JP4817722B2 - Image forming apparatus - Google Patents

Description

  In the present invention, a detection toner image is formed in an inter-image region between toner images repeatedly formed on an image carrier, and the toner image on the image carrier is contacted with the image carrier to a recording material. The present invention relates to the removal of toner adhering to a transfer member in an image forming apparatus in which a transfer member to be transferred is in contact with a region between images of an image carrier.

  In recent years, there has been an increasing demand for stabilization of image quality of electrophotographic image forming apparatuses.

  Therefore, when a plurality of toner images are repeatedly formed on the image carrier, a detection toner image is formed in an inter-image region between the toner images on the image carrier and the detection result of the detection toner image. The image quality is stabilized by increasing the frequency of controlling the toner image forming conditions based on the above.

  On the other hand, the transfer member that contacts the image carrier when the toner image on the image carrier is transferred to the recording material is also in contact with the inter-image region where the toner image to be transferred to the recording material does not exist. As a result, it is possible to suppress the occurrence of vibration associated with the contact and separation of the transfer member with respect to the image carrier, to narrow the area between the images, and to increase the number of images that the image forming apparatus can form per unit time. Can do.

Here, when the transfer member is in contact with the inter-image region, the fog toner or the detection toner image in the inter-image region adheres to the transfer member. To remove the toner This deposition, while the transfer member is in contact with the inter-image area, (for example, Patent cleaning electric field is made the form of moving toner adheres electrostatically image bearing member to a transfer member References 1 and 2).

  However, the toner is not sufficiently removed from the transfer member to which the detected toner image adheres, and there is a problem that the toner adheres to the surface of the recording material in contact with the transfer member.

The above object is achieved by the image forming apparatus according to the present invention. In summary , according to the first aspect of the present invention ,
A moving image carrier;
A toner image forming means for forming a preparative toner image on the image bearing member,
A transfer member for forming a transfer nip for transferring the toner image formed on the image carrier to a recording material;
Detecting means for detecting a detection toner image formed on the image carrier by the toner image forming means ;
And control means for variably controlling a toner image forming condition based-out before Symbol toner image forming means on the result of said detecting means,
During continuous image formation in which images are continuously formed on a plurality of recording materials, the transfer member is cleaned by applying a bias having the same polarity as the normal polarity of the toner and a bias having the opposite polarity to the transfer member during image formation. Cleaning means,
In continuous image formation, in the image forming apparatus in which the transfer member presses the image carrier during image formation and in the transfer process, and the toner image forming unit can form a detection toner image during predetermined image formation. ,
At the time of continuous image formation, after the formed detection toner image passes through the transfer nip portion, a bias having the same polarity as the normal polarity of the toner and a bias having the opposite polarity are alternately applied to the transfer member by the cleaning unit. There is provided an image forming apparatus characterized in that the number of repetitions and the cleaning time are made larger than the number of repetitions and the cleaning time when the detected toner image is not formed.
According to a second aspect of the invention,
A moving image carrier;
Toner image forming means for forming a toner image on the image carrier;
A transfer member for forming a transfer nip for transferring the toner image formed on the image carrier to a recording material;
Detecting means for detecting a detection toner image formed on the image carrier by the toner image forming means;
Control means for variably controlling toner image forming conditions of the toner image forming means based on the result of the detecting means;
Cleaning means for cleaning the transfer member by applying a bias having the same polarity as the normal polarity of toner and a reverse polarity bias to the transfer member in contact with the image carrier;
In the image forming apparatus in which the toner image forming unit is capable of forming a detected toner image during predetermined image formation and during post-rotation,
After the detected toner image formed in the state where the transfer member and the image carrier are in contact with each other, the cleaning means applies a bias having the same polarity as the normal polarity of the toner and a bias having a reverse polarity. As for the number of repetitions and the cleaning time for alternately applying to the transfer member, the case where it is performed during post-rotation is smaller than the case where it is performed during image formation, respectively.
During the pre-rotation of the next image forming job after the end of the post-rotation, a bias having the same polarity as the normal polarity of the toner and a bias having a reverse polarity are alternately applied to the transfer member by the cleaning unit. An image forming apparatus is provided that performs cleaning.

According to the present invention, even when the detected toner image adheres to the secondary transfer roller 26 (transfer member) and the amount of toner adhering to the recording material increases, sufficient toner removal can be performed, and recording can be performed. The problem that the toner adheres to the surface of the material that contacts the secondary transfer roller 26 (transfer member) can be solved. That is, the toner amount per unit area of the detected toner image is larger than the toner amount per unit area of the fog toner. For this reason, the time for forming the cleaning electric field for removing the toner of the detected toner image is set longer than the time for forming the cleaning electric field for removing the fog toner, thereby causing the secondary transfer roller 26 (transfer member) to move. The toner in the detected toner image adhering could be sufficiently removed.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
The present invention can be embodied in the electrophotographic color image forming apparatus shown in FIG. Therefore, an electrophotographic color image forming apparatus which is an embodiment of the image forming apparatus of the present invention will be described in detail with reference to FIG.

  In this embodiment, the image forming apparatus is supported by support rollers 29a, 29b, and 29c, which are intermediate transfer members serving as image carriers, and an endless intermediate transfer belt 28 that runs in the direction of arrow X within the main body. It has. The intermediate transfer belt 28 is formed of a dielectric resin film such as polycarbonate, polyethylene terephthalate, or polyvinylidene fluoride. The recording material 8 taken out from a paper feed cassette (not shown) is supplied to a secondary transfer portion of the intermediate transfer belt 28 through a registration roller 32.

  Above the intermediate transfer belt 28, an image forming portion P as a toner image forming unit is disposed. The image forming part P is composed of four parts Pa, Pb, Pc, and Pd, and Pa, Pb, Pc, and Pd are arranged in series. Pa, Pb, Pc, and Pd constituting the image forming unit have substantially the same configuration, except that magenta, cyan, yellow, and black toner images are formed.

  Pa, Pb, Pc, and Pd constituting the image forming unit include a photosensitive drum 21 (21a, 21b, 21c, and 21d) that is rotatably arranged. In this embodiment, the photosensitive drum 21 (21a, 21b, 21c, 21d) is exposed around the contact charging device 22 (22a, 22b, 22c, 22d), which is charging means, and the charged photosensitive drum 21, An exposure device 80 (80a, 80b, 80c, 80d) that is an exposure unit that forms an electrostatic image, a developing device 23 (23a, 23b, 23c, 23d) that constitutes the developing unit, and a cleaning device 25 that constitutes a cleaning unit ( Process devices such as 25a, 25b, 25c, and 25d) are arranged. The Pa, Pb, Pc, and Pd developing devices 23 (23a, 23b, 23c, and 23d) constituting the image forming unit respectively store magenta toner, cyan toner, yellow toner, and black toner charged to negative polarity. Has been.

  The photosensitive drum 21a is uniformly charged to a negative polarity by the contact charging device 22a.

  Laser light based on a magenta component color image signal of an original is projected onto a negatively charged photosensitive drum 21a via a polygon mirror (not shown) or the like, and an electrostatic latent image is formed on the photosensitive drum 21a. The developing device 23a supplies magenta toner charged to a negative polarity to develop it, and the electrostatic latent image is visualized as a magenta toner image. When this toner image arrives at the primary transfer portion where the photosensitive drum 21a and the intermediate transfer belt 28 come into contact with the rotation of the photosensitive drum 21a, the positive polarity applied to the primary transfer roller 24a as the primary transfer means. The magenta toner image on the photosensitive drum 21a is transferred to the intermediate transfer belt 28 by the primary transfer bias (primary transfer).

  When the portion carrying the magenta toner image on the intermediate transfer belt 28 moves to Pb of the image forming unit, a cyan toner image has been formed on the photosensitive drum 21b in the same manner as described above at Pb of the image forming unit. This cyan toner image is transferred onto the intermediate transfer belt 28 from the magenta toner image. Here, also in Pb of the image forming unit, the same charging / bias application as Pa is performed, and a cyan toner image is formed and transferred to the intermediate transfer belt 28. In addition, in Pc and Pd of the image forming unit, which will be described later, the same charging and bias application as Pa described above is performed, and a yellow toner image and a black toner image are formed and transferred to the intermediate transfer belt 28.

Similar to the magenta toner image and cyan toner image transferred to the intermediate transfer belt 28, as the intermediate transfer belt 28 moves, the yellow toner image and the black toner image are respectively transferred to the primary transfer portions Pc and Pd of the image forming unit. Are superimposed and transferred onto the magenta toner image and the cyan toner image, and by this time, the recording material 8 from the paper feeding cassette reaches the secondary transfer portion via the registration roller 32 and serves as a secondary transfer means. The four color toner images on the intermediate transfer belt 28 are collectively transferred onto the recording material 8 by a positive polarity secondary transfer bias applied to the secondary transfer roller 26 which is a conductive sponge-like rubber roller ( Secondary transfer).
Here, a secondary transfer bias is applied to the secondary transfer roller 26 from a power source 70.

  Further, a support roller 29b provided to face the secondary transfer roller 26 via the intermediate transfer belt 28 is electrically grounded.

  The secondary transfer residual toner after the secondary transfer and the toner discharged by the cleaning operation of the secondary transfer roller 26 are cleaned by the cleaning device 11 attached to the intermediate transfer belt 28 to prepare for the next image formation. . The cleaning device 11 in this embodiment employs a blade cleaning method in which urethane rubber is spring-pressed with a predetermined contact pressure.

  Finally, the recording material 8 onto which the four color toner images have been transferred is separated from the intermediate transfer belt 28 and then conveyed to the fixing device 9 by the conveyance belt 27. In the fixing device 9, heat and pressure are applied to the recording material 8 by a pair of rollers 9 a and 9 b to fix the toner image on the recording material 8.

  The image forming apparatus of this embodiment uses a two-component developer in which toner and carrier are mixed in the developing device 23. In the developing device 23 using the two-component developer as in this embodiment, the mixing ratio T / D ratio (D = T + C) of the developer toner (T) and the carrier (C) (the toner concentration of the developer). Hereinafter, it is important to keep the T / D ratio constant, and toner replenishment control (ATR) for keeping the T / D ratio constant is executed. Next, toner supply control in this embodiment will be described with reference to FIG.

  As shown in FIG. 2, in this embodiment, a copy original 101 is projected by a reader unit 51, the original image is decomposed into a large number of pixel units, and a photoelectric conversion signal corresponding to the density of each pixel is output. To do. The output from the reader unit 51 is transmitted to the image signal processing circuit 52, and the image signal processing circuit 52 forms a pixel image signal having an output level corresponding to the density of the pixel for each pixel.

  In order to control the amount of toner supplied to the developing device 23 by the video count method, the level of the output signal of the image signal processing circuit 52 is counted for each pixel and integrated by the video counter 53. An integrated value C1 obtained by integrating the output signals for each pixel corresponds to the amount of toner consumed by the developing device 23 to form one image (toner image) of the original 101.

  The integration signal C1 is applied to the CPU 54 and stored in the RAM 55. The CPU 54 calculates the rotation driving time of the conveying screw 61 required to supply the toner corresponding to the amount of toner consumed by the developing device 23 from the hopper 12 to the developing device 23 based on the integration signal C1. The driving circuit 63 is controlled, and the motor 62 is driven for the above time to replenish toner.

  However, if the T / D ratio is controlled only by the video count type ATR, the toner hopper is replenished depending on the change in the toner state such as the fluidity of the toner and the bulk density depending on the humidity and the leaving state. Since variations in accuracy occur, toner replenishment with respect to the expected consumption cannot be performed well, and the T / D ratio gradually fluctuates. Therefore, a patch image (toner pattern image) as a detected toner image is periodically formed on the intermediate transfer belt 28, the actual toner concentration of the developer in the developing device 23 is obtained, and the T / D ratio fluctuation is corrected. ATR of the patch detection method is performed.

  According to the present embodiment, as shown in FIG. 2, a video count ATR is formed by combining a reader unit 51 and a video counter 53 and the like. Further, the patch includes a detection sensor (detection means) 41 that detects a density by irradiating a toner patch image serving as a reference image from a light source such as an LED and detecting reflected light by a light receiving element such as a photo diode. A detection type ATR is formed. In this embodiment, the detection sensor 41 is arranged at the position of the intermediate transfer belt support roller 29a on the upstream side of the secondary transfer roller 26 on the intermediate transfer belt 28, as can be seen with reference to FIG. .

  In this embodiment, with the above configuration, the density of the patch image is detected by the density sensor 41, and the T / D ratio represented by the output signal is set to an appropriate value of the T / D ratio set in advance and stored in the RAM 55. On the other hand, the CPU 54 as the control means determines whether the toner is high or low, and corrects the toner supply.

  That is, based on the detection result of the patch image of the density sensor 41, the CPU 54 variably controls the T / D ratio (image forming condition). In general, correction by the patch detection method ATR is performed at the time of post-rotation after the end of the image forming operation after a predetermined number of image forming operations, or between the Nth and N + 1th image forming (that is, a predetermined number of times). (Between papers).

  As shown in FIG. 3, the patch image is formed on the intermediate transfer belt 28 and detected by the detection sensor 41.

Patch images, magenta used in the image forming apparatus of the present embodiment, cyan, yellow, and black toners used are respectively 1 tsuzuic one form, it is a total of four formation.

  The four patch images are arranged so as to overlap in the traveling direction of the intermediate transfer belt (arrow X in the figure).

  That is, a patch image is formed in the inter-image region between the Nth image and the (N + 1) th image (toner image) on the intermediate transfer belt 28.

Further, when a patch image is formed in the inter-image region, after the patch image passes through the secondary transfer roller 26, the secondary transfer roller 26 is in contact with the secondary transfer roller 26 between the image regions. Is applied with a cleaning bias, and the toner of the patch image adhering to the secondary transfer roller 26 is removed. This cleaning bias will be described in detail later.

  In this embodiment, N = 100, and patch detection ATR correction is performed every time printing is performed on 100 sheets of paper.

  In this embodiment, the secondary transfer roller 26 is also in contact with the inter-image area of the intermediate transfer belt 28 where no image (toner image) transferred to the transfer material 8 exists.

  The fog toner adheres to the inter-image area of the intermediate transfer belt 28. For this reason, even when a patch image is not formed in the inter-image area, the secondary transfer roller 26 contacts the inter-image area, so that the toner adheres to the secondary transfer roller 26.

The fog toner has a smaller amount of toner per unit area than the patch image, but when a large amount of image formation is repeatedly performed, the toner adhering to the secondary transfer roller 26 is transferred to the back surface of the paper (the surface on which the toner image is transferred). Cause the toner to adhere to the back surface of the toner.

  Therefore, every time a certain number of images are formed, a cleaning bias is applied to the secondary transfer roller 26, and the fog toner adhering to the secondary transfer roller 26 is removed.

  Here, if the fixed number is M sheets, the secondary transfer roller 26 is in contact with the inter-image area between the M-th image and the (M + 1) -th image on the intermediate transfer belt 28. A cleaning bias is applied to the secondary transfer roller 26, and the fog toner adhering to the secondary transfer roller 26 is removed. This cleaning bias will be described in detail later.

  In this embodiment, M = 50, and the fog toner is removed from the secondary transfer roller 26 every time printing is performed on 50 sheets of paper.

  A sequence diagram of the secondary transfer bias in this embodiment including these controls will be described with reference to FIGS.

  FIG. 4 shows a cleaning bias while ATR correction is applied during continuous image formation, a patch image is formed in the inter-image area, and the secondary transfer roller 26 is in contact with the inter-image area where the patch image is formed. It is a sequence diagram in case where is applied.

  FIG. 5 is a sequence diagram in the case where the cleaning bias is applied while the ATR correction is not performed during continuous image formation and the secondary transfer roller 26 is in contact with the inter-image region where the patch image is not formed. It is.

  FIG. 6 shows a cleaning bias while the secondary transfer roller 26 is in contact with an inter-image area where no patch image is formed while patch detection ATR correction is performed during post-rotation after the image forming operation is completed. It is a sequence diagram when no is applied.

  FIG. 7 is a sequence diagram in the case where the cleaning bias is not applied while the secondary transfer roller 26 is in contact with the inter-image area where no patch image is formed without patch detection ATR correction. .

  In this embodiment, during normal image formation, as shown in FIG. 7, when the image forming operation is started, the secondary transfer roller 26 rotates once as cleaning of the secondary transfer roller 26 in accordance with the pre-rotation of the photosensitive drum. After applying a bias of -500V, which is opposite in polarity to the transfer bias, similarly, a bias of + 500V having the same polarity as the transfer bias is applied for one turn. Thereafter, in synchronization with the image forming operation, approximately +2 KV is applied as a transfer bias at the timing when the recording material reaches the secondary transfer roller. At the time of continuous image formation, the operation of once turning off the transfer bias between sheets and starting to apply the transfer bias again at the timing when the next recording material comes is repeated. After the last recording material passes through the secondary transfer roller, a post-rotation cleaning sequence is started. In this embodiment, −500 V and +500 V are applied for the time of one rotation of each secondary transfer roller at the time of post-rotation, and then the secondary transfer bias is turned off to end the post-rotation operation.

  Subsequently, when image formation of the next print job is started, as the cleaning bias of the secondary transfer roller 26 in accordance with the pre-rotation of the photosensitive drum, a bias having a polarity opposite to the transfer bias for one rotation of the secondary transfer roller 26 is performed. , -500V is applied, and in the same manner, a bias having the same polarity as the transfer bias, + 500V, is applied for one round. Thereafter, in synchronization with the image forming operation, approximately +2 KV is applied as a transfer bias at the timing when the transfer material reaches the secondary transfer roller.

  Note that the transfer bias and the cleaning bias are not limited to the values shown above, but appropriately change depending on the recording material, environment, durability, and the like.

  Further, as shown in FIG. 5, in the sequence of cleaning the fog toner adhering to the secondary transfer roller 26 between the papers during the continuous image formation, the secondary transfer roller 26 is located in the area between the images during the continuous image formation. During the contact, after applying a cleaning bias of −500 V and +500 V for each rotation, the normal image forming operation is repeated again in accordance with the timing at which the next transfer material enters the secondary transfer roller nip. In the case where the patch operation does not enter during rotation, as in the sequence shown in FIG. 6, −500 V and +500 V are applied for the duration of one round of the secondary transfer roller 26 respectively, and then the secondary transfer bias is turned off. To complete the post-rotation operation.

  Furthermore, as shown in FIG. 4, in the sequence of patch detection ATR correction between sheets during continuous image formation, the patch image passes through the secondary transfer roller nip portion, that is, the contact portion with the secondary transfer roller 26. During this time, a −100 V bias having a polarity opposite to the transfer bias is continuously applied to the secondary transfer roller 26 to prevent contamination of the secondary transfer roller with the patch image as much as possible. After the patch image has passed through the secondary transfer roller nip, after the cleaning bias of −500 V and +500 V is alternately applied for one turn for each time of the secondary transfer roller, the next recording material is transferred to the secondary transfer roller nip. When the normal image forming operation is repeated again in accordance with the timing of entering the part, and when the patch operation is not performed at the time of the post-rotation, −500 V and +500 V are set to one turn of the secondary transfer roller as in FIG. After the time is applied, the secondary transfer bias is turned off to end the post-rotation operation.

  Next, a secondary transfer bias sequence when patch detection ATR correction is included in the post-rotation will be described with reference to FIG.

  As shown in FIG. 6, when patch detection ATR correction is entered at the post-rotation timing at the end of image formation, the patch image is similar to the sequence between sheets in FIG. 4 while it passes through the secondary transfer roller nip. In addition, a −100 V bias having a polarity opposite to the transfer bias is continuously applied to the secondary transfer roller 26 to prevent contamination of the secondary transfer roller with the patch image as much as possible. After the patch image has passed through the secondary transfer roller nip portion, a cleaning bias of −500 V and +500 V is applied for a time corresponding to two rounds of the secondary transfer roller 26. Thereafter, in order to prevent in-machine contamination due to the adhered toner on the intermediate transfer belt 28, the adhered toner retransferred from the secondary transfer roller 26 to the intermediate transfer belt 28 is cleaned by the cleaning device 11 attached on the intermediate transfer belt 28. Then, the post-rotation operation is finished.

Subsequently, when the image formation of the next print job Ru is started, with the rotation before the photosensitive drum 21, a cleaning of the secondary transfer roller 26, one turn of the secondary transfer roller 26, the transfer bias having a reverse polarity After applying a bias of −500 V, similarly, a bias of +500 V having the same polarity as the transfer bias for one rotation of the secondary transfer roller 26 is applied. Thereafter, in synchronization with the image forming operation, approximately +2 KV is applied as a transfer bias at the timing when the recording material 8 reaches the secondary transfer roller 26.

  In this way, the cleaning bias is applied to the secondary transfer roller 26 in contact with the inter-image region where the patch image is not formed, and the cleaning bias is applied to the secondary transfer roller 26 in contact with the inter-image region where the patch image is formed. By setting the time longer than the time, the toner adhering to the secondary transfer roller 26 could be sufficiently removed.

In addition, when the patch image is formed on the intermediate transfer belt 28 at the timing of post-rotation at the end of the print job, the time during which the cleaning bias is applied to the secondary transfer roller is set to the intermediate transfer belt 28. When the patch image was not formed, the toner attached to the secondary transfer roller 26 could be sufficiently removed by making the cleaning bias longer than the time during which the cleaning bias was applied to the secondary transfer roller 26.

That is, when the toner patch image is formed on the intermediate transfer belt 28 in the inter-image region between the last image of the previous print job and the first image of the next print job, the inter-image region is touched. Application time of the cleaning bias applied to the secondary transfer roller 26 (that is, a bias having the same polarity as the normal polarity of the toner and a bias having the opposite polarity after the toner patch image has passed through the transfer nip portion are alternately 2 The number of repetitions applied to the next transfer roller and the cleaning time) are the application time of the cleaning bias applied to the secondary transfer roller 26 in contact with the image area when the toner patch image is not formed in this image area (ie, the cleaning time ). During the cleaning, the number of repetitions of applying a bias having the same polarity as the normal polarity of the toner and a bias having the opposite polarity to the secondary transfer roller alternately By longer than), it was possible to sufficiently remove the toner adhering to the secondary transfer roller 26.

Example 2
FIG. 8 shows the cleaning time of the secondary transfer roller 26 after the ATR correction of the patch detection method is entered at the post-rotation timing at the end of image formation in the image forming apparatus described in the first embodiment, and the next The result of examining the range in which the back contamination of the recording material 8 that comes first when the cleaning time of the secondary transfer roller 26 during rotation is changed is shown.

  The above examination method is as follows.

  First, as described with reference to FIG. 4 in the first embodiment, while the patch image passes through the secondary transfer roller nip portion, a −100 V bias having a polarity opposite to the transfer bias is continuously applied to the secondary transfer roller. Further, contamination of the secondary transfer roller 26 by the patch image is prevented as much as possible. Next, after the patch image passed through the secondary transfer roller nip portion, the cleaning time of the secondary transfer roller 26 in the post-rotation was changed, and the post-rotation operation was terminated.

  Also, in the secondary transfer roller 26 in the pre-rotation at the start of the next image formation, after changing the cleaning time of the secondary transfer roller 26, it is determined whether or not the first recording material 8 is stained on the back side. It was.

  The horizontal axis in FIG. 8 represents the post-rotation cleaning time after the patch image has passed, and the vertical axis represents the cleaning time during the pre-rotation. The unit was the time for one round of the secondary transfer roller.

  As a result of the examination, as shown in FIG. 8, the total time T2 + T3 of the cleaning time T2 of the secondary transfer roller 26 after the patch image performed at the time of the post-rotation and the cleaning time T3 of the secondary transfer roller 26 at the time of the pre-rotation is obtained. It has been found that the backside contamination of the next recording material 8 can be prevented by setting the time T1 or longer, that is, T1 ≦ T2 + T3, in which the contamination of the secondary transfer roller 26 due to the patch image can be sufficiently cleaned.

Accordingly, as shown in FIG. 9, when patch detection ATR correction is entered at the post-rotation timing at the end of image formation, the patch image is moved between the papers in FIG. 4 while passing through the secondary transfer roller nip. Similar to the sequence, a −100 V bias having a polarity opposite to the transfer bias is continuously applied to the secondary transfer roller 26 to prevent contamination of the secondary transfer roller with the patch image as much as possible. After the patch image passes through the secondary transfer roller nip portion, a cleaning bias of −500 V and +500 V is applied for a time corresponding to one round of the secondary transfer roller 26. That is, after the toner patch image passes through the transfer nip portion, the post-rotation is performed with respect to the number of repetitions and the cleaning time in which the bias having the same polarity as the normal polarity of the toner and the bias having the opposite polarity are alternately applied to the secondary transfer roller. In the case where the operation is performed during the image formation, each is made smaller than the case where the operation is performed during the image formation. Thereafter, the intermediate transfer belt 28 is rotated until the transfer toner that has been retransferred from the secondary transfer roller 26 to the intermediate transfer belt 28 is cleaned by the transfer cleaning blade 11 in order to prevent in-machine contamination due to the adhesion toner on the intermediate transfer belt 28. After that, the post-rotation operation is finished.
That is, in the embodiment shown in FIG. 9, a bias having the same polarity as the normal polarity of the toner and a bias having a reverse polarity are alternately applied after the toner patch image passes through the transfer nip portion. The number of repetitions applied to the next transfer roller 26 and the cleaning time are N1 and T1, respectively, and the number of repetitions and cleaning times performed during post-rotation are N2 and T2, respectively, before the next image forming job after the end of the post-rotation. When the number of repetitions and the cleaning time performed during rotation are N3 and T3,
N1 = N2 + N3,
T1 = T2 + T3
It is said.
Even if the secondary transfer roller cleaning time in the post-rotation is shortened, the secondary transfer cleaning operation for each round of the secondary transfer roller 26 is always performed in the next pre-rotation. The transfer roller 26 can be cleaned, and the back contamination due to the toner adhering to the secondary transfer roller 26 can be reduced.

  FIG. 10 shows a sequence in the case where the patch detection type ATR correction is not included in the post-rotation timing after the end of image formation in this embodiment.

  In this embodiment, when the patch detection type ATR correction is not applied at the timing of post-rotation after the end of image formation, the cleaning bias is not applied to the secondary transfer roller 26 at the time of post-rotation.

Also in this embodiment, the time when the cleaning bias is applied to the secondary transfer roller when the toner patch image is formed on the intermediate transfer belt 28 at the timing of post-rotation at the end of the print job, when the patch image on the intermediate transfer belt 28 is not formed, by longer than the time the cleaning bias is applied to the secondary transfer roller, it is possible to sufficiently remove the toner adhering to the secondary transfer roller 26 did it.

  That is, when a patch image is formed on the intermediate transfer belt 28 in the inter-image area between the last image of the previous print job and the first image of the next print job, the area 2 in contact with the inter-image area 2 The application time of the cleaning bias applied to the secondary transfer roller 26 is longer than the application time of the cleaning bias applied to the secondary transfer roller 26 in contact with the image area when no patch image is formed in the image area. By increasing the length, the toner adhering to the secondary transfer roller 26 could be sufficiently removed.

  Table 1 shows the results of examination of the present example and the conventional examples 1 and 2 and the comparative example 1 which were actually performed as a comparison.

  As described above, as in the conventional example 1, the secondary transfer roller only needs to apply the cleaning bias after the patch image between the sheets passes through the secondary transfer roller for a period of one round of the secondary transfer roller as in the conventional example 1. 26 is insufficiently cleaned, and the next recording material is stained. As the cleaning bias, forward and reverse biases are applied for a time corresponding to at least two rounds of the secondary transfer roller 26 to reduce backside contamination.

  Further, as in Comparative Example 1, even if the bias value applied to the secondary transfer roller 26 is increased, the effect does not change greatly, and there is a bias value necessary for flowing a transfer current of a certain value or more. I found it good.

  Note that the cleaning time in the post-rotation is not necessarily in units of one rotation, and when the pre-rotation time is short, the time until the first recording material reaches the secondary transfer portion is the pre-rotation cleaning. By setting the time T1-T3 as the post-rotation secondary transfer roller cleaning time T2, there is no influence on the first copy time, and after patch image formation is performed by post-rotation. It is possible to minimize the rotation time.

Example 3
FIG. 11 shows a secondary transfer bias sequence according to the third embodiment of the present invention. This embodiment can also be embodied by the image forming apparatus described in the first embodiment, and the description of the first embodiment is used for the description of the overall configuration of the image forming apparatus.

  According to the graph of FIG. 8, in this embodiment, the secondary transfer roller 26 is cleaned in order to minimize the post-rotation time at the time of post-rotation at the end of image formation, regardless of the presence or absence of image control by the pattern image. The post-rotation operation was completed without any problems. The same applies to normal post-rotation. Then, at the time of pre-rotation at the start of the next image formation, after the cleaning bias of −500 V and +500 V is alternately applied for the time corresponding to the two rounds of the secondary transfer roller 26, the recording material 8 is continuously transferred to the secondary transfer. A sequence in which a normal image forming operation is repeated in accordance with the timing of entering the roller nip portion. Other sequences are the same as those in the first and second embodiments.

  In this embodiment, the sequence when the patch detection type ATR correction is not entered at the timing of post-rotation after the end of image formation is performed by the sequence shown in FIG.

  Even if the secondary transfer roller 26 is not cleaned in the post-rotation as in the present embodiment, the cleaning operation is performed for the rotation time of two or more rotations of the forward and reverse biases in the next pre-rotation. Further, it is possible to prevent the back dirt on the recording material 8.

  Also in this embodiment, when a patch image is formed on the intermediate transfer belt 28 in the inter-image area between the last image of the previous print job and the first image of the next print job, The cleaning bias is applied to the secondary transfer roller 26 in contact with the area, and the cleaning bias is applied to the secondary transfer roller 26 in contact with the image area when no patch image is formed in the image area. By making it longer than the application time, the toner adhering to the secondary transfer roller 26 could be sufficiently removed.

Example 4
FIG. 12 shows a secondary transfer bias sequence according to the fourth embodiment of the present invention. This embodiment can also be embodied by the image forming apparatus described in the first embodiment, and the description of the first embodiment is used for the description of the overall configuration of the image forming apparatus.

  In the present embodiment, for example, a sequence is performed in a pre-rotation when image information can already be output when the user opens the door cover. At this time, after the user closes the door, first, a pattern image for preventing color misregistration is formed on the intermediate transfer belt, and this is detected by the sensor 41 to perform color misregistration control. It may be a sequence that enters.

  In the color misregistration control, based on the detection result of the pattern image for preventing color misregistration by the detection sensor 41, the exposure timing and the exposure position, which are image forming conditions as the exposure conditions for the photosensitive drum 21 of the exposure device 80, are variably controlled. And correct color misregistration.

  Even in this case, as shown in FIG. 12, while the pattern image (detection toner image) for preventing color misregistration passes through the secondary transfer roller nip portion, the secondary transfer roller 26 has a polarity of −100 V, which is opposite in polarity to the transfer bias. The bias is continuously applied to prevent the secondary transfer roller 26 from being contaminated by the pattern image as much as possible. After the pattern image passes through the secondary transfer roller nip portion, the recording material 8 is subjected to secondary transfer continuously after the cleaning bias of −500 V and +500 V is alternately applied for the duration of two rotations of the secondary transfer roller 26. The normal image forming operation is repeated in accordance with the timing of entering the roller nip portion. The subsequent sequence is the same as in the first embodiment.

  FIG. 13 shows a sequence when a pattern image for preventing color misregistration is not formed during the previous rotation in this embodiment.

  When the image forming operation (print job) is started, as the secondary transfer roller 26 is cleaned in accordance with the pre-rotation of the photosensitive drum, a bias having a polarity opposite to the transfer bias, −500 V is applied for one rotation of the secondary transfer roller 26. Thereafter, a bias of the same polarity as the transfer bias, +500 V, is similarly applied for one round. Thereafter, in synchronization with the image forming operation, approximately +2 KV is applied as a transfer bias at the timing when the recording material reaches the secondary transfer roller.

As in this embodiment, when a pattern image for preventing color misregistration is formed on the intermediate transfer belt 28 during the pre-rotation of the print job, the time during which the cleaning bias is applied to the secondary transfer roller 26 is set as the intermediate transfer belt 26. When the pattern image for preventing color misregistration is not formed on the belt 28, the cleaning bias is made longer than the time for which the secondary transfer roller 26 is applied, so that the toner adhering to the secondary transfer roller 26 is sufficiently obtained. Could be removed.

Example 5
In the above embodiment, the image forming apparatus of the present invention is configured to include the intermediate transfer belt 28 as an intermediate transfer member. However, the present invention is not limited to the image forming apparatus having such a configuration.

  FIG. 14 shows a schematic configuration of another embodiment of the image forming apparatus of the present invention. In this embodiment, the image forming apparatus is an image forming apparatus such as an electrophotographic monochromatic copying machine or a printer, and includes a photosensitive drum 21 as an image carrier disposed rotatably. Around the photosensitive drum 21, process devices such as a charging device 22, a developing device 23, and a cleaning device 25 are arranged. A developer is stored in the developing device 23.

  Laser light L based on the image signal of the original is projected onto the photosensitive drum 21 via a polygon mirror (not shown) or the like, and an electrostatic latent image is formed on the photosensitive drum 21, and toner is supplied to the photosensitive drum 21 from the developing device 23. Then, the electrostatic latent image is visualized as a toner image.

  The photosensitive drum has a configuration in which a photosensitive layer 211 is provided on the surface of a metal roller 212, but the metal roller is electrically grounded.

  When the toner image visualized on the photosensitive drum 21 reaches the transfer portion, a bias is applied from a power source 70 to a transfer roller 24 as a transfer means to which a transfer bias is applied, and the toner image is sent in synchronization with the timing. The recording material 8 is transferred. Finally, the recording material 8 separated from the photosensitive drum is fixed by the fixing device 9.

  The adhered toner remaining on the photosensitive drum 21 as it is is cleaned by the cleaning device 25.

  In such an image forming apparatus, the density detection pattern image 30 formed on the photosensitive drum 21 for image control is directly transferred to the transfer roller 24 as a transfer member that rotates in contact with the photosensitive drum 21 at the transfer nip portion. 24 adheres to the surface.

  In the image forming apparatus of the present embodiment, the image sensor such as toner replenishment control is performed by detecting the density of the image pattern on the photosensitive drum 21 by the detection sensor 41 disposed between the developing device 23 and the transfer roller 24. Is going.

  Also in this embodiment having such a configuration, the transfer roller 24 has the same sequence as the cleaning of the secondary transfer roller 26 in Embodiments 1 to 4, that is, FIGS. By implementing the sequence shown in FIGS. 9 to 12, it is possible to obtain the same effects as in the above-described embodiment, to reduce the back dirt of the transfer roller 24, and to shorten the time during post-rotation. Is also possible.

  In the first to fifth embodiments, when a patch image is formed in the inter-image area, the secondary transfer roller 26 is applied with biases of +500 V and −500 V on the secondary transfer roller 26 in contact with the image area. When a patch image is not formed in the inter-image area, a bias of +500 V and −500 V is applied to the secondary transfer roller 26 in contact with the image area, respectively. For one rotation.

  However, when a patch image is formed in the inter-image region, as shown in FIG. 15 as an example, a bias of −500 V is applied to the secondary transfer roller 26 in contact with this image region, and the secondary transfer roller 26 2 When a rotation time is applied and no patch image is formed in the inter-image area, as shown in FIG. 16, as an example, a bias of −500 V is applied to the secondary transfer roller 26 in contact with the image area. It is also possible to apply the roller 26 for one rotation time.

1 is a schematic overall configuration diagram of an embodiment of an image forming apparatus of the present invention. FIG. 3 is a schematic configuration diagram illustrating an embodiment of toner replenishment control of the image forming apparatus according to the present invention. FIG. 3 is a schematic configuration diagram of a patch image formed in an inter-image region on the intermediate transfer member of the present invention. FIG. 5 is a sequence diagram of a secondary transfer bias when patch detection type ATR correction is performed during continuous image formation in the image forming apparatus of the present invention. FIG. 6 is a sequence diagram in the case where the cleaning bias of the secondary transfer roller is applied without ATR correction of the patch detection method during continuous image formation in the image forming apparatus of the present invention. FIG. 6 is a sequence diagram of a secondary transfer bias according to an embodiment when patch detection type ATR correction is performed during post-rotation in the image forming apparatus of the present invention. FIG. 5 is a sequence diagram of a secondary transfer bias when patch detection type ATR correction is not performed in the image forming apparatus of the present invention. It is a graph which shows the examination result of the cleaning time of a secondary transfer roller. FIG. 11 is a sequence diagram of a secondary transfer bias according to another embodiment when patch detection type ATR correction is performed during post-rotation in the image forming apparatus of the present invention. FIG. 11 is a sequence diagram of a secondary transfer bias according to another embodiment when patch detection type ATR correction is not performed during post-rotation in the image forming apparatus of the present invention. FIG. 11 is a sequence diagram of a secondary transfer bias according to another embodiment when patch detection type ATR correction is performed during post-rotation in the image forming apparatus of the present invention. FIG. 7 is a sequence diagram of a secondary transfer bias when color misregistration control is performed during pre-rotation in the image forming apparatus of the present invention. FIG. 6 is a sequence diagram of a secondary transfer bias when color misregistration control is not performed during pre-rotation in the image forming apparatus of the invention. It is a schematic block diagram of the other Example of the image forming apparatus of this invention. FIG. 10 is another sequence diagram of the secondary transfer bias when patch detection type ATR correction is performed during continuous image formation in the image forming apparatus of the present invention. In the image forming apparatus of the present invention, another sequence diagram when the cleaning bias of the secondary transfer roller is applied without the ATR correction of the patch detection method during continuous image formation.

Explanation of symbols

8 Recording material 11 Intermediate transfer belt cleaning device 21 (21a, 21b, 21c, 21d) Photosensitive drum (image carrier)
22 (22a, 22b, 22c, 22d) Charging device (charging means)
23 (23a, 23b, 23c, 23d) Developing device (developing means)
24 (24a, 24b, 24c, 24d) Primary transfer roller (primary transfer means)
25 (25a, 25b, 25c, 25d) Cleaning device (cleaning means)
26 Secondary transfer roller (secondary transfer means)
28 Intermediate transfer belt (intermediate transfer member, image carrier)
30 Pattern image for density detection 41 Detection sensor (detection means)
70 Power supply 80 (80a, 80b, 80c, 80d) Exposure apparatus (exposure means)

Claims (6)

A moving image carrier;
A toner image forming means for forming a preparative toner image on the image bearing member,
A transfer member for forming a transfer nip for transferring the toner image formed on the image carrier to a recording material;
Detecting means for detecting a detection toner image formed on the image carrier by the toner image forming means ;
And control means for variably controlling a toner image forming condition based-out before Symbol toner image forming means on the result of said detecting means,
During continuous image formation in which images are continuously formed on a plurality of recording materials, the transfer member is cleaned by applying a bias having the same polarity as the normal polarity of the toner and a bias having the opposite polarity to the transfer member during image formation. Cleaning means,
In continuous image formation, in the image forming apparatus in which the transfer member presses the image carrier during image formation and in the transfer process, and the toner image forming unit can form a detection toner image during predetermined image formation. ,
At the time of continuous image formation, after the formed detection toner image passes through the transfer nip portion, a bias having the same polarity as the normal polarity of the toner and a bias having the opposite polarity are alternately applied to the transfer member by the cleaning unit. An image forming apparatus , wherein the number of repetitions and the cleaning time are larger than the number of repetitions and the cleaning time when the detected toner image is not formed. The transfer member is a roller that rotates in contact with the image carrier, and the transfer member rotates at least twice during a cleaning time after the detection toner image is formed, and the detection toner image is not formed. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus rotates at least once during the cleaning time.   3. The toner image forming unit forms a toner image using a plurality of colors of toner, and the detection toner image forming unit uses the plurality of colors of toner to form a plurality of detection toner images. Image forming apparatus.   The image forming apparatus according to claim 3, wherein the plurality of detected toner images overlap with each other in a moving direction of the image carrier. A moving image carrier;
Toner image forming means for forming a toner image on the image carrier;
A transfer member for forming a transfer nip for transferring the toner image formed on the image carrier to a recording material;
Detecting means for detecting a detection toner image formed on the image carrier by the toner image forming means;
Control means for variably controlling toner image forming conditions of the toner image forming means based on the result of the detecting means;
Cleaning means for cleaning the transfer member by applying a bias having the same polarity as the normal polarity of toner and a reverse polarity bias to the transfer member in contact with the image carrier;
In the image forming apparatus in which the toner image forming unit is capable of forming a detected toner image during predetermined image formation and during post-rotation,
After the detected toner image formed in the state where the transfer member and the image carrier are in contact with each other, the cleaning means applies a bias having the same polarity as the normal polarity of the toner and a bias having a reverse polarity. As for the number of repetitions and the cleaning time for alternately applying to the transfer member, the case where it is performed during post-rotation is smaller than the case where it is performed during image formation, respectively.
During the pre-rotation of the next image forming job after the end of the post-rotation, a bias having the same polarity as the normal polarity of the toner and a bias having a reverse polarity are alternately applied to the transfer member by the cleaning unit. An image forming apparatus for cleaning. The number of repetitions and the cleaning time performed during image formation are N1, T1,
The number of repetitions and the cleaning time performed during the post-rotation are N2, T2,
When the number of repetitions and the cleaning time performed during the pre-rotation of the next image forming job after the end of the post-rotation are N3 and T3, respectively.
N1 = N2 + N3,
T1 = T2 + T3
The image forming apparatus according to claim 5, wherein:

Images