Abstract:
A testing method for rangefinders is described and saves developing time of a required rangefinder. The method sets a default parameter of a rangefinder for emitting pulses, emits the firing pulses toward a target using an emission module according to the parameter, receives reflected pulses from the target and straylight according to the parameter by an receiving module; generates S/N data of the received pulse and the straylight with a testing system, resets the parameter or changing some components with different feature if no target signal can be recognized from the S/N data and repeats steps  2  to  4  until a target signal is recognized from the S/N data; and configures the rangefinder with the default parameter or the substitute component with which the target signal can be recognized from the S/N data.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a testing method used in rangefinders, and more particularly, to a testing method that saves the developing time of laser rangefinders.  
       BACKGROUND OF THE INVENTION  
       [0002]     From ancient times to the present, distance estimation is always very important for humanity in daily life. From the measuring tape to the geometrical rangefinder, people are always searching for a faster and more accurate measuring tool and more efficient method for solving the problem of distant measurement.  
         [0003]     Since conventional measuring tools, such as the geometrical rangefinder, need to be set up on a specific ground and operated by a person, errors and inaccuracy are inevitable.  
         [0004]     Therefore,when laser rangefinders be invented and appear in the market, it&#39;s very popularly with people. Reference is made to  FIG. 1 , which illustrates the basic principle of the laser rangefinder  10 . First, the laser rangefinder  10  emits a signal  102  of laser beam to the target  12  and records the emission time. The signal  102  possesses some certain pattern for ease of recognition. After the signal  102  arrives the target  12 , an inverse reflected signal  104  is produced according to optical theorem. The laser rangefinder  10  receives the reflected signal  104  and records the reception time. The reception time minus the emission time is the transmission time of the whole transmission process. Since the velocity of light is 3×108 meters per second, the transmission time multiplied by the velocity of light and then divided by 2 is the distance between the laser rangefinder  10  and the target  12 . However, even though the laser rangefinder can measure the distance quickly and precisely, the velocity of light is so great that it is complicated for the laser rangefinder to precisely estimate distance. Further, owing to the complexity of adjusting the laser rangefinder, laser rangefinders are always expensive and thus not popular with people.Besides, since laser rangefinders have a variety of applications, such as estimating distances, the physical property of the space being estimated, such as a water surface with high humidity, and other conditions using the principle of distance estimation with a laser beam, such as speed estimators used by police, the adjustment of emitted signals and received signals determines the quality of laser rangefinders. However, due to the shortage of integrated testing methods, only testing apparatus with individual estimating property can be chosen in accordance with the need in developing when producing current laser rangefinders. Such apparatus is expensive, inefficient and wastes time and effort. Hence, it has become important to set up a testing method that is flexible and can be used in every kind of laser rangefinder.  
       SUMMARY OF THE INVENTION  
       [0005]     An objective of the present invention is to provide a testing method for laser rangefinders in which every parameter of a laser rangefinder can be flexibly set to obtain the optimum value.  
         [0006]     According to the aforementioned objectives, the present invention uses a testing system to test a rangefinder. The testing system comprises a central processing unit, a display unit, and a memory unit, and the rangefinder comprises an emission module, a receiving module, and an analog/digital converter. The parameters for emission times, emission power of the laser, and receiving threshold voltages are set, and an emission module emits firing pulses toward a target in accordance with the default parameters. After the target reflects the pulses, the receiving module receives and filters the reflected pulses and accompanying stray-light according to the preset receiving threshold voltages, and then generates an analog signal. The analog signal will be converted to a digital signal via an analog/digital converter and sent back to the testing system and saved in a memory unit. The central processing unit accesses and analyzes the data in the memory unit to obtain its signal/noise ratio (S/N), and converts the same into visual data for display on the display unit. User checks the visual data on the display unit, and judges if the S/N meets the ideal value. The S/N is usually shown as a logarithm, in which the higher the value, the bigger the difference of the strength between the signal and the noise, i.e. the strength of the signal is bigger. If the S/N is too low, the parameters can be reassigned or the components with better features are substituted until the rangefinder achieves an optimum S/N ratio.  
         [0007]     Accordingly, the advantages of the present invention are as follows. First, the system collects and analyzes the original data of the laser rangefinder for different optical systems, emission voltages, threshold voltages for received signals, and the natural environment, and displays the signal/noise chart. Second, the system in the present invention can speed the testing process and the the parameters setting in the laser rangefinder to meet the requirements in every application.  
         [0008]     The following will describe the present invention in detail with reference to the drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The foregoing aspects and many of the attendant advantages of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0010]      FIG. 1  illustrates the basic principle of a conventional laser rangefinder;  
         [0011]      FIG. 2  illustrates the system block diagram according to the embodiment of the present invention;  
         [0012]      FIG. 3  illustrates the method flow diagram according to the embodiment of the present invention;  
         [0013]      FIG. 4  illustrates the example of processing the receiving signal emitted three times;  
         [0014]      FIG. 5  illustrates the schematics of accumulated showing up times/the distance according to the received signal;  
         [0015]      FIG. 6  illustrates the S/N chart according to the received signal;  
         [0016]      FIG. 7  illustrates an ideal schematics of accumulated showing up times/the distance; and  
         [0017]      FIG. 8  illustrates an ideal S/N chart. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     Reference is made to  FIG. 2 , which provides a block diagram of the present invention including the master units required in testing. The present invention uses a testing system  20  to control the motion of the laser rangefinder  22 , to process the reflected signals received and convert them into graphical S/N data for display on the display unit  206 . The testing system  20  mainly comprises the central processing unit  202 , the memory unit  204 , and the display unit  206 ; the laser rangefinder  22  mainly comprises the emission module  222 , the receiving module  224 , and the analog/digital (A/D) converter  226 . The central processing unit  202  herein is, for example, a microprocessor, a micro controller, or any apparatus with operation ability. Further, the memory unit  204  herein is, for example, a memory, a hard disk or any storage apparatus, and the display unit  206  is, for example, a cathode ray tube monitor (CRT), a liquid crystal display (LCD), or any apparatus with graphical display function. The testing system  20  is any apparatus comprising these three units, such as a computer, a workstation, or a personal digital assistant (PDA). Further, as well known by those skilled in the art, the input/output interface and buses needed for the testing system will be configured respectively in accordance with different systems.  
         [0019]     The aforementioned testing system  20  is mainly used to set flexibly the parameters of the laser rangefinder  22  to control the emission times and the power of the laser of the emission module  222  and the receiving threshold voltage of the receiving module  224  in the laser rangefinder  22 . The testing system  20  also processes the reflected analog signals from the target received by the receiving module  224 , converts them into digital signals via the analog/digital converter  226 , then statistically analyzes the signals to S/N data and plots them in visual chart with the central processing unit  202 , and finally outputs the same to the display unit  206  as reference for parameter adjustment by a user.  
         [0020]     The aforementioned central processing unit  202  is mainly used to control the motion of the emission module  222 , and perform the processing, analysis, and conversion of the received signals.  
         [0021]     The aforementioned memory unit  204  is mainly used to save control programs and receive signals.  
         [0022]     The aforementioned display unit  206  is mainly used to display the visual chart converted, analyzed, and plotted by the central processing unit  202 .  
         [0023]     The aforementioned emission modules  222  is connected to the central processing unit  202 , and drives the laser to emit according to the control signals from the central processing unit  202 .  
         [0024]     The aforementioned receiving module  224  is connected to the analog/digital converter  226 , and mainly used to receive the reflected signals from the target and straylight, and output an analog signal to the analog/digital converter  226 .  
         [0025]     The aforementioned analog/digital converter  226  is mainly used to receive the analog signal from the receiving module  224 , and convert it into a digital signal.  
         [0026]     The following will describe the procedure of the present invention with reference to the flow diagram. Reference is made to  FIG. 3  and  FIG. 2 . Steps are as follows.  
         [0027]     First, the parameter of the testing system  20  (step  30 ) is predetermined to control the emission times and the power of the firing pulses and the receiving threshold voltage of the receiving module  224  in the laser rangefinder  22 . Next, according to the parameter, the emission module  222  is commanded to emit a plurality of firing pulses toward a target (step  31 ). Meanwhile, according to the parameter, a receiving threshold voltage of the receiving module  224  to receive the reflected firing pulses from the target and stray-light is set (step  32 ), and an analog signal is output. Then, the analog signal is converted into a digital signal by the analog/digital converter  226  (step  33 ), and the digital signal is returned to the testing system  20  and saved in the memory unit  204 . Afterwards, the central processing unit  202  accesses the digital signal. Since the digital signal not only contains the reflected firing pulses, but also may contain the background noise with a different signal level, the central processing unit  202  needs to analyze and sum up all the values, compare the value of every emission signal in turn, and conclude to plot the S/N distribution chart of the signal to recognize the real target signal (step  34 ).  
         [0028]     The following examples describe the procedure of how the reflected digital signal from the target is analyzed and plotted in the S/N chart, and the timing and results of parameter adjustment.  
       EXAMPLE 1  
       [0029]     Reference is made to  FIG. 4 . If the predetermined emission time of the laser rangefinder  22  is three, and the inner clock signal is  40 , the first reflected signal from the target received by the receiving module is  41  and the second and the third reflected signals from the target are  42  and  43 , respectively. The signals  41 ,  42 , and  43  are converted into the digital signals  401 ,  402 , and  403 , respectively, through the analog/digital converter  226  in accordance with the inner clock signal  40 , and saved in the form of values in the memory unit  204  in order. The values are denoted  401 ′,  402 ′, and  403 ′ in order. At this moment, the central processing unit  202  computes the relative distance by multiplying the velocity of light by one half the time difference between the time of the emission module  222  emitting the pulse signal and the time of the receiving module  224  receiving the reflected signal. The digital signal  401 , for example, when the signal level “1” first shows up, might be the reflected signal from the target. If 3 clock signal cycles have passed between emitting the signal and receiving the reflected signal, and the clock signal cycle is 0.11 microseconds, then the signal cycle is 0.11×3=0.33 microseconds, the time for the laser light to travel to the target and back one time. Therefore, the distance is time (0.33/2=0.167 microsecond) multiplied by the velocity of light (3×108 meters per second), which is 50 meters. All the possible distance of the targets of the digital signals  401 ,  402 , and  403  can be derived in the same way. If the X-axis denotes the distance and the Y-axis denotes the accumulated showing up times, then the distribution will be as shown in  FIG. 5 . According to the ratio of the strength of the target signal (i.e. the strength of the signal 100 meter far) to the strength of the noise in every distance, and in the form of logarithm (db), a S/N chart in which the X-axis denotes the distance and the Y-axis denotes the strength ratio (db) as shown in  FIG. 6  will be plotted and shown in the display unit  206 , whereby users can distinguish the strength of the target signal from the background noise. It can be derived from  FIG. 5  that due to the insufficient emission times of sampling, the distribution of S/N in  FIG. 6  is too average to properly judge the target signal. Hence, the emission times needs to be reset (step  37 ).  
         [0030]     If the emission times is reset to 100 and steps  31  to  35  repeated to convert the reflected signal and compute the distance, a distribution chart in which the X-axis denotes the distance and the Y-axis denotes the accumulated showing up times as shown in  FIG. 7  will be plotted. According to the ratio of the strength of the target signal (i.e. the strength of the signal 100 meter far) to the strength of the noise in every distance, and in the form of logarithm (db), a S/N chart in which the X-axis denotes the distance and the Y-axis denotes the strength ratio (db) as shown in  FIG. 8  will be plotted and shown in the display unit  206 . As shown in  FIG. 8 , it is an ideal S/N distribution chart, whereby users can clearly determine the real distance of the target. Users can store the setting of the emission times in the laser rangefinder  22  (step  36 ) and finish the procedure of the whole system. Furthermore, the correction of the emitting parameter includes not only the emission times, but also the emission power. If the ideal S/N distribution cannot be acquired after repeatedly resetting the emission times, users may try to adjust the emission power to meet the demand. Reference is made to example 2.  
       EXAMPLE 2  
       [0031]     The emission power of laser usually needs to be reduced to avoid excessive background noise when measuring a close target. On the contrary, the emission power of laser usually needs to be raised to increase the discrimination of the target when measuring the distant targets. Therefore, a failure to acquire the ideal S/N distribution after repeatedly resetting the emission times indicates the necessity of adjusting the emission power of the laser. At this time, the emission power needs to be reset (step  37 ) and steps  31  to  35  repeated to convert the reflected signal and compute the distance as in example 1. A S/N chart in which the X-axis denotes the distance and the Y-axis denotes the strength ratio of the signal/noise will be plotted and shown in the display unit  206 . As shown in  FIG. 8 , it is an ideal S/N distribution chart, whereby users can clearly determine the distance of the target. Users can store the setting of the emission power in the laser rangefinder  22  (step  36 ) and finish the procedure of the whole system. However, if the ideal S/N distribution cannot be acquired after repeatedly resetting the emission times and the emission power, the receiving threshold voltage of the receiving module may need to be corrected. Reference is made to example 3.  
       EXAMPLE 3  
       [0032]     The receiving threshold voltage decides the least voltage of the receiving module to receive signals, and thus can filter out unnecessary noise. However, if the the target is too far away, the reflected signal may be so weak that the threshold voltage will filter it, and therefore, the receiving module cannot receive the reflected signal. At this time, the threshold voltage of the receiving module needs to be reset (step  37 ) and steps  31  to  35  repeated. Finally, the setting of the parameter is saved in the laser rangefinder  22 . Moreover, the property of the components will also affect the ideal of the S/N chart. Hence, the choices of the components are necessary and important during the developing of the laser rangefinder. Reference is made to example 4.  
       EXAMPLE 4  
       [0033]     The components of the laser rangefinder comprise the emission module, the receiving module, and the analog/digital converter. If the power of the emission module, the receiving sensitivity of the receiving module, and the analyzing ability of the analog/digital converter are insufficient, the requirements will not be satisfied however the parameters are set. At this time, one or several components need to be changed (step  37 ) and steps  31  to  35  repeated. The component is installed in the laser rangefinder  22  to finish the whole procedure.  
         [0034]     Hence, the advantages of the present invention are as follows. First, the system can collect and analyze the original data of the laser rangefinder in different optical systems, emission voltages, receiving voltages, receiving threshold voltages, and the natural environment, and display the signal/noise chart. Second, the system in the present invention can accelerate the testing and the setting of the parameters in the laser rangefinder to perform precision estimation.  
         [0035]     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative of the present invention rather than limiting of the present invention. It is intended that various modifications and similar arrangements be covered within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.