Apparatus and method for detecting when a web is not being perforated

摘要

The present invention provides a web perforating apparatus which includes a system for detecting and indicating when a blade in the apparatus is broken, dull or otherwise not perforating the web. The apparatus is typically used with rewinders or other similar machines that produce perforated sheets of products, such as paper, using sets of stationary anvil blades and rotating perforating blades. The apparatus comprises at least one anvil including a blade holder and an anvil blade which is positioned within the blade holder. The blade holder is formed of an insulating material for electrically isolating the anvil blade from the machine frame of the rewinder. An electrical conductor is coupled to the anvil blade for supplying an electric current to the anvil blade from a current source. The apparatus also includes at least one grounded perforating blade for moving relative to the anvil blade and cooperating with the anvil blade to perforate the web at predetermined points along its length. The perforating blade will contact the anvil blade after perforating the web. A closed circuit is formed and maintained along the anvil blade at points where the blades are in contact with each other. The apparatus further includes means for detecting if a closed circuit has been formed and maintained along the anvil blade when the perforating blade moves into a position where the blades should contact each other.