JPH01217476A - Electrophotographic recorder - Google Patents

Abstract

PURPOSE:To realize multistage gradation expression by providing a parallel planar lens between a photosensitive body and an LED head provided so that it faces to the photosensitive body and using a lens which has a refraction ratio distribution where the refraction ratio is decreased from center toward an outer edge part along with the moving direction of the photosensitive body. CONSTITUTION:A refraction ratio distribution type lens (a Selfoc lens) 3 and a one-way refraction ratio distribution type slab lens 4 as the parallel planar lens are disposed each in parallel to the axis direction of the photosensitive body 1 between the LED head 2 and a photosensitive body drum 1. When the emitting light from the LED head 2 passes the lens 4, the light is refracted according to the refraction ratio distribution where the refraction ratio is decreased from the center toward the outer edge part along with the moving direction of the photosensitive body 1, and the refraction is not changed in the axis direction of the photosensitive body 1. Therefore, circular beam shape is changed into elliptical beam shape the minor axis direction which is same as the moving direction of the photosensitive body 1. And besides, since the axis length of the ellipse is changed by changing LED conducting time, the area of a dot is changed and gradation at every dot is safely performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrophotographic recording device using an LED head.

[Prior Art] In an electrophotographic recording device using a conventional LED head, L
So that the light from the ED head is focused on the photoreceptor,
A gradient index lens array is arranged between the LED light emitting element and the photoreceptor. In order to express gradation, the so-called density matrix method, dither method, etc. using a threshold value matrix are used, and for example, one pixel is divided into 16
It consists of dots and by selecting the number of dots, 1
A gradation expression of 7 gradations is obtained.

[Problem to be solved] Traditionally, the light emitting surface of an LED head is approximately square;
When this light is imaged onto a photoreceptor, it becomes a nearly circular beam, which becomes very unstable when performing dot-by-dot gradation. Furthermore, in the conventional method described above,
The apparent resolution and the number of gradations are contradictory, and in order to satisfy both, a very high resolution of the printer itself is required. For example, to obtain 32 or more gradations and 6 dots/mu or more, the printer resolution must be 36 dots/+
am is required, which is very difficult.

SUMMARY OF THE INVENTION An object of the present invention is to stably perform gradation for each dot, thereby making it possible to express multiple gradations.

[Means for Solving the Problems] In order to achieve the above object, in the electrophotographic recording apparatus of the present invention, a parallel plate is provided between a photoreceptor and an LED head provided to face the photoreceptor. A lens having a shape of a shape is provided, and this lens has a refractive index distribution such that the refractive index decreases from the center toward the outer end along the direction of movement of the photoreceptor.

[Function] In the electrophotographic recording device configured as described above, the LED
While the light emitted from the head passes through the lens, it is refracted in accordance with the refractive index distribution such that the refractive index decreases from the center to the outer edge along the direction of movement of the photoconductor, and does not change in the width direction of the photoconductor. . For this reason, the circular beam shape changes to an elliptical beam shape whose minor axis is the direction of movement of the photoreceptor. By changing the energization time of the LED, the length of the short axis of this ellipse changes, so the area of one dot changes, and the gradation of each dot is stably performed.

[Example] In FIG. 1, LED heads 2 are arranged parallel to the axial direction of a photoreceptor drum 1 and at predetermined intervals.

Between the LED head 2 and the photoconductor drum 1, a refractive index distribution type lens (SELFOC lens) 3 and a unidirectional refractive index distribution type slab lens 4 as parallel plate lenses are provided, respectively, in the axial direction of the photoconductor 1. It is arranged parallel to.

In the unidirectional refractive index gradient type slab lens 4 shown in FIG. 2, the X direction, which is the thickness direction, is a line L on the surface of the photoreceptor drum 1 where the output beam from the lens is formed (FIG. 1).
is placed at right angles to. Therefore, the Y direction, which is the width direction of the lens 4, corresponds to the axial direction of the photoreceptor drum 1, and the X direction, which is the length direction of the lens 4, corresponds to the radial direction of the photoreceptor drum 1. The refractive index n of this unidirectional refractive index gradient type slab lens 4 is as shown in FIG.
It exhibits a refractive index distribution that gradually decreases from the center toward the outer end in the X direction, and a constant refractive index in the Y and X directions. That is, since the X direction coincides with the direction of movement of the photoreceptor, the light passing through the lens is refracted so as to converge toward the center only in the direction of movement of the photoreceptor.

Further, the gradient index lens 3 exhibits a refractive index distribution that gradually decreases from the center toward the outer end in the X direction and the Y direction, similar to the X direction in FIG. 3 described above.

Therefore, in FIG. 4, the substantially square light emitted from the light emitting surface of the LED head 2 passes through the gradient index lens 3 and is squeezed in the XY force direction to become a minute, substantially circular beam a. Since this light enters the parallel plate-shaped lens 4, it is a substantially circular incident light, but it converges toward the center in the X direction to become an elliptical outgoing light C. This elliptical emitted light C reaches the surface of the photoreceptor drum 1, and is formed on the surface as an elliptical beam d having a large oblateness.

Also, since the photosensitive drum 1 is rotating at a constant speed, the LE
The area of one dot can be changed by changing the energization time of the D head. For example, if the energization time is lengthened and the pulse width is increased, a dot with a shape extending in the short axis direction will be formed. The area of the dot becomes wider.

In such a configuration, as mentioned earlier, 4X4-1
When one pixel is made up of six dots, not only can 17 gradations be expressed by selecting the number of dots, but even finer gradation can be expressed by changing the area of one dot. By combining these, multi-level gradation expression becomes possible.

Furthermore, since the elliptical beam d always converges toward the center of the gradient index lens 3 and forms an image on the photoreceptor drum 1, even if there are manufacturing errors or installation errors in the LED head, the photoreceptor drum The imaging position of the elliptical beam d on 1 becomes approximately constant, which has the effect of facilitating assembly and improving the reliability of the device.

[Effect] Since the present invention is configured as described above,
It is possible to image the light emitted from the LED head into an elliptical beam with a large oblateness on the surface of the photoreceptor, which has excellent gradation and stability, and allows multi-step gradation expression for each dot.

Furthermore, even if there is some manufacturing error or some positional error in the mounting of the LED head, the imaging position of the elliptical beam on the photoreceptor surface remains almost constant, improving the reliability of the device.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a schematic configuration of the present invention, Fig. 2 is an enlarged perspective view showing the XYZ directions of a parallel plate lens, Fig. 3 is a refractive index distribution diagram of a parallel plate lens, and Fig. 4 FIG. 2 is a perspective view showing a change in beam shape due to a parallel plate-like lens. 1... Photoreceptor, 2... LED head, 4... Parallel flat lens. that's all

Claims (1)

[Claims] A photoreceptor and an LED provided opposite the photoreceptor.
A parallel plate-shaped lens is provided between the head and the lens, and the lens is characterized in that the refractive index is distributed such that it decreases from the center toward the outer end along the moving direction of the photoreceptor. An electrophotographic recording device.