Rotational speed sensor having micromechanical structure and method for operating rotational speed sensor

Abstract

The invention relates to a rotational speed sensor having a micromechanical structure and having a mass vibrator, the mass vibrator being drivable by means of a drive device for driving vibrations, the rotation speed sensor is configured to protect the micromechanical structure and during a time interval of a detected free-fall condition, the free-fall condition is represented by a signal by means of a free-fall signal supplied to the rotation speed sensor, and the rotation speed sensor is configured to protect the micromechanical structure and during the time interval of the detected free-fall condition, the rotation speed sensor is configured to detect the rotation speed of the micromechanical structure. The rotational speed sensor is further configured in such a way that the drive device drives the mass vibrator again for an operational drive vibration of the mass vibrator, immediately after receiving a further free-fall signal indicating the end of the free-fall condition by means of the signal, the reduction in the amplitude of the drive vibrations is achieved more quickly than a reduction in the simple damping process of the drive vibrations corresponding to the mass vibrator.

Description

Technical Field

[0001] The invention relates to a rotational speed sensor having a micromechanical structure and a mass vibrator. Background Art

[0002] Micromechanical rotational speed sensors (hereinafter also referred to as IMUs - inertial measurement units) are already known from the prior art in a variety of embodiments. The common operating principle here is to detect the rotational speed by the action of Coriolis forces that are dependent on the rotational speed. For this purpose, one or more mass vibrators are set in periodic motion by means of an electrically driven movement, so that a force that acts not only perpendicularly to the direction of movement but also perpendicularly to the rotation vector is achieved by rotation. In this case, the periodic motion is maintained by a drive structure; the mass vibrator is coupled to the substrate of the micromechanical sensor via spring elements.

[0003] Such tachometer sensors with continuous drive excitation are prone to particles in the MEMS core during repeated drop tests, which sometimes generate electrical shorts that lead to generally significantly larger static / dynamic offset shifts in one or more axes of the gyroscope, sometimes accompanied by increased noise.

[0004] Therefore, the present invention is intended to address the problem of particle generation in the MEMS core of a tachometer sensor if (a) the mass vibrator is driven from its resting position or into vibratory motion by a tachometer sensor and (b) if the IMU (either independently or as part of an electronic device) is faced with an impact with a surface due to a free fall (under gravity) greater than about 10 cm.

[0005] Methods for detecting a free-falling body based on a parameter of a signal of an acceleration sensor are known. The parameter of the measured acceleration (in g) is defined as follows:

[0006]

[0007] Here, and is the acceleration (in g) in the direction of the corresponding axis.

[0008] Typically, a threshold is used as the basis: below which the sensor is considered free fall; the threshold is defined as Acc thres This value is close to ~0 g and typically depends on the temperature and often on further specifications, such as defined acceleration excursions (according to the manufacturing process or welding process), which are often product-specific.

[0009] The typical output data rate (ODR) provided by known rotational speed sensors is approximately 200 Hz, resulting in a corresponding detection interval of 5 ms, i.e. new data is generated every 5 ms. Due to the length of this time interval, delays can occur in the detection of free fall. If the drive movement or drive actuation is stopped when the free fall signal is detected, the natural decay process of the excited movement of the mass vibrator may last longer than the free fall, so that the problem of particle generation in the MEMS core still exists during the impact. Summary of the invention

[0010] Against this background, the object of the present invention is to provide a rotational speed sensor which can actively reduce the amplitude of the drive vibration by signaling a free fall situation with the aid of a free fall signal supplied to the rotational speed sensor and reducing the amplitude of the drive vibration of the oscillator mass more quickly than a reduction corresponding to a simple attenuation process of the drive vibration of the oscillator mass. This advantageously ensures a higher safety for the sensor in a free fall situation.

[0011] Compared to sensors known from the prior art, the rotational speed sensor according to the invention has the following advantages: after obtaining a signal indicating a free fall situation (by means of the rotational speed sensor), the vibration movement of the mass vibrator (or the amplitude of the vibration movement), in particular the driving vibration of the mass vibrator, can be reduced particularly effectively and in particular relatively quickly, so that in particular the particle generation in the event of an impact can be minimized. Since a free fall situation must be detected only after a certain delay (after its actual occurrence), it is assumed in the context of the invention that there is a minimum duration of the free fall or a minimum duration of the free fall situation (e.g. a value that can be parameterized based on the specific application, e.g. a few tens of ms up to about 80 ms to 100 ms, corresponding to a fall height of several centimeters in the presence of a gravitational acceleration of about 1 g, i.e. near the earth's surface), so that in the event of a possible imminent collision / impact an interrupt signal can be output to the rotational speed sensor. According to the invention, after the free fall signal is obtained, the excitation of the harmonic vibrations of the mass vibrator of the rotation speed sensor, which was previously carried out by means of the drive electrodes, is actively weakened (or the amplitude of the excitation is reduced or the excitation is interrupted) in such a way that the particle generation in the event of a possible subsequent impact is minimized as much as possible. Therefore, according to the invention, it is advantageously possible to protect the rotation speed sensor from damage in a free fall situation - or in particular at the end of the free fall situation (or thereafter). If the IMU is no longer in free fall (or the free fall situation is no longer detected), the drive to the rotation speed sensor is reset to standard operating conditions again. According to the invention, preferably, the possibility for actively interrupting or for weakening the amplitude of the vibration is implemented in particular directly as part of a control loop for maintaining a setpoint value for the drive vibration, whereby it is particularly possible to quickly and actively influence the excitation of the vibration of the mass vibrator.

[0012] According to the invention, a rotational speed sensor is provided, which has a micromechanical structure and a mass vibrator, wherein the mass vibrator can be driven to perform a drive vibration by means of a drive device, wherein the rotational speed sensor is configured to protect the micromechanical structure and is configured in such a way that a reduction in the amplitude of the drive vibration is achieved during a time interval of a detected free fall situation, wherein the free fall situation is signaled or detected by means of a free fall signal supplied to the rotational speed sensor, wherein the rotational speed sensor is further configured in such a way that - immediately after receiving a further free fall signal which signals the end of the free fall situation - the drive device again drives the mass vibrator to perform an operational drive vibration of the mass vibrator, wherein the reduction in the amplitude of the drive vibration is achieved more rapidly than a reduction corresponding to a simple decay process of the drive vibration of the mass vibrator.

[0013] Advantageous embodiments and developments of the invention are apparent from the dependent claims and from the description with reference to the figures.

[0014] According to a preferred embodiment of the invention, the rotational speed sensor is configured such that a drive device for causing a drive vibration of the mass vibrator is controlled by means of a drive control device having an amplifier device and the drive control device generates a drive control signal for causing the drive of the mass vibrator, and such that during a first part of the time interval of the detected free fall situation, the amplifier device is operated in an operating mode with the smallest possible amplification factor, wherein the amplifier device is in particular designed as an operational amplifier. By actively intervening in the excitation of the vibration of the mass vibrator in this way (in particular by changing (reducing) the setpoint value), the drive vibration can be reduced more quickly (or its amplitude can be reduced) compared to the duration of a natural decay or decay.

[0015] According to another preferred embodiment of the invention, the rotation speed sensor is configured such that the drive device for causing the drive vibration of the mass vibrator is controlled by means of a drive control device having a phase inversion device, so that the drive control device generates a drive control signal for causing the drive of the mass vibrator, and so that during the first part of the time interval of the detected free fall situation, the phase inversion device generates the drive control signal as a phase-inverted drive control signal. By means of such an inversion, the drive vibration can be reduced particularly quickly or the amplitude of the drive vibration can be reduced.

[0016] According to another preferred embodiment of the invention, the rotational speed sensor is configured such that the drive and / or the drive control signal is switched off in a second part of the time interval of the detected free fall situation, wherein the second part of the time interval of the detected free fall situation begins in particular after the end of the first part, in particular immediately after the first part or - separated in time from the first part - after a predetermined waiting time. This effectively prevents the risk of further increased vibrations or the occurrence of oscillation effects of the system due to active intervention in the drive vibrations by the smallest possible amplification factor or also - in particular - by reversal after a certain time.

[0017] According to another preferred specific embodiment of the invention, the rotational speed sensor is configured in such a way that the free fall situation is detected if the measured acceleration acting on the rotational speed sensor is detected as being less than an acceleration threshold value.

[0018] According to another preferred embodiment of the invention, the rotational speed sensor has an acceleration sensor or is connected to the acceleration sensor, wherein the rotational speed sensor is configured such that if the measured acceleration acting on the rotational speed sensor is detected as less than an acceleration threshold value, a free fall situation is detected and a free fall signal is generated. According to the invention, this can be realized according to a variety of variants; for example, it is conceivable that the free fall signal generated by the acceleration sensor (Accel) is provided to the rotational speed sensor in an inertial sensor structure (especially in the form of a so-called combined ASIC-including not only the acceleration sensor (Accel) but also the rotational speed sensor (Gyro)); here, it can be advantageously provided that the signal processing of Accel and Gyro runs via the same data path. Therefore, when sending the free fall signal, this does not necessarily have to be a conventional sensor-to-sensor communication. Alternatively or superimposed thereon, according to the invention, according to an embodiment variant, it is also provided that the corresponding signal (free fall signal) is triggered by a microcontroller or a motion processor-inside or outside the device, that is, inside or outside the inertial sensor structure.

[0019] According to the present invention, in a method for operating a rotational speed sensor, the rotational speed sensor has a micromechanical structure and has a mass vibrator, which can be driven to perform a drive vibration by means of a drive device, wherein the rotational speed sensor is configured to protect the micromechanical structure and is configured in such a way that a reduction in the amplitude of the drive vibration is achieved during a time interval of a detected free fall situation, wherein the free fall situation is indicated by a signal by means of a free fall signal supplied to the rotational speed sensor, wherein the rotational speed sensor is further configured in such a way that - immediately after receiving a further free fall signal which indicates the end of the free fall situation by a signal - the drive device again drives the mass vibrator to perform an operating drive vibration of the mass vibrator, wherein the reduction in the amplitude of the drive vibration is achieved more rapidly than a reduction corresponding to a simple decay process of the drive vibration of the mass vibrator. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The schematic diagram shows a control loop (feedback loop of a drive control loop or a drive control device) for an actuating or detecting electrode of a rotational speed sensor having an amplifier device and having a phase inversion device indicated and integrated into the control loop.

[0021] Figure 2 The schematic diagram shows the time profile of the drive amplitude during active interruption or reduction of the amplitude of the drive oscillation. DETAILED DESCRIPTION

[0022] In the various figures, identical components are always provided with the same reference symbols and are therefore usually also each named or mentioned only once.

[0023] exist Figure 1 Schematically—for rotational speed sensor 1 —a control circuit 3 for drive electrodes 2 or actuation and detection electrodes of a micromechanical structure 2 of rotational speed sensor 1 (a feedback loop of a drive control circuit 3 or of a drive control device 3 ).

[0024] For the sake of simplicity, the drive electrodes are not specifically labeled with reference numerals, but should be considered as part of the micromechanical structure 2. Figure 1 In the exemplary schematic diagram in FIG. 1 , the drive control loop or drive control device 3 has an amplifier device 31. According to the invention, the amplifier device 31 is in particular an operational amplifier. In addition, the drive control loop or drive control device 3 supplies a drive control signal 32 back to the micromechanical structure 2 for causing the mass vibrator to be driven (for the sake of simplicity, the mass vibrator is also not shown in FIG. 1 ). Figure 1 In addition, the drive control loop or drive control device 3 has—in a manner known per se—an input 34 for a reference signal and a control device 35 .

[0025] According to a first embodiment variant or implementation of the present invention, in order to reduce the drive vibration (amplitude) of the mass vibrator (excited by the drive control device 3) more quickly or more effectively, the amplifier device 31 is adjusted or operated so that the amplifier device 31 is operated with the smallest possible amplification factor at least during a certain time interval (the first part of the time interval of the detected free fall condition) (in the operating mode); according to the first embodiment variant or implementation of the present invention, in particular, there is no phase inversion device 33 integrated into the control loop.

[0026] According to a second embodiment variant or embodiment of the invention, such a phase reversal device 33 is provided as part of the control loop or the drive control device 3; Figure 1 33. According to the second embodiment of the present invention, in order to more quickly or more effectively reduce the drive vibration (amplitude) of the mass vibrator (excited by the drive control device 3), at least during a certain time interval (the first part of the time interval of the detected free fall condition), the phase reversal device 33 generates the drive control signal 32 as a phase-inverted drive control signal.

[0027] According to the invention, according to both embodiments, it is advantageously possible to achieve a reduction in the amplitude of the drive oscillation that is as rapid as possible—in any case significantly faster than is achievable by a simple damping process of the drive oscillation of the oscillator mass.

[0028] exist Figure 2 This is schematically illustrated in , wherein the time profile of the drive amplitude 101 is shown by way of example during a time interval 100 of a detected free fall situation with active interruption or reduction of the amplitude of the drive vibration: the drive amplitude 101 is shown constant in time before the start of the time interval 100 - corresponding to a predetermined target amplitude (as a setpoint value). During a first part 110 of the time interval 100 of the detected free fall situation, the drive amplitude 101 drops strongly (more strongly than according to a natural decay process). This is achieved, for example, by the amplifier device 31 being operated in an operating mode with the smallest possible amplification factor (so that a significantly lower amplitude setpoint value is generated, which can be reached in a very short time due to the feedback) or by the drive control signal 32 (for causing the drive of the mass vibrator) being applied with a phase difference of 180° via the phase reversal device 33. As Figure 2 As shown, the second part 120 of the time interval 100 of the detected free fall situation begins in particular after the end of the first part 110, in particular either directly after the first part 110 or at a time interval from the first part 110. In the second part 120 of the time interval 100 of the detected free fall situation, in particular the drive device and / or the drive control signal 32 are switched off, so that - in any case with the beginning of the second part 120 of the time interval 100 and starting from the significantly reduced amplitude of the drive oscillation - a natural decay process occurs.

[0029] According to a first embodiment, during a first part 110 of the time interval 100 of the detected free fall situation, the amplifier device 31 is operated with the smallest possible amplification factor, i.e. the amplitude nominal value is reduced to the smallest possible value by means of the amplification of the amplifier device 31. The expected time until this drive amplitude is reached is in the order of a few milliseconds (-0.10 msec). 0 )ms)—significantly faster than the natural decay (of the amplitude) of the drive vibrations due to the damping in the core (MEMS core) of the mechanical structure 2. For example, after 5 ms (during the first part 110 of the time interval 100), the drive is switched off (the second part 120 of the time interval 100) in order to allow the remaining drive amplitude to decay naturally. If Acc mag >Acc thres If again, the free fall situation no longer exists (ie the end of the free fall has been reached): the amplification of the amplifier device 31 is reset to the set value and the drive electrode is switched on again.

[0030] According to a second embodiment, a phase inversion device 33 is present in the feedback loop of the control loop: the phase inversion device 33 in the feedback loop inverts the phase of the drive oscillation or drive control signal 32 (by means of a phase difference of 180°), whereby the drive amplitude decreases significantly more rapidly during the first part 110 of the time interval 100 compared to a natural decay. This phase change can be realized or displayed, for example, by recording an inversion bit in a register map, whereby the phase inversion device 33 is configured in such a way that such a phase change is implemented in accordance with the inversion bit. In the order of a few milliseconds (~O(10 0 )ms) on the determined waiting time t wait Afterwards, ie after a first part 110 of the time interval 100 (depending in particular on the ASIC FE), the drive electrodes are switched off in order to ensure that they do not increase the drive amplitude (vibration amplitude) further (with a changed phase position). mag >Acc thres Once again, the free fall condition no longer exists (ie the end of the free fall is reached) and the phase reversal device 33 returns from the 180° phase shift to 0° and the drive electrode is switched on again.

Claims

1. A rotational speed sensor (1) having a micromechanical structure (2) and a mass vibrator, wherein: The mass vibrator can be driven to perform a driven vibration by means of a drive device, wherein the rotational speed sensor (1) is configured to protect the micromechanical structure (2) and is configured to achieve a reduction in the amplitude (101) of the driven vibration during a time interval (100) of a detected free fall situation, wherein the free fall situation is signaled by means of a free fall signal supplied to the rotational speed sensor (1), wherein the rotational speed sensor (1) is further configured such that - immediately after receiving a further free fall signal which signals the end of the free fall situation - the drive device drives the mass vibrator again to perform an operational driven vibration of the mass vibrator, It is characterized in that the amplitude (101) of the drive vibration is reduced more rapidly than a reduction corresponding to a simple damping process of the drive vibration of the vibrator mass.

2. The rotation speed sensor (1) according to claim 1, characterized in that The rotation speed sensor (1) is configured as follows: - controlling a drive device for causing a drive vibration of the mass vibrator by means of a drive control device (3) having an amplifier device (31), - causing the drive control device (3) to generate a drive control signal (32) for causing the mass vibrator to be driven, and - causing the amplifier device (31) to be operated in an operating mode with a minimum possible amplification factor during a first part (110) of a time interval (100) of a detected free-fall situation, The amplifier device (31) is designed in particular as an operational amplifier.

3. The rotational speed sensor (1) according to any one of the preceding claims, characterized in that The rotation speed sensor (1) is configured as follows: - enabling a drive device for causing a driving vibration of the mass vibrator to be controlled by means of a drive control device (3) having a phase inversion device (33), - causing the drive control device (3) to generate a drive control signal (32) for causing the mass vibrator to be driven, and -- so that during a first part (110) of a time interval (100) of a detected free fall condition, the phase inversion device (33) generates the drive control signal (32) as a phase-inverted drive control signal.

4. The rotational speed sensor (1) according to any one of the preceding claims, characterized in that The rotational speed sensor (1) is configured to shut down the drive device and / or the drive control signal (32) in a second part (120) of the time interval (100) of the detected free fall situation, wherein the second part (120) of the time interval (100) of the detected free fall situation starts in particular after the end of the first part (110), in particular directly after the first part (110) or - separated in time from the first part (110) - after a predetermined waiting time.

5. The rotational speed sensor (1) according to any one of the preceding claims, characterized in that The rotational speed sensor (1) is configured such that the free fall situation is detected if the measured acceleration acting on the rotational speed sensor (1) is detected as being less than an acceleration threshold value.

6. The rotational speed sensor (1) according to any one of the preceding claims, characterized in that The rotational speed sensor (1) has an acceleration sensor or is connected to an acceleration sensor, wherein the rotational speed sensor is configured such that the free fall situation is detected and the free fall signal is generated if the measured acceleration acting on the rotational speed sensor (1) is detected as being less than an acceleration threshold value.

7. A method for operating a rotational speed sensor (1) having a micromechanical structure (2) and a mass vibrator, wherein: The mass vibrator can be driven to perform a driven vibration by means of a drive device, wherein the rotational speed sensor (1) is configured to protect the micromechanical structure (2) and is configured to achieve a reduction in the amplitude (101) of the driven vibration during a time interval (100) of a detected free fall situation, wherein the free fall situation is signaled by means of a free fall signal supplied to the rotational speed sensor (1), wherein the rotational speed sensor (1) is further configured such that - immediately after receiving a further free fall signal which signals the end of the free fall situation - the drive device drives the mass vibrator again to perform an operational driven vibration of the mass vibrator, It is characterized in that the amplitude (101) of the drive vibration is reduced more rapidly than a reduction corresponding to a simple damping process of the drive vibration of the vibrator mass.

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