| 摘要 |
A method and apparatus for controlling the speed of a traveling web being driven along a path by means of first and second drive rollers located at spaced positions along the path. An emitter device is provided for directing a radiation signal at the traveling web at a predetermined location along the path between the first and second drive rollers so as to be reflected thereby, and a detector device is provided for detecting the reflected radiation signal and for generating a position indication signal indicative of the position of the detector relative to the traveling web at the predetermined location. In response to the position indication signal, the detector device is caused to move so as to maintain a predetermined position with respect to the traveling web at the predetermined location. This movement of the detector in turn causes an appropriate control device to control the speed of the first drive roller relative to the speed of the second drive roller so as to maintain a predetermined relationship between the speeds of the first and second drive rollers. By utilizing this type of arrangement in which a radiation signal is reflected by the traveling web itself, it is possible to position the emitter and/or detector within the field or range of movement of the path along which the web travels.
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