Abstract:
The present invention is a method and an apparatus of a laser range detector, a delay circuit is comprised for generating a plurality of delay signals. With the delay signal, the precision of detecting could be improved without faster clock signals or higher power consumption.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/487,623 filed Jan. 20, 2000, now abandoned which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a laser range detector and more particularly pertains to a method and apparatus for a laser range detector to detect a distance precisely. 
     2. Description of the Related Art 
     It is convenient to use a laser beam to detect the distance from a laser range detector to a target point. 
     FIG. 1 of the drawings illustrates a structure of a laser range detector in the prior art. A MPU  130  outputs a trigger signal to a clock unit  120 , the clock unit  120  receives the trigger signal and outputs an emitting signal to an emitter  110  and outputs a clock signal to a sampler  160 . The emitter  110  receives the emitting signal and outputs a pulse S 0  to a target point and a receiver  150  receives a pulse S 1  reflected from the target point, the features of the pulse S 1 , for example, the waveform or the period are similar to the pulse S 0 . The receiver  150  outputs the pulse S 1  to the sampler  160 . The sampler  160  samples the pulse S 1  according to the clock signal and outputs pulse clock data corresponding to the pulse S 1  to a register  170 . The register  170  stores the pulse clock data. The MPU  130  receives the pulse clock data from the register  170  and calculates the time between the pulse S 0  and S 1 , then calculates the distance to a target point. 
     A problem with the laser range detector is the precision of the detection. As illustrated in FIG. 2, a pulse S 0  is output by a laser range detector, a pulse S 1  and a pulse S 2  are reflected by the target and are received by a laser range detector, wherein the pulse S 1  and S 2  are sampled at the same clock so the distances calculated are the same (both at 122 th  clock). In fact, the distances are different because the pulse S 11  and S 21  are not the same. A faster clock generator can improve the precision of the detection because a pulse can be sampled more times. But a faster clock generator is expensive and a circuit working at a faster clock is complicated. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing disadvantage inherent in the laser range detector in the prior art, it is one object of the present invention to provide a method and an apparatus to detect a distance precisely for a laser range detector. 
     To attain the object, the present invention provides a method for a laser range detector to detect a distance precisely. The method including the following steps: first, emitting a first signal to a target; second, receiving a second signal which is the first signal reflected by the target; then generating one or more delay signals; then generating a plurality of pulse clock data from sampling the second signal or the delay signals; then calculating a precise time according to the pulse clock data; and calculating a precise distance according to the precise time, wherein each delay signal is delayed for a multiple default time from the second signal and the period of the second signal is smaller than the default time. 
     To attain the object,.the present invention provides an apparatus for a laser range detector to generate a plurality of delay signals, the apparatus including: an input terminal for inputting a second signal; and one or more delay units for generating one or more delay signals; and a switching circuit for selectively outputting one of the second signals or the delay signals; wherein the feature of the delay signal is similar to the second signal. 
     To attain the object, the present invention provides an apparatus for a laser range detector to detect a distance precisely, the apparatus including: a processor for calculating a precise time and a precise distance; and a clock generator for outputting clock signals; and an emitter for emitting a first signal to a target; and a receiver for receiving a second signal collided from a target; and a delay circuit for passing the second signal and outputting one or more delay signals; and a sampler for sampling the second signal or the delay signals; and-a register for storing a plurality of pulse clock data corresponding to the second signal or the delay signals; wherein the feature of the second signal and the delay signals are similar to the first signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein: 
     FIG. 1 illustrates a block diagram of a laser range detector in the prior art; 
     FIG. 2 illustrates a timing diagram of pulse signals; 
     FIG. 3 illustrates a block diagram of a preferred embodiment of the invention; 
     FIG. 4 illustrates a block diagram of a preferred embodiment of a delay circuit of the invention; and 
     FIG. 5 illustrates a timing diagram of the prefer embodiment; 
     FIG. 6 illustrates a flow diagram of the method for improving the precision of the invention. 
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the drawings, FIG. 3 illustrates a block diagram of a preferred embodiment of the invention. A MPU  230  outputs a trigger signal to a clock unit  220 . The clock unit  220  receives the trigger signal and outputs an emitting signal to an emitter  210  and outputs a clock signal to a sampler  270 . The emitter  210  receives the emitting signal and outputs a pulse S 0  to a target and a receiver  250  receives a pulse S 1  reflected by the target, the feature of the pulse S 1 , for example, the waveform or the period, are similar to the pulse S 0 . Then, the receiver  250  outputs a pulse S 11  to a delay circuit  260 . The delay circuit  260  receives the pulse S 11  and generates one or more delayed pulses, such as a pulse S 12 . Wherein the pulse S 12  is delayed for a default time from the pulse S 11  and the period of the clock signal is smaller than the default time. The delay circuit  260  outputs the pulse S 11  and the pulse S 12  to the sampler  270 . The sampler  270  samples the pulse S 11  and S 12  according to the clock signal and outputs a plurality of pulse clock data corresponding to the pulse S 11  and S 12  to a register  280 , the register  280  stores the pulse clock data. The MPU  230  reads the pulse data from the register  280  and calculates the time between the pulse S 0 , S 11  and S 12  then calculates the distance to a target point precisely. 
     FIG. 4 illustrates a block diagram of a preferred embodiment of a delay circuit of the invention. The delay circuit  260  includes a plurality of delay units and a plurality of TTL units, wherein one TTL unit corresponds to one delay unit. One delay unit  261   a  and one TTL unit  262   a  are illustrated in the delay circuit  260 . However, it is understood that any number of delay units and TTL Units can be used. In this embodiment, the pulse S 11  is input to the delay circuit  260 . The delay unit  262   a  outputs a pulse S 12  according to the pulse S 11  to a TTL unit  262   a , the TTL unit  262   a  alters the waveform of the pulse S 12  and outputs a square wave of the pulse S 12  to a switching circuit  268 . Each delay unit delays the pulse S 11  for a multiple of a default time, for example, the pulse S 12  is delayed from the pulse S 11  for a default time as shown as in FIG.  2 . It is understood that if the delay circuit  260  further comprises a delay unit  261   b  and a TTL unit  262   b , a pulse S 13  generated from the delay unit  261   b  delays the pulse S 11  for twice the default time. A third delay unit would delay the pulse S 11  for three times the default time and so on. The switching circuit  268  passes the pulse S 11  or S 12 , wherein the switching circuit  268  is a N to 1 or gate. 
     The default time can be selected according to the delay unit and the TTL unit within the delay circuit. For the default delay time setting, we choose accuracy number (R) according to the desired accuracy and delay circuit unit performance from the following formula:          t   k     =       (     Q   *   d     )     -         M   k     *   d     R                              
     where t k  is the kth delay time, M k =k and R are the accuracy number, k is the natural number from 0 to R-1, d is the operated clock period and set as 12.192*10 −9  seconds, and Q is the delay number (Q&gt;R). 
     For example, for achieving the d/2 accuracy, the accuracy number R is 2 and the other parameters are: K=0, 1; Q=3; t 0 =3d; t 1 =3d−d/2. If k=1, Q=3, M k =1 and R=2 then t 1 =3*d−[(1*d)/2]=2.5d. If k=2 then t 2 =5d and so on. Therefore, the pulse S 12  delays the pulse S 11  for 2.5 clock periods and the pulse S 13  delays the pulse S 11  for 5 clock periods and so on. It is understood that the default time is larger than one clock period so the second signal and each delay signal corresponding to the second signal can be sampled particularly. 
     On the basis of the time difference between the pulse S 11  and S 12 , the pulse S 11  is sampled at the 122 th  clock and the pulse S 12  is sampled at the 124 th  clock. In the preferred embodiment a precise time can be calculated with the pulse S 11  and the pulse S 12  and S 13  and so on. An indefinite time can be calculated with the tine between the pulse S 0  and the pulse S 11 , then the indefinite time can be corrected with the time between the pulse S 0  and the pulse S 11  and the pulse S 12  and so on. For example, a precise time Tprecise is calculated with the following equation:        Tprecise   =       T   o     +             ∑     k   =   1       R   -   1                         (       t   k     -     T   o       )     ×   k       -     Q   ×   d       R     .                              
     wherein the T 0  is the time between the emitted pulse and the pulse received from the receiver and the time T k  is between the emitted pulse and the k th  delay pulse. For example, T 0  is the time between pulse S 0  and the pulse S 11 , e.g. T 0  is 122*d=1.4874E-6 seconds. T 1  is the time between pulse S 0  and the pulse S 12 , e.g. T 1  is 124*d=1.5118E-6 seconds. Therefore, the Tprecise=1.4996E−6−1.5d=1.481E-6. 
     A distance can be calculated by a time. A precise distance Xprecise is calculated by the following equation:        Xprecise   =       Tprecise   *   3.28      E8     2                            
     wherein 3.28*E8 is the speed of light in meters. Therefore, the precise distance Xprecise is 1.481E-6*3.28E8/2=243 meter. 
     If a second pulse S 21  is reflected with the target in FIG. 5, and a delay pulse S 22  is generated by the delay circuit  260 , the pulse S 11  and the pulse S 21  are sampled at the same time, but the pulse S 22  is sampled at the 125 th  clock. In this case, Tprecise is 1.487E-6 and another Xprecise is a  244  meter. In the prior art, because the signal S 11  and S 21  could have been sampled at the 122 th  clock, the time Tprecise and the distance Xprecise have been measured simultaneously. Hence the laser range detector in the preferred embodiment detects a range from a target precisely. 
     As illustrated in FIG. 6, the present invention provides a method of a laser range detector. In step  510 , a first signal is emitted to a target. The first signal is emitted from a laser range detector. In step  520 , a second signal which is the first signal reflected by the target is received. The laser range detector detects a second signal reflected by the target and the feature of the second signal is similar to the first signal, wherein the feature includes the waveform or the period and so on. In step  530 , one or more delay signals are generated. A delay circuit in the laser range detector not only passes the second signal but also generates one or more delay signals. In step  540 , a plurality of pulse clock data is generated from sampling the second signal or the delay signals. A sampler in the laser range detector samples the second signal or the delay signals according to a clock signal generated from a clock generator, then outputs a plurality of pulse clock data to a register. The pulse clock data is the clock number of the second signal and the delay signals. And in step  550 , a precise time is calculated according to the pulse clock data. A MPU in the laser range detector calculates the precise time from the pulse clock data stored in the register. And in step  560 , a precise distance is calculated according to the precise time. The MPU in the laser range detector calculates the precise distance according to the precise time. 
     Finally, while the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.