JP2006220848A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus designed such that a user's waiting time is reduced, productivity is high, process control accuracy is improved by correct detection of the density and position information of a toner pattern, and stable image quality is ensured. <P>SOLUTION: The image forming apparatus detects the density or position information of a toner pattern on an intermediate transfer body with a prescribed timing by an image density detection means, and exerts process control based upon the result of the detection. In the image forming apparatus, when the toner pattern is formed, a secondary transfer roller is separated from an intermediate transfer body, then an image is formed with such a timing that a toner pattern formed by an image forming unit located furthest downstream in the direction of the movement of the intermediate transfer body first comes to the detecting area of the image density detecting means. That is, where image formation is carried out for Y, C, M, and K in that order, images are actually formed for K, M, C, and Y in that order. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a plotter.

In a so-called tandem color image forming apparatus having a plurality of image forming units, a toner pattern (detection pattern, patch pattern) is formed on an image carrier in order to make the image density and image position constant. Is widely known in which various processes are controlled based on the detection result.
However, due to such process control, a “waiting time (hereinafter also simply referred to as a waiting time)” that cannot be used by the user has occurred. In recent years, reduction of this waiting time has been demanded.

  On the other hand, in an image forming apparatus that does not have a cleaning mechanism for cleaning a secondary transfer roller that transfers an image from an intermediate transfer belt to paper (recording medium) for the purpose of saving space and reducing costs, If a non-transferred image that is not transferred onto paper adheres to the secondary transfer roller, problems such as back stains occur during normal image formation. In addition, the secondary transfer roller needs to be separated from the intermediate transfer belt.

In an apparatus in which the secondary transfer roller needs to be separated when creating the toner pattern as described above, due to the contact / separation operation, creation is not in time between normal images, and the gap between sheets is increased. Therefore, it will be a waiting time.
In such an image forming apparatus, the contact and separation of the secondary transfer roller with respect to the intermediate transfer belt adversely affects the image and the toner pattern due to vibration, noise, and the like.
In order to avoid this problem, conventionally, after the image is created, the process is once stopped, the secondary transfer roller is separated and then raised again to form a toner pattern, and the toner pattern passes through the secondary transfer portion. When there is an image to be continuously formed after the process is stopped, the waiting time has been increased because the process is started again after the secondary transfer roller is brought into contact with the intermediate transfer belt.
In order to solve such a problem, in the technique described in Japanese Patent Laid-Open No. 2002-123052, the secondary transfer roller is separated after the toner pattern passes the final color portion of the primary transfer.

JP 2002-123052 A JP 2003-186278 A JP 2003-167406 A

However, in order to eliminate the influence of the contact / separation operation of the secondary transfer roller, it is premised that a series of toner patterns enter between the primary transfer site and the secondary transfer site of the most downstream image forming unit. It cannot be applied to key patterns.
Also, for the purpose of reducing the waiting time, a patent is also disclosed in which the control operation is interrupted when there is an image formation instruction (image formation instruction) during execution of these process controls. Yes.
However, as soon as toner pattern image formation is started from the upstream image formation unit in the same order as normal image formation, the untransferred image on the intermediate transfer belt passes through the secondary transfer portion even if an interruption command is issued immediately. Otherwise, the secondary transfer roller cannot be brought into contact, and then normal image formation is started. Therefore, even though the control operation is interrupted in order to give priority to normal image formation, it is quite normal. There was a problem of not being able to enter the image forming operation.

  Therefore, the present invention can reduce the waiting time of the user, is highly productive, can accurately detect the density and position information of the toner pattern, can improve the accuracy of the process control, and has a stable image quality. The main purpose is to provide a forming apparatus.

  In order to achieve the above object, according to the first aspect of the present invention, there are provided a plurality of image forming units for forming an image on an image carrier, and a toner image formed by these image forming units is superimposed on an intermediate transfer member. And transferring the superimposed toner images onto a recording medium in a batch by a secondary transfer means that can be moved toward and away from the intermediate transfer member. In the image forming apparatus that detects the density or position information of the toner pattern by the image density detection means and performs process control based on the detection result, when creating the toner pattern, the secondary transfer means is used as the intermediate transfer After being separated from the body, the toner pattern by the image forming unit located on the most downstream side in the moving direction of the intermediate transfer body first comes to the detection site of the image density detection means. Characterized by image formation in Una timing.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, prior to the separation operation of the secondary transfer means, the predetermined charging in which the image forming conditions of the plurality of image forming units are different from normal image forming. It is switched to a potential, and when the region where the toner pattern is formed on the intermediate transfer member comes into contact with each image forming unit, the switched potential is set.

  According to the first aspect of the present invention, when creating a toner pattern, it is necessary to wait for a time until the most upstream color reaches the position of the image density detecting means by performing image formation from the most downstream development color. Since the toner pattern can be generated at an early stage, the waiting time can be reduced and the usability can be improved.

  According to the second aspect of the present invention, stable developing ability can be detected by aligning the charging conditions of a plurality of image forming units to a predetermined potential. By switching the charging potentials of the plurality of image forming units prior to the separation operation, in addition to the effect of claim 1, stable detection can be performed even if the downstream image formation unit performs image formation immediately after the separation operation. The pattern can be detected and the image quality can be stabilized.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
First, an overview of the overall configuration of an electrophotographic laser printer (hereinafter also simply referred to as “printer”) as an image forming apparatus according to the present embodiment will be described with reference to FIG.
The printer 100 includes process cartridges 6Y, 6C, 6M, and 6K as four image forming units for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, C, M, and K). ing. These use Y, C, M, and K toners of different colors as image forming substances, but the other configurations are the same and are replaced when the lifetime is reached.
The structure of the process cartridge 6Y for generating a Y toner image will be described as a representative. As shown in FIG. 2, a drum-shaped photosensitive member 1Y as an image carrier, a drum cleaning device 2Y, a charge eliminating device (not shown). ), A charging device 4Y, a developing device 5Y, and the like. The process cartridge 6Y can be attached to and detached from the printer 100 main body, and consumable parts can be replaced at a time.

The charging device 4Y uniformly charges the surface of the photoreceptor 1Y that is rotated in the clockwise direction in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1Y is exposed and scanned by the laser light L to carry an electrostatic latent image for Y.
The Y electrostatic latent image is developed into a Y toner image by the developing device 5Y using Y toner. Then, intermediate transfer is performed on an intermediate transfer belt 8 as an intermediate transfer member.
The drum cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process. The static eliminator neutralizes residual charges on the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. The other process cartridges 6C, 6M, and 6K have the same configuration, and similarly, C, M, and K toner images are formed on the photoreceptors 1C, 1M, and 1K, and the intermediate transfer belt 8 is formed. Transcribed.

  As shown in FIG. 1, an exposure device 7 is disposed below the process cartridges 6Y, 6C, 6M, and 6K in the drawing. The exposure device 7 serving as a latent image forming unit irradiates each of the photoconductors in the process cartridges 6Y, 6C, 6M, and 6K with a laser beam L emitted based on the image information. By this exposure, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 1Y, 1C, 1M, and 1K. The exposure device 7 has a well-known configuration in which a laser beam L emitted from a light source is irradiated onto a photoconductor via a plurality of optical lenses and mirrors while scanning with a polygon mirror that is rotationally driven by a motor. .

On the lower side of the exposure apparatus 7 in the drawing, a sheet feeding unit having a sheet feeding cassette 26, a sheet feeding roller 27 incorporated in the sheet feeding cassette 26, a pair of registration rollers 28, and the like are disposed.
A plurality of transfer sheets S as recording media are stored in the sheet feed cassette 26, and a sheet feed roller 27 is in contact with each uppermost transfer sheet S. When the paper feed roller 27 is rotated counterclockwise in the figure by a driving means (not shown), the uppermost transfer paper S is fed toward the rollers (nip) of the registration roller pair 28. The registration roller pair 28 rotationally drives both rollers so as to sandwich the transfer sheet S, but temporarily stops rotating immediately after the sandwiching. Then, the transfer sheet S is sent out toward a secondary transfer nip described later at an appropriate timing. In the sheet feeding unit having such a configuration, a recording medium conveying unit is configured by a combination of a sheet feeding roller 27 and a registration roller pair 28 as a timing roller pair. The recording medium transporting unit transports the transfer paper S from a paper feed cassette 26 serving as a storage unit to a secondary transfer nip described later.

Above the process cartridges 6Y, 6C, 6M, and 6K in the drawing, a transfer unit 15 that moves the intermediate transfer belt 8 endlessly while being stretched is disposed.
In addition to the intermediate transfer belt 8, the intermediate transfer unit 15 includes four primary transfer bias rollers 9Y, 9C, 9M, and 9K, a cleaning device 10, and the like. A secondary transfer backup roller 12, a cleaning backup roller 13, a tension roller 14 and the like are also provided. The intermediate transfer belt 8 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers while being stretched around these three rollers.
The primary transfer bias rollers 9Y, 9C, 9M, and 9K sandwich the intermediate transfer belt 8 that is moved endlessly between the photoreceptors 1Y, 1C, 1M, and 1K to form primary transfer nips, respectively. Yes. In these methods, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 8.

All the rollers except the primary transfer bias rollers 9Y, 9C, 9M, and 9K are electrically grounded. The intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, C, M, and K along with the endless movement thereof, and Y, C, and M on the photoreceptors 1Y, 1C, 1M, and 1K. , K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 8.
The secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 between the secondary transfer roller 19 as a transfer member and forms a secondary transfer nip. The four-color toner image formed on the intermediate transfer belt 8 is transferred to the transfer paper S at the secondary transfer nip.
Untransferred toner that has not been transferred to the transfer sheet S adheres to the intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the cleaning device 10.

In the secondary transfer nip, the transfer sheet S is sandwiched between the intermediate transfer belt 8 and the secondary transfer roller 19 whose surfaces move in the forward direction, and is conveyed in the opposite direction to the registration roller pair 28 side. When the transfer sheet S sent out from the secondary transfer nip passes between rollers of the fixing device 20, the four-color toner image transferred to the surface is fixed by heat and pressure. Thereafter, the transfer sheet S is discharged out of the apparatus through the pair of discharge roller pairs 29. A stack unit 30 is formed on the upper surface of the printer main body, and the transfer sheets S discharged to the outside by the discharge roller pair 29 are sequentially stacked on the stack unit 30.
Under the stack unit 30, toner cartridges 2Y, 32M, 32C, and 32K are arranged.

In FIG. 1, a reflection type photosensor 40 as an image density detection means is disposed above the secondary transfer backup roller 12 so as to output a signal corresponding to the light reflectance on the intermediate transfer belt 8. It is configured.
The reflection type photosensor 40 has a sufficient difference between the amount of reflected light on the surface of the intermediate transfer belt 8 and the amount of reflected light of a reference pattern image (toner pattern) to be described later, of the diffused light detection type or the regular reflection light detection type. Whichever value can be used is used. The role of the reflective photosensor 40 will be described later.

FIG. 3 is a block diagram showing a part of the electric circuit of the laser printer. In the figure, control unit 150 is electrically connected to toner image forming units (process cartridges) 6Y, 6M, 6C, 6K, optical writing unit 7, paper feed cassette 26, registration roller pair 28, transfer unit 15, reflection type. The photo sensor 40 and the like are controlled. The control unit 150 includes a CPU 150a that controls the arithmetic unit and the like, and a RAM 150b that stores data.
The controller 150 is formed on the intermediate transfer belt 8 at a predetermined timing such as when a main power supply (not shown) is turned on, when waiting after a predetermined time has elapsed, or when waiting after outputting a predetermined number of sheets or more. It is configured to detect the density of the toner pattern and control each process so that it maintains the target density.

FIG. 4 is a schematic diagram showing the reference pattern image P (Py, Pc, Pm, Pk). In the figure, the reference pattern image P is composed of four reference images arranged at intervals of 5 mm. In this laser printer, each reference image 101 is 15 mm long × 12 mm wide and is formed through a gap of 5 mm.
Therefore, the lengths of the reference pattern images Py, Pc, Pm, and Pk on the intermediate transfer belt 8 are L3 = 75 mm, respectively. The reference pattern images Py, Pc, Pm, and Pk are transferred so as to be arranged on the intermediate transfer belt 8 without overlapping, unlike the toner images of the respective colors formed during the printing process. By such transfer, one pattern block constituted by the reference pattern images Py, Pc, Pm, and Pk of each color is formed on the intermediate transfer belt 8. The image forming potential at this time is set to the same charging potential and developing bias as the image portion for each color.

FIG. 5 is a schematic diagram showing the installation pitch of the photosensitive drum 1. As illustrated, the photosensitive drums 1Y, 1C, 1M, and 1K are set to L1 = 100 mm and L2 (1) = 95 mm, respectively.
In FIG. 5, a reflection type photosensor 40 as an image density detecting means is disposed on the upper right side of the transfer unit 15 including the intermediate transfer belt 8 in the drawing. Each reference pattern image on the intermediate transfer belt 8 is moved with endless movement and detected by the reflective photosensor 40, and then removed by the cleaning device 10 of the transfer unit 15.
The reflective photosensor 40 reflects the amount of light reflected from each reference image 101 constituting the reference pattern images Py1, Pc1, Pm1, and Pk1 from the front end to the rear end of the first pattern block PB1. A voltage signal corresponding to the amount of reflection is detected by a method described later, and sequentially output to the control unit 150.
The control unit 150 sequentially calculates the image density of each reference image 101 based on the voltage signals sequentially sent from the reflection type photosensor 40 and stores it in the RAM 150b. Note that the diffused light detection type is desirable for the reflective photosensor 40 in that it can detect a high density portion of color toner.

Image forming and toner pattern forming operations will be described based on the flowchart of FIG.
When a normal image forming operation is instructed, the secondary transfer roller is brought into contact with the intermediate transfer belt 8 (S1), and the process is started to form an image (S2). Next, it is determined whether or not it is the execution timing of the process control (S3). If it is not the execution timing, the secondary transfer cleaning is started (S10).
Here, the toner attached to the secondary transfer roller 19 is reversed onto the intermediate transfer belt 8 by applying a secondary transfer bias opposite to that at the time of image formation only at the timing between the secondary transfer portions of the paper. The secondary transfer roller 19 is cleaned by applying an electric field. Here, the toner adhering to the intermediate transfer belt 8 is cleaned by the cleaning device 10.

Next, it is determined whether or not there is an image (S11). If there is an image, the process returns to S2, and if there is no image, the secondary transfer roller 19 is separated to end the process (S12).
If it is the process control timing in S3, a toner pattern is formed following the previous image (S4). As shown in FIG. 4, the toner pattern at this time is formed such that Py, Pc, Pm, Pk and the normal image are not overlapped on the intermediate transfer belt 8 in the order of image formation.
Next, it is determined whether or not these toner patterns have passed through the primary transfer portion of the final color (the most downstream image forming unit) and the top of the toner pattern has come to a predetermined position before the secondary transfer roller 19 ( In step S5, the secondary transfer roller 19 is moved away from the transfer belt 8 when it comes (S6).
Next, the density of the toner pattern is detected by the reflective photosensor 40 (S7), and process control is executed (S8). In parallel with this, along with the end of toner pattern density detection, the secondary transfer roller 19 is brought into contact with the intermediate transfer belt 8 (S9).

As described above, when the pattern length (L3) as shown in FIG. 4 is shorter than the most downstream primary transfer position to secondary transfer roller position (L2 = L2 (1) + L2 (2)), it is continuously. A stable toner pattern can be detected by creating a toner pattern and controlling the contact and separation timing of the secondary transfer roller 19.
However, when a plurality of toner patterns are formed as a gradation pattern, L3> L2, and the secondary transfer roller 19 needs to be separated while the pattern is being formed. In addition, the toner pattern image is disturbed and an accurate toner pattern cannot be detected.

For this reason, conventionally, as shown in FIGS. 10 and 11, after the secondary transfer roller 19 is separated, a continuous gradation pattern is created. In FIG. 11, the image and the pattern actually have respective colors, but are omitted here and are distinguished by Y, C, M, and K (the same in FIG. 8).
However, in this method, since image formation is started from the most upstream Y (yellow), the time for the Y pattern to reach the position of the reflective photosensor 40 is wasted. That is, as shown in FIG. 11, the time for the Y pattern to reach the position of the reflective photosensor 40 becomes longer. For example, when the interval from separation to contact of the secondary transfer roller 19 is the waiting time Wt, the result As a result, the waiting time Wt becomes longer. In FIG. 11, a symbol J indicates a superimposed image.

In this embodiment, control for shortening the waiting time Wt is performed. Hereinafter, the control operation will be described.
The gradation pattern is created as follows. When the timing for creating the gradation pattern (for example, when the predetermined number of sheets is reached or when the main power is turned on), the photosensitive drums 1Y, 1C, 1M, and 1K are first uniformly charged while rotating.
Unlike the uniform charging potential (for example, −700 V) set for each color during normal printing, this charging is gradually increased. The developing units 6Y, 6C, 6M, and 6K develop the electrostatic latent image for the reference pattern image by scanning with the laser beam. By this development, bias development pattern images of the respective colors are formed on the photosensitive drums 1Y, 1C, 1M, and 1K. During development, the control unit 150 performs control so that the value of the developing bias applied to the developing roller 51 of each developing unit 6 is also gradually increased. Table 1 shows the set potential at this time.

While the potential is set for a predetermined color, the laser writing level of the corresponding color is set to 255 (full power), and the other image forming units are charged (DC) -700 V and developing bias -550 V. The laser writing level is fixed at 0.
The potential setting conditions are not necessarily set as shown in Table 1, and the toner pattern is formed under the process conditions necessary for process control.
The bias development pattern images of these colors are transferred so as to be arranged on the intermediate transfer belt 8 without overlapping. By this transfer, a pattern block constituted by the reference pattern image of each color is formed on the intermediate transfer belt 8.
When the reference image of each reference pattern image in the pattern block passes through the position facing the reflective photosensor 40 as the intermediate transfer belt 8 moves endlessly, the amount of reflected light is detected and an electric signal is detected. It is output to the control unit 150. The control unit 150 calculates the light reflectance of each reference image based on the output signals sequentially sent from the reflection type photosensor 40, and stores it in the RAM 150a as density pattern data.

The pattern block that has passed the position facing the reflective photosensor 40 is cleaned by the cleaning device 10.
The toner adhesion amount for each image forming potential thus obtained, so-called development γ characteristics, is used for determining the image forming potential of a normal image, controlling the toner density, etc., but is widely known as a control method. However, although details are omitted, for example, well-known means can be applied as process control means.
For example, a technique described in Japanese Patent Application Laid-Open No. 2002-132097 can be cited as density control based on toner pattern density detection. Further, as a control of the image position by detecting the position of the toner pattern, there is a technique described in Japanese Patent No. 2642351.

Next, the control operation will be described with reference to FIGS.
When it is determined in S3 of FIG. 7 that the process control execution timing is determined, first, detection pattern creation conditions are sequentially set from the upstream Y image forming unit (S4). In other words, prior to the separation operation of the secondary transfer roller 19, the charging potential is switched to a predetermined charging potential different from normal image formation. Specifically, each color has a charging potential of −700 V and a developing bias of −550 V.
Next, the secondary transfer roller is separated (S5). Next, a detection pattern is created (S6). What is important at this time is that the image is created from the K image forming unit at the most downstream position as shown in FIG.
A pattern is formed by sequentially switching the image forming condition of K to the potential shown in Table 1. That is, when the region where the toner pattern is formed on the intermediate transfer belt 8 comes into contact with each image forming unit, the potential is switched (the potential shown in Table 1). At this time, the area of the intermediate transfer belt 8 coming to the K primary transfer site is where the other image forming units have passed with the setting of the charging potential of −700 V and the developing bias of −550 V.

When K is over, the pattern is created by successively switching the imaging conditions of M, which is the next upstream positional relationship, to the potentials shown in Table 1. At this time, K is set to a predetermined charging potential of −700 V and a developing bias of −550 V.
In this way, it is very important that not only the color units to be imaged but also the image forming conditions for other colors are set to predetermined conditions.
FIG. 9 shows data in which the charging potential of the image forming unit, the transfer rate, and the reverse transfer rate are plotted. Here, the primary transfer performs the constant current transfer bias control used in this system. As can be seen from the figure, the higher the charging potential, the worse the transfer rate (the rate at which toner is transferred from the photoconductor to the intermediate transfer belt), and the lower the charging potential, the reverse transfer rate (the toner returns from the intermediate transfer belt to the photoconductor). It can be seen that the ratio is worse.

As a matter of course, the image of the upstream image forming unit (station) passes through the primary transfer portion of the other image forming unit, so that the final charge potential can be determined by the set charging potential without overlapping the pattern on the intermediate transfer belt 8. Thus, the amount of toner remaining on the intermediate transfer belt 8 changes.
Accordingly, the toner that is finally transferred onto the intermediate transfer belt 8 even if the developing ability is constant, unless the charging potential of the other image forming unit when forming the toner pattern is appropriately set. The amount of adhesion changes.

As described above, unlike the normal image forming order, by forming an image from the downstream image forming unit, unnecessary time waiting for the Y toner pattern to move is eliminated, so that the secondary transfer unit Even in a system that requires contact and separation, it is possible to form a long toner pattern in a short time. That is, as shown in FIG. 8, the waiting time Wt can be shortened compared to the case of FIG.
In this way, all the patterns are imaged (S6), the toner adhesion amount is detected (S7), and process control is executed (S8). Thereafter, the secondary transfer roller is contacted (S9).
Next, it is determined whether or not normal image formation is continued (S11). If there is no subsequent image formation, the secondary transfer roller is separated (S12). Complete the control operation.

Specific process conditions in the present embodiment are as follows.
As the photosensitive member 1, an organic photosensitive member (OPC) is used, and the charging device 4 is a charging roller. Light that is uniformly charged to -200 to -2000V is irradiated with laser light corresponding to the image of the document. Writing is performed to form an electrostatic latent image.
The toner is negatively positively developed using a negatively chargeable toner to form a toner image on the photoreceptor 1. As the intermediate transfer belt 8, an intermediate transfer belt made of a thermosetting resin having a thickness of 0.10 mm, a width of 246 mm, and an inner peripheral length of 796 mm was used, and the moving speed of the intermediate transfer belt 8 was set to 150 mm / sec.
When the volume resistivity of the entire intermediate transfer belt 8 formed of such a material was measured, it was 10 ⁷ to 10 ¹² Ωcm.
Each volume resistivity is measured by applying a voltage of 100 V for 10 seconds using the measuring method described in JIS K6911. Further, the surface resistivity of the intermediate transfer belt 8 was measured by a resistance measuring instrument “HI-Lester IP” manufactured by Mitsubishi Oil Chemical Co., Ltd. and found to be 10 ⁹ to 10 ¹⁴ Ω / □. This surface resistivity can be measured by the surface resistance measuring method described in JIS K 6911, in addition to using the resistance measuring instrument. As the secondary transfer roller 19, a roller made of urethane foam resin having a diameter of 26 mm and a width of 230 mm was used.

1 is a schematic front view of a laser printer as an image forming apparatus according to an embodiment of the present invention. It is an enlarged schematic front view of a process cartridge corresponding to a yellow image. It is a control block diagram. FIG. 3 is a schematic plan view showing a toner pattern arrangement state. It is a figure which shows the arrangement | positioning relationship of a photoreceptor. 6 is a flowchart illustrating a creation operation when the entire length of a toner pattern is short. 10 is a flowchart illustrating a creation operation when the entire toner pattern is long. 6 is a timing chart illustrating a creation operation when the entire toner pattern is long. It is a graph which shows the relationship between a charging potential, a transfer rate, and a reverse transfer rate. 10 is a flowchart showing a creation operation when the entire length of a toner pattern in the related art is long. 10 is a timing chart illustrating a creation operation in the case where the entire length of a conventional toner pattern is long.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor as image carrier 6 Process cartridge as image forming unit 8 Intermediate transfer belt as intermediate transfer member 19 Secondary transfer roller as secondary transfer means 40 Reflective photosensor P as image density detection means P Toner pattern S Transfer paper as recording medium

Claims (2)

There are multiple image forming units that form images on the image carrier, and the toner images formed by these image forming units can be transferred onto the intermediate transfer member for primary transfer, and contacted and separated from the intermediate transfer member. A secondary transfer unit that collectively transfers the superimposed toner images onto a recording medium, and the density or position information of the toner pattern on the intermediate transfer member is detected by the image density detection unit at a predetermined timing. In an image forming apparatus that performs process control based on the detection result,
When creating the toner pattern, after the secondary transfer means is separated from the intermediate transfer member, the toner pattern by the image forming unit located on the most downstream side in the moving direction of the intermediate transfer member is first subjected to the image density. An image forming apparatus characterized in that an image is formed at a timing such that it comes to a detection part of a detection means. The image forming apparatus according to claim 1.
Prior to the separation operation of the secondary transfer means, the image forming conditions of the plurality of image forming units are switched to a predetermined charging potential different from the normal image forming, and the toner pattern on the intermediate transfer member is formed. An image forming apparatus having a switched potential when an area to be contacted with each image forming unit.

Images