JP3684098B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat plate type image forming apparatus comprising an anode and a cathode. More specifically, the present invention relates to a novel image forming apparatus that avoids various damages related to abnormal discharge.
[0002]
[Prior art]
In recent years, flat image forming apparatuses composed of an anode and a cathode have been extensively researched and developed, and examples of electron sources used include those composed of field emission elements, surface conduction electron emission elements, and the like. Can be mentioned. As an example using the former field emission device, US Pat. No. 5,142,184 has been proposed. As an example using the latter surface conduction electron-emitting device, US Pat. No. 5,066,883 has been proposed.
[0003]
Although there are differences in the structure of the electron source and the driving method, the common feature is that it has a cathode consisting of an electron source composed of a plurality of electron-emitting devices and an anode close to the cathode. It is. The distance between the cathode and the anode is approximately several hundred μm to several mm. The point to be noted here is that a large capacitance is generated because the wiring for the cathode and the connection and the anode electrode for attracting electrons are close to each other.
[0004]
A high positive potential of several kilovolts to several tens of kilovolts is usually applied to the anode in order to attract electrons. Therefore, a large amount of electric charge is accumulated between both the anode and the cathode. Note that in this specification, the substrate on which the anode is formed is abbreviated as an anode substrate, and the substrate on which the cathode located opposite to the substrate on which the anode is formed is abbreviated as a cathode substrate. When such a large potential difference is applied between narrow electrodes, that is, in a strong electric field situation, abnormal discharge may occur between the anode and the cathode substrate. The abnormal discharge referred to here refers to a state in which a current flows which is related to driving and which is distinguished from a regular or expected emission current emitted from an electron source. For example, it refers to a discharge with a large current that causes a short circuit between the anode and the cathode.
[0005]
Such an abnormal discharge is considered to occur when there is an insufficient vacuum between the cathode and the anode substrate, or when there is a problem that an abnormal electric field can be caused in the electrode shape. Once such an abnormal discharge occurs, damage to the electrodes and the like due to current concentration, or, in severe cases, destruction of the element connected to the abnormal discharge part via the wiring leads to arc discharge in a vacuum. There is a case. This arc discharge results in a large current, and due to the large amount of Joule heat caused by the current, not only the element in the abnormal discharge part is destroyed, but also the evaporated particles may cause a short circuit of other elements and wiring. Further, it is considered that the current concentration destabilizes the potential of the cathode and the wiring for connection, and as a result, damages to the elements connected via the wiring.
[0006]
Conventionally, when an arc discharge occurs as such an abnormal discharge, during the arc discharge, a large current flows from an external voltage source through the anode and further through an ionized vacuum and flows as an electric arc to the emitter (cathode). Japanese Patent Application Laid-Open No. 08-106847 discloses a technique for providing an inductor between an anode and an external voltage source for the purpose of limiting the current. The abnormal discharge used in this specification includes the above-described arc discharge.
[0007]
[Problems to be solved by the invention]
Therefore, it is most important not to cause an abnormal discharge between the anode and the cathode. However, in the case of a realistic image forming apparatus constituted by a large number of elements, it is possible to prevent it completely with a high yield. is important. Therefore, in the unlikely event that an abnormal discharge occurs, it is important to take measures to alleviate the damage, which has been eagerly desired.
[0008]
The technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 08-106847 is schematically shown in FIG. In FIG. 5, 21 is a substrate, 22 is a cathode electrode, 23 is an emitter, 24 is a cathode conductor, 25 is an insulator, 26 is a gate, 27 is an anode, 28 is an inductor, 29 is a resistor, and 30 is a voltage source. This technique uses a field emission device as an electron-emitting device and is supplied from a voltage source 30 in connection with the arc discharge between the anode 27 and the emitter 23 while the arc discharge is generated between the anode 27 and the emitter 23 (cathode). By providing the inductor 28, the current is substantially limited. That is, when arc discharge occurs and the potential of the anode 27 decreases, the injection of charges from the external power source is limited in time.
[0009]
However, in a large-screen image forming apparatus with a large capacitance between the anode and the cathode substrate, the amount of charge accumulated on the anode and the cathode substrate is large, and this charge corresponds to a decrease in the potential of the anode at the start of abnormal discharge. There is a problem of moving through the discharge path. When this charge movement is performed instantaneously, the current value becomes considerably large. Of course, this current cannot be observed as a current flowing into the anode from the external power source, that is, cannot be suppressed by the above-described method of limiting the injection of charges from the external power source. This is to restore the lowered anode potential in the event of abnormal discharge, in other words, only as a current that charges the capacitor composed of the anode and cathode substrate, or as a current that sustains the arc as a result of arc discharge. Because it was observed.
[0010]
The present inventors confirmed that the movement of the electric charge according to the decrease in the potential of the anode occurs on a time scale of about μsec or less by measuring the temporal change of the anode potential during abnormal discharge. Yes. In addition, as a result of preliminary examination described later, it has been confirmed that a current corresponding to the decrease in the potential of the anode flows through the discharge path, thereby causing damage.
[0011]
Therefore, an object of the present invention is to suppress the current corresponding to the decrease in the anode potential from flowing through the discharge path.
[0012]
[Means for Solving the Problems]
The configuration of the present invention made to solve the above problems will be described below.
[0013]
The present invention includes an electron source, an image forming apparatus of anodic or Ranaru plate type electron source is a potential to attract the electrons emitted applied, a means for detecting abnormal discharge image forming region, the abnormal discharge An image forming apparatus comprising: means for discharging between the electron source and the anode in a non- image forming area outside the image forming area when the image is detected .
[0016]
Specifically, by detecting abnormal discharge, the charge accumulated between the anode and the cathode is quickly released through the non-image forming area. Thereby, at the start of abnormal discharge, the potential difference between the anode and the cathode, which is essential for abnormal discharge such as arc discharge, can be reduced. This makes it possible to avoid arc discharge or to significantly reduce its scale.
[0017]
As means for detecting the abnormal discharge described above, there are means for detecting the amount of change in the anode potential and the precursor development of abnormal discharge. In addition, the cathode is composed of an electron source composed of a plurality of electron-emitting devices, and the means for detecting abnormal discharge is a voltage observed superimposed on the applied voltage in relation to driving of the electron source, or a current corresponding thereto. It may be. The means for discharging in the non-image forming area may be any means as long as it has excellent responsiveness and can flow a large current instantaneously.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
An image forming apparatus to which the present invention is applied will be described below. FIG. 1 is a schematic diagram showing the configuration of the present invention. In FIG. 1, 1 is an anode substrate, 2 is a cathode substrate on which electron-emitting devices are formed, 3 is a means for detecting abnormal discharge, 4 is an image forming region, 5 is a high-voltage power supply, and 6 is a non-image. A means for discharging in the forming area, 7 indicates a resistance or inductance for limiting the current from the high-voltage power supply 5, and 8 indicates a signal for operating the means 6 for discharging in the non-image forming area from the detecting means 3.
[0019]
Next, the operation principle will be described. In order to function as an image forming apparatus, a high positive potential of several kilovolts to several tens of kilovolts is usually applied to the anode substrate 1 in order to give a sufficient acceleration voltage to the electron beam. Under such circumstances, controlled electrons are emitted from the electron-emitting devices formed in the image forming area of the cathode substrate 2 to cause the phosphor (not shown) formed in the image forming area of the anode substrate 1 to emit light. . The electron flow in this case is distinguished from the abnormal discharge in the present invention.
[0020]
Further, the current related to the image formation is small, and the decrease in the anode potential due to the current related to the image formation can be almost ignored. The anode substrate 1 and the cathode substrate 2 are normally kept in a vacuum, and the distance between the anode substrate 1 and the cathode substrate 2 is smaller than the mean free path of emitted electrons.
[0021]
Even in such a situation, abnormal discharge may be suddenly observed. The reason for this cannot be clearly limited, but for example, there is a case where there is a problem that an abnormal electric field can be brought about in the electrode shape formed on the cathode substrate 2. In order to specify the start of abnormal discharge, for example, it is possible to measure the change in the anode potential with an electrometer provided in the vicinity of the anode substrate 1. When an abnormal discharge occurs and a potential change greater than a certain threshold is observed, the electric charge stored in the anode is released by discharging in the non-image forming area in the image forming apparatus.
[0022]
In this case, if the time required for observing abnormal discharge and discharging in the non-image forming area is sufficiently short, the current flowing through the space in the image forming area via the anode and cathode vacuum can be cut off or reduced. As a result, the damage that should have occurred on the cathode in the image forming area can be greatly reduced.
[0023]
When the discharge is completed in the non-image forming area, the current from the high-voltage power supply 5 defines the potential of the anode again if no current flows through the space between the anode substrate 1 and the cathode substrate 2 in the image forming area. It flows as a charging current that restores to the value of. This makes it possible to suppress damage due to abnormal discharge.
[0024]
[Preliminary detection]
An experiment was conducted with the system schematically shown in FIG. 2 for the purpose of clarifying the time change of the anode potential during abnormal discharge and the process in which damage occurs. In FIG. 2, 9 is a switch for separating the high-voltage power supply 5 and the anode substrate 1, and 10 is an electrometer. Moreover, about the thing which is common in the site | part shown in FIG. 1, the same number is shown and duplication description is abbreviate | omitted. The capacitance between the anode substrate 1 and the cathode substrate 2 is about 200 pF.
[0025]
First, a high voltage of about 6 kV is applied to the anode substrate 1 to drive the cathode substrate 2 so as to reach the anode substrate 1 in the form of an electronic pulse. At this time, a cathode substrate 2 having an electron source arrangement and connection in a matrix structure was used, and only one arbitrary row was selected and driven at 10 Hz. At this time, the switch 9 is opened every time immediately before electrons are emitted from the cathode substrate 2, and is closed again after the emission of electrons is completed. The switch 9 was a vacuum switch that can be opened and closed by applying a pulse.
[0026]
When driving in such a situation, the switch 9 is disconnected from the high-voltage power source 5 every time the electrons are emitted, so that a decrease in the anode potential due to the emitted electrons can be observed with the electrometer 10. The amount of potential decrease is determined by the amount of emitted electrons. In this experiment, the amount of emitted electrons was set so that the potential drop was less than 3% with one pulse. Under such circumstances, driving was performed until abnormal discharge occurred.
[0027]
When the time change of the indicated voltage of the electrometer 10 when the abnormal discharge was observed was measured, the graph shown in FIG. 3 was obtained. In the graph of FIG. 3, the horizontal axis indicates time, the left vertical axis indicates the potential, and the right vertical axis indicates the current flowing from the anode substrate 1 to the cathode substrate 2, which is obtained from the time differentiation of the potential. The current flowing from the anode substrate 1 to the cathode substrate 2 due to the abnormal discharge can be obtained by the product of the potential time derivative and the capacitance. From FIG. 3, it is understood that a current of about 11 A at the maximum flows in this experiment about 200 nanoseconds after the start of the potential drop of the anode. In FIG. 3, the time when the time on the horizontal axis is zero is the start time of electron emission related to driving.
[0028]
Next, after the abnormal discharge was observed, it was inspected whether the element selected for driving was defective. As a result, it was found that the elements corresponding to three pixels were greatly damaged. As a result, it was understood that a current corresponding to a decrease in the potential of the anode may flow through the discharge path and cause damage.
[0029]
【Example】
Hereinafter, the present invention will be described based on examples.
[0030]
[Example 1]
FIG. 4A shows a configuration diagram of an image forming apparatus constituted by the anode substrate 1 and the cathode substrate 2. FIG. 4B shows a part of the image forming apparatus. In this embodiment, a surface electric type electron-emitting device is used as an electron-emitting device, and a cathode substrate 2 composed of electron sources arranged in a matrix, a phosphor 18 for performing color display, and a metal back 19 made of Al are formed. The prepared anode substrate 1 was used. It will be understood from the above description that the image forming apparatus of the present invention is not particularly limited as an electron source.
[0031]
The image forming area is formed by the following configuration. 12 is an x-direction wiring, 13 is a y-direction wiring, 15 is a surface conduction electron-emitting device, 18 is a phosphor, and 19 is a metal back. The surface conduction electron-emitting device 15 is provided with opposing device electrodes. By applying a voltage of about 15 V between the device electrodes, a device current If flows between the electrodes, and at the same time, electron emission occurs. Done. In this example, a device composed of 720 elements in the y direction (n = 720) and 240 elements in the x direction (m = 240) was used.
[0032]
On the other hand, the non-image forming area is formed by the following configuration. 32 is a + side wiring, 33 is a-side wiring, and is connected to the electron-emitting device 34 in a ladder shape by opposing device electrodes. These wirings are configured to be electrically insulated from the electron source 14 including the x-direction wiring 12 and the y-direction wiring 13 in the image forming area.
[0033]
As shown in FIG. 4A, an anode electrode 36 is formed on the side of the anode substrate 1 facing the cathode substrate 2 of the non-image forming portion and is electrically connected to the metal back 19. In this embodiment, a surface conduction electron-emitting device is used as a means for discharging in the non-image forming region, but it is not particularly limited. Since the phosphor 18 is not formed on the anode substrate 1 in the non-image forming region, no light is emitted during discharge.
[0034]
Reference numeral 16 denotes a rear plate that supports the cathode substrate 2, reference numeral 17 denotes a glass substrate, and reference numeral 20 denotes a support frame that fixes the anode substrate 1 and the cathode substrate 2. The rear plate 16, the glass substrate 17, and the support frame 20 constitute an envelope of a sealed container. The abnormal discharge detection means is an electrometer 10 provided near the anode substrate 1 and also has a counter for checking the number of times of control. When the potential fluctuation of the electrometer 10 is measured to be 20 V or more, a voltage of about 20 v is applied between the element electrodes of the electron-emitting device 34 through the + side wiring 32 and the − side wiring 33 and through the discharge monitoring power source 35. The system configuration is such that the discharge occurs in the non-image forming area and the short circuit occurs.
[0035]
Now, a high voltage of 10 kV is applied to the anode, and the x-direction wiring 12 of the cathode substrate 2, specifically, Dox1, Dox2,... Dox (m−1), Doxm, and the y-direction wiring 13, specifically, Doy1. , Doy2,... Doy (n−1), Doyn are driven to drive an unillustrated driver unit to display an image in the image forming area. In this state, a durability test for 1000 hours was performed while displaying various images. As a result, three abnormal discharges were detected by the counter of the abnormal discharge detection means 3, and control related to the present invention, that is, a non-image forming area. This was performed three times through control of applying a voltage between the + side wiring 32 and the − side wiring 33 from the discharge monitoring power source 35 in FIG. Further, even after 1000 hours, no image defect or the like due to abnormal discharge was observed, and a good image was maintained.
[0036]
From this, it was shown that the image forming apparatus of the present invention is effective in reducing damage caused by abnormal discharge.
[0037]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, it is possible to effectively control various damages such as image defects due to abnormal discharge.
[0038]
In addition, since the discharge voltage is detected and controlled in the non-image forming area when an abnormal discharge occurs, the influence of the image forming area on the electron-emitting devices can be prevented, and long-time image formation can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of an image forming apparatus used for preliminary examination.
FIG. 3 is a graph showing a change with time of an anode potential measured by a preliminary study and a current flowing from the anode to the cathode.
FIG. 4 is a schematic diagram of an image display unit configured with an image forming region in which surface conduction electron-emitting devices are arranged in a matrix and a non-image forming region in which surface conduction electron-emitting devices are arranged in a ladder shape in the embodiment. is there.
FIG. 5 is a schematic diagram showing a conventional technique for limiting arc current.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Anode 2 Cathode board 3 Abnormal discharge detection means 4 Image formation area 5 High voltage power supply 6 Means to discharge in non-image formation area 7 Resistance or inductance for limiting current from high voltage power supply 8 Signal 9 For shutting off the high voltage power supply of the anode Switch 10 Electrometer 12 X direction wiring 13 Y direction wiring 14 Electron source 15 Surface conduction electron-emitting device 16 Rear plate 17 supporting cathode substrate 2 Glass substrate 18 Phosphor 19 Metal back 20 Alead substrate 1 and cathode substrate 2 are fixedly supported Frame 21 Substrate 22 Cathode electrode 23 Emitter 24 Cathode conductor 25 Insulator 26 Gate 27 Anode 28 Inductor 29 Resistance 30 Voltage source 32 + Side wiring 33 −Side wiring 34 Surface conduction electron-emitting device 35 Power source 36 for starting discharge 36 Electrode

Claims (2)

An electron source, an image forming apparatus of anodic or Ranaru plate type potential is applied to attract electrons electron source emits,
Means for detecting abnormal discharge in the image forming area;
An image forming apparatus comprising: means for discharging between the electron source and the anode in a non-image forming area outside the image forming area when the abnormal discharge is detected . The means for discharging includes an electron-emitting device provided in the non-image forming region, and the electron-emitting device and the electron-emitting device included in the electron source in the image forming region are electrically connected. The image forming apparatus according to claim 1, wherein there is no image forming apparatus.

Images