Patent Publication Number: US-2010126271-A1

Title: Inertial velocity sensor signal processing circuit and inertial velocity sensor device including the same

Description:
TECHNICAL FIELD 
     The present invention relates to an inertial velocity sensor signal processing circuit used together with an inertial velocity sensor for detecting an inertial velocity, and an inertial velocity sensor device including the inertial velocity sensor signal processing circuit. 
     BACKGROUND ART 
     Inertial velocity sensors, such as angular velocity sensors and acceleration sensors, are used in a wide variety of fields including hand movement detection for digital cameras, attitude control for mobile units (such as aircrafts, automobiles, robots, and ships) and the guidance of missiles and spacecraft. In recent years, as a result of development in circuit microfabrication techniques, progress is being made in the digitalization of an inertial force detection circuit for detecting an inertial force based on a signal from a sensor device. An example inertial force detection circuit that is configured using a digital circuit is disclosed in Japanese Laid-Open Patent Application Publication No. 2002-188925 (Patent Document 1). In the technique disclosed in Patent Document 1, a signal according to an inertial force from a sensor device is converted into a digital signal by an analog/digital circuit. At the same time, a square-wave signal corresponding to an oscillation frequency is generated by an oscillator circuit, and by using the square-wave signal, an inertial force component is detected from the digital signal. The digitalization of the inertial force detection circuit can reduce influences of offset voltage variations, which are typical of analog signals, and enhance accurate detection of the inertial force. 
     As in the above, high detection accuracy is required in inertial velocity sensor devices, and at the same time, failure detection is also important. Japanese Patent No. 2728300 (Patent Document 2) discloses an inertial velocity sensor device having a built-in testing function for detecting failures. In this inertial velocity sensor device, a signal for detecting failures is generated based on an oscillation frequency of a drive circuit by using a demodulator; the output of the demodulator is integrated by an integrator; and the output of the integrator is monitored to detect a failure condition. 
     Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2002-188925 
     Patent Document 2: Japanese Patent No. 2728300 
     DISCLOSURE OF INVENTION 
     Problems to be solved by the invention 
     In the inertial velocity sensor device disclosed in Patent Document 2, however, an operation clock signal for detecting failures is generated based on a frequency of an inertial velocity sensor element, and thus, in the case where the inertial velocity sensor element is not in the normal operation, failure detection is impossible. 
     An object of the present invention is to provide a circuit capable of detecting an abnormal condition even if the inertial velocity sensor element is not in the normal operation. 
     Means for solving the problems 
     According to an aspect of the present invention, an inertial velocity sensor signal processing circuit is used together with an inertial velocity sensor element and includes a first signal processing circuit which operates with a first clock and a second signal processing circuit which operates with a second clock which does not synchronize with the first clock. In the above inertial velocity sensor signal processing circuit, the second signal processing circuit operates with the second clock which does not synchronize with the first clock, and therefore, the second signal processing circuit can operate even when the first clock is in an abnormal condition. 
     It is preferable that the first clock is supplied from a first oscillator circuit which operates based on a frequency of the inertial velocity sensor element. In the above inertial velocity sensor signal processing circuit, the second signal processing circuit can operate even when the inertial velocity sensor element is not in the normal operation. 
     It is preferable that the inertial velocity sensor signal processing circuit further includes a clock input terminal to which the second clock is supplied, wherein the second signal processing circuit receives the second clock supplied to the clock input terminal. Alternatively, the inertial velocity sensor signal processing circuit further includes a second oscillator circuit configured to supply the second clock, wherein the second signal processing circuit receives the second clock from the second oscillator circuit. 
     According to another aspect of the present invention, an inertial velocity sensor device includes the inertial velocity sensor signal processing circuit and the inertial velocity sensor element. 
     It is preferable that in the inertial velocity sensor device, the second signal processing circuit outputs an abnormal condition detection signal when the second signal processing circuit detects an abnormal condition of the inertial velocity sensor device. In the inertial velocity sensor device, the second signal processing circuit can detect an abnormal condition of the inertial velocity sensor device even when the inertial velocity sensor element is not in the normal operation. 
     It is preferable that the inertial velocity sensor device further includes an abnormal condition handling circuit controlled by the abnormal condition detection signal, wherein the abnormal condition handling circuit operates with the second clock. In the inertial velocity sensor circuit, the abnormal condition handling circuit can operate even when the inertial velocity sensor element is not in the normal operation. 
     EFFECTS OF THE INVENTION 
     As described in the above, the abnormal condition of an inertial velocity sensor device can be detected even if an inertial velocity sensor element is not in the normal operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a configuration of an inertial velocity sensor device according to Embodiment 1 of the present invention. 
         FIG. 2  shows an example configuration of an inertial velocity sensor element of  FIG. 1 . 
         FIG. 3  shows an example internal configuration of a drive circuit of  FIG. 1 . 
         FIG. 4  shows an example internal configuration of an inertial force detection circuit of  FIG. 1 . 
         FIG. 5  shows an example internal configuration of an abnormal condition detection circuit of  FIG. 1 . 
         FIG. 6  shows a configuration of an inertial velocity sensor device according to Embodiment 2 of the present invention. 
         FIG. 7  shows an example internal configuration of an inertial force detection circuit of  FIG. 6 . 
         FIG. 8  shows a modification of the inertial force detection circuit of  FIG. 6 . 
         FIG. 9  shows a configuration of an inertial velocity sensor device according to Embodiment 3 of the present invention. 
     
    
    
     DESCRIPTION OF CHARACTERS 
     
         
         
           
               11  inertial velocity sensor element 
               12  drive circuit 
               13  inertial force detection circuit 
               14  abnormal condition detection circuit 
               15  CR oscillator 
               101  monitor amplifier 
               102  automatic gain control (AGC) amplifier 
               103  drive amplifier 
               104  comparator 
               105  input amplifier 
               106  synchronous detector 
               107  low-pass filter 
               108  output amplifier 
               141 ,  142  comparators 
               143  NAND circuit 
               144  counter 
               21  PLL circuit 
               22  inertial force detection circuit 
               201  input amplifier 
               202  low-pass filter 
               203  analog/digital converter 
               204  synchronous detector 
               205  digital filter 
               206  output controller 
               31  temperature monitoring circuit 
               32  EEPROM 
               33  control circuit 
           
         
       
    
     EXAMPLE EMBODIMENT 
     Embodiments of the present invention will be described in detail below, with reference to the drawings. In the drawings, like reference characters have been used to designate identical or equivalent elements, and explanation thereof is not repeated. 
     Embodiment 1 
       FIG. 1  shows a configuration of an inertial velocity sensor device according to Embodiment 1 of the present invention. The inertial velocity sensor device includes an inertial velocity sensor element  11 , a drive circuit  12 , an inertial force detection circuit  13 , an abnormal condition detection circuit  14 , and a CR oscillator  15 . 
     &lt;Inertial Velocity Sensor&gt; 
     The inertial velocity sensor element  11  oscillates according to a frequency and an amplitude of a drive signal Sd from the drive circuit  12  to output an oscillation signal So corresponding to the oscillation, and outputs a sensor signal Si corresponding to an inertial force (e.g., Coriolis force) applied to the inertial velocity sensor element  11 . For example, as shown in  FIG. 2 , the inertial velocity sensor element  11  includes a tuning-fork body  11 F, a piezoelectric element  11 A for drive, a piezoelectric element  11 B for oscillation detection, and piezoelectric elements PDa and PDb for angular velocity detection. The tuning-fork body  11 F includes a pair of tuning-fork pieces each twisted to a right angle at a middle part, a connecting part that connects one end of one of the tuning-fork pieces with one end of the other tuning-fork piece, and a support pin provided to the connecting part to serve as a rotation axis. The piezoelectric element  11 A for drive oscillates the tuning-fork piece for drive according to the frequency and amplitude of the drive signal Sd from the drive circuit  12 . As a result, resonance occurs between the tuning-fork piece for drive and the tuning-fork piece for detection. By this tuning-fork oscillation, electric charge is generated in the piezoelectric element  11 B for oscillation detection (in other words, the oscillation signal So is generated). When an angular velocity is generated, electric charge according to Coriolis force is generated in the piezoelectric elements PDa and PDb for angular velocity detection (in other words, the sensor signal Si is generated). 
     &lt;Drive Circuit&gt; 
       FIG. 3  shows an example internal configuration of the drive circuit  12  of  FIG. 1 . The drive circuit  12  adjusts the frequency and amplitude of the drive signal Sd according to the oscillation signal So from the inertial velocity sensor element  11 . In the drive circuit  12 , a monitor amplifier  101  converts the oscillation signal So from the inertial velocity sensor element  11  into voltage, and an automatic gain control (AGC) amplifier  102  changes its gain such that the voltage supplied to a drive amplifier  103  has a constant value. The drive amplifier  103  controls the amplitude of the drive signal Sd according to an output of the automatic gain control amplifier  102 . By adjusting the drive signal Sd according to the oscillation signal So as in the above, a maximum oscillation amplitude and an oscillation frequency of the inertial velocity sensor element  11  are maintained constant. Further, a comparator  104  converts the oscillation signal So into a square-wave signal and outputs the square-wave signal as a clock signal CLK 1 . 
     &lt;Inertial Force Detection Circuit&gt; 
       FIG. 4  shows an internal configuration of the inertial force detection circuit  13  of  FIG. 1 . The inertial force detection circuit  13  extracts an inertial force component (an analog signal corresponding to an inertial force applied to the inertial velocity sensor element  11 ) from the sensor signal Si output from the inertial velocity sensor element  11 , using the clock signal CLK 1  from the drive circuit  12  as an analog detection signal. In the inertial force detection circuit  13 , an input amplifier  105  converts the sensor signal Si from the inertial velocity sensor element  11  into voltage, and a synchronous detector  106  extracts the inertial force component from an output of the input amplifier  105  using the analog detection signal (the clock signal CLK 1  from the drive circuit  12 ). A low-pass filter  107  allows only a low-frequency component of the analog signal extracted by the synchronous detector  106  to pass for the purpose of such as removing noise, and an output amplifier  108  amplifies an output of the low-pass filter  107  and outputs the amplified signal as an inertial force detection signal S 13  (analog value). 
     &lt;Abnormal Condition Detection Circuit&gt; 
     Turning back to  FIG. 1 , the abnormal condition detection circuit  14  determines whether the operating condition of the drive circuit  12  is normal or abnormal, based on a monitor signal M 12  for monitoring the operating condition of the drive circuit  12 . Further, the abnormal condition detection circuit  14  synchronizes with a clock signal CLK 2  from the CR oscillator  15  to measure a period in which the operating condition of the drive circuit  12  is abnormal (an abnormal condition period), and outputs an abnormal condition detection signal Sa when the abnormal condition period obtained by the measurement reaches an abnormal condition detection period (a predetermined period). Each of the drive circuit  12  and the inertial force detection circuit  13  performs an error handling on receipt of the abnormal condition detection signal Sa from the abnormal condition detection circuit  14 . 
     For example, in the case where the operating condition of the drive circuit  12  is monitored based on a direct-current voltage inside the automatic gain control amplifier  102  of the drive circuit  12 , the abnormal condition detection circuit  14  includes, as shown in  FIG. 5 , a window comparator which is composed of comparators  141  and  142  and a NAND circuit  143 , and a counter  144  which operates in synchronization with the clock signal CLK 2  from the CR oscillator  15 . Reference voltages REF 1  and REF 2  are for specifying a normal voltage range, and the reference voltage REF 1  is higher than the reference voltage REF 2 . The abnormal condition detection circuit  14  determines that the operating condition of the drive circuit  12  is abnormal if a voltage value of the monitor signal M 12  (a voltage value of the direct-current voltage inside the automatic gain control amplifier  102 ) is out of the normal voltage range specified by the reference voltages REF 1  and REF 2 . 
     As described in the above, the abnormal condition detection circuit  14  operates in synchronization with the clock signal CLK 2  from the CR oscillator  15  (e.g., a clock signal whose frequency is not based on a frequency of the inertial velocity sensor element  11 ), and not with a signal whose frequency is based on the frequency of the inertial velocity sensor element  11  (e.g., the clock signal CLK 1 ). Thus, the abnormal condition detection circuit  14  can detect the abnormal condition of the drive circuit  12  even when the inertial velocity sensor element  11  is not in the normal operation. 
     The abnormal condition detection circuit  14  may be configured such that it can detect not only an abnormal condition of the drive circuit  12  but also abnormal conditions of other parts of the inertial velocity sensor device (such as the inertial force detection circuit  13 ). 
     &lt;Error Handling&gt; 
     Now, the error handlings by the drive circuit  12  and the inertial force detection circuit  13  are described. 
     In the drive circuit  12 , the drive amplifier  103  gradually reduces the amplitude of the drive signal Sd on receipt of the abnormal condition detection signal Sa from the abnormal condition detection circuit  14 . This makes it possible to suppress abrupt variations in the drive signal Sd and prevent destruction of the inertial velocity sensor element  11 . The drive circuit  12  may be configured such that the drive amplifier  103  stops outputting the drive signal Sd when the abnormal condition detection signal Sa is output from the abnormal condition detection circuit  14 . 
     In the inertial force detection circuit  13 , the output amplifier  108  fixes a voltage value of the inertial force detection signal S 13  on receipt of the abnormal condition detection signal Sa from the abnormal condition detection circuit  14 . Alternatively, the output amplifier  108  gradually reduces the voltage value of the inertial force detection signal S 13  on receipt of the abnormal condition detection signal Sa from the abnormal condition detection circuit  14 . This makes it possible to suppress abrupt variations in the inertial force detection signal S 13 . The inertial force detection circuit  13  may be configured such that the output amplifier  108  stops outputting the inertial force detection signal S 13  when the abnormal condition detection signal Sa is output from the abnormal condition detection circuit  14 . 
     Embodiment 2 
       FIG. 6  shows a configuration of an inertial velocity sensor device according to Embodiment 2 of the present invention. This inertial velocity sensor device includes an inertial force detection circuit  23  in place of the inertial force detection circuit  13  shown in  FIG. 1 , and further includes a PLL circuit  21  which generates an operation clock CLK 3  by multiplying the clock signal CLK 1  output from the drive circuit  12 . The other parts of the configuration are the same as those in  FIG. 1 . 
     &lt;Inertial Force Detection Circuit&gt; 
       FIG. 7  shows an internal configuration of the inertial force detection circuit  23  of  FIG. 6 . The inertial force detection circuit  23  converts the sensor signal Si output from the inertial velocity sensor element  11  into a digital sensor signal, and then extracts an inertial force component (a digital signal corresponding to the inertial force applied to the inertial velocity sensor element  11 ) from the digital sensor signal, using a digital detection signal (a detection signal generated based on the operation clock CLK 3  output from the PLL circuit  21 ). In the inertial force detection circuit  23 , an analog/digital (A/D) converter  203 , a synchronous detector  204 , a digital filter  205 , and an output controller  206  operate in synchronization with the operation clock CLK 3  output from the PLL circuit  21 . 
     An input amplifier  201  converts the sensor signal Si output from the inertial velocity sensor element  11  into voltage, and a low-pass filter  202  allows only a low-frequency component of an output of the input amplifier  201  to pass for the purpose of such as removing noise. The analog/digital converter  203  carries out an analog/digital conversion of an output of the low-pass filter  202 , and thereby obtains a digital sensor signal. The synchronous detector  204  generates a digital detection signal based on the operation clock CLK 3 , and using the digital detection signal, extracts an inertial force component (a digital signal corresponding to an inertial force) from the digital sensor signal obtained by the analog/digital converter  203 . The digital filter  205  allows only a low-frequency component of the digital signal extracted by the synchronous detector  204  to pass for the purpose of removing noise components. The output controller  206  outputs an output of the digital filter  205  as an inertial force detection signal S 23  (digital value). Further, the output controller  206  gradually reduces the digital value indicated by the inertial force detection signal S 23 , on receipt of the abnormal condition detection signal Sa from the abnormal condition detection circuit  14 . This makes it possible to suppress abrupt variations in the inertial force detection signal S 23 . The inertial force detection circuit  23  may be configured such that the output controller  206  stops outputting the inertial force detection signal S 23  when the abnormal condition detection signal Sa is output from the abnormal condition detection circuit  14 . 
     In the signal processing device disclosed in Patent Document 1, a digital detection signal is generated based on a clock signal from an oscillator circuit, while in the inertial velocity sensor device according to the present embodiment, the digital detection signal is generated using the oscillation signal So output from the inertial velocity sensor element  11 . Digital detection signals in synchronization with the sensor signal Si can thus be easily generated, and alias and beat can be suppressed. 
     &lt;Modification of Inertial Force Detection Circuit&gt; 
     The inertial velocity sensor device of  FIG. 6  may include an inertial force detection circuit  23   a  of  FIG. 8  in place of the inertial force detection circuit  23 . The inertial force detection circuit  23   a  shown in  FIG. 8  extracts an inertial force component (an analog signal corresponding to an inertial force applied to the inertial velocity sensor element  11 ) from the sensor signal Si output from the inertial velocity sensor element  11 , using an analog detection signal (the clock signal CLK 1  from the drive circuit  12 ), and then converts the inertial force component into a digital signal. In the inertial force detection circuit  23   a , the analog/digital (A/D) converter  203 , the digital filter  205 , and the output controller  206  operate in synchronization with the operation clock CLK 3  from the PLL circuit  21 . The synchronous detector  204  extracts an inertial force component of the output of a low-pass filter  202  using the clock signal CLK 1  from the drive circuit  12 , and outputs the inertial force component to the analog/digital converter  203 . 
     Embodiment 3 
       FIG. 9  shows a configuration of an inertial velocity sensor device according to Embodiment 3 of the present invention. This inertial velocity sensor device includes a temperature monitoring circuit  31 , an EEPROM  32 , and a control circuit  33  in addition to the configuration shown in  FIG. 6 . The abnormal condition detection circuit  14  detects not only an abnormal condition of the drive circuit  12 , but also abnormal conditions of the PLL circuit  21 , the inertial force detection circuit  23 , the temperature monitoring circuit  31  and the EEPROM  32 . Here, the drive circuit  12 , the abnormal condition detection circuit  14 , the PLL circuit  21 , the inertial force detection circuit  23 , the temperature monitoring circuit  31 , and the control circuit  33  are included in the same semiconductor integrated circuit (or the same package). 
     &lt;Abnormal Condition Detection Circuit&gt; 
     The abnormal condition detection circuit  14  does not only receive the monitor signal M 12  for monitoring the operating condition of the drive circuit  12 , but also receives monitor signals M 21 , M 23 , M 31  and M 32  for monitoring the operating conditions of the PLL circuit  21 , the inertial force detection circuit  23 , the temperature monitoring circuit  31  and the EEPROM  32 . The abnormal condition detection circuit  14  determines whether the operating conditions of the drive circuit  12 , the PLL circuit  21 , the inertial force detection circuit  23 , the temperature monitoring circuit  31  and the EEPROM  32  are normal or abnormal based on the monitor signals M 12 , M 21 , M 23 , M 31  and M 32 . The abnormal condition detection circuit  14  synchronizes with the clock signal CLK 2  output from the CR oscillator  15  to measure a period in which the operating condition of the circuit is abnormal (an abnormal condition period), for each of the drive circuit  12 , the PLL circuit  21 , the inertial force detection circuit  23 , the temperature monitoring circuit  31  and the EEPROM  32 . Further, the abnormal condition detection circuit  14  outputs the abnormal condition detection signal Sa when the abnormal condition period of at least one of the drive circuit  12 , the PLL circuit  21 , the inertial force detection circuit  23 , the temperature monitoring circuit  31  and the EEPROM  32  reaches an abnormal condition detection period (a predetermined period). The abnormal condition detection circuit  14  may be configured to output the abnormal condition detection signal Sa based on the determination result of the operating conditions, without measuring the abnormal operation period. 
     &lt;Temperature Monitoring Circuit&gt; 
     The temperature monitoring circuit  31  measures a temperature of the semiconductor integrated circuit (or the package) and outputs the measurement result as a temperature monitoring signal S 31 . 
     &lt;EEPROM&gt; 
     The EEPROM  32  stores control information for controlling the operation of the drive circuit  12  (such as an amplification factor and an offset of the automatic gain control amplifier  102 ) and control information for controlling the operation of the inertial force detection circuit  23  (such as an amplification factor and an offset of the output controller  206 ). 
     &lt;Control Circuit&gt; 
     The control circuit  33  operates in synchronization with the clock signal CLK 2  output from the CR oscillator  15  and outputs control signals C 12  and C 23  for controlling the drive circuit  12  and the inertial force detection circuit  23  based on the temperature monitoring signal S 31  from the temperature monitoring circuit  31 , the control information stored in the EEPROM  32 , and the abnormal condition detection signal Sa from the abnormal condition detection circuit  14 . 
     For example, the control circuit  33  reads the control information from the EEPROM  32 , and based on the control information, controls parameters (such as an amplification factor and an offset) of each of the drive circuit  12  and the inertial force detection circuit  23 , thereby implementing normal operations of the drive circuit  12  and the inertial force detection circuit  23 . Further, the control circuit  33  determines that the semiconductor integrated circuit has an abnormal temperature when the temperature indicated by the monitoring signal S 31  exceeds a given temperature, and makes the drive circuit  12  and the inertial force detection circuit  23  perform error handlings. The control circuit  33  makes the drive circuit  12  and the inertial force detection circuit  23  perform error handlings, also when the control circuit  33  receives the abnormal condition detection signal Sa from the abnormal condition detection circuit  14 . 
     The control circuit  33  may be configured such that the control circuit  33  carries out reset processing when the temperature indicated by the monitoring signal S 31  exceeds a given temperature or when the abnormal condition detection signal Sa is output from the abnormal condition detection circuit  14 . In the reset processing, the control circuit  33  temporarily stops the operations of the drive circuit  12  and the inertial force detection circuit  23  and rereads the control information from the EEPROM  32  to reset the parameters of each of the drive circuit  12  and the inertial force detection circuit  23 . The above control enables a restart of normal operations of the drive circuit  12  and the inertial force detection circuit  23 . 
     As described in the above, the control circuit  33  operates in synchronization with the clock signal CLK 2  from the CR oscillator  15  (a clock signal whose frequency is not based on a frequency of the inertial velocity sensor element  11 ), and not with the signal whose frequency is based on a frequency of the inertial velocity sensor element  11  (e.g., the clock CLK 3 ). The control circuit  33  can therefore control the drive circuit  12  and the inertial force detection circuit  23  even when the inertial velocity sensor element  11  is not in the normal operation. 
     Moreover, inclusion of the drive circuit  12 , abnormal condition detection circuit  14 , PLL circuit  21 , inertial force detection circuit  23 , temperature monitoring circuit  31 , and control circuit  33  in the same semiconductor integrated circuit (or same package) eliminates the need for wiring on board and the need for interrupt control by a microcomputer. Further, placing the temperature monitoring circuit  31  and the abnormal condition detection circuit adjacent to each other can improve accuracy in detecting self-heating. 
     The inertial velocity sensor element  11  may also be included in the same semiconductor integrated circuit (or the same package) in which the drive circuit  12 , abnormal condition detection circuit  14 , PLL circuit  21 , inertial force detection circuit  23 , temperature monitoring circuit  31 , and control circuit  33  are included. In other words, the inertial velocity sensor element  11  and the signal processing circuits (drive circuit  12 , abnormal condition detection circuit  14 , PLL circuit  21 , inertial force detection circuit  23 , temperature monitoring circuit  31 , and control circuit  33 ) may be formed as different modules, or may be formed as SiP (System in Package) in which the inertial velocity sensor element  11  and the signal processing circuits are sealed in the same package, or as a module in which the inertial velocity sensor element  11  and the signal processing circuits are embedded together. 
     Same effects are obtained in the inertial velocity sensor device of  FIG. 9  even if the inertial force detection circuit  23  is replaced with the inertial force detection circuit shown in  FIG. 4  or  FIG. 8 . 
     Other Embodiments 
     Although the example in which the CR oscillator  15  is included in the inertial velocity sensor device is described in the above embodiments, the CR oscillator  15  may be provided outside the inertial velocity sensor device. Specifically, the inertial velocity sensor device may be provided with a clock input terminal, and the clock signal CLK 2  may be supplied to the abnormal condition detection circuit  14  and the control circuit  33  through the clock input terminal. 
     The shape of the inertial velocity sensor element  11  is not limited to a tuning-fork shape, but may be a regular triangle prism, square prism, ring and other shapes. The inertial velocity sensor element  11  may be composed of a plurality of inertial velocity sensor elements. 
     INDUSTRIAL APPLICABILITY 
     As described in the above, an inertial velocity sensor device of the present invention can detect an abnormal condition even if an inertial velocity sensor element is not in the normal operation, and thus, is suitable as a device for detecting an inertial force in mobile units (such as aircrafts, automobiles, robots, and ships), mobile phones, cameras, video game equipment and others.