Patent ID: 8446574
Filing Date: 2013-05-21
Classification: G01P,G01S

Abstract:
1. A velocity measuring device comprising: a semiconductor laser emitting a laser beam at a web that is a physical object that is under conveyance by a conveying device from a sending side to a receiving side; an oscillating wavelength modulator causing the semiconductor laser to operate so as to alternatingly be in a first oscillating interval wherein the oscillating wavelength continuously increases monotonically and a second oscillating interval wherein the oscillating wavelength continuously decreases monotonically; a detector detecting an electric signal that includes an interference waveform that is produced through a self-coupled effect between a laser beam that is emitted from the semiconductor laser and a return beam from the web; a signal extractor counting the number of interference waveforms included in the output signal of the detector during the first emitting interval and the second emitting interval; a sign applier applying a positive or negative sign to the most recent counting result by the signal extractor; a distance-proportional count calculator calculating a distance-proportional count, which is a number of interference waveforms that is proportional to an average distance between the semiconductor laser and the web, through calculating the average value of the number of interference waveforms, using a signed counting result wherein signs have been applied by the sign applier; and a velocity calculator calculating the velocity of the web from the distance-proportional count calculated by the distance-proportional count calculator; wherein the sign applier apply a positive or negative sign to the most recent counting result of the signal extractor depending on a magnitude relationship with twice the distance-proportional count calculated using the most recent counting result and a counting result prior to that counting result by the signal extractor, depending on whether or not the directions of increase or decrease of the counting results of the signal extractor match or do not match, or depending upon the change in the average value of the counting results.