JP3084425B2 - Method and apparatus for removing foreign matter from cathode 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 method and an apparatus for removing foreign matter adhering to a shadow mask during the production of a cathode ray tube such as a color cathode ray tube by using an electron gun of the cathode ray tube itself.

[0002]

2. Description of the Related Art When foreign matter adheres to a shadow mask, a portion of the screen where the foreign matter adheres becomes a black point when a raster screen is formed, and a defect such as emission of light of another color occurs, so that foreign matter does not adhere to the shadow mask. Great care is taken in the manufacturing process. By the way, in a color cathode ray tube or the like, for example, after a shadow mask is attached to a face panel, a step of fusing the face panel and the funnel with low-melting glass and performing vacuum evacuation sealing is performed. For this reason, there is no effective method for removing foreign matter adhering to the shadow mask after the evacuation sealing step, and defective products may be generated.

As a countermeasure, as a method of removing foreign matter adhering to the shadow mask after the evacuation sealing step, there has been a method of removing foreign matter by applying mechanical vibration. This is described, for example, in JP-A-50-105267, JP-A-54-152858, JP-A-55-136439, and
These are disclosed in, for example, JP-A-59-16246 and JP-A-62-69435.

Japanese Patent Laid-Open Publication No. Sho 56-35343 discloses a method of removing foreign matter adhering to a shadow mask by using an electron beam of a cathode ray tube after the evacuation sealing step. This is a method in which the deflection circuit of the cathode ray tube is switched from a raster deflection circuit to a DC deflection circuit, the electron beam is spotted, aligned with the foreign matter, and the foreign matter is dissolved and removed by continuously irradiating a predetermined beam current for a predetermined time. ,
In the case of using an electron beam from a television cathode ray tube, an average foreign substance is dissolved and removed in about 3 minutes.

[0005]

Among the conventional methods for removing foreign matter as described above, the method of applying mechanical vibration is effective for foreign matter having extremely low adhesion strength, but is actually robust to shadow masks. There are many foreign matters adhering to or melt-adhering to the shadow mask, and it is difficult to remove the foreign matters only by slightly applying vibration to the shadow mask. Further, when strong vibration is applied, there is a disadvantage that the shadow mask is deformed.

On the other hand, the method of using the electron beam of the cathode ray tube itself is a method of dissolving and removing a foreign substance by continuously irradiating a predetermined beam current amount to the foreign substance for a predetermined time.
During the irradiation with the electron beam, the mask near the foreign matter is also continuously irradiated for a predetermined time. For example, in the case of a display monitor tube, the hole diameter of a shadow mask is about 120 μm, the hole pitch is about 300 μm, and the size of foreign matter is often about 100 to 200 μm. Since the diameter is about 500 to 600 μm when observed on the tube surface, the beam current density distribution on the mask surface is a Gaussian distribution, and its 3σ value is the beam radius (25
0-300 μm), foreign matter (100-200 μm)
Energy input to m) is at most 10% of total energy
It is about. This means that in a real cathode ray tube, most of the beam irradiation energy is injected into the phosphor through the mask and the holes in the mask.

Therefore, in the continuous irradiation method, most of the irradiated electron beam is irradiated to the fluorescent screen from the mask as well as the gap between the hole of the mask and the foreign matter and at the place where there is no foreign matter, not only the mask.
The phosphor itself is also continuously heated for a predetermined time.

[0008] The continuous heating of the shadow mask by beam current irradiation at the time of removing such foreign matter causes local thermal deformation due to the rise in the temperature of the mask, and the relative distance between the electron gun and the mask changes, thereby causing a problem on the screen. Continuous irradiation of the phosphor with excessive beam current causes local thermal damage of the phosphor, resulting in a decrease in brightness of the phosphor, as well as defects on the screen. .

In an experiment using an actual cathode ray tube by the present inventors, when the electron beam diameter is reduced to about 700 μm by observing the electron beam on the tube surface and the beam current is changed for 10 seconds, the beam current amount is reduced to 40 μA or less. Although the mask does not adversely affect the heat, a result of 50 μA or more is that the mask is deformed which adversely affects the screen such as color shift.

As described above, in the conventional method of continuously irradiating an electron beam for a predetermined time to remove foreign matter,
It is necessary to limit the beam current per unit area and unit time so as not to cause thermal deformation of the mask and thermal damage to the phosphor, and the removal effect of foreign substances having low melting point and low sublimation point is recognized. However, on the contrary, there is a problem that the effect of removing foreign substances having a high melting point and a high sublimation point is extremely poor.

[0011] After experimentally using a real cathode ray tube to remove foreign matter under the above-described continuous beam irradiation conditions that do not cause thermal deformation of the mask, the tube is disassembled and the EMPA (Electoron M
As a result of analyzing foreign matter that was difficult to remove by the icroBeam Analysis) method, the difficult-to-remove substances were “graphite conductive paint” coated inside the funnel to establish electrical conduction between the anode button and the mask, and other “glass”. And high melting point materials such as "iron-based".

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. After the step of evacuating and sealing the cathode ray tube, the electron beam of the cathode ray tube itself is used to thermally deform the mask and to remove the phosphor. Provided is a method and an apparatus for removing foreign matter of a cathode ray tube, which can effectively remove not only foreign matter having a low melting point and a low sublimation point but also foreign matter having a high melting point and a high sublimation point attached to a mask without causing thermal damage. The purpose is to do.

[0013]

According to the present invention, there is provided a method for removing foreign matter from a cathode ray tube, which scans an electron beam over the entire surface of a shadow mask of the cathode ray tube using an electron gun of the cathode ray tube itself, and emits fluorescent light from outside the cathode ray tube. Observe the light emission state of the light surface, detect the presence or absence of foreign matter attached to the shadow mask and the position of the foreign matter from the observation data, deflect the spot-shaped electron beam and align it with the foreign matter. To remove foreign matter.

The foreign matter removing device for a cathode ray tube according to the present invention includes means for raster-scanning an electron beam on a tube surface, and means for detecting a position of a foreign matter attached to a shadow mask from a light emitting state of a fluorescent screen on the tube surface. Means for converging the spot diameter of the electron beam to a predetermined size; means for adjusting the deflection position of the spot-shaped electron beam; means for intermittently turning on and off the electron beam; Means for discretely and minutely moving the intermittent irradiation position.

[0015]

According to the first aspect of the present invention, the foreign matter is intermittently irradiated with an electron beam having a high current density, thereby preventing damage to the phosphor and thermal deformation of the shadow mask without causing the foreign matter. Is instantaneously heated to a high temperature, and is removed by sublimation, burning or dissolution evaporation.

According to the second aspect of the present invention, the electron beam emission area is maintained at a constant size at the time of alignment, whereby the beam current density is maintained at a constant level. Thus, large foreign matter is also removed.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. (Embodiment 1) FIG. 1 is an apparatus configuration diagram showing a method and an apparatus for removing foreign matter from a cathode ray tube according to the present invention. Example 1
Japanese Patent Application Laid-Open No. H10-157,199 shows a case in which a foreign substance adhering to a shadow mask of a color cathode ray tube as a cathode ray tube is removed using a monochromatic electron beam of the color cathode ray tube itself.

In the figure, 1 is a face panel of a color cathode ray tube, 2 is a fluorescent screen formed on the inner surface of the face panel 1,
Reference numeral 3 denotes a shadow mask mounted inside the face panel 1, and 4 denotes an internal magnetic shield plate previously mounted on the shadow mask 3. Reference numeral 5 denotes a glass or foreign matter made of an organic substance or the like attached to the shadow mask 3.

On the other hand, the electron gun section includes cathodes 6 corresponding to red (R), green (G), and blue (B), and a heater 7 for heating the cathodes 6 to generate thermoelectrons. Are first and second grid electrodes 8 and 9 for controlling a beam current drawn from the cathode 6, a focusing electrode 10 for converging the electrons passing through the second grid electrode 9, and accelerating the converged electrons to the shadow mask 3. Acceleration electrode 11 for irradiation
Are installed in this order.

Reference numeral 12 denotes an electron beam applied to the shadow mask 3, and reference numeral 13 denotes an internal conductive film. This internal conductive film 13
Is electrically connected to the shadow mask 3, the internal magnetic shield plate 4 and the accelerating electrode 11, and further connected to a high voltage power supply (usually +24 KV to +27 KV) 15 through the anode button 14. The cathode 6 is connected to a cathode switching circuit 19, the heater 7 is connected to a heater power supply 18, the second grid electrode 9 is connected to a second grid power supply 17, and the focusing electrode 10 is connected to a focusing power supply 16.

Reference numeral 20 denotes a deflection coil for deflecting the electron beam 12, to which a raster scanning signal circuit 21 and a DC deflection control circuit 22 are connected via a switching circuit 23. Also the first
The grid electrode 8 has a DC voltage generator 24, a pulse oscillator 25
Are connected via a switching circuit 26 and a first grid control amplifier 27. Reference numeral 28 denotes an ITV camera for observing the fluorescent screen 2 from outside the cathode ray tube.

Next, the foreign matter 5 adhering to the shadow mask 3
A series of operations for removing is described. (Operation for detecting foreign matter 5 adhering to shadow mask 3)
First, the cathode switching circuit 19 selects, for example, the cathode 6 corresponding to green G, the switching circuit 23 selects the raster scanning signal generation circuit 21 side to operate the deflection coil 20, and further the switching circuit 26 generates a DC voltage. Then, a predetermined voltage (negative voltage) is applied to the first grid electrode 8 via the first grid control amplifier 27. This is a single color (green)
The entire surface of the shadow mask 3 is raster-scanned by obtaining the electron beam 12, and the light emission state of the fluorescent screen 2 is observed from outside the face panel 1.

When the foreign matter 5 is adhered to the shadow mask 3, the screen corresponding to the foreign matter 5 causes the electron beam 12 to be irradiated with the foreign matter 5.
The fluorescent material does not emit light because it is not illuminated by the fluorescent screen 2 and is observed as a black spot. When an enlarged image is taken by setting the field of view of the ITV camera 28 at this black point position, it is observed as shown in FIG. In the figure, the white circles indicate where the green phosphor emits light, and 29 indicates a black shadow where the green light should be emitted due to the foreign matter 5 adhering to the holes of the shadow mask 3. Part.

(Operation for Positioning Electron Beam 12 on Detected Foreign Material 5) First, in FIG. 1, with the cathode switching circuit 19 selecting the cathode 6 corresponding to green G, the switching circuit 23 switches the DC deflection control circuit 22 side. , And switching circuit 26
Select the pulse oscillator 25 side.

FIG. 3A shows the output voltage waveform of the pulse oscillator 25, and FIG. 3B shows the output voltage waveform of the first grid control amplifier 27, that is, the voltage waveform applied to the first grid electrode 8.
(c) is a beam current output waveform. As shown in FIG. 3 (a), a pulse having a pulse height _VPJ is emitted from the pulse oscillator 25, the polarity is inverted and amplified by the first grid control amplifier 27, and the pulse height V _PJ is outputted as shown in FIG. 3 (b). _ef (<0) is a pulse applied to the first grid electrode 8, whereby the electron beam of the green G-mentioned beam current I _B shown in FIG. 3 (c)
12 is emitted in pulse form.

The beam spot is moved to the vicinity of the detected foreign substance 5 while adjusting the horizontal deflection and the vertical deflection of the beam spot by the DC deflection control circuit 22. Next, the voltage of the focusing power supply 16 is adjusted so that the electron beam 12 is converged and the emission diameter on the fluorescent screen 2 is set to a predetermined size. FIG. 4 shows the state of phosphor emission on the tube surface at this time. Broken line
Only the part indicated by the white circle in the circle surrounded by HC is reflected as green.
At this time, the diameter of a circle indicated by a broken line HC (hereinafter referred to as a light emission circle) is considered to be a light emission diameter on the fluorescent screen 2.

Normally, even in the same tube type, the beam diameter slightly changes even when the same convergence voltage is applied due to the difference in beam convergence characteristics due to the difference between the central portion and the end portion of the screen or individual differences of electron guns even within the same tube type. . The same occurs between different pipe types, for example, between a TV pipe and a display monitor pipe due to a difference in pipe size. However, for any tube type, if the convergence voltage is finely adjusted so that the diameter of the light emitting circle HC on the tube surface of the convergent beam is always constant, the size of the light emitting circle HC corresponds to the beam diameter. Therefore, regardless of the target pipe type,
An electron beam having substantially the same beam current density can be irradiated, and irradiation conditions for removing foreign matter without causing thermal deformation of the shadow mask and damage to the phosphor can be standardized.

After setting the light emission diameter to a predetermined size in this manner, the center of the light emission circle HC coincides with the center of the black shadow 29 caused by the foreign matter 5 while further finely adjusting the horizontal deflection and the vertical deflection. Position. This state is shown in FIG. When the electron beam 12 is aligned with the foreign matter 5 in this manner, the electron beam 12 is turned on and off to form a pulse. The pulse condition at this time is as follows. Without changing the beam current value (corresponding to the pulse voltage level), the pulse width is set to be much smaller (about one tenth) than the pulse width at the time of removing foreign matter.

FIGS. 6A and 6B are waveform diagrams showing the pulse waveforms of the electron beam 12 when the light emitting circle HC is aligned and when foreign matter is removed. FIG. 6A shows the position alignment, and FIG. Each pulse waveform at the time of removing foreign matter is shown. In order to efficiently remove the foreign matter adhering to the shadow mask, it is extremely important to accurately align the electron beam with the foreign matter found on the tube surface and irradiate the position with the electron beam. Detection of the position of a foreign substance on the tube surface and alignment of the electron beam with the foreign substance are usually performed visually. In order to improve the accuracy of this operation, enlarged observation by the ITV camera 28 is used as an auxiliary means.

The simplest method of matching the position of the electron beam to the foreign matter with the point of the electron beam irradiation for removing the foreign matter is to use both the beam current amount and the pulse duty during the alignment and the foreign matter removal. Under the same conditions. However, if such a method is employed, the emission intensity of the phosphor on the tube surface at the time of alignment becomes extremely strong, and the aperture value of the camera lens of the ITV camera 28 remains the same as that at the time of detecting the position of the foreign matter. When this is imaged, blooming is caused, the size of the emission diameter, and the target foreign matter 5
Is extremely difficult to observe, and the beam alignment work becomes difficult. This is the same problem when performing visual observation without using the ITV camera 28.

There are two methods for preventing the ITV camera 28 from blooming when observing the diameter of the luminescent circle HC of the phosphor on the tube surface during alignment with the foreign matter. (1) At the stage of aligning with the foreign matter, change the aperture of the camera lens of the ITV camera 28 to increase the aperture value (decrease the aperture ratio), or use a filter (for example, an ND filter) compared to the time of detecting the foreign matter position. A method of attaching a camera to a camera lens to take an image. (2) A method in which the emission intensity of the phosphor is controlled by limiting the amount of charge of the irradiation beam per unit time to the phosphor while keeping the aperture value of the camera lens the same as when detecting the position of the foreign matter.

In the method (1), complicated operations such as a diaphragm operation of a camera lens and a filter are interposed at the stage of shifting from the detection of the position of the foreign matter to the positioning of the foreign matter. Therefore, considering the specific means for realizing the above (2), there are the following two cases. At the time of positioning, the beam current amount is reduced without changing the pulse duty compared with the time of removing foreign matter. Conversely, the pulse duty is changed by reducing the pulse width without changing the beam current amount or by increasing the pulse period.

The method described above has the following disadvantages.
That is, in an actual cathode ray tube, it is difficult to assemble the electrodes and the phosphor of the electron gun in a state where they are completely aligned, and it is difficult to maintain a configuration in which the electromagnetic field distribution is completely axisymmetric. Therefore, when the beam current amount is changed, there is a problem that the focus point of the electron beam moves.

The relationship as shown in FIG. 6, which realizes the method employed in the method of the present invention, that is, by changing the pulse width or pulse period without changing the beam current amount, the electron beam orbit or the electron beam The convergence state is preserved, and the beam position and beam diameter applied to the foreign matter on the shadow mask are kept the same at the time of alignment and at the time of removing the foreign matter, without moving the focus point.

(Operation for Removing Foreign Material 5) After the electron beam is aligned with the foreign material 5 as described above, the foreign material 5 is removed at this position. The pulse condition of the pulse oscillator 25 is shown in FIG.
In the same beam current and beam current I _B at the time of registration shown in (a), and long pulse width t _p2 (about 10 times as shown in FIG. 6 (b) with respect to the pulse width t _P1 during alignment ) Is generated at a predetermined pulse cycle for a predetermined time (time from the start to the end of the pulse train generation). At this time, the beam current value and the ratio between the pulse width and the pulse period, that is, the pulse duty, are determined in advance by experimentation or the like to obtain a condition area where the thermal deformation of the shadow mask 3 and the thermal deterioration of the fluorescent screen 2 are not given. Set within.

The basic idea of removing foreign matter by irradiating an electron beam is to convert the kinetic energy of the electron beam into heat to melt and burn the foreign matter. The physical quantities that are the points for this are the acceleration voltage Vk, the beam current density Id, and the input power integration time Tp. Assuming that all the energy of the electrons is converted into heat when the foreign matter is irradiated with the electron beam, the thermal energy Je per unit area is represented by the following equation. Je = Vk ・ Id ・ Tp

Normally, when an electron beam from a cathode ray tube is used, Vk is fixed at +27 kV, so that the element that can change Je is the beam current density Id or the input integration time T.
p. Therefore, in order to selectively apply high thermal energy to foreign matter, the following concept is basically required.
It will be described based on.

(1) Irradiation at High Peak Current Density To obtain high thermal energy Je, first, increase the beam current density Id. FIG. 8A is an explanatory diagram showing the relationship between the foreign matter 5 and the thermal energy distribution. In the graph, the vertical axis represents the beam current density Id (A / m ² ), and the horizontal axis represents the diameter of the light emitting circle HC. The position in the direction is shown. As shown in FIG. 8A, if the current density distribution of the electron beam on the focal plane follows a Gaussian distribution, it can be seen that increasing the peak current is effective.

[0039] (2) from the viewpoint of the convergence thermal energy of the electron beam effectively turned to foreign matter 5, increasing the ratio I _s / I _B of the input beam current I _s to the foreign matter to the total beam current I _B I do. FIG. 8 (b) is an explanatory diagram showing the relationship between the heat energy applied to the foreign matter 5 and the heat energy deviating from the foreign matter 5. In the figure, both the vertical and horizontal axes are the same as those shown in FIG. 8 (a). It is. FIG.
As is clear from (b), it is desirable to converge the electron beam .

(3) Intermittent irradiation of beam Heat energy Je can be increased by converging the electron beam, increasing the beam current Id and increasing the input power integration time Tp. However, when high thermal energy is applied continuously over time, there is a concern that thermal deformation of the mask and thermal damage to the phosphor may occur due to heat accumulation in the mask and the phosphor. Therefore, the input power integration time Tp is time-divided, and the heat energy is provided intermittently by alternately providing a heat energy input period and a pause period. Reduce damage.

FIG. 8 (c) is an explanatory view showing the relationship between the case where the electron beam is intermittently irradiated as in the present invention and the case where the electron beam is continuously irradiated as in the prior art. Assuming that the beam current density Id (A / m ² ) and the input power integration time Tp in the conventional method shown in the upper part of FIG. Tp is divided into N times, and the beam current density Id (A / m ² ) and the applied power integrated time are set to αTp for each pulse, and by performing N times, the same applied power integrated time Tp as in the case of continuous irradiation is obtained. It is set so that αTp × N can be obtained.

FIG. 9 shows a comparison of irradiation conditions between the conventional continuous irradiation method and the intermittent irradiation method according to the present invention. (1) Continuous irradiation method Irradiation energy density E that does not damage mask and phosphor
c (joules / m ² ) is given by the following equation (1). Ec = Vk · Jc · Tc (1) where Vk: acceleration voltage (volt) Jc: irradiation current density (A / m ² ) Tc: continuous irradiation time

(2) Intermittent Irradiation Method Assuming that the continuous irradiation time Tc is divided into N pulse irradiations, the irradiation energy density Ep (Joule / m ² ) per pulse is given by the following (2). Ep = Vk · Jp · Tp (2) where Jp: irradiation current density per pulse (A / m ² ) Tp: pulse time width (sec) Also, equation (3) holds. Ep = Tc / N (3) From the above equations (1) to (3), the following equation (4) is obtained. Jc / Jp = Tp / (Tc / N) = Tp / Fp (4) where Jp> Jc Fp: pulse period, so that pulse duty Dp (= Tp / Fp) = Jc
/ Jp, the beam current amount, pulse width, and pulse period are set.

Based on the idea that the amount of energy input per unit area and per unit time is the same between continuous irradiation and intermittent irradiation, the combination of the beam current amount and the pulse duty value as the intermittent irradiation conditions is There are various possibilities. However, naturally, thermal deformation to the mask,
The range of this combination is naturally limited by the restriction of not damaging the phosphor. In experiments using actual cathode ray tubes, even under intermittent irradiation conditions where thermal deformation is not applied to the mask,
It has been confirmed that the phosphor may be damaged. This suggests that in intermittent irradiation with a high beam current density, attention must be paid to the phosphor damage rather than the mask.

Therefore, from the viewpoint of avoiding phosphor damage,
The one-shot irradiation time Tp for preventing the phosphor from being damaged by single beam irradiation (one-shot irradiation) is experimentally obtained using the beam current amount as a parameter, and the beam current amount and pulse duty value in intermittent irradiation. In setting the combination with the above, the shot time per pulse (corresponding to the pulse width) is set to be at least equal to or less than the obtained Tp.

(Processing after foreign matter removal) When the removal of foreign matter 5 is completed, the whole screen is returned to the raster scan screen again, and it is observed whether or not foreign matter 5 has been surely removed. At this time, the electron beam 12
It is also observed at the same time whether the luminance of the phosphor near the portion where the foreign matter 5 was present is not reduced by the influence of the irradiation. Conventionally, this confirmation work largely relies on a sensitivity test, and the judgment may be different depending on the operator.

Therefore, a quantitative decision is made using the video signal of the ITV camera 28. More specifically, as shown in FIG. 7A, an enlarged image of the fluorescent screen 2 after removing the foreign substance is taken by the ITV camera 28, and the fluorescent substance 30- which has been observed as a black shadow 29 before the foreign substance is removed. The video signal of the horizontal scanning one line 31 of the ITV camera 28 passing through the line 2 is taken out, and the signal voltage level is compared with the surrounding phosphors 30-1, 30-3, 30-4 to obtain the phosphor 30-. 2 is quantitatively determined.

FIGS. 7B and 7C show the video signal level on the vertical axis and each phosphor on the horizontal axis. If there is no thermal damage, each of the phosphors 30-1 and 30-2 as shown in FIG.
The video signal level is the same from ~ 30-4.
If there is damage, the video signal level will be lower than that of the other phosphors, as shown in FIG. 7 (c).

Next, the effect of the first embodiment will be described. (Effectiveness of Intermittent Beam Irradiation for Removal of Foreign Substances) The following describes that the intermittent irradiation of the electron beam 12 is more effective for removing foreign substances by heating than the conventional continuous irradiation method. Figure
Fig. 10 shows the results obtained by simulating the temporal transition of the temperature rise due to mask heating near the irradiation position when irradiating a spot-shaped electron beam to the foreign matter that closes the hole of the shadow mask under the following conditions with a computer FIG.

The conditions for the simulation are as follows. The thickness of the mask is a value actually applied to a cathode ray tube, the size is 500 mm square, and the outer peripheral surface is fixed in a room temperature environment. The material of the mask is Invar (Fe + Ni36%), and the physical properties of specific heat, specific gravity, thermal conductivity, and emissivity (assuming a blackened film) are used. The mask has only one hole, and the hole diameter is actually
100 About several microns, but 1
mm. The foreign material is made of Invar made of the same material as the mask, the thickness is also the same as the actual mask thickness, and a disk-shaped foreign material having a diameter of 1 mm covers the hole of the mask. Although only heat conduction is considered for heat transport between the foreign matter and the mask, it is hardly considered that the hole side surface and the disk foreign matter are in close contact with each other, so that the thermal contact ratio η (0 ≦ η ≦ 1) is obtained. An artificial parameter is introduced and multiplied by the close contact area to obtain a substantial thermal contact area. The accelerating voltage of the irradiating electron beam is +27 kV in a normal cathode ray tube, the spatial distribution of the beam intensity is an axially symmetric Gaussian distribution, and the beam diameter is 2 mm in full width at half maximum (the actual electron beam of the cathode ray tube is In the above observation, it is possible to converge to about 500-600 μm).

FIG. 10A shows an irradiation spot center position (R = 0) when continuous irradiation is performed for 10 seconds at a beam current of 50 μA,
5 is a graph showing a temporal transition of a temperature rise at each position of R = 2.1 mm and R = 5.1 mm from this position. FIG. 10 (b) shows the temperature rise at each position of R = 0, 2.1 and 5.1 when the beam current is 5 mA, the beam on time (irradiation time) is 10 ms, and the off time is 990 ms, that is, when intermittent irradiation is performed at a frequency of 10 Hz for 10 seconds. 5 is a graph showing a time transition of the graph.

In each of FIGS. 10 (a) and 10 (b), the heat energy is 13.5 joules. In the case of continuous irradiation: Je [27 KV] x [0.05 mA] x [10 sec
] = 13.5 Joules In case of intermittent irradiation; Je [27 KV] x [5 mA] x [0.01 sec
] X [10 shots] = 13.5 joules Further, it is assumed that the foreign matter adheres to the edge of the hole of the mask to such an extent that it touches lightly (conditional thermal contact ratio η = 0).

From the result, the following can be understood. (1) The biggest feature of the temperature rise transition due to intermittent irradiation is that it exhibits a sawtooth-like change in which the temperature rises and falls periodically. (2) The above characteristics are remarkable near the beam irradiation point, and the farther from the irradiation point, the same temperature rise as in continuous irradiation having the same average heat input is exhibited. (3) Even if it is near the beam irradiation point, if the time course of the sawtooth change in temperature is traced, the temperature rise will be the same as that of continuous irradiation with the same average heat input. From the above, it can be said that intermittent irradiation of the beam is synonymous with "realizing instantaneous high-temperature heating of the beam irradiation region while maintaining the time average temperature equal to the temperature during continuous irradiation".

(Effect of Avoiding Thermal Deformation of Mask by Intermittent Beam Irradiation) As described above, the beam diameter on the tube surface is set to about 700 μm between the actual cathode rays, and the beam current amount is set to 40 μm.
From the experimental results that thermal irradiation is not adversely affected on the mask when the continuous irradiation is performed for 10 seconds at A or less, and from the conclusion described above,
To ensure that the input energy amount of the beam per unit area and unit time is the same between continuous irradiation and intermittent irradiation,
By properly setting the beam current amount and the intermittent irradiation duty (the ratio of the electron beam on time to the on / off cycle of the electron beam), it is possible to irradiate a beam with a high current density without affecting the mask, and Expected high-temperature heating removal.

(Embodiment 2) The embodiment 2 is provided with a drive system capable of turning on and off the electron beam to the cathode 6 for realizing the intermittent irradiation of the electron beam.
FIG. 11 is an apparatus configuration diagram showing the configuration of the second embodiment. In the second embodiment, instead of the DC voltage generator 24, the pulse oscillator 25, the switching circuit 26, and the first grid control amplifier 27 of the first embodiment shown in FIG. The cathode switching circuit 19 is connected to the electrode 8 and is selectively switchable between a cathode cutoff power supply 31 and a pulse oscillator 25.

That is, the cathode switching circuit 19 has three sets of changeover switches SB, SG, SR, and each changeover switch SB, SG, SR is connected to each cathode 6 corresponding to B, G, R of the cathode ray tube. It has a contact 19a, a contact 19b connected to the cathode cutoff power supply 31, and a contact 19c connected to the beam current monitor 32, and the contact 19a can be selectively connected to the contact 19b or 19c. The beam current monitor 32
Is connected to a pulse oscillator 25 via a cathode amplifier 34 and a changeover switch 33 in the middle. The ITV camera 28 is connected to a monitor TV 36 via a cursor generator 35.
, And to the synchroscope 37.

Next, the operation of the second embodiment will be described. First, the switches SB and SR in the cathode switching circuit 19 are switched, and
Each of the B and R cathodes 6 is connected to a cathode cutoff power supply 31, and the switch SG is switched to ground only the G cathode 6 by the changeover switch 33. 1st grid power supply 30
Is adjusted and an appropriate negative voltage is applied to the first grid electrode 8, a positive voltage (for example, +100) is applied to the cathodes 6 corresponding to B and R from the cathode cutoff power supply 31.
Since V) is applied, the electron beam from the cathode 6 corresponding to B and R is cut off, and the electron beam is emitted only from the cathode 6 corresponding to G. At this time, at the same time, the switching circuit 23 selects the raster scanning signal generation circuit 21 side, and the deflection coil 20 is operated. As a result, raster scanning over the entire surface using a monochromatic (green) beam current is realized.

When the foreign matter 5 adheres to the shadow mask 3, the screen corresponding to the foreign matter 5 is observed as a black dot. When the field of view of the ITV camera 28 and the aperture value of the camera lens are set at this black point position and an enlarged image is taken, it is observed as in FIG. 2 of the first embodiment. Next, the voltage of the first grid power supply 30 is adjusted again, a negative voltage is applied to the first grid electrode 8, and the beam current monitor 32 is monitored so that a predetermined beam current is obtained while monitoring. The switching circuit 23 selects the DC deflection control circuit 22 and switches the switch 33 to connect the cathode 6 corresponding to G to the pulse oscillator 25 via the cathode amplifier 34. When the pulse oscillator 25 is operated to generate a positive rectangular voltage, the electron beam 12 is emitted in a pulse form from the cathode 6 corresponding to G.

This state is shown as a signal waveform in FIG.
It is 12. FIG. 12A shows the output voltage waveform of the pulse oscillator 25,
FIG. 12B shows the output voltage waveform of the cathode amplifier 34, that is, the applied voltage waveform of the cathode 6 corresponding to G, and FIG. 12C shows the beam current output waveform. The DC deflection control circuit 22 moves the beam spot to the vicinity of the detected foreign matter 5 while adjusting the horizontal deflection and vertical deflection of the beam spot. A diagram displayed on the monitor television 36 such that the voltage of the focusing power supply 16 is adjusted so that the emission diameter on the fluorescent screen 2 becomes a predetermined size.
13, the setting is made with reference to the cursor window KW as shown in FIG. The size of the diameter of the light emitting circle HC is observed by enlarging and imaging the portion while keeping the aperture value of the camera lens of the ITV camera 28 the same as when detecting the foreign matter.

FIGS. 13 and 14 show FIGS. 4 and 5 in the first embodiment.
The center of the cursor window KW is moved to match the center of the black shadow 29, and the center of the emission circle HC is adjusted while finely adjusting the horizontal deflection and vertical deflection of the beam spot while referring to this. The setting is made so as to match the center of the black shadow 29 as shown in FIG. Other operations are substantially the same as those in the first embodiment.

(Embodiment 3) In Embodiment 3, the case where the cathode voltage is driven as a means for intermittently irradiating the electron beam by turning it on and off has been described. The same operation can be achieved by driving the voltage, the second grid voltage, and the acceleration voltage). In the third embodiment, the first grid voltage drive method is employed.

FIG. 15 is an apparatus configuration diagram showing the configuration of the third embodiment. In the third embodiment, two sets of switches SW ₁ and SW ₂ are provided in the switching circuit 23, and the contact 23 a of each switch is connected to the deflection coil 20, and each contact 23 b is connected to the raster operation signal generation circuit 21.
Further, each contact 23c is connected to the DC deflection control circuit 22 respectively. The cathode switching circuit 19 has three sets of switches SB and S
G and SR have their respective contacts 19a connected to the cathodes 6 corresponding to B, G and R, and the contact 19b has a beam current monitor 32.
Further, each contact 19c is connected to a cathode cutoff power supply 31 respectively. The ITV camera 28 is connected to a monitor television 36 and a synchroscope 37 via a cursor generator 35.

In the third embodiment, the cathode 6 corresponding to G is selected by the control of the cathode switching circuit 19, and the raster scanning signal generation circuit 21 is selected by the switching circuit 23.
And a predetermined negative voltage is applied to the first grid electrode 8 via the first grid control amplifier 27. Thereby, raster scanning of a single color (green) is realized in a state where a predetermined beam current is obtained.

When aligning the electron beam 12 with the detected foreign matter, the switching circuit 26 selects the pulse oscillator 25 side. The output voltage of the pulse oscillator 25 is inverted and amplified by the first grid control amplifier 27, and the first grid electrode 8
, Whereby the electron beam 12 is turned on and off, and is intermittently irradiated.

The method of adjusting the deflection position of the beam spot to the foreign matter, removing the foreign matter by intermittent irradiation, and observing the phosphor screen after the removal is substantially the same as in the first embodiment. If the applied voltage is changed in the same manner, the beam can be intermittently irradiated even by driving the second grid voltage and the acceleration voltage.

(Embodiment 4) When the foreign matter 5 adhering to the shadow mask 3 is relatively large, as shown in FIGS. 5 and 14, the center of the light emitting circle HC on the fluorescent screen 2 is In some cases, the foreign matter 5 cannot be sufficiently removed simply by aligning with the center of the shadow 29 and irradiating at that position. The fourth embodiment solves this problem, and a function of slightly deflecting the beam irradiation point on the foreign matter 5 is added to the first embodiment.

FIG. 16 is an apparatus configuration diagram showing the configuration of the fourth embodiment, and includes a minute deflection circuit 39 and an analog addition circuit 40. The DC deflection control circuit 22 and the minute deflection circuit 39 are connected to the switching circuit 23 via an analog addition circuit 40, and the minute deflection circuit 39 and the pulse oscillator 25 are mutually connected. In such a fourth embodiment, a DC deflection control circuit
After selecting the 22 side and aligning the electron beam irradiation point with the center of the black shadow 29, the pulse oscillator 25 is operated to irradiate the foreign matter 5 with the electron beam 12 in a pulse shape for a predetermined time. When the predetermined time has elapsed, a trigger signal is input from the pulse oscillator 25 to the minute deflection control circuit 34, and the minute deflection control circuit 34 generates a constant minute DC voltage.

This minute DC voltage is added to the DC voltage of the DC deflection circuit 22 by the analog addition circuit 40, and the deflection coil
The electron beam 12 is deflected to a position slightly moved from the first irradiation point. In parallel with this, a reverse trigger signal is sent from the micro deflection control circuit 34 to the pulse oscillator 25, and the pulse beam is irradiated for a predetermined time. In this manner, the beam irradiation point moves minutely one after another while changing the position near the foreign matter 5. For setting each of these minute deflection positions, a memory is provided in the minute deflection control circuit 39,
This can be realized by storing in advance as minute deflection voltage data corresponding to the position. Other configurations and operations are substantially the same as those of the first embodiment, and corresponding portions are denoted by the same reference numerals and description thereof will be omitted.

(Embodiment 5) FIG. 17 is an apparatus configuration diagram showing Embodiment 5 of the present invention. In the fifth embodiment, in order to remove a large foreign matter, a configuration that is a more specific example of the fourth embodiment is provided. The two sets of switches SW _1, SW ₂ to the switching circuit 23 is provided in this embodiment 5, the changeover switch SW _1, SW
₂ is a contact 23a connected to the deflection coil 20, a contact 23b connected to the output terminals X and Y of the raster scanning signal generation circuit 21, respectively.
And the contacts 23c connected to the output terminals of the analog summing amplifiers 41 and 42, respectively.
and c can be selectively connected to each other.

One input terminal of the analog voltage addition amplifier 41 is connected to the output terminal of the DC deflection control circuit 22, and the other input terminal is connected to the output terminal of the minute deflection control circuit 39. One input terminal is the output terminal of the DC deflection control circuit 22, and the other input terminal is the micro deflection control circuit.
Each is connected to 39 outputs. The pulse oscillator 25 has a stop terminal supplied with a signal from the micro deflection control circuit 39, and a start terminal supplied with a start switch from an OR gate 44.
The logical sum signal of the signal from the SW and the signal obtained by time-delaying the positive trigger pulse of the micro deflection control circuit 39 is input. When a positive pulse is input to the start terminal, oscillation starts, and the signal is input to the stop terminal. Oscillation is stopped when this is done. The pulse signal oscillated from the pulse oscillator 25 is supplied to the cathode amplifier 34, the changeover switch 33, the beam current monitor 32,
The signal is supplied to the cathode 6 via the cathode switching circuit 19 and to the trigger pulse generation circuit 45.

The trigger pulse generation circuit 45 includes a pulse oscillator 25
, And a trigger signal is supplied to the micro-deflection control circuit 39 when a predetermined set count value is reached. The micro-deflection control circuit 39 has a built-in memory, and sends and receives data to and from the computer 43.
The micro-deflection voltage data D _X and D _Y input from the memory 43 are stored in the memory, the positive trigger pulse input from the trigger pulse generation circuit 45 is counted, and two types of the micro-deflection voltage are stored in the memory according to the count value. .DELTA.X and .DELTA.Y are output to the analog voltage addition amplifiers 41 and 42 and to the pulse oscillator 25.

FIG. 18 shows the micro deflection control circuit 39 shown in FIG.
5 is a block diagram showing a more specific configuration of a trigger pulse generation circuit 45. FIG. The trigger pulse generation circuit 45 includes a pulse counter 50, a digital switch 51, and a comparator 52. The pulse input from the pulse oscillator 25 is counted by the pulse counter 50, and the count value and the setting input from the digital switch 51 are output. Pulse value and comparator 52
, A positive trigger pulse is generated, and the pulse counter 50 is reset and output to the trigger pulse counter 82, the OR gate 85, and the delay circuit 88 in the micro deflection control circuit 39.

The micro-deflection control circuit 39 includes memories 70 and 71. Each of the memories 70 and 71 is connected to an address bus via bus drivers 72 and 76 and a data bus via bus drivers 74 and 78, respectively. Each of them is connected to the computer 43 and has a trigger pulse counter 82 and a bus driver 75, 79 on a data bus via bus drivers 73, 77, respectively.
Digital-to-analog converter on the data bus with
Connected to 80,81. Further, a control signal line is connected between the computer 43, each of the memories 70 and 71, and each of the bus drivers 72 to 79, so that transmission and reception of data through the data buses and other timings are controlled. It has become.

A comparator 83 included in the micro-deflection control circuit 51 compares a pulse input from the trigger pulse counter 82 with a set count value input from the digital switch 84. At the same time as resetting, a positive trigger signal is output to one input terminal of the OR gate 85. When a positive trigger pulse is input from either the comparator 83 or 52, the OR gate 85 outputs a positive signal to the AND gate 86.

The other input terminal of the AND gate 86 has a switch
A voltage from a constant voltage source or a ground voltage is applied via 87, and when a constant voltage is applied, a positive signal is output from the AND gate 86 to the stop terminal of the pulse oscillator 25,
The oscillation of the pulse oscillator 25 is stopped. The delay circuit 88 delays the positive trigger pulse signal input from the comparator 52 with time and outputs the delayed signal to the OR gate 44. The OR gate 44 outputs a positive signal to the start terminal of the pulse oscillator 25 when a signal from the start switch SW or the delay circuit 88 is input.

In the memories 70 and 71, minute deflection data is previously input from the computer 43 and stored in areas corresponding to the addresses. FIG. 19 (a) is a conceptual diagram showing the data contents of the memory 71, the data 0 in a region corresponding to each of the address 0,1~N the memory _{70, DX 1, DX 2 ...} DX
_N and the memory 71 also has data DY ₁ , DY ₂ … DY _N
Are entered respectively.

[0077] Now, for example, data DX _N from the memory 70,
In the case where DY _N from the memory 71 is read out respectively, small voltage displacement as the deflection coil 20 shown in FIG. 19 (b) (Δ
X _n , ΔY _n ) is added to the main deflection voltage amount and given. Note that the data DX ₁ and DY _{1 as} shown in FIG.
Data DX ₂ and DY ₂ are more read than data DX ₂
The amount of minute voltage displacement to be set is greater when DX _N and DY _N are read.

Next, the operation of the fifth embodiment will be described with reference to a time chart shown in FIG. When aligning the electron beam with respect to the foreign matter, the changeover switch 87 is set to the ground potential side, and the stop terminal of the pulse oscillator 25 is set to logic 0 via the AND gate 86 so that pulses can be continuously oscillated. The pulse condition at this time is the same as the pulse voltage level (corresponding to the beam current amount) as compared with the time of foreign substance removal performed later, and only the pulse duty is changed. When the alignment of the electron beam to the foreign object is completed under such conditions,
Turn off the start switch SW to stop the pulse oscillation.

At the time of removing foreign matter, only the pulse duty is adjusted, and the pulse generator 25 can be controlled by an external signal through the AND gate 86 by the changeover switch 87. First, the start switch SW is turned on, and a pulse oscillation start signal (SA) as shown in FIG. 20 (a) is given to the start terminal of the pulse oscillator 25 through the OR gate 44. A pulse train signal (SB) as shown is output. At this time, the first memory 70 and the second memory
The address indication value of 71 is zero, and the data O (ΔX ₀ , ΔY ₀ , where ΔX ₀ = ΔY ₀ = 0) shown in FIG.
Is read out, the minute voltage displacement amount becomes zero, and the deflection position at the end of the alignment is held.

When the pulse count of the pulse train reaches the value n set by the digital switch 51, the trigger pulse signal (SC) shown in FIG.
Is generated, and the first memory 70 is output from the trigger pulse counter 82.
And the address indication value of the second memory 71 changes to 1.
At this time, displacement amount data DX ₁ and DY ₁ are read from the first memory 70 and the second memory 71, respectively, and the corresponding minute voltage displacement amount (Δ
X ₁ , ΔY ₁ ) is added to the main deflection voltage amount from the DC deflection circuit 22 and applied to the deflection coil 20.

On the other hand, the trigger pulse signal (SC) is supplied to the OR gate 85
To the stop terminal of the pulse oscillator 25 to stop the oscillation. Thereafter, after a slight time delay (tc) shown in FIG. 20 by the delay circuit 88, the pulse oscillator 25 starts oscillating again. As described above, after a predetermined number n of pulse oscillations (intermittent irradiation of the beam) are performed at the predetermined deflection position, the pulse oscillation is temporarily stopped, the pulse oscillation is moved to the next minute deflection position, and after a slight time delay, the pulse oscillation is performed again. The operation of starting pulse oscillation is sequentially performed. When the number of such operations reaches the number N set by the digital switch 84, the intermittent irradiation of the beam accompanying the minute deflection is completed.

(Embodiment 6) In Embodiments 1 to 5, the electron beam
The method of adjusting the voltage of the focusing power supply 16 so that the diameter of the light emitting circle HC on the fluorescent screen 2 always becomes a predetermined size when aligning the 12 with the foreign matter 5 has been described. If the light emission diameter changes according to the position of the tube surface with the voltage kept constant, the pulse width may be changed accordingly.

For example, if the emission diameter at the center of the tube surface is D ₁ and the emission diameter at the end is D ₂ (usually D ₁ ≦ D ₂ ),
Assuming that the pulse irradiation condition of the electron beam 12 for removing foreign matter at the center of the tube surface is set to the beam current I _b1 and the pulse width W _p1 , the beam current I _b2 and the pulse width W _p2 at the end are _calculated as follows. Set as follows. The beam current I _b2 = I _b1 and the pulse width W _p2 = (D ₂ / D ₁ ) ² · W _p1 in order to equalize the irradiation electron quantity per pulse. The adjustment is made by

(Embodiment 7) In Embodiments 1 to 6, the configuration in which the foreign matter 5 is removed by using a monochromatic beam (for example, green) is shown. However, a method of simultaneously using three-color beams (red, green, and blue) is also considered. Can be Embodiment 7 achieves this. Fig. 21
Is a device configuration diagram showing a seventh embodiment, in which the cathode switching circuit 19 is removed from the configuration of FIG. 1 so that three cathodes 6 are simultaneously operated. In such an embodiment, the beam current value obtained from each cathode 6 may be 1 / of that in the first to sixth embodiments using a monochromatic beam. Therefore, even if the electron beam 12 passes through the hole of the shadow mask 3 and reaches the phosphor screen 2 at the moment when the foreign matter 5 is removed, the adverse effect of thermal deterioration on the phosphor can be greatly reduced. .

(Results of Comparative Test) The driving circuit shown in the second embodiment (pulse driving method of the cathode) or the third embodiment (pulse driving method of the first grid) is added to the actual television driving circuit, and the conventional method is applied. The beam current was increased by about one digit compared with the intermittent irradiation. As a result, it was confirmed that 362 pipes could be rescued compared to 602 pipes, and foreign matter removal rate improved by about 60%. Here, the foreign matter removal rate is the ratio of the number of tubes rescued by removing foreign matter to the total number of tubes to which beam irradiation is applied.

When the foreign matter is an electrically insulating material such as glass, a negative charge is charged at the time of raster scanning, and the trajectory of the electron beam passing through the side surface of the foreign matter is bent by the repulsion by the Coulomb force. However, since the surrounding area of the black shadow emits another color on the tube surface because the phosphor of another color is also irradiated, a foreign matter defect (glasses) emitting another color on such a tube surface.
With respect to, a considerable number of, but not all, foreign matter defects could be eliminated. Further, after removing the foreign matter, the luminance of the phosphor at that position was observed with a video signal of the ITV camera, and it was confirmed that there was no change from that before irradiation.

On the other hand, in the conventional method, a mask,
The beam diameter was reduced to about 1-0.7 mm by observing on the tube under the constraint that the phosphor was not adversely affected by heat.
As a result of continuous irradiation at 40 μA for 10 seconds, the foreign matter removal rate was about 30%. The foreign substances that were not removed include “graphite conductive paint (carbon-based material)”, “glasses”,
It was a high melting point material such as "iron-based".

[0088]

According to the first aspect of the present invention, since a foreign substance is intermittently irradiated with an electron beam having a high current density, a foreign substance having a high melting point, which has been difficult by the conventional continuous irradiation method, can be subjected to thermal deformation of the shadow mask or the like. Only foreign matter can be effectively removed without causing thermal damage to the phosphor. Further, in the second aspect of the present invention, since a means for slightly moving the intermittent irradiation position of the electron beam is provided, it is possible to effectively remove a large foreign matter.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an enlarged view of a phosphor screen at the time of detecting foreign matter according to the first embodiment of the present invention.

FIG. 3 is a signal waveform diagram of a beam generating unit according to the first embodiment of the present invention.

FIG. 4 is an enlarged view of a phosphor screen showing a light emitting area at the time of alignment according to the first embodiment of the present invention.

FIG. 5 is an enlarged view of a phosphor screen according to the first embodiment of the present invention, in which the center of the light emitting area and the center of the black shadow coincide with each other.

FIG. 6 is a diagram comparing and contrasting an irradiation pulse condition when aligning an electron beam with a foreign substance and a pulse condition when removing a foreign substance according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram of measurement of phosphor luminance after foreign matter removal according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a basic concept of foreign matter removal according to the present invention.

FIG. 9 is a diagram comparing and contrasting irradiation conditions between a conventional continuous electron beam irradiation method and an intermittent irradiation method according to the present invention.

FIG. 10 is a diagram showing the results of computer simulation of the temperature rise transition caused by mask heating when an electron beam is irradiated by the method of the present invention and when irradiation is performed by the conventional method.

FIG. 11 is an apparatus configuration diagram showing a second embodiment of the present invention.

FIG. 12 is a signal waveform diagram of a beam generation unit of the device according to the second embodiment of the present invention.

FIG. 13 is an enlarged view of a phosphor screen showing a light emitting area at the time of alignment according to a second embodiment of the present invention.

FIG. 14 is an enlarged view of a phosphor screen according to a second embodiment of the present invention, in which the center of the light emitting area and the center of the black shadow coincide with each other.

FIG. 15 is an apparatus configuration diagram showing a third embodiment of the present invention.

FIG. 16 is an apparatus configuration diagram showing a fourth embodiment of the present invention.

FIG. 17 is an apparatus configuration diagram showing a fifth embodiment of the present invention.

FIG. 18 is a block diagram showing a detailed configuration of a trigger pulse generation circuit and a minute deflection control circuit in a device configuration diagram according to a fifth embodiment of the present invention.

FIG. 19 is a conceptual diagram showing a data configuration stored in a memory in a minute deflection control circuit in Embodiment 5 of the present invention.

FIG. 20 is a diagram for explaining the operation timing of the device according to the fifth embodiment of the present invention.

FIG. 21 is an apparatus configuration diagram showing a seventh embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Face panel 2 Fluorescent surface 3 Shadow mask 5 Foreign material 6 Cathode 8 First grid electrode 9 Second grid electrode 10 Focusing electrode 12 Electron beam 19 Cathode switching circuit 20 Deflection coil 21 Raster scanning signal generation circuit 22 DC deflection control circuit 23,26 Switching circuit 25 Pulse oscillator 27 First grid control amplifier 28 ITV camera 29 Black shadow 30 First grid power supply 31 Cathode cut-off power supply 32 Beam current monitor 34 Cathode amplifier 39 Micro deflection control circuit 43 Computer 45 Trigger pulse generation circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeo Sasaki 8-1-1 Tsukaguchi Honcho, Amagasaki-shi, Hyogo Mitsubishi Electric Corporation Production Technology Laboratory (72) Inventor Minoru Kobayashi 8-1-1, Tsukaguchi-Honcho, Amagasaki-shi, Hyogo No. 1 Mitsubishi Electric Corporation Production Technology Laboratory (72) Inventor Ryuji Ueda 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation Production Technology Laboratory (72) Inventor Takuji Oda Tsukaguchi, Amagasaki City, Hyogo Prefecture 8-1-1 Honcho Mitsubishi Electric Corporation Production Technology Research Laboratory (72) Inventor Akio Yoshida 8-1-1 Honcho Tsukaguchi Honcho Amagasaki City, Hyogo Mitsubishi Electric Corporation Production Technology Research Laboratory (72) Inventor Owaki Tadayoshi No. 1 Baba Zojo, Nagaokakyo-shi, Kyoto Prefecture Mitsubishi Electric Corporation Kyoto Works (72) Inventor Yamasaki Saki Akihiko Kyoto 1 Baba Zujo, Nagaokakyo-shi, Mitsubishi Mitsubishi Electric Co., Ltd.Kyoto Works (72) Inventor Masaaki Kinoshita 1 Baba Zojo, Nagaokakyo-shi, Kyoto, Japan Mitsubishi Electric Co., Ltd.Kyoto Works (72) Inventor Toshiaki Fukunishi No. 1, Ichiba Baba Zhousho, Mitsubishi Electric Corporation, Kyoto Works (56) References JP-A-56-35343 (JP, A) JP-A-55-136439 (JP, A) JP-A-54-152858 (JP, A) A) JP-A-62-69435 (JP, A) JP-A-50-105267 (JP, A) JP-A-59-16246 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) H01J 9/38 H01J 9/42

Claims (9)

(57) [Claims] 1. An electron beam is scanned over the entire surface of a shadow mask of a cathode ray tube using an electron gun of the cathode ray tube itself, and a light emitting state of a fluorescent screen is observed from outside the cathode ray tube. A cathode ray tube characterized in that the presence or absence of a foreign substance and the position of the foreign substance are detected, the spot-shaped electron beam is deflected to align with the foreign substance, and then the electron beam is intermittently irradiated to remove the foreign substance. Foreign matter removal method. 2. The method according to claim 1, wherein the spot-like irradiation of the electron beam is performed in a pulsed manner at the time of positioning with respect to the foreign matter, and the pulse condition is such that the beam current amount is the same as that at the time of removing the foreign matter, and only the pulse duty is changed. 2. The method for removing foreign matter from a cathode ray tube according to 1. 3. The method according to claim 1, wherein the size of a light emitting area of the electron beam on the phosphor screen when the spot-shaped electron beam is aligned with the foreign matter is made constant by adjusting the focusing voltage of the electron beam. The method for removing foreign matter from a cathode ray tube according to the above. 4. The size of a light-emitting area on a fluorescent screen of an electron beam changes when a focusing voltage for the electron beam is set to a predetermined value when a spot-shaped electron beam is aligned with a foreign substance. 3. The method according to claim 1, wherein the pulse duty at the time of removing the foreign matter is changed accordingly. 5. The unit area of the electron beam and the amount of irradiation energy per unit time are determined so that the mask does not thermally deform and the phosphor is not damaged when continuously irradiated with the electron beam. 2. The method for removing foreign matter from a cathode ray tube according to claim 1, wherein the value is equal to or less than the maximum irradiation energy amount per unit time. 6. The method for removing foreign matter from a cathode ray tube according to claim 1, wherein, at the time of removing the foreign matter, an intermittent irradiation position of the electron beam is slightly moved near the foreign matter. 7. The method for removing foreign matter from a cathode ray tube according to claim 1, wherein electron beams corresponding to three colors of red, green and blue are used. 8. After the foreign matter is removed, the entire surface is raster-scanned, and the fluorescent screen is enlarged and imaged by an ITV camera.
The change in luminance of the phosphor at the position corresponding to the foreign matter removal part
The measurement is performed using a video signal level obtained by a V camera.
7. The method for removing foreign matter from a cathode ray tube according to any one of 6. 9. A means for raster-scanning an electron beam on a tube surface, a means for detecting a position of a foreign substance attached to a shadow mask from a light emitting state of a fluorescent surface on the tube surface, and a method for setting a spot diameter of the electron beam to a predetermined size. Means for adjusting the deflection position of the spot-shaped electron beam, means for intermittently turning on and off the electron beam, and means for discretely moving the intermittent irradiation position of the electron beam. Means for removing foreign matter from a cathode ray tube.