Abstract:
An instrument for use in alignment, plumb and leveling functions includes a laser diode projecting a beam through a liquid contained in a vessel. Floating in the liquid is a compensator float which includes telescope optics so as to diminish the angle of rays leaving the telescope as compared to rays entering the telescope. The laser beam passes through the liquid and through the telescope, exiting from a window at the top or side of the instrument. By selecting the proper relationship between the telescope&#39;s magnification and the index of refraction of the liquid, the instrument is made to correct for small tilt angles of its housing. Various embodiments are disclosed for projecting upward or downward plumb beams, level beams or both.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to hand tools, and in particular the invention is concerned with a compact hand tool for projecting plumb and level reference beams of visible light for precise alignment. 
     A system for generating reference beams based on first generating a plumb beam of light is the invention described herein. Many self-leveling plumb laser beam generators have used ball bearings, wires, and springs. There are also many instruments which have used electronic sensors and motors to level the projector as required. A low cost automatic self-leveling laser instrument is described in U.S. Pat. Nos. 5,459,932, 5,524,352, 5,541,727, and 5,619,802 assigned to the same assignee as the present invention. The instruments of those patents are similar in application to the present invention. The disclosure of those patents is incorporated herein by reference. 
     In Swierski, U.S. Pat. No. 5,184,406, the instrument of which is shown in FIG. 1, a battery operated laser projector 1 is mounted in a float 2 which floats in a partially closed pan 8 of water 6. Although this does produce a plumb beam of light, there are many disadvantages to this system. The lack of liquid containment makes it difficult to transport and set up. The accuracy can be adversely affected by mishandling of the float or the battery insertion. 
     SUMMARY OF THE INVENTION 
     The present invention uses a floating telescope to generate a plumb beam of laser light by redirecting a laser beam using a telescope which is floating below the surface of a liquid. The axis of the floating telescope is always vertical because of the location of the center of gravity and the center of buoyancy in the same way a boat or submarine remains vertical at sea. The laser module is located below the bath of liquid and projects a collimated laser beam up through the vessel and through the floating telescope and out an exit window of the instrument. The compensatory effect of the telescope combined with changes of index of refraction as the beam passes through the telescope and the vessel produces a fully compensated plumb laser beam emanating from the upper end of the vessel. The vessel is sealed, and problems of prior floating plumb beam generators described above are overcome. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic elevational section view showing a plumb laser beam generator according to prior art. 
     FIGS. 2 and 3 are schematic elevational section views showing a plumb beam generator according to the invention. 
     FIG. 4 is a simplified schematic view serving to illustrate the principles of the invention. 
     FIG. 5 is a view similar to FIG. 4, schematically indicating the device as tilted and illustrating the compensating effects of the telescope and the indices of refraction. 
     FIG. 6 is an elevational section view showing one preferred embodiment of a tilt compensating instrument of the invention. 
     FIG. 7 is a view similar to FIG. 6 but showing the instrument housing tilted and the exit beam remaining plumb. 
     FIG. 8 is an elevational section view showing another preferred embodiment in which the laser beam is directed downwardly rather than upwardly, but involving the same principles. 
     FIG. 9 is a schematic elevation view showing a variation in which the vessel contains two liquids of different densities, as an arrangement for keeping the floating telescope below the surface of the liquid. 
     FIG. 10 is an elevational section view showing an instrument with a floating telescope to produce a level beam despite tilt of the housing. 
     FIG. 11 is an elevation view in section showing another embodiment of an instrument which is similar to that of FIG. 6 but with an exit window providing fine adjustment. 
     FIGS. 12, 13, and 14 are sectional views, somewhat schematic, showing a self-leveling pentaprism device for producing a level beam from a plumb beam generator as in FIG. 6. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the schematic view of FIG. 2, the number 20 corresponds to the instrument of the invention generally. A laser module 22 produces a collimated laser beam 24 which passes through a lower window 26 and into a transparent liquid 28. 
     A cylindrical floating telescope 30 is contained in a sealed, preferably cylindrical vessel 32 which is partially filled with the liquid 28. The telescope consists of two lenses 34 and 36 and an air space between. Generally speaking, a telescope magnifies the angle between incoming rays so that it may be more easily seen. In this case the magnification is approximately three times. A collimated light beam entering the telescope defined by the lenses 34 and 36 remains collimated as it exits the telescope. In this invention the light travels in the opposite direction from that of a viewing telescope so that the angle of the ray relative to the axis of the telescope is reduced by the power of the telescope. 
     The weight of the float 30 is chosen so that two appendages 38 on the floating telescope protrude above the surface. In this way the telescope&#39;s optical path is always in the fluid and the float is free to align itself to the vertical. The effects of surface tension at the locations where the appendages 38 exit the fluid are negligible because of their size. 
     A re-entrant section 42 of the vessel further ensures that the exit window is and remains in the fluid. An air pocket 44 is present to allow the volume of fluid in the vessel to change with temperature without causing vessel-distorting pressure changes. 
     A lower portion 46 of the float 30 fits the diameter of the vessel closely to keep the lens centered on the beam. 
     FIG. 3 shows schematically the beam path for a tilted compensator. Note that the angle of the beam changes within the telescope as well as at the exit window, due to passage through the lenses and refraction index of the liquid. The final beam is, however, vertical. 
     FIG. 4 may be used in a first order analysis of the optical path. The light beam and axis of the vessel and telescope are aligned in the vertical direction. In this case the beam passes vertically through the system. 
     In FIG. 5 the housing of the vessel is tilted so that the beam makes an angle A with the vertical. The angle of the beam entering the telescope is A and the optics of the telescope reduce the angle to A/M where M is the magnification, i.e., optical power, of the telescope. The angle between the beam and the normal to the exit window, as the beam approaches, is now A-A/M. B is the angle the exiting beam makes with the normal to the exit window. From Snell&#39;s Law sin B=n sin (A-A/M), where n=index of refraction of the liquid. By setting B equal to A and approximating the sin A=A (for small A), we arrive at the compensation condition, M=[n/(n-1)]. In such a system the exit beam remains plumb or pointed in the vertical direction even though the platform on which it is resting is not level. 
     FIG. 6 is a section view of the compensator according to a preferred embodiment, showing a laser diode 52 in a laser diode holder 53 below a transparent liquid vessel 54. A lens 56 collimates the beam. The liquid 58 is a transparent liquid, for example, turpentine or kerosene. These liquids provide sufficient damping of the float motion while allowing quick response. The laser beam 60 from the diode is expanded by optics in a lower telescope half 62 which is registered to an upper telescope half 64. The two halves fit together, one into the other, registering the distance between the two optics which include lenses 63 and 65. In this way the telescope&#39;s upper and lower pieces may be fitted together without adjustment. These parts may be molded out of clear plastic and chemically sealed with a solvent. Two or more small diameter plastic cylinders or rods 66 at the top of the upper telescope half 64 serve to keep the telescope float below the surface of the liquid. A reentrant window 68 keeps the region above the lens under the fluid surface. A wide section of material 70 at the bottom of the lower telescope half ensures that the center of gravity is well below the center of buoyancy. A raised ring or lip 72 on the floor of the liquid vessel 54 keeps the lower optical surface centered on the laser beam. A spherical surface 74 between the laser diode holder and the liquid vessel allows the alignment or calibration of the compensator. 
     FIG. 7 shows the instrument as in FIG. 6 except that the housing 54 has been tilted. Note that the floating telescope orientation remains vertical. 
     FIG. 8 is a cross sectional view of a preferred embodiment of a compensator 80 in which the beam is directed in the vertically down direction using the same principles. The liquid vessel 82 has been rearranged to capture the floating telescope 84 at its top where the negative lens 86 is located. In this case the exit beam 88 is downwardly directed. 
     FIG. 9 is a schematic view showing an alternate arrangement for keeping the floating telescope below the surface of the liquid. A liquid 98 of high density and a liquid 99 of low density are placed in the same vessel. The density of the float is adjusted to a value between the liquids. The value of M, the telescope magnification, is selected to provide the necessary compensation as described previously. If the indices of refraction of the two liquids differ, the formula becomes somewhat more complicated than described above, but it can nonetheless be solved. In this way the float is held below the surface of the liquids by hydrostatic forces. As in the above embodiments, the weight distribution in the float is selected so that the float remains upright. 
     FIG. 10 is a section view showing a floating telescope design used to produce a level beam. It uses the same principles described above. The floating telescope compensator instrument is described generally by the number 100. A laser diode 102 produces a laser beam 104 which is first collimated by a lens 106. The beam passes into a transparent housing 108 filled with a transparent liquid 110. A float 112 has two built-in lenses 111, 113 which minify the angle of the incoming beam. The float is free to orient itself to the vertical and remains below the surface of the liquid. Small cylindrical pegs 114 help maintain the float just below the surface. 
     In an alternate preferred embodiment 115 shown in section view FIG. 11, fine calibration of the instrument can be achieved by tilting the exit window 68. This embodiment is otherwise similar to that of FIG. 6, and reference numbers correspond to those used in FIG. 6. The transparent housing 54 is open at its top and is sealed by a window-bearing member 116 which has a spherical surface 118 which fits snugly in the open housing as shown. By tilting of this member, small deviations of the plumb beam may be introduced for the purpose of calibration of the compensator. An adhesive (not shown) can be used to seal the member 116 to the housing at the spherical surface. 
     A level reference beam can be created from the plumb beam by using a self-leveling pentaprism as shown generally by 120 in FIG. 12. A pentaprism 122 is hung by a flexible suspension member 124 from a support member 126 on the inside of a cap 128. A hole 130 in the cap allows the beam to exit the cap. This flexible member need only level approximately in one axis (tilting in and out of the page in FIG. 12) to produce an accurate 90 degree deviation of the beam. The flexible member 124 may be made of thin or very flexible rubber to combine flexibility with damping. 
     An inside lip 132 allows the cap 128 to fit over the plumb beam generator shown in FIG. 6. By rotating the cap by hand a level reference plane can be defined with the exiting horizontal beam 134. The lip can also provide some height adjustment by allowing the cap to slide up and down on the upper edge of the housing of the device shown in FIG. 6. 
     FIG. 13 is a section view of the pentaprism hanging from the cap, from a 90 degree rotated vantage point as compared to FIG. 12. FIG. 14, similar to FIG. 13, shows how the flexible member 122 allows the pentaprism to self level in one axis, the self-leveling now being within the plane of the drawing. 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to this preferred embodiment will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.