JP4316211B2 - X-ray generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray generator provided with an X-ray tube or the like.
[0002]
[Prior art]
An X-ray generator is an apparatus incorporating an X-ray tube that emits X-rays, and is widely used for medical or industrial diagnostic apparatuses. Various X-ray tubes have been put into practical use depending on the use of the X-ray generator. For example, when inspecting the fine structure of an inspection object with X-rays, an X-ray tube having a focal dimension of an electron beam on an anode target, which is an X-ray generation region, of about several μm to several tens of μm, so-called micro A focus X-ray tube is used (see, for example, JP-A-2001-273860).
[0003]
The above-described microfocus X-ray tube has a structure in which, for example, an anode target that emits X-rays and a cathode are disposed in a vacuum vessel. The cathode includes a cathode electrode that generates an electron beam by heating with a heater, a grid electrode that controls a tube current, a focus electrode that controls a focal dimension of the electron beam on the anode target, and the like.
[0004]
In an X-ray tube having such a configuration, for example, a cathode electrode, an anode target, or a grid electrode is generally set to a ground potential, and a predetermined tube voltage is applied to the anode target. The operation state of the X-ray tube is adjusted, for example, by controlling the voltage applied to the focus electrode and the grid electrode. When controlling the voltage applied to the focus electrode, a focus electrode power source for generating a focus voltage to be applied to the focus electrode is used separately from the anode target power source for generating the tube voltage.
[0005]
However, in the method of controlling the focus voltage, if the tube voltage applied to the anode target or the focus voltage applied to the focus electrode varies, such as pulsation, it affects the focus shape of the electron beam, making it difficult to form a micro focus. become. That is, when the minimum focal shape of the electron beam, it is important to maintain a proportional relationship between the tube voltage and the focus voltage as indicated by symbol P in FIG. 6, for example. When the tube voltage or the focus voltage fluctuates, the proportional relationship as shown in FIG. 6 is not maintained, and it becomes difficult to form a micro focus. According to the experiment by the present inventor, it has been confirmed that when the ratio of the tube voltage to the focus voltage varies by 0.15%, the focal diameter is greatly affected.
[0006]
In contrast to the above-mentioned points, for example, in Japanese Patent Laid-Open No. 7-29532, the focus electrode is set to the ground potential, and the cathode electrode is applied to the cathode electrode at a constant ratio in conjunction with the change in the voltage applied to the anode target. An X-ray generator that changes the applied voltage is described. According to such a conventional X-ray generator, the focus electrode maintains the ground potential and does not fluctuate. Therefore, even if pulsation or the like occurs in the voltage applied to the anode target, the micro focus can be kept stable. Can do.
[0007]
However, since the X-ray generator described in the above publication needs to set the focus electrode to the ground potential, there are significant restrictions on the device configuration. For example, in the conventional X-ray generator, it is common to set the anode target and the grid electrode to the ground potential, but the microfocus formation method described in the above publication is applied to such an X-ray generator. I can't do it. For this reason, even when the anode target or grid electrode is set to the ground potential, there is a need for a technique that can suppress the influence of voltage fluctuations on the formation of the micro focus of the electron beam.
[0008]
In the microfocus X-ray tube, a bias voltage is applied between the cathode electrode and the grid electrode, and the current (tube current) of the electron beam that generates X-rays is controlled by this bias voltage. When such a tube current control method is applied, it is general to provide a power source for generating a bias voltage independently.
[0009]
[Problems to be solved by the invention]
However, in the above-described tube current control method, an excessive tube current flows in the X-ray tube when the bias voltage power supply fails. Such an excessive tube current causes the anode target to melt and the like, leading to deterioration of the characteristics of the X-ray tube and further destruction. Therefore, when the tube current is controlled by the bias voltage applied to the cathode electrode, it is desired to improve the reliability and safety.
[0010]
An object of the present invention is to provide an X-ray generator capable of suppressing the influence of voltage fluctuations on the focus formation of an electron beam even when the anode target and the grid electrode are set to the ground potential. is there. Another object of the present invention is to provide an X-ray generator with improved reliability and safety by preventing excessive tube current from flowing when the tube current is controlled by a bias voltage applied to the cathode electrode. There is to do.
[0011]
[Means for Solving the Problems]
The present onset Ming, a cathode electrode for generating an electron beam, a grid electrode for controlling the flow of the electron beam in which the cathode electrode is generated, a focus electrode for focusing said electron beams, which are focused by the focusing electrode An anode target that emits X-rays by electron beam collision, a bias voltage generator that generates a bias voltage to be applied between the cathode electrode and the grid electrode, and a tube voltage generator that generates a tube voltage to be applied to the anode target And a voltage dividing unit that divides the tube voltage to generate a focus voltage and divides the focus voltage to generate a cathode voltage, and the voltage dividing unit applies the focus voltage to the focus electrode. And an X-ray generator that combines the cathode voltage and the bias voltage generated by the bias voltage generator. .
[0012]
In the X-ray generator of the present invention, since the focus voltage is generated by dividing the tube voltage, the proportional relationship between the tube voltage and the focus voltage can be maintained even if the tube voltage varies such as pulsation. . Therefore, the influence of fluctuations in the tube voltage on the focal size of the electron beam is suppressed, and as a result, it is possible to form a fine focal point of the electron beam with good reproducibility.
[0013]
To generate a cathode voltage by applying the focus voltage min dividing section to is found, it you are characterized for combining the bias voltage the cathode voltage and the bias voltage generating unit generates. In addition , the cathode voltage generated in the voltage dividing section is set to such a magnitude that the tube current does not flow when a voltage of the same magnitude is applied between the cathode electrode and the grid electrode, thereby enhancing the safety of the X- ray generator. It becomes possible to raise.
[0014]
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, modes for carrying out the present invention will be described.
[0016]
FIG. 1 is a diagram showing a configuration of an X-ray generator according to a reference example of the present invention. The X-ray generator shown in the figure has a microfocus X-ray tube 10. The microfocus X-ray tube 10 is entirely composed of a vacuum vessel 11. A cathode 12 is arranged on one side of the vacuum vessel 11, and an anode 13 is arranged on the other side. The anode 13 has an anode target 14.
[0017]
The cathode 12 is, for example, a cathode electrode 15 that generates an electron beam e, a heater 16 that heats the cathode electrode 15, a grid electrode 17 that controls the flow (for example, tube current) of the electron beam e, and the electron beam e. And a focus electrode 18 for controlling the focus shape of the electron beam formed on the anode target 14.
[0018]
In the X-ray generator of this reference example , the grid electrode 17 is set to the ground potential G. An output variable tube voltage generator 19 is connected between the anode target 14 and the ground potential G, and a positive tube voltage Vt is applied to the anode electrode 14 with respect to the grid electrode 17. The tube voltage Vt is controlled to a predetermined value.
[0019]
Further, an output variable bias voltage generator 20 is connected between the cathode electrode 15 and the ground potential G, and a positive bias voltage Vb is applied to the grid electrode 17 to the cathode electrode 15. The tube current of the X-ray tube 10 is controlled by the bias voltage Vb between the cathode electrode 15 and the grid electrode 17. The heater 16 is supplied with predetermined power of DC or AC from the heater voltage generator 21.
[0020]
A voltage divider 31 is connected in parallel to both ends of the tube voltage generator 19. The voltage dividing unit 31 includes two resistors R ₁ and R ₂ . These two resistors R ₁ and R ₂ are connected in series, and are, for example, a first resistor R ₁ and a second resistor R _{2 in} order from the higher potential side of the tube voltage generator 19. The connection point a between the first resistor R ₁ and the second resistor R ₂ is connected to the focus electrode 18, and the voltage across the _second resistor R ₂ forms the focus voltage Vf.
[0021]
That is, the voltage divider 31 divides the tube voltage Vt based on the first resistor R ₁ and the second resistor R ₂ , and generates the focus voltage Vf across the second resistor R ₂ . A focus voltage Vf generated by dividing the tube voltage Vt by the voltage divider 31 is applied between the focus electrode 18 and the ground potential G. A positive focus voltage Vf is applied to the focus electrode 18 with respect to the grid electrode 17.
[0022]
In the X-ray generator having the above-described configuration, the electron beam e generated at the cathode electrode 15 is controlled by the grid electrode 17 and the tube current is further focused by the focus electrode 18 and collides with the anode target 14. Due to the collision of the electron beam e with the anode target 14, X-rays are emitted from the anode target 14 in the direction of the arrow Y, for example. At this time, the focus voltage Vf applied to the focus electrode 18 is related to the tube voltage Vt.
Vf = Vt × R ₂ / (R ₁ + R ₂ ) (1)
It becomes.
[0023]
(1) As can be seen from the equation, the focus voltage Vf and the tube voltage Vt has a proportional relationship as shown in FIG. Since the proportional relationship between the focus voltage Vf and the tube voltage Vt is basically maintained even when the tube voltage Vt varies such as pulsation, the influence of the variation of the tube voltage Vt on the focal diameter of the electron beam is reduced. be able to. As a result, it is possible to form a fine focus of the electron beam on the anode target 14 with good reproducibility.
[0024]
Thus, according to the X-ray generator of the reference example , it is possible to reduce the influence of the voltage fluctuation on the formation of the focus of the electron beam, so that the fine focus of the electron beam on the anode target 14 can be reproduced with high reproducibility. It becomes possible to form. Furthermore, since the tube voltage Vt is divided by the voltage divider 31 to generate the focus voltage Vf, it is necessary to provide a focus voltage generator separately from the tube voltage generator 19 as in the conventional X-ray generator. In addition, the apparatus configuration of the X-ray generator can be simplified. In this embodiment, the grid electrode 17 is set to the ground potential G. However, for example, the same operation is performed when the anode target 14 is set to the ground potential.
[0025]
Next, an X-ray generator according to the first embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of the X-ray generator according to the first embodiment of the present invention. In FIG. 2, parts corresponding to those in FIG.
[0026]
In the X-ray generator shown in FIG. 2, the voltage dividing sections 31 are connected in parallel to both ends of the tube voltage generating section 19 as in the above-described reference example . However, the voltage dividing section 31 includes three resistors R ₁ , R ₂₁ , and R ₂₂ . These three resistors R ₁ , R ₂₁ , and R ₂₂ are connected in series. For example, the first resistor R ₁ , the second resistor R _21, and the second resistor are sequentially arranged from the higher potential side of the tube voltage generator 19. 3 resistor R ₂₂ .
[0027]
The connection point a between the _first resistor R ₁ and the second resistor R ₂₁ is connected to the focus electrode 18 as in the reference example, and the voltage across the two resistors R ₂₁ and R ₂₂ is focused. A voltage Vf is applied between the focus electrode 18 and the ground potential G. The focus voltage Vf is a positive voltage with respect to the grid electrode 17.
[0028]
In the X-ray generator of the first embodiment , the function of the voltage dividing unit 31 relating to the generation of the focus voltage Vf is the same as that of the reference example , and the focus voltage Vf is proportional to the tube voltage Vt. That is, the focus voltage Vf is related to the tube voltage Vt.
_{Vf = Vt × (R 21 +} R 22) / (R 1 + R 21 + R 22) ...... (2)
It becomes. In this way, the focus voltage Vf and the tube voltage Vt have a proportional relationship as shown in FIG. 6 , and the influence of fluctuations in the tube voltage Vt on the focal diameter of the electron beam can be reduced.
[0029]
In the X-ray generator of the first embodiment , the connection point b between the second resistor R ₂₁ and the third resistor R _{22 in} the voltage divider 31 is further connected to the cathode electrode 15 via the bias voltage generator 20. It is connected. That is, the voltage divider 31 divides the focus voltage Vf based on the second resistor R ₂₁ and the third resistor R ₂₂ , and the cathode electrode 15 is positive with respect to the grid electrode 17 at both ends of the third resistor R _22. A cathode voltage Vc (not shown) as a voltage is generated. The cathode voltage Vc generated at both ends of the third resistor R ₂₂ is combined with the output voltage of the bias voltage generator 20.
[0030]
Here, the bias voltage generator 20 in FIG. 2 is connected to the grid electrode 17 so that the cathode electrode 15 has a negative voltage, and a negative output voltage Vb ′ (not shown) is applied to the cathode electrode 15. Applied. Since the connection point b between the second resistor R ₂₁ and the third resistor R ₂₂ is connected to the positive terminal of the bias voltage generator 20, the cathode electrode 15 has both ends of the third resistor R ₂₂ . The difference between the voltage (cathode voltage) Vc and the output voltage Vb ′ of the bias voltage generator 20 is supplied.
[0031]
By the way, in the microfocus X-ray tube, the tube current is controlled by the bias voltage Vb between the cathode electrode 15 and the grid electrode 17 as described above. Further, there is a relationship as indicated by the symbol Q in FIG. 3 between the bias voltage Vb and the focus voltage Vf. In FIG. 3, the horizontal axis indicates the focus voltage [V], the vertical axis indicates the bias voltage [V], and the straight line Q indicates the tube current cutoff bias voltage.
[0032]
As shown in FIG. 3, with the tube current cut-off bias voltage Q as a boundary, a region above which the tube current does not flow is a region above which a tube current flows. In other words, the tube current does not flow unless the bias voltage Vb is smaller than the tube current cutoff bias voltage Q with respect to a certain focus voltage Vf. The symbol Q1 indicates the case where the tube current is 40 μA.
[0033]
As can be seen from the relationship in FIG. 6 , when the operating range of the tube voltage Vt is, for example, 0 to 80 kV, the adjustment range of the focus voltage Vf is 0 to 2000 V. In this case, from the relationship of FIG. 3, the adjustment range of the bias voltage Vb through which the tube current flows is, for example, 0 to 150V. In the reference example shown in FIG. 1, the bias voltage generator 20 in which the bias voltage Vb in such a range (for example, 0 to 150 V) is connected to the grid electrode 17 so that the cathode electrode 15 becomes a positive voltage. The output voltage is adjusted directly.
[0034]
On the other hand, in the voltage divider 31 of the first embodiment shown in FIG. 2, the voltage (cathode voltage) Vc generated across the third resistor R ₂₂ is proportional to the focus voltage Vf. That is, the voltage at the connection point b between the second resistor R ₂₁ and the third resistor R ₂₂ (the voltage Vc across the third resistor R ₂₂ ) is:
_{Vc = Vf × R 21 / (} R 21 + R 22) ...... (3)
It can be seen that this is proportional to the focus voltage Vf. Further, since the focus voltage Vf is proportional to the tube voltage Vt, the cathode voltage Vc and the tube voltage Vt are in a proportional relationship.
[0035]
Therefore, in the X-ray generator of the first embodiment , the cathode voltage Vc generated at both ends of the third resistor R ₂₂ is applied between the cathode electrode 15 and the grid electrode 17 with the same magnitude as this. In such a case, the tube current does not flow, that is, the tube current cut-off bias voltage Q shown in FIG. 3, and the tube current cut-off cathode voltage Vc and the generated voltage Vb ′ of the bias voltage generator 20 are combined. Applied to the cathode electrode 15. In this case, the tube current cutoff cathode voltage Vc changes along a straight line of the tube current cutoff bias voltage Q (FIG. 3), for example.
[0036]
Further, as can be seen from the relationship shown in FIG. 3, when the tube current is passed, the generated voltage Vb ′ of the bias voltage generator 20 may be controlled only in the direction of lowering the tube current cutoff cathode voltage Vc. That is, the tube current cutoff cathode voltage Vc which is a positive voltage and the generated voltage Vb ′ of the bias voltage generating unit 20 which is a negative voltage are synthesized, and the difference between them is applied to the cathode electrode 15 as the bias voltage Vb (= Vc−Vb). ′) Is applied to control the tube current.
[0037]
For this reason, the generated voltage Vb ′ of the bias voltage generating unit 20 necessary for controlling the tube current can be set to a range of 0 to 30 V, for example. The tube current can be sufficiently controlled with such a narrow generated voltage Vb ′. Therefore, the configuration and control of the bias voltage generator 20 can be simplified. Further, even when the bias voltage generator 20 fails, the tube current cut-off cathode voltage Vc is applied to the cathode electrode 15 from the voltage divider 31 so that an excessive tube current flows and the anode target 14 melts. Can be prevented.
[0038]
Here, the relationship between the tube current and the generated voltage Vb ′ of the bias voltage generator 20 when the focus voltage Vf is changed will be described with reference to FIG. The vertical axis in FIG. 4 is the tube current [μA], the horizontal axis is the generated voltage Vb ′ [V] of the bias voltage generator 20, the reference V1 is the focus voltage Vf of 400V, the reference V2 is the focus voltage of 1000V. Is the case. As described above, even when the range of the generated voltage Vb ′ of the bias voltage generator 20 is a narrow range of 0 to 30 V, for example, the tube current can be controlled to a necessary range.
[0039]
According to the X-ray generator of the first embodiment described above, since the focus voltage Vf is generated by dividing the tube voltage Vt by the voltage divider 31, the influence of voltage fluctuations on the focus formation of the electron beam. Can be reduced. Further, since the difference between the tube current cutoff cathode voltage Vc generated by the voltage divider 31 and the generated voltage Vb ′ of the bias voltage generator 20 is applied to the cathode electrode 15 as the bias voltage Vb, the bias voltage generator 20 The configuration and control can be simplified.
[0040]
In addition, even when the bias voltage generating unit 20 fails, the tube current cut-off cathode voltage Vc is applied to the cathode electrode 15 from the voltage dividing unit 31, so that the characteristic degradation of the X-ray tube 10 due to excessive tube current or It becomes possible to prevent destruction. That is, the reliability and safety of the X-ray generator can be greatly improved. In this embodiment, the case where the grid electrode 17 is set to the ground potential G has been described. However, for example, the same operation is performed when the anode target 14 is set to the ground potential.
[0041]
Next, an X-ray generator according to a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram showing a configuration of an X-ray generator according to the second embodiment of the present invention. In FIG. 5, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals, and a part of overlapping description is omitted.
[0042]
In the X-ray generator of the second embodiment , the anode target 14, that is, the anode 12 is grounded G. In addition, a high voltage generation unit 22 that generates a power supply voltage to be supplied to the microfocus X-ray tube 10 and a control unit 30 that controls the high voltage generation unit 22 are provided. The high voltage generation unit 22 is made of, for example, an insulator. It is stored. The function of the voltage divider 31 is the same as that of the first embodiment described above.
[0043]
In the second embodiment , a negative voltage generated by the tube voltage generator 19 is applied to the grid electrode 17. Further, the tube voltage detection unit 32 detects the output voltage of the tube voltage generation unit 19. The tube voltage comparison unit 33 compares the tube voltage value V 1 detected by the tube voltage detection unit 32 with the set tube voltage set value V 0. This comparison data is sent to the tube voltage control unit 34, and the tube voltage control unit 34 controls the tube voltage generation unit 19 so that the tube voltage value V1 is equal to the tube voltage set value V0.
[0044]
The tube current I1 flowing between the cathode electrode 15 and the anode target 14 is detected by the tube current detector 35. The tube current comparison unit 36 compares the tube current value I1 detected by the tube current detection unit 35 with the set tube current set value I0. The comparison data is sent to the bias voltage control unit 37, and the bias voltage generation unit 20 is controlled by the bias voltage control unit 37 so that the tube current value I1 is equal to the tube current set value I0. The heater voltage generator 21 is controlled by a heater voltage controller 38.
[0045]
In the X-ray generator having the above-described configuration, the electron current is emitted from the cathode electrode 15 by heating by the heater 16, and a tube current flows. The electron beam e emitted from the cathode electrode 15 is controlled in tube current by the grid electrode 17, further focused by the focus electrode 18 and collides with the anode target 14, and X-rays are emitted from the anode target 14 in the arrow Y direction. Is done.
[0046]
According to the X-ray generator of the second embodiment described above, an optimum focus voltage can be applied to the focus electrode 18 even if the voltage of the anode target 14 changes due to pulsation or the like. This makes it possible to form a fine focus of the electron beam on the anode target 14 with good reproducibility. As in the first embodiment described above, the control range of the bias voltage can be reduced, and the tube current with high resolution can be stably controlled with a simple control circuit.
[0047]
[0048]
[0049]
[0050]
[0051]
[0052]
[0053]
[0054]
【The invention's effect】
According to the X-ray generator of the present invention, it is possible to suppress the influence of voltage fluctuations on the focus formation of an electron beam. Therefore, it is possible to form a fine focus of the electron beam on the anode target with good reproducibility. Furthermore, the reliability and safety of the X-ray generator can be improved. Such an X-ray generator of the present invention is effectively used as a medical or industrial diagnostic apparatus.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration and a circuit configuration of an X-ray generator according to a reference example of the present invention.
FIG. 2 is a diagram showing a schematic configuration and a circuit configuration of the X-ray generator according to the first embodiment of the present invention.
FIG. 3 is a characteristic diagram showing a relationship between a tube voltage and a focus voltage of the X-ray generator in the embodiment of the present invention.
FIG. 4 is a characteristic diagram showing the relationship between the output voltage of the bias voltage generator of the X-ray generator and the tube current in the first embodiment of the present invention.
FIG. 5 is a diagram showing a schematic configuration and a circuit configuration of an X-ray generator according to a second embodiment of the present invention.
FIG. 6 is a characteristic diagram showing the relationship between tube voltage and focus voltage in the X-ray generator .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Microfocus X-ray tube 11 ... Vacuum container 12 ... Cathode 13 ... Anode 14 ... Anode target 15 ... Cathode electrode 16 ... Heater 17 ... Grid electrode 18 ..Focus electrode 19 ... tube voltage generator 20 ... bias voltage generator
31 · · dividing section e · · · electron beam Vt · · · tube voltage Vf · · · focusing voltage Vb · · · bias voltage _{R 1, R 2, R 21} , resistor R ₂₂ · · · division part

Claims (6)

The collision of the cathode electrode that generates the electron beam, the grid electrode that controls the flow of the electron beam generated by the cathode electrode, the focus electrode that focuses the electron beam, and the electron beam focused by the focus electrode An anode target that emits X-rays; a bias voltage generator that generates a bias voltage to be applied between the cathode electrode and the grid electrode; a tube voltage generator that generates a tube voltage to be applied to the anode target; and the tube A voltage dividing unit that divides the voltage to generate a focus voltage, and divides the focus voltage to generate a cathode voltage. The voltage dividing unit applies the focus voltage to the focus electrode, and the cathode voltage X-ray generation instrumentation, characterized by combining the bias voltage the bias voltage generating unit generates the . 2. The cathode voltage generated by the voltage dividing unit is set to a magnitude that prevents tube current from flowing when a voltage of the same magnitude is applied between the cathode electrode and the grid electrode. X-ray generator. The X-ray generator according to claim 1, wherein the voltage divider is connected in parallel to the tube voltage generator. The voltage dividing unit is configured by connecting a first resistor, a second resistor, and a third resistor in series from the higher potential side of the tube voltage generating unit, and the first resistor and the first resistor are connected in series. 2. The X-ray generator according to claim 1, wherein a connection point between the second resistor and the third resistor is connected to a focus electrode, and a connection point between the second resistor and the third resistor is connected to a bias voltage generator.  A cathode electrode for generating an electron beam, a grid electrode for controlling a flow of the electron beam generated by the cathode electrode, a focus electrode for focusing the electron beam, and an X-ray by collision of the electron beam focused by the focus electrode An X-ray tube having an anode target that emits, a bias voltage generation unit that generates a bias voltage to be applied between the cathode electrode and the grid electrode, and a tube current that flows through the X-ray tube, A bias voltage control unit that compares the tube current with a reference value and controls the bias voltage generated by the bias voltage generation unit, a tube voltage generation unit that generates a tube voltage to be applied to the anode target, and the tube voltage Tube voltage control for detecting the tube voltage generated by the generator, comparing the detected tube voltage with a reference value, and controlling the tube voltage And a voltage dividing unit that divides the tube voltage to generate a focus voltage, and divides the focus voltage to generate a cathode voltage. The voltage dividing unit applies the focus voltage to the focus electrode. An X-ray generator that synthesizes the cathode voltage and the bias voltage generated by the bias voltage generator. 6. The cathode voltage generated by the voltage dividing unit is set to a magnitude that prevents tube current from flowing when a voltage of the same magnitude is applied between the cathode electrode and the grid electrode. X-ray generator.

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