JP2000071515A - Image forming device - Google Patents

Abstract

(57) [Summary] [Problem] It is possible to easily absorb the difference between individual components of a plurality of components,
An object of the present invention is to provide an image forming apparatus capable of performing stable image formation. A plurality of laser beams oscillated from a plurality of laser oscillators of a laser exposure device are reflected by a polygon mirror to expose the surface of a photosensitive drum to form an electrostatic latent image. The CPU 62 determines the image density of the toner image formed on the photosensitive drum by the laser beam oscillated from any one of the laser oscillators.
And the detected image density is stored in the memory 93 as a reference value. Subsequently, the CPU individually adjusts the light output of each of the other laser oscillators so that the image density of the toner image formed by the laser beam oscillated from the other laser oscillator matches the reference value.

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 a copying machine and a printer for forming an image by an electrophotographic method, and more particularly to an image forming apparatus for forming an image using a plurality of laser beams.

[0002]

2. Description of the Related Art Electrophotographic copying machines, printers, and the like are widely known as image forming apparatuses. For example, in an electrophotographic copying machine, the surface of a photoreceptor drum is uniformly charged by a charging charger and then exposed to form an electrostatic latent image corresponding to a desired image on the drum surface. And
The electrostatic latent image is developed with the developer supplied from the developing device to form a developer image, and the developer image is transferred onto transfer paper by a transfer charger to form an image.

As this type of image forming apparatus, a multi-beam type image forming apparatus that exposes a photosensitive drum using a plurality of laser beams has been provided. According to this image forming apparatus, the exposure unit includes a plurality of laser oscillators, reflects a laser beam emitted from each of the laser oscillators by a polygon mirror or the like, and scans the photosensitive drum, so that the laser beam is statically placed on the drum surface. An electrostatic latent image is formed.
By exposing the photosensitive drum using a plurality of laser beams, it is possible to form an image at a high speed without extremely increasing the rotation speed of the polygon mirror.

In this type of image forming apparatus, in order to form a stable image, individual differences between a plurality of laser oscillators and other individual differences in an image forming section are eliminated, and the laser beam from each laser oscillator is used for proper image formation. It is necessary to be able to form a perfect image.

Therefore, conventionally, as one method, prior to assembling the image forming apparatus, a laser oscillator is selected or manual adjustment of the laser oscillator alone is performed to absorb the solidity between the plurality of laser oscillators. The way has been taken. Also, as another method, after assembling the image forming apparatus, a method of manually adjusting each part by checking an actual output image, a method of adjusting by controlling using a single beam, or an output image using a dedicated sensor There is a method of automatically adjusting the size of the image.

[0006]

However, as described above, when a laser oscillator is selected before assembling the image forming apparatus, the production cost is increased and how an actual output image appears. I can't judge. Also, when performing manual adjustment with the laser oscillator alone,
A great deal of adjustment time is required and it is not possible to determine how the actual output image will appear.

Further, when the actual output image is confirmed after the image forming apparatus is assembled and manual adjustment of each part is performed, it takes a long time for adjustment, reduction in manufacturing efficiency and increase in manufacturing cost. Adjustment by control using a single beam
This is an adjustment other than the laser oscillator, and it is also difficult to adjust the formed image in pixel units. Similarly, when an output image is automatically adjusted using a dedicated sensor, development costs for the dedicated sensor are required, and the number of sensors to be used increases, resulting in an increase in manufacturing cost. Further, since the adjustment is performed only for the laser oscillator, no effect can be expected for other image quality fluctuation factors.

Thus, in the case of the conventional multi-beam type image forming apparatus, in order to improve the performance, the manufacturing cost is increased, and when the use environment is different, the individual difference of the laser oscillator is absorbed. In addition, it becomes difficult to absorb the difference between the individual photosensitive drums.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus capable of easily absorbing a difference between individual components of a plurality of components and performing stable image formation. It is in.

[0010]

In order to achieve the above object, an image forming apparatus according to the present invention exposes an image carrier by exposing a surface of an image carrier with a plurality of laser beams oscillated from a plurality of laser oscillation means. Exposure means for forming a latent image, developing means for developing an electrostatic latent image formed on the image carrier with a developer to form a developer image, and developer formed on the image carrier Detecting means for detecting the image density of the image, and detecting the image density of the developer image formed on the image carrier by a laser beam oscillated from any one of the laser oscillating means, The detected image density is used as a reference value, and the other image density is adjusted so that the image density of the developer image formed on the image carrier by the laser beam oscillated from another laser oscillating unit matches the reference value. Laser oscillation means It is characterized by comprising respectively adjusting means independently adjusting the.

According to the image forming apparatus having the above configuration, the adjusting means first forms a developer image on the image carrier using the laser beam oscillated from any one of the laser oscillating means, and The image density of the developer image is detected by the detecting means, and the detected image density is stored as a reference value. Subsequently, the adjusting means forms a developer image by using a laser beam oscillated from any one of the other laser oscillating means, detects the image density of the developer image by the detecting means, and detects the detected image density. The other laser oscillation means are individually adjusted one by one so that coincides with the reference value.

According to another aspect of the present invention, there is provided an image forming apparatus comprising: an exposure unit configured to expose a surface of an image carrier with a plurality of laser beams oscillated from a plurality of laser oscillation units to form an electrostatic latent image; Developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image, and detecting means for detecting the image density of the developer image formed on the image carrier And one of the above laser oscillation means.
The image density of the developer image formed on the image carrier is detected by the detecting means by the laser beam oscillated from one of the two, so that the detected image density matches a predetermined reference value set in advance. Adjusting means for individually adjusting each laser oscillation means.

According to the image forming apparatus having the above-described structure, the adjusting means first forms a developer image on the image carrier using a laser beam oscillated from any one of the laser oscillating means, and forms the developer image. The image density of the developed developer image is detected by a detection unit. Then, the detected image density is
The laser oscillation means is adjusted so as to match a preset reference value. Subsequently, the adjusting unit similarly adjusts the other laser oscillating units, and individually adjusts the plurality of laser oscillating units one by one based on a predetermined reference value.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine will be described below in detail with reference to the drawings. FIG. 1 shows an image forming section of a digital copying machine. The image forming section includes, as an image carrier, a photosensitive drum 12 made of, for example, arsenic selenium. It is rotatably provided at a substantially central portion in the housing of the above. Around the photoreceptor drum 12, a charging charger 1 functioning as a charging unit
1. Laser exposure apparatus 10 functioning as exposure means, developing device 13 functioning as developing means, transfer charger 14 functioning as transfer means, peeling charger 15, peeling claw 1
6, a cleaning device 17, and a static elimination lamp 18 are sequentially arranged. Further, an image density sensor 20 functioning as a detecting unit is provided between the developing device 13 and the transfer charger 14.

An image density sensor 20 for detecting the image density of the toner image formed on the surface of the photosensitive drum 12 is provided between the developing device 13 and the transfer charger 14.
FIG. 2 shows an inspection image C formed on the surface of the photosensitive drum 12.
Is detected by the image density sensor 20. The image density sensor 20 has a substantially elliptical detection area D on the surface of the photoconductor drum.
The density of the image formed thereon can be detected.

The image density sensor 20 has a light emitting section (not shown) for emitting detection light toward an inspection area D on the surface of the photosensitive drum 12, and a light receiving section for receiving light reflected from the surface of the photosensitive drum. Then, an output voltage is output to the CPU 62 (see FIG. 4) as an image density signal according to the amount of light received by the light receiving section. The light emitting unit of the image density sensor 20 is a CPU 62
Is controlled by the light source driver 108 (see FIG. 4).

Next, the laser exposure apparatus 10 will be described in detail. As shown in FIG. 3, the laser exposure apparatus 10 is a multi-beam type exposure apparatus, and for example, semiconductor laser oscillators 31a and 31 as four laser oscillation units.
b, 31c, 31d, and each of the laser oscillators 3
1a to 31d simultaneously form an image one scanning line at a time, thereby enabling high-speed image formation without extremely increasing the rotation number of the polygon mirror.

That is, the laser oscillator 31a is driven by the laser driver 32a, and the output laser beam is
After passing through a collimator lens (not shown), the mirror 33
a. The laser beam reflected by the mirror 33a passes through the half mirrors 34a and 34b, and is incident on a polygon mirror 35 as a polygon mirror.

The polygon mirror 35 is rotated at a constant speed by a polygon motor 36 driven by a polygon motor driver 37. As a result, the reflected light from the polygon mirror 35 scans in a fixed direction at an angular velocity determined by the rotation speed of the polygon motor 36. The laser beam scanned by the polygon mirror 35 is scanned at a constant speed by passing through the laser beam due to the f-θ characteristic of an f-θ lens (not shown).

The laser oscillators 31b, 31c, 31d are:
The laser beams driven and output by the laser drivers 32b, 32c, and 32d, respectively, pass through a collimator lens (not shown), and are then mirrored by mirrors 33b, 33c.
The light 33d is reflected by the half mirrors 34a, 34b and 34c, and enters the polygon mirror 35, respectively. The path of the laser beam after the polygon mirror 35 is the same as that of the laser oscillator 31a described above, and passes through the f-θ lens and scans the photosensitive drum 12 at a constant speed.

The laser drivers 32a to 32d are:
Each has a built-in auto power control (APC) circuit, and the laser oscillators 31a to 31d always emit light at the emission power level set by the CPU 62.

Thus, the separate laser oscillators 31
Laser beams output from a, 31b, 31c, and 31d are combined by half mirrors 34a, 34b, and 34c, and four laser beams travel in the direction of polygon mirror 35.

Therefore, the four laser beams can scan the photosensitive drum 15 at the same time. When the rotation speed of the polygon mirror 35 is the same as that of the conventional single beam, the four laser beams are four times faster. Images can be recorded.

As shown in FIG. 4, the control system of the laser exposure apparatus 10 includes a CPU 6 for controlling the operation of the entire copying machine.
The CPU includes a memory 93, a control panel 53, an external communication interface (I / F) 54,
The laser drivers 32a, 32b, 32c, and 32d, the polygon mirror motor driver 37, the synchronization circuit 55, the image data interface (I / F) 56, the light source driver 108, and the image density sensor 20 are connected.

The synchronization circuit 55 includes an image data I / F 5
6, page memory 58, external interface (I / F)
The image processing unit 57 and the scanner unit 1 are connected to the image data I / F 56 in order.

When a copying operation is performed by the copying machine having the above configuration, an image of a document set on a document table is read by the scanner unit 1 and sent to the image processing unit 57. The image processing unit 57 performs, for example, well-known shading correction, various filtering processes, gradation processing, gamma correction, and the like on the image signal from the scanner unit 1.

The image data from the image processing section 57 is sent to an image data I / F 56. Image data I / F56
Are four laser drivers 32a, 32b, 32c, 3
It plays the role of distributing image data to 2d. The synchronization circuit 55 generates a clock for matching the exposure start position of each laser beam, and synchronizes the image data I / F 56 with each laser driver 32 in synchronization with the clock.
The image data is sent out to a, 32b, 32c, and 32d as a laser modulation signal.

As described above, by transferring the image data while synchronizing the exposure start timings of the respective laser beams, an image can be formed (to a correct position) synchronized in the main scanning direction. .

The copying machine is configured to output not only a copying operation but also image data input from the outside via an external I / F 59 connected to the page memory 58. The image data input from the external I / F 59 is temporarily stored in the page memory 58 and then sent to the synchronization circuit 55 via the image data I / F 56.

The laser drivers 32a, 32b, 32c,
Reference numeral 32d denotes a laser oscillator that emits a laser beam in accordance with a laser modulation signal synchronized with the scanning of the laser beam from the synchronization circuit 55, and forcibly emits a laser oscillator 31a, 31b, irrespective of image data by a forced emission signal from the CPU 62.
31c and 31d have a function of individually emitting light.

This function is performed by each of the laser oscillators 31a and 31a.
In addition to confirming the operating states of b, 31c, and 31d, it is also used to forcibly emit light from each of the laser oscillators 31a, 31b, 31c, and 31d when performing optical output adjustment between laser beams, which will be described later. Can be

The CPU 62 supplies the power at which the respective laser oscillators 31a, 31b, 31c and 31d emit light to the respective laser drivers 32a, 32b, 32c and 3d.
Set for 2d. The setting of the beam power is changed in accordance with a change in process conditions, detection of a laser beam passage position, and the like.

The memory 93 stores information necessary for control. For example, the memory 93 stores print area information corresponding to each laser beam, a reference value of image density, and the like.
Immediately after the power is turned on, the laser exposure device 10 can be brought into a state where image formation is possible.

In the multi-beam type copying machine configured as described above, in order to form a stable image,
It is necessary to adjust the laser exposure apparatus 10 so that there is no individual difference between a plurality of laser oscillators. Therefore, next, the adjustment operation of the laser exposure apparatus 10 will be described.

First, the drive current of the laser beam, light output characteristics, characteristics of the photosensitive drum, and the like will be described. FIG.
It shows a laser light output (light emission amount) P with respect to a drive current If in a general laser oscillator, and a hatched portion in the drawing shows an LED light emission region. Due to its characteristics, a laser oscillator emits light like an LED until a certain amount of drive current is supplied, and emits light as a laser only when a higher drive current is supplied. Then, at the time of laser emission, an optical output substantially proportional to the drive current can be obtained.

Assuming that the input image data is the same, the laser oscillator a. b. The light intensity distribution of each laser beam obtained when the three drive currents c are supplied is as shown in FIG. In this figure, the vertical axis indicates the light intensity, and the horizontal axis indicates the scanning position of the laser beam. The peak value of the light intensity changes according to the magnitude of the drive current, and the spread of the low light intensity portion is substantially constant without being affected by the drive current.

FIG. 6B shows the surface potential of the photosensitive drum at the exposure position when the photosensitive drum is exposed by the laser beams having the above three light intensities. FIG. 6C shows the photosensitive drum after development. 3 shows a pattern formed on a body drum.

The photosensitive drum has such a characteristic that the surface potential is reduced in accordance with the light output of the laser beam, but the surface potential is not reduced further even after a laser exposure of a certain value or more. Therefore, as can be seen from FIGS. 6B and 6C, the density and size of the toner pattern formed on the photosensitive drum increase as the light output of the laser beam increases, and there is light output. When the value is larger than the value, the density itself is stable without changing, and only the size increases.

From the various characteristics described above, in order to form a stable image in a multi-beam type copying machine, the laser exposure device 10 is adjusted so that the light outputs of a plurality of laser oscillators are adjusted to predetermined values. It is desirable. Hereinafter, the adjustment operation of the laser exposure apparatus 10 will be described with reference to the flowchart shown in FIG.

This adjustment operation adjusts the other laser oscillators with the toner density of a pattern image formed using a laser beam emitted from one arbitrary laser oscillator as a target value. That is, the CPU 62 first selects any one of the laser oscillators, forms an electrostatic latent image on the surface of the photosensitive drum by a laser beam from this laser oscillator, and further develops the toner image by a developing device. I do. Subsequently, the toner density of the formed toner image is detected by the density detection sensor 20, and the detection result is stored in the memory 93 as a target value.

Next, the laser oscillator is changed to another one, and a toner image is formed on the photosensitive drum in the same manner as described above. Subsequently, the toner density of the formed toner image is detected and compared with the target value stored in the memory 93.
If the detected toner concentration is different from the target value,
The light output of the laser oscillator is adjusted, and toner image formation, density detection, and light output adjustment are repeated until the light output matches the target value. By performing the above operation for all the laser oscillators, it is possible to absorb the difference in the exposure amount due to the individual difference between the plurality of laser oscillators and to make it equal to a predetermined value.

For example, as shown in FIG. 8A, when there are variations in the optical outputs P1 and P2 with respect to the drive current I1 supplied to the two laser oscillators, the toner formed by the laser beam from each laser oscillator The statue is
As shown in FIG. 8B, the toner densities Q1 and Q2 are different from each other, and as shown in FIG. 8C, the size of the photosensitive drum in the longitudinal direction is almost the same, but the size in the rotating direction of the photosensitive drum. Will not match.

Here, the drive current of the second laser oscillator is set so that Q2 = Q1 by the above-described adjustment operation, with the toner density Q1 of the toner image formed by the laser beam from the first laser oscillator as the target value. Changing to I2,
As shown in FIG. 9A, the first laser oscillator and the second
The toner images formed by the laser oscillators have the same toner density and size.

In the above-described adjustment operation, since the other laser oscillators are adjusted based on the toner density of the toner image formed by the first laser oscillator selected first, the size of the toner image by the first laser oscillator is ideal. The size is desirable, but it may be deviated from the ideal size. For example, when the size of the toner image by the first laser oscillator is larger than the ideal size, if another laser oscillator is adjusted based on the size, the size of the toner image by each laser oscillator becomes larger than the ideal size. . In this case, the resolution required for the copying machine cannot be satisfied, and when a plurality of laser oscillators are turned on simultaneously, the formed toner images partially overlap. Since the exposure potential of the overlapping portion is lower than the exposure potential of the non-overlapping portion, a difference occurs in the toner density, and density unevenness occurs.

Therefore, in order to solve such a problem,
It is more preferable to adjust the laser exposure apparatus 10 in the following procedure. That is, as shown in FIG. 10, first, the CPU 62 simultaneously emits light from all the laser oscillators with a sufficiently large optical output, detects the toner density QT of the formed toner image, and temporarily stores it in the memory 92. Subsequently, each laser oscillator is individually caused to emit light by using an appropriate drive current, and the toner density q of each formed toner image is determined.
n is detected.

Next, the smallest one of the detected toner densities is set as the target value qt in the memory 93.
To memorize. Subsequently, a toner image is formed and the toner density is detected using each of the other laser oscillators, and the light output of each laser oscillator is adjusted so that the toner density matches the target value qt.

After the adjustment of all the laser oscillators is completed,
All the laser oscillators emit light at the same time, and the toner density Qn of the formed toner image is detected. Detected toner concentration Q
n is compared with the toner concentration QT stored in the memory 93, and if QT <Qn, the drive currents of all laser oscillators are simultaneously changed to adjust the optical output. And Qn is QT
By repeating this operation until the value becomes equal to the above, all laser oscillators can be adjusted while solving the above problem.

Further, another adjustment operation for solving the above-mentioned problem will be described with reference to the flowchart of FIG. First, the CPU 62 selects an arbitrary one of the plurality of laser oscillators, and detects the toner density of the toner image formed by causing only the laser oscillator to emit light. Then, it is determined whether or not the detected toner density matches an optimum target value stored in the memory 93 in advance.

If the result of the determination indicates that the detected value is deviated from the target value, the light output of the laser emitter is adjusted, and laser emission, toner density detection, and toner density determination are performed until the target value matches the detected value. repeat. Then, after the toner densities match, toner image formation, toner density detection, and optical output adjustment are performed individually for the other laser oscillators, and the adjustment operation of each laser oscillator is repeated until the laser output equals the target value.

Thus, the toner density and size of the toner image formed by each laser oscillator can be adjusted to a predetermined optimum value in a relatively short time. Accordingly, there is no individual difference between the plurality of laser oscillators, and thereafter, stable image formation can be performed.

The problem described above can also be solved by optimizing the development characteristics of the copying machine after adjusting the light output of the laser exposure apparatus 10 shown in FIG. First, the developing characteristics will be described. As shown in FIG. 12, when a toner image is formed on the photoconductor drum, the surface of the photoconductor drum 12 is uniformly charged by the charging charger 11 so as to have a predetermined potential V0. You. When a portion where a toner image is to be formed is exposed by the laser exposure device 10, the surface potential of the exposed portion changes to the OV side and becomes the exposure potential VL lower than the developing bias VB.

Subsequently, the toner negatively charged by the developing unit 13 is supplied to an exposed portion on the photosensitive drum to form a toner image. Here, the potential difference between the charging potential V0 and the developing bias VB is represented by the background potential VBG and the developing bias VB.
The potential difference between B and the exposure potential VL is defined as a contrast potential VC. Note that the exposure potential is a potential when the irradiation time (input data per pixel) in one pixel of the laser exposure apparatus is maximized. Through such a process, a toner image is formed on the photosensitive drum.

On the other hand, when the grid bias that determines the charging potential V0 is increased, the charging potential V0 on the surface of the photosensitive drum and the exposure potential VL when exposed with a constant amount of laser beam are both shown in FIG. It changes in an increasing direction. Therefore, by changing the grid bias, the background potential VBG and the contrast potential VC also change.

When the contrast potential VC changes, as shown in FIG. 14A, the characteristics of the toner density with respect to the input image data greatly change on the higher toner density side. Further, when the background potential VBG changes, FIG.
As shown in the figure, the characteristic on the side where the toner density is low greatly changes contrary to the contrast potential.

By optimizing the development characteristics utilizing such characteristics, the size of the toner image formed by each laser oscillator can be adjusted to an appropriate size. That is, first, as shown in FIGS. 15 and 16, the high density image A and the low density image B
Are arranged in the sub-scanning direction and sandwich a space where no image is formed. Then, the image density sensor 2
Based on 0, the toner densities of the high-density image A and the low-density image B are respectively detected, and it is determined whether or not the toner densities match the target values stored in the memory 93 in advance.

If the result of the determination is that they do not match, the deviation from the target value is calculated for each of the images A and B, and the contrast potential VC and the background potential VB are calculated from the calculation results.
The correction amount of G is calculated. Then, the operation amounts of the grit bias VG and the developing bias VB corresponding to these correction amounts are calculated, and VG and VB are set. Such an operation is repeated until the detected toner concentration matches the target value.

This control does not directly detect the charging potential V0 and the exposure potential VL, but converges on the initially set optimum developing characteristics if the light quantity is constant. Therefore,
First, by adjusting the laser exposure apparatus 10, the light outputs of all the laser oscillators are made to coincide with each other, and then the above-described development characteristic optimization control is performed, so that the exposure size of each laser oscillator is set to an ideal size. It becomes possible.

According to the copier of the multi-beam system configured as described above, individual differences between a plurality of laser oscillators can be easily and inexpensively absorbed, and stable image formation can be achieved. Further, it is possible to absorb a difference between components of a component other than the laser oscillator, such as a difference between individual photosensitive drums. Further, it is possible to adjust an electrophotographic process including exposure conditions without outputting an actual image.

The present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the present invention. For example, when forming a binary image, as in the above-described embodiment, the effect can be obtained by adjusting the drive current of the laser oscillator and aligning the light output. Further, it is necessary to adjust the image density also for the halftone portion.

FIG. 17 shows a change in toner density when the pulse width data is changed after adjusting the light output of each laser oscillator. The horizontal axis represents pulse width data defining the light emission time in one pixel. The vertical axis indicates the toner density. It is assumed that all the pixels emit light when the pulse width data is FF, and that the light output of the laser oscillator has already been adjusted in the FF state.

As shown in FIG. 17, by adjusting the optical output, the toner density in the pulse width data FF of the laser oscillators 1 and 2 is equal to Qmax. When formed, the toner concentration becomes Q1 in the laser oscillator 1 and Q2 in the laser oscillator 2, and the toner concentration varies. This is caused by the response characteristics of the laser oscillator, the difference between the individual laser drivers, and the like.

When an image is formed in such a state in which the toner density varies, the output image becomes jagged as shown in FIG. On the other hand, a laser driver or a CPU of a copying machine generally has a conversion unit that converts image data input from a scanner unit or an external I / F into pulse width data of a laser beam. The conversion data is stored in a memory, and the conversion data in the memory is read into a conversion unit when an image is formed, and pulse width data is output based on the read data.

Therefore, when outputting an image having the toner density Q1, the laser oscillator 1 sets the pulse width data to 80,
In the laser oscillator 2, by changing the conversion data table stored in the memory so that the pulse width data becomes A0, the relationship between the input data to the laser driver and the toner density is matched for all laser oscillators. Can be.

More specifically, as shown in FIG. 19, after adjusting the light output of each laser oscillator, a toner image is formed by an arbitrary laser oscillator, and the toner density is detected by an image density sensor. Then, the detected toner density is compared with a predetermined target value, and if different, the pulse width data is changed. Until the detected toner density matches a predetermined target value, toner image formation, density detection, and pulse width data adjustment are repeatedly performed.

When the toner density matches the target value, the conversion data in the table in the memory is rewritten according to the adjustment of the pulse width data. Subsequently, the pulse width data is adjusted for the other laser oscillators by the same operation as described above, and all the laser oscillators are individually adjusted. This optimizes the driving conditions of the laser oscillator in the halftone,
A stable image can be formed at a low cost even for a multivalued image.

The present invention is applicable not only to the above-described copying machine but also to, for example, a full-color image forming apparatus. FIG. 20 shows a four-drum color printer as a full-color image forming apparatus. In this color printer, four photosensitive drums 12Y, 12M, 12
C and 12K are arranged in parallel with each other, and a toner image of each color is formed on each photosensitive drum using yellow (Y), magenta (M), cyan (C), and black (K) toners. A color image is obtained by separately forming these toner images and sequentially transferring these toner images to one transfer sheet.

More specifically, the four-drum type color printer includes four image forming units 5Y, 5M, 5C, and 5K corresponding to four color images. These image forming units 5Y, 5M, 5C, and 5K are provided with photosensitive drums 12Y, 12M, 12C, and 12K, and chargers 11Y, 11M, and
11C, 11K, developing units 13Y, 13M, 13C, 13
K, transfer rollers 14Y, 14M, 14C, and 14K, a cleaning device (not shown), and the like. Above these image forming units 5Y, 5M, 5C, and 5K, a laser exposure device 10 is provided. The laser exposure device includes yellow (Y), magenta (M), cyan (C), and black (K). Are provided with four laser oscillators 31Y, 31M, 31C, and 31K, respectively.

Below the image forming units 5Y, 5M, 5C and 5K, there are four photosensitive drums 12Y, 12M, 12C and 1
A transport belt 100 that travels in contact with 2K is provided, and the transport belt is driven to travel at the same speed as the peripheral speed of the photosensitive drum. The transfer paper is transferred to the transport belt 100 after being charged by a charging roller or the like, and is transported by the transport belt while being electrostatically attracted to the transport belt.

Then, the image forming units 5Y, 5M, 5C, 5
K, four color toner images are formed on the photosensitive drum, and these toner images are
Thus, the image data is sequentially transferred onto the transfer paper conveyed at a predetermined timing. The transfer material on which the toner images of the four colors are superimposed is sent to the fixing device 102, where the toner image is melted and fixed on the transfer paper and then discharged.

In the color printer configured as described above, the laser exposure device 10 includes four laser oscillators 31Y, 31M, 31C, and 31K corresponding to Y, M, C, and K. It is necessary to adjust the driving conditions individually. For color printers, Y,
Since images of various colors are formed by combining the four colors of M, C, and K, if the driving conditions of the four laser oscillators do not match, the images appear in different colors.

Therefore, the color printer according to the present embodiment is provided with an image density sensor 20 provided opposite to the transport belt 100 between the image forming section 5K on the paper discharge side and the fixing device 102, and the The density sensor detects the toner density of an image formed on the transfer paper conveyed by the conveyance belt.

The four laser oscillators 31Y, 31M, 31
When adjusting the driving conditions of C and 31K, as shown in FIG. 21, the CPU 62 first selects the image forming unit 5Y,
By causing the laser oscillator 31Y to emit light, a toner image is formed on the transfer paper. Then, the toner density of the formed toner image is detected by the image density sensor 20,
The detection result is compared with a predetermined target value stored in the memory 93 in advance.

If the detected toner density does not match the target value, the CPU 62 changes the drive current of the laser oscillator 31Y to adjust the light output. Then, again, the image forming unit 5
The toner image formation by Y, toner density detection, and comparison with the target value are performed, and the above operation is repeated until the detected toner density matches the target value.

Subsequently, by the same operation, the optical outputs of the laser oscillators 31M, 31C and 31K are sequentially adjusted individually, and the toner concentrations of all the laser oscillators are adjusted so as to match the target values.

When a toner image is formed by each of the image forming units, as shown in FIG. 22A, the toner images are continuous in the main scanning direction and have a constant interval in the sub scanning direction, for example, every other line. A pattern toner image is formed. Or,
As shown in FIG. 22B, the toner image has a pattern that is continuous in the sub-scanning direction and is spaced at a constant interval in the main scanning direction.
As shown in (c), the toner density may be detected using a toner image of a pattern that is spaced at a constant interval in both the main scanning direction and the sub-scanning direction. By using such a toner image, adjustment of the laser oscillator can be performed with less toner consumption.

In the color printer configured as described above, similarly to the above-described embodiment, it is possible to easily and inexpensively absorb the individual difference between a plurality of laser oscillators, and to form an image capable of performing stable color reproduction. Can be realized. Further, it is possible to absorb a difference between components of a component other than the laser oscillator, such as a difference between individual photosensitive drums. Further, it is possible to adjust an electrophotographic process including exposure conditions without outputting an actual image.

[0077]

As described above in detail, according to the present invention, in an image forming apparatus for forming an image by using a plurality of laser beams, a difference between individual components of a plurality of components can be easily absorbed and stable. An image forming apparatus capable of forming an image can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an image forming unit of a multi-beam type copying machine according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a photosensitive drum and an image density sensor of the copying machine.

FIG. 3 is a block diagram schematically showing a configuration of a laser exposure apparatus of the copying machine.

FIG. 4 is a block diagram schematically showing a configuration of a control system of the copying machine.

FIG. 5 is a graph showing a relationship between a driving current of a laser oscillator and an optical output in the laser exposure apparatus.

FIG. 6 is a diagram showing a relationship among a laser beam light output, an exposure amount, and a toner adhesion amount by the laser oscillator.

FIG. 7 is a flowchart showing an adjusting operation of the laser exposure apparatus.

FIG. 8 is a diagram showing a difference in characteristics between two laser oscillators.

FIG. 9 is a diagram showing characteristics of the two laser oscillators after adjustment.

FIG. 10 is a flowchart showing another adjustment operation of the laser exposure apparatus.

FIG. 11 is a flowchart showing still another adjustment operation of the laser exposure apparatus.

FIG. 12 is a diagram for explaining a surface potential of a photosensitive drum when forming a toner image.

FIG. 13 is a graph showing a relationship between a grid bias and a drum surface potential.

FIG. 14 is a graph showing a relationship between input data and toner density.

FIG. 15 is a perspective view showing a state in which toner images having different densities are formed on the photosensitive drum.

FIG. 16 is a flowchart showing an image adjusting operation by controlling development characteristics of the photosensitive drum.

FIG. 17 is a graph showing a relationship between pulse width data and toner density.

FIG. 18 illustrates an example of a formed toner image.

FIG. 19 is a flowchart showing a halftone adjustment operation of the laser exposure apparatus.

FIG. 20 is a diagram schematically showing a color printer according to another embodiment of the present invention.

FIG. 21 is a flowchart showing an adjustment operation of the laser exposure device in the color printer.

FIG. 22 is a diagram showing a pattern of a toner image used in the adjustment operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Laser exposure apparatus 12 ... Photoconductor drum 12a ... Exposure position 13 ... Developer 20 ... Image density sensor 31a, 31b, 31c, 31d ... Laser driver 35 ... Polygon mirror 62 ... CPU 93 ... Memory

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA12 AA16 AA17 AA33 AA54 AA61 AA63 AA66 BA67 CB80 2H027 DA10 DE02 EA02 EC06 EC07 EF07 2H030 AA03 BB02 BB13 BB36 2H076 AB06 AB09 AB34 DA07 DA17 DA17

Claims (2)

[Claims] An exposure means for exposing a surface of the image carrier with a plurality of laser beams oscillated from a plurality of laser oscillation means to form an electrostatic latent image; and an electrostatic device formed on the image carrier. Developing means for developing a latent image with a developer to form a developer image; detecting means for detecting an image density of the developer image formed on the image carrier; and one of the laser oscillation means The image density of the developer image formed on the image carrier by the laser beam oscillated from is detected by the detecting means, and the laser oscillated from another laser oscillating means using the detected image density as a reference value Adjusting means for individually adjusting the other laser oscillation means so that the image density of the developer image formed on the image carrier by the beam coincides with the reference value. Image formation apparatus. 2. An exposure means for exposing the surface of an image carrier with a plurality of laser beams oscillated from a plurality of laser oscillation means to form an electrostatic latent image, and an electrostatic device formed on said image carrier. Developing means for developing a latent image with a developer to form a developer image; detecting means for detecting an image density of the developer image formed on the image carrier; and one of the laser oscillation means The image density of the developer image formed on the image carrier by the laser beam oscillated from is detected by the detection means, so that the detected image density matches a predetermined reference value set in advance, An image forming apparatus comprising: adjusting means for individually adjusting each laser oscillation means.