Image forming apparatus

Abstract

To appropriately adjust a transfer voltage to an image preferred by a user.SOLUTION: An image forming apparatus has: an image carrier 44b; transfer means 45b; application means 76; an output mode execution unit 31d that outputs a chart 100; a density information acquisition unit 3 that is related to density of a test image on a recording material; a setting unit 30 that sets a transfer voltage on the basis of the density information; and an input unit 70 that receives input of instruction information. The execution unit 31d can control to transfer a plurality of first test images with first density on the recording material S, and can control to transfer a plurality of second test images with second density higher than the first density to the recording material S. According to the instruction information input to the input unit 70, the setting unit 30 can set a first transfer voltage by using at least the information on the density of the first test images (priority to half tone), or can set a second transfer voltage by using at least the information on the density of the second test images without using the information on the density of the first test images (priority to solid image).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, with the conventional adjustment mode, for example, when using a recording material with strict transferability (it is difficult to set transfer conditions that will result in good transferability), the user may not be able to select the optimum adjustment value for the image that is actually output. Generally, the higher the density of the toner image to be transferred, the larger the absolute value of the transfer voltage required. However, when using a recording material with strict transferability, for example, it may be difficult to transfer images ranging from halftones to solid images well with a single transfer voltage.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to enable a user to adjust the transfer voltage appropriately for the image that has priority. [Means for solving the problem]

[0008] The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus including an image carrier that carries a toner image, transfer means that transfers the toner image from the image carrier to a recording material in a transfer unit, application means that applies a transfer voltage to the transfer means, an execution unit that controls to execute an output mode in which a chart is output by transferring a plurality of test images onto the recording material using different transfer voltages, an acquisition unit that acquires density information related to the density of the test images on the recording material, a setting unit that sets the transfer voltage based on the density information acquired by the acquisition unit, and an input unit that inputs instruction information, and the execution unit controls to transfer a plurality of first test images, each having a first density on the image carrier, onto the recording material. and can be controlled to transfer a plurality of second test images, the density of which on the image carrier is a second density higher than the first density, onto a recording material, and the setting unit can set a first transfer voltage using the density information of at least the first test image of the first and second test images, or set a second transfer voltage using the density information of at least the second test image of the first and second test images, in accordance with instruction information input by the input unit. [Effects of the Invention]

[0009] According to the present invention, the user can adjust the transfer voltage appropriately for the image that he or she prefers. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic block diagram of a control system of the 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 a chart output in an adjustment mode. [Figure 7] FIG. 10 is a schematic diagram of a chart output in an adjustment mode. [Figure 8] FIG. 4 is a flowchart showing an outline of the procedure of an adjustment mode in the first embodiment. [Figure 9] FIG. 10 is a schematic diagram of a paper type category selection screen. [Figure 10] FIG. 10 is a schematic diagram of a paper feed unit selection screen. [Figure 11] FIG. 10 is a schematic diagram of a secondary transfer voltage adjustment screen in the first embodiment. [Figure 12] FIG. 10 is a graph showing the transition of the secondary transfer voltage when a chart is output. [Figure 13(a)] 10 is a table showing an example of the relationship between patch numbers of a chart and adjustment values. [Figure 13(b)] 10 is a table showing an example of the relationship between patch numbers of a chart and adjustment values. [Figure 13(c)] 10 is a table showing an example of the relationship between patch numbers of a chart and adjustment values. [Figure 14] FIG. 10 is a graph showing the transition of the secondary transfer voltage when a chart is output. [Figure 15] 10A and 10B are schematic diagrams for explaining a method for detecting the position of a trigger patch. [Figure 16] FIG. 4 is a graph illustrating a halftone priority mode in the first embodiment. [Figure 17] FIG. 10 is a graph illustrating a solid image priority mode in the first embodiment. [Figure 18] FIG. 10 is a flowchart showing an outline of the procedure of an adjustment mode in the second embodiment. [Figure 19] FIG. 10 is a schematic diagram of a secondary transfer voltage adjustment screen in the second embodiment. [Figure 20] FIG. 10 is a graph illustrating a low-density halftone priority mode in the second embodiment. [Figure 21] FIG. 10 is a graph illustrating a high-density halftone priority mode in the second embodiment. [Figure 22] FIG. 10 is a graph illustrating a solid image priority mode in the second embodiment. [Figure 23] FIG. 11 is a flowchart showing an outline of the procedure of an adjustment mode in the third embodiment. [Figure 24] FIG. 11 is a schematic diagram of a secondary transfer voltage adjustment screen in the third embodiment. [Figure 25] FIG. 11 is a graph illustrating a low-density priority mode in the third embodiment. [Figure 26] FIG. 11 is a graph illustrating a high-density priority mode in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0012] [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.

[0013] 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.

[0014] 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.

[0015] 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 the intermediate transfer unit 44). 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.

[0016] 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.

[0017] 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 power supply 73 applies a predetermined charging voltage (charging bias) to the charging roller 52 during the charging process.

[0018] 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.

[0019] 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 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 as described above, is directly delivered 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 reversing conveyance path 7 by the reversing conveyance roller 12, which serves as a reversing conveyance member. In the reversing 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 the double-sided conveyance roller 13, which serves as a double-sided conveyance member. The recording material S thus supplied again to the secondary transfer section N2 has a toner image transferred and fixed on the second side, and is then delivered from the delivery section 6 to the sensing unit 3. In this way, the image forming apparatus 1 (printer unit 2) of this embodiment is capable of double-sided printing (automatic double-sided printing, duplex printing), in which an image is formed on both sides of a single recording material S. The reversing conveyance path 7, the reversing conveyance roller 12, the double-sided conveyance roller 13, and the like constitute a double-sided mechanism 14. The recording material S on which the 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 below, 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.

[0026] 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.

[0027] The image forming apparatus 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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 the ROM 32 and 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. The 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 set 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 and the secondary transfer voltage storage unit / calculation unit 31f) functions as a setting unit that sets the secondary transfer voltage based on the density information acquired by the acquisition unit.

[0036] 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.

[0037] 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.

[0038] 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 for both sides of the recording material S in the adjustment mode, the recording material S with charts formed on both sides 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.

[0039] 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.

[0040] 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.

[0041] As shown in FIG. 2, the sensing unit 3 is connected to the control unit 30, and is capable of transferring information read by the first and second line sensors 91 and 92 (density information relating to density) to the control unit 30.

[0042] In this embodiment, the chart is read by the sensing unit 3, but the present invention is not limited to this configuration. For example, the image reading unit 80 may be provided with a function for reading the chart. In that case, the operator places the chart discharged from the image forming apparatus 1 (printer unit 2) in the image reading unit 80. Furthermore, devices equivalent to the first and second line sensors 91 and 92 may be installed in the conveyance path of the printer unit 2.

[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) determines 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 determines 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 determined 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 determining 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 the adjustment amount ΔV corresponding to the adjustment value. As will be described later, this adjustment value 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 (secondary transfer voltage storage unit / calculation unit 31f) 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, an 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 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 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 image density is presented based on the luminance information (density information) of the patches 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 secondary transfer voltage setting.

[0056] 6. Charts Next, the chart 100 output in the adjustment mode of this embodiment will be described. In this embodiment, different charts 100 are output depending on the size of the recording material S used to output the chart 100. The length of the recording material S in the conveyance direction of the recording material S is also referred to simply as the "conveyance direction length," and the length of the recording material S in a direction substantially perpendicular to the conveyance direction of the recording material S is also referred to simply 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 the 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 the 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") 100L, 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] The large chart data (also referred to as "L chart data"), which is the image data defining the L chart 100L, 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 100L corresponding to the image data cropped from this L chart data is output according to the size of the recording material S. 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 scanning 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 100L 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 100L includes 11 pairs of blue (B) solid patches 101, black (Bk) solid patches 102, and black halftone (BkHT) patches 103 aligned in the width direction, in the conveyance direction of the recording material S. In this embodiment, the output of the exposure device 42 during non-image formation is 0, and the output of the exposure device 42 during image formation of the Bk solid patch 102 is 255. The output of the exposure device 42 during image formation of the BkHT patch 103 is 128. Note that a solid patch (solid image) is an image with the maximum toner coverage. Furthermore, a halftone (halftone) patch (halftone image) can be formed with a toner coverage of approximately 10 to 80% of the toner coverage of a solid image, typically approximately 40 to 60%. In the L chart 100L in FIG. 6, 100L(1) indicates the first side, and 100L(2) indicates the second side. After passing through the secondary transfer unit N2, the second side passes through the sensing unit 3 without changing its orientation, while the first side passes through the reverse transport path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer unit N2 and when passing through the sensing unit 3. In FIG. 6, the thin arrow indicates the transport direction of the chart when passing through the secondary transfer unit N2, and the thick arrow indicates the transport direction of the chart when passing through the sensing unit 3. In this embodiment, the leading patches of the B solid patch 101, Bk solid patch 102, and BkHT patch 103 when passing through the sensing unit 3 are patches for acquiring position information (also referred to here as "trigger patches") 101T, 102T, and 103T, respectively. These trigger patches 101T, 102T, and 103T are used to accurately detect the positions of the patch rows when read by the first and second line sensors 91 and 92. Of the B solid patch 101, Bk solid patch 102, and BkHT patch 103, the remaining ten patches, excluding trigger patches 101T, 102T, and 103T, are patches for acquiring brightness information (density information) (here, also referred to as "adjustment patches") 101A, 102A, and 103A. A different secondary transfer voltage Vtr is applied to each of the adjustment patches 101A, 102A, and 103A, 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 and 15 mm wide in the transport direction, and the patches are spaced 15 mm apart in the transport direction of the recording material S. Furthermore, on the first side 100L(1) and the second side 100L(2) of the L chart 100L, the patches 101 to 103 are arranged so that they do not overlap on the front and back of the recording material S. This is to avoid the effect of show-through on the detected brightness when read by the first and second line sensors 91 and 92. The effect of show-through on the detected brightness is a concern when the recording material S is thin paper with a small basis weight.

[0061] Figure 7 is a schematic diagram showing a small chart (also called an "S chart") 100S, 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 279.4 mm (the long side of LTR size) or more.

[0062] The small chart data (also referred to as "S chart data"), which is the image data defining the S chart 100S, 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 A4 (landscape feed) or LTR (landscape feed), the S chart 100S corresponding to the 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 fit the size of the recording material S, based on the leading edge in the scanning 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 100S is A4 size (landscape feed) (210 mm long in the transport direction x 297 mm wide), image data of 205 mm long in the transport 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 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.

[0063] The S chart 100S has 12 sets of blue (B) solid patches 101, black (Bk) solid patches 102, and black halftone (BkHT) patches 103 arranged side by side in the width direction across two sheets of recording material S. By using two sheets of recording material S to form the chart, the S chart 100S ensures the same number of patches as the L chart 100L, allowing for equivalent adjustments. In the S chart 100S in FIG. 7, 100S(1-1) indicates the first sheet of the first side, 100S(1-2) indicates the second sheet of the first side, 100S(2-1) indicates the first sheet of the second side, and 100S(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 direction, while the first side passes through the reverse conveyance path 7 once. Therefore, the orientation of the first side is different when it passes through the secondary transfer portion N2 and when it passes through the inside of the sensing unit 3. In FIG. 7, the thin arrow indicates the transport direction of the chart when it passes through the secondary transfer portion N2, and the thick arrow indicates the transport direction of the chart when it passes through the inside of 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, the Bk solid patch 102, and the BkHT patch 103 when they pass through the inside of the sensing unit 3 are trigger patches 101T, 102T, and 103T, respectively, for acquiring position information. These trigger patches 101T, 102T, and 103T are used to accurately detect the positions of the patch rows when they are read by the first and second line sensors 91 and 92. Of the B solid patch 101, Bk solid patch 102, and BkHT patch 103, the remaining 10 patches, excluding trigger patches 101T, 102T, and 103T, are adjustment patches 101A, 102A, and 103A for acquiring luminance information (density information). A different secondary transfer voltage Vtr is applied to each of the adjustment patches 101A, 102A, and 103A, and they are transferred onto the recording material S.

[0064] As described above, in this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm long and 15 mm wide in the transport direction, and the patches are spaced 15 mm apart in the transport direction of the recording material S. Furthermore, on the first side 100S(1-1) and 100S(1-2) of the S chart 100S and the second side 100S(2-1) and 100S(2-2), the patches 101 to 103 are arranged so that they do not overlap on the front and back of the recording material S. This is to avoid the effect of show-through on the detected brightness when the first and second line sensors 91 and 92 read the image. The effect of show-through on the detected brightness is a concern when the recording material S is thin paper with a small basis weight.

[0065] Considering the reading by the first and second line sensors 91 and 92, it is desirable that the size of each patch (especially the adjustment patch) be somewhat large. 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 be reduced. In this embodiment, the patch size in the L chart 100L 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 may be set so that the secondary transfer voltage can be switched.

[0066] 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 10 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.

[0067] 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 279.4 mm or more in width (the long side of LTR size). In this embodiment, as long as the size is larger than this, not only standard sizes but also any size of recording material S can be used by the operator, for example, by inputting and specifying the size through the operation unit 70 or external device 200. Note that 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, etc.

[0068] In this embodiment, when adjusting the secondary transfer voltage for only one side of the recording material S (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 100L, the chart 100L(2) in FIG. 6 is formed on the first side of one sheet of recording material S during the image forming operation for single-sided printing, and output. When outputting the S chart 100S, the charts 100S(2-1) and 100S(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, during the image forming operation for single-sided printing, and output. In other words, when adjusting the secondary transfer voltage for both sides of the recording material S (secondary transfer voltage for the first and second sides during double-sided printing) (also referred to as "double-sided adjustment"), the chart for the second side is output during the image forming operation for single-sided printing without passing through the reverse conveyance 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 conveyance 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.). 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.

[0069] The chart design is not limited to that described in this embodiment. For example, the adjustment patches are not limited to B solid images, Bk solid images, and BkHT images. For example, the solid patches may be either B solid images or Bk solid images, or other single-color solid images, or solid images of other secondary colors or mixed colors (multi-colors), either alone or in combination. The halftone patches are not limited to black, but may be other single-color halftone images, or other halftone images of other secondary colors or mixed colors (multi-colors). The density of the halftone patches is also not limited to that described in this embodiment. The color and density of the patches may be changeable by the user depending on the image to be output. Such changes can be made, for example, from the operation unit 70 or the external device 200. The shape and number of the adjustment patches may also 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. The shape of the trigger patches is also not limited to that described in this embodiment. Also, depending on the chart reading method, a trigger patch may not always be necessary.

[0070] 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.

[0071] 7. Adjustment mode operation Next, the operation of the adjustment mode in this embodiment will be described. Fig. 8 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. The following symbols will be used in the following description.

[0072] 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

[0073] 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. 9 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 be configured to allow 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.

[0074] FIG. 10 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. 10 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. 10, "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 (paper feed unit [1], paper feed unit [2] in FIG. 10), 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, for example, 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.

[0075] FIG. 11 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. 11 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 708a that selects whether the adjustment mode is to be performed on one side or both sides, and the like. The secondary transfer voltage adjustment screen 706 also includes a priority image selection unit 708b that selects the density of the image to be optimized in the adjustment mode, and an adjustment execution button 709 that starts chart formation. As will be described in detail later, in this embodiment, the priority image selection unit 708b allows the user to select a priority image from two options: "halftone" and "solid image." By inputting a value into the adjustment value display section 707, secondary transfer can be performed with the recording material assigned voltage offset from the default recording material assigned 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 into the adjustment value display section 707, with the default value being 0. When 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) of the adjustment value display section 707 corresponds to ΔN=1 with ΔV=150V (i.e., changing the adjustment value N by 1 changes the adjustment amount ΔV by 150V). For example, when 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. When executing the adjustment mode, the operator selects whether to perform double-sided adjustment or single-sided adjustment in the single-sided / double-sided selection area 708a, selects a priority image in the priority image selection area 708b, and then presses (operates) the adjustment execution button 709. The contents entered in the single-sided / double-sided selection area 708a and the priority image selection area 708b are saved in RAM 33. In this way, the contents entered in determining the adjustment conditions (S1) are saved in RAM 33 and are reflected in subsequent processing.

[0076] 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.

[0077] 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.

[0078] Thereafter, the control unit 30 (adjustment processing unit 31d) executes output of the chart (S4). At this time, the control unit 30 (adjustment processing unit 31d) selects a chart according to the size of the recording material S and outputs the selected chart.

[0079] FIG. 12 is a graph showing the transition of the output of the secondary transfer power supply 76 when forming the L chart 100L. FIG. 12(a) shows the first side during double-sided adjustment, and FIG. 12(b) shows the second side during double-sided adjustment. In the case of the first side, ten consecutive adjustment patches 101A-103A are secondarily transferred onto the recording material S, and then trigger patches 101T-103T are secondarily transferred onto the recording material S, respectively. The adjustment patches 101A-103A are arranged in order of increasing adjustment value N from the smallest adjustment value N. Note that the patch numbers of the adjustment patches 101A-103A increase in order as the adjustment value N increases, 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 of the patches 101-103 has passed through the secondary transfer. There is a slight time lag before the output of the secondary transfer power supply 76 switches, but by switching at the above timing, the output of the secondary transfer power supply 76 switches in the margins between each patch. For the second side, the arrangement of the adjustment patches 101A-103A and the trigger patches 101T-103T is reversed compared to 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.

[0080] In this embodiment, the amplitude (change in one step) ΔV (reference numeral 801 in FIG. 12) 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."

[0081] 13(a) to 13(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. 13(a) shows the case where the adjustment value amplitude ΔN=1, FIG. 13(b) shows the case where the adjustment value amplitude ΔN=2, and FIG. 13(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 to 103A 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-103A for n=1-10 do not fall within the adjustment range of ±20. In such cases, the patch corresponding to the current adjustment value N0 is shifted away from n=5 so that all of the adjustment patches 101A-103A for n=1-10 fall within the adjustment range of ±20. This allows all of the adjustment patches 101A-103A to be used effectively.

[0082] In the case of the L chart 100L, when the chart is secondarily transferred to the recording material S, trigger patches 101T to 103T are located on the trailing edge of the first side and the leading edge of the second side. The trigger patches 101T to 103T are used to detect the patch positions when the sensing unit 3 reads the chart. Therefore, the trigger patches 101T to 103T must be transferred at the minimum density required for that purpose. An extremely high or low secondary transfer voltage poses the risk of making it impossible to read the trigger patches 101T to 103T. Therefore, in this embodiment, when the trigger patches 101T to 103T are secondarily transferred to the recording material S, a voltage corresponding to patch number n=5 (the voltage indicated by the dotted line with reference numeral 800 in FIG. 12) is applied. Note that the method for setting the secondary transfer voltage applied when the trigger patches 101T to 103T 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.

[0083] FIG. 14 is a graph showing the transition of the output of the secondary transfer power supply 76 when forming an S chart 100S. FIG. 14(a) shows the first side during double-sided adjustment, and FIG. 14(b) shows the second side during double-sided adjustment. In the case of the S chart 100S, the chart is divided into the first sheet 100S (1-1) of the first side, the second sheet 100S (1-2) of the first side, the first sheet 100S (2-1) of the second side, and the second sheet 100S (2-2) of the second side, and trigger patches 101T to 103T are arranged on each. However, in the case of the S chart 100S, the magnitude and timing of the output of the secondary transfer power supply 76 basically operate in the same way as in the case of the L chart 100L.

[0084] As described above, when the operator selects single-sided adjustment in the single-sided / double-sided selection section 708a on the secondary transfer voltage adjustment screen 706, the following is performed. When outputting the L chart 100L, the chart 100L(2) in FIG. 6 is output. When outputting the S chart 100S, the charts 100S(2-1) and 100S(2-2) in FIG. 7 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.

[0085] When the chart is output, the control unit 30 (adjustment processing unit 31d) first determines whether the high voltage (secondary transfer voltage) is saturated (S5). "Saturation of high voltage" refers to a state in which the secondary transfer voltage Vtr has reached (stuck at) the upper or lower limit of the output voltage of the secondary transfer power supply 76. The secondary transfer power supply 76 has an upper limit for its output voltage, and although this depends on the specifications of the high-voltage power supply, in this embodiment the upper limit for the output voltage (absolute value) of the secondary transfer voltage 76 is 6.5 kV.

[0086] For example, if the outer secondary transfer roller 45b has been used for a long period of time, or if the image forming apparatus 1 is used in a low-temperature, low-humidity environment, the electrical resistance of the secondary transfer section N2 increases, and the secondary transfer partial voltage Vb increases (increases in absolute value). As another example, if the current adjustment value N0 is extremely large, such as +20, adjustment is performed around the current adjustment value N0 = +20, which inevitably increases the secondary transfer voltage Vtr (increases in absolute value). In such a case, the secondary transfer voltage Vtr reaches the output upper limit of the secondary transfer power supply 76, and the secondary transfer voltage cannot be adjusted when the chart is output. If the secondary transfer voltage Vtr for all adjustment patches 101A to 103A (patch numbers, adjustment values) has reached the output upper limit of the secondary transfer power supply 76, adjustment itself is impossible, so the control unit 30 (adjustment processing unit 31d) uses the smallest adjustment value (NA = the smallest N in the chart) is determined (S6). The reason for using the smallest adjustment value is to increase the possibility of selecting an adjustment value that is far from the upper output limit of the secondary transfer power supply 76 when adjustment is performed again. At this time, the control unit 30 (adjustment processor 31d) may also cause the operation unit 70 or the external device 200 to display a message such as "optimal adjustment was not performed" or "check the life of the outer secondary transfer roller." In this way, the control unit 30 (adjustment processor 31d) may perform control to notify the user that the secondary transfer voltage adjustment was not performed appropriately.

[0087] Furthermore, when the image forming apparatus 1 is used in a high-temperature, high-humidity environment, the default recording material distribution voltage Vp is low (small absolute value), and as a result of offsetting the adjustment value to the negative side, the secondary transfer voltage Vtr may become negative. Also, when the current adjustment value N0 is extremely small, such as -20, adjustment is performed around the current adjustment value N0 = -20, which inevitably results in a low secondary transfer voltage Vtr (small absolute value). In the configuration of this embodiment, it is theoretically unlikely that a negative secondary transfer voltage Vtr would be optimal, so in this embodiment, Vtr is limited to 0V or more. If the secondary transfer voltage Vtr for all adjustment patches 101A to 103A (patch numbers, adjustment values) is 0V, the control unit 30 (adjustment processing unit 31d) cannot perform adjustment at all, and therefore, the largest adjustment value (N A(=the largest N in the chart) is determined (S6). The reason for using the largest adjustment value is to increase the possibility of selecting an adjustment value that will result in the secondary transfer voltage Vtr being 0 V or higher when readjusting. At this time, the control unit 30 (adjustment processor 31d) may display a message such as "optimal adjustment was not performed" on the operation unit 70 or the external device 200. In this manner, the control unit 30 (adjustment processor 31d) may perform control to notify the user that the secondary transfer voltage adjustment was not performed appropriately. While the secondary transfer voltage Vtr is limited to 0 V or higher in this embodiment, other limitations may also be imposed. For example, if there is a lower limit value that can be stably applied as the secondary transfer voltage, a value other than 0 V may be used. Furthermore, the recording material distribution voltage Vp may be restricted from becoming negative, and the lower limit of the secondary transfer voltage Vtr may be set to the secondary transfer portion voltage Vb.

[0088] If some or all of the adjustment patches 101A-103A (patch numbers, adjustment values) are not in the "high-voltage saturated" state, the control unit 30 (adjustment processor 31d) proceeds to step S7. In this embodiment, if some of the adjustment patches 101A-103A are in the "high-voltage saturated" state, the control unit 30 (adjustment processor 31d) controls the adjustment values ​​N of those patches so that they are not included in the candidates for the recommended secondary transfer voltage adjustment value N in subsequent processing. This is to prevent secondary transfer from being performed at a recording material distribution voltage Vp that differs from the adjustment value N determined in the adjustment mode when the secondary transfer partial voltage Vb fluctuates. In other words, if the adjustment value N is in the "high-voltage saturated" state, it may be impossible to set an appropriate secondary transfer voltage Vtr if the usage environment, etc., changes.

[0089] Next, the control unit 30 (adjustment processor 31d) determines whether the current is fluctuating correctly (S7). In this embodiment, to make this determination, the control unit 30 (adjustment processor 31d) acquires, using the current detection sensor 76b, the current that flows through the secondary transfer unit N2 when each of the adjustment patches 101A-103A passes through the secondary transfer unit N2 during chart output, and stores the acquired current in the RAM 33. In this embodiment, the method for this determination is as follows.

[0090] I(n): Current of the nth tuning patch α: coefficient where n=1 to 9 I(n+1)≧I(n)×α

[0091] In the above formula, α is a coefficient approximately equal to 1. That is, the control unit 30 (adjustment processor 31d) checks whether the secondary transfer current I(n+1) (absolute value) of the nth adjustment value, which has the larger secondary transfer voltage Vtr, is α times or more greater than the secondary transfer current I(n) (absolute value) of the nth adjustment value. If the above formula is not true, it is likely that the secondary transfer currents of the adjustment patches 101A-103A (patch number, adjustment value) are not properly distributed across the chart. Examples of such cases include when the electrical resistance of the recording material S is uneven across its surface, or when the electrical resistance of the recording material S is so low that current flows through the recording material S to components (such as conveying rollers or guides) that contact the recording material S near the secondary transfer station N2. In such cases, the control unit 30 (adjustment processor 31d) determines that adjustment is difficult and terminates the adjustment mode with the current adjustment value unchanged (S8). In this embodiment, α is set to 1. However, α does not necessarily have to be 1. For example, by setting α to a value greater than 1, adjustment may be performed only when the current is definitely fluctuating. Also, α may have different values ​​for the first and second sides. In particular, α may be less than 1 for the first side, which may have large variations in the amount of moisture within the surface depending on the storage conditions of the recording material S. Furthermore, if the above formula is not satisfied, the control unit 30 (adjustment processing unit 31d) may cause the operation unit 70 to display a message such as "optimal adjustment was not performed" or "the recording material S may not be able to be adjusted." In this way, the control unit 30 (adjustment processing unit 31d) may perform control to notify the user that the secondary transfer voltage adjustment may not have been performed appropriately.

[0092] Once the control unit 30 (adjustment processing unit 31d) has confirmed that the current is fluctuating as intended, it reads the chart using the sensing unit 3 and controls the unit to calculate the brightness and variance of each adjustment patch 101A to 103A as described below (S9).

[0093] 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-103A based on the positions of the trigger patches 101T-103T of the chart as follows. FIG. 15 is a schematic diagram illustrating an example of a method for identifying the positions of the trigger patches 101T-103T from the image 110 read by the first and second line sensors 91 and 92. An L chart 100L(2) is used as an example. First, a line 112 located in the margin between the edge 111 of the chart (recording material S) and the trigger patches 101T-103T in the conveyance direction of the recording material S as it passes through the sensing unit 3 is roughly set. The average luminance value of line 112 is then read from the read chart information. 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 to 103T. If it is not determined to be an edge, the process repeats for each line toward the upstream side in the conveyance direction of the recording material S as it passes through the sensing unit 3, and an edge line 113 is found. Next, a line 114 located in the margin between the edge 111 of the chart (recording material S) and the trigger patch 103T in the width direction is set based on a rough positional relationship. The average luminance value of line 114 is then read from the read chart information. 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 patch 103T. If it is not determined to be an edge, the process repeats for each line toward the right side in the width direction in FIG. 15, and an edge line 115 is found. 15 is the right side when the surface of the recording material S facing the first and second line sensors 91 and 92 is viewed with the leading edge of the recording material S facing up in the conveyance direction as it passes through the inside of the sensing unit 3. Note that similar edge detection is performed in the width direction between trigger patches 103T and 102T, and between 102T and 101T.The above edge detection method makes it possible to detect the positions of the trigger patches 101T to 103T in the image 110. Note that the above edge detection method is an example, and the edge detection method 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.

[0094] Once the control unit 30 (adjustment processing unit 31d) has identified the position of each of the adjustment patches 101A-103A, it calculates the average brightness value and variance value of each of the adjustment patches 101A-103A and stores them in RAM 33. That is, for the nth adjustment patch, the average brightness value and variance value calculated using the following formulas are stored in RAM 33.

[0095]

number

[0096] In this embodiment, B(m) is detected as a signal value ranging from low brightness 0 to high brightness 255. The average brightness is a parameter that reflects density (i.e., correlates with density) (the lower the brightness, the higher the density). Furthermore, the inventors' studies have revealed that the variance is a parameter that is sensitive to transferability when the recording material S has unevenness. The smaller the average brightness and variance, the better the transferability. In this embodiment, a method for determining the recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) for the secondary transfer voltage setting using the average brightness will be mainly described, but the variance may also be used, as described below. Note that if only one of the average brightness and variance is used, the calculation of the other value does not need to be performed.

[0097] In this embodiment, the brightness read from the information of the image read by the sensing unit 3 is B (blue) brightness for the B solid patch 101, and G (green) brightness for the Bk solid patch 102 and the BkHT patch 103. 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.

[0098] 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.

[0099] Next, the control unit 30 (adjustment processor 31d) uses the calculated average luminance value and variance value (particularly the average luminance value in this embodiment) to select a patch (patch number, adjustment value) with good transferability. In this embodiment, at this time, the control unit 30 (adjustment processor 31d) refers to the input result of the priority image selector 708b stored in RAM 33 (S10). In this embodiment, specifically, in S10, it is determined whether or not the halftone priority mode has been selected.

[0100] In other words, as mentioned above, generally, the higher the density of the toner image to be transferred, the larger the absolute value of the secondary transfer voltage required. However, when using a recording material S with difficult transfer characteristics, it may be difficult to transfer images ranging from halftones to solid images satisfactorily with a single secondary transfer voltage. An example of a recording material S with difficult transfer characteristics is embossed paper, which has a more uneven surface than plain paper. With embossed paper, the depressions in the paper surface tend to create gaps between the intermediate transfer belt 44b and the paper surface at the secondary transfer section N2. When the secondary transfer voltage is high (high in absolute value), the discharge in these gaps tends to reduce image density. This effect can be more pronounced in halftone images, which have a lower toner load than solid images. Therefore, if such recording materials S are frequently used to output halftone images, adjusting the secondary transfer voltage to improve the transfer characteristics of solid images may result in undesirable results. Therefore, in this embodiment, the secondary transfer voltage is adjusted according to the priority image selected by the priority image selection unit 708b.

[0101] When "halftone" is selected in the priority image selection unit 708b, the control unit 30 (adjustment processing unit 31d) performs adjustment in "halftone priority mode" and selects adjustment values ​​that optimize the transferability of halftone toner images. When "solid image" is selected in the priority image selection unit 708b, the control unit 30 (adjustment processing unit 31d) performs adjustment in "solid image priority mode" and selects adjustment values ​​that optimize the transferability of high-density toner images such as solid images. In the following description of the process for selecting patches with good transferability, the B solid patch 101, Bk solid patch 102, and BkHT patch are assumed to be adjustment patches 101A, 102A, and 103A, respectively.

[0102] The halftone priority mode will now be described. FIG. 16 is a graph illustrating the process of selecting patches with good transferability in the halftone priority mode. FIG. 16(a) shows an example of the average luminance value obtained for each patch number of the BkHT patches 103. FIG. 16(b) shows an example of the average luminance value obtained for each patch number of the Bk solid patches 102. FIG. 16(c) shows an example of the average luminance value obtained for each patch number of the B solid patches 101. In the halftone priority mode, the control unit 30 (adjustment processor 31d) first narrows down the adjustment values ​​for the BkHT patches 103 (S11). As shown in FIG. 16(a), in this embodiment, in S11, the patch numbers are narrowed down to those equal to or less than the value (threshold L1) obtained by multiplying the lowest average luminance value by a coefficient of 1.2. In the illustrated example, the patch numbers are narrowed down to patch numbers 1 to 5. Next, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​for the Bk solid patches 102 (S12). As shown in FIG. 16(b), in this embodiment, in S12, the patch numbers narrowed down in S11 are narrowed down to patch numbers equal to or less than the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L2). In the example shown, patch numbers 1 to 5 narrowed down in S11 are narrowed down to patch numbers 3 to 5. Finally, the control unit 30 (adjustment processor 31d) narrows down the adjustment value using the B solid patch 101 (S13). As shown in FIG. 16(c), in this embodiment, in S13, the patch number with the lowest average luminance value is selected from the patch numbers narrowed down in S11 and S12. In the example shown, patch number 5 is selected from patch numbers 3 to 5 narrowed down in S11 and S12. Then, the control unit 30 (adjustment processor 31d) narrows down this patch number 5(n A ) is the recommended adjustment value (N A ) (S16).

[0103] The solid image priority mode will now be described. FIG. 17 is a graph illustrating the process of selecting patches with good transferability in the solid image priority mode. FIG. 17(a) shows an example of the average luminance value obtained for each patch number of the BkHT patches 103. FIG. 17(b) shows an example of the average luminance value obtained for each patch number of the Bk solid patches 102. FIG. 17(c) shows an example of the average luminance value obtained for each patch number of the B solid patches 101. The average luminance values ​​shown in FIGS. 17(a), (b), and (c) are assumed to be the same as the average luminance values ​​shown in FIGS. 16(a), (b), and (c). In the solid image priority mode, the control unit 30 (adjustment processing unit 31d) does not narrow down the adjustment values ​​using the BkHT patches 103, but narrows down the adjustment values ​​using the Bk solid patches 102 (S14). As shown in FIG. 17(b), in this embodiment, in S14, the patch numbers are narrowed down to those equal to or less than the lowest average luminance value multiplied by a coefficient of 1.2 (threshold L2). In the example shown, the patch numbers are narrowed down to patch numbers 3 to 8. Next, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​using the B solid patch 101 (S15). As shown in FIG. 17(c), in this embodiment, in S15, the patch number with the lowest average luminance value is selected from the patch numbers narrowed down in S14. In the example shown, patch number 8 is selected from patch numbers 3 to 8 narrowed down in S14. Then, the control unit 30 (adjustment processor 31d) narrows down this patch number 8 (n A ) is the recommended adjustment value (N A ) (S16).

[0104] In this way, the adjustment value N selected in the halftone priority mode and the solid image priority mode is A This is due to the difference in whether narrowing down is performed using the BkHT patch 103 or not, and the halftone priority mode, which has narrowed down the settings, is able to select an adjustment value with a lower secondary transfer voltage (smaller absolute value).

[0105] Note that, in both the BkHT patch 103 and the Bk solid patch 102 narrowing down, the coefficient values ​​are not limited to the above numerical values, and the narrowing down method is not limited to the above method. For example, a method of pre-storing a brightness tolerance value in the ROM 32 or a method of extracting a certain number of patch numbers in ascending order of average brightness value is conceivable. In this embodiment, the transferability is determined using the average brightness value, but it may also be determined using a variance value. Transferability may also be determined using both the average brightness value and the variance value. The variance value is effective for detecting density unevenness within a patch. For example, when narrowing down the adjustment values ​​using solid patches, in addition to narrowing down using the average brightness value (e.g., extracting a certain number of patch numbers in descending order of average brightness value), narrowing down using the variance value (e.g., selecting the patch number with the smallest variance value) may be performed. Furthermore, depending on the conditions of the image forming apparatus 1 and the recording material S during adjustment, it is possible that the adjustment results for the prioritized image will not differ.

[0106] The control unit 30 (adjustment processor 31d) calculates the adjustment value N selected as above. A 11 on the display unit 70a of the operation unit 70 (S17). 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) or the like of the operation unit 70 to input the value into the adjustment value display unit 707, and then operates 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) (S18). 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 operator operates the confirmation unit 710 without changing the adjustment value, the control unit 30 (adjustment processor 31d) stores the adjustment value determined by the control unit 30 in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S18). This ends the adjustment mode.

[0107] As described above, in this embodiment, the image forming apparatus 1 includes the image carrier 44b that carries a toner image, transfer means 45b that transfers the toner image from the image carrier 44b to the recording material S at the transfer section N2, application means 76 that applies a transfer voltage to the transfer means 45b, an execution unit (in this embodiment, the adjustment processor 31d of the control unit 30) that controls to execute an output mode in which a chart 100 is formed by transferring a plurality of test images onto the recording material S using different transfer voltages, an acquisition unit 3 that acquires density information related to the density of the test images on the recording material, a setting unit (in this embodiment, the adjustment processor 31d and secondary transfer voltage storage unit / calculation unit 31f of the control unit 30) that sets the transfer voltage based on the density information acquired by the acquisition unit 3, and an input unit (in this embodiment, the adjustment processor 31d and secondary transfer voltage storage unit / calculation unit 31f of the control unit 30) that inputs instruction information. In the embodiment, the control unit 31 has an operation unit 70), and the execution unit 31d is capable of controlling the transfer of a plurality of first test images having a first density on the image carrier to the recording material S, and is also capable of controlling the transfer of a plurality of second test images having a second density on the image carrier that is higher than the first density to the recording material S, and the setting unit 30 is capable of setting the first transfer voltage using density information of at least the first test image of the first and second test images (halftone priority) according to instruction information input by the input unit 70, or setting the second transfer voltage using density information of at least the second test image of the first and second test images without using density information of the first test image of the first test image (solid image priority).

[0108] In this embodiment, the setting unit 30 sets the first transfer voltage using density information of the first test image and the second test image. More specifically, in this embodiment, the setting unit 30 sets the first transfer voltage based on information regarding the transfer voltage when a first test image, of the plurality of first test images, whose density information satisfies a predetermined condition, is transferred onto the recording material S, and the transfer voltage when a second test image, of the plurality of second test images, whose density information satisfies a predetermined condition, is transferred onto the recording material S. In this embodiment, the absolute value of the second transfer voltage is equal to or greater than the absolute value of the first transfer voltage. Also, in this embodiment, the setting unit 30 sets the second transfer voltage based on information regarding the transfer voltage when a second test image, of the plurality of second test images, whose density information satisfies a predetermined condition, is transferred onto the recording material S. Also, in this embodiment, the execution unit 31d controls the chart 100 formed by transferring the first test image and the second test image onto the recording material S to be output. The execution unit 31d may be controllable to execute a first output mode in which only the first test image of the first and second test images is transferred onto the recording material S to output the chart 100, or to execute a second output mode in which only the second test image of the first and second test images is transferred onto the recording material S to output the chart 100, in accordance with instruction information input by the input unit 70. In this embodiment, the first test image is a halftone image, and the second test image is a solid image. In this embodiment, the acquisition unit 3 acquires density information of the test image on the recording material when the recording material S on which the chart has been formed is discharged from the image forming apparatus 1.

[0109] As described above, according to this embodiment, the priority image (halftone priority, solid image priority) selected by the user in the adjustment mode can be reflected in the adjustment value. Therefore, according to this embodiment, the secondary transfer voltage can be appropriately adjusted for the image prioritized by the user.

[0110] [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.

[0111] The operation of the adjustment mode in this embodiment will be described. Fig. 18 is a flowchart showing an outline of the procedure of the adjustment mode in this embodiment. In Fig. 18, the same processes as those in the adjustment mode in embodiment 1 shown in Fig. 8 are given the same step numbers as in Fig. 8, and detailed explanations will be omitted as appropriate. In embodiment 1, there were two levels of options for the prioritized image, but in this embodiment, there are three levels of options for the prioritized image.

[0112] 19 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 in this embodiment. In this embodiment, the secondary transfer voltage adjustment screen 706 differs from embodiment 1 in that a priority image selection section 708c is used to select the density of an image to be optimized in the adjustment mode. In this embodiment, the priority image selection section 708c allows the user to select a priority image from three options: "low density halftone," "high density halftone," and "solid image." The content input in determining the adjustment conditions (S1) is saved in RAM 33 and reflected in subsequent processing.

[0113] The low-density halftone priority mode will now be described. FIG. 20 is a graph illustrating the process of selecting patches with good transferability in the low-density halftone priority mode. FIG. 20(a) shows an example of the average luminance value obtained for each patch number of the BkHT patch 103. FIG. 20(b) shows an example of the average luminance value obtained for each patch number of the Bk solid patch 102. FIG. 20(c) shows an example of the average luminance value obtained for each patch number of the B solid patch 101. In the low-density halftone priority mode, the control unit 30 (adjustment processing unit 31d) first narrows down the adjustment values ​​for the BkHT patch 103 (S21). As shown in FIG. 20(a), in this embodiment, in S21, the patch numbers are narrowed down to those equal to or less than the value (threshold L3) obtained by multiplying the lowest average luminance value by a coefficient of 1.1. In the illustrated example, patch numbers 1 to 4 are narrowed down. Next, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​using the Bk solid patch 102 (S22). As shown in FIG. 20(b), in this embodiment, in S22, the patch numbers narrowed down in S21 are narrowed down to patch numbers equal to or less than the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L4). In the example shown, patch numbers 1 to 4 narrowed down in S21 are narrowed down to patch numbers 3 to 4. Finally, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​using the B solid patch 101 (S23). As shown in FIG. 20(c), in this embodiment, in S23, the patch number with the lowest average luminance value is selected from the patch numbers narrowed down in S21 and S22. In the example shown, patch number 4 is selected from patch numbers 3 to 4 narrowed down in S21 and S22. Then, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​using the B solid patch 101. A ) is the recommended adjustment value (N A ) (S16).

[0114] The high-density halftone priority mode will now be described. FIG. 21 is a graph illustrating the process of selecting patches with good transferability in the high-density halftone priority mode. FIG. 21(a) shows an example of the average luminance value obtained for each patch number of the BkHT patch 103. FIG. 21(b) shows an example of the average luminance value obtained for each patch number of the Bk solid patch 102. FIG. 21(c) shows an example of the average luminance value obtained for each patch number of the B solid patch 101. The average luminance values ​​shown in FIGS. 21(a), (b), and (c) are assumed to be the same as those shown in FIGS. 20(a), (b), and (c). Even in the high-density halftone priority mode, the control unit 30 (adjustment processor 31d) first narrows down the adjustment values ​​for the BkHT patch 103 (S24). As shown in FIG. 21(a), in this embodiment, in S24, the patch numbers are narrowed down to those equal to or less than the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L3'). As described above, the coefficient used to narrow down the BkHT patch 103 in the high-density halftone priority mode is different from the coefficient used to narrow down the BkHT patch 103 in the low-density halftone priority mode. This coefficient in the high-density halftone priority mode is larger than this coefficient in the low-density halftone priority mode. In other words, narrowing down the adjustment values ​​using the BkHT patch 103 in the high-density halftone priority mode is more lenient than narrowing down the adjustment values ​​using the BkHT patch 103 in the low-density halftone priority mode. In the illustrated example, patch numbers 1 to 5 are narrowed down. Next, the control unit 30 (adjustment processing unit 31d) narrows down the adjustment values ​​using the Bk solid patch 102 (S25). As shown in FIG. 21(b), in this embodiment, in S25, patch numbers narrowed down in S24 to patch numbers equal to or less than the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L4). In the illustrated example, patch numbers 1 to 5 narrowed down in S24 to patch numbers 3 to 5. Finally, the control unit 30 (adjustment processing unit 31d) narrows down the adjustment values ​​using the B solid patch 101 (S26). As shown in Fig. 21(c) in this embodiment, in S26, the patch number with the lowest average luminance value is selected from the patch numbers narrowed down in S24 and S25.In the illustrated example, patch number 5 is selected from patch numbers 3 to 5 narrowed down in steps S24 and S25. Then, the control unit 30 (adjustment processing unit 31d) selects patch number 5(n. A ) is the recommended adjustment value (N A ) (S16).

[0115] The solid image priority mode will now be described. FIG. 22 is a graph illustrating the process of selecting patches with good transferability in the solid image priority mode. FIG. 22(a) shows an example of the results of acquiring the average luminance value for each patch number of the BkHT patches 103. FIG. 22(b) shows an example of the results of acquiring the average luminance value for each patch number of the Bk solid patches 102. FIG. 22(c) shows an example of the results of acquiring the average luminance value for each patch number of the B solid patches 101. The average luminance values ​​shown in FIGS. 22(a), (b), and (c) are assumed to be the same as the average luminance values ​​shown in FIGS. 20(a), (b), and (c). In the solid image priority mode, the control unit 30 (adjustment processing unit 31d) does not narrow down the adjustment values ​​using the BkHT patches 103, but narrows down the adjustment values ​​using the Bk solid patches 102 (S27). As shown in FIG. 22(b), in this embodiment, in S27, the patch numbers are narrowed down to those equal to or less than the lowest average luminance value multiplied by a coefficient of 1.2 (threshold L4). In the example shown, the patch numbers are narrowed down to patch numbers 3 to 8. Next, the control unit 30 (adjustment processor 31d) narrows down the adjustment value using the B solid patch 101 (S28). As shown in FIG. 22(c), in this embodiment, in S28, the patch number with the lowest average luminance value is selected from the patch numbers narrowed down in S27. In the example shown, patch number 8 is selected from patch numbers 3 to 8 narrowed down in S27. Then, the control unit 30 (adjustment processor 31d) narrows down this patch number 8 (n A ) is the recommended adjustment value (N A ) (S16).

[0116] In this way, the adjustment values ​​selected in the low density halftone priority mode, the high density halftone priority mode, and the solid image priority mode are N A This is due to the difference in whether narrowing down is performed using the BkHT patch 103 or the difference in the degree of narrowing down, and the mode that prioritizes low density can select an adjustment value with a lower secondary transfer voltage (smaller absolute value).

[0117] Note that, whether narrowing down the number of patches using the BkHT patch 103 or the Bk solid patch 102, the coefficient values ​​are not limited to the above numerical values, and the narrowing down method is not limited to the above method. For example, a method of pre-storing brightness tolerance values ​​in ROM 32 or a method of extracting a certain number of patch numbers in ascending order of average brightness value is conceivable. Furthermore, the adjustment value between the low-density halftone priority mode and the solid image priority mode may be set to the high-density halftone priority mode. Furthermore, in this embodiment, the transferability is determined using the average brightness value, but it may also be determined using the variance value. It is also possible to determine the transferability using both the average brightness value and the variance value. Furthermore, depending on the conditions of the image forming apparatus 1 and the recording material S during adjustment, there may be no difference in the adjustment results depending on the prioritized image.

[0118] Thus, in this embodiment, depending on the instruction information input by the input unit 70, the setting unit 30 can set the first transfer voltage using the density information of at least the first test image of the first and second test images (priority on low-density halftones), set the second transfer voltage using the density information of at least the second test image of the first and second test images without using the density information of the first test image of the first and second test images (priority on solid images), or set the third transfer voltage using the density information of at least the first test image of the first and second test images (priority on high-density halftones). In this embodiment, the setting unit 30 is configured to set the first transfer voltage and the third transfer voltage using density information of the first test image and the second test image. The first transfer voltage is set based on information regarding the transfer voltage when a first test image, of the plurality of first test images whose density information satisfies a predetermined first condition, is transferred to the recording material S, and the second test image, of the plurality of second test images whose density information satisfies the predetermined condition, is transferred to the recording material S. The third transfer voltage is set based on information regarding the transfer voltage when a first test image, of the plurality of first test images whose density information satisfies a predetermined second condition different from the first condition, is transferred to the recording material S, and the second test image, of the plurality of second test images whose density information satisfies the predetermined condition, is transferred to the recording material S. In this embodiment, the absolute value of the third transfer voltage is equal to or greater than the absolute value of the first transfer voltage, and the absolute value of the second transfer voltage is equal to or greater than the absolute value of the third transfer voltage.

[0119] As described above, according to this embodiment, in the adjustment mode, the priority image selected by the user (low-density halftone priority, high-density halftone priority, solid image priority) can be reflected in the adjustment value. Therefore, according to this embodiment, the secondary transfer voltage can be appropriately adjusted for the image prioritized by the user.

[0120] [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.

[0121] The operation of the adjustment mode in this embodiment will be described. Fig. 23 is a flowchart showing an outline of the procedure of the adjustment mode in this embodiment. In Fig. 23, the same steps as those in the adjustment mode in embodiment 1 shown in Fig. 8 are given the same step numbers as in Fig. 8, and detailed explanations will be omitted as appropriate. In embodiment 1, the chart formed in the adjustment mode was the same regardless of the prioritized image, but in this embodiment, the chart formed in the adjustment mode is changed depending on the prioritized image.

[0122] 24 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 in this embodiment. In this embodiment, the secondary transfer voltage adjustment screen 706 differs from embodiment 1 in that a priority image selection unit 708d for selecting the density of an image to be optimized in the adjustment mode is provided. In this embodiment, the priority image selection unit 708d allows the user to select a priority image from two options: "low density" and "high density." The content input in determining the adjustment conditions (S1) is saved in RAM 33 and is reflected in subsequent processing.

[0123] In this embodiment, after ATVC control (S3), the control unit 30 (adjustment processor 31d) first refers to the input result from the priority image selector 708d (S31). Specifically, in this embodiment, in S31, it is determined whether or not the low-density priority mode is selected. If "low density" is selected in the priority image selector 708b, the control unit 30 (adjustment processor 31d) performs adjustment in the "low-density priority mode." If "high density" is selected, the control unit 30 (adjustment processor 31d) performs adjustment in the "high-density priority mode." In this embodiment, the control unit 30 (adjustment processor 31d) changes the density of the BkHT patch 103 according to the prioritized image (S32, S33). That is, in this embodiment, the control unit 30 (adjustment processor 31d) sets the density of the BkHT patch 103 to a light intermediate tone in the "low-density priority mode" (S32). In this embodiment, when the output of the exposure device 42 during non-image formation is set to 0 and the output of the exposure device 42 during image formation of the Bk solid patch 102 is set to 255, the output of the exposure device 42 during image formation of the BkHT patch 103 in the "low density priority mode" is set to 96. On the other hand, the control unit 30 (adjustment processor 31d) sets the density of the BkHT patch 103 to a dark intermediate tone in the "high density priority mode" (S33). In this embodiment, when the output of the exposure device 42 during non-image formation is set to 0 and the output of the exposure device 42 during image formation of the Bk solid patch 102 is set to 255, the output of the exposure device 42 during image formation of the BkHT patch 103 in the "high density priority mode" is set to 192. As described above, the control unit 30 (adjustment processor 31d) sets the density of the BkHT patch 103 according to the prioritized image and outputs the chart (S4). The arrangement of the patches on the chart is the same as in the first embodiment. The processes from S5 to S9 are also the same as in the first embodiment.

[0124] After S9, the control unit 30 (adjustment processing unit 31d) enters the process of selecting a patch with good transferability. In this embodiment, the narrowing down conditions for the adjustment value in the BkHT patch 103 are not changed depending on the image to be prioritized. In other words, the transferability is confirmed by the BkHT patch 103 (S34), the transferability is confirmed by the Bk solid patch (S35), the transferability is confirmed by the B solid patch (S36), and the adjustment value N AThe determination of (S16) is performed in the same way regardless of the prioritized image. In this embodiment, the density of the BkHT patch 103 itself differs depending on the prioritized image, so even if the narrowing down conditions are not changed in this way, differences occur in the narrowing down results.

[0125] An example of adjustment in low-density priority mode will be described. FIG. 25 is a graph illustrating the process of selecting patches with good transferability in low-density priority mode. FIG. 25(a) shows an example of the results of acquiring average luminance values ​​for each patch number of the BkHT patches 103. FIG. 25(b) shows an example of the results of acquiring average luminance values ​​for each patch number of the Bk solid patches 102. FIG. 25(c) shows an example of the results of acquiring average luminance values ​​for each patch number of the B solid patches 101. The control unit 30 (adjustment processor 31d) first narrows down the adjustment values ​​for the BkHT patches 103 (S34). As shown in FIG. 25(a), in this embodiment, in S34, the patch numbers are narrowed down to those equal to or less than the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L5). In the illustrated example, the patch numbers are narrowed down to patch numbers 1 to 4. Next, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​for the Bk solid patches 102 (S35). As shown in FIG. 25(b), in this embodiment, in S35, the patch numbers narrowed down in S34 are narrowed down to patch numbers equal to or less than the lowest average luminance value multiplied by a coefficient of 1.2 (threshold L6). In the illustrated example, patch numbers 1 to 4 narrowed down in S34 are narrowed down to patch numbers 3 to 4. Finally, the control unit 30 (adjustment processor 31d) narrows down the adjustment value using the B solid patch 101 (S36). As shown in FIG. 25(c), in this embodiment, in S36, the patch number with the lowest average luminance value is selected from the patch numbers narrowed down in S34 and S35. In the illustrated example, patch number 4 is selected from patch numbers 3 to 4 narrowed down in S34 and S35. Then, the control unit 30 (adjustment processor 31d) narrows down this patch number 4 (n A ) is the recommended adjustment value (N A ) (S16).

[0126] An example of adjustment in high-density priority mode will be described. FIG. 26 is a graph illustrating the process of selecting patches with good transferability in high-density priority mode. FIG. 26(a) shows an example of the results of acquiring average luminance values ​​for each patch number of the BkHT patches 103. FIG. 26(b) shows an example of the results of acquiring average luminance values ​​for each patch number of the Bk solid patches 102. FIG. 26(c) shows an example of the results of acquiring average luminance values ​​for each patch number of the B solid patches 101. The control unit 30 (adjustment processing unit 31d) first narrows down the adjustment values ​​using the BkHT patches 103 (S34). Compared to the average luminance values ​​of the BkHT patches 103 in the high-density priority mode shown in FIG. 26(a) and those in the low-density priority mode shown in FIG. 25(a), patch numbers with low luminance (good transferability, high density) have shifted to the higher voltage side. As shown in FIG. 26(a), in this embodiment, in S34, the patch numbers are narrowed down to those equal to or less than the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L5'). In the illustrated example, the patch numbers are narrowed down to 1 to 6. Next, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​using the Bk solid patch 102 (S35). As shown in FIG. 26(b), in this embodiment, in S35, the patch numbers narrowed down in S34 are narrowed down to those equal to or less than the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L6). In the illustrated example, the patch numbers 1 to 6 narrowed down in S34 are narrowed down to patch numbers 3 to 6. Finally, the control unit 30 (adjustment processor 31d) narrows down the adjustment values ​​using the B solid patch 101 (S36). As shown in FIG. 26(c), in this embodiment, in S36, the patch number with the lowest average luminance value is selected from the patch numbers narrowed down in S34 and S35. In the illustrated example, patch number 6 is selected from patch numbers 3 to 6 narrowed down in S34 and S35. Then, the control unit 30 (adjustment processing unit 31d) selects this patch number 6 (n A ) is the recommended adjustment value (N A ) (S16).

[0127] In this way, the adjustment value selected in the low density priority mode and the high density priority mode is N A This is due to the difference in density of the BkHT patch 103 used for adjustment, and the mode that prioritizes low density can select an adjustment value with a lower secondary transfer voltage (smaller absolute value).

[0128] The density of the BkHT patch 103 is not limited to the above numerical values, and may be directly specified by the user or may be changeable depending on the image that the user actually outputs. Such changes may be made, for example, from the operation unit 70 or the external device 200. In addition, in this embodiment, the transferability is determined using the average luminance value, but it may also be determined using the variance value. It may also be determined using both the average luminance value and the variance value. Furthermore, depending on the conditions of the image forming apparatus 1 and the recording material S at the time of adjustment, it is possible that no difference will be made in the adjustment results depending on the prioritized image.

[0129] Thus, in this embodiment, in addition to the first test image and second test image described above, the execution unit 31d can control the transfer of multiple third test images, each having a third density on the image carrier that is higher than the second density, onto the recording material S, and the setting unit 30 sets the first transfer voltage using density information of the first test image and the third test image (prioritizing low density), and sets the second transfer voltage using density information of the second test image and the third test image (prioritizing high density). More specifically, in this embodiment, the setting unit 30 sets the first transfer voltage based on information regarding the transfer voltage when a first test image, of the plurality of first test images, whose density information satisfies a predetermined condition, is transferred onto the recording material S, and the setting unit 30 sets the second transfer voltage based on information regarding the transfer voltage when a third test image, of the plurality of third test images, whose density information satisfies a predetermined condition, is transferred onto the recording material S. In this embodiment, the absolute value of the second transfer voltage is equal to or greater than the absolute value of the first transfer voltage. In this embodiment, the execution unit 31d can be controlled, in accordance with instruction information input by the input unit 70, to execute a first output mode in which only the first and third test images of the first, second, and third test images are transferred onto the recording material S to output a chart 100 formed thereon, or to execute a second output mode in which only the second and third test images of the first, second, and third test images are transferred onto the recording material S to output a chart 100 formed thereon. In this embodiment, the first and second test images are halftone images, and the third test image is a solid image.

[0130] As described above, according to this embodiment, in the adjustment mode, the priority image (low density priority, high density priority) selected by the user can be reflected in the adjustment value. Therefore, according to this embodiment, the secondary transfer voltage can be appropriately adjusted for the image prioritized by the user.

[0131] [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.

[0132] 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.

[0133] In the above-described embodiment, the control unit determines the adjustment amount (adjustment value) of the secondary transfer voltage for any one selected priority image in a single adjustment mode. Alternatively, the control unit may determine and store the adjustment amounts (adjustment values) of the secondary transfer voltage for multiple (or all) of the priority image options in a single adjustment mode. Before or after the multiple adjustment amounts (adjustment values) are determined and stored in this manner, the operator can select a priority image in the same manner as in the above-described embodiment. The control unit can then set the secondary transfer voltage using one of the stored adjustment amounts (adjustment values) that corresponds to the priority image selected by the operator.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] In the above-described embodiment, the chart was read using inline image sensors (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 into 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 recording material. Furthermore, for example, the chart output in the adjustment mode may be read by an image reading unit prepared separately from the image forming apparatus 1. In this case, information on the read image, luminance information (density information) of the read patch, or information on the adjustment value (adjustment amount) selected based on the information and processed by an external device can be input to the image forming apparatus 1. This information can 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.

[0138] 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.

[0139] 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]

[0140] 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 80 Image reading unit 91 First line sensor 92 Second line sensor 100 Charts 100L Large Chart (L Chart) 100S Small Chart (S Chart) 101 B Solid Patch 102 Black solid patch 103 BkHT patch 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; an application unit that applies a voltage to the transfer device; a detection unit that detects density information relating to the density of an image on a recording material to which the image is transferred by the transfer device; a control unit that executes an operation of a setting mode in which, during non-image formation, a plurality of test images are transferred onto a recording material by applying a plurality of different test voltages to the transfer device, and a transfer voltage to be applied to the transfer device during image formation is set based on a detection result of the test images transferred onto the recording material, detected by the detection unit; A reception unit that receives instruction information; having When an operation of the setting mode is executed to set the transfer voltage in a single-sided mode for forming an image on one side of a predetermined recording material, the reception unit is capable of receiving the instruction information for selectively specifying a mode to be executed from a plurality of modes including a first setting mode in which the transfer voltage set in the setting mode satisfies a first predetermined condition, and a second setting mode in which the transfer voltage set in the setting mode satisfies a second predetermined condition different from the first predetermined condition, the test images include a plurality of first test images having a first density on a recording material and a plurality of second test images having a second density on a recording material, the second density being higher than the first density; An image forming apparatus, characterized in that the first specified condition includes a first condition regarding the plurality of first test images, and the second specified condition includes a second condition regarding the plurality of first test images, the second condition being different from the first condition.

2. An image forming apparatus as described in claim 1, characterized in that in the first setting mode, the transfer voltage is set to prioritize the transferability of an image of a first density, and in the second setting mode, the transfer voltage is set to prioritize the transferability of an image of a second density higher than the first density.

3. In a case where the transfer voltage can be set so as to satisfy that an image density after the plurality of first test images are transferred is equal to or greater than a first threshold value, and an image density after the plurality of second test images are transferred is equal to or greater than a second threshold value, When the first setting mode is selected, the transfer voltage is set so that the image density after the plurality of first test images are transferred is equal to or greater than the first threshold value, and the transfer voltage is set so that the image density after the plurality of second test images are transferred is equal to or greater than the second threshold value, 2. The image forming apparatus according to claim 1, characterized in that, when the second setting mode is selected, the transfer voltage is set so that the image density after the multiple first test images are transferred is less than the first threshold value, and the transfer voltage is set so that the image density after the multiple second test images are transferred is greater than or equal to the second threshold value.

4. An image forming apparatus as described in claim 1, characterized in that the transfer voltage set in the second setting mode is equal to or higher than the transfer voltage set in the first setting mode.

5. The image forming apparatus of claim 3, characterized in that the first test image is a halftone image, and the second test image is a solid image.

Images