1. The industry has identified four key approaches for collaborative robot-human interaction:
Safety-rated monitored stop
Hand-guiding
Speed and separation monitoring
Power and force limiting
2. Developers will need to determine which approach or combination of approaches best fits their application.
SAFETY RATED MONITORED STOP
1. The safety-rated monitored stop works well in applications where the operator interacts with the robot only under specific conditions, such as loading or unloading the robot’s end-effector or performing inspections on work in progress.
2. In this type of interaction, the robot operates autonomously within a protected workspace that is monitored to detect any human presence.
3. The human operator initiates a safety-rated stop before entering that workspace, and while the operator is within the workspace, the robot remains powered but stationary.
4. When the operator exits the workspace, the robot automatically resumes its autonomous operation.
5. Should someone enter the monitored workspace without initiating the safety-rated stop, the system will initiate a protective stop that will shut down system power.
HAND-GUIDING
1. In the hand guiding scenario, the operator initiates a safety-rated stop before entering the robot’s workspace, then goes on to use a hand guiding mechanism to reposition the robotic arm before triggering the robot's next operation.
2. The hand guiding mechanism may involve simply grasping the robot arm and manipulating it, or it can involve the use of a handheld control device to command the robot's motion.
3. An application such as robotic lift assistance can utilize a hand-guided collaboration.
SPEED AND SEPARATION
1. Speed and separation monitoring are useful in situations where the operator and robot frequently share the same workspace and the operator is able to move freely within that space.
2. In this scenario the system monitors the human's distance from the robot, working to maintain a minimum protective separation distance at all times
3. When the two are at a safe separation distance—so that there is no possibility of contact—the robot is free to move at full speed.
4. Should the separation lessen, the robot continues working but slows, serving to reduce the effort required to bring the robot to a complete stop.
5. When the separation becomes too small, the robot comes to a safety-rated stop to ensure that there is no possibility for it to cause an injury.
1. The power and force limiting approach is especially useful in applications where human-robot contact is highly likely.
2. To use the approach, the robot must be capable of sensing when unusual forces have been applied to the mechanism so that it can detect and react to contact.
3. The robot should also be designed to minimize potential contact force, such as by avoiding sharp edges and pinch points, incorporating surface padding, and limiting movement speed.
4. The application should be designed so that contact is infrequent and avoidable, with care taken to evaluate what types of contact (transient or quasi-static) might occur and what body parts might be involved.
5. The application design should also aim to minimize the opportunities for quasi-static contact and prevent contact with head, neck, or throat altogether.
ROBOTIC SYSTEM SAFETY FEATURES
1. Developers selecting a robot for a collaborative application should keep in mind how they might implement one or more of these mitigation methods.
2. The robot's physical design as well as the systems that control it are all factors to evaluate in determining how readily safety measures can be implemented.
Source: www.digikey.com/en/articles/how-to-safely-incorporate-cobots-in-industrial-workplaces
