JPH0267155A - Led printer - Google Patents

Abstract

PURPOSE:To enhance the printing quality by compact apparatus constitution by forming a non-reflecting coating layer for preventing the reflection of the incident light from an LED to the incident surface of a condensing lens. CONSTITUTION:A non-reflecting coating layer 28 is provided to the incident surface of a SELFOC lens array 27. Since the reflectivity of the incident surface of the SELFOC lens array 127 to the light emitted from an LED becomes 0 by said coating layer 28, flare light can be perfectly cut. As a result, the printing quality of an LED printer can be enhanced markedly by merely forming the coating layer to the part corresponding to the incident surface of a condensing lens and, therefore, the complication of apparatus constitution and an increase of the number of parts can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an LED printer that converges light from an LED onto a photosensitive drum via a condensing lens to form a latent image.

Figures 2 to 4 show the structure of the optical system in this type of LED printer. The optical system 2 includes a light source L for exposure on a ceramic substrate 21 attached to the surface of the Aβ substrate 20.
ED22 and drive IC23 that controls its light emission
The LED chip 2 is bonded with a gold wire 25 via a pattern 24 (gold plating is often used to reduce resistivity) placed in the middle of each die.
2 and a drive IC 23 are electrically connected. Note that the LED 22 has a size of 50 μm x 50 μm as shown in FIG. 300 ljm chip 22a
Approximately 0 of them are arranged in a line and emit light with a single wavelength of approximately 740 nm. Further, 26 in the figure is a cover for attaching the entire LED array to the main body of the device.

Below the optical system 2 is a SELFOC lens (a product name of Nippon Sheet Glass Co., Ltd.) as shown in Figure 2 (however, it is drawn upside down in Figure 2) and Figure 9. , a type of condensing lens) The array 27 is attached to the holder 26a.
The light emitted from the LED 22 is focused and exposed onto the photosensitive drum 7 to form a latent image on which character information is written. Note that FIG. 9 is a front view showing the optical system 2 in order to explain the flare light F described below, and 26 in the figure is a holder or cover for attaching the entire optical system 2 to the main body of the device.

However, in order to improve the printing quality in an LED printer, as shown by the broken line in FIG. It is necessary to eliminate as much as possible the adverse effects of the flare light F, which re-enters the SELFOC lens array 27 after being reflected again by the pattern 24, the gold wire 25, and other high-reflectance parts.

FIG. 10 is a graph showing the potential distribution of the latent image, and FIG. 11 is an explanatory diagram showing the adverse effects of flare light F.

As shown in FIG. 10, in an LED printer that uses N-P C (negative-positive) development, the surface potential of the photosensitive drum 7 is set to approximately 1,600 V during charging.
. On the other hand, by applying a bias voltage of -450 V to the developer side and providing a potential difference of -150 V,
The purpose is to prevent "fogging" from occurring in the developed image and obtain a good print (image) as shown in FIG. 11(a).

Here, "cover j" is as shown in Figure 11(b),
In this case, it refers to a printing defect in which many black dots are generated around the developed characters, and the black dots are caused by toner scattering. In FIG. 10, ■i is the surface potential of the photosensitive drum 7 when the photosensitive drum 7 is exposed to the incident light from the LED chip 22. In FIG.

However, in this case, when the flare light F shown by the broken line in FIGS. 9 and 10 is incident, the potential distribution of the latent image of the flare light F shown by the broken line has a shape that is wider than that of the incident light shown by the solid line. . For this reason, as shown in the figure, the potential difference in this portion becomes small, which reduces the effect of applying the bias voltage as described above, resulting in r-fogging, which impairs printing quality. like this,
The adverse effects of the flare light F become a bigger problem because the flare light F increases as the printing rate increases, that is, the image includes more black images.

Therefore, in order to prevent the above-mentioned "fogging" from occurring and improve printing quality, measures are taken to cut the flare light F re-entering the SELFOC lens array 27, whose aperture angle is normally selected to be about 20'. As an example of countermeasures, the position of the pattern 24 may be changed to the third position.
A possible method is to set it at a position farther from the LED chip 22 than the position shown in the figure to prevent the light reflected from the pattern 24 from entering again.

However, such a method leads to an increase in the size of the device configuration, and is not in keeping with the current situation where there is a trend to make the entire printer more compact.

The present invention has been made in view of the current situation, and it is an object of the present invention to provide an LED printer that can improve printing quality with a compact device configuration.

The present invention provides an LED printer in which light from an LED is converged on a photosensitive drum via a condensing lens to form a latent image, in which reflection of incident light from the LED is performed. The present invention is characterized in that an anti-reflection coating layer for preventing this is formed on the incident surface of the condenser lens.

Moreover, instead of the anti-reflection coating layer, a coating layer formed by laminating a plurality of high refractive index substances and low refractive index substances is formed on the incident surface of the condenser lens, and the transmittance of this coating layer is is set to a value corresponding to the transmittance determined by the aperture angle of the condenser lens and the wavelength of the incident light from the LED.

In this case, if the first method is used, the light from the LED is not reflected by the incident surface of the condenser lens, so the generation of flare light can be reduced.

Furthermore, in the case of the second method, only the light directly incident from the LED is incident on the condenser lens due to the filter function of the coating layer, so that the occurrence of flare light can be similarly reduced.

fruit Embodiments of the present invention will be specifically described below based on the drawings.

Fig. 1 is a front view showing the peripheral structure of the photosensitive drum in an LED printer, Fig. 2 is a perspective view showing the optical system, Fig. 3 is a plan view showing an enlarged view of the main parts of the optical system, and Fig. 4 is the main part of the optical system. The side view and FIG. 5 are enlarged front views of essential parts showing a coating layer formed on the entrance surface of the SELFOC lens array.

First, the image forming process of the LED printer will be outlined based on FIG. The photosensitive drum 7 is designed to rotate in the clockwise direction indicated by the arrow mark in the figure, and is first given a negative charge by the charger 1 placed outside the photosensitive drum 7, and then by the optical system placed downstream of the charger 1. 2
As a result, a latent image with character information written thereon is formed.

Then, the negatively charged toner is developed by the developing device 3, and the visualized image is transferred onto paper (not shown) by the transfer charger 4, thereby forming an image on the paper. Thereafter, the residual toner on the photosensitive drum 7 is removed by the cleaner 5, and the residual charge is removed by the eraser 6.

Since the structure of the optical system 2 shown in FIGS. 2 to 4 is as described above, a description of the overlapping parts will be omitted, and only the different parts shown in FIG. 5 will be described below.

As shown in FIG. 5, the entrance surface of the SELFOC lens array 27 has a refractive index n of 1.38 on the upper surface side (incidence side) and an optical film thickness of λ. A thin film 28a made of a material M g F z with a refractive index of 1.63 and an optical thickness of λ is placed on the lower surface side. /4 material AIZO:l thin film 28b
A coating layer 28 is provided by laminating the following layers.

However, λ. is the wavelength of the light emitted from the LED 22 (hereinafter referred to as emitted light) (as described above, a single wavelength of <740 nm).

In Figure 6, the vertical axis shows the reflectance R [%], and the horizontal axis shows the wavelength λ (nm
) is a graph showing the reflectance characteristics of the coating layer 28. As is clear from FIG. 6, in the case of this coating layer 28, the reflectance R of the incident surface of the SELFOC lens array 27 for emitted light with a wavelength of 740 nm is
is O, so flare light due to reflection from the SELFOC lens array 27 can be completely cut out.

FIG. 7 shows a modification of the coating layer. This coating layer 29 includes a thin film 29h made of a high refractive index substance (for example, TtO□) having a refractive index n of 2.35 and an optical thickness of λ/4, and a thin film 29h having a refractive index n of 1.46. It is a multi-coat formed by alternately laminating, for example, 20 thin films 291 made of a low refractive index material (for example, 5iOt) and having an optical thickness of λ/4 or λ/8. Regarding the laminated form, as shown in FIG. 7, the top layer is a thin film 29L with a thickness of λ/8, the 2nd to 20th layers are even-numbered layers with a thin film 29H of λ/4, and the odd-numbered layers are a thin film 29L with a thickness of λ/4. Layer ff)li29L of λ/4. However, λ in this case is 9QQnm.

In Figure 8, the vertical axis shows the transmittance T (%), and the horizontal axis shows the wavelength λ (n
FIG. 3 is a graph showing the transmittance characteristics of the coating layer 29 when the incident angle is 20" and 30". however,
The angle of incidence here refers to the angle with respect to the optical axis.

As can be seen from FIG. 8, when the incident angle is 20° for incident light with a wavelength of 740 nm, the transmittance T is 90%, which is 1. When the incident angle is 30°, the transmittance T is 1%. In addition, in Fig. 8, the transmittance T when the incident angle is between 20° and 30'' is the same as the transmittance curve when the incident angle is 20'' and 30°.
is between the transmittance curves for .

Therefore, according to FIG. 8 and the correlation between the aperture angle and the incident angle of the Selfoc lens array 27, when forming the coating layer 29 on the incident surface of the Selfoc lens array 27 with an aperture angle of 20'' as in the present invention, , LED chip 22
Only the emitted light of , that is, the incident light with a wavelength of 740 nm is transmitted,
Other disturbance light such as reflected light with an incident angle greater than 20° does not pass through the coating layer 29, and the flare light is cut off. In other words, such a coating layer 2
9 functions as a filter that allows only the light emitted from the LED chip 22 to pass through.

According to the present invention described above, it is possible to reduce the generation of flare light that adversely affects printing quality, so LED
In addition to the performance advantage of dramatically improving the print quality of the printer, this can be achieved by simply forming a coating layer on the part corresponding to the entrance surface of the condenser lens, which reduces the complexity of the device configuration and There is also a structural advantage that an increase in the number of parts can be avoided.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the peripheral structure of the photosensitive drum in an LED printer, Fig. 2 is a perspective view showing the optical system, Fig. 3 is a plan view showing an enlarged view of the main parts of the optical system, and Fig. 4 is the main part of the optical system. A side view, FIG. 5 is an enlarged front view of the main part showing the coating layer formed on the entrance surface of the SELFOC lens array, and FIG. 6 shows the reflectance R [%] on the vertical axis and the wavelength λ (nm) on the horizontal axis. It is a graph showing the reflectance characteristics of the coating layer. Fig. 7 is an enlarged front view of the main part showing a modification of the coating layer, and Fig. 8 shows the transmittance T (%) on the vertical axis and the wavelength λ(n) on the horizontal axis.
Fig. 9 is a graph showing the transmittance characteristics of the coating layer when the incident angle is 20'' and 306 mm). Fig. 9 is a front view showing the optical system to explain flare light, and Fig. 10 is A graph showing the potential distribution of the latent image, and FIG. 11 is an explanatory diagram showing the bad influence of flare light. 2... Optical system, 22... LED chip, 27...
SELFOC lens array, 28.29...Coating layer, F...Flare light Fig. 1 Fig. 3 Fig. 2 Fig. 4 Fig. 5 Fig. λ[,,ml Fig. 6 Fig. 8 Fig. 8 [ nml

Claims (2)

[Claims] (1) In an LED printer in which light from an LED is converged on a photosensitive drum via a condensing lens to form a latent image, a non-reflective coating layer is provided on the photosensitive drum to prevent reflection of incident light from the LED. An LED printer characterized in that an LED printer is formed on an incident surface of a condenser lens. (2) In an LED printer in which light from an LED is converged on a photosensitive drum via a condensing lens to form a latent image, a material with a high refractive index and a material with a low refraction are provided on the incident surface of the condensing lens. A coating layer is formed by laminating a plurality of materials with a certain ratio, and the transmittance of this coating layer corresponds to the transmittance determined by the aperture angle of the condenser lens and the wavelength of the incident light from the LED. An LED printer characterized in that it is set to a value.