Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/039,205 filed Jan. 19, 2005. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     This invention relates to apparatus for providing a reference laser beam and, more particularly, to a laser beam transmitter having an improved lighthouse structure. The lighthouse of the present invention effectively seals the transmitter against moisture and dirt. Further, this lighthouse is rugged, while also facilitating repair should a glass panel be broken during use of the transmitter. 
     Laser beam systems have been employed in numerous surveying and construction applications. In one such system, disclosed in U.S. Pat. No. 4,062,634, issued to Rando et al, a laser beam transmitter produces a rotating laser beam which establishes a reference plane. The reference plane swept by the rotating beam is used as an elevational reference over an entire work area, such as for example a construction site. Also, the system employs one or more laser beam detectors, placed at considerable distances from the transmitter, for intercepting the rotating laser beam in the reference plane. These detectors may be carried on earthmoving equipment and used by the operators of the equipment to determine proper elevation at various points throughout the work area. 
     In a laser beam transmitter of this type, the horizontal rotating reference laser beam is produced by projecting the beam generally upward, and then redirecting it ninety degrees within a pentaprism assembly. The pentaprism assembly, which typically uses a pair of mirrors rather than a prism to produce the needed double reflection, is rotated about a vertical axis within the projecting apparatus to cause the resulting horizontal beam to rotate, thereby defining the reference plane. If desired, the beam may be rotated in a plane that is tilted by a specified amount with respect to horizontal, thereby providing a tilted reference plane. 
     To adapt the reference laser beam transmitter for use in surveying and construction applications under a variety of field conditions, the transmitter is provided with a waterproof housing having an upper, transparent lighthouse assembly within which the pentaprism assembly rotates and through which the laser beam is projected. In the transmitter shown in the &#39;634 patent, the lighthouse assembly includes four upstanding flat transparent panes of glass of high optical quality which are joined together at their side edge surfaces so as to form a square in cross section. The lower edges of the panes are mounted within recessed seats formed in an upper rim of the housing, while the upper edges of the panes are mounted within recessed seats formed within a top casing of the housing. Gaskets seal the upper and lower edges of the panes. Four posts extend between the top casing of the housing and upper rim of the housing and apply sufficient compressive force to pull them together and lock the panes into their seats. The four posts are aligned radically outward from the corners of the lighthouse assembly. Where the panes meet at the corners they have forty-five degree beveled side edges that mate and are further sealed by a suitable adhesive, such as a silicone adhesive. 
     While this lighthouse construction performs well, it requires careful grinding of the individual glass panes to precise dimensions to bevel the side edge surfaces that form the corner junctures of the lighthouse. The assembly of the lighthouse also requires precise positioning of the panes relative to one another, before they were adhered together. Additionally, this lighthouse construction is not as rugged as might be desired. Several lighthouse constructions have been used to overcome these difficulties. One such construction, similar to that in the &#39;634 patent, is shown in U.S. Pat. No. 4,776,672, issued Oct. 11, 1988. In the lighthouse to which the &#39;672 patent is directed, a plurality of transparent panes are arranged in a generally polygonal cross-sectional shape. The window structure has spaced corners formed by pairs of adjacent ones of the opposite side edge portions of the panes. The side edge portions of the panes in each pair are offset relative to one another in forming a respective corner. The offset position of the side edge portions of each pair in forming a respective corner exposes only an interior edge on one of the adjacent side edge portions to laser light being transmitted through the window structure. The path of laser light through the adjacent side edge portions forming the corner is thereby affected only by one interior edge on the respective one of the adjacent side edge portions of the panels at each corner. This reduces the care with which the edges of the panes must be adhesively bonded, but does not deal with the issue of ruggedness. 
     Another lighthouse construction is shown in U.S. Pat. No. 4,662,707, issued May 5, 1987. The &#39;707 patent discloses a lighthouse configured as a cylindrical lighthouse of molded acrylic resin. The lighthouse has no corners and, therefore, no problems of the type associated with joining together flat panes at the corners. A difficulty with the cylindrical configuration, however, is that the rays of laser light at the periphery of the beam will tend to diverge laterally from the center of the beam after being refracted twice as they pass through the lighthouse. To overcome this difficulty, an additional correction lens is provided in the &#39;707 transmitter, to minimize the generally horizontal beam divergence. While this effectively eliminates several limitations encountered with respect to prior art lighthouses, it also requires the addition of a component, the lens, and the resulting inaccuracies. 
     Accordingly, it is seen that there is a need for an improved lighthouse construction in which additional optical components are not required. Further, there is a need for a lighthouse construction in which the lighthouse is rugged, and easily constructed. 
     SUMMARY OF THE INVENTION 
     These difficulties are overcome by a laser transmitter, and a lighthouse for such a transmitter, constructed according to the present invention. The laser transmitter projects a beam of laser light and rotates the beam about an axis that is generally normal to the beam. The transmitter includes a lighthouse for enclosing the laser beam source, at least in part. The lighthouse, which permits the beam of laser light to be projected there through, includes a plurality of transparent panels. 
     The panels may be held in place by a panel support of elastomeric material in a peripheral configuration such that they surround the laser beam source. Each of the transparent panels has a trapezoid shape, with upper and lower parallel edges, with the upper edge being shorter than the lower edge. Each of the transparent panels has an isosceles trapezoid shape with right and left non-parallel edges. The right and left non-parallel edges are beveled. 
     The panel support of elastomeric material engages the plurality of transparent panels and supports the panels in a peripheral configuration such that they surround the laser beam source. The panel support defines a plurality of openings for receiving the transparent panels. The plurality of panels comprises four panels, each generally trapezoidal in shape, and the plurality of openings comprises four trapezoidal openings. Preferably, each of the panels has an isosceles trapezoid shape and substantially parallel upper and lower edges. The upper edge is shorter than the lower edge, and the panels further have right and left non-parallel beveled edges. The panel support defines retaining grooves along at least some of the edges of each of the four trapezoidal openings. The panels are received into the grooves and held in place in the panel support. 
     Accordingly, it is an object of the present invention to provide an improved, more rugged lighthouse construction for a laser transmitter. Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a portion of a laser transmitter constructed according to the present invention, with portions broken away and in section to reveal interior structure; 
         FIG. 2  is a side view of a lighthouse panel support according to the present invention; 
         FIG. 3  is a sectional view of the lighthouse panel support of  FIG. 2 , taken generally along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a top plan view of the lighthouse panel support of  FIG. 2 ; 
         FIG. 5  is a sectional view of the lighthouse panel support of  FIG. 4 , taken generally along line  4 - 4  in  FIG. 4 ; 
         FIG. 6  is a front view of a transparent panel used in the lighthouse of  FIG. 2 ; 
         FIG. 7  is a rear view of a transparent panel used in the lighthouse of  FIG. 2 ; 
         FIG. 8  is a top view of a transparent panel used in the lighthouse of  FIG. 2 ; and 
         FIG. 9  is a side view of a second embodiment of a transmitter, with an inverted lighthouse, and with portions broken away to reveal interior structure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention relates to an improved laser transmitter and an improved lighthouse for use in such transmitters. Reference is made to  FIG. 1  of the drawings, which shows a laser transmitter  10  constructed according to the present invention for projecting a beam  12  of laser light in a reference plane. The apparatus  10  includes a housing  14 , a laser  16  in the housing  14  for generating the laser beam  12 , and a beam diverting assembly  18  mounted for receiving the laser beam  12 ′ from the laser  16  and deflecting the laser beam outwardly from the housing in the reference plane as beam  12 . The laser  16  may be any laser beam source, such as, for example, a helium-neon gas laser with appropriate optics for producing a low-power collimated output beam in the red band of the light spectrum. The beam diverting assembly  18  is preferably a pentaprism assembly which redirects light beam  12 ′ in a perpendicular direction as beam  12 . As is known, the pentaprism assembly has a pair of reflecting surfaces (not shown) which are accurately aligned to divert the beam from the vertical axis to a direction perpendicular thereto. 
     The transmitter  10  has an arrangement, including a motor (not shown), for rotating the beam diverting assembly  18  about a vertical axis. As the assembly  18  is rotated, the beam  12  is rotated about the vertical axis and swept through the horizontal reference plane. 
     A lighthouse  20  overlies the beam diverting assembly  18 . The lighthouse  20  is mounted on the housing  14  to allow transmission of the laser beam  12  therethrough, while sealing the housing  14  in conjunction with a lighthouse cover  22 . The cover  22  is supported over the lighthouse  20  by posts  24  which extend between the housing and the cover at the corners of the lighthouse  20 . The lighthouse  20  includes a plurality of transparent panels  26  arranged circumferentially around the beam diverting assembly  18 , and a panel support  28  of elastomeric material for holding the transparent panels  26  in position. 
     One of the transparent panels  26  is shown in  FIGS. 6-8 . The panel  26 , preferably made of optical grade glass, has a front surface  30  and rear surface  32 . Surfaces  30  and  32  are substantially parallel to each other so that any refraction experienced by the beam  12  entering the panel  26  is offset by an equal and substantially opposite refraction experienced by the beam  12  as it exits the panel  26 . As illustrated in  FIGS. 6 and 7 , each of the transparent panels  26  is shaped substantially as an isosceles trapezoid having upper and lower parallel edges  34  and  36 , respectively. The upper edges  34  are shorter than the lower edges  36 . Each of the transparent panels  26  also has right and left non-parallel, beveled edges  38  and  40 , respectively. It should be appreciated that the upper edges  34  are shorter than the lower edges  36  because the transparent panels are not vertically positioned in the lighthouse  20 , but are pitched rearward slightly, as shown in  FIG. 1 . The lighthouse  20  could, however, have transparent panels that tilt back slightly if desired, in which case the lower edges of the panels would be longer than their upper edges. Such a lighthouse construction is shown in  FIG. 9 , in which structures that correspond to structures in  FIG. 1  are given like reference numerals. 
     The lighthouse panel support  28  is made of an elastomeric material that holds the transparent panels  26  in position in the lighthouse. As seen in  FIGS. 2-5 , the panel support  28  defines a plurality of trapezoidal openings  42  that receive the transparent panels  26 . The panel support  28  further defines retaining grooves  44 ,  46 ,  48 , and  50  along the edges of each of the trapezoidal openings. The panels  26  are received into these grooves and held in place. 
     Because the openings  42  and surrounding grooves are the same size as the panels  26 , each panel is inserted into a corresponding opening in the support  28  by stretching and deforming the panel support  28  slightly, temporarily enlarging an opening  42 . The panel support  28  then returns to its unreformed shape and firmly securely engages the periphery of the panel, forming a seal around the panel periphery at the same time. It will be noted that after the panels  26  are mounted in the openings  42  in the lighthouse panel support  28 , the elastomeric support  28  is positioned on the housing  14  such that its lower edge is received into a mating seat  52  ( FIG. 1 ). The sealing of the lighthouse  20  is then completed by lighthouse cover  22  and mating seat  54  that engages and seals the top edge of the support  28 . 
     The panel support  28  of elastomeric material supports the four transparent panels  26  in a peripheral configuration such that they surround the laser beam source  16 . The openings  42  of the panel support are beveled and narrowed at  56  to minimize the amount of the beam  12  that is blocked as the beam  12  is swept past the edges of each of the openings  42 . Note that at the top and bottom of the grooves  48  and  50 , at points were the beam  12  will be unaffected, the support  28  defines shoulders  58  which add additional backing to support the side edges  38  and  40  of the panels  26 . 
     The lighthouse of the present invention has a number of advantages. First, it is extremely rugged. If the transmitter is inadvertently subject to an impact, such as for example would result from being dropped, the support  28 , made of elastomeric material, cushions the impact to the panels. This makes it less likely that a panel will be broken than is the case with a lighthouse in which there is glass-to-glass contact at the lighthouse corners. Further, if a panel should be damaged during operation of the transmitter, the transmitter need not be taken out of service for an extended period for repairs. No adhesive is required to replace a transparent panel, and this can be accomplished with relative ease. 
     While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the business form disclosed herein may be made without departing from the scope of the invention, which is defined in the appended claims.

Technology Category: 3