Device for determining the rotational speed

Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration

Reexamination Certificate

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Details

C073S504130

Reexamination Certificate

active

06205838

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention is based on a device for determining a rate rotation.
The use of rotation rate sensors that utilize the Coriolis effect is known in conjunction with systems for dynamic control in motor vehicles. Such rotation rate sensors typically comprise one or more masses that are set into mechanical oscillation at the frequency f
s
by an electrical oscillator circuit. These mechanical oscillations act on one or more acceleration sensors, which upon a rotation of the system also measure the Coriolis acceleration acting on the oscillating masses. From the excitation and acceleration signals, the rotation rate of the system can be determined with the aid of a suitable evaluation circuit.
An additional electrical test signal that is fed to the acceleration sensor or acceleration sensors can be used to cause an additional, arbitrarily generated acceleration to act upon the sensor. In this way, information on the properties of the acceleration sensor and the downstream evaluation circuits can for instance be obtained. It is thus also possible to detect errors, and especially systematic errors. This is especially important because rotation rate sensors that evaluate the Coriolis effect has systematic errors, whose effect on the measurement signal must be minimized by a suitable choice of evaluation method. Such systematic errors can be classified in one of the following types of error:
a) The acceleration sensor or sensors are sensitive not merely in the direction of the Coriolis acceleration to be measured but in other directions as well.
b) The mechanical oscillator that is set into oscillation by the electrical circuit has unintended oscillation components in the direction of the Coriolis acceleration.
c) Electrical feedthrough of the oscillation signal to the acceleration signal is possible.
To evaluate the output signals of rotation rate sensors, until now circuits have been used that are designed as analog circuits for signal processing. Such evaluation circuits, with which the rotation rate can be determined from the output signals of a rotation rate sensor and with which moreover monitoring the operability of the sensor or of the evaluation circuit is made possible, are described in International Patent Application WO 96/21138.
The known device for determining a rotation rate includes a rotation rate sensor which operates on the principle of a resonant oscillation gyrometer and is excited by means of an amplitude-regulated oscillator loop. This sensor is used for instance to ascertain the yaw speed of a vehicle. To that end, the effect of the Coriolis acceleration, which is a measure for the actual yaw speed, is evaluated. To monitor the operability of the sensor or of the associated electronics, an additional voltage, for instance in the form of a Bite function, is fed in at certain selectable times, and the reaction of the system to this additional voltage is evaluated for error detection.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a device for determining a rate rotation which avoids the disadvantages of the prior art.
In keeping with these objects, one feature of present invention resides, briefly stated, in a device for determining a rotation rate, in which the oscillation voltage which is proportional to the instantaneous speed of the oscillatable body is picked up and digitized, the output voltage is digitized or is already generated as a digital signal, and from two digitally presented voltages, the transfer function is formed, which simulates all interference components at the rotation rate of zero and is the point of departure for determination of the rotation rate.
The device of the invention has the advantage over the known device that purely digital signal processing is done, while in the known device an analog circuit is employed. The use of adaptive methods of digital signal processing enables advantageous system identification and a system simulation. Sensor errors can be compensated for successfully by the adaptation processes. The digital evaluation circuit according to the invention is advantageously fully integratable and has no problems of synchronism and drift of the individual components. The circuit is calibration-free, except for a scaling factor.
These advantages are attained in that both the oscillation voltage and the electrical acceleration signal are evaluated jointly, with digitizing of the signals being done beforehand. In a first evaluation method, the digitized signals are subjected to an adaptive system identification, as a result of which the transfer function of the sensor system between the oscillation signal and the acceleration signal is simulated. With the aid of this transfer function, the rotation rate can be determined. In this method, all the relevant factors are simulated by means of the system identification. However, constant rotation rates that persist for a long time are compensated for.
In a second method, in which in addition a test signal U
T
that excites the acceleration sensors is used, even long-persisting constant rotation rates are ascertained, even though at the same time a fast adaptation rate is possible. In this method, a system identification of the transfer function between the test signal U
T
and the acceleration signal U
2
is performed, and with the aid of this the rotation rate is determined. By using the test signal, malfunctions of the sensor or of the associated digital evaluation circuit can advantageously be detected as well.


REFERENCES:
patent: 5426970 (1995-06-01), Florida et al.
patent: 5889193 (1999-03-01), Pfaff et al.
patent: WO 96/21138 (1994-12-01), None

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