Abstract: A reference mark configuration for an interferometric miniature grating encoder readhead using fiber optic receiver channels is provided. The readhead includes primary fibers that provide reference mark primary signals processed to generate a reference signal with accuracy of approximately 0.2 microns. The readhead may include secondary fibers used to generate reference mark secondary signals processed to generate a reference signal with accuracy of approximately 20 nanometers. Spatial filter masks configured for the secondary fiber optic receiver channels provide two spatially periodic secondary signals arising from interference fringes outside of the receiving area of the primary fiber optic receiver channels. The secondary signals are out of phase with one another and their spatial frequency is higher than that of the primary signals. A signal crossing of the reference mark secondary signals is identified that is spatially adjacent to a signal crossing of the reference mark primary reference signals.

Abstract: A correlation function peak finding method for an image correlation displacement sensing system is provided. The method may include capturing a reference image and a displaced image, and searching for an initial peak correlation function value point (CFVP) with pixel-level resolution based on correlating the reference image and displaced images at a plurality of offset positions. Then a complete set of CFVPs may be determined at each offset position in an analysis region surrounding the initial peak CFVP. Then a preliminary correlation function peak location is estimated with sub-pixel resolution, based on CFVPs included in the analysis region. Finally, curve-fitting operations are performed to estimate a final correlation function peak location with sub-pixel accuracy, wherein the curve-fitting operations apply a windowing function and/or a set of weighting factors that is/are located with sub-pixel resolution based on the preliminary sub-pixel correlation function peak location.

Abstract: A reference mark configuration for an interferometric miniature grating encoder readhead using fiber optic receiver channels is provided. The readhead includes “primary” fibers that provide reference mark primary signals processed to generate a reference signal with accuracy of approximately 0.2 microns. The readhead may include “secondary” fibers used to generate reference mark secondary signals processed to generate a reference signal with accuracy of approximately 20 nanometers. Spatial filter masks configured for the secondary fiber optic receiver channels provide two spatially periodic secondary signals arising from interference fringes outside of the receiving area of the primary fiber optic receiver channels. The secondary signals are out of phase with one another and their spatial frequency is higher than that of the primary signals. A signal crossing of the reference mark secondary signals is identified that is spatially adjacent to a signal crossing of the reference mark primary reference signals.

Abstract: A fiber optic readhead and scale arrangement for measuring displacement provides a reference position indication. The scale includes a scale track comprising a first type of track portion providing first level of zero order reflectance, such as a grating, and a reference mark providing a second level of zero order reflectance, such as a mirror. The reference mark is configured with certain length or boundary spacing dimensions determined based on certain fiber optic receiver channel aperture dimensions in the readhead. In some configurations a fiber optic readhead and track that provides the reference position indication is separate from a fiber optic readhead and track that provides periodic incremental measurement signals. In some configurations an integrated fiber optic readhead and an integrated track structure provide both the reference position indication and the periodic incremental measurement signals.

Abstract: A correlation function peak finding method for an image correlation displacement sensing system is provided. The method may include capturing a reference image and a displaced image, and searching for an initial peak correlation function value point (CFVP) with pixel-level resolution based on correlating the reference image and displaced images at a plurality of offset positions. Then a complete set of CFVPs may be determined at each offset position in an analysis region surrounding the initial peak CFVP. Then a preliminary correlation function peak location is estimated with sub-pixel resolution, based on CFVPs included in the analysis region. Finally, curve-fitting operations are performed to estimate a final correlation function peak location with sub-pixel accuracy, wherein the curve-fitting operations apply a windowing function and/or a set of weighting factors that is/are located with sub-pixel resolution based on the preliminary sub-pixel correlation function peak location.

Abstract: An acoustic log for vessels includes a transmitter which sends a signal within a lobe region and at least two receivers provided for receiving signals reflected from a reference for determining the velocity component of a vessel relative to the reference in the measuring direction determined by the two receivers. The log further includes a transducer device with five crystals serving as transmitter and receiver elements for transmitting and receiving acoustic signals, and being arranged such that combinations in pairs of the crystals define twelve measuring directions regularly distributed around revolution.

Abstract: Apparatus for measuring a vessel's velocity relative to a reference location includes a transmitter on board the vessel for transmitting a coherent signal toward a reference location from where the coherent signal is reflected, and a receiver on board the vessel which includes at least four spaced-apart receiver transducers. The coherent signal transmitted by the transmitter is within a lobe range that is substantially common to the receiver transducers, the signals reflected by the reference location comprising at least two acoustic signals that are similar in character but different in timing from each other, the difference in timing being a function of the distance in the direction of measurement between the spaced-apart receiver transducers and further being a function of the vessel's velocity, the received signals comprising reflections from every point on the reference location within the lobe range.

Abstract: Apparatus for measuring a vessel's velocity relative to a reference location includes a transmitter on board the vessel for transmitting a coherent signal toward a reference location from where the coherent signal is reflected, and a receiver on board the vessel which includes at least two spaced-apart receiver transducers. The coherent signal transmitted by the transmitter is within a lobe range that is substantially common to the at least two receiver transducers, the signals reflected by the reference location comprising at least two acoustic signals that are similar in character but different in timing from each other, the difference in timing being a function of the distance in the direction of measurement between the spaced-apart receiver transducers and further being a function of the vessel's velocity, the received signals comprising reflections from every point on the reference location within the lobe range.