Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a resonant element used as an angular velocity sensor, acceleration sensor, filter, or the like, and to a vibration adjustment method therefor.  
           [0003]    2. Description of the Problems Leading to the Present Invention  
           [0004]    [0004]FIG. 9A is a perspective view showing a previous resonant element invented by the inventor of the present invention. FIG. 9B is a sectional view taken along the line I-I in FIG. 9A.  
           [0005]    The resonant element shown in FIGS. 9A and 9B is a resonant element  1  which is a microelement produced utilizing a conventional silicon micromachining technique and the like. The resonant element  1  is produced by forming a nitride film  3  on a silicon fixed substrate  2 , then forming a polysilicon film  4  thereover, and forming these films  3  and  4  into a predetermined set pattern by dry etching or the like.  
           [0006]    As shown in FIGS. 9A and 9B, above the top surface  2   a , which is a plane in the X-Y plane direction of the fixed substrate  2 , a vibrator  5  is disposed in a state isolated from the fixed substrate  2 . The vibrator  5  functions as a planar vibrating body  6 . The vibrator  5  is supported via support beams  7  so as to be vibratable in the X-direction. One end side of each of the support beams  7  is fixed to the fixed substrate  2  via a fixing portion  8 .  
           [0007]    On the right and left sides (as viewed in FIG. 9A) of the vibrator  5 , movable-side comb electrodes  10  ( 10   a  and  10   b ) are each formed outwardly in the X-direction, and fixed-side comb electrodes  11  ( 11   a  and  11   b ) are each disposed inwardly in the X-direction at positions opposed to the movable-side comb electrodes  10  and interdigitated therewith in a spaced relationship. The movable-side electrodes  10  and the fixed-side comb electrodes  11  are each connected to outside electrode pads (not shown) via conductive patterns (not shown), and thereby form exciting means  12 .  
           [0008]    For example, when AC voltages which are different in phase from each other by 180°, are applied to the fixed-side comb electrodes  11   a  and  11   b  while maintaining the movable-side comb electrodes  10   a  and  10   b  at a predetermined constant voltage (0 volt for example), electrostatic forces in directions opposite to each other occur between the movable-side comb electrodes  10   a  and the fixed-side comb electrodes  11   a , and between these movable-side comb electrodes  10   b  and the fixed-side comb electrodes  11   b , and by these electrostatic forces, the vibrator  5  is caused to be subjected to an excitation vibration in the X-direction.  
           [0009]    In the resonant element  1  with the above-described features, when the resonant element  1  is rotated around the Y-axis while being caused to be subjected to an excitation vibration in the X-direction, as described above, a Coriolis force occurs in the Z-direction orthogonal to the X-Y plane direction. This Coriolis force is applied to the vibrator  5  (planar vibrating body  6 ), and the vibrator  5  vibrates in the direction of the Coriolis force. By measuring the electric signal corresponding to the magnitude of the vibration amplitude of the vibrator  5  due to the Coriolis force occurring at this time, for example, the magnitude of a rotational angular velocity can be detected.  
           [0010]    In the case where the resonant element  1  is used as an angular velocity sensor, there is provided a detecting portion for measuring the electric signal corresponding to the magnitude of vibration amplitude of the vibrator  5  due to a Coriolis force.  
           [0011]    When the resonant element  1  is produced, the resonance frequency of the vibrator  5  (planar vibrating body  6 ) in the direction of a Coriolis force (Z-direction) is previously set at the design stage to the resonance frequency in the X-direction, and the shape, dimensions, weight, etc. of the vibrator  5  are designed and implemented so that the resonance frequency is obtained. In many cases, however, the shape, dimensions, weight, etc. of the vibrator  5  are not implemented as designed because of the machining accuracy of the silicon micromachining technique. Accordingly, deviation of the resonance frequency of the vibrator  5  from the designed frequency often occurs. If the vibration of the vibrator  5  is in a resonant state, the amplitude thereof is greatly amplified by virtue of the Q (quality factor) value related to the structure, but if the frequency deviates, a problem arises in that the amplitude is not amplified nearly as much, resulting in the sensitivity of the resonant element being significantly reduced. It is therefore necessary to adjust the resonance frequency of the vibrator  5  to the set frequency in design by performing trimming with respect to the vibrator  5  and/or the support beams  7  by, for example, a complicated machining process.  
           [0012]    The resonant element  1  is, however, a minute element, therefore, it is practically impossible, because of the accuracy of conventional mechanical trimming techniques, to perform trimming of the minute planar vibrating body  6  and/or the support beams  7  so as to have the desired dimensions, shape, and weight, etc. It has, therefore, been difficult to adjust the resonance frequency of the planar vibrating body  6  to a set value.  
           [0013]    In the resonant element  1 , therefore, a conductive layer  15  for providing an electrostatic attractive force  14  is provided on the fixed substrate  2  at the position opposed to the vibrator  5  with an interval interposed in the Z-direction, as illustrated in FIGS. 9A and 9B.  
           [0014]    As shown in FIG. 9A, the conductive layer  15  is connected to a conductive pad  17  via a conductive pattern  16 . By controlling the voltage to be applied to the conductive layer  15  via the conductive pattern  16  and conductive pad  17 , the resonance frequency of the vibrator  5  is adjustable to a set value.  
           [0015]    Once a DC voltage is applied to the conductive layer  15 , an electrostatic attractive force acts on the vibrator  5 , and this acts on the vibrator  5  as an electrostatic spring. Specifically, when the vibrator  5  vibrates in a direction such that the vibrator  5  approaches the fixed substrate  2 , the electrostatic attractive force acts in the direction such that the amplitude is increased, so that the application of the DC voltage to the conductive layer  15  has an effect of generating a force in the direction opposite to the direction of the force of a mechanical spring. This results in a reduction in the resonance frequency of the vibrator  5  in the Z-direction. Since this reduced amount of the resonance frequency varies in accordance with the magnitude of the electrostatic attractive force  14  applied, a fine-adjustment of the resonance frequency of the vibrator  5  from the natural frequency thereof to the lower frequency side can be performed by adjusting the magnitude of the DC voltage applied to the conductive layer  15 .  
           [0016]    Utilizing this effect, by designing the natural resonance frequency of the vibrator  5  in the Z-direction to be slightly higher than the most sensitive resonance frequency (the frequency equal to the resonance frequency in the X-direction), in other words, by designing the resonance frequency of the vibrator  5  in the Z-direction to be higher than the resonance frequency thereof in the excitation vibrational direction by the exciting means  12 , the vibrator  5  can be resonated at a predetermined resonance frequency by adjusting the magnitude of the DC voltage applied to the conductive layer  15 .  
           [0017]    However, although the adjustment of the resonance frequency for the vibrator  5  has been performed by providing the conductive layer  15 , in some cases, characteristics such as S/N (signal-to-noise) ratio have deteriorated due to an increase in the noise of the resonant element  1 .  
           [0018]    Investigation by the present inventor into the reason for the deterioration of the characteristics, has found that the deterioration of characteristics is attributable to the vibrating conditions of the vibrator  5 .  
           [0019]    [0019]FIGS. 8A and 8B each show vibrating states of the vibrator  5  in the X-Z plane, observed in experiments by the present inventor. If there is no angular velocity around the Y-axis when the vibrator  5  is caused to be subjected to an excitation vibration, it is desirable that vibrator  5  be subjected to an excitation vibration in the X-direction horizontally along the plane  2   a  in the X-Y plane direction of the fixed substrate  2 , as illustrated in FIG. 10C, and substantially without deflection in the Z-direction as shown in FIG. 8B.  
           [0020]    In contrast to this, in some cases, the vibrator  5  vibrates as shown in FIGS. 10A and 10B, and as illustrated in FIG. 8A, the vibrations of the vibrator  5  are in states deflecting by a large amount in the Z-direction which is the detection direction of a Coriolis force. In such cases, the resonant element  1  has been found to deteriorate in characteristics.  
           [0021]    The present inventor, therefore, has noted that the deflection of the vibrator  5  in the Z-direction is attributable to the tilt of the vibrator  5  with respect to the substrate plane of the fixed substrate  2 , and has proposed various resonant elements  1  each having excitation deflection inhibiting means for correcting the tilt of the vibrator  5  and for inhibiting the deflection of the vibrator  5  in the Z-direction.  
           [0022]    [0022]FIG. 6A is a perspective view showing one example of a previously proposed resonant element  1 , and FIG. 6B is a sectional view taken along the line I-I in FIG. 6A. Here, in FIGS. 6A and 6B, the same components as those of the resonant element  1  in FIGS. 9A and B are identified by the same reference numerals, and repeated descriptions of the common components are omitted. It is to be noted that the resonant element  1  shown in FIGS. 6A and 6B is disclosed in Japanese patent application Nos. 11-197096 and 11-344648 and the corresponding U.S. and European patent applications.  
           [0023]    In the resonant element  1  shown in FIGS. 6A and 6B, conductive layers  20  and  21  are disposed on the plane in the X-Y plane direction of the fixed substrate  2  so as to be opposed to each other with a gap in the X-direction therebetween, and to be opposed to the right or left (as viewed in FIG. 6A) edge area with a gap interposed. The conductive layers  20  and  21  are conductively connected to conductive pads  24  and  25  via conductive patterns  22  and  23 , respectively. In the resonant element  1  shown in FIG. 6A and 6B, the conductor layers  20  and  21  constitute excitation deflection inhibiting means.  
           [0024]    By individually applying DC voltages to the conductive layers  20  and  21  via the conductive patterns  22  and  23 , and the conductive pads  24  and  25 , respectively, electrostatic attractive forces  26  and  27  occur between the conductive layers  20  and  21 , and the vibrator  5 . The tilt of the vibrator  5  can be corrected by adjusting each of the right and left electrostatic attractive forces  26  and  27  to the vibrator  5  through adjusting each of the voltages to be applied to the conductive layers  20  and  21 .  
           [0025]    Specifically, if the vibrator  5  tilts downwardly to the right as indicated by a broken line α in FIG. 6B, a DC voltage higher than that applied to the conductive layer  21  is applied to the conductive layer  20 . Thereby, the electrostatic attractive force  26  acting on the left edge area of the vibrator  5  opposed to the conductive layer  20  becomes larger than the electrostatic attractive force  27  acting on the right edge area of the vibrator  5  opposed to the conductive layer  21 , so that the left edge area of the vibrator  5  is pulled toward the fixed substrate  2  side more strongly than the right edge area of the vibrator  5 , whereby the downward tilt to the right is corrected.  
           [0026]    If the vibrator  5  tilts upwardly to the right as indicated by a broken line β in FIG. 6B, a DC voltage higher than that applied to the conductive layer  20  is applied to the conductive layer  21 . Thereby, the electrostatic force  27  becomes larger than the electrostatic force  26 , so that the right edge area of the vibrator  5  is pulled toward the fixed substrate  2  side more strongly than the left edge area of the vibrator  5 , whereby the downward tilt to the right is corrected.  
           [0027]    In the resonant element  1  shown in FIG. 6, by providing the conductive layers  20  and  21 , the tilt of the vibrator  5  can be corrected, which leads to an improvement in the vibrating conditions of the vibrator  5 .  
           [0028]    Meanwhile, in order to find the optimum applied voltage to the conductive layers  20  and  21  for correcting the tilt of the vibrator  5 , the present applicant has performed the following vibration adjustments for the vibrator  5 , utilizing a large-scale vibration measuring system  30  as shown in FIG. 7.  
           [0029]    For example, a resonant element  1  is disposed on a specimen holding stand  31 , driving means (not shown) for AC voltage application is conductively connected to the fixed side comb electrodes  11 , and first DC bias applying means  32  is conductively connected to the conductive layer  20  via the electrode pad  24  and the conductive pattern  22 . In the same manner, second DC bias applying means  33  is conductively connected to the conductive layer  20  via the electrode pad  25  and the conductive pattern  23 .  
           [0030]    Then, in the state wherein the vibrator  5  is caused to be subjected to an excitation vibration by the driving means, the vibrator  5  under excitation vibration is radiated by laser rays  35  from a laser displacement meter  34 . By utilizing the reflected laser rays from the vibrator  5 , signals in response to displacements in the X-direction and in the Z-direction of the vibrator  5  are outputted from the laser displacement meter  34  to an oscilloscope  36 .  
           [0031]    The vibrating conditions of the vibrator  5  in the X-Z plane can be viewed on the screen of the oscilloscope  36 . While viewing the screen of the oscilloscope  36 , a vibration adjustment operator individually varies the magnitudes of the voltages to be applied to the conductive layers  20  and  21 , by controlling the first and second DC bias applying means  32  and  33 , respectively. Thereby, the vibration adjustment operator obtains the optimum values of the applied voltage to the conductive layers  20  and  21 , wherein the deflection of the vibrator  5  in the Z-direction can be eliminated, or suppressed to a very small amount.  
           [0032]    In this manner, vibration adjustments for the vibrator  5  utilizing the vibration measuring system  30  shown in FIG. 7 are performed.  
           [0033]    After the optimum values of the applied voltage to the conductive layers  20  and  21  have been obtained as described above, the resonant element  1  is removed from the specimen holding stand  31  of the vibration measuring system  30 , and then, for example, is built into a predetermined sensor device or the like. The sensor device into which the resonant element  1  having the conductive layers  20  and  21  shown in FIGS. 6A and 6B is to be built, is provided with means for individually applying DC voltages to the conductive layers  20  and  21 , and the means is set so that voltages having the optimum values are each applied to the conductive layers  20  and  21 . This allows the vibrator  5  of the resonant element  1  to be subjected to an ideal excitation vibration in the X-direction without deflection in the Z-direction, and allows the resonant element  1  to be improved in characteristics.  
           [0034]    However, there has been a problem that, in order to obtain the above-described optimum values of the applied voltages to the conductive layers  20  and  21 , a large-scale and costly vibration measuring system  30  is required. Also, as described above, the vibration adjusting method for the vibrator  5  has been a manual method such that the operator obtains the optimum values of the applied voltages to the conductive layers  20  and  21  by controlling the first and second DC bias applying means  32  and  33 , respectively, while viewing the screen of the oscilloscope  36 . As a result, the vibration adjustment is both costly and time consuming.  
           [0035]    Furthermore, as described above, since the operator performs the vibration adjustment for the vibrator  5  based on vibration conditions (vibrational loci) of the vibrator  5  in the X-Z plane while viewing the screen of the oscilloscope  36 , there is a problem in that an improvement in the adjustment accuracy is limited by the skill of the operator.  
           [0036]    Moreover, in accordance with the vibration adjustment method as described above, after the optimum value of the applied voltage to the conductive layers  20  and  21  has been obtained by the vibration measuring system  30 , the resonant element  1  is removed from the specimen holding stand  31  of the vibration measuring system  30 , and is built into a predetermined sensor device or the like. Therefore, even though the optimum values of the applied voltages to the conductive layers  20  and  21  have been obtained by the vibration measuring system  30 , for example, the stresses within the support beams  7  of the resonant element  1  can change when the resonant element  1  is removed from the specimen holding stand  31  and is built into a predetermined sensor device, and thereby the optimum voltage values of the applied voltages to the conductive layers  20  and  21  can change into different voltages from the optimum voltages values. In such a case, the vibrator  5  of the resonant element  1  in the sensor device will not be subject to an optimum excitation vibration.  
           [0037]    If the optimum voltage value of the applied voltage to the conductive layers  20  and  21  has thus changed, it will be necessary to again dispose the resonant element  1  in the vibration measuring system  30  and to again perform the above-described vibration adjustment. This is very troublesome, however, and it is virtually impracticable after the resonant element  1  has been built into the sensor device.  
         SUMMARY OF THE INVENTION  
         [0038]    The present invention solves the above-described problems. It is a first object of the present invention to allow the vibration adjustment for the vibrator for inhibiting the deflection of the vibrator (vibrating body) in the Z-direction during the excitation vibration thereof in the X-direction to be easily performed, without the need for a large-scale apparatus. It is a second object to facilitate the automation of the vibration adjustment for the vibrator. It is a third object to provide a resonant element allowing the vibration adjustment for the vibrator to be performed in the state wherein the vibrator has been built into the sensor device.  
           [0039]    In order to achieve the objects, the present invention has the following constitutions as means for solving the above-described problems. In accordance with a first aspect, the resonant element includes a vibrating body vibratable in orthogonal X- and Z-directions; exciting means for causing the vibrating body to be subjected to an excitation vibration in the X-direction; excitation deflection detecting means for detecting the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction; and excitation deflection inhibiting means for inhibiting the deflection of the vibrating body in the Z-direction.  
           [0040]    The resonant element in accordance with another aspect constitutes an angular velocity sensor for detecting the angular velocity around a Y-axis orthogonal to the X- and Z-direction based on the vibration of the vibrating body in the Z-direction by a Coriolis force, and the angular velocity sensor has Z-direction vibration detecting means for detecting the vibration of the vibrating body in the Z-direction, the Z-direction vibration detecting means also serving as excitation deflection detecting means.  
           [0041]    In accordance with another aspect, the excitation deflection detecting means is constituted of a detecting electrode for detecting the variation in the electrostatic capacity with respect to the vibrating body in response to the vibration of the vibrating body in the Z-direction, and the excitation deflection detecting means detects the variation in the detected electrostatic capacity by the detecting electrode during the excitation vibration thereof in the X-direction, as a deflection of the vibrating body in the Z-direction.  
           [0042]    In accordance with another aspect, the vibrating body is disposed so as to be opposed to the plane of the X-Y plane direction of the fixed substrate, and the vibrating body constitutes a planar vibrating body supported by the fixed substrate via support beams so as to be vibratable in the X-direction.  
           [0043]    In accordance with another aspect, the invention is directed to a vibration adjustment method for a resonant element which includes a vibrating body vibratable in orthogonal X- and Z-directions, exciting means for causing the vibrating body to be subjected to an excitation vibration in the X-direction, a detecting electrode for detecting the variation in the electrostatic capacity with respect to the vibrating body in response to the vibration thereof in the Z-direction; and excitation deflection inhibiting means which give electrostatic attractive forces to the vibrating body and which inhibit the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction by the electrostatic attractive forces. In the vibration adjustment method in accordance with this aspect, the variation in the detected electrostatic capacity by the detecting electrode is detected as a deflection of the vibrating body in the Z-direction, while the vibrating body is caused to be subjected to an excitation vibration in the X-direction by the exciting means; and the electrostatic attractive forces given to the vibrating body by the excitation deflection inhibiting means are controlled in the direction such that the variation in the detected electrostatic capacity by the detecting electrode is canceled.  
           [0044]    The vibration adjustment method for a resonant element in accordance with another aspect converts the detected electrostatic capacity by the detecting electrode into a voltage, the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction is detected based on the variation in the voltage.  
           [0045]    The vibration adjustment method for a resonant element in accordance with another aspect, converts the detected electrostatic capacity by the detecting electrode into a voltage using capacity-voltage converting means comprising FET.  
           [0046]    In a vibration adjustment method for a resonant element in accordance with another aspect, the resonant element constitutes an angular velocity sensor for detecting the angular velocity around the Y-axis by a Coriolis force based on the vibration of the vibrating body in the Z-direction. The angular velocity sensor has Z-direction vibration detecting means for detecting the vibration of the vibrating body in the Z-direction utilizing the variation in the electrostatic capacity; and capacity-voltage converting means for converting the detected electrostatic capacity by the detecting electrode into a voltage, the Z-direction vibration detecting means also serving as excitation deflection detecting means; and the capacity-voltage converting means also serves as capacity-voltage converting means for detecting an excitation deflection.  
           [0047]    In the present invention, when performing vibration adjustment for the resonant element by providing the resonant element with excitation deflection detecting means and excitation deflection inhibiting means, the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction is detected by the excitation deflection detecting means, and the excitation deflection inhibiting means are adjusted in a direction such that the deflection in the Z-direction is eliminated. Thereby, the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction can be inhibited, and the vibrating body can be caused to be subjected to an ideal excitation vibration in the X-direction. This makes it possible to avoid the problem of the characteristics deterioration of the resonant element caused by the deflection of the vibrating body in the Z-direction.  
           [0048]    Since the resonant element is in itself provided with the excitation deflection detecting means, there is no need for large-scale equipment for measuring the vibrating conditions of the vibrating body as described above, which leads to a reduction in equipment cost.  
           [0049]    Also, since the vibration adjustment for the vibrator of the resonant element can be performed in the state wherein the vibrator has been built in the sensor device, it is possible to prevent the problem that, even though the vibration adjustment for the vibrating body has been performed stresses, for example, within the support beams supporting the vibrating body change when the resonant element is built into the sensor device, resulting in the vibrating body not being subjected to an ideal excitation vibration.  
           [0050]    For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.  
           [0051]    Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S)  
       [0052]    [0052]FIG. 1 is an explanatory view showing an embodiment of a resonant element in accordance with the present invention, together with the main construction of a characteristic vibration adjusting system.  
         [0053]    [0053]FIG. 2 is a graph showing an example of the voltage waveform in response to the electrostatic capacity between a vibrator and a detecting electrode.  
         [0054]    [0054]FIG. 3 is a graph showing an example of the variation in the voltage in response to the electrostatic capacity between a vibrator and a detecting electrode in accordance with the variation in the applied voltage to conductive layers.  
         [0055]    [0055]FIG. 4 is an explanatory view showing an example of a main circuit configuration of the sensor device into which a resonant element as an angular velocity sensor is to be built.  
         [0056]    [0056]FIGS. 5A and 5B are explanatory views showing another embodiment of a resonant element.  
         [0057]    [0057]FIGS. 6A and 6B are explanatory views illustrating an example of a previous resonant element.  
         [0058]    [0058]FIG. 7 is a model diagram illustrating an example of a previous system for performing the vibration adjustment for a resonant element.  
         [0059]    [0059]FIGS. 8A and 8B are explanatory views illustrating an example of a vibrating state of a vibrating body in a X-Z plane.  
         [0060]    [0060]FIGS. 9A and 9B are explanatory views illustrating another previous example of a resonant element.  
         [0061]    [0061]FIGS. 10A to  10 B are explanatory views illustrating movements of a vibrating body in the X-Z plane.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0062]    Hereinbelow, the embodiments in accordance with the present invention will be described based on the drawings.  
         [0063]    [0063]FIGS. 1A and 1B show one embodiment of a resonant element  1  in accordance with the present invention, together with a vibration adjustment system for characterizing the resonant element. In the descriptions of this embodiment, the same components as the above described examples of previous resonant elements are identified by the same reference numerals, and repeated explanations of the common components are omitted.  
         [0064]    The resonant element  1  shown in FIGS. 1A and 1B can be used as an acceleration sensor, angular velocity sensor, pressure sensor, filter, or the like. The resonant element  1  has substantially the same construction as the proposed resonant element shown in FIG. 6, but this embodiment is characterized in that a detecting electrode  40  which is an excitation deflection detecting means is disposed on the top surface  2   a  of the fixed substrate  2  so as to be opposed to and spaced from the vibrator  5 .  
         [0065]    Since the vibrator  5  is formed of polysilicon and has electric conductivity, it is possible, by forming the above-mentioned detecting electrode  40 , to detect, by the detecting electrode  40 , variation in the spacing between the top surface  2   a  of the fixed substrate  2  and the vibrator  5 , that is, the vibration (deflection) of the vibrator  5  in the Z-direction, as a variation in the electrostatic capacity,  
         [0066]    When the resonant element  1  is used as an angular velocity sensor, for example, the detecting electrode  40  similar to the above-described one, is formed on the top surface  2   a  of the fixed substrate  2  as Z-direction vibration detecting means, in order to detect the vibration amplitude of the vibrator  5  in the Z-direction due to a Coriolis force. In such a case, the Z-direction vibration detecting means (detecting electrode  40 ) also serves as excitation deflection detecting means.  
         [0067]    The characteristic vibration adjusting system in this embodiment shown in FIG. 1 is arranged to perform a vibration adjustment with respect to the resonant element  1  having the above-described excitation deflection detecting means (detecting electrode  40 ), and comprises a first DC voltage applying means  41 , a second DC voltage applying means  42 , capacity-voltage converting means  43 , an amplifier  44 , and driving means  45 .  
         [0068]    The first and second DC voltage applying means  41  and  42  are conductively connected to conductive layers  20  and  21 , respectively, and have a capability of applying DC voltages to the respective conductive layers  20  and  21  and of changing the magnitude of the DC voltages to be applied.  
         [0069]    The capacity-voltage converting means  43  comprises FET  46  and a source resistor  47 . As shown in FIG. 1, the gate -side of the FET  46  is conductively connected to the detecting electrode  40 , one end side of the source resistor  47  is connected to the source-side of the FET  46 , and the other end side of the source resistor  47  is grounded.  
         [0070]    In the capacity-voltage converting means  43 , the voltage corresponding to the electrostatic capacity between the vibrator  5  and the detecting electrode  40  occurs at the connection point P between the source-side of the FET  46  and the source resistor  47 . In other words, the capacity-voltage converting means  43  converts the electrostatic capacity between the vibrator  5  and the detecting electrode  40  into a voltage and outputs the voltage from connection point P. The amplifier  44  is connected to the connection point P and amplifies and outputs the voltage corresponding to the electrostatic capacity between the vibrator  5  and the detecting electrode  40 .  
         [0071]    In the vibration adjusting system in this illustrated embodiment, since the capacity-voltage converting means  43  converts the electrostatic capacity detected by the detecting electrode  40  into a voltage, the vibration (deflection) of vibrator  5  in the Z-direction can be detected as a voltage variation.  
         [0072]    The driving means  45  comprises an AC power source  48  and a phase inversion portion  49 . One of the fixed-side comb electrodes  11   a  and  11   b  of the resonant element  1  is conductively connected to the AC power source  48  directly, and the other is conductively connected to the AC power source  48  via the phase inversion portion  49 . By this driving means  45 , AC voltages which are different in phase from each other by 180° are applied respectively to the fixed-side comb electrodes  11   a  and  11   b  of the resonant element  1 , and thereby the vibrator  5  can be subjected to an excitation in the X-direction.  
         [0073]    A vibration adjusting method for the resonant element  1  may include, for example, conductively connecting an oscilloscope (not shown) to the output-side of the amplifier  44  and then subjecting the vibrator  5  to an excitation vibration in the X-direction, while viewing the waveform of the voltage output by the amplifier  44  is viewed on the screen of the oscilloscope.  
         [0074]    In some cases, even though no angular velocity around the Y-axis is applied during the excitation vibration of the vibrator  5 , a voltage waveform as indicated by a solid line A in FIG. 2 is viewed with the oscilloscope, the voltage waveform varying in response to the excitation vibration of the vibrator  5  in the X-direction.  
         [0075]    In such a case, since deflection in the Z-direction arises during the excitation vibration of the vibrator  5 , a vibration adjustment for the vibrator  5  is performed. For example, while viewing the voltage waveforms shown up on the screen of the oscilloscope, the DC voltages to be each applied to the conductive layers  20  and  21  are varied by controlling the first DC voltage applying means  41  or the second DC voltage applying means  42 . The applied voltages for the conductive layers  20  and  21  at the time when the voltage waveform on the screen of the oscilloscope becomes a waveform wherein substantially no vibration amplitude can be seen and wherein the voltage converges into a given voltage, as indicated by the dotted line B in FIG. 2, i.e., at the time when the variation in the detected electrostatic capacity by the detecting electrode  40  disappears, or is substantially removed, is detected as the voltage optimum for the vibration adjustment for the vibrator  5 .  
         [0076]    For example, when a voltage waveform indicated by the solid line A in FIG. 2 is viewed on the screen of the oscilloscope, for example, in the state wherein the conductive layer  20  of the resonant element  1  is maintained at a given voltage (0 volt for example), the applied voltage for the conductive layer  21  is varied by variably controlling the second voltage applying means  42  while viewing the voltage waveform on the screen of the oscilloscope. The voltage at the time when the voltage waveform on the screen of the oscilloscope converges into a waveform wherein substantially no vibration amplitude can be seen, as indicated by the dotted line B in FIG. 2, is detected as the optimum voltage for the conductive layer  21 . This detected optimum voltage for the conductive layer  21 , and the fixed voltage (0 volt for example) of the above-described conductive layer  20  are detected as the voltages optimum for the vibrator  5 .  
         [0077]    Conversely, of course, the applied voltage for the conductive layer  20  may be varied in the state wherein the conductive layer  21  is maintained at a given voltage (0 volt for example), and the voltage at the time when the voltage waveform on the screen of the oscilloscope converges into a vibration amplitude wherein substantially no vibration amplitude can be seen, as indicated by the dotted line B in FIG. 2, may be detected as the optimum voltage for the conductive layer  20 , whereby the voltage optimum for the vibration adjustment for the vibrator  5  is detected. Or, the voltage optimum for the vibration adjustment for the vibrator  5  may be detected by individually varying the applied voltages for the conductive layers  20  and  21  and thereby obtaining the optimum voltages to the conductive layers  20  and  21 .  
         [0078]    As described above, by performing the vibration adjustment for the vibrator  5  through controlling the applied voltage to the conductive layers  20  and  21 , the vibrator  5  can be caused to be subjected to an ideal excitation vibration substantially without deflection in the Z-direction.  
         [0079]    The above-described effect has been verified in experiments by the present inventor. In these experiments, the present inventor has built the resonant element  1  having a characteristic construction in this embodiment into the vibration adjusting system shown in FIG. 1, and in the state wherein the conductive layer  20  is fixed at a given voltage (0 volt for example), the inventor has investigated as to how the voltage waveform output by the connection point P of the above-described capacity-voltage converting means varies as the applied voltage V 21  to the above-described conductive layer  21  is varied.  
         [0080]    [0080]FIG. 3 is a graph illustrating the experimental results. In FIG. 3, the horizontal axis designates the applied voltage to the conductive layer  21 , and the vertical axis designates the amplitude of the voltage waveform output by the connecting point P of the capacity-voltage converting means  43 . In the above-described experiments, the detecting electrode  40  has dimensions of 0.5×0.5 mm, and the interval between the detecting electrode  40  and the vibrator  5  is 2 mm. The vibrator  5  is caused to be subjected to an excitation vibration in the X-direction under the frequency of 7.623 kHz.  
         [0081]    As shown in FIG. 3, as the applied voltage V 21  to the above-described conductive layer  21  is varied, the amplitude of the voltage waveform output by the connection point P of the capacity-voltage converting means  43  varies, and the amplitude of the voltage waveform at the connection point P is minimized at the point Q (at this point, the applied voltage V 21  is 9.34 V). In accordance with the investigated movement of the vibrator  5  in the X-Z plane, the vibrator  5  exhibited loci as shown in FIG. 8B. That is, as illustrated in FIG. 10C, the vibrator  5  was being subjected to an excitation vibration horizontally in the X-direction along the plane of the fixed substrate in the X-Y plane direction, and substantially without deflection in the Z-direction.  
         [0082]    As shown in these experimental results, by performing the vibration adjustment for the vibrator  5  so that the variation in the detected electrostatic capacity by the detecting electrode  40  is canceled, the vibrator  5  can be caused to be subjected to an excitation in the X-direction.  
         [0083]    [0083]FIG. 4 shows one example of a main circuit configuration of the sensor device  50  into which a resonant element  1  as an angular velocity sensor has been built. In the sensor device  50 , the vibrator  5  is caused to be subjected to an excitation vibration in the X-direction by applying AC voltages which are different in the phase from each other by 180°to the fixed-side comb electrodes  11   a  and  11   b , respectively, of the resonant element  1  by driving means  45 . At the same time, a Coriolis force is applied to the vibrator  5  due to the angular velocity around the Y-axis. Variation in the electrostatic capacity with respect to the vibrator  5  resulting from vibration of the vibrator  5  in the Z-direction is output by the detecting electrode  40 , and the electrostatic capacity is converted into a voltage by the capacity-voltage converter  43 . The voltage after the conversion is amplified by the amplifier  44 , and is applied to a phase detection portion  53  via a BPF (band-pass filter)  51  and a phase shifter  52 .  
         [0084]    The phase detection portion  53  takes in the AC voltage output by an AC power source  48  as a reference signal, and performs a phase detection with respect to the voltage applied by the phase shifter portion  52  utilizing the reference signal. The signal obtained by this phase detection is output as a detecting signal for angular velocity around the Y-axis via a LPF (low-pass filter) and the amplifier  55 .  
         [0085]    As shown in FIG. 4, the angular velocity sensor  50  has the first and second AC voltage applying means  41  and  42 , the capacity-voltage converting means  43 , the amplifier  44 , and the driving means  50  which constitute the vibration adjusting system shown in FIG. 1. Therefore, when performing a vibration adjustment for the resonant element  1  as an angular velocity sensor, it is possible, after building the resonant element  1  into the sensor device  50 , to utilize, for vibration adjustment, the above-described first and second AC voltage applying means  41  and  42 , the capacity-voltage converting means  43 , the amplifier  44 , and the driving means  50  to perform a vibration adjustment for the resonant element  1 .  
         [0086]    In accordance with this embodiment, since the resonant element  1  is constituted so as to have a detecting electrode  40 , and to detect the deflection of the vibrator  5  in the Z-direction by this detecting electrode utilizing the variation in the electrostatic capacity, the vibration adjustment can be performed by the simple vibration adjusting system shown in FIG. 1, without the need to use a large-scale vibration measuring system, such as the system shown in FIG. 7.  
         [0087]    Since the vibration adjustment for the vibrator  5  can be easily performed, the time required for the vibration adjustment for the vibrator  5  can be reduced, and the adjustment cost can be reduced. Also, since this embodiment is constituted so that the deflection of the vibrator  5  in the Z-direction is detected utilizing the variation of the electrostatic capacity, the deflection of the vibrator  5  in the Z-direction can be detected with a much higher accuracy than the case where the deflection of the vibrator  5  in the Z-direction is detected utilizing laser rays as described above. This results in an improvement in the accuracy of the vibration adjustment for the vibrator  5 .  
         [0088]    Furthermore, in addition to having a simple construction, the characteristic vibration adjusting system in this embodiment has features, as described above, such as to detect the deflection of the vibrator  5  in the Z-direction utilizing the variation in the electrostatic capacity, to convert the electrostatic capacity into a voltage, and to detect the variation in the electrostatic capacity based on the variation in the voltage. Therefore, the automation of the vibration adjustment wherein the optimum value of the applied voltages for the above-described conductive layers  20  and  21  are obtained utilizing the variation in the voltage in response to the deflection of the vibrator  5  in the Z-direction, can be easily achieved.  
         [0089]    Moreover, in the case of an angular velocity sensor, since there is provided Z-direction vibration detecting means (detecting electrode  40 ) for detecting the vibration of the vibrator  5  in the Z-direction due to a Coriolis force, the Z-direction vibration detecting means can be caused to do double duty as excitation deflection detecting means for vibration adjustment. Thereby, the vibration adjustment can be performed easily and with a high accuracy as describe above without the need to change the design.  
         [0090]    In addition, since the units constituting the vibration adjusting system shown in FIG. 1 are incorporated in the sensor device  50  into which the resonant element  1  as an angular velocity sensor is to be built, the vibration adjustment of the angular velocity sensor can be performed in the state wherein the angular velocity sensor has been built into the sensor device  50 . This make it possible to prevent the occurrence of the problem that, even though vibration adjustment has been performed, the stresses within the support beams  7  of the vibrator  5  change when the resonant element  1  is built into the sensor device  50 , and the optimum applied voltages to the conductive layers  20  and  21  change with the result that the vibrator  5  of the angular velocity sensor cannot be appropriately caused to be subjected to an excitation vibration without deflection in the Z-direction.  
         [0091]    The present invention is not limited to the above-described embodiment, but various embodiments may be adopted. For example, in the above-described embodiment, the detecting electrode  40  is disposed on the fixed substrate  2 , but, for example, when there is a cover member covering the upper side of the vibrator  5  with an interval interposed, the detecting electrode  40  may be disposed at the area opposed to the vibrator  5  on the cover member. Or, the detecting electrodes  40  may be provided on both of the fixed substrate  2  and the cover member. The same goes for the conductive layers  20  and  21 . That is, the conductive layers  20  and  21  may be provided not only on the fixed substrate  2 , but also on the above-mentioned cover member, or may be provided on both of the fixed substrate  2  and the cover member.  
         [0092]    Also, the detecting electrode  40  is disposed so as to be opposed to the central area of the vibrator  5  with a gap interposed. However, the detecting electrodes  40  may be, for example, disposed so as to be opposed to both edge areas of the vibrator  5  with a gap in the X-direction therebetween.  
         [0093]    Also, the configuration of the resonant element  1  is not limited to that of the embodiment illustrated. The present invention can be applied to resonant elements  1  having various configurations. For example, the present invention can be applied to the resonant element  1  as shown in FIGS. 5A and 5B. In FIGS. 5A and 5B, a cavity (depression)  57  is formed in the top surface  2   a  which is a plane in the X-Y plane direction of the fixed substrate  2  which is made of glass. The bottom surface  57   a  ofthis cavity  57 , like the top surface  2   a , forms a plane in the X-Y plane and a planar vibrating body  6  is disposed so as to be opposed to the bottom surface  57   a  with a gap interposed in the Z-direction.  
         [0094]    The planar vibrating body  6  shown in FIGS. 5A and 5B is a combined body wherein a weight  9  is connected to the inside of a frame body  60  by four connection beams (detecting beams)  61 . The weight  9  has a square shape, and each of the connection beams has a L-letter shape. The tips of the shorter sides  62  of the L-letter shaped connection beams  61  each communicates with and are connected to the four corners of the weight  9 . The longer sides  63  of the L-shaped connection beams  61  are each extended from the shorter sides  62  along the sides of the frame body  60  via a gap, and the tips of the extension portions thereof each communicates with and are connected to the comers of the frame body  60 .  
         [0095]    A plurality of fixing portions  8  (four fixing portions in the figure) is each fixedly disposed on the fixed substrate  2  with gaps therebetween so as to surround the planar vibrating body  6 , and the planar vibrating body  6  is fixedly supported by hooked-claw shaped support beams (driving beams)  7  so as to be vibratable in the X-direction.  
         [0096]    On both right and left sides (as viewed in FIG. 5A) of the planar vibrating body  6 , movable-side comb electrodes  10  ( 10   a  and  10   b ) are formed outwardly in the X-direction, and fixed-side comb electrodes  11  ( 11   a  and  11   b ) are each extended from the fixing portion  64  so as to be interdigitated with the above-mentioned movable-side comb electrodes  10  with a gap interposed. These movable-side comb electrodes  10  and fixed-side comb electrodes  11  make up exciting means.  
         [0097]    The resonant element  1  of FIGS. 5A and 5B, similarly to the embodiment shown in FIG. 1, is provided with conductive layers  20  and  21 , and detecting electrode  40  which is excitation deflection detecting means for detecting the deflection of the weight  9  (planar vibrating body  6 ) in the Z-direction. By performing vibration adjustment in the same manner as vibration adjustment is performed for the embodiment of FIG. 1, the weight  9  (planar vibrating body  6 ) can be caused to be subjected to an ideal excitation vibration.  
         [0098]    As explained above, in accordance with the present invention, since the resonant element  1  is provided with excitation deflection inhibiting means, as well as the resonant with excitation deflection detecting means, the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction can be detected, and the deflection of the vibrating body in the Z-direction can be inhibited by the above-described excitation deflection inhibiting means, without the need for large-scale equipment for measuring the vibrating conditions of the vibrating body. Thereby, the vibrating body can be caused to be subjected to an ideal excitation vibration in the X-direction without deflection in the Z-direction, and hence it is easy to improve characteristics of the resonant element.  
         [0099]    In the resonant element constituting an angular velocity sensor, since it is possible to make the Z-direction vibration detecting means do double-duty as excitation vibration deflection detecting means, a resonant element having superior characteristics can be provided without a large change in design.  
         [0100]    In the excitation vibration deflection detecting means constituted of detecting means for the variation in the electrostatic capacity with respect to the vibrating body in response to the vibration thereof in the Z-direction, since the deflection of the vibrating body in the Z-direction can be detected with a high accuracy by a very simple construction, it is possible to inhibit more surely the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction, which provides a resonant element having more excellent characteristics.  
         [0101]    The invention is applicable to a vibrating body which is a planar vibrating body disposed so as to be opposed to the plane in the X-Y plane direction and supported by a fixed substrate so as to be vibratable in the X-direction. More specifically, since the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction has a significant adverse effect on characteristics of the resonant element, it is very effective to provide the above-described constructions characterizing the present invention.  
         [0102]    In accordance with the present invention, it is possible to perform a vibration adjustment for the vibrating body without the need for large-scale equipment, thereby reducing adjustment cost.  
         [0103]    Further, in accordance with the present invention, it is possible to further increase the accuracy of vibration adjustment for the vibrating body, and to easily perform a vibration adjustment for the vibrating body, which leads to a reduction in the time required for the vibration adjustment for the vibrating body.  
         [0104]    In the resonant element in accordance with the present invention wherein the resonant element constitutes an angular velocity sensor, and wherein the Z-direction vibration detecting means and the capacity-voltage converting means incorporated in the sensor device into which the angular velocity is to be built, also serve a function of vibration adjustment, since the vibration adjustment for the vibrator can be performed in the state wherein the vibrator has been built in the sensor device, it is possible to prevent the occurrence of the problem that the deflecting state of the vibrating body in the Z-direction after assembly becomes different from that at the time of vibration adjustment, and that the deflection of the vibrating body in the Z-direction during the excitation vibration thereof in the X-direction occurs despite the performed vibration adjustment.  
         [0105]    While preferred embodiments of the invention have been disclosed, various modes of carrying out the principles disclosed herein are contemplated as being within the scope of the following claims. Therefore, it is understood that the scope of the invention is not to be limited except as otherwise set forth in the claims.

Technology Category: g