Contouring objects which have a great deal of surface relief is often a challenge difficult to address with standard techniques because of the dynamic range involved. In particular, to produce a moire pattern over a large depth range requires a large depth-of-field and hence fairly course grating patterns. Removing the grating image from the resultant moire pattern is difficult since the grating is typically clearly resolved and comparable in period to the moire pattern. This paper describes a large depth-of-field moire projection system which uses remote reconstruction of the more fringes. The reconstruction system removes the grating lines via optical processing techniques, then analyzes the resulting clean moire using phase shift analysis within the optical processor. The output of the optical filtering is very high quality moire data over large depth ranges without any grating pattern present to disrupt the analysis. Potential application of this approach for use with photographic based field measurements is discussed.
The measurement of part diameters is an important factor in metal turning operations, increased production demands have suggested the use of methods that adjust subsequent cuts depending on the previous operations. This paper describes the design of a laser based gage made specifically for measuring parts on the machine tool to a high accuracy. The tri-beam gage uses three beams of light to measure the local curvature of the part in a manner similar to a V-block gage. The diffraction of the light beams that touch the sides of the part are sensed by a detector array. The distinctive diffraction pattern is correlated to locate the edge of the shadow to a very high precision. The properties of this design include: calibration that is independent of the machine tool scales, non-contact damage free operation, high speed of measurement, low cost of the gage, and the ability to measure parts in motion. This paper will describe the design considerations of this gage including issues of design angle of the V, light source coherence, thermal drift, noise effects, stability, and accuracy.
Phase shifted moire interferometry is one of the most effective tools for obtaining a full-field depth map. The major draw back of the technique is the two pi ambiguity which limits the measurement depth range to one fringe or requires the counting of fringes across the image. In either case, only a relative measurement is obtained, no information is available about the absolute distance to the camera. By moving the moire projection system (field shifting) the period of the moire pattern is changed allowing extraction of absolute depth information. We have built an instrument, employing field shifted moire to produce a full field depth map with 12 bits of depth resolution. The performance and applications of this instrument are discussed.