JP2006220991A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus preventing the interior of the apparatus from being soiled with toner extruded from edges and toner from being wastefully consumed, adequately making printing on areas prescribed by a user, and requiring no calibration for margin-free printing, and degrading no productivity in regular printing. <P>SOLUTION: The color image forming apparatus includes: a detection means for detecting the passage of the position of the leading or trailing edge of a recording material; and a correction means for controlling the correction of amounts of a plurality of toner images protrusions from the recording material. When the toner images are protruded from the recording material or when margin-free printing is carried out such that images are printed up to areas near the edges, the amounts of the plurality of toner image protrusions are controlled according to the detection result of the passage detection means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus such as a copying machine, a printer, and a fax machine using an electrophotographic process.

  In an image forming apparatus such as a copying machine, a printer, or a fax machine, an electrophotographic system using toner is often used. Conventionally, in these electrophotographic image forming apparatuses, an image is printed with a certain margin (edge) provided from the edge of the paper.

  However, as printer demand has diversified in recent years, not only electrophotographic image forming apparatuses but also printed materials output by the inkjet method or other printing methods can be used as catalogs or pamphlets, or silver salts. Opportunities to use as an alternative to photography are increasing. With such applications such as catalogs, pamphlets and silver salt photo substitution, there is an increasing demand for marginless printing. In particular, for electrophotographic image forming apparatuses, it is strongly desired to realize marginless printing for business use because of its high productivity.

  However, when performing marginless printing in a conventionally known electrophotographic image forming apparatus, the edge portion of the toner image formed on the image carrier and the edge portion of the recording material to be conveyed are accurately detected. It needs to be well synchronized. This is because the following problems occur when the edge portion of the toner image and the edge portion of the recording material cannot be synchronized.

  1. A margin occurs even though marginless printing is specified.

  2. The toner that protrudes from the edge of the recording material adheres to the electrostatic conveyance belt and the secondary transfer roller that electrostatically conveys the recording material, and causes back dirt and toner scattering in the apparatus.

  3. Excess toner that protrudes from the edge of the recording material wastes toner.

  4). Since the portion of the toner image that protrudes from the edge of the recording material is not printed on the recording material, only a narrow area is actually printed with respect to the image area specified by the user, and the area intended by the user is accurate. Cannot be displayed.

  Although it is possible to suppress the occurrence of the margin 1 by increasing the extra portion (the amount of protrusion), the amount of toner that protrudes from the edge portion of the recording material is increased, resulting in problems 2, 3, and 4. It becomes a trade-off relationship such as increasing.

  However, it has been very difficult in the past to synchronize the edge portion of the recording material and the edge portion of the toner image at a level required for borderless printing.

  As a workaround for such a problem, for example, Patent Document 1 proposes a method of using a recording material having a structure in which a half cut is inserted so that a blank portion can be cut off. Alternatively, Patent Document 2 proposes a method in which a backup member that is slightly larger than the recording material is transported simultaneously with the recording material, and toner positioned outside the recording material is transferred to the backup member. .

  In any of these methods, the margin portion is cut off every time borderless printing is performed, and the backup member is ejected and discarded every time printing is performed. That was a waste. In addition, since a cut-off portion is generated in the image area designated by the user, the area intended by the user cannot be displayed accurately.

  In order to avoid such a problem, it is necessary to strictly control the edge portion of the recording material and the edge portion of the toner image in synchronization. For this purpose, it is necessary to accurately grasp and control the transport position of the recording material.

  However, although the reference size (length) is determined for the recording material, it is not strictly a constant value and varies depending on the paper manufacturer and lot. This is a level that poses no problem in normal printing, but cannot be ignored in a situation where strict registration control such as borderless printing is required. If the margin is increased and the amount of protrusion is increased with respect to this variation, the above-described problem occurs.

  For example, according to Patent Document 3, registration control is performed by a calibration operation that directly reads a distance between a toner image formed on a recording material and an edge portion of the recording material, so that control accuracy can be improved. is there.

  However, an output product on which a calibration pattern is printed is discharged for each calibration operation, and waste is caused such as discarding it. In addition, such calibration can perform registration control with appropriate accuracy immediately after execution, but as the printing operation is repeated, the conveyance speed of the recording material varies as described above. In particular, the stability is insufficient for a case where strict registration control is required, such as borderless printing.

JP 2001-205936 A JP 2004-045457 A Japanese Patent Laid-Open No. 10-186752

  When strictly controlling the edge portion of the recording material and the edge portion of the toner image, as described above, the conveyance position of the recording material must be accurately grasped and controlled.

  However, although the reference size (length) is determined for the recording material, it is not strictly a constant value and varies depending on the paper manufacturer and lot. Further, the recording material is not always conveyed to the transfer position at the same timing. This is because the shape of the loop formed before reaching the transfer position varies depending on the stiffness of the recording material depending on the type of recording material, the atmospheric environment, and the recording material leaving condition. The speed of the registration roller also varies depending on individual differences in the image forming apparatus, and the loop shape varies. Since marginless printing is specified during borderless printing, it is not possible to create a margin when strict synchronization is made between the edge of the recording material and the edge of the toner image. Take a margin on the protruding side.

  Therefore, it is necessary to increase the amount of protrusion at the leading edge of the image by the variation in the loop formation of the recording material, and the amount of protrusion at the trailing edge of the image by the variation in the size (length) of the recording material. Therefore, it is easy to cause backside contamination and toner scattering in the machine, and wasteful toner consumption increases. Further, by taking a large amount of protrusion, only a narrow area is actually printed with respect to the image area designated by the user, and the area intended by the user cannot be displayed accurately. In particular, this effect becomes more significant as the size of the non-recording material is smaller.

  In view of the above problems, the present invention synchronizes the front and rear end edge portions of the recording material and the front and rear end edge portions of the toner image even when performing borderless printing, for example, without causing a margin and the edge portion. During normal printing without the need for calibration to perform borderless printing, it is possible to accurately print the area intended by the user by suppressing the occurrence of internal contamination and wasteful toner consumption due to the protruding toner. An object of the present invention is to provide a color image forming apparatus capable of borderless printing without impairing productivity.

  The present invention is a color image forming apparatus having the following configuration.

A plurality of image carriers, an exposure device for creating an electrostatic latent image on the image carrier in accordance with an image signal, a plurality of developing devices for visualizing the electrostatic latent images as toner images, and the image carrier Transfer bias applying means for directly transferring the toner image to the transfer material or primary transfer to the intermediate transfer medium and then secondary transfer to the transfer material, and to-be-transferred on the recording material In an image forming apparatus having a heat fixing device for heat fixing a toner image as a permanent image,
A detection unit that detects passage of the leading end position or the trailing end position of the recording material; and a correction unit that performs correction control of an amount of protrusion of a plurality of toner images from the recording material. When performing so-called borderless printing that prints out or to the same area, the amount of protrusion of a plurality of toner images is controlled based on the detection result of the passage detecting means.

  As a result, for example, even when borderless printing is performed, the edge portion of the recording material and the edge portion of the toner image can be synchronized, so that there is no margin and internal contamination due to the toner protruding from the edge portion. This reduces the occurrence of toner and wasteful toner consumption, allows the user's intended area to be printed accurately, and does not require calibration to perform borderless printing, without impairing productivity during normal printing. An image forming apparatus capable of borderless printing can be provided.

  Also, each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material, and the recording material Compared with each time required for moving the distance from the passage detection position of the passage detection means to the position where the toner image on each carrier is transferred, the former is shorter in all the image carriers. It is also preferable that the control means controls the amount of protrusion of all toner images based on the passage detection result.

  As a result, in all toner images forming a color image, there is no margin, and the occurrence of in-machine contamination and wasteful toner consumption due to the toner protruding from the edge portion is suppressed, and the area intended by the user is printed accurately. it can.

  Also, each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material, and the recording material Is compared with each time required to move the distance from the passage detection position of the passage detection means to the position where the toner image of each carrier is transferred, at least one of the former has a long relationship. The first image forming unit described above and at least one second image forming unit in which the former is in a short relationship, and the control means is configured to use the second image forming unit based on the passage detection result. It is also preferable to control the amount of protrusion of at least one or more toner images.

  As a result, the distance between the detection means and the transfer position can be shortened, so that the image forming apparatus can be reduced in size, and the second image forming apparatus that can feed back the detection result of the detection means to the protruding amount protrudes from the edge portion. The occurrence of in-machine contamination due to toner and wasteful toner consumption can be suppressed.

A plurality of image carriers, an exposure device that creates an electrostatic latent image on the image carrier in accordance with an image signal, a plurality of developing devices that visualize the electrostatic latent images as toner images, and a recording material. A recording material carrier to be carried and conveyed, an adsorption member that electrostatically adsorbs the recording material to the recording material carrier at an adsorption position, and a toner image on the image carrier are directly covered. Transfer bias applying means for transferring to a transfer material or primary transfer to an intermediate transfer medium and then secondary transfer to a transfer material, and an unfixed toner image transferred onto the recording material permanently In an image forming apparatus having a heat fixing device for heat fixing as an image,
Correction means for performing correction control of the amount of protrusion of a plurality of toner images that protrudes from the recording material, and when performing so-called borderless printing in which the toner image protrudes from the recording material or prints up to an equivalent area. A suction detection means for detecting a current or a voltage due to the suction bias when the material reaches the suction position; a detection result when the recording material of the suction detection means enters the suction position; and a recording material It is also preferable to control the amount of protrusion of a plurality of toner images based on the detection result of the suction detection means when the toner leaves the suction position.

  Accordingly, the edge of the recording material can be detected even when borderless printing is performed, for example, without newly providing a passage detection means for detecting the passage of the leading / earning end position by detecting the leading / rear end position using the suction member. And the edge portion of the toner image can be synchronized, so that no margin is generated, the occurrence of in-machine contamination due to the toner protruding from the edge portion and unnecessary toner consumption can be suppressed, and the edge An image forming apparatus capable of borderless printing without impairing productivity during normal printing without requiring calibration for performing blank printing can be provided.

  Further, the value of the suction bias until the arrival of the leading edge of the recording material at the suction position is detected is different from the value of the suction bias after the arrival of the leading edge of the recording material at the suction position is detected. Is also suitable.

  Thereby, appropriate electrostatic adsorption of the recording material can be performed, and more stable recording material conveyance can be performed.

  Further, the value of the suction bias until the arrival of the leading end of the recording material at the suction position is detected is set to at least one of the temperature and humidity of the environment in the image forming apparatus main body, the type of the recording material, and the process speed. It is also suitable to change according to conditions.

  As a result, appropriate electrostatic adsorption of the recording material can be performed regardless of the temperature and humidity of the environment in the main body of the image forming apparatus, the type of recording material, and the process speed, and more stable recording material conveyance can be performed. Can do.

  It is also preferable that the means for applying the adsorption bias has a constant voltage bias applying means, and the detecting means is a current detecting means.

  Thus, more stable bias control and more accurate front / rear end position detection can be performed in appropriate electrostatic attraction of the recording material.

  It is also preferable that the means for applying the adsorption bias has a constant current bias applying means, and the detecting means is a voltage detecting means.

  Thus, more stable bias control and more accurate front / rear end position detection can be performed in appropriate electrostatic attraction of the recording material.

  According to the present invention, even when borderless printing is performed, the leading and trailing edge portions of the recording material and the leading and trailing edges of the toner image can be synchronized, so that no margin is generated and the edge portion Production during normal printing without the occurrence of internal contamination and wasteful toner consumption due to protruding toner, accurate printing of the user's intended area, and no need for calibration for borderless printing Borderless printing that does not impair the performance is possible.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. It is not intended that the scope of the present invention be limited to the following embodiments.

<Embodiment 1>
A configuration of a color image forming apparatus according to the present embodiment is shown in FIG.

  In the full-color image forming apparatus using the direct transfer type tandem system shown in FIG. 1, an electrostatic attraction conveyance belt (hereinafter simply referred to as “conveyance belt”) 14 as a transfer means is provided with a drive 22 roller, a driven roller 25, It is wound around each of the tension rollers 13a and 13b.

  Process stations 31Y, 31M, 31C, and 31Bk, which are image forming portions for yellow, magenta, cyan, and black, are arranged along the circumferential surface of the conveyance belt, and the conveyance belt 14 is in the direction of the arrow in the figure. By rotating, the recording material P is sequentially conveyed to each process station.

  Each process station is attachable to and detachable from the image forming apparatus main body as a process cartridge, and each process cartridge includes photosensitive drums 1Y to 1Bk, primary chargers 2Y to 2Bk, developing devices 8Y to 8Bk, and cleaning device 10Y. -10Bk are integrated together.

  The controller unit 45 arranged in the apparatus main body sends image signals corresponding to the image information to the scanner units 11Y to 11Bk at a predetermined timing, and the optical information 12Y to 12Bk corresponding to the image signals is sent from each scanner unit to each process. The photosensitive drums 1Y to 1Bk in the process station are irradiated and latent images are formed on the photosensitive drums 1Y to 1Bk. Further, when the photosensitive drums 1Y to 1Bk advance in the direction of the arrow, the latent images are developed by the developing devices 8Y to 8Bk to become toner images.

  In an electrophotographic image forming apparatus, for example, when a negative organic semiconductor electrophotographic photosensitive member (OPC photosensitive member) is used as a photosensitive drum and an exposed portion in which negative charges are attenuated by exposure is developed, the negative electrode A developer containing a neutral toner is used.

  The photosensitive drums 1Y to 1Bk in each process station are in contact with transfer rollers 4Y to 4Bk, which are transfer charging means, via a conveyor belt 14, and transfer biases from transfer bias power sources 32Y to 32Bk are applied to the transfer rollers 4Y to 4Bk. Is applied. As described above, when a developer containing negative toner is used, a positive transfer bias is applied to the transfer roller from a transfer bias power source.

  When the recording material P is fed into the image forming apparatus from the paper feeding cassette 15 or the like by the paper feeding rollers 17 and 18, first, in order to synchronize the image forming operation and the conveyance of the recording material P, a pair of registration rollers 19A. , 19B. Thereafter, the electromagnetic clutch 41 is operated at a predetermined timing, and the power of the feeding motor 42 is transmitted to the registration roller 19A to start the rotation of the registration roller pair 19A, 19B. Led to.

  Then, the recording material P sequentially passes through each process station, and the respective color toner images developed on the photosensitive drums 1Y to 1Bk in the above-described process are successively transferred. Further, when a transfer bias is applied from the transfer bias power sources 32Y to 32Bk to the transfer rollers 4Y to 4Bk, a charge is applied to the recording material P, and the recording material P to which the charge is applied polarizes the conveyance belt 14. As a result, it is conveyed while being electrostatically attracted to the conveying belt 14.

  Thereafter, the color image of the unfixed toner is heated and pressed by the fixing device 21 to become a permanently fixed image.

  The image forming apparatus includes an environment sensor 50. The bias, fixing, and fixing conditions for charging, developing, and transfer can be changed according to the atmospheric environment (temperature, humidity) in the image forming apparatus. It has become. Thus, it is used for adjusting the density of the toner image formed on the recording material P and for achieving optimum transfer and fixing conditions.

As the conveyor belt 14, PVDF (vinylidene fluoride resin), ETFE (tetrafluoroethylene-ethylene copolymer resin), polyimide, PET (polyethylene terephthalate) having a thickness of 50 to 200 μm and a volume resistivity of about 10 ⁹ to 10 ¹⁶ Ωcm. ), A resin film such as polycarbonate, or a base layer of rubber having a thickness of about 0.5 to 2 mm, for example, EPDM, which is coated with, for example, urethane rubber dispersed with a fluorine resin such as PTFE And use.

  The conveyor belt 14 does not normally carry a toner image directly on its surface, but it can cause contamination toner to adhere to the conveyor belt 14 due to jamming or ground fog on a non-image area, density detection, etc. In operation, a detection patch may be carried directly on the conveyor belt 14. In order to clean such toner on the conveyor belt 14, a cleaning bias having a polarity opposite to that at the time of transfer is applied to the transfer rollers 4Y to 4Bk at each process station 31, and the contaminated toner on the conveyor belt 14 is exposed. The cleaning process of transferring to the drums 1Y to 1Bk and recovering to the drum cleaners 10Y to 10Bk is performed at a predetermined timing.

  The recording material P that has passed through the fixing device 21 is discharged to the discharge tray 20 by the action of the discharge roller pairs 13A, 13B and 14A, 14B, or the recording material when performing duplex printing. When the rear end of P passes through the S portion, the paper discharge roller pair 14A, 14B rotates in the reverse direction, and the recording material P is switched back and passes through the double-sided conveyance path D and is again guided to the registration roller portion.

  At the position between the driven roller 25 and the photosensitive drum 1Y, a protrusion amount correction sensor 30 is arranged on the conveyor belt 14, so that the passage timing of the front and rear ends of the recording material P can be accurately detected. ing. In this embodiment, a non-contact optical sensor is used as the protrusion amount correction sensor.

  A sensor 43 is installed between the discharge roller pairs 13A, 13B and 13A, 13B so that the toner image formed on the edge of the recording material P and the recording material P can be detected.

  A conventionally known sensor can be used as the sensor 43. For example, a combination of an infrared light emitting element such as an LED and a light receiving element such as a photodiode can be used. In the present embodiment, a color sensor composed of a white LED and a charge storage sensor with an RGB on-chip filter is used.

  Next, a case where borderless printing is executed using the image forming apparatus will be described.

  In a normal printing operation, the image forming operation is performed at a predetermined timing set in advance. As a result, for example, the image forming operation is performed with the upper and lower margins of the recording material P set to 5 mm.

  On the other hand, at the time of borderless printing, the upper margin and the lower margin of the recording material P are set to 0 mm, and a certain predetermined amount of protrusion is set in the image forming apparatus to perform printing.

  Hereinafter, a method of correcting the protrusion amount at the time of borderless printing will be described.

  First, a method for correcting the amount of protrusion at the tip during borderless printing will be described.

  The amount of protrusion of the leading edge during borderless printing is set with a margin so as not to generate a blank even with respect to variations in the shape of the loop formed before the recording material P reaches the transfer position.

  Here, the amount of protrusion of the leading end is corrected by detecting the passage timing of the leading end of the recording material P by the protrusion amount correcting sensor 30. This operation will be described below.

  When the image forming operation is performed in this image forming apparatus, the registration roller rotation ON timing is used under the reference conditions (the type of the recording material P, the atmosphere environment, the recording material leaving state, the registration roller speed). The time until the passage timing of the leading edge is Xa sec. Further, during the actual image forming operation, the time from the ON timing of the registration roller rotation to the passing timing of the tip is assumed to be Ya sec. By using the difference time ΔTa (= Xa−Ya) sec between Xa and Ya at this time and the process speed Zmm / sec at the time of image formation, the tip protrusion amount Aa mm is set as follows.

Aa = Z × ΔTa
The protrusion amount Aa is calculated by the arithmetic and control unit 40, and the print signal is corrected by the controller unit. By doing so, the leading edge portion of the recording material P and the leading edge portion of the toner image can be synchronized.

  Next, a method for correcting the amount of protrusion of the trailing edge during borderless printing will be described.

  The amount of protrusion of the trailing edge during borderless printing is set with a margin so that no margin is generated even when the length of the recording material P varies.

  Here, the protruding amount of the trailing edge is corrected by detecting the passage timing of the trailing edge of the recording material P by the protruding amount correction sensor 30. This operation will be described below.

  When the image forming operation is performed in the image forming apparatus, the leading edge portion of the recording material P having the reference length passes through the trailing edge portion from the passage timing detected by the protrusion amount correction sensor 30. The time until the timing is Xb sec. In addition, the passage timing from the leading edge of the recording material P detected by the protrusion amount correction sensor 30 during the actual image forming operation to the trailing edge is Yb sec. By using the difference time ΔTb (= Xb−Yb) sec between Xb and Yb and the process speed Zmm / sec at the time of image formation, the protrusion amount Ab mm is set as follows.

Ab = Z × ΔTb
The amount A of protrusion is calculated by the arithmetic and control unit 40, and the print signal is corrected by the controller unit. By doing so, the trailing edge portion of the recording material P and the trailing edge portion of the toner image can be synchronized.

  As described above, here, the description has been made assuming that the edge portion of the recording material P and the edge portion of the toner image are completely synchronized (at the same position). Even under various conditions, in order to prevent the margin part from being generated in the relationship of the edge part of the edge toner image of the recording material P, it may be desirable to increase the amount of protrusion as much as possible. In this case, the amount of protrusion of the leading and trailing edges of the toner image may be slightly increased, for example, 0.5 mm or 1.0 mm.

  By using the present invention, it is possible to minimize the occurrence of in-machine contamination and wasteful toner consumption due to the toner protruding from the edge portion.

  In the present embodiment, the printing operation is performed with the amount of protrusion corrected for both the leading and trailing edges. Therefore, the magnification of the image can be made almost equal to the size of the recording material P. In other words, the vertical length of the recording material P may be added to the vertical length of the recording material P in consideration of the variation in the length of the recording material P, and a slight margin of the protrusion at the front and rear ends. Assuming that the thickness is Tmm and the horizontal length is Ymm, it is sufficient that the toner image can be formed if the vertical length is T + 2 mm and the horizontal length is (T + 2) × Y ÷ Tmm. That is, the image magnification is treated as an image of (T + 2) ÷ T times, and the portion exceeding the width of the recording material P is cut off.

  Here, depending on the shape of the recording material P, the longer the paper, the more likely it is to be affected by the skew in the paper conveyance, so a margin in the lateral direction (thrust direction) is required. Depending on conditions such as the type and the atmospheric environment, the paper conveyance accuracy (degree of skew) of the image forming apparatus may be somewhat deteriorated, so that a margin in the lateral direction (thrust direction) is required. At this time, when the lateral length is (T + 2) × Y ÷ Tmm as described above, the lateral amount (thrust direction) protrusion amount margin is slightly insufficient, and the lateral direction (thrust direction) protrusion amount margin In some cases, a more marginless printed image can be obtained by further increasing. In such a case, the magnification of the image may be further increased as the amount of protrusion in the horizontal direction increases.

  By doing so, although the cut-out width of the image exceeding the width of the recording material P becomes larger, the amount of protrusion of the leading and trailing ends of the recording material can be corrected and handled in the same manner, and an effect can be obtained. Can do.

  On the other hand, in the relationship between the edge portion of the recording material P and the edge portion of the toner image in the conventional image forming apparatus, the amount of protrusion is usually required to be about 3 mm at both the front end and the rear end in order not to generate a blank portion. Therefore, problems such as in-machine contamination due to toner protruding from the edge portion and wasteful toner consumption occur.

  When the protrusion amount is 3 mm at both the front and rear ends, the vertical length of the recording material P is Tmm and the horizontal length is Ymm. Is T + 6 mm, and the horizontal length is (T + 6) × Y ÷ Tmm. In other words, the image magnification is handled as (T + 6) ÷ T times, and the portion exceeding the paper width becomes a cut-off portion, and the ratio of the image cut-out becomes large, so that the area intended by the user cannot be printed accurately. End up. In particular, the ratio of the cut-off amount increases as the small-size paper is printed.

  By using the present invention, such a problem can be drastically improved.

  In the case of applying the present invention, the electrostatic latent image created on each image carrier is necessary to move the distance from the exposure start position to the transfer position of the recording material P. Each time is preferably shorter than each time required to move the distance from the passage detection position of the recording material P to the position where the toner image on each carrier is transferred. . When this condition is not satisfied, when the recording material P detects the passage by the protrusion amount correction sensor 30, the toner image formation for the protrusion amount has already started, and the protrusion is detected. This is because the amount cannot be corrected.

  However, even in that case, each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material P is different. However, as long as there is a station whose relationship is shorter than the time required for the recording material P to move the distance from the passage detection position of the passage detection means to the position where the toner image of each carrier is transferred, The present invention can be applied to the corresponding station to obtain the effect.

  However, when the amount of protrusion cannot be corrected in some stations, the magnification of the image cannot be made substantially equal to the size of the recording material P. That is, for a station where the amount of protrusion cannot be corrected, the amount of protrusion of about 3 mm is required at both the front and rear ends as in the conventional image forming apparatus. Therefore, the area where the toner image can be formed is T + 6 mm in the vertical length and (T + 6) × Y ÷ Tmm in the horizontal length. And for stations that can correct the amount of protrusion, the amount of protrusion can be adjusted, so by correcting the print signal so as not to write a toner image, the occurrence of in-machine contamination and wasteful toner consumption due to toner protruding from the edge portion can be avoided. Can be suppressed.

  As described above, according to the present invention, in the full-color image forming apparatus using the direct transfer tandem system, the passage amount of the recording material P is detected by the protrusion amount correction sensor 30 and the protrusion amount is corrected, for example. Even when borderless printing is performed, the leading and trailing edge portions of the recording material P are synchronized with the edge portion of the leading and trailing edge toner image, and no margin is generated, and in-machine contamination due to toner protruding from the edge portion is generated. Borderless printing that suppresses wasteful toner consumption, accurately prints the user's intended area, and does not require calibration for borderless printing and does not impair productivity during normal printing It is possible to provide a possible image forming apparatus.

<Embodiment 2>
In the first embodiment, in the full-color image forming apparatus using the direct transfer type tandem method, the protruding timing is detected by the protruding amount correction sensor 30 to correct the protruding amount. The present embodiment differs in that the sticking roller 28 is used instead of the sticking amount correction sensor 30 and the sticking current detection circuit 34 detects the passage timing of the recording material P to correct the sticking amount. The other configuration of the present embodiment is basically the same as that of the first embodiment. In FIG. 2, the same members as those in FIG.

  FIG. 2 shows the configuration of the image forming apparatus used in this embodiment.

  Also in the present embodiment, image forming operations are performed at predetermined timings in the process stations 31Y to 31Bk in the same manner as described with reference to FIG. 1, whereby each color of each color is formed on the photosensitive drums 1Y to 1Bk. A toner image is formed.

  When the recording material P is fed into the image forming apparatus from the paper feeding cassette 15 or the like by the paper feeding rollers 17 and 18, first, in order to synchronize the image forming operation and the conveyance of the recording material P, a pair of registration rollers 19A. , 19B and then guided to a suction portion where the recording material P and the transport belt 14 are sucked.

  In the suction unit, for example, a suction roller 28 as a suction member is opposed to the driven roller 25 via the transport belt 14 and sandwiches the transport belt 14 and the recording material P. A charge is applied to the recording material P when a voltage is applied to the suction roller 28 from the suction bias power source 32A, which is a high voltage source, and the recording material P to which the charge is applied polarizes the transport belt 14. It is electrostatically attracted to the conveyor belt 14.

  Further, there is an adsorption current detection circuit 34 between the adsorption roller 28 and the adsorption bias power supply 32A, and the value of the current that flows when the adsorption bias is applied is measured. In the arithmetic control circuit 40, the resistance of the recording material P is measured. And the optimum transfer bias can be selected.

  The recording material P adsorbed on the conveyance belt 14 in this way sequentially passes through each process station, and the respective color toner images developed on the photosensitive drums 1Y to 1Bk in the above-described steps are transferred one after another. Thereafter, the unfixed toner color image is heated and pressed by the fixing device 21 to become a permanent image.

  The conveyor belt 14 does not normally carry a toner image directly on its surface, but it can cause contamination toner to adhere to the conveyor belt 14 due to jamming or ground fog on a non-image area, density detection, etc. In operation, a detection patch may be carried directly on the conveyor belt 14. In order to clean such toner on the conveyor belt 14, a cleaning bias having a polarity opposite to that at the time of transfer is applied to the transfer rollers 4Y to 4Bk at each process station 31, and the contaminated toner on the conveyor belt 14 is exposed. The cleaning process of transferring to the drums 1Y to 1Bk and recovering to the drum cleaners 10Y to 10Bk is performed at a predetermined timing.

  In the present embodiment, the timing at which the front and rear ends of the recording material P during the image forming operation change is the timing at which the value of the current flowing through the suction roller changes.

  First, a method for determining the passage timing of the leading end of the recording material P will be described.

Specifically, before the recording material P passes, a constant voltage is applied to the suction roller 28 by the suction bias power source 32A, and the current value flowing at that time is measured by the suction current detection circuit 34 and calculated. It is monitored by taking it into the control circuit 40. When the leading edge of the recording material P passes, the current flowing when a constant voltage is applied decreases (after passing the leading edge of the paper) due to the resistance of the recording material P. The passage timing is detected from this phenomenon. As timing used as passage timing,
1. 1. Timing when current starts to decrease Timing settled after current decrease 3.1 An intermediate timing between 3.1 and 2 is conceivable, but basically any one of 1 to 3 may be used because a difference from the reference timing (Xsec) is used. In the present embodiment, the timing 3 is set as the passage timing.

  Next, a method for determining the passage timing of the trailing edge of the recording material P will be described.

When the rear end of the recording material P passes, the current flowing when a constant voltage is applied increases (after passing the rear end of the paper) due to the resistance of the recording material P. The passage timing is detected from this phenomenon. As timing used as passage timing,
1. 1. Timing when current starts to increase Timing settled after current increase 3.1 The intermediate timing between 3.1 and 2 is conceivable, but basically any one of 1 to 3 may be used because the difference from the reference timing (Xsec) is used. In the present embodiment, the timing 3 is set as the passage timing.

  The effect of using this embodiment is the same as that of Embodiment 1 in principle, and the same effect can be obtained. That is, the amount of protrusion is corrected by detecting the passage timing of the leading and trailing edges of the recording material P during the image forming operation using the timing at which the value of the current flowing through the suction roller changes, and as a result, the edge of the recording material P is corrected. And the edge portion of the toner image can be synchronized.

  In this embodiment, as a further effect, since the suction roller 28 is used, a stable recording material transportability (and thus accurate image recording performance) is obtained by transporting the belt while electrostatically attracting. It is done. Further, it is possible to achieve high image quality by detecting the resistance of the recording material P and determining an appropriate transfer bias.

  Further, the edge portion of the recording material P and the edge portion of the toner image are synchronized at the time of borderless printing without using a new sensor (without increasing the cost) so as to detect the timing at which the recording material P passes through the front and rear ends. Can do. Furthermore, when a non-contact optical sensor is used as the protrusion amount correction sensor 30, it is possible to maintain superiority against the problem that it is difficult to detect the front and rear end passage timing of the transmissive recording material P.

  In the present embodiment, the method has been described in which a constant voltage is applied by the suction bias power source 32A and the current value flowing at that time is monitored by the suction current detection circuit 34. However, the present invention is not limited to this method. For example, a method may be used in which a current is supplied using a constant current power source as the suction bias power source and the voltage value at that time is monitored by the suction voltage detection circuit.

  The application timing of the suction bias may be any timing until the recording material P reaches the suction roller 28. Further, the adsorption voltage is different between the voltage for detecting passage of the recording material P at the front and rear ends, the voltage for detecting the resistance of the recording material P, and the voltage for attracting the transfer material P to the transfer belt 14. A value may be used.

  Further, the suction bias to be used may be changed using the temperature / humidity detection result of the environmental sensor 50. Since the moisture content of the recording material P varies depending on the temperature and humidity in the image forming apparatus and the resistance value may vary accordingly, the optimum adsorption bias value setting for detecting the recording material P is also possible. It is because it changes with it. As described above, an optimum suction bias setting value according to the atmospheric environment of the image forming apparatus is prepared in advance, and the suction bias setting value is set based on the data measured by the environment sensor 50, so that a more accurate recording material is recorded. The P passage timing and the resistance value can be detected, and the recording material P can be more stably conveyed by electrostatic attraction.

  Furthermore, when changing the process speed to increase the resolution of image drawing or improving the fixing property, or when changing the suction condition to an optimum value depending on the thickness or type of the recording material P to be used, etc. However, it is preferable to change the suction bias according to each condition because more accurate detection and more stable electrostatic suction conveyance can be performed.

  In the case of applying the present invention, the electrostatic latent image created on each image carrier is necessary to move the distance from the exposure start position to the transfer position of the recording material P. Each time is preferably shorter than each time required to move the distance from the position where the recording material P passes through the suction roller 28 to the position where the toner image on each carrier is transferred. . If this condition is not satisfied, when the passage of the recording material P is detected by the suction roller 28, the toner image has already been formed.

  However, even in that case, each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material P is different. However, as long as there is a station whose relationship is shorter than the time required for the recording material P to move the distance from the detection position of the suction roller 28 to the position where the toner image of each carrier is transferred, The present invention can be applied to the corresponding station to obtain the effect.

  However, when the amount of protrusion cannot be corrected in some stations, the magnification of the image cannot be made substantially equal to the size of the recording material P. That is, for a station where the amount of protrusion cannot be corrected, the amount of protrusion of about 3 mm is required at both the front and rear ends as in the conventional image forming apparatus. However, for stations where the amount of protrusion can be corrected, the amount of protrusion can be adjusted, so by correcting the print signal so that toner images are not written, the occurrence of internal contamination and wasteful toner consumption due to toner protruding from the edge portion can be avoided. The effect of suppressing can be acquired.

  As described above, according to the present invention, in the full-color image forming apparatus using the direct transfer type tandem method, the sticking roller 28 is used, and the sticking current detection circuit 34 detects the passage timing of the recording material P, thereby protruding. By correcting the amount, for example, even when borderless printing is performed, the edge portion of the recording material P and the edge portion of the toner image are synchronized, and there is no margin, and the inside of the machine by the toner protruding from the edge portion Reduces contamination and wasteful toner consumption, accurately prints the area intended by the user, and does not require calibration to perform borderless printing, thereby impairing productivity during normal printing It is possible to provide an image forming apparatus capable of printing without margins.

<Embodiment 3>
In the second embodiment, in the color image forming apparatus using the direct transfer type tandem method, the sticking roller 28 is used, and the sticking current detection circuit 34 detects the passage timing of the recording material P, whereby the amount of protrusion is determined. Corrected. In the present embodiment, in the color image forming apparatus using the intermediate transfer type tandem method, the sticking roller 28 is used, and the sticking current detection circuit 34 detects the passage timing of the recording material P, whereby the amount of protrusion is determined. The correction is different.

  FIG. 3 shows an intermediate transfer type tandem image forming apparatus used in this embodiment. The image forming apparatus of this example is a laser beam printer using an electrophotographic process, and is a full-color image forming apparatus including a plurality of process stations and an intermediate transfer belt as an intermediate transfer member.

  The intermediate transfer belt 27 is wound around each of a drive 22 roller, a secondary transfer counter roller 26, and a tension roller 13.

  On the peripheral surface of the intermediate transfer belt 27, yellow, magenta, cyan, and black image forming units, that is, process stations 31Y to 31Bk for the respective colors are arranged.

  Each process station is attachable to and detachable from the image forming apparatus main body as a process cartridge, and each process cartridge includes photosensitive drums 1Y to 1Bk, primary chargers 2Y to 2Bk, developing devices 8Y to 8Bk, and cleaning device 10Y. -10Bk are integrated together.

  The controller unit 45 arranged in the apparatus main body sends image signals corresponding to the image information to the scanner units 11Y to 11Bk at a predetermined timing, and the optical information 12Y to 12Bk corresponding to the image signals is sent from each scanner unit to each process. The photosensitive drums 1Y to 1Bk in the process station are irradiated and latent images are formed on the photosensitive drums 1Y to 1Bk. Further, when the photosensitive drums 1Y to 1Bk advance in the direction of the arrow, the latent images are developed by the developing devices 8Y to 8Bk to become toner images.

  In an electrophotographic image forming apparatus, for example, when a negative organic semiconductor electrophotographic photosensitive member (OPC photosensitive member) is used as a photosensitive drum and an exposed portion in which negative charges are attenuated by exposure is developed, the negative electrode A developer containing a neutral toner is used.

  The photosensitive drums 1Y to 1Bk in each process station are in contact with primary transfer rollers 4Y to 4Bk, which are primary transfer charging means, via the intermediate transfer belt 27, and the primary transfer rollers 4Y to 4Bk are in contact with the primary transfer rollers 4Y to 4Bk. A primary transfer bias is applied from the transfer bias power sources 32Y to 32Bk. When a developer containing negative toner is used as described above, a positive transfer bias is applied to the transfer roller from a transfer bias power source.

  The respective color toner images are sequentially primary-transferred onto the intermediate transfer belt 27 at the respective primary transfer portions facing the primary transfer rollers 4Y to 4Bk as transfer means, and four colors of yellow, magenta, cyan, and black are obtained. A full color image on which the toner image is superimposed is once formed on the intermediate transfer belt 27.

As the intermediate transfer belt 27, PVDF (vinylidene fluoride resin), ETFE (tetrafluoroethylene-ethylene copolymer resin), polyimide, PET (thickness: 50 to 200 μm, volume resistivity: about 10 ⁹ to 10 ¹⁶ Ωcm) Polyethylene terephthalate), polycarbonate, or other resin film, or about 0.5 to 2 mm in thickness, for example, EPDM or other rubber base layer, for example urethane rubber dispersed with fluorine resin such as PTFE Is used by coating.

  In a normal printing operation, when the recording material P is fed into the image forming apparatus from the paper feeding cassette 15 or the like by the pickup roller 16 and the paper feeding rollers 17 and 18, first, the four colors formed on the intermediate transfer belt are formed. In order to synchronize the toner image and the conveyance of the recording material P, for example, a synchronous rotating body in the form of a roller, that is, a registration roller 19A and a registration counter roller 19B (hereinafter referred to as “registration roller pair 19A, 19B”). After being sandwiched between the recording material P and the conveying belt 14, the recording material P and the conveying belt 14 are guided to a suction portion at a predetermined timing.

  In the suction unit, for example, a suction roller 28 as a suction member is opposed to the driven roller 25 via the transport belt 14 and sandwiches the transport belt 14 and the recording material P. When a voltage is applied to the suction roller 28 from the suction bias power source 32A, which is a high voltage source, a charge is applied to the recording material P, and the recording material P to which the charge is applied polarizes the transport belt 14. Thus, the toner is conveyed to the secondary transfer portion while being electrostatically attracted to the conveyance belt 14.

  Further, there is an adsorption current detection circuit 34 between the adsorption roller 28 and the adsorption bias power supply 32A, and the value of the current that flows when the adsorption bias is applied is measured. In the arithmetic control circuit 40, the resistance of the recording material P is measured. And the optimum secondary transfer bias can be selected.

  In the secondary transfer portion, the four-color toner images formed on the intermediate transfer belt 27 by the action of the secondary transfer roller 28 applied with a bias from the secondary transfer bias power source 33 are secondarily transferred collectively.

  The recording material P that has completed the transfer process is conveyed to the fixing device 21 where it is heated and pressurized to fix the toner image on the surface of the recording material as a permanent image.

  The recording material P that has passed through the fixing device is discharged to the discharge tray 20 by the action of the discharge roller pairs 13A, 13B and 14A, 14B.

  On the other hand, residual transfer toner remaining on the intermediate transfer belt 27, contamination toner caused by jam of the recording material or ground fog in the non-image portion of the photosensitive drum 1, or registration mark or density on the intermediate transfer belt 27. The toner formed as the detection pattern is collected by the belt cleaner 24.

  In addition, although the electrostatic conveyance belt 14 does not normally carry a toner image directly on the surface, contaminated toner adheres to the conveyance belt 14 due to jamming or ground fog on a non-image portion, etc. There is. Such toner on the conveyor belt 14 is collected by a belt cleaner 35.

  The image forming apparatus has an environment sensor 50, and the charging and developing, primary transfer, secondary transfer bias and fixing conditions depend on the atmospheric environment (temperature, humidity) in the image forming apparatus. Can be changed. Thus, it is used for adjusting the density of the toner image formed on the recording material P and for achieving optimum transfer and fixing conditions. Further, the image forming apparatus includes a media sensor 51, and by determining the type of the recording material P, the transfer bias and the fixing conditions can be changed according to the type of the recording material. It is used to achieve optimum transfer and fixing conditions for the recording material P.

  In the present embodiment, as in the second embodiment, the timing at which the front and rear ends of the recording material P during the image forming operation change is the timing at which the value of the current flowing through the suction roller changes.

  The effect of using this embodiment is the same as that of Embodiment 1 in principle, and the same effect can be obtained.

  In other words, the amount of protrusion is corrected by detecting the passage timing of the recording material P during the image forming operation using the timing at which the value of the current flowing through the suction roller changes, and as a result, the edge portion of the recording material P is corrected. The edge portion of the toner image can be synchronized.

  In the present embodiment, the method has been described in which a constant voltage is applied by the suction bias power source 32A and the current value flowing at that time is monitored by the suction current detection circuit 34. However, the present invention is not limited to this method. For example, a method may be used in which a current is supplied using a constant current power source as the suction bias power source and the voltage value at that time is monitored by the suction voltage detection circuit.

  The application timing of the suction bias may be any timing until the recording material P reaches the suction roller 28. The adsorption voltage has different voltage values for detecting the passage of the recording material P, for detecting the resistance of the recording material P, and for detecting the transfer material P on the transfer belt 14. It may be used.

  Further, the suction bias to be used may be changed using the temperature / humidity detection result of the environmental sensor 50. Since the moisture content of the recording material P fluctuates depending on the temperature and humidity in the image forming apparatus and the resistance value may fluctuate accordingly, the optimum adsorption bias value setting for detecting the transfer material is accordingly accompanied. Because it changes. As described above, an optimum suction bias setting value according to the atmospheric environment of the image forming apparatus is prepared in advance, and the suction bias setting value is set based on the data measured by the environment sensor 50, so that a more accurate recording material is recorded. The passage timing and resistance value of P can be detected, and the recording material P can be more stably conveyed by electrostatic attraction.

  Furthermore, when changing the process speed to increase the resolution of image drawing, to improve fixability, or when changing the adsorption conditions to the optimum value depending on the thickness or type of transfer material used, etc. It is preferable to change the suction bias according to each condition because more accurate detection and more stable electrostatic suction conveyance can be performed.

  In the case of applying the present invention, the electrostatic latent image created on each image carrier is necessary to move the distance from the exposure start position to the transfer position of the recording material P. Each time is preferably shorter than each time required to move the distance from the position where the recording material P passes through the suction roller 28 to the position where the toner image on each carrier is transferred. . If this condition is not satisfied, when the passage of the recording material P is detected by the suction roller 28, the toner image has already been formed.

  However, even in that case, the time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material P is as follows: As long as there is a station whose relationship is shorter than the time required to move the distance from the position where the recording material P passes the detection position of the suction roller 28 to the position where the toner image of each carrier is transferred, this is true. The present invention can be applied to a station to obtain an effect.

  However, when the amount of protrusion cannot be corrected in some stations, the magnification of the image cannot be made substantially equal to the size of the recording material P. That is, for a station where the amount of protrusion cannot be corrected, the amount of protrusion of about 3 mm is required at both the front and rear ends as in the conventional image forming apparatus. However, for stations where the amount of protrusion can be corrected, the amount of protrusion can be adjusted, so by correcting the print signal so that toner images are not written, the occurrence of internal contamination and wasteful toner consumption due to toner protruding from the edge portion can be avoided. The effect of suppressing can be acquired.

  In particular, the time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material P is such that the recording material P has There are many cases where there are stations that are longer than the time required to move the distance from the detection position of the suction roller 28 to the position where the toner image of each carrier is transferred.

  In the present embodiment, the method of correcting the protrusion amount by using the suction roller 28 and detecting the passage timing of the leading end or the trailing end of the recording material P by the suction current detection circuit 34 has been described. However, as in the first embodiment, a method of correcting the protrusion amount by detecting the passage timing of the recording material P by the protrusion amount correction sensor 30 may be used.

  As described above, according to the present invention, in the color image forming apparatus using the intermediate transfer type tandem system, the sticking roller 28 is used, and the sticking current detection circuit 34 detects the passage timing of the recording material P, thereby protruding. By correcting the amount, for example, even when borderless printing is performed, the edge portion of the recording material P and the edge portion of the toner image are synchronized, and there is no margin, and the inside of the machine by the toner protruding from the edge portion Suppresses the occurrence of contamination and wasteful toner consumption, can accurately print the area intended by the user, and does not require calibration to perform borderless printing, thereby impairing productivity during normal printing It is possible to provide a color image forming apparatus capable of printing without margins.

1 is a configuration cross-sectional view of a color image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is a cross-sectional view of a color image forming apparatus according to Embodiment 2 of the present invention. FIG. 6 is a structural cross-sectional view of a color image forming apparatus according to Embodiment 3 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 14 Electrostatic adsorption conveyance belt 19A Registration roller 19B Registration counter roller 27 Intermediate transfer belt 28 Adsorption roller 30 Projection amount correction sensor 32A Adsorption bias power supply 34 Adsorption current detection circuit 40 Arithmetic control device 45 Controller unit P Recording material

Claims (12)

A plurality of image carriers, an exposure device for creating an electrostatic latent image on the image carrier in accordance with an image signal, a plurality of developing devices for visualizing the electrostatic latent images as toner images, and the image carrier Transfer bias applying means for directly transferring the toner image to the transfer material or primary transfer to the intermediate transfer medium and then secondary transfer to the transfer material, and to-be-transferred on the recording material In a color image forming apparatus having a heat fixing device for heat fixing a toner image as a permanent image,
A detection unit that detects passage of the leading end position or the trailing end position of the recording material; and a correction unit that performs correction control of an amount of protrusion of a plurality of toner images from the recording material. A color image forming apparatus that controls the amount of protrusion of a plurality of toner images based on the detection result of the passage detection means when performing so-called borderless printing that protrudes or prints up to an equivalent area.   Each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material, and the recording material passes through Compared with the time required to move the distance from the detection position of the detection means to the position where the toner image of each carrier is transferred, the former is shorter in all image carriers, and the control is performed. 2. A color image forming apparatus according to claim 1, wherein said means controls the amount of protrusion of all toner images based on said passage detection result.   Each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material, and the recording material passes through When comparing each time required to move the distance from the passing detection position of the detection means to the position where the toner image of each carrier is transferred, at least one or more of the former is in a long relationship. A first image forming unit and at least one second image forming unit in which the former is in a short relationship, and the control means is configured to control at least one of the second image forming units based on the passage detection result. 2. The color image forming apparatus according to claim 1, wherein an amount of protrusion of the two or more toner images is controlled. A plurality of image carriers, an exposure device that creates an electrostatic latent image on the image carrier in accordance with an image signal, a plurality of developing devices that visualize the electrostatic latent images as toner images, and a recording material A recording material carrier, an adsorption member that electrostatically adsorbs the recording material to the recording material carrier at an adsorption position, and a toner image on the image carrier that directly transfers a toner image on the image carrier A transfer bias applying means for transferring the toner image onto the intermediate transfer medium, and then transferring the toner image onto the transfer material as a permanent image. In a color image forming apparatus having a heat fixing device for heat fixing,
Correction means for performing correction control of the amount of protrusion of a plurality of toner images that protrudes from the recording material, and when performing so-called borderless printing in which the toner image protrudes from the recording material or prints up to an equivalent area. A suction detection means for detecting a current or a voltage due to the suction bias when the material reaches the suction position; a detection result when the recording material of the suction detection means enters the suction position; and a recording material The color image forming apparatus according to claim 1, wherein the amount of protrusion of the plurality of toner images is controlled based on a detection result of the suction detection unit when the toner leaves the suction position.   Each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material, and the recording material passes through Compared with the time required to move the distance from the detection position of the detection means to the position where the toner image of each carrier is transferred, the former is shorter in all image carriers, and the control is performed. 5. The color image forming apparatus according to claim 4, wherein the means controls the amount of protrusion of all toner images based on the passage detection result.   Each time required for the electrostatic latent image created on each image carrier to move the distance from the exposure start position to the transfer position of the recording material, and the recording material Comparing each time required for moving the distance from the passage detection position of the passage detection means to the position where the toner image of each carrier is transferred, at least one or more of the former is in a long relationship. A first image forming unit and at least one second image forming unit in which the former is in a short relationship, and the control means is configured to control at least one of the second image forming units based on the passage detection result. 5. The color image forming apparatus according to claim 4, wherein the amount of protrusion of the two or more toner images is controlled.   The value of the suction bias until the arrival of the leading end of the recording material at the suction position is detected is made different from the value of the suction bias after the arrival of the leading end of the recording material at the suction position is detected. A color image forming apparatus according to any one of claims 4 to 7.   The value of the suction bias until the arrival of the leading end of the recording material at the suction position is detected is set to at least one of the conditions of temperature and humidity of the environment in the image forming apparatus main body, the type of recording material, and the process speed The color image forming apparatus according to any one of claims 4 to 7, wherein the color image forming apparatus is changed accordingly.   9. The color image forming apparatus according to claim 4, wherein the means for applying the suction bias includes a constant voltage bias application means, and the suction detection means is a current detection means.   9. The color image forming apparatus according to claim 4, wherein the means for applying the suction bias includes a constant current bias application means, and the suction detection means is a voltage detection means.   11. The color image forming apparatus according to claim 1, wherein the amount of protrusion corrected by the protrusion amount correcting unit is a protrusion amount of a plurality of toner images protruding from the leading end of the recording material.   The color image forming apparatus according to claim 1, wherein the amount of protrusion corrected by the protrusion amount correcting unit is a trailing edge protruding amount of a plurality of toner images protruding from the trailing edge of the recording material. .

Images