US Patent 7768549 Machine safety system with mutual exclusion zone

A safety system receives access monitoring information from sensors to detect intrusion into a mutual exclusion zone by either an operator or mechanical equipment. The border of the mutual exclusion zone is segmented into portals that allow both the operator and equipment to access a common work area such as for loading material. When intrusion into one of the portals is detected, intrusion into any other selected portals triggers a safety violation. Access to the mutual exclusion zone via the other portals is prohibited until the interior of the zone is determined to be empty again.