Development and Application of a Safety-Related Control System Implementing a Safety Function for a CNC Milling Machine

The safety of small CNC (Computer Numerical Control) milling machines is typically ensured through organizational measures. However, when such a CNC milling machine is used in a manner that may involve contact with untrained individuals or children (e.g., for demonstration purposes), it becomes essential to ensure safety through appropriate technical measures. The required safety can be achieved by implementing safety functions to mitigate identified hazards. This paper addresses the design and application of a Safety-Related Control System (SRCS) that implements safety functions for a small CNC milling machine. A notable aspect of this implementation is that commonly available sensors (e.g., optical barriers) with a defined Safety Integrity Level (SIL) are unsuitable for small CNC milling machines in size, cost, and performance parameters. For instance, these sensors might fail to detect the entry of a child’s hand. Consequently, it was necessary to design suitable custom sensors for realizing an SRCS. The paper also demonstrates the achieved SIL for the implemented safety functions.