How to safely incorporate cobots in industrial workplaces
unloading the robot’s end-effector or performing inspections on work in progress. In this type of interaction, the robot operates autonomously within a protected workspace that is monitored to detect any human presence. 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. When the operator exits the workspace, the robot automatically resumes its autonomous operation. 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. 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. 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. An application such as robotic lift assistance can utilize a hand- guided collaboration. 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. In this scenario the system monitors the human's distance from the robot, working to maintain a minimum protective separation distance at all times
( Figure 4 ). 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. Should the separation lessen, the robot continues working but slows, serving to reduce the effort required to bring the robot to a complete stop. 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. Defining the distances for each stage in this approach requires understanding the robotic system's movement capabilities. The system should be designed so that once the monitors detect a human moving toward the protected space, the robotic mechanisms come to a complete stop before the human can reach that space. In order to calculate suitable separation distances, developers need to know: n How fast the robot and human move n The system's reaction time to detect the potential intrusion n How long it takes for the robot to stop moving after it receives a command The workspace layout can help simplify the definition and monitoring of safety zones for the speed and separation monitoring approach. In one example, the layout creates inherent safety zones ( Figure 5 ). A workbench separates the human from the robot's operating space, in which the robot
these mitigation methods. 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. Typically, however, robot vendors have worked to make their systems safety ready. For example, the Agilus robot kit family from KUKA, includes a smartPAD touch operator panel for hand-guided control and the KR C4 system controller with integrated safety features. The optional KUKA.SafeOperation software completes the package. The kits’ arms come with various reach lengths, including 540 millimeters (mm) (KR 3 R540), 900 mm (KR 6 R900-2), and 1100 mm (KR 10 R1100-2) ( Figure 6 ).
Figure 5: Workspace design can create inherent safety zones. (Image source: Richard A. Quinnell)
can freely move at full speed. The robot can automatically reduce speed when it enters the collaborative areas at the sides of the workbench, which are laid out to limit opportunities for quasi-static contact. The reduced speed minimizes risk in this area by reducing potential transient contact force and maximizing the opportunity for avoiding any hazards. Mechanical stops can prevent the robotic mechanism from ever entering the human's operating area, eliminating risk. Such an arrangement would require only minimal monitoring of the robot's operating space for human intrusion to ensure a high degree of system safety. The power and force limiting approach is especially useful in applications where human-robot contact is highly likely. 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. 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. 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. 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 Developers selecting a robot for a collaborative application should keep in mind how they might implement one or more of
Stop
Figure 6: Compact industrial robots such as the KUKA Agilus KR 3 are designed with safety as a major consideration and can safely share workspace and collaborate with human operators if industry standards are followed during setup. (Image source: Kuka Robotics)
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Figure 4: Speed and separation monitoring identifies zones around the robot that define its safe operation. (Image source: Richard A. Quinnell)
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