When a power switch is turned on, first and second analog switches are turned on while a third analog switch is turned off. Accordingly, at the time of starting, a forced excitation driving circuit supplies to a vibrator an oscillation output pulse which is substantially at the resonance frequency of the vibrator, thereby forcibly driving the vibrator in an excitation manner. Thereafter, when the vibrator substantially attains its stationary state and thereby the charged voltage of a capacitor reaches a threshold value of an inverter, the first and second analog switches are turned off while the third analog switch is turned on. Accordingly, the output of a self-excitation circuit is supplied to the electrode of the vibrator so as to vibrate the vibrator in a self-excitation manner.
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9. A self-excitation circuit for driving a vibrator in a self-excitation manner,
said self-excitation circuit comprising:
a converting means for converting a first sine wave voltage indicative of a state of vibration of said vibrator into a square wave voltage which becomes a first predetermined level when said first square sine wave voltage is greater than a predetermined reference level while becoming a second predetermined level when said first square sine wave voltage is smaller than said predetermined reference level;
a filter for filtering a second sine wave voltage, which has a frequency identical to a frequency of said first sine wave voltage, from said square wave voltage; and
a phase shifter for adjusting a phase of said second sine wave voltage, which has been filtered by said filter, such that an amplitude of vibration of said vibrator is substantially maximized.
1. An angular velocity meter comprising:
a vibrator and
a self-excitation driving circuit for driving said vibrator in a self-excitation manner,
said self-excitation driving circuit comprising:
a converting means for converting a first sine wave voltage indicative of a state of vibration of said vibrator into a square wave voltage which becomes a first predetermined level when said first square sine wave voltage is greater than a predetermined reference level while becoming a second predetermined level when said first square sine wave voltage is smaller than said predetermined reference level;
a filter for filtering a second sine wave voltage, which has a frequency identical to a frequency of said first sine wave voltage, from said square wave voltage; and
a phase shifter for adjusting a phase of said second sine wave voltage, which has been filtered by said filter, such that an amplitude of vibration of said vibrator is substantially maximized.
2. A meter according to
3. A meter according to
5. A meter according to
6. A meter according to
7. A meter according to
a first piezoelectric crystal layer;
at least three electrodes formed on an upper surface of said first piezoelectric crystal layer; and
an electrode formed on a lower surface of said first piezoelectric crystal layer.
0. 10. A self-excitation circuit according to claim 9, wherein said converting means includes a zero-cross comparator.
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where m is the mass of the vibrator, v is the vibration speed of the vibrator, and Ω is the rotational angular velocity.
In a conventional vibration angular velocity meter, problems are posed in manufacturing inexpensive, compact vibrators. More specifically, when the manufacturing process includes the process of joining piezoelectric ceramic plates to metal vibrators, piezoelectric ceramic plates must be joined to vibrator side surfaces one by one. This process needs much time, posing difficulty in realizing mass production. In the process, the workability deteriorates as the size of each vibrator decreases. When electrodes are to be formed on the side surface of cylindrical piezoelectric ceramic member, the electrodes must be formed on vibrators one by one by using a roll type printing machine. In addition, each vibrator must be polarized. Such a process is not suitable for mass production and a reduction in size either.
If electrodes are two-dimensionally formed on a ceramic plate consisting of a piezoelectric or electrostrictive material, compact vibrators can be manufactured in large quantities at once. In consideration of such a technique, there is provided a piezoelectric vibration angular velocity meter having a unimorph structure including a metal or ceramic base member in the form of a quadratic prism, a vibrator constituted by a piezoelectric or electrostrictive member in the form of a quadratic prism, an inner electrode formed between the base member and the piezoelectric or electrostrictive member, and an outer electrode formed on the side surface of the piezoelectric or electrostrictive member which is located on the opposite side to the inner electrode.
Note that the ceramic material includes a glass material, a sintered polycrystalline material, a synthetic single crystal, and the like.
Unimorph vibrators can be manufactured in large quantities by joining a piezoelectric or electrostrictive ceramic or plate having electrode patterns formed on both the surfaces to a metal or ceramic plate having the same size as that thereof, and cutting the resultant structure. In addition, if the electrode patterns are formed by lithography, and the joint plate is cut with a precision cutter, compact unimorph vibrators can be manufactured with good reproducibility.
Nonrestraint fundamental vibration of a unimorph vibrator is excited by using a so-called piezoelectric lateral effect by applying a voltage between an inner electrode as a ground electrode on a piezoelectric or electrostrictive member and the middle electrode of three divided outer electrodes. The vibration, therefore, is caused in a direction perpendicular to the electrode surface. When the vibrator rotates about the axis of the vibrator, the vibrator is bent within the electrode surface owing to the Coriolis force. This bending due to the Coriolis force is detected by the two detection electrodes of the three divided outer electrodes which are located on both sides.
At this time, since piezoelectric signals are generated in the Coriolis force detection electrodes upon driving of the vibrator, actual signals are signals obtained by synthesizing signals originating from the Coriolis force and signals originating from the driving of the vibrator. The signals generated in the two detection electrodes have the same frequency, are opposite in phase with respect to the Coriolis force, and are in phase with respect to the driving operation. If, therefore, differential voltages between the signals are obtained, only signals almost originating from the Coriolis force can be obtained.
The vibrator, however, need not be designed such that the resonance in the driving direction matches the resonance frequency in the Coriolis force direction. For example, even if a resonant state is not set in a driving operation, unimorph vibration with a large displacement can be used, and resonance in the Coriolis force direction can be used only for detection. For this purpose, the vibrator my be subjected to unimorph driving at the resonance frequency in the Coriolis force direction. With such a vibrator, the resonance matching step can be omitted.
An inexpensive, compact piezoelectric vibration angular velocity meter similar to the one described above can be manufactured by using a metal plate as a member constituting a unimorph structure instead of a ceramic material such as silica glass. In this case, the metal member can be used as parts of electrodes and leads.
As described above, according to the present invention, inexpensive, compact vibration angular velocity meters can be provided in large quantities.
An AC voltage having a frequency near the resonance frequency of the fundamental cantilever natural oscillation of the uniform vibrator PED3 is applied to the piezoelectric plate 110 to cause resonant vibration of the vibrator. When the vibration is caused in the direction (indicated by “V” in
If the vibrator is caused to vibrate under cantilever vibration conditions with one end of the vibrator being fixed, and the other end being set in a nonrestraint state, the vibrator can be easily fixed, and lead lines can be joined to electrode portions on the fixed portion which does not vibrate. Therefore, an almost ideal vibration state can be obtained. This device has a unimorph structure including a rectangular parallellepiped base member consisting of a metal or ceramic material, a vibrator constituted by a parallellepiped piezoelectric or electrostrictive member joined to the base member, an inner electrode formed between the base member and the piezoelectric or electrostrictive member, and outer electrodes on the opposite side surface of the piezoelectric or electrostrictive member to the inner electrode. One end of the vibrator is fixed.
Cantilever vibration allows the vibrator to be easily fixed, and also allows lead lines to be connected to the fixed portion which does not vibrate so that an ideal vibration state can be easily attained. The vibrator is preferably shaped into a quadratic prism, which allows easy formation of a unimorph structure and easy adjustment of the resonance frequency.
By vibrating the piezoelectric or electrostrictive element as an excitation means, fundamental cantilever vibration of the unimorph vibrator can be excited. Vibration is caused in a direction perpendicular to the electrode surface. When the vibrator rotates about the axis of the vibrator, the vibrator is bent within the electrode surface owing to the Coriolis force. Of the signals generated in the two divided outer electrodes, the signals originating from the Coriolis force have opposite phases between the two electrodes, and the signals originating from the driving operation are in phase. If, therefore, the differential signal between the two signals is obtained, only the signals almost originating from the Coriolis force can be obtained.
If three divided outer electrodes are formed on a piezoelectric or electrostrictive member constituting a unimorph structure, the middle electrode is used for excitation to excite fundamental cantilever natural oscillation. If the electrodes on both sides are used for detection, and the differential voltage between the two signals generated in the two electrodes is obtained, signals originating from the Coriolis force can be obtained.
According to the above method, a vibration angular velocity meter having an ideal vibration condition can be easily provided. In addition, inexpensive, compact vibrators can be manufactured in large quantities by forming an electrode pattern on a large ceramic plate by printing, photolithography, or the like, joining a metal or ceramic plate to the ceramic plate, and cutting the resultant structure.
In order to maintain high positioning precision in the subsequent steps, the peripheral portion of the joint plate constituted by the these plates is cut in the direction of thickness with a dicing saw to align the side surfaces of the two plates (
A photoresist 1311 is coated on the electrode 1304. Predetermined areas of the photoresist 1311 are exposed by using an exposure apparatus. The photoresist 1311 is exposed such that exposed areas having the same width are arranged at equal intervals. The non-exposed areas of the photoresist 1311 are etched to form a resist pattern corresponding to an electrode pattern (
This resist 1311 is used as a protective mask. The exposed portions of the silver electrode 1304 are removed by using the reactive ion etching (RIE) method (
When an AC voltage having a frequency near the nonrestraint vibration fundamental resonance frequency in the Coriolis force direction is applied to a driving piezoelectric member 302 via driving elements 308 and 310, vibration is excited in the direction V. The vibration caused at this time causes no resonance because the frequency of the applied AC voltage is lower than the vibration fundamental basic resonance frequency. However, since the element PED6 has a bimorph structure, a sufficiently large amplitude can be obtained by applying a proper voltage. Detection outer electrodes 304 and 305 are separated from the central axis of the vibrator PED6 to maintain the balance of vibration and prevent coupling of vibration caused by the driving operation in the Coriolis force direction.
When the vibrator rotates about the axis of the vibrator PED6, Coriolis forces are generated. Since the frequency of an AC voltage used for a driving operation is equal to the vibration fundamental resonance frequency in the Coriolis force direction, a resonant state is set once the vibrator is bent by the Coriolis forces. As a result, an amplitude of a quality factor multiple (sever 10 to several 1,000 times) of vibration of a static amplitude obtained by piezoelectric strain can be obtained.
Coriolis force signals are detected by the divided electrodes. This detection principle is the same as that in the first embodiment.
If electrodes are two-dimensionally formed on a ceramic plate consisting of a piezoelectric or electrostrictive material, compact vibrators can be manufactured in large quantities at once. In consideration of such a technique, there is provided a piezoelectric vibration angular velocity meter comprising a vibrator having a bimorph structure constituted by a first member made of a piezoelectric or electrostrictive material in the form of a quadratic prism and a second member made of a piezoelectric or electrostrictive material in the form of a quadratic prism, an inner electrode formed between the first and second members, and outer electrodes formed on the opposite surfaces of the first and second members to the inner electrode.
Bimorph vibrators can be manufactured in large quantities at once by joining two piezoelectric or electrostrictive plates respectively having electrode patterns formed on upper and lower surfaces and having the same size, and cutting the resultant structure. In addition, if the electrode patterns are formed by reactive etching, and the joint ceramic plate is cut with a precision cutter, compact bimorph vibrators can be manufactured with good reproducibility.
Nonrestraint fundamental vibration of a bimorph vibrator is excited by using a so-called piezoelectric lateral effect by applying a voltage between an inner electrode in the bimorph shape as a ground electrode and the outer electrode on the driving piezoelectric or electrostrictive member. The vibration, therefore, is caused in a direction perpendicular to the electrode surface. When the vibrator rotates about the axis of the vibrator, the vibrator is bent within the electrode surface owing to the Coriolis forces. This bending due to the Coriolis forces is detected by the detection piezoelectric or electrostrictive member.
According to the above arrangement, since a piezoelectric signal is generated in the Coriolis force detection element upon driving of the vibrator, detection of the Coriolis forces imposes a heavy load on an electrical system in practice. For this reason, the outer electrode on the detection piezoelectric or electrostrictive member is divided into two electrodes with reference to the central line of the vibrator in the axial direction. Signals generated in the two electrodes have the same frequency and opposite phases with respect to the Coriolis forces and are in phase with respect to the driving operation. If, therefore, the differential voltages between these signals are obtained, only the signals almost originating from the Coriolis forces can be obtained.
If a cross-section of the vibrator is square, and the resonance frequencies in the Coriolis force direction and the driving direction can be matched with each other, the vibrator can be driven at a frequency near the resonance frequency with a simple oscillation circuit by feeding back outputs from the detection electrodes. Therefore, the vibration based on the Coriolis forces is set in a resonant state, and the detection sensitivity improves.
In order to omit the cumbersome process of matching resonance frequencies, the vibrator has a rectangular cross-section to intentionally shift the resonance frequencies in the two directions. With this operation, a bimorph driving operation which allows a large amplitude without driving the vibrator in a resonant state can be realized, and the frequency of the AC voltage for this driving operation is used as the resonance frequency of the fundamental vibration in the Coriolis force direction. In addition, if the vibrator is driven at a frequency higher than the fundamental resonance frequency in a bimorph driving operation, vibration cannot be stably caused because of, e.g., coupling with a high-order mode. For this reason, the vibrator has a rectangular cross-section shorter in the electrode surface direction than in the other direction.
As a method of fixing the vibrator, a method of fixing the vibrator at positions corresponding to the nodes of nonrestraint fundamental vibration is most simple and hence preferable.
According to the above method of the present invention, inexpensive, compact vibration angular velocity meters can be provided in large quantities.
A support portion 610 has a hole (cavity) OP1 in its center. In this hole OP1, the piezoelectric element is constituted by the rectangular parallellepiped members 601 and 602, the electrodes 606, 608, and 609, and the adhesive layer 607. One end portion of the piezoelectric element is fitted in the hole OP1 of the support portion 610. The size of the opening of this hole OP1 is almost equal to the area of a cross-section of the piezoelectric element in a direction perpendicular to the longitudinal direction. Although the piezoelectric element and the support portion 610 are fixed to each other with an adhesive layer 611, they may be fixed to each other with a screw.
A lead line 606a is electrically connected to the electrodes 606 and 608. This lead line 606a is in contact with the inner surface of the hole OP1 of the support portion 610 as well as the electrodes 606 and 608. A lead line 605a is electrically connected to the electrode 605. This lead line 605a is in contact with the inner surface of the hole OP1 of the support portion 610 as well as the electrode 605. A lead line 609a is electrically connected to the electrode 609. The lead line 609a is in contact with the inner surface of the hole OP1 of the support portion 610 as well as the electrode 609.
In this case, when the vibrator rotates about the vibrator axis, a Coriolis force is generated in the direction indicated by “Fc” in
When an AC voltage having a frequency near the cantilever vibration fundamental resonance frequency in the Coriolis force direction is applied to a driving piezoelectric member 602 via a driving electrode 609, vibration is excited in the direction indicated by “V” in
When the vibrator rotates about the axis of the vibrator, a Coriolis force is generated. Since the frequency of the AC voltage used for a driving operation is equal to the cantilever vibration fundamental resonance frequency in the Coriolis force direction, a resonant state occurs once the vibrator is bent by the Coriolis force. As a result, an amplitude of a quality factor multiple (several 10 to several 1,000 times) of vibration of a static amplitude obtained by piezoelectric strain can be obtained.
A signal based on a Coriolis force is detected by the divided electrodes. When the Coriolis force indicated by “Fc” in
Each embodiment described above has exemplified the angular velocity meter using the vibrator in the form of a quadratic prism. However, as shown in
This element also includes a second member 731 consisting of a piezoelectric crystal and having two parallel surfaces. The second member 731 is fixed to the third electrode 735 via one of these two surfaces. A fourth electrode 736 is formed on the surface of one of the two surfaces of the second member 731. These piezoelectric members are respectively polarized in the directions indicated by arrows PD1 and PD2. The directions indicated by the arrows PD1 and PD2 are perpendicular to the surface of the electrode 735.
An AC voltage is applied between the electrodes 735 and 736. By obtaining the difference between a voltage signal output across the electrodes 737a and 735 and a voltage signal output across the electrodes 737b and 375, the strain amount of this element can be detected, and hence the angular velocity can be detected.
An AC voltage is applied between the electrode 835 and an electrode 836. By obtaining the difference between a voltage signal output across an electrode 837a and the electrode 835 and a voltage signal output across an electrode 837b and the electrode 835, the strain amount of this element can be detected, and hence the angular velocity can be detected.
If a columnar vibrator is vibrated under cantilever vibration conditions with one end of the vibrator being fixed, and the other end being set in a nonrestraint state, the vibrator can be easily fixed, and lead lines can be joined to electrode portions on the fixed portion which does not vibrate. Therefore, an almost ideal vibration state can be obtained. The present invention is based on such an idea.
According to the present invention, there is provided a piezoelectric vibration angular velocity meter comprising a columnar vibrator partly or completely made of a piezoelectric or electrostrictive member, an excitation means for exciting the vibrator, and a detection means for detecting a Coriolis force generated in the vibrator, wherein one end of the vibrator is fixed.
In addition, the vibrator of the piezoelectric vibration angular velocity meter of the present invention has a unimorph or bimorph structure. That is, there is provided a piezoelectric vibration angular velocity meter comprising a base member made of a metal or ceramic material in the form of a quadratic prism, and a vibrator made of a piezoelectric or electrostrictive material in the form of a quadratic prism and joined to the base member, or a vibrator constituted by a first member made of a piezoelectric or electrostrictive material in the form of a quadratic prism and a second member made of a piezoelectric or electrostrictive material in the form of a quadratic prism.
Cantilever vibration allows the vibrator to be easily fixed, and also allows lead lines to be connected to the fixed portion which does not vibrate so that an ideal vibration state can be easily attained.
The vibrator preferably has the shape of a quadratic prism, triangular prism, or column because it allows easy adjustment of resonance frequencies and easy formation of the vibrator.
Driving (excitation) of the vibrator and detection of a Coriolis force are performed by using the piezoelectric or electrostrictive effect.
In forming a vibrator by using a piezoelectric or electrostrictive ceramic material, a material in the form of a quadratic prism, e.g., a plate-like material, is preferably used because it facilitates polarization.
When a unimorph vibrator is to be used, a piezoelectric or electrostrictive element as an excitation means is arranged near the vibrator (on the vibrator or the support portion for fixing the vibrator), and a voltage is applied to the element to excite fundamental cantilever vibration of the unimorph vibrator.
When a bimorph vibrator is to be used, an inner electrode is used as a ground electrode, and a voltage is applied between the inner electrode and an outer electrode on a piezoelectric or electrostrictive member for a driving operation, i.e., excitation. With this operation, fundamental cantilever vibration of the bimorph vibrator is excited by using a so-called piezoelectric lateral effect.
In either the unimorph structure or the bimorph structure, vibration is caused in a direction perpendicular to the electrode surface. When the vibrator rotates about the axis of the vibrator, the vibrator is bent within the electrode surface owing to Coriolis forces. Of the signals generated in the two divided outer electrodes for detection, the signals originating from the Coriolis forces have opposite phases, but the signals originating from the driving operation are in phase. If, therefore, the differential signal between the two signals is obtained, only the signal almost originating from the Coriolis force can be obtained.
If the outer electrode on a piezoelectric or electrostrictive member is divided into three electrodes, the middle electrode is used for excitation to execute fundamental cantilever natural oscillation. If the electrodes on the two sides of the middle electrode are used for detection, and the differential voltage between the voltages generated in the two electrodes is obtained, a signal originating from a Coriolis force can be obtained.
If the vibrator has a square cross-section, and the resonance frequencies in the Coriolis force direction and the driving direction can be matched with each other, the vibrator can be driven at a frequency near the resonance frequency with a simple oscillation circuit by feeding back outputs from detection electrodes. Vibration based on a Coriolis force is set in a resonant state to improve the detection sensitivity.
In order to omit the cumbersome process of matching resonance frequencies, the vibrator has a rectangular cross-section to intentionally shift the resonance frequencies in the two directions. With this operation, a bimorph driving operation which allows a large amplitude without driving the vibrator in a resonant state can be realized, and the frequency of the AC voltage for this driving operation is used as the resonance frequency of the fundamental vibration in the Coriolis force direction. In addition, if the vibrator is driven at a frequency higher than the fundamental resonance frequency in a bimorph driving operation, vibration cannot be stably caused because of, e.g., coupling with a high-order mode. For this reason, the vibrator preferably has a rectangular cross-section shorter in the coriolis force direction than in the other direction.
In joining two piezoelectric or electrostrictive ceramic plates to each other, a metal plate as a so-called shim member can be inserted between the two plates to increase the displacement amount of the bimorph structure.
As described above, according to the present invention, a vibration angular velocity meter having an ideal vibration state can be easily provided.
In addition, inexpensive, compact vibrators can be manufactured in large quantities by forming a plurality of electrode patterns on a large ceramic plate by a printing technique, photolithography, or the like, joining a metal or ceramic plate thereto, and cutting the resultant structure.
As has been described above, the piezoelectric vibration angular velocity meter of the present invention includes a columnar unimorph or bimorph vibrator made of a piezoelectric or electrostrictive member, an excitation electrode for exciting the vibrator, and a detection electrode for detecting a Coriolis force generated in the vibrator. In the meter, an ideal vibration state can be attained by fixing one end of the vibrator.
In the following, a self-excitation circuit which drives a vibrator of a piezoelectric vibrational angular velocity meter or the like in a self-excitation manner will be explained. First, the schematic configuration of the self-excitation circuit in accordance with the following embodiments will be explained.
This self-excitation circuit is constituted by an inverting amplifier 1004 which inversely amplifies a signal from a signal detecting piezoelectric element 1002 in the upper portion of a vibrator 1001 and a low-pass filter 1005 which adjusts the phase of the output signal of the inverting amplifier 1004. The output side of the low-pass filter 1005 is connected to a driving piezoelectric element 1003 for the vibrator 1001.
The inverting amplifier 1004 is constituted by an operational amplifier 1006 and resistors 1007, 1008, and 1009. The low-pass filter 1005 is constituted by resistors 1010 and 1011 and capacitors 1012 and 1013 as two steps of RC filters.
Here, the vibrator 1001 is configured such that piezoelectric elements are respectively bonded to two side surfaces of a triangle pole made of a metal. Each of these piezoelectric elements comprises a piezoelectric layer and electrodes respectively formed on both sides thereof. One of these piezoelectric elements is the above-mentioned detecting piezoelectric element 1002, whereas the other is the above-mentioned driving piezoelectric element 1003. Also, the above-mentioned triangle pole is grounded.
According to this self-excitation circuit, the signal output from the detecting electrode 1002 is inversely amplified by the inverting amplifier 1004 and the phase of thus amplified voltage is adjusted by the low-pass filter 1005, whose output is supplied, as a driving voltage, to the driving electrode 1003 of the vibrator 1001. Accordingly, a positive feedback is provided so as to attain a loop gain of 1 or higher, whereby the vibrator 1001 is driven in a self-excitation manner.
While the vibrator is likely to become mechanically and electrically unstable, the positively fed-back voltage (driving voltage) may become unstable in thus configured self-excitation circuit of
The following self-excitation circuits and the piezoelectric vibrational angular velocity meter using the same can stabilize driving voltage regardless of the mechanical and electrical unstableness of the vibrator, thereby stabilizing the amplitude at the self-excitation vibration of the vibrator while preventing the abnormal oscillation at frequencies other than the resonance frequency of the vibrator from occurring.
First, the outline of the following embodiments will be explained.
The self-excitation circuit of the first embodiment is a self-excitation circuit for driving a vibrator in a self-excitation manner and comprises a converting means for converting a first sine wave voltage indicative of a state of vibration of the vibrator into a square wave voltage which becomes a first predetermined level when the first square wave voltage is greater than a predetermined reference level while becoming a second predetermined level when the first square wave voltage is smaller than the predetermined reference level; a filter for filtering a second sine wave voltage, which has a frequency identical to that of the first sine wave voltage, from the square wave voltage; and a phase shifter for adjusting the phase of the second sine wave voltage, which has been filtered by the filter, such that the amplitude of vibration of the vibrator is substantially maximized.
The self-excitation circuit of the second embodiment comprises a current/voltage converter which receives one input signal from the vibrator as an electric current signal and converts the electric current signal into a voltage signal, while the converting means converts the output of the current/voltage converter, as the first sine wave voltage, into the square wave voltage.
The self-excitation circuit of the third embodiment comprises a means for receiving one input signal from the vibrator as a voltage signal, while the converting means converts this voltage signal, as the first sine wave voltage, into the square wave voltage.
The self-excitation circuit of the fourth embodiment comprises a means for receiving a plurality of input signals from the vibrator and attaining a voltage signal corresponding to the sum of the plurality of input signals, while the converting means converts the voltage signal corresponding to the sum of the plurality of input signals, as the first sine wave voltage, into the square wave voltage.
In the self-excitation circuit of the fifth embodiment, the means for attaining a voltage signal corresponding to the sum of the plurality of input signals has a plurality of current/voltage converters which respectively receive the plurality of input signals as electric current signals and convert these electric current signals into voltage signals.
In the self-excitation circuit of the sixth embodiment, the means for attaining a voltage signal corresponding to the sum of the plurality of input signals has a means for receiving the plurality of input signals respectively as voltage signals.
In the self-excitation circuit of the seventh embodiment, the converting means includes a zero-cross comparator.
The self-excitation circuit of the eighth embodiment further comprises an attenuator 1042 for attenuating the output of the zero-cross comparator.
In the self-excitation circuit of the ninth embodiment, the attenuator comprises a potential dividing circuit including a variable resistor.
The piezoelectric vibrational angular velocity meter of the tenth embodiment comprises a vibrator and a self-excitation circuit for driving the vibrator in a self-excitation manner.
In the piezoelectric vibrational angular velocity meter of the eleventh embodiment, the vibrator in the tenth embodiment comprises first and second members each made of a rectangular parallelopiped piezoelectric member; a first electrode formed between a first side surface of the first member and a first side surface of the second member; second and third electrodes 1033 and 1034 respectively formed at both side positions on a second side surface of the first member opposite to the first side surface thereof or respectively formed on third and fourth side surfaces of the first member neighboring the first side surface thereof; and a fourth electrode 1035 formed on a second side surface of the second member opposite to the first side surface thereof.
In the piezoelectric vibrational angular velocity meter of the twelfth embodiment, the vibrator in the eleventh embodiment further comprises a fifth electrode formed at substantially the center position of the second side surface of the first member.
In the piezoelectric vibrational angular velocity meter of the thirteenth embodiment, the vibrator in the tenth embodiment comprises a member made of a columnar piezoelectric material and a plurality of band-like electrodes formed on the outer peripheral surface of this member so as to extend in the axial direction thereof.
In the piezoelectric vibrational angular velocity meter of the fourteenth embodiment, the vibrator in the tenth embodiment comprises a member made of a metal formed like a polygonal (higher than triangle) pole and a plurality of piezoelectric elements respectively bonded to a plurality of side surfaces of the member.
The above-mentioned converting means converts the first sine wave voltage indicative of the state of vibration of the vibrator into a square wave voltage having a predetermined level. The first sine wave voltage is obtained on the basis of one or a plurality of input signals from the vibrator. While the amplitude of the first sine wave voltage may fluctuate due to mechanical and electrical unstableness of the vibrator, the level of the square wave voltage is always maintained at the predetermined level. From the square wave voltage, the second sine wave voltage having a frequency identical to that of the first sine wave voltage is filtered by the filter. Accordingly, regardless of the fluctuation in amplitude of the first sine wave voltage, namely, regardless of the mechanical and electrical unstableness of the vibrator, the amplitude of the second sine wave voltage is securely held at a predetermined level. Then, the phase of the second sine wave voltage is adjusted by the phase shifter such that the amplitude of vibration of the vibrator is substantially maximized. The output of the phase shifter is supplied, as a driving voltage, to the vibrator so as to provide a positive feedback. Consequently, the vibrator is driven in a self-excitation manner.
Accordingly, regardless of the mechanical and electrical unstableness of the vibrator, the amplitude of the driving voltage supplied to the vibrator is held at a predetermined level and stabilized. Therefore, the amplitude of the self-excited vibration of the vibrator is stabilized, thereby preventing the vibrator from abnormally oscillating at frequencies other than the resonance frequency thereof.
When the vibrator configured in accordance with the eleventh or twelfth embodiment is adopted as the vibrator, a large number of such vibrators can be made at once, for example, when two sheets of piezoelectric plates in which electrode patterns have been formed on both sides thereof are bonded together and then cut. Also, when the electrode patterns are formed by reactive etching or the like and the bonded plates are cut by a precision cutting machine or the like, small vibrators can be made with a favorable reproducibility.
In the following, self-excitation circuits in accordance with embodiments will be explained in further detail with reference to the drawings.
First, the vibrator 1020 will be explained with reference to
As shown in
In this embodiment, each of the first and second members 1030 and 1031 is made of a piezoelectric ceramic (e.g., lead zirconate titanate (PZT)) and has a thickness of 0.5 mm, a width of 1.0 mm, and a length of 9.0 mm. The present invention, however, should not be restricted to such a size. The direction of polarization of the first member 1030 is the upward direction in
Since the vibrator 1020 is thus configured, a large number of such vibrators can be made at once. Namely, when a piezoelectric plate in which a number of electrode patterns for the electrodes 1033 and 1034 and a number of electrode patterns constituting a part of the electrode 1032 have been formed for the number of vibrators 1020 beforehand and a piezoelectric plate in which a number of electrode patterns for the electrode 1035 and a number of electrode patterns constituting the other part of the electrode 1032 have been formed for the number of vibrators 1020 beforehand are bonded together by means of the above-mentioned adhesive and then cut into the individual vibrators 1020, the large number of vibrators 1020 can be made at once. Also, when the electrode pattern formation by reactive etching or the like and the cutting of the bonded plates by a precision cutting machine or the like are effected, the vibrator 1020 having a small size can be made with a favorable reproducibility.
In this vibrator 1020, for example, the electrode 1032 is used as a reference electrode (earth electrode), the electrodes 1033 and 1034 are used as Coriolis force detecting electrodes, and the electrode 1035 is used as a vibrator excitation electrode (driving electrode). Also, one or both of the electrodes 1033 and 1034 are used for taking out the input signal for the self-excitation circuit, namely, used for taking out the signal for attaining a voltage indicative of the state of vibration of the vibrator 1020 for self-excitation. When an excitation voltage is applied to the electrode 1035 while using the electrode 1032 as a reference electrode, the second member 1031 is subjected to bending vibration in a direction (vertical direction in
Here, as the material for each of the members 1030 and 1031, a piezoelectric material having a large Q value is selected in order for the vibrator 1020 to efficiently vibrate upon application of the driving voltage thereto and to generate a high voltage due to the vibration thereof. Also, it is preferable for the vibrator 1020 to have resonance frequencies in its thickness direction and width directions substantially coincide with each other. When they coincide with each other, the vibrator 1020 has a substantially square cross section. For example, this frequency matching operation is effected as, while the vibrator 1020 is vibrated, its side surface is shaven with laser or the like so as to adjust the resonance frequency.
Next, with reference to
As shown in
The input side of the current/voltage converter 1040 acts as an input terminal of the self-excitation circuit 1021 and is connected to the electrode 1033 (which may be the electrode 1034, of course) of the vibrator 1020. When a sine wave AC voltage with the resonance frequency of the vibrator 1020 is applied (by a voltage follower constituted by an operational amplifier 1072 as will be explained later) between the electrode 1035 and the electrode 1032, the vibrator 1020 vibrates in a direction perpendicular to the surfaces of the electrodes 1032 and 1035. Upon this vibration, a sine wave with the resonance frequency of the vibrator 1020 is generated from the electrodes 1033 and 1034 due to a piezoelectric effect.
As shown in
The voltage signal (sine wave voltage) output from the current/voltage converter 1040 is shown in (a) of
The zero-cross comparator 1041 is constituted by means of an operational amplifier 1054 and converts the output (which corresponds to the sine wave voltage indicative of the state of vibration of the vibrator 1020 in this embodiment) of the current/voltage converter 1040 into a square wave voltage which has a positive power source voltage level (e.g., +3 V) when the output of the current/voltage converter 1040 is greater than zero level (potential of the electrode 1032) while having a negative power source voltage level (e.g., −3 V) when the output of the current/voltage converter 1040 is smaller than zero level. In this case, regardless of the amplitude of the input waveform, the square wave voltage is output with its amplitude being securely set by the zero-cross comparator 1041 at an output amplitude determined by the power source voltage. In
The attenuator 1042 is constituted by a potential dividing circuit composed of a resistor 1055 and a variable resistor 1056 and outputs the output (square wave voltage) of the zero-cross comparator 1041 with its amplitude being attenuated according to the potential dividing ratio thereof. The amplitude of the square wave voltage output from the attenuator 1042 can be arbitrarily set as the variable resistor 1056 is adjusted. The output of the attenuator 1042 is shown in (c) of
The band-pass filter 1043 is a state variable filter constituted by operational amplifiers 1057 to 1059, resistors 1060 to 1065, and a capacitor 1066 and only transmits therethrough frequencies near the resonance frequency of the vibrator 1020. Namely, from the square wave voltage output from the attenuator 1042, the band-pass filter 1043 filters the sine wave voltage having a frequency identical to that of the output voltage of the current/voltage converter 1040. In this embodiment, with respect to the input square wave voltage output from the attenuator 1042, the band-pass filter 1043 outputs a sine wave voltage having an inverted phase (due to the fact that the phases of the input current and the output voltage are inverted by the current/voltage converter 1040) and a constant amplitude with the resonance frequency of the vibrator 1020. Its output waveform is shown in (d) of
As shown in (d) of
The phase shifter 1044 adjusts the phase of the sine wave voltage, which has been filtered by the band-pass filter 1043, such that the amplitude of the vibration of the vibrator 1020 is substantially maximized. Its output waveform is shown in (e) of
To the output side of the phase shifter 1044, the input side of the voltage follower composed of the operational amplifier 1072 is connected, while the output side of this voltage follower acts as the output terminal of the self-excitation circuit 1021, which is connected to the electrode 1035 of the vibrator 1020. Accordingly, the output of the phase shifter 1044 is supplied to the electrode 1035 by way of the voltage follower so as to provide a positive feedback with the resonance frequency of the vibrator 1020, whereby the vibrator 1020 can be efficiently and correctly driven in a self-excitation manner. Here, the voltage follower composed of the operational amplifier 1072 may be omitted as well, thereby making the output side of the phase shifter 1044 as the output terminal of the self-excitation circuit 1021.
The configurations of the current/voltage converter 1040, zero-cross comparator 1041, attenuator 1042, filter 1043, and phase shifter 1044 should not be restricted to those mentioned above, however.
According to the self-excitation circuit 1021 explained in the foregoing, regardless of the fluctuation in the amplitude of the sine wave voltage ((a) in
In the following, with reference to
The piezoelectric vibrational angular velocity meter shown in
Since the signals corresponding to Coriolis force are generated at the electrodes 1033 and 1034 with phases opposite to each other, the voltage signals output from the respective current/voltage converters 1040 and 1080 are sine waves whose amplitudes change due to the Coriolis force in phases opposite to each other. Accordingly, when the sum of their outputs is formed by the adder 1090, their changes are supposed to be offset against each other, thereby making a constant output regardless of the Coriolis force. Actually, however, due to a slight difference between the areas of the electrodes 1033 and 1034, local positional differences in characteristics of PZT, and other mechanical and electrical unstableness of the vibrator 1020, the output (sum output) of the adder 1090 may not become constant, whereby the amplitude in the output of the adder 1090 may fluctuate.
However, the sine wave voltage signal having thus changed amplitude is input into the zero-cross comparator 1041 such that its output is converted into a rectangular voltage whose amplitude is determined by the power source voltage and thereby does not depend on the amplitude output of the input. The functions of the attenuator 1042, band-pass filter 1043, and phase shifter 1044 subsequent thereto are the same as those in the case of the self-excitation circuit 1021 shown in
Accordingly, also in this embodiment, the amplitude of the self-excited vibration of the vibrator 1020 is stabilized, thereby preventing the vibrator 1020 from oscillating at frequencies other than the resonance frequency thereof.
In the following, a piezoelectric vibrational angular velocity meter in accordance with another embodiment will be explained with reference to
The piezoelectric vibrational angular velocity meter shown in
Accordingly, also in this embodiment, the amplitude of the self-excited vibration of the vibrator 1020 is stabilized, thereby preventing the vibrator 1020 from oscillating at frequencies other than the resonance frequency thereof.
In the following, a piezoelectric vibrational angular velocity meter in accordance with another embodiment will be explained with reference to
The piezoelectric vibrational angular velocity meter shown in
Next, another example of vibrators used in the piezoelectric vibrational angular velocity meter in accordance with the present invention will be explained with reference to
This vibrator 1200 differs from the vibrator 1020 shown in
This vibrator 1200 can be combined with the self-excitation circuits 1021 and 1110 shown in
Also, in the piezoelectric vibrational angular velocity meters shown in
This vibrator 1210 differs from the vibrator 1020 only in that the electrodes 1033 and 1034 are not formed on the upper surface (second surface) of the first member 1030 but respectively formed at the third and fourth side surfaces of the first member 1030 neighboring the first side surface (lower surface) of the first member 1030. It is clear that the vibrator 1210 is substantially equivalent to the vibrator 1020.
As in the case of the vibrator 1200 shown in
This vibrator 1220 differs from the vibrator 1200 shown in
Also, in the piezoelectric vibrational angular velocity meters shown in
This vibrator 1230 differs from the vibrator 1020 only in that the electrode 1035 formed on the second side surface (lower surface in
While the vibrator 1020 shown in
Since the vibrator 1230 does not utilize the piezoelectric phenomenon of the second member 1031 at all and thus the second member 1031 is piezoelectrically inactive, not only piezoelectric materials but also inherently piezoelectrically inactive materials such as alumina and glass may be used as the material for the second member 1031.
When this vibrator 1230 is used in the piezoelectric vibrational angular velocity meters shown in
Also, in the piezoelectric vibrational angular velocity meters shown in
This vibrator 1240 differs from the vibrator 1230 shown in
In the following, a still another example of the vibrator used in the piezoelectric vibrational angular velocity meter in accordance with the present invention will be explained with reference to
In this vibrator 1300, PZT plates (i.e., piezoelectric elements) 1320, 1330, 1340, and 1350, each of which has a length of 1.6 mm, a width of 3 mm, and a thickness of 0.3 mm with electrodes (not depicted) formed by silver paste on both sides thereof are respectively bonded to four side surfaces of a metal pole (column) 1310 made of an elinvar alloy having a square cross section, whose each side is 2 mm, with a length of 15 mm. The sizes of the respective portions should not be restricted to those mentioned above, however.
The PZT plate 1320 is used for exciting the vibrator by an inverse piezoelectric effect, whereas the PZT plate 1330 is used for generating a voltage upon vibration of the vibrator 1300 due to a piezoelectric effect. The PZT plates 1340 and 1350 are used for sensing Coriolis force generated when the vibrator is rotated around an axis which is in parallel to the longitudinal direction thereof so as to have an angular velocity. As the metal pole 1310 is used as an earth electrode, the electrode at the surface of each of the PZT plates 1320, 1330, 1340, and 1350 in contact with the metal pole 1310 has an earth potential. The PZT plate 1320 vibrates due to the sine wave voltage applied thereto. Upon this vibration, the metal pole 1310 vibrates so as to form irregularities in the thickness direction of the PZT plate 1320. The PZT plate 1330 vibrates so as to follow the metal pole 1310, whereby a voltage having a frequency identical to that of the vibration is generated due to a voltage effect. At the Coriolis vibration sensing electrodes 1340 and 1350, voltages corresponding to the Coriolis force are generated in phases inverted with respect to each other with frequencies identical to each other and identical to the frequency of the vibrator.
In the case of this vibrator 1300, the self-excitation circuits shown in
In the following, a still another example of the vibrator used in the piezoelectric vibrational angular velocity meter in accordance with the present invention will be explained with reference to
In this vibrator 1400, PZT plates (i.e., piezoelectric elements) 1420, 1430, and 1440 each of which has a length of 1.4 mm, a width of 3 mm, and a thickness of 0.3 mm with electrodes (not depicted) formed by silver paste on both sides thereof are respectively bonded to three side surfaces of a metal pole (column) 1410 having an equilateral triangular cross section, whose each side is 2 mm, with a length of 15 mm. The sizes of the respective portions should not be restricted to those mentioned above. As in the case of the metal pole 1310 of the vibrator 1300 shown in
In the case of this vibrator 1400, the self-excitation circuits shown in
In the following, a still another example of the vibrator used in the piezoelectric vibrational angular velocity meter in accordance with the present invention will be explained with reference to
In this vibrator 1500, band-like electrodes 1520, 1530, 1540, 1550, and 1560 are formed on the side surface of a PZT cylinder 1510 having a diameter of 2 mm and a length of 14 mm so as to extend in the longitudinal direction thereof in parallel to each other as shown in
In the case of this vibrator 1500, the self-excitation circuits shown in
The vibrator used in the piezoelectric vibrational angular velocity meter in accordance with the present invention should not be restricted to the vibrators mentioned above. Also, though the foregoing embodiments refer to the cases where the self-excitation circuit in accordance with the present invention is used for driving the vibrator of the piezoelectric vibrational angular velocity meter in a self-excitation manner, the self-excitation circuit of the present invention can be used for vibrating the vibrator of other apparatuses or the like in a self-excitation manner.
As explained in the foregoing, the above-mentioned piezoelectric vibrational velocity meter can stabilize the driving voltage regardless of the mechanical and electrical unstableness of the vibrator, thereby stabilizing the amplitude of the self-excited vibration of the vibrator while preventing the vibrator from abnormally oscillating at frequencies other than the resonance frequency thereof.
In the following, a piezoelectric vibrational angular velocity meter in accordance with another embodiment will be explained. A piezoelectric vibrational angular velocity meter utilizing normal and inverse piezoelectric effects comprises a vibrator, an excitation driving means for driving the vibrator in an excitation manner, and a detecting means for detecting Coriolis force generated due to a rotation of the vibrator, thereby detecting the Coriolis force generated due to the rotation of the vibrator. The piezoelectric vibrational angular velocity meter is adopted as angular velocity sensor, manual blurring sensor, and the like and has a number of achievements.
In the vibrator 2001, piezoelectric elements 2005, 2006, and 2007 each of which has electrodes (not depicted) respectively formed on both sides thereof are attached to respective side surfaces of a vibration substrate 2004 formed as an equilateral triangular pole made of an elinvar alloy. The two piezoelectric elements 2005 and 2006 are used for detection, whereas the remaining piezoelectric element 2007 is used for driving.
The two input terminals of the detection circuit 2003 are respectively connected to the piezoelectric elements 2005 and 2006. Also, the two input terminals of the self-excitation driving circuit 2002 are respectively connected to the piezoelectric elements 2005 and 2006, while the output terminal thereof is connected to the piezoelectric element 2007.
The self-excitation driving circuit 2002 is constituted by an adder circuit 2010 composed of two resistors 2008 and 2009; an inverting amplifier 2015 composed of an operational amplifier 2011 and resistors 2012 to 2014; and a low-pass filter 2020 composed of two steps of RC filters formed by resistors 2016 and 2017 and capacitors 2018 and 2019.
The output voltages from the piezoelectric elements 2005 and 2006 are added together at the adder 2010 and then inversely amplified by the inverting amplifier 2015. The phase of thus amplified voltage is adjusted by the low-pass filter 2020 so as to be supplied to the piezoelectric element 2007 as a driving voltage. Consequently, a positive feedback is provided so as to attain a loop gain of 1 or higher, whereby the vibrator 2001 is driven in a self-excitation manner.
The detection circuit 2003 takes out the differential between the output voltages from the piezoelectric elements 2005 and 2006, for example, so as to attain the detection signal corresponding to the Coriolis force acting on the vibrator 2001.
In this piezoelectric vibrational angular velocity meter, however, since only the self-excitation driving circuit 2002 is used as an excitation driving circuit for driving the vibrator 2001 in an excitation manner, the rise time after the self-excitation driving circuit 2001 is started till the amplitude of vibration of the vibrator 2001 attains a measurable amplitude (stationary state) is long.
In particular, since the piezoelectric constant of the piezoelectric material forming the vibrator 2001 is highly dependent on temperature, it greatly varies upon temperature in this piezoelectric vibrational angular velocity meter. When the environmental temperature in use is low, for example, at a temperature not higher than 0° C., the rise time for the vibrator 2001 becomes remarkably long.
Accordingly, in cases where this piezoelectric angular velocity meter 2001 is used for measuring Coriolis force in real time, for example, in order to detect manual blurring of a still camera and vibrations other than the manual blurring, a time lag may occur in the measured value when the measurement is effected after the stationary state is attained or reproducibility cannot be attained when the measurement is effected before the stationary state is achieved. Accordingly, it has not been suitable for the measurement in which a rapid rise time is required.
In
In view of such circumstances, the following embodiments provide excitation driving circuits and methods as well as piezoelectric vibrational angular velocity meters using the same by which the rise time for the vibrator can be reduced. First, the outline of the embodiments will be explained.
The excitation driving circuit of the first embodiment is an excitation driving circuit for driving a vibrator in an excitation manner and comprises a self-excitation driving circuit for driving the vibrator in a self-excitation manner and a forced excitation circuit CV for forcibly driving the vibrator PED1 when started.
The excitation driving circuit of the second embodiment further comprises, in the excitation driving circuit of the first embodiment, a means by which, when an amplitude level of a signal indicative of the state of vibration of the vibrator becomes a predetermined level or higher, the excited driving of the vibrator by the forced excitation driving circuit is nullified while only the excited driving of the vibrator by the self-excitation driving circuit is made effective.
The excitation driving circuit of the third embodiment further comprises, in the excitation driving circuit of the first embodiment, a means by which, after a predetermined time has passed from the starting time, the excited driving of the vibrator by the forced excitation driving circuit is nullified while only the excited driving of the vibrator by the self-excitation driving circuit is made effective.
The excitation driving circuit of the fourth embodiment is an excitation driving circuit for driving a vibrator in an excitation manner and comprises a self-excitation driving circuit for driving the vibrator in a self-excitation manner and a pulse signal applying means for forcibly applying a predetermined pulse to an input portion of the self-excitation driving circuit when started.
The excitation driving circuit of the fifth embodiment further comprises, in the excitation driving circuit of the fourth embodiment, a means by which, when an amplitude level of a signal indicative of the state of vibration of the vibrator becomes a predetermined level or higher, the application of the pulse signal by the pulse signal applying means is nullified.
The excitation driving circuit of the sixth embodiment further comprises, in the excitation driving circuit of the fifth embodiment, a means by which, after a predetermined time has passed from the starting time, the application of the pulse signal by the pulse signal applying means is nullified.
The piezoelectric vibrational angular velocity meter of the seventh embodiment is a piezoelectric vibrational angular velocity meter comprising a vibrator and wherein the excitation driving circuit is that in accordance with one of the first to sixth embodiments.
The excitation driving method in accordance with the eighth embodiment is an excitation driving method for driving a vibrator in an excitation manner, wherein, after the vibrator is forcibly driven in an excitation manner when started, the vibrator is driven in an self-excitation manner.
According to the excitation driving circuits of the first to third embodiments of the present invention, while the vibrator is driven in a self-excitation manner by the self-excitation driving circuit, it is forcibly driven in an excitation manner by the forced excitation driving circuit when started. Accordingly, the rise time of the vibrator can be reduced as compared with the conventional cases. Therefore, Coriolis force can be appropriately measured in real time in such cases as detection of manual blurring of still camera or vibration other than the manual blurring.
Though the forced excited vibration of the vibrator by the forced excitation driving circuit is important for reducing the rise time of the vibrator when started, it is unnecessary and may rather deteriorate the self-excitation of the vibrator after the vibration of the vibrator has reached its stationary state. Accordingly, it is preferable that, when the vibration of the vibrator attains the stationary state or a state in the proximity thereof, the excited driving of the vibrator by the forced excitation driving circuit be nullified while the excited driving of the vibrator by the self-excitation circuit alone be made effective. In this case, the excited driving of the vibrator by the forced excitation driving circuit may be nullified while the excited driving of the vibrator by the self-excitation circuit alone is made effective when the amplitude level of the signal indicative of the state of vibration of the vibrator is at a predetermined level or higher as in the case of the excitation driving circuit of the second embodiment. Alternatively, the excited driving of the vibrator by the forced excitation driving circuit may be nullified while the excited driving of the vibrator by the self-excitation circuit alone is made effective after a predetermined time has passed from the starting time as in the case of the excitation driving circuit of the third embodiment.
Also, in the excitation driving circuits of the fourth to sixth embodiments, no forced excitation driving circuit is provided independently from the self-excitation driving circuit. However, the pulse signal applying means applies a predetermined pulse signal to the input portion of the self-excitation circuit when started. Due to this predetermined pulse signal, the self-excitation driving circuit operates as the forced excitation driving circuit. Namely, while a signal from the vibrator indicative of the state of vibration thereof is normally applied to the self-excitation driving circuit such that the vibrator is driven by the self-excitation driving circuit in a self-excitation manner, at the time of starting, the predetermined pulse signal is input to the input portion of the self-excitation driving circuit such that the vibrator is forcibly excited by the self-excitation driving circuit. Accordingly, the rise time of the vibrator can be reduced by the excitation driving circuits of the fourth to sixth embodiments as well.
Also, as mentioned above, the forced excited driving of the vibrator is unnecessary and may rather deteriorate the self-excitation of the vibrator after the vibration of the vibrator has reached its stationary state. Accordingly, it is preferable that, when the vibration of the vibrator attains the stationary state or a state in the proximity thereof, the forced excited driving of the vibrator be nullified while the self-excited driving of the vibrator alone be made effective. In this case, the application of the pulse signal by the pulse signal applying means may be nullified when the amplitude level of the signal indicative of the state of vibration of the vibrator is at a predetermined level or higher as in the case of the excitation driving circuit of the fifth embodiment. Alternatively, the application of the pulse signal by the pulse signal applying means may be nullified after a predetermined time has passed from the starting time as in the case of the excitation driving circuit of the sixth embodiment.
Also, according to the piezoelectric vibrational angular velocity meter of the seventh embodiment, since it has the excitation driving circuit of any of the first to sixth embodiments, the rising time of the vibrator is reduced. Accordingly, Coriolis force can be appropriately measured in real time in such cases as detection of manual blurring of still camera or vibration other than the manual blurring.
Further, according to the excitation driving method of the eighth embodiment, since the vibrator is forcibly driven in an excitation manner when started and then driven in a self-excitation manner, the rise time for the vibrator can be reduced as in the case of the excitation driving circuits of the first to sixth embodiments. In the following, the foregoing embodiments of the present invention will be explained in further detail with reference to the drawings.
In the following, the excitation driving circuits and methods as well as the piezoelectric vibrational angular velocity meters using the same will be explained in further detail with reference to the drawings.
As shown in
First, the vibrator 1200 is shown in
With reference to
Next, the excitation driving circuit 2031 will be explained with reference to
The excitation driving circuit 2031 comprises a self-excitation driving circuit 2050 for driving the vibrator 1200 in a self-excitation manner and a forced excitation circuit 2051 for forcibly driving the vibrator 1200 in an excitation manner when started.
The input terminal of the self-excitation driving circuit 2050 is connected to the electrode 1201 of the vibrator 1200, whereas the output terminal of the self-excitation driving circuit 2050 is connected to the electrode 1035 of the vibrator 1200 by way of an analog switch 2080 as will be explained later. The self-excitation driving circuit 2050 is constituted by an inverting amplifier 2064 composed of an operational amplifier 2060 and resistors 2061 to 2063 and a low-pass filter 2069 composed of two steps of RC filters comprising resistors 2065 and 2066 and capacitors 2067 and 2068. The configuration of the self-excitation driving circuit 2050 should not be restricted thereto, however. The output voltage from the electrode 1201 is inversely amplified by the inverting amplifier 2064. The phase of thus amplified voltage is adjusted by the low-pass filter 2069. When the analog switch 2080 is on, thus phase-adjusted voltage is supplied to the electrode 1035 as a driving voltage by way of the analog switch 2080. As a result, a positive feedback is provided so as to attain a loop gain of 1 or higher, whereby the vibrator 1200 is driven in a self-excitation manner. According to this self-excitation driving circuit 2050, simple harmonic oscillation of the vibrator 1200 with bending in the direction (thickness direction) perpendicular to the surfaces of the electrodes 1034 and 1033 can be attained.
As mentioned previously, the electrode 1032 of the vibrator 1200 is used as a reference electrode so as to be maintained at potential Vref(=VCC/2, e.g., 2.5 V) by means of a power source circuit which is not depicted. Here, VCC indicates a power source voltage (e.g., 5 V).
On the other hand, the forced excitation driving circuit 2051 is constituted by an oscillation circuit comprising a Schmitt trigger inverter 2070, a resistor 2071, and a capacitor 2072. The configuration of the forced excitation driving circuit 2051 should not be restricted thereto, however. When both of a power switch 2090 (corresponding to a start switch, contact, or the like in this embodiment) and an analog switch 2080, which will be explained later, are on, the power source voltage VCC is supplied to the power source terminal of the Schmitt trigger inverter 2070 and thus the forced excitation driving circuit 2051 performs an oscillating operation, whereby an oscillation output pulse is attained from the output terminal of the Schmitt trigger inverter 2070. The values of the resistor 2071 and capacitor 2072 are selected such that the oscillation frequency substantially coincides with the mechanical resonance frequency of the vibrator 1200. Also, the output terminal of the Schmitt trigger inverter 2070 (output terminal of the forced excitation driving circuit 2051) is connected to the electrode 1035 of the vibrator 1200 by way of an analog switch 2082 which will be explained later. When the analog switch 2082 is on, the oscillation output pulse is supplied to the electrode 1035 as a driving voltage by way of the analog switch 2082.
Further, as shown in
In this embodiment, the analog switches 2080, 2081, and 2082, inverters 2083 and 2084, resistor 2085, capacitor 2086, and diode 2087 constitute a means by which, when the amplitude level of a signal indicative of the state of vibration of the vibrator 1200 becomes a predetermined level or higher, the excited driving of the vibrator 1200 by the forced excitation driving circuit 2051 is nullified while the excited driving of the vibrator 1200 by the self-excitation driving circuit 2050 alone is made effective. Namely, by way of the diode 2087 and resistor 2085, the capacitor 2086 is charged with the output of the forced excitation driving circuit 2051 as the signal indicative of the state of vibration of the vibrator 1200. The charged voltage (output of the RC low-pass filter constituted by the resistor 2085 and capacitor 2086) corresponds to the amplitude level of the output of the self-excitation driving circuit 2050. Until the level of thus charged voltage reaches a threshold value VTH1 of the inverter 2084 (the level of the charged voltage being set so as to reach the threshold value VTH1 of the inverter 2084 when the output of the forced excitation driving circuit 2051 substantially attains its stationary state, i.e., when the vibration of the vibrator 1200 substantially attains its stationary state), the outputs of the inverter 2084 and 2083 are respectively set to high and low levels. Consequently, the analog switch 2080 is turned off, while the analog switches 2081 and 2082 are turned on, whereby the excited driving of the vibrator 1200 by the forced excitation driving circuit 2051 is made effective while the excited driving of the vibrator 1200 by the self-excitation driving circuit 2050 is nullified. Then, after the level of the charged voltage of the capacitor 2086 has reached the threshold value VTH1 of the inverter 2084, the outputs of the inverter 2084 and 2083 are respectively set to low and high levels. Consequently, the analog switch 2080 is turned on, while the analog switches 2081 and 2082 are turned off, whereby the excited driving of the vibrator 1200 by the forced excitation driving circuit 2051 is nullified while the excited driving of the vibrator 1200 by the self-excitation driving circuit 2050 alone is made effective. Though the output of the self-excitation driving circuit 2050 is used as the signal indicative of the state of vibration of the vibrator 1200 in this embodiment, the signal derived from the electrode 1201, for example, may be used therefor as well.
Next, with reference to the timing chart shown in
In
First, at time t10, the power switch 2090 is turned on so as to start the apparatus ((a) in
At time t11 where the charged voltage of the capacitor 2086 has reached the threshold value VTH1 of the inverter 2084 (the vibrator being substantially in its stationary state at this point in this embodiment), the analog switches 2081 and 2082 are turned off whereas the analog switch 2080 is turned on. Accordingly, the forced excitation driving circuit 2051 stops its oscillating operation, while the output terminal of the inverter 2070 is separated from the electrode 1035. Also, the output of the self-excitation driving circuit 2050 is supplied to the electrode 1035 by way of the analog switch 2080, whereby the vibrator 1200 is driven in a self-excitation manner with the resonance frequency of the vibrator 1200. As a result, as shown in (e) of
In this embodiment, at the starting (period t10 to t12), the vibrator 1200 is forcibly driven in an excitation manner by the forced excitation driving circuit 2051, whereby the rise time t10 to t12 for the vibrator 1200 is greatly reduced as compared with conventional cases even when the environmental temperature in use changes.
Next, a piezoelectric vibrational angular velocity meter in accordance with another embodiment will be explained with reference to
The piezoelectric vibrational angular velocity meter of this embodiment differs from that shown in
In this embodiment, between a terminal of the power switch 2090 opposite to the power source and the ground (0 V), the capacitor 2105 and the resistor 2103 are connected in series. Also, between the terminal of the power switch 2090 opposite to the power source and the ground (0 V), the resistor 2104 used for discharge is connected. The middle point of the connection between the capacitor 2105 and the resistor 2103 is connected to the input terminal of the inverter 2102. The output of the inverter 2102 is connected to the control terminal 2080c of the analog switch 2080 and the input terminal of the inverter 2101. The output terminal of the inverter 2101 is connected to the respective control terminals 2081c and 2082c of the analog switches 2081 and 2082.
In this embodiment, the analog switches 2080, 2081, and 2082, inverters 2101 and 2102, resistors 2103 and 2104, and capacitor 2105 constitute a means by which, after a predetermined time has passed from the starting point, the excited driving of the vibrator 1200 by the forced excitation driving circuit 2051 is nullified while the excited driving of the vibrator 1200 by the self-excitation driving circuit 2050 alone is made effective. Namely, when the power switch 2090 is turned on, an electric current successively flows through the capacitor 2105 and the resistor 2103 such that the capacitor 2105 is charged, whereby the voltage of the input terminal of the inverter 2102 gradually decreases from the power source voltage VCC which is attained immediately after the power switch 2090 is turned on. Until the voltage of the input terminal of the inverter 2102 has reached a threshold value VTH2 of the inverter 2102 (the level of the input terminal of the inverter 2102 being set so as to reach the threshold value VTH2 of the inverter 2102 when the output of the forced excitation driving circuit 2051 substantially attains its stationary state, i.e., when the vibration of the vibrator 1200 substantially attains its stationary state) after a predetermined time which is determined by the time constants of the capacitor 2105 and resistors 2103 and 2104, the outputs of the inverter 2102 and 2101 are respectively set to low and high levels. Consequently, the analog switch 2080 is turned off, while the analog switches 2081 and 2082 are turned on, whereby the excited driving of the vibrator 1200 by the forced excitation driving circuit 2051 is made effective while the excited driving of the vibrator 1200 by the self-excitation driving circuit 2050 is nullified. Then, after the voltage of the input terminal of the inverter 2102 has reached the threshold value VTH2 of the inverter 2102, the outputs of the inverter 2101 and 2102 are respectively set to low and high levels. Consequently, the analog switch 2080 is turned on, while the analog switches 2081 and 2082 are turned off, whereby the excited driving of the vibrator 1200 by the forced excitation driving circuit 2051 is nullified while the excited driving of the vibrator 1200 by the self-excitation driving circuit 2050 alone is made effective.
Next, with reference to the timing chart shown in
In
First, at time t20, the power switch 2090 is turned on so as to start the apparatus ((a) in
At time t21 where the voltage at the input terminal of the inverter 2102 has reached the threshold value VTH2 of the inverter 2102 (the vibrator being substantially in its stationary state at this point in this embodiment) after a predetermined time has passed from the starting point t20, the analog switches 2081 and 2082 are turned off whereas the analog switch 2080 is turned on. Accordingly, the forced excitation driving circuit 2051 stops its oscillating operation, while the output terminal of the inverter 2070 is separated from the electrode 1035. Also, the output of the self-excitation driving circuit 2050 is supplied to the electrode 1035 by way of the analog switch 2080, whereby the vibrator 1200 is driven in a self-excitation manner with the resonance frequency of the vibrator 1200. As a result, as shown in (e) of
Also in this embodiment, at the starting (period t20 to t22), the vibrator 1200 is forcibly driven in an excitation manner by the forced excitation driving circuit 2051, whereby the rise time t20 to t22 for the vibrator 1200 is greatly reduced as compared with the above-mentioned comparative angular velocity meter even when the environmental temperature in use changes.
Next, a piezoelectric vibrational angular velocity meter in accordance with another embodiment will be explained with reference to
The piezoelectric vibrational angular velocity meter of this embodiment differs from that shown in
In this embodiment, the circuit 2051 functions as a pulse signal applying means for forcibly applying a predetermined pulse signal to the input portion of the self-excitation driving circuit 2050 when started, while also being used as a forced excitation driving circuit. Namely, the oscillation output pulse from the circuit 2051 is also applied to the input terminal of the self-excitation driving circuit 2050 by way of the diode 2110 so as to be used as the predetermined pulse signal. Also, the oscillation output pulse from the circuit 2051 is applied to the electrode 1201 by way of the diode 2110 and used as a driving signal for forcibly driving the vibrator 1200 in an excitation manner. Here, the vibrator 1200 also vibrates when the driving signal is applied to the electrode 1201. Accordingly, in this embodiment, when the oscillation output pulse is generated from the circuit 2051, this oscillation output pulse is applied to the input terminal of the self-excitation driving circuit 2050. Then, the output of the self-excitation driving circuit 2050 generated in response thereto is applied to the electrode 1035 of the vibrator 1200 so as to forcibly vibrate the vibrator 1200, while the oscillation output is applied to the electrode 1201 so as to forcibly vibrate the vibrator 1200. Here, when the oscillation output pulse from the circuit 2051 is applied to the input terminal of the self-excitation driving circuit 2050, the self-excitation driving circuit 2050 operates as the forced excitation driving circuit.
However, for example, a reverse-current preventing diode may be inserted so as to prevent the oscillation output pulse of the circuit 2051 from being applied to the electrode 1201 such that the circuit 2051 is merely used as the pulse signal applying means without being used as the forced excitation driving circuit. In this case, the analog switch 2081, inverter 2084, resistor 2085, capacitor 2086, and diode 2087 constitute only a means by which, when the amplitude level of a signal indicative of the state of vibration of the vibrator 1200 becomes a predetermined level or higher, the application of the pulse signal by the circuit 2051 as the pulse signal applying means is nullified.
Next, the operation of the piezoelectric vibrational angular velocity meter in accordance with this embodiment shown in
First, at time t10, the power switch 2090 is turned on so as to start the apparatus ((a) in
At time t11 where the charged voltage of the capacitor 2086 has reached the threshold value VTH1 of the inverter 2084 (the vibrator being substantially in its stationary state at this point in this embodiment), the analog switch 2081 is turned off. Accordingly, the forced excitation driving circuit 2051 stops its oscillating operation. Therefore, the forced excitation of the vibrator 1200 is terminated, while the vibrator 1200 is driven in a self-excitation manner by the output of the self-excitation driving circuit 2050 alone. As a result, as shown in (e) of
Also in this embodiment, at the starting (period t10 to t12), the vibrator 1200 is forcibly driven in an excitation manner, whereby the rise time t10 to t12 for the vibrator 1200 is greatly reduced as compared with the above-mentioned comparative angular velocity meter even when the environmental temperature in use changes.
Next, a piezoelectric vibrational angular velocity meter in accordance with another embodiment will be explained with reference to
The piezoelectric vibrational angular velocity meter of this embodiment differs from that shown in
In this embodiment, as in the case of the piezoelectric vibrational angular velocity meter shown in
However, for example, a reverse-current preventing diode may be inserted so as to prevent the oscillation output pulse of the circuit 2051 from being applied to the electrode 1201 such that the circuit 2051 is merely used as the pulse signal applying means without being used as the forced excitation driving circuit. In this case, the analog switch 2081, invertors 2101 and 2102, resistors 2103 and 2104, and capacitor 2105 constitute only a means by which, after a predetermined time has passed from the starting point, the application of the pulse signal by the circuit 2051 as the pulse signal applying means is nullified.
Next, the operation of the piezoelectric vibrational angular velocity meter in accordance with this embodiment shown in
First, at time t2o, the power switch 2090 is turned on so as to start the apparatus ((a) in
At time t21 where the voltage of input terminal of the inverter 2102 has reached the threshold value VTH2 of the inverter 2102 (the vibrator being substantially in its stationary state at this point in this embodiment) after a predetermined time has passed from the starting point t20, the analog switch 2081 is turned off. Accordingly, the forced excitation driving circuit 2051 stops its oscillating operation. Therefore, the forced excitation of the vibrator 1200 is terminated while the vibrator 1200 is driven in a self-excitation manner by the output of the self-excitation driving circuit 2050 alone. As a result, as shown in (e) of
Also in this embodiment, at the starting (period t20 to t22), the vibrator 1200 is forcibly driven in an excitation manner by the forced excitation driving circuit 2051, whereby the rise time t20 to t22 for the vibrator 1200 is greatly reduced as compared with the above-mentioned comparative angular velocity meter even when the environmental temperature in use changes.
Next, a piezoelectric vibrational angular velocity meter in accordance with another embodiment will be explained with reference to
The piezoelectric vibrational angular velocity meter of this embodiment differs from that shown in
In this embodiment, a circuit composed of resistors 2103 and 2104 and a capacitor 2105 forms a forced excitation driving circuit CV, while functioning as a pulse signal applying means for forcibly applying a predetermined pulse signal to the input portion of the self-excitation driving circuit 2050 when started. Namely, when started, a single pulse is output from the middle point of the connection between the capacitor 2105 and the resistor 2103. This single pulse is applied to the electrode 1201 by way of the diode 2120 and used as a driving signal for forcibly driving the vibrator 1200 in an excitation manner. Also, this single pulse is applied to the input terminal of the self-excitation driving circuit 2050 by way of the diode 2120 and used as the predetermined pulse signal. Accordingly, in this embodiment, when the single pulse is generated, it is applied to the input terminal of the self-excitation driving circuit 2050. The output of the self-excitation driving circuit 2050 generated in response thereto is applied to the electrode 1035 of the vibrator 1200 so as to forcibly excite the vibrator 1200, while the oscillation output pulse is applied to the electrode 1201 so as to forcibly excite the vibrator 1200.
Next, the operation of the piezoelectric vibrational angular velocity meter in accordance with this embodiment shown in
In
First, at time t30, the power switch 2090 is turned on so as to start the apparatus ((a) in
Also in this embodiment, at the starting (initial part at the starting in this embodiment), the vibrator 1200 is forcibly driven in an excitation manner by the forced excitation driving circuit, whereby the rise time t30 to t31 for the vibrator 1200 is greatly reduced as compared with the above-mentioned comparative angular velocity meter even when the environmental temperature in use changes.
Here, in the embodiments shown in
Also, in the embodiments shown in
When this vibrator 1020 is used, one terminal of the resistor 2061 may be connected to the electrode 1033 or 1034 in
Also, in the embodiments shown in
Further, in the embodiments shown in
Also, in the embodiments shown in
Further, the vibrator 1300 shown in
Further, the vibrator 1400 shown in
Further, the vibrator 1500 shown in
In the following, a camera using such a self-excitation driving circuit will be explained.
A power source or battery BT accommodated within the camera supplies an electric power to the system within the camera. As a shutter release button 407 is pushed down, the camera performs an image capturing operation. As the shutter release button 407 is pushed down, a switch 90 is turned on, whereby a driving electric power is supplied to each of the angular velocity meters JY1 and JY2. Namely, as the shutter release button 407 is pushed down, the potential of an input terminal 18c becomes VCC. When the input voltage VCC is applied to the input terminal of the forced excitation circuit CV, namely, the joint between the resistor 2103 and the capacitor 2105, one pulse of voltage is applied to a center electrode 3 by way of the joint between the resistor 2104 and the capacitor 2105 and then by way of the diode 2120. Accordingly, one pulse of voltage is applied between a ground electrode 6 of the vibrator and the center electrode 3, whereby an upper piezoelectric crystal layer 1 bends in its thickness direction. At this time, the input pulse voltage transmitted through the diode 2120 is also applied to the input terminal of the self-excitation circuit 1021.
The input pulse current which flows into the current/voltage converting circuit 1040 from the forced excitation circuit CV in response to the input pulse voltage is converted into a pulse voltage. Thus converted pulse voltage is input into the comparator 1041 from which the component of this voltage greater than zero level is output as the high level. The amplitude of the square wave voltage output from the comparator 1041 is adjusted by the potential dividing circuit 1042. The square wave voltage transmitted through the potential dividing circuit 1042 is transmitted through the band-pass filter 1043 so as to be converted into a sine wave voltage. The sine wave voltage output from the band-pass filter 1043 is input into the phase shifter 1044.
The phase shifter 1044 adjusts the phase of the input voltage such that the phase of the sine wave voltage output therefrom equals to the phase of the input voltage of the self-excitation circuit 1021. Accordingly, the pulse voltages are applied between the center electrode 3 and ground electrode 6 of the vibrator and between the lower surface electrode 9 and ground electrode 6 of the vibrator from the forced excitation circuit CV and the self-excitation circuit 1021, respectively, whereby the vibrator greatly bends in its thickness direction. Therefore, the rise time for the vibrator can be reduced. Also, a voltage due to a piezoelectric effect is generated between the center electrode 3 and ground electrode 6 of the upper piezoelectric crystal layer 1 which has bent in the thickness direction. This voltage is input into the self-excitation circuit 1021 again, whereby the vibration of the vibrator continues. When the vibrator rotates while vibrating, Coriolis force is imparted to the vibrator, thereby warping the vibration of the vibrator.
At each of left and right electrodes 4 and 5 of the vibrator, an AC voltage, in which the voltage generated by the Coriolis force is superposed on the voltage generated by the vibration, is generated. The alternating currents flowing through the vibrator due to these AC voltages are converted into AC voltages by current/voltage converting circuits 1080a and 1080b, respectively. The current/voltage converting circuits 1080a is constituted by an operational amplifier 1082a, a resistor 1083a, and a capacitor 1084a; whereas the current/voltage converting circuits 1080b is constituted by an operational amplifier 1082b, a resistor 1083b, and a capacitor 1084b. A differential amplifier 558 outputs the difference between these AC voltages, namely, the voltage component generated in response to the Coriolis force. Assuming that the angular velocity is Ω and the velocity of vibration of the vibrator in its thickness direction is V, Coriolis force F is in proportion to Ω×V. At the time when the velocity of vibration V is maximized, namely, when the vibrator is at the neutral position (phase of vibration =0°), the Coriolis force F is maximized and, accordingly, the sine wave voltage (phase of AC voltage =90°) generated by the Coriolis force is also maximized.
Consequently, the phase of the electric signal corresponding to the Coriolis force output from the differential amplifier 558 is shifted from the phase of the AC signal for vibrating the vibrator by about 90°. A phase shifter 562 makes the phases of these signals coincide with each other. A multiplier 559 synchronously detects and then outputs the multiplication of these signals, namely, the voltage signal corresponding to the Coriolis force output from the differential amplifier 558. This voltage signal corresponding to the Coriolis force is smoothed by the low-pass filter 560. Then, its gain is adjusted by a gain adjustment amplifier 561. Subsequently, it is digitized by an A/D converter 501 so as to be input into a central processing unit 502 within the camera as an angular velocity data (X axis). The configuration of the angular velocity meter JY2 is identical to that of the angular velocity meter JY1. The signal output from the angular velocity meter JY2 is digitized by the A/D converter 501 so as to be input into the central processing unit 502 within the camera as an angular velocity data (Y axis). Based on thus detected angular velocity data, the central processing unit 502 controls motors 401 and 402 so as to move an image pickup lens 404. Here, the central processing unit 502 moves the lens 404 as explained with reference to
The vibrator used in the piezoelectric vibrational angular velocity meter in accordance with the present invention should not be restricted to the foregoing vibrators. Any of the foregoing vibrators or piezoelectric vibrational angular velocity meters can be applied to the above-mentioned camera. The excitation driving circuit can also be used when vibrators of other apparatuses and the like are driven in an excitation manner.
From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.
The basic Japanese Application Nos. 207080/1994 (6-207080) filed on Aug. 31, 1994, 207081/1994 (6-207081) filed on Aug. 31, 1994, 207082/1994 (6-207082) filed on Aug. 31, 1994, 115693/1995 (7-115693) filed on May 15, 1995, 170152/1995 (7-170152) filed on Jun. 13, 1995, and 209242/1995 (7-209242) filed on Jul. 25, 1995 are hereby incorporated by reference.
Fujii, Toru, Sango, Yoshinori, Hattori, Tetsuo, Hattori, legal representative, Tomoko
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