The European Norm of Standards has defined integrated safety technology at the servo drive level that is scalable from drive interlocks to "safety-on-board" safe motion. Implementing safety standards at the drive provides the shortest reaction time, less than two msec, easy installation from discrete I/O to safety bus systems, and less work for machinery OEMs. Safe motion limits axis movements by defining axis parameters such as torque and speed during selected machine states. Safety-relevant data is transferred and handled in two channels using independent microprocessors. If a discrepancy of monitored parameters is detected in one of the channels, the drive system goes to a safe status.
How will safe motion in the drive enhance productivity? Safe motion reduces downtime because operators can make machine changes more quickly and easily, and remove jams without going through the lock-out procedures we have today. During setup, when most injuries occur, operators can be in the work zone and setup the machine faster and more easily than we can today. Safe motion boosts machine safety because most crashes, plus damage to workpieces and fixturing, happen during setup mode. Setup of the machine, switching product recipes or batches and making teach points in robotics applications are the types of situations where productivity will be improved.
How has Europe taken safe motion and built it into a specification? European companies needed to set standards in a specification that could be used throughout Europe without dealing with every local regulation on wiring practices and mechanical lockout procedures. They are trying to balance productivity, human safety and machine safety by establishing guidelines and training everyone in the standards. Hopefully we'll see it gaining more support in the U.S.
What has the approach been in the U.S.? OSHA and the ANSI machinery committee recognize that this type of safety system will improve productivity and machine safety. But the guidelines have not been put into their documents yet. In the U.S., there are many regulatory bodies and we're behind.
A strong push in the U.S. will come from the big users who are looking at this technology anyway. They will ask, "will we have a safer environment and overall safer machines, reduce damage to machines and have more productive equipment?" When they see the answer is "yes," I believe they will push the regulatory bodies to incorporate safe motion into their standards.
What changes in machinery safety guidelines are important at this point? The biggest thing is for software/firmware to be recognized as a redundant system that is safe for both humans and machinery. The idea behind safe motion is that in the drive itself you have all of the monitoring conditions for the different states the machine can go into. Maximum torques, speeds and travel limits are all set within the drive, and redundantly monitored. We need more education to help people understand how this works.