JPS63296068A - Device for correcting reproduction of gradation - Google Patents

Abstract

PURPOSE:To constantly hold the reproducibility of the gradation of an image, against the variation of an electrified state of a toner attended with an environmental fluctuation, by varying a spot diameter of an image forming light on an image carrying body. CONSTITUTION:A photosensitive drum 1d is electrified, a light beam is radiated from a laser beam scanner 16d by a controller CTL 26, and the position 27 of the drum 1d is exposed. Subsequently, in the CTL 26, the bright potential of the drum 1d for realizing the target density is decided definitely, and the irradiating light quantity from the scanner 16d therefor is also determined. The CTL 26 selects one from in light passing ports 30a-30d whose sizes are different, respectively, provided on a rotary plate 30, and sets it as a passing port of parallel rays which have passed through a collimator lens 31. In such a way, a spot diameter of light is changed, and an ideal gradation property is reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a gradation reproduction correction device in an image forming apparatus that forms images using an electrophotographic method.

(Prior Art) Conventionally, in image forming apparatuses using the center-f photography method, various control methods as described below have been carried out in order to obtain images with appropriate density.

First, as a method for controlling the dark potential of an image carrier, a potential sensor detects the surface potential of the image carrier after being charged by a negative charger, and changes in the surface potential from a predetermined dark potential are examined. If the fluctuation exceeds the permissible value, adjust the discharge of the above-mentioned 12 electric appliance or immerse the grid in the humidity of the above-mentioned area, and reduce the voltage applied to the grid. By adjusting 1. A method has been used to adjust the surface potential of the image bearing member after it has been charged by the secondary charger, and to suppress the difference between the surface potential and a predetermined dark potential to within a certain range.

Also, as a method for controlling the bright potential of a 5Ijt carrier.

Serious crime - next (17 by (t? After being electrocuted?FI)
The surface potential of the image carrier exposed to light by the light source for the image forming area is detected by the potential sensor, the variation of the surface potential from a predetermined bright potential is checked, and if the variation exceeds a permissible limit; The method includes adjusting the surface potential of the image bearing member after light emission from "A" by adjusting the light emission 1j- of the light source, and suppressing the difference between the surface potential and a predetermined bright potential within the above-mentioned allowable range. has been carried out.

Next, as a toner concentration control method, the ratio of toner to carrier in the developing device is detected, the amount of variation in this ratio from a predetermined ratio is checked, and if the amount of variation exceeds a permissible value, the amount of variation in the ratio is determined. The difference between the actual ratio of toner and carrier in the developing device and the predetermined ratio can be tolerated by setting the amount of toner supplied to the developing device in section A. ) Methods have been used to suppress it within the limits.

However, by using the method for controlling the dark potential and bright potential of the image bearing member and the method for controlling the toner concentration described in L in combination, the surface potential of the latent image on the image bearing member and the ratio of toner to carrier in the developing device can be adjusted. Even if the toner is maintained in a proper state, there is a problem in that the densities of the finally formed =r-view images change due to environmental fluctuations because the charging state of the toner itself is dependent on the environment.

Therefore, as a control method to maintain the image density at an appropriate level even if the charged state of the toner changes depending on the environment, fluctuations in the image density due to environmental changes are absorbed by changing the set brightness potential, and the image density is adjusted accordingly. = A method has been proposed to hold it constant.

(Problem to be solved by the invention) However, in the conventional example, there is almost no environmental dependence of the image density on the bright potential from the dark potential level to the bright potential near the development bias level, and the image fR density is large for the bright potential near the maximum image density, so if you change the irradiation light so that the maximum image density is constant, the pulse width at which the image density starts to appear depending on the irradiation light In addition, in the range from the developing bias level to the bright potential at which the maximum image density can be obtained, the relationship between the image density and the bright potential is closer to a straight line in an environment where image density is more likely to occur, Environment F where concentration is difficult to occur
In the case of
Due to the non-linearity of the curve, a problem has arisen in that the gradation from blank paper to maximum image density changes.

(Means and effects for solving the problems) The present invention is as follows.
This was created in consideration of the actual situation, in which a latent image is formed by pulse modulating a light source in an image forming unit having an image carrier, and the visible image obtained by developing the latent image is transferred to a transfer material. an image forming apparatus configured to transfer and fix the image onto the image forming apparatus, and comprising a control means for controlling fluctuations in image aperture due to environmental changes by adjusting the brightness of the light source and changing the bright potential of the image carrier. In the apparatus, by changing the spot diameter of the light emitted from the light source and forming an image on the image carrier according to the combination of the bright potential and the image density, the toner is removed due to environmental changes. This is to ensure that the gradation of one image is maintained constant even when the charging state changes.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

1 to 3 show an image forming apparatus according to the present invention. First, the overall configuration will be explained using PfS3 diagram.
The image forming apparatus main body lO includes a plurality of image forming units Pa.
. The transfer material 6 whose transfer has been completed in each image forming unit Pa, Pb, Pc, and Pd is sent to the fixing device 7 from the left side of the conveyor belt 8.
is discharged from the main body lc.

First, second, third and fourth image forming units Pa, Pb
, Pc and Pd are photosensitive drums (image drum special) la
, lb, lc and ld.

h of each of the photosensitive tram la, lb, lc and ld
Charging paths 15a, 15b, 15c and 15d are provided on the left side of a.

Further, laser beam scanners 16a and 16b are installed in the F portions of &A optical drums la, lb, lc, and ld.

16c and 16d are provided, respectively. These laser beam scanners 16a, 16b.

16c and 16d are semiconductor lasers, polygon mirrors, f
Chargers J15a and 15b are composed of an O-lens, etc., and are laser beams that receive an input of an electrical digital image signal and are modulated in accordance with the signal.

The photosensitive trams 15c, 15d and the developing devices 3a, 3b, 3c, 3d are scanned in the generatrix direction of the photosensitive trams la, lb, lc, and ld to expose them.

Specifically, the laser beam scanner 16a of the first image forming unit Pa receives a pixel signal corresponding to the yellow component image of the color image, and the laser beam scanner 16b of the first image forming unit Pa receives a pixel signal corresponding to the magenta component image. The pixel signals are input manually, and the laser beam scanner 16c of the third image forming unit Pc and the laser beam scanner lad of the fourth image forming unit Pd receive pixel signals corresponding to the shear component image and pixel signals corresponding to the black component image. pixel signals are respectively input.

The paper feeding mechanism 13 includes a paper feeding guide 51 and a sensor 52. When the transfer material 6 is inserted into the paper feeding guide 51, the sensor 52 detects the tip of the transfer material 6, and the photosensitive tram la, lb
, lc, and ld, and at the same time drive the drive rollers 11, 12.96 to rotate the conveyor belt 8. Further, the transfer material 6 fed to the conveyor belt 8 receives corona discharge from the attraction charger 59 and is reliably attracted to the surface of the conveyor belt 8. In the example, charging for adsorption! The polarity of the high voltage 159°62 is set to be opposite, and the polarity of the charger 62 is set to be the transfer m-electron W4a, 4b, 4c.

It has the same polarity as 4d.

The leading edge of the transfer paper 6 is each sensor 60a, 60b.

61C, 60d1til! When the signal is disconnected, image formation is sequentially started on the rotating photosensitive trams la, lb, lc, and ld.

When the transfer material 6 passes through the fourth image forming unit Pd, the transfer material 6 enters the fixing device 7 from the conveyor belt 8, fixes the image thereon, and is then discharged from the discharge 1114.

FIG. 2 shows in detail the special rlk portion of the L image forming apparatus. In 1A, 20 is a potential sensor, I+!
Detects the surface potential of the optical drum. 21 is an electrometer,
When the potential sensor 20 is connected, it is also connected to the controller 26, and information on the surface position of the photosensitive tram LD is sent to the controller 26.22
is the test batch and is the visible image transferred onto the conveyor belt. Reference numeral 23 denotes a concentration sensor exposure section which irradiates light to detect the concentration of the test batch 22. The light emitted from the density sensor exposure fi 23 and passed through the conveyor belt 8 and the test batch 22 is transmitted to the density sensor light receiving section 24.
The light is received by 25 is a densitometer, which is connected to the C degree sensor exposure section 23 and the concentration sensor light receiving section 24, and is also connected to the controller 26;
The concentration information of the test batch 22 is sent to the controller 26. The controller 26 includes a laser beam scanner 1.
6d is connected so that the amount of irradiation light can be changed according to the potential information and the concentration information. 2
7 is a light irradiation position, and the laser beam scanner 16d
The light from is focused on this area. A reader 28 reads the IX draft and sends the image data of the draft to the controller 26 via a data transmission line 29.

FIG. 1 shows the laser beam scanner 16d in detail. In FIG. 8, numeral 30 indicates a plurality of light passages r130a and 30b, each having a different size.

A rotary plate with holes 30c and 30d, and a central axis 32
Rotation ii (structured in a Noh manner) around the center.

A collimator lens 31 makes the light emitted from the laser diode 33 more visible.

Incidentally, image density data for bright potentials as shown in the graph of FIG. 4 is previously input to the controller 26. The horizontal axis of the graph represents the bright potential, and the vertical axis represents the concentration.Curve 0 represents the characteristics in the environment where the concentration is the highest relative to the bright potential.Curve 1 represents the characteristics in the environment where the concentration is the lowest relative to the bright potential. It represents the characteristics in environment F. In other words, even if the charge state of the toner changes by 1 μm due to environmental changes and the density is affected, the density for each bright potential will never leave the region surrounded by curves a and b.TRD
vLL represents the target concentration, and the concentration TRD must be maintained accurately under any circumstances.
is the f-choki concentration TR under the environment where the characteristics of curve a can be obtained.
vLH is a bright potential that realizes the concentration TRD in an environment where the characteristics of the curve are obtained. In other words, the eye e! under each environment! The bright potential that realizes the concentration TRD is between vLL and vL.

Ru.

In addition, DL is ItI in an environment where the characteristics of a curved line can be obtained.
D1 is the concentration with respect to the bright potential VLL, and Dl is the concentration with respect to the bright potential VL11 in an environment where the characteristics of curve a can be obtained. After all, for the bright potential from vLL to V, , H, the concentration is between DL and Dll. Therefore, the concentration data for the bright potential only needs to have concentration data for the bright potential between at least the vLL and the vLH, where Vd is the dark potential.

Next 1. I: An image density control method using the apparatus described above will be explained. First, the photosensitive tram ld is charged, and then light is irradiated from the laser beam scanner lad according to a command from the controller 26, and the light irradiation position of the photosensitive tram ld is determined! ! 27 is exposed. Then, following the movement of the photosensitive drum ld in the direction of the arrow, the exposure section reaches below the potential sensor 20, and the potential is detected. This is the so-called bright potential, and its value is sent from the electrometer 21 to the controller 26.

In the controller 26, an attempt is first made to set the bright potential of the photosensitive drum ld to the vLL shown in FIG. Therefore, the detected bright potential and the VLL are compared, and if the difference is within the allowable range, a command is issued to the laser beam scanner 16d to adjust the irradiation output, and the bright potential of the photosensitive tram ld is adjusted. Bring it closer to 1. Then, when the difference between the bright potential detected in one scan and the vLL falls within the allowable range, development is performed and the formed NF image is transferred to the conveying belt 8. This is the test patch 22 mentioned above. Moreover, when the difference between the bright potential detected again and the above-mentioned VLL is greater than the tolerance value, the ilj degree is adjusted.Of course, when the bright potential is detected for the first time,
, if the difference is already within the scope of deception, there is no need to immediately develop the image.

Now, the transferred test batch pattern 22 is carried by the conveyor belt 8 and reaches the positions of the density sensor exposure section 23 and the density sensor light reception section 24, and its image density is detected. Its concentration is shown as DI in FIG. The detected concentration information is sent to the controller 2 via the meter 25.
6 and into the controller 26, the light potential vLL
The detected concentration is stored as data.

Next, the controller 26 changes the bright potential of the photosensitive tram ld to E.
Attempt to set the above VLH in the same manner as described above. That is, the detected bright potential and the above v, 4. Compare with
If necessary, adjust the amount of light irradiated by the laser beam scanner 16d, and when the difference between the bright potential and vLll falls within the allowable range, perform development, transfer the test batch 22 to the conveyor belt 8L, and adjust the density. The density is detected by the sensor exposure fi 23 and the density sensor light receiving section 24, and the density is shown as D2 in FIG. And controller 2
6, the bright potential vLll is stored as data in the form of detected concentration D2.

Next item, 1: Two sets of Day 9 (Vt, t,, D
I) By comparing and calculating (vLH4, Dz) with the two characteristic curves a and b in Fig. 4, the two points in No. 41A (VLL, D, ) and (V Lll, D 2
) The dotted line C in FIG. 4 is the result of categorizing the concentrations of IgI'iIt between 1 and 2.

Then, based on the data in the dotted line C, the [1 building part TRD]
Select the bright potential that achieves this and decide it as the bright potential in that environment F++! ! ! 'ci, the set bright potential is set as the bright potential at the point P where the dotted line C intersects the straight line extending along the horizontal axis passing through (0, TRD) in FIG. M.I.
The J1 potential is shown as VLCL/41'ill.

Next, the second controller 26 sets the IJJ potential of the photosensitive drum ld to VLc in the same manner as when setting the voltages to vLL and vLH. is formed and its concentration is detected. Then, it is checked whether the difference between the detected concentration and the target concentration TRD is within an allowable value, and if it is, the control path is set to r, and if it is not, the control path is set to r.

The amount of light irradiated from the laser beam scanner 16d is finely adjusted to keep the difference between the density of the test batch 22 and the target density TRD within an allowable value.

In this manner, the bright potential of the photosensitive tram ld to be realized by the IJ marking section TRD is determined, and the amount of light irradiated from the laser beam scanner 16d to realize the 111 potential is also determined. 30, each having a different size of light passing through Iff 30a,
One of 30 b, 30 c, and 30 d is selected and set as the passage port for the parallel light that has passed through the collimator lens 31. The selection is made so that ideal gradation is reproduced. The reproduction of ideal gradation will be explained with reference to FIG.

FIG. 5 shows image density data. It shows the relationship between image densities actually formed (actual image densities). 5th LA
The horizontal axis represents image density data, and MAX is an image density data value meaning the maximum image density. The vertical axis is the actual image*a
TRD is the maximum image density as described above.

The straight line β represents the ideal gradation reproducibility, and the curves α and γ represent the characteristics when only the maximum image density is controlled constant in each environment mode, and the single gradation reproducibility is not corrected.

Furthermore, as the spot diameter of the irradiated light on the photosensitive drum L is decreased, the gradation changes in the direction of γ→β→α, and on the contrary, as the spot diameter is increased, the gradation changes. changes in the direction of γ→β→α.
Then, the controller 26 includes the TRD.
Which light passes through the rotating plate 30 depending on the bright potential 1
1, the ideal gradation level 11 effect, that is, the state of β in FIG. -30d.

It should be noted that - of the wing light passing through the collimator lens 31
・Since some portions may be cut off by the light passing 11, the light 1. )
Adjust the voltage and return it to the light potential set for the serious crime, and end the crime.

As a result, even if the charging state of the toner changes due to environmental changes, not only the maximum image density but also the gradation can be reproduced in an ideal state.

In the serious crime embodiment, light passage ports of different sizes are used as means for changing the spot diameter of the light irradiated onto the photosensitive tram L, but light passage ports of different shapes may be used.

In addition, the spot diameter may be adjusted by changing the distance between the optical system that focuses light on the photosensitive drum and the photosensitive drum, or by using a plurality of parallel plane plates with different curvatures and different thicknesses from air. Alternatively, one of them may be prepared, and one of them may be selected and inserted between the optical system and the photosensitive drum.

(Effects of the Invention) As described above, according to the present invention, even if the charging state of the toner changes due to environmental changes, it is possible to always maintain a constant image density and ideal gradation.

[Brief explanation of the drawing]

Fig. 1 is an enlarged perspective view of the main parts of an embodiment of the present invention, Fig. 2 is a side view of the main parts of the image forming apparatus, Fig. 3 is a general configuration diagram of the same, and Fig. 41.4 is a bright potential and image density. FIG. 5 is a graph showing the relationship between image C-plane data and actual image density. Pa, Pb, Pc, Pd---image forming unit, la, lb, lc, 1d---photosensitive tram (image carrier), 3a, 3b, 3c, 3d-developing device,
6 - Transfer material, 16a, 16b, 16c, 16d - Laser beam scanner, 20... Potential center, 22
...Test patch, 23.24...Concentration sensor,
26... Controller, 30a, 30b, 30c. 30d... Light passing 11.33... Laser diode.

Claims (1)

[Claims] 1. A latent image is formed by pulse width modulating a light source in an image forming unit having an image carrier, and a visible image obtained by developing the latent image is transferred to a transfer material. , an image forming apparatus configured to fix the image, and comprising a control means for controlling fluctuations in image density due to environmental changes by adjusting the light amount of the light source and changing the bright potential of the image carrier; A gradation reproduction correction device characterized by changing a spot diameter of light emitted from the light source and formed on the image carrier, depending on a combination of bright potential and image density. 2. The gradation reproduction correction device according to claim 1, wherein the spot diameter is adjusted by changing the cross-sectional area or cross-sectional shape of the parallel light irradiated onto the image carrier. 3. The gradation reproduction correction device according to claim 1, wherein the spot diameter is adjusted by changing the distance between the image carrier and an optical system that focuses light onto the image carrier. 4. The spot diameter is adjusted by inserting a plane parallel plate having a different refractive index from air between the optical system that focuses light on the image carrier and the image carrier. The gradation reproduction correction device according to item 1.