| 摘要 |
<p>In the transfer of a web from reel to reel in a web/reel assembly respective speed detectors 56, 58 generate electrical pulses at rates proportional to their reel speeds for monitoring the web movement. The time to produce a given number of pulses from each reel is determined and the ratio between the measured results is utilised to provide the ratio of the speeds of the reels. Knowing other parameters characterising the type of web/reel assembly the web position can be determined from this ratio. By the use of further means, 66, 68, 80, the information can be employed to control web movement to bring the web to a required position and/or to indicate its instantaneous position. The invention has particular application to controlling and operating magnetic tapes, especially cassette tapes, e.g. to effect a high speed search for a target playback and/or recording position. <IMAGE></p> |
