Abstract:
Various embodiments of the invention integrate multiple shock-robust single-axis MEMS gyroscopes into a single silicon substrate while avoiding the complexities typically associated with designing a multi-drive control system for shock immune gyroscopes. In certain embodiments of the invention, a shock immune tri-axial MEMS gyroscope is based on a driving scheme that employs rotary joints to distribute driving forces generated by two sets of driving masses to individual sensors, thereby, simplifying the control of the gyroscope.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is related to and claims the priority benefit of commonly-assigned U.S. Patent Application Ser. No. 61/994,57, filed on May 16, 2014, titled “Shock Robust Integrated Multi-Axis MEMS Gyroscope,” listing inventors Lorenzo Bertini and Alessandro Rocchi, which application is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     A. Technical Field 
     The present invention relates to micro-electro-mechanical-system (MEMS) gyroscopes. More particularly the invention relates to MEMS systems, devices, and methods to operate multi-axial MEMS gyroscopes and provide immunity against environmental mechanical disturbances. 
     B. Background of the Invention 
     In recent years, the market for MEMS gyroscopes has seen rapid increases in the demand for MEMS gyroscopes designed for applications such as consumer electronics and automotive. As a result, two distinctive trends have crystallized in the development of modern gyroscopes. 
     First, the trend to miniaturization of gyroscopes has led to designs that integrate multiple MEMS sensors into a single device that is capable of simultaneously sensing angular velocity around multiple spatial axes. An example of multi-axial integration of gyroscopic sensors for low-end devices, where small size is a key design parameter, is presented in U.S. patent application serial number 2011/0094301. Second, immunity to environmental disturbances such as vibrations, shock and other sudden impact of forces has become a key requirement in the high-end gyroscopic device market. An example of a shock-robust gyroscope that is designed to counteract environmental disturbances by electrical and mechanical means is presented in U.S. patent application serial number 2013/0269469. 
     At a glance, it appears that integrating multi-axial sensors into high-end gyroscopic devices would allow for more sophisticated and demanding applications in the consumer market as well as reduce cost for automotive applications. However, high-end shock-robust gyroscopes are inherently complex devices that incorporate redundant differential structures. A direct integration of a three single-axis high-end gyroscope on the same silicon substrate poses complex challenges that have not been mastered to date. In addition, the increase in complexity of designing a suitable control system has kept the above-mentioned two trends practically distinct thus far. 
     While some efforts are being undertaken to design stabilization and shock robustness features into MEMS gyroscopes that, for example, could prevent accidents and potentially save lives in safety-related applications, the automotive field continues to rely on independent single-axis high-end gyroscopes integrated at board level. Ideally, these gyroscopes would always remain operative even in scenarios in which disturbing forces from shock events are transmitted to the appropriate sensing circuit of the MEMS gyroscope so as to maintain directional stability by distinguishing between the different contributions of forces that cause displacement of proof masses, detecting unwanted spinning, etc., and taking appropriate corrective action in various shock scenarios. 
     What is needed are designs that successfully combine the advantages of the two above-mentioned trends to create reliable, shock-robust, multi-axis gyroscopic sensors. 
     SUMMARY OF THE INVENTION 
     The disclosed systems and methods provide for an electro-mechanical driving system that allows to drive three individual single-axis gyroscopes with a plurality of driving masses. 
     In particular, in various embodiments of the invention a mechanical component of a driving system is based on a set of rotary joints that distributes driving forces in a manner such as to adjust the direction of the driving motion in accordance with the needs of a plurality single-axis gyroscopes. 
     By integrating three single-axis shock-robust gyroscopes into a single silicon substrate, the core design of each gyroscope and, hence, its performance in terms of shock robustness is maintained, while avoiding the complexities typically associated with designing a multi-drive control system for shock immune gyroscopes. 
     Certain features and advantages of the present invention have been generally described here; however, additional features, advantages, and embodiments presented herein will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims hereof. Accordingly, it should be understood that the scope of the invention is not limited by the particular embodiments disclosed in this summary section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that this is not intended to limit the scope of the invention to these particular embodiments. 
         FIG. 1  is an illustration of an exemplary system of shock-robust gyroscopic sensors in a tri-axial gyroscope configuration that is driven by a single driving mechanism, according to various environment of the invention. 
         FIG. 2  is an illustration of another exemplary system of shock-robust gyroscopic sensors in a multi-axis gyroscope configuration driven by a single driving mechanism, according to various environment of the invention. 
         FIG. 3  is an illustration of an exemplary system of non-shock-robust gyroscopic sensors in a tri-axial gyroscope configuration driven by a single driving mechanism, according to various environment of the invention. 
         FIG. 4  is a flowchart of an illustrative process for shock cancellation in a multi-axis gyroscope configuration driven by a single driving mechanism, in accordance with various embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, described below, may be performed in a variety of ways and using a variety of means. Those skilled in the art will also recognize that additional modifications, applications, and embodiments are within the scope thereof, as are additional fields in which the invention may provide utility. Accordingly, the embodiments described below are illustrative of specific embodiments of the invention and are meant to avoid obscuring the invention. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearance of the phrase “in one embodiment,” “in an embodiment,” or the like in various places in the specification are not necessarily referring to the same embodiment. 
     Furthermore, connections between components or between method steps in the figures are not restricted to connections that are affected directly. Instead, connections illustrated in the figures between components or method steps may be modified or otherwise changed through the addition thereto of intermediary components or method steps, without departing from the teachings of the present invention. In this document the terms “joint” and “rotary joint” refer to any kind of hinge, pivoting means, or coupling mechanics recognized by persons skilled in the art. 
       FIG. 1  is an illustration of an exemplary system of shock-robust gyroscopic sensors in a tri-axial gyroscope and driven by a single driving mechanism, according to various embodiments of the invention. The system in  FIG. 1  combines three individual axial gyroscopes  180 - 184  within a single device to create tri-axial gyroscope  100 . Gyroscope  184  is a Z-gyroscope, while gyroscopes  180  and  182  are two identical in-plane gyroscopes. As shown in  FIG. 1 , in-plane gyroscopes  180 ,  182  are oriented placed in a mirror image arrangement to each other across Y-axis  194  and at 45 degree angles to the Y-axis  194  in the X-Y plane. 
     Gyroscopic sensors  180 - 184  take advantage of the Coriolis effect to determine when an angular rate is applied to tri-axial gyroscope  100 . It is understood that gyroscopic sensors  180 - 184  comprise internal proof masses (schematically represented at  186 ) that are displaced by Coriolis forces. Generally, Coriolis forces can be used to measure an angular rate according to the following principle: 
     Capacitive sense electrodes within each gyroscope measure the displacement of gyro masses in a sense direction orthogonal to the respective driving direction as a capacitive change, which is a function of a rotation of the respective gyroscope. For example, when a Coriolis force acts on the gyroscope  180  in response to an angular velocity applied to tri-axial gyroscope  100 , the sense electrodes associated with the proof masses  186  convert the displacement induced by Coriolis force in a capacitive change that is proportional to the applied angular velocity. Typically, an ASIC processes gyroscopic sensor signals in order to determine the angular velocity in relation to the sensor&#39;s environment and to adjust the frequency and amplitude required to maintain the harmonic oscillation of the actuator, here, driving masses  102 ,  104 . 
     In detail, when a mass (e.g., proof mass  186 ) in a tri-axial gyroscope is driven to move with a certain velocity along a first axis (e.g., X-axis  192 ) of an orthogonal coordinate system and is exposed to an angular rotation about a second axis (e.g., Z-axis  196 ), the Coriolis effect typically causes a proof mass  186  to be displaced in a third direction (Y-axis  194 ) by a Coriolis force that is directly proportional to the angular rate to be measured. Using MEMS technology, this displacement can be detected by appropriate electronics, e.g., by capacitive sensor elements (typically comb electrodes or plate electrodes) to which a voltage is applied to detect variations in position (i.e., a change in capacitance or electric voltage) as a measure of that angular rotation. 
     In example in  FIG. 1 , Z-gyroscope  184  is driven along Y-axis  194  and sensitive to deflections along X-axis  192 , for rotations about Z-axis  196 , i.e., out-of-plane. In-plane gyroscope  180  is driven at a positive 45 degree angle relative to Y-axis  194  and sensitive to deflections along Z-axis  196 , for rotations perpendicular to its driving direction in the X-Y plane. Similarly, in-plane gyroscope  182  is driven at a negative 45 degree angle relative to Y-axis  194  and is sensitive to deflections along Z-axis  196  for rotations perpendicular to its driving direction in the X-Y plane. 
     The driving scheme is facilitated by a set of rotary joints  110 ,  112 ,  120 ,  122 ,  124 ,  150 ,  152 ,  160 ,  162 , and  164 , which includes first and second subsets of rotary joints  120 ,  122 ,  124  and  160 ,  162 , and  164  respectively, that by their rotation about Z-axis  196  create push-pull forces that transfer the translational motion of driving masses  102 ,  104  that takes place in the Y-axis direction  194  to each individual gyroscope  180 - 184  in the XY-plane. In other words, the set of rotary joints  120 - 124  and  160 - 164  distributes the driving force to the proof masses  186  of the individual gyroscopes  180 - 184 . It is noted that without an integrated mechanical system that controls the interaction between driving masses  102 ,  104  and gyroscopes  180 - 184 , each gyroscope  180 - 184  would require a separate electrical control loop. 
     In one embodiment, mechanical excitation for gyroscopes  180 - 184  is advantageously provided by only a single electrical system comprising drive elements (not shown) that excite both driving masses  102 ,  104  into harmonic oscillation along a spatial axis, e.g., Y-axis  194 . Masses  102 ,  104  are typically electrostatically actuated by electrodes (not shown) so as to oscillate along Y-axis  194  and deliver mechanical forces to individual gyroscopes  180 - 184 . This substantially simplifies the design of the control system (not shown) that drives and controls driving masses  102 ,  104 . One skilled in the art will appreciate that masses  102 ,  104  may be implemented in any suitable orientation and geometry. 
     In example in  FIG. 1 , each of rotary joint  110 - 112 ,  120 - 124 ,  150 - 152 , and  160 - 164  is coupled to either mass  102 ,  104 , gyroscope  180 - 184 , or another one of joint  110 - 112 ,  120 - 124 ,  150 - 152 , and  160 - 164  and rotates around its respective central anchoring point  170 . One set of joints  110 - 112  and its symmetrical counterpart  150 - 152  constrain the motion of driving masses  102 ,  104  to be synchronous and antiphase. 
     In detail, when mass  102  moves in negative direction  106  along Y-axis  194 , mass  104  moves in positive direction  108  along Y-axis  194 . This antiphase motion is suitable to generate forces  174  that directly excite Z-gyroscope  184 . Joints  120 - 124  and  160 - 164  transform the movement of driving mass  102 ,  104  along Y-axis  194  into antiphase movements at +/−45 degrees relative to Y-axis  194  in plane X-Y, so as to excite in-plane gyroscopes  180  and  182 , respectively. For example, when joint  120  rotates clockwise, the rotary motion is transferred to joints  122  and  124  that then rotate counter-clockwise and clockwise, respectively. This generates forces  172  that actuate in-plane gyroscope  180 . Joints  160 - 164  correspondingly effect in-plane gyroscope  182 . 
     It is understood that the number of locations on joints  122  at which a force may be applied can be adjusted according to the particular implementation. While in some cases this may prevent the use of shock-robust gyroscopes, it still enables operation of the gyroscope in a single-drive tri-axial gyroscope configuration. It is further understood that while gyroscopes  180 ,  182 , due to their mirror-image design in-plane, may be identical, this is not intended as a limitation on the scope of the present invention. One of skill in the art will appreciate that other joint arrangements and orientations for gyroscopes  180 ,  182  are feasible without deviating from the scope of the invention. Finally, while detailed descriptions of joints and additional anchoring to frames, for example, for driving joints are omitted for brevity and clarity, it is understood that joints  110 - 112 ,  120 - 124 ,  150 - 152 , and  160 - 164  may be implemented by any method known in the art. 
       FIG. 2  is an illustration of another exemplary system of shock-robust gyroscopic sensors in a multi-axis gyroscope that is driven by a single driving mechanism, according to various environment of the invention. In a manner similar to  FIG. 1 , multi-axial gyroscope  200  in  FIG. 2  combines at least three individual axial gyroscopes  280 - 284  into a single device. Unlike in  FIG. 1 , in-plane gyroscopes  280  and  282  are oriented parallel to Y-axis  194  and X-axis  192 , respectively, rather than being placed in a mirror image arrangement about a certain spatial axis. Gyroscope  284  is an out-of-plane Z-gyroscope oriented parallel to Y-axis  194 . 
     In example in  FIG. 2 , in-plane gyroscope Y-gyroscope  280  and out-of-plane Z-gyroscope  284  are driven along X-axis  192 , while in-plane gyroscope X-gyroscope  282  is driven along Y-axis  194 . Y-gyroscope  280  is sensitive to deflections along Z-axis  196  for rotations about Y-axis  194 ; X-gyroscope  282  is sensitive to deflections along Z-axis  196  for rotations about X-axis  192 ; and Z-gyroscope  284  is sensitive to deflections along Y-axis  194  for rotations about Z-axis  196 . 
     In one embodiment, the set of rotary joints  222  rotates about Z-axis  196  to create push-pull forces that transfer the motion of two sets of driving masses  202 - 208  and  212 - 218  in the Y-axis direction  194  to individual gyroscopes  280 - 284  located in the XY-plane so as to distribute the actuating driving force to each individual gyroscope  280 - 284 . In a manner similar to  FIG. 1 , the system of masses  202 - 208  and  212 - 218  in  FIG. 2  may be electrostatically actuated by electrodes to oscillate along Y-axis  194  and deliver the mechanical forces required to oscillate internal masses of gyroscopes  280 - 284 . 
     In one embodiment, rotary joint  222  is coupled to at least to one of masses  202 - 218  or another rotary joint  222  and rotates about its respective center anchor  170  to generate pairs of antiphase motions along both X-axis  192  and Y-axis  194 . The arrangement of joints  222  constrains the motion of the sets of driving masses  202 - 208 ,  212 - 218  to be synchronous and antiphase (e.g., when set  202 - 208  moves in negative direction along Y-axis  194 , set  212 - 218  consistently moves in positive direction along Y-axis  194 ). The synchronous motion generates driving forces that enable the operation of shock-robust gyroscopes  280 - 284 . For example, force  172  may drive four internal masses of shock-robust gyroscope  280 , as shown in  FIG. 2 . 
     In one embodiment, the location denoted with numeral  286  in  FIG. 2  may be used to hold a redundant X-gyroscope or Z-gyroscope that is not shown in  FIG. 2 . That location may also be used to hold dummy masses (also not shown), e.g., for the purpose of improving sensor symmetry about X-axis  192 . 
       FIG. 3  is an illustration of an exemplary system of non-shock-robust gyroscopic sensors arranged as a tri-axial gyroscope and driven by a single driving mechanism, according to various environment of the invention. System  300  comprises in-plane gyroscopes  380  and  382  and out-of-plane Z-gyroscope  384 . Similar to  FIG. 2 , gyroscopes  380  and  384  are oriented parallel to X-axis  192 , while gyroscope  382  is oriented parallel to Y-axis  194 . X-gyroscope  380  is sensitive to deflections along Z-axis  196  for rotations about X-axis  192 ; Y-gyroscope  382  is sensitive to deflections along Z-axis  196  for rotations about Y-axis  194 ; and Z-gyroscope  384  is sensitive to deflections along Y-axis  194  for rotations about Z-axis  196 . 
     In one embodiment, a set of rotary joints  322  rotates about Z-axis  196  to create push-pull forces that transfer the motion of two sets of driving masses  302 - 306  and  312 - 316  in the Y-axis direction  194  to individual gyroscopes  380 - 384  located in the XY-plane so as to distributes the actuating driving force to each individual gyroscope  380 - 384 . System of masses  302 - 316  may be electrostatically actuated by electrodes to oscillate along Y-axis  194  and deliver the mechanical forces to gyroscopes  380 - 384 . 
     Again, each of rotary joint  322  is coupled to at least to one of masses  302 - 316  or another rotary joint  332  and rotates about its respective center anchor  170  to generate pairs of antiphase motions along both X-axis  192  and Y-axis  194 . The arrangement of joints  322  constrains the motion of the sets of driving masses  302 - 306  and  312 - 316  to be synchronous and antiphase (e.g., when set  302 - 306  moves in negative direction along Y-axis  194 , set  312 - 316  moves in positive direction along Y-axis  194 ). 
     In this example, only two forces  372  are required to actuate gyroscope  380 , so that only two masses internal to gyroscope  380  are connected to joints  322 . As a result, without more, this configuration would be insufficient to drive the number of masses required to operate the shock-robust gyroscopes shown in  FIG. 1  and  FIG. 2 . 
       FIG. 4  is a flowchart of an illustrative process for shock cancellation in a multi-axis gyroscope configuration driven by a single driving mechanism, in accordance with various embodiments of the invention. The process for shock cancellation starts at step  402  by providing multiple shock-robust single-axis gyroscopes. The gyroscopes may be in-plane gyroscopes, out-of-plane gyroscopes or any combination thereof. 
     At step  404 , driving forces are distributed to the shock-robust single-axis gyroscopes via a joint system, for example, a rotary joint system. 
     Finally, at step  406 , the shock-robust single-axis gyroscopes are driven electro-mechanically by at least two masses, for example, by synchronous, antiphase motions as controlled by an external control system. 
     It will be appreciated by those skilled in the art that fewer or additional steps may be incorporated with the steps illustrated herein without departing from the scope of the invention. No particular order is implied by the arrangement of blocks within the flowchart or the description herein. 
     It will be further appreciated that the preceding examples and embodiments are exemplary and are for the purposes of clarity and understanding and not limiting to the scope of the present invention. It is intended that all permutations, enhancements, equivalents, combinations, and improvements thereto that are apparent to those skilled in the art, upon a reading of the specification and a study of the drawings, are included within the scope of the present invention. It is therefore intended that the claims include all such modifications, permutations, and equivalents as fall within the true spirit and scope of the present invention.