Abstract:
A three axes MEM accelerometer system includes three MEM accelerometer sensors and a MEM sensor board including a MEM sensor control circuit for the accelerometer sensors. The accelerometer sensors are mounted mutually orthogonally. At least two coplanar mounting members have a first surface coplanar with a connection pad on the surface of the sensor board. A second surface is inclined to the surface of the board for mounting a MEM accelerometer sensor. An electrical conductor array interconnects the MEM accelerometer sensor with the connection pad on the board.

Description:
RELATED APPLICATIONS AND PRIORITY CLAIM 
       [0001]    This application is a divisional application of prior U.S. patent application Ser. No. 10/142,127 filed on May 9, 2002, which is hereby incorporated herein by reference, and to which this application claims priority. 
     
    
     RELATED APPLICATIONS 
       [0002]    This invention was made with U.S. Government support under Contract No. F33615-98-C-108 awarded by DARPA MMIMU. The Government may have certain rights in the subject invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    This invention relates to a coplanar mounting member for a MEM sensor, and more particularly such to a member for use in three axes MEMs systems such as accelerometers and gyroscopes. 
       BACKGROUND OF THE INVENTION 
       [0004]    Micro-electro-mechanical (MEM) sensors such as gyroscopes, accelerometers, vibration sensors, and microphones must be mounted in close proximity to an application specific integrated circuit (ASIC) control chip to realize optimum instrument performance. The path length of sensitive electrical nodes is typically held to 0.25 inches or less to minimize parasitic capacitance and noise susceptibility. This requirement, combined with the need to measure rotation or acceleration along three orthogonal axes in micromechanical inertial sensor assemblies (MMISA) has constrained system architectures to those typified by the competent munition advanced technology demonstration (CMATD) system shown in  FIG. 1 . 
         [0005]    The MMISA in  FIG. 1  occupies approximately 8 in 3  of the 16 in 3  available volume of the device. In order to reduce this volume it has been proposed to place each instrument at an angle. For example, in CMATD systems, the three gyro and three accel instruments are mounted on separate circuit boards which are in turn mounted orthogonal to each other. A circuit backplane and flexible cabeling are used to interconnect these six instruments. In order to reduce this volume it has been proposed to place the three gyro instruments onto a single circuit board and the three accel instruments onto single circuit board, which allows for a substantial reduction in redundant component. The challenge is in mounting the three gyro and three accel sensor devices orthogonal to each other on a coplanar surface while maintaining the close proximity to their associated ASICs. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of this invention to provide an improved coplanar mounting member for a MEM sensor. 
         [0007]    It is a further object of this invention to provide such an improved coplanar mounting member which reduces the size of MEM sensor systems such as inertial guidance systems. 
         [0008]    It is a further object of this invention to provide such an improved coplanar mounting member which reduces the redundancy in the MEM sensor control circuits. 
         [0009]    It is a further object of this invention to provide such an improved coplanar mounting member which reduces the cost of such MEM sensor systems through reduction in number of components, enables less complex cabling, and improves reliability. 
         [0010]    It is a further object of this invention to provide such an improved coplanar mounting member which permits the same MEM sensor to be used for in plane and out-of-plane sensing, e.g., three identical gyroscopes or three identical accelerometers. 
         [0011]    It is a further object of this invention to provide such an improved coplanar mounting member which avoids the instability of the sense axes of non-coplanar mounted MEM sensors. 
         [0012]    The invention results from the realization that more compact smaller, and more reliable MEM sensor systems can be made using one or more coplanar mounting members which include a first surface coplanar with a connection pad on the surface of a MEM sensor board containing the MEM sensor controls circuits, a second surface inclined to the surface of the board for mounting a MEM sensor and an electrical conductor array for interconnecting the MEM sensor with the connection pad on the board. 
         [0013]    This invention features a coplanar mounting member for a MEM sensor including a first surface coplanar with a connection pad on the surface of the MEM sensor board containing the MEM sensor control circuit. There is a second surface inclined to the surface of the board for mounting a MEM sensor and an electrical conductor array for interconnecting the MEM sensor with the connection pad on the board. 
         [0014]    In a preferred embodiment the second surface may be inclined at approximately 35°, 54°, or at 90° to the board. The MEM sensor may be an inertial sensor and may be a gyroscope sensor or an accelerometer sensor. The sensor board may include an ASIC; the MEM sensor may be integral with the second surface. 
         [0015]    The invention also features a three axes MEMs accelerometer system including three MEM accelerometer sensors and a MEM sensor board including a MEM sensor control circuit for the accelerometer sensors. The accelerometer sensors are mounted mutually orthagonally. There are at least two coplanar mounting members having a first surface coplanar with a connection pad on the surface of the sensor board. The second surface is inclined to the surface of the board for mounting a MEM accelerometer sensor. An electrical conductor array interconnects the MEM accelerometer sensor with the connection pad on the board. 
         [0016]    In a preferred embodiment there may be two coplanar mounting members and the second surface may be inclined at approximately 90°. There may be three coplanar mounting members and each may have a second surface inclined at approximately 54°. 
         [0017]    The invention also features a three axes MEMs gyroscope system including three MEM gyroscope sensors and a MEM sensor board including a MEM sensor control circuit for the gyroscope sensors. The gyroscopes are mounted mutually orthogonally. There is at least one coplanar mounting member having a first surface coplanar with a connection pad on the surface of the sensor board and a second surface inclined to the surface of the board for mounting a MEM gyroscope sensor. There is an electrical conductor array for interconnecting the MEM gyroscope sensor with the connection pad on the board. 
         [0018]    In a preferred embodiment there may be one coplanar mounting member and the second surface may be approximately 90°. There may be three coplanar mounting members and each second surface may be at approximately 35°. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]    Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
           [0020]      FIG. 1  is a three dimensional schematic view of a prior art inertial guidance system in a typical application in a tactical missile; 
           [0021]      FIG. 2  is a schematic top view of a three axes gyroscope instrument using a coplanar mounting member according to this invention; 
           [0022]      FIG. 3  is a schematic bottom view of the device in  FIG. 2 ; 
           [0023]      FIG. 4  is a view similar to  FIG. 2  of an alternative embodiment of a gyroscope system using three coplanar mounting members according to this invention; 
           [0024]      FIG. 5  is a side schematic sectional elevational view of the device of  FIG. 4 ; 
           [0025]      FIG. 6  is a schematic bottom view of two axes accelerometer instruments using two coplanar mounting members according to this invention; 
           [0026]      FIG. 7  is a schematic top view of the device of  FIG. 6 ; 
           [0027]      FIG. 8  is a view similar to  FIG. 6  of an alternative embodiment of the three axes accelerometer system using three coplanar mounting members according to this invention; 
           [0028]      FIG. 9  is a side schematic sectional elevational view of the device of  FIG. 8 ; 
           [0029]      FIG. 10  is a three dimensional view of a coplanar mounting member according to this invention which may be used in the systems of  FIGS. 2-9 . 
           [0030]      FIG. 11  is a view similar to  FIG. 10  of an alternative embodiment of a coplanar mounting member according to this invention; and 
           [0031]      FIG. 12  is a view similar to that of  FIGS. 10 and 11  of a coplanar mounting member according to this invention whose second surface for mounting a MEM sensor is at 90°. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    There is shown in  FIG. 1  a typical prior art inertial guidance system  10  including a three axes gyroscope system  12  and a three axes accelerometer system  14  mounted in the body  16  of tactical missile  18 . Three axes gyroscope system  12  includes three separate gyroscope instruments,  20 ,  22 , and  24 , which are arranged in mutually perpendicular planes. Each gyroscope instrument  20 ,  22  and  24  includes its own gyroscope MEM sensor which is an in-plane sensor. That is, the sensing axis of each of the MEM sensors  20 ,  22 ,  24  is within the plane of the instrument which also contains the associated control circuits. The three axes accelerometer system  14  includes three accelerometer instruments,  26 ,  28  and  30 . Together the six instruments make up an inertial guidance system which occupies approximately 8 cubic inches of the available 16 cubic inches in the body  16 . The accelerometers sense out-of-plane or normal to the plane of their instrument which also contains a control circuit. In addition these instruments typically include an application specific integrated circuit (ASIC) usually on the back side of the instrument. The instrument has a control circuit related to the sensor on one side and on the other, the associated ASIC, and the support layer between may be a printed circuit board, or laminar structure, a ceramic board, or any other kind of suitable support structure. 
         [0033]    In accordance with this invention a single printed circuit board or other support structure  40 ,  FIGS. 2 and 3 , can be used to support all three MEM sensors, such as gyroscope sensors  42 ,  44  and  46 . Gyroscope sensors  42  and  44  sense g x  (arrow  43 ) direction and g y  (arrow  45 ) direction, respectively, and are mounted directly on connection pads  48  and  50 , which are interconnected with the rest of the control circuitry  52  on board  40 . In order for the third MEM&#39;s gyroscope sensor  46  to provide the mutual perpendicularity sense g z  direction (arrow  47 ) as required, it is mounted on a surface  53  of coplanar mounting member or wedge  54 . The lower surface  55  of mounting member  54  is mounted to connection pad  56 . Also visible in  FIG. 3  is the ASIC circuits  62 . Because of the compact construction shown in the device of  FIGS. 2 and 3  a number of redundant components can be eliminated in the control circuit which is made to serve all three sensors  42 ,  44  and  46 . The three ASICs  62 , one associated with each of the MEM sensors are located on the bottom of printed circuit board or other support  40 . 
         [0034]    In  FIGS. 2 and 3  the MEM gyroscope sensor  46  is shown mounted vertically on a coplanar mounting member  54  or perpendicular, to the plane of the board  40 . This is not a necessary limitation of the invention. For example, as shown in  FIGS. 4 and 5 , three wedges or coplanar mounting members  70 ,  72  and  74  can be mounted directly to connection pads  76 ,  78  and  80  on board  82 . Each wedge or coplanar mounting member  70 ,  72 ,  74  connects on one surface with its associated connection pad  76 ,  78 , and  80 , and on its second surface, with the gyroscope sensor  84 ,  86  and  88 , respectively. In the plan view of  FIG. 4  it can be seen that the three wedges  70 ,  72 , and  74 , and their associated MEM&#39;s gyroscope sensors  84 ,  86  and  88  are spaced a 120° apart. In addition, in three dimensional space they are mutually orthogonal as shown in  FIG. 5 . The arrows  90 ,  92 , and  94  indicate the direction of sense of each of the MEM gyroscope sensors. 
         [0035]    Also shown in  FIG. 5  are the mounting surfaces  100  and  102  of mounting member  72  and mounting surfaces  104  and  106  of mounting member  74 . Note: all the mounting members  70 ,  72 ,  74  have an angle of approximately 35° to maintain the 90° mutual perpendicularity required of the three MEM gyroscope sensors. Also shown in  FIGS. 4 and 5  are the control circuit  81  and ASIC circuits  108 . 
         [0036]    Although thus far the invention has been described with respect to a three-axes gyroscope system, it may also be used to create a three-axes accelerometer system as shown in  FIGS. 6 and 7 , where printed circuit board  120  contains typical sensor control circuit  122  and three connection pads  124 ,  126 , and  128 . Pad  124  contacts a coplanar mounting member  130  whose first surface contacts connection pad  124  and whose second surface  134  receives MEM&#39;s accelerometer sensor  136 . Connection pad  126  receives the first surface  138  of coplanar mounting member  140  whose second surface  142  receives MEM accelerometer sensor  144 . The third MEM sensor  146  does not require a special coplanar mounting member but mounts directly to connection pad  128 . The accelerometers all have out of plane or perpendicular sensing axes a x , a y , a z ; thus MEM accelerometer sensors  144  and  136  sense in the X and Y axis, respectively, to board  120 , while the MEM sensors  146  senses in Z axis direction with respect to board  120 . Again, the associated ASICs  160  are mounted on the underside of board  120 . 
         [0037]    In an alternate embodiment,  FIGS. 8 and 9 , each of the MEM&#39;s accelerometer sensors  170 ,  172 , and  174  is mounted on a coplanar mounting member  176 ,  178  and  180 , which mount to connection pads  182 ,  184 , and  186  on printed circuit board  188 , which also contains the electronic circuits  190  associated with the MEM accelerometer sensors. These three MEM sensors  170 ,  172 , and  174  are spaced a 120° apart on board  188  and as can be seen from  FIG. 9 , they are mutually perpendicularly mounted by virtue of their approximately 54° angle in each of the wedges. 
         [0038]    The sense axes  200 ,  202 , and  204  of each of the MEM accelerometer sensors  170 ,  172 , and  174  are perpendicular to the plane of those sensors and are mutually perpendicular to each other as can be seen in  FIG. 9  where the wedges have the angle of approximately 54° to board  188  in order to create the mutual perpendicularity between the three axes  200 ,  202 , and  204 . Also shown in  FIG. 9  is the presence of the associated ASICs  210  on the underside of board  188 . 
         [0039]    The coplanar mounting member of this invention may include a ceramic wedge  220 ,  FIG. 10 , which has a first surface  222 , for mounting to a connection pad, and a second surface  224  for receiving a MEM sensor  226  of whatever type. An array of conductors  228  is provided to interconnect the sensor  226  with the appropriate connection pad at first surface  222 . The angle of the wedge as shown at  230  may be approximately 35° for a gyroscope sensor, or approximately 54° for an accelerometer sensor. More accurately, those angles are 35.688° and 54.312°, respectively. Although in  FIG. 10  the wedge  220  and MEM sensor  226  are shown as discrete parts, this is not a necessary limitation of the invention, for, as shown in  FIG. 11 , the MEM sensor  226   a  may be formed integrally as a part of surface  224   a  of wedge  220   a . The second surface for mounting the MEM sensor is not limited to approximately 35° or approximately 54° or any other specific angle. For example, it can be any angle, including 90°, as shown at angle  230   b ,  FIG. 12 , such as where it is used in the embodiments of  FIGS. 2 and 3 , or  FIGS. 6 and 7 , or as shown in  FIG. 12 , where the sensor  226   b  and wedge  220   b  are once again shown as discrete parts. 
         [0040]    Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
         [0041]    Other embodiments will occur to those skilled in the art and are within the following claims: