Abstract:
Disclosed is a data recorder for munitions. The data recorder includes a power source, a processor, and an acceleration sensor. The data recorder further includes a trigger validation feature which is operably coupled to the data recorder to verify the occurrence of a secondary environmental/input event. This envisioned data recorder can contain a digital or analog device as a primary or secondary trigger. Data from an accelerometer is stored in FRAM memory.

Description:
FIELD 
     The present disclosure relates to a data recorder for munitions and, more particularly, to a data recorder capable of withstanding in high deceleration forces during a munition impact event. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. A method currently exists for recording acceleration and deceleration (analog) events and discrete electrical signals (digital) for various munitions. This method consists of assembling three main items. These items are the actual data recorder in the form of a processor, a power source, and an acceleration sensor or sensors. As seen in  FIG. 1 , all three of these components are typically electrically connected with wires. 
     Sometimes, the data recorder, power source, and acceleration sensor or combinations of these components are installed in a separate housing instead of “floating” inside an available cavity. In this case, the separate housing is typically filled with wax and/or glass beads or equivalent supporting media. In some cases, cabling/wires that extend outside of the test article are connected to some/all of the components for power and communication. In general, it is difficult to assemble the items discussed above due to the fact that these items are generally placed in a munition as an afterthought. Often, these assemblies are rather unsophisticated and use, for example, wooden dowels and tape have been used to assemble the battery, data recorder, and sensor together prior to placement into a warhead. Subsequent installation of the wax/glass beads, to increase the likelihood the assembly will survive, leads to significant room for error, i.e. insufficient fill leading to movement of components resulting in broken wires. Wax/glass beads are messy to work with and typically require clean up of the work area after initial installation. Disassembly of the items from the projectile is also challenging. Often wires will break during disassembly, possibly leading to component damage and, more importantly, the loss of test data stored in volatile memory. 
     In the prior art system discussed above, the data recorder starts to acquire and permanently store data after it has received an external signal. This signal can be caused, for example, by a circuit that is closed (or opened) after a munition is launched or impacts a surface. The circuit is typically closed (or opened) by way of an acceleration sensing switch composed of a mass, a spring and an electrical contact(s). When the acceleration becomes large enough, the mass overcomes the counteracting force from the spring thus closing (or opening) the circuit through the electrical contact(s). 
     Most current data recorders require power to be applied to the data recorder at all times during and after the event of interest. If power to the data recorder module is lost at any time, all the data is lost. This is due to what is known as “volatile memory” or memory that requires power to be maintained after it has been recorded. For current data recorders that use non volatile (EEPROM or flash based) memory, any loss in power during an impact event causes a complete loss of data. This occurs because the data is not actually permanently recorded onto the non-volatile memory until the end of the event. Memory write speeds prevents the “real time” recording of this data in EEPROM during an actual impact event. Additionally, current data recorders rely on only one trigger event to start the recording sequence. This means that a false/premature trigger event can lead to capturing erroneous data. 
     As such, the current data recording prior art systems offer the following disadvantages: 1) Items are placed in a munition as an “after thought” causing improperly supported assemblies leading to an increased risk of broken wires and data recorder component damage; 2) Difficulty installing and controlling the supporting fill, leading to possible movement of components, thus leading to broken components/wires; 3) Failure of the external power source, i.e. a broken battery leads during an impact event lead to partial or total loss of data; 4) Disassembly can cause components to be damaged, power to be lost, and requires clean up due to wax/glass beads; 5) Momentary/permanent loss of power for volatile memory and EEPROM/Flash non volatile memory to the data recorder (i.e. broken power wire, damaged battery etc.) can lead to total loss of data; and 6) A premature trigger event can lead to incorrect data being permanently recorded. 
     It is an object of the present teachings to provide a data recording assembly for munitions that integrates the power source, data recorder, and sensors in a package that overcomes at least one of these problems above. Additionally this data recorder contains features that are intended to increase the probability that as much data as possible will be recovered after an impact event. These features and a general description of the device are discussed below. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     Disclosed is a data recorder for munitions. The data recorder includes a power source, a processor, and an acceleration sensor. The data recorder further includes a trigger verification module or validation feature which is operably coupled to the data recorder to verify the occurrence of a secondary environmental/input event. This envisioned data recorder can contain a digital or analog device as a primary or secondary trigger. 
     In another embodiment, the data recorder utilizes a power supply, an accelerometer sensor, and a processor. Associated with the processor is a ferroelectric or FRAM memory, which is used to record signals indicative of measurements from the acceleration sensor. The acceleration data is stored within the FRAM in real time. 
     In another embodiment of the invention, a data recorder for munitions is provided which utilizes an internal power system. The internal power system has a secondary power supply in the form of a bank of capacitors which are directly coupled to the processor and sensors and are utilized during an impact event should power from the intended power source be interrupted during a deceleration event. 
     In another embodiment, a data recorder system for recording the deceleration of a munition is disclosed. The munition has a primary deceleration axis. The system has a plurality of electrical connections between power, control, and sensor modules. At least one of the electrical connections have pin and socket interfaces where the pin and socket are generally parallel to the primary deceleration axis. 
     In another embodiment, the munitions data recorder is provided having a power module, a processor, and a first accelerometer module. Disposed between the accelerometer module and its sensors are a plurality of pin and socket interfaces. The pin interface between the sensor and the accelerometer module is generally disposed along a primary deceleration axis. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present invention. 
         FIG. 1  represents a prior art munition and data recorder construction; 
         FIG. 2  represents the deceleration curve for a munition impact having a launch impact event; 
         FIG. 3  represents an exterior view of the data recorder according to the present teachings; 
         FIG. 4  represents a cross-sectional view of the data recorder shown in  FIG. 3 ; 
         FIGS. 5 and 6  represent top and bottom views of the sensor module shown in  FIG. 3 ; 
         FIG. 7  represents an interface of the modules; 
         FIGS. 8 and 9  represent perspective views of the sensor module with its casing removed; 
         FIGS. 10 and 11  represent top and bottom perspective views of the data recorder module shown in  FIG. 3 ; 
         FIGS. 12 and 13  represent top and bottom perspective views of the power source shown in  FIG. 3 ; 
         FIG. 14  represents an accelerometer module plugged into a sensor module circuit; 
         FIGS. 15   a - 15   c  represent perspective views of an accelerometer module using a surface mount accelerometer; 
         FIG. 15   d  shows an accelerometer module using an accelerometer that has wire leads; 
         FIG. 16   a - 16   b  represent perspective views of the interface wiring between the module and exterior systems; 
         FIG. 17  represents a diagram of an interface connection of the data acquisition module, the data recorder; the external power source and the communications input/output; 
         FIG. 18  represents a graphical user interface (GUI) to program the data recorder shown in  FIG. 3 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Generally, the munitions data recorder  20  and associated components shown in  FIGS. 4-17 , are designed specifically to survive a munition&#39;s impact or launch in a particular orientation. The teaching herein, however, can be applied to data recording in munitions having any orientation. The munition data recorder  20  is generally formed of a sensor module  22 , data recorder module  24 , and power supply  26 . 
       FIG. 2  represents tri-axial data readout from a munitions launch. As can be seen, one data channel exhibits significantly higher acceleration than the other channels. This higher acceleration represents acceleration along the primary acceleration axis  33  during an impact event. 
     As shown in  FIGS. 5-9 , the sensor module  22  is responsible for housing the accelerometer(s)  23  and associated signal conditioning circuitry  25 . Optionally, this module holds four accelerometers  23  (two axial and two lateral). The sensor module  22 , however, is not limited to this configuration, but it can be configured as desired to hold any number of accelerometers  23  in any desired orientation. The other configurations may not have the benefits described below. 
       FIG. 7  represents the coupling of the sensor module  22  with the data recording module  24 . Shown is the use of interface pins and sockets which are generally parallel to the primary deceleration axis. This interface can be a Mill-Max receptacle, part number 0351-0, and the pins are based on Mill-Max part number 3124. Optionally, additional accelerometer modules can be coupled to the sensor module at an axis generally perpendicular to the primary deceleration axis. This interface allows the selective attachment of a plurality of different accelerometers to the processor. 
     The sensor module  22  contains power conditioning circuitry  25  that provides the power to the entire data recorder. It additionally can contain a bank of capacitors, or batteries, that will act as a secondary source of power for the module for up to ˜75 ms if power from the power source module  26  is lost. The sensor module  22  also is responsible for passing electrical signals from the external interface to data recorder module  24  and power to the power supply module  26  through appropriate pin/socket interfaces  29 . 
     As shown in  FIGS. 10 and 11 , the data recorder module  24  which is electrically and physically coupled to the sensor module  22 , is responsible for processing and storing analog and digital data acquired from the accelerometers  23  and other pre-defined inputs. Optionally, the data recorder module  24  accepts four analog and five digital inputs and one digital output, but has the capability for expansion. Additionally, two independent secondary triggers are also available through the digital inputs (not shown). 
     Upon application of power to the recorder module  24 , following configuration, the recorder module  24  begins recording pre-event data and awaiting a trigger signal from an accelerometer  23  and/or from at least one independent trigger defined by the configuration settings. While awaiting a trigger signal, the data can be stored in a continuous “first in first out” FIFO loop within memory using the memory size defined by the configuration settings. The receipt of a trigger signal serves as a marker which shows the halting of the recording of pre-event data and begins recording data contiguously until the end of memory or exhaustion of available power. Care is taken not to overwrite data of an impact event by the FIFO loop in memory. 
     It is envisioned the data recorder module  22  can utilize ferroelectric random access memory (FRAM or FeRAM). The use of FRAM allows the data recorder module to store incoming data in non-volatile memory immediately at bus speed without delayed writes to non-volatile memory. This allows the recording of the data in “real time” during a munitions impact or acceleration event. This FRAM is coupled to the accelerometer(s) through the processor. As previously mentioned, RAM memory requires sustained power even following the recording event in order to retrieve data. FLASH EEPROM memory involves long write cycles in reference to an event. Therefore, all data must exist in volatile memory (RAM) until post-event processing and transfer can occur. As such, it is envisioned that the sensor module  22  can be disassembled after an impact event and the data recorder module  24  or FRAM from the data recorder module can be individually accessed to access the data from an impact event. In the event the recorder is undamaged, the data can also be retrieved from the intact module  20 . 
     As shown in  FIGS. 12 and 13 , the power supply module  26  is the primary source of power for the data recorder module  24 . It is envisioned a bank of capacitors or a battery can be used to power the system. As mentioned earlier, a secondary or subset of the capacitor battery bank  32  can be found in the sensor module  22 , thereby providing power back-up. The two power sources  32  are combined through diodes and are charged by a power source external to the data recorder to either prior to or after installation of the data recorder  20  into the munition. This external power source is typically cut at some point during the test event. 
     The modules  22 ,  24 ,  26  are attached electrically by way of pins and receptacles. The pins and receptacles are generally parallel to a primary deceleration axis  33  (see  FIG. 2 ). This configuration eliminates the wires that often break during testing. Returning briefly to  FIGS. 4 and 5 , mechanical locating features  38  formed on the external housing  34  help ensure correct alignment as well as preventing relative rotation of the housings. This relative rotation can be the source of failure in electrical connections. In this example, the modules  22 ,  24 ,  26  can be held together axially inasmuch as the module  20  is under compression as part of an assembly in the projectile. The exterior housing  34  of one module can seat within an external groove  37  defined within an adjacent housing. However, fasteners, epoxy, welding etc. can be used to hold the modules  22 ,  24 , and  26  together if required. 
     As best seen in  FIG. 14 , the accelerometers are electrically connected to the sensor module  22  using a similar pin socket configuration. The example shown in  FIG. 14  shows one method for interfacing with a specific type of accelerometer package with the sensor module  22 . The sensor module  22  has been designed such that it can interface with other accelerometer packages. Optionally, an accelerometer  23  can be mounted in a configuration which allows the accelerometer module  23  to bear against a bearing surface  39  which is perpendicular to the impact axis.  FIG. 7  shows how an accelerometer package  23  is mounted into an aperture  41  defined in a bearing surface  39  by walls  43  which define the aperture. The sensor assembly is supported axially and radially. 
     As seen in  FIGS. 16   a - 17 , the external interface in this configuration is provided by a circuit board  45  that has pins that plug into receptacles inside the sensor module  22 . Wires are soldered to this board to make connections between the sensor module  22  and outside stimuli, and for power and communications. 
     Using this configuration allows for fast electrical connection of the data recorder with external sources. If wires that connect to the circuit board are severed they can be easily replaced allowing the circuit board assembly to be reused. This interface could also occur using a connector or other standard electrical connection technique. 
     As seen in  FIG. 17 , there are three main sections to the electrical interface. Shown is the RS 422 interface with the data recorder used to upload/download test configurations and data. This configuration is not limited to RS 422, as other communication configurations can be used. Next to the RS 422 is the power input and return. The remaining section is for digital signal monitoring. In this configuration, up to four digital signals can be monitored (more signals can be monitored if required). The first three signals require their own power and reference (ground). The last signal (Ext 4 ) is driven by a +5V output from the data recorder. This signal can be used to monitor events that do not have there own power source. The +5V output can also be used to drive Ext 1  through Ext 3  in some circumstances. 
     As seen in  FIG. 18 , Graphical User Interface (GUI) can be used to communicate to the data recorder module  20  via serial communication (i.e. RS-422). This allows the user to specify the percentage of pre-event (pre-trigger) data, record time, trigger inputs etc. The design of this recorder allows for analog triggers in addition to digital triggers. The user specifies the configuration using the GUI and then downloads it to the data recorder module  24 , via the sensor module  22 . 
     During the use of the data recorder, false triggers are typically a concern when installing a projectile with a data recorder into the launch vehicle, i.e. a Howitzer, sled track, aircraft, and air gun. For example, a false trigger could be caused by excessive rattling while positioning a projectile in a Howitzer. This false trigger could prematurely trigger the data recorder thereby causing the data recorder to complete its acquisition before the projectile is fired. To alleviate the effect of a false trigger, the data recorder is optionally equipped with a trigger validation feature. The validation is based on verification of an additional trigger input after the primary trigger input has been received. If the verification trigger was found inactive at the completion of the data recorder&#39;s acquisition, then the recorder assumes the previous trigger was invalid and resets back into the pre-trigger mode and, thus, continues to store data in the FIFO mode. An example of a trigger validation event is the external power source being eliminated after the power source wires are cut when the Howitzer is fired. Additionally, sensors can be used to detect munitions spin or lack thereof. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.