Method and system for monitoring a sensor arrangement

A method and system for monitoring a sensor arrangement comprising a vibrating gyroscope, wherein the vibrating gyroscope is used as a resonator and forms part of at least one control circuit that excites the vibration gyroscope by feeding an excitation signal with its natural frequency. An output signal is tapable from the vibrating gyroscope from which the excitation signal is derivable by filtering and amplification.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2006/065882, filed on Aug. 31, 2006. Priority is claimed on German application No. 10 2005 043 559.9, filed Sep. 12, 2005.

BACKGROUND OF THE INVENTION

The invention relates to a method and an arrangement for monitoring a sensor arrangement comprising a vibration gyroscope which includes a resonator and is forms part of at least one control circuit which excites the vibration gyroscope by feeding an exciter signal at its natural frequency, where an output signal can be tapped off from the vibration gyroscope and the exciter signal is derived from the output signal by filtering and amplification.

For example EP 0 461 761 B1 discloses rotational speed sensors in which a vibration gyroscope is excited in two axes which are oriented radially with respect to a main axis, for which purpose a primary and a secondary control circuit are provided with corresponding transducers on the vibration gyroscope. If such rotational speed sensors are used in vehicles for stabilizing the movement of the vehicle, a fault-free function of the rotational speed sensors is an important precondition for reliable operation of the motor vehicle. For this reason, various devices and methods for monitoring and rotational speed sensors have already been disclosed, for example, by WO 2005/01378 A1, where redundant analog components and further digital components are used for monitoring.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve sensor monitoring and to detect malfunctions or failures as far as possible in advance.

The object of the present invention is also to improve the monitoring and to detect malfunctions or failures as far as possible in advance.

These and other objects and advantages are achieved with the method of the invention by first calculating a first value of the change in temperature compared to the measurement from the difference between the current value of the natural frequency and a value of the natural frequency which has been previously measured during adjustment, stored in a memory and measured at a reference temperature, and from the temperature coefficient of the natural frequency. A second value of the change in temperature compared to the measurement is then+ calculated from the difference between the output variables of a temperature sensor at the current temperature and at the reference temperature stored in the memory and the temperature coefficient of the temperature sensor. In addition, the two calculated values are compared, and a fault signal is generated when there is a deviation which exceeds a predefined amount.

In relevant sensor arrangements, a temperature sensor and a microcontroller are usually present in any case so that no additional hardware expenditure is necessary to perform the method in accordance with the invention. However, the method of the invention may be implemented as a software program.

If the vibration gyroscope in a sensor arrangement is not in direct thermally conducting contact with the circuits of the sensor arrangement, the circuits generally assume a higher temperature than the vibration gyroscope during operation. Here, in order to permit a correct comparison, an embodiment of the method of the invention provides for the inclusion in the calculation of a correction temperature which takes into account thermal conditions which have changed in comparison to the adjustment of the temperature sensor.

Preferably, the correction temperature is calculated from the measured power loss of an integrated circuit which contains the temperature sensor, e.g., from the power loss which has been measured during the adjustment and stored in the memory, and from the thermal resistance of the integrated circuit with respect to the surroundings.

The invention also comprises an arrangement for monitoring a sensor arrangement comprising means to calculate a first value of a change in temperature from the difference between the current value of the natural frequency and a value of the natural frequency which has been previously measured during adjustment and stored in a memory, and from the temperature coefficient of the natural frequency, order to calculate a second value of a change in temperature from the difference between the output variables of a temperature sensor at the current temperature and at the measurement temperature, and the temperature coefficient of the temperature sensor, in order to compare the two calculated values, and to generate a fault signal when there is a deviation which exceeds a predefined amount.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The sensor arrangement and parts thereof are illustrated as block circuit diagrams. However, it is not the intention to limit the sensor arrangement of the invention to an implementation using individual circuits which correspond to the depicted blocks. The sensor arrangement according to the invention can instead be advantageously implemented by using highly integrated circuits. This can be achieved using microprocessors which, given suitable programming, perform the processing steps illustrated in the block circuit diagrams.

With reference to the FIGURE, sensor arrangement has a vibration gyroscope1with two inputs2,3for a primary exciter signal PD and a secondary exciter signal SD. The excitation is effected by suitable transducers, for example, electromagnetic transducers. The vibration gyroscope also has two outputs4,5for a primary output signal PO and a secondary output signal SO. These signals forward the respective vibration to spatially offset locations on the gyroscope. Such gyroscopes are known, for example, from EP 0 307 321 A1 and are based on the effect of the Coriolis force.

The vibration gyroscope1constitutes a high quality filter in which the distance between the input2and the output4is part of a primary control circuit6, and the distance between the input3and the output5is part of a secondary control circuit which is not illustrated since it is not necessary to explain it in order to understand the invention. The primary control circuit6serves to excite oscillations at the resonant frequency of the vibration gyroscope1of, for example, 14 kHz. Here, excitation is effected in an axis of the vibration gyroscope with respect to which the oscillation direction which is used for the secondary control circuit is offset by 90°. In the secondary control circuit (not illustrated), the signal SO is split into two components, one of which can be tapped, after suitable processing, as a signal which is proportional to the rotational speed.

In both control circuits, a significant part of the signal processing is performed digitally. The clock signals which are necessary for the signal processing are generated in a quartz-controlled, digital frequency synthesizer10whose clock frequency is, for example, 14.5 MHz in the example illustrated. For application of the method in accordance with the invention, the primary control circuit is essentially considered, for which reason an exemplary embodiment of the primary control circuit is illustrated inFIG. 1.

The control circuit has an amplifier11for the output signal PO to which an anti-alias filter12and an analog/digital converter13are connected. Multipliers14,15, to which carriers Ti1and Tq1are fed, are used to perform splitting of the output signal into an in-phase component and a quadrature component. Each of the two components subsequently passes through a (sinx/x) filter16,17and a low pass filter18,19. The filtered real part is fed to a PID controller20which controls the digital frequency synthesizer. As a result, a phase control circuit which creates the correct phase angle of the carriers Ti1and Tq1is closed. Furthermore, a carrier Tq2is generated and it is modulated in a circuit22with the output signal of a further PID controller21which receives the low pass-filtered imaginary part. The output signal of the circuit22is fed to the input2of the vibrating gyroscope1as exciter signal PD. Depending on the conditions, it is possible to provide other controllers, for example PI controllers instead of the PID controllers.

In order to implement the method in accordance with the invention, a microcontroller27is provided which controls the individual steps of the method and has access to a nonvolatile memory28which is embodied as an EEPROM. In addition, a temperature sensor which is present in many sensor circuits in any event for the method according to the invention is used, where the temperature sensor is composed of an actual sensor29and an analog/digital converter30. A bus system31interconnects the specified components to one another, the digital frequency synthesizer10, and to the circuit22.

In an embodiment of the adjustment method when the sensor arrangement is manufactured, the value FORT of the natural frequency of the vibration gyroscope which was measured and the temperature at which the measurement was performed, in the form of the output voltage VRT of the temperature sensor29, are written into the memory28.

For the purpose of monitoring, these variables are read out from the memory28from time to time during operation and for comparison purposes, the variables are compared with the respectively current natural frequency, while taking into account the current temperature measured with the sensor29(output voltage VTA). The comparison is based, for example, on the following equations:
Tadelta1=(FOTA−FORT)/TCFO
Tadelta2=(VTA−VRT)TCv
Here, Tadelta2 is the change in temperature which is detected using the temperature sensor, Tadelta1is the change in temperature detected on the basis of the change in the frequency, TCvis the temperature coefficient of the temperature sensor29which is stored in the memory, FOTAis the current frequency, FORTis the frequency which is stored in the memory and TCFOis the temperature coefficient of the natural frequency of the vibration gyroscope which is likewise stored in the memory.

The current value of the natural frequency can be acquired from the respective setting of the divider of the digital frequency synthesizer10and its clock frequency. However, it is also possible to calculate the current value using a frequency measuring device which is composed of a further amplifier24, a Schmitt trigger25and a counter26.

In an ideal case, Tadelta1and Tadelta2are identical; if a difference assumes values which exceed a predefined amount, it is possible to infer that one of a plurality of possible faults is present and, for example, a fault can be signaled in the form of the activation of a warning lamp or can be stored in the memory to be available for later diagnostic purposes.

In order to take into account a loss of power to the circuit which contains at least the primary control circuit6, which is different from the adjustment, the power drain I of the circuit is measured using a measuring resistor32with the value R. The operating voltage U for the circuit is fed to a connection33and distributed to the various components via a circuit node34. The voltage drop Uiat the measuring resistor32is amplified in an amplifier35by a factor v and fed to the analog/digital converter30via a multiplexer36. The microcontroller27then calculates the power loss according to the equation P=U*I=U*Ui/(R*v). During the adjustment, the power loss PRTand the associated ambient temperature TRTare stored in the memory.

The power loss which is calculated during operation is denoted by PAin the text which follows.

It is therefore possible to calculate a correction temperature, specifically as Tkor=TRT+(PA−PRT)*RTH, where RTHsignifies the thermal resistance between the circuit and the surroundings. The abovementioned equation for calculating Tadelta2is therefore supplemented as follows:
Tadelta2kor=Tadelta2−Tkor

As already mentioned above, when there is a lack of identity a fault signal can be output, specifically if:
Tadelta1≈Tadelta2kor.