  This work presents methods for the seamless execution of arbitrary spherical
trajectories with a seven-degree-of-freedom robotic arm as a sample holder. The
sample holder is integrated into an existing X-ray computed tomography setup.
We optimized the path planning and robot control algorithms for the seamless
execution of spherical trajectories. A precision-manufactured sample holder
part is attached to the robotic arm for the calibration procedure. Different
designs of this part are tested and compared to each other for optimal coverage
of trajectories and reconstruction image quality.
  We present experimental results with the robotic sample holder where a sample
measurement on a spherical trajectory achieves improved reconstruction quality
compared to a conventional circular trajectory. Our results demonstrate the
superiority of the discussed system as it outperforms single-axis systems by
reaching nearly 82\% of all possible rotations.
  The proposed system is a step towards higher image reconstruction quality in
flexible X-ray CT systems. It will enable reduced scan times and radiation dose
exposure with task-specific trajectories in the future, as it can capture
information from various sample angles.
