JPH03144671A - Optical writing device - Google Patents

Abstract

PURPOSE:To vary the size in a subscanning direction reasonably by providing a fine deflecting means which deflects a light beam by a fine quantity in the subscanning direction in a picture element unit of image data, and a light beam modulating means which imposes pulse-width modulation upon the light beam in the picture element unit according to image data written on a photosensitive body. CONSTITUTION:This device is provided with the fine deflecting means 2 which deflects the light beam by the fine quantity in the subscanning direction in picture element units of the image data and the light beam modulating means 6 which imposes pulse- width modulation upon the light beam in a picture element unit according to the image data written on the photosensitive body 4. Therefore, the light beam while deflected in a main scanning direction is deflected through the fine deflecting means 2 by the fine quantity in the subscanning direction in the picture element unit, so the light beam modulating means 6 imposes pulse-width modulation upon the light beam which travels slantingly and repeatedly along the main scanning line according to the image data. Consequently, picture element sizes can be switched fast in the picture element unit and the size of the picture elements can be varied reasonably in both the main scanning direction and subscanning direction.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical writing device for an image forming apparatus.

[Conventional technology]

In general, image forming devices such as laser printers and digital copiers have high speeds that meet the needs of users.

Improvements in performance such as high image quality are progressing.

Therefore, the optical writing device used in the image forming apparatus is also required to have high speed and high pixel density.1 For example, while using a high-output semiconductor laser, the beam spot (hereinafter simply referred to as "spot") must also be narrowed down to a small size. ing.

However, not all image data has a high pixel density, and when handling image data with a low pixel density, such as when enlarging and printing small screen image data, the size of the pixels to be printed also increases. Must.

Further, when the image data is composed of pixels having gradations, it is necessary to vary the size of each pixel according to the gradation data.

In such cases, an electrical method is to take advantage of the fact that increasing the amount of light irradiated on the photoreceptor effectively increases the spot diameter, and vary the spot diameter by changing the output of the semiconductor laser that is the light source. There is something to do.

There is also a method that changes the pixel size by modulating the pulse width of a pulse signal that drives a semiconductor laser, for example.

On the other hand, as a mechanical method, for example, there is a method in which the spot diameter is changed by slightly blurring the spot by shifting the coupling position of the optical system that forms the spot in the optical axis direction.

[Problem to be solved by the invention]

However, although the electrical method allows the pixel size to be switched at high speed, increasing the output of the semiconductor laser too much can shorten its lifespan and cause negative effects such as photoreceptor fatigue, so it is not effective. There is a limit to the range in which the spot diameter can be changed.

Furthermore, although the method of changing the pulse width allows the pixel size to be freely changed in the main scanning direction, it hardly changes in the sub-scanning direction, so that the visual effect of the finished image cannot be expected to be very good.

On the other hand, with the mechanical method, the spot changes while remaining almost circular, and the spot diameter can be varied over a wide range, but it requires a complex and highly accurate active system to subtly move the optical system, which increases the pixel size. Because the time required for switching is slow, high-speed switching, for example, not only in pixel order but also in scanning line order, is impossible, and in practice, only page-by-page switching is possible.The invention was made in view of the above points. It is an object of the present invention to provide an optical writing device which is capable of high-speed switching of one pixel size and whose size, particularly in the sub-scanning direction, can be changed easily.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an optical writing device that deflects a light beam in the main scanning direction to write an image on a photoreceptor. It is provided with a minute deflection means for deflecting the light beam, and a light beam modulation means for pulse width modulating the light beam for each pixel according to the image data written on the photoreceptor.

[For production]

According to the optical writing device configured in this way, while being mainly deflected in the main scanning direction, it is deflected by a small amount in the sub-scanning direction in pixel units by the micro-deflection means, so that the skewing is performed along the main scanning line. Since the repeating light beam is pulse width modulated for each pixel by the light beam modulation means according to the image data, 1
The pixel size can be switched at high speed for each pixel, and the pixel size can be easily changed in both the main scanning direction and the sub-scanning direction.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a perspective view and a block diagram respectively showing the schematic configuration of a mechanical system and a control system of a first embodiment of an optical writing device of the present invention.

In the figure, the coordinate axes are the X-axis (positive) in the main scanning direction (right), the Y-axis (positive) in the sub-scanning direction (top), and
Therefore, the description will be made with the normal direction as the Z axis (the direction in which light travels is negative).

This optical writing device includes a light source unit 1 that emits a modulated light beam, a Y deflector 2 that is minute deflection means that deflects the light beam in the sub-scanning direction, and an X deflector that deflects the light beam in the main-scanning direction. 3, a mechanical system consisting of an fθ lens 5 that images the deflected light beam as a spot on the photoreceptor 4, and a write control section 6 that controls the mechanical system and also serves as a light beam modulation means. It consists of a system.

The light source section 1 consists of a semiconductor laser 7 and a collimator lens 1a. The semiconductor laser 7 outputs a laser beam that is turned on and off according to a pulse width modulated opening signal input from the write control section 6, and the collimator lens 1a converts the laser light into a narrow parallel light beam and emits it upward (in the X direction).

The Y deflector 2 is composed of a Y polygon mirror 10, a motor 11, a Y synchronization sensor 12, and a relay lens 13. The Y polygon mirror 10 is rotated clockwise ( It is rotating in the direction of arrow A).

Therefore, the parallel light beam incident in the X direction from the light source section 1 is transmitted by the Y polygon mirror 10.

Centered around the reflection point 10a, the light is repeatedly Y-deflected from top to bottom (in the direction of arrow Be''J) near the X direction, and is directed toward the X polarizer 3.

The X deflector 3 consists of an X polygon mirror 15, a motor 16, and an X synchronization sensor 17, and the X polygon mirror 15 is rotated clockwise (arrow C ) is rotating.

Therefore, the light beam incident in the X direction from the Y deflector 2 is deflected by the X polygon mirror 15.

From the reflection point 15a, the light is repeatedly deflected in X direction from left to right (in the X direction) centering on one or two directions, and is directed toward the fθ lens 5.

If this continues, the reflection point 15a on the mirror surface of the X polygon mirror 15 will move up and down, so in order to cover this, each mirror surface constituting the X polygon mirror 15 and fθ
The vertical width of the lens 5 must be widened.

However, a relay lens 13 is provided between the Y polygon mirror 10 and the X polygon mirror 15, and the respective reflection points 10a, 15. If the image of the reflection point 10a is focused on the reflection point 15a, the position of the reflection point 15a will not move, so the vertical width of the X polygon mirror 15 and the fθ lens 5 will be widened. There's no need.

Instead, the parallel light beam incident on the relay lens 13 forms a spot at the rear focal point position 13a of the relay lens 13, and the spot moves in the -V force direction arrow D), so the X polygon The light beam reflected by the mirror 15 is deflected from bottom to top (in the V direction).

The fθ lens 5 focuses the spot on the focal position 13a on the photoreceptor 4.
Since the re-imaged spot is adjusted to be re-imaged on the surface of 1!, the re-imaged spot is on the main scanning 1! (coinciding with the X axis in Fig. 1), with a slight width in the sub-scanning direction (V direction) by the Y deflector 2,
Main scanning is performed from left to right (X direction).

The photoreceptor 4 is made of a silver salt emulsion film or a photosensitive resin film if the image forming apparatus uses a normal photographic method, or a thin film of a photoconductor if the image forming apparatus uses an electrophotographic method. An image (latent image) is formed on the photoreceptor 4 by being held by the rotating holding drum 8 and sub-scanned as shown in FIG.

The Y synchronization sensor 12 and the X synchronization sensor 17 are arranged in close proximity above the relay lens 13 and on the left side of the photoreceptor 4, respectively, and detect the incidence of the light beam to determine timing standards for pixel and line modulation of the light beam, respectively. A synchronization signal corresponding to the following is output to the write control section 6.

The write control unit 6 includes a CPU, a ROM, and a R
It is composed of a microcomputer consisting of AM, Ilo, etc., and controls the motor 11° 1B to a predetermined rotation speed based on the print mode, such as the type of image, its size, and pixel density, input in advance from the host CPU 20, and
Synchronous sensor 17°Y While timing is determined by the synchronizing signal from the Y synchronizing sensor 12, the host CPU input 2
A drive signal pulse width modulated for each pixel is output to the semiconductor laser 7 according to the image data inputted from 0.

Pulse width modulation of the light beam.

FIG. 2 is an explanatory diagram showing an example of the locus of a spot formed on the photoreceptor 4 and the state of a written latent image in response to an active signal pulse width modulated for each pixel.

Figure 2 (A) is an example of pixel data, Figure 2 (B) is a waveform diagram of the active signal, and Figure 2 (C) and (D) are spot spots when the Y deflector 2 is in operation and at rest, respectively. The locus and state of the latent image are shown, and the trajectory is shown by solid lines and broken lines when the light beam is on and off, and the latent image is shown by the range surrounded by thin lines. Therefore, FIG. 3D is the same as the conventional optical writing device in which pulse width modulation is applied to each pixel.

For example, the pixel data of one line of image data having five levels from "0" (no modulation) to "4" (full modulation) is as shown in FIG.
...'', the pulse-modulated active signal will be as shown in FIG.

Here, if the linear velocities of the X and Y deflections of the spot on the photoreceptor 4 are equal, then FIG. 2(C).

As shown in , the trajectory of the spot becomes a sawtooth pattern tilted at 45 degrees for each pixel with respect to the main scanning direction (χ direction), and the on/off modulation of the light beam is performed on the diagonal line as shown by the solid line. appears in

In general, the laser beam spot has a light intensity distribution close to a crab-dimensional Gaussian distribution, so the range of the latent image on the beam splitter 4 is shown surrounded by ate in Figures (C) and (D). It becomes like that.

Comparing Fig. 2 (C) and (D), it is found that in the case of Fig. 2 (D), for example, the pixel data is "...32..."
...31...'', the latent image is continuous and the gradation power 1 cannot be expressed correctly.

On the other hand, according to the optical writing device of this embodiment, "...43...
Even if the drive signals are continuous as in “...”, the second
As shown in Figure (C), since the latent images are separated, even if the effective spot diameter is slightly offset, it is not affected by the light amount distribution and the gradation can be expressed more accurately.

Although the diagrams shown in FIGS. 2(B) and 2(C) are simplified for the purpose of explanation, in reality, not all of the light beam is written on the photoreceptor 4, but the first In order to irradiate the Y synchronous sensor 12 shown in the figure (X synchronous sensor 17 for each line)
Since a light beam on section (same as when irradiating the modulator) (which is turned off by the output of the Y synchronization signal) and a light beam off or blanking section for timing on both sides of the modulation section are required, the modulation section The time allocated to the signal (signal writing time) becomes shorter.

Such a case can be solved, for example, by slightly tilting the direction of deflection by the Y deflector 2 from the y (i11 scan) direction toward the X (main scan) direction and by increasing the linear velocity.

FIG. 3 is an explanatory diagram showing an example of the state of the drive signal, Y synchronization signal, spot locus, and latent image when the linear velocity is increased by tilting the Y deflector 2 in this way. ) is the same as the example shown in FIG. 2(A).

Figures 3(E) and (C) show the drive signal and Y
It is a waveform diagram showing a synchronization signal, and the figure (D) is a waveform diagram showing a synchronization signal.
) is supported.

The drive current shown in FIG. 3(B) consists of a light beam on part that irradiates the Y synchronization sensor 12, a modulation part according to pixel data, and a blanking part provided before and after the modulation part. In the beam on section, when the Y synchronization sensor 12 detects the irradiation light and outputs the Y synchronization signal shown in FIG.

The light beam enters the modulation section at a predetermined timing from the Y synchronization signal, is emitted for a time corresponding to the pulse width according to the pixel data, and then is turned off, and shifts from the off state to the post-blanking section.

Since the direction of deflection by the Y deflector 2 has rotated slightly clockwise, the starting point of the trajectory of a certain pixel is relative to the end of the trajectory of the previous pixel, as shown in Figure 3 (D). You will start from a position that is on the left side (-x direction), that is, slightly back.

The two point #I lines in Fig. 3 (B) to (D) are shown by connecting temporally corresponding points. Therefore, in Fig. 3 (D), the initial part S of the trajectory is In the light beam on part for synchronization, the next part b! corresponds to the front blanking section, the following section m corresponds to the modulation section, and the last section b2 corresponds to the rear blanking section.

Of these, only the modulation part m is actually written on the photoreceptor 4, and the light beam-on part S is the blanking part before and after the light beam has not yet entered the effective aperture of the relay lens 13. Although part of bitb2 is within the effective aperture, it is not written because the light beam is off.

Therefore, the latent image shown surrounded by thin lines is similar to the latent image shown in FIG. 2(C).

FIG. 4 is a perspective view and a block diagram showing the schematic configuration of the mechanical system and control system of the second embodiment, and the same parts as those of the first embodiment shown in FIG. 1 are denoted by the same reference numerals. For omitting the explanation, the second embodiment uses the Y polarizer 2 using the polygon mirror of the first embodiment as described in J, J, A, P, (English journal of the Japanese Society of Applied Physics) Vol. 24-2. (1985), "Optical polarizer using rPLZT ceramics" (Utsunomiya et al.).

This is replaced with a Y polarizer 20 that uses a photoelectric deflection element that deflects a light beam according to a deflection voltage, and the Y synchronization sensor 12 and relay lens 13 are no longer necessary.

FIG. 5 is a perspective view showing an example of the configuration of the Y polarizer 20, and FIG. 6 is a diagram showing an example of its deflection characteristics.

As shown in FIG. 5, the Y polarizer 20 consists of a polarizer 21 which is a polarizing element and a rectangular parallelepiped photoelectric deflection element 22 made of PLZT ceramics. A triangular electrode pair 23 is provided on the side surface.

When a deflection voltage is applied to the electrode pair 23 from the DC power supply 24,
Since the refractive index of the portion of the PLZT ceramic sandwiched between the electrode pair 23 changes, a difference in refractive index occurs along the hypotenuse of the electrode pair 23, that is, the boundary between the portion to which the deflection voltage is applied and the portion to which the deflection voltage is not applied. The light beam is deflected in a plane that includes the optical axis and is parallel to the electrode pair 23.

FIG. 6 is a diagram showing an example of the deflection angle characteristics with respect to the deflection voltage, and FIGS. 6A and 6B show the polarization angle (°) of the horizontal and vertical polarization components, respectively, on the vertical axis.

The horizontal axis indicates the electric field strength (V/m++) due to the deflection voltage.

As is clear from the figure, since the horizontally polarized component and the vertically polarized component of the light beam are deflected in opposite directions when a deflection voltage is applied, the light emitted from the light source 1 is By converting the beam into a polarized beam by a polarizer 21 and passing it through a photoelectric deflection element 22, only the horizontal or vertical polarized component 1, for example, the vertically polarized component with a large deflection angle, is used.

In FIG. 4, the light beam emitted from the light source unit 1 in the χ direction is deflected from bottom to top ( arrow Fy'/direction) is deflected by a minute angle, and the X deflector 3
incident on .

Since the components after the X deflector 3 are the same as those in the first embodiment, their explanation will be omitted, but the Y polarizer 20 is different from the Y polarizer 2 (FIG. 1) because it has no movable parts due to its structure.

Since the relay lens 13 can be placed immediately adjacent to the X polygon mirror 15 of the X polarizer 3, the relay lens 13 is not necessary.

Therefore, since the parallel light beam reaches the fθ lens 5, the rear focal point of the fθ lens 5 only needs to be at the position of the photoreceptor 4.

In addition, this Y deflector 20 has an extremely fast response (several MHz
), and the deflection angle is determined according to the deflection voltage (correctly its square).
There is no need for 2.

The drive signal for the semiconductor laser 7 may also have a simple waveform as shown in FIG. 2(B) instead of a complicated waveform as shown in FIG. 3(B).

Furthermore, the locus of the spot written on the photoreceptor 4 is not limited to the sawtooth wave created by repeated scanning in one direction as shown in FIG. 2(C), but for example as shown in FIG. 7(A). As shown, even if the waveform is a triangular wave (or sine wave) whose unit (period) is two pixels, pulse width modulation may be performed according to the waveform.

Alternatively, if the number of gradations is small and strict gradation expression is not required, and a component in the sub-scanning direction is sufficient, the polarizer 21 can be removed.

The full intensity of the light beam may be used for writing.

FIGS. 7(B) and 7(C) respectively show the loci of the spot when the polarizer 21 is removed and a deflection voltage that writes, for example, a sawtooth wave or a triangular wave is applied to the photoelectric deflection element 22.

As is clear from the above explanation, by changing the period of pulse width modulation for each pixel using the light beam modulation means,
The pixel size in the main scanning direction can be set arbitrarily.

Furthermore, by changing the amplitude in the sub-scanning direction using a Y deflector, the aspect ratio of the pixel size can be arbitrarily set.

Therefore, the pixel size in the main scanning direction and the sub-scanning direction can be arbitrarily set depending on the purpose.

Furthermore, although the optical writing device according to the present invention has been explained using an embodiment using a semiconductor laser as a light source, the light source may be a gas laser, a discharge lamp, or an arc lamp, and the wavelength range may be infrared, visible, or ultraviolet. It is fine as long as it is suitable for your body.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to provide an optical writing device that is capable of high-speed switching of one pixel size, and can also easily change the size, especially the size in the sub-scanning direction. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view and a block diagram showing a schematic configuration of a first embodiment of an optical writing device according to the present invention. 2 and 3 are partially enlarged views showing waveform diagrams of laser abrasion current, etc. for the image data and an example of formed images, and FIG. 4 is a perspective view showing a schematic configuration of a second embodiment of the present invention. and block diagram. FIG. 5 is a perspective view showing an example of the configuration of the Y deflector, FIG. 6 is a diagram showing an example of the deflection characteristics, and FIG. 7 is a partially enlarged view showing an example of the formed image. 1... Light source section 2.20... Y deflector (minor deflection means) 3... X deflector (means for deflecting in the main scanning direction) 4... Photoreceptor 6. 26... Writing Control unit (light beam modulation means) 7...
・Semiconductor laser Figure 1M2 (A) Figure 3 (A) Figure 4 Figure s6

Claims (1)

[Scope of Claims] 1. In an optical writing device that writes an image on a photoreceptor by deflecting a light beam in the main scanning direction, the light beam is deflected by a minute amount in units of pixels of image data in the sub-scanning direction. An optical writing device comprising: a deflection means; and a light beam modulation means for pulse width modulating the light beam for each pixel according to the image data written on the photoreceptor.