Abstract:
The present invention aims to present an angular velocity sensor having a self diagnosis function. An angular velocity sensor of the present invention includes a driving part for stably vibrating a driving part of a sensor element having a driver part and a detector part for detecting an angular velocity and detection means for detecting the angular velocity of the sensor element and obtains a self diagnosis signal for a malfunction by detecting a mechanical coupling signal obtained at the detection means.

Description:
This is a divisional application of Ser. No. 08/776,443, filed Apr. 17, 1997, now U.S. Pat. No. 5,939,630, which is a 371 of PCT/JP96/01445, filed May 29, 1996. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an angular velocity sensor having a self diagnosis function. 
     BACKGROUND OF THE INVENTION 
     A conventional tuning fork type, angular velocity sensor has detector plates at the top of two driver plates of the tuning fork type driving part facing in the orthogonal direction. When an angular velocity is applied at a continuous driving state of the driving part, the angular velocity is detected by the output of the detector plates vibrating in opposite direction to each other corresponding to the applied angular velocity. 
     In an angular velocity sensor in accordance with the prior art, a tightly sealed space is formed by a lid  2 , which is made of resin. Lid  2  is attached at an aperture of a case  1 , also made of resin, of which one end is open, as shown in FIG.  18 . 
     Inside the tightly sealed space, a circuit board  3  and a metallic weight plate  4  are contained. Supporting pins  5  are attached at four corners inside the case  1  and weight plate  4  and circuit board  3  are elastically supported and fixed by the supporting pins  5 . Dampers  6  made of rubber are attached at the four corners of weight plate  4  for the elastic support. Supporting legs  7  made of resin are put between damper  6  and circuit board  3 . Supporting pins  5  are crashed at the tips toward the circuit board  3  side after penetrating dampers  6 , supporting legs  7  and circuit board  3 . Thus, circuit board  3  and weight plate  4  are elastically supported and fixed. A metallic supporting pin  8  is inserted and fixed vertically to weight plate  4 , on the circuit board  3  side, as shown in FIG.  19 . One end of a metallic, supporting pin  9 , is inserted, is fixed to supporting pin  8 , and is parallel to weight plate  4 . The diameter of supporting pin  9  is about one fifth of the diameter of supporting pin  8 . Furthermore supporting pin  9  is made of metallic material having elasticity such as a piano wire, wherein the other end of supporting pin  9  fixed by soldering to a metal plate  10 . 
     One end of each metallic driver plates  11  and  12 , facing other across supporting pins  8  and  9 , is fixed to each side of metal plate  10 . Plate-shaped piezoelectric elements  11   a  and  12   a  are fixed on the surfaces of metallic driver plates  11  and  12 , respectively. In this way, the tuning fork type driving part is formed. The other ends of driver plates  11  and  12  are twisted orthogonally so that piezoelectric elements  11   a  and  12   a  and other plate-shaped piezoelectric elements  13   a  and  14   a  are fixed on detector plates  13  and  14 , as shown in FIG.  19 . In this way, the detector part is formed. A sensor element is composed of the driver part and the detector part. 
     There is a problem of a usual angular velocity sensor however. Namely, the usual sensor has no ability to judge detected information, drawn to a malfunction of the components, as such, nor the ability to send such information, judged to be a malfunction of the components, to the outside. 
     The present invention aims to be able to detect, from the outside, the state in which the sensor can not perform a correct detection resulting from partial damage, thereby providing a highly reliable angular velocity sensor. 
     SUMMARY OF THE INVENTION 
     To achieve the purpose, an angular velocity sensor of the present invention includes drive means including a sensor element having a driver part and a detector part for detecting an angular velocity, a driver circuit for supplying a driving signal to the driving part of the sensor element and a monitor circuit to which a monitor signal is supplied from the sensor element and stably driving and vibrating the driver part of the sensor element by applying the output of the monitor circuit to the driver circuit through an AGC (automatic gain control) circuit, detection means including a charging amplifier to which an output of the detector part of the sensor element is supplied and a synchronous detector to which an output of the charging amplifier is supplied through a band pass filter and detecting an output of the band pass filter synchronizing with a driving signal from the drive means and outputting an angular velocity signal, and self diagnosis means receiving a mechanical coupling signal obtained from the detection means other than an angular velocity signal detecting abnormality of the sensor element and outputting a self diagnosis signal. 
     According to the above composition, by making the mechanical coupling signal always obtained from the detection, means a signal for self diagnosis because of its composition, whether the angular velocity signal is in a state which can perform a normal detection can be detected or not and because the mechanical coupling signal surely generates, it is unnecessary to independently provide means for generating the mechanical coupling signal arid not only the composition is very simple and can be highly reliable for self diagnosis but also it is possible to know the timing which the characteristic becomes stable after the sensor start to work and to utilize an sensor output more early. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an angular velocity sensor in accordance with a first exemplary embodiment of the present invention. 
     FIG. 2 shows waveforms at various points of the angular velocity sensor. 
     FIG. 3 is a block diagram of an angular velocity sensor in accordance with a second exemplary embodiment of the present invention. 
     FIG. 4 shows waveforms at various points of the angular velocity sensor. 
     FIG. 5 is a block diagram of an angular velocity sensor in accordance with a third exemplary embodiment of the present invention. 
     FIG. 6 shows waveforms at various points of the angular velocity sensor. 
     FIG. 7 is a block diagram of an angular velocity sensor in accordance with a fourth exemplary embodiment of the present invention. 
     FIG. 8 shows waveforms at various points of the angular velocity sensor. 
     FIG. 9 is a block diagram of an angular velocity sensor in accordance with a fifth exemplary embodiment of the present invention. 
     FIG. 10 shows waveforms at various points of the angular velocity sensor. 
     FIG.  11 ( a ) is an expanded squint view of an essential part of the angular velocity sensor. 
     FIG.  11 ( b ) is a cross sectional view of the essential part of the angular velocity sensor. 
     FIG.  11 ( c ) is an equivalent circuit diagram of the angular velocity sensor. 
     FIG. 12 is a circuit diagram showing a circuit configuration of the principal part of the angular velocity sensor. 
     FIG. 13 is a block diagram of an angular velocity sensor in accordance with a sixth exemplary embodiment of the present invention. 
     FIG. 14 is a circuit diagram of the essential part of the angular velocity sensor. 
     FIG. 15 shows waveforms at various points of the angular velocity sensor. 
     FIG. 16 is a block diagram of an angular velocity sensor in accordance with a seventh exemplary embodiment of the present invention. 
     FIG. 17 shows waveforms at various points of the angular velocity sensor. 
     FIG. 18 is a squint view for assembling an essential part of an angular velocity sensor in accordance with the prior art. 
     FIG. 19 is an expanded squint view of an essential part of the angular velocity sensor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Exemplary Embodiment 
     FIG. 1 is a circuit diagram of an angular velocity sensor of an angular velocity sensor in accordance with a first exemplary embodiment of the present invention. An alternating signal of about 1 Vp-p and 1.5 kHz is applied to a piezoelectric element  11   a  of a driver plate  11  as a sensor element from a driver circuit. Accordingly, driver plates  11  and  12  start a tuning fork vibration inward and outward against a supporting pin  9  as a center. A voltage proportional to the applied signal is induced at a piezoelectric element  12   a  of a driver plate  12  by a tuning fork vibration and becomes a monitor signal A shown as waveform A in FIG. 12 at point A in FIG. 1, after passing a current amplifier  16  and a band pass filter  17 . This signal is fed back to a driver circuit  15  through a full wave rectifier  18  and an AGC circuit  19  and thus a driving signal is automatically controlled in its amplitude. 
     In the detector part, when piezoelectric elements  13   a  and  14   a  detect an angular velocity, both piezoelectric elements  13   a  and  14   a  output angular velocity signals of +Q. These angular velocity signals are shown in FIG. 2 as waveforms B and C. These angular velocity signals are then synthesized at point D, shown in FIG. 1, thus becoming an angular velocity signal shown in FIG. 2 as waveform D. Angular velocity signal D is outputted from an output terminal  24  passing through a charging amplifier  20 , a band pass filter  21 , a synchronous detector  22  and a low pass filter  23 . The angular velocity signals at points E, F and G shown in FIG. 1 are shown in FIG. 2 as waveforms E, F and G, respectively. 
     In the exemplary embodiment, although detector plates  13  and  14  have to be set orthogonally against driver plates  11  and  12 , it is essentially difficult to put them in true orthogonal directions and moreover it is impossible to make piezoelectric elements  13   a  and  14   a  quite the same in size and attaching method. As a result, piezoelectric elements  13   a  and  14   a  always generate mechanical coupling signals shown in FIG. 2 as waveform B and C other than the angular velocity signals described above. In this case, piezoelectric elements  13   a  and  14   a  are pasted on the same side surfaces of detector plates  13  and  14  and the centers of gravity of detector plates  13  and  14  deviate a little toward the pasted sides of piezoelectric elements  13   a  and  14   a . Therefore, when driver plates  11  and  12  make a tuning fork vibration, for example when they open outward, they open leaning toward the sides of piezoelectric elements  13   a  and  14   a . Accordingly, mechanical coupling signals generated at piezoelectric elements  13   a  and  14   a  are in a reciprocal phase as shown in FIG. 2 as waveforms B and C and when the mechanical coupling signals are synthesized at point D shown in FIG. 1, the synthesized mechanical coupling signal becomes small. The synthesized mechanical coupling signal is amplified at a charging amplifier  20  and an amplifier  15 , rectified at a rectifier  27  and then the signal level is judged at a judge circuit  28  and the judged result is outputted from a signal output terminal  29 . The signals at points H, I and J shown in FIG,  1  are shown in FIG. 2 as waveforms H, I and J, respectively. When signal I outputted from filter  27  is between level a and level b, the output of judge circuit  28  is in a low level as shown in FIG. 2 as waveform J and is outputted from terminal  29 . 
     In the case in which, for example, detector plate  14  shown in FIG. 1 is damaged or its lead wire is broken, both the angular velocity signal and the mechanical coupling signal from piezoelectric element  14   a  become zero after malfunction, as shown in FIG. 2 as waveform C. As a result, only a mechanical coupling signal from piezoelectric element  13   a  appears at point D shown in FIG.  1  and it becomes a much larger mechanical coupling signal than before. Therefore, the output of filter  27  becomes larger than level a shown in waveform I of FIG. 2 and a high level signal is outputted from judge circuit  28  as shown in FIG. 2 as waveform J. When both detector plates  13  and  14  are damaged or both lead wires are broken, the output of filter  27  becomes smaller than level b shown in waveform I of FIG. 2 and a high level signal is also outputted from judge circuit  28  as shown in FIG. 2 as waveform J. When such a high level signal is outputted, information that the angular velocity sensor is malfunctioning is transmitted. 
     Second Exemplary Embodiment 
     FIG. 3 is a circuit diagram of an angular velocity sensor in accordance with a second exemplary embodiment of the present invention. In this exemplary embodiment, a synchronous detector  30  is inserted between amplifier  25  and filter  27 . A synchronous detection is executed, by using a feedback signal from the feedback circuit, for a driving signal. Such a driving signal is a phase shifted signal from the signal of point A at phase shifter  31  shown in FIG.  3 . In other words, because the mechanical coupling signal flowing in amplifier  25  contains an angular velocity signal, the level of the mechanical coupling signal is brought close to a correct value by canceling the angular velocity signal. The signal shown in FIG. 4 as waveform A flowing at point A shown in FIG. 3 is delayed by 90 degrees at phase shifter  31 . If the output from amplifier  25  is detected synchronized with a signal H delayed by 90 degrees (shown in FIG. 4 as waveform H), the angular velocity signal is canceled as shown in FIG. 4 as waveform H and it is possible to bring the mechanical coupling signal level inputted to filter  27  close to a correct value. 
     Third Exemplary Embodiment 
     FIG. 5 is a circuit diagram of an angular velocity sensor in accordance with a third exemplary embodiment of the present invention. In this exemplary embodiment, when the mechanical coupling signals outputted from piezoelectric elements  13   a  and  14   a  are added at point D, shown in FIG. 5, the sum is made zero as an initial setting. While the sums are not zero in the first and second exemplary embodiments, in the third exemplary embodiment, the sum of the mechanical coupling signals outputted from piezoelectric elements  13   a  and  14   a  is made zero by trimming either detector plate  13  or  14  at the initial setting. It is shown in FIG. 6 as waveform D. For example, at a normal state before a malfunction such as a damage of detector  14  or a break of lead wire, no mechanical coupling signal generates at point D shown in FIG.  5 . However, after the malfunction, the mechanical coupling signal from piezoelectric element  14   a  is hard to generate and the mechanical coupling signal appears at point D, as shown in FIG. 6 as waveform D. As a result, the output of judge circuit  28  is a high level at the malfunction as shown in FIG. 6 as waveform J. A signal informing the angular velocity sensor&#39;s malfunction is then outputted from signal output terminal  29  through a logical sum circuit  32 , as shown in FIG. 6 as waveform L. In this exemplary embodiment, A driving signal for feedback, that is an output of full wave rectifier  18 , is supplied to togic sum circuit  32  through judge circuit  33 . It aims to be able to inform the malfunction from signal output terminal  29 , even when driver plates  11  and  12  are not driven. Therefore, the driving signal is made to be supplied to logical sum circuit  32  through judge circuit  33 . Judge circuit  33  outputs a high level when the feedback signal is zero because driver plates  11  and  12  are not driven and outputs a signal informing the malfunction from signal output terminal  29  through logical sum circuit  32 . 
     In the case of a composition to input the output of charging amplifier  20  to amplifier  25  as a self diagnosis means as shown in the first exemplary embodiment, in the second and the third exemplary embodiments, when a signal exceeding an input range of synchronous detector  22  is inputted from band pass filter  21 , the output signal at output terminal  24  sometimes varies although no angular velocity signal is added. In this case, it is desirable to change to input the output signal of band pass filter  21  to amplifier  25 , to set to detect saturation of synchronous detector  22  as a criterion for judging and to match a time constant of filter  27  with a time constant of low pass filter  23 . 
     Fourth Exemplary Embodiment 
     FIG. 7 is a circuit diagram of an angular velocity sensor in accordance with a fourth exemplary embodiment of the present invention. Also in this exemplary embodiment, an initial setting is made so that when the mechanical coupling signals from piezoelectric elements  13   a  and are added, their sum becomes zero by trimming either detector plate  13  or  14 , like in the third exemplary embodiment. The signal from piezoelectric element  13   a  is amplified at a charging amplifier  20   a , the signal from piezoelectric element  14   a  is amplified at a charging amplifier  20   b , they are added at adder  34  and the sum signal is outputted from output terminal  24  as an angular velocity signal after being processed. A signal subtracted the output of charging amplifier  20   b  from the output of charging amplifier  20   a  at subtracter  35  is outputted from signal output terminal  29  as a self diagnosis signal after being processed. Waveforms at the points in FIG. 7 are shown in FIG.  8 . Amplifier  25 , rectifier  26  and filter  27  can be omitted. Although the explanation was made using a tuning fork type angular velocity sensor, it is possible to detect a malfunction using the mechanical coupling signal in an angular velocity sensor of triangular prism type, solid cylinder type, tuning fork type or tubular type because such additional types of angular velocity sensors also generate a mechanical coupling signal. 
     Fifth Exemplary Embodiment 
     FIG. 9 is a circuit diagram of an angular velocity sensor in accordance with a fifth exemplary embodiment of the present invention. 
     An alternating signal of about 1 Vp-p and 1.5 kHz is applied from a driver circuit  15  to a piezoelectric element  11   a  of a driver plate  11 . Driver plates  11  and  12  start tuning fork vibration inward and outward against a supporting pin  9  as a center. A voltage proportional to an applied signal is induced at a piezoelectric element  12   a  of driver plate  12  by tuning fork vibration and is outputted from point A as a monitor signal after passing through a current amplifier  16  and a band pass amplifier  17 . The output signal is shown in FIG. 10 as waveform A. This signal fed back to a driver circuit  15  through an AGC (Automatic Grain Control) circuit  19  and the level of the driving signal is controlled to be always constant at point A. In the detector part, the signals from piezoelectric elements  13   a  and  14   a  are synthesized at point D and the synthesized signal is supplied to a charging amplifier  20 . The monitor signal from point A synchronized with a tuning fork vibration is attenuated by an attenuator  36  and is supplied to a non-inverted input terminal of a charging amplifier  20  after passing through a injector  37 . The output of charging amplifier  20  is outputted from an output terminal  24  through a band pass filter  21 , a synchronous detector  22  and a low pass filter  23 . Signal waveforms at point I (the output of attenuator  36 ), H (the output of injector  37 ), E (the output of charging amplifier  20 ), F (the output of synchronous detector  22 ) and G (the output of low pass filter  23 ) are shown in FIG. 10 as waveforms I, H, E, F and G, respectively. 
     In this exemplary embodiment, piezoelectric element  13   a  detecting an angular velocity is glued an detector plate  13  through adhesive  8  and a silver electrode  13   b  is formed on piezoelectric elements  13   a  as shown in FIG.  11 ( a ). 
     Detector plate  13 , piezoelectric elements  13   a  and silver electrode  13   b  form a parallel plate capacitor as shown in FIG.  11 ( b ) and its equivalent circuit is shown in FIG.  11 ( c ). The capacity of a capacitor formed by piezoelectric element  13   a  is expressed by equation (1). 
     
       
         Cs 1 =ε* S/d   (1) 
       
     
     ε: permitivity of piezoelectric element, 
     S: area of the electrode and 
     d: thickness of piezoelectric element. 
     Similarly, the capacity of a capacitor formed by, piezoelectric element  14   a  is expressed by equation (2). 
     
       
         Cs 2 =ε* S/d   (2) 
       
     
     ε: permitivity of piezoelectric element, 
     S: area of the electrode and 
     d: thickness of piezoelectric element. 
     There are following relations between the sensitivities of piezoelectric elements detecting an angular velocity and capacities Cs 1  and Cs 2  expressed by equations (1) and (2). 
     The sensitivity is proportional to area S and capacity C is proportional to area S, therefore the sensitivity is proportional to capacity C. Therefore, if a capacity variation can be detected, a sensitivity variation can be conjectured and it is possible to detect a sensitivity abnormality. 
     Now, monitor signal A at point A is attenuated at attenuator  36  as shown in waveform I of FIG.  10  and supplied to injector  37 . Injector  37  is composed of, for example, a capacitor and a resistor shown in FIG. 12 and a signal phase shifted against monitor signal A as shown in waveform H of FIG. 10 is supplied to non-inverted input terminal of charging amplifier  20 . However, because the inverted input and the non-inverted input of charging amplifier  20  have virtually the same potential, the signal from injector  37  supplied to the non-inverted input terminal appears also at the inverted input terminal of charging amplifier  20  as shown by waveform D in FIG.  10 . 
     As a result, a displacement current ID shown by waveform D (broken line) of FIG. 10 generates at capacity components Cs 1  and Cs 2  of piezoelectric elements  13   a  and  14   a  connected to the inverted input terminal and a voltage shown by waveform E of FIG. 10 is outputted from charging amplifier  20 . The output voltage ve at point E is expressed by equation (3). 
     
       
           ve=Vm*α* (1/C 0 )*(Cs 1 +Cs 2 )* ID∠φ   (3) 
       
     
     ve: output voltage E (Vp-p) of charging amplifier, 
     Vm: monitor voltage (Vp-p), 
     α: attenuation factor (0&lt;α&lt;1) of attenuator  36 , 
     ∠φ: phase shift (0°&lt;φ&lt;90°) by injector  37 , 
     C 0 : feedback capacity (pF) of charging amplifier  20 , 
     and 
     ID: displacement current (pA). 
     Signal Vout obtained from output terminal  24  is expressed by equation (4). 
     
       
         Vout= A*D*Vm*α* (1/C 0 )*(Cs 1 +Cs 2 )* ID *sin φ  (4) 
       
     
     D: detection constant of synchronous detector  22  and 
     A: dc gain of low pass filter  23 . 
     Because signal E shown in FIG. 10 is phase shifted by ∠φ against monitor signal A, signal E is detected at synchronous detector  22  after being amplified at band pass filter  21 . Only a signal component corresponding to the phase shift is extracted, amplified at low pass filter  23  and outputted from terminal  24  as a dc off-set component. Usually, it is good to adjust the off-set voltage of the output, for example 2.5 V, considering this dc off-set component. 
     From equation (3), because signal E shown in FIG. 10 is proportional to capacity Cs 1  or Cs 2  of piezoelectric element  13   a  or  14   a  for angular velocity detection, respectively, for example, when a disconnection occurs at point B or C shown in FIG. 9, there is a signal level variation as shown by waveforms E and F of FIG.  10  and as a result, the voltage level at output terminal  24  varies. The abnormality is judged as a sensor malfunction by, for example, threshold judgment of this level variation. 
     Because the input signal of injector  37  is obtained from a monitor signal of the drive circuit and the output signal is applied to the input terminal of charging amplifier  20 , whenever any component or any part of the tuning fork, the drive circuit or the-detection circuit malfunction, a signal appears at output terminal  24  as a variation of the dc off-set component and it is always possible to detect a sensor malfunction. 
     Sixth Exemplary Embodiment 
     FIG. 13 is a circuit diagram of an angular velocity sensor in accordance with a sixth exemplary embodiment of the present invention. In addition to the fifth exemplary embodiment, the input of injector  37  is made selectable to connect to the output of attenuator  36  or to the ground by a switch  38  controlled by an external signal from a control terminal  39 . A circuit diagram of the essential part is shown in FIG.  14  and waveforms are shown in FIG.  15 . 
     Because monitor signal I attenuated at attenuator  36  is usually in a state of disconnection to injector  37  by switch  38 , monitor signal I is not transmitted to injector  37  and accordingly, the sensor outputs are in an ordinary state. When a signal shown by waveform J of FIG. 15 such as a check signal from computer is applied to control terminal  39  shown in FIG. 13, switch  38  closes and signal I from attenuator  36  is transmitted to injector  37 . As a result, the signals at each point vary as shown by waveforms H, D, E and F of FIG. 15 and an off-set voltage linked to a check signal applied to control terminal  39  generates at output terminal  24 , as shown by waveform G of FIG.  15 . Because this off-set variation is determined by equation (4) of the fifth exemplary embodiment, it is possible to know a sensor abnormality by monitoring this offset variation. 
     Seventh Exemplary Embodiment 
     FIG. 16 is a circuit diagram of an angular velocity sensor in accordance with a seventh exemplary embodiment of the present invention. The waveforms are shown in FIG.  17 . The seventh exemplary embodiment details when an input terminal of the external signal is used in common with output terminal  29  of judge circuit  28 . Judge circuit  28  monitors, for example, output E of charging amplifier  20  and detects an abnormal voltage generated by, for example, an abnormal shock or vibration given to the tuning fork from the outside and outputs a signal to inform an abnormality from terminal  29  to the outside. Although the control signal input terminal of switch  38  is used in common with output terminal  29 , the connect/disconnect logical value is set to be inverse against the logical output of the judge circuit  28 . Therefore, in an ordinary state in which switch  38  is not working, an abnormal voltage generated by an abnormal shock or vibration of the tuning fork given from the outside is detected and the abnormality is informed to the outside. In a state in which the sensor is checked, by inputting a check signal from terminal  29  and monitoring the sensor output of terminal  24 , a multifunction diagnosis for malfunction can be made using only one terminal and a high cost performance is realized. 
     In the case in which connect/disconnect logical value of switch  38  is set to be equal to the logical value of judge circuit  28 , it is possible to transfer to a self diagnosis mode by forcibly working switch  38  by the logical output of judge circuit  28  and it is possible to keep outputting a signal as an abnormality detection state at terminal  29  until a reset signal for a self diagnosis mode is supplied from the outside. 
     Here, although an exemplary embodiment in which a sensor working state is informed using a sensor signal is described, it is possible to offset adjust the sensor output. In this case, it is good to adjust an attenuation amount by attenuator  36  or adjust the off-set by adjusting the phase shift amount by injector  37 . It is possible to temperature compensate for the sensor output by making an attenuation amount or a phase shift amount vary with temperature, using a temperature sensitive element. 
     It is similar, if the output of injector  37  is applied to band pass filter  21  and synchronous detector  22 . 
     Thus, an angular velocity sensor of the present invention can detect from a state of the mechanical coupling signal whether the angular velocity signal is in a state which can perform a correct detection or not. Moreover, because the mechanical coupling signal is always generated, it is unnecessary to provide independent means for generating the mechanical coupling signal and the composition of the sensor becomes very simple and highly reliable for self diagnosis.