Abstract:
The present invention relates to a method for laser ranging with high precision and high efficient, a method for identifying distance mode automatically during laser ranging process, and a laser ranger with high precision, high efficient and low power waste. The accuracy of ranging is increased through multi classes of receiving process; the accuracy of ranging is further increased through the selection of distance mode and the adjustment of receiving sensitivity before the measuring steps are executed; the accuracy of ranging is further increased through executing jitter judgment on obtained distance measured values to discard the distance measured values that do not satisfy the setting conditions and judge whether the number of remaining distance measured values satisfies the setting quantity requirement; and the present invention is also of simple structure, high measurement efficiency, and low power waste.

Description:
CROSS REFERENCE TO THE RELATED PATENT APPLICATIONS 
       [0001]    The present application claims priorities of the Chinese patent application No. 200820163236.7 filed on Aug. 21, 2008 and the Chinese patent application No. 200910138155.0 filed on Apr. 29, 2009, which applications are incorporated herein by reference. 
       FIELD OF INVENTION 
       [0002]    The present invention relates to an apparatus for laser ranging in the field of laser range measuring, more particularly, a hand held, portable laser ranging apparatus; the present invention also relates to a method for laser ranging. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    Portable laser ranger is one of the development trends of laser ranger, and as an apparatus that can be carried or moved conveniently, portable laser ranger is widely used in engineering projects, such as architecture, traffic and etc., and in sports entertainment, such as golf, hunt and etc. The power supply for portable laser ranger usually depends on battery, which puts a higher requirement for the low power-waste, the system stability, and the measurement accuracy performances of laser ranger. 
         [0004]    The disadvantages of apparatus and method for laser ranging disclosed in U.S. Pat. Nos. 5,612,779, 6,226,077, 5,652,651 and 5,926,259 are described as follows:
       (1) The ranging accuracy is low;   (2) The power waste is large, which makes the range finders do not meet the mini-type and portable requirements thereof. The drive voltage for emitting laser pulses is from 110V to 140V, and the bias voltage of avalanche diode in receiving circuit is 50V or higher. The high voltages aforementioned are acquired through raising up a low-tension battery by a booster circuit and then dividing the gotten high voltage, which is of low conversion efficiency and high power waste, and brings interferences and radiations to the circuit of apparatus, furthermore, influences the ranging stability of laser ranger.   (3) The operation of exiting laser ranger as disclosed in U.S. Pat. No. 5,926,259 is complicated, and the error of which is bigger as well by reason of the manual choice of distance modes according to different weather condition and measured object;   (4) Lack of anti-shake function. Any kinds of tiny shaking of hand-hold side are enlarged more and more tremendous in measured object side while the distance between measured object and laser ranger is getting larger, and a bigger deviation is formed. So the excellent shaking identification function is powerful for the accuracy of a laser ranger.       
 
       SUMMARY OF THE INVENTION 
       [0009]    The first object of present invention is to provide a method for laser ranging with high precision and high efficient; 
         [0010]    The second object of present invention is to provide a method for identifying distance mode automatically during laser ranging process; 
         [0011]    The third object of present invention is to provide a laser ranger with high precision, high efficient and low power waste. 
         [0012]    According to one exemplary embodiment, the present invention relates to a method for laser ranging, which comprises the steps of: 
         [0013]    (1) Select a distance mode and then adjust the receiving sensitivity of reflected signal according to selected distance mode; 
         [0014]    (2) Set the number of laser pulse groups emitted during a measurement process as G D , the number of laser pulses included in one laser pulse group as I D , the maximum of absolute difference between two measured distance values arranged consecutively in first class receiving process as D A , the maximum of absolute difference between two virtual distance values sequenced consecutively in second class receiving process as D B , the minimum number of distance values included in an element association with maximum length gotten from each laser pulse group in the first class receiving process as D; 
         [0015]    (3) Emit G D  laser pulse groups to a target in a way of time diversity, each of the laser pulse group includes I D  ranging pulses with the same period, the ranging pulses reflect by the target and receive by a receiving circuit, I D  measured distance values correspondence to each of the ranging pulses are obtained after computing, and then execute Step (4) and Step (5) in turn on each laser pulse group; 
         [0016]    (4) First-class receiving process: arrange the I D  measured distance values according to the numerical value thereof; compute the difference between two consecutive measured distance values; the measured distance values sequenced consecutively and whose absolute difference values are smaller than or equal to the maximum absolute difference value D A  are combined in one element association, and the element association with the maximum element quantity is set to be a maximum length element association D max  of current group; 
         [0017]    (5) Set the number of measured distance values included in the maximum length element association D max  as x; compare x and set minimum number of distance values included in an element association with maximum length gotten from one laser pulse group D, if x≧D, the laser pulse group that the maximum length element association D max  belongs to is effective; process the x measured distance values by means of mean smoothing, and then obtain a first-class distance computation value; save the first-class distance computation value and return to Step (3) to process the measured distance values obtained from the next group of laser pulses; if the laser pulse group processed in this step is the last group of laser pulse, execute the subsequent steps; if x&lt;D, the laser pulse group that the maximum length element association D max  belongs to is noneffective, emit another group of laser pulse, and execute Step (4) and Step (5) in order to obtained I D  measured distance values; 
         [0018]    (6) Second class receiving process: arrange saved virtual distance values according to the numerical value thereof; compute the difference between two consecutive virtual distance values; the virtual distance values sequenced consecutively and whose absolute difference values are smaller than or equal to the maximum absolute difference value D B  are combined in one element association, and the element association with the maximum element quantity is set to be a maximum length element association for second class receiving processing D′ max ; the number of virtual distance values included in the maximum length element association D′ max ; is set as y; 
         [0019]    (7) Process the y virtual distance values by means of mean smoothing, and obtain a second class distance computation value, output the second class distance computation value as the result of current measurement process; end the measurement. 
         [0020]    The final measurement result is obtained by emitting multi groups of laser pulses, calculating and adjusting to get virtual first class distance measured value of each groups of laser pulses, and executing the second receiving process on multi first class distance measured values. When the first class distance computation value is determined to be noneffective for each group of laser pulses emitting in Step (3), another group of laser pulses will be emit; as a substitution, execute Step (4) to Step (5) to I D  distance measured values gotten from the re-emitted laser pulse group till a virtual first class computation value is gotten; and then, go back to process distance measured values gotten from the next group of laser pulses; if the process aforementioned is the executed on the last emitting group of laser pulses of Step (3), go to subsequent steps. The execution of Step (5) ensures the number of samples of distance measured values gotten from each group of laser pulses; the first class distance computation value obtained on the basis of a certain amount of distance measured values is more accurate. The second class receiving process executed after Step (5) is a farther process on multi virtual distance values gotten from the first class receiving process to increase the accuracy of measurement to a higher level. 
         [0021]    As the first preferable embodiment, the minimum number of distance virtual values included in the maximum length element association of the second class receiving process E and the time limit of one measurement T n  are set in step (2), and the real-time timing variable t is initialized in step (2) as well, there is a step (6.1) executed between step (6) and step (7), which is, compare the number of distance virtual values included in the maximum length element association D′ max ; and set minimum number of distance virtual values included in the maximum length element association of the second class receiving process E, if y&lt;E, and the real-time timing variable t≧T n , end current measurement and output an error indication. The minimum number of distance virtual values included in the maximum length element association of the second class receiving process E, the time limit of one measurement T n  could be set through the ways of manual setting and automatic setting, wherein, the setting value of minimum number E is equal to or less than the number of groups emitted during one ranging process G D . If the number of distance virtual values y included in the maximum length element association D′ max  is less than the set minimum number E, but measurement is overtime, the present measurement process is judged to end. Step (6.1) ensures the sample numbers of distance virtual values which are used for mean value smoothing process during second class receiving process, and the final ranging result is obtained based on curtain numbers of samples, which further ensures the accuracy as a following Step of Step (5) (which ensures the sample numbers of distance measured values of each laser pulse group). 
         [0022]    Furthermore, or as the second preferable embodiment, a process is executed after at least one step of step (1) to step (7), which is, compare the real-timing variable t and set time limit of one measurement T n , if t&gt;T n , the measurement is end and an overtime indication is output. For the purpose of preventing endless loop, a real-time timing variable t is further set, and the time limit of one measurement process is T n . During the in-order execution from Step (1) to Step (7), the judgment of time-consuming is executed after each Step, if consumed time is more than preset time-limit, current measurement process should be end, and output an overtime indication, which helps operators find out system error as soon as possible and avoids spending time on unwitting wait, and increases the ranging efficiency as well. The time limit T n  could be set through at least one way of manual setting and ex-factory setting. 
         [0023]    As the third preferable embodiment, the receiving sensitivity of reflected signal adjustment comprises the steps of: 
         [0024]    (1) Set pulse-width reference values of reflected laser pulse signal correspondence to each of the distance modes, Q 1 ˜Q a , wherein, the distance mode A i  is corresponding to the pulse-width reference values of reflected laser pulse signal Q i , i is a positive integer from 1 to a; 
         [0025]    (2) Emit a laser pulse group, and then measure the pulse width WI(i) of reflected laser pulse signal, wherein, i is a positive integer from 1 to a; 
         [0026]    (3) Compare the pulse width of reflected laser pulse signal WI(i) and the pulse-width reference value Q i  of selected distance mode Ai, if WI(i)≦Q i , the current sensitivity control parameter is fitness, end the sensitivity adjustment; if WI(i)&gt;Q i , the current sensitivity control parameter is unfitness, adjust the sensitivity control parameter, and return to execute Step (2) and Step (3). 
         [0027]    There are many interference signals between the emissive source and the subject, such as solar ray, laser pulse signals reflected by interferential subjects and etc. If the interference signals are received and processed as distance measured values, the final ranging result would be influenced deeply. So a suitable receiving sensitivity should be choose under the premise of getting the distance mode of current measured subject, to shield the interference signals. Compare with manual setting way, the automatic sensitivity adjusting way is more accuracy. The manual setting way is based on the experience of operator, predicted value, or prior ranging data in a large part, which is a choice of sensitivity based on estimated values. But, the automatic sensitivity adjusting way finds out the distance interval the measured subject belongs to firstly, chooses a suitable distance mode, compare the pulse width of reflected laser pulse signal and the pulse-width reference value of selected distance mode and adjust the receiving sensitivity of laser pulse reflecting signals. 
         [0028]    As the first preferable embodiment of the sensitivity adjustment step described above, in Step (2), the select of the distance mode and the measurement of the pulse width WI(i) both are based on one laser pulse group. 
         [0029]    As the second preferable embodiment of the sensitivity adjustment step described above, in step (2), the select of the distance mode is base on a first laser pulse group, and the measurement of the pulse width WI(i) is base on a second laser pulse group emitted after the first laser pulse group. 
         [0030]    The pulse width WI(i) of reflected signals could be acquired through two ways alternatively: the first way is computing the pulse width of emitting signals coupled with the process of distance mode selection; the second way is emitting another group of laser pulses for receiving sensitivity adjustment after the distance mode is determined. The first way is of lower power waste and higher efficiency, but the second way is of higher accuracy. 
         [0031]    As the third preferable embodiment of the sensitivity adjustment step described above, the adjustment of sensitivity is made through adjusting the threshold voltage of a comparator. When the threshold voltage of comparator is lower, interference signals are easier to pass through the comparator and get into the subsequence circuit thereof; oppositely, if the threshold voltage of comparator is higher, interference signals are harder to pass through the comparator. When stronger shield capability to interference signals is needed, the threshold voltage of comparator should be increased to make the receiving end be with lower receiving sensitivity to reflected signals, which means, the threshold voltage of comparator and the receiving sensitivity are in inverse proportion, a lower threshold voltage of comparator is correspondence to a higher receiving sensitivity of reflected signals. 
         [0032]    As the forth preferable embodiment, the maximum of absolute jitter difference between two consecutive distance measured values is set as D s  in Step (2), Step (5.1) and Step (5.2) are executed between Step (5) and Step (6), which are, 
         [0033]    (5.1) compute the jitter difference between two adjacent measured distance values after sequencing, the measured distance values sequenced consecutively and whose absolute jitter difference are smaller than or equal to the maximum of absolute jitter difference D s  are combined in one element association, and the element association with the maximum element quantity is set to be a maximum length element association D″ max , set the number of measured distance values included in the maximum length element association D″ max  is z; 
         [0034]    (5.2) compare z and set minimum number of distance approximations include in each of the laser pulse groups D, if z≧D, the laser pulse group including the maximum length element association D″ max  is effective, return to step (3) and process the measured distance values obtained by next group of laser pulses; if z&lt;D, the laser pulse group including the maximum length element association D″ max  is noneffective, emit another group of laser pulses, and execute Step (4) to Step (5.2) on obtained I D  measured distance values. A tiny shaking in ranging operating end might be magnified larger and larger in the measured subject end along with the increasing of ranging distance, which makes a large deviation between the distance measured value and the actual subject distance. The distance measured values with lager margin of variation as a result of shaking should be discarded in Step (5) in order to increase the accuracy of measurement. Besides, the jitter difference between two adjacent measured distance values after sequencing should be smaller than set numbers of elements, which ensures the subsequence steps are executed on the basis of a certain amount of distance measured values, and further increases the accuracy of measurement. 
         [0035]    A method for selecting a distance mode in laser ranging, which comprises the steps of: 
         [0036]    (1) Divide the extreme measure distance Ia into a distance intervals [0˜I1], (I 1 ˜I 2 ), . . . (I a-1 ˜I a ), Iε[0,a], each of the intervals is corresponding to one distance mode, which are A 1 ˜A a , a≧1, the distance modes A 1 ˜A a  are corresponding to a parameter configurations of ranging circuit; 
         [0037]    (2) Set a laser pulse group with I D  laser pulses, divide the I D  laser pulses into a sub-groups, each of which includes I g  ranging pulses, namely, I D =a×I g ; 
         [0038]    (3) Select a distance mode which is correspondence to target distance interval, and then emit a sub-group of laser pulses to the interval; process the measured distance values reflected into the receiving circuit and got calculated distance values of the interval; 
         [0039]    (4) Compare the calculated distance values with the upper distance limit and the lower distance limit of the interval, if the calculated distance values are greater than the lower distance limit, and smaller than the upper distance limit as well, the target is in the interval, and the distance mode that the interval is correspondence to is chosen to be current operating mode for the target; or not, the target is not in the interval, select another distance interval as target distance interval, return to execute step (3). 
         [0040]    The distance between measured subject and ranging operation end (the emitting end of laser pulses) influences the ranging result to a certain extent. The uncontrollable factors laser pulses met during flight are increased along with the increasing distance between a measured subject and the ranging operation end. To determine the spatial position of measured subject and configure different ranging circuit parameters according to the distance interval the measured subject belongs to before the ranging steps are executed on measured subject can increase the accuracy of ranging steps executed subsequently. 
         [0041]    As the first preferable embodiment, the extreme flying distance of each sub-group of laser pulses is the upper distance limit of the distance interval which is correspondence to the sub-group. Suppose that a measured subject is located at the largest distance position of one distance interval from the laser pulse emitting end. In order to make the laser pulse signals of emitted laser pulse group can cover a whole distance interval; the longest flight distance of laser pulses of a laser pulse group is set to be equal with the upper limit distance value of the distance interval corresponding to the laser pulse group. The parameters of laser pulse signals driving circuit are configured according to the aforementioned principle. 
         [0042]    Furthermore, a levels of drive current are adopted when a sub-groups of laser pulses are emitting respectively, the drive current used for emitting laser pulses to the distance interval which is nearer to the emitting point is smaller than the drive current used for emitting laser pulses to the distance interval which is farther to the emitting point. The flight distance of laser pulse signals of each group is adjusted through adjusting the value of driving current. The drive current configured to laser pulse group with longer flight distance is larger than the drive current configured to laser pulse group with shorter flight distance. 
         [0043]    As the second preferable embodiment, a time-control times is set corresponding to the distance intervals respectively; laser pulses reflected into the receiving circuit in the corresponding time-control time of current distance interval are shielded as noisy signal; reflected signals getting into the receiving circuit after corresponding time-control time of current distance interval are regard as effective measured distance values, and calculated distance values of current interval are gotten by processing the effective measured distance values. To avoid the reflection of laser pulses by other interferential subjects other than measured subject, and getting an error distance ranging value, time-control time is set. 
         [0044]    Furthermore, the time-control time corresponding to a farther distance interval from the emitting point of laser pulses is longer than the time-control time corresponding to a nearer distance interval to the emitting point. The purpose of setting time-control time is to avoid the reflection of laser pulses by other interferential subjects located between measured subject and laser emitting end, and getting an error distance ranging value, so the duration of time-control time is adjusted according to the distance between a distance interval and laser pulse emitting point. 
         [0045]    As the third preferable embodiment or a preferable embodiment of the first or the second embodiment, the parameters of ranging circuit at least include drive current for laser emitting, and the time-control time. 
         [0046]    An apparatus for laser ranging, comprising: 
         [0047]    a power supply, supplying power to the laser ranging apparatus; 
         [0048]    a laser pulses emitting unit, emitting laser pulse signals, the emitted laser pulses get to a target through lens; 
         [0049]    a laser pulses receiving unit, receiving signals getting into the laser ranging apparatus; 
         [0050]    a receiving sensitivity adjusting unit, adjusting the receiving sensitivity of the laser pulse receiving unit, reflected laser pulses go through lens, the laser pulses receiving unit, and the receiving sensitivity adjusting unit connected with the laser pulses receiving unit in turn; 
         [0051]    a time-interval measuring unit, controlling the time-sequence of emitting laser pulse, computing the time-interval between the laser pulse emitting and the receiving thereof, measuring the pulse-width of reflected laser pulse signals, the time-interval measuring unit is connected with the laser pulse emitting unit and the receiving sensitivity adjusting unit; 
         [0052]    a micro-processor (MCU), connected with the time-interval measuring unit, the micro-processor (MCU) receives the information of emitting time-sequence, the time-interval of laser pulses, and the pulse-width of emitting signals, and moreover, chooses the distance modes, adjusts the receiving sensitivity, estimates the shaking-extent of measured distance values, and process the measured distance values of target to obtain ranging result according to received information and measured distance values. 
         [0053]    As the first preferable embodiment, laser pulses emitting unit comprises, 
         [0054]    a laser emitter, generating laser pulse signals; 
         [0055]    a switching circuit, connected with the laser emitter, when the switching circuit is on, the laser emitter emits laser pulses; 
         [0056]    a driving circuit, connected with the switching circuit, the driving circuit drives the laser emitter to emit laser pulse signal by controlling the on and off of the switching circuit, the output current of the driving circuit is one of the diverse driving currents; 
         [0057]    a sampling circuit of count start signal, getting the time message of the emitting instant of laser pulse, and outputting the time message to the time-interval measuring unit. 
         [0058]    As the second preferable embodiment, laser pulses receiving unit comprises a photoelectric conversion element, which converts received laser signals to electrical signals; the receiving sensitivity adjusting unit comprises, 
         [0059]    an amplifying circuit, connected with the photoelectric conversion element, the amplifying circuit amplifies the electrical signals output from the photoelectric conversion element; 
         [0060]    a comparator, connected with the amplifying circuit, the comparator converts the analog signals output from the amplifying circuit to digital signals, and outputs the digital signals to the time interval measuring unit; 
         [0061]    a D-A converter, converting the digital control signals output from the time interval measuring unit to analog signals, and outputting which to the comparator; 
         [0062]    the time interval measuring unit computes the pulse-width values of the digital signals output from the comparator, and outputs an adjustment signal to the D-A converter according to the result thereof, the comparator adjusts the threshold voltage according to the adjustment signal. 
         [0063]    As the third preferable embodiment, time interval measuring unit comprises, 
         [0064]    a clock generator, generating clock signal; 
         [0065]    a timing and processing module, comprising,
       a logic control unit, connected with the micro-processor (MCU) and the laser pulse emitting unit, the input end of the logic control unit receives the time message of the emitting instant of laser pulses;   a counter, controlled by the logic control unit to count the clock signal, the input end of the counter for inputting counting signals is connected with the clock generator, and the counting control end thereof is connected with the logic control unit;   a flip-latch, latching the count value of the counter, the flip-latch is connected with the micro-processor (MCU) through a paralleled to serial interface, and transmits the count value to the micro-processor (MCU) through the paralleled to serial interface, the micro-processor (MCU) computes to obtain distance value according to the count value;       
 
         [0069]    the logic control unit controls the start-stop time of latching the emitted laser pulses of flip-latch according to the input time message of the emitting instance of laser pulses and the receiving time thereof. 
         [0070]    The advantages of present invention are described as follows: 
         [0071]    The accuracy of ranging is increased through multi classes of receiving process; 
         [0072]    The accuracy of ranging is further increased through the selection of distance mode and the adjustment of receiving sensitivity before the measuring steps are executed; 
         [0073]    The accuracy of ranging is further increased through executing jitter judgment on obtained distance measured values to discard the distance measured values that do not satisfy the setting conditions and judge whether the number of remaining distance measured values satisfies the setting quantity requirement; 
         [0074]    The present invention is also of simple structure, high measurement efficiency, and low power waste. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0075]      FIG. 1  is a block diagram of the present invention; 
           [0076]      FIG. 2  is a circuit diagram of the laser pulse emitting unit according to the present invention; 
           [0077]      FIG. 3  is a block diagram of the receiving sensitivity adjusting unit according to the present invention; 
           [0078]      FIG. 4  is a block diagram of the timing and processing module according to the present invention; 
           [0079]      FIG. 5  is an operation flow diagram of the laser ranging method according to the laser ranging method of present invention;  FIG. 5  is separated into  FIG. 5   a  and  5   b;    
           [0080]      FIG. 6  is an operation flow diagram of the first class receiving process and the validity determinant process of distance values of the laser ranging method shown in  FIG. 5 ; 
           [0081]      FIG. 7  is an operation flow diagram the shaking-extent estimation process of the laser ranging method shown in  FIG. 5 ; 
           [0082]      FIG. 8  is an operation flow diagram of the receiving sensitivity adjustment process of the laser ranging method shown in  FIG. 5 ; 
           [0083]      FIG. 9  is an operation flow diagram of the distance mode selection method according to the present invention;  FIG. 9  is separated into  FIG. 9   a  and  9   b.    
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0084]    Through the embodiments described subsequently and the drawings combined with, the technique detailed of the present invention could be fully understood. 
         [0085]    A method for laser ranging, which comprises the steps of: 
         [0086]    (1) Select a distance mode and then adjust the receiving sensitivity of reflected signal according to selected distance mode; 
         [0087]    (2) Set the number of laser pulse groups emitted during a measurement process as G D , the number of laser pulses included in one laser pulse group as I D , the maximum of absolute difference between two measured distance values arranged consecutively in first class receiving process as D A , the maximum of absolute difference between two virtual distance values sequenced consecutively in second class receiving process as D B , the minimum number of distance values included in an element association with maximum length gotten from each laser pulse group in the first class receiving process as D, the maximum of absolute jitter difference between two consecutive distance measured values as D s ; 
         [0088]    (3) Emit G D  laser pulse groups to a target in a way of time diversity, each of the laser pulse group includes I D  ranging pulses with the same period, the ranging pulses reflect by the target and receive by a receiving circuit, I D  measured distance values correspondence to each of the ranging pulses are obtained after computing, and then execute Step (4) and Step (5) in turn on each laser pulse group; 
         [0089]    (4) First-class receiving process: arrange the I D  measured distance values according to their numerical value thereof, compute the difference between two consecutive measured distance values; the measured distance values sequenced consecutively and whose absolute difference values are smaller than or equal to the maximum absolute difference value D A  are combined in one element association, and the element association with the maximum element quantity is set to be a maximum length element association Dmax of current group; 
         [0090]    (5) Set the number of measured distance values included in the maximum length element association D max  as x; compare x and set minimum number of distance values included in an element association with maximum length gotten from one laser pulse group D, if x≧D, the laser pulse group that the maximum length element association D max  belongs to is effective; process the x measured distance values by means of mean smoothing, and then obtain a first-class distance computation value; save the first-class distance computation value as a virtual distance value; if x&lt;D, the laser pulse group that the maximum length element association D max  belongs to is noneffective, emit another group of laser pulses, and execute Step (4) and Step (5) in order to obtained I D  measured distance values; 
         [0091]    (5.1) compute the jitter difference between two adjacent measured distance values after sequencing, the measured distance values sequenced consecutively and whose absolute jitter difference are smaller than or equal to the maximum of absolute jitter difference Ds are combined in one element association, and the element association with the maximum element quantity is set to be a maximum length element association D″ max , set the number of measured distance values included in the maximum length element association D″ max  is z; 
         [0092]    (5.2) compare z and set minimum number of distance approximations include in each of the laser pulse groups D, if z≧D, the laser pulse group including the maximum length element association D″ max  is effective, return to step (3) and process the measured distance values obtained by next group of laser pulses; if z&lt;D, the laser pulse group including the maximum length element association D″ max  is noneffective, emit another group of laser pulses, and execute Step (4) on obtained I D  measured distance values; 
         [0093]    (5.3) return to Step (3) to process the measured distance values obtained from the next group of laser pulses; if the laser pulse group processed in this step is the last group of laser pulses, execute the subsequent steps; 
         [0094]    (6) Second class receiving process: arrange saved virtual distance values according to the numerical value thereof; compute the difference between two consecutive virtual distance values; the virtual distance values sequenced consecutively and whose absolute difference values are smaller than or equal to the maximum absolute difference value D B  are combined in one element association, and the element association with the maximum element quantity is set to be a maximum length element association for second class receiving processing D′ max ; the number of virtual distance values included in the maximum length element association D′ max ; is set as y; 
         [0095]    (6.1) compare the number of distance virtual values included in the maximum length element association D′ max ; and set minimum number of distance virtual values included in the maximum length element association of the second class receiving process E, if y&lt;E, and the real-time timing variable t≧T n , end current measurement and output an error indication; or not, emit another group of laser pulses, and go back to execute Step (4) to the gotten I D  measured distance values; 
         [0096]    (7) Process the y virtual distance values by means of smoothing, and obtain a second class distance computation value, output the second class distance computation value as the result of current measurement process; end the measurement. 
         [0097]    The final measurement result is obtained by emitting multi groups of laser pulses, calculating and adjusting to get virtual first class distance measured value of each groups of laser pulses, and executing the second receiving process on multi first class distance measured values. When the first class distance computation value is determined to be noneffective for each group of laser pulses emitting in Step (3), another group of laser pulses will be emit; as a substitution, execute Step (4) to Step (5) to ID distance measured values gotten from the re-emitted laser pulse group till a virtual first class computation value is gotten; and then, go back to process distance measured values gotten from the next group of laser pulses; if the process aforementioned is the executed on the last emitting group of laser pulses of Step (3), go to subsequent steps. The execution of Step (5) ensures the number of samples of distance measured values gotten from each group of laser pulses; the first class distance computation value obtained on the basis of a certain amount of distance measured values is more accurate. The second class receiving process executed after Step (5) is a farther process on multi virtual distance values gotten from the first class receiving process to increase the accuracy of measurement to a higher level. Likewise, more classes of receiving process could be set; and the selection of element association with maximum length and mean value processing would be executed on each class of receiving process to increase the accuracy of measurement. If producers want to further ensure the accuracy of gotten distance value, a third class receiving process or more subsequence receiving processes could be executed. Take third class receiving process for example, a third class distance computation value is obtained through executing Step (3) to Step (7) repeatedly, and executing the selection of element association with maximum length and mean value processing described in Step (6) to Step (7) on multi second class distance computation values repeatedly. More classes of receiving process can be concluded by the skilled in the art, and there is no more detailed description. 
         [0098]    In this embodiment, the selection of distance mode and the adjustment of receiving sensitivity of reflected signal could be carried out by manual and automatic setting alternatively. If the way of manual setting is adopted, operator chooses a suitable distance mode and receiving sensitivity of reflected signals according to actual situation through visual range estimation and some predictable information combined with. If the way of automatic settings is adopted, system decides a distance mode and sensitivity of reflected signals intelligently in Step (1) according to the actual situation of a subject, such as the distance between the laser pulse emitting point and the subject and the pulse width of laser pulse reflecting signals, through loading a distance mode selection program and a sensitivity adjustment program in which. Likewise, the parameters setting could also be carried out by manual and automatic ways alternatively in Step (2). If the manual way is adopted, operator could choose suitable parameters according to expected ranging accuracy, for example, if you want to achieve a high measurement accuracy, you could increase at least one parameter of the number of laser pulse groups emitted during one measuring process G D  and the number of laser pulses included in one group of laser pulses I D  and decrease at least one of the maximum of absolute difference between two measured distance values arranged consecutively in first class receiving process as D A  and the maximum of absolute difference between two virtual distance values sequenced consecutively in second class receiving process as D B , or increase the minimum number of distance values included in an element association with maximum length gotten from each laser pulse group in the first class receiving process as D, the parameters aforementioned could be preset as fixed values before the apparatus leave factory. 
         [0099]    The minimum number of distance virtual values included in the maximum length element association of the second class receiving process E, the time limit of one measurement T n  could be set through the ways of manual setting and automatic setting, wherein, the setting value of minimum number E is equal to or less than the number of groups emitted during one ranging process G D . If the number of distance virtual values y included in the maximum length element association D′ max  is less than the set minimum number E, but measurement is overtime, the present measurement process is judged to end. Step (6.1) ensures the sample numbers of distance virtual values which are used for mean value smoothing process during second class receiving process, and the final ranging result is obtained based on curtain numbers of samples, which further ensures the accuracy as a following Step of Step (5) (which ensures the sample numbers of distance measured values of each laser pulse group). Such kind of judgment process could also be added in Step (6.1), which is if y&lt;E and t&lt;T n , emit another group of laser pulses, and execute Step (4) to Step (5) on received I D  distance measured values, and then execute Step (6) to Step (7) on distance virtual values, which means that a new group of laser pulses could be emitted as long as the measurement is not overtime, Step (7) would not be executed until the limit setting y≧E is satisfied. 
         [0100]    Optionally, a process is executed after at least one step of Step (1)˜Step (7), which is, compare the real-timing variable t and set time limit of one measurement T n , if t&gt;T n , the measurement is end and an overtime indication is output. For the purpose of preventing endless loop, a real-time timing variable t is further set, and the time limit of one measurement process is T n . During the in-order execution from Step (1) to Step (7), the judgment of time-consuming is executed after each Step, if consumed time is more than preset time-limit, current measurement process should be end, and output an overtime indication, which helps operators find out system error as soon as possible and avoids spending time on unwitting wait, and increases the ranging efficiency as well. The time limit T n  could be set through at least one way of manual setting and ex-factory setting. 
         [0101]    A tiny shaking in ranging operating end might be magnified larger and larger in the measured subject end along with the increasing of ranging distance, which makes a large deviation between the distance measured value and the actual subject distance. The distance measured values with lager margin of variation as a result of shaking should be discarded in Step (5) in order to increase the accuracy of measurement. Besides, the jitter difference between two adjacent measured distance values after sequencing should be smaller than set numbers of elements, which ensures the subsequence steps are executed on the basis of a certain amount of distance measured values, and further increases the accuracy of measurement. In Step (2), the minimum number of distance values D might be set in the way of manual setting or system presetting. 
         [0102]    Step (5.1) and Step (5.2) could also be executed on the maximum length element association D max  after validity determinant of Step (5), which means to sequence the distance measured values in the maximum length element association D max  in value order, compute the jitter difference between two adjacent measured distance values after sequencing, choose a maximum length element association D″ max , and compare the number of measured distance values included in the maximum length element association D″ max  z and set minimum number of distance approximations include in each of the laser pulse groups D, and at last, judge the validity of laser pulse group which the maximum length element association D max  corresponds to. Step (4 ) to Step (5) and Step (5.1) to Step (5.2) could be executed synchronously, and choose the first obtained result of this two synchronous execution processes as a final result. 
         [0103]    A ranging quality factor Q m , a shaking factor S, and a ranging resolution ratio R 1  are set, according to empirical formulas, the maximum of absolute jitter difference D S =S×Q m ×R 1 . 
         [0104]    The receiving sensitivity of reflected signal adjustment comprises the steps of: 
         [0105]    (1) Set pulse-width reference values of reflected laser pulse signal correspondence to each of the distance modes, Q 1 ˜Q a , wherein, the distance mode A i  is corresponding to the pulse-width reference values of reflected laser pulse signal Q i , i is a positive integer from 1 to a; 
         [0106]    (2) Emit a laser pulse group, and then measure the pulse width WI(i) of reflected laser pulse signal, wherein, i is a positive integer from 1 to a; 
         [0107]    (3) Compare the pulse width of reflected laser pulse signal WI(i) and the pulse-width reference value Q i  of selected distance mode Ai, if WI(i)≦Q i , the current sensitivity control parameter is fitness, end the sensitivity adjustment; if WI(i)&gt;Q i , the current sensitivity control parameter is unfitness, adjust the sensitivity control parameter, and return to execute Step (2) and Step (3). 
         [0108]    In Step (2), the pulse width WI(i) of reflected signals could be measured through the ways mentioned below alternatively: 1. the select of the distance mode and the measurement of the pulse width WI(i) both are based on one laser pulse group; 2. the select of the distance mode is base on a first laser pulse group, and the measurement of the pulse width WI(i) is base on a second laser pulse group emitted after the first laser pulse group. The first way is of lower power waste and higher efficiency, but the second way is of higher accuracy. 
         [0109]    The adjustment of sensitivity is made through adjusting the threshold voltage of a comparator. When the threshold voltage of comparator is lower, interference signals are easier to pass through the comparator and get into the subsequence circuit thereof; oppositely, if the threshold voltage of comparator is higher, interference signals are harder to pass through the comparator. When stronger shield capability to interference signals is needed, the threshold voltage of comparator should be increased to make the receiving end be with lower receiving sensitivity to reflected signals, which means, the threshold voltage of comparator and the receiving sensitivity are in inverse proportion, a lower threshold voltage of comparator is correspondence to a higher receiving sensitivity of reflected signals. 
         [0110]    There are many interference signals between the emissive source and the subject, such as solar ray, laser pulse signals reflected by interferential subjects and etc. If the interference signals are received and processed as distance measured values, the final ranging result would be influenced deeply. So a suitable receiving sensitivity should be choose under the premise of getting the distance mode of current measured subject, to shield the interference signals. Compare with manual setting way, the automatic sensitivity adjusting way is more accuracy. The manual setting way is based on the experience of operator, predicted value, or prior ranging data in a large part, which is a choice of sensitivity based on estimated values. But, the automatic sensitivity adjusting way finds out the distance interval the measured subject belongs to firstly, chooses a suitable distance mode, compare the pulse width of reflected laser pulse signal and the pulse-width reference value of selected distance mode and adjust the receiving sensitivity of laser pulse reflecting signals. 
         [0111]    A method for selecting a distance mode in laser ranging, which comprises the steps of: 
         [0112]    (1) Divide the extreme measure distance Ia into a distance intervals [0˜I1], (I 1 ˜I 2 ), . . . , (I a-1 ˜I a ), Iε[0,a], each of the intervals is corresponding to one distance mode, which are A 1 ˜A a , a≧1, the distance modes A1˜Aa are corresponding to a parameter configurations of ranging circuit, the parameters of ranging circuit at least include drive current for laser emitting, and the time-control time. 
         [0113]    (2) Set a laser pulse group with I D  laser pulses, divide the I D  laser pulses into a sub-groups, each of which includes I g  ranging pulses, namely, I D =a×I g ; 
         [0114]    (3) Select a distance mode which is correspondence to target distance interval, and then emit a sub-group of laser pulses to the interval; process the measured distance values reflected into the receiving circuit and got calculated distance values of the interval; 
         [0115]    (4) Compare the calculated distance values with the upper distance limit and the lower distance limit of the interval, if the calculated distance values are greater than the lower distance limit, and smaller than the upper distance limit as well, the target is in the interval, and the distance mode that the interval is correspondence to is chosen to be current operating mode for the target; save current ranging current parameter configuration and continue to execute subsequence ranging steps on current subject; or not, the target is not in the interval, select another distance interval as target distance interval, return to execute step (3). 
         [0116]    The extreme flying distance of each sub-group of laser pulses is the upper distance limit of the distance interval which is correspondence to the sub-group. A levels of drive current are adopted when a sub-groups of laser pulses are emitting respectively, the drive current used for emitting laser pulses to the distance interval which is nearer to the emitting point is smaller than the drive current used for emitting laser pulses to the distance interval which is farther to the emitting point. 
         [0117]    A time-control times is set corresponding to the distance intervals respectively; laser pulses reflected into the receiving circuit in the corresponding time-control time of current distance interval are shielded as noisy signal; reflected signals getting into the receiving circuit after corresponding time-control time of current distance interval are regard as effective measured distance values, and calculated distance values of current interval are gotten by processing the effective measured distance values. The time-control time corresponding to a farther distance interval from the emitting point of laser pulses is longer than the time-control time corresponding to a nearer distance interval to the emitting point. 
         [0118]    The distance between measured subject and ranging operation end (the emitting end of laser pulses) influences the ranging result to a certain extent. The uncontrollable factors laser pulses met during flight are increased along with the increasing distance between a measured subject and the ranging operation end. To determine the spatial position of measured subject and configure different ranging circuit parameters according to the distance interval the measured subject belongs to before the ranging steps are executed on measured subject can increase the accuracy of ranging steps executed subsequently. 
         [0119]    Suppose that a measured subject is located at the largest distance position of one distance interval from the laser pulse emitting end. In order to make the laser pulse signals of emitted laser pulse group can cover a whole distance interval; the longest flight distance of laser pulses of a laser pulse group is set to be equal with the upper limit distance value of the distance interval corresponding to the laser pulse group. The parameters of laser pulse signals driving circuit are configured according to the aforementioned principle; the flight distance of laser pulse signals of each group is adjusted through adjusting the value of driving current. The drive current configured to laser pulse group with longer flight distance is larger than the drive current configured to laser pulse group with shorter flight distance. 
         [0120]    To avoid the reflection of laser pulses by other interferential subjects other than measured subject, and getting an error distance ranging value, time-control time is set. In present embodiment, the purpose of setting time-control time is to avoid the reflection of laser pulses by other interferential subjects located between measured subject and laser emitting end, and getting an error distance ranging value, so the duration of time-control time is adjusted according to the distance between a distance interval and laser pulse emitting point. Concretely, compute the time from emitting a laser pulse to the lower limit value of a distance interval to return to the receiving circuit according to the flight speed of laser pulse, and shield the reflected laser pulse signals under the computed time. In actual measurement process, the time-control time gotten through aforementioned computing method could be decreased or increased. 
         [0121]    An apparatus for laser ranging, comprising: 
         [0122]    a power supply  14 , supplying power to the laser ranging apparatus; 
         [0123]    a laser pulses emitting unit  11 , emitting laser pulse signals, the emitted laser pulses get to a target through lens  01 ; 
         [0124]    a laser pulses receiving unit  17 , receiving signals getting into the laser ranging apparatus; 
         [0125]    a receiving sensitivity adjusting unit  12 , adjusting the receiving sensitivity of the laser pulse receiving unit  17 , reflected laser pulses go through lens  02 , the laser pulses receiving unit  17 , and the receiving sensitivity adjusting unit  12  connected with the laser pulses receiving unit in turn; 
         [0126]    a time-interval measuring unit  13 , controlling the time-sequence of emitting laser pulse, computing the time-interval between the laser pulse emitting and the receiving thereof, measuring the pulse-width of reflected laser pulse signals, the time-interval measuring unit  13  is connected with the laser pulse emitting unit  11 , the receiving sensitivity adjusting unit  12 , and MCU  15 ; 
         [0127]    a micro-processor (MCU)  15 , connected with the time-interval measuring unit  13 , the micro-processor (MCU)  15  receives the information of emitting time-sequence, the time-interval of laser pulses, and the pulse-width of emitting signals, and moreover, chooses the distance modes, adjusts the receiving sensitivity, estimates the shaking-extent of measured distance values, and process the measured distance values of target to obtain ranging result according to received information and measured distance values; 
         [0128]    a monitor  16 , controlled by the MCU  15 , and displays ranging result and error information; 
         [0129]    an input keyboard  18 , inputs external control information to the MCU  15 . 
         [0130]    The laser pulses emitting unit  11  comprises, a laser emitter  23 , generating laser pulse signals; a switching circuit  22 , connected with the laser emitter  23 , when the switching circuit is on, the laser emitter  23 emits laser pulses; a driving circuit  21 , connected with the switching circuit, the driving circuit drives the laser emitter to emit laser pulse signal by controlling the on and off of the switching circuit, the output current of the driving circuit is one of the diverse driving currents; a sampling circuit of count start signal  24 , getting the time message of the emitting instant of laser pulse, and outputting the time message to the time-interval measuring unit. 
         [0131]    The laser pulses receiving unit comprises a photoelectric conversion element D 1 , which converts received laser signals to electrical signals. 
         [0132]    The receiving sensitivity adjusting unit  12  comprises, an amplifying circuit  32 , connected with the photoelectric conversion element D 1 , the amplifying circuit amplifies the electrical signals output from the photoelectric conversion element; a comparator  33 , connected with the amplifying circuit  32 , the comparator  33  converts the analog signals output from the amplifying circuit  32  to digital signals, and outputs the digital signals to the time interval measuring unit  13 ; a D-A converter  34 , converting the digital control signals output from the time interval measuring unit  13  to analog signals, and outputting which to the comparator  33 ; the time interval measuring unit  13  computes the pulse-width values of the digital signals output from the comparator  33 , and outputs a adjustment signal to the D-A converter  34  according to the result thereof; the comparator  33  adjusts the threshold voltage according to the adjustment signal. 
         [0133]    The time interval measuring unit  13  comprises a clock generator, a timing-and-processing module  133 , furthermore: 
         [0134]    The clock generator generates clock signal, and comprises TCXO (Temperature-compensation Crystal Oscillator)  131  and PLL (phase-locked loop)  132 , the TCXO  131  generates clock signals after frequency doubling by PLL  132 ; 
         [0135]    The timing and processing module  133 , comprising, a logic control unit  41 , connected with the micro-processor (MCU)  15  and the laser pulse emitting unit  11 , the input end of the logic control unit receives the time message of the emitting instant of laser pulses; a counter  42 , controlled by the logic control unit  41  to count the clock signal, the input end of the counter  42  for inputting counting signals is connected with the clock generator, and the counting control end thereof is connected with the logic control unit  41 ; a flip-latch  43 , latching the count value of the counter, the flip-latch is connected with the micro-processor (MCU)  15  through a paralleled to serial interface, and transmits the count value to the micro-processor (MCU) through the paralleled to serial interface  44 , the micro-processor (MCU)  15  computes to obtain distance value according to the count value; the logic control unit  41  starts the counter  42  according to the timing information of the emitting moment of laser pulses, and controls the flip-latch  43  save the count value of counter  42  according to the receiving moment of laser pulses. 
         [0136]    Combine with the laser ranging apparatus and the method described above; the present invention will be further described as followed: 
         [0137]    Turn on the source to actuate the apparatus, input each ranging parameters, such as the number of laser pulse groups emitted during a measurement process as G D , the number of laser pulses included in one laser pulse group as I D  and so on by input keyboard  18 , each of the parameters mentioned above might be set through different ways, such as system presetting, manual selection, presetting in factory, and input values manually with the instruction of system, the parameter setting modulation is selected according to actual need, and there is not going to give more examples; MCU  15  records each of set ranging parameters; 
         [0138]    Firstly, the distance mode choice step is executed; the driving circuit is controlled to output corresponding driving current according to the distance interval which the current emitting laser pulse group corresponding to, the laser emitter  23  emits a laser pulse group, and the sampling circuit of count start signal  24  acquires the timing information of the emitting moment of each laser pulse, the logic control unit  41  controls the counter  42  to count the clock signal of clock generator after receives the timing information, current count value will be latched in the flip-latch  43  for further processing by MCU  15  when the laser pulse receiving unit  17  or the logic control unit  41  receives reflected laser pulse signals, if the latching time of count value is the moment that the logic control unit  41  receives the reflected laser pulse, a system processing delay time should be deducted in processing phase; during the signal receiving process, MCU  15  assigns different time-control time for each group of laser pulses, laser pulse signals get into the photoelectric conversion element D1 under the time-control time are shield automatically; during the emitting process, the time-interval measuring unit  13  controls the emitting time sequence of laser pulses; 
         [0139]    Secondly, MCU  15  processes the count values output from the flip-latch  43 , which are corresponding to every laser pulses, to obtain the flight distance of each laser pulses, namely, the distance measured values; the distance mode selection step is executed and circuit parameters, such as driving circuit, time-control time, which are the selected distance mode corresponding to are saved; 
         [0140]    Thirdly, as to the reflected laser pulse signals including in the laser pulse group corresponding to determined distance mode, the time-interval measuring unit  13  computes to obtain the pulse width of emitting signals, and outputs the computation values to MCU  15 ; and then the sensitivity adjustment step is executed, if current receiving sensitivity is inappropriate, a processing result is output to the time-interval measuring unit  13 , the time-interval measuring unit  13  outputs an adjusting signal to the D-A converter  34  according to the processing result, the comparator  34  adjusts the threshold voltage thereof according to the adjusting signal; 
         [0141]    In the end, the distance measurement step is executed; the acquirement of distance measured values adopts the same method as the distance mode selection process aforementioned, the detailed execution steps of MCU  15  is described above. 
         [0142]    Elements disposed in a portable and hand-hold laser ranger is preferable to be of low power waste, in order to decrease the power waste and extent the use time.