Patent attributes
A velocity deviation measuring device includes: a laser driver that causes a semiconductor laser to oscillate; a counting portion that counts run lengths of binary signals wherein interference waveforms included in the output of a photodiode that converts the output of the semiconductor laser into an electric signal have been binarized; and a calculating portion that calculates the deviation in the surface velocity of a web from the counting result by the counting portion. The counting portion binarizes the interference waveform synchronized to a sampling clock, measures the respective run lengths of the binary signal during a reference interval and a comparison interval, creates respective frequency distributions of the run lengths for the reference interval and the comparison interval, and calculates, respectively, for the reference interval and the comparison interval, the total numbers of run lengths that are at or above a threshold value Th, from the frequency distribution.
