JP2013108929A - Vibration type gyro with high accuracy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration type gyro including a structure capable of reducing a bias output by correcting a quadrature error.SOLUTION: In a vibration type gyro, a Y direction component can be electrically detected as a quadrature error because capacitance between a drive mass body 6 and a fixed electrode 24 varies when the Y direction component is included in drive vibration. Since an initial capacitance between the drive mass body 6 and the fixed electrode 24 is different from an initial capacitance between electrodes for angular velocity detection, and a magnitude of each quadrature error is also different from each other, an output signal from which a quadrature error is subtracted can be obtained by converting respective capacitance variations into voltages by a C-V conversion circuit, adjusting the voltages by a variable amplifier so as to make the amplitudes of the voltages equal, making respective phases equal, and outputting the difference.

Description

  The present invention relates to a vibration type gyro manufactured by MEMS technology or the like, and more particularly, to a vibration type gyro in which high accuracy is achieved by compensating for leakage output.

  By so-called micromachining technology developed rapidly since the 1990s, for example, a bulk silicon wafer bonded on a silicon substrate or glass substrate having an insulating film is processed by chemical etching such as wet etching or dry etching, and mechanical A technique has been established for forming a large number of sensor structures in a single process by forming a simple sensor structure. Sensors based on such micro electro mechanical system (MEMS) technology include acceleration sensors and vibration-type gyros, and are used in many fields such as automobiles, inertial navigation, digital cameras, game machines, and the like.

  In the capacitance detection type MEMS gyro, a driving force is applied from a fixed part to a movable part supported via a beam, and the movable part is vibrated in one direction parallel to the substrate surface. When the angular velocity is input here, the movable electrode for detecting the angular velocity included in the movable portion is displaced in the direction perpendicular to the driving direction by the Coriolis force, and the distance between the movable electrode and the fixed electrode provided on the substrate is the input acceleration. It changes depending on the size. The change in capacitance between the electrodes at this time is detected and used as a sensor output.

  As a structure of the capacitance detection type MEMS gyro, there is a structure in which a movable part is a so-called double gimbal type. In this configuration, a driving mass body for driving is supported from a fixed portion via an elastic beam, and a detection mass body and a movable electrode for detecting angular velocity are supported from the driving mass body via different beams. A feature of this structure is that the detection mass body vibrates with the same movement as the drive mass body.

  For example, Patent Document 1 discloses a rotational angular velocity sensor having a rectangular frame 3. Here, a vibrating mass body 1 is disposed in the frame 3, and the vibrating mass body 1 is interposed via four webs 4. The frame 3 is coupled to be displaceable in a certain direction.

JP 2007-101553 A

  The driving vibration of the driving mass is ideally perpendicular to the detection direction, and the movable electrode is not displaced in the detection direction unless there is an angular velocity input. However, due to the asymmetry of the structure that occurs in the manufacturing process and the driving force including some components in the detection direction, the movable electrode is displaced in the detection direction, and the capacitance change is output despite no angular velocity input. May end up. This is called a quadrature error (leakage output), which generates a bias output that is an output when no angular velocity is input, leading to instability of the gyro.

  Therefore, an object of the present invention is to provide a vibrating gyroscope having a structure capable of correcting the quadrature error and reducing the bias output.

  In order to achieve the above object, the first invention of the present application is supported by the fixing portion via the fixing portion provided on the support substrate and the first support beam, and is driven to vibrate in the X direction in the plane. A driving mass body configured to be supported by the driving mass body via a second support beam and configured to be able to vibrate in the Y direction within the plane and perpendicular to the X direction; A movable electrode for detecting angular velocity provided on the detection mass body, and a fixed electrode for detection provided on the support substrate so as to be opposed to the movable electrode, both in the X direction and in the Y direction. In a vibrating gyroscope in which the detection mass body is displaced in the Y direction by a Coriolis force generated by an angular velocity around an orthogonal Z-direction axis, the drive mass body is arranged at a certain interval with respect to the drive mass body. The capacitance between When the monitor fixed electrode is configured to be changed only by the displacement of the mass body in the Y direction, and the drive vibration of the drive mass body includes a Y direction component, the drive mass body and the monitor Provided is a vibration type gyro that outputs a change in capacitance generated between a fixed electrode and a fixed electrode as a monitor signal.

  According to a second invention, in the first invention, a capacitance between the drive mass body and the fixed electrode for monitoring, and a static electricity between the movable electrode and the fixed electrode for detection of the detection mass body. The monitor fixed electrode is arranged so that the capacitance is the same and the sign of the capacitance change with respect to the change in the Y direction is reversed, and the monitor fixed electrode and the detection fixed electrode are electrically connected. Provide a vibrating gyroscope.

  According to a third invention, in the first invention, the driving mass body is arranged at a certain distance from the driving mass body, has a capacitance between the driving mass body, and is applied with a voltage. A vibrating gyroscope further comprising a detection direction drive electrode configured to generate an electrostatic force and displace the drive mass body in the Y direction by the electrostatic force.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the vibration gyroscopes are arranged in two pairs, and the two sets of drive mass bodies have vibration modes that vibrate in opposite phases to each other in the X direction. A vibrating gyroscope connected to each other by a connecting beam having elasticity is provided.

  According to a fifth invention, in the first or fourth invention, a change in capacitance between the drive mass body and the fixed electrode for monitoring, the movable electrode of the detection mass body, and the fixed electrode for detection The change in capacitance between the two voltages is converted into a voltage using a CV conversion circuit, and the two voltages are converted using a variable amplifier so that the amplitudes of the two converted voltages match. A vibrating gyroscope is provided that is configured to output a difference between two voltages having adjusted amplitudes by adjusting one or both of them in phase.

  According to the present invention, a detected displacement (quadrature error) due to drive vibration generated in a vibration type gyro can be detected also in a drive mass body. In the present invention, since the driving mass body and the detection mass body move in the same manner due to the driving vibration, the quadrature error can be separated from the sensor output by using the error signal detected in the driving mass body, and unnecessary bias output. To improve stability.

1 is a plan view showing a vibrating gyroscope according to a first embodiment of the present invention. It is sectional drawing which follows the II-II line of the gyro of FIG. It is sectional drawing which follows the III-III line of the gyro of FIG. It is a top view which shows the vibration-type gyro which concerns on the 2nd Embodiment of this invention. It is a top view which shows the vibration-type gyro which concerns on the 3rd Embodiment of this invention. It is a top view which shows the vibrating gyroscope which concerns on the 4th and 5th embodiment of this invention.

  FIG. 1 is a plan view showing a basic structure of a vibrating MEMS gyroscope 1 according to the first embodiment of the present invention. FIGS. 2 and 3 are respectively taken along lines II-II and III-III in FIG. It is sectional drawing which shows the cut surface along. Basically, this MEMS gyro vibrates a movable part supported by a substrate in a plane parallel to the substrate, and when an angular velocity about an axis perpendicular to the substrate surface is input, the Coriolis that acts in the horizontal plane of the substrate. The displacement due to force is detected.

  As can be seen from FIGS. 2 and 3, the present embodiment is formed by performing micromachining on a bonded substrate obtained by anodically bonding a single crystal silicon substrate 100 and a support substrate 102 such as glass as an insulating material by a micromachining technique. Is done. A cavity is processed in advance in a part of the support substrate 102, and the silicon substrate 100 is not bonded to the support substrate 102 in the processed portion, and is a structure having a degree of freedom with respect to the support substrate 102.

  As shown in FIG. 1, the first support beams 4 (four in the illustrated example) are attached to the fixing portions 2 (four in the illustrated example) corresponding to the portion where the support substrate 102 and the silicon substrate 100 are joined. The substantially rectangular drive mass body 6 is supported through the gap. The first support beam 4 is configured such that the rigidity in the X direction is lower than the rigidity in the other direction so that the drive mass body 6 can vibrate in the X direction (left and right direction in FIG. 1) within the substrate surface. Yes. Inside the drive mass body 6, a substantially rectangular detection mass body 10 is supported via second support beams 8 (four in the illustrated example). The second support beam 8 is configured such that the rigidity in the Y direction is lower than the rigidity in the other direction so that the detection mass body 10 can vibrate in the Y direction (vertical direction in FIG. 1) within the substrate surface. Yes.

  The driving mass body 6 is provided with a comb-like protrusion 12, and a driving comb electrode 14 and a driving monitoring comb electrode 16 are arranged on the support substrate 102 so as to face the protrusion 12. . The intervals between the comb teeth are equal, and the protrusion 12 and the comb electrodes 14 and 16 are insulated via the space and the support substrate 102.

  The detection mass body 10 is also provided with a comb-like protrusion 18, and a detection comb-tooth electrode 20 is disposed on the support substrate 102 so as to face the protrusion 18. As shown in FIG. 1, the intervals between the comb teeth are not equal, and the protrusions 18 and the detection comb electrodes 20 are arranged so that the narrow portion and the wide portion are alternating. Further, the protrusion 18 and the detection comb electrode 20 are insulated via a space and a support substrate.

  In addition, the support substrate 102 is provided with a monitor fixed electrode 24 that is separated from one end (the upper end 22 in the illustrated example) of the driving mass body 6 facing the Y direction. The fixed electrode 24 and the driving mass body 6 are insulated via the space and the support substrate 102.

  The vibratory gyro configured as described above can be manufactured by applying the following micromachining process.

  First, wet etching is performed so that a predetermined gap is formed between a supporting substrate such as glass and the movable member of the gyro. At this time, as a region that should not be etched, a portion other than a portion where a gap is formed is protected by applying a semiconductor photolithography technique or the like, for example, by forming a resist mask in advance.

  Next, the support substrate and the silicon substrate are bonded by an anodic bonding method or the like. The bonded substrate is polished from the silicon substrate side so that the silicon substrate has a predetermined thickness, and selective sputtering of a conductive metal such as Cr & Au is performed in an area required as a bonding pad. Then, an electrode pad (not shown) is formed. Further, using a mask material such as photoresist on the surface side (polished side) of the bonded silicon substrate, a resist pattern of a structure as shown in the plan view of FIG. 1 is applied using photolithography technology. To make. Also in this case, the region that should not be etched is protected by the resist mask.

  Next, through etching is performed in the thickness direction of the silicon substrate by dry etching using an RIE apparatus or the like. The basic structure of the vibrating gyroscope can be manufactured by the manufacturing process to which the micromachining technology as described above is applied.

Next, the operation of the vibration type gyro will be described. For example, Coriolis in the Y-axis direction that occurs when rotation about the Z-axis (rotational angular velocity Ωz) perpendicular to both the X-axis and the Y-axis is applied to the detection mass body of the mass M that vibrates at the speed Vx in the X-axis direction. The absolute amount of force c is
Fc = 2MVxΩz
It is represented by For this reason, in the vibration type gyro that detects the angular velocity by detecting the displacement of the detection mass body due to the Coriolis force Fc, it is necessary to excite the drive mass body at the velocity Vx. As a method for this, for example, a comb drive method using an electrostatic force is used.

When the sum of the DC voltage V _DC and the AC voltage V _AC is applied between the driving comb electrode 14 and the driving mass body 6 including the comb-shaped protrusions 12, the driving is equal to the voltage cycle of V _AC. Force is generated. Since the drive mass body 6 is a so-called spring mass structure supported by the first support beam 4 having low rigidity in the X direction, it has a vibration mode that vibrates in the X direction. Therefore, the drive mass body 6 vibrates by resonance by matching the frequency of _{VAC with} the frequency of this vibration mode. On the other hand, the detection mass body 10 is supported by the driving mass body 6 and has a structure that is difficult to move in the X direction with respect to the driving mass body 6. Drive vibration. The vibration speed Vx is detected as an electrostatic capacitance change by the monitoring comb-teeth electrode 16 through an electric circuit, and is used for controlling the drive vibration.

  Although the above-described driving method is called an electrostatic driving method, an electromagnetic driving method can also be applied, and the structure and operation principle in that case will be briefly described below. From one of the fixed parts 2, through one of the first support beams 4, through one side parallel to the Y axis of the driving mass 6, to another fixed part 2 through another first support beam 4 A metal wiring film insulated from the silicon substrate via an insulating film is disposed on the surface of the silicon substrate. Permanent magnets are arranged in parallel to the silicon substrate and the metal wiring film at a predetermined distance so that a perpendicular magnetic field acts on the metal wiring film. At this time, a Lorentz force is generated in the metal wiring film by passing a current through the metal wiring film. Since the Lorentz force is generated in the X direction, the driving mass body 6 can be vibrated by resonance by setting the current flowing through the metal wiring film to an AC current having the same frequency as that of the driving vibration mode.

  When the driving mass body 6 and the detection mass body 10 vibrate in the X direction as described above, if the angular velocity Ωz acts in a direction perpendicular to the paper surface of FIG. 1 (Z direction), the driving mass body 6 and the detection mass body. The body 10 has a Coriolis force Fc. Since the drive mass body 6 is supported by a structure that is difficult to move in the Y direction, the drive mass body 6 is hardly displaced in the Y direction. However, since the detection mass body 10 is supported so as to move easily in the Y direction, it is displaced and vibrated by Coriolis force. As a result, the electrostatic capacitance between the comb-shaped protrusion 18 provided on the detection mass body 10 and the detection fixed comb electrode 20 changes, and the angular velocity Ωz is detected by electrically reading this. can do.

  Ideally, the detected capacitance changes only when an angular velocity is input, but the capacitance also changes when the detection mass 10 is displaced in the Y direction due to other factors. To do. For example, if there are manufacturing variations in the four first support beams 4 that support the drive mass body 6, the Y direction component is included in the drive vibration. Further, since the detection mass body 10 is supported with high rigidity in the driving direction (X direction) with respect to the driving mass body 6, it vibrates integrally with the driving mass body 6. Therefore, when the Y direction component is included in the drive vibration, the detection mass body 10 is displaced in the Y direction, and a capacitance change that becomes an error component occurs.

  Here, when the Y direction component is included in the drive vibration, the capacitance between the drive mass body 6 and the monitor fixed electrode 24 changes, so that the Y direction component is electrically used as a quadrature error. Can be detected. The initial capacity between the driving mass 6 and the fixed electrode 24 is different from the initial capacity of the electrode for detecting the angular velocity, and the size of the quadrature error is also different. Therefore, each capacitance change is converted into a voltage by a CV conversion circuit, one or both voltages are adjusted by a variable amplifier so that the amplitudes of the voltages match, and a phase difference is output to output a difference. An output signal from which the char error has been subtracted can be obtained. In this way, the bias output can be reduced and the stability of the gyro can be increased.

  Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment generally has a structure in which two gyro structures according to the first embodiment are arranged in the X direction, and both gyro structures are connected to each other by a central connection spring 26. The left and right drive mass bodies 6a and 6b are connected by a connecting spring 26, thereby having a so-called reverse-phase vibration mode in which they are brought into contact with and separated from each other in the X direction. The drive mass bodies 6a and 6b are vibrated in reverse phase by applying a drive signal having the same frequency as the vibration mode to the drive comb electrodes 14a and 14b for driving the left and right drive mass bodies 6a and 6b, respectively. be able to. In addition, about the member which has a function equivalent to the thing of embodiment of FIG. 1, "a" is attached to a left structure, "b" is attached to a right structure, and detailed description is abbreviate | omitted.

  When the left and right driving mass bodies 6a and 6b vibrate in reverse phase as described above, if the angular velocity Ωz acts in the direction perpendicular to the paper surface of FIG. 4 (Z direction), the left and right driving mass bodies 6a and 6b respectively The detection mass bodies 10a and 10b supported by the second support beams 8a and 8b generate a reverse phase Coriolis force Fc, and the detection mass bodies 10a and 10b are displaced in the Y direction.

  However, if acceleration in any direction is input here, capacitance change occurs in the electrode for detecting angular velocity, resulting in erroneous detection. Therefore, as described in the first embodiment, the quadrature error is obtained on each of the left and right sides, and this is subtracted, and the output due to acceleration can be subtracted by detecting the left and right output signals differentially. it can. Note that the processing by the CV conversion circuit and the variable amplifier in the first embodiment can also be applied to this embodiment.

  Next, a third embodiment of the present invention will be described with reference to FIG. In addition, about the member which has a function equivalent to the thing of embodiment of FIG. 1, the same referential mark is attached | subjected and detailed description is abbreviate | omitted. In the first embodiment, the capacitance change in the angular velocity detection electrodes (comb electrodes 18 and 20) and the capacitance change in the monitor fixed electrode 24 in the detection direction of the driving mass 6 appear in the same phase. However, the third embodiment has a structure in which the phase is reversed.

  Specifically, the third embodiment basically has a spring mass structure equivalent to that of the first embodiment, but the monitor fixed electrode 28 corresponding to the monitor fixed electrode 24 in the first embodiment is As shown in FIG. 5, the structure is moved to a line-symmetric position with respect to the X axis. The initial capacity of the comb-teeth electrodes 18 and 20 for detecting the angular velocity and the initial capacity of the fixed electrode 28 and the driving mass body 6 are the same. The fixed electrode 28 and the detection comb electrode 20 are electrically connected by means such as wire bonding.

  In the third embodiment, when the drive mass body 6 is displaced in the + Y direction in FIG. 5, the detection mass body 10 is similarly displaced in the + Y direction, and the interval between the comb electrodes 18 and 20 is reduced, so that the distance between both electrodes is reduced. The capacitance of increases. On the other hand, since the interval between the monitor fixed electrode 28 and the drive mass body 6 is widened, the capacitance between the fixed electrode 28 and the drive mass body 6 is reduced. Here, the initial capacity between the comb electrodes 18 and 20 and the initial capacity between the fixed electrode 28 and the driving mass body 6 are the same, and their capacity changes are in opposite phases. Furthermore, since the fixed electrode 28 and the comb electrode 20 for detection are electrically connected, the total capacity change when the driving mass body 6 is displaced in the Y direction is offset or greatly reduced, resulting in a quadrature Errors can be suppressed.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. The fourth embodiment generally has a structure in which means for applying an electrostatic force to the driving mass is added to the first embodiment. In addition, about the member which has a function equivalent to the thing of embodiment of FIG. 1, the same referential mark is attached | subjected and detailed description is abbreviate | omitted.

  As shown in FIG. 6, the detection direction driving fixed electrode 30 is disposed below the driving mass body 6, specifically, at a position that is substantially line-symmetric with respect to the monitoring fixed electrode 24 and the X axis. The driving mass body 6 and the fixed electrode 30 are insulated from each other with a certain distance, and the driving mass body 6 and the fixed electrode 30 have a capacitance.

  Here, when a DC voltage and an AC voltage are applied to the detection direction driving electrode 30, an electrostatic force is generated on the driving mass body 6 and can be vibrated at the frequency of the AC voltage. That is, as described in the first embodiment, the condition for minimizing the quadrature error can be obtained by adjusting the magnitude and phase of the AC voltage while monitoring the quadrature error by the fixed electrode 24. .

  The fifth embodiment to be described next is structurally equivalent to the fourth embodiment, but the operation method is different. First, a DC voltage and an AC voltage are applied to the detection direction driving fixed electrode 30 to vibrate the driving mass body 6 in the Y direction. This vibration is a sine wave vibration, the amplitude of which greatly exceeds the quadrature error that occurs during normal driving vibration, and the amplitude can be controlled by monitoring with the fixed electrode 24.

  On the other hand, a similar sinusoidal vibration is also applied to the angular velocity detection electrode 20, and the capacitance change is detected here. Since the capacitance change and the displacement due to the angular velocity appear superimposed on the sine wave vibration, the error component is greatly increased by subtracting the sine wave vibration from the sensor output by the signal processing as described in the first embodiment. It becomes possible to detect the angular velocity signal reduced to a minimum.

  The present invention utilizes the fact that the movable electrode of the detection mass body performs the same drive vibration as the drive mass body, and the output detected at this time corresponds to a quadrature error. That is, if the displacement in the detection direction of the driving mass is output as a change in capacity, the output can also be regarded as a quadrature error. Therefore, by providing the fixed electrode for monitoring so as to face the driving mass body, it becomes possible to detect a change in the capacity of the driving mass body, that is, a quadrature error.

  As described above, the initial capacity between the movable electrode of the detection mass body and the comb electrode for detection is the same as the case where the initial capacity between the drive mass body and the fixed electrode for monitoring is the same. It may be the case. In the former case, the fixed electrode for monitoring is arranged so that the signs of the capacitance changes are reversed, and the fixed electrode and the detection comb fixed electrode are electrically connected to output. The quadrature error can always be zero, and only the output due to the capacitance change due to the angular velocity can be detected.

  On the other hand, in the latter case, by adjusting and subtracting the output quadrature error so as to be the same value by an amplifier circuit or the like, it becomes possible to detect only the output due to the capacitance change due to the angular velocity. However, this method can also be applied to the former case.

  Moreover, by applying a force in the detection direction from the outside to the drive mass body and vibrating it, it is possible to obtain a signal that is equal to or higher than the quadrature error output due to the angular velocity, such as separation, amplification, subtraction, etc. Processing becomes easy.

2 Substrate 6 Driving Mass 10 Detection Mass 14 Driving Comb Electrode 16 Driving Monitoring Comb Electrode 20 Detection Monitoring Comb Electrode 24, 28 Monitoring Fixed Electrode 30 Detection Direction Driving Fixed Electrode

Claims (5)

A fixing portion provided on the support substrate;
A driving mass supported by the fixed portion via a first support beam and configured to drive and vibrate in the X direction in a plane;
A detection mass body supported by the drive mass body via a second support beam and configured to vibrate in the Y direction within the plane and perpendicular to the X direction;
A movable electrode for angular velocity detection provided on the detection mass body;
A fixed electrode for detection provided on the support substrate so as to be opposed to the movable electrode,
In the vibration type gyro in which the detection mass body is displaced in the Y direction by the Coriolis force generated by the angular velocity around the axis in the Z direction orthogonal to both the X direction and the Y direction,
Fixed electrode for monitoring, which is arranged at a certain interval with respect to the driving mass body, and is configured such that the capacitance between the driving mass body and the driving mass body changes only by displacement in the Y direction of the driving mass body. Have
A vibration-type gyro that outputs a change in capacitance generated between the drive mass body and the monitor fixed electrode as a monitor signal when the drive vibration of the drive mass body includes a Y-direction component.   Regarding the change in the Y direction, the electrostatic capacity between the drive mass body and the fixed electrode for monitoring is the same as the electrostatic capacity between the movable electrode of the detection mass body and the fixed electrode for detection. The vibrating gyroscope according to claim 1, wherein the monitor fixed electrode is disposed so that a sign of capacitance change of the monitor is reversed, and the monitor fixed electrode and the detection fixed electrode are electrically connected.   The drive mass body is arranged at a certain interval, has a capacitance between the drive mass body and generates an electrostatic force when a voltage is applied, and the drive is performed by the electrostatic force. The vibrating gyroscope according to claim 1, further comprising a detection direction driving electrode configured to displace the mass body in the Y direction.   The vibrating gyroscopes are arranged in two rows and are connected to each other by a connecting beam having elasticity in the X direction so that the two sets of driving mass bodies have vibration modes that vibrate in mutually opposite phases. The vibrating gyroscope according to claim 1. A change in capacitance between the driving mass body and the fixed electrode for monitoring and a change in capacitance between the movable electrode of the detection mass body and the fixed electrode for detection are expressed as CV. Convert each into voltage using the conversion circuit,
Using a variable amplifier, adjust one or both of the two voltages so that the amplitudes of the two converted voltages match,
The vibratory gyroscope according to claim 1 or 4, wherein a difference between two voltages whose amplitudes are adjusted is configured to output a difference in phase.

Images