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Safe Motion Technology -
Safe motion technology is available for the machines themselves as one layer in the mechanical architecture [8]. Safe motion technology deploys an independent check that the robot is performing as commanded. This second independent check on top of the machine’s traditional controller is so reliable that it is internationally recognized as an approved approach to safety when deployed properly. Note this check is that the machine is performing as commanded, it is not a check that the machine is commanded to perform safely. This very much points out the need for higher-level safety systems that verify the machine is commanded to move, or not move, in a safe fashion. Operational modes currently supported by the safe motion technology include:
• safe operational stop - drives are in
standing still, but all control functions are still active and motion at any joint triggers an automatic safety response;
• safe reduced velocity or increment - a reduced velocity or a limited increment is enabled and exceeding limited velocity or increment values triggers an automatic safety response;
• safe direction - a safe direction of movement is monitored and changes in the monitored direction of movement is followed by an automatic safety response;
• safe positioning - a safe absolute position range is defined and leaving the allowed position range is followed by an automatic safety response.
The notion of layered safety deploys different facets of safety across different time frames and different sensing technologies. Components of safety in the long term include installation, training, support, hardware maintenance, software maintenance and finally decommissioning, dismantlement and disposal. Components of safety in the medium term typically focus on trajectory scaling with vision, motion and presence sensors used to create zones that define allowable speeds and behaviors. Finally, we find reactive control that comes into play in the immediate pre- and post-contact time frames. The pre-contact sensors include infrared, ultrasonic, capacitive and inductive sensors.
Pre-contact sensors are found in automatic pedestrian doors. The post-contact sensors include force and torque sensors at the tool, force and torque sensors at the joints, and tactile sensors on the surface of the structure. Note that simply stopping motion is not necessarily a safe response.
Ultimately, the collaborative robotics safety challenge becomes a multi-criteria decision making problem. Automatic decision making based on input from these different sensing technologies across the different spans of time presents complex issues of data normalization and multi-criteria fusion [9].
Conclusion - Collaborative robotics is undeniably upon us. We see it in applications ranging from robots and people packing boxes together in huge warehouses; to nurses, doctors and remote-controlled robots working together in the operating room. These applications demand a layered, multi-criteria approach to robotic system safety that leverages lessons learned from experience already gained in collaborative robotics.
REFERENCES
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