Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-09-09
2002-03-26
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C310S363000
Reexamination Certificate
active
06360600
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an angular velocity sensor which can be employed in various control systems, such as a vehicle motion/behavior control system as well as a navigation system, or in a video camera for compensating the operator's hand movement, and more particularly to an angular velocity sensor which detects an angular velocity using a piezoelectric vibrator.
Japanese Unexamined Patent Application No. 8-210860, published in 1996, discloses a conventional angular velocity sensor which comprises a piezoelectric vibrator configured into a tuning fork with a pair of arm bars and a connecting bar. According to this angular velocity sensor, the vibrator causes a predetermined vibration in a driving direction along which the arm bars are arrayed. When the sensor is subjected to an angular velocity, a Coriolis force derived from the angular velocity is detected as a vibration change of the vibrator caused in a sensing direction normal to the driving direction.
Japanese Unexamined Utility Application No. 5-71715, published in 1993, discloses another angular velocity sensor employing a lead wire arrangement according to which terminals of lead wires are located adjacent to a vibrator to shorten the length of each lead wire in the air.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel, accurate and reliable angular velocity sensor.
Another object of the present invention is to provide a manufacturing method for fabricating this angular sensor.
Another object of the present invention is to provide a piezoelectric vibrator element used in this angular sensor.
In order to accomplish the above-described and other related objects, one aspect of the present invention provides an angular velocity sensor with a vibrator. The vibrator comprises a piezoelectric body configured into a predetermined shape having at least one pair of arm bars and a connecting bar. Electrodes are formed on an outer surface of the piezoelectric body. At least one drive electrode receives an alternating voltage to vibrate the arm bars in a drive axis direction along which the arm bars are arrayed. At least one sensing electrode detects a vibration caused in a sensing axis direction normal to the drive axis direction. The outer surface of the piezoelectric body comprises a front face and a rear face both being U-shaped. The drive electrode and the sensing electrode are formed on the front face, while a first reference electrode having a predetermined reference potential is formed on the rear face. At least one second reference electrode is formed on at least one side face of the aim bars of the piezoelectric body at a position corresponding to the sensing electrode. The second reference electrode is connected to the first reference electrode formed on the rear face.
Preferably, at least one additional sensing electrode is formed on the rear face at a predetermined arm portion corresponding to the sensing electrode, and at least one short-circuit electrode is formed on the side face of the arm bars to connect the additional sensing electrode to the sensing electrode.
Preferably, at least one ground electrode is formed on the front face at a predetermined position of the arm bars, and at least one short-circuit electrode is formed on the side face to connect the ground electrode to the first reference electrode.
Preferably, at least one monitor electrode is formed on the front face at a predetermined position of the arm bars, and the monitor electrode detects a vibration caused in the drive axis direction.
Preferably, the piezoelectric body is polarized from the front face to the rear face or vice versa by applying a predetermined voltage between the electrodes formed on the front and rear faces, and the electrodes formed on the side faces of the arm bars are fabricated after finishing the polarization of the piezoelectric body.
Preferably, the electrodes formed on the side faces of the arm bars are made of a low-temperature hardening type conductive resin.
Preferably, metallic wires are wire bonded to the electrodes formed on the front face of the piezoelectric body.
Preferably, a bonding position of a metallic wire connected to the sensing electrode formed on the front face is offset toward the connecting bar.
Preferably, the vibrator is secured to a base member, and the metallic wires are connected to terminals provided on the base member for inputting and outputting signals.
Another aspect of the present invention provides a manufacturing method for an angular velocity sensor. According to this manufacturing method, a first step is performed for forming the drive electrode and at least one polarizing electrode on a U-shaped front face of the piezoelectric body, and for forming a common electrode on a U-shaped rear face at a region corresponding to the drive electrode and the polarizing electrode. The polarizing electrode is positioned closer to a distal end of a corresponding arm bar than the drive electrode. Succeeding to the first step, a second step is performed for polarizing the piezoelectric body by applying a predetermined polarization voltage between the common electrode formed on the rear face and the electrode formed on the front face. Then, succeeding to the second step, a third step is performed for forming the sensing electrode on at least one side face of the piezoelectric body at a predetermined arm portion corresponding to the polarizing electrode.
Preferably, the first step includes a formation of at least one monitor electrode on the front face for monitoring a vibrating condition of a corresponding arm bar in the drive axis direction, so that the monitor electrode is interposed between the polarizing electrode and the drive electrode. The second step includes an application of the polarization voltage between the monitor electrode and the common electrode for polarizing the piezoelectric body.
Preferably, the first step includes a formation of at least one pad electrode on the front face for outputting a detection signal. The third step includes a formation of at least one lead electrode on at least one side face for connecting the sensing electrode and the pad electrode.
Preferably, the pad electrode is formed at a predetermined arm portion closer to a distal end of a corresponding arm bar than the polarizing electrode or at a predetermined arm portion closer to the connecting bar than the polarizing electrode.
Preferably, the first step includes a formation of at least one ground electrode on the front face for connecting the common electrode to a reference potential. The third step includes a formation of at least one short-circuit electrode on at least one side face for connecting the common electrode to the ground electrode.
Preferably, a processing temperature for the electrode formed on the side face in the third step is lower than a Curie temperature of the piezoelectric body.
Preferably, a conductive resin, hardening at a temperature lower than the Curie temperature of the piezoelectric body, is used for the formation of the electrode formed on the side face in the third step.
Preferably, a metallic deposition is used for forming the electrode on the side face in the third step.
Another aspect of the present invention provides an angular velocity sensor with a vibrator, a base plate and a supporter interposed between the vibrator and the base plate. The vibrator comprising a piezoelectric body having at least one polygonal arm bar and electrodes formed on the piezoelectric body. The electrodes include at least one drive electrode, at least one outlet electrode and at least one sensing electrode formed on a first face of the piezoelectric body, and a common electrode formed on an opposing second face of the piezoelectric body. The common electrode is integrally connected to the outlet electrode on the first face. The base plate confronts with the second face. The supporter supports the vibrator to the base plate. The piezoelectric body is polarized in an X-axis direction from the first face to the second face. Th
Kamimura Rikiya
Kuroki Hisao
Denso Corporation
Kwok Helen
Pillsbury & Winthrop LLP
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