1. Field of the Invention
This invention generally relates to apparatus for aligning objects and more particularly to a portable system utilizing a laser for enabling an operator to quantify alignment and misalignments precisely.
2. Description of Related Art
There are a number of applications where it is important to obtain precise alignment between two elements or among three or more elements and particularly to quantify any misalignments that may exist. Examples in which such alignments are beneficial include aligning two or more machine elements, such as machine beds or shafts to a common plane or axis. Another example includes measuring surface flatness to ascertain any variance of a surface from a common plane.
The need for such alignment applications has led to the development of different apparatus specifically designed for an application. U.S. Letters Pat. No. 3,603,688 (1971) to Smith-Vaniz depicts an alignment apparatus with a laser light source and a remote target object. The target object includes an array of photocells for sensing and indicating the displacement of a centroid of an impinging laser beam from a reference point in the array. The laser light source establishes a beam pattern of contrasting light intensity indicative of the centroid of the beam. The target photocell array is designed to maximize sensitivity. The annunciation of any misalignment is in the form of two meters that indicate displacement in x and y directions. The alignment apparatus is used by directing a laser beam along a projection axis and then moving the object until the meters null. There appears to be no provision in such a system for providing surface flatness or other similar measurements or for providing a direct reading of the amount of any misalignment by numeric display.
U.S. Letters Pat. No. 3,723,013 (1973) to Stirland et al. discloses an alignment system that utilizes intermediate photodetectors with central apertures and a terminal photodetector. Each photodetector has four quadrants of active area. The centers are aligned on an axis of a laser beam. Output signals are utilized to indicate alignment or the degree of misalignment of the centers with respect to the axis of the laser beam. Such a system seems to require multiple detectors that can become costly to implement.
U.S. Letters Pat. No. 3,826,576 (1974) to Stewart discloses an alignment system in which a laser beam passes through a lens assembly to create a focusable diverging planar light beam that is projected tangentially to an object surface and onto a screen rearwardly of the object. Any increase in the size of the object into the beam interrupts the beam image on the screen. While such a system does provide some indication of surface flatness, it appears it will only detect extensions of the surface into the beam. Areas of reduced dimension would seem to go undetected. Moreover, this system does not appear to quantify any misalignment.
U.S. Letters Pat. No. 5,233,761 (1993) to Guaraldi et al. discloses a method for aligning multiple machine units by positioning precisely located, cylindrical alignment markers in the various elements to be aligned. A laser beam can then be directed along a desired line and through axial bores in the markers. The various machine elements are positioned until the laser beam passes through all alignment markers. Alternatively, when end surfaces of the alignment markers lie in a common plane, the laser beam can be directed through radial bores found in the markers. Nothing in this patent discloses any quantification of misalignment.
U.S. Letters Pat. No. 5,507,097 (1996) to Duey et al. discloses an apparatus for inspecting machine tie bars. A laser is mounted to project a laser beam normally to a support and parallel to the desired axis of a tie bar. A receiver in the form of a photocell target mounts on the tie bar and generates voltages that are processed in a separate control unit and computer to provide angular and lateral deviations of the laser beam from the axis of the target thereby to indicate tie bar straightness and squareness.
Each of the foregoing references appears limited to a specific application. For example, the Smith-Vaniz patent seems directed primarily to moving an object to a particular location, but does not seem readily adapted to measure surface flatness. Moreover, such alignment systems generally require a trained operator. Given the single-purpose designs and requirements for training and the expense of such systems, many companies can not afford to purchase such equipment and employ such individuals on a full-time basis. Consequently, they employ a subcontractor to perform alignments. The use of subcontractors oftentimes introduces scheduling problems and intolerable delays which further increases the costs of the alignment procedure.