Partial Feed Detection

In applications where the press runs at higher speeds, or when the feed cycle is long, it may be impossible to stop the press in time to avoid die damage caused by misfeeds.   If the press crankshaft is past the critical angle before the material finishes feeding, the wise thing to do is to set the full feed sensor to top stop the machine to minimize the chances of sticking the press on bottom.

If you have such an application, you don't necessarily have to accept that you will crash the die on every short feed.   If fact, there's an easy way to detect some (if not most) short feeds in such applications:   Simply check the strip progression during the feed while there is still time to stop the press.

The photo below shows two proximity sensors that are being used to detect feed progression.   This die runs at a high enough speed so that there is not sufficient time to stop the press by the time the feed is complete.

The sensor in the background detects full feed progression, and is set to top-stop the machine in the event of an error.   The sensor in the foreground is located so that it detects the strip about halfway through the feed progression.   When the die is running normally, the partial feed sensor will detect the strip during the progression before the critical angle.   This sensor is set to emergency-stop the press.

This arrangement is effective at preventing die damage due to misfeeds because short-feeds are much more common than over-feeds, and most causes of short-feeds (such as roll slippage, improper setup, and partially pulled slugs) occur at the beginning of the feed cycle.