JP3033609B2 - Power supply mechanism for rotating cathode X-ray tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply mechanism for supplying electric power to a filament for emitting an electron beam of a rotary cathode X-ray tube apparatus for irradiating X-rays from all around the object.

[0002]

2. Description of the Related Art A rotating cathode X-ray tube has a ring-shaped rotating cathode that is magnetically levitated and an anode target that is installed and fixed, opposed to each other in a vacuum vessel that surrounds the entire circumference of a subject. The rotating cathode is provided with a filament that emits thermoelectrons toward the fixed anode. When the rotating cathode is rotated at high speed (approximately 100 km / h per hour) while emitting thermoelectrons from the filament toward the target, X-rays are radiated toward the subject from all directions around the target, resulting in high-speed CT. A scan is performed. in this way,
It is necessary to supply electric power for heating the filament rotating at high speed.

[0003] The conventional power supply mechanism, as shown in the cross-sectional view of FIG.
Ring-shaped slip ring 20 connected to two lead wires
And a contact 21 that contacts the slip ring 20 and supplies electric power from a power supply 22 installed outside the vacuum vessel 1 to the fillant 7.

[0004]

As described above, since the rotating cathode 3 rotates at a high speed of about 100 km / h, the contact 21 is worn out by the frictional force at the contact surface between the contact 21 and the slip ring 20. I do. The following problems are caused by the fine particles generated by this depletion.

[0005] 1. Fine particles may scatter in the vacuum vessel 1 and enter the orbit of the thermoelectrons drawn from the filament 7. Then, the fine particles of the contact 21 as a conductor also collide with the anode target 4 together with the thermoelectrons. The point of collision between the thermoelectrons and the anode target 4 is the X-ray generation point. If fine particles of the contact 21 intervene here, the X-ray generation rate is significantly reduced. In addition, since the fine particles collide with the anode target 4, the anode target 4 may be damaged. 2. It is necessary to perform a frequent replacement operation in which the life of the contact 21 is significantly reduced due to the frictional heat, and the cost associated therewith is also high.

[0006] To completely eliminate such problems,
All that is required is to supply power to the rotating cathode in a non-contact state.
However, since the filament, which is a load, is attached to the rotating cathode rotating at high speed by magnetic levitation, there is a problem to be solved in realizing the above-mentioned non-contact power supply. One is that the contactless power supply becomes unstable due to the vibration of the rotating cathode.

That is, when performing non-contact power supply, a certain gap is provided for the rotating cathode, and the gap is used as a power transmission path. At this time, if the rotating cathode vibrates and the length of the air gap changes, the length of the power transmission path changes, and the power supply state becomes unstable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to provide a rotating cathode X capable of supplying electric power in a stable and non-contact manner to a filament attached to the rotating cathode. An object of the present invention is to provide a power supply mechanism for a wire tube.

[0009]

The present invention has the following configuration to achieve the above object. That is, the present invention is a power supply mechanism of a rotary cathode X-ray tube for supplying power to a filament for thermionic emission attached to a rotary cathode floating in a vacuum vessel, wherein a power transmission coil for the filament is provided. A secondary magnetic core to be wound is provided on the rotating cathode, and a primary magnetic core forming a magnetic path together with the secondary magnetic core is installed at a required gap from the rotating cathode, and excitation is applied to the primary magnetic core. A power receiving coil connected to the unit and a detection coil for detecting a change in magnetic flux due to a change in the length of the magnetic path are wound, and the excitation unit is controlled so that the output of the detection coil has a preset value. A control means for performing the control.

[0010]

The operation of the present invention is as follows. That is, an electromotive force is generated in the power transmission coil by the electromagnetic induction effect via the gap, and power is supplied to the filament. During this power supply, the rotating cathode is in a non-contact state. When the length of the air gap, that is, the length of the magnetic path changes due to the vibration of the rotating cathode during power supply, the detection coil detects a change in the magnetic flux due to the change in the magnetic path length and outputs it to the control means. The control means controls the excitation unit so that the output of the detection coil becomes a set value. As a result, a change in magnetic flux due to a change in magnetic resistance is corrected, and an electromotive force induced in the power transmission coil is stabilized.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a rotating cathode X-ray tube. In the figure, reference numeral 1 denotes a hollow ring-shaped vacuum container having a subject insertion hole 2 formed at the center. In this vacuum vessel 1,
A ring-shaped rotating cathode 3 and an anode target 4 are arranged. The rotating cathode 3 is levitated and supported by a plurality of magnetic bearing coils 5 arranged on the outer peripheral surface of the vacuum vessel 1, and is controlled by energizing a ring-shaped stator (not shown) also arranged on the outer peripheral surface. It is driven to rotate around the axis X of the subject insertion hole 2. On the other hand, the anode target 4 is
Is fixedly supported on the inner peripheral side surface of the.

On the surface of the rotating cathode 3 facing the anode target 4, a filament 7 for emitting thermoelectrons toward the anode target 4 is attached. Filament 7
Is connected to the power transmission coil 8, and the power transmission coil 8 is
It is wound around a "U" -shaped secondary magnetic core 9 embedded therein.

The primary magnetic core 9 is separated from the rotating cathode 3 by a required gap length Lg so as to face the end face of the secondary magnetic core 9.
10 are fixedly installed. As shown in FIG. 2, the primary magnetic core 10 includes two ring-shaped members 11a, 11a around an axis X.
b are arranged so as to be opposed to the two end faces of the secondary side magnetic core 9, respectively, and are bridged at one point. The bridge 11 c has a power receiving coil 12 and a detection coil 13.
And is wrapped around.

FIG. 3 is a circuit diagram of a power feeding mechanism constituted by using a gap transformer having a gap length of Lg as described above. Receiving coil 12 wound on primary magnetic core 10
Is connected to an excitation unit 14 that generates a high AC voltage, and the excitation unit 14 is configured to be controlled by the output voltage of the differential amplifier 15. One input of the differential amplifier 15 is connected to a reference power supply E, and the other input is connected to a rectifier circuit 16 including a diode D for rectifying an output current of the detection coil 13, a capacitor C, and a resistor R. Reference numeral 17 denotes a DC high voltage power supply for applying a DC high voltage to the anode target 4.

According to the power supply mechanism having such a configuration, when a primary current is applied from the excitation unit 14 to the power receiving coil 12, a magnetic flux is generated in the primary magnetic core 10, and the magnetic flux passes through a gap having a length of Lg. And passes through the inside of the secondary magnetic core 9. As a result, an electromotive force is induced in the power transmission coil 8 and power is supplied to the filament 7. This power causes the filament 7 to generate heat, and the thermoelectrons are attracted to the high potential anode target 4, and X-rays 18 are generated from the collision point of the thermoelectrons of the anode target 4. During this time, since the rotating cathode 3 is rotating at a high speed, the X-rays 18
, And tomography is performed in a short time.

In this manner, power is supplied to the filament 7 in a state of non-contact with the rotating cathode 3 rotating at a high speed.
The gap length Lg is changed by the vibration of
The problem remains that stable power supply cannot be performed.
The detection coil 13 solves this problem.

With the change of the gap length Lg, the primary magnetic core
Since the magnetic path length formed from 10 to the secondary magnetic core 9 changes, the magnetic resistance changes. This change in the magnetic resistance appears as a change in the rate of the temporal change of the magnetic flux, and the electromotive force induced in the power transmission coil 8 fluctuates. Similarly, the output current of the detection coil 13 also fluctuates. This output current is rectified by a diode D and a capacitor C, applied to a resistor R, and converted into a DC voltage.

The differential amplifier 15 amplifies the difference voltage between the output voltage of the detection coil 13 and the reference voltage of the power supply E (the voltage corresponding to the output voltage of the detection coil 13 when the gap length Lg does not change). This is given as a control voltage to the excitation unit 14. Excitation section 14 performs feedback control of the primary current flowing through power receiving coil 12 so that the applied control voltage becomes “0”. As a result, the variation of the magnetic flux passing through the magnetic path from the primary magnetic core 10 to the secondary magnetic core 9 via the gap length Lg, that is, the variation of the induced electromotive force is corrected.

By varying the primary current to the power receiving coil 12 as described above, the fluctuation of the induced electromotive force due to the change in the gap length Lg caused by the vibration of the rotating cathode 3 is corrected, so that the power supply to the filament 7 is stabilized. Become

In the above-described embodiment, as shown in FIG. 2, the secondary magnetic core 9 is formed in a "U" shape, and the primary magnetic core 10 is formed in a ring shape which is installed and fixed in a posture facing the secondary magnetic core. However, the correspondence may be reversed. That is, the secondary magnetic core 9 formed in a ring shape in the rotating cathode 3.
And a primary magnetic core 10 formed in a “U” shape is installed and fixed at an opposing position separated by a gap length Lg. However, in this case, since the weight of the rotating cathode 3 increases, it is necessary to increase the electric power applied to the magnetic bearing coil 5 in order to float, and the configuration illustrated and described in the embodiment can be said to be a preferable example.

In the embodiment, the number of the filaments 7 is one.
Although there is only one, a plurality of fillants 7 may be provided for the purpose of speeding up tomography.

[0022]

As is apparent from the above description, according to the power supply mechanism of the rotary cathode X-ray tube of the present invention, the power is transmitted to the filament by the electromagnetic induction through the air gap. The power supply is performed in a non-contact state with respect to the rotating cathode, and the problem of the conventional mechanism for supplying power while contacting the rotating cathode can be solved. In addition, even if the length of the air gap changes due to the vibration of the rotating cathode that floats in the air and rotates at high speed, the detection coil detects the change in the magnetic flux corresponding to the change, and the control unit corrects the power reception so that it is corrected. Since the current to the coil is adjusted, the electromotive force induced in the power transmission coil, that is, the power supplied to the filament can be stabilized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a rotating cathode X-ray tube according to an embodiment of the present invention.

FIG. 2 is a plan view showing a positional relationship between a primary magnetic core and a secondary magnetic core.

FIG. 3 is a circuit diagram showing a schematic configuration of a power supply mechanism.

FIG. 4 is a partial cross-sectional view of a rotating cathode X-ray tube according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vacuum container 3 ... Rotating cathode 7 ... Filament 8 ... Power transmission coil 9 ... Primary magnetic core 10 ... Secondary magnetic core 12 ... Power receiving coil 13 ... Detection coil 14 ・ ・ ・ Exciter 15 ・ ・ ・ Differential amplifier

Claims (1)

(57) [Claims] 1. A power supply mechanism of a rotary cathode X-ray tube for supplying power to a filament for emitting thermoelectrons attached to a rotary cathode floating in a vacuum vessel, wherein a power transmission coil is wound around the filament. A secondary core is provided on the rotating cathode, and a primary core forming a magnetic path together with the secondary core is installed at a required gap from the rotating cathode. And a detection coil that detects a change in magnetic flux due to a change in the length of the magnetic path, and controls the excitation unit so that the output of the detection coil becomes a preset value. Rotating cathode X equipped with control means
Wire tube power supply mechanism.