JP2500733B2 - Laser distance measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser range finder,
In particular, the present invention relates to a laser range finder that projects a pulsed laser beam toward a target and measures the distance to the target based on the time from when the laser beam is projected until the reflected light reflected by the target is received.

[0002]

2. Description of the Related Art This type of laser distance measuring device generates a pulsed laser beam in a light transmitting section and projects the pulsed laser beam onto a target which is an object for distance measurement. The light receiving portion receives the laser light reflected by the target, and measures the time from the laser light emitting time at the light transmitting portion to the laser light receiving time at the light receiving portion (hereinafter, this time is referred to as reflection time), The distance to the target is measured from the relationship between this time and the speed of light. Here, at the time of detecting the laser light emission time at the light transmitter and the laser light reception time at the light receiver, the light reception signal level obtained by optoelectrically converting the light intensity of each laser light is set to a predetermined threshold. The time is detected when the received light signal level reaches a threshold value by comparing with the value.

In this case, since the laser light having a substantially constant light intensity is generated in the light transmitting section, the projection time of the laser light can be detected with high accuracy. On the other hand, in the light receiving section, when the target reflectance is different, the intensity of the received light is changed accordingly, so the time at which the light receiving signal level obtained therefrom reaches the threshold value is also changed. As a result, the reflection time, which is the basis of distance measurement, is changed, and an error occurs in distance measurement. For example, when the target reflectance is high, the light receiving signal level of the pulsed laser light received has a high peak value, so that the rising edge also becomes sharp,
The threshold is reached in a short time. On the other hand, when the target reflectance is low, the signal level of the received laser light has a low peak value, so that the rising edge becomes gentle,
It takes longer to reach the threshold. Therefore, the time difference between the times when the threshold value is reached appears as an error in distance measurement.

Therefore, conventional measures have been taken to correct the rising error of the signal. For example, in the one disclosed in Japanese Patent Laid-Open No. 2-49180, the received signal obtained by the light receiving unit is decomposed for each delay time of a plurality of buffers to measure the received pulse width, and the center of the received pulse width is measured. The reflection time is obtained as the light reception time and correction is performed. Further, in the technique disclosed in Japanese Patent Laid-Open No. 3-81687, the center of the pulse width of the projected laser light and the center of the pulse width of the received signal are respectively obtained, and the reflection time is calculated from the center time of each of these pulse widths. Is to seek. Further, the one disclosed in Japanese Patent Application No. 2-101291 attempts to eliminate the rise error by controlling the gain of the amplifier based on the signal level of the received laser beam and keeping the received signal level constant. .

[0005]

As described above, in the conventional distance measuring apparatus, an attempt has been made to eliminate the influence of the rising of the light receiving signal level in order to eliminate the distance measuring error due to the fluctuation of the already received signal level. . However, in the method of detecting the pulse width, it is necessary to detect the pulse width time of a signal having an extremely short pulse width, and it is actually difficult to detect such a pulse width time, and the detection error In consideration of the above, it is difficult to detect with high accuracy so as to eliminate the above-mentioned rising error in distance measurement. In this case, if the pulse width is measured by using the delay time of the buffer, it is not possible to obtain the resolution of the distance measurement below the distance that the buffer has the delay time. Further, when the light intensity of the received laser light is high and the light receiving detector is saturated and the received pulse width is widened backward, the detection error at the center of the pulse width becomes large and the distance measurement error becomes large. The problem may occur. Further, in the method of controlling the gain of the amplifier, it is required to control the gain control at a high response speed. Therefore, in order to realize this, it is necessary to use a high-speed operation element in the control circuit, which is expensive. There is a risk that problems such as The purpose of the present invention is to
It is an object of the present invention to provide a laser distance measuring device which has a relatively simple structure and eliminates an error in distance measurement caused by a difference in reflectance of a target and enables high-precision distance measurement.

[0006]

According to the present invention, a pulsed laser beam is projected onto a target, reflected light from the target is received, and the target is based on the time from the projection of the laser beam to the reception. In a laser range finder that measures the distance to, a photodetector that detects the received laser light as an electrical signal, a log amplifier that logarithmically amplifies the output of this photodetector, and a part of the output of the log amplifier is delayed. Delay element to
A peak hold circuit that holds the peak value of another part of the output of the log amp, a level shifter that obtains a voltage that is lower than the peak value by a certain voltage, and a light reception signal that compares the output of the delay element and the output of the level shifter. And a comparator for outputting. Here, the comparator uses the signal from the level shifter as a threshold value, and outputs the light reception time signal when the signal from the delay element reaches this threshold value. It also has a counter display section that receives the start signal that is output at the same time as the laser beam projection and that receives the light reception signal from the comparator as the stop signal. The counter display section displays the time from the start signal to the stop signal. Is measured, and the distance to the target is calculated from the measured time and light speed.

[0007]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a laser distance measuring device according to the present invention. The light transmitting section 10 is provided with a pulse generating section 11 and outputs a trigger signal. The laser light generator 12 generates pulsed laser light based on the trigger signal. This laser light is projected onto the target O, which is the object of distance measurement, through the light transmission optical system 13. Further, a timing signal is output from the laser light generator 12 based on the laser light generated, and this timing signal is input to a counter display unit 30 described later as a start signal SS for measuring a reflection time during distance measurement. . The timing signal (start signal) SS monitors, for example, generated laser light,
The obtained signal is compared with the threshold value, and the signal is output when the signal level exceeds the threshold value.

On the other hand, the light receiving section 20 has a light receiving optical system 21 for receiving the laser light reflected by the target O, and the laser light condensed by the light receiving optical system 21 is converted into a voltage corresponding to the light intensity. It has a photodetector 22 for converting to. The received light signal photoelectrically converted by the photodetector 22 is the log amplifier 2
3 and is logarithmically amplified here. The output of the log amplifier 23 is divided into two, and one is input to one input terminal of the comparator 25 through the delay element 24 set to a predetermined delay time. Also, the halved amplifier 23
The other output of is input to the peak hold circuit 26.
The peak hold circuit 26 holds the peak voltage of the output of the log amplifier 23 and outputs it. The peak hold circuit 26 includes a pulse generator 11 of the light transmitter 10.
It is reset each time by the trigger signal ST generated in. The peak voltage output from the peak hold circuit 26 is input to the level shifter 27, where it is shifted to a voltage lower by a certain voltage than the peak voltage. Further, the shifted voltage is applied to the comparator 2
It is input to the other input terminal of No. 5.

The comparator 25 compares the output of the log amplifier 23 input through the delay element 24 with the shifted peak voltage as a threshold voltage, and when the output reaches the threshold voltage, a stop signal is output. The SP is input to the counter display unit 30. Counter display section 30
Starts the time measurement based on the start signal SS and ends the measurement when the stop signal SP is input to obtain the reflection time. Further, calculation is performed using the obtained reflection time and light velocity, the distance to the target is calculated, and this is displayed.

The operation of the distance measuring device having the above configuration will be described with reference to the timing chart of FIG. Based on the trigger signal SS generated by the pulse generation unit 11, the laser light generation unit 12 generates pulsed laser light, and the laser light is monitored by the laser light generation unit 12 and the electric signal S1 obtained from this laser light is monitored.
((A) in the figure) is compared with a predetermined threshold value TH1, and a timing signal SS ((b) in the figure) is generated when the signal level exceeds the threshold value. Is input to the counter display unit 30. On the other hand, the reflected light from the target O passes through the light receiving optical system 21 and the photodetector 2
2 detects and a pulsed light receiving signal is obtained ((c) in the same figure). When this light reception signal is logarithmically amplified by the log amplifier 23, the output voltage level Vp of the photodetector 22 becomes a signal S2 amplified by two digits or more. Here, log amplifier 2
Even if the voltage level of the peak value changes , the light receiving signal incident on the signal No. 3 is always kept constant until it reaches the 1 / n level, while this light receiving signal is
The ordinate scale of the output voltage of the signal amplified in 23 is a uniform output scale. That is, the input voltage VIN and the output voltage VOUT of the log amp have a relationship represented by the following equation. VIN = D · Vo · exp [- (t-to) / E] ^{2 VOUT = A (logVIN + B} ) + C where, A-E are constants.

Then, this voltage signal is divided into two, and one of them is made a signal S3 delayed by a predetermined time T2 by the delay element 24 ((d) in the figure). The delayed voltage signal S3 is input to the + input terminal of the comparator 25.
Here, the predetermined time T2 which is the delay time is the received light signal
Must be at least 1/2 the pulse width of
Yes, it is generally preferable to set the pulse width to a value larger than the pulse width.
Good Further, the other amplified voltage signal S2 is input to the peak hold circuit 26 and the peak voltage is held, so that the output becomes the peak voltage, and this peak voltage is shifted to the low voltage side by the constant voltage by the level shifter ( The output TH2 is shown in FIG.
Is input to the-input terminal. In the comparator 25, the delayed voltage signal S3 ((d) in the figure) is set with the shifted voltage TH2 ((e) in the figure) as a threshold voltage.
(F) is output from the comparison result, and this is input to the counter display unit 30 as a stop signal SP. In the counter display unit 30, the start signal SS ((b) in the figure) from the laser light generation unit 12,
The reflection time T1 is measured based on each rising time of the stop signal SP ((f) in the figure). At this time, time t
The reflection time is a value obtained by subtracting the delay time T2 of the delay element from the time T1 obtained from the difference between 1 and t2, that is, T1-T2 = T. The target distance measurement is performed by performing calculation using the reflection time T and the light speed C.

Therefore, in this apparatus, one peak voltage of the output from the log amplifier 23 is held by the peak hold circuit 26 as shown in FIG. The voltage A shifted to the side is compared with the other voltage B output from the log amplifier 23 and delayed by the delay element 24. As a result, the voltages A and B are output from the comparator 25.
Is output as waveform C rising at the cross point of
The rising signal of the signal C serves as a stop signal SP to the counter display unit 30. Here, the constant voltage ΔV
Is the output voltage of the log amp 23 with respect to the lowest light receiving level
Set to a value smaller than. Then, when the input voltage VIN of the log amplifier 23 changes, for example, when the constant D is 1, 1/10, 1/100, as shown in FIG. 4, the log amplifier 23 changes according to the change of the input voltage level. The output level of the log amplifier 23 varies depending on the output level.
Since the logarithmic output is amplified by and the ordinate scale is uniform, and in the comparator 25, each output level is compared with a voltage shifted to the low voltage side by a constant voltage ΔV with respect to each peak voltage. , The constant timing t2 is always detected regardless of the fluctuation of the output level.

As described above, according to this laser range finder, it is possible to detect the time of the same waveform portion of the received light signal even when the received signal level is changed.
As a result, the reflected light amount of the pulsed laser light projected from the light transmitter fluctuates because the target reflectance differs, and even if the signal level obtained by receiving this fluctuates, the reflected light is received. The timing time can be accurately detected, and highly accurate distance measurement can be realized based on the light reception time. Therefore, it is not necessary to detect the pulse width as in the conventional case, and even in the case of a laser beam having an extremely short pulse width, it is possible to detect the time with high accuracy and improve the accuracy of distance measurement. Further, it is not necessary to use a high-speed operation element in the control circuit, and it is possible to avoid the cost increase with a simple configuration.

[0014]

As described above, according to the present invention, after the received light signal is amplified by the log amp, a part of the output is delayed and the other part is peak-held so that the peak value is kept at a constant level. Since the light reception time is detected by shifting and comparing the delayed signals based on this shifted value, the reflected light from the target is irrespective of the level of the light reception signal, that is, regardless of the difference in the reflectance of the target. The time when the light is received can be detected with high accuracy, and the accuracy of distance measurement obtained based on this time can be improved. Further, since it is not necessary to detect the pulse width and control the gain, there is an effect that the circuit configuration can be simplified and the cost of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a laser range finder of the present invention.

FIG. 2 is a timing chart for explaining the operation of the laser range finder of the present invention.

FIG. 3 is a signal waveform diagram for explaining the operation of the comparator.

FIG. 4 is a signal waveform diagram for explaining a comparison operation in a comparator at different signal levels.

[Explanation of symbols]

 10 Light Transmitter 11 Pulse Generator 12 Laser Light Generator 20 Light Receiver 22 Photodetector 23 Log Amplifier 24 Delay Element 25 Comparator 26 Peak Hold Circuit 27 Level Shifter 30 Counter Display O Target

Claims (3)

(57) [Claims] 1. A light transmitting unit for projecting pulsed laser light onto a target, and a light receiving unit for receiving reflected light from the target, wherein the target is based on the time from the projection of the laser light to the light reception. In a laser range finder that measures the distance of a photodetector, a photodetector that detects received laser light as an electrical signal, a log amplifier that logarithmically amplifies the output of this photodetector, and a part of the output of the log amplifier are delayed. A delay element, a peak hold circuit that holds some other peak value of the output of the log amp, a level shifter that obtains a voltage lower than the peak value by a certain voltage, and the delay element output and the level shifter output are compared. And a comparator that outputs a light reception signal. 2. The laser distance measuring apparatus according to claim 1, wherein the comparator uses the signal from the level shifter as a threshold value and outputs a light reception time signal when the signal from the delay element reaches this threshold value. 3. A counter display unit to which a start signal output simultaneously with the projection of laser light is input and a light reception signal from a comparator is input as a stop signal, and the counter display unit changes the start signal to the stop signal. 3. The laser distance measuring device according to claim 1, wherein the distance to the target is calculated from the measured time and the speed of light.