Image forming apparatus

Abstract

To suppress the occurrence of a one side loop caused by an image even when a loop sensor is not arranged.SOLUTION: An image forming apparatus includes an intermediate transfer belt 7, a secondary transfer device 8, a fixing device 17, a fixing motor 212, and an engine control unit 202, and when image information on one end side from a center in a direction orthogonal to a conveyance direction of a recording material P is defined as first image information and image information on the other end side is defined as second image information, the engine control unit 202 controls a conveyance speed in a fixing unit based on left-right difference information that is a difference between the first image information and the second image information.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, such as a copying machine, a printer, or a facsimile machine that forms an image by electrophotography. [Background technology]

[0002] In an image forming apparatus, a loop sensor is provided between a transfer means and a fixing means to detect the amount of loop of the recording material, and the conveying speed of the recording material is controlled based on the detection result of the loop amount. For example, Patent Document 1 discloses a method in which a plurality of loop sensors are provided in a direction perpendicular to the conveying direction of the recording material, and the conveying speed of the recording material is controlled so that a defective image does not occur even if a loop occurs on only one side (hereinafter referred to as a one-side loop). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-215430 Summary of the Invention [Problem to be solved by the invention]

[0004] Among image forming devices, there are those that cannot accommodate multiple loop sensors as in the past because the distance between the transfer means and the fixing means has been shortened in order to reduce size, and there are also image forming devices that do not have multiple loop sensors in order to reduce costs.

[0005] The present invention has been made under these circumstances, and has as its object to suppress the occurrence of one-sided loops caused by images even when a loop sensor is not provided. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) An image forming apparatus comprising: an image carrier on which a toner image corresponding to image information is formed; a transfer means for transferring the toner image formed on the image carrier to a recording material in a transfer section; a fixing means for fixing the toner image transferred to the recording material to the recording material in a fixing section; a drive means for driving the fixing means; and a control means for controlling the conveying speed of the recording material in the fixing section by controlling the drive means, wherein, when, of the image information, image information on one end side of the center in a direction perpendicular to the conveying direction of the recording material is defined as first image information and image information on the other end side is defined as second image information, the control means controls the conveying speed in the fixing section based on the difference between the first image information and the second image information. [Effects of the Invention]

[0008] According to the present invention, even when a loop sensor is not provided, it is possible to suppress the occurrence of one-sided loops caused by images. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic cross-sectional view of an image forming apparatus according to first and second embodiments [Figure 2] Control block diagram of the image forming apparatus according to the first and second embodiments [Figure 3] Schematic cross-sectional view of a transfer device and a fixing device in Examples 1 and 2 [Figure 4] FIG. 10 is a diagram illustrating the occurrence of a one-sided loop in single-sided printing in Example 1. [Figure 5] FIG. 10 is a diagram illustrating the occurrence of a one-sided loop in double-sided printing in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0010] <Overall configuration of image forming apparatus> The overall configuration of an image forming apparatus will be described using FIG. 1. The image forming apparatus shown in Example 1 is a laser printer that uses an electrophotographic process as an image forming means. The color image forming apparatus 100 (hereinafter referred to as printer 100) shown in FIG. 1 includes four cartridges 5Y, 5M, 5C, and 5K that are detachable from the main body. Each cartridge 5Y, 5M, 5C, and 5K has the same structure but differs in that it forms images using toner of different colors, namely, yellow (Y), magenta (M), cyan (C), and black (K). Note that the reference symbols YMCK will be omitted hereinafter except when describing a specific cartridge. Each cartridge 5 includes a photosensitive drum 1, a charging roller 2, and a developing roller 3 as a developing means. An exposure device 6 is disposed below the cartridge 5 and exposes the photosensitive drum 1 based on an image signal.

[0011] The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2, and then exposed to light by the exposure device 6, forming an electrostatic latent image of the desired image. The electrostatic latent image formed on the photosensitive drum 1 is developed into a toner image by the developing roller 3, forming a toner image.

[0012] The intermediate transfer belt unit is composed of an intermediate transfer belt 7 as an image carrier, a drive roller 10, and a tension roller 11. Furthermore, primary transfer rollers 4 are disposed inside the intermediate transfer belt 7 facing each photosensitive drum 1, and a voltage is applied to the transfer rollers 4 from a power source (not shown). As a result, the toner images on the photosensitive drums 1 are transferred sequentially onto the intermediate transfer belt 7 (hereinafter referred to as primary transfer). Thereafter, the four color toner images are transported to a secondary transfer device 8 in a superimposed state.

[0013] The paper feed conveying device 12 has a paper feed roller 14 that feeds the recording material P from a paper feed cassette 13 that stores the recording material P, and a pair of conveying rollers 15 that convey the fed recording material P. The recording material P conveyed from the paper feed conveying device 12 is conveyed by a pair of registration rollers 16 to a secondary transfer device 8, where the toner image on the intermediate transfer belt 7 is transferred (hereinafter referred to as secondary transfer). The toner image is transferred onto the recording material P as it is conveyed through a nip portion (transfer portion) between a secondary transfer roller 9 and a drive roller 10. After the toner image transfer, the recording material P has the toner image fixed by a fixing device 17 and is then discharged outside the printer 100 by a pair of discharge rollers 20, completing the image formation operation for single-sided printing. The fixing device 17 has a fixing film 18 and a pressure roller 19. When the toner image is transferred onto the recording material P, the intermediate transfer belt 7 functions as an image carrier in the configuration shown in FIG. 1. Some printers do not have an intermediate transfer belt, in which case the toner image is transferred from the photosensitive drum to the recording material P, and the photosensitive drum functions as the image carrier. In this case, the transfer section is the part where the toner image is transferred from the photosensitive drum to the recording material.

[0014] The printer 100 is capable of double-sided printing on the recording material P. When double-sided printing is performed on the recording material P, the trailing edge of the recording material P that has passed through the fixing device 17 passes the position of the double-sided flapper 21, and then the position of the double-sided flapper 21 is first switched to the double-sided conveyance path side. Furthermore, a reversing clutch (not shown) that determines the rotation direction of the discharge roller pair 20 switches the rotation direction of the discharge roller pair 20 to the double-sided conveyance path side. The conveyance direction of the recording material P is reversed, and the recording material P is conveyed to the double-sided conveyance path. In the double-sided conveyance path, the recording material P is conveyed by the double-sided conveyance roller pair 22 and the main body merging roller pair 23, and is conveyed to the registration roller pair 16. After the registration roller pair 16, the same process as for the first side is performed, and the recording material P is discharged outside the printer 100 after passing through the fixing device 17. The printer control device 200 will be described later.

[0015] <Printer control device> The printer control device 200 of the first embodiment will be described with reference to FIG. 2. The printer control device 200 includes a video controller 201 that creates image data to be printed and issues print instructions, and an engine control unit 202 that controls each component within the printer 100. The engine control unit 202 includes a central processing unit (CPU), read-only memory (ROM), random-access memory (RAM), and a timer. The engine control unit 202 controls the printer 100 by executing a program pre-stored in the ROM using the CPU while using the RAM as a temporary work area. When controlling the printer 100, the engine control unit 202 controls various timings using a timer. The engine control unit 202 may include an application specific integrated circuit (ASIC) or a micro processing unit (MPU). The number of CPUs, timers, ROMs, and RAMs is not limited to one, and may be multiple. Furthermore, other storage media such as a hard disk or optical disk may be used as the storage medium.

[0016] When the video controller 201 receives a print instruction from an external device such as a personal computer, it issues a print start instruction to the engine control unit 202. When the engine control unit 202 receives the instruction from the video controller 201, it controls the paper transport of the recording material P by the paper transport control unit 203, controls the image forming operation by the image formation control unit 204, and controls the temperature of the fixing device 17 by the fixing control unit 205. In the printer control device 200 of the first embodiment, the video controller 201 calculates information about the left-right difference of an image, which will be described later, and notifies the engine control unit 202 of the information.

[0017] <Configuration of transfer device and fixing device> Using FIG. 3, the configurations of the secondary transfer device 8 as a transfer means and the fixing device 17 as a fixing means in the first embodiment will be described. The secondary transfer device 8 is composed of an intermediate transfer belt 7, a drive roller 10, and a secondary transfer roller 9. The intermediate transfer belt 7 is an endless belt having a circumference of 800 mm and a surface layer coated on a base layer made of a resin with an adjusted resistance. The drive roller 10 is a roller with an outer diameter of φ26 and a rubber layer on a pipe-shaped core metal. It rotates by a main motor 211 (see FIG. 2), thereby rotating the intermediate transfer belt 7. The secondary transfer roller 9 is a roller with an outer diameter of φ20 and a rubber layer with an adjusted resistance on a core metal. It presses against the intermediate transfer belt 7 with a pressure of approximately 6 kgf and rotates in response to the rotation of the intermediate transfer belt 7. The recording material P is sandwiched and transported between the intermediate transfer belt 7 and the secondary transfer roller 9, and during this transport process, a voltage is applied to the secondary transfer roller 9 from a power source (not shown), thereby transferring the toner image on the intermediate transfer belt 7 to the recording material P.

[0018] The fixing device 17 is composed of a fixing film 18, a pressure roller 19, a heater 24, and a thermistor 25 as a temperature detection means. The fixing film 18 is a cylindrical film with an outer diameter of φ24, which has an elastic layer and a surface layer provided on a resin base layer. The elastic layer is made of a heat-resistant elastic material for the purposes of improving fixing properties and uniform gloss. The surface layer is made of a heat-resistant material with good releasability, such as fluororesin, for the purpose of improving separability from the recording material P.

[0019] The pressure roller 19 is a roller with an outer diameter of 25 mm, which includes a core shaft, at least one elastic layer, and a surface layer. The elastic layer is made of a heat-resistant elastic material such as silicone rubber to ensure the width of the fixing nip (fixing portion) formed by the fixing film 18 and the pressure roller 19. The width refers to the length in the direction perpendicular to the conveyance direction of the recording material P. The surface layer is made of a heat-resistant material with good releasability, such as fluororesin, to prevent contamination.

[0020] The heater 24 is a resistance heating element provided in the internal space of the fixing film 18 and contacts the inner circumferential surface of the fixing film 18 to rapidly heat the fixing film 18. The temperature of the heater 24 is detected by a thermistor 25 that is in contact with the back surface of the substrate on which the heater 24 is mounted. The detection result of the thermistor 25 is output as a detection signal to the fixing control unit 205. The fixing control unit 205, which serves as a temperature control means, controls the heater 24 to reach a predetermined target temperature based on the detection signal of the thermistor 25.

[0021] The pressure roller 19 contacts the outer peripheral surface of the fixing film 18 and is driven to rotate by a fixing motor 212 (see FIG. 2) which is a driving means, and the fixing film 18 is rotated in accordance with the rotation of the pressure roller 19. With the heater 24 controlled to a predetermined target temperature, the recording material P is guided to the fixing nip portion and is sandwiched and conveyed between the fixing film 18 and the pressure roller 19. During the conveyance process, heat and pressure are applied to the recording material P, and the unfixed toner image is fixed to the recording material P. As the recording material P is conveyed through the fixing nip portion between the fixing film 18 and the pressure roller 19, the unfixed toner image is fixed.

[0022] The printer 100 of the first embodiment has the capability of outputting an A3 size recording material P at 15 ppm (pages per minute) at a conveying speed of 150 mm / s for both single-sided printing and double-sided printing. The printer 100 also has a main motor 211 and a fixing motor 212, and the drive roller 10 and pressure roller 19 can be driven and controlled at different conveying speeds by a paper conveyance control unit 203.

[0023] <Explanation of one-sided loop caused by image> Using Figure 4, we will explain the phenomenon of one-sided loops, for example, when a one-sided loop occurs due to an image. Figure 4(A) shows the behavior of the recording material P between the secondary transfer device 8 and the fixing device 17 when a black (K) image is printed on one side (first side) of the recording material P in single-sided printing. Figure 4(B) is a diagram of the intermediate transfer belt 7 and the fixing film 18 in the longitudinal direction Dr as viewed from the direction of arrow x1 in Figure 4(A). Here, the longitudinal direction Dr is a direction perpendicular to the conveyance direction of the recording material P and is the direction of the rotation axes of the drive roller 10 and the pressure roller 19. Meanwhile, Figure 4(A) is a cross-sectional view as viewed from the direction of arrow y1 in Figure 4(B).

[0024] In Figure 4(B), the trajectory at the end of region R_P1K where black (K) toner is present on recording material P is trajectory P1K in Figure 4(A), and the trajectory at the end of region R_P1W where there is no toner on recording material P is trajectory P1W in Figure 4(A). In the case of an image in which toner is unevenly distributed on only one side like this, the conveyance speed of recording material P in secondary transfer device 8 is slower on trajectory P1K on the side where there is toner than on trajectory P1W on the side where there is no toner. This is because the toner in Example 1 is a spherical toner made of resin, and the presence of toner (toner before fixing) reduces the frictional force between intermediate transfer belt 7 and recording material P.

[0025] In Figure 4(A), trajectory P1K shown by a dashed line is the trajectory of the recording material P on the side where toner is present, and trajectory P1W shown by a solid line is the trajectory of the recording material P on the side where toner is not present. The amount of loop is smaller on the trajectory P1K side, where the conveying speed of the recording material P in the secondary transfer device 8 is slower, than on the trajectory P1W side. This difference in loop amount accumulates toward the rear end of the recording material P, causing a one-sided loop. In a high-humidity environment, if the recording material P is recycled paper, the one-sided loop may become larger (develop) and cause paper wrinkles.

[0026] <Explanation of one-sided loop cancellation control in the first embodiment> In the first embodiment, when the engine control unit 202 as a control means determines that an image will have a one-side loop based on the difference between the left and right image information (hereinafter referred to as left-right difference information of the image), it increases the conveying speed of the fixing device 17 to eliminate the one-side loop. Here, if one end side of the center in the longitudinal direction of the recording material P or the image formed on the recording material P is defined as the left side, the right side is the other end side of the center in the longitudinal direction.

[0027] In the first embodiment, the image information is the coverage rate, and the left-right difference in coverage rate, specifically, the coverage rate of the left half of the image (first image information) and the coverage rate of the right half of the image (second image information), is used as the left-right difference information of the image. Here, the coverage rate indicates the proportion (%) of the recording material P covered by toner in a predetermined area, and is expressed by the following formula (2). In the first embodiment, the video controller 201 acquires the coverage rate, i.e., the proportion of the number of non-white pixels to the total number of pixels in the predetermined area, based on the image data. Furthermore, the predetermined area is defined as the left and right halves of the largest image to be transferred to one sheet of recording material P, and the acquired left-right difference therebetween is expressed as the left-right difference in coverage rate (%), by the following formula (1). Difference in coverage (%) = coverage of the left half of the image (%) - coverage of the right half of the image (%) (1) Coverage (%) = Number of non-white pixels / Total number of pixels x 100 (2)

[0028] In the first embodiment, the left-right difference is obtained between the left half of the image, i.e., the left half, and the right half, i.e., the right half, but this is not limited to this. The left-right difference may also be obtained using image information of, for example, one-third or one-quarter areas on the left and right sides, symmetrically with respect to the center in the longitudinal direction, as long as the information on the left and right difference can be obtained based on information extracted on the left and right. Furthermore, with regard to the conveyance direction, image information from the leading edge to the trailing edge of the recording material P is used, but this is not limited to this. For example, image information within an area in the conveyance direction of the recording material P that corresponds to the conveyance distance between the transfer unit and the fixing unit may also be used.

[0029] Table 1 is a table (countermeasure control table) showing the absolute value of the difference between the left and right coverages used in the one-side loop elimination control in the first embodiment and the speed increase amount of the fixing device 17 relative to the secondary transfer device 8. It should be noted that the table in Table 1 is assumed to be stored in a storage medium such as the above-mentioned ROM. [Table 1]

[0030] When the video controller 201 receives the image data, it calculates the difference in left and right coverage using equation (1) and notifies the engine control unit 202 along with a print start command. The engine control unit 202 determines the amount of speed increase for the fixing device 17 based on the received difference in left and right coverage according to Table 1, and controls the speed of the fixing device 17 using the paper transport control unit 203.

[0031] For example, when the absolute value of the difference (%) in coverage between the left and right sides is 60% or more and less than 80%, the engine control unit 202 controls the conveying speed of the fixing device 17 so that the conveying speed at the fixing device 17 increases by 1% compared to the conveying speed at the secondary transfer device 8, based on Table 1. Specifically, the engine control unit 202 controls the conveying speed of the recording material P by the pressure roller 19 by controlling the fixing motor 212 via the paper conveyance control unit 203. Similarly, when the difference (%) in coverage between the left and right sides is 80% or more and less than 100%, the engine control unit 202 controls the conveying speed of the fixing device 17 so that the conveying speed at the fixing device 17 increases by 2% compared to the conveying speed at the secondary transfer device 8, based on Table 1. Furthermore, when the difference (%) in coverage between the left and right sides is 100%, as shown in FIG. 4B, the engine control unit 202 controls the conveying speed of the fixing device 17 so that the conveying speed at the fixing device 17 increases by 3% compared to the conveying speed at the secondary transfer device 8, based on Table 1. That is, the engine control unit 202 controls the conveying speed in the fixing device 17 relative to the conveying speed in the secondary transfer device 8 to increase as the absolute value (%) of the difference in coverage between the left and right sides increases.

[0032] By controlling in this manner, the recording material P is pulled by the fixing device 17, and the trajectory P1W on the side where there is no toner in Figure 4(A) approaches the trajectory P1K on the side where there is toner, thereby suppressing the occurrence of a one-sided loop.

[0033] <Effects of Control in Example 1> To confirm the effect of Example 1, the incidence of paper wrinkles was compared and the results are shown in Table 2. The confirmation was carried out in an environment of a temperature of 30°C and a humidity of 80%. GFR070-A3 size (Canon recycled paper) was used as the recording material P, and a black (K) image was formed on half of one side, and 30 sheets were printed continuously using single-sided printing. [Table 2]

[0034] When control to increase the conveying speed of the fixing device 17 was not performed (no speed increase of the fixing device), paper wrinkles occurred on 3 out of 30 sheets. On the other hand, when the countermeasure control of Example 1 was performed, no paper wrinkles occurred. From the results in Table 2, it was confirmed that the countermeasure control of Example 1 had a lower paper wrinkle occurrence rate and suppressed the occurrence of one-sided loops caused by images. In the first embodiment, a method for suppressing the occurrence of one-sided loops due to images by controlling the conveying speed of the fixing device 17 based on information about the left-right difference of the image has been described.

[0035] <Modification> In the first embodiment, the left-right difference in coverage (%) is used as the left-right difference information of the image, but this is not limiting, and the image information may be, for example, a printing rate. Specifically, the printing rate of the left half of the image (first image information) and the printing rate of the right half of the image (second image information) are used. That is, the following left-right difference in printing rate may be used. Here, the printing rate indicates the ratio (%) of the sum of the number of pixels of each color to the total number of pixels, and is expressed by the following formula (4). The video controller 201 acquires the number of pixels based on the image data. Furthermore, the difference (left-right difference) between the printing rate of the left half of the image and the printing rate of the right half of the image is acquired and expressed as the left-right difference in printing rate (%), using the following formula (3). Difference in print rate (%) = print rate (%) of left half of image - print rate (%) of right half of image (3) Print rate (%) = (yellow pixels + magenta pixels + cyan pixels + black pixels) / total pixels x 100 (4)

[0036] As in Table 1, the greater the difference (%) in the printing rate between the left and right sides, the more likely one-sided loops are to occur, and the more likely paper wrinkles are to occur. For this reason, the engine control unit 202 controls the conveying speed in the fixing device 17 to increase by a larger amount relative to the conveying speed in the secondary transfer device 8, as the absolute value of the difference (%) in the printing rate between the left and right sides increases.

[0037] As described above, according to the first embodiment, even when no loop sensor is provided, it is possible to suppress the occurrence of one-sided loops caused by images. [Example]

[0038] In the second embodiment, in double-sided printing, based on the left-right difference information of the image on the first side, one-sided looping is suppressed when the second side is transported by the secondary transfer device 8. The configurations of the image forming device, transfer device, and fixing device in the second embodiment are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0039] <Explanation of one-sided loop occurring on the second side due to image-related reasons> Using Figure 5, we will explain the phenomenon in which a one-sided loop occurs on the second side due to an image on the first side during double-sided printing. Figure 5(A) is a diagram showing the behavior of the recording material P between the secondary transfer device 8 and the fixing device 17 on the second side when a black (K) image is printed on one side of the recording material P on the first side and a text image is printed across the entire surface of the recording material P on the second side during double-sided printing. Figure 5(B) is a diagram showing the secondary transfer roller 9, pressure roller 19, and the first side of the recording material P as viewed from the direction of arrow x2 in Figure 5(A). Meanwhile, Figure 5(A) is a cross-sectional view as viewed from the direction of arrow y2 in Figure 5(B).

[0040] In FIG. 5B, the trajectory at the end of region R_P2K where there is a black fixed image on the first side of recording material P is trajectory P2K (FIG. 5A), and the trajectory at the end of region R_P2W where there is no fixed image on the first side of recording material P is trajectory P2W (FIG. 5B). Note that a fixed image refers to an image that has been subjected to a fixing process by fixing device 17. In this way, in the case of an image where the fixed image is unevenly distributed on only one side of the first side, the conveying speed of recording material P on the second side of secondary transfer device 8 is faster on trajectory P2K on the side where there is a fixed image on the first side than on trajectory P2W on the side where there is no fixed image on the first side. This is because the fixed toner, which is the fixed image, increases the frictional force between secondary transfer roller 9 and recording material P.

[0041] In Figure 5(A), trajectory P2K shown by a solid line is the trajectory of the second side of the recording material P on the side where there is a fixed image on the first side, and trajectory P2W shown by a dashed line is the trajectory of the second side of the recording material P on the side where there is no fixed image on the first side. The amount of loop is larger on the trajectory P2K side, where the conveying speed of the recording material P in the secondary transfer device 8 is faster, than on the trajectory P2W side. This difference in loop amount accumulates toward the rear end of the recording material P, causing a one-sided loop. If the recording material P is recycled paper in a high-humidity environment, the one-sided loop may develop and cause paper wrinkles.

[0042] <Explanation of measures in Example 2> In the second embodiment, when the engine control unit 202 determines from the left-right difference information of the image on the first side that the image will have a one-sided loop on the second side, it increases the conveying speed of the fixing device 17 on the second side to eliminate the one-sided loop. In the second embodiment, the left-right difference in coverage is used as the left-right difference information of the image. The coverage (%) is calculated using the following formula (6), and the left-right difference in coverage (%) is calculated using the following formula (5). Difference in coverage (%) = coverage of the left half of the image (%) - coverage of the right half of the image (%) (5) Coverage (%) = Number of non-white pixels / Total number of pixels x 100 (6)

[0043] Table 3 is a table (countermeasure control table for the second side) showing the absolute value of the difference between the left and right coverage rates for the first side used in the countermeasure control in Example 2 and the speed increase amount of the fixing device 17 relative to the secondary transfer device 8 for the second side. Note that the table of Table 3 is assumed to be stored in a storage medium such as the above-mentioned ROM. [Table 3]

[0044] When the video controller 201 receives the image data, it calculates the difference in left and right coverage on the first side and notifies the engine control unit 202 along with a print start command. The engine control unit 202 determines the amount of speed increase for the fixing device 17 based on the received difference in left and right coverage according to Table 3, and controls the speed of the fixing device 17 on the second side using the paper transport control unit 203.

[0045] When the absolute value of the left-right difference (%) in coverage on the first side is 60% or more and less than 80%, the engine control unit 202 controls the conveying speed of the fixing device 17 so that the conveying speed at the fixing device 17 increases by 3% compared to the conveying speed at the secondary transfer device 8 for the second side, based on Table 3. Specifically, the engine control unit 202 controls the conveying speed of the recording material P by the pressure roller 19 by controlling the fixing motor 212 via the paper conveyance control unit 203. Similarly, when the left-right difference (%) in coverage on the first side is 80% or more and less than 100%, the engine control unit 202 controls the conveying speed of the fixing device 17 so that the conveying speed at the fixing device 17 increases by 4% compared to the conveying speed at the secondary transfer device 8, based on Table 3. Furthermore, when the left-right difference (%) in coverage on the first side is 100%, as shown in FIG. 5B, the engine control unit 202 controls the conveying speed of the fixing device 17 so that the conveying speed at the fixing device 17 increases by 5% compared to the conveying speed at the secondary transfer device 8, based on Table 3. That is, the engine control unit 202 controls the conveying speed at the fixing device 17 relative to the conveying speed at the secondary transfer device 8 on the second side so that the larger the absolute value (%) of the difference between the left and right coverage rates on the first side, the larger the increase in the conveying speed at the fixing device 17 relative to the conveying speed at the secondary transfer device 8 on the second side.

[0046] By controlling in this manner, the recording material P is pulled by the fixing device 17, and the trajectory P2K on the side where there is a fixed image on the first side in Figure 5(A) approaches the trajectory P2W on the side where there is no fixed image on the first side, thereby suppressing the occurrence of a one-sided loop.

[0047] <Effects of Control in Example 2> Table 4 shows the results of a comparison of paper wrinkle occurrence rates to confirm the effects of Example 2. The confirmation was carried out in an environment with a temperature of 30°C and humidity of 80%. GFR070-A3 size (Canon recycled paper) was used as the recording material P, with a black (K) image on one half of one side of the first side and a text image on the entire second side, and 30 sheets were printed continuously using double-sided printing. The control of Example 1 was also applied to the first side. [Table 4]

[0048] When control to increase the conveying speed of the fixing device 17 was not performed (no speed increase of the fixing device), paper wrinkles occurred on 5 out of 30 sheets. On the other hand, when the countermeasure control of Example 2 was performed, paper wrinkles did not occur. The results in Table 4 confirm that the countermeasure control of Example 2 had a lower paper wrinkle occurrence rate and suppressed the occurrence of one-sided loops on the second side caused by the image on the first side.

[0049] In the above, in the second embodiment, a method for suppressing the occurrence of one-sided loops due to an image by controlling the conveying speed in the fixing device for the second side based on the left-right difference information of the image on the first side has been described. Note that in the second embodiment, the speed control of the fixing device 17 for the recording material P on the second side is determined based on the left-right difference information of the image on the first side, but it may also be determined by adding the left-right difference information of the image on the second side. Also, instead of the coverage rate, control may be performed based on the printing rate as in the modified example of the first embodiment.

[0050] As described above, according to the second embodiment, even when no loop sensor is provided, it is possible to suppress the occurrence of one-sided loops caused by images.

[0051] <Other embodiments> The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0052] The disclosure of this embodiment includes the following configuration. (Configuration 1) an image carrier on which a toner image is formed according to image information; a transfer unit that transfers the toner image formed on the image carrier onto a recording material at a transfer unit; a fixing unit for fixing the toner image transferred onto the recording material to the recording material at a fixing unit; a driving means for driving the fixing means; a control unit that controls the driving unit to control a conveying speed of the recording material in the fixing unit; Equipped with When the image information on one end side of the center in a direction perpendicular to the conveyance direction of the recording material is defined as first image information and the image information on the other end side is defined as second image information, The image forming apparatus is characterized in that the control means controls a conveying speed in the fixing unit based on a difference between the first image information and the second image information. (Configuration 2) the image forming apparatus is capable of forming images on both sides of a recording material, The image forming apparatus according to configuration 1, characterized in that the control means controls the conveying speed in the fixing section of the recording material on which an image has been formed on the second side based on the difference between the first image information and the second image information on the first side. (Configuration 3) 3. The image forming apparatus according to claim 1, wherein the control unit controls the conveying speed in the fixing unit to be faster than the conveying speed in the transfer unit based on the difference. (Configuration 4) The image forming apparatus according to Configuration 3, wherein the control unit increases the increase in the conveying speed in the fixing unit relative to the conveying speed in the transfer unit as the difference increases. (Configuration 5) 5. The image forming apparatus according to any one of configurations 1 to 4, wherein the image information is a ratio of the number of non-white pixels to the total number of pixels. (Configuration 6) 5. The image forming apparatus according to any one of configurations 1 to 4, wherein the image information is a printing rate. (Configuration 7) The image forming apparatus according to any one of Configurations 1 to 6, wherein the fixing means includes a cylindrical film, a heater provided in an internal space of the film, and a pressure roller that contacts the outer peripheral surface of the film and forms the fixing section together with the heater via the film. [Explanation of symbols]

[0053] 7 Intermediate transfer belt 9 Secondary transfer roller 10 Drive roller 17 Fixing device 202 Engine control unit

Claims

1. an image carrier on which a toner image is formed according to image information; a transfer unit that transfers the toner image formed on the image carrier onto a recording material at a transfer unit; a fixing unit for fixing the toner image transferred onto the recording material to the recording material at a fixing unit; a driving means for driving the fixing means; a control unit that controls the driving unit to control a conveying speed of the recording material in the fixing unit; Equipped with When the image information on one end side of the center in a direction perpendicular to the conveyance direction of the recording material is defined as first image information and the image information on the other end side is defined as second image information, The image forming apparatus is characterized in that the control means controls a conveying speed in the fixing unit based on a difference between the first image information and the second image information.

2. the image forming apparatus is capable of forming images on both sides of a recording material, 2. The image forming apparatus according to claim 1, wherein the control means controls the conveying speed in the fixing section of the recording material having an image formed on its second side based on the difference between the first image information and the second image information on the first side.

3. 2. The image forming apparatus according to claim 1, wherein the control unit controls the conveying speed in the fixing unit to be faster than the conveying speed in the transfer unit based on the difference.

4. 4. The image forming apparatus according to claim 3, wherein the control unit increases the increase in the transport speed in the fixing unit relative to the transport speed in the transfer unit as the difference increases.

5. 2. The image forming apparatus according to claim 1, wherein the image information is a ratio of the number of non-white pixels to the total number of pixels.

6. 2. The image forming apparatus according to claim 1, wherein the image information is a printing rate.

7. 7. The image forming apparatus according to claim 1, wherein the fixing means comprises a cylindrical film, a heater provided in the internal space of the film, and a pressure roller that contacts the outer surface of the film and forms the fixing section together with the heater via the film.

Images