| 摘要 |
<p>The invention relates to an edge sensing apparatus for a running web of material with a support on which at least one sensing element is arranged. Known apparatuses of this type have either a mechanical sensor arm which actuates electrical contacts when there is a deviation or an opto-electronic sensing element which scans the edge of the web of material without contact. When the mechanical sensor arm is used, it is difficult to derive exact signals which indicate the movement of the edge in a very small space without convergence. Opto-electronic sensing elements, on the other hand, cannot be used with certain web materials or web edges. According to the invention, this is avoided by providing a digital sensing element and a mechanical sensing element, the digital sensing element plotting the edge indirectly via the mechanical sensing element when the latter is in an operating position and plotting the edge of the web of material directly when the mechanical sensing element is moved from the operating position into a passive position.</p> |
