Reflector and reference point surveying method

Abstract

To provide a reflector and a reference point surveying method having a simple structure and capable of detecting the incident direction of a light beam to the reflector without changing a measuring reference point regardless of the incident direction of the light beam.SOLUTION: The direction detector includes an image-forming lens (4) and a light-receiving sensor (5), and is configured such that principal rays 11a, 11b, 11c, and 11d that are incident so as to pass through the center of the ball lens and are transmitted through the ball lens are reflected by an outer face of the spherical crown and an inner face of the spherical crown or a face of the ball lens and are then incident on the direction detector. The direction detector is configured to detect the incident direction of the main light beam with respect to the main optical axis based on a light receiving position 5d of the light receiving sensor when the main light beam is incident on the imaging lens and is imaged on the light receiving sensor by the imaging lens.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reflector that retroreflects a light beam such as a laser beam and a method for measuring a reference point. [Background technology]

[0002] In laser surveying, a reflector that retroreflects distance measurement light is used as the measurement target. The reflector is attached to a pole that indicates the measurement point, and typically a full-circle prism that retroreflects a wide range of laser light is used as the reflector.

[0003] The full-circumference prism is made up of a combination of multiple corner cube prisms, and in addition to having a complex structure, the retroreflection point (measurement reference point) may shift slightly depending on the direction of the incident light, which can cause measurement errors in distance, vertical angle, and horizontal angle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent Application Publication No. 4343272 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a reflector and a reference point surveying method that has a simple structure, does not change the measurement reference point regardless of the incident direction of a light ray, and is capable of detecting the incident direction of a light ray on the reflector. [Means for solving the problem]

[0006] The present invention relates to a reflector including a ball lens, a spherical crown joined to the ball lens, and a direction detector disposed on a principal optical axis passing through the center of the ball lens, the direction detector including an imaging lens and a light-receiving sensor, and configured so that a principal ray of light incident on the ball lens passes through the center of the ball lens and is transmitted through the ball lens is reflected by the outer surface of the spherical crown and the inner surface of the spherical crown or the surface of the ball lens, and then enters the direction detector, and the principal ray is incident on the imaging lens and formed into an image on the light-receiving sensor by the imaging lens, and the direction detector is configured to detect the incident direction of the principal ray with respect to the principal optical axis based on the light-receiving position of the light-receiving sensor.

[0007] The present invention also relates to a reflector in which the ball lens is a concentric multi-sphere formed by laminating glass materials in multiple layers.

[0008] The present invention also relates to a reflector in which the joint between the ball lens and the spherical crown is optically discontinuous.

[0009] The present invention also relates to a reflector that is calibrated so that light rays are incident from outside the spherical crown so that they are imaged on the light-receiving sensor, changes in the light-receiving position of the light rays due to environmental changes are detected, and errors in direction detection are corrected based on the detected changes.

[0010] Furthermore, the present invention relates to a control point surveying method using the above-mentioned reflector, in which the reflector is installed at at least known point 2 of known points 1 and 2, a surveying device is installed at new point 1, known points 1 and 2 are measured by the surveying device, new point 1 is made known by resection, the direction angle of new point 1 is detected with the reflector at known point 2, the surveying device is then installed at new point 2, known point 2 is measured from new point 2, the direction angle of new point 2 is detected with the reflector at known point 2, and new point 2 is made known based on the direction angles of new point 1 and new point 2 detected by the reflector and the measurement results of measuring known point 2 from new point 2. [Effects of the Invention]

[0011] According to the present invention, a ball lens, a spherical crown joined to the ball lens, and a direction detector are disposed on a principal optical axis passing through the center of the ball lens, the direction detector including an imaging lens and a light-receiving sensor, and configured so that a principal ray of light incident to pass through the center of the ball lens and transmitted through the ball lens is reflected by the outer surface of the spherical crown and the inner surface of the spherical crown or the surface of the ball lens, and then incident on the direction detector, and the direction detector is configured so that the principal ray is incident on the imaging lens and is imaged on the light-receiving sensor by the imaging lens, and the incident direction of the principal ray with respect to the principal optical axis is detected based on the light-receiving position of the light-receiving sensor, thereby providing the excellent effect that the measurement reference point does not change regardless of the incident direction of the light ray, and that it is possible to detect the incident direction of the light ray on a reflector. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing an optical system of a reflector according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram illustrating a first modified example of the present embodiment. [Figure 3] FIG. 10 is a diagram illustrating a second modified example of the present embodiment. [Figure 4] FIG. 10 is a diagram illustrating a third modified example of the present embodiment. [Figure 5] FIG. 10 is a diagram showing an optical system of a reflector according to a second embodiment. [Figure 6] (A) and (B) are explanatory diagrams of the conventional resection method for measuring new points. [Figure 7] 1A and 1B are explanatory diagrams showing a method for measuring new points in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] FIG. 1 shows an optical system of a reflector 1 according to an embodiment of the present invention, and the support structure and support members for the optical elements that make up the optical system are not shown.

[0015] The reflector 1 according to this embodiment uses a spherical ball lens 2 as a retroreflector. A ball lens reflector does not require correction because no error occurs in the orientation of the reflector relative to the incident light.

[0016] The ball lens 2 has a refractive index of 1.9 to 2.1 for the target wavelength and has the optical property of retroreflecting on-axis light passing through the center of the sphere. In this embodiment, a ball lens with a refractive index of 2.0 is used.

[0017] A spherical cap 3 is provided on the opposite incident side of the ball lens 2. The spherical cap 3 is a transparent body, and has the shape of a hollow sphere with a part removed.

[0018] The inner surface of the spherical cap 3 is a spherical surface with the same diameter as the radius of the outer surface of the ball lens 2, and is cemented to the ball lens 2 so as to cover the apex of the non-incident side of the ball lens 2. The inner surface of the spherical cap 3 is in close contact with the outer surface of the ball lens 2.

[0019] The outer surface of the spherical crown 3 is spherical, and the outer diameter of the spherical crown 3 is such that the required thickness is achieved, and the center of the outer surface of the spherical crown 3 is positioned away from the center of the ball lens 2. Alternatively, the outer surface of the spherical crown 3 is formed aspherical.

[0020] Here, the cemented surface between the ball lens 2 and the spherical crown 3 is referred to as surface A, and the outer surface of the spherical crown 3 is referred to as surface B.

[0021] An optical axis passing through the center of ball lens 2 and the center of spherical crown 3 is defined as main optical axis O, and an imaging lens 4 consisting of a group of convex lenses and a light-receiving sensor 5 are provided on main optical axis O that passes through ball lens 2 and spherical crown 3. The imaging lens 4 forms an image of the light beam from spherical crown 3 on light-receiving sensor 5.

[0022] The light receiving sensor 5 is a collection of pixels, each of which has pixel coordinates (x:y) with the main optical axis O as the origin, and the pixel coordinates identify the position on the light receiving sensor 5. Each pixel outputs position information (pixel coordinates) along with a light receiving signal. A 2D image sensor such as a CMOS or CCD is used as the light receiving sensor 5.

[0023] The imaging lens 4, the light receiving sensor 5, etc. constitute a direction detector 31 (described later).

[0024] A first beam splitter film 7 is formed on the surface A. The first beam splitter film 7 may be formed on the entire surface A, or may be formed only in the center of the surface A. The first beam splitter film 7 is set to have a high reflection ratio and a low transmission ratio, so that it reflects at least half of the light and transmits the rest. For example, the reflection / transmission ratio is set to 90% / 10%. The surface A may be the inner surface of the spherical cap 3 or the surface of the ball lens 2. The center of the surface A refers to the effective range of the entire light beam reflected by the surface A.

[0025] Here, the reason for increasing the reflectance of the first beam splitter film 7 is to obtain the amount of light necessary for distance measurement and tracking, since the retroreflected light from the ball lens 2 is very weak.

[0026] A second beam splitter film 8 is formed on the surface B. The second beam splitter film 8 may be formed on the entire surface of the surface B, or may be formed only in the central portion. The second beam splitter film 8 has a reflection / transmission ratio of 50% / 50% for maximum efficiency. The central portion of the surface B refers to the effective range of the entire light beam that is transmitted through the surface B.

[0027] The following describes the state of the light beam when the first beam splitter film 7 is formed on surface A and the second beam splitter film 8 is formed on surface B. In this embodiment, the maximum incident angle of view is approximately 130°.

[0028] First, the light beam (principal ray 11a) on the principal optical axis O (incident angle of view 0°) passes through the center of the ball lens 2, with 90% retroreflected by surface A and 10% transmitted. 50% of the transmitted principal ray 11a is reflected by surface B, and 90% of that reflected by surface B is reflected by surface A, with a further 50% transmitted through surface B, and is imaged on the light-receiving sensor 5 by the imaging lens 4. The image position of the principal ray 11a on the light-receiving sensor 5 is the intersection of the principal optical axis O and the light-receiving sensor 5, i.e., the center of the light-receiving sensor 5. The pixel located in the center outputs position information (0,0) along with a light-receiving signal.

[0029] Next, for example, when a light beam (principal ray 11d) enters ball lens 2 from above at 65° (maximum angle of view) in Figure 1, chief ray 11d passes through the center of ball lens 2, is reflected by surface A by 90%, and is retroreflected 65° upward.

[0030] Furthermore, 10% of the principal ray 11d that has passed through surface A is reflected successively by surfaces B and A, passes through surface B, is subjected to the refraction action of the spherical crown 3, and is incident on the imaging lens 4, which then forms an image at the light-receiving position 5d of the light-receiving sensor 5. The pixel at light-receiving position 5d outputs a light-receiving signal and position information (xd, yd).

[0031] At this time, the angle of view of the exit point of the chief ray 11d at the spherical cap 3 is 30°, which is less than half the angle of view of the incident light.

[0032] Furthermore, 10% of chief ray 11c, which is incident at a smaller angle of view than chief ray 11d, is transmitted through surface A, is reflected successively by surfaces B and A, is transmitted through surface B, is refracted by the spherical crown 3, is collected near the imaging lens 4, is incident on the imaging lens 4, and is imaged by the imaging lens 4 at the light-receiving position 5c of the light-receiving sensor 5. The pixel at light-receiving position 5c outputs a light-receiving signal and position information (xc, yc).

[0033] Regarding the chief ray 11b that is incident at an even smaller angle of view than the chief ray 11c, the chief ray 11b that passes through the surface A is similarly reflected successively by the surfaces B and A, and then emerges from the spherical crown 3, is condensed, and is imaged at the light-receiving position 5b of the light-receiving sensor 5 by the imaging lens 4.

[0034] Therefore, a chief ray incident from an angle of view deviated from the chief optical axis O is similarly reflected successively by surfaces A and B, then emitted from the spherical crown 3, and imaged by the imaging lens 4 on the light-receiving sensor 5. Furthermore, the light-receiving position of the chief ray on the light-receiving sensor 5 corresponds to the incident angle of view of the chief ray on the ball lens 2, and the incident angle of view, i.e., the incident direction (retroreflection direction) of the chief ray relative to the main optical axis O, can be determined from the light-receiving position information.

[0035] Next, regarding the amount of light received by the light receiving sensor 5, for example, the principal ray 11a is transmitted through surface A, reflected through surface B, reflected through surface A, and transmitted through surface B before entering the imaging lens 4. Since the reflection / transmission ratio of surface A is 90% / 10% and the reflection / transmission ratio of surface B is 50% / 50%, the amount of light received by the light receiving sensor 5 is 1×0.1×0.5×0.9×0.5=0.0225=2.25% of the incident light amount 1. Meanwhile, the amount of retroreflected light is 1×0.9=90%.

[0036] As described above, by including the reflection processes at surfaces A and B, the exit angle of view is 1 / 2 or less of the maximum incident angle of view, which makes it possible to reduce the size of the imaging lens 4 and significantly shorten the optical axis length on the light-receiving sensor 5 side.

[0037] For example, compared to Patent Document 1, the overall length is reduced by 25%, the maximum diameter is reduced by 13%, and the angle is increased by 40%.

[0038] It should be noted that the transmittances of the first beam splitter film 7 and the second beam splitter film 8 described above are merely examples. For example, for the first beam splitter film 7 on surface A, if the target of this reflector is a specification for a distance of up to 100 m, the amount of reflected light needs to be increased, so transmission:reflection=1:10, and if the target is a distance of up to 30 m, transmission:reflection=1:1 to minimize variations in the amount of light transmitted and reflected by the beam splitter film. Needless to say, the transmittance is selected appropriately depending on the situation in which this reflector is used.

[0039] FIG. 2 shows a first modified example of this embodiment.

[0040] In the first modification, the ball lens 2 is made of a plurality of glass materials in order to improve the retroreflection performance of the ball lens 2.

[0041] In this modified example, ball lens 2 is a concentric multi-sphere 13, which is constructed by using a solid sphere 13a at the center and by closely polymerizing hollow spheres 13b and 13c in multiple layers on sphere 13a, and polymerizing spheres 13b and 13c by combining hemispheres 13b1 and 13b2, and hemispheres 13c1 and 13c2, respectively.

[0042] 3 shows a second modified example, which is also constructed of two glass materials to improve retroreflection performance. A partial spherical body 14b of a required thickness is bonded to one spherical body 14a. The partial spherical body 14b is designed so that light rays incident on the spherical body 14a are retroreflected by the outer surface of the partial spherical body 14b, and the partial spherical body 14b covers the maximum angle of view of the incident light rays.

[0043] Fig. 4 shows a third modified example. In Fig. 4, the same components as those shown in Fig. 1 are denoted by the same reference numerals.

[0044] In the third modified example, a small gap g is formed between the ball lens 2 and the spherical crown 3. Alternatively, the ball lens 2 and the spherical crown 3 are configured to be optically discontinuous.

[0045] By forming the gap g, the degree of freedom in design increases and aberration correction (retroreflection performance) becomes easier.

[0046] Furthermore, off-axis chief rays 11b, 11c, and 11d (chief rays other than chief ray 11a) pass through surface B and are reflected by surfaces A and B, but the formation of gap g causes the angle of incidence on surface B to be greater than a predetermined angle, resulting in total reflection, reducing the loss of light in the peripheral areas and improving efficiency. Therefore, efficiency is improved for high-angle incident rays that are disadvantageous in terms of aberration correction. While there is originally a difference in reach distance between the center and periphery of the sensor due to general lens performance, the increased efficiency caused by total reflection has the effect of extending the reach distance in the peripheral areas, and is effective in extending the reach distance overall.

[0047] Fig. 5 shows a second embodiment, which aims to improve the direction detection accuracy in the first embodiment. In Fig. 5, the same reference numerals are used to designate the same components as those shown in Fig. 1, and their explanation will be omitted.

[0048] The optical components that make up the reflector, such as the ball lens 2, undergo thermal expansion or changes in refractive index due to temperature changes. The thermal expansion and changes in refractive index cause changes in the image position when the light passes through the ball lens 2, spherical cap 3, and imaging lens 4 and is focused on the light-receiving sensor 5.

[0049] With respect to a desired chief ray, for example, chief ray 11d, a change in temperature changes the image formation position (light receiving position) of the chief ray 11d on the light receiving sensor 5. This change in the light receiving position appears as an error in direction detection.

[0050] In this embodiment, a change in the light receiving position corresponding to a temperature change is obtained in advance, and the detection direction by the light receiving sensor 5 is corrected based on the change in the light receiving position.

[0051] An LED 15 that emits inspection light is provided in contact with or close to the outer surface of the spherical cap 3, and the LED 15 irradiates inspection light 16 toward the ball lens 2. The inspection light 16 is reflected by the ball lens 2, passes through the spherical cap 3, enters the imaging lens 4, and forms an image on the light-receiving sensor 5. The inspection light 16 may have the same wavelength as the light actually used in surveying, such as distance-measuring light, or it may have a different wavelength. Although the LEDs 15 are provided in two locations in the figure, they may also be provided in one location.

[0052] The irradiation direction of the inspection light 16 is set to be the same as the optical path of a principal ray having a known incident angle, for example, a principal ray 11d'.

[0053] In a steady state, for example, when the ambient temperature is 20° C., the distance measuring light is incident on the reflector 1 as the principal ray 11d', and the light receiving position at the light receiving sensor 5 is detected.

[0054] Next, at an ambient temperature of 20° C., the LED 15 irradiates the inspection light 16, and the light receiving position of the light receiving sensor 5 for the inspection light 16 is set to the same as the light receiving position for the distance measuring light. The light receiving position of the inspection light 16 at this time is set as the reference value.

[0055] Next, the environmental temperature is set to 30°C, the LED 15 irradiates the inspection light 16, and if the light-receiving position of the light-receiving sensor 5 changes, this change can be determined to be due to a change in the environmental temperature. Therefore, by correcting the direction detected by the light-receiving sensor 5 based on this change in the light-receiving position, accurate direction detection can be performed.

[0056] Furthermore, by acquiring in advance the change in the light receiving position of the inspection light 16 corresponding to a predetermined temperature change, for example, a temperature change from -10°C to 40°C, it is possible to correct detection errors caused by environmental changes.

[0057] In this embodiment, the position where the LED 15 is provided may be any location outside the range through which the distance measurement light passes, for example, referring to Fig. 1, any location outside the range of 60 degrees around the main optical axis O. Therefore, the LED 15 may be provided at multiple locations to obtain multiple reference values.

[0058] In this embodiment, since it is sufficient that the incident optical path of the inspection light 16 coincides with the optical path of the chief ray, the LED 15 does not necessarily have to be installed on the outer surface of the spherical crown 3, and may be installed away from the reflector 1 in a location that is not affected by temperature changes. Alternatively, a separate inspection light irradiating device may be used to irradiate the inspection light 16 onto the reflector 1, and while changing the ambient temperature and the incident angle of the inspection light 16, the light-receiving position on the light-receiving sensor 5 may be detected to obtain data relating to the incident angle and ambient temperature. If the ambient temperature of the reflector 1 changes during actual measurement, the direction detected by the light-receiving sensor 5 may be corrected based on this data.

[0059] Furthermore, since the inspection light 16 only needs to be received by the light receiving sensor 5, it may be incident so as to form an image on the light receiving sensor 5.

[0060] Next, the control point surveying method will be described.

[0061] First, a conventional surveying method for performing control point surveying will be described with reference to FIGS. 6(A) and 6(B).

[0062] STEP: 01 Install a surveying device at new point 1, install reflective targets at known point 1 and known point 2, measure known point 1 and known point 2 with the surveying device, determine the coordinates of new point 1 using the intersection method, and make new point 1 known. The point that has been made known is called known point 3.

[0063] Install a surveying device at new point 2, leave the reflective target at known point 2 as is, and install a reflective target at known point 3. Use the surveying device to measure known points 2 and 3 from new point 2, and make new point 2 known in the same way as in STEP:01.

[0064] Next, a control point surveying method of the present invention using the reflector 1 of the above embodiment will be described with reference to FIGS. 7(A) and 7(B).

[0065] STEP 11: A surveying device is installed at new point 1, a reflective target is installed at known point 1, and the reflector 1 (including direction detector 31) of the present invention is installed at known point 2. The coordinates of new point 1 are determined by the method of intersection, and new point 1 is made known. The known new point 1 is made known point 3.

[0066] STEP 12: At this time, the direction detector 31 of the reflector 1 receives the distance measuring light and detects the direction angle of the installation point (known point 3) of the surveying instrument from the light reception result. The direction angle (horizontal angle) at this time is defined as A.

[0067] STEP 13: The surveying equipment is moved to the next measurement point (new point 2) and installed at new point 2. At this time, the reflector 1 at known point 2 is maintained in the initial installation state.

[0068] STEP 14: Known point 2 is measured from new point 2 using a surveying device. The reflector 1 (direction detector 31) receives the distance measurement light and detects the direction angle (horizontal angle) B of new point 2 from known point 2 based on the received light. The horizontal angle C between known point 3 and new point 2 is calculated as (BA).

[0069] New point 2 is made known based on this horizontal angle C and the measurement results of known point 2 using the surveying equipment at new point 2.

[0070] In the present invention, when making the new point 2 known, there is no need to set a target at the known point 3, so the measurement work time is reduced. [Explanation of symbols]

[0071] 1 reflector 2. Ball Lens 3 ball crown 4 Imaging lenses 5 Light receiving sensor 7 First beam splitter film 8 Second beam splitter film 15 LED 16 Inspection light 31 Direction detector

Claims

1. a ball lens, a spherical crown joined to the ball lens, and a direction detector disposed on a principal optical axis passing through the center of the ball lens, the direction detector including an imaging lens and a light-receiving sensor, configured so that a principal ray of light incident on the ball lens so as to pass through the center of the ball lens and transmitted through the ball lens is reflected by the outer surface of the spherical crown and the inner surface of the spherical crown or the surface of the ball lens, and then incident on the direction detector, the direction detector being configured so that the principal ray is incident on the imaging lens and is imaged on the light-receiving sensor by the imaging lens, and the direction detector detects the incident direction of the principal ray with respect to the principal optical axis based on the light-receiving position of the light-receiving sensor.

2. 2. The reflector according to claim 1, wherein the ball lens is a concentric multi-sphere formed by laminating glass materials in multiple layers.

3. 2. The reflector according to claim 1, wherein the joint between the ball lens and the spherical cap is optically discontinuous.

4. 2. The reflector according to claim 1, wherein a light beam is incident from outside the spherical crown so as to be imaged on the light receiving sensor, a change in the light receiving position of the light beam due to an environmental change is detected, and an error in direction detection is corrected based on the detected change.

5. A control point surveying method using the reflector of claim 1, comprising the steps of: installing the reflector of claim 1 at at least known point 2 of known points 1 and 2; installing a surveying instrument at new point 1; measuring known points 1 and 2 with the surveying instrument; making new point 1 known by resection; detecting a direction angle of new point 1 with a reflector at known point 2; installing the surveying instrument at new point 2; measuring known point 2 from new point 2; detecting a direction angle of new point 2 with a reflector at known point 2; and making new point 2 known based on the direction angle of new point 1 and the direction angle of new point 2 detected by the reflector and the measurement results of measuring known point 2 from new point 2.

Images