An optoelectronic apparatus and a technique for its operation have been developed to facilitate and accelerate the measurement of distances of the order of tens of feet to within error limits of about ±1/8 in. (about 3 mm). In the original application, the distance to be measured [≈ 66 ft (≈20 m)] is that between the axes of rotation of the front and rear tires of the space shuttle orbiter as it rests in a ground-based processing facility. Previously, this distance was determined in a tedious procedure that involved measurements of component horizontal distances between floor points found by dropping plumb bobs. (This distance is used, along with other measurements, to locate the center of gravity of the orbiter.) The apparatus and technique could also be used for similar purposes in other settings; for example, to measure perpendicular distances between wall frames in situations in which tape measures cannot be used, to establish fence lines, or to lay out football grids.
The figure illustrates the apparatus and its use in the original application, in which the rear tires rest on the floor and the front tires rest on a platform about 3 ft (≈0.9 m) above the floor. The major components of the apparatus are (1) a laser rangefinder and (2) laser line projectors that include two battery-powered laser-diode modules with collimating optics. Each laser-diode module generates a continuous-wave beam with a power of 3 mW at a wavelength of 670 nm. The modules are aimed to point the beams downward, and the beams are made to pass through a cylindrical diverging lens to spread the beams into fans oriented in a nominally vertical plane; the modules are aligned to project coincident vertical lines as viewed from the side and collinear horizontal lines as viewed from the top.
The rangefinder is aligned precisely with respect to the laser-diode modules and the diverging lens so that the line of sight of the rangefinder is perpendicular to the plane defined by the beams from the laser-diode modules. This line of sight is thus nominally horizontal.
The apparatus is mounted on a tripod between the rear tires, with the rangefinder at approximately the height of the front tire hub. (Exact matching of heights is not necessary in this application because the geometry is such that even at a height difference as large as a few inches, the difference between the horizontal distance and the measured distance is less than the allowable error of 1/8 in.) A target is mounted on the front tire hub. The position and orientation of the apparatus are adjusted until the bright lines projected by the fan beams strike the hubs of both rear tires and the beam from the rangefinder strikes the center of the target. Then the distance is measured by use of the rangefinder, which produces a digital readout. The measurement range is from
This work was done by James P. Strobel, Jimmy D. Polk, William D. Haskell, and Robert C. Youngquist formerly of I-NET, Inc., for Kennedy Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Physical Sciences category.
Inquiries concerning rights for the commercial use of this invention should be addressed to
the Technology Programs and Commercialization Office
Kennedy Space Center
Refer to KSC-11980.