Calibration of Robotic Manipulator Systems for Cone-Beam Tomography Imaging

Abstract

Abstract-Iterative reconstruction of tomographic data relies on the precise knowledge of the geometric properties of the scan system. Common tomography systems such as rotational tomography, C-arm systems, helical scanners or tomosynthesis scanners generally use motions described by few rotational or linear motion axis. We are interested in applications in nondestructive testing, where objects might have large aspect rations and complex shapes. For these problems, more complex scan trajectories are required which can be achieved with robotic manipulator systems that have several linear or rotational degrees of freedom.For the geometric calibration of our system, instead of using an approach that scans a calibrated phantom with markers at known relative position, we propose an approach that uses one (or several) markers with unknown relative positions. The fiducial marker is then moved by a known amount along one degree of freedom, thus tracing out a "virtual" phantom. Using the assumed spacial locations of the markers together with the locations of the markers on the imaging plane, we use a nonlinear optimisation method to estimate the orientation of the linear and rotational manipulator axis, the detector and source location and the detector orientation.

Complex 3D scan trajectories for industrial cone-beam computed tomography using a hexapod

“…The specifications of the supplier (max. ±0.5 µm and ±12 µrad) and results in the literature using a similar hexapod for Computed Laminography [30] suggest that this assumption is valid.…”

Spatial resolution of a laboratory based X-Ray cone-beam laminography scanning system for various trajectories

“…Instead, an approach based on Ref. [58] is used here where one or several markers with unknown relative positions are imaged but with the manipulator in different configurations. These projection images contain sufficient information for an accurate characterization of the system geometry, including test object location, source location, detector location and orientation and the alignment of linear and rotational manipulator axes.…”

“…These projection images contain sufficient information for an accurate characterization of the system geometry, including test object location, source location, detector location and orientation and the alignment of linear and rotational manipulator axes. The accuracy of this method relies on the manipulator system's accuracy which was found in [58] to allow the geometry to be estimated with sufficient accuracy to guarantee average geometric errors in the projected image to be below pixel size.…”

“…For rotational axis calibration, the manipulator was rotated through a range of rotational offsets (60 0 ), Fig.5 (c). Geometric information was then extracted as described in [58]. Table. 2 for both FDK and CGLS.…”

Selection and evaluation of spherical acquisition trajectories for industrial computed tomography

“…However, driven by the space and flexibility limitations of conventional systems, very flexible or even robot-based configurations have emerged in recent years [24]. In particular for the latter, several new challenges also appeared that are related to calibration [25], positioning accuracy [26] or the reconstruction method [27,28]. Such set-ups have been installed for instance at the French Alternative Energies and Atomic Energy Commission (CEA) [28,29] or at the car manufacturer BMW in cooperation with the Fraunhofer institute (‘RoboCT’ [24,30,31]).…”