JP3198585B2 - Transmission optical system of lightwave 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 transmission optical system of a lightwave distance measuring device. More specifically, the present invention relates to a transmission optical system of a lightwave distance measuring device for transmitting transmission light on an annular zone.

[0002]

2. Description of the Related Art As a conventional lightwave distance measuring device, there is known a lightwave distance measuring device which projects transmission light in a ring shape. For example, Japanese Patent Application Laid-Open No. 51-20866 discloses that a ring-shaped transmission light is projected toward a target, and reception light reflected by the target passes through light in a hollow region of the ring-shaped transmission light. What is received and received is disclosed.

[0003] In addition, LEs conventionally used as light sources
A lightwave distance measuring device using a near-infrared laser having a higher luminance than D as a light source is known. The near-infrared laser supplies a laser beam having a Gaussian intensity distribution.

[0004]

However, in the conventional optical distance measuring apparatus as described above, the diameter of the opening at the exit end of the objective system and the diameter of the Gaussian beam at the exit end of the objective system (Gaussian distribution shape). The transmission efficiency of the transmitted light was not considered because no optimization was performed with respect to the distance from the position where the intensity was 1 / e ² to the position where the intensity of the Gaussian distribution became the maximum intensity. Was sometimes worse. When the transmission efficiency of the transmission light is low, the intensity of the transmission light at the target point is reduced, and there is a possibility that the distance measurement accuracy may be reduced.

Accordingly, the present invention has been made in view of the above problems,
An object of the present invention is to provide a transmission optical system of a lightwave distance measuring device capable of causing transmission light to reach a target point with high transmission efficiency.

[0006]

In order to achieve the above-mentioned object, according to the present invention, a light source for supplying transmission light having a Gaussian intensity distribution and an object for projecting the transmission light from the light source toward a target. The transmission optical system of the lightwave distance measuring device having the system
The distance in the light beam cross-sectional direction from the position where the intensity of the Gaussian distribution at the exit end of the objective system becomes 1 / e ² to the position where the intensity of the Gaussian distribution becomes the maximum intensity is ω, and the objective system emits light. Assuming that the aperture diameter at the end is D and the diameter of the hollow area of the transmitted light at the exit end of the objective system is d, 0.76 + 0.63d / D-0.19 (d / D) ² <2ω / D <0.96+ 1.15d / D-0.47 (d / D) ² is satisfied.

[0007]

In the transmission optical system of the lightwave distance measuring device according to the present invention,
The aperture diameter D at the exit end of the transmission optical system, the diameter d of the hollow region of the transmission light flux in the annular zone, and the diameter ω of the Gaussian beam (the intensity of the Gaussian distribution at the exit end of the transmission optical system is 1 / e ² (The distance in the light beam cross-sectional direction from the position where the intensity becomes the maximum intensity of the Gaussian distribution) to satisfy the above-mentioned conditional expression. This conditional expression specifies that the light intensity at the target point is 95% or more of the maximum intensity.

[0008] Under the influence of the aperture diameter D at the exit end of the transmission optical system, the transmission light causes diffraction spread when it reaches the target point. Here, the above conditional expression is such that even at the beam center of the transmission light and at a position deviated to some extent from the beam center (4.5% of the Airy disk diameter of the intensity distribution at the target point), the light intensity has the maximum value at that position. Since the intensity is defined to be 95% or more of the intensity, even if the target point deviates slightly from the extension of the optical axis of the transmission optical system, it is possible to make the transmission light of high light intensity reach the target point.

Here, exceeding the upper limit of the conditional expression is not preferable because the light intensity of the transmission light at the position of 4.5% of the diameter of the Airy disk is weakened. If the lower limit of the conditional expression is exceeded, the light intensity at the beam center position of the transmitted light is weakened, which is not desirable.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1 which shows a cross-sectional view passing through the optical axis of a lightwave distance measuring apparatus according to the present invention. In FIG. 1, the transmission optical system of the lightwave distance measuring apparatus according to the present invention includes an objective lens 1, an optical path splitter 5 disposed behind the objective lens 1, which reflects only infrared light and transmits visible light, It comprises a light source section 8 having an infrared laser for emitting infrared transmission light, and a transmission / reception light splitter 6 for reflecting a light beam from the light source section 8 toward an optical path splitter 5.

The receiving optical system includes an objective lens 1 and
An optical path splitter 5 that reflects and splits received light that is infrared light, a light receiving unit 10 that photoelectrically converts the received light, and a transmission / reception light splitter 6 that guides the received light reflected by the optical path splitter 5 to the light receiving unit 10. It consists of. Here, the transmission / reception light splitter 6 has a transmission area formed at the center and an annular reflection film 6a formed around the transmission area. For this reason, the transmission / reception optical splitter
The transmission light from the light source unit 8 reaching the reflection film 6a is reflected toward the optical path splitter 5 to be converted into a ring-shaped transmission light, and the reception light from the target traveling from the optical path splitter 5 to the light receiving unit 10 is reflected. Let through.

Further, in the lightwave distance measuring apparatus of this embodiment, the focusing lens 2, the focusing screen 3, and the eyepiece are provided behind the optical path splitter 5 in order to visually observe the target with visible light from the target point. A lens 4 is provided. Then, the visible light from the target point passes through the objective lens 1, passes through the focusing lens 2 that can move in the optical axis direction for focusing, and combines the objective lens 1 and the focusing lens 2. An image is formed on the reticle 3 arranged at the focal position. The image on the reticle 3 is magnified and observed through the eyepiece 4. The collimating optical system includes an objective lens 1, a focusing lens 2, a reticle 3, and an eyepiece 4.

Next, the function of the lightwave distance measuring apparatus according to this embodiment at the time of distance measurement will be described. First, the collimating optical system is used to adjust the lightwave distance measuring device so as to face the corner cube as the target point. Thereafter, the transmitting light is transmitted toward a corner cube (not shown). At this time, the transmission light (infrared light) from the light source unit 8 is emitted from the objective lens 1 in the state of a transmission / reception light splitter 6, an optical path splitter 5, and an annular light flux, and travels toward a corner cube. Then, the reflected light reflected by the corner cube enters from the center of the objective lens 1, and then enters the light receiving unit 10 via the optical path splitter 5 and the transmission / reception light splitter 6. Then, the received light incident on the light receiving unit 10 is photoelectrically converted. Further, reference light (not shown) is also photoelectrically converted. Then, the phase difference between the received light and a reference light (not shown) is measured, and the distance from the reference point in the lightwave distance measuring device to the corner cube is calculated.

In the above distance measurement, the corner cube is arranged at the target point. However, if the strong light can reach the target point, the corner cube becomes unnecessary and the distance can be measured. . Next, optimization of transmission light will be described. FIG. 2A shows a state of light intensity distribution near the exit end of the objective lens 1 (the transmission optical system 20), and FIG. 2B shows an intensity distribution at a target point. Then, in FIG. 2A, D indicates the opening diameter of the exit end of the objective lens 1 (transmission optical diameter 20), and d indicates
It shows the diameter of the hollow area of the orbicular transmission light flux.

Here, as shown in FIG. 2A, the intensity I of the transmitted light at a point at a distance x from the center of the transmitted light near the exit end of the objective lens 1 in the light beam cross-sectional direction is, as shown in FIG. Assuming that the distance from the position where the intensity of the maximum intensity is 1 / e ² of the maximum intensity to the position where the intensity is the maximum is ω, I∝exp [ ⁻² × ² · ω ⁻² ]〕 (1)

As shown in FIG. 2B, the transmitted light is affected by the aperture diameter D at the exit end of the transmission optical system 20.
Diffraction spread occurs before reaching the target point. When considering the intensity distribution of the transmitted light that has caused this diffraction spread, it is preferable that the target point be located at 30% to 50% of the Airy disk having this intensity distribution. Of course, if the target is sufficiently large, there is no need to consider the above, but it is difficult to manufacture a corner cube as a sufficiently large target. Further, the amount of reflected light may be increased by combining a large number of corner cubes. However, since the transmission optical system of the lightwave distance measuring apparatus according to the present embodiment uses a transmission light beam with high coherency, it is reflected by different corner cubes. The received light has a phase shift. For this reason, when receiving by the receiving optical system, the received lights reflected by different corner cubes cause interference, and it is not always possible to perform accurate ranging.

Here, the spread angle θ of the transmitted light corresponding to this Airy disk is expressed as follows: θ = 1.22λ / D ‥‥ (2) Here, λ is the wavelength of the transmitted light. Then, the rectangular coordinates (x,
y), the intensity of the transmitted light in the θ direction I (θ _X , θ
_{y) is, I (θ x, θ y} ) = C | ∬dxdyω -1 · exp ^{[(x 2 + y 2) ω} -2 ] exp ^{[-i · 2π · λ -1 (θ} x · x + θ y · y )] | ² ‥‥ (3). Here, θ _X : the angle of the light spreading direction in the X direction, θ _y : the angle of the light spreading direction in the Y direction, and C: the proportionality constant.

Here, since the total energy of the light beam emitted from the light source section 8 is constant, when ω changes, the energy density at the center is proportional to ω ^-2 . Therefore, (3)
Ω ⁻¹ in the equation indicates that when ω changes, the portion representing the amplitude in equation (3) is proportional to ω ⁻¹ . Next, based on the above equation (3), a calculation result is shown for the intensity distribution when the light beam emitted from the transmission optical system according to the present embodiment reaches the target point.

First, when projecting a transmission light having no hollow area, that is, a transmission light having a normal circular cross section where the hollow rate α is α≡d / D = 0, ω = D / 2 FIG. 3 (a) shows the result of calculating the intensity distribution at the time of ω = 0.9
FIG. 3B shows the result of calculating the intensity distribution at D / 2.
Shown in 3A and 3B, the vertical axis represents the intensity I.
And the horizontal axis is θ. Here, on the horizontal axis, O
Indicates the center, and A, B, and C indicate the positions distant from the center O by 30%, 4.5%, and 100% of the diameter of the Airy disk, respectively. Further, when ω = D / 2, the constant C in Expression (3) is normalized so that the intensity at the center becomes 1, and the intensity distributions in FIGS. 3A and 3B are shown.

Here, comparing FIGS. 3 (a) and 3 (b),
According to the value of ω with respect to the aperture D of the exit end of the transmission optical system,
It can be seen that the intensity distribution changes. FIG. 4 shows the intensity distribution I _O1 at the beam center O when the value of ω with respect to the diameter D of the exit end of the transmission optical system changes, the intensity distribution I _A1 at the 30% position A of the Airy disk, and The intensity distribution I _B1 at the position B of 4.5% of the Airy disk is shown. Here, the range in which the intensity at each position becomes 95% or more of the maximum intensity is regarded as an allowable range, and becomes 95% or more of the maximum value of the intensity in the intensity distributions I _O1 , I _A1 , and I _B1. Select the intersection of each range.

The common part at this time is 0.76 <2ω / D <0.96 (4). In this embodiment, the value of ω at the exit end of the transmission optical system is changed by appropriately setting the magnification and the like of the transmission optical system. When the value of ω satisfies the above expression (4), the transmitted light with high light intensity is at the beam center O, at the position A of 30% of the Airy disk, and at the position B of 4.5% of the Airy disk. Reach the target point.

Next, when projecting the transmission light in a ring-shaped light beam state onto a target, the hollowing rate α is α 抜 け d / D = 0.
In the case of 2, the calculation result of the intensity distribution when ω = D / 2 is shown in FIG. 5A, and the intensity distribution when ω = 1.05 · D / 2 is shown in FIG. 5B. . Then, FIG. 5 (a),
In (b), the vertical axis is the intensity I and the horizontal axis is θ. Here, on the horizontal axis, O indicates the beam center, and A, B, and C indicate 30%, 4.
The positions that are distant from the center O by 50% and 100% are shown.
Then, so that the intensity of the center O of ω = D / 2 becomes 1,
The intensity distributions of FIGS. 5A and 5B are shown by normalizing the constant C of the equation (3).

5 (a) and 5 (b), FIG.
As in the cases (a) and (b), it can be seen that the intensity distribution changes depending on the value of ω with respect to the aperture D of the exit end of the transmission optical system. FIG. 6 shows the intensity distribution I _O2 of the beam center O when the value of ω with respect to the diameter D of the exit end of the transmission optical system is changed.
The intensity distribution I _A2 at the position A of 30% of the Airy disk and the intensity distribution I at the position B of 4.5% of the Airy disk
_B2 is shown. Here, as described above, the range of ω that is 95% or more of the maximum intensity in the intensity distribution I _O1 , and ω that is 95% or more of the maximum intensity in the intensity distribution I _A2.
When a common part of the range of ω, which is 95% or more of the maximum intensity in the intensity distribution I _B2 , is selected, 0.895 <2ω / D <1.185 (5)

Further, when the hollow ratio α is α≡d / D = 0.3
, The intensity distribution when ω = D / 2 is shown in FIG.
FIG. 7 shows the intensity distribution when ω = 1.1 · D / 2.
(B). 7A and 7B, the vertical axis represents the intensity I and the horizontal axis represents θ. Here, on the horizontal axis, O indicates a beam center position, and A, B, C
Are 30%, 4.5%, and 10% of the diameter of the Airy disk, respectively.
It shows a position separated by a certain distance. Then, when ω = D / 2, the constant C in Expression (3) is normalized so that the intensity at the center becomes 1, and the intensity distributions in FIGS. 7A and 7B are shown.

When comparing FIGS. 7A and 7B, FIG.
As in the cases of (a) and (b), the port at the exit end of the transmission optical system
The intensity distribution changes depending on the value of ω with respect to the diameter D.
I understand. FIG. 8 shows the relationship between the diameter D of the exit end of the transmission optical system.
Intensity distribution at the beam center position O when the value of ω is changed
I_O3, 30% of Airy disk intensity distribution I at position A
_A3And 4.5% of Airy disk strength at position C
Distribution I_B3Are respectively shown. Where
Thus, the intensity distribution I_O3Ω which is 95% of the maximum intensity
Range, intensity distribution I_A3Range of ω which is 95% of the maximum intensity
Enclosure, intensity distribution I _B3Range of ω which is 95% of the maximum intensity
When the common part of the box and the box is selected, 0.945 <2ω / D <1.27 (6)

Similarly, consider the case where the hollowing rate further increases. When the hollow ratio α = 0.6, the range of 2ω / D at which the strength is optimal is found to be 1.07 <2ω / D <1.48 (7). When the ratio α is 0.95, 1.2 <2ω / D <1.64 ‥‥ (8).

From the above equations (4) to (8), 2ω
As can be seen from the range of / D, the optimum value of ω for the transmission light with high light intensity to reach the target point changes depending on the hollow ratio α. Next, FIG. 9 shows the relationship between the value of ω with respect to the diameter D of the exit end of the transmission optical system and the hollow ratio α. From FIG. 9, the lower limit of the performance of the transmission optical system of the lightwave distance measuring apparatus, that is, the lower limit of the range in which the transmission efficiency of the transmission light is the best is 2ω / D = 0.76 + 0.63d / D−0.19 (d / D) ² ‥‥ (9), and the upper limit value is 2ω / D = 0.96 + 1.15d / D−0.47 (d / D) ² ‥‥ (10).

Therefore, from the equations (9) and (10), it is found that 0.76 + 0.63d / D-0.19 (d / D) ² <2ω / D <0.96 + 1.15d / D-0.47 (d / D) ² ‥ If the transmission optical system is configured so as to satisfy (11), transmission light with high light intensity can be transmitted to the target point. When a reflection type objective lens having a primary mirror such as a concave mirror and a secondary mirror such as a convex mirror is used, the secondary mirror may cause a center shield (hollow area) at the exit end of the objective lens. . At this time, since the center shielding ratio is d / D, if the reflection type objective lens is configured to satisfy the above equation (11), the transmission light can be supplied to the target with high transmission efficiency. It goes without saying that you can do it.

The optical system for projecting a light source having a Gaussian intensity distribution is not limited to the optical system having an annular transmission light as in the embodiment shown in FIG. In an optical system that projects transmission light having a normal circular cross section, it is desirable that the above expression (4) is satisfied. As described above, if the transmission optical system is configured so as to satisfy the above equation (11), the transmission light can be transmitted to the target object under extremely high transmission efficiency without being restricted by the type of the objective lens. Since it can be guided, the present invention is not limited to the transmission optical system of the lightwave distance measuring apparatus shown in the embodiment, but can be applied to other transmission optical systems.

[0030]

As described above, according to the present invention, the diameter of the exit end of the transmission optical system of the optical distance measuring apparatus and the diameter of the Gaussian beam at the exit end are optimized, so that high transmission efficiency can be achieved. Thus, the transmission light can reach the target point. Therefore, it is possible to improve the ranging accuracy of the lightwave distance measuring device.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lightwave distance measuring apparatus according to the present invention.

FIG. 2 is a diagram showing an intensity distribution of transmission light at a target point.

FIG. 3 is a diagram showing an intensity distribution when α = 0.

FIG. 4 is a diagram showing the dependence of the intensity at α = 0 on ω.

FIG. 5 is a diagram showing an intensity distribution when α = 0.2.

FIG. 6 is a diagram showing the dependence of the intensity at α = 0.2 on ω.

FIG. 7 is a diagram showing an intensity distribution when α = 0.3.

FIG. 8 is a diagram showing the dependence of the intensity at ω = 0.3 on ω.

FIG. 9 is a diagram showing that an optimum ω has α dependency.

[Description of Signs of Main Parts] 1 ‥‥ Objective lens 5 ‥‥ Optical path splitter 6 ‥‥ Transmit and receive light splitter 8 ‥‥ Light source unit 10 ‥‥ Light receiving unit 20 ‥‥ Transmission optical system

Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01S ⁷ /48-7/51 G01S 17/00-17/95 G01B 11/00-11/30

Claims (1)

(57) [Claims] 1. A transmission optical system of a lightwave distance measuring device comprising: a light source for supplying transmission light having a Gaussian intensity distribution; and an objective system for projecting the transmission light from the light source toward a target. The intensity of the Gaussian distribution at the exit end of the objective system is 1 /
e is the distance in the light beam cross-sectional direction of the transmission light from the position where e ² is the position where the intensity of the Gaussian distribution is the maximum intensity.
0.76 + 0.63d / D-0.19 (d / D), where D is the aperture diameter at the exit end of the objective system and d is the diameter of the hollow area of the transmitted light at the exit end of the objective system. ² <2ω / D <0.96 + 1.15d / D-0.4
7 (d / D) ^2. A transmission optical system of a lightwave distance measuring device, characterized by satisfying ² (d / D) ² .