JPH09114257A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reduction in image density and occurrence of irregularity in an image prior to the reduction in the image density by detecting if a devel oper is in a state liable to generate the reduction in image density before the image density is reduced and supplying toner to a developer, based on the detection. SOLUTION: A patch image is formed on the surface of a recording paper 71 in such a manner that printing conditions for the path image and an effective image formed in an effective image region are made different to make the image density of the patch image higher than that of the effective image. This patch image is detected by a density detecting sensor 87. Then, a printer control part 1 controls a toner supplying device, based on the detection value, to supply the toner to the developer in a developer tank 64 by the toner supplying device.

Description

Detailed Description of the Invention

[0000]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile and a printer, and more specifically, it detects the image density of an image formed on a recording material and, based on the result, a developer. The present invention relates to an image forming apparatus that replenishes toner.

[0001]

2. Description of the Related Art As a conventional image forming apparatus, there is known an image forming apparatus which is provided with a conveying means for conveying a recording material and a developing means for developing a latent image with a developer to form a toner image on the surface of the recording material. ing. In this image forming apparatus, the toner in the developer is consumed as the developing operation is continued, and the toner concentration of the developer is lowered. When the toner density decreases, the image formed on the recording material starts to have unevenness.
Then, when the toner density further decreases, the density of the image formed on the recording material decreases. Therefore, in order to prevent the deterioration of the image quality due to the decrease of the toner concentration, it is necessary to replenish the developer with the toner before the deterioration of the image quality occurs.

Therefore, when the image density detecting means detects that the image density of the image formed on the recording material has decreased, the toner replenishing device replenishes the toner in the developer tank with toner, and An image forming apparatus is known in which the toner density is prevented from dropping too much (Japanese Patent Laid-Open No. 62-1441).
84). According to this apparatus, it is possible to prevent the toner density of the developer from further decreasing and the image density of the image formed on the recording material from further decreasing.

[0003]

However, this apparatus detects a decrease in the image density that has already occurred and then replenishes the toner. Therefore, prior to the actual decrease of the image density, it is detected that the developer is likely to cause the decrease of the image density,
By supplying toner to the developer at that stage, it is impossible to prevent the toner concentration of the developer from being lowered, that is, the image density of the image to be formed from being lowered. Therefore,
In this apparatus, toner replenishment is performed after the image density has already decreased, so it is possible to prevent the occurrence of image unevenness that occurs prior to the image density decrease when the toner density of the developer decreases. Can not.

Therefore, the present applicant previously provided a patch image for image density detection outside the effective image area with a density higher than the maximum image density of the effective image formed in the effective image area of the recording material. An image forming apparatus is proposed in which toner is replenished before the density of an effective image in the effective image area is decreased by forming the image and detecting the decrease in the image density of the patch image. The present invention further embodies this.

The present invention has been made in view of the above points, and it is an object of the present invention that the developer is liable to cause a decrease in the image density before the decrease in the image density occurs. It is possible to prevent the decrease in the image density by supplying the toner to the developer based on the detection, and it is also possible to prevent the occurrence of the image unevenness that occurs prior to the decrease in the image density. An object is to provide an image forming apparatus.

[0006]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention comprises a conveying means for conveying a recording material and a latent image forming means for forming a latent image on the surface of the recording material. A developing device that develops a latent image using a developer to form a toner image on the recording material, a developer tank that supplies the developer to the developing device, and a toner that supplies toner to the developer tank. A replenishing device, a patch image forming unit for forming a patch image for image density detection in a patch area provided outside the effective image region of the recording material, and the recording material formed by the patch image forming unit. Image density detecting means for detecting the image density of the patch image, and the toner replenishment amount replenished by the toner replenishing device to the developer in the developer tank based on the detection result by the image density detecting means. A toner supply amount controlling means for controlling,
In the image forming apparatus having the above, the patch image forming unit sets the printing conditions for the both so that the image density of the patch image is higher than the image density of the effective image formed in the effective image area. It is characterized by being configured to be different.

An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the latent image forming means is formed by using a latent image carrier, and the latent image carrier has the above-mentioned effect. It is characterized in that the patch area outside the image area is charged with a charging potential higher than that of the effective image area.

An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first aspect, wherein the latent image forming means is formed by using a latent image carrier, and the latent image carrier has the above-mentioned effect. The bias potential when transferring the latent image in the patch area outside the image area to the recording material is higher than the latent image transfer bias potential when transferring the latent image in the effective image area to the recording material. It is characterized by being configured in.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the latent image forming means is constituted by using an exposing means, and the patch latent image is within the effective image area. It is characterized in that it is formed with an exposure amount higher than the exposure amount for forming a latent image having the maximum image density of the effective image formed in the above.

An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the first aspect, wherein the conveying means forms a developing speed for developing the patch latent image portion within the effective image area. It is characterized in that it is configured to be slower than the developing speed at the time of developing the latent image.

An image forming apparatus according to a sixth aspect is the image forming apparatus according to the second, third, fourth, or fifth aspect, in which the patch images are present in the vicinity of the front end portion and the rear end portion of the recording material in the transport direction. It is characterized in that they are formed respectively.

According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth aspect, the patch image is continuously formed from the vicinity of the leading end to the vicinity of the trailing end of the recording material in the transport direction. It is characterized by that.

In the image forming apparatus according to any one of claims 1 to 7, a printing condition different from the printing condition of the effective image such that the density is higher than the maximum density of the effective image formed in the effective image area. The image density of the patch image formed under the conditions is detected by the image density detecting means. Then, prior to the fact that the density of the effective image actually decreases by this detection, it is detected that the decrease in the image density is likely to occur. Further, the toner replenishing device replenishes the toner to the developer tank based on the detection result of the image density detecting means. Therefore, it is possible to prevent the deterioration of the effective image, and it is possible to prevent the occurrence of image unevenness in the effective image area that occurs prior to the decrease of the image density of the effective image. Hereinafter, such an operation will be described with reference to FIG.

FIG. 2 is a graph showing the relationship between the number of image formations and the image density, the characteristic line a shows the relationship between the number of image formations and the image density in the effective image, and the characteristic line b.
Shows the relationship between the number of images formed and the image density in the patch image. In this apparatus, if the initial toner density is higher than a certain value, an effective image can be obtained even if the toner density is lowered until image formation of a fixed number of n1 images is performed as indicated by the characteristic line a. The concentration of does not decrease. When image formation is further performed from n1 sheets, the toner density of the developer further decreases, and the image density of the effective image starts to decrease. Therefore, in the conventional apparatus, the decrease in the image density is detected when the number of formed images is n2, and the toner is replenished to the developer. However, prior to the decrease in the image density, unevenness occurs in the effective image on which the recording material after the n3th image formation (area A) is formed, and the occurrence of this image unevenness is detected by the conventional apparatus. I couldn't.

Therefore, in the image forming apparatus according to the first aspect, a patch portion image having a higher density than the effective image formed in the effective image area is formed in the patch portion area, and the image density of the patch portion image is detected. The toner is replenished to the developer based on the detected value. That is, as shown by the characteristic line b, the decrease in the density of the patch image occurs at the time of the n4th sheet, which is before the n3th sheet where unevenness occurs in the effective image. Therefore, in this apparatus, the image density detection unit detects the decrease in the image density of the patch image, and at this time, the toner is replenished to the developer. Therefore, in this device,
Toner is supplied to the developer before unevenness occurs in the effective image. However, in the patch portion image, unevenness is also generated in the area (next area) of the n5th sheet before the n4th sheet before the image density is reduced. However, the patch image is used exclusively for detecting the image density, and even if unevenness occurs, it does not cause a problem.

FIG. 3 is a graph showing the relationship between the latent image potential of the recording material and the image density, where the vertical axis shows the image density and the horizontal axis shows the latent image potential. According to this graph, it can be seen that the image density becomes higher as the latent image potential on the recording material becomes higher, and the image density does not further rise at a certain latent image potential. Here, in order to form the image density of the patch image to be higher than the maximum image density of the effective image, the latent image potential of the effective image may be set to p1 and the latent image potential of the patch image may be set to p2. By thus changing the printing conditions for the effective image and the patch image, the image densities d1 and d2 at this time are changed.
2 correspond to the characteristic lines a and b in FIG. 2, respectively. Therefore, when the latent image potential p2 of the patch image is set higher than the latent image potential p1 of the effective image, the solid image density decreases when the toner density decreases. The high patch image density decrease occurs earlier than the effective image density decrease. Therefore, by detecting the density decrease of the patch image by the density detecting means, it is possible to detect the decrease of the toner density before the image unevenness occurs.

Particularly, in the image forming apparatus according to the second aspect, the portion on the latent image carrier on which the latent image for the patch image is formed is higher than the portion on which the effective image is formed in the effective image area. The latent image carrier is charged so as to have a charging potential. Then, a latent image and a patch latent image of an effective image are formed on each of these portions, and a latent image transfer bias is applied to the latent image carrier to transfer the latent image on the latent image carrier onto a recording material. To do. Thus, when the latent image on the recording material is developed by the developing device, the image density of the patch image is higher than the maximum image density of the effective image formed in the effective image area.

Particularly, in the image forming apparatus of the third aspect, the latent image transfer bias for transferring the latent image from the latent image carrier to the recording material is more than the transfer bias of the effective image formed in the effective image area. Is also applied so that the transfer bias of the patch image becomes higher. As a result, when the latent image on the recording material is developed by the developing device, the image density of the patch image is higher than the maximum image density of the effective image formed in the effective image area.

Particularly, in the image forming apparatus according to the fourth aspect, the exposure means causes the patch latent image formed on the latent image carrier to have the maximum image density of the effective image formed in the effective image area. The latent image carrier is exposed with an exposure amount that is higher than the exposure amount when the latent image is formed. By developing the latent image formed by this exposure by the developing device, the image density of the patch image is higher than the maximum image density of the effective image formed in the effective image area. .

FIG. 4 is a graph showing the relationship between the developing speed of the recording material and the image density, where the vertical axis represents the image density and the horizontal axis represents the developing speed of the recording material. According to this graph, it can be seen that the image density becomes higher as the developing speed of the recording material becomes slower, and becomes darker at a certain speed. Here, in order to form the image density of the patch image to be higher than the maximum image density of the effective image, the development speed of the effective image may be set to v1 and the development speed of the patch image may be set to v2. By thus changing the printing conditions for the effective image and the patch image, the image densities d1 and d2 at this time are changed.
2 correspond to the characteristic lines a and b in FIG. 2, respectively. Therefore, when the developing speed v2 of the patch image is made slower than the developing speed v1 of the effective image, when the toner density decreases, the patch image of the solid image density is high. The density decrease occurs earlier than the density decrease of the effective image. Therefore, by detecting the density decrease of the patch image by the density detecting means, it is possible to detect the decrease of the toner density before the image unevenness occurs.

Therefore, particularly in the image forming apparatus of claim 5, when the conveying means develops the patch latent image at a speed higher than the developing speed at which the latent image formed in the effective image area is developed. By transporting the recording material so that the developing speed is slowed, the image density of the patch image is higher than the maximum image density of the image formed in the effective image area.

Further, in the image forming apparatus according to the sixth aspect, the image density detecting means detects the image density in the patch image formed near the leading end of the recording material in the transport direction. Then, based on the detection result, the toner replenishing device replenishes the developer in the developer tank with toner. afterwards,
The image density detecting means detects the image density of the patch image formed in the vicinity of the trailing edge of the recording material in the conveyance direction by the developer supplied with the toner, and the image unevenness is caused by the toner supply performed earlier. Check if it has been resolved.
Then, when the image unevenness is not eliminated, the toner is replenished to the developer again at this point.

Further, in the image forming apparatus according to the seventh aspect, the image density detecting means detects the image density in the patch image which is continuously formed from the vicinity of the leading end to the vicinity of the trailing end of the recording material in the transport direction. . Then, based on the detection result, the toner replenishing device replenishes the developer in the developer tank with toner. Therefore, even if the effective image is being formed, if the image density is lowered, the toner is immediately replenished to the developer at that point. (Hereinafter, margin)

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] A first embodiment in which the present invention is applied to a color printer which is a wet image forming apparatus will be described below. FIG. 5 is a front view showing a schematic configuration of the color printer according to this embodiment. An electrostatic recording sheet (hereinafter referred to as a recording sheet) 71 as a recording material is wound in a roll shape with the recording surface facing outside, and is attached to the printer body as a recording sheet roll 70 by a paper tube holder (not shown). A flat surface portion 11b is formed on a part of the outer peripheral portion 11a of the clamp drum 11 as a conveying means for mounting the recording paper 71 fed from the recording paper roll, and the flat surface portion 11b includes
The clamp claw 12 as a recording paper fixing member that holds the leading edge of the recording paper 71, and the flat surface portion 11b when the recording paper 71 is ejected
An eject pin 13 for lifting the upper recording paper 71 is provided. The clamp claw 12 and the eject pin 13 are integrally attached to respective rotary shafts provided inside the clamp drum 11, and the respective rotary shafts project outward from the end surface of the clamp drum 11. Then, the opening / closing operation of the clamp claw 12 and the eject pin 13
In order to perform the in-and-out operation of the clamp drum 11, a cam-shaped lever (not shown) is attached to the shaft end of each rotating shaft outside the end surface of the flange portion of the clamp drum 11, and the cam-shaped lever is attached to the side plate of the printer. A pin (not shown) that moves in the rotation axis direction of the clamp drum 11 is provided so as to make contact with the lever of the clamp drum 11 as needed.

When mounting the recording paper 71 on the clamp drum 11, first, the rotation of the clamp drum 11 is temporarily stopped when the flat surface portion 11b reaches the paper feeding position (almost the uppermost position). At this time, the clamp claw 12 is open.
When the front end of the recording paper 71 is inserted into the nip portion of the paper feed roller 74 via the guide roller 72 and the cutter 73, the front end is detected by a paper sensor (not shown). Then, the leading end of the recording paper 71 hits the clamp claw 12 to such an extent that it slightly buckles. After that, when the clamp drum 11 rotates in the direction of the arrow, the cam-shaped lever of the clamp claw 12 and the pin on the side plate side of the printer are disengaged, the clamp claw 12 is closed, and the recording paper 71 is gripped. When the drum 11 rotates, the recording paper 7
1 is wound around the surface of the clamp drum 11. The clamp drum 11 is temporarily stopped when it rotates to an angle at which the recording paper 71 is wound up to a predetermined length, and the cutter 73 operates to separate the recording paper 71 from the roll section 70 side.

Around the clamp drum 11, a photoconductor drum 21 as an image carrier, an exposure device for exposing the photoconductor drum 21 to the photoconductor, and an electrostatic latent image transferred onto the recording paper 71 are provided. A wet developing device or the like for developing using a developing solution in which toner is dispersed in a liquid carrier is provided.

The above-mentioned exposure apparatus includes a laser diode (not shown), a polygon mirror 31 and a drive motor for the polygon mirror 31, a beam expander (not shown), and f-.
a lens group 32 such as a θ lens and a cylindrical lens,
First mirror 33, second mirror 34, synchronization detection mirror 3
5, the synchronization detection sensor 36 and the like. The laser light emitted from the LD is reflected by the surface of the polygon mirror 31,
The lens is narrowed down through the lens group 32, and the first mirror 33,
The laser light focused by the second mirror 34 and focused reaches the surface of the photoconductor drum 21, whereby the recorded image is written on the photoconductor drum 21 as an electrostatic latent image. L
The optical path length from D to the surface of the photoconductor drum 21 is 3
The diameter of the laser beam narrowed by 2 is set to be the minimum. In the present embodiment, the LD, the polygon mirror 31, the lens group 32 and the like are integrally formed on a base, and the optical path length is adjusted by moving the base in the left-right direction in FIG.

The electrostatic latent image formed on the photoconductor drum 21 by the exposure device is transferred onto the recording paper 71 between the clamp drum 11 and the electrostatic latent image formed on the photoconductor on the recording paper 71. The electrostatic latent image is transferred to form an electrostatic latent image that is in a mirror image relationship with the electrostatic latent image formed on the photosensitive drum. The electrostatic latent image transferred to the recording paper 71 is transferred by a slit developing head (hereinafter referred to as a developing head) 60 of a wet developing device.
It is developed with the developing solution 10 and visualized.

FIG. 6 shows a simplified structure of the wet developing device.
Shown in The wet developing device will be described later. This wet developing device is provided with a developing head 6
0, suction pump 61, solenoid valve 62, developer tank 64,
It is composed of a developer supply pipe 65, a developer recovery pipe 66, and the like. The developing head 60 includes yellow (y), magenta (m), cyan (c), black (b)
k), there are five special colors (sp), and they are formed in a shape so as to come into close contact with the surface of the clamp drum 11, and are radially arranged with a distance of about 2 mm from the clamp drum 11 when not developing. . Further, at least one developing groove 60a extending in the axial direction of the clamp drum 11 is engraved on the surface of the developing head 60 facing the clamp drum 11.

As shown in FIG. 7, cams 50 of the same shape are provided at both ends of the developing head 60 in the longitudinal direction, and each cam shaft 50a is synchronized by a developing device vertical movement motor and a chain (not shown). It is driven to rotate. The cam 50 has such a shape that the developing heads 60 can be moved up and down separately for each 1/10 rotation. Also,
The cam follower 52 is fixed to the fixed shaft 53 by the developing head 60.
The cam follower 52 is attached at one end thereof so as to be rotatable around a rotation shaft 54 on the printer body side. And the cam follower 52
The roller 55 attached to the other end of the developing device is in contact with the outer peripheral surface of the cam 50, and is between the pin (not shown) provided on the printer body side and the pin 60b at the lower end of the developing head 60. By the spring 51 stretched around the developing head 6,
0, the cam follower 52 is pressed against the cam 50, so that the developing head 6 is rotated according to the rotation of the cam 50.
0 moves up and down. In FIG. 7, the reference numerals of the members provided corresponding to the colors of yellow, magenta, cyan, black, and special colors are y, m, c, bk, and s, respectively.
The subscript of p is attached.

At the time of development by the above-mentioned wet developing device, FIG.
As shown in FIG. 3, when the clamp drum 11 rotates in the direction of the arrow and the leading edge of the recording paper 71 on which the electrostatic latent image is formed passes a position facing the developing head 60, a cam shaft is driven by a drive motor (not shown). 50a is rotated by 1/10 rotation,
The developing head 60 is pressed against the surface of the clamp drum 11 via the cam 50 fixedly mounted on the cam shaft 50a, and is brought into close contact with the recording paper 71.

Then, the developing head 6 is moved by the recording paper 71.
With the development groove 60a of 0 being substantially sealed, the suction pump 6
1 makes the sealed developing groove 60a negative pressure,
The developer 10 is the developer tank 64, the developer supply pipe 6
5, the developing solution is supplied to the developing groove 60a of the developing head 60 by circulating among the developing head 60, the developing solution recovery pipe 66, the suction pump 61, and the developing solution tank 64.
The electrostatic latent image transferred on the recording paper 71 is developed.

Then, after the rear end of the image forming portion of the recording paper 71 has passed the position facing the developing head 60, the electromagnetic valve 62
The supply of the developing solution 10 is stopped by the
A squeeze of 0 is performed. After this squeeze ends, the suction pump 61 is stopped and the cam shaft 50a moves to 1/1
The development head 60 rotates 0 revolutions, and the developing head 60
Separated from 1. At this time, if the squeeze is not complete, the developing solution 10 remains on the rear portion of the recording paper 71, so the blotter roller 41 completely removes the remaining solution. Further, the recording paper 71 and the blotter roller 41 are dried by the fan 42.

After the above-mentioned development, the residual potential remains on the recording paper 71. In the next step, in order to prevent color mixture, the static elimination scorotron 43 removes the residual potential to remove the residual potential. When the development by all the developing heads 60 is completed, the clamp drum 11 is driven to the paper discharge position, the clamp claws 12 are opened, and the eject pin 13 is released.
Is ejected, the leading end of the recording paper 71 is lifted from the clamp drum 11, and the recording paper 71 is ejected to the paper ejection table 77.

FIG. 8 is a block diagram of a control system of the color printer according to this embodiment. As shown in FIG. 8, the control system includes a printer control unit 1, a printer input unit 2, a printer output unit 3, an operation unit 4, and a writing unit 5.

FIG. 9 is a flow chart of control of the color printer of this embodiment. When the power of the printer is turned on (step S1), the developing head 60, the clamp drum 11, and the electrostatic latent image writing section 5 are initialized (initial setting) (step S2). When the developing head 60 is initialized, the developing head home position sensor of the printer input unit 2 in FIG. 8 detects the home position between the developing head 60 and the cam 50. Here, the home position is
In this state, all the developing heads 60 are lowered, and the developing head 60 that is raised next is set to be the developing head 60 of the first color used in the image forming process. When the power of the printer is turned on, the output of the developing head home position sensor is checked. If the current position of the cam 50 is the home position, it does not operate. If it is not the home position, the cam shaft 50a The developing device vertical movement motor that is driving is turned on to operate the cam 50 to bring the cam 50 to the home position.

After the initialization of the developing head 60 is completed, the clamp drum 11 is initialized. The drum home position sensor of the printer input unit 2 shown in FIG. 8 detects the detection unit on the clamp drum 11. It is confirmed that the clamp drum 11 is rotationally driven and the rotational position (angle) of the clamp drum 11 can be recognized until the drum drive motor is turned on and the drum home position sensor detects the detection unit on the clamp drum 11. Then, the motor for the polygon mirror 31 turns off.
Then, the rotation of the polygon mirror 31 is stabilized, and then the power source of the LD drive system is turned on.

Next, the clamp drum 11 rotates, and at a predetermined position, the sheet feeding solenoid is turned on to open the clamp claw 12 and bring the clamp portion to a position right above. Is set to the paper feed standby state (step S3).

Next, in the paper feed standby state, the recording paper 71 is set on the clamp portion of the clamp drum 11, and the user depresses a predetermined switch of the operation portion 4 to place the recording paper 71 on the clamp drum 11. The winding operation is started. When the recording paper 71 is roll paper, a cutting operation is performed and the paper feeding operation is completed (step S4).

Next, the clamp drum 11 continues to rotate,
With the recording paper 71 wound, it is stopped at the READY position waiting for the start of the electrostatic latent image writing operation (step S5).

Next, the user presses a predetermined switch of the operation unit 4 to write and develop the electrostatic latent image (step S6). That is, when the user presses the switch, the clamp drum 11 starts to rotate, and the static elimination LEDs arranged around the photosensitive drum 21.
24, the power supply for the charging charger 23, etc. are turned on. The clamp drum 11 continues to rotate, the detection unit on the clamp drum 11 is detected by the write start position detection sensor, and the detected value is input to the printer control unit 1. At this time, a write start signal is output from the printer control unit 1 to the writing unit 5, and formation of an electrostatic latent image on the photoconductor drum 21 is started. Further, the electrostatic transfer power supply used for transferring the electrostatic latent image from the photosensitive drum 21 to the recording paper 71 on the clamp drum 11 is turned on. After the formation of the electrostatic latent image for one sheet of recording paper 71 and the electrostatic transfer are completed by the above operation, the power supply for the charging charger 23 and the electrostatic transfer power are turned off, and the electrostatic latent image forming operation is performed. finish.

The leading edge of the electrostatic latent image on the recording paper 71 is formed just before the photosensitive drum 21 at the time when the electrostatic latent image forming operation is completed, and the clamp drum 11 continues to rotate, The clamp portion of the clamp drum 11 is sent to the position of the developing head 60. 5 developing heads 6
When the developing head to be used out of 0 (hereinafter referred to as an active developing head) reaches the developing head raising position between the clamp portion on the recording paper 71 and the leading end portion of the electrostatic latent image, the drive motor for the cam shaft 50a. Is turned on to raise the active developing head. At this time, the clamp drum 11
There is a method of temporarily stopping the process and waiting for the active developing head to rise, and a method of raising the active developing head without stopping the clamp drum 11. This method
It can be selected depending on whether or not the distance between the clamp portion on the recording paper 71 and the tip of the electrostatic latent image can be sufficiently set. For example, when the distance is sufficient, the clamp drum 11 is not stopped and is activated. There is no problem even if the developing head is raised.

When the raising of the active developing head is completed, the developing device vertical movement motor that rotationally drives the cam shaft 50a is stopped. Then, rotate the clamp drum 11,
The pump 61 and the solenoid valve 62 corresponding to the raised active developing head are turned on. By this operation, the developing solution 10
Is supplied to the developing groove 60a in the active developing head,
Development is started. Then, when the development is started, the blower fan 42 is turned on. As the development is continued, the clamp portion of the recording paper 71 reaches the position of the static elimination scorotron 43, and at that time, the power source of the static elimination scorotron 43 for discharging the recording paper is turned on.

When the development is completed, the electromagnetic valve 62 is turned off to collect the developer 10, and when the collection is completed, the pump 61 is collected.
And the active developing head is lowered. When the clamp portion of the recording paper 71 reaches the position of the static elimination scorotron 43 again, the recording paper static elimination power source and the blower fan 42 are turned off.

After the writing and development of the electrostatic latent image for the first color is completed, the clamp drum 11 continues to rotate as it is, and the writing and development of the electrostatic latent image corresponding to the next color are started for a predetermined number of times. When the writing and development of the electrostatic latent image are completed, the recording paper discharging operation is started (step S7).

In the recording paper discharge operation, the discharge solenoid is turned on at a position where the clamp portion has passed just above, the clamp claw 12 is opened at the discharge position, and the clamp drum 11 remains as it is.
Rotation is continued (step S
8). After that, the clamp drum 11 continues to rotate,
It stops at the paper feeding position as after the initial setting.

In the control of the printer described above, the rotation speed of the clamp drum 11 at the time of writing and developing the electrostatic latent image is restricted by the process conditions, but at other times, it can be rotated at an arbitrary speed. Therefore, in order to shorten the printing operation time, it is effective to rotate the clamp drum 11 at a high speed except when writing the electrostatic latent image and developing the electrostatic latent image. Further, when the rotation speeds of the clamp drum 11 at the time of writing the electrostatic latent image and at the time of developing can be made to coincide with each other, the printing operation time can be shortened by simultaneously writing and developing the electrostatic latent image. be able to. In that case, when raising the active developing head, the clamp drum 1
1 is not stopped, and the electrostatic latent image writing operation and the developing operation are performed in the same cycle.

When the printing is repeated in the apparatus having the configuration and operation described above, the toner in the developing solution tank 64 is consumed and the toner concentration of the developing solution 10 decreases, so that the recording sheet 71 is formed. The resulting image (toner image) becomes uneven, or the image density of the image is reduced. Therefore, in this embodiment, the recording paper 71
The patch image is formed so that the density of the patch image for image density detection formed outside the effective image area is higher than the maximum density of the image formed in the effective image area. The image density detecting means for detecting the density of the patch image, and the toner replenishing device for replenishing the developing solution in the developing solution tank 64 with toner based on the detection result obtained by the image density detecting means are provided. It prevents deterioration of image quality. Further, the developing device whose outline has been described above also has a configuration other than that shown above in order to apply it to a device provided with the image density detecting means and the toner replenishing device. Hereinafter, these points will be described.

FIG. 1 is an explanatory view showing the construction of this developing device in detail. The developing device includes a developing head 60, a suction pump 61, a developing solution tank 64, and a developing solution supply pipe 6.
5. The developer recovery pipe 66 is provided as described above. In addition to that, the developer supply pipe 6 is added.
5 and the inside of the developer recovery pipe 66, a communication pipe 80, a circulation valve 81 composed of an electromagnetic three-way valve provided at a connection portion between the developer supply pipe 65 and the communication pipe 80, and a communication with the developer recovery pipe 66. It is provided with a stirring valve 82, which is an electromagnetic three-way valve, which is provided at a connecting portion with the pipe 80.
Further, one end of a toner replenishing pipe 85 communicates with the communication pipe 80, and the other end of the toner replenishing pipe 85 communicates with a toner container 84 having replenishment toner 83 stored therein. ing. A toner replenishing valve 86, which is an electromagnetic valve, is provided in a portion of the toner replenishing pipe 85 extending from the toner container 84 to the communication pipe 85.

The density of the image developed on the transfer paper 71 is detected in the vicinity of the recording paper 71 conveyed to the clamp drum 11 where the latent image has been developed by the developing head 60. A density detection sensor 87 is provided as an image density detection means for inputting the detection result to the printer control unit 1. In the above description, the printer control unit 1 corresponds to toner replenishment amount control means. Further, the pump 61, the circulation valve 81, the communication pipe 80, the stirring valve 82, the toner container 84, the toner replenishing pipe 85, and the toner replenishing valve 86 constitute a toner replenishing device that replenishes the developer tank 64 with toner.

Further, an LD for adjusting the exposure light amount of the LD
A control circuit 100, a charging control circuit 110 that controls the charging potential of the photosensitive drum 21, and a bias control circuit 120 that controls the latent image transfer bias voltage from the photosensitive drum 21 to the recording paper 71 on the clamp drum 11. A rotation control circuit 130 for controlling the rotation speed of the clamp drum 11,
A negative pressure control circuit 140 that adjusts the negative pressure of the pump 61 is provided, and each can be controlled by a control signal from the printer control unit 1.

The operation of detecting the density of the image formed on the recording paper 71 in this apparatus configured as described above, and the toner replenishing device causes the developing solution in the developer tank 64 to be developed based on the detected value of the image density. The operation of replenishing the liquid with toner will be described below. 10 and 11 are flowcharts showing the control of the image density detection and the toner replenishing operation in this embodiment, and the control of steps S4 to S6 in the control of the embodiment described above with reference to FIG. Is shown in detail. In the present embodiment, a so-called positive / positive process is adopted in which a negatively charged latent image is transferred onto the recording paper 71 on the negatively charged photosensitive drum 21 and is developed with positive polarity toner.

In this apparatus, as described above, when the power of the printer is turned on, the developing head 60 and the clamp drum are initialized, and the paper is fed to the printer in the paper feed standby state. Hereinafter, description will be given with reference to FIG. When the paper feeding operation ends, the printer enters the READY state, and printing starts (step S101), the printer control unit 1
The bias control circuit 120 is controlled so that the latent image transfer bias is applied to the photosensitive drum 21 (step S1).
02). Next, by controlling the charging control circuit 110,
The effective image area on the photosensitive drum 21 is charged (step S103). Next, the LD control circuit 100
Is controlled to expose the image area. Then, the photosensitive drum 21 is driven to rotate together with the rotation of the clamp drum 11 in a state where a predetermined latent image transfer bias is applied between the photosensitive drum 21 and the clamp drum 11, and the recording paper 71 wound around the clamp drum 11 is rotated. Transfer the latent image (step S10)
4). Here, in step S105, it is determined whether or not the latent image of the effective image portion is transferred to the recording paper 71. If the transfer is not completed, the process returns to step S104, and if the transfer is completed, in the next step S106, Turn off the exposure.
Then, in step S107, the printer control unit 1 controls the charging control circuit 110 to switch the charging amount.

Here, the developing process employed in this embodiment is a positive / positive process, and when the charge amount of the photosensitive drum 21 is increased, the latent image potential transferred to the recording paper 71 is also increased. Therefore, the charging control circuit is configured to charge the patch latent image forming area of the photoconductor drum 21 with a charging amount such that the density of the patch image for image density detection is higher than the maximum density of the effective image portion. It controls 110. As a result, a patch image having a high solid image density causes a decrease in image density due to a decrease in toner density earlier than an image in the effective image portion, and the density of the patch image is detected by the density detection sensor 87, whereby image unevenness is detected. It is possible to detect the decrease in toner concentration before the occurrence of.

Then, the patch latent image formed on the photosensitive drum 21 charged as described above is transferred to the recording paper 71. Here, it is determined whether or not the transfer of the patch latent image is completed in step S109, and if the transfer is not completed, the process returns to step S108, and if the transfer is completed, the charging and the latent image transfer are performed in the next step S110. Turn off bias application. Then, step S1 at which development is started
11. The specific operation for developing the electrostatic latent image is as described above.

The distance from the effective image portion to the patch image portion is determined by the charge amount switching time and the distance between the charger and the transfer portion onto the recording paper 71. In the present embodiment, the charge amount is switched after the transfer of the effective image portion is completed. Therefore, when the charge amount switching time and the distance between the charger and the transfer portion onto the recording paper 71 are set to be close to each other, the effective image is changed. The distance from the area to the patch image area is short, which is preferable.

Next, when the developing operation in FIG. 11 is started (step S111), the density detecting sensor 87 is used.
Detects the image density of the patch image formed outside the effective image area of the recording paper 71 (step S11).
2). Then, the detection result is input to the printer control unit 1 and compared with a specified density preset in the printer control unit 1 to determine whether the density is less than or equal to the specified density (step S113). If the density is below the specified concentration, the toner replenishment operation described later is performed to replenish the developer tank 64 with a required amount of toner (step S11
4). On the other hand, if the density in the patch image exceeds the specified density, the toner replenishing operation is not performed. Then, in the next recording paper discharge operation (step S115), the recording paper is discharged, and a series of operations is completed. (Hereinafter, margin)

Next, the toner replenishing device operates the developer tank 6
A specific operation of replenishing the developing solution in 4 with toner will be described. FIG. 12 is a flowchart showing the control of the toner replenishing operation, and shows the control of step S114 of FIG. 11 in detail. When replenishing the toner, the printer controller 1 first turns on the power to the circulation valve 81.
As the FF, the valve 81 is brought into a state in which the side of the developing solution tank 64 of the developing solution supply pipe 65 and the communication pipe 80 communicate with each other (step S201). Next, the printer control unit 1 turns on the power supply to the stirring valve 82 to bring the developing solution tank 64 side of the developing solution recovery pipe 66 into communication with the communication pipe 80 (step S202). By such control, the circulation valve 81, the communication pipe 80, the agitation valve 8 from the developer tank 64.
2, and a developer recovery pipe 6 provided with a pump 61
A circulation path for the developer to reach the developer tank 64 again via 6 is formed.

With the circulation path formed, the printer control device 1 drives the pump 61 to generate a negative pressure in the flow path (step S203). This negative pressure is
It is adjusted by the negative pressure control circuit described above. Then, the developing solution in the developing tank 64 circulates in the circulation path by the adjusted negative pressure, and the toner dispersed in the developing solution is agitated (step S204). Further, when negative pressure is generated in the circulation path, the printer control unit 1 turns on the power supply to the toner supply valve 86 (step S20).
5) The toner container 84 and the communication pipe 80 are brought into communication with each other. As a result, the toner in the toner container 84 is sucked out by the negative pressure, and the communication pipe 80 and the stirring valve 8
2. The developer tank 64 is replenished through the developer collecting pipe 66 (step S206). After that, the printer control unit 1 turns off the power supply to the toner supply valve 86 (step S207), and the toner container 84 and the communication pipe 8 are connected.
In the state where 0 is disconnected, the toner supply from the toner container 84 is stopped. In this state, the pump 61 is continuously driven for a while to circulate the developer in the circulation path to stir, and then the stirring valve 82 is deenergized (step S208) and the pump 6 is pumped.
The power supply to No. 1 is turned off (step S209), and toner replenishment is completed.

[Second Embodiment] A second embodiment in which the present invention is applied to a color printer which is an image forming apparatus will be described below. The basic configuration of this embodiment is the same as that of the first embodiment, and the difference is that the printing condition for making the image density of the patch image higher than the maximum image density in the effective image area is the charging condition. Instead of controlling the amount of charge on the photosensitive drum 21 by the charger 23, a method of controlling the latent image transfer bias to the photosensitive drum 21 is used. Therefore, the control of the latent image transfer bias to the photoconductor drum 21 will be described below, and the description of the other parts will be omitted. The developing process is a so-called negative / positive process in which a negatively charged latent image is transferred onto the recording paper 71 using the positively charged photosensitive drum 21 and is developed with positive polarity toner.

FIG. 13 is a flow chart showing the control from the start of printing to the end of development. The operation other than the operation shown in FIG. 13 to which the following description is added is the same as the operation of the first embodiment described above with reference to FIG. 9. As in the first embodiment, when the printer is powered on, the developing head 60
And the clamp drum 11 are initialized, and then the paper is fed to the printer in the paper feed standby state and printing is started (step S301), and the printer is in a state of waiting for writing of the electrostatic latent image. Next, the user operates the operation unit 4
When a predetermined switch is operated, the printer control unit 1 turns on the latent image transfer bias and applies the predetermined latent image transfer bias to the photoconductor drum 21.
0 is controlled (step S302). Next, the charging control circuit is turned on to uniformly charge the photosensitive drum 21 by the charging charger 23 (step S303). Then, the LD exposes the image portion onto the photosensitive drum 21.
Then, in the state where a constant latent image transfer bias is applied between the photosensitive drum 21 and the clamp drum 11, the photosensitive drum 21 is driven to rotate and the latent image formed on the photosensitive drum 21 is exposed. The image is transferred from the body drum 21 to the recording paper 71 (step S304). Then, in step S305, it is determined whether or not these processes are completed. When it is determined that the exposure and latent image transfer for the effective image portion are completed, the exposure and charging are turned off in the next step S306.

Next, the printer control section 1 switches the bias control circuit 120 so as to increase the latent image transfer bias potential of the patch image portion (step S307). Here, the higher the bias potential, the higher the latent image potential transferred to the recording paper 71. As described with reference to FIGS. 2 and 3, the higher the latent image potential, the higher the image density. Therefore, by increasing the exposure light amount, a high density image can be obtained. For this reason, the printer control unit 1 of the present embodiment uses the bias control circuit 12
0 is switched so that the bias potential of the patch image portion is higher than the bias potential of the effective image. Then, a patch latent image is formed on the photosensitive drum 21, and the patch latent image for image density detection is transferred to the vicinity of the trailing edge of the recording paper outside the effective image area of the recording paper 71 (step S308). Then, it is determined in step S309 whether or not this process is completed, and when it is determined that the transfer of the patch latent image is completed,
In the next step S310, the latent image transfer bias is turned off. In this way, the electrostatic latent image is written on the recording paper 71, and the electrostatic latent image is formed on the recording paper 71. Then, development of the electrostatic latent image by the developing head 60 or the like is started (step S311). Since this developing operation is the same as that in the first embodiment, its explanation is omitted.

The distance from the effective image portion to the patch image portion is determined by the latent image transfer bias switching time and the distance between the charger and the transfer portion onto the recording paper 71. In this embodiment, since the latent image transfer bias is switched after the transfer of the effective image portion is completed, the latent image transfer bias switching time and the distance between the charger and the transfer portion to the recording paper 71 are set to be close. Then, the distance from the effective image portion to the patch image portion becomes short, which is preferable.

[Third Embodiment] A third embodiment in which the present invention is applied to a color printer which is an image forming apparatus will be described below. The basic configuration of this embodiment is the same as that of the second embodiment, and the difference is that the method for making the image density of the patch image higher than the maximum image density in the effective image area is a photosensitive drum. In place of the method of controlling the latent image transfer bias to 21, the exposure amount of the LD to the photoconductor drum 21 is controlled. Therefore, the control of the exposure amount of the LD on the photosensitive drum 21 will be described below, and the description of the other parts will be omitted. The developing process is a negative / positive process similar to that in the second embodiment. FIG. 14 is a flowchart showing the control from the start of printing to the end of development. The operation other than the operation shown in FIG. 14 to which the following description is added is the same as the operation of the first embodiment described above with reference to FIG. As in the first embodiment, the printer power is turned on.
Then, the developing head 60 and the clamp drum 11 are initialized, and then the paper is fed to the printer that is in the paper feed standby state and printing is started (step S40).
1) The printer is in a state of waiting for writing of an electrostatic latent image. Next, when the user presses a predetermined switch of the operation unit 4, the printer control unit 1 turns on the latent image transfer bias and sets the bias control circuit 120 to apply the predetermined latent image transfer bias to the photosensitive drum 21. Control (step S4
02). Next, the charging control circuit 110 is controlled to uniformly charge the photosensitive drum 21 by the charging charger 23 (step S403). Then, the LD exposes the image portion onto the photosensitive drum 21. The latent image formed on the photoconductor drum 21 is generated by the photoconductor drum 21 being driven and rotated while a constant latent image transfer bias is applied between the photoconductor drum 21 and the clamp drum 11. The image is transferred from the photosensitive drum 21 to the recording paper 71 (step S404). Then, in step S405, it is determined whether or not these processes are completed. If it is determined that the exposure and the latent image transfer for the effective image portion are completed, the exposure amount of the LD is switched in the next step S406.

Here, the latent image potential transferred to the recording paper 71 can be increased as the amount of light emitted from the LD onto the photosensitive drum 21 is increased. In addition, FIG. 2 and FIG.
As described above, since the higher the latent image potential, the higher the image density, it is possible to obtain a high density image by increasing the exposure light amount. Therefore, the printer control unit 1 of the present embodiment switches the LD control circuit 100 so that the exposure light amount of the patch image portion is larger than the exposure light amount of the effective image.

Then, a patch latent image is formed with an exposure light amount larger than that for forming an effective image on the photosensitive drum 21, and an image is formed outside the effective image area of the recording paper 71 near the trailing edge of the recording paper. The patch latent image for density detection is transferred (step S407). Then, in step S408, it is determined whether or not this process is completed. If it is determined that the transfer of the patch latent image is completed, the charging, the latent image transfer bias, and the exposure are turned off in the next step S409. In this way, the electrostatic latent image is written on the recording paper 71, and the electrostatic latent image is formed on the recording paper 71. Then, development of the electrostatic latent image by the developing head 60 or the like is started (step S410). Since this developing operation is the same as that in the first embodiment, its explanation is omitted.

[Fourth Embodiment] The fourth embodiment in which the present invention is applied to a color printer which is a wet image forming apparatus will be described below. This embodiment also has the same basic configuration as that of the first embodiment. The difference is that the control for forming the image density of the patch image at a density higher than the maximum image density in the effective image area is performed by the photoconductor. Instead of controlling the charge amount of the drum 21, the rotation speed of the clamp drum 11 is controlled. Therefore, the rotation speed control of the clamp drum 11 will be described below, and the description of the other parts will be omitted.

FIG. 15 is a flowchart showing the control from the start of printing to the end of development. The operation other than the operation shown in FIG. 15 to which the following description is added is the same as the operation of the first embodiment described above with reference to FIG. As in the first embodiment, when the printer is powered on, the developing head 60
And the clamp drum 11 are initialized, and then the paper is fed to the printer which is in the paper feed standby state and printing is started (step S501), and this printer waits for writing of the electrostatic latent image. Then, the photosensitive drum 2
1 is applied with a predetermined latent image transfer bias, the charging charger 23 is turned on, and the image portion is exposed by the LD.
Then, in the state where a constant latent image transfer bias is applied between the photosensitive drum 21 and the clamp drum 11, the photosensitive drum 21 is driven to rotate and the latent image formed on the photosensitive drum 21 is exposed. The image is transferred from the body drum 21 to the recording paper 71 (step S502). Then, the effective image portion is developed (step S503). Next, the printer controller 1
However, the rotation speed control circuit 130 is switched so as to reduce the rotation speed of the clamp drum 11 (step S50).
4).

Here, as described with reference to FIGS. 2 and 4, the image density can be increased as the developing speed on the recording paper 71 is decreased. Therefore, the rotation speed control circuit 130 is switched so that the development speed v2 of the patch image is slower than the development speed v1 of the effective image. As a result, when the toner density decreases due to use over time, the image density of the patch image is reduced earlier than the effective image, and the decrease in toner concentration is detected before image unevenness occurs.

Then, in step S505, the patch latent image is developed at a developing speed v2 slower than the developing speed v1 of the effective image portion. In this way, when both the effective image portion and the patch image portion have been developed, the developing operation ends (step S506).

According to the above-described first to fourth embodiments, the density of the patch image is formed on the recording paper 71, which is conveyed by the clamp drum 11 and is actually printed, higher than the image density of the effective image area. Therefore, the image deterioration is more likely to occur in the patch image before the effective image is deteriorated such as density unevenness due to the toner consumption over time. Then, by detecting such a patch image density by the density detection sensor 87,
It is possible to detect the occurrence of a decrease in density. Therefore, when the decrease in the density of the patch image portion is detected based on the detection, the toner can be immediately supplied to the developing solution.
Therefore, it is possible to prevent the occurrence of image deterioration on the effective image.

[Fifth Embodiment] A fifth embodiment in which the present invention is applied to a printer which is a wet image forming apparatus will be described below. This embodiment has the same configuration as the third embodiment. That is, it has the same configuration as the printer shown in FIG. The difference between the two lies in the method of forming the patch image formed on the recording paper 71 and the operation of detecting the patch image density. Therefore, the operation will be described, and description of other parts will be omitted.

FIG. 16 is an explanatory diagram showing the distribution of each image on the surface of the recording paper 71 on which the image is formed in the fifth embodiment. As shown in FIG. 16, the patch area A is an area other than the effective image area B and is in the conveyance direction of the recording paper 71 (see FIG.
6 is provided at two locations in the vicinity of the front end portion C and in the vicinity of the rear end portion D in the direction indicated by the arrow 6), and patch images are formed in the respective patch areas. That is, in the first to fourth embodiments, the patch image is formed only at one location in the patch area A near the rear end portion D, whereas in the fifth embodiment, the patch images are formed at the two locations. .

In determining the position occupied by each image area on the surface of the recording paper 71, it is desirable to secure a certain distance between the patch area A on the front end portion C side and the effective image area B. If there is a certain distance, the effective image area B
Before the latent image is developed, the time for replenishing the developing device with the toner is secured based on the density of the image detected in the patch area A on the tip portion C side. If a sufficient distance cannot be secured, the conveyance of the recording paper 71 due to the rotation of the clamp drum 11 is once stopped, toner is replenished with the developer during that time, and then the latent image in the effective image area is developed. It is desirable to do. Further, it is desirable to secure a certain distance between the effective image area B and the patch area A on the rear end portion D side.

FIG. 17 is a flow chart showing the control of the image forming operation in this embodiment. The operation other than the operation shown in FIG. 17, to which the following description is added, is the same as the operation of the first embodiment outlined with reference to FIG. As in the other embodiments, when the power of the printer is turned on, the developing head 60 and the clamp drum 11 are initialized, and then the paper is fed to the printer in the paper feed standby state (step S601). The printer waits for writing of the electrostatic latent image. Next, the user operates the operation unit 4
When a predetermined switch is operated, the printer control unit 1
The bias control circuit 1 turns on the latent image transfer bias and applies a predetermined latent image transfer bias to the photosensitive drum 21.
20 is controlled (step S602). Then, the charger 23 is turned on to uniformly charge the photoconductor drum 21 (step S603). Next, in order to form a patch latent image, the LD control circuit 100 is controlled to switch to increase the exposure light amount (step S604). Then, the patch image is exposed on the photosensitive drum 21 by the LD to form a patch latent image. Then, the photosensitive drum 21
When a constant latent image transfer bias is applied between the photosensitive drum 21 and the clamp drum 11, the photosensitive drum 21 is driven to rotate, so that the patch latent image formed on the photosensitive drum 21 by the exposure is exposed. Body drum 21 to recording paper 71
(Step S605). Then, in step S606, it is determined whether or not these processes are completed. If it is determined that the exposure and latent image transfer for the patch image portion are completed, then the LD control circuit is formed in order to form an effective image. Control 100 to switch the exposure light amount back to the original value (step S607). Then, step S6
At 08, the effective image area is exposed and the latent image is transferred onto the recording material 71. Then, in step S609, it is determined whether or not these processes are completed. When it is determined that the exposure and latent image transfer for the effective image portion are completed, the LD control circuit 100 is formed again for patch latent image formation. Control to switch to increase the exposure light amount (step S61).
0). Here, steps S610 to S612
Is the same as steps S604 to S606 described above, and a description thereof will be omitted. Then, in step S61
If it is determined in step 2 that exposure and latent image transfer for the patch image portion have been completed, charging, latent image transfer bias application, and exposure are turned off (step S613). In this way, on the recording paper 71, a patch latent image, a latent image of an effective image,
The latent images are written in the order of patch latent images, and the recording paper 7
A latent image is formed at 1. Then, these latent images are developed by the developing head 60 or the like (step S614). Since this developing operation is the same as that in the first embodiment, its explanation is omitted.

FIG. 18 is a flow chart showing the control of the image density detection and toner replenishing operation performed by the printer control section 1. Steps S701 and S702
Then, the development of the patch area A on the leading end portion C side of the recording paper 71 is performed. In step S703, the density detection sensor 87 detects the image density of the patch image. When this detected value is input to the printer control unit 1, the printer control unit 1 compares the detected value with a prescribed density required to obtain a good image that is measured and stored in advance. Is performed (step S704). Here, as a result of comparison, if the density in the patch image is equal to or higher than the specified density, toner is not replenished and the effective image area B is developed (step S706). On the other hand, if the density in the patch image is equal to or lower than the specified density, the toner replenishing device replenishes the developing solution in the developing solution tank 64 with toner as described above (step S705), and then the effective image area B
Will be developed (step S706).
Regarding the operation of developing the effective image area B,
The description is omitted because it is the same as that of the first embodiment. Further, the processing from the next step S707 to step S710 shows the processing of developing the patch area A near the trailing edge of the recording sheet and the processing of detecting the density of the patch image, and the processing from step S702 to step S705. Since it is similar to the above, this explanation is also omitted. When the above process is completed, the recording paper 71 is ejected (step S711) and the printing operation is completed (step S712).

According to the fifth embodiment, after the toner is replenished to the developing solution based on the density of the patch area A near the front end portion C of the recording paper 71 in the transport direction, the development in which the toner is replenished is performed. An image is formed on the patch area A near the rear end portion D of the recording paper 71 in the transport direction by the liquid,
Check whether the concentration is equal to or higher than the specified concentration. Then, when the density is equal to or lower than the specified density, toner is replenished to the developing solution again at that time. As described above, it is possible to confirm whether or not the decrease in the image density has been eliminated by the toner replenishment, so that the deterioration in the image quality due to the decrease in the toner density can be surely prevented as compared with the first to fourth embodiments. You can (Hereinafter, margin)

[Sixth Embodiment] A sixth embodiment in which the present invention is applied to a printer which is a wet image forming apparatus will be described below. FIG. 19 is a front view showing a schematic configuration of the printer of this embodiment. The configuration of this printer is basically the same as that of the first embodiment. The difference between the two is
In order to replenish toner during printing, there is no circulation path for toner replenishment and agitation for connecting the circulation valve 81 and the supply valve 86, which is provided in the printer of No.
The point where the toner replenishing pipe 85 is directly connected to the developer collecting pipe 66 and the patch area A as shown in FIG.
In the area other than the effective image area B, the recording paper 71 is continuously formed from the front end portion C side to the rear end portion D side in the transport direction (the direction shown by the arrow in FIG. 20).

FIG. 21 is a flow chart showing the control of the image density detection and the toner replenishing operation in this embodiment. The operation other than the operation shown in FIG. 21 to which the following description is added is the same as the operation of the first embodiment outlined with reference to FIG. Similar to the other embodiments, when the printer is powered on, the developing head 60 and the clamp drum 11
Are initialized, and then the paper is fed to the printer which is in the paper feed standby state (step S801), and the printer is in a state of waiting for writing of the electrostatic latent image. Next, when the user operates a predetermined switch of the operation unit 4, the printer control unit 1 turns on the latent image transfer bias,
The bias control circuit 120 is controlled so as to apply a predetermined latent image transfer bias to the photosensitive drum 21 (step S
802). Then, the charging control circuit 110 is controlled to uniformly charge the photosensitive drum 21 by the charging charger 23 (step S803).

Here, in the present embodiment, as shown in FIG. 20, the patch area A formed in the area other than the effective image area B is arranged from the leading end portion C side to the trailing end portion D side of the recording paper 71 in the conveying direction. Since the LDs are formed without breaks, both the patch image portion and the effective image portion are exposed while the LD scans one line. As described above, the density of the patch image portion needs to be higher than the density of the effective image portion. Therefore, in forming such an image, only one patch image portion is large during one line scanning. LD so that it is exposed with the amount of exposure light
The exposure light amount is switched (steps S804, S8
05).

In the illustrated example, the patch image is formed on the left side of the effective image, but it may be on the right side. However, in this case, it is necessary to change the arrangement of the density detection sensor 87 accordingly.

The latent image thus formed is transferred onto the recording paper 71 (step S806), and it is determined in step S807 whether or not the transfer is completed for all lines, and the process is repeated until all lines are completed. When the transfer of the latent image is completed, the charging, the latent image transfer bias application, and the exposure are all performed.
Set to F (step S808). In this way, the patch latent image and the latent image of the effective image are written on the recording paper 71. Then, these latent images are developed by the developing head 60 or the like (step S809). Since this developing operation is the same as that in the first embodiment, its explanation is omitted.

FIG. 22 is a flow chart showing the control relating to the density detection. In step S810, it is determined whether or not the developing operation of step S809 is completed. If the development is completed, the recording paper 71 is discharged in the recording paper discharging operation (step S811), and the series of operations is completed. On the other hand, during development, in step S812,
The density detection sensor 87 detects the density of the patch image portion. As described in the first embodiment, this detection result is input to the printer control unit 1 and compared with a predetermined density preset by the printer control unit 1 to determine whether or not the density is less than or equal to the predetermined density ( Step S81
3). If the concentration is below the specified concentration, the toner replenishing operation described later is performed to supply a required amount of toner to the developer tank 64.
Replenish inside (step S814).

FIG. 23 is a flow chart showing the control of the toner replenishing device in step S814. When toner supply is started in step S901, first, the supply valve 86 is opened to establish communication between A and B (step S90).
2). Here, during development, a negative pressure is applied such that the toner in the toner container 84 is sucked out, and by connecting A and B, the toner is contained in the developer in the developer tank 64. It is replenished (step S903). At this time, since the toner is replenished in the flow path of the developer, the negative pressure may change at the same time as the toner is replenished, and the flow rate of the developer may change accordingly. Therefore, the printer control unit 1 controls the negative pressure by the negative pressure control circuit 140 so that the negative pressure does not change during toner supply (step S904). After replenishing a certain amount of toner, the replenishment valve 86 is closed (step S905) and the toner replenishment is stopped. At this time, the negative pressure control circuit 140 restores the negative pressure before toner replenishment. (Step S906)
Toner supply control is ended.

According to this embodiment, the density detection sensor 8 detects the image density in the patch image which is formed seamlessly from the vicinity of the front end to the vicinity of the rear end of the recording paper 71 in the transport direction.
7 detects. Then, based on the detection result, the toner replenishing device replenishes the developer in the developer tank 64 with toner. Therefore, even if the effective image is being formed, if the image density of the effective image is lowered, the toner is immediately replenished to the developer at that time, so that the image density is lowered in the effective image. Can be prevented.

[0086]

According to the image forming apparatus of the first to seventh aspects, prior to the actual reduction of the density of the effective image, it is detected that the reduction of the image density is likely to occur. Then, the toner replenishing device replenishes the toner to the developer tank before the image density of the effective image is reduced based on the detection. Therefore, as compared with an apparatus in which the toner density of an effective image that has already occurred is detected and then toner is replenished afterwards, the image density at the time when the toner density of the developer starts to decrease decreases. By so doing, it is possible to prevent the occurrence of unevenness in the effective image that occurs prior to the decrease in image density, and always form an image with stable density.

Particularly, according to the image forming apparatus of claim 4,
Since the patch image is formed by the exposure means, the patch image is formed at any position within the image forming range on the recording material and outside the effective image area during the normal printing operation. There is an advantage that can be done.

Particularly, according to the image forming apparatus of claim 5,
Since the density of the patch image can be formed to be higher than the image density of the image in the effective image area simply by slowing down the developing speed, it is possible to increase the charging potential of the latent image carrier or to the latent image carrier, for example. The bias applied voltage of, or
Since the amount of exposure of the latent image carrier by the exposing means is not increased, the load on the latent image carrier can be reduced and deterioration of the latent image carrier can be prevented. .

Particularly, according to the image forming apparatus of claim 6,
Toner is replenished to the developer based on the density of the patch image provided near the tip of the recording material in the transport direction,
After that, by detecting the density of the patch image formed in the vicinity of the rear end portion in that direction, it is confirmed whether the image unevenness has been eliminated by the toner replenishment previously performed. Then, if the image unevenness is not eliminated, the toner is replenished again at this point. For this reason, when the toner concentration of the developer is lowered, the toner is surely replenished, and it is possible to reliably prevent the image concentration from being lowered.

Further, according to the image forming apparatus of the seventh aspect, even if the effective image is being formed, if the image density of the effective image is lowered, the toner is immediately supplied to the developer at that time. Since it is performed, it is possible to prevent the image density from being lowered in the effective image.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a developing device in a printer according to a first embodiment.

FIG. 2 is a graph showing the relationship between the number of printed sheets and the solid image density.

FIG. 3 is a graph showing a relationship between a recording paper latent image potential and image density.

FIG. 4 is a graph showing the relationship between developing speed and image density.

FIG. 5 is an explanatory diagram showing a schematic configuration of the printer according to the first embodiment.

FIG. 6 is an explanatory view showing a developing device of the printer according to the first embodiment in a simplified manner.

FIG. 7 is an explanatory view showing an elevating mechanism of a developing head of the developing device.

FIG. 8 is a block diagram showing a control system of the printer according to the first embodiment.

FIG. 9 is a flowchart showing control of the printer according to the first embodiment.

FIG. 10 is a flowchart showing control from latent image formation to development of the printer according to the first embodiment.

FIG. 11 is a flowchart showing control relating to density detection of the printer according to the first embodiment.

FIG. 12 is a flowchart showing control of toner supply operation of the printer according to the first embodiment.

FIG. 13 is a flowchart showing control from latent image formation to development of the printer according to the second embodiment.

FIG. 14 is a flowchart showing control from latent image formation to development of the printer according to the third embodiment.

FIG. 15 is a flowchart showing control from latent image formation to development of the printer according to the fourth embodiment.

FIG. 16 is an explanatory diagram showing a recording sheet printed by a printer according to a fifth embodiment.

FIG. 17 is a flowchart showing control from latent image formation to development of the printer according to the fifth embodiment.

FIG. 18 is a flowchart showing control of development and density detection of the printer according to the fifth embodiment.

FIG. 19 is an explanatory diagram showing a schematic configuration of a developing device in the printer according to the sixth embodiment.

FIG. 20 is an explanatory diagram showing a recording sheet printed by a printer according to a sixth embodiment.

FIG. 21 is a flowchart showing control from latent image formation to development of the printer according to the sixth embodiment.

FIG. 22 is a flowchart showing control relating to density detection of the printer.

FIG. 23 is a flowchart showing control of the toner supply device of the printer.

[Explanation of symbols]

 1 Printer Controller 10 Developer 11 Clamp Drum 21 Photosensitive Drum 60 Developer Head 61 Suction Pump 64 Developer Tank 65 Developer Supply Pipe 66 Developer Recovery Pipe 71 Recording Paper 80 Communication Pipe 81 Circulation Valve 82 Stirring Valve 83 Toner 84 Toner Container 85 Toner supply pipe 86 Toner supply valve 87 Density detection sensor 100 LD control circuit 110 Charging control circuit 120 Bias control circuit 130 Rotation speed control circuit 140 Negative pressure control circuit

Claims (7)

[Claims] 1. A conveying means for conveying a recording material; a latent image forming means for forming a latent image on the surface of the recording material; and a latent image developed with a developer to form a toner image on the recording material. Developing device, a developer tank for supplying a developer to the developing device, a toner replenishing device for replenishing the developer tank with toner, and a patch portion area provided outside the effective image area of the recording material, A patch image forming means for forming a patch image for image density detection; an image density detecting means for detecting the image density of the patch image formed on the recording material by the patch image forming means; An image forming apparatus comprising: a toner replenishment amount control unit that controls the replenishment amount of toner replenished to the developer in the developer tank by the toner replenishment device based on the detection result, The patch image forming unit is configured to have different printing conditions so that the image density of the patch image is higher than the image density of the effective image formed in the effective image area. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the latent image forming means is formed by using a latent image carrier, and the patch portion region of the latent image carrier is outside the effective image region. Is configured to be charged with a charging potential higher than that of the effective image area. 3. The image forming apparatus according to claim 1, wherein the latent image forming means is formed by using a latent image carrier, and the patch image area of the latent image carrier is outside the effective image area. The image is characterized in that the bias potential when transferring the latent image of No. 1 to the recording material is higher than the latent image transfer bias potential when transferring the latent image of the effective image area to the recording material. Forming equipment. 4. The image forming apparatus according to claim 1, wherein the latent image forming means comprises an exposing means, and the patch latent image is the highest effective image formed in the effective image area. An image forming apparatus configured to be formed with an exposure amount higher than an exposure amount for forming a latent image having a density. 5. The image forming apparatus according to claim 1, wherein the transporting means is used to develop the patch latent image portion at a developing speed and to develop the latent image formed in the effective image area. An image forming apparatus characterized by being configured to be slower than the speed. 6. The image forming apparatus according to claim 2, 3, 4, or 5, wherein the patch image is formed in the vicinity of the front end and the rear end of the recording material in the transport direction. A characteristic image forming apparatus. 7. The image forming apparatus according to claim 5, wherein the patch image is continuously formed from the vicinity of the leading end portion of the recording material to the vicinity of the trailing end portion thereof in the transport direction.