Patent ID: 7286639

Claim:
A focal spot sensing device comprising: a housing that resists x-ray beams; an opening disposed in a wall of the housing that allows an x-ray beam to enter the housing; and a sensor device disposed in the housing for interpreting a position of the x-ray beam for calculating a position of a focal spot, the sensor device being disposed in the housing such that an area of the x-ray allowed to fall on the sensor device changes in both position and size at the sensor device in response to movement of the focal spot in a plane parallel to the plane of the sensor device; wherein the opening is sized such that the x-ray beam at a surface of the sensor device is less than a total sensitive area of the sensor device; wherein the sensor device includes at least three detector elements; wherein a first and a second of the at least three detector elements are arranged next to each other and are aligned with a first axis parallel to the plane of the sensor device, and the first and a third of the at least three detector elements are arranged next to each other and are aligned with a second axis parallel to the plane of the sensor device, the second axis being perpendicular to the first axis; wherein the opening and the at least three detector elements are disposed such that the x-ray beam passing through the opening is allowed to strike more than two of the at least three detector elements, but only on just a portion of each of the at least three detector elements capable of receiving the x-ray beam, the portion being less than 100% of a sensitive area of an associated detector element; wherein a change in output signal of each detector element of the sensor device is responsive to a change in position and size of the area of x-ray allowed to fall on each detector element of the sensor device in response to the movement of the focal spot; and wherein the change in output signal is a position indicator for the focal spot in two dimensions.