Abstract:
An indoor monitoring system for a structure comprises an unmanned floating machine provided with a propeller to float and move in the air inside a structure; a distance measuring unit on said machine to measures a distance between said machine and an inner wall surface of the structure; an inertial measurement unit on said machine to identify the attitude of the body of said machine; an image-capturing unit on said machine to capture an image of a structural body on the side of said machine; a control unit which controls said machine remotely; a flight position information acquiring unit which uses information from the distance measuring unit and the inertial measurement unit to acquire information relating to the current position of said machine; and a monitor unit which displays image information from the image-capturing unit and the position information from the flight position information acquiring unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a national stage of PCT International Application No. PCT/JP2015/051360, filed on Jan. 20, 2015, which claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2014-136868 filed in Japan on Jul. 2, 2014. 
     
    
     FIELD 
       [0002]    The present invention relates to an indoor monitoring system and method for a structure. 
         [0003]    For example, a boiler furnace used at a thermal power plant needs to be opened during construction and periodically after starting operation so that a worker enters the inside to conduct maintenance inspection. During this maintenance inspection, it is necessary to define a portion to be inspected, but it is difficult to accurately grasp the portion to be inspected visually because the capacity of the boiler furnace is large. Thus, a height position and a lateral position of the portion to be inspected have been conventionally measured and marked using a measuring tape or the like to grasp where the worker is or a maintenance inspection position, but such a method requires not only erection of scaffolding for the worker and installation of a gondola but also a lot of efforts, cost, and inspection periods. 
         [0004]    Thus, a technique has been conventionally proposed to clean up the inside of a structure such as a stack using an unmanned inspection apparatus (Japanese Laid-open Patent Publication No. 6-73922). However, this proposal also requires a cradle to install a wire, and efforts, cost and inspection periods are required for the preparation thereof. 
         [0005]    In addition, application of an unmanned inspection technique, which does not require erection of scaffolding using an unmanned aircraft and GPS (Global Positioning System), has been proposed for an outdoor structure (Japanese Patent Application National Publication (Laid-Open) No. 2011-530692). 
         [0006]    However, since electric waves from satellites do not reach indoor structures such as the inside of a boiler and a stack, it is difficult to obtain a flight position using the GPS and to stably maneuver the unmanned aircraft. Thus it is difficult to use the existing inspection technique using the unmanned aircraft. 
         [0007]    In this regard, a system in which indoor flight without using a GPS is possible has been also proposed (EP 1901153 A). 
         [0008]    However, a characteristic point (or a pattern) needs to be provided on the ground instead of the GPS in the proposal of Patent Literature 3, and there is a problem that a place where this characteristic point (or the pattern) can be installed is limited. In addition, since the structure such as the boiler furnace and the stack has a closed space whose inside is dark, there is a problem that it is difficult to confirm the characteristic point. 
         [0009]    Accordingly, there has been a request for emergence of an indoor monitoring system for a structure that is capable of unmanned inspection which reliably obtains internal position information in a closed indoor structure such as a boiler furnace and a stack and also capable of reducing efforts, cost, inspection periods by omitting erection of scaffolding, for example. 
       SUMMARY 
       [0010]    It is an object of the present disclosure to at least partially solve the problems in the conventional technology. 
         [0011]    According to one aspect, there is provided an indoor monitoring system for a structure comprising: an unmanned floating machine including a floating means which levitates the unmanned floating machine inside the structure by remote control; a distance measurement unit which is mounted to the unmanned floating machine and configured to measure a distance between the unmanned floating machine and an inner wall surface of the structure; an inertial measurement unit which is mounted to the unmanned floating machine and configured to obtain an attitude of a body of the unmanned floating machine; an imaging unit which is mounted to the unmanned floating machine and configured to image a structural body on the wall surface side of the structure; an operation unit which is configured to remotely control the unmanned floating machine; a flight position information acquisition unit which is configured to acquire current position information of the unmanned floating machine based on information from the distance measurement unit and information from the inertial measurement unit; and a monitor unit which is configured to display image information from the imaging unit and position information from the flight position information acquisition unit, wherein the flight position information acquisition unit is further configured to execute a horizontal-direction distance measuring step of measuring horizontal distance information between the unmanned floating machine and the inner wall surface of the structure using the distance measurement unit, an attitude angle acquiring step of acquiring an attitude angle of the unmanned floating machine using the inertial measurement unit, a horizontal-direction distance correcting step of correcting the horizontal distance information using the attitude angle acquired in the attitude angle acquiring step, a horizontal-direction distance acquiring step of acquiring distances between the inner wall surface of the structure and the unmanned floating machine in at least two different horizontal directions around the unmanned floating machine based on a yaw angle acquired by the inertial measurement unit, and a horizontal-direction current position information acquiring step of acquiring current position information in a horizontal direction from existing horizontal cross-sectional shape information of the structure. 
         [0012]    According to one aspect, there is provided a An indoor monitoring method for a structure which uses an unmanned floating machine including a floating means which levitates the unmanned floating machine inside the structure by remote control, the method comprising: a distance measurement step executed in the unmanned floating machine and measuring a distance between the unmanned floating machine and an inner wall surface of the structure; an inertial measurement step executed in the unmanned floating machine and obtaining an attitude of a body of the unmanned floating machine; an imaging step executed in the unmanned floating machine and imaging a structural body on the wall surface side of the structure; an operation step of remotely controlling the unmanned floating machine; a flight position information acquisition step of acquiring current position information of the unmanned floating machine based on information from the distance measurement step and information from the inertial measurement step; and a monitor displaying step of displaying image information from the imaging step and position information from the flight position information acquisition step, wherein in the flight position information acquisition step, a horizontal-direction distance measuring step of measuring horizontal distance information between the unmanned floating machine and the inner wall surface of the structure by the distance measurement step is executed, an attitude angle acquiring step of acquiring an attitude angle of the unmanned floating machine by the inertial measurement step is executed, a horizontal-direction distance correcting step of correcting the horizontal distance information using the attitude angle acquired in the attitude angle acquiring step is executed, a horizontal-direction distance acquiring step of acquiring distances between the inner wall surface of the structure and the unmanned floating machine in at least two different horizontal directions around the unmanned floating machine based on a yaw angle acquired in the inertial measurement step is executed, and a horizontal-direction current position information acquiring step of acquiring current position information in a horizontal direction from existing horizontal cross-sectional shape information of the structure is executed. 
         [0013]    According to one aspect, there is provided an indoor monitoring system for a structure comprising: an unmanned floating machine including a floating means which levitates the unmanned floating machine inside the structure by remote control; a distance measurement unit which is mounted to the unmanned floating machine and configured to measure a distance between the unmanned floating machine and an inner wall surface of the structure; an inertial measurement unit which is mounted to the unmanned floating machine and configured to obtain an attitude of a body of the unmanned floating machine; an imaging unit which is mounted to the unmanned floating machine and configured to image a structural body on the wall surface side of the structure; an operation unit which is configured to remotely control the unmanned floating machine; a flight position information acquisition unit which is configured to acquire current position information of the unmanned floating machine based on information from the distance measurement unit and information from the inertial measurement unit; and a monitor unit which is configured to display image information from the imaging unit and position information from the flight position information acquisition unit, wherein the flight position information acquisition unit is further configured to execute a horizontal-direction distance measuring step of measuring horizontal distance information between the unmanned floating machine and the inner wall surface of the structure using the distance measurement unit, when the unmanned floating machine is controlled inside the structure by the remote control to turn along the inner wall surface of the structure after rising by a predetermined distance repeatedly till the unmanned floating machine arrives at a predetermined height, an attitude angle acquiring step of acquiring an attitude angle of the unmanned floating machine using the inertial measurement unit, a horizontal-direction distance correcting step of correcting the horizontal distance information using the attitude angle acquired in the attitude angle acquiring step, a horizontal-direction distance acquiring step of acquiring distances between the inner wall surface of the structure and the unmanned floating machine based on a yaw angle acquired by the inertial measurement unit, and a horizontal-direction current position information acquiring step of acquiring current position information in a horizontal direction from existing horizontal cross-sectional shape information of the structure. 
         [0014]    According to one aspect, there is provided an indoor monitoring method for a structure which uses an unmanned floating machine including a floating means which levitates the unmanned floating machine inside the structure by remote control, the method comprising: a distance measurement step executed in the unmanned floating machine and measuring a distance between the unmanned floating machine and an inner wall surface of the structure; an inertial measurement step executed in the unmanned floating machine and obtaining an attitude of a body of the unmanned floating machine; an imaging step executed in the unmanned floating machine and imaging a structural body on the wall surface side of the structure; an operation step of remotely controlling the unmanned floating machine; a flight position information acquisition step of acquiring current position information of the unmanned floating machine based on information from the distance measurement step and information from the inertial measurement step; and a monitor displaying step of displaying image information from the imaging step and position information from the flight position information acquisition step, wherein in the flight position information acquisition step, a horizontal-direction distance measuring step of measuring horizontal distance information between the unmanned floating machine and the inner wall surface of the structure is executed using the distance measurement step, when the unmanned floating machine is controlled inside the structure by the remote control to turn along the inner wall surface of the structure after rising by a predetermined distance repeatedly till the unmanned floating machine arrives at a predetermined height, an attitude angle acquiring step of acquiring an attitude angle of the unmanned floating machine is executed using the inertial measurement step, a horizontal-direction distance correcting step of correcting the horizontal distance information using the attitude angle acquired in the attitude angle acquiring step is executed, a horizontal-direction distance acquiring step of acquiring distances between the inner wall surface of the structure and the unmanned floating machine based on a yaw angle acquired in the inertial measurement step is executed, and a horizontal-direction current position information acquiring step of acquiring current position information in a horizontal direction from existing horizontal cross-sectional shape information of the structure is executed. 
         [0015]    The above and other objects, features, advantages and technical and industrial significance of this disclosure will be better understood by reading the following detailed description of presently preferred embodiments of the disclosure, when considered in connection with the accompanying drawings. 
         [0016]    According to the present invention, it is possible to perform the unmanned inspection which reliably obtains the position information inside the structure, for example, the boiler furnace, the stack, or the like, and it is also possible to achieve the significant reduction of efforts, cost, inspection periods by omitting the scaffolding erection, for example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic view of an unmanned floating machine according to a first embodiment. 
           [0018]      FIG. 2  is a schematic view illustrating an aspect of inspection of a boiler furnace according to the first embodiment. 
           [0019]      FIG. 3  is a block configuration diagram of an indoor monitoring system for a structure according to the first embodiment. 
           [0020]      FIG. 4  is a block configuration diagram of another indoor monitoring system for a structure according to the first embodiment. 
           [0021]      FIG. 5  is a diagram illustrating an example of a scan range in a case where a laser scanner is used as a distance measurement unit according to the first embodiment. 
           [0022]      FIG. 6  is a diagram illustrating three aspects of an attitude position of the unmanned floating machine according to the first embodiment. 
           [0023]      FIG. 7  is a flowchart of position monitoring in the horizontal direction according to the first embodiment. 
           [0024]      FIG. 8  is a flowchart of position monitoring in the height direction according to the first embodiment. 
           [0025]      FIG. 9  is a diagram illustrating an example of acquisition of a current position in the horizontal direction according to the first embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Incidentally, the present invention is not limited by the embodiments, and further, encompasses any configuration obtained by combining the respective embodiments when there are a plurality of embodiments. 
       First Embodiment 
       [0027]      FIG. 1  is a schematic view of an indoor monitoring system for a structure according to a first embodiment.  FIG. 2  is a schematic view illustrating an aspect of inspection of a boiler furnace according to the first embodiment.  FIG. 3  is a block configuration diagram of an indoor monitoring system for a structure according to the first embodiment. As illustrated in  FIGS. 1 to 3 , the indoor monitoring system for the structure according to the present embodiment is provided with: an unmanned floating machine  11  with propellers  22 , for example, as a floating means which levitates and moves the unmanned floating machine inside a closed structure  50 , for example, a boiler furnace or the like by remote control; a distance measurement unit (for example, a laser scanner, an ultrasonic sensor, or the like)  12  which is mounted to the unmanned floating machine  11  and measures a distance between the unmanned floating machine  11  and an inner wall surface of the structure  50 ; an inertial measurement unit (IMU) which is mounted to the unmanned floating machine  11  and obtains an attitude of a body of the unmanned floating machine; an imaging unit (a still image imaging unit  13 A and a video imaging unit  13 B)  13  which is mounted to the unmanned floating machine  11  and images a structure (for example, piping, fitting or the like) on a wall surface side of the structure  50 ; an operation unit  15  which remotely controls the unmanned floating machine  11 ; a flight position information acquisition unit  16  which acquires current position information of the unmanned floating machine  11  based on information (signal) of the distance measurement unit  12  and information (signal) of the inertial measurement unit; and a monitor unit  14  which displays image information from the imaging unit  13  and position information from the flight position information acquisition unit  16 . Incidentally,  12   a  represents a laser light emitting portion. 
         [0028]    Further, the flight position information acquisition unit  16  is configured to execute: a distance measuring step (step  1 : S- 1 ) of measuring a horizontal distance information (r(t),α s ) between the unmanned floating machine  11  and the inner wall surface of the structure  50  using the distance measurement unit  12 ; an attitude angle acquiring step (step  2 : S- 2 ) of acquiring an attitude angle of the unmanned floating machine  11  using the inertial measurement unit; a distance correcting step (step  3 : S- 3 ) of correcting the horizontal distance information (r(t),α s ) using the attitude angle acquired in step  2 ; a distance acquiring step (step  4 : S- 4 ) of acquiring distances of at least two points (any two points among front (L f (t)) and left (L L (t)), front (L f (t)) and right (L R (t)), back (L B (t)) and left (L L (t)), and back (L B (t)) and right (L R (t))) on the front, back, right and left of the unmanned floating machine  11  on the basis of a yaw angle acquired by the inertial measurement unit; and a horizontal-direction current position information acquiring step (step  5 : S- 5 ) of acquiring current position information in the horizontal direction from existing horizontal cross-sectional shape information of the structure  50 . 
         [0029]    In the present embodiment, the structure  50 , which has a simple shape (whose cross-sectional shape is a rectangle or a circle), for example, a boiler furnace, a stack, or the like, is set as a target of inspection. Since the inside of the structure  50  is the target, provided is a system that monitors a flight position (current flight position information) of the unmanned floating machine  11  using the distance measurement unit (for example, the laser scanner, the ultrasonic sensor, or the like)  12  which does not use a GPS and the inertial measurement unit (IMU) which belongs a sensor group used for attitude control of the unmanned floating machine  11 . 
         [0030]    In the present embodiment, the unmanned floating machine  11  is operated by the operation unit  15  while confirming the flight position of the unmanned floating machine  11  and an image (a damaged portion) using the monitor unit  14  of a personal computer PC in a ground station positioned outside the closed structure (boiler furnace)  50 , thereby performing inspection of an inner wall of a closed space of the boiler furnace  50 , as illustrated in  FIG. 2 . 
         [0031]    During the inspection, the unmanned floating machine  11  is introduced from an entrance of the boiler furnace  50  illustrated in  FIG. 2 , thereafter is raised by a predetermined distance inside the boiler furnace  50 , and is turned along inner surfaces of walls in the four directions by operating the operation unit  15  on the ground side. Thereafter, the unmanned floating machine  11  is raised again by a predetermined distance, and is turned along the inner wall surfaces in the four directions in the same manner. This operation is repeated until the top of the boiler furnace  50  is inspected, and then, the unmanned floating machine  11  is lowered, thereby ending the inspection. 
         [0032]    A degree of damage such as a crack in the piping on the inner surface is inspected using the imaging unit. During this inspection, it is possible to confirm the flight position and the damaged portion of the closed indoor structure on the monitor unit  14  according to the present embodiment, and thus, it is possible to perform unmanned inspection that reliably obtains the internal position information. 
         [0033]    The perimeter of the unmanned floating machine  11  is protected by an body guard portion  21  (a front-side guard portion  21 A, a left-side guard portion  21 B, a right-side guard portion  21 C, and a back-side guard portion  21 D), and there is provided the propeller  22  as the floating means on each upper surface of four corners of the body guard portion  21 , the distance measurement unit  12  mounted at a center portion of a body  21 E, the still image imaging unit  13 A positioned on a part of the front-side guard portion  21 A, and the video imaging unit  13 B positioned on the back-side guard portion  21 D via a support portion  13   b , as illustrated in  FIG. 1 . Incidentally, the distance measurement unit  12  scans a predetermined angle (±135° in the present embodiment) and can be turned by a turning means (not illustrated). 
         [0034]    Here, any one of the still image imaging unit  13 A and the video imaging unit  13 B may be used as the imaging unit  13  to confirm the internal information. 
         [0035]    Hereinafter, a description will be given regarding procedure of position monitoring in a case where the laser scanner is used as the distance measurement unit  12  in the present embodiment. 
         [0036]    &lt;Monitoring in Horizontal Direction&gt; 
         [0037]    (1) First, a distance (r(t),α s ) is acquired by the distance measurement unit  12  to implement monitoring in the horizontal direction. 
         [0038]    Here,  FIG. 5  illustrates an example of a scan range of the laser scanner. In the present embodiment, a scanner-type range sensor, “UTM-30 LX (product name)” manufactured by HOKUYO AUTOMATIC CO., LTD. is used. 
         [0039]    As illustrated in  FIG. 5 , this scanner-type range sensor is a two-dimensional scanning-type optical distance sensor, which measures a distance to an object to be inspected while performing scanning with laser light, and a scan angle is±135° with 0° as the center thereof. 
         [0040]    In  FIG. 5 , a distance (r) is an actually measured distance obtained when measurement is performed up to an inner wall  50   a  from the laser scanner of the distance measurement unit  12 , and α is an angle at the measured scanning step thereof. A scanning step (s) for measurement in this device is set to every 0.25°. 
         [0041]    (2) Next, attitude angles including a pitch angle (θ(t)), a yaw angle (ψ(t)), a roll angle (φ(t)) of the unmanned floating machine  11  are acquired by the inertial measurement unit (IMU). 
         [0042]      FIG. 6  is a diagram illustrating three aspects of an attitude position of the unmanned floating machine according to the first embodiment. 
         [0043]    The inertial measurement unit (IMU) is a device that detects angles (or angular velocities) and accelerations in three axes governing a motion. 
         [0044]    Here, the upper stage of  FIG. 6  illustrates an aspect of vertical rotation of the unmanned floating machine  11  which is turning (the pitch (θ)) where the front-side guard portion  21 A (on a nose side) facing the inner wall  50   a  side is raised or lowered. The middle stage of  FIG. 6  illustrates an aspect of horizontal rotation of the body of the unmanned floating machine  11  which is turning (the yaw (ψ)) where a direction of a nose is shifted right and left, and the left-side guard portion  21 B and the right-side guard portion  21 C swing right and left. The lower stage of  FIG. 6  is an aspect of rotation about an axis in a travel direction of the unmanned floating machine  11  which is turning (the roll (φ)) where the body is tilted right and left. Incidentally, the right and left of the body are based on the travel direction thereof. 
         [0045]    Next, a position monitoring measuring step will be described with reference to  FIG. 3 . 
         [0046]    The flight position information acquisition unit  16  is configured to obtain a real distance based on actual distance information of the distance measurement unit  12  and the attitude angle information of the inertial measurement unit (IMU). This is because there is a need for correction of the measured distance since the unmanned floating machine  11  is not always capable of flying constantly according to XY coordinates. 
         [0047]      FIG. 7  is a flowchart of position monitoring in the horizontal direction according to the first embodiment. 
         [0048]    The measurement in the horizontal direction is performed through step  1  (S- 1 ) to step  5  (S- 5 ). 
         [0049]    Prior to this measurement, an initial direction information acquiring step (S- 0 ) of acquiring initial direction information, obtained when the unmanned floating machine  11  is positioned at the bottom inside the structure  50 , is provided in the present embodiment, but this step may be omitted. 
         [0050]    1) Step  1  is the horizontal-direction distance measuring step (S- 1 ) of measuring the horizontal distance information (r(t),α s ) between the unmanned floating machine  11  and the inner wall  50   a  of the structure  50  using the distance measurement unit  12 . 
         [0051]    2) Step  2  is the attitude angle acquiring step (S- 2 ) of acquiring the attitude angle of the unmanned floating machine  11  using the inertial measurement unit (IMU). 
         [0052]    3) Step  3  is a horizontal-direction distance correcting step (S- 3 ) of correcting the horizontal distance information (r(t),α s ) using the attitude angle acquired in step  2  (S- 2 ). 
         [0053]    4) Step  4  is a horizontal-direction distance acquiring step (S- 4 ) of acquiring distances of at least two points (any two points among front (L F (t)) and left (L L (t)), front (L F (t)) and right (L R (t)), back (L B (t)) and left (L L (t)), and back (L B (t)) and right (L R (t))) on the front, back, right and left of the unmanned floating machine  11  on the basis of the yaw angle (ψ) acquired by the inertial measurement unit (IMU), as illustrated in  FIG. 9 . 
         [0054]    5) Step  5  is the horizontal-direction current position information acquiring step (S- 5 ) of acquiring the current position information in the horizontal direction from the existing horizontal cross-sectional shape information of the structure  50 . 
         [0055]    It is possible to acquire the real distance information in the horizontal direction on consideration of the attitude angle at the time of measurement of the unmanned floating machine  11  by executing step  1  (S- 1 ) to step  5  (S- 5 ). 
         [0056]    Here, the correction of the measured distance using the attitude angle acquired in step  3  (S- 3 ) is performed as follows. 
         [0057]    A laser measurement point obtained as (r(t),α s ) is transformed into coordinates (x R ,y R ). This coordinate transformation is obtained by the following Formula (1). 
         [0000]    
       
         
           
             
               
                 
                   
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         [0058]    Transformation of a corrected measurement point (x′(t),y′(t)) into a rotation coordinate system is obtained by the following Formula (2). 
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         [0059]    A value obtained from Formula (2) is transformed into a coordinate system (r,α) of laser measurement. This coordinate transformation is obtained by the following Formula (3). 
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                     ) 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0060]    Next, each distance on the front, back, right and left of the unmanned floating machine  11  is obtained on the basis of the yaw angle ψ (t) acquired by the inertial measurement unit (IMU) in step  4  (S- 4 ). However, when a scan angle is out of a predetermined scan range, the obtained data is not employed as a distance from a wall side. 
         [0061]    Scan angle data where a scan angle α l =ψ (t) is set as a front distance L F (t). 
         [0062]    Scan angle where a scan angle α 2 =ψ (t)−90° is set as a left distance L L (t). 
         [0063]    Scan angle where a scan angle α 3 =ψ (t)+90° is set as a right distance L R (t). 
         [0064]    Scan angle where a scan angle α 4 =ψ(t)+180° is set as a back distance L B (t). 
         [0065]    In the final step  5  (S- 5 ), a current position (x(t),y(t)) is acquired from the existing horizontal cross-sectional shape using measurable distances (at least two of the front, back, right and left distance). 
         [0066]    Accordingly, it is possible to acquire the real current position, and it is possible to confirm the imaging information imaged in this current position and the position information by the monitor unit  14 . 
         [0067]    When this measurement of the position information is performed every time when the unmanned floating machine  11  travels, it is possible to reliably obtaining the position information continuously. 
         [0068]    &lt;Monitoring in Height Direction&gt; 
         [0069]      FIG. 8  is a flowchart of position monitoring in the height direction according to the first embodiment. 
         [0070]    An initial direction information acquiring step (S- 10 ) of acquiring an initial direction information uses the information obtained in the initial direction information acquiring step (S- 0 ) of acquiring the initial direction information in the horizontal direction. 
         [0071]    The measurement in the height direction is performed through the following step  11  (S- 11 ) to step  14  (S- 14 ). 
         [0072]    6) Step  11  is a height-direction distance measuring step (S- 11 ) of measuring the distance information (L D (t),α S ) between the unmanned floating machine  11  and the structure  50  on the lower side in the height direction using the distance measurement unit  12 . 
         [0073]    Here, the measurement in the height direction using laser light is performed using a reflective optical system such as a mirror (not illustrated). When an irradiation distance of the laser light does not reach as the unmanned floating machine  11  is raised, distance information (L U (t),α s ) on the upper side may be measured by causing the laser light to be reflected to the upper side. 
         [0074]    7) Step  12  is an attitude angle acquiring step (S- 12 ) of acquiring an attitude angle of the unmanned floating machine  11  using the inertial measurement unit (IMU). 
         [0075]    8) Step  13  is a height-direction distance correcting step (S- 13 ) of correcting the distance information (L D (t)) in the height direction using an attitude angle (φ(t),θ(t)) acquired in step  12  (S- 12 ). 
         [0076]    9) Step  14  is a height-direction current position information acquiring step (S- 14 ) of acquiring current position information in the height direction from existing vertical cross-sectional shape information of the structure  50 . 
         [0077]    In the correction in step  13  (S- 13 ), a corrected measurement point (z′(t)) is obtained from the following Formula (4). 
         [0000]      z′=z cos α cos β  (4)
 
         [0078]    Therefore, it is possible to transform the actually measured distances in the horizontal direction and the height direction into the real distances and to reliably acquire the position information. 
         [0079]    As a result, it is possible to perform the inspection that reliably obtains the measurement position using the unmanned floating machine inside the structure  50  where it is difficult to use the GPS. As a result, it is unnecessary to erect scaffolding inside the structure  50  as in the related art, and it is possible to significantly reduce efforts, cost, and inspection periods for internal inspection. 
         [0080]      FIG. 3  is a block configuration diagram of an indoor monitoring system for a structure according to the first embodiment.  FIG. 4  is a block configuration diagram of another indoor monitoring system for a structure according to the first embodiment. 
         [0081]    As illustrated in  FIG. 3 , the present embodiment is a case in which position information processing is executed on the unmanned floating machine  11  side. 
         [0082]    In the present embodiment, the flight position information acquisition unit  16  is mounted at a predetermined portion (not illustrated) on the unmanned floating machine  11  side, and here, acquires real current position information and transmits the acquired real current position information to the ground side by a transmission unit  13   a  to display the information on the monitor unit  14 . 
         [0083]    Incidentally, the operation of the unmanned floating machine  11  is performed in such a manner that a reception unit  15   a  receives a signal from the operation unit  15  and a flight command is issued to a floating machine driving unit  19 . 
         [0084]    In addition, the imaging information of the imaging unit  13  (the still image imaging unit  13 A and the video imaging unit  13 B)  13  is transmitted to the ground side by the transmission unit  13   a  at the same time and displayed on the monitor unit  14  in the present embodiment. 
         [0085]    With respect to this, another example illustrated in  FIG. 4  is a case in which the position information processing is performed on a controller terminal side of the personal computer PC on the ground. 
         [0086]    In this example, the flight position information acquisition unit  16  is mounted to the controller terminal of the PC on the ground side (base station), and information (signal) of the distance measurement unit  12  and information (signal) of the inertial measurement unit (IMU) are transmitted to the ground side by the transmission unit  13   a . Further, the received information is processed by the flight position information acquisition unit  16  to acquire real current position information, and this acquired current position information is displayed on the monitor unit  14 . 
         [0087]    Although the imaging information imaged by the imaging unit  13  is transmitted by the transmission unit  13   a  in the present embodiment, the present invention is not limited thereto, and for example, may be configured such that the imaging information is temporarily stored in a memory unit of the imaging unit on the unmanned floating machine  11  side, the information is transmitted to the ground station side after ending measurement, and the imaging information and the position information are processed to match each other. 
         [0088]    As described above, it is possible to perform the unmanned inspection which reliably obtains the position information inside the structure  50 , for example, the boiler furnace, the stack, or the like, and it is possible to achieve the significant reduction of efforts, cost, inspection periods by omitting erection of scaffolding, for example, according to the present embodiment. 
       Second Embodiment 
       [0089]    Although the measurement of the distance measurement unit  12  is performed to obtain the information of the single point in the first embodiment, the present invention is not limited thereto, and the accuracy in position measurement may be improved based on measurement information at multiple points. 
         [0090]    That is, multiple points are extracted and averaged based on the scan angle in the distance measurement unit  12  to obtain each distance in the calculation of distances in the horizontal direction and the height direction. Further, when more than half of the multiple points is abnormal for distance measurement or unmeasurable, such points are not used for the position monitoring. 
         [0091]    As a result, it is possible to reduce influence of a distance acquisition error. 
         [0092]    The present disclosure has been made in view of the above-described problems, and an object thereof is to provide an indoor monitoring system and method for a structure that is capable of unmanned inspection which reliably obtains internal position information, and also capable of reducing efforts, cost, inspection periods by omitting erection of scaffolding, for example. 
         [0093]    Although this disclosure has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.