Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-02-15
2001-08-07
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06269697
ABSTRACT:
TECHNICAL FIELD
This invention relates to an acceleration sensor using piezoelectric element and, more particularly, to a sensor capable of detecting respective acceleration components in multi-dimensional axes directions and capable of detecting respective angular velocity components about multi-dimensional axes.
BACKGROUND ART
In automobile industry and machinery industry, etc., there has been increased demand for sensors capable of precisely detecting physical quantity such as acceleration or angular velocity. Particularly, small sensors capable of detecting these physical quantities every two-dimensional or three-dimensional respective components-are demanded.
As such small sensors, a novel sensor which has been developed by the same inventor as that of the present application has been disclosed in the Japanese Patent Application Laid Open No. 5-26744/1993 publication. In this novel sensor, plural sets of detection elements comprised of a piezoelectric element are prepared and these sets of detection elements are disposed on a flexible substrate. This novel sensor is of a structure in which a working body is attached on the flexible substrate so that when external force is applied to the working body, bending takes place in the flexible substrate. This bending is transmitted to the piezoelectric element, and charges corresponding to the bending are produced in the piezoelectric element. Thus, the applied external force is detected on the basis of such charges produced. This is the fundamental principle of the novel sensor. Since a way of bending changes in dependency upon the direction of the applied external force, an approach is employed to detect the state of charges produced with respect to plural piezoelectric elements disposed at predetermined respective positions, thereby making it possible to detect magnitude and direction of the applied force. Moreover, in the Japanese Patent Laid Open Application No. 7-43226/1995 publication, a technology for permitting similar detection by lesser number of detection elements is disclosed.
On the other hand, in the International Laid Open No. W094/23272 publication based on the Patent Cooperation Treaty, there is disclosed an angular sensor in which plural piezoelectric elements are similarly disposed on a flexible substrate to thereby detect angular velocity components about respective three-dimensional axes. This angular velocity sensor utilizes the principle that when an object is oscillated in the Y-axis direction in the state where angular velocity &ohgr;x about the X-axis is applied, Coriolis force is exerted in the Z-axis direction. Namely, an a.c. voltage is applied to a predetermined piezoelectric element disposed on the flexible substrate to oscillate the working body attached on the flexible substrate in the Y-axis direction. In this case, since when angular velocity &ohgr;x about the X-axis is applied, Coriolis force is exerted on the working body in the Z-axis direction, the working body is caused to undergo displacement in the Z-axis direction. This displacement is detected by charges that the piezoelectric element produces to thereby indirectly detect the applied angular velocity &ohgr;x.
In the case where acceleration components or angular velocity components with respect to three-dimensional directions are detected by a single sensor, the technologies which have been proposed until now-are required to dispose a large number of electrodes at predetermined positions, resulting in the problem that the structure becomes complicated as a whole. In sensors of such complicated structure, there takes place the problem that miniaturization becomes difficult, so mass-productivity is poor.
DISCLOSURE OF THE INVENTION
In view of the above, an object of this invention is to provide an acceleration/angular velocity sensor using a piezoelectric element which is simple in structure, is suitable for miniaturization and mass-approachability, and is capable of detecting acceleration components and/or angular velocity components relating to multi-dimensional direction.
In order to attain such an object, the sensor according to this invention has features as described below.
(1) A first mode of this invention resides in an acceleration sensor using a piezoelectric element for detecting acceleration components in plural coordinate axis directions in an XYZ three-dimensional system, the sensor comprising a piezoelectric element in a plate form, five upper electrodes formed on an upper surface of the piezoelectric element and a lower electrode formed at a position facing to the respective upper electrodes on a lower surface of the piezoelectric element,
wherein an origin of the XYZ three-dimensional coordinate system is defined substantially at a central position of the upper surface of the piezoelectric element,
wherein the piezoelectric element extends along an XY plane and includes a central portion around the origin, a flexible portion with flexibility surrounding the central portion and a peripheral portion surrounding the flexible portion, so that said central portion and said peripheral portion are caused to undergo displacement relative to each other by bending of the flexible portion,
wherein either one of the central portion and the peripheral portion is fixed to a sensor casing as a fixed portion, and the other is supported as a working portion in a state to be displaced by force applied in respective coordinate axis directions, and
wherein the five upper electrodes are constituted with a first upper electrode formed in a negative region with respect to the X-axis and having a shape symmetrical with respect to the X-axis, a second upper electrode formed in a positive region with respect to the X-axis and having a shape symmetrical with respect to the X-axis, a third upper electrode formed in a negative region with respect to the Y-axis and having a shape symmetrical with respect to the Y-axis, a forth upper electrode formed in a positive region with respect to the Y-axis and having a shape symmetrical with respect to the Y-axis and a fifth upper electrode formed in a region surrounding a periphery of the origin, at least each portion of these respective upper electrodes being located on the flexible portion,
the acceleration sensor further comprising,
force detecting means for detecting a force in a particular axis direction applied to the working portion on the basis of charges produced in the upper electrodes, and
circuit means for outputting a detected value by the force detecting means with respect to the particular axis direction as an electric signal so as to carry out detection of acceleration in the particular axis direction.
(2) A second mode of this invention resides in an acceleration sensor using a piezoelectric element according to the first mode,
wherein an annular groove to surround a periphery of the origin is formed at the lower surface of the piezoelectric element, a thickness of the portion where the annular groove is formed is caused to be thinner than a thickness of others, and the portion thin in thickness is used as a flexible portion.
(3) A third mode of this invention resides in an acceleration sensor using a piezoelectric element for detecting acceleration components in plural coordinate axis directions in an XYZ three-dimensional system, the sensor comprising a piezoelectric element in a plate form, five upper electrodes formed on an upper surface of the piezoelectric element, a lower electrode formed at a position facing to the respective upper electrodes on a lower surface of the piezoelectric element and a strain generative body in a plate form for supporting the lower electrode from below,
wherein an origin of the XYZ three-dimensional coordinate system is defined substantially at a central position of an upper surface of the strain generative body,
wherein the strain generative body extends along an XY plane and includes a central portion around the origin, a flexible portion with flexibility surround surrounding the flexible portion, so that said central portion and said peripheral portion ar
Kwok Helen
Ladas and Parry
Wacoh Corporation
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