Abstract:
The disclosed system provides headgear, i.e., a Firefighter Helmet, with forward illumination that also acts as a personal rescue detection system for quickly finding a downed of lost firefighter. More specifically, the headgear includes a forward illuminating light that has unique characteristics that are easily detected in a smoke filled space by using a handheld photodetector probe that is tuned to the exact characteristics of the light source. The handheld probe has a somewhat narrow directional response to allow a directed search for a downed firefighter or other emergency personnel in a smoke filled noisy environment that hinders normal visual and audible search methods. The handheld photodetector probe produces a unique audio tone that is proportional in volume to the intensity of the exact-characteristics-light-source thus allowing a sweeping motion of the probe to immediately determine the relative direction to a firefighter who is down or requiring assistance. An illuminated visual display also indicates the strength of the unique tone.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to forward illumination of a firefighter&#39;s path with a light source which also acts as part of a personal rescue detection system for quickly finding a downed or lost firefighter in a smoke filled space. More specifically, the present invention includes a light source having characteristics which are detected by a handheld photodetector probe. The probe has a very high sensitivity to the light source, several thousand times more sensitive than the human eye, and also has a narrow field of view which provides a directional response to the light source. 
       BACKGROUND OF THE INVENTION 
       [0002]    Time is extremely critical when trying to find a lost or downed firefighter. His air supply and the temperature of the surrounding environment limit the firefighter&#39;s survival time. Typical methods to find and rescue a firefighter in a burning structure usually involve visual methods such as following hose lines or seeing a flashing light signal. These methods can be severely hampered in a very dense smoke-filled space making it virtually impossible to find a lost or downed firefighter in a timely manner. 
         [0003]    Personal alert safety systems (PASS) are also commonly used today to locate firefighters in distress. The PASS devices produce an audible signal which, in some cases, varies in volume depending upon where the source is to aid in locating the firefighter in distress. 
         [0004]    Following the audible signal to its source locates the distressed firefighter. However, the PASS device location method can also be severely hampered by the high noise level of a raging fire which masks changes in the volume of an audible signal. PASS devices may also be equipped with flashing strobe lights which are intended to be visible and guide a rescuer, but such lights currently in use are severely hampered by dense smoke. 
         [0005]    The present invention solves these problems by providing a rescue system which penetrates dense smoke and is unaffected by the noise of a raging fire. The beam from the helmet-mounted element of the present invention not only illuminates a firefighter&#39;s forward path as he moves about inside a burning structure, but also, because of its frequency and intensity, is easily and quickly detected by the field of view of a handheld probe element in the hands of a rescuer. 
       SUMMARY OF THE INVENTION 
       [0006]    The rescue system of the present invention provides a forward illumination for a firefighter working in an enclosed space while fighting a fire and also a personal rescue system for the firefighter if he should be overcome comprising an element with a forward illuminating light source modulated with a photometric characteristic and an element with a handheld photodetector probe tuned to the photometric characteristic of the light source. 
         [0007]    Accordingly, it is an object of the present invention to provide a firefighter rescue system which discriminates between the noise and smoke in a structure which is on fire and a light from a lamp worn by a downed firefighter. 
         [0008]    It is a further object of this invention to provide a firefighter rescue system utilizing a light receiving unit which is responsive to a lamp worn by a downed firefighter and translates the light beam from the lamp into an audible signal for a rescuer holding the receiving unit to follow. 
         [0009]    It is a further object of this invention to provide a firefighter rescue system with a narrow beam which readily penetrates a smoke-filled atmosphere. 
         [0010]    Other features and advantages of the present invention will become apparent to those skilled in the art of designing rescue systems for firefighters from a consideration of the following disclosure of this invention in the accompanying drawings and detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  depicts a firefighter&#39;s helmet having a forwardly directed headlight mounted in the shield on its crown and a probe unit with a wand facing the headlight cooperatively tuned to the beam emitted from the headlight; 
           [0012]      FIG. 2  is an enlarged cross-sectional view of a portion of the distal end of the wand shown in  FIG. 1  taken along the line  2 - 2  in  FIG. 1 ; 
           [0013]      FIG. 3  is a schematic representation of the helmet light circuit for the headlight of the present invention shown in  FIG. 1 ; 
           [0014]      FIG. 4  is a block diagram of the circuits assembled in the probe unit shown in  FIG. 1 ; 
           [0015]      FIG. 5  is a detailed schematic drawing of a transimpedance amplifier circuit engaged to a photodiode and a voltage amplifier circuit contained in the probe unit shown in  FIG. 1 ; 
           [0016]      FIG. 6  is a detailed schematic drawing of a 2-stage bandpass filter circuit engaged to the voltage amplifier circuit shown in  FIG. 5  and contained in the probe unit shown in  FIG. 1 ; 
           [0017]      FIG. 7  is a detailed schematic drawing of a second voltage amplifier circuit engaged to the bandpass filter circuit shown in  FIG. 6  and an audio power amplifier circuit engaged to the second voltage amplifier circuit, both of which circuits are contained in the probe unit shown in  FIG. 1 ; and 
           [0018]      FIG. 8  is a detailed schematic drawing of an illuminated visual display circuit engaged to the circuits shown in  FIG. 7  and contained in the probe unit shown in  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Referring to the drawings in particular, the invention embodied therein comprises a firefighter helmet with a forward illumination light and a handheld photodetector probe. The forward illumination light and the handheld photodetector probe provide a method and apparatus to locate a firefighter who may be down or requiring assistance inside a smoke-filled environment. 
         [0020]    The firefighter helmet  100  shown in  FIG. 1  is a firefighter&#39;s basic helmet with a crown  1  and a conventional leather shield  2  mounted on the front of crown  1 . The forward illuminating light  3  has a narrow beam  3 A and is mounted in the leather shield so that the beam is directed slightly downwardly in order to illuminate the firefighter&#39;s path. The spectral characteristics of the light  3  are selected to provide the best visual penetration of the smoke and fumes encountered in most common structure fires. However, the frequency and intensity of the beam  3 A is modulated by an electronic circuit which encodes a photometric characteristic easily detected by the handheld photodetector probe  102  shown in  FIGS. 1 and 2 . 
         [0021]    The helmet light circuit  103  diagrammed in  FIG. 3  provides the modulation needed to produce the photometric characteristic of the light beam  3 A. This circuit is a free-running oscillator with an integrated circuit operating in an astable mode. One such oscillator may be an MC1455 TIMER which is illustrated diagrammatically at 9. The pulse-repetition-rate of that oscillator is 1,666 hertz and the ON-period duty cycle of the oscillator&#39;s output is three percent. The output is coupled to driver transistor  10  via resistor  11 . The driver transistor  10  provides the necessary current gain to power a plurality of high intensity light emitting diodes  12 . The maximum current for the light emitting diodes  12  is limited by resistors  13 . The entire circuit  103  is powered by a single rechargeable battery  14  via ON-OFF switch  15 . An external 12-volt DC source (not shown) may be connected to power jack  17  for recharging of battery  14 . The maximum charging current for the battery is limited by resistor  16 . 
         [0022]    Operating the illuminating LEDs  12  at 1,666 hertz provides a flash rate that is too fast for the human eye to discern, thus providing what appears to be steady-state illumination. Operating the illuminating LEDs  12  at a three percent ON-period duty cycle allows the LEDs&#39; current to be overdriven by a factor of 33. This very low duty cycle and very high overdrive current produces a very high intensity light beam that is 3300 percent of the normal steady-state LED light intensity without exceeding the maximum allowable LED power dissipation. 
         [0023]    The handheld photodetector probe unit  102 , depicted in  FIGS. 1 and 2 , includes an electronics enclosure  4  and a wand  5 . The enclosure  4  is disposed at the proximal end  5 A of wand  5 . Also, a photodiode  6  is recessed in a bushing  7  adjacent the distal end  5 B of wand  5 . Recessing the photodiode in the bushing provides a sharply defined field-of-view  8  which is sufficiently narrow to direct a search to the source of beam  3 A by panning the distal end  5 B of wand  5 . Electrical wires  6 A within the probe wand  5  convey electrical signals from the photodiode  6  to a photometer circuit  104  (see  FIG. 4 ) mounted within the electronics enclosure  4 . 
         [0024]      FIG. 4  depicts the overall combination of circuits which comprise photometer circuit  104  for the handheld photodetector probe  102 . This combination incorporates several individual electronic circuits cascaded one after another to amplify a signal from the photodiode  6 , which signal is generated as the photodiode  6  encounters and tracks light beam  3 A. The six individual circuits which are schematically illustrated are: a transimpedance amplifier ( FIG. 5 ), a voltage amplifier ( FIG. 5 ), a 2-stage active bandpass filter ( FIG. 6 ), a second voltage amplifier ( FIG. 7 ), an audio power amplifier ( FIG. 7 ), and an illuminated visual display ( FIG. 8 ). 
         [0025]    The photodiode  6  receives all of the light that is within the defined field-of-view  8  and converts it to a current which is proportional to the intensity of the light. The output of photodiode  6  connects to the inverting (negative) and non-inverting (positive) inputs of amplifier  19 . That amplifier is connected in a transimpedance configuration to produce a voltage at the output of amplifier  19  which is proportional to the photodiode  6 &#39;s current. The transimpedance circuit also contains a solid-state diode  20  arranged in a negative feedback loop which produces a logarithmic response, i.e., an output voltage proportional to the logarithm of the photodiode current, thus preventing amplifier  19  from becoming saturated and non-responsive when the photodiode  6  is exposed to very bright light. Resistor  21  limits the current through the photodiode  6  in order to protect it from excessive current. The output voltage from amplifier  19  is a complex signal that has both steady-state (DC) and fluctuating (AC) components. The DC component of the output voltage is proportional to the steady-state intensity of the ambient light conditions detected by the photodiode  6 . The AC component of the output voltage is superimposed on the DC component and is proportional to any fluctuations in the intensity of the light detected by the photodiode  6 . 
         [0026]    The output of the amplifier  19  is AC-coupled to the input of amplifier  22  through capacitor  27 , thus blocking the DC voltage component of amplifier  19 &#39;s output signal in order to prevent amplifier  22  from becoming saturated and non-responsive. The AC component of amplifier  19 &#39;s output signal is passed on to the input of amplifier  22  by capacitor  27 . Amplifier  22  is connected with a stage gain of 100, i.e., amplifying the signal from capacitor  27  by a factor of 100 to produce an output signal which is 100 times the AC component of amplifier  19 &#39;s output. 
         [0027]    The output of amplifier  22  is coupled to the input of the active bandpass filter  23 . The active bandpass filter  23  is tuned to respond only to the frequency of the helmet light  3 A and provides additional amplification for the helmet light  3 A while discriminating against other fluctuating light sources such as flames or room lighting. When the active bandpass filter  23  receives the helmet light frequency (1,666 hertz), it resonates producing a sinusoidal output voltage. The amplitude of the sinusoidal output voltage is proportional to the helmet light intensity received by the photodiode  6 . 
         [0028]    The output of the active bandpass filter  23  is coupled to the input of amplifier  24  for further amplification, i.e., with a stage gain of 100, thus providing additional amplification for very weak signals from the filter  23 . 
         [0029]    The output of amplifier  24  is coupled to the input of audio power amplifier  25  for further current amplification in order to drive an audio output device  26  which converts an electrical signal to one which the human ear can hear. Dual earphones may be used in order to help exclude ambient noise in the audio signal from the probe. 
         [0030]    The output of amplifier  25  is also connected to the input of an illuminated visual display  28  that indicates the received strength of the helmet light signal, for example, a yellow light emitting diode which illuminates a bargraph, displays signal strength and is easily visible in a dark, smoke filled environment, as shown. 
         [0031]    One manner of cascading the circuitry described above is illustrated in  FIGS. 5 through 8 . Looking first at  FIG. 5 , photodiode  6  is connected to the input of transimpedance amplifier  19 . Transimpedance amplifier  19  is composed of operational amplifier  201 , resistor  21 , solid-state diode  20 , resistor  202  and capacitor  203 . The operational amplifier  201  is connected in a transimpedance configuration with solid-state diode  20  and resistor  21  to produce an output voltage that is proportional to the logarithm of the input current from photodiode  6  current. Resistor  21  limits the maximum current to prevent damage to photodiode  6 . Resistor  202  limits the maximum gain of amplifier  201  when photodiode  6  is under dark conditions providing additional electronic noise immunity. Capacitor  203  limits the high frequency response of amplifier  201  providing added noise immunity to radio frequency interference. 
         [0032]    The output of transimpedance amplifier  19  is AC-coupled to the input of voltage amplifier  22  by capacitor  27 . Capacitor  27  blocks any DC component at transimpedance amplifier  19  output, allowing only the AC component of transimpedance amplifier  19  output to input to voltage amplifier  22 . 
         [0033]    Voltage amplifier  22  is composed of operational amplifier  204 , resistors  205 ,  206  and  207 , and capacitor  208 . Operational amplifier  204  is connected in the non-inverting voltage amplifier configuration with the stage gain set by resistors  205  and  206 . Resistor  207  provides input bias current balancing to reduce output offset drift. Capacitor  208  limits the high frequency response of amplifier  204  providing added noise immunity to radio frequency interference. Capacitor  209  blocks any DC component at amplifier  204  output, allowing only the AC component of amplifier  204  output to input the next stage, which is the active bandpass filter shown in  FIG. 6 . 
         [0034]    Looking at  FIG. 6 , the active bandpass filter  23  is comprised of two identical operational amplifier stages  301 , resistors  302 ,  303 ,  304 , and capacitors  305  and  306 . Each stage is connected in the multiple feedback bandpass configuration, a configuration which is commonly referred to as a two-stage active bandpass filter. The parameters of this circuit are: Q, the quality or sharpness of the center frequency cutoff; G, the passband gain or amplification factor; and f, the center frequency. All of the resistor and capacitor values interact to affect all of these circuit parameters, but can be equated as follows and solved simultaneously. C in these equations represents the value of capacitors  305  and  306 , which are equal. The input resistor  302  is equal to Q/(G*2*Pi*f*C). The attenuator resistor  303  is equal to Q/((2*Q 2 −G)*2*π*f*C). The feedback resistor  304  is equal to Q/Pi*f*C). The passband gain, G, is equal to 1/((R 302 /R 304 )*2). The center frequency, f, is equal to (1/(2*Pi*C))*((R 302 +R 303 +R 304 ))̂0.5. Capacitor  307  blocks any DC component at active filter  23  output, allowing only the AC component of active filter  23  output to input to the next stage, which is the voltage amplifier  24  shown in  FIG. 7 . 
         [0035]    Looking at  FIG. 7 , the voltage amplifier  24  is comprised of operational amplifier  401 , resistors  402 ,  403 ,  404 , and capacitor  405 . Operational amplifier  401  is connected in a non-inverting voltage amplifier configuration with the stage gain set by resistors  402  and  403 . Resistor  404  provides input bias current balancing to reduce output offset drift. Capacitor  405  limits the high frequency response of amplifier  401  providing added noise immunity to radio frequency interference. The output of amplifier  401  is connected to potentiometer  406  providing a means to adjust signal amplitude. The output of potentiometer  406  is connected to the input of audio power amplifier  25  by capacitor  407 . Capacitor  407  blocks any DC component at the potentiometer  406  output, allowing only the AC component of potentiometer  406  output to input to audio power amplifier  25 . 
         [0036]    Audio power  25  is an integrated circuit  408  connected to provide a gain of  20 . Input resistor  409  provides a fixed input impedance for the capacitively coupled input signal from potentiometer  406 . Resistor  410  and capacitor  411  provide the gain control network to set the gain to  20  in the audio frequency spectrum. Capacitor  412  is the power supply bypass filter capacitor that prevents integrated circuit  408  from feeding back into the power supply. Capacitor  413  is an internal bypass capacitor that improves integrated circuit  408  stability. Capacitor  414  is the output bypass capacitor that removes high frequency hiss from the audio output signal. Capacitor  415  and resistor  416  provide the conventional output decoupling network to block the quiescent DC voltage at integrated circuit  408  output, allowing only the AC signal component to pass through to earphone jack  417 . Earphone jack  417  provides a means to connect the audio output to any conventional audio listening device. 
         [0037]      FIG. 8  depicts the circuitry to implement the illuminated visual display  28 . This circuitry consists of AC log amplifier  501  (logamp), voltage amplifier  502 , display driver  503 , LED bar display  504 , sync generator  505 , sync notch generators  506  and  507 , and sync gating transistor  508 . AC logamp  501  is an operational amplifier connected in the transimpedance configuration with input resistor  509  and solid-state diodes  512  and  513  to produce an output voltage that is proportional to the logarithm of the input voltage from audio power amplifier output  25  output. Since the audio signal is AC, the circuit is bi-directional, with diode  512  producing the logarithm of the positive half-cycle and diode  513  producing the logarithm of the negative half-cycle. Resistor  510  limits the maximum gain of the logamp when the audio signal is near zero providing additional electronic noise immunity. Capacitor  511  limits the high frequency response of the logamp providing added noise immunity to radio frequency interference. Capacitor  514  blocks any DC component at logamp  501  output, allowing only the AC component of the logamp  501  output to input to the next stage, voltage amplifier  502 . 
         [0038]    Voltage amplifier  502  is an operational amplifier connected as an inverting amplifier. Input resistor  515  and feedback resistor  516  set the stage gain. Capacitor  517  limits the high frequency response of amplifier  501  providing added noise immunity to radio frequency interference. 
         [0039]    Solid-state diode  518  rectifies the AC audio signal from voltage amplifier  502  to provide a DC analog signal to the input of display driver  503 . Capacitor  519  and resistor  520  provide an R-C filter circuit to remove ripple from the DC signal. 
         [0040]    Display driver  503  is an integrated circuit that converts the DC analog input signal into digital output signals to drive a ten segment LED bar display  504 . Resistors  521 ,  522  and  523  form a voltage divider to provide the reference voltage that determines the full-scale response of the display. 
         [0041]    LED bar display  504  is strobed ON by sync gating transistor  508  only when the received signal is at or near the fundamental frequency of the helmet light. Capacitor  525  provides energy storage to power the LED display between strobe pulses from transistor  508 . Only the top nine LED segments actively display the amplitude of the analog signal. The bottom segment is biased ON continuously by resistor  524  to indicate when the power is turned on. 
         [0042]    The sync generator  505  consists of an integrated circuit voltage comparator, resistors  526  and  527 , and solid-state diode  528 . The input signal to the sync generator is from the output of voltage amplifier  24 , shown in  FIG. 7 . When the input signal is positive, the comparator output is OFF, producing a LOGIC 1 signal to the inputs of the sync notch generators  506  and  507  via resistor  526  and diode  528 . When the input signal is negative, the comparator output is ON, conducting to signal ground, producing a LOGIC 0 signal to the inputs of the sync notch generators  506  and  507  via resistor  527 . This action generates a square wave digital pulse train that is at the same frequency as the input signal. 
         [0043]    The sync notch generators  506  and  507  consist of two missing pulse detectors (MPD) in a single integrated circuit. Each MPD is a retriggerable one-shot multivibrator. The time constant for sync notch generator  506  is set by capacitor  529  and resistor  530  for a frequency slightly lower than the fundamental helmet light frequency, producing a continuous LOGIC 0 at the not-Q output any time the input signal is at or above the helmet light frequency. The time constant for sync notch generator  507  is set by capacitor  531  and resistor  532  for a frequency slightly higher than the fundamental helmet light frequency, producing a digital pulse train at the Q output any time the input signal is at or below the helmet light frequency. Diodes  533  and  534  and resistor  535  logically AND these two signals to produce the sync notch to gating transistor  508  that strobes the display ON when the helmet light signal frequency is detected. 
         [0044]    While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. One other such embodiment would allow a plurality of light sources that have unique identities encoded in the specific characteristics of each light source providing a unique photometric signature for each light source, and a handheld photodetector probe that can be set to detect the unique identity of a particular light source thus refining the search for a particular firefighter.