JP2005345961A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of guaranteeing stable image density over a long period of time. <P>SOLUTION: In the image forming apparatus having an image carrier, a charging means, an image information writing means and a developing means for developing an electrostatic latent image with developer to be a toner image, the toner image is transferred to recording material on a recording material carrier from the image carrier so as to form the image on the recording material. The apparatus is provided with a density control means for obtaining desired image density, by reading at least one toner image for detection formed on the image carrier by using an optical detection means and changing an image forming condition, based on the result of detection read by the optical detection means. When the variation of the image forming condition, calculated from the result of the detection read by the optical detection means, exceeds a previously set limit value, the next control interval is decided according to the difference between the calculated variation of the image forming condition and the limiting value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that obtains an image by transferring a toner image onto a recording material by an electrophotographic system or an electrostatic recording system.

  As an example of this type of image forming apparatus, FIG. 1 shows a color image forming apparatus.

  1 is a schematic configuration diagram of a color image forming apparatus. In the illustrated color image forming apparatus, the rotary developing device 3 includes a magenta toner developing device 3M, a cyan toner developing device 3C, a yellow toner developing device 3Y, and A black toner developing device 3K is used. The rotary developing unit 3 is rotatably supported by a rotation support device (not shown), and the color toner developing units 3M, 3C, 3Y, and 3K sequentially face the photosensitive drum 4 and develop with each color toner. Is called.

  Thus, the photosensitive drum 4 is rotationally driven at a predetermined angular velocity, and the surface thereof is uniformly charged by the charger 8. Next, a laser beam is exposed and scanned onto the photosensitive drum 4 by an exposure device that is ON / OFF controlled according to image data of the first color (for example, magenta), whereby the first color is transferred onto the photosensitive drum 1. And the electrostatic latent image is developed and visualized by the first color magenta toner developing device 3M. The visualized toner image of the first color is transferred to the recording material 6 adsorbed on the surface of the transfer drum 5 that is rotationally driven while being pressed against the photosensitive drum 4 with a predetermined pressing force.

  The steps up to the above transfer are similarly repeated for other toners (cyan, yellow, black), and a toner image visualized by each color toner contained in each developing device 3C, 3Y, 3K is transferred onto the transfer drum 5 each time. A color image is formed by sequentially transferring and laminating on the supported recording material 6, and this color image is fixed to the recording material 6 by the fixing device 7, and the recording material 6 on which the color image is fixed is discharged outside the apparatus. Is done.

  Incidentally, in recent years, especially with the increase in full-color output, there has been a demand for density stability and gradation stability of output images. In particular, in order to maintain a stable density over a long period of time, the following technique is known as an image density control method for an image forming apparatus such as a copying machine or a printer using an electrophotographic system.

  In other words, an image forming condition table corresponding to the environmental state and the number of durable sheets is stored in advance, the environment around the image forming apparatus is detected by an output from an environmental sensor provided in the image forming apparatus, and This is a method of detecting the durable number of the image forming apparatus or the process unit by a provided number counter and selecting an appropriate image forming condition from the image forming condition table based on the detection result.

  However, in the above method, when the status of the image forming apparatus deviates from the image forming condition table due to an accidental cause or the like, it is difficult to respond accordingly and follow subtle changes in the image forming apparatus. There is a disadvantage that it can not.

  Further, a specific toner patch is formed on the photosensitive drum or the transfer body, the density of the toner patch is detected by a density sensor, and image forming conditions are selected based on the detected density so that the desired density is obtained. A technique for controlling an image forming apparatus has been proposed. In this case, since the control is performed by detecting the actually formed toner density, the control according to the state of the image forming apparatus is possible, and a stable image density can be obtained over a long period of time. Then, the density control according to the state of the image forming apparatus can be performed as much as possible by frequently executing the density control as described above at the time of rising after standing for a long time or for each regular number of sheets (for example, Patent Documents). 1).

  In recent years, there has been a demand for a reduction in running cost regardless of color or monochrome. For example, an image forming apparatus using an amorphous silicon photoconductor drum that has a life nearly 100 times longer than that of a conventional organic photoconductor. It has been developed.

JP 2003-156904 A

  In order to maintain an appropriate image density in an image forming apparatus using the above-described density control technique, it is desirable to increase the frequency of density control as much as possible.

  However, in recent years, improvement in productivity and the like has been demanded in the market, and frequent downtime due to control causes a decrease in throughput. On the other hand, when the density control interval is sparse to improve productivity, control is performed to obtain a desired image density with a small control interval, which may cause a rapid density fluctuation after the control. In such a case, it is possible to prevent rapid fluctuations in the image density after the control by providing a certain upper and lower limit value in the control range, but it takes time to converge to the desired image density, and as a result As a result, it is difficult to stabilize the image density.

  In addition, when long-life amorphous silicon photoconductors are used with an emphasis on lowering running costs, the density fluctuation of specific toner patches for density detection increases due to uneven charging potential, which is a drawback inherent to amorphous silicon. Therefore, there is a problem that the accuracy of the control itself cannot be obtained.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of guaranteeing a stable image density over a long period of time.

  In order to achieve the above object, the present invention forms an electrostatic latent image on an image carrier, a charging means for applying a charging bias to charge the image carrier, and a charging surface of the image carrier. Image information writing means and developing means for developing the electrostatic latent image as a toner image with a developer, and transferring the toner image from the image carrier to a recording material on the recording material carrier on the recording material In an image forming apparatus for forming an image, at least one detection toner image formed on the image carrier is read by an optical detection unit, and a desired image formation condition is changed by changing the image forming condition based on the read detection result. A density control means for obtaining an image density is provided, and when the amount of change in the image forming condition calculated from the detection result read by the optical detection means exceeds a preset limit value, the calculation is performed. And determining the next control interval according to a difference between the limit value change amount and the image forming conditions are.

  The present invention also provides an image carrier, charging means for applying a charging bias to charge the image carrier, and image information writing means for forming an electrostatic latent image on the charging surface of the image carrier. And developing means for developing the electrostatic latent image as a toner image with a developer. After the toner image is transferred from the image carrier onto the intermediate transfer member to form an image on the intermediate transfer member, intermediate transfer is performed. In an image forming apparatus for transferring an image from a body onto a recording material, at least one detection toner image formed on the intermediate transfer body is read by an optical detection unit, and image forming conditions are determined based on the read detection result. A density control unit is provided to obtain a desired image density by changing, and a change amount of the image forming condition calculated from the detection result read by the optical detection unit exceeds a preset limit value. If, and determines the next control interval according to a difference between the limit value and the change amount of the calculated image formation condition.

  According to the present invention, at least one detection toner image formed on the image carrier or the intermediate transfer member is read by the optical detection means, and the image forming condition is changed based on the read detection result, thereby changing the desired image formation condition. In the image forming apparatus having the density control means for obtaining the image density, if the amount of change in the image forming condition calculated from the read detection result exceeds a preset limit value, the calculated image forming condition Since the next control interval is determined according to the difference between the amount of change and the limit value, rapid fluctuations in image density before and after the control are suppressed, and the accuracy depends on the material configuration and the accuracy of the optical detection means. Thus, it is possible to obtain an image having a stable density over a long period of time.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
FIG. 1 is a schematic configuration diagram of an electrophotographic color image forming apparatus according to Embodiment 1 of the present invention.

  In the reader unit A of the illustrated color image forming apparatus, a document 101 placed on a platen glass 102 is irradiated by a light source 103, and reflected light from the document 101 is incident on a CCD sensor 105 via an optical system 104. Imaged. The CCD sensor 105 generates red, green, and blue color component signals for each line sensor by a group of red, green, and blue CCD line sensors arranged in three rows.

  These reading optical system units convert the document 101 into an electric signal data string for each line by scanning in the direction of the arrow.

  Further, an abutting member 107 that abuts the position of the original 101 on the original platen glass 102 to prevent the original 101 from being placed obliquely, and a white level of the CCD sensor 105 on the surface of the original table glass 101 are determined. A reference white plate 106 for performing the shading in the thrust direction of the CCD sensor 105 is disposed.

  Thus, the image signal obtained by the CCD sensor 105 is subjected to image processing by the reader image processing unit 108, sent to the printer unit B, and subjected to image processing by the printer control unit 109.

  Next, the printer unit B will be described.

  In FIG. 1, a primary charger 8 as a charging unit is a corona charger, and the charging unit 8 uniformly charges the surface of the photosensitive drum 4 to a negative polarity by applying a bias.

  The image data is converted into laser light through a laser driver and laser light source 110 included in the printer image processing unit 109, and the laser light is reflected by the polygon mirror 1 and the mirror 2 to be uniformly charged. 4 is irradiated. By this laser light irradiation, an electrostatic latent image is formed on the photosensitive drum 4, and the photosensitive drum 4 on which the electrostatic latent image is formed rotates in the direction of the arrow shown in the drawing.

  The rotary developing device 3 visualizes the electrostatic latent image on the photosensitive drum 4 and houses magenta, cyan, yellow, and black developing devices 3M, 3C, 3Y, and 3K. . These four developing devices 3M, 3C, 3Y, and 3K are rotatably held by a rotation shaft, and rotate around the rotation shaft while being held during image formation. For example, the magenta toner developing device 3M Stops at a position facing the photoconductive drum 4, and the developing sleeve in the magenta toner developing device 3 </ b> M opposes the photoconductive drum 4 with a minute interval (about 400 μm), and the static image formed on the photoconductive drum 4 is formed. The electrostatic latent image is developed and visualized as a magenta toner image. Different color toner images, that is, a cyan toner image, a yellow toner image and a black toner image are formed in the same manner. When developing the electrostatic latent image on the photosensitive drum 4, the cyan toner developing device 3C, The developing device 3Y and the black toner developing device 3K are sequentially rotated and stopped at a position facing the photosensitive drum 4 to perform development.

  When the above developing operation is completed, the developing sleeves in all the developing devices 3M, 3C, 3Y, and 3K in the rotary developing device 3 are separated to a position where they do not contact the photosensitive drum 4, and this position is set as the home. Position. By setting the home position in this way, the toner in the developing units 3M, 3C, 3Y, 3K is prevented from inadvertently adhering to the surface of the photosensitive drum 4, and the developing units 3M, 3C, 3Y, 3K are prevented. It is possible to prevent the toner stored in the toner from being mixed.

  The transfer drum 5 carries and conveys a recording material by an adsorbing means, is rotatably supported, and is rotationally driven by a motor (not shown).

  The cleaning device 9 cleans the residual toner on the photosensitive drum 4 after the toner image visualized by the developing devices 3M, 3C, 3Y, and 3K is transferred to the recording material on the transfer drum 5, and is discarded. The toner is stored in the cleaning container and is exchanged when the cleaning container is full.

  The fixing device 7 heats and fixes the toner image on the recording material. The fixing device 7 includes a fixing roller 7a for applying heat to the recording material and a pressure roller 7b for pressing the recording material against the fixing roller 7a. It is composed of rollers.

  Further, an LED light source 10 (having a main wavelength at about 960 nm) and a photodiode 11 are provided for detecting the amount of reflected light of the toner patch pattern formed on the photosensitive drum 4.

  FIG. 2 is a block diagram showing the configuration of the image forming apparatus according to the present embodiment.

  As shown in FIG. 2, the printer image processing unit 109 includes an LUT 25, a PWM 26, an LD driver 27, a CPU 28, a pattern generator 29, a ROM 30, a test pattern storage unit 31, a RAM 32, and a density conversion circuit 42. A, It can communicate with the printer engine unit 100.

  The printer image processing unit 109 controls the photosensor 40, the primary charger 8, the laser light source 110, the surface potential sensor 12, and the rotary developing device 3 disposed around the photosensitive drum 4 of the printer engine unit 100. . Note that the photosensor 40 includes an LED 10 and a photodiode 11.

  The printer engine unit 100 is provided with an environmental sensor 33 that measures the amount of moisture in the air in the machine.

  The surface potential sensor 12 is provided upstream of the rotary developing device 3 (upstream with respect to the rotation direction of the photosensitive drum 4), and the surface potential sensor 12 includes the grid potential of the primary charger 8 and the rotary developing device 3. The development bias is controlled by the CPU 28 as will be described later.

  Next, a method for controlling the maximum density in the image forming apparatus according to the present embodiment will be described.

  In the image forming apparatus according to this embodiment, the optimum maximum is obtained by finely adjusting the contrast potential obtained at the previous density control with the contrast potential obtained from the density data obtained by detecting a predetermined toner patch by the photosensor 40. It is configured to control the concentration. In the present embodiment, the density control is performed every 500 regular sheets.

  Here, the maximum density control method will be described with reference to FIGS. FIG. 3 is a diagram showing the relationship between the image density and the contrast potential, and FIG. 4 is a flowchart showing the density control procedure.

  First, the previous control contrast potential Vcont0 is obtained from the previous density control result. Here, the contrast potential Vcont is a differential voltage between the developing bias Vdc and the surface potential Vl of the exposed photosensitive drum 4 as shown in FIG. 5, and the larger the Vcont, the higher the maximum density. It has become.

  As described above, a plurality of toner patches are formed with a certain potential width (50 V in the present embodiment) around the contrast potential Vcont0 obtained by the previous control. In this embodiment, as shown in FIG. 3, a total of five toner patches of Vcont0-100V, Vcont0-50V, Vcont0, Vcont0 + 50V, Vcont0 + 100V are formed at the maximum signal value 255 level, The density is detected by a photosensor 40 installed facing the drum 4.

  FIG. 6 shows a processing circuit for processing a signal from the photosensor 40 including the LED 10 and the photodiode 11 facing the photosensitive drum 4. Near-infrared light from the photosensitive drum 4 incident on the photosensor 40 is converted into an electric signal by the photosensor 40, and the output voltage of 0 to 5 V is 0 to 255 level by the A / D conversion circuit 41. Converted to a digital signal. Then, it is converted into a density by the density conversion circuit 42. Note that the photosensor 40 used in the present embodiment is configured to detect only regular reflection light from the photosensitive drum 4.

  FIG. 7 shows the relationship between the output of the photosensor 40 and the output image density when the density on the photosensitive drum 4 is changed stepwise by the area gradation of each color.

  The output of the photosensor 40 when the toner is not attached to the photosensitive drum 4 is set to 5V, that is, 255 level.

  As can be seen from FIG. 7, as the area coverage by each toner increases and the image density increases, the output of the photosensor 40 becomes smaller than that of the photosensitive drum 4 alone. From these characteristics, by having a table 42a (see FIG. 6) for converting the sensor output signal dedicated to each color into a density signal, the density signal can be read with high accuracy for each color.

  The five predetermined toner patches that have been imaged are detected by the photosensor 40 and converted into density signals to obtain five pairs of contrast potential-density relationships. Five obtained data are linearly approximated by the method of least squares, and an appropriate contrast potential Vcont1 is calculated so as to obtain a desired target density Dtarget.

As the image forming apparatus, the previous control contrast potential Vcont0 and appropriate contrast potential Vcont1
Is stored as an offset level ΔVcont. Originally, the difference ΔVcont between the contrast potential Vcont0 at the previous control and the appropriate contrast potential Vcont1 obtained by the current control should be very small.

However, the contrast potential Vcont0 at the previous control and the current proper contrast potential Vcont1 are caused by factors such as environmental fluctuations, durability fluctuations, toner charge amount fluctuations, the ratio of toner and magnetic carrier in the developing unit, and the like.
When the difference ΔVcont becomes large, the contrast potential largely fluctuates before and after the control, and as a result, a rapid density fluctuation as shown in FIG. 8 occurs.

Therefore, in the present embodiment, the contrast potential Vcont0 at the previous control and the current proper contrast potential Vcont1.
When the difference ΔVcont exceeds the preset change limit value | Vlimit |, ΔVcont = Vlimit is set.

  Here, the change limit value Vlimit needs to be set to a maximum value within a range in which a sudden density fluctuation does not occur, based on the development density and contrast potential characteristic curves. According to the experiment of the present inventor, in the image forming apparatus according to the present embodiment, the contrast potential required for changing the reflection density by 0.1 is about 20 V. The value Vlimit = 20V. Here, if ΔVcont obtained as a result of the control is 60V, ΔVcont> Vlimit, and therefore ΔVcont = 20V.

  However, in actuality, although ΔVcont = 60V, only 20V is controlled in order to suppress rapid density fluctuations. Therefore, in order to converge to an appropriate density, a plurality of density controls will be executed every 500 sheets in the future. It is necessary to be executed twice and it is difficult to maintain an appropriate concentration.

Therefore, in this embodiment, ΔVcont obtained by the control is compared with the change limit value Vlimit, and if ΔVcont ≦ Vlimit, Vcont = Vcont0 + ΔVcont, and if ΔVcont> Vlimit, Vcont = Vcont0. + Vlimit as a ratio Vlimit to the control interval
The interval until the next control is newly calculated by multiplying / ΔVcont.

That is, assuming that Vcont before control is 160V (= Vcont0), if ΔVcont obtained by this control is 60V, Vlimit
Since Vcont exceeds 20V, the newly calculated Vcont is 160 + 20 = 180V, and the next control is performed after 167 sheets with 500 × (20/60) = 167 for a control interval of 500 sheets. To do.

  By performing the above control, as shown in FIG. 9, the contrast potential is not greatly changed before and after the control, so that rapid density fluctuations are suppressed and the unachieved part for the desired image density is not achieved. By shortening the interval until the next control in accordance with the amount of contrast potential not achieved, it is possible to increase the convergence rate for a desired image density.

  Further, in this embodiment, even when the accuracy when detecting a predetermined toner patch by the photosensor 40 is not obtained, the control result is limited. Therefore, a large variation in density due to poor control accuracy occurs. In addition to being able to prevent this, the control frequency is made variable accordingly, so that the convergence rate to the appropriate concentration can be increased. For example, when density detection is performed using the photosensor 40 as in the present embodiment, the higher the density level, the more the detection dynamic range decreases in proportion to this, and the detection accuracy accordingly increases. Will go down.

  In addition, in an image forming apparatus using an amorphous silicon photoconductor, there is a possibility that sufficient detection accuracy may not be obtained due to the influence of uneven charging potential peculiar to amorphous silicon. However, this embodiment is applied. Thus, stable control can be performed with the same configuration as the conventional one.

  As described above, according to the present embodiment, in an image forming apparatus that controls density by forming a predetermined toner pattern on a photosensitive drum and detecting the density with a density sensor, the image density before and after the control is controlled. Since the convergence rate to the desired density can be increased by determining the next control timing based on the control result, it is possible to guarantee a stable image density over a long period of time. It becomes possible.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  In this embodiment, an example applied to an image forming apparatus using an intermediate transfer member is shown. In this embodiment, a photo sensor is provided on the intermediate transfer member to detect the density of the patch toner.

  FIG. 10 is a schematic configuration diagram of the image forming apparatus according to the present embodiment. The printer unit B includes a rotary developing device 3 in which developing units 3M, 3C, 3Y, and 3K for magenta, cyan, yellow, and black are accommodated. The configuration in which the developing devices 3M, 3C, 3Y, and 3K move to the developing position and perform development when necessary is the same as in the first embodiment.

  The toner images formed on the photosensitive drum 4 according to the image information of each color are sequentially transferred onto the intermediate transfer member 51, and in the case of full color, the four-color toner image is transferred onto the intermediate transfer member 51. After that, the recording material 6 is collectively transferred to the recording material 6 fed from the paper feeding unit, and the recording material 6 is discharged outside the apparatus through a fixing process of the toner image by the fixing device 7 to be a full color print.

  In the case of the configuration shown in the first embodiment, a toner patch used for image density control is formed on the photosensitive drum 4, but the surface of the photosensitive drum 4 is deteriorated due to deterioration factors such as shaving and scratches during durability. Reading fluctuation factors are remarkable, which is not preferable from the viewpoint of long-term stability.

  Therefore, the present embodiment is characterized in that a photosensor 40 used for image density control is provided on an intermediate transfer member 51 that is less likely to deteriorate than the photosensitive drum 4 and is expected to obtain further stability. Yes. Other configurations are the same as those of the first embodiment.

  Thus, also in the present embodiment, when density control is performed by forming a predetermined toner pattern on the intermediate transfer member 51 and detecting the density by the density sensor, the image density before and after the control is controlled. Suppressing rapid changes and determining the next control timing based on the control result can increase the convergence rate to the desired density, thus ensuring stable image density over a long period of time. It becomes.

  In this embodiment, the toner patch is read on the intermediate transfer member 51. However, the present invention can be applied if a configuration in which the toner patch is read on a transfer belt or the like that conveys the recording material is employed. is there.

  Further, in the present embodiment, a reflective sensor is used. However, if a highly transmissive material is used for the intermediate transfer member or the transfer belt, a configuration using a transmissive sensor is naturally applicable.

  The present invention is useful for an image forming apparatus that forms an image by an electrophotographic system or an electrostatic recording system.

1 is a schematic configuration diagram of a color image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a control block diagram of the color image forming apparatus according to Embodiment 1 of the present invention. It is a figure which shows the relationship between the image density and contrast potential which show the density control method of Embodiment 1 of this invention. It is a flowchart which shows the density | concentration control procedure of Embodiment 1 of this invention. It is the schematic which shows contrast potential. It is a flowchart from a photo sensor to density | concentration conversion. It is a figure which shows the relationship between a photosensor output and image density. It is the schematic which shows the density | concentration fluctuation | variation by the conventional density | concentration control method. It is the schematic which shows the density | concentration fluctuation | variation by the density | concentration control method of Embodiment 1 of this invention. It is a schematic block diagram of the color image forming apparatus which concerns on Embodiment 2 of this invention.

Explanation of symbols

3 Rotating developing device 4 Photosensitive drum (image carrier)
5 Transfer drum 6 Recording material 7 Fixing device 8 Primary charger 9 Cleaner 10 LED
DESCRIPTION OF SYMBOLS 11 Photodiode 12 Surface potential sensor 40 Photosensor 51 Intermediate transfer body 100 Printer engine 105 CCD sensor 109 Printer control part 110 Semiconductor laser

Claims (16)

An image carrier, a charging unit that applies a charging bias to charge the image carrier, an image information writing unit that forms an electrostatic latent image on a charging surface of the image carrier, and the electrostatic latent image. An image forming apparatus for developing a toner image with a developer as a toner image, and transferring the toner image from the image carrier to a recording material on the recording material carrier to form an image on the recording material.
There is provided density control means for obtaining a desired image density by reading at least one detection toner image formed on the image carrier by optical detection means and changing image forming conditions based on the read detection result. When the change amount of the image forming condition calculated from the detection result read by the optical detection unit exceeds a preset limit value, the calculated change amount of the image forming condition and the limit value An image forming apparatus characterized in that a next control interval is determined in accordance with the difference between the two.   The image forming condition is changed to a limit value when a change amount of the image forming condition calculated from a detection result read by the optical detection unit exceeds a preset limit value. The image forming apparatus according to 1.   When the change amount of the image formation condition calculated from the detection result read by the optical detection unit exceeds a preset limit value, the image formation condition is set to the calculated change amount of the image formation condition. 2. The image forming apparatus according to claim 1, wherein the value is changed to a value obtained by adding a limit value to a value obtained by multiplying a certain ratio.   The image forming condition to be changed based on the detection result read by the optical detection unit includes at least one of a charging potential, a developing potential, and an exposure light amount. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the control by the density control unit is executed according to a preset frequency.   The image forming apparatus according to claim 1, wherein the optical detection unit detects a density of the detection toner image formed on the image carrier.   The optical detection means detects in advance an area on the image carrier that is not carrying an image before the detection toner image is formed. Image forming apparatus. An image carrier, a charging unit that applies a charging bias to charge the image carrier, an image information writing unit that forms an electrostatic latent image on a charging surface of the image carrier, and the electrostatic latent image. And developing the toner image with a developer as a toner image. The toner image is transferred from the image carrier onto the intermediate transfer member to form an image on the intermediate transfer member, and then the image is transferred from the intermediate transfer member to the recording material. In the image forming apparatus to be transferred onto
There is provided density control means for obtaining a desired image density by reading at least one detection toner image formed on the intermediate transfer member by an optical detection means and changing image forming conditions based on the read detection result. When the change amount of the image forming condition calculated from the detection result read by the optical detection unit exceeds a preset limit value, the calculated change amount of the image forming condition and the limit value An image forming apparatus characterized in that a next control interval is determined in accordance with the difference between the two.   The image forming condition is changed to a limit value when a change amount of the image forming condition calculated from a detection result read by the optical detection unit exceeds a preset limit value. 9. The image forming apparatus according to 8. When the change amount of the image formation condition calculated from the detection result read by the optical detection unit exceeds a preset limit value, the image formation condition is set to the calculated change amount of the image formation condition. 9. The image forming apparatus according to claim 8, wherein the value is changed to a value obtained by adding a limit value to a value obtained by multiplying a predetermined ratio.
Image forming apparatus.   11. The image forming condition to be changed based on a detection result read by the optical detection unit includes at least one of a charging potential, a developing potential, and an exposure light amount. The image forming apparatus described.   11. The image forming apparatus according to claim 8, wherein the control by the density control unit is executed in accordance with a preset frequency.   13. The image forming apparatus according to claim 8, wherein the optical detection unit detects a density of the detection toner image formed on the intermediate transfer member.   14. The image forming apparatus according to claim 8, wherein the optical detection unit detects in advance an area on the intermediate transfer member on which the image is not carried before the toner image for detection is formed. .   9. The image forming apparatus according to claim 1, further comprising an image carrier position information detecting unit that detects position information of the image carrier.   9. The image forming apparatus according to claim 1, wherein the optical detection unit is a regular reflection type sensor.

Images