JPH05160975A - Image formation device - Google Patents

Abstract

PURPOSE:To form an image of high quality whose jag is inconspicuous without varying picture element density nor picture element size. CONSTITUTION:When a code specifying upward or downward movement is inputted, an up/down control part 310 applies an ultrasonic wave of frequency fau (for upward movement) or fad (for downward movement) to an AOM 20 through a D/A converter 311 and a V/F converter 312 and the AOM 20 deflects a light beam emitted from a laser light source in a subscanning direction. Consequently, the deflected light beam is reflected by a mirror surface of a polygon mirror and made incident on a photosensitive drum, on which an electrostatic latent images of picture elements to be printed by movement in the subscanning direction is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus,
In particular, the present invention relates to an image forming apparatus using an electrophotographic system that performs exposure with a light beam.

[0002]

2. Description of the Related Art An optical printer, which is one of electrophotographic image forming apparatuses, can print at high speed and with high resolution (high quality) as compared with other various printers, and is quieter than impact type printers. It has the advantage that there is almost no noise. This optical printer was mainly high-priced and the device itself was large, so it was mainly used for general-purpose computers and CAs.
It was mainly used in print output devices for D / CAM,
At present, compact and low-priced desktop optical printers have been commercialized, and are rapidly becoming popular as print output devices for office computers and personal computers. Further, because of the high printing quality, the demand is increasing as a printing apparatus for desktop publishing (DTP: DeskTop Publishing) such as in-house printing.

By the way, laser printers are the mainstream of such optical printers, and their resolution is currently 300 dpi.
(dot per inch) is the mainstream. Therefore,
The print data output from the host computer is also 300dp
Many are compatible with i.

However, at a resolution of 300 dpi, jaggies (jagged lines) are noticeable in diagonal lines and the like, and high print quality in the original sense cannot be obtained. This drawback can be solved by increasing the pixel density. However, increasing the pixel density increases the capacity of the page buffer (page memory) built into the laser printer body and increases the accuracy of the printer engine (sub scanning). In addition to the cost increase due to the higher precision of the rotation control mechanism of the photosensitive drum and the higher precision rotation control of the polygon mirror (rotating polygon mirror), etc., for more accurate position control in the direction (paper feed direction) The following compatibility issues arise.

At present, the mainstream bitmap fonts for 300 dpi cannot be used. The already widely used 300dpi compatible image input devices (image scanner, etc.) will no longer be usable.

Therefore, as a method of eliminating jaggies without increasing the pixel density, pixels in the page buffer are cut out in a predetermined size and shape, and the cut out pattern (sample window) is used. R in advance
When a matching template is found by sequentially comparing with a plurality of templates written in OM (read only memory), the central pixel in the cutout pattern is moved to the left or right by a predetermined distance, and the pixel is also moved. By changing the size of 12 stages and printing,
There has been proposed a method for improving image quality by reducing crushing of dots and making jaggies inconspicuous (USP 4,847,
641).

[0007]

However, the above-mentioned U
The method of SP4,847,641 has a drawback in that it is not possible to completely correct a horizontal line.

It is an object of the present invention to realize an image forming apparatus having a pixel density similar to the conventional one, in which jaggies are not conspicuous and printing of a line close to horizontal is good, and which has a high printing quality.

[0009]

FIG. 1 is a block diagram showing the principle of the present invention. The present invention comprises a light beam scanning means for scanning a light beam on a photosensitive holding carrier, and a control means for turning on / off the light beam according to a video signal corresponding to image information to be output, It is premised on an image forming apparatus for forming an image on a holding carrier.

The instructing means 1 obtains the density information of the recording pixel and the density information of the peripheral pixels of the recording pixel based on the video signal, and from this density information, the recording position of the recording pixel with respect to the standard recording position. Move to the left or right or up or down, or to the left or right and up or down to instruct to form the image of the recording pixel.

The changing means 2 changes the direction of the light beam according to the instruction of the instructing means 1. This changing means 2 is
For example, as described in claim 2, it has an incident surface on which a light beam is incident, is arranged so as to give a passing light beam to the light beam scanning means, and the change instruction of the instruction means 1 is an ultrasonic wave of a predetermined frequency. It consists of a given acousto-optic modulator.

Further, as described in claim 3, the ultrasonic wave applied to the ultrasonic element of the acousto-optic modulator is generated by, for example, a piezoelectric element (Piezo-Electric Element). This piezoelectric element is made of, for example, quartz (SiO ₂ ), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ),
It is composed of lithium niobate (LiNbO ₃ ).

[0013]

The instructing means 1 causes the video signal to be input every time it is input.
Based on the video signal, the density information of the recording pixel and the density information of the peripheral pixels of the recording pixel are obtained, and from this density information, the instruction information for instructing the image forming position of the recording pixel is output to the changing unit 2. ..

When the changing means 2 designates the leftward or rightward movement of the print position by the input instruction information, the change means 2 prints the light emission timing of the light beam of the laser light source at the standard position. It is controlled to be earlier (when moving to the left) or slower (when moving to the right). Further, if the print information is designated to move upward or to the right by the instruction information, it is possible to specify an upward movement of the irradiation position of the light beam emitted from the laser light source on the photosensitive drum. Controls in the positive sub-scanning direction (the same direction as the sub-scanning direction), or in the case of downward movement, in the negative sub-scanning direction (direction opposite to the sub-scanning direction).

Therefore, it is possible to print by moving the pixel not only in the main scanning direction (left and right) but also in the sub scanning direction (up and down) by an arbitrary distance. Further, since the movement control of the left and right and the upper and lower print positions can be independently performed, by combining the left / right movement and the upper / lower movement, the print position of the pixel can be at least the left, for example. ,right,
45 ° above, below and diagonally left, 45 ° diagonally right, 45 ° diagonally left
You can move in 8 ways, at 45 degrees and 45 degrees diagonally to the right.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic diagram showing an overall configuration of an optical system in a reversal development type laser printer in which toner is attached to an exposed portion, which is an embodiment of the present invention.

In FIG. 1, a laser light source 10 is composed of, for example, a semiconductor laser or the like, and generates a light beam (laser beam) by a current pulse applied from a controller (not shown). The light beam having the elliptical FFF (far field pattern) is converted into parallel light through a collimator lens (not shown) and then a cylinder for correcting the tilt of the polygon mirror. The light enters the vertical controller 20 through the lens.

The vertical controller 20 is, for example, an AOM.
(Acoustic Optical Modulator) and the like, which outputs the first-order diffracted light deflected from the incident parallel light by a predetermined angle in a predetermined direction. AO
M is, for example, a bulk-type ultrasonic element such as TeO ₂ single crystal, PbMoO ₄ single crystal, or tellurite glass. When an ultrasonic wave is applied from the outside, the ultrasonic wave and the parallel light interact with each other. , The parallel light is deflected in the sub-scanning direction. That is, a phase diffraction grating (period = ultrasonic wavelength λ
_{When a} ) occurs and the parallel light is incident at an angle satisfying the Bragg condition, the parallel light undergoes Bragg diffraction and is divided into zero-order and first-order diffracted light. Where the ultrasonic frequency f _a
Is changed by Δf _{a, the} diffraction angle θ of the first-order diffracted light is changed.
Is modulated as in equation (1) below.

[0019]

[Equation 1]

The lambda: wavelength of light outside the AOM v _a: Ultrasonic velocity polygon mirror (rotary polygon mirror) applied to the AOM 30 is by reflecting light beams incident from the vertical direction controller 20, the light beam It has eight mirror surfaces 31 for scanning the photosensitive drum 40 in the main scanning direction, and its rotation is controlled by a motor (not shown).

Further, the polygon mirror 30 and the photosensitive drum 4
An fθ lens, for example, is arranged between 0 and 0. This f
The θ lens converts the light beam reflected by the Borgone mirror 30 from a constant angular velocity motion to a constant velocity motion on the surface of the photosensitive drum 40 to correct scanning distortion, and also has a function of narrowing the light beam. is doing.

Further, instead of providing the above fθ lens,
The mirror surface of the Borgon mirror 30 may be subjected to processing for correcting scanning distortion. The photosensitive drum 40 is a drum that rotates at a constant speed in the rotation direction A shown in FIG. 2 on the surface of which a photoconductor such as an organic photoconductor (OPC), CdS, Se, amorphous Si, or Se-Te system is applied. By irradiation (exposure) of the reflected light by the polygon mirror 30, an electrostatic latent image of a printed image is formed on the surface thereof.

Next, FIG. 3 shows the configuration of the printer head control circuit of the control unit (printer controller) of the laser printer of the embodiment. This control circuit includes a data cutout unit 100 and a pixel position conversion unit 200. The data cutout unit 100 is a bitmap memory (page memory)
From the image data of one page is sequentially cut out in units of 5 × 5 pixels with the pixel to be printed at the center, and the cut-out 5
The image pattern of × 5 pixels is output to the pixel position conversion unit 200.

The pixel position conversion unit 200 receives the input 5 ×
An image pattern of 5 pixels is sequentially compared with a plurality of prestored templates, and if there is a matching template, the central pixel of 5 × 5 pixels (print target pixel)
Change the print position of.

The data slicing section 100 includes five line buffers 110-1, 110-2, ... 110- for storing image data for one row of the bit map memory.
5, those line buffers 110-1, 110-2,
... Five 5-bit shift registers 120-1, 120-2, ... 120 provided corresponding to 110-5
-5, and an address counter 140 that outputs a read address to the bitmap memory.

The line buffers 110-1, 110-2,
... 110-5 stores image data of five consecutive rows in the bitmap memory. The storage order is the scanning order in the sub-scanning direction.

5-bit shift registers 120-1, 12
0-2, ... 120-5 correspond to the corresponding line buffers 110-1, 110-2 ,.
5 bits of pixels sequentially shifted by one pixel are input and stored in the scanning order from 5 in the main scanning direction.

The address counter 140 outputs an address signal to the bit map memory and causes the line buffers 110-1, 110-2, ... 110-5 to store the pixel.

Next, the circuit configuration of the pixel position conversion unit 200 will be described. The comparator 210 serially inputs 5 × 5 pixels, that is, 25-bit pixels serially from the 5-bit shift registers 120-1 to 120-5, and compares them with the 5 × 5 pixel template (50 bits) input from the rotator 240. To do. The data of each pixel of the template is
Since it has three-value information of "black", "white", and "unspecified" (either black or white may be used), it is composed of 2 bits. Therefore, the 5 × 5 pixel template is composed of 50-bit serial data. If the two match, the comparator 210 outputs a match signal to the selector 260 and the rotator 240.

The template storage section 220 stores a plurality of 5 × 5 pixel templates each having 50 bits.
For example, it comprises a ROM (Read Only Memory) and the like.
An example of the template stored in the template storage unit 220 is shown in FIG. In the figure, white circles 301 are white dots, black circles 302 are black dots, and hatched circles 3
Reference numeral 03 denotes a pixel which is not a comparison target and may be either a black dot or a white dot. Then, in the template storage unit 220, the data of each pixel consists of 2 bits as described above. That is, a pixel which is a white dot is represented by "00", a pixel which is a black dot is represented by "01", and an unspecified pixel is represented by "10". In the template, the data (dot information) of each pixel is stored in the order of the numbers attached in FIG. Therefore,
For example, the template of 5 × 5 pixels shown in FIG.
"10 10 10 10 10 10 (1st line), 00 00 00 00 00 (2
Line), 00 01 01 01 01 (line 3), 01 10 10 10 10
(4th line), 10 10 10 10 10 (5th line) ". Then, the template shown in FIGS. 4A to 4C has an address “0” in the template storage unit 220.
It is stored in order from. It should be noted that this template storage unit 220 is rotated 90 degrees counterclockwise about the center pixel,
Only one template is stored for templates that have the same rotation target relationship when rotated to 80 ° and 270 °, and only multiple templates that are not in rotational symmetry are stored efficiently. ing. That is, 5 × 5
The number of patterns that a pixel can take is 2 ²⁵ , but the number of templates to be stored can be reduced to 1/4, that is, 2 ²³ by adopting the storage method described above. Furthermore, as shown in FIG. 4, the number of templates n _p stored in the template storage unit 220 is further reduced by designating the pixels on the outer side of 5 × 5 pixels as the pixels outside the comparison symmetry.

The counter 230 receives "0" to "n" in response to a count-up signal applied from the comparator 210.
It is an n-ary counter that counts up to (n = n ^p -1) and adds the count value to the template storage unit 220 as an address signal.

The rotator 240 has a template storage section 22.
The 50-bit template output from 0 is initially output to the comparator 210 as it is, but after the output,
If the match detection signal is not added from the comparator 210 after a predetermined time has elapsed, 50 bits obtained by rotating the template 90 °, 180 °, 270 ° counterclockwise until the match signal is added. The template is sequentially output to the comparator 210 at predetermined time intervals.

The modified pattern code storage unit 250 corresponds to each template stored in the template storage unit 220 (including the template obtained by each rotation of 90 °, 180 °, 270 °) from the bitmap memory. A correction pattern code that specifies the print correction position of the cut-out 5 × 5 pixel center pixel is stored. As described above, in the comparator 210, with respect to one template stored in the template storage unit 220, 90 °, 180 ° around the center pixel in the counterclockwise direction.
Since the patterns obtained by rotating the rotation angle of 270 ° and 270 ° are also compared, the modified pattern code storage unit 250 stores the n _p 4 stored in the template storage unit 220.
Double, that is, 4n _p correction pattern codes are stored in association with the template stored in the template storage unit 220 (see FIG. 6). And rotator 2
2-bit template rotation information output from 40 (00: no rotation, 01: 90 ° rotation, 10: 180 ° rotation, 11:
270 ° rotation) is input as the lower 2 bits of the address signal, and the count value output from the counter 230 is input as the upper bits of the address signal (see FIG. 7).

The correction pattern codes stored in the correction pattern code storage unit 250 are "0001", "0010", "1000", "1001", "101" shown in FIGS. 8 (b) to (i).
There are eight types of 4-bit values of "0", "0100", "0101", and "0110".

The high-order 2 bits of the correction pattern code specify the movement correction of the print position in the upward or downward direction (10:
Upper, 01: Lower) and lower 2 bits specify the print position movement correction to the left or right (10: left, 01: right). Further, as shown in FIG. 9A, the uncorrected pattern code when the print position is not changed is “0000”. In the figure, a black dot 401 indicates a corrected print position of a central pixel of 5 × 5 pixels cut out from the bitmap memory, and a white dot 402 indicates an uncorrected print position (standard position) of the central pixel. Shows.

The selector 260 outputs 4 from "0000" output from the register 270 when the coincidence detection signal is not added from the comparator 210 even after a lapse of a predetermined time.
When the bit value is selectively output to the three-state register 280 as a code (printing position code) indicating the printing position of the central pixel (printing target pixel), but the coincidence detection signal is added from the comparator 210 within the predetermined time. , The 4-bit correction pattern code output from the correction pattern code storage unit 250 is selectively output to the three-state register 280 as the print position code of the central pixel.

The three-state register 280 outputs the 4-bit printing position code of the central pixel output from the selector 260 and the 1-bit dot information (1: black) of the central pixel output from the data cutout unit 100. , 0: white) is output to the printer head control unit, which will be described later, every time an enable signal is applied from the timing control unit 290 at a predetermined cycle.

The timing controller 290 divides the basic clock supplied from a clock generator (not shown) and outputs a strobe signal to the selector 260 and an enable signal to the three-state register 280 at a predetermined cycle. To do. Further, the reset signal of the counter 230 or the like is output at a predetermined timing.

Next, the three-state register 280.
FIG. 9 shows a circuit configuration of a printer head controller which controls the printer head (optical system) shown in FIG. 2 based on the 5-bit information output from the printer.

The printer head control unit includes an up-and-down direction control unit 310 for changing the black dot printing position in the up-and-down direction,
A left-right direction control unit 320 that changes the printing position of the black dots in the left-right direction.

The vertical direction control unit 310 includes a D / A converter (digital / analog converter) 311 and its D / A.
V / to which the voltage output from the converter 311 is input
It comprises an F converter 312 and the AOM (acousto-optic modulator) 313 connected to the V / F converter 312 by a coaxial cable 313.

The D / A converter 311 is the same as that shown in FIG.
The corrected pattern code (“000” output from the three-state register 280 of the pixel position conversion unit 200 shown in FIG.
The upper 2 bits of "0" (including uncorrected) are input, and the value of the 2 bits is converted into a corresponding voltage value. There are three types of 2-bit values, "00" (uncorrected), "10" (upward movement), and "01" (downward movement). The D / A converter 311 performs conversion into voltage values as shown below according to the above three types of values.

“00” → O “10” → V _u “01” → V _{d The} V / F converter 312 is an ultrasonic wave generator composed of a piezoelectric element or the like, and it depends on the voltage value applied from the D / A converter 311. The ultrasonic wave having the frequency f _a is generated, and the ultrasonic wave is applied to the AOM 20 via the coaxial cable 313. In this case, the V / F converter 312 is the D / A converter 31.
When the voltage applied from 1 is OV, ultrasonic waves are not oscillated. Further, the light beam AOM20 is incident when the voltage V _u, oscillates an ultrasonic wave of a frequency f _au deflect such incident on the mirror surface of the lower polygon mirror 30 shown in FIG. 3, the V _d Occasionally, the AOM 20 generates an ultrasonic wave having a frequency f _ad that deflects the incident light beam so as to be incident above the mirror surface of the polygon mirror 30. Therefore, the AOM 20 uses the laser light source 10 according to the frequency f _a of the ultrasonic wave applied from the V / F converter 312.
A light beam (incident light beam) that is incident through the collimator lens and the cylinder lens is deflected as described below and is incident on the mirror surface of the Borgone mirror 30.

When ultrasonic waves are not applied, the incident light beam is not deflected and is incident on the mirror surface of the Borgone mirror 30 as it is. Therefore, in this case, the exposure position of the black dot is the standard position.

When an ultrasonic wave having a frequency f _au is applied, the incident light beam is deflected so as to be incident below the mirror surface of the Borgone mirror 30 than usual. Therefore, in this case, the exposure position of the black dot moves to a position printed above the standard position during printing.

When an ultrasonic wave having a frequency f _ad is applied, the incident light beam is deflected so as to be incident above the mirror surface of the Borgon mirror 30 than usual. Therefore, in this case, the exposure position of the black dot moves to a position where the black dot is printed below the standard position during printing.

Next, the circuit configuration of the left / right direction control section 320 will be described. The decoder 321 decodes the lower 2 bits of the modified pattern code input from the three-state register 280 to generate three output terminals Y ₀ , Y ₁ ,
Any one of Y ₂ is made active (“H” level) and the corresponding data select terminal A (Y
₀ and connection), connected to the B (Y _1), and outputs the C (connected to the Y _2).

The counter 322 has a basic clock C inside.
It has a clock generator consisting of a crystal oscillator etc. that generates LK _B , and from its basic clock CLK _B ,
Three types of clock pulses CLK _l , CLK _c , and CLK having different phases in which the rising timings of the pulses are shifted by 1/3 of the pulse width T as shown in FIGS. 10 (a), (b), and (c).
_R to generate their clock pulses CLK _l , CLK
_c and CLK _R are output to the data input terminals D ₀ , D ₁ and D ₂ of the selector 323, respectively. The clock pulses CLK _l , CLK _c , and CLK _R are signals that control the light emission time of the laser light source 10, and are output to the laser driver 400 via the selector 323. Also the counter 322
Also outputs the strobe signal STROBE to the selector 323.

A truth table showing the operation of the selector 323 is shown in FIG. The above clock pulses CLK _l , CLK
_R is a signal for moving the exposure position of each black dot to the left and right of the standard position, for example, by 1/3 of the diameter d of the black dot. Also, the clock pulse CL
_Kc is a signal for exposing a black dot at a standard position.

The laser driver 400 is the selector 32.
3 output clock pulses CLK _l , CLK _c ,
Alternatively, the laser light source 10 composed of a semiconductor laser is driven based on CLK _R , and the clock pulses CLK _l , CL
The laser light source 10 emits a light beam while K _c or CLK _R is at the H level.

Next, the operation of the embodiment having the above configuration will be described. First, the data cutout unit 100 inputs pixel data of five consecutive lines from the bitmap memory to the line buffers 110-1 to 110-5.

Then, the line buffers 110-1 to 110-1
Image data for 5 lines stored in 110-5 is 5
Cut out in units of × 5 pixels, 5 bit shift register 1
20-1 to 120-5.

The line buffers 110-1 to 110-
5 has 2 bits at the right end and 2 at the left end as shown in FIG.
Bit dummy pixel data 501 is stored. In addition, the pixel data of the first row of the bit map memory, along with the above-mentioned 4-bit dummy pixel data, are stored in the line buffer 11
0-3, the line buffer 110-
Dummy pixel data 501 is stored in all 1, 110-2. This is because the print position for the central pixel is determined by the cutout pattern of 5 × 5 pixels.

Here, the operation of the pixel position conversion unit 200 will be described with reference to FIG. 13 by taking two concrete patterns of 5 × 5 pixels. First, the pattern of 5 × 5 pixels as shown on the right side of FIG.
Is input to the comparator 210, the comparator 210 first compares the pixel pattern with the template stored in the first address (= address “0”) of the template storage unit 220. If they do not match, then the template is compared with the template rotated 90 ° counterclockwise by the rotator 240. If the two do not match in the comparison, then the rotator 240
A comparison is made with the template rotated by 80 °, and if the two do not match in the comparison, further comparison is performed with the template pattern rotated by 270 ° by the rotator 240.

If the 5 × 5 pixel pattern shown in FIG. 13A does not match the template rotated by 270 °, the comparator 240 outputs a count-up signal to the counter 230. By this,
The counter 230 counts up from “0” to “1” and outputs the address signal “1” to the template storage unit 220. Then, the template stored at the address “1” from the template storage unit 220 is the rotator 240.
The comparator 210 sequentially changes the pattern of 5 × 5 pixels shown in FIG. 13 (a) to 0 ° (unrotated), 90 °, in the same manner as the template of the address “0” described above.
Compare with the template of address "2" rotated to 180 and 270 degrees.

In the same manner, the templates stored at the addresses "3", "4", ... Are sequentially read from the template storage unit 220 until the matching templates are input to the comparator 210. 0 ° (unrotated), 90 °, 180 of template of each address
A comparison is made with the template obtained by rotating counterclockwise at °, 270 °.

Then, the template (including the template obtained by rotating at 90 °, 180 ° or 270 °) stored at an arbitrary address of the template storage unit 220 input to the comparator 210 is the data cutout unit 100. When it matches the pattern of 5 × 5 pixels shown in FIG. 13 (a) which is cut out from the image and input to the comparator 210, the comparator 210 outputs a match signal to the selector 2
Output to 60.

At this time, the selector 260 is input with the correction pattern code “0010” shown in FIG. 8C output from the correction pattern code storage unit 250. When the coincidence signal is applied from the comparator 210, the selector 260 selectively outputs the modified pattern code of “0010” to the three-state register 280 at the timing when the strobe signal is applied from the timing control circuit 290.

The three-state register 280 includes a 5-bit shift register 120-3 of the data cutout unit 100.
"Black" or "white" of the above center pixel output from
1-bit dot data indicating that the three-state register 280 is input to the timing control unit 290.
When the enable signal is applied from the above, the upper 2 bits "00" of the modified pattern code of "0010" are supplied to the D / A converter 311 of the vertical direction control unit 310 shown in FIG. Decoder 32 of control unit 320
Output to 1. Then, the dot data “1” (black) of the central pixel is further output to the laser driver 400.

In this case, since the digital data applied to the D / A converter 311 in the vertical direction control section 310 is "00", no ultrasonic wave is applied to the AOM 20.
On the other hand, in the left-right direction control unit 320, the selector 32
3, the clock CLK ₁ shown in FIG. 10A is selectively output to the laser driver 400.

As described above, since the dot data of "1" indicating the black dot printing is added to the laser driver 400, the laser driver 400 lasers for the time corresponding to the pulse generation period T of the clock pulse CLK _l. The light source 10 is controlled to generate a light beam.

By the above operation, the electrostatic latent image on the photosensitive drum 40 of the central pixel is moved to the left by 1/3 pixel from the standard position as shown on the right side of FIG. 13 (a). And is formed at a position where it is printed. Similarly,
In the case of the pattern of 5 × 5 pixels shown on the upper left side of FIG. 13B, the correction pattern code storage unit 250
The modified pattern code of "0100" shown in (g) is selector 2
It is output to 60. In this case, 2-bit data "01" is input to the D / A converter 311 of the vertical direction control unit 310, the V / F converter 312 oscillates and outputs the ultrasonic wave of the frequency f _ad , and the coaxial cable Add to AOM 20 via 313.

On the other hand, the decoder 3 of the left / right direction controller 320
The 2-bit data “00” is input to 21 and the selector 323 outputs the clock pulse CLK _c shown in FIG. 10B output from the counter 322 to the laser driver 323. Since the dot data of "1" (black) is input from the three-state register 280 to the laser driver 323, the center pixel is 1/3 pixel from the standard position as shown in the upper right of FIG. 13 (b). The generation time of the light beam of the laser light source 10 is controlled so that the image is printed just below.

In USP 4,847,641, in this case, as shown in the lower right part of FIG. 13B, the print position of the central pixel is not changed, and the central pixel is printed in a smaller size than usual. I was doing For this reason, the black dots 601 and the black dots 603 shown in FIG. 6B may appear discontinuous. In this embodiment, since the pixel size is not changed, such a phenomenon does not occur.
As is clear from the comparison between before and after correction shown in (a) and (b), jaggies are eliminated and the contour is printed smoothly.

FIG. 14 is a timing chart showing the overall operation of this embodiment. 5-bit shift registers 120-1 to 120-1 in the data cutout unit 100
The loading of 5 × 5 pixels from the line buffers 110-1 to 110-5 to 20-5 is performed at a constant cycle T _ls as shown in FIG. This constant period T _ls is the photosensitive drum 4
It corresponds to a period for forming an electrostatic latent image of 1 pixel at 0.

After the 5 × 5 pixels are loaded into the 5-bit shift registers 120-1 to 120-5, the 5 × 5 pixels are loaded into the comparator 210 at the rising timing of the pulse shown in FIG. It Comparator 2
The 10 holds the loaded 5 × 5 pixels for a certain period of time T _lc (see FIG. 7B).

Subsequently, at the rising timing of the pulse shown in FIG. 7C, the counter 230 first outputs the address signal “0” to the template storage section 220. Next, at the pulse rising timing shown in FIG. 3D, the address “0” output from the template storage unit 220 is output.
The template stored in the is loaded into the rotator 240. The template is output from the rotator 240 to the comparator 210, and the 5 × 5 pixel pattern is compared with the template by the comparator 210. Then, as described above, until the comparator 210 detects the template matching the 5 × 5 pixels, the 5 × 5 pixels and the plurality of templates stored in the template storage unit 2220 are
The storage order is sequentially compared.

Then, at the rising timing of the pulse generated just before the end of the period T _ls shown in FIG.
4 corresponding to the matching template from the selector 260
Either the bit modified pattern code or “0000” (when there is no matching template) stored in the register 270 is output to the three-state register 280.

Next, FIG. 15 shows an example of a timing chart when the comparator 210 detects a matching template. The data cutout unit 100 and the pixel position conversion unit 200 operate in synchronization with the basic clock shown in FIG.

First, after the arbitrary 5 × 5 pixel pattern stored in the bit map memory is loaded into the shift registers 120-1 to 120-5 at the timing shown in FIG. At the rising timing of the pulse shown in (c), the pattern of 5 × 5 pixels is the comparator 21.
Loaded to zero.

Then, the counter 230 outputs the address signal "0" at the rising timing of the pulse shown in FIG.
Is output to the template storage unit 220, and the template stored in the address “0” of the template storage unit 220 is loaded into the rotator 240 at the pulse rising timing shown in FIG.

Subsequently, the template (non-rotation) and the template obtained by rotating the template 90 ° and 180 ° counterclockwise at the rising timing of the pulse shown in FIG.
Is output to.

Then, at the pulse rising timing shown in (g) of FIG.
The 5 × 5 pixel pattern loaded at the rising timing of the pulse shown in (c) and the above templates are sequentially compared.

Then, as shown in FIG. 7H, when the comparator 210 detects that the template rotated 180 ° counterclockwise matches the pattern of 5 × 5 pixels, it selects a match detection signal. Output to 260.

When the coincidence detection signal is added, the selector 260 outputs the correction pattern code output from the correction pattern code storage section 250 at the timing shown in FIG.
It is selectively output to the three-state register 280 at the rising timing of the pulse shown in FIG.

The above-described operation is performed by the template storage unit 22.
The same applies to templates stored after the address "1" of 0 (however, the comparator 2
10 detects a template that matches the loaded 5 × 5 pixel pattern).

Next, the operation when the comparator 210 does not detect a template that matches the loaded 5 × 5 pixel pattern will be described with reference to the timing chart of FIG.

In this case, (d), (e), (f) in FIG.
As shown in (g), first, the template storage unit 2 is changed by the address signal “0” output from the counter 230.
The template stored in the address “0” from 20 is output to the rotator 240.

Then, at every constant time interval T _R , the rotator 2
40 to the template (0 °) of the above address “0”,
Counterclockwise the template 90 °, 180 °, 270 °
The templates obtained by rotating the image are sequentially output to the comparator 210, and the comparator 210 sequentially compares the four types of templates with the loaded 5 × 5 pixel pattern. If the template does not match any of the templates, the comparator 210
A count-up signal is output to the counter 230, which causes the counter 230 to count up by "1", and this time, the address signal "1" is transferred to the template storage unit 2.
Output to 20.

As a result, the template storage section 220 outputs the template stored at the address "1" to the rotator 240. Then, again, the rotator 240
From the above, the template (0 °) of the address “1” and the template is rotated counterclockwise 90 times at regular time intervals T _R.
The template obtained by rotating by 180 °, 180 °, 270 ° is output to the comparator 210, and the comparator 210 compares the template with the 5 × 5 pixel pattern which is sequentially loaded. If no matching template is detected in any of the comparisons, the count-up signal is output again to the counter 230, and the count value of the counter 230 is increased from "1" to "2".

As a result, the template storage unit 22
The template stored in the address “2” from 0 is output to the rotator 240, and thereafter, the above-mentioned address “0”,
Comparing with the template of "1", the comparator 210 compares the template of address "2" with the loaded pattern of 5x5 pixels. Then, the templates stored in the template storage unit 220 are sequentially read and compared in the order of address until the comparator 210 detects a template that matches the loaded 5 × 5 pixel pattern. If all the templates stored in the template storage unit 220 do not match the loaded 5 × 5 pixel pattern,
The comparator 210 does not output the coincidence detection signal to the selector 260. Therefore, in this case, the selector 260 selectively outputs the pattern code “0000” stored in the register 270 to the three-state register 280.
As a result, 2 bits of "00" are output to both the vertical direction control unit 310 and the horizontal direction control unit 320 shown in FIG. 9, and the laser driver 400 is shown in FIG.
Is input a clock pulse CLK _c shown in, the laser driver 400, if the central pixel of the 5 × 5 pixels was black dots, the light emission timing of the laser light source 10 so that the center pixel is printed in the standard position Control. In this case, in the vertical direction control unit 310, the AO
Since no ultrasonic wave is applied to M20, the light beam emitted from the laser light source 10 is incident on the mirror surface of the polygon mirror 30 without being deflected by the AOM 20. Therefore, the electrostatic latent image on the photosensitive drum 40 of the central pixel is
It is formed so as to be printed in a standard position.

As described above, in the present embodiment, each template of 5 × 5 pixels stored in the template storage section 220 is not only output by the rotator 240 as it is, but also 90 °, 180 °, 270 ° Since it is rotated clockwise and is output to the comparator 210,
Not only does the memory capacity of the template storage unit 220 become smaller, but when compared with the method of directly outputting the template without passing through the rotator 240, the template storage unit 220 having the same memory capacity can store templates of many patterns.

Further, in the present embodiment, FIG.
As shown in (i), the print position can be moved up to eight types, but the present invention is not limited to this, and the number of types of ultrasonic waves to be added to the AOM is increased, and further, the laser is added. By increasing the types of clock pulses input to the driver, it is possible to control the movement direction of the print position in more directions, and the movement distance can be controlled in more steps. Such control can be realized, for example, by adding not only the moving direction but also information indicating the moving distance in the correction pattern code.

In the above embodiment, the AOM (acousto-optic modulator) is used as the means for deflecting the light beam, but the light deflecting means is not limited to this element.
All other elements capable of deflecting light at high speed may be used.

Further, in the above-described embodiment, the template pattern is compared with a plurality of pixels including the target pixel in order to determine whether or not the recording position of the target pixel should be shifted. May be discriminated by a neural network.

Further, the laser light source has been described as a semiconductor laser which is turned on / off according to a video signal given from the printer controller, but a gas laser may be used.

In this case, it is necessary to further provide an AOM for turning on / off the light beam from the gas laser.

[0088]

According to the present invention, the print position of a pixel can be controlled not only in the main scanning direction (left and right) but also in the sub scanning direction (up and down). High-quality printing that enables excellent printing is possible. It also has the advantage that the currently used 300-dpi bitmap fonts can be used as they are.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a diagram showing a configuration of an optical system of a laser printer which is an embodiment of the present invention.

FIG. 3 is a block diagram showing a circuit configuration of a data cutout unit and a pixel position control unit.

FIG. 4 is a diagram showing an example of a template.

FIG. 5 is a diagram illustrating an arrangement order of dot information of each pixel of a template.

FIG. 6 is a diagram showing a correspondence relationship between storage positions of templates stored in a template storage unit and correction pattern codes stored in a correction pattern code storage unit.

FIG. 7 is a diagram showing a configuration of an address signal input to a correction pattern code storage unit.

FIG. 8 is a diagram showing a correction pattern and its code.

FIG. 9 is a block diagram showing a circuit configuration of a printer head controller.

FIG. 10 is a diagram showing three types of clock pulses output from a counter in the left / right direction control unit.

FIG. 11 is a diagram showing a truth table of a selector in the left / right direction control unit.

FIG. 12 is a diagram illustrating pixels stored in a line buffer.

FIG. 13 is a diagram showing an example of a method for correcting the print position of a pixel in this embodiment.

FIG. 14 is a timing chart showing the overall operation of this embodiment.

FIG. 15 is a timing chart showing an example of an operation when there is a template that matches a cut-out pixel pattern.

FIG. 16 is a timing chart illustrating an operation when there is no template that matches a cut-out pixel pattern.

[Explanation of symbols]

 1 instruction means 2 change means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Sato 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Tomohisa Mikami 1015, Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (3)

[Claims] 1. A light beam scanning means for scanning a light beam on a photosensitive image carrier, and a control means for turning on / off the light beam according to a video signal corresponding to image information to be output. An image forming apparatus for forming an image on the image carrier, wherein density information of a recording pixel and density information of peripheral pixels of the recording pixel are obtained based on the video signal, and the recording pixel is obtained from the density information. An instruction unit (1) for instructing to form the image of the recording pixel by moving the recording position of (1) to the left or right or up and down, or to the left and right and up and down with respect to the standard recording position; An image forming apparatus comprising: a changing unit (2) for changing the direction of the light beam. 2. The changing means (2) has an incident surface on which a light beam is made incident, and is arranged so as to give a passing light beam to the light beam scanning means, and a change instruction of the instructing means is at a predetermined frequency. The image forming apparatus according to claim 1, wherein the image forming apparatus is an acousto-optic modulator that is given by ultrasonic waves. 3. The image forming apparatus according to claim 2, wherein the ultrasonic wave applied to the ultrasonic element of the acousto-optic modulator is generated by a piezoelectric element.