JPH03243814A - Angular velocity sensor - Google Patents

Abstract

PURPOSE:To obtain this highly reliable sensor which does not vary in sensitivity even in the case of receiving a thermal shock by structuring the sensor by sticking piezoelectric bimorph elements for driving and piezoelectric bimorph elements for detection on each other across an intermediate electrode. CONSTITUTION:The piezoelectric bimorph elements 2 for driving and piezoelectric bimorph elements 1 for detection are stacked and joined by joining members 6 having their vibrating directions so that they are intersected orthogonally with each other and the joined couples are joined in tuning fork structure by electrode blocks 3 to be the joining members. The elements 2 and 1 are two piezoelectric bimorph elements which are stuck together across the intermediate electrode and a resistance body is connected between the electrode and intermediate electrode on both sides of the bimorph elements structure. Further, a conductive adhesive 9 which has a specific resistance value is used to join the elements 2 and 1 and thus a resistance connection between electrodes on both sides of each piezoelectric bimorph element is made. Consequently, charges which are generated on both sides of the elements 2 and 1 owing to a thermal shock are discharged through the resistance body and the elements are prevented from breaking.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a gyroscope, and particularly to an angular velocity sensor using vibration of a piezoelectric element.

BACKGROUND OF THE INVENTION Conventionally, a mechanical rotary gyro has been mainly used as an inertial navigation device using a gyroscope to determine the direction of a moving object such as an airplane or a ship.

Although this method can provide stable orientation, since it is mechanical, the device is large-scale and costly, and it is difficult to apply it to equipment that is desired to be miniaturized.

On the other hand, there is a vibration type angular velocity sensor that vibrates an object without using rotational force and detects the r Coriolis force 1 from a vibrated sensing element. Many of these structures employ piezoelectric and electromagnetic mechanisms.

In these cases, the mass that makes up the gyro does not move at a constant speed, but instead vibrates. Therefore, when an angular velocity is applied, the Coriolis force occurs as a vibration torque with a frequency equal to the frequency of the mass. The principle of a vibration type angular velocity sensor is to measure angular velocity by detecting vibrations caused by this torque, and in particular, many sensors using piezoelectric bodies have been devised. (Journal of the Japan Institute of Aeronautics and Astronautics Vol. 23, No. 257, pages 339-350) The structure of a general angular velocity sensor based on the above principle is shown in FIG.

As shown in the figure, a detection piezoelectric element 1 and a driving piezoelectric element 2
are orthogonally joined by a joining member 6, and joined to a tuning fork structure by an electrode block 3. This tuning fork structure is supported by a support rod 4 and fixed to a hess 5. Note that 7 is a lead wire, 8 is a lid pin, and 9 is an adhesive. Since the vibration of the drive piezoelectric element 2 must be transmitted to the detection piezoelectric element 1, the bonding member 6 is made of alumina-based ceramics that have a high bending elastic modulus and have little temperature change, and the adhesive 9 is I use an evokino type material with high adhesive strength.

In order to operate the conventional angular velocity sensor configured as described above, first, in order to drive the pair of driving piezoelectric elements 2, the opposing surfaces are used as a common electrode, and an AC signal is connected between the opposing surfaces and the outer surfaces. multiply. The driving piezoelectric element 2 to which the signal is applied begins to vibrate symmetrically around the electrodes 3, which is what is called a tuning fork vibration, and when angular velocity is added to this, a Coriolis force is generated, and the angular velocity is detected. can.

Problems to be Solved by the Invention The angular velocity sensor having the conventional configuration described above has the following problems.

In other words, when subjected to thermal shock, the sensitivity deteriorated. That is, when a piezoelectric bimorph element is used as the piezoelectric element,
The detection and drive piezoelectric bimorph elements are composed of two pieces of piezoelectric ceramics, and the intermediate electrode on the bonded surface is electrically connected to the outside.
Since it is only through the capacitance of the piezoelectric ceramic and its insulation resistance, when a thermal shock is applied, the electric charge generated by the pyroelectric effect is charged to the intermediate electrode. If a piezoelectric bimorph element is constructed by bonding two pieces of piezoelectric ceramic to a metal reinforcing plate, the piezoelectric effect is caused by the strain caused by the difference in expansion coefficient between the metal reinforcing plate and the piezoelectric ceramic. The generated charge is superimposed on the charge generated by the pyroelectric effect, and the intermediate electrode is charged. If the voltage generated by this charging exceeds the coercive voltage of the piezoelectric ceramic, it destroys the piezoelectric ceramic and deteriorates the sensitivity of the piezoelectric bimorph element.

Deterioration in the sensitivity of the detection piezoelectric bimorph element results in deterioration in the sensitivity of the angular velocity sensor. When the degree of sensitivity deterioration of the drive bimorph element is small, the amplitude adjustment function of the drive circuit increases the amplitude amount and the vibration speed. Since the "Coriolis force" is proportional to the speed of vibration, the sensitivity of the angular velocity sensor will increase to compensate for its degradation. When the degree of sensitivity deterioration of the driving bimorph element is large and exceeds the range of the amplitude adjustment function of the driving circuit, the sensitivity of the angular velocity sensor decreases.

The present invention takes these problems into consideration and aims to provide a highly reliable angular velocity sensor whose sensitivity does not change even when subjected to thermal shock.

Means for Solving the Problems In order to achieve the above object, the present invention has a driving piezoelectric bimorph element, a sensing piezoelectric bimorph element, and a driving piezoelectric bimorph element and a sensing piezoelectric bimorph element whose vibration directions are perpendicular to each other. The piezoelectric bimorph element for driving and the piezoelectric bimorph for sensing element are connected to each other via an intermediate electrode. It has a structure of a piezoelectric bimorph element made by bonding two pieces together.
A resistor is connected between the electrodes on both sides of this piezoelectric bimorph element structure and the intermediate electrode.

In addition, by using a conductive adhesive with a certain specific resistance value to bond the first bonding member to the drive piezoelectric bimorph element and the detection piezoelectric bimorph element, this conductive adhesive allows each piezoelectric bimorph element to A resistive connection is made between the electrodes on both sides and the middle electrode.

Function: The angular velocity sensor of the present invention having the above configuration is characterized in that the electric charge generated at both ends of the piezoelectric bimorph element due to thermal shock is discharged through the resistor connected to both side electrodes and the intermediate electrode of the piezoelectric bimorph element, and is not charged. Do not destroy bimorph elements. Furthermore, if a conductive adhesive is used to bond the first bonding member, the electrodes on both sides and the intermediate electrode exposed on the end face of each piezoelectric bimorph element are connected with a certain resistance value, so a similar effect can be obtained. can get. Therefore, it is possible to obtain a highly reliable angular velocity sensor whose sensitivity does not change even when subjected to thermal shock.

Embodiment FIG. 1 is a perspective view showing an embodiment of the angular velocity sensor according to the present invention as well as a conventional example.The structure thereof, as already described, includes a piezoelectric bimorph element l for detection and a piezoelectric bimorph element for drive. The adhesive 9 used to join the joining member 6 that orthogonally joins the elements 2 is an adhesive and also contains a metal oxide high resistance fiber of 100 kΩ to 100 MΩ.
It also serves as a resistor. Since the adhesive also serves as a resistor, no new steps are required in manufacturing this angular velocity sensor. The operating principle as an angular velocity sensor is the same as that of the conventional example.

If the external temperature of the angular velocity sensor changes drastically, heat cannot be uniformly conducted to the detection piezoelectric bimorph element 1 and the drive piezoelectric bimorph element 2, so charges are generated in these elements due to the pyroelectric effect. . However, since the adhesive 9 attached to the electrode exposed at the end of the element discharges this charge, it is not charged to a high voltage, and the sensitivity of the angular velocity sensor is stabilized. In addition, although the resistance value of the adhesive 9 is limited to 100 MΩ or less here, it is possible to insulate the outside of the sensor to slow down the temperature change of the angular velocity sensor, or to improve the heat conduction inside the sensor. By making heat conduction uniform to the piezoelectric bimorph element 1 for use and the piezoelectric bimorph element 2 for driving, the effects of the present invention can be expected even at a resistance value of 100 MΩ or more.

Further, in this embodiment, the resistance value of the adhesive 9 is set to 100Ω or more, but since the driving frequency of the angular velocity sensor of this embodiment is 1 kHz, this is to prevent signals at that frequency from being attenuated. Therefore, as long as the angular velocity sensor has a high driving frequency, the effects of the present invention can be expected even if the resistance is less than 100Ω.

In this embodiment, a metal oxide is used as the high-resistance material contained in the adhesive 9, but a conductive filler such as metal or carbon may be used in an appropriate amount. If the adhesive strength of the adhesive 9 is important, a resistor may be provided separately from the adhesive 9.

Effects of the Invention As is clear from the above explanation, according to the present invention, the electrodes on both sides of the two piezoelectric elements constituting the bimorph element, that is, the electrodes on both sides and the intermediate electrode of the bimorph element, have a resistance of 100 to 100 MΩ. By electrically connecting a resistor in parallel, the electric charge generated across the piezoelectric bimorph element due to thermal shock is discharged through this resistor.
Since it is not charged, it will not destroy the piezoelectric bimorph element.
A highly reliable angular velocity sensor whose sensitivity does not change even when subjected to thermal shock can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing the configuration of an angular velocity sensor according to an embodiment of the present invention and a conventional example. 1...Piezoelectric bimorph element for detection, 2...
... Drive piezoelectric bimorph element, 3... Electrode block (second bonding member), 6... Bonding member (
first bonding member), 9...adhesive.

Claims (2)

[Claims] (1) A driving piezoelectric element, a sensing piezoelectric element, a first joining member for stacking and joining the driving piezoelectric element and the sensing piezoelectric element so that their vibration directions are perpendicular to each other, and a pair of the joined elements. and a second bonding member for bonding to a tuning fork structure, the driving piezoelectric element and the detection piezoelectric element are two piezoelectric bimorph elements bonded together via an intermediate electrode, and the two piezoelectric An angular velocity sensor with a resistor connected between the electrodes on both sides of a bimorph element and the intermediate electrode. (2) A conductive adhesive having a certain specific resistance value is used to bond the first bonding member to the drive piezoelectric element and the detection piezoelectric element, and both sides of the drive piezoelectric element and the detection piezoelectric element are bonded to each other. Claim 1: A resistance connection is made between the electrode and the intermediate electrode.
The angular velocity sensor described.