Image forming apparatus

Abstract

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

Description

[Technical Field]

[0001] This invention relates to image forming apparatus such as photocopiers, printers, and facsimile machines that use electrophotographic or electrostatic recording methods. [Background technology]

[0002] In image forming apparatuses using electrophotography or similar methods, a toner image formed on an image carrier such as a photoreceptor or intermediate transfer body is transferred to a recording material. The transfer of the toner image from the image carrier to the recording material is often performed by applying a transfer voltage to a transfer member, such as a transfer roller, which contacts the image carrier to form a transfer area. The transfer voltage can be determined based on a transfer portion voltage corresponding to the electrical resistance of the transfer area detected during a pre-rotation process before image formation, and a recording material portion voltage corresponding to a preset type of recording material. This allows for setting an appropriate transfer voltage according to environmental fluctuations, the usage history of the transfer member, and the type of recording material.

[0003] However, because the types and conditions of recording materials used in image formation vary, the default recording material distribution voltage may result in an excess or deficiency in the transfer voltage. Therefore, it has been proposed to provide an adjustment mode that adjusts the set transfer voltage according to the recording material actually used in image formation.

[0004] Patent Document 1 proposes an image forming apparatus capable of performing an adjustment mode to adjust the setting voltage of the secondary transfer voltage. In this adjustment mode, a chart is output on a single recording material in which multiple patches (test images) are transferred, with the secondary transfer voltage switched for each patch. The density of each patch is then detected, and the optimal secondary transfer voltage conditions are selected according to the detection results. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-37185 [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0007] In particular, when the recording material used for chart output is small in size, there is less margin when forming patches, making it easier for the patches to overlap on the front and back of the recording material when adjusting the transfer voltage during double-sided printing. As a result, the adjustment of the transfer voltage during double-sided printing according to the detection results of the patch density may not be appropriate.

[0008] Therefore, the objective of the present invention is to enable appropriate adjustment of the transfer voltage during double-sided printing, even when the recording material used for chart output is small in size. [Means for solving the problem]

[0009] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier for carrying a toner image, a transfer means for transferring the toner image from the image carrier to a recording material in a transfer unit, an application means for applying a transfer voltage to the transfer means, a fixing means for fixing the toner image transferred to the recording material in a fixing unit, a double-sided mechanism for transporting a recording material to perform double-sided printing, in which the toner image is transferred to the first surface of the recording material in the transfer unit, the toner image is fixed to the first surface of the recording material in the fixing unit, the toner image is then transferred to the second surface of the recording material in the transfer unit, and the toner image is fixed to the second surface of the recording material in the fixing unit to form an image on both sides of the recording material, and an execution unit that executes an output mode for outputting a chart formed by transferring a plurality of test images to the recording material with different transfer voltages in order to adjust the transfer voltage, wherein the execution unit outputs the chart for adjusting the transfer voltage in the double-sided printing. The image forming apparatus is characterized in that, when executing the output mode, if the width in a direction substantially perpendicular to the transport direction of the recording material to which the test image is transferred is a first width, it executes a first output mode that outputs the chart formed by transferring the test image for adjusting the transfer voltage of the first side of the double-sided print and the test image for adjusting the transfer voltage of the second side of the double-sided print onto the first and second sides of a single recording material, respectively; and if the width of the recording material to which the test image is transferred is a second width smaller than the first width, it executes a second output mode that outputs the chart formed by transferring the test image for adjusting the transfer voltage of the first side of the double-sided print and the test image for adjusting the transfer voltage of the second side of the double-sided print onto one side of another recording material, respectively. [Effects of the Invention]

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

[0011] [Figure 1]It is a schematic cross-sectional view of an image forming apparatus. [Figure 2] It is a block diagram showing a schematic configuration of a control system of an image forming apparatus [Figure 3] It is a flowchart showing an outline of a secondary transfer voltage control procedure. [Figure 4] It is a graph showing an example of voltage-current characteristics obtained by secondary transfer voltage control. [Figure 5] It is a table showing an example of a recording material sharing voltage table. [Figure 6] It is a schematic diagram of an L chart output in adjustment mode. [Figure 7] It is a schematic diagram of an S chart output in adjustment mode. [Figure 8] It is a schematic diagram of an R chart output in adjustment mode. [Figure 9] It is a flowchart showing an outline of a procedure in adjustment mode. [Figure 10] It is a schematic diagram of a paper type category selection screen. [Figure 11] It is a schematic diagram of a paper feed unit selection screen. [Figure 12] It is a schematic diagram of a secondary transfer voltage adjustment screen. [Figure 13] It is a graph showing the transition of the secondary transfer voltage at the time of chart output. [Figure 14(a)] It is a table showing an example of the relationship between the patch number and the adjustment value of the chart. [Figure 14(b)] It is a table showing an example of the relationship between the patch number and the adjustment value of the chart. [Figure 14(c)] It is a table showing an example of the relationship between the patch number and the adjustment value of the chart. [Figure 15] It is a graph showing the transition of the secondary transfer voltage at the time of chart output. [Figure 16] It is a schematic diagram for explaining a method of detecting the position of a trigger patch. [Figure 17] It is a graph for explaining a method of selecting a recommended adjustment value. [Figure 18] It is a schematic diagram of an R chart in Example 2. [Figure 19] This is a schematic diagram of the L chart in Example 3. [Figure 20] This is a schematic diagram of the S chart in Example 3. [Modes for carrying out the invention]

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

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

[0014] The printer unit 2 includes a paper feeding unit 4, an image forming unit 5, a control unit 30, a data transfer unit 6 to the sensing unit 3, an operation unit 70, an image reading unit 80, and the like. In Figure 1, only one paper feeding unit 4 is shown, but the printer unit 2 may have multiple paper feeding units 4. Inside the main body 10 of the image forming apparatus 1 (printer unit 2), there is a temperature sensor 71 (Figure 2) capable of detecting the internal temperature of the main body 10 (internal temperature), and a humidity sensor 72 (Figure 2) capable of detecting the internal humidity of the main body 10 (internal humidity). The temperature sensor 71 and humidity sensor 72 are examples of environmental detection means for detecting environmental information, which is at least one of the temperature or humidity inside or outside the image forming apparatus 1, respectively. The printer unit 2 can form a four-color full-color image on a recording material (sheet, transfer material) S based on image information (image signal) from the image reading unit 80 or an external device 200 (Figure 2). External devices 200 include host devices such as personal computers, or digital cameras and smartphones. The recording material S is on which a toner image is formed, and specific examples include paper such as plain paper and cardboard, as well as paper substitutes such as synthetic resin sheets (synthetic paper) and overhead projector sheets.

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

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

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

[0018] The surface of the rotating photosensitive drum 51 is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by the charging roller 52. In this embodiment, the charging roller 52 is a rubber roller positioned in contact with the surface of the photosensitive drum 51. The charging roller 52 rotates in conjunction with the rotation of the photosensitive drum 51. A charging power supply 73 (Figure 2), which serves as a means for applying a charging voltage (charging voltage application unit), is connected to the charging roller 52. The charging bias power supply 73 applies a predetermined charging voltage (charging bias) to the charging roller 52 during the charging process.

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

[0020] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by the developing device 20 when toner is supplied, and a toner image (toner image, developer image) is formed on the photosensitive drum 51. In this embodiment, the developing device 20 contains a two-component developer comprising non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as the developer. Toner is supplied to the developing device 20 from the toner bottle 41. The developing device 20 has a developing sleeve 24 as a developer carrier (developing member). The developing sleeve 24 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). A magnetic roller, which is a roller-shaped magnet, is fixedly positioned inside the developing sleeve 24 so as not to rotate relative to the main body (developing container) of the developing device 20. The developing sleeve 24 carries the developer and transports it to the developing area facing the photosensitive drum 51. A developing power supply 74 (Figure 2) is connected to the developing sleeve 24 as a developing voltage application means (developing voltage application unit). The developing bias power supply 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 as the charging polarity of the photosensitive drum 51 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 51, where the absolute value of the potential has decreased after uniform charging treatment and exposure (reverse developing method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0021] An intermediate transfer belt 44b, which is an intermediate transfer body composed of an endless belt as a second image carrier, is positioned opposite the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer belt 44b is wrapped around a plurality of tension rollers (support rollers), namely a drive roller 44a, a tension roller 44d, and a secondary transfer inner roller 45a, and is stretched under a predetermined tension. The intermediate transfer belt 44b is movable (rotatable) and carries the toner image. The drive roller 44a is rotationally driven by a motor (not shown) as a driving means, causing the intermediate transfer belt 44b to rotate (move around). The tension roller 44d controls the tension of the intermediate transfer belt 44b to be constant. The tension roller 44d is subjected to a force that pushes the intermediate transfer belt 44b from the inner circumferential surface side to the outer circumferential surface side by the biasing force of a spring (not shown) as a biasing means. This force applies a tension of approximately 2 to 5 kg in the circumferential direction (direction of surface movement) to the intermediate transfer belt 44b. The secondary transfer inner roller 45a also constitutes the secondary transfer apparatus 45, as will be described later. The intermediate transfer belt 44b is driven by the drive roller 44a and rotates (circumferentially moves) in the direction of arrow R2 (clockwise) in Figure 1 at a predetermined circumferential speed (process speed) corresponding to the circumferential speed of the photosensitive drum 51. On the inner circumferential surface side of the intermediate transfer belt 44b, primary transfer rollers 47y, 47m, 47c, and 47k are arranged, corresponding to the four photosensitive drums 51y, 51m, 51c, and 51k, respectively. In this embodiment, the primary transfer roller 47 is positioned opposite the photosensitive drum 1 via the intermediate transfer belt 44b and sandwiches the intermediate transfer belt 44b between itself and the photosensitive drum 51. As a result, the primary transfer roller 47 contacts the photosensitive drum 51 via the intermediate transfer belt 44b, forming a primary transfer section (primary transfer nip section) N1 where the photosensitive drum 51 and the intermediate transfer belt 44b are in contact. The tension rollers other than the drive roller 44a and each of the primary transfer rollers 47y, 47m, 47c, and 47k rotate in conjunction with the rotation of the intermediate transfer belt 44b. In addition, a belt cleaning device 60, which serves as an intermediate transfer body cleaning means, is positioned on the outer circumferential surface side of the intermediate transfer belt 44b, facing the drive roller 44a via the intermediate transfer belt 44b.The intermediate transfer unit 44 is composed of an intermediate transfer belt 44, tension rollers 44a, 44d, 45a, primary transfer rollers 47y, 47m, 47c, 47k, a belt cleaning device 60, and the like.

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

[0023] On the outer circumferential surface of the intermediate transfer belt 44b, a roller-type secondary transfer member, the secondary transfer outer roller 45b, is positioned opposite the secondary transfer inner roller 45a, which acts as an opposing member via the intermediate transfer belt 44b. The secondary transfer outer roller 45b, together with the secondary transfer inner roller 45a, constitutes the secondary transfer device 45 as a secondary transfer means. The secondary transfer outer roller 45b contacts the secondary transfer inner roller 45a via the intermediate transfer belt 44b, forming a secondary transfer section (secondary transfer nip section) N2 where the intermediate transfer belt 44b and the secondary transfer outer roller 45b are in contact. The toner image formed on the intermediate transfer belt 44b is secondarily transferred in the secondary transfer section N2 to the recording material S, which is held between the intermediate transfer belt 44b and the secondary transfer outer roller 45b and transported (passing through the secondary transfer section N2) by the action of the secondary transfer device 45. In this embodiment, a positive polarity secondary transfer voltage is applied to the secondary transfer outer roller 45b, thereby secondary transferring the negative polarity toner image on the intermediate transfer belt 44b onto the recording material S. The recording material S is fed from the paper feeding unit 4 in parallel with the toner image formation operation described above, and is transported to the secondary transfer unit N2 by the register roller 11, which is a transport member provided on the transport path P, in time with the toner image on the intermediate transfer belt 44b.

[0024] Thus, the secondary transfer device 45 is configured to include a secondary transfer inner roller 45a as an opposing member and a secondary transfer outer roller 45b as a secondary transfer member. A secondary transfer power supply 76 (Figure 2), which serves as a secondary transfer voltage application means (secondary transfer voltage application unit), is connected to the secondary transfer outer roller 45b. During the secondary transfer process, the secondary transfer power supply 76 applies a predetermined secondary transfer voltage to the secondary transfer outer roller 45b, which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner. A voltage detection sensor 76a, which serves as a voltage detection means (voltage detection unit) for detecting the output voltage, and a current detection sensor 76b, which serves as a current detection means (current detection unit) for detecting the output current, are connected to the secondary transfer power supply 76 (Figure 2). In this embodiment, the core metal of the secondary transfer inner roller 45a is connected to ground potential. When the recording material S is supplied to the secondary transfer unit N2, a constant voltage controlled secondary transfer voltage with the opposite polarity 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 6.5 kV is applied, and a current of about 15 to 100 μA is passed through, thereby secondary transferring the toner image on the intermediate transfer belt 44b onto the recording material S. In this embodiment, the secondary transfer inner roller 45a is connected to ground potential, and a voltage is applied to the secondary transfer outer roller 45b from the secondary transfer power supply 76. Alternatively, a voltage may be applied to the secondary transfer inner roller 45a, which is the secondary transfer member, from the secondary transfer power supply 76, and the secondary transfer outer roller 45b, which is the opposing member, may be connected to ground potential. In this case, a DC voltage with the same polarity as the normal charging polarity of the toner is applied to the secondary transfer inner roller 45a.

[0025] The recording material S onto which the toner image has been transferred is transported to a fixing device 46, which serves as a fixing means. The fixing device 46 includes a fixing roller 46a and a pressure roller 46b. The fixing roller 46a has a built-in heater as a heating means. The pressure roller 46b is pressed toward the fixing roller 46a, forming a fixing section (fixing nip section) N3 where the fixing roller 46a and the pressure roller 46b come into contact. The recording material S, which carries the unfixed toner image, is heated and pressurized in the fixing section N3 by being transported while sandwiched between the fixing roller 46a and the pressure roller 46b. As a result, the toner image is fixed (melted and solidified) onto the recording material S. The temperature of the fixing roller 46a (fixing temperature) is detected by a fixing temperature sensor 77 (Figure 2) and controlled by a control unit 30.

[0026] In the case of single-sided printing, where an image is formed on one side of the recording material S, the recording material S, with the toner image fixed to one side as described above, is transferred directly from the transfer unit 6 to the sensing unit 3. On the other hand, in the case of double-sided printing, where an image is formed on both sides of the recording material S, the recording material S, with the toner image fixed to the first side as described above, is transported to the inversion transport path 7 by an inversion transport roller 12 or the like, which acts as an inversion transport member. In the inversion transport path 7, the recording material S with the toner image fixed to the first side is turned over and supplied again to the secondary transfer unit N2 by a double-sided transport roller 13 or the like, which acts as a double-sided transport member. The recording material S supplied again to the secondary transfer unit N2 in this way has the toner image transferred to the second side and fixed, and then is transferred from the transfer unit 6 to the sensing unit 3. In this way, the printer unit 2 of this embodiment is capable of performing double-sided printing (automatic double-sided printing, double-sided printing) by forming an image on both sides of a single recording material S. The double-sided mechanism 14 is composed of the inversion transport path 7, the inversion transport roller 12, the double-sided transport roller 13, and the like. The recording material S on which the image has been formed passes through the inside of the sensing unit 3 and is discharged (output) to the discharge unit 8 located outside the sensing unit 3 (image forming apparatus 1). In the adjustment mode described later, when a chart formed by transferring patches to the recording material S is output, the patches on the chart are read as the recording material S passes through the inside of the sensing unit 3, and then the recording material S is discharged to the discharge unit 8.

[0027] After the primary transfer, the photosensitive drum 51 is electrostatically discharged from its surface by the pre-exposure device 54. Furthermore, toner remaining on the photosensitive drum 51 during the primary transfer process that was not transferred to the intermediate transfer belt 44b (primary transfer residue toner) is removed and recovered from the surface of the photosensitive drum 51 by the drum cleaning device 55. The drum cleaning device 55 has a cleaning blade as a cleaning member. The cleaning blade is a plate-shaped member that contacts the photosensitive drum 51 with a predetermined pressing force. The cleaning blade is in contact with the surface of the photosensitive drum 51 in a counter-direction with respect to the rotation direction of the photosensitive drum 51, such that the tip of its free end faces upstream in the rotation direction of the photosensitive drum 51. Additionally, toner remaining on the intermediate transfer belt 44b during the secondary transfer process that was not transferred to the recording material S (secondary transfer residue toner) and other adhering materials such as paper dust are removed and recovered from the surface of the intermediate transfer belt 44b by the belt cleaning device 60. In this embodiment, the belt cleaning device 60 is configured to have a cleaning blade similar to the drum cleaning device 55. The toner and other materials collected by the drum cleaning device 55 and the belt cleaning device 60 are transported to a collection container (not shown) and stored there.

[0028] Furthermore, the printer unit 2 can also form single-color or multi-color images, such as a black-only image, using image forming units 50 for several of the desired single colors or four colors.

[0029] 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. Furthermore, the primary transfer roller 47 has an electrical resistance value of 1 × 10⁻¹⁰. 5 ~1 × 10 8 A roller with a value of Ω (N / N (measured at 23°C, 50%RH, with 2kV applied)) can be suitably used.

[0030] In this embodiment, the intermediate transfer belt 44b is an endless belt having a two-layer structure consisting of a base layer and a surface layer from the inner circumferential surface side. Suitable materials for the base layer include resins such as polyimide and polycarbonate, or various types of rubber containing an appropriate amount of carbon black as an antistatic agent. The thickness of the base layer is, for example, 0.05 to 0.15 mm. Suitable materials for the surface layer include resins such as fluororesin. The surface layer reduces the adhesion of toner to the surface of the intermediate transfer belt 44b, facilitating the transfer of toner to the recording material S in the secondary transfer section N2. The thickness of the surface layer is, for example, 0.0002 to 0.020 mm. Suitable materials for the surface layer include 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, a surface layer can be formed on this substrate by dispersing one or more types of powders or particles, such as fluororesin, or particles with different particle sizes, as a material that reduces surface energy and enhances lubricity. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5 × 10⁻⁶ 8 ~1 × 10 14 The friction coefficient is Ω·cm (23℃, 50%RH), and the static friction coefficient is 0.15~0.6 (23℃, 50%RH, HEIDON type 94i). In this embodiment, the intermediate transfer belt 44b has a two-layer structure, but it may also be a single-layer structure of the material corresponding to the base layer described above.

[0031] 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 electrical resistance value of the secondary transfer outer roller 45b is 1 × 10⁻¹⁰. 5 ~1 × 10 8 A roller with a value of Ω (N / N (measured at 23°C, 50%RH, with 2kV applied)) can be suitably used.

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

[0033] Furthermore, an automatic document transport device 81 and an image reading unit 80 are arranged on the upper part of the main body 10 of the device. The automatic document transport device 81, as a document transport means, automatically transports a sheet such as recording material S on which an image (text or image) of the document is formed to the reading position of the image reading unit 80 (which may consist of at least a part of the platen glass 82 described later). The image reading unit 80, as a reading means, can read the image on the sheet transported to the reading position by the automatic document transport device 81. The image reading unit 80 can also read the image on a sheet such as recording material S on which an image (text or image) of the document is formed, which is placed on the platen glass 82. The image reading unit 80 is configured to illuminate the sheet with a light source (not shown) and read the image on the sheet with an image reading element (not shown) at a predetermined dot density. In other words, the image reading unit 80 optically reads the image on the sheet and converts it into an electrical signal.

[0034] 2. Control Modes Figure 2 is a block diagram illustrating the schematic configuration of the control system of the image forming apparatus 1 in this embodiment. As shown in Figure 2, the control unit 30 is composed of a computer. The control unit 30 includes, for example, a CPU 31, a ROM 32 (including a rewritable one) that stores programs for controlling each part, a RAM 33 that temporarily stores data, and an input / output circuit (I / F) 34 that inputs and outputs signals to and from the outside. The CPU 31 is a microprocessor that oversees the entire control of the image forming apparatus 1 and is the main component of the system controller. The CPU 31 is connected to the paper feeding unit 4, the image forming unit 5, the transfer unit 6, the operation unit 70, the sensing unit 3, and the image reading unit 80 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 image forming control sequences for forming images on the recording material S. For example, the control unit 30 is connected to a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, and a secondary transfer power supply 76, each of which is controlled by signals from the control unit 30. Furthermore, the control unit 30 is connected to a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power supply 76, and a fixing temperature sensor 77. Signals detected by each sensor are input to the control unit 30.

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

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

[0037] Here, the image forming apparatus 1 executes a job (image output operation, print job), which is a series of operations that form and output an image on one or more recording materials S, initiated by a single start instruction. A job generally includes an image forming process, a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials S, and a post-rotation process. The image forming process is the period during which the electrostatic image, toner image, primary transfer, secondary transfer, and fixing of the toner image are performed for the image to be actually formed and output on the recording materials S. The image forming time (image forming period) refers to this period. More specifically, the timing of the image forming time differs depending on the position where each of these processes—electrostatic image formation, toner image formation, primary transfer, secondary transfer, and fixing of the toner image—is performed. The pre-rotation process is the period during which preparatory operations are performed before the image forming process, from when a start instruction is input until the image is actually formed. The paper-to-paper process (image-to-image process) is the period corresponding to the space between recording materials S when image forming is performed continuously on multiple recording materials S (continuous image forming). The post-rotation process is the period during which the image forming process is followed by tidying up (preparation) operations. The non-image forming period is the period other than the image forming process, and includes the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation process, which is the preparation operation when the image forming apparatus 1 is powered on or when it returns from sleep mode.

[0038] 3. Sensing Unit Configuration Next, we will describe the configuration of the sensing unit 3, which has the function of reading the output chart in the adjustment mode for adjusting the setting voltage of the secondary transfer voltage.

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

[0040] Furthermore, a first press roller 93 is positioned opposite the first line sensor 91, and a second press roller 94 is positioned opposite the second line sensor 92. When reading the chart, the first and second press rollers 93 and 94 stabilize the posture of the recording material S, thereby stabilizing the reading result. The recording material S that has passed through the sensing unit 3 is discharged to the discharge section 8.

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

[0042] As shown in Figure 2, the sensing unit 3 is connected to the control unit 30, and can transmit information (concentration information related to concentration) read by the first and second line sensors 91 and 92 to the control unit 30.

[0043] 4. Control of secondary transfer voltage Next, the control of the secondary transfer voltage will be explained. Figure 3 is a flowchart illustrating the general procedure for controlling the secondary transfer voltage in this embodiment. Generally, there are two methods for controlling the secondary transfer voltage: constant voltage control and constant current control. In this embodiment, constant voltage control is used.

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

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

[0046] Next, the control unit 30 (ATVC control process unit 31b) acquires information regarding the electrical resistance of the secondary transfer unit N2 by ATVC control (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, with the secondary transfer outer roller 45b and the intermediate transfer belt 44b in contact, the secondary transfer power supply 76 supplies multiple predetermined voltage levels to the secondary transfer outer roller 45b. The current value while the predetermined voltage is supplied is detected by the current detection sensor 76b, and the relationship between voltage and current (voltage-current characteristics) as shown in Figure 4 is acquired. The control unit 30 (ATVC control process unit 31b) writes this information on the relationship between voltage and current to the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f). This relationship between voltage and current changes according to the electrical resistance of the secondary transfer unit N2. Alternatively, a predetermined current at multiple levels may be supplied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b, and the voltage value generated at that time may be detected by the voltage detection sensor 76a. In the configuration of this embodiment, the relationship between voltage and current is not such that the current changes linearly (proportionally) with respect to voltage, but rather the current changes in such a way that it can be expressed as a polynomial of order two or higher of the voltage. Therefore, in this embodiment, in order to express the relationship between voltage and current as a polynomial, the predetermined voltage or current supplied when acquiring information on the electrical resistance of the secondary transfer unit N2 is set to three or more multi-stage values.

[0047] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines the voltage value to be applied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b (S106). In other words, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines the voltage value Vb required to flow the target current Itarget in the secondary transfer unit N2 when there is no recording material S, based on the target current Itarget written to the RAM 33 in S104 and the relationship between voltage and current determined in S105. This voltage value Vb corresponds to the secondary transfer partial voltage (transfer voltage of the electrical resistance of the secondary transfer unit N2). In addition, the ROM 32 stores information for determining the recording material partial voltage (transfer voltage of the electrical resistance of the recording material S) Vp, as shown in Figure 5. This information is set as table data showing the relationship between the environmental moisture content (absolute moisture content) and the recording material partial voltage Vp for each basis weight category of the recording material S (corresponding to the paper type category). Furthermore, since the electrical resistance of the recording material S increases due to a decrease in moisture content after passing through the fixing device 46, separate tables are prepared for the first and second sides. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the recording material distribution voltage Vp from the above table data based on the job information acquired in S101 and the environmental information acquired in S103. The table data for calculating the recording material distribution voltage Vp, as shown in Figure 5, has been determined in advance through experiments or other means. The control unit 30 can also determine the environmental moisture content based on the temperature information acquired by the temperature sensor 71 and the humidity information acquired by the humidity sensor 72. In addition, if an adjustment value has been set by the adjustment mode for adjusting the secondary transfer voltage setting value, which will be described later, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the adjustment amount ΔV corresponding to that adjustment value. As will be described later, this adjustment amount ΔV is stored in the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) when it has been set by the adjustment mode. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates Vb+V+ΔV, which is the sum of Vb, Vp, and ΔV, as the secondary transfer voltage Vtr to be applied from the secondary transfer power supply 76 to the secondary transfer outer 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) to the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f).

[0048] Here, the recording material voltage Vp can change not only due to information related to the electrical resistance of the recording material S (such as basis weight), but also due to the surface properties of the recording material S. Therefore, the table data above may be set so that the recording material voltage Vp changes depending on information related to the surface properties of the recording material S. In this embodiment, information related to the electrical resistance of the recording material S (and further information related to the surface properties of the recording material S) is included in the job information acquired in S101. However, the image forming apparatus 1 may be provided with measuring means for detecting the thickness of the recording material S and the surface properties of the recording material S, and the recording material voltage Vp may be determined based on the information obtained by this measuring means.

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

[0050] Regarding the primary transfer unit N1, the same ATVC control as described above is performed from the start of the job until the toner image is transported to the primary transfer unit N1, but a detailed explanation is omitted here.

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

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

[0053] Conversely, if the secondary transfer voltage is excessively high, abnormal discharge may occur, resulting in image defects, or the charge of the toner may reverse due to discharge in the secondary transfer section N2, leading to a decrease in transferability. For example, this could occur if the electrical resistance of the recording material S is lower than the value assumed for each paper type category (corresponding to the recording material distribution voltage Vp), or if the moisture content of the recording material S increases (hygroscopic) due to storage conditions, causing a decrease in electrical resistance. In such cases, it is desirable to lower the setting voltage of the secondary transfer voltage (reduce its absolute value) by lowering the recording material distribution voltage Vp.

[0054] Therefore, it is desirable for operators, such as users or service personnel, to adjust (change) the recording material distribution voltage Vp according to the recording material S actually used for image formation, thereby adjusting (changing) the secondary transfer voltage setting voltage during job execution to an optimal value. In other words, it is sufficient to select the optimal recording material distribution voltage Vp + ΔV (adjustment amount) according to the recording material S actually used for image formation. This adjustment can be performed by the following method. For example, the operator can output the image to be output, switching the secondary transfer voltage for each recording material S, and check for any image defects in the output image to determine the optimal secondary transfer voltage setting voltage (more specifically, the recording material distribution voltage Vp + ΔV). However, with this method, the amount of wasted recording material S increases, and it may take a long time, as it involves repeatedly outputting images and adjusting the secondary transfer voltage setting voltage.

[0055] Therefore, in this embodiment, the image forming apparatus 1 is capable of executing an adjustment mode for adjusting the setting voltage of the secondary transfer voltage. In this adjustment mode, a chart is output in which multiple patches of representative colors (test images, test patterns, test toner images) are transferred to the recording material S actually used for image formation, with the setting voltage of the secondary transfer voltage being switched for each patch. Based on the results of reading the output chart by the sensing unit 3, the optimal setting voltage of the secondary transfer voltage (more specifically, the recording material distribution voltage Vp + ΔV) is determined. In particular, in this embodiment, based on the brightness information (density information) of the solid patch (a patch of a solid image which is an image with the maximum amount of toner applied) on the chart, a recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) for optimizing the density of the solid image is presented. This reduces the need for the operator to visually check for image defects, thereby reducing the operator's workload and making it possible to adjust the setting of the secondary transfer voltage more appropriately.

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

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

[0058] The large chart data (also called "L chart data"), which is the image data that defines the L chart 100, corresponds to the maximum paper size. The image size of the L chart data is approximately 13 inches (≒330 mm) in width and 19.2 inches (≒487 mm) in length in the transport direction. Depending on the size of the recording material S, the L chart 100 corresponding to the image data cut from this L chart data is output. At this time, the image data is cut from the L chart data to match the size of the recording material S, with the leading edge in the reading direction and the center in the width direction as the reference point. Figure 6 shows the case where the size of the recording material S is A3 size (portrait feed). For example, if the recording material S used to output the L chart 100 is A3 size (portrait feed) (width 297 mm × transport direction length 420 mm), image data with a size of 292 mm in width and transport direction length 415 mm is cut from the L chart data. Then, an image corresponding to this cropped image data is formed on an A3-sized (portrait orientation) recording material S, with a margin of 2.5 mm at each end, based on the leading edge in the reading direction and the center in the width direction. This margin is typically around 2 to 10 mm.

[0059] The L-chart 100 has 11 pairs of blue (B) solid patches 101 and black (Bk) solid patches 102 arranged side by side in the width direction, all aligned in the direction of transport of the recording material S. In the L-chart 100 in Figure 6, 100(1) shows the first side and 100(2) shows the second side. The second side passes through the secondary transfer section N2 and then through the inside of the sensing unit 3 without changing orientation, while the first side passes through the reversal transport path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer section N2 and when passing through the inside of the sensing unit 3. In Figure 6, the transport direction of the chart when passing through the secondary transfer section N2 is shown by a thin arrow, and the transport direction of the chart when passing through the inside of the sensing unit 3 is shown by a thick arrow. In this embodiment, the leading patches of the B solid patch 101 and Bk solid patch 102 as they pass through the inside of the sensing unit 3 are position information detection patches (also referred to here as "trigger patches") 101T and 102T, respectively. These trigger patches 101T and 102T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101 and Bk solid patch 102, the remaining 10 patches each, excluding the trigger patches 101T and 102T, are brightness information (density information) acquisition patches (also referred to here as "adjustment patches") 101A and 102A. Adjustment patches 101A and 102A are each transferred to the recording material S with different secondary transfer voltages Vtr applied.

[0060] In this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm in length and 40 mm in width in the transport direction, and a 15 mm gap is maintained between B solid patches 101 and between Bk solid patches 102 in the transport direction of the recording material S. Considering the readings by the first and second line sensors 91 and 92, if the size of each patch (especially the adjustment patch) is too small, the reading results will vary greatly due to the influence of unevenness in the recording material S (unevenness in the unevenness caused by paper fibers, etc.). Therefore, it is desirable for each patch (especially the adjustment patch) to have a relatively large area, approximately 600 mm². 2The above is desirable. However, if the size of each patch (especially the adjustment patch) is made too large, the number of secondary transfer voltages Vtr that can fluctuate within the chart will decrease. In this embodiment, the patch size in the L chart 100 is set to allow the secondary transfer voltage Vtr to fluctuate in 10 steps. In addition, the patch spacing in the transport direction of the recording material S is set to allow switching of the secondary transfer voltage, and a spacing of 15 mm or more is desirable.

[0061] Furthermore, on the first side 100(1) and the second side 100(2) of the L chart 100, the B solid patch 101 and the Bk solid patch 102 are arranged so that they do not overlap on the front and back sides of the recording material S. This is to avoid the influence of back-image reflection on the detection brightness when read by the first and second line sensors 91 and 92, as will be explained in more detail later.

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

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

[0064] In the S chart 103, pairs of blue (B) solid patches 101 and black (Bk) solid patches 102 are arranged side by side in the width direction, spanning two recording materials S and arranged in the direction of transport of the recording materials S, for a total of 12 pairs. In the S chart 103, by using two recording materials S to form the chart, the same number of patches as the L chart 100 is secured, and equivalent adjustments can be made. In the S chart 103 in Figure 7, 103(1-1) shows the first sheet of the first side, 103(1-2) shows the second sheet of the first side, 103(2-1) shows the first sheet of the second side, and 103(2-2) shows the second sheet of the second side. After passing through the secondary transfer section N2, the second side passes through the inside of the sensing unit 3 without changing orientation, but the first side passes through the reversal transport path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer section N2 and when passing through the inside of the sensing unit 3. In Figure 7, the transport direction of the chart as it passes through the secondary transfer section N2 is indicated by a thin arrow, and the transport direction of the chart as it passes through the inside of the sensing unit 3 is indicated by a thick arrow. In this embodiment, with respect to the patches formed on one surface of the recording material S, the leading patches of the B solid patch 101 and Bk solid patch 102 as they pass through the inside of the sensing unit 3 are trigger patches 101T and 102T for detecting position information, respectively. These trigger patches 101T and 102T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101 and Bk solid patch 102, the remaining 10 patches each, excluding the trigger patches 101T and 102T, are adjustment patches 101A and 102A for acquiring brightness information (density information). The adjustment patches 101A and 102A are each transferred to the recording material S with different secondary transfer voltages Vtr applied.

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

[0066] Furthermore, on the first side 103(1-1), 103(1-2) and the second side 103(2-1), 103(2-2) of the S chart 103, the B solid patch 101 and Bk solid patch 102 are arranged so that they do not overlap on the front and back sides of the recording material S. This is to avoid the influence of back-image reflection on the detection brightness when read by the first and second line sensors 91 and 92, as will be explained in more detail later.

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

[0068] The R-chart data, which is the image data defining the R-chart 104, corresponds to half the maximum paper size, similar to the S-chart data. The image size of the S-chart data is approximately 13 inches wide (≒330 mm) x 9.6 inches long in the transport direction (≒243 mm). When the size of the recording material S is A5R (width 148.5 mm x transport direction length 210 mm) or STMTR (width 139.7 mm x transport direction length 215.9 mm), the R-chart 104 corresponding to the image data cut from this R-chart data is output according to the size of the recording material S. In this case, the image data is cut from the R-chart data to match the size of the recording material S, with the leading edge in the reading direction and the center in the width direction as the reference point. Figure 8 shows the case when the size of the recording material S is A5R. For example, if the recording material S used for outputting the R chart 104 is A5 size (vertical feed) (width 148.5 mm x length in the transport direction 210 mm), then image data measuring 148.5 mm in width and 210 mm in length in the transport direction is cropped from the R chart data. Then, an image corresponding to this cropped image data is formed on the A5 size (vertical feed) recording material S, with a margin of 2.5 mm at each end, based on the leading edge in the reading direction and the center in the width direction. This margin is typically around 2 to 10 mm.

[0069] In the R chart 104, pairs of blue (B) solid patches 101 and black (Bk) solid patches 102 are arranged side by side in the width direction, spanning across two recording materials S and in the direction of transport of the recording materials S, for a total of 12 pairs. In the R chart, for each side of the recording material S, two recording materials S are used to form the chart, similar to the S chart 103, thereby ensuring the same number of patches as the L chart 100 and enabling equivalent adjustments. In the R chart 104 in Figure 8, 104(1-1) represents the first sheet of the first face, 104(2-1) represents the first sheet of the second face, 104(1-2) represents the second sheet of the first face, 104(2-2) represents the second sheet of the second face, 104(1-3) represents the third sheet of the first face, 104(2-3) represents the third sheet of the second face, 104(1-4) represents the fourth sheet of the first face, and 104(2-4) represents the fourth sheet of the second face. The second face passes through the secondary transfer section N2 and then through the inside of the sensing unit 3 without changing orientation, but the first face passes through the reversal transport path 7 once. Therefore, the orientation of the first face is different when passing through the secondary transfer section N2 and when passing through the inside of the sensing unit 3. In Figure 8, the transport direction of the chart when passing through the secondary transfer section N2 is shown by a thin arrow, and the transport direction of the chart when passing through the inside of the sensing unit 3 is shown by a thick arrow. In this embodiment, with respect to the patches formed on one surface of the recording material S, the leading patches of the B solid patch 101 and Bk solid patch 102 as they pass through the sensing unit 3 are trigger patches 101T and 102T, respectively, for acquiring position information. These trigger patches 101T and 102T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101 and Bk solid patch 102, the remaining 10 patches each, excluding the trigger patches 101T and 102T, are adjustment patches 101A and 102A for acquiring brightness information (density information). The adjustment patches 101A and 102A are each transferred to the recording material S with different secondary transfer voltages Vtr applied.

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

[0071] Thus, in R Chart 104, the first side of recording material S, which forms a patch on the second side, is left blank without forming a patch. Similarly, the second side of recording material S, which forms a patch on the first side, is also left blank without forming a patch. This is because, with narrow recording material S, there is less margin other than the patch, making it difficult to arrange the patches so that they do not overlap on the front and back of the recording material S, as in L Chart 100 and S Chart 103. If the patches overlap on the front and back of the recording material S, the patch on the first side may affect the detection brightness of the patch on the second side due to bleed-through, and vice versa, potentially making accurate brightness detection impossible. Therefore, to detect brightness more accurately, for recording material S of a size where patches may overlap on the front and back, the patch on the first side and the patch on the second side are transferred to separate recording material S. This effect of bleed-through on detection brightness tends to be particularly noticeable with recording material S with a small basis weight. For example, the effect of this back-facing on the detection brightness is as follows: (Base weight: 150 g / m²) 2 This tendency is particularly pronounced with the following recording material S. Furthermore, the thinner the recording material S, the more pronounced this effect tends to be.

[0072] Furthermore, in this embodiment, the second side of the recording material S, on which a patch is formed on the first side, is left blank without forming a patch, and the recording material S is output after performing the image formation operation for double-sided printing. As a result, by detecting the brightness of the patch after the patch formed on the first side has passed through the fuser 46 twice, the same surface state of the toner image as in actual double-sided printing can be detected, and more appropriate adjustment values ​​can be selected.

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

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

[0075] In this embodiment, the size of the recording material S usable for chart output is set to a length of 210 mm (short side of A4 size) or more in the transport direction and a width of 139.7 mm (short side of STMT size) or more. However, the size of the recording material S usable for chart output is not limited to that of this embodiment and can be set as appropriate according to the maximum paper feed size of the image forming apparatus 1. In addition to standard sizes, it may also be possible to use recording material S of any size, for example, by having the operator input and specify it from the control unit 70 or external device 200.

[0076] Furthermore, in this embodiment, when adjusting only the secondary transfer voltage during single-sided printing (also referred to here as "single-sided adjustment"), the following procedure is followed. When outputting the L chart 100, the chart 100(2) in Figure 6 is formed on the first surface of one recording material S using the single-sided printing image formation operation and output. When outputting the S chart 103, the charts 103(2-1) and 103(2-2) in Figure 7 are formed on the first surface of the first recording material S and the first surface of the second recording material S, respectively, using the single-sided printing image formation operation and output. When outputting the R chart 104, the charts 104(2-3) and 104(2-4) in Figure 8 are formed on the first surface of the first recording material S and the first surface of the second recording material S, respectively, using the single-sided printing image formation operation and output. In other words, when adjusting the secondary transfer voltage of the first and second sides during double-sided printing (also referred to here as "double-sided adjustment"), the chart for the second side is output during the single-sided printing image formation operation without passing through the inversion transport path 7. Furthermore, the chart is read using the second line sensor 92 of the sensing unit 3. This allows single-sided adjustment to be performed without changing the orientation of the read image compared to double-sided adjustment, and because the recording material S does not pass through the inversion transport path 7, downtime (time when the image cannot be output for adjustment, etc.) is minimized. It is also possible to use the adjustment result of the first side during double-sided adjustment to set the secondary transfer voltage during single-sided printing.

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

[0078] Also, for example, assuming that the operator visually checks, information such as the patch number described later is printed in relation to each set of patches in the conveyance direction of the recording material S as identification information indicating the setting of the secondary transfer voltage when transferring each patch to the recording material S. Also, for example, assuming that the operator visually checks, information such as the front side (first side) and the back side (second side) is printed on the corresponding side as identification information indicating whether it is a chart for adjusting the first side or a chart for adjusting the second side.

[0079] 7. Operation in adjustment mode Next, the operation in the adjustment mode in this embodiment will be described. FIG. 9 is a flowchart showing an overview of the procedure in the adjustment mode in this embodiment. Here, the case where the operator causes the image forming apparatus 1 to execute the adjustment mode via the operation unit 70 of the image forming apparatus 1 will be described as an example. The role of the operation unit 70 for causing the image forming apparatus 1 to execute the adjustment mode may be performed by an external device 200 such as a personal computer. Also, the following symbols will be used in the following description.

[0080] N: Adjustment value (=-20 to +20) N0: Current adjustment value (before executing the adjustment mode) N A : Selected adjustment value n: Patch number of the adjustment patch (n = 1 to 10 in ascending order of adjustment value) n0: Patch number corresponding to the current adjustment value (corresponding to the adjustment value N0) n A : Selected patch number (corresponding to the adjustment value N A ) T: Symbol indicating the trigger patch

[0081] First, the control unit 30 (adjustment process unit 31d) acquires information on the recording material S that the operator wants to adjust (size of the recording material S, paper type category) and information on the adjustment conditions, which are input by the operator (S1). Figure 10 is a schematic diagram of the paper type category selection screen 700 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1. The paper type category selection screen 700 displays the paper type categories of the recording material S that can be set in the image forming apparatus 1. By pressing (operating) the adjustment button 701, the operator can proceed to the adjustment mode to adjust the setting voltage of the secondary transfer voltage. Note that the paper type category selection screen 700 may also provide access to screens for changing other image forming conditions, such as fixing conditions, in addition to adjusting the secondary transfer voltage. Furthermore, in order to retain the default settings for each paper type category, the paper type categories may be duplicated to RAM 33 or ROM 32 using the duplicate button 702 before the adjustment mode can be executed. The duplicated paper type category 703 is saved under a different name in RAM33 or ROM32, and for that paper type category 703, image formation will be performed using the default settings, except for conditions where the settings have been changed.

[0082] Figure 11 is a schematic diagram of the paper feed unit selection screen 704 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1. When the paper type category of the recording material S for which the adjustment mode is to be executed is selected, the paper feed unit selection screen 704 shown in Figure 11 is displayed. The paper feed unit selection screen 704 displays the paper type category of the recording material S stored in the paper feed unit 4, which has been set in advance by the operator from the operation unit 70 or the like, and the size detected by the recording material size detection sensor (not shown) provided in each paper feed unit 4. For example, "Plain paper 1_copy (64~75g / m²)" 2 This section describes the case where ")" is selected and the adjustment mode is executed. In the example in Figure 11, multiple paper feeders (paper feeder [1], paper feeder [2], paper feeder [3]) are set to "Plain paper 1_copy (64~75g / m²)". 2The following is stored: ) . Also, when the size of the recording material S is compatible with the adjustment mode, the operator can press (operate) the selection button 705. If the paper type category or the size of the recording material S is not compatible with the adjustment mode, the selection button 705 may be grayed out or otherwise prevented from being pressed (operated) by the operator. In addition, if the recording material S required to execute the adjustment mode is not already stored in any of the paper feed units 4, the operator may be able to exit the paper feed unit selection screen 704 by pressing a back button (not shown) or the like.

[0083] Figure 12 is a schematic diagram of the secondary transfer voltage adjustment screen 706 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1. When the paper type category of the recording material S for which the adjustment mode is to be executed is selected, and the paper feed unit 4 in which the recording material S is stored is selected, the secondary transfer voltage adjustment screen 706 shown in Figure 12 is displayed. The secondary transfer voltage adjustment screen 706 includes an adjustment value display unit 707 that displays the current adjustment value, a single-sided / double-sided selection unit 708 that selects whether the target of the adjustment mode is single-sided or double-sided, and an adjustment execution button 709 that starts the formation of a chart. By inputting a value into the adjustment value display unit 707, it becomes possible to perform secondary transfer with the recording material distribution voltage offset from the default recording material distribution voltage Vp stored in the ROM 32 for the corresponding paper type category. In this embodiment, integer values ​​from -20 to +20 can be input as the adjustment value N in the adjustment value display unit 707, and the default value is 0. If the adjustment value N is 0, the default recording material distribution voltage Vp corresponding to the paper type category recorded in ROM 32 is used as is. The value (adjustment value N) in the adjustment value display unit 707 corresponds to ΔN=1 as ΔV=150V (that is, changing the adjustment value N by 1 changes the adjustment amount ΔV by 150V). For example, if N=-5 is entered in the adjustment value display unit 707, the default recording material distribution voltage Vp is offset by -750V (=-5 × 150) and used as the recording material distribution voltage. When the operator performs the adjustment mode, they select whether to perform double-sided adjustment or single-sided adjustment using the single-sided / double-sided selection unit 708, and then press the adjustment execution button 709 (perform the operation).

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

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

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

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

[0088] In this embodiment, the amplitude of the secondary transfer voltage (change in one step) ΔV (indicated by 801 in Figure 13) when the chart is transferred to the recording material S is switched by the secondary transfer partial voltage Vb. In this embodiment, when the secondary transfer partial voltage Vb is 2000V or higher, the amplitude of the secondary transfer voltage ΔV is set to 450V, which corresponds to the adjustment value amplitude ΔN=3 (three steps of the adjustment value N). When the secondary transfer partial voltage Vb is 1500V or higher and less than 2000V, the amplitude of the secondary transfer voltage ΔV is set to 300V, which corresponds to the adjustment value amplitude ΔN=2 (two steps of the adjustment value N). When the secondary transfer partial voltage Vb is less than 1500V, the amplitude of the secondary transfer voltage ΔV is set to 150V, which corresponds to the adjustment value amplitude ΔN=1 (one step of the adjustment value N). This is because, in order to confirm the current sensitivity of the secondary transfer, it is considered more efficient to increase the range of change in the secondary transfer voltage in one step as the secondary transfer partial voltage Vb increases, thereby widening the range of change in the secondary transfer current across the entire chart. In this embodiment, the amplitude ΔV (swing amplitude ΔN of the adjustment value) of the secondary transfer voltage when the chart is transferred to the recording material S is automatically selected according to the result of ATVC control, but it may also be possible to allow the operator to directly select it on the secondary transfer voltage adjustment screen 706 or the like. Furthermore, it may also be possible to allow the operator to choose whether to "automatically select" or "directly specify" the amplitude ΔV (swing amplitude ΔN of the adjustment value) of the secondary transfer voltage when the chart is transferred to the recording material S.

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

[0090] In the case of L-chart 100, when the chart is secondarily transferred to the recording material S, trigger patches 101T and 102T are located on the trailing edge of the first side of the paper and the leading edge of the second side. Trigger patches 101T and 102T are used for detecting the position of the patches when the sensing unit 3 reads the chart. Therefore, trigger patches 101T and 102T need to be transferred with the minimum density required for this purpose. Extremely high or extremely low secondary transfer voltages pose a risk of preventing the reading of trigger patches 101T and 102T. Therefore, in this embodiment, when secondary transferring trigger patches 101T and 102T to the recording material S, a voltage corresponding to patch number n=5 (the voltage indicated by the dotted line of reference numeral 800 in Figure 13) is applied. Note that the method for setting the secondary transfer voltage applied when secondary transferring trigger patches 101T and 102T to the recording material S is not limited to the method of this embodiment described above. For example, one could set the secondary transfer voltage higher (to a larger absolute value) to minimize weak transfer (transfer failure due to a weak transfer voltage), or control the secondary transfer voltage with a constant current to transfer at the minimum required concentration.

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

[0092] As mentioned above, if the operator selects single-sided adjustment in the single-sided / double-sided selection section 708 of the secondary transfer voltage adjustment screen 706, the following procedures are followed: When outputting the L chart 100, the chart 100(2) in Figure 6 is output. When outputting the S chart 103, the charts 103(2-1) and 103(2-2) in Figure 7 are output. When outputting the R chart, the charts 104(2-3) and 104(2-4) in Figure 8 are output. In other words, the chart for the second side when performing double-sided adjustment is output without passing through the inversion transport path 7 during the single-sided print image formation operation. The chart is read using the second line sensor 92 of the sensing unit 3. This allows single-sided adjustment to be performed with minimal downtime, as the orientation of the read image does not change from that during double-sided adjustment, and the recording material S does not pass through the inversion transport path 7.

[0093] When the chart is output, the control unit 30 (adjustment process unit 31d) reads the chart using the sensing unit 3 and controls it to calculate the brightness and dispersion of each adjustment patch 101A, 102A as follows (S11).

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

[0095] Once the control unit 30 (adjustment process unit 31d) has identified the location of each adjustment patch 101A, 102A, it calculates the average luminance value and variance value and stores them in the RAM 33. In other words, for the nth patch, the average luminance value and variance value calculated by the following formula are stored in the RAM 33.

[0096]

number

[0097] The average luminance value (average luminance value) is a parameter that is close to (i.e., correlates with) density. Furthermore, our inventors' research has shown that the variance value is a parameter that is sensitive to the transferability when the recording material S has irregularities. In this embodiment, the average luminance value and variance value are calculated for both the B solid patch 101 and the Bk solid patch 102. In this embodiment, the recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) for the setting voltage of the secondary transfer voltage is determined using this average luminance value and variance value.

[0098] In this embodiment, the brightness read from the image information read by the sensing unit 3 is B brightness for the B solid patch 101 and G brightness for the Bk solid patch 102. The choice of which of the RGB brightnesses to use is not limited to this, and the average value of the three brightnesses or the grayscale brightness that is not decomposed into RGB may also be used.

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

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

[0101] Figure 17(a) shows an example of the acquisition results for the average luminance value of B beta patch 101, and Figure 17(b) shows an example of the acquisition results for the average luminance value of Bk beta patch 102. Furthermore, Figure 17(c) shows an example of the acquisition results for the average luminance value of B beta patch 101 grouped as described later, and Figure 17(d) shows an example of the acquisition results for the variance value of B beta patch 101.

[0102] First, the control unit 30 (adjustment process unit 31d) searches for the lowest average brightness value among the Bk solid color patches 102. Then, it controls the system to narrow down the patch numbers (i.e., adjustment values) to those that fall within a predetermined threshold γ1 range, from the lowest average brightness value to the higher end of that range (S12). In the case of Figure 17(b), the patch numbers with the lowest average brightness value (minimum brightness) are n=4, 5, and 6, and the narrowed-down patch numbers are n=1, 2, 3, 4, 5, 6, and 7. This allows the system to narrow down the patch numbers (i.e., adjustment values) to those where the Bk solid color has been transferred to a certain extent. The threshold γ1 should be small if the transferability of the Bk solid color is important, and large if the transferability of the B solid color is important.

[0103] Next, the control unit 30 (adjustment process unit 31d) calculates the average brightness value (also called "group brightness") of three B-beta patches 101, including the patch numbers before and after it, for each narrowed-down patch number (i.e., the adjustment value). Then, the control unit 30 (adjustment process unit 31d) selects the group with the lowest calculated group brightness (S13). The group brightness for the nth patch is expressed by the following formula.

[0104]

number

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

[0106] In this case, adjustment using a chart only allows adjustment to patches of a certain density. Therefore, correction may be applied to the group selected here. For example, a threshold γ2 for the lowest group brightness can be set in advance. Then, check if there is a group brightness within the range of threshold γ2 on the side of the lowest group brightness that falls within the range of threshold γ2, on the side of the lowest group brightness that falls within the range of threshold γ2, with a patch number (i.e., adjustment value) smaller than the patch number of the group with the lowest group brightness. If there is, the selected group may be changed to the group with the patch number (i.e., adjustment value) of that group brightness. This correction makes it possible to select a patch number (i.e., adjustment value) of a group that is as close as possible to the onset of secondary color transferability. This can suppress cases where the secondary transfer voltage Vtr is too high for users who mainly output monochrome or halftone images. In this embodiment, the correction (forward adjustment) of the adjustment value using the threshold γ2 as described above is adopted. In the case of Figure 17(c), the group with patch number n=6 (i.e., patches with patch numbers n=5, 6, and 7) is selected.

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

[0108] As mentioned above, adjustments using a chart can only be made to patches of a certain density. Therefore, corrections may be made to the selected patch number (i.e., the adjustment value). If the user primarily outputs monochrome or halftone images, the correction can be made to make the adjustment value as small as possible. In this case, for example, as with group brightness, a threshold γ3 for the smallest variance value is set in advance. Then, among the patch numbers with variance values ​​that fall within the range of threshold γ3 from the smallest variance value to the larger variance value, the smallest patch number (i.e., the adjustment value) may be selected. Conversely, if the emphasis is on reliably transferring secondary color images, the correction can be made to make the adjustment value as large as possible. In this case, for example, as shown in Figure 17(a), a threshold γ4 is set in advance to the higher side of the average brightness value of the selected patch number. Then, for example, the difference between the average brightness value of the selected patch number n=6 and the average brightness value of the previous patch number n=5 is compared with threshold γ4. If this difference in average brightness value is greater than threshold γ4, it can be determined that the transferability of secondary colors is established at patch number n=5. In such cases, fluctuations in the toner's charge level or the moisture content of the recording material S can lead to a risk of insufficient transfer field for secondary colors. In this embodiment, a correction was adopted to ensure reliable transfer of such secondary colors. In the case of Figure 17(a), the difference between the average brightness value of the selected patch number n=6 and the average brightness value of the previous patch number n=5 is greater than the threshold γ4, so patch number n=7, which is one size larger than the selected patch number n=6, is selected.

[0109] Following the above selection flow for adjustment values, the control unit 30 (adjustment process unit 31d) selects the preferred patch number n for transferability. A and the corresponding adjustment value N A This is decided (S15).

[0110] Note that the selection flow for adjustment values ​​in this embodiment is just one example, and the selection flow for adjustment values ​​is not limited to that of this embodiment. For example, group brightness B grThis calculation was performed using three patches, but it may also be performed using four or more patches, or even just two patches. Also, Group Brightness B gr While this method is effective for selecting a stable adjustment range with good transferability, the adjustment value may also be selected directly from the average luminance value and variance value without using this method. In particular, depending on the setting of threshold γ1 and the transferability of the recording material S, it may not be possible to select a group luminance; in such cases, the adjustment value may be selected directly from the average luminance value and variance value without using the group luminance. Furthermore, while the variance value is effective for detecting density unevenness within a patch, it is not always necessary to use it. In addition, the transferability of the Bk solid may be adjusted by methods other than narrowing down by threshold γ1. For example, the patch number (i.e., the adjustment value) in which the average luminance value of the Bk solid patch is the lowest (highest density) and the average luminance value of the B solid patch is the lowest (highest density) may be selected.

[0111] The control unit 30 (adjustment process unit 31d) then selects the adjustment value N as described above. A The adjustment value N is displayed on the display unit 70a of the operation unit 70, on the adjustment value display unit 707 of the secondary transfer voltage adjustment screen 706 as shown in Figure 12 (S16). The operator determines whether the displayed content of the secondary transfer voltage adjustment screen 706 is correct and adjusts the displayed adjustment value N A If you do not want to change it, select the confirmation unit 710 (OK button 710a or Apply button 710b). On the other hand, the operator selects the displayed adjustment value N AIf you wish to change the value, you input it into the adjustment value display unit 707 by operating the numeric keypad (not shown) on the operation unit 70 and select the confirmation unit 710 (OK button 710a or apply button 710b). If the adjustment value has been changed, the control unit 30 (adjustment process unit 31d) stores the adjustment value entered by the operator in the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) (S17). The operator can visually check the output chart to determine whether the display content of the secondary transfer voltage adjustment screen 706 is correct. On the other hand, if the adjustment value has not been changed and the confirmation unit 710 is selected, the control unit 30 (adjustment process unit 31d) stores the determined adjustment value as is in the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) (S17). This completes the adjustment mode.

[0112] 8. Effects Experiments were conducted to confirm the effectiveness of this embodiment in both this embodiment and the comparative example. In the comparative example, under the same conditions as in this embodiment, where R chart 104 is output and double-sided adjustment is performed, a chart in which the front and back patches of the recording material S overlap is output and double-sided adjustment is performed. That is, in the comparative example, 104(1-1) in Figure 8 is output as the first side of the first sheet, and 104(2-3) in Figure 8 is output as the second side of the first sheet, which is its reverse side. Also, 104(1-2) in Figure 8 is output as the first side of the second sheet, and 104(2-4) in Figure 8 is output as the second side of the second sheet, which is its reverse side.

[0113] In the experiment, the image quality of solid black (B) and solid black (Bk) images was investigated after executing the adjustment mode. The recording material S used was a smooth, high-quality paper with a basis weight of 68 g / m². 2 The paper is a type of embossed paper with a non-smooth surface and a basis weight of 87 g / m². 2The experiment was conducted using paper and paper. The results are shown in Table 1. Table 1 shows the adjustment values ​​after running the adjustment mode, and the image quality when printing a solid B image and a solid Bk image on both sides afterward. Image quality was rated as "○ (Good)" if there were no problems, and "× (Poor)" if image defects occurred due to the setting of the secondary transfer voltage. Since similar results were obtained for the first and second sides of the double-sided print, Table 1 shows the result for one side as a representative example.

[0114] [Table 1]

[0115] In this embodiment, when using high-quality paper, there were no abnormalities in image quality. However, in the comparative example, a lower secondary transfer voltage was selected, resulting in transfer defects in the solid B image. In the comparative example, it is thought that in the adjustment mode, the presence of back-pattern bleed-through caused a false detection of a higher density for the solid B patch corresponding to a lower secondary transfer voltage, resulting in an inappropriate adjustment value.

[0116] Furthermore, when using embossed paper, there were no abnormalities in image quality in this embodiment, whereas in the comparative example, a higher adjustment value for the secondary transfer voltage was selected than in this embodiment, resulting in density unevenness (roughness) in the solid black image. In the comparative example, it is thought that in the adjustment mode, the presence of back-facing patch caused a false detection that the density of the solid black patch corresponding to the high secondary transfer voltage was high, resulting in an inappropriate adjustment value. In other words, with embossed paper, in the secondary transfer section N2, the indentation on the paper surface easily creates a gap between the intermediate transfer belt 44b and the paper surface, and when the secondary transfer voltage is high, the discharge in this gap tends to lighten the image density. However, it is thought that the image density is not lightened due to back-facing, leading to a false detection and a higher setting of the secondary transfer voltage. In this embodiment, there is no effect from back-facing, and the adjustment is performed appropriately.

[0117] In this embodiment, all patches were arranged in L chart 100 and S chart 103 so as not to overlap on the front and back of the recording material S, but the present invention is not limited to this embodiment. At a minimum, the patches should be arranged so that the portion used to adjust the secondary transfer voltage of the patch transferred to the first side and the portion used to adjust the secondary transfer voltage of the patch transferred to the second side do not overlap on the front and back of the recording material S. For example, for adjustment patches, the entirety of each patch should not overlap on the front and back of the recording material S, while for trigger patches and images such as identification information such as patch numbers when printed, the entirety or part of them may overlap on the front and back of the recording material S. Also, for adjustment patches, as described above, it is sufficient that at least the portion from which density information is read for adjusting the secondary transfer voltage does not overlap on the front and back of the recording material S.

[0118] Furthermore, as mentioned above, the effect of back-printing on the detection brightness tends to be particularly pronounced with recording material S that has a low basis weight. Therefore, only when the basis weight of the recording material S used to output the R chart 104 is less than or equal to a predetermined basis weight, the adjustment chart for the first side and the adjustment chart for the second side may be formed and output on separate recording materials S, one side at a time. For example, a basis weight of 150 g / m² 2In the case of the recording material S described below, the adjustment chart for the first side and the adjustment chart for the second side can be formed and output on separate recording materials S, one side at a time. In this case, if the basis weight of the recording material S used to output the R chart 104 is greater than the predetermined basis weight, the R chart 104 can be output in the same manner as the comparative example described above. In other words, for recording material S of a size where patches may overlap on the front and back sides, and where the basis weight is less than or equal to the predetermined basis weight, the patches for the first side and the patches for the second side are transferred to separate recording materials S. On the other hand, even for recording material S of a size where patches may overlap on the front and back sides, if the basis weight is greater than the predetermined basis weight, the patches for the first side and the patches for the second side can be transferred to the first and second sides of a single recording material S, respectively. In the case of recording material S that is large enough to arrange patches on both sides without overlapping, regardless of the basis weight, it is preferable from the viewpoint of reducing downtime to transfer the patches on the first and second sides, respectively, arranged in this manner, to the first and second sides of a single sheet of recording material S.

[0119] As described above, in this embodiment, the image forming apparatus 1 includes an image carrier 44b that carries a toner image, a transfer means 45 that transfers the toner image from the image carrier 44b to the recording material S in a transfer unit N2, an application means 76 that applies a transfer voltage to the transfer means 45, a fixing means 46 that fixes the toner image transferred to the recording material S in a fixing unit N3, a double-sided mechanism 14 that transports the recording material S in order to perform double-sided printing in which an image is formed on both sides of the recording material S by transferring the toner image to the first surface of the recording material S in a transfer unit N2 and fixing the toner image to the first surface of the recording material S in a fixing unit N3, then transferring the toner image to the second surface of the recording material S in a transfer unit N2 and fixing the toner image to the second surface of the recording material S in a fixing unit N3, and an execution unit 31d that executes an output mode that outputs a chart formed by transferring multiple test images to the recording material S with different transfer voltages in order to adjust the transfer voltage. Furthermore, when the execution unit 31d executes an output mode to output a chart for adjusting the transfer voltage in double-sided printing, it is possible to execute the following first output mode and second output mode. When the width of the recording material S to which the test image is transferred is a first width, the execution unit 31d executes a first output mode to output charts 100 and 103 formed by transferring a test image for adjusting the transfer voltage of the first side of double-sided printing and a test image for adjusting the transfer voltage of the second side of double-sided printing onto the first and second sides of a single recording material, respectively. Also, when the width of the recording material S to which the test image is transferred is a second width smaller than the first width, the execution unit 31d executes a second output mode to output charts 104 formed by transferring a test image for adjusting the transfer voltage of the first side of double-sided printing and a test image for adjusting the transfer voltage of the second side of double-sided printing onto one side of another recording material S, respectively.

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

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

[0122] [Example 2] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in 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 in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0123] In this embodiment, R chart 104 differs from that in Embodiment 1. However, in this embodiment, L chart 100 and S chart 103 are the same as in Embodiment 1.

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

[0125] As shown in Figure 18, in this embodiment, the first and second sheets have patches formed only on the first surface, and after passing through the secondary transfer section N2, they pass through the inside of the sensing unit 3 without changing orientation. Also, the recording material S that has patches formed on the second surface does not have patches formed on the first surface, but only on the second surface, and after passing through the secondary transfer section N2, it passes through the inside of the sensing unit 3 without changing orientation. In Figure 18, the transport direction of the chart when passing through the secondary transfer section N2 is indicated by a thin arrow, and the transport direction of the chart when passing through the inside of the sensing unit 3 is indicated by a thick arrow.

[0126] In other words, in this embodiment, 104(1-1) and 104(1-2) of the R chart 104 in Figure 18 are formed on the first surface of the recording material S during a single-sided printing image formation operation and output, and are read by the second line sensor 92 of the sensing unit 3 without changing orientation. Also, 104(2-3) and 104(2-4) of the R chart 104 in Figure 18 are formed on the second surface of the recording material S during a double-sided printing image formation operation and output, and are read by the second line sensor 92 of the sensing unit 3 without changing orientation. In this embodiment, the first and second recording materials S on which the adjustment chart for the first surface is formed go to the sensing unit 3 without passing through the inversion transport path 7, thus reducing downtime compared to Embodiment 1.

[0127] Similar to Example 1, in this embodiment, on the surface where the patches are formed, the leading patches of the B solid patch 101 and Bk solid patch 102 as they pass through the sensing unit 3 are trigger patches 101T and 102T, respectively, for detecting position information. The remaining 10 patches each of the B solid patch 101 and Bk solid patch 102, excluding the trigger patches 101T and 102T, are adjustment patches 101A and 102A for acquiring brightness information (density information).

[0128] Thus, in this embodiment as well, similar to Embodiment 1, in the R chart 104, the first surface of the recording material S on which a patch is formed on the second surface is left blank without forming a patch. Also, the second surface of the recording material S on which a patch is formed on the first surface is left blank without forming a patch.

[0129] In this embodiment, when performing single-sided adjustment, the image forming operation for single-sided printing forms and outputs the charts 104(1-1) and 104(1-2) in Figure 18 on the first surface of the first recording material S and the first surface of the second recording material S, respectively. In this case, the charts are output without passing through the inversion transport path 7, and the charts are read using the second line sensor 92 of the sensing unit 3. It is also possible to use the adjustment result of the first surface during double-sided adjustment to set the secondary transfer voltage during single-sided printing.

[0130] Furthermore, in this embodiment, the secondary transfer voltage applied when outputting the chart is the voltage shown in Figure 15(b) for surfaces where patches are formed, and the voltage corresponding to patch number n=5 (the voltage shown by the dotted line labeled 800 in Figure 15) for blank surfaces.

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

[0132] As described above, this embodiment provides the same effects as in Embodiment 1, while also reducing the downtime for the adjustment mode using the R chart 104 compared to Embodiment 1.

[0133] [Example 3] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in 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 in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0134] In this embodiment, L chart 100 and S chart 103 differ from those in Embodiment 1. On the other hand, as will be described later, in this embodiment, R chart 104 is the same as in Embodiment 1 or Embodiment 2.

[0135] Figure 19 is a schematic diagram showing the L-chart 100 in this embodiment. In this embodiment as well, similar to Embodiment 1, the L-chart 100 is a chart for cases where the transport direction length of the recording material S is 420 mm (long side of A3 size) or more, and the width of the recording material S is 279.4 mm (long side of LTR size) or more.

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

[0137] As described above, in the L chart 100 of this embodiment, in addition to the B solid patch 101 and Bk solid patch 102 similar to those in the L chart 100 of Embodiment 1 shown in Figure 6, a Bk halftone patch 106 is also arranged. The configuration of the B solid patch 101 and Bk solid patch 102 in this embodiment is the same as that of the B solid patch 101 and Bk solid patch in Embodiment 1. Now, when the leading edge of the transport direction of the recording material S as it passes through the inside of the sensing unit 3 is facing upwards, the surfaces of the recording material S on the first and second line sensors 91 and 92 are viewed as follows. In other words, in this embodiment, the Bk halftone patch 106 is positioned adjacent to the right side of the B solid patch 102 and adjacent to the edge of the chart (recording material S). Also, in this embodiment, the Bk halftone patch (gray patch) 106 is formed with 50% of the toner amount of the Bk solid patch 102. In this embodiment, the size of the Bk halftone 106 is approximately 15 mm in length and 15 mm in width in the transport direction, and the Bk halftone patches 106 are spaced 15 mm apart in the transport direction of the recording material S.

[0138] Here, if the width of the recording material S is wide, the behavior of the edges in the width direction of the recording material S tends to be unstable, for example, the edges in the width direction of the recording material S may absorb moisture and become wavy. Therefore, if the width of the recording material S is wide, image defects due to discharge are likely to occur at the edges in the width direction of the recording material S during secondary transfer. Such image defects due to discharge are easily detected in halftone images. For this reason, it is desirable to place the Bk halftone patch 106 adjacent to the edges in the width direction of the recording material S. It is preferable to place the Bk halftone patch 106 in a range of about 50 mm inward from the edges in the width direction of the recording material S, and more preferably in a range of about 10 to 30 mm inward from the edges in the width direction of the recording material S. The Bk halftone patch 106 may be continuous to the edges in the width direction of the recording material S, or it may be placed with a margin of about 2.5 mm at the edges in the width direction of the recording material S, as in Example 1. This margin is typically about 2 to 10 mm. Furthermore, the Bk halftone patch 106 can be formed with a toner load of approximately 10-80% of the toner load of the Bk solid patch 102, typically with a toner load of approximately 40-60%. Note that the halftone patch is not limited to black; it may also be a halftone image of other single colors, other secondary colors, or even more complex mixed colors (multi-color).

[0139] Furthermore, on the first side 100(1) and the second side 100(2) of the L chart 100, the B solid patch 101, the Bk solid patch 102, and the Bk halftone patch 106 are arranged so that they do not overlap on the front and back sides of the recording material S. This is to avoid the influence of back-image reflection on the detection brightness when read by the first and second line sensors 91 and 92, as explained in Example 1.

[0140] Figure 20 is a schematic diagram showing the S chart 103 in this embodiment. In this embodiment as well, similar to Embodiment 1, the S chart 103 is a chart for cases where the length of the recording material S in the transport direction is 210 mm (short side of A4 size) or more and less than 420 mm (long side of A3 size), and the width of the recording material S is 160 mm or more.

[0141] In this embodiment, the S chart 103 has a total of 12 sets of blue (B) solid patches 101, black (Bk) solid patches 102, and black (Bk) halftone patches 106 arranged side by side in the width direction, spanning across two recording materials S and in the transport direction of the recording materials S. In the S chart 103 of Figure 20, 103(1-1) shows the first sheet of the first side, 103(1-2) shows the second sheet of the first side, 103(2-1) shows the first sheet of the second side, and 103(2-2) shows the second sheet of the second side. Also in Figure 20, the transport direction of the chart when passing through the secondary transfer section N2 is indicated by a thin arrow, and the transport direction of the chart when passing inside the sensing unit 3 is indicated by a thick arrow. In this embodiment, the leading patches of the B solid patch 101, Bk solid patch 102, and Bk halftone patch 106 as they pass through the sensing unit 3 are trigger patches 101T, 102T, and 106T, respectively, for detecting position information. These trigger patches 101T, 102T, and 106T are used to accurately detect the position of the patch rows when read by the first and second line sensors 91 and 92. Of the B solid patch 101, Bk solid patch 102, and Bk halftone patch 106, the remaining 10 patches each, excluding the trigger patches 101T, 102T, and 106T, are adjustment patches 101A, 102A, and 106A for acquiring brightness information (density information). The adjustment patches 101A, 102A, and 106A are each applied to a different secondary transfer voltage Vtr and transferred to the recording material S.

[0142] As described above, in the S chart 103 of this embodiment, in addition to the B solid patch 101 and Bk solid patch 102 similar to those in the S chart 103 of Embodiment 1 shown in Figure 7, a Bk halftone patch 106 is also arranged. The configuration of the B solid patch 101 and Bk solid patch 102 in this embodiment is the same as that of the B solid patch 101 and Bk solid patch in Embodiment 1. When the leading edge of the transport direction of the recording material S as it passes through the inside of the sensing unit 3 is facing upwards, and the surfaces of the recording material S on the first and second line sensors 91 and 92 are viewed, the following is observed. In other words, in this embodiment, the Bk halftone patch 106 is positioned adjacent to the right side of the B solid patch 102 and adjacent to the edge of the chart (recording material S). Also, in this embodiment, the Bk halftone patch (gray patch) 106 is formed with 50% of the toner amount of the Bk solid patch 102. In this embodiment, the size of the Bk halftone 106 is approximately 15 mm in length and 15 mm in width in the transport direction, and the Bk halftone patches 106 are spaced 15 mm apart in the transport direction of the recording material S. The arrangement and density of the Bk halftone patches 106 can be set in the same way as described for the L chart 100.

[0143] Furthermore, on the first side 103(1-1), 103(1-2) and the second side 103(2-1), 103(2-2) of the S chart 103, the B solid patch 101, Bk solid patch 102, and Bk halftone patch 106 are arranged so that they do not overlap on the front and back sides of the recording material S. This is to avoid the influence of back-image bleed on the detection brightness when read by the first and second line sensors 91 and 92, as explained in Example 1.

[0144] On the other hand, in this embodiment, the R chart 104 is the same as in Embodiment 1 (Figure 8) or Embodiment 2 (Figure 18). That is, the R chart 104 has a solid B patch 101 and a solid Bk patch 102, but no Bk halftone patch 106. Also, in the R chart 104, the first side of the recording material S on which a patch is formed on the second side is left blank without a patch. Similarly, the second side of the recording material S on which a patch is formed on the first side is left blank without a patch. This is because, with a narrow recording material S, it is difficult to arrange three types of patches in the width direction, and it is also difficult to arrange the patches so that they do not overlap on the front and back of the recording material S.

[0145] In other words, as mentioned above, when the width of the recording material S is wide, the behavior of the edges of the recording material S in the width direction tends to be unstable, making it easy for image defects due to discharge to occur at the edges of the recording material S in the width direction during secondary transfer. Since such image defects due to discharge are easily detected in halftone images, Bk halftone patches 106 were placed adjacent to the edges in the width direction in L chart 100 and S chart 103. In contrast, when the width of the recording material S is small, the behavior of the edges of the recording material S in the width direction tends to be stable. Therefore, there is less need to consider image defects due to discharge at the edges of the recording material S in the width direction. On the other hand, density changes due to changes in secondary transfer voltage are easier to detect in solid images than in halftone images. For this reason, in R chart 104, Bk halftone patches 106 were not placed, and B solid patch 101 and Bk solid patch 102 were left.

[0146] In this embodiment, the operation of the adjustment mode is the same as that in Embodiment 1, which was described with reference to Figure 9. However, in this embodiment, when using the L chart 100 and S chart 103, the recommended adjustment amount (more specifically, the corresponding adjustment value) of the secondary transfer voltage is determined based on the readings of the B solid patch 101, Bk solid patch 102, and Bk halftone patch 106 by the sensing unit 3 (S12-S15). In Embodiment 1, as described with reference to Figure 17, the optimal range of the secondary transfer voltage was narrowed using the brightness information (density information) of the Bk solid patch (monochromatic solid patch) 102. Then, the optimal adjustment amount (more specifically, the corresponding adjustment value) of the secondary transfer voltage was determined from the narrowed range using the brightness information (density information) of the B solid (secondary color solid) patch. In this embodiment, similarly, the optimal range of the secondary transfer voltage can be narrowed down using the brightness information (density information) of the Bk solid patch (monochromatic solid patch) 102 and the brightness information (density information) of the Bk halftone patch (halftone patch) 106. For example, the optimal range can be narrowed down for each of the Bk solid patch 102 and the Bk halftone patch 106 in the same manner as in Embodiment 1, and then further narrowed down to the range where both optimal ranges overlap. Then, using the brightness information (density information) of the B solid (secondary color solid) patch, the optimal adjustment amount for the secondary transfer voltage (more specifically, the corresponding adjustment value) can be determined from the narrowed range. This makes it possible to set the optimal secondary transfer voltage while also considering image defects caused by discharge that tend to occur at the edges in the width direction of the recording material S. The process for determining the recommended adjustment amount for the secondary transfer voltage when using the R chart 104 can be the same as in Embodiment 1.

[0147] Thus, in this embodiment, the number of test images in the width direction substantially perpendicular to the transport direction of the recording material S in chart 104, output in the second output mode, is less than the number of test images in the width direction substantially perpendicular to the transport direction of the recording material S in charts 100 and 103, output in the first output mode. In particular, in this embodiment, charts 100 and 103, output in the first output mode, have solid image test images and halftone image test images arranged side by side in the width direction, while chart 104, output in the second output mode, has only the solid image test images among the solid image test images and halftone image test images. Furthermore, in this embodiment, the halftone image test images are arranged adjacent to the end of the recording material S in the width direction.

[0148] As described above, this embodiment provides the same effects as in Embodiment 1, and also makes it possible to set a more appropriate secondary transfer voltage when outputting a chart using a wide recording material S.

[0149] [Example 4] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in 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 in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0150] This embodiment describes modified methods for reading charts output in adjustment mode and selecting adjustment values.

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

[0152] Furthermore, even when an operator visually checks the chart to select a preferred adjustment amount for the secondary transfer voltage, if the double-sided adjustment patches overlap on the front and back of the recording material S, there is a possibility of making an incorrect judgment regarding transferability. Therefore, even in configurations where the image forming apparatus 1 does not have a function to select adjustment values ​​based on the chart reading results, and the operator visually checks the chart to select a preferred adjustment amount for the secondary transfer voltage, the present invention is still effective. In this case as well, when the recording material S is large enough that the patches on the front and back may overlap, the possibility of the operator making an incorrect judgment regarding transferability can be reduced by transferring the first and second patches to separate recording materials S.

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

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

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

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

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

[0158] Furthermore, in the above-described embodiment, the image forming apparatus had a printer unit and a sensing unit, each unitized separately, but the present invention is not limited to this embodiment. With such a configuration, for example, the units can be separated, and the functions of the sensing unit can be provided as an extended function of the image forming apparatus. However, the configuration of the printer unit and the configuration of the sensing unit in the above-described embodiment may be arranged and integrated within a single housing, for example.

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

[0160] 2 Image forming apparatus 3. Sensing Unit 4 Paper feed section 7 Reversal transport path 8 Discharge section 30 Control Unit 70 Operation section 76 Secondary Transfer Power Supply 91 First line sensor 92 Second line sensor 100 Large Chart (L Chart) 101 B Beta Patch 102 Black Beta Patch 103 Small Chart (S Chart) 104 R Chart N2 Secondary Transfer Section

Claims

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

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

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

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

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

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

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

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

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

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

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

Images