Device for detecting jamming in a forming die - uses high voltage spark between jammed workpiece and electrode on the die

The system for detecting the presence of a workpiece in a press tool is used in automatically operating deep drawing presses, and ensures that no new blank is fed into a die before the previous workpiece has been ejected. This prevents production of scrap and protects the dies. The detector is stable against impact, dirt and heat. An electrical pulse is generated when a workpiece is still in the die and the machine is stopped. This arrangement uses an electrical spark which is generated on a jammed workpiece which acts as an electrode. This spark generates a pulse which interrupts the feed of a workpiece blank to the die. The spark is generated between the electrode (10) arranged on the edge of the die (13) and connected to a high voltage source (7) which can be a piezo crystal or an induction coil.