Patent Application
20070041502
1. Field of the Invention
The invention concerns an x-ray apparatus as well as a method for the operation thereof.
2. Description of the Prior Art
X-ray apparatuses are generally known having the basic arrangement of a cathode and an anode mounted opposite the cathode in a vacuum-sealed housing. To generate x-ray radiation, a high voltage is applied between the cathode and the anode and the cathode is heated. An electron beam directed toward the anode forms, causing x-ray radiation and heat to be generated upon the electronics in the beam striking the anode. The surface of the anode deforms (warps) due to the repeated generation of heat with high gradient formation. An appearance known as “orange skin” forms. As a result, if a protective layer is provided on the surface of the anode, it can detach from the anode surface.
The formation of such plastic deformations on the surface and, if applicable, the detachment of a protective layer, lead to a reduced performance yield in the course of time.
An object of the invention is to provide a method for operation of an x-ray apparatus as well as an x-ray apparatus with such a performance decrease is reduced in the course of long-term operation of the x-ray apparatus.
This object is achieved according to the invention by controlling an applied current or an applied voltage such that the current strength or the voltage is steadily increased to the operating current strength or the operating voltage from an activation point in time until the expiration of a predetermined time segment.
The “applied current” can be either the current that is applied to accelerate electrons emitted by the cathode to generate an electron beam between the cathode and the anode, or the current that is applied to the cathode for heating thereof. Similarly, the “applied voltage” can be the voltage applied between the cathode and the anode, which accelerates electrons emitted by the cathode toward the anode, or the voltage that is applied to the cathode to heat the cathode. Naturally it is also possible to vary both applied currents or voltages in the sense of the present invention such that a steady heating or cooling of the anode is achieved.
As a result, the formation of thermoshock stresses on the surface of the anode (and, as a result of this, plastic deformations) can be minimized to a significant degree. A protective layer that may be provided on the anode surface does not flake off (spall). The x-ray apparatus can be operated over a long time span with constant performance yield.
As used herein, “steadily” encompasses a continuous as well as a discontinuous increase of the current or of the voltage up to operating current strength or operating voltage. A discontinuous increase, for example, can be a stepped increase. The aforementioned time segment is selected such that the anode is not heated suddenly but rather continuously and the formation of thermoshock stresses is therewith avoided.
In an embodiment of the invention, the aforementioned time segment is a first time segment, and the current or the voltage is controlled such that the operating current strength or, respectively, the operating voltage is steadily decreased to the initial value from a shutdown point in time until the expiration of a second time segment. In particular a fast cooling from high temperature values and a formation of thermoshock stresses associated therewith can be avoided. The formation of unwanted plastic deformations on the surface of the anode can be minimized further.
The first and/or the second time segment is/are advantageously 0.5 to 2 seconds. In practice, neither time segment practically limits the availability of the x-ray apparatus, particularly an x-ray apparatus with a fixed anode. Nonetheless, a distinct improvement of the performance yield of such an x-ray apparatus can be achieved with such relatively short time segments, even over a long time span.
The above object also is achieved in accordance with the invention by an x-ray apparatus having a control unit that controls an applied current or an applied voltage such that the operating current strength or the operating voltage is steadily increased to the operating current strength or the operating voltage from an activation point in time until the expiration of a time segment.
As noted above the “applied current” can be either the current that is applied to accelerate electrons emitted by the cathode to generate an electron beam between the cathode and the anode, or the current that is applied to the cathode for heating thereof. Similarly, the “applied voltage” can be the voltage applied between the cathode and the anode, which accelerates electrons emitted by the cathode toward the anode, or the voltage that is applied to the cathode to heat the cathode. Both currents or voltages can be varied to achieve a steady heating or cooling of the anode. An excellent performance yield can be achieved with the x-ray device, even over a long time span.
The aforementioned control unit can be a conventional device that is modified to cause the current or the voltage of the x-ray tube to be steadily increased to a predetermined operating current strength or a predetermined operating voltage. Naturally a device for regulation (i.e., with feedback) can be used instead of a device for control. The temperature of the anode or the intensity of the x-ray radiation radiated from the anode can be used as a control variable.
According to an advantageous embodiment, the current or the voltage can be controlled with the control unit such that the operating current strength or the operating voltage is steadily lowered to the initial value from a shutdown point in time until the expiration of a second time segment. A “steady” increase or lowering as used herein encompasses a continuous or a discontinuous increase or lowering. A discontinuous increase or lowering, for example, can be a stepped increase or lowering. Since the current or the voltage is not suddenly lowered upon shutdown but rather is steadily lowered according to a predetermined time delay, cooling of the anode can be achieved with prevention of the formation of thermoshock stresses. Plastic deformations on the anode thus can be avoided, and an essentially constant performance yield of the x-ray apparatus thus can be achieved even over a long time span.
The first and/or the second time segment is/are advantageously 0.5 to 2 seconds. In practice the aforementioned time segments have proven to be sufficient to avoid the thermoshock stresses on the surface of the anode.
In a manner similar to that shown in
The steady increase or decrease of the current I or voltage U charging the anode shown in
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 039 186.9 | Aug 2005 | DE | national |
