JPH11248898A - Electron beam irradiation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a blown out filament immediately after initiation of current supply to a filament even in the case of breake of only one filament. SOLUTION: An electron beam irradiation device is provided with a filament voltage measuring means measuring the filament voltage Vf across the filament and a blown out filament detection circuit 42 which is given the measured filament voltage Vf. The blown out filament detection circuit 42 has a reference voltage setter 44 and a comparator 46. The reference voltage setter 44 is for setting a reference voltage R against the filament voltage Vf and it increases the reference voltage R with elapsing of time after the initiation of current supply to the filament, and makes it constant after a specific time. The comparator 46 compares the filament voltage Vf with the reference voltage R and outputs a blown out filament detection signal S when the former Vf is larger than the latter R.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam irradiation method having a plurality of electron-emitting filaments connected in parallel to each other and controlling the total filament current flowing through all the filaments to be constant. Regarding the device,
More specifically, the present invention relates to a means for detecting the disconnection of a single filament immediately after the start of energization of the filament even when the filament is disconnected.

[0002]

2. Description of the Related Art FIG. 5 shows an example of an electron beam irradiation apparatus.
This electron beam irradiation device includes an electron beam accelerator 2 for accelerating and extracting an electron beam 8 and a power supply device 20 for supplying necessary electric power.

In this example, the electron beam accelerator 2 is of a non-scanning type which does not scan the electron beam 8, and is drawn from a plurality of filaments 6 provided in a cylindrical vacuum vessel 4 and connected in parallel with each other. The electron beam 8 extracted by the electrode 10 is accelerated by a potential difference between the filament 6 and the vacuum container 4, is transmitted through the window foil 12, is extracted out of the vacuum container 4, and is irradiated on the irradiation object 14. . Each filament 6 is made of, for example, tungsten.

The power supply device 20 includes an insulating transformer 24 for supplying electric power from the ground potential portion, a filament transformer 26 connected to the insulating transformer 24 and supplying electric power for heating the filament 6, Filament transformer 2
6 is connected between the neutral point N of the secondary winding 26b and the extraction electrode 10, and a direct current extraction voltage Ve (for example, 300) between the filament 6 and the extraction electrode 10 with the former being a negative electrode.
V) and an acceleration power supply for applying a DC acceleration voltage Va (for example, about 300 kV) between the filament 6, the vacuum vessel 4 and the window foil 12 via the filament transformer 26 with the former being a negative electrode. 28. The voltage after the secondary winding 24b of the insulating transformer 24 becomes negative high potential. These are housed in a pressure vessel 22 filled with an insulating gas (for example, SF ₆ gas), and
0. The reason why the extraction power supply 30 is connected to the neutral point N of the secondary winding 26b of the filament transformer 26 is to apply the extraction voltage Ve as uniformly as possible in the longitudinal direction of the filament 6.

The filament voltage Vf applied to the entire filaments 6 and the filament current If flowing through the filaments 6 are determined by the electric / optical converter 32.
To an optical signal 34, and the optical / electrical converter 3 in the ground potential portion
6, where it is again converted into an electric signal and supplied to the control device 38. The control device 38 is composed of, for example, a sequencer, and controls the voltage regulator 40 to control the voltage supplied to the insulating transformer 24 and the filament voltage Vf so that the filament current If supplied as described above becomes constant. Control. Thus, the amount of electrons emitted from all the filaments 6 is stabilized, and the dose of the electron beam 8 is stabilized.

If even one of the filaments 6 breaks, the uniformity of the dose distribution of the electron beam 8 extracted from the electron beam accelerator 2 deteriorates. In 38, disconnection detection is performed as follows.

That is, the filament voltage Vf when a predetermined filament current If flows is compared with a constant reference voltage R ₀ (see FIG. 6), and when the filament voltage Vf exceeds the reference voltage R ₀ , the filament is disconnected. Is determined. This is because in this electron beam irradiation apparatus, the filament current If is controlled to be constant as described above. Under such a constant filament current control, even if one of the plurality of filaments 6 connected in parallel is disconnected. , The parallel combined resistance value of the filament 6
This is because the filament voltage Vf at both ends becomes larger.

[0008]

The above-mentioned filament voltage Vf is, for example, several minutes (for example, about 2 to 3 minutes) after the start of energization even if each filament 6 is normal (that is, not broken). As shown in FIG. 6, there is a tendency to gradually increase. For example, it rises from about 4.6 V to about 5.0 V and becomes stable. This is because the filament 6 generally has a characteristic that the resistance value is small when the temperature is low.

On the other hand, since a large number of filaments 6 are usually connected in parallel, the change in filament voltage Vf when only one filament is broken is very small. For example, the total number of the filaments 6 is 34. In this case, the change of the filament voltage Vf when one wire is broken is about 2.9%.
It is. Conventionally, in order to detect the change in the filament voltage Vf, the reference voltage R ₀ is set to a value slightly smaller than the 2.9% increase of the filament voltage Vf in a stable state, for example, 5.1V.

However, even when the reference voltage R ₀ is set as described above, the filament voltage Vf is low for a few minutes after the start of energization of the filament 6 even under normal conditions. Even if one wire breaks, the filament voltage Vf does not exceed the reference voltage _R0 . For example,
About 30 seconds after the start of energization, the filament voltage Vf becomes 4.7.
Even if one filament 6 breaks at about V, the filament voltage Vf is only about 4.8V. Therefore, the conventional electron beam irradiation apparatus cannot detect such a disconnection, and the disconnection detection is not complete.

Accordingly, it is a main object of the present invention to be able to detect even if one filament is broken immediately after the start of energization of the filament.

[0012]

According to a first aspect of the present invention, there is provided a first electron beam irradiation apparatus for setting filament voltage measuring means for measuring a filament voltage at both ends of the filament and setting a reference voltage for the filament voltage. The reference voltage is increased with the passage of time from the start of energization of the filament, and is made constant after a lapse of a predetermined time, and the filament voltage measured by the filament voltage measurement unit and the reference voltage setting unit are used. A comparison means for comparing with a set reference voltage and outputting a disconnection detection signal when the former is larger than the latter is provided (claim 1).

According to the above construction, the reference voltage set by the reference voltage setting means is increased with the lapse of time from the start of energization of the filament and is kept constant after the lapse of a predetermined time. In response to the filament voltage rising for a while after the start of energization, the reference voltage can always be made closer to the normal filament voltage. Therefore, even if one filament is disconnected, the disconnection can be detected immediately after the current supply to the filament is started.

A second electron beam irradiation apparatus according to the present invention comprises:
A plurality of filament voltage measuring means for measuring a filament voltage at both ends of the filament, and a filament voltage measuring means for comparing the filament voltage measured by the filament voltage measuring means with a reference voltage, and outputting a disconnection detection signal when the former is larger than the latter. Comparing means having different reference voltages and selectively activating the plurality of comparing means, and measuring the elapsed time from the start of energizing the filament, And a timer control means for sequentially activating the comparison means having a larger reference voltage as the time becomes longer (claim 2).

According to the above configuration, as the elapsed time from the start of energizing the filament increases, the comparing means having the larger reference voltage is sequentially activated by the timing control means. In response to the filament voltage rising for a while afterwards, the reference voltage of the comparison means to be activated can always be made closer to the normal filament voltage. Therefore, even if one filament is disconnected, the disconnection can be detected immediately after the current supply to the filament is started.

[0016]

FIG. 1 is a block diagram showing an example of a filament disconnection detecting circuit of an electron beam irradiation apparatus according to the present invention. The configuration of the entire electron beam irradiation apparatus is shown in FIG.
Since this is the same as that described above, reference is made to it, and redundant description is omitted here.

The electron beam irradiating apparatus of this embodiment includes a filament disconnection detecting circuit 42 shown in FIG. The filament disconnection detecting circuit 42 is provided in the control device 38 shown in FIG. 5, for example, but may be provided in another place.

The filament disconnection detecting circuit 42 includes:
From the optical / electrical converter 36 described above, the filament voltage Vf
Is given. That is, in this example, the electric / optical converter 32 and the optical / electric converter
Constitutes a filament voltage measuring means for measuring the filament voltage Vf at both ends. The filament voltage measuring means supplies the filament voltage Vf.

The filament disconnection detecting circuit 42 includes a reference voltage setting device (reference voltage setting means) 44 and a comparator (comparing means) 46 in this example.

The reference voltage setting unit 44 sets a reference voltage R with respect to the filament voltage Vf, and increases the reference voltage R with the lapse of time from the start of energization of the filament 6 and after a predetermined time has elapsed. Keep it constant. For example, as in the example shown in FIG. 2, the reference voltage R is increased stepwise (stepwise) over a plurality of stages so as to substantially follow the rising curve of the filament voltage Vf after the start of energization.

More specifically, assuming that the time from the start of energization to the filament 6 is t seconds, the reference voltage for 0 ≦ t <15 is R ₁ , and the reference voltage for 15 ≦ t <30 is R ₁ . Is R ₂ , and the reference voltage during 30 ≦ t <60 is R ₃ , 60 ≦ t
The reference voltage during <90 is R ₄ , and the reference voltage during 90 ≦ t is R ₅ . Here, R ₁ <R ₂ <R ₃ <R ₄ <R ₅ . For example, when the rising curve of the filament voltage Vf is as shown in FIGS. 2 and 6, R ₁ = 4.7 V, R _{2
= 4.8V, R 3 = 4.9V,} R 4 = 5.0V, R 5 =
Set to 5.1V. By doing so, the reference voltage R is set to Vf <R <1.029 at any time after the start of energization.
Vf. Vf is a normal filament voltage, and 1.029 Vf is 34
The magnitude of the filament voltage when one of the filaments 6 is broken.

The comparator 46 compares the filament voltage Vf given as described above with the reference voltage R, and outputs a disconnection detection signal S when the former Vf is larger than the latter R.

According to the above configuration, the reference voltage R set by the reference voltage setting unit 44 is increased with the lapse of time from the start of energization of the filament 6 and is kept constant after the lapse of a predetermined time, so that the filament 6 is normally operated. Even in this case, the reference voltage R can always be brought close to the normal filament voltage Vf in response to the filament voltage Vf rising for a while after the start of energization. Therefore, even if one filament 6 is disconnected, the disconnection can be accurately detected immediately after the start of energization of the filament 6. As a result, it is possible to quickly prevent the occurrence of defective irradiation with poor dose distribution uniformity due to the filament disconnection.

The filament disconnection detecting circuit 42
The filament break detection circuit 4 described later (see FIG. 3)
It has an advantage that only one comparing means is required as compared with 2.

The number of steps for raising the reference voltage R stepwise as described above is not necessarily limited to the five steps in the above example, and may be smaller or larger. If the number is reduced, the accuracy of disconnection detection is reduced. If the number is increased, the accuracy of disconnection detection is improved, but the setting of the reference voltage R in the voltage setting device 44 is complicated. Also, the reference voltage R is
It may be changed in a curved line along with the rise of the filament voltage Vf. In such a case, the disconnection detection accuracy is further improved, but the setting of the reference voltage R in the reference voltage setting device 44 becomes more complicated. Therefore, the filament 6 is 34
In this case, it is usually preferable to change the reference voltage R in steps of four to five steps.

However, as the number of filaments 6 is smaller, the rise of the filament voltage Vf at the time of disconnection of one filament is greater. Therefore, when the number of filaments 6 is smaller, the disconnection detection accuracy is not so good even if the setting of the reference voltage R is coarse. Does not drop.

The period during which the reference voltage R is changed as described above is usually about 2 to 3 minutes from the start of energization of the filament 6, and about 5 minutes is sufficient for a long time. This is because the filament voltage Vf normally stabilizes during that time.

The filament disconnection detecting circuit 4 as described above
Instead of 2, a filament disconnection detection circuit 42 as shown in FIG. 3 may be used. The filament disconnection detecting circuit 42 includes a plurality of (five in this example) comparing means 5.
1 to 55 and a timing control means 58.

Different reference voltages R _{1 to} R ₅ are set in the respective comparing means 51 to 55. This reference voltage R ₁ to R _5, for example the reference voltage R ₁ to R described above
_These are the same values as ₅ (see FIG. 2 etc.). Each of the comparing means 51 to 55 is connected to the optical / electrical converter 36 in the same manner as described above.
And the reference voltage R ₁
To R ₅ and the compared respectively, and outputs the disconnection detection signal S when the filament voltage Vf is higher than the reference voltage.

The timer control means 58 selectively activates the plurality of comparison means 51 to 55. In addition, the elapsed time from the start of energization of the filament 6 is measured, and as the elapsed time becomes longer, the comparison means having the larger reference voltage is sequentially activated. For example, if the elapsed time from the start of energization to the filament 6 is t seconds, the comparison unit 51 is activated during 0 ≦ t <15,
During ≤t <30, the comparison means 52 is activated, and 30≤t <
The comparison means 53 is activated during 60, the comparison means 54 is activated during 60 ≦ t <90, and the comparison means 55 is activated during 90 ≦ t.

In this case, the filament disconnection detection circuit 42
FIG. 4 shows a flow chart of the disconnection detecting operation in.
Also in this example, similarly to the example of FIG. 1, the filament voltage Vf after the start of energization is determined using a reference voltage that approximates a stepwise change in the filament voltage Vf over time, and the filament voltage Vf is determined. 6 can be detected. Therefore, even if one filament 6 is disconnected, the disconnection can be accurately detected immediately after the start of energization of the filament 6.

The filament disconnection detecting circuit 42 as shown in FIG. 3 can be easily constituted by using, for example, a microcomputer. Further, since the above-described control device 38 usually has a microcomputer, the microcomputer may be used to configure the filament disconnection detection circuit 42.

In the case of the filament disconnection detecting circuit 42 of this example, as in the case of the filament disconnection detecting circuit 42 of FIG. Although the disconnection detection accuracy is improved, the control and the like become complicated.
In the case of about this number, it is preferable to use 4 to 5 steps.

[0034]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, the reference voltage set by the reference voltage setting means increases with the lapse of time from the start of energization of the filament and is kept constant after the lapse of a predetermined time, so that the filament operates normally. Even in this case, the reference voltage can always be made closer to the normal filament voltage in response to the filament voltage rising for a while after the start of energization. Therefore, if the filament is 1
Even in the event of a main disconnection, the disconnection can be accurately detected immediately after the start of energization of the filament.

According to the second aspect of the present invention, as the elapsed time from the start of energization to the filament is increased by the time control means, the comparison means having the larger reference voltage is sequentially activated, so that the filament is normal. Even when the filament voltage rises for a while after the start of energization, the reference voltage of the activated comparison means can always be made to approach the normal filament voltage. Therefore, even if one filament is disconnected, the disconnection can be accurately detected immediately after the start of energization of the filament.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a filament disconnection detection circuit of an electron beam irradiation device according to the present invention.

FIG. 2 is a diagram showing an example of a change in a filament voltage and a reference voltage in the electron beam irradiation apparatus according to the present invention.

FIG. 3 is a block diagram showing another example of the filament disconnection detection circuit of the electron beam irradiation device according to the present invention.

FIG. 4 is a flowchart illustrating an example of a disconnection detection operation in the filament disconnection detection circuit illustrated in FIG. 3;

FIG. 5 is a diagram illustrating an example of an electron beam irradiation device.

FIG. 6 is a diagram showing an example of changes in a filament voltage and a reference voltage in a conventional electron beam irradiation device.

[Explanation of symbols]

 6 Filament 32 Electric / Optical Converter 34 Optical Signal 36 Optical / Electric Converter 38 Controller 42 Filament Disconnection Detection Circuit 44 Reference Voltage Setter 46 Comparator 51-55 Comparison Means 58 Clock Control Means

Claims (2)

[Claims] An electron beam irradiation apparatus having a plurality of electron-emitting filaments connected in parallel to each other and controlling a total filament current flowing through all the filaments to be constant. A filament voltage measuring means for measuring a filament voltage at both ends, and a reference voltage for the filament voltage, wherein the reference voltage is increased with the lapse of time from the start of energization of the filament, and after a lapse of a predetermined time, A reference voltage setting means for making constant, a comparison between a filament voltage measured by the filament voltage measuring means and a reference voltage set by the reference voltage setting means, and a disconnection detection signal output when the former is larger than the latter. Means for irradiating an electron beam. 2. An electron beam irradiation apparatus having a plurality of electron-emitting filaments connected in parallel to each other and controlling a total filament current flowing through all the filaments to be constant. Filament voltage measuring means for measuring the filament voltage at both ends, and a plurality of comparing means for comparing the filament voltage measured by the filament voltage measuring means with a reference voltage and outputting a disconnection detection signal when the former is larger than the latter. And the reference voltages are different from each other, and the plurality of comparing means are selectively switched to be activated, and the elapsed time from the start of energization to the filament is measured, and the elapsed time is large. A timing control means for sequentially activating a comparison means having a larger reference voltage as much as possible. Line irradiation equipment.