Reconstruction algorithms in X-ray computed tomography assume a particular geometrical alignment of the instrument components: X-ray source, sample stage, and detector. Motion errors and misalignments in the actual instrument contribute to errors in the reconstruction. In previous work, we presented an object-based procedure to measure the instrument geometrical alignment at a single position of the sample rotation stage along its linear translation axes. Here, we present an object-based method to determine error motions of the sample stage manipulator in cone-beam X-ray computed tomography instruments. The proposed method is applied with a reference object comprising calibrated sphere center positions to determine error motions of the stage as it is translated along the nominal magnification axis from the X-ray source towards the detector. Results agree with previous reference measurements performed using laser interferometers and electronic levels, albeit at a loss of sensitivity at lower imaging magnifications when the projected object occupies progressively smaller areas of the detector image. To compensate for the lower sensitivity, we propose a solution based on having a limited set of reference objects of various sizes to be used along the entire magnification range of the sample stage.

X射线计算机断层摄影中的重建算法假定仪器组件（X射线源，样品台和检测器）具有特定的几何对齐方式。实际仪器中的运动误差和未对准会导致重建误差。在以前的工作中，我们提出了一个基于对象的过程，以测量样品旋转台沿其线性平移轴的单个位置处的仪器几何对准。在这里，我们提出了一种基于对象的方法来确定锥束X射线计算机断层扫描仪器中样品台操纵器的误差运动。所提出的方法与包括校准球体中心位置的参考对象一起应用，以确定载物台沿标称放大轴从X射线源向检测器平移时的错误运动。结果与先前使用激光干涉仪和电子水准仪进行的参考测量结果吻合，尽管当投影的物体逐渐占据检测器图像的较小区域时，在较低的成像放大倍数下灵敏度会下降。为了补偿较低的灵敏度，我们提出了一种解决方案，该解决方案基于在样品台的整个放大倍率范围内使用的各种尺寸的有限参考对象集。