JPH08171242A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of obtaining image density which is nearly coincident with aimed density based on the first image forming operation after halt period even though such environment as the humidity of the peripheral atmosphere of the device is largely changed during the halt period of the image forming device. CONSTITUTION: This image forming device is provided with an image producing means 3 forming a toner image on an image carrier 2 in accordance with image information and transfers the toner image on a recording sheet 4 so as to form a recorded image. This image forming device is provided with a measurement controlling means 5 making the means 3 repeatedly produce a reference patch for measuring density at a specified standard interval, a density measuring means 6 detecting the density of the patch 1 formed on the image carrier 2, a density controlling means 7 setting and changing image producing parameter on the means 3 based on the detection signal of the means 6, an environment measuring means 8 measuring the environment on the peripheral atmosphere of the means 3, and a patch producing interval controlling means 9 changing the interval for producing the reference patch 1 from a standard interval to a shortened interval based on the measurement result of the means 8.

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 or a laser printer, and more specifically, to a density change of a density measuring reference patch formed on an image carrier such as a photoconductor. The present invention relates to an image forming apparatus that controls the potential of an electrostatic latent image and the amount of toner supplied to a developing device.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a laser printer, the image density of a recorded image is easily influenced by environmental factors such as temperature and humidity. For example, copying using a general two-component developer. In the machine, the image density tends to decrease in a low humidity environment, and the image density tends to increase in a high humidity environment. Therefore, in order to always maintain a constant image density, the contrast potential of the electrostatic latent image formed on the image carrier, the developing bias potential applied in the developing process, the toner concentration of the developer in the developing device, etc. It is necessary to precisely control the image forming parameters according to changes in environmental factors.

Therefore, conventionally, a toner image having a specific pattern (hereinafter, this toner image is referred to as a reference patch) is formed on an image carrier, and the density of the reference patch is optically measured, and the measurement result is obtained. A method of controlling various image forming parameters relating to the formation of a toner image based on the above is widely used (JP-A-63-106672, JP-A-1-).
295281, etc.). In this method, when the image density changes due to changes in environmental factors, this can be measured as the density change of the reference patch, and if the image forming parameter is controlled based on the measured density of the reference patch, the image density will be substantially reduced. It has the advantage that it can be kept constant.

Here, if the reference patch forming interval is too frequent, the toner consumption increases and it also leads to contamination of the inside of the apparatus, and the image forming operation cannot be performed during the preparation of the reference patch. Therefore, the productivity of recorded images per unit time is reduced. On the contrary, if the creation interval is too long, the control of the image density cannot sufficiently follow the change of the environmental factor, and the image density tends to change. For this reason, it is necessary to set the interval for creating the reference patch to an optimum interval for each image forming apparatus.
In the copying machine disclosed in Japanese Patent No. 45986, etc., the reference patch formation interval is determined according to the number of copies.

[0005]

By the way, the cause of the change of the image density due to the change of the environmental factors is, in particular, the change of the charge amount of the toner due to the change of the humidity. Therefore, if the humidity in the room in which the image forming apparatus is installed changes significantly during the rest period of the image forming operation, the image density greatly deviates from the target density when the image forming operation is performed after the rest period.

However, since the toner is actually agitated in the developing unit to obtain a charge amount according to the humidity at that time, the toner is charged during the pause period of the image forming operation in which the toner is not agitated. If the amount of toner does not completely follow changes in humidity and the toner is agitated with the start of the image forming operation, the amount of charge on the toner will change rapidly according to the humidity at that time. become.

Therefore, even if the reference patch is created before the first image forming operation after the rest period and the image forming parameters of the toner image are set according to the density thereof, the image forming operation is started and the inside of the developing device is started. When the toner is agitated, the image density changes abruptly until the charge amount of the toner stabilizes at the charge amount according to the humidity, and the image density set in the image forming parameters is the target image density. There was a problem that it could not be maintained.

FIG. 8 illustrates this phenomenon by taking the case where the copying machine is left overnight as an example. FIG. 8A shows a change in humidity in the copying machine installation room, and FIG. The change in the toner charge amount and the accompanying change in the image density are shown.
For example, when the copier is used in an air-conditioned room, there is almost no change in humidity during the day when the air-conditioning equipment is operating, and therefore there is no change in the toner charge amount. It is kept almost constant.

Here, it is assumed that the air conditioner is stopped and the copying machine is left overnight, and the humidity in the room rises compared with the previous day. Since copying is not performed during the night when the toner is left unattended, the toner in the developing device is not agitated, and even if the humidity greatly rises, the change in the toner charge amount is slight. But,
When the copier was started the next morning, the toner inside the developing device was agitated as the number of copies increased, and the toner charge amount drastically decreased in response to high humidity, and the image density drastically increased. Will rise. Then, when the charge amount of the toner becomes a value according to the humidity and becomes stable, the image density also becomes stable. Further, when the room is air-conditioned and the humidity gradually decreases, the charge amount of the toner also gradually increases, and accordingly, the image density also gradually decreases.

Therefore, as shown in the above-mentioned prior art, a reference patch is formed and image forming parameters are set before the first copy job is started in the morning, and thereafter, a reference patch is formed for every fixed number of copies. Then, the imaging parameters are set again. FIG. 9 shows a change in image density at this time, and a broken line shows a change in image density when a reference patch is not formed for comparison.

In this case, if the number of copies increases and the charge amount of the toner becomes stable according to the humidity, the change in the image density with respect to the change in humidity is also small. Therefore, as shown in FIG. Even if the creation interval is long, the image density can be maintained at a substantially target density. But,
Immediately after the start of the copy job, unless the creation interval of the reference patch is sufficiently short, the image density changes significantly before the next reference patch is formed, and as shown in FIG. There is a problem that the concentration deviates greatly.

In order to deal with such a problem, it is sufficient to set the interval for forming the reference patch to be sufficiently short. However, the problem is that the humidity greatly changes during the pause period of the image forming operation. Since only this occurs, the number of times the reference patch is created becomes excessive when the toner charge amount is stable depending on humidity, resulting in an increase in toner consumption, contamination in the device, and unit time as described above. There arises a problem that the productivity of the recorded image per hit is lowered.

On the other hand, in the image forming apparatus disclosed in Japanese Unexamined Patent Publication No. 6-230675, when it is predicted that the change of the toner charge amount is large based on the pause time of the image forming operation and the change of humidity during the pause. As a pre-stage before starting the actual image forming operation, only toner agitation is performed to stabilize the toner charge amount prior to the image forming operation. However, if only toner agitation is performed before the image forming operation is started, image formation cannot be performed during that time.
For example, the so-called first copy time from when the copy start switch of the copying machine is pressed until the first copy is ejected becomes long, which causes a problem that the productivity of recorded images decreases. In addition, since the toner does not come in and out of the developing device by the stirring of the toner, there is a problem that the developer including the carrier is deteriorated and the life thereof is shortened if this is frequently performed.

The present invention has been made in view of the above problems, and an object of the present invention is when the environment such as the humidity of the surrounding atmosphere of the image forming apparatus is greatly changed during the rest period of the apparatus. Even if there is, it is an object of the present invention to provide an image forming apparatus capable of obtaining an image density that substantially matches the target density from the first image forming operation after the rest period.

[0015]

In order to achieve the above object, the image forming apparatus of the present invention forms an image forming toner image on the image carrier 2 according to image information as shown in FIG. An image forming apparatus comprising means 3 for transferring the toner image onto a recording sheet 4 to form a recorded image, wherein reference patches 1 for density measurement are repeatedly formed on the image forming means 3 at predetermined standard intervals. Measurement control means 5, a density measurement means 6 for detecting the density of the reference patch 1 formed on the image carrier 2, and an image formation in the image formation means 3 based on the detection signal of the density measurement means 6. The density control means 7 for setting and changing the parameters, the environment measuring means 8 for measuring the environment in the atmosphere around the image forming means 3, and the creation interval of the reference patch 1 based on the measurement result of the environment measuring means 8 Reduced from standard interval And it is characterized in that it comprises a creation interval control means 9 for changing the septum.

In the above technical means, the image forming means 3 is a series of steps for forming a toner image on the image carrier 2 such as a photosensitive drum, that is, a charging process.
The design can be changed as appropriate as long as the latent image forming process and the developing process can be sequentially performed, and specifically, it includes a charging device, an exposure optical system, a developing device, and the like.

The image forming parameters in the image forming means 3 are various conditions that affect the density of the toner image, and specifically include the contrast potential of the electrostatic latent image and the developing bias potential. Here, the contrast potential of the electrostatic latent image is determined by the charging potential of the image carrier 2 by the charger and the exposure intensity of the image carrier by the exposure optical system. Further, in an image forming apparatus of a type that temporarily holds image information as electrical image data such as a laser printer, the gradation characteristic of the image data is also one of the toner image forming conditions.

Further, the environment measuring means 8 may be any one as long as it can measure the humidity in the image forming apparatus which is considered to have the greatest influence on the image density, and directly measures the humidity. Alternatively, the humidity may be predicted by measuring the temperature.

Further, as the above-mentioned production interval control means 9,
If it is determined from the measurement result of the environment measuring means 8 that the environment changes greatly, the interval for creating the reference patch can be shortened from the standard interval. However, at the beginning of the image forming operation, the change in the image density due to the change of environmental factors is large, but the image density becomes stable as the image forming operation is repeated. It is preferable to restore the patch creation interval to the standard interval.

[0020]

According to the above technical means, the environment measuring means measures the environment of the atmosphere around the image forming means, and based on the measurement result, the reference patch forming interval is changed from the predetermined standard interval to the shortening interval. Therefore, even when environmental factors such as humidity change significantly during the pause period of the image forming operation, and the image density changes abruptly at the beginning of the image forming operation after the pause period, the detection signal of the density measuring unit does not change. Based on this, the image forming parameters are finely set and changed, and the image density does not largely deviate from the target density.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming apparatus of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 2 shows a first embodiment of a color copying machine to which the present invention is applied. In the figure, reference numeral 20 is a photosensitive drum, 21 is a charging corotron for precharging the surface of the photosensitive drum 20, 22 is a scanner unit for reading image information of an original 222, 228 is on the photosensitive drum 20 charged by the charging corotron 21. Raster scanning device (hereinafter referred to as ROS) for writing an electrostatic latent image, 23
Is four developing devices 2 in which toner images of black (K), cyan (C), magenta (M), and yellow (Y) are stored.
3K, 23C, 23M, 23Y are rotatably arranged,
A rotary developing unit appropriately switched and selected, 25 is a cleaner for removing the residual toner on the photosensitive drum 20, and 26 is an erase lamp for removing the residual charge on the photosensitive drum 20.

In this embodiment, the scanner unit 22
Is an exposure lamp 223 for irradiating the original 222 set on the platen 221 with a light beam and the exposure lamp 2
Carriage 2 for moving 23 over the original 222 area
24, a reflection mirror 225 that guides the beam from the surface of the original 222 by the exposure lamp 223 along a predetermined path, a CCD sensor 226 that converts the beam from the surface of the original 222 into a digital signal for each color component, and the surface of the original 222. And an image forming lens 227 which forms an image of the beam from the image sensor on the CCD sensor 226. In addition, the ROS 228
Is a semiconductor laser 228a that emits a laser beam based on the image data of each color component captured by the CCD sensor 226, and a polygon mirror 228b that distributes and deflects the beam from the semiconductor laser 228a in the main scanning direction of the photosensitive drum 20, It is composed of an image forming lens 228c for forming an image of the beam from the semiconductor laser 228a along a line in the main scanning direction of the photosensitive drum 20 and a reflecting mirror 228d for regulating the beam path.

The photosensitive drum 20 is located between the writing position and the developing position of the electrostatic latent image on the photosensitive drum 20.
An electrometer 27 for measuring the charging potential of the photosensitive drum 20 is provided, while an optical sensor 28 for measuring the density of the reference patch formed on the photosensitive drum 20 is provided between the developing position and the transfer position. There is. The optical sensor 28 is a reflection type optical sensor in which an LED illuminates the photosensitive drum and the amount of reflected light is measured by a photodiode. Further, a hygrometer (not shown) for measuring relative humidity is provided in the copying machine.

On the other hand, reference numeral 31 indicates that the recording sheet 30 is wound and held on the peripheral surface, and the photosensitive drum 20 is attached to the recording sheet 30.
This is a transfer drum that sequentially multiple-transfers the toner images of the respective color components. The transfer drum 31 includes an adsorption corotron 41 that charges the drum sheet 35 when holding the recording sheet 30,
A transfer corotron 42 for transferring the toner image on the photosensitive drum 20 to the recording sheet 30 side, and a destaticizing corotron 43 for destaticizing the recording sheet 30 for which the final color transfer process has been completed,
A cleaning charge-removing corotron 44 for removing charges on the drum sheet 35 after the final color transfer process, a cleaning brush 45 for cleaning paper dust and the like adhering to the drum sheet 35 after the final color transfer process, and a recording sheet. Three
An inner pressing roll 46 that pushes up the drum sheet 35 from the inside when peeling 0 is provided, and a peeling finger 47 that peels the recording sheet 30. Reference numeral 48 indicates the recording sheet 30 supplied from a sheet feeding cassette (not shown).
Is a sheet conveying system that conveys to the suction corotron 41 portion at a predetermined timing according to each mode.

Further, reference numeral 50 is a fixing device for inserting the recording sheet 30 after the transfer process and fixing the unfixed toner image on the recording sheet 30. In this embodiment, a heating device having a heater incorporated therein is used. The recording sheet 30 from the transfer drum 31 is conveyed to the fixing device 50 via the guide plate 53. The recording sheet 30 is composed of a roll 51 and a pressure roll 52 arranged in pressure contact with the heating roll 51. Further, reference numeral 54 is a fuser outlet roll that conveys the recording sheet 30 that has passed through the fixing device 50, and 55 is the fixing device 50.
The fuser outlet switch for detecting the trailing edge of the recording sheet 30 that has passed through the recording sheet 30, 56 is a discharge tray in which the fixed recording sheet 30 is accommodated, and 57 is a discharge tray 56.
Is an exit roll for sending out.

In the color copying machine configured as described above, first, when the user operates the copy start switch, the original 222 is scanned and the photoconductor drum 20 is scanned.
An electrostatic latent image corresponding to black K is written on the top. On the other hand, in the rotary developing unit 23, the black developing device 23K is set at a position facing the photoconductor drum 20, and the electrostatic latent image is developed by the black developing device 23K with a slight delay from the writing timing. Then, the black K toner image thus formed is transferred to the recording sheet 30 held on the transfer drum 31. Further, when the developing process by the black developing device 23K is completed, the developing device is replaced until the transfer drum 31 completes one rotation cycle, and the yellow developing device 23Y is exposed by the 90 ° rotation of the rotary developing unit 23. It is set at a position facing the body drum 20.

After that, these operations are repeated every one rotation cycle of the transfer drum 31, and the toner images of yellow Y, magenta M, and cyan C are held on the transfer drum 31 from the photosensitive drum 20 each time. The image is transferred to the recording sheet 30, and a superposed toner image is formed on the recording sheet 30 by four color toner images. Then, the recording sheet 30 on which the cyan C toner image has been transferred is peeled off from the transfer drum 31 as it is, passes through the fixing device 50, and then the discharge tray 56.
Is discharged to.

FIG. 3 is a block diagram showing the control system of this color copying machine. First, in the scanner unit 22, C
The image data read by the CD sensor 226 is the amplifier 6
After being amplified to an appropriate level by 0, the A / D converter 61
Is converted into an 8-bit digital signal. After the shading correction and the gap correction, the density converter 62 converts the reflectance data into density data and sends the density data to the image processing unit.

The image data sent to the image processing unit is first subjected to basic image processing as a color copying machine, that is, color signal conversion, black reproduction (UCR), MTF processing, etc., in the color conversion unit 63, and black. , Yellow, cyan, and magenta image data. Next, the image data of each color is sent to the first gamma correction 64, and the ROS 22 of each copying machine is
8 and the color tone correction is performed in accordance with the tone characteristics peculiar to the image forming unit.

The image data for which the first gamma correction 64 has been completed in this way is converted into analog data by the D / A converter 68, and then a signal of a predetermined period sent from the triangular wave generator 70 by the comparator 69. And is converted into binary image data by pulse width modulation. FIG. 4 is a diagram for explaining binarization of image data in a comparator, in which input analog image data is compared with a triangular wave, and a portion where the analog image data is larger than the triangular wave is "0" and a portion where it is smaller is "1". The image data is binarized as. The binary image data is sent to the laser driver 71 of the optical section.
The semiconductor laser 228a of the ROS 228 is turned off when the image data is "0", and is turned on when the image data is "1".

The image processing section includes a photoconductor drum 20.
A patch signal generating means 72 for generating an image signal when forming a reference patch is provided on the upper portion, and generates reference patch data having an image area ratio of 50%. The analog image data and the reference patch data described above are input to the second selector 73 controlled by the controller 74, and only one of the data is compared with the triangular wave by the comparator 69 and binarized.

On the other hand, the image forming section has an electrometer 27 and an optical sensor.
Sensor 28 and the photosensor drum based on the detection signals of the hygrometer.
The density of the toner image formed on the upper 20 is controlled to be constant.
Controller 74, the control signal of this controller 74
Grid voltage V of the charger 21 according to the number_GChange obi
The control signal of the electric appliance control unit 75 and the controller 74
The voltage is applied to each developing device of the rotary developing unit 23 accordingly.
Developing bias voltage V _BBias control unit to change the
76 is provided. Also, rotary development unit
A toner supply device 77 is connected to each of the 23 developing devices.
The toner according to the control signal of the controller 74.
It is supposed to be replenished. Furthermore, the control
The controller 74 also controls the laser light amount controller 78 of the optical unit.
Control signal is transmitted, and the laser driver 71
The amount of light emitted by the conductor laser 228a is adjusted.
There is.

In the color copying machine of the present embodiment having the above-mentioned structure, immediately after the main power is turned on or 4
The image density control is performed as follows when the copy job is performed for the first time after the copy job is not performed for a time or longer.

First, the controller 74 is used in the copying machine.
When the copy start switch is pressed, the image formation condition setting mode
Start the operation and follow the flow chart shown in Fig. 5.
Grid potential V of electric appliance 21_GS, ROS 228 laser light
Quantity L_DS, Development bias potential V _BTo determine.

In the controller 74, the target dark potential V _HS , the target exposure portion potential V _LS , and the fog prevention potential difference V _C from the target dark potential V _HS to the developing bias potential V _B are stored in advance, and based on these, V _GS , L _DS and V _B are determined. Explaining along the flowchart, first, the controller 74 sends a control signal to the charger control unit 75 to charge the photoconductor drum 20 with different grid voltages V _G1 and V _G2 . Then, using the electrometer 27, the dark potential V at that time
_H1 and V _H2 are measured (ST1), and the grid potential V _GS required to obtain the target dark potential V _HS is calculated by the following formula (ST
2).

[0036]

[Equation 1]

Next, the photosensitive drum 20 is charged by using the grid potential V _GS obtained in ST2, while the controller 74 requests the patch signal generating means 72 to generate the reference patch data, and the second selector 73 is used. Is requested to select the reference patch data. As a result, the reference patch data is binarized and supplied to the laser driver 71, and an electrostatic latent image corresponding to the reference patch data is formed on the photosensitive drum 20. At this time, the controller 74
Sends a control signal to the laser light amount control unit 78 to expose the ROS 22 to the photosensitive drum 20 using two kinds of laser light amounts L _D1 and L _D2 . Then, for each of the reference patches to measure the exposed portion potential V _L1, V _L2 with electrometer (ST3), calculated by the following formula amount of laser light L _DS required to obtain the target exposed portion potential V _LS (ST4).

[0038]

[Equation 2]

Next, the developing bias potential V _B is calculated using the target dark potential V _HS and the fog prevention potential difference V _C (ST5),
The calculated grid potential V _{GS is set} to the charger control unit 75, the laser light amount L _{DS is set} to the laser light amount control unit 78, and the developing bias potential V _B is set to the developing bias control unit 76 (S).
T6).

After that, the controller 74 again requests the patch signal generating means 72 to generate the reference patch data, and uses the set grid potential V _GS and laser light amount L _DS to electrostatic latent image on the photosensitive drum. Form an image. Then, this time is developed using the set developing bias potential V _B to form a reference patch on the photosensitive drum 20 (ST
7). The density of the formed reference patch is the optical sensor 28.
The controller 74 corrects the laser light amount L _DS set in the laser light amount controller 78 or the toner amount replenished from the toner supply device to the developing device 23 based on the detection signal of the optical sensor 28 (ST8).

This ST7 is performed for each color toner while replacing the developing device 23, and after the replenishment amounts of all four color toners are controlled, the image forming condition setting mode is ended. This ends the image forming condition setting mode.

On the other hand, when the image forming condition setting mode ends and the copy job actually starts, the controller 74 requests the patch signal generating means 72 to generate reference patch data for each predetermined copy number N, and the exposure is performed. Body drum 20
Form a reference patch on top. Then, the density of the formed reference patch is detected by the optical sensor 28, and the laser light amount L set in the laser light amount control unit 78 based on the detection signal.
_The amount of toner supplied from the _DS and toner supply device 77 to the developing device 23 is corrected. In the copying machine of this embodiment, the initial setting is made so that the reference patch is formed with the number of copies N = 10 as the standard interval.

FIG. 6 is a flowchart showing an image density control program after the copy job is started. When the copy start switch is turned on, the controller 74 measures the in-machine humidity H _on from the detection signal of the hygrometer (ST1) prior to the actual start of the copy job, and the measured value H _on and the end of the previous copy job are completed. Humidity H at the time of
The absolute value ΔH of the difference from _end is calculated (ST2). Then, the calculated ΔH is compared with the judgment reference value H ₀ stored in advance in the controller 74 (ST3). If ΔH exceeds the judgment reference value H ₀ , the humidity change during the suspension of the copy job is large. Then, the interval for creating the reference patch after the start of the copy job is changed to the shortened interval N = 2 (ST4). On the other hand, if ΔH is less than the determination reference value H ₀ in ST3, it is determined that the humidity change during the suspension of the copy job is small, and the reference patch creation interval remains unchanged at the standard interval N = 10.

Next, when the image forming condition setting mode (see FIG. 5) ends and the copy job starts (ST5), the controller 74 counts up the copy number CNT (ST6), and the copy number CNT becomes the reference patch. It is checked whether or not it matches the creation interval N (ST7). If the copy number CNT does not match the reference patch creation interval N, it is checked whether all copy jobs have been completed (ST8), and if not completed, ST6 and ST7 are repeated. On the other hand, the number of copies CNT
If it is determined that the reference patch creation interval N matches the reference patch creation interval N, the controller 74 creates a reference patch on the photoconductor drum 20, detects the density of the reference patch, and supplies the laser light amount L _DS or the toner supplied to the developing device 23. Correct the amount (ST
9).

Here, the laser light amount L _DS is corrected by selecting the offset value α to be added to the target exposure portion potential V _LS based on the detection signal of the optical sensor 28, and when the reference patch density is low, the offset value α is added. α is a negative value, and the offset value α is a positive value when the reference patch density is high. If the offset value α is a negative value, the new laser light amount L _DS ′ obtained by calculation becomes large and the image portion potential drops,
The difference between the image portion potential and the developing bias potential increases, and the image density increases. On the contrary, if the offset value α is a positive value, a new laser light amount L _DS ′ obtained by calculation is obtained.
Becomes smaller, the image portion potential increases, the difference between the image portion potential and the developing bias potential becomes smaller, and the image density decreases. As a result, the image density can be promptly corrected to the target density from the first copy after forming the reference patch.

When the image density is controlled in ST9 in this way, the counted number of copies is changed to CNT.
= 0 is reset (ST10), and then it is checked whether or not the reference patch has been created 10 times since the start of the copy job (ST11). If the reference patch is created 10 times, the reference patch creation interval is the standard interval N.
= 10 again (ST12), and it is checked in ST8 whether or not all the copy jobs have been completed. If not completed, ST6 and ST7 are repeated.

If all the copy jobs have been completed in ST8, the controller 74 measures the in-machine humidity H _end at that time from the detection signal of the hygrometer, stores this, and ends the control program.

In this embodiment, in ST2 and ST3 of the flowchart shown in FIG. 6, the in-machine humidity H _on at the start of the copy job and the in-machine humidity H at the end of the previous copy job are set.
The absolute value ΔH of the difference from _end is calculated, and this is used as the judgment reference value H ₀
However, the measured in-machine humidity H _on itself may be compared with another judgment reference value H ₁ stored in advance in the controller 74, and if H _on exceeds H ₁ , the process may proceed to ST4. This is because the charge amount of the toner becomes unstable in a high humidity environment, and the image density easily changes rapidly.

FIG. 7 shows the fluctuation of the image density when the image density control of this embodiment performed as described above is applied to the specific example shown in FIG. If the copier is left overnight and is activated the next morning, the image forming condition setting mode described above is executed before the start of the copy job, so the image density of the first copy is approximately the target. It matches the concentration. After that, since the toner charge amount sharply decreases as the number of cohesive sheets increases, the image density should normally sharply increase as indicated by the broken line. However, in this embodiment, when the absolute value of the difference in the in-machine humidity before and after the downtime of the copying machine is larger than the judgment reference value H ₀ , the reference patch is created not at the standard interval N = 10 but at the shortening interval N = 2. Therefore, the image density does not largely deviate from the target density, and it is possible to maintain the image density substantially at the target density even before the charge amount of the toner stabilizes to the charge amount corresponding to the in-machine humidity. it can.

Further, after the charge amount of the toner becomes commensurate with the humidity and the fluctuation of the image density becomes slight, the image density is maintained at the target density without frequently forming the reference patch. Therefore, if the reference patch is formed 10 times from the start of the copy job as in this embodiment and then the creation interval is restored from the shortened interval N = 2 to the standard interval N = 10, the toner consumption amount can be reduced. In addition to being able to suppress it, dirt inside the copying machine can also be reduced, and
It is also possible to improve the productivity of recorded images per unit time.

In the present embodiment, the standard patch creation interval N is set to the standard interval N = 10 and the shortened interval N = 2. The creation interval N may be switched in several steps according to the size of the. By doing so, the image density can be finely corrected according to the degree of change in the toner charge amount, and the image quality can be further improved.

[0052]

As described above, according to the image forming apparatus of the present invention, the environment of the atmosphere around the image forming means is measured by the environment measuring means, and the reference patch forming interval is based on the measurement result. Is shortened from the predetermined reference interval, the image density does not deviate significantly from the target density even when environmental factors such as humidity change significantly during the pause period of the image forming operation, and after the pause period. It is possible to obtain an image density that substantially matches the target density from the first image forming operation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an image forming apparatus of the present invention.

FIG. 2 is a schematic view showing an embodiment of a color copying machine to which the present invention is applied.

FIG. 3 is a block diagram showing a control system of the color copying machine according to the embodiment.

FIG. 4 is an explanatory diagram showing an operation of the comparator according to the example.

FIG. 5 is a flowchart showing an image forming condition setting mode according to an embodiment.

FIG. 6 is a flowchart illustrating a procedure of image density control during execution of a copy job according to the embodiment.

FIG. 7 is a diagram illustrating a specific example of image density control in the embodiment.

FIG. 8 is a diagram showing changes in humidity and changes in toner charge amount and image density corresponding thereto.

FIG. 9 is a diagram illustrating a specific example of image density control in the related art.

[Explanation of symbols]

1 ... Reference patch, 2 ... Image carrier, 3 ... Image forming means, 4 ... Recording sheet, 5 ... Measurement control means, 6 ... Density measuring means, 7 ...
Concentration control means, 8 ... Environment measuring means, 9 ... Creation interval control means

Claims (2)

[Claims] 1. An image forming apparatus comprising an image forming unit for forming a toner image according to image information on an image carrier, and transferring the toner image onto a recording sheet to form a recorded image, the image forming apparatus comprising: Measurement control means for repeatedly creating a density measurement reference patch in the image forming means at standard intervals, density measurement means for detecting the density of the reference patch formed on the image carrier, and this density measurement means Density control means for setting and changing the image forming parameter in the image forming means based on the detection signal, environment measuring means for measuring the environment in the atmosphere around the image forming means, and the above based on the measurement result of the environment measuring means An image forming apparatus comprising: a creation interval control unit that changes a creation interval of a reference patch from the standard interval to a shortened interval. 2. The image according to claim 1, wherein the creation interval control means restores the creation interval of the reference patch to the reference interval after creating the reference patch a predetermined number of times at the shortening interval. Forming equipment.