JPH05277096A - Rotary cathode x-ray tube - Google Patents

Abstract

PURPOSE:To achieve a smaller size and a reduction in cost of an X-ray tube by checking extension of a feeder mechanism when two filaments for generating X rays are set. CONSTITUTION:Internal switches SW1 and SW2 are provided to switch the polarity of a DC power source 13 according to an operation signal of an external switch to heat filaments 6a and 6b and diode elements 7a and 7b different in polarity are mounted in the course of a circuit for connecting the DC power source 13 and the filament 6a and the DC power source 13 and the filament 6b. The conduction of the diode elements 7a and 7b is switched separately by changing the polarity of the DC power source 13 to switch the connection between the filament 6a and 6b and the DC power source 13. This can reduce the number of feeder mechanisms for connecting the filaments 6a and 6b and the DC power source 13 to one only thereby obviating the need for the extension thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an X-ray CT apparatus for making a tomographic image of an object, and in particular, by rotating a cathode equipped with an electron beam emitting section for X-ray generation. The present invention relates to a rotating cathode X-ray tube that irradiates X-rays from the entire circumference of a specimen.

[0002]

2. Description of the Related Art The rotary cathode X-ray tube proposed in recent years is
In a vacuum envelope of a shape that surrounds the entire circumference of the subject, a ring-shaped rotating cathode that is magnetically levitated and a ring-shaped fixed anode that is fixedly installed are arranged to face each other.
Attached is a filament that emits thermoelectrons towards a fixed anode. When the rotating cathode is rotated at high speed while emitting thermoelectrons from the filament toward the fixed anode, the collision point (X-ray focus) between the thermoelectrons and the fixed anode draws a circular orbit around the subject, and X-rays are emitted from the circumferential direction.

The filaments can be mounted at any position on the circumference of the rotary cathode corresponding to the circular orbit. Therefore, for example, two filaments are installed on the circumference and these filaments are alternately switched and used. can do.

When the same two filaments are installed, when one of the filaments reaches the end of its life, it can be switched to the other filament to continue X-ray photography, and a filament forming a large focal point and a filament forming a small focal point. If and are installed, those filaments can be switched and used according to the photographing conditions, which is practically convenient.

[0005]

By the way, in order to light the filament that emits thermoelectrons, it is necessary to install a power source outside the rotary cathode X-ray tube to supply power to the filament. As a general power feeding mechanism, an annular slip ring connected to the lead wire of the filament is integrally attached to the rotating cathode, and a power feeding brush that makes contact with the slip ring while sliding is installed in the envelope. The power supply brush and the power supply unit are connected to each other to supply the power from the power supply unit to the filament.

Alternatively, Japanese Patent Application No. 2-326665 filed by the present applicant
As described in "Power Supply Mechanism to Rotating Body" in Japanese Patent Application No. 3-318343 and "Power Supply Mechanism to Rotating Body" in Japanese Patent Application No. 3-318343, molten metal is placed in a container installed in an envelope or a rotating cathode. A mechanism is conceivable in which the terminal of the power source section and the lead wire of the filament are electrically connected via this molten metal.

If two filaments accompanied by such a power feeding mechanism are installed for the above-mentioned reason, two sets of power feeding mechanisms for individually connecting the power source section and the two filaments are required, and the rotating cathode is required. However, there is a problem in that the size of the enclosure becomes larger and the envelope becomes larger accordingly. Furthermore, in the power feeding mechanism that uses the slip ring and the power feeding brush as its components, it is necessary to add the slip ring and the power feeding brush.
The number of fine particles generated due to the wear of the power feeding brush increases, and the following problems are promoted.

(1) Fine particles may be scattered in the vacuum envelope and enter the orbits of the thermoelectrons extracted from the filament. Then, the particles of the power feeding brush, which is a conductor, also collide with the fixed anode together with the thermoelectrons. The collision point between the thermoelectrons and the fixed anode becomes the X-ray generation point, but if the particles of the power feeding brush intervene there, the X-ray generation rate will significantly decrease. Further, since the fine particles collide with the fixed anode, the fixed anode may be damaged.

(2) The fine particles cause discharge in the vacuum envelope, which deteriorates the withstand voltage characteristics of the rotary cathode X-ray tube and reduces the vacuum degree of the vacuum envelope.

Further, in a power feeding mechanism using a molten metal as its component, the amount of relatively expensive molten metal (mainly gallium alloy etc.) used increases, so that the manufacturing cost of the rotary cathode X-ray tube increases. There are also problems.

The present invention has been made in view of the above circumstances, and eliminates the need for an additional power feeding mechanism associated with the addition of filaments, thus reducing the size of a rotary cathode X-ray tube, improving reliability, and reducing costs. An object is to provide a rotatable cathode X-ray tube that can be designed.

[0012]

In order to achieve the above object, the present invention has the following constitution. That is, according to the present invention, an annular rotating cathode that supports and rotates an electron beam emitting portion for generating X-rays, and an annular fixed anode that is fixedly installed at a position facing the rotating cathode are provided in an annular vacuum container. In a rotating cathode X-ray tube in which a power supply unit for supplying electric power to the electron beam emitting unit is installed outside the vacuum vessel, two electron beam emitting units for generating X-rays are attached to the rotating cathode, It is characterized in that a rectifying element is attached in the middle of each circuit connecting the electron beam emitting section and the power source section so as to have different polarities, and means for switching the polarity of the power source section is provided.

[0013]

The function of the present invention is as follows. By switching the polarity of the power supply, the rectifying elements with different polarities are alternately switched between the conductive state and the cutoff state.
The connection between the individual electron beam emitting units and the power supply unit is selected. Therefore, the two electron beam emitting parts and the power source part may have the same contact point, and the power supply mechanism may correspond to one electron beam emitting part.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a vertical sectional view of a rotary cathode X-ray tube according to a first embodiment of the present invention. An annular rotating cathode 2 and a fixed anode 3 are provided in an annular envelope 1 made of stainless steel that has been evacuated. The center hole 4 of the envelope 1 is an insertion hole for a subject (not shown).

The outer peripheral portion of the rotating cathode 2 is formed of a magnetic material, and is floatably supported inside the envelope 1 by an electromagnet device 5 arranged along the outer periphery of the envelope 1.
It is rotated at about 10 Hz by the rotating magnetic field formed by the stator provided in the electromagnet device 5.

Two filaments 6a and 6b for emitting thermionic rays for X-ray generation are mounted on the surface of the rotating cathode 2 facing the fixed anode 3, and the filaments 6a and 6b on the side opposite to the filament mounting surface are mounted. An annular container 8 having two chambers open toward the center of rotation is integrally attached to the surface. The container 8 is formed of an electrically insulating material such as plastic, and the molten metal 9 is housed inside. Molten metal 9
For this reason, it is preferable to use a metal having a relatively low melting point so as to omit the installation of a heater and the like, and moreover, it is hard to be vaporized in a vacuum state. For example, a Ga-In alloy (gallium-indium alloy) having a melting point of 17 degrees Celsius or a Ga-In alloy having a melting point of 5 degrees Celsius
In-Sn alloy (gallium-indium-tin alloy) and the like.

The lead wires of the two filaments 6a and 6b are connected to terminals provided on the bottom surfaces of the two chambers of the container 8 (corresponding to the outer peripheral portion of the container 7) and in contact with the molten metal 9. ing. For example, diode elements 7a and 7b as rectifying elements are provided in the middle of connection between the filaments 6a and 6b and their terminals. As shown in the circuit diagram of FIG. 2, the polarity of each diode element 7a and 7b is It is the opposite. A power supply terminal 10, which is inserted from the openings of the two chambers of the container 8 (corresponding to the inner periphery of the container 8) and comes into contact with the molten metal 8,
Reference numeral 11 is attached to the wall surface of the envelope 1, and is connected to a power supply control unit 12 installed outside the envelope 1.

As shown in the circuit diagram of FIG. 2, the power supply controller 12 has a DC power supply 13 for lighting the filament, a controller 14 for adjusting the output of the DC power supply 12, and a polarity of the output of the external switch 15. Internal switch SW that switches according to the operation signal
1 and SW2. Internal switch SW1
Is for switching the connection between the positive side terminal of the DC power supply 13 and the power supply terminals 10 and 11, and the internal switch SW2 is for switching between the negative side terminal of the DC power supply 13 and the power supply terminals 10 and 11.

According to the apparatus having the above structure, the molten metal 9 accumulated below the container 8 in a state where the rotating cathode 2 is stopped receives centrifugal force due to the rotation of the rotating cathode 2 and the container 8
It is urged by the outer peripheral part (bottom part) and is uniformly distributed there. Therefore, the molten metal 9 is not splashed up at the contact portions with the power supply terminals 10 and 11 fixedly attached to the envelope 1, and scattering from the opening of the container 8 to the outside is prevented. The power supply terminals 10 and 11 and the filaments 6a and 6b are electrically connected in a stable state.

Selection of the filaments 6a and 6b is performed by operating the external switch 15. That is, the internal switches SW1 and S1 are driven by the operation signal of the external switch 15.
When both W2 connect the internal a-side terminal and the DC power supply 13, the positive side terminal of the DC power supply 13 and the power supply terminal 10 are connected, and the negative side terminal of the DC power supply 13 and the power supply terminal 11 are connected. , Current Ia from power supply terminal 10 to power supply terminal 11
Flows.

For this current Ia, the diode element 7a
Are connected in the forward direction, and one diode element 7b
Are connected in the opposite direction, the diode element 7a is in a conducting state, the diode element 7b is in a blocking state, and the filament 6a and the DC power source 12 are connected and lighted.

Next, when the external switch 15 is switched, the internal switches SW1 and SW2 both connect the internal b-side terminal and the DC power source 13, and the positive side terminal of the DC power source 13 and the power source terminal 11 are connected. , The negative side terminal of the DC power supply 13 and the power supply terminal 10 are connected, and the power supply terminal 11 to the power supply terminal 10 are connected.
A current Ib that flows toward is flowing.

For this current Ib, the diode element 7a
Are connected in the reverse direction and the diode element 7b is connected in the forward direction, so that the diode element 7a is in the cutoff state,
The diode element 7b becomes conductive and the filament 6
b and the DC power supply 13 are connected and lighted.

Since the two filaments 6a and 6b can be selected by switching the polarity of the DC power source 13 as described above, the container of the molten metal 9 for electrically connecting the DC power source 13 and each filament. 8 may be one. Also,
As shown in FIG. 3, the power controller 12 and the filament 6a,
Even when 6b is connected to the slip ring 30 and the power feeding brush 31, only one set of the slip ring 30 and the power feeding brush 31 is required.

[0025]

As is apparent from the above description, according to the rotary cathode X-ray tube of the present invention, by switching the polarity of the power source section, each rectifying element having a different polarity is alternately turned on and off. And the connection between the two electron beam emitters and the power supply unit is selected. Therefore, even if the two electron beam emitters are installed, the power from the power supply unit is supplied to these electron beam emitters. The power supply mechanism to be used only needs to correspond to one electron beam emission part, and the problems associated with the addition of the power supply mechanism have been solved.
It is possible to reduce the size of the wire tube, improve reliability, and reduce costs.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a rotary cathode ray tube device according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram for heating two filaments.

FIG. 3 is a longitudinal sectional view of another rotating cathode X-ray tube to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Enclosure 2 ... Rotating cathode 3 ... Fixed anode 6a, 6b ... Filament 7a, 7b ... Diode element 12 ... Power supply control part 15 ... External switch SW1, SW2 ... Internal switches

Claims (1)

[Claims] 1. An annular vacuum container is provided with an annular rotary cathode that supports and rotates an electron beam emitting portion for generating X-rays, and an annular fixed anode that is fixedly installed at a position facing the rotary cathode. In a rotating cathode X-ray tube in which a power supply unit for supplying electric power to the electron beam emitting unit is installed outside the vacuum container, two electron beam emitting units for generating X-rays are attached to the rotating cathode. A rotating cathode X, characterized in that a rectifying element is attached in the middle of each circuit connecting the electron beam emitting section and the power source section so as to have different polarities, and means for switching the polarity of the power source section is provided. Line tube.