What is the concept of safe motion? How does it apply to robotics?

Safe motion is the capability of providing motion control functions at an integrity level high enough to reliably provide risk reduction in safe dependent applications. An integrity level is the measure of the predicted failure rate of a control function. Risk, the possibility of harm in relationship to the potential degree of severity, must be reduced to a tolerable level in a safety application. A given integrity level ensures the possibility of harm occurring is sufficiently reduced to be tolerable for a safety related function. These integrity levels and design requirements are now defined in IEC 61800.

Safe motion extends the safeguarding of hazardous motion beyond the traditional dropping of power to the motors when personnel are exposed to a hazard. With safe motion, these are some of the new safe functions available by allowing power to continue to flow to the drives and to the motors:

• Safe torque off
• Safe controlled deceleration to a stop
• Safe operational stop (safe stand still)
• Safely limiting speed or torque
• Monitoring a position or maintaining a speed 

Protective measures implemented in traditional control systems such as reduced speed and hold-to-run functions can be further enhanced through this higher integrity.

In robotics, new applications are now available to the user. The international standard ISO 10218, for robotic safeguarding, is defining new applications for safe motion.

Setting safety related axis limits and defining safety zones in three dimensional spaces is allowing easier reduction of the restricted space of a robot to provide maximum clearance while minimizing the work cell.

ISO 10218 allows for collaborative operation between the robot and the human. In this application the robot may be allowed to stay in automatic, with power available to the motors and possibly continue its motion. The robot may safely limit its speed and if necessary top in a safe standstill mode (safe operational stop) while the operator works on a part in the robots gripper. A safe operational stop is characterized by the halting of motion, but keep torque output on the motors to resisting external forces. Coupled with sophisticated presence sensing technology, all the variations of this application have not been thought of yet.