Image forming device

Abstract

To provide an image forming apparatus that can appropriately set a secondary transfer voltage applied to a second surface of a double-sided print.SOLUTION: There is provided an image forming apparatus 1 that has reading means that acquires information on the density of a first test image on a first surface and a second test image on a second surface of a double-sided chart, and can set transfer voltage in double-sided image formation. The image forming apparatus 1 has an execution unit that executes operations to output the double-sided chart so that the first test image and the second test image do not overlap on the front and back of a recording material S, and the execution unit has: an acquisition unit that acquires first information on the amount of adjustment of transfer voltage during transfer to the first surface based on information on the density of the first test image, and acquires information on the amount of adjustment of transfer voltage during transfer to the second surface based on information on the density of the second test image; a correction unit that corrects second information to acquire information on the amount of adjustment of transfer voltage during transfer to the second surface; and a setting unit that sets the transfer voltage during transfer to the first surface based on the first information and sets the transfer voltage during transfer to the second surface based on third 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] Conventionally, in image forming apparatuses using electrophotography or the like, a toner image is electrostatically transferred from an image carrier to a recording material such as paper. This transfer is often performed by applying a transfer voltage to a transfer member that contacts the image carrier to form a transfer section. In an image forming apparatus using an intermediate transfer method, a toner image formed on a first image carrier such as a photosensitive drum is primarily transferred onto a second image carrier such as an intermediate transfer belt, and then secondarily transferred onto the recording material. The secondary transfer in an image forming apparatus using an intermediate transfer method will be further described below as an example.

[0003] In order to obtain a high-quality image product, it is important 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 charge amount of the toner on the intermediate transfer body, the toner image cannot be sufficiently transferred from the intermediate transfer body onto the recording material, and the desired image density cannot be obtained. This image defect (low density) is sometimes called "grainy (grainy omission)". In addition, if the secondary transfer voltage is too high, a discharge occurs at the secondary transfer section, and the charge polarity of the toner on the intermediate transfer body is reversed due to the discharge, and the toner image on the intermediate transfer body cannot be partially transferred onto the recording material, and the image may become partially blank. This image defect (blank omission) is sometimes called "punch-through" or "strong blank omission".

[0004] The secondary transfer voltage can be determined based on a transfer portion voltage corresponding to the electrical resistance of the secondary transfer portion detected in a pre-rotation process before image formation, and a recording material portion voltage corresponding to a preset type of recording material. This makes it possible to set an appropriate secondary transfer voltage according to environmental fluctuations, the usage history of the transfer member, the type of recording material, etc.

[0005] However, since the types and conditions of recording materials used in image formation are various, depending on the recording material, the preset default recording material distribution voltage may result in an excess or deficiency in the secondary transfer voltage. Therefore, it has been proposed to provide an image forming apparatus with an adjustment mode that enables the setting value of the secondary transfer voltage to be adjusted 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 value of the secondary transfer voltage. In this adjustment mode, a chart (adjustment chart) is output in which a plurality of patches (test images) are transferred onto one sheet of recording material by switching the secondary transfer voltage (test voltage) for each patch. This chart is read by a reading unit provided in the image forming apparatus, and the density of each patch is detected. Then, depending on the detection result, an appropriate secondary transfer voltage condition is selected. Also, in this adjustment mode, the secondary transfer voltage for the second side of a double-sided print is set based on the density of the patch of the chart formed on the second side of the recording material, in the portion that overlaps with the patch of the chart formed on the first side and the portion that does not overlap with it. [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] However, it has been found that when the secondary transfer voltage for the second side of a double-sided print is set based on the chart for the second side of a double-sided chart in which charts are formed on both sides of a recording material, the following problem occurs.

[0009] In other words, due to the effect of switching and applying the secondary transfer voltage for each patch when forming the chart on the first side, the density of the patches of the chart on the first side changes according to the applied secondary transfer voltage.

[0010] Therefore, when forming the chart on the second side, the patches on the first side have non-uniform density, which can make it difficult to accurately detect the density of the patches on the second side when the scanning unit detects the density of the patches due to the effect of the density of the patches on the first side.

[0011] Furthermore, as described above, when forming the chart on the second side, the first side has patches on the first side that are not uniform in density, i.e., have a non-uniform amount of toner. This may cause variations in the secondary transfer current required for secondary transfer of the patches of the chart on the second side. In other words, when secondary transfer of each patch of the chart on the second side is performed, the toner distribution voltage varies depending on the patches of the chart on the first side. As a result, during double-sided printing, depending on the image density of the image on the first side, the effect of the toner layer (toner distribution voltage) on the first side during secondary transfer to the second side may differ from that during adjustment mode, and this may result in, for example, a shortage of secondary transfer current.

[0012] Due to these factors, it may not be possible to appropriately set the secondary transfer voltage for the second side of a double-sided print.

[0013] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an image forming apparatus capable of appropriately setting a secondary transfer voltage for the second side of a double-sided print. [Means for solving the problem]

[0014] 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 forming unit that forms a toner image, a transfer unit that transfers the toner image formed by the image forming unit onto a recording material, a power source that applies a voltage to the transfer unit, a reading unit that reads the image on the recording material, a first chart formed by applying a plurality of first test voltages from the power source to the transfer unit to transfer a plurality of first test images onto a first side of the recording material, and a read unit that reads the first test images from the power source to the transfer unit. Source? Then, a plurality of second test voltages are applied to the transfer section. Multiple second test images a control unit that executes an output process for outputting a double-sided chart having the first and second charts formed by transferring the first and second test images to the second side of the recording material, the control unit executing a process in a mode in which a transfer voltage for transferring an image to the first side in double-sided image formation is set based on a detection result of the plurality of first test images read by the reading unit, and a transfer voltage for transferring an image to the second side in double-sided image formation is set based on a detection result of the plurality of second test images read by the reading unit, the control unit executes the output process so that the plurality of first test images on the first side of the recording material do not overlap the plurality of second test images on the second side of the recording material, the control unit executes a predetermined selection process in which one image of the plurality of images is selected based on a detection result when the plurality of images are detected by the reading unit, and the control unit executes a process in which a transfer voltage for transferring an image to the first side in double-sided image formation is set based on a detection result of the plurality of second test images read by the reading unit, When the transfer voltage for transferring an image to the first side in double-sided image formation is set, the control unit selects one first test image from the multiple first test images by the predetermined selection process, and sets the transfer voltage for transferring an image to the first side in double-sided image formation based on the selected first test image; and when the transfer voltage for transferring an image to the second side in double-sided image formation is set in the processing of the mode, the control unit selects one second test image from the multiple second test images by the predetermined selection process, and based on the selected second test image, sets a voltage whose absolute value is greater than the absolute value of the test voltage when the selected second test image is transferred as the transfer voltage for transferring an image to the second side in double-sided image formation, regardless of the detection result of the multiple first test images by the reading unit. Effect of the Invention

[0015] According to the present invention, it is possible to appropriately set the secondary transfer voltage for the second side of a double-sided print. [Brief description of the drawings]

[0016] [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 flowchart showing an outline of a procedure for controlling a secondary transfer voltage. [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. 13 is a schematic diagram of a chart output in an adjustment mode. [Figure 7] FIG. 13 is a schematic diagram of a chart output in an adjustment mode. [Figure 8] FIG. 11 is a flowchart illustrating an example of a procedure of an adjustment mode. [Figure 9] 11 is a schematic diagram showing an example of a secondary transfer voltage adjustment screen. FIG. [Figure 10] 11 is a graph illustrating an example of a relationship between an adjustment value of a secondary transfer voltage and an average brightness value. [Figure 11] FIG. 11 is a graph showing an example of the relationship between the amount of applied toner and the toner distribution voltage. [Figure 12] 6A and 6B are schematic diagrams for explaining a method of determining an adjustment value of a secondary transfer voltage. [Figure 13] FIG. 11 is a schematic cross-sectional view of another example of an image forming apparatus. [Figure 14] FIG. 11 is a graph showing an example of a relationship between a recording material distribution voltage and a toner distribution voltage. [Figure 15] FIG. 11 is a flowchart showing an outline of a process for setting a secondary transfer voltage during double-sided printing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0018] [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.

[0019] As shown in FIG. 1, the image forming apparatus 1 includes an apparatus 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. Inside the apparatus main body 10, an environment detection unit is provided, such as a temperature sensor 71 (FIG. 2) capable of detecting the temperature inside the apparatus, and a humidity sensor 72 (FIG. 2) capable of detecting the humidity inside the apparatus. 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 signal) 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, and specific examples thereof include plain paper, a synthetic resin sheet that is a substitute for plain paper, cardboard, and an overhead projector sheet.

[0020] The printer section 40 can form an image on the recording material S fed from the feeding section (feeding device) 90 based on image information. The printer section 40 has 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 section 40 also has an intermediate transfer unit 44, a secondary transfer device 45, and a fixing section 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 provided corresponding to each color may be generally described by omitting the suffixes y, m, c, and k indicating that the element is for any one 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.

[0021] 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 a first image carrier. It also has a charging roller 52, which is a roller-type charging member as a charging means. It also has an exposure device 42 as an exposure means. It also has a developing device 20 as a developing means. It also has a pre-exposure device 54 as a charge removing 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 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 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 including 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 (aluminum in this embodiment) such as aluminum or non-magnetic stainless steel. 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.

[0026] 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 intermediate transfer body formed of an endless belt as a second image carrier. The intermediate transfer belt 44b is wound around a driving roller 44a, a driven roller 44d, and a secondary transfer inner roller 45a 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) 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) as a biasing member 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.

[0027] 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.

[0028] 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. The primary transfer roller 47 has an electrical resistance of 1×10 5 ~1×10 8A roller of Ω (N / N (measured at 23° C., 50% RH), 2 kV applied) can be preferably used. 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 for forming 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 preferably used. The thickness of the base layer is, for example, 0.05 to 0.15 mm. As an elastic material for forming 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 preferably used. The thickness of the elastic layer is, for example, 0.1 to 0.500 mm. As a material for forming the surface layer, a resin such as fluororesin can be preferably used. The surface layer reduces the adhesion of the toner to the surface of the intermediate transfer belt 44b, making it easier to transfer 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 fluororesin, or particles with different particle sizes, as a material that reduces surface energy and increases lubricity, in this base material. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5×10 8 ~1×10 14 The surface roughness 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 have a single layer structure of a material equivalent to the above-mentioned base layer.

[0029] 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 45a, 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, which 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.

[0030] 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. The secondary transfer outer roller 45b has an electrical resistance of 1×10 5 ~1×10 8 A roller of Ω (N / N (23° C., 50% RH) measurement, 2 kV applied) can be suitably used.

[0031] The recording material S is fed from the 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 as a recording material storage section. In this embodiment, the image forming apparatus 1 is provided with a plurality of recording material cassettes 91 (91a, 91b) in which the recording material S is stored. 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) as a feeding member. The recording material S sent to the conveying path 93 is conveyed to a registration roller pair 43 as a conveying member by a conveying roller pair 94 as a conveying member. The skew of the recording material S is corrected by the registration roller pair 43, and the timing is matched with the toner image on the intermediate transfer belt 44b, and the recording material S is supplied 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.

[0032] 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).

[0033] 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 constituted by the discharge path 48a, the pair of discharge rollers 48b, the discharge port 48c, the discharge tray 48d, and the like. 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 on which the toner image has been fixed after passing 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 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. 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. In double-sided printing, the recording material S after the toner image is fixed on the first side is guided to the reverse conveying path 12. The recording material S is reversed in conveying direction by the switchback roller pair 13 provided in the reverse conveying path 12 and guided to the double-sided conveying path 14. The recording material S is then sent to the conveying path 93 by the re-conveying roller pair 15 provided in the double-sided conveying path 14, conveyed to the registration roller pair 43, and supplied to the secondary transfer section N2 by the registration roller pair 43. Thereafter, the recording material S is subjected to the second transfer of the toner image on the second side in the same manner as in the image formation on the first side, and after the toner image is fixed, it is discharged to the discharge tray 48d. The reverse 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.

[0034] 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.

[0035] A reading section (reading device) 80 as a reading means is disposed on the upper portion of the device body 10. The reading section 80 includes an automatic document feeder (automatic document feeder (ADF)) 81 as a document transporting means (document transporting 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. In this embodiment, the reading section 80 can sequentially read the image of the document (recording material S on which an image is formed) placed on the platen glass 82 by the reading element 85 via the optical system 84 while scanning and exposing the image by the movable light source 82. In this case, the reading section 80 sequentially illuminates the document placed on the platen glass 82 by the moving light source 83, and sequentially forms an image of the reflected light from the document on the reading element 85 via the optical system 84. This allows the image of the document to be read by the reading element 85 at a predetermined dot density. In this embodiment, the reading unit 80 can sequentially expose the image of the document conveyed by the automatic document feeder 81 to light by 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 unit 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 image of the document to be read by the reading element 85 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. In this way, the reading unit 80 optically reads the image on the recording material S placed on the platen glass 82 or conveyed 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-size recording material S, such as A3 size, and two sheets of small-size recording material S, such as A4 size, side by side on the platen glass 82. Also, 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. Also, the automatic document feeder 81 can automatically read images on both sides of the recording material S.

[0036] For example, when the image forming apparatus 1 operates as a copier, the image of the document read by the reading unit 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 unit 80 is also used to read the patches of the chart (to obtain density information (luminance information)) in the adjustment mode.

[0037] 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 means, a ROM 32 as a storage means for storing programs for controlling each unit, a RAM 33 as a storage means for temporarily storing data, and an input / output circuit (I / F) 34 for inputting and outputting signals to and from the outside. The CPU (arithmetic unit) 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 printer 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.

[0038] 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 operate the operation unit 70 to cause the image forming apparatus 1 to execute a job (described later). The control unit 30 receives a signal from the operation unit 70 and operates various devices of the image forming apparatus 1. 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.

[0039] 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. 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 value of the secondary transfer voltage. The adjustment mode will be described in detail later.

[0040] In this embodiment, the control unit 30 (image formation process unit 31c) can switch between a multiple color mode in which a primary transfer voltage is applied to multiple primary transfer units N1 to form a multiple color image, 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 a monochrome image.

[0041] 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.

[0042] 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.

[0043] First, when the control unit 30 (pre-image formation preparation process unit 31a) acquires job information from the operation unit 70 or the external device 200, it starts the job operation (S101). This job information includes image information specified by the operator and information 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, normal paper, thick paper, etc.", which is related to the thickness of the recording material S. The information on the recording material S (recording material information) includes any information that can distinguish the recording material S, such as attributes based on general characteristics such as plain paper, fine paper, glossy paper, glossy paper, coated paper, embossed paper, thick paper, thin paper, etc. (so-called paper type category), numerical values ​​or numerical ranges of basis weight, thickness, size, stiffness, etc., or brands (including manufacturers, product names, product numbers, etc.). Each recording material S distinguished by the information on the recording material S can be considered as constituting a type of recording material S. The information on the recording material S may be included in information on a print mode 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 information on the print mode. The control unit 30 (pre-image formation preparation process unit 31a) writes the job information to the RAM 33 (S102).

[0044] 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.

[0045] 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) 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 (S105). That is, in a state in which the secondary transfer outer roller 45b and the intermediate transfer belt 44b are in contact with each other, a predetermined voltage of multiple levels is supplied from the secondary transfer power source 76 to the secondary transfer outer roller 45b. 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 the information on the relationship between the voltage and the current in the RAM 33 (or the secondary transfer voltage storage unit / calculator 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.

[0046] 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 flow the target current Itarget in a 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 carrying voltage (transfer voltage for the electrical resistance of the secondary transfer portion N2). Note that it is also possible to apply the target current Itarget from the secondary transfer power source 76 to the secondary transfer outer roller 45b by constant current control, detect the voltage value at that time by the voltage detection sensor 76a, and set the detected voltage as the voltage value Vb. Also, information for determining the recording material partial carrying voltage (transfer voltage for the electrical resistance of the recording material S) Vp, as shown in FIG. 5, is stored in the ROM 32. In this embodiment, this information is set as table data indicating the relationship between the moisture amount of the atmosphere for each classification (corresponding to the paper type category) of the basis weight of the recording material S and the recording material shared voltage Vp. The control unit 30 (pre-image formation preparation process unit 31a) can obtain the moisture amount 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 shared 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 value 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 this 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. Then, the control unit 30 writes this Vtr (=Vb+Vp+ΔV) in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f).The table data for calculating the recording material distribution voltage Vp as shown in FIG. 5 is previously obtained through experiments or the like.

[0047] 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.

[0048] 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).

[0049] 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.

[0050] 3. Overview of Adjustment Mode Next, the adjustment mode (simplified adjustment mode) for adjusting the set value of the secondary transfer voltage will be described.

[0051] 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 the standard recording material S. In this case, the setting value 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 appropriate transfer. In other words, 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 the value assumed as the standard value. In this case, the setting value of the secondary transfer voltage using the default recording material distribution voltage Vp set in advance may not be enough 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 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 recording material S may absorb moisture, and thus the electrical resistance may be lower than the value assumed as the standard value, making it easier for discharge to occur. In this case, the setting value 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 secondary transfer voltage by lowering the recording material voltage Vp, for example.

[0052] For this reason, it may be desirable for an operator such as a user or a service person to adjust (change) the setting value of the secondary transfer voltage during job execution to an appropriate value by, for example, 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 appropriate recording material assigned voltage Vp+ΔV (adjustment amount) according to the recording material S actually used for image formation.

[0053] This adjustment can be performed by the following method. That is, for example, an operator outputs the image he 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, with this method, since the output of the image and the adjustment of the setting value of the secondary transfer voltage are repeated, more recording material S may be wasted and the adjustment may take a long time.

[0054] 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 by transferring a plurality of patches (test images) of representative colors to the recording material S actually used for image formation by switching the secondary transfer voltage (test voltage) for each patch, and outputting the chart. 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 shared voltage Vp+ΔV). In this embodiment, in the adjustment mode, the control unit 30 presents information on a recommended adjustment amount ΔV of the set value of the secondary transfer voltage based on the result of reading the density information (brightness information) of the patch (typically a solid image patch) on the chart by the reading unit 80. 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 set value of the secondary transfer voltage.

[0055] 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. 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. 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 by 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.

[0056] Here, the size of the recording material S is indicated by 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 a direction (width direction) substantially perpendicular to the conveying direction of the recording material S when passing through the secondary transfer portion N2. The recording material length is the length in a direction substantially parallel to the conveying direction of the recording material S when passing through the secondary transfer portion N2.

[0057] Fig. 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). Fig. 6(a) shows a large chart 100La when outputting a single-sided chart (or the first side when outputting a double-sided chart). Fig. 6(b) shows a large chart 100Lb on the second side when outputting a double-sided chart.

[0058] Fig. 7 shows a small-size chart (hereinafter also referred to as "small chart") 100S (100Sa, 100Sb) that is 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). Figs. 7(a) and (b) respectively show the first and second small charts 100Sa when a single-sided chart is output (or the first side when a double-sided chart is output). Figs. 7(c) and (d) respectively show the first and second small charts 100Sb on the second side when a double-sided chart is output.

[0059] 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. 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 loading amount of the blue solid is 200%. In addition, the black solid is an image with 100% black (K) toner. 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 value 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 eleven stages of secondary transfer voltage settings 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 ten stages of secondary transfer voltage settings are arranged. In addition, the chart 100 may be provided with front / back identification information 105 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 at least one of the first side (front side) or second side (back side) of the recording material S.

[0060] 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 in the width direction to the very end of the chart 100 (there may be a margin, as described later). 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 that are different so that the absolute values ​​are successively 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 a plurality of secondary transfer voltages whose absolute values ​​are made different in sequence to become smaller.

[0061] 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.

[0062] The maximum size of the recording material S that can be used in the image forming apparatus 1 of this embodiment is 13 inches (about 330 mm) x 19.2 inches (about 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 x 19.2 inches or less and A3 (297 mm x 420 mm) or more, a chart corresponding to the 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 conveying direction and the leading edge of the large chart 100L in the conveying direction (the upper edge 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. Also, in this embodiment, the image data is cut so that a margin of 2.5 mm is provided at the ends (both ends in the width direction and both ends in the conveying direction in this embodiment). For example, when the large chart 100L is output on 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 on each end. Then, the large chart 100L corresponding to the image data is output on an A3 (297 mm x 420 mm) recording material S with the leading edge center as a reference. When a recording material S with a width smaller than 13 inches is used, the size in the width direction of the halftone patch 103 at the end in the width direction becomes smaller. Also, when a recording material S with a width smaller than 13 inches is used, the margin at the trailing edge 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 eleven patch sets 101 to 103 of the large chart 100L are arranged within a range of 387 mm in length 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.

[0063] 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.

[0064] Furthermore, in this embodiment, regardless of the size of the recording material S, the solid blue patch 101 and the solid black patch 102 are arranged on the first side (front side) and second side (back side) of the double-sided chart so as not to overlap on the front and back of the recording material S. In this embodiment, the patch interval in the width direction is set to 5.4 mm. This is to suppress the patch density on the second side from varying due to the patch density on the first side, and to more accurately adjust the secondary transfer voltage on the second side.

[0065] In addition, in this embodiment, in addition to standard sizes, the operator can also input and specify from the operation unit 70 or external device 200, for example, to output the chart 100 using recording material S of any size (free size).

[0066] 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 patch groups whose test voltage is changed 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.

[0067] 5. Adjustment mode operation Next, the operation of the adjustment mode in this embodiment will be described. FIG. 8 is a flow chart showing an outline of the procedure of the adjustment mode in this embodiment. FIG. 9 is a schematic diagram showing an example of an adjustment screen 300 for setting the adjustment mode. Note that here, an example is taken of a case where the above-mentioned large chart 100L is formed as the chart 100. Also, 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, for simplicity, the recording material on which the chart is formed may be simply referred to as a "chart".

[0068] The adjustment screen 300 will be described with reference to FIG. 9. In this embodiment, the control unit 30 (adjustment process unit 31d) displays the adjustment screen 300 as shown in FIG. 9 on the display unit 70a of the operation unit 70. The adjustment screen 300 has a voltage setting unit 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. The adjustment screen 300 also has an output side selection unit 302 for selecting whether the chart 100 is 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 (OK button) 304 for confirming the setting, and a cancel button 305 for canceling the change of the setting. 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.

[0069] 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 of "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 150V for each level of adjustment value, and the chart 100 is output. In addition, the chart 100 is output by operating the chart output button 303. Then, in this embodiment, after the chart 100 is output, the voltage setting unit 301 displays a recommended adjustment value of the secondary transfer voltage that the control unit 30 has determined based on the reading result of the chart 100 by the reading device 80. The operator can change the adjustment value displayed on the voltage setting unit 301. When the OK button 104 is operated in a state in which the adjustment value determined by the control unit 30 or the adjustment value changed by the operator is selected in the voltage setting unit 301, the adjustment value of the secondary transfer voltage is finalized. 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.

[0070] 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 set 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. On this recording material setting screen, it is possible to input (select) information (paper type category, size, etc.) of the recording material S to be used. Then, for example, the operator operates an adjustment mode start button provided corresponding to each recording material S on the recording material setting screen. Then, 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.

[0071] Next, the control unit 30 (adjustment processor 31d) acquires information on the setting of the center voltage value of the secondary transfer voltage when the chart 100 is formed and the setting of whether to output a single-sided chart or a double-sided chart, which are input by the operator on the adjustment screen 300 (S202). Next, when the operator operates the chart output button 303 on the adjustment screen 300, the control unit 30 (adjustment processor 31d) acquires information on the electric low resistance of the secondary transfer unit N2 in the same operation as the ATVC control prior to outputting the chart 100 (S203). In this embodiment, as described above, a quadratic or higher polynomial (quadratic in this embodiment) of the relationship between the voltage and the current according to the electric resistance of the secondary transfer unit N2 is acquired. Then, the control unit 30 (adjustment processor 31d) sets the secondary transfer voltage Vtr=Vb+Vp+ΔV based on the acquired information on the electric resistance and the information on the center voltage value set on the pre-output adjustment screen 300a, and outputs the chart 100 (S204). At this time, the control unit 30 (adjustment processor 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 increments of 150 V. Here, since a case where a large chart 100L is output is taken as an example, the control unit 30 (adjustment processor 31d) controls the chart 100 to be output having 11 patch sets as described above. For example, if the recording material shared voltage Vp in the environment when the adjustment mode is executed is 2500 V and Vb obtained by ATVC control is 1000 V, the image formation of the chart 100 is performed while changing the secondary transfer voltage in increments of 150 V from 2750 V to 4250 V.

[0072] Next, the control unit 30 (adjustment process unit 31d) obtains density information (luminance information) of the patches of the output chart 100 (S205). In this embodiment, the output chart 100 is set by the operator in the reading unit 80 (for example, the automatic document feeder 81) and is read by the reading unit 80. When a double-sided chart is output, each of the first and second sides of the double-sided chart is read by the reading unit 80. Then, the control unit 30 (adjustment process unit 31d) obtains RGB luminance 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 process unit 31d) can display on the operation unit 70 to prompt the operator to set the chart 100 in the reading unit 80. Also, the control unit 30 (adjustment process unit 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 obtain the average brightness value of each patch ("average brightness value") (S206). When a double-sided chart is output, the average brightness value of each patch is obtained for each of the first and second sides of the double-sided chart. Through this process, for each of the first and second sides of the recording material S, a relationship between the voltage level (adjustment value) and the average brightness value of the patch (information regarding the transition of the density of the patch with respect to the change in the secondary transfer voltage) as shown in FIG. 10 as an example is obtained. 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 blue solid patch. Note that the brightness data of B is used for the blue solid patch.

[0073] Next, the control unit 30 (adjustment processor 31d) obtains a judgment value of an appropriate secondary transfer voltage based on the relationship between the acquired adjustment value and the average brightness value (S207). In this embodiment, the control unit 30 (adjustment processor 31d) determines the adjustment value at which the average brightness value is minimum (the density is maximum) as the judgment value of the appropriate secondary transfer voltage. In other words, if the absolute value of the secondary transfer voltage is smaller than the appropriate value, the toner cannot be transferred to the recording material S, and the image density may become low ("low density"). In this case, the average brightness value obtained becomes large. On the other hand, if the absolute value of the secondary transfer voltage is larger than the appropriate value, the charge is injected into the toner, and the charge polarity of the toner becomes the opposite polarity to the normal charge polarity. Therefore, an image defect called "punch-through" or "strong pass-through" may occur in which the toner once transferred to the recording material S returns to the intermediate transfer belt 44b. In this case, the image density becomes low and the average brightness value obtained becomes large. Therefore, when the adjustment value has the smallest average brightness value, the image density is highest, and it can be said to be an appropriate secondary transfer voltage. When a single-sided chart is output, a judgment value of the appropriate secondary transfer voltage for single-sided printing is obtained based on the results of reading the single-sided chart.When a double-sided chart is output, a judgment value of the appropriate secondary transfer voltage for each of the first and second sides of double-sided printing is obtained based on the results of reading each of the first and second sides of the double-sided chart.

[0074] Then, the control unit 30 (adjustment processing unit 31d) determines the judgment value obtained based on the relationship between the above-mentioned adjustment value and the average brightness value as the recommended adjustment value for the secondary transfer voltage for single-sided printing or the first side of double-sided printing (S208).

[0075] Next, the control unit 30 (adjustment processor 31d) judges whether or not the judgment value for the second side of the double-sided print has been acquired (whether or not a double-sided chart has been output) (S209). If the control unit 30 (adjustment processor 31d) judges that the judgment value for the second side of the double-sided print has not been acquired (a double-sided chart has not been output), the process proceeds to S211. On the other hand, if the control unit 30 (adjustment processor 31d) judges that the judgment value for the second side of the double-sided print has been acquired (a double-sided chart has been output), the control unit 30 (adjustment processor 31d) corrects the judgment value for the secondary transfer voltage for the second side of the double-sided print and determines a recommended adjustment value for the secondary transfer voltage (S210).

[0076] Here, the determination of the recommended adjustment value of the secondary transfer voltage for the second side of double-sided printing (correction of the judgment value) in this embodiment will be described.

[0077] In this embodiment, as described above, the solid blue patches on the first and second sides of the double-sided chart used in the process of determining the recommended adjustment value for the secondary transfer voltage in the adjustment mode are arranged so as not to overlap on the front and back of the recording material S. This prevents the density of the patches on the second side from varying due to the density of the patches on the first side.

[0078] However, as described above, when forming the chart for the second side, the density of the first side is not uniform, that is, the amount of toner is not uniform, and therefore the secondary transfer current may vary when the patches of the chart for the second side are secondarily transferred. In other words, for an image of any image density output by the user, the influence of the toner on the back side does not need to be considered for the first side of a single-sided print and a double-sided print. Therefore, by determining the judgment value obtained based on the relationship between the above-mentioned adjustment value and the average brightness value as the recommended adjustment value for the secondary transfer voltage, the secondary transfer voltage can be appropriately adjusted. On the other hand, for the second side of a double-sided print, the secondary transfer current during the secondary transfer of the second side changes depending on the amount of toner on the first side, which is the back side. Figure 11 shows the toner amount M / S [mg / cm2] of the first side during the secondary transfer of the second side of a double-sided print, obtained by experiment. 211 is a graph showing an example of the relationship between the amount of toner applied to the first side and the toner distribution voltage (transfer voltage for the electrical resistance of the toner layer) Vt [V] by the toner on the first side. As shown in FIG. 11, as the amount of toner applied to the first side increases, the toner distribution voltage Vt applied to the toner layer on the first side increases. Therefore, depending on the image density of the image output by the user, the judgment value obtained based on the relationship between the above-mentioned adjustment value and the average brightness value may cause image defects due to insufficient secondary transfer current. In particular, this may be noticeable under conditions where the contribution of the electrical resistance of the toner layer to the electrical resistance of the recording material S and the toner layer on the first side in the secondary transfer section N2 is large (the ratio of the toner distribution voltage to the recording material distribution voltage and the toner distribution voltage is large).

[0079] Therefore, in this embodiment, taking the above relationship into consideration, the control unit 30 (adjustment processor 31d) corrects the judgment value for the second side of a double-sided print, which is calculated based on the relationship between the above-mentioned adjustment value and the average brightness value, in S210. In this embodiment, the control unit 30 (adjustment processor 31d) adds a predetermined adjustment value (this adjustment value for the correction amount is also called a "correction value") of a predetermined correction amount [V] to the judgment value. In particular, in this embodiment, a correction value of +1 level is added to the judgment value so that the correction amount [V] becomes the adjustment value +1 level. FIG. 12 is a graph diagram that shows a schematic method of determining a recommended adjustment value of the secondary transfer voltage for the second side of a double-sided print by correcting the judgment value by adding the correction value. As shown in the figure, a secondary transfer current shortage that may occur due to a fluctuation in the secondary transfer current of the second side according to the toner amount of the first side can be compensated for by adding the correction value to the judgment value of the secondary transfer voltage. In this embodiment, the correction value is set to the adjustment value +1 level, but is not limited to this. The correction value may be preset through experiments or the like so as to compensate for a shortage of secondary transfer current during secondary transfer of the second side of a double-sided print, which may occur depending on the image density of the image output by the user.

[0080] Next, the control unit 30 (adjustment process unit 31d) displays the recommended adjustment value of the secondary transfer voltage determined in S208 and S210 on the display unit 70a of the operation unit 70 on the adjustment screen 300 as shown in FIG. 9 (S211). 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 voltage setting unit 301a for the front surface displays the adjustment value determined in S208. The voltage setting unit 301b for the back surface displays the adjustment value determined in S210. The operator can determine whether the displayed adjustment value is acceptable based on the display contents 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 OK button 304 on the adjustment screen 300. On the other hand, if the operator wants to change the displayed adjustment value, the operator inputs the changed value in the voltage setting section 301 (301a, 301b) of the adjustment screen 300 and operates the OK button 304. Therefore, the control unit 30 (adjustment processor 31d) judges whether the adjustment value has been changed (S212). If the adjustment value is not changed and the OK button 304 is operated, the control unit 30 (adjustment processor 31d) stores the adjustment value determined in S208 and S210 in the RAM 33 (or the secondary transfer voltage storage section / calculation section 31f) (S213). On the other hand, if the adjustment value has been changed, the control unit 30 (adjustment processor 31d) stores the adjustment value input by the operator in the RAM 33 (or the secondary transfer voltage storage section / calculation section 31f) (S214). Note that instead of or in addition to the adjustment value, an adjustment amount ΔV calculated as described below may be stored. This ends the adjustment mode.

[0081] 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 on 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 the 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. Then, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) uses the calculated adjustment amount ΔV to calculate the recording material shared voltage Vp+ΔV after adjustment, and uses this 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.

[0082] 6.Effects Thus, the image forming apparatus 1 of this embodiment includes an image carrier (intermediate transfer belt) 44b that carries a toner image, a transfer member (secondary transfer outer roller) 45b that forms a transfer section (secondary transfer section) N2 that transfers the toner image from the image carrier 44b to the recording material S, an application section (secondary transfer power source) 76 that applies a voltage to the transfer member 45b, a first chart 100La formed by applying a plurality of first test voltages to the transfer member 45b by the application section 76 to transfer a plurality of first test images onto a first side of the recording material S, and a first chart 100La formed by applying a plurality of second test voltages to the transfer member 45b by the application section 76. The control unit 31d has an execution unit (in this embodiment, the adjustment processor 31d has the function of the execution unit) that executes an output operation to output a double-sided chart 100 having a first test image and a second test image 100Lb formed by transferring the first test image and the second test image to the second side of the recording material S, and a reading means (reading unit) 80 that acquires information on the density of the first test image and the second test image of the double-sided chart 100, and based on the information acquired from the double-sided chart 100 by the reading means 80, it is possible to set a transfer voltage to be applied to the transfer member 45b by the application unit 76 during transfer in double-sided image formation in which toner images are transferred sequentially to the first and second sides of the recording material S. In this embodiment, the execution unit 31d executes the output operation so that the first test image and the second test image do not overlap on the front and back of the recording material S. In addition, in this embodiment, image forming apparatus 1 includes an acquisition unit (in this embodiment, adjustment processor 31d has the function of the acquisition unit) that acquires first information regarding the adjustment amount of transfer voltage when transferring to the first side in double-sided image formation based on information about the first test voltage and information about the density of the first test image acquired by reading means 80, and acquires second information regarding the adjustment amount of transfer voltage when transferring to the second side in double-sided image formation based on information about the second test voltage and information about the density of the second test image acquired by reading means 80, and a correction unit (in this embodiment, adjustment processor 31d has the function of the correction unit) that corrects the second information using correction information to acquire third information regarding the adjustment amount of transfer voltage when transferring to the second side in double-sided image formation.), and a setting unit (in this embodiment, secondary transfer voltage storage unit / calculation unit 31f has the function of the setting unit) that sets the transfer voltage at the time of transfer of the first side in double-sided image formation based on the first information, and sets the transfer voltage at the time of transfer of the second side in double-sided image formation based on the third information. Also, in this embodiment, image forming apparatus 1 has output unit (control unit) 30 that outputs a signal for displaying the first information and the third information. Also, in this embodiment, image forming apparatus 1 has a storage unit (RAM 33 and secondary transfer voltage storage unit / calculation unit 31f) that stores the first information and the third information.

[0083] In this embodiment, the correction unit 31d acquires correction information so as to increase the absolute value of the transfer voltage during transfer of the second side in double-sided image formation. It is also possible to configure the correction unit 31d to acquire correction information so as to decrease the absolute value of the transfer voltage during transfer of the second side in double-sided image formation. That is, in the above embodiment, the possibility of image defects occurring due to insufficient transfer current caused by fluctuations in the transfer current during transfer of the second side has been described, but as described above, image defects may also occur due to excessive transfer current. Therefore, depending on the configuration of the image forming apparatus, correction may be performed in the direction of decreasing the absolute value of the transfer voltage so as to suppress image defects occurring due to excessive transfer current caused by fluctuations in the transfer current during transfer of the second side.

[0084] In addition, in this embodiment, the acquiring unit 31d acquires the first information based on information on a first test voltage at the time of transfer of a first test image among the plurality of first test images, the information on density acquired by the reading means 80 conforming to a first condition set in advance, and acquires the second information based on information on a second test voltage at the time of transfer of a second test image among the plurality of second test images, the information on density acquired by the reading means 80 conforming to a second condition set in advance. Typically, the first condition and the second condition are the same. In this embodiment, the first condition and the second condition are that the average density value is maximum (the average brightness value is minimum). Furthermore, in this embodiment, the image forming apparatus 1 has an input section (operation section 70, adjustment screen 300) for inputting information regarding the adjustment amount of the transfer voltage during transfer of at least one of the first or second sides in double-sided image formation in response to operation by the operator when an output operation is executed, and when information regarding the adjustment amount of the transfer voltage during transfer of the second side in double-sided image formation is input from the input section, the setting section 31f sets the transfer voltage during transfer of the second side in double-sided image formation based on the input information.

[0085] As described above, according to this embodiment, in the adjustment mode, the blue solid patches on the first and second sides of the double-sided chart are arranged so as not to overlap on the front and back of the recording material S. This makes it possible to suppress the variation in density of the patch on the second side due to the influence of the density of the patch on the first side. Also, according to this embodiment, in the adjustment mode, the recommended adjustment value of the secondary transfer voltage for the second side of the double-sided print is determined by adding a predetermined correction value to the judgment value obtained based on the relationship between the acquired adjustment value and the average brightness value. In other words, the judgment value is corrected so as to compensate for a secondary transfer current shortage during secondary transfer of the second side of the double-sided print, which may occur depending on the image density of the image output by the user, and the recommended adjustment value of the secondary transfer voltage for the second side of the double-sided print is determined. This makes it possible to suppress the occurrence of a secondary transfer current shortage due to the influence of the toner distribution voltage of the toner on the first side during secondary transfer of the second side of the double-sided print. Therefore, according to this embodiment, it is possible to appropriately set the secondary transfer voltage for the second side of the double-sided print.

[0086] The method of obtaining the judgment value of the secondary transfer voltage (adjustment value) is not limited to the above-mentioned method. In this embodiment, the judgment value is obtained based on extracting the adjustment value at which the luminance average value is minimum (the density is maximum), but the method is not limited to this. For example, a representative value such as a central value among the adjustment values ​​at which the luminance average value is equal to or less than a predetermined value may be determined as the recommended adjustment value of the secondary transfer voltage. In addition, the judgment value may be obtained based on extracting an adjustment value of a luminance stable region where the standard deviation of the luminance average value obtained sequentially for each of a predetermined number of adjustment values ​​is minimum, or an adjustment value of a luminance stable region where the luminance difference of the patch between adjacent adjustment values ​​is equal to or less than a predetermined value. The judgment value may be obtained based on information regarding the relationship between the secondary transfer voltage when the patch is formed and the density (luminance) of the patch.

[0087] In this embodiment, the luminance data is acquired using a solid blue patch, which is a multi-color (multi-color), but this is not limited to this. For example, instead of blue, secondary colors such as red and green may be used, or single colors such as yellow, magenta, cyan, and black may be used. Halftone patches may also be used.

[0088] In this embodiment, the reading unit 80 is used as the reading unit to read the chart 100 set by the operator as shown in FIG. 1, but the present invention is not limited to such an embodiment. The reading unit may be a reading unit that reads the chart 100 when the chart 100 is output from the image forming apparatus 1. For example, as shown in FIG. 13, an in-line image sensor 86 may be provided downstream of the fixing unit 46 in the conveying 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 to 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.

[0089] [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 given the same reference numerals as those of the image forming apparatus of embodiment 1, and detailed explanations are omitted.

[0090] In the first embodiment, in the adjustment mode, a predetermined correction value is added to the judgment value of the secondary transfer voltage (adjustment value) based on the relationship between the acquired adjustment value and the average brightness value, and a recommended adjustment value of the secondary transfer voltage for the second side of a double-sided print is determined. This correction value is preset to compensate for a shortage of secondary transfer current during secondary transfer of the second side of a double-sided print, which may occur depending on the image density of the image output by the user. In particular, in the first embodiment, a +1 level correction value is added to the judgment value based on the relationship between the adjustment value and the average brightness value so that the correction amount [V] is the adjustment value +1 level, and a recommended adjustment value of the secondary transfer voltage for the second side of a double-sided print is determined.

[0091] FIG. 14 is a graph showing an example of the relationship between the recording material distribution voltage Vp and the toner distribution voltage Vt of the toner on the first side during the secondary transfer of the second side of a double-sided print, which was obtained by an experiment. As shown in FIG. 14, as the recording material distribution voltage Vp decreases, the toner distribution voltage Vt increases. That is, under the condition where the recording material distribution voltage Vp decreases, the contribution of the electrical resistance of the toner layer to the electrical resistance of the recording material S and the toner layer on the first side at the secondary transfer section N2 increases. Therefore, under the above conditions, there is a possibility that the deviation between the adjustment value of the secondary transfer voltage for the second side of a double-sided print determined in the adjustment mode and the appropriate adjustment value of the secondary transfer voltage for an arbitrary image output by the user becomes large. For example, the condition where the recording material distribution voltage Vp becomes small includes thin paper with a small basis weight (or thickness) and a high temperature and high humidity usage environment. As a result, under the above conditions, in the control of the first embodiment, the toner distribution voltage Vt cannot be fully compensated for during the secondary transfer of the second side of a double-sided print, and image defects may occur due to a shortage of secondary transfer current.

[0092] Therefore, in this embodiment, the secondary transfer voltage for the second side of double-sided printing is corrected according to the recording material shared voltage Vp and further according to the toner shared voltage for the first side.

[0093] 15 is a flow chart showing an outline of a procedure for setting the secondary transfer voltage when performing double-sided printing in this embodiment. In this embodiment, when performing double-sided printing, ATVC control is performed, and the overall operation of setting the secondary transfer voltage for each of the first and second sides of double-sided printing using the result of ATVC control and the adjustment value set in the adjustment mode is the same as in the first embodiment. In this embodiment, the overall operation of the adjustment mode is generally the same as in the first embodiment. However, in this embodiment, in the adjustment mode, for all of single-sided printing, the first side of double-sided printing, and the second side of double-sided printing, a judgment value based on the relationship between the adjustment value and the average brightness value acquired as described in the first embodiment is determined and stored as the adjustment value of the secondary transfer voltage.

[0094] When a double-sided print job is started, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) executes ATVC control and acquires information on the adjustment value (judgment value) stored in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S301). At this time, the control unit 30 (adjustment processing unit 31d) acquires information on the adjustment value (judgment value) corresponding to the information on the recording material S specified in the double-sided print job. If the adjustment mode has not been executed before the double-sided print job, the stored adjustment value (here, the judgment value) is assumed to be "0". If the adjustment mode has not been executed before the job, the process of setting the secondary transfer voltage as described here may be omitted and image formation may be performed using a default secondary transfer voltage.

[0095] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) sets the secondary transfer voltage Vtr for the first side in the same manner as described in the first embodiment using the adjustment value (judgment value) determined in the adjustment mode (S302). That is, the adjustment amount ΔV is calculated as ΔV=adjustment value×150[V]. Then, the calculated adjustment amount ΔV is used to calculate the adjusted recording material shared voltage Vp+ΔV, which is then used to calculate the secondary transfer voltage Vtr (=Vb+Vp+ΔV).

[0096] Meanwhile, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) corrects the adjustment value (judgment value) determined in the adjustment mode as follows and sets the secondary transfer voltage Vtr for the second side (S303). That is, in this embodiment, the control unit 30 (adjustment processing unit 31d) calculates a corrected adjustment value by adding a value obtained by multiplying the adjustment value +1 level by Vt / Vp to the judgment value of the secondary transfer voltage for the second side of double-sided printing determined in the adjustment mode. Here, Vt is the toner distribution voltage by the toner of the first side during secondary transfer to the second side, Vp is the recording material distribution voltage during secondary transfer to the second side, and Vt / Vp represents the ratio of the toner distribution voltage Vt by the toner of the first side to the recording material distribution voltage Vp during secondary transfer to the second side. Then, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) sets the secondary transfer voltage Vtr in the same manner as described in the first embodiment using the calculated corrected adjustment value. That is, the adjustment amount ΔV is calculated as ΔV = corrected adjustment value × 150 [V]. Then, the calculated adjustment amount ΔV is used to calculate the adjusted recording material shared voltage Vp + ΔV, and this is used to calculate the secondary transfer voltage Vtr (= Vb + Vp + ΔV).

[0097] Then, the control unit 30 (image forming process unit 31c) performs the image forming operation (secondary transfer) using the secondary transfer voltages Vtr for the first and second sides that are set as described above (S304).

[0098] Although not shown in the drawings, in this embodiment, the secondary transfer voltage Vt for single-sided printing is set in the same manner as the secondary transfer voltage Vtr for the first side of double-sided printing.

[0099] Here, the control unit 30 (adjustment processor 31d) can obtain Vp and Vt used to obtain the adjustment value of the secondary transfer voltage for the second side as follows. In this embodiment, the control unit 30 (adjustment processor 31d) refers to the recording material shared voltage Vp from table data as shown in FIG. 5, which is stored in advance in the ROM 32. That is, the control unit 30 (adjustment processor 31d) obtains the corresponding recording material shared voltage Vp from table data as shown in FIG. 5, based on the information of the recording material S used in the double-sided print job and the environmental information. In this embodiment, the control unit 30 (adjustment processor 31d) also refers to the toner shared voltage Vt from information (table data and calculation formula) for obtaining the toner shared voltage, which is stored in advance in the ROM 32 based on the relationship in FIG. 11 and FIG. 14. That is, the control unit 30 (adjustment processor 31d) obtains the toner amount of the first side during the secondary transfer of the second side based on the image information of the first side. This toner application amount is obtained (for example, average value) based on image information of images formed on the first side of all or some of the recording materials S in the double-sided print job, and can be used to set the secondary transfer voltage for the second side of all the recording materials S in the job. Alternatively, this toner application amount is obtained (for example, average value) based on image information of images formed on the first side of each recording material S in the double-sided print job, and can be used to set the secondary transfer voltage for the second side of the corresponding recording material S. This toner application amount for the first side may be obtained for a predetermined area including at least a part of the area to which the toner image for the second side is transferred. In addition, the control unit 30 (adjustment processing unit 31d) obtains the recording material application voltage Vp and the toner application voltage Vt corresponding to the toner application amount obtained as described above, based on information (table data or calculation formula) showing the relationship between the recording material application voltage Vp and the toner application voltage Vt as shown in FIG. 14, which is obtained in advance for each toner application amount (which may be for each predetermined toner application amount division). Then, the control unit 30 (adjustment processing unit 31d) uses these Vp and Vt to obtain the Vt / Vp ratio.

[0100] In this embodiment, the adjustment value of the secondary transfer voltage for the second side of double-sided printing is obtained according to the Vt / Vp ratio. In this case, the adjustment value when the recording material distribution voltage Vp (absolute value) is a second value smaller than the first value is larger than the adjustment value when the recording material distribution voltage Vp is a first value, and the adjustment value when the toner distribution voltage Vt is a fourth value larger than the third value is larger than the adjustment value when the toner distribution voltage Vt (absolute value) is a third value. However, the present invention is not limited to such an embodiment. For example, the toner distribution voltage for the first side may be considered to be approximately constant (predetermined value), and the adjustment value of the secondary transfer voltage for the second side of double-sided printing may be obtained according to the recording material distribution voltage Vp. In this case, the adjustment value when the recording material distribution voltage Vp is a second value smaller than the first value is larger than the adjustment value when the recording material distribution voltage Vp (absolute value) is a first value. This corresponds to obtaining an adjustment value of the secondary transfer voltage for the second side of a double-sided print according to the Vt / Vp ratio using the toner distribution voltage Vt considered to be substantially constant. In addition, for example, when a predetermined recording material S (such as thin paper with a basis weight in a predetermined range) is used or in a predetermined environment (such as a high-temperature, high-humidity environment), the recording material Vp may be considered to be substantially constant (a predetermined value) and an adjustment value of the secondary transfer voltage for the second side of a double-sided print may be obtained according to the toner distribution voltage Vt. In this case, the adjustment value when the toner distribution voltage Vt (absolute value) is a fourth value greater than the third value is larger than the adjustment value when the toner distribution voltage Vt is a third value. This corresponds to obtaining an adjustment value of the secondary transfer voltage for the second side of a double-sided print according to the Vt / Vp ratio using the recording material distribution voltage Vp considered to be substantially constant.

[0101] Thus, in this embodiment, the image forming apparatus 1 has an output unit that outputs a signal for displaying the first information and the second information. In this embodiment, the setting unit 31f sets the transfer voltage for the second side transfer based on the third information acquired by the correction unit 31d when performing double-sided image formation. In this embodiment, the image forming apparatus 1 has a storage unit (RAM 33 and secondary transfer voltage storage unit / calculation unit 31f) that stores the first information and the second information. In this embodiment, the setting unit 31f sets the transfer voltage for the second side transfer based on the third information acquired by the correction unit 31d when performing double-sided image formation. The correction unit 31d can acquire the correction information based on information on the recording material S on which double-sided image formation is performed. In this case, the correction unit 31d acquires the correction information so that the absolute value of the correction amount indicated by the correction information when the absolute value of the recording material shared voltage applied to the recording material S at the transfer portion N2 during the transfer of the second side based on the information of the recording material S is a first value is larger than the absolute value of the correction amount indicated by the correction information when the absolute value of the recording material shared voltage is a second value smaller than the first value. The recording material shared voltage can be acquired from a value that is determined in advance based on the type of the recording material S (basis weight, thickness, etc.) and further environmental information (at least one of the temperature and humidity inside or outside the image forming apparatus 1). The recording material shared voltage may also be acquired by measuring it in the image forming apparatus 1. For example, when the recording material S is in the transfer portion N2, a voltage of a predetermined voltage value Vtr is applied to the transfer portion N2 to detect the current value that flows. This can be performed, for example, when a margin on the leading edge side of the recording material S in the transport direction during image formation of the first or second side is in the transfer portion N2. The transfer portion carrying voltage Vb is calculated by applying the detected current value to the relationship between voltage and current when there is no recording material S at the transfer portion N2, which is calculated by the above-mentioned ATVC control or a control similar thereto. The recording material carrying voltage Vp can be calculated by subtracting the calculated transfer portion carrying voltage Vb from the voltage value Vtr. Information on the electrical resistance of the recording material S may also be used as information on the recording material S.There is a correlation between the electrical resistance of the recording material S and the recording material shared voltage. When the electrical resistance of the recording material S is relatively high, the recording material shared voltage is relatively high, and when the electrical resistance of the recording material S is relatively low, the recording material shared voltage is relatively low. The recording material shared voltage can also be seen as information on the electrical resistance of the recording material S. The correction unit 31d can also acquire correction information based on information on the amount of toner transferred to the first side in double-sided image formation. In this case, the correction unit 31d acquires correction information so that the absolute value of the correction amount indicated by the correction information when the absolute value of the toner shared voltage applied to the toner on the first side at the transfer unit N2 during transfer of the second side based on the information on the amount of toner is a fourth value that is greater than the third value is larger than the absolute value of the correction amount indicated by the correction information when the absolute value of the toner shared voltage is a third value.

[0102] As described above, according to this embodiment, the secondary transfer voltage for the second side of double-sided printing can be set more appropriately in accordance with the recording material S and the image on the first side when double-sided printing is performed.

[0103] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0104] In the above 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.

[0105] In addition, in the above-described embodiment, the image forming apparatus is configured to allow an operator to change information regarding the amount of adjustment of the transfer voltage determined by the image forming apparatus in the adjustment mode, but the image forming apparatus may be configured not to allow the operator to change the information.

[0106] In the above embodiment, the operation performed on the operation unit of the image forming apparatus may be performed on an external device. That is, the case where the adjustment mode is executed by the operator via the operation unit 70 of the image forming apparatus 1 has been described, but the adjustment mode may be executed by the operator via the external device 200 such as a personal computer. In this case, the same settings as those in the above embodiment can be performed via a screen displayed on the display unit of the external device 200 by the driver program of the image forming apparatus 1 installed in the external device 200.

[0107] In the above embodiment, the secondary transfer voltage is controlled to a constant voltage, but the secondary transfer voltage may be controlled to a constant current. In the above embodiment, in the configuration in which the secondary transfer voltage is controlled to a constant voltage, the secondary transfer voltage is adjusted by adjusting the target voltage when the secondary transfer voltage is applied in the adjustment mode. In the configuration in which the secondary transfer voltage is controlled to a constant current, the secondary transfer voltage can be adjusted by adjusting the target current when the secondary transfer voltage is applied in the adjustment mode.

[0108] Furthermore, the detection result of the current or voltage may be an average value of a plurality of sampling values ​​acquired at a predetermined sampling interval at one detection timing, etc. Furthermore, when the transfer voltage is controlled to a constant voltage, the voltage value may be detected (recognized) from an 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 an output instruction value for the power supply.

[0109] 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 being a color image forming apparatus, but may be a monochrome image forming apparatus. For example, the present invention may be applied to a transfer section in an image forming apparatus configured to form a toner image on a photosensitive drum as an image carrier, and then directly transfer the toner image to a recording material in the transfer section. Furthermore, the present invention can be implemented in various applications, such as printers, various printing machines, copiers, FAX machines, and multifunction machines. [Explanation of symbols]

[0110] 1. Image forming device 30 Control section 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 section S recording material

Claims

1. an image forming unit that forms a toner image; a transfer section for transferring the toner image formed by the image forming section onto a recording material; A power source that applies a voltage to the transfer unit; A reading unit that reads an image on a recording material; a control unit that executes an output process to output a double-sided chart having a first chart formed by applying a plurality of first test voltages to the transfer unit from the power source to transfer a plurality of first test images onto a first side of a recording material, and a second chart formed by applying a plurality of second test voltages to the transfer unit from the power source to transfer a plurality of second test images onto a second side of the recording material, the control unit executing a process in a mode in which a transfer voltage for transferring an image onto the first side in double-sided image formation is set based on a detection result of the plurality of first test images read by the reading unit, and a transfer voltage for transferring an image onto the second side in double-sided image formation is set based on a detection result of the plurality of second test images read by the reading unit; having the control unit executes the output process such that the first test images on a first side of a recording material do not overlap with the second test images on a second side of the recording material; the control unit executes a predetermined selection process in which one image is selected from the plurality of images based on a detection result when the plurality of images are detected by the reading unit; when the transfer voltage for transferring an image to the first side in the double-sided image formation is set in the processing of the mode, the control unit selects one first test image from among the plurality of first test images by the predetermined selection processing, and sets the transfer voltage for transferring an image to the first side in the double-sided image formation based on the selected first test image; When the transfer voltage for transferring an image to the second side in the double-sided image formation is set in the processing of the mode, the control unit selects one second test image from the plurality of second test images by the predetermined selection processing, and based on the selected second test image, sets a voltage having an absolute value greater than the absolute value of the test voltage when the selected second test image is transferred as the transfer voltage for transferring an image to the second side in the double-sided image formation, regardless of the detection result of the plurality of first test images by the reading unit.

1. An image forming apparatus comprising:

2. The image forming apparatus according to claim 1, characterized in that the control unit sets the transfer voltage for transferring an image to the second side in the double-sided image formation based on the selected second test image and an adjustment value obtained by adding a predetermined value to the test voltage when the selected second test image is transferred.

3. 3. The image forming apparatus according to claim 2, wherein the predetermined value corresponds to one level when the test voltage is changed to a plurality of levels in the processing of the mode.

4. an input unit for inputting information for adjusting the transfer voltage for transferring an image to at least one of the first side and the second side in the double-sided image formation in response to an operation by an operator, The image forming apparatus according to claim 1, characterized in that, when information for adjusting the transfer voltage for transferring an image to a second side in the double-sided image formation is input from the input unit, the control unit sets the transfer voltage adjusted by an operator via the input unit as the transfer voltage for transferring an image to the second side.

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