JPH0363712B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a light wave distance measuring device in which the objective lens of a collimating optical system is also used as a light wave distance measuring optical system. The present invention relates to a coaxial type light wave distance measuring device that uses the other semicircular side for light reception.

(Background of the Invention) Conventionally, various light wave distance measuring devices are known in which the objective lens of a collimating optical system is also used as a light wave ranging optical system, and the optical path between the collimating optical system and the light wave ranging optical system is branched. Various types of optical path splitter configurations have also been realized. A coaxial optical distance measuring device that uses one semicircular side of the objective lens aperture for transmitting light and the other semicircular side for receiving light is generally tilted at a 45 degree angle to the optical axis. The optical path of the ranging optical system is branched using a semi-transparent mirror, but this increases the thickness of the prism with the semi-transparent mirror in the optical axis direction. The optical path becomes longer, and the overall structure of the device has to be larger. Furthermore, since the distance measuring light is generally infrared light, it is effective to use a dichroic mirror as the optical path splitter, but since dichroic mirrors are generally formed of multilayer thin films, their characteristics are well known. The performance deteriorated as the incidence became oblique, and there was still room for improvement in this respect. It is well known in thin film technology that when dichroic mirrors are used, reducing the angle of incidence will improve their performance and make them easier to manufacture.Based on this, the angle of incidence on dichroic mirrors was made smaller than 45 degrees. The composition is JP-A-57-
This is proposed in Publication No. 86771. however,
Even in the optical distance measuring device disclosed herein, the center thickness of the prism serving as an optical path splitter is still large, which is disadvantageous for downsizing the collimating optical system.

(Object of the invention) The object of the present invention is to eliminate the above-mentioned drawbacks,
It is an object of the present invention to provide a light wave distance measuring device having a compact configuration and excellent operability without increasing the optical path length of a collimating optical system.

(Summary of the Invention) The present invention provides a collimating optical system having an objective lens and an eyepiece, an optical path splitter disposed between the objective lens and the eyepiece, and an optical path split by the optical path splitter. a transmitted light reflecting member and a received light reflecting member that are integrally arranged on the optical axis of the objective lens, and a light source that supplies transmitted light to the transmitted light reflecting member and receives a luminous flux from the received light reflecting member. In the coaxial optical distance measuring device comprising a light receiving member, the optical path splitter includes an entrance surface formed substantially perpendicular to the optical axis of the collimation optical system, a first exit surface substantially parallel thereto, and a first exit surface substantially parallel to the entrance surface. The prism includes a semi-transmissive mirror surface obliquely disposed between an incident surface and the first exit surface, and the prism totally reflects the light beam reflected by the semi-transmissive mirror surface on the incident surface, and and a second exit surface that transmits the light beam totally reflected by the surface, and further includes an appropriate angle θ between the normal to the semi-transparent mirror surface of the optical path splitter and the optical axis of the collimation optical system. We have found a range.

That is, in the present invention, the optical path splitter is configured to split the optical path by twice reflecting with a semi-transmissive mirror surface and a total reflection surface. The thickness of the prism block in the optical axis direction required to extract the optical path of the system can be considerably reduced, making it possible to create a compact optical distance measuring device without significantly increasing the optical path length of the collimating optical system. That is.
In the present invention, the semi-transparent mirror surface is defined to include a dichroic mirror surface that can separate reflected light and transmitted light according to their wavelength ranges.

(Example) Hereinafter, the present invention will be explained based on Examples.

FIG. 1 is an optical path diagram showing the configuration of an embodiment of a light wave distance measuring device according to the present invention. An objective lens 1, a focusing lens 2, an erecting prism 3, a focusing plate 4, and an eyepiece 5 are arranged in this order to constitute a collimating optical system. Between the objective lens 1 and the focusing lens 2,
An optical path splitter 6 having a dichroic mirror surface for reflecting infrared light and transmitting visible light is arranged.

The optical path splitter 6 consists of a rectangular prism P1 and a trapezoidal prism P2 that are bonded together at a slope D as a dichroic mirror surface, and includes an entrance surface 6a perpendicular to the optical axis A of the objective lens 1, and a first exit parallel to this. It has a surface 6b. The dichroic mirror surface D, which is a semi-transparent mirror surface, has the function of reflecting infrared light and transmitting visible light at the same time, and the infrared light reflected here is totally reflected by the incident surface 6a, and then passes through the trapezoidal prism. The light passes through the second exit surface 6c corresponding to the slope of P2. Therefore, visible light for collimation is emitted from the first exit surface 6a, and infrared light for distance measurement is emitted from the second exit surface 6c.

Here, the angle of incidence θ on the dichroic mirror surface D, that is, the angle between the optical axis A of the objective lens 1 and the normal to the dichroic mirror surface D is determined as follows.

First, regarding the lower limit of θ, in order to make the optical path splitter compact, the incident light flux from the objective lens 1 and the reflected light flux from the dichroic mirror surface D must be superimposed on the entrance surface 6a of the optical path splitter. Therefore, the entrance surface must be a transparent total reflection surface, not a mirror surface. Therefore, subject to the restriction of the critical angle at the incident surface 6a, when the refractive index of the prism P2 is n, it is necessary to satisfy the condition θ>1/2·arcsin1/n (1). At the same time,
When θ becomes smaller, the optical path of the ranging light emitted from the optical path splitter 6 becomes nearly parallel to the optical axis of the collimating optical system. This makes it difficult to arrange the distance measuring optical element group including the lens 12 and the like.

On the other hand, regarding the upper limit of θ, the larger θ is, the greater the thickness in the optical axis direction of the optical path splitter for branching the optical path of the ranging optical system from the optical path of the collimating optical system, that is, the thickness of the entrance/exit surface 6a and the first exit surface 6a. The distance from the surface 6b increases, making the collimating optical system longer.
Also, the optical axis of the distance measuring optical system reflected by the dichroic mirror surface D is the incident surface 6a as a total reflection surface.
The intersection point Q becomes farther from the optical axis of the collimating optical system as θ increases and approaches 45 degrees, so the second prism P2 becomes larger and the entire device becomes larger. Furthermore, as is well known in thin film technology, as the incident angle θ increases, the characteristics of the dichroic prism deteriorate, so the incident angle cannot be set very large, and it becomes difficult to manufacture thin films.

From the above viewpoint, the angle θ that the normal line of the dichroic mirror surface D makes with the optical axis of the objective lens needs to be specifically set in the range of 15°<θ<45°. In this example, a configuration in which θ is 30 degrees is adopted.

In addition, it is desirable to form a transmitting part without any vapor deposition in a minute region near the position where the dichreuz mirror surface D intersects with the optical axis A of the objective lens. It is possible to have the same function as a board. It is effective to attach a filter that absorbs the infrared light for distance measurement to the bottom surface 6d of the first prism P1 in order to prevent the reflected light from this surface from becoming noise. It is also possible to change the angle so that the reflected light does not enter the receiving light optical path. It is preferable that the refractive index of both prisms P1 and P2 sandwiching the dichroic mirror surface D be equal to the refractive index of the adhesive bonding the prisms.

Now, a negative lens 7 as an auxiliary lens is provided on the optical path of the distance measuring optical system branched by the optical path splitter 6 made of a prism having a dichroic mirror surface as described above.
A so-called Galileo-type afocal system is formed with this negative lens. Therefore, objective lens 1
A beam of light from an object at infinity entering the lens 7 becomes a parallel beam of light after exiting from the negative lens 7. On the optical path of such a parallel light beam, a transmitted light reflecting member 8 for reflecting the transmitted light and a received light reflecting member 9 for reflecting the received light are provided with the optical axis as a boundary. The transmitted light reflecting member 8 has an entrance surface 8a and an exit surface 8b that are perpendicular to each other, and a 45-degree slope 8c is a silver-deposited back mirror that has high reflectance in the infrared and visible regions. The transmitted light reflecting member 8 is joined and supported by a 45-degree first inclined surface 9a formed on the received light reflecting member 9 by an inclined surface 8c. The received light reflecting member 9 has a second slope 9b formed on the surface reflecting surface at a 45-degree angle opposite to the first slope 9a.
The second slope 9b is formed as a surface mirror having a thin film deposited thereon so as to maximize the reflectance of infrared light for distance measurement. The optical path of the transmitted light and the optical path of the received light by both reflecting members are configured to be perpendicular to the optical axis of the objective lens and located on the same straight line.

The transmitting light optical path and the receiving light optical path, which are branched from each other by the transmitting light reflecting member 8 and the receiving light reflecting member 9, still maintain a parallel light flux, and the transmitting positive lens 11 is provided in the transmitting light optical path, and the receiving light optical path is A positive receiving lens 12 is arranged in each optical path. A light emitting diode 10 as a light source is provided on the focal point of the positive transmission lens 11, and a photodiode 13 as a light receiving member is provided on the focal point of the positive receiving lens 12. Here, a transmission optical path of the ranging optical system is formed by the light source 10, the transmission lens 11, the transmission light reflection member 8, the negative lens 7, the optical path splitter 6, and the objective lens 1. The lens 7, the received light reflecting member 9, the receiving lens 12 and the light receiving member 13 form a receiving optical path of the distance measuring optical system. Further, a reference light optical path is formed by an optical path that directly reaches the light receiving member 13 from the light source 10 via the transmitting lens 11 and the receiving lens 12.

In the basic configuration of such a distance measuring optical system, a background light cut filter 14 is provided between the receiving reflection member 9 and the receiving lens 12 to cut out light of wavelengths other than the received light that enters as noise. It is located. In order to switch between the transmission light and the reference light, an optical path switch 15 that is rotatable about a rotation axis eccentric from the optical axis of the transmission lens is provided.
A rotary filter 16 is provided between the light source 10 and the transmitting lens 11 and is provided between the receiving lens 12 and the light receiving member 13 to equalize the intensity of the received light and the reference light. In addition, a light shielding plate 17 is arranged along the optical axis of the objective lens 1 and the negative lens 7 so that the transmitted light does not directly enter the receiving optical path or the reference optical path, and the reference light does not enter the receiving optical path. is provided. As shown in the side view of FIG. 2A and the plan view of FIG. The near-axis portion 17b is formed into a bent portion to prevent transmitted light from entering the receiving optical path.

Between the transmitting lens 11 and the negative lens 7, between the negative lens 7 and the receiving lens 12, and the transmitting lens 11
The parallel system between the receiving lens 12 and the receiving lens 12 has the following advantages.

First, in general, regarding transmission optical systems, assuming that the size of the light source is constant, the shorter the focal length of the transmission optical system as a whole, the larger the transmission angle, which widens the allowable range for distance measurement. In the configuration of the present invention, the transmitting lens 11
By changing the focal length of the transmitting optical system, the focal length of the transmitting optical system as a whole can be shortened without significantly changing the total length of the transmitting optical system, and there is a high degree of freedom in designing the basic configuration. Second, since the distance measuring light is infrared light, it is necessary to remove the background light cut filter 14 to adjust the distance measuring optical system, but the background light cut filter is placed in the parallel light beam. Therefore, there is no focus shift or optical axis shift due to the insertion and removal of this filter, and it is possible to perform sufficient adjustment for infrared light through visible light observation. Furthermore, since the light beam incident on the background light cut filter is neither convergent nor diverging, there is no risk of being adversely affected by the angular characteristics of the multilayer thin film forming this filter. Thirdly,
Since the optical path of the reference optical system is shared by a part of the transmitting optical system and a part of the receiving optical system, the structure is simple and does not require a dedicated member as the reference optical system. Since the member 13 is coaxial, adjustment can be made extremely easily and accurately.

In the above embodiment, the light source was placed at the focal position of the transmitting lens, and the light receiving member was placed at the focal position of the receiving lens. Needless to say, it can be configured to guide each luminous flux.

(Effects of the Invention) As described above, according to the present invention, since the optical path splitter for branching the optical path of the ranging optical system from the optical path of the collimating optical system is constituted by a small prism,
The entire device can be made compact. In addition, since the distance measuring optical system can be inserted without making the optical path of the collimating optical system very long, the collimating telescope can be rotated freely and has excellent operability, as well as the optical system of the conventional theodolite. It is possible to configure a light wave distance measuring device relatively easily without making major changes. It goes without saying that the light wave distance measuring device according to the present invention is effective not only for intensity modulating the transmitted light for distance measurement, but also for distance measurement using pulsed light.

[Brief explanation of drawings]

FIG. 1 is an optical path diagram showing the configuration of an embodiment of a light wave distance measuring device according to the present invention, and FIGS. 2A and 2B are a side view and a plan view of a light shielding plate provided in the distance measuring optical system. [Explanation of symbols of main parts], 1...Objective lens,
2... Focusing lens, 5... Eyepiece lens, 6... Optical path splitter, 7... Negative lens, 8... Transmitted light reflecting member, 9... Receiving light reflecting member, 10... Light source, 11
...Transmission lens, 12...Reception lens, 13...
Light receiving member, P1...first prism, P2...second
prism.

Claims (1)

[Scope of Claims] 1. A collimating optical system having an objective lens and an eyepiece; an optical path splitter disposed between the objective lens and the eyepiece; A transmitted light reflecting member and a received light reflecting member are integrally arranged on the optical axis of the objective lens, and a light receiving member receives a light beam from a light source that supplies transmitted light to the transmitted light reflecting member and the received light reflecting member. In the coaxial optical distance measuring device, the optical path splitter includes an entrance surface formed substantially perpendicular to the optical axis of the collimation optical system, a first exit surface substantially parallel to this, and the entrance surface. and a semi-transmissive mirror surface obliquely installed between the first exit surface and the prism, the prism totally reflects the light beam reflected by the semi-transparent mirror surface on the incident surface, and also transmits light onto the incident surface. Therefore, the angle θ between the normal to the semi-transparent mirror surface of the optical path splitter and the optical axis of the collimation optical system is 15°<θ< A light wave ranging device characterized by a range of 45°.