Abstract:
A laser surveying instrument, comprising a rotating unit for projecting a laser beam by rotary irradiation, a main unit for rotatably supporting the rotating unit, and a sealing means for sealing between the rotating unit and the main unit, wherein the sealing means comprises annular ridges formed on the main unit concentrically to the rotation center of the rotating unit, and annular grooves formed on the rotating unit so that the annular ridges are engaged in the annular grooves and gaps are formed between the annular ridges and the annular grooves, the annular ridges and the annular grooves being arranged concentrically to each other and disposed in double arrangement, and wherein the sealing means further comprises a route bent and crooked in a radial direction by the gaps, and a cavity disposed at least at one point along the route and having larger volume than the volume of the gap.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a laser surveying instrument for projecting a laser beam in rotary irradiation and for forming a reference plane and a reference line. In particular, the present invention relates to a laser surveying instrument with waterproof function. 
         [0002]    As a type of laser surveying instrument used for forming a reference plane and a reference line, which are required for operations of civil engineering work, building and construction project, etc. a laser surveying instrument for projecting a laser beam in rotary irradiation is known. 
         [0003]    A laser surveying instrument has a rotating unit for deflecting and projecting a laser beam. By rotating the rotating unit, a reference plane or a reference line is formed by the laser beam. 
         [0004]    The laser surveying instrument may be used under outdoor conditions, and the laser surveying instrument must have waterproof function so that the laser surveying instrument can also be used under rainy weather. 
         [0005]    A laser surveying instrument with waterproof function has been known in the past, which has waterproof structure to enclose the rotating part by a cover with transparency. A type of laser surveying instrument having simple and inexpensive waterproof structure is disclosed in U.S. Pat. No. 6,643,004. 
         [0006]    Referring to  FIG. 6 , description will be given below on a conventional type laser surveying instrument. 
         [0007]    Inside a housing  1 , a rotation mechanism accommodating unit  3  is movably supported in two directions perpendicularly crossing each other via a gimbal supporting unit  2 . A rotation shaft  4  extending in a vertical direction is rotatably supported on the rotation mechanism accommodating unit  3 . The rotation shaft  4  is connected with a motor  5 , and an encoder  6  is mounted on the rotation shaft  4 . 
         [0008]    On the upper end of the rotation shaft  4 , a rotary head  7  is mounted, and a light emitter  8  is accommodated in the rotary head  7 . The light emitter  8  comprises a laser diode  9 , a collimating lens  10 , a rod lens  11 , etc. A laser beam  13  emitted from the laser diode  9  is projected as linear luminous fluxes extending in a vertical direction. 
         [0009]    The upper portion of the rotation mechanism accommodating unit  3  is protruding upward from the housing  1 . A gap between the housing  1  and the rotation mechanism accommodating unit  3  is sealed by a bellows  14 , and the protruding portion of the rotation mechanism accommodating unit  3  and the rotary head  7  are enclosed by a cover  15 . The cover  15  has a light projection window  16 , and the laser beam  13  is projected through the light projection window  16 . 
         [0010]    When the laser diode  9  is turned on and the motor  5  is rotated, the rotary head  7  is rotated via the rotation shaft  4  so that the laser beam  13  is rotated in a horizontal direction. 
         [0011]    A labyrinthine seal  17  serving as a waterproof means is provided between the rotary head  7  and the rotation mechanism accommodating unit  3 , and a gap between the rotary head  7  and the rotation mechanism accommodating unit  3  is sealed by the labyrinthine seal  17 . 
         [0012]    Now, referring to  FIG. 7 , description will be given on the labyrinthine seal  17 . 
         [0013]    On the upper surface of the rotation mechanism accommodating unit  3 , annular projected rims (ridges)  18  and annular grooves  19 , each having cross-sectional profile in rectangular shape, are disposed concentrically and in double arrangement respectively. On the lower surface of the rotary head  7 , annular grooves  21  and annular ridges  22  are arranged concentrically. The annular ridge  18  is movably engaged in the annular groove  21 , and the annular groove  19  is movably engaged with the annular ridge  22 . The annular ridge  18  and the annular groove  21  as well as the annular groove  19  and the annular ridge  22  are not in contact with each other. A narrow space  23  with cross-sectional profile in crank-like shape is formed in the radial direction. 
         [0014]    Because the bending space  23  with crank-like shape is formed between the rotation mechanism accommodating unit  3  and the rotary head  7 , the intrusion of water, dust, etc. from outside to the inner space of the rotation mechanism accommodating unit  3  can be prevented. The rotary head  7  can be rotated without any resistance because the rotating portion is not contact with the fixed portion in the labyrinthine seal  17 . 
         [0015]    It is preferable that the space  23  is small for the purpose of preventing direct intrusion of rainwater on rainy day or under windy and rainy weather or the like. If the space  23  is small, capillary phenomenon occurs. In such case, gradual intrusion of water from outside cannot be prevented. 
         [0016]    Therefore, by the conventional type water preventive means, perfect waterproof effect cannot be necessarily obtained when the surveying instrument is used under severe rainy condition or under rainy weather for long time. 
       SUMMARY OF THE INVENTION 
       [0017]    It is an object of the present invention to provide a laser surveying instrument, by which it is possible to improve the waterproof function of the water preventing means disposed between the rotating portion and the fixed portion, and to have better water preventing function. 
         [0018]    To attain the above object, the present invention provides a laser surveying instrument, which comprises a rotating unit for projecting a laser beam by rotary irradiation, a main unit for rotatably supporting the rotating unit, and a sealing means for sealing between the rotating unit and the main unit, wherein the sealing means comprises annular ridges formed on the main unit concentrically to the rotation center of the rotating unit, and annular grooves formed on the rotating unit so that the annular ridges are engaged in the annular grooves and gaps are formed between the annular ridges and the annular grooves, the annular ridges and the annular grooves being arranged concentrically to each other and disposed at least in double arrangement, and wherein the sealing means further comprises a route bent and crooked in a radial direction by the gaps, and a cavity disposed at least at one point along the route and having larger volume than the volume of the gap. Also, the present invention provides the laser surveying instrument as described above, wherein the annular ridges at least include a first annular ridge formed at an outer position and a second annular ridge formed at an inner position, wherein the second annular ridge is higher than the first annular ridge, and the cavity is formed at a point closer to the first annular ridge between the second annular ridge and the annular groove where the second annular ridge is engaged. Further, the present invention provides the laser surveying instrument as described above, wherein an eave protruding in an outward direction is provided on an upper end of the second annular ridge, the cavity is disposed under the eave, and a lower surface of the eave is at a position higher than the first annular ridge. Also, the present invention provides the laser surveying instrument as described above, wherein at least inner peripheral surface of at least one of the annular ridges is tilted in an outward direction toward the upper end. Further, the present invention provides the laser surveying instrument as described above, wherein the rotating unit is mounted so as to sandwich a flat plate which is a part of the main unit, the first annular ridge and the second annular ridge are disposed on an upper surface of the flat plate, a third annular ridge is formed on a lower surface of the flat plate, and an annular groove where the third annular ridge is inserted on non-contact basis is formed on a portion of the rotating unit to face toward the lower surface. Also, the present invention provides the laser surveying instrument as described above, wherein a fourth annular ridge is further formed on the portion of the rotating unit to face toward the lower surface, wherein an eave protruding toward the center is provided on an upper end of the fourth annular ridge, and a cavity is formed under the eave. Further, the present invention provides the laser surveying instrument as described above, wherein the cavity has gap and volume sufficient to avoid capillary phenomenon. 
         [0019]    According to the present invention, there are provided a rotating unit for projecting a laser beam by rotary irradiation, a main unit for rotatably supporting the rotating unit, and a sealing means for sealing between the rotating unit and the main unit, and the sealing means comprises annular ridges formed on the main unit concentrically to the rotation center of the rotating unit, and annular grooves formed on the rotating unit so that the annular ridges are engaged in the annular grooves and gaps are formed between the annular ridges and the annular grooves, the annular ridges and the annular grooves being arranged concentrically to each other and disposed at least in double arrangement, and the sealing means further comprises a route bent and crooked in a radial direction by the gaps, and a cavity disposed at least at one point along the route and having larger volume than the volume of the gap. As a result, the intrusion of water and dust can be prevented by using a route with windings and bendings. Also, capillary phenomenon can be excluded by the cavity, and the intrusion of water can be prevented. 
         [0020]    Also, according to the present invention, the annular ridges at least include a first annular ridge formed at an outer position and a second annular ridge formed at an inner position, and the second annular ridge is higher than the first annular ridge, and the cavity is formed at a point closer to the first annular ridge between the second annular ridge and the annular groove where the second annular ridge is engaged. The water intruding by running over the first annular ridge is trapped and stays in the cavity, and the intrusion of water to the inner space is suppressed. When the surface level of the water staying in the cavity is higher than the first annular ridge, the intrusion of the water into the inner space can be prevented by the pressure of the water trapped and staying in the cavity. 
         [0021]    Further, according to the present invention, an eave protruding in an outward direction is provided on an upper end of the second annular ridge, the cavity is disposed under the eave, and a lower surface of the eave is at a position higher than the first annular ridge. When the surface level of the water staying in the cavity is higher than the first annular ridge, the intrusion of the water into the inner space can be prevented by a pressure of the staying water. Also, the intrusion of the water staying in the cavity into the inner space can be prevented when the main unit is tilted or placed at lateral position. 
         [0022]    Also, according to the present invention, at least inner peripheral surface of at least one of the annular ridges is tilted in an outward direction toward the upper end. When the main unit is tilted or the main unit is pulled down, the intruding water in the route can be effectively discharged to outside by gravitational force. 
         [0023]    Further, according to the present invention, the rotating unit is mounted so as to sandwich a flat plate which is a part of the main unit, the first annular ridge and the second annular ridge are disposed on an upper surface of the flat plate, a third annular ridge is formed on a lower surface of the flat plate, and an annular groove where the third annular ridge is inserted on non-contact basis is formed on a portion of the rotating unit to face toward the lower surface. Water and dust intruding to the central portion are further sealed by the third annular ridge and the annular groove on the rear side, and effective water-preventive and dust preventive effects can be attained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a cross-sectional view of a laser surveying instrument according to an embodiment of the present invention; 
           [0025]      FIG. 2  is a partial cross-sectional view to show an essential portion of a first embodiment of the invention; 
           [0026]      FIG. 3  is a partial cross-sectional view to show an essential portion of a second embodiment of the invention; 
           [0027]      FIG. 4  is a partial cross-sectional view to show an essential portion of a third embodiment of the invention; 
           [0028]      FIG. 5  is a partial cross-sectional view to show an essential portion of a fourth embodiment of the invention; 
           [0029]      FIG. 6  is a cross-sectional view of a laser surveying instrument according to the prior art; and 
           [0030]      FIG. 7  is an enlarged view to show a sealing part in the laser surveying instrument according to the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Description will be given below on the best mode for carrying out the present invention referring to the attached drawings. 
         [0032]      FIG. 1  shows a laser surveying instrument  24  according to the present invention.  FIG. 1  shows a condition where the laser surveying instrument  24  is installed at longitudinal position. 
         [0033]    The laser surveying instrument  24  comprises a rotating unit  57  (to be described later) for projecting a laser beam by rotary irradiation and a main unit  25  for rotatably supporting the rotating unit  57 . 
         [0034]    First, description will be given on the main unit  25 . 
         [0035]    A supporting shelf  27  is installed inside a housing  26 . A light emitter accommodating tube  28  is mounted so as to penetrate the supporting shelf  27  in a vertical direction. A connecting portion to connect the light emitter accommodating tube  28  with the supporting shelf  27  is designed in form of a spherical seat (bearing seat)  29  so that the light emitter accommodating tube  28  can be tilted in any direction as desired. 
         [0036]    The light emitter accommodating tube  28  has two tilting arms extending in two directions, which perpendicularly cross each other. One of the tilting arms is an X-axis tilting arm  30  extending in an X-axis direction (left-to-right direction with respect to the paper surface in  FIG. 1 ), and the other is a Y-axis tilting arm (not shown) extending in a Y-axis direction (vertical direction with respect to the paper surface in  FIG. 1 ). The light emitter accommodating tube  28  is designed in cylindrical shape with a hollow portion inside. The central axis of the light emitter accommodating tube  28  is aligned with a Z-axis direction (up-to-bottom direction with respect to the paper surface), and the central axis is aligned with an optical axis  34  of a light emitter  33  accommodated inside the light emitter accommodating tube  28 . 
         [0037]    At a tip of each of the X-axis tilting arm  30  and the Y-axis tilting arm, an engaging pin  35  (only one of them is shown) is mounted, and the engaging pin  35  is connected to one of tilting mechanisms  36  (only one of them is shown). Because the tilting mechanisms  36  (only one of them is shown) have the same mechanism, description will be given below only on one of the tilting mechanisms  36 . 
         [0038]    The tilting mechanism  36  has a screw shaft  38  installed in an up-to-bottom direction. The screw shaft  38  is rotatably supported, and a tilting gear  39  is attached on a lower end of the screw shaft  38 . A tilt driving gear  40  is engaged with the tilting gear  39 , and the tilt driving gear  40  is rotated by a leveling motor  41 . 
         [0039]    A nut block  42  is engaged on the screw shaft  38  by threading. Connecting pins  43  are projecting in horizontal direction on the nut block  42 , and the connecting pins  43  and the engaging pin  35  are slidably engaged with each other. 
         [0040]    On the light emitter accommodating tube  28 , there are provided an X-axis tilt sensor  45  for detecting the tilting in an X-axis direction, a Y-axis tilt sensor  46  for detecting the tilting in a Y-axis direction, and a Z-axis tilt sensor  47  for detecting the tilting in a Z-axis direction under the condition that the laser surveying instrument  24  is installed in a lateral direction. 
         [0041]    On a certain portion of the light emitter accommodating tube  28 , i.e. a portion, which does not interfere with the X-axis tilting arm  30  and the Y-axis tilting arm, a motor supporting seat  49  is disposed. A scanning motor  50  is mounted on the motor supporting seat  49 , and a scan driving gear  51  is mounted on an output shaft of the scanning motor  50 . 
         [0042]    A ceiling plate  53  is mounted on an upper end of the light emitter accommodating tube  28 . A bellows  54  made of rubber are disposed between the ceiling plate  53  and the upper end of the housing  26  so that the ceiling plate  53  is liquid-tightly sealed with the housing  26  and the ceiling plate  53  can be tilted in any direction as desired with respect to the housing  26 . 
         [0043]    The light emitter  33  comprises a laser diode  55  as a light source, an objective lens  56 , etc. The laser diode  55  and the objective lens  56  are arranged on the optical axis  34  in this order from the bottom to the top. 
         [0044]    The rotating unit  57  is rotatably mounted so as to be stretched over the ceiling plate  53  and the light emitter accommodating tube  28 . Description will be given below on the rotating unit  57 . 
         [0045]    The upper end of the light emitter accommodating tube  28  is to serve as a rotation shaft  58  of the rotating unit  57 . A prism holder  59  is rotatably mounted on the rotation shaft  58  via a bearing, and a pentagonal prism  61  is mounted on the prism holder  59 . On the upper surface of the pentagonal prism  61 , a wedge prism  62  is disposed, and the boundary surface between the wedge prism  62  and the pentagonal prism  61  is designed as a half-mirror. The pentagonal prism  61  deflects the optical axis  34  in a horizontal direction so that the laser beam emitted from the laser diode  55  is projected in a horizontal direction, while a part of the laser beam is allowed to pass through the pentagonal prism  61  and is projected in a vertical direction. 
         [0046]    On the prism holder  59 , a rotating unit cover  63  to cover the pentagonal prism  61  is provided, and the rotating unit cover  63  is rotated integrally with the pentagonal prism  61 . On the rotating unit cover  63 , there are arranged a light projection window  64  for projecting the laser beam in a horizontal direction and a light projection window  65  for projecting the laser beam in a vertical direction. 
         [0047]    At the outside of a lower portion of the prism holder  59 , a rotating plate  66  is fitted. The rotating plate  66  is positioned on the lower side of the ceiling plate  53  so that the ceiling plate  53  is sandwiched between the rotating plate  66  and the rotating unit  57 . On outer periphery of the rotating plate  66 , a gear is provided. The gear is engaged with the scan driving gear  51 , and the outer periphery of the rotating plate  66  serves as a scanning gear  67 . 
         [0048]    On a portion between the rotating portion (including the rotating unit cover  63 , the rotating plate  66 , etc.) and the fixed portion such as the ceiling plate  53 , etc., a sealing means is disposed to prevent the intrusion of rainwater and dust so that the laser surveying instrument  24  can be used in outdoor condition on rainy day or under dusty environment. The sealing means include a first sealing means  68  installed between the ceiling plate  53  and the rotating unit cover  63  and a second sealing means  69  installed between the ceiling plate  53  and the rotating plate  66 . 
         [0049]    Now, referring to  FIG. 2 , description will be given on the sealing means. 
         [0050]    A central portion  70  of the rotating plate  66  is protruded in an upward direction. The protruded central portion  70  movably passes through the central region of the ceiling plate  53 . On the upper surface of the ceiling plate  53 , a first annular ridge  71  with its center on the optical axis  34  is formed to be protruded. At an inner position than the first annular ridge  71 , a second annular ridge  72  is formed to be protruded. Further, a third annular ridge  73  is formed to be protruded at an inner position than the second annular ridge  72 . The third annular ridge  73  is at a position to face to the central portion  70  with a certain gap between them. 
         [0051]    The cross-sectional profile of the first annular ridge  71  has a height h 1 . Its outer peripheral surface runs perpendicularly to the upper surface of the ceiling plate  53 . Its inner peripheral surface is tilted in the outward direction. The cross-sectional profile of the second annular ridge  72  has a height h 2 . The second annular ridge  72  is designed in hook-shaped form and has an eave  72   a  protruding in the outward direction at its upper end. The lower surface of the eave  72   a  has a height h 3 . The cross-sectional profile of the third annular ridge  73  is designed in rectangular shape, and the upper surface of the third annular ridge  73  is lower than the upper surface of the ceiling plate  53 . 
         [0052]    Between the first annular ridge  71  and the second annular ridge  72 , there is provided a first annular groove  74 . Between the second annular ridge  72  and the third annular ridge  73 , there is provided a second annular groove  75 . 
         [0053]    On the lower surface of the rotating unit cover  63 , a third annular groove  76  concentric with the first annular ridge  71  is formed. A fourth annular groove  77  concentric with the third annular groove  76  is formed at a position inside the third annular groove  76 . On the boundary between the third annular groove  76  and the fourth annular groove  77 , there is formed a fourth annular ridge  78 , and a fifth annular ridge  79  is formed along the inner peripheral surface of the rotating unit cover  63 . 
         [0054]    The cross-sectional profile of the third annular groove  76  is approximately similar to the shape of the first annular ridge  71 . The first annular ridge  71  is engaged into the third annular groove  76 , and a gap with the same width is formed between the first annular ridge  71  and the third annular groove  76 . 
         [0055]    The cross-sectional profile of the second annular ridge  72  is approximately in rectangular shape. The second annular ridge  72  is movably engaged in the fourth annular groove  77 . A gap is formed between the fourth annular groove  77  and the second annular ridge  72 , and a first water trap  81  is disposed under the eave  72   a . The first water trap  81  is a cavity with sufficient volume to trap and reserve the intruding water. The first water trap  81  is so designed that sufficient gap and volume can be kept to at least avoid capillary phenomenon. 
         [0056]    When the fifth annular ridge  79  is engaged into the second annular groove  75 , a gap is formed between the second annular groove  75  and the fifth annular ridge  79 , and the second annular groove  75  fulfills the function as a second water trap. The second water trap is so designed that sufficient gap and volume can be kept to at least avoid capillary phenomenon. 
         [0057]    The first annular ridge  71 , the second annular ridge  72 , the third annular groove  76 , the fourth annular groove  77 , etc. make up together the first sealing means  68 . 
         [0058]    On the lower surface of the ceiling plate  53 , a sixth annular ridge  82  is formed near the central portion  70 . On the upper surface of the rotating plate  66 , a seventh annular ridge  84  is formed so that a fifth annular groove  83  is formed in ring-like shape. The sixth annular ridge  82  is placed into the fifth annular groove  83 . A gap is formed between the fifth annular groove  83  and the sixth annular ridge  82 , and the fifth annular groove  83  fulfills the function as a third water trap. The third water trap is so designed that sufficient gap and volume can be kept to at least avoid capillary phenomenon. 
         [0059]    The third annular ridge  73 , the sixth annular ridge  82 , the fifth annular groove  83 , etc. make up together the second sealing means  69 . 
         [0060]    The intrusion of rainwater and dust is prevented by the first sealing means  68 . When rainwater and dust pass through the first sealing means  68 , rainwater and dust are further prevented by the second sealing means  69  from entering the inner space of the housing  26 . Depending on the environmental conditions where the laser surveying instrument is used, either one of the first sealing means  68  or the second sealing means  69  may not be used. 
         [0061]    Next, description will be given on operation of the laser surveying instrument. 
         [0062]    First, description will be given on a case where the laser surveying instrument  24  is installed at longitudinal position. 
         [0063]    When the laser surveying instrument  24  is installed, leveling of the laser surveying instrument  24  is performed. 
         [0064]    Tilting in the X-axis direction and tilting in the Y-axis direction are detected by the X-axis tilt sensor  45  and the Y-axis tilt sensor  46  respectively. Based on the results of detection by the X-axis tilt sensor  45  and the Y-axis tilt sensor  46 , the leveling motors  41  (only one of them is shown) are driven. The nut blocks  42  are moved up and down. The X-axis tilting arm  30  and the Y-axis tilting arm (not shown) are tilted, and adjustment is made so that the X-axis tilt sensor  45  and the Y-axis tilt sensor  46  detect horizontal position. When the X-axis tilt sensor  45  and the Y-axis tilt sensor  46  detect the horizontal position, the light emitter accommodating tube  28 , i.e. the optical axis  34 , is at vertical position, and the optical axis of the exit light deflected by the pentagonal prism  61  is set in a horizontal direction. 
         [0065]    When the laser diode  55  is turned on, the laser beam is emitted, and turned to parallel luminous fluxes by the objective lens  56 . The laser beam is deflected by the pentagonal prism  61  and is projected in a horizontal direction. 
         [0066]    By driving the scanning motor  50 , the scanning gear  67  is rotated via the scan driving gear  51 . Further, the rotating plate  66 , the prism holder  59  and the pentagonal prism  61  are rotated integrally with the scanning gear  67 , and the laser beam is projected within a horizontal plane by rotary irradiation, and a horizontal reference plane is formed by the laser beam. When the laser beam scans over an object such as a wall surface, a horizontal reference line is formed. 
         [0067]    From the light projection window  65 , a laser beam to form a vertical reference line is projected. 
         [0068]    When the laser surveying instrument  24  is installed at lateral position so that the light emitter accommodating tube  28  is placed at horizontal position, tilting of the light emitter accommodating tube  28  is detected by the Z-axis tilt sensor  47 . Based on the result of detection by the Z-axis tilt sensor  47 , the leveling motor  41  is driven, and leveling is performed so that the Z-axis tilt sensor  47  detects horizontal position. 
         [0069]    Under the condition that the Z-axis tilt sensor  47  detects the horizontal position, because the projecting direction of the laser beam perpendicularly crosses the optical axis  34 , a vertical reference plane is formed when the laser beam is projected by rotary irradiation. 
         [0070]    Through the light projection window  65 , the laser beam is projected in a horizontal direction. By aligning the laser beam with a target point, a vertical reference plane to perpendicularly cross the target is formed. 
         [0071]    As described above, the rotating unit cover  63  and the rotating plate  66  to constitute the rotating unit  57  are not in contact with the ceiling plate  53 , and this is a structure to reduce the rotation resistance of the rotating unit  57 . The first sealing means  68  and the second sealing means  69  are provided between the rotating unit  57  and the ceiling plate  53 . 
         [0072]    Description will be given below on the effects of the first sealing means  68  and the second sealing means  69  to prevent the intrusion of water and dust. In the following description, an example is taken on the prevention of water intrusion. It is supposed here that the laser surveying instrument  24  is installed at vertical position in outdoor conditions under windy and rainy weather. 
         [0073]    When rain falls on the laser surveying instrument  24  from above in diagonal direction, because the first annular ridge  71  is engaged into the third annular groove  76  and the space between the first annular ridge  71  and the third annular groove  76  is narrow, direct intrusion of rainwater through a gap entrance  85  between the rotating unit cover  63  and the ceiling plate  53  is prevented. On the other hand, rainwater may enter through the narrow gap between the first annular ridge  71  and the third annular groove  76  due to capillary phenomenon, and rainwater may ooze out to the first water trap  81 . By the presence of the first water trap  81 , the intrusion of water due to capillary phenomenon is interrupted. 
         [0074]    The oozing water is trapped in the first water trap  81 . When the water surface level trapped in the water trap  81  rises up to a level higher than the lower end of the fourth annular ridge  78 , a pressure is applied to push out the water between the first annular ridge  71  and the third annular groove  76  by the water trapped in the water trap, and the intrusion of rainwater is prevented as balancing is kept between the pressure and the oozing caused by capillary phenomenon. 
         [0075]    Further, when the surface level of the water in the first water trap  81  exceeds the height h 1  of the first annular ridge  71 , a pressure of the water trapped in the trap applies a power to discharge the water to outside on the water trapped in the trap, and further intrusion of rainwater is prevented. Specifically, the intruding water stays in the first water trap  81 , and it fulfills the function of water seal. 
         [0076]    When the force of the intruding rain water is higher than the pressure of the water from the first water trap  81  due the force of wind or the like, the water running over the second annular ridge  72  stays in the second annular groove  75 . Further, when the intruding water runs over the third annular ridge  73 , the water stays in the fifth annular groove  83 , and the seventh annular ridge  84  prevents the intruding water from falling down inside the housing  26 . 
         [0077]    The space from the gap entrance  85  to the fifth annular groove  83  serves as a complicatedly crooked route with the water traps inbetween, and the spacce causes high resistance to the flow. Therefore, much time is required until the intruding water reaches the fifth annular groove  83 . This gives ample time for operations such as the measurement and the like by the surveying instrument. 
         [0078]    Next, description will be given on a case where the laser surveying instrument  24  is installed at lateral position, e.g. a case where the laser surveying instrument  24  is rotated in a clockwise direction by an angle of 90° in  FIG. 1 . 
         [0079]    Referring to  FIG. 2 , it is a condition where  FIG. 2  is rotated clockwise by an angle of 90° and the gap entrance  85  is at lower position. Then, the water staying in the first water trap  81  and in the second annular groove  75  moves down toward the gap entrance  85  due to the gravitational force. Therefore, even when the rainwater enters the first water trap  81  and the second annular groove  75  and when the water is staying there, the water is discharged by placing the laser surveying instrument  24  at lateral position. 
         [0080]    On the other hand, when assumption is made on a case where the first water trap  81  on the opposite side is at upper position, the water staying in the first water trap  81  flows down along the first water trap  81  in annular shape and flows out via the gap entrance  85 . On the first water trap  81 , which is at upper position, the eave  72   a  of the second annular ridge  72  is set in vertical position, and the eave  72   a  fulfills the function as an embankment. This prevents the staying water from moving toward the center. 
         [0081]    Therefore, when the water entering the first water trap  81  and the second annular groove  75  is stopped and stays there, and if the laser surveying instrument  24  is placed at lateral position, most of the intruding water can be discharged toward outside. 
         [0082]      FIG. 3  shows a second embodiment of the invention. When the laser surveying instrument  24  is placed at lateral position, the intruding water can be effectively discharged toward outside in this embodiment. 
         [0083]    The inner peripheral surface of the second annular ridge  72  is tilted so that the second annular ridge  72  is spread in an upward direction, and the outer peripheral surface of the eave  72   a  is tilted so that it is spread in a downward direction. The groove wall of the fourth annular groove  77  (inner peripheral surface of the fourth annular ridge  78 ) is tilted so that the groove wall runs in parallel to the inner peripheral surface of the second annular ridge  72  and the outer peripheral surface of the eave  72   a . An eave  73   a  protruding outward is formed on the upper end of the third annular ridge  73 , and an eave  84   a  protruding in an inward direction is formed on the upper end of the seventh annular ridge  84 . 
         [0084]    By tilting the inner peripheral surface of the second annular ridge  72  and the outer peripheral surface of the eave  72   a , a route between the second annular ridge  72  and the fourth annular groove  77  runs in a vertical direction or tilted in a downward direction. As a result, the water in the gap can easily moved downward, and the intruding water can be effectively discharged to outside. Because the eave  73   a  is formed, the water trapped in the second annular groove  75  is prevented from entering inside, and the water trapped in the second annular groove  75  can be discharged to outside. The eave  84   a  fulfills the function as an embankment to the water staying in the fifth annular groove  83 , and the water is prevented from falling into the inner space of the housing  26 . 
         [0085]    It may be so designed that only the inner peripheral surface of one of the second annular ridge  72  and the fourth annular ridge  78  is tilted. 
         [0086]      FIG. 4  shows a third embodiment of the invention. In this third embodiment, the eave  72   a  of the second annular ridge  72  in the first embodiment is not used. 
         [0087]    In the third embodiment, the height of the second annular ridge  72  is h 2 , and this is higher than the height h 1  of the first annular ridge  71 . When the surface level of the water staying in the first water trap  81  is increased to higher than the height h 1 , a pressure by the water staying in the first water trap  81  applies a power to discharge the water to outside, and this prevents the intrusion of the rainwater. 
         [0088]      FIG. 5  shows a fourth embodiment of the invention. In this fourth embodiment, the first annular ridge  71  and the third annular groove  76  are formed in double arrangement. By forming the first annular ridge  71  and the third annular groove  76  in double arrangement, sealing capability up to the first water trap  81  are increased, and water preventing effect as the entire first sealing means  68  can be increased. 
         [0089]    As described above, according to the present invention, non-contact type sealing means can be provided by the crooked and bent route of the gap, and the first water trap  81  to exclude capillary phenomenon is arranged in the middle of the crooked route of the gap. As a result, the intrusion of water due to capillary phenomenon can be prevented. Because the water trap is provided, the time required for the intrusion of water into the laser surveying instrument  24  can be made longer. The water staying in the water trap can be discharged to outside by tilting or pulling down the laser surveying instrument  24 . This makes it possible to use the laser surveying instrument  24  for longer time under bad weather conditions. 
         [0090]    It is so designed that a pressure is applied to discharge the water by the water which is accumulated in the first water trap  81 . As a result, the intrusion of water from outside can be prevented, and water which exceeds a predetermined water surface level can be discharged to outside. This makes it possible to use the laser surveying instrument for longer time under bad weather conditions. 
         [0091]    Next, description will be given on dust preventive effect. 
         [0092]    Dust intrudes with the flow of the air, which is a compressed fluid. The sealing means according to the present invention has a route, which is very narrow and complicatedly crooked. This means that the route gives high resistance to the moving of the fluid. Further, the route has a multiple of windings and bendings, which are perpendicularly or almost perpendicularly bent. The intrusion of dust to inner space can be blocked because the dust in the air flow collides with or is brought into contact with the bending portions. Because the water traps with large volume are disposed at the midpoints, the flow of the intrusion air stagnates at the water traps, and this prevents the intrusion of the dust into the inner space. Therefore, sufficient sealing effect can be provided to the flow of dust.