Optical: systems and elements – Collimating of light beam
Reexamination Certificate
2000-03-09
2001-09-18
Mack, Ricky (Department: 2873)
Optical: systems and elements
Collimating of light beam
C033S286000
Reexamination Certificate
active
06292303
ABSTRACT:
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
Casella Anthony J.
Hamar Laser Instruments, Inc.
Hespos Gerald E.
Mack Ricky
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