Patent Publication Number: US-2013239679-A1

Title: Three-axis gyroscope

Description:
BACKGROUND 
     Sensors and devices for detecting and measuring position, angular orientation, displacement, velocity and acceleration are sought after in numerous areas of endeavor. Navigation, consumer electronics, geology, and oil exploration are just a few such areas. Reduced size and production cost of such devices are also desirable. The present teachings address the foregoing and related concerns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments will now be described, by way of example, reference to the accompanying drawings, in which: 
         FIG. 1  depicts a plan view of a single-axis gyroscopic sensor according to one example of the present teachings; 
         FIG. 1A  depicts a plan view flexure detail of the sensor of  FIG. 1 ; 
         FIG. 1B  depicts a plan view of an alternative flexure detail for a sensor; 
         FIG. 2  depicts a plan view of a single-axis gyroscopic sensor according to another example; 
         FIG. 3  depicts a plan view single-axis gyroscopic sensor according to still another example; 
         FIG. 4  depicts a plan schematic view of a three-axis gyroscope in accordance with the present teachings; 
         FIG. 5  depicts a table of behavioral characteristics of the gyroscope of  FIG. 4 ; 
         FIG. 6  depicts a plan schematic view of a three-axis gyroscope and accelerometer device in accordance with the present teachings. 
     
    
    
     DETAILED DESCRIPTION 
     Introduction 
     Apparatus and methods related to measuring angular velocities in three-space are provided, Plural drive masses are distributed in a plane and are force-oscillated in two orthogonal directions such that gyration of the collective is performed. Sense masses are coupled by flexures to the drive masses and are each displaceable along a respective single degree of freedom. Such displacements occur in response to angular velocities about a vector orthogonal to the particular degree of freedom of a given sense mass. Electronic circuitry measures the respective sense mass displacements and provides corresponding signaling. The drive masses and sense masses can be formed such that a microelectromechanical system (MEMS) device is defined. 
     In one example, an apparatus includes a plurality of drive masses disposed in a plane. The drive masses are configured to be simultaneously oscillated in two orthogonal directions in the plane. The apparatus also includes a plurality of sense masses, Each sense mass is configured to be displaced within a respective single-axis range in response to angular velocity of the apparatus about a vector orthogonal to the respective single-axis range. Each drive mass supports one or more of the sense masses. 
     In another example, a microelectromechanical system (MEMS) device includes a substrate and a plurality of drive masses supported in overlying relationship to the substrate. The drive masses are distributed in a plane. The drive masses are configured to be gyrated as an entity by way of forced oscillations in two orthogonal axes in the plane. The MEMS device also includes a plurality of pairs of sense masses. Each pair is supported by a respective one of the drive masses. Each sense mass is displaceable in a single degree of freedom in response to angular velocity of the MEMS device about a vector orthogonal to the respective degree of freedom of that sense mass. 
     First Illustrative Sensor 
     Attention is now turned to  FIG. 1 , which depicts a plan view of single-axis gyroscopic sensor (sensor)  100 . The sensor  100  is illustrative and non-limiting in accordance with the present teachings. Thus, other sensors and gyroscopic devices incorporating such other sensors are also contemplated. The sensor  100  is depicted in a three-axis frame of reference defined by mutually orthogonal vectors “X”, “Y” and “Z”. 
     The sensor  100  includes a drive mass  102 . The drive mass  102  is formed from a solid material. The drive mass is suspended within the sensor frame by a plurality of flexures (not shown) allowing it to displace along the “X” axis. The sensor  100  also includes a sense mass  104  suspended within the drive mass  102  by way of a plurality of flexures  106  extending there between. The respective flexures  106  are configured such that the sense mass  104  can be displaced within a “Y” axis as indicated by the double-arrow D 1 . Thus, the sense mass  104  is supported within and surrounded by the drive mass  102 , and is defined by a single degree of freedom along the “Y” axis. 
     In one example, the drive mass  102 , the sense mass  104  and the respective flexures  106  are formed from a silicon wafer by way of photolithography such that the sensor  100  is defined by a monolithic structure. Other suitable materials or formative processes can also be used. In one example, the sensor  100  is defined by an overall length (“Y”) of 2.0 millimeters, a width (“X”) of 1.5 millimeters, and a relatively uniform thickness (“Z”) of 0.2 millimeters. Other suitable respective dimensions can also be used. 
     Typical normal operation of the sensor  100  is as follows: the drive mass  102  is oscillated (or vibrated) along the “X” axis as indicated by the double-arrow D 2  by way of a drive device or apparatus discussed in further detail below. The sense mass  104  is coupled to the drive mass  102  so as to oscillate in a corresponding manner. That is, forced oscillation or stimulus of the drive mass  102  in the “X” axis does not result in significant displacement of the sense mass  104  in the “Y” axis, provided that the sensor  100  is angularly stationary. In one example, the sensor  100  is oscillated in the “X” axis at about 6,000 Hertz with a peak-to-peak amplitude of about 10 micrometers. Other suitable frequencies or amplitudes can also be used. 
     However, rotation of the sensor  100  about the “Z” axis, during forced oscillation in the “X” axis, results in a corresponding displacement of the sense mass  104  along the “Y” axis. This displacement is attributable to the Coriolis effect. The magnitude of the sense mass  104  displacement along “Y” corresponds to the angular velocity about “Z”, while the sign or direction of displacement corresponds to the direction of rotation about the “Z” axis. Measurement of the magnitude and/or direction of displacement of the sense mass  104  can thus be correlated to the angular velocity and rotational sense about “Z”. The sensor  100  is thus also referred to herein as a “Z” axis sensor  100 . 
     Reference is now made to  FIG. 1A , which depicts a plan view of a detail of the sensor  100 . A flexure  106  extends from a corner portion of the sense mass  104  coupling it with the drive mass  102 . Each flexure  106  is thus defined by a single supporting extension. 
     Reference is made now to  FIG. 1B , which depicts a plan view of a flexure  120 , in accordance with the present teachings. The flexure  120  is an alternative form to that of the flexure  106 . The flexure  120  includes two respective extensions  122  ultimately coupling the sense mass  104  to the drive mass  102 . The flexure  120  is generally more complex in form than the flexure  106 , but offers relatively greater and more linear displacement along the “Y” axis, and greater structural strength and resistance to displacement of the sense mass  104  all directions except along the “Y” axis. Other suitable flexure forms can also be used. 
     Second Illustrative Sensor 
     Attention is now turned to  FIG. 2 , which depicts a plan view of single-axis gyroscopic sensor (sensor)  200 . The sensor  200  is illustrative and non-limiting in accordance with the present teachings. Thus, other sensors and gyroscopic devices incorporating such various sensors are also contemplated. The sensor  200  is depicted in a mutually orthogonal, three-axis frame of reference. In one example, the sensor  200  is defined by length, width and thickness dimensions equivalent to those described above for the sensor  100 . Other suitable dimensions can also be used. 
     The sensor  200  includes a drive mass  202  formed from a solid material, The drive mass is suspended within the device frame by a plurality of flexures (not shown) allowing it to displace along the “X” axis. The sensor  200  also includes a sense mass  204  suspended within the drive mass  202  by way of a plurality of flexures  206  extending there between. The respective flexures  206  are configured such that the sense mass  204  can be displaced in a cantilever-like manner along the “Z” axis as indicated by the directional indicator D 3 . The sense mass  204  is therefore supported within and surrounded by the drive mass  202 , and is defined by a single degree of freedom along the “Z” axis. 
     In one example, the drive mass  202 , the sense mass  204  and the respective flexures  206  are formed from a silicon wafer by way of photolithography such that the sensor  200  is defined by a monolithic structure. Other suitable materials or formative processes can also be used. 
     Typical normal operation of the sensor  200  is as follows: the drive mass  202  is oscillated (or vibrated) along the “X” axis as indicated by the double-arrow D 2 . The sense mass  204  is coupled to the drive mass  202  so as to oscillate in a corresponding manner, such that forced oscillation of the drive mass  202  in the “X” axis does not result in significant displacement of the sense mass  204  in the “Z” axis under non-rotational conditions. 
     Rotation of the sensor  200  about the “Y” axis during oscillation in the “X” axis results in a corresponding cantilever displacement of the sense mass  204  along the “Z” axis. The magnitude of the sense mass  204  displacement along “Z” corresponds to the angular velocity about “Y”, while the sign or direction of displacement corresponds to the rotational sense about the “Z” axis. The sensor  200  is thus also referred to herein as a “Y” axis sensor  200 . 
     Third Illustrative Sensor 
     Attention is now turned to  FIG. 3 , which depicts a plan view of single-axis gyroscopic sensor (sensor)  300 . The sensor  300  is illustrative and non-limiting in accordance with the present teachings. Thus, other sensors and gyroscopic devices incorporating such various sensors are also contemplated. The sensor  300  is depicted in a mutually orthogonal, three-axis frame of reference. In one example, the sensor  300  is essentially equivalent to the sensor  200 , rotated ninety degrees in the X-Y plane. In one example, the sensor  300  is defined by length, width and thickness dimensions equivalent to those described above for the sensor  100 . Other suitable dimensions can also be used. 
     The sensor  300  includes a drive mass  302  suspended within the device frame by a plurality of flexures, and a sense mass  304  suspended there within by way of a plurality of flexures  306 , all formed from a solid material. The respective flexures  306  are configured such that the sense mass  304  is displaceable along a “Z” axis as indicated by the directional indicator D 3 . The sense mass  304  is therefore defined by a single degree of freedom along the “Z” axis. 
     In one example, the drive mass  302 , the sense mass  304  and the respective flexures  306  are formed from a silicon wafer by way of photolithography such that the sensor  300  is defined by a monolithic structure. Other suitable materials or formative processes can also be used. 
     Typical normal operation of the sensor  300  is as follows: the drive mass  302  is oscillated (or vibrated) along the “Y” axis as indicated by the double-arrow D 1 , as discussed in further detail below. The sense mass  304  is coupled to the drive mass  302  so as to oscillate in a corresponding manner, such that forced oscillation of the drive mass  302  in the “Y” axis does not result in significant displacement of the sense mass  304  in the “Z” axis under non-rotational conditions. 
     Rotation of the sensor  300  about the “X” axis during oscillation in the “Y” axis results in a corresponding cantilever displacement of the sense mass  304  along the “Z” axis. The magnitude of the sense mass  304  displacement along “Z” corresponds to the angular velocity about “X” while the sign or direction of displacement corresponds to the direction of rotation about the “Z” axis. The sensor  300  is thus also referred to herein as an “X” axis sensor  300 . 
     Illustrative Gyroscope 
     Reference is now made to  FIG. 4 , which depicts a plan schematic view of a three-axis gyroscope (gyroscope)  400  in accordance with the present teachings. The gyroscope  400  is illustrative and non-limiting with respect to the present teachings. Other suitable gyroscopes can be defined and used in accordance there with. The gyroscope  400  is depicted in a mutually orthogonal, three-axis frame of reference. In one example, the gyroscope  400  is formed so as to define at least a portion of a microelectromechanical systems (MEMS) device. Other configurations or structures according to the present teachings can also be defined and used. 
     The gyroscope  400  includes a frame  402 . In one example, the frame  402  is defined by a silicon wafer or portion thereof. Other suitable materials can also be used, The frame  402  supports various elements of the gyroscope  400  as described below. The frame  402  is bonded or otherwise joined to an underlying wafer (or substrate)  403 . The frame  402  and the substrate  403  are fixed to one another such that no relative motion occurs between them during normal operations. 
     The gyroscope  400  also includes drive masses  404 ,  406 ,  408  and  410 , respectively. The drive masses  404 - 410  are coupled or connected to one another by way of respective distance-fixing (or offset maintaining) extensions  412 , and are connected to (i.e., suspended within) the frame  402  by way of respective flexures (or elastic elements)  413 . In one example, the drive masses  404 - 410 , the extensions  412  and the flexures  413  are formed from a silicon wafer by way of photolithography such that a monolithic entity  414  is defined. Other suitable constructs can also be used. The    
     The drive mass  404  is formed to define an “X” axis sensor  416  analogous to the sensor  300  described above, and a “Z” axis sensor  418  analogous to the sensor  100  described above. Thus, the drive mass  404  serves as a common drive mass for the two respective sensors  416  and  418 . 
     In turn, the drive mass  406  is formed to define a “Y” axis sensor  420  analogous to the sensor  200  described above, and a “Z” axis sensor  422 . The drive mass  408  is formed to define a “Z” axis sensor  422 , and an “X” axis sensor  424 . Furthermore, the drive mass  410  is formed to define a “Z” axis sensor  428 , and a “Y” axis sensor  430 . Thus, the drive masses  404 - 410  collectively define two “X” axis sensors, two “Y” axis sensors and four “Z” axis sensors. 
     The substrate  403  includes or defines a central post or standard  432  that extends away from a planar aspect of the substrate  403 . The drive masses  404 - 410  are mechanically coupled to the standard  432  by way of respective elastic or “spring” elements  434 . In another example, the standard  432  and the elastic elements  434  are omitted. The drive masses  404 - 410  are coupled to, or are otherwise affected by, one or more electrostatic drivers. Non-limiting examples of such electrostatic drivers (or actuators) are described in U.S. Pat. No. 5,986,381 to Hoen et al., issued Nov. 16, 1999, and which is herein incorporated by reference in its entirety. Other suitable drivers can also be used. 
     Specifically, the drive masses  404  and  408  are coupled to be force oscillated along the “Y” 0  axis as depicted by the double-arrow D 1 , The drive masses  406  and  410  are coupled to be force oscillated along the “X” axis as depicted by the double-arrow D 2 . In one example, the respective oscillations in the X-Y plane are sinusoidal in waveform and offset by ninety degrees of phase angle from each other, resulting in full gyrations (i.e., three-hundred sixty degrees) of the coupled drive masses  404 - 410 . The immediate foregoing behavior is also attributable to the distance (or spacing) fixing characteristic of the extensions  412 , which can be characterized by a slight bending or flexing. Other suitable forced oscillations or stimulus techniques can also be used. 
     The forced oscillations of the drive masses  404 - 410  in the X-Y plane cause the sensors  416 - 430  to exhibit respective displacements in accordance with respective rotations (i.e., angular velocities) of the gyroscope  400  about the three mutually-orthogonal axis due to Coriolis forces. For example, rotation of the gyroscope  400  about the “Z” axis results in corresponding displacements of the “Z” axis sensors  418 ,  422 ,  424  and  428 . In another example, rotation about the “Y” axis results in corresponding displacements of the “Y” axis sensors  420  and  430 . Analogous behavior is exhibited by the “X” axis sensors  416  and  426 . 
     Simultaneous angular velocities about two or three of the mutually-orthogonal axis results in simultaneous displacements of the corresponding sensors  416 - 430 . Capacitance-based sensors, for example, can be used to provide electrical signals corresponding to such respective displacements of the sensors  416 - 430  during normal operations. Non-limiting examples of such capacitance-based sensors are described in U.S. Pat. No. 7,484,411 to Walmsley, issued Feb. 3, 2009, and which is herein incorporated by reference in its entirety. Other suitable displacement sensing and measuring techniques can also be used. 
     Illustrative Behavioral Characteristics 
     Attention is turned now to  FIG. 5 , which depicts a table  500  of behavioral characteristics in accordance with the present teachings. The table  500  corresponding to normal operating behaviors of the gyroscope  400  described above. Other suitable devices defined by other behaviors in accordance with the present teachings can also be used. 
     The table  500  includes a column of mass velocities  502  corresponding to the forced motions of the drive masses  404 - 410 . The table  500  also includes a column of rotations  504  corresponding to angular velocity of the gyroscope  400  about respective axis. The table further includes a column  506  of sense mass displacements corresponding to the response behaviors of the respective sensors  416 - 430 . 
     For example, when the drive masses  404 - 410  are being forced in the positive “X” direction and the gyroscope  400  is being rotated in a clockwise sense about the “Z” axis, the sense masses of the “Z” axis sensors  418 ,  422 ,  424  and  428  will exhibit respective displacements along the negative “Y” axis. In another example, when the drive masses  404 - 410  are being forced in the negative “X” direction and the gyroscope  400  is being rotated in a clockwise sense about the “Y” axis, the sense masses of the “Y” axis sensors  420  and  430  will exhibit respective displacements along the positive “Z” axis, and so on. 
     Angular senses for clockwise rotations as depicted in the table  500  are as indicated by the orthogonal vectors icon  508 . In turn, the directional responses of the sense masses (i.e., positive or negative) would be the opposite of those indicated for counter-clockwise rotations of the gyroscope  400 . 
     Illustrative Gyroscope and Accelerometer 
     Reference is now made to  FIG. 6 , which depicts a plan schematic view of a three-axis gyroscope and accelerometer (sensing device)  600  in accordance with the present teachings. The sensing device  600  is illustrative and non-limiting with respect to the present teachings. Other suitable sensing devices can be defined and used in accordance there with. The sensing device  600  is depicted in a mutually orthogonal, three-axis frame of reference. In one example, the sensing device  600  is formed so as to define at least a portion of a microelectromechanical systems (MEMS) device. Other configurations or structures according to the present teachings can also be defined and used. 
     The sensing device  600  includes a frame  602  defined, for non-limiting example, by a silicon wafer or other suitable material. The frame  602  overlies a supporting wafer (or substrate)  603 . The sensing device  600  also includes drive masses  604 - 610 , respectively, each defining (or including) respective “X”, “Y” or “Z” axis sensors analogous to those described above (e.g., sensors  416 - 430 ). 
     The drive masses  604 - 610  are coupled to each other by way of substantially rigid extensions  612 , and are suspended within the frame  602  by way of flexures or elastic elements  613  so as to be force oscillated in two orthogonal directions in the X-Y plane. Thus, the sensing device  600  includes a monolithic entity  614  that is analogous in structure and operation to the monolithic entity  414  of the gyroscope  400 . 
     The sensing device  600  also includes respective accelerometers  616 ,  618 ,  620 ,  622  and  624  bonded or anchored to the frame  602 . In particular, the accelerometer  616  provides electrical signaling corresponding to accelerations along the “Z” axis. In turn, the accelerometers  618  and  622  provide electrical signaling corresponding to accelerations along the “Y” axis. Furthermore, the accelerometers  620  and  624  provide electrical signaling corresponding to accelerations along the “X” axis. The drive masses  604 - 610  can be coupled to a structure  617  that is fixed to or extending from the underlying wafer  603  by way of respective elastic or “spring” elements  626 . In another example, the structure  617  and the elastic elements  626  are not present. 
     The sensing device  600  also includes displacement measuring electronic circuitry (circuitry)  628 . The circuitry  628  can include or be defined by a microprocessor, a state machine, an application-specific integrated circuit (ASIC), and so on. The circuitry  628  is configured to receive signals from the respective sense masses and to provide an electronic signaling output  630  to communicate angular velocities in three-space as detected by the sensing device  600 . Such signals can be received from the sense masses by way of capacitive or other suitable detection schemes. 
     The sensing device  600  is configured to provide electrical signaling corresponding to accelerations and angular velocities in three-space. One having ordinary skill in the motion and position sensing or related arts can appreciate that such signals can be digitally quantified, filtered or otherwise processed for use in determining acceleration or velocity, displacement, angular rotation or orientation with respect to a frame of reference, and so on. Non-limiting examples of applications contemplated by the present teachings include cellular or “smart” phones, portable computing devices, geological sensing apparatus, inertial navigation systems, platform or antenna stabilization apparatus, and so on. 
     In general and without limitation, the present teachings contemplate vibratory gyroscopes and sensing devices that include gyroscopes formed and packaged as MEMS devices. Such a gyroscope includes a plurality of drive masses distributed in a plane, each drive mass supporting or formed to define a pair of respective sense masses (i.e., sensors). Each sense mass is coupled by flexure suspension to the corresponding drive mass so as to be defined by a single degree of freedom or displaceable axis. Accelerometers can also be included with a gyroscope within a single MEMS form-factor. 
     Stimulus devices, such as electrostatic drives, are used to forcibly oscillate the drive masses in two orthogonal directions within the plane such that a full gyrating motion is controllably sustained. Rotation of the gyroscope about any one or more of the mutually-orthogonal axis in three-space results in displacement of those respective sense masses configured to react to the corresponding Coriolis forces. 
     Capacitive sensing or other detection determines the respective displacements of the sense masses and electronic signaling corresponding to the displacements is provided. Such signals can be quantified or processed accordingly such that angular velocities, angular accelerations, relative changes in orientation and so on can be determined. Movement, position, rotation, displacement and other characteristics can be determined (e.g., by known mathematical operations such as time integration), recorded and used in any number of apparatus or system in accordance with the present teachings. 
     In general, the foregoing description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent to those of skill in the art upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation and is limited only by the following claims.