Vibration control apparatus

Abstract: A vibration control apparatus comprises a vibration member having a surface with a resonance point. A piezoelectric element that is split in the direction of the vibration member width into first and second portions, is adhered to the surface of the vibration member. A drive apparatus is connected to the first and second portions of the piezoelectric element via first and second impedance elements for exciting the piezoelectric element with an A.C. signal. A feedback circuit is connected between the first and second portions of the piezoelectric element and the drive apparatus. The feedback circuit picks out the components of a voltage on the first and second portions of the piezoelectric element caused by a strain of the first and second portions of the piezoelectric element and feeds these voltages back to control the drive apparatus. The invention vibration control apparatus may be incorporated in a gyro to simplify the construction of the gyro.

Description: Field of the Invention The present invention relates to a vibration control apparatus, for use, for example, in a vibration gyroscope. In particular, the invention relates to a vibration control apparatus that offers a constantly stabilized self-induced vibration in a vibrator element that is excited using a piezoelectric element. In addition, the functions of drive, feedback and detection are performed in a vibration gyro using only one piezoelectric element having two portions. Background of the Invention A prior art vibration control apparatus using two piezoelectric elements is illustrated in FIG 1. In FIG 1, vibrator 4 comprises drive piezoelectric element 2 and feedback piezoelectric element 3 which are both adhered onto one surface of vibration member 1. The output of drive apparatus 5 is supplied directly to drive piezoelectric element 2 while the output of feedback piezoelectric element 3 is fed back directly to drive apparatus 5 so as to form a vibration control apparatus that provides a constantly stabilized self-induced vibration to vibrator 4. With prior technology of this sort, the word of assembling vibrator 4 is troublesome because it is necessary to adhere at least the drive and feedback piezoelectric elements 2 and 3 to vibration member 1. In addition, the vibration created by drive piezoelectric element 2 is transmitted to vibration member 1 via adhesive layer 6 used for the piezoelectric element 2, after which feedback output is provided through adhesive layer 7 used for feedback piezoelectric element 3. This leads to problems of unstable vibration in vibrator 4 because it is easily affected by the characteristic differences between these two piezoelectric elements 2 and 3 and by the temperature dependence of these adhesive layers 6 and 7. Such a prior art vibration control using two piezoelectric elements is known from DE-A-3 926 504. An important application of a vibration control apparatus of the type discussed above is to a vibration gyroscope or gyro. Prior art vibration gyros which incorporate vibration control apparatus are sown as block diagrams in FIG 2 and FIG 3. The vibration gyro shown in FIG 2 comprises drive piezoelectric element 8 adhered to a a first surface of vibration member 1 that is rectangular in cross-section, with feedback piezoelectric element 9 adhered to the surface opposite the first surface. The detector piezoelectric elements 10 and 11 are adhered to two more surfaces at right angles to the others to make vibrator 4. By supplying output from drive apparatus 5 to drive piezoelectric element 8 while feeding back output from feedback piezoelectric element 9 to drive apparatus 5, vibrator 4 gives a prescribed self-induced vibration in the direction of axis X in an orthogonal three-dimensional coordinate system. Under such self-induced vibration, when vibrator 4 is rotated around axis Z, vibration is induced in the Y axis direction by the Coriolis force, and voltages accompanying this vibration in the Y axis direction are formed respectively in the detection piezoelectric elements 10 and 11. These voltages are transmitted successively through differential amplifier 12, synchronous detector 13 and direct current amplifier 14 so as to obtain an indication of the angular velocity of vibrator 4 as the output of the amplifier 14. An alternative prior art vibration gyro is illustrated in FIG 3. The vibration gyro shown in FIG 3 includes vibrator 4 for self-induced vibration in the X axis direction. This vibration is driven by the drive piezoelectric elements 15 and 16 which are adhered respectively to two surfaces of vibration member 1 that is triangular in cross-section. The feedback piezoelectric element 17 is adhered to another surface. The output from feedback piezoelectric element 17 is fed to drive apparatus 5. The feedback piezoelectric element 17 controls the output from drive apparatus 5 to drive piezoelectric elements 15 and 16 respectively via resistances 18 and 19. The drive piezoelectric elements 15 and 16 also serve as detection piezoelectric elements. The voltages formed by the piezoelectric elements 15 and 16 are differentially amplified by the differential amplifier 12. The output of the differential amplifier 12 is processed by the synchronous detector 13 and amplified by the D.C. amplifier 14. At the output of the amplifier 14, it is possible to detect the Coriolis force in the Y axis direction generated by vibrator 4 being rotated around axis Z, that is, to detect the angular velocity. With the vibration gyro shown in FIG 2, the respective piezoelectric elements 8, 9, 10 and 11 are all adhered to vibration member 1 by epoxy resin or other adhesives, creating problems in lack of stability in the self-induced vibration of vibrator 4 because of variations in vibration conditions caused by changes in the strength, elasticity and other properties of the adhesives brought about by changes, for example, in ambient temperature. Such problems may also result from the characteristic differences between drive piezoelectric element 8 and feedback piezoelectric element 9. There are also problems of variations in adhesive properties over time that cause hysteresis in drive conditions, and problems originating from variations in adhesive strength of the detection piezoelectric elements 10 and 11. Also, variations in the properties of the several piezoelectric elements 8, 9, 10 and 11 and asymmetry in the sectional shape of vibration member 1 cause so-called offset voltages to occur because vibration in the Y axis direction, that does not occur ideally when vibrator 4 is not rotating, does occur in actuality. The size and other features of this offset voltage also change depending on the drive voltage and other drive conditions. Also in the case of this prior technology it is necessary to adhere each piezoelectric element to each surface of vibration member 1 with. high precision, causing troublesome problems in assembly labor for vibrator 4. With the prior technology shown in FIG 3, drive piezoelectric elements 15 and 16 are also used as detection piezoelectric elements, making it possible to decrease the changes in offset voltage brought about by changes in the adhesive under the prior technology shown in FIG 2. However, even with this prior technology there still remains problems similar to those described above relative to vibration conditions because feedback piezoelectric element 17 is still furnished separately in the same manner as in FIG 2. US-A-3 520 195 describes a vibration gyroscope comprising a vibratory rod having coupled thereto first and second orthogonally arranged piezoelectric elements. The first piezoelectric element is energized to produce vibrations of the vibratory rod in a first transverse direction, and the second piezoelectric element develops a voltage in response to Coriolis force induced vibrations in a second transverse direction, which are produced by rotational motion of said rod about its axis. Further general prior art referring to the detection of angular velocity is also known from FR-A-2 096 135. In view of the disadvantages of using a plurality of piezoelectric elements in a vibration control apparatus it is desirable to reduce the necessary number of piezoelectric elements. This is achieved by the features of claim 1. By providing a feedback circuit for controlling a drive apparatus such that the drive apparatus excites a piezoelectric element, having two portions disposed in the direction of the vibration member width wherein the feedback circuit connects the piezoelectric element to the drive apparatus for generating a voltage indicative of a strain of the piezoelectric element, it is possible to produce a vibration control apparatus that provides a stable self-induced vibration of the vibration member. Since the vibration control of the present invention uses each portion of the piezoelectric element for the dual functions of driving and feedback, the assembly of such a vibration control apparatus is simplified. In an illustrative embodiment, the present invention is directed to a vibration control apparatus. The vibration control apparatus comprises a vibration member having a surface with a resonance point. A piezoelectric element having two portions is attached to the surface of the vibration member with the resonance point. A drive apparatus is connected via impedance elements to the portions of the piezoelectric element to drive the piezoelectric element with an AC drive voltage. A feedback circuit is connected between the piezoelectric element and the drive apparatus to control the drive apparatus. The feedback circuit includes, for example, a differential amplifier, for differentiating between the output voltage of the impedance element (or equivalently, the voltage obtained at the connection between the portions of the piezoelectric element and the impedance element) and an AC reference voltage, which reference voltage is Illustratively generated from the drive voltage, so as to generate a control voltage for the drive apparatus. The piezoelectric element produces strain when stress is applied to it. The piezoelectric effect produces an electric displacement that is proportional to the stress. On the other hand, when an electric field is applied thereto, an electric displacement is produced and an inverse piezoelectric effect produces a strain that is proportional to the electric field. Consequently, when an alternating current charge is applied to the piezoelectric element by means of impedance elements, a voltage is observed in the connection between the piezoelectric element and the impedance element that is made up of the impressed alternating current voltage and the voltage that accompanies the strain of the piezoelectric element. The feedback circuit serves to separate out the voltage related to the strain of the piezoelectric member and returns this voltage to the drive apparatus to control the drive apparatus. With this vibration control apparatus, the dual functions of drive and feedback are provided using a piezoelectric element having two portions adhered to one surface of the vibration member. The two portions of the piezoelectric element cause strain and thus vibration in the vibrator by means of the piezoelectric effect of the piezoelectric element. The voltages produced by the inverse piezoelectric effect of the piezoelectric element are separated from the combined voltages present at the connection between the portions of the piezoelectric element and the impedance elements by the feedback circuit. Because of this, the inventive apparatus is capable of making it easier to assemble the vibrator as compared to the case when a plurality of piezoelectric elements are adhered to different surface of the vibration member. The inventive apparatus also makes it possible to carry out stabilized self-induced vibration in the vibrator by efficiently reducing the effects of differences in characteristics between piezoelectric elements and effects such as physical changes in the adhesive layers. The vibration control apparatus may be incorporated in a vibration gyro. In an embodiment, the vibration gyro of this invention comprises a piezoelectric element having two portions which is adhered to one surface of a vibration member that is polygon-shaped in cross-section. A vibrator is formed by first and second portions disposed on one surface in the direction of vibration member width. Each portion is connected with a single drive apparatus via corresponding impedance elements. A feedback circuit connects the electrodes of each portion back to the drive apparatus. The feedback circuit comprises, for example 1) an adder for adding the output voltages of the impedance elements (or equivalently the voltages in the connections between the electrodes and the corresponding impedance elements) and a differential amplifier that performs differential amplification of the resulting sum with a reference alternating current voltage, or 2) first and second differential amplifiers for differentially amplifying the output voltages of the impedance elements and first and second reference A.C. voltages, and an adder for adding the outputs of the differential amplifiers. Each A.C. reference voltage is the voltage of a connection between an impedance element and a capacitive element that connects to the drive apparatus via the impedance element. When stress is applied to a piezoelectric element it causes strain and an electric displacement form that is proportional to the stress because of the piezoelectric effect. When an electric field is applied, the strain that occurs with the electric displacement is proportional to the electric field because of the inverse piezoelectric effect. Consequently when an A.C. voltage is applied to the piezoelectric element via an impedance element, a voltage is detected at the connection between a portion of the piezoelectric element and an impedance element that is a combination of the alternating current voltage applied and the voltage created by the strain of the portion of the piezoelectric element. The feedback circuit separates out the voltages related to strain and uses the separated voltage to control the drive apparatus. With the vibration gyro of the present invention, the three functions of drive, feedback and detection are performed by a piezoelectric element having two portions by means of separating and removing the voltages created by the strains in each direction of the piezoelectric element. By these means the vibration gyro of the present invention can decrease the effects of adhesives on drive conditions, can control hysteresis in drive conditions even when there are temperature cycles present, and can suppress changes in offset voltage to satisfactorily small amounts. Further, the vibration gyro of the present invention can make vibrator assembly work very quick and easy because only a single piezoelectric element having two portions is adhered. Brief Description of the Drawing FIG 1 illustrates a prior art vibration control apparatus. FIG 2 and FIG 3 illustrates prior art gyros. FIG 4 illustrates a vibration control apparatus in accordance with the present invention. FIG 5 and FIG 6 illustrate gyros in accordance with the present invention. Detailed Description of the Invention FIG 4 is a block diagram that shows an example of this invention, wherein parts that are identical with parts already discussed for prior technology are given the same numbers. Here vibrator 4 is constructed by adhering a single piezoelectric element 20 to one surface of vibration member 4 having a resonance point by means of adhesive layer 21. Drive apparatus 5 is attached to this piezoelectric element 20 by means of impedance element Z 1 and this drive apparatus 5 is also connected to capacitive element 22 by means of another impedance element Z 2 , so that the output of drive apparatus 5 can be supplied both to piezoelectric element 20 and to capacitive element 22. Here also connection 23 between piezoelectric element 20 and impedance element Z 1 and connection 24 between impedance element Z 2 and capacitive element 22 are both connected to differential amplifier 25, and this differential amplifier 25 is in turn connected to drive apparatus 5. Differential amplifier 25 functions so that it obtains the difference between the outputs from the respective connections 23 and 24 and feeds back the differential output to drive apparatus 5. Further, in this sort of circuit construction of the respective impedance elements Z 1 and Z 2 may be of any resistance types, capacitive types or induction types, although it is preferred that they each have the same performance, and the capacitance of capacitive element 22 should be identical to that of piezoelectric element 20. With such a vibration control apparatus, the voltage output of connection 24 between impedance element Z 2 and capacitive element 22 becomes equivalent to the applied alternating current voltage at connection 23 when piezoelectric element 20 is considered as a simple capacitive element, so that the outputs of the two connections 23 and 24 are subtracted at differential amplifier 25 to separate out the voltage produced by the strain of piezoelectric element 20, consequently making it possible to provide stabilized self-induced vibration to vibrator 4 by feeding back the differential output as a feedback signal to drive apparatus 5. So by following this invention it is possible to have a single piezoelectric element function as an piezoelectric element for both drive and for feedback. It is possible to make the work of adhering the piezoelectric element to the vibration member and consequently the work of assembling the vibrator extremely easy. It is possible to remove the effects on self-induced vibration of the different characteristics of a plurality of piezoelectric elements, and it is possible to greatly reduce the effects on self-induced vibration imparted by variations in the physical forms of a plurality of adhesive layers. As indicated above, the inventive vibrator and associated control apparatus may be incorporated in a gyro. FIG 5 is a block diagram of an example of a gyro according to the invention, wherein portions that are identical to portions shown for prior technology in the drawings have the same numbers. In this example of an embodiment, vibrator 4 is constructed by adhering a single piezoelectric element 26 to one surface of the vibration member 1 which has a rectangular shape in cross-section. The electrode of this piezoelectric element 26 is split along the width of vibration member 1 to make split electrodes 26a and 26b. Further, the entire piezoelectric element 26 is split instead of just the electrode. Here drive apparatus 5 is connected to split electrodes 26a and 26b via the respective impedance elements Z 3 and Z 4 . The drive apparatus is also connected to capacitive element 27 via another impedance element Z 5 , and these are all capable of receiving alternating current voltage from drive apparatus 5. The voltage at the connections 28 and 29 between the split electrodes 26a and 26b and impedance elements Z 3 and Z 4 are added at adder 20. Then at differential amplifier 25 the output from adder 30 and the output from connection 31 between impedance element Z 5 and capacitive element 27 are differentially amplified, the result being fed back to drive apparatus 5. It is also possible to use any of resistance types, capacitive types or induction types as the said several impedance elements Z 3 , Z 4 and Z 5 . Further, the two connections 28 and 29 are connected to differential amplifier 12 and this differential amplifier 12 is connected in succession to synchronous detector 13 and direct current amplifier 14 in the same manner as in prior technology. When a vibration gyro is constructed as above, it is possible to impart self-induced vibration in the X axis direction to vibrator 4 by means of impressing an alternating current voltage from drive apparatus 5 onto split electrodes 26a and 26b. Under such vibration conditions, the outputs from the respective connections 28 and 29 are each the combined output of the supply voltage from drive apparatus 5 and the voltage output via the respective split electrode 26a and 26b from the strain of piezoelectric element 26. Consequently, these combined voltages, after being added by adder 30, are processed by differential amplifier 25 so as to obtain only the voltage created by the vibration in the X axis direction, and when this is fed back to drive apparatus 5 it is possible to stabilize the self-induced vibration of vibrator 4 sufficiently. Under such self-induced vibration of vibrator 4, when this vibrator 4 is rotated around axis Z, a vibration in the Y axis direction is created in vibrator 4 based on the Coriolis force, and this creates a difference in the output voltages of connections 28 and 29. Here the two output voltages are differentially amplified at differential amplifier 12 to make it possible to do separation detection of the voltage accompanying the formation of the Coriolis force. FIG 6 is a block diagram showing another example of a gyro which incorporates a vibration control apparatus of this invention. In this example, drive apparatus 5 is connected to the respective split electrodes 26a and 26b via the respective impedance elements Z 3 and Z 4 . The drive apparatus 5 is also connected to the respective capacitive elements 32 and 33 via the other respective impedance elements Z 6 and Z 7 . The respective connections 28 and 29 are connected to adder 34 via the respective differential amplifiers 35 and 36 that differentially amplify with respect to a reference alternating current voltage. Differential amplifier 35 differentially amplifies the output of impedance element Z 6 from connection 37 and the output impedance element Z 3 from connection 28. The differential amplifier 36 differentially amplifies the outputs of impedance element Z 7 from connection 38 and impedance element Z 4 from connection 29. Thus, adder 34 separates out only the voltage generated by the vibration of vibrator 4 in the X axis direction by means of adding these two differential amplification outputs, so that the detection voltage is fed back to drive apparatus 5 to give stabilized self-induced vibration to vibrator 4. With such a vibration gyro, the Coriolis force occurring during vibration of vibrator 4 can be separated and detected by inputting the respective outputs of connections 28 and 29 into another differential amplifier 12. Further, although in the foregoing, the outputs of connections 28 and 29 are input directly into differential amplifier 12, it is possible to input the outputs from the respective differential amplifiers 35 and 36 into differential amplifier 12. Also, in either of the examples in FIG 5 and FIG 6 it is possible to have a vibration member 1 with a cross-section in a polygon shape other than rectangular. As will be clear from what was said above, in the embodiments of FIGs 5 and 6, this invention makes it possible to provide stabilized self-induced vibration merely by furnishing a single piezoelectric element on one surface of the vibration member without furnishing a special feedback piezoelectric element, and also makes it possible to detect angular velocity with high precision. That is, by having a single piezoelectric element perform the three functions of drive, feedback and detection, it becomes possible to decrease the effects of adhesive on drive conditions sufficiently, to effectively control formation of hysteresis in drive conditions when, for example, temperature cycles are present. It is also possible to suppress offset voltage changes to a sufficiently small level. As a result it is possible to provide constantly stabilized self-induced vibration while maintaining high detection precision. And in addition, because it is possible to construct the vibrator by adhering only a single piezoelectric element to vibration member 1, it is possible to do assembly of the vibrator very quickly and easily. In addition, assembly of the vibrator can be accomplished very quickly and easily because the vibrator can be constructed with only one piezoelectric element having two portions adhered to one surface of vibrator 1.

Claims: Vibration control apparatus comprising: a vibration member (1); a piezoelectric element (20) fixed to a surface of the vibration member (1); a drive apparatus (5) for exciting said piezoelectric element with an A.C. drive voltage; and a feedback circuit for controlling the drive apparatus such that the drive apparatus excites the piezoelectric element (20) at a frequency suitable for causing the vibration member to vibrate at a predetermined frequency, characterized in that said piezoelectric element is split in the direction of vibration member width into first and second portions; said first and second portions of said piezoelectric element are connected to said drive apparatus (5) via first and second impedance elements (Z3,Z4), respectively; said feedback circuit connects said first and second portions of said piezoelectric element to said drive apparatus (5) for generating a first voltage indicative of a strain of said first portion and for generating a second voltage indicative of a strain of said second portion, wherein each of said first and second portions of said piezoelectric element performs the dual functions of driving and feedback. Vibration control apparatus of claim 1, wherein said feedback circuit includes means (30) for obtaining the sum of the first and second voltages, and differential means (25) for obtaining the difference between the sum and an A.C. reference voltage. Vibration control apparatus of claim 1 wherein said feedback circuit includes first differential means (35) for differentiating between said first voltage and a first A.C. reference voltage, second differential means (36) for differentiating between said second voltage and a second A.C. reference voltage, and means (34) for summing the output of said first and second differential means and feeding the result back to said driving apparatus (5). Vibration control apparatus of claim 2 or 3 further comprising a circuit for obtaining said A.C. reference voltage comprising a third impedance element (Z 5 ;Z 6 ,Z 7 ) connected to said drive apparatus(5) and a capacitor (27;32,33) connected to said third impedance element. Vibration control apparatus of any of claims 2-4 further comprising differential means (12) for differentiating said first and second voltages to obtain an output indicative of an angular velocity.

Inventors: TERAJIMA KOKICHI, TERAJIMA, KOKICHI, TERAJIMA, KOKICHI, C/O AKAI ELECTRIC CO., LTD.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI ELECTRIC CORPORATION
Application year: 1992
Main classification: G01C19
IPC codes: G01C19, H01L41