Image forming device

Abstract

To appropriately adjust transfer voltage during double-sided printing even if a recording material used for output of a chart is a recording material with a small size.SOLUTION: An image forming apparatus has an execution unit that executes an output mode for outputting a chart formed by transferring a plurality of test images to a recording material with different transfer voltages in order to adjust transfer voltage. In adjusting the transfer voltage in double-sided printing, when the recording material has a first width, the execution unit executes a first output mode for outputting a chart formed by transferring a test image for adjusting the transfer voltage on a first surface and a test image for adjusting the transfer voltage on a second surface to the first surface and the second surface of one recording material, respectively, and when the recording material has a second width smaller than the first width, executes a second output mode for outputting charts formed by transferring the test image for the first surface and the test image for the second surface to one sides of different recording materials.SELECTED DRAWING: Figure 8

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 uses an electrophotographic or electrostatic recording method. [Background technology]

[0002] In image forming apparatuses using electrophotography or the like, a toner image formed on an image carrier, such as a photoreceptor or intermediate transfer member, is transferred to a recording material. Transfer of the toner image from the image carrier to the recording material is often achieved by applying a transfer voltage to a transfer member, such as a transfer roller, that contacts the image carrier to form a transfer section. The transfer voltage can be determined based on a transfer section voltage corresponding to the electrical resistance of the transfer section, detected during a pre-rotation process before image formation, and a recording material voltage corresponding to a preset type of recording material. This allows an appropriate transfer voltage to be set depending on environmental fluctuations, the usage history of the transfer member, the type of recording material, and the like.

[0003] However, since the types and conditions of recording materials used in image formation vary, the transfer voltage may be excessive or insufficient with the preset default recording material voltage. Therefore, it has been proposed to provide an adjustment mode that adjusts the set transfer voltage depending on the recording material actually used in image formation.

[0004] Patent Document 1 proposes an image forming apparatus capable of executing an adjustment mode for adjusting the set voltage of the secondary transfer voltage. In this adjustment mode, a chart is output by transferring a plurality of patches (test images) onto a single sheet of recording material while switching the secondary transfer voltage for each patch. The density of each patch is then detected, and the optimal secondary transfer voltage conditions are selected based on the detection results. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-37185 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when adjusting the transfer voltage during double-sided printing in the above-mentioned adjustment mode, if the patch positions on the first and second sides overlap on the front and back of the recording material, the density may not be detected accurately due to the influence of bleed-through. For example, the density of the patch on the first side may be erroneously detected as darker than it actually is due to the influence of the patch on the second side.

[0007] In particular, if the recording material used to output the chart is small, there is little margin when the patches are formed, so when adjusting the transfer voltage for double-sided printing, the patches are likely to overlap on the front and back of the recording material, which may result in inappropriate adjustment of the transfer voltage for double-sided printing according to the detection results of the patch density.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to make it possible to appropriately adjust the transfer voltage during double-sided printing even when the recording material used to output the chart is small. [Means for solving the problem]

[0009] The above object is achieved by the image forming apparatus according to the present invention. According to one aspect an image carrier that carries a toner image; and a transfer unit that transfers the toner image from the image carrier to a recording material. Device and the transcription Device Apply transfer voltage to Voltage application Department and a fixing unit that fixes the toner image transferred onto the recording material to the recording material. Device and, a control unit that is capable of performing a double-sided mode operation in which toner images are formed on both sides of a recording material, and that is capable of performing an output mode operation in which a chart is output by transferring a plurality of test images, including a plurality of first test images and a plurality of second test images, to the recording material, the test images being formed by applying different transfer voltages for adjusting the transfer voltage applied during the double-sided mode operation. and, During execution of the operation in the output mode, the control unit is capable of selectively executing a first operation in which the first test image formed on the first side of a recording material is fixed to the first side of the recording material by the fixing device, and then the second test image is transferred to the second side of the recording material, and a second operation in which the first test image formed on the first side of a first recording material is fixed by the fixing device, and then the first recording material is output without forming the plurality of test images on the second side of the first recording material, and then a second recording material is passed through the fixing device without forming the plurality of test images on the first side of the second recording material, and then the second test image is transferred to the second side of the second recording material. An image forming apparatus characterized by is provided . According to another aspect of the present invention, there is provided an image carrier that carries a toner image, a transfer device that transfers the toner image from the image carrier to a recording material at a transfer section, a voltage application section that applies a transfer voltage to the transfer device, a fixing device that fixes the toner image transferred to the recording material to the recording material at a fixing section, and a test image forming device that is capable of performing a double-sided mode operation in which toner images are formed on both sides of the recording material and that is formed by transferring a plurality of test images, including a plurality of first test images and a plurality of second test images, to the recording material, and that is formed by applying different transfer voltages for adjusting the transfer voltage applied during the double-sided mode operation. and a control unit capable of executing an operation in an output mode in which a test image is output, wherein during execution of the operation in the output mode, the control unit controls the image forming operation so that the first test image formed on the first side of a first recording material is fixed by the fixing device, the first recording material is then output without forming the test image on the second side of the first recording material, and then a second recording material is passed through the fixing device without forming the test image on the first side of the second recording material, and then the second test image is transferred to the second side of the second recording material. [Effects of the Invention]

[0010] According to the present invention, even when the recording material used to output the chart is small, the transfer voltage can be appropriately adjusted during double-sided printing. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] 1 is a block diagram showing a schematic configuration of a control system of an image forming apparatus; [Figure 3] FIG. 10 is a flowchart illustrating an outline of a procedure for controlling a secondary transfer voltage. [Figure 4] FIG. 10 is a graph showing an example of voltage-current characteristics obtained in secondary transfer voltage control. [Figure 5] 10 is a table showing an example of a recording material distribution voltage table. [Figure 6] FIG. 10 is a schematic diagram of an L chart output in the adjustment mode. [Figure 7] FIG. 10 is a schematic diagram of an S chart output in the adjustment mode. [Figure 8] FIG. 10 is a schematic diagram of an R chart output in the adjustment mode. [Figure 9] FIG. 10 is a flowchart showing an outline of the procedure of the adjustment mode. [Figure 10] FIG. 10 is a schematic diagram of a paper type category selection screen. [Figure 11] FIG. 10 is a schematic diagram of a paper feed unit selection screen. [Figure 12] FIG. 10 is a schematic diagram of a secondary transfer voltage adjustment screen. [Figure 13] FIG. 10 is a graph showing the transition of the secondary transfer voltage when a chart is output. [Figure 14(a)] 10 is a table showing an example of the relationship between patch numbers of a chart and adjustment values. [Figure 14(b)] 10 is a table showing an example of the relationship between patch numbers of a chart and adjustment values. [Figure 14(c)] 10 is a table showing an example of the relationship between patch numbers of a chart and adjustment values. [Figure 15] FIG. 10 is a graph showing the transition of the secondary transfer voltage when a chart is output. [Figure 16] 10A and 10B are schematic diagrams for explaining a method for detecting the position of a trigger patch. [Figure 17] FIG. 10 is a graph illustrating a method for selecting a recommended adjustment value. [Figure 18] FIG. 10 is a schematic diagram of an R chart in Example 2. [Figure 19] FIG. 10 is a schematic diagram of an L chart in Example 3. [Figure 20] FIG. 10 is a schematic diagram of an S chart in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0013] [Example 1] 1. Configuration of image forming device FIG. 1 is a schematic cross-sectional view of an image forming apparatus (image forming system) 1 of this embodiment. In this embodiment, the image forming apparatus 1 is configured by combining a printer unit 2 that forms an image and a sensing unit 3 that reads a chart to adjust a secondary transfer voltage. In this embodiment, the printer unit 2 is configured as a tandem full-color printer that employs an intermediate transfer method and is capable of forming a full-color image on a recording material S using an electrophotographic method. Note that the recording material S is sometimes referred to as "paper," but as will be described later, the recording material S is not limited to paper.

[0014] The printer unit 2 includes a paper feeder 4, an image forming unit 5, a control unit 30, a transfer unit 6 for the sensing unit 3, an operation unit 70, an image reading unit 80, and the like. While FIG. 1 shows only one paper feeder 4, the printer unit 2 may include multiple paper feeders 4. Furthermore, a temperature sensor 71 (FIG. 2) capable of detecting the temperature (internal temperature) inside the device body 10 and a humidity sensor 72 (FIG. 2) capable of detecting the humidity (internal humidity) inside the device body 10 are provided inside the device body 10 of the image forming apparatus 1 (printer unit 2). The temperature sensor 71 and the humidity sensor 72 are examples of environmental detection means for detecting environmental information, such as at least one of the temperature and humidity inside or outside the image forming apparatus 1. The printer unit 2 can form a four-color full-color image on a recording material (sheet, transfer material) S based on image information (image signals) from the image reading unit 80 or an external device 200 (FIG. 2). Examples of the external device 200 include a host device such as a personal computer, a digital camera, a smartphone, etc. The recording material S is a material on which a toner image is formed, and specific examples include paper such as plain paper and cardboard, as well as synthetic resin sheets (synthetic paper) that are substitutes for paper, and sheets for overhead projectors.

[0015] The image forming unit 5 is capable of forming an image based on image information on a recording material S that is fed from the paper feed unit 4 and moves within a conveying path (conveying route) P. The image forming unit 5 has a plurality of image forming units, namely, first, second, third, and fourth image forming units 50y, 50m, 50c, and 50k that form images of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. The image forming unit 5 also has an intermediate transfer unit 44, a secondary transfer device 45, a fixing device 46, and the like. Elements in the image forming units 50y, 50m, 50c, and 50k that have the same or corresponding functions or configurations may be generally described by omitting the suffixes y, m, c, and k that indicate that the element is for one of the colors Y, M, C, and Bk.

[0016] The image forming unit 50 has a photosensitive drum 51, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as a first image carrier. The image forming unit 50 also has a charging roller 52, which is a roller-type charging member serving as charging means. The image forming unit 50 also has an exposure device 42, which is an exposure device. The image forming unit 50 also has a developing device 20, which is a developing means. The image forming unit 50 also has a primary transfer roller 47, which is a roller-type primary transfer member serving as primary transfer means (the primary transfer roller 47 also constitutes an intermediate transfer unit 44, which will be described later). The image forming unit 50 also has a pre-exposure device 54, which is a charge removing device. The image forming unit 50 also has a drum cleaning device 55, which is a photosensitive member cleaning device. The image forming unit 50 also has a toner bottle 41, which is a developer supply container. The image forming unit 50 forms a toner image on an intermediate transfer belt 44b, which will be described later.

[0017] The photosensitive drum 51 is movable (rotatable) and carries an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 51 is a negatively charged organic photoconductor (OPC) with an outer diameter of 30 mm. The photosensitive drum 51 has an aluminum cylinder as a base and a surface layer formed on its surface. In this embodiment, the surface layer has three layers: an undercoat layer, a photocharge generation layer, and a charge transport layer, which are coated and stacked on the base in the following order. When an image formation operation starts, the photosensitive drum 51 is rotated in the direction of arrow R1 in FIG. 1 (counterclockwise) at a predetermined peripheral speed (process speed) by a motor (not shown) as a driving means.

[0018] The surface of the rotating photosensitive drum 51 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the charging roller 52. In this embodiment, the charging roller 52 is a rubber roller disposed in contact with the surface of the photosensitive drum 51. The charging roller 52 is rotated in accordance with the rotation of the photosensitive drum 51. A charging power supply 73 (FIG. 2) serving as a charging voltage application means (charging voltage application unit) is connected to the charging roller 52. The charging bias power supply 73 applies a predetermined charging voltage (charging bias) to the charging roller 52 during the charging process.

[0019] The surface of the charged photosensitive drum 51 is scanned and exposed by the exposure device 42 based on image information, and an electrostatic image is formed on the photosensitive drum 51. In this embodiment, the exposure device 42 is a laser scanner. The exposure device 42 emits laser light in accordance with image information of separated colors output from the control unit 30, and scans and exposes the surface (outer peripheral surface) of the photosensitive drum 51.

[0020] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by the developing device 20, which supplies toner to the developing device 20. The toner image (toner image, developer image) is formed on the photosensitive drum 51. In this embodiment, the developing device 20 contains a two-component developer containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier). Toner is supplied to the developing device 20 from a toner bottle 41. The developing device 20 has a developing sleeve 24 as a developer carrier (developing member). The developing sleeve 24 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). A roller-shaped magnet roller is fixed inside the developing sleeve 24 so as not to rotate relative to the main body (developing container) of the developing device 20. The developing sleeve 24 carries the developer and transports it to a development region facing the photosensitive drum 51. A developing power supply 74 (FIG. 2) is connected to the developing sleeve 24 as a developing voltage application unit (developing voltage application section). During the development process, the development bias power supply 74 applies a predetermined development voltage (development bias) to the development sleeve 24. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 51 (negative polarity in this embodiment) adheres to the exposed portion (image portion) on the photosensitive drum 51, which has been uniformly charged and then exposed to light, thereby reducing the absolute value of the potential (reverse development method). In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative polarity.

[0021] An intermediate transfer belt 44b, which is an intermediate transfer body formed of an endless belt and serves as a second image carrier, is disposed facing the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer belt 44b is wound around a plurality of support rollers (driving rollers), including a drive roller 44a, a tension roller 44d, and a secondary transfer inner roller 45a, and is stretched with a predetermined tension. The intermediate transfer belt 44b is movable (rotatable) while carrying a toner image. The drive roller 44a is driven to rotate by a motor (not shown) serving as a driving means, causing the intermediate transfer belt 44b to rotate (circulate). The tension roller 44d controls the tension of the intermediate transfer belt 44b to be constant. A spring (not shown) serving as a biasing means applies a force to the tension roller 44d to push the intermediate transfer belt 44b from its inner peripheral surface toward its outer peripheral surface. This force applies a tension of approximately 2 to 5 kg to the intermediate transfer belt 44b in the circumferential direction (the direction of movement of the surface). The inner secondary transfer roller 45a also constitutes a secondary transfer device 45, as described below. The drive force is transmitted to the intermediate transfer belt 44b by the drive roller 44a, causing the intermediate transfer belt 44b to rotate (circumferentially move) in the direction of arrow R2 (clockwise direction) in FIG. 1 at a predetermined circumferential speed (process speed) corresponding to the circumferential speed of the photosensitive drum 51. Primary transfer rollers 47y, 47m, 47c, and 47k are arranged on the inner circumferential surface of the intermediate transfer belt 44b, corresponding to the four photosensitive drums 51y, 51m, 51c, and 51k, respectively. In this embodiment, the primary transfer roller 47 is arranged in a position facing the photosensitive drum 1 with the intermediate transfer belt 44b interposed therebetween, and the intermediate transfer belt 44b is sandwiched between the primary transfer roller 47 and the photosensitive drum 51. As a result, the primary transfer roller 47 comes into contact with the photosensitive drum 51 via the intermediate transfer belt 44b, forming a primary transfer portion (primary transfer nip portion) N1 where the photosensitive drum 51 and intermediate transfer belt 44b come into contact. The tension rollers other than the drive roller 44a and the primary transfer rollers 47y, 47m, 47c, and 47k are rotated in accordance with the rotation of the intermediate transfer belt 44b. In addition, a belt cleaning device 60 serving as intermediate transfer body cleaning means is disposed on the outer circumferential surface of the intermediate transfer belt 44b at a position facing the drive roller 44a across the intermediate transfer belt 44b.The intermediate transfer belt 44, tension rollers 44a, 44d, and 45a, primary transfer rollers 47y, 47m, 47c, and 47k, and belt cleaning device 60 constitute an intermediate transfer unit 44.

[0022] The toner image formed on the photosensitive drum 51 is primarily transferred onto the rotating intermediate transfer belt 44b at the primary transfer portion N1 by the action of the primary transfer roller 47. A primary transfer power supply 75 (FIG. 2) serving as a primary transfer voltage application means (primary transfer voltage application portion) is connected to the primary transfer roller 47. During the primary transfer process, the primary transfer power supply 75 applies a predetermined primary transfer voltage (primary transfer bias), which is a DC voltage of opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, to the primary transfer roller 47. A voltage detection sensor 75a serving as a voltage detection means (voltage detection portion) for detecting the output voltage and a current detection sensor 75b serving as a current detection means (current detection portion) for detecting the output current are connected to the primary transfer power supply 75 (FIG. 2). In this embodiment, primary transfer power supplies 75y, 75m, 75c, and 75k are provided for primary transfer rollers 47y, 47m, 47c, and 47k, respectively, and the primary transfer voltages applied to primary transfer rollers 47y, 47m, 47c, and 47k can be individually controlled. In this embodiment, a positive primary transfer voltage is applied to primary transfer roller 47, thereby causing a negative toner image on photosensitive drum 51 to be primarily transferred onto intermediate transfer belt 44b. For example, when a full-color image is formed, the Y, M, C, and Bk toner images formed on photosensitive drums 51y, 51m, 51c, and 51k are superimposed one on top of the other and transferred onto intermediate transfer belt 44b.

[0023] On the outer peripheral surface of the intermediate transfer belt 44b, a roller-type secondary transfer member, an outer secondary transfer roller 45b, is disposed at a position facing the inner secondary transfer roller 45a, which serves as an opposing member, across the intermediate transfer belt 44b. The outer secondary transfer roller 45b, together with the inner secondary transfer roller 45a, constitutes a secondary transfer device 45 serving as a secondary transfer means. The outer secondary transfer roller 45b abuts against the inner secondary transfer roller 45a via the intermediate transfer belt 44b, forming a secondary transfer portion (secondary transfer nip portion) N2 where the intermediate transfer belt 44b and the outer secondary transfer roller 45b come into contact. At the secondary transfer portion N2, the toner image formed on the intermediate transfer belt 44b is secondarily transferred by the action of the secondary transfer device 45 onto the recording material S, which is sandwiched between the intermediate transfer belt 44b and the outer secondary transfer roller 45b and transported (passing through the secondary transfer portion N2). In this embodiment, a positive secondary transfer voltage is applied to the outer secondary transfer roller 45b, thereby secondarily transferring the negative toner image on the intermediate transfer belt 44b onto the recording material S. The recording material S is fed from the paper feed unit 4 in parallel with the above-mentioned toner image formation operation, and is conveyed to the secondary transfer unit N2 by a registration roller 11 as a conveying member provided on the conveying path P in synchronization with the toner image on the intermediate transfer belt 44b.

[0024] As described above, the secondary transfer device 45 includes an inner secondary transfer roller 45a as an opposing member and an outer secondary transfer roller 45b as a secondary transfer member. A secondary transfer power supply 76 (FIG. 2) serving as a secondary transfer voltage application unit (secondary transfer voltage application unit) is connected to the outer secondary transfer roller 45b. During the secondary transfer process, the secondary transfer power supply 76 applies a predetermined secondary transfer voltage, which is a DC voltage of a polarity opposite to the normal charge polarity of the toner (positive polarity in this embodiment), to the outer secondary transfer roller 45b. A voltage detection sensor 76a serving as a voltage detection unit (voltage detection unit) for detecting the output voltage and a current detection sensor 76b serving as a current detection unit (current detection unit) for detecting the output current are connected to the secondary transfer power supply 76 (FIG. 2). In this embodiment, the core of the inner secondary transfer roller 45a is connected to ground potential. When the recording material S is supplied to the secondary transfer unit N2, a constant-voltage controlled secondary transfer voltage of a polarity opposite to the normal charge polarity of the toner is applied to the outer secondary transfer roller 45b. In this embodiment, a secondary transfer voltage of, for example, 1 to 6.5 kV is applied, and a current of approximately 15 to 100 μA flows, thereby secondarily transferring the toner image on the intermediate transfer belt 44b onto the recording material S. In this embodiment, the inner secondary transfer roller 45a is connected to a ground potential, and a voltage is applied to the outer secondary transfer roller 45b from the secondary transfer power supply 76. Alternatively, a voltage may be applied from the secondary transfer power supply 76 to the inner secondary transfer roller 45a as the secondary transfer member, and the outer secondary transfer roller 45b as the opposing member may be connected to a ground potential. In this case, a DC voltage of the same polarity as the normal charging polarity of the toner is applied to the inner secondary transfer roller 45a.

[0025] The recording material S onto which the toner image has been transferred is transported to a fixing device 46 serving as a fixing means. The fixing device 46 has a fixing roller 46a and a pressure roller 46b. The fixing roller 46a incorporates a heater serving as a heating means. The pressure roller 46b is pressed against the fixing roller 46a, forming a fixing portion (fixing nip portion) N3 where the fixing roller 46a and the pressure roller 46b come into contact. The recording material S carrying the unfixed toner image is heated and pressurized as it is conveyed while being sandwiched between the fixing roller 46a and the pressure roller 46b in the fixing portion N3. This causes the toner image to be fixed (melted and adhered) to the recording material S. The temperature (fixing temperature) of the fixing roller 46a is detected by a fixing temperature sensor 77 (FIG. 2) and controlled by the control unit 30.

[0026] In the case of single-sided printing, in which an image is formed on one side of the recording material S, the recording material S, on which the toner image has been fixed on one side as described above, is passed as is from the delivery section 6 to the sensing unit 3. On the other hand, in the case of double-sided printing, in which an image is formed on both sides of the recording material S, the recording material S, on which the toner image has been fixed on one side as described above, is conveyed to the reversal conveyance path 7 by a reversal conveyance roller 12 or the like serving as a reversal conveyance member. In the reversal conveyance path 7, the recording material S, on which the toner image has been fixed on the first side, is turned over and supplied again to the secondary transfer section N2 by a double-sided conveyance roller 13 or the like serving as a double-sided conveyance member. The recording material S, which has been supplied again to the secondary transfer section N2 in this way, has a toner image transferred and fixed on the second side, and is then passed from the delivery section 6 to the sensing unit 3. In this way, the printer unit 2 of this embodiment is capable of performing double-sided printing, in which an image is formed on both sides of a single sheet of recording material S (automatic double-sided printing, double-sided printing , double-sided mode) can be performed. A double-sided mechanism 14 is made up of the reversing conveying path 7, the reversing conveying rollers 12, the double-sided conveying rollers 13, etc. The recording material S on which an image has been formed passes through the inside of the sensing unit 3 and is discharged (output) to a discharge section 8 provided outside the sensing unit 3 (image forming apparatus 1). When a chart formed by transferring patches onto the recording material S is output in an adjustment mode described later, the patches on the chart are read as the recording material S passes through the inside of the sensing unit 3, and then the recording material S is discharged to the discharge section 8.

[0027] After the primary transfer, the surface of the photosensitive drum 51 is neutralized by a pre-exposure device 54. Toner remaining on the photosensitive drum 51 without being transferred to the intermediate transfer belt 44b during the primary transfer process (primary transfer residual toner) is removed from the surface of the photosensitive drum 51 and collected by a drum cleaning device 55. The drum cleaning device 55 has a cleaning blade as a cleaning member. The cleaning blade is a plate-shaped member that contacts the photosensitive drum 51 with a predetermined pressure. The cleaning blade contacts the surface of the photosensitive drum 51 in a counter direction to the rotation direction of the photosensitive drum 51, with the tip of its free end facing upstream in the rotation direction of the photosensitive drum 51. Toner remaining on the intermediate transfer belt 44b without being transferred to the recording material S during the secondary transfer process (secondary transfer residual toner) and other deposits such as paper dust are removed from the surface of the intermediate transfer belt 44b and collected by a belt cleaning device 60. In this embodiment, the belt cleaning device 60 is configured with a cleaning blade, just like the drum cleaning device 55. The collected materials such as toner collected by the drum cleaning device 55 and the belt cleaning device 60 are transported to a collection container (not shown) and accumulated therein.

[0028] The printer unit 2 can also form a monochrome or multicolor image, such as a black monochrome image, using image forming units 50 for a desired monochrome color or for some of the four colors.

[0029] In this embodiment, the primary transfer roller 47 has an elastic layer of ion-conductive foam rubber (NBR rubber) and a core metal. The outer diameter of the primary transfer roller 47 is, for example, 15 to 20 mm. The primary transfer roller 47 has an electrical resistance of 1×10 5 ~1×10 8 A roller of Ω (measured at N / N (23° C., 50% RH), applied voltage of 2 kV) can be suitably used.

[0030] In this embodiment, the intermediate transfer belt 44b is an endless belt having a two-layer structure consisting of a base layer and a surface layer from the inner circumferential surface side. The base layer can be made of a resin such as polyimide or polycarbonate, or various rubbers containing an appropriate amount of carbon black as an antistatic agent. The thickness of the base layer is, for example, 0.05 to 0.15 mm. The surface layer can be made of a resin such as fluororesin. The surface layer reduces the adhesion of toner to the surface of the intermediate transfer belt 44b, facilitating the transfer of toner to the recording material S at the secondary transfer section N2. The thickness of the surface layer is, for example, 0.0002 to 0.020 mm. The surface layer can be made of a single resin material such as polyurethane, polyester, or epoxy resin, or two or more elastic materials such as elastic rubber, elastomer, or butyl rubber. A surface layer can be formed by dispersing one or more types of powder or particles, such as fluororesin, or other materials with different particle sizes, which are used to reduce surface energy and increase lubricity. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5×10 8 ~1×10 14 The static friction coefficient is 0.15 to 0.6 (23°C, 50% RH, HEIDON type 94i) and the resistance to friction is Ω·cm (23°C, 50% RH). Although the intermediate transfer belt 44b has a two-layer structure in this embodiment, it may have a single layer structure made of a material equivalent to the above-mentioned base layer.

[0031] In this embodiment, the outer secondary transfer roller 45b has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the outer secondary transfer roller 45b is, for example, 20 to 25 mm. The outer secondary transfer roller 45b has an electrical resistance of 1×10 5 ~1×10 8 A roller of Ω (measured at N / N (23° C., 50% RH), applied voltage of 2 kV) can be suitably used.

[0032] In each image forming unit 50, the photosensitive drum 51 and at least one of the charging roller 52, developing device 20, and drum cleaning device 55 acting as process means may be integrated into a process cartridge. This unit may be detachable from the apparatus main body 10.

[0033] An automatic document feeder 81 and an image reading unit 80 are also disposed on the upper portion of the apparatus main body 10. The automatic document feeder 81, serving as a document feeding means, automatically feeds a sheet, such as a recording material S on which an original image (text or image) is formed, to a reading position of the image reading unit 80 (which may be configured as at least a part of a platen glass 82, described later). The image reading unit 80, serving as a reading means, is capable of reading an image on the sheet conveyed to the reading position by the automatic document feeder 81. The image reading unit 80 is also capable of reading an image on a sheet, such as a recording material S on which an original image (text or image) is formed, placed on the platen glass 82. The image reading unit 80 is configured to illuminate the sheet with a light source (not shown) and read the image on the sheet at a predetermined dot density using an image reading element (not shown). In other words, the image reading unit 80 optically reads the image on the sheet and converts it into an electrical signal.

[0034] 2. Control mode FIG. 2 is a block diagram showing the schematic configuration of the control system of the image forming apparatus 1 of this embodiment. As shown in FIG. 2, the control unit 30 is configured by a computer. The control unit 30 includes, for example, a CPU 31, a ROM 32 (including a rewritable one) that stores programs for controlling each unit, a RAM 33 that temporarily stores data, and an input / output circuit (I / F) 34 that inputs and outputs signals to and from the outside. The CPU 31 is a microprocessor that controls the overall control of the image forming apparatus 1 and is the main system controller. The CPU 31 is connected to the paper feed unit 4, image forming unit 5, delivery unit 6, operation unit 70, sensing unit 3, and image reading unit 80 via the I / F circuit 34, and exchanges signals with these units and controls their operation. The ROM 32 stores an image formation control sequence for forming an image on the recording material S. For example, the control unit 30 is connected to a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, and a secondary transfer power supply 76, each of which is controlled by signals from the control unit 30. Also connected to the control unit 30 are a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of a primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of a secondary transfer power supply 76, and a fixing temperature sensor 77. Signals detected by each sensor are input to the control unit 30.

[0035] The operation unit 70 has operation buttons (such as a numeric keypad) as input means, and a display unit 70a consisting of a liquid crystal panel or the like as display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as input means. An operator such as a user or a service representative can input instructions to the control unit 30 to execute a job (described below) by operating the operation unit 70. The control unit 30 can receive signals from the operation unit 70 and control various devices of the image forming apparatus 1 to operate and execute the job. The image forming apparatus 1 can also execute a job based on image formation signals (image data, control commands) from an external device 200 such as a personal computer.

[0036] In this embodiment, the control unit 30 includes an image formation preparation processor 31a, an ATVC control processor 31b, an image formation processor 31c, and an adjustment processor 31d. The control unit 30 also includes a primary transfer voltage storage / calculation unit 31e and a secondary transfer voltage storage / calculation unit 31f. These processing units and storage / calculation units may be provided as part of the CPU 31 or RAM 33. For example, the control unit 30 (more specifically, the image formation processor 31c) can be controlled to execute a job as described above. The control unit 30 (more specifically, the ATVC control processor 31b) can be controlled to execute ATVC control (setting mode) of the primary transfer unit N1 and the secondary transfer unit N2. ATVC control will be described in detail later. The control unit 30 (more specifically, the adjustment processor 31d) can be controlled to execute an adjustment mode that adjusts the setting voltage of the secondary transfer voltage. The adjustment mode will be described in detail later. In this embodiment, the control unit 30 (more specifically, the adjustment processor 31d) functions as an execution unit that executes an operation (output mode) to output a chart in an adjustment mode, which will be described later. Also, in this embodiment, the sensing unit 3 constitutes an acquisition unit that acquires density information related to the density of a test image on a chart in an adjustment mode, which will be described later. Also, in this embodiment, the control unit 30 (more specifically, the adjustment processor 31d) functions as a setting unit that sets a secondary transfer voltage based on the density information acquired by the acquisition unit.

[0037] Here, the image forming apparatus 1 executes a job (image output operation, print job) that is a series of operations that starts with a single start command and forms and outputs an image on one or more recording materials S. The job generally includes an image formation process, a pre-rotation process, a sheet-to-sheet process when forming images on multiple recording materials S, and a post-rotation process. The image formation process is a period during which electrostatic image formation, toner image formation, primary transfer of the toner image, secondary transfer, and fixing of the toner image are performed for the image that will actually be formed and output on the recording materials S. This period is referred to as the image formation period. More specifically, the timing of the image formation process varies depending on the positions where the electrostatic image formation, toner image formation, primary transfer of the toner image, secondary transfer, and fixing processes are performed. The pre-rotation process is a period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image formation process. The sheet-to-sheet process (inter-image process) is a period corresponding to the interval between recording materials S when image formation is performed continuously on multiple recording materials S (continuous image formation). The post-rotation process is a period in which a rearrangement operation (preparatory operation) is performed after the image forming process. The non-image formation time (non-image formation period) is a period other than the image formation time, and includes the pre-rotation process, the sheet interval process, the post-rotation process, and further the pre-multiple rotation process which is a preparatory operation when the image forming apparatus 1 is turned on or when it returns from a sleep state.

[0038] 3. Sensing unit configuration Next, the configuration of the sensing unit 3 having the function of reading the chart output in the adjustment mode for adjusting the set voltage of the secondary transfer voltage will be described.

[0039] As shown in FIG. 1, a conveying path P through which the recording material S passes is provided inside the sensing unit 3, and a first line sensor 91 and a second line sensor 92 are provided on either side of the conveying path P. The first line sensor 91 is disposed upstream of the second line sensor 92 in the conveying direction of the recording material S, facing the conveying path P from below in FIG. 1. The second line sensor 92 is disposed downstream of the first line sensor 91 in the conveying direction of the recording material S, facing the conveying path P from above in FIG. 1. In this embodiment, when adjusting the secondary transfer voltage during double-sided printing in the adjustment mode, the recording material S on which a chart has been formed passes through the conveying path P inside the sensing unit 3 so that the upper side in FIG. 1 is the second side and the lower side in FIG. 1 is the first side. In other words, the first line sensor 91 faces the first side of the recording material S, and the second line sensor 92 faces the second side of the recording material S, so it is possible to read the chart images (patches) formed on both sides of the recording material S in a single pass of the recording material S.

[0040] Furthermore, a first pressure roller 93 is disposed at a position facing the first line sensor 91, and a second pressure roller 94 is disposed at a position facing the second line sensor 92. When reading the chart, the first and second pressure rollers 93, 94 stabilize the posture of the recording material S, thereby stabilizing the reading results. After passing through the sensing unit 3, the recording material S is discharged to the discharge section 8.

[0041] For example, a CIS (contact image sensor) or the like can be suitably used as the first and second line sensors 91 and 92. In this embodiment, the first and second line sensors 91 and 92 are each capable of reading a chart at a resolution of about 300 dpi. In this embodiment, the image data read by the first and second line sensors 91 and 92 is treated by the control unit 30 as brightness values ​​of 0 to 255 for each of RGB.

[0042] As shown in FIG. 2, the sensing unit 3 is connected to the control unit 30, and is capable of transferring information (density information) read by the first and second line sensors 91 and 92 to the control unit 30.

[0043] 4. Secondary transfer voltage control Next, the control of the secondary transfer voltage will be described. Fig. 3 is a flowchart showing an outline of the procedure for controlling the secondary transfer voltage in this embodiment. Generally, the control of the secondary transfer voltage is performed using constant voltage control or constant current control, but this embodiment uses constant voltage control.

[0044] First, when the control unit 30 (pre-image formation preparation process unit 31a) acquires job information from the operation unit 70 or the external device 200, it starts the job operation (S101). This job information includes image information specified by the operator and information about the recording material S. This information about the recording material S includes information about the size of the recording material S and information about the type of recording material S (so-called "paper type category"), such as "thin paper, plain paper, thick paper, etc." The type of recording material S includes any information that can distinguish the recording material S, such as attributes based on general characteristics such as plain paper, thick paper, thin paper, glossy paper, coated paper, brand, product number, basis weight, and thickness. The control unit 30 (pre-image formation preparation process unit 31a) writes this job information to the RAM 33 (S102).

[0045] Next, the control unit 30 (image formation preparation process unit 31a) acquires environmental information detected by the temperature sensor 71 and humidity sensor 72 (S103). Also, ROM 32 stores information indicating the correlation between the environmental information and the target current Itarget for transferring the toner image on the intermediate transfer belt 44b onto the recording material S. Based on the environmental information read in S103, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the target current Itarget corresponding to the environment from information indicating the relationship between the environmental information and the target current Itarget. Then, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) writes this target current Itarget to RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) (S104). The reason for changing the target current Itarget according to the environmental information is that the amount of charge on the toner varies depending on the environment. The target current Itarget in this embodiment is a secondary transfer current value that is determined in advance using the image forming apparatus 1 for each environment, at which an image with the maximum toner amount (in this embodiment, a full solid secondary color image) can be transferred.

[0046] Next, before the toner image on the intermediate transfer belt 44b and the recording material S onto which the toner image is transferred reach the secondary transfer portion N2, the control unit 30 (ATVC control processor 31b) acquires information about the electrical resistance of the secondary transfer portion N2 using ATVC (Active Transfer Voltage Control) (S105). That is, while the secondary transfer outer roller 45b and the intermediate transfer belt 44b are in contact with each other, the secondary transfer power supply 76 supplies a predetermined voltage at multiple levels to the secondary transfer outer roller 45b. The current value while the predetermined voltage is being supplied is detected by the current detection sensor 76b, and the relationship between the voltage and the current (voltage-current characteristics) as shown in FIG. 4 is acquired. The control unit 30 (ATVC control processor 31b) writes the information about the relationship between the voltage and the current to the RAM 33 (or the secondary transfer voltage storage unit / calculator 31f). This relationship between the voltage and the current changes depending on the electrical resistance of the secondary transfer portion N2. Alternatively, the secondary transfer power supply 76 may supply a predetermined current at multiple levels to the outer secondary transfer roller 45b, and the voltage value generated at that time may be detected by the voltage detection sensor 76a. In the configuration of this embodiment, the relationship between the voltage and the current is not one in which the current changes linearly (proportional) to the voltage, but rather one in which the current changes in a manner that is expressed by a polynomial of the second degree or higher of the voltage. Therefore, in this embodiment, the predetermined voltage or current supplied when acquiring information about the electrical resistance of the secondary transfer unit N2 is multi-staged at three or more points so that the relationship between the voltage and the current can be expressed by a polynomial.

[0047] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the voltage value to be applied from the secondary transfer power supply 76 to the outer secondary transfer roller 45b (S106). That is, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the voltage value Vb required to apply the target current Itarget when no recording material S is present at the secondary transfer portion N2, based on the target current Itarget written to the RAM 33 in S104 and the voltage-current relationship calculated in S105. This voltage value Vb corresponds to the secondary transfer partial voltage (transfer voltage corresponding to the electrical resistance of the secondary transfer portion N2). Also, the ROM 32 stores information for calculating the recording material partial voltage Vp (transfer voltage corresponding to the electrical resistance of the recording material S), as shown in FIG. 5. This information is set as table data indicating the relationship between the environmental moisture content (absolute moisture content) and the recording material partial voltage Vp for each basis weight category (corresponding to the paper type category) of the recording material S. Furthermore, since the recording material S, once it has passed through the fixing device 46, has a reduced moisture content and an increased electrical resistance, separate tables are prepared for the first and second sides. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the recording material assigned voltage Vp from the table data based on the job information acquired in S101 and the environmental information acquired in S103. The table data for calculating the recording material assigned voltage Vp, such as that shown in FIG. 5, was previously obtained through experiments. The control unit 30 can also calculate the environmental moisture content based on temperature information acquired by the temperature sensor 71 and humidity information acquired by the humidity sensor 72. If an adjustment value is set in an adjustment mode for adjusting the secondary transfer voltage setting, which will be described later, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates an adjustment amount ΔV corresponding to the adjustment value. As will be described later, this adjustment amount ΔV is stored in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) when set in the adjustment mode. The control unit 30 (secondary transfer voltage memory unit / calculation unit 31f) calculates Vb+Vp+ΔV by adding the above Vb, Vp, and ΔV as the secondary transfer voltage Vtr to be applied from the secondary transfer power source 76 to the outer secondary transfer roller 45b when the recording material S passes through the secondary transfer unit N2.Then, the control unit 30 writes this Vtr (=Vb+Vp+ΔV) into the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f).

[0048] Here, the recording material voltage Vp may change depending on the surface properties of the recording material S in addition to information related to the electrical resistance of the recording material S (such as basis weight). Therefore, the table data may be set so that the recording material voltage Vp also changes depending on information related to the surface properties of the recording material S. In this embodiment, information related to the electrical resistance of the recording material S (and further information related to the surface properties of the recording material S) is included in the job information acquired in S101. However, it is also possible to provide a measuring means for detecting the thickness and surface properties of the recording material S in the image forming apparatus 1, and to determine the recording material voltage Vp based on information obtained by this measuring means.

[0049] Next, the control unit 30 (image forming process unit 31c) executes image formation, sends the recording material S to the secondary transfer unit N2, and controls to apply the secondary transfer voltage Vtr determined as described above to perform secondary transfer (S107). Thereafter, the control unit 30 (image forming process unit 31c) repeats S107 until all images of the job have been transferred onto the recording material S and output (S108).

[0050] Regarding the primary transfer portion N1, the same ATVC control as above is performed from the time the job is started until the toner image is transported to the primary transfer portion N1, but a detailed description thereof will be omitted here.

[0051] 5. Adjustment Mode Overview Next, a simple adjustment mode (herein simply referred to as "adjustment mode") for adjusting the set voltage of the secondary transfer voltage will be described. Depending on the type and condition of the recording material S used for image formation, the moisture content and electrical resistance of the recording material S may differ significantly from those of a standard recording material S. In this case, the set voltage of the secondary transfer voltage using the default recording material distribution voltage Vp that is set in advance as described above may not be able to perform proper transfer.

[0052] First, if the secondary transfer voltage is insufficient, the toner on the intermediate transfer belt 44b cannot be sufficiently transferred to the recording material S, resulting in a decrease in image density. For example, this may occur if the electrical resistance of the recording material S is higher than the value (corresponding to the recording material assigned voltage Vp) assumed for each paper type category, or if the moisture content of the recording material S has decreased (become dry) due to storage conditions of the recording material S, causing the electrical resistance to increase. In such cases, it is desirable to increase the set voltage of the secondary transfer voltage (increase the absolute value) by, for example, increasing the recording material assigned voltage Vp.

[0053] Conversely, if the secondary transfer voltage is higher than necessary, abnormal discharge may occur, resulting in poor image quality, or the discharge at the secondary transfer section N2 may reverse the charge on the toner, resulting in poor transfer performance. For example, this may occur if the electrical resistance of the recording material S is lower than the value (corresponding to the recording material voltage Vp) assumed for each paper type category, or if the storage conditions of the recording material S cause the recording material S to absorb more moisture and its electrical resistance to decrease. In such cases, it is desirable to lower the set voltage of the secondary transfer voltage (reduce its absolute value) by, for example, lowering the recording material voltage Vp.

[0054] Therefore, it is desirable for an operator, such as a user or a service technician, to adjust (change) the set voltage of the secondary transfer voltage to an optimal value during job execution, for example by adjusting (changing) the recording material assigned voltage Vp depending on the recording material S actually used for image formation. In other words, it is sufficient to be able to select the optimal recording material assigned voltage Vp+ΔV (adjustment amount) depending on the recording material S actually used for image formation. This adjustment can be performed using the following method. For example, the operator can output the desired image while switching the secondary transfer voltage for each sheet of recording material S, check the output image for image defects, and then determine the optimal set voltage of the secondary transfer voltage (more specifically, the recording material assigned voltage Vp+ΔV). However, this method may result in more recording materials S being wasted and take more time because the image output and adjustment of the set voltage of the secondary transfer voltage must be repeated.

[0055] Therefore, in this embodiment, the image forming apparatus 1 can execute an adjustment mode for adjusting the set voltage of the secondary transfer voltage. In this adjustment mode, a chart is output by transferring multiple patches (test images, test patterns, test toner images) of representative colors onto the recording material S actually used for image formation, with the set voltage of the secondary transfer voltage being changed for each patch. The output chart is then read by the sensing unit 3, and the optimal set voltage of the secondary transfer voltage (more specifically, the recording material distribution voltage Vp+ΔV) is determined based on the results. In particular, in this embodiment, a recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) for optimizing the density of a solid image is presented based on the luminance information (density information) of a solid patch (a patch of a solid image with the maximum toner amount) on the chart. This reduces the need for the operator to visually check for image defects, reducing the burden on the operator and enabling more appropriate adjustment of the setting of the secondary transfer voltage.

[0056] 6. Charts Next, the chart output in the adjustment mode of this embodiment will be described. In this embodiment, a different chart is output depending on the size of the recording material S used to output the chart. The length of the recording material S in the conveyance direction of the recording material S is simply referred to as the "conveyance direction length," and the length of the recording material S in the direction substantially perpendicular to the conveyance direction of the recording material S is simply referred to as the "width." The conveyance direction of the recording material S is substantially parallel to the sub-scanning direction (the direction of movement of the surfaces of the photosensitive drum 51 and intermediate transfer belt 44b), and the direction substantially perpendicular to the conveyance direction of the recording material S (also referred to here as the "width direction") is substantially parallel to the main scanning direction (the direction substantially perpendicular to the direction of movement of the surfaces of the photosensitive drum 51 and intermediate transfer belt 44b). The lengths of the chart, image data defining the chart, or patches formed on the chart in the directions corresponding to the "conveyance direction length" and "width" of the recording material S are also simply referred to as the "conveyance direction length" and "width," respectively.

[0057] Figure 6 is a schematic diagram showing a large chart (also called an "L chart") 100, which is a chart when the length of the recording material S in the conveying direction is 420 mm or more (the long side of A3 size) and the width of the recording material S is 279.4 mm or more (the long side of LTR size).

[0058] Large chart data (also referred to as "L chart data"), which is image data defining the L chart 100, corresponds to the maximum paper size. The image size of the L chart data is approximately 13 inches wide (≒ 330 mm) x 19.2 inches long (≒ 487 mm) in the transport direction. The L chart 100 corresponding to image data cropped from this L chart data is output according to the size of the recording material S. At this time, the image data is cropped from the L chart data to fit the size of the recording material S, based on the leading edge in the reading direction and the center in the width direction. Figure 6 shows the case where the size of the recording material S is A3 size (portrait feed). For example, if the recording material S used to output the L chart 100 is A3 size (portrait feed) (297 mm wide x 420 mm long in the transport direction), image data with a size of 292 mm wide x 415 mm long in the transport direction is cropped from the L chart data. An image corresponding to this cut-out image data is then formed on an A3 size (portrait feed) recording material S, with a 2.5 mm margin on each side, based on the leading edge in the reading direction and the center in the width direction. This margin is typically about 2 to 10 mm.

[0059] The L chart 100 has a total of 11 pairs of blue (B) solid patches 101 and black (Bk) solid patches 102 arranged side by side in the width direction, aligned in the conveyance direction of the recording material S. In the L chart 100 in FIG. 6, 100(1) indicates the first side, and 100(2) indicates the second side. After passing through the secondary transfer portion N2, the second side passes through the sensing unit 3 without changing its orientation, while the first side passes through the reverse conveyance path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer portion N2 and when passing through the sensing unit 3. In FIG. 6, the conveyance direction of the chart when passing through the secondary transfer portion N2 is indicated by a thin arrow, and the conveyance direction of the chart when passing through the sensing unit 3 is indicated by a thick arrow. In this embodiment, the leading patches of the B solid patch 101 and the Bk solid patch 102 as they pass through the inside of the sensing unit 3 are patches for detecting position information (also referred to herein as "trigger patches") 101T and 102T, respectively. These trigger patches 101T and 102T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101 and the Bk solid patch 102, excluding the trigger patches 101T and 102T, the remaining ten patches are patches for acquiring luminance information (density information) (also referred to herein as "adjustment patches") 101A and 102A. Different secondary transfer voltages Vtr are applied to the adjustment patches 101A and 102A, respectively, and they are transferred onto the recording material S.

[0060] In this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm long x 40 mm wide in the conveyance direction, and there is a 15 mm gap between the B solid patches 101 and between the Bk solid patches 102 in the conveyance direction of the recording material S. Considering reading by the first and second line sensors 91 and 92, if the size of each patch (especially the adjustment patch) is too small, it will be affected by uneven texture of the recording material S (unevenness in the unevenness of the paper fibers, etc.), and the reading results will vary greatly. Therefore, it is desirable that the size of each patch (especially the adjustment patch) be somewhat large in area, and it is preferable that it be 600 mm 2The above is desirable. However, if the size of each patch (especially the adjustment patch) is made too large, the number of times the secondary transfer voltage Vtr fluctuates within the chart will decrease. In this embodiment, the patch size in the L chart 100 is set to allow the secondary transfer voltage Vtr to fluctuate in 10 steps. In addition, the patch spacing in the conveyance direction of the recording material S is set so that the secondary transfer voltage can be switched, and is desirably 15 mm or more.

[0061] On the first side 100(1) and the second side 100(2) of the L chart 100, the B solid patch 101 and the Bk solid patch 102 are arranged so as not to overlap on the front and back of the recording material S. This is to avoid the influence on the detected brightness due to show-through when read by the first and second line sensors 91 and 92, as will be described in detail later.

[0062] Figure 7 is a schematic diagram showing a small chart (also called an "S chart") 103, which is a chart when the length of the recording material S in the conveying direction is 210 mm (the short side of A4 size) or more and less than 420 mm (the long side of A3 size) and the width of the recording material S is 160 mm or more.

[0063] The small chart data (also referred to as "S chart data"), which is the image data defining the S chart 103, corresponds to half the size of the maximum paper size. The image size of the S chart data is approximately 13 inches wide (≒ 330 mm) x 9.6 inches long (≒ 243 mm) in the conveying direction. When the size of the recording material S is A4 (landscape feed) or LTR (landscape feed), the S chart 103 corresponding to image data cropped from this S chart data is output according to the size of the recording material S. At this time, the image data is cropped from the S chart data to match the size of the recording material S, based on the leading edge in the reading direction and the center in the width direction. Figure 7 shows the case where the size of the recording material S is A4 size (landscape feed). For example, when the recording material S used to output the S chart 103 is A4 size (landscape feed) (210 mm long in the conveying direction x 297 mm wide), image data of 205 mm long in the conveying direction x 292 mm wide is cropped from the S chart data. An image corresponding to this cut-out image data is then formed on an A4 size (horizontal feed) recording material S, with a margin of 2.5 mm on each side, based on the leading edge in the reading direction and the center in the width direction. This margin is typically about 2 to 10 mm.

[0064] The S chart 103 has a total of 12 pairs of blue (B) solid patches 101 and black (Bk) solid patches 102 arranged side by side in the width direction across two sheets of recording material S in the conveyance direction of the recording material S. By using two sheets of recording material S to form the chart, the S chart 103 ensures the same number of patches as the L chart 100, allowing for equivalent adjustments. In the S chart 103 in FIG. 7, 103(1-1) indicates the first sheet of the first side, 103(1-2) indicates the second sheet of the first side, 103(2-1) indicates the first sheet of the second side, and 103(2-2) indicates the second sheet of the second side. After passing through the secondary transfer portion N2, the second side passes through the sensing unit 3 without changing its orientation, while the first side passes through the reverse conveyance path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer portion N2 and when passing through the sensing unit 3. In FIG. 7, the thin arrow indicates the direction of transport of the chart as it passes through the secondary transfer portion N2, and the thick arrow indicates the direction of transport of the chart as it passes through the sensing unit 3. In this embodiment, with respect to the patches formed on one side of the recording material S, the leading patches of the B solid patch 101 and the Bk solid patch 102 as they pass through the sensing unit 3 are trigger patches 101T and 102T, respectively, for detecting position information. These trigger patches 101T and 102T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101 and the Bk solid patch 102, the remaining ten patches, excluding the trigger patches 101T and 102T, are adjustment patches 101A and 102A for acquiring luminance information (density information). Different secondary transfer voltages Vtr are applied to the adjustment patches 101A and 102A, respectively, and they are transferred to the recording material S.

[0065] As described above, in this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm long x 40 mm wide in the conveying direction, and there is a 15 mm gap between the B solid patches 101 and between the Bk solid patches 102 in the conveying direction of the recording material S.

[0066] On the first side 103(1-1), 103(1-2) and the second side 103(2-1), 103(2-2) of the S chart 103, the B solid patches 101 and the Bk solid patches 102 are arranged so as not to overlap on the front and back of the recording material S. This is to avoid the influence on the detected brightness due to show-through when read by the first and second line sensors 91, 92, as will be described in detail later.

[0067] Figure 8 is a schematic diagram showing a small size vertical feed chart (also called an "R chart") 104, which is a chart when the length of the recording material S in the conveying direction is 210 mm (the short side of A4 size) or more and less than 420 mm (the long side of A3 size) and the width of the recording material S is 139.7 mm (the short side of STMT size) or more and less than 160 mm.

[0068] Like the S chart data, the R chart data, which is image data defining the R chart 104, corresponds to half the maximum paper size. The image size of the S chart data is approximately 13 inches wide (≈330 mm) x 9.6 inches long (≈243 mm) in the transport direction. When the size of the recording material S is A5R (148.5 mm wide x 210 mm long in the transport direction) or STMTR (139.7 mm wide x 215.9 mm long in the transport direction), the R chart 104 corresponding to image data cropped from this R chart data is output according to the size of the recording material S. At this time, the image data is cropped from the R chart data to fit the size of the recording material S, based on the leading edge in the reading direction and the center in the width direction. Figure 8 shows the case where the size of the recording material S is A5R. For example, if the recording material S used to output the R chart 104 is A5 size (portrait feed) (width 148.5 mm x length in the conveying direction 210 mm), image data of a size of 148.5 mm width x 210 mm length in the conveying direction is cut out from the R chart data. An image corresponding to this cut-out image data is then formed on the A5 size (portrait feed) recording material S, with a 2.5 mm margin on each end, based on the leading edge in the reading direction and the center in the width direction. Note that this margin is typically about 2 to 10 mm.

[0069] The R chart 104 has a total of 12 pairs of blue (B) solid patches 101 and black (Bk) solid patches 102 arranged side by side in the width direction, across two sheets of recording material S, arranged in the conveyance direction of the recording material S. In the R chart, by using two sheets of recording material S to form the chart for each side of the recording material S, as in the case of the S chart 103, the same number of patches as the L chart 100 can be secured, and equivalent adjustments can be made. In the R chart 104 in FIG. 8, 104(1-1) indicates the first sheet of the first side, 104(2-1) indicates the first sheet of the second side, 104(1-2) indicates the second sheet of the first side, 104(2-2) indicates the second sheet of the second side, 104(1-3) indicates the third sheet of the first side, 104(2-3) indicates the third sheet of the second side, 104(1-4) indicates the fourth sheet of the first side, and 104(2-4) indicates the fourth sheet of the second side. After passing through the secondary transfer portion N2, the second side passes through the sensing unit 3 without changing its orientation, but the first side passes through the reverse conveying path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer portion N2 and when passing through the sensing unit 3. In FIG. 8, the conveying direction of the chart when passing through the secondary transfer portion N2 is indicated by a thin arrow, and the conveying direction of the chart when passing through the sensing unit 3 is indicated by a thick arrow. In this embodiment, with regard to the patches formed on one side of the recording material S, the leading patches of the B solid patch 101 and the Bk solid patch 102 as they pass through the inside of the sensing unit 3 are trigger patches 101T and 102T, respectively, for acquiring position information. These trigger patches 101T and 102T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101 and the Bk solid patch 102, the remaining ten patches excluding the trigger patches 101T and 102T are adjustment patches 101A and 102A for acquiring luminance information (density information). Different secondary transfer voltages Vtr are applied to the adjustment patches 101A and 102A, and they are transferred to the recording material S.

[0070] As described above, in this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm long x 40 mm wide in the conveying direction, and there is a 15 mm gap between the B solid patches 101 and between the Bk solid patches 102 in the conveying direction of the recording material S.

[0071] As described above, in the R chart 104, the first side of a recording material S on which a patch is formed on the second side is left blank without a patch. Similarly, the second side of a recording material S on which a patch is formed on the first side is left blank without a patch. This is because, with a narrow recording material S, there is less white space other than the patches, making it difficult to arrange the patches without overlapping on the front and back of the recording material S, as with the L chart 100 and S chart 103. If patches overlap on the front and back of the recording material S, the patches on the first side may affect the detected luminance of the patches on the second side due to bleed-through, and the patches on the second side may affect the detected luminance of the patches on the first side, potentially making it impossible to accurately detect luminance. Therefore, to detect luminance more accurately, for recording materials S of a size where patches may overlap on the front and back, the patches on the first and second sides are transferred to separate recording materials S. The effect of bleed-through on the detected luminance tends to be particularly pronounced with recording materials S with small basis weights. For example, the effect of this bleed-through on detection brightness is as follows: 2 This tends to be more pronounced with the following recording material S. Also, the thinner the recording material S, the more pronounced this effect tends to be.

[0072] In this embodiment, the second side of the recording material S on which a patch is formed on the first side is left blank without a patch, and the recording material S is output by performing a double-sided printing image forming operation. As a result, by detecting the brightness of the patch formed on the first side after the patch has passed through the fixing device 46 twice, it is possible to detect the same surface condition of the toner image as in actual double-sided printing, and select a more appropriate adjustment value.

[0073] Whether patches overlap on the front and back of the recording material S is determined by the relationship between the patch width, the number of patches arranged in the width direction, and the width of the recording material S. When the number of patches arranged in the width direction is N and the patch width is L, if the width of the recording material S is smaller than N×L×2, it is impossible to arrange the patches so that they do not overlap on the front and back of the recording material S. Therefore, when outputting a chart using a recording material S with a width smaller than N×L×2, the patches on the first side and the patches on the second side are transferred to separate recording materials S. In this embodiment, the patch width L is 40 mm and the number of patches arranged in the width direction is 2. Therefore, when outputting a chart using a recording material S with a width of less than 160 mm, the R chart 104 is output. Note that even if the width of the recording material S is N×L×2 or more, if the patches overlap on the front and back of the recording material S due to the patch arrangement position, the patches on the first side and the patches on the second side may be transferred to separate recording materials S.

[0074] It is preferable that patches are not formed near the leading and trailing ends in the conveyance direction of the recording material S (for example, within a range of about 20 mm inward from the edge). This is because there may be image defects that occur only at the leading or trailing end of the recording material S, and it may be difficult to determine whether or not the image defects are caused by the secondary transfer voltage.

[0075] In this embodiment, the size of the recording material S that can be used to output the chart is 210 mm or more in length in the conveying direction (the short side of A4 size) and 139.7 mm or more in width (the short side of STMT size). However, the size of the recording material S that can be used to output the chart is not limited to that in this embodiment, and can be set appropriately depending on the maximum paper size that can be passed through the image forming apparatus 1. In addition to standard sizes, the operator may specify a size of recording material S through the operation unit 70 or external device 200, for example, so that any size of recording material S can be used.

[0076] In this embodiment, when adjusting only the secondary transfer voltage during single-sided printing (also referred to as "single-sided adjustment"), the following is done. When outputting the L chart 100, the chart 100(2) in FIG. 6 is formed on the first side of one sheet of recording material S in the image forming operation for single-sided printing and output. When outputting the S chart 103, the charts 103(2-1) and 103(2-2) in FIG. 7 are formed on the first side of the first sheet of recording material S and the first side of the second sheet of recording material S, respectively, in the image forming operation for single-sided printing and output. When outputting the R chart 104, the charts 104(2-3) and 104(2-4) in FIG. 8 are formed on the first side of the first sheet of recording material S and the first side of the second sheet of recording material S, respectively, in the image forming operation for single-sided printing and output. That is, when adjusting the secondary transfer voltages for the first and second sides during double-sided printing (also referred to here as "double-sided adjustment"), the chart for the second side is output during the image formation operation for simplex printing without passing through the reverse conveying path 7. The chart is read using the second line sensor 92 of the sensing unit 3. This allows the orientation of the read image to remain the same as during double-sided adjustment, and the recording material S does not pass through the reverse conveying path 7, so that single-sided adjustment can be performed while minimizing downtime (time during which an image cannot be output due to adjustments, etc.). The adjustment results for the first side during double-sided adjustment can also be used to set the secondary transfer voltage during simplex printing.

[0077] Furthermore, the chart design is not limited to that of this embodiment. For example, the adjustment patches are not limited to a B solid image and a Bk solid image. The adjustment patches may be, for example, either a B solid image or a Bk solid image, or may be other single-color solid images, solid images of other secondary colors or mixed colors (multi-colors), or halftone images. Furthermore, for example, the shape and number of adjustment patches may be changed depending on the configuration of the image forming apparatus 1, the size of the recording material S corresponding to the chart output, the reading method, etc. Furthermore, the shape and number of trigger patches are not limited to that of this embodiment. Furthermore, trigger patches may not necessarily be required depending on the chart reading method, etc.

[0078] Also, assuming that an operator will visually check, for example, information such as a patch number, which will be described later, may be printed in association with each set of patches in the conveyance direction of the recording material S as identification information indicating the setting of the secondary transfer voltage when each patch is transferred to the recording material S. Also, assuming that an operator will visually check, for example, information such as front side (first side) or back side (second side) may be printed on the corresponding side as identification information indicating whether it is a chart for adjustment on the first side or a chart for adjustment on the second side.

[0079] 7. Adjustment mode operation Next, the operation of the adjustment mode in this embodiment will be described. Fig. 9 is a flowchart showing an outline of the procedure of the adjustment mode in this embodiment. Here, an example will be described in which an operator causes the image forming apparatus 1 to execute the adjustment mode via the operation unit 70 of the image forming apparatus 1. The role of the operation unit 70 that causes the image forming apparatus 1 to execute the adjustment mode may be played by an external device 200 such as a personal computer. Furthermore, the following symbols will be used in the following description.

[0080] N: Adjustment value (=-20 to +20) N0: Current (before executing adjustment mode) adjustment value N A : selected adjustment value n: Patch number of the adjustment patch (n=1 to 10, starting from the smallest adjustment value) n0: Patch number corresponding to the current adjustment value (corresponding to adjustment value N0) n A : Selected patch number (adjustment value N A (corresponding to T: Trigger patch code

[0081] First, the control unit 30 (adjustment processing unit 31d) acquires information about the recording material S that the operator wants to adjust (the size of the recording material S, the paper type category) and information about the adjustment conditions, which are input by the operator (S1). FIG. 10 is a schematic diagram of a paper type category selection screen 700 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment processing unit 31d) in S1. The paper type category selection screen 700 displays paper type categories for the recording material S that can be set in the image forming apparatus 1. The operator can proceed to an adjustment mode for adjusting the set voltage of the secondary transfer voltage by pressing (operating) an adjustment button 701. Note that the paper type category selection screen 700 may also provide access to a screen for changing other image formation conditions, such as fixing conditions, in addition to adjusting the secondary transfer voltage. Furthermore, in order to retain the default settings for each paper type category, the adjustment mode may be executed after copying the paper type category to RAM 33 or ROM 32 using a copy button 702. The copied paper type category 703 is stored in the RAM 33 or the ROM 32 under a different name, and image formation is performed for the paper type category 703 with the default settings except for the conditions for which the settings have been changed.

[0082] FIG. 11 is a schematic diagram of a paper feed unit selection screen 704 that is displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment processing unit 31d) in S1. When the paper type category of the recording material S for which the adjustment mode is to be performed is selected, the paper feed unit selection screen 704 shown in FIG. 11 is displayed. The paper feed unit selection screen 704 displays the paper type category of the recording material S stored in the paper feed units 4 that has been set in advance by the operator via the operation unit 70 or the like, and the size detected by a recording material size detection sensor (not shown) provided in each paper feed unit 4. For example, "Plain Paper 1_Copy (64-75 g / m 2 )" is selected and the adjustment mode is executed. In the example of FIG. 11, "Plain Paper 1_Copy (64-75 g / m 2) is stored. In addition, when the size of the recording material S is compatible with the adjustment mode, the operator can press (operate) the selection button 705. In the case of a paper type category that is not compatible with the adjustment mode or a size of the recording material S that is not compatible with the adjustment mode, the selection button 705 may be grayed out so that the operator cannot press (operate) it. In addition, when the recording material S for executing the adjustment mode is not stored in any of the paper feed units 4 in advance, the operator may be able to temporarily exit the paper feed unit selection screen 704 by using a back button (not shown) or the like.

[0083] FIG. 12 is a schematic diagram of a secondary transfer voltage adjustment screen 706 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment processing unit 31d) in S1. When the paper type category of the recording material S for which the adjustment mode is to be performed is selected and the paper feed unit 4 containing that recording material S is selected, the secondary transfer voltage adjustment screen 706 shown in FIG. 12 is displayed. The secondary transfer voltage adjustment screen 706 includes an adjustment value display unit 707 that displays the current adjustment value, a single-sided / double-sided selection unit 708 that selects whether the adjustment mode is to be performed on one side or both sides, and an adjustment execution button 709 that starts chart formation. By inputting a value into the adjustment value display unit 707, secondary transfer can be performed with the recording material voltage offset from the default recording material voltage Vp stored in ROM 32 for the corresponding paper type category. In this embodiment, an integer value between −20 and +20 can be input as the adjustment value N in the adjustment value display unit 707, with the default value being 0. If the adjustment value N is 0, the default recording material assigned voltage Vp corresponding to the paper type category stored in ROM 32 is used as is. The value (adjustment value N) in the adjustment value display section 707 corresponds ΔN=1 to ΔV=150V (i.e., changing the adjustment value N by 1 changes the adjustment amount ΔV by 150V). For example, if N=-5 is input into the adjustment value display section 707, a value obtained by offsetting the default recording material assigned voltage Vp by -750V (=-5×150) is used as the recording material assigned voltage. To execute the adjustment mode, the operator selects whether to perform double-sided adjustment or single-sided adjustment in the single-sided / double-sided selection section 708, and then presses (operates) the adjustment execution button 709.

[0084] When the adjustment execution button 709 is pressed (operated), the control unit 30 (adjustment processor 31d) executes density correction control (S2). The density correction control is performed to ensure that an appropriate amount of toner is placed on the intermediate transfer belt 44b before adjusting the secondary transfer voltage. The control unit 30 (adjustment processor 31d) forms toner patches for density correction control while changing the outputs of the charging power supply 73, the developing power supply 74, the exposure device 42, etc., and controls the primary transfer of the toner patches onto the intermediate transfer belt 44b. The control unit 30 (adjustment processor 31d) then determines the image formation conditions for chart output by measuring the toner amount of the toner patches on the intermediate transfer belt 44b using a patch detection sensor (not shown). Note that density correction control does not necessarily need to be executed every time the adjustment mode is executed. The control unit 30 (adjustment processor 31d) may determine whether to execute density correction control based on, for example, the number of images formed, environmental changes, or the elapsed time since the previous density correction control was executed.

[0085] Thereafter, the control unit 30 (adjustment processor 31d, ATVC control processor 31b) executes ATVC control (S3). Details of the ATVC control are as described above.

[0086] Thereafter, the control unit 30 (adjustment processor 31d) executes output of the chart (S4 to S10). At this time, the control unit 30 (adjustment processor 31d) selects a chart according to the size of the recording material S and outputs the selected chart. First, the control unit 30 (adjustment processor 31d) determines whether the length of the recording material S in the conveying direction is 420 mm or more (S4). If the control unit 30 (adjustment processor 31d) determines in S4 that the length of the recording material S in the conveying direction is 420 mm or more ("Yes"), it controls to output one L chart 100 as shown in FIG. 6 (S5). At this time, the control unit 30 (adjustment processor 31d) controls to form and output charts on one or both sides of the recording material S as described above, depending on whether single-sided or double-sided adjustment is being performed. Furthermore, if the control unit 30 (adjustment processor 31d) determines in S4 that the length of the recording material S in the conveying direction is less than 420 mm ("No"), it determines whether the width of the recording material S is 160 mm or more (S6). If the control unit 30 (adjustment processor 31d) determines in S6 that the width of the recording material S is 160 mm or more ("Yes"), it controls to output two S charts 103 shown in FIG. 7 (S7). Note that at this time, the control unit 30 (adjustment processor 31d) controls to form and output charts on one or both sides of the recording material S as described above, depending on whether single-sided adjustment or double-sided adjustment is being performed. Furthermore, if the control unit 30 (adjustment processor 31d) determines in S6 that the width of the recording material S is less than 160 mm ("No"), it determines whether double-sided adjustment is being performed (S8). If the control unit 30 (adjustment processor 31d) determines in S8 that double-sided adjustment is being performed ("Yes"), it controls so that the four R charts 104 in Fig. 8 are output in a double-sided print image forming operation (S9). If the control unit 30 (adjustment processor 31d) determines in S8 that single-sided adjustment is being performed ("No"), it controls so that the two R charts 104, 104(2-3) and 104(2-4) in Fig. 8, are output in a single-sided print image forming operation (S10).

[0087] FIG. 13 is a graph showing the transition of the output of the secondary transfer power supply 76 when the L chart 100 is secondarily transferred to the recording material S. FIG. 13(a) shows the first side during double-sided adjustment, and FIG. 13(b) shows the second side during double-sided adjustment. In the case of the first side, ten consecutive adjustment patches 101A and 102A are secondarily transferred to the recording material S, and then trigger patches 101T and 102T are secondarily transferred to the recording material S. The adjustment patches 101A and 102A are arranged in order from the smallest adjustment value N to the largest adjustment value N. The patch numbers of the adjustment patches 101A and 102A increase sequentially in accordance with the increase in the adjustment value N, with n=1 for the patch number corresponding to the smallest adjustment value N and n=10 for the patch number corresponding to the largest adjustment value N. In addition, in the case of the first side, the recording material distribution voltage Vp for setting the secondary transfer voltage Vtr uses values ​​from a table stored in ROM 32 for the first side. The timing for switching the secondary transfer voltage when the chart is secondarily transferred to the recording material S is after each patch 101, 102 has passed the secondary transfer section N2. There is a slight time lag in switching the output of the secondary transfer power supply 76, but by switching at the above timing, the output of the secondary transfer power supply 76 is switched in the margins between each patch. For the second side, the arrangement of the adjustment patches 101A, 102A and the trigger patches 101T, 102T is reversed from the first side, and the recording material distribution voltage Vp uses values ​​from a table stored in ROM 32 for the second side. However, switching of the secondary transfer voltage and other operations are performed in the same way as for the first side.

[0088] In this embodiment, the amplitude (change in one step) ΔV (reference numeral 801 in FIG. 13 ) of the secondary transfer voltage when the chart is secondarily transferred to the recording material S is changed by the secondary transfer partial voltage Vb. In this embodiment, when the secondary transfer partial voltage Vb is 2000 V or more, the amplitude ΔV of the secondary transfer voltage is set to 450 V, which corresponds to an adjustment value amplitude ΔN=3 (three steps of the adjustment value N). Furthermore, when the secondary transfer partial voltage Vb is 1500 V or more but less than 2000 V, the amplitude ΔV of the secondary transfer voltage is set to 300 V, which corresponds to an adjustment value amplitude ΔN=2 (two steps of the adjustment value N). Furthermore, when the secondary transfer partial voltage Vb is less than 1500 V, the amplitude ΔV of the secondary transfer voltage is set to 150 V, which corresponds to an adjustment value amplitude ΔN=1 (one step of the adjustment value N). This is because, in order to check the current sensitivity of the secondary transfer characteristics, it is considered more efficient to increase the amount of change in the secondary transfer voltage in one step as the secondary transfer partial voltage Vb increases, since this increases the amount of change in the secondary transfer current for the entire chart. In this embodiment, the amplitude ΔV of the secondary transfer voltage (amplitude ΔN of the adjustment value) when the chart is secondarily transferred to the recording material S is automatically selected according to the results of ATVC control, but it may also be possible for the operator to directly select it on the secondary transfer voltage adjustment screen 706, etc. Furthermore, it may also be possible for the operator to select whether the amplitude ΔV of the secondary transfer voltage (amplitude ΔN of the adjustment value) when the chart is secondarily transferred to the recording material S is "automatically selected" or "directly specified."

[0089] 14(a) to 14(c) show a list of the current adjustment value N0 and the secondary transfer voltage adjustment value N applied to each patch number n for each adjustment value amplitude ΔN (secondary transfer voltage amplitude ΔV) and for each of the first and second sides in this embodiment. FIG. 14(a) shows the case where the adjustment value amplitude ΔN=1, FIG. 14(b) shows the case where the adjustment value amplitude ΔN=2, and FIG. 14(c) shows the case where the adjustment value amplitude ΔN=3. When the current adjustment value N0 is 0, patch number n=5 corresponds to the current adjustment value N0=0, n=1 to 4 correspond to smaller adjustment values ​​in ΔN intervals, and n=6 to 10 correspond to larger adjustment values ​​in ΔN intervals. When the current adjustment value N0 is other than 0, the adjustment value corresponding to each adjustment patch 101A, 102A is uniformly offset. Furthermore, if the current adjustment value N0 is fixed at n=5, when the current adjustment value N0 is large on the positive or negative side, there may be cases where all of the adjustment patches 101A, 102A for n=1 to 10 do not fall within the adjustment range of ±20. In such cases, the patch corresponding to the current adjustment value N0 is shifted from n=5 so that all of the adjustment patches 101A, 102A for n=1 to 10 fall within the adjustment range of ±20. This allows all of the adjustment patches 101A, 102A to be used effectively.

[0090] In the case of the L chart 100, trigger patches 101T and 102T are located on the trailing edge of the first side and the leading edge of the second side when the chart is secondarily transferred to the recording material S. The trigger patches 101T and 102T are used to detect the patch positions when the chart is read by the sensing unit 3. Therefore, the trigger patches 101T and 102T must be transferred at the minimum density required for that purpose. An extremely high or low secondary transfer voltage may result in the trigger patches 101T and 102T not being readable. Therefore, in this embodiment, when the trigger patches 101T and 102T are secondarily transferred to the recording material S, a voltage corresponding to patch number n=5 (the voltage indicated by the dotted line 800 in FIG. 13 ) is applied. Note that the method for setting the secondary transfer voltage applied when the trigger patches 101T and 102T are secondarily transferred to the recording material S is not limited to the method described above. For example, one possible method is to set the secondary transfer voltage higher (to a larger absolute value) to minimize weak transfer (poor transfer due to weak transfer voltage), or to control the secondary transfer voltage to a constant current to transfer at the minimum required density.

[0091] FIG. 15 is a graph showing the transition of the output of the secondary transfer power supply 76 when the charts are secondarily transferred onto the recording material S in the cases of the S chart 103 and the R chart 104. FIG. 15(a) shows the first side during double-sided adjustment, and FIG. 15(b) shows the second side during double-sided adjustment. In the case of the S chart 103 and the R chart 104, the chart is divided into the first sheet of the first side (103(1-1) or 104(1-1)), the second sheet of the first side (103(1-2) or 104(1-2)), the first sheet of the second side (103(2-1) or 104(2-3)), and the second sheet of the second side (103(2-2) or 104(2-4)), and trigger patches 101T and 102T are arranged on each of them. However, in the cases of the S chart 103 and the R chart 104, the magnitude and timing of the output of the secondary transfer power supply 76 are basically the same as in the case of the L chart 100. In this embodiment, a voltage corresponding to patch number n=5 (the voltage value indicated by the dotted line with reference numeral 800 in FIG. 15) is applied to the entire blank surface of the R chart 104 (104(2-1), 104(2-2), 104(1-3), 104(1-4)).

[0092] As described above, when the operator selects single-sided adjustment in the single-sided / double-sided selection section 708 on the secondary transfer voltage adjustment screen 706, the following is performed. When outputting the L chart 100, the chart 100(2) in FIG. 6 is output. When outputting the S chart 103, the charts 103(2-1) and 103(2-2) in FIG. 7 are output. When outputting the R chart, the charts 104(2-3) and 104(2-4) in FIG. 8 are output. In other words, the chart for the second side when performing double-sided adjustment is output in the image forming operation for simplex printing without passing through the reverse conveying path 7. The chart is read using the second line sensor 92 of the sensing unit 3. This allows single-sided adjustment to be performed without changing the orientation of the read image from that during double-sided adjustment and without the recording material S passing through the reverse conveying path 7, minimizing downtime.

[0093] When the chart is output, the control unit 30 (adjustment processing unit 31d) reads the chart using the sensing unit 3, and controls the calculation of the luminance and variance of each of the adjustment patches 101A and 102A as follows (S11).

[0094] The first and second line sensors 91 and 92 of the sensing unit 3 read the first and second charts at a resolution of 300 dpi, respectively. The image information read by the first and second line sensors 91 and 92 of the sensing unit 3 is stored in the RAM 33. The control unit 30 (adjustment processing unit 31d) calculates the positions of the adjustment patches 101A and 102A based on the positions of the trigger patches 101T and 102T of the chart as follows. FIG. 16 is a schematic diagram illustrating an example of a method for identifying the positions of the trigger patches 101T and 102T from the image 110 read by the first and second line sensors 91 and 92. First, a line 112 located in the margin between the edge 111 of the chart (recording material S) and the trigger patches 101T and 102T in the conveyance direction of the recording material S as it passes through the sensing unit 3 is roughly determined. Then, the average luminance value of the line 112 is read from the read chart information. At this time, if the average luminance value is smaller than a predetermined threshold (if the density is greater than a predetermined value), it is determined to be an edge of the trigger patches 101T and 102T. If it is not determined to be an edge, the process repeats line by line toward the upstream side in the conveyance direction of the recording material S as it passes through the sensing unit 3 to find an edge line 113. Next, a line 114 located in the margin between the edge 111 of the chart (recording material S) and the trigger patches 101T and 102T in the width direction is set based on a rough positional relationship. Then, the average luminance value of the line 114 is read from the read chart information. At this time, if the average luminance value is smaller than a predetermined threshold (if the density is greater than a predetermined value), it is determined to be an edge of the trigger patches 101T and 102T. If it is not determined to be an edge, the process repeats line by line toward the right side in the width direction in FIG. 16 to find an edge line 115. The right side in the width direction in Figure 16 above is the right side when viewing the surface of the recording material S facing the first and second line sensors 91, 92 with the leading edge of the recording material S facing up as it passes through the inside of the sensing unit 3. Note that the above edge detection method is just one example, and edge detection is not limited to the above method. For example, a method different from that in this embodiment may be used depending on the chart design.

[0095] After the control unit 30 (adjustment processing unit 31d) has identified the positions of the adjustment patches 101A and 102A, it calculates the average brightness value and variance value and stores them in RAM 33. That is, for the nth patch, the average brightness value and variance value calculated by the following formulas are stored in RAM 33.

[0096]

number

[0097] The average luminance value (average luminance value) is a parameter that is close to density (i.e., correlated with density). Furthermore, the inventors have found through their studies that the variance value is a parameter that is sensitive to the transferability when the recording material S has unevenness. In this embodiment, the average luminance value and variance value are calculated for both the B solid patch 101 and the Bk solid patch 102. In this embodiment, the average luminance value and variance value are used to determine the recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) for the set voltage of the secondary transfer voltage.

[0098] In this embodiment, the brightness read from the information of the image read by the sensing unit 3 is B brightness for the B solid patch 101 and G brightness for the Bk solid patch 102. Which of the RGB brightnesses is used does not have to be in this order, and the average value of the three brightnesses or grayscale brightness that is not resolved into RGB may also be used.

[0099] Furthermore, when calculating the variance value, it is necessary to temporarily store the luminance value read out for each pixel, which may result in a high load on the control unit 30 and a long adjustment mode. In such cases, the luminance may be divided into several ranges from 0 to 255, the frequency of each pixel may be counted, and the variance value may be calculated from a digital histogram. The number of luminance ranges and the spacing between them can be changed as appropriate depending on the characteristics of the first and second line sensors 91 and 92 and the processing capacity of the control unit 30. Furthermore, since the luminance histogram differs depending on the paper type category, the number of luminance ranges and the spacing between them may be changed depending on the paper type category.

[0100] Next, the control unit 30 (adjustment processing unit 31d) controls to select a patch with good transferability from the average luminance value and variance value of the adjustment patches 101A and 102A as follows (S12 to S15). Note that in the following explanation of the process for selecting a patch with good transferability using Figure 17, the B solid patch 101 and the Bk solid patch 102 are assumed to be the adjustment patches 101A and 102A, respectively.

[0101] Fig. 17(a) shows an example of the result of acquiring the average luminance value of the B solid patch 101, and Fig. 17(b) shows an example of the result of acquiring the average luminance value of the Bk solid patch 102. Fig. 17(c) shows an example of the result of acquiring the average luminance value of the B solid patch 101 grouped as described below, and Fig. 17(d) shows an example of the result of acquiring the variance value of the B solid patch 101.

[0102] First, the control unit 30 (adjustment processing unit 31d) finds the lowest average luminance value among the Bk solid patches 102. Then, control is performed to narrow down the patch numbers (i.e., adjustment values) to those that fall within a range of a preset threshold γ1 on the higher luminance side from the lowest average luminance value (S12). In the case of FIG. 17(b), the patch numbers with the lowest average luminance values ​​(lowest luminance) are n=4, 5, and 6, and the narrowed-down patch numbers are n=1, 2, 3, 4, 5, 6, and 7. This makes it possible to narrow down the patch numbers (i.e., adjustment values) to which the Bk solid has been transferred to a certain extent. The threshold γ1 should be small when emphasis is placed on the transferability of the Bk solid, and large when emphasis is placed on the transferability of the B solid.

[0103] Next, the control unit 30 (adjustment processor 31d) calculates the average luminance value (here, also referred to as "group luminance") of the three B solid patches 101, including the patch numbers before and after it, for each of the narrowed-down patch numbers (i.e., adjustment values). Then, the control unit 30 (adjustment processor 31d) selects the set (group) with the lowest calculated group luminance (S13). The group luminance for the nth patch is expressed by the following formula:

[0104]

number

[0105] Figure 17(a) shows the average luminance value of the B solid patch 101, and Figure 17(c) shows the average luminance value of the B solid patch 101 converted into group luminance. In Figure 17(c), the group with patch number n=7 (i.e., patches with patch numbers n=6, 7, and 8) has the lowest group luminance.

[0106] Here, adjustment using a chart can only be performed on patches of a certain density. Therefore, correction may be performed on the group selected here. For example, a threshold value γ2 for the lowest group luminance is preset. Then, a check is made to see if there is a group luminance that falls within the threshold value γ2 on the side of patch numbers (i.e., adjustment values) smaller than the patch number of the group with the lowest group luminance, from the lowest group luminance to the higher side. If there is, the selected group may be changed to the group with the patch number (i.e., adjustment value) of that group luminance. This correction makes it possible to select a patch number (i.e., adjustment value) of a group that is as close as possible to the rise of the secondary color transfer characteristics. This prevents cases where the secondary transfer voltage Vtr is too high for users who mainly output monochrome images or halftone images. In this embodiment, the above-described correction (advancement) of the adjustment value using the threshold value γ2 is adopted. In the case of Figure 17(c), the group with patch number n=6 (i.e., patches with patch numbers n=5, 6, and 7) is selected.

[0107] Next, the control unit 30 (adjustment processing unit 31d) selects the patch with the lowest variance value within the selected group (S14). In the case of Fig. 17(d), the variance value of patch number n=6 is the smallest.

[0108] As described above, adjustments using a chart can only be made to patches of a certain density. Therefore, corrections can be made to the selected patch numbers (i.e., adjustment values). For users primarily outputting monochrome or halftone images, corrections can be made to minimize the adjustment values. In this case, for example, as in the case of group luminance, a threshold γ3 for the smallest variance value is preset. Then, among the patch numbers with variance values ​​that fall within the range of the threshold γ3 from the smallest variance value toward the larger variance value, the smallest patch number (i.e., adjustment value) can be selected. Conversely, when emphasis is placed on the reliable transfer of secondary color images, corrections can be made to maximize the adjustment values. In this case, for example, as shown in FIG. 17(a), a threshold γ4 is preset on the higher average luminance side of the average luminance value of the selected patch number. Then, for example, the difference between the average luminance value of the selected patch number n=6 and the average luminance value of the previous patch number n=5 is compared with the threshold γ4. If this difference in average luminance value is greater than the threshold γ4, it can be determined that the secondary color transfer performance is enhanced in patch number n=5. In such a case, there is a risk that the transfer electric field for the secondary color will be insufficient due to fluctuations in the charge amount of the toner or fluctuations in the moisture content of the recording material S. In this embodiment, the above-mentioned correction is adopted to ensure that the secondary color is transferred. In the case of Figure 17(a), the difference between the average luminance value of the selected patch number n=6 and the average luminance value of the previous patch number n=5 is greater than the threshold value γ4, so patch number n=7, which is one greater than the selected patch number n=6, is selected.

[0109] Following the above flow of selecting the adjustment value, the control unit 30 (adjustment processing unit 31d) selects the patch number n with the preferable transferability. A and the corresponding adjustment value N A is determined (S15).

[0110] The selection flow of the adjustment value in this embodiment is an example, and the selection flow of the adjustment value is not limited to that in this embodiment. grAlthough the group luminance B is calculated using three patches, it may be calculated using four or more patches, or may be calculated using two patches. gr Although the threshold γ1 is effective for selecting an adjustment range with stable and favorable transferability, it is also possible to select an adjustment value directly from the average luminance value and variance value without using this. In particular, depending on the setting of the threshold γ1 and the transferability of the recording material S, it may not be possible to select a group luminance. In such cases, it is also possible to select an adjustment value directly from the average luminance value and variance value without using the group luminance. Also, while the variance value is effective for detecting density unevenness within a patch, it is not necessarily necessary to use it. Furthermore, the transferability of the Bk solid may be adjusted by a method other than narrowing down the results using the threshold γ1. For example, it is possible to select the patch number (i.e., the adjustment value) for which the Bk solid patch has the lowest average luminance value (highest density) and the B solid patch has the lowest average luminance (highest density).

[0111] The control unit 30 (adjustment processor 31d) calculates the adjustment value N selected as above. A 12 on the display unit 70a of the operation unit 70 (S16). The operator determines whether the displayed content of the secondary transfer voltage adjustment screen 706 is acceptable, and then selects the displayed adjustment value N. A If the operator does not want to change the adjustment value N AIf the operator wishes to change the adjustment value, the operator operates the numeric keypad (not shown) of the operation unit 70 or the like to input the value into the adjustment value display unit 707, and selects the confirmation unit 710 (OK button 710a or apply button 710b). If the adjustment value has been changed, the control unit 30 (adjustment processor 31d) stores the adjustment value input by the operator in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S17). The operator can determine whether the display content of the secondary transfer voltage adjustment screen 706 is acceptable by, for example, visually checking the output chart. On the other hand, if the adjustment value has not been changed and the confirmation unit 710 is selected, the control unit 30 (adjustment processor 31d) stores the determined adjustment value as is in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S17). This completes the adjustment mode.

[0112] 8.Effects An experiment to confirm the effects of this embodiment was conducted for this embodiment and a comparative example. In the comparative example, under the conditions in which the R chart 104 is output to perform double-sided adjustment in this embodiment, a chart in which patches on the front and back of the recording material S overlap is output to perform double-sided adjustment. That is, in the comparative example, 104(1-1) in FIG. 8 is used as the chart for the first side of the first sheet, and 104(2-3) in FIG. 8 is output as the chart for the second side of the first sheet, which is the back side of that. Also, 104(1-2) in FIG. 8 is used as the chart for the first side of the second sheet, and 104(2-4) in FIG. 8 is output as the chart for the second side of the second sheet, which is the back side of that.

[0113] In the experiment, the image quality when a B solid image and a Bk solid image were output after the adjustment mode was executed was examined. The experiment was carried out on recording material S, which was a fine-quality paper with a smooth surface and a basis weight of 68 g / m. 2 and 87g / m2 embossed paper with a non-smooth surface. 2The test was carried out using paper of the same color. The results are shown in Table 1. Table 1 shows the adjustment values ​​after running the adjustment mode, and the image quality when a solid B image and a solid Bk image were subsequently output in double-sided printing. The image quality was rated as "Good" if there were no problems, and "Poor" if an image defect occurred due to the secondary transfer voltage setting. Note that similar results were obtained for the first and second sides of the double-sided printing, so Table 1 shows the results of one side as a representative.

[0114] [Table 1]

[0115] When using high-quality paper, there were no abnormalities in the image quality in this example, but in the comparative example, an adjustment value that resulted in a lower secondary transfer voltage than in this example was selected, and transfer omissions were observed in the B solid image. In the comparative example, it is thought that in the adjustment mode, bleed-through of the patch occurred, causing the density of the B solid patch corresponding to the low secondary transfer voltage to be erroneously detected as being high, and the adjustment value became inappropriate.

[0116] Furthermore, when embossed paper was used, the present example showed no abnormalities in image quality, whereas the comparative example selected an adjustment value resulting in a higher secondary transfer voltage than the present example, resulting in uneven density (roughness) in the black solid image. In the comparative example, bleed-through of the patch occurred in the adjustment mode, leading to a false detection that the density of the black solid patch corresponding to the high secondary transfer voltage was high, resulting in an inappropriate adjustment value. In other words, with embossed paper, depressions in the paper surface at the secondary transfer section N2 tend to create gaps between the intermediate transfer belt 44b and the paper surface. When the secondary transfer voltage is high, the discharge in these gaps tends to reduce the image density. However, bleed-through leads to a false detection that the image density is not reduced, resulting in a high secondary transfer voltage. In this example, there is no effect of bleed-through, and the adjustment is appropriate.

[0117] In this embodiment, in the L chart 100 and the S chart 103, all patches are arranged so that they do not overlap on the front and back of the recording material S. However, the present invention is not limited to this configuration. It is sufficient that the patches are arranged so that at least the portion of the patch used to adjust the secondary transfer voltage of the patch transferred to the first side and the portion of the patch used to adjust the secondary transfer voltage of the patch transferred to the second side do not overlap on the front and back of the recording material S. For example, while the entire adjustment patches are arranged so that they do not overlap on the front and back of the recording material S, images such as trigger patches and identification information such as patch numbers when printed may be arranged so that they overlap in whole or in part on the front and back of the recording material S. Furthermore, as described above, it is sufficient that at least the portions of the adjustment patches from which density information is read to adjust the secondary transfer voltage do not overlap on the front and back of the recording material S.

[0118] As mentioned above, the effect of show-through on the detected brightness tends to be particularly noticeable on recording materials S with small basis weights. Therefore, only when the basis weight of the recording material S used to output the R chart 104 is equal to or less than a predetermined basis weight, the first-side adjustment chart and the second-side adjustment chart may be formed on separate recording materials S and output. For example, when the basis weight is 150 g / m 2In the case of the recording material S described below, the adjustment chart for the first side and the adjustment chart for the second side can be formed on one side each on separate recording materials S and output. In this case, if the basis weight of the recording material S used to output the R chart 104 is greater than the predetermined basis weight, the R chart 104 can be output in the same manner as in the comparative example described above. That is, if the recording material S is large enough that patches may overlap on both sides and has a basis weight equal to or less than the predetermined basis weight, the patches on the first side and the patches on the second side are transferred to separate recording materials S. On the other hand, even if the recording material S is large enough that patches may overlap on both sides, if the basis weight is greater than the predetermined basis weight, the patches on the first side and the patches on the second side can be transferred to the first and second sides, respectively, of a single recording material S. In the case of a recording material S of a size that allows patches to be arranged on the front and back without overlapping, it is preferable to transfer the patches on the first and second sides arranged in this manner to the first and second sides of a single recording material S, respectively, regardless of the basis weight, from the standpoint of reducing downtime, etc.

[0119] As described above, in this embodiment, the image forming apparatus 1 includes an image carrier 44b that carries a toner image, a transfer means 45 that transfers the toner image from the image carrier 44b to the recording material S at a transfer section N2, an application means 76 that applies a transfer voltage to the transfer means 45, a fixing means 46 that fixes the toner image transferred to the recording material S to the recording material S at a fixing section N3, a double-sided mechanism 14 that transports the recording material S to perform double-sided printing in which a toner image is transferred to the first side of the recording material S at the transfer section N2 and fixed to the first side of the recording material S at the fixing section N3, and then a toner image is transferred to the second side of the recording material S at the transfer section N2 and fixed to the second side of the recording material S at the fixing section N3, thereby forming images on both sides of the recording material S, and an execution section 31d that executes an output mode in which a chart is output in which multiple test images are transferred to the recording material S at different transfer voltages in order to adjust the transfer voltage. When executing an output mode for outputting a chart for adjusting the transfer voltage for double-sided printing, the execution unit 31d can execute the following first output mode and second output mode. When the width of the recording material S onto which the test image is transferred in a direction substantially perpendicular to the conveyance direction is a first width, the execution unit 31d executes the first output mode in which a test image for adjusting the transfer voltage for the first side in double-sided printing and a test image for adjusting the transfer voltage for the second side in double-sided printing are transferred onto the first and second sides of a single recording material, respectively, to output charts 100 and 103. When the width of the recording material S onto which the test image is transferred is a second width smaller than the first width, the execution unit 31d executes the second output mode in which a test image for adjusting the transfer voltage for the first side in double-sided printing and a test image for adjusting the transfer voltage for the second side in double-sided printing are transferred onto one side of a separate recording material S, respectively, to output charts 104.

[0120] In this embodiment, the execution unit 31d controls to execute the second output mode when the width of the recording material S to which the test image is transferred is smaller than a predetermined width. Furthermore, the execution unit 31d can also control to execute the second output mode when the width of the recording material S to which the test image is transferred is smaller than N×L×2, where L is the width of the test image in the width direction substantially perpendicular to the conveyance direction of the recording material S and N is the number of test images in the width direction. Furthermore, in this embodiment, the execution unit 31d controls in the first output mode so that the portion of the test image transferred to the first side of the recording material S used to adjust the transfer voltage and the portion of the test image transferred to the second side of the recording material S used to adjust the transfer voltage do not overlap on the front and back of the recording material S. In particular, in this embodiment, the execution unit 31d controls in the first output mode so that the entire test image transferred to the first side of the recording material S and the entire test image transferred to the second side of the recording material S do not overlap on the front and back of the recording material S. In this embodiment, the execution unit 31d controls the duplex mechanism 14 to transfer a test image for adjusting the transfer voltage for the second side in double-sided printing onto the second side of the recording material S that has been transported to the transfer unit N2 by the duplex mechanism 14 without a test image transferred onto the first side. In this embodiment, the execution unit 31d controls the duplex mechanism 14 to transport the recording material S, on the first side of which a test image for adjusting the transfer voltage for the first side in double-sided printing has been transferred, to the transfer unit N2, and to eject the recording material S from the image forming apparatus 1 after passing through the transfer unit N2 and the fixing unit N3 without transferring the test image onto the second side. In this embodiment, the image forming apparatus 1 includes an acquisition unit 3 that acquires density information regarding the density of the test image on the chart, and a setting unit 30 that sets the transfer voltage based on the density information acquired by the acquisition unit 3. In this embodiment, the acquisition unit 3 acquires density information of the test image on the chart when the recording material S on which the chart has been formed is ejected from the image forming apparatus 1.

[0121] As described above, according to this embodiment, even if the size of the recording material S used to output the chart in the adjustment mode is small, it is possible to avoid detecting density information when patches overlap on the front and back of the recording material S. Therefore, according to this embodiment, it is possible to select an appropriate secondary transfer voltage according to the density information of the patches. Therefore, according to this embodiment, even if the size of the recording material S used to output the chart is small, it is possible to appropriately adjust the secondary transfer voltage during double-sided printing.

[0122] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0123] In this embodiment, the R chart 104 is different from that in the first embodiment. Note that in this embodiment, the L chart 100 and the S chart 103 are the same as those in the first embodiment.

[0124] FIG. 18 is a schematic diagram showing an R chart 104 in this embodiment. In this embodiment, as in the first embodiment, the R chart 104 is a chart for a case where the length of the recording material S in the conveying direction is 210 mm (the short side of A4 size) or more and less than 420 mm (the long side of A3 size) and the width of the recording material S is 139.7 mm (the short side of STMT size) or more and less than 160 mm. In the R chart 104 in FIG. 18, 104(1-1) indicates the first sheet of the first side, 104(1-2) indicates the second sheet of the first side, 104(1-3) indicates the third sheet of the first side, 104(2-3) indicates the third sheet of the second side, 104(1-4) indicates the fourth sheet of the first side, and 104(2-4) indicates the fourth sheet of the second side. The configuration of the patches formed on the R chart 104 in this embodiment is the same as that of the R chart 104 in the first embodiment.

[0125] 18, in this embodiment, the first and second sheets have patches formed only on their first sides, and after passing through the secondary transfer portion N2, they pass through the inside of the sensing unit 3 without changing their orientation. Also, for recording material S on which patches are to be formed on the second side, patches are not formed on the first side, but only on the second side, and after passing through the secondary transfer portion N2, they pass through the inside of the sensing unit 3 without changing their orientation. In FIG. 18, the conveying direction of the chart when passing through the secondary transfer portion N2 is indicated by a thin arrow, and the conveying direction of the chart when passing through the inside of the sensing unit 3 is indicated by a thick arrow.

[0126] That is, in this embodiment, 104(1-1) and 104(1-2) of the R chart 104 in FIG. 18 are formed on the first side of the recording material S in an image forming operation for single-sided printing, output, and read by the second line sensor 92 of the sensing unit 3 without changing the orientation. Also, 104(2-3) and 104(2-4) of the R chart 104 in FIG. 18 are formed on the second side of the recording material S in an image forming operation for double-sided printing, output, and read by the second line sensor 92 of the sensing unit 3 without changing the orientation. In this embodiment, the first and second sheets of recording material S on which the adjustment chart for the first side has been formed head toward the sensing unit 3 without passing through the reverse conveyance path 7, and therefore downtime can be reduced compared to the first embodiment.

[0127] As in the first embodiment, in this embodiment, on the surface on which the patches are formed, the leading patches of the B solid patch 101 and the Bk solid patch 102 as they pass through the sensing unit 3 are trigger patches 101T and 102T, respectively, for detecting position information. Of the B solid patch 101 and the Bk solid patch 102, the remaining 10 patches excluding the trigger patches 101T and 102T are adjustment patches 101A and 102A for acquiring brightness information (density information).

[0128] In this embodiment, as in the first embodiment, the first surface of the recording material S on which a patch is to be formed is left blank without a patch on the second surface of the R chart 104. Also, the second surface of the recording material S on which a patch is to be formed is left blank without a patch on the first surface.

[0129] In this embodiment, when single-sided adjustment is performed, the charts 104(1-1) and 104(1-2) in FIG. 18 are formed and output on the first side of the first sheet of recording material S and the first side of the second sheet of recording material S, respectively, in the image forming operation for single-sided printing. In this case, the charts are output without passing through the reversing conveyance path 7, and the charts are read using the second line sensor 92 of the sensing unit 3. Note that the adjustment results for the first side during double-sided adjustment can also be used to set the secondary transfer voltage for single-sided printing.

[0130] In addition, in this embodiment, the secondary transfer voltage applied when outputting the chart is the voltage shown in Figure 15(b) for the surface on which the patch is formed, and the voltage corresponding to patch number n=5 (the voltage shown by the dotted line with symbol 800 in Figure 15) for the blank surface.

[0131] Thus, in this embodiment, in the second output mode (R chart output operation) described above, the execution unit 31d controls the recording material S, on the first side of which a test image for adjusting the transfer voltage for the first side in double-sided printing, to be discharged from the image forming device 1 without being transported to the transfer unit N2 by the double-sided mechanism 14.

[0132] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained, and the downtime for the adjustment mode using the R chart 104 can be reduced more than that of the first embodiment.

[0133] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0134] In this embodiment, the L chart 100 and the S chart 103 are different from those in the first embodiment. On the other hand, as will be described later, in this embodiment, the R chart 104 is the same as in the first or second embodiment.

[0135] 19 is a schematic diagram showing an L chart 100 in this embodiment. In this embodiment, as in embodiment 1, the L chart 100 is a chart for when the length in the conveying direction of the recording material S is 420 mm or more (the long side of A3 size) and the width of the recording material S is 279.4 mm or more (the long side of LTR size).

[0136] In this embodiment, the L chart 100 has a total of 11 pairs of blue (B) solid patches 101, black (Bk) solid patches 102, and black (Bk) halftone patches 106 arranged side by side in the width direction, aligned in the conveyance direction of the recording material S. In the L chart 100 in FIG. 19, 100(1) indicates the first side, and 100(2) indicates the second side. Also in FIG. 19, the conveyance direction of the chart when passing through the secondary transfer portion N2 is indicated by a thin arrow, and the conveyance direction of the chart when passing through the inside of the sensing unit 3 is indicated by a thick arrow. In this embodiment, the leading patches of the B solid patch 101, Bk solid patch 102, and Bk halftone patch 106 when passing through the inside of the sensing unit 3 are trigger patches 101T, 102T, and 106T, respectively, for detecting position information. These trigger patches 101T, 102T, and 106T are used to accurately detect the position of the patch array when read by the first and second line sensors 91 and 92. Of the B solid patch 101, Bk solid patch 102, and Bk halftone patch 106, the remaining 10 patches, excluding the trigger patches 101T, 102T, and 106T, are adjustment patches 101A, 102A, and 106A for acquiring luminance information (density information). Different secondary transfer voltages Vtr are applied to the adjustment patches 101A, 102A, and 106A, and they are transferred onto the recording material S.

[0137] As described above, in the L chart 100 of this embodiment, in addition to the B solid patch 101 and Bk solid patch 102 similar to those of the L chart 100 of Embodiment 1 shown in FIG. 6, a Bk halftone patch 106 is also arranged. The configurations of the B solid patch 101 and Bk solid patch 102 in this embodiment are the same as those of the B solid patch 101 and Bk solid patch in Embodiment 1. Here, when the leading edge of the recording material S in the conveying direction as it passes through the sensing unit 3 is facing up and the surface of the recording material S facing the first and second line sensors 91 and 92 appears as follows. That is, in this embodiment, the Bk halftone patch 106 is arranged adjacent to the right side of the B solid patch 102 and adjacent to the edge of the chart (recording material S). Furthermore, in this embodiment, the Bk halftone patch (gray patch) 106 is formed with a toner amount that is 50% of the toner amount of the Bk solid patch 102. In this embodiment, the size of the Bk halftone 106 is approximately 15 mm long and 15 mm wide in the conveying direction, and the Bk halftone patches 106 are spaced apart by 15 mm in the conveying direction of the recording material S.

[0138] When the recording material S is wide, the behavior of the widthwise edges of the recording material S is likely to become unstable, for example, the widthwise edges of the recording material S may absorb moisture and become wavy. Therefore, when the recording material S is wide, image defects due to discharge are likely to occur at the widthwise edges of the recording material S during secondary transfer. Such image defects due to discharge are easily detected using halftone images. Therefore, it is desirable to arrange the Bk halftone patches 106 adjacent to the widthwise edges of the recording material S. The Bk halftone patches 106 are preferably arranged within a range of approximately 50 mm inward from the widthwise edges of the recording material S, and more preferably within a range of approximately 10 to 30 mm inward from the widthwise edges of the recording material S. The Bk halftone patches 106 may be continuous to the widthwise edges of the recording material S, or may be arranged with a margin of approximately 2.5 mm at each widthwise edge of the recording material S, as in Example 1. This margin is typically approximately 2 to 10 mm. Furthermore, the Bk halftone patch 106 can be formed with a toner amount of about 10 to 80%, and typically about 40 to 60%, when the toner amount of the Bk solid patch 102 is taken as 100%. Note that the halftone patch is not limited to black, and may be another single-color halftone image, or a halftone image of another secondary color or a mixed color (multi-color) of more than one color.

[0139] On the first side 100(1) and the second side 100(2) of the L chart 100, the B solid patch 101, the Bk solid patch 102, and the Bk halftone patch 106 are arranged so as not to overlap on the front and back of the recording material S. This is to avoid the influence on the detected brightness due to show-through when read by the first and second line sensors 91 and 92, as described in the first embodiment.

[0140] 20 is a schematic diagram showing the S chart 103 in this embodiment. In this embodiment, as in the first embodiment, the S chart 103 is a chart for the case where the length of the recording material S in the conveying direction is 210 mm or more (the short side of A4 size) and less than 420 mm (the long side of A3 size) and the width of the recording material S is 160 mm or more.

[0141] In this embodiment, the S chart 103 has a total of 12 sets of blue (B) solid patches 101, black (Bk) solid patches 102, and black (Bk) halftone patches 106 arranged side by side in the width direction, across two sheets of recording material S, arranged side by side in the conveyance direction of the recording material S. In the S chart 103 in FIG. 20, 103(1-1) indicates the first sheet of the first side, 103(1-2) indicates the second sheet of the first side, 103(2-1) indicates the first sheet of the second side, and 103(2-2) indicates the second sheet of the second side. Also in FIG. 20, the conveyance direction of the chart when passing through the secondary transfer portion N2 is indicated by a thin arrow, and the conveyance direction of the chart when passing through the inside of the sensing unit 3 is indicated by a thick arrow. In this embodiment, the leading patches of the B solid patch 101, the Bk solid patch 102, and the Bk halftone patch 106 as they pass through the sensing unit 3 are trigger patches 101T, 102T, and 106T, respectively, for detecting position information. These trigger patches 101T, 102T, and 106T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101, the Bk solid patch 102, and the Bk halftone patch 106, excluding the trigger patches 101T, 102T, and 106T, the remaining ten patches are adjustment patches 101A, 102A, and 106A for acquiring luminance information (density information). Different secondary transfer voltages Vtr are applied to the adjustment patches 101A, 102A, and 106A, and they are transferred to the recording material S.

[0142] As described above, the S chart 103 of this embodiment includes a B solid patch 101 and a Bk solid patch 102 similar to those of the S chart 103 of the first embodiment shown in FIG. 7 , and also includes a Bk halftone patch 106. The configurations of the B solid patch 101 and the Bk solid patch 102 in this embodiment are the same as those of the B solid patch 101 and the Bk solid patch 102 in the first embodiment. When the leading edge of the recording material S in the conveying direction as it passes through the sensing unit 3 is facing up, the surface of the recording material S facing the first and second line sensors 91 and 92 appears as follows: That is, in this embodiment, the Bk halftone patch 106 is located adjacent to the right side of the B solid patch 102 and adjacent to the edge of the chart (recording material S). Furthermore, in this embodiment, the Bk halftone patch (gray patch) 106 is formed with a toner amount that is 50% of the toner amount of the Bk solid patch 102. In this embodiment, the size of the Bk halftone patches 106 is approximately 15 mm long and 15 mm wide in the transport direction, and the Bk halftone patches 106 are spaced 15 mm apart in the transport direction of the recording material S. The arrangement and density of the Bk halftone patches 106 can be set in the same way as described for the L chart 100.

[0143] On the first side 103(1-1), 103(1-2) and the second side 103(2-1), 103(2-2) of the S chart 103, the B solid patch 101, the Bk solid patch 102, and the Bk halftone patch 106 are arranged so as not to overlap on the front and back of the recording material S. This is to avoid the effect on the detected brightness due to show-through when read by the first and second line sensors 91, 92, as described in the first embodiment.

[0144] On the other hand, in this embodiment, the R chart 104 is the same as in embodiment 1 (FIG. 8) or embodiment 2 (FIG. 18). That is, the R chart 104 has a B solid patch 101 and a Bk solid patch 102 arranged thereon, but no Bk halftone patch 106 arranged thereon. In addition, in the R chart 104, no patch is formed on the first side of the recording material S on whose second side a patch is to be formed, and the first side is left blank. In addition, no patch is formed on the second side of the recording material S on whose first side a patch is to be formed, and the second side is left blank. This is because, with a recording material S having a small width, it is difficult to arrange three types of patches in the width direction, and it is also difficult to arrange the patches so that they do not overlap on the front and back of the recording material S.

[0145] That is, as described above, when the recording material S is wide, the behavior of the widthwise edges of the recording material S tends to be unstable, and image defects due to discharge are likely to occur at the widthwise edges of the recording material S during secondary transfer. Because such image defects due to discharge are easily detected in halftone images, the L chart 100 and the S chart 103 have Bk halftone patches 106 arranged adjacent to the widthwise edges. In contrast, when the width of the recording material S is small, the behavior of the widthwise edges of the recording material S tends to be stable. Therefore, there is less need to consider image defects due to discharge at the widthwise edges of the recording material S. Meanwhile, density changes due to changes in secondary transfer voltage are easier to detect in solid images than in halftone images. Therefore, the R chart 104 does not have the Bk halftone patch 106, and instead has the B solid patch 101 and the Bk solid patch 102.

[0146] In this embodiment, the operation of the adjustment mode is the same as in the first embodiment described with reference to FIG. 9. However, in this embodiment, when the L chart 100 and the S chart 103 are used, the recommended adjustment amount of the secondary transfer voltage (more specifically, the corresponding adjustment value) is determined based on the results of reading the B solid patch 101, the Bk solid patch 102, and the Bk halftone patch 106 by the sensing unit 3 (S12 to S15). In the first embodiment, as described with reference to FIG. 17, the optimal range of the secondary transfer voltage was narrowed using the luminance information (density information) of the Bk solid patch (single-color solid patch) 102. Then, the luminance information (density information) of the B solid (secondary-color solid) patch was used to determine the optimal adjustment amount of the secondary transfer voltage (more specifically, the corresponding adjustment value) from the narrowed range. In this embodiment, similarly, the optimal range of the secondary transfer voltage can be narrowed down using the luminance information (density information) of the Bk solid patch (single-color solid patch) 102 and the luminance information (density information) of the Bk halftone patch (halftone patch) 106. For example, it is possible to narrow down the optimal range for each of the Bk solid patch 102 and the Bk halftone patch 106 in the same manner as in the first embodiment, and then further narrow down the range to one where both optimal ranges overlap. Then, the luminance information (density information) of the B solid (secondary color solid) patch can be used to determine the optimal adjustment amount of the secondary transfer voltage (more specifically, the corresponding adjustment value) from the narrowed range. This makes it possible to set an optimal secondary transfer voltage that takes into account the image defects caused by discharge that tend to occur at the widthwise edges of the recording material S. Note that the process of determining the recommended adjustment amount of the secondary transfer voltage when using the R chart 104 may be the same as in the first embodiment.

[0147] As described above, in this embodiment, the number of test images in the width direction, which is approximately perpendicular to the conveyance direction of the recording material S, in the chart 104 output in the second output mode is smaller than the number of test images in the width direction, which is approximately perpendicular to the conveyance direction of the recording material S, in the charts 100 and 103 output in the first output mode. In particular, in this embodiment, the charts 100 and 103 output in the first output mode have solid test images and halftone test images arranged side by side in the width direction, and the chart 104 output in the second output mode has only the solid test image of the two test images. Furthermore, in this embodiment, the halftone test image is arranged adjacent to the edge of the recording material S in the width direction.

[0148] As described above, according to this embodiment, the same effects as in embodiment 1 can be obtained, and when outputting a chart using a wide recording material S, it is possible to set a more appropriate secondary transfer voltage.

[0149] [Example 4] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0150] In this embodiment, a modified example of a method for reading a chart output in the adjustment mode and a method for selecting adjustment values ​​will be described.

[0151] In Examples 1 to 3, the chart was read using an in-line image sensor (first and second line sensors 91 and 92) in the adjustment mode. This reduces the burden on the operator. However, the present invention is not limited to this configuration. For example, the operator may set the chart output in the adjustment mode in the image reading unit 80 as an acquisition unit, and the image reading unit 80 may read the chart. In this manner, the acquisition unit 80 may be configured to receive the recording material S on which the chart is formed and ejected from the image forming apparatus 1, and acquire density information of the test image on the chart. Also, for example, the operator may read the chart output in the adjustment mode using an image reading unit prepared separately from the image forming apparatus 1, and input information about the read image or luminance information (density information) of the read patch into the image forming apparatus 1. This information may be input via a network, via a storage medium from the operation unit 70, or directly by the operator using key input from the operation unit 70. In this case, the control unit 30 of the image forming apparatus 1 can present a recommended adjustment amount for the secondary transfer voltage based on the input image information and brightness information (density information) in the same manner as in the above-described embodiment.

[0152] Furthermore, even when an operator visually checks the chart to select a preferred adjustment amount for the secondary transfer voltage, if the patches for double-sided adjustment overlap on the front and back of the recording material S, there is a possibility that the operator will make an erroneous judgment about the transferability. For this reason, the present invention is also effective when the image forming apparatus 1 does not have the function of selecting an adjustment value based on the results of reading the chart, and the operator visually judges the chart to select a preferred adjustment amount for the secondary transfer voltage. In this case, too, when the recording material S is of a size that may cause patches to overlap on the front and back, the patches on the first side and the patches on the second side are transferred to separate recording materials S, thereby reducing the possibility that the operator will make an erroneous judgment about the transferability.

[0153] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0154] In the above-described embodiment, the transfer voltage is adjusted using an adjustment value corresponding to a predetermined adjustment amount, but the adjustment amount may be directly set on an adjustment screen, for example.

[0155] Furthermore, in the above-described embodiment, the operations performed on the operation unit of the image forming apparatus can be performed on an external device. That is, although the case where the adjustment mode is executed by an operator via the operation unit 70 of the image forming apparatus 1 has been described, the adjustment mode may also be executed by an operation via an external device 200 such as a personal computer. In this case, settings similar to those in the above-described embodiment can be performed via a screen displayed on the display unit of the external device 200 by a driver program of the image forming apparatus 1 installed in the external device 200.

[0156] Furthermore, in the above-described embodiment, a configuration in which the secondary transfer voltage is constant voltage controlled has been described, but the secondary transfer voltage may also be constant current controlled. In the above-described embodiment, in a configuration in which the secondary transfer voltage is constant voltage controlled, the secondary transfer voltage is adjusted by adjusting the target voltage when the secondary transfer voltage is applied using the adjustment mode. In a configuration in which the secondary transfer voltage is constant current controlled, the secondary transfer voltage can be adjusted by adjusting the target current when the secondary transfer voltage is applied using the adjustment mode.

[0157] Furthermore, the current detection result or voltage detection result may be the average value of multiple sampling values ​​acquired at a predetermined sampling interval at one detection timing, etc. Furthermore, when the transfer voltage is controlled to a constant voltage, the voltage value may be detected (recognized) from the output instruction value for the power supply, and when the transfer voltage is controlled to a constant current, the current value may be detected (recognized) from the output instruction value for the power supply.

[0158] In the above-described embodiment, the printer unit and the sensing unit are each individually configured in the image forming apparatus, but the present invention is not limited to this configuration. This configuration allows, for example, the units to be separable, and the sensing unit function to be provided as an extended function of the image forming apparatus. However, the printer unit configuration and the sensing unit configuration in the above-described embodiment may be integrated, for example, by being disposed in a single housing.

[0159] Furthermore, the image forming apparatus is not limited to a tandem-type image forming apparatus, but may be an image forming apparatus of another type. Furthermore, the image forming apparatus is not limited to an image forming apparatus capable of forming full-color images, but may be an image forming apparatus capable of forming only monochrome (black and white or monocolor) images. For example, the present invention may be applied to a transfer unit in an image forming apparatus configured to form a toner image on a photosensitive drum as an image carrier and then transfer the toner image directly to a recording material in the transfer unit. Furthermore, the image forming apparatus may be an image forming apparatus for various purposes, such as a printer, various printing machines, copiers, fax machines, and multifunction machines. [Explanation of symbols]

[0160] 2. Image forming device 3 Sensing Unit 4 Paper feed section 7 Reversing transport path 8 Discharge section 30 Control Unit 70 Operation section 76 Secondary transfer power supply 91 First line sensor 92 Second line sensor 100 Large Chart (L Chart) 101 B Solid Patch 102 Black solid patch 103 Small Chart (S Chart) 104 R Chart N2 Secondary transfer unit

Claims

1. an image carrier that carries a toner image; a transfer device that transfers a toner image from the image carrier to a recording material at a transfer section; a voltage application unit that applies a transfer voltage to the transfer device; a fixing device that fixes the toner image transferred onto the recording material to the recording material at a fixing section; a control unit capable of executing a double-sided mode operation in which toner images are formed on both sides of a recording material, and also capable of executing an output mode operation in which a chart is output by transferring a plurality of test images, including a plurality of first test images and a plurality of second test images, onto the recording material, the test images being formed by applying different transfer voltages for adjusting the transfer voltage applied during the double-sided mode operation; and During the execution of the output mode operation, the control unit: a first operation in which the first test image formed on the first side of the recording material is fixed to the first side of the recording material by the fixing device, and then the second test image is transferred to the second side of the recording material; and a second operation in which the first test image formed on the first side of a first recording material is fixed by the fixing device, the first recording material is then output without forming the plurality of test images on the second side of the first recording material, and a second recording material is then passed through the fixing device without forming the plurality of test images on the first side of the second recording material, and the second test image is then transferred to the second side of the second recording material; An image forming apparatus characterized in that:

2. The image forming apparatus described in Claim 1, characterized in that during execution of the operation of the output mode, the control unit executes the first operation when the width of the recording material onto which the test image is transferred is a first width, and executes the second operation when the width of the recording material onto which the test image is transferred is a second width narrower than the first width.

3. An image forming apparatus as described in claim 1, characterized in that when the width of each of the test images in a width direction approximately perpendicular to the conveying direction of the recording material is L and the number of the test images in the width direction is N, the control unit controls to perform the second operation when the width of the recording material onto which the test images are transferred is narrower than N x L x 2.

4. The device further includes a double-sided conveying mechanism that, during operation in the double-sided mode, transfers a toner image onto one side of a recording material, then fixes the toner image onto the first side of the recording material by the fixing device, and then inverts the recording material and conveys it to the transfer section; The image forming apparatus described in claim 1, characterized in that during the execution of the second operation, the control unit controls the test image formed on the first side of the first recording material to be fixed by the fixing device, and then the first recording material to be transported to the transfer section by the double-sided transport mechanism, and then the first recording material to be transported without transferring the test image to the second side of the first recording material, passing through the transfer section and the fixing section, and then the first recording material to be discharged from the image forming apparatus.

5. The apparatus further includes a double-sided conveying mechanism that, during operation in the double-sided mode, transfers a toner image onto one side of a recording material, then fixes the toner image onto the first side of the recording material by the fixing device, and then inverts the recording material and conveys it to the transfer section; The image forming apparatus described in claim 1, characterized in that during execution of the second operation, the control unit controls the first test image formed on the first side of the first recording material to be fixed by the fixing device, and then the first recording material to be discharged from the image forming apparatus without being transported to the transfer section by the double-sided transport mechanism.

6. The image forming apparatus described in Claim 1, characterized in that during execution of the first operation, the control unit controls the area of ​​the recording material used to transfer the first test image onto the first side of the recording material and the area of ​​the recording material used to transfer the second test image onto the second side of the recording material so that they do not overlap each other on the front and back of the recording material.

7. The image forming apparatus described in Claim 1, characterized in that during execution of the first operation, the control unit controls the first test image transferred to the first side of the recording material and the second test image transferred to the second side of the recording material so that they do not overlap each other on the front and back of the recording material.

8. An image forming apparatus as described in claim 1, characterized in that in the width direction approximately perpendicular to the conveying direction of the recording material, the number of test images in the chart output by the second operation is less than the number of test images in the chart output by the first operation.

9. 9. The image forming apparatus according to claim 8, wherein the chart output in the first operation includes a solid test image and a halftone test image arranged side by side in the width direction, and the chart output in the second operation includes the solid test image but does not include the halftone test image.

10. 10. The image forming apparatus according to claim 9, wherein the halftone test image is arranged adjacent to an end of the recording material in the width direction.

11. An image carrier that carries a toner image; a transfer device that transfers a toner image from the image carrier to a recording material at a transfer section; a voltage application unit that applies a transfer voltage to the transfer device; a fixing device that fixes the toner image transferred onto the recording material to the recording material at a fixing section; a control unit capable of executing a double-sided mode operation in which toner images are formed on both sides of a recording material, and also capable of executing an output mode operation in which a chart is output by transferring a plurality of test images, including a plurality of first test images and a plurality of second test images, onto the recording material, the test images being formed by applying different transfer voltages for adjusting the transfer voltage applied during the double-sided mode operation; and An image forming apparatus characterized in that, during execution of the operation in the output mode, the control unit controls the image forming operation so that the first test image formed on the first side of a first recording material is fixed by the fixing device, and then the first recording material is output without forming the test image on the second side of the first recording material, and then a second recording material is passed through the fixing device without forming the test image on the first side of the second recording material, and then the second test image is transferred to the second side of the second recording material.

Images