JPH01115648A - Image forming device - Google Patents

Abstract

PURPOSE:To enhance an image quality, by a method wherein a recording signal having a pulse width coincident with a printing pattern is selected for printing. CONSTITUTION:Input image information is successively inputted to a shift register 251 in synchronism with an image clock. A relation between a pixel and a plurality of pixels adjacent thereto in the image information in the shift register 251 is judged by an isolated black pixel judgement circuit 252 and an isolated white pixel judgement circuit 253. A black pixel among a white pixel group is judged by the isolated black pixel judgement circuit 252, and a white pixel among a black pixel group is judged by the isolated white pixel judgement circuit 253. For a black pixel among a white pixel group, the pulse width of a recording signal is set large by a recording signal pulse width set circuit 254. For a white pixel among a black pixel group, the pulse width of a recording signal is set small by the recording signal pulse width set circuit 254. A pattern change-over signal 261 is inputted to a recording signal change- over circuit 260 to change-over a character printing and a graphic printing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus for an electrostatic recording section in a laser printer, facsimile, etc.

(Prior art) In conventional laser printers, facsimile machines, etc., a charged photoconductor is irradiated with a beam in the main scanning direction to obtain an electrostatic latent image, and toner is attached to the electrostatic latent image to develop it. It is well known that recorded images are obtained by fixing.

In this type of image forming apparatus, printing patterns are broadly divided into character printing and graphic printing. In the case of character printing, solid black looks more beautiful, whereas in the case of graphic printing, thin lines ( The better the halftones appear, the more beautiful the image will look. For this reason, if the image forming method is adapted to one method, the other pattern cannot be printed beautifully.

Therefore, conventionally, process conditions such as development bias, L
By adjusting D power, etc., a compromise between both patterns was achieved. Therefore, satisfactory images were not formed in either pattern. Additionally, the machine was unstable depending on the installation environment.

(Problems to be Solved by the Invention) Among such conventional laser printers, facsimile machines, etc., there is no one that prints based on a recording signal that matches character printing and graphic printing, which have different printing patterns. In addition, when developing by so-called negative/positive development in this type of image forming apparatus, due to the properties of the photoreceptor and developing material, compared to the part where multiple images are successively scanned with a laser beam in the main scanning direction, Isolated 1-pixel points or 1-pixel-width line portions, or paired portions of 1-pixel-width lines (black and white) were faded, and these portions could not be reproduced satisfactorily.

An object of the present invention is to improve the quality of images by selecting and printing a recording signal with a pulse width that matches a printing pattern.

(Structure and Operation) In order to achieve the above object, the present invention provides a storage means for sequentially storing a plurality of pixels before and after a pixel of interest in recorded information in synchronization with a pixel clock, and isolated black pixel discriminating means for discriminating an isolated black pixel pattern in which a pixel is a black pixel and the plurality of pixels before and after it are all white pixels; isolated white pixel discriminating means for discriminating an isolated white pixel pattern in which all of the plurality of pixels are black pixels, and an isolated black pixel discriminating means for determining the recording signal of the pixel of interest to have a pulse width larger than the standard according to the output of the isolated black pixel discriminating means; Recording signal pulse width setting means for making the pulse width of the recording signal of a black pixel before or after a pixel of interest smaller than a standard according to the output of the isolated white pixel discriminating means, and image information content of character printing and graphic printing. The present invention is characterized by comprising means for switching the recording signal according to.

According to the present invention, when receiving print data from the host computer, the character controller determines whether the sent data is character printing or graphic printing,
The results are transmitted to the CPU in the main controller through the video interface. Depending on the print content, the CPU sets the pattern switching signal to low level for character printing, and holds the pattern switching signal to high level for graphic printing. Also, when the operator wants to print graphics, turn on the pattern changeover switch.
When you want to print characters, turn off the pattern changeover switch. The character controller determines whether character printing or graphic printing is to be performed by checking the state of the pattern changeover switch, transmits the result to the CPU in the main control via the video interface, and sends a pattern changeover signal as described above depending on the print content. Hold low or high.

The basic operation of the present invention is that the information to be recorded, which is sequentially supplied in the main scanning direction, is sequentially input into the storage means in synchronization with the pixel clock. The storage means has a capacity to store the pixel of interest and a plurality of pixels before and after it, and the contents stored in the storage means change from moment to moment by being sequentially shifted by the pixel clock, and the contents are changed from moment to moment for each pixel clock. The isolated black pixel discrimination means and the isolated white pixel discrimination means monitor a pattern consisting of a pixel of interest and a plurality of pixels before and after it, and detect a pattern in which a black pixel is isolated in a continuous white pixel part and a pattern in which a white pixel is isolated in a continuous black pixel part. When this occurs, a signal indicating the occurrence is output from the isolated black pixel discriminating means or the isolated white pixel discriminating means. In response to the output, when a black isolated pattern is detected by the recording signal pulse width setting means, the pulse width of the recording signal of the pixel of interest is set to the standard recording signal pulse width (for example, the period T of one pixel clock). 80%) or a larger pulse width (for example, 100% of the period T of one pixel clock). Further, when a white isolated pattern is detected, the pulse width of the recording signal of the pixel of interest is set to a pulse width smaller than the pulse width of the standard recording signal (for example, 50% of the cycle T of one pixel clock).

(Example) Hereinafter, an example in which the present invention is used in a laser printer will be described in detail.

FIG. 4 is a perspective view showing the appearance of the laser printer of this embodiment.

This laser printer is roughly divided into a printer upper unit 1 and a printer lower unit 2. A paper feed tray 3 for placing and holding transfer paper is removably attached to the lower unit 2, and a paper discharge switching knob 4 is also provided. The upper unit 1 has an operation panel 5. Font cartridge insertion slot6. An emulation card insertion lower is provided. An upper paper ejection tray 9 is provided on the upper surface of the cover 8.

The operation panel 5 includes switches for setting the transfer paper size and various other printing conditions. The font cartridge insertion slot 6 is used to insert a font cartridge, that is, a cartridge in which font information is stored.
It sends font information to the character controller.

The emulation card insertion lower is for connecting an emulation card to a character controller for matching the host computer and this laser printer depending on the type of the host computer.

The paper discharge switching knob 4 is used to switch whether the transfer paper that has been printed in the laser printer is discharged to the upper paper discharge tray 9 or straightly in the direction of arrow A.

The upper printer unit 1 and the lower printer unit 2 are hinged together on the back side of the figure, and are fixedly held to each other by a locking mechanism on the front side.

If the lock lever knob 10 protruding from the front of the cover 8 is pushed up to release the lock mechanism, the printer upper unit 1 can be rotated and lifted from the pull link lower unit 2, as shown in FIG. This two-part structure facilitates maintenance work and facilitates replacement of the photoreceptor, developer, and the like.

FIG. 6 is a side sectional view of the laser printer in which the upper printer unit 1 and the lower printer unit 2 are connected to each other.

The drum-shaped photoreceptor 11 disposed approximately in the center of the printer lower unit 2 is driven and rotated in a clockwise direction, and is first subjected to a discharging action by the electrification charger 12 .

The charge wire 13 of the charger 12 is connected to the photoreceptor 11
The surface of the photoreceptor 11 is charged in the axial direction by this discharge.

The charged photoreceptor 11 is exposed to an image by a laser exposure device 14 . As shown in FIG. 7, the laser exposure device 14 includes a polygon mirror 16 rotated clockwise by a scanner motor 15, a laser diode (LD) unit 17, a first cylindrical lens 18, and a first mirror 19. , a spherical lens 20 , and a second mirror 21 .

The LD unit 17 includes a semiconductor laser diode (LD
) is built in, and this laser diode LD emits an image signal writing laser beam based on the image signal. As shown in FIG. 8, this laser beam is transmitted through the first cylindrical lens 18. It passes through the first mirror 19 and enters the spherical lens 20.

The laser beam is focused by a spherical lens 20, refracted slightly upward, and irradiated onto one surface of the polygon mirror 16. ' The laser beam irradiated in this way is transmitted to the second mirror 21
The reflected light passes through the second cylindrical lens 22 and is guided onto the photoreceptor 11. At this time, the laser beam is scanned on the second mirror 21, and therefore on the photoreceptor 11, in the main scanning direction according to the rotation of the polygon mirror 16. This optical scanning is repeated for each surface of the polygon mirror 16, and at the same time, the photoreceptor 11 rotates in a direction perpendicular to the main scanning direction, that is, in the sub-scanning direction. A latent image is formed.

The semiconductor laser used in this embodiment emits light of a single wavelength, and has a wavelength of about 780±10 nrn at room temperature. However, the sensitivity range of photoreceptors is generally considerably lower than this, and most of them have a peak at 500 nm or less. In addition, since laser light is a coherent single wavelength light, it may be reflected off the base of the photoreceptor drum (for example, aluminum), causing multiple exposure.
A defect called moiré occurs. In addition, the light energy received by the photoreceptor is determined by the amount of light x the time, but there is a reciprocity law in which the sensitivity changes depending on whether the amount of light is decreased and the time is lengthened, or when the amount of light is increased and the time is shortened. For photoreceptors, this is particularly a problem with a control method in which the amount of light from a single conductor laser is changed depending on the irradiation position as in this embodiment.

The photoreceptor in this example is a PC photoreceptor made of an organic material, and is made of an aluminum drum as a drum base, on which titanium dioxide, a white pigment, is added to an alcohol-soluble polyamide resin. It has an underlayer having a thickness of 4 pm. Further, there is a layer made of trisazo pigment having a thickness of about 0.2 pm as a charge generation layer for absorbing light and generating charge carriers, and further on top of that, there is a layer made of trisazo pigment having a thickness of about 0.2 pm. As a charge transport layer for transporting charge carriers, about 2
A layer made of an α-phenylstilbene compound having a thickness of 2 μm is provided. The peak of the sensitivity range is 750nm
However, it has sufficient sensitivity even in the range of 500 nm to 820 nm. It has a charge transport layer made of an α-phenylstilbene compound, which has good drift mobility (responsiveness) and has succeeded in eliminating the reciprocity law. In addition, titanium dioxide, a white pigment, plays an important role in preventing the formation of a 'moist layer'.

Although not shown, in order to generate synchronization pulses, a synchronization detection sensor is provided that detects passage of a laser beam through a specific position for each scan in the main scanning direction.

The output pulse of this sensor generates other synchronous clock pulses for image writing control.

Returning to FIG. 6, the electrostatic latent image formed on the photoreceptor 11 by the laser exposure device 14 is conveyed to the developing roller 23 as the photoreceptor 11 rotates. The developing roller 23 is rotated counterclockwise while lightly contacting the photoreceptor 11 . Further, the developing roller 23 has
Toner 26 contained in the developer tank 24 is supplied by a toner supply roller 25 that is disposed at the bottom of the developer tank 24 and rotates counterclockwise. Therefore, the electrostatic latent image on the photoreceptor 11 carried to the developing roller 23 is developed into a visible image by the toner carried by the developing roller 23.

This toner image is then conveyed to a transfer position, which is a position opposite the transfer charger 27. 28 is a toner layer thickness regulating blade, and 29 is a toner cartridge.

While the above process is being executed, one sheet of transfer paper at the uppermost position among the transfer papers 30 stacked on the paper feed tray 3 is brought into pressure contact with the paper feed roller 31 which is driven and rotated in a clockwise direction. The friction pad 32 separates the paper from other sheets and sends it to the nip portion of the upper and lower transport rollers 33 . '34, the photoreceptor 11 is transported to the transfer position.

The conveyed transfer paper is superimposed on the toner image on the photoreceptor 11 at the transfer position, and is subjected to discharge by the transfer charger 27. Due to this discharge, the toner image on the photoreceptor 11 is transferred to the transfer paper. When the transfer is completed, light from a static elimination lamp 35 placed next to the transfer charger 27 is irradiated onto the photoreceptor 11 through the transfer paper, eliminating both the surface potential of the photoreceptor and the electrical potential charged when the transfer paper passes. .

The transfer paper whose potential has been weakened is separated from the photoreceptor 11 by its own weight and sent to a heat fixing device including a heating roller 36 and a pressure roller 37. The transfer paper and the toner image transferred thereon are heated by the heating roller 36 and are subjected to pressure from above and below by both rollers 36, 37, and as a result, the toner image is fused and fixed onto the transfer paper. A heater 38 is provided inside the heating roller 36 to heat the heating roller 36.

After the fixing, the transfer paper is peeled off from the heating roller 36 by a peeling claw 39 and sent to a paper discharge roller 40. A paper ejection switching claw 41 is provided at a downstream position of the paper ejection roller 40.
This switching claw 41 can be operated by turning the paper ejection switching knob 4.
It can be switched between the solid line position and the broken line position in FIG. When the switching claw 41 is at the solid line position, the transfer paper coming out from the paper ejection roller 40 is moved between the paper ejection guide member 42 and the paper ejection guide plates 43 and 44.
It passes through the conveyance path formed by the upper paper ejection roller 45.
The paper is discharged to the upper paper discharge tray 9. On the other hand, when the paper ejection switching claw 41 is at the position shown by the broken line, the transfer paper coming out of the paper ejection roller 40 is ejected linearly in the direction of arrow A to the outside of the printer.

Toner that does not contribute to the transfer and remains on the photoreceptor 11 after the transfer is completed is neutralized by the neutralization lamp 35 and scraped off from the photoreceptor 11 by the cleaning blade 46 . The scraped off toner is collected by toner collection roller 4.
7 into the toner collection tank 48. The photoreceptor 11 cleaned by the cleaning blade 46 is
It is charged again by the charger 12.

The surface of the heating roller 36 is made conductive, and the charge on the transfer paper is removed through the conductive surface. In order to impart electrical conductivity to the heating roller, a method can be used, for example, in which carbon is mixed into the base of the roller such as Teflon.

The paper feed tray 3 is detachably attached to the printer lower unit 2. Moreover, this paper feed tray 3 has a pressing lever 49 (
A projecting portion 50 (FIG. 4) projects downward, and a projecting portion 51 is provided on the bottom surface behind it.

This allows the paper feed tray 3 to sit comfortably and eliminates paper slippage.

When the inner cover 52 is attached, as shown in FIG. 6, it covers the paper feed roller 31 and prevents dust from adhering to the paper feed roller 31. The paper feed roller 31 is protected.

FIG. 9 is a diagram showing a control circuit of this laser printer.

The power input section 160 is connected to a commercial power source via an AC plug 161, and includes a main switch 162 and a noise filter 163. One side of the power from the power input unit 160 is supplied to the main controller power supply unit 165 via the interlock switch 164,
The other side is the character controller power supply section 166
is supplied to

The main controller power supply section 165 includes a noise filter 167, a constant voltage circuit 168. It has a semiconductor relay 169. The constant voltage circuit 168 mainly performs AC/DC conversion, and the main controller 176 and charger 12
and power pack 177 for developing bias, power pack 178 for transfer charger (27). Main motor 53
．． Various operating devices 179 (paper feed clutch solenoid 212
2 Paper transport latch solenoid 213. Total counter solenoid 214. latching solenoid 217), etc. The semiconductor relay 169 turns on and off the power supply for controlling the temperature of the heater 38 in the heating roller 36 .

A thermistor 235 for temperature control is attached to the heater 38, and the thermistor 235 is placed closest to the position where the minimum width transfer material, such as an envelope, will pass, to perform accurate temperature control.

The interlock switch 164 is turned off when the upper unit 1 is lifted, and the power supply section 1 for the main controller is turned off.
This is to stop power supply to 65. This character controller power supply section 166 is connected to a noise filter 174.
It has a constant voltage circuit 175, and the character controller 18
Drive 0.

As shown in FIG. 6, the main controller 176 is attached to the electrical chassis 181 in the printer unit 1, and is responsible for the charging,
Controls the overall printer process such as exposure, development, and transfer. The main controller 176 also includes a CPU 186
．． Phase synchronization section 1872 composed of a gate array; display drive section 188. Scanner synchronization detection section 189. Scanner motor driver 190. It has a video interface 191 and a recording signal control section 200. This recording signal control section 200 is the core of the present invention, and will be explained in detail later.

Character controller 180 is main controller 1
76, it is attached to the electrical chassis 181, and the character information sent from the computer 182 to the host 1 is sent to the CPU 1 via the interface 183.
84, where a character signal corresponding to the character information is formed.

That is, the character controller 180 that receives print data from the host computer 182 determines whether the sent print data is character printing or graphic printing.

The host computer 182 is the character controller 1
When sending print data to the computer 80, there are usually a text mode (for character printing) and a graphic mode.

Which mode it is in is determined by sending certain specific data before sending the print data.

FIG. 10 shows an example of the operation flow at this time.

After turning on the main switch 162, each CP in the character controller 180 and main controller 176
If U184 and 186 are both set to character printing, if the ASCII code ESC, -3 is sent, it is set to graphic printing, and if the ASCII code is sent ESC-4, the graphic mode is exited and character printing is determined. As a result, the character controller 180 determines that it is in the graphic mode when it receives the ASCII code ESC-3 sent from the host computer 182, and prints graphics to the CPU 186 of the main controller 176 via the video interface 191. If an ESC-4 is sent, do the same and tell them that it is character printing.

Based on the above results, the CPU 186 sets the pattern switching signal to low level for character printing, maintains the pattern switching signal at high level for graphic printing, and controls the recording signal control unit 200 of FIG. 1, which will be described later. This is characterized in that it is input to the recording signal switching circuit 260 as a pattern switching signal 261.

The display drive section 188 drives the operation panel 5. As shown in FIG. 4, the operation panel 5 includes a rotary type switch 192 for instructing the CPU 186 regarding the size of the transfer paper placed on the paper feed tray 3; button switch 193. A group of LEDs 194 are provided for various indications.

When the operator wants to print graphics, he turns on a pattern changeover switch (not shown) in the operation panel 5, and when he wants to print characters, he turns off the pattern changeover switch in the operation panel 5. by this,
The CPU 184 of the character controller 180 is
Character printing or graphic printing is determined by checking the state (ON, 0FF) of the pattern changeover switch, and the result is transmitted to CPU 186 in main controller 17.6 via video interface 191. The subsequent operation is characterized by inputting the pattern switching signal 261 to the recording signal switching circuit 260 of the recording signal control section 200 in FIG. 1 in the same way as when it is sent from the host computer 182. .゛The phase synchronization unit 187 synchronizes with the printing process executed by the CPU 186, and synchronizes the laser exposure device 1.
The laser diode Lt) in 4 is driven. Further, a synchronization detection signal from the optical fiber 54 is received via the synchronization detection unit 189 to control the light emission timing of the laser diode LD. Furthermore, the scanner motor 15 is controlled via a scanner motor driver 190.

The video interface 191 exchanges control data with the character controller 180 and also transmits a clock signal, which serves as a reference for control, to the character controller 180.

Inside the main controller 176, there are two voltage converters 2 consisting of a 3-terminal regulator, a DC/DC converter, etc.
10 and 221 are provided, and these voltage converters generate voltages for controlling drive motors, solenoids, etc. of each device.

Various operating device sensors 218 (registration sensor 219, paper ejection sensor 220
．． Toner over sensor 221. Paper end sensor 222. Latch sensor 223. Toner end sensor 22
4) is provided.

FIG. 1 shows the main controller 176 shown in FIG.
FIG. 2 is a block diagram illustrating a configuration of a recording signal control section 200, which is a core part of the present invention.

As shown in FIG. 1, input image information is sequentially input to the shift register 251 in synchronization with the image clock, and a pixel with image information (pixel of interest) in the input shift register 251 and a plurality of adjacent pixels are The relationship is determined by the isolated black pixel determination circuit 252 and the isolated white pixel determination circuit 253, the isolated black pixel determination circuit 252 determines the black pixel sandwiched between the white pixel groups, and the white pixel sandwiched between the black pixel groups is isolated. The white pixel discrimination circuit 253 discriminates. Then, according to the determination result, in the case of a black pixel sandwiched between white pixel groups, the pulse width of the recording signal is set larger by the recording signal pulse width setting circuit 254, In Case of,
The recording signal pulse width setting circuit 254 sets the pulse width of the recording signal.
It is set to a smaller value.

In the above configuration, the CPU 184 of the character controller 180 determines whether character printing or graphic printing is performed from the host computer 182 or the operation panel 5 as described above, and the main controller 1 to roller 176 CPU of
186. Here, the recording signal switching circuit 260
A pattern switching signal 261 is input to the printer to switch between character printing and graphic printing.

FIG. 2 shows an example of the specific configuration of FIG. 1. The shift register 251 has five D flip-flops, -2, -1, +1, . +2, and five consecutive pixels in one line of input monochrome image information (third line in Figure 3) are shifted and input sequentially by the pixel clock (first line in Figure 3). be.

The isolated black pixel discrimination circuit 252 consists of an AND circuit, and the input of the AND circuit is outputted to the center flip-flop, and -2 and -1 to the remaining flip-flops.
, to +1. and +2 Q outputs, and by performing an AND operation on them, the central flip-flop K receives black pixel information, and the other flip-flops receive -2,
-1, +1. When +2 contains white pixel information.

An isolated black pixel information panel B (line 5 in FIG. 3) is output. This isolated black pixel information pulse has a width corresponding to the pulse width for one pixel of input image information (period T of the pixel clock).
It has a pulse width T) of 10'0%.

The isolated white pixel discrimination circuit 253 consists of an AND circuit, and the inputs of the AND circuit are connected to the Q output of the center flip-flop and the -Q- outputs of the remaining flip-flops, and their AND operation is performed. By doing this, white pixel information is transferred to the central flip-flop K.
-2 to other flip-flops, -1 to other flip-flops, +1 to other flip-flops. +2 to
When the black pixel information is contained in the black pixel information, the isolated white pixel information pulse C (line 6 in FIG. 3) is output.

The recording signal pulse width setting circuit 254 includes a D flip-flop 2 for setting the output to a low level at 100 with a delay of one pixel clock when the isolated white pixel information pulse C is obtained.
55, a delay circuit 256 that delays the pixel clock for a predetermined period, and a pattern of pixel information in the shift register 251, such as one black pixel in a white pixel group and a white pixel in a black pixel group. an AND circuit 257 for setting the pulse width of the black pixel recording signal (that is, the standard pulse width, which is 80% pulse intensity of the period T of one pixel clock, that is, 0.8T) for a pattern other than that of the black pixel; , a not-AND circuit 258 for setting a 50% pulse width (0,5T) signal from the τ output to the flip-flop and the pixel clock, and based on the outputs of the AND circuits 252 and 257 and the NOT-AND circuit 258, recording is performed. It consists of a NOR circuit 259 that generates a signal, and a recording signal switching circuit 260 that operates in response to a pattern switching signal 261.

The operation of the recording signal control section configured as above will be explained with reference to the time chart of FIG. 3.

In this embodiment, depending on the data pattern in the shift register 251, the width of the recording signal corresponding to the information in the flip-flop is set to one of three widths. That is,
The pattern of image information in the shift register 251 is black for the flip-flop K, -2 for the other flip-flops, -1 for the other flip-flops, +1 for the other flip-flops, and so on. When the pattern is such that white is input to +2, a recording signal with a large pulse width (the 100% width recording signal) is generated, and black information is recorded in the flip-flop. Also, the image information pattern in the shift register 251 is white for the flip-flop K, -2 for the other flip-flops, -1 for the other flip-flops, +1 for the other flip-flops, and so on. When the pattern is such that black is input to +2, a recording signal with a small pulse width (the 50% width recording signal) is generated with a delay of one clock, and +1 black information is recorded in the flip-flop. Also,
When the image information pattern in the shift register 251 is other than the above two patterns, a standard pulse width (the 80% recording signal) is generated, and black information is recorded in the flip-flop. In this way, recording a black pixel in a pattern in which a black pixel is isolated in a group of white pixels increases the pulse width than the standard, and recording a black pixel adjacent to a white pixel in a pattern in which a white pixel is isolated in a group of black pixels increases the pulse width more than the standard. Pixel recording is performed by reducing the pulse width from the standard.

A pixel clock (
3) is given, and image information is input while being shifted in synchronization with this clock.

Let us take as an example the case where the image information is input in the order of "white, black, white, black and white, black and white, black and white, black and white, black and white" (line 3 in FIG. 3). The Q output 3Q (line 4 in FIG. 3) to the third flip-flop of the shift register serves as an output section for information to be recorded (hereinafter referred to as pixel information of interest).

In the flip-flop adjacent to the flip-flop K~2. −1°K+1. The content of +2 is information on neighboring pixels that precede or follow the pixel of interest.

■ Creation of a recording signal for an isolated black pixel When the first black pixel a in the image information example (line 3 in FIG. 3) is shifted to the flip-flop K, the remaining flip-flops have -2, -1, Since the contents of +1°K+2 are all white pixels, the output of the black isolation discrimination circuit 252 becomes a high-level pulse b (FIG. 3, line 5). The pulse width of the pulse b is the same as the time width T of one pixel clock, and this black isolation information is input to the NOR circuit 259, and the recording signal C of the isolated black pixel with the time width T (bottom row of FIG. 3) is output.

■ Generation of a recording signal for a black pixel following an isolated white pixel A white pixel d is input to the flip-flop K, -2 to the remaining flip-flops, -1 to the remaining flip-flops, +1 to the remaining flip-flops, and so on. When +2 are all black pixels, a pulse e is outputted from the white isolation determination circuit 253 (line 6 in FIG. 3). flip flop 2
55 is inverted at the first pixel clock after the pulse e is input, and a low-level pulse f is output at the output π (7th line in Figure 3), so the duration of this pulse f is During this period, the output of the AND circuit 257 is at a low level regardless of other inputs (line 8 in FIG. 3).

On the other hand, since the pixel clock and the 3Q output of the flip-flop are input to the not-and circuit 258, when there is a black pixel in the flip-flop K and it is a half cycle of the latter level of the pixel clock, it becomes high level (the 3Q output of the flip-flop). Figure 3, line 9). In recording a black pixel following this isolated white pixel, the outputs of the black isolated discrimination circuit 252 and the AND circuit 257 are both at low level, and the not AND circuit 258
The recording signal that is the output of the NOR circuit 259 is at a high level during the latter 0.5T period of the pixel clock (in this embodiment, the duty ratio of the pixel clock is set to 0.5T). Small pulse width of 0.5T h
It becomes. Therefore, by narrowing the recording width of the black pixel g following the isolated white pixel d, the recording of the isolated white pixel d results in i being more emphasized than the standard.

■ Generation of recording signals in patterns other than the isolated black pixel and isolated white pixel If the pixel pattern in the shift register 251 is other than the isolated white pixel pattern and the isolated black pixel pattern,
No output is generated to the isolated black pixel discrimination circuit 252.

Furthermore, since the isolated white pixel discrimination circuit 253 also does not produce an output, the flip-flop 255 is not inverted and the 6Q output is at a high level. The delay circuit 256 delays pixel locking by a certain period of time (0.2T in this embodiment), and its delayed output (second row in FIG. 3) is input to an AND circuit 257. The inverted output 3Q to the flip-flop by the AND circuit 257 and the 6Q output of the flip-flop 255 (
The AND output of the delayed pixel clock (line 7 of FIG. 3) and the delayed pixel clock (line 2 of FIG. 3) is the 3Q output (line 4 of FIG. 3) when the content of the flip-flop is a black pixel. , m, n,
(inverted outputs for p and o) are at a high level, and the output of the AND circuit 257 is at a high level during the positive half cycle of the delayed pixel clock (line 8 in FIG. 3).

On the other hand, when the flip-flop K is a black pixel, the output of the NOT-AND circuit 258 becomes high level during the latter half cycle of the pixel clock (line 9 in FIG. 3).

Isolated black pixel discrimination circuit 252. The outputs of the AND circuit 257 and the NOT AND circuit 258 are input to a NOR circuit 259, and the NOR circuit 259 forms a superimposed and inverted recording signal. That is, the waveform on the 8th line of FIG. 3 and the waveform on the 9th line are superimposed and inverted to form the waveform of the recording signal on the 10th line of FIG. 3. Taking pixel information k that is not an isolated pixel as an example, there is a slight difference between the output q of the AND circuit 257 and the output r of the NOT AND circuit 258, so by superimposing them, the output S of the NOR circuit 259 becomes , 0,8 which is the standard pulse width in this example.
T is obtained.

■ Character printing and graphic printing switching process When the pattern switching signal 261 is input to the recording signal switching circuit 260 and is at a high level, the recording signal A (bottom row in FIG. 3) generated by the recording signal pulse width setting circuit 254 is ) is the recording signal for graphic printing.

Furthermore, when the pattern switching signal is at low level, the recording signal B (3 in the 4th line of FIG. 3) generated by the shift register 251 is
Let Q) be the recording signal for character printing.

The above recording signal A (bottom row in Figure 3) is subjected to pulse width control, so it may be a point of one pixel, a vertical line of one pixel width, a horizontal line, a diagonal line, or a pair of vertical lines of one pixel width line. It can sufficiently reproduce horizontal lines, etc., and is suitable for graphic patterns.

In addition, since the recording signal B (line 4 in FIG. 3) is the image information itself, the pulse width of the black pixel is wider than the recording signal A by the delay circuit 256, so the solid black pattern is printed neatly. This makes it suitable for character patterns.

In the above explanations of the embodiments ■ to ■, when a white pixel isolated pattern is detected, the pulse width of the recording signal of the black pixel immediately after the pixel of interest is reduced, but the pulse width of the recording signal of the black pixel immediately after the pixel of interest is reduced. The pulse width of the pixel recording signal may be reduced.

(Effects of the Invention) As described above, the present invention improves image quality by selecting a recording signal with a pulse width that matches the printing pattern of character printing and graphic printing.

Further, according to the present invention, basically, when a black pixel is isolated in a continuous white part in the main scanning direction, it is detected and the pulse width of the recording signal of the black pixel is increased. , it is possible to sufficiently reproduce points of one pixel and lines (vertical lines, diagonal lines) having a width of one pixel.

Further, according to the present invention, if a white pixel is isolated in a continuous black part in the main scanning direction, it is detected, and the pulse width of the recording signal of the black pixel immediately before or after the white pixel is reduced. By doing so, it is possible to sufficiently reproduce a point of one pixel or a line (vertical line, diagonal line) having a width of one pixel.

In addition, in cases other than the black isolated pattern or white isolated pattern described above, in a mode in which the recording signal of the black pixel is set slightly smaller than the one pixel clock width, vertical lines of pairs of lines of one pixel width such as black and white, Horizontal lines can be reproduced satisfactorily.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of a recording signal control section of a laser printer to which the present invention is applied, FIG. 2 is a diagram showing an example of a specific configuration of the recording signal control section of FIG. 1, and FIG. 3 is a configuration block diagram of a recording signal control section of a laser printer to which the present invention is applied. Figure 4 is a perspective view showing the external appearance of a laser printer to which the present invention is applied, and Figure 5 is an open upper unit of the laser printer shown in Figure 4. FIG. 6 is a side sectional view of the laser printer in which the printer upper unit 1 and printer lower unit 2 are coupled together; FIG. 7 is a plan view of the laser exposure device; and FIG. 8 is the laser exposure device. Optical path diagram of the device, No. 9
The figure shows a control circuit of this laser printer, and FIG. 10 is a diagram showing an operation flowchart for character printing and graphic printing. DESCRIPTION OF SYMBOLS 1... Printer upper unit, 2... Printer lower unit, 3... Paper feed tray, 4... Paper output selection knob, 5... Operation panel, 6... Font cartridge insertion slot, 7 ...Emulation card insertion slot, 8.Cover, 9.Upper paper output tray, 10.Lock lever knob, 11.Drum-shaped photoreceptor, 12.Charger, 13.
...Charge wire, 14...Laser exposure device, 1
5... Scanner motor, 16... Polygon mirror, 17... Laser diode (LD) unit,
18...first cylindrical lens, 19...
First mirror, 20... Spherical lens, 21.
...Second mirror, 22...Second cylindrical lens, 23...Developing roller, 24...Developing tank,
25... Toner supply roller, 26... Toner,
27... Transfer charger, 28... Toner layer thickness regulating blade, 29... Toner cartridge, 30
...Transfer paper, 31...Paper feed roller, 32...
Friction pad, 33. 34... Upper/lower conveyance roller, 35... Static elimination lamp, 36... Heating roller, 37... Pressure roller, 38... Heater, 3
9... Peeling claw, 40... Paper ejection roller, 41...
- Paper ejection switching claw, 42... Paper ejection guide member, 43° 44... Paper ejection guide plate, 45... Upper paper ejection roller,
46...Cleaning blade, 47...Toner collection roller, 48...Toner collection tank, 49...
・Press lever, 50... overhanging portion, 51...
Projection part, 52... Inner cover, 53... Main motor, 54... Optical fiber, 160...
Power input section, 161... AC plug, 162...
・Main switch, 163.167, 174...Noise filter, 164...Interlock switch,
165...Power supply unit for main controller, 1
66...Power supply unit for character controller, 1
68.175... Constant voltage circuit, 169... Semiconductor relay, 176... Main controller, 177.
...Power back for developing bias, 179...Various operating equipment, 180...Character controller,
181...Electrical chassis, 182...Host computer, 183...Interface, 184.
186...cpu, 187...phase synchronization unit, 18
8...Display drive unit, 189・Synchronization detection unit, 190・
... Scanner motor driver, 191 ... Video interface, 192 ... Rotary type switch, 193 ... Button switch, 194 ... LED group for various displays, 200 ... Recording signal control section, 210 , 211...Voltage converter, 212...Paper feed clutch solenoid, 213...Paper transport latch solenoid, 214...Total force counter solenoid, 217...Latching solenoid, 218...
・Various operating device sensors, 219... Registration sensor, 220... Paper discharge sensor, 22]... Toner over sensor, 222... Paper end sensor,
223... Latch sensor, 224... Toner end sensor, 235... Thermistor for temperature control,
251... Shift register, 252... Isolated black pixel discrimination circuit, 253... Isolated white pixel discrimination circuit, 25
4... Recording signal pulse width setting circuit, 255... Flip-flop, 256... Delay circuit, 257...
・AND circuit, 258...not AND circuit, 25
9...NOR circuit, 260...Recording signal switching circuit. Patent Applicant Ricoh Co., Ltd. - Figure 10 Procedural Amendment (self-imposed January 22, 1988) Commissioner of the Patent Office Kunio Ogawa 1, Indication of the case: Japanese Patent Application No. 1982-273529 2, Title of the invention: Image formation Device 3, relationship with the case of the person making the amendment Patent applicant address 1-3-6 Nakamagome, Ota-ku, Tokyo Name (674) Ricoh Co., Ltd. Representative
Hama 1) Hiro 4, Agent 5, Number of inventions increased by amendment 0S C) Corrected to J. (2) Change the “recording signal waveform” in the first line of page 32 to “
Correct it to ``Waveform of recording signal A''. (3) On page 32, line 12 of the same page, “(Figure 3, number 10)
Figure 3, Figure 10” is corrected. (4) r recording signal B (3rd
3Q) in line 4 of the figure) is changed to ``recording signal B (line 11 of figure 3)
” he corrected. (5) "Recording signal A (bottom line in Figure 3)" on page 32, line 18 is corrected to "recording signal A (line 10, page 32)." (6) "Recording signal B (line 4 in Figure 3)" on the third line of page 33 is corrected to "recording signal B (line 11 in Figure 3)." (7) Figure 3 is corrected as shown in the attached drawing. that's all

Claims (2)

[Claims] (1) storage means for sequentially storing a plurality of pixels before and after a pixel of interest in recorded information in synchronization with a pixel clock;
isolated black pixel determining means for determining an isolated black pixel pattern in which the pixel of interest in the storage means is a black pixel, and the plurality of pixels before and after the pixel are all white pixels; and the pixel of interest in the storage means is a white pixel. isolated white pixel discriminating means for discriminating an isolated white pixel pattern in which the plurality of pixels before and after the pixel pattern are all black pixels; and an isolated black pixel discriminating means for determining the recording signal of the pixel of interest with a pulse width different from that of the standard. recording signal pulse width setting means for setting the pulse width of a recording signal of a black pixel before or after a pixel of interest to be smaller than a standard according to the output of the isolated white pixel discriminating means; and character printing and graphics. An image forming apparatus comprising: means for switching the recording signal according to image information content of printing. (2) The image according to claim (1), wherein the means for switching the recording signal according to the image information content of character printing and graphic printing is based on an input signal from a host computer or an operation panel. Forming device.