Abstract:
Various embodiments of the invention allow for increased shock robustness in gyroscopes. In certain embodiments, immunity against undesired forces that corrupt signal output is provided by a chessboard-pattern architecture of proof masses that provides a second layer of differential signals not present in existing designs. Masses are aligned parallel to each other in a two-by-two configuration with two orthogonal symmetry axes. The masses are driven to oscillate in such a way that each mass moves anti-parallel to an adjacent proof mass. In some embodiments of the invention, a mechanical joint system interconnects proof masses to suppress displacements due to mechanical disturbances, while permitting displacements due to Coriolis forces to prevented erroneous sensor signals.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Application Ser. No. 61/993,626 titled “Systems and Methods for MEMS Gyroscope Shock Robustness,” filed May 15, 2014. by Alessandro Rocchi, Lorenzo Bertini, and Eleonora Marchetti, which application is hereby incorporated herein by reference in its entirety and from which application priority is hereby claimed. 
     
    
     BACKGROUND 
       [0002]    A. Technical Field 
         [0003]    The present invention relates to rate sensors. More particularly, the invention relates to systems, devices, and methods of providing shock robustness for MEMS rate of rotation sensors, such as gyroscopes. 
         [0004]    B. Background of the Invention 
         [0005]    MEMS gyroscopes are sensors that when continuously excited by driving electronics to perform a primary oscillation can sense a rotation rate about one or more axes by detecting deflections of mechanical structures that result from forces caused by the Coriolis effect. 
         [0006]    A common problem of MEMS gyroscopes is that it may be exposed to different types of external mechanical disturbances, such as shock, vibrations, and other undesirable environmental mechanical noise that can negatively impact the sensor&#39;s excitation and rate measurement. In general, a shock is a combination of forces and momentum with arbitrary orientation within a three-dimensional system of coordinates. In other words, mechanical disturbances may comprise six components—three translational and three rotational components. 
         [0007]    External mechanical disturbances have numerous side effects, including the creation of spurious output signals that falsify the sensor&#39;s reading, e.g., when a shock event induces a deflection similar to a to-be-detected deflection created by a Coriolis force. The two superimposing signals may corrupt the rate measurement. Second, when shock events are great enough to cause the proof masses within the gyroscope to contact stopper structures that are attached to the substrate and designed to limit the displaceability of the masses, they lose some of their kinetic energy, and the sensor&#39;s primary oscillation will have to be restarted during which time the entire device remains inoperable. 
         [0008]    Shock robustness of gyroscopes, especially in automotive and similar applications, is a highly desirable feature that would allow gyroscopes to remain functional and deliver accurate electric output signals even in scenarios when the device is subject to certain levels of mechanical disturbance. 
         [0009]    What is needed are devices, systems, and methods for system designers to overcome the above-described limitations. 
       SUMMARY OF THE INVENTION 
       [0010]    The disclosed systems and methods increase shock robustness in both single-axis and multi-axis rate sensors such as gyroscopes. In particular, certain embodiments of the invention provide sensor immunity against interference from translational and rotational shock conditions acting, such as shock, vibrations, and other undesirable environmental mechanical noise that are likely to generate spurious electrical differential output signals that, in turn, would be erroneously interpreted as a rotational speed, thus falsifying the sensor&#39;s reading. 
         [0011]    In various embodiments of the invention, shock robustness is facilitated by a chessboard-pattern architecture of proof masses that provides a second layer of differential signals not present in existing designs. Masses are aligned parallel to each other in a two-by-two configuration with two orthogonal symmetry axes. The masses are driven to oscillate in such a way that each mass moves anti-parallel to an adjacent proof mass. 
         [0012]    In some embodiments, electrodes located underneath movably suspended proof masses are arranged in a chessboard-pattern and connected as balanced differential pairs in order to electrically cancel the effect of mechanical disturbances such as linear and angular accelerations. This immunizes the sensor against undesired forces that could otherwise superimpose with desired Coriolis forces and impact the accuracy of the output signal. 
         [0013]    In some embodiments, electrodes associated with the masses are configured in a two-by-two chessboard-pattern, and one mass from each pair of masses is electrically coupled to another pair so as to form a balanced differential electrical pair. In addition, a mechanical joint system coupled to the proof masses inhibits displacements of masses provoked by undesired mechanical disturbances, such as linear accelerations and angular accelerations, while permitting displacements due to the desired Coriolis forces. In other words, mechanical disturbances are prevented from causing unwanted movements that may lead to erroneous output signals or sensor malfunction. 
         [0014]    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 
         [0015]    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. 
           [0016]      FIG. 1A  shows primary motion for a typical MEMS gyroscope. 
           [0017]      FIG. 1B  shows secondary motion for a typical MEMS gyroscope. 
           [0018]      FIG. 2A  shows the respective effect of translational shock for a common implementation of a MEMS gyroscope. 
           [0019]      FIG. 2B  shows the respective effect of rotational shock for a common implementation of a MEMS gyroscope. 
           [0020]      FIG. 3A  shows the effect of translational shock for an implementation of a MEMS gyroscope having a mechanical joint. 
           [0021]      FIG. 3B  shows the effect of rotational shock for an implementation of a MEMS gyroscope having a mechanical joint. 
           [0022]      FIG. 4A  is a general illustration of primary motion in a “chessboard” configuration of proof masses according to various embodiments of the invention. 
           [0023]      FIG. 4B  is a general illustration of secondary motion in a chessboard configuration of proof masses according to various embodiments of the invention. 
           [0024]      FIG. 5A  illustrates the effect of translational shock for the chessboard configuration in  FIG. 4 . 
           [0025]      FIG. 5B  illustrates the effect of rotational shock for the chessboard configuration in  FIG. 4 . 
           [0026]      FIG. 6  is an exemplary application of a mechanical joint system to the chessboard configuration in  FIG. 4  according to various embodiments of the invention. 
           [0027]      FIG. 7  schematically illustrates primary motion according to various embodiments of the invention. 
           [0028]      FIG. 8A  and  FIG. 8B  illustrate examples of primary joint systems according to various embodiments of the invention. 
           [0029]      FIG. 9  illustrates secondary motion in a “yaw rate sensor” implementation according to various embodiments of the invention. 
           [0030]      FIG. 10  illustrates secondary motion in a “pitch rate sensor” implementation according to various embodiments of the invention. 
           [0031]      FIG. 11A  and  FIG. 11B  illustrate examples of secondary joint systems in a yaw rate sensor according to various embodiments of the invention. 
           [0032]      FIG. 11C  illustrates an exemplary out-of-plane gyroscope comprising primary and secondary joint systems according to various embodiments of the invention. 
           [0033]      FIG. 11D  illustrates the primary joint system of  FIG. 8B  implemented into the out-of-plane gyroscope shown in  FIG. 11C . 
           [0034]      FIG. 11E  illustrates the secondary joint system of  FIG. 11B  implemented into the out-of-plane gyroscope shown in  FIG. 11C . 
           [0035]      FIG. 11F  illustrates an exemplary in-plane gyroscope comprising primary and secondary joint systems according to various embodiments of the invention. 
           [0036]      FIG. 11G  illustrates the primary joint system of  FIG. 8A  implemented into the in-plane gyroscope shown in  FIG. 11F . 
           [0037]      FIG. 11H  illustrates the secondary joint system of  FIG. 12B  implemented into the in-plane gyroscope shown in  FIG. 11F . 
           [0038]      FIG. 12A  and  FIG. 12B  illustrate examples of secondary joint systems in a pitch rate sensor according to various embodiments of the invention. 
           [0039]      FIG. 13  illustrates an exemplary arrangement for the sensing electrodes in a pitch rate sensor implementation, according to various embodiments of the invention. 
           [0040]      FIG. 14  illustrates an exemplary arrangement for the sensing electrodes for a yaw rate sensor implementation, according to various embodiments of the invention. 
           [0041]      FIG. 15  is a flowchart of an illustrative process for facilitating shock robustness in rate sensors in accordance with various embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]    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. 
         [0043]    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. 
         [0044]    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. 
         [0045]    In this document the terms “primary” motion, mode, and axis refers to the driving motion of proof masses and the terms “secondary” motion, mode, and axis, generally, refers to sensing operations. Detailed descriptions of components, such as driving electronics, joints, and anchoring to frames, for example for driving the joints, are omitted for brevity and clarity. Further, the term “shock” includes any type of translational and angular acceleration, vibration, and mechanical noise. 
         [0046]      FIG. 1A  shows primary motion for a typical MEMS gyroscope, while  FIG. 1B  shows secondary motion for a typical MEMS gyroscope. Masses  104 ,  106  in  FIG. 1A  are excited from their resting positions (indicated by dashed lines) to perform an oscillatory movement along the primary axis parallel to electrode  150 ,  152  until masses  104 ,  106  reach their maximum deflection. Electrode  150 ,  152  is connected an electric circuit (not shown) to measure the distance between masses  104 ,  106  and electrode  150 ,  152  via determining capacitance, as those of ordinary skill in the art will appreciate. 
         [0047]    However, if system  100  is exposed to a rotation about the sensitive axis (here rate axis  103 ), the Coriolis effect creates oscillating forces  114 ,  116  along secondary axis  102  that will be detected by electrode  150 ,  152  as a differential signal. Oscillating forces  114 ,  116  occur in addition to the driving motion (not shown in  FIG. 1B ). In detail, Coriolis force  114  causes mass  104  to travel a distance away from electrode  150 , thereby, lowering the capacitance. At the same time, Coriolis force  116  causes mass  106  to move toward electrode  152 , which decreases the distance to electrode  150  and increases the capacitance accordingly. This change in position is detected as a variation in capacitance due Coriolis forces and can be measured as a differential signal on electrode  150 ,  152  that is proportional to the angular rate to be determined. 
         [0048]      FIG. 2A  and  FIG. 2B  show the respective effects of translational and rotational shock for a common implementation of a MEMS gyroscope. Same numerals as in  FIG. 1  denote similar elements. As can be deduced from  FIG. 2A , an external linear acceleration of masses  104 ,  106  induced by force  210  in a translational direction results in a common mode signal rather than a differential error signal, as both masses  104 ,  106  are affected by the same variation in capacitance, thus, creating a zero differential electric output signal. Therefore, by using two proof masses  104 ,  106  as compared using to a single mass, linear acceleration can be ignored or isolated and canceled from the output signal so as to eliminate the impact of this type of external shock. 
         [0049]    In contrast, angular acceleration  211  around the rate axis, e.g., an unwanted spinning pulse of the MEMS gyroscope about the rate axis, is more problematic. Such a shock event acts to induce an unequal displacement of both masses  104 ,  106  along the secondary axis, i.e., in the same direction as the to-be-detected Coriolis force, which, by definition, is also normal to the axis of rotation. A shown in  FIG. 2B , the unequal forces cause mass  106  to move closer to electrode  152  while causing mass  104  to move away from electrode  150 . Since the resulting parasitic signals superimpose the sensing signal from which they cannot be easily distinguished, parasitic signal components cannot be canceled by appropriate electronic circuitry. As a result, the output signal will include an error component due to the effect of the shock and erroneously indicate an angular rate. 
         [0050]    In general, errors that generate common mode signals are relatively easy to deal with, because unlike in single mass architectures in which an uncorrected superposition of undesired motion vectors due to perturbation always results in a falsification of the output signal, common mode signals due to a common mode movement of masses  104  and  106  can at least be partially canceled to reduce the effect of certain unwanted acceleration components. However, architecture  250  remains vulnerable to external perturbation due to certain shock events. 
         [0051]    Some existing approaches utilize coupling joint system  302  between masses  104  and  106  (shown in  FIG. 3A  and  FIG. 3B ) in order to reduce defections caused by translational force  210 . However, the usefulness of such a design is limited to reducing only translational motion in system  302 . These designs cannot reduce the effects of all types of shock. In particular, coupling joint system  302  cannot prevent motion caused by rotational acceleration  211  for the purpose of avoiding erroneous readings by electrode  150 ,  152 . 
         [0052]    Therefore, it would be desirable to have systems and methods available that increase the shock robustness of both single and multi-axial sensors against all types of shock so as to ensure accurate sensor readings. 
         [0053]      FIG. 4A  and  FIG. 4B  generally illustrate primary and secondary motion in a chessboard configuration of movable proof masses in a sensing device according to various embodiments of the invention. For clarity, components such as springs, anchors, frames, and actuators are omitted. In  FIG. 4A  and  FIG. 4B , four essentially equal masses  402 - 408  are movably suspended within a base frame and disposed above their respective electrodes  150 - 156 . Masses  402 - 408  are aligned parallel to each other, as two balanced differential pairs, in a two-by-two configuration that has two orthogonal symmetry axes. The primary motion, secondary motion, and associated electrode connections are arranged in a “chessboard” configuration that adds another layer of differential signals not present in existing designs. 
         [0054]    In operation, masses  402 - 408  in  FIG. 4A  are constantly driven to perform an oscillatory motion along primary axis  101  that is parallel to electrode  150 - 156 . Movable proof mass  402  is driven in the same direction as mass  408 , whereas masses  404  and  406  are driven in the opposite direction along the same primary axis. Electrode  150 - 156  is configured to detect movements of masses  402 - 408  along the secondary axis  102 .  FIG. 4B  illustrates how masses  402 - 408  move along the secondary axis due to Coriolis forces that are generated by an angular rate around the rate axis  103 , which is the rate to be measured by system  450 . One skilled in the art will appreciate that masses  402 - 408  may comprise any suitable shape. 
         [0055]    In both the primary and secondary oscillation, all four masses  402 - 408  move along parallel paths, and each mass  402 - 408  moves anti-phase with two adjacent masses and in-phase with diametrically opposite mass. For example, when Coriolis force  114 ,  120 , the force to be measured, moves mass  402 ,  408  along the secondary axis toward electrode  150  and  156 , respectively, at the same time, Coriolis force  116 ,  118 , which acts in the opposite direction with respect to the Coriolis force  114 ,  120 , moves mass  404 ,  406  away from electrode  152 ,  154 . In this example, electrode  150  and  156  are coupled with each other and the output signal is sent to an electric reading circuit (e.g., an ASIC), while electrode  152  and  154  are coupled to produce a second output signal. From both output signals one electrical differential signal representative of the desired Coriolis force is obtained. One of ordinary skill in the art will appreciate that while only planar electrodes are shown in the figures, electrodes  150 - 156  may be shaped in any other manner known in the art, including as capacitive finger electrodes, known as comb electrodes. 
         [0056]      FIGS. 5A and 5B  illustrates the effect of undesired external translational and rotational acceleration on proof masses in the chessboard configuration in  FIG. 4 . For clarity, components similar to those shown in  FIG. 4  are labeled in the same manner. For purposes of brevity, a description of their function is not repeated here. External translational force  510  caused by, for example a linear acceleration, moves all masses  402 - 408  parallel along the secondary axis. The resulting equal change in capacitance between masses  402 - 408  and electrodes  150 - 156  generates no unwanted electrical differential output signal. Instead a common mode signal is generated and only wanted angular rate is measured. 
         [0057]    Similarly, in case of unwanted angular acceleration  511 , for example, when masses  404  and  408  are accelerated to a greater extent than masses  402  and  406 , the distance between mass  404 ,  408  and electrode  152 ,  156  will decrease, while the distance between mass  402 ,  406  and electrode  150 ,  154  will increase, such that the overall change in capacitance experienced by electrodes  152  and  154  and electrodes  150  and  156  remains essentially equal, again, rejecting unwanted differential signals that may lead to erroneous output signals. 
         [0058]    The architecture of system  400 ,  450  reliably generates a common mode signal on electrodes  150 - 156  that electrically cancels the effect of mechanical disturbances so as to not impact the accuracy of the output signal, i.e., the reading of the gyroscope. As such, system  400 ,  450  is much more immune against mechanical shock due to both linear acceleration and momentum irrespective of orientation. 
         [0059]    It is envisioned that one system per sensing axis may be arranged to create a multi-axis gyroscope. It is noted that the shown symmetry is applied only to the four masses  402 - 408 . However, other structures of the sensor may be arranged in any suitable manner with respect to the two symmetry axes of the chessboard configuration. 
         [0060]      FIG. 6  is an exemplary application of a mechanical joint system to the chessboard configuration in  FIG. 4  to reduce deflections caused by environmental perturbations according to various embodiments of the invention. System  600  has two orthogonal symmetry axes, as can be easily seen. System  600  comprises essentially equal masses  402 - 408 , which are suspended above electrode  150 - 156 , respectively, and coupled to each other with rotary joint  610 - 616 . In a manner similar to  FIG. 4A  and  FIG. 4B , masses  402 - 408  are movably arranged within a base frame and disposed above their respective electrodes  150 - 156  as two balanced differential pairs in a two-by-two configuration that has two orthogonal symmetry axes. Examples of primary and secondary operative motion for mass  402 - 408  are similar to this given with respect to  FIG. 4A  and  FIG. 4B . 
         [0061]    In one embodiment, each rotary joint  610 - 616  is formed by combing a rigid and a flexible body, such as a spring, and an anchor point that may be fixed to the base frame (not shown) that holds masses  402 - 408  in place. By employing rotary joints  610 - 616 , mass  402  is forced to move in tandem with mass  408  and mass  404  is forced to move in tandem with mass  406 . As a result, any common mode motion, such as the one discussed with respect to  FIG. 5A  or  FIG. 5B , is mechanically suppressed while continuing to permit regular secondary motion. In detail, by preventing masses that are designed to move in the same direction (e.g., mass  402  and  408 ) to move at different rates by using rotary joints  610 - 616 , forces caused by, e.g., angular acceleration around the rate axis and other unwanted disturbances are prevented from both vectorially adding to wanted Coriolis forces and, thus, corrupting the output signal. Furthermore, in addition to the electrical rejection discussed above with respect to  FIG. 4A  through  FIG. 5B , this mechanical constraint prevents the masses from touching the stopper structures and, thereby, helps to prevent the need to restart the primary motion. 
         [0062]    In one embodiment, a similar set of rotary joints is used to effectively inhibit unwanted motions resulting from motion in the primary direction. The direction of primary motion is schematically captured in  FIG. 7 . In another embodiment, rotary joints are used to effectively inhibit unwanted motions in both the primary and secondary direction. 
         [0063]      FIG. 8A  and  FIG. 8B  illustrate examples of primary rotary joint systems according to various embodiments of the invention. In example system  800 ,  850 , masses  402 - 408  are attached to fixed mechanical hinges  814  via flexible mechanical hinges  820 . Each fixed mechanical hinge  814  is coupled to a flexible mechanical hinge  820  via rigid arm  830 . It is noted that any other possible configuration of masses and rotatable joint system may be used in accordance with the goals of the present invention. It is also noted that although the previous description is primarily focused on improving the shock robustness of “pitch rate” sensors having an in-plane rate axis and an out-of-plane secondary motion, this is not intended as a limitation on the scope of the invention, as the principles of the present invention are equally applicable to, for example, “yaw rate” sensors that have an out-of-plane rate axis and an in-plane secondary motion. 
         [0064]    In one embodiment, in a yaw rate sensor implementation, the secondary motion is such that proof masses  402 - 408  move in the same direction along 102 secondary axis that is in-plane and orthogonal to primary axis  101  and rate axis  103 , as shown in  FIG. 9 . In this example, the plane of motion is parallel to the plane of the substrate on which the MEMS gyroscope is placed. The gyroscope is sensitive to rotation about the axis that protrudes out of the plane of the drawing, i.e., forming a z-gyroscope. 
         [0065]    In one embodiment, in a “pitch rate sensor” implementation, the secondary motion is such that proof masses  402 - 408  move in the same direction along secondary axis  103  that is normal to the plane of the substrate, as shown in  FIG. 10 , i.e., the gyroscope is sensitive to rotation about rate axis  102  that is an in-plane axis orthogonal to primary axis  101 . In either case, each of the proof masses moves in-phase with the diametrically opposite one and in anti-phase with respect to the remaining two masses. In other words, at any given instant, the velocity of mass  402  has the same orientation of velocity as mass  408 , while the velocity of mass  404  and mass  406  has the opposite orientation. 
         [0066]      FIG. 11A  and  FIG. 11B  illustrate structures that comprise a secondary rotary joint system that constrains a secondary motion of proof masses in a yaw rate sensor according to various embodiments of the invention. In a manner similar to  FIG. 8 , joints are formed by fixed mechanical hinges  814  coupled to flexible components, such as flexible mechanical hinges  820 , a rigid body (arm  830 ), and an anchor point fixed to a base frame that is not shown in  FIG. 11A-11B . In operation, system  1100 ,  1150  permits a primary motion in the driving direction as well as secondary motion along the secondary axis, while practically suppressing all spurious motions along the secondary axis, such that only the Coriolis force is effective. One of ordinary skill in the art will appreciate that any other configuration of masses, joints, etc., and additional anchoring, frames, decoupling structures, etc., is possible to achieve the principles in accordance with the present invention. 
         [0067]    In one embodiment, in order to achieve a complete mechanical rejection, displacement of masses  402 - 408  along rate axis  103  is inhibited by one of primary joints, secondary joints, a combination of primary and secondary joints, or by additional mechanical constraints. In one embodiment, several mechanical components act as both primary and secondary joint. It is understood that the primary and secondary joint systems be independent from each other. 
         [0068]    Examples of rotary joints that constrain the primary and the secondary motion while inhibiting the spurious motions, for a yaw rate sensor implementation as well as a pitch rate sensor implementation, are shown in  FIG. 11C  through  FIG. 11D .  FIG. 11E  illustrates an exemplary yaw rate sensor comprising the primary joint system of  FIG. 8B  and the secondary joint system of  FIG. 11B .  FIG. 11D  illustrates the sensor of  FIG. 11C  during the primary motion, while  FIG. 11E  illustrates the same sensor during the secondary motion. Similarly,  FIG. 11F  illustrates an exemplary pitch rate sensor comprising the primary joint system of  FIG. 8A  and the secondary joint system of  FIG. 12B .  FIG. 11G  illustrates the sensor of  FIG. 11F  during the primary motion, while  FIG. 11H  illustrates the same sensor during the secondary motion. 
         [0069]      FIG. 12A  and  FIG. 12B  illustrate structures that comprise a secondary rotary joint system to constrain a secondary motion of proof masses in a pitch rate sensor according to various embodiments of the invention. Device  1200 ,  1250  comprise proof masses  402 - 408  that are connected to each other by a joint system comprising frame  1230 ,  1232  torsion spring  1220 ,  1222 , and anchor  1210 . Anchor  1210  is typically affixed to the substrate and connected to frame  1230 ,  1232  via torsion spring  1220 ,  1222 . Torsion spring  1220 ,  1222  enables frame  1230 ,  1232 , which is rotatably disposed between adjacent masses  402 - 408 , to move about the primary and secondary axis, respectively, by pivoting around anchor  1210 . Frame  1230 ,  1232  is suspended on anchor  1210  with torsion spring  1220 ,  1222  and connected to masses  402 - 408  via respective joint  1240 . 
         [0070]    In operation, in addition to oscillating motions at the same driving frequency, device  1200 ,  1250  constrains the displacement of proof masses  402 - 408  in sensing direction, i.e., normal to the plane of the substrate (not shown). Masses  402  and  408  are constrained to move, along this axis, in an opposite direction with respect to the movement of masses  404  and  406 . Therefore, sensing motions due to Coriolis forces generated by an angular rate around the rate axis are enabled, while the motions caused by undesired mechanical disturbances are prevented from acting on masses  402 - 408  and interfering with electrical output signals. Restricting movements in this manner allows for rejection of spurious motions resulting from shock conditions. For example, if device  1200  is subjected to a parasitic load that would move masses  402 ,  406  with the same orientation towards their respective electrodes (not shown), frame  1230  will prevent this kind of displacement as not compliant with corresponding torsion spring  1220 . 
         [0071]      FIG. 13  illustrates an exemplary arrangement for the sensing electrodes in a pitch rate sensor implementation, according to various embodiments of the invention. The configuration of sensing electrodes  1350 - 1356  in system  1300  may vary depending on the particular implementation. In one embodiment, in order to achieve electrical rejection, sensing electrodes  1350 - 1356  are designed so as to facilitate detection of displacement of the four main masses (indicated by dashed lines) in the secondary direction. With respect to at least one of the symmetry axes of the main masses, system  1300  is connected in an anti-symmetrical configuration, such that electrodes  1350  and  1356  are electrically coupled to each other, and electrodes  1352  and  1354  are electrically coupled to each other. In this example, electrodes  1350 - 1356  are situated on a different plane with respect to the moving masses. 
         [0072]    In example in  FIG. 14 , the “yaw rate sensor” implementation, electrodes  1402  are constructed as static structures that are built in to the same plane as moving masses  402 - 408 .  FIG. 14  shows an exemplary arrangement for sensing electrodes for a yaw rate sensor implementation. It is noted that, as with the embodiments discussed with respect to  FIG. 4A  through  FIG. 5B , the concepts presented in  FIG. 6  through  FIG. 14  may be duplicated or triplicated, as needed, to create multi-axis sensors, such as gyroscopes, that are sensitive motion about all axes. In addition it is envisioned that any number and combination of masses may be utilized, for example, in order compensate for any imperfections in the manufacture of  402 - 408 . 
         [0073]      FIG. 15  is a flowchart of an illustrative process for facilitating shock robustness in rate sensors in accordance with various embodiments of the invention. In one embodiment, at step  1502 , shock robustness is enabled by setting proof masses (e.g., adjacent proof masses) into an anti-phase oscillatory motion in a first plane, for example, along a gyroscope drive axis. 
         [0074]    At step  1504 , at least one of the proof masses is operated in-phase in an oscillatory motion with another (e.g., diametrically opposing) proof mass located in a plane parallel to the drive axis, such that the two masses move in-phase and at the same rate. Together with the anti-phase movement of the adjacent proof masses, this suppresses a common mode motion between masses located in planes orthogonal to the drive axis. 
         [0075]    At step  1506 , a measured sensing signal is received from a plurality of sensing electrodes. 
         [0076]    Finally, at step  1508 , an angular rate is determined in a sensing direction, without interference from deflection of elements caused by shock movements impacting the gyroscope, which otherwise would erroneously indicate a rotational acceleration. 
         [0077]    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. 
         [0078]    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.