JPH04250076A - Optically writing head - Google Patents

Abstract

PURPOSE:To remove unevenness in a light quantity distribution of a fluorescent tube without reducing a light quantity with a simple construction to obtain a uniform light quantity distribution to form an image with a little unevenness of an image density. CONSTITUTION:A substrate 1 is securely held so that at least the top surface thereof is shaped into a substantially cylindrical surface which is gently projected on the side of a cathode. A distance between the substrate 1 and the cathode 5 is increased from the center part to the end part. Namely, where a distance at the center part is tc and a distance at the end part is te, a relation tc < te is held.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to optical writing heads, and more particularly to optical writing heads using fluorescent tubes. for example,
It is applied to image output devices such as digital copying machines, facsimile machines, and printers.

0002

[Prior Art] Conventionally, digital copying machines, facsimiles,
In various electrophotographic image output devices such as printers, solid-state scanning is one of the methods for converting information signals corresponding to the image to be recorded into optical information and writing it on a photoreceptor, which uses a light emitting diode (LED) array. Solid-state scanning write heads using fluorescent tubes together with liquid crystal shutter arrays are being put into practical use.

[0003] Solid-state scanning writing heads using fluorescent tubes are disclosed in, for example, Japanese Utility Model Application Publication No. 1-169257 and Japanese Utility Model Application No. 1-16.
As shown in Japanese Patent No. 9258, a large number of anode electrodes each having minute phosphor dots formed thereon are arranged in an array in the main scanning direction to form a light emitting segment, and thermionic electrons emitted from the cathode are selected according to image information. The material is guided to the phosphor on the anode electrode which is electrically energized to emit light,
The information signal is suitably converted into optical information. The light emitted from the light emitting segment is imaged onto the photoreceptor surface via an imaging optical system.

FIGS. 12(a) and 12(b) are configuration diagrams of a conventional phosphor dot array tube. FIG. 12(a) is a perspective view of the entire tube, and FIG. FIG. In the figure,
31 is a glass substrate, 32 is an anode electrode, 33 is a phosphor, 34 is an insulating layer, 35 is a grid electrode, 36 is a face glass, and 37 is a cathode electrode. In fluorescent tubes,
The substrate 31 has a long plate shape, and a large number of anode electrodes 32 are formed on the substrate 31 so as to extend from the side edges of the substrate 31 toward the center. Each anode electrode 32 is provided with a phosphor 33 by appropriate means such as electrodeposition, and a large number of phosphors 33 are arranged in a straight line in a dot shape. A mesh-like grid electrode 35 with a constant thickness is provided on the base of each anode electrode 32 with an insulating layer 34 in between. This grid electrode 35 extends along both side edges of the glass substrate 31, and the two grid electrodes 35 are placed so as to sandwich each phosphor 33 at a substantially constant interval. Both grid electrodes 35, 35 are covered with a transparent face glass 36 having a U-shaped vertical surface.

[0005] A closed space formed by the face glass 36 and the glass substrate 31 is kept in a vacuum. Two cathode electrodes 37, 37 are stretched in the closed space with a predetermined tension applied thereto. The cathode electrodes 37, 37
is arranged above the grid electrodes 35, 35,
It is provided so as to extend along the longitudinal direction of the glass substrate 31. Thermionic electrons are emitted from the cathode electrodes 37, 37 due to Joule heat obtained by energizing the cathode electrodes 37, 37. When a voltage is applied to the selected anode electrode 32, the thermoelectrons are accelerated and controlled by the grid electrodes 35, 35, and the phosphor 3 on the anode electrode 32 to which the voltage is applied is
3 and causes the phosphor 33 to emit light with a predetermined brightness. That is, the brightness of the phosphor 33 is varied depending on the amount of thermoelectron control by the grid electrode 35.

Incidentally, as shown in FIG. 13, an alternating current voltage is normally applied to the cathode electrode 37 by a center tap type alternating current power supply. In this case, an AC potential is applied to both ends of the cathode electrode 37, but only an intermediate potential is applied to the central part. On the other hand, the amount of thermoelectrons emitted from the cathode electrode 37 is
The phosphor 3 is increased or decreased in accordance with the applied voltage, and as shown in FIG.
The brightness (vertical axis) fL of is increased or decreased by a quadratic function characteristic.

For this reason, in conventional fluorescent tubes, the amount of thermionic emission at both end portions of the cathode electrode where the voltage is high is increased, the luminance of the phosphor in those portions increases, and the amount of thermionic emission at the central portion of the cathode is decreased. As a result, the luminance of the phosphor in that area becomes low. Therefore, unevenness will occur in the phosphor 33. Therefore, when an optical writing head using a fluorescent tube is used in an image output device, the above-mentioned unevenness in the light amount distribution of the fluorescent tube appears as density unevenness on the image, causing a reduction in image quality.

[0008] Therefore, for example, Japanese Patent Laid-Open No. 16832/1983
Publication No. 1, JP-A-62-184759, JP-A-6
According to Publication No. 2-168463, in a device using a phosphor dot array, unevenness in light intensity distribution occurs due to differences in cathode filament voltage (it tends to be low in the center and high at both ends). In order to eliminate this and make the light intensity distribution uniform, the structure of the phosphor dot array itself and the electrical drive conditions are being devised. Furthermore, Japanese Utility Model Publication No. 1-21804 discloses that in an apparatus using an LED array, variations in the amount of light of each LED array can be electrically corrected to be made to be at approximately the same level. However, even if we try to devise the structure of the phosphor dot array itself and the electrical drive conditions (generally by varying the emission time), in reality, it is technically extremely difficult, the correction circuit is complex, and the electrical burden is high. It is also large and expensive.

[0009] Furthermore, in the conventional method as described above, an attempt is made to make the light intensity distribution uniform by reducing the light intensity in the areas where the amount of light is large (both ends) and aligning it with the area where the amount of light is small (the center). Most of them were things. In addition, an optical writing head using the above-mentioned fluorescent tube (Utility Model Publication No.
169257, Utility Model Application Publication No. 1-169258)
In some cases, a fluorescent tube is placed in an optical writing head to correct warping by sandwiching the substrate between a rigid support plate and a housing, or by bonding the substrate to the support plate. Therefore, the substrate of the fluorescent tube is usually held flat within the optical writing head.

0010

[Purpose] The present invention has been made in view of the above-mentioned circumstances, and has a simple configuration that eliminates unevenness in the light intensity distribution of fluorescent tubes without reducing the light intensity, and achieves a uniform light intensity distribution to improve image density. The purpose of this invention is to provide an optical writing head that can form images with less unevenness.

[0011]

[Structure] In order to achieve the above objects, the present invention provides (1)
Phosphors arranged at a predetermined pitch on a substrate, a cathode (cathode line) stretched above the phosphors with a predetermined tension applied substantially parallel to the direction in which the phosphors are arranged, and a voltage applied to the cathode. an optical writing device comprising: a fluorescent tube that selectively causes the phosphor to emit light using electrons emitted by the fluorescent tube; and an imaging optical system that receives light emitted from the fluorescent tube and forms an image on a photoreceptor. In the head, the fluorescent tube is fixed and held with the substrate bent such that the distance between the substrate and the cathode increases from the center to both ends in the direction in which the fluorescent substances are arranged. This is a characteristic feature. Hereinafter, the present invention will be explained based on examples.

FIGS. 1(a) and 1(b) are configuration diagrams for explaining one embodiment of a fluorescent tube used in an optical writing head according to the present invention, and FIG. It is an enlarged view of the part. In the figure, 1 is a substrate, 2 is an anode electrode, 3 is a phosphor, 4 is a face glass, and 5 is a cathode. The substrate 1 is a long glass plate, and a large number of anode electrodes 2 are formed on the substrate 1, and phosphors 3 are formed and arranged in dots on the anode electrodes 2. Further, above the phosphor 3, a cathode 5 is provided with appropriate tension via an elastic body such as a spring.
It is stretched straight so that it hardly bends. Further, the cathode 5 is supported at both ends by supports (not shown) disposed on the substrate 1, and is held on the substrate 1 so as to be substantially parallel to the arrangement direction of the phosphors 3.

[0013] The substrate 1 is fixed and held so that at least its upper surface forms a gentle, generally cylindrical shape with a convex surface facing the cathode side, and the distance between the substrate 1 and the cathode 5 is set from the center to both ends. It seems to get bigger as you go. That is, the relationship between the distance tc at the center and the distance te at both ends is tc<te. Since the thicknesses of the phosphor 3 and the anode electrode 2 are sufficiently smaller than the distance between the substrate and the cathode, the same can be said about the distance between the phosphor and the cathode and the distance between the anode and the cathode.

Now, an AC voltage is applied to both ends of the cathode 5 to emit electrons, and a positive potential (E) is applied to the anode electrode 2.
When b) is applied, electrons are transferred to the phosphor 3 on the anode electrode 2.
This causes the phosphor 3 to emit light, but at this time,
The average electric field strength generated in the space between the cathode and the substrate is stronger at the center than at both ends. That is, Eb/t
c>Eb/te.

Generally, the luminance of a phosphor increases as the distance from the cathode decreases. this is,
This is because as the distance becomes smaller, the solid angle with respect to the phosphor dot increases and the probability of collision with the phosphor dot increases, or the stronger electric field causes the electrons to be drawn toward the anode electrode and collide with the phosphor dot. This is because the number of electrons that

Therefore, by holding the substrate in a warped manner so that the distance between the substrate and the cathode increases from the center to both ends, the unevenness in the light intensity distribution of the fluorescent tube caused by the thermionic emission ability of the cathode can be properly corrected. Corrected. In other words, when a fluorescent tube is used with a flat substrate, the distance between the substrate and the cathode is always te (tc=t
e) As shown by the solid line in Figure 2, the light intensity at the center is lower than at both ends, but this can be fixed by warping the board.
By setting <te, the amount of light in the central part is increased, and as shown in Fig. 2
As shown by the dotted line, the light intensity distribution is made uniform.

In other words, a major feature of the present invention is that the light intensity distribution can be made uniform by increasing the light intensity in areas where the light intensity is low. Furthermore, there is no need to change the structure of the fluorescent tube itself. Note that the specific amount of warpage of the board, that is, the value of Δt=te-tc, is 1 mm.
A value below this level is appropriate. In other words, for a fluorescent tube used in an optical writing head, the distance t between the substrate and the cathode is 0.
Values of the order of 3-3 mm may be used. If the lower limit is exceeded, the cathode may come into contact with other parts in the tube, such as the phosphor and the grid, damaging the phosphor or the cathode itself, and there is also the risk of short-circuiting between the electrodes. Furthermore, if the upper limit is exceeded, the luminance of the phosphor decreases, making it difficult to use it as an optical writing head. If the value of Δt is about 5 to 10% or more with respect to the value of t, the light amount distribution can be corrected, but if it is 1 mm or more,
There are problems with the strength of the substrate (possibility of damage) and the possibility of exceeding the limit of the depth of field of the imaging optical system.

FIG. 3 is a block diagram of an optical writing head using the fluorescent tube shown in FIG. 1. In the figure, 12 is a photosensitive surface, 13 is an optical writing head, 14 is a fluorescent tube, and 15 is a roof mirror. Lens array, 15a is a roof mirror array, 15b is a lens array, 16 is a housing, 17 is a hole, 18 is an elastic member, 19 is a screw, 20 is a support plate, 21 is a mirror, 22 is a slit, 23 is a presser plate, 24 is an internal space, and other parts having the same functions as in FIG. 1 are given the same reference numerals.

A fluorescent tube 14 is disposed on the support plate 20 of the optical writing head 13 via an elastic member 18 as required, and the support plate 20 is given a predetermined rigidity and the fluorescent tube 14 is The tube 14 is held by screws 19 so that the substrate 1 is sandwiched between the support plate 20 and the housing 16. A hole 17 is formed in the housing 16, and the light emitted from the phosphor 3 of the fluorescent tube 14 and transmitted through the face glass 4 is emitted upward through the hole 17, and is deflected by about 90 degrees by the mirror 21. It is reflected at an angle of , and enters the roof mirror lens array 15 . The light reflected and converged by the roof mirror lens array 15 is reflected by the mirror 21
The light passes through the lower transparent portion of the light beam and is further irradiated through the flare prevention slit 22 so as to converge onto the photoreceptor 12 .

FIG. 4 is a configuration diagram of the roof mirror lens array. At least a roof mirror array 15a (a roof mirror array formed continuously at a predetermined pitch) and a lens array 15b (a large number of imaging lenses successively arranged in parallel at the same pitch as the roof mirror array) It is used as a 1-magnification imaging element. The imaging optical system is not limited to the roof mirror lens array, and other imaging elements or lens systems such as a Selfox lens can be used. Roof mirror lens array 15
is the space 2 inside the housing from the opposite direction to the photoreceptor 12 side.
4 and installed at a predetermined position within the housing 16, and is stably held by being pressed by the holding plate 23 via a plate spring or the like.

[0021] Here, a method for holding the fluorescent tube substrate in a warped manner will be described. First, a first holding method is shown in FIG. The fluorescent tube is sandwiched between the upper and lower sides of the fluorescent tube by rigid holding members (for example, the support plate 20 and the housing 16) having arcuate curves with convex and concave surfaces, and the upper and lower holding members are tightened with screws 19 or the like. The substrate 1 is held by the holding member (
Alternatively, the fluorescent tube is fixedly held by following the arc-shaped curve of the guide portion of the holding member. At this time, an elastic member is used as necessary. Alternatively, the substrate of the fluorescent tube may be sandwiched from above and below as shown by arrow B in FIG. 6, or it may be sandwiched from above and below using the face glass and the substrate as shown by arrow C in FIG. good.

Next, a second holding method is shown in FIG. A convex protrusion 10 may be provided at the center of the holding member 20, and convex protrusions 11 may be provided at both ends of the holding member 16 to sandwich the fluorescent tube. Of course, a spacer or another member such as an elastic member as a spacer can be used instead of the convex projection. When using an elastic member as a spacer, it is necessary to set the thickness in consideration of the amount of deformation.

FIG. 8 is a side view of the configuration shown in FIG. 5, viewed from the slit side. The support plate 20 has a convex surface on the substrate side, and the lower surface of the housing 16 has a concave shape, and a fluorescent tube is sandwiched between the housing 16 and the substrate 1 with an elastic member 18 interposed between the support plate 20 and the substrate 1. The substrate 1 is held and fixed by screws 19 so that the shape of the substrate 1 is warped by a predetermined amount (Δt).

FIG. 9 is a side view of the structure shown in FIG. 7, viewed from the slit side. A convex portion is provided at both ends of the lower surface of the housing 16 in the center of the support plate 20, and a fluorescent tube is held and fixed to the convex portion by sandwiching it from above and below via an elastic member 18, thereby warping the substrate. be. The amount of warpage of the board can be adjusted by tightening the screws 19.

FIG. 10 is another example of a side view corresponding to the configuration shown in FIG. 7, viewed from the slit side. An elastic member 1 is provided at the center of the support plate 20 and at both ends of the lower surface of the housing 16.
8 was installed, fluorescent tubes were sandwiched from above and below, and screws were secured. When the screw 19 is tightened, the substrate of the fluorescent tube can be warped by an amount corresponding to the thickness of the elastic member serving as a spacer. Furthermore, since the fluorescent tube can be held fixed even when the screws 19 are not tightened, the amount of warpage of the substrate 1 can be adjusted by adjusting the way the screws are tightened.

[0026] In the above embodiments, the method of warping the substrate was shown, but this is only an example, and various other methods can be considered. That is, the fluorescent tube may be fixed and held within the optical writing head by bending the substrate of the fluorescent tube by a predetermined amount. Note that FIG. 11 is a side view showing a typical example in which a fluorescent tube is held so that its substrate is kept on a substantially flat surface.

[0027]

[Effects] As is clear from the above description, the present invention has the following effects. The fluorescent tube was fixed and held with the substrate bent so that the distance between the substrate and the cathode increased from the center to both ends in the direction in which the phosphors were arranged. Unevenness in the light amount distribution can be removed without reducing the light amount, and a uniform light amount distribution can be obtained. Therefore, an optical writing head that can obtain images with less density unevenness can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining one embodiment of a fluorescent tube used in an optical writing head according to the present invention.

FIG. 2 is a diagram showing a light amount distribution of a fluorescent tube.

FIG. 3 is a configuration diagram of an optical writing head using the fluorescent tube shown in FIG. 1;

FIG. 4 is a configuration diagram of a roof mirror lens array.

FIG. 5 is a diagram for explaining a first holding method for warping the substrate of a fluorescent tube.

FIG. 6 is a diagram showing another example of the first holding method.

FIG. 7 is a diagram for explaining a second holding method for warping the substrate of a fluorescent tube.

FIG. 8 is a side view of the structure shown in FIG. 5, seen from the slit side.

FIG. 9 is a side view of the structure shown in FIG. 7, seen from the slit side.

10 is another example of a side view seen from the slit side corresponding to the configuration shown in FIG. 7. FIG.

FIG. 11 is a side view showing an example in which a fluorescent tube and a substrate are held on a substantially flat surface.

FIG. 12 is a configuration diagram showing a conventional fluorescent tube.

FIG. 13 is a diagram showing a potential distribution applied to a cathode electrode.

FIG. 14 is a diagram showing the relationship between cathode electrode voltage and brightness.

[Explanation of symbols]

1 Board 2 Anode electrode 3. Phosphor 4 Face glass 5 Cathode

Claims (1)

[Claims] 1. Phosphors arranged at a predetermined pitch on a substrate, a cathode stretched above the phosphors under a predetermined tension substantially parallel to the direction in which the phosphors are arranged, and a cathode attached to the cathode. A light comprising a fluorescent tube that selectively causes the phosphor to emit light by electrons emitted by applying a voltage, and an imaging optical system that receives the light emitted from the fluorescent tube and forms an image on a photoreceptor. In the writing head, a fluorescent tube was fixed and held with the substrate bent such that the distance between the substrate and the cathode increased from the center to both ends in the direction in which the phosphors were arranged. An optical writing head characterized by: