Abstract:
A laser range finder scope for measuring the distance between a target and the scope based on the time-of-flight of laser impulses is disclosed as including means for transmitting laser impulses toward the target and generating a first time signal corresponding to the transmission; means for receiving laser impulses reflected from the target and generating a second time signal corresponding to the reception; means for delaying said first time signal to provide a third time signal; means for calculating the time-of-flight by comparing said second time signal and third time signal; and a scope with a reticle with a plurality of indicia selectively lightable to each indicate the appropriate reticle scale to aim at the target.

Description:
[0001]    This invention relates to a laser range finder scope, in particular such a range finder scope used for determining the distance of a target. 
       BACKGROUND OF THE INVENTION 
       [0002]    A known approach to measuring distance of a target is to measure the time of flight of a narrow beam of light emitted from the measuring system to and back from the target, and to calculate the distance of the target on the basis of the time that has elapsed. In a laser range finder, the pulse of light is a beam of laser. 
         [0003]    Some such laser range finders are incorporated with a scope, or called telescopic sight, which is used for magnifying the image of the target for viewing and giving an accurate point of aim for weapons, such as firearms, airguns and crossbows. Such scopes come with a variety of different reticles, ranging from the traditional crosshairs to complex recticles designed to allow the shooter to estimate accurately the range to the target, to compensate for the bullet drop, and so on. 
         [0004]    In such conventional laser range finder scopes, the measured distance is usually projected onto the scopes. This not only obstructs part of the image as viewed by the shooter, but the shooter also has to carry out calculation before adjusting the leveling of the weapon for accurate shooting. It is thus an object of the present invention to provide a laser range finder scope in which the aforesaid shortcomings are mitigated, or at least to provide a useful alternative to the public. 
       SUMMARY OF THE INVENTION 
       [0005]    According to a first aspect of the present invention, there is provided a laser range finder scope for measuring the distance between a target and the scope based on the time-of-flight of laser impulses; including means for transmitting laser impulses toward the target and generating a first time signal corresponding to the transmission; means for receiving laser impulses reflected from the target and generating a second time signal corresponding to the reception; means for delaying said first time signal to provide at least a third time signal; means for calculating the time-of-flight by comparing said second time signal and said third time signal; and a scope with a reticle with a plurality of indicia selectively lightable to each indicate the appropriate reticle scale to aim at the target. 
         [0006]    According to a second aspect of the present invention, there is provided a method for indicating the distance of a target based on the time-of-flight of laser impulses; including steps of transmitting laser impulses toward the target; generating a first time signal corresponding to the transmission; receiving laser impulses reflected from the target; generating a second time signal corresponding to the reception; delaying said first time signal to provide at least a third time signal; calculating the time-of-flight by comparing said second time signal and said third time signal; calculating the distance of the target based on the calculated time of flight; and lighting one of a plurality of indicia on a reticle of a scope to indicate the appropriate reticle scale to aim at the target. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0008]      FIG. 1  is a schematic diagram showing the lens arrangement of a laser range finder scope according to a preferred embodiment of the present invention; 
           [0009]      FIG. 2  is a schematic diagram showing the operational arrangement of the laser range finder scope of  FIG. 1 ; 
           [0010]      FIG. 3  is a schematic diagram showing a circuit arrangement of the laser range finder scope of  FIG. 1 ; 
           [0011]      FIG. 4A  is a conventional reticle; 
           [0012]      FIG. 4B  is a recticle of the laser range finder scope of  FIG. 1 ; 
           [0013]      FIG. 5  shows a first delay arrangement of the laser range finder scope of  FIG. 1 ; and 
           [0014]      FIG. 6  shows a second delay arrangement of the laser range finder scope of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    As shown in  FIGS. 1 and 2 , a laser range finder scope according to a preferred embodiment of the present invention includes a lens assembly  9  with a number of optical lens, including an object lens  19  and an ocular lens  18 , arranged for manipulating light  21  from a target to magnify the image of the target for viewing by a shooter at  17 . A reticle  16  is positioned in the lens assembly  9  for providing accurate aiming resolution and guidance, in a manner to be discussed below. 
         [0016]    When in use, a shooter presses a button  10  to activate a circuit  11  to generate a signal pulse to drive a laser diode  12  to emit an infra-red laser beam  22  towards the target. The laser beam  22  is outputted from the laser range finder scope through an optical lens  13  to reduce output noise. Laser  23  falling onto and reflected by the target is detected by an Avalanche photodiode (APD)  15  via an optical lens  14  for reducing the noise in the received signals caused by the environment. The APD  15  converts the optical signals into electrical signals to enable the circuit  11  to calculate the distance of the target. In particular, the circuit  11  calculates the time-of-flight between transmission of the laser beam  22  and reception of the laser beam  23  reflected by the target. 
         [0017]    Turning now to  FIG. 3 , upon pressing of the button  10 , the circuit  11  activates a pulse generator  25  to trigger a laser diode driver  26 , which provides power to activate a laser diode  27  to emit a narrow laser beam  22 . The APD  15  detects the laser light  23  reflected from the target, converts the signals into electrical signals, and feeds the converted signals to a time-to-distance converter  29 . The time-to-distance converter  29  calculates the time-of-flight of the emitted laser  22  and the reflected light  23 , with reference to time signals of a system clock  28 . Thus, choosing a system clock  28  with a higher frequency can increase the resolution of distance measurement. Data outputted by the time-to-distance converter  29  are fed to a combination logic circuit  31  for mapping the data output with a certain output pattern on the reticle  16 . 
         [0018]    The combination logic circuit  31  also controls the operation of the converter  29  and a status control logic  32 . When the APD  15  does not receive any reflected laser beam and the converter  29  reaches full state (overflows), the combination logic circuit  31  will reset the converter  29  and provide signals to the status control logic  32  indicative of an overflow at the converter  29 . 
         [0019]    If the status control logic  32  receives signals indicating that the converter  29  overflows, the status control logic  32  will determine whether the converter  29  is to recalculate the time of flight or not on the basis of the control from the system clock  28  and the pulse generator  25 . The status control logic  32  also provides an overall control, with an interface  34  allowing the shooter to implement input switch control and displaying the current status of the system. 
         [0020]    The status control logic  32 , the time-to-distance converter  29 , and the combination logic circuit  31  are all integrated into a complex programmable logic device (CPLD) or a field-programmable gate array (FPGA) type integrated circuit (IC)  24 , which affords a small size circuit, short gate-to-gate propagation time, low cost, and the ability to implement a high speed circuit. 
         [0021]      FIG. 4A  shows a conventional reticle  35 , which displays in word form  37  the distance of the target measured by a conventional laser range finder scope, e.g. “Distance: 120 Meters”. For example, in this conventional reticle  35 , the centre reticle  38  is set for a 100-meter shooting distance, the next upper reticle scale  39  is 20 meters less than the centre reticle  38 , i.e. 80 meters, whereas the next lower reticle scale  40  is 20 meters more than that of the centre reticle  38 , i.e. 120 meters. Thus, if the measured distance is 120 meters, the shooter should aim the reticle scale  40  at the target, whereas if the measured distance is 80 meters, the shooter should aim the reticle scale  39  at the target. A disadvantage associated with this conventional reticle  35  (and thus a laser range finder scope with this conventional reticle  35 ) is that the shooter has to carry out calculation before arriving at the proper reticle scale for aiming. It also means that the shooter has to know the pre-set shooting distance of the centre reticle  38  and the difference of distance between successive reticle scales. 
         [0022]    According to the present invention, a new reticle  135  is provided, and as shown in  FIG. 4B . In this reticle  135 , once the laser range finder scope according to this invention determines the distance between the scope and the target, it does not display the distance on the reticle  135  in word form, but will light up one of a number of lightable dots to indicate the reticle scale which the shooter should use for aiming at the target. In this way, the shooter does not have to carry out any calculation, nor to know the distance difference between successive reticle scales. 
         [0023]    Assuming that in the new reticle  135 , the centre reticle  138  is set for a 100-meter shooting distance, the next upper reticle scale  139  is 20 meters less than the centre reticle  138 , i.e. 80 meters, whereas the next lower reticle scale  140  is 20 meters more than that of the centre reticle  38 , i.e. 120 meters. If the measured distance of the target is 100 meters, only the red dot on the reticle scale  138  will light up; if the measured distance is 120 meters, only the red dot on the reticle scale  140  will light up; and if the measured distance is 80 meters, only the red dot on the reticle scale  139  will light up, and so on. The shooter then simply aims the lighted red dot on the reticle  135  at the magnified image of the target for shooting. 
         [0024]    As a first implementation of a time-to-distance converter  29 , and as shown in  FIG. 5 , a time-to-distance converter  29  includes a shift register  42  with a number of registers (Register  1 , Register  2 , . . . Register n) connected in series, which provides a fixed time delay function, and the time delay propagates from one register to another. When a shooter presses the button  10 , simultaneously with the transmission of the laser beam  22 , a start measure signal  45  is generated and received at the input of Register  1 , and the shift register  42  begins generating the time delay from register to register, with the time delay based on the frequency of the system clock  28 . 
         [0025]    Each register (Register  1 , Register  2 , . . . Register n) is connected with a respective AND gate  43  for inputting different time delay for output by the respective AND gate  43 . The APD  15 , upon reception of the reflected laser signal, also outputs signals to the input of the AND gates  43 . Only one AND gate  43  will have an operational logic high of both the APD  15  input and the register input, and the time delay of that AND gate  43  is taken as the time that has elapsed between transmission and reception of the laser beam, and to be used for arriving at the distance between the scope and the target. Such an arrangement can minimize the number of components if the measured distance levels is relatively small, say up to ten distance levels. 
         [0026]    A more sophisticated arrangement of a time-to-distance converter  29  is shown in  FIG. 6 , in which a counter  147  is provided for counting the number of delay cycles which a shift register  142  has run. When a shooter presses the button  10 , simultaneously with the transmission of the laser beam  22 , a start measure signal  145  is generated and received at the input of Register  1 , and the shift register  142  begins generating the time delay from register to register, with the time delay based on the frequency of the system clock  28 . 
         [0027]    Each register (Register  1 , Register  2 , . . . Register n) is connected with a respective AND gate  143  for inputting different time delay for output by the respective AND gate. The APD  15 , upon reception of the reflected laser signal, also outputs signals to the input of the AND gates  143 . Only one AND gate  143  will have an operational logic high of both the APD  15  input and the register input. The counter  147  counts the number of cycles of running of the shift register  142 . The counter output  148  is multiplied by the current delay time value from the current shift register  142  to calculate the time delay, corresponding to the time-of-flight of the laser pulse. In such an arrangement, it only requires a shift register with eight registers and a 4-bit counter to provide up to 8*6−1 (i.e. 127) time delay levels. 
         [0028]    It should be understood that the above only illustrates examples whereby the present invention may be carried out, and that various modifications and/or alterations may be made thereto without departing from the spirit of the invention. 
         [0029]    It should also be understood that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any appropriate sub-combinations.