Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-07-23
2001-08-21
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
Reexamination Certificate
active
06276206
ABSTRACT:
REFERENCE TO RELATED APPLICATION
The present application stresses the priority of German Patent Application 197 02 392.4 of Jan. 24, 1997 and the German Utility Patent 297 09 688.5 of Jun. 3, 1997, the disclosure content of which also is a subject of the present invention.
AREA OF THE INVENTION
The invention concerns an accelerometer for detecting inertial forces. Essentially, changes independent of time are understood as static position changes and essentially, time-dependent changes are understood as dynamic position changes.
PRIOR ART
An accelerometer of this kind is known from GB 2 022 822 A with a phase boundary between a liquid and air in a vessel. In this case, light is beamed through the phase boundary, detection means detecting the varying reflective index as a result of a motion of the sensor and this the phase boundary. Differential means are provided which make it possible to differentiate a time-dependent change of the phase boundary based on a vibration from a change dependent on time and based on simple motion. Evaluation means make it possible to determine the time-dependent change in the phase boundary as acceleration in stages.
A sensor completely filled with gas and liquid, in the case of which measuring sections are formed with a reflex light barrier, is known from WO 87/05569. A change in the reflection behavior is evaluated as an acceleration signal for triggering an occupant-protection device of a motor vehicle. However, low deceleration values cannot be determined reliably with this.
A sensor, in the case of which a phase boundary is detected between an external, approximately ring-shaped electrode and a central electrode, is known from FR-A 2 311 310. In this way it is not possible to interrogate the measuring sections in each case, so that this sensor is not in a position to make static changes differentiable from dynamic changes.
An accelerometer with a phase boundary between two media is known from GB-A 2 032 110, two measuring sections being formed between two emitting elements and one sensing element separated therefrom. The difference values detectable thereby are not free of environmental influences, such as, e.g., an aging of the sensor or evaporation of liquid, but in particular the sensor is not capable of differentiating dynamic positional changes from static positional changes of the phase boundary.
An acceleration sensor of this kind is known from U.S.-A No. 39,929,512. Two media, a liquid medium and a gaseous medium, which form a phase boundary between them, are provided in a housing. In the case of an acceleration, electrodes, which detect the positional change of the phase boundary from gradual determination of the acceleration, are provided as detection means. If a sensor of this type is turned out of the zero position, an acceleration signal is produced, although an acceleration has not actually taken place. A comparable device is known from U.S. Pat. No. 3,442,023.
A sensor, which in particular is suited for detecting the wetting of a surface, in an optical and also capacitative way, is known as a detection element from WO-A 95/01561. The detection is performed at least at two measuring sections, which are acted upon alternately, the measured values being detected with the same timing, e.g. by light or field sensitive elements. The measured values detected are fed to a comparator for difference value formation and a detection signal is determined from this. This detection signal is leveled as compared with zero with the use of a time constant adjusted to the respective application purpose, so that outside influences can be largely suppressed. For the leveling the output power of the sensor or the amplification power of the receiver is regulated on the basis of the signal determined. The leveling also makes a relatively rapid dynamic time-dependent detection of the changes possible.
Further there are known to be accelerometers which have great mass inertias, so that, in particular, in the case of use in a motor vehicle the regular motions of the vehicle at the time of driving along streets or in uneven terrain do not lead to accelerations. Therefore a corresponding acceleration signal is produced only when there is a strong acceleration, more precisely a deceleration, e.g. in the case of an accident. A sensor of this type is used, e.g. for triggering the air bag.
SUMMARY OF THE INVENTION
Starting from this prior art, the object of the present invention is to create an accelerometer reacting to acceleration and deceleration sensitively, but which produces almost no signal if the sensor is turned out of the zero position.
This object is attained by means of an accelerometer.
The accelerometer comprises a vessel having several separable and immiscible media held therein, wherein at most one medium is gaseous and the other media are liquid; at least one phase boundary formed between the media; a detector which detects a static positional change of the phase boundary in the case of an appearance of acceleration; and an evaluator which evaluates a dynamic positional change for gradual determination of the acceleration. The detector detects the positional change of phase boundaries which are formed by at least three separable and immiscible media as a detection signal, at least two of media being liquid. The detector determines the detection signal as an acceleration signal and feeds the acceleration signal to the evaluator. The media form at least two phase boundaries as a discriminating means for discriminating the dynamic positional change from the static positional change.
In this case different media are arranged over one another, the positional changes of the phase boundary between these media being detected in the case of the appearance of an acceleration. Of course, in order to differentiate accelerations to be detected from static positional changes, differentiation means are provided which make the time-dependent dynamic changes detectable so long as it is not a matter of accelerations remaining constant for a longer time, such as e.g., the constant radial acceleration of a car body moving uniformly.
Thus different media are arranged over one another so that in the case of a positional change of the accelerometer with velocity remaining the same, almost no signal is emitted, since the phase boundaries between the different media follow this motion uniformly. On the other hand, if there is an acceleration or deceleration, the phase boundaries behave differently with respect to time because of their different physical properties, so that these two phase boundaries provide a dynamic, unambiguous gradual acceleration signal as a differentiation means since in the case of acceleration or deceleration the separation of the phase boundaries from one another changes.
Alternatively, in the case of a configuration with e.g. only one phase boundary and a differentiation means connected at the outlet side for detecting the positional change a dynamic positional change can be detected. The unambiguous nature of the acceleration signal is achieved by the fact that, as in the case of the previously known sensor, the detection signal determined is compared with zero with a time constant, so that a time-dependent signal detection which also changes unambiguously with the position of the phase boundary results. Preferably the time constant is chosen here so that the signals detected are leveled faster than in the case of normal operation; in particular in the case of the preferred area of application in motor vehicles in the case of normal driving, accelerations and decelerations as a result of the acceleration of the vehicle or as a result of braking of the vehicle result. In this way at least one slow rotation, as results in the case of the motion of a vehicle, e.g., at the time of the transition from driving up a mountain to driving down a valley, are differentiated from a rapid deceleration at the time of braking.
Further advantages result from the sub-claims and the following description of preferred specific embodiments.
REFERENCES:
patent:
Colburn LLP Cantor
Kwok Helen
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