Measuring and testing – Instrument proving or calibrating – Volume of flow – speed of flow – volume rate of flow – or mass...
Patent
1991-08-14
1994-03-22
Chapman, John E.
Measuring and testing
Instrument proving or calibrating
Volume of flow, speed of flow, volume rate of flow, or mass...
73517R, G01P 2100
Patent
active
052953866
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an apparatus for detecting a physical quantity acting as an external force, e.g., a force exerted on a working body, an acceleration exerted on a weight body, or a magnetism exerted on a magnetic body. Particularly, this invention relates to a signal processing circuit, a testing method, and a manufacturing method for a force sensor serving as a main part of such a detector, and a structure of this force sensor.
BACKGROUND ART
In recent years, there have been proposed force sensors including, arranged on a semiconductor substrate, resistance elements having the property of piezo resistance wherein the electric resistance varies in dependency upon a mechanical deformation to detect a force from changes in resistance values of the resistance elements. Further, acceleration sensors or magnetic sensors to which such force sensors are applied are also proposed. In either detector, a strain generative body partially having flexibility is used to detect a mechanical deformation produced in the strain generative body as changes in electric resistance of the resistance elements. A working body is provided for exerting a force on the strain generative body. If a weight body responsive to acceleration is used as the working body, an acceleration sensor is provided. Further, if a magnetic body responsive to magnetism is used as the working body, a magnetic sensor is provided.
For example, in U.S. Pat. No. 4905523, U.S. patent applications No. 295210, No. 362399, No. 470102, and No 559381, force/acceleration/magnetic sensors according to the invention of the inventor of this application are disclosed. Further, in U.S. patent application No. 526837, a novel manufacturing method for a sensor of this kind is disclosed.
The force sensors disclosed in these patent materials can detect a direction and a magnitude of an external force applied to a predetermined working point on the basis of changes in resistance values of resistance elements formed on a single crystal substrate. If a weight body is formed at the working point, it is also possible to detect, as a force, an acceleration exerted on the weight body. Accordingly, this permits application as an acceleration sensor. Further, if a magnetic body is formed at the working point, it is also possible to detect, as a force, magnetism exerted on the magnetic body. Accordingly, this permits application as a magnetic sensor.
However, the conventional force sensors (or acceleration sensors, or magnetic sensors based on the same principle) have the problem that there may occur interference in the output characteristic with respect to respective axial directions of two-dimensions or three-dimensions. For example, in the case of the three dimensional acceleration sensor, components in the X-axis, Y-axis and Z-axis directions of an acceleration exerted on a predetermined working point must be independently detected, respectively. In the case of conventional sensors, however, these components in respective axial directions interfere with each other. As a result, a detected value of the component in one axial direction was influenced to some extent by detected values of components in other axial directions. Such an interference is not preferable because it lowers reliability of measured values.
With the above in view, a first object of this invention is to provide a signal processing circuit capable of obtaining correct detected values free from interference of the components in other axial directions.
In order to mass produce such sensors to deliver them on the market, it is necessary to conduct a test or inspection at the final stage of the manufacturing process. The test for the force sensor can be carried out relatively with ease. Namely, this test may be accomplished by applying a force of a predetermined magnitude to the working point in a predetermined direction to check a detected output at this time. However, the test for the acceleration sensor or the magnetic sensor becomes more complicated. Since the sensor body is in a seale
REFERENCES:
patent: 4941354 (1990-07-01), Russell et al.
patent: 5060504 (1991-10-01), White et al.
patent: 5103667 (1992-04-01), Allen et al.
H. V. Allen et al., "Accelerometer Systems with Self-Testable Features," Sensors and Actuators, 20 (1989), pp. 153-161.
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