JP4506408B2 - Laser distance monitoring system - Google Patents

Description

 The present invention relates to a laser distance monitoring system that sequentially measures a distance to a measurement object using a laser distance measuring device and monitors displacement or shape change of the measurement object.

  Conventionally, when monitoring changes in terrain and the like, as shown in FIG. 9, the reflection element 2 is attached to a position (hereinafter referred to as an observation point) where a measurement object 1 such as a mountainside is to be observed. Illumination light having directivity from the light projecting unit 4, for example, a highly directional laser diode (Patent Document 1), a light emitting element, or an illumination lamp (Patent Document 2) through the illumination lens 5 at a separated position. Reflected light that is projected toward the reflecting element 2 and reflected by the reflecting element 2 in substantially the same direction as the incident direction is input to the light receiving unit 7 through the condenser lens 6, and the calculation processing unit 8 performs the illumination. An optical distance measuring device 3 that calculates the distance D to the observation point based on the time from when the light is projected until it is received by the light receiving element 2 is installed, and the arithmetic processing unit 8 of the optical distance measuring device 3 is installed. Or the distance D to the observation point or Calculated amount of change ΔD and D, to monitor the displacement or terrain variation of the measurement object 1 observation point based on these calculation results are known (see Patent Documents 1 and 2).

  In any of the optical distance monitoring devices using the above-described conventional optical distance measuring device 3, as the reflecting element 2, as shown in FIGS. 10 (a) and 10 (b), a corner reflector (Patent Document 1). Or a spherical reflector (Patent Document 2) is used, and in general, when it is mounted several tens to hundreds of meters away from the light projecting unit 4, The target (target) of the beam or luminous flux projected from the unit 4 is very small as viewed from the light projecting unit 4 and is substantially point-like.

 In a conventional optical distance monitoring device used in combination with such a single type of reflection element 2, the projection direction of the light beam projected from the light projecting unit 4 is always set to the target, that is, the reflection element 2. Since it is impossible to measure the distance to the observation point if it is outside the measurement range corresponding to the reflection region, it is essential to aim at the point target. Accordingly, when this type of optical distance monitoring device is in operation, the observation object 1 is always observed while adjusting one of the elevation angle or horizontal angle of the light projecting unit 4 and the light receiving unit 7 or the elevation angle and horizontal angle. Control is performed so as to follow the point, and thus the point-like reflection region of the reflection element 2, that is, the so-called reflection spot (target). Such target tracking control is performed by the direction control device 25 in the device of Patent Document 1 and by the (transit) control device 5 in the device of Patent Document 2.

In the optical distance monitoring device that measures the distance in cooperation with the single-type reflection element 2 of the conventional type, as described above, the target of the projection light from the light projecting unit 4 is very small. When the projection light from the light projecting unit 4 deviates from the target during operation of the monitoring device, that is, out of the measurement range, its automatic repair is difficult, distance measurement becomes impossible, and stability and reliability are insufficient. is there. This problem is particularly serious when used unattended and regularly for distance monitoring. Further, the direction control device of the projection light is required to have high accuracy and high response, and not only the control circuit or the device itself is expensive, but also the cost of the entire monitoring device becomes very expensive. .
JP-A-7-159162 JP-A-4-348217

  As described above, the distance monitoring device based on the conventional optical distance measurement has a narrow pinpoint effective measuring range of the reflecting element that cooperates with the device, and has stable and reliable operation. There was a drawback that it was insufficient and the manufacturing cost was expensive.

  In addition, since the reflective element tends to deviate from the effective measurement range of the distance monitoring device, the distance monitoring device constantly adjusts the elevation angle or horizontal angle of the optical axis of the light projecting unit and the light receiving unit, that is, the observation point of the measurement object, that is, In order to search for the target (reflective element), there were problems such as wear and malfunction of the drive mechanism of the distance monitoring device, and the battery for driving the drive mechanism did not last long.

  The present invention was devised to solve the above-described problem, and it is possible to easily and easily aim the target of the projection light used for distance measurement, and reduce the target deviation of the projection light as much as possible. Laser that can prevent wear and malfunction of the drive mechanism of the distance monitoring device, reduce power consumption, and easily and quickly return to the measurement range even if the target is out of the effective range of distance monitoring The object is to provide an optical distance monitoring system.

The invention according to claim 1 is a plate-like reflection which has a reflection area of a predetermined area at the observation point of the measurement object and reflects the laser beam incident on the reflection area in the substantially same direction as the incident direction. A light projecting means for projecting a laser beam toward a reflection region of the reflector at a position spaced from the measurement object, and a light receiving means capable of receiving the laser light reflected by the reflector Driving means for rotating the optical axes of the light projecting means and the light receiving means, and laser light received by the light receiving means is projected from the light projecting means and reflected by the reflection region of the reflector. That is, a recognition unit that determines whether or not the observation point of the measurement object is out of the measurement range corresponding to the reflection region of the reflector, and the observation point of the measurement object by the recognition unit is the measurement range Off When it is recognized that not, while rotating movement within a predetermined range of the optical axis of said light projecting means and light receiving means by said drive means, said reflected by the reflector from the projection point of the laser light from said light projecting means And a laser distance measuring means comprising an arithmetic processing means for measuring a time until the light is received by the light receiving means and calculating a shortest distance to the observation point of the measurement object based on the measurement time. The laser distance measuring means sequentially measures the distance of the observation point of the measurement object, the calculation processing means calculates the change amount ΔD of the measurement distance D, and the measurement object is based on the change amount ΔD. This is a laser distance monitoring system configured to monitor displacement or shape change.

According to a second aspect of the present invention, the distance measurement point of the measurement object is periodically measured by the laser distance measurement means, and the measurement object is recognized by the recognition means in the laser distance measurement means at the start of each distance measurement. When the observation point is recognized as being out of the measurement range of the laser distance measuring means, the driving means rotates the optical axes of the light projecting means and the light receiving means so that the observation point of the measurement object is 2. The laser distance monitoring system according to claim 1, wherein the laser distance monitoring system is automatically adjusted so as to be included in a measurement range.

According to a third aspect of the present invention, the rotational movement of the optical axes of the light projecting means and the light receiving means is within a predetermined range including the position at the time of the previous distance measurement by combining the vertical rotational movement and the horizontal rotational movement. 3. The laser distance monitoring system according to claim 2, wherein scanning is performed.

According to a fourth aspect of the present invention, the rotational movement of the optical axes of the light projecting means and the light receiving means is spirally started from the position at the previous distance measurement by combining the vertical rotational movement and the horizontal rotational movement. 3. The laser distance monitoring system according to claim 2, wherein the laser distance monitoring system is rotated .

  According to the laser distance monitoring system of the first aspect of the present invention, it is possible to monitor a change in the distance of the measurement object in the laser light projection direction (front-rear direction), and the reflector attached to the measurement object is a predetermined reflector. Therefore, the reflector does not immediately deviate from the measurement range with respect to the horizontal and vertical displacements. Therefore, since the frequency of driving the driving means is reduced, it is possible to reduce the wear and malfunction of the driving mechanism, the consumption of the battery for operating the driving means, and the like.

  According to the laser distance monitoring system of the second aspect of the present invention, the vertical axis and the horizontal axis of the transit mechanism are automatically rotated only when the observation object is periodically removed and the measurement object is out of the measurement range. It is ideal for unmanned observation because it is driven to find the measurement object.

  According to the laser distance monitoring system of the third aspect of the present invention, when the measurement object is out of the measurement range, the laser distance measuring device is scanned in a wide range in the vertical direction or the horizontal direction to reflect the reflected light from the reflector. Therefore, the moved (displaced) measurement object can be easily and quickly found.

  According to the laser distance monitoring system of claim 4 of the present invention, when searching for a measurement object that is out of the measurement range, it moves by scanning the projection light in a spiral shape starting from the position at the previous distance measurement. The measurement object that has been (displaced) can be found faster, and the measurement can be completed in a short time.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows the concept of the configuration of a laser distance monitoring system according to an embodiment of the present invention, and is used for monitoring, for example, a change in terrain with time due to an earthquake or the like, a movement of a building with time, and the like. Monitoring of deviations or changes in topography, movement of buildings, and the like is performed by measuring a displacement at a predetermined position in the measurement object 1 to be monitored.

 In FIG. 1, land is shown as the measurement object 1. For example, a flat reflector 12 having a reflection area of 80 cm × 100 cm, for example, at a predetermined point (observation point) near the top of a hilly area. It is installed, for example, on a sign post. For example, a laser distance measuring device 10 that measures the distance D to the observation point in cooperation with the reflector 12 is disposed at a saddle point separated by about 300 m from the observation point. The distance D to the observation point is measured and the displacement of the observation point is evaluated based on the change amount ΔD of the distance D calculated from the measurement distance D. For example, whether or not a threshold value indicating a danger limit is exceeded is determined. Then, the deformation of the hilly area is monitored.

  As shown in FIG. 3A, the reflector 12 is formed by arranging cube mirrors 13 known per se on the substrate surface of the reflector 12 as shown in FIG. 3C. In this case, it is desirable that the size of each cube mirror 13 is 1/10 or less of the beam diameter of the laser light projected from the light projecting unit 25. As shown in FIG. 3 (a), the cube mirror 13 has three reflecting surfaces that are perpendicular to each other and have a shape in which one corner of the cube is cut off. The light incident from the ABC plane in the figure is The light is reflected once by the reflecting surface and comes out of the ABC surface again.

  As shown in FIG. 3B, the laser beam projected from the light projecting unit 25 of the laser distance measuring device 10 is reflected in a reflection region formed by laying many cube mirrors 13 on the substrate surface of the reflector 12. Even if the incident angle changes, the reflection point is reflected so that the incident angle and the reflection angle are equal to each other, so the reflected light is reflected in substantially the same direction as the incident direction (the reflected light is parallel to the incident light), The distance D to the observation point can be measured.

  As shown in FIG. 2, the laser distance measuring instrument 10 generally includes a light projecting unit 25 that projects laser light, a light receiving unit 28, a recognition unit 32, an arithmetic processing unit 34, a transit mechanism unit 40, and the transit mechanism unit 40. Drive circuit (41, 51) and a drive control unit 36. Although not shown, a laser for supplying electric power to electronic components, driving components such as a motor, etc. is mounted in the laser distance measuring instrument 10.

The light projecting unit 25 is composed of a semiconductor laser element (LD element) 22 used for distance measurement, for example, that outputs a pulsed laser beam with an output of 300 mW, and a laser driving circuit 23. For example, a photodiode (light receiving element) 26 having an optical-electrical conversion characteristic selected in accordance with the semiconductor laser element (laser diode) 22 and an amplification circuit 27 for amplifying the output from the light receiving element 26 are included. Is done. The laser light emitted from the light projecting unit 25 passes through an appropriate objective lens (not shown) as in the conventional optical distance measuring device 3, and the measuring device housing 15 described later with reference to FIG. The light is emitted from the projection window 16. On the other hand, of the laser light projected from the light projecting unit 25, the reflected light reflected by the reflection region of the reflector 12 or the laser light reflected from other objects around the reflector 12 is described later. 4 is received through a light receiving window 18 of the measuring instrument housing 15 and a condenser lens (not shown).

  The recognition unit 32 is, for example, a series shown in FIG. 7 which will be described in detail later according to a predetermined recognition operation program stored in a memory area in the central processing unit 30 of the laser distance measuring device 10 configured using a microprocessor. The laser beam received by the light receiving means is projected from the light projecting means and reflected by the reflection region of the reflector, that is, the observation point of the measurement object. Is determined to be out of the measurement range corresponding to the reflection area of the reflector.

  The arithmetic processing unit 34 calculates the distance from the laser distance measuring device 10 to the observation point of the measuring object 1 based on the measurement time performed by the laser distance measuring device 10 in the central processing unit 30. The measurement range in which the observation point of the measurement object 1 is determined by the recognition unit (circuit) 32 according to the size (area) of the reflection region of the reflector 12, that is, the laser beam projected from the light projecting unit 25. When it is recognized that the light can be reflected toward the light receiving unit 28 and, therefore, it is recognized that the distance D to the observation point can be calculated by the reflected light, the laser from the light projecting unit 25 is recognized. The time from the light projection time to the time when the light is reflected by the reflector 12 and received by the light receiving unit 28 is measured, and the measurement object is observed based on the measurement time and the propagation speed (light speed) of the laser light. Calculate the distance to the point.

  The transit mechanism section 40 includes a vertical axis rotation mechanism section 42 as shown in FIG. 5 and a horizontal axis rotation mechanism section 52 as shown in FIG.

  The vertical shaft rotating mechanism unit 42 mounts a table 45 on a vertical shaft 44 fixed to the base 43 and can rotate the table 45 around the vertical shaft 44 via an electric motor 47 and a belt 48 fixed to the base 43. It is a mechanism part built by attaching to the. A horizontal shaft 54 is attached to a pair of support columns 53 standing and fixed on the rotary table 45 of the vertical shaft rotation mechanism 42 so as to be rotatable via an electric motor 57 and a belt 58, and rotates around the horizontal shaft 54. The horizontal axis rotating mechanism 52 is constructed by mounting the measuring instrument housing 15 as possible.

 When the vertical axis rotation mechanism unit 42 is rotationally driven via an electric motor 47, the measuring instrument housing 15, that is, the light projecting unit 25 and the light receiving unit 28 are horizontally arranged around the vertical axis 44 according to the rotation angle. The horizontal angle of the optical axes of the light projecting unit 25 and the light receiving unit 28 and thus the horizontal angle projected from the light projecting unit 25 toward the reflection region of the reflector 12 can be changed. On the other hand, when the horizontal axis rotation mechanism 52 is driven to rotate through the electric motor 57, the measuring instrument housing 15, that is, the light projecting unit 25 and the light receiving unit 28 are moved around the horizontal axis 54 according to the rotation angle. It rotates around the horizontal axis 54 and changes the elevation angle of the optical axes of the light projecting unit 25 and the light receiving unit 28, and thus the elevation angle of the laser light projected from the light projecting unit 25 toward the reflection region of the reflector 12. be able to.

  The electric motor 47 of the vertical axis rotation mechanism unit 42 is rotationally driven by a vertical axis rotation drive circuit 41 that is program-controlled by a drive control unit 36 configured in the central processing unit 30. On the other hand, the electric motor 57 of the horizontal axis rotation mechanism unit 52 is rotationally driven by a horizontal axis rotation drive circuit 51 that is program-controlled by a drive control unit 36 configured in the central processing unit 30.

When the recognizing unit 32 recognizes that the laser light projected from the light projecting unit 25 is out of the measurement range determined corresponding to the reflection region of the reflector 12 attached to the measurement target 1, the drive control unit 36 to control the rotation angle of the electric motor 47 by controlling the vertical axis rotation drive circuit 41, and in accordance with the rotation angle of the electric motor 47, the horizontal angle of the light projecting unit 25, and hence the reflection region of the reflector 12. On the other hand, the optical axis of the laser light projected from the light projecting unit 25 is rotated and moved in the horizontal direction. On the other hand, when the recognition unit 32 recognizes that the laser light projected from the light projecting unit 25 is out of the measurement range determined corresponding to the reflection region of the reflector 12, the drive control unit 36 rotates the horizontal axis. The drive circuit 51 is controlled to control the rotation angle of the electric motor 57, and the elevation angle of the light projecting unit 25 changes according to the rotation angle of the electric motor 57, so that the light is projected onto the reflection region of the reflector 12. The optical axis of the laser light projected from the unit 25 rotates in the vertical direction.

  Various measurement data obtained by the laser distance measuring instrument 10 can be communicated with a remote monitoring device 61 configured by using a computer via a general-purpose communication interface 38 of RS-232C, for example. In the apparatus 61, the measurement distance D data collected by the laser distance measuring device 10 set in each place can be centrally managed.

  Next, when the displacement of the observation point on the terrain is regularly monitored using the laser distance measuring device 10, the observation point on the measuring object 1 is suddenly greatly displaced, and the projection light from the light projecting unit 25. Will be described with reference to an operation flow diagram of the recognition unit 32 in FIG. 7 for an automatic recovery operation in the case where the distance measurement cannot be performed because the measurement distance of the laser distance measuring device 10 is out of range.

  Now, it is assumed that the displacement of the observation point of the previous measurement object 1 is normal, and laser light is projected from the light projecting unit 25 in step S1 at the start of the current measurement.

 In step S <b> 2, it is determined by the recognition unit 32 whether the laser light projected from the light projecting unit 25 is within the measurement range. This determination is based on whether the distance D calculated by the arithmetic processing unit 34 based on the laser beam received by the light receiving unit 28 after the laser beam is emitted from the light projecting unit 25 is extremely large or infinite. Alternatively, the determination is made based on whether the amount of light received by the light receiving unit 28 is zero or below a specified value. That is, if the laser light projected from the light projecting unit 25 is reflected by the reflector 12, it is determined as YES because it is within the measurement range, and the process proceeds to step S7. The distance D to the observation point is calculated based on the time from the time when the laser beam is projected from the unit 25 to the time when the light is received by the light receiving unit 28.

 In this case, in the reflection region of the reflector 12 when the shortest distance is calculated among the distances calculated while changing the drive amounts of the vertical axis rotation mechanism unit 42 and the horizontal axis rotation mechanism unit 52 within a predetermined range. The distance to the reflection point of the laser beam is determined as the distance D to the observation point.

On the other hand, if the determination by the recognition unit 32 is determined to be NO, the process proceeds to step S3, where it is determined that the observation point is out of the measurement range, and the operations of steps S4 to S6 are repeatedly executed. In step S4, the drive control unit 36 drives the transit mechanism unit 40 by a small angle, and the optical axis of the laser light projected from the light projecting unit 25 rotates slightly in the horizontal and vertical directions in the reflection region of the reflector 12. Moved.

 Next, in step S5, similarly to step S1, the laser diode 22 of the light projecting unit 25 is driven to project the laser beam toward the reflection region of the reflector 12, and is received by the light receiving unit 28 as in step S2. Based on the calculation result of the distance D or the measurement result of the amount of received light by the laser light, it is determined whether or not it is out of the measurement range. However, it is repeatedly executed until the determination in step S6 becomes YES.

By repeatedly executing this routine, the laser beam projected from the light projecting unit 25 while changing the horizontal angle of the vertical axis rotation mechanism unit 42 of the transit mechanism unit 40 and the elevation angle of the horizontal axis rotation mechanism unit 52 by a minute angle. the optical axis is small amount and at a time rotational movement in the horizontal direction and the vertical direction in the reflection area of the reflector 12, so that the laser light projected from the light projecting unit 25 is reflected within the measurement range in the reflection region of the reflector 12 Adjusted to

 As described above, the plate-like reflector 12 that has the reflection area of a predetermined area and reflects the laser light incident on the reflection area in the substantially same direction as the incident direction is attached to the measurement object, and the laser distance is obtained. When the measurement is performed, the observation point does not deviate from the reflection area for a slight vertical and horizontal displacement of the measurement object, and the change in the distance between the laser distance measuring instrument and the measurement object continues. Since it can measure and the drive frequency of the transit mechanism part of a laser distance measuring device can be suppressed, abrasion and malfunction of a drive part can be prevented and power consumption can be suppressed.

In executing the routine from step S4 to step S6, when the transit mechanism unit 40 is driven by the drive control unit 36, the vertical axis rotation mechanism unit 42 and the horizontal axis rotation mechanism unit 52 are driven, for example, the previous time. A measurement range in the reflection region of the reflector 12 by rotating the optical axis of the projection laser light from the light projecting unit 25 in the vertical and horizontal directions starting from a point that is a predetermined distance away from the position at the time of distance measurement. Adjust to reflect inside. That is, the projection laser beam can be aimed at the reflector 12. FIG. 8A shows a state in which the optical axes of the light projecting means 25 and the light receiving means 28 are changed in a raster shape by combining the vertical rotation movement and the horizontal rotation movement. It continues to run 査 by the projection laser beam for certain rectangular range around the (measured at a previous point in time deviates from the measurement range) previous distance measurement time. In this manner, a reflector that is out of the measurement range can be detected at high speed.

In executing the routine from step S4 to step S6, when the transit mechanism 40 is driven by the drive controller 36, the vertical axis rotating mechanism 42 or the horizontal axis rotating mechanism 52 is simultaneously moved within a predetermined angle range. The laser light projected from the light projecting unit 25 is reflected by rotating the optical axes of the light projecting means 25 and the light receiving means 28 in a spiral shape starting from the position at the previous distance measurement while sequentially changing the rotation angle at It can also be adjusted to reflect within the measurement range in the 12 reflection regions. FIG. 8B shows a state in which the optical axes of the light projecting means 25 and the light receiving means 28 are rotationally moved in a spiral shape. It will expand the detection range in a spiral shape by performing the rotational movement of the rotational movement and lateral longitudinal direction of the optical axis of the projection laser beam alternately. According to this method, the reflector can be found faster than the detection operation in a raster shape as shown in FIG.

 The laser distance monitoring system of the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.

It is a basic composition conceptual diagram of the laser distance monitoring system of the present invention. It is a block diagram of the laser distance monitoring system of one Example of this invention. FIG. 3A is a configuration explanatory diagram of a flat reflector applicable to the present invention, FIG. 3A is a basic configuration explanatory diagram of a constituent cube mirror, FIG. 3B is a reflected light path diagram of the cube mirror, FIG. (C) is a partially enlarged plan view of a reflector in which a large reflective surface is formed by laying a large number of cube mirrors on the same plane. It is an external appearance perspective view of a laser distance measuring device. It is a schematic plan view of the vertical axis | shaft rotation mechanism part in the said laser distance measuring device. It is a schematic side view of the horizontal axis | shaft rotation mechanism part in the said laser distance measuring device. It is an operation | movement flowchart of the recognition part in the laser distance monitoring system of this invention. FIG. 8A is an explanatory diagram showing an operation of detecting an appropriate reflection point in a reflection region of a reflector of a projection laser beam in a laser distance measuring device. FIG. 8A shows an operation concept of a raster type detection method, and FIG. ) Shows the operation concept of the spiral detection method. It is a block diagram which shows the basic composition of the conventional optical distance measuring device. FIG. 10A is a schematic sectional view of a corner reflector , and FIG. 10B is a schematic sectional view of a spherical reflector. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement object 10 Laser distance measuring device 12 Reflector 13 Cube mirror 22 Laser diode 23 Laser drive circuit 25 Light projection part 26 Light receiving element 28 Light reception part 30 Microprocessor 32 Recognition part 34 Operation processing part 36 Drive control part 38 Communication interface 40 Transit mechanism 41 Vertical axis rotation drive circuit 42 Vertical axis rotation mechanism 51 Horizontal axis rotation drive circuit 52 Horizontal axis rotation mechanism 61 Remote monitoring device 62 Communication cable

Claims (4)

At the observation point of the measurement object, a plate-like reflector that has a reflection area of a predetermined width and reflects the laser light incident on the reflection area in a direction substantially the same as the incident direction is attached. A light projecting means for projecting a laser beam toward the reflection area of the reflector, a light receiving means capable of receiving the laser light reflected by the reflector, and the light projecting means and the light receiving means. Driving means for rotating the optical axis of the laser beam, and whether the laser light received by the light receiving means is projected from the light projecting means and reflected by the reflection region of the reflector, that is, the measurement object Recognizing means for determining whether or not the observation point is out of the measurement range corresponding to the reflection region of the reflector, and when the observation point of the measurement object is recognized as not out of the measurement range by the recognition means While rotating movement within a predetermined range of the optical axis of said light projecting means and light receiving means by said driving means, is received by the photodetection means is reflected by the reflector from the projection point of the laser light from said light projecting means a laser distance measuring means and a processing means to calculate the shortest distance to the observation point of the object to be measured based on the measuring time arranged with measuring the time up to the point that,
The laser distance measuring means sequentially measures the distance of the observation point of the measurement object, and the calculation processing means calculates the amount of change ΔD of the measurement distance D. Based on the change amount ΔD, the measurement object A laser distance monitoring system configured to monitor displacement or shape change. The laser distance measuring means periodically measures the distance of the observation point of the measurement object, and at the start of each distance measurement, the laser distance measurement means recognizes the observation point of the measurement object by the laser distance measurement means. When the driving means rotates the optical axes of the light projecting means and the light receiving means so that the observation point of the measurement object is included in the measurement range. 2. The laser distance monitoring system according to claim 1, wherein the laser distance monitoring system is adjusted automatically. The rotation movement of the optical axes of the light projecting means and the light receiving means is performed by scanning within a predetermined range including the position at the time of the previous distance measurement by combining vertical rotation movement and horizontal rotation movement. 2. The laser distance monitoring system according to 2. The rotational movement of the optical axes of the light projecting means and the light receiving means is characterized by rotating in a spiral shape starting from the position at the previous distance measurement by combining vertical rotational movement and horizontal rotational movement. Item 3. The laser distance monitoring system according to Item 2.

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