Image formation device

Abstract

To achieve improvement in usability by reducing an output of an adjustment chart.SOLUTION: When implementing an adjustment mode to a prescribed recording material larger than a reading area of a reading device, a control unit is configured to: output a first chart including a plurality of first test images to a first area of the prescribed recording material that is the same in size as the reading area of the reading device; output a second chart including a plurality of second test images to a second area different from the first area that is the same in size as the reading area of the reading device, in the same surface as a surface having the first chart formed; and implement the adjustment mode on the basis of a first detection result read by the reading device when the first chart is set at a prescribed reading position, and a second detection result read by the reading device when the second chart is set to the prescribed reading position.SELECTED DRAWING: Figure 11

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] Conventionally, as an image forming apparatus using an electrophotographic method or the like, there is an intermediate transfer type in which a toner image formed on an image carrier such as a photosensitive drum is primarily transferred onto an intermediate transfer body such as an intermediate transfer belt, and then secondarily transferred from the intermediate transfer body onto a recording material. The primary transfer is performed by applying a primary transfer voltage to a primary transfer section where the image carrier and the intermediate transfer body come into contact, and the secondary transfer is performed by applying a secondary transfer voltage to the secondary transfer section when the recording material passes through the secondary transfer section where the intermediate transfer body and the secondary transfer member come into contact.

[0003] In order to obtain a high-quality image product, it is necessary to set the secondary transfer voltage at an appropriate value when electrostatically transferring the toner image on the intermediate transfer body onto the recording material. If the secondary transfer voltage is not sufficient for the amount of charge held by the toner on the intermediate transfer body, the toner image may not be transferred sufficiently onto the recording material, resulting in a failure to obtain a desired image density. In addition, if the secondary transfer voltage is too high, discharge may occur at the secondary transfer section, which may cause the charge polarity of the toner on the intermediate transfer body to be reversed, resulting in a "blank area" where the toner image on the intermediate transfer body cannot be transferred in part.

[0004] The amount of charge required for the secondary transfer of the toner on the intermediate transfer body onto the recording material varies depending on the size of the recording material, the area ratio of the toner image, etc. Therefore, the secondary transfer voltage supplied to the secondary transfer section is often applied as a constant voltage that outputs a constant voltage corresponding to a predetermined current density. In this case, a transfer current corresponding to a predetermined voltage can be secured in the crucial part where the toner image is to be transferred, regardless of the current flowing outside the recording material or in the part of the recording material where there is no toner image.

[0005] The secondary transfer voltage can be determined based on a transfer portion voltage corresponding to the electrical resistance of the secondary transfer portion detected during a pre-rotation process before image formation, and a recording material distribution voltage corresponding to a preset type of recording material. This allows an appropriate secondary transfer voltage to be set according to environmental fluctuations, the use history of the transfer member, the type of recording material, and the like. However, since the types and conditions of recording materials used in image formation are various, the secondary transfer voltage may be excessive or insufficient with a preset default recording material distribution voltage. Therefore, it has been proposed to provide an image forming apparatus with an adjustment mode that adjusts the set voltage of the transfer voltage according to the recording material actually used in image formation.

[0006] 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 a plurality of patches (test images) are formed on one sheet of recording material is output with the secondary transfer voltage switched for each patch. This chart is read by a reading device provided in the image forming apparatus, and the density of each patch is detected. Then, the optimal secondary transfer voltage condition is selected according to the detection result. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-37185 A Summary of the Invention [Problem to be solved by the invention]

[0008] When using the above chart, the adjustment chart was output so that the size of the chart would fit within the maximum size that the reading device can read. For example, consider a case where an adjustment chart is output on a recording material that is 297 mm in the main scanning direction and 1200 mm in the sub-scanning direction in an image forming device with a reading area of ​​a pressure plate type reading device that is 297 mm in the main scanning direction and 420 mm in the sub-scanning direction. The adjustment chart is output within the range of the reading area of ​​the reading device (297 mm in the main scanning direction and 420 mm in the sub-scanning direction), and nothing is printed outside of that, so it becomes a margin. If the adjustment was not completed in one go, it was necessary to output another adjustment chart on the same paper type, perform the reading operation, and make the adjustment. Outputting the adjustment chart multiple times and increasing the number of operations by the operator to replace it with the reading device may reduce usability.

[0009] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an image forming apparatus capable of reducing the number of times adjustment charts are output and improving usability. [Means for solving the problem]

[0010] The above object is achieved by the image forming apparatus according to the present invention. In summary, a typical configuration of the present invention includes an image carrier that carries a toner image, an intermediate transfer body to which the toner image is primarily transferred from the image carrier, a transfer member forming a transfer section for performing a secondary transfer of the toner image from the intermediate transfer body to a recording material, an application section that applies a voltage to the transfer member, a discharge section that discharges the recording material on which the toner image transferred in the transfer section is fixed and an image is formed, a reading device capable of reading an image on the recording material set at a predetermined reading position, and an adjustment mode in which the application section applies a plurality of test voltages to the transfer member to output a chart on which a plurality of test images are sequentially transferred, and the secondary transfer voltage applied to the transfer member by the application section during the secondary transfer is adjusted based on the reading result read by the reading device when the chart is set at the predetermined reading position. and a control unit, wherein when the control unit executes the adjustment mode on a predetermined recording material that is larger than a reading area of ​​the reading device, the control unit causes a first chart including a plurality of first test images to be output in a first area of ​​the predetermined recording material, and causes a second chart including a plurality of second test images to be output in a second area different from the first area on the same side as the side on which the first chart is formed, and the control unit is configured to execute the adjustment mode based on a first detection result read by the reading device when the first chart is set at the predetermined reading position and the second chart is not set at the predetermined reading position, and a second detection result read by the reading device when the second chart is set at the predetermined reading position and the first chart is not set at the predetermined reading position. Effect of the Invention

[0011] According to the present invention, the number of adjustment charts to be output can be reduced, and usability can be improved. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a block diagram showing a control system of the image forming apparatus. [Diagram 3] FIG. 11 is a flow chart showing an outline of a procedure for controlling secondary transfer. [Figure 4] 6 is a graph showing voltage-current characteristics obtained by controlling a secondary transfer voltage. FIG. [Diagram 5] FIG. 4 is a schematic diagram showing an example of a table of recording material distribution voltages. [Figure 6] FIG. 1 is a schematic diagram of a large size chart. [Figure 7] FIG. 1 is a schematic diagram of a chart for a small size. [Figure 8] FIG. 11 is a diagram showing the correspondence between the colors of the page determination patches and the page numbers. [Figure 9] FIG. 11 is a flowchart illustrating a procedure for a process of determining an adjustment value according to the first embodiment. [Figure 10] FIG. 13 is a diagram of a setting screen for an adjustment mode. [Figure 11] FIG. 1 is a schematic diagram showing a chart printed on a long sheet of paper that is larger than the reading area of ​​a reading device. [Figure 12] FIG. 13 is a diagram showing a setting screen for an adjustment mode showing a reading status; [Figure 13] 7 is a diagram illustrating a procedure of a process for determining an adjustment value of a secondary transfer voltage. [Figure 14] FIG. 13 is a diagram showing the relationship between patch numbers and average luminance values ​​of patches. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the image forming apparatus according to the present invention will be described in more detail 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 according to this embodiment. The image forming apparatus 1 according to this embodiment is a tandem type multifunction machine (having the functions of a copier, printer, and facsimile machine) that employs an intermediate transfer method and is capable of forming full-color images using an electrophotographic method.

[0015] As shown in FIG. 1, the image forming apparatus 1 includes an apparatus main body 10, a reading device 80, a feeding section 90, an image forming section 40, a discharge section 48, a control section 30, an operation section 70, and the like. Inside the apparatus main body 10, a temperature sensor 71 (FIG. 2) capable of detecting the temperature inside the apparatus, a humidity sensor 72 (FIG. 2) capable of detecting the humidity inside the apparatus, and the like are provided. The image forming apparatus 1 can form a four-color full-color image on a recording material (sheet, transfer material, recording medium) S in response to image information (image signal) from the reading device 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, and specific examples thereof include plain paper, a synthetic resin sheet that is a substitute for plain paper, cardboard, and an overhead projector sheet.

[0016] The image forming section 40 can form an image on the recording material S fed from the feeding section (feeding device) 90 based on image information. The image forming section 40 has image forming units 50y, 50m, 50c, 50k, toner bottles 41y, 41m, 41c, 41k, exposure devices 42y, 42m, 42c, 42k, an intermediate transfer unit 44, a secondary transfer device 45, and a fixing section 46. The image forming units 50y, 50m, 50c, 50k form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Elements having the same or corresponding functions or configurations provided corresponding to these four image forming units 50y, 50m, 50c, 50k may be generally described by omitting the suffixes y, m, c, and k of the reference numerals indicating that the elements are for any of the colors. The image forming apparatus 1 can also form a monochrome image, such as a black monochrome image, or a multi-color image, using a desired single or several image forming units 50.

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

[0018] The photosensitive drum 51 is movable (rotatable) while carrying an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 51 is a negatively charged organic photoconductor (OPC) having an outer diameter of 30 mm. The photosensitive drum 51 has an aluminum cylinder as a base and a surface layer formed on the surface of the aluminum cylinder. In this embodiment, the surface layer has three layers, an undercoat layer, a photocharge generation layer, and a charge transport layer, which are applied and laminated on the base in the following order. When an image forming operation is started, 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 source 73 (FIG. 2) is connected to the charging roller 52. The charging power source 73 applies a predetermined charging voltage (charging bias) to the charging roller 52 during the charging process.

[0020] The charged surface of the 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 circumferential surface) of the photosensitive drum 51.

[0021] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by supplying toner by the developing device 20, and a toner image is formed on the photosensitive drum 51. In this embodiment, the developing device 20 contains a two-component developer having non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. 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 such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). Inside the developing sleeve 24, a roller-shaped magnet roller is fixed and arranged so as not to rotate relative to the main body (developing container) of the developing device 20. The developing sleeve 24 carries the developer and transports it to a developing area facing the photosensitive drum 51. A developing power source 74 (FIG. 2) is connected to the developing sleeve 24. The developing power source 74 applies a predetermined developing voltage (developing bias) to the developing sleeve 24 during the developing 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 so as to face the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer unit 44 has an intermediate transfer belt 44b, which is an endless belt serving as an intermediate transfer body. The intermediate transfer belt 44b is wound around a driving roller 44a, a driven roller 44d, and a secondary transfer inner roller 45a serving as a plurality of tension rollers (support rollers), and is stretched with a predetermined tension. The intermediate transfer belt 44b is movable (rotatable) while carrying a toner image. The driving 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 controls the tension of the intermediate transfer belt 44b to a constant value. A force is applied to the driven roller 44d by a tension spring (not shown) serving as a biasing member serving as a biasing means, so as to push the intermediate transfer belt 44b from the inner peripheral surface side to the outer peripheral surface side. This force applies a tension of about 2 to 5 kg in the transport direction of the intermediate transfer belt 44b. The secondary transfer inner roller 45a constitutes the secondary transfer device 45, as described later. The intermediate transfer belt 44b receives a driving force as the driving roller 44a is rotated and driven, and rotates (moves around) in the direction of the arrow (clockwise direction) in the figure at a predetermined circumferential speed corresponding to the circumferential speed of the photosensitive drum 51. In addition, primary transfer rollers 47y, 47m, 47c, and 47k, which are roller-type primary transfer members as primary transfer means, are arranged on the inner circumferential surface side of the intermediate transfer belt 44b in correspondence with the photosensitive drums 51y, 51m, 51c, and 51k. The primary transfer roller 47 holds the intermediate transfer belt 44b between itself 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. The primary transfer power supply 75 applies a primary transfer voltage (primary transfer bias) which is a DC voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) to the primary transfer roller 47 during the primary transfer process. For example, when a full-color image is formed, the toner images of yellow, magenta, cyan, and black formed on the photosensitive drums 51y, 51m, 51c, and 51k are primarily transferred in sequence onto the intermediate transfer belt 44b so as to be superimposed on each other. A voltage detection sensor 75a for detecting an output voltage and a current detection sensor 75b for detecting an 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] Here, in this embodiment, the primary transfer roller 47 has an elastic layer of ion conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the primary transfer roller 47 is, for example, 15 to 20 mm. A roller having an electrical resistance value of 1×105 to 1×108 Ω (measured at N / N (23° C., 50% RH), 2 kV applied) can be suitably used as the primary transfer roller 47. In this embodiment, the intermediate transfer belt 44b is an endless belt having a three-layer structure including a base layer, an elastic layer, and a surface layer in the following order from the inner peripheral surface side to the outer peripheral surface side. As a material constituting the base layer, a material containing an appropriate amount of carbon black as an antistatic agent in a resin such as polyimide or polycarbonate or various rubbers can be suitably used. The thickness of the base layer is, for example, 0.05 to 0.15 mm. As an elastic material constituting the elastic layer, a material containing an appropriate amount of an ion conductive agent in various rubbers such as urethane rubber or silicone rubber can be suitably used. The thickness of the elastic layer is, for example, 0.1 to 0.500 mm. As a material constituting the surface layer, a resin such as a fluororesin can be suitably used. The surface layer reduces the adhesion of the toner to the surface of the intermediate transfer belt 44b, and facilitates the transfer of the toner to the recording material S at the secondary transfer section N2 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 a 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. Then, the surface layer is formed by dispersing one or more types of powder or particles such as a fluororesin, or particles with different particle sizes, as a material that reduces surface energy and increases lubricity, on this base material. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5×108 to 1×1014 Ω·cm (23° C., 50% RH) and a hardness of MD1 hardness of 60 to 85° (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). Note that although the intermediate transfer belt 44b has a three-layer structure in this embodiment, it may have a single layer structure of a material equivalent to the above-mentioned base layer.

[0025] On the outer peripheral surface side of the intermediate transfer belt 44b, a secondary transfer outer roller 45b, which is a roller-type secondary transfer member as a secondary transfer means and which constitutes the secondary transfer device 45 together with the secondary transfer inner roller 44a, is arranged. The secondary transfer outer roller 45b sandwiches the intermediate transfer belt 44b between itself and the secondary transfer inner roller 45a. As a result, the secondary transfer outer roller 45b abuts against 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 abut. The toner image formed on the intermediate transfer belt 44b is secondarily transferred onto the recording material S that is being conveyed while being sandwiched between the intermediate transfer belt 44b and the secondary transfer outer roller 45b in 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] Thus, in this embodiment, the secondary transfer device 45 is configured to have the secondary transfer inner roller 45a as an opposing member and the secondary transfer outer roller 45b as a secondary transfer member. The secondary transfer inner roller 45a is disposed facing the secondary transfer outer roller 45b via the intermediate transfer belt 44b. A secondary transfer power source 76 (FIG. 2) as a voltage application means (application unit) is connected to the secondary transfer outer roller 45b. The secondary transfer power source 76 applies a secondary transfer voltage (secondary transfer bias) that is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner to the secondary transfer outer roller 45b during the secondary transfer process. 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 source 76 (FIG. 2). Also, in this embodiment, the core metal of the secondary transfer inner roller 45a is connected to the ground potential. That is, in this embodiment, the secondary transfer inner roller 45a is electrically grounded (connected to the 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 secondary transfer outer 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 is passed, so that the toner image on the intermediate transfer belt 44b is secondarily transferred onto the recording material S. In this embodiment, the secondary transfer power source 76 applies a DC voltage to the secondary transfer outer roller 45b to apply the secondary transfer voltage to the secondary transfer portion N2, but the present invention is not limited to this embodiment. For example, the secondary transfer power source 76 may apply a DC voltage to the secondary transfer inner 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 secondary transfer inner roller 45a as the secondary transfer member, and the secondary transfer outer roller 45b as the opposing member is electrically grounded. In this embodiment, the secondary transfer outer roller 45b has an elastic layer of ion conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the secondary transfer outer roller 45b is, for example, 20 to 25 mm. In addition, a roller having an electrical resistance value of 1×105 to 1×108 Ω (measured at N / N (23°C, 50% RH), applied with 2 kV) can be suitably used as the secondary transfer outer roller 45b.

[0027] The recording material S is fed from a feeding section 90 in parallel with the above-mentioned toner image forming operation. That is, the recording material S is stacked and stored in a recording material cassette 91 serving as a recording material storage section. The recording material S stored in the recording material cassette 91 is sent to a conveying path 93 by a feeding roller 92 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 the 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 section 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 section 90.

[0028] The recording material S onto which the toner image has been transferred is transported to a fixing section (fixing device) 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 by being sandwiched between the fixing roller 46a and the pressure roller 46b and transported. This causes the toner image to be fixed (melted and fixed) 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 on which the toner image has been fixed is conveyed through a discharge path 48a by a pair of discharge rollers 48b as a conveying member, and is discharged (output) from a discharge port 48c and stacked on a discharge tray 48d provided outside the apparatus main body 10. A discharge section (discharge device) 48 is configured by the discharge path 48a, the pair of discharge rollers 48b, the discharge port 48c, the discharge tray 48d, and the like. In this embodiment, the image forming apparatus 1 is capable of double-sided image formation (double-sided printing, automatic double-sided printing) in which images are formed on both sides of the recording material S. Between the fixing section 46 and the discharge port 48c, a reversing conveying path 12 is provided for turning over the recording material S after the toner image has been fixed on the first side and supplying it again to the secondary transfer section N2. During double-sided image formation, the recording material S after the toner image has been fixed on the first side is guided to the reversing conveying path 12. The recording material S is reversed in the conveying direction by a switchback roller pair 13 provided in the reversing conveying path 12 and 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 section 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 in the image formation on the first side, and the toner image is fixed and then discharged to a discharge tray 48d. The reversing conveying path 12, the switchback roller pair 13, the double-sided conveying path 14, the re-conveying roller pair 15, etc. constitute a double-sided conveying section (double-sided conveying device) 11. By the operation of the double-sided conveying section 11, images can be formed on both sides of one recording material S.

[0030] The surface of the photosensitive drum 51 after the primary transfer is neutralized by a pre-exposure device 54. In addition, 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 scrapes off deposits from the surface of the rotating photosensitive drum 51 with a cleaning blade as a cleaning member that contacts the surface of the photosensitive drum 51 and stores the deposits in a cleaning container. The cleaning blade is contacted with the surface of the photosensitive drum 51 with a predetermined pressing force so that the tip of the free end side faces the upstream side of the rotation direction of the photosensitive drum 51 in a counter direction. In addition, the intermediate transfer unit 44 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 device 80 serving as a reading means (reading section) is disposed on the upper portion of the apparatus main body 10. The reading device 80 has an automatic document transport device (automatic document feeder (ADF)) 81 serving as a document transport means (document transport section), 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.

[0032] In this embodiment, the reading device 80 can sequentially read the image of the original (recording material S on which an image is formed) placed on the platen glass 82 with the reading element 85 via the optical system 84 while scanning and exposing the image with the movable light source 82. In this case, the reading device 80 sequentially illuminates the original placed on the platen glass 82 with the moving light source 83, and sequentially forms an image of the light reflected from the original on the reading element 85 via the optical system 84. This allows the image of the original to be read at a predetermined dot density by the reading element 85. The platen glass 82 forms a reading surface that supports the recording material S so that the reading device 80 can read it.

[0033] In this embodiment, the reading device 80 can sequentially expose the image of the document conveyed by the automatic document feeder 81 to the light source 82 as the document is conveyed, and sequentially read the image by the reading element 85 via the optical system 84. In this case, the reading device 80 sequentially illuminates the document passing a predetermined reading position on the platen glass 82 with the light source 83, and sequentially forms a reflected light image 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. The automatic document feeder 81 automatically conveys the document so that it passes through the reading position of the reading device 80 in a state where the document is separated one by one. The automatic document feeder 81 constitutes a conveying device that sequentially conveys the recording material S so that the reading device 80 can read the recording material S.

[0034] In this way, the reading device 80 optically reads an image on the recording material S that is placed on the platen glass 82 or transported by the automatic document feeder 81, and converts it into an electrical signal. In this embodiment, the reading device 80 can arrange one sheet of large-sized recording material S, such as A3 size, or two sheets of small-sized recording material S, such as A4 size, side by side on the platen glass 82. In this embodiment, the reading device 80 can continuously transport a plurality of recording materials S, such as A3 size or A4 size, loaded on the document placement section of the automatic document feeder 81 to the above-mentioned reading position. In addition, the automatic document feeder 81 can automatically read images on both sides of the recording material S.

[0035] For example, when the image forming apparatus 1 operates as a copier, the image of the document read by the reading device 80 is sent to the image processing unit of the control unit 30 as image data of three colors, for example, red (R), green (G), and blue (B) (each 8 bits). In the image processing unit, the image data of the document is subjected to a predetermined image processing as necessary, and is converted into image data of four colors, yellow, magenta, cyan, and black. The image processing includes shading correction, positional deviation correction, brightness / color space conversion, gamma correction, frame erasure, and color / movement editing. The image data corresponding to the four colors, yellow, magenta, cyan, and black, are sequentially sent to the exposure devices 42y, 42m, 42c, and 42k, respectively, and the above-mentioned image exposure is performed according to this image data. In addition, as will be described in detail later, the reading device 80 is also used to read the patches of the chart (to obtain density information (luminance information)) in the adjustment mode.

[0036] FIG. 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus 1 of this embodiment. As shown in FIG. 2, the control unit 30 is composed of a computer. The control unit 30 has, for example, a CPU 31 as an arithmetic control unit, a ROM 32 as a storage unit for storing programs for controlling 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 31 is a microprocessor that controls the overall control of the image forming apparatus 1, and is the main body of the system controller. The CPU 31 is connected to the feeding unit 90, the image forming unit 40, the discharge unit 48, and the operation unit 70 via the input / output circuit 34, and exchanges signals with each of these units and controls the operation of each of these units. The ROM 32 stores an image formation control sequence for forming an image on the recording material S, etc. 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.

[0037] The operation unit 70 has an input unit such as an operation button as an input means, and a display unit 70a consisting of a liquid crystal panel as a display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as an input means. An operator such as a user or a service person can execute a job (described later) by operating the operation unit 70. The control unit 30 operates various devices of the image forming apparatus 1 upon receiving a signal from the operation unit 70. The image forming apparatus 1 can also execute a job based on an image formation signal (image data, control command) from an external device 200 such as a personal computer.

[0038] In this embodiment, the control unit 30 has 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 has a primary transfer voltage storage / calculation unit 31e and a secondary transfer voltage storage / calculation unit 31f. These processing units and storage / calculation units may be provided as part of the CPU 31 or the RAM 33. For example, the control unit 30 (more specifically, the image formation processor 31c) can execute a job as described above. 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. The 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 voltage of the secondary transfer voltage. The adjustment mode will be described in detail later.

[0039] Here, the image forming apparatus 1 executes a job (image output operation, print job) which is a series of operations for forming and outputting an image on a single or multiple recording materials S, which is started by one start instruction. The job generally includes an image forming process, a pre-rotation process, a paper-interval process in the case of forming an image on multiple recording materials S, and a post-rotation process. The image forming process is a period in which the formation of an electrostatic image of an image to be actually formed on the recording material S and output, the formation of a toner image, the primary transfer of the toner image, and the secondary transfer are performed, and the image formation time (image formation period) refers to this period. More specifically, the timing of the image formation time differs depending on the position where each of the processes of forming the electrostatic image, forming the toner image, the primary transfer of the toner image, and the secondary transfer is performed. The pre-rotation process is a period in which a preparatory operation is performed before the image forming process, from when a start instruction is input until the image actually starts to be formed. The paper-interval process is a period corresponding to the period between recording materials S when image formation is performed continuously on multiple recording materials S (continuous image formation). The post-rotation process is a period in which an arrangement operation (preparatory operation) is performed after the image forming process. Non-image formation (non-image formation period) refers to a period other than image formation, and includes the above-mentioned pre-rotation process, paper interval process, post-rotation process, and also the pre-multiple-rotation process, which is a preparatory operation when the image forming apparatus 1 is turned on or when it returns from a sleep state.

[0040] 2. Secondary transfer voltage control Next, the control of the secondary transfer voltage will be described. Fig. 3 is a flow chart showing an outline of the procedure for controlling the secondary transfer voltage in this embodiment. Generally, the control of the secondary transfer voltage is classified into constant voltage control and constant current control, but in this embodiment, the constant voltage control is used.

[0041] First, the control unit 30 (pre-image formation 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 on the recording material S. This information on the recording material S may include the size (width, length) of the recording material S on which the image is 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 or not. In particular, in this embodiment, the information on the recording material S includes information on the size of the recording material S and information on the category of the recording material S (so-called paper type category) such as "thin paper, plain paper, thick paper, etc." related to the thickness of the recording material S. Note that the information on the recording material S (recording material information) includes attributes (so-called paper type category) based on general characteristics such as plain paper, fine paper, glossy paper, glossy paper, coated paper, embossed paper, thick paper, thin paper, etc. The information on the recording material S includes any information that can distinguish the recording material S, such as the numerical values ​​or numerical ranges of basis weight, thickness, size, and stiffness, or the brand (including manufacturer, product name, model number, etc.). Each recording material S distinguished by the information on the recording material S can be considered to constitute a type of recording material S. The information on the recording material S may be included in print mode information that specifies the operation settings of the image forming apparatus 1, such as "plain paper mode" and "thick paper mode," or may be replaced by the print mode information. The control unit 30 (pre-image formation preparation process unit 31a) writes the job information to the RAM 33 (S102).

[0042] Next, the control unit 30 (pre-image formation preparation process unit 31a) acquires environmental information detected by the temperature sensor 71 and humidity sensor 72 (S103). In addition, 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) obtains 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. Then, the control unit 30 writes this target current Itarget into the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S104). The reason why the target current Itarget is changed according to the environmental information is because the charge amount of the toner changes depending on the environment. The information indicating the relationship between the environmental information and the target current Itarget is obtained in advance by experiments or the like.

[0043] Next, the control unit 30 (ATVC control processor 31b) obtains information on the electrical resistance of the secondary transfer unit N2 by ATVC (Active Transfer Voltage Control) (S105). The ATVC control is performed before the toner image on the intermediate transfer belt 44b and the recording material S to which the toner image is transferred reach the secondary transfer unit N2. In addition, the ATVC control supplies a predetermined voltage of multiple levels from the secondary transfer power source 76 to the secondary transfer outer roller 45b in a state in which the secondary transfer outer roller 45b and the intermediate transfer belt 44b are in contact with each other. Then, the current value when 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 obtained. The control unit 30 writes information on the relationship between the voltage and the current in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f). The relationship between the voltage and the current changes depending on the electrical resistance of the secondary transfer unit 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 one in which the current changes so as to be expressed by a polynomial of the voltage that is equal to or greater than the second degree (a quadratic expression in this embodiment). Therefore, in this embodiment, the predetermined voltage or current supplied when acquiring information regarding 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.

[0044] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines the voltage value to be applied from the secondary transfer power source 76 to the secondary transfer outer roller 45b (S106). That is, the control unit 30 determines the voltage value Vb required to pass the target current Itarget in the state where the recording material S is not present in the secondary transfer portion N2 based on the target current Itarget written in the RAM 33 in S104 and the relationship between the voltage and current determined in S105. This voltage value Vb corresponds to the secondary transfer partial voltage (transfer voltage for the electrical resistance of the secondary transfer portion N2). Also, the ROM 32 stores information for determining the recording material shared voltage Vp (transfer voltage for 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 moisture amount of the atmosphere and the recording material shared voltage Vp for each classification (corresponding to the paper type category) of the basis weight of the recording material S. The control unit 30 (pre-image formation preparation process unit 31a) can obtain the moisture content of the atmosphere based on the environmental information (temperature and humidity) detected by the temperature sensor 71 and the humidity sensor 72. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains the recording material distribution voltage Vp from the above table data based on the job information obtained in S101 and the environmental information obtained in S103. Furthermore, when an adjustment value is set by an adjustment mode that adjusts the set voltage of the secondary transfer voltage, which will be described later, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains an adjustment amount ΔV corresponding to the adjustment value. As will be described later, when the adjustment amount ΔV is set by the adjustment mode, it is stored in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f). The control unit 30 calculates Vb+Vp+ΔV by adding the above Vb, Vp, and ΔV as the secondary transfer voltage Vtr to be applied from the secondary transfer power source 76 to the outer secondary transfer roller 45b when the recording material S passes through the secondary transfer unit N2. The control unit 30 then writes this Vtr (=Vb+Vp+ΔV) to the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f). The table data for calculating the recording material shared voltage Vp as shown in FIG. 5 is previously obtained by experiments or the like.

[0045] Here, the recording material voltage Vp may change depending on the surface properties of the recording material S in addition to the 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 the information related to the surface properties of the recording material S. In this embodiment, the 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, the image forming apparatus 1 may be provided with a measuring means for detecting the thickness and surface properties of the recording material S, and the recording material voltage Vp may be calculated based on the information obtained by this measuring means.

[0046] 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 to the recording material S and output (S108).

[0047] Incidentally, with regard to the primary transfer portion N1 as well, the same ATVC control as described above is performed from the start of a job until the toner image is transported to the primary transfer portion N1, but a detailed description thereof will be omitted here.

[0048] 3. Overview of Adjustment Mode Next, the adjustment mode (simplified adjustment mode) for adjusting the set voltage of the secondary transfer voltage will be described.

[0049] 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 be significantly different from those of a standard recording material S. In this case, the setting voltage of the secondary transfer voltage using the default recording material distribution voltage Vp set in advance as described above may not be able to perform optimal transfer. That is, the secondary transfer voltage must first be a voltage necessary for transferring the toner on the intermediate transfer belt 44b to the recording material S. In addition, the secondary transfer voltage must be suppressed 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 a value assumed as a standard value. In this case, the setting voltage of the secondary transfer voltage using the default recording material distribution voltage Vp set in advance may be insufficient 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 setting voltage of the secondary transfer voltage by increasing the recording material distribution voltage Vp, for example. Conversely, 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 the electrical resistance lower than the value assumed as the standard value, and making it easier for discharge to occur. In this case, the set voltage of the secondary transfer voltage using the preset default recording material voltage Vp may cause image defects due to abnormal discharge. Therefore, in this case, it is desirable to lower the set voltage of the secondary transfer voltage by, for example, lowering the recording material voltage Vp.

[0050] Therefore, it may be desirable for an operator such as a user or a service person to adjust (change) the set voltage of the secondary transfer voltage during execution of a job to an optimal value by adjusting (changing) the recording material assigned voltage Vp according to the recording material S actually used for image formation. In other words, it may be desirable to select an optimal recording material assigned voltage Vp+ΔV (adjustment amount) according to the recording material S actually used for image formation. This adjustment may be performed by the following method. That is, for example, an operator outputs an image to be output while switching the secondary transfer voltage for each sheet of recording material S, checks the output image, and determines the optimal set voltage of the secondary transfer voltage (more specifically, the recording material assigned voltage Vp+ΔV). However, in this method, since the output of the image and the adjustment of the set voltage of the secondary transfer voltage are repeated, the amount of recording material S that is wasted may increase, and the adjustment may take a long time.

[0051] Therefore, in this embodiment, the image forming apparatus 1 is provided with an adjustment mode for adjusting the set voltage of the secondary transfer voltage. In this adjustment mode, a chart on which a plurality of patches (test images) of representative colors are formed on the recording material S actually used for image formation is output while switching the set voltage of the secondary transfer voltage for each patch. Then, based on the result of reading the output chart by the reading device 80, the optimal set voltage of the secondary transfer voltage (more specifically, the recording material distribution voltage Vp+ΔV) can be determined. In this embodiment, in the adjustment mode, information on the recommended adjustment amount ΔV of the set voltage of the secondary transfer voltage is presented based on the density information (luminance information) of the patch on the chart (typically a patch of a solid image). This reduces the need for the operator to visually check the image on the chart, thereby reducing the burden on the operator, and makes it possible to more appropriately adjust the setting of the secondary transfer voltage.

[0052] 4. Charts Next, a chart (adjustment image, test page) output in the adjustment mode in this embodiment will be described. FIGS. 6 and 7 are schematic diagrams of a chart 100 in this embodiment. In this embodiment, in the adjustment mode, two types of charts 100 shown in FIGS. 6 and 7 are output according to the size of the recording material S used. Here, the size of the recording material S is indicated by the recording material width (length in the main scanning direction)×recording material length (length in the sub-scanning direction). The recording material width is the length in a direction (width direction) approximately perpendicular to the conveying direction of the recording material S when passing through the secondary transfer portion N2. Also, the recording material length is the length in a direction approximately parallel to the conveying direction of the recording material S when passing through the secondary transfer portion N2.

[0053] FIG. 6 shows a large size chart (hereinafter also referred to as a "large chart") 100L that is output when using a large size recording material S such as A3 (297 mm x 420 mm) or ledger (approximately 280 mm x 432 mm).

[0054] FIG. 7 shows small-size charts (hereinafter also referred to as "small charts") 100Sa and 100Sb that are output when using a small-size recording material S such as A4 landscape (297 mm x 210 mm) or letter landscape (approximately 280 mm x 216 mm).

[0055] Considering visual confirmation by an operator, the larger the size of the patch of the chart output in the adjustment mode, the easier it is to confirm image defects. However, if the patch is large, the number of patches that can be formed on one sheet of recording material S is reduced. The shape of the patch can be a square or the like. The color of the patch can be determined depending on the image defect to be confirmed and the ease of confirmation. For example, when the secondary transfer voltage is increased from a low value, the lower limit of the secondary transfer voltage can be determined from the voltage value at which a patch of a secondary color such as red, green, or blue can be properly transferred. In addition, when the operator visually confirms, the upper limit of the secondary transfer voltage can be determined from the voltage value at which an image defect occurs in a halftone patch due to a high secondary transfer voltage when the secondary transfer voltage is further increased.

[0056] 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. In the large chart 100L of FIG. 6, eleven sets of the width direction patch sets 101-103 are arranged in the transport direction. In the small chart 100S of FIG. 7, ten sets of the width direction patch sets 101-103 are 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 of the maximum density level. In this embodiment, the blue solid is a superposition of 100% magenta (M) toner and 100% cyan (C) toner, and the toner coverage of the blue solid is 200%. Also, a halftone image is an image with a toner amount of 10 to 80% when the toner amount of a solid image is 100%. Also, in this embodiment, the chart 100 is provided with patch identification information 104 corresponding to each of the patch sets 101 to 103, for identifying the setting of the secondary transfer voltage applied to each patch set. This patch identification information 104 may be a value corresponding to the adjustment value of the secondary transfer voltage, which will be described later. In the large chart 100L of FIG. 6, eleven pieces of patch identification information 104 (in this embodiment, eleven pieces from -5 to 0 to +5) corresponding to the setting of the secondary transfer voltage in eleven stages are arranged. In the small chart 100S of FIG. 7, ten pieces of patch identification information 104 (in this embodiment, five pieces from -4 to 0 on the first sheet and five pieces from +1 to +5 on the second sheet) corresponding to the setting of the secondary transfer voltage in ten stages are arranged.

[0057] The size of the patch is required to be a size that allows an operator to easily judge the presence or absence of an image defect. The transferability of the blue solid patch 101 and the black solid patch 102 is difficult to judge when the patch size is small, so the patch size is preferably 10 mm square or more, and more preferably 25 mm square or more. In the halftone patch 103, image defects caused by discharge that occur when the secondary transfer voltage is increased often become image defects such as white dots. This image defect tends to be easier to judge even for a small image compared to the transferability of a solid image. However, since it is easier to see if the image is 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. In addition, the interval between the patch sets 101 to 103 in the transport direction may be set so that the secondary transfer voltage can be switched. In this embodiment, the blue solid patch 101 and the black solid patch 102 are each a square of 25.7 mm×25.7 mm (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 end of the chart 100 in the width direction. In this embodiment, the interval between the patch sets 101 to 103 in the transport direction is 9.5 mm. The secondary transfer voltage is switched at the timing when the part on the chart 100 corresponding to this interval 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 (test voltages) that are different so that the absolute values ​​are sequentially increased. However, the present invention is not limited to such an 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 transport direction of the recording material S when the chart 100 is formed, using multiple secondary transfer voltages (test voltages) whose absolute values ​​are different from each other so that they become smaller in sequence.

[0058] It is preferable that patches are not formed in the vicinity of the leading and trailing ends in the transport direction of the recording material S (for example, within a range of about 20 to 30 mm inward from the edge). This is for the following reason. That is, among the ends in the transport direction of the recording material S, there may be an image defect that occurs only at the leading or trailing end in the transport direction, but not at the ends in the width direction. In this case, it may be difficult to determine whether the image defect has occurred due to the fluctuation of the secondary transfer voltage.

[0059] The size of the recording material S that can be placed on the reading device 80 of this embodiment is up to 13 inches (about 330 mm) x 19.2 inches (about 487 mm). That is, the reading area of ​​the reading device 80 is 13 inches (about 330 mm) x 19.2 inches (about 487 mm). The large chart 100L in FIG. 6 corresponds to the recording material S of this size. When the size of the recording material S is 13 inches x 19.2 inches or less and A3 (297 mm x 420 mm) or more, a chart corresponding to image data cut 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 cut according to 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 (top end in the figure) are aligned, and the center of the recording material S in the width direction and the center of the large chart 100L in the width direction are aligned, and the image data is cut out. In this embodiment, the image data is cut out so that a margin of 2.5 mm is provided at the ends (both ends in the width direction and both ends in the transport direction in this embodiment). For example, when the large chart 100L is output onto an A3 (297 mm x 420 mm) recording material S, image data in the range of 292 mm x 415 mm is cut out so that a margin of 2.5 mm is provided at each end. Then, the large chart 100L corresponding to the image data is output onto an A3 (297 mm x 420 mm) recording material S based on the leading edge center. When a recording material S with a width smaller than 13 inches is used, the size of the halftone patch 103 in the width direction at the end in the width direction becomes smaller. Furthermore, when a recording material S with a width smaller than 13 inches is used, the margin at the rear end in the transport direction becomes smaller. As described above, 11 patch sets of -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 the transport direction so that they fit within a length of 415 mm in the transport direction when the size of the recording material S is A3.

[0060] In this embodiment, when a recording material S smaller than A3 (297 mm x 420 mm) is used, the small chart 100S in FIG. 7 is output. The small chart 100S in FIG. 7 corresponds to a size smaller than A5 (vertical feed) to A3 (297 mm x 420 mm) (i.e., a length 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 of the small chart 100S is 13 inches x 210 mm. In the width direction, the halftone patch 103 becomes smaller according to the size of the recording material S. In the transport direction, the five patch sets are arranged to fit within a length of 167 mm in the transport direction, and the margin at the rear end becomes longer according to the length of the recording material S in the transport direction of 210 to 419 mm. In the case of 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, in order to increase the number of patches, the chart is divided into two sheets, and a total of ten patch sets are formed, five sets from -4 to 0 and five sets from +1 to +5. Note that the small chart 100S omits the -5 patch set from the large chart 100L.

[0061] Also, a trailing edge identification patch 106 for determining the arrangement of the chart, a page determination patch 107 for determining the reading order, and a page identification number 105 for allowing the operator to determine the reading order are provided. A black band that is the trailing edge identification patch 106 is printed at the trailing edge of the chart, and the orientation of the read image is corrected based on the trailing edge identification patch 106. Also, the page determination patch 107 is printed in the same main scanning direction as the trailing edge identification patch 106. In this embodiment, the page is identified by color, and FIG. 8 shows the correspondence between the color of the page determination patch 107 and the page number. The page determination patch 107 is information for the control unit 30 to determine the reading order. That is, it is identification information for determining which chart is read by the reading device 80 when multiple charts (for example, the first chart and the second chart) are output on a long paper (N1=2) that is larger than the reading area of ​​the reading device as described later.

[0062] In this embodiment, in addition to standard sizes, the operator can also input and specify from the operation unit 70 or external device 200, to output the chart 100 using recording material S of any size (free size).

[0063] 5. Adjustment mode operation Next, the operation of the adjustment mode in this embodiment will be described. Fig. 9 is a flow chart showing an outline of the procedure of the adjustment mode in this embodiment. Fig. 10 is a schematic diagram showing an example of a setting screen for the adjustment mode. Here, an example is taken of a case where an operator inputs an instruction from the operation unit 70 of the image forming apparatus 1 to execute the adjustment mode. Also, an example is taken of a case where an operator reads density information (brightness information) of a patch by placing a recording material S on which a chart 100 has been formed on the platen glass 82 of the reading device 80. For simplicity, the recording material on which a chart has been formed may be simply referred to as a "chart".

[0064] The setting screen of the adjustment mode will be described. In this embodiment, the control unit 30 (adjustment process unit 31d) displays a setting screen 300 of the adjustment mode as shown in FIG. 10(a) on the display unit 70a of the operation unit 70. The setting screen 300 has an output instruction unit (chart output button) 303 for instructing the output of the chart 100. The setting screen 300 also has a confirmation unit (OK button) 304 for confirming the setting, and a cancel button 405 for canceling the change of the setting. The setting screen 300 also has a message display unit 306 for displaying various messages related to the adjustment mode. In this embodiment, a start button 307 provided on the operation unit 70 adjacent to the display unit 70a functions as an input unit for inputting an instruction to start reading the chart 100 to the reading device 80. However, a display (button) functioning as the input unit may be provided on the setting screen 300 displayed on the display unit 70a.

[0065] When the adjustment value "0" is selected in the voltage setting unit 301, the secondary transfer voltage (more specifically, the recording material assigned voltage Vp) is set to a specified value (table value) that is preset for the currently selected recording material S. In this case, the secondary transfer voltage (more specifically, the recording material assigned voltage Vp) may be set to a value that is currently set for the currently selected recording material S. In this case, the central voltage value (the value corresponding to the patch set of 0 in the chart 100) of the secondary transfer voltage (more specifically, the recording material assigned voltage Vp) at the time of outputting the chart 100 is set to that value. In addition, when an adjustment value other than "0" is selected, in this embodiment, the secondary transfer voltage (more specifically, the recording material assigned voltage Vp) is adjusted by an adjustment amount ΔV of 150V for each level of the adjustment value. In this case, the central voltage value of the secondary transfer voltage (more specifically, the recording material assigned voltage Vp) at the time of outputting the chart 100 is set to that value. After the adjustment value is selected, the chart output button 303 is operated to output the chart 100 at the selected center voltage value. After the adjustment value is selected, the OK button 104 is operated to confirm the adjustment value of the secondary transfer voltage. The control unit 30 (adjustment process unit 31d) acquires information on settings such as the center voltage value input via the setting screen 300 on the operation unit 70, and stores the information in a storage unit (RAM 33, secondary transfer voltage storage unit / calculation unit 31f, etc.) as necessary.

[0066] The procedure of the adjustment mode will be described. First, when the operator inputs information (paper type category, size, etc.) of the recording material S to be used in the adjustment mode, the control unit 30 (adjustment process unit 31d) causes the display unit 70a to display a setting screen 300 for the adjustment mode (S201). At this time, the control unit 30 (adjustment process unit 31d) causes the display unit 70a to display the setting screen 300 in response to the operation of a button or the like provided on the input screen for the information of the recording material S displayed on the display unit 70a for calling up the setting screen 300 for the adjustment mode. The control unit 30 (adjustment process unit 31d) acquires the information of the recording material S input by the operator on the input screen, and adjusts the secondary transfer voltage in association with the information of the recording material S. Note that the information of the recording material S may be acquired from information previously set in association with the recording material cassette 91 by selecting the recording material cassette 91 in which the recording material S to be used in the adjustment mode is stored.

[0067] Next, the control unit 30 (adjustment processor 31d) acquires the setting of the center voltage value of the secondary transfer voltage when outputting the chart 100 and the information on the paper feed stage to be used, which are input by the operator on the setting screen 300 (S202). Next, the control unit 30 (adjustment processor 31d) acquires a signal indicating that the operator has operated the chart output button 303 on the setting screen 300 (S203). Then, prior to outputting the chart 100, the control unit 30 (adjustment processor 31d) acquires a quadratic or higher polynomial (a quadratic equation in this embodiment) of the relationship between the voltage and the current according to the electric low resistance of the secondary transfer unit N2 by an operation similar to that of the above-mentioned ATVC control (S204).

[0068] Next, the control unit 30 (adjustment processing unit 31d) determines whether the length L in the transport direction of the recording material S used in the adjustment mode is longer than the length R of the long side of the reading device 80 (the length of the long side of the recording material S that can be placed on the reading device 80) (S205). Since the reading device 80 in this embodiment can hold recording materials S up to 13 inches by 19.2 inches, in this embodiment, it is determined whether the length Z in the transport direction of the recording material S used in the adjustment mode is longer than 19.2 inches.

[0069] If in S205 the length of the recording material S in the transport direction is longer than the length of the long side of the reading device 80, the number N1 of large charts 100L that can be printed is calculated from the length Z of the recording material S in the transport direction and the length R (=19.2 inches) of the long side of the reading device using formula (1) (S206). N1 = Z / R = Z / 19.2 (1) For example, if the length Z of the recording material S, on which the chart is to be printed, in the transport direction is 40 inches, formula (1) will calculate a value of 2 or more, and if the length Z of the recording material S in the transport direction is 60 inches, formula (1) will calculate a value of 3 or more.

[0070] Next, the control unit 30 (adjustment processing unit 31d) determines whether N1 calculated in S206 is equal to or greater than 2 (S207).

[0071] Then, the secondary transfer voltage (test voltage) is set based on the acquired information on the relationship between voltage and current and the information on the center voltage value set on the setting screen 300. Then, while changing the secondary transfer voltage every 150V, control is performed so as to output a predetermined large chart 100L according to the size of the recording material S (S208). FIG. 11 is a schematic diagram of a case where a chart is printed on a long sheet of paper (N1=2) larger than the reading area of ​​the reading device. If N1≧2 in S207, the large chart 100L is transferred twice in succession to the recording material S as shown in FIG. 11 while switching the secondary transfer voltage, and is then fixed. That is, the large chart 100L (first chart) is transferred to the first area of ​​the recording material S, and the large chart 100L (second chart) is transferred to the second area of ​​the recording material S. The first and second areas of the recording material S are disposed adjacent to each other in the recording material conveying direction, and the first area is disposed downstream of the second area in the recording material conveying direction. The first and second regions of the recording material S are on the same surface of the recording material S. The first region of the recording material S has the same size as the reading region of the reading device 80, and the second region of the recording material S has the same size as the reading region of the reading device 80. At this time, the identification information 104 is printed as -10 to 11, the page identification number 105 is printed as 1 and 2, and the page determination patch 107 is printed as cyan and magenta. In this embodiment, the absolute value of the test voltage when transferring the patch sets 101 to 103 is set to be sequentially larger as the identification information 104 becomes larger. Therefore, the absolute value of the test voltage when transferring the patch sets 101 to 103 formed in the second region of the recording material S is larger than the maximum absolute value of the test voltage of the patch sets 101 to 103 formed in the first region of the recording material S.

[0072] If N1≧3, the large chart 100L is similarly printed three times in succession on the recording material S. As shown in FIG. 8 regarding the correspondence between the colors of the page determination patch 107 and the page numbers, cyan, magenta, and yellow are printed in this case.

[0073] On the other hand, if the length Z in the transport direction of the recording material S used in S205 is shorter than the length R of the long side of the reading device 80, or N1<2 in S207, it is determined that it is not possible to print multiple charts 100. Then, the chart 100 according to the size of the recording material S is printed while switching the secondary transfer voltage (S209).

[0074] Next, the control unit 30 (adjustment processing unit 31d) displays, for example, a screen as shown in FIG. 10(b) on the setting screen 300, and prompts the operator to set the adjustment chart printed on the recording material S in the reading device 80 (S210).

[0075] When the operator sets the chart and presses the start button 307 on the operation unit 70, the chart is read by the reading device 80 (S211).

[0076] Next, the control unit 30 (adjustment processing unit 31d) judges whether all the printed charts have been read (S212). If it is judged that all the printed adjustment charts have not been read, the control unit 30 prompts the operator to set an adjustment chart, and repeats the reading operation until all the charts have been read. In this embodiment, since the adjustment charts are identified by the page determination patch 107, it is also possible to display the current reading status on the setting screen 300, as shown in FIG. 12. If the image has been read once, it is also possible to inform the setting screen 300 that it has already been read.

[0077] When the control unit 30 (adjustment processing unit 31d) determines that all of the printed adjustment charts have been read, it performs a process of determining an adjustment value for the secondary transfer voltage (S213). FIG. 13 is a flow chart showing an outline of an example of the procedure of this process. Here, a case where the large chart 100L in FIG. 6 is read by the reading device 80 is taken as an example. Also, a case where the luminance data of a solid blue patch 101 is used as the density information (luminance information) of the patch for determining the adjustment value for the secondary transfer voltage is taken as an example. Also, for convenience, the above-mentioned adjustment values ​​-5 to +5 will be described as corresponding to patch numbers 1 to 11, respectively.

[0078] The control unit 30 (adjustment processor 31d) acquires RGB luminance data (8 bits) of each solid blue patch that is read from the large chart 100L set in the reader 80 by the operator and stored in the RAM 33 (S301). Next, the control unit 30 (adjustment processor 31d) calculates the average luminance value Lave_B(N) (N=1 to 10) of each patch using the luminance data acquired in S301 (S302). By the process of S302, for example, information indicating the relationship between the patch number (voltage level, adjustment value) and the average luminance value of the patch as shown in FIG. 14 is acquired. Next, the control unit 30 (adjustment processor 31d) calculates the standard deviation Lave_stdev(n) (n=1 to 7) of the average luminance value for every four patch numbers (N to N+3) in order from the smallest patch number to the largest patch number (S303). Next, the control unit 30 (adjustment processor 31d) extracts patch numbers N to N+3 (stable brightness region) in which the standard deviation Lave_stdev(n) of the brightness average value is the smallest (S304). Next, the control unit 30 (adjustment processor 31d) selects the largest patch number among the patch numbers in which the recording material distribution voltage Vp+ΔV (absolute value) determined from the adjustment value corresponding to each patch number extracted in S304 is equal to or less than a predetermined upper limit value (S305). That is, an adjustment value in which the brightness average value of the blue solid patch 101 is the smallest (the density is the largest) is selected within a range in which the recording material distribution voltage Vp+ΔV does not exceed the upper limit value. Note that the upper limit value is set in advance, for example, according to the paper type category of the recording material S from the viewpoint of suppressing image defects due to a secondary transfer voltage that is too high. Then, the control unit 30 (adjustment processor 31d) determines the adjustment value corresponding to the patch number selected in S305 as a candidate for a preferred setting of the secondary transfer voltage, and stores it in the RAM 33 (S306). By such processing, in FIG. 14, a patch number where the decrease in the average brightness (increase in density) is saturated, for example, an adjustment value corresponding to patch number -2, is determined as a candidate.

[0079] The color of the patch from which the luminance data is obtained is not limited to blue, and other colors such as red and green may be used, or a single solid color of YMCK may be used. Halftone luminance data may also be obtained.

[0080] In this embodiment, the adjustment amount of the secondary transfer voltage is determined based on sequentially obtaining the standard deviation of the luminance data of the patches for each of a plurality of patch numbers and extracting the patches in the luminance stable region. However, the method of determining the adjustment amount of the secondary transfer voltage is not limited to this method. For example, the adjustment amount of the secondary transfer voltage may be determined based on sequentially obtaining the luminance difference between the patches of adjacent patch numbers and extracting the patches in the luminance stable region where the luminance difference is equal to or less than a predetermined value.

[0081] 6.Effects As described above, when an adjustment chart is printed on a recording material larger than the reading device, it is possible to reduce the output of the adjustment chart and improve usability by effectively utilizing the margins of the recording material. [Explanation of symbols]

[0082] 30 Control section 44b Intermediate transfer belt 45a Secondary transfer inner roller 45b Secondary transfer outer roller 46 Fixing section 80 Reading device 100 Charts N2 Secondary transfer section S recording material

Claims

1. an image carrier that carries a toner image; an intermediate transfer member onto which a toner image is primarily transferred from the image carrier; a transfer member forming a transfer section for performing a secondary transfer of a toner image from the intermediate transfer body to a recording material; an application unit that applies a voltage to the transfer member; a discharge section that discharges a recording material on which the toner image transferred by the transfer section is fixed and an image is formed; a reading device capable of reading an image on a recording material set at a predetermined reading position; a control unit that executes an adjustment mode in which a chart on which a plurality of test images are sequentially transferred by applying a plurality of test voltages to the transfer member by the application unit, and that adjusts a secondary transfer voltage applied to the transfer member by the application unit when the secondary transfer is executed based on a reading result by the reading device when the chart is set at the reading position; having the control unit, when executing the adjustment mode on a specified recording material larger than a reading area of ​​the reading device, causes a first chart including a plurality of first test images to be output in a first area of ​​the specified recording material, and causes a second chart including a plurality of second test images to be output in a second area different from the first area on the same side as the side on which the first chart is formed, and the adjustment mode is executed based on a first detection result read by the reading device when the first chart is set at the specified reading position and the second chart is not set at the specified reading position, and a second detection result read by the reading device when the second chart is set at the specified reading position and the first chart is not set at the specified reading position.

2. 2. The image forming apparatus according to claim 1, wherein the control unit executes the adjustment mode on the specified recording material such that first identification information for an operator to identify that the outputted chart is the first chart and second identification information for an operator to identify that the outputted chart is the second chart are output.

3. 2. The image forming apparatus according to claim 1, wherein, when the control unit executes the adjustment mode for the predetermined recording material, first discrimination information for discriminating whether the chart read by the reading device is the first chart, and second discrimination information for discriminating whether the chart read by the reading device is the second chart are output.

4. 2. The image forming apparatus according to claim 1, wherein the first chart is positioned downstream of the second chart in the transport direction of the recording material, the absolute value of the test voltage when the multiple first test images are transferred is set to be gradually increased from the downstream side to the upstream side in the transport direction of the recording material, and the absolute value of the test voltage when the multiple second test images are transferred is set to be greater than the maximum absolute value of the test voltage when the multiple first test images are transferred and to be gradually increased from the downstream side to the upstream side in the transport direction of the recording material.

5. 2. The image forming apparatus according to claim 1, further comprising a display unit that displays information, wherein when the control unit executes the adjustment mode for the specified recording material, the control unit causes the display unit to display information regarding the reading status of the first chart and the second chart by the reading device.

Images