Abstract:
The present invention provides apparatus and a method for projecting an indication of alignment. The invention features forming a first output beam, and a second output beam that is substantially perpendicular to the first output beam. The first output beam indicates level, the second output beam indicates plumb, and the first and second output beams together indicate square.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a laser-based tool for indicating level, plumb and/or square. 
       BACKGROUND 
       [0002]    Portable devices capable of indicating level, plumb and square alignment have been useful in the construction and carpentry trades for some time. The advent of laser technology has seen the use of portable laser emitting devices capable indicating level and plumb, as well as level, plumb and square alignments simultaneously. 
         [0003]    In some prior art tools, alignment is indicated with beams that form points of light or “spots” on a surface against which they are projected. In some prior art tools, an invisible “line” can be imagined between two or more opposing and aligned spots to provide an alignment line. Other tools indicate alignment with beams that form the image of a straight line on the surface against which they are projected, that is, they project linear alignment beams. 
         [0004]    Such devices typically require some sort of tilt-compensation mechanism or self-leveling mechanism, to avoid the introduction of error when operated from a non-level surface. However, even with a tilt-compensation or self-leveling mechanism, such tools typically can only accurately indicate level and plumb within a range of inclinations of the tool relative to level. To avoid a user inadvertently relying on an erroneous indication of alignment, some tools provide an indication to the user, when the user is attempting to use the tool outside of a predefined range of inclinations, for example, by ceasing projection of alignment beams or causing the alignment beams to blink. 
       SUMMARY 
       [0005]    The present invention provides apparatus and a method projecting alignment lines. In general, in one aspect, the invention features an apparatus for projecting an indication of alignment. The apparatus includes a housing, a projection unit and a damper to dampen pendular motion of the projection unit. The projection unit is pendulously suspended in the housing to project output beams to indicate level, plumb and square and includes a vertical projection module and a horizontal projection module. Each of the vertical and horizontal projection modules include (1) a laser emitting diode to emit a laser beam incident on a collimator, (2) a collimator configured to collimate the laser beam into a collimated beam and project the collimated beam on a planar reflective surface; (3) a planar reflective surface orientated at an angle of approximately 45° to a path of the collimated beam projected from the collimator and configured to divert the path of the collimated beam approximately 90° and toward a partial-conical reflective surface; and (4) a partial-conical reflective surface formed from approximately 180° of an exterior surface of a cone and configured to reflect the diverted collimated beam into an approximately 180° fanned output beam. The vertical projection module generates a substantially vertical output beam and the horizontal projection module generates a substantially horizontal output beam, the vertical and horizontal output beams being projected from the housing in different but generally perpendicularly related directions. The output beams can be used to indicate level, plumb and square alignment. 
         [0006]    Implementations of the invention may include one or more of the following features. The vertical projection module and the horizontal projection module can be positioned within the apparatus such that the vertical output beam and the horizontal output beam both emanate from a same face of the apparatus. Each collimator can be an aspheric lens and each collimated beam can have an elliptically shaped cross-section. The apparatus may further include at least one battery to provide power to the laser emitting diodes of the projection unit. 
         [0007]    The apparatus may include an error indicator to indicate when the housing is inclined such that the accuracy of the level and plumb directions are compromised; and an override to deactivate the error indicator, whereby the output beams can be used at least to indicate square alignment. The error indicator can suspend projection of the vertical and horizontal output beams. The error indicator can indicate the housing is inclined such that the accuracy of the level and plumb directions is compromised, when the housing is inclined in any direction in the range of approximately plus or minus 4 to 9 degrees from horizontal. In another implementation, the error indicator indicates the housing is inclined such that the accuracy of the level and plumb directions is compromised, when the housing is inclined in any direction more than approximately 9 degrees from horizontal. The override can include digital circuitry to deactivate the error indicator in response to a user input. 
         [0008]    The damper can include a magnet mounted in the housing below the projection unit and a damping plate rigidly suspended from the projection unit, such that the damping plate is positioned above the magnet with a gap maintained therebetween sufficiently small that eddy currents are generated in the damping plate by motion thereof above the magnet. 
         [0009]    The apparatus can further include a user interface configured to receive a user input, wherein: in response to a first user input, the projection unit projects a horizontal output beam that can be used to indicate level; in response to a second user input, the projection unit projects a vertical output beam having a generally perpendicular relationship to the horizontal output beam, whereby the vertical output beam can be used indicate plumb; in response to a third user input, the projection unit projects simultaneously the horizontal and vertical output beams, whereby the output beams can be used to indicate simultaneously level, plumb and square; and in response to a fourth user input, the override is employed to deactivate the error indicator, and the projection unit simultaneously projects the horizontal and vertical output beams, whereby the output beams can be used to at least indicate square. 
         [0010]    The vertical projection module can be mounted relative the housing at an angle γ relative to a vertical axis of the housing such that the approximately 180° fanned output beam from the vertical projection module is rotated approximately the angle γ from a vertical orientation. In one implementation, the angle γ is approximately 15°. In another implementation, the laser emitting diode included in the vertical projection module is orientated such that the laser beam emitting therefrom has a substantially elliptical cross-section with a long axis of the ellipse orientated at an angle γ relative to a vertical orientation, such that the approximately 180° fanned output beam is rotated approximately the angle γ from a vertical orientation. 
         [0011]    In general, in another aspect, the invention features a method for projecting an indication of alignment. The method includes projecting a first laser beam and a second laser beam and collimating the first laser beam into a first collimated beam and collimating the second laser beam into a second collimated beam. The first collimated beam is incident on a first planar reflective surface and diverted approximately 90° toward an approximately 180° first partial-conical reflective surface, and reflected to form a first output beam fanning approximately 180° in a first direction. The second collimated beam is incident on a second planar reflective surface and diverted approximately 90° toward an approximately 180° second partial-conical reflective surface, and reflected to form a second output beam fanning approximately 180° in a second direction. The first output beam indicates level, the second output beam indicates plumb, and the first and second output beams together indicate square. 
         [0012]    Implementations of the invention may include one or more of the following features. The method can further include providing an error indicator to indicate an error in the accuracy of the first and second output beams as indicators of level and plumb respectively; and deactivating the error indicator, such that the first and second output beams can be used at least to indicate square. The output beams can be projected in the image of substantially straight lines. 
         [0013]    In general in another aspect the invention features an apparatus for projecting an indication of alignment, the apparatus including a housing, a projection unit and a damper to dampen pendular motion of the projection unit. The projection unit is pendulously suspended in the housing to project at least one output beam. The projection unit includes at least one projection module that includes: (1) a laser emitting diode to emit a laser beam incident on a collimator, (2) a collimator configured to collimate the laser beam into a collimated beam and project the collimated beam on a planar reflective surface; (3) a planar reflective surface orientated at an angle of approximately 45° to a path of the collimated beam projected from the collimator and configured to divert the path of the collimated beam approximately 90° and toward a partial-conical reflective surface; and (4) a partial-conical reflective surface formed from approximately 180° of an exterior surface of a cone and configured to reflect the diverted collimated beam into an approximately 180° fanned output beam. 
         [0014]    Implementations of the apparatus may include one or more of the following features. The laser emitting diode can emit a laser beam having a substantially elliptical cross-section. The collimator can be an aspheric lens. 
         [0015]    In general, in another aspect, the invention features a laser projection module. The laser projection module includes a laser emitting diode, a collimator, a planar reflective surface and a partial-conical reflective surface. The laser emitting diode emits a laser beam incident on the collimator. The collimator is configured to collimate the laser beam into a collimated beam and project the collimated beam on the planar reflective surface. The planar reflective surface is orientated at an angle of approximately 45° to a path of the collimated beam projected from the collimator and configured to divert the path of the collimated beam approximately 90° and toward the partial-conical reflective surface. The partial-conical reflective surface is formed from approximately 180° of an exterior surface of a cone and configured to reflect the diverted collimated beam into an approximately 180° fanned output beam. 
         [0016]    Implementations of the invention may include one or more of the following features. The laser emitting diode can emit a laser beam having a substantially elliptical cross-section. The collimator can be an aspheric lens. The planar reflective surface can be a plane mirror. 
         [0017]    The invention can be implemented to realize one or more of the following advantages. The use of a planar reflective surface to divert the laser beam path in conjunction with a conical reflective surface allows the tool to provide the desired functionality while requiring a relatively small footprint. The tool can be implemented in a compact and lightweight configuration, which a user can operate with one hand, leaving a free hand to make alignment marks and facilitating use in confined spaces, e.g., window and door openings. Additionally, the tool provides approximately 180° fanned output beams provided longer projected alignment images (i.e., vertical and horizontal lines projected onto a wall for example). 
         [0018]    Prior art laser alignment tools typically required precise adjustments between the diode and the optics within a module during manufacturing and post-assembly. Although assembling the laser alignment tool described herein will require some adjustments, e.g., to set the vertical and horizontal projection modules perpendicular to each other as well as level and plumb, the need for the somewhat tedious adjustments required for some prior art tools is alleviated. The laser alignment tool includes an error indicator permitting a user to operate the tool to accurately indicate level, plumb and square alignment, knowing the tool will be disabled, or the user will be otherwise notified, if the tool is positioned such that indications of level and plumb alignments may be inaccurate. A user has the option of deactivating the error indicator, to permit use of the tool to indicate square alignment when the tool is in virtually any position, including positions that would not accurately indicate level and plumb. 
         [0019]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description, the drawings, and the claims. 
     
     
       DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a laser-based tool and a schematic representation of two output beams. 
           [0021]      FIG. 2A  is a front view of the laser-based tool of  FIG. 1  tilted to one side. 
           [0022]      FIG. 2B  is a side view of the laser-based tool of  FIG. 1  tilted to one end. 
           [0023]      FIG. 3  is a schematic representation of a laser-based tool projecting alignment lines onto a floor surface. 
           [0024]      FIG. 4  is a rear view of the laser-based tool of  FIG. 1 . 
           [0025]      FIGS. 5A and 5B  show a support frame of a laser-based tool. 
           [0026]      FIG. 5C  shows a projection unit of a laser-based tool. 
           [0027]      FIG. 6  is a side view of the laser-based tool of  FIG. 1  including a schematic representation of two output beams. 
           [0028]      FIG. 7  is an exploded view of a horizontal projection module. 
           [0029]      FIGS. 8A and 8B  are schematic representations of the paths of laser beams within the horizontal projection module shown in  FIG. 7 . 
           [0030]      FIG. 9A  is a schematic representation of a path of a laser beam within a vertical projection module. 
           [0031]      FIG. 9B  is a schematic representation of a path of a laser beam within a vertical projection module mounted at an angle. 
           [0032]      FIGS. 10A and 10B  are schematic representations of a path of a laser beam in a projection module. 
           [0033]      FIGS. 11A and 11B  are views of a projection unit and a portion of a support frame. 
           [0034]      FIGS. 12A-C  are top, front and side views respectively of a laser-based tool. 
       
    
    
       [0035]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0036]    Referring to  FIG. 1 , a laser alignment tool  100  is shown capable of indicating level, plumb and square alignment. The tool  100  includes a housing  102  having a window  116 , from which output beams  118 ,  120  are projected. The beams  118 ,  120  have a substantially perpendicular arrangement with each other and form vertical and horizontal alignment indicators respectively. In one implementation, an alignment indicator can be the image of a substantially straight line on the surface against which an output beam is projected. In another embodiment an alignment indicator can be a point of light on a surface against which the output beam is projected. Alternatively, two or more points of light can be projected, connected by an imaginary straight line, the straight line being an alignment line, and the points of light used as alignment indicators. 
         [0037]    The vertical alignment indicator  118  can be used to indicate plumb, the horizontal alignment indicator  120  can be used to indicate level, and both alignment indicators  118 ,  120  together can be used to indicate square. In the embodiment shown, the housing includes an upper wall  104 ; a base  106 ; side walls  108 ,  110 ; a rear wall  112 ; and a front wall  114 . The front wall  114  and portions of the side wall  108 ,  110  and upper wall  104  include the window  116 . Although in the embodiment shown, the window  116  extends across multiple faces, the vertical and horizontal output beams  118 ,  120  both emanate from a single face of the tool. Other embodiments are possible, such as a housing including rounded walls or a cylindrically shaped housing, or a differently configured window  116 , e.g., one or more circular shaped windows. 
         [0038]    The tool  100  includes a projection system or unit for projecting the output beams  118 ,  120 , wherein a light source and all necessary optical components for projecting the output beams are mounted in a fixed relationship to each other, preferably in a single unit. A self-leveling feature includes pendulously suspending the projection unit from a support frame, for example, by a gimbal mount, or other methods of pendulous suspension, such as by a spring or wire flexures, as known in the art. In one implementation, a self-aligning platform driven by a servo-motor and controlled by one or more sensors can be used. The tool  100  is preferably operated by setting the base  106  on a substantially level surface, however the self-leveling feature can allow for accurate level and plumb alignment indicators when the tool  100  is inclined within a certain range from horizontal, referred to herein as the “accuracy range”. 
         [0039]    Referring to  FIGS. 2A and 2B , the tool  100  is shown as tilted from side-to-side at an angle θ from a horizontal plane  126  ( FIG. 2A ), and tilted from front-to-back at an angle θ from the horizontal plane  126  ( FIG. 2B ). The accuracy range, meaning the range of angle θ within which the tool  100  can provide accurate level and plumb alignment indicators, depends in part on the geometry of the tool  100 . In the embodiment shown, where the tool  100  is sized to fit comfortably within the palm of a human hand, the accuracy range is between approximately 0° and plus or minus a maximum inclination in the range of approximately 4 to 7 degrees from horizontal. However, in another embodiment having a larger housing, for example, the accuracy range can be approximately plus or minus 0 to 9 degrees from horizontal. 
         [0040]    The tool  100  can include an error indicator that operates to notify a user when the tool  100  is inclined from horizontal beyond the accuracy range, thereby compromising the integrity of the plumb and level alignment indicators  118 ,  120 . The error indicator can include a cut-off mechanism that cuts off power to the laser emitting diodes when the cut-off mechanism senses the housing is inclined beyond the accuracy range, ceasing projection of the output beams. An example of such a cut-off mechanism is described in U.S. Pat. No. 5,144,487, issued Sep. 1, 1992, for “Portable Laser Device for Alignment Tasks” to William Hersey, the entire contents of which are hereby incorporated by reference. In this manner, the user is notified that the tool  100  is inclined beyond the accuracy range, and the tool  100  is effectively disabled, thus not allowing the inadvertent use of inaccurate level and plumb alignment indicators. A further example of a cut-off mechanism is described below in reference to  FIG. 11 . In another embodiment, the error indicator can be a mechanism causing the output beams to blink. 
         [0041]    Although the alignment indicators  118 ,  120  may not accurately indicate plumb and level when the tool  100  is inclined beyond the accuracy range, the indicators  118 ,  120  together can still accurately indicate a square alignment. That is, the alignment indicators  118 ,  120  maintain their perpendicular relationship to one another, and although not indicating true horizontal or true vertical, can still indicate a true 90° angle. A drawback of the error indicators described above is that the tool  100  is effectively disabled once inclined beyond the accuracy range, thus not permitting a user the option of using the tool  100  to indicate square alignment outside the accuracy range. 
         [0042]    To allow a user the option of using the tool  100  to indicate square alignment when the tool  100  is inclined beyond the accuracy range, the tool  100  further includes an override mechanism, allowing a user to deactivate the error indicator. The tool  100  can therefore be used to indicate square alignment when in virtually any position, without regard to the accuracy range that is relevant only to the level and plumb alignment indicators. Referring to  FIG. 3 , a use for the tool  100  when inclined beyond the accuracy range is exemplified. In this example, a user requires square alignment indicators to be projected onto a floor  130 , for the purpose of laying tiles square to one another on the floor surface. By deactivating the error indicator, the tool  100  can be inclined at 90° from horizontal, such that the window  116  is substantially parallel with the floor  130  and output beams  118 ,  120  are directed toward the floor  130 , providing square alignment indicators  132 ,  134  on the floor surface. A variety of other uses in the construction and carpentry trades, for example, are also imaginable, such as projecting alignment indicators on a ceiling for mounting lighting fixtures. 
         [0043]    In one embodiment, the tool  100  can include a user-friendly interface for interacting with a user. Referring to  FIG. 4 , the rear wall  112  of the tool  100  is shown. The rear wall has an inclined portion  138 , which includes a button  140  and a light  142 . In this embodiment, a user can operate the tool  100  as follows. Starting with the tool  100  powered down, the light  142  is not illuminated, indicating the tool  100  is in the OFF position. A first press of the button  140  powers up the tool  100  and projects the horizontal linear output beam  120 , providing a horizontal alignment indicator, with the error indicator activated. The light  142  shines green, indicating that the power is ON, and that the error indicator is activated. 
         [0044]    A second press of the button  140  turns off the horizontal output beam  120 , and projects the vertical linear output beam  118 , providing a vertical alignment indicator. The light  142  continues to shine green, indicating the power is ON and the error indicator is activated. 
         [0045]    A third press of the button  140  turns on the horizontal linear output beam  120 , projecting both output beams and providing both horizontal and vertical alignment indicators  120 ,  118 . The light  142  shines green, indicating the power is ON and the error indicator is activated. 
         [0046]    A fourth press of the button  140  causes the override mechanism to deactivate the error indicator. The output beams continue to be projected, providing both horizontal and vertical alignment indicators. The light  142  now shines red, indicating that the power is ON, but that the error indicator has been deactivated. By changing the color emitted from the light  142 , the user is notified that the error indicator is not activated, and that the tool  100  may provide inaccurate level and plumb alignment indicators, although the alignment indicators can still be used to provide square alignment. 
         [0047]    A fifth press of the button  140  powers down the tool  100 , and the light  142  does not shine, indicating the tool  100  is in the OFF position. The next press of the button  140  would start the above described cycle over again. 
         [0048]    The user interface shown in  FIG. 4  is one embodiment: however, any other convenient arrangement can be used to interact with a user, such as multiple buttons, an LCD or the like. 
         [0049]    In one embodiment, the error indicator and override mechanism can be embodied in an implementation of the tool  100  as follows. Referring to  FIGS. 5A and 5B , the tool  100  can include a support frame  200 , located within the tool housing  102 , from which a projection unit  202  can be pendulously suspended by a gimbal mount  204 . 
         [0050]    Referring particularly to  FIGS. 5A and 5B , the support frame  200  includes a generally U-shaped, rigid portion  206  forming two sidewalls  207  and a base  209 . An upper portion  208  is attached within the U-shaped portion  206 , for example, by using screws, and provides a receiving surface for a gimbal mount  204  used to suspend the projection unit  202 . The U-shaped portion  206  and upper portion  208  are preferably made from a metal, such as aluminum, that is sufficiently rigid, yet lightweight. Other metals can be used, for example, stainless steel. Soft, padded members can be positioned on either side of the upper portion to absorb impact on the tool  100  typical to its use in the construction and carpentry trades. An energy absorbent stop[see  212  in  FIG. 11A ] can be positioned within the U-shaped member to limit motion of the projection unit  202  when suspended within the support frame  200 . The padded members and stop can be made of rubber, such as 40 durometer EPDM rubber. A magnet  260 , used in a damping system described further below, is affixed to the interior of the base of the U-shaped portion  206 . 
         [0051]    Referring particularly to  FIG. 5C , the projection unit  202  includes a vertical projection module  214  and a horizontal projection module  216 . The vertical projection module  214  projects beam  118  and fans approximately 180°. In the implementation shown, the beam  118  is projected at an angle of β from vertical, as shown more clearly in  FIG. 6 . This implementation allows the plumb beam to project overhead and behind the tool  100 , even when the tool  100  is held relatively close to a surface (e.g., a wall) directly in front of the tool. Having the beam project overhead and behind in this manner can be desirous for performing certain tasks. In other implementations, the beam  118  can be projected with no angle (i.e., β=0) or can be projected downwardly, i.e., in the opposite direction. The angle β can vary depending on the desired projection path of the beam  118 . In one implementation, the angle β is approximately 15°. 
         [0052]    The horizontal projection module  216  projects beam  120  and fans approximately 180°. Referring to  FIG. 7 , an exploded view of the horizontal projection module  216  is shown. The horizontal projection module  216  includes a laser emitting diode  218  mounted within a diode mount  220 . The diode mount  220  couples to a lens mount  222  used to mount a lens  224 . In this implementation, the lens  224  is an aspheric lens. The lens  224  and lens mount  222  couple to the main body  226  of the horizontal projection module  216 . The path of a laser beam emitting from the laser emitting diode  218  is deflected by a flat mirror  228  and a reflective conical surface  230 , as described in further detail below. 
         [0053]    In one implementation, the laser emitting diode  218  can be selected to emit visible light having a wavelength between about 630 to 650 nanometers (nm), such as model DL-4038-31 available from Sanyo Semiconductor Corporation in San Diego, Calif., and model HL6332G available from Hitachi Semiconductor (America) Inc. of San Jose, Calif., which emit visible light at a wavelength of 635 nm at a power of 10 milliwatts. In other implementations, different diodes can be used. 
         [0054]    Referring to  FIG. 8A , an enlarged side view of the horizontal projection module  216  is shown with the path of the laser beam emitted from the laser emitting diode  218  illustrated. For illustrative purposes, not all elements of the horizontal projection module  216  are shown, for example, the mounting elements  220 ,  222  and the main body  226  are not displayed. The laser beam  232  initially emits from the laser emitting diode  218  and is incident on the lens  224 . In this implementation, the laser emitting diode  218  emits an elliptically shaped laser beam  232  that is expanding at approximately 8 degrees in one axis and 30 degrees in a perpendicular axis. Passing the laser beam  232  through the lens  224  has the effect of producing a collimated beam  234  maintaining the elliptical cross-section, as depicted more clearly in  FIG. 8B . The beam  234  is incident on the plane mirror  228  at an angle Δ. In the implementation shown, the angle Δ is approximately 45°. If the angle varies substantially from 45°, the intensity of the beam incident on the partial-conical reflective surface  230  is affected. The plane mirror  228  diverts the beam  234  downwardly toward the partial-conical reflective surface  230 . The partial-conical reflective surface  230  fans the beam  234  out into the approximately 180° fanned output beam  120 . 
         [0055]    In the implementation shown, the partial-conical reflective surface  230  is approximately one half (i.e., 180°) the surface of a cone  236 . In another implementation, a semi-cone can be used, since only half of the surface of a full cone is used. The cone  236  is positioned beneath the plane mirror  228  such that the beam  234  is incident on only the front face of the cone  236 , the front face being the partial-conical reflective surface  230 . By only reflecting the beam  234  from the partial-conical reflective surface  230  (i.e., the front face), the beam  234  is fanned out by only 180°. By contrast, if the beam  234  were incident on the apex of the cone  236 , the beam  234  would fan out 360°. In this implementation, since the fanned output beam  120  projects in front of the tool  100 , the remaining 180° of a fanned 360° beam would be wasted, i.e., reflected back into the tool  100 , and the output beam  120  would be less intense than if the beam  234  is entirely reflected off of just the front face of the cone  236 . Accordingly, by positioning the cone  236  beneath the plane mirror  228  as shown, so that the beam  234  is incident on just the front face of the cone  236 , the resulting fanned laser beam is concentrated in the desired 180° fanned direction. 
         [0056]    In other implementations, more or less of the surface of the cone can be used to reflect the beam  234  either less than or greater than 180°, by shifting the position of the cone  236  relative to the plane mirror  228 . 
         [0057]    The path of a laser beam within the vertical projection module  214  is similar to what was described above with respect to the horizontal projection module  216 , however, the entire module is rotated by approximately 90 degrees about its own axis. Referring to  FIGS. 9A and 9B , the laser beam path for the vertical projection module  214  is shown. Again, for illustrative purposes, not all elements of the vertical projection module  214  are shown, in particular, the mounting elements and the main body are not displayed. The laser beam  238  initially emits from the laser emitting diode  240  and is incident on the lens  242 . In this implementation, the laser beam  238  has an elliptical cross-section. Passing the laser beam  238  through the lens  242  has the effect of producing a collimated beam  244 , maintaining the elliptical cross-section, as depicted more clearly at reference numeral  245 . The long axis of the beam  244  is orientated vertically, as compared to the long axis of the beam  234  in the horizontal projection module  216 , which is orientated horizontally. The beam  244  is incident on the plane mirror  246  at an angle. In the implementation shown, the angle is approximately 45°. The plane mirror  246  diverts the beam  244  laterally toward the partial-conical reflective surface  248 . The partial-conical reflective surface  248  fans the beam  244  out into the approximately 180° fanned output beam  118 . 
         [0058]    As described above in reference to the horizontal projection module  216 , in the implementation shown, the partial-conical reflective surface  248  is approximately one half (i.e., 180°) the surface of a cone  250 . In another implementation, a semi-cone can be used, since only half of the surface of a full cone is used. The cone  250  is positioned relative to the plane mirror  246  such that the beam  244  is incident on only the front face of the cone  250 , the front face being the partial-conical reflective surface  248 . By only reflecting the beam  244  from the partial-conical reflective surface  248  (i.e., the front face), the beam  244  is only fanned out 180°. 
         [0059]    Referring to  FIG. 9B , in one implementation, the vertical projection module  214  can be orientated at an angle γ relative to vertical. As result, the projected output beam  118  angles upwardly at the angle γ. As discussed above, angling the output beam  118  in this manner provides the plumb line not only directly in front of the tool  100 , but above and behind the tool  100 . In some applications, having the plumb beam projecting overhead (e.g., onto a ceiling) can be desirous. In one implementation, the angle γ can range between approximately 0 to 30 degrees. 
         [0060]    Referring to  FIGS. 10A and 10B , an angled output beam can alternatively be achieved by rotating the laser emitting diode  240  relative to the plane mirror  246 , rather than angling the entire vertical projection module  214 .  FIG. 10A  shows a projection module, which can be either the vertical or horizontal projection module. For illustrative purposes, we shall describe the figures in reference to the vertical projection module  214 . In  FIG. 10A , the laser emitting diode  240  is orientated parallel to an axis  241  representing a vertical orientation of the output beam  118 . The laser beam is diverted by the plane mirror  246 , incident on the partial-conical reflective surface and reflected as the substantially 180° fanned output beam  118  having a vertical orientation. In  FIG. 10B , the laser emitting diode  240  has been rotated such that the long axis of the elliptically shaped laser beam exiting the lens  242  is at an angle as compared to the long axis of the laser beam shown in  FIG. 10A , i.e., at an angle relative to a vertical orientation. As a result, the laser beam is incident on a different portion of the cone  250 , although still only over a span of approximately 180°. The reflected, fanned output beam is therefore still fanned at substantially 180°, but angled by the same angle relative to the output beam shown in  FIG. 10A , i.e., angle Φ. 
         [0061]    The fanned vertical and horizontal linear output beams  118 ,  120  project vertical and horizontal alignment indicators respectively. The brightness of the projected alignment indicators can vary, depending in part on the strength of the laser beam emitted from the laser emitting diode. An implementation using the laser emitting diodes described above can produce highly visible, bright alignment indicators. 
         [0062]    In the implementation described above, the laser emitting diodes  218  and  240  emitted laser beams with an elliptical cross-section. In other implementations, the emitted laser beams can have different cross-sections, e.g., circular or oval. In the implementation described above a plane mirror  228  and  248  was used to divert the laser beams emitted from the laser emitting diodes  218 ,  240 . A plane mirror is just one example of a planar reflective surface that can be used to divert the laser beams and other configurations of planar reflective surfaces can be used. 
         [0063]    In the implementation described above, the laser beams emitted from the laser emitting diodes  218 ,  240  were collimated by a lens  224 ,  242 , and in particular an aspheric lens. In other implementations, different configurations of optical elements can be used to collimate the laser beams. 
         [0064]    In the implementation described above the partial-conical reflective surfaces  230 ,  248  were formed on cones  236 ,  250 . The cones  236 ,  250  can be full cones, as shown, or can be partial cones. In one implementation, the cones  236 ,  250  are made from diamond turned aluminum. Other configurations of cones can be used, for example, a cast glass cone or a mirrored glass cone. The apex angle of the cones  236 ,  250  is substantially 90°. If the apex angle varies significantly from 90°, the resulting output beams tend not to be planar, but rather flare up at the edges. 
         [0065]    In the implementation described above, two projection modules were included, both a vertical and horizontal project module  214 ,  216 . In other implementations, more or fewer projection modules can be included. The configuration of the projection modules relative to one another can vary. For example, although in the implementation described, both output beams emanated from a single face of the tool, in other implementations it may be desirable to have one or more output beams emanate from different faces of the tool. 
         [0066]    An important feature of a portable laser alignment device is to contain the device within a relatively small housing. The tool  100  is configured such that the tool  100  can fit comfortably within the palm of a human hand, and is sufficiently lightweight to allow a user to operate the tool while holding it in one hand, and conveniently carry it on a tool belt when not in use. The use of a planar reflective surface to divert the laser beam path plays an important role in allowing the tool  100  to be configured into such a small footprint. Both the vertical and horizontal output beams can be projected from the same face of the tool, allowing for a more compact design. 
         [0067]    The projection unit  202  can include a damping system to limit pendular motion when the tool is set down on a surface, such as the damping system described in U.S. Pat. No. 5,144,487, previously incorporated herein by reference. Referring again to  FIG. 5B , such a damping system can include the magnet  260  secured to the inside of the base  206  of the support frame  200 , and a copper damping plate  264  attached to a lower surface of the projection unit  202 . The damping plate  264  is formed and positioned such that a precise gap  270  is maintained at a predetermined width when the damping plate  264  is in motion over the magnet  260 . In one implementation, the gap  270  is approximately 0.025 of an inch. 
         [0068]    The gap  270  is sufficiently small such that motion of the damping plate  264  causes eddy currents to be generated in the plate  264 . Interaction of the eddy currents in the damping plate  264  with the magnetic field of the magnet  260  causes damping of pendular motion of the projection unit  202 . The damping force may depend on the mass and thickness of the magnet  260 , the dimension of the gap  270  and the thickness of the copper plate  264 . Preferably the magnet  260  is a neodymium magnet approximately three-quarters of an inch in diameter and a quarter of an inch thick. The damping plate  264  is preferably three-quarters of an inch thick and has a maximum diameter of 0.625 inches at its widest point and a minimum diameter of 0.500 at its narrowest point. Other types of magnets may be used and other arrangements of one or more magnets may be used to accomplish the damping function, as is known in the art. In addition, other shapes and/or materials can be used for the damping plate, as is also known in the art. Alternatively, the “plate” can be an integral portion of the projection unit. 
         [0069]    The laser emitting diodes  218 ,  240  can be powered by a rechargeable battery located in a battery compartment within the housing  102 . The battery is connected to the diodes  218 ,  240  by a connector extending from the battery terminal. The connector can be an ultraflexible micro-miniature conductor obtainable from New England Electric Wire Company of Lisbon, N.H. The connector is lead to an on-off switch attached to the housing  102 . The connector is then lead through the gimbal mount  204  and connected to the laser emitting diodes  218 ,  240 . Leading the connector through the gimbal mount  204  is one technique to ensure the connector has a negligible effect on the balance of the projection unit  202 . 
         [0070]    Provision is made to prevent excessive motion of the projection unit  202  when the tool  100  is set down on a surface which is far from level. Referring to  FIG. 11A , an energy absorbent stop  212  is positioned such that when the tool  100  is inclined at approximately plus or minus seven degrees (7°) or greater from the horizontal, the damping plate  264  contacts the stop  212 , thus limiting further relative movement between the projection unit  202  and the support frame  200 . 
         [0071]    As discussed above, the tool  100  can include a cut-off switch that will cut off power to the laser emitting diodes  218 ,  240  when the housing  102  is inclined in any direction plus or minus a predetermined angle from horizontal. In the embodiment shown, the predetermined angle can be approximately plus or minus 6°, however, the angle can vary depending on the geometry of the tool  100 , and, as already discussed above, can be in a range of approximately plus or minus 4 to 9 degrees. 
         [0072]    Referring to  FIGS. 11A and 11B , views of the support frame  200  and the projection unit  202  are shown. More particularly, in  FIG. 11B , a partially exploded view of a portion of the support frame  200  and the projection unit  202  and is shown. The cut-off mechanism can include a wire flexure  272  attached to and protruding above the upper portion of the projection unit  202 . The cut-off mechanism further includes a small metal plate  274  attached to the top of the support frame  200 , the plate  274  including an aperture  276 . The aperture  276  is sized and positioned such that the wire flexure  272  projects through the center of the aperture  276  when the projection unit  202  is suspended from the support frame  200 . The wire flexure  272  carries a charge from the projection unit  202 , which is charged due to the rechargeable battery used to power the laser emitting diodes  218 ,  240 . When the housing  102  is inclined beyond the accuracy range, for example 7° from horizontal, the wire flexure  272  contacts the metal interior of the aperture  276 , which in essence behaves as a contact switch, indicating to the laser power drive that power to the laser emitting diodes  218 ,  240  should be cut-off, which can be accomplished, in one example, by conventional digital logic. Other embodiments are possible using different cut-off switches, for example, an omni-directional mercury switch. 
         [0073]    As discussed above, the tool  100  includes an override mechanism to allow a user to deactivate the cut-off switch described above. As already described with reference to  FIG. 4 , in one implementation, the user can deactivate the cut-off switch by pressing a button electrically connected to a circuit board mounted to the central core of the projection unit  202 . Digital circuitry within the circuit board can be used to deactivate or reactivate the cut-off switch in response to an electrical input received from the button. Other means for deactivating the cut-off switch can also be used, for example, firmware. The circuit board can also control power to the laser emitting diodes  218 ,  240 . 
         [0074]    As discussed above, using the plane mirrors in conjunction with the conical reflective surfaces to direct the laser beams, combined with the damping system, advantageously allows the tool  100  to be embodied within a relatively compact housing with a relatively low overall weight. Referring to  FIGS. 12A-C , in one embodiment, the tool  100  can be dimensioned to have a height X of approximately 3.3 inches, a width Y of approximately 2 inches and a length Z of approximately 2.8 inches. In this configuration, the tool  100  can have a tool weight of approximately 10 ounces. 
         [0075]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.