Abstract:
A system for sensing projectile velocity and position having a plurality of support members positioned in a path of said projectile. Each support member has an aperture with a resistive trace supported in the aperture. The resistive trace can be separated by the projectile&#39;s passage. A sensing circuit is joined to each resistive trace and provides a signal indicating separation of the resistive trace. This signal is provided to a logic circuit which provides a single signal indicating separation of each said resistive trace. A data acquisition system provides an output indicating said projectile velocity and position with respect to time.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention generally relates to a system for sensing the speed and time-position history of an underwater projectile, over the entire length of a run, for the Adaptable High Speed Underwater Munition (AHSUM) project. More particularly, the invention relates to a sensing circuit for providing a state output of a plurality of sensors used in the testing of an underwater projectile. The state output is used to determine a position and speed of the projectile during an entire run thereof through the plurality of screens. 
     (2) Description of the Prior Art 
     The known Adaptable High Speed Underwater Munition(AHSUM) project needed to record the speed and position of the projectile over the entire length of the underwater firing range. This provides valuable acceleration and deceleration data during the course of the test. Due to data acquisition channel limitations and a large number of sensors, a method was required to provide the speed and position data for the entire run over a single channel. 
     Thus, a problem exists in the art whereby there is a need for a sensing device which is able to sense both the speed and time position history of an underwater projectile over the entire length of a test range. 
     The following patents, for example, disclose various types of devices for determining projectile position and velocity, but do not disclose a device for sensing projectile velocity or time-position history using a sensing circuit according to the aspects of the present invention. 
     U.S. Pat. No. 4,147,055 to Wood et al.; and 
     U.S. Pat. No. 5,210,488 to McKeag. 
     Specifically, the patent to Wood et al. discloses an apparatus for measurement and correlation of chamber pressure and projectile position. The data is accomplished using an array of photo transistors, illuminated by collimated light, which photo transistors are sequentially switched off due to the interruption of the collimated light by the passing projectile. Pulses generated thereby may be displayed on an oscilloscope along with the pressure-time trace. 
     The patent to McKeag discloses a velocity measurement system for determining velocity of a launched projectile in a launch tube in an underwater environment. The system includes a transformer with secondary coils arranged in discrete groups with an increment of insulation shielding each of the groups of coils from the water therearound, the insulation increments being connectable to the projectile and being successively separable from the groups of secondary coils to expose such groups of coils successively to the water to short out such coils and reduce the voltage of the transformer secondary, and means for converting the speed of voltage reduction to the velocity of the projectile in the tube. In the case of launch of the projectile from a submarine, at least preprocessing of the voltage of the secondary is performed in the launch tube, and the pre-processed signal is passed to within the pressure hull of the submarine via a sealed electrical connector in the breech door of the launch tube to provide sub-safe conditions. 
     It should be understood that the present invention would in fact enhance the functionality of the above patents by providing a simplified device for sensing projectile velocity in an underwater environment. 
     SUMMARY OF THE INVENTION 
     Therefore it is an object of this invention to provide a device for sensing projectile velocity. 
     Another object of this invention is to provide a device for sensing projectile time-position history along with velocity in an underwater environment. 
     A still further object of the invention is to provide circuitry which is an accurate and inexpensive method to measure the velocity and time-position history of a projectile under the water. 
     Yet another object of this invention is to provide a device for sensing projectile velocity and time-position history in an underwater environment which is simple to manufacture and easy to use. 
     In accordance with one aspect of this invention, there is provided a system for sensing projectile velocity and position having a plurality of support members positioned in a path of said projectile. Each support member has an aperture with a resistive trace supported in the aperture. The resistive trace can be separated by the projectile&#39;s passage. A sensing circuit is joined to each resistive trace and provides a signal indicating separation of the resistive trace. This signal is provided to a logic circuit which provides a single signal indicating separation of each said resistive trace. A data acquisition system provides an output indicating said projectile velocity and position with respect to time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which: 
     FIG. 1 is a side plan view of a first preferred embodiment of the present invention; and 
     FIG. 2 is a diagrammatic view of the circuitry used in the preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In general, the present invention is directed to an apparatus for sensing a speed and time-position history of an underwater projectile, sensed over an entire length of a run for the adaptable high speed underwater munition (AHSUM) project. 
     The testing utilizes both a break screen arrangement as shown in FIG. 1 and a sensing device used in connection with the break screens as shown more particularly in FIG.  2 . 
     Referring first to FIG. 1, there is shown a plurality of break screen members  10 . Each break screen  10  includes at least a support plate  12  having an opening formed therein for passage of a projectile  14  therethrough as discharged from a gun  30 . The opening may be of any shape suitable for a clean passage of the projectile  14 , however, a circular opening was utilized in actual testing of the device. The support plate  12  is typically made from steel because the steel plate  12  is not only used as a fastening surface for the break screen  10 , but as a barricade to protect the surrounding facility and personnel in the event the projectile  14  strays off course. 
     The break screen  10  is further constructed of plastic sheets or film  16 , similar to a transparency. A continuous resistive trace  18  winds its way back and forth across the flat surface of the film  16  and is sandwiched between two of the sheets of film  16 . It is understood that alternative forms of capture and/or windings of the continuous resistive trace may be used in connection with one or more of the sheets of film  16 , and such modifications are intended to be included within the scope of the invention. Both ends of the resistive trace are connected to the input of the control circuitry shown in further detail in FIG.  2  and described more fully in the following. 
     With regard to the arrangement shown in FIG. 1, the device for sensing projectile velocity preferably utilizes a plurality of break screens  10 . In FIG. 1 there are a series of five break screens  10 , all spaced a predetermined distance D apart. By shooting the projectile  14  through a series of break screens  10 , set up along the full length of the underwater firing range, the test engineers can measure the time interval between the opening of consecutive screens  10  in order to measure velocity of the projectile  14  as well as a position of the projectile  14  during the run. The velocity of the projectile  14  is ultimately found by measuring the travel time (T 2 −T 1 ) between two consecutive break screens  10  separated by a distance D. 
     By recording the speed and position of the projectile  14  over the entire length of the underwater firing range valuable acceleration and deceleration data is obtained during the course of the test. Due to data acquisition channel limitations and large number of break screens  10 , a method was required to provide the speed and position data for the entire run over a single channel. Referring now more particularly to FIG. 2, it will be understood that the sensing and control circuitry processes the state of the plurality of break screens  10 , and the following describes the circuit that was designed to accomplish this goal. 
     The circuitry described herein is able to receive and condition signals received from at least twelve break screens  10  evenly spaced in the underwater firing range. The resistance of each of the break screens  10  is approximately 1 Kohm before being broken by the projectile  14 , and the resistance increases by a few orders of magnitude after being punctured. If the break screen  10  were in air, the resistance would be infinite (open circuit), but in water the resistance is lower due to the conductivity of the water. 
     One end of each resistance trace  18  is connected to circuit ground  28 . The other end of each screen  10  is connected to a positive input of individual voltage comparator  20  circuits. The voltage comparator  20  can be any voltage comparator such as that manufactured by and identified as LP365A. A negative input of these voltage comparators  20  is connected to individual potentiometers  22  that are adjusted at a desired comparator transition voltage level (i.e., 10 V). The comparator transition voltage provides a threshold voltage at which an output of the comparator will change. A positive input of the comparator  20  is connected to a midpoint of a two-resistor voltage divider  24 . The two resistor voltage divider  24  is made up of a fixed resistance pull-up resistor  26  (pulled up to positive 15VDC) and the resistive trace  18  connected to circuit ground  28 . In this embodiment, the positive inputs to the comparators  20  (SCREEN_IN to SCREEN 12 _IN) will be approximately 2.36 VDC when the traces  18  are intact and will rise to between 14 and 15 VDC when the traces  10  are broken by the projectile  14 . Comparators  20  and the other logic circuitry contained herein use a non-asserted or low state of 0VDC and an asserted or high state of 5 VDC. Once a trace  18  is broken and the positive input of the comparator  20  crosses the 10 VDC threshold, the output of the comparator  20  will change from a normally low state (0 VDC) to a high output state (5 VDC). Thus, while the trace  18  is intact, prior to impact by the projectile  14 , the comparator  20  outputs a low signal. Immediately following impact of the projectile  14  on the trace  18 , the trace  18  opens, thus opening a bottom half of the potentiometer voltage divider  22  allowing the positive input to the comparator  20  to be pulled high. This causes the comparator  20  to output a high signal (5VDC). The comparator output signal is input to a programmable array logic device  32  (PAL). 
     The PAL  32  is an integrated circuit that contains discrete logic devices that can be programmed and reconfigured. Each comparator  20  output signal is routed to the clock input of a D-flip-flop latch  34  programmed in the PAL  32 . The D-input of each flip-flop  34  is permanently connected to a logically high input. The flip-flop  34  provides a latched high signal when the trace  18  is broken and prevents this latched output from changing in the event of variances at the output of the comparator  20 . 
     The output of the flip-flops  34  are labeled SCREEN 1 _LATCHED through SCREEN 12 _LATCHED. The latched values can be cleared via an external logical high RESET pulse to the D-flip-flop reset input  38  that is generated by the activation of a manual switch  39 . This reset input  38  is normally held low via a pull-down resistor  26 . These latched signals are sent through buffers  36 , such as 74LS244 buffers manufactured by Texas Instruments which provide the appropriate output drive current for the next stage of the circuit. The outputs of the buffers  36  are fed through resistor voltage dividers  37  made up of 10 Kohm and 2 Kohm resistors. These dividers  37  reduce the 5VDC buffer outputs to approximately 0.8VDC. The twelve resistor divider outputs are fed to the twelve 470 Kohm resistor inputs of a summing amplifier  40 . 
     The output of the summing amplifier  40  is passed through a unity gain inverting amplifier  42  to cancel the inverting action of the summing amplifier  40  and to accommodate input characteristics of a data acquisition system  46 . The data summing amplifier  40  receives a divided latched high signal from each D flip flop  34  for each of the break screen channels (output of the break screen). As the projectile  14  passes through successive break screens  10 , the latched signals will be delayed in time. The output of this inverting amplifier  42  is called SCREEN_SUM. The SCREEN_SUM output is initially 0VDC but will increase in increments of approximately 0.8VDC as each of the successive screens  10  are broken. A time trace of this output resembles a staircase waveform. Each step of the waveform represents the breaking of a break screen  10 . By simply measuring the time between steps on the waveform, a measurement of the time it takes the projectile  14  to travel between adjacent break screens  10  (T 2 −T 1 ) is obtained. Knowing the distance D between the respective screens enables an accurate calculation of the speed and time history of the projectile. This process is repeated over the length of the entire run of break screens  10  in order to measure the speed of the projectile from the muzzle of the gun to the end of the test range. The outputs of the latches remain high until a reset signal is provided to the PAL  32  via an external manual switch  39  connected to a RESET input  38  of the PAL  32 . 
     The above circuitry provides an accurate and inexpensive method to measure the velocity and time-position history of a projectile fired underwater. The circuitry only requires a single data acquisition channel to capture and record the state of multiple break screens located down the length of the firing range allowing for simplified calculation of the projectile velocity and acceleration/deceleration rates. 
     Alternatives to the embodiment shown include the use of a sensing coil around the plate instead of a break screen in order to sense the projectile passing through the plate. The projectile would be either constructed from magnetic material or have a magnetic insert. 
     Finally, it is anticipated that the invention herein will have far reaching applications other than those of underwater projectile testing projects. 
     This invention has been disclosed in terms of certain embodiments. It will be apparent that many modifications can be made to the disclosed apparatus without departing from the invention. Therefore, it is the intent of the appended claims to cover all such variations and modifications as come within the true spirit and scope of this invention.