Method for determining the detection sensitivity of a rotational speed sensor

Abstract

A method for determining the detection sensitivity of a rotational speed sensor, wherein the rotational speed sensor has an oscillation system (1), is proposed, characterized in that in a first step a first quadrature signal of the oscillation system (1) is determined, in a second step a controlled change of the transfer function of the oscillation system (1) is carried out, in a third step a second quadrature signal of the oscillation system (1) is determined, and in a fourth step the detection sensitivity is determined on the basis of the first and second quadrature signals. Furthermore, a method for determining the detection sensitivity of a rotational speed sensor is proposed, wherein the rotational speed sensor has a first oscillation system (1) and a second oscillation system.

Description

Technical Field

[0001] The present invention starts with a method for determining the detection sensitivity of a speed sensor, wherein the speed sensor has an oscillation system. Background Technology

[0002] Speed ​​sensors, as known from existing technology, are limited in performance by adverse effects such as drift in detection sensitivity, which can lead to misinterpretation of measurement results in the absence of compensation or correction. Therefore, speed sensors typically incorporate compensation mechanisms to counteract the drift in measurement results.

[0003] This drift in sensitivity depends on many factors, such as environmental influences like temperature or humidity, or mechanical stress, aging, etc. The actual physical cause of the drift is usually based on the mechanical effects on the spring-mass system (FMS) of the sensor. These mechanical effects, in turn, cause changes in the amplitude response (gain characteristic curve) and / or phase response (phase characteristic curve). The amplitude and phase responses are determined by the transfer function (or system function) of the spring-mass system, which characterizes the system's frequency-dependent response in such a way that it describes the relationship between the input signal (e.g., the drive signal) and the output signal (e.g., the amplitude of the drive mode or the probe mode, or the associated electrical signal). For different models of oscillating systems, the transfer function in analytical form is known. In particular, for damped oscillations of a system consisting of a mass and a linear spring, the following correlation with the frequency ω of the input signal is derived (the size factor of the gain G(ω) is omitted here):

[0004]

[0005]

[0006] Here, ω0 represents the natural frequency (determined by the mass and spring constant) and Q represents the quality factor of the oscillating system. When the system's spring constant (and therefore natural frequency) changes, the gain and phase characteristic curves are affected by the effects mentioned above in terms of their slope and position relative to the frequency axis. On the other hand, the direction of the characteristic curves may also be affected by changes in the system's quality due to temperature variations. Changes in gain or phase, in turn, affect the measured signal (see Equation 3 below), which is not based on actual changes in rotational speed, thus introducing measurement errors and reducing detection sensitivity. To identify drift without resorting to a reference excitation (i.e., a known external rotational speed), the orthogonality (denoted by Quad in the formula) present in every practical micromechanical system can be fully utilized. Orthogonality produces a force effect, or an additional quantity on the detected signal, independent of the rotational speed Ω, which is phase-shifted by 90° relative to the useful signal generated by the rotational speed. However, both signal quantities are proportional to the sensitivity G. Due to the phase shift, the orthogonal signal s can be demodulated. Quad With the detection signal s Ω Separation.

[0007] s Ω =G*Ω+C*Quad*φ (3)

[0008] s Quad =C*Quad (4)

[0009] This situation is fully utilized in methods known in the prior art to determine sensitivity variations. This is achieved by temporarily and artificially enhancing the orthogonality of the oscillation detection device electrostatically through electrodes additionally integrated into the sensor. The altered output signal is then compared during operation with a reference value determined through prior calibration. Conclusions regarding the sensitivity variation can then be derived from the ratio of the output signal to the reference value. However, this method has drawbacks, including the associated additional design overhead and space requirements for the additional electrodes on the sensor. Therefore, it is desirable to achieve the measurement of sensitivity drift without additional mechanical overhead. Furthermore, the methods described above in the prior art can only determine temperature-dependent variations in the gain and phase characteristic curves of the oscillation system. Conversely, shifts in the characteristic curves due to additional interference effects (e.g., mechanical stress in the micromechanical structure forming the sensor) can only be determined under certain conditions. Summary of the Invention

[0010] In this context, the objective of this invention is to propose a method for obtaining information about possible drift in detection sensitivity without incurring the aforementioned disadvantages.

[0011] The method according to the present invention has the following advantages over the prior art: it eliminates the need for artificial influence on the orthogonality of the oscillating system, and in particular, eliminates the need for additional electrodes required for this purpose. This method provides an efficient way to determine the sensitivity variation of an oscillating system (hereinafter also referred to as a spring-mass system or simply FMS). The FMS can particularly relate to the detection device of a speed sensor. Here, the detection of this variation is independent of possible orthogonal variations and is also almost independent of temperature. This method makes it possible to determine the position of the transfer function (TF) or the position of the operating point on the gain characteristic curve or phase characteristic curve determined by the transfer function. In this way, not only the detection sensitivity can be determined, but also the phase variation (regardless of temperature effects). This, in particular, leads to the possibility of establishing a correction factor, or a correction factor function or table, which can be used to compensate for sensitivity drift and phase drift during sensor operation. Based on the measurement results determined in this method, the temperature-dependent absolute phase difference and the temperature-independent relative phase difference can be determined, which can be used as other indicators for additional influence factors.

[0012] Each of the possibilities mentioned above can be realized without the additional electrodes used in the prior art, especially in the case of a detection device. Furthermore, these possibilities are independent of the applied rotational speed and therefore can be applied without other limitations during sensor operation. It is also conceivable to use additional electrodes to influence the FMS, and to use these additional electrodes in a manner complementary to the method according to the invention, in order to improve the accuracy of possible compensations and thus contribute to the absolute determination of sensitivity independent of rotational speed.

[0013] The concept of this invention is based on the following basic idea: inducing a controlled change in the transfer function (i.e., amplitude response and / or phase response), and determining the relative change in gain or phase shift at a fixed drive frequency to determine the position of the transfer function relative to the frequency axis. At a pre-given drive frequency, conclusions about the actual gain can only be drawn from the probe signal if the applied rotational speed is known. According to Equation 3 (in addition to the quadrature components that can be determined by demodulation), the probe signal also contains a product of gain G and rotational speed Ω, thus the separation of these two effects cannot be achieved solely based on the probe signal. Instead, in the method according to the invention, quadrature components s are determined for at least two different gains (caused by the controlled change in the transfer function). Quad Therefore, sufficient information is available to determine the true gain.

[0014] Using Equation 4, we can derive the orthogonal signal s belonging to the transformed transfer function. Quad,i,Δ =s Quad,i+Δs Quad (Variables belonging to the changed transfer function are labeled with an additional index Δ below, and differences are indicated by a Δ label placed before the variable) and orthogonal signals s belonging to the unchanged transfer function. Quad,i The ratio v i :

[0015]

[0016] As can be seen from the equation, the ratio established in this way is independent of orthogonality. After changing the transfer function, the following applies to the output signal of the rotational speed:

[0017] s Ω，i，Δ =(G i +ΔG i )Ω(φ i +Δφ i (6)

[0018] Based on ratio v i The determination of gain can be described by way of controlled horizontal shifts (especially by corresponding shifts in the natural frequency) of the gain characteristic curves and phase characteristic curves given by Equations 1 and 2 (see [reference]). Figure 3 Since, according to Equation 1, the gain increases strictly monotonically below the natural frequency and decreases strictly monotonically above the natural frequency, a region can be defined in which the ratio v i Allowing for a single, definitive conclusion regarding the location of the operating point. A similar approach can be implemented based on the phase characteristic curve, i.e., by inferring the location of the characteristic curve from mechanical phase changes. If currently unknown external influences (e.g., mechanical stress) act on the FMS of the actuator or probe unit and cause a change in the natural frequency ω0→ω i Then the ratio also changes from v0 to v i . Figure 4 This process is illustrated graphically in a more general form.

[0019] The above-described embodiments (which describe the inventive concept in detail with a controlled horizontal offset as an example) can be transferred to a general case, in which the largely arbitrary, reproducible, and controlled influence of the transfer function of the oscillating spring-mass system can be used to determine the operating point on the gain and phase characteristic curves given by the transfer function, and thus ultimately determine the sensitivity change caused by external influences.

[0020] In addition to using the offset of the natural frequency as a compensation method (whether by mechanical or inductive modification), this method can also be used for other functions or alternative applications.

[0021] According to a preferred embodiment, in the second step, a controlled change is made to the natural frequency of the oscillating system and / or a controlled change is made to the quality factor of the oscillating system. According to Equations 1 and 2, the natural frequency ω0 and the quality factor Q determine the shape and position of the gain characteristic curve and the phase characteristic curve. Here, the quality factor essentially determines the width of the curve, i.e., the descent at the left and right edges of the maximum value, while the natural frequency determines the position of the characteristic curve relative to the frequency axis. Therefore, both variables can be used in the method of the present invention to change the transfer function in a controlled and reversible manner, and enable the determination of the sensitivity drift through the aforementioned measurements of orthogonal signals.

[0022] According to a particularly preferred embodiment, the change in natural frequency is achieved through a controlled change in the spring constant of the oscillating system. The spring constant, together with the mass of the oscillating object, determines the natural frequency of the oscillating system, so that an increase or decrease in the spring constant directly results in a shift in the natural frequency, which, as described above, can be used to determine sensitivity drift.

[0023] According to a preferred embodiment, in a fifth step, following the third step and preceding the fourth step, further controlled changes to the transfer function are performed, and other orthogonal signals of the speed sensor are determined. In the fourth step, the detection sensitivity is determined based on the first, second, and other orthogonal signals. In this way, by repeating the second and third steps of the method according to the invention once or multiple times, the accuracy of the obtained sensitivity drift can be advantageously improved. In the simplest case, for example, the sensitivity drift can be obtained in each repetition, and a suitable selection or average value can be formed from the values ​​thus obtained.

[0024] According to a preferred embodiment, in a fifth step following the fourth step, a compensation parameter for the detection signal is determined based on the detection sensitivity determined in the fourth step. This is to enable the ratio v i For compensation, a matrix or function can be pre-established (under initial conditions), which will calculate the changed ratio v. i This is combined with a compensation factor CF. This can be achieved, for example, by measuring the ratio v over a defined area. i And for each of these values, a corresponding correction factor is determined. In the simplest case, the correction factor can be established by comparing the quadrature signal belonging to the offset natural frequency with the reference signal:

[0025]

[0026] Figure 4The process is illustrated graphically in a more general form. Because the measurement is performed under initial conditions, the orthogonality is unaffected by any changes, and therefore the correction factor is independent of any possible variations in orthogonality. The calculated correction factor can then be applied in another step to the (orthogonally compensated) output signal of the demodulated probe channel:

[0027]

[0028] This yields results that have already been measured under the initial conditions, without the need to measure orthogonal orthogonal variations. Figure 5 The process is illustrated graphically in a more general form. Similarly, correction factors for mechanical phase changes can be calculated and applied.

[0029] Another subject of the invention is a method according to another technical solution of the invention. One method according to the invention is based on the controlled variation of the transfer function of an oscillating system, while this variant uses two oscillating systems with the same sensor, which differ in a defined manner in terms of their transfer functions. Ratio v i Accordingly, it is given by the orthogonal signals of the two systems, that is, in Equation 5, the variable s Quad,i Given by the orthogonal signal of the first oscillating system, and the variable s Quad,i,Δ The orthogonal signal from the second oscillating system is given. However, the above considerations apply directly.

[0030] According to a preferred embodiment, the quality factor of the first oscillating system is equal to the quality factor of the second oscillating system, wherein the mass of the first oscillating system is different from the mass of the second oscillating system, and / or the spring constant of the first oscillating system is different from the spring constant of the second oscillating system. In this embodiment, the difference in the transfer functions of the two systems is caused by the mass, spring constant, and / or quality factor. Here, the mass, together with the spring constant, determines the natural frequency, thereby providing another possibility for shifting the natural frequencies of the two systems relative to each other by increasing or decreasing the mass.

[0031] According to a preferred embodiment, in a fifth step following the fourth step, compensation parameters for the detection signal are determined based on the detection sensitivity determined in the fourth step. The compensation parameters are determined in a manner similar to that described above for the case of a single oscillating system.

[0032] The following embodiments can be understood as variations of the method according to one technical solution of the present invention (changing the transfer function of an oscillating system) and the method according to another technical solution of the present invention (two oscillating systems with different transfer functions).

[0033] According to a preferred embodiment, the speed sensor has a register with multiple pairs of values ​​for detection sensitivity and compensation parameters. The compensation parameter is determined either by selecting a value from the register or by an analytical, particularly linear, relationship between the detection sensitivity and the compensation parameter. Therefore, depending on the choice of operating point, a linear relationship between the detection signal ratio v and the compensation factor CF can be approximately assumed. This allows the factor to be obtained instead of using tables, and CF can then be calculated by multiplying v by the factor.

[0034] According to a preferred embodiment of the method, a first detection signal is determined in a first step and a second detection signal is determined in a second step, wherein, in a sixth step following the fourth step, the temperature effect on the mechanical phase of the oscillating system is calculated based on the first and second detection signals. Based on equations 3 and 4 and the shift in the detection mode, the following relationship can be calculated for the absolute phase change:

[0035]

[0036] Since the same FMS is studied and a ratio is formed under the condition of natural frequency shift, the horizontal position on the gain characteristic curve determined by the method according to the invention is almost independent of temperature effects. However, in this way, the effects of thermal interference cannot be identified or compensated. However, the phase change caused by the shift of the natural frequency is calculated as an absolute value and is therefore a function of temperature. Therefore, in a variation of the method of the invention, the absolute phase change can be used as an indicator for temperature effects.

[0037] Another subject of the invention is a speed sensor having an oscillation system and a control unit, wherein the speed sensor, and particularly the control unit, is configured to implement a method according to one technical solution of the invention. Another subject is a speed sensor having first and second oscillation systems and a control unit, wherein the speed sensor, and particularly the control unit, is configured to perform a method according to another technical solution of the invention, or configured to perform both a method according to one technical solution of the invention and a method according to another technical solution of the invention. The above-described embodiments of the method according to the invention are directly transferred to embodiments of the speed sensor according to the invention. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of an oscillating system, which is formed by an elastically supported mass and can be excited to oscillate via an electrode device.

[0039] Figure 2The transfer function of the oscillating system is illustrated by showing the gain characteristic curves of the driving oscillation and the probe oscillation, as well as the phase characteristic curve of the probe oscillation.

[0040] Figure 3 A flowchart of the initialization process is shown, in which multiple values ​​of the compensation parameters are determined.

[0041] Figure 4 A flowchart of the compensation process is shown, in which compensation parameters for the detection signal are determined.

[0042] Figure 5 Showing the method used to determine the ratio v i The flowchart. Detailed Implementation

[0043] Figure 1 This is a schematic diagram of the oscillation system 1 used in a speed sensor. Here, the oscillation system 1 includes a vibrating mass 2, which is elastically coupled to the sensor substrate via a spring device 3 and can be excited to oscillate (drive oscillation or drive mode) by an electrostatic alternating field. A common possibility for speed determination is that, in addition to the drive mode, the vibrating mass 2 has another oscillation mode, which extends, for example, in a direction perpendicular to the drive oscillation and serves as a detection mode. The speed applied to the sensor causes coupling between the drive mode and the detection mode, so that the amplitude of the detection mode (which depends on the strength of the coupling and therefore on the applied speed) can be used to measure the speed. In addition to this coupling, the actual sensor additionally has two modes of (undesired) coupling, generally referred to as the orthogonal effect, which results in speed-independent excitation of the detection mode. The measurement signal contains two components, where, however, the orthogonal signal can be separated from the useful signal by demodulation. As shown in the figure, the measurement signal can be detected by the change in capacitance associated with the detection oscillation, which is formed by the mass 2 and the measuring electrode 4 fixed to the substrate. Furthermore, the spring constant of the system can be matched by measuring the bias voltage 5 of the electrodes, and thus the natural frequency can be shifted. This represents a simple possibility for causing a controlled change in the transfer function according to the invention, since the transfer function is shifted toward a higher or lower frequency when the natural frequency is increased or decreased.

[0044] Figure 2This is a graph illustrating the gain and phase curves generated by the offset of the inherent frequency at the driving frequency, which operates with a phase-locked loop (PPL) at its global maximum. It shows the gain characteristic curve 10 (upper part) for the driving mode, two mutually offset gain characteristic curves 11 and 12 (middle part) for the probe mode, and two mutually offset phase characteristic curves 13 and 14 (lower part) for the probe mode. The frequencies are plotted on the horizontal axis 6. The vertical axis 7 of the upper graph corresponds to the gain G. drive The vertical axis 8 of the central figure corresponds to the gain G. sense The vertical axis 9 of the lower figure corresponds to the phase φ. sense The vertical quantities are logarithmic.

[0045] One embodiment of the method according to the present invention is based on the following scheme: comparing the gain or phase of the oscillating system 1 at different natural frequencies. Figure 2 The transfer function of the sensor, given by Equations 1 and 2, for the sensor consisting of a driving FMS (upper) and a sensing FMS (middle and lower), is graphically illustrated using gain or phase characteristic curves 10, 11, 12, 13, and 14. In this example, the sensing FMS is affected by the increase in the spring constant, thereby affecting the system's natural frequency ω0, and thus characteristic curves 11 and 13 as a whole shift towards a higher frequency (indicated by arrow 15). The difference between the curves can be easily obtained by analyzing the corresponding quadrature signals. As can be seen from Equation 5, the ratio of the quadrature signals directly corresponds to the ratio v of the gains (i.e., at the driving frequency, these gains correspond to the values ​​16 and 16' of gain characteristic curves 11 and 12). i In the diagram, the driving frequency is marked by the vertical line 35, and the maximum gain G is obtained corresponding to the driving mode. drive The frequency of time. The edges of characteristic curve 11 (and its corresponding offset portion 12) have a strictly monotonically increasing trend to the left of the maximum value and a strictly monotonically decreasing trend to the right of the maximum value. This is due to the ratio v. i The value of , in the region where both characteristic curves are monotonic, allows for a unique and definitive deduction of the operating point given the known shift in the natural frequency. The method according to the invention utilizes this situation to determine the true gain from the ratio.

[0046] Figure 3 The sensor initialization process is shown, where, for the ratio v i Collect different values ​​of the compensation parameter belonging to CF i (v iFor simplicity, the process is described here and below based on a specific implementation using a shift in the inherent frequency, where, however, the controlled variation of the transfer function can be easily transferred to the general case. This process is particularly automated by the sensor's control unit.

[0047] Initialization begins in box 17, and in box 18, it is first determined whether the desired number of measurement points has been reached. Initially, no measurements exist, so the natural frequency of the FMS is shifted in box 20, and then the quadrature signal is measured in box 21. The ratio v is determined from the measured values ​​and the values ​​of the quadrature signal belonging to the unshifted natural frequency. i Determine the correction factor CF in box 22. i =v i / v, and in 23 it is used as the allocation CF i (v i The data is stored, for example, in a register. The sequence 18, 20, 21, 22, 23 is repeated until the desired number of measurement points is determined in 18, and the process ends in 19.

[0048] Figure 4 The procedure for compensating for sensitivity or phase changes caused by interference is shown. After starting the procedure in step 24, the ratio v is determined in step 25. i And in 26, the corresponding correction factor CF is called from 28. i (v i (CF) i (v i (This can exist as a table or a function, for example). The process ends in 27.

[0049] Figure 5 Showing the ratio v i The established procedure. After starting at 29, the orthogonal signal s is measured in 30. Quad,i In step 31, the inherent frequency of the FMS is shifted, and in the subsequent step 32, the corresponding quadrature signal s is measured. Quad,i,Δ Then, calculate the ratio v in 33. i =s Quad,i,Δ / s Quad,i And the process ends in step 34.

Claims

1. A method for determining the detection sensitivity of a speed sensor, wherein, The speed sensor has an oscillation system (1), characterized in that... In the first step, the first orthogonal signal of the oscillation system (1) is determined. In the second step, a controlled change is performed on the transfer function of the oscillating system (1). In the third step, the second orthogonal signal of the oscillation system (1) is determined, and In the fourth step, the detection sensitivity is determined based on the first and second orthogonal signals, wherein the detection sensitivity is determined based on the ratio of the first and second orthogonal signals, and the ratio of the first and second orthogonal signals corresponds to the gain ratio. In the second step, a controlled change is made to the natural frequency of the oscillation system (1) and / or a controlled change is made to the quality factor of the oscillation system (1). Specifically, at a fixed driving frequency, the relative change in gain or phase shift is calculated to determine the position of the transfer function relative to the frequency axis. The first orthogonal signal and the second orthogonal signal are orthogonal signals present in the oscillation system (1), and the orthogonal signals are caused by an orthogonal effect independent of rotational speed, which leads to the excitation of the detection mode independent of rotational speed.

2. The method according to claim 1, characterized in that, The natural frequency is changed by the controlled change of the spring constant of the oscillating system (1).

3. The method according to claim 1 or 2, wherein, In a fifth step, which follows the third step and precedes the fourth step, other controlled changes to the transfer function are performed and other orthogonal signals of the speed sensor are determined, wherein, in the fourth step, the detection sensitivity is determined based on the first, second and other orthogonal signals.

4. The method according to claim 1 or 2, wherein, In the fifth step following the fourth step, compensation parameters for the detection signal are determined based on the detection sensitivity determined in the fourth step.

5. A method for determining the detection sensitivity of a speed sensor, wherein, The speed sensor has a first oscillation system (1) and a second oscillation system, wherein the transfer function of the first oscillation system (1) is different from the transfer function of the second oscillation system, characterized in that... In the first step, the first orthogonal signal of the first oscillation system (1) is determined. In the second step, the second orthogonal signal of the second oscillation system is determined, and In the fourth step, the detection sensitivity is determined based on the first and second orthogonal signals, wherein the detection sensitivity is determined based on the ratio of the first and second orthogonal signals, and the ratio of the first and second orthogonal signals corresponds to the gain ratio. Wherein, the first orthogonal signal is an orthogonal signal existing in the first oscillation system (1), the second orthogonal signal is an orthogonal signal existing in the second oscillation system, the orthogonal signal is caused by an orthogonal effect independent of rotational speed, the orthogonal effect leads to the excitation of the detection mode independent of rotational speed.

6. The method according to claim 5, wherein, The quality factor of the first oscillation system (1) is equal to the quality factor of the second oscillation system, wherein the mass of the first oscillation system (1) is different from the mass of the second oscillation system, and / or the spring constant of the first oscillation system (1) is different from the spring constant of the second oscillation system.

7. The method according to claim 5 or 6, wherein, In the fifth step following the fourth step, compensation parameters for the detection signal are determined based on the detection sensitivity determined in the fourth step.

8. The method according to claim 7, wherein, The speed sensor has a register having multiple pairs of values ​​for the detection sensitivity and the compensation parameter, wherein the compensation parameter is determined by selecting a value from the register, or wherein the compensation parameter is determined by an analytical relationship between the detection sensitivity and the compensation parameter.

9. The method according to claim 8, wherein, The analytical relationship between the detection sensitivity and the compensation parameter is linear.

10. The method according to claim 5 or 6, wherein, In the first step, a first detection signal is determined, and in the second step, a second detection signal is determined, wherein in the sixth step following the fourth step, the temperature effect on the mechanical phase of the oscillation system (1) is determined based on the first detection signal and the second detection signal, as well as the first detection signal and the second detection signal.

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