Abstract:
The purpose of the present invention is to achieve accurate angular velocity detection even when an angular velocity detection sensor is set in an environment in which oscillation and electromagnetic noise have significant influence. Provided is an angular velocity detection device which has an oscillating body displaceable in first and second directions that are perpendicular to each other, and which detects, as an angular velocity, a displacement of the oscillating body in the second direction while the oscillating body is being oscillated in the first direction, wherein in accordance with a frequency change in a drive signal for oscillating the oscillating body in the first direction, the frequency of a servo signal for detecting the angular velocity from the quantity of displacement in the second direction is changed (see  FIG. 1 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an oscillation-type angular velocity sensor. More specifically, the present invention relates to an angular velocity sensor that reduces influences of change in resonance frequency of displacement signal of oscillating body. 
       BACKGROUND ART 
       [0002]    Patent Literatures 1, 2, and 3 listed below, for example, disclose devices regarding methods for controlling oscillating-type angular velocity sensors with high precision. 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: JP Patent No. 3729191 
         [0004]    Patent Literature 2: JP Patent Publication (Kokai) No. 2000-105125 A 
         [0005]    Patent Literature 3: JP Patent Publication (Kokai) No. H08-007070 A (1996) 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    In an antiskid brake system for securing safety of running automobiles, it is required to keep the precision of sensors detecting angular velocities caused by skids or turnings on compacted snow roads or frozen roads at high level. In terms of such technical problems, Patent Literature 1 discloses an example where angular velocities are detected by servo-control. Patent Literature 2 discloses an example where an oscillating body is driven at a resonant frequency by frequency adjusting control. Patent Literature 3 discloses an example where sensor data for multiple cycles is sampled to perform digital control. 
         [0007]    However, if an angular velocity sensor is placed in an environment, such as an engine room, where the temperature varies within wide range and vibration or electromagnetic noise has significant effects, further techniques are required for keeping precision of sensors in addition to the techniques mentioned above. 
         [0008]    An objective of the present invention is to achieve angular velocity detection with high precision even if the angular velocity detection sensor is placed in an environment where vibration or electromagnetic noise has significant effects. 
       Solution to Problem 
       [0009]    The angular velocity detection device according to the present invention comprises an oscillating body displaceable in a first and a second direction perpendicular to each other, the angular velocity detection device detecting, as an angular velocity, a displacement of the oscillating body in the second direction when the oscillating body is oscillating in the first direction, wherein the angular velocity detection device changes a frequency of a servo signal for detecting an angular velocity based on a displacement amount of the oscillating body in the second direction in accordance with a change in frequency of a drive signal that oscillates the oscillating body in the first direction. 
       Advantageous Effects of Invention 
       [0010]    With an angular velocity detection device according to the present invention, angular velocity detection with high precision is achieved even if the angular velocity detection sensor is placed in an environment where vibration or electromagnetic noise has significant effects. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]    [ FIG. 1 ]  FIG. 1  is a block diagram of a sensor control circuit according to a first example. 
           [0012]    [ FIG. 2 ]  FIG. 2  is a diagram showing a frequency-magnitude characteristic in an oscillation axis direction and in a detection axis direction. 
           [0013]    [ FIG. 3 ]  FIG. 3  is a timing chart of a drive frequency adjustment unit of the first example. 
           [0014]    [ FIG. 4 ]  FIG. 4  is a time chart showing a servo-control of the first example. 
           [0015]    [ FIG. 5 ]  FIG. 5  is a time chart showing a change in frequency of a servo signal of the first example. 
           [0016]    [ FIG. 6 ]  FIG. 6  is a block diagram of a control circuit of an angular velocity sensor using a digital signal processor of a second example. 
           [0017]    [ FIG. 7 ]  FIG. 7  is a block diagram of an antiskid brake system of an example. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    Hereinafter, examples of the present invention will be described using  FIGS. 1-7 . 
         [0019]    Firstly, a first example will be described using  FIGS. 1-5 . 
         [0020]    An angular velocity detection element  101  of the present example comprises : an oscillator  102  that has a certain mass and that oscillates in an oscillation axis direction at an oscillation frequency (resonant frequency) fd; a fixed electrode (external force application means)  103  that exerts an electrostatic force for adjusting the oscillation magnitude and the oscillation frequency of the oscillator  102  in the oscillation direction; fixed electrodes (displacement detection means)  104  and  105  that detect the oscillation magnitude and the oscillation frequency of the oscillator  102  according to change in capacitance; fixed electrodes (displacement detection means)  106  and  107  that detect, according to change in capacitance, displacements of the oscillator  102  in the direction perpendicular to the oscillation axis caused by the Coriolis force due to application of angular velocity; and fixed electrodes (servo signal application means)  108  and  109  that exert electrostatic force to the oscillator  102  so that the Coriolis force to the oscillator  102  is canceled. 
         [0021]    The angular velocity detection device further comprises: a capacitance detector  110  that detects displacements of the angular velocity detection element  101  in the oscillation direction by detecting the difference between the capacitance between the angular velocity detection element  101  and the fixed electrode  104  and the capacitance between the angular velocity detection element  101  and the fixed electrode  105 ; an AD convertor that converts the output from the capacitance detector  110  into digital signals; a synchronous detector  131  including a multiplier  113  that performs synchronous detection using a detection signal Φ1; and a drive frequency adjustment unit  151  including an integrator  118  that adds the output from the synchronous detector  131  at a constant interval. 
         [0022]    The angular velocity detection device further comprises a drive magnitude adjustment unit  152  including: a subtractor  117  that calculates the difference between the output from the synchronous detector  131  and a preconfigured value in a magnitude reference value register  125 ; and an integrator  119  that adds the output from the subtractor  117  at a constant interval. 
         [0023]    The angular velocity detection device further comprises: a capacitance detector  112  that detects displacements of the oscillator  102  due to the Coriolis force by detecting the difference between the capacitance between the oscillator  102  and the fixed electrode  106  and the capacitance between the oscillator  102  and the fixed electrode  107 , and that converts the displacements into digital signals; an AD convertor  146  that converts the output from the capacitance detector  112  into digital signals; a multiplier  115  for performing synchronous detection using a detection signal Φ2 which phase is delayed by a phase adjuster  116  by 90 degree; and an angular velocity detection unit  153  including an integrator  120  that adds the output from the multiplier  115  at a constant interval. 
         [0024]    The angular velocity detection device further comprises a servo signal generator  154  including a multiplier  121  that multiplies the output from the integrator  120  with the detection signal Φ1. 
         [0025]    The angular velocity detection device further comprises: a VCO (voltage control oscillator)  122  that outputs a base clock in accordance with the output from the integrator  118 ; and a clock generator  123  that performs frequency division with respect to the output from the VCO  122  to output the drive signal and the detection signal Φ1. 
         [0026]    The angular velocity detection device further comprises: a characteristics corrector  139  that corrects the output from the angular velocity sensor in accordance with the output from the temperature sensor  137 ; a diagnosis unit  142  that performs self-diagnosis with respect to each of the functions in the sensor; and a communication unit  143  that outputs the sensor output to external devices. 
         [0027]    Next, the operation will be described.  FIG. 2  shows frequency characteristics of the angular velocity detection element  101  in the oscillation axis direction and in the detection axis direction.  FIG. 2  shows that the oscillation magnitude in the oscillation axis direction reaches the peak at the resonant frequency and decreases rapidly from the peak.  FIG. 2  also shows that the magnitude becomes significantly small when driven at frequencies other than the resonant frequency and the magnitude in the detection axis direction also decreases simultaneously. The frequency of displacement oscillation in the detection axis direction due to generation of angular velocity matches with the oscillation frequency in the oscillation axis direction. Therefore, in order to increase the magnitude in the detection axis direction, it is necessary to constantly drive the oscillation axis direction at the resonant frequency. 
         [0028]    For the reason stated above, the drive frequency adjustment unit  151  adjusts the frequency of the drive signal so that the oscillation of the oscillator  102  in the drive direction becomes resonated. The fixed electrodes  104  and  105  detect the displacement of the angular velocity detection element  101  due to the drive signal and then input the displacement into the capacitance detector  110 . The synchronous detector  131  performs synchronous detection with respect to the displacement signal of the oscillator acquired through the capacitance detector  110  and the AD convertor  145  to detect the oscillation displacement in the oscillation axis direction. The integrator  118  integrates the signal acquired by the synchronous detector  131 . 
         [0029]      FIG. 3  shows a time chart of the drive frequency adjustment unit  151 . The drive signal and the displacement signal have a characteristic that their phases are different from each other by 90 degree in resonant state, namely when fv (drive signal frequency)=fd (resonant frequency in the oscillation axis direction). Therefore, when performing synchronous detection with respect to the displacement signal using the detection signal Φ1, the drive signal and the displacement signal are resonated if the outputs of the synchronous detection are mutually canceled. At that time, the output from the integrator  118  converges into a constant value. The signal acquired by the integrator  118  is outputted into the VCO  122 . The clock generator  123  generates the drive signal. As shown in the time chart of  FIG. 3 , the base clock outputted from the VCO is controlled so that its frequency is constantly an integer multiple of that of the drive signal. 
         [0030]    Next, the drive magnitude adjustment unit  152  adjusts the magnitude of the drive signal so that the magnitude of the oscillation of the oscillator  102  in the drive direction matches with the value in the magnitude reference value register  125 . The synchronous detector  131  performs synchronous detection with respect to the displacement signal of the oscillator acquired through the AD convertor  145  to detect the oscillation displacement in the oscillation axis direction. The subtractor  117  calculates the difference between the displacement and the target value and the integrator  119  integrates the difference. When the output from the synchronous detector  131  matches with the magnitude reference value register  125 , the difference becomes zero. As a result, the output from the integrator  119  converges into a constant value. The signal acquired by the integrator  119  is outputted into the multiplier  124 . The multiplier  124  multiplies the output from the clock generator  123  with the output from the drive magnitude adjustment unit  152  to generate the drive signal. 
         [0031]      FIG. 4  shows a time chart of the servo control. The angular velocity detector  153  detects the displacement of the oscillator  102  in the detection axis direction (perpendicular to the oscillation axis) due to the Coriolis force using the fixed electrodes  106 ,  107  and the capacitance detector  112 . The synchronous detector  132  performs synchronous detection with respect to the detected displacement signal of the oscillator acquired through the capacitance detector  112  and the AD convertor  146 , thereby detecting the oscillation displacement perpendicular to the oscillation axis. The integrator  120  integrates the signal acquired by the synchronous detector  132 . The servo signal generator  154  applies an electric voltage to the fixed electrodes  108  and  109  to cancel the displacement by the Coriolis force to the oscillator using the electrostatic force generated between the electrodes and the oscillator. Namely, a servo control is performed in which a signal is fed back to the sensor such that the displacement of the oscillator  102  due to the Coriolis force in the direction perpendicular to the oscillation axis becomes zero. Specifically, the multiplier  121  multiplies the Φ1 to generate a detection servo signal in order to feed back the signal acquired by the integrator  120  into the oscillator  102 . The detection servo signal is applied to the fixed electrode  108  of the oscillator  102  and the inverted detection servo signal inverted by the polarity reverser  126  is applied to the fixed electrode  109 , thereby canceling the detected displacement oscillation. The output from the integrator  120  when the displacement oscillation is canceled is outputted as the angular velocity detection signal. 
         [0032]      FIG. 5  is a time chart of the servo signal generator  154 . The detection servo signal is generated from the Φ1 outputted from the clock generator  123 , similarly to the drive signal. Therefore, if the resonant frequency of the oscillator  102  is fd, the drive frequency adjustment unit  151  adjusts the frequency of the output Φ1 of the clock generator  123  as fd and the frequency of the drive signal becomes fd. When a displacement occurs due to angular velocity in this state, since the frequency of the displacement oscillation in the detection axis direction is fd, the detected displacement can be suppressed by feeding back the detection servo signal of frequency fd. On the other hand, the resonant frequency of the oscillator may be f1 due to manufacturing tolerance, or the resonant frequency fd at normal temperature may change into f1 due to increase of peripheral temperature. In such cases, the drive frequency adjustment unit  151  adjusts the frequency of the output Φ1 of the clock generator  123  as f1 and the frequency of the drive signal becomes f1. When a displacement occurs due to angular velocity in this state, since the frequency of the displacement oscillation in the detection axis direction is f1, the detected displacement can be suppressed by feeding back the detection servo signal of frequency f1. 
         [0033]    The characteristics corrector  139  performs, with respect to the angular velocity output and the acceleration output in two directions, temperature correction and high-frequency noise reduction using a low-pass filter in accordance with the detection value of the temperature sensor  137 . The diagnosis unit  142  performs diagnosis for driving function and angular velocity detecting function regarding angular velocity detection. The communication unit  143  sends, to external devices, the three sensor outputs in which the characteristics corrector  139  corrects the characteristics and the diagnosis result by the diagnosis unit  142 . 
         [0034]    As described above, the displacement oscillation of the oscillator in the detection axis direction can be suppressed with high precision by controlling the frequency of the servo signal so that it matches with the resonant frequency of the oscillator  102  constantly. Thus the angular velocity can constantly be detected with high precision even under influences of vibration or electromagnetic noise. Further, it is not necessary to adjust individual tolerances of resonant frequency of the detection element when shipping and the individual tolerances can be automatically adjusted. 
         [0035]    Next, a second example will be described using  FIG. 6 . 
         [0036]    The sensor control in this example is implemented using two DSPs (Digital Signal Processor), namely DSP-A  204  and DSP-B  205  and using control programs stored in two ROMs (Read Only Memory), namely ROM-A  202  and ROM-B  203 . The VCO  122  is a means for generating clocks at a frequency of integer multiple of the resonant frequency of the angular velocity detection element  101  in the oscillation axis direction, as described in the example of  FIG. 1 . An address counter  201  is a counter that simply counts up according to the base clock inputted from the VCO  122 . 
         [0037]    The DSP-A  204  performs processes of the synchronous detector  131 , the drive frequency adjustment unit  151 , the drive magnitude adjustment unit  152 , the angular velocity detector  153 , and the servo signal generator  154  described in  FIG. 1 . The DSP-B  205  performs processes of the characteristics corrector  138  and the diagnosis unit  142 . A PROM  207  is a memory storing coefficients of integration and coefficients of characteristics correction. A RAM  207  is a temporal storing buffer to pass the result calculated by the DSP-A  204  to the DSP-B  205 . 
         [0038]    Next, the operation will be described. The two DSPs, namely the DSP-A  204  and the DSP-B  205  operate in accordance with the base clock outputted from the VCO  122 . The DSP-A  204  repeatedly performs, at the frequency four times as high as the resonant frequency, the processes from the synchronous detector  131  to the servo signal generator  154  stored from the 0-th address to the last address (e.g. 255-th address) of the ROM-A  202  as one cycle. The DSP-B  205  repeatedly performs, at the one-fourth frequency of the resonant frequency, the processes of the characteristics corrector  139  and the diagnosis unit  142  stored from the 0-th address to the last address (e.g. 4095-th address) of the ROM-B  203  as one cycle. Therefore, during the DSP-B  205  performs its one cycle process, the DSP-A  204  performs 16 cycles of its one cycle. The two ROMs, namely the ROM-A  202  and the ROM-B  203  are configured such that no effective address skipping occurs such as process branch of conditional judgment or subroutine call and such that the 0-th address to the last address are simply repeated. Therefore, as shown in the time chart of  FIG. 2 , when the resonant frequency changes the output from the VCO  122  follows the change. Thus the base clocks inputted into the DSP-A  204  and the DSP-B  205  change. Accordingly, the process repetition frequency of the DSP-A  204  is constantly kept as four times as high as the resonant frequency and the process repetition frequency of the DSP-B  205  is constantly kept as one-fourth of the resonant frequency. As a result, the servo signal outputted from the servo signal generator  154  can be controlled to constantly match with the resonant frequency of the oscillator  102  in the oscillation direction. 
         [0039]    This achieves adjusting the frequency of the drive signal in the oscillation axis direction and the frequency of the servo signal in the detection axis direction so that they match with the resonant frequency in accordance with the change in the resonant frequency of the detection element. Thus the displacement oscillation in the detection axis direction caused at the same frequency as that of the oscillation in the oscillation axis direction can be suppressed, thereby achieving angular velocity detection with high precision even under influences of vibration or electromagnetic noise. 
         [0040]      FIG. 7  is a system configuration example of an antiskid brake system equipping the present invention. A control unit  1  is a function that detects signs of skids or turnings of the running car using multiple sensors to control the brake of the car so that the skids or turnings are suppressed. An angular velocity sensor  11  is a sensor that detects angular velocities caused when turning of the running car occurs. An acceleration sensor  12  is a sensor that detects the velocity of the running car caused when skids of the running car occurs. A car speed sensor  13  is a sensor that detects the speed of the running car. A rudder angle sensor  14  is a sensor that detects the angle of the handle of the car. An ECU  10  is an engine control unit (hereinafter, referred to as ECU) that keeps the posture of the car according to the outputs from the above-mentioned multiple sensors. A hydraulic pressure unit  2  is a function that controls the brake pressure of the four wheels via hydraulic pressure in accordance with the control by the ECU  10 . A brake device  3  is a function that applies brake force by the friction between a brake disc  6  and a brake pad  5  of a wheel  4  via hydraulic pressure. The above-mentioned system is placed near the engine of the car. Thus the operating environment is within high temperature from −40 Celsius degree to +125 Celsius degree. If the angular velocity sensor  11  is equipped in the control unit  1  along with the ECU  10 , the resonant frequency of the detection element of the angular velocity sensor  11  fluctuates due to the wide range temperature variation. If the present invention is applied in the above-stated environment, the drive frequency and the frequency of the detection servo signal can be controlled to match with the fluctuated resonant frequency, thereby acquiring precise angular velocity outputs. 
       REFERENCE SIGNS LIST 
       [0041]      101 : angular velocity detection element 
         [0042]      102 : oscillator 
         [0043]      103 : fixed electrode (external force application means) 
         [0044]      104 ,  105 ,  106 ,  107 : fixed electrode (displacement detection means) 
         [0045]      108 ,  109 : fixed electrode (servo signal application means) 
         [0046]      110 ,  112 : capacitance detector 
         [0047]      113 ,  115 ,  121 ,  124 : multiplier 
         [0048]      116 : phase adjuster 
         [0049]      117 : subtractor 
         [0050]      118 ,  119 ,  120 : integrator 
         [0051]      122 : VCO (Voltage Control Oscillator) 
         [0052]      123 : clock generator 
         [0053]      125 : magnitude reference value register 
         [0054]      137 : temperature sensor 
         [0055]      138 ,  145 ,  146 : AD converter 
         [0056]      139 : characteristics corrector 
         [0057]      142 : diagnosis unit 
         [0058]      143 : communication unit 
         [0059]      147 : DA converter 
         [0060]      151 : drive frequency adjustment unit 
         [0061]      152 : drive magnitude adjustment unit 
         [0062]      153 : angular velocity detector 
         [0063]      154 : servo signal generator 
         [0064]      201 : address counter 
         [0065]      202 : ROM-A 
         [0066]      203 : ROM-B 
         [0067]      204 : DSP-A 
         [0068]      205 : DSP-B 
         [0069]      206 : PROM 
         [0070]      207 : RAM 
         [0071]      301 ,  302 ,  303 ,  304 : register