Acceleration sensor

Details Acceleration sensor Acceleration sensor

1996-11-21

1998-11-03

Williams, Hezron E.

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

D7351409, D73862581, D7351433, D73715, D73720, D73726, 338 2, 338 4, G01P 1500

Patent

active

058311653

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an acceleration sensor that detects an acceleration of an object to which the sensor is attached based on pressure changes caused by the inertia of the medium filling the sensor.
2. Description of the Related Art
There have been proposed various types of acceleration sensors for detecting the acceleration of an object to which the sensor is attached by detecting pressure changes. An acceleration sensor 70 illustrated in FIG. 16 is an example of such a sensor. The acceleration sensor 70 includes a cylindrical sensor mount 72 mounted on a circuit board 71. A diaphragm type semiconductor pressure sensitive sensor chip (hereinafter simply referred to as a sensor chip), on which diffusion gauges 73 are formed, is provided in the sensor mount 72. Silicon gel 75 having a required density fills the interior of the sensor mount 72 to cover the sensor chip 74. In the acceleration sensor 70 having the above structure, acceleration of an object to which the sensor 70 is attached causes the silicon gel 75 to fluctuate in response to the acceleration. The pressure caused by the fluctuation of the silicon gel 75 is transmitted to the sensor chip 74 and therefore strains the sensor chip 74. A force is applied to the diffusion strain gauge 73 in accordance with the strain. The diffusion strain gauge 73 then senses the force applied thereto and outputs an electrical signal in accordance with the acceleration as a detection signal. In other words, since the sensor chip 74 is subjected to the pressure of the silicon gel 75, the sensor chip 74 is therefore most susceptible to the pressure caused by acceleration in the vertical direction with respect to the circuit board 71 (direction z in the figures). The principle detectable direction of the acceleration sensor 70 is therefore its vertical direction (direction z in the figures).
FIG. 17 shows another acceleration sensor 80. In the acceleration sensor 80, a weight portion 84 is attached to a silicon substrate 81 by a cantilever 82. A diffusion strain gauge 83 is provided at the proximal portion of the cantilever 82. The silicon substrate 81 surrounds the weight portion 84 with a predetermined space therebetween. In the acceleration sensor 80 of the above structure, acceleration of an object to which the sensor 80 is attached causes the weight portion 84 to bend in response to the acceleration. This strains the proximal portion of the cantilever 82. A force is applied to the diffusion strain gauge 83 in accordance with the strain. The diffusion strain gauge 83 then senses the force and outputs an electrical signal in accordance with the acceleration as a detection signal. The weight portion 84 therefore bends most when the object and the acceleration sensor 80 are accelerated in the vertical direction with respect to the weight portion 84 (direction z in the figures). This allows a strong detection signal to be produced. The principle detectable direction of the acceleration sensor 80 is therefore its vertical direction (direction z in the figures).
There has been also proposed a three dimensional acceleration sensor for detecting accelerations in a vertical direction (z direction) as well as horizontal directions (x and y directions). FIGS. 18 and 19 show such an acceleration sensor 90. The acceleration sensor 90 has a weight portion 91 having a shape of a truncated pyramid supported by cantilevers 92 to 95. The cantilevers 92 to 95 have diffusion strain gauges 96 to 99 on their top surfaces, respectively. In the acceleration sensor 90 of the above structure, as in the case of the acceleration sensor 80, acceleration of an object to which the sensor 80 is attached causes the weight portion 91 to bend in response to the acceleration. This strains the cantilevers 92 to 95. Force is applied to the diffusion strain gauges 96 to 99 in accordance with the strain. The diffusion strain gauges 96 to 99 then sense the force applied thereto and issue detection signals in accordance with the accelerat

REFERENCES:
patent: 5461922 (1995-10-01), Koen
patent: 5509308 (1996-04-01), Iwata et al.

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