Abstract:
A device for controlling a video camera in underwater high speed photography in a first aspect includes a plurality of spaced break screen or sense coil members, a projectile for launch through the series of break screen or sense coil members, a video camera operated to video at a predetermined timing upon release of the projectile, and a source of illumination to aid in the video photography. A trigger device such as a break screen or sense coil is positioned immediately up-range of the video camera. With a time delay programmed into a Programmable Array Logic (PAL), a control circuitry receives the trigger information and creates a timed signal to control the operation of the video camera. In accordance with another aspect of this invention, the control circuitry includes discrete logic devices programmed such that gating of the video camera is controlled by the control circuitry at the time the projectile passes the lens of the camera.

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 relates high speed photography, and to a circuit for triggering a video camera located between two sensors. More specifically, the video camera is triggered by a projectile passing through a break screen on an underwater range. 
   (2) Description of the Prior Art 
   The Adaptable High Speed Underwater Munition (AHSUM) project needed a method to obtain video images of underwater projectiles during the course of their test series. Prior to this time, there was no satisfactory means of obtaining the video images that were needed, nor was there a device applicable to a variety of conditions. 
   The following patents, for example, disclose various types of video photography, including underwater photography and circuits in connection therewith, but do not disclose a device for controlling an underwater video camera for the purpose of taking underwater video of a high speed projectile.
         U.S. Pat. No. 4,335,944 to Marshall;   U.S. Pat. No. 4,418,999 to Baxter;   U.S. Pat. No. 4,447,896 to Rines;   U.S. Pat. No. 4,713,686 to Ozaki et al.; and   U.S. Pat. No. 4,970,597 to Shepard.       

   Specifically, the patent to Marshall discloses improvements in underwater elapsed time strobe-camera apparatus and the like involving sonar-triggering by a sonar beam generated co-axially with and about the camera lens axis and, as a result of novel circuits, size-reduction and packaging, adaptability for portability, with ancillary novel features of automatic predetermination of number of pictures and indication thereof. 
   Baxter discloses a synchronizing circuit which enables a desired phenomena to occur, such as the discharge of a flash illuminating means at a precise point along the path of travel of an article irrespective of the speed of the article in that path. The circuit utilizes two spaced sensors upstream of the precise point. The sensors are operable to detect the passage of the article and each sensor is connected to respective counter. When sensor detects the passage of the article it starts its respective counter counting in one direction at one particular counting rate. When the second sensor detects the passage of the article it causes its respective counter to count in the opposite direction from the value of the count in the first count at a different but faster counting rate. The circuit includes gate means which determine when the count has returned to a predetermined count to then cause said phenomena to occur. 
   The patent to Rines is concerned with problems of energy conservation and more effective utilization at desired critical times only in, for example, sonar-triggered underwater elapsed time strobe photography of objects or scenes or in applications having similar problems; and accomplishing such and other ends by restricting optical and sonar monitoring to relatively low periodicity intervals until the desired object has come within range, whereupon the apparatus automatically changes mode to take rapid successive strobe photographs or other records supplemented by contemporaneous sonar recording. 
   The patent to Ozaki et al. discloses a high speed, instantaneous multi-image recorder having a video camera, sensor unit and light projector. A frame memory is connected to the video camera, a flash tube is joined to the light projector, and a retarder is joined to the sensor unit. The flash tube is connected to the retarder, and a monitor is connected to the frame memory. The video camera, sensor unit and light projector are directed toward a moving object which is, for example, a golf club. When the golfer swings the club, the sensor unit detects the club, the light projector flashes, and the video camera picks up the golf ball and club head at the moment of impact. Thus, the video camera catches many instantaneous poses within a frame. Many such images picked up in a signal frame of the video camera are displayed on the monitor screen for analysis. 
   Shepard discloses a method of imaging a high speed event. A multiplicity of frames, or image fields, are output from a camera which scans repeated occurrences of the event. Selected data representing individual portions of frames are accumulated in essentially random order. The selected data are used to construct a composite image of the high speed event. 
   It should be understood that the present invention would in fact enhance the functionality of the above patents by providing a control device for an underwater video camera and triggering the underwater video camera at the precise time necessary for acquiring desired video frames, particularly in a test environment. 
   SUMMARY OF THE INVENTION 
   Therefore it is an object of this invention to provide a device for controlling a video camera in underwater photography. 
   A further object of the invention is to provide a circuitry which is an accurate and inexpensive method to control a timing of operation of a video camera in underwater high speed photography. 
   Yet another object of this invention is to provide a device and circuitry for controlling a timing operation of a video camera in underwater high speed photography which is simple to manufacture and easy to use. 
   In accordance with one aspect of this invention, there is provided a device for controlling a video camera in underwater high speed photography. The device includes a plurality of spaced sensors, a projectile for launch through the series of sensors, a camera or video camera having a shutter opened at a predetermined timing prior to release of the projectile and closing at a predetermined timing subsequent to release of the projectile, and an illumination source for providing a light source at the same time as the projectile passes in front of the camera. A sensor is positioned immediately-uprange of the camera. A control circuit receives the sensor information and creates a timed signal to control the activation of the video camera. 
   In accordance with another aspect of this invention, the control circuitry includes a first D flip flop for receiving a signal output from a break screen upon passing of a projectile therethrough, the first D flip flop additionally having a constant voltage applied thereto and a resulting latched output signal. An AND gate receives an output signal of the first D flip flop, the AND gate additionally having a clock signal and a resulting output clock signal only when the latched output signal from the first D flip-flop is high. An N-bit counter receives the output clock signal from the AND gate. The N-bit counter provides a count to delay generation logic. Upon lapse of a predetermined length of time the delay generation logic provides a delayed control signal. A second D flip-flop receives the delayed control signal, and additionally has a constant voltage applied thereto and a resulting latched output signal, wherein a rising edge of an output generated by the second D flip-flop identifies a beginning of a camera activation window. A second AND gate receives the output signal of the second D flip flop. The second AND gate additionally receives a clock signal. The second AND gate outputs a second output clock signal to a second independent N-bit counter. A second delay generation logic block receives the output of the second N-bit counter, and outputs a second delayed control signal upon lapse of a predetermined count. A third D flip-flop receives the second delayed control signal from the second delay generation logic, and additionally has a constant voltage applied thereto and a resulting latched output signal. A rising edge of the output generated by the third D flip-flop identifies an end of the camera activation window. An exclusive OR gate receives outputs from each of the second D flip-flop and the third D flip-flop, the exclusive OR gate producing a high pulse from the time delayed trig out goes high to the time second delay goes high. The output of the exclusive OR gate is compared using an AND Gate with an externally generated camera clock square wave. The camera clock signal is provided by a separate function generator. The frequency of the square wave dictates the number of pulses that will occur in the activation window and hence the number of times the camera will be gated. The output of the AND gate is buffered via a separate non-inverting buffer and then sent to the camera trigger. 
   The camera is controlled by the control circuitry at the exact moment the projectile passes the lens of the camera. 

   
     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 plan view of a first preferred embodiment of the present invention; 
       FIG. 2  is a diagrammatic view of the circuitry used in the preferred embodiment of the invention; and 
       FIG. 3  is a timing diagram of the preferred embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In general, the present invention is directed to a control circuitry for controlling an underwater video camera for the purpose of taking underwater video images of a high speed projectile tested in the Adaptable High Speed Underwater Munition (AHSUM) project. The control circuitry essentially senses when the projectile has passed through a break screen or sensing coil and provides a trigger signal in response thereto. The control circuitry uses this trigger to enable its novel timing scheme to turn on the video camera at the exact time required to acquire the video images. 
   Referring first to  FIG. 1 , there is shown a simple diagram of the test set up including a plurality of sensing devices  10  all spaced a predetermined distance D apart. These sensing devices  10  can be either sensing coils or break screens. Each sensing device  10  is mounted to a steel 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 the actual device. The steel plate  12  is not only used as a fastening surface for the sensing device  10 , but as a barricade to protect the surrounding facility and personnel in the event the projectile  14  strays off course. 
   The sensing device  10  may be further constructed as a break screen having clear plastic sheets or film  16 , similar to a transparency. A continuous resistive trace (not shown) winds its way back and forth from one side of the film  16  to the other and is sandwiched between two of the sheets of film  16 . It is understood that alternative forms of capture may be used in place 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 a control circuitry described in detail in co-pending application entitled Underwater High Speed Projectile Break Screen Based Speed Sensing Circuit. 
   Referring further to  FIG. 1 , there is additionally shown a video camera  20  opposed to a source of illumination such as an incandescent light  22 . The video camera  20  may be mounted to a base  24  if desired. While the incandescent light  22  is used for the purposes of illustration, other sources of illumination having the same or similar constant output may be suitable for use in the present invention. 
   It is not possible to operate a standard video camera and capture a series of images of the projectile passing by at high speed. Therefore, a high speed gated intensified video camera  20  must be used to take high speed video images. By providing the video camera with a packet of high speed digital trigger pulses at the exact time the projectile  14  is passing allows the user to automatically gate the video camera  20  and gather multiple images of the projectile  14 . The number of pulses included in the pulse packet dictates the number of images taken by the camera  20 . The control circuitry  25  is activated when the projectile  14  passes through the break screen or voltage sense coil  10  located immediately uprange from the camera equipment  20 . 
   The control circuitry  25  joined to the camera  20  is activated when the projectile passes through the break screen or voltage sensing coil  10  located immediately up-range of the camera equipment  20 . A time delay must be incorporated to compensate for the time required for the projectile to reach the camera equipment after passing through the break screen or voltage sense coil. 
   FIG.  2  and  FIG. 3  describe the control circuitry  25  that receives the break screen or coil voltage trigger information and then creates the appropriate timed trigger signal to control the underwater camera  20 . The control circuitry  25  receives the input trigger information either as an open circuit from the break screen  10  or as a voltage spike from a sensing coil which detects the presence of a magnetic projectile  14  passing through it. This signal is sent to an input voltage comparator  26  that outputs a logical high pulse (5 Volts). This pulse is sent to the input of a timing circuitry which may be programmed in a programmable array logic (PAL) device. Referring now in detail to  FIG. 2 , the circuitry programmed in the PAL is shown therein. All discrete logic labels are used in the description strictly for explanation purposes. The signal and component labels match those appearing in the figures. The waveforms produced by the control circuitry  25  in order to properly control the high speed video camera  20  are depicted in FIG.  3 . 
   The voltage comparator signal is sent to the clock input of a first D-flip-flop  32  that is programmed internally in the PAL. The D-input of the first flip-flop  32  is permanently connected to a logical high source (5 Volts). The first flip-flop  32  provides a latched logical high signal when a projectile passes through the sensor  10 . Flip flop  32  prevents output changes in the event of fluctuations at the comparator output. The output of the first flip-flop  32  is labeled as TRIGGER_IN_LATCHED. 
   This signal of TRIGGER_IN_LATCHED is sent to a first AND gate labeled  34 . The other input of the AND gate  34  is a 1 MHz square wave generated by a quartz crystal based oscillator  35  and is labeled CRYSTAL_IN. Oscillator  35  preferably provides a 1 MHz clock signal. 
   The main purpose of oscillator  35  is to provide a stable clock to the counters programmed in the PAL. This AND gate  34  acts as a switch which is activated, allowing the clock signal through, only when the TRIGGER_IN_LATCHED signal is a logical high. The output of the first AND gate  34  is sent to the clock input of a first N-Bit Counter  36 . The size in bits (N) of the counter  36  depends on the sum of: 1) the length of time delay required between the initial triggering of the control circuitry by the sensor  10  and the time the first image is desired; and 2) the length time the camera  20  is to acquire images. 
   The output of the N-Bit Counter  36  is sent to a first delay generation logic section  38 . The first delay generation logic section  38  contains logic that utilizes one of ten user defined/jumper selectable preprogrammed delay times. The delay time selected is actually the number of counter transitions that must occur before allowing the output of this logic section to become a high logic state. The counter  38  starts at zero and will only start incrementing once the oscillator clock signal is enabled via the first AND gate  34 . Once the N-Bit Counter  36  reaches the time delay value selected by the user, a high pulse is output from the first delay generation logic  38  and fed into the clock input of a second D flip-flop  40 . 
   Once again the D-input of the flip-flop  40  is permanently connected to a logical high source. Therefore, the rising edge of the first delay generation logic output will permanently latch an output signal of the second flip-flop  40  high. The latched signal is labeled DELAYED_TRIG_OUT. The rising edge of DELAYED_TRIG_OUT signifies the beginning of the camera activation window. The next step in the control circuitry is to create an additional delay signal. 
   The DELAYED_TRIG_OUT signal is input to a second two-input AND gate  42 . The other input of the AND gate  42  is a clock signal from oscillator  35 . The output of the AND gate  42  is sent to the clock input of a second N-Bit Counter  44 . The size in bits (N) of the second N-Bit Counter  44  depends upon the maximum possible length of the activation window required by the video camera  22 . The N-Bit output of this counter  44  is output to a second delay generation logic block  46 . This section contains logic that utilizes user selectable preprogrammed delay times. The delay time selected is actually the number of counter transitions that must occur before allowing the output of this logic section  46  to generate a logical high signal. The counter  44  starts at zero and will only start incrementing once the input clock is enabled via the second AND gate  42 . 
   Once the N-Bit Counter  44  reaches the time delay value selected by the user, a high pulse is output from the delay logic  46  and fed into the clock input of a third D-flip-flop  48 . Once again the D-input of the flip-flop  48  is permanently connected to a logical high source. Therefore, this rising edge will latch the output of the flip-flop  48  to a high signal. The latched signal is labeled SECOND_DELAY. The rising edge of the SECOND_DELAY signifies the end of the camera activation window. 
   Each of the DELAYED_TRIG_OUT and SECOND_DELAY are fed to the two inputs of an exclusive-OR gate  50  which produces a high pulse (activation window) which is high from the time the DELAYED_TRIG_OUT goes high to the time the SECOND_DELAY goes high. The exclusive OR output is provided to a third AND gate  52  with an externally generated square wave signal from a second function generator  51 . The frequency of the square wave signal dictates the number of pulses that will occur in the activation window and hence the number of times the camera will be gated. Typically, it is desirable to capture three to ten frames during passage of the projectile. The output signal, labeled WINDOW_OF_PULSES, is buffered via a separate non-inverting buffer  53  whose open collector is pulled up to a logical high and then sent to the camera trigger. 
   When programmed correctly, the video camera  20  will be enabled by the activation window at the exact moment the projectile  14  passes the lens of the video camera  20 . 
   The above circuitry provides an accurate and inexpensive method to control an underwater video camera  20  for high speed photographic imaging purposes. The circuitry is programmable which provides flexibility and greatly minimizes the need for circuit modifications as test requirements and conditions (i.e., projectile speed) vary. 
   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.