JPS6349779A - Image density correcting device - Google Patents

Abstract

PURPOSE:To uniform image density by correcting the exposure time of laser light based on a turn-on time data input corresponding to electrostatic charging irregularity characteristic and then correcting the exposure time of the laser light based on turn-on time data corresponding to sensitivity irregularity characteristics which are inputted thereafter. CONSTITUTION:When an input device 3 inputs turn-on time data regarding the light part potential characteristics of a photosensitive drum 17 to a correcting circuit 2d, the circuit 2d computes the laser exposure corrected time when a specific quantity of laser light is emitted. The exposure time of the laser light is corrected to raise the lowest light part potential to the highest light part potential. Then, the device 3 inputs turn-on time data 3b regarding the dark part potential characteristics of the drum 17 to the correcting circuit 2d, the circuit 2d computes the laser exposure time when a specific quantity of laser light is emitted. This operation is performed as to all picture elements in the generating line direction of the drum 17 to uniform the electrostatic charging potential of all picture elements in the generating line direction of the drum 17.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image recording device that forms an image by scanning a photoreceptor with a laser beam modulated according to an image signal.
In particular, the present invention relates to an apparatus that corrects uneven density of a formed image in accordance with uneven axial sensitivity of a photoreceptor.

[Conventional technology]

Conventionally, in this type of device, scanning is divided in the main and sub-scanning directions from a reader (original reading device) or computer, etc.
The read image signal is modulated into an on/off signal of a semiconductor laser, which is scanned at a constant speed through a mirror-finished rotating polygon mirror (polygon mirror) for each mj in the axial direction of a cylindrical rotating photoreceptor. A static latent image is formed on a photoreceptor rotating at a constant speed.Then, development, transfer, and fixation are performed by a known electrophotographic process on a recording medium to be transported.
For example, it is configured to be able to fix an image developed on recording paper.

The above-mentioned photoreceptors have conventionally had some sensitivity unevenness, and it is difficult to suppress the aforementioned sensitivity unevenness within 20 V in manufacturing, especially in amorphous silicon photoreceptors formed by plasma CVD, etc. In an electrophotographic device having a laser optical system, such as a laser beam printer, it is difficult to obtain a uniform potential due to the unevenness of the amount of incident light due to interference.

For this reason, in an image recording device that uses a halogen lamp or a fluorescent lamp as a light source, a single or multiple slit in the optical path from the light source to the surface of the photoreceptor is used to prevent uneven axial sensitivity of the photoreceptor. By setting the irradiation light amount to 31fffi, the latent image potential is made uniform and image unevenness is corrected.

[Problem that the invention seeks to solve]

However, in an image recording apparatus having a laser scanning optical system, the surface potential of the photoreceptor is controlled to be uniformly charged by a charger in preparation for one image formation, but is it possible to charge the surface potential of the photoreceptor uniformly in the direction of the generatrix of the photoreceptor? There was a problem in that j1 electric unevenness occurred, resulting in uneven image density. Further, even when exposed to laser light based on image data, sensitivity unevenness occurs in the direction of the generatrix of the photoreceptor, resulting in image density, and there is a problem in that similar density unevenness occurs. It is technically difficult to improve these density unevenness by adjusting the light amount by adjusting the exposure width, and at present there is a strong desire for improvement.

In addition, in the case of a laser scanning optical system, when exposing an original, it is possible to shorten the laser emission time by exposing the black background or character area of the original, rather than exposing the white background of the original or the ground area of the display. , Laser spot hemline.

Reversal development has been widely used because it is effective in preventing deterioration in latent image resolution due to fluctuations and the like. In this case, since the potential of the bright area corresponds to the black background area of the image, there is a problem in that the sensitivity unevenness of the photoreceptor not only causes unevenness in image density, but also deteriorates the image quality.

This invention was made to solve the above-mentioned problems, and it corrects the unit dot emission time of the laser beam based on the axial charging unevenness characteristics and sensitivity unevenness characteristics of the photoreceptor. By eliminating density unevenness in the axial direction,
An object of the present invention is to obtain an image density correction device that can obtain uniform image density.

[Means for solving problems]

The image density correcting device for a photoreceptor according to the present invention has an image density correction device according to the charging unevenness characteristics and the sensitivity unevenness characteristics in the generatrix direction of the photoreceptor.
An input means for inputting lighting time data of an image signal for each pixel, and correcting the exposure time of the laser beam based on the lighting time data inputted by the input means according to charging unevenness characteristics, and after completion of this correction, A correction means is provided for correcting the exposure time of the laser beam based on lighting time data corresponding to sensitivity unevenness characteristics inputted from the input means.

[Effect]

In this invention, when the lighting time data of the image signal for each pixel is input from the input means in accordance with the sensitivity unevenness characteristics and the charging unevenness characteristics in the generatrix direction of the photoreceptor, the correction means adjusts the lighting time according to the charging unevenness characteristics. The exposure time of the laser beam is corrected based on the time data, and after the correction is completed, the exposure time of the laser beam is corrected based on the lighting time data corresponding to the sensitivity unevenness characteristic inputted from the input means.

〔Example〕

FIG. 1 is a block diagram for explaining the configuration of a laser beam printer showing an embodiment of the present invention.] is a league section, which is composed of an image reading section 1a, an amplifier 1b, and an A/D converter 1c. , the image reading section 1a is composed of an image sensor such as a CCD. 2 is the printer section, PW
It is composed of an M converter 2a, a laser driver 2b, a laser unit 2C, a correction circuit 2d, etc. P.W.
The M converter 2d'' performs pulse width modulation on/off of the laser beam based on the image information sent from the A/D converter 1C.The laser unit 2c modulates the laser beam LBI based on the correction data 3d described later. The correction circuit 2d emits a laser beam LB2 based on the correction data 3b.The correction circuit 2d converts the PWM converter based on the correction data (lighting time data) 3a corresponding to the sensitivity unevenness characteristics of the photoreceptor inputted from the input device 3. 2
The pulse width of the modulation signal output from a is corrected by a predetermined amount.

The corrected laser exposure signal is output to the laser driver 2b which also serves as exposure means of the present invention. Further, the correction circuit 2d sends a laser exposure signal to the laser driver 2 to emit a predetermined amount of laser light based on correction data (lighting time data) 3b input from the input device 3 according to the charging unevenness characteristics.
Send to b. The input device 3 is a digitizer that inputs lighting time data of an image signal for each pixel according to sensitivity unevenness characteristics and charging unevenness characteristics in the generatrix direction of the photoreceptor recorded on paper such as a data sheet, or the lighting time data. It is composed of a magnetic card or ROM chip, etc., in which is written in advance.

FIG. 2 is a diagram for explaining the laser exposure operation of a laser beam printer showing an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

In this figure, ]1 is a DC controller, which has a BD synchronization signal generation circuit 11a and sends a video signal to a laser driver 2b. 12 is a scanner driver circuit, D
The scanner motor 13 is driven at a constant speed based on a drive signal sent from the C controller 11. 14
is a rotating polygon mirror, which is composed of, for example, 10 mirror surfaces, rotates in the direction of the arrow at a constant speed by the scanner motor 13, deflects the laser beam emitted from the laser unit 2c, and directs it to the imaging lens. 15. Scanning mirror 16
A photosensitive drum 17 made of, for example, an amorphous silicon photosensitive member is horizontally scanned with the laser beam deflected through the photosensitive drum 17 . A scanning mirror 18 guides the deflected laser beam to the fiber cable 191. The fiber cable 19 sends a deflected laser beam, that is, a beam detect signal (BD double signal) serving as an image writing start signal to the BD synchronization signal generation circuit 11a.

FIG. 3 is a characteristic diagram for explaining the correction data 3a, 3b input from the input means 3 shown in FIG. 2, where the vertical axis shows the surface potential (V) and the horizontal axis shows the axial direction of the photoreceptor. R(ff
lff1). Note that the dark area average potential is the surface potential of 4
This is the case of 00 (V).

In this figure, 21 is the bright area potential characteristic (sensitivity unevenness characteristic)
, point A indicates the highest potential in the bright area, and point B indicates the lowest potential in the bright area. VLI indicates the highest potential value in the bright area, and Vl,2 indicates the lowest potential value in the bright area. 22 indicates dark area potential characteristics (charging unevenness characteristics), point 0 indicates sampling potential, point D indicates the highest potential in the dark area, and point E indicates the lowest potential in the dark area. V.D.
+ indicates the highest potential value in the dark area, and VD2 indicates the lowest potential value in the dark area.

Next, referring to FIG. 3, the correction circuit 2d shown in FIG.
The operation will be explained.

First, the bright area potential characteristics 2 of the photosensitive drum 17 are input from the input device 3.
1 (see Figure 3) is input to the correction circuit 2d, the correction circuit 2d performs laser exposure correction to emit a predetermined amount of laser light based on equations (1) and (2) below. Calculate time TB and TC.

TE = (VLB - Vl2) 0 K 1
...... (1) TC= (VLC-
Vl2) Zero K 1 -...- (2) However, K1 is such that the amount of laser light when one pixel is fully lit is, for example, 4.0
If μJ/cm2, then = 64/400 = 0.1
6 (light emission unit/V).

Therefore, the potential unevenness (Vte-Vl2) at point B is 30 (
V), and the image signal emission time of this dot is 61
/64 (3D/3F (hexadecimal)), the lighting time after correction is 57 (61-10, 16*301=57
), and the light amount of 3.8 pJ/cm2 is: 3,6 p,
Corrected to J 7cm2. As a result, the surface potential at point B increases to the surface potential at point A. In addition, by performing the same process for the 0 point, the surface potential is similarly changed to A.
The surface potential of the photosensitive drum 1 can be raised to
The surface potential of all pixels in the direction of the bus line of No. 7, that is, the bright area potential can be made uniform.

Next, uniformization of the dark potential will be explained.

FIG. 4 is a diagram for explaining the E-■4 characteristics of the photosensitive drum 17 shown in FIG. Exposure amount (p-J
7cm2).

In this figure, 31 indicates the EV characteristic, K2 is the slope of the EV characteristic 31 (ΔE/Δv (where ΔE indicates the light quantity variation, and ΔV indicates the surface potential difference)) However, it is known that, for example, in the case of an amorphous silicon photoreceptor, the EV characteristic 31 becomes a straight line, that is, a linear function.
E of amorphous silicon photoconductor compared to OPC photoconductor
Since the -V characteristic 31 has the best linearity, sensitivity correction control becomes simple. In addition, in this embodiment, the photosensitive drum 17 is made of an amorphous silicon photosensitive material because it has excellent strength and durability. First, when the lighting time data 3b regarding the dark area potential characteristic 22 (see FIG. 3) of the photosensitive drum 17 is inputted from the input device 3 to the correction circuit 2d, the correction circuit 2d calculates the following equations (3) and (4). Laser exposure time TD, T for emitting a predetermined amount of laser light based on
Calculate F.

TD=(Vo −VE)0 to 2・・・・・・(
3) TF = (VF - VE) zero K 2
= (4) The calculated laser exposure times TD and TF are sent from the correction circuit 2d to the laser driver 2b, and the laser unit 2C exposes the laser beam LB2 before the image writing start position based on the laser exposure times TD and TF. drum 1
7, the charged potential at points D and F of the photosensitive drum 17 can be set to, for example, an average dark area potential of 400 (V). By performing this operation on all pixels in the generatrix direction of the photosensitive drum 17, the charged potentials of all the pixels in the generatrix direction of the photosensitive drum 17 can be made uniform.

Incidentally, in the above embodiment, a case has been described in which the photoreceptor 7 is exposed using a single rotary multi-facet 14 in a single-chip device.
Since the focus precision of the laser beam LB2 for correcting the dark potential is not required as compared to the focus precision of I, the laser beam LB2 may be swung from another polygon mirror. Further, the number of laser elements may be increased as appropriate.

Furthermore, since the amount of exposure of the laser beam LB2 for correcting the dark area potential only needs to be small, it is preferable to attenuate the light with an ND filter or to shift the wavelength of the laser beam LB2 from the peak sensitivity wavelength of the photosensitive drum 17.

In addition, when the photosensitive drum 17 is made of an amorphous silicon photoreceptor, the peak sensitivity is 680 to 700 nm, so the wavelength of a normal semiconductor laser is 778 to 788 nm.
If a semiconductor laser is used, the semiconductor laser will oscillate in a sensitivity range that is considerably lower than its peak sensitivity. Therefore, by using a semiconductor laser having a wavelength near Boonffi, the sensitivity is about half that of a normal semiconductor laser, and control is possible without drastically lowering the laser power. However, what happens when the wavelength exceeds 820r+m? 12 Since it mainly affects, use 800.
It is desirable to keep it within a range of nm or more and 820r+m or less.

〔Effect of the invention〕

As described above, the present invention includes an input means for inputting lighting time data of an image signal for each pixel in accordance with charging unevenness characteristics and sensitivity unevenness characteristics in the generatrix direction of a photoconductor, and charging data inputted by this input means. The exposure time of the laser beam is corrected based on the lighting time data corresponding to the unevenness characteristics, and after this correction is completed, the exposure time of the laser beam is corrected based on the lighting time data corresponding to the sensitivity unevenness characteristics inputted from the input means. Since a correction means for correction is provided, the photoreceptor can be charged uniformly in the generatrix direction, and sensitivity unevenness of the photoreceptor drum can be accurately corrected not only in the bright area potential but also in the intermediate tones, and image density can be made uniform. Has excellent advantages.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining the configuration of a laser beam printer according to an embodiment of the present invention [A], and FIG. 2 is a block diagram for explaining the laser exposure operation of a laser beam printer according to an embodiment of the present invention. 3 are characteristic diagrams for explaining the correction data inputted from the input means shown in FIG. 2, and FIG. 4 is a diagram for explaining the EV characteristics of the photoreceptor according to the present invention. In the figure, 1 is a league part, 2 is a printer part, 2d is a correction circuit, and 3 is an input device. Figure 1 Figure 2 Figure 3 Figure 4 - Exposure amount

Claims (3)

[Claims] (1) In an image recording device that forms an image by scanning a photoreceptor with a laser beam modulated according to an image signal, each pixel is determined in units of one pixel according to charging unevenness characteristics and sensitivity unevenness characteristics in the generatrix direction of the photoreceptor. an input means for inputting lighting time data of the image signal of the image signal; and correcting the exposure time of the laser beam based on the lighting time data inputted by the input means according to the charging unevenness characteristics; An image density correction apparatus comprising: a correction means for correcting the exposure time of the laser beam based on lighting time data corresponding to the sensitivity unevenness characteristic inputted from an input means. (2) The exposure means directs the laser beam to the generatrix of the photoreceptor based on the lighting time data corrected by the correction means in accordance with the charging unevenness characteristics inputted by the input means immediately before the image writing position in the rotational direction of the photoreceptor. An image density correction device according to claim 1, wherein the image density correction device performs exposure in a direction. (3) The image density correction device according to claim (1), wherein the photoreceptor is an amorphous silicon photoreceptor.