JP2011178038A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly correct a density while suppressing an increase in expenses when a D/A converter is used. <P>SOLUTION: The image forming apparatus includes an image carrier comprised of a cylindrical member and configured to carry a toner image on the peripheral surface, a laser beam irradiation means for irradiating the image carrier with a laser beam to form an electrostatic image on the surface of the image carrier, a digital signal generation means for generating a digital signal indicating a correction point of the quantity of a laser beam with which the main scanning line of the image carrier is irradiated, a D/A converter for converting the digital signal into an analog signal and outputting the analog signal to the laser beam irradiation means, and a control means for controlling the D/A converter. The image forming apparatus forms a toner image by causing toner to adhere to the electrostatic latent image of the image carrier, wherein the control means shifts the timing of sampling to the D/A converter for each main scanning line. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus that forms an electrostatic latent image on a photosensitive drum by scanning with a laser beam, the density in the main scanning direction due to variations in sensitivity of the photosensitive drum in the main scanning direction and unevenness in the amount of laser beam main scanning by the optical system. Unevenness occurs. For example, the density unevenness can be reduced if the optical system or photosensitive drum is expensive. However, solving this problem with this method is expensive. Therefore, as a method for reducing the density unevenness while suppressing the cost, a method of electrically correcting the density in the main scanning direction is used.

  For example, as the technique, there has been proposed a technique for adjusting the amount of laser beam light by finely changing the pulse width of a laser beam control signal (pulse signal) for each image. As another method, a method for feedback correction of the amount of light (see Patent Document 1 below) has been proposed. In this method, a history of values of current supplied to the laser diode is stored for each image formation, and a current value supplied to the laser diode is determined for each image formation based on the history.

JP 2006-198894 A

  By the way, in the above prior art, the amount of light is adjusted by finely changing the pulse width of the laser beam control signal (pulse signal) for each image. However, since this method requires highly accurate PWM control, an increase in cost is inevitable. Further, since the necessary density correction is to be performed in units larger than one pixel, actually, so high-accuracy PWM control is not necessary. In the method of Patent Document 1, a D / A converter is used in the light quantity correction control circuit. However, when a high-resolution D / A converter cannot be used in terms of cost, smooth density correction becomes difficult because the resolution is low.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to enable smooth density correction while suppressing an increase in cost when a D / A converter is used.

  In order to achieve the above object, according to the present invention, as a first solving means relating to an image forming apparatus, an image carrier comprising a cylindrical member and carrying a toner image on the circumferential surface, and the image carrier. Laser beam irradiation means for forming an electrostatic latent image on the surface by irradiating the laser beam, and a digital signal for generating a digital signal indicating a correction point of the light amount of the laser beam irradiated to the main scanning line of the image carrier The image carrier includes: a generating unit; a D / A converter that converts the digital signal into an analog signal and outputs the analog signal to the laser beam irradiation unit; and a control unit that controls the D / A converter. An image forming apparatus for forming a toner image by adhering toner to an electrostatic latent image, wherein the control means sets the sampling timing for each main scanning line. To adopt a means of shifting to the converter.

  In the present invention, as the second solving means relating to the image forming apparatus, in the first solving means, the control means causes the D / A converter to repeat the sampling timing shift at a constant scanning cycle. Adopt the means.

  In the present invention, as the third solving means relating to the image forming apparatus, in the first or second solving means, the control means employs means for irregularly shifting the sampling timing shift.

  According to the present invention, the sampling timing when the light amount correction data is converted into the light amount correction analog signal is shifted for each main scanning line. Thereby, it is possible to make the density correction apparently inconspicuous. That is, in the present embodiment, when using a D / A converter, smooth density correction can be performed while suppressing an increase in cost.

FIG. 2 is a functional block diagram of a copying machine A according to an embodiment of the present invention; 1 is a perspective front view showing a schematic configuration of a copying machine A according to an embodiment of the present invention. It is a figure showing functional composition of optical scanning device 63 of copying machine A concerning an embodiment of the present invention. 6 is a graph showing a light quantity correction analog signal of the copying machine A according to the embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings.
First, the configuration of the copying machine A according to the present embodiment will be described.
As shown in FIG. 1, the copier A of the present embodiment includes a CPU (Central Processing Unit) 1, a ROM (Read Only Memory) 2, a RAM (Random Access Memory) 3, an image reading unit 4, and an image data storage unit 5. A sheet conveyance / image forming unit 6 and an operation display unit 7 are provided.

The CPU 1 copies the copying machine A based on the control program stored in the ROM 2, the original image data stored in the image data storage unit 5, the print image data, the facsimile image data, and the operation instruction input from the operation display unit 7. To control the overall operation. The details of the control processing of the CPU 1 will be described later as the operation of the copying machine A.
The ROM 2 is a non-volatile memory that stores a control program executed by the CPU 1 and other data.
The RAM 3 is a volatile memory used as a working area as a temporary storage destination of data when the CPU 1 executes a control program and performs various operations.

The image reading unit 4 includes an ADF (automatic document feeder) and a CCD (Charge Coupled Device) sensor, and causes the CCD sensor to read images of documents sequentially fed by the ADF under the control command of the CPU 1. Document image data based on the image is output to the CPU 1. On the other hand, the CPU 1 stores the document image data in the image data storage unit 5.
The image data storage unit 5 includes an external storage device such as a hard disk and / or a semiconductor memory such as a flash memory, and stores document image data read by the image reading unit 4 under the control of the CPU 1.

  The paper transport / image forming unit 6 transfers toner to the image forming paper transported from the paper tray based on the image data in the image data storage unit 5 under the control command of the CPU 1, and performs the toner fixing process. As shown in FIG. 2, a photosensitive drum (image carrier) 61, a charging device 62, a light scanning device 63, a developing device 64, a cleaning unit 65, a fixing device 66, and the like are formed. It is the composition provided with.

The photosensitive drum 61 is a cylindrical member on the surface of which an electrostatic latent image is formed. The photosensitive drum 61 extends in the depth direction of FIG. 2, and the toner adheres to the electrostatic latent image on the peripheral surface thereof, thereby removing the toner from the toner. An image is formed.
The charging device 62 is disposed so as to face the photosensitive drum 61, and the peripheral surface of the photosensitive drum 61 is charged.

The optical scanning device 63 is disposed at a position where scanning can be performed facing the peripheral surface of the photosensitive drum 61, and the surface of the photosensitive drum 61 is scanned electrostatically by the irradiated laser beam L. It forms a latent image.
As shown in FIG. 3, the optical scanning device 63 includes an optical housing 631, a light source 632, a rotating polyhedron 633, an fθ lens 634, a reflection mirror 635, a CPU 1, a D / A converter 636, a driver IC (Integrated Circuit) 637, and a BD mirror. 638 and a BD sensor 639. The CPU 1, the ROM 2, and the RAM 3 constitute a digital signal generation unit and a control unit in the present embodiment. Further, the light source 632 and the driver IC 637 constitute laser beam irradiation means in the present embodiment.

  The optical housing 631 houses the light source 632, the rotating polyhedron 633, the fθ lens 634, the reflecting mirror 635, the BD mirror 638, and the BD sensor 639, and the light source 632, the rotating polyhedron 633, and the fθ lens 634 therein. The reflection mirror 635, the BD mirror 638, and the BD sensor 639 are fixed.

The light source 632 emits a laser beam L under the control of the CPU 1, and emits the laser beam L in the horizontal direction toward the peripheral surface of the rotating polyhedron 633.
The rotating polyhedron 633 is a mirror having a polygonal shape in plan view and a peripheral surface as a reflecting surface. The rotating polyhedron 633 is driven to rotate about the vertical direction as a rotation axis by a rotation driving motor arranged under the control of the CPU 1. The The rotating polyhedron 633 rotates counterclockwise as indicated by the arrow in FIG.
The fθ lens 634 has a constant scanning speed in the scanning of the laser beam L reflected by the rotating polyhedron 633. That is, the fθ lens 634 acts optically so that the laser beam L is scanned at a constant speed on the peripheral surface of the photosensitive drum 61.
The reflection mirror 635 is a plate material having a rectangular reflection surface that reflects the laser beam L.

The CPU 1 controls the overall operation of the copying machine A as described above. That is, the CPU 1 controls the irradiation operation of the laser beam L of the light source 632 and the rotation operation of the rotating polyhedron 633. Then, the CPU 1 outputs a digital control signal to the D / A converter 636 when controlling the light source 632.
The D / A converter 636 converts the digital control signal input from the CPU 1 into an analog voltage signal and outputs the analog voltage signal to the driver IC 637.
The driver IC 637 converts the analog voltage signal input from the D / A converter 636 into a current signal and outputs the current signal to the light source 632. The light source 632 controls the light amount of the laser beam L based on the current signal.

The BD mirror 638 is a mirror that reflects the laser beam L reflected by the rotating polyhedron 633 toward the BD sensor 639. The rotating polyhedron 633 moves the reflection direction of the laser beam L emitted from the light source 632 in the main scanning direction, that is, moves it from the upper direction to the lower direction in FIG. The electrostatic latent image is formed. At that time, the rotating polyhedron 633 reflects the laser beam L toward the BD mirror 638 before reflecting the laser beam L to the image region on the main scanning line. The amount of laser beam L incident on the BD mirror 638 is higher than the laser beam L on the image area.
The BD sensor 639 outputs to the CPU 1 a BD pulse signal having a period corresponding to the rotational speed (laser scanning speed) of the rotating polyhedron 633 based on the laser beam L incident from the BD mirror 638.

The developing device 64 develops an image based on the electrostatic latent image on the peripheral surface of the photosensitive drum 61 by supplying toner to the peripheral surface of the photosensitive drum 61, and is provided for the photosensitive drum 61. .
The cleaning unit 65 includes a cleaning roller and a cleaning blade that remove toner remaining on the photosensitive drum 61 after the image is transferred from the photosensitive drum 61 to the image forming paper. Oppositely arranged so as to be contactable.
The fixing device 66 applies heat and pressure to fix the toner transferred from the photosensitive drum 61 to the image forming paper on the image forming paper, and is arranged in the conveyance path of the image forming paper.

  The operation display unit 7 includes a start key, a stop / clear key, a power key, a numeric keypad (numerical value input key), a touch panel, and other various operation keys, and outputs operation instructions for each key to the CPU 1. Under the control, various screens are displayed on the touch panel.

Next, the operation of the copying machine A according to the present embodiment having the above configuration will be described.
First, a user who wants to copy a document with the copying machine A sets the document on the ADF of the image reading unit 4. Then, the user causes the copier A to start copying by pressing a start key included in the operation display unit 7.

  Then, the CPU 1 causes the light source 632 to irradiate the laser beam L based on the image data stored in the image data storage unit 5. At that time, the CPU 1 outputs light amount correction data, which is a digital control signal, to the D / A converter 636. The light amount correction data is a digital control signal indicating a correction point of the light amount of the laser beam L irradiated to the main scanning line of the photosensitive drum 61. In the copying machine A, by correcting the light amount of the laser beam L in the main scanning line of the photosensitive drum 61, density unevenness caused by sensitivity variation in the main scanning direction of the photosensitive drum is corrected.

  When the light amount correction data is input, the D / A converter 636 converts the light amount correction data into a light amount correction analog signal that is an analog voltage signal, and outputs the light amount correction analog signal to the driver IC 637. The driver IC 637 converts the light amount correction analog signal into a current signal and outputs the current signal to the light source 632. The light source 632 controls the light amount of the laser beam L based on the current signal.

As a feature of the present embodiment, the CPU 1 shifts the sampling timing for converting the light amount correction data into the light amount correction analog signal by the D / A converter 636 for each main scanning line. The above operation will be specifically described with reference to FIG.
When the CPU 1 irradiates the first main scanning line of the photosensitive drum 61 with the laser beam L, the CPU 1 causes the D / A converter 636 to sample the light amount correction data and the first light amount correction analog signal ((a) in FIG. 4). Reference).

Then, when irradiating the second main scanning line of the photosensitive drum 61 with the laser beam L, the CPU 1 converts the light amount correction data into the D / A converter 636 at a timing shifted by 1 / 3T from the first light amount correction analog signal. To generate a second light quantity correction analog signal (see FIG. 4B).
When the CPU 1 irradiates the third main scanning line of the photosensitive drum 61 with the laser beam L, the CPU 1 converts the light amount correction data into the D / A converter 636 at a timing shifted by 2 / 3T from the first light amount correction analog signal. To generate a third light quantity correction analog signal (see FIG. 4C).

  Then, when irradiating the fourth main scanning line of the photosensitive drum 61 with the laser beam, the CPU 1 causes the D / A converter 636 to sample the light amount correction data at the same timing as the first main scanning line. That is, the CPU 1 causes the D / A converter to repeat the sampling timing shift with three as one cycle. By shifting the sampling timing in this manner, when the sampling rate of the D / A converter 636 is low, finer and smoother density correction is applied to the image than when sampling is always performed at the same timing. Visual effect is obtained.

  For example, even if there are 90 correction points in the light amount correction data for one main scanning line, when the D / A converter 636 can sample only 30 points for the light amount correction data, the D / A converter 636 is used. If sampling is always performed at the same timing, the density of the main scanning line always changes at the same 30 correction points, so that the correction roughness becomes conspicuous. However, if the sampling timing is shifted, the density changes at 30 different correction points for each main scanning line, so that a visual effect as if smooth density correction is applied to the image is obtained.

  As described above, in this embodiment, the CPU 1 shifts the sampling timing when the light amount correction data is converted into the light amount correction analog signal to the D / A converter for each main scanning line. Thereby, since the density changes at different correction points for each main scanning line, a visual effect can be obtained as if smooth density correction is performed on the image. Further, since it can be realized only by shifting the sampling timing of the D / A converter, it can be realized at a low cost.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above-described embodiment, the control unit causes the D / A converter to repeat the sampling timing shift with a constant scanning cycle with three main scanning lines as one cycle. It is not limited to.
For example, the sampling timing may be shifted irregularly.

A ... copier, 1 ... CPU (digital signal generation means, control means), 2 ... ROM (digital signal generation means, control means), 3 ... RAM (digital signal generation means, control means), 4 ... image reading section, DESCRIPTION OF SYMBOLS 5 ... Image data storage part, 6 ... Paper conveyance / image formation part, 7 ... Operation display part, 61 ... Photosensitive drum (image carrier), 62 ... Charging device, 63 ... Optical scanning device, 631 ... Optical housing, 632 ... Light source (laser beam irradiating means), 633... Rotating polyhedron, 634... Fθ lens, 635... Reflecting mirror, 636... D / A converter, 637 ... Driver IC (laser beam irradiating means), 638. 64 ... developing device, 65 ... cleaning unit, 66 ... fixing device

Claims (3)

An image carrier comprising a cylindrical member and carrying a toner image on the circumferential surface thereof; a laser beam irradiating means for forming an electrostatic latent image on the surface of the image carrier by irradiating the image carrier with a laser beam; A digital signal generating means for generating a digital signal indicating a correction point of the light amount of the laser beam irradiated to the main scanning line of the carrier; and the digital signal is converted into an analog signal, and the analog signal is applied to the laser beam irradiation means. An image forming apparatus comprising a D / A converter for outputting and a control means for controlling the D / A converter, and forming a toner image by attaching toner to an electrostatic latent image of the image carrier,
The image forming apparatus characterized in that the control means shifts the sampling timing to the D / A converter for each main scanning line.   The image forming apparatus according to claim 1, wherein the control unit causes the D / A converter to repeatedly shift a sampling timing at a constant scanning period. The image forming apparatus according to claim 1, wherein the control unit shifts a sampling timing shift irregularly.

Images