Three dimensional metrology – R. J. Hocken et al.

The article presents the results of research into the three dimensional measurement process using a classically designed measuring machine. This machine has been retrofitted with laser interferometers to provide a stable metric and is controlled by a minicomputer. Machine motions are programmable in a high level interactive language. Data links are provided to a larger computer for sophisticated data processing.

The authors created, with the lasers., a machine independent coordinate system based at a point. Measurements made in this reference frame are transformed in to the coordinate system of the measured object using the techniques ·of rigid body kinematics. The error terms inherent to the mechanical design {yaw, pitch, straightness, etc.) are measured over the machine volume 4811 x 2411 x 1011, on a cubic lattice of spacing two (2) inches. These error tenns are stored as matrices and used to correct the data during a measurement.

A measurement history on these error terms is being compiled. Real time instrumental drifts due to temperature and other external effects are removed using cross referenced measurement algorithms. Errors that cannot be assessed by calibration, such as axis non-orthogonality, are obtained by measuring the object in different angalar positions within the measurement volume. This technique, which we call multiple redundancy, allows the assessment of all metric errors which do not commute wHh the finite rotation matrix.