X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
1999-05-06
2001-08-07
Church, Craig E. (Department: 2876)
X-ray or gamma ray systems or devices
Source
Electron tube
C378S125000
Reexamination Certificate
active
06272205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an X-ray radiator, of the type having a rotary X-ray tube with an allocated deflecting magnet system with at least one current-conducting coil for generating a magnetic deflecting field.
2. Description of the Prior Art
In X-rays radiators of the type described in U.S. Pat. No. 4,993,055, the complete X-ray tube rotates in a cooling medium which is enclosed by the radiator housing. For this reason, the emitter usually must emit the electrons on the axis of rotation, these electrons being accelerated by the high voltage between the emitter—which represents the cathode—and the anode. These electrons without further auxiliary means, i.e. if undeflected, would propagate straight ahead to the anode. To deflect the electron beam onto the provided focal spot outside the anode center, there needs to be an additional force on the electrons. This is produced by a magnetic field which is generated by the deflecting magnet system. The magnitude of the magnetic field becomes larger as the speed of the electrons increases, because of the Lorentz force. The deflection current which is carried by the coil and the high voltage of the X-ray tube thus have a functional connection.
Dependent on the different radiological applications, X-ray tubes are operated at different high voltages. As explained, in X-ray radiators with rotating bulb tubes, the deflecting current of the deflection system must be set dependent on the high voltage which is employed. Consequently, the control of the magnet system, i.e. the control of the coil current, must receive as a control signal representative of the level of the high voltage of the tube, so that the corresponding coil current can be set. Conventional X-ray radiators operate in such a way that the deflecting coil current is stored, as a function of the high voltage, in a database of the control computer for the radiator. Thus, by means of electronics and a controllable direct current source for the deflecting current, the deflecting current can be adjusted corresponding to the applied high voltage and can be fed to the X-ray radiator via additional cables. This control design is entirely acceptable for a new X-ray device. Problems arise, however, when an apparatus with a conventionally assembled X-ray tube is to be retrofitted to function as a rotating bulb X-ray radiator. Since these radiators are based on different characteristics, the voltage generator would also have to be retrofitted, so that the two elements are compatible and an adequate control of the radiator is possible. Although it would be possible to transmit, in turn, the high voltage signal at the generator side to the radiator as a separate signal via an additional line, this is disadvantageous to the extent that additional cable has to be laid and corresponding additional terminals have to be provided at the radiator itself.
German OS 31 36 881 and European Application 0 138 486 teach tapping a reference voltage which is proportional to the high voltage pending at an X-ray tube, for obtaining a focusing voltage corresponding to the high voltage, or for controlling an inverter.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an X-ray radiator of the abovementioned type which can be integrated into an existing X-ray device by retrofitting without the assembly of additional lines, and which enables an operation of the X-ray device without a retrofitting of the voltage generator.
The object is achieved in accordance with the invention in an X-ray radiator of the abovementioned type, wherein at least one reference signal is tapped which is dependent on the existing high voltage, and the coil current is adjusted by a control unit dependent on the reference signal.
From the high voltage presently existing at the X-ray tube, the inventive X-ray radiator generates the corresponding control signal for the adjustment of the coil current itself. This means that an X-ray radiator can be retrofitted without complications, since in this regard it functions autarkically with respect to the generator in reference to the coil current control. Based on the reference signal, which is proportional to the existing high voltage, the control unit is able to adjust the coil current corresponding to the high voltage which is currently present.
As long as the tube is operated such that the high voltage is at only the cathode or at the anode, it is enough to tap only one reference signal and to feed it to the control unit. However, since usually one-half of the high voltage is at the anode and one-half is at the cathode, an anode-side reference signal can be tapped and a cathode-side reference signal can be tapped, with the current control being dependent on the sum of the two reference signals. This dual tapping of reference signals assures that possible voltage fluctuations or shifts, which can lead to differences between the respective voltages pending at the cathode and anode sides, are reliably detected, and the high voltage which actually exists can be detected correctly, so that the current control can correctly ensue.
In the case where it is either guaranteed that the voltages at the cathode and anode sides are held extremely constant, equaling U/2, for example, or that they are in a predetermined ratio which is kept constant and varies extremely insignificantly, if at all, tapping of only one anode-side or one cathode-side reference signal can be done, in which case the control unit generates the control signal for the coil current dependent on the known ratio. In the case where the sub-voltages equal U/2, respectively, the control unit merely doubles the reference signal, while in cases of different ratios, the tapped reference signal is correspondingly further processed and weighted. As a result of the voltage constancy, the high voltage can be obtained exactly and the coil current can be controlled exactly in this case. The reference signal or the sum of the two reference signals preferably should be less than 40 V, particularly less than 20 V. A signal of about 10 V has proven appropriate.
To easily generate the coil current to be adjusted with reference to the presently existing high voltage, a control characteristic describing the coil current as a function of the tube voltage can be stored in the control unit, and using this characteristic the control signal for the coil current can be generated on the basis of the reference signal.
A concrete circuit for tapping the reference voltage can include at least one voltage divider, connected between the high voltage and ground and which communicates with the control unit. In the case where the voltage is at the anode and cathode sides, two voltage dividers can be inventively provided, one of which is connected to the high voltage at the anode side, and the other of which is connected to the high voltage at the cathode side, both preferably being connected to a common ground point. For selecting the level (portion) of the existing high voltage which is tapped, the (or each) voltage divider can include a serpentine resistor. With such a voltage divider it is possible to tap a selected fraction of the pending high voltage as the reference signal. The control unit itself can be inventively arranged in the interior of the radiator housing, which is advantageous particularly with respect to the retrofitting, since there are co parts projecting from the radiator housing in this case. Furthermore, cable bushings through the radiator housing are not necessary. An external arrangement is of course also possible, however.
Besides the X-radiator itself, the invention also relates to an X-ray devic having an X-radiator of the inventive type.
REFERENCES:
patent: 4334153 (1982-06-01), Stehman et al.
patent: 4993055 (1991-02-01), Rand et al.
patent: 5822395 (1998-10-01), Schardt et al.
patent: 0 138 486 (1985-04-01), None
Hell Erich
Schardt Peter
Church Craig E.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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