Method for aligning a rotation rate sensor

The invention relates to a method for aligning a rotation rate sensor with a vibration gyroscope, the first input and the first output of which is part of a primary control circuit. Said control circuit excites the vibration gyroscope to vibrate at its natural frequency by supplying it with an excitation signal. The second input and the second output of the vibration gyroscope is part of a secondary control circuit. An output signal can be gathered from the second output and said signal is demodulated after amplification and analog to digital conversion to give an in-phase component and a quadrature component. After filtering, these components are modulated and composed to give a driver signal that is supplied to the second input and a rotation rate signal is derived from the in-phase component. The inventive method is characterized in that, when the vibration gyroscope remains motionless, correction values are added to the in-phase components and to the quadrature component which correction values are changed until the in-phase component and the quadrature component reach a minimum each. The correction values are stored in a non-volatile memory and are used when the rotation rate sensor is operated.

CROSS REFERENCE TO RELATED APPLICATIONS

BACKGROUND OF THE INVENTION

The invention relates to a method for adjustment of a rotation rate sensor having a vibration gyro, which, with a first input and a first output, is part of a primary control loop which excites the vibration gyro by supplying an excitation signal to the first input at its natural frequency, in which case the vibration gyro, with a second input and with a second output, is also part of a secondary control loop, in which case an output signal can be tapped off from the second output and, after amplification and analog/digital conversion, is demodulated to form an in-phase component and a quadrature component, in which case the components are modulated again after filtering and are combined to form a driver signal which is supplied to the second input, and in which case a rotation rate signal is derived from the in-phase component.

In the case of rotation rate sensors having a vibration gyro, which are operated with the measures mentioned in the introduction being carried out, not only is the variation in the output signal caused by the Coriolis force included in the rotation rate signal, but also an inadvertent phase shift which is caused by delay times in the components which form the at least one control loop.

SUMMARY OF THE INVENTION

An object of the present invention is to minimize the influences of the inadvertent phase shift on the rotation rate signal of a rotation rate sensor caused by delay times in the components of at least one control loop of the rotation rate sensor.

According to the invention, this object is achieved in that, when the vibration gyro is not moving, correction values are added to the in-phase components and to the quadrature components and are varied until the in-phase component and the quadrature component are each at a minimum, and in that these correction values are stored in a non-volatile memory and are used during operation of the rotation rate sensor.

The method according to the invention is preferably carried out within a final adjustment process during the production of the rotation rate sensor. The non-volatile memory is in this case used for even further correction and initialization variables, and therefore does not need to be provided just for the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The exemplary embodiment as well as parts of it are admittedly shown in the form of block diagrams. However, this does not mean that the arrangement according to the invention is restricted to an implementation using individual circuits corresponding to the blocks. In fact, the arrangement according to the invention can be implemented particularly advantageously using large-scale-integrated circuits. In this case, microprocessors may be used which, when suitably programmed, carry out the processing steps illustrated in the block diagrams.

FIG. 1shows a block diagram of an arrangement having a vibration gyro1with two inputs2,3for a primary excitation signal PD and a secondary excitation signal SD. The excitation is provided by means of suitable transducers or converters, for example electromagnetic transducers. The vibration gyro furthermore has two outputs4,5for a primary output signal PO and a secondary output signal SO. These signals reproduce the respective vibration at physically different points in the gyro. Gyros such as these are known, for example, from EP 0 307 321 A1 and are based on the Coriolis force effect.

The vibration gyro1represents a high Q-factor filter, in which the path between the input2and the output4is part of a primary control loop6, and the path between the input3and the output5is part of a secondary control loop7. The primary control loop6is used to stimulate oscillations at the resonant frequency of the vibration gyro at, for example, 14 kHz. The stimulation is in this case applied on one axis of the vibration gyro with respect to which the oscillation direction that is used for the secondary control loop is offset through 90°. The signal SO is split in the secondary control loop7into two quadrature components, one of which is passed via a filter8to an output9, from which a signal which is proportional to the rotation rate can be tapped off.

A major proportion of the signal processing is carried out digitally in both control loops6,7. The clock signals which are required for signal processing are produced in a crystal-controlled digital frequency synthesizer10, whose clock frequency in the illustrated example is 14.5 MHz. The primary control loop will not be described, since this is not necessary for understanding of the exemplary embodiment.

The secondary control loop7is illustrated in the form of a block diagram inFIG. 2and contains an amplifier25, an anti-aliasing filter26and an analog/digital converter27. Splitting into the real part and the imaginary part is carried out with the aid of multipliers28,29, to which the amplified and digitized signal SO is supplied, with the I and Q components, which have not yet been separated, and the carriers Ti1and Tq1.

The two components then each pass through a (sinx/x) filter30,31and a low-pass filter32,33, respectively. Two signals R1and R2, which represent the rotation rate to be measured by the rotation rate sensor, are derived by means of a preprocessing circuit34from the filtered real part. The signals R1and R2differ in that the signal R2does not occupy the entire amplitude range for example from 0V to +5V that is possible with the circuit technology that is used. The signal R2is set to zero in order to output a fault message, which the connected system identifies as a fault message.

The low-pass filters32,33are followed by a respective adder35,36. The two components Si and Sq, respectively, are then remodulated with the carriers Ti2and Tq2, by means of multipliers37,38. An addition process at39once again results in a 14 kHz oscillation, which is converted in an output driver40to a current which is suitable for stimulation of the vibration gyro1.

The frequency synthesizer10is controlled in a manner that is not illustrated in any more detail in order to carry out the modulation process at28with a phase angle i and the demodulation process at29with a phase angle q. This means that an in-phase component I is demodulated at28, and a quadrature component Q is demodulated at29.

However, the in-phase components and the quadrature components are corrupted by variations in the delay times in the various circuits involved. The measurement result, that is to say the rotation rate signal, is therefore corrupted.

In order to avoid this, an adjustment process is carried out in which correction variables k1and k2, which are produced in a device41, are added to the filtered components by means of the adders35,36, with the correction values k1and k2being chosen such that they result in a phase shift in the excitation signal SD and thus also in the output signal SO. The changeover switches42are then in the illustrated position. During the adjustment process, the predetermined value ranges of the correction values k1, k2are passed through. At the same time, a check is carried out in a device43to determine whether the in-phase component and the quadrature component are each zero or have assumed a minimum. If this is the case, the correction values k1, k2which are produced in the device41are then stored in an EEPROM44. During normal operation, the changeover switches42are in the right-hand position and the correction values as determined during the adjustment process are read from the EEPROM44and are supplied to the adders35,36.