| 摘要 |
PURPOSE:To calculate and display the running amount of a tape by detecting variations in the lamination amount of the tape on both sides of the center of the small window of a cassette half through a two-split photodetector and a differential amplifier, and then processing the detection output. CONSTITUTION:A reflector 28 is irradiated with a uniform light beam through the optical system in the figure. This beam 22 passes through the interval part between winding parts of a tape, and is collected to a two-split photodetector 31 through a cylindrical convex lens 30. The photodetection surface of the photodetector 31 is split into two parts right and left, and signals which correspond to the quantities of detected light at both the parts are inputted to a differential amplifier 33. Therefore, a detection output VD is the difference signal between the left and right signals of the two-split photodetector 31. The detection output VD is processed by a center position detecting circuit 34 to calculate an intermediate position M(t), an averaging circuit 35 remove the influence of the eccentricity of a hub to obtain a mean value M, and a tape-running-time arithmetic circuit 37 calculates a tape running time (t) from the M. At this time, tape thickness (d) is set and nonlinear correction is performed to display the running time and the running amount of the tape. |
