Method for operating a micromechanical angular rate sensor with a sensor element as part of a vibrating structure and micromechanical angular rate sensor with a sensor element as part of a vibrating structure

Abstract

A method for operating a micromechanical angular rate sensor with a sensor element as part of a vibrating structure, as well as a micromechanical angular rate sensor with a sensor element as part of a vibrating structure, is proposed. wherein the micromechanical angular rate sensor comprises a drive with a drive control loop for driving a vibration of the vibrating structure along a drive direction due to a drive voltage, wherein to drive the vibration of the vibrating structure it is subjected to the drive voltage and to an offset voltage, wherein the vibration amplitude of the vibrating structure is detected by means of the drive control loop and is controlled by adjusting the drive voltage.

Description

State of the art

[0001] The invention relates to a method for operating a micromechanical angular rate sensor with a sensor element as part of a vibrating structure according to the preamble of claim 1.

[0002] In such methods for operating a micromechanical angular rate sensor, particularly as part of an IMU (inertial measurement unit), a vibrating structure is driven into vibration along a drive direction by means of a drive with a drive control loop, and is thereby typically deflected or excited up to a target amplitude of this vibration, for example, 8 micrometers. For this purpose, the vibrating structure is subjected to a drive voltage. In addition to the drive voltage, the vibrating structure is also typically subjected to or pre-charged with an offset voltage. This is because the offset voltage has an amplifying effect on both the detection of a detection signal and the (drive) force acting during the drive excitation.Thus, the vibration amplitude of the vibrating structure is proportional to the product of the applied offset voltage and the driving voltage.

[0003] The drive control loop measures the vibration amplitude of the vibrating structure, compares it to the target amplitude, and adjusts or controls the drive voltage (and consequently the vibration amplitude). In the prior art, adjusting the vibration amplitude of the vibrating structure, or—in the case of an insufficient vibration amplitude, particularly due to a drop in the offset voltage—increasing the vibration amplitude, is usually achieved by a (short-term) disproportionately increasing adjustment or increase of the drive voltage.As a result of the disproportionate increase in the drive voltage, it is possible (without this being the intended goal) that the adjusted vibration amplitude, which is generally proportional to the product of the adjusted drive voltage and the applied offset voltage, is excited – at least briefly – beyond the target amplitude (or a comparable length) of the vibrating structure. In detail, the vibration amplitude is detected by separate structures (drive detection), i.e., by structures that are distinct from the actual (drive) structures used to generate the driving force. These drive detection structures are typically also subjected to the offset voltage. The drive control loop is oriented according to this detection signal from the drive detection. If the offset voltage now decreases, the detection signal also decreases (even if the drive or...The vibratory structure would continue to oscillate with the target amplitude. This leads to overcompensation of the drive excitation. A critical range thus arises in which the vibratory structure is excited to oscillate with a modified amplitude that exceeds the target amplitude, potentially causing damage to the vibratory structure and / or the micromechanical angular rate sensor. Specifically, at a typical oscillation frequency of, for example, 35 kHz, mechanical contact (between the vibratory structure and a substrate-fixed structure surrounding the vibratory structure, particularly within a cavity) can occur 35,000 times per second, resulting in significant potential for damage.Therefore, a drop in the offset voltage (into a critical range) can lead to critical behavior and a correspondingly high potential for damage to the micromechanical gyroscope.

[0004] A drop in the offset voltage into a critical range can be caused, for example, by mobile particles within the surrounding structure, particularly within a cavity of the micromechanical angular rate sensor (due to a short circuit or shunt between the applied offset voltage and, for example, the ground potential). These mobile particles can arise primarily from mechanical overload of the vibrating structure within the surrounding structure or cavity (e.g., mechanical impacts between the vibrating structure and the surrounding structure or cavity), but also during manufacturing processes. In particular, a shunt caused by the mobile particles between the offset voltage and the ground potential can thus lead to a drop in the offset voltage, especially into a critical range. Disclosure of the invention

[0005] Against this background, the task is to provide a method for operating a micromechanical angular rate sensor with a sensor element as part of a vibrating structure, which does not have the aforementioned disadvantages.

[0006] The inventive method for operating a micromechanical angular rate sensor with a sensor element as part of a vibrating structure has the advantage over the prior art that the operation of the micromechanical angular rate sensor in a critical range of the applied offset voltage is technically controlled. This is achieved by directly or indirectly detecting the offset voltage applied to the vibrating structure and reducing the drive voltage or switching off the drive of the micromechanical angular rate sensor when a determined value of the applied offset voltage lies within a predetermined value interval. This results in the need for readjustment or...The adjustment of the drive voltage, which is implemented for values ​​of the applied offset voltage outside the specified value range, is at least modified or controlled differently for values ​​within the specified value range – due to the reduction of the drive voltage or the deactivation of the drive of the micromechanical gyroscope. Thus, according to the invention, it is advantageously possible to prevent the effect of the otherwise (i.e., according to prior art control methods) disproportionate increase in the drive voltage (in the case of a drop in the applied offset voltage) and the resulting potential increase of the adapted vibration amplitude of the vibrating structure beyond its target amplitude (or a comparable length) by reducing the drive voltage or by deactivating the drive of the micromechanical gyroscope.Preferably, for an applied offset voltage, which experiences a brief voltage drop (i.e., falls into the critical range or the specified value interval) particularly due to a short circuit or shunt with, for example, the ground potential, the adjusted vibration amplitude of the vibrating structure is not regulated beyond the target amplitude (or a comparable length or maximum deflection). Reducing the drive voltage or switching off the drive of the micromechanical gyroscope thus prevents permanent damage, as mechanical overload or mechanical contact (shocks and collisions) between the vibrating structure and the surrounding structure is prevented.

[0007] By monitoring the applied offset voltage and thereby preventing damage to the micromechanical gyroscope, both a permanent failure of the micromechanical gyroscope can be avoided and a fault analysis can be enabled: If a micromechanical gyroscope is completely destroyed (e.g., due to exceeding the target amplitude for too long), the original cause of the fault (which led to the drop in the applied offset voltage) can no longer be clearly determined; however, if the micromechanical gyroscope is not destroyed, the original cause of the failure can still be determined.

[0008] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0009] According to an advantageous embodiment of the invention, the offset voltage has a setpoint, wherein the predetermined value interval is defined as a range of the setpoint of the offset voltage, the range extending from 50% or greater than 50% to 90% or less than 90% of the setpoint. This limitation to a range between 50% and 90% of the setpoint advantageously enables the operation of the gyroscope to be designed effectively, since a drop in the applied offset voltage outside this range does not substantially lead to an exceedance of the target amplitude (or a comparable length) of the vibrating structure (despite the disproportionate adjustment of the drive voltage).

[0010] According to an advantageous embodiment of the invention, the reduction of the drive voltage or the switching off of the drive of the micromechanical angular rate sensor is provided for within a time interval of up to one millisecond, in particular up to 100 microseconds, and more preferably up to 10 microseconds. This advantageously ensures effective and efficient operation of the micromechanical angular rate sensor.

[0011] According to an advantageous embodiment of the invention, the setpoint is provided to be in a range of up to 50 volts, in particular up to 25 volts, and preferably from 8 to 20 volts. This advantageously ensures effective and efficient operation of the micromechanical gyroscope.

[0012] Further objects of the invention are a micromechanical rate gyroscope with a sensor element as part of a vibrating structure, a controller and a micromechanical rate gyroscope system with a controller and a micromechanical rate gyroscope according to the dependent device claims.

[0013] The micromechanical angular rate sensor according to the invention, with a sensor element as part of a vibrating structure, proves to be advantageous compared to the prior art in that the micromechanical angular rate sensor can be technically controlled in a critical range of the offset voltage. This is achieved by configuring the micromechanical angular rate sensor such that the offset voltage applied to the vibrating structure is detected directly or indirectly, and the drive voltage is reduced or the drive of the micromechanical angular rate sensor is switched off when a determined value of the applied offset voltage lies within a predetermined value interval.

[0014] The advantages and features described in connection with the embodiments of the inventive method for operating a micromechanical gyroscope with a sensor element as part of a vibrating structure can be applied to the micromechanical gyroscope with a sensor element as part of a vibrating structure, the controller and the micromechanical gyroscope system.

[0015] An embodiment of the present invention is shown in the drawing and explained in more detail in the following description.

[0016] Brief description of the drawings: Fig. Figure 1 shows in a very schematic representation a micromechanical rotation rate sensor with a sensor element as part of a vibrating structure according to an embodiment of the present invention. Fig. Figure 2 shows a diagram in which a detected applied offset voltage and an adapted vibration amplitude of the vibrating structure of a micromechanical angular rate sensor according to the state of the art are schematically plotted. Embodiments of the invention:

[0017] Fig. Figure 1 shows a highly schematic representation of a micromechanical angular rate sensor 100 with a sensor element as part of a vibrating structure 120 according to an embodiment of the present invention. The micromechanical angular rate sensor 100 comprises a drive 110 with a drive control loop for driving an oscillation of the vibrating structure 120 along a drive direction due to a drive voltage 201. Furthermore, to drive the oscillation of the vibrating structure 120, it is subjected to the drive voltage 201 and to an offset voltage 200. In particular, the application of the offset voltage 200 to the vibrating structure 120 has an amplifying effect on the detection of a detection signal and on a driving force acting within the oscillation. As a result, the oscillation amplitude is generally proportional to the product of the applied offset voltage 200 and the drive voltage 201.

[0018] Furthermore, the vibration amplitude or maximum displacement of the vibrating structure 120 is detected by the drive control loop and adjusted by modifying the drive voltage 201. Specifically, the drive control / excitation and the drive detection / monitoring are typically performed using two separate structures. Within this framework, the vibration amplitude is compared to a target amplitude, for example, 8 micrometers, and if the vibration amplitude deviates from the target amplitude, it is adjusted by modifying the drive voltage 201 so that the vibration amplitude matches the target amplitude. This adjustment is achieved (in the case of an insufficient vibration amplitude) primarily by a disproportionate increase in the drive voltage 201.Thus, a decrease in the applied offset voltage 200 (while the drive voltage 201 remains constant) can lead to a reduction in the vibration amplitude, and consequently, due to the drive control loop, a disproportionate increase in the drive voltage 201 occurs. This, in turn, causes an increase in the vibration amplitude of the vibrating structure 120. Therefore, the vibration amplitude of the vibrating structure is adjusted.

[0019] In prior art gyroscopes, a critical range can occur, particularly with regard to the drop in the offset voltage 200, for which the vibration amplitude is controlled beyond the target amplitude (or a comparable length). This represents a critical behavior because, when the vibration amplitude increases beyond the target amplitude, usually only a few micrometers remain before the vibrating structure 120 impacts the surrounding structure. According to the prior art, this also means that the vibrating structure 120 may be damaged within this critical range of the applied offset voltage 200, or damage may occur within the micromechanical gyroscope 100. A drop in the applied offset voltage 200 (into the critical range) can therefore lead to critical behavior and a correspondingly high potential for damage in prior art gyroscopes.

[0020] The drop in the offset voltage 200 applied to the vibrating structure 120 into the critical range can be triggered, for example, by mobile particles or abrasion particles. These mobile particles can originate primarily within the surrounding structure (cavity or sensor housing) due to mechanical overload, especially impacts or collisions, with the vibrating structure 120, or they can occur as a result of the manufacturing or production process. With respect to the applied offset voltage 200, the mobile particles can cause a short circuit or shunt with, for example, the ground potential. In particular, a resistive shunt caused by the mobile particles between the applied offset voltage 200 and the ground potential can thus lead to a drop in the applied offset voltage 200, especially into the critical range.In other words, such mobile particles can (with a low probability) temporarily land at a point in the surrounding structure where, in particular as a shunt, for example through a resistive voltage divider with 1MOhm to 1 TOhm, between the applied offset voltage 200 and another potential, for example the ground potential, they can cause the applied offset voltage 200 to drop into the critical range.

[0021] According to the invention, the offset voltage 200 applied to the vibrating structure 120 is detected directly or indirectly, and the drive voltage 201 is reduced or the drive 110 of the micromechanical gyroscope 100 is switched off when a determined value of the applied offset voltage 200 lies within a predetermined value interval (which is related to the critical range). Thus, it is possible to technically control the operation of the micromechanical gyroscope 100 within the critical range of the applied offset voltage 200. The negative effect of the disproportionately increasing drive voltage 201, described above and occurring in the prior art, is therefore prevented within the critical range or the predetermined value interval of the applied offset voltage 200 (i.e., when the applied offset voltage 200 drops), particularly when triggered by a short circuit or shunt circuit.The disproportionate increase in the drive voltage 201 is counteracted by reducing or even switching off the micromechanical gyroscope in order to protect the micromechanical gyroscope from potential damage (due to mechanical overload or shocks and collisions between the vibrating structure 120 and the surrounding structure). In particular, the operation of the gyroscope 100 is monitored, preferably with regard to the applied offset voltage 200. This monitoring and the resulting prevention of damage prevent both a permanent failure of the micromechanical gyroscope 100 and enable fault analysis.In the case of a completely destroyed micromechanical gyroscope 100, which is avoided according to the invention, the original source of the error can no longer be clearly determined and thus the original cause of failure can still be determined in the case of the micromechanical gyroscope according to the invention.

[0022] Fig.Figure 2 shows a diagram schematically plotting the adjusted vibration amplitude 210 of the vibrating structure 120 of the micromechanical angular rate sensor 100, resulting from the drive control loop, against the measured applied offset voltage 200 in angular rate sensors according to the prior art. This diagram illustrates an example of the course of the adjusted vibration amplitude 210 of the vibrating structure 120 as it is generated in the prior art. The diagram depicts the specified value interval 104, a target value 102 of the applied offset voltage 200, and a proportionality range 105 between the applied offset voltage 200 and the adjusted vibration amplitude 210 of the vibrating structure 120 (for comparatively small values ​​of the applied offset voltage 200).Furthermore, the diagram shows a characteristic curve 101 (which is related to the target amplitude or a comparable length) for the adjusted vibration amplitude 210, as well as a range 103 in which the adjusted vibration amplitude 210 lies above the characteristic curve 101. Here, the characteristic curve 101 marks a range above which the adjusted vibration amplitude 210 is too large, or above which damage within the micromechanical angular rate sensor 100 is possible due to the adjusted vibration amplitude 210. The value interval 104 thus includes a range of values ​​for the offset voltage 200 in which the adjustment of the vibration amplitude 210, associated with this deviation of the applied offset voltage 200 (from the target value 102), lies above the characteristic curve 101.

[0023] According to the invention, it is therefore provided that for measured values ​​of the offset voltage 200 within the predetermined value interval 104 (for which a critical applied offset voltage 200 is assumed and thus related to the critical range), the drive voltage is reduced or the drive of the micromechanical gyroscope is switched off. In particular, this value interval 104 is defined according to the invention as a range of the setpoint 102 of the offset voltage 200, wherein this range extends from 50% to 90% of the setpoint 102. Thus, according to the invention, it is advantageously achieved both for values ​​of the applied offset voltage 200 outside this predetermined value interval 104 and for values ​​within the predetermined value range 104 that a drive voltage 201 regulated by the drive control loop does not lead to an exceedance of the adapted vibration amplitude 210 via the characteristic curve 101.For offset voltage values ​​200 (less than, for example, 50 percent of the setpoint 102), this is already the case. For values ​​greater than, for example, 90 percent of the setpoint 102, the effect of the commonly used readjustment of the drive voltage 201 is also not such that it generates a vibration amplitude 210 above the characteristic curve 101.

[0024] In a preferred embodiment of the invention (not shown here), the setpoint 102 of the applied offset voltage 200 lies in a range of up to 50 volts, in particular up to 25 volts, and more preferably from 8 to 20 volts. In a further preferred embodiment of the invention (also not shown here), the reduction of the drive voltage 201 or the switching off of the drive 110 of the micromechanical angular rate sensor 100 takes place within a time interval of up to one millisecond, in particular up to 100 microseconds, and more preferably up to 10 microseconds, in order to keep the number of mechanical stops (in the case of an increase in the adapted vibration amplitude 210 of the vibrating structure 120 beyond the characteristic curve 101) as low as possible.

[0025] By monitoring the applied offset voltage 200 (or a voltage correlated with the applied offset voltage 200) – by direct or indirect detection of the offset voltage 200 – the drive 110 of the micromechanical angular rate sensor 100, in particular of the vibrating structure 120, can be reduced or deactivated according to the invention in the case of certain deviations from the setpoint 102. If the cause of the voltage drop, for example a mobile particle within the surrounding structure, for example the cavity, changes its position during the next start of the drive 110 of the micromechanical angular rate sensor 100 and thus resolves a shunt across the offset voltage 200, the normal operation of the micromechanical angular rate sensor 100 can be continued. If the shunt persists, the start of the micromechanical angular rate sensor 100 is aborted until the particle moves again.This may lead to a temporary disruption or interruption of operation, but permanent damage is avoided. Even in the unlikely event that the particle does not move further, this is advantageous because it allows for a more precise fault analysis.

Claims

[1] Method for operating a micromechanical angular rate sensor (100) with a sensor element as part of a vibrating structure (120), wherein the micromechanical angular rate sensor (100) comprises a drive (110) with a drive control loop for driving a vibration of the vibrating structure (120) along a drive direction due to a drive voltage (201), wherein, to drive the vibration of the vibrating structure (120), it is subjected to the drive voltage (201) and to an offset voltage (200), wherein the vibration amplitude of the vibrating structure (120) is detected by means of the drive control loop and controlled by adjusting the drive voltage (201), characterized by, that the offset voltage (200) applied to the vibrating structure is detected directly or indirectly and the drive voltage is reduced or the drive of the micromechanical gyroscope is switched off when a determined value of the applied offset voltage (200) lies within a specified interval (104). [2] Method according to claim 1, characterized by , that the vibration amplitude of the vibrating structure (120) is proportional to the product of the offset voltage (200) and the drive voltage (201), wherein the offset voltage (200) has a setpoint (102), wherein the specified interval of values ​​(104) is defined as a range of the setpoint (102) of the offset voltage (200). [3] Method according to any one of the preceding claims, characterized by, that the reduction of the drive voltage (201) or the switching off of the drive (110) of the micromechanical rotation rate sensor (100) takes place within a time interval of up to one millisecond, in particular up to 100 microseconds, in particular preferably up to 10 microseconds. [4] Method according to any one of the preceding claims, characterized by , that the setpoint (102) is in a range of up to 50 volts, in particular up to 25 volts, and in particular preferably from 8 to 20 volts. [5] Micromechanical angular rate sensor (100) with a sensor element as part of a vibrating structure (120), wherein the micromechanical angular rate sensor (100) comprises a drive (110) with a drive control loop for driving a vibration of the vibrating structure (120) along a drive direction due to a drive voltage (201), wherein the micromechanical rotation rate sensor (100) is configured such that, to drive the vibration of the vibrating structure (120), it is subjected to the drive voltage (201) and to an offset voltage (200), wherein the micromechanical rotation rate sensor (100) is further configured such that the vibration amplitude of the vibrating structure (120) is detected by means of the drive control loop and controlled by adjusting the drive voltage (201), characterized by , that the micromechanical angular rate sensor (100) is configured such that the offset voltage (200) applied to the vibrating structure is detected directly or indirectly and the drive voltage is reduced or the drive of the micromechanical angular rate sensor is switched off when a determined value of the applied offset voltage (200) lies within a specified value interval (104). [6] Controller configured to execute a computer-implemented method according to claims 1 to 4, wherein the controller is further configured to monitor an offset voltage and, in the event of a configurable deviation from a setpoint, to deactivate a drive of a micromechanical gyroscope system. [7] Micromechanical rate gyroscope system comprising a controller according to claim 6 and a micromechanical rate gyroscope according to claim 5.

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