Multibody dynamics with joint modeling and trajectory optimization for the breeding blanket vertical transporter robot

The vertical maintenance of breeding blanket (BB) segments weighing as much as 180t at future fusion power plants like EU-DEMO will be a vital activity enabling plant safety and availability. The BB vertical transporter (BBVT) is a robotic arm with 7 kinematic joints, characterized by a unique and complex mechanical structure, and specifically designed for this challenging task. Sub-centimeter accuracy is required in manipulating the BB segments out of the vacuum vessel through the upper port without collision. Detailed modeling is required before sophisticated control strategies can be developed. In the literature, the dynamic modeling of robotic arms often omits detailed joint modeling to reduce complexity. As such, this work builds on the kinematic model of the BBVT by describing the rigid-body dynamics and filling gaps in the modeling of joints, enabling the loads and motions of actuators and transmission components to be calculated. The previously defined waypoints are interpolated to cubic trajectories and the recursive Newton–Euler inverse dynamics algorithm is applied to obtain the realistic joint loads, helping verify the preliminary design. Then, an inverse-dynamics-based trajectory optimization is performed to estimate the quickest valid BB segment removal times, yielding 41 to 52min per BB segment or a total of 5.24days of handling for a 16-sector tokamak. The model and results are also verified with a BBVT simulation in MSC ADAMS. These developments support the further modeling and design of the BBVT to achieve resilient control and safe BB maintenance in a challenging nuclear environment.