Patent Application
20200284583
The present invention relates to a MEMS device and a corresponding operating method.
Although arbitrary optical devices and systems are also applicable, the present invention and the underlying problem thereof are explained on the basis of micromechanical rotation rate sensor devices.
For some time, rotation rate sensors (gyroscopes) including oscillatory micromechanical structures have been used in the automotive field and in consumer electronics for measuring elements. In addition, such oscillatory micromechanical structures are used in the present configurations of micromirrors, which are used in microprojectors and microscanners, for example, for LIDAR.
A rotation rate sensor including two sensitive axes is discussed, for example, in WO 2009/059639 A1. A micromirror including a resonant operation is discussed, for example, in WO 2013/091939 A1.
These and similar applications use the oscillatory micromechanical structures, which have oscillation modes (eigenmodes or useful modes), which are utilized for the intended function. The rotation rate sensors use, for example, drive modes to set detection structures into resonant oscillations. These structures in turn detect rotation rates via the measurement of the occurring Coriolis accelerations with the aid of detection modes. Micromirrors use specific oscillation modes to deflect the micromirror as intended.
The drive of the oscillatory micromechanical structures is carried out electrostatically or piezoelectrically, however, other drives are also known, for example, electromagnetic or dynamic drives, etc.
Oscillatory micromechanical structures, as are used in the above-mentioned systems or similar systems, in principle have, in addition to the desired useful modes (for example, for drive and detection), (countably) infinite oscillation modes, however, some of which may result in undesirable, interfering effects.
Thus, rotation rate sensors again and again display undesirable properties in their offset behavior, for example, so-called offset jumps. These effects occur if, in addition to the useful modes, one or multiple further parasitic spurious modes are also excited, which may result in interferences in the detection signals due to their oscillation forms. In the case of micromirrors, it may occur, for example, that larger deflections of the micromirror are not possible under certain circumstances, since the drive energy goes into other parasitic spurious modes and excites spurious oscillations. These spurious oscillations may under certain circumstances even result in undesirable mechanical impacts or in the worst case in structural fractures.
Attempts have heretofore been made to avoid the described disadvantages in that parasitic spurious modes are prevented from being placed precisely at integer multiples of the drive frequencies in the configuration of the oscillatory micromechanical structures. The excitation of the parasitic spurious modes by harmonic waves (integer multiples) of the drive frequencies is thus avoided. In practice, however, it has to be stated that due to manufacturing tolerances, it is not possible to guarantee that the multiples of the drive frequencies remain free of parasitic spurious modes. The statistical distributions of the frequencies of the parasitic spurious modes over the manufacturing tolerances is often so broad that over the plurality of the exemplars, the resonant frequencies of parasitic spurious modes are nonetheless encountered in some exemplars and under specific circumstances in these exemplars, the parasitic spurious oscillations are excited and cause corresponding problems.
Internal resonances may also exist in the mode spectrum in every configuration. These include, for example, three-mode (three-wave) mixtures and four-mode (four-wave) mixtures. These internal resonances may be excited by nonlinearities, in particular if the oscillation frequencies of the modes meet certain mathematical relationships, which are called internal resonance conditions. For the example of a three-mode mixture, the internal resonance condition is given by f1+f2≅f3, f1, f2, and f3 denoting the resonant frequencies of the oscillation modes. The more poorly the mathematical condition is met, the more difficult it is for the excitation of parasitic modes by nonlinearities to take place. Accordingly, configuration measures may be made, which in turn may not prevent the occurrence of the parasitic spurious modes due to the manufacturing tolerances, however.
An underlying aspect of the present invention is that undesirable parasitic oscillations are counteracted with the aid of an adjusting device, which applies an electromagnetic interaction to one or multiple affected system components.
An electromagnetic interaction is understood here as the generic term for static and dynamic, electric, magnetic, or electromagnetic interactions.
The present invention creates a MEMS device as described herein and a corresponding operating method as described herein.
Refinements are the subject matter of the particular further descriptions herein.
An underlying aspect of the present invention is to provide an adjusting device in the area of the system component susceptible to spurious modes, which is configured in such a way that by applying an electromagnetic interaction to the system component, it counteracts a parasitic spurious mode to which the system component is susceptible.
According to one refinement, the adjusting device includes a DC voltage generating unit for generating a DC voltage and one or multiple electrodes, which are configured in such a way that an electrostatic field may be applied to the system component via the electrodes. Such an adjusting device is easily integratable.
According to a further refinement, the DC voltage generating unit is controllable, regulatable, or settable. This may increase the accuracy in the case of nonlinearities.
According to a further refinement, the adjusting device includes an AC voltage generating unit for generating an AC voltage and one or multiple electrodes, which are configured in such a way that an electrodynamic field may be applied to the system component via the electrodes.
According to a further refinement, the AC voltage generating unit is controllable, regulatable, or settable. This may increase the accuracy in the case of nonlinearities.
According to a further refinement, the electrodes are situated perpendicularly to an oscillation direction of the system component. The effective interaction area may thus be made large.
According to a further refinement, the electrodes are situated in parallel to an oscillation direction of the system component. The distance may thus be selected to be small.
According to a further refinement, the system component includes one or multiple counter electrodes which interact with the electrodes.
According to a further refinement, the counter electrodes are molded at the system component. Additional electrode area may thus be formed on the system component.
According to a further refinement, the counter electrodes are applied as a coating to the system component.
According to a further refinement, the system component is a spring unit or a bar unit.
According to a further refinement, the DC voltage generating unit and/or the AC voltage generating unit are controllable proportionally to an oscillation deflection or oscillation speed of the system component. Effective feedback may thus be established.
Further features and advantages of the present invention are explained hereafter on the basis of specific embodiments with reference to the figures.
In the figures, identical reference numerals identify identical or functionally-identical elements.
In
An adjusting device 50 is provided in the area of system component 1, which is configured in such a way that by applying an electromagnetic interaction W to system component 1, it counteracts a parasitic spurious mode to which system component 1 is susceptible.
Adjusting device 50 may be, as already mentioned above, electrostatic, electrodynamic, magnetostatic, magnetodynamic, electromagnetostatic, or electromagnetodynamic, or also piezoelectric, inter alia. In the specific embodiments described hereafter, only an electrostatic and an electrodynamic interaction are described as the electromagnetic interaction to simplify the description.
Adjusting device 50 may either be preprogrammed or be controllable or regulatable.
In
A first electrode 31 and a second electrode 32 are provided in their plate plane perpendicular to oscillation direction SR on opposing sides adjacent to system component 1a.
Furthermore, a DC voltage generating unit 30 is provided for generating a DC voltage, which is connected to electrodes 31, 32 in such a way that an electrostatic field may be applied to system component 1a via electrodes 31, 32. DC voltage generating unit 30 may be settable or controllable or regulatable, as schematically shown by the arrow. However, this is not necessarily required, but rather is to be considered optional.
DC voltage generating unit 30 and the two electrodes 31, 32 form adjusting device 51 in this first specific embodiment.
As shown in
An adaptation of the resonant frequency of system component 1a is carried out during operation by adjusting device 51, whereby the influence of the parasitic spurious modes is eliminated or strongly reduced. In particular, the rigidity of system component 1a becomes less due to the electrostatic interaction and the resulting resonant frequency becomes smaller. It may be set in such a way that the resonant frequency is no longer at a multiple of the drive frequency or does not meet the internal resonance condition, due to which excitation to spurious oscillations cannot take place.
In the second specific embodiment according to
As in the first specific embodiment, AC voltage generating unit 40 changes the rigidity of system component 1a in the form of the spring, in order to shift the resonant frequency to eliminate the spurious mode.
The AC voltage generating unit 40 may optionally be settable or controllable or regulatable, but may also be set to a constant value established empirically or by simulation.
AC voltage generating unit 40 and the two electrodes 31, 32 form adjusting device 52 in this example.
Furthermore, it is possible both in the first and in the second specific embodiment and also in the specific embodiments described hereafter to configure DC voltage generating unit 30 or AC voltage generating unit 40 to be regulatable in such a way that the applied DC voltage or AC voltage, respectively, is proportional to the deflection or proportional to the speed of the spurious parasitic oscillations of system component 1a. Further electrodes (not shown) for detecting the deflection or speed may be provided for this purpose.
In the third specific embodiment, system component 1b is a bar, which is connected via springs 101, 102 to remaining oscillatory micromechanical system 100 according to
In the fourth specific embodiment, in contrast to the third specific embodiment, an analog AC voltage generating unit 40 is provided as part of adjusting device 54 as in the second specific embodiment. Otherwise, the fourth specific embodiment corresponds to the third specific embodiment.
According to
In the fifth specific embodiment, adjusting device 55 is formed by DC voltage generating unit 30 and electrode 31″.
In this fifth specific embodiment, it is advantageous that in the case of the arrangement in parallel to oscillation direction SR of system component 1a (in the form of the spring), the distance to system component 1a may be small in relation to the above specific embodiments, which results in a strong electrostatic attractive force.
In the fifth specific embodiment, the distance may thus be selected to be smaller. If the attractive force is nonetheless not sufficient in the fifth specific embodiment, it may be increased by a counter electrode which is also moved, as described hereafter.
In
In the sixth specific embodiment, adjusting device 56 is formed by the DC voltage generating unit and electrodes 31′″, 32′″.
Otherwise, the structure of the sixth specific embodiment is identical to that of the fifth specific embodiment.
Although the present invention was described on the basis of exemplary embodiments, it is not restricted thereto. In particular, the mentioned materials and topologies are only by way of example and are not restricted to the explained examples.
As already mentioned above, in addition to electrostatic and electrodynamic interaction, other electromagnetic interactions may also be used, for example, piezoelectric layers or magnetic layers or current-conducting conductors being applied to corresponding system components of the oscillatory micromechanical structure.
The present invention is also not restricted to the system components shown, but rather is applicable to any arbitrary one-piece or multipart system components.
The ascertainment of the spurious resonances to be eliminated may be carried out either empirically in a calibration mode or by a corresponding simulation.
The present invention is also applicable not only to rotation rate sensors or micromirrors, but rather to any arbitrary oscillatory micromechanical systems.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 217 009.3 | Sep 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/075431 | 9/20/2018 | WO | 00 |
