JP3390283B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, etc., 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.

[0002]

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 is lowered, the toner replenishing device replenishes the toner in the developer tank with the 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.

[0004]

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.

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 an optical writing medium for forming a latent image to be carried on the recording material .
A developing unit that forms a toner image on the recording material by developing a latent image using a developer under application of a developing bias; a developer tank that supplies the developer to the developing device; Image formation provided with a toner replenishing device for replenishing toner to the developer tank, and a toner replenishing amount control means for controlling the replenishing amount of toner replenished by the toner replenishing device to the developer in the developer tank. in the apparatus, a plurality of locations in the patch image formed on the effective image area outside of said recording medium
Image and the image density detecting means for detect the concentration of the image density of the portion of the number of the plurality detected by the image density detecting means,
Provided processing means for obtaining a difference between the maximum value and the minimum value, the light
Optical writing by writing means, latent image in effective image area
In addition to forming a latent image of the patch image,
The optical density of the patch image is
Solid image in the effective image area (image with 100% image area ratio)
Image density when the image is formed
The toner replenishment amount control means is obtained by the processing means.
It is characterized in that the toner replenishment amount is controlled based on the difference in density . Invention of Claim 2
Is the patch image in the image forming apparatus according to claim 1.
From the vicinity of the leading edge to the trailing edge of the recording material in the transport direction.
It is characterized in that it is formed seamlessly up to the vicinity of the part
It is a thing. The invention of claim 3 is the image of claim 1 or 2.
In the forming device, the patch image is
The above-mentioned recording material is formed near the leading edge and near the trailing edge, respectively.
It is characterized by being made. Claim 4
The invention provides the image forming apparatus according to claim 1 or 2, wherein:
A certain amount of toner has been supplied by the toner supply device.
The above highest among patch images developed with later developer
Is the difference between the value and the minimum value greater than or equal to a predetermined allowable value?
Determination means for determining whether or not the difference is not less than the allowable value
If it is determined that the
It is characterized in that an indicating means is provided. Claim
According to a fifth aspect of the invention, in the image forming apparatus according to the first or second aspect,
The light transmittance of the liquid developer supplied to the developing device is measured.
And a toner concentration sensor for detecting the toner concentration ,
Initial developer pre-detected by toner concentration sensor
The initial toner density of the inside is stored and
According to the detection result of the
In the developer only when it becomes necessary to replenish the toner
Measurement of the toner density of the
The initial toner concentration by comparing with the initial toner concentration
Toner density configured to determine whether or not it has returned to
A determination means is provided. Claim
The invention of claim 6 is the image forming apparatus according to claim 5, wherein
The initial toner concentration is based on the time when the liquid developer is transported.
The provision of correction means configured to correct
It is a feature.

[0007]

[Action] In the image forming apparatus according to claim 1 to 6, a plurality of points detects the image density of the patch unit image formed at a lower concentration than the maximum concentration of the active image to be formed on the effective image area by the image density detecting means . Then, using these detected values, the difference between the highest value and the lowest value in the patch image is obtained.
It Such a patch image is recorded by the optical writing means.
Image density of patch image is
When a solid image (image with an image area ratio of 100%) is formed on
It is formed so that it is lower than the image density. Due to this , prior to the actual reduction of the density of the effective image,
It is detected that the image density is likely to decrease. Then , based on the detection, the toner replenishing device replenishes the toner to the developer tank. Therefore, it is possible to prevent the deterioration of the effective image and prevent the occurrence of the unevenness of the effective image 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 solid image density and the density unevenness on the image. The vertical axis represents the solid image density and the horizontal axis represents the density unevenness. The characteristic line p shows the relationship between the solid image density at the developer concentration before the toner is consumed and the density unevenness on the image, and the characteristic line q is the solid image density after the toner is consumed and the image. The relationship with the upper density unevenness is shown. As indicated by the characteristic lines p and q, it can be seen that the higher the density of the solid image, the less the density unevenness. In the density difference y when the toner is not consumed, the density unevenness does not occur even if the density of the solid image is low, as shown by the characteristic line p. Here, if the solid image density for density measurement for detecting density unevenness is set to b, the density unevenness becomes very small before the toner is consumed. Therefore, when the solid image density is set to the maximum density a, naturally, The density unevenness is very small. The characteristic lines p and q at the density difference y or less
Coincides with the vertical axis. Solid image density is symbol b in the figure
In the characteristic line p before the toner is consumed, the density unevenness is very small and is not noticeable. However, as the toner is consumed, the characteristic line q has a characteristic as shown by the characteristic line q. Even if the solid image density b is the same, the density unevenness becomes large, and if the solid image density b becomes low, the density unevenness becomes more remarkable.

By the way, in general, when an image is formed on an electrostatic latent image on a recording paper by using a developing device, it is known that the toner is less likely to adhere to the recording paper and the density unevenness is more likely to occur. This phenomenon becomes more prominent when the developer concentration decreases as toner is consumed. In a normal printer, since the gradation is expressed by the area ratio of dots, the solid image portion (100
%) And the intermediate density portion (for example, 50%) are electrostatic latent images having the same potential difference, the density unevenness is more noticeable in the solid image portion. That is, assuming that the potential difference of the electrostatic latent image on the recording paper is, for example, 70 V, it is 7 in the solid image portion (100%).
The dots of 0 V potential are present on the entire surface of the recording paper, and the dots are present every other dot in the intermediate density portion (for example, 50%). For this reason, in the intermediate density portion whose area ratio is smaller than the image area ratio of the solid image density, or in the highlight portion whose area ratio is smaller than the intermediate density portion, there is a portion that is not originally printed. ,
Even if a small amount of density unevenness occurs, it is less noticeable, and conversely, if a small amount of density unevenness occurs, it becomes noticeable.

Therefore, in the image forming apparatus according to the first to seventh aspects, as described above, when the developer density decreases, the density unevenness is more noticeable in the solid image than in the intermediate density portion and the highlight portion. Paying attention to, the density is lower than that of the image formed in the effective image area, and the image area ratio is 100.
By forming the% patch image outside the effective image area, the occurrence of density unevenness is easily detected. And
The image density in the patch image is detected at a plurality of points, and the developer is replenished with an amount of toner corresponding to the difference between the detected values. That is, the density unevenness that occurs in a patch image with an image area ratio of 100% is extremely small, and the density is at a limit to the extent that density unevenness is not noticeable even in the intermediate density portion and the highlight portion where the image area ratio is smaller than the solid image density. The difference x is previously determined by an experiment. Further, when the density difference between solid image densities exceeds the set value x, the amount of toner to be replenished to the developer until the density difference becomes y is also obtained in advance by experiments. It should be noted that the density difference y is obtained when a new developing solution or the developing solution is replaced and the printing operation for the first sheet is performed. Then, the image density in the patch image is detected by the image density detecting means at a plurality of positions, and the processing means calculates the density difference from the highest value and the lowest value of the detected values, for example. If the density difference is equal to or greater than the set value x, it is determined that the image density has decreased, and the toner amount previously obtained as the amount for returning to the density difference y is supplied to the developer. Therefore, with this device,
By detecting the density in the patch image and detecting the density unevenness of the patch image that occurs before the effective image area, the toner is applied to the developer before the density unevenness occurs in the image formed in the effective image area. To replenish.

In the image forming apparatus of the second aspect, the image density detecting means detects the image density at a plurality of positions in the patch image which is formed seamlessly from the leading end to the trailing end of the recording material in the transport direction. Then, the toner replenishing device replenishes the developer in the developer tank with toner based on the density difference in the patch image. 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.

In the image forming apparatus of the third aspect, the image density detecting means detects the image densities at a plurality of positions in the patch image formed near the front end of the recording material in the transport direction. Then, the toner replenishing device replenishes the developer in the developer tank with toner based on the density difference in the patch image. After that, the plurality of image density detecting means detects the image density of the patch image formed in the vicinity of the rear end portion in the transport direction of the recording material by the developer to which the toner has been supplied, and the toner supply previously performed. Check if the image unevenness has been eliminated by. Then, when the image unevenness is not eliminated, the toner is replenished to the developer again at this point.

[0013] In the image forming apparatus according to claim 4, after the toner supply is made with respect to the developing agent, to detect the image density at a plurality of locations in the patch image, the density difference obtained by the processing means, more tolerance The determining means determines whether or not When the density difference is equal to or more than the allowable value,
It is considered that the developer deteriorates with time and the developing ability is lowered, and the image density does not increase even if the toner is replenished, and the display device displays a message to prompt replacement of the developer.

In the image forming apparatus according to claim 5 or 6 , the toner replenishment amount control means controls only when toner is replenished to the developer based on the density difference.
The toner concentration sensor starts measuring the toner concentration in the developer supplied to the developing device. Then, by continuously comparing with the initial toner concentration during the measurement, it is determined whether or not the initial toner concentration has returned. Therefore, when replenishing the toner to the developer, it is not necessary to determine in advance the amount to be replenished, and the optimum amount of toner is replenished to the developer each time.

Here, when the liquid developer circulates in the toner replenishing device, the toner particles in the liquid developer are crushed into fine particles, and the light transmittance thereof becomes low. Therefore,
When a toner concentration sensor that detects that the toner concentration in the liquid developer is high when the light transmittance is low is used, when the crushing occurs, the toner concentration is not actually high. Nevertheless, it will be erroneously detected as becoming high. Therefore, in the image forming apparatus of the sixth aspect , the initial toner concentration is corrected according to the time when the liquid developer is circulated by the pump. Therefore, in this apparatus, the toner in the liquid developer is pulverized, and even if the toner concentration of the liquid developer is increased by the pulverization, the reference initial toner concentration is corrected corresponding to this toner concentration. The toner is replenished based on this corrected density, and the amount of toner replenished to the liquid developer is accurately controlled.

[0016]

[Embodiment 1] 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. 3 is a front view showing a schematic configuration of the color printer according to this embodiment. Electrostatic recording paper as recording material (hereinafter referred to as recording paper)
71 is wound in a roll shape with the recording surface facing outward, and is attached to the printer body as a recording paper roll 70 by a paper tube holder (not shown). A flat surface portion 11b is formed on a part of an outer peripheral portion 11a of a clamp drum 11 as a conveying means for mounting the recording paper 71 fed from the recording paper roll, and the front end of the recording paper 71 is formed on the flat surface portion 11b. A clamp claw 12 serving as a recording paper fixing member to be gripped and an eject pin 13 for lifting the recording paper 71 on the flat surface portion 11b when the recording paper 71 is ejected are 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. A cam-shaped lever (not shown) is attached to the shaft end of each rotary shaft outside the end surface of the flange portion of the clamp drum 11 in order to open and close the clamp claw 12 and move the eject pin 13 in and out. On the side plate side of the printer, a pin (not shown) that moves in the rotation axis direction of the clamp drum 11 is provided so as to come into contact with the cam-shaped lever 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 (hereinafter referred to as LD) (not shown), a polygon mirror 31, a drive motor therefor, 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 this embodiment, the LD and the polygon mirror 3
1. 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. 4 is a simplified diagram of the 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. 5, 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. 5, 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 moves to the clamp drum 1.
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 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. 6 is a block diagram of the control system of the color printer according to this embodiment. As shown in FIG. 6, the control system comprises 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. 7 is a flow chart of control of the color printer of this embodiment. Printer power is O
If N (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 initializing the developing head 60, as shown in FIG.
The developing head home position sensor of the printer input unit 2 inside detects the home position of the developing head 60 and the cam 50. Here, the home position is a state in which all the developing heads 60 are all lowered, and
The developing head 60 which moves up next is 1 in the image forming process.
In this state, the developing head 60 for the second color to be used is set. 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,
Turn on the developing device vertical movement motor that drives the cam shaft 50a.
Then, the cam 50 is operated 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. 6 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 paper feeding solenoid is turned on to bring the clamp portion directly above while opening the clamp claw 12, and the clamp drum 11 is stopped to stop the printer. 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 part of the clamp drum 11, and the user presses a predetermined switch of the operation part 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 end 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 developing solution 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 and the writing and development of the electrostatic latent image corresponding to the next color are started, and the clamp drum 11 is started 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 above printer control, 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 whose construction and operation have been outlined above, the toner in the developer tank 64 is consumed and the toner concentration of the developer 10 is lowered, so that the recording paper 71 is formed. The resulting image (toner image) becomes uneven, or the image density of the image is reduced. Therefore, in this embodiment, the developer tank 64 is based on a plurality of image density detecting means for detecting the density of the image formed on the recording paper 71 and the difference between the detection values obtained by the plurality of image density detecting means. A toner replenishing device that replenishes the developing solution with toner is provided to prevent the deterioration of the 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 plurality of density detection sensors 87 are provided as 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.

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 develop based on the detected value of the image density. The operation of replenishing the liquid with toner will be described below. FIG. 8 is a flow chart showing the control of the image density detection and the toner replenishing operation in this embodiment, and details of the control of step S4 to step 6 in the control of the embodiment outlined with reference to FIG. It is shown.

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 (step S101). The state of waiting for writing the latent image is entered (see FIG. 7). Next, when the user presses a predetermined switch of the operation unit 4, the electrostatic latent image is written, and the electrostatic latent image is formed on the recording paper 71 (step S102). Then, this electrostatic latent image is transferred to the developing head 60.
And the like (step S103). The specific operation for forming the electrostatic latent image and the specific operation for developing the electrostatic latent image are as described above. Here, not only the effective area in which the original image of the recording material 71 is to be formed but also the patch image other than this effective area is formed. That is, optical writing on the surface of the photosensitive drum 21 by the writing unit 5 is performed not only on the portion corresponding to the effective area on the surface but also on the portion corresponding to the patch image area on the surface. Then, each latent image formed by this optical writing is transferred to the recording material and developed by the developing device, so that an image is formed not only in the effective image area but also in the patch area.

The density of the patch image formed in this patch area is lower than the image density of the effective image formed in the effective image area. In order to reduce the density of the patch image, a weak electric charge may be applied to the portion of the recording paper 71 corresponding to the patch image portion when the photosensitive drum 2 is optically written.

Next, the density detection sensor 87 detects the densities at a plurality of points in the patch image and inputs the detected values to the printer control section 1 (step S104). Then, the printer control unit 1 selects the highest value and the lowest value from these detected values (step S105), and
The density difference is calculated from the highest value and the lowest value (step S
106). This density difference is compared with a prescribed density difference required to obtain a good image that is measured and stored in advance (step S107). Here, as a result of comparing the density differences, if the density difference in the patch image is equal to or larger than the specified value, the toner replenishing device causes the developer tank 6 to perform the toner replenishing operation.
Toner is supplied to the developer in step 4 (step S10).
8). On the other hand, if the density difference in the patch image is less than the specified value, the toner replenishing operation is not performed. Then, in the next recording paper discharge operation (step S109), the recording paper is discharged, and a series of operations is completed.

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. 9 is a flow chart showing the control of the toner replenishing operation, and shows the control of step S108 of FIG. 8 in detail. When replenishing the toner, first, the printer control unit 1 turns off the energization of the circulation valve 81 to bring the valve 81 into a state in which the developing solution tank 64 side of the developing solution supply pipe 65 and the communication pipe 80 communicate with each other. (Step S201). Next, the printer control unit 1 causes the stirring valve 82
Is turned on to turn on the state where the developing solution tank 64 side of the developing solution recovery pipe 66 and the communication pipe 80 are in communication with each other (step S202). By such control, the circulation of the developing solution from the developing solution tank 64 to the developing solution tank 64 again via the circulation valve 81, the communication pipe 80, the stirring valve 82, and the developing solution recovery pipe 66 provided with the pump 61. A path is formed.

With the circulation path formed, the printer controller 1 drives the pump 61 to generate a negative pressure in the flow path (step S203). Then, due to this negative pressure, the developing solution in the developing tank 64 circulates in the circulation path, 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 toner supply valve 86 (step S205), and the toner container 84 is turned on.
And the communication pipe 80 are in communication with each other. As a result, the toner in the toner container 84 is sucked by the negative pressure and is replenished to the developing solution tank 64 via the communication pipe 80, the stirring valve 82, and the developing solution recovery pipe 66 (step S206). After that, the printer control unit 1 turns off the power supply to the toner supply valve 86 (step S20).
7) With the toner container 84 and the communication pipe 80 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 turned off (step S208) and the pump 61 is turned on. OFF
Then (step S209), toner supply is completed.

In this embodiment, since the density of the patch image is formed lower than the image density of the effective image area,
Before the effective image is deteriorated such as density unevenness, the patch image is more likely to be deteriorated. Therefore, it is possible to prevent the occurrence of image deterioration on the effective image by detecting the occurrence of density unevenness from the image density detected at a plurality of positions in the patch image and supplying toner to the developing solution based on the detection. I can .

[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 lies in the developing device and the toner replenishing device. Therefore, the developing device and the toner replenishing device will be described, and description of other parts will be omitted.

FIG. 10 is an explanatory view showing the structure of this developing device. This developing device is similar to the developing device of the first embodiment in that the developing head 60, the suction pump 61, and the developing solution tank 6 are provided.
4, a developer supply pipe 65, and a developer recovery pipe 66. However, the communication pipe 80 included in the developing device according to the first embodiment is not included. Further, in the developing device of Embodiment 1, the toner container 84 is attached to the communication pipe 80 via the toner supply pipe 85, but in this embodiment, the toner supply pipe 85 is connected to the developer recovery pipe 66. It is installed. Further, in the developing device of the first embodiment, the electromagnetic three-way valve is used as the circulation valve 81. However, the circulation valve 81 of this embodiment is the developer supply pipe 6
5 is composed of an electromagnetic valve for connecting and disconnecting the side of the developing solution tank 64 and the side of the developing head 60 of the pipe.

Further, in the vicinity of the recording paper 71 conveyed to the clamp drum 11, a plurality of density detecting sensors 87 as image density detecting means are provided as in the first embodiment. In addition, in this embodiment, the pump 61, the circulation valve 81, 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.

The operation of detecting the image densities in the patch image formed on the recording paper 71 at a plurality of points in this embodiment configured as described above and the density difference obtained from the detected value of the image density are used. Based on the toner supply device, the developer tank 64
The operation of replenishing the developing solution with toner will be described below. FIG. 11 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. 11 to which the following description is added is the same as the operation of the first embodiment described above with reference to FIG. 7.

As in the first embodiment, the printer is powered on.
Then, 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 S301), and the printer waits for writing of the electrostatic latent image. . Next, when the user presses a predetermined switch of the operation unit 4, the electrostatic latent image is written and the electrostatic latent image is formed on the recording paper 71 (step S302). Then, development of the electrostatic latent image by the developing head 60 or the like is started (step S
303). Since the electrostatic latent image forming operation and the developing operation are the same as those in the first embodiment, the description thereof will be omitted. Further, similarly to the first embodiment, step S302 and step S
In 303, a patch image is formed in a region other than the effective image area of the recording paper 71. In this embodiment, FIG.
As shown in FIG. 7, the patch area A is provided in an area other than the effective image area B without a break from the leading end portion C side to the trailing end portion D side in the conveyance direction of the recording paper 71 (the direction shown by the arrow in FIG. There is. The image density of the patch image formed outside the effective image area of the recording paper 71 is lower than the image density of the effective image.

During the developing operation, the density detection sensor 87 detects the image density at a plurality of points on the patch image and inputs the detected values to the printer controller 1 (step S306). Then, the printer control unit 1 selects the highest value and the lowest value from these detected values (step S307), and obtains the density difference from the highest value and the lowest value (step S308). This density difference is compared with a prescribed density difference required for obtaining a good image that is measured and stored in advance (step S309). Here, as a result of comparing the density differences, if the density difference in the patch image is equal to or less than the specified value, the toner supply operation is not performed and the development is ended. On the other hand, if the density difference in the patch image is not less than the specified value, the toner replenishing operation is performed by the toner replenishing device by the following steps as the toner replenishing operation.
Add toner to the developer inside.

When performing such toner replenishment, the toner supply valve 86 is turned on by the control of the printer controller 1 to turn on the toner container 84 and the developer recovery pipe 66.
And are communicated with each other via the toner supply pipe 85 (step S310). Then, in this state, toner is replenished from the toner container 84 to the developing solution in the developing solution tank 64 (step S311). Since this toner replenishment operation is performed during printing, negative pressure fluctuation due to toner replenishment may be adjusted (step S3).
12). Then, from step S313 to step S31
In step 6, the same processing as step S306 to step S309 is performed, and comparison is made with the density difference of the specified image required to obtain a good image that is measured and stored in advance (step S316). Then, when the density difference in the patch image reaches the specified density difference, the printer controller 1 turns off the power supply to the toner replenishing valve 86 (step S317), and the developer in the developer tank 64 is supplied with the toner. Toner supply is stopped (step S318). Then, in step S304, it is determined whether or not the development is completed. If it is not completed, step S306 is repeated again. If the development is completed, the recording paper 71 is discharged in the recording paper discharging operation of step S305 (step S109), and a series of operations is ended.

In this embodiment, the recording paper 71 which is conveyed by the clamp drum 11 and is actually printed.
In the above, by detecting the density in the patch image where density unevenness occurs before the effective image at multiple points,
Occurrence of uneven density is detected. Therefore, when density unevenness is detected based on the detection, the toner can be immediately replenished to the developing solution even during printing. Therefore, it is possible to prevent the occurrence of image deterioration on the effective image.

[Third Embodiment] A third 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, and the difference lies in the developing device and the toner replenishing device. Therefore, the developing device and the toner replenishing device will be described, and description of other parts will be omitted.

FIG. 13 is an explanatory view showing the structure of the developing device according to this embodiment. This developing device is characterized by including a bias applying circuit 90 as a bias applying means for applying a bias to the developing head 60 in response to a command from the printer controller 1 in addition to the components of the developing device of the first embodiment. A positive bias, which is set to be lower than the highest potential on the recording paper when an image is formed in the effective image area, is applied to the developing head 60. The solid image in the patch area is formed by this bias.
Except for this point, the developing device has the same configuration as that of the developing device according to the first embodiment. As the electrostatic recording paper 71 of this embodiment, a recording paper having a multilayer structure of a dielectric layer, a conductive layer, a base, and a conductive layer in order from the surface is used, and a toner having a positive charging property is used. .

Based on the operation of detecting the densities in the patch image formed on the recording paper 71 at a plurality of points in this embodiment configured as described above, and the density difference obtained from the detected value of the image density. The operation of the toner replenishing device for replenishing the developer in the developer tank 64 with toner will be described below. FIG. 14 is a flowchart showing the control of the image density detection and the toner replenishing operation in this embodiment. In addition, the operation other than the operation shown in FIG.
The operation is the same as that of the first embodiment outlined with reference to FIG.

As in the first embodiment, the printer is powered on.
Then, 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 S401), and the printer waits for writing of the electrostatic latent image. . Next, when the user presses a predetermined switch of the operation unit 4, the electrostatic latent image of the portion corresponding to the effective image formed in the effective image area is written, and the electrostatic latent image is formed on the recording paper 71. (Step S402). Then, this electrostatic latent image is developed by the developing head 60 or the like (step S403), and an effective image is formed. Since the electrostatic latent image forming operation and the developing operation are the same as those in the first embodiment, the description thereof will be omitted.

Then, the recording paper 71 on which an effective image is formed
When the patch area located near the rear end of the recording paper 71 comes into contact with the developing head 60, the printer controller 1 controls the bias applying circuit 90 to turn on the power to the circuit. , A positive bias is applied to the developing head 60 by the bias circuit 90 (step S40).
4). Then, the developing head 60 to which the bias is applied develops an area corresponding to the patch image portion of the recording paper 71 to form a patch portion image. Hereinafter, the processes from step S406 to step S411 are the same as step S104 to step S10 in the first embodiment.
Since it is the same as the processing up to 9, the description is omitted.

Also in this embodiment, the image density of the patch image is formed to be lower than the image density of the effective image formed in the effective image area. For this purpose, the bias applying circuit is configured so that the force of attracting toner by the patch image formed on the recording paper 71 by the developing head 60 is weaker than the force of attracting toner by the latent image corresponding to the effective image portion. The bias applied to the developing head 60 by 90 may be set. The operation of the toner replenishing device for replenishing the toner in the developing solution tank 64 is the same as that in the first embodiment, and therefore its explanation is omitted.

According to this embodiment, the bias applying circuit 9
By applying a voltage to the developing head 60 at 0 and developing the recording paper 71 by the head, a patch image having a lower image density than the effective image can be formed.

Example 4 Hereinafter, Example 4 in which the present invention is applied to a printer which is a wet image forming apparatus will be described. This embodiment has the same structure as the third embodiment. That is, it has the same configuration as the printer shown in FIG. The difference between the two is that the toner replenishing device uses the developer in the developer tank 64 based on the operation of detecting the image density of the image formed on the recording paper 71 and the density difference obtained from the detected value of the image density. The operation is to replenish the toner. Therefore, I will explain the operation,
Description of other parts will be omitted.

FIG. 15 is an explanatory diagram showing the distribution of each image on the surface of the recording paper 71 on which the image is formed according to this embodiment. As shown in FIG. 15, 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.
5 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 5), and a patch image is formed in each patch region. That is, in the third embodiment, the patch image is formed only in one place in the patch area A near the rear end portion D, whereas in the third embodiment, the patch image is formed.
It is formed in two places.

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 developing the latent image in, the time for replenishing the developing device with toner is secured based on the density difference of the image detected in the patch area A. 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. 16 is a flow chart showing the control of the image density detection and toner supply operation in this embodiment. The operation other than the operation shown in FIG. 16 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, 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 in the paper feed standby state (step S501), and the printer waits for writing of the electrostatic latent image. . Next, when the user operates a predetermined switch of the operation unit 4, the electrostatic latent image of the portion corresponding to the effective image formed in the effective image area is written, and the electrostatic latent image is formed on the recording paper 71. (Step S502). Then, the recording paper 71 is conveyed, the developing head comes into contact with the patch area A located in the vicinity of the leading end portion C of the recording paper 71 in the conveying direction, and the development of the patch area A is started (step S503). Next, the printer controller 1 controls the bias applying circuit 90 to turn on the power supply to the circuit, and the bias circuit 90 applies the bias to the developing head 60 (step S504). Then, the patch area A is developed by the developing head 60 to which the bias is applied to form a patch image (step S505). Then, the densities at a plurality of points of this patch image are detected by the density detection sensor 8
7 detects and inputs the detected value to the printer control unit 1 (step S506).

Then, the printer control unit 1 selects the highest value and the lowest value from these detected values (step S5).
07), and the density difference is obtained from the highest value and the lowest value (step S508). This density difference is compared with a prescribed density difference necessary for obtaining a good image that is measured and stored in advance (step S509). Here, as a result of comparing the density differences, if the density difference in the patch image is equal to or more than the specified value, the toner replenishing device replenishes the developer in the developer tank 64 with toner (step S510), and then the effective image area. The development of B is performed (step S511). On the other hand, if the density difference in the patch image is less than the specified value, toner is not replenished and the effective image area B is developed (step S51).
1). Since the operation of developing the effective image area B is the same as that in the first embodiment, the description thereof will be omitted.

Then, the development of the effective image area B is completed,
The recording paper 71 is conveyed, and a rear end portion D of the recording paper in the conveyance direction is conveyed.
When the developing head comes into contact with the patch area A located in the vicinity, the printer controller 1 controls the bias applying circuit 90 to turn on the current to the circuit, and the bias circuit 90 applies the bias to the developing head 60. This is done (step S512, step S513). Then, the patch area A is developed by the developing head 60 to which the bias is applied to form a patch image. Since the processes from step S514 to step S519 are the same as the processes from step S104 to step S109 in the first embodiment, the description thereof will be omitted.

According to this embodiment, after the toner is replenished to the developing solution based on the density difference of the patch area A near the front end portion C of the recording paper 71 in the transport direction, the development to which the toner is replenished is performed. Recording paper 7 in the transport direction due to liquid
An image is formed on the patch area A near the rear end portion D of No. 1, and it is confirmed whether the density difference is equal to or less than the reference value. Then, if the density difference is equal to or larger than the reference value, the toner is replenished to the developer again at that time. Therefore, it is possible to reliably prevent the deterioration of the image quality due to the decrease of the toner concentration.

By the way, step S510 of the above embodiment.
In, even though the developer was replenished with toner,
The image developed by the developer with the toner replenished may not be a good image. In this case, it is considered that the toner changes with time and the developing power thereof is weakened. Therefore, the following process, that is, it is determined whether or not the density difference when a plurality of positions on the image developed by the developer in the state where the toner is replenished is detected is within an allowable value. If the allowable value is exceeded, a message may be displayed on the operation panel or the like, or a warning or the like may be blinked or lit to control the display to prompt the operator to replace the developer. .

[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 is for preventing the risk of continuing to use the developing solution having a lowered developing ability as it is, and has the same configuration as that of the third embodiment. That is, it has the same configuration as the printer shown in FIG. The difference is that whether or not the density difference is within an allowable value is determined, and if the density difference is greater than or equal to the allowable value, a process is added to display so as to prompt the operator to replace the developer. Especially. Therefore, the operation will be described, and description of other parts will be omitted.

FIG. 17 is a flow chart showing the control of the image density detection and toner replenishing operation, and the developer replacement display processing in this embodiment. The operation other than the operation shown in FIG. 17 is performed by the first embodiment outlined with reference to FIG.
Is the same as the operation of. In addition, step S6 in FIG.
The processing from 01 to step S609 is also performed from step S101 to step S109 in FIG. 8 in the first embodiment.
Since it is the same as the processing up to this point, the description is omitted.

The processing from step S610 to step S619 shows the processing performed in the next printing operation when the toner is replenished in step S608. In other words, after the toner is replenished, it is judged whether the cause of the density unevenness is due to the lack of toner or the deterioration of the developing ability of the developing solution by the density difference of the image printed immediately after replenishing the toner. The printing operation processing of is specially provided. Steps S611 to S616 are the same as the above steps S601 to S606, and step S617 is the same as step S617.
Based on the density difference obtained in 616, it is determined whether the density is equal to or more than the allowable value. Then, if it is less than or equal to the allowable value, the recording paper discharging operation is performed as it is (step S61
9), finish printing. On the other hand, if the density difference is equal to or more than the allowable value, a display prompting the replacement of the developing solution is displayed in step S618, and then the recording paper discharging operation of step S619 is performed to complete the printing. It should be noted that the above-mentioned allowable value is obtained in advance by experiments or the like, and is set to a limit density difference in which the density difference does not return to the original level even after toner replenishment, and density unevenness occurs if the printing operation is continued as it is.

According to this embodiment, the replacement of the developing solution is promoted when the density difference in the patch image after the toner is replenished exceeds the permissible value. You can prevent the risk of continued use. For this reason, it is possible to prevent problems such as density unevenness or image density reduction even if toner is replenished due to a reduction in the developing ability of the developer. Therefore, the image density can always be stabilized.

Although the example in which the present invention is applied to the printer having the same configuration as that of the third embodiment has been described above, the present invention is a printer in which the bias applying device 90 is added to the printer described in the second embodiment, that is, It can also be applied to a printer in which the bias applying device 90 is added to the printer shown in FIG .

[Sixth Embodiment] A sixth embodiment in which the present invention is applied to a color printer which is a wet image forming apparatus will be described below. In this embodiment, the basic configuration is the same as the first embodiment.
The difference lies in the developing device and the toner replenishing device. Therefore, the developing device and the toner replenishing device will be described, and description of other parts will be omitted.

FIG. 18 is an explanatory view showing the structure of the developing device according to this embodiment. In addition to the components of the developing device according to the first embodiment, this developing device transmits light as a developer concentration detecting means for detecting the concentration of the developer supplied from the developer tank 64 to the developing head 60. Has a sensor. The light transmission sensor 95 receives the light emitted from the light emitting element 95a and transmitted through the developing solution by the light receiving element 95b, and measures the amount of the received light with respect to the emitted light to measure the light in the developing solution. The concentration of the developing solution is detected from the transmittance of the light passing therethrough. When the toner concentration of the developer is high, it becomes difficult for light to pass therethrough, so the light transmittance shows a low value. On the other hand, when the toner concentration of the developing solution is low, light easily passes therethrough, and thus the light transmittance shows a high value. In addition,
The developing device has the same configuration as that of the developing device according to the first embodiment except that the light transmitting sensor 95 is provided. That is, this developing device
Similar to the developing device of the first embodiment, the developing head 60, the suction pump 61, the developing solution tank 64, the developing solution supply pipe 65,
Developer recovery pipe 66, communication pipe 80, circulation valve 81,
A stirring valve 82 and a toner supply pipe 85 are provided, and a light transmission sensor 95 is additionally provided. Further, in this embodiment, the pump 61, the circulation valve 81, the communication pipe 80, the stirring valve 82, the toner container 84, the toner supply pipe 85, the toner supply valve 86, and the light transmission sensor 95 are
A toner replenishing device that replenishes the developer tank 64 with toner is configured.

Based on the operation of detecting the densities of the images in the patch image on the recording paper 71 at a plurality of points in this embodiment configured as described above, and the density difference obtained from the detected value of the image density. The operation of the toner replenishing device for replenishing the developer in the developer tank 64 with toner will be described below. FIG. 19 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. 19 to which the following description is added is the same as the operation of the first embodiment described above with reference to FIG. 7.

When the power of the printer is turned on, first, 1
Before the first sheet is printed, the light transmission sensor 95 measures the transmittance of the developing solution (step S701). The measured value at this time is stored in the printer control unit 1 or an external storage device (step S702). In the following processing, steps S703 to S708 are
Step S101 to Step S in the first embodiment
Since the processing is the same as that up to 106, the description is omitted.
In step S709, it is determined whether or not the density difference is greater than or equal to the set value, and if it is less than or equal to the set value, the recording paper discharge operation in step S714 is performed. On the other hand, when it is equal to or larger than the set value, the light transmission sensor 95 again measures the transmittance of the developing solution supplied to the developing head 60 under the control of the printer control unit 1 (step S710), and then the developing solution. Toner supply to the tank 64 is started (step S71).
1). Then, the light transmission sensor 95 continuously measures the toner concentration of the developer being replenished with toner, and the developer is replenished until the toner concentration stored in step S702 is reached (steps 712 and 713). When the toner supply is completed, the recording paper discharging operation of step S714 is performed. With that, a series of processing is completed. The second and subsequent prints are processed by omitting steps 701 and 702, and thereafter, the same process is performed until the developer is replaced. Therefore, it is necessary to keep the transmittance stored even when the power is turned off.

In this embodiment, it is not necessary to predetermine the amount of toner to be replenished to the developing solution, and the toner concentration of the developing solution supplied to the developing head 60 is the toner concentration required to obtain a good image. Toner is replenished until it becomes.

In this apparatus, when the developing solution is circulated by the pump 61, the toner may be crushed into fine particles and the light transmittance thereof may be lowered. Since this device determines that the toner concentration of the developer is high when the light transmittance is low, in such a case, it may be erroneously detected that the toner concentration is high even though the toner concentration is low. Therefore, in order to avoid such a situation, it is desirable to correct the reference value for determining that the toner concentration is good according to the time during which the developer circulates by the pump 61. In particular,
The change in the light transmittance of the developing solution with respect to the driving time of the pump 61 is stored in the printer controller 1 as a data table. Then, the drive time of the pump 61 is measured every time printing is performed, the data table is referred to according to the measured value, and the reference value is corrected. When a large amount of toner is replenished in the developer, it is considered that the toner in the developer has not been made into fine particles due to the replenishment, and the reference value is reset. On the other hand, when a small amount of toner is replenished in the developer, it depends on the ratio between the amount of replenished toner that is not pulverized and the amount of toner that is present in the developer in advance and that is pulverized. The data in the data table is corrected, and this value is used to correct the reference value.

In the above description of each embodiment, only one density detecting sensor 87 is provided, the image density is detected at a plurality of points by the sensor 87, and the density is detected from the highest value and the lowest value of the detection result. Although the apparatus for obtaining the difference and supplying the toner to the developing solution based on the difference in density is shown, the density detection sensor 8
7, a plurality of detection values obtained from these sensors may be used to obtain an average value of detection values higher and lower than a predetermined value, and the difference between the average values may be determined as a density difference. good. According to this, as compared with the case where only one density detection sensor 87 is provided, it is possible to reduce the influence on the obtained density difference when the detection error is large or when the abnormal value is detected.

[0085]

According to the image forming apparatus of the first to sixth 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. Also,
The image density detector detects multiple image densities in the patch image.
Location and obtain the difference in concentration from these average values.
The toner is replenished based on this density difference.
Detects the concentration only at the location, and based on this detected concentration
-Compared to the case of replenishment, the error of detection of image density is smaller.
Since it is possible to reduce the
It is possible to prevent the toner replenishing device from being controlled. sand
That is, the state where toner should be replenished originally
However, the toner is not replenished and the toner is replenished.
To prevent toner replenishment even if there is no need for
You can

According to the image forming apparatus of the second aspect , 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. It is possible to prevent the image density from being reduced in the effective image.

According to the image forming apparatus of the third aspect , the developer is replenished with toner based on the density of the patch image provided in the vicinity of the front end of the recording material in the transport direction, and then the rear end in that direction. By detecting the densities of patch images formed in the vicinity, 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.

According to the image forming apparatus of the fourth aspect , when the developer deteriorates with time and a good image cannot be obtained even if the toner is replenished, the display means displays that fact. To do. Therefore, the developer can be replaced according to the display, and the deterioration of the image quality of the effective image due to the continued use of the deteriorated developer can be prevented.

According to the image forming apparatus of the fifth aspect , the development in the developer tank is carried out until the density of the developer supplied to the developing apparatus reaches a predetermined density required for forming a good image. Toner is replenished to the agent. Therefore, an optimum amount of toner is replenished each time toner is replenished without calculating the replenishment amount in advance, and the toner replenishment amount is prevented from becoming excessive or insufficient. be able to.

According to the image forming apparatus of the sixth aspect , even when the liquid developer is circulated by the pump and the toner in the liquid developer is crushed and made into fine particles, at this time, the reference value is determined according to the density. Since the density is corrected, the density of the liquid developer supplied to the developing device will not be erroneously detected. Therefore, an accurate amount of toner is supplied to the liquid developer.

[Brief description of 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 an explanatory view showing the operation of the invention.

FIG. 3 is an explanatory diagram showing a schematic configuration of a printer according to a first embodiment.

FIG. 4 is an explanatory view showing a developing device of the printer in a simplified manner.

FIG. 5 is an explanatory view showing a lifting mechanism of a developing head of the developing device.

FIG. 6 is a block diagram showing a control system of the printer.

FIG. 7 is a flowchart showing control of the printer.

FIG. 8 is a flowchart showing control of a toner supply device of the printer.

FIG. 9 is a flowchart showing control of toner supply operation of the printer.

FIG. 10 is an explanatory diagram showing a schematic configuration of a developing device in the printer according to the second embodiment.

FIG. 11 is a flowchart showing control of a toner supply device of the printer.

FIG. 12 is an explanatory diagram showing a recording sheet printed by the printer.

FIG. 13 is an explanatory diagram showing a schematic configuration of a developing device in a printer according to a third embodiment.

FIG. 14 is a flowchart showing control of a toner supply device of the printer.

FIG. 15 is an explanatory diagram showing a recording sheet printed by a printer according to a fourth example.

FIG. 16 is a flowchart showing control of the toner supply device of the printer.

FIG. 17 is a flowchart showing control of the toner replenishing device in the printer according to the fifth embodiment.

FIG. 18 is an explanatory diagram showing a schematic configuration of a developing device in a printer according to a sixth embodiment.

FIG. 19 is a flowchart showing control of the toner supply device of the printer.

[Explanation of symbols]

1 Printer control unit 10 Developer 11 Clamp drum 21 photoconductor drum 60 developing 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 Stirrer valve 83 toner 84 toner container 85 Toner supply pipe 86 Toner supply valve 87 Concentration detection sensor 90 bias application circuit 95 Light transmission sensor

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Claims (6)

(57) [Claims] 1. A conveying means for conveying a recording material and an optical writing device for forming a latent image to be carried on the recording material.
And developing a latent image with a developer under application of a developing bias,
A developing device for forming a toner image on the recording material, a developer tank for supplying a developer to the developing device, a toner replenishing device for replenishing the developer tank with toner, and the toner replenishing device for the developer tank. in the image forming apparatus and a toner supply amount controlling means for controlling the supply amount of toner to be replenished to the developer in a plurality of locations in the patch image formed on the effective image area outside of said recording medium and the image density detecting means for detect the image density, image density portion of the number of the plurality detected by the image density detecting means
A processing means for determining the difference between the highest value and the lowest value of the effective image area by the optical writing by the optical writing means.
Not only the latent image of the patch image but also the latent image of the patch image,
The optical writing of the patch image
A solid image (image area ratio 100% in the effective image area)
Image) is lower than the image density when formed
Performed urchin, the toner supply amount control means, determined by said processing means Concentration
An image forming apparatus characterized in that the toner replenishment amount is controlled on the basis of the difference . 2. The image forming apparatus according to claim 1, wherein the patch image is continuously formed from the vicinity of the front end portion of the recording material to the vicinity of the rear end portion thereof in the transport direction. 3. The image forming apparatus according to claim 1, 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. 4. A difference between the maximum value and the minimum value in a patch image developed with a developer after a certain amount of toner is replenished by the toner replenishing device is a predetermined allowable value or more. determination means for determining whether or, if the difference is determined to be equal to or greater than the allowable value, according to claim 1 or 2, characterized in that a display means for performing display to prompt the replacement of the developer Image forming device. 5. A toner concentration sensor for detecting a toner concentration by measuring a light transmittance of the liquid developer supplied to the developing device, and an initial toner in an initial developing solution which is previously detected by the toner concentration sensor. The density is stored, and the measurement of the toner density in the developing solution is started only when the toner replenishment from the toner replenishing device to the developer tank is required based on the detection result of the image density detecting means, and the measurement is performed. 3. A toner concentration determining means configured to determine whether or not the initial toner concentration has been returned by continuously comparing the initial toner concentration for a period of time.
Image forming device. 6. The image forming apparatus according to claim 5, further comprising a correction unit configured to correct the initial toner concentration based on a time when the liquid developer is conveyed.