Dual Check Safety - http://www.fanucrobotics.com/products/vision-software/AtoZ.aspx
DCS enables the user to save money on safety hardware and to reduce the size of the robot cell. Hardware savings are realized by the elimination of safety rings and limit switches. The cell size can be reduced by reducing the travel of the robot to the required operating space which allows the guarding to be placed closer to the robot "inside the maximum operating space of the robot". DCS also provides the ability to dynamically restrict the travel of the robot. The robot operating space can be dynamically controlled by tying external devices (such as a safety mat) to standard safety rated inputs on the robot controller.