JP2910452B2 - 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 method for emitting a laser pulse toward a target, receiving the laser pulse reflected by the target, and measuring a time difference between the emission time and the reception time of the laser pulse to the target. The present invention relates to a laser distance measuring device for obtaining a distance.

[0002]

2. Description of the Related Art FIG. 8 shows, for example, OPTICAL ENGI.
NEERING, April 1992, Vol. 3
1, No. 4, a block diagram of a laser distance measuring device described in pp. 768-781, wherein 1 is a laser oscillator, 2 is a laser power supply, 3 is a partial reflecting mirror, 4 is a transmission optical system, and 5 is a first photodiode. , 6 are receiving optical systems, 7
Is a second photodiode, 8 is an amplifier circuit, 9 is a signal processing circuit, 10 is a display, 11 is a collimating optical system, 12 is a reticle, 13 is a relay lens, and 14 is an eyepiece.

Next, the operation will be described. In FIG. 8, a laser oscillator 1 is driven by a laser power supply 2 and oscillates pulsed laser light (laser pulse). The laser pulse is partially reflected by the partial reflecting mirror 3 in the direction of the first photodiode 5 and partially reflected by the first photodiode 5.
And is detected. The signal output from the first photodiode 5 is input to the signal processing circuit 9 as a start signal. On the other hand, the laser pulse transmitted through the partial reflecting mirror 3 is emitted toward a target by the transmission optical system 4. The laser pulse reflected by the target is condensed by the receiving optical system 6, detected by the second photodiode 7, and output as a stop signal. The stop signal is amplified to a required level by an amplifier 8 and input to a signal processing circuit 9. The signal processing circuit 9 starts the clock when the start signal is input, and stops the clock when the stop signal is input. Then, the distance R to the target is obtained by the equation (1) using the elapsed time Δt of the timepiece and the light speed C, and the result is displayed on the display 10. R = C · Δt / 2 (1)

On the other hand, a target forms an image on the reticle 12 by the collimating optical system 11. The reticle 12 is a transparent plate on which a cross mark is marked, and when looking through the eyepiece 14, the cross mark and the target appear to overlap in the field of view. The center of the cross mark coincides with the optical axis of the collimating optical system 11, and furthermore, the transmitting optical system 4, the receiving optical system 6, and the collimating optical system 1
1 have the same optical axis. Therefore, if the target is aimed at the center of the cross mark by looking through the eyepiece lens 14, the target can be accurately irradiated with the laser pulse, and the target can be measured.

Incidentally, the receiving optical system 6 has a configuration shown in FIG. 9 in more detail. In the figure, 7 is a second photodiode, 15 is a first condenser lens, 1
6 is a pinhole, 17 is a collimating lens, 18 is an optical filter, and 19 is a second condenser lens. The laser pulse reflected by the target is focused by the first focusing lens 15, passes through a pinhole 16 provided at the focusing point, is collimated by a collimating lens 17, passes through an optical filter 18, The light is condensed again by the second condenser lens 19 and enters the second photodiode 7. The optical filter 18 is used to transmit light having a wavelength near the wavelength of the laser pulse and cut off unnecessary background light.
Is used to limit the viewing angle of the receiving optical system 6 as shown in FIG. In the figure, L _{1 to} L ₃ are optical axes, and the angle θr between the optical axes L ₂ and L ₃ passing through the end of the pinhole 16 is the viewing angle. Pinhole 16, X in FIG. 10 so that the optical axes L ₁ passing through the center coincides with the optical axis of the transmission optical system 4 and collimating optics 11 are installed is finely adjusted in the Y direction.

The laser oscillator 1 uses a Q switch to obtain a laser pulse having a narrow pulse width and a large peak power. EO-Q switch as Q switch,
AO-Q switches and rotating prisms are well known. EO-Q switch, thereby changing the polarization of the laser beam instantaneously by switching the high voltage of a few hundred V~ several thousand V was applied to the material, such as LiNbO ₃ having an electro-optic effect at a high speed. Further, the AO-Q switch inputs a microwave pulse of several W into a material having an acousto-optic effect, generates a pulse-like elastic wave, and instantaneously changes the direction of laser light. In addition, a rotating prism is a prism that uses one of a pair of reflecting mirrors constituting a laser resonator as a prism and rotates this prism at a high speed by a motor to instantaneously configure or destroy the configuration of the laser resonator. is there. The drive circuits for these Q switches are included in the laser power supply 2.

Further, in FIG. 8, since the second photodiode 7 is very easy to pick up noise, it is mounted on the same substrate as the amplifier circuit 8 and is used as a preamplifier among multi-stage amplifiers constituting the amplifier circuit 8 as much as possible. It is connected with a short line length and is electrically shielded. here,
The amplifier circuit 8 is composed of a multi-stage amplifier as described above because the laser pulse reflected by the target received by the second photodiode 7 has a very small amount of light, so that the single-stage amplifier performs signal processing. This is because the signal does not have a sufficient level to be processed by the circuit 9. As the electric shield, a method of covering at least the preamplifier of the second photodiode 7 and the multistage amplifier with a grounded conductive case is often used. In addition, the amplification circuit 8,
The signal processing circuit 9, the display 10, the first photodiode 5, the laser oscillator 1 and the laser power supply 2 are connected to each other by an electric cable.

[0008]

Since the conventional laser distance measuring apparatus is constructed as described above, when an EO-Q switch is used as a Q switch, a high voltage is switched at a high speed, so that a large electric distance is required. Noise occurs. Alternatively, when an AO-Q switch is used as the Q switch,
Since it is necessary to generate a high-power microwave pulse, a large electric noise is also generated. Or Q
When a rotating prism is used as a switch, since the motor rotates at high speed, a large electric noise is also generated. These generated noises penetrate from the electric cable connecting the first photodiode 5 and the signal processing circuit 9 and enter the signal processing circuit 9 as a false start signal, causing the clock to operate erroneously, resulting in erroneous ranging. There was a problem of doing.

Further, since the conventional laser range finder is constructed as described above, the second photodiode 7 is
In order to receive the laser pulse condensed by the first condenser lens 19, it is necessary to fix the laser pulse on the substrate of the amplifier circuit 8, so that the position thereof must be aligned with the condenser lens 19 within a limited range. . For this reason, the workability is extremely poor, and when the second photodiode 7 is positioned and then fixed on the amplifier circuit 8 substrate, pressure is applied to the second photodiode 7 and the second collection It is difficult to fix the optical lens 19 at the optimum position, and it is difficult to fix the optical lens 19 at the optimum position. As the temperature changes, the position of the second condenser lens 19 gradually shifts, and the amount of the laser pulse incident on the second photodiode decreases. Further, since the second photodiode 7 and the amplifier circuit 8 must always be installed at the light condensing position of the second condenser lens 19, there is no freedom of the installation position, and the amplifier circuit 8 has a large noise when the Q switch is operated. It is difficult to install the device near the laser power supply 2 and the Q switch, which generates noise, and noise during the operation of the Q switch penetrates the amplifier circuit 8 to degrade the signal-to-noise ratio of the received signal. there were.

Further, since the conventional laser distance measuring apparatus is configured as described above, the viewing angle of the receiving optical diameter 6 is limited.
In order to align the pinhole 16 so that the optical axis of the receiving optical system 6 coincides with the optical axis of the transmitting optical system 4, as shown in FIG. Is incident on the pinhole 16 by the third condenser lens 21 via the optical filter 18, and the parallelism between the output light of the first condenser lens 15 and the laser pulse emitted from the transmission optical system 4 is determined. While observing with a collimator, the pinhole 16 is aligned so that the two are parallel. At this time, every time the pinhole 16 is displaced for alignment, the light of the lamp 20 does not sufficiently enter the pinhole 16 and the third condenser lens 21 is also adjusted.
I have to do it. Therefore, there is a problem that it takes a very long time to align the optical axes of the receiving optical system 6 and the transmitting optical system 4.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and does not cause erroneous distance measurement due to noise at the time of Q-switch operation, does not cause a positional shift between a receiving optical system and a photodiode, and has a transmitting optical system. It is an object of the present invention to obtain a laser distance measuring apparatus that can easily align the optical axes of a system and a receiving optical system.

[0012]

In a laser distance measuring apparatus according to the present invention, a photodiode for generating a start signal is mounted on the same substrate as a signal processing circuit, and a part of a laser pulse emitted from a laser oscillator is converted to an optical fiber. At one end and input to the photodiode at the other end.

Further, in the laser distance measuring apparatus according to the present invention, a condensing lens for condensing a laser pulse reflected on a receiving optical system as a target, and a view angle of the receiving optical system are limited.
Having a core diameter and its numerical aperture NA, the receiving optical system
Let D and f be the aperture diameter and focal length of
Consists of an optical fiber having a numerical aperture of ≧ D / (2f)
Then, one end of the optical fiber is focused by the focusing lens.
A photo-sensor that is installed at a point and the other end generates a stop signal.
It is modularized with iod.

Further, in the laser distance measuring apparatus according to the present invention, the laser distance measuring device is located at the light condensing point of the light condensing lens.
Light emitted from the end face toward the condenser lens enters from outside.
An optical connector for providing power is provided.

[0015]

According to the present invention, the photodiode for generating the start signal sends the start signal to the signal processing circuit on the same substrate. The optical fiber guides the laser pulse to the photodiode, and the means for inputting the laser light to the photodiode inputs the laser pulse guided by the optical fiber to the photodiode with low loss.

An optical fiber provided in the receiving optical system receives a laser pulse reflected at a target at one end from a condensing lens and guides the laser pulse to the other end modularized with a photodiode. Limit the viewing angle of the system. Above at the other modular end
The laser pulse is transmitted from the optical fiber to the photo diode.
To the password.

Further, the optical fiber of the receiving optical system is divided into a plurality of optical fibers from the optical connector when the optical axes of the receiving optical system 6 and the transmitting optical system 4 are aligned, and the optical fiber is positioned closest to the condenser lens. The split optical fiber that receives the laser pulse from the condenser lens receives light from an optical connector and emits the light from the condenser lens.

[0018]

【Example】

Embodiment 1 FIG. Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing Embodiment 1 of the laser distance measuring apparatus of the present invention. In the drawing, 1 is a laser oscillator, 2 is a laser power supply, 3 is a partial reflecting mirror, 4 is a transmitting optical system, 5 is a first photodiode, 6 is a receiving optical system, 7
Is a second photodiode, 8 is an amplifier circuit, 9 is a signal processing circuit, 10 is a display, 11 is a collimating optical system, 12 is a reticle, 13 is a relay lens, 14 is an eyepiece, 22
Is an optical fiber.

Next, the operation will be described. The operation is almost the same as that of the conventional example shown in FIG. A part of the laser pulse oscillated from the laser oscillator 1 is reflected by the partial reflecting mirror 3 in the direction of the optical fiber 22, and a part of the reflected laser pulse further enters from one end (A end) of the optical fiber 22. Then, it is guided to the other end (end B). The laser pulse emitted from the end B is condensed by a lens 23 and detected by a first photodiode 5 as shown in FIG. 2, for example. Alternatively, as shown in FIG. Detection is performed by bringing the light receiving element surface of the first photodiode 5 closer to the B end. The first photodiode 5 is mounted on the same substrate as the signal processing circuit 9 and sends a start signal generated by receiving the laser pulse to the signal processing circuit 9 through a short wiring patterned on the substrate. .

As described above, in the conventional example, the first photodiode 5 and the signal processing circuit 9 are connected by the electric cable, whereas in the present invention, the first photodiode 5 and the signal processing circuit 9 are connected. Are connected by short wires on the same substrate, and a laser pulse for generating a start signal is guided to the photodiode 5 by the optical fiber 22, so that large noise generated at the time of the Q switch operation does not easily enter. The generation of a false start signal can be prevented. Although an example in which a photodiode is used as an element for detecting a laser pulse has been described above, an avalanche photodiode or another light detection element may be used.

Embodiment 2 FIG. Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. The block diagram of the present invention is the same as that of the conventional example of FIG. 8, but the configuration of the receiving optical system 6 shown in FIG. 9 is different. FIG. 4 is a configuration diagram of the receiving optical system 6 of the laser distance measuring apparatus of the present invention. In the figure, 7 is the second
, 15 is a first condenser lens, 18 is an optical filter, 19 is a first condenser lens, and 24 is an optical fiber.

Next, the operation will be described. Since the operation of the laser distance measuring device is almost the same as that of the conventional example shown in FIG. 8, a portion of the receiving optical system 6 different from the conventional example will be described with reference to FIG. The laser pulse reflected by the target is condensed by the first condensing lens 15, and is received at one end (A end) of the optical fiber 24 set at the condensing point and is received at the other end (B end).
End). The laser pulse emitted from the B end of the optical fiber 24 is condensed by the second condenser lens 19 and passes through the optical filter 18 to the second photodiode 7.
And is detected. Here, the first condenser lens 15
The core also in the A end face of the optical fiber 24 set at the light condensing point corresponds to the pinhole in FIG. 9 and limits the viewing angle of the receiving optical system 6 as in FIG. In this case, the core diameter corresponds to the pinhole diameter, but in the optical fiber 24, the numerical aperture other than the core diameter is a factor that limits the viewing angle of the reception optical diameter 6. In order for the viewing angle to be limited only by the core diameter, the first
A lens having a numerical aperture large enough to receive the laser pulse condensed by the condensing lens 15 may be selected. For example, in FIG. 4, the aperture diameter of the first condenser lens 15 is D
The numerical aperture NA of the optical fiber 24 may satisfy Expression (2), where f is the focal length. NA ≧ D / (2f) (2)

On the other hand, the second photodiode 7 is fixed on the same substrate as the amplifier circuit 8 as in the prior art, and is connected to the preamplifier of the multistage amplifiers constituting the amplifier circuit 8 with a line length as short as possible. And an electrical shield is applied. In the present invention, the positioning of the receiving optical system 6 and the second photodiode 7 is performed by the optical fiber 2 shown in FIG.
The B end of No. 4, the second condenser lens 19 and the second photodiode 7 are aligned with each other. The above optical fiber 2
The laser pulse emitted from the B end of No. 4 is condensed by the second condensing lens 19 through the optical filter 18 into a spot smaller than the light receiving element area of the second photodiode 7, and is condensed by the second photodiode 7. Light is received without loss. Actually, a module in which these three members are precisely aligned and modularized is commercially available as a photodiode module with an optical fiber, and if these are used, there is no need to bother the three members. If the above-mentioned modularization is also carried out, the workability is good and easy because the receiving optical system 6 and the amplifying circuit 8 can be carried out separately by the above three persons, and the modularization and optical fiber What is necessary is just to fix to the said amplifier circuit 8 in the state made into the photodiode module. In this case, since no pressure is applied to the second photodiode 7 at the time of fixing as in the conventional example, there is no displacement between the second photodiode 7 and the second condenser lens 19, and even if there is a temperature change. The three members are always held at the optimum positions without the occurrence of the position shift. Therefore, the amount of laser pulse incident on the second photodiode 7 does not decrease due to the displacement.

Further, the substrate of the amplifier circuit 8 to which the second photodiode 7 is fixed can be installed at an arbitrary place by the optical fiber 24. For this reason, it is possible to avoid the vicinity of the laser power supply 2 and the Q switch, which generate large noise during the operation of the Q switch, or to install them electrically shielded from the laser power supply 2 and the Q switch, thereby preventing the noise from entering the amplifier circuit 8. , The required signal-to-noise ratio of the received signal can be ensured.

Although an example in which a photodiode is used as an element for detecting a laser pulse has been described above, an avalanche photodiode or another light detection element may be used. Further, when the light receiving element area of the second photodiode 7 is sufficiently larger than the core cross-sectional area of the optical fiber 24, the second condenser lens 19 is omitted, and as shown in FIG. The laser pulse emitted from the end can be directly received by the second photodiode 7 via the optical filter 18.

Embodiment 3 FIG. Hereinafter, a third embodiment of the present invention will be described. In the present invention, the optical fiber 24 of the receiving optical system shown in FIG.
Optical fiber 25, a first optical connector 26 attached to one end of the first optical fiber 25, a second optical fiber 2
7. This is replaced with an optical system including a second optical connector 28 attached to one end of the second optical fiber 27.

In the receiving optical system of the laser distance measuring apparatus according to the present invention, when receiving the laser pulse reflected by the target, the laser pulse is focused by the first focusing lens 15 and set at the focusing point. The light is received at the end A of the first optical fiber 25 and guided to the first optical connector 26. The first optical connector 26 is connected to a second optical connector 28, and the laser pulse is guided to the B end of the second optical fiber 27. The laser pulse emitted from the end B of the second optical fiber 27 is incident on the second photodiode 7 and detected in the same manner as in FIG. 4 or FIG. Here, the core in the end face A of the first optical fiber 25 limits the viewing angle of the receiving optical system 6 as in FIG.

Next, when the optical axis of the receiving optical system 6 coincides with the optical axis of the transmitting optical system 4 when assembling the laser distance measuring apparatus according to the present invention, the light of the lamp 20 is collected as shown in FIG. The light is made incident on the first optical connector 26 by the optical lens 21, and while the parallelism between the output light of the first condenser lens 15 and the laser pulse emitted from the transmission optical system 4 is observed by a collimator, both are parallelized. The A end of the first optical fiber 25 is aligned so as to be as follows. In this system, once the light of the lamp 20 is made incident on the first optical connector 26 by the third condenser lens 21, the position of the end A of the first optical fiber 25 can be adjusted even when the position of the end of the lamp 20 is adjusted. The positional relationship between the third condenser lens 21 and the first optical connector 26 may be fixed. Therefore, every time the pinhole 16 is shifted for alignment as in the conventional example, the third
Does not have to be aligned, and the optical axes of the receiving optical system 6 and the transmitting optical system 4 can be easily aligned, which can be performed in a very short time. In the above description, the case where there is one optical connector connection portion between the first optical connector 26 and the second optical connector 28 is shown, but a plurality of optical connector connection portions may be provided.

[0029]

As described above, according to the present invention, a photodetector for generating a start signal, which is mounted on the same substrate as a signal processing circuit, and a part of a laser pulse emitted from a laser oscillator are transmitted to one side of an optical fiber. Is received at one end and emitted from the other end, and this emitted light is input to a photodetector that generates a start signal mounted on the same substrate as the signal processing circuit. This makes it difficult for noise to penetrate, and has the effect of suppressing generation of a false start signal due to noise and preventing erroneous distance measurement.

Further, according to the present invention, a laser pulse reflected at a target by an optical fiber whose one end is located at a condensing position of a receiving optical system is received, and a stop signal is transmitted from the other end of the optical fiber. Since the light is input to the generated photodetector, the receiving optical system and the amplifier circuit can be separated and the other end of the optical fiber can be aligned with the photodetector to form a module. Since the photodetector is fixed to the amplifying circuit, even after the fixation, the other end of the optical fiber and the photodetector are not displaced from each other, so that the light quantity of the laser pulse incident on the photodetector can be prevented from decreasing. effective. Furthermore, since the substrate of the amplifier circuit can be installed at an arbitrary place, it is possible to avoid the vicinity of a laser power supply or a Q switch which generates a large noise when the Q switch is operated, or to install the circuit electrically shielded from these. Thus, it is possible to prevent noise from invading the amplifier circuit and to secure a required signal-to-noise ratio of a received signal.

Further, according to the present invention, the optical fiber of the receiving optical system is provided with at least one connecting portion by an optical connector from one end to the other end, so that it can be used at the time of assembling the laser distance measuring apparatus. in the receiving optical axis alignment between the optical system and the transmission optical system, the optical axis adjustment of the reception optical system
At the time, while inputting the light of the lamp into the conventional pinhole,
The beam was adjusted with respect to the condenser lens.
Fiber is the above pinhole that limits the viewing angle of the receiving optical system
Of the lamp from the above optical connector to have the function of
This light is input and emitted from the end of the condenser lens side.
The position of the end may be adjusted with respect to the condenser lens. For this reason,
There is no relationship between the part that inputs the lamp light and the part that adjusts the position
The effect that the optical axis alignment can be performed in a very short time
is there.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a laser distance measuring apparatus according to the present invention.

FIG. 2 is a diagram illustrating a method of coupling an optical fiber and a photodiode in the first embodiment of the laser distance measuring apparatus according to the present invention.

FIG. 3 is a diagram showing another method of coupling the optical fiber and the photodiode in the first embodiment of the laser distance measuring apparatus of the present invention.

FIG. 4 is a configuration diagram showing a receiving optical system in a laser distance measuring apparatus according to a second embodiment of the present invention.

FIG. 5 is a diagram showing another configuration of the receiving optical system in Embodiment 2 of the laser distance measuring apparatus of the present invention.

FIG. 6 is a diagram showing a configuration of an optical fiber in Embodiment 3 of the laser distance measuring apparatus of the present invention.

FIG. 7 is a diagram showing an optical axis alignment method of a receiving optical system in a third embodiment of the laser distance measuring apparatus according to the present invention.

FIG. 8 is a block diagram of a conventional laser distance measuring apparatus.

FIG. 9 is a configuration diagram showing a receiving optical system of a conventional laser distance measuring device.

FIG. 10 is a diagram showing how a pinhole limits a viewing angle.

FIG. 11 is a diagram showing an optical axis alignment method of a receiving optical system in a conventional laser distance measuring device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser oscillator 2 laser power supply 3 partial reflecting mirror 4 transmitting optical system 5 first photodiode 6 receiving optical system 7 second photodiode 8 amplifying circuit 9 signal processing circuit 10 display 11 collimating optical system 12 reticle 13 relay lens 14 eyepiece 15 first condenser lens 16 pinhole 17 collimator lens 18 optical filter 19 second condenser lens 20 lamp 21 third condenser lens 22 optical fiber 23 lens 24 optical fiber 25 first optical fiber 26 First optical connector 27 Second optical fiber 28 Second optical connector

Claims (2)

(57) [Claims] A laser beam is emitted toward a target, and
The above laser light reflected or scattered by the
The light is focused and detected by a photodetector to detect the distance to the target.
In the laser distance measuring apparatus for calculating the distance, the receiving optical system
The condensing lens and the core that limits the viewing angle of the receiving optical system
And the numerical aperture is NA.
When the aperture and focal length are D and f, respectively, NA ≧ D
/ (2f) and an optical fiber having a numerical aperture of
Place one end of the optical fiber at the focal point of the condenser lens.
And the other end is modularized with the photodetector.
Laser distance measuring device characterized by the above-mentioned. 2. The optical fiber according to claim 1 , wherein said condensing lens is provided on said optical fiber.
Light is emitted from the end face located at the light spot toward the condenser lens
That an optical connector for inputting light from outside is provided.
The laser distance measuring apparatus according to claim 1, wherein: