Vibration gyroscope and method for adjusting vibration-gyroscope characteristics

Abstract: A vibration gyroscope (10) includes a vibrator (12). The vibrator (12) has a vibration member (14) formed in a regular triangular prism shape. On side faces of the vibration member (14), three piezoelectric elements (16a, 16b, 16c) are formed, respectively. Two of the piezoelectric elements (16a, 16b) are connected to the input terminal of an oscillation circuit (20) through resistors (18a, 18b) which serve as the loads of the two piezoelectric elements (16a, 16b), respectively. The output terminal of the oscillation circuit (20) is connected to the other piezoelectric element (16c). The former piezoelectric elements (16a, 16b) are also connected to the non-inverting input terminal and the inverting input terminal of a differential amplifier circuit (22), respectively. By changing the impedances of the resistors (18a, 18b), the characteristics of the vibration gyroscope (10) is adjusted.

Description: The present invention relates to a vibration gyroscope and a method for adjusting the characteristics of the same, and more particularly, to a vibration gyroscope having a detecting device for obtaining a signal corresponding to a rotation angular velocity and a method for adjusting the characteristics of the same. Fig. 6 is a diagram showing an example of a conventional vibration gyroscope. A vibration gyroscope 1 shown in Fig. 6 includes a vibrator 2. The vibrator 2 includes a vibration member 3 having a regular triangular prism shape. The vibration member 3 is made from, for example, permanently elastic metal materials such as elinvar. At nearly the centers of the three side faces of the vibration member 3, three piezoelectric elements 4a, 4b, and 4c are formed, respectively. These piezoelectric elements 4a to 4c each include a piezoelectric layer made up of ceramic. Each piezoelectric element is provided with electrodes at both primary surfaces of the piezoelectric layer. One electrode on a primary surface of the piezoelectric layer is adhered to a side face of the vibration member and the other electrode, which is disposed on the other primary surface of the piezoelectric layer, is used for signal input and output. In the vibrator 2, two piezoelectric elements 4a and 4b are used for feedback and detection, and the other piezoelectric element 4c is used for driving. Two piezoelectric elements 4a and 4b are connected to the input terminal of an oscillation circuit 6 through resistors 5a and 5b which serve as the loads of the piezoelectric elements. In this case, to use the vibration gyroscope with the highest synchronous-detection efficiency, the impedances of the resistors 5a and 5b are set equal to the impedances of piezoelectric element 4a and 4b, which serve as detecting elements, in a matching condition, respectively. The impedance Z of a piezoelectric element in a matching condition is expressed by Z = 1/(2πfC), where f indicates the frequency of a driving signal and C indicates the capacitance of the piezoelectric element. The output terminal of the oscillation circuit 6 is connected to piezoelectric element 4c. Piezoelectric elements 4a and 4b are connected to the non-inverting input terminal and the inverting input terminal of a differential amplifier circuit 7, respectively. The output terminal of the differential amplifier circuit 7 is connected to the input terminal of a synchronous- detection circuit 8. The output terminal of the synchronous-detection circuit 8 is connected to the input terminal of a smoothing circuit 9. When a driving signal output from the oscillation circuit 6 is applied to piezoelectric element 4c in the vibration gyroscope 1 shown in Fig. 6, the vibration member 3 vibrates in the direction perpendicular to the primary surfaces of piezoelectric element 4c. When the vibration gyroscope 1 rotates about the axis of the vibration member 3 in this state, the direction of vibration of the vibration member 3 changes due to the Coriolis force. Then, a signal according to the rotation angular velocity is generated between two piezoelectric elements 4a and 4b. This signal is detected by the differential amplifier circuit 7. The signal output from the differential amplifier circuit 7 is synchronously detected by the synchronous-detection circuit 8, and the output signal of the synchronous-detection circuit 8 is smoothed by the smoothing circuit 9. Therefore, the rotation angular velocity is detected from the output signal of the smoothing circuit 9 in this vibration gyroscope 1. In the vibration gyroscope 1 shown in Fig. 6, the relationship between temperature and sensitivity change rate without any compensation are determined by the temperature characteristics of the ceramic in the piezoelectric layers of piezoelectric elements 4a and 4b, which serve as detecting elements. To obtain the desired relationship between temperature and sensitivity change rate, the level of a driving signal is changed with the use of a thermistor or diode in a driving-signal processing system including the oscillation circuit 6. Alternatively, the gain of a detected signal is changed with the use of a thermistor or diode in a detected-signal processing system including the differential amplifier circuit 7, the synchronous-detection circuit 8, and the smoothing circuit 9. When a thermistor or diode is used, however, the cost of the vibration gyroscope increases due to high cost of the thermistor or diode, and the number of used components also increases. To improve the response of the vibration gyroscope 1 shown in Fig. 6, the vibration frequency of the vibrator is increased or the vibrator material is changed. However, to increase the vibration frequency of the vibrator, the size and the shape of the vibrator need to be changed and changes of the circuit constants in the peripheral circuits are also required. These factors cause high cost. To change the vibrator material, the vibrator needs to be changed and changes of the circuit constants in the peripheral circuits are also required. These factors also increase cost. U.S. Patent No. 4,791,815 discloses a cyclically driven gyro having a tuning fork structure portion, on which two rectangular piezoelectric elements are secured. Each of the rectangular piezoelectric elements is fixed to a cantilever supported at a joint with the tuning fork structure portion. The tuning fork structure portion is excited by a drive circuit. Each of the piezoelectric elements is connected to a preamplifier for converting the capacitive, high input impedance outputs of the piezoelectric elements into low output impedance voltage signals. The output signals of each preamplifier are added and the added signal is input into a signal processing circuit for obtaining an output signal indicative of an angular rate applied to the tuning fork structure portion. Accordingly, it is an object of the present invention to provide an inexpensive vibration gyroscope having desired response characteristics. Another object of the present invention is to provide an inexpensive, good-response vibration gyroscope. These objects are achieved by a vibration gyroscope in accordance with claim 1. Still another object of the present invention is to provide a method for inexpensively adjusting the characteristics of a vibration gyroscope. This object is achieved by a method in accordance with claim 5. In one aspect of the present invention, the impedance of the loads is made lower than the impedance of the detecting elements in a matching condition to improve the response of the vibration gyroscope. In still another aspect of the present invention, the impedance of the loads is made higher than the impedance of the detecting elements in a matching condition to improve the response of the vibration gyroscope. The desired response is a desired relationship between temperature and sensitivity change rate. In accordance with the foregoing aspects of the invention, a thermistor or diode is not required to obtain the desired relationship between temperature and sensitivity change rate, decreasing the cost of the vibration gyroscope. Additionally, it is not necessary to increase the vibration frequency of the vibrator or to change the vibrator material, in order to improve the response. Thus, further reducing the cost of the vibration gyroscope. The foregoing objects are achieved in a further aspect of the present invention through the provision of a method for adjusting the characteristics of a vibration gyroscope which has at least a first detecting element for obtaining a signal corresponding to a rotation angular velocity, including the step of connecting at least a first load to the first detecting element, the impedance of the first load being different than the impedance of the first detecting element and having a value commensurate with a desired response. In accordance with one aspect of the method, the vibrator includes a second detection element, and the method further includes connecting a second load to the second detection element, the impedance of the second load being different than the impedance of the second detection element and having a value commensurate with a desired response. In accordance with the method for adjusting the characteristics of a vibration gyroscope, a thermistor or a diode is not required, and it is not necessary to increase the vibration frequency of the vibrator or to change the vibrator material, in order to improve the response. The cost of the vibration gyroscope is reduced. According to the present invention, an inexpensive vibration gyroscope having the desired relationship between temperature and sensitivity change rate is obtained. According to the present invention, an inexpensive, good-response vibration gyroscope is also obtained. Furthermore, according to the present invention, a method for inexpensively adjusting the characteristics of a vibration gyroscope is obtained. The above-described objects, other objects, features, and advantages of the present invention will be further clarified by detailed descriptions in the description of the preferred embodiment which will be mentioned below by referring to the drawings. Fig. 1 is a diagram showing a vibration gyroscope according to an embodiment of the present invention. Fig. 2 is a graph indicating the relationship between temperature and sensitivity change rate of the vibration gyroscope shown in Fig. 1. Fig. 3 is a graph indicating the relationship between impedance and phase lag of a resistor in the vibration gyroscope shown in Fig. 1. Fig. 4 is a graph indicating the relationship between impedance and sensitivity change rate of a resistor in the vibration gyroscope shown in Fig. 1. Fig. 5 is a diagram showing a vibration gyroscope according to another embodiment of the present invention. Fig. 6 is a diagram showing a conventional vibration gyroscope. Fig. 1 is diagram showing a vibration gyroscope according to an embodiment of the present invention. A vibration gyroscope 10 shown in Fig. 1 includes a vibrator 12. The vibrator 12 has a vibration member 14 which is formed, for example, in a regular triangular prism shape. The vibration member 14 is formed, for example, by permanently elastic metal materials, such as elinvar and an iron-nickel alloy. At nearly the centers of the three side faces of the vibration member 14, three piezoelectric elements 16a, 16b, and 16c are formed, respectively. These piezoelectric elements 16a to 16c each include a piezoelectric layer made up of ceramic. Each piezoelectric element is provided with electrodes at both primary surfaces of the piezoelectric layer. One electrode on a primary surface of the piezoelectric layer is adhered to a side face of the vibration member 14 and the other electrode, which is disposed on the other primary surface of the piezoelectric layer, is used for signal input and output. In the vibrator 12, two piezoelectric elements 16a and 16b are used for feedback and detection, and the other piezoelectric element 16c is used for driving. Two piezoelectric elements 16a and 16b are connected to the input terminal of an oscillation circuit 20 through resistors 18a and 18b which serve as the loads of the piezoelectric elements. The output terminal of the oscillation circuit 20 is connected to piezoelectric element 16c. Two piezoelectric elements 16a and 16b are also connected to the non-inverting input terminal and the inverting input terminal of a differential amplifier circuit 22, respectively. The output terminal of the differential amplifier circuit 22 is connected to the input terminal of a synchronous-detection circuit 24. The output terminal of the synchronous-detection circuit 24 is connected to the input terminal of a smoothing circuit 26. When a driving signal output from the oscillation circuit 20 is applied to piezoelectric element 16c in the vibration gyroscope 10, the vibration member 14 vibrates in the direction perpendicular to the primary surfaces of piezoelectric element 16c. When the vibration gyroscope 10 rotates about the axis of the vibration member 14 in this condition, the direction of vibration of the vibration member 14 changes due to the Coriolis force. Then, a signal according to the rotation angular velocity is generated between two piezoelectric elements 16a and 16b, which serve as detecting elements. This signal is detected by the differential amplifier circuit 22. The signal output from the differential amplifier circuit 22 is synchronously detected by the synchronous-detection circuit 24, and the output signal of the synchronous-detection circuit 24 is smoothed by the smoothing circuit 26. Therefore, the rotation angular velocity is detected from the output signal of the smoothing circuit 26 in this vibration gyroscope 10. In this vibration gyroscope 10, the desired relationship between temperature and sensitivity change rate can be obtained by differentiating the impedances of the resistors 18a and 18b from those of piezoelectric elements 16a and 16b in a matching condition. The details will be described below. Fig. 2 shows the relationship between temperature and sensitivity change rate at 25°C with sensitivity being used as a reference in the vibration gyroscope 10 with the impedances of piezoelectric elements 16a and 16b in a matching condition being set to 15 kΩ and those of the resistors 18a and 18b being set to 12, 15, or 18 kΩ. As clearly understood from the graph shown in Fig. 2, when the impedances of the resistors 18a and 18b are set to the same (15 kΩ) as those of piezoelectric elements 16a and 16b in a matching condition, the relationship between temperature and sensitivity change rate has a negative gradient. When the impedances of the resistors 18a and 18b are set to smaller (12 kΩ) than those of piezoelectric elements 16a and 16b in a matching condition, the relationship between temperature and sensitivity change rate has a substantially flat gradient. In contrast, when the impedances of the resistors 18a and 18b are set to larger (18 kΩ) than those of piezoelectric elements 16a and 16b in a matching condition, the relationship between temperature and sensitivity change rate has a large negative gradient. When the impedances of the resistors 18a and 18b are set to smaller or larger than those of piezoelectric elements 16a and 16b in a matching condition, the response of the vibration gyroscope 10 is improved. The details will be described below. Fig. 3 shows the phase lag of the signal output from the smoothing circuit 26 against the rotation angular velocity in the vibration gyroscope 10 with a rotation angular velocity of 30 Hz being applied and with the impedances of piezoelectric elements 16a and 16b in a matching condition being set to 15 kΩ and those of the resistors 18a and 18b being set to 5.6 to 33 kΩ. As clearly understood from the graph shown in Fig. 3, when the impedances of the resistors 18a and 18b are set to the same as those (15 kΩ) of piezoelectric elements 16a and 16b in a matching condition, the phase lag of the output signal is large. When the impedances of the resistors 18a and 18b are set to smaller or larger than those (15 kΩ) of piezoelectric elements 16a and 16b in a matching condition, the phase lag of the output signal becomes small. When the impedances of the resistors 18a and 18b are set to larger than those of piezoelectric elements 16a and 16b in a matching condition, the detecting sensitivity of the vibrator increases and the S/N ratio is improved. The details will be described below. Fig. 4 shows the sensitivity change rate of the vibration gyroscope 10 with the impedances of piezoelectric elements 16a and 16b in a matching condition being set to 15 kΩ and those of the resistors 18a and 18b being set to 15 to 33 kΩ. As clearly understood from the graph shown in Fig. 4, when the impedances of the resistors 18a and 18b are set to larger than those (15 kΩ) of piezoelectric elements 16a and 16b in a matching condition, the detecting sensitivity of the vibrator increases and the S/N ratio is improved. In the above-described vibration gyroscope 10, two piezoelectric elements 16a and 16b are used for feedback and detection, and the other piezoelectric element 16c is used for driving. The vibration gyroscope may be configured such that two piezoelectric elements 16a and 16b serve as driving means and detecting means and the other piezoelectric element 16c is used as feedback means. In this case, as shown in Fig. 5, the piezoelectric element 16c is connected to the input terminal of the oscillation circuit 20, and the output terminal of the oscillation circuit 20 is connected to piezoelectric elements 16a and 16b through resistors 18a and 18b which serve as the loads of piezoelectric elements 16a and 16b. Two piezoelectric elements 16a and 16b are also connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier circuit 22, respectively. The output terminal of the differential amplifier circuit 22 is connected to the input terminal of the synchronous-detection circuit 24, and the output terminal of the synchronous-detection circuit 24 is connected to the input terminal of the smoothing circuit 26. In the vibration gyroscope shown in Fig. 5, with the impedances of resistors 18a and 18b which serve as the loads of piezoelectric elements 16a and 16b acting as detecting elements being set appropriately, the desired relationship between temperature and sensitivity change rate is obtained and the response is improved, in the same way as in the vibration gyroscope shown in Fig. 1. In addition, the detecting sensitivity of the vibrator increases and the S/N ratio is improved. In the above-described embodiments, a vibration member having a regular triangular prism shape is used. The vibration member may have another prism shape such as a cylindrical shape and a quadrangular prism shape. In the above-described embodiments, three piezoelectric elements are used. Only two piezoelectric elements for driving and detection may be used. The number of piezoelectric elements used can be changed.

Claims: A vibration gyroscope (10) comprising: a vibrator (12) having a first detecting element (16a) and a second detecting element (16b) for obtaining a signal corresponding to a rotation angular velocity, the first detecting element (16a) having an impedance, and the second detecting element having an impedance; a first load (18a) having an impedance, the first load being connected between the first detecting element (16a) and an oscillation circuit (20) for generating a driving signal for driving the vibrator (12), the driving signal having a driving frequency; a second load (18b) having an impedance, the second load being connected between the second detecting element (16a) and the oscillation circuit (20); and wherein the impedance of the first detecting element (16a) in a matching condition is determined by a capacitance of the first detecting element (16a) and the driving frequency, and wherein the impedance of the second detecting element (16b) in a matching condition is determined by a capacitance of the second detecting element (16b) and the driving frequency; characterized in that the impedance of the first load (18a) is different than the impedance of the first detecting element (16a) in a matching condition, the impedance of the second load (18b) is different than the impedance of the second detecting element (16b) in a matching condition, and the first and second load impedances have values which are selected to achieve a desired relationship between temperature and sensitivity change rate, an increased detection sensitivity, or a desired response. A vibration gyroscope (10) in accordance with claim 1, wherein the impedance of the first load (18a) and the impedance of the second load (18b) are lower than the respective impedances of the first detecting element (16a) and the second detecting element (16b) in a matching condition. A vibration gyroscope (10) in accordance with claim 1, wherein the impedance of said first load (18a) and the impedance of the second load (18b) are higher than the respective impedances of the first detecting element (16a) and the second detecting element (16b) in a matching condition. A vibration gyroscope according to claim 5, wherein the first and second loads (18a, 18b) are first and second resistors. A method for adjusting characteristics of a vibration gyroscope (10) which comprises a vibrator having a first detecting element (16a) and a second detecting element (16b), the first detecting element (16a) having an impedance and the second detecting element having an impedance, for obtaining a signal corresponding to a rotation angular velocity, the method comprising the steps of: connecting a first load (18a) having an impedance between the first detecting element (16a) and an oscillation circuit (20) for generating a driving signal for driving the vibrator (12), the driving signal having a driving frequency; and connecting a second load (18b) having an impedance between the second detecting element (16a) and the oscillation circuit (20); and wherein the impedance of the first detecting element (16a) in a matching condition is determined by a capacitance of the first detecting element (16a) and the driving frequency, and wherein the impedance of the second detecting element (16b) in a matching condition is determined by a capacitance of the second detecting element (16b) and the driving frequency; characterized in that the impedance of the first load (18a) is different than the impedance of the first detecting element (16a) in a matching condition, the impedance of the second load (18b) is different than the impedance of the second detecting element (16b) in a matching condition, and the first and second load impedances have values which are selected to achieve a desired relationship between temperature and sensitivity change rate, an increased detection sensitivity, or a desired response. A method in accordance with claim 5, wherein the impedances of the first load (18a) and the second load (18b) are lower than the respective impedances of the first detecting element (16a) and the second detecting element (16b) in a matching condition. A method in accordance with claim 5, wherein the impedance of the first load (18a) and the impedance of the second load (18b) are higher than the respective impedances of the first detecting element (16a) and the second detecting element (16b) in a matching condition.

Inventors: EBARA KAZUHIRO, FUJIMOTO KATSUMI, EBARA, KAZUHIRO, FUJIMOTO, KATSUMI
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1996
Main classification: G01C19
IPC codes: G01P9, G01C19