Image forming apparatus

Abstract

To provide an image forming apparatus that appropriately adjusts setting voltage for secondary transfer voltage even for a recording material having electric resistance unevenness occurring in a plane, in a configuration in which air is blown to the recording material during feeding of the recording material.SOLUTION: An image forming apparatus 1 has: an image carrier 44b; a transfer member 45b; a detection unit that detects voltage and current when voltage is applied to a transfer unit N2; acquisition units 91, 92 that acquire image density information on a recording material; a control unit 30 that executes an adjustment mode for outputting a chart and setting transfer voltage during image formation; and a feeding unit 4 including a blowing unit 49 that blows air to a leading end of the recording material S. The control unit sets the transfer voltage during image formation on the basis of a detection result from the detection unit when images for density acquisition on the recording material S on which the chart is formed passes through the transfer unit N2, a detection result from the detection unit when an area of the recording material S closer to the leading end than an area to which the images for density acquisition are transferred passes through the transfer unit N2, and information on the density of the plurality of images for density acquisition.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a copying machine, a printer, or a facsimile machine, that uses an electrophotographic or electrostatic recording method. [Background technology]

[0002] In an image forming apparatus using an electrophotographic method or the like, a toner image formed on an image carrier such as a photoreceptor or an 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 that contacts the image carrier to form a transfer section. The transfer voltage can be determined based on a transfer portion voltage corresponding to the electric resistance of the transfer section detected during a pre-rotation process before image formation, and a recording material distribution voltage corresponding to a preset type of recording material. This makes it possible to set an appropriate transfer voltage according to environmental fluctuations, the use history of the transfer member, the type of recording material, and the like.

[0003] However, since the types and conditions of recording materials used in image formation are various, the transfer voltage may be excessive or insufficient with the preset default recording material distribution voltage. Therefore, it has been proposed to provide an adjustment mode that adjusts the set voltage of the transfer voltage according to the recording material actually used in image formation.

[0004] Patent Document 1 proposes an image forming apparatus capable of executing an adjustment mode for adjusting the set voltage of the secondary transfer voltage. In this adjustment mode, a chart is output by transferring a plurality of patches (test images) onto one sheet of recording material while switching the secondary transfer voltage for each patch. Then, the density of each patch is detected, and the optimal secondary transfer voltage condition is selected according to the detection result.

[0005] Here, as a configuration of a feeding section that feeds (feeds) a recording material toward a transfer section, a configuration in which air is blown onto the recording material to separate and feed the recording material is known (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-37185 A [Patent Document 2] JP 2013-107738 A Summary of the Invention [Problem to be solved by the invention]

[0007] The above-described adjustment mode makes it possible to easily adjust the set voltage of the secondary transfer voltage in accordance with the type and condition of the recording material.

[0008] However, when there is unevenness in the electrical resistance within the surface of the recording material, it may be difficult to appropriately adjust the set voltage of the secondary transfer voltage using the conventional method.

[0009] In particular, in image forming apparatuses that use an "air feeding" method in which air is blown onto a stack of recording materials to separate them before feeding them to a transfer section, uneven electrical resistance within the surface of the recording material is likely to become large. This is because the moisture content of the recording material at the points where the air is blown decreases, causing a local increase in the electrical resistance of the recording material.

[0010] Even if the adjustment mode is performed on such a recording material using a conventional method, there are cases in which the set voltage of the secondary transfer voltage cannot be appropriately adjusted so as to apply a sufficient transfer voltage to the area where the air is blown.

[0011] Therefore, an object of the present invention is to make it possible to appropriately adjust the set voltage of the secondary transfer voltage even for recording materials that have uneven electrical resistance within the surface, in a configuration in which air is blown onto the recording material when the recording material is fed. [Means for solving the problem]

[0012] The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus including an image carrier that carries a toner image, a transfer member forming a transfer section that transfers the toner image from the image carrier to a recording material, an application section that applies a transfer voltage to the transfer section for transferring the toner image from the image carrier to the recording material, a detection section that detects the voltage and current when a voltage is applied to the transfer section, an acquisition section that acquires information on the density of an image on the recording material, a control section that is controllable to apply a plurality of test voltages to the transfer section, form and output a chart in which a plurality of density acquisition images made of toner images are respectively transferred to the recording material, acquire information on the density of the plurality of density acquisition images of the chart by the acquisition section, and execute an adjustment mode to set the transfer voltage during image formation, and a feeding section that feeds the recording material toward the transfer section, and the feeding section detects the density of the plurality of density acquisition images of the chart, and the control section detects the density of the plurality of density acquisition images of the chart, and executes an adjustment mode to set the transfer voltage during image formation, and a control section that is controllable to execute an adjustment mode ... and a feeding section equipped with a blowing section which blows air onto a leading edge of the recording material in the transport direction of the recording material as it is sent out from the feeding section, and the control section sets the transfer voltage during image formation based on a detection result of the detection section when an area on the recording material on which the chart is formed, onto which at least one of the multiple density acquisition images is transferred, passes through the transfer section, a detection result of the detection section when a predetermined area within the image formation area of ​​the recording material on which the chart is formed, which is on the leading edge side of the area on which the multiple density acquisition images are transferred, passes through the transfer section, and information regarding the densities of the multiple density acquisition images acquired by the acquisition section.

[0013] According to another aspect of the present invention, a recording medium recording apparatus includes an image carrier that carries a toner image, a transfer member that forms a transfer section that transfers the toner image from the image carrier to a recording material, an application section that applies a transfer voltage to the transfer section for transferring the toner image from the image carrier to the recording material, a detection section that detects a voltage and a current when a voltage is applied to the transfer section, an acquisition section that acquires information regarding the density of an image on the recording material, and a control section that is controllable to execute an adjustment mode in which a plurality of test voltages are applied to the transfer section, and a chart is formed and output in which a plurality of density acquisition images made of toner images are respectively transferred to the recording material, and information regarding the densities of the plurality of density acquisition images of the chart is acquired by the acquisition section and the transfer voltage during image formation is set, and a feeding section that feeds the recording material toward the transfer section, the feeding section having a blowing section that blows air from a blowing port onto the recording material when the recording material is sent out from the feeding section, The control unit acquires a first current detected by the detection unit when a predetermined voltage is applied to the transfer unit when a first region of the recording material on which the chart is formed, to which the density acquisition image is transferred, passes through the transfer unit, a voltage-current characteristic based on a detection result from the detection unit when at least one second region of the recording material on which the chart is formed, to which the density acquisition image is transferred and which is farther from the blowing port than the first region when the recording material is sent out from the feed unit, passes through the transfer unit, and a second current calculated based on the voltage-current characteristic and the predetermined voltage, and when the first current is smaller than the second current by a predetermined value or more, sets the transfer voltage during image formation based on a difference between the second current and the first current and information on the densities of the multiple density acquisition images acquired by the acquisition unit. Effect of the Invention

[0014] According to the present invention, in a configuration in which air is blown onto a recording material when the recording material is fed, it is possible to appropriately adjust the set voltage of the secondary transfer voltage even for a recording material on which unevenness in electrical resistance occurs within the surface. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus; [Diagram 3] FIG. 11 is a flowchart illustrating an outline of a procedure for controlling a secondary transfer voltage. [Figure 4] 6 is a graph showing an example of a voltage-current characteristic obtained by secondary transfer voltage control; [Diagram 5] 11 is a table showing an example of a recording material shared voltage table. [Figure 6] FIG. 13 is a schematic diagram of an L chart output in the adjustment mode. [Figure 7] FIG. 13 is a schematic diagram of an S chart output in the adjustment mode. [Figure 8] FIG. 11 is a flow chart showing an outline of a procedure of an adjustment mode. [Figure 9] FIG. 13 is a schematic diagram of a paper type category selection screen. [Figure 10] FIG. 13 is a schematic diagram of a paper feed unit selection screen. [Figure 11] FIG. 13 is a schematic diagram of a secondary transfer voltage adjustment screen. [Figure 12] 6 is a graph showing a transition of a secondary transfer voltage when a chart is output. FIG. [Figure 13(a)] 11 is a table showing an example of a relationship between patch numbers of a chart and adjustment values. [Figure 13(b)] 11 is a table showing an example of a relationship between patch numbers of a chart and adjustment values. [Figure 13(c)] 11 is a table showing an example of a relationship between patch numbers of a chart and adjustment values. [Figure 14] 6 is a graph showing a transition of a secondary transfer voltage when a chart is output. FIG. [Figure 15] FIG. 11 is a graph showing an example of voltage-current characteristics acquired when a chart is output. [Figure 16] 5A and 5B are schematic diagrams for explaining a method for detecting the position of a trigger patch. [Figure 17] FIG. 11 is a graph illustrating a method for selecting a recommended adjustment value. [Figure 18] FIG. 11 is a graph illustrating a method for correcting an adjustment value. [Figure 19] 3A and 3B are schematic cross-sectional views for explaining an air blowing section and schematic views of a recording material. [Figure 20] 13 is a graph showing another example of the transition of the secondary transfer voltage when the chart is output. FIG. [Figure 21] FIG. 11 is a graph showing another example of voltage-current characteristics acquired when the chart is output. [Figure 22] 13 is a graph showing another example of the transition of the secondary transfer voltage when the chart is output. FIG. [Diagram 23] FIG. 10 is a graph illustrating another example of a method for correcting an adjustment value. [Figure 24] 10A and 10B are schematic diagrams of a recording material for explaining another example of the air blowing section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0017] [Example 1] 1. Configuration of image forming device 1 is a schematic cross-sectional view of an image forming apparatus (image forming system) 1 of this embodiment. In this embodiment, the image forming apparatus 1 is configured by combining a printer unit 2 that forms an image and a sensing unit 3 that reads a chart to adjust a secondary transfer voltage. In this embodiment, the printer unit 2 is configured as a tandem-type full-color printer that employs an intermediate transfer method and is capable of forming a full-color image on a recording material S using an electrophotographic method. Note that the recording material S is sometimes referred to as "paper," but as will be described later, the recording material S is not limited to paper.

[0018] The printer unit 2 includes a paper feed section (feed section) 4, an image forming section 5, a control section 30, a transfer section 6 to the sensing unit 3, an operation section 70, an image reading section 80, and the like. In FIG. 1, only one paper feed section 4 is shown, but the printer unit 2 may be provided with a plurality of paper feed sections 4. In addition, a temperature sensor 71 (FIG. 2) capable of detecting the temperature (internal temperature) inside the device body 10 and a humidity sensor 72 (FIG. 2) capable of detecting the humidity (internal humidity) inside the device body 10 are provided inside the device body 10 of the image forming device 1 (printer unit 2). The temperature sensor 71 and the humidity sensor 72 are examples of environment detection means for detecting environmental information, which is at least one of the temperature and humidity inside or outside the image forming device 1. The printer unit 2 can form a four-color full-color image on a recording material (sheet, transfer material) S based on image information (image signal) from the image reading section 80 or an external device 200 (FIG. 2). Examples of the external device 200 include a host device such as a personal computer, a digital camera, a smartphone, etc. The recording material S is a material on which a toner image is formed, and specific examples thereof include paper such as plain paper and thick paper, as well as a synthetic resin sheet (synthetic paper) that is a substitute for paper, and a sheet for an overhead projector.

[0019] The paper feed section 4 has a cassette 43 as a recording material storage section, a paper feed member (feeding member) 48 such as a paper feed roller and a paper feed belt, and an air blowing section (air handling device) 49 as a recording material handling means. The paper feed section 4 blows air to the recording materials S stored in a stacked state in the cassette 43 using the air blowing section 49 to sort them, and sends out the topmost recording material S using the paper feed member 48 to feed it toward the secondary transfer section N2 described later. If the stacked recording materials S are attracted to each other, there is a possibility that they will be fed in multiples. Therefore, the air blowing section 49 blows air near the leading edge of the recording materials S in the conveying direction when they are sent out from the paper feed section 4 to sort them before feeding them. In this way, the paper feed section 4 blows air to sort the stack of recording materials S, making it easier to feed the recording materials S one by one.

[0020] The image forming section 5 is capable of forming an image based on image information on a recording material S that is fed from the paper feed section 4 and moves in a conveying path (conveying route) P. The image forming section 5 has a plurality of image forming units, namely, first, second, third and fourth image forming units 50y, 50m, 50c and 50k that form images of yellow (Y), magenta (M), cyan (C) and black (Bk), respectively. The image forming section 5 also has an intermediate transfer unit 44, a secondary transfer device 45, a fixing device 46 and the like. Elements having the same or corresponding functions or configurations in each of the image forming units 50y, 50m, 50c and 50k may be generally described by omitting the suffixes y, m, c and k of the reference characters indicating that the elements are for any one of the colors Y, M, C and Bk.

[0021] The image forming unit 50 has a photosensitive drum 51 which is a rotatable drum-type (cylindrical) photosensitive body (electrophotographic photosensitive body) 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 an intermediate transfer unit 44 described later). The image forming unit 50 also has a pre-exposure device 54 as a charge removing means. The image forming unit 50 also has a drum cleaning device 55 as a photosensitive body 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 an intermediate transfer belt 44b described later.

[0022] The photosensitive drum 51 is movable (rotatable) while carrying an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 51 is a negatively charged organic photoconductor (OPC) having an outer diameter of 30 mm. The photosensitive drum 51 has an aluminum cylinder as a base and a surface layer formed on the surface of the aluminum cylinder. In this embodiment, the surface layer has three layers, an undercoat layer, a photocharge generation layer, and a charge transport layer, which are applied and laminated on the base in the following order. When an image forming operation is started, the photosensitive drum 51 is rotated in the direction of the arrow R1 in FIG. 1 (counterclockwise direction) at a predetermined peripheral speed (process speed) by a motor (not shown) as a driving means.

[0023] The surface of the rotating photosensitive drum 51 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the charging roller 52. In this embodiment, the charging roller 52 is a rubber roller arranged in contact with the surface of the photosensitive drum 51. The charging roller 52 rotates in accordance with the rotation of the photosensitive drum 51. A charging power source 73 (FIG. 2) serving as a charging voltage application means (charging voltage application section) is connected to the charging roller 52. The charging power source 73 applies a predetermined charging voltage (charging bias) to the charging roller 52 during the charging process.

[0024] The charged surface of the photosensitive drum 51 is scanned and exposed by the exposure device 42 based on image information, and an electrostatic image is formed on the photosensitive drum 51. In this embodiment, the exposure device 42 is a laser scanner. The exposure device 42 emits laser light in accordance with image information of separated colors output from the control unit 30, and scans and exposes the surface (outer peripheral surface) of the photosensitive drum 51.

[0025] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by supplying toner by the developing device 20, and a toner image (toner image, developer image) is formed on the photosensitive drum 51. In this embodiment, the developing device 20 contains a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. Toner is supplied to the developing device 20 from a toner bottle 41. The developing device 20 has a developing sleeve 24 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). Inside the developing sleeve 24, a magnet roller, which is a roller-shaped magnet, is fixed and arranged so as not to rotate relative to the main body (developing container) of the developing device 20. The developing sleeve 24 carries the developer and transports it to a developing area facing the photosensitive drum 51. A developing power source 74 (FIG. 2) as a developing voltage application means (developing voltage application unit) is connected to the developing sleeve 24. During the development process, the development power supply 74 applies a predetermined development voltage (development bias) to the development sleeve 24. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 51 (negative polarity in this embodiment) adheres to the exposed portion (image portion) on the photosensitive drum 51, which has been uniformly charged and then exposed to light, thereby decreasing the absolute value of the potential (reverse development method). In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative polarity.

[0026] An intermediate transfer belt 44b, which is an intermediate transfer body formed of an endless belt as a second image carrier, is disposed so as to face the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer belt 44b is wound around a driving roller 44a, a tension roller 44d, and a secondary transfer inner roller 45a as a plurality of tension rollers (support rollers) and stretched with a predetermined tension. The intermediate transfer belt 44b is movable (rotatable) while carrying a toner image. The driving roller 44a is driven to rotate by a motor (not shown) as a driving means, and rotates (moves in a circular motion) the intermediate transfer belt 44b. The tension roller 44d controls the tension of the intermediate transfer belt 44b to a constant level. A force is applied to the tension roller 44d by a spring (not shown) as a biasing means, so as to push the intermediate transfer belt 44b from the inner peripheral surface side toward the outer peripheral surface side. Due to this force, the intermediate transfer belt 44b is applied with a tension of about 2 to 5 kgf in the circumferential direction (surface moving direction, process proceeding direction). The secondary transfer inner roller 45a also constitutes the secondary transfer device 45, as described later. The intermediate transfer belt 44b rotates (moves around) in the direction of arrow R2 in FIG. 1 (clockwise direction) at a predetermined circumferential speed (process speed) corresponding to the circumferential speed of the photosensitive drum 51 by the driving force transmitted by the driving roller 44a. On the inner peripheral 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 arranged at a position facing the photosensitive drum 1 via the intermediate transfer belt 44b, and sandwiches the intermediate transfer belt 44b between the photosensitive drum 51 and the primary transfer roller 47. As a result, the primary transfer roller 47 comes into contact with the photosensitive drum 51 via the intermediate transfer belt 44b, forming a primary transfer portion (primary transfer nip portion) N1 where the photosensitive drum 51 and the intermediate transfer belt 44b come into contact with each other. The tension rollers other than the drive roller 44a and the primary transfer rollers 47y, 47m, 47c, and 47k are rotated in accordance with the rotation of the intermediate transfer belt 44b. In addition, a belt cleaning device 60 is disposed as an intermediate transfer body cleaning means on the outer circumferential surface side of the intermediate transfer belt 44b at a position facing the drive roller 44a via the intermediate transfer belt 44b.The intermediate transfer belt 44, the tension rollers 44a, 44d, and 45a, the primary transfer rollers 47y, 47m, 47c, and 47k, the belt cleaning device 60, and the like constitute an intermediate transfer unit 44.

[0027] The toner image formed on the photosensitive drum 51 is primarily transferred onto the rotating intermediate transfer belt 44b by the action of the primary transfer roller 47 in the primary transfer section N1. A primary transfer power supply 75 (FIG. 2) is connected to the primary transfer roller 47 as a primary transfer voltage application means (primary transfer voltage application section). The primary transfer power supply 75 applies a predetermined primary transfer voltage (primary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, to the primary transfer roller 47 during the primary transfer process. A voltage detection sensor 75a as a voltage detection means (voltage detection section) that detects the output voltage, and a current detection sensor 75b as a current detection means (current detection section) that detects the output current are connected to the primary transfer power supply 75 (FIG. 2). In this embodiment, the primary transfer power sources 75y, 75m, 75c, and 75k are provided for the primary transfer rollers 47y, 47m, 47c, and 47k, respectively, and the primary transfer voltages applied to the primary transfer rollers 47y, 47m, 47c, and 47k can be individually controlled. In this embodiment, a positive primary transfer voltage is applied to the primary transfer roller 47, so that a negative toner image on the photosensitive drum 51 is primarily transferred onto the intermediate transfer belt 44b. For example, when a full-color image is formed, the toner images of Y, M, C, and Bk formed on the photosensitive drums 51y, 51m, 51c, and 51k are multiple-transferred so as to be sequentially superimposed on the intermediate transfer belt 44b.

[0028] On the outer peripheral surface side of the intermediate transfer belt 44b, a secondary transfer outer roller 45b, which is a roller-type secondary transfer member, is disposed at a position facing the secondary transfer inner roller 45a 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 a secondary transfer device 45 as a secondary transfer means. The secondary transfer outer roller 45b abuts against the secondary transfer inner roller 45a via the intermediate transfer belt 44b, forming a secondary transfer portion (secondary transfer nip portion) N2 where the intermediate transfer belt 44b and the secondary transfer outer roller 45b are in contact with each other. The toner image formed on the intermediate transfer belt 44b is secondarily transferred by the action of the secondary transfer device 45 at the secondary transfer portion N2 onto the recording material S that is sandwiched between the intermediate transfer belt 44b and the secondary transfer outer roller 45b and transported (passing through the secondary transfer portion N2). In this embodiment, a positive secondary transfer voltage is applied to the outer secondary transfer roller 45b, whereby a negative toner image on the intermediate transfer belt 44b is secondarily transferred onto the recording material S. The recording material S is fed from the paper feed unit 4 in parallel with the above-mentioned toner image forming operation, and is conveyed to the secondary transfer unit N2 by the registration roller 11 as a conveying member provided on the conveying path P in synchronization with the toner image on the intermediate transfer belt 44b.

[0029] Thus, the secondary transfer device 45 is configured to have the inner secondary transfer roller 45a as an opposing member and the outer secondary transfer roller 45b as a secondary transfer member. A secondary transfer power source 76 (FIG. 2) as a secondary transfer voltage application means (secondary transfer voltage application section) is connected to the outer secondary transfer roller 45b. The secondary transfer power source 76 applies a predetermined secondary transfer voltage, which is a DC voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), to the outer secondary transfer roller 45b during the secondary transfer process. A voltage detection sensor 76a as a voltage detection means (voltage detection section) that detects the output voltage and a current detection sensor 76b as a current detection means (current detection section) that detects the output current are connected to the secondary transfer power source 76 (FIG. 2). In this embodiment, the core metal of the inner secondary transfer roller 45a is connected to a ground potential. Then, when the recording material S is supplied to the secondary transfer section N2, a constant voltage controlled secondary transfer voltage of a polarity opposite to the normal charging polarity of the toner is applied to the outer secondary transfer roller 45b. In this embodiment, for example, a secondary transfer voltage of 1 to 6.5 kV is applied, and a current of about 15 to 100 μA is passed, so that the toner image on the intermediate transfer belt 44b is secondarily transferred onto the recording material S. In this embodiment, the secondary transfer inner roller 45a is connected to a ground potential, and a voltage is applied to the secondary transfer outer roller 45b from the secondary transfer power source 76. Alternatively, a voltage may be applied from the secondary transfer power source 76 to the secondary transfer inner roller 45a as the secondary transfer member, and the secondary transfer outer roller 45b as the opposing member may be connected to a ground potential. In this case, a DC voltage of the same polarity as the normal charging polarity of the toner is applied to the secondary transfer inner roller 45a.

[0030] The recording material S onto which the toner image has been transferred is conveyed to a fixing device 46 as a fixing means. The fixing device 46 has a fixing roller 46a and a pressure roller 46b. The fixing roller 46a incorporates a heater as a heating means. The pressure roller 46b is pressed against the fixing roller 46a to form a fixing section (fixing nip section) N3 where the fixing roller 46a and the pressure roller 46b come into contact with each other. The recording material S carrying the unfixed toner image is heated and pressurized by being sandwiched between the fixing roller 46a and the pressure roller 46b in the fixing section N3 and conveyed. As a result, the toner image is fixed (melted and fixed) onto the recording material S. The temperature (fixing temperature) of the fixing roller 46a is detected by a fixing temperature sensor 77 (FIG. 2) and controlled by the control unit 30.

[0031] In the case of single-sided printing, in which an image is formed on one side of the recording material S, the recording material S on which the toner image is fixed on one side as described above is delivered as is from the delivery section 6 to the sensing unit 3. On the other hand, in the case of double-sided printing, in which an image is formed on both sides of the recording material S, the recording material S on which the toner image is fixed on the first side as described above is conveyed to the reverse conveying path 7 by the reverse conveying roller 12 as a reverse conveying member. By being switched back in the reverse conveying path 7, the recording material S on which the toner image is fixed on the first side is reversed in the conveying direction and turned over, and is supplied again to the secondary transfer section N2 by the double-sided conveying roller 13 as a double-sided conveying member. The recording material S supplied again to the secondary transfer section N2 in this way has a toner image transferred and fixed on the second side, and is then delivered from the delivery section 6 to the sensing unit 3. In this way, the printer unit 2 of this embodiment is capable of performing double-sided printing (automatic double-sided printing, double-sided printing) in which an image is formed on both sides of one recording material S. A double-sided mechanism 14 is configured by the reversing conveying path 7, the reversing conveying rollers 12, the double-sided conveying rollers 13, etc. The recording material S on which an image has been formed passes through the inside of the sensing unit 3 and is discharged (output) to a discharge section 8 provided outside the sensing unit 3 (image forming apparatus 1). When a chart formed by transferring a patch to the recording material S is output in an adjustment mode described later, the patch on the chart is read as the recording material S passes through the inside of the sensing unit 3, and then the recording material S is discharged to the discharge section 8.

[0032] The surface of the photosensitive drum 51 after the primary transfer is neutralized by the pre-exposure device 54. In addition, toner (primary transfer residual toner) remaining on the photosensitive drum 51 without being transferred to the intermediate transfer belt 44b during the primary transfer process is removed from the surface of the photosensitive drum 51 and collected 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 is abutted against the photosensitive drum 51 with a predetermined pressing force. The cleaning blade is abutted against the surface of the photosensitive drum 51 in a counter direction to the rotation direction of the photosensitive drum 51 so that the tip of the free end side faces the upstream side in the rotation direction of the photosensitive drum 51. In addition, toner (secondary transfer residual toner) remaining on the intermediate transfer belt 44b without being transferred to the recording material S during the secondary transfer process and adhesions such as paper powder are removed from the surface of the intermediate transfer belt 44b and collected by the belt cleaning device 60. In this embodiment, the belt cleaning device 60 is configured to have a cleaning blade like the drum cleaning device 55. The toner and other collected materials collected by the drum cleaning device 55 and the belt cleaning device 60 are transported to a collection container (not shown) and accumulated therein.

[0033] The printer unit 2 can also form a monochrome or multi-color image, such as a black monochrome image, using the image forming units 50 for a desired single color or for some of the four colors.

[0034] In this embodiment, the primary transfer roller 47 has an elastic layer of ion conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the primary transfer roller 47 is, for example, 15 to 20 mm. The primary transfer roller 47 has an electrical resistance of 1×10 5 ~1×10 8 A roller of Ω (N / N (23° C., 50% RH) measurement, 2 kV applied) can be suitably used.

[0035] In this embodiment, the intermediate transfer belt 44b is an endless belt having a two-layer structure of a base layer and a surface layer from the inner peripheral surface side. As a material for constituting the base layer, a resin such as polyimide or polycarbonate, or various rubbers containing an appropriate amount of carbon black as an antistatic agent can be suitably used. The thickness of the base layer is, for example, 0.05 to 0.15 mm. As a material for constituting the surface layer, a resin such as fluororesin can be suitably used. The surface layer reduces the adhesion of the toner to the surface of the intermediate transfer belt 44b, making it easier to transfer the toner to the recording material S at the secondary transfer portion N2. The thickness of the surface layer is, for example, 0.0002 to 0.020 mm. As a material for the surface layer, for example, 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 can be used as the base material. A surface layer can be formed by dispersing one or more types of powder or particles of fluororesin or the like, or particles of different particle sizes, as a material that reduces surface energy and enhances lubricity, on the base material. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5×10 8 ~1×10 14 The static friction coefficient is 0.15 to 0.6 (23°C, 50% RH, HEIDON type 94i). Although the intermediate transfer belt 44b has a two-layer structure in this embodiment, it may have a single layer structure made of a material equivalent to the above-mentioned base layer.

[0036] In this embodiment, the secondary transfer outer roller 45b has an elastic layer of ion conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the secondary transfer outer roller 45b is, for example, 20 to 25 mm. The secondary transfer outer roller 45b has an electrical resistance of 1×10 5 ~1×10 8 A roller of Ω (N / N (23° C., 50% RH) measurement, 2 kV applied) can be suitably used.

[0037] In each image forming unit 50, the photosensitive drum 51 and at least one of the charging roller 52, the developing device 20, and the drum cleaning device 55 acting on the photosensitive drum 51 as a process means may be integrated into a process cartridge. This unit may be detachable from the apparatus main body 10.

[0038] In addition, an automatic document feeder 81 and an image reading unit 80 are arranged on the upper part of the device main body 10. The automatic document feeder 81 as a document feeder automatically feeds a sheet such as a recording material S on which an image (text or image) of an original is formed to a reading position of the image reading unit 80 (which may be configured as at least a part of a platen glass 82 described later). The image reading unit 80 as a reading unit can read an image on a sheet conveyed to the reading position by the automatic document feeder 81. The image reading unit 80 can also read an image on a sheet such as a recording material S on which an image (text or image) of an original is formed, which is arranged on the platen glass 82. The image reading unit 80 is configured to illuminate the sheet with a light source (not shown) and read the image on the sheet at a predetermined dot density by an image reading element (not shown). In other words, the image reading unit 80 optically reads the image on the sheet and converts it into an electrical signal.

[0039] 2. Control mode FIG. 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus 1 of this embodiment. As shown in FIG. 2, the control unit 30 is configured by a computer. The control unit 30 has, for example, a CPU 31, a ROM 32 (including a rewritable one) that stores programs for controlling each unit, a RAM 33 that temporarily stores data, and an input / output circuit (I / F) 34 that inputs and outputs signals to and from the outside. The CPU 31 is a microprocessor that controls the entire control of the image forming apparatus 1, and is the main body of the system controller. The CPU 31 is connected to the paper feed unit 4, the image forming unit 5, the delivery 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 an image formation control sequence for forming an image on the recording material S. For example, a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, and a secondary transfer power supply 76 are connected to the control unit 30, and each of these is controlled by a signal from the control unit 30. Also connected to the control unit 30 are a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of a primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of a secondary transfer power supply 76, and a fixing temperature sensor 77. Signals (information) indicating the detection results of each sensor are input to the control unit 30.

[0040] The operation unit 70 has operation buttons (such as a numeric keypad) as input means, and a display unit 70a consisting of a liquid crystal panel as display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as input means. An operator such as a user or a service person can input an instruction to the control unit 30 to execute a job (described later) by operating the operation unit 70. The control unit 30 can receive a signal from the operation unit 70 and control various devices of the image forming apparatus 1 to operate and execute a job. The image forming apparatus 1 can also execute a job based on an image formation signal (image data, control command) from an external device 200 such as a personal computer.

[0041] In this embodiment, the control unit 30 has an image formation pre-preparation processor 31a, an ATVC control processor 31b, an image formation processor 31c, and an adjustment processor 31d. The control unit 30 also has a primary transfer voltage storage / calculation unit 31e and a secondary transfer voltage storage / calculation unit 31f. These processing units and storage / calculation units may be provided as part of the CPU 31 or the RAM 33. For example, the control unit 30 (more specifically, the image formation processor 31c) can be controlled to execute a job as described above. The control unit 30 (more specifically, the ATVC control processor 31b) can be controlled to execute ATVC control (setting mode) of the primary transfer unit N1 and the secondary transfer unit N2. The ATVC control will be described in detail later. The control unit 30 (more specifically, the adjustment processor 31d) can be controlled to execute an adjustment mode that adjusts the setting voltage of the secondary transfer voltage. The adjustment mode will be described in detail later.

[0042] Here, the image forming apparatus 1 executes a job (image output operation, print job) which is a series of operations for forming and outputting an image on one or more recording materials S, which is started by one start instruction. The job generally includes an image forming process, a pre-rotation process, a paper-interval process in the case of forming images on multiple recording materials S, and a post-rotation process. The image forming process is a period during which electrostatic image formation, toner image formation, primary transfer of the toner image, secondary transfer, and fixing of the image to be actually formed on the recording material S are performed, and 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 the processes of electrostatic image formation, toner image formation, primary transfer of the toner image, secondary transfer, and fixing is performed. The pre-rotation process is a period during which a preparatory operation is performed before the image forming process, from when a start instruction is input until the image actually starts to be formed. The paper-interval process (image-interval process) is a period corresponding to the period between recording materials S when image formation is performed continuously on multiple recording materials S (continuous image formation). The post-rotation process is a period in which a tidying operation (preparatory operation) is performed after the image forming process. The non-image forming time (non-image forming period) is a period other than the image forming time, and includes the above-mentioned pre-rotation process, the sheet interval process, the post-rotation process, and further the pre-multiple rotation process which is a preparatory operation when the image forming apparatus 1 is turned on or when it returns from a sleep state.

[0043] 3. Sensing unit configuration Next, a configuration of the sensing unit 3 having a function of reading a chart output in an adjustment mode for adjusting a set voltage of the secondary transfer voltage will be described.

[0044] As shown in FIG. 1, a conveying path P through which the recording material S passes is provided inside the sensing unit 3, and a first line sensor 91 and a second line sensor 92 are provided so as to sandwich the conveying path P from the front and back. The first line sensor 91 is disposed upstream of the second line sensor 92 in the conveying direction of the recording material S and faces the conveying path P from the bottom in FIG. 1. The second line sensor 92 is disposed downstream of the first line sensor 91 in the conveying direction of the recording material S and faces the conveying path P from the top in FIG. 1. In this embodiment, when adjusting the secondary transfer voltage during double-sided printing in the adjustment mode, the recording material S on which the chart is formed passes through the conveying path P inside the sensing unit 3 so that the upper side in FIG. 1 is the second side and the lower side in FIG. 1 is the first side. In other words, the first line sensor 91 faces the first side of the recording material S, and the second line sensor 92 faces the second side of the recording material S, so that it is possible to read the chart images (patches) formed on both sides of the recording material S in one pass of the recording material S.

[0045] In addition, a first pressure roller 93 is disposed at a position facing the first line sensor 91, and a second pressure roller 94 is disposed at a position facing the second line sensor 92. When reading the chart, the first and second pressure rollers 93, 94 stabilize the posture of the recording material S to stabilize the reading result. The recording material S that has passed through the sensing unit 3 is discharged to the discharge section 8.

[0046] For example, a CIS (contact image sensor) can be suitably used as the first and second line sensors 91 and 92. In this embodiment, the first and second line sensors 91 and 92 can each read a chart at a resolution of about 300 dpi. In this embodiment, the image data read by the first and second line sensors 91 and 92 is treated as brightness values ​​of 0 to 255 for each of RGB in the control unit 30.

[0047] As shown in FIG. 2, the sensing unit 3 is connected to the control unit 30, and is capable of transferring information read by the first and second line sensors 91 and 92 (density information relating to density) to the control unit 30.

[0048] 4. Secondary transfer voltage control Next, the control of the secondary transfer voltage will be described. Fig. 3 is a flow chart showing an outline of the procedure for controlling the secondary transfer voltage in this embodiment. Generally, the control of the secondary transfer voltage is classified into constant voltage control and constant current control, but this embodiment uses constant voltage control.

[0049] First, when the control unit 30 (pre-image formation preparation process unit 31a) acquires job information from the operation unit 70 or the external device 200, it starts the operation of the job (S101). The job information includes image information designated by the operator and information on the recording material S. The recording material S information includes information on the size of the recording material S and information on the type of the recording material S (so-called "paper type category") such as "thin paper, plain paper, thick paper, etc." The type of the recording material S includes any information that can distinguish the recording material S, such as attributes based on general characteristics such as plain paper, thick paper, thin paper, glossy paper, coated paper, etc. (so-called "paper type category"), brand, product number, basis weight, thickness, etc. The control unit 30 (pre-image formation preparation process unit 31a) writes the job information to the RAM 33 (S102).

[0050] Next, the control unit 30 (pre-image formation preparation process unit 31a) acquires environmental information detected by the temperature sensor 71 and humidity sensor 72 (S103). In addition, the ROM 32 stores information indicating the correlation between the environmental information and the target current Itarget for transferring the toner image on the intermediate transfer belt 44b onto the recording material S. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains the target current Itarget corresponding to the environment from the information indicating the relationship between the environmental information and the target current Itarget based on the environmental information read in S103. Then, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) writes this target current Itarget into the RAM 33 (or the 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 charge amount of the toner changes depending on the environment. The target current Itarget in this embodiment is a secondary transfer current value that is obtained in advance by using the image forming apparatus 1 for each environment, and that allows an image with the maximum toner amount (in this embodiment, a secondary color full-surface solid image) to be transferred.

[0051] Next, the control unit 30 (ATVC control processor 31b) obtains information on 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, in a state in which the secondary transfer outer roller 45b and the intermediate transfer belt 44b are in contact with each other, a predetermined voltage of multiple levels is supplied from the secondary transfer power source 76 to the secondary transfer outer roller 45b. Then, the current value when the predetermined voltage is being supplied is detected by the current detection sensor 76b, and the relationship between the voltage and the current (voltage-current characteristics) as shown in FIG. 4 is obtained. The control unit 30 (ATVC control processor 31b) writes information on the relationship between the voltage and the current in the RAM 33 (or the secondary transfer voltage storage unit / calculator 31f). This relationship between the voltage and the current changes depending on the electrical resistance of the secondary transfer unit N2. Alternatively, a predetermined current of multiple levels may be supplied from the secondary transfer power source 76 to the outer secondary transfer roller 45b, and the voltage value generated at that time may be detected by the voltage detection sensor 76a. In the configuration of this embodiment, the relationship between the voltage and the current is not one in which the current changes linearly (proportional) to the voltage, but one in which the current changes so as to be expressed by a polynomial of the voltage that is equal to or greater than the second degree (a quadratic expression in this embodiment). Therefore, in this embodiment, the predetermined voltage or current supplied when acquiring information regarding the electrical resistance of the secondary transfer portion N2 is multi-staged at three or more points so that the relationship between the voltage and the current can be expressed by a polynomial.

[0052] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines a voltage value to be applied from the secondary transfer power source 76 to the secondary transfer outer roller 45b (S106). That is, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines a voltage value Vb required for flowing the target current Itarget in a state in which the recording material S is not present in the secondary transfer portion N2, based on the target current Itarget written in the RAM 33 in S104 and the relationship between the voltage and current determined in S105. This voltage value Vb corresponds to a secondary transfer partial voltage (transfer voltage for the electrical resistance of the secondary transfer portion N2). Also, the ROM 32 stores information for determining the recording material shared voltage (transfer voltage for the electrical resistance of the recording material S) Vp, as shown in FIG. 5. This information is set as table data indicating the relationship between the environmental moisture amount (absolute moisture amount) and the recording material shared voltage Vp for each basis weight classification for each paper type category of the recording material S. In addition, since the recording material S that has passed through the fixing device 46 once has a lower moisture content and therefore an increased electrical resistance, separate tables are prepared for the first and second sides. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains the recording material shared voltage Vp from the above table data based on the job information obtained in S101 and the environmental information obtained in S103. The table data for obtaining the recording material shared voltage Vp as shown in FIG. 5 is obtained in advance by experiments or the like. The control unit 30 can obtain the environmental moisture amount based on the temperature information obtained by the temperature sensor 71 and the humidity information obtained by the humidity sensor 72. In addition, when an adjustment value is set by an adjustment mode that adjusts the set value of the secondary transfer voltage, which will be described later, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains an adjustment amount ΔV corresponding to the adjustment value. As will be described later, when the adjustment amount ΔV is set by the adjustment mode, it is stored in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f). The control unit 30 (secondary transfer voltage memory unit / calculation unit 31f) calculates Vb+Vp+ΔV by adding the above Vb, Vp, and ΔV as the secondary transfer voltage Vtr to be applied from the secondary transfer power source 76 to the secondary transfer outer roller 45b when the recording material S passes through the secondary transfer section N2.Then, the control unit 30 writes this Vtr (=Vb+Vp+ΔV) into the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f).

[0053] Here, the recording material shared voltage Vp may change depending on the surface properties of the recording material S in addition to the information related to the electrical resistance of the recording material S (such as basis weight). Therefore, the table data may be set so that the recording material shared voltage Vp also changes depending on the information related to the surface properties of the recording material S. In this embodiment, information related to the electrical resistance of the recording material S (and further information related to the surface properties of the recording material S) is included in the job information acquired in S101. However, it is also possible to provide a measuring means for detecting the thickness and surface properties of the recording material S in the image forming apparatus 1, and to obtain the recording material shared voltage Vp based on the information obtained by this measuring means.

[0054] Next, the control unit 30 (image forming process unit 31c) executes image formation, sends the recording material S to the secondary transfer unit N2, and controls to apply the secondary transfer voltage Vtr determined as described above to perform secondary transfer (S107). Thereafter, the control unit 30 (image forming process unit 31c) repeats S107 until all images of the job have been transferred to the recording material S and output (S108).

[0055] Incidentally, with regard to the primary transfer portion N1 as well, the same ATVC control as described above is performed from the start of a job until the toner image is transported to the primary transfer portion N1, but a detailed description thereof will be omitted here.

[0056] 5. Adjustment Mode Overview Next, a simple adjustment mode (herein also referred to as "adjustment mode") for adjusting the set voltage of the secondary transfer voltage will be described. Depending on the type and condition of the recording material S used for image formation, the moisture content and electrical resistance value of the recording material S may be significantly different from those of a standard recording material S. In this case, there is a possibility that proper transfer cannot be performed with the set voltage of the secondary transfer voltage using the default recording material distribution voltage Vp that is preset as described above.

[0057] 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, and the density of the image decreases. For example, this may occur when the electrical resistance of the recording material S is higher than the value (corresponding to the recording material assigned voltage Vp) assumed for each paper type category, or when the moisture content of the recording material S has decreased (dried) due to the storage conditions of the recording material S, causing the electrical resistance to increase. In such cases, it is desirable to increase the set voltage of the secondary transfer voltage (increase the absolute value) by, for example, increasing the recording material assigned voltage Vp.

[0058] Conversely, if the secondary transfer voltage is higher than necessary, abnormal discharge may occur, resulting in poor image quality, or the charge of the toner may be inverted due to discharge at the secondary transfer portion N2, resulting in poor transferability. For example, this may occur when the electrical resistance of the recording material S is lower than the value (corresponding to the recording material distribution voltage Vp) assumed for each paper type category, or when the storage conditions of the recording material S cause the amount of moisture contained in the recording material S to increase (absorb moisture) and the electrical resistance to decrease. In such cases, it is desirable to lower the set voltage of the secondary transfer voltage (reduce the absolute value) by lowering the recording material distribution voltage Vp, for example.

[0059] Therefore, it is desired that an operator such as a user or a service person adjusts (changes) the recording material distribution voltage Vp according to the recording material S actually used for image formation, and adjusts (changes) the set voltage of the secondary transfer voltage when a job is executed to an optimal value. In other words, it is sufficient to be able to select an 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, an operator outputs an image to be output while switching the secondary transfer voltage for each sheet of recording material S, checks whether there is an image defect generated in the output image, and determines the optimal set voltage of the secondary transfer voltage (more specifically, the recording material distribution voltage Vp+ΔV). However, in this method, the output of the image and the adjustment of the set voltage of the secondary transfer voltage are repeated, so that more recording materials S are wasted and it takes time.

[0060] Therefore, in this embodiment, the image forming apparatus 1 can execute an adjustment mode for adjusting the set voltage of the secondary transfer voltage. In this adjustment mode, a chart is outputted by transferring a plurality of patches (test image, test pattern, test toner image) of representative colors to the recording material S actually used for image formation, with the set voltage of the secondary transfer voltage being switched for each patch. Then, based on the result of reading the outputted chart by the sensing unit 3, the set voltage of the optimal 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 that is an image of the maximum toner amount) 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 the presence or absence of image defects, and reduces the burden on the operator while more appropriately adjusting the setting of the secondary transfer voltage.

[0061] 6. Charts Next, a chart (adjustment chart) output in the adjustment mode in this embodiment will be described. In this embodiment, different charts are output according to the size of the recording material S used to output the chart. The length of the recording material S in the conveying direction of the recording material S is simply called the "conveying direction length", and the length of the recording material S in the direction approximately perpendicular to the conveying direction of the recording material S is simply called the "width". The conveying direction of the recording material S is approximately parallel to the sub-scanning direction (the moving direction of the surface of the photosensitive drum 51 or the intermediate transfer belt 44b), and the direction approximately perpendicular to the conveying direction of the recording material S (here, also called the "width direction") is approximately parallel to the main scanning direction (the direction approximately perpendicular to the moving direction of the surface of the photosensitive drum 51 or the intermediate transfer belt 44b). The lengths of the chart, image data defining the chart, or patches formed on the chart in the directions corresponding to the "conveying direction length" and "width" of the recording material S are also simply called the "conveying direction length" and "width", respectively.

[0062] FIG. 6 is a schematic diagram showing a large chart (also called an "L chart") 100, which is a chart when the length of the recording material S in the transport direction is 420 mm or more (the long side of A3 size) and the width of the recording material S is 279.4 mm or more (the long side of LTR size).

[0063] Large chart data (also called "L chart data"), which is image data defining the L chart 100, corresponds to the maximum paper size. The image size of the L chart data is approximately 13 inches (≈330 mm) wide x 19.2 inches (≈487 mm) long in the transport direction. The L chart 100 corresponding to the image data cut from this L chart data is output according to the size of the recording material S. At this time, the image data is cut from the L chart data according to the size of the recording material S based on the leading edge in the reading direction and the center in the width direction. FIG. 6 shows a case where the size of the recording material S is A3 size (portrait feed). For example, when the recording material S used to output the L chart 100 is A3 size (portrait feed) (width 297 mm x transport direction length 420 mm), image data with a size of 292 mm wide x 415 mm long in the transport direction is cut from the L chart data. Then, an image corresponding to this cut-out image data is formed on an A3 size (portrait feeding) recording material S with a margin of 2.5 mm on each end based on the leading edge in the reading direction and the center in the width direction. Note that this margin is typically about 2 to 10 mm.

[0064] In the L chart 100, a total of 11 pairs of blue (B) solid patches 101 and black (Bk) solid patches 102 arranged side by side in the width direction are arranged side by side in the conveying direction of the recording material S. In the L chart 100 in FIG. 6, 100(1) indicates the first side, and 100(2) indicates the second side. After passing through the secondary transfer portion N2, the second side passes through the inside of the sensing unit 3 without changing its orientation, but the first side passes through the reversing conveying path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer portion N2 and when passing through the inside of the sensing unit 3. In FIG. 6, the conveying direction of the chart when passing through the secondary transfer portion N2 is indicated by a thin arrow, and the conveying 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 and the Bk solid patch 102 when passing through the inside of the sensing unit 3 are patches for detecting position information (also referred to as "trigger patches" here) 101T and 102T, respectively. The 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 the Bk solid patch 102, the remaining ten patches excluding the trigger patches 101T and 102T are patches for acquiring luminance information (density information) (also referred to as "adjustment patches" here) 101A and 102A. The adjustment patches 101A and 102A are transferred to the recording material S by applying different secondary transfer voltages Vtr to each patch.

[0065] In this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm long by 40 mm wide in the transport direction, and there is a 15 mm gap between the B solid patches 101 and between the Bk solid patches 102 in the transport direction of the recording material S. Considering reading with the first and second line sensors 91, 92, if the size of each patch (especially the adjustment patch) is too small, it will be affected by uneven texture of the recording material S (unevenness in the unevenness of the paper fibers, etc.), which will increase the variability in the reading results. Therefore, it is desirable for the size of each patch (especially the adjustment patch) to be somewhat large in area, and it is preferable for the area to be no larger than 600 mm. 2The above is desirable. However, if the size of each patch (especially the adjustment patch) is made too large, the number of times the secondary transfer voltage Vtr fluctuates within the chart will decrease. In this embodiment, the patch size is set to allow the secondary transfer voltage Vtr to fluctuate in 10 steps in the L chart 100. Also, the interval between each patch in the conveying direction of the recording material S is set so that the secondary transfer voltage can be switched, and is desirably 15 mm or more.

[0066] In this embodiment, the B solid patch 101 and the Bk solid patch 102 on the first side 100(1) and the second side 100(2) of the L chart 100 are arranged so as not to overlap on the front and back of the recording material S. This is to avoid the influence on the detected brightness due to show-through when reading with the first and second line sensors 91 and 92. This show-through is likely to occur especially with recording material S having a small basis weight.

[0067] FIG. 7 is a schematic diagram showing a small chart (also called an "S chart") 103, which is a chart when the length of the recording material S in the transport direction is 210 mm (the short side of A4 size) or more and less than 420 mm (the long side of A3 size) and the width of the recording material S is 160 mm or more.

[0068] Small chart data (also called "S chart data"), which is image data defining the S chart 103, corresponds to half the size of the maximum paper passing size. The image size of the S chart data is approximately 13 inches (≈330 mm) wide x 9.6 inches (≈243 mm) long in the transport direction. When the size of the recording material S is A4 (horizontal feed) or LTR (horizontal 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 according to the size of the recording material S based on the leading edge in the reading direction and the center in the width direction. FIG. 7 shows the case where the size of the recording material S is A4 size (horizontal feed). For example, when the recording material S used to output the S chart 103 is A4 size (horizontal feed) (210 mm long in the transport direction x 297 mm wide), image data of 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 the cut-out image data is formed on an A4 size (horizontal feed) recording material S with a margin of 2.5 mm on each end, based on the leading edge in the reading direction and the center in the width direction. Note that this margin is typically about 2 to 10 mm.

[0069] In the S chart 103, a set of blue (B) solid patches 101 and black (Bk) solid patches 102 arranged side by side in the width direction are arranged across two sheets of recording material S, with a total of 12 sets arranged side by side in the conveying direction of the recording material S. In the S chart 103, two sheets of recording material S are used to form the chart, so that the same number of patches as the L chart 100 can be secured and the same adjustment can be performed. In the S chart 103 in FIG. 7, 103(1-1) indicates the first sheet of the first side, 103(1-2) indicates the second sheet of the first side, 103(2-1) indicates the first sheet of the second side, and 103(2-2) indicates the second sheet of the second side. After passing through the secondary transfer portion N2, the second side passes through the inside of the sensing unit 3 without changing its orientation, but the first side passes through the reversing conveying path 7 once. Therefore, the orientation of the first side is different when passing through the secondary transfer portion N2 and when passing through the inside of the sensing unit 3. In FIG. 7, the conveying direction of the chart when passing through the secondary transfer portion N2 is indicated by a thin arrow, and the conveying direction of the chart when passing through the inside of the sensing unit 3 is indicated by a thick arrow. In this embodiment, for the patches formed on one side of the recording material S, the leading patches of the B solid patch 101 and the Bk solid patch 102 when passing 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. The remaining ten patches of each of the B solid patch 101 and the Bk solid patch 102, excluding the trigger patches 101T and 102T, are adjustment patches 101A and 102A for acquiring luminance information (density information). The adjustment patches 101A and 102A are transferred to the recording material S by applying different secondary transfer voltages Vtr to each other.

[0070] As described above, 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 there is a 15 mm gap between the B solid patches 101 and between the Bk solid patches 102 in the transport direction of the recording material S.

[0071] In this embodiment, the B solid patches 101 and the Bk solid patches 102 are arranged so as not to overlap on the front and back of the recording material S 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. This is to avoid the influence on the detected brightness due to show-through when read by the first and second line sensors 91, 92. This show-through is likely to occur especially with recording material S having a small basis weight.

[0072] In this embodiment, the size of the recording material S usable for outputting the chart is 210 mm or more in length in the transport direction (the short side of A4 size) and 160 mm or more in width. However, the size of the recording material S usable for outputting the chart is not limited to that in this embodiment, and can be set appropriately depending on the maximum paper passing size of the image forming apparatus 1. Also, in addition to standard sizes, the operator may specify the size through the operation unit 70 or the external device 200, so that a recording material S of any size can be used.

[0073] In this embodiment, the image forming apparatus 1 is capable of selecting, in the adjustment mode, whether to adjust only the secondary transfer voltage during single-sided printing (also referred to as "single-sided adjustment" here), or to adjust the secondary transfer voltages for the first and second sides during double-sided printing (also referred to as "double-sided adjustment" here). However, to facilitate understanding of the present invention, the embodiment will be described with reference to the case where "double-sided adjustment" is performed. The case where "single-sided adjustment" is performed will be described in embodiment 3.

[0074] The design of the chart is not limited to that of this embodiment. For example, the adjustment patch is not limited to a B solid image and a Bk solid image. The adjustment patch may be, for example, either a B solid image or a Bk solid image, or may be another single-color solid image, a solid image of another secondary color or a mixed color (multi-color) of more than one color, or a halftone image. For example, the shape and number of the 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. The shape of the trigger patch is also not limited to that of this embodiment. Depending on the chart reading method, etc., the trigger patch is not necessarily required.

[0075] Also, assuming that an operator will visually check, for example, information such as a patch number, which will be described later, may be printed in association with each set of patches in the transport 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, assuming that an operator will visually check, for example, information such as front side (first side) or back side (second side) may be printed on the corresponding side as identification information indicating whether it is a chart for adjusting the first side or a chart for adjusting the second side.

[0076] 7. Adjustment mode operation Next, the operation of the adjustment mode in this embodiment will be described. Fig. 8 is a flow chart showing an outline of the procedure of the adjustment mode in this embodiment. Here, a case where an 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 that causes the image forming apparatus 1 to execute the adjustment mode may be played by an external device 200 such as a personal computer. The following symbols will be used in the following description.

[0077] N: Adjustment value (=-20 to +20) N0: Current (before adjustment mode is executed) adjustment value N A : selected adjustment value n: Patch number of the adjustment patch (n=1 to 10, starting from the smallest adjustment value) n0: Patch number corresponding to the current adjustment value (corresponding to adjustment value N0) n A : Selected patch number (adjustment value N A (corresponding to T: Trigger patch code D: A code indicating the position where the electrical resistance of the area where the air is blown is detected

[0078] First, the control unit 30 (adjustment processing unit 31d) acquires information on the recording material S that the operator wishes to adjust (size, paper type category (and basis weight) of the recording material S) and information on the adjustment conditions, which are input by the operator (S1). FIG. 9 is a schematic diagram of a paper type category selection screen 700 that is displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment processing unit 31d) in S1. The paper type category selection screen 700 displays paper type categories of the recording material S that can be set in the image forming apparatus 1. The operator can proceed to an adjustment mode for adjusting the set voltage of the secondary transfer voltage by pressing (operating) an adjustment button 701. Note that the paper type category selection screen 700 may be configured to allow access to a screen for changing other image forming conditions such as fixing conditions in addition to adjusting the secondary transfer voltage. In addition, in order to leave the default settings of each paper type category, the adjustment mode may be executed after copying the paper type category to the RAM 33 or ROM 32 using a copy button 702. The copied paper type category 703 is stored in the RAM 33 or the ROM 32 under a different name, and image formation is performed with the default settings for that paper type category 703 except for the conditions for which the settings have been changed.

[0079] FIG. 10 is a schematic diagram of a 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 performed is selected, the paper feed unit selection screen 704 shown in FIG. 10 is displayed. The paper feed unit selection screen 704 displays the paper type category of the recording material S stored in the paper feed unit 4 that is set in advance by the operator via the operation unit 70 or the like, and the size detected by a recording material size detection sensor (not shown) provided in each paper feed unit 4. For example, "Plain Paper 1_Copy (64-75 g / m 2 10, a case will be described in which "Plain Paper 1_Copy (64-75 g / m 2 )" is stored. Also, in the case of a size of the recording material S that is compatible with the adjustment mode, the operator can press (operate) the selection button 705. In the case of a paper type category that is not compatible with the adjustment mode or a size of the recording material S that is not compatible with the adjustment mode, the selection button 705 may be grayed out so that the operator cannot press (operate) it. Also, in the case where the recording material S for executing the adjustment mode is not stored in advance in any of the paper feed units 4, for example, the operator may be able to temporarily exit the paper feed unit selection screen 704 by using a back button (not shown) or the like.

[0080] FIG. 11 is a schematic diagram of a secondary transfer voltage adjustment screen 706 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1. When the paper type category of the recording material S for which the adjustment mode is to be performed is selected and the paper feed unit 4 in which the recording material S is stored is selected, the secondary transfer voltage adjustment screen 706 shown in FIG. 11 is displayed. The secondary transfer voltage adjustment screen 706 has an adjustment value display unit 707 in which the current adjustment value is displayed, a single-sided / double-sided selection unit 708 in which the adjustment mode is to be performed for single-sided or double-sided, an adjustment execution button 709 for starting chart formation, and the like. By inputting a value into the adjustment value display unit 707, it becomes possible to perform secondary transfer in a state in which the recording material assigned voltage is offset from the default recording material assigned voltage Vp stored in the ROM 32 for the corresponding paper type category. In this embodiment, an integer value 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. When the adjustment value N is 0, the default recording material voltage Vp corresponding to the paper type category recorded in the ROM 32 is used as is. The value (adjustment value N) of the adjustment value display section 707 corresponds ΔN=1 to ΔV=150V (i.e., when the adjustment value N is changed by 1, the adjustment amount ΔV changes by 150V). For example, when N=-5 is input to the adjustment value display section 707, a value obtained by offsetting the default recording material voltage Vp by -750V (=-5×150) is used as the recording material voltage. When the operator executes the adjustment mode, he or she selects whether to perform double-sided adjustment or single-sided adjustment in the single-sided / double-sided selection section 708, and then presses (operates) the adjustment execution button 709. However, as described above, in this embodiment, the case where "double-sided adjustment" is performed will be described.

[0081] When the adjustment execution button 709 is pressed (operated), the control unit 30 (adjustment process unit 31d) executes the density correction control (S2). The density correction control is for making a state in which a certain 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 a toner patch for the density correction control while changing the output of the charging power source 73, the developing power source 74, the exposure device 42, etc., and controls the primary transfer of the toner patch onto the intermediate transfer belt 44b. Then, the control unit 30 (adjustment process unit 31d) determines the image formation conditions at the time of outputting the chart by measuring the toner amount (density) of the toner patch on the intermediate transfer belt 44b by a patch detection sensor (not shown). It is not necessary to execute the density correction control every time the adjustment mode is executed. The control unit 30 (adjustment process unit 31d) may determine whether or not to execute the density correction control based on, for example, the number of images formed, environmental changes, and elapsed time since the previous density correction control was executed.

[0082] Next, the control unit 30 (the adjustment processor 31d and the ATVC control processor 31b) executes the ATVC control (S3). The details of the ATVC control are as described above.

[0083] Thereafter, the control unit 30 (adjustment processor 31d) controls to output the chart (S4 to S6). At this time, the control unit 30 (adjustment processor 31d) selects a chart according to the size of the recording material S, and controls to output the selected chart. The control unit 30 (adjustment processor 31d) judges whether the length of the recording material S in the conveying direction is 420 mm or more (S4). If the control unit 30 (adjustment processor 31d) judges in S4 that the length of the recording material S in the conveying direction is 420 mm or more ("Yes"), it controls to output one L chart 100 in FIG. 6 (S5). Also, if the control unit 30 (adjustment processor 31d) judges in S4 that the length of the recording material S in the conveying direction is less than 420 mm ("No"), it controls to output two S charts 103 in FIG. 7 (S6). In S5 and S6, the control unit 30 (adjustment processing unit 31d) performs control so that charts are formed and output on one or both sides of the recording material S depending on whether single-sided adjustment or double-sided adjustment is performed. However, as described above, in this embodiment, the case where "double-sided adjustment" is performed will be described.

[0084] FIG. 12 is a graph showing the transition of the output of the secondary transfer power source 76 when the L chart 100 is secondarily transferred to the recording material S. FIG. 12(a) shows the first side during double-sided adjustment, and FIG. 12(b) shows the second side during double-sided adjustment. In the case of the first side, after ten adjustment patches 101A and 102A are consecutively secondarily transferred to the recording material S, trigger patches 101T and 102T are secondarily transferred to the recording material S. The adjustment patches 101A and 102A are arranged in order from the smallest adjustment value N to the largest adjustment value N. The patch numbers of the adjustment patches 101A and 102A are set to n=1 for the patch number corresponding to the smallest adjustment value N and n=10 for the patch number corresponding to the largest adjustment value N, and increase in order in response to an increase in the adjustment value N. In addition, in the case of the first side, the recording material shared voltage Vp for setting the secondary transfer voltage Vtr uses a value from a table stored in the ROM 32 for the first side. The timing for switching the secondary transfer voltage when the chart is secondarily transferred to the recording material S is after each patch 101, 102 has passed the secondary transfer portion N2. Although there is a slight time lag in switching the output of the secondary transfer power supply 76, by switching at the above timing, the output of the secondary transfer power supply 76 is switched in the margins between each patch. In the case of the second side, the arrangement of the adjustment patches 101A, 102A and the trigger patches 101T, 102T is reversed from that of the first side, and the recording material shared voltage Vp uses a value from a table stored in ROM 32 for the second side. However, switching of the secondary transfer voltage and other operations are performed in the same manner as for the first side.

[0085] In this embodiment, the amplitude (change in one step) ΔV (reference numeral 801 in FIG. 12) of the secondary transfer voltage when the chart is secondarily transferred to the recording material S is switched by the secondary transfer partial voltage Vb. In this embodiment, when the secondary transfer partial voltage Vb is 2000V or more, the amplitude ΔV of the secondary transfer voltage is set to 450V, which corresponds to the amplitude ΔN=3 of the adjustment value (three steps of the adjustment value N). When the secondary transfer partial voltage Vb is 1500V or more and less than 2000V, the amplitude ΔV of the secondary transfer voltage is set to 300V, which corresponds to the amplitude ΔN=2 of the adjustment value (two steps of the adjustment value N). When the secondary transfer partial voltage Vb is less than 1500V, the amplitude ΔV of the secondary transfer voltage is set to 150V, which corresponds to the amplitude ΔN=1 of the adjustment value (one step of the adjustment value N). This is because, in order to check the current sensitivity of the secondary transfer property, it is considered more efficient to increase the change width of the secondary transfer voltage in one step as the secondary transfer partial voltage Vb increases, since this increases the change width of the secondary transfer current for the entire chart. In this embodiment, the amplitude ΔV of the secondary transfer voltage (amplitude ΔN of the adjustment value) when the chart is secondarily transferred to the recording material S is automatically selected according to the result of ATVC control, but it may also be possible for the operator to directly select it on the secondary transfer voltage adjustment screen 706 or the like. Furthermore, it may also be possible for the operator to select whether the amplitude ΔV of the secondary transfer voltage (amplitude ΔN of the adjustment value) when the chart is secondarily transferred to the recording material S is "automatically selected" or "directly specified."

[0086] 13(a) to 13(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 (amplitude ΔV of the secondary transfer voltage) and for each of the first and second sides in this embodiment. FIG. 13(a) shows the case where the adjustment value amplitude ΔN=1, FIG. 13(b) shows the case where the adjustment value amplitude ΔN=2, and FIG. 13(c) shows the case where the adjustment value amplitude ΔN=3. When the current adjustment value N0 is 0, patch number n=5 corresponds to the current adjustment value N0=0, n=1 to 4 correspond to the small adjustment value side at ΔN intervals, and n=6 to 10 correspond to the large adjustment value side at ΔN intervals. When the current adjustment value N0 is other than 0, the adjustment value corresponding to each adjustment patch 101A, 102A is offset uniformly. Furthermore, if the current adjustment value N0 is fixed at n=5, when the current adjustment value N0 is large on the positive or negative side, there will be cases where all of the adjustment patches 101A, 102A for n=1 to 10 do not fall within the adjustment range of ±20. In such cases, the patch corresponding to the current adjustment value N0 is shifted from n=5 so that all of the adjustment patches 101A, 102A for n=1 to 10 fall within the adjustment range of ±20. This allows all of the adjustment patches 101A, 102A to be used effectively.

[0087] In the case of the 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 and the leading edge of the second side. The trigger patches 101T and 102T are used to detect the positions of the patches when the chart is read by the sensing unit 3. Therefore, the trigger patches 101T and 102T need to be transferred at a minimum density required for that purpose. If the secondary transfer voltage is extremely high or extremely low, there is a risk that the trigger patches 101T and 102T cannot be read. Therefore, in this embodiment, when the trigger patches 101T and 102T are secondarily transferred to the recording material S, a voltage corresponding to patch number n=5 (a voltage indicated by a dotted line with reference numeral 800 in FIG. 13) is applied.

[0088] Furthermore, in the case of the L chart 100, when the chart is secondarily transferred to the recording material S, there is a blank area (margin) where the patch 101 is not formed in the image formation area (area where a toner image can be formed) at the leading edge of the paper on the first side and the trailing edge of the paper on the second side. In this embodiment, an area for acquiring information about the electrical resistance near the leading edge of the recording material S in the transport direction when the recording material S is sent out from the paper feed unit 4 (described later) is set in this area. In this embodiment, when the area for acquiring information about the electrical resistance of the recording material S near the leading edge of the recording material S in the transport direction when the recording material S is sent out from the paper feed unit 4 (hereinafter also referred to as "position D (or electrical resistance detection position D)") passes through the secondary transfer unit N2, a voltage corresponding to patch number n=5 (a voltage indicated by a dotted line with reference numeral 800 in FIG. 13) is applied.

[0089] In this manner, in this embodiment, when the positions of the trigger patches 101T, 102T on the recording material S and the position D near the leading edge of the recording material S in the transport direction when sent out from the paper feed unit 4 pass the secondary transfer unit N2, a voltage of patch number n=5 (a voltage indicated by a dotted line with reference numeral 800 in FIG. 13) is applied. In particular, in this embodiment, a voltage corresponding to patch number n=5 (a voltage indicated by a dotted line with reference numeral 800 in FIG. 13) is applied to almost the entire area other than the adjustment patches 101A, 102A within the image formation area of ​​the recording material S in the transport direction when passing through the secondary transfer unit N2.

[0090] The method of setting the secondary transfer voltage applied when the trigger patches 101T and 102T are secondarily transferred to the recording material S is not limited to the method of this embodiment as described above. For example, the secondary transfer voltage may be set higher (larger absolute value) to suppress weak dropout (transfer failure due to weak transfer voltage) at the minimum, or the secondary transfer voltage may be controlled at a constant current to transfer at the minimum required density. Similarly, the voltage applied at position D is not limited to the setting in this embodiment. The voltage applied at position D may be obtained with sufficient accuracy information on the electrical resistance near the leading edge of the recording material S in the conveying direction when it is sent out from the paper feed unit 4 (more specifically, the current difference ΔId described later). This voltage may be set to a voltage higher (larger absolute value) than the voltage corresponding to patch number n=5, or may be set to a voltage lower (smaller absolute value) than the voltage corresponding to patch number n (see embodiment 2). In addition, it is preferable that this voltage be the same value as the voltage for any patch number n from the viewpoint of simplification of control, but it may be a different value.

[0091] FIG. 14 is a graph showing the transition of the output of the secondary transfer power source 76 when the chart is secondarily transferred to the recording material S in the case of the S chart 103. FIG. 14(a) shows the first side during double-sided adjustment, and FIG. 14(b) shows the second side during double-sided adjustment. In the case of the S chart 103, the chart is divided into the first sheet of the first side (103(1-1)), the second sheet of the first side (103(1-2)), the first sheet of the second side (103(2-1)), and the second sheet of the second side (103(2-2)), and trigger patches 101T and 102T are arranged on each side, and a position D is set. However, in the case of the S chart 103, the magnitude and timing of the output of the secondary transfer power source 76 are basically the same as in the case of the L chart 100. Note that the position D may be set only for either the first or second sheet, for example, for the first sheet.

[0092] In addition, the control unit 30 (adjustment processing unit 31d) controls the current detection sensor 76b to detect the current when the recording material S passes through the secondary transfer portion N2 when the chart is output (S7). The current detection timing is, first, the timing when the positions (hereinafter also referred to as "adjustment patch positions 1 to 10") on the recording material S where the adjustment patches 101A and 102A of patch numbers 1 to 10 are transferred pass through the secondary transfer portion N2. Also, it is the timing when the position D on the recording material S passes through the secondary transfer portion N2. Also, it is the timing when the position (hereinafter also referred to as "trigger patch position T") on the recording material S where the trigger patches 101T and 102T are transferred pass through the secondary transfer portion N2. Note that the current is detected multiple times while each of the above positions (areas) passes through the secondary transfer portion N2, and the average value can be used for control as the detection result of the current when each position (area) passes through the secondary transfer portion N2. Adjustment patch positions 1 to 10, trigger patch position T, and position D are each represented by the center in the transport direction of the recording material S. This allows the control unit 30 (adjustment processing unit 31d) to obtain the relationship between voltage and current when the chart is output. Fig. 15 is a graph showing the relationship between voltage and current (voltage-current characteristics) obtained when the chart is output in this embodiment.

[0093] Here, the position D is set so as to include a location where air is blown in the paper feed section 4 near the leading edge of the recording material S in the transport direction when it is sent out from the paper feed section 4. FIG. 19(a) is a schematic cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 51) of the air blowing section 49 of the paper feed section 4 in this embodiment. FIG. 19(b) is a schematic view showing a location where air is blown onto the recording material S in the paper feed section 4 in this embodiment. The air blowing section 49 is configured to have a fan 49a, a duct 49b, a handling nozzle 49c, and the like. When the feeding operation of the recording material S is started under the control of the control section 30, the fan 49a is operated and air is sucked into the duct 49b. Then, this air is blown from the handling nozzle (blow port) 49c onto some of the uppermost recording materials S, including the topmost one, of the stack of recording materials S contained in the cassette 43. At this time, air is blown from the leading end side to the trailing end side as indicated by the arrow E against the leading end of the recording material S in the transport direction when it is sent out from the paper feed unit 4. In this embodiment, the handling nozzle 49c is provided at a plurality of locations (three locations from the center and both ends in this embodiment) in the width direction of the recording material S. When air is blown, several sheets of recording material S including the top sheet of the stack of recording materials S in the cassette 43 float up. Then, the top recording material St is sent out from the cassette 43 by the paper feed member 48 (FIG. 1) such as a paper feed roller or a paper feed belt as indicated by the arrow F. The air blowing unit 49 may further include a separation nozzle 49d that blows air so as to further separate the recording materials S that have been sorted by the air from the handling nozzle 49c.

[0094] As shown in FIG. 19B, the portion Sa of the recording material S where the air is blown may be dried by the air and have a higher electrical resistance than the other portion Sb. Therefore, a position D is set at a position including the portion Sa where the air is blown in the conveying direction when the recording material S is sent out from the paper feed unit 4 (a position where the electrical resistance of the recording material S may increase due to the air being blown during paper feed), and when this position D passes through the secondary transfer unit N2, a voltage is applied to the secondary transfer outer roller 45b, and the current is detected by the current detection sensor 76b. This makes it possible to determine whether the electrical resistance of the recording material S at the position D has been caused to vary in electrical resistance by the blowing of air, by comparing the electrical resistance of the recording material S at the adjustment patch position where the air is not blown.

[0095] Although toner is present at the adjustment patch position, the electrical resistance of the toner in the electrical resistance of the recording material S and the toner when the adjustment patch position passes through the secondary transfer portion N2 is sufficiently smaller than the electrical resistance of the recording material S. Therefore, the presence or absence of toner at the position D and the adjustment patch position can be ignored when determining the electrical resistance unevenness within the surface of the recording material S. By detecting the electrical resistance (current that flows when a predetermined voltage is applied) of the recording material S at the adjustment patch position and the position D, the electrical resistance unevenness in the area where the adjustment patch is transferred can be detected, and the adjustment value, which will be described later, can be corrected more accurately. In addition, by detecting the electrical resistance (current that flows when a predetermined voltage is applied) within the image formation area of ​​the recording material S, the set voltage of the secondary transfer voltage when the toner image is transferred to the recording material S during image formation can be adjusted more accurately.

[0096] In this embodiment, the control unit 30 (adjustment processing unit 31d) compares the relationship between the voltage applied and the detected current at adjustment patch positions 1 to 10 (a polynomial, particularly a quadratic expression, in this embodiment) with the relationship between the voltage applied and the detected current at position D. Then, a current difference ΔId is calculated and stored in RAM 33 (S8). It can be determined that the larger the current difference ΔId is, the more the electrical resistance of the recording material S is locally increased due to the influence of air. To explain further with reference to FIG. 15, the control unit 30 (adjustment processing unit 31d) obtains an approximation of the relationship between the voltage applied and the detected current at adjustment patch positions 1 to 10 using a quadratic function (I=a×V 2 +b×V+c). Then, the control unit 30 (adjustment processing unit 31d) applies the voltage Vtr at the position D and detects the current Id, and calculates the current difference ΔId using the following formula: ΔId=(a×Vtr 2 +b×Vtr+c)-Id In the case of double-sided adjustment, the relationship between the voltage applied and the detected current at adjustment patch positions 1 to 10 and the current difference ΔId are acquired and calculated for each of the first and second sides. In the case of the S chart 103, for example, the current detected at position D on either the first or second sheet can be used for each of the first and second sides, or the average value of the current detected at position D on the first and second sheets can be used. Also, the current may be detected only at position D on either the first or second sheet for each of the first and second sides. Usually, the first sheet of recording material S and the second sheet of recording material S that are continuously fed for output of the S chart 103 can be considered to have the same degree of in-plane electrical resistance unevenness.

[0097] As described above, position D is set at a position including the area Sa where air is blown near the leading edge in the transport direction when the recording material S is sent out from the paper feed unit 4. In order to accurately detect uneven electrical resistance within the surface of the recording material S caused by the blowing of air, in relation to a configuration for effectively handling air, position D is preferably within 50 mm from the leading edge to the trailing edge of the recording material S in the transport direction when the recording material S is sent out from the paper feed unit 4. In this embodiment, position D is set at a position 20 mm from the leading edge to the trailing edge of the recording material S in the transport direction when the recording material S is sent out from the paper feed unit 4 (more specifically, for example, an area with a length of 15 mm in the transport direction with said position as the center of the transport direction of the recording material S).

[0098] When the chart is output, the control unit 30 (adjustment processing unit 31d) reads the chart with the sensing unit 3, and controls the calculation of the luminance and variance of each of the adjustment patches 101A and 102A as follows (S9).

[0099] The first and second line sensors 91 and 92 of the sensing unit 3 read the first and second charts at a resolution of 300 dpi, respectively. The image information read by the first and second line sensors 91 and 92 of the sensing unit 3 is stored in the RAM 33. The control unit 30 (adjustment processing unit 31d) calculates the positions of the adjustment patches 101A and 102A based on the positions of the trigger patches 101T and 102T of the chart as follows. FIG. 16 is a schematic diagram for explaining an example of a method for identifying the positions of the trigger patches 101T and 102T from the image 110 read by the first and second line sensors 91 and 92. First, in the conveying direction of the recording material S when passing through the inside of the sensing unit 3, a line 112 located in a margin between an edge 111 of the chart (recording material S) and the trigger patches 101T and 102T is set from a rough positional relationship. Then, the average luminance value of the line 112 is read from the information of the read chart. At this time, if the average luminance value is smaller than a predetermined threshold value (if the density is larger than a predetermined value), it is determined to be an edge of the trigger patches 101T and 102T. If it is not determined to be an edge, the process repeats line by line toward the upstream in the conveying direction of the recording material S when passing through the inside of the sensing unit 3 to find an edge line 113. Next, a line 114 located in the margin between the edge 111 of the chart (recording material S) and the trigger patches 101T and 102T in the width direction is set based on a rough positional relationship. Then, the average luminance value of the line 114 is read out from the information of the read chart. At this time, if the average luminance value is smaller than a predetermined threshold value (if the density is larger than a predetermined value), it is determined to be an edge of the trigger patches 101T and 102T. If it is not determined to be an edge, the process repeats line by line toward the right side in the width direction in FIG. 16 to find an edge line 115. 16 is the right side in the width direction when the surface of the recording material S facing the first and second line sensors 91 and 92 is viewed with the leading edge side in the transport direction of the recording material S facing up as it passes through the inside of the sensing unit 3. Note that the above edge detection method is an example, and edge detection is not limited to the above method. For example, a method different from that in this embodiment may be used depending on the chart design.

[0100] When the control unit 30 (adjustment processing unit 31d) identifies the positions of the adjustment patches 101A and 102A, it calculates the average luminance value and the variance value and stores them in the RAM 33. That is, for the nth adjustment patch, the average luminance value and the variance value calculated by the following formula are stored in the RAM 33.

[0101]

number

[0102] The average luminance value (average luminance value) is a parameter close to density (i.e., correlated with density). Furthermore, the inventors have found through their studies that the variance value is a parameter that is sensitive to the transferability when the recording material S has unevenness. In this embodiment, the average luminance value and the variance value are calculated for both the B solid patch 101 and the Bk solid patch 102. In this embodiment, the average luminance value and the variance value are used to determine a recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) for the set voltage of the secondary transfer voltage.

[0103] In this embodiment, the luminance read from the information of the image read by the sensing unit 3 is B luminance for the B solid patch 101, and G luminance for the Bk solid patch 102. Which of the RGB luminances is used does not have to be in this order, and it may also be the average value of the three luminances, or a grayscale luminance that is not resolved into RGB.

[0104] In addition, when calculating the variance value, it is necessary to temporarily store the luminance of each pixel that has been read out, which may lead to a high load on the control unit 30 and a long time for the adjustment mode. In such a case, the luminance from 0 to 255 may be divided into several sections, the frequency of each pixel may be counted, and the variance value may be calculated from a digital histogram. The number of luminance sections to be divided into and the intervals may be appropriately changed depending on the characteristics of the first and second line sensors 91, 92 and the processing capacity of the control unit 30. In addition, since the luminance histogram differs depending on the paper type category, the number of luminance sections to be divided into and the intervals may be changed depending on the paper type category.

[0105] Next, the control unit 30 (adjustment processing unit 31d) performs control to select a patch with good transferability from the average luminance value and variance value of the adjustment patches 101A, 102A as follows (S10 to S12). In the explanation of the process of selecting a patch with good transferability, it is assumed that the B solid patch 101 and the Bk solid patch 102 are the adjustment patches 101A and 102A, respectively.

[0106] Fig. 17(a) shows an example of the result of acquiring the average luminance value of the B solid patch 101, and Fig. 17(b) shows an example of the result of acquiring the average luminance value of the Bk solid patch 102. Fig. 17(c) shows an example of the result of acquiring the average luminance value of the B solid patch 101 grouped as described below, and Fig. 17(d) shows an example of the result of acquiring the variance value of the B solid patch 101.

[0107] First, the control unit 30 (adjustment processor 31d) searches for the lowest average luminance value among the Bk solid patches 102. Then, the control unit 30 (adjustment processor 31d) controls to narrow down the patch numbers (i.e., adjustment values) that fall within a range of a threshold value γ1 preset on the higher luminance side from the lowest average luminance value (S10). In the case of FIG. 17(b), the patch numbers with the lowest average luminance value (lowest luminance) are n=4, 5, 6, and the narrowed-down patch numbers are n=1, 2, 3, 4, 5, 6, 7, 8. This makes it possible to narrow down the patch numbers (i.e., adjustment values) to which the Bk solid has been transferred to a certain degree. The threshold value γ1 should be small when the transferability of the Bk solid is emphasized, and large when the transferability of the B solid is emphasized.

[0108] Next, the control unit 30 (adjustment processor 31d) calculates the average luminance value (herein also referred to as "group luminance") of the three B solid patches 101 including the patch numbers before and after each of the narrowed down patch numbers (i.e., adjustment values). Then, the control unit 30 (adjustment processor 31d) selects the set (group) with the lowest calculated group luminance (S11). The group luminance for the nth patch is expressed by the following formula:

[0109]

number

[0110] Fig. 17(a) shows the average luminance value of the B solid patch 101, and Fig. 17(c) shows the average luminance value of the B solid patch 101 converted into group luminance. In the case of Fig. 17(c), the group with patch number n=7 (i.e., the patches with patch numbers n=6, 7, and 8) has the lowest group luminance.

[0111] Here, in the adjustment using the chart, adjustment can only be performed for patches of a certain density. Therefore, correction may be performed for the group selected here. For example, a threshold value γ2 for the lowest group luminance is set in advance. Then, on the side of a patch number (i.e., an adjustment value) smaller than the patch number of the group with the lowest group luminance, it is checked whether there is a group luminance that falls within the range of the threshold value γ2 from the lowest group luminance to the higher luminance side. Then, if there is, the group to be selected may be changed to the group of the patch number (i.e., an adjustment value) of that group luminance that is as close as possible to the rise of the transferability of the secondary color. This correction makes it possible to select a patch number (i.e., an adjustment value) of a group as close as possible to the rise of the transferability of the secondary color. This makes it possible to suppress the occurrence of a case where the secondary transfer voltage Vtr is too high for a user who mainly outputs monochrome images or halftone images. In this embodiment, the correction (advancement) of the adjustment value by the threshold value γ2 as described above is adopted. Then, in the case of FIG. 17(c), the group of patch number n=6 (i.e., patches of patch numbers n=5, 6, and 7) is selected.

[0112] Next, the control unit 30 (adjustment processing unit 31d) selects the patch with the lowest variance value within the selected group (S12). In the case of Fig. 17(d), the variance value of patch number n=6 is the smallest.

[0113] The above-described flow for selecting the adjustment value is merely an example, and other examples are also possible. For example, gr Although three patches are used for the calculation, four or more patches may be used for the calculation, or two patches may be used for the calculation. gris effective for selecting an adjustment range with good transferability, but the adjustment value may be selected directly from the average luminance value and the variance value without using this. In particular, depending on the setting of the threshold value γ1 and the transferability of the recording material S, it may not be possible to select the group luminance. In that case, the adjustment value may be selected directly from the average luminance value and the variance value without using the group luminance. Also, the variance value is effective for detecting density unevenness in the adjustment patch, but it is not necessarily required to use this. Also, the transferability of the Bk solid may be adjusted by a method other than narrowing down by the threshold value 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 of the B solid patch is the lowest (highest density) may be selected.

[0114] Next, the control unit 30 (adjustment processor 31d) compares the current difference ΔId stored in the RAM 33 in S8 with a predetermined threshold value (S13). If the current difference ΔId is equal to or greater than the predetermined threshold value, it can be determined that the recording material S is significantly dried by the air during paper feeding, and the electrical resistance of the area where the air is blown is higher than other areas, causing electrical resistance unevenness within the surface of the recording material S. In this case, even if the adjustment value selected so far is used, the transfer current may be insufficient at the area where the air is blown. Therefore, if the current difference ΔId is equal to or greater than the predetermined threshold value in S13, the control unit 30 (adjustment processor 31d) corrects the adjustment value selected so far (S14).

[0115] FIG. 18 is a graph diagram for explaining a method of correcting an adjustment value using a current difference ΔId in this embodiment. FIG. 18 shows the relationship between voltage and current (voltage-current characteristics) acquired when outputting a chart similar to that of FIG. 15. The voltage value corresponding to the adjustment value selected in S12 is set as Vt1. The control unit 30 (adjustment processing unit 31d) calculates this voltage value Vt1 by calculating the relationship between the voltage applied at adjustment patch positions 1 to 10 and the detected current (I=a×V 2 +b×V+c) to calculate a current value It1 that flows corresponding to this voltage value Vt1. That is, the current value It1 is calculated by the following formula: It1=a×Vt1 2+b×Vt1+c The control unit 30 (adjustment processor 31d) also calculates a corrected current value It2 by adding the current difference ΔId to the current value It1. That is, the current value It2 can be calculated by the following formula: It2 = It1 + ΔId The control unit 30 (adjustment processor 31d) calculates the current value It2 based on the relationship between the voltage applied at adjustment patch positions 1 to 10 and the detected current (I=a×V 2 +b×V+c) to calculate the corrected voltage value Vt2. It2=a×Vt2 2 +b×Vt2+c Then, calculate the voltage value Vt2 such that

[0116] Then, the control unit 30 (adjustment processing unit 31d) selects the patch number n to which the voltage closest to the voltage value Vt2 has been applied as the final adjustment value. A The corresponding adjustment value N A is selected as the recommended adjustment value (S15). In the case of double-sided adjustment, the adjustment value is corrected using the current difference ΔId by using the current detection results for the first and second sides, respectively. Note that if the current difference ΔId is smaller than a predetermined threshold in S13, the control unit 30 (adjustment processing unit 31d) can determine that the influence of air during paper feeding is small (uneven electrical resistance within the surface of the recording material S is within an acceptable range), and therefore there is no need to correct the adjustment value selected up to that point. In this embodiment, the predetermined threshold for the current difference ΔId is set to 5 μA. In other words, in this embodiment, if the current difference ΔId is 5 μA or more, the adjustment value selected in S12 is corrected in S14, and the corrected adjustment value is set as the recommended adjustment value N. A On the other hand, in this embodiment, when the current difference ΔId is less than 5 μA, the adjustment value selected in S12 is adopted as the recommended adjustment value N A It will be adopted as such.

[0117] The control unit 30 (adjustment processor 31d) determines the adjustment value N A11 on the display unit 70a of the operation unit 70 in the adjustment value display area 707 of the secondary transfer voltage adjustment screen 706 as shown in FIG. 11 (S16). The operator determines whether the displayed content of the secondary transfer voltage adjustment screen 706 is acceptable, and selects the displayed adjustment value N A If the operator does not want to change the adjustment value N A If the operator wishes to change the adjustment value from the above, he / she operates the numeric keypad (not shown) of the operation unit 70 to input the adjustment value to the adjustment value display unit 707 and selects the confirmation unit 710 (OK button 710a or application button 710b). The operator can determine whether the display content of the secondary transfer voltage adjustment screen 706 is acceptable by, for example, visually checking the output chart. If the adjustment value is changed, the control unit 30 (adjustment process unit 31d) stores the adjustment value input by the operator in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S17). On the other hand, if the adjustment value is not changed and the confirmation unit 710 is selected, the control unit 30 (adjustment process unit 31d) stores the adjustment value determined as described above in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) as is (S17). This ends the adjustment mode.

[0118] 8. Effects An experiment to confirm the effect of this embodiment was carried out for this embodiment and a comparative example. In the comparative example, an adjustment mode was carried out under conditions in which the adjustment value was not corrected using the current detection result at the location where air was blown during paper feeding.

[0119] The experiment was carried out on recording material S with a basis weight of 300 g / m 2A thick paper of this size was used. This is because when thick paper with a larger basis weight than plain paper is used as the recording material S, the difference in electrical resistance between the area where air was blown in the paper feed section 4 and other areas is likely to be significant, and differences in transferability due to uneven electrical resistance are likely to occur. Table 1 shows the adjustment value after the adjustment mode is performed and the image quality of the center of the recording material S and the area where air was blown during paper feed. The image quality is indicated as "good" if there is no problem, and "poor" if an image defect occurs due to the setting of the secondary transfer voltage. Note that similar results were obtained for the first and second sides of a double-sided print, so Table 1 shows the results of one side as a representative.

[0120] [Table 1]

[0121] In the comparative example, an adjustment value was selected in the adjustment mode that resulted in a lower secondary transfer voltage than in this embodiment. This resulted in some images being output with transfer defects in the areas where air was blown during paper feed. This is thought to be because the comparative example was unable to select an appropriate adjustment value in the adjustment mode, as it was not possible to take into account the fact that the electrical resistance of the areas where air was blown during paper feed was high.

[0122] In contrast, in this embodiment, the adjustment value selected in the adjustment mode did not cause any image quality abnormality, and a good image was output. Thus, in this embodiment, in the adjustment mode, an appropriate adjustment value can be selected even for the recording material S on which electrical resistance unevenness has occurred within the surface. In other words, in this embodiment, the influence of the air blowing during paper feeding can be suppressed, and the secondary transfer voltage can be appropriately adjusted.

[0123] In this embodiment, the relationship between the voltage and the current when the chart is output is approximated by a quadratic equation, but this is not limited to this. The relationship between the voltage and the current when the chart is output can be approximated by a straight line or a polynomial of degree two or higher, depending on the configuration of the image forming apparatus 1, etc.

[0124] Furthermore, in this embodiment, the voltage-current characteristics are obtained using the applied voltages and detected currents at multiple adjustment patch positions when the chart is output, and the current difference ΔId is obtained from the current detected when a predetermined voltage is applied at position D and the current corresponding to the predetermined voltage in the voltage-current characteristics. However, the present invention is not limited to this embodiment, and the current difference ΔId may be obtained from the current detected when a predetermined voltage is applied at position D and the current detected at an adjustment patch position where the same predetermined voltage as that applied at position D is applied.

[0125] Thus, in this embodiment, the image forming apparatus 1 includes an image carrier (intermediate transfer belt) 44b that carries a toner image, a transfer member 45b that forms a transfer portion N2 that transfers the toner image from the image carrier 44b to a recording material S, an application unit 76 that applies a transfer voltage to the transfer portion N2 for transferring the toner image from the image carrier 44b to the recording material S, detection units 76a, 76b that detect the voltage and current when a voltage is applied to the transfer portion N2, acquisition units 91, 92 that acquire information regarding the density of an image on the recording material, a control unit 30 that is controllable to execute an adjustment mode in which a plurality of test voltages are applied to the transfer portion N2 to form and output a chart in which a plurality of density acquisition images made of toner images are respectively transferred to the recording material S, acquire information regarding the density of the plurality of density acquisition images of the chart by the acquisition units 91, 92, and set the transfer voltage during image formation, and ... and a feeding section 4 which feeds the recording material S in a conveying direction of the recording material S when it is sent out from the feeding section 4, and which is provided with a blowing section 49 which blows air onto a leading end portion of the recording material S in the conveying direction of the recording material S when it is sent out from the feeding section 4. A control section 30 sets a transfer voltage during image formation based on a detection result of the detection sections 76a, 76b when an area (adjustment patch positions 1-10) on the recording material S on which a chart is formed, to which at least one of the plurality of density acquisition images is transferred, passes through the transfer section N2, a detection result of the detection sections 76a, 76b when a predetermined area (position D) on the leading end side of the area to which the plurality of density acquisition images is transferred, in the conveying direction of the recording material S when it is sent out from the feeding section 4, passes through the transfer section N2, and information on the densities of the plurality of density acquisition images acquired by the acquisition sections 91, 92.In this embodiment, the control unit 30 acquires a first current detected by the detection unit 76b when a predetermined voltage is applied to the transfer unit N2 when the specified area (position D) passes through the transfer unit N2, a voltage-current characteristic based on the detection results of the detection units 76a, 76b when an area to which at least two of the multiple density acquisition images are transferred passes through the transfer unit N2, and a second current calculated based on the voltage-current characteristic and the specified voltage, and when the first current is smaller than the second current by a predetermined value or more, sets the transfer voltage during image formation based on the difference between the second current and the first current (current difference ΔId) and information regarding the density of the multiple density acquisition images acquired by acquisition units 91, 92. The control unit 30 may acquire a first current detected by the detection unit 76b when a predetermined voltage is applied to the transfer unit N2 when the predetermined area passes through the transfer unit N2, and a second current detected by the detection unit 76b when the predetermined voltage is applied to the transfer unit N2 when an area to which a predetermined density acquisition image of the plurality of density acquisition images is transferred passes through the transfer unit N2, and when the first current is smaller than the second current by a predetermined value or more, set the transfer voltage during image formation based on the difference between the second current and the first current and information on the density of the plurality of density acquisition images acquired by the acquisition units 91 and 92. Here, when the first current is smaller than the second current by the predetermined value or more, the control unit 30 sets the transfer voltage so that the absolute value of the transfer voltage during image formation is larger than when the first current is not smaller than the second current by the predetermined value or more. In this embodiment, the predetermined area is an area on the recording material S on which a chart is formed, to which an image made of a toner image is not transferred. However, as described below, the above-mentioned specified area may also be an area on the recording material S on which the chart is formed, onto which a specified image consisting of a toner image for detecting the position of the density acquisition image is transferred (see Example 3).

[0126] As described above, according to this embodiment, even if air is blown onto the recording material S during feeding, causing electrical resistance unevenness within the surface of the recording material S, the secondary transfer voltage can be adjusted in consideration of the transfer current required for the area where the air is blown. Therefore, according to this embodiment, it is possible to appropriately adjust the secondary transfer voltage.

[0127] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted. In this embodiment, as in embodiment 1, a case where "double-sided adjustment" is performed will be described.

[0128] This embodiment differs from the first embodiment in the method of applying voltage when outputting the chart in the adjustment mode.

[0129] Fig. 20 is a graph showing the transition of the output of the secondary transfer power supply 76 when the L chart 100 is secondarily transferred to the recording material S. Fig. 20(a) shows the first side during double-sided adjustment, and Fig. 20(b) shows the second side during double-sided adjustment. In this embodiment, patch number n=5 (the voltage indicated by the dotted line with reference numeral 800 in Fig. 20) is applied at trigger patch position T, and the same voltage as the adjacent patch number (patch number n=1 on the first side, patch number n=10 on the second side) is applied at position D.

[0130] FIG. 21 is a graph showing the relationship between voltage and current (voltage-current characteristics) acquired when the chart is output in this embodiment. FIG. 21(a) shows the relationship between voltage and current acquired on the first side, and FIG. 21(b) shows the relationship between voltage and current acquired on the second side. In this embodiment, too, in S8 of FIG. 8, the current difference ΔId can be calculated in the same manner as in embodiment 1. That is, the control unit 30 (adjustment processing unit 31d) calculates the relationship between the voltage applied at adjustment patch positions 1 to 10 and the detected current by approximating it with a quadratic function (I=a×V2 +b×V+c). Then, the control unit 30 (adjustment processing unit 31d) applies the voltage Vtr at the position D and detects the current Id, and calculates the current difference ΔId using the following formula: ΔId=(a×Vtr 2 +b×Vtr+c)-Id In the case of double-sided adjustment, the relationship between the applied voltage and the detected current at adjustment patch positions 1 to 10 and the current difference ΔId are acquired and calculated for each of the first and second sides.

[0131] Other aspects of the adjustment mode, such as the method of correcting the adjustment value using the current difference ΔId in S14 of FIG.

[0132] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained, and the control of the secondary transfer power supply 75 can be simplified.

[0133] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1 and detailed explanations are omitted.

[0134] In this embodiment, a case where single-sided adjustment is performed will be described. When single-sided adjustment is performed, the relationship between the location where air is blown during paper feeding and the trigger patch position is different from when double-sided adjustment is performed described in embodiment 1.

[0135] When adjusting only the secondary transfer voltage during single-sided printing ("single-sided adjustment"), the following charts are output in the adjustment mode. When outputting the L chart 100, the chart 100(2) in FIG. 6 is formed on the first side of one sheet of recording material S in the image forming operation for single-sided printing and output. When outputting the S chart 103, the chart 103(2-1) and the chart 103(2-2) in FIG. 7 are formed on the first side of the first sheet of recording material S and the first side of the second sheet of recording material S, respectively, in the image forming operation for single-sided printing and output. That is, when adjusting the secondary transfer voltage for the first and second sides during double-sided printing ("double-sided adjustment"), the chart for the second side is output in the image forming operation for single-sided printing without passing through the reversing conveying path 7. The chart is read using the second line sensor 92 of the sensing unit 3. This allows the orientation of the read image to be kept the same as during double-sided adjustment, and the recording material S does not pass through the reversal conveying path 7, so downtime (time during which an image cannot be output due to adjustment, etc.) can be minimized while performing single-sided adjustment.

[0136] 22 is a graph showing the transition of the output of the secondary transfer power supply 76 when the L chart 100 is secondarily transferred to the recording material S in single-sided adjustment. In this embodiment, the trigger patch position T is close to the point where air was blown when the paper was fed (the trigger patch position T is included in the point where air was blown when the paper was fed). Therefore, in this embodiment, the current difference ΔId is found using the relationship between the voltage applied at the trigger patch position T and the detected current. In other words, in this embodiment, the trigger patch position T also serves as an area ("position D") for acquiring information about the electrical resistance of the recording material S near the leading edge of the recording material S in the transport direction when it is sent out from the paper feed unit 4.

[0137] The trigger patches 101T and 102T are used to detect the position of the patches when the chart is read by the sensing unit 3. Therefore, even if the electrical resistance of the recording material S at that location increases when air is blown onto it during feeding, causing a slight decrease in transferability, this poses almost no problem.

[0138] Other aspects of the adjustment mode, such as the method of calculating the current difference ΔId in S8 of FIG. 8 and the method of correcting the adjustment value using the current difference ΔId in S14 of FIG.

[0139] As described above, according to this embodiment, it is possible to obtain the same effects as those of the first embodiment while suppressing the downtime during single-sided adjustment.

[0140] [Example 4] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1 and detailed explanations are omitted.

[0141] It is preferable to set the adjustment patch position at a location other than the location where air is blown near the leading edge of the recording material S in the transport direction when it is sent out from the paper feed unit 4, that is, at a location where the change in electrical resistance caused by air being blown when the paper is fed is sufficiently small. However, depending on the chart design, it is also possible that the adjustment patch position is set at a location where air is blown when the paper is fed. For example, in such a case, the adjustment patch position may also be used as an area ("position D") for acquiring information about the electrical resistance of the recording material S near the leading edge of the recording material S in the transport direction when it is sent out from the paper feed unit 4.

[0142] FIG. 23(a) is a graph showing an example of the relationship between voltage and current (voltage-current characteristics) acquired when the chart is output in a case where the adjustment patch position is also used as position D. The figure shows, as an example, an example of the case where an L chart 100 is output (first side of double-sided adjustment) in a configuration having an air blowing unit 49 similar to that of the above-mentioned embodiment, in a case where adjustment patch position 1 is included in the area where air was blown during paper feed. It is known in advance that adjustment patch position 1 is a position where the electrical resistance of the recording material S may increase due to air being blown thereto during paper feed. In this case, in S8 of FIG. 8, the current difference ΔId can be calculated as follows. That is, the control unit 30 (adjustment processing unit 31d) calculates the relationship between the voltage applied at adjustment patch positions 2 to 10 excluding adjustment patch position 1 (which also serves as position D) and the detected current by approximating it with a quadratic function (I=a×V 2 +b×V+c). Then, the control unit 30 (adjustment processing unit 31d) applies the voltage Vtr at adjustment patch position 1 (which also serves as position D) and detects the current Id. The current difference ΔId is calculated by the following formula: ΔId=(a×Vtr 2 +b×Vtr+c)-Id It can be calculated as follows:

[0143] Other aspects of the adjustment mode, such as the method of correcting the adjustment value using the current difference ΔId, are the same as in the first embodiment. The relationship between the voltage applied at the adjustment patch positions 2 to 10 and the detected current may be used to correct the adjustment value. If the current difference ΔId is equal to or greater than a predetermined threshold, the density information at the adjustment patch position 1 may not be used to select the adjustment value. Note that the same control as above can be performed in the case of single-sided adjustment. In addition, in the case of the second side of double-sided adjustment, if the adjustment patch position 10 is included in the area where air was blown during paper feeding, the same control can be performed using the detection result of the current at the adjustment patch position 10 instead of the adjustment patch position 1.

[0144] FIG. 23(b) is a graph showing another example of the relationship between voltage and current (voltage-current characteristics) acquired when the chart is output in a case where the adjustment patch position is also used as the position D. The figure shows an example of an L chart 100 output in a configuration having an air blowing unit 49 that blows air from both ends in the width direction toward the center near the center of the recording material S in the conveying direction when it is sent out from the paper feed unit 4. FIG. 24 is a schematic diagram showing the position where air is blown onto the recording material S in the paper feed unit 4 in this case. For example, it is assumed that the adjustment patch position 5 is included in the portion where air is blown onto the recording material S during paper feed. It is known in advance that the adjustment patch position 5 is a position where the electrical resistance of the recording material S may increase due to air being blown onto the recording material S during paper feed. In this case, in S8 of FIG. 8, the current difference ΔId can be obtained as follows. That is, the control unit 30 (adjustment processor 31d) obtains a relationship between the voltage applied at adjustment patch positions 1 to 4 and 6 to 10, excluding adjustment patch position 5 (which also serves as position D), and the detected current by approximating it with a quadratic function (I=a×V 2 +b×V+c). Then, the control unit 30 (adjustment processing unit 31d) applies the voltage Vtr at adjustment patch position 5 (which also serves as position D) and detects the current Id. The current difference ΔId is calculated by the following formula: ΔId=(a×Vtr 2 +b×Vtr+c)-Id It can be calculated as follows:

[0145] Other aspects of the adjustment mode, such as the method of correcting the adjustment value using the current difference ΔId, are the same as in the first embodiment. The relationship between the voltage applied and the detected current at the adjustment patch positions 1 to 4 and 6 to 10 may also be used to correct the adjustment value. If the current difference ΔId is equal to or greater than a predetermined threshold, the density information at adjustment patch position 5 may not be used to select the adjustment value. Note that the same control as above can be performed in the case of single-sided adjustment. Also, in the case of double-sided adjustment, the same control can be performed on the second side using the detection result of the current at the adjustment patch position that also serves as position D.

[0146] 23(a) and 23(b), the relationship between voltage and current may be found by using the detection results at all adjustment patch positions. Then, only when an index (correlation coefficient) for observing the relationship between data satisfies a predetermined condition (for example, falls below a predetermined value), the relationship between voltage and current may be found by using the detection results at adjustment patch positions excluding the adjustment patch position that also serves as position D.

[0147] Furthermore, the adjustment patch position that also serves as position D is not limited to being one. If there are multiple adjustment patch positions to which air may be blown during paper feed, thereby increasing the electrical resistance of the recording material S, the voltage and current can be found using the detection results of the adjustment patch positions excluding these. Then, the relationship between the voltage and current can be compared with the detection result at at least one of the multiple adjustment patch positions that also serve as position D to find the current difference ΔId.

[0148] Thus, the image forming apparatus 1 has a feeding section 4 which feeds the recording material S toward the transfer section N2, and which is equipped with a blowing section 49 which blows air from a blowing port (handling nozzle) 49c (Figure 19(a)) onto the recording material S as the recording material S is sent out from the feeding section 4. In this embodiment, the control unit 30 acquires a first current detected by the detection unit when a predetermined voltage is applied to the transfer unit when a first area of ​​the recording material S on which a chart is formed, to which an image for density acquisition is transferred, passes through the transfer unit N2, a voltage-current characteristic based on the detection results of the detection units 76a, 76b when at least one second area of ​​the recording material S on which a chart is formed, to which an image for density acquisition is transferred and which is farther from the blowing port 49c than the first area, passes through the transfer unit N2 when the recording material S is sent out from the feed unit 4 (more specifically, when the recording material S is placed on the feed unit 4 to be sent out), and a second current calculated based on the voltage-current characteristic and the predetermined voltage, and when the first current is smaller than the second current by a predetermined value or more, sets the transfer voltage during image formation based on the difference between the second current and the first current (current difference ΔId) and information on the densities of the multiple images for density acquisition acquired by the acquisition units 91, 92. Here, when the first current is smaller than the second current by the predetermined value or more, the control unit 30 sets the transfer voltage so that the absolute value of the transfer voltage during image formation is larger than when the first current is not smaller than the second current by the predetermined value or more. Note that the configuration described in the first embodiment corresponds to the case where the first region is a region on the recording material S on which the chart is formed, to which an image made of a toner image is not transferred. Also, the configuration described in the third embodiment corresponds to the case where the first region is a region on the recording material S on which the chart is formed, to which a predetermined image made of a toner image for detecting the position of the density acquisition image is transferred.

[0149] As described above, according to this embodiment, the adjustment value of the secondary transfer voltage is corrected using the current detection results at the adjustment patch position included in the area where air is blown during paper feed, thereby achieving the same effect as in embodiment 1.

[0150] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0151] In the above embodiment, the transfer voltage is adjusted using an adjustment value corresponding to a predetermined adjustment amount, but the adjustment amount may be directly set on an adjustment screen, for example.

[0152] In the above embodiment, the operation performed on the operation unit of the image forming apparatus may be performed on an external device. That is, the case where the adjustment mode is executed by the operator via the operation unit 70 of the image forming apparatus 1 has been described, but the adjustment mode may be executed by the operator via the external device 200 such as a personal computer. In this case, the same settings as those in the above embodiment can be performed via a screen displayed on the display unit of the external device 200 by the driver program of the image forming apparatus 1 installed in the external device 200.

[0153] In the above embodiment, the secondary transfer voltage is controlled to a constant voltage, but the secondary transfer voltage may be controlled to a constant current. In the case where the secondary transfer voltage is controlled to a constant current, the secondary transfer voltage can be adjusted by adjusting the target current or the initial voltage when the secondary transfer voltage is applied in the adjustment mode.

[0154] Furthermore, the detection result of the current or voltage may be an average value of a plurality of sampling values ​​acquired at a predetermined sampling interval at one detection timing, etc. Furthermore, when the transfer voltage is subjected to constant voltage control, the voltage value may be detected (recognized) from an output instruction value for the power supply, and when the transfer voltage is subjected to constant current control, the current value may be detected (recognized) from an output instruction value for the power supply.

[0155] In the above embodiment, the printer unit and the sensing unit are each unitized in the image forming apparatus, but the present invention is not limited to such an embodiment. By configuring in this manner, for example, it is possible to separate the units and provide the function of the sensing unit 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 embodiment may be integrated by being arranged in, for example, a single housing.

[0156] In the above embodiment, the chart was read using the in-line image sensor (first and second line sensors) in the adjustment mode. That is, in the above embodiment, the acquisition unit that acquires information about the density of the image on the recording material acquires information about the density of the density acquisition image on the chart when the recording material on which the chart is formed is discharged from the image forming apparatus. This reduces the burden on the operator. However, the present invention is not limited to such an embodiment, and for example, the chart output in the adjustment mode may be set by the operator in the image reading unit 80 (FIG. 1) as the acquisition unit, and the chart may be read by the image reading unit 80. In this way, the acquisition unit that acquires information about the density of the image on the recording material may acquire information about the density of the density acquisition image on the chart when the recording material on which the chart is formed and discharged from the image forming apparatus is set.

[0157] Also, as mentioned above, when thick paper having a basis weight larger than that of plain paper is used as the recording material, the difference in electrical resistance between the portion where the air is blown in the paper feed section and the other portion is likely to be significant, and the difference in transferability due to uneven electrical resistance is likely to occur. Therefore, for example, only when thick paper having a basis weight equal to or greater than a predetermined value is used as the recording material, control using the detection result of the current at position D (correction of the adjustment value) as described in the above embodiment may be performed.

[0158] Furthermore, the image forming apparatus is not limited to a tandem type image forming apparatus, and may be an image forming apparatus of another type. Furthermore, the image forming apparatus is not limited to an image forming apparatus capable of forming a full-color image, and may be an image forming apparatus capable of forming only a monochrome (black and white or monochromatic) image. For example, the present invention may be applied to a transfer unit in an image forming apparatus configured to form a toner image on a photosensitive drum as an image carrier and transfer the toner image directly to a recording material in the transfer unit. Furthermore, the image forming apparatus may be an image forming apparatus for various purposes, such as a printer, various printing machines, a copier, a FAX, or a multifunction machine. [Explanation of symbols]

[0159] 1. Image forming device 2 Printer unit 3 Sensing Unit 4 Paper feed section 30 Control section 49 Air blowing section 76 Secondary transfer power supply 91 First line sensor 92 Second line sensor 100 Large Chart (L Chart) 101 B Solid Patch 102 Bk solid patch 103 Small Chart (S Chart) N2 Secondary transfer section

Claims

1. an image carrier that carries a toner image; a transfer member forming a transfer section for transferring a toner image from the image carrier to a recording material; an application section that applies a transfer voltage to the transfer section for transferring a toner image from the image carrier to a recording material; a detection unit that detects a voltage and a current when a voltage is applied to the transfer unit; an acquisition unit that acquires information regarding the density of an image on a recording material; a control unit that is controllable to execute an adjustment mode in which a plurality of test voltages are applied to the transfer unit, a chart is formed by transferring a plurality of density acquisition images, each of which is made of a toner image, onto a recording material, and the chart is output, and information regarding the densities of the plurality of density acquisition images of the chart is acquired by the acquisition unit, and the transfer voltage during image formation is set; a feeding section that feeds the recording material toward the transfer section, the feeding section including a blowing section that blows air onto a leading end of the recording material in a conveying direction of the recording material when the recording material is sent out from the feeding section; having an image forming apparatus characterized in that the control unit sets the transfer voltage during image formation based on a detection result of the detection unit when an area on the recording material on which the chart is formed, onto which at least one of the multiple density acquisition images is transferred, passes through the transfer unit; a detection result of the detection unit when a predetermined area within the image forming area of ​​the recording material on which the chart is formed, which is on the leading edge side of the area on which the multiple density acquisition images are transferred in the transport direction of the recording material when it is sent out from the feed unit, passes through the transfer unit; and information regarding the densities of the multiple density acquisition images acquired by the acquisition unit.

2. The control unit acquires a first current detected by the detection unit when a predetermined voltage is applied to the transfer unit when the predetermined area passes through the transfer unit, a voltage-current characteristic based on the detection result of the detection unit when an area to which at least one of the plurality of density acquisition images is transferred passes through the transfer unit, and a second current calculated based on the voltage-current characteristic and the predetermined voltage, and when the first current is smaller than the second current by a predetermined value or more, sets the transfer voltage during image formation based on a difference between the second current and the first current and information regarding the densities of the plurality of density acquisition images acquired by the acquisition unit.

3. The control unit acquires a first current detected by the detection unit when a predetermined voltage is applied to the transfer unit when the predetermined area passes through the transfer unit, and a second current detected by the detection unit when the predetermined voltage is applied to the transfer unit when an area to which a predetermined density acquisition image of the plurality of density acquisition images is transferred passes through the transfer unit, and when the first current is smaller than the second current by a predetermined value or more, sets the transfer voltage during image formation based on the difference between the second current and the first current and information regarding the density of the plurality of density acquisition images acquired by the acquisition unit.

4. The image forming apparatus according to claim 2 or 3, characterized in that the control unit sets the transfer voltage so that, when the first current is smaller than the second current by the specified value or more, the absolute value of the transfer voltage during image formation is larger than when the first current is not smaller than the second current by the specified value or more.

5. 2. The image forming apparatus according to claim 1, wherein the predetermined area is an area of ​​the recording material on which the chart is formed, onto which a toner image is not transferred.

6. 2. The image forming apparatus according to claim 1, wherein the predetermined area is an area on a recording material on which the chart is formed, onto which a predetermined image consisting of a toner image for detecting the position of the density acquisition image is transferred.

7. an image carrier that carries a toner image; a transfer member forming a transfer section for transferring a toner image from the image carrier to a recording material; an application section that applies a transfer voltage to the transfer section for transferring a toner image from the image carrier to a recording material; a detection unit that detects a voltage and a current when a voltage is applied to the transfer unit; an acquisition unit that acquires information regarding the density of an image on a recording material; a control unit that is controllable to execute an adjustment mode in which a plurality of test voltages are applied to the transfer unit, a chart is formed by transferring a plurality of density acquisition images, each of which is made of a toner image, onto a recording material, and the chart is output, and information regarding the densities of the plurality of density acquisition images of the chart is acquired by the acquisition unit, and the transfer voltage during image formation is set; a feeding section that feeds the recording material toward the transfer section, the feeding section including a blowing section that blows air from a blowing port onto the recording material when the recording material is sent out from the feeding section; having the control unit acquires a first current detected by the detection unit when a predetermined voltage is applied to the transfer unit when a first region of the recording material on which the chart is formed, to which the density acquisition image is transferred, passes through the transfer unit; a voltage-current characteristic based on a detection result from the detection unit when at least one second region of the recording material on which the chart is formed, to which the density acquisition image is transferred, which is farther from the blowing port than the first region when the recording material is sent out from the feed unit, passes through the transfer unit; and a second current calculated based on the voltage-current characteristic and the predetermined voltage; and when the first current is smaller than the second current by a predetermined value or more, sets the transfer voltage during image formation based on a difference between the second current and the first current and information on the densities of the multiple density acquisition images acquired by the acquisition unit.

8. The image forming apparatus according to claim 7, characterized in that the control unit sets the transfer voltage so that, when the first current is smaller than the second current by the predetermined value or more, the absolute value of the transfer voltage during image formation is larger than when the first current is not smaller than the second current by the predetermined value or more.

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