METHOD FOR DETERMINING A DETECTION SENSITIVITY OF A ROTATION RATE SENSOR

Abstract

A method for determining a detection sensitivity of a rotation rate sensor, the rotation rate sensor including an oscillatory system. A first quadrature signal of the oscillatory system is determined in a first step. A controlled change of a transfer function of the oscillatory system takes place in a second step. A second quadrature signal of the oscillatory system is determined in a third step. The detection sensitivity is determined in a fourth step on the basis of the first and second quadrature signal. A method is also described for determining a detection sensitivity of a rotation rate sensor, the rotation rate sensor including one first oscillatory system and one second oscillatory system.

Claims

1. A method for determining a detection sensitivity of a rotation rate sensor, the rotation rate sensor including an oscillatory system, the method comprising: in a first step, determining a first quadrature signal of the oscillatory system; in a second step, performing a controlled change of a transfer function of the oscillatory system; in a third step, determining a second quadrature signal of the oscillatory system; and in a fourth step, determining the detection sensitivity based on the first quadrature signal and the second quadrature signal.

2. The method as recited in claim 1, wherein, in the second step, a controlled change of an inherent frequency of the oscillatory system takes place and/or a controlled change of a quality factor of the oscillatory system takes place.

3. The method as recited in claim 2, wherein the change of the inherent frequency takes place via a controlled change of a spring constant of the oscillatory system.

4. The method as recited in claim 1, wherein further controlled changes of the transfer function take place and further quadrature signals of the rotation rate sensor are determined in a fifth step following the third step and preceding the fourth step, the detection sensitivity being determined in the fourth step based on the first, second and further quadrature signals.

5. The method as recited in claim 1, wherein a compensation variable for a detection signal is determined in a fifth step following the fourth step based on the detection sensitivity determined in the fourth step.

6. A method for determining a detection sensitivity of a rotation rate sensor, the rotation rate sensor including one first oscillatory system and one second oscillatory system, a transfer function of the first oscillatory system differing from a transfer function of the second oscillatory system, the method comprising: in a first step, determining a first quadrature signal of the first oscillatory system; in a second step, determining a second quadrature signal of the second oscillatory system; and in a fourth step, determining the detection sensitivity based on the first quadrature signal and the second quadrature signal.

7. The method as recited in claim 6, wherein a quality factor of the first oscillatory system is identical to a quality factor of the second oscillatory system, and/or a mass of the first oscillatory system differs from a mass of the second oscillatory system and/or a spring constant of the first oscillatory system differs from a spring constant of the second oscillatory system.

8. The method as recited in claim 6, wherein a compensation variable for a detection signal is determined in a fifth step following the fourth step based on the detection sensitivity determined in the fourth step.

9. The method as recited in claim 5, wherein: (i) the rotation rate sensor includes a register that includes a plurality of value pairs of the detection sensitivity and of the compensation variable, the compensation variable being determined via selection of a value from the register, or (ii) the compensation variable is determined via an analytical, linear correlation between the detection sensitivity and the compensation variable.

10. The method as recited in claim 1, wherein a first detection signal is determined in the first step and a second detection signal is determined in the second step, a temperature effect on a mechanical phase of the oscillatory system being ascertained in a sixth step following the fourth step based on the first detection signal and the second detection signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a schematic representation of an oscillatory system, which is formed by a flexibly mounted mass and may be stimulated by an electrode arrangement to oscillate.

[0031] FIG. 2 illustrates the transfer function of an oscillatory system via a representation of the amplification characteristic curves of the drive and detection oscillation and of the phase characteristic curve of the detection oscillation.

[0032] FIG. 3 shows the flowchart of an initializing process, in which a plurality of values of the compensation variable is determined.

[0033] FIG. 4 shows the flowchart of a compensation process, in which a compensation variable for the detection signal is determined.

[0034] FIG. 5 shows the flowchart for determining the relationship v.sub.i.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0035] FIG. 1 is a schematic illustration of an oscillatory system 1 as it is used in rotation rate sensors. Oscillatory system 1 includes here a seismic mass 2, which is flexibly coupled via a spring arrangement 3 to the sensor substrate and may be stimulated by an electrostatic alternating field to oscillate (drive oscillation or drive mode). One common option for determining the rotation rate is that in addition to the drive mode, oscillatory mass 2 includes a further oscillation mode, which extends, for example, along a direction perpendicular to the drive oscillation and serves as a detection mode. A rotation rate present at the sensor effectuates a coupling of drive mode and detection mode so that the amplitude of the detection mode (which is a function of the strength of the coupling and thus of the present rotation rate) may be utilized for measuring the rotation rate. In addition to this coupling, real sensors also include (usually undesirable) couplings of the two modes, which are generally referred to as quadrature effects and result in an excitation of the detection mode regardless of the rotation rate. The measured signal contains both components; the quadrature signal, however, may be separated by demodulation from the useful signal. The measured signal may be detected as indicated in the figure by the change associated with the detection oscillation of the capacitance formed by mass 2 and a measuring electrode 4 fixed relative to the substrate. Via a bias voltage 5 of the measuring electrode, it is also possible to adapt the spring constant of the system and thus to achieve a shift of the inherent frequency. This represents one simple possibility for effectuating the controlled change of the transfer function according to the present invention, since the transfer function is shifted toward higher or lower frequencies when the inherent frequency is increased or reduced.

[0036] FIG. 2 is a representation of the amplification curve and phase curve generated by shifting the inherent frequency at a drive frequency, which operates with a phase-locked loop, PPL, in the global maximum. Shown is amplification characteristic curve 10 of the drive mode (above), and two amplification characteristic curves 11, 12 shifted with respect to one another of the detection mode (center) and two phase characteristic curves 13, 14 of the detection mode (below) shifted with respect to one another are shown. The frequency in each case is plotted on horizontal axis 6. Vertical axis 7 of the upper graphic corresponds to amplification G.sub.drive, vertical axis 8 of the middle graphic corresponds to amplification G.sub.sense, and vertical axis 9 of the lower graphic corresponds to phase ϕ.sub.sense. The vertical plotting is logarithmic in each case.

[0037] One specific embodiment of the method according to the present invention is based on the approach of comparing the amplification or phase of an oscillatory system 1 at different inherent frequencies. FIG. 2 represents graphically the transfer functions provided by equations 1 and 2 for a sensor made up of a drive-SMS (above) and a detection SMS (middle and below) via amplification characteristic curve and phase characteristic curve 10, 11, 12, 13, 14. The detection SMS in this example has been influenced by an increase in the spring constant, as a result of which inherent frequency ω.sub.0 of the system, and thus characteristic curves 11, 13 are shifted in their totality toward higher frequencies (indicated by arrow 15). The difference in the curves is easily possible by evaluating the associated quadrature signals. As is apparent from equation 5, the relationship of the quadrature signals corresponds directly to the relationship v.sub.i of the amplifications, i.e., to values 16 and 16′ of amplification characteristic curves 11 and 12 at the drive frequency. The drive frequency is identified in the figure by vertical line 35 and corresponds to the frequency at which the drive mode experiences maximum amplification G.sub.drive. The flanks of characteristic curve 11 (and those of its shifted counterpart 12) exhibit a strictly monotonically ascending profile left of the maximum and a strictly monotonically descending profile to the right thereof. Conclusions about the operating point in the ranges in which both characteristic curves are monotonic may be clearly drawn from the value of the relationship v.sub.i at a known shift of the inherent frequency. This fact is utilized by the method according to the present invention in order to determine from the relationship the true amplification.

[0038] FIG. 3 shows the sequence of an initialization of the sensor, in which the associated values of compensation variable CF.sub.i(v.sub.i) are collected for various values of relationship v.sub.i. For the sake of simplicity, the sequences are described here and in the following based on the specific implementation with the aid of the shift of the inherent frequency, a transfer to the general case of a controlled change of the transfer function being readily possible, however. The processes are carried out, in particular, in an automated manner by a control unit of the sensor.

[0039] The initialization is started in block 17 and it is initially established in block 18 whether the desired number of measuring points is achieved. Initially, no measured values are present, so that in block 20 the inherent frequency of the SMS is shifted and the quadrature signal is subsequently measured in block 21 and the relationship v.sub.i is determined from the measured value and from the value of the quadrature signal belonging to the unshifted inherent frequency. Correction factor CF.sub.i=v.sub.i/v is determined in block 22 and stored in block 23 as assignment CF.sub.i(v.sub.i), for example, in a register. Sequence 18, 20, 21, 22, 23 is repeated until it is determined in block 18 that the desired number of measured points is achieved and the process is ended in block 19.

[0040] FIG. 4 shows the sequence of a compensation of a sensitivity change or phase change due to disruptive influences. Once the process has been started in 24, the relationship v.sub.i is determined in 25, and in 26 the associated correction factor CF.sub.i(v.sub.i) is retrieved from 28 (CF.sub.i(v.sub.i) may be present here, for example, as a table or also as a function). The process is ended in 27.

[0041] FIG. 5 shows the sequence of the determination of the relationship After start 29, quadrature signal s.sub.Quad,i is measured in 30. The inherent frequency of the SMS is shifted in step 31 and associated quadrature signal s.sub.Quad,i,Δ is measured in subsequent step 32. Relationship v.sub.i=s.sub.Quad,i,Δ/s.sub.Quad,i is then calculated in 33 and the sequence is ended in 34.