Sensor element, sensor device, force detection apparatus, and robot

A sensor element includes a first reference potential side terminal located between a first signal side terminal and a second signal side terminal along a first axis passing through the first signal side terminal and the second signal side terminal in a plan view from a direction in which a first piezoelectric element and a second piezoelectric element are stacked and a second reference potential side terminal located between the first signal side terminal and the second signal side terminal along the first axis in the plan view from the direction. The first axis is located between the first reference potential side terminal and the second reference potential side terminal in the plain view from the direction.

BACKGROUND

1. Technical Field

The present invention relates to a sensor element, sensor device, force detection apparatus, and robot.

2. Related Art

Recently, piezoelectric elements each having a structure in which electrodes are provided between a plurality of piezoelectric materials and outputting electric charge according to an applied external force have been known as sensor elements for force detection (for example, see Patent Document 1 (JP-A-2015-87333)). In the sensor element, piezoelectric materials having different crystal directions are stacked, and the element may detect external forces in different axis directions. Further, the element uses quartz crystal as the piezoelectric materials and has excellent characteristics including a wider dynamic range, higher rigidity, higher natural frequency, higher withstanding load, etc., and may be widely used for industrial robots.

However, the sensor element disclosed in Patent Document 1 outputs output signals according to external forces from two different axis directions respectively from two side terminals provided on the same side surface of the sensor element. Accordingly, the two side terminals are placed close to each other, and there is a problem that noise is generated in the output signals output from the respective side terminals due to capacitive coupling and electromagnetic coupling between the side terminals.

SUMMARY

A sensor element according to an aspect of the invention includes a stacking structure having surrounding side surfaces in which a plurality of reference potential electrodes, a first piezoelectric element, a first signal electrode placed in a position with the first piezoelectric element between at least one of the plurality of reference potential electrodes and itself and extracting a signal of the first piezoelectric element, a second piezoelectric element, a second signal electrode placed in a position with the second piezoelectric element between at least one of the plurality of reference potential electrodes and itself and extracting a signal of the second piezoelectric element are stacked, a first signal side terminal placed on the side surface and electrically connected to the first signal electrode, a second signal side terminal placed on the side surface and electrically connected to the second signal electrode, a first reference potential side terminal placed on the side surface and electrically connected to at least one of the reference potential electrodes, and a second reference potential side terminal placed on the side surface and electrically connected to at least one of the reference potential electrodes, wherein, in a plan view from a direction of the stacking, the first reference potential side terminal is located between the first signal side terminal and the second signal side terminal on the side surface on one side of a first axis passing through a position of the first signal side terminal and a position of the second signal side terminal, and the second reference potential side terminal is located between the first signal side terminal and the second signal side terminal on the side surface on the other side of the first axis.

In the sensor element according to the aspect of the invention, it is preferable that the first signal side terminal and the second signal side terminal are placed point-symmetrically with respect to a geometrical center of the sensor element in the plan view, and the first reference potential side terminal and the second reference potential side terminal are placed point-symmetrically with respect to the geometrical center of the sensor element in the plan view.

In the sensor element according to the aspect of the invention, it is preferable that the first piezoelectric element has a first piezoelectric material and a second piezoelectric material having a polarization direction opposite to a polarization direction of the first piezoelectric material, the first signal electrode is placed between the first piezoelectric material and the second piezoelectric material, the first piezoelectric material, the first signal electrode, and the second piezoelectric material are placed between two of the plurality of reference potential electrodes, the second piezoelectric element has a third piezoelectric material and a fourth piezoelectric material having a polarization direction opposite to a polarization direction of the third piezoelectric material, the second signal electrode is placed between the third piezoelectric material and the fourth piezoelectric material, and the third piezoelectric material, the second signal electrode, and the fourth piezoelectric material are placed between two of the plurality of reference potential electrodes.

In the sensor element according to the aspect of the invention, it is preferable that the first piezoelectric element has a plurality of sets of the first piezoelectric material, the second piezoelectric material, and the first signal electrode placed between the first piezoelectric material and the second piezoelectric material, and the second piezoelectric element has a plurality of sets of the third piezoelectric material, the fourth piezoelectric material, and the second signal electrode placed between the third piezoelectric material and the fourth piezoelectric material.

In the sensor element according to the aspect of the invention, it is preferable that the plurality of reference potential electrodes include a first reference potential electrode, a second reference potential electrode, a third reference potential electrode, and a fourth reference potential electrode, the first piezoelectric material is placed between the first reference potential electrode and the first signal electrode, the second piezoelectric material is placed between the second reference potential electrode and the first signal electrode, the third piezoelectric material is placed between the third reference potential electrode and the second signal electrode, the fourth piezoelectric material is placed between the fourth reference potential electrode and the second signal electrode, the first reference potential side terminal is electrically connected to the first reference potential electrode and the second reference potential electrode, the second reference potential side terminal is electrically connected to the third reference potential electrode and the fourth reference potential electrode, the first reference potential side terminal and the third reference potential electrode and the fourth reference potential electrode are electrically insulated, and the second reference potential side terminal and the first reference potential electrode and the second reference potential electrode are electrically insulated.

In the sensor element according to the aspect of the invention, it is preferable that the first piezoelectric material, the second piezoelectric material, the third piezoelectric material, and the fourth piezoelectric material are quartz crystal.

A sensor device according to an aspect of the invention includes the sensor element according to the above described aspect, a base member in which the sensor element is placed, a lid member connected to the base member and forming a housing space for housing the sensor element with the base member, a first circuit containing an electronic component placed on the base member within the housing space and electrically connected to a first signal side terminal and a first reference potential side terminal, and a second circuit containing an electronic component placed on the base member within the housing space and electrically connected to a second signal side terminal and a second reference potential side terminal, wherein the first circuit is placed on one side of the sensor element and the second circuit is placed on the other side of the sensor element in a plan view of the base member.

In the sensor device according to the aspect of the invention, it is preferable that, in the sensor element, the first signal side terminal and the second signal side terminal are placed point-symmetrically with respect to a geometrical center of the sensor element in the plan view, the first reference potential side terminal and the second reference potential side terminal are placed point-symmetrically with respect to the geometrical center, and the first circuit and the second circuit are placed point-symmetrically with respect to the geometrical center.

In the sensor device according to the aspect of the invention, it is preferable that the lid member is connected to the base member having a connecting portion, a wire connecting the first signal side terminal and the electronic component of the first circuit is placed apart from the connecting portion, and a wire connecting the second signal side terminal and the electronic component of the second circuit is placed apart from the connecting portion.

In the sensor device according to the aspect of the invention, it is preferable that the first circuit includes a plurality of the electronic components, the second circuit includes a plurality of the electronic components, and wires connecting between the electronic components contained in the respective first circuit and the second circuit are placed apart from the connecting portion.

A force detection apparatus according to an aspect of the invention includes a first board, a second board, and the sensor device according to the above described aspect placed between the first board and the second board.

A robot according to an aspect of the invention includes a base, an arm connected to the base, and the force detection apparatus according to the above described aspect.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

As below, a sensor element, sensor device, force detection apparatus, and robot as aspects according to the invention will be explained in detail based on embodiments shown in the accompanying drawings.

First Embodiment

First, a sensor device according to the first embodiment of the invention is explained.

FIG. 1is a plan view of the sensor device according to the first embodiment of the invention.FIG. 2is a sectional view along line A-A inFIG. 1.FIG. 3is a sectional view along line B-B inFIG. 1.FIG. 4is a plan view of the sensor device shown inFIG. 1.FIG. 5is a side view showing a manufacturing method of the sensor device shown inFIG. 1.FIG. 6is a sectional view of a sensor element of the sensor device shown inFIG. 1.FIG. 7is a perspective view of the sensor element shown inFIG. 6.FIG. 8is a plan view of the sensor device shown inFIG. 1.FIG. 9is a circuit diagram of a first circuit of the sensor device shown inFIG. 1.FIG. 10is a circuit diagram of a second circuit of the sensor device shown inFIG. 1.FIG. 11is a sectional view along line C-C inFIG. 8.

Hereinafter, for convenience of explanation, three axes orthogonal to one another are referred to as “A-axis”, “B-axis, and “C-axis”, and the tip end sides of arrows showing the respective axes are referred to as “plus sides” and the tail end sides are referred to as “minus sides”. Further, directions parallel to the A-axis are referred to as “A-axis directions (first directions)”, directions parallel to the B-axis are referred to as “B-axis directions (second directions)”, and directions parallel to the C-axis are referred to as “C-axis directions (third directions)”. Furthermore, the plus side in the C-axis direction is also referred to as “upper” and the minus side in the C-axis direction is also referred to as “lower”. A view as seen from the C-axis direction (a plan view of a base member21) is also referred to as “plan view”.

The sensor device1shown inFIG. 1has a package2, a sensor element3housed in the package2, a first circuit4A, and a second circuit4B. The sensor device1is sandwiched from the C-axis directions and used with the sensor element3pressurized, for example, as a force detection apparatus100, which will be described later. External forces (a shear force in the A-axis direction and a shear force in the B-axis direction) applied to the sensor device1are transmitted to the sensor element3via the package2, and signals based on the applied external forces are output from the sensor element3and the output signals are processed in the first circuit4A and the second circuit4B.

Note that, in the embodiment, as the sensor element3, a configuration in which a first piezoelectric element31and a second piezoelectric element32, which will be described later, are stacked is exemplified, but the sensor element is not limited to that. A sensor device in which a first element and a second element that output electric charge according to the external forces are respectively independently placed may be employed.

In the plan view, the package2is in a nearly rectangular shape having the long axis along the A-axis directions and the short axis along the B-axis directions. The package2has the base member21and a lid member24joined to the base member21. An air-tight housing space S is formed inside of the package2, and the sensor element3, the first circuit4A, and the second circuit4B are respectively housed in the housing space S. The sensor element3, the first circuit4A, and the second circuit4B are housed in the package2, and thereby, these respective parts may be protected (dust-proof, water-proof) from the outside world. Particularly, the first circuit4A and the second circuit4B are protected from water (moisture), and thereby, deterioration and variations of the characteristics of the first circuit4A and the second circuit4B due to water may be suppressed.

The atmosphere of the housing space S is not particularly limited, but preferably in a vacuum state or a state nearly the vacuum state (reduced-pressure state). Specifically, the housing space S is preferably from 0.01 Pa to 1000 Pa. Thereby, the deterioration and variations of the characteristics of the first circuit4A and the second circuit4B may be effectively suppressed. Note that the housing space S may be not only in the vacuum state but also replaced by an inert gas such as nitrogen, argon, or helium.

As shown inFIGS. 2 and 3, the base member21has a base part22and a bottom member23. The base part22has a concave portion221opening in the upper surface, a concave portion222opening in the lower surface, and a through hole223penetrating the center parts of the bottom surfaces of the concave portions221,222. Further, the bottom member23has a plate shape and joined to the bottom surface of the concave portion222to close the lower opening of the through hole223. Accordingly, the through hole223and the bottom member23form a concave portion224opening in the center part of the bottom surface of the concave portion221. The sensor element3is placed to be inserted into the concave portion224, and a lower surface3bof the sensor element3is joined to the upper surface of the bottom member23via an adhesive29.

As shown inFIG. 2, the base part22has a concave portion225located on the minus side of the concave portion224in the A-axis direction and opening in the bottom surface of the concave portion221. A circuit element45A of the first circuit4A is placed in the concave portion225. Further, as shown inFIG. 3, the base part22has a concave portion226located on the plus side of the concave portion224in the A-axis direction and opening in the bottom surface of the concave portion221. A circuit element45B of the second circuit4B is placed in the concave portion226. As will be described later, the circuit elements45A,45B have larger heights (thicknesses) than the other circuit elements of the first, second circuits4A,4B. Accordingly, the concave portions225,226are formed in the base member21and the circuit elements45A,45B are placed therein, and thereby, the height of the package2may be made smaller.

As shown inFIG. 1, a wire46A of the first circuit4A and a wire46B of the second circuit4B are provided on the base part22. At least parts of the wires46A,46B are respectively placed on the bottom surface of the concave portion221. Further, as shown inFIGS. 2 and 3, a plurality of external terminals28exposed outside of the package2and electrically connected to the first circuit4A and the second circuit4B are provided on the lower surface of the base part22.

The constituent material of the base part22is preferably a material having an insulation property and e.g. various ceramics including oxide ceramics such as alumina or zirconia, carbide ceramics such as silicon carbide, nitride ceramics such as silicon nitride as a principal component. Thereby, the base part22having appropriate rigidity and a good insulation property is obtained. Accordingly, the package2is harder to be damaged due to deformation of the package2and the sensor element3, the first circuit4A, and the second circuit4B housed inside may be protected more reliably.

The constituent material of the bottom member23is not particularly limited to, but includes various metal materials e.g. stainless steel, kovar, copper, iron, carbon steel, titanium, etc. Of the materials, kovar is particularly preferable. Thereby, the bottom member23having higher rigidity and appropriately elastically deforming when stress is applied thereto is obtained. Accordingly, an external force may be properly transmitted via the bottom member23to the sensor element3and likelihood of breakage of the bottom member23by the external force may be reduced. Further, kovar has a coefficient of thermal expansion closer to the ceramics as the constituent material of the base part22, and thermal stress (distortion due to the difference in coefficient of thermal expansion between the base part22and the bottom member23) is harder to be generated in the base member21and output drift due to thermal stress may be effectively suppressed.

The lid member24has a plate shape and joined to the upper surface of the base part22to close the opening formed on the plus side of the concave portion221in the C-axis direction via a seal member20. As shown inFIGS. 2, 3, and 4, the lid member24has a center portion241, an outer edge portion242surrounding the center portion241and having a frame shape along the outer edge, and a coupling portion243located between the center portion241and the outer edge portion242and coupling these portions. The lid member24is joined to the upper surface of the base part22via the seal member20in the outer edge portion242. Further, the center portion241is located on the opposite side (the plus side in the C-axis direction) to the bottom member23with respect to the outer edge portion242, and the coupling portion243is inclined in a tapered shape to connect the outer edge portion242and the center portion241.

As described above, the lid member24is formed in a hat shape, and thereby, the height of the outer periphery part of the package2may be made smaller and the package2may be downsized by the amount of height decrease. The boundary parts between the center portion241, the coupling portion243, and the outer edge portion242are flexed, and thereby, stress applied to the lid member24may be relaxed and absorbed. Accordingly, separation of the lid member24may be suppressed. Particularly, as shown inFIG. 5, the lid member24is joined to the upper surface of the base part22using seam welding, and stress generated by pressing of a roller electrode RE to the outer edge portion242and thermal stress generated by heating of the lid member24by the roller electrode RE may be effectively relaxed and absorbed by the above described deformation. Therefore, breakage of the lid member24may be effectively suppressed, and further, the housing space S may be air-tightly sealed more reliably. Note that the shape of the lid member24is not particularly limited, but may be e.g. a flat plate shape or, inversely to the embodiment, the center portion241may be recessed.

The constituent material of the lid member24is not particularly limited to, but includes various metal materials e.g. stainless steel, kovar, copper, iron, carbon steel, titanium, etc. like the above described bottom member23. Of the materials, kovar is particularly preferable. Thereby, like the bottom member23, the external force may be transmitted more correctly by the sensor element3and breakage of the lid member24by the external force may be reduced. Note that the constituent material of the lid member24may be the same as or different from the constituent material of the bottom member23, but is preferably the same. Thereby, the external force applied to the package2may be transmitted more correctly by the sensor element3.

The sensor element3has a function of outputting electric charge Qa (first output signal) according to a component of the external force applied to the sensor element3in the A-axis direction and electric charge Qb (second output signal) according to a component of the external force applied to the sensor element3in the B-axis direction. As shown inFIG. 6, the sensor element3has the first piezoelectric element31that outputs the electric charge Qa according to the external force in the A-axis direction (shear force), the second piezoelectric element32that outputs the electric charge Qb according to the external force in the B-axis direction (shear force), and a pair of supporting boards33,34.

As shown inFIG. 6, the first piezoelectric element31has a configuration in which a first reference potential electrode311, a first piezoelectric material312, a first signal electrode313, a second piezoelectric material314, and a second reference potential electrode315are stacked sequentially from the downside (the minus side in the C-axis direction). That is, the first piezoelectric material312, the first signal electrode313, and the second piezoelectric material314are placed between the two reference potential electrodes311,315. Note that the first signal electrode313is an electrode for extraction of the signal of the first piezoelectric element31.

The second piezoelectric element32is stacked on the first piezoelectric element31, and has a configuration in which a third reference potential electrode321, a third piezoelectric material322, a second signal electrode323, a fourth piezoelectric material324, and a fourth reference potential electrode325are stacked sequentially from the downside (the minus side in the C-axis direction). That is, the third piezoelectric material322, the second signal electrode323, and the fourth piezoelectric material324are placed between the two reference potential electrodes321,325. Note that the second signal electrode323is an electrode for extraction of the signal of the second piezoelectric element32.

The sensor element3has a stacking structure in which the first piezoelectric element31and the second piezoelectric element32formed by stacking of the plurality of electrodes and the plurality of piezoelectric materials are stacked. Note that the order of the stacking of the first piezoelectric element31and the second piezoelectric element32in the C-axis direction may be opposite, or the first piezoelectric element31and the second piezoelectric element32may be placed side by side, not stacked.

The first piezoelectric material312, the second piezoelectric material314, the third piezoelectric material322, and the fourth piezoelectric material324are respectively formed using quartz crystal. Thereby, the sensor element3having good characteristics including higher sensitivity, wider dynamic range, and higher rigidity is obtained. In the first piezoelectric material312, the X-axis (electrical axis) as the crystal axis of the quartz crystal is directed toward the right side (the plus side in the A-axis direction) inFIG. 6and, in the second piezoelectric material314, the X-axis of the quartz crystal is directed toward the left side (the minus side in the A-axis direction) inFIG. 6. Accordingly, the second piezoelectric material314is polarized in the opposite direction to the polarization direction of the first piezoelectric material312. Further, in the third piezoelectric material322, the X-axis of the quartz crystal is directed toward the far side of the paper (the plus side in the B-axis direction) inFIG. 6and, in the fourth piezoelectric material324, the X-axis of the quartz crystal is directed toward the near side of the paper (the minus side in the B-axis direction) inFIG. 6. Accordingly, the fourth piezoelectric material324is polarized in the opposite direction to the polarization direction of the third piezoelectric material322. These respective piezoelectric materials312,314,322,324are formed using Y cut quartz crystal plates (quartz crystal plates having thicknesses along the Y-axis (mechanical axis) of quartz crystal).

Note that the piezoelectric materials312,314,322,324may have configurations using another piezoelectric material than quartz crystal. The other piezoelectric material than quartz crystal includes e.g. topaz, barium titanate, lead titanate, lead zirconate titanate (PZT: Pb (Zr,Ti)O3), lithium niobate, and lithium tantalate.

The reference potential electrodes311,315(321),325are respectively electrically connected to the ground potential GND. The first signal electrode313is electrically connected to the first circuit4A, and the second signal electrode323is electrically connected to the second circuit4B. The constituent materials of these reference potential electrodes311,315(321),325and signal electrodes313,323are not particularly limited to, but include e.g. nickel, gold, titanium, aluminum, copper, iron, chromium, or an alloy containing the metals. One of the materials may be used or two or more of the materials may be combined (stacked, for example) for use.

The pair of supporting boards33,34are placed to sandwich the stacking structures of the piezoelectric elements31,32from top and bottom. Specifically, the supporting board33is placed on an upper surface3aof the stacking structure of the piezoelectric elements31,32and the supporting board34is placed on the lower surface3b. Thereby, the reference potential electrodes311,325may be covered by the supporting boards33,34, and the reference potential electrodes311,325may be protected and unintended conduction because of contact between the reference potential electrodes311,325and the package2may be suppressed.

The supporting boards33,34are formed using quartz crystal. The supporting board33has the same configuration as the adjacent fourth piezoelectric material324. That is, the supporting board33is formed using a Y cut quartz crystal plate and the X-axis of the quartz crystal is directed toward the near side of the paper (the minus side in the B-axis direction) inFIG. 6like the fourth piezoelectric material324. Similarly, the supporting board34has the same configuration as the adjacent first piezoelectric material312. That is, the supporting board34is formed using a Y cut quartz crystal plate and the X-axis of the quartz crystal is directed toward the right side (the plus side in the A-axis direction) inFIG. 6like the first piezoelectric material312. As described above, the supporting board33has the same configuration as the adjacent fourth piezoelectric material324and the supporting board34has the same configuration as the adjacent first piezoelectric material312, and thereby, the coefficients of thermal expansion of these may be the same and output drift due to thermal expansion may be effectively reduced.

Note that the crystal axis of the supporting board33is not necessarily aligned with the crystal axis of the fourth piezoelectric material324, and the crystal axis of the supporting board34is not necessarily aligned with the crystal axis of the first piezoelectric material312. Or, the supporting boards33,34may be respectively formed using other piezoelectric materials than piezoelectric materials, or using other materials without conductivity than quartz crystal. Or, the supporting boards33,34may be omitted.

As shown inFIG. 7, the overall shape of the sensor element3is a rectangular parallelepiped shape. That is, the sensor element3has the upper surface3aas an upper surface of the supporting board33, the lower surface3bas a lower surface of the supporting board34, and four side surfaces3c,3d,3e,3fconnecting these upper surface3aand lower surface3b. Further, on the side surface3cfacing the minus side in the B-axis direction, a first reference potential side terminal391electrically connected to the respective reference potential electrodes311,315(321),325and a second signal side terminal392electrically connected to the second signal electrode323are provided apart in the width direction (A-axis direction). Note that, in the embodiment, the first reference potential side terminal391is located on the minus side in the A-axis direction and the second signal side terminal392is located on the plus side in the A-axis direction.

On the side surface3eopposed to the side surface3cand facing the plus side in the B-axis direction, a second reference potential side terminal393electrically connected to the respective reference potential electrodes311,315(321),325and a first signal side terminal394electrically connected to the first signal electrode313are provided apart in the width direction (A-axis direction). Note that, in the embodiment, the first signal side terminal394is located on the minus side in the A-axis direction and the second reference potential side terminal392is located on the plus side in the A-axis direction.

That is, as shown inFIG. 8, the first reference potential side terminal391is located between the first signal side terminal394and the second signal side terminal392on the side surfaces3c,3fon one side (the minus side in the A-axis direction) of a first axis L3passing through the position of the first signal side terminal394and the position of the second signal side terminal392in the plan view from the direction in which the piezoelectric elements31,32are stacked. Further, the second reference potential side terminal393is located between the first signal side terminal394and the second signal side terminal392on the side surfaces3d,3eon the other side (the plus side in the A-axis direction) of the first axis L3. Note that, inFIG. 8, the first axis L3passes through the center (geometrical center) O of the sensor element3in the plan view, however, does not necessarily pass through the center O as long as the axis passes through the position of the first signal side terminal394and the position of the second signal side terminal392.

As described above, the first reference potential side terminal391and the second reference potential side terminal393electrically connected to the ground potential GND are placed between the first signal side terminal394and the second signal side terminal392. Accordingly, the distance between the two signal side terminals392,394may be made wider, noise generated due to capacitive coupling and electromagnetic coupling between the signal side terminals392,394may be reduced, and deterioration of the electric charges Qa, Qb (output signals) output according to the external forces due to noise may be reduced.

The first signal side terminal394and the second signal side terminal392are placed point-symmetrically (rotationally symmetrically by 180°) with respect to the center (geometrical center) O of the sensor element3in the plan view, and the first reference potential side terminal391and the second reference potential side terminal393are placed point-symmetrically with respect to the center O of the sensor element3in the plan view. Note that the center O may be the geometrical center O of the sensor element3in the plan view in a wide sense and may be the geometrical center of the upper surface3ain a narrow sense.

As described above, the first signal side terminal394and the second signal side terminal392are placed point-symmetrically with respect to the center O of the sensor element3in the plan view, and the first reference potential side terminal391and the second reference potential side terminal393are placed point-symmetrically with respect to the center O of the sensor element3in the plan view. Accordingly, detection characteristics of the first piezoelectric element31and the second piezoelectric element32may be made nearly equal to each other, the electric charge Qa (first output signal) according to the external force in the A-axis direction (shear force) and the electric charge Qb (second output signal) according to the external force in the B-axis direction (shear force) may be extracted with balance, and the applied external forces may be detected with higher accuracy and output from the first signal side terminal394and the second signal side terminal392.

The respective side terminals391,392,393,394are provided on the side surfaces3c,3e, and thereby, the electrical connection between the sensor element3and the first circuit4A and the second circuit4B may be easily made.

The shape of the sensor element3is not particularly limited, but may be any shape including e.g. a circular shape, elliptical shape, triangular shape, quadrangular shape except square (rectangular shape, trapezoidal shape, parallelogram shape, or the like), polygonal shape with five or more vertexes, or odd shape.

As above, the sensor element3is explained. As shown inFIGS. 2 and 3, the lower surface3bof the sensor element3is joined to the bottom surface of the concave portion224(the upper surface of the bottom member23) of the package2via the insulating adhesive29. The adhesive29is not particularly limited, but e.g. acrylic resin, phenol resin, silicone resin, epoxy resin, or the like may be used.

Further, as shown inFIGS. 2 and 3, under natural conditions, the upper surface3aof the sensor element3is placed apart to face the center portion241of the lid member24. Thereby, application of unintended stress (other stress than that to be detected) to the sensor element3sandwiched between the bottom member23and the lid member24and production of output drift may be effectively suppressed. Note that the upper surface3aof the sensor element3is not limited to that, but may be in contact with the center portion241of the lid member24. Or, an adhesive (e.g. the same adhesive as the adhesive29) may be provided between the upper surface3aof the sensor element3and the center portion241of the lid member24, and the sensor element3and the lid member24may be joined via the adhesive.

As above, the sensor element3is explained. In the sensor element3, as described above, the first reference potential side terminal391is located between the first signal side terminal394and the second signal side terminal392on the side surfaces3c,3fon one side (the minus side in the A-axis direction) of the first axis L3passing through the position of the first signal side terminal394and the position of the second signal side terminal392in the plan view from the direction in which the piezoelectric elements31,32are stacked. Further, the second reference potential side terminal393is located between the first signal side terminal394and the second signal side terminal392on the side surfaces3d,3eon the other side (the plus side in the A-axis direction) of the first axis L3. Accordingly, the first reference potential side terminal391and the second reference potential side terminal393electrically connected to the ground potential GND are placed between the first signal side terminal394and the second signal side terminal392, and thereby, the distance between the two signal side terminals392,394may be made wider, noise generated due to capacitive coupling and electromagnetic coupling between the signal side terminals392,394may be reduced, and deterioration of the electric charges Qa, Qb (output signals) output according to the external forces due to noise may be reduced.

The first signal side terminal394and the second signal side terminal392are placed point-symmetrically (rotationally symmetrically by 180°) with respect to the center O of the sensor element3in the plan view, and the first reference potential side terminal391and the second reference potential side terminal393are placed point-symmetrically with respect to the center O of the sensor element3in the plan view. Accordingly, the detection characteristics of the first piezoelectric element31and the second piezoelectric element32may be made nearly equal to each other, the electric charge Qa (first output signal) according to the external force in the A-axis direction (shear force) and the electric charge Qb (second output signal) according to the external force in the B-axis direction (shear force) may be extracted with balance, and the applied external forces may be detected with higher accuracy and output from the first signal side terminal394and the second signal side terminal392.

In the first piezoelectric element31, the first piezoelectric material312, the first signal electrode313, and the second piezoelectric material314having the polarization direction opposite to the polarization direction of the first piezoelectric material312are placed between the first reference potential electrode311and the second reference potential electrode315. In the second piezoelectric element32, the third piezoelectric material322, the second signal electrode323, and the fourth piezoelectric material324having the polarization direction opposite to the polarization direction of the third piezoelectric material322are placed between the third reference potential electrode321and the fourth reference potential electrode325. Accordingly, the configurations of the first piezoelectric element31and the second piezoelectric element32may be simpler and the high-sensitivity sensor element3may be obtained.

Further, the first piezoelectric material312, the second piezoelectric material314, the third piezoelectric material322, and the fourth piezoelectric material324are respectively formed using quartz crystal. Thereby, the sensor element3having good characteristics including higher sensitivity, wider dynamic range, and higher rigidity may be obtained.

Next, the first circuit4A and the second circuit4B of the sensor device1will be explained.

The first circuit4A and the second circuit4B are respectively housed in the housing space S of the package2. As shown inFIG. 8, in the plan view of the base member21, the first circuit4A is located on one side (the minus side in the A-axis direction) with respect to the sensor element3and the second circuit4B is located on the other side (the plus side in the A-axis direction) with respect to the sensor element3. The first circuit4A is a circuit that processes the electric charge Qa output from the sensor element3and the second circuit4B is a circuit that processes the electric charge Qb output from the sensor element3. As described above, the first circuit4A and the second circuit4B are placed on the sides opposite to each other via the sensor element3, and thereby, the circuits may be placed as far away from each other as possible. Accordingly, interferences between the first circuit4A and the second circuit4B may be reduced, and noise from the second circuit4B superimposed on the electric charge Qa or noise from the first circuit4A superimposed on the electric charge Qb may be effectively suppressed. Thus, tolerance to noise may be improved, and the electric charge Qa may be accurately processed by the first circuit4A and the electric charge Qb may be accurately processed by the second circuit4B.

The first circuit4A is a circuit that converts the electric charge Qa into a voltage Va (charge/voltage conversion circuit) and, as shown inFIG. 9, has a resistor41A to which the electric charge Qa is input, a capacitor43A (capacitor part) that changes the electric charge Qa, an operational amplifier42A (amplifier) that amplifies the voltage by the electric charge Qa, a switching element44A, and a wire46A.

Of these circuit elements, the resistor41A and the capacitor43A are respectively provided on the bottom surface of the concave portion221, and the operational amplifier42A and the switching element44A are integrated as a circuit element45A and provided on the bottom surface of the concave portion225. Further, regarding the resistor41A, the capacitor43A, and the circuit element45A as electronic components, the first signal side terminal394of the sensor element3and the resistor41A, the resistor41A and the capacitor43A, and the capacitor43A and the circuit element45A are respectively electrically connected via the wire46A. The wire46A is electrically connected to the first reference potential side terminal391and the first signal side terminal394of the sensor element3via conducting connecting members261,264(e.g. various kinds of metal paste including Ag paste, Cu paste, Au paste). Thereby, the circuit shown inFIG. 9is realized.

In the embodiment, the resistor41A and the capacitor43A are electrically connected to the wire46A by flip-chip implementation using a conducting bump such as a gold (Au) bump, and the circuit element45A is electrically connected to the wire46A via a bonding wire BW. Note that the method of electrically connecting the resistor41A, the capacitor43A, and the circuit element45A and the wire46is not particularly limited. Or, the operational amplifier42A and the switching element44A may be separately formed.

The second circuit4B is a circuit that converts the electric charge Qb into a voltage Vb (charge/voltage conversion circuit) and has the same configuration as the above described first circuit4A. That is, as shown inFIG. 10, the second circuit4B has a resistor41B to which the electric charge Qb is input, a capacitor43B (capacitor part) that charges the electric charge Qb, an operational amplifier42B (amplifier) that amplifies the voltage by the electric charge Qb, a switching element44B, and a wire46B.

Of these circuit elements, the resistor41B and the capacitor43B are respectively provided on the bottom surface of the concave portion221, and the operational amplifier42B and the switching element44B are integrated as a circuit element45B and provided on the bottom surface of the concave portion226. Further, regarding the resistor41B, the capacitor43B, and the circuit element45B as electronic components, the second signal side terminal392of the sensor element3and the resistor41B, the resistor41B and the capacitor43B, and the capacitor43B and the circuit element45B are respectively electrically connected via the wire46B. The wire46B is electrically connected to the second reference potential side terminal393and the second signal side terminal392of the sensor element3via conducting connecting members262,263(e.g. various kinds of metal paste including Ag paste, Cu paste, Au paste). Thereby, the circuit shown inFIG. 10is realized.

In the embodiment, the resistor41B and the capacitor43B are electrically connected to the wire46B by flip-chip implementation using a conducting bump such as a gold (Au) bump, and the circuit element45B is electrically connected to the wire46B via a bonding wire BW. Note that the method of electrically connecting the resistor41B, the capacitor43B, and the circuit element45B and the wire46B is not particularly limited. Or, the operational amplifier42B and the switching element44B may be separately formed.

Here, as shown inFIG. 11, the wire46A electrically connecting the first signal side terminal394and the resistor41A of the first circuit4A is placed apart from a connecting portion26provided on the base part22. That is, the wire is placed at a distance of a length G from a side wall27of the connecting portion26, and the length G is equal to or larger than 0.1 mm and preferably equal to or larger than 0.2 mm. Note that the connecting portion26includes two boards26A,26B in annular shapes without center parts, and the lid member24is joined thereto via the seal member20and the housing space S for housing the sensor element3is formed.

The wire46A electrically connecting the first signal side terminal394and the resistor41A of the first circuit4A is placed apart from a connecting portion26, and thereby, a leak current generated between the wire46A and the seal member20may be minimized and draft characteristics of the sensor device1may be improved.

The wire46B electrically connecting the second signal side terminal392and the resistor41B of the second circuit4B is placed apart from the connecting portion26like the wire46A, and thereby, a leak current generated between the wire46B and the seal member20may be minimized and the draft characteristics of the sensor device1may be improved.

The wires46A,46B electrically connecting between the electronic components contained in the respective first circuit4A and the second circuit4B are placed apart from the connecting portion26. That is, the wire46A electrically connecting the resistor41A and the capacitor43A and the wire46B electrically connecting the resistor41B and the capacitor43B are placed apart from the connecting portion26.

As described above, the wires46A,46B are placed apart from the connecting portion26, and thereby, the leak currents generated between the wires46A,46B and the seal member20provided on the connecting portion26may be minimized and the draft characteristics of the sensor device1may be improved.

In the first circuit4A, the circuit element45A is thicker than the other electronic components, i.e., the resistor41A and the capacitor43A. Accordingly, in the embodiment, the concave portion225is formed on the bottom surface of the concave portion221and the circuit element45A is provided on the bottom surface of the concave portion225. Thereby, the height of the circuit element45A may be suppressed, and thus, increase of the height of the package2may be suppressed and the placement space of the bonding wire BW may be easily secured on the circuit element45A.

Similarly, in the second circuit4B, the circuit element45B is thicker than the other electronic components, i.e., the resistor41B and the capacitor43B. Accordingly, in the embodiment, the concave portion226is formed on the bottom surface of the concave portion221and the circuit element45B is provided on the bottom surface of the concave portion226. Thereby, the height of the circuit element45B may be suppressed, and thus, the increase of the height of the package2may be suppressed and the placement space of the bonding wire BW may be easily secured on the circuit element45B. Note that the concave portions225,226may be omitted and the circuit elements45A,45B may be placed on the bottom surface of the concave portion221.

Further, as shown inFIG. 4, in the first circuit4A, in the plan view, all of the resistor41A, the capacitor43A, and the circuit element45A are placed to overlap with the center portion241of the lid member24. As described above, the center portion241of the lid member24is offset toward upside of the other portion (outer edge portion242). Accordingly, contact between the resistor41A, the capacitor43A, and the circuit element45A and the lid member24may be suppressed and breakage and malfunction of the first circuit4A may be suppressed.

Similarly, in the second circuit4B, in the plan view, all of the resistor41B, the capacitor43B, and the circuit element45B are placed to overlap with the center portion241of the lid member24. Accordingly, contact between the resistor41B, the capacitor43B, and the circuit element45B and the lid member24may be suppressed and breakage and malfunction of the second circuit4B may be suppressed. Note that the placement is not limited to that, but at least one of the resistors41A,41B, the capacitors43A,43B, and the circuit elements45A,45B may be placed in positions not to overlap with the center portion241in the plan view, for example.

The first circuit4A and the second circuit4B are housed in the package2, and thereby, the first circuit4A and the second circuit4B may be protected and dust-proofness and water-proofness may be improved. Particularly, the first circuit4A and the second circuit4B are protected from water (moisture), and thereby, deterioration of the characteristics of these circuits may be effectively suppressed. For example, the capacitors43A,43B are parts that charge the electric charges Qa, Qb from the sensor element3and easily affected by the leak current depending on humidity. Further, the offset voltages on the input sides of the operational amplifiers42A,42B fluctuate due to humidity. As described above, the first circuit4A and the second circuit4B contain the circuit elements easily affected by water (humidity). Accordingly, these first circuit4A and second circuit4B are housed in the package2to be waterproof, and thereby, deterioration and variations of the circuit characteristics may be effectively suppressed and the electric charges Qa, Qb may be converted into the voltages Va, Vb with higher accuracy. Therefore, according to the sensor device1, the applied external forces may be detected with higher accuracy.

The first circuit4A and the second circuit4B are housed in the package2, and thereby, for example, compared to the case where the first circuit4A and the second circuit4B are placed outside of the package2, the wire lengths of the wires46A,46B may be made shorter. Accordingly, tolerance to noise of the first circuit4A and the second circuit4B is improved.

The first circuit4A and the second circuit4B are symmetrically placed with respect to the sensor element3in the plan view. Specifically, in the embodiment, the first circuit4A and the second circuit4B are placed point-symmetrically (rotationally symmetrically by 180°) with respect to the center (geometrical center) O of the sensor element3. Thereby, the circuit characteristics (wire lengths, environmental influences, etc.), i.e., charge/voltage conversion characteristics of the first circuit4A and the second circuit4B may be made nearly equal to each other. Accordingly, the electric charge Qa (first output signal) according to the external force in the A-axis direction (shear force) and the electric charge Qb (second output signal) according to the external force in the B-axis direction (shear force) may be extracted with balance, and the applied external forces may be detected with higher accuracy.

Note that the point-symmetric placement of the first circuit4A and the second circuit4B with respect to the center O refers to point-symmetric placement of at least respective circuit elements (resistors41A,41B, capacitors43A,43B, and circuit elements45A,45B) with respect to the center O, and preferably refers to further point-symmetric placement of the wires46A,46B with respect to the center O. Further, the point-symmetric placement of the first circuit4A and the second circuit4B with respect to the center O includes e.g. errors that may be made in design or manufacture and is not necessarily limited to complete point-symmetric placement. In the plan view, the point-symmetric placement includes not only the case where the point of symmetry of the first circuit4A and the second circuit4B coincides with the center O but also the case where the point of symmetry is not at the center O in a range overlapping with the sensor element3.

The first circuit4A and the second circuit4B are placed point-symmetrically with respect to the center O, and accordingly, in the sensor element3, the first signal side terminal394to which the electric charge Qa is output is placed on the side surface3efacing the plus side in the B-axis direction, and the second signal side terminal392to which the electric charge Qb is output is placed on the side surface3efacing the minus side in the B-axis direction. Further, the connecting member264connecting the first circuit4A and the first signal side terminal394is placed on the plus side in the B-axis direction with respect to the sensor element3, and the connecting member262connecting the second circuit4B and the second signal side terminal392is placed on the minus side in the B-axis direction with respect to the sensor element3. According to the arrangement, the first circuit4A and the second circuit4B may be placed point-symmetrically with respect to the center O of the sensor element3by the simpler arrangement. Particularly, in the embodiment, the first signal side terminal394is placed toward the first circuit4A side (the minus side in the A-axis direction) of the side surface3e, and thereby, the length of the wire connecting the first signal side terminal394and the resistor41A may be made shorter. Similarly, the second signal side terminal392is placed toward the second circuit4B side (the plus side in the A-axis direction) of the side surface3c, and thereby, the length of the wire connecting the second signal side terminal392and the resistor41B may be made shorter.

As above, the sensor device1is explained. In the sensor device1, as described above, in the plan view of the base member21, the first circuit4A is located on one side (the minus side in the A-axis direction) with respect to the sensor element3and the second circuit4B is located on the other side (the plus side in the A-axis direction) with respect to the sensor element3. Accordingly, the first circuit4A and the second circuit4B are placed on the sides opposite to each other via the sensor element3, and thereby, the circuits may be placed as far away from each other as possible. Therefore, interferences between the first circuit4A and the second circuit4B may be reduced, and noise from the second circuit4B superimposed on the electric charge Qa (first output signal) or noise from the first circuit4A superimposed on the electric charge Qb (second output signal) may be effectively suppressed. Thus, tolerance to noise may be improved, and the electric charge Qa may be accurately processed by the first circuit4A and the electric charge Qb may be accurately processed by the second circuit4B. As a result, the sensor device1that may accurately detect the applied external forces may be obtained.

The first circuit4A and the second circuit4B are symmetrically placed with respect to the sensor element3in the plan view. Specifically, the first circuit4A and the second circuit4B are placed point-symmetrically (rotationally symmetrically by 180°) with respect to the center of the sensor element3. Thereby, the circuit characteristics (wire lengths, environmental influences, etc.), i.e., charge/voltage conversion characteristics of the first circuit4A and the second circuit4B may be made nearly equal to each other. Accordingly, the electric charge Qa according to the external force in the A-axis direction (shear force) and the electric charge Qb according to the external force in the B-axis direction (shear force) may be extracted with balance, and the applied external forces may be detected with higher accuracy.

The wire46A electrically connecting the first signal side terminal394and the resistor41A of the first circuit4A and the wire46B electrically connecting the second signal side terminal392and the resistor41B of the second circuit4B are placed apart from the connecting portion26, and thereby, the leak currents generated between the wires46A,46B and the seal member20may be minimized and the draft characteristics of the sensor device1may be improved.

The wires46A,46B electrically connecting between the electronic components contained in the respective first circuit4A and the second circuit4B are placed apart from the connecting portion26. That is, the wire46A electrically connecting the resistor41A and the capacitor43A and the wire46B electrically connecting the resistor41B and the capacitor43B are placed apart from the connecting portion26, and thereby, the leak currents generated between the wires46A,46B and the seal member20provided on the connecting portion26may be minimized and the draft characteristics of the sensor device1may be improved.

Second Embodiment

Next, a sensor device according to the second embodiment of the invention will be explained.

FIG. 12is a sectional view of a sensor element of the sensor device according to the second embodiment of the invention.

A sensor element30aof the sensor device according to the embodiment is the same as the sensor element3of the sensor device of the above described first embodiment mainly except that the configuration of the sensor element30ais different. In the following description, the sensor element30aof the sensor device of the second embodiment will be explained with focus on the differences from the above described first embodiment and the explanation of the same items will be omitted. Further, inFIG. 12, the same configurations as those of the above described first embodiment have the same signs.

As shown inFIG. 12, in the sensor element30aof the sensor device according to the embodiment, a first piezoelectric element31ahas two sets of the first piezoelectric material312, the second piezoelectric material314, and the first signal electrode313placed between the first piezoelectric material312and the second piezoelectric material314, and a second piezoelectric element32ahas two sets of the third piezoelectric material322, the fourth piezoelectric material324, and the second signal electrode323placed between the third piezoelectric material322and the fourth piezoelectric material324.

Specifically, the first piezoelectric element31ahas a configuration in which the first reference potential electrode311, the first piezoelectric material312, the first signal electrode313, the second piezoelectric material314, the second reference potential electrode315, a fifth piezoelectric material316, a third signal electrode317, a sixth piezoelectric material318, and a fifth reference potential electrode319are stacked sequentially from the downside (the minus side in the C-axis direction).

Further, the second piezoelectric element32ais stacked on the first piezoelectric element31aand has a configuration in which the third reference potential electrode321, the third piezoelectric material322, the second signal electrode323, the fourth piezoelectric material324, the fourth reference potential electrode325, a seventh piezoelectric material326, a fourth signal electrode327, an eighth piezoelectric material328, and a sixth reference potential electrode329are stacked sequentially from the downside (the minus side in the C-axis direction).

The first piezoelectric material312and the fifth piezoelectric material316have the same polarization direction and the second piezoelectric material314and the sixth piezoelectric material318have a polarization direction opposite to the first piezoelectric material312. Further, the third piezoelectric material322and the seventh piezoelectric material326have the same polarization direction and the fourth piezoelectric material324and the eighth piezoelectric material328have a polarization direction opposite to the third piezoelectric material322.

The reference potential electrodes311,315,319(321),325,329are respectively electrically connected to the ground potential GND via the first reference potential side terminal391and the second reference potential side terminal393. Further, the first signal electrode313and the third signal electrode317are respectively electrically connected to the first circuit4A via the first signal side terminal394, and the second signal electrode323and the fourth signal electrode327are respectively electrically connected to the second circuit4B via the second signal side terminal392.

According to the configuration, the configurations of the first piezoelectric element31aand the second piezoelectric element32amay be simpler and the sensor element30awith higher sensitivity may be obtained.

Note that, in the embodiment, two of the first piezoelectric elements31and two of the second piezoelectric elements32of the sensor element3of the sensor device of the first embodiment are respectively stacked, however, not limited to that. The respective three or more of the first piezoelectric elements31and the second piezoelectric elements32may be stacked. Thereby, the sensor element with even higher sensitivity may be obtained.

According to the above described second embodiment, the same advantages as those of the above described first embodiment may be offered.

Third Embodiment

Next, a sensor device according to the third embodiment of the invention will be explained.

FIG. 13is a sectional view of a sensor element of the sensor device according to the third embodiment of the invention.

A sensor element30bof the sensor device according to the embodiment is the same as the sensor element3of the sensor device of the above described first embodiment mainly except that the configuration of the sensor element30bis different. In the following description, the sensor element30bof the sensor device of the third embodiment will be explained with focus on the differences from the above described first embodiment and the explanation of the same items will be omitted. Further, inFIG. 13, the same configurations as those of the above described first embodiment have the same signs.

As shown inFIG. 13, in the sensor element30bof the sensor device according to the embodiment, an insulating board35is placed between a first piezoelectric element31band a second piezoelectric element32b.

In the first piezoelectric element31b, the first piezoelectric material312is placed between the first reference potential electrode311and the first signal electrode313, and the second piezoelectric material314is placed between the second reference potential electrode315and the first signal electrode313. In the second piezoelectric element32b, the third piezoelectric material322is placed between the third reference potential electrode321and the second signal electrode323, and the fourth piezoelectric material324is placed between the fourth reference potential electrode325and the second signal electrode323.

Further, the first reference potential side terminal391is electrically connected to the first reference potential electrode311and the second reference potential electrode315and electrically connected to a first ground potential GND, and the second reference potential side terminal393is electrically connected to the third reference potential electrode321and the fourth reference potential electrode325and electrically connected to a second ground potential GND. Accordingly, the first reference potential side terminal391and the third reference potential electrode321and the fourth reference potential electrode325are electrically insulated, and the second reference potential side terminal393and the first reference potential electrode311and the second reference potential electrode315are electrically insulated.

According to the configuration, the first reference potential side terminal391and the second reference potential side terminal393may be electrically insulated, and crosstalk to the electric charges Qa, Qb (output signals) output from the first signal side terminal394and the second signal side terminal392and the influence by capacitance coupling between the two signal side terminals may be reduced. Therefore, the sensor element30bwith higher sensitivity may be obtained.

According to the above described third embodiment, the same advantages as those of the above described first embodiment may be offered.

Fourth Embodiment

Next, a sensor device according to the fourth embodiment of the invention will be explained.

FIG. 14is a plan view of a sensor element of the sensor device according to the fourth embodiment of the invention.

A sensor element30cof the sensor device according to the embodiment is the same as the sensor element3of the sensor device of the above described first embodiment mainly except that the configuration of the sensor element30cis different. In the following description, the sensor element30cof the sensor device of the fourth embodiment will be explained with focus on the differences from the above described first embodiment and the explanation of the same items will be omitted. Further, inFIG. 14, the same configurations as those of the above described first embodiment have the same signs.

As shown inFIG. 14, in the sensor element30cof the sensor device according to the embodiment, a first signal side terminal394cis placed on the side surface3fand a second signal side terminal392cis placed on the side surface3d. Further, a first reference potential side terminal391cand a second reference potential side terminal393care placed on the side surfaces3c,3e, respectively, like the first embodiment.

According to the configuration, the first signal side terminal394cmay be placed closer to the first circuit4A, and the second signal side terminal392cmay be placed closer to the second circuit4B. Therefore, the length of the wire connecting the first signal side terminal394cand the resistor41A may be made even shorter. Similarly, the length of the wire connecting the second signal side terminal392cand the resistor41B may be made even shorter. In the wire (46A) connecting the first signal side terminal394cand the resistor41A and the wire (46B) connecting the second signal side terminal392cand the resistor41B may be made harder to be affected by noise.

Further, the first signal side terminal394cand the second signal side terminal392care placed in the direction in which the first circuit4A, the sensor element30c, and the second circuit4B are arranged (A-axis direction), and thereby, the distance between the sensor element30cand the connecting portion26forming the concave portion221of the package2may be made shorter in the direction in which the first reference potential side terminal391cand the second reference potential side terminal393care arranged (B-axis direction). Accordingly, the length of the package2in the B-axis direction may be made shorter, the package2may be downsized, and the sensor device may be downsized.

According to the above described fourth embodiment, the same advantages as those of the above described first embodiment may be offered.

Fifth Embodiment

Next, a sensor device according to the fifth embodiment of the invention will be explained.

FIG. 15is a plan view of a sensor element of the sensor device according to the fifth embodiment of the invention.

A sensor element30dof the sensor device according to the embodiment is the same as the sensor element3of the sensor device of the above described first embodiment mainly except that the configuration of the sensor element30dis different. In the following description, the sensor element30dof the sensor device of the fifth embodiment will be explained with focus on the differences from the above described first embodiment and the explanation of the same items will be omitted. Further, inFIG. 15, the same configurations as those of the above described first embodiment have the same signs.

As shown inFIG. 15, in the sensor element30dof the sensor device according to the embodiment, a third signal side terminal396and a third reference potential side terminal395are placed on the side surface3d, and the third reference potential side terminal395is placed between the second signal side terminal392and the third signal side terminal396.

The third signal side terminal396is electrically connected to a signal electrode of a third piezoelectric element provided within the sensor element30dand outputting electric charge Qc according to an external force (compression/tensile force) in the C-axis direction. Further, the third reference potential side terminal395is electrically connected to a reference potential electrode of the third piezoelectric element, electrically connected to the first reference potential side terminal391and the second reference potential side terminal393, and electrically connected to the ground potential GND.

Note that the first reference potential side terminal391, the second reference potential side terminal393, and the third signal side terminal396may be electrically insulated.

According to the configuration, regarding the external forces applied to the sensor element30d, the component in the C-axis direction may be detected in addition to the component in the A-axis direction and the component in the B-axis direction, and the sensor element30dhaving the detection axes in the three axis directions may be obtained.

According to the above described fifth embodiment, the same advantages as those of the above described first embodiment may be offered.

Sixth Embodiment

Next, a force detection apparatus according to the sixth embodiment of the invention will be explained.

FIG. 16is a perspective view of the force detection apparatus according to the sixth embodiment of the invention.FIG. 17is a longitudinal sectional view of the force detection apparatus shown inFIG. 16.FIG. 18is a cross sectional view of the force detection apparatus shown inFIG. 16.FIG. 19is a sectional view of a sensor device placed in the force detection apparatus.

Hereinafter, for convenience of explanation, three axes orthogonal to one another are referred to as “α-axis”, “β-axis, and “γ-axis”, and the tip end sides of arrows showing the respective axes are referred to as “plus sides” and the tail end sides are referred to as “minus sides”. Further, directions parallel to the α-axis are referred to as “α-axis directions”, directions parallel to the β-axis are referred to as “β-axis directions”, and directions parallel to the γ-axis are referred to as “γ-axis directions”. Furthermore, the plus side in the γ-axis direction is also referred to as “upper” and the minus side in the γ-axis direction is also referred to as “lower”. A view as seen from the γ-axis direction is referred to as “plan view”.

A force detection apparatus100shown inFIG. 16is a six-axis force sensor that can detect six axis components of an external force applied to the force detection apparatus100. The six axis components include translational force (shear force) components in the respective directions of the three axes orthogonal to one another (in the drawings, the α-axis, β-axis, and γ-axis) and rotational force (moment) components about the respective three axes.

The force detection apparatus100has a plurality (four in the embodiment) of the sensor devices1placed at equal intervals (90° intervals) around a center axis A1(γ-axis) thereof, and a case5housing the sensor devices1. In the force detection apparatus100, the respective sensor devices1output detection signals according to external forces applied to the respective sensor devices1and the detection signals are processed, and thereby, the six axis components of the external force applied to the force detection apparatus100are detected. As below, the respective parts of the force detection apparatus100will be explained.

As shown inFIG. 16, the case5has a first case member6, a second case member7placed apart from the first case member6, and a side wall part8provided in the outer peripheral parts of the first case member6and the second case member7.

As shown inFIG. 17, the first case member6has a top plate61(first base part) and four wall parts62(first pressurization parts) provided on the lower surface of the top plate61and placed at equal intervals (90° intervals) around the center axis A1. A through hole611along the center axis A1is formed in the center part of the top plate61. Further, as shown inFIG. 18, a plurality of through holes621into which pressurization bolts50, which will be described later, are inserted are formed in the respective wall parts62. Inner wall surfaces620(inner surfaces) of the respective wall parts62are flat surfaces perpendicular to the top plate61.

As shown inFIG. 17, the second case member7has a bottom plate71(second base part) and four wall parts72(second pressurization parts) provided on the upper surface of the bottom plate71and placed at equal intervals (90° intervals) around the center axis A1to face the above described four wall parts62. A through hole711along the center axis A1is formed in the center part of the bottom plate71. Further, the respective wall parts72have projecting portions73projecting toward the opposed wall parts62side, and top surfaces730of the projecting portions73are parallel to the inner wall surfaces620and face the inner wall surfaces620at predetermined distances (distances into which the sensor devices1can be inserted). As shown inFIG. 18, a plurality of female screw holes721with which the tip end portions of the pressurization bolts50are screwed together are formed in the respective wall parts72.

The side wall part8has a cylindrical shape and the upper end portion and the lower end portion thereof are fastened to the first case member6and the second case member7by e.g. screwing, fitting, or the like. Further, the four sensor devices1are housed in a space S1(the inner space of the force detection apparatus100) surrounded by the side wall part8, the top plate61of the first case member6, and the bottom plate71of the second case member7.

In the above described case5, an upper surface60of the first case member6functions as e.g. an attachment surface to be attached to an end effector170(attached member) of a robot1000, which will be described later, and a lower surface70of the second case member7functions as e.g. an attachment surface for arm to be attached to an arm1200of the robot1000to be described later.

The outer shape of the case5in the plan view is a circular shape, however, not limited to that. For example, any shape including a polygonal shape such as a triangular shape, quadrangular shape, or pentagonal shape, an elliptical shape, and an odd shape may be employed. In the embodiment, the respective wall parts62are formed by the top plate61and other members and fastened to the top plate61, however, may be integrally formed with the top plate61. Similarly, in the embodiment, the respective wall parts72are formed by the bottom plate71and other members and fastened to the bottom plate71, however, may be integrally formed with the bottom plate71.

The constituent materials of the first case member6, the second case member7, and the side wall part8are respectively not particularly limited, but e.g. metal materials such as aluminum and stainless steel, ceramics, or the like may be used. Note that the constituent materials of the first case member6, the second case member7, and the side wall part8may be the same as one another or not.

As shown inFIG. 18, in a plan view, the four sensor devices1are placed to be symmetric with respect to a line segment CL passing through the center axis A1and parallel to the β-axis. Further, as shown inFIG. 17, the respective sensor devices1are located between the top plate61and the bottom plate71. Furthermore, the respective sensor devices1are located between the wall parts62and the wall parts72(projecting portions73) and sandwiched by the wall parts62and the wall parts72(projecting portions73). Specifically, as shown inFIG. 19, the respective sensor devices1are placed between the wall parts62and the wall parts72with the base members21of the packages2facing the wall parts72sides and the lid members24facing the wall parts62sides. In addition, the bottom members23of the base members21are in contact with the top surfaces730of the projecting portions73and the center portions241of the lid members24are in contact with the inner wall surfaces620of the wall parts62.

As shown inFIG. 18, the pressurization bolts50couple the wall parts62and the wall parts72, and thereby, the first case member6and the second case member7are fastened. Further, the pressurization bolts50are fastened, and thereby, the sensor devices1(sensor elements3) located between the wall parts62and the wall parts72are pressurized. That is, under natural conditions, compression forces in directions shown by arrows P inFIG. 19are applied to the sensor elements3. In this manner, the sensor elements3are pressurized under natural conditions, and thereby, the six axis components of the external force applied to the force detection apparatus100may be accurately detected. Note that the fastening forces of the pressurization bolts50are appropriately adjusted, and thereby, the pressure applied to the sensor elements3may be adjusted.

A pair of the pressurization bolts50are provided for each sensor device1, and the pair of pressurization bolts50are located on both sides of the sensor device1. Note that the placement of the pressurization bolts50is not particularly limited. Further, the pressurization bolts50may be provided as necessary, but may be omitted if not necessary.

The force detection apparatus100has an external force detection circuit (not shown), and the external force detection circuit may detect (calculate) a translational force component Fα in the α-axis direction, a translational force component Fβ in the β-axis direction, a translational force component Fγ in the γ-axis direction, a rotational force component Mα about the α-axis, a rotational force component Mβ about the β-axis, and a rotational force component Mγ about the γ-axis based on the voltages Va, Vb output from the respective sensor devices1. The external force detection circuit may include e.g. an AD converter and an arithmetic circuit such as a CPU connected to the AD converter.

As above, the force detection apparatus100is explained. As described above, the force detection apparatus100includes the top plate61(first board), the bottom plate71(second board), and the sensor devices1(the sensor devices according to the invention) provided between the top plate61and the bottom plate71. According to the force detection apparatus100, the sensor devices1are provided, and thereby, the external force may be detected with higher accuracy.

Seventh Embodiment

Next, a robot according to the seventh embodiment of the invention will be explained.

FIG. 20is a perspective view of the robot according to the seventh embodiment of the invention.

A robot1000shown inFIG. 20may perform work of feeding, removing, carrying, assembly, etc. of objects including precision apparatuses and components forming the apparatuses. The robot1000is a single-arm robot, the so-called six-axis vertical articulated robot. The robot1000has a base1100, a robot arm1200rotatably coupled to the base1100, a force detection apparatus100, and an end effector1700.

The base1100is a part fixed to e.g. a floor, wall, ceiling, movable platform, or the like. The robot arm1200has an arm1210(first arm), an arm1220(second arm), an arm1230(third arm), an arm1240(fourth arm), an arm1250(fifth arm), and an arm1260(sixth arm). These arms1210to1260are sequentially coupled from the proximal end side toward the distal end side. The respective arms1210to1260are rotatable with respect to the adjacent arms or base1100.

The force detection apparatus100is connected to the distal end of the arm1260. The force detection apparatus100detects forces (including moment) applied to the end effector1700attached to the distal end of the force detection apparatus100. The end effector1700is a tool for work on an object as a work object of the robot1000and includes a hand having a function of gripping the object. Note that the end effector1700is not limited to the hand, but a tool for the details of work or the like of the robot1000e.g. a screwing tool for screwing, fitting tool for fitting, or the like may be used.

The robot1000has drive units (not shown) including motors that rotate one arm with respect to the other arm (or base1100). Further, the robot1000has angle sensors (not shown) that detect rotation angles of the rotation shafts of the motors.

As above, the robot1000is explained. As described above, the robot1000includes the base1100, the robot arm1200(arm) connected to the base1100, and the force detection apparatus100(the force detection apparatus according to the invention). According to the robot1000, the force detection apparatus100is provided and, for example, the external force detected by the force detection apparatus100is fed back to a control unit (not shown) having a function of controlling the robot1000, and thereby, work may be executed more precisely. Further, the robot1000may sense contact of the end effector1700with an obstacle or the like based on the external force detected by the force detection apparatus100. Accordingly, the robot1000may easily perform an obstacle avoidance action, object damage avoidance action, etc., and may execute work more safely.

Note that the force detection apparatus100may be provided between the adjacent arms (for example, between the arms1240,1250). Or, the robot1000may be another robot e.g. a scalar robot, dual-arm robot, or the like. Or, the number of arms of the robot1000is six in the embodiment, however, may be one to five, seven, or more.

As above, the sensor elements3,30a,30b,30c,30d, the sensor device1, the force detection apparatus100, and the robot1000according to the invention are explained based on the illustrated embodiments, however, the invention is not limited to those. The configurations of the respective parts may be replaced by arbitrary configurations having the same functions. Further, other arbitrary configurations may be added to the invention. Furthermore, the sensor elements3,30a,30b,30c,30d, the sensor device1, and the force detection apparatus100may be incorporated into another apparatus than the robot1000e.g. a vehicle such as an automobile.

As below, the details derived from the embodiments will be described. For example, the sensor elements3,30a,30b,30c,30dhave the following features.

The sensor element includes a stacking structure having surrounding side surfaces in which a plurality of reference potential electrodes, a first piezoelectric element, a first signal electrode placed in a position with the first piezoelectric element between at least one of the plurality of reference potential electrodes and itself and extracting a signal of the first piezoelectric element, a second piezoelectric element, a second signal electrode placed in a position with the second piezoelectric element between at least one of the plurality of reference potential electrodes and itself and extracting a signal of the second piezoelectric element are stacked, a first signal side terminal placed on the side surface and electrically connected to the first signal electrode, a second signal side terminal placed on the side surface and electrically connected to the second signal electrode, a first reference potential side terminal placed on the side surface and electrically connected to at least one of the reference potential electrodes, and a second reference potential side terminal placed on the side surface and electrically connected to at least one of the reference potential electrodes, wherein, in a plan view from a direction of the stacking, the first reference potential side terminal is located between the first signal side terminal and the second signal side terminal on the side surface on one side of a first axis passing through a position of the first signal side terminal and a position of the second signal side terminal, and the second reference potential side terminal is located between the first signal side terminal and the second signal side terminal on the side surface on the other side of the first axis.

Thereby, the first reference potential side terminal and the second reference potential side terminal as reference potentials are placed between the first signal side terminal and the second signal side terminal, and thus, the distance between the two signal side terminals may be made wider, noise generated due to capacitive coupling and electromagnetic coupling between the two signal side terminals may be reduced, and deterioration of electric charges Qa, Qb (output signals) output according to external forces due to noise may be reduced.

In the above described sensor element, it is preferable that the first signal side terminal and the second signal side terminal are placed point-symmetrically with respect to a geometrical center of the sensor element in the plan view, and the first reference potential side terminal and the second reference potential side terminal are placed point-symmetrically with respect to the geometrical center of the sensor element in the plan view.

Thereby, the first signal side terminal and the second signal side terminal are point-symmetrically placed and the first reference potential side terminal and the second reference potential side terminal are point-symmetrically placed, respectively, and thus, detection characteristics of the first piezoelectric element and the second piezoelectric element may be made nearly equal to each other. Further, the electric charge Qa (first output signal) according to the external force in the A-axis direction (shear force) and the electric charge Qb (second output signal) according to the external force in the B-axis direction (shear force) may be extracted with balance, and the applied external forces may be detected with higher accuracy and output from the first signal side terminal and the second signal side terminal.

In the above described sensor element, it is preferable that the first piezoelectric element has a first piezoelectric material and a second piezoelectric material having a polarization direction opposite to a polarization direction of the first piezoelectric material, the first signal electrode is placed between the first piezoelectric material and the second piezoelectric material, the first piezoelectric material, the first signal electrode, the second piezoelectric material are placed between two of the plurality of reference potential electrodes, and the second piezoelectric element has a third piezoelectric material and a fourth piezoelectric material having a polarization direction opposite to a polarization direction of the third piezoelectric material, the second signal electrode is placed between the third piezoelectric material and the fourth piezoelectric material, and the third piezoelectric material, the second signal electrode, and the fourth piezoelectric material are placed between two of the plurality of reference potential electrodes.

Thereby, the configurations of the first piezoelectric element and the second piezoelectric element are simpler, and the sensor element with high sensitivity may be obtained.

In the above described sensor element, it is preferable that the first piezoelectric element has a plurality of sets of the first piezoelectric material, the second piezoelectric material, and the first signal electrode placed between the first piezoelectric material and the second piezoelectric material, and the second piezoelectric element has a plurality of sets of the third piezoelectric material, the fourth piezoelectric material, and the second signal electrode placed between the third piezoelectric material and the fourth piezoelectric material.

Thereby, the sensor element with higher sensitivity may be obtained by the simple configuration of a combination of a plurality of the first piezoelectric elements and a plurality of the second piezoelectric elements.

In the above described sensor element, it is preferable that the plurality of reference potential electrodes include a first reference potential electrode, a second reference potential electrode, a third reference potential electrode, and a fourth reference potential electrode, the first piezoelectric material is placed between the first reference potential electrode and the first signal electrode, the second piezoelectric material is placed between the second reference potential electrode and the first signal electrode, the third piezoelectric material is placed between the third reference potential electrode and the second signal electrode, the fourth piezoelectric material is placed between the fourth reference potential electrode and the second signal electrode, the first reference potential side terminal is electrically connected to the first reference potential electrode and the second reference potential electrode, the second reference potential side terminal is electrically connected to the third reference potential electrode and the fourth reference potential electrode, the first reference potential side terminal and the third reference potential electrode and the fourth reference potential electrode are electrically insulated, and the second reference potential side terminal and the first reference potential electrode and the second reference potential electrode are electrically insulated.

Thereby, the first reference potential side terminal and the second reference potential side terminal may be electrically insulated, and crosstalk to the electric charges Qa, Qb (output signals) output from the first signal side terminal and the second signal side terminal and the influence by capacitance coupling between the two signal side terminals may be reduced. Therefore, the sensor element with higher sensitivity may be obtained.

In the above described sensor element, it is preferable that the first piezoelectric material, the second piezoelectric material, the third piezoelectric material, and the fourth piezoelectric material are quartz crystal.

Thereby, the configurations of the first piezoelectric element and the second piezoelectric element are simpler, and the sensor element having good properties including higher sensitivity, wider dynamic range, and higher rigidity may be obtained.

For example, the sensor device1has the following features.

The sensor device includes the above described sensor element, a base member in which the sensor element is placed, a lid member connected to the base member and forming a housing space for housing the sensor element with the base member, a first circuit containing an electronic component placed on the base member within the housing space and electrically connected to a first signal side terminal and a first reference potential side terminal, and a second circuit containing an electronic component placed on the base member within the housing space and electrically connected to a second signal side terminal and a second reference potential side terminal, wherein the first circuit is placed on one side of the sensor element and the second circuit is placed on the other side of the sensor element in a plan view of the base member.

Thereby, the first circuit and the second circuit may be placed apart with the sensor element in between. Accordingly, interferences between the first circuit and the second circuit may be reduced, and noise from the second circuit superimposed on a first signal or noise from the first circuit superimposed on a second signal may be effectively suppressed. Thus, the first signal may be accurately processed by the first circuit and the second signal may be accurately processed by the second circuit. As a result, the sensor device that may accurately detect the applied external force and exhibit good force detection characteristics may be obtained.

In the above described sensor device, it is preferable that, in the sensor element, the first signal side terminal and the second signal side terminal are placed point-symmetrically with respect to a geometrical center of the sensor element in the plan view, the first reference potential side terminal and the second reference potential side terminal are placed point-symmetrically with respect to the geometrical center, and the first circuit and the second circuit are placed point-symmetrically with respect to the geometrical center.

Thereby, the first circuit and the second circuit are placed point-symmetrically with respect to the sensor element, and the circuit characteristics (wire lengths, environmental influences, etc.), i.e., charge/voltage conversion characteristics of the first circuit and the second circuit may be made nearly equal to each other. Accordingly, the electric charge Qa according to the external force in the A-axis direction (shear force) and the electric charge Qb according to the external force in the B-axis direction (shear force) may be extracted with balance, and the applied external forces may be detected with higher accuracy.

In the above described sensor device, it is preferable that the lid member is connected to the base member having a connecting portion, a wire connecting the first signal side terminal and the electronic component of the first circuit is placed apart from the connecting portion, and a wire connecting the second signal side terminal and the electronic component of the second circuit is placed apart from the connecting portion.

Thereby, a leak current generated between the wire connecting the first signal side terminal and the electronic component of the first circuit and the wire connecting the second signal side terminal and the electronic component of the second circuit and a seal member provided in the connecting portion may be minimized and draft characteristics of the sensor device may be improved.

In the above described sensor device, it is preferable that the first circuit includes a plurality of the electronic components, the second circuit includes a plurality of the electronic components, and wires connecting between the electronic components contained in the respective first circuit and second circuit are placed apart from the connecting portion.

Thereby, a leak current generated between the wires connecting between the electronic components contained in the respective first circuit and second circuit and the seal member provided in the connecting portion may be minimized and draft characteristics of the sensor device may be improved.

For example, the force detection apparatus100has the following features.

The force detection apparatus includes a first board, a second board, and the above described sensor device placed between the first board and the second board.

According to the force detection apparatus, the above described sensor device is provided and the external forces may be detected with higher accuracy.

For example, the robot1000has the following features.

The robot includes a base, an arm connected to the base, and the above described force detection apparatus.

According to the robot, the above described force detection apparatus is provided and more precise work may be executed.

The entire disclosure of Japanese Patent Application No. 2018-061415, filed Mar. 28, 2018, is expressly incorporated by reference herein.