Abstract:
A laser apparatus is provided for producing a plurality of mutually perpendicular laser beams, the apparatus includes a laser generated for producing a diverging laser beam. At least one beam splitter is disposed to be impinged upon by the diverging input laser beam. The beam splitter reflects a portion of the diverging input laser beam 90° and permits passage of the remainder of the diverging laser beam. Collimating lenses are disposed to be impinged upon by the diverging laser beams leaving the beam splitter. The collimating lenses are fixed at right angles to one another. As a result, the collimating lenses will produce collimated output laser beams that are perpendicular to one another despite any angular shifting of the diverging beams impinging upon the collimating lenses.

Description:
This application claims benefit of Provisional No. 60/123,635 filed Mar. 10, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to laser apparatuses, and, more particularly, to a laser apparatus for assessing alignment of a plurality of spaced-apart structural elements. 
     2. Description of the Related Art 
     Laser alignment systems include a laser for generating a laser beam and a light-sensitive target cell. The target cell is operative to generate electrical signals that identify the location of the center of energy of the laser beam impinging on the target cell. The light-sensitive target cell typically is mounted in a housing, and the housing is mounted to a structural element that must be aligned to another structural element or to some pre-established frame of reference. The laser is fixedly mounted to the other structural member or in proximity to the frame of reference. The laser then directs a beam on the light-sensitive target cell, and the target cell produces signals to identify both the position and the angular alignment of the target cell relative to the laser beam. Adjustments can be made to the structure on which the target is mounted so that the center of the target cell is positioned on the center of energy of the laser beam and so that the target cell is aligned substantially perpendicular to the laser beam. 
     Some prior art laser alignment systems employ a penta-prism. The penta-prism receives an input laser beam and permits a plurality of internal reflections. As a result of these reflections, an output laser beam emerges from the penta-prism at precisely right angles to the input laser beam. The penta-prism then may be rotated about the axis defined by the input laser beam. As a result, the output laser beam will sweep a perfectly flat laser plane. Systems of this type typically are used with a plurality of light-sensitive target cells mounted to a plurality of structural elements that require alignment relative to the laser reference plane. A system of this type is shown in U.S. Pat. No. 4,297,031. 
     U.S. Pat. No. 5,307,368 discloses a laser apparatus for generating up to three mutually perpendicular laser planes. In a first embodiment shown in U.S. Pat. No. 5,307,368 the apparatus is formed with three separate laser sources, and three separate beam adjustment means. Hamar Laser Instruments, Inc. manufactures and sells a laser apparatus, Model No. 723, formed in accordance with the first embodiment of U.S. Pat. No. 5,307,368. Hamar Model No. 723 is very effective and precise, but also is relatively expensive. The cost of the Hamar Model No. 723 laser apparatus can be reduced by using a single laser source, rather than three separate laser sources, and U.S. Pat. No. 5,307,368 shows three embodiments which utilize a single laser source to simultaneously produce three mutually perpendicular planes. Specifically, beam splitters and/or fiber optic elements are used to split a single laser beam into three separate beams. However, for each of these embodiments, beam adjustment means are provided for each of the resulting split laser beams to achieve mutual perpendicularity. Unfortunately, the costs of the beam adjustment means also are relatively high. 
     It is an object of the subject invention to provide a laser apparatus which utilizes a single laser source to simultaneously generate a plurality of laser planes. 
     It is also an object of the subject invention to provide a laser apparatus without beam adjustment means for simultaneously generating a plurality of laser planes arranged to be generally mutually perpendicular. 
     SUMMARY OF THE INVENTION 
     The above-stated objects are met by a laser apparatus which utilizes a single laser source that generates a diverging input laser beam. The apparatus utilizes the housing disclosed in U.S. Pat. No. 5,307,368, and may be used in conjunction with the rotating scanners or penta-prisms as disclosed in U.S. Pat. No. 5,307,368. A first beam splitter, preferably having 30% reflectivity, is placed in the path of the diverging input beam to reflect a portion of the beam in a direction perpendicular to the path of the input laser beam. Also, a second beam splitter, preferably having 50% reflectivity, is placed in the path of the diverging laser beam that passes through the first beam splitter to re-direct a portion of the laser beam in a direction perpendicular to the path of the input laser beam and perpendicular to the path of the first reflected beam. Collimating lenses are placed respectively in the paths of the three diverging beams, and collimate the respective beams. With this structural arrangement, three collimated output laser beams are generated which are mutually perpendicular. 
     The collimating lenses ensure substantial mutual perpendicularity of the output laser beams despite angular misalignment of the laser source relative to the beam splitters. In particular, angular shifting of a diverging beam relative to a collimating lens will cause the output beam to shift laterally, but will not affect the angular alignment of the output beam. Stated differently, regardless of the angle of a diverging input beam impinging on a collimating lens, the output beam will always be parallel to its alignment prior to the angular shifting of the input beam. With the apparatus of the subject invention, any angular shift of the generated diverging input laser beam will result in lateral shifting of the respective collimated output laser beams, but the perpendicular alignment of the collimated output laser beams will remain intact. 
     As is readily apparent, complex beam adjustment means are not required for use with this invention. The initial positioning of the collimating lenses to obtain three perpendicular output laser beams is all the adjustment that is required. Once the collimating lenses have been positioned to generate three mutually perpendicular output laser beams, the collimating lenses are immovably fixed to the housing using techniques known by those skilled in the art. The fixed collimating lenses, in combination with the single diverging input laser beam and the beam splitters, ensure the consistent generation of three perpendicular collimated output beams. 
     As a further enhancement apertures are formed in the housing of the apparatus or in structure between the beam splitters and the collimating lenses so that the resulting beams pass through the apertures. The apertures have considerably smaller diameters than the diameters of the resulting output beams themselves. In this manner, the respective beams “overflood” the apertures with only portions of the beams actually passing through the apertures. Thus, where the resulting beams are laterally shifted as the result of angular misalignment of the laser source relative to the beam splitters, the overflooded apertures ensure that the beams emitted from the apparatus remain constant in shape. More importantly, even though the beam approaching the aperture may shift, the portion of the beam emerging from the aperture will remain constantly along the same respective path. Thermal instability and settling of components, which may cause angular misalignment of the laser source and hence the input laser beam has no affect on the mutual perpendicularity of the output beams due to the combination of the diverging input laser beam, the beam splitters, the fixed collimating lenses and the overflooded apertures. Nevertheless it is preferred that the housing be formed of strain-free steel to minimize structural settling. 
     It should be noted that the method disclosed in U.S. Pat. No. 5,307,368 for achieving mutually perpendicular laser planes may be utilized herein for establishing perpendicularity between resulting output beams. Instead of adjusting the beams with beam adjustment means as in U.S. Pat. No. 5,307,368, the perpendicular arrangement of the beams is achieved by laterally shifting the respective collimating lenses. As used herein, “lateral shifting”, and any derivative phrases thereof, is defined as movement in a direction transverse to, but not necessarily perpendicular to, the central longitudinal axis of a laser beam. 
     As an additional feature, where fine adjustment is desired, a tilt plate may be placed in the path of at least two, preferably all three, of the resulting beams between the respective beam splitters and the respective collimating lenses. The tilt plates allow for fine adjustment in pitch and yaw of the output beams, as disclosed in U.S. Pat. No. 5,307,368. 
     As a further feature of the subject invention, the laser source can be located remotely from the apparatus, and the laser source may produce a straight beam, rather than a diverging, laser beam. A converging lens is placed in the path of the straight laser beam to cause convergence of the beam. The converging lens is formed with a focal length to focus the converging laser beam at the common focus of the three split beams—i. e., the focus point of the converging laser beam is located at the equivalent point where the diverging laser source emits a laser beam as described above. Thus, in effect, the converging laser beam is the equivalent of the diverging laser beam described above. Beyond the focus point, the converging laser beam diverges and interacts with the apparatus as described above. 
     These and other features of the invention will be better understood through a study of the following detailed description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a laser apparatus in accordance with the invention. 
     FIG. 2 is a schematic illustration of a first embodiment of the internal components of the apparatus. 
     FIG. 3 is a schematic of the first embodiment of the invention shown with additional features. 
     FIG. 4 is a schematic of a second embodiment of the internal components of the apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a laser apparatus  100  in accordance with the subject invention. The apparatus  100  includes a rigid substantially cubical housing  112  with a hollow interior in which the various optical and electrical components of the apparatus  100  are mounted. Three substantially adjacent mutually perpendicular faces  126 ,  128  and  130  of the housing  112  are provided with apertures through which mutually perpendicular laser beams will project as described further below. The faces  126 ,  128  and  130  further are provided with scanner head  132 ,  134  and  136 . The scanner heads are mounted to be selectively pivoted between a first position where the scanner heads are spaced from the apertures in the respective faces  126 ,  128  and  130  and a second position, shown in FIG. 1, where the scanner heads  132 ,  134  and  136  overlie the apertures. The scanner heads  132 ,  134  and  136  each include a penta-prisir that is operative to reflect a laser beam through precisely 90°. The scanner heads  132 ,  134  and  136  also are operative to rotate about the axis of the laser beam projecting through the respective apertures. Thus, the scanner heads effectively sweep the flat laser planes P 1 , P 2  and P 3 . The laser planes will be mutually perpendicular to one another. The structural and functional features of the housing  112  and the scanner heads  132 ,  134  and  136  are substantially the same as in the above-described U.S. Pat. No. 5,307,368. However, the optical and electrical components of the apparatus of the subject invention differ significantly from U.S. Pat. No. 5,307,368 as explained further below and as illustrated in FIGS. 2-4. 
     FIG. 2 is a schematic illustration of a first embodiment of the invention, wherein a laser source  10 , such as a laser diode, is provided for generating a single diverging input laser beam  12 . A first beam splitter  14  is disposed in the path of the diverging input laser beam  12  to reflect and re-direct a portion of the input laser beam  12 . It is preferred, that the reflectivity of the first beam splitter  14  be selected to re-direct 30% of the diverging input laser beam  12 . As a result of the beam splitting, a first resulting output beam  16  is generated. The non-reflected portion of the diverging input laser beam  12  passes through the beam splitter  14  to generate a laser beam designated with the reference numeral  12 A. Both the beam  12 A and the first resulting output beam  16  are diverging. 
     A second beam splitter  18  is disposed in the path of the beam  12 A. The beam  12 A impinges on the second beam splitter  18  and causes a portion of the beam  12 A to be reflected and re-directed as a second resulting output beam  20 . The non-reflected portion of the beam  12 A passes through the second beam splitter  18  to define a third resulting output beam  22 . Both the second resulting beam  20  and the third resulting beam  22  are diverging. 
     The first and second beam splitters  14  and  18  are disposed such that the first, second, and third resulting output beams  16 ,  20 , and  22  are generally perpendicular. In other words, the first resulting output beam  16  is generally perpendicular to both the second resulting output beam  20  and to the third resulting output beam  22 . Likewise, the second resulting output beam  20  is generally perpendicular to both the first resulting beam  16  and to the third resulting beam  22 , whereas, the third resulting output beam  22  is generally perpendicular to both the first resulting beam  16  and to the second resulting output beam  20 . Due to optical and mechanical inaccuracies of the laser source  10 , the beam splitters  14  and  18 , their mounting and their housing, precise perpendicularity cannot and need not be achieved. However, in forming an apparatus in accordance with the subject invention, the laser source  10  and the first and second beam splitters  14  and  18  are fixed within the housing to increase the likelihood of maintaining the generally perpendicular arrangement. 
     First, second, and third collimating lenses,  24 ,  26 , and  28 , are disposed respectively in alignment with the first, second, and third resulting output beams  16 ,  20 , and  22 , respectively, to be impinged thereon. Preferably, the collimating lenses  24 - 28  are laser or achromatic lenses. As the respective first, second, and third resulting output beams  16 ,  20 , and  22  pass through the first, second, and third collimating lenses  24 ,  26 , and  28 , respectively, the beams  16 ,  20  and  22  are collimated to generate first, second, and third collimated output laser beams  16 A,  20 A, and  22 A, respectively. 
     The apparatus is formed such that the collimating lenses  24 - 28  initially are disposed in the paths of first, second and third resulting output beams  16 ,  20 , and  22 , respectively. Using the methodology disclosed in U.S. Pat. No. 5,307,368, the collimating lens  24 - 28  are laterally shifted to achieve substantial perpendicularity between the first, second and third collimated laser beams  16 A,  20 A and  22 A. Having achieved substantial mutual perpendicularity (i.e., to within acceptable tolerances), the collimating lenses  24 - 28  are immovably fixed to the housing using techniques known by those skilled in the art. 
     The combination of the beam splitters  14  and  18 , and the collimating lenses  24 ,  26 ,  28 , advantageously allows for maintaining substantial perpendicularity between the collimated output beams  16 A,  20 A, and  22 A, even if angular shifting of the diverging input laser beam  12  occurs relative to the beam splitters  14  and  18 . In particular, an angular shift of the laser beam  12  results in angular shifting of the first, second, and/or third resulting output beams,  16 ,  20 , and  22 . The angular shifting of the first, second and third resulting beams  16 ,  20 , and  22 , however, is of no consequence, since the respective collimated laser beams  16 A,  20 A, and  22 A, are simply shifted laterally with no angular change. For example, as shown in FIG. 1, a change in location of impingement of the first resulting output beam  16  on the first collimating lens  24  results in the first collimated beam  16 A shifting laterally from the position shown in solid lines to a position represented by a beam in dashed lines indicated with reference numeral  16 B. The two collimated beams  16 A and  16 B are parallel, and, therefore, the collimated laser beam  16 B maintains its original perpendicularity to both the second and third collimated laser output beams  20 A and  22 A. Accordingly, any shifting of the first, second, and third resulting output beams  16 ,  20 , and  22  will result in lateral shifting of the first, second, and third collimated output beams  16 A,  20 A, and  22 A, respectively, with the initial, mutually perpendicularity being unaffected. 
     FIG. 3 shows an embodiment where more accurate perpendicularity between the first, second, and third collimated laser output beams  16 A,  20 A, and  22 A can be attained. In particular, tilt plates  30 , formed in accordance with the teachings of U.S. Pat. No. 5,307,368 are provided between the beam splitters  14  and  18  and the respective collimating lens  24 ,  26  and  28 . It is preferred that three of the tilt plates  30  be utilized, thus, having one of the tilt plates  30  corresponding to each of the first, second, and third resulting output beams  16 ,  20 , and  22 . Alternatively, two of the tilt plates  30  may be utilized, with one of the first, second, and third resulting beams  16 ,  20 , and  22  not being provided with a tilt plate  30 . As shown in FIG. 2, the tilt plate  30  is disposed in alignment with the respective first, second, or third resulting beam  16 ,  20 , or  22 , intermediate the respective beam splitters  14 ,  18 , and collimating lens  24 - 28 . As disclosed in U.S. Pat. No. 5,307,368, the passage of the respective first, second, and third resulting beams  16 ,  20 , and  22 , through one of the tilt plates  30  results only in lateral shifting, with the output from the tilt plate  30  being parallel to the input. However a shifting of the point of impingement of the diverging output beam  16 ,  20  or  22  on the associated collimating lens  24 ,  26  or  28  enables fine tuning of the angular alignment of the output collimated beam  16 A,  20 A or  22 A. Consequently, the tilt plates  30  allow for fine tuning the locations of impingement of the respective first, second, and third resulting beams  16 ,  20 , and  22  on the collimating lenses  24 - 28  to achieve higher accuracy in perpendicularity between the collimated output laser beams  16 A,  20 A, and  22 A. As, mentioned above, two of the tilt plates  30  may be utilized, wherein two of the collimated laser beams  16 A,  20 A, and  22 A are adjusted using the tilt plates  30  relative to a non-adjustable collimated laser beam to achieve more accurate mutual perpendicularity. 
     As a further feature, “overflooded” apertures, such as those disclosed in U.S. Pat. No. 5,307,368, may also be utilized with the subject invention. In FIG. 3, an aperture  32  is schematically shown superimposed on the collimating lens  26 . However, as disclosed in U.S. Pat. No. 5,307,368 the aperture  32  may actually be formed in the housing of the apparatus and is positioned to allow the passage therethrough of the second collimated laser beam  28 . Likewise, apertures  32  may be provided for the first and third collimated laser beams  16 A and  22 A. As explained in U.S. Pat. No. 5,307,368, the apertures  32  are formed with a smaller diameter than the collimated laser beams  16 A,  20 A, and  22 A to cull the respective beam and allow only a central high energy portion of the beam to pass through the aperture. Consequently, the overflooded apertures  32  increase the likelihood that laser beams of constant cross-section are emitted from the apparatus, and that the emitted beams remain constantly along the same paths, even though lateral shifting of the beam within the housing may occur. 
     As an alternative embodiment, a laser source may be used with the apparatus formed in accordance with the subject invention with is located remotely from the housing of the apparatus. Referring to FIG. 4, a laser source  34  is provided for generating a straight input laser beam rather than the diverging beam described above. The straight laser beam is directed to impinge upon and pass through a converging lens  36  to define a converging laser beam  38 . The converging lens  36  is formed with a focal length f which causes the converging laser beam  38  to converge to a focus point  40 . The focus point  40  is located relative to the first beam splitter  14  at an equivalent position as the laser source  10  described above. As shown in FIG. 3, the converging laser beam  38  diverges beyond the focus point  40  to be the equivalent of the diverging laser beam  12  described above. In all other respects, the embodiment shown in FIG. 3 functions as described above. It should be noted that the focal length f of the converging lens  36  is to be identical to the focal lengths of the collimating lenses  24 - 28 .