| 摘要 |
<p>PURPOSE:To precisely detect a revolving speed of a rotary drum and a carrier speed of a magnetic tape by irradiating a tape-like medium to wrap the rotary drum and an exposed part of the rotary drum with measuring laser light by an optical system for detecting laser Doppler speed. CONSTITUTION:Laser light from a laser diode 32 is divided into two by a beam splitter 36, and is reflected by mirrors 38 and 40 and incident upon the same measuring point 48. The measuring point 48 is set on the upper periphery of the magnetic tape 12 traveling along the rotary drum 10 and also in the exposed part of an upper drum 10B under rotation on its upward side from the tape periphery. A beam reflected by the measuring point 48 is incident upon a photodetector 44, and a signal for showing the rotating speed of the rotary drum 10 and a signal for showing the traveling speed of the magnetic tape 12 are obtained at the same time from a signal of a laser Doppler frequency obtained from an output of this photodetector. Consequently, the revolving speed of the rotary drum 10 and the traveling speed of the magnetic tape 12 are controlled in simple and small size constitution.</p> |
