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HAZARDOUS AREAS


waste to be disposed of is growing at an overwhelming rate worldwide. Automation is increasingly required to handle nuclear waste, but the nuclear industry is reluctant of fully autonomous robotic control methods for safety reasons, and remote-controlled industrial robots are preferred in hazardous environments. However, such complex tasks as remote-controlled gripping or cutting of unknown objects with the help of joysticks and video surveillance cameras are difficult to control and sometimes even impossible. To simplify this process, the National Centre


T


for Nuclear Robotics led by Extreme Robotics Lab at the University of Birmingham in the UK is researching automated handling options for nuclear waste. The robot assistance system developed there enables “shared” control to perform complex manipulation tasks by means of haptic feedback and vision information provided by Ensenso 3D camera. The operator, who is always present in the loop can retain control over the robot’s automated actions, in case of system failures.


ApplicAtion


Anyone who has ever tried out a fairground grab machine can confirm it: Manual control of grab arms is anything but trivial. As harmless as it is to fail when trying to grab a stuffed bunny, failed attempts can be as dramatic when handling radioactive waste. To avoid damage with serious consequences for humans and the environment, the robot must be able to detect the radioactive objects in the scene extremely accurately and act with precision. The operator literally has it in his hands, it is up to him to identify the correct gripping positions. At the same time, he must correctly assess the inverse kinematics (backward transformation) and correctly determine the joint angles of the robot’s arm elements in order to position it correctly and avoid collisions. The assistance system developed by


he decommissioning of nuclear facilities poses major challenges for operators. Whether decommissioning or safe containment, the amount of nuclear


hanDlE with caRE


Robot-assisted system with Ensenso 3D camera for


safe handling of nuclear waste


the British researchers simplifies and speeds up this task immensely: with a standard industrial robot equipped with a parallel jaw gripper and an Ensenso N35 3D camera. The system autonomously scans unknown


waste objects and creates a 3D model of them in the form of a point cloud. This is extremely precise because Ensenso 3D cameras work according to the principle of spatial vision (stereo vision), which is modelled on human vision. Two cameras view the object from different positions. Although the image content of both camera images appear identical, they show differences in the position of the objects viewed. Since the distance and viewing angle of the cameras as well as the focal length of the optics are known, the Ensenso software can determine the 3D coordination of the object point for each individual image pixel. In this case, the scene is captured using different scanning positions of the camera and


combined to get a complete 3D surface from all viewing angles. Ensenso’s calibration routines help transform the individual point clouds into a global coordinate system, which improves the complete virtual image. The resulting point cloud thus contains all the spatial object information needed to communicate the correct gripping or cutting position to the robot. With the help of the software, the Enseno


3D camera takes over the perception and evaluation of the depth information for the operator, whose cognitive load is considerably reduced as a result. The assistance system combines the haptic features of the object to be gripped with a special gripping algorithm. “The scene cloud is used by our system to


automatically generate several stable gripping positions. Since the point clouds captured by the 3D camera are high-resolution and dense, it is possible to generate very precise gripping positions for each object in the scene. Based on this, our “hypothesis ranking algorithm” determines the next object to pick up, based on the robot’s current position,” explains Dr Naresh Marturi, senior research scientist at the National Centre for Nuclear Robotics. (The principle is similar to that of the skill game Mikado, where one stick must be taken away at a time without moving any other sticks). The determined path guidance enables the


robot to navigate smoothly and evenly along a desired path to the target gripping position. Like a navigation system, the system supports the operator in guiding the robot arm to the safe grasp, if necessary, also past other unknown and dangerous objects. The system calculates a safe corridor for this and helps the operator not to leave the corridor through haptic feedback. The system maps the operator’s natural hand


26 JUlY/aUGUSt 2022 | inDUStRial compliancE


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