Acceleration sensor and process for its production

Details Acceleration sensor and process for its production Acceleration sensor and process for its production

1994-02-04

1995-05-16

Powell, William

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

73704, 216 87, 216 39, 216 83, G01P 1508, B44C 122

Patent

active

054150434

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an acceleration sensor and a process for producing the sensor.


BACKGROUND OF THE INVENTION

Acceleration sensors, in which an electric contact is closed through the deflection of a spring-mass system, have already been disclosed by the German Patent 29 23 029. In these sensors, the deflection of the spring-mass system is linear to the acceleration. The movement of the spring-mass system is damped to improve the switching performance of the sensor. The German Patent 37 27 142 has already disclosed processes for producing sensors by irradiating a plastic layer through a mask with X-ray radiation, dissolving out the irradiated regions, and galvanically filling the thus created negative sensor matrix with a metal.


SUMMARY OF THE INVENTION

In contrast, the advantage of the sensor according to the invention is that the spring-mass system of the sensor is not deflected until a predetermined acceleration value is exceeded. This makes it possible for the sensor signal to be evaluated quite simply. Another advantage to be considered is that the contact closing takes place very reliably and entails only negligible bouncing. Therefore, large currents can also flow through the sensor according to the invention. In addition, mechanical spring-mass systems are particularly insensitive.
The spring-mass system and the contacts are produced quite simply on an insulating, plate-shaped substrate. Because the walls of the metal structures are oriented predominantly at right angles to the substrate, the clearances among the sensor structures are precisely defined. Since the contact points are made of another material, the resistance of the contact is diminished. The properties of the springs, which are designed as bending bars, can be calculated quite simply. The desired non-linear switching performance of the spring-mass system is realized with springs that show a slight curvature. Springs, which are straight, but are not aligned parallel to one another, demonstrate the same switching performance. With the smallest degree of complexity, the sensors are able to be realized with a seismic mass between two bearing blocks and, in each case, with a spring between the bearing blocks and the seismic mass. By adding electrostatic actuators, the sensors can be switched arbitrarily through the application of a voltage. The functioning of the sensors is checked in this manner. An especially simple design of the electrostatic actuators consists of comb-shaped electrodes that mate into one another. The damping and thus the dynamic response of the sensors is influenced through the formation of a small gap between the spring-mass system and the contact block. The damping is adjusted by means of additional venting slits. The responsivity of the sensors is influenced through the application of an electric voltage between the contact block and the seismic mass.
One advantage of the process according to the invention is that the sensors are produced with small manufacturing tolerances. Another advantage to consider is the fact that the disclosed process allows a parallel production of a plurality of sensors and, thus, lowers the manufacturing costs for the individual sensors. Producing sensors by means of X-ray radiation is advantageous due to the low expenditure entailed by small series. In mass production, it is more cost-effective to mold plastic structures. The application of additional X-ray irradiation makes it possible to produce metal structures out of different materials.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sensor according to the invention in the original position;
FIG. 2 a sensor in the deflection position;
FIG. 3 a sensor with straight helical springs;
FIG. 4 the contact points;
FIG. 5 a sensor with additional actuators;
FIG. 6 a sensor with a specially designed contact block;
FIG. 7 a detail of the gap between the contact block and the seismic mass;
FIGS. 8 and 9 the production of the sensor.


DETAILED DESCRIPTION

In FIG. 1 and FIG. 2, 1 denotes the spri

REFERENCES:
patent: 2930863 (1960-03-01), Pasieka
patent: 4855544 (1989-08-01), Glenn
patent: 4893509 (1990-01-01), MacIver et al.
patent: 5025346 (1991-06-01), Tang et al.
patent: 5045152 (1991-09-01), Sickafus
patent: 5129983 (1992-07-01), Greiff

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