JP3228577B2 - Automatic vertical angle compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical angle automatic compensator used for surveying instruments, measuring instruments, etc., for measuring a change in the amount of inclination or for holding the optical axis of the instrument vertically. It is.

[0002]

2. Description of the Related Art When various types of surveying are performed in a surveying instrument, a measuring instrument, or the like, it is necessary to compensate for the reference plane of the surveying instrument, the measuring instrument, or the verticality of the optical axis.

Conventionally, these compensations are automatically performed.
When a pendulum body such as a lens or a prism is suspended in a pendulum shape by three or more suspension lines, when the surveying instrument or the measuring instrument body is inclined, the pendulum body is braked by a braking mechanism such as a magnetic type. In some cases, the optical path is automatically compensated.

As a method for detecting the inclination of a reference surface of a main body such as a surveying instrument or a measuring instrument, there is a method utilizing reflection on a free liquid level.

In this method, a light beam is made incident on a free liquid surface, and a change in the optical axis of reflected light of the light beam is detected by a light receiver. When mercury or the like is used as a liquid having a free liquid surface, if a light beam is incident perpendicularly to the free liquid surface, a reflection angle having the same sensitivity to the inclination of the liquid surface in all two-dimensional directions will be obtained. And the inclination of the reference plane can be detected.

However, in practice, liquids such as mercury described above are difficult to use from the viewpoint of cost and safety, and transparent liquids such as silicone oil are practically used. When a transparent liquid is used, total reflection is used, but since there is a critical angle between the liquid and air, in order to totally reflect the light flux on the liquid surface, the incidence of the light flux on the free liquid surface is the critical angle. Is necessary for the incident angle θ. Thus, in the conventional tilt detecting device using the free liquid surface, a light beam is incident on the free liquid surface at a predetermined angle.

When the light beam is incident on the free liquid surface at a predetermined angle, the change in the reflection angle of the reflected light in two different directions with respect to the inclination of the liquid surface is not uniform.
Therefore, in the tilt detecting device using the free liquid level, a measure must be taken against the non-uniform change in the reflection angle. For this reason, light beams of two different optical axes are made incident on the free liquid surface at a predetermined angle, the reflected light is received by the light receiver, and each light receiver detects the light receiving position in only one direction, and Based on the change in the light receiving position, the inclination with respect to the two optical axes is detected, and the reference plane inclination of a surveying instrument, a measuring instrument, or the like with respect to a horizontal plane is calculated from the detected inclination of the two optical axes, and compensation is performed based on the calculation result. I have.

[0008]

However, the former of the prior art described above has a complicated structure because the pendulum is suspended, and the work of suspending the pendulum at the time of assembling the device is not easy. Adjustment was also difficult. Further, the length of the suspension wire changes with the lapse of time, so that it is difficult to maintain the accuracy. In addition, since a special braking device for braking the pendulum body is required, this also causes the structure of the device to be complicated. Further, there is a problem that the suspension structure of the pendulum body is delicate and weak against impact.

On the other hand, the latter using total reflection of the free liquid surface is easy to assemble and adjust, has no change over time because there is no hanging wire, and can make the liquid a sealed structure, so that it has impact resistance and environmental resistance. Excellent in nature. Furthermore, since liquid is used, braking can be performed by utilizing the viscosity of the liquid, and there is an advantage that a braking device is not required. There are various advantages of the automatic vertical angle compensating device which suspends a pendulum body. The problem has been solved.

However, since light beams having two different optical axes are incident on the free liquid surface at a predetermined angle with respect to the free liquid surface, the configuration of the apparatus is complicated because the light beam projection system is composed of two optical systems. There was a problem of becoming.

In view of such circumstances, the present invention utilizes the total reflection of the free liquid surface, detects the inclination of the reference surface only with a single-axis optical system, or performs automatic compensation of the vertical line. It was done.

[0012]

According to the present invention, there is provided a liquid filling container in which a transparent liquid is filled so as to form a free liquid surface, and a luminous flux totally reflected at the free liquid surface at a predetermined angle to the free liquid surface. A light projecting system for projecting, a mirror for vertically reflecting the light beam reflected on the free liquid surface, and a reflection angle of the optical axis provided at a required position in an optical path of the reflected light beam and corresponding to a change in the incident angle of the optical axis. And a lens system for equalizing the change in all directions and canceling the change in the angle of the reflected optical axis corresponding to the change in the incident angle of the optical axis.

[0013]

The sensitivity of the change in the reflection angle when the angle of incidence of the light beam with respect to the free liquid surface changes relative to the free liquid surface depends on the inclination direction of the free liquid surface. This difference in sensitivity is optically corrected, and the light flux reflected in the vertical direction by the mirror optically offsets the relative inclination of the free liquid level,
The luminous flux reflected in the vertical direction always keeps vertical.

[0014]

An embodiment of the present invention will be described below with reference to the drawings.

First, a light beam is incident on the free liquid surface at a predetermined angle, and when the light beam is totally reflected at the free liquid surface, the free liquid surface is inclined relative to the light beam. The difference in the sensitivity of the change in the reflection angle with respect to the direction will be described with reference to FIGS.

Actually, the free liquid surface is kept horizontal and the incident direction of the light beam changes. However, the following description is based on the assumption that the incident direction of the light beam is constant and the free liquid surface is inclined.

In FIG. 1, reference numeral 1 denotes a free liquid surface, and it is assumed that an incident light beam 2 is incident on the free liquid surface 1 at an angle θ. The free liquid level 1
And an xz coordinate plane formed by the coordinate axes x and z, and the coordinate axis perpendicular to the coordinate plane is y. It is assumed that the optical axis of the incident light beam 2 exists in a coordinate plane formed by the coordinate axes z and y. From this state, if the free liquid surface 1 is inclined by an angle α about the coordinate axis x, the optical axis of the reflected light beam 3 moves in the yz coordinate plane, and the reflection angle changes by ξ1x in the yz coordinate plane. . In this case, the relationship between the liquid surface displacement angle α and the reflected displacement angle ξ1x is ξ1x =
2α, and in this case, the reflection displacement angle ξ2x in the xy coordinate plane does not occur. In the figure, reference numeral 14 denotes a mirror.

On the other hand, as shown in FIG. 2, if the free liquid surface 1 is inclined at an angle α about the coordinate axis z, the reflected light beam 3 separates from the xy coordinate plane and the yz coordinate plane, respectively. Moving. Accordingly, a reflection displacement angle ξ1z and a reflection displacement angle ξ2z appear on the xy coordinate plane and the yz coordinate plane, respectively. Further, the relationship between the reflection displacement angle ξ1z and the liquid surface displacement angle α of the free liquid surface 1 is

[0019]

[Number 1] ^{ξ1z = cos -1 (cos 2 θ} cos2α + sin 2 θ) ξ2z = π / 2- cos -1 ((1- cos2α) sinθ cosθ)

Where α = 10 ′, θ = 50
If °, ξ2z = 1.7 ″, and ξ2z is a value that can be ignored in terms of precision.

[0021]

２1x ′ = 2nαξ1z ′ = n · cos ⁻¹ (cos ² θ cos 2α + sin ² θ).

Therefore, the sensitivity to the liquid surface displacement angle α differs between the reflection displacement angle ξ1x 'and the reflection displacement angle ξ1z'. In the present invention, the reflected displacement angle ξ1x ′ and the reflected displacement angle ξ
The difference in sensitivity of the displacement angle from 1z 'is corrected by optical means and the same sensitivity is obtained, so that an optical axis constantly deviating at a constant rate in all directions is obtained.

Further description will be made with reference to FIG.

In the figure, reference numeral 4 denotes a liquid enclosing container provided in the main body of a measuring instrument or the like, and a free liquid level 1 is formed by the liquid sealed in the liquid enclosing container 4. A light beam emitted from a light source 6 is projected onto the free liquid surface 1 at a predetermined angle through a collimating lens 5 so as to be totally reflected on the free liquid surface 1, and the optical axis of the light beam is as described above. Like yz
Position in the coordinate plane.

With the free liquid level 1 not inclined,
A cylindrical lens system 9 having a pair of cylindrical lenses 7 and 8 and a reflection mirror 14 are arranged along the optical axis of the reflected light beam 3 totally reflected by the free liquid surface 1. Each of the cylindrical lenses 7 and 8 has a curvature in only one direction, and the cylindrical lens 7 has a convex cylindrical lens and a cylindrical lens 8 having a focal length f1.
Is a concave cylindrical lens having a focal length f2.

The light beam transmitted through the cylindrical lens system 9 is reflected in the vertical direction by a reflection mirror 14, and the light beam reflected by the reflection mirror 14 is reflected by the convex lens 1.
The beam expander 12 composed of 0 and 11 is transmitted. If the focal length of the convex lens 10 is f3 and the focal length of the convex lens 11 is f4, the distance between the convex lens 10 and the convex lens 11 is set to f3 + f4.

The cylindrical lens system 9 may be provided on the optical path after being reflected by the reflection mirror 14.

The operation will be described below.

First, as shown in FIG. 4A, when a light beam enters from the direction of the radius of curvature of the cylindrical lens 7, an angle between the reflected light beam 3 and the optical axis of the cylindrical lens 7, an incident angle a, The relationship with the exit angle a ′ from the cylindrical lens 8 is as follows:

[0030]

## EQU3 ## a '= (f1 / f2) a.

As shown in FIG. 4B, the angle between the reflected light beam 3 and the optical axis of the cylindrical lens 7 when the light beam enters from a plane including the generatrix of the curved surface of the cylindrical lens 7, and the incident angle. a, the relationship with the exit angle a ′ from the cylindrical lens 8 is

[0032]

## EQU4 ## a = a '.

Here, the cylindrical lens system 9 is disposed as shown in FIG. 4A with respect to the movement of the reflected light beam 3 when the free liquid surface 1 is inclined about the z-axis. Therefore, for the movement of the reflected light beam 3 when the free liquid surface 1 is tilted about the x-axis, the arrangement of the cylindrical lens system 9 is arranged as shown in FIG.

Thus, in FIG. 3, the set incident angle θ to the liquid is 50 °, the inclination angle of the apparatus, that is, the inclination angle α of the free liquid surface 1 =
Assuming that 10 ′ and the refractive index of the liquid n = 1.4, the reflection displacement angle ξ1x ′ when the free liquid surface 1 is tilted about the x-axis and the case where the free liquid surface 1 is tilted about the z-axis according to Equation 2. Are the reflection displacement angles 、 1z 'of 1x' = 28 'and ξ1z' = 1, respectively.
8 '. Therefore, there is a sensitivity difference of (ξ1x '/ ξ1z') = 1.555 times between the reflection displacement angle ξ1x 'and the reflection displacement angle ξ1z'. Therefore, in this condition,

[0035]

５1x ′ = 2nα and ξ1z ′ = 1.286nα.

Therefore, from equation 2, (f 1 / f 2) = 2 /
If 1.286, the displacement angle ξ1z ′ of the optical axis transmitted through the cylindrical lens system 9 is 1.286nα × 2 /
1.286 = 2nα, and after transmission through the cylindrical lens system 9, ξ1x ′ = ξ1z ′. Even if the free liquid surface 1 is inclined in any direction, the reflection displacement angle always has the same sensitivity to this inclination. Is obtained.

Further, when the light beam transmitted through the cylindrical lens system 9 and reflected upward by the reflection mirror 14 is transmitted through the beam expander 12, the angular magnification of the beam expander 12 is 1 / 2n times. If,
The optical axis after transmission is

[0038]

(6) (ξ1x ′ = ξ1z ′ = 2nα) × １ ／ n = α

The final optical axis after transmission through the beam expander 12 is always perpendicular to the free liquid surface 1, that is, vertical. Here, the focal length of the convex lens 10 is f3
If the focal length of the convex lens 11 is f4, the angular magnification of the expander 12 is f3 / f4.
Is selected, the angular magnification can be set to 1 / 2n.

Next, the cylindrical lens system 9 is rotated by 90 ° with respect to the embodiment shown in FIG.

[0041]

## EQU7 ## (f2 / f1) = 1.555 (f3 / f4) = 1 / 1.286n.

FIG. 5 shows the relationship between the incidence and emission of the reflected light beam 3 when the cylindrical lens system 9 is rotated by 90 °.
This will be described in (A) and (B).

As described above, the reflection displacement angle of the optical axis of the reflected light beam 3 with respect to the free liquid surface 1 is represented by the inclination angle α of the free liquid surface 1,
When the set incident angle θ of the light beam and the refractive index n of the liquid are set, the reflection displacement angle ξ1x ′ = 2 when the free liquid surface 1 is inclined about the x-axis.
When the free liquid surface 1 is inclined about the center of the nα z-axis, the reflection displacement angle ξ1
Since z ′ = 1.286nα, the reflection displacement angle ξ1x ′ is transmitted through the cylindrical lens system 9

[0044]

８1x ′ = 2nα × 1 / 1.555 = 1.286nα

Thus, the reflection displacement angle ξ1z 'is maintained as it is after passing through the cylindrical lens system 9, and

[0046]

Ξ1z ′ = 1.286nα.

Further, as described above, the beam expander 1
Since the angular magnification of 2 is f3 / f4 = 1 / 1.286n,

[0048]

(Ξ1x ′ = ξ1z ′) × (f3 / f4) = 1.286nα / 1.286n = α

As described above, the optical axis can always be maintained vertical.

Referring to FIG. 6, another embodiment of the present invention will be described.

In the other embodiment, the combination of the cylindrical lens system 9 and the beam expander 12 shown in FIG. 3 is replaced with an expander 13 having a pair of toric lenses 15 and 16. The toric lenses 15 and 16 are lenses having different focal points in the x direction and the z direction. The focal points in the x direction are f1x and f2x, and the focal points in the z direction are f1z and f2z.

[0052]

## EQU11 ## f1x / f2x = 1 / 1.286n f1z / f2z = 1 / 2n

Then, as shown in FIGS. 7A and 7B, the exit angle from the toric lens 16 can be set to α.
Again, the optical axis can always be maintained vertical.

As described above, according to the present invention, the optical axis of the emitted light beam can always be maintained vertically. An application example of the present invention will be described below.

FIG. 8 shows a pentaprism or a pentamirror 17 rotatably arranged on the optical axis of the light beam emitted from the beam expander 12. Then, the pentamirror 17 is further rotated to form a horizontal reference plane by the emitted light. That is, the present invention can be applied to a leveling device.

FIG. 9 shows still another application example.

In this application example, a telescope system 18 is provided on the light source side in the embodiment shown in FIG. 3, and this configuration makes it possible to use it as a vertical device.

In the above configuration, when actually used, the inclination of all the components is usually limited. Therefore, in use, it is necessary to detect whether the inclination is within the required inclination limit. The following configuration may be added to such a request.

In the application example shown in FIG . 10, a half mirror 40 is provided in place of the above-described reflection mirror 14, and the reflected light beam from the free liquid surface 1 is divided into a vertically reflected light beam 41 and a transmitted light beam 42. . The transmitted light flux 42 passes through the convex lens 43 and is received by the light receiving element 46 through a pinhole 45 formed in the light shielding plate 44. The pinhole 45 is disposed at the focal point of the convex lens 43. Further, the diameter of the pinhole 45 is set to a size corresponding to the range of limitation.

When the entire structure is tilted, the light beam reflected from the free liquid surface 1 shifts the optical axis. Since the configuration has the cylindrical lens system 9 as described above, the reflected light beam exhibits uniform sensitivity in all directions with respect to the inclination angles of all the configurations. The transmitted light flux 42 is received by the light receiving element 46 through the convex lens 43 and the pinhole 45. By the way, since the pinhole 45 and the light receiving element 46 are arranged at the focal point of the convex lens 43, if the focal length of the convex lens 43 is f0, the optical axis of the pinhole 45 is f0 · tanξ0 with respect to the reflection displacement angle ξ0. Move on.

When the amount of movement becomes equal to or greater than the required inclination limit, the diameter of the pinhole 45 is determined so that the amount of light received by the light receiving element 46 becomes equal to or less than a predetermined amount of light.

By monitoring the amount of light received by the light receiving element 46, it is possible to determine whether or not the inclination of all components is within the limit angle.

For example, the incident angle θ on the free liquid surface 1 is 50
°, inclination limit angle α = 10 ′ of all components, refractive index of liquid n =
Assuming that the 1.4, the focal length f0 of the convex lens 43 is 100 mm, and the diameter of the pinhole is R, the deviation of the optical axis after passing through the cylindrical lens system 9 is ξ0 = 2nα as described above. Therefore, the movement amount 1 of the optical axis in the pinhole 45 (the focal position of the convex lens 43) is

[0064]

L = f0 * tan ＝ 0 = 100 * tan (2 * 1.4 * 10/60) = 0.81

When the pinhole 45 is formed to have this diameter, as shown in FIG. 11, when the beam spot of the transmitted light beam 42 moves by 0.81 mm, the pinhole 45 is removed.
, The amount of light received by the light shielding plate 44 decreases. Therefore, by stopping the light emission of the light source 6 when this light amount decrease is detected, it is possible to use the light source 6 only in the required range.

The pinhole 45 may be omitted, and the light receiving element 46 may be a light receiving element such as a CCD, and the position of the beam spot may be detected by the light receiving element 46.

Next, a specific example of the above-described liquid filling container 4 will be described with reference to FIGS.

The liquid enclosing container 4 is fixed to the apparatus main body together with another lens system, or is configured as a part of the apparatus. In this case, when the device is used in an environment where a temperature difference occurs, for example, when the device is carried out from indoors to outdoors, a temperature distribution occurs inside the liquid sealed in the liquid sealing container 4. When a temperature distribution occurs inside the liquid, the refractive index also shows a distribution corresponding to the temperature distribution, so that the optical axis is refracted inside the liquid. The specific example of the liquid filling container 4 shown in FIGS. 12 and 13 solves such a problem.

The details will be described below.

An inner case 21 similar to the outer case 20 is provided inside the inverted trapezoidal outer case 20. A flat space 22 is formed along the upper side surface of the inner case 21, and a light introduction path 23 and a light extraction path 24 communicating with the space 22 are formed. The axis of the light introduction path 23 coincides with the optical axis of the incident light beam, and the axis of the light exit path 24 coincides with the optical axis of the reflected light beam 3 when the free liquid surface 1 is horizontal. .

The heat transfer plate 25 is fixed to the bottom of the space 22. The heat transfer plate 25 has a window hole 26 formed at the center thereof so that an incident light beam and a reflected light beam can pass therethrough. Further, the light introduction path 2
3 and a stopper 27 made of transparent glass is fixed to the upper end of each of the light guide paths 24, and the stopper 27 hermetically seals a transparent liquid 28. The amount of the transparent liquid 28 is determined so as to form a free liquid surface.

The outer case 20 accommodates the inner case 21 and has a required surrounding space 2 around the inner case 21.
9 is formed. Further, the light introducing path 23 of the outer case 20 is
A transparent glass window 30 and a glass window 31 are provided at positions where the respective axes of the light guide paths 24 pass. The outer case 20 has an air-tight structure, and the surrounding space 29 is evacuated or filled with gas.

The outer case 20 and the inner case 21 are made of a material having a low thermal conductivity such as a synthetic resin in order to suppress heat radiation and heat absorption to the outside.

As described above, the space 22 in which the transparent liquid 28 is sealed is flat and thin, and the heat transfer plate 25
Is provided, the speed of heat propagation is increased, and the uniformity of the temperature of the transparent liquid 28 in the temperature change state is improved.
Further, the surrounding space 29 forms a heat insulating layer with respect to the transfer of heat to and from the inner case 21, and suppresses the temperature change of the transparent liquid 28 or the temperature change speed.

Thus, the occurrence of a difference in temperature distribution inside the transparent liquid 28 is suppressed, and the refraction of the optical axis of the light beam and the change in the sectional shape of the light beam due to the change in the refractive index can be prevented. In addition, the stability is increased with respect to environmental temperature changes, and the measurement accuracy is improved.

Next, FIG. 14 shows another specific example of the liquid filling container 4, in which the inner case 21 is covered with an outer case 20 made of a heat insulating material without forming a surrounding space 29 around the inner case 21. , The inner case 21 by the outer case 20.
Is formed with a heat insulating layer around.

It is needless to say that the shape of the liquid enclosing container 4 is not limited to the above embodiment.

[0078]

As described above, according to the present invention, since the reflection of the free liquid surface which maintains the horizontal level is always used, a high level of assembling technique is not required unlike the conventional pendulum type angle compensator. It is easy to assemble, and instead of suspending the optical member like a conventional pendulum-type angle compensator, it is sufficient to inject the liquid into the liquid enclosing container. There is no variation in assembling accuracy due to the difference between them.Moreover, since the liquid is completely sealed, there is no change over time, so it is excellent in environmental resistance, and it can be braked by using the viscosity of the liquid against external vibrations and shocks. It exhibits various excellent effects such as not requiring a complicated braking device.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a change in a reflection angle of a reflected light beam when a free liquid surface is inclined.

FIG. 2 is an explanatory diagram illustrating a change in a reflection angle of a reflected light beam when a free liquid surface is inclined.

FIG. 3 is a configuration diagram of one embodiment of the present invention.

FIGS. 4A and 4B are explanatory diagrams showing changes in the optical axis of a transmitted light beam with respect to a cylindrical lens system.

FIGS. 5A and 5B are explanatory diagrams showing changes in the optical axis of a transmitted light beam with respect to a cylindrical lens system.

FIG. 6 is an explanatory view showing another embodiment of the present invention.

FIGS. 7A and 7B are explanatory diagrams showing changes in the optical axis of a transmitted light beam with respect to a toric lens expander.

FIG. 8 is an explanatory diagram showing an application example of the present invention.

FIG. 9 is an explanatory diagram showing another application example of the present invention.

FIG. 10 is an explanatory diagram showing still another application example of the present invention.

FIG. 11 is an explanatory diagram showing a relationship between a beam spot and a pinhole in still another application example.

FIG. 12 is a front sectional view showing a specific example of the liquid filling container.

FIG. 13 is a view taken in the direction of arrows AA in FIG. 12;

FIG. 14 is a front sectional view showing another specific example of the liquid filling container.

[Explanation of symbols]

 Reference Signs List 1 free liquid surface 2 incident light beam 3 reflected light beam 4 liquid enclosure 6 light source 9 cylindrical lens system 12 beam expander 14 reflection mirror 17 pentaprism, pentamirror 18 telescope system 28 transparent liquid 45 pinhole 46 light receiving element

Continued on the front page (72) Inventor Takaaki Yamazaki 75-1, Hasunumacho, Itabashi-ku, Tokyo Inside Topcon Co., Ltd. Document JP-A-49-127657 (JP, A) JP-A-59-30521 (JP, A) JP-A-61-108908 (JP, A) JP-A-61-132819 (JP, A) 204515 (JP, A) JP-A-63-179208 (JP, A) JP-A-63-222214 (JP, A) JP-A-4-93910 (JP, A) JP-A-5-256647 (JP, A) JP-A-6-137870 (JP, A) JP-A-6-147892 (JP, A) JP-A-6-147897 (JP, A) JP-B-45-4208 (JP, B1) (58) (Int.Cl. ⁷ , DB name) G01C 5/02 G01C 9/00 G01C 15/12

Claims (7)

(57) [Claims] A liquid-filled container filled with a transparent liquid so as to form a free liquid surface; a light projecting system for projecting a light beam to be totally reflected at the free liquid surface onto the free liquid surface at a predetermined angle; A mirror that reflects the light flux reflected by the free liquid surface in a vertical direction, and a change in the reflection angle of the optical axis corresponding to the change in the incident angle of the optical axis, which is provided at a required position in the optical path of the reflected light flux, is equal in all directions; And a lens system for canceling a change in the angle of the reflected optical axis corresponding to a change in the incident angle of the optical axis. 2. A vertical optical system according to claim 1, further comprising an optical path changing means for emitting a light beam in a horizontal direction on a vertical optical axis transmitted through the lens system, wherein said optical path changing means is rotatable about a vertical axis. Direction angle automatic compensation device. 3. The automatic vertical angle compensator according to claim 1, wherein a telescope system is provided on a side of the light beam incident on the free liquid surface. 4. A half mirror is used as a mirror that reflects a reflected light beam in a vertical direction, a light beam transmitted through the half mirror is received by a light receiving element, and the movement of the optical axis of the transmitted light beam is detected by the light receiving element. The vertical angle automatic compensation device according to claim 1. 5. The method according to claim 1, wherein the transparent liquid is sealed in a plate-like space.
Vertical angle automatic compensation device. 6. The automatic vertical angle compensator according to claim 5, wherein a heat transfer plate is provided on a bottom surface of the plate-shaped space. 7. The automatic vertical angle compensator according to claim 1, wherein a heat insulating layer is formed around the inner case filled with the transparent liquid.