Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration
Reexamination Certificate
2000-03-29
2002-08-06
Le, N. (Department: 2858)
Measuring and testing
Instrument proving or calibrating
Speed, velocity, or acceleration
C073S001380, C073S504130, C073S504120, C073S504140, C073S504150, C073S504160
Reexamination Certificate
active
06427518
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to an apparatus for determining a rotation rate, with an oscillatory body on which a plurality of electromechanical converters are mounted, of which at least a first converter is caused to oscillate mechanically by an electric driver signal generated in a first circuit arrangement, and at least a second converter is caused to oscillate mechanically by an electric damping signal generated in a second circuit arrangement, and at least a third converter emits an electric sensor damping signal which corresponds to the oscillation of the body in the location where the at least third converter is mounted ,the sensor damping signal being fed back to the input of the second circuit arrangement.
This type of apparatus which generally works according to the principle of a vibration gyrometer is known, for example, from DE-44 47 005 A1. The electromechanical converters present in the apparatus, generally piezo-electric elements, evaluate the effect of the Coriolis acceleration which serves as a measure for a rotation rate at which the oscillatory body rotates. This known apparatus is therefore well suited for use in connection with systems for controlling driving dynamics in motor vehicles, since the detected Coriolis acceleration can be used as a measure for the current yaw rate of the vehicle.
In the case of the known apparatus, the oscillatory body is realized as a thin-walled hollow cylinder made from an elastic material. On the cylinder wall, eight piezo-elements are arranged at a uniform distance of 45 degrees relative to one another. The piezo-elements arranged, for example, at the positions of 0 degrees, 90 degrees, 180 degrees and 270 degrees work together with an oscillator stage. The piezo-elements arranged in the positions of 45 degrees, 135 degrees, 225 degrees and 315 degrees work together with a damping stage. The piezo-elements arranged in the positions of 0 and 180 degrees are caused to oscillate mechanically by an oscillator driver stage. The piezo-elements arranged in the positions at 90 and 270 degrees emit a signal which corresponds to the oscillation of the hollow cylinder in the location where the piezo-elements are arranged. The signal emitted by the piezo-elements arranged in the 90-degree and 270-degree positions is fed back to the input of the circuit arrangement for generating the electric oscillator driver signal in such a way that this results in an oscillator oscillating at its resonant frequency.
The hollow cylinder is oscillated by the piezo-electric elements which are arranged at the positions of 0 and 180 degrees and which are mechanically oscillated by the oscillator driver stage. The hollow cylinder oscillates in such a way that nodal points form at the positions of 45 degrees, 135 degrees, 225 degrees and 315 degrees when it is in a steady state. If a rotation rate acts on the hollow cylinder from outside, the steady state of the hollow cylinder is disturbed because of the Coriolis acceleration. The system is detuned in such a way that the position of the nodal points shifts. Because of this, the hollow cylinder carries out oscillations in the locations where the nodes were previously.
The piezo-elements arranged in the 45-degree and 225-degree positions can be oscillated mechanically using a damping driver stage. The piezo-elements arranged in the positions of 135 degrees and 315 degrees emit a signal which corresponds to the oscillation of the hollow cylinder at the location where they are arranged. The signal emitted by the piezo-elements arranged in the positions of 135 and 315 degrees is fed back to the input of the circuit arrangement which is provided for the excitation of the piezo-elements arranged in the positions of 45 degrees and 225 degrees in such a way that the oscillations in the positions of 135 degrees and 315 degrees are compensated approximately to zero.
The voltage fed back to the input of the circuit arrangement for the excitation of the piezo-elements arranged in the positions of 45 degrees and 225 degrees is a measure of the detuning of the hollow cylinder caused by the effect of a rotation rate on the oscillating hollow cylinder. This signal can therefore be used as a measure of the rotation rate.
For adaptation to a circuit arrangement for further processing of the signal, the known apparatus provides an amplifier with adjustable amplification. Although the output signal of the known apparatus can be adjusted by the amplifier, the known apparatus has the disadvantage that it does not provide for the possibility of tuning or balancing the circuit with respect to the tolerances of the component parts. This has disadvantageous results especially when, as provided in the known circuit arrangement, the possibility is provided for adding an interference signal by means of which the perfect functioning of the circuit arrangement is tested in a so-called self-test.
In order to carry out the self-test, the signal which is emitted by the piezo-elements arranged in the positions of 90 degrees and 270 degrees and which is fed back to the input of the oscillator driver stage is guided to an amplifier and guided via a switch to the input of the damping driver stage provided for the excitation of the piezo-elements arranged in the positions of 45 degrees and 225 degrees. This detunes the system in the same manner as is effected under the effect of a rotation rate. Since the magnitude of the self-test signal is determined, the output signal must reach a certain magnitude because of the detuning if the apparatus is working correctly. If this is not the case, it indicates that the apparatus is not working properly.
Since the output signal which is generated because of the interference signal is supposed to correspond to a predetermined rotation rate and be independent of the adaptation carried out by the output amplifier, the amplifier for generating the self-test signal can also be adjusted with respect to its amplification. The independence of the output signal from the adaptation effected by the output amplifier is achieved in that the inputs of the amplifier for adjusting the amplification are coupled together and work in opposite directions.
Tolerances of component parts cannot be compensated for, however, by adapting the self-test signal by means of the amplifier which is adjustable with respect to amplification. In particular, differences between the dynamic systems behavior or transient response of the piezo-elements of the damping stage and the piezo-elements of the oscillator stage cannot be compensated for by adjusting the self-test signal.
However, as regards the self-test, a perfect functioning of the known circuit arrangement is only guaranteed if the transient responses are identical so that they cancel each other. Since this is not the case in practice, an incorrect self-test value is obtained. A correspondingly large expenditure on circuitry is required in order to overcome this problem. Adapting the transient response to an integrated circuit, the known circuit arrangement generally being constructed as such, is overridden by the process parameters of semiconductor production and is therefore difficult to do with the desired accuracy. In the case of the known circuit arrangement, a systematic correction is therefore effected by two capacitive voltage dividers of different values in the hybrid circuit following the circuit arrangement. However, this is disadvantageous because this step has a temperature response made up of the transient response and the capacitive voltage divider.
SUMMARY OF THE INVENTION
It is the object of the present invention to construct an apparatus of the type mentioned in the beginning in such a way that it can be tuned in a simple manner.
This object and others which will be made more apparent hereinafter are attained in an apparatus for determining a rotation rate, with an oscillatory body on which a plurality of electromechanical converters are mounted, of which at least a first converter is caused to oscillate mechanically by an electric drive
Abendroth Manfred
Miekley Klaus
Hamdan Wasseem H.
Le N.
Robert & Bosch GmbH
Striker Michael J.
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