# Patent

## Title
Gyro module

## Abstract

A gyro module includes: two gyro element pieces outputting a signal, the signal being obtained by combining a signal of an angular velocity of a first detection axis and a signal of an angular velocity of a second detection axis; and an arithmetic circuit for performing an addition and a subtraction with respect to the signal outputted from the two gyro element pieces. The two gyro element pieces are a first gyro element piece and a second gyro element piece. The first and second gyro element pieces are arranged such that a detection sensitivity polarity of the first detection axis of the first gyro element piece is same as that of the second gyro element piece, and a detection sensitivity polarity of the second detection axis of the first gyro element piece and that of the second gyro element piece are inverted.

## Background
BACKGROUND
1. Technical Field
The present invention relates to a two-axis gyro module.
2. Related Art
Related art gyro sensors have been formed such that sensors including one detection axis each are combined so as to perform a multi-axis detection. For example, a multi-axial semiconductor sensor disclosed in JP-A-2003-28646 is formed such that three sensor blocks to which semiconductor sensors capable of performing one-axis detection (angular velocity sensors or acceleration sensors) are respectively attached are joined to each other and fixed. Further, a multi-axis detecting vibration gyro disclosed in JP-A-7-306047 includes a plurality of planar substrates provided with a vibration gyro and a signal processing circuit, and has a shape of a quadrangular prism or a rectangular column formed by standing the planar substrates with respect to one of the plurality of planar substrates so as to detect rotation angular velocities in multi-axial directions.
The above gyro sensor performing the multi-axial detection mounts a sensor element having a detection axis for one-axis, so that in a case of performing a two-axial detection, for example, one sensor element has to be stood perpendicular to the other sensor. In this case, the gyro sensor has an approximate L-shape from a lateral view, so that the gyro sensor can not be made low-profile and it produces a useless space in a module. Namely, in the gyro sensor performing the two-axis detection (Z-axis detection and Y-axis detection), the detection axis that the gyro sensor needs has to be matched with the detection axis of the sensor element. Therefore, the detection axis of the sensor element for the Z-axis detection needs to be perpendicular to the detection axis of the sensor element for the Y-axial detection. Thus the height of the gyro sensor depends on the width of a main surface of the sensor element that is stood. Therefore, even if a thin sensor element is used, the gyro sensor can not be sufficiently miniaturized.
Further, in the related art gyro sensors performing the multi-axial detection, one of sensor elements mounted thereon has been used for one-axis detection. Namely, each of the sensor elements detects an angular velocity at each detection axis. Therefore, in terms of an output of the gyro sensor, an output of one detection axis is an output of one sensor element. In addition, even if a signal outputted from the sensor element includes noise, the signal is used as it is in the following process. Therefore, if the signal level is increased, the noise is also increased. Further, if a filter and the like are provided so as to remove the noise, the circuit becomes large.
SUMMARY
An advantage of the present invention is to provide a gyro module that can detect angular velocities of two axes.
A gyro module according to an aspect of the invention, includes: two gyro element pieces outputting a signal that is obtained by combining a signal of an angular velocity of a first detection axis and a signal of an angular velocity of a second detection axis; and an arithmetic circuit for performing an addition and a subtraction with respect to the signal outputted from the two gyro element pieces. The two gyro element pieces are a first gyro element piece and a second gyro element piece. The first and second gyro element pieces are arranged such that a detection sensitivity polarity of the first detection axis of the first gyro element piece is same as that of the second gyro element piece, and a detection sensitivity polarity of the second detection axis of the first gyro element piece and that of the second gyro element piece are inverted.
Therefore, signals outputted from the gyro element pieces can be separated into angular velocity components around the first detection axis and angular velocity components around the second detection axis.
Since each of the two gyro element pieces includes two detecting axes, the first gyro element piece does not need to be stood to be disposed with respect to the second gyro element piece as related art. The gyro module employs the two gyro element pieces for separating the angular velocity components around the first and second axes. However, the module has such a structure that the first axes of the two gyro element pieces are matched and the second axes of them are inverted, so that main surfaces of the two gyro element pieces can face the same direction or the inverted directions. Thus, they do not need to be stood. Therefore, the gyro module can be made low-profile.
Further, the angular velocities of the first and second axes can be obtained such that the signals outputted from the two gyro element pieces are added up, being able to increase the signal level. Therefore, even if the signals outputted from the gyro element pieces include noise, the signals are added up to increase the signal level, being able to make the signal level larger than the noise. Therefore, a signal outputted from the gyro module includes small noise, having high accuracy.
In the gyro module according to the aspect, each of the gyro element pieces may include a base, two connecting arms extending in a symmetry direction from the base as a center, driving arms extending in the symmetry direction from the connecting arms as centers, and two detecting arms extending in an orthogonal direction to the connecting arms and in the symmetry direction from the base as the center; and the detecting arms may include a weight part.
Thus, the gyro element pieces are double T-shaped gyro sensors. The signals outputted from the double T-shaped gyro sensors can be separated into angular velocity components around the first detection axis and angular velocity components around the second detection axis, being able to obtain outputs of the first and the second axes.
In the gyro module of the aspect, each of the gyro element pieces may include a base, two connecting arms extending in a symmetry direction from the base as a center, driving arms extending in the symmetry direction from the connecting arms as centers, and two detecting arms extending in an orthogonal direction to the connecting arms and in the symmetry direction from the base as the center; and the detecting arms may include a weight part being wider than the detecting arms.
Thus, the gyro element pieces are double T-shaped gyro sensors. With the double T-shaped gyro sensors, sensitivity ratio between the first detection axis and the second detection axis becomes one to one. Therefore, an output of one detection axis can not be smaller than an output of the other detection axis, so that a gain and the like do not need to be changed depending on the outputs of the detection axes. Thus the signal process can be simplified.
At least one of the two gyro element pieces may be a double tuning fork vibration gyro sensor.
Therefore, a signal outputted from the double tuning fork vibration gyro sensor can be separated into angular velocity components around Y-axis and angular velocity components around Z-axis, being able to obtain outputs of these axes.
The gyro element pieces may be made of a crystal plate, and the first and the second detecting axes may be an optical axis and a mechanical axis of quartz crystal axes.
Therefore, signals outputted from the gyro element pieces can be separated into angular velocity components around the optical axis and angular velocity components around the mechanical axis, being able to obtain outputs of these axes.
The gyro module of the aspect, further includes: a comparison unit comparing a signal level of an adding result of the arithmetic circuit with a signal level of a subtracting result of the arithmetic circuit so as to measure time during which the signal levels are matched; and an alarm unit raising an alarm in response to a signal outputted from the comparison unit.
With this structure, even if the gyro element piece breaks down, the break down can be informed.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
FIG. 1 is a block diagram of a gyro module.
FIG. 2 is a schematic perspective view showing a gyro element piece.
FIG. 3 is a schematic bottom view illustrating a state that one gyro sensor element piece is turned around in a planar direction with respect to the other gyro sensor element piece.
FIG. 4 is a schematic perspective view illustrating a state that one gyro sensor element piece is turned over in an up and down direction with respect to the other gyro sensor element piece.
FIG. 5 is a schematic sectional view showing a two-axis gyro module structured with one package.
FIG. 6 is a schematic perspective view showing a gyro element.
FIG. 7 is a schematic planar view showing a double tuning fork vibration gyro sensor.



DESCRIPTION OF EXEMPLARY EMBODIMENTS
A gyro module according to an embodiment of the present invention will be now described. FIG. 1 is a block diagram of a gyro module. A two-axis gyro module 10 includes two gyro element pieces 30 having a first detection axis and a second detection axis. The two gyro element pieces 30 have the same detection sensitivity polarities with respect to angular velocities around respective first detection axes and have inverted detection sensitivity polarities with respect to the angular velocities around respective second detection axes.
To the gyro element pieces 30, an oscillation circuit which is not shown is coupled at an input side, and an arithmetic circuit 20 is coupled at an output side. The oscillation circuit vibrates a driving arm of the gyro element pieces 30. The arithmetic circuit 20 includes an addition circuit 22 and a subtraction circuit 24 that are coupled to the output side of each of the gyro element pieces 30. The addition circuit 22 adds up signals based on angular velocities that are detected by the respective gyro element pieces 30 to output a signal. The subtraction circuit 24 subtracts a signal based on the angular velocity that is detected by one of the gyro element pieces 30 from a signal based on the angular velocity that is detected by the other of the gyro element piece 30 so as to output a signal. The output of the addition circuit 22 is an output of the first detection axis (first detection axis output) and the output of the subtraction circuit 24 is an output of the second detection axis (second detection axis output).
To a poststage of the addition circuit 22 and the subtraction circuit 24, a comparison unit 26 is coupled. The comparison unit 26 compares an output value of the addition circuit 22 to an output value of the subtraction circuit 24. To a poststage of the comparison unit 26, an alarm unit 28 is coupled and raises an alarm based on an alarm transmitting signal received from the comparison unit 26.
Here, the circuit diagram of FIG. 1 briefly shows a coupling structure of the gyro element pieces and the arithmetic circuit. However, a concrete structure of a poststage circuit of each of the gyro element pieces 30 in the two-axis gyro module 10 is such that, for example, a charge amplifier circuit is provided to each detecting arm 40 (two charge amplifier circuits are provided to one gyro element piece 30). The charge amplifier circuit converts a detecting signal (electric charge) detected with a detecting electrode described later of the gyro element piece 30 into a voltage signal.
Further, the two-axis gyro module 10 includes a differential amplifier circuit for amplifying an output signal from the above two charge amplifier circuits; a synchronous detection circuit for synchronously detecting an output signal from the differential amplifier circuit and an output signal from the oscillator; and a low pass filter for removing a high frequency signal from an output of the synchronous detection circuit.
Further, the two-axis gyro module 10 includes a structure for supplying an output signal from the low pass filter to the addition circuit 22 and the subtraction circuit 24.
The gyro element pieces 30 are structured as follows. FIG. 2 is a schematic perspective view showing a gyro element piece. This gyro element piece 30 is so-called a double T-shaped gyro sensor. The gyro element piece 30 is made of a Z-cut crystal plate that is cut out at the XY plane composed of X-axis (electric axis) and Y-axis (mechanical axis) of the quartz crystal. A main surface of the crystal plate is a main surface of the gyro element piece 30. Z-axis (optical axis) is in an orthogonal direction of the XY plane.
The gyro element piece 30 includes a rectangle shaped base 32 within the XY plane. In the XY-plane, the base 32 is provided with connecting arms 34 extending in a direction parallel to X-axis from the center of respective edge sides parallel to Y-axis of the base 32. Namely, the base 32 is provided with the connecting arm 34 extending in a +X direction (X-axis arrow direction) and the connecting arm 34 extending in −X direction that is an inverse direction of the +X direction in an integrated manner. At the end part (end part in X-axis direction) or the intermediate part (intermediate part in X-axis direction) of the connecting arm 34, driving arms 36 extending in a direction parallel to Y-axis are provided, within the XY plane. Namely, at the end part or the intermediate part of each of the connecting arms 34, the driving arm 36 extending in +Y direction (Y-axis arrow direction) and the driving arm 36 extending in −Y direction are provided in an integrated manner with the connecting arm 34. The driving arm 36 extending in −Y direction is disposed symmetrically to the driving arm 36 extending in +Y direction with the connecting arm 34 as a center. At the end part of each driving arm 36, a weight part 38 having a rectangular shape and larger width in X-axis direction than the driving arm 36 is integrated with the driving arm 36.
The base 32 is provided with detecting arms 40 extending in a direction parallel to Y-axis from the center of edge sides thereof that are parallel to X-axis. Namely, the base 32 is provided with the detecting arm 40 extending in +Y direction and the detecting arm 40 extending in −Y direction in an integrated forming manner. At the end part of each detecting arm 40, a weight part 42 having a rectangular shape and larger width in X-axis direction than the detecting arm 40 is formed integral with the detecting arm 40. The width in X-axis direction of the weight part 42 provided to the end part of the detecting arm 40 is larger than that of the weight part 38 provided to the end part of the driving arm 36. If the width of the weight part 42 is indicated with D, and the width of the weight part 38 is indicated with d, a relation of a formula 5d<D<10d is satisfied. That is, the width D of the weight part 42 is set to be 5 to 10 times as large as the width d of the weight part 38. The width D of the weight part 42 provided to the end part of the detecting arm 40 is set as above so as to efficiently obtain torsional vibration of the detecting arm 40 in an angular velocity detection of Y-axis rotation system.
On both surfaces that are parallel to the XY plane of the driving arm 36 and the detecting arm 40, a groove 44 is provided at the center of the width in X-axis direction. A metal film for a driving electrode or a detecting electrode is provided in a whole inner surface of the groove 44. Thus an electric field can be efficiently generated between the driving electrode or the detecting electrode formed on a surface parallel to a ZY plane of the driving arm 36 or the detecting arm 40 and the electrode provided to the groove 44, being able to miniaturize the gyro element piece 30. Here, each driving arm 36 is provided with the driving electrode that is not shown and each detecting arm 40 is provided with the detecting electrode that is not shown. The driving electrode and the detecting electrode are coupled in one and one correspondence with a resonator element side mount electrode 48 (refer to FIG. 3, 4) provided to a back surface of the base 32. The resonator element side mount electrode 48 is a connecting point with an electrode of a package side when the gyro element piece 30 is housed in the package.
In the gyro element piece 30, if an electric signal (a driving signal) from the oscillator is supplied through the resonator element side mount electrode 48 to the driving electrode, the driving arms 36 bend and vibrate (perform bending vibration) symmetrically to each other. Namely, the driving arm 36 shown on the left side of FIG. 2 and the driving arm 36 shown on the right side of the figure vibrate line-symmetrically with respect to a line passing through the gravity center and being parallel to Y-axis. If an angular velocity around Z-axis is added during such driving vibration of the gyro element piece 30, the driving arms 36 are subject to the Coriolis force of Y-axis direction. Then the detecting arm 40 bends and vibrates (performs detecting vibration) in X-axis direction due to the effect of the Coriolis force, so that an electric signal is outputted from the resonator element side mount electrode 48 via the detecting electrode. In addition, if an angular velocity around Y-axis is added during the driving vibration of the gyro element piece 30, the detecting arm 40 performs torsional vibration (detecting vibration). This torsional vibration is a vibration mode obtained by combining the flexure vibration of the detecting arm 40 in X direction caused by the Coriolis force and the flexure vibration in Z direction. Then the electric signal is outputted from the detecting electrode due to the torsional vibration. Here, the Coriolic force is not generated in a case of rotation around X-axis, so that the electric signal is not outputted from the gyro element piece 30.
The gyro element piece 30 is structured as above, so that a ratio between sensitivity for detecting an angular velocity around Z-axis and that around Y-axis becomes one to one.
Here, the gyro element piece 30 can be manufactured by photolithography processing technique, being able to be miniaturized. In addition, the gyro element piece 30 can be miniaturized and the sensitivity can be improved also by providing the weight parts 38, 42 and the groove 44 to the driving arm 36 and the detecting arm 40.
In order to separate components of the respective detection axes from the output signal of the gyro element pieces 30, the two-axis gyro module 10 matches the sensitivity polarity of the first detection axis of one of the gyro element pieces 30 to that of the other of the gyro element pieces 30, and inverts the detection sensitivity polarities between the second detection axis of the one of the gyro element pieces 30 and that of the other of the gyro element pieces 30.
For the structure, it is only necessary to prepare two gyro element pieces 30 having same structure and dispose them such that the other of the gyro element piece 30 is rotated by 180 degrees around Z-axis with respect to the one of the gyro element pieces 30 (symmetric arrangement) as shown in FIG. 3. Namely, in the one of the gyro element pieces 30 shown in the left side of FIG. 3, the +Y-direction is toward the upper side of the figure, the +Z-direction is toward the front side orthogonal to the figure, and the +X-direction is toward the right side of the figure. On the other hand, the other of the gyro element pieces 30 shown in the right side of FIG. 3 is obtained by turning around by 180 degrees in the planar direction with respect to the one of the gyro element pieces 30, so that the +Y-direction is toward the lower side of the figure, the +Z-direction is toward the front side orthogonal to the figure, and the +X-direction is toward the left side of the figure. When the gyro element pieces 30 are disposed as above, the first detection axes become Z-axis, and the second detection axes become Y-axis.
Here, Z-axes of the gyro element pieces 30 may be matched completely, and may be matched approximately depending on detecting accuracy required for the two-axis gyro module 10. In the same manner, the direction of Y-axis of the one of the gyro element pieces 30 may be inverted by completely 180 degrees and may be inverted approximately depending on the detecting accuracy required for the two-axis gyro module 10.
If Z-axes are matched completely and Y-axes are inverted by completely 180 degrees, the two-axis gyro module 10 having high detecting accuracy is achieved.
FIG. 3 does not show the driving electrode and the detecting electrode coupled to the resonator element side mount electrode 48. FIG. 3 does not show the groove 44 provided to the driving arm 36 and the detecting arm 40, either.
Further, the gyro element pieces 30 also can be disposed as shown in FIG. 4 so as to match the detection sensitivity polarities of the first detection axes of the gyro element pieces 30 and invert the detection sensitivity polarities of the second detection axes. It is only necessary to prepare two gyro element pieces 30 having the same structure and turn over the other of the gyro element pieces 30 with respect to the one of the gyro element pieces 30 in an up and down direction. In the one of the gyro element pieces 30 shown in the upper side of FIG. 4, the +Y-direction is toward the lower right side of the figure, the +Z-direction is toward the lower side of the figure, and the +X-direction is toward the upper right side of the figure. On the other hand, the other of the gyro element pieces 30 shown in the lower side of FIG. 4 is obtained by turning over by 180 degrees in the up and down direction with respect to the one of the gyro element pieces 30, so that the +Y-direction is toward the lower right side of the figure, the +Z-direction is toward the upper side of the figure, and the +X-direction is toward the lower left side of the figure. When the gyro element pieces 30 are disposed as above, the first detection axes become Y-axis, and the second detection axes become Z-axis.
Here, Y-axes of the gyro element pieces 30 may be matched completely, and may be matched approximately depending on the detecting accuracy required for the two-axis gyro module 10. In the same manner, the directions of Z-axes of the gyro element pieces 30 may be inverted by completely 180 degrees and may be inverted approximately depending on detecting accuracy required for the two-axis gyro module 10.
If Y-axes are matched completely and Z-axes are inverted by completely 180 degrees, the two-axis gyro module 10 having high detecting accuracy is achieved.
FIG. 4 omits to show the driving electrode and the detecting electrode coupled to the resonator element side mount electrode 48. FIG. 4 omits to show the groove 44 provided to the driving arm 36 and the detecting arm 40, as well.
The two-axis gyro module 10 can be structured with one package. FIG. 5 is a schematic sectional view showing a two-axis gyro module structured with one package. The two-axis gyro module 10 includes a package base 62. The package base 62 is provided with concave parts 64 that open upward and downward. The concave parts 64 have the same structures, so that the structure of the concave part 64 open upward will be described as an example here. The concave part 64 has lateral a surface formed step-like. To a part corresponding to the upper surface of the step part 68, a package side mount electrode 66 for mounting the gyro element piece 30 is provided. The bottom surface of the concave part 64 open upward is an area for firmly fixing an integrated circuit (IC) chip 58. To such the concave part 64, a pattern (not shown) conducting the IC chip 58 and the package side mount electrode 66 is provided. Further, an external terminal 70 is provided on the back surface of the package base 62, and a pattern (not shown) conducting the external terminal 70 and the IC chip 58 is provided.
The gyro element piece 30 is disposed above an intermediate substrate 50. The intermediate substrate 50 is provided with a lead 52 (a lead electrode). The end part of the lead 52 is coupled with the resonator element side mount electrode 48 of the gyro element piece 30. The base end part of the lead 52 is laid out to the edge part of the intermediate substrate 50 so as to be coupled to the package side mount electrode 66.
The IC chip 58 is firmly fixed to the bottom surface of the convex part 64 and includes the oscillation circuit in the inside or on the surface thereof. The IC chip 58 is provided to each concave part 64. One of the IC chips 58 is provided with necessary circuits such as the arithmetic circuit 20 and the comparison unit 26 as well as the oscillating circuit. Here, the two IC chips 58 may be integrated into one. At a part corresponding to the upper surface of the step part 68 provided to the concave part 64 open upward, the intermediate substrate 50 coupled with the gyro element piece 30 is disposed. Thus the gyro element piece 30 conducts with the IC chip 58, and the IC chip 58 conducts with the external terminal 70. The gyro element pieces 30 are mounted on the package base 62 in a manner inverting each other in the up and down direction, so that the first detection axes become Y-axis and the second detection axes become Z-axis.
The concave parts 64 are provided with lids 72 at their openings so as to be sealed. Thus the gyro element pieces 30 are vacuum-sealed. As structured as above, the two-axis gyro module 10 can be structured with one package 60.
Here, two concave parts 64 may be vacuum-sealed individually in the vacuum-sealing process.
Also, the insides of the two concave parts 64 may be vacuumed in one vacuuming process.
In order to realize this process, a through-hole for communicating the concave part 64 on upper side with the concave part 64 on the lower side is simply formed within the package base 62 (at the bottom surface of the concave part 64 open upward, for example). Accordingly, after the opening of one concave part 64 is covered by the lid 72, the other concave part 64 is vacuum-processed before being sealed. Thus, gas inside the one concave part 64 is exhausted through the through-hole, being able to vacuum the insides of the two concave parts 64 in one vacuum-process.
As above, the vacuum-sealing process can be simplified.
In addition, in a case where the two IC chips 58 are integrated, the intermediate substrate 50 provided with one gyro element piece 30 can be mounted on the bottom surface of the concave part 64 open upward.
Namely, if there is only one IC chip 58, one concave part 64 simply houses only the gyro element piece 30, so that the package side mount electrode 66 to be coupled with the base end part of the lead 52 can be disposed at the bottom surface of the concave part 64.
Accordingly, the step part 68 is, unnecessary in the concave part 64, effectively making the two-axis gyro module 10 low-profile.
Further, the distance between the two gyro element pieces 30 in the Z-axis direction becomes shorter, making the difference (absolute value) between detecting results of angular velocities with respect to Y-axis rotation detected by the two gyro element pieces 30 small.
The two-axis gyro module 10 with one package can be structured also as follows. The gyro element pieces 30 are arranged opposed to each other on upper and lower sides (front and back surfaces) of the intermediate substrate 50 with the lead 52. In this case, it is only necessary to match the first detection axes of the gyro element pieces 30 disposed on the upper side and on the lower side of the intermediate substrate 50 and invert the second detection axes of the gyro element pieces 30. Then the intermediate substrate 50 mounting the two gyro element pieces 30, and the IC chips 58 are mounted on the package base having one concave part open upward (the package base includes the step part, provided with the package side mount electrode that is coupled to the base end part of the lead, in the inside thereof). Further, the lid is bonded on the upper surface of the package so as to vacuum-seal the gyro element pieces 30 and the like. With such structure, the two gyro element pieces 30 and the IC chips 58 can be housed in the package having one concave part.
With such the structure, the distance between the two gyro element pieces 30 in the Z-axis direction becomes shorter, making the difference (absolute value) between detecting results of angular velocities with respect to Y-axis rotation detected by the two gyro element pieces 30 small. In addition, the sealing process (connecting process) with the lid 72 is performed simply once, so that the two-axis gyro module 10 with high manufacturing efficiency can be obtained.
Wire-bonding may be applied for coupling the IC chips 58 with circuit lines on the package base 62, and also the IC chips 58 may be face-down bonded to the package base 62 by flip-chip bonding and the like.
In a case where the IC chips 58 are face-down bonded, a space corresponding to the height of a loop of wiring in the Z-axis direction is not required like a case of the wire-bonding, so that the height of the step part 68 can be made low.
Thus, the distance between the two gyro element pieces 30 in the Z-axis direction can be made shorter than in the case where the IC chips 58 are wire-bonded, being able to make the difference (absolute value) between detecting results of angular velocities with respect to Y-axis rotation detected by the two gyro element pieces 30 small.
Further, the two-axis gyro module 10 with one package may be structured such that two intermediate substrates 50 provided each with one gyro element piece 30 are disposed in the planar direction in a concave part provided singularly to the package base (an arrangement shown in FIG. 3), the IC chips 58 are also disposed there, and the lid is bonded on the upper surface of the package base.
Further, the two-axis gyro module 10 may have a structure in which the two gyro element pieces 30 are arranged side-by-side on one intermediate substrate 50 in the planar direction.
Furthermore, the two-axis gyro module 10 may be structured such that each of the gyro element pieces 30 is housed in one package and then the packages are combined. FIG. 6 is a schematic perspective view showing a gyro element. FIG. 6 omits to show the lid, the lead, the package side mount electrode, the external electrode, and the IC chip.
This gyro element 80 houses one gyro element piece 30 in one package 82 thereof. The gyro element piece 30 is fixed to the intermediate substrate 50 with the lead as is the case described with reference to FIG. 5. A package base 84 mounting the gyro element piece 30 has a concave part 86 open upward, and the package side mount electrode is provided in the concave part 86. On the back surface of the package base 84, the external terminal is provided. The IC chip is firmly bonded to the bottom surface of the concave part 86, and is conducted to the external terminal. Above the IC chip, the intermediate substrate 50 is disposed in a manner allowing the gyro element piece 30 to face upward. In this case, the lead provided to the intermediate substrate 50 is coupled to the package side mount electrode, so that the gyro element piece 30 is conducted with the IC chip. Then the lid is bonded to the upper surface of the package base 84 so as to vacuum-seal the gyro element piece 30. Thus, the gyro element 80 is obtained.
Then two gyro elements 80 shown in FIG. 6 are combined to be arranged so as to form the two-axis gyro module 10. The two gyro elements 80 are denoted as a first gyro element 80 and a second gyro element 80. For combining and arranging them, the first gyro element 80 is turned around in the planar direction with respect to the second gyro element 80. Consequently, the gyro element pieces 30 are arranged as shown in FIG. 3. Also, for combining and arranging them, the first gyro element 80 may be turned over in the up and down direction with respect to the second gyro element 80 and disposed. Consequently, the gyro element pieces 30 are arranged as shown in FIG. 4.
After the respective gyro elements 80 are disposed as above, the periphery of them is covered by resin mold material so as to form one package. In a case where the two-axis gyro module 10 is formed with two gyro elements 80 as above, it is only necessary to provide the arithmetic circuit 20, the comparison unit 26, and the like to one of the IC chips housed in the packages 82.
While the structure housing the IC chips 58 in the package 60 has been described above, the IC chips 58 may be mounted outside of the package 60.
In this case, especially in the structure that two gyro element pieces 30 are piled as shown in FIG. 5, the external terminal 70 is conducted with the detecting electrode and the two intermediate substrates 50 can be mounted at the bottom surface of the concave part open upward and the upper surface of the concave part open downward.
Therefore, the distance between the two gyro element pieces 30 in the Z-axis direction can be made shorter, being able to make the difference (absolute value) between detecting results of angular velocities with respect to Y-axis rotation detected by the two gyro element pieces 30 small.
An operation of such two-axis gyro module 10 is as follows. In the gyro element pieces 30, the electric signal is supplied from the oscillating circuit to the driving electrode so as to vibrate the driving arms 36. If the angular velocity around the first detection axis and the angular velocity around the second axis are added to each of the gyro element pieces 30, the detecting arms 40 provided to the respective gyro element pieces 30 vibrate. The vibration is converted into an electric signal to be outputted. The signal is inputted into the addition circuit 22 and the subtraction circuit 24. The addition circuit 22 adds up the signal inputted from the one of the gyro element pieces 30 and the signal inputted from the other of the gyro element pieces 30. The addition circuit 22 removes angular velocity components around axes of which the detecting sensitivity polarities are inverted (the second detection axes) and obtains angular velocity components around axes of which the detecting sensitivity polarities are matched (the first detection axes). The addition circuit 22 outputs a signal obtained by adding up the angular velocity components around the first axes in the respective gyro element pieces 30, so that the level of the output signal is twice as high as that of the inputted signal. The output of the addition circuit 22 is the first detection axis output of the two-axis gyro module 10.
On the other hand, the subtraction circuit 24 subtracts the signal inputted from the one of the gyro element pieces 30 from the signal inputted from the other of the gyro element pieces 30. The subtraction circuit 24 removes angular velocity components around axes of which the detecting sensitivity polarities are matched (the first detection axes) and obtains angular velocity components around axes of which the detecting sensitivity polarities are inverted (the second detection axes). The subtraction circuit 24 performs subtraction between the components of which the detection sensitivity polarities are inverted, so that the level of the outputted signal is twice as high as that of the inputted signal. The output of the subtraction circuit 24 is the second detection axis output of the two-axis gyro module 10.
In a case where the rotation axis of the two-axis gyro module 10 is an axis that is inclined in an angular direction of which the angle is formed with Z-axis within YZ plane in XYZ coordinate illustrated on the left side of FIG. 3, the angular velocity around Z-axis and the angular velocity around Y-axis are mixed to be generated in the two gyro element pieces 30.
Thus, a detection signal in which the detection signal component with respect to the angular velocity around Z-axis overlaps the detection signal component with respect to the angular velocity around Y-axis is outputted from the detecting electrode of the gyro element piece 30.
Here, in this case as well, the polarities are inverted between variation of the detection signal component of the one of the gyro element pieces 30 and variation of the detection signal component of the other of the gyro element pieces 30 with respect to variation of the angular velocity around Y-axis.
Therefore, if the detection signals of the two gyro element pieces 30 are added up at the addition circuit 22, the detection signal components with respect to the angular velocities around Z-axis of which the polarities are same are added up but the detection signal components with respect to the angular velocities around Y-axis of which the polarities are different are subject to subtraction as a consequence.
Accordingly, only the detecting result with respect to the angular velocity around Z-axis is obtained as the first detection axis output.
If the detection signals of the two gyro element pieces 30 are subject to subtraction at the subtraction circuit 24, the detection signal components with respect to the angular velocities around Z-axis of which the polarities are same are subject to subtraction but the detection signal components with respect to the angular velocities around Y-axis of which the polarities are different are added up as a consequence.
Accordingly, only the detecting result with respect to the angular velocity around Y-axis is obtained as the second detection axis output.
Thus, the two-axis gyro module 10 can separately detect the detection component of the angular velocities around Z-axis and the detection component of the angular velocities around Y-axis.
If the gyro element pieces 30 are arranged such that the one of the gyro element pieces 30 is turned upside down with respect to the other of the gyro element pieces 30, the first detection axes are Y-axis. In addition, if they are arranged such that the one of the gyro element pieces 30 is turned around in the planar direction with respect to the other of the gyro element pieces 30, the first detection axes are Z-axis.
In a case where only angular velocities around the first detection axes are added to the gyro element pieces 30, the addition circuit 22 adds up the outputted signals outputted from the respective gyro element pieces 30 to output a signal having a level twice as high as that of the inputted signal. On the other hand, in the subtraction circuit 24, if the signals outputted from the respective gyro element pieces 30 are subject to subtraction, the output becomes zero. In a case where angular velocities around the second detection axes are added to the respective gyro element pieces 30, the subtraction circuit 24 subtracts the signal outputted from the one of the gyro element pieces 30 from the signal outputted from the other of the gyro element pieces 30 to output a signal having a level twice as high as that of the inputted signal. On the other hand, in the addition circuit 22, if the signals are added up, the output becomes zero.
The comparison unit 26 inputs the signals outputted from the addition circuit 22 and the subtraction circuit 24 so as to compare whether the levels of the signals are same or not. When the levels of signals are same and the time during which the levels are kept to be same is longer than the predetermined time as a result of the comparison, the comparison unit 26 judges that at least one gyro element piece 30 has a trouble. Then the comparison unit 26 outputs an alarm transmitting signal to the alarm unit 28. The alarm unit 28 alarms in response to the alarm transmitting signal so as to inform that the gyro element piece 30 has a trouble. The alarm unit 28 may be provided to electronic equipment to which the two-axis gyro module 10 is to be mounted.
The two-axis gyro module 10 structured as above includes two gyro element pieces 30 having two detection axes each. In the module 10, the detection sensitivity polarities of the first detection axes of the respective gyro element pieces 30 are matched and the detection sensitivity polarities of the second detection axes are inverted. Therefore, components of the first detection axes and those of the second detection axes can be separated by performing an addition or a subtraction to the outputs of the gyro element pieces 30. Namely, the two-axis gyro module 10 can separate the components of the angular velocities around the first detection axes from the components of the angular velocities around the second detection axes to obtain the outputs of the first and second axes.
Further, if the two-axis gyro module 10 houses double T-shaped gyro element pieces 30 in a package, the module 10 can detect an angular velocity around the detection axis that is in an orthogonal direction to the main surface, even though the gyro element pieces 30 are arranged such that the main surfaces thereof are along the bottom surface of the package. Thus the two-axis gyro module 10 does not need to dispose the gyro element pieces 30 in a perpendicularly standing manner as related art, so that the module 10 can be made low-profile even in both cases where the two gyro element pieces 30 are arranged in a planar direction and in a piling direction. The two-axis gyro module 10 can detect two axes even though the main surfaces of the gyro element pieces 30 are arranged in a parallel manner, providing no useless space. Therefore, the thickness size of the gyro element pieces 30 can be reflected to the thickness size of the two-axis gyro module 10, being able to miniaturize the two-axis gyro module 10 as a result. If the gyro element pieces 30 are arranged side by side in a planar direction, the two-axis gyro module 10 can be made low-profile. If the gyro element pieces 30 are arranged adjacent in up and down direction, the planar size of the two-axis gyro module 10 can be made smaller.
Since the output of one detection axis is obtained by adding up two outputs of the two gyro element pieces 30, the two-axis gyro module 10 can increase the signal level twice as high as that in related art. Therefore, even if the signals outputted from the gyro element pieces 30 include noise, the level of the noise does not change but the signal level is increased in the arithmetic circuit 20. Thus the two-axis gyro module 10 can make the signal level higher than a noise, thereby being highly accurate. In addition, since the two-axis gyro module 10 does not need a filter and the like, the module 10 does not become large and fewer signal processes are required.
If the two-axis gyro module 10 has such structure that two gyro element pieces 30 are arranged in a planar direction in the concave part singularly provided to one package, the intermediate substrate 50 can be formed within the same plane, being able to improve the accuracy of the plane that mounts the gyro element pieces 30. Even if the surface to which the intermediate substrate 50 is provided inclines with respect to the horizontal direction, the inclining angles of the two gyro element pieces 30 are same, being able to simplify the process for adjusting the inclining angle.
Further, if the two-axis gyro module 10 is structured such that the two gyro element pieces 30 are housed in one package or such that two gyro elements 80 are joined to each other, they can be mounted such that the directions of the two gyro element pieces 30, that is, the directions of the first detection axes and the second detection axes are adjusted. Therefore, even a case where the two-axis gyro module 10 is mounted on a mounting board does not produce any shift between the first detection axes and shift between the second detection axes. On the other hand, in a case where the gyro elements each housing one gyro element piece are mounted individually to one package without being joined, problems that the gyro elements rotates in a planar direction, for example, sometimes happen while the gyro elements are disposed on the mounting substrate and fixed. In this case, it is difficult to adjust the direction of each detection axis, causing variation between the directions of respective detection axes. Therefore, the two-axis gyro module 10 can accurately detect the angular velocities of two axes.
Further, the two-axis gyro module 10 employs the double T-shaped gyro sensor described above as the gyro element piece 30, so that the detection sensitivity of Z-axis can be made equal to that of Y-axis. Thus the module 10 does not need an adjustment for equalizing the detection sensitivity of Z-axis and that of Y-axis, so that the module 10 only needs processes for adding and subtracting at the arithmetic circuit 20. On the other hand, a case where sensitivities of the first detection axis and the second detection axis are different needs a process for equalizing the sensitivities of the first and second detection axes. In this case, a process for equalizing the detection sensitivities is needed in addition to the processes of adding and subtracting at the arithmetic circuit 20, increasing the signal process.
While the structure that the double T-shaped gyro sensor is employed as the gyro element piece 30 is described in the above embodiment, it should be noted that the present invention is not limited to the embodiment. The gyro element piece 30 may be a double tuning fork vibration gyro sensor.
FIG. 7 is a schematic planar view showing a double tuning fork vibration gyro sensor. This double tuning fork vibration gyro sensor 90 is made of a Z-cut crystal plate that is cut out at XY-plane formed of X-axis and Y-axis. A main surface of the crystal plate is a main surface of the double tuning fork vibration gyro sensor 90. Z-axis is in an orthogonal direction of the XY plane.
The double tuning fork vibration gyro sensor 90 includes two resonating arms 92. At both end part of the resonating arms 92, double tuning fork supporting parts 94 are provided. To an opposite side to a side coupled with the resonating arm 92, a support fixing part 98 is coupled via a detecting part 96. The resonating arm 92 serves as a driving part and is provided with a driving electrode (not shown) on its surface. With an electric signal applied to this driving electrode, the resonating arms 92 perform a flexure vibration in which the resonating arms 92 come close to and away from each other. In addition, a detecting electrode (not shown) is provided to the surface of the detecting part 96. If an angular velocity is added, the double tuning fork vibration gyro sensor 90 is subject to the Coriolis force, generating the flexure vibration corresponding to the force. Since the detecting part 96 also vibrates in the flexure vibration, the vibration of the detecting part 96 is converted into an electric signal with the detecting electrode so as to be outputted. The double tuning fork vibration gyro sensor 90 structured as above can detect angular velocities around Y-axis and around Z-axis. Therefore, the two-axis gyro module 10 can employ the double tuning fork vibration gyro sensor 90 as the gyro element piece 30.
While the two-axis gyro module described above employs crystal for the gyro element piece 30 and the gyro element 80, the present invention is not limited to it. The gyro element piece may be made of other piezoelectric material other than crystal, and may be a micro electro mechanical system (MEMS) that is formed with fine processing technique for silicon.

## Claims

1. A gyro module, comprising:
two gyro element pieces outputting a signal, the signal being obtained by combining a signal of an angular velocity of a first detection axis and a signal of an angular velocity of a second detection axis; and
an arithmetic circuit for performing an addition and a subtraction with respect to the signal outputted from the two gyro element pieces, wherein the two gyro element pieces are a first gyro element piece and a second gyro element piece; and the first and second gyro element pieces are arranged such that a detection sensitivity polarity of the first detection axis of the first gyro element piece is same as that of the second gyro element piece, and a detection sensitivity polarity of the second detection axis of the first gyro element piece and that of the second gyro element piece are inverted, wherein
each of the gyro element pieces includes a base, two connecting arms extending in a symmetry direction from the base as a center, driving arms extending in the symmetry direction from the connecting arms as centers, and two detecting arms extending in an orthogonal direction to the connecting arms and in the symmetry direction from the base as the center; and the detecting arms include a weight part being wider than the width of the weight part of the driving arms such that the relationship between the width of the weight part of the driving arms and detecting arms satisfies the equation 5d≦D≦10d, where d corresponds to the width of the weight part of the driving arms and D corresponds to the width of the weight part of the detecting arms.

2. The gyro module according to claim 1, wherein at least one of the two gyro element pieces is a double tuning fork vibration gyro sensor.

3. The gyro module according to claim 1, wherein the gyro element pieces are made of a crystal plate, and the first and the second detection axes are an optical axis and a mechanical axis of quartz crystal axes.

4. The gyro module according to claim 1, further comprising:
a comparison unit comparing a signal level of an adding result of the arithmetic circuit with a signal level of a subtracting result of the arithmetic circuit so as to measure time during which the signal levels are matched; and
an alarm unit raising an alarm in response to a signal outputted from the comparison unit.