INERTIAL SENSOR

An inertial sensor includes a resonator, a mounting board, and an actuator. The resonator has a first drive mode and a second drive mode. The mounting board has a plurality of electrode portions arranged at a distance from each other and surrounding the resonator. The actuator is configured to vibrate in a z-axis direction. The z-axis direction is a direction orthogonal to a planar direction of the mounting board. The actuator is further configured to vibrate the resonator in the z-axis direction to cause a resonance mode.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority from Japanese Patent Application No. 2023-090967 filed on Jun. 1, 2023. The entire disclosure of the above application is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an inertial sensor.

BACKGROUND

In recent years, a system for autonomous driving of a vehicle has been developed. This type of system requires a highly accurate self-position estimation technique. For example, a self-position estimation system including GNSS and IMU has been developed for so-called level3autonomous driving. GNSS is abbreviation for Global Navigation Satellite System. IMU is abbreviation for Inertial Measurement Unit, and is, for example, a six-axis inertial sensor including a three-axis gyro sensor and a three-axis acceleration sensor. In the future, in order to realize a level4or higher autonomous driving, IMU with higher accuracy than the current one is required.

SUMMARY

The present disclosure provides an inertial sensor including a resonator, a mounting board, and an actuator. The resonator has a first drive mode and a second drive mode. The mounting board has a plurality of electrode portions arranged at a distance from each other and surrounding the resonator. The actuator is configured to vibrate in a z-axis direction. The z-axis direction is a direction orthogonal to a planar direction of the mounting board. The actuator is further configured to vibrate the resonator in the z-axis direction to cause a resonance mode.

DETAILED DESCRIPTION

Next, a relevant technology is described only for understanding the following embodiments. An inertial sensor according to the relevant technology includes a resonator as a vibrating body and a substrate on which a plurality of electrodes is formed. The electrodes are arranged apart from each other along a circumferential direction around the resonator and surround the resonator at a predetermined distance. The inertial sensor causes the resonator to resonate in a first vibration mode and a second vibration mode in a planar direction of the substrate by an electrostatic force from some of the electrodes, and detects an angle of rotation applied to the resonator based on a change in electrostatic capacitance between the resonator and the electrodes.

In order to operate this type of inertial sensor in a whole angle mode, it is necessary to perform control for making an amplitude of the resonator constant, control for making a quadrature error between a first drive axis and a second drive axis zero, control for feeding back a measured angle, and control for maintaining resonance. In the control in the whole angle mode, the angle detection accuracy may be reduced due to the influence of an error in obtaining the direction of the vibration standing wave, a time delay in calculation, a drift due to a drive gain difference between the first drive axis and the second drive axis, and the like.

An inertial sensor according to an aspect of the present disclosure includes a resonator, a mounting board, and an actuator. The resonator has a first drive mode and a second drive mode. The mounting board has a plurality of electrode portions arranged at a distance from each other and surrounding the resonator. The actuator is configured to vibrate in a z-axis direction. The z-axis direction is a direction orthogonal to a planar direction of the mounting board. The actuator is further configured to vibrate the resonator in the z-axis direction to cause a resonance mode.

According to this aspect, the inertial sensor includes the resonator having the first drive mode and the second drive mode, the mounting board having the plurality of electrode portions surrounding the resonator, and the actuator that excites the resonator in the z-axis direction. In this inertial sensor, the resonator is vibrated in the z-axis direction by the actuator vibrating in the z-axis direction orthogonal to the planar direction of the mounting board, not by an external force along the planar direction, that is, the xy plane direction, and a resonance mode is caused. Therefore, the inertial sensor has a configuration in which the actuator can apply vibration energy to the resonator without hindering a rotational direction of vibration when the resonator is driven, which is a direction along the xy plane. Therefore, the inertial sensor can restrict a decrease in the accuracy of angle detection during operation in a whole angle mode.

Embodiments of the present disclosure will be described below with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals for description.

First Embodiment

An inertial sensor1according to a first embodiment will be described with reference toFIGS.1to5.

InFIG.1, in order to facilitate understanding of the configuration of the inertial sensor1, outlines of first electrode portions53and electrode films531, which will be described later, located in another cross section are indicated by broken lines. InFIG.2, in order to facilitate understanding of the configuration of the inertial sensor1, a lower substrate4, an upper substrate5, and a resonator2, which will be described later, of the inertial sensor1are partially omitted, and a cross-sectional configuration of the resonator2is partially illustrated.

Hereinafter, for convenience of description, as shown inFIG.2, one direction of a planar direction of a mounting board3is referred to as an “x-axis direction”, a direction orthogonal to the x-axis direction on the same plane is referred to as a “y-axis direction”, and a normal direction with respect to an xy plane is referred to as a “z-axis direction”. A direction along the xy plane direction may be referred to as a “horizontal direction”. The x, y, and z-axis directions in the drawings other thanFIG.2correspond to the x, y, and z-axis directions inFIG.2, respectively. Further, in the present specification, “upper” or “upward” represents a direction along the z-axis direction in the view and represents a direction along the arrow, and “lower” or “downward” represents the opposite direction to the upper or upward. Furthermore, in the present description, a state in which the inertial sensor1, the resonator2, or the mounting board3is viewed from the upper side in the z-axis direction may be referred to as a “top view”.

A basic configuration of the inertial sensor1of the present embodiment will be described. For example, as shown inFIG.1, the inertial sensor1includes the resonator2, the mounting board3, an actuator6, a housing7, and a lid member8. The resonator2, the mounting board3, and the actuator6are accommodated in the housing7and covered with the lid member8. The inertial sensor1can detect an angular velocity applied to the inertial sensor1and a rotation angle based on a change in capacitance between a part of the resonator2capable of vibrating in a first drive mode and a second drive mode to be described later and the first electrode portions53of the mounting board3. In the present specification, a case where the inertial sensor1is configured as a whole angle mode gyro sensor will be described as a representative example. Note that the whole angle mode can also be referred to as an integral gyro, and may be hereinafter referred to as “WA”.

In the present embodiment, for example, as shown inFIG.3, the resonator2is a micro vibrator having a three-dimensional symmetric structure including a curved surface portion21and a connection portion22. The curved surface portion21has an outline defined by a three-dimensional curved surface having a hemispherical shape. In the present disclosure, the term “hemispherical shape” includes a substantially hemispherical shape. The connection portion22extends from a vertex of the substantially hemispherical shape formed by the curved surface portion21toward the center of the hemispherical shape. In the resonator2, the curved surface portion21has, for example, a bowl-shaped three-dimensional curved surface. The resonator2exhibits a Q factor of the vibration that is 105 or more.

In the resonator2of the present embodiment, for example, a base portion having the curved surface portion21and the connection portion22is formed of a reflow material made of glass with additive, metal glass, silicon, or the like. Examples of glass with additive include quartz glass and borosilicate glass. The base portion of the resonator2may be formed of a reflow material that is capable of forming the curved surface portion21having a three-dimensional curved surface and the connection portion22and is capable of vibrating in a wine-glass mode or an n=2 mode to be described later, and is not limited to the above-described material examples. The resonator2is a thin member and is formed, for example, by processing a thin base made of the material described above in a formation process described later, so that the curved surface portion21and the connection portion22are thin on the order of micrometers, such as in a range from 10 micrometers (μm) to 100 μm. A dimension of the resonator2in a direction along a thickness direction of the mounting board3, that is, a direction orthogonal to the planar direction of the mounting board3is referred to as a height. The resonator2has a bird bath shape in a millimeter-size. For example, the height of the resonator2is 2.5 mm, and an outer diameter of a rim211defined by a front surface2ais 5 mm.

When the resonator2is manufactured, for example, a quartz plate having a thickness of 100 μm or less is set in a mold (not shown) including a concave portion and a support portion that supports a part of the quartz plate at the center of the concave portion when the quartz plate is heated and softened, and the inside of the concave portion is vacuumed while the quartz plate is softened by heating means such as flame. Accordingly, the curved surface portion21is formed. For example, in this step, a portion of the quartz plate supported by the support portion of the mold (not shown) becomes the connection portion22having a bottomed cylindrical shape recessed with respect to the curved surface portion21, and a portion protruding outward from the concave portion remains without being processed, but is removed in a subsequent step. Then, for example, the concave portion of the mold (not shown) is returned to normal pressure, the quartz plate on which the curved surface portion21having the hemispherical shape is removed from the mold, and the quartz plate is sealed with a sealing material made of any curable resin material. Thereafter, for example, unnecessary portions of the quartz plate after processing the sealing material are removed by polishing and chemical mechanical polishing (CMP), and then the sealing material is completely removed by any method such as heating or a chemical solution, and the quartz plate is taken out. The base portion of the resonator2is manufactured by, for example, the manufacturing process as described above, but the present disclosure is not limited to this manufacturing method, and other methods may be adopted. For example, the base portion of the resonator2may be formed by removing an unnecessary portion outside the curved surface portion21by laser processing without sealing the quartz plate in which the curved surface portion21and the connection portion22are formed. Thereafter, the resonator2can be manufactured by forming a surface electrode23on the base portion of the resonator2by any film forming method.

An end of the curved surface portion21opposite to the connecting portion22is referred to as the rim211. The rim211has, for example, a substantially cylindrical shape. Here, the term “substantially cylindrical shape” includes not only a cylindrical shape in which the diameter from an upper end to a lower end of an outer surface and an inner surface of the rim211is the same, but also a cylindrical shape in which the diameter varies from the upper end to the lower end. In other words, the curved surface portion21has the rim211that is an annular portion having an annular curved shape. When the resonator2is mounted on the mounting board3with a surface having a larger outer diameter as the front surface2aand a surface opposite to the frost surface2aas a rear surface2b, the front surface2aof the rim211faces the first electrode portions53of the mounting board3at intervals therebetween. The resonator2is mounted such that the intervals between the rim211and the first electrode portions53are equal to each other. When the resonator2is mounted on the mounting board3, the curved surface portion21including the rim211is in a midair state without contacting other members. In the present embodiment, the resonator2has a structure in which the rim211in the midair state can vibrate in a wine glass mode when mounted on the mounting board3, and can also be referred to as a vibrator.

The connection portion22is a connection portion connected to another member such as the mounting board3, and is, for example, a bottomed cylindrical recessed portion. However, the connection portion22is not limited thereto, and may have a substantially columnar shape. When the connection portion22is a bottomed cylindrical recessed portion, a recessed bottom surface22aon the front surface2acan be, for example, a suction surface used for suction conveyance when the resonator2is mounted on the mounting board3. A surface of the connection portion22opposite to the recessed bottom surface22a, that is, a surface on the rear surface2bis a mounting surface22bfacing the mounting board3.

The surface electrode23is formed of, for example, but not limited to, a laminated film including an adhesion layer and a conductive payer. The adhesion layer is formed on the front surface2aand the rear surface2bis made of chromium or titanium. The conductive layer is formed on the adhesion layer and is made of any conductive material such as gold or platinum. The front surface electrode23is formed on the front surface2aand the back surface2bof the resonator2by any film forming method such as sputtering, vapor deposition, CVD, or ALD. CVD is an abbreviation for Chemical Vapor Deposition. ALD is an abbreviation for Atomic Layer Deposition. For example, the surface electrode23is formed on at least the mounting surface22band the front surface2aof the rim211, and these portions are electrically connected to each other. The surface electrode23may have a solid shape that covers the entire front and rear surfaces of the resonator2, or may have a pattern shape that is patterned by a photolithography etching method or the like and covers a part of the front and rear surfaces. In the resonator2, for example, a portion of the surface electrode23covering the mounting surface22bof the connection portion22is connected to the mounting board3via a bonding member52made of a conductive material.

As shown inFIG.1, for example, the mounting board3includes the lower substrate4and the upper substrate5, which are joined to each other. For example, the mounting board3is obtained by performing etching processing and wiring film formation on the lower substrate4made of borosilicate glass, which is an insulating material, then anodically bonding the upper substrate5made of silicon, which is a semiconductor material, to the lower substrate4, and performing patterning. The mounting board3includes, for example, a plurality of inner frame portions51, the plurality of first electrode portions53disposed apart from each other so as to surround the inner frame portions51, and a second electrode portion54disposed apart from the plurality of first electrode portions53and surrounding the first electrode portions53on the upper substrate5. In addition, the mounting board3includes, for example, an annular groove41surrounding the plurality of inner frame portions51while separating the inner frame portion51from the plurality of first electrode portions53, and a plurality of wires42straddling the inside and the outside of the groove41, for example, on the lower substrate4.

For example, as shown inFIG.2, the groove41is a groove provided between the inner frame portion51and the plurality of first electrode portions53, and is formed by wet etching. The groove41has a dimension corresponding to the outer diameter of the rim211of the resonator2, and is provided to prevent the rim211from coming into contact with the mounting board3when the resonator2is mounted on the mounting board3.

The wires42are made of, for example, a conductive material such as aluminum, are disposed to pass between the plurality of first electrode portions53, and are electrically independent of the plurality of first electrode portions53. For example, one end of each of the wires42is connected to the inner frame portion51and the other end is connected to the second electrode portion54while straddling the groove41in the lower substrate4, and the wires42electrically connect the inner frame portion51and the second electrode portion54. Thus, the mounting board3can apply a voltage to the surface electrode23of the resonator2via the second electrode portion54, the wires42, and the inner frame portion51.

The inner frame portion51is formed together with the plurality of first electrode portions53and the second electrode portion54, for example, by performing dry etching such as DRIE on the upper substrate5anodically bonded to the lower substrate4. DRIE is an abbreviation for Deep Reactive Ion Etching. The inner frame portion51has, for example, an annular shape in the top view, and is configured such that the connection portion22of the resonator2can be inserted into a region surrounded by the inner frame portion51. In other words, the inner frame portion51has a frame body shape surrounding a bonding region that is a region of the mounting board3located immediately below the mounting surface22bof the resonator2. For example, the resonator2is mounted on the mounting board3by disposing the bonding member52in a region of the mounting board3surrounded by the inner frame portion51, mounting the connection portion22of the resonator2on the bonding member52, and heating and solidifying the bonding member52.

The bonding member52is made of, for example, a conductive material such as sintered silver or gold-tin, and fixes the connection portion22of the resonator2to the mounting board3. The bonding member52fixes the resonator2to the mounting board3in a state of covering the mounting surface22bof the connection portion22and a part of a side surface of the connection portion22adjacent to the mounting surface22b. The bonding member52may be a conductive material that can be bonded to the resonator2and the surface electrode23, and a conductive material other than the above-described examples may be used.

The first electrode portions53are disposed apart from each other, and, for example, as shown inFIG.1, an electrode film531is formed on the upper surface of each of the first electrode portions53. For example, wires (not shown) are connected to the electrode films531, so that the first electrode portions53are electrically connected to an external circuit board (not shown) to enable control of the potential. For example, the first electrode portions53are disposed to be separated from each other at equal intervals so as to form one ring on the xy plane while surrounding the rim211of the resonator2when viewed from above. When the resonator2is mounted, the first electrode portions53are separated from the rim211of the resonator2by a predetermined distance, and form a capacitor with the resonator2. That is, the mounting board3can detect the capacitance between the mounting board3and the resonator2via the first electrode portions53. A part of the first electrode portions53is used as a detection electrode for detecting the capacitance. The first electrode portions53positioned in the direction corresponding to the first drive mode of the resonator2are used as first detection electrodes, and the first electrode portions53positioned in the direction corresponding to the second drive mode are used as second detection electrodes.

The second electrode portion54has, for example, one frame shape surrounding the inner frame portion51and the first electrode portions53disposed around the inner frame portion51in the top view. The second electrode portion54includes, for example, at least one electrode film541made of aluminum or the like on an upper surface, and a wire (not shown) is connected to the electrode film541. The second electrode portion54may be connected to the surface electrode23of the resonator2via at least the wires42, and may have a configuration capable of applying a voltage. The second electrode portion54may have a shape other than the frame shape, or a plurality of second electrode portions54may be disposed.

The actuator6is a driving device that vibrates the resonator2in the z-axis direction, and is, for example, a piezoelectric, electrostatic, or electromagnetic element that can vibrate in the z-axis direction. In the present embodiment, for example, the actuator6is separately manufactured by a known actuator manufacturing method as a body separated from the mounting board3, and is disposed on an inner bottom surface of the housing7. The actuator6is connected to, for example, a wire (not shown) provided in the housing7, and can vibrate in the z-axis direction by voltage application from an external power supply. The mounting board3is bonded to a surface of the actuator6opposite to a surface facing the housing7by an adhesive layer (not shown), and the actuator6vibrates the resonator2bonded to the mounting board3in the z-axis direction. The actuator6has, for example, substantially the same planar size as that of the mounting board3, and the mounting board3is bonded to the actuator6with the outlines thereof in the xy plane aligned with each other. However, the present disclosure is not limited thereto, and the actuator6may have a planar size larger than that of the mounting board3, and a part of the actuator6may protrude from the mounting board3.

Hereinafter, for convenience of description, a vibration mode in which the number of antinodes and the number of nodes in the vibration amplitude of the rim211are the same at n (n: an integer of 2 or more) in the top view when resonator2is vibrated in the planar direction is referred to as a “planar resonance mode”. In the planar resonance mode, the resonator2vibrates along the planar direction of the xy-axis direction and also vibrates in the z-axis direction. When the resonator2is vibrated in the z-axis direction, vibration in the xy plane direction is excited. The actuator6serves to vibrate the resonator2in the z-axis direction to excite vibration in the horizontal direction and generate a resonance mode corresponding to the planar resonance mode. Hereinafter, excitation of the resonator2in the z-axis direction by the actuator6is referred to as “z-axis excitation”, and a resonance mode corresponding to the planar resonance mode and generated in the resonator2by the z-axis excitation is referred to as “z-axis resonance mode”. Details of the z-axis resonance mode of the resonator2by the actuator6will be described later.

The housing7is, for example, a package member in which a base portion is made of an insulating material such as ceramic and at least the resonator2and the mounting board3are accommodated. The housing7has, for example, electrode pads, internal wires, and external terminals (not shown), and is connected to the first electrode portions53and the second electrode portion54of the mounting board3and the actuator6by wires or the like, and has a structure capable of electrically connecting these members to the external power supply.

The lid member8is a member that is attached to the housing7with an adhesive (not shown) and covers the opening portion of the housing space of the resonator2and the mounting board3in the housing7. The lid member8may be made of, for example, the same insulating material as that of the housing7, or may be made of an insulating material different from that of the housing7. In the present embodiment, the lid member8constitutes, together with the housing7, a package member that encloses the resonator2, the mounting board3, and the actuator6of the inertial sensor1.

The above is the basic configuration of the inertial sensor1.

Next, the z-axis excitation and a z-axis vibration mode of the resonator2by the actuator6will be described with reference toFIGS.4A to4F.

InFIGS.4A,4B,4D, and4E, for ease of viewing, only a part of the resonator2including the rim211is illustrated in a simplified manner, and the outline of the part in the z-axis vibration mode is indicated by any of a broken line, a one-dot chain line, and a two-dot chain line. InFIG.4D, in order to facilitate understanding of the first detection electrodes53A and the second detection electrodes53B which will be described later, the detection electrodes53A and53B are hatched although a cross section is not illustrated.

For example, the resonator2can be vibrated in the xy plane direction, that is, the horizontal direction by applying an electrostatic force from some of the first electrode portions53, and can be set to the planar resonance mode. However, in the inertial sensor1, during the whole angle operation, the resonator2is set to the z-axis resonance mode similar to the planar resonance mode by vibrating the actuator6in the z-axis direction instead of the external force along the horizontal direction such as the electrostatic force from the first electrode portions53.

Specifically, for example, as shown inFIG.4A, the resonator2is vibrated in the z-axis direction by the actuator6, and the curved surface portion21including the rim211is displaced in the vertical direction. At this time, for example, as shown inFIG.4B, assuming that the y-axis direction is vertical and the x-axis direction is horizontal, the rim211of the resonator2is in a vibration state in which displacement in the horizontal direction indicated by a two-dot chain line and displacement in the vertical direction indicated by a one-dot chain line are alternately repeated in association with the vertical displacement along the z-axis direction. That is, when the resonator2is vibrated in the z-axis direction by the actuator6, the vibration of the rim211in the horizontal direction is excited. The z-axis resonance mode of resonator2shown inFIG.4Bis a standing wave vibration pattern in which antinodes and nodes in the vibration amplitude of the rim211are the same at n=2 in the top view. Hereinafter, the z-axis resonance mode shown inFIG.4Bis referred to as “n=2 mode”.

For example, when the resonator2is excited in the z axis at a resonance frequency at which the planar resonance mode in which the antinodes and the nodes in the amplitude of the rim211are n=2 is generated, the resonator2is in a vibration state of the n=2 mode. In the standing wave vibration pattern of the n=2 mode, for example, as shown inFIG.4, in the top view, a first drive mode in a vibration direction indicated by a solid arrow and a second drive mode in a vibration direction indicated by a broken arrow occur in the resonator2. In the n=2 mode, the second drive mode occurs in a direction inclined by 45 degrees with respect to the direction of the first drive mode. In the n=2 mode, for example, as shown inFIG.4D, some of the first electrode portions53positioned in the direction of the first drive mode are set as the first detection electrodes53A, and some of the first electrode portions53positioned in the direction of the second drive mode are set as the second detection electrodes53B, so that the rotation angle during the whole angle operation can be detected.

Note that, in the resonator2, the z-axis resonance mode during the whole angle operation is not limited to n=2. For example, as shown inFIG.4E, the z-axis resonance mode may be a resonance mode in which antinodes and nodes in the amplitude of the rim211are n=3 in the top view, or may be a higher-order resonance mode. In the resonance mode of n=3, for example, as shown inFIG.4F, the second drive mode in the vibration direction indicated by the broken-line arrow occurs in a direction inclined by 30 degrees with respect to the direction of the first drive mode in the vibration direction indicated by the solid-line arrow.

In the whole angle operation, the inertial sensor1drives the actuator6to set the resonator2in the z-axis excitation mode, thereby generating the first drive mode and the second drive mode. At this time, in a state in which no rotation is applied to the inertial sensor1, the vibration directions in the first drive mode and the second drive mode remain linear and do not change, for example, as indicated by double-headed arrows inFIG.4C. On the other hand, when rotation is applied to the inertial sensor1in which the resonator2is in the z-axis excitation mode, the vibration direction of the resonator2rotates. At this time, in the inertial sensor1, the vibration amplitude, the quadrature error, the vibration direction, and the phase difference φ of the resonator2can be calculated from the detection signal according to the change in the capacitance between the resonator2and the detection electrodes53A and53B. In the inertial sensor1, for example, maintenance control of the resonance frequency in the z-axis excitation mode is performed based on the phase difference q detected by the control circuit10described below.

[Control Circuit for Whole Angle Operation]

Next, an example of the control circuit10used for processing in a whole angle operation mode in the inertial sensor1will be described with reference toFIG.5.

For example, as shown inFIG.5, the control circuit10includes a whole angle calculation unit (WACU)11that executes various calculations in the whole angle operation mode, a PLL12for maintaining the z-axis resonance mode of the resonator (RES)2, and a drive circuit (DRC)152that inputs a drive signal to the actuator6. Note that PLL is an abbreviation for Phase Locked Loop. The PLL12maintains a constant phase difference between the input signal to the actuator6and the output signal of the amplitude.

The control circuit10further includes, for example, an oscillator (OSC)153that controls an oscillation frequency based on a signal from the PLL12, PIDs131and132that correct a signal from the whole angle calculation unit11, and a modulation unit (MDU)14that modulates signals from the oscillator153and the PIDs131and132. PID is an abbreviation for Proportional Integral Differential. The PID131performs correction for making the vibration amplitude of the resonator2constant, and inputs the corrected signal to the modulation unit14. The PID132corrects the quadrature error in the z-axis resonance mode of the resonator2to zero, and inputs the corrected signal to the modulation unit14. The control circuit10further includes, for example, a DAC151that converts a digital signal output from the modulation unit14into an analog signal, and the drive circuit152inputs a drive signal to the actuator (ACT)6based on the analog signal input from the DAC151. DAC is an abbreviation for Digital to Analog Converter.

The control circuit10further includes, for example, detection circuits (DTC)161and162that detect electrostatic capacitances between the resonator2and some of the detection electrodes of the first electrode portions53, and ADCs171and172that convert analog signals from the detection circuits161and162into digital signals. The control circuit10further includes, for example, demodulation units (DMU)181and182that demodulate the digital signals from the ADCs171and172and the input signal from the oscillator153, and the detection signal from the resonator2is input to the whole angle calculation unit11via the demodulation units181and182. ADC is an abbreviation for Analog to Digital Converter.

The whole angle calculation unit11includes, for example, an energy calculation unit (ECU)111, a quadrature calculation unit (QCU)112, an angle calculation unit (ACU)113, and a phase calculation unit (PCU)114. The energy calculation unit111calculates the vibration amplitude of the resonator2. The quadrature calculation unit112performs calculation for making the quadrature error in the z-axis resonance mode of the resonator2zero. The angle calculation unit113calculates an angle θ of the rotation applied to the inertial sensor1during the whole angle operation. The phase calculation unit114calculates a phase of the signal input to the actuator6and a phase of the vibration amplitude of the resonator2. The whole angle calculation unit11outputs, for example, a signal corresponding to the calculation result of the energy calculation unit111to the PID131, a signal corresponding to the calculation result of the quadrature calculation unit112to the PID132, and a signal corresponding to the calculation result of the phase calculation unit114to the PLL12.

When the amplitude amount of the vibration of the resonator2is E and the quadrature error is Q, the amplitude amount E, the quadrature error Q, the rotation angle θ, and the phase difference q are calculated by, for example, the following Equations 1 to 4, respectively.

In Equations 1 to 4, xcand xsare respectively the amplitude of the in-phase component and the amplitude of the 90-degree phase component demodulated at an angular frequency ω of an oscillator by the demodulation unit181. In Equations 1 to 4, ycand ysare respectively the amplitude of the in-phase component and the amplitude of the 90-degree phase component demodulated at an angular frequency ω of an oscillator by the demodulation unit182.

The above is the basic configuration of the control circuit10of the inertial sensor1. The control circuit10is not limited to the example shown inFIG.5, and may be appropriately changed within a possible range. For example, in the above description, the PLL12is configured by a digital circuit block of the control circuit10, but may be configured by an analog circuit block connected to the resonator2. If the resonator2is configured to be excited in the vibration mode in which the resonator2vibrates in the first drive mode or the second drive mode, the inertial sensor1operates in principle. Therefore, the actuator6does not necessarily need to vibrate at the natural frequency of the resonator2.

Next, an inertial sensor100and a control circuit110of the inertial sensor100according to a comparative example will be described with reference toFIG.6andFIG.7. Here, differences from the inertial sensor1and the control circuit10of the inertial sensor1will be mainly described.

For example, as shown inFIG.6, the inertial sensor100of the comparative example does not include the actuator6, uses some of the first electrode portions53as drive electrodes, and applies an electrostatic force from the drive electrodes to the resonator2to set the planar resonance mode. That is, during operation, the inertial sensor100of the comparative example applies an external force to the resonator2from the xy plane direction, that is, the horizontal direction, and sets the resonator2to the planar resonance mode. However, in the inertial sensor100of the comparative example, when rotation is applied from the outside, two forces along the horizontal plane, that is, an external force caused by the rotation and an electrostatic force from some of the first electrode portions53serving as the drive electrodes are applied to the resonator2. Since the electrostatic force generated by the drive electrodes is along the same horizontal direction as the external force generated by the rotation, the electrostatic force also affects the rotation of the resonator2in the vibration direction. Therefore, in the inertial sensor100of the comparative example, when rotation is applied from the outside, in order to maintain the planar resonance mode, it is necessary to perform adjustment in consideration of displacement due to the rotation.

The control circuit110is used in the whole angle operation mode. For example, as shown inFIG.7, the control circuit110further includes an angle conversion calculation unit (ACCU)19to which signals from the PIDs131and132and a signal corresponding to the calculation result of the rotation angle θ by the angle calculation unit113are input. The angle conversion calculation unit19is used to feed back the rotation angle θ calculated by the angle calculation unit113to the angle of the vibration standing wave of the resonator2in the control for making the amplitude amount of the resonator2constant and the control for making the quadrature error zero. The angle conversion calculation unit19inputs signals to modulation units (MDU)141and142. The control circuit110further includes the modulation unit142, a DAC154, and a drive circuit (DRC)155in addition to the modulation unit141, the DAC151, and the drive circuit152in order to apply the electrostatic force from the drive electrodes to the resonator2from two or more different directions in the xy plane direction.

The inertial sensor100of the comparative example requires feedback of the rotation angle θ as described above, and the detection accuracy of the rotation angle decreases due to the influence of an error in obtaining the direction of the vibration standing wave, a time delay of calculation, a drift due to a drive gain difference between the first drive axis and the second drive axis, and the like. The first drive axis and the second drive axis are drive electrodes corresponding to the first drive mode and drive electrodes corresponding to the second drive mode of the resonator2, respectively.

In contrast, the inertial sensor1has a configuration in which the resonator2is set to the z-axis excitation mode by the z-axis excitation using the actuator6instead of the first electrode portions53. That is, in the inertial sensor1, even when a rotational force along the horizontal direction is applied from the outside and the vibration direction of the resonator2rotates, the influence of the actuator6vibrating in the z-axis direction on the rotation direction of the vibration is restricted. Furthermore, in the driving of the resonator2, since the control force by the z-axis excitation of the actuator6is directly input in the current vibration direction of the resonator2, the feedback of the rotation angle during the whole angle operation is not required. Therefore, in the inertial sensor1, the influence of the error in obtaining the direction of the vibration standing wave, the time delay in calculation, the drift due to the drive gain difference between the first drive axis and the second drive axis, and the like is reduced, and improvement in detection accuracy of the rotation angle is expected.

According to the present embodiment, the inertial sensor1can restrict a decrease in the accuracy of the angle detection during the whole angle mode operation.

Second Embodiment

An inertial sensor1according to a second embodiment will be described with reference toFIG.8.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that the arrangement of the actuator6is changed, for example, as shown inFIG.8. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, for example, as shown inFIG.8, the actuator6is disposed at a portion of the mounting board3located immediately below the connection portion22of the resonator2. For example, the actuator6is directly formed on the mounting board3by a process different from a process of forming the mounting board3, or is formed separately from the mounting board3and disposed on the mounting board3. In the present embodiment, the actuator6is connected to, for example, a wire (not shown) formed on the mounting board3, and vibrates in the z-axis direction when a drive voltage is applied from an external drive circuit to perform the z-axis excitation of the resonator2. The actuator6is disposed, for example, in a region of the mounting board3surrounded by the inner frame portion51, and is connected to the connection portion22of the resonator2by the bonding member52.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Third Embodiment

An inertial sensor1according to a third embodiment will be described with reference toFIG.9.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that the actuator6is configured as a part of the mounting board3, for example, as shown inFIG.9. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, the actuator6is a MEMS actuator formed integrally with the mounting board3. The MEMS is an abbreviation for Micro Electro Mechanical Systems. In the present embodiment, for example, the actuator6is formed on the upper substrate5by a semiconductor process, is connected to an external power supply by a wire (not shown) formed on the mounting board3, and vibrates in the z-axis direction. In the present embodiment, for example, as shown inFIG.9, the lower substrate4has a through hole43formed in a region located immediately below the actuator6, the through hole43allowing the outside of the mounting board3and the region immediately below the actuator6to communicate with each other. The actuator6is, for example, a diaphragm type parallel plate device formed integrally with the inner frame portion51in a region surrounded by the inner frame portion51, and is in a midair state not in direct contact with the lower substrate4. In the present embodiment, the resonator2is bonded to the actuator6by the bonding member52, and the actuator6vibrates in the z-axis direction to perform the z-axis excitation.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Fourth Embodiment

An inertial sensor1according to a fourth embodiment will be described with reference toFIG.10.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that, for example, as shown inFIG.10, the actuator6is formed on the mounting board3and the arrangement is changed. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, for example, as shown inFIG.10, the actuator6is formed outside the second electrode portion54in the mounting board3, and is integrated with the mounting board3. In the present embodiment, the actuator6is, for example, an electrostatic silicon actuator mainly made of silicon, and is formed by a semiconductor process. The actuator6has, for example, one symmetrical structure such as an annular shape centered on the resonator2in the top view, or a structure in which multiple actuators6are formed and arranged symmetrically centered on the resonator2.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Fifth Embodiment

An inertial sensor1according to a fifth embodiment will be described with reference toFIG.11.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that the actuator6is attached to a part of the package at a position not in contact with the resonator2and the mounting board3, for example, as shown inFIG.11. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, for example, as shown inFIG.11, the actuator6is disposed on an inner surface of the lid member8facing the opening portion of the housing7. The actuator6is attached to the inner surface of the lid member8by, for example, an adhesive layer (not shown), and is connected to a wire (not shown) or the like, so that a drive voltage from an external drive circuit can be applied to the actuator6. In the present embodiment, for example, the actuator6vibrates along the z-axis direction on the inner surface of the lid member8, and performs the z-axis excitation of the entire package and the resonator2. Alternatively, the actuator6may be configured to function as a drive electrode for applying an electrostatic force along the z-axis direction to the resonator2and perform the z-axis excitation of the resonator2.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Sixth Embodiment

An inertial sensor1according to a sixth embodiment will be described with reference toFIG.12.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that the actuator6is attached to an outer surface of the package, for example, as shown inFIG.12. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, for example, as shown inFIG.12, the actuator6is disposed on the outer surface corresponding to the bottom surface of the package. The actuator6is attached to, for example, the outer surface of the bottom surface of the housing7opposite to the inner surface on which the mounting board3is mounted by an adhesive layer (not shown). In the present embodiment, the actuator6is connected to, for example, a wire (not shown), and vibrates along the z-axis direction when a drive voltage is applied from an external drive circuit, thereby performing the z-axis excitation of the entire package and the resonator2. The actuator6is not limited to have the same planar size as the bottom surface of the housing7, and may have a planar size smaller than the bottom surface and be attached to a part of the bottom surface. The dimensions, arrangement, and the like of the actuator6can be appropriately changed.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Seventh Embodiment

An inertial sensor1according to a seventh embodiment will be described with reference toFIG.13.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that the actuator6is attached to the outer surface of the package, for example, as shown inFIG.13. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, for example, as shown inFIG.13, the actuator6is disposed on an outer surface corresponding to a side surface of the package. For example, the actuator6is attached to the surfaces of the housing7and the lid member8along the z-axis direction by an adhesive layer (not shown) so as to straddle these surfaces. In the present embodiment, the actuator6is connected to, for example, a wire (not shown), and vibrates along the z-axis direction when a drive voltage is applied from an external drive circuit. The actuator6vibrates in the z-axis direction on the side surface of the package to perform the z-axis excitation of the entire package and the resonator2.

It is not necessary that the actuator6has the same planar size as the side surface of the package including the housing7and the lid member8as long as the actuator6can perform the z-axis excitation of the resonator2. The actuator6may have a planar size smaller than the side surface. The dimensions, the arrangement, and the like of the actuator6can be appropriately changed.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Eighth Embodiment

An inertial sensor1according to an eighth embodiment will be described with reference toFIG.14.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that the actuator6is attached to the outer surface of the package, for example, as shown inFIG.14. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, for example, as shown inFIG.14, the actuator6is disposed on an outer surface of the lid member8of the package. The actuator6is bonded to the outer surface of the lid member8by an adhesive layer (not shown) or the like, and vibrates in the z-axis direction to perform the z-axis excitation of the entire package and hence the resonator2. In the present embodiment, the actuator6is connected to, for example, a wire (not shown), and a drive voltage is applied from an external drive circuit. It is not necessary that the planar size of the actuator6is the same as that of the lid member8as long as the actuator6can perform the z-axis excitation of the resonator2. The planar size of the actuator6may be smaller than that of the lid member8as in the fifth embodiment.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Ninth Embodiment

An inertial sensor1according to a ninth embodiment will be described with reference toFIGS.15to17.

InFIGS.16and17, similarly toFIG.4D, the trajectory of the outer portion of the resonator2facing the plurality of first electrode portions53in the first drive mode is indicated by a one-dot chain line, and the trajectory of the outer portion in the second drive mode is indicated by a two-dot chain line. In addition, inFIGS.16and17, similarly toFIG.4D, the directions corresponding to the first drive mode of the resonator2are indicated by solid arrows, and directions corresponding to the second drive mode of the resonator2are indicated by broken arrows. AlthoughFIGS.16and17do not show cross sections, for ease of understanding, detection electrodes53A and53B among the first electrode portions53are hatched. In addition, the resonator2is hatched inFIG.17for the same reason.

The inertial sensor1of the present embodiment is different from that of the first embodiment in that the resonator2has a two-dimensional symmetric structure, for example, as shown inFIG.15. The following describes the difference between the present embodiment and the first embodiment.

In the present embodiment, for example, as shown inFIGS.15and16, the resonator2has a disk-like plate shape, and a central portion of the resonator2is connected to the mounting board3. In the resonator2, a portion on an outer side in a radial direction with a portion connected to the mounting board3as an axis is positioned above the groove41, and a portion other than the connection portion is in the midair state. In the mounting board3of the present embodiment, the width of the groove41in the radial direction is larger than that of each of the above embodiments. In the resonator2, the portion in the midair state is vibrated by the z-axis excitation by the actuator6, and the vibration state of the first drive mode or the second drive mode shown inFIG.16is obtained. Among the first electrode portions53, some of the first electrode portions53located in the vibration direction of the resonator2in the first drive mode are the first detection electrodes53A, and some of the first electrode portions53located in the vibration direction of the resonator2in the second drive mode are the second detection electrodes53B.

For example, as shown inFIG.17, the resonator2may have an annular two-dimensional symmetric structure in the top view. In this case, the resonator2includes, for example, a support portion (not shown) that is connected to the annular portion and is thinner than the annular portion, the support portion extends to the outside or the inside of the annular portion in a midair state, and an end portion of the support portion is connected and fixed to the mounting board3. The annular portion of the resonator2is in the midair state in which the annular portion is spaced apart from the mounting board3, and enters the z-axis resonance mode by the z-axis excitation by the actuator6as indicated by the one-dot chain line and the two-dot chain line inFIG.17. At this time, among the first electrode portions53, the first detection electrodes53A are positioned on the vibration direction of the first drive mode of the annular portion of the resonator2, and the second detection electrodes53B are positioned on the vibration direction of the second drive mode. In the example shown inFIG.15, the actuator6has the same arrangement as that of the first embodiment. However, the arrangement of the actuator6is not limited to the example shown inFIG.15, and may have the same arrangement or configuration as that of any one of the second to eighth embodiments.

The present embodiment also provides the inertial sensor1that can achieve effects similar to those of the first embodiment.

Other Embodiments

Although the present disclosure has been made in accordance with the embodiments, it is understood that the present disclosure is not limited to such embodiments and structures. The present disclosure encompasses various modifications and variations within the scope of equivalents. In addition, various combinations and modes, and further, other combinations and modes including one element of these alone, or thereabove, or therebelow, are also comprised within the scope or concept range of the present disclosure.

A controller (for example, the control circuit10) and the method described in the present disclosure may be implemented by a special purpose computer which is configured with a memory and a processor programmed to execute one or more particular functions embodied in computer programs of the memory. Alternatively, the controller and the method described in the present disclosure may be implemented by a special purpose computer configured as a processor with one or more special purpose hardware logic circuits. Alternatively, the controller and the method described in the present disclosure may be implemented by one or more special purpose computer, which is configured as a combination of a processor and a memory, which are programmed to perform one or more functions, and a processor which is configured with one or more hardware logic circuits. The computer program may be stored, as instructions to be executed by a computer, in a tangible non-transitory computer-readable medium.

The constituent element(s) of each of the above embodiments is/are not necessarily essential unless it is specifically stated that the constituent element(s) is/are essential in the above embodiment, or unless the constituent element(s) is/are obviously essential in principle. A quantity, a value, an amount, a range, or the like referred to in the description of the embodiments described above is not necessarily limited to such a specific value, amount, range or the like unless it is specifically described as essential or understood as being essential in principle. Further, in each of the above embodiments, when the shape of an element or the positional relationship between elements is mentioned, the present disclosure is not limited to the specific shape or positional relationship unless otherwise particularly specified or unless the present disclosure is limited to the specific shape or positional relationship in principle.