A Hemispherical Resonator Gyroscope (HRG) is a type of gyroscope that utilizes a thin hemispherical shell resonator that is often anchored to a base by a relatively thicker stem. The hemispherical shell is typically driven to a flexural resonance by electrostatic forces generated by conductive electrodes deposited on a fused-quartz shell. The HRG's gyroscopic effect is produced by the inertial property of flexural standing waves produced in the shell. Notably, HRGs are extremely reliable because of their lack of moving parts. However, HRGs are expensive to manufacture due to the high costs of the precision ground and polished hollow quartz hemispherical shells utilized. Furthermore, these manufacturing techniques fundamentally limit the minimum size of HRGs, deeming them unsuitable for certain platforms having size and weight limitations.
Glass-blown Micro-Electro-Mechanical Systems (MEMS) HRGs are one type of HRG that have been produced in laboratories, exhibiting high quality-factors (e.g., Q-factors >1 million) and long ring-down times (e.g., >250 secs). However, in order to function as gyroscopes, vibratory motion must be induced in these HRGs. One approach is to deposit metal conductors on the HRG, and utilize the metal conductors to induce the vibratory motion through electrostatic actuation. However, the presence of the metal conductors significantly degrades the ultra-low-loss acoustic resonance of the HRG. Another approach is to utilize a piezoelectric structure to induce the vibratory motion in the HRG, but this approach generates a significant amount of un-wanted vibration because the vibratory motion induced by the piezoelectric structure must be coupled to the HRG through its stem.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, the need exists in the art for a technique that can be utilized to overcome the above-described problems associated with, for example, the utilization of metal conductors and/or piezoelectric structures to induce vibratory motion in HRGs.
The embodiments of the present disclosure provide methods and systems for optical excitation of acoustic resonance in hemispherical resonator gyroscopes and will be understood by reading and studying the following specification.
In one embodiment, a resonator gyroscope device comprises: a sealed vacuum cavity; a resonator positioned within the sealed vacuum cavity, wherein the resonator comprises a resonating shell coupled to a stem; at least one light source, that is utilized to generate an optical excitation signal directed onto the resonating shell of the resonator; a controller coupled to the at least one light source; at least one optical signal interrogation device; and measurement processor coupled to the at least one optical signal interrogation device; wherein the controller controls the at least one light source to selectively heat a portion of the resonating shell in a manner that excites the resonating shell into a state of resonance; wherein the at least one optical signal interrogation device measures a movement of a standing wave in the resonating shell and the measurement processor outputs rotational data based on the movement measured by the at least one optical signal interrogation device.
Embodiments of the present disclosure can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which:
In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize features relevant to the present disclosure. Reference characters denote like elements throughout the figures and text.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of specific illustrative embodiments in which the embodiments may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense.
HRG 100 comprises a resonator 102 that includes a micro-shell referred to herein as a resonating shell 107 and a stem 104 that anchors the resonator 102 to a substrate 106. Throughout this disclosure, the resonator 102 may alternately be referred to as a “hemispherical” resonator 102. Similarly, the resonating shell 107 may alternately be referred to as a “hemispherical” resonator 102. It should be noted that the “hemispherical” prefix used herein is intended as generally descriptive adjective and not intended to implicate that the shape of the element is perfectly hemispherical or a perfect half-sphere. For example, resonator elements having what may be referred to as “bird-bath”, “bubble”, “elliptical” or “wine-glass” shapes may be considered hemispherical elements. It should be understood that a “hemispherical” element may comprise additional features, such as a stem, for securing or mounting the element in place. In other embodiments, the resonator 102 and/or resonating shell 107 may comprise a hemitoroidal shape (such as illustrated in U.S. Pat. No. 8,631,702, which is incorporated herein by reference) a cylindrical shell, or otherwise having cylindrical symmetry. It should be understood that a resonator gyroscope comprising a resonating shell with any of the alternative shapes just described would still generally be referred to by those of ordinary skill in the relevant art as a hemispherical resonator gyroscope (HRG). It should also be understood that the embodiments disclosed herein are not limited to microscale resonator gyroscopes, but may be applied to macro-scale resonator gyroscopes as well.
In the embodiment shown in
In one embodiment, the resonator 102 comprises a glass-blown resonator made of fused silica formed into a 3-dimensional shell resonator utilizing a MEMS fabrication process. In some embodiments, the stem 104 is anchored to the substrate 106 via a glass frit or bonded to the substrate 106 by other techniques. The resonator 102 is located within vacuum cavity 103 that is at least partially evacuated and sealed. In some embodiments, during fabrication the vacuum cavity 103 may be completely evacuated and the backfilled with a gas to a desired pressure in order to provide a desired level of dampening on the resonator 102.
The hemispherical resonator gyroscope 100 further comprises at least one light source 108 that is utilized to generate optical excitation signals (e.g., light beams) that are directed at the resonating shell 107 of the resonator 102. In some embodiments, light beams generated by the light source 108 are directed into the vacuum cavity 103 by a waveguide 109 coupled to an output of the light source 108. In alternate embodiments, waveguide 109 may be implemented, for example, by rigid waveguide elements, optical fibers, an on-chip integrated optical waveguide, a multi-chip waveguide (for example, where a resonator shell 107 and the optical components are on separate, but interacting and optionally bonded die), or a combination thereof. In some embodiments, light source(s) 108 may be implemented on-chip with the vacuum cavity 103 and resonator 102 elements. In other embodiments the light source(s) 108 may be implemented off-chip and the light from light source(s) 108 brought to the vacuum cavity by one or more waveguides 109.
It should be noted that although
In the embodiment shown in
The measurement processor 112 may then convert the data from the optical signal interrogation device 110 into rotational data, such as an angle of rotation and/or a rotation rate with respect to rotation about the axis 101 of the resonator 102. In some embodiments, data received from the optical signal interrogation device 110 may be provided as feedback by the measurement processor 112 to the controller 105 for adjusting operation of the light source(s) 108 or for other purposes. The controller 105 may be implemented, for example, using a processor coupled to a memory, an application specific integrating circuit (ASIC), or similar processing device configured to execute application-specific digital/analog instructions and may comprises a suitable sine wave generator or other signal generator which may provide an output to the light source(s) 108 for modulating the output from the light source(s) 108. In some embodiments, the functions associated with the measurement processor 112 and controller 105 may both be implemented by a single processing device.
In operation, the light beams generated from the light source(s) 108 are directed onto the resonator 102 in order to selectively heat portions of the resonating shell 107 in a controlled manner so as to excite the resonating shell 107 into a state of resonance (for example, to excite the resonating shell 107 into a fundamental resonance consisting of an acoustic standing wave having a primary and secondary wave around the perimeter of the shell, also known as the (N=2) mode), as illustrated in
In any event, the resonating shell 107 is illuminated by the excitation signal 310 (at one or more locations and generated by one or more light sources 108) so that the optical radiation can be strongly absorbed by the resonator 102 and thereby induce a significant amount of vibrational motion in the resonating shell 107. In one embodiment, with the excitation signal 310 amplitude modulated at the mechanical resonance frequency of the resonating shell 107, standing waves form in the resonating shell 107 resulting in nodes 312 and anti-nodes 314 in the N=2 mode. Reference 107a represents an undistorted resonating shell 107 not excited to resonate, whereas reference 107b represents the distortion of resonating shell 107 when excited to resonance. Nodes 312 occur at points on the perimeter of the resonating shell 107 where no displacement occurs during each vibrational cycle of the standing wave. In contrast, the anti-nodes 314 are points on the perimeter of the resonating shell 107 that undergo a maximum displacement during each vibrational cycle of the standing wave.
In some embodiments, the controller 105 outputs a control signal (for example, an approximately 10 kHz sine wave signal) which causes the light source(s) 108 to output an amplitude modulated excitation signal 310 (for example, a 4.8 μm wavelength optical signal) modulated at approximately 10 kHz (1). One side of the resonating shell 107 is illuminated by the excitation signal 310 and absorbs the excitation signal. The resonating shell 107 becomes differentially stressed to excite the N=2 mode (e.g., nodes 312 and anti-nodes 314). As previously mentioned, movement of the standing wave around the resonating shell 107 will occur in response to a rate input (i.e., a rotation of the device about axis 101). Accordingly, in some embodiments, the actuation of resonance in the resonating shell 107 by the excitation signal 310 may be adjusted by the controller 105 (for example, using feedback from the optical signal interrogation device 110 and/or measurement processor 112) to account for that rotation.
As described above with respect to
In some embodiments, the optical signal interrogation device 110 may comprise, for example, a laser vibrometer (such as a laser doppler vibrometer, for example) or an interferometer, or other motion sensing technology, utilized to detect the motion of the nodes 312 and/or anti-nodes 314 in order to measure the rotation of the standing wave in the resonator 102. In some embodiments, a portion of the excitation light beam directed at the resonating shell 107 is coupled to the optical signal interrogation device 110, which detects the motion of the nodes 312 and/or the anti-nodes 314. The frequency data associated with the detected motion is then coupled from the optical signal interrogation device 110 to the measurement processor 112 accumulation and analysis. In some embodiments, the optical excitation signals 310 enter the vacuum cavity 103 via a window in the vacuum cavity (which may comprise, for example, a calcium fluoride or borosilicate window). Similarly, the optical signal interrogation device 110 may detect the motion of the nodes 312 and/or the anti-nodes 314 via a window in the vacuum cavity (which may comprise, for example, a calcium fluoride or borosilicate window). Alternatively, an on-chip integrated optical waveguide, a bonded chip waveguide system, or a multi-chip waveguide may be incorporated to facilitate detect the motion of the nodes 312 and/or the anti-nodes 314 by the optical signal interrogation device 110.
The method 400 begins at 410 with heating a resonating shell of a hemispherical responator by applying a light beam directed onto the resonating shell, wherein the light beam has an optical wavelength absorbed by the resonating shell. The method proceeds to 420 with producing a fundamental resonance in the resonating shell by controlling (e.g. cycling or modulating) the light beam, wherein the fundamental resonance generates a standing wave in the resonating shell having two pairs of nodes and anti-nodes. The method proceeds to 430 with measuring a motion of the nodes and/or anti-nodes to measure a rotation of the standing wave and to 440 with generating an output signal as a function of the rotation of the standing wave.
Although
Example 1 includes a resonator gyroscope device, the gyroscope device comprising: a sealed vacuum cavity; a resonator positioned within the sealed vacuum cavity, wherein the resonator comprises a resonating shell coupled to a stem; at least one light source that generates an optical excitation signal directed onto the resonating shell of the resonator; a controller coupled to the at least one light source; at least one optical signal interrogation device; and a measurement processor coupled to the at least one optical signal interrogation device; wherein the controller controls the at least one light source to selectively heat a portion of the resonating shell in a manner that excites the resonating shell into a state of resonance; wherein the at least one optical signal interrogation device measures a movement of a standing wave in the resonating shell and the measurement processor outputs rotational data based on the movement measured by the at least one optical signal interrogation device.
Example 2 includes the gyroscope device of example 1, wherein the controller causes the at least one light source to amplitude modulate the optical excitation signal at a resonance frequency of the resonating shell.
Example 3 includes the gyroscope device of any of examples 1-2, wherein the optical excitation signal directed onto the resonating shell is controlled by the controller to form a standing wave in the resonating shell having nodes and anti-nodes; and wherein the optical signal interrogation device measures the movement of the standing wave by measuring movement of one or both of the nodes and anti-nodes.
Example 4 includes the gyroscope device of any of examples 1-3, wherein the controller controls the at least one light source to: energize or de-energize the optical excitation signal; pulse or cycle the optical excitation signal; amplitude modulate the optical excitation signal; adjust a wavelength of the optical excitation signal.
Example 5 includes the gyroscope device of any of examples 1-4, wherein data received from the optical signal interrogation device is utilized to provide feedback by the measurement processor to the controller for adjusting operation of the at least one light source.
Example 6 includes the gyroscope device of any of examples 1-5, wherein the optical signal interrogation device comprises, a vibrometer or an interferometer.
Example 7 includes the gyroscope device of any of examples 1-6, wherein the optical excitation signal is directed into the vacuum cavity by a waveguide coupled to an output of the at least one light source.
Example 8 includes the gyroscope device of any of examples 1-7, wherein the optical excitation signal is split and directed into the vacuum cavity to illuminate the resonating shell at different locations.
Example 9 includes the gyroscope device of any of examples 1-8, wherein the at least one light source comprises a first light source emitting a first optical excitation signal and a second light source emitting a second optical excitation signal; wherein the first optical excitation signal and the second optical excitation signal illuminate the resonating shell at different locations.
Example 10 includes the gyroscope device of any of examples 1-9, wherein the at least one light source is located within the vacuum cavity.
Example 11 includes the gyroscope device of any of examples 1-10, wherein the resonator comprises a Micro-Electro-Mechanical Systems (MEMS) resonating shell fabricated from a material comprising one of: Quartz, fused silica, fluoride, calcium fluoride, borosilicate, a lithium-aluminosilicate glass-ceramic, or other forms of glass.
Example 12 includes the gyroscope device of any of examples 1-11, wherein the controller adjust application of the optical excitation signal to account for rotation detected by the optical signal interrogation device.
Example 13 includes a method for optical excitation of acoustic resonance in a resonator gyroscope, the method comprising: heating a resonating shell of a resonator by applying a light beam directed onto the resonating shell, wherein the light beam has an optical wavelength absorbed by the resonating shell, and wherein the resonator is located within a vacuum cavity; producing a fundamental resonance in the resonating shell by controlling the light beam, wherein the fundamental resonance generates a standing wave in the resonating shell having a node and anti-node; measuring a motion of one or both of the node or anti-node to measure a rotation of the standing wave; and generating an output signal as a function of the rotation of the standing wave.
Example 14 includes the method of example 13, further comprising: utilizing the light beam directed onto the resonating shell, forming a standing wave in the resonating shell having nodes and anti-nodes; and measuring the movement of the standing wave by measuring movement of one or both of the nodes and anti-nodes.
Example 15 includes the method of any of examples 13-14, further comprising: modulating the light beam at a resonance frequency of the resonating shell.
Example 16 includes the method of any of examples 13-15, the method further comprising: directing the light beam into the vacuum cavity by utilizing a waveguide coupled to an output of a light source generating the light beam.
Example 17 includes the method of any of examples 13-16, the method further comprising: generating the light beam from at least one light source located within the vacuum cavity.
Example 18 includes the method of any of examples 13-17, further comprising: splitting the light beam; and directing the light beam into the vacuum cavity to illuminate the resonating shell at different locations.
Example 19 includes the method of any of examples 13-18, wherein the resonator comprises a Micro-Electro-Mechanical Systems (MEMS) resonating shell fabricated from a material comprising one of: Quartz, fused silica, fluoride, calcium fluoride, borosilicate, a lithium-aluminosilicate glass-ceramic, or other forms of glass.
Example 20 includes the method of any of examples 13-19, wherein measuring a motion of one or both of the node or anti-node to measure a rotation of the standing wave comprises measuring the motion by utilizing a vibrometer or an interferometer.
It should be understood that elements of the above described embodiments and illustrative figures may be used in various combinations with each other to produce still further embodiments which are explicitly intended as within the scope of the present disclosure.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the presented embodiments. Therefore, it is manifestly intended that embodiments be limited only by the claims and the equivalents thereof.
This application claims priority to, and the benefit of, U.S. Provisional Patent Application No. 62/774,556 titled “SYSTEM AND METHODS FOR OPTICAL EXCITATION OF ACOUSTIC RESONANCE IN HEMISPHERICAL RESONATOR GYROSCOPES” filed on Dec. 3, 2018, which is incorporated herein by reference.
Number | Date | Country | |
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62774556 | Dec 2018 | US |