Image forming device

Abstract

To prevent the occurrence of "break through" in a configuration including an adjustment mode for adjusting the settings of transfer voltage based on a result of detection of the density of test images on a chart.SOLUTION: An image forming apparatus 1 has: an image carrier 44b; a transfer member 45b; an application unit 76 that applies voltage to the transfer member 45b; an execution unit 30 that executes an output operation to output a chart 100 formed by applying, with the application unit 76, a plurality of test voltages to the transfer member 75b and transferring a plurality of test images to a recording material S; a density acquisition unit 80 that acquires density information on the density of the test images on the chart 100; environment acquisition units 71, 72 that acquire environment information on at least either one of the temperature or the humidity of an environment; and a setting unit 30 that sets a transfer voltage. The setting unit 30 can set the transfer voltage based on the density information and the environment information.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 other methods, a toner image formed on an image carrier such as a photoreceptor or intermediate transfer member is transferred to a recording material. The 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. In image forming apparatuses using the intermediate transfer method, a toner image formed on a first image carrier is first transferred onto a second image carrier, and then secondarily transferred onto the recording material.

[0003] The transfer voltage can be determined based on a transfer portion 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 recording material type. 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, etc.

[0004] 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 image forming apparatus with an adjustment mode that adjusts the set transfer voltage depending on the recording material actually used in image formation.

[0005] Patent Document 1 proposes an image forming apparatus equipped with an adjustment mode for adjusting the set voltage of the secondary transfer voltage. In this adjustment mode, a chart in which multiple patches (test images) are formed on a single sheet of recording material is output with the secondary transfer voltage switched for each patch. Then, the image density of each patch is detected, and the optimal secondary transfer voltage conditions are selected based on the detection results. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-37185 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it has been found that the above-mentioned conventional image forming apparatus has the following problems.

[0008] When the recording material is subjected to discharge during transfer, the toner in the discharged areas is not transferred, resulting in spot-like blank areas (hereinafter referred to as "punch-through"). This image defect is easily apparent in halftone images. However, it is difficult to distinguish the difference between the occurrence of "punch-through" and the absence of "punch-through" in terms of image density. For this reason, in the adjustment mode, the secondary transfer voltage may be adjusted higher even when "punch-through" is occurring. "Punch-through" is particularly likely to occur in low-humidity environments where discharge is likely to occur.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to suppress the occurrence of "punch-through" in a configuration that has an adjustment mode for adjusting the setting of the transfer voltage based on the detection result of the density of a test image of a chart. [Means for solving the problem]

[0010] 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, a transfer member that forms a transfer section that transfers the toner image from the image carrier to a recording material, an application section that applies a voltage to the transfer member, an execution section that executes an output operation in which the application section applies a plurality of test voltages to the transfer member to transfer a plurality of test images onto the recording material, and outputs a chart formed by the application section, a density acquisition section that acquires density information relating to the density of the test images on the chart, an environment acquisition section that acquires environmental information relating to at least one of the temperature and humidity of the environment, and a setting section that sets a transfer voltage to be applied to the transfer member by the application section during the transfer, and the setting section is capable of setting the transfer voltage based on the density information and the environmental information. an adjustment amount acquiring unit that acquires adjustment amount information relating to an adjustment amount for adjusting the transfer voltage based on the test voltage information and the density information; and a correction amount acquiring unit that acquires correction amount information relating to a correction amount for correcting the adjustment amount information so as to reduce an absolute value of the transfer voltage based on the environmental information, wherein the setting unit is capable of setting the transfer voltage based on the adjustment amount information and the correction amount information. The image forming apparatus is characterized in that: [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress the occurrence of "punch-through" in a configuration that has an adjustment mode that adjusts the setting of the transfer voltage based on the detection result of the density of the test image of the chart. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a block diagram showing a control system of the image forming apparatus. [Figure 3] FIG. 10 is a flowchart illustrating a procedure for controlling a secondary transfer voltage. [Figure 4] FIG. 10 is a graph showing voltage-current characteristics obtained by controlling a secondary transfer voltage. [Figure 5] FIG. 10 is a schematic diagram showing an example of a table of recording material distribution voltages. [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. 10 is a flowchart illustrating an example of a procedure in an adjustment mode. [Figure 9] FIG. 10 is a schematic diagram showing an example of a setting screen for an adjustment mode. [Figure 10] FIG. 10 is a graph illustrating an example of the relationship between the adjustment value of the secondary transfer voltage and the average brightness value. [Figure 11] FIG. 10 is a schematic diagram showing an example of an adjustment table for correcting an adjustment value. [Figure 12] FIG. 10 is a schematic cross-sectional view of another example of an image forming apparatus. [Figure 13] FIG. 10 is a flowchart illustrating another example of the procedure of the adjustment mode. [Figure 14] FIG. 10 is a schematic diagram showing another example of the setting screen for the adjustment mode. [Figure 15] FIG. 10 is a schematic diagram showing an example of a detailed setting screen in an adjustment mode. DETAILED DESCRIPTION OF THE INVENTION

[0013] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0014] [Example 1] 1. Configuration and operation of image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 1 of this embodiment. The image forming apparatus 1 of this embodiment is a tandem multifunction machine (having the functions of a copier, printer, and facsimile machine) that employs an intermediate transfer system and is capable of forming full-color images using an electrophotographic system.

[0015] As shown in FIG. 1, the image forming apparatus 1 includes a main body 10, a reading unit 80, a feeding unit 90, a printer unit 40, a discharge unit 48, a control unit 30, an operation unit 70, and the like. The main body 10 also includes an environment detection unit, such as a temperature sensor 71 (FIG. 2) capable of detecting the internal temperature and a humidity sensor 72 (FIG. 2) capable of detecting the internal humidity. The environment detection unit may detect at least one of the temperature and humidity inside or outside the image forming apparatus 1. The image forming apparatus 1 can form a four-color full-color image on a recording material (sheet, transfer material, recording medium, media) S in response to image information (image signals) from the 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, and a smartphone. The recording material S is a material on which a toner image is formed. Specific examples include plain paper, a synthetic resin sheet (a substitute for plain paper), cardboard, and overhead projector sheet.

[0016] The printer unit 40 is capable of forming an image based on image information on a recording material S fed from a feeding unit (feeding device) 90. The printer unit 40 includes four image forming units 50y, 50m, 50c, and 50k as a plurality of image forming sections, and four toner bottles 41y, 41m, 41c, and 41k. The printer unit 40 also includes an intermediate transfer unit 44, a secondary transfer device 45, and a fixing unit 46. The image forming units 50y, 50m, 50c, and 50k form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Elements having the same or corresponding functions or configurations and provided for each color may be generally described by omitting the suffixes y, m, c, and k indicating the element for one of the colors. The image forming apparatus 1 can also form monochrome images, such as black monochrome images, or multicolor images using a single or several desired image forming units 50.

[0017] The image forming unit 50 has the following components. First, it has a photosensitive drum 51, which is a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as a first image carrier. It also has a charging roller 52, which is a roller-type charging member serving as charging means. It also has an exposure device 42 serving as exposure means. It also has a developing device 20 serving as development means. It also has a pre-exposure device 54 serving as charge removal means. It also has a drum cleaning device 55 serving as photosensitive member cleaning means. The image forming unit 50 forms a toner image on an intermediate transfer belt 44b, which will be described later. In the image forming unit 50, the photosensitive drum 51 and the charging roller 52, developing device 20, and drum cleaning device 55 serving as process means acting on the photosensitive drum 51 are integrated into a unit to form a process cartridge that is detachable from the apparatus main body 10.

[0018] 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 the arrow in the figure (counterclockwise direction) at a predetermined process speed (circumferential speed) by a motor (not shown) as a driving means.

[0019] 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 that comes into contact with the surface of the photosensitive drum 51 and rotates in accordance with the rotation of the photosensitive drum 51. A charging power supply 73 (FIG. 2) 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.

[0020] 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.

[0021] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by the developing device 20 by supplying toner, thereby forming a toner image 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. The developing sleeve 24 is made of a non-magnetic material (aluminum in this embodiment) such as aluminum or non-magnetic stainless steel. A roller-shaped magnet roller is fixed inside the developing sleeve 24 so as not to rotate relative to the main body (developer container) of the developing device 20. The developing sleeve 24 carries the developer and transports it to a development area facing the photosensitive drum 51. A developing power supply 74 (FIG. 2) is connected to the developing sleeve 24. The developing power supply 74 applies a predetermined developing voltage (developing bias) to the developing sleeve 24 during the development process. In this embodiment, toner charged with the same polarity (negative in this embodiment) as the charge polarity of the photosensitive drum 51 adheres to the exposed portion (image portion) on the photosensitive drum 51, which has been uniformly charged and then exposed to light to reduce the absolute value of the potential (reverse development). In this embodiment, the normal charge polarity of the toner, which is the charge polarity of the toner during development, is negative.

[0022] The intermediate transfer unit 44 is disposed opposite the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer unit 44 has an intermediate transfer belt 44b, which is an intermediate transfer body formed of an endless belt and serves as a second image carrier. The intermediate transfer belt 44b is wound around a plurality of tension rollers (support rollers), including a drive roller 44a, a driven roller 44d, and a secondary transfer inner roller 45a, and is tensioned 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. The driven roller 44d is a tension roller that keeps the tension of the intermediate transfer belt 44b constant. A tension spring (not shown), which serves as a biasing member, applies a biasing force to the driven roller 44d, pushing 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 transport direction. The inner secondary transfer roller 45a constitutes a secondary transfer device 45, as will be described later. The intermediate transfer belt 44b receives a driving force as the drive roller 44a is driven to rotate, and rotates (circumferentially moves) in the direction of the arrow (clockwise) in the figure at a predetermined peripheral speed corresponding to the peripheral speed of the photosensitive drum 51. Furthermore, primary transfer rollers 47y, 47m, 47c, and 47k, which are roller-type primary transfer members serving as primary transfer means, are arranged on the inner peripheral surface of the intermediate transfer belt 44b, corresponding to the photosensitive drums 51y, 51m, 51c, and 51k, respectively. The primary transfer rollers 47 sandwich the intermediate transfer belt 44b between themselves 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) N1 where the photosensitive drum 51 and the intermediate transfer belt 44b come into contact with each other.

[0023] 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. A primary transfer power supply 75 (FIG. 2) is connected to the primary transfer roller 47. During the primary transfer process, the primary transfer power supply 75 applies a 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. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on the photosensitive drums 51y, 51m, 51c, and 51k are sequentially primarily transferred onto the intermediate transfer belt 44b so as to be superimposed on each other. A voltage detection sensor 75a that detects the output voltage and a current detection sensor 75b that detects 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 the primary transfer rollers 47y, 47m, 47c, and 47k, respectively, and the primary transfer voltages applied to the primary transfer rollers 47y, 47m, 47c, and 47k can be individually controlled.

[0024] 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 8A roller with a resistance of Ω (N / N (measured at 23°C, 50% RH, applied voltage of 2 kV) can be suitably used. In this embodiment, the intermediate transfer belt 44b is an endless belt having a three-layer structure, including, from the inner circumferential surface side to the outer circumferential surface side, a base layer, an elastic layer, and a surface layer, in the following order. 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 elastic layer can be made of an elastic material such as various rubbers, including urethane rubber or silicone rubber, containing an appropriate amount of an ion conductive agent. The thickness of the elastic layer can be, for example, 0.1 to 0.500 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, which will be described later. The thickness of the surface layer is, for example, 0.0002 to 0.020 mm. In this embodiment, the surface layer uses, as its base material, one type of resin material such as polyurethane, polyester, or epoxy resin, or two or more types of elastic materials such as elastic rubber, elastomer, or butyl rubber. The surface layer is then formed by dispersing one or more types of powder or particles, such as fluororesin, or particles of different particle sizes, as a material that reduces surface energy and increases lubricity into this base material. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5×10 8 ~1×10 14 The resistance is Ω·cm (23°C, 50% RH), and the hardness is 60 to 85° (MD1 hardness) (23°C, 50% RH). In this embodiment, the static friction coefficient of the intermediate transfer belt 44b is 0.15 to 0.6 (23°C, 50% RH, HEIDON type 94i). Although the intermediate transfer belt 44b has a three-layer structure in this embodiment, it may also have a single layer structure made of a material equivalent to the above-mentioned base layer.

[0025] On the outer peripheral surface of the intermediate transfer belt 44b, there is disposed a secondary transfer outer roller 45b, which is a roller-type secondary transfer member and constitutes the secondary transfer device 45 together with the secondary transfer inner roller 45a. The secondary transfer outer roller 45b sandwiches the intermediate transfer belt 44b between itself and the secondary transfer inner roller 45a. This causes the secondary transfer outer roller 45b to contact the secondary transfer inner roller 45a via the intermediate transfer belt 44b, forming a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 44b and the secondary transfer outer roller 45b come into contact. The toner image formed on the intermediate transfer belt 44b is secondarily transferred onto the recording material S being conveyed while being sandwiched between the intermediate transfer belt 44b and the secondary transfer outer roller 45b at the secondary transfer portion N2. In this embodiment, a secondary transfer voltage (secondary transfer bias) is applied to the secondary transfer outer roller 45b during the secondary transfer process.

[0026] As described above, in this embodiment, 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. The inner secondary transfer roller 45a is disposed opposite the outer secondary transfer roller 45b across the intermediate transfer belt 44b. A secondary transfer power supply 76 (FIG. 2) serving as a voltage application unit (application unit) is connected to the outer secondary transfer roller 45b. During the secondary transfer process, the secondary transfer power supply 76 applies a secondary transfer voltage (secondary 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 outer secondary transfer roller 45b. A voltage detection sensor 76a that detects the output voltage and a current detection sensor 76b that detects the output current are connected to the secondary transfer power supply 76 (FIG. 2). Furthermore, in this embodiment, the core of the inner secondary transfer roller 45a is connected to ground potential. That is, in this embodiment, the inner secondary transfer roller 45a is electrically grounded (connected to ground). When the recording material S is supplied to the secondary transfer portion N2, a constant-voltage controlled secondary transfer voltage of a polarity opposite to the normal charging polarity of the toner is applied to the outer secondary transfer roller 45b. In this embodiment, for example, a secondary transfer voltage of 1 to 7 kV is applied, and a current of 40 to 120 μA flows, thereby secondarily transferring the toner image on the intermediate transfer belt 44b to the recording material S. Note that in this embodiment, the secondary transfer power supply 76 applies a DC voltage to the outer secondary transfer roller 45b to apply the secondary transfer voltage to the secondary transfer portion N2, but the present invention is not limited to this configuration. For example, the secondary transfer power supply 76 may apply a DC voltage to the inner secondary transfer roller 45a to apply the secondary transfer voltage to the secondary transfer portion N2. 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 as the secondary transfer member, and the outer secondary transfer roller 45b as the opposing member is electrically grounded. In this embodiment, the outer secondary transfer roller 45b has an elastic layer of ion-conductive foam 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.

[0027] The recording material S is fed from a feeding unit 90 in parallel with the above-described toner image formation operation. That is, the recording material S is stacked and stored in a recording material cassette 91 serving as a recording material storage unit. In this embodiment, the image forming apparatus 1 is provided with a plurality of recording material cassettes 91 (91a, 91b), each storing a recording material S. The recording material S stored in each recording material cassette 91 is sent to a conveying path 93 by a feeding roller 92 (92a, 92b) serving as a feeding member. The recording material S sent to the conveying path 93 is conveyed to a registration roller pair 43 serving as a conveying member by a conveying roller pair 94 serving as a conveying member. The registration roller pair 43 corrects skew of the recording material S and synchronizes the timing with the toner image on the intermediate transfer belt 44b before supplying it to the secondary transfer unit N2. The recording material cassette 91, the feeding roller 92, the conveying path 93, the conveying roller pair 94, and the like constitute the feeding unit 90.

[0028] The recording material S onto which the toner image has been transferred is transported to a fixing section (fixing device, fuser) 46 as a fixing means. The fixing section 46 has a fixing roller 46a and a pressure roller 46b. The fixing roller 46a has a built-in heater as a heating means. The recording material S carrying the unfixed toner image is heated and pressurized as it is sandwiched and transported between the fixing roller 46a and the pressure roller 46b. This causes the toner image to be fixed (melted and adhered) onto the recording material S. The temperature (fixing temperature) of the fixing roller 46a is detected by a fixing temperature sensor 77 (FIG. 2).

[0029] The recording material S with the fixed toner image is conveyed along a discharge path 48a by a pair of discharge rollers 48b and other conveying members, and discharged (output) through a discharge opening 48c and stacked on a discharge tray 48d provided outside the apparatus main body 10. The discharge path 48a, the pair of discharge rollers 48b, the discharge opening 48c, and the discharge tray 48d constitute a discharge section (discharge device) 48. In the case of single-sided printing (single-sided image formation) in which an image is formed on one side of the recording material S, the recording material S with the fixed toner image on one side that has passed through the fixing section 46 is discharged directly to the discharge tray 48d as described above. In this embodiment, the image forming apparatus 1 is also capable of double-sided printing (automatic double-sided printing, double-sided image formation) in which images are formed on both sides of the recording material S. A reversing conveyance path 12 is provided between the fixing section 46 and the discharge opening 48c to turn over the recording material S after the toner image has been fixed on the first side and feed it again to the secondary transfer section N2. During double-sided printing, the recording material S, after a toner image has been fixed on its first side, is guided to a reverse conveying path 12. The conveying direction of the recording material S is reversed by a switchback roller pair 13 provided in the reverse conveying path 12, and the recording material S is guided to a double-sided conveying path 14. The recording material S is then sent to a conveying path 93 by a re-conveying roller pair 15 provided in the double-sided conveying path 14, conveyed to a registration roller pair 43, and supplied to a secondary transfer unit N2 by the registration roller pair 43. Thereafter, a toner image is secondarily transferred to the second side of the recording material S in the same manner as when an image was formed on the first side. After the toner image is fixed, the recording material S is discharged to an output tray 48d. The reverse conveying path 12, the switchback roller pair 13, the double-sided conveying path 14, the re-conveying roller pair 15, and the like constitute a double-sided conveying unit (double-sided conveying device) 11. By operating the double-sided conveying unit 11, images can be formed on both sides of a single sheet of recording material S.

[0030] After the primary transfer, the surface of the photosensitive drum 51 is neutralized by a pre-exposure device 54. Furthermore, deposits such as toner (primary transfer residual toner) remaining on the photosensitive drum 51 without being transferred to the intermediate transfer belt 44b during the primary transfer process are removed from the photosensitive drum 51 and collected by a drum cleaning device 55. The drum cleaning device 55 uses a cleaning blade as a cleaning member that contacts the surface of the photosensitive drum 51 to scrape off deposits from the surface of the rotating photosensitive drum 51 and collect the scraped deposits in a cleaning container. The cleaning blade is contacted with the surface of the photosensitive drum 51 with a predetermined pressure so that the tip of its free end faces upstream in the counter direction of the rotation direction of the photosensitive drum 51. The intermediate transfer unit 44 also has a belt cleaning device 60 as an intermediate transfer body cleaning means. Deposits such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 44b without being transferred to the recording material S during the secondary transfer process are removed from the intermediate transfer belt 44b and collected by the belt cleaning device 60.

[0031] A reading unit (reading device) 80 serving as a reading means is disposed on the upper portion of the apparatus main body 10. The reading unit 80 includes an automatic document feeder (ADF) 81 serving as a document transport means (document transport unit), a platen glass 82, a light source 83, an optical system 84 including a group of mirrors 84a and an imaging lens 84b, and a reading element 85 such as a CCD. In this embodiment, the reading unit 80 sequentially reads an image of a document (recording material S on which an image has been formed) placed on the platen glass 82 using the reading element 85 via the optical system 84 while scanning and exposing the document using the movable light source 82. In this case, the reading unit 80 sequentially illuminates the document placed on the platen glass 82 using the moving light source 83, and sequentially forms an image of the light reflected from the document on the reading element 85 via the optical system 84. This allows the reading element 85 to read the image of the document at a predetermined dot density. In this embodiment, the reading unit 80 sequentially exposes images of documents conveyed by the automatic document feeder 81 to light using a light source 82 as the documents are conveyed, and sequentially reads the images using a reading element 85 via an optical system 84. In this case, the reading unit 80 sequentially illuminates documents passing a predetermined reading position on the platen glass 82 using a light source 83, and sequentially forms light images reflected from the documents on the reading element 85 via the optical system 84. This allows the reading element 85 to read the images of the documents at a predetermined dot density. The automatic document feeder 81 automatically conveys the documents so that they pass the reading position of the reading unit 80 one by one, separated from one another. In this way, the reading unit 80 optically reads images on a recording material S placed on the platen glass 82 or conveyed by the automatic document feeder 81 and converts the images into electrical signals. The automatic document feeder 81 can automatically read images on both sides of the recording material S.

[0032] For example, when the image forming apparatus 1 operates as a copier, the document image scanned by the scanning unit 80 is sent to the image processing unit of the control unit 30 as image data for three colors, red (R), green (G), and blue (B) (8 bits each). The image processing unit performs predetermined image processing on the document image data as needed, converting it into image data for four colors, yellow, magenta, cyan, and black. Examples of the image processing include shading correction, misalignment correction, brightness / color space conversion, gamma correction, border removal, and color / movement editing. The image data for the four colors, yellow, magenta, cyan, and black, are sequentially sent to the exposure devices 42y, 42m, 42c, and 42k, respectively, where the aforementioned image exposure is performed in accordance with this image data. As will be described in detail later, the scanning unit 80 is also used to scan the chart patches (obtain density information (brightness information)) in the adjustment mode.

[0033] 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 as a calculation control unit, a ROM 32 as a storage unit for storing programs that control each unit, a RAM 33 as a storage unit for temporarily storing data, and an input / output circuit (I / F) 34 for inputting and outputting signals to and from the outside. The CPU (calculation unit) 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 feed unit 90, printer unit 40, discharge unit 48, and operation unit 70 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. A charging power supply 73, a developing power supply 74, a primary transfer power supply 75, and a secondary transfer power supply 76 are connected to the control unit 30, and each of these is controlled by a signal 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 an input unit such as operation buttons 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 operate the operation unit 70 to cause the image forming apparatus 1 to execute a job (described below). The control unit 30 receives signals from the operation unit 70 and operates various devices of the image forming apparatus 1. The image forming apparatus 1 can also execute jobs 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 RAM 33. For example, the control unit 30 (more specifically, the image formation processor 31c) can execute a job. The control unit 30 (more specifically, the ATVC control processor 31b) can execute ATVC control (setting mode) of the primary transfer unit and the secondary transfer unit. ATVC control will be described in detail later. The control unit 30 (more specifically, the adjustment processor 31d) can execute an adjustment mode that adjusts the setting value of the secondary transfer voltage. The adjustment mode will be described in detail later.

[0036] In this embodiment, the control unit 30 (image forming process unit 31c) can switch between a multi-color mode in which a primary transfer voltage is applied to multiple primary transfer units N1 to form images in multiple colors, and a monochrome mode in which a primary transfer voltage is applied to only one primary transfer unit N1 out of the multiple primary transfer units N1 to form images in a single color.

[0037] Here, the image forming apparatus 1 executes a job (image output operation, print job) that is a series of operations that starts with a single start command and forms and outputs an image on one or multiple 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, and secondary transfer of the toner image are performed for the image that is actually 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 differs depending on the positions where the electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer 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 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 during which tidying up operations (preparatory operations) are performed after the image formation process. Non-image formation time (non-image formation period) refers to a period other than image formation time, and includes the above-mentioned pre-rotation process, paper interval process, post-rotation process, and also the pre-multi-rotation process, which is a preparatory operation when the image forming device 1 is turned on or when it returns from a sleep state.

[0038] 2. 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.

[0039] First, the control unit 30 (image formation pre-preparation process unit 31a) starts the job operation when it acquires job information from the operation unit 70 or the external device 200 (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 may include the size (width, length) of the recording material S on which the image is to be formed, information related to the thickness of the recording material S (thickness, basis weight, etc.), and information related to the surface properties of the recording material S, such as whether the recording material S is coated paper. In particular, in this embodiment, the information about the recording material S includes information about the size of the recording material S and information about the category of the recording material S (so-called paper type category), such as "thin paper, plain paper, thick paper, etc.", which is related to the thickness of the recording material S. The information about the recording material S (recording material information) includes any information that can distinguish the recording material S, such as attributes based on general characteristics (so-called paper type categories) such as plain paper, high-quality paper, glossy paper, coated paper, embossed paper, thick paper, and thin paper; numerical values ​​or numerical ranges for basis weight, thickness, size, and rigidity; or brand (including manufacturer, product name, and product number). Each recording material S distinguished by the information about the recording material S can be considered to constitute a type of recording material S. The information about the recording material S may also be included in print mode information, such as "plain paper mode" or "thick paper mode," that specifies the operational settings of the image forming apparatus 1, or may be replaced by the print mode information. The control unit 30 (image formation preparation process unit 31a) writes this job information to RAM 33 (S102).

[0040] 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). The 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. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the target current Itarget corresponding to the environment from the information indicating the relationship between the environmental information and the target current Itarget based on the environmental information read in S103. The control unit 30 then writes this target current Itarget to the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S104). The reason the target current Itarget is changed according to the environmental information is because the amount of charge on the toner varies depending on the environment. The information indicating the relationship between the environmental information and the target current Itarget is calculated in advance through experiments or the like.

[0041] 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) control (S105). That is, while the outer secondary transfer 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 outer secondary transfer 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 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. 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 so as to be expressed by a polynomial of the voltage that is quadratic or higher (a quadratic equation in this embodiment). Therefore, in this embodiment, the predetermined voltage or current supplied when acquiring information related to the electrical resistance of the secondary transfer portion 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.

[0042] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the voltage value to be applied from the secondary transfer power supply 76 to the outer secondary transfer roller 45b (S106). That is, based on the target current Itarget written to the RAM 33 in S104 and the voltage-current relationship calculated in S105, the control unit 30 calculates the voltage value Vb required to apply the target current Itarget when no recording material S is present at the secondary transfer portion N2. This voltage value Vb corresponds to the secondary transfer partial voltage (transfer voltage corresponding to the electrical resistance of the secondary transfer portion N2). Alternatively, the target current Itarget may be applied from the secondary transfer power supply 76 to the outer secondary transfer roller 45b by constant current control, the voltage value detected by the voltage detection sensor 76a, and the detected voltage may be used as the voltage value Vb. Also, the ROM 32 stores information for calculating the recording material partial voltage Vp (transfer voltage corresponding to the electrical resistance of the recording material S), as shown in FIG. 5. In this embodiment, this information is set as table data indicating the relationship between the atmospheric moisture content and the recording material voltage Vp for each basis weight category (corresponding to a paper type category) of the recording material S. The control unit 30 (image formation preparation process unit 31a) can determine the atmospheric moisture content based on environmental information (temperature and humidity) detected by the temperature sensor 71 and humidity sensor 72. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines the recording material voltage Vp from the table data based on the job information acquired in S101 and the environmental information acquired in S103. Furthermore, if an adjustment value is set in an adjustment mode that adjusts the secondary transfer voltage setting, which will be described later, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines an adjustment amount ΔV corresponding to the adjustment value. As will be described later, this adjustment amount ΔV is stored in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) when set in the adjustment mode. The control unit 30 calculates Vb+Vp+ΔV by adding together Vb, Vp, and ΔV as the secondary transfer voltage Vtr to be applied to the outer secondary transfer roller 45b from the secondary transfer power supply 76 while the recording material S is passing through the secondary transfer unit N2. Then, the control unit 30 writes this Vtr (=Vb+Vp+ΔV) to the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f).The table data for determining the recording material voltage Vp as shown in FIG. 5 is determined in advance through experiments or the like.

[0043] 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 thickness of the recording material S (thickness, basis weight, etc.). 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 thickness 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 the information obtained by this measuring means.

[0044] 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 applies 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 the process of S107 until all images of the job have been transferred onto the recording material S and output (S108).

[0045] 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.

[0046] 3. Adjustment Mode Overview Next, the adjustment mode (simplified adjustment mode) for adjusting the set value of the secondary transfer voltage will be described.

[0047] 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 secondary transfer voltage setting using the default recording material voltage Vp, as previously set, may not perform proper transfer. In other words, the secondary transfer voltage must first be sufficient to transfer the toner on the intermediate transfer belt 44b to the recording material S. Furthermore, the secondary transfer voltage must be limited to a voltage that does not cause abnormal discharge. However, depending on the type and condition of the recording material S actually used for image formation, the electrical resistance may be higher than the standard value. In this case, the secondary transfer voltage setting using the default recording material voltage Vp may not be sufficient to transfer the toner on the intermediate transfer belt 44b to the recording material S. Therefore, in this case, it is desirable to increase the secondary transfer voltage, for example by increasing the recording material voltage Vp. Furthermore, depending on the type and condition of the recording material S actually used for image formation, the moisture content of the recording material S may be reduced, making it more susceptible to discharge. In this case, if the secondary transfer voltage is set to a preset default recording material voltage Vp, image defects may occur due to abnormal discharge. Therefore, in this case, it is desirable to lower the secondary transfer voltage by, for example, lowering the recording material voltage Vp.

[0048] Therefore, it may be desirable for an operator such as a user or a service person to adjust (change) the set value of the secondary transfer voltage during job execution to an appropriate value by adjusting (changing) the recording material voltage Vp according to the recording material S actually used for image formation. In other words, it may be desirable to select an appropriate recording material voltage Vp+ΔV (adjustment amount) according to the recording material S actually used for image formation.

[0049] This adjustment can be performed by the following method: For example, an operator outputs the image he or she wants to output while switching the secondary transfer voltage for each sheet of recording material S, checks the output image, and determines an appropriate setting value for the secondary transfer voltage (more specifically, the recording material shared voltage Vp+ΔV). However, this method involves repeatedly outputting the image and adjusting the setting value for the secondary transfer voltage, which can result in more recording material S being wasted or can take a long time to adjust.

[0050] Therefore, in this embodiment, the image forming apparatus 1 is provided with an adjustment mode for adjusting the set value of the secondary transfer voltage. In this adjustment mode, a chart is formed and output by transferring multiple patches (test images) of representative colors onto the recording material S actually used for image formation, while switching the secondary transfer voltage (test voltage) for each patch. Then, based on the output chart, it is possible to determine an appropriate set value of the secondary transfer voltage (more specifically, the recording material distribution voltage Vp+ΔV). In this embodiment, in the adjustment mode, the control unit 30 presents information regarding the recommended adjustment amount ΔV of the set value of the secondary transfer voltage based on the results of reading density information (brightness information) of patches (typically solid image patches) on the chart using the reading unit 80. This reduces the need for the operator to visually check the image on the chart, thereby reducing the operator's operational burden and enabling more appropriate adjustment of the set value of the secondary transfer voltage.

[0051] 4. Charts Next, the chart (adjustment image, test page) output in the adjustment mode of this embodiment will be described. FIGS. 6 and 7 are schematic diagrams of a chart 100 in this embodiment. In this embodiment, two types of charts 100 are output in the adjustment mode, broadly classified according to the size of the recording material S used, as shown in FIGS. 6 and 7. FIG. 6 shows a chart 100 output when the length of the recording material S in the conveying direction is 420 to 487 mm. FIG. 7 shows a chart 100 output when the length of the recording material S in the conveying direction is 210 to 419 mm. Note that in this embodiment, charts can be formed and output on both sides of the recording material S even in the adjustment mode, so that the secondary transfer voltages during secondary transfer to the first side (front side) and the second side (back side) in double-sided printing can be adjusted, respectively. FIGS. 6 and 7 show a chart when a chart is formed on one side of the recording material S (hereinafter also referred to as a "single-sided chart") and a chart when a chart is formed on both sides of the recording material S (hereinafter also referred to as a "double-sided chart"), respectively. In this embodiment, the chart 100 is formed in a full-color mode operation. Also, a double-sided chart is formed by a double-sided printing operation using the double-sided conveying unit 11 described above.

[0052] Here, the size of the recording material S is expressed as recording material width (length in the main scanning direction) x recording material length (length in the sub-scanning direction). The recording material width is the length in the direction (width direction) substantially perpendicular to the conveyance direction of the recording material S when passing through the secondary transfer portion N2. The recording material length is the length in the direction substantially parallel to the conveyance direction of the recording material S when passing through the secondary transfer portion N2.

[0053] Figure 6 shows a large-size chart (hereinafter also referred to as "large chart") 100L (100La, 100Lb) that is output when using a large-size recording material S such as A3 (297mm x 420mm) or ledger (approximately 280mm x 432mm). Figure 6(a) shows the large chart 100La when outputting a single-sided chart (or the first side when outputting a double-sided chart). Figure 6(b) shows the large chart 100Lb when outputting a double-sided chart.

[0054] Figure 7 shows small-size charts (hereinafter also referred to as "small charts") 100S (100Sa, 100Sb) that are output when using small-size recording material S, such as A4 landscape (297 mm x 210 mm) or letter landscape (approximately 280 mm x 216 mm). Figures 7(a) and (b) show the first and second small charts 100Sa when outputting a single-sided chart (or the first side when outputting a double-sided chart). Figures 7(c) and (d) show the first and second small charts 100Sb when outputting a double-sided chart (or the second side when outputting a double-sided chart).

[0055] In this embodiment, the chart 100 has a patch set in which one blue solid patch 101, one black solid patch 102, and two halftone patches 103 are arranged in the width direction. The large chart 100L in FIG. 6 has 11 width direction patch sets 101-103 arranged in the transport direction. The small chart 100S in FIG. 7 has 10 width direction patch sets 101-103 arranged in the transport direction. In this embodiment, the halftone patch 103 is a gray (black halftone) patch. Here, the solid image is an image with the maximum density level. In this embodiment, the blue solid is a combination of 100% magenta (M) toner and 100% cyan (C) toner, and the toner coverage of the blue solid is 200%. The black solid is an image with 100% black (K) toner. A halftone image (halftone image) is an image with a toner coverage of 10 to 80%, assuming that the toner coverage of a solid image is 100%. In this embodiment, the chart 100 includes patch identification information 104 associated with each of the patch sets 101 to 103, for identifying the secondary transfer voltage setting value applied to each patch set. This patch identification information 104 may correspond to the secondary transfer voltage adjustment value, which will be described later. The large chart 100L in FIG. 6 includes eleven pieces of patch identification information 104 (11 pieces, from -5 to 0 to +5, in this embodiment) corresponding to eleven levels of secondary transfer voltage settings. The small chart 100S in FIG. 7 includes ten pieces of patch identification information 104 (five pieces, from -4 to 0, on the first sheet and five pieces, from +1 to +5, on the second sheet, in this embodiment) corresponding to ten levels of secondary transfer voltage settings. In addition, the chart 100 may have front / back identification information 105 provided on at least one of the first side (front side) or second side (back side) of the recording material S, which indicates that it is the first side (front side) or the second side (back side) of the recording material S.

[0056] The patch size is required to be large enough to allow an operator to easily determine whether or not there is an image defect. Because it is difficult to determine the transferability of the blue solid patch 101 and the black solid patch 102 when the patch size is small, the patch size is preferably 10 mm square or larger, and more preferably 25 mm square or larger. Image defects caused by discharges that occur when the secondary transfer voltage is increased in the halftone patch 103 often appear as white dots. Compared to the transferability of solid images, these image defects tend to be easier to determine even with small images. However, because images are easier to see when they are not too small, in this embodiment, the width of the halftone patch 103 in the transport direction is set to the same as the width of the blue solid patch 101 and the black solid patch 102 in the transport direction. Furthermore, the spacing between the patch sets 101 to 103 in the transport direction may be set to allow for switching of the secondary transfer voltage. In this embodiment, the blue solid patch 101 and the black solid patch 102 are each a 25.7 mm x 25.7 mm square (one side is approximately parallel to the width direction). In this embodiment, the halftone patches 103 at both ends in the width direction each have a width of 25.7 mm in the transport direction and extend to the very edge of the chart 100 (a margin, as described below, may be present). In this embodiment, the spacing between the patch sets 101 to 103 in the transport direction is 9.5 mm. The secondary transfer voltage is switched when the portion of the chart 100 corresponding to this spacing passes through the secondary transfer portion N2. In this embodiment, the patch sets 101 to 103 of the chart 100 are sequentially transferred from the upstream side to the downstream side in the transport direction of the recording material S when the chart 100 is formed, using a plurality of secondary transfer voltages whose absolute values ​​are sequentially increased. However, the present invention is not limited to this embodiment. Each patch set 101 to 103 of the chart 100 may be transferred sequentially from the upstream side to the downstream side in the conveying direction of the recording material S when the chart 100 is formed, using a plurality of secondary transfer voltages whose absolute values ​​are different from each other so as to successively decrease.

[0057] It is preferable that patches are not formed near the leading and trailing ends of the recording material S in the conveying direction (for example, within a range of about 20 to 30 mm inward from the edge). This is for the following reason: Among the ends of the recording material S in the conveying direction, there may be an image defect that occurs only at the leading or trailing end in the conveying direction, but not at the end in the width direction. In this case, it may be difficult to determine whether the image defect is caused by fluctuating the secondary transfer voltage.

[0058] The maximum size of the recording material S that can be used with the image forming apparatus 1 in this embodiment is 13 inches (approximately 330 mm) × 19.2 inches (approximately 487 mm), and the large chart 100L in FIG. 6 corresponds to this size of recording material S. When the size of the recording material S is 13 inches × 19.2 inches or less and A3 (297 mm × 420 mm) or larger, a chart corresponding to image data that is cropped from the image data of the large chart 100L shown in FIG. 6 according to the size of the recording material S is output. At this time, in this embodiment, the image data is cropped to fit the size of the recording material S based on the center of the leading edge. That is, the leading edge of the recording material S in the transport direction and the leading edge of the large chart 100L in the transport direction (the top edge in the figure) are aligned, and the center of the width of the recording material S and the center of the large chart 100L in the width direction are aligned, and the image data is cropped. Furthermore, in this embodiment, the image data is cropped so that a margin of 2.5 mm is provided at the ends (both ends in the width direction and the transport direction in this embodiment). For example, when a large chart 100L is output onto an A3 (297 mm x 420 mm) recording material S, image data within a 292 mm x 415 mm range is cropped, leaving 2.5 mm margins at each end. The large chart 100L corresponding to this image data is then output onto an A3 (297 mm x 420 mm) recording material S, with the leading edge centered as the reference. When a recording material S with a width smaller than 13 inches is used, the widthwise size of the halftone patches 103 at the widthwise edges becomes smaller. Furthermore, when a recording material S with a width smaller than 13 inches is used, the margin at the trailing edge in the conveying direction becomes smaller. As described above, 11 patch sets ranging from -5 to 0 to +5 are arranged on the large chart 100L. The 11 patch sets 101 to 103 of the large chart 100L are arranged within a range of 387 mm in length in the conveying direction so that they fit within a length of 415 mm in the conveying direction when the size of the recording material S is A3.

[0059] In this embodiment, when a recording material S smaller than A3 (297 mm × 420 mm) is used, the small chart 100S shown in FIG. 7 is output. The small chart 100S shown in FIG. 7 corresponds to sizes smaller than A5 (portrait feed) and A3 (297 mm × 420 mm) (i.e., lengths in the transport direction of 210 to 419 mm). As described above, the small chart 100S has a total of 10 patch sets: five sets of -4 to 0 on the first sheet and +1 to +5 on the second sheet. The size of the image data for the small chart 100S is 13 inches × 210 mm. In the width direction, the halftone patches 103 are smaller to match the size of the recording material S. In the transport direction, the five patch sets fit within a length of 167 mm in the transport direction, and the margin at the trailing edge is longer to match the length of the recording material S in the transport direction of 210 to 419 mm. For recording material S with a length in the transport direction of 210 to 419 mm, only five patch sets can be formed in the transport direction on one sheet. Therefore, to increase the number of patches, the chart is divided into two sheets, and five sets from -4 to 0 and five sets from +1 to +5 are formed, for a total of 10 patch sets. Note that the small chart 100S omits the -5 patch set from the large chart 100L.

[0060] Furthermore, in this embodiment, regardless of the size of the recording material S, the blue solid patch 101 and the black solid patch 102 are arranged on the first side (front side) and second side (back side) of the double-sided chart so that they do not overlap on the front and back of the recording material S. In this embodiment, the patch spacing in the width direction is set to 5.4 mm. This is to suppress variations in the patch density on the second side due to the influence of the patch density on the first side, and to more accurately adjust the secondary transfer voltage on the second side.

[0061] In addition, in this embodiment, in addition to standard sizes, the chart 100 can also be output using recording material S of any size (free size) by the operator specifying it through input from the operation unit 70 or external device 200, for example.

[0062] Here, one chart 100 may be formed on one side of one sheet of recording material S, or may be formed separately on one side of each of multiple sheets of recording material S (i.e., one set of charts having one set of patches whose test voltage changes stepwise). In the above example, the large chart 100La (first side) and the large chart 100Lb (second side) each correspond to one chart. Also, in the above example, the first and second small charts 100Sa (first side) collectively correspond to one chart. Similarly, the first and second small charts 100Sb (second side) collectively correspond to one chart.

[0063] 5. 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. FIG. 9 is a schematic diagram of a setting screen (adjustment screen) 300 for the adjustment mode in this embodiment. Note that, here, an example is taken of a case where the large chart 100L described above is formed as the chart 100. Also, here, an example is taken of a case where the operator inputs instructions from the operation unit 70 of the image forming apparatus 1 to execute the adjustment mode. Also, for simplicity, the recording material on which the chart is formed may be simply referred to as a "chart."

[0064] First, the adjustment screen 300 will be described with reference to FIG. 9. In this embodiment, the control unit 30 (adjustment processing unit 31d) displays the adjustment screen 300 shown in FIG. 9 on the display unit 70a of the operation unit 70. The adjustment screen 300 has voltage setting units 301 (301a, 301b) for setting adjustment values ​​of the secondary transfer voltage for the first side (front side) and the second side (back side) of the recording material S, respectively. The adjustment screen 300 also has an output side selection unit 302 for selecting whether the chart 100 is to be output on one side or both sides of the recording material S. The adjustment screen 300 also has an output instruction unit (chart output button) 303 for instructing the output of the chart 100. The adjustment screen 300 also has a confirmation unit 304 (OK button 304a, apply button 304b) for confirming the settings, and a cancel button 305 for canceling the setting changes. The control unit 30 (adjustment processing unit 31d) can acquire information regarding various settings input via the adjustment screen 300 on the operation unit 70, and store the information in a memory unit (RAM 33, secondary transfer voltage memory unit / calculation unit 31f, etc.) as necessary.

[0065] In this embodiment, before the chart 100 is output, the adjustment value displayed on the voltage setting unit 301 indicates the center voltage value (the value corresponding to the patch “0” on the chart) of the secondary transfer voltage (more specifically, the recording material distribution voltage Vp) when the chart 100 is formed. When the adjustment value “0” is selected in the voltage setting unit 301 and the chart 100 is output, the center voltage value is set to a specified value (table value) that is preset for the currently selected recording material S. The adjustment value displayed on the voltage setting unit 301 can be changed by the operator. When an adjustment value other than “0” is selected and the chart 100 is output, the center voltage value is changed by an adjustment amount ΔV of 150 V for each level of the adjustment value, and the chart 100 is output. In addition, the chart 100 is output by operating the chart output button 303. In this embodiment, after the chart 100 is output, the voltage setting unit 301 displays a recommended adjustment value for the secondary transfer voltage that the control unit 30 (adjustment processing unit 31d) determined based on the results of reading the chart 100 by the reading device 80. The operator can change the adjustment value displayed on the voltage setting unit 301. In the voltage setting unit 301, the adjustment value of the secondary transfer voltage is confirmed by operating the confirmation unit 304 while the adjustment value determined by the control unit 30 (adjustment processing unit 31d) or the adjustment value changed by the operator is selected. Note that before the chart 100 is output, the adjustment value displayed on the voltage setting unit 301 may indicate the adjustment value currently set for the currently selected recording material S.

[0066] Next, the procedure of the adjustment mode will be described with reference to FIG. 8. First, the control unit 30 (adjustment processor 31d) acquires information (paper type category, size, etc.) of the recording material S selected by the operator and for which the operator wishes to adjust the setting value of the secondary transfer voltage (S201). For example, the control unit 30 (adjustment processor 31d) displays a recording material setting screen for setting the recording material S on the display unit 70a of the operation unit 70. This recording material setting screen allows the operator to input (select) information about the recording material S to be used (paper type category, size, etc.). Then, for example, the operator operates an adjustment mode start button provided corresponding to each recording material S on the recording material setting screen. In response, the control unit 30 (adjustment processor 31d) displays an adjustment screen 300 for setting the adjustment mode, as shown in FIG. 9, on the display unit 70a of the operation unit 70. That is, in this embodiment, the control unit 30 (adjustment processing unit 31d) acquires information about the recording material S in response to the operator operating the start button for the adjustment mode, and starts processing of the adjustment mode in which the set value of the secondary transfer voltage is adjusted in association with the information. Note that the information about the recording material S may be acquired from information that is previously set in association with the recording material cassette 91, for example, by selecting the recording material cassette 91 that contains the recording material S to be used in the adjustment mode.

[0067] Next, the control unit 30 (adjustment processor 31d) acquires information entered by the operator on the adjustment screen 300, such as the setting of the center voltage value of the secondary transfer voltage when forming the chart 100 and the setting of whether to output a single-sided chart or a double-sided chart (S202). Next, when the operator operates the chart output button 303 on the adjustment screen 300, the control unit 30 (adjustment processor 31d) acquires environmental information detected by the temperature sensor 71 and humidity sensor 72 prior to outputting the chart 100 (S203). The control unit 30 (adjustment processor 31d) calculates the moisture content (absolute moisture content) of the ambient atmosphere based on the environmental information (temperature and humidity) detected by the temperature sensor 71 and humidity sensor 72. Furthermore, prior to outputting the chart 100, the control unit 30 (adjustment processor 31d) acquires information regarding the electrical resistance of the secondary transfer unit N2 through an operation similar to ATVC control (S204). In this embodiment, as described above, a quadratic or higher polynomial (in this embodiment, a quadratic equation) of the relationship between voltage and current corresponding to the electrical resistance of the secondary transfer portion N2 is acquired. Then, the control unit 30 (adjustment processing unit 31d) sets the secondary transfer voltage Vtr=Vb+Vp+ΔV based on the acquired information about the electrical resistance and the information about the center voltage value set on the adjustment screen 300, and outputs the chart 100 (S205). At this time, the control unit 30 (adjustment processing unit 31d) adjusts the image data of the chart 100 according to the size of the recording material S as described above, and controls the chart 100 to be output while changing the adjustment amount ΔV in 150 V increments. In this example, a case where a large chart 100L is output is illustrated, and therefore the control unit 30 (adjustment processing unit 31d) controls the chart 100 to be output having 11 patch sets as described above. For example, if the recording material voltage Vp in the environment when the adjustment mode is executed is 2500V and Vb obtained by ATVC control is 1000V, an image of chart 100 is formed while changing the secondary transfer voltage in 150V increments from 2750V to 4250V.

[0068] Next, the control unit 30 (adjustment processor 31d) acquires density information (brightness information) of the patches of the output chart 100 (S206). In this embodiment, the output chart 100 is set in the reading unit 80 (for example, the automatic document feeder 81) by the operator and read by the reading unit 80. If a double-sided chart is output, each of the charts on the first and second sides of the double-sided chart is read by the reading unit 80. Then, the control unit 30 (adjustment processor 31d) acquires RGB brightness data (8 bits) of each patch of solid blue based on the reading result of the reading unit 80. At this time, the control unit 30 (adjustment processor 31d) can display on the operation unit 70 a message prompting the operator to set the chart 100 in the reading unit 80. Furthermore, the control unit 30 (adjustment processor 31d) can control the reading unit 80 to read the chart 100 in response to the operator operating a start button (not shown) on the operation unit 70. Next, the control unit 30 (adjustment processing unit 31d) uses the acquired brightness data (density data) to determine the average brightness value of each patch ("average brightness value") (S207). When a double-sided chart is output, the average brightness value of each patch is determined for each of the first and second sides of the double-sided chart. This process, for example, obtains the relationship between the adjustment value (voltage level) and the average brightness value of the patch (information regarding the transition of the image density of the patch relative to changes in the secondary transfer voltage) as shown in FIG. 10. The horizontal axis of FIG. 10 indicates the adjustment value (-5 to 0 to +5) indicating each voltage level, and the vertical axis indicates the average brightness value of the solid blue patch. Note that the brightness data of B is used for the solid blue patch.

[0069] Next, the control unit 30 (adjustment processor 31d) provisionally determines a recommended adjustment value for the secondary transfer voltage based on the relationship between the acquired adjustment value and the average luminance value (S208). In this embodiment, the control unit 30 (adjustment processor 31d) provisionally determines the adjustment value that minimizes the average luminance value (maximizes the average image density value) as the recommended adjustment value for the secondary transfer voltage. In other words, if the absolute value of the secondary transfer voltage is smaller than the appropriate value, the toner may not be transferred to the recording material S, resulting in a low image density (known as "grainy or grainy image loss"). In this case, the resulting average luminance value is high. On the other hand, even if the absolute value of the secondary transfer voltage is larger than the appropriate value, charge may be injected into the toner, causing the toner's charge polarity to become opposite to its normal charge polarity. This may result in an image defect in which toner once transferred to the recording material S returns to the intermediate transfer belt 44b (known as "strong image loss"). In this case, the image density is low and the resulting average luminance value is high. Therefore, the adjustment value that minimizes the average luminance value provides the highest image density and is considered to be the appropriate secondary transfer voltage. When a single-sided chart is output, the recommended adjustment value of the secondary transfer voltage for single-sided printing is provisionally determined based on the results of reading the single-sided chart. When a double-sided chart is output, the recommended adjustment value of the secondary transfer voltage for each of the first and second sides of double-sided printing is provisionally determined based on the results of reading the first and second sides of the double-sided chart.

[0070] Next, the control unit 30 (adjustment processor 31d) modifies (corrects) the provisionally determined recommended adjustment value of the secondary transfer voltage, and performs a process (modification process) to determine a recommended adjustment value of the secondary transfer voltage (S209). In this embodiment, the control unit 30 (adjustment processor 31d) performs this modification process based on environmental information (moisture content of the ambient atmosphere) and print side information (single-sided printing or double-sided printing, and if double-sided printing, first side or second side).

[0071] The correction process in this embodiment will now be described in more detail. As previously mentioned, when the recording material S is subjected to discharge during transfer, the toner in the affected area is not transferred, resulting in an image defect known as "punch-through," resulting in white spots. Experiments have shown that the lower the humidity of the environment in which the image forming apparatus 1 is installed, the more likely "punch-through" occurs. This is thought to be because low humidity reduces the electrical permittivity of the material surface, causing it to become charged and making it more likely for discharge within the paper (discharge occurring within the thickness of the recording material S) to occur. Punch-through is also more likely to occur on the second side of a double-sided print because the moisture content of the recording material P decreases after passing through the fixing unit 46. Punch-through is more likely to occur on halftone images. However, it is difficult to distinguish the presence or absence of "punch-through" in terms of image density. Therefore, in the adjustment mode, the secondary transfer voltage may be adjusted higher even when "punch-through" is occurring. As a result, the risk of "punch-through" occurring may be increased in low-humidity environments where discharge is more likely to occur, especially on the second side of a double-sided print.

[0072] Therefore, in this embodiment, an adjustment table showing the amount of modification of the provisionally determined recommended adjustment value of the secondary transfer voltage according to environmental information (moisture content of the ambient atmosphere) and print surface information, as shown in FIG. 11, is preliminarily generated and stored in ROM 32. In FIG. 11, "-1" means that the provisionally determined adjustment value of the secondary transfer voltage is modified by "1" to be smaller. As shown in FIG. 11, when the moisture content of the ambient atmosphere is low, the provisionally determined adjustment value of the secondary transfer voltage is modified to be smaller. Furthermore, since the moisture content of the recording material S is lower on the second side due to passing through the fixing unit 46, "punch-through" is more likely to occur on the first side than on the first side. Therefore, the adjustment value is modified to be smaller than that on the first side (including single-sided printing). Specifically, for example, when the relationship shown in FIG. 10 is obtained, adjustment value 3, which normally provides the smallest average luminance, is selected as the recommended adjustment value for the secondary transfer voltage. However, as described above, although it is difficult to determine the image density, "punch-through" may occur in a low-humidity environment or on the second side. Therefore, in this embodiment, for example, if the moisture content of the ambient atmosphere is 0.9 g / kg and it is the first side, adjustment value 2 (A in FIG. 10) is selected (i.e., the provisionally determined adjustment value 3 is corrected to adjustment value 2). Also, for example, if the moisture content of the ambient atmosphere is 0.9 g / kg and it is the second side, adjustment value 1 (B in FIG. 10) is selected (i.e., the provisionally determined adjustment value 3 is corrected to adjustment value 1).

[0073] As shown in FIG. 11 , in this embodiment, for the first side, the provisionally determined adjustment value of the secondary transfer voltage is corrected when the moisture content of the ambient atmosphere is equal to or less than a first threshold (0.9 g / kg). For the second side, the provisionally determined adjustment value of the secondary transfer voltage is corrected when the moisture content of the ambient atmosphere is equal to or less than a second threshold (8.9 g / kg), which is greater than the first threshold (0.9 g / kg). When the moisture content of the ambient atmosphere is equal to or less than the first threshold, the absolute value of the correction value for the second side is greater than the absolute value of the correction value for the first side, assuming that the moisture content of the ambient atmosphere is the same. For both the first and second sides, the adjustment value of the secondary transfer voltage can be corrected in multiple stages so that the absolute value of the correction value increases as the moisture content of the ambient atmosphere decreases. For convenience, the correction process is described as being performed in S209 of FIG. 8 , but this correction process also includes cases where no correction is performed, such as when the moisture content of the ambient atmosphere is sufficiently high. Furthermore, for example, before provisionally determining the recommended adjustment value for the secondary transfer voltage, it may be determined based on environmental information or print surface information that if it is not necessary, the correction process will not be performed (skipped), thereby omitting the process of S209.

[0074] Next, the control unit 30 (adjustment processor 31d) displays the recommended adjustment value of the secondary transfer voltage determined (corrected) in S208 and S209 on the adjustment screen 300 as shown in FIG. 9 on the display unit 70a of the operation unit 70 (S210). As described above, after the chart 100 is output, the voltage setting unit 301 (301a, 301b) displays the recommended adjustment value of the secondary transfer voltage determined by the control unit 30. The operator can determine whether the displayed adjustment value is acceptable based on the display content of the adjustment screen 300 and the output chart 100. If the operator does not want to change the displayed adjustment value, he or she simply operates the confirmation unit 304 on the adjustment screen 300. On the other hand, if the operator wants to change the displayed adjustment value, he or she inputs the changed value into the voltage setting unit 301 (301a, 301b) on the adjustment screen 300 and operates the confirmation unit 304. Therefore, the control unit 30 (adjustment processor 31d) determines whether the adjustment value has been changed (S211). If the adjustment value is not changed and the confirmation unit 304 is operated, the control unit 30 (adjustment processor 31d) stores the adjustment value decided (modified) in S208 and S209 in RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) (S212). On the other hand, if the adjustment value is changed, the control unit 30 (adjustment processor 31d) stores the adjustment value input by the operator in RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) (S213). This ends the adjustment mode.

[0075] Note that instead of or in addition to the adjustment value, an adjustment amount ΔV calculated as described below may be stored. The same applies to the correction of the adjustment value, and the adjustment amount ΔV may be corrected directly.

[0076] When a subsequent job using the recording material S to be adjusted is executed, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) sets the secondary transfer voltage according to the stored adjustment value until the next adjustment is performed. That is, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) sets the secondary transfer voltage during image formation based on information about the recording material S used during image formation and information stored in the storage unit (RAM 33 or secondary transfer voltage storage unit / calculation unit 31f) corresponding to that information. In this embodiment, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the adjustment amount ΔV as ΔV = adjustment value × 150 [V] according to the adjustment value stored in the adjustment mode as described above. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) then uses the calculated adjustment amount ΔV to calculate the adjusted recording material shared voltage Vp + ΔV, which is then used to calculate the secondary transfer voltage Vtr (= Vb + Vp + ΔV) during normal image formation. When double-sided printing is performed, the secondary transfer voltages for the first and second sides are set as described above.

[0077] 6.Effects As described above, the image forming apparatus 1 of this embodiment includes an image carrier 44b that carries a toner image, a transfer member 45b that forms a transfer section N2 that transfers the toner image from the image carrier 44b to the recording material S, an application section 76 that applies a voltage to the transfer member 45b, an execution section (in this embodiment, the control section 30 has the function of the execution section) that performs an output operation in which the application section 76 applies multiple test voltages to the transfer member 45b to transfer multiple test images to the recording material S to form a chart 100 and output the chart 100, a density acquisition section 80 that acquires density information regarding the density of the test images on the chart 100, environment acquisition sections 71 and 72 that acquire environmental information regarding at least one of the environmental temperature and humidity, and a setting section (in this embodiment, the control section 30 has the function of the setting section) that sets the transfer voltage to be applied to the transfer member 45b by the application section 76 during transfer, and the setting section 30 is capable of setting the transfer voltage based on the density information and the environmental information. Furthermore, the image forming apparatus 1 of this embodiment includes an adjustment amount acquisition unit (in this embodiment, the control unit 30 has the function of the adjustment amount acquisition unit) that acquires adjustment amount information regarding the adjustment amount for adjusting the transfer voltage based on the test voltage information and the density information, and a correction amount acquisition unit (in this embodiment, the control unit 30 has the function of the correction amount acquisition unit) that acquires correction amount information regarding the correction amount for correcting the adjustment amount information so as to reduce the absolute value of the transfer voltage based on the environmental information, and the setting unit 30 can set the transfer voltage based on the adjustment amount information and the correction amount information. Furthermore, in this embodiment, the correction amount acquisition unit 30 acquires the correction amount information for correcting the adjustment amount information so as to reduce the absolute value of the transfer voltage when the moisture content indicated by the environmental information is equal to or less than a predetermined threshold.

[0078] In this embodiment, the adjustment amount acquisition unit 30 acquires first adjustment amount information regarding the adjustment amount for adjusting the transfer voltage on the first side of double-sided image formation based on the test voltage information and the density information regarding the test image formed on the first side of the recording material S, and acquires second adjustment amount information regarding the adjustment amount for adjusting the transfer voltage on the second side of double-sided image formation based on the test voltage information and the density information regarding the test image formed on the second side of the recording material S. The correction amount acquisition unit 30 also acquires first correction amount information regarding the correction amount for correcting the first adjustment amount information and second correction amount information regarding the correction amount for correcting the second adjustment amount information based on the environmental information. The setting unit 30 can set the transfer voltage on the first side of double-sided image formation based on the first adjustment amount information and the first correction amount information, and can set the transfer voltage on the second side of double-sided image formation based on the second adjustment amount information and the second correction amount information. In this embodiment, when the moisture content of the environment indicated by the environmental information is the same, the amount of change in the absolute value of the transfer voltage indicated by the second correction amount information is larger than the amount of change in the absolute value of the transfer voltage indicated by the first correction amount information. Also, in this embodiment, when the moisture content indicated by the environmental information is equal to or less than a predetermined first threshold, the correction amount acquisition unit 30 acquires the first correction amount information for correcting the first adjustment amount information so as to reduce the absolute value of the transfer voltage, and when the moisture content indicated by the environmental information is equal to or less than a predetermined second threshold that is greater than the first threshold, the correction amount acquisition unit 30 acquires the second correction amount information for correcting the second adjustment amount information so as to reduce the absolute value of the transfer voltage.

[0079] As described above, according to this embodiment, in a configuration having an adjustment mode that adjusts the setting of the transfer voltage based on the detection results of the density of the chart test image, it is possible to suppress the occurrence of "punch-through."

[0080] The method for determining (provisionally determining) the recommended adjustment value for the secondary transfer voltage is not limited to the above-described method. In this embodiment, the recommended adjustment value for the secondary transfer voltage is determined (provisionally determined) based on extracting the adjustment value that minimizes the average luminance value (maximizes the average image density value). However, the method is not limited to this. For example, a representative value, such as the median value, among the adjustment values ​​that result in an average luminance value equal to or less than a predetermined value may be determined as the recommended adjustment value for the secondary transfer voltage. Alternatively, the recommended adjustment value for the secondary transfer voltage may be determined based on extracting an adjustment value in a luminance stable region where the standard deviation of the average luminance values ​​sequentially calculated for each predetermined number of adjustment values ​​is minimized, or an adjustment value in a luminance stable region where the luminance difference between patches between adjacent adjustment values ​​is equal to or less than a predetermined value. The recommended adjustment value for the secondary transfer voltage may be determined (provisionally determined) based on information regarding the relationship between the secondary transfer voltage and the image density (luminance) of the patch when the patch is formed. Then, in the correction process, the recommended adjustment value for the secondary transfer voltage determined (provisionally determined) in this manner may be corrected in accordance with environmental information (and further information about the print surface).

[0081] In this embodiment, a solid blue patch, which is a multi-color (multi-level color), is used as the color of the patch from which brightness data is acquired, but this is not limited to this. For example, secondary colors such as red or green may be used instead of blue, or single colors such as yellow, magenta, cyan, or black may be used. Halftone patches may also be used.

[0082] Furthermore, in this embodiment, the reading unit 80 that reads the chart 100 set by the operator as shown in FIG. 1 is used as the reading unit, but the present invention is not limited to this configuration. Alternatively, a reading unit that reads the chart 100 when it is output from the image forming apparatus 1 may be used as the reading unit. For example, as shown in FIG. 12, an in-line image sensor 86 may be provided downstream of the fixing unit 46 in the conveyance direction of the recording material S. In this case, when the chart 100 is output from the image forming apparatus 1, the image sensor 86 can read the chart 100 and obtain density information (brightness information) of the patch. In this way, the reading unit may obtain information regarding the density of the test image of the chart 100 on the recording material output from the image forming apparatus 1. Alternatively, the reading unit may obtain information regarding the density of the test image of the chart 100 on the recording material when the recording material S on which the chart 100 is formed is output from the image forming apparatus 1.

[0083] In this embodiment, the adjusted secondary transfer voltage value is saved in the adjustment mode. However, the adjusted secondary transfer voltage value before the adjustment may be saved in the adjustment mode, and when an image is actually output, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) may correct and use the adjusted value based on environmental information (and information about the print surface). This reduces the risk of "punch-through" occurring depending on the conditions when the image is actually output.

[0084] [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.

[0085] 1. Overview of this Example In the first embodiment, when conditions are such that "punch-through" is likely to occur, the adjustment value of the secondary transfer voltage is lowered to a setting that reduces the risk of "punch-through." However, this may result in the image density of a secondary color, such as blue, deviating from its optimal value. More specifically, since the secondary transfer voltage is corrected to a lower value (smaller absolute value), the image density may decrease slightly.

[0086] Therefore, in this embodiment, the operator can select whether to prioritize the image density of the secondary color or the suppression of "punch-through," thereby making it possible to adjust the transfer voltage to suit the usage situation more appropriately.

[0087] 2. Adjustment mode operation Next, the operation of the adjustment mode in this embodiment will be described. Fig. 13 is a flowchart showing an outline of the procedure of the adjustment mode in this embodiment. Fig. 14 is a schematic diagram of a setting screen (adjustment screen) 300a for the adjustment mode in this embodiment. Fig. 15 is a schematic diagram of a detailed setting screen 300b for the adjustment mode in this embodiment. Note that the operation of the adjustment mode in this embodiment is generally similar to the operation of the adjustment mode in embodiment 1, so differences will mainly be described.

[0088] First, the adjustment screen 300a of this embodiment will be described. The adjustment screen 300a of this embodiment, shown in FIG. 14, has an advanced settings button 306 added to the adjustment screen 300 of the first embodiment shown in FIG. 9. When the advanced settings button 306 is operated, the control unit 30 (adjustment processing unit 31d) causes the display unit 70a of the operation unit 70 to display the advanced settings screen 300b shown in FIG. 15. The advanced settings screen 300b has a priority image selection section 307 for selecting a prioritized image. In this embodiment, the priority image selection section 307 allows the user to select a "high density image" or "halftone." A "high density image" refers to an image that uses a large amount of toner, such as a solid image or an image of a secondary color (red, blue, or green), and requires a transfer voltage with a relatively large absolute value for good transfer. Furthermore, a "halftone" refers to an image that is primarily light-colored and uses a relatively small amount of toner per unit area of ​​the recording material S.

[0089] "Poke-through" is more likely to be apparent in halftones. Therefore, when "halftones" is selected by the priority image selection unit 307, the process of correcting the provisionally determined recommended adjustment value of the secondary transfer voltage described in the first embodiment is performed to reduce the risk of "poke-through." On the other hand, when "high density image" is selected by the priority image selection unit 307, the process of correcting the provisionally determined recommended adjustment value of the secondary transfer voltage described in the first embodiment is not performed (skip).

[0090] Next, the procedure of the adjustment mode in this embodiment will be described with reference to Fig. 13. In the flowchart of Fig. 13, the same or corresponding processes as those in the flowchart of Fig. 8 described in embodiment 1 are assigned the same step numbers (S201 to S213) as in embodiment 1. Detailed descriptions of these processes will be omitted as appropriate.

[0091] In this embodiment, after the operator selects a priority image in the priority image setting section 307 of the detail setting screen 300b, the operator operates the confirmation section (OK button) 308 of the detail setting screen 300b. Then, the control unit 30 (adjustment processor 31d) stores the priority image setting input by the operator in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S301). Note that the default setting for the priority image may be a "high density image" or a "halftone." Thereafter, the control unit 30 (adjustment processor 31d) returns the display on the display unit 70a of the operation unit 70 to the adjustment screen 90a of FIG. 18.

[0092] In this embodiment, the control unit 30 (adjustment processor 31d) provisionally determines the recommended adjustment value of the secondary transfer voltage (S208), and then determines whether the setting of the prioritized image is "halftone" (S302). If the setting of the prioritized image is "halftone," the control unit 30 (adjustment processor 31d) performs a correction process for the provisionally determined recommended adjustment value of the secondary transfer voltage to reduce the risk of "punch-through" as in the first embodiment (S209). On the other hand, if the setting of the prioritized image is not "halftone" (i.e., it is a "high-density image"), the control unit 30 (adjustment processor 31d) does not perform (skips) the correction process for the provisionally determined recommended adjustment value of the secondary transfer voltage.

[0093] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained, and an appropriate secondary transfer voltage can be set according to the image prioritized by the operator.

[0094] In this embodiment, the mode for selecting a prioritized image is adopted in order to intuitively display the setting purpose to the operator, but the method for displaying the setting items is not limited in any way. For example, an ON / OFF button for the correction process may be provided on the setting screen for the adjustment mode (including the detailed setting screen) so that the ON / OFF of the correction process for the adjustment value of the secondary transfer voltage described in the first embodiment can be set more directly. In this case, the default setting for the correction process may be OFF or ON.

[0095] Furthermore, in this embodiment, when suppression of "punch-through" is prioritized, the adjustment value of the secondary transfer voltage is corrected to be lowered, and when image density is prioritized, this correction is not made. Conversely, for example, when a "high density image" is selected, as in this embodiment, the adjustment of the secondary transfer voltage may be corrected to be higher. In other words, in addition to a mode in which the recommended adjustment value of the secondary transfer voltage determined based on information about the relationship between the secondary transfer voltage when forming the patch and the density (brightness) of the patch is corrected to be lowered, at least one of a mode in which the adjustment value is not corrected or a mode in which the adjustment value is corrected to be higher can be selected.

[0096] Furthermore, in this embodiment, the priority image was selected on the detailed setting screen 300b in FIG. 15 . However, whether or not to execute the adjustment value correction process may also be selected based on the image data of the image to be actually output. More specifically, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) can perform correction of the secondary transfer voltage adjustment value based on the image data acquired during job execution if there are many halftone images. For example, if the area ratio of halftone images in the image formation area (area where a toner image can be formed) of one sheet of recording material P or in the image to be formed therein is equal to or greater than a predetermined threshold, the secondary transfer voltage adjustment value can be corrected to be lowered. This reduces the risk of "punch-through" depending on the image to be actually output. Note that even when controlling the correction process based on image data in this way, similar to the above, it is possible to select at least one of a mode in which the secondary transfer voltage adjustment value is corrected to be lowered, a mode in which the adjustment value is not corrected, or a mode in which the adjustment value is corrected to be increased. For example, if the area ratio of high density images (such as solid images or secondary color images) in the image forming area of ​​one sheet of recording material P or in the image formed there is equal to or greater than a predetermined threshold, the adjustment value of the secondary transfer voltage can be set not to be corrected or can be corrected to increase the adjustment value.

[0097] In this manner, the image forming apparatus 1 may have an input unit capable of inputting information to the setting unit 30 instructing the setting unit 30 to set the transfer voltage based on adjustment amount information that has not been corrected by the correction amount information. The image forming apparatus 1 may also have an input unit capable of inputting information to the setting unit 30 instructing the setting unit 30 to set the transfer voltage based on adjustment amount information that has not been corrected by the correction amount information and that has been corrected to increase the absolute value of the transfer voltage. When the information is input to the setting unit 30 in response to an operator's operation, as in this embodiment, the input unit may be the operation unit 70 or the like provided in the image forming apparatus 1. The information may also be input to the setting unit 30 in response to an operator's operation of an external device 200 connected to the image forming apparatus 1. In this case, the input unit may be the input / output circuit 34 or the like that inputs information from the external device 200 to the setting unit 30. When the information is input to the setting unit 30 during image formation as described above, the control unit 30 may have the function of the input unit.

[0098] [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.

[0099] 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.

[0100] Furthermore, in the above-described embodiment, the image forming device is configured so that the operator can change the information regarding the adjustment amount of the transfer voltage determined by the image forming device in the adjustment mode, but it may also be configured so that the information cannot be changed.

[0101] 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.

[0102] 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.

[0103] Furthermore, the current detection result or voltage detection result may be the average value of multiple sampled 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.

[0104] Furthermore, the present invention is not limited to tandem-type image forming apparatuses, but can also be applied to other types of image forming apparatuses. The image forming apparatus is not limited to a color image forming apparatus, but may also be a monochrome image forming apparatus. For example, the present invention may be applied to the transfer unit of 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. The present invention can also be implemented in a variety of applications, such as printers, various printing machines, copiers, fax machines, and multifunction machines. [Explanation of symbols]

[0105] 1. Image forming device 30 Control Unit 31d Adjustment Process Section 31f Secondary transfer voltage storage unit / calculation unit 44b Intermediate transfer belt 45b Secondary transfer outer roller 70 Operation section 80 Reading unit 100 Charts N2 Secondary transfer unit S recording material

Claims

1. an image carrier that carries a toner image; a transfer member forming a transfer section that transfers a toner image from the image carrier to a recording material; an application unit that applies a voltage to the transfer member; an execution unit that executes an output operation in which a plurality of test voltages are applied to the transfer member by the application unit, and a chart is output by transferring a plurality of test images onto a recording material; a density acquisition unit that acquires density information regarding the density of the test image on the chart; an environment acquisition unit that acquires environmental information related to at least one of the temperature and humidity of the environment; a setting unit that sets a transfer voltage to be applied to the transfer member by the application unit during the transfer; and the setting unit is an image forming apparatus capable of setting the transfer voltage based on the density information and the environmental information, an adjustment amount acquisition unit that acquires adjustment amount information regarding an adjustment amount for adjusting the transfer voltage based on the test voltage information and the density information; a correction amount acquiring unit that acquires correction amount information relating to a correction amount for correcting the adjustment amount information so as to reduce the absolute value of the transfer voltage based on the environmental information; and The image forming apparatus is characterized in that the setting section is capable of setting the transfer voltage based on the adjustment amount information and the correction amount information.

2. 2. The image forming apparatus according to claim 1, wherein the correction amount acquisition unit acquires the correction amount information to correct the adjustment amount information so as to reduce the absolute value of the transfer voltage when the moisture amount indicated by the environmental information is equal to or less than a predetermined threshold.

3. 3. The image forming apparatus according to claim 1, further comprising an input unit capable of inputting information into the setting unit that instructs the setting of the transfer voltage based on the adjustment amount information that has not been corrected by the correction amount information.

4. The image forming apparatus according to claim 1 or 2, characterized in that the setting unit has an input unit capable of inputting information instructing the setting of the transfer voltage based on the adjustment amount information that has not been corrected by the correction amount information and has been corrected to increase the absolute value of the transfer voltage.

5. the adjustment amount acquisition unit acquires first adjustment amount information relating to an adjustment amount for adjusting the transfer voltage on the first side of double-sided image formation based on the test voltage information and the density information relating to the test image formed on the first side of the recording material, and acquires second adjustment amount information relating to an adjustment amount for adjusting the transfer voltage on the second side of double-sided image formation based on the test voltage information and the density information relating to the test image formed on the second side of the recording material; the correction amount acquisition unit acquires, based on the environmental information, first correction amount information relating to a correction amount for correcting the first adjustment amount information and second correction amount information relating to a correction amount for correcting the second adjustment amount information; the setting unit is capable of setting the transfer voltage for a first side of double-sided image formation based on the first adjustment amount information and the first correction amount information, and is capable of setting the transfer voltage for a second side of double-sided image formation based on the second adjustment amount information and the second correction amount information; 2. The image forming apparatus according to claim 1, wherein when the moisture content of the environment indicated by the environmental information is the same, the amount of change in the absolute value of the transfer voltage indicated by the second correction amount information is greater than the amount of change in the absolute value of the transfer voltage indicated by the first correction amount information.

6. The image forming apparatus of claim 5, wherein the correction amount acquisition unit acquires the first correction amount information to correct the first adjustment amount information so as to reduce the absolute value of the transfer voltage when the moisture amount indicated by the environmental information is equal to or less than a predetermined first threshold, and acquires the second correction amount information to correct the second adjustment amount information so as to reduce the absolute value of the transfer voltage when the moisture amount indicated by the environmental information is equal to or less than a predetermined second threshold that is greater than the first threshold.

Images