JP3407399B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic digital copying machine and a laser beam printer, and more particularly to an image forming apparatus capable of correcting density unevenness of an image.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus such as an electrophotographic digital copying machine or a laser beam printer, for example, a semiconductor laser is used to scan and expose a laser beam on a photosensitive drum in accordance with input image data. Then
There is a configuration in which an electrostatic latent image corresponding to image data is formed on a photosensitive drum and the electrostatic latent image is developed to form a black and white or color image.

By the way, in such digital copying machines and laser beam printers, there is an increasing demand for higher image quality, and as one of them, halftone (halftone) gradation reproducibility is required. . In order to reproduce the halftone gradation in the digital copying machine or the like, the semiconductor laser is not simply turned on and off, but the emission time of the semiconductor laser is changed according to the gradation data. 2. Description of the Related Art An image data conversion device is used that converts gradation data into an analog signal and generates a pulse width modulation signal having a pulse width according to the gradation data.

As this image data conversion device, there is, for example, a device configured as shown in FIG.

In FIG. 16, reference numeral 100 denotes 8-bit 400-line gradation data input from an image reading device, a computer or the like via an I / F circuit (not shown), and 101 denotes 8-bit quantization of the gradation data 100. A D / A converter having a function of decomposing into an analog signal (256 gradations), a gradation data clock 103 of 400 lines is set to 1
A 1/2 frequency divider that divides the frequency by 1/2, and a triangular waveform generator 104 that generates a triangular waveform that is synchronized with the 200-line gradation data clock 105 that is frequency-divided by 1/2 by the 1/2 frequency divider. A low-pass filter 106 removes a high-frequency line segment from the 8-bit quantized data 107 output from the D / A converter 101, and a 8-bit quantization 108 removes the high-frequency line segment from the low-pass filter 106. A comparator for comparing the data 109 with the triangular wave signal 110 output from the triangular waveform generator 104, and 111 is a pulse width modulation signal output from the comparator 108 to a laser driving circuit (not shown).

In the image data conversion device, gradation data 100 having gradation information for each pixel to be printed is input from an image reading device, a host computer or the like (not shown) through an I / F circuit (not shown). Then, the input gradation data 100 is D / A converted by the D / A converter 101 having a quantization resolution of 8 bits based on the 400-line gradation data clock 103 and converted into the analog signal. The key data 107 is sent to the comparator 108 via the low-pass filter 106. In addition, the triangular waveform generator 104 uses the 400-line gradation data clock 10
5 is divided into 1/2 by the 1/2 divider 102.
A 200-line triangular wave signal 110 is generated in synchronization with the 0-line gradation data clock 105, and this triangular wave signal 110 is also sent to the comparator 108. The comparator 108 compares the triangular wave signal 110 with the gradation data 109 that has been converted into an analog signal and from which high frequency components have been removed, and the gradation data 109 is compared.
A pulse width modulation signal 111 having a length proportional to the gradation information is output, and this output is sent to the laser driving circuit (not shown) as the pulse width modulation signal 111.

By the way, in a digital copying machine or the like in which the image data converting apparatus having the above-mentioned structure is used,
The image data conversion device converts the image data according to the gradation information, and the semiconductor laser is modulated using the image data converted according to the gradation information. Then, a laser beam emitted from the semiconductor laser is used to scan and expose a laser beam on the photoconductor drum according to the input image data to form an electrostatic latent image on the photoconductor drum according to the image data. By developing this electrostatic latent image with a developing device, a black and white or color image is formed.

At this time, the surface of the photosensitive drum is uniformly charged by the charger, and then the laser beam is scanned and exposed according to the image data to form an electrostatic latent image as described above. . The electrostatic latent image formed on the photosensitive drum is developed by a developing device arranged so as to face the surface of the photosensitive drum. In this developing device, a developing roll, which is driven to rotate with a developer carried on the surface thereof, is arranged in proximity to the surface of the photoconductor drum with a predetermined gap, and a predetermined developing bias is applied to the developing roll. To develop the electrostatic latent image formed on the photosensitive drum.

[0009]

However, the above-mentioned prior art has the following problems. That is, in the image forming apparatus such as the electrophotographic digital copying machine, due to variations in manufacturing and assembling, image forming means such as a developing device, a main charging device, and a transfer charging device used for image formation and a photosensitive member are used. The gap with the body drum may be different on the front side and the back side of the apparatus, and there is a problem that the density of the obtained copy becomes uneven. For example, the center axis of the photoconductor drum and the developing roll of the developing device may not be parallel to each other, and the gap between the photoconductor drum and the developing roll may be different on the front side and the back side of the apparatus. In this way, if there is a variation in the gap between the photoconductor drum and the developing roll between the front side and the back side of the apparatus, a laser beam of constant intensity is scanned and exposed on the photoconductor drum to form an electrostatic latent image. However, there is a problem that the development density of the electrostatic latent image is not constant between the front side and the back side of the apparatus and a density gradient occurs. Particularly, in the color image forming apparatus, since color images are formed by superposing color toner images of three to four colors, unevenness in density of each color toner image is finally caused to cause color unevenness when superposed. Therefore, there is a problem that the image quality is remarkably deteriorated. At that time, in order to obtain the uniformity in which the color difference is not noticeable in the color image from the low density portion to the medium density portion (density 0.4), the density difference in the single color before being combined (output of the single color The concentration is about 0.
As 2), it is considered that it should be within 0.04.

Particularly, in adjusting the distance from the center of the drive shaft of the photosensitive drum to the surface of the developing roller, the gap between the surface of the photosensitive drum and the developing roller has a great influence on the developing characteristics. It is important for uniform image quality as well as management of various rotation fluctuations.

However, strict adjustment of the distance from the center of the drive shaft of the photosensitive drum to the surface of the developing roll requires a large amount of adjustment work time. Therefore, the range of variation is substantially ± 50 μm. Since the adjustment error occurs, a density difference of about 0.05 occurs, and if variations due to other factors such as the main charger, laser light amount, and transfer efficiency are included, the uniformity of the image will be improved. Since then, it was not at a satisfactory level. Further, the above-mentioned adjustment work requires a jig made with a particularly high precision, and it is practically impossible to perform the readjustment on the spot when the developing device fails. In the above description, the two-component developing system is taken as an example. However, when the non-magnetic one-component developing system is adopted, the developing characteristics are more outstanding than in the two-component developing system, so that the density is higher. There was a problem that there was a difference.

By the way, as a method of setting the gap between the surface of the photoconductor drum and the surface of the developing roll to a constant value with high accuracy, there is a system of using a tracking roll contacting the surface of the photoconductor drum. However, due to dirt on the tracking roll, the gap between the surface of the photoconductor drum and the surface of the developing roll may change, or a band-like density difference due to uneven rotation of the photoconductor drum, that is, banding may easily occur. In the case of a color image forming apparatus aiming for high efficiency, there is a surface that is difficult to put into practical use.

As a known density correction method, the output density of the copy can be adjusted by adjusting the gap between the corotron wire, grid, shield, etc. of the main charger and the photosensitive drum, or by adjusting the distribution of the exposure light amount. Is known, but when forming a color image by superposing toner images of a plurality of colors on one photoconductor drum using a developing device of three to four colors, the above-mentioned method is used. It was difficult to correct the density every time.

Further, in the image forming apparatus such as the digital copying machine, as a technique applicable to prevent the occurrence of a density gradient without the image density being constant on the front side and the back side of the apparatus, For example, JP-A-62-23597
There is one disclosed in Japanese Patent Laid-Open No. 2. This Japanese Patent Laid-Open No. 62-2
An image recording apparatus according to Japanese Patent No. 35972 is an electrophotographic image recording apparatus which records an image by scanning a laser beam modulated by an image signal on a photoconductor, and corresponds to a sensitivity characteristic deviation distribution of the photoconductor. A storage means for storing data, and a means for controlling and correcting the exposure time by the laser beam based on the image signal according to the data stored in the storage means in synchronization with the scanning position of the photoconductor It was done.

The technique disclosed in Japanese Patent Laid-Open No. 62-235972 will be described more specifically. As shown in FIG. 17, after converting the image data 120 into an analog signal by a D / A converter 121, the image data 120 is converted into an analog signal. The in-out adjustment circuit 1 is added to the image data 122 converted into the analog signal.
The sawtooth wave 124 generated by 23 is added by the adder 125. The sawtooth wave 124 generated by the in-out adjustment circuit 123 is ROS (Raster O
SOS detected from the output scanner)
(Start Of Scan) signal 126 or lin
Based on the e sync signal, a predetermined gradient is set so as to correct the concentration gradient. Then, the sawtooth wave 1 is added to the image data 122 converted into the analog signal.
The signal 127 obtained by adding 24 is compared with the triangular wave signal 129 output from the triangular wave generation circuit 128 by the comparator 130, and the density gradient corrected image signal 13
1 to generate an image signal 13 in which the density gradient is corrected.
1 is output to a laser driving circuit (not shown).

Further, in the image forming apparatus such as the laser beam printer, as shown in FIG. 18, the image forming density D _out is changed based on the gradation information C _in (for example, 256 gradations) of the input image data. By doing so, gradation reproduction of the image is performed. At that time, in reproducing the gradation of this image, the image on the low density side of about 0 to 8% is invisible to the human eye. It is necessary to perform image density adjustment on the low density side, which is so-called legible correction, that is, whether to make the state visible from the information C _in . Therefore, in the image forming apparatus such as the laser beam printer, as shown in FIGS. 19 and 20, the triangular wave 129 generated by the triangular wave generation circuit 128 is superimposed with the voltage 133 of the DC component generated by the resilient adjustment circuit 132. As a result, the resilience correction, which is the image density adjustment on the low density side, is performed.

Therefore, the above-mentioned JP-A-62-235972 is used.
In an image forming apparatus such as a laser beam printer to which the technique disclosed in the publication is applied, the image density is converted into an analog signal in order to correct a density gradient that is not constant between the front side and the back side of the apparatus. When the in-out density correction is performed by adding a sawtooth wave to the image data, the density gradient is corrected and the image density can be made constant on the front side and the back side of the apparatus, but the reproduced image density is As the value shifts to the high concentration side or the low concentration side,
Every time the out density correction is performed, the so-called legible correction for adjusting the visible density on the low density side must be redone, and the density adjustment operation of the apparatus becomes complicated.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art. The first object of the present invention is to easily adjust the unevenness of the density of a color toner image. An object is to provide a possible image forming apparatus.

A second object of the present invention is that even when an in-out density correction is performed to correct a density gradient in which the image density is not constant on the front side and the back side of the apparatus, each time the correction is performed. Another object of the present invention is to provide an image forming apparatus capable of easily performing the density adjusting operation of the apparatus without having to redone so-called legible correction again.

[0020]

The above-mentioned technical problems are as follows.
In the image forming apparatus according to the first aspect of the present invention, the exposure unit irradiates the photosensitive member with the scanning light modulated by the image signal to form an electrostatic latent image, and the electrostatic latent image is developed. In an image forming apparatus for forming an image, a storage unit for storing characteristic information according to an image forming characteristic of the exposure unit in the scanning direction, and a simple exposure light amount in the scanning direction of the exposure unit based on the storage information of the storage unit It is configured to include a correction signal generation unit that forms a signal that increases or simply decreases, and an image signal correction unit that superimposes the signal output from the correction signal generation unit and the image signal to output.

The image forming apparatus according to claim 1 of the present invention is, in addition to the above configuration, an adjusting means for outputting an adjusting signal for adjusting the reproduction start density of the image signal, and a scanning by the exposing means. Sampling means for sampling the correction signal by the correction signal generating means after a predetermined time from the start point, and adjustment signal correcting means for correcting the output of the adjusting means using the correction signal sampled by the sampling means are provided. It is configured.
Further, in the image forming apparatus according to claim 2 of the present invention, in the image forming apparatus according to claim 1,
A parameter changing unit for changing the ratio of the simple increase or the simple decrease by the correction signal generating unit during one scan in the main scanning direction by the exposure unit based on the storage information of the storage unit is configured. .

[0022]

In the image forming apparatus according to the first aspect of the present invention, the characteristic information corresponding to the image forming characteristic of the exposure means in the scanning direction is stored in the storage means in advance, and the storage information stored in the storage means is stored. A signal for simply increasing or simply decreasing the exposure light amount in the scanning direction of the exposure means is formed by the correction signal generating means based on the information, and the signal output from the correction signal generating means and the image signal are superimposed to correct the image signal. Means for irradiating the photosensitive member with scanning light modulated by the signal output from the image signal correcting means to form an electrostatic latent image, and developing the electrostatic latent image to form an image. This makes it possible to easily adjust the unevenness of the density of the color toner image.

Further, in the image forming apparatus according to the first aspect of the present invention, the adjustment signal for adjusting the reproduction start density of the image signal is output by the adjustment means, and the correction is performed after a predetermined time from the scanning start time by the exposure means. The correction signal by the signal generating means is sampled by the sampling means,
The output of the adjusting unit is corrected by the adjusting signal correcting unit using the correction signal sampled by the sampling unit, thereby correcting the density gradient in which the image density is not constant on the front side and the back side of the apparatus. out
Even when the density is corrected, the so-called resilient (l
The density adjustment operation of the apparatus can be easily performed without the need to redo the (egible) correction again.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows an electrophotographic digital color image forming apparatus as an embodiment of the image forming apparatus according to the present invention.

The digital color image forming apparatus 1 includes an image reading device 4 for reading an original document (not shown) placed on the platen glass 2 on its upper portion as an RGB analog image signal by a scanner 3 having an image sensor or the like. I have it. The RGB analog image signal read by the image reading device 4 is converted into a KYMC image signal by the image processing device 5 and temporarily stored in a memory provided inside the image processing device 5. Then, the image processing device 5 sequentially outputs image data of each color of cyan (C), magenta (M), yellow (Y), and black (K) at a predetermined timing.

Further, the above digital color image forming apparatus 1
Is a color image forming apparatus main body 6 under the image processing apparatus 5.
The color image forming apparatus main body 6 is equipped with
The photoconductor drum 7 is arranged so as to be rotationally driven at a predetermined speed in the arrow direction. In the main body 6 of the color image forming apparatus, the surface of the photoconductor drum 7 is uniformly charged to a predetermined potential by the charger 8 and then the photoconductor drum 7 is charged.
On the surface of the image processing device 5, cyan (C) is generated by the exposure device 9 based on the image data of cyan (C), magenta (M), yellow (Y), and black (K) output from the image processing device 5. , Magenta (M), yellow (Y), black (K)
The images of the respective colors are sequentially exposed to form an electrostatic latent image.
At that time, the surface potential of the photosensitive drum 7 is detected by the surface electrometer 10 at a predetermined timing, and the surface potential of the photosensitive drum 7 is controlled to a predetermined potential. The electrostatic latent image formed on the photoconductor drum 7 corresponds to the cyan (C), magenta (M), yellow (Y), and black (K) developing devices 11C, 11M, 11Y, 1
It is developed by 1K and becomes a toner image. The density of the toner image formed on the photosensitive drum 7 is appropriately detected by the density sensor 12.
According to the detection result of 2, the developing devices 11C, 11M, 11Y,
The supply of toner into 11K is controlled, and the image density is controlled.

The toner image formed on the photosensitive drum 7 is sequentially transferred to the transfer paper P held on the transfer drum 13 by the charging of the transfer corotron 14, and the photosensitive drum 7 and the transfer drum 13 rotate four times. By,
On the transfer sheet P held on the transfer drum 13, four color toner images of cyan (C), magenta (M), yellow (Y), and black (K) are transferred in a multiple manner. The transfer paper P on which the toner image is transferred is supplied from the paper feed tray 15 and electrostatically adsorbed and held on the surface of the transfer drum 13 by the charging of the adsorption corotron 16.

The transfer paper P on which the toner images of four colors have been transferred from the photosensitive drum 7 is separated from the transfer drum 13 by being charged by the separating corotron 17, and is heated by the fixing device 18 by heat and pressure. After undergoing the fixing process, it is discharged to the outside of the apparatus and a color image is formed.

After the multi-transfer process of the four-color toner images is completed, the surface of the photosensitive drum 9 is cleaned by the cleaning device 19a to remove residual toner and the like, and is discharged by the discharging device 19b to remove the charge. In preparation for the next color image forming step.

By the way, in this embodiment, the storage means for storing the characteristic information according to the image forming characteristics in the scanning direction of the exposure means, and the exposure light amount in the scanning direction of the exposure means based on the storage information of the storage means. It is configured to include a correction signal generating means for forming a signal for simply increasing or simply decreasing, and an image signal correcting means for superimposing and outputting the signal output from the correction signal generating means and the image signal. .

FIG. 1 is a block diagram showing an image density control section of the laser beam printer constructed as described above.

In FIG. 1, reference numeral 40 is gradation data having a resolution of 400 lines / inch of 8 bits, which is inputted from an image reading device or a computer through an I / F circuit (not shown), and 41 is the gradation data 40. To a 8-bit quantized analog signal (256 gradations), a D / A converter, 42 is a storage circuit for storing characteristic information according to image forming characteristics of the exposure apparatus 11 in the scanning direction, 43 Is a signal which, in synchronization with the SOS signal (scan start signal) 44 output from the exposure device 11, forms a signal that simply increases or decreases the exposure light amount in the scanning direction of the exposure device 11 based on the stored information in the storage circuit 42. The correction signal generator 45 performs a simple increase of the 8-bit quantized analog signal (256 gradations) 46 output from the correction signal generator 43. Is an analog adder that superimposes a signal 47 for simple reduction, 48 is a 1/2 frequency divider that divides a 400-line gradation data clock 49 into 1/2 200-line gradation data clock 50, and 51 is this 200 line A triangular wave generating circuit for generating a triangular wave signal 52 of 200 lines based on the gradation data clock 50, 53 is an 8-bit quantized analog signal (25 which is output from the analog adder 45).
6 gradations) signal 4 that simply increases or decreases 46
7 is a low-pass filter for removing high frequencies of the signal 54, 54 is a signal 54 in which a signal 47 for simply increasing or decreasing is superimposed on the analog signal (256 gradations) 46 from which high frequencies are removed by the low-pass filter 53.
And a triangular wave signal 52 output from the triangular waveform generator 51, and outputs a pulse width modulation signal 55 having a pulse width according to the gradation data 40.

FIG. 3 is a block diagram showing a charge pump type correction signal generator as the correction signal generator.

In FIG. 3, the counter circuit 61 resets the counter each time the SOS (scan start signal) 44 is input from the exposure device 11, and at the same time, validates the image area signal IMA as shown in FIG. When the counting of the 400-line gradation data clock 49 is started and the total number of pixels in the main scanning image area is counted, the IMA is disabled.

As the charge pump D / A converter 62 of FIG. 3, for example, a complement current output type is used. The charge pump D / A converter 62 outputs I _OUT and I _OUT ^* as shown in FIG. 6 according to an input 8-bit charge parameter. One of the outputs I _OUT ^* of the charge pump D / A converter 62 drives the current mirror circuit 63 to generate a current I _C. This current I _C follows the following equation (1). I _C = I _OUT ^* R1 / R2 (1) Now, if R1 = R2 is set, I _C = I _OUT ^* .

Further, the potential V of the charging capacitor 64
_C is 0V because the analog switch 65 is connected to the ground potential 0V while IMA, which is the output of the counter circuit 61, is invalid. On the other hand, when IMA, which is the output of the counter circuit 61, becomes valid, V _C changes according to the equation (2). V _C = ∫ (I _OUT ^* −I _OUT ) · dt = (I _OUT ^* −I _OUT ) · t (2) where the integral is taken from 0 to t.

This relationship is shown in FIG. In this way
A sawtooth-shaped potential waveform is created as the output potential V _C of the charging capacitor 64, and is input as a correction signal 47 to the analog adder 45 through the buffer amplifier 66.

At this time, the maximum correction potential V _CMAX is (I _OUT ^*
-I _OUT ) · T. The magnitude of this correction is (I _OUT
^* -I _OUT ) proportional to D / A for charge pump
It can be changed by the input data of the converter 62.

With the above construction, the digital copying machine according to this embodiment can easily adjust the unevenness of the density of the color toner image as follows.

That is, in the image density control section of this digital copying machine, as shown in FIG. 1, 8-bit 400-line gradation input from an image reading device, a host computer or the like via an I / F circuit (not shown). The data 40 is sent in synchronization with the 400-line gradation data clock 49. The gradation data 40 is D having a quantization resolution of 8 bits.
After being converted into the analog signal 46 by the A / A converter 41, the analog signal 46 is converted into the analog adder 45.
Is input to one side.

Further, the correction signal generator 43 synchronizes with the SOS (scan start signal) 44, and the sawtooth wave 4 as shown in FIG.
7 is generated. The sawtooth wave 47 is adjusted in the scanning direction of the exposure apparatus 11 by adjusting the charge parameters shown in FIG. 3 based on the characteristic information stored in the storage circuit 42 according to the image forming characteristics of the exposure apparatus 11 in the scanning direction. The image forming characteristic is corrected, and the image density is generated with a predetermined gradient and voltage so that the image density becomes uniform on the front side and the back side of the apparatus. Then, the sawtooth wave 47 output from the correction signal generator 43 is added to the analog signal 46 by the analog adder 45.

Further, the 200-line synchronous triangular waveform generator 51
Then, the frequency divided by 2 by the 1/2 frequency divider 48 is 2
The triangular wave signal 52 is output in synchronization with the gradation data clock 50 of the 00 line. The triangular wave signal 52 output from the triangular waveform generator 51 is compared with an analog signal 54 in which the high frequency component is removed through a low pass filter 53 from an analog signal 54 on which the sawtooth wave 47 is superimposed by a comparator 54, From the comparator 54, a pulse width modulation signal 55 having a pulse width according to the gradation data 40 is output to a laser drive circuit (not shown).

Therefore, even when a density gradient different in image density occurs between the front side and the back side of the apparatus due to the inclination of the gap between the photoconductor drum and the developing device at the time of manufacturing and assembling the digital copying machine. By adjusting the slope of the sawtooth wave 47 output from the correction signal generator 43, the sawtooth wave 47 having the adjusted slope is superimposed on the analog signal 46 indicating the grayscale data by the adder 45. The voltage value of the analog signal 46 indicating is corrected to be low on either the front side or the back side of the device having high density and the end side of the device having low density is corrected to be high. The comparator 54 compares the analog signal 54 indicating the gradation data corrected in this way with the triangular wave signal 52 output from the triangular waveform generator 51.
Outputs a pulse width modulation signal 59 having a pulse width corresponding to the analog signal 46 indicating the gradation data.

Therefore, in the digital copying machine or the like, it is possible to easily adjust the unevenness of the density of the color toner image.

As described above, in the image data conversion device of the digital copying machine, the gradation data 40 of the color image color-separated by the image processing device 7 is D / A converted, and the exposure data is scanned during one exposure scanning time. The lighting time of the laser light is controlled by comparing with the triangular wave signal 52 of the scanning cycle having a wave height difference corresponding to the density correction amount stored for each color. In addition, by adjusting the voltage level of the triangular wave signal 52,
It is possible to change the shade of the image. The exposure control is to convert the gradation data 40 of the image into the lighting time. In order to faithfully reproduce the input gradation data 40, a portion of one pixel having a total lighting time is used for density correction. Need to be allocated. That is, if one pixel total lighting time (T) ≧ maximum image signal lighting time (T _S ) + maximum density correction time (T _C ), the input gradation data 40 can be faithfully reproduced without being damaged. become. If the condition is not satisfied, in the color image information, the shadow portion may be crushed or the background portion may be developed with the toner. In order to effectively perform the density correction, it is necessary to increase the maximum density correction time (T _C ), but if it is set too large, the maximum image signal does not form a solid image, and a white line is formed between pixels. There is a problem that "is entered. Therefore, in the above-mentioned density correction method, it is necessary to perform appropriate distribution. It has been found that (T _C / T) * 100 ≦ 30 is suitable for satisfying the above-mentioned factors for the following reasons. This density correction method of the image forming apparatus is intended to correct the uneven density of the image forming apparatus by superimposing the density correction signal on the image signal. This image forming apparatus uses 8 bits (0
If the input image signal occupies the whole area from 0 to 255 when it has an image input signal width of
It is clear that this density correction method cannot perform faithful reproduction in a strict sense. However, for example, when an image reading apparatus and an image processing apparatus are connected to this image forming apparatus and the apparatus is used as a copying apparatus, an image is formed substantially without fog on the background even for various original paper qualities. This is practically important, and this is the purpose of so-called resilient adjustment. For magenta, cyan, and black, as shown in FIG. 21 (FIG. 21 shows the target data of the density curve represented by the magenta solid line and the upper and lower limit values thereof represented by the broken line and the alternate long and short dash line), By adjusting so that the development is started with an input signal of 8%, it is possible to obtain a level that is acceptable even for the quality of the paper of a commonly used document and for the jump of the highlight part. . In some cases, due to variations in equipment,
In some cases, it may be preferable to set it at around 12%. However, if the setting exceeds 15%, a defect becomes conspicuous with respect to jumping in the highlight portion, so the upper limit practically used is 15%. On the high density side, the density of about 1.7 is the highest for an ordinary document, so it is possible to set the charging potential and the light amount so that the density becomes 1.7 when the input signal is 100%. In order to reproduce high density areas included in photographic development, etc. to the extent that there is no problem, it is necessary to set a density of 1.7 at 85% of the input signal and set a margin area from 85% to 100%. desirable. As described above, it can be said that it is practically desirable to provide a substantial margin area of 15% for each of the low density and the high density. Thus, one pixel total lighting time (T) and 1 pixel maximum density correction time (T _C) is (T _C / T) * 100
Limiting the upper limits of both corrections so that ≦ 30 is an important requirement for faithfully reproducing the input tone data, and corrections exceeding this range cause problems in the highlight portion and the high density portion. Will occur.

As a result, the density can be corrected for each color, and the color difference can be minimized.

As described above, according to the present invention, for example, it is possible to easily correct the density in a short time by the key input from the control panel, and it is also easy to return to the state before the correction. The point is superior to the mechanical adjustment used in the conventional correction method. Therefore, in consideration of these advantages, it is easy to apply to a monochrome digital image output device or a tandem type color image output device. FIG. 7 shows a modification of the second embodiment, in which an analog adder is connected after the 200-line synchronous triangular waveform generator, and the signals of the correction signal generator are added here. Generally, since the triangular wave signal has a higher frequency component than the image signal, the circuit design is easier with the configuration of FIG. 1, but the image density can be corrected with the configuration of FIG. 7. Further, as a further modified example, a configuration as shown in FIGS. 22 and 23 is also possible.
In the above embodiment, the sawtooth-shaped correction signal is generated using one charge parameter, but as shown in FIG. 22, the counter circuit 61 outputs the inflection point signal CP and the selector 67 switches between the two charge parameters. And FIG.
As shown in, the slope of V _C can be changed at the inflection point, and the density can be corrected more accurately. To further increase the charge parameter, the inflection point signal may be increased to 2 bits or 3 bits and sequentially switched by the selector.

Second Embodiment FIG. 8 shows a second embodiment of the present invention. The same parts as those of the above-mentioned embodiment are designated by the same reference numerals and explained. In this embodiment, the correction signal generator 43 is used. By adjusting the gradient of the sawtooth wave 47 output from the image density gradient, the correction voltage is not superimposed on the image density gradient, but the correction voltage is individually superimposed on the image data per pixel. It is possible to correct the density.

That is, at the time of manufacturing and assembling the above-mentioned digital copying machine, due to the inclination of the gap between the photoconductor drum and the developing device, as shown in FIG. A different concentration gradient may occur on the EOS side. Therefore, in this embodiment, as shown in FIG. 8, an up / down counter 70 is provided,
To the up / down counter 70, a gradation data clock and SOS (scan start signal) are input, as well as count initial value addition data and an up / down switching signal. The count initial value addition data and the up / down switching signal are set so that the density gradient is corrected along the scanning direction along the axial direction of the photosensitive drum so that the density gradient becomes constant. The digital signal output from the up / down counter 70 is converted into an analog signal by the D / A converter 71 and input to the analog adder 54.

In the above-described structure, in this embodiment, as shown in FIG. 8, 8-bit 400-line gradation data 40 input from an image reading device, a host computer or the like via an I / F circuit (not shown) is used. , 400-line gradation data clock 49 is sent in synchronization. This gradation data 40
Is converted into an analog signal 46 by a D / A converter 41 having a quantization resolution of 8 bits, and then this analog signal 46 is input to one of the analog adders 45.

The up / down counter 70 is SO
In synchronization with the S (scan start signal) 44, a predetermined number of counts is down-counted in the count initial value addition data, and the output signal from the up / down counter 70 is converted into an analog voltage by the D / A converter. As shown in FIG. 9, 72 has a predetermined slope that decreases from the front (SOS) side to the back (EOS) side of the apparatus. The offset voltage 72 output from the D / A converter 71 is added to the analog signal 46 by the analog adder 45.

Further, the triangular wave generating circuit 51 outputs the triangular wave signal 52 in synchronization with the gradation data clock 50. The triangular wave signal 52 output from the triangular wave generator 51 is, as shown in FIG.
Is compared with a superimposed analog signal 54 by a comparator 54, and a pulse width modulation signal 55 having a pulse width corresponding to the gradation data 40 is output from the comparator 54 to a laser driving circuit (not shown).

Therefore, even when a density gradient different in image density occurs between the front side and the back side of the apparatus due to the inclination of the gap between the photosensitive drum and the developing device at the time of manufacturing and assembling the digital copying machine. , Up-down counter 7
By adjusting the gradient of the offset voltage output from 0, the adder 45 superimposes the offset voltage 47 having the adjusted gradient on the analog signal 46 indicating the grayscale data. The voltage value is corrected lower on the near side of the device with high density,
The end side of the device with low density is corrected to be high. Then, the analog signal 54 indicating the gradation data corrected in this way
And a triangular wave signal 52 output from the triangular waveform generator 51.
By comparing and with the comparator 54, the comparator 54 outputs a pulse width modulation signal 59 having a pulse width corresponding to the analog signal 46 indicating the grayscale data.

Therefore, in the digital copying machine or the like, it becomes possible to correct the unevenness of the density of the color toner image.

The other structure and operation are the same as those of the above-mentioned embodiment, and the explanation thereof is omitted.

Third Embodiment FIG. 12 shows a laser beam printer as a third embodiment of the image forming apparatus according to the present invention.

In FIG. 12, reference numeral 21 denotes a photosensitive drum as an image bearing member.
Is driven to rotate at a predetermined rotation speed in the direction of the arrow by a driving means (not shown). Around the photoconductor drum 21, a scorotron charger 22 for uniformly charging the surface of the photoconductor drum 21, a laser optical system 23, and developers of respective colors of yellow, magenta, cyan, and black are housed. Four color developing devices 24a, 24b, 24c, 24d and transfer charger 2
5 and an intermediate transfer belt 26 that transfers and holds the toner images of the respective colors sequentially formed on the photosensitive drum 21 in an overlapping state are sequentially arranged along the rotation direction of the photosensitive drum 21. Further, around the intermediate transfer belt 26, the toner images of a predetermined number of colors that are superimposed on each other on the intermediate transfer belt 26 are conveyed to a position facing the intermediate transfer belt 26 at a predetermined timing. Transfer paper 2
Transfer roll 2 for batch transfer onto 0
7, the recording sheet 20 as a recording medium on which the toner images of the predetermined number of colors are transferred, are conveyed to a fixing device 29 described below, and on the recording sheet 20 conveyed by the conveying belt 28. Fixing device 2 for fixing a toner image
9 and 9 are arranged.

As the scorotron charger 22 for uniformly charging the surface of the photosensitive drum 21, two or more discharge wires are provided so that stable and uniform charging can be performed even during image formation of the second and subsequent colors. It is preferable to use the scorotron charger used.

Further, the color developing devices 24a, 24b,
As the components 24c and 24d, for example, a two-component developing device having a known configuration can be used. In particular, the tips of the spikes of the two-component developer composed of toner and carrier are the surface of the photoconductor drum 21 and the second color. Subsequent photosensitive drum 21
The two-component developer carried on the developing roll is arranged so that the spikes of the two-component developer are opposed to the surface of the photoconductor drum 21 through a gap so as not to come into contact with the toner image formed above. Further, each of the color developing devices 24a, 2
The developing bias applied to 4b, 24c, and 24d is a DC voltage (DC + AC voltage) superimposed with an AC voltage so as not to disturb the toner image formed on the photoconductor drum 21 and to obtain a desired high image quality. ) Is applied, and for example, the AC component of the developing bias is adjusted.

FIG. 13 is a schematic diagram showing a laser optical system used in the laser beam printer of FIG.

The laser optical system 23 is composed of a dual semiconductor laser array 31 driven by a laser drive circuit described later, a collimator lens 32, a polygon mirror 33, and an fθ lens 34.
Then, the semiconductor laser array 31 is turned on and off by being modulated by a laser drive circuit described later, and emits a plurality of laser beams 35 which are modulated by a so-called pulse width modulation method. This semiconductor laser array 3
The plurality of laser beams 35 emitted from No. 1 are irradiated onto the surface of the polygon mirror 33 through the collimator lens 32, and the polygon mirror 3 rotating at high speed.
3 is reflected and deflected by the surface of the photosensitive drum 3, and is transferred onto the photosensitive drum 21 via the fθ lens 34 in the main scanning direction (photosensitive drum
Scanning exposure is carried out along the (axis direction).

In the laser beam printer constructed as described above, after the surface of the photoconductor drum 21 is uniformly charged to a predetermined potential by the scorotron charger 22, the surface of the photoconductor drum 21 is subjected to laser optical scanning. An image corresponding to the image information of the first color is scanned and exposed by the system 23 to form an electrostatic latent image. The first color electrostatic latent image formed on the photosensitive drum 21 is developed into a toner image by a first color developing device, for example, a yellow color developing device 24a. The first color yellow toner image is electrostatically transferred onto the intermediate transfer belt 26 by the transfer charger 25. Thereafter, the photosensitive drum 21 on which the toner image of the first color is formed is subjected to the charging, exposing, and developing steps again for a predetermined number of colors in the same manner as above without passing through the transfer step and the cleaning step. Photoconductor drum 21
The four color toner images of yellow, magenta, cyan, and black that are sequentially formed on top of each other are sequentially transferred onto the intermediate transfer belt 26 in a state of being superimposed on each other. The four-color toner images formed on the intermediate transfer belt 26 are collectively transferred onto the recording paper 20 by a transfer roll 27 that contacts the intermediate transfer belt 26 via the recording paper 20 at a predetermined timing. After the transfer, the recording sheet 20 is conveyed to the fixing device 29 by the conveying belt 28. The fixing device 29 fixes the toner images of four colors on the recording paper 20 in a state of being melted and mixed, and the recording paper 20 is ejected out of the machine to complete the color image forming process.

On the surface of the photoconductor drum 21 after the transfer process, the charge of the residual toner is erased by a charge remover (not shown), and the charge is removed after the residual toner is removed by a cleaning device having a blade. The residual charge is further erased by the lamp, and the next color image forming step is prepared.

In this embodiment, as the laser beam printer, an apparatus for forming a full-color image by using the intermediate transfer belt 26 has been described, but the invention is not limited to this, and it is formed on the photosensitive drum. A toner image of a full color is formed by sequentially transferring the toner images of the respective colors to a recording paper or an intermediate transfer medium held on the intermediate transfer drum, or a plurality of photosensitive drums are provided. Even a so-called tandem type color image forming apparatus or the like that forms a full-color image by sequentially transferring a plurality of toner images formed on the recording paper that is sequentially conveyed to the transfer position of each photoconductor drum Of course good things.

FIG. 14 is a block diagram showing the image density controller of the laser beam printer constructed as described above.

By the way, in this embodiment, the storage means for storing the characteristic information according to the image forming characteristic in the scanning direction of the exposure means, and the exposure light quantity in the scanning direction of the exposure means are simply based on the storage information of the storage means. It is configured to include a correction signal generation unit that forms a signal that increases or simply decreases, and an image signal correction unit that superimposes the signal output from the correction signal generation unit and the image signal to output.

In FIG. 14, reference numeral 40 denotes gradation data input from an image reading device, a computer or the like via an I / F circuit (not shown) and having 8-bit resolution of 400 lines / inch. Reference numeral 41 denotes the gradation data 40. Is a D / A converter having a function of decomposing an 8-bit quantized analog signal (256 gradations), 42 is an SOS signal (scan reference signal) or line s output from a laser optical system
i to generate an in-out adjustment sawtooth wave for correcting the concentration gradient between the front side and the back side of the apparatus in synchronization with the sync 43
An n-out adjustment sawtooth wave generation circuit 44 is provided for in-o conversion to the 8-bit quantized analog signal (256 gradations) 45.
An adder that superimposes the ut adjusting sawtooth wave 46, 47 is a triangular wave generating circuit that generates a 200-line triangular wave signal 48 based on the grayscale data clock, and 49 is an 8-bit quantized signal output from the adder 44. Analog signal (256 gradations)
A comparator 50 for comparing a signal 50 in which 45 and a sawtooth wave 46 are superimposed with a triangular wave signal 48 output from the triangular wave generating circuit 47, and 51 is the SOS signal (scan reference signal) or li.
A counter for measuring a predetermined time t after the input of ne sync 43, and 53, when the counter 51 outputs a count-up pulse signal 52, a sawtooth wave output from the sawtooth wave generation circuit 42 at that time. A sample hold circuit for sampling and holding the value of 46, 54
Is a D / A converter for resilience adjustment that outputs a DC voltage for resilience adjustment, and 55 is the sample hold circuit 5 described above.
Sample hold value 56 of sawtooth wave 46 output from 3
In order to control the voltage of the triangular wave signal 48 generated by the triangular wave generating circuit 47 based on the added value, the DC voltage 57 for resilience adjustment output from the resilient adjustment D / A converter 54 is added. Is an adder circuit.

In the laser beam printer according to this embodiment having the above-described structure, in-out density correction for correcting the density gradient in which the image density is not constant on the front side and the back side of the apparatus is performed as follows. Even if it is performed, it is not necessary to re-execute so-called legible correction each time, and the density adjustment operation of the apparatus can be easily performed.

That is, in the image density control section of this laser beam printer, as shown in FIG. 14, 8-bit 400-line gradation input from an image reading device, a host computer or the like via an I / F circuit (not shown). Data 40
Is transmitted in synchronization with a 400-line gradation data clock (not shown). The gradation data 40 is converted into an analog signal 45 by a D / A converter 41 having an 8-bit quantization resolution, and then the analog signal 45 is
It is input to one of the adders 44.

The sawtooth wave generation circuit 42 for the in-out adjustment is, as shown in FIG. 15, SOS or line.
A sawtooth wave 46 is generated based on the sync signal 43, and the sawtooth wave 46 output from the sawtooth wave generation circuit 42 is added to the analog signal 45 by the adder 44.

Further, the above SOS or line syn
The counter 51 measures the elapsed time from the input of the c signal 43, and the SOS or line sync signal 4
When a predetermined time t elapses after 3 is input, the counter 51 outputs a pulse signal 52 as shown in FIG. Then, the sample hold circuit 53
The voltage value of the sawtooth wave 46 output from the sawtooth wave generation circuit 42 when the pulse signal 52 is input is sampled and held. The voltage value 56 of the sawtooth wave 46 sample-held by the sample-hold circuit 53 is added by the adder circuit 55 to the D / A converter 5 for resilience adjustment.
4 is added to the DC voltage 57 outputted from the No. 4 and outputted to the triangular wave generating circuit 47. The triangular wave generating circuit 47 generates the triangular wave signal 48 with the voltage value 58 output from the adding circuit 55 as a reference, that is, with the voltage value 58 as a bias value.

Then, in the comparator 49, as shown in FIG. 15, the analog signal 45 indicating the gradation data to which the sawtooth wave 46 is added is compared with the triangular wave signal 48 outputted from the triangular wave generating circuit 47. Then, the pulse width modulation signal 59 is output to a laser driving circuit (not shown).

Therefore, even when a density gradient different in image density between the front side and the back side of the apparatus occurs due to the inclination of the gap between the photoconductor drum and the developing device at the time of manufacturing the laser beam printer, etc. By adjusting the slope of the sawtooth wave 46 output from the in-out adjustment sawtooth wave generation circuit 42, the sawtooth wave 46 having the adjusted slope is superimposed on the analog signal 45 indicating the grayscale data by the adder 44, The voltage value of the analog signal 45 indicating the gradation data is
Either the front side or the back side of the device with high density is corrected to be low, and the end side of the device with low density is corrected to be high. The comparator 49 compares the analog signal 45 indicating the gradation data corrected in this way with the triangular wave signal 48 output from the triangular wave generation circuit 47. A pulse width modulation signal 59 having a pulse width corresponding to the analog signal 45 indicating is output.

At this time, as shown in FIG. 15, the triangular wave signal 48 output from the triangular wave generating circuit 47 has a reference bias voltage determined by the voltage at the point a of the sawtooth wave 46. Therefore, in the above laser beam printer, when correcting the density gradient in which the image density differs between the front side and the back side of the apparatus, the gradient of the sawtooth wave 46 output from the in-out adjustment sawtooth wave generation circuit 42 is adjusted. Even in this case, the analog signal 45 on which the voltage value of the sawtooth wave 46 at the point a is superposed is the triangular wave signal 48 whose reference is always the bias voltage determined by the voltage at the point a of the sawtooth wave 46.
Will be compared with. Therefore, regardless of whether the sawtooth wave 46 has a steep slope or a gentle slope, the analog signal 45 is converted into the pulse width modulation signal 59 with the voltage at the point a of the sawtooth wave 46 as a reference, so that the in-out Even if adjustment is performed, the pulse width modulation signal 59 corresponding to the point a of the sawtooth wave 46
Has a constant pulse width, and the density at the location corresponding to point a of the printed image is always kept at a certain value.

Therefore, in the laser beam printer, even when the image density adjustment on the low density side called the legible correction is performed, this resilient correction is performed based on the density of the place corresponding to the point a of the print image. By doing so, the resilience correction can be performed independently of the in-out adjustment operation. Therefore, even if the in-out density correction is performed to correct the density gradient in which the image density is not constant on the front side and the back side of the apparatus, it is not necessary to re-execute so-called resilient correction each time, and the density adjustment of the apparatus is performed. The operation can be performed easily.

If the predetermined time t set by the counter 51 is set to a value corresponding to the position of the density detecting device (ESV sensor or the like) used in the laser beam printer, the density detecting device detects the density. The CPU can read the density, and by changing the set value of the resilience adjustment D / A converter 54 according to the detected density read by the CPU, feedback can be applied, and automatic resilience adjustment can be easily performed. Becomes

[0078]

The invention described in claim 1 of the present invention is
With the above configuration and operation, it is possible to easily adjust the unevenness of the density of the color toner image.

The invention according to claim 1 of the present invention has the above-described configuration and operation, and corrects a density gradient in which the image density is not constant on the front side and the back side of the apparatus. Even when the out density correction is performed, it is not necessary to repeat the so-called legible correction each time, and it is possible to provide the image forming apparatus in which the density adjustment operation of the apparatus can be easily performed.

[Brief description of drawings]

FIG. 1 is a block diagram of a control unit showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram showing a color image forming apparatus as an embodiment of the image forming apparatus according to the present invention.

FIG. 3 is a block diagram showing a control unit.

FIG. 4 is a timing chart showing operation timing.

FIG. 5 is a timing chart showing operation timing.

FIG. 6 is a chart showing control data.

FIG. 7 is a block diagram of a controller showing another embodiment of the image forming apparatus according to the present invention.

FIG. 8 is a block diagram of a control unit showing still another embodiment of the image forming apparatus according to the present invention.

FIG. 9 is a graph showing a concentration gradient.

FIG. 10 is a graph showing the slope of the offset voltage.

FIG. 11 is a waveform diagram showing a control waveform.

FIG. 12 is a block diagram showing a color image forming apparatus as another embodiment of the image forming apparatus according to the present invention.

FIG. 13 is a block diagram showing a laser writing device.

FIG. 14 is a block diagram of a controller showing still another embodiment of the image forming apparatus according to the present invention.

FIG. 15 is a timing chart showing the operation of the device shown in FIG.

FIG. 16 is a block diagram showing a control unit in a conventional image forming apparatus.

FIG. 17 is a block diagram showing a control unit in another conventional image forming apparatus.

FIG. 18 is a graph illustrating the resilience adjustment.

FIG. 19 is a timing chart showing the operation of the conventional device.

FIG. 20 is a timing chart showing the operation of the conventional device.

FIG. 21 is a graph showing the operation of another embodiment of the present invention.

FIG. 22 is a block diagram showing a control unit in still another embodiment of the present invention.

23 is a timing chart showing the operation of the embodiment shown in FIG.

[Explanation of symbols]

40 gradation data, 41 D / A converter, 42 storage circuit, 43 correction signal generator, 45 analog adder, 51 triangular waveform generator, 54 comparator.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Ishii 2274 Hongo, Ebina City, Kanagawa Fuji Zerox Co., Ltd. (56) References JP-A-63-49778 (JP, A) JP-A-1-261680 ( (58) Fields investigated (Int.Cl. ⁷ , DB name) B41J 2/44 G03G 15/00 G03G 15/04 G03G 15/043

Claims (2)

(57) [Claims] 1. An image forming apparatus for irradiating a photosensitive member with scanning light modulated by an image signal onto a photosensitive member to form an electrostatic latent image, and developing the electrostatic latent image to form an image. Storage means for storing characteristic information corresponding to image forming characteristics in the scanning direction of the exposure means, and correction for forming a signal for simply increasing or decreasing the exposure light amount in the scanning direction of the exposure means based on the storage information of the storage means. A signal generation unit, an image signal correction unit that superimposes the signal output from the correction signal generation unit and the image signal and outputs the signal, and an adjustment signal that adjusts the reproduction start density of the image signal.
The adjusting means and the exposure means after a predetermined time from the start of scanning by the exposing means.
A sampler for sampling the correction signal generated by the correction signal generating means.
And sampling means, San by the sampling means the output of said adjusting means
Adjustment signal correction for correction using the pulled correction signal
An image forming apparatus comprising the means. 2. A parameter changing means for changing the ratio of the simple increase or the simple decrease by the correction signal generating means during one scan in the main scanning direction by the exposing means based on the storage information of the storage means. The image forming apparatus according to claim 1, wherein: