JPH0272979A - Intermediate tone image recorder for laser beam printer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus such as a laser printer that records images in multiple gradations using a black and white dot configuration.

[Conventional technology]

Conventionally, there is a dot matrix method as one of the methods for forming halftones. If an n x n matrix is used, 22+1 gradations can be reproduced (dither method). For example 2
In the case of a x2 dot matrix, one dot is formed in each of the four divided sections, which means there are five gradations (no dots are counted as 1)! li - can be reproduced. Another method is the #degree pattern method, but what is important in gradation expression is the relationship between gradation expression ability and resolution. In other words, if the value of 9 is increased, the number of tones will be larger (although the resolution will be lower).Also, there are two types of patterns: dot-dispersed type and dot-concentrated type, but the dot-dispersed type does not reduce the resolution but has fewer gradation types. The concentrated dot type has the disadvantage of having a large number of gradation formulas (but on the other hand, it has the disadvantage of lowering the resolution. Conventionally, in order to satisfy both the gradation ability and the resolution, the dot concentration type has the disadvantage of reducing the value of The method of expressing images using micropixels (fine dots that do not even reach a single pixel), which divides one pixel into multiple values, has been defeated.In the case of laser beam printers, pulse width modulation and light intensity are used to control the lighting time of the laser. It performs brightness modulation to change the brightness of the pixels and controls the fine pixels that are divided into multi-value clusters in the laser scanning direction.

The conventional device divides one dot pixel into five micropixels as described in Japanese Patent Application Laid-Open No. 61-214663, and
Obtain 6 gradations with each pixel. If the pattern is a concentrated dot type, a 5×5 dither matrix provides 46 levels of gradation.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, when viewed in terms of fine pixels, it becomes a 15×6 matrix, and the number of gradations is 46. i.e. 6×
Although the number of gradations is 46 in a 6-dot matrix, in terms of fine pixel dots, the number of gradations is 46 in a 15×6 fine pixel dot matrix, which is a commonly used dither method.

An object of the present invention is to control the size of the above-mentioned fine pixel dots and obtain more gradations with a smaller number of dots.

[Means for solving the problem] The purpose of the above is to control the laser beam diameter on the photosensitive drum of the laser beam printer.9 By changing the size of the fine pixel mark, an increase in the number of gradations can be achieved. be done.

For the above purpose, if the lighting time and driving current of the laser used to print fine pixel dots are constant, when the spot diameter of the laser beam on the photosensitive drum is changed, the fine pixel dots will also change corresponding to the spot diameter. We have confirmed that.

For the purpose mentioned above, there is no problem whether the gradation pattern is a dot concentrated type or a dot dispersed type, there is no deterioration in resolution, a large number of gradations can be obtained, and halftone pixel recording can be achieved.

Next, a means for changing the spot diameter of the laser beam on the photosensitive drum will be described. A semiconductor laser is used as the laser. A laser beam emitted from a semiconductor laser diverges, but is cosimated through a coupling lens into a convergent beam that is close to a parallel beam. Furthermore, the luminous flux of the collimated laser beam is controlled by a beam waist position adjustment strip (K).

This optical system will be described later. The beam exiting the slit passes through a cylindrical lens and forms an image on the reflecting surface of a rotating polygon mirror. The reflected beam from the polygon mirror reaches the photosensitive drum after passing through the fe optical system. The spot diameter on the photosensitive drum changes depending on the width of the slit. Focusing on this point, we changed the spot diameter. In other words, the width as seen on the optical axis is changed by rotating a plate provided with slits.

[Effect]

In the above configuration, as a device for rotating the slit plate, a motor such as a stepping motor whose rotation angle can be precisely controlled is used, and a centimeter for detecting the rotation angle is provided. A rotary encoder is used as the center/f for measuring the rotation angle. A stepping motor rotates using pulses, and some motors have a resolution of 1 or less per pulse.

Some rotary encoders output 20,000 pulses per revolution.

Therefore, by using such a device, the rotation angle of the slit plate can be varied and positioned with better precision.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall configuration of the optical system of the beam printer of the present invention. In FIG. 1, 1 is a semiconductor laser that emits a laser beam, and 2 is a coupling lens that collimates the diverging beam emitted from the laser 1 into a convergent beam that is nearly parallel. 3 is a metal plate having slits. This slit 9 will be described later. The slit plate is provided with a motor 4 for rotating the plate and a centimeter 5 for measuring the rotation angle. The beam passing through the slit plate 3 enters the cylinder 9 cal lens B. The cylindrical lens 6 is a lens that has power only in the j-scanning direction (here, the scanning direction of the laser is called the main scanning direction, and the direction perpendicular thereto, that is, the rotational direction of the photosensitive drum 12 is called the sub-scanning direction. connects agl on the reflective surface of the rotating polygon mirror 7. The rotating polygon mirror 7 is rotated at a constant speed by a motor 8, and changes the reflection angle of the light beam reflected by the mirror surface with time, thereby deflecting and scanning the light beam. It is something that allows you to do this.

The reflected beam from the rotating polygon mirror 7 passes through a flat reflecting mirror 10 on a spherical single lens 9, is reflected by a toric-shaped reflecting mirror 11 (hereinafter referred to as a toric reflecting mirror), and is irradiated onto a photosensitive drum 12.

Here, the spherical lens 9 and the toric-shaped reflecting mirror are f-
It has a θ characteristic. The plane reflecting mirror 10 is for guiding the laser beam to the photosensitive drum 12 and has no characteristic effect.

FIG. 2 is a sectional view showing each element and a laser beam in a plane perpendicular to the scanning plane along the optical axis of the optical scanning device of the present invention. After the light beam emitted from the laser light source 1 is cosimated by the coupling lens 2, it is passed through a slit plate 3 in order to adjust the beam diameter dt entering the cylindrical lens 6IC. The cylindrical lens 6 focuses the light beam only in the sub-scanning direction to form a line image on the reflective surface 7 of the deflection device.

Further, the beam reflected on the reflecting surface 7 is imaged on the photosensitive drum 12 by the spherical lens 9 and the tosic reflector 11 and K at a scanning speed of -.

In FIG. 2, FIG. 3 shows the relationship between the beam spot diameter on the photosensitive drum 12 (portion A) when the beam diameter d incident on the cylindrical lens 6, that is, the width d of the slit, is changed. be.

In FIG. 3, the horizontal axis is the distance from the photosensitive drum surface, and the vertical axis is the beam spot diameter in the sub-scanning direction. The horizontal axis indicates 0 on the drum surface, the negative direction represents the optical system side, and the positive direction represents the inside of the drum surface. Actual If816 to If17 in the figure indicate the spot diameter in the sub-scanning direction when the beam diameter d is changed. Compared to the solid line 16, the busy beam diameter d of 14°15.16.17 is thicker.The results in Figure 3 show that the beam waist diameter does not change, but the position changes, confirmed by the experimental pressure. The spot diameter in the sub-scanning direction on the drum surface was
13 is 90μm, 14 is 75μm shoulder, 15
70. The case of αIIs+16 is 75μ ugly and 17
In the case of 90 μm. Therefore, it can be seen that by changing the width d of the slit 3, the spot diameter in the sub-scanning direction on the photosensitive drum 12 changes.

Next, the slit plate 5Vc will be described.

A schematic diagram of changing the width d of the slit plate 3 is shown in red in Fig. 4. If the slit width when placed perpendicular to the Lede beam is d, then when the slit plate 3 is tilted from 0 by IC#, the slit width as seen on the optical axis becomes d-cos-θ.

For example, the slit width when the inclination angle θ is 60 is d/2
becomes. By rotating in this manner, the slit width d can be easily changed.

Further, as shown in FIG. 5, there is no problem even if a slit is provided in the cylindrical shape 18 and the cylindrical shape is rotated. Such a cylindrical shape is easier to rotate.

The slit shown in FIGS. 4 and 5 is not rotated once, but if the maximum rotation angle is set to 60 and the rotation step is set to 15 as described above, the slit width can be switched in 5 steps.

That is, the spot diameter in the sub-scanning direction can be changed in five steps, and the width of the change is proportional to the cos function.

Next, the apparatus 1 for rotating the slit will be described.

One embodiment of the device is shown in FIG.

In FIG. 6, reference numeral 19 denotes a microcomputer, and when a command for rotation angle and normal/inversion is transmitted from the host computer 28, the microcomputer 19 sends the microcomputer 28 to the mi/inversion circuit 2.
0 and the pulse generator 21, respectively. The number of pulses is output from the pulse generator 21 in accordance with the data, and the excitation direction of the stepping motor 4 is determined by the positive/inverted Ig pressure in the drive circuit 22, and the rotation angle is determined by the number of pulses.

Here, the stepping motor 4 moves with a pulse signal, and
The rotation angle is determined by pulses, and reversal is possible by reversing the excitation direction, so it is suitable for this type of positioning.

A rotary encoder 5 is connected to this device in order to measure the rotation angle with high precision. The rotary empuder 5 replaces rotation with a pulse signal, and some high-precision models output tens of thousands of pulses in one revolution (360). For example, if 10,000 pulses are output, the resolution will be 0.056°/pulse. Therefore, for a rotation angle of 15 degrees, the number of pulses is 416, which is accurate (the rotation angle can be measured).Also, for the detection 27 of positive and reverse, pulse signals with different phases are generally output. Therefore, it is possible to determine whether the phase of the other signal is ahead or behind based on 1. Therefore, by inputting the pulse signal to the counter circuit 26 and counting the number of pulses, the rotation angle can be determined. Good accuracy (can be measured.

Therefore, the fluctuation range of the slit can also be determined with high precision.

Next, we will discuss the gradation expression when using this device.

First, FIGS. 7 and 8 show the relationship between the printing pattern of fine pixel dots and the laser lighting time. When fine pixel dots are printed with a constant spot diameter, the dot diameter in the main scanning direction is determined by the laser lighting time, and the dot diameter in the regular scanning direction is determined by the spot diameter.

The dither method described first in FIG. 9 will be explained. In order to record a halftone image, each pixel 29 is arranged in a matrix, for example, 2×2 fine pixels 60 as shown in FIG.
If you compose it more! Five levels of intermediate tones are obtained by a black and white combination of +1 (all white pixels are counted as 1) micropixels, that is, by distribution of white micropixels and black micropixels.

Furthermore, in the present invention described so far, the spot diameter can be changed by changing the width of the slit 3, so the area of the fine pixel can be changed. The situation is shown in FIG.

FIG. 10 shows the case (1) in FIG. 9, but if the width d of the slit 3 can be changed in five steps as described above, one fine pixel dot can be changed as shown in FIG. Also obtains 5 gradations. Therefore, a greater number of gradations can be expressed in the pixels of the 2×2 dot matrix than in the past.

〔Effect of the invention〕

As explained above, according to the present invention, when a pixel is composed of a plurality of fine pixel dots, it is possible to change the size of the fine pixel dots, so that a larger number of gradations than the conventional dither method can be achieved. You can get it. In addition, this method can reduce the dot matrix's niceness, so there is no deterioration in resolution (・.

[Brief explanation of the drawing]

Figure 1 is a diagram of the configuration of an optical system according to an embodiment of the present invention, Figure 2 is a diagram of the principle of changing the spot diameter in a cross section perpendicular to the scanning direction, and Figure 3 is a diagram of the principle of changing the slit width. Figure 4 is a diagram showing the decrease in slit width when the slit plate is tilted, and Figure 5 is a diagram showing the change in spot diameter with respect to the distance from the photosensitive drum surface. A configuration diagram showing the decrease in slit width due to inclination, Figure 6 is a system block diagram for rotating the slit plate, Figure 7 is an explanatory diagram of the printing pattern of fine pixel dots, and Figure 8 corresponds to the printing dots in Figure 7. FIG. 9 is an explanatory diagram showing the lighting time of the laser, FIG. 9 is a halftone representation of a 2×2 matrix by micropixels, and FIG. 10 is a state diagram of the micropixel dots with respect to changes in spot diameter according to the present invention. DESCRIPTION OF SYMBOLS 1... Laser light source, 2... Coupling lens, 3... Slit plate, 4... Stebbing motor, 5... Rotary encoder, 6... Cylindrical lens, 7...
... Rotating polygon mirror, 9 ... Spherical lens, 11 ... Toric reflector, 12 ... Photosensitive drum, 19 ... Microcomputer, 21 ... Pulse generator, 20 ...
- Positive/inversion circuit, 22... Drive circuit, 26... Pulse counter circuit, 27... Positive/inversion detection circuit, 29.
...Small pixels, 30...pixels. Column f concave 5 rotary engo 57' tz KL dora person 6
Cylindrical length (tm) → Drum PIT battle j Concave concave 1st collection → Main scanning direction diagram

Claims (1)

[Claims] 1. In an optical scanning device having a light beam generator, a deflection device for scanning the light beam, an optical system having f.0 characteristics, and a slit capable of varying the spot diameter of the light beam on the surface of the photosensitive drum, the slit is The slit width on the optical axis is made variable by tilting the photosensitive drum, the spot diameter of the light beam on the surface of the photosensitive drum is changed, and the number of gradations is increased by changing the size of the fine pixel dots that constitute the pixels. A halftone image recording device for a laser beam printer, characterized by: