Picker International, Inc.

William E Szabo

Theodore A Resnick

Walter A Dupuis

Donald A Hescht

Narasimha R Koka

An x-ray tube (10) of a CT scanner has a rotating anode and rotor combination which is propelled by AC currents applied to run and phase windings (42, 46) by a starter (22). A monitor (24) includes Hall effect current detectors (40, 44) which detect the actual current flowing through the run and phase windings. The detected analog current values, voltage values, and the like are multiplexed (132) and digitized in a preselected order by an analog to digital converter (60) and stored in that order in a FIFO memory (62). A microprocessor (64) performs a Fourier transform (94, 96) to convert the digital run and phase signals into frequency spectra. The run and phase frequency spectra are compared (100, 102, 104, 106) with frequency spectra indicative of rotor speed, bearing wear, anode vibration, failure of the anode to rotate, and other conditions, analyzed for symmetry or other characteristics, or the like (FIG. 5 ) to generate digital run and phase reference signals. An error amplifier (54) controls a pulse width modulator ( 56) or other power amplifier controls in accordance with a deviation between analog reference signals converted from the digital signals by a reference digital to analog converter (66) and the actually sensed run and phase signals (40, 44) to adjust the starter. A direct coupled driver (122) adjusts DC offsets in the drive currents to maintain balance and drive efficiency.

High speed starter operations monitor

An x-ray tube (10) imaging system, such as a computed tomography scanner, includes a cathode (40) for generating a stream of electrons. A rotating anode (42) is placed in a path of the electron stream and generates x-rays as a result of collisions therewith. An induction rotor (44) causes rotation of the anode as a result of electromagnetic interaction with a stator (48) comprised of two windings: a run winding (50) and a phase winding (52). The run winding and the phase winding are connected to three nodes (54, 58, 60), one of which is common to both. The three nodes are actively driven with run, common, and phase signals, respectively. Actively driving the three nodes increases bus drive voltage over 40% over that achieved by half-bridge drives.

Biphase quadrature drive for an x-ray tube rotor

A calibration pattern (FIG. 2) is utilized to adjust the calibration of a video monitor (C) and a multi-format camera (D). The multi-format camera (D) includes a video display (12) and photographic equipment (20) internally therein such that received signals indicative of an image are turned into a photograph. The test pattern includes a first region (30) having a background (34) and a series of holes or dots (36) thereon. Each hole has progressively greater contrast with the first background such that the number of visible holes is indicative of whether the video monitor and multi-format camera are in proper calibration. A second region (40) is similar to the first region but has gray holes on a white background. A third region (50) has a plurality of tuning fork-like subregions having different gray scales levels. The brightness of a fourth region (70) varies sinusoidally. A fifth region (80) has square holes and a sixth region (90) has circular holes. The holes are of incrementally displaced brightness levels against a black or white background. The camera is initially calibrated in a conventional manner using photodensitometer measurements. To verify the calibration subsequently, another photograph is taken and the number of visible subregions in each region are compared with the reference photograph. The brightness and contrast calibration of the video monitor are adjusted until the number of visible subregions matches the reference photograph.

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North Olmstead, OH, United States of America

William E Szabo