Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Patent
1998-06-12
2000-06-20
Moller, Richard A.
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
73514, 73340, 7351417, G01P 1508
Patent
active
060764031
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The field of the invention is that of electromagnetic accelerometers including a moving mass and piezoelectric gauges for detecting the displacement of this mass and controlling a system that controls the position of this mass, using phenomena of electromagnetic induction. This type of accelerometer can be produced, in particular, from silicon wafers using technologies derived from those developed from the manufacture of integrated circuits and can, in particular, be used in geophones for making a very detailed analysis of the nature of the Earth's strata in order to detect any sources of oil.
DISCUSSION OF THE BACKGROUND
In general, the strain gauges of an electromagnetic accelerometer are intended, by means of an electronic circuit, to generate a supply current for a coil which, using phenomena of electromagnetic induction, compensates for a displacement of the moving mass under the effect of external conditions, for example of seismic movements involved in geophone applications. The magnitude of the acceleration experienced by the moving mass is deduced from the value of the supply current to the coil needed to prevent the displacement of the moving mass. The overall principle of operation of this type of accelerometer is described in FIG. 1.
A moving mass 2 is suspended by arms 80 and 81 from a fixed frame 3. The moving mass, the suspension arms and the fixed frame may advantageously be made from silicon wafers. A coil 6 is attached to the moving mass 2. This coil is associated with a magnetic circuit consisting of two pole pieces and the pole pieces define two gaps for routing the magnetic field of a permanent magnet 5 the axis of magnetization of which is perpendicular to the surface of the moving mass 2. Suspension arms, for example the upper arms 80 and 81, include strain gauges 10, which constitute detectors of the displacement of the moving mass. These strain gauges are intended, by means of an electronic circuit 11, to generate a supply current I for the coil 6 so that using phenomena of electromagnetic induction, they can compensate for a displacement of the moving mass 2 under the effect of external conditions, for example seismic movements. Compensation for the displacement of the moving mass 2 under the action of the electromagnetic-induction forces takes place along a direction depicted by the double-headed arrow F which corresponds to the axis of magnetization of the magnet 5. The magnitude of the displacement that the moving mass 2 would have experienced under the effect of the external conditions is deduced from the value of the current I needed by the control system to prevent the displacement of the moving mass. The value of the current I is extracted, for example, by means of a resistor R, in the form of a voltage between two output terminals C and D.
A limit on the sensitivity of this kind of accelerometer lies in the stiffness of the suspension arms, which are typically made of silicon, which means that a low force exerted on the moving mass causes no displacement thereof.
Now, in applications such as those for which the present invention is intended, and which have to do with identifying the Earth's strata, very high sensitivity is absolutely essential. This kind of device operates according to the following principle. Excitation sources placed at ground level send mechanical waves into the ground, and these act on accelerometers. The response of the said accelerometers provides information on the nature of the Earth's strata encountered by the mechanical waves created.
SUMMARY OF THE INVENTION
In order to solve the problem of the positive stiffness of the suspension arms of the moving masses present in electromagnetic accelerometers like those described earlier, the subject of the invention is an accelerometer which uses a magnetic motor with negative stiffness, opposing the positive stiffness of the suspension arms and contributing to increasing the sensitivity of the said accelerometer.
More specifically, the subject of t
REFERENCES:
patent: 4314202 (1982-02-01), Okubo
patent: 4446741 (1984-05-01), Sirokorad et al.
patent: 4473768 (1984-09-01), Kerr et al.
patent: 5693883 (1997-12-01), Giroud et al.
Giroud Pierre
Guillemin Pierre
Migeon Andre
Pedraza-Ramos Sylvie
Moller Richard A.
Sextant Avionique
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