| 摘要 |
PURPOSE:To confirm the residual amount of a tape by irradiating light onto the surface of a magnetic tape and detecting and calculating the displacement of a reflected light where the reflecting angle is changed in response to the change in the number of turns of the tape around a reel. CONSTITUTION:The incident angle and the reflected angle of a laser ray 24 are changed in response to the change in the radius of winding of the magnetic tape 21 and the incident position to a photodetecting sensor 25 is displaced linearly. This displacement is expressed as a function of radius of the tape. Thus, this function is set in an arithmetic circuit 31, the incident position of the laser ray 24 in the photodetecting sensor 25 is converted electrically and inputted to the circuit 31 to calculate the radius of winding of the magnetic tape 21 of a supply reel 2 and obtain the residual amount of the tape. |
