JP2001138571A - Led printer head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED printer head which can prevent an image quality deterioration because of a reflecting light generated when a light emitted from an LED array is reflected by a lens array surface and by a member in the periphery of the LED array. SOLUTION: A light-shielding plate 1 is interposed between an LED array 42 and a collecting rod lens array 45. A slit-shaped trough hole 2 is formed in a main scanning direction to the light-shielding plate. Moreover, an AR coating is provided on the face of the light-shielding plate opposite to a collecting rod lens 45a. The lens 45a is arranged at a position outside a line connecting an LED array element 42a and a projection point 71b on a photoreceptor 71, so that the light from the element 42a is brought into and out of the lens 45a slantwise. The through hole 2 is positioned on a line connecting the element 42a and the lens 45a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a printer head of an LED array printer, and more particularly, to an LED printer head provided with an LED array (light emitting diode array) as a micro light source array.
The LED printer head can be widely applied to writing units such as an optical printer, a copying machine, a facsimile, and a scanner.

[0002]

2. Description of the Related Art With the development of information devices for small offices (small offices) and home offices, the demand for printers for outputting various types of paper information has been increasing. Such a printer needs to be able to output high-resolution images and characters in monochrome or color. Also, with the increase in demand, the above-mentioned printer requires higher resolution, higher output speed,
It is required to be compact and inexpensive.

As an example of a printer satisfying these requirements, there is an electrophotographic optical printer using LEDs. In this method, since the LED array is used as a light source, it can be configured more easily and compactly than an optical printer having a writing optical system using a semiconductor laser, and each LED array element performs writing in parallel. It is relatively easy to achieve high-speed output. Further, an optical printer using an LED array element (LED array chip) has an advantage that it is more resistant to deformation of an optical system due to vibration and heat than an optical printer of a laser raster system.

FIG. 3 is a schematic cross-sectional view showing a writing system including a photosensitive drum and an optical system in a conventionally used optical printer. In this writing system, the light 32 emitted from the LED array light source 31 passes through the same-magnification imaging optical system 33, and only the light that has entered the field of view of the same-magnification imaging optical system 33 condenses on the photosensitive drum 34. Then, the photosensitive surface 34a is exposed.

It is said that the image quality of the LED array printer is inferior to that of the laser raster printer, but one of the reasons is the deformation of the image formation such as uneven line width of the image. The cause of line width unevenness is LED
Variations in point images (dots) formed by the array on the photosensitive surface (irradiated surface) of the photosensitive member are mentioned.

FIG. 4 is a cross-sectional view showing an example of the structure of a conventional LED printer head and a cause of the point image variation occurring in the LED printer head. In this printer head, the substrate 44 having the following components
Deployed within. That is, on this substrate 44,
An LED array 42 having a large number of dot-shaped LED array chips 42a arranged in a line;
3 and these LED array chips 42
a and the driver IC 43 are electrically connected by a bonding wire (not shown).

A light-condensing rod lens array 45, in which a large number of light-condensing rod lenses 45a are arranged, is provided above the housing 41 and immediately above the LED array chip 42a. Further, a photosensitive drum (not shown) is provided to face the light-collecting rod lens array 45.

In this LED printer head, a desired LED array chip 42
Then, dot light is emitted to a, and the dot light is transmitted through a predetermined rod lens 45a of the light-collecting rod lens array 45 to form an image on the photosensitive surface of the photosensitive drum.

However, the light emitted from the light emitting area of the LED array chip 42a is almost completely diffused light, and there is no directivity of only the output light (outgoing light) 42b, and some diffused light is
As shown in FIG.
The light is reflected at 43 or the like and becomes reflected scattered light 42c. And
Such reflected and scattered light 42c enters the light-collecting rod lens array 45 and is transmitted, resulting in the formation of these latent images on the photosensitive drum. When printing is performed in this state,
Protruding print unevenness, commonly called whiskers, occurs and causes deterioration of print quality.

An LED printer head that solves the above problem is disclosed in Japanese Utility Model Publication No. 6-5814. As shown in FIG. 5, this printer head has a pair of light shielding plates 51, 51 opposed to each other on both sides of an optical path that linearly connects the LED array 42 and the light-condensing rod lens array 45. . That is, in this LED printer head, of the light from the LED array chip 42a, only the light (outgoing light 42b) directed to the condensing rod lens 45a passes through the optical path and is reflected in the housing 41. The generated disturbance light such as the reflected scattered light 42c is shielded by the light shielding plate 51 so that the disturbance light does not reach the light collecting rod lens 45a. Thereby, the disturbance light is blocked by the light shielding plate 51,
Since light does not enter the light collecting rod lens 45a, the occurrence of printing unevenness is prevented.

[0011]

However, according to the study by the present inventor, it has been found that even if the countermeasure shown in FIG. 5 is taken, another problem still remains. Hereinafter, this will be described with reference to FIGS. FIG. 6 is a schematic explanatory view of the structure of the main part of the LED printer head, in which the output light 42b from the LED array chip 42a and the reflected light 61 generated by the reflection on the surface of the condensing rod lens 45a.
Is shown. FIG. 7 shows an example of the structure in the vicinity of the LED light emitting portion (chip body) of the LED array.
FIG. 9 is a schematic explanatory view showing an arrangement relationship between a D array chip 42a and wirings 52 and electrodes 53 (bonding pads) for operating the D array chip 42a.

In FIG. 6, the LED array chip 42a
A part of the light coming out of the lens and entering the condensing rod lens 45a is reflected by the surface of the lens 45a, and the reflected light 61
The vicinity of the ED array chip 42a is irradiated. In general, the surface of a rod lens constituting a condensing rod lens array has a refractive index distribution and does not have a uniform refractive index, so that it is difficult to apply an anti-reflection coating (AR coating). Therefore, it is difficult to suppress such light reflection on the lens surface.

[0013] As shown in FIG.
In the vicinity of the ED array chip 42c, this chip 42a
52 for supplying a current to the
An electrode 53 and the like for connecting to the outside by bonding are arranged. However, when the reflected light 61 on the surface of the rod lens 45a is applied to the vicinity of the LED light emitting portion, the light is further reflected by the wiring 52 and the electrode 53. As a result, an abnormal light emitting point near the LED light emitting portion Occurs.
Then, the reflected light (light from the emission light point) and the LED
Both the outgoing light 42b from the array chip 42a enters the rod lens 45a, and these light
a is transmitted light 62 from the photoconductor 71
On the photosensitive surface 71a (writing surface) of the recording medium, causing variations in dots and, consequently, deterioration of image quality. In FIG. 6, reference numeral 71b denotes the photosensitive surface 71.
It is a projection point on a.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an LED printer in which light emitted from an LED array is condensed on a photosensitive surface of a photoreceptor via a rod lens array. When the light emitted from the LED array is reflected on the surface of the lens array,
An object of the present invention is to provide an LED printer head capable of preventing deterioration of image quality and having a high quality image stably formed by adopting a structure that does not further reflect light from members around the ED array.

[0015]

An LED according to claim 1
The printer head has an LED array in which a plurality of LED array elements are arranged, and a plurality of light-condensing rod lenses for condensing light emitted from the LED array elements and forming an image on a photoconductor. L with lens array
In the ED print head, a light-shielding plate in which a slit-shaped light-transmitting hole is formed and a surface facing the light-collecting rod lens is non-reflective is provided between the LED array and the lens array. The light-transmitting hole transmits light from the LED array element and enters the light-collecting rod lens, but the light reflected by the light-collecting rod lens does not pass through the light-transmitting hole. It is characterized by being formed in.

According to the present invention, light emitted from the LED light-emitting portion and reflected on the surface of the light-collecting rod lens array is transmitted to the LED light-emitting portion and its peripheral portion (these portions are located behind the light-shielding plate). ) Can be prevented from being emitted, so that the occurrence of an abnormal light spot near the LED light emitting portion can be prevented. Hereinafter, this will be described in detail.

(1) Light reflected from the rod lens array hits the light shielding plate and is blocked. The slit-shaped light-transmitting hole of the light-shielding plate transmits light from the LED light-emitting unit and makes it incident on the rod lens array, but is located at a position where reflected light from the rod lens array transmits through this light-transmitting hole. Not formed. For this reason, since the reflected light does not hit the LED light emitting portion and its peripheral portion, the reflected light from the rod lens array does not reflect on the LED light emitting portion and its peripheral portion and enter the rod lens array. .

(2) Light reflected from the rod lens array impinges on the light shielding plate. However, for example, antireflection processing (AR processing) is performed on the upper surface (the surface on the side facing the rod lens array) of the light shielding plate, or an AR film is attached. For this reason, the light hitting the light-shielding plate (which is absorbed by the light-shielding plate) does not indirectly enter the rod lens array.

(3) As described above, the reflected light from the rod lens array does not hit the LED light emitting portion and its peripheral portion, and the reflected light from the rod lens array does not reflect on the light shielding plate. Therefore, only the light emitted from the LED light emitting unit will shine on the rod lens array,
This achieves the object of the present invention.

The slit-shaped light-transmitting holes of the light-shielding plate are
It may be a through-hole formed in the light-shielding plate, or a pair of light-shielding plates may be separated and opposed, and the opposed gap may be a light-transmitting hole. The form of the photoreceptor is not limited, and may be, for example, a drum shape or a belt shape.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view showing the main structure of the LED printer head. FIG. 2 shows this L
How to arrange the light shielding plate in the ED printer head, and
FIG. 4 is a schematic cross-sectional view showing the operation, which is a cross-sectional view taken along a plane orthogonal to the main scanning direction.

In the LED printer head, the light shielding plate 1 having a predetermined configuration is provided at a predetermined position between the LED array 42 and the light-collecting rod lens array 45 as described below. The light shielding plate 1 has a slit-shaped light transmitting hole 2 formed in the main scanning direction (the direction in which the LED array elements 42a of the LED array 42 are arranged). The surface of the light shielding plate 1 facing the light-collecting rod lens 45a is AR (Anti-Reflect).
ion) Non-reflective because of coating.

Further, the light-collecting property is located at a position (right side of this straight line in FIG. 2) deviating from a straight line (not shown) connecting the LED array element 42a and the projection point (imaging point) 71b on the photosensitive member 71. The rod lenses 45a are arranged, and the slit-shaped light transmitting holes 2 of the light shielding plate 1 are positioned on a straight line (not shown) connecting the LED array element 42a and the condensing rod lens 45a. With such a configuration, the light transmitting holes 2 are LE
Although the light from the D array element 42a is transmitted and made incident on the rod lens 45a, the reflected light 61 from the rod lens 45a does not pass through the slit-shaped light transmitting hole 2.

The structures of the LED array 42 and the light-condensing rod lens array 45 are the same as those of the known one. However, the latter will be briefly described. A large number of cylindrical rod lenses 45a are formed by a pair of holding members facing each other. Board 45
b and 45b are inserted in an aligned state, and a non-reflective and non-transparent resin 45c is inserted into the space between the two holding plates.
Is filled.

According to the above configuration, since abnormal light emission does not occur near the LED light emitting portion, in the LED printer equipped with the LED printer head, abnormal thickening of dots is suppressed, and variation in dots is suppressed, and image quality is improved. Is greatly improved.

[0026]

As is apparent from the above description, according to the present invention, the light emitted from the LED light emitting portion and reflected on the surface of the condensing rod lens array does not irradiate the vicinity of the LED light emitting portion. Therefore, occurrence of an abnormal light spot near the LED light emitting unit is prevented. As a result, there is the effect that abnormal thickening of the dots is suppressed, the variation of the dots is suppressed, and a significant improvement in image quality can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a main structure of an LED printer head according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a procedure for arranging a light shielding plate in the LED printer head of FIG. 1 and its operation.

FIG. 3 is a schematic cross-sectional view illustrating a main structure of a writing system in a conventional optical printer.

FIG. 4 is a cross-sectional view showing a main part structure of a conventional LED printer head.

FIG. 5 is an LED disclosed in Japanese Utility Model Publication No. 6-5814.
FIG. 3 is a cross-sectional view illustrating a main part structure of the printer head.

6 is a schematic cross-sectional view for explaining a problem in the LED printer head of FIG.

FIG. 7 shows LE in a general LED printer head.
FIG. 4 is a schematic explanatory view showing a structural example near a D light emitting unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light-shielding plate 2 slit-shaped light-transmitting hole 31 LED array light source 32 outgoing light 33 unit-magnification imaging optical system 34 photosensitive drum 34 a photosensitive surface 41 housing 42 LED array 42 a LED array chip 42 b outgoing light 42 c reflected and scattered light 43 driver IC 44 Substrate 45 Light collecting rod lens array 45a Light collecting rod lens 45b Holding plate 45c Resin 51 Light shielding plate 52 Wiring 53 Electrode 61 Reflected light 62 Transmitted light 71 Photoconductor 71a Photosensitive surface 71b Projection point

Claims (1)

[Claims] 1. An LED array in which a plurality of LED array elements are arranged, and a plurality of light-condensing rod lenses for condensing light emitted from the LED array elements and forming an image on a photoconductor. LED with lens array made of
In the print head, a slit-shaped light-transmitting hole is formed, and a light-shielding plate in which a surface facing the light-collecting rod lens is non-reflective is provided between the LED array and the lens array. The light transmitting hole transmits light from the LED array element and enters the light collecting rod lens, but is formed at a position where light reflected by the light collecting rod lens does not pass through the light transmitting hole. An LED printer head characterized in that: