Abstract:
An inertial measurement unit is described that includes a first subassembly comprising one or more inertial sensors, a second subassembly comprising support electronics for the one or more inertial sensors, and at least one pair of mating connectors configured to provide an interface between the first subassembly and the second subassembly.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &amp; DEVELOPMENT 
       [0001]    The United States Government has acquired certain rights in this invention pursuant to Contract No. DAAH01-03-C-R314 issued by the Department of the Army. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to packaging of sensor devices, and more specifically, to methods and systems for segregating sensors within a housing. 
         [0003]    Typically, the supporting electronics for sensor devices are intermingled with the sensor devices within a housing. Such sensor devices, for example, gyroscopes, accelerometers and the like, require an extensive, both in time and cost, calibration process. When there is a failure in the supporting electronics, these sensor devices may be disturbed during the removal and replacement process of the failed electronic component(s). Such a disturbance often results in the need to recalibrate the sensor devices. 
         [0004]    Sensor devices and supporting electronics have often been intermingled in order to keep a size of a housing incorporating both within one or more specified dimensions. However, the sizes of supporting electronics are continually being reduced with, for example, multiple discrete components being included into programmable logic devices and the like. The size reduction associated along with other factors have made it possible to consider reconfiguration of the packaging for such sensor based devices. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    In one aspect, an inertial measurement unit is provided that comprises a first subassembly comprising one or more inertial sensors, a second subassembly comprising support electronics for the one or more inertial sensors, and at least one pair of mating connectors configured to provide an interface between the first subassembly and the second subassembly. 
         [0006]    In another aspect, a method for fabricating an inertial measurement unit is provided. The method comprises providing a first subassembly having one or more inertial sensors mounted therein, providing a second subassembly including support electronics therein for the one or more inertial sensors, and interconnecting the first subassembly and the second subassembly to form a housing for the inertial measurement unit. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an illustration of an assembled inertial measurement unit (IMU). 
           [0008]      FIG. 2  is an illustration of a gyroscope, accelerometer, and support electronics subassembly of the IMU of  FIG. 1 . 
           [0009]      FIG. 3  is an illustration of a power supply subassembly of the IMU of  FIG. 1 . 
           [0010]      FIG. 4  is a block diagram of the IMU of  FIG. 1 , depicting boundaries between the subassemblies of  FIGS. 2 and 3 . 
           [0011]      FIG. 5  is a flow diagram illustrating build and rework processes associated with the IMU of  FIG. 1 . 
           [0012]      FIG. 6  is an illustration of an assembled IMU having segregated sensor and support electronics subassemblies. 
           [0013]      FIG. 7  is an illustration of a gyroscope and accelerometer subassembly of the IMU of  FIG. 6 . 
           [0014]      FIG. 8  is an illustration of a support electronics subassembly of the IMU of  FIG. 6 . 
           [0015]      FIG. 9  is a block diagram of the IMU of  FIG. 6 , depicting boundaries between the subassemblies of  FIGS. 7 and 8 . 
           [0016]      FIG. 10  is a flow diagram illustrating build and rework processes associated with the IMU of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]      FIG. 1  is an illustration of a known assembled inertial measurement unit (IMU)  10 . As further described below with respect to  FIGS. 2-4 , IMU  10  includes both a gyroscope, accelerometer, and support electronics subassembly  12  and a power supply subassembly  14 . 
         [0018]      FIG. 2  is an illustration of gyroscope, accelerometer, and support electronics subassembly  12  of IMU  10 . As seen in  FIG. 2 , gyroscope, accelerometer, and support electronics subassembly  12  includes multiple electronic components  20  mounted on a circuit board  22  which are hard wired to the gyroscopes and accelerometers which are mounted beneath circuit board  22 . A plurality of connectors  24  are also mounted on circuit board  22  which provide an interface to external power sources and further provide an interface to external systems that receive the inertial data that is output from IMU  10 . Additionally, connectors  24  also provide an interface for reprogramming and calibration of a processing device which is also mounted on circuit board  22 . 
         [0019]      FIG. 3  is an illustration of power supply subassembly  14  of IMU  10  of  FIG. 1 . Referring again to  FIG. 1 , it is apparent that  FIG. 3  illustrates an underside  30  of power supply subassembly  14 , and that power supply subassembly  14  includes openings  32  that allow power supply subassembly  14  to be placed onto gyroscope, accelerometer, and support electronics subassembly  12 . In this configuration, connectors  24  extend through openings  32  of power supply subassembly  14 . 
         [0020]      FIG. 4  is a block diagram  50  of IMU  10  (shown in  FIG. 1 ). Block diagram  50  illustrates functional boundaries between gyroscope, accelerometer, and support electronics subassembly  12  and power supply subassembly  14  respectively illustrated in  FIGS. 2 and 3 . Power supply subassembly  14  include a power supply  52  which receives power from an external source and converts the received power to levels needed for operation of the various components of gyroscope, accelerometer, and support electronics subassembly  12 . 
         [0021]    Gyroscope, accelerometer, and support electronics subassembly  12  includes three gyroscopes  60 , associated with the three axes, X, Y, and Z, and three accelerometers  62 , also associated with the three axes. Outputs from gyroscopes  60  and accelerometers  62  are typically amplified utilizing respective gain components  64  and  66  whose outputs are input into A/D converter  68 . An output of A/D converter  68  is then provided to a processing device  70 , which is programmed to output data to external systems that is representative of the inertial conditions experienced by gyroscopes  60  and accelerometers  62 . 
         [0022]    While gyroscope, accelerometer, and support electronics subassembly  12  is illustrated as having the five major components described above, those skilled in the art will realize that many additional electronic components are utilized in the fabrication of gyroscope, accelerometer, and support electronics subassembly  12 . Typical examples of such electronic components include protective devices that counteract any electrostatic voltages that may become present on the individual connector contacts, logic for allocating A/D converter  68  among the three gyroscopes  60  and accelerometers  62 , support components for processing device  70 , and the like. 
         [0023]      FIG. 5  is a flow diagram  80  illustrating build and rework processes associated with IMU  10 . Processes include an electronics assembly process  82 , a mechanical assembly process  84 , and a sensor assembly process  86 . An IMU integration process  88  is indicative of the fabrication of the IMU  10 , and specifically, fabrication of gyroscope, accelerometer, and support electronics subassembly  12  and power supply subassembly  14  based on the electronics assembly process  82 , the mechanical assembly process  84 , and the sensor assembly process  86 . IMU integration process  88  is further indicative of the fabrication of the IMU  10  from the completed gyroscope, accelerometer, and support electronics subassembly  12  and power supply subassembly  14 . An IMU environmental process  90  is performed to ensure that the completed IMU  10  is able to withstand the rigorous environment to which it will be exposed during its operation. 
         [0024]    An IMU calibration process  92  is performed to characterize the gyroscopes  60  and accelerometers  62 , such that the data contained within the outputs received from gyroscope, accelerometer, and support electronics subassembly  12  are as expected. As is known, there are variations between individual gyroscopes  60  and accelerometers  62  due to their mechanical nature, and as represented by the flow diagram  80  of  FIG. 5 , the IMU calibration process  92  is the most time consuming of all the processes utilized to build and/or rework an IMU  10 . Upon completion of the IMU calibration process  92 , the IMU IO is accepted for use within a vehicle or other application through an IMU acceptance process  94 . 
         [0025]    There are problems associated with the rework and repair processes associated with IMU  10 . Specifically, when there is a failure in the supporting electronics, the gyroscopes  60  and accelerometers  62 , collectively referred to as sensor devices, may be disturbed during the removal and replacement process of the failed electronic component(s). Such a disturbance often results in the need to recalibrate the IMU  10 . As illustrated in  FIG. 5 , the IMU calibration process  92  is the most time consuming, and likely most expensive, especially when associated with rework of an IMU  10 . 
         [0026]      FIG. 6  is an illustration of an assembled IMU  100  having segregated sensor and support electronics subassemblies. Specifically, and as described in further detail below, IMU  100  includes a gyroscope and accelerometer subassembly  102  and a support electronics subassembly  104 . As also further described below, the segregation of components and packaging may allow, at least for a portion of reworked IMUs  100 , that calibration processes, for example, similar to the above described IMU calibration process, need not be repeated for certain repairs and rework of IMUs  100   
         [0027]      FIG. 7  is an illustration of a gyroscope and accelerometer subassembly  102  of IMU  100 . Gyroscope and accelerometer subassembly  102  includes three gyroscopes  110 ,  112 , and  114 , as well as three accelerometers  120 , which are housed within a single package. A plurality of connectors  130 ,  132 , and  134  are utilized to provide power to gyroscopes  110 ,  112 , and  114  and accelerometers  120 . Connectors  130 ,  132 , and  134  are further configured to conduct the signals originating from gyroscopes  110 ,  112 , and  114 , and accelerometers  120  for further processing before being output from IMU  100  as further described below. 
         [0028]      FIG. 8  is an illustration of support electronics subassembly  104  of IMU  100 . As seen in the Figure, support electronics subassembly  104  includes three connectors  140 ,  142 , and  144  which are configured to mate with connectors  130 ,  132 , and  134  (shown in  FIG. 7 ) effectively interconnecting gyroscopes  110 ,  112 , and  114 , and accelerometers  120  with their support electronics, which is described below with respect to  FIG. 9 . 
         [0029]      FIG. 9  is a block diagram  170  of the IMU of  FIG. 6 , depicting boundaries between the subassemblies  102  and  104  which are respectively shown in  FIGS. 7 and 8 . More specifically, block diagram  170  illustrates functional boundaries between gyroscope and accelerometer subassembly  102  and support electronics subassembly  104 . 
         [0030]    Support electronics subassembly  104  includes a power supply  180  which receives power from an external source and converts the received power to levels needed for operation of the various components of gyroscope and accelerometer subassembly  102  and support electronics subassembly  104 . 
         [0031]    Support electronics subassembly  104  further includes gain components  182  and  184  that receive and amplify outputs from gyroscopes  110 ,  112 , and  114  and accelerometers  120 . Outputs of gain components  182  and  184  are then input into A/D converter  186 . An output of A/D converter  186  is then provided to a processing device  188 , which is programmed to output data to external systems that is representative of the inertial conditions experienced by gyroscopes  110 ,  112 , and  114  and accelerometers  120 . 
         [0032]    Gyroscope and accelerometer subassembly  102  as described herein includes three gyroscopes  110 ,  112 , and  114 , associated with the three axes, X, Y, and Z, and three accelerometers  120 , also associated with the three axes. Output from these sensor devices are respectively input into gain components  182  and  184  (e.g., amplifiers), respectively, as described above. 
         [0033]    While support electronics subassembly  104  is illustrated as having power supply  180 , gain components  182  and  184 , A/D converter  186 , and processing device  188 , those skilled in the art will realize that many additional electronic components are utilized within support electronics subassembly  104 , and that each of the above listed components is fabricated using a number of distinct electronic components. Typical examples of such additional electronic components are described hereinabove, and such examples should not be construed as limiting. 
         [0034]      FIG. 10  is a flow diagram  200  illustrating improved rework processes that are associated with IMU  100  of  FIGS. 6-9 . Specifically, the processes include an electronics assembly process  202 , a mechanical assembly process  204 , and a sensor assembly process  206 . An IMU integration process  208  is indicative of the fabrication of the IMU  100 , and specifically, fabrication of gyroscope and accelerometer subassembly  102  and support electronics subassembly  104  based on the electronics assembly process  202 , the mechanical assembly process  204 , and the sensor assembly process  206 . IMU integration process  208  is further indicative of the fabrication of the IMU  100  from the completed gyroscope and accelerometer subassembly  102 , and support electronics subassembly  104 . An IMU environmental process  210  is performed to ensure that the completed IMU  100  is able to withstand the rigorous environment to which it will be exposed during its operation. Finally, upon completion of the IMU environmental process  210 , the IMU  100  is accepted for use within a vehicle or other application through an IMU acceptance process  212 . 
         [0035]    Contrasted to IMU  10  described above, there is no time consuming and expensive IMU calibration process as there is with IMU  10 . As the gyroscopes and accelerometers are separate from the support electronics, there is no disturbance of these devices as a support electronics subassembly  104  is removed and/or replaced during a repair. 
         [0036]    As explained by the descriptions of the above described embodiments, providing an IMU with segregated housing portions for sensors and support electronics, such as IMU  100 , eliminates or reduces the amount of time for sensor calibration, at least as compared to known IMUs, after a repair or removal process. As the housing portions are segregated, repair and replacement of the support electronics subassemblies to not affect orientations or calibrations of the gyroscopes and accelerometers in the other subassembly. As described above, IMUs that have commingled sensors and support electronics are more likely to have to calibrate their sensors after a repair or replacement of a portion of the support electronics. 
         [0037]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.