The invention relates generally to x-ray tubes and, more particularly, to a magnetic coupler drive for transmitting torque to the rotating anode of the x-ray tube.
X-ray systems typically include an x-ray tube, a detector, and a bearing assembly to support the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then emits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in a computed tomography (CT) package scanner.
X-ray tubes include a rotating anode structure for the purpose of distributing the heat generated at a focal spot. An x-ray tube cathode provides a focused electron beam that is accelerated across a cathode-to-anode vacuum gap and produces x-rays upon impact with the anode. Because of the high temperatures generated when the electron beam strikes the target, it is necessary to rotate the anode assembly at high rotational speed.
The anode is typically rotated by an induction motor having a cylindrical iron-copper or copper rotor built into a cantilevered axle that supports a disc-shaped anode target and an iron stator structure with copper windings that surrounds an elongated neck of the x-ray tube. Specifically, the rotor resides inside the x-ray tube and is attached to the bearing/anode shaft, with the stator assembly residing outside the x-ray tube in either air or oil for cooling thereof. In operation, the stator functions to generate a magnetic field between the stator and the rotor by having a high current passed through a plurality of windings included therein. The high current passing through the stator windings generates the magnetic field, thereby transmitting torque from the stator to the rotor according to known DC motor principles.
The rotor-stator arrangement of typical x-ray tubes, with the rotor residing inside the x-ray tube and the stator assembly residing outside the x-ray tube, presents limits on the motor efficiency and performance that can be achieved. For example, the large rotor-stator gap resulting from placement of the rotor inside the x-ray tube vacuum and the stator assembly outside the x-ray tube vacuum significantly reduces motor efficiency. Additionally, the rotor-stator arrangement requires cooling mechanisms for cooling the stator windings due to the large currents (e.g., 5-17 amps) needed therein to overcome motor inefficiency.
Therefore, it would be desirable to have a method and apparatus for driving the rotating anode with improved efficiency. It would further be desirable for such an apparatus to operate at a lower temperature, require less input power, and occupy less space outside the x-ray tube housing.
The invention is directed to an apparatus, and method of manufacturing thereof, that transmits torque to the rotating anode of an x-ray tube. A magnetic coupler drive is provided that transmits torque from an outer magnetic rotor assembly positioned outside the vacuum chamber to an inner magnetic rotor assembly positioned within the vacuum chamber.
Therefore, in accordance with one aspect of the invention, an x-ray tube includes a housing enclosing a vacuum chamber, a cathode positioned within the vacuum chamber and configured to emit electrons, and an anode positioned within the vacuum chamber to receive the electrons emitted from the cathode and configured to generate a beam of x-rays from the electrons. The x-ray tube also includes a magnetic coupler drive configured to rotate the anode, the magnetic coupler drive further including an inner rotor frame positioned within the vacuum chamber and an outer rotor frame positioned outside the vacuum chamber and adjacent the inner rotor frame. The magnetic coupler drive also includes an inner rotor magnet mounted to the inner rotor frame and an outer rotor magnet mounted to the outer rotor frame. The inner rotor magnet and the outer rotor magnet interact to generate a magnetic field therebetween to transfer torque from the outer rotor to the inner rotor such that, when the outer rotor rotates about the inner rotor, torque is transferred from the outer rotor to the inner rotor, thereby causing the anode to rotate.
In accordance with another aspect of the invention, a method of manufacturing an x-ray tube includes the steps of positioning a cathode in a vacuum chamber, positioning an anode within the vacuum chamber to receive electrons emitted from the cathode and generate a beam of x-rays, and attaching an inner rotor assembly that includes a first magnet to the anode within the vacuum chamber. The method also includes the step of positioning an outer rotor assembly outside the vacuum chamber and about the inner rotor assembly, the outer rotor assembly including a second magnet configured to interact with the first magnet to generate a magnetic field therebetween. The method further includes the step of attaching a drive motor to the outer rotor assembly outside the vacuum chamber to drive the outer rotor assembly.
In accordance with yet another aspect of the invention, an x-ray tube includes a housing enclosing a vacuum chamber, a cathode positioned within the vacuum chamber and configured to emit electrons, and an anode positioned within the vacuum chamber to receive the electrons emitted from the cathode and configured to generate a beam of x-rays from the electrons. The x-ray tube also includes a magnetic coupler drive configured to rotate the anode, with the magnetic coupler drive further including a drive motor configured to generate rotational power and an outer magnetic rotor assembly coupled to the drive motor to receive rotational power therefrom, the outer magnetic rotor assembly being positioned outside the housing. The magnetic coupler drive also includes an inner magnetic rotor assembly coupled to the anode by way of a bearing shaft and being positioned within the vacuum chamber adjacent the outer magnetic rotor assembly. The outer magnetic rotor assembly and the inner magnetic rotor assembly are configured so as to generate magnetic fields to transfer the rotational power from the outer rotor to the inner rotor.
Various other features and advantages will be made apparent from the following detailed description and the drawings.
The drawings illustrate preferred embodiments presently contemplated for carrying out the invention.
In the drawings:
As shown in
A processor 20 receives the analog electrical signals from the detector 18 and generates an image corresponding to the object 16 being scanned. A computer 22 communicates with processor 20 to enable an operator, using operator console 24, to control the scanning parameters and to view the generated image. That is, operator console 24 includes some form of operator interface, such as a keyboard, mouse, voice activated controller, or any other suitable input apparatus that allows an operator to control the x-ray system 10 and view the reconstructed image or other data from computer 22 on a display unit 26. Additionally, console 24 allows an operator to store the generated image in a storage device 28 which may include hard drives, floppy discs, compact discs, etc. The operator may also use console 24 to provide commands and instructions to computer 22 for controlling a source controller 30 that provides power and timing signals to x-ray source 12.
Referring now to
As shown in
The bearing assembly 40 includes a center shaft 52 attached to the inner rotor assembly 44 at first end 54 and attached to the anode 38 at second end 56. A front inner race 58 and a rear inner race 60 rollingly engage a plurality of front balls 62 and a plurality of rear balls 64, respectively. Bearing assembly 40 also includes a front outer race 66 and a rear outer race 68 configured to rollingly engage and position, respectively, the plurality of front balls 62 and the plurality of rear balls 64. A stem 70 is also included in bearing assembly 40 and is supported by the x-ray tube 12.
As further shown in
A detailed view of magnetic coupler drive 76 is shown in
As shown in
The magnets 82, 86 of inner rotor assembly 44 and outer rotor assembly 72 are positioned adjacent one another, being separated by a wall of rotor can 78, and are radially aligned relative to bearing shaft 52 such that magnet 82 of inner rotor assembly 44 interacts with magnet 86 of outer rotor assembly 72 to generate a magnetic field therebetween and transmit torque from the outer rotor assembly 72, in air, to the inner rotor assembly 44 of the rotating anode bearing shaft 52, in vacuum 36. Accordingly, a gap 88 between the inner rotor assembly 44 and the outer rotor assembly 72 (i.e., rotor-rotor gap) is minimized to provide for an efficient transfer of torque from outer rotor assembly 72 to inner rotor assembly 44. Thus, according to an exemplary embodiment of the invention, the rotor-rotor gap 88 is formed to be approximately 5 mm in width.
In operation, drive motor 74 of magnetic coupler drive 76 provides rotational power or torque to outer rotor assembly 72 by way a drive shaft 90. Drive motor 74 may be configured as any known type of DC motor, for example. The transfer of rotational power to outer rotor assembly 72 by drive motor 74 (by way of drive shaft 90) thus causes outer rotor assembly 72 to rotate about inner rotor assembly 44. As outer rotor assembly 72 rotates about inner rotor assembly 44, the outer rotor magnet 86 is thus caused to rotate about inner rotor magnet 82. The rotation of outer rotor magnet 86 about inner rotor magnet 82 causes torque to be transferred from the outer rotor assembly 72 to the inner rotor assembly 44. That is, the magnetic field generated by the interaction between outer rotor magnet 86 and inner rotor magnet 82 provides for a transfer of torque from outer rotor assembly 72 to inner rotor assembly 44 upon rotation of the outer rotor magnet 86 about the inner rotor magnet 82.
The construction of magnetic coupler drive 76 as including a magnetic outer rotor assembly 72 and a magnetic inner rotor assembly 44 results in several advantages from a motor drive having a typical rotor-stator arrangement. For example, magnetic coupler drive 76 has a reduced size as compared to a typical rotor-stator arrangement. According to an exemplary embodiment, an inner diameter of the outer rotor frame 84 is between 60 and 90 mm. Additionally, as magnetic coupler drive 76 transfers torque from the outer rotor assembly 72 to the inner rotor assembly 44 by way of the interaction between outer rotor magnet 86 and inner rotor magnet 82, without the need to provide a “high” current to a stator, the magnetic coupler drive 76 generates no heat. The magnetic coupler drive 76 thus does not require cooling as apposed to stator windings of a typical rotor-stator arrangement, which must be cooled due to the large currents needed to overcome motor inefficiency. Furthermore, the magnetic coupler drive 76 operates at a lower power than typical rotor-stator drives based on the decreased size of the rotor-rotor gap 88 in the magnetic coupler drive 76. According to an exemplary embodiment, magnetic coupler drive 76 operates with a drive current provided to drive motor 74 on the order of 0.5 amps to 1 amp, as compared to the 5 amps to 17 amps needed to operate typical rotor-stator drives.
According to an embodiment of the invention, x-ray tube 12 can be incorporated into an x-ray system, for example.
Therefore, according to one embodiment of the invention, an x-ray tube includes a housing enclosing a vacuum chamber, a cathode positioned within the vacuum chamber and configured to emit electrons, and an anode positioned within the vacuum chamber to receive the electrons emitted from the cathode and configured to generate a beam of x-rays from the electrons. The x-ray tube also includes a magnetic coupler drive configured to rotate the anode, the magnetic coupler drive further including an inner rotor frame positioned within the vacuum chamber and an outer rotor frame positioned outside the vacuum chamber and adjacent the inner rotor frame. The magnetic coupler drive also includes an inner rotor magnet mounted to the inner rotor frame and an outer rotor magnet mounted to the outer rotor frame. The inner rotor magnet and the outer rotor magnet interact to generate a magnetic field therebetween to transfer torque from the outer rotor to the inner rotor such that, when the outer rotor rotates about the inner rotor, torque is transferred from the outer rotor to the inner rotor, thereby causing the anode to rotate.
According to another embodiment of the invention, a method of manufacturing an x-ray tube includes the steps of positioning a cathode in a vacuum chamber, positioning an anode within the vacuum chamber to receive electrons emitted from the cathode and generate a beam of x-rays, and attaching an inner rotor assembly that includes a first magnet to the anode within the vacuum chamber. The method also includes the step of positioning an outer rotor assembly outside the vacuum chamber and about the inner rotor assembly, the outer rotor assembly including a second magnet configured to interact with the first magnet to generate a magnetic field therebetween. The method further includes the step of attaching a drive motor to the outer rotor assembly outside the vacuum chamber to drive the outer rotor assembly.
According to yet another embodiment of the invention, an x-ray tube includes a housing enclosing a vacuum chamber, a cathode positioned within the vacuum chamber and configured to emit electrons, and an anode positioned within the vacuum chamber to receive the electrons emitted from the cathode and configured to generate a beam of x-rays from the electrons. The x-ray tube also includes a magnetic coupler drive configured to rotate the anode, with the magnetic coupler drive further including a drive motor configured to generate rotational power and an outer magnetic rotor assembly coupled to the drive motor to receive rotational power therefrom, the outer magnetic rotor assembly being positioned outside the housing. The magnetic coupler drive also includes an inner magnetic rotor assembly coupled to the anode by way of a bearing shaft and being positioned within the vacuum chamber adjacent the outer magnetic rotor assembly. The outer magnetic rotor assembly and the inner magnetic rotor assembly are configured so as to generate magnetic fields to transfer the rotational power from the outer rotor to the inner rotor.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.