force detecting device
2000 shown in FIG. 8A, electrodes and rock crystal substrates are
alternately stacked within a cylindrical container 420 between a
base 311 and a base 312 and are pressed and fixed by the base 311
and the base 312.
[0053] The electrodes and the rock crystal substrates housed in the
cylindrical container 420 are stacked as follows. From the side of
the base 311, a sensor device 1101 in which sensor elements 101,
102 are stacked in the same configuration as the sensor device 1100
according to the another form of the third embodiment, followed by
a sensor device 1102 in which sensor elements 101, 102 are stacked
in the same configuration as the sensor device 1100, and then a
sensor device 1200 in which sensor elements 201, 202 are stacked.
In the sensor devices 1101, 1102, 1200 thus stacked, the GND
electrodes 30 except the GND electrode contacting the bases 311,
312 are shared by the sensor devices 1101, 1102, 1200.
[0054] As shown in FIG. 8B, the arrangement of the sensor device
1102 is in a direction that results from rotating the sensor device
1101 by an angle of 90.degree. about the V-axis. That is, the
L-axis of the sensor device 1101 which detects a force along the
L-axis is aligned with the Hx-axis, and the sensor device 1102 is
arranged by rotating the L-axis by an angle of 90.degree. about the
V-axis and aligning the L-axis with the Hy-axis. Thus, forces along
the Hx-axis and Hy-axis can be detected. Moreover, the sensor
device 1200 which detects a force in the N-axis direction is
arranged by aligning the N-axis with the V-axis. Thus, a force
along the V-axis can be detected. In this manner, the force
detecting device 2000 incorporating the sensor devices 1101, 1102,
1200 can detect forces in the Hx, Hy and V directions, that is, in
triaxial directions.
[0055] If a force is applied to the bases 311, 312 of the force
detecting device 2000 thus configured, based on the electric charge
generated in the sensor device 1101, 1102, 1200, vector data of the
applied external force including force components of Hx, Hy and V
directions obtained by an Hx direction arithmetic unit 610 based on
the electric charge of the sensor device 1101, by an Hy direction
arithmetic unit 620 based on the electric charge of the sensor
device 1102, and by a V direction arithmetic unit 630 based on the
electric charge of the sensor device 1200, are outputted to a
control device, not shown, with the Hx, Hy and V direction
arithmetic units 610, 620, 630 being provided in an arithmetic
device 600 as an arithmetic unit. The electric charge excited in
the GND electrode 30 is grounded and discharged by GND 640 provided
in the arithmetic device 600.
[0056] As described above, the force detecting device 2000
according to this embodiment can be a small-sized force detecting
device by having electrodes and rock crystal substrates as
piezoelectric substrates stacked in one direction. Also, the force
detecting device of this embodiment can be formed by stacking
electrodes and rock crystal substrates of simple shapes and
therefore can be a low-cost force detecting device.
[0057] FIGS. 9A and 9B schematically show a six-axis force
detecting device 3000 which uses the force detecting device 2000
according to the above embodiment and is capable of torque
detection. FIG. 9A is a plan view. FIG. 9B is a sectional view
taken along C-C' shown in FIG. 9A. As shown in FIGS. 9A and 9B, the
six-axis force detecting device 3000 has a configuration in which
four force detecting devices 2000 are fixed by bases 321, 322. By
employing this six-axis force detecting device 3000, it is possible
to find the torque about each of the Hx-axis, Hy-axis and V-axis
based on the distance between the four force detecting devices 2000
that are arranged and the force obtained by each force detecting
device 2000.
Fifth Embodiment
[0058] FIG. 10 is an external view showing the configuration of a
robot 4000 using the force detecting device 2000 according to the
third embodiment or the six-axis force detecting device 3000. The
robot 4000 includes a body portion 4100, an arm portion 4200, a
robot hand portion 4300 and the like. The body portion 4100 is
fixed, for example, on a floor, wall, ceiling, movable trolley or
the like. The arm portion 4200 is provided movably in relation to
the body portion 4100. An actuator, not shown, which generates a
motive force to rotate the arm portion 4200, a control unit which
controls the actuator, and the like are arranged inside the body
portion 4100.
[0059] The arm portion 4200 includes a first frame 4210, a second
frame 4220, a third frame 4230, a fourth frame 4240 and a fifth
frame 4250. The first frame 4210 is connected to the body portion
4100 in a rotatable or bendable manner via a rotation-bending axis.
The second frame 4220 is connected to the first frame 4210 and the
third frame 4230 via a rotation-bending axis. The third frame 4230
is connected to the second frame 4220 and the fourth frame 4240 via
a rotation-bending axis. The fourth frame 4240 is connected to the
third frame 4230 and the fifth frame 4250 via a rotation-bending
axis. The fifth frame 4250 is connected to the fourth frame 4240
via a rotation-bending axis. Under the control of the control unit,
the arm portion 4200 operates as each of the frames 4210 to 4250
rotates or bends in a complex manner about each rotation-bending
axis.
[0060] The robot hand portion 4300 is attached on the side of the
fifth frame 4250 of the arm portion 4200 that is opposite to the
connecting part with the fourth frame 4240. The robot hand portion
4300 includes a robot hand 4310 which can grip an object, and a
robot hand connecting portion 4320 in which a motor to rotate the
robot hand 4310 is arranged. The robot hand portion 4300 is
connected to the fifth frame 4250 by the robot hand connecting
portion 4320.
[0061] In the robot hand connecting portion 4320, the force
detecting device 2000 according to the third embodiment or the
six-axis force detecting device 3000 is arranged in addition to the
motor. Thus, when the robot hand portion 4300 is moved to a
predetermined operating position under the control of the control
unit, contact with an obstacle or contact with an object in
response to an operation command to exceed a predetermined
position, or the like, can be detected as a force by the force
detecting device 2000 or the six-axis force detecting device 3000.
This force can be fed back to the control unit of the robot 4000 so
that an evasive action can be executed.
[0062] Using such a robot 4000, a robot that can easily carry out
an obstacle avoiding operation, an object damage avoiding operation
and the like, which cannot be realized by traditional position
control, and that can perform safe and fine work, can be provided.
The technique is not limited to this embodiment and can also be
applied to, for example, a two-arm robot.
Example
[0063] FIGS. 11A and 11B are graphs showing the amount of electric
charge generated when a force is applied to the sensor element 100
according to the first embodiment and the sensor element 200
according to the second embodiment. The result of calculating the
amount of electric charge in relation to the angle .theta. in the
case of the sensor element 100 is shown in FIG. 11A. The result of
calculating the amount of electric charge in relation to the angle
.lamda. in the case of the sensor element 200 is shown in FIG. 11B.
The piezoelectric substrate is made of a rock crystal with a plane
size of 5 mm by 5 mm and a thickness of 200 .mu.m. F.alpha.=500N
and F.gamma.=500N are applied in the illustrated directions.
[0064] As shown in FIG. 11A, in the case where the sensor element
100 according to the first embodiment is used, compared with a
general Y-cut plate with .theta.=0.degree., an amount of electric
charge exceeding the amount of electric charge in the case of
.theta.=0.degree. can be obtained if .theta. is increased within a
range of 0.degree.<.theta.<20.degree..
[0065] As shown in FIG. 11B, in the case where the sensor element
200 according to the second embodiment is used, compared with a
general X-cut plate with .lamda.=0.degree., an amount of electric
charge exceeding the amount of electric charge in the case of
.lamda.=0.degree. can be obtained if .lamda. is within a range of
25.degree..ltoreq..lamda..ltoreq.85.degree..
* * * * *