JPH071761A - Printer - Google Patents

Abstract

PURPOSE: To facilitate generation of a shading or a halftone by generating a spot having a variable size by providing a means that is coupled to a light emitting means and controls widths of a series of pulses applied to the light emitting means. CONSTITUTION: A control logical section 82 transfers data stored in a format memory 84 to buffer memories 86, 88. The data is processed by a D/A converter 90 for driving a pulse width modulator(PWM) 92. The PWM 92 generates a driving signal 93 for controlling to drive a laser device 19 to be switched on or off and to generate the series of pulses, then the modulated dot 70 having a variable size is generated. A personal computer 98 and a document scanner 95 can be used for supplying an input image to a print system 80. The control logical section 82 comprises a central processing unit capable of retrieving data from a read-only-memory storing a dot pattern.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method and apparatus for obtaining grayscale output from an electronic printer. In particular, the present invention forms "superpixels" of groups of differently sized printed dots and modulates drive signals that illuminate a photoconductive drum that selectively applies electrostatic ink to the paper. The present invention relates to a technique for creating various gray densities for obtaining high quality graphics output by forming dots of various sizes.

[0002]

2. Description of the Related Art One of the problems faced by conventional ink jet printers and laser printers is "2.
It means that only "value" printouts can be generated. In other words, conventional ink jet printers and laser printers obtain printed output by either applying small dots of ink or toner to a portion of the paper, or leaving it blank to leave that portion of the paper blank. Complex graphic images, such as photographs, require more sophisticated techniques to print intermediate gray densities between the black and white extremes. In conventional printers, the physical size of printed dots is changed in order to obtain a continuous tone density. For example, in newspapers, photographs are composed of many ink dots of different sizes.
Although these dots are discrete from each other,
To the human eye, these dot sizes or densities are mixed and appear as a set of images.

[0003] Conventional electronic printers are capable of sufficiently high performance for print output of simple shapes such as characters and symbols, but are generally not sufficient when more complicated graphics output is required. As computer users find more and more uses for electronic devices, the demand for more sophisticated and versatile electronic printers continues to grow. Thus, the problem of designing a highly accurate and cost-effective printer capable of obtaining a high quality gray scale brings great challenges to designers and development engineers in the field of electronic printer technology. It was. If a durable, yet powerful grayscale printer could be made using the latest inkjet or laser technology, it would represent a major technological advance in the computer peripherals industry. If improved performance is achieved with such innovative devices, it will satisfy the long-felt need in the art and save considerable time and money for printing equipment manufacturers. It seems to be.

[0004]

OBJECTS OF THE INVENTION It is an object of the present invention to improve the quality of grayscale printing using laser printer technology in grayscale electronic printing systems.

[0005]

SUMMARY OF THE INVENTION Improved print quality is achieved by precisely controlling the size of the ink dots applied to the paper during the printing cycle. The size of the printed ink dots depends on the width of the modulation signal (modulated signal) that drives the light source of the electronic printer used to implement the invention.

An embodiment of the present invention comprises a laser printer having a rotating photosensitive charging drum. As the drum rotates, the laser beam is scanned across the drum surface in a raster fashion. When the laser beam illuminates a point on the drum, the surface potential of the drum changes. Then, electrostatic ink material called toner is sprayed onto the charging drum and is attracted to the portion of the drum exposed to the laser beam. The toner is then transferred to the paper and fixed (fused) to the paper by the roller and the heater. The toner and paper form a permanently printed page corresponding to the electrostatic image written on the rotating drum by the scanning laser beam. The present invention is
It is an improvement over conventional electronic printers by modulating the pulse width produced by the laser beam. The amount of toner adhering to the drum is proportional to the illuminance of the laser light (that is, the exposure amount per unit area) that scans the drum surface from one end to the other, so the duration of the laser beam on the pixel area on the drum is By controlling, a variable size toner spot is formed during printout. These controllable variable-sized toner spots result in shading or shading that is generally considered unattainable and unobtainable by conventional electronic printers that only use uniformly sized printed dots. Halftoning is possible. The present invention can be implemented in either laser printers or light emitting diode printers. Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the accompanying drawings.

[0007]

1 (a) is a schematic perspective view of a portion of a laser printer 10 known to those of ordinary skill in the electronic printing art which may be used to practice the present invention. The cylindrical photosensitive drum 11 is driven by a motor (not shown) and rotates in the direction indicated by arrow 12. The drum 11 is made of metal and is usually coated with a photoconductive organic material. During the printing process, the drum 11 is constantly rotating, sometimes several revolutions per print page. Before the image is applied to a given portion of the print, the drum's electrostatic surface 13 is treated to hold the desired electrostatic image by physically and electrostatically cleaning the drum. There must be. Physical cleaning is done by a rubber cleaning blade (not shown) that scrapes the particles left over from the previous cycle from the drum 11 into the residue sump. After that, the rotating drum 11 is electrostatically cleaned by an erasing lamp in a cleaning / erasing unit 14 provided above the surface thereof. These erasing lamps irradiate the photosensitive material (photoconductive material) of the drum 11 to neutralize the electric charges previously on the drum 11. The surface 13 of the electrostatic drum (rotary drum) 11 thus cleaned is then conditioned by applying a uniform negative charge. This negative charge is applied by the high voltage corona charge generator 16. The rotating tram 11 uses the photosensitive material as a corona charge generator 16
Through the ionization region formed by. In this ionization region,
Negative charges move from the corona charge generator 16 to the surface of the drum 11. The drum 11 rotating past the corona charge generator 16 is provided with a uniformly distributed potential of minus 600 volts on its surface 13. During writing, a laser beam 18 is used to focus the laser light on selected portions of the surface 13 of the photoconductive drum 11 to discharge the surface potential of the drum in those selected areas. The laser beam 18 is generated by a small solid-state semiconductor laser diode 19, and the rotating polygon mirror foil 2
0 scans the surface of the drum 13 end to end. An electrostatic pattern is formed on the surface 13 of the drum 11 by discharging the drum 11 with a laser beam (laser beam) 18, and this electrostatic pattern is subsequently formed on paper using electrostatic ink called toner 27. Transcribed.

The laser beam 18 is pulsed on and off by simply turning on and off the power supply alternately. The laser light 18 generated from the diode 19 becomes a parallel light beam having a clear cross-sectional contour by a collimator lens (not shown), and is incident on the polygonal scanning mirror 20 while being focused by a cylindrical lens (not shown). The scanning mirror 20 is
It has six faces and is rotated at a constant speed by a scanner motor (not shown). As the scanning mirror 20 rotates, the laser beam 18 sweeps the drum surface 11 from one end to the other in a direction indicated by an arrow 23. The swept laser beam 18 is focused on the drum surface 11 along a horizontal line. While the drum rotates, the laser beam 18 sweeps over substantially the entire length of the drum 11, and the entire surface 13 of the drum is exposed to the laser beam 18 according to the raster pattern. The speed of the scanner motor that rotates the scanning mirror 20 and the speed of the main motor that rotates the drum 11 are synchronized, and the beam is 1 / E for each successive sweep of the laser beam 18.
Move down the surface of the drum 11 by 300 inches.
The laser (diode) 19 is driven on and off at high speed in order to obtain a modulation pulse that irradiates a small light spot every 1/300 inch in the horizontal direction along the horizontal line on the drum.
This shutter effect, combined with the operation of the drum, is 300 dots vertically and 30 dots horizontally per square inch of the drum surface.
This produces a 0 dot picture element or pattern of pixels.

After the laser beam 18 scans the drum 11 from one end to the other, an invisible electrostatic latent image is formed on the drum surface (photosensitive surface) 13. Laser beam 1
The portion of the drum surface 13 not exposed to light 8 is at a potential of minus 600 volts as before, but the portion exposed to laser light is discharged to about 100 volts.
When each portion of the drum surface 13 passes inside the developing portion 24, a developer called toner 27 is sprinkled on the drum surface 13. The developing unit 24 converts the electrostatic latent image on the photoconductive drum 13 into a visible image.

The toner 27 is a powdery substance made of black plastic resin bonded to iron particles. Toner 27
The iron inside is attracted to a metal rotary charging cylinder having a permanent magnet (not shown) provided along the length direction. The plastic particles of toner 27 obtain a negative surface charge by rubbing against a charging cylinder connected to a negative DC bias power supply. When the toner 27 is sprinkled on the drum surface 13, due to this negative electrostatic charge, it is attracted to the region of the drum surface 13 exposed to the laser beam 18 and at the same time repelled from the region not exposed to the laser beam. To be done. Further, in order to further promote the action of the toner particles to overcome the attraction force of the magnet, and to draw the toner particles 27 back to the charging cylinder from the region of the drum surface 13 which has not been exposed or discharged by the laser beam 18, it is made of metal. A high voltage AC signal is applied to the charging cylinder. This AC signal changes the force and direction of the electric field between the charging cylinder and the drum 11 at high speed, and causes the charged toner particles 27 to generate a high-frequency vibration force.
This force ensures that the toner particles in the end discharge area of the drum surface 13 will have some degree of mobility and will have a momentum required to move little by little towards the larger discharged area on the drum surface 13. Can have

The transfer section 28A transfers the toner 27 image on the drum surface 13 onto the paper 26. The paper 26 contacts the drum surface and moves at the same speed. Paper 26 is arrow 2
Move in the direction indicated by 9. The transfer unit 28A transfers the developed visible image from the drum 13 to the paper 26. Paper 2
A positive charge is generated by a corona assembly (not shown) on the paper surface opposite to the side where 6 contacts the drum 13. The stronger positive charge on the paper 26 strips the negatively charged toner particles 27 from the surface of the drum 11. Alternatively,
A charging roller may be used instead of the corona assembly. The fixing units 28B and 28C including the roller and the heat source are
The toner 27 is melted and forced by heat and pressure into the paper 26 to form a permanently printed page.

FIG. 1 (b) illustrates a light emitting diode printhead 30 that is different from the previous embodiments that can be used in practicing the present invention. The light emitting diode printhead 30 is well known to those skilled in the electronic printing arts and includes a substrate 32 and a driver chip 3.
6 has an array of discrete light emitting diodes (LEDs) 34 coupled thereto. This print head 30 is shown in FIG.
It can be used in place of the laser diode 19 and the scanning mirror 20 of the printer 10 shown in FIG. These light emitting diodes are attached to the drum surface 1 as the drum 11 rotates.
It is arranged close to the drum 11 so as to irradiate a small portion of 3.

FIG. 2 (a) is a graph 38 showing the change in the surface potential of the photoconductor drum when the photoconductor drum 11 is illuminated by the powerful collimated beam of rays 18.
Indicate. FIG. 2B shows a curve 40 in which the change in print density is plotted against the change in brightness of the beam 18 incident on the photoconductive drum 11.

FIG. 3 (a, b and c) illustrates the general principle of standard dot matrix printing. Figure 3
In (a), a pattern 42 of ink dots on the paper is shown. Each dot 44 occupies one square section in a matrix called pixel 46. Figure 1
The laser printer shown in FIG.
When a line consisting of four consecutive dots as shown in FIG. 3 is drawn, the control signal causes the laser 19 to cause the drum 11 to produce an exposure pattern 50 such as the pattern shown in FIG. Scan it. Then, this exposure pattern 50 is also called a drum surface potential in FIG.
A drum voltage 52 as shown in (c) is applied, and this potential is finally transferred to a printing medium such as paper and fixed as a printed image. FIG. 4 illustrates the introduction of the concept of superpixels used in the present invention. 4 (a) and 4 (b), just as in the case of FIG.
And (c) show a pattern 54 of dots 56 in a pixel 58, an exposure pattern 60, and a drum voltage 62, respectively.
Indicates. The difference between FIG. 4 and FIG. 3 is that in FIG. 4, a boundary called “super pixel boundary” 64 formed by combining four pixels into one super pixel is added. The number of pixels 58 in superpixel 66 can be any number, but in this embodiment, a superpixel of 2 × 2 regular pixels is used.

FIG. 5 illustrates the modulation process used in the present invention. FIG. 5A shows a dot pattern 6 consisting of a large number of dots 70 of different sizes printed on each pixel 71 within the superpixel boundary 72.
8 is shown. Dots 44 of uniform size shown in FIGS.
, And 56, they are simply in or out of pixels 46 or 58. The role of each dot 44 or 56 of these single sizes is essentially that of binary printing. On the contrary,

The function of the dot 70 shown in FIG. 5 is completely different. Depending on the modulation drive signal that creates the modulation drum voltage 78,
Each dot 70 can be made smaller or larger than the dots of uniform size shown in FIGS. 3 and 4 and can be changed. The last dot line 74 in FIG.
It is formed by the exposure level 76 and the corresponding drum voltage 78 shown in FIGS.
A longer duration at exposure level 76, i.e. a larger pulse width, lowers drum voltage 78 by itself. The lower the drum voltage 78, the more toner 2
7 is attracted to the photosensitive drum 11, and a larger dot 70
Is formed.

FIG. 6 is a block diagram of the circuitry used in an embodiment of the electronic grayscale printing system of the present invention, generally indicated at 80. System 80 of this embodiment
Is a control logic unit 82, a page format memory 84,
It consists of multi-line buffer memories 86 and 88, a digital-to-analog (D / A) converter 90, a pulse width modulator 92, and a print engine control system 94. Also, FIG.
The laser diode 19 as shown in FIG. A grayscale document scanner 96 and a personal computer (PC) / imaging software 98 are connected as peripherals to the system 80. The page format memory 84 stores instructions for determining the print format. The control logic unit 82 transfers the data stored in the format memory 84 to the buffer memories 86 and 88. The data from memories 86 and 86 are pulse width modulator (PWM) 92
Are processed by the D / A converter 90 that drives the. PW
The M92 produces a drive signal 93 that is controlled by driving the laser 19 on and off to produce a series of pulses, which ultimately produces a modulated or variable size dot 70. The control logic 82 also governs the operation of the print engine control system 94, which in turn controls the drum 11
And operation of a motor that rotationally drives the scanning mirror 20 and D / A
It controls the operation of the modulator 90 and the PWM 92. Personal computer 98 and document scanner 95 can be used to provide an input image to printing system 80. The control logic unit 82 is a central processing unit (CP) capable of retrieving data from a read only memory (ROM) that stores a dot pattern called a font.
U). It is also possible to insert a ROM cartridge into a socket (not shown) provided on the outer surface of the laser printer to add another font. CPU is
It controls communication between the printer and external devices such as a personal computer 98.

[0018]

As is apparent from the above description, the improvement of the print quality according to the present invention, particularly the improvement of the gray scale print quality, is achieved by accurately controlling the size of the print dots. The size of the dot is determined by changing the width of the pulse generated by the laser beam. This makes it possible to create variable-sized spots, which facilitates shading and halftone generation. Therefore, if this technique is applied to a printer, extremely high quality printing becomes possible and a high performance printer can be provided.

[Brief description of drawings]

FIG. 1a is a schematic diagram of a typical laser printer.

FIG. 1b is a schematic diagram of a typical KED printer.

FIG. 2a is a characteristic diagram showing a change in surface potential of a photosensitive drum when the photosensitive drum is irradiated with a light beam.

FIG. 2b is a characteristic diagram showing the relationship between the density of light incident on the photosensitive drum and the print density.

FIG. 3a is a diagram showing print dots in a conventional printer.

FIG. 3b is a diagram showing an exposure state in a conventional printer.

FIG. 3c is a diagram showing drum potential in a conventional printer.

FIG. 4a is a diagram showing the concept of a super pixel according to the present invention.

FIG. 4b is a diagram showing the concept of a super pixel according to the present invention.

FIG. 4c is a diagram showing a concept of a super pixel according to the present invention.

FIG. 5a is a diagram showing the concept of a modulation technique according to the present invention.

FIG. 5b is a diagram showing the concept of the modulation technique according to the present invention.

FIG. 5c is a diagram showing the concept of the modulation technique according to the present invention.

FIG. 6 is a block diagram of a portion for performing electronic gray scale printing in the printer of the present invention.

[Explanation of symbols]

Reference numeral 10: laser printer, 11: drum, 13: drum surface, 14: cleaning / erasing unit, 16: high-voltage charging unit, 18:
Laser beam, 19: laser, 26: paper, 27: toner, 30: LED print head, 36: drive chip

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[Procedure amendment]

[Submission date] October 21, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

Figure 1a

Figure 1b

Figure 2a

Figure 2b

FIG. 3a

FIG. 3b

[Fig. 3c]

[Figure 4]

[Figure 5]

[Figure 6]

Claims (4)

[Claims] 1. A photosensitive unit for forming an electrostatic image on a surface, a light irradiation unit for irradiating the surface with a light beam to change the potential of the surface, and a developing unit for forming an electrostatic latent image on the surface. A transfer unit for supplying an ink medium to the print medium, a fixing unit for fixing the ink medium on the print medium, and a width of a series of pulse signals coupled to the light irradiating unit and applied to the light irradiating unit. A printer including means. 2. The printer according to claim 1, wherein the light irradiation unit includes a laser diode and a light scanning unit. 3. The printer according to claim 1, wherein the light emitting means has a print head including a plurality of light emitting diodes. 4. Generating a drive signal having a time interval corresponding to a desired print dot size; exposing a rotating photosensitive drum with a light beam having a time interval controlled by the drive signal; A gray scale printing method, comprising: supplying an electrostatic ink medium to the surface of the drum having a potential determined by, and transferring the ink medium from the drum to a print medium to generate gray scale.