METHOD FOR DETERMINING, MEASURING AND/OR MONITORING PROPERTIES OF A SENSOR SYSTEM

Abstract

A method for determining, measuring and/or monitoring properties of a sensor system. In the method, a controlled change of at least one system parameter of the sensor system takes place in such a way that prior to the controlled change, the system parameter includes a first value and assumes at least one further value as a result of the controlled change. At least one characteristic variable of the sensor system and/or a change of the at least one characteristic variable of the sensor system is/are determined for the at least one further value of the system parameter. The determination, measuring and/or monitoring of properties of the sensor system take place based the at least one further value of the system parameter and the at least one characteristic variable determined in the second step and/or the change of the at least one characteristic variable.

Claims

1. A method for determining and/or measuring and/or monitoring properties of a sensor system, the method comprising the following: in a first step, a controlled change of at least one system parameter of the sensor system taking place in such a way that prior to the controlled change, the system parameter includes a first value and assumes at least one further value as a result of the controlled change; in a second step, determining at least one characteristic variable of the sensor system and/or a change of the at least one characteristic variable of the sensor system, for the at least one further value of the system parameter; in a third step, determining and/or measuring and/or monitoring of properties of the sensor system based on the at least one further value of the system parameter and based on the at least one characteristic variable determined in the second step and/or based on the change of the at least one characteristic variable.

2. The method as recited in claim 1, wherein in the third step, a change of the properties of the sensor system is determined with respect to a reference state, the reference state being determined during an end adjustment subsequent to the manufacture of the sensor system.

3. The method as recited in claim 2, wherein in a step following the third step, at least one sensor parameter is changed, the change of the sensor parameter effectuating a correction of a measured signal of the sensor system.

4. The method as recited in claim 1, wherein in the third step, a comparison of the characteristic variable of the sensor system determined in the second step and/or the change of the at least one characteristic variable, with a threshold value is carried out, a sensor response being generated in a subsequent step.

5. The method as recited in claim 1, wherein the sensor includes a movable structure, which is configured in such a way that as a result of a physical stimulus acting on the movable structure, a deflection of the movable structure is effectuated in a detection direction, the system parameter changed in the first step in a controlled manner directly influencing the deflection generated by the physical stimulus and/or a measured signal read out from the sensor system.

6. The method as recited in claim 5, wherein the physical stimulus is an inertial force or a gas pressure or a liquid pressure.

7. The method as recited in claim 5, wherein the changed system parameter is a potential present between the movable structure and a readout structure, the potential being an electrode voltage present between an electrode fixed to the substrate and the movable structure of the sensor system.

8. The method as recited in claim 1, wherein the changed system parameter is an operating temperature of the sensor system, the change of the operating temperature taking place as a result of a targeted change of an operating mode of the sensor system or of parts of the sensor system.

9. The method as recited in claim 8, wherein the parts of the sensor system include evaluation electronics.

10. The method as recited in claim 5, wherein the characteristic variable determined in the second step corresponds to the measured signal without an external physical stimulus.

11. The method as recited in claim 1, wherein the sensor system is a rotation rate sensor and includes a movable structure which is configured in such a way that it is excitable for carrying out a drive movement, the drive movement proceeding along a drive direction differing from a detection direction.

12. The method as recited in claim 11, wherein the changed system parameter is an oscillation amplitude of the movable structure.

13. The method as recited in claim 11, wherein the characteristic variable determined in the second step is a phase position of a detection oscillation of the movable structure with respect to a drive oscillation of the movable structure.

14. The method as recited in claim 11, wherein a deflection in the detection direction and the drive movement are coupled in such a way that the drive movement causes a quadrature deflection, which is in phase with the drive movement, the characteristic variable of the sensor system being a quadrature value.

15. The method as recited in claim 14, wherein in the third step, at least two data points are generated based on the characteristic variable of the sensor system determined in the second step and/or based on the change of the at least one characteristic variable, a model function being adapted to the data points using a compensating calculation, the model function containing at least one model parameter, which is fixed at a value by the compensating calculation, the determination and/or measuring and/or monitoring of properties of the sensor system taking place based on a value of the model parameter.

16. The method as recited in claim 15, wherein the system parameter is an electrode voltage and the data points are formed by an inverse of the quadrature values and by associated electrode voltages.

17. The method as recited in claim 15, wherein a first quadrature voltage is applied between the movable structure and a first quadrature electrode fixed to the substrate, and a second quadrature voltage is subsequently applied between the movable structure and a second quadrature electrode fixed to the substrate, the changed system parameter being a further voltage at a detection electrode and the characteristic variable being a change of the quadrature value produced by the quadrature voltages as a function of the further voltage at the detection electrode.

18. The method as recited in claim 14, wherein the system parameter is a voltage present at a detection electrode fixed to the substrate, and the characteristic variable is a change of the quadrature value produced by the voltage, the voltage present at the detection electrode including at least two phases and the change of the quadrature value being produced by variation of one or of both of the two phases.

19. A sensor system, comprising: a control and evaluation unit configured to determine and/or measure and/or monitor properties of a sensor system, the control and evaluation unit being configured to perform the following: in a first step, a controlled change of at least one system parameter of the sensor system taking place in such a way that prior to the controlled change, the system parameter includes a first value and assumes at least one further value as a result of the controlled change; in a second step, determining at least one characteristic variable of the sensor system and/or a change of the at least one characteristic variable of the sensor system, for the at least one further value of the system parameter; in a third step, determining and/or measuring and/or monitoring of properties of the sensor system based on the at least one further value of the system parameter and based on the at least one characteristic variable determined in the second step and/or based on the change of the at least one characteristic variable.

20. The sensor system as recited in claim 19, wherein the sensor system is a microelectromechanical sensor system.

21. The sensor system as recited in claim 19, wherein the sensor system includes a device for changing the system parameter, and the control unit and evaluation unit is configured to change at least one sensor parameter via the device based on the properties of the sensor system ascertained in the third step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 schematically shows a representation of a sensor system including a resiliently mounted mass, whose deflection is measured by an electrode system fixed to the substrate.

[0037] FIG. 2 schematically shows a representation of the method according to an example embodiment of the present invention.

[0038] FIG. 3 schematically shows a representation of the self-calibration of the sensor system, in accordance with an example embodiment of the present invention.

[0039] FIG. 4 schematically shows a representation of the monitoring of the sensor properties, in accordance with an example embodiment of the present invention.

[0040] FIG. 5 illustrates the determination of the sensitivity change by the progress of the quadrature as a function of the electrode voltage.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0041] A schematic representation of a sensor system 1 designed as a rotation rate sensor is depicted in FIG. 1. The system includes a substrate 40 and an oscillating mass 2, which is mounted via a mounting 44 fixed to the substrate and a spring arrangement 3 in an oscillatory manner with respect to substrate 40. Mass 2 may be excited to oscillate in a drive direction 41 in parallel to substrate 40. Due to a rotation rate present from the outside, velocity-related Coriolis forces act on mass 2, which cause an additional deflection in detection direction 42. In order to determine this deflection, the system includes a detection electrode 46 fixed to the substrate which, together with mass 2, forms a capacitive system, whose capacitance is a function of the distance between mass 2 and electrode 46 and may be measured via a voltage V.sub.CM 5 present between mass 2 and electrode 46. A change of this voltage 5 influences the electrostatic properties of system 1 and modifies, in particular, the rest position of mass 2 and the correlation between resetting force and deflection in detection direction 42. Thus, the electrostatic contribution to the electromechanical stiffness of vibratory system 1 in the detection direction may be changed via voltage 5 (indicated by spring symbol 43). This mechanism allows, in particular, the natural frequency to be influenced in a targeted manner with respect to detection direction 42. With this aid of a gradual change of voltage 5, it is possible to determine a characteristic progress Q(V.sub.CM) of the quadrature signal as a function of voltage 5, which may be used as a type of “fingerprint” of the system and, in particular, allows for conclusions to be drawn about a change of the detection sensitivity.

[0042] A schematic representation of method 10 according to the present invention is shown in FIG. 2. Sensor system 1 in this case includes one or multiple parameters P.sub.i, i=1, . . . , n, which may be changed in a fixed manner and, in particular, may each assume different values P.sub.i(W.sub.j), j=1, . . . , n.sub.i. Prior to first step 11 of method 10, the parameters have an initial value P.sub.i(W.sub.1) and are then changed in first step 11 in such a way that they assume one or multiple values P.sub.i(W.sub.1).fwdarw.P.sub.i(W.sub.j), j=2, . . . , n.sub.i differing from P.sub.i(W.sub.1). In determination step 12, one or multiple characteristic variables C.sub.k, k=1, . . . , m of the system is/are determined for each value or combination of values of the system parameters, so that a data set C.sub.k,j.sub.1.sub., . . . , j.sub.n results that includes the respective value of n-th characteristic variable C.sub.k, which results after the change P.sub.i(W.sub.1).fwdarw.P.sub.i(W) of system parameter P.sub.i. Thus, in step 13, certain properties E of sensor 1 may be determined or estimated E=ƒ(C.sub.k,j.sub.1.sub., . . . , j.sub.n) with the aid of data set C.sub.k,j.sub.1.sub., . . . , j.sub.n and on the basis of an underlying physical understanding or of suitable empirical correlations. This procedure may be repeated at an arbitrary point in time t.sub.l, l=1, . . . , o, among other things, an initial implementation after the end adjustment, a further after start-up and thereafter at regular intervals during the service life of the sensor is possible. This results in a data set C(t.sub.l).sub.k,j.sub.1.sub., . . . , j.sub.n, which allows not only properties of sensor 1 to be determined at various point in time t.sub.l, but also changes of properties to be determined ΔE(t.sub.l.sub.1.fwdarw.t.sub.l.sub.2)=ƒ(C(t.sub.l).sub.k,j.sub.1.sub., . . . , j.sub.n.fwdarw.C(t.sub.l.sub.2).sub.k,j.sub.1.sub., . . . , j.sub.n) between various points in time t.sub.l.sub.1,t.sub.l.sub.2 and for monitoring, diagnosing and self-calibrating the sensor system during the service life.

[0043] The sequence of a self-calibration of sensor 1 is represented in FIG. 3. The self-calibration involves an embodiment of method 10 according to the present invention, where in third step 13, a determination 21 of the change of the sensor properties with respect to a reference state takes place. The reference state in this case may be determined, in particular, during the end adjustment subsequent to the manufacture of sensor system 1. In this way, method 10 may be used to determine the change of the properties of sensor system 1 with respect to a reference state at point in time t.sub.1, ΔE(t.sub.1.fwdarw.t.sub.l)=ƒ(C(t.sub.1).sub.k,j.sub.1.sub., . . . , j.sub.n.fwdarw.C(t.sub.l).sub.k,j.sub.1.sub., . . . , j.sub.n)). In a step 22 following third step 13, at least one sensor parameter is then changed, the change being capable, for example, of effectuating a correction of a measured signal of the sensor system. In this way, a targeted change of one or of multiple sensor parameters P.sub.i(W.sub.1).fwdarw.P.sub.i(W.sub.j.sub.i) may be carried out in step 22, with the aim of correcting changed sensor properties E(t.sub.1, P.sub.i(W.sub.1))≈E(t.sub.l,P.sub.i(W.sub.j.sub.i)). One typical application here would be, for example, a self-calibration of the sensitivity of sensor system 1 carried out at regular intervals in order to achieve an accuracy preferably constant over the entire service life.

[0044] A monitoring of sensor system 1 is represented in FIG. 4 as a further embodiment of method 10 according to the present invention. To monitor the sensor properties, a comparison 31 is carried out in third step 13, in which the value of the characteristic variable at point in time t.sub.l (or the change of this variable with respect to a reference state) is compared with a threshold value. In comparison 31, it is checked whether the characteristic variable is below or above the threshold value (C(t.sub.l).sub.k,j.sub.1.sub., . . . , j.sub.n≤Const. or C(t.sub.l).sub.k,j.sub.1.sub., . . . , j.sub.n>Const.). As a function of this comparison 31, a sensor response is then generated in a subsequent step 32:

[00004]$S\left(t_l\right)=\{\begin{array}{c}0.Math.{C\left(t_l\right)}_{k,j_1,\mathrm{.Math.},j_n}\le \mathrm{Const}.\\ 1.Math.{C\left(t_l\right)}_{k,j_1,\mathrm{.Math.},j_n}>\mathrm{Const}.\end{array}$

[0045] One possible application here would be a monitoring of the correct operability of the sensor system and, in the case of a no longer acceptable deviation, the triggering of a suitable message to the user.

[0046] FIG. 5 illustrates the determination of the sensitivity change with the aid of the quadrature as a function of electrode voltage V.sub.CM. In the lower graphic, vertical axis 51 corresponds to the measured relative change of the quadrature, whereas vertical axis 52 in the upper graphic corresponds to the relative deviation of the detection sensitivity determined therefrom. In both cases, electrode voltage V.sub.CM is plotted on respective horizontal axis 50. Within the scope of a self-calibration, a gradual change of electrode voltage 5 is carried out and a measurement of the associated quadrature values results in data points 53 shown, which reflect progress 54 of the relative change of the quadrature as a function of voltage 5. Since the corresponding correlation reacts sensitively to changes of the sensor, in particular, to a drift of the detection sensitivity, progress 54 may be used as a type of “fingerprint,” at which a sensitivity drift may be read out. In the case shown, a slight change is revealed by a comparison of reference curve 54 with curve 55 determined in the end calibration of the manufacturing process, which is reflected in particular, in a difference between the slopes of associated tangents 57 and 56. In turn, the relative deviation of the detection sensitivity from the reference value is plotted in the upper graphic (the values belonging to reference curve 54 are thus constantly zero and coincide with the horizontal axis). The difference between sensitivities 58 and 59 correlates with the different tangent slopes in the lower graphic, so that the “fingerprint” determined by the self-calibration may be used for estimating the sensitivity drift.