Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2003-04-04
2004-09-21
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
Reexamination Certificate
active
06792806
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an acceleration sensor for detecting an acceleration, and more particularly to an acceleration sensor for detecting an acceleration by sliding vibration, which is exerted when an acceleration is applied, and to an acceleration sensor device constructed by storing this acceleration sensor in a package.
An acceleration sensor is installed in equipment to monitor an abnormal condition of the equipment by detecting an acceleration and vibration of the equipment. For example, the acceleration sensor is used to prevent errors in reading and writing data resulting from vibration and shock in a hard disk drive, to prevent hand shaking in a video camera, to actuate an air bag in a vehicle, etc.
With a reduction in size and an increase in the performance of equipment in which an acceleration sensor is to be installed, there has been a demand for the development of a small-sized, high-performance acceleration sensor capable of being mounted on a surface of the equipment. As such a small-sized acceleration sensor, an acceleration sensor using a piezoelectric element has been conventionally put into practice. Disclosed examples of such an acceleration sensor include an acceleration sensor which detects an acceleration by using a deflection of a piezoelectric single crystal (Japanese Patent Application Laid-Open Nos. 10-206456/1998 and 11-211748/1999) and an acceleration sensor which detects an acceleration by using a deflection of piezoelectric ceramic (Japanese Patent Application Laid-Open No. 6-273439/1994).
Acceleration sensors using the deflection of a piezoelectric single crystal or the deflection of piezoelectric ceramic as mentioned above can improve the detection sensitivity by increasing the deflection to increase the stress. Thus, in order to improve the detection sensitivity for high performance, the mass needs to be increased to produce a larger deflection, causing a problem that the acceleration sensor becomes heavier and larger in size. On the other hand, when the piezoelectric element is made thicker, it does not easily deflect and causes a problem that the detection sensitivity is lowered. Then, in order to improve the detection sensitivity, there have been proposals to make the piezoelectric element thinner, to stick two pieces of extremely thin piezoelectric elements together, etc. However, such proposals are associated with problems that the fabrication process is complicated and the cost is increased.
Therefore, the applicant of the present invention proposed an acceleration sensor capable of detecting an acceleration with good sensitivity by a small-sized structure (Japanese Patent Application Laid-Open No. 2000-97707). This acceleration sensor comprises a vibrator and a weight section which is connected and supported at a position different from the position of the center of gravity of an assembly of the vibrator and weight section, and obtains the magnitude of an applied acceleration by detecting the amount of characteristic (sliding vibration) of the vibrator corresponding to an angular moment exerted in the weight section when the acceleration is applied. The present inventors are pursuing the development and improvement of such an acceleration sensor that has a small-sized structure and a high detection sensitivity without increasing the size of the vibrator to achieve high performance because it detects sliding vibration instead of deflective vibration.
BRIEF SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above-mentioned circumstance, and its object is to provide an acceleration sensor which is an improvement of the acceleration sensor proposed in Japanese Patent Application Laid-Open No. 2000-97707 and capable of realizing a further reduction in size and cost while maintaining high performance.
Another object of the present invention is to provide an acceleration sensor which does not limit sliding vibration (or, shearing strain) of a vibrator for the purpose of preventing a lowering of the detection performance.
Still another object of the present invention is to provide an acceleration sensor capable of improving the connectivity between a vibrator and a weight section.
Yet another object of the present invention is to provide an acceleration sensor device having a package structure capable of storing such an acceleration sensor efficiently without deteriorating its detection performance.
An acceleration sensor of the first aspect of the present invention comprises a vibrator provided with an electrode and subject to a sliding vibration; and a weight section connected to the vibrator and supported at a position different from the position of the center of gravity of an assembly of the vibrator and weight section, wherein the weight section is provided with a wiring pattern connected to the electrode, the vibrator detects an angular moment about the support point as sliding vibration, which is exerted in the weight section when an acceleration is applied, and an electrical signal corresponding to the applied acceleration is output from the electrode through the wiring pattern. In this structure, the weight section is provided with the wiring pattern for drawing an electrical signal corresponding to an acceleration to be detected, and also functions as a signal detecting substrate. Therefore, it is not necessary to newly provide a signal detecting substrate, resulting in a simplified structure and a reduction in the cost.
In an acceleration sensor of the second aspect of the present invention, a detection portion for sliding vibration of the vibrator is divided by electrodes which are a plurality of divided electrode parts. Since the detection portion for sliding vibration of the vibrator is divided into a plurality of parts by the electrodes, the detection section of the vibrator can be divided simply, thereby achieving a reduction in the cost.
In an acceleration sensor of the third aspect of the present invention, the detection portion for sliding vibration of the vibrator is divided by the electrodes which are a plurality of divided electrode parts and by a groove connected to the electrodes. Since the detection portion for sliding vibration of the vibrator is divided into a plurality of parts by the formation of the groove, the detection portion of the vibrator is certainly divided and a number of acceleration sensors are readily manufactured, thereby achieving a reduction in the cost.
In an acceleration sensor of the fourth aspect of the present invention, the vibrator has substantially a rectangular parallelepiped shape, and the groove has a depth of not less than 10% of the thickness of the vibrator. Since the groove is formed to have a depth of not less than 10% of the thickness of the vibrator in the process of dividing the detection portion of the vibrator into a plurality of parts by the formation of the groove, it is possible to achieve not only a reduction in the cost, but also an improvement in the detection sensitivity.
In an acceleration sensor of the fifth aspect of the present invention, a position where the detection portion is divided is a position where a charge distribution by the sliding vibration is substantially zero. Since the detection portion of the vibrator is divided at a position where the angular moment of the weight section is substantially zero, i.e., a position where the charge distribution by the sliding vibration of the vibrator is substantially zero, it is possible to achieve not only a reduction in the cost, but also an improvement in the detection sensitivity.
In an acceleration sensor of the sixth aspect of the present invention, the vibrator and weight section have substantially a rectangular parallelepiped shape, and a length (width) of the vibrator in an acceleration detecting direction is not more than a length (width) of the weight section in the acceleration detecting direction. It is therefore possible to reduce an error signal (crosstalk) generated when an acceleration in a direction different from that of an acceleratio
Ishikawa Hiroshi
Tanaka Hiroshi
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