JP2002318475A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten time for controlling image density by maintaining the quality of an image formed by simultaneously using a plurality of beams over the lapse of time with simple constitution. SOLUTION: A beam scanning direction is divided to patch data forming areas for controlling the image density corresponding to the respective beams, and image density sensors as many as the beams are provided corresponding to the respective patch data forming areas. Then, the image density is controlled by detecting the density of patch data by the respective beams formed on an image carrier or an intermediate transfer body by the image density sensor, and controlling the light quantity of the beam other than a reference beam set previously so that the density of the patch data formed by the beam other than the reference beam may be equal to the density of the patch data formed by the reference beam.

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 using a plurality of beams.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. H11-11948 discloses an image forming apparatus for controlling image density by providing a plurality of patch data.
There is a technique disclosed in Japanese Patent Application Publication No. 0 (1999). However, this technique is not related to multi-beams, requires a new sensor configuration, takes time to control the density of multiple beams, and when a degraded beam is generated among multiple beams, image formation is not possible. Can not be done.

[0003]

An object of the present invention is to maintain the quality of an image formed by simultaneously using a plurality of beams with a simple configuration over time, to shorten the time required for image density control, and to reduce the image density control. An object of the present invention is to provide an image forming apparatus capable of reducing the number of sensors for image formation, reducing the size and cost of the image forming apparatus, and extending the life of an image forming apparatus using a plurality of beams simultaneously. .

[0004]

The present invention has the following configuration to achieve the above object. (1). An image forming apparatus in which a plurality of beams emitted from a light source are arranged in a sub-scanning direction on an image carrier, and a plurality of lines of latent images are simultaneously formed on the image carrier by one beam scanning, the beam scanning direction comprising: Are divided into patch data formation areas for image density control corresponding to the respective beams, and the same number of image density sensors as the beams are provided corresponding to the respective patch data formation areas, and are provided on the image carrier or the intermediate transfer body. The patch data density of each beam to be formed is detected by the image density sensor so that the patch data density formed by beams other than the reference beam is equal to the patch data density formed by the preset reference beam. The density of an image is controlled by controlling the amount of light of a beam other than the reference beam. (2). An image forming apparatus in which a plurality of beams emitted from a light source are arranged in a sub-scanning direction on an image carrier, and a plurality of lines of latent images are simultaneously formed on the image carrier by one beam scanning, the beam scanning direction comprising: The patch data for image density control corresponding to each beam is sequentially formed in the same area, and formed on the image carrier or the intermediate transfer body with a single image density sensor provided in the patch data formation area The density of the patch data formed by the beams other than the reference beam is equal to the density of the patch data formed by the preset reference beam. The density of the image is controlled by controlling the amount of light (claim 2). (3). An image forming apparatus, wherein a plurality of beams emitted from a light source are arranged in a sub-scanning direction on an image carrier, and a plurality of lines of latent images are simultaneously formed on the image carrier by a single beam scan. The patch data for image density control is formed by one preset reference beam among the beams, and the image carrier is formed by the single preset reference beam by a single image density sensor provided in the patch data formation area. The density of one reference beam image is controlled by detecting the density of patch data formed on the upper or intermediate transfer member, and the light amount of the remaining beam is adjusted to the predetermined value.
The density of an image formed by the remaining beams is controlled by controlling the amount of light to be equal to that of the two reference beams (claim 3). (4). In the image forming apparatus according to any one of (1) to (3), density control of an image performed by detecting patch data density with an image density sensor includes various bias voltage controls related to an image forming process, toner control, and the like. The replenishment and the light quantity control of the beam as the image forming means are performed alone or in combination (claim 4). (5). In the image forming apparatus according to any one of (1) to (4), when the image density detected by the image density sensor is lower than a preset density, priority is given to bias control and toner replenishment. When the image density detected by the image density sensor is higher than a preset density, the density control is performed with priority given to the light quantity control of the beam. (6). An image forming apparatus in which 2n (n: an integer) beams emitted from a light source are arranged in a sub-scanning direction on an image carrier, and a plurality of lines of latent images are simultaneously formed by one beam scanning. When all the 2n beams cannot be used for image formation due to deterioration, an odd condition is determined according to the order in which the 2n beams are arranged in the sub-scanning direction. A means for maintaining the forming operation is provided (claim 6). (7). An image forming apparatus in which 2n (n: an integer) beams emitted from a light source are arranged in a sub-scanning direction on an image carrier, and latent images of different lines are simultaneously formed by one beam scanning. When all of the 2n beams cannot be used for image formation due to deterioration, the 2n beams are equally divided into a plurality of groups, and all beams in the group including the deteriorated beam are prohibited from use, and at the same time, use is prohibited. There is provided means for switching data to be supplied to the beam to supply to a usable beam, and lowering an image output speed according to the number of beams whose use is prohibited, thereby maintaining an image forming operation. (8). In the image forming apparatus described in (6) or (7), image data density control is performed by detecting patch data density formed by one preset reference beam among a plurality of beams, and controlling the light quantity of the remaining beams. In an image forming apparatus that controls the density of an image with the remaining beams by controlling the same light amount as the predetermined one reference beam, if the light source that emits the predetermined reference beam deteriorates, A new reference beam is selected, patch data for image density control is formed with the selected reference beam, and a single image density sensor provided in a patch data formation area is used to select the selected one reference beam. The density of the patch data formed by the beam is detected, the image density is controlled, and the light amount of the remaining beam is the same as the light amount of the beam newly selected as the reference beam. Control to, it was decided to maintain the image forming operation (claim 8). (9). In the image forming apparatus according to any one of (1) to (8), the image forming apparatus includes a plurality of image forming units arranged to face a moving surface of the intermediate transfer body, and the image forming unit is a single image carrier. And one writing means, at least two developing means for developing the electrostatic latent image formed on the image carrier by the writing means, and switching means for selectively selecting and driving the developing means. (Claim 9). (10). (1) The image forming apparatus according to any one of (1) to (9), wherein the patch data is used as solid data, and after controlling the light amount by the patch data, various bias voltage controls related to the image forming process, The image density is controlled by the replenishment, and the pulse width for controlling the beam lighting time is changed to express the gradation of the image.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1] Example Corresponding to Claim 1 In FIG. 1 showing a schematic configuration of an image forming unit in an image forming apparatus according to the present invention, a beam Lb emitted from a light source 1 is directed in the direction of an arrow. After being deflected and scanned by the rotating polygon mirror 2 and passed through a scanning optical element (fθ lens 3 is shown as a representative example), it is scanned in the direction of arrow 5 on a drum-shaped photoconductor 4 as an image carrier. . Although not shown, synchronization detection for detecting a beam Lb to be scanned and generating a signal serving as a writing start reference in the main scanning direction on the scanning start side (upstream of arrow 5) which is one end side of the photoconductor 4 is performed. A plate is arranged.

The light source 1 has a plurality of (two in this case, for the sake of simplicity of explanation) light beams, and two beams emitted from the light source 1 are applied on the photosensitive member 4 in the main scanning direction as shown in FIG. The beam Lb is arranged so as to form an image adjacent to the beam Lb in the sub-scanning direction perpendicular to the direction.

In FIG. 2, when a printing operation is started, latent images of lines L11 and L21 are formed on the photosensitive member 4 in a first scan, and latent images of lines L12 and L22 are formed in a second scan. Data is sequentially formed as a latent image for each two lines.

When an image of the same page is formed by combining data formed by different beams as described above, it is necessary to equalize image densities formed by different beams in order to form high-quality images. . On the other hand, the image forming apparatus performs image density control in a standby state where there is no print instruction or when a predetermined number of prints is reached.

In order to perform image density control, according to the first aspect of the present invention, the beam scanning direction is divided into patch data forming areas for image density control corresponding to each beam, and the same number of image densities as the number of beams are used. A sensor is provided corresponding to each patch data formation area.

When the number of light sources is n, the main scanning width, which is the scanning width of the beam Lb, is divided into n as shown in FIG. 1, and the image (toner) density sensor is placed at a beam scanning position corresponding to the divided area. Provided.

FIG. 3 shows an example of an image forming unit of the image forming apparatus.
, Around the photoreceptor 4, in the order of the rotation indicated by the arrow 6, the charging brush 7, the irradiation unit 9 of the writing beam Lb, the developing device 10, and the transfer of the toner image to the intermediate transfer belt 11 as an intermediate transfer body An intermediate transfer position 12 is provided. In the developing device 10, the developing roller 15
Faces the photoconductor 4 and transfers the toner to the photoconductor,
The part to be developed is referred to as a development position 16.

At the intermediate transfer position 12, at the time of transfer, the intermediate transfer belt 11 comes into contact with the photoconductor 4, and the toner image on the photoconductor 4 is transferred. To perform the intermediate transfer, an intermediate transfer charger (not shown) is provided inside the intermediate transfer belt 11. A cleaning blade 13 is provided around the intermediate transfer belt 11 so as to be able to freely contact and separate from the intermediate transfer belt 11. A portion where the cleaning blade 13 contacts the intermediate transfer belt 11 is referred to as a cleaning position 14.

In FIG. 3, the image density sensor is a photoconductor 4
Above, a section A from the developing position 14 to the intermediate transfer position 12 toward the upstream side in the rotation direction of the photoconductor 4 as indicated by an arrow 6, or on the intermediate transfer belt 11, from the intermediate transfer position 11 to the intermediate transfer transfer belt. 11 is provided at an arbitrary position in a section B until reaching the cleaning position 14 toward the downstream side in the rotation direction of the motor 11.

Control Method When shifting to the image density control mode, each beam is
The light is turned on so that patch data can be created in an area previously set in advance. The lighting timing is shown in FIG. In FIG. 4, Lsync is a synchronization detection signal and the interval between rising pulses indicates one scanning period.

The interval between the rising pulses of the beams BM-1, BM-2,... BM-N is a lighting period for creating patch data of each beam, and a period during which the beam actually scans the photosensitive member 4 (effective scanning period). ) Is divided into n. Lighting is continued at the timing shown in FIG. 4 so that the patch data width becomes several cm in the sub-scanning direction.

When the patch data is formed, density detection by the image density sensor is simultaneously performed for each beam, and the detected density of the patch data formed by a preset reference beam and the beam other than the reference beam are formed. The light amounts of the beams other than the reference beam are controlled as necessary so that the detected densities of the patch data become equal.

In FIG. 5 showing a processing block for such control, the beams BM-1, BM-2,.
The image density sensors corresponding to N are denoted by SE-1 and SE-2.
... SE-N. Each image density sensor SE-1, SE-
2... SE-N are detected by the CPU at the port P corresponding to each of the image density sensors SE-1, SE-2.
T-1, PT-2 ... PT-N are simultaneously loaded and AD
After the conversion, it is stored in the register as the patch data density.

The patch data density of each beam stored in the register is compared with the patch data density of the reference beam.
BM-2 ... Driver DV- that drives and controls BM-N
1, a signal for controlling the amount of light to be equal to DV-2... DV-N is output.

When the density of the patch data formed by each beam becomes equal to the density of the patch data formed by the reference beam by the light quantity control, the patch data density formed by the preset reference beam becomes the predetermined image density. Various bias adjustments and toner replenishment are performed as necessary to control image density.

[2] Example Corresponding to Claim 2 The image forming apparatus according to this embodiment sequentially forms patch data for image density control corresponding to each beam in the same area in the beam scanning direction. , A single image density sensor is provided corresponding to the patch data formation area.

An arbitrary area in the beam scanning (main scanning) direction is defined as a patch data forming area, and one image (toner) density sensor is provided at a beam scanning position corresponding to the area. The image density sensor extends from the developing position 16 of the photosensitive member 4 shown in FIG. 3 to the intermediate transfer position 12 toward the downstream side in the rotation direction of the photosensitive member 4 as shown in FIG. Section A or intermediate transfer position 1 on intermediate transfer body belt 11
It is provided at an arbitrary position in a section B from 2 to the cleaning position 14 toward the downstream side in the rotation direction of the intermediate transfer belt 11.

Control Method When shifting to the image density control mode, each beam is turned on so that patch data can be created in a preset area.
The lighting timing is shown in FIG. Here, the beam B described above is used.
The same area as the area formed by M-1 is defined as a patch data formation area.

Each of the beams is turned on in the order of the beams BM-1, BM-2,... BM-N. Lighting at the timing shown in FIG. 6 is continued for each beam so that the patch data width in the sub-scanning direction becomes several cm. When the patch data is formed, density detection by the image density sensor is performed,
The light amounts of the beams other than the reference beam are controlled as necessary so that the detection density of the patch data formed by the preset reference beam is equal to the detection density of the patch data formed by the beams other than the reference beam.

FIG. 7 shows a processing block. The detection signal of the image density sensor SE is a port PT corresponding to the sensor of the CPU.
The signal is taken into -S, subjected to AD conversion, and stored in a register. The patch data density of each beam stored in the register is compared with the patch data density of the reference beam, and as a result, as necessary, the CPU drives and controls the light source that emits each beam. A signal for controlling the amount of light to be equal to -N is output.

Each beam BM-1, BM-
2. When the density of the patch data formed by the BM-N becomes equal, various bias adjustments and toner replenishment are performed as necessary so that the density of the patch data formed by the preset reference beam becomes a predetermined density, and the image is formed. Is performed.

[3] An example corresponding to claim 3 The image forming apparatus according to the present invention provides a patch for controlling image density using a predetermined reference beam among a plurality of beams in an arbitrary region in the beam scanning direction. Data is formed, and one image density sensor is provided corresponding to the patch data formation area.

The image density sensor includes the photosensitive member 4 shown in FIG.
In the section A from the developing position 16 to the intermediate transfer position 12 toward the downstream side in the rotational direction of the transfer position photoconductor 4, or in the rotational direction downstream of the intermediate transfer transfer belt 11 from the intermediate transfer position 12 on the intermediate transfer belt 11. It is provided at an arbitrary position in the section B up to the cleaning position 14 toward the side.

Control Method When shifting to the image density control mode, a preset reference beam is turned on to generate patch data. While the patch data width in the sub-scanning direction is several centimeters, the lighting of the beam is continued.

When the patch data is formed, density detection by the image density sensor is performed, and the light amount of the reference beam is adjusted so that the detected density of the patch data formed by the preset reference beam becomes equal to the preset image density. The process supply bias and the toner supply amount are controlled. When the density control with the reference beam set in advance is completed, the light amount of the beam other than the reference beam becomes equal to the set reference beam light amount using a PD (photo detector) which is a light amount detector built in the light source that emits each beam. The density of the image is controlled by controlling as needed.

First, the processing in the block diagram shown in FIG. 8 is performed. The detection signal of the image density sensor SE is taken into a port of the CPU corresponding to the image density sensor SE, and is stored in a register after AD conversion. The density data of the reference beam taken into the register is compared with the set image density data, and as a result, the CPU controls the light amount of the reference beam BM, the bias power supply 18 relating to the image density, and the toner supply control for controlling the toner supply amount. Each control value for the unit is specified as needed to control the density of the reference beam.

When the density control of the reference beam is completed, as shown in the block of FIG.
1, BM-2... BM-N are turned on, and the outputs of light amount detectors PD1, PD2.
Then, the image density control is performed by controlling the light amounts of the respective beams other than the reference beam so as to be the same as the set reference beam light amount.

[4] Example Corresponding to Claim 4 In the invention according to this example, the density control of the image performed by detecting the patch data density by the image density sensor includes various bias voltage controls related to the image forming process, toner control, and the like. Replenishment and light amount control of the beam as the image forming means are performed alone or in combination.

[5] An example corresponding to claim 5 The image forming apparatus according to this example provides a density of patch data formed by a preset one reference beam among a plurality of beams in an arbitrary region in the beam scanning direction. Is detected, and the image density control procedure is changed according to the comparison result between the detected density and the set image density.

If the detected density is lower than the set image density, control is performed so as to increase the image density by controlling the process bias value and supplying toner. At this time, if necessary, control is performed so that the light amounts of the beams other than the reference beam become equal to the reference beam light amount.

The light quantity of the reference beam is controlled only when the image density does not reach the set value even by the process bias value control and toner replenishment. When the reference beam light amount is controlled, control is performed so that the remaining beam light amounts are also equal to the reference beam light amount.

On the other hand, when the detected density is higher than the set image density, the set reference beam light amount is controlled to lower the image density. After reducing the set reference beam light amount to set the image density to a set value, the remaining beam light amount is controlled to be the same as the reference beam light amount. Only when the image density does not reach the set value even within the set light amount range of the beam, the process bias value control and the toner supply control are performed to control the image density. [6] Example Corresponding to Claim 6 An example of the image forming apparatus according to this example is shown. The beam scanning direction is divided into a plurality of patch data forming areas for image density control corresponding to each beam, and the same number of image density sensors as the beams are provided corresponding to each patch data forming area to form patch data. Then, the density detection by the image density sensor is simultaneously performed on each beam, and the reference beam is set so that the detection density of the patch data formed by the preset reference beam and the detection density of the patch data formed by other than the reference beam become equal. Other beam powers are controlled as necessary.

Here, when there is a beam other than the reference beam whose light amount does not become the same as the reference beam amount within the set light amount range, the beam is determined to be deteriorated and its use as a writing beam is prohibited. However, when the number of beams is even (2n: n = 1, 2,...), The image forming operation is maintained as follows.

When the deteriorated beams are odd-numbered in the arrangement order in the sub-scanning direction, the use of all odd-numbered beams is prohibited and the image forming operation is maintained. At this time, the image data transfer clock frequency and image data in the main scanning direction are converted as necessary. Similarly, when the even-numbered beams are deteriorated, the even-numbered beams are prohibited from being used, and the image forming operation is maintained.

FIG. 10 shows an arrangement of image dots. The case of four beams will be described for ease of explanation.
In FIG. 10, a circle means a dot, a number in the dot (circle) indicates the order of image data, and 11 in the circle indicates the first line, that is, one pixel of line 1 (beam 1), 21 in the circle is the second line, that is, one pixel of line 2 (beam 2), 31 in the circle is the third line, one pixel of line 3 (beam 3), and 41 in the circle is four lines It means the eye, that is, one pixel of the line 4 (beam 1) (hereinafter, the same).

FIG. 10A shows a state in which an image is formed normally without a deteriorated beam, and FIGS. 10B and 10B show a state of image formation when the beam deterioration is found and even-numbered beams are thinned out. (C) and FIG. 10 (d).

FIG. 10B shows the case where the clock frequency and image data in the main scanning direction are used without being changed.
(C) is an example in which data in the main scanning direction is thinned out for each pixel as in the sub-scanning direction.

Further, the clock frequency is reduced by half to
The image data shown in FIG. 1C is expanded in the main scanning direction, and FIG.
0 (d) can also be used. FIG. 10 (c)
Although the dots appear to be spaced apart, the actual beam shape is an elongated ellipse in the sub-scanning direction, and by arranging the beams so that each dot overlaps in the sub-scanning direction, as described above, Even if the image is formed by thinning out, the image quality is not significantly reduced. [7] Example Corresponding to Claim 7 An example of the image forming apparatus according to this example will be described. In the same manner as described in the example corresponding to claim 6, if there is a beam other than the reference beam that does not have the same light amount as the reference beam within the set light amount range, the beam is determined to be deteriorated. Although the use as a writing beam is prohibited, when the plurality of beams are even (2n: n = 1, 2,...), The image forming operation is maintained as follows.

The plurality of beams are divided into a plurality of groups of adjacent beams having the same number of beams in accordance with the arrangement order of the deteriorated beams in the sub-scanning direction. At the same time, switching the image data to be supplied to the beam of the group that was supplied to the supply of the beam of the available group, and at the same time, reducing the image output speed (linear velocity) according to the number of beams that could not be used, to perform the image forming operation. maintain.

FIG. 11 shows an arrangement of image dots. The case of four beams will be described for ease of explanation.
The notation is based on FIG. FIG. 11A shows a state in which an image is normally formed without beam deterioration, and FIGS. 11B and 11C show image forming states in a case where beam deterioration is found and a beam is thinned out. Shown in

FIG. 11B shows the case where the beam of the line 1 which is the first (first in the arrangement order in the sub-scanning direction) line has deteriorated. FIG. 11C shows the case where the beam of the second line 2 has deteriorated. Is the case.

In FIG. 11B, the image is divided into four groups, one beam at a time, the first group (leading beam) is prohibited, the remaining three beams are used, and the linear velocity is reduced to 3/4. Perform formation.

In FIG. 11C, as shown in the figure, the beam is divided into two groups each of two beams, and the first group, that is, the beam 1 of the line 1 is prohibited from being used, and the image is formed only in the second group. The linear velocity at this time is reduced to 1/2.

If the beam on line 3 is deteriorated,
When the beam of the last fourth line 4 is deteriorated, the beam is divided into four groups as shown in FIG. 11 (b) and the beams used are limited.
As described above, the image formation is performed similarly by switching the data supply and changing the linear velocity.

FIG. 1 showing the state of the scanning line by each beam.
In FIG. 12, FIG. 12A shows a case where there is no deteriorated beam and four lines are simultaneously drawn by one (second) scan. In the next second scan, each line is moved in the sub-scanning direction by four pitches at an interline pitch starting from p1 (corresponding to line 1 in FIG. 11), and four lines are drawn starting from the position of p2.

FIG. 12B shows the case where the deteriorated first beam (corresponding to line 1 in FIG. 11) is prohibited from being used, and three lines (line 2 and line 3 in FIG. 11) are scanned in the first (first) scan. , Line 4) at the same time. In the next second scan, line 1 whose use is prohibited is changed to line 3
In the sub-scanning direction, three lines (line 2, line 3, and line 4 in FIG. 11) are simultaneously drawn by moving the sub-scanning direction by three pitches from p1 to p3 in order to overlap with.

In order to enable such writing, each line has a linear velocity of the photosensitive member 4 of 1 in the case of FIG.
Then, the linear velocity is reduced to 3/4 here. Thus, the line movement distance p1 to p3 for each scan = [FIG.
(P1−p2) × 3/4 in (a), and no line omission occurs due to prohibition of use of the deteriorated beam.

FIG. 12C shows the first and second (FIG. 1)
In the case where the use of these beams was prohibited due to the deterioration of the beams of line 1 and line 2 in 1)
Two lines (line 3 and line 4) are drawn in the second (eye) scan. In the next second scan, in order to make line 1 and line 2 which are prohibited from use overlap line 3 and line 2 overlap line 4, the line is moved in the sub-scanning direction by two pitches between lines p1 to p4 at a line pitch. 2 lines (line 3 and line 4 in FIG. 11) at the same time.

In order to enable such writing, each line has a linear velocity of the photosensitive member 4 in the case of FIG.
Then, the linear velocity is reduced to で は here. Thereby, the line movement distance p1 to p4 for each scan = [FIG.
(P1-p2) / 2 in (a), and line omission does not occur due to prohibition of use of the deteriorated beam.

FIG. 13 shows a method of supplying image data. FIG.
3 (a) is a normal case where there is no degraded beam. Image data to be output is buffered in a line memory or a frame memory and output to each beam according to a control signal.

In the case of four beams, line data is updated and supplied every four lines for each beam. Here, when the beam BM-1 is degraded as described above and the remaining three beams BM-2, BM-3 and BM-4 are used to form an image, as shown in FIG. The data output is switched so that the line data is updated and supplied to each beam. (In the figure: n = 1, 2, 3,...) Even when a plurality of beams have deteriorated, the same means can be used as long as the deteriorated beams can be grouped and collected as a use prohibition group as described above. [8] An example corresponding to claim 8 The image forming apparatus according to the present example detects the density of patch data formed by one preset reference beam among a plurality of beams in an arbitrary region in the beam scanning direction. When controlling the beam light amount, the process supply bias and the toner supply amount so that the detected density becomes equal to the preset image density, when the light source that emits the preset reference beam is deteriorated, a new reference is made from the remaining beams. Is selected to form patch data for image density control, and a single image density sensor provided in a patch data formation area is used to form a single beam selected as the new reference beam. The density of the patch data is detected to perform image density control, and the light amount of the remaining beam is controlled to be the same as the light amount of the new reference beam. It is intended to maintain.

[9] Example Corresponding to Claim 9 The image forming apparatus according to this example is an example in which the present invention is applied to an image forming apparatus called two stations. FIG. 14 shows an embodiment. This image forming apparatus has two image forming means (station 1, station 2) below an intermediate transfer belt 110 as an intermediate transfer member. Station 1,
The station 2 includes one image carrier (photoconductors 4a and 4b), writing means (polygon mirror 22, mirror M, etc.), and each of the image carriers (photoconductors 4a and 4b).
At least two developing means (24a, 24a 'for station 1) for developing an electrostatic latent image formed thereon by writing means (polygon mirror 22, mirror M, etc.);
Station 2 includes 24b and 24b ′) and a switching unit that selectively selects and drives these two developing units, and transfers the color images formed by the plurality of image forming units onto the intermediate transfer belt 110. Is an image forming apparatus that generates an image of a plurality of colors by superimposing.

In the following description of the structure, the constituent members of the station 1 are indicated by adding a suffix a to the numerals, and the constituent members of the station 2 are indicated by the suffix b to the numerals. , And the contents are the same, so station 1 will be mainly described and station 2 will not be described.

The writing means arranges a plurality of beams emitted from the respective light sources in the sub-scanning direction on the photoconductors 4a and 4b by using the same polygon mirror 22 and scans the beams at the same time at high speed, as described above. A full-color image is output.

Further, as for the constituent members, the developing means 24a is provided with a stirring means and developing rollers 26a, 26a ', and the developing rollers 26a', 26a, the intermediate transfer belt 110 around the photosensitive member 4a in the direction of rotation. , A charging brush 28a, a writing beam irradiation unit, and the like. Further, the intermediate transfer belt 110 facing the photoconductor 4a
A transfer brush 29a is provided on the back side of the transfer brush 29a.

The intermediate transfer belt 110 is stretched between two rollers. On the upper stretch surface, the above-described image density sensor 30 according to the present invention and the rotational position of the intermediate transfer belt 110 are detected. A belt mark sensor 32 is provided.

Further, a cleaning blade 130 is provided opposite to the right pulley supporting the intermediate transfer belt 110 so as to be able to contact and separate from the belt.
A paper transfer roller 34 is provided so as to be able to contact and separate from the belt in opposition to the pulley on the left side that supports the belt.

The paper stored in the paper feed cassette 36 is fed out from the paper feed roller 46, follows the paper feed path indicated by the dashed line, passes through the registration roller 38, and transfers the image on the intermediate transfer belt 110 by the paper transfer roller 34. The toner image is transferred and fixed via a fixing roller 40, and is discharged via a conveyance roller to a discharge tray 42.
Is discharged on top. Reference numeral 44 denotes a manual feed roller pair for manual feed, reference numeral 48 denotes an engine board, and reference numeral 50 denotes an image data storage unit.

Assuming that the total length of the intermediate transfer belt 110 is L and the length corresponding to the length of the intermediate transfer belt 110 in the moving direction at the time of paper transfer is m, the outline of the color image forming process when L = m + α is as follows. It is. (1). In the station 1, the color A developed by the developing means 24a 'is transferred onto the intermediate transfer belt 110. (2). The B color developed by the developing unit 24b in the station 2 is overlaid and transferred onto the A color on the intermediate transfer belt to obtain A and B color toner images, and the A and B color toner images are developed in the station 1 by the developing unit 24a. C
The colors are superimposed and transferred to obtain A, B, and C toner images on the intermediate transfer belt 110. At this point, the intermediate transfer belt 110 makes one rotation.

(3). A, B, C obtained in step (2)
In the station 2, the developing means 24
The D color developed by b ′ is transferred to A, B,
The full-color image is transferred to the paper transfer roller 34 by superimposing and transferring the C color.
To transfer onto paper (first sheet). The transfer to the first sheet is performed during the second rotation of the intermediate transfer belt 110. (4). When a plurality of color prints are to be taken, the A-color toner image is transferred by the station 1 and the B-color toner image is superimposed by the station 2 at the same time as the transfer of the D-color toner image by the station 2 in the step (3). Transfer to obtain A and B color toner images.

(5). The C toner image is added to the A and B toner images obtained in the process (4) by the station 1.
Subsequently, the D color toner image is superimposed and transferred by the station 2 and is transferred to a second transfer paper. The transfer to the second sheet is performed at the fourth point of the intermediate transfer belt 110. (6). The third and subsequent prints are obtained at the sixth rotation of the intermediate transfer belt 110 by repeating the steps from the step (3).

In the above description, for example, color A is magenta,
B is yellow, C is cyan, and D is black.

An example of the switching means for selectively selecting and driving the developing means will be described.

Referring to FIG.
The gear 82G is a rotating shaft 4 of the developing roller driving motor 90-1.
Directly connected to 00-1. The rotation shaft 400-1 is also a rotation fulcrum of the rotation member 64-1. A gear 80G and a gear 81G are meshed with the gear 82G.
The gear 81G meshes with the first gear 74G according to the turning position of the turning member 64-1, and at this time, the mesh between the gear 80G and the second gear 79G is released. Alternatively, the gear 80
G meshes with the second gear 79G, at which time the mesh between the gear 81G and the first gear 74G is released.

In order to perform such switching, a cam follower 402 is provided at a tip of an arm portion extending in a radial direction from the rotation shaft 400-1 at a part of the rotating member 64-1, and the cam follower 402 is attached to the eccentric cam 404. The eccentric cam 404 is rotationally driven by a motor 408 as a switching drive source.

With this configuration, the turning member 64-1 is swung in accordance with the turning position of the eccentric cam 404, and the gear 80
G and 81G mesh with the first gear 74G and the second gear 79G, and switch to a non-meshing state.

The first gear 74G is meshed with a gear for driving the developing roller 26a 'via an intermediate gear train (not shown). The second gear 79G is meshed with a gear for driving the developing roller 26a via an intermediate gear train (not shown).

Therefore, according to the rotational position of the eccentric cam 404, the developing roller 26a 'is driven without driving the developing roller 26a'.
a, or the developing roller 26a 'can be driven without driving the developing roller 26a.

Here, the eccentric cam 404, the spring 406, the rotating member 64-1, the gears 80G and 81G, and the first gear 7
4G, the second gear 79G to the developing rollers 26a, 26
The gear train up to the a 'driving gear constitutes switching means for selectively selecting and driving the developing means. The driving and non-driving of the developing rollers 26b and 26b 'for the station 2 are also switched by the same switching means.

[10] An example corresponding to claim 10 The image forming apparatus according to this example controls the light amount of the beam using the patch data as solid data, regulates the maximum image density, and varies the pulse width for modulating and driving the beam. The gradation expression is performed by changing the beam exposure time (dot shape) on the image carrier by changing the beam lighting time. Just set the drive current to be supplied to the light source to obtain the required light amount, which is necessary at the time of power (drive current) modulation.
There is no need to determine the bias current change due to aging and the slope of the current-light output characteristics.

[0075]

According to the first aspect of the present invention, since a plurality of densities are simultaneously detected by a plurality of patch data, image density control can be performed in a short time.

According to the second aspect of the present invention, since the image density of a plurality of beams is controlled by one image density sensor, the size and cost of the image forming apparatus can be reduced.

According to the third aspect of the present invention, since the image density of a plurality of beams is controlled by one image density sensor, the size and cost of the image forming apparatus can be reduced. For the beams other than the reference beam, the density control is performed only by the light amount without creating the patch data, so that the image density control can be performed in a short time. In addition, it is not affected by process condition variations.

According to the fourth aspect of the present invention, the size and cost of the image forming apparatus can be reduced, and the image density can be controlled in a short time and with high accuracy.

According to the fifth aspect of the present invention, the life of the light source is extended by controlling the drive current of the light source that cannot be replaced preferentially, so that the image formation can be performed with stable image quality. The device can be used for a long time.

According to the sixth aspect of the present invention, even when the light source is deteriorated, the image forming apparatus can be continuously used by reducing the image density.

According to the seventh aspect of the present invention, even when the light source is deteriorated, the image forming apparatus can be continuously used by reducing the image output speed.

According to the eighth aspect of the present invention, even when the light source is deteriorated, the image forming apparatus with stable image quality can be continuously used by lowering the image density or lowering the image output speed. .

According to the ninth aspect of the present invention, a full-color image having a stable image density can be output at a high speed by a small / low-cost image forming apparatus.

According to the tenth aspect of the present invention, it is possible to obtain an image forming apparatus capable of outputting a tone image with good reproducibility at a high speed even when the use environment changes.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of an image forming unit in an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing writing beams arranged on a photosensitive member in a sub-scanning direction.

FIG. 3 is a front view illustrating an example of an image forming unit of the image forming apparatus.

FIG. 4 is a timing chart showing the lighting timing of each beam.

FIG. 5 is a processing block diagram of light amount control of a beam according to an output of an image density sensor.

FIG. 6 is a timing chart showing lighting timing of a beam for patch data.

FIG. 7 is a processing block diagram of light amount control of a beam according to an output of an image density sensor.

FIG. 8 is a processing block diagram of light intensity control of a beam according to an output of an image density sensor.

FIG. 9 is a block diagram for controlling image density.

10A is a diagram showing a sheet for image formation when an image is formed normally without a degraded beam, and FIG.
FIGS. 10B, 10C, and 10D are views showing the state of image formation when beam deterioration is found and even-numbered beams are thinned out.

FIG. 11A is a diagram showing an image dot array when an image is formed normally without beam deterioration, and FIGS. 11B and 11C show beam deterioration. FIG. 5 is a diagram illustrating a state of image formation when a beam is thinned out.

12A is a diagram of a write line when there is no deteriorated beam, FIG. 12B is a diagram of a write line when the use of the first deteriorated beam is prohibited, and FIG. () Is a drawing of a write line when the use of the first and second beams is prohibited.

FIG. 13A is a view for explaining a method of supplying image data in a normal case where there is no deteriorated beam, and FIG.
FIG. 3 is a diagram illustrating a method of supplying image data in which data output is switched so that line data is updated every three lines and supplied to each beam.

FIG. 14 is a configuration diagram of an image forming apparatus.

FIG. 15 is a front view of a main part of a switching unit of the developing unit.

[Explanation of symbols]

 4 Photoconductor 11 Intermediate transfer belt

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/043 G03G 21/00 372 21/00 500 B41J 3/00 D 21/14 F-term (Reference) 2C362 AA07 AA10 AA54 AA65 BA48 2H027 DA09 DA10 DE02 DE10 EA02 EA05 EA06 EA20 EC03 EC06 EC07 EC10 EE03 EK11 EK15 2H030 AA03 AB02 BB02 BB13 BB24 BB33 BB34 BB36 BB38 BB42 2H076 AB06 AB01 DA19 DA19

Claims (10)

[Claims] An image forming apparatus for arranging a plurality of beams emitted from a light source in a sub-scanning direction on an image carrier, and simultaneously forming a plurality of lines of latent images on the image carrier by one beam scanning. The beam scanning direction is divided into patch data forming areas for image density control corresponding to the respective beams, and the same number of image density sensors as the beams are provided corresponding to the respective patch data forming areas. The density of the patch data formed by each beam formed on the intermediate transfer member is detected by the image density sensor, and the density of the patch data formed by the predetermined reference beam is changed to the patch data formed by the beam other than the reference beam. An image forming apparatus, wherein the density of an image is controlled by controlling the light amounts of beams other than the reference beam so that the densities become equal. 2. An image forming apparatus for arranging a plurality of beams emitted from a light source in a sub-scanning direction on an image carrier, and simultaneously forming a plurality of lines of latent images on the image carrier by one beam scanning. The patch data for controlling the image density corresponding to each beam is sequentially formed in the same area in the beam scanning direction, and a single image density sensor provided in the patch data formation area is used to form the patch data on the image carrier or in the middle. By detecting the pattern data density of each beam formed on the transfer body,
The density of the image is controlled by controlling the light quantity of the beam other than the reference beam so that the patch data density formed by the beam other than the reference beam becomes equal to the density of the patch data formed by the preset reference beam. Image forming apparatus. 3. An image forming apparatus for arranging a plurality of beams emitted from a light source in a sub-scanning direction on an image carrier, and simultaneously forming a plurality of lines of latent images on the image carrier by one beam scanning. A predetermined one of the plurality of beams.
One reference beam forms patch data for image density control, and a single image density sensor provided in the patch data formation area uses the one reference beam set in advance on the image carrier or the intermediate transfer member. By detecting the density of the patch data to be formed, controlling the density of the image of one preset reference beam, and controlling the light quantity of the remaining beam to be the same as the light quantity of the preset one reference beam, An image forming apparatus for controlling the density of an image formed by a beam. 4. An image forming apparatus according to claim 1, wherein the density control of the image performed by detecting the patch data density with an image density sensor includes various bias voltages related to an image forming process. An image forming apparatus which performs control, toner replenishment, and light amount control of a beam serving as an image forming means alone or in combination. 5. An image forming apparatus according to claim 1, wherein when the image density detected by the image density sensor is lower than a preset density, priority is given to bias control and toner supply. An image forming apparatus that performs density control by performing a density control with priority given to a light quantity control of a beam when an image density detected by an image density sensor is higher than a preset density. 6. An image forming apparatus for arranging 2n (n: integer) beams emitted from a light source in a sub-scanning direction on an image carrier and simultaneously forming a plurality of lines of latent images by one beam scanning. When the light source is deteriorated and all of the 2n beams cannot be used for image formation, odd beams are determined according to the order in which the 2n beams are arranged in the sub-scanning direction, and the deteriorated beams coincide with the odd beams. An image forming apparatus having means for prohibiting the use of the image forming apparatus and maintaining the image forming operation. 7. An image forming apparatus for arranging 2n (n: integer) beams emitted from a light source in a sub-scanning direction on an image carrier, and simultaneously forming latent images of different lines by one beam scanning. When the light source deteriorates and all of the 2n beams cannot be used for image formation, the 2n beams are equally divided into a plurality of groups, and all beams in the group including the deteriorated beams are prohibited. At the same time, switching the data to be supplied to the use-prohibited beam to supply to the usable beam, and lowering the image output speed according to the number of beams whose use is prohibited to maintain the image forming operation. Image forming apparatus. 8. An image forming apparatus according to claim 6, wherein a density of patch data formed by one preset reference beam among a plurality of beams is detected to perform image density control, and the remaining beams are controlled. In an image forming apparatus that controls the light amount of the reference beam to be the same as the light amount of the preset one reference beam to control the density of the image with the remaining beams, if the light source that emits the preset reference beam is deteriorated, A new reference beam is selected from among the beams, patch data for image density control is formed with the selected reference beam, and a single image density sensor provided in a patch data formation area is used to select the selected reference beam. The density of the patch data formed by one reference beam is detected and image density control is performed, and the light amount of the remaining beam is determined based on the light beam of the beam newly selected as the reference beam. An image forming apparatus, wherein the same amount of light is controlled to maintain an image forming operation. 9. The image forming apparatus according to claim 1, further comprising: a plurality of image forming units arranged to face a moving surface of the intermediate transfer body, wherein one image forming unit is provided. An image carrier, one writing unit, at least two developing units for developing an electrostatic latent image formed by the writing unit on the image carrier, and switching for selectively selecting and driving the developing unit And an image forming apparatus. 10. The image forming apparatus according to claim 1, wherein the patch data is set as solid data, and after controlling the light amount by the patch data, various bias voltages involved in an image forming process are provided. An image forming apparatus characterized in that image density is controlled by controlling and replenishing toner, and gradation expression of an image is performed by changing a pulse width for controlling a lighting time of a beam.