Laser rangefinder and method for digital signal processing thereof
View Patent ↗A method for digital signal processing is disclosed. Reflected laser signals are received and digitized to generate corresponding digital signals. The digital signals are accumulated to generate an accumulated signal. A digital filtering operation is applied to the accumulated signal to generate a filtered signal. A maximum signal value for the filtered signal is found and a threshold value is set accordingly. It is determined whether the maximum signal value is less than the threshold value, and, if not, a distance value is calculated.
1. A method for digital signal processing, comprising:
(a) sequentially emitting x signals and receiving the reflected signals;
(b) digitizing the reflected signals to corresponding digital signals;
(c) accumulating the digital signals to generate an accumulated signal;
(d) applying a digital filtering operation to the accumulated signal to generate a filtered signal;
(e) finding a maximum signal value for the filtered signal and setting a threshold value according to the accumulated signal;
(f) determining whether the maximum signal value is less than the threshold value; and
(g) if the maximum signal value is not less than the threshold value, calculating a distance value;
wherein the threshold value is represented by a first function f(x), wherein, if x1>x2, f(x1)≧f(x2) then [f(x1)/x1]≦[f(x2)/(x2)].
2. The method for digital signal processing as claimed in claim 1 , wherein the step (a) further comprises:
(a1) predefining a maximum number of emitting pulses y; and
(a2) sequentially emitting signals for the reflection signals.
3. The method for digital signal processing as claimed in claim 2 , wherein, when the number of emitting signals x is equal to the maximum emitting signals y and the maximum signal value is less than the threshold value, then displaying a no-target message.
4. The method for digital signal processing as claimed in claim 1 , wherein the step (e) further comprises calculating noise data N according to the accumulated signal and setting the threshold value as a second function g(x)=M+k×N based on the noise data N, where M represents an average value of the accumulated signal and k is a predefined parameter.
5. The method for digital signal processing as claimed in claim 4 , wherein the noise data N is a root-mean-square value or a mean absolute difference value of the accumulated signal minus the average value M.
6. The method for digital signal processing as claimed in claim 4 , wherein g(x)=M+k(x)×N, k(x) is a function of the number of emitting laser pulses x, and k(x1)≦k(x2) if x1>x2.
7. The method for digital signal processing as claimed in claim 1 , wherein the step (d) implements the digital filtering operation to the accumulated signal using a moving average method.
8. The method for digital signal processing as claimed in claim 1 , wherein the step (c) further comprises:
(c1) subtracting fixed pattern noise from the accumulated signal to obtain a correct signal for the accumulated signal and implementing the digital filtering operation according to the correct signal.
9. A method for digital signal processing, comprising:
(a) predefining a maximum number of emitting laser pulses y;
(b) shooting a first laser signal;
(c) receiving a first reflected laser signal corresponding to the first laser signal;
(d) digitizing and accumulating the first reflected laser signal to generate a first digital signal;
(e) applying a digital filtering operation to the first digital signal to generate a filtered signal;
(f) finding a maximum signal value for the filtered signal and setting a threshold value is according to the first digital signal;
(g) determining whether the maximum impulse signal value is less than the threshold value; and
(h) if the maximum impulse signal value is not less than the threshold value, calculating a distance value;
wherein the step (g) further comprises:
(g1) if the maximum signal value is less than the threshold value, and the number of laser pulses emitting x is equal to the maximum number of emitting laser pulses y, displaying a no-target message;
(g2) if the number of laser pulses emitting x is less than the maximum number of emitting laser pulses y, shooting a second laser signal and correspondingly receiving a second optical reflected laser signal;
(g3) digitizing and accumulating the second reflected laser signal to generate a second digital signal; and
(g4) accumulating the first and second digital signals to obtain an accumulated signal and repeating the steps (e)˜(h).
10. The method for digital signal processing as claimed in claim 9 , further comprising calculating noise data N according to the accumulated signal and setting the threshold value as a function g(x)=M+k×N based on the noise data N, where M represents an average value of the accumulated signal and k is a predefined parameter.
11. The method for digital signal processing as claimed in claim 10 , wherein the noise data N is the root-mean-square value or the mean absolute difference value of the accumulated signal minus the average value M.
12. The method for digital signal processing as claimed in claim 11 , wherein g(x)=M+k(x)×N , k(x) is a function of the number of emitting laser pulses x, and k(x1)≦k(x2) if x1>x2.
13. The method for digital signal processing as claimed in claim 9 , further comprising implementing the digital filtering operation to the accumulated signal using a moving average method.
14. A laser rangefinder, comprising:
a laser transmitter, sequentially emitting laser signals;
a receiving module, receiving reflected laser signals;
a data processing unit, digitally converting and accumulating the reflected laser signals to obtain an accumulated signal;
a filter, applying a digital filtering operation to the accumulated signal to generate a filtered signal;
a microprocessor, determining a maximum signal value for the accumulated signal, setting a threshold value according to the filtered signal, and determining whether the maximum pulse signal value is less than the threshold value, and, if not, calculating a distance value;
wherein the threshold value is represented by a first function f(x), (a function of the number of emitting laser pulses x), wherein, if x1>x2, f(x1)≧f(x2) and [f(x1)/x1]≦[f(x2)/(x2).
15. The laser rangefinder as claimed in claim 14 , wherein the microprocessor further calculating noise data N according to the accumulated signal and sets the threshold value as a second function g(x)=M+k(x)×N based on the noise data N, where M represents an average value of the accumulated signal and k(x) represents a predefined parameter, wherein k(x1)≦k(x2) if x1>x2.
16. The laser rangefinder as claimed in claim 14 , wherein the filter further subtracts fixed pattern noise from the accumulated signal to obtain a correct signal for the accumulated signal and implementing the digital filtering operation according to the correct signal.