Abstract:
A gyroscope assembly comprises a shaft and a flexure device mounted on the shaft. The flexure device includes three concentric plates. A first pair of diametrically opposed hinges connected the inner plate and the central plate. A second pair of diametrically opposed hinges spaced 90° apart from the first pair of hinges connects the outer plate and the inner plate. The hinges define two perpendicular sensing axis and form a gimbal so that rotations of the outer plate about the sensing axes may be detected.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to rotation sensors and particularly to two degree of freedom dry tuned gyroscopes that include a spinning mass, electro-optic signal pickoffs for sensing motion of the gyroscope case relative to the spinning mass and forcing coils with associated magnets to maintain the spinning mass in a fixed orientation relative to the gyroscope case to provide closed loop operation. 
         [0002]    Prior art devices within this gyroscope class utilize a spinning mass that is supported relative to the gyroscope case by a flexure. When the gyroscope case is subjected to angular inputs, the gyroscope case moves relative to the spinning mass. A position transducer determines the change in position of the case relative to the spinning mass. The position transducer and associated electronics produce an electrical signal that is fed to a torquer coil that is mounted on the gyroscope case. A magnet assembly located in the spinning mass produces a magnetic filed that interacts with the current flowing in the torquer coil. This interaction produces a force that restores the spinning mass to a null position. The torquer current provides a measurement of the input angular rate to the gyroscope case. The flexure of the current device is formed of a metal that requires electro-discharge-machining to form the flexure in the required configuration. 
         [0003]    The primary disadvantage of the prior art is the use of separate structures that are combined into one assembly. These separate structures interact to limit performance of the device. Furthermore, the piece parts of the assembly require tight tolerances and costly manufacturing techniques for final assembly. Also current devices require post processing to achieve the required angular spring rates. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides a gyroscope assembly that overcomes the foregoing described deficiencies of the prior art. A gyroscope assembly according to the present invention is an all silicon device comprising a spinning mass, hinges, gimbals and a connecting structure. The gyroscope assembly according to the present invention reduces the number of piece parts and complicated assembly techniques as compared to the prior art. Another advantage of the present invention is that rotational stops are micro-machined and fusion bonded to the gimbal. Micro-machining and silicon bonding processes allow the assemblies to be produced in a low cost batch process and provide the ability to tune the angular spring rate without using a post machining tuning process. The all-silicon structure of the present invention minimizes mechanical stresses developed over the operating temperature range, which provides improved performance. The present invention includes a metallization pattern on the rotor, which provides a simplification of the rotor angular position sensor, or pickoff. 
         [0005]    A gyroscope assembly according to the present invention comprises a shaft and a flexure device mounted to the shaft. The flexure device has an inner flexure portion formed generally as a thin cylindrical plate having a central passage therethrough. The flexure device is mounted on the shaft so that the shaft passes through the central passage. The flexure device further includes an outer flexure portion formed as a thin cylindrical plate having a central opening having a diameter such that the inner flexure portion fits within the central opening spaced apart from the outer flexure portion. A first hinge is arranged to join a first outer edge portion of the inner flexure portion with a first inner edge portion of the outer flexure device. A second hinge is arranged to join a second outer edge portion of the inner flexure portion with a second inner edge portion of the outer flexure device. The outer flexure portion has a rotational degree of freedom about a sensing axis defined by a line through the first and second hinges. 
         [0006]    The flexure device preferably includes a first inner flexure passage spaced radially inward from the first hinge arranged to form a first thin-walled inner flexure portion near the first hinge and a second inner flexure passage is spaced radially inward from the second hinge to form a second thin-walled inner flexure portion near the second hinge. A first outer flexure passage is spaced radially outward from the first hinge arranged to form a first thin-walled outer flexure portion near the first hinge, and a second outer flexure passage spaced radially inward from the second hinge arranged to form a second thin-walled outer flexure portion near the second hinge. 
         [0007]    The gyroscope assembly of claim according to the present invention preferably has a rotor mounted on an outer rim portion of the outer flexure portion. 
         [0008]    The gyroscope assembly according to the present invention may alternatively comprise a laminated rotor mounted on the outer flexure portion near the outer rim. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an exploded perspective view of a two degree of freedom gyroscope assembly according to the present invention; 
           [0010]      FIG. 2  is a cut away perspective view of the assembled gyroscope assembly of  FIG. 1 ; 
           [0011]      FIG. 3  is a top plan view of the gyroscope assembly of  FIGS. 1 and 2 ; 
           [0012]      FIG. 4  is a bottom perspective view of a flexure device that may be included in the invention as shown in  FIGS. 1-3  with a surface metallization formed thereon; 
           [0013]      FIG. 5  is a cross sectional view of the invention as shown in  FIGS. 1-4 ; 
           [0014]      FIG. 6  is a cut away perspective view of a two degree of freedom gyroscope assembly according to the present invention having a laminated rotor; 
           [0015]      FIG. 7  is a perspective view of the two degree of freedom gyroscope assembly of  FIG. 6 ; 
           [0016]      FIG. 8  is a cross sectional view of the embodiment of the invention shown in  FIGS. 6 and 7 ; 
           [0017]      FIG. 9  is a cut away perspective view of a one degree of freedom gyroscope assembly according to the present invention; 
           [0018]      FIG. 10  bottom plan view of the embodiment of the invention shown in  FIG. 9 ; 
           [0019]      FIG. 11  is a top plan view of the invention as shown in  FIG. 9 ; and 
           [0020]      FIG. 12  is a cross sectional view of the embodiment of the invention shown in  FIGS. 9-11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  is an exploded perspective view of a gyroscope assembly  20  according to the present invention. A flexure device  22  formed generally as a thin cylinder having a central passage  24  therethrough is mounted on a shaft  26 . The shaft  26  is preferably formed as a stepped cylinder having a base  28 . The shaft  26  includes a mounting post  30  having a diameter smaller than the base diameter extending perpendicularly from the base  28 . The shaft  26  and the base  28  are axially aligned. A rotor  23  may be connected to an outer edge  25  of the flexure device. 
         [0022]    A first stop device  32  is mounted on the mounting post  30 . The stop device  32  formed generally as a thin plate having a plurality of substantially identical vanes  34 - 37  extending from a central region  40 . A cylindrical passage  42  having a diameter that is approximately identical to the diameter of the mounting post  26  is formed in the central region  40 . The vanes  34 - 37  preferably are spaced 90° apart around the central region  40 . The central region  40  is thicker than the vanes  34 - 37  and has a hub  41  around the passage  42  and facing a central region  43  (shown in  FIG. 2 ) of the flexure device  22 . The vanes  34 - 37  thus are spaced apart by a small gap  45  from the flexure device  22 . 
         [0023]    The central passage  24  of the flexure device  22  also has a diameter that is substantially identical to the diameter of the mounting post  30 . As shown in  FIGS. 1 ,  2  and  5 , the flexure device  22  is mounted on the shaft  26  such that the first stop device  32  is between the flexure device  22  and a ledge  44  formed at the juncture of the base  28  and the mounting post  30 . A second stop device  46  that preferably is substantially identical to the first stop device  32  is mounted on the mounting post  30  such that the flexure device  22  is retained between the first and second stop devices  32  and  48 . 
         [0024]    A plurality of vanes  48 - 51  extend from a central region  54  of the second stop device  46 . The second stop device  46  also includes a hub  56  around a central passage  58 . The hub contacts a portion  60  of the flexure device  22  to form a small gap  57  between the vanes  48 - 51  and a surface  62  of the flexure device  22 . 
         [0025]    Referring to  FIGS. 1-5 , the flexure device  22  may be seen to comprise an inner section  22 A, an intermediate section  22 B and an outer section  22 C. The inner section  22 A is connected to the intermediate section  22 B via a pair of hinges  62  and  64 . Except for the hinges  62  and  64 , the inner section  22 A and the intermediate section  22 B are separated by a pair of arcuate passages  66  and  68  formed in the flexure device  22 . The hinges  62  and  64  are preferably located 180° apart and are sized such that the arcuate passages  66  and  68  are nearly semicircular. The hinges  62  and  64  may have a generally T-shaped cross sections. 
         [0026]    A pair of passages  70  and  72  is formed in the inner section  22 A radially spaced by small distances from the inner sides of the hinges  62  and  64 , respectively. Another pair of passages  74  and  76  is formed in the intermediate section  22 B radially spaced by small distances from the outer sides of the hinges  62  and  64 , respectively. The passages  70  and  72  cooperate with the passages  66  and  68  to form thin-walled portions  78  and  80  as shown in  FIG. 3  in the inner flexure section  22 A near the inner sides of the hinges  62  and  64 . The passages  74  and  76  cooperate with the passages  66  and  68  to form thin-walled portions  82  and  84  in the intermediate flexure section  22 B near the outer sides of the hinges  62  and  64 . 
         [0027]    Referring to  FIG. 3 , the hinge  62  may be formed as a thin bridge  63  connecting the inner flexure section  22 A and the intermediate flexure section  22 B between the thin-walled portions  78  and  80 . The hinge  64  may be formed as a thin bridge  65  connecting the inner flexure section  22 A and the intermediate flexure section  22 B between the thin-walled portions  82  and  84 . 
         [0028]    The gyroscope assembly  20  also includes a pair of hinges  90  and  92  between the intermediate flexure section  22 B and the outer flexure section  22 C. The hinge  90  is formed as a bridge  94  between a first thin-walled section  96  of the intermediate flexure section  22 B and a second thin-walled section  98  of the outer flexure section  22 C. The hinge  92  is formed as a bridge  100  between a first thin-walled section  102  of the intermediate flexure section  22 B and a second thin-walled section  104  of the outer flexure section  22 C. Except for the hinges  90  and  92 , the intermediate flexure section  22 B and the outer flexure section  22 C are separated by a pair of arcuate passages  106  and  108  in the flexure  22 . 
         [0029]    A pair of passages  110  and  112  is formed in the intermediate section  22 B radially spaced by small distances from the inner sides of the hinges  92  and  94 , respectively. Another pair of passages  114  and  116  is formed in the outer section  22 C radially spaced by small distances from the outer sides of the hinges  92  and  94 , respectively. The passages  110  and  112  cooperate with the passages  106  and  108  to form the thin-walled portions  96  and  98  in the intermediate flexure section  22 B near the inner sides of the hinges  92  and  94 . The passages  114  and  116  cooperate with the passages  106  and  108  to form the thin-walled portions  102  and  104  in the intermediate flexure section  22 B near the outer sides of the hinges  106  and  108 . 
         [0030]    Referring to  FIGS. 1-5 , the intermediate flexure section  22 B has an inner edge  120  that is supported by the pair of hinges  62  and  64  and an outer edge  122  that is supported by the pair of hinges  92  and  94 . The hinges  62  and  64  are arranged to be diametrically opposite one another. The hinges  92  and  94  are also diametrically opposite one another and are angularly displaced by 90° from the hinges  62  and  64 . The hinges  62 ,  64 ,  92  and  94  have a degree of compliance such that the intermediate flexure section  22 B functions as a gimbal for displacements. 
         [0031]    As shown in the  FIG. 4 , the inner flexure portion  22 A includes a plurality of projections  124 - 127  extending radially outward therefrom. The projections  124  and  125  extend into the passage  66 , and the projections  126  and  127  extend into the passage  68  toward the inner edge  120  of the central flexure section  22 B. The outer flexure section  22 C includes radially extending projections  130 - 133 . The projections  130  and  131  extend radially inward into the passage  106  toward the outer edge  122  of the central flexure portion  22 B. The projections  124 - 127  and  130 - 133  function as stops to limit radial displacement of the central flexure portion  22 B. 
         [0032]    Referring to  FIG. 4 , the gyroscope assembly  20  includes a metallization layer  136  formed on a portion  138  of the outer flexure assembly  22 C. The metallization layer  136  is used to form a pickoff for signals that may be processed to determine the rotation rate detected by the gyroscope assembly  20 . 
         [0033]    The rotor  23  may be formed generally as a thin walled cylinder having an inner wall  140  that is fastened to an outer edge portion  142  of the outer flexure section  22 C. Thus, the rotor  23  and the outer flexure section  22 C are mounted to the gimbal formed by the central flexure section  22 B. As shown in  FIGS. 2 and 5 , the rotor  23  may include a ledge  144  formed in the inner wall  140  to aid in forming a secure connection between the rotor  23  and the outer edge  142  of the outer flexure section  22 C. 
         [0034]    The outer flexure portion  22 C has two rotational degrees of freedom defined by lines extending through the inner opposing hinge pair  62 ,  64  and the outer hinge pair  90 ,  92 . Rotation about these axes is detected as being a change in a capacitance determined by the position of the pickoff metallization layer  136 . In a preferred embodiment of the invention the outer flexure section  22 B may have an angular displacement of about 0.5° about rotational axes defined by the two hinge pairs  62 ,  64  and  90 ,  92 . Upon detection of a rotation, a feedback signal is applied to null the signal pickoff output. The feedback signal is processed to determine the rotation rate. 
         [0035]      FIGS. 6-8  illustrate an alternative embodiment of the invention that includes a laminated rotor  150  that comprises a first silicon layer  152  placed on a first surface portion  154  near the outer edge  25  of the outer flexure section  22 C. A first metallization layer  156  is formed on an outer surface  158  of the first silicon layer  152 . The laminated rotor  150  also includes a second silicon layer  160  placed on a second surface portion  162  near the outer edge  25  of the outer flexure section  22 C. A second metallization layer  164  is formed on an outer surface  166  of the first silicon layer  160 . 
         [0036]    Except for having the laminated rotor  150  instead of the one-piece rotor  23 , the embodiment of the invention shown in  FIGS. 6-8  is substantially identical to the embodiment shown in  FIGS. 1-5 . 
         [0037]      FIGS. 9-12  illustrate a one-degree of freedom gyroscope assembly  170 . The gyroscope assembly  170  includes a flexure assembly  172 . The flexure assembly  172  is formed to comprise an inner flexure section  174  and an outer flexure section  176 . A mounting post  28  passes through a central passage  178  in the inner flexure section  174 . Stop devices  32  and  46  are mounted on the mounting post  28  as described above with reference to  FIGS. 1-3  and  5 . 
         [0038]      FIG. 10  is a bottom plan view of the gyroscope assembly  170  showing a pickoff metallization  177  formed on the outer flexure section  176 . 
         [0039]    Passages  180  and  182  are formed between the inner flexure section  174  and the outer flexure section  176 . Hinges  184  and  186  extend between the inner flexure section  174  and the outer flexure section  176 . A pair of passages  190  and  192  is formed in the inner flexure section  174  radially spaced by small distances from the inner sides of the hinges  184  and  186 , respectively. Another pair of passages  194  and  196  is formed in the outer flexure section  176  radially spaced by small distances from the outer sides of the hinges  184  and  186 , respectively. The passages  190  and  192  cooperate with the passages  180  and  182  to form thin-walled portions  200  and  202  in the inner flexure section  174  near the inner sides of the hinges  184  and  186 . The passages  194  and  196  cooperate with the passages  180  and  182  to form thin-walled portions  204  and  206  in the outer flexure section  176  near the outer sides of the hinges  106  and  108 . The hinges  184  and  186  are spaced apart by 180° so that the outer flexure portion  174  has a single rotational degree of freedom about a line extending through the hinges  184  and  186 . 
         [0040]    The gyroscope assembly  170  includes a plurality of radial displacement  210 - 213  stops that limit the range of radial movement of the inner flexure section  174  relative to the outer flexural section  176 . 
         [0041]    The various components of the invention are preferably fabricated using Micro-Electro-Mechanical Systems (MEMS) techniques. MEMS is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology. While electronics are typically fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes), micromechanical components are fabricated using compatible “micromachining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.